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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NotesPayableToRelatedPartiesMember_lbl" xml:lang="en-US">NotesPayableToRelatedParties [Member]</link:label>
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      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:to="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_lbl" xml:lang="en-US">Related Party [Axis]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_CurrentPortionFourMember" xlink:label="VSTA_CurrentPortionFourMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CurrentPortionFourMember" xlink:to="VSTA_CurrentPortionFourMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CurrentPortionFourMember_lbl" xml:lang="en-US">CurrentPortionFour [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MaximumMember" xlink:label="us-gaap_MaximumMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_MaximumMember" xlink:to="us-gaap_MaximumMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_MaximumMember_lbl" xml:lang="en-US">Maximum [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeStatementLocationAxis" xlink:label="us-gaap_IncomeStatementLocationAxis" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeStatementLocationAxis" xlink:to="us-gaap_IncomeStatementLocationAxis_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_IncomeStatementLocationAxis_lbl" xml:lang="en-US">Income Statement Location [Axis]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MinimumMember" xlink:label="us-gaap_MinimumMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_MinimumMember" xlink:to="us-gaap_MinimumMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_MinimumMember_lbl" xml:lang="en-US">Minimum [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockCompensationPlanMember" xlink:label="us-gaap_StockCompensationPlanMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockCompensationPlanMember" xlink:to="us-gaap_StockCompensationPlanMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_StockCompensationPlanMember_lbl" xml:lang="en-US">Stock Incentive Plan [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:to="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_lbl" xml:lang="en-US">Antidilutive Securities [Axis]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_Note1Member" xlink:label="VSTA_Note1Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_Note1Member" xlink:to="VSTA_Note1Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_Note1Member_lbl" xml:lang="en-US">Note 1 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_Note2Member" xlink:label="VSTA_Note2Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_Note2Member" xlink:to="VSTA_Note2Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_Note2Member_lbl" xml:lang="en-US">Note 2 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueInputsLevel1Member" xlink:label="us-gaap_FairValueInputsLevel1Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueInputsLevel1Member" xlink:to="us-gaap_FairValueInputsLevel1Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FairValueInputsLevel1Member_lbl" xml:lang="en-US">Fair Value, Inputs, Level 1 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueByFairValueHierarchyLevelAxis_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis_lbl" xml:lang="en-US">Fair Value, Hierarchy [Axis]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="us-gaap_FairValueInputsLevel2Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueInputsLevel2Member" xlink:to="us-gaap_FairValueInputsLevel2Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FairValueInputsLevel2Member_lbl" xml:lang="en-US">Fair Value, Inputs, Level 2 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="us-gaap_FairValueInputsLevel3Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueInputsLevel3Member" xlink:to="us-gaap_FairValueInputsLevel3Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FairValueInputsLevel3Member_lbl" xml:lang="en-US">Fair Value, Inputs, Level 3 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_SeniorNote1Member" xlink:label="VSTA_SeniorNote1Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SeniorNote1Member" xlink:to="VSTA_SeniorNote1Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SeniorNote1Member_lbl" xml:lang="en-US">Senior Note1 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_SeniorNote2Member" xlink:label="VSTA_SeniorNote2Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SeniorNote2Member" xlink:to="VSTA_SeniorNote2Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SeniorNote2Member_lbl" xml:lang="en-US">Senior Note 2 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_SeniorNote3Member" xlink:label="VSTA_SeniorNote3Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SeniorNote3Member" xlink:to="VSTA_SeniorNote3Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SeniorNote3Member_lbl" xml:lang="en-US">Senior Note 3 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_SeniorNote4Member" xlink:label="VSTA_SeniorNote4Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SeniorNote4Member" xlink:to="VSTA_SeniorNote4Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SeniorNote4Member_lbl" xml:lang="en-US">Senior Note 4 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_SeniorNote5Member" xlink:label="VSTA_SeniorNote5Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SeniorNote5Member" xlink:to="VSTA_SeniorNote5Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SeniorNote5Member_lbl" xml:lang="en-US">Senior Note 5 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_SeniorNonCurrentMember" xlink:label="VSTA_SeniorNonCurrentMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SeniorNonCurrentMember" xlink:to="VSTA_SeniorNonCurrentMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SeniorNonCurrentMember_lbl" xml:lang="en-US">Senior NonCurrent [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_SevenPercentNotesPayableAprilTwoThousandElevenMember" xlink:label="VSTA_SevenPercentNotesPayableAprilTwoThousandElevenMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SevenPercentNotesPayableAprilTwoThousandElevenMember" xlink:to="VSTA_SevenPercentNotesPayableAprilTwoThousandElevenMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SevenPercentNotesPayableAprilTwoThousandElevenMember_lbl" xml:lang="en-US">Seven% Note [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_SevenPercentNoteCurrentPortionMember" xlink:label="VSTA_SevenPercentNoteCurrentPortionMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SevenPercentNoteCurrentPortionMember" xlink:to="VSTA_SevenPercentNoteCurrentPortionMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SevenPercentNoteCurrentPortionMember_lbl" xml:lang="en-US">Seven % Current [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_SevenPercentNoncurrentMember" xlink:label="VSTA_SevenPercentNoncurrentMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SevenPercentNoncurrentMember" xlink:to="VSTA_SevenPercentNoncurrentMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SevenPercentNoncurrentMember_lbl" xml:lang="en-US">Seven % Noncurrent [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_MAndFNoteBMember" xlink:label="VSTA_MAndFNoteBMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_MAndFNoteBMember" xlink:to="VSTA_MAndFNoteBMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_MAndFNoteBMember_lbl" xml:lang="en-US">M F Note B [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_MandFNoteAMember" xlink:label="VSTA_MandFNoteAMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_MandFNoteAMember" xlink:to="VSTA_MandFNoteAMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_MandFNoteAMember_lbl" xml:lang="en-US">M F Note A [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_BurrPilgerMayerMember" xlink:label="VSTA_BurrPilgerMayerMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_BurrPilgerMayerMember" xlink:to="VSTA_BurrPilgerMayerMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_BurrPilgerMayerMember_lbl" xml:lang="en-US">BurrPilgerMayer [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_DesjardinsMember" xlink:label="VSTA_DesjardinsMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_DesjardinsMember" xlink:to="VSTA_DesjardinsMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_DesjardinsMember_lbl" xml:lang="en-US">Desjardins [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_McCarthyTetraultMember" xlink:label="VSTA_McCarthyTetraultMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_McCarthyTetraultMember" xlink:to="VSTA_McCarthyTetraultMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_McCarthyTetraultMember_lbl" xml:lang="en-US">McCarthyTetrault [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_MayTwoThousandElevenMorrisonFoersterMember" xlink:label="VSTA_MayTwoThousandElevenMorrisonFoersterMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_MayTwoThousandElevenMorrisonFoersterMember" xlink:to="VSTA_MayTwoThousandElevenMorrisonFoersterMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_MayTwoThousandElevenMorrisonFoersterMember_lbl" xml:lang="en-US">UniversityHealthNote1 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ServiceProviderNotesTotalMember" xlink:label="VSTA_ServiceProviderNotesTotalMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ServiceProviderNotesTotalMember" xlink:to="VSTA_ServiceProviderNotesTotalMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ServiceProviderNotesTotalMember_lbl" xml:lang="en-US">Service Provider Notes Total [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ServiceProvidersCurrentMember" xlink:label="VSTA_ServiceProvidersCurrentMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ServiceProvidersCurrentMember" xlink:to="VSTA_ServiceProvidersCurrentMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ServiceProvidersCurrentMember_lbl" xml:lang="en-US">Service Providers Current [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ServiceProvidersNoncurrentMember" xlink:label="VSTA_ServiceProvidersNoncurrentMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ServiceProvidersNoncurrentMember" xlink:to="VSTA_ServiceProvidersNoncurrentMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ServiceProvidersNoncurrentMember_lbl" xml:lang="en-US">Service Providers Noncurrent [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_InsuranceCompanyMember" xlink:label="VSTA_InsuranceCompanyMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_InsuranceCompanyMember" xlink:to="VSTA_InsuranceCompanyMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_InsuranceCompanyMember_lbl" xml:lang="en-US">Insurance Company [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_VendorMember" xlink:label="VSTA_VendorMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_VendorMember" xlink:to="VSTA_VendorMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_VendorMember_lbl" xml:lang="en-US">Vendor [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_VendorCurrentMember" xlink:label="VSTA_VendorCurrentMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_VendorCurrentMember" xlink:to="VSTA_VendorCurrentMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_VendorCurrentMember_lbl" xml:lang="en-US">Vendor Current [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_TenPercenCurrentMember" xlink:label="VSTA_TenPercenCurrentMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_TenPercenCurrentMember" xlink:to="VSTA_TenPercenCurrentMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_TenPercenCurrentMember_lbl" xml:lang="en-US">TenPercentCurrent [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_UnrelatedPartiesMember" xlink:label="VSTA_UnrelatedPartiesMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_UnrelatedPartiesMember" xlink:to="VSTA_UnrelatedPartiesMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_UnrelatedPartiesMember_lbl" xml:lang="en-US">Unrelated Parties [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_UnrelatedPartiesCurrentMember" xlink:label="VSTA_UnrelatedPartiesCurrentMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_UnrelatedPartiesCurrentMember" xlink:to="VSTA_UnrelatedPartiesCurrentMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_UnrelatedPartiesCurrentMember_lbl" xml:lang="en-US">Unrelated Parties Current [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_UnrelatedPartiesNoncurrentMember" xlink:label="VSTA_UnrelatedPartiesNoncurrentMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_UnrelatedPartiesNoncurrentMember" xlink:to="VSTA_UnrelatedPartiesNoncurrentMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_UnrelatedPartiesNoncurrentMember_lbl" xml:lang="en-US">Unrelated Parties Noncurrent [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_CatoNote1Member" xlink:label="VSTA_CatoNote1Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CatoNote1Member" xlink:to="VSTA_CatoNote1Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CatoNote1Member_lbl" xml:lang="en-US">Cato Note 1 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_CatoNote2Member" xlink:label="VSTA_CatoNote2Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CatoNote2Member" xlink:to="VSTA_CatoNote2Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CatoNote2Member_lbl" xml:lang="en-US">Cato Note 2 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_RelatedPartiesAggregateMember" xlink:label="VSTA_RelatedPartiesAggregateMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_RelatedPartiesAggregateMember" xlink:to="VSTA_RelatedPartiesAggregateMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_RelatedPartiesAggregateMember_lbl" xml:lang="en-US">Related Parties Aggregate [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_RelatedPartiesCurrentMember" xlink:label="VSTA_RelatedPartiesCurrentMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_RelatedPartiesCurrentMember" xlink:to="VSTA_RelatedPartiesCurrentMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_RelatedPartiesCurrentMember_lbl" xml:lang="en-US">Related Parties Current [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_RelatedPartiesNoncurrentMember" xlink:label="VSTA_RelatedPartiesNoncurrentMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_RelatedPartiesNoncurrentMember" xlink:to="VSTA_RelatedPartiesNoncurrentMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_RelatedPartiesNoncurrentMember_lbl" xml:lang="en-US">Related Parties Noncurrent [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_RelatedPartiesAfterDiscountMember" xlink:label="VSTA_RelatedPartiesAfterDiscountMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_RelatedPartiesAfterDiscountMember" xlink:to="VSTA_RelatedPartiesAfterDiscountMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_RelatedPartiesAfterDiscountMember_lbl" xml:lang="en-US">Related Parties After Discount [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ServiceProvidersAfterDiscountMember" xlink:label="VSTA_ServiceProvidersAfterDiscountMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ServiceProvidersAfterDiscountMember" xlink:to="VSTA_ServiceProvidersAfterDiscountMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ServiceProvidersAfterDiscountMember_lbl" xml:lang="en-US">Service Providers After Discount [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_SeniorNoteTotalMember" xlink:label="VSTA_SeniorNoteTotalMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SeniorNoteTotalMember" xlink:to="VSTA_SeniorNoteTotalMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SeniorNoteTotalMember_lbl" xml:lang="en-US">Senior Note Total [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_SeniorNoteNoncurrentMember" xlink:label="VSTA_SeniorNoteNoncurrentMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SeniorNoteNoncurrentMember" xlink:to="VSTA_SeniorNoteNoncurrentMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SeniorNoteNoncurrentMember_lbl" xml:lang="en-US">Senior Note Noncurrent [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_SeniorNote7Member" xlink:label="VSTA_SeniorNote7Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SeniorNote7Member" xlink:to="VSTA_SeniorNote7Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SeniorNote7Member_lbl" xml:lang="en-US">SeniorNote 7 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_TenpercentTotalMember" xlink:label="VSTA_TenpercentTotalMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_TenpercentTotalMember" xlink:to="VSTA_TenpercentTotalMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_TenpercentTotalMember_lbl" xml:lang="en-US">Ten% Total [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_TenPercentNoncurrentMember" xlink:label="VSTA_TenPercentNoncurrentMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_TenPercentNoncurrentMember" xlink:to="VSTA_TenPercentNoncurrentMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_TenPercentNoncurrentMember_lbl" xml:lang="en-US">Ten % Noncurrent [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_MFNoteAMember" xlink:label="VSTA_MFNoteAMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_MFNoteAMember" xlink:to="VSTA_MFNoteAMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_MFNoteAMember_lbl" xml:lang="en-US">MF Note A [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ServiceProviderTotalMember" xlink:label="VSTA_ServiceProviderTotalMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ServiceProviderTotalMember" xlink:to="VSTA_ServiceProviderTotalMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ServiceProviderTotalMember_lbl" xml:lang="en-US">Service Providers Total [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_MFNoteBMember" xlink:label="VSTA_MFNoteBMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_MFNoteBMember" xlink:to="VSTA_MFNoteBMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_MFNoteBMember_lbl" xml:lang="en-US">MF Note B [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_UnivHealthMember" xlink:label="VSTA_UnivHealthMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_UnivHealthMember" xlink:to="VSTA_UnivHealthMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_UnivHealthMember_lbl" xml:lang="en-US">Univ Health Note [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ServiceNotesCurrentMember" xlink:label="VSTA_ServiceNotesCurrentMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ServiceNotesCurrentMember" xlink:to="VSTA_ServiceNotesCurrentMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ServiceNotesCurrentMember_lbl" xml:lang="en-US">Service Note Current [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ServiceNotesNoncurrentMember" xlink:label="VSTA_ServiceNotesNoncurrentMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ServiceNotesNoncurrentMember" xlink:to="VSTA_ServiceNotesNoncurrentMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ServiceNotesNoncurrentMember_lbl" xml:lang="en-US">Service Notes Noncurrent [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_TenPercenNoncurrentMember" xlink:label="VSTA_TenPercenNoncurrentMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_TenPercenNoncurrentMember" xlink:to="VSTA_TenPercenNoncurrentMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_TenPercenNoncurrentMember_lbl" xml:lang="en-US">TenPercenNoncurrent [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_SeniorNotesTotalMember" xlink:label="VSTA_SeniorNotesTotalMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SeniorNotesTotalMember" xlink:to="VSTA_SeniorNotesTotalMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SeniorNotesTotalMember_lbl" xml:lang="en-US">Senior Notes Total [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ServiceProvidersTotalMember" xlink:label="VSTA_ServiceProvidersTotalMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ServiceProvidersTotalMember" xlink:to="VSTA_ServiceProvidersTotalMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ServiceProvidersTotalMember_lbl" xml:lang="en-US">Service Providers Aggregate [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_RelatedPartiesTotalMember" xlink:label="VSTA_RelatedPartiesTotalMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_RelatedPartiesTotalMember" xlink:to="VSTA_RelatedPartiesTotalMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_RelatedPartiesTotalMember_lbl" xml:lang="en-US">Related Parties [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_Warrant1Member" xlink:label="VSTA_Warrant1Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_Warrant1Member" xlink:to="VSTA_Warrant1Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_Warrant1Member_lbl" xml:lang="en-US">Warrant 1 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ClassOfWarrantOrRightAxis" xlink:label="us-gaap_ClassOfWarrantOrRightAxis" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ClassOfWarrantOrRightAxis" xlink:to="us-gaap_ClassOfWarrantOrRightAxis_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ClassOfWarrantOrRightAxis_lbl" xml:lang="en-US">Class of Warrant or Right [Axis]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_Warrant2Member" xlink:label="VSTA_Warrant2Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_Warrant2Member" xlink:to="VSTA_Warrant2Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_Warrant2Member_lbl" xml:lang="en-US">Warrant 2 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_Warrant3Member" xlink:label="VSTA_Warrant3Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_Warrant3Member" xlink:to="VSTA_Warrant3Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_Warrant3Member_lbl" xml:lang="en-US">Warrant 3 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_Warrant4Member" xlink:label="VSTA_Warrant4Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_Warrant4Member" xlink:to="VSTA_Warrant4Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_Warrant4Member_lbl" xml:lang="en-US">Warrant 4 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_Warrant5Member" xlink:label="VSTA_Warrant5Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_Warrant5Member" xlink:to="VSTA_Warrant5Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_Warrant5Member_lbl" xml:lang="en-US">Warrant 5 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_Warrant6Member" xlink:label="VSTA_Warrant6Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_Warrant6Member" xlink:to="VSTA_Warrant6Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_Warrant6Member_lbl" xml:lang="en-US">Warrant 6 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_Warrant7Member" xlink:label="VSTA_Warrant7Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_Warrant7Member" xlink:to="VSTA_Warrant7Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_Warrant7Member_lbl" xml:lang="en-US">Warrant 7 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_Warrant8Member" xlink:label="VSTA_Warrant8Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_Warrant8Member" xlink:to="VSTA_Warrant8Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_Warrant8Member_lbl" xml:lang="en-US">Warrant 8 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_Warrant9Member" xlink:label="VSTA_Warrant9Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_Warrant9Member" xlink:to="VSTA_Warrant9Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_Warrant9Member_lbl" xml:lang="en-US">Warrant 9 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_Warrant10Member" xlink:label="VSTA_Warrant10Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_Warrant10Member" xlink:to="VSTA_Warrant10Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_Warrant10Member_lbl" xml:lang="en-US">Warrant 10 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_Warrant11Member" xlink:label="VSTA_Warrant11Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_Warrant11Member" xlink:to="VSTA_Warrant11Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_Warrant11Member_lbl" xml:lang="en-US">Warrant 11 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_Warrant12Member" xlink:label="VSTA_Warrant12Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_Warrant12Member" xlink:to="VSTA_Warrant12Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_Warrant12Member_lbl" xml:lang="en-US">Warrant 12 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_Warrant13Member" xlink:label="VSTA_Warrant13Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_Warrant13Member" xlink:to="VSTA_Warrant13Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_Warrant13Member_lbl" xml:lang="en-US">Warrant 13 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_WarrantModificationMember" xlink:label="VSTA_WarrantModificationMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_WarrantModificationMember" xlink:to="VSTA_WarrantModificationMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_WarrantModificationMember_lbl" xml:lang="en-US">Warrant Modification [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:label="us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:to="us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_lbl" xml:lang="en-US">Equity Method Investee, Name [Axis]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_PlatinumModificationsMember" xlink:label="VSTA_PlatinumModificationsMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PlatinumModificationsMember" xlink:to="VSTA_PlatinumModificationsMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PlatinumModificationsMember_lbl" xml:lang="en-US">Platinum Modifications [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_PrivatePlacement2013Member" xlink:label="VSTA_PrivatePlacement2013Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PrivatePlacement2013Member" xlink:to="VSTA_PrivatePlacement2013Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PrivatePlacement2013Member_lbl" xml:lang="en-US">2013 Private Placement [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_Note3Member" xlink:label="VSTA_Note3Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_Note3Member" xlink:to="VSTA_Note3Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_Note3Member_lbl" xml:lang="en-US">Note 3 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_Note4Member" xlink:label="VSTA_Note4Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_Note4Member" xlink:to="VSTA_Note4Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_Note4Member_lbl" xml:lang="en-US">Note 4 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_USNIHMember" xlink:label="VSTA_USNIHMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_USNIHMember" xlink:to="VSTA_USNIHMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_USNIHMember_lbl" xml:lang="en-US">US NIH [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="us-gaap_TypeOfArrangementAxis" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TypeOfArrangementAxis" xlink:to="us-gaap_TypeOfArrangementAxis_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_TypeOfArrangementAxis_lbl" xml:lang="en-US">Type of Arrangement and Non-arrangement Transactions [Axis]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_UHNMember" xlink:label="VSTA_UHNMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_UHNMember" xlink:to="VSTA_UHNMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_UHNMember_lbl" xml:lang="en-US">UHN [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_CatoMember" xlink:label="VSTA_CatoMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CatoMember" xlink:to="VSTA_CatoMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CatoMember_lbl" xml:lang="en-US">Cato [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_CBVNoteMember" xlink:label="VSTA_CBVNoteMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CBVNoteMember" xlink:to="VSTA_CBVNoteMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CBVNoteMember_lbl" xml:lang="en-US">CBV Note [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_CRLNoteMember" xlink:label="VSTA_CRLNoteMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CRLNoteMember" xlink:to="VSTA_CRLNoteMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CRLNoteMember_lbl" xml:lang="en-US">CRL Note [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OfficerMember" xlink:label="us-gaap_OfficerMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OfficerMember" xlink:to="us-gaap_OfficerMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OfficerMember_lbl" xml:lang="en-US">Officer [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SubsequentEventMember" xlink:label="us-gaap_SubsequentEventMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SubsequentEventMember" xlink:to="us-gaap_SubsequentEventMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_SubsequentEventMember_lbl" xml:lang="en-US">Subsequent Event [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="us-gaap_SubsequentEventTypeAxis" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SubsequentEventTypeAxis" xlink:to="us-gaap_SubsequentEventTypeAxis_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_SubsequentEventTypeAxis_lbl" xml:lang="en-US">Subsequent Event Type [Axis]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_WarrantMember" xlink:label="us-gaap_WarrantMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_WarrantMember" xlink:to="us-gaap_WarrantMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_WarrantMember_lbl" xml:lang="en-US">Warrant [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_SeniorNote6Member" xlink:label="VSTA_SeniorNote6Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SeniorNote6Member" xlink:to="VSTA_SeniorNote6Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SeniorNote6Member_lbl" xml:lang="en-US">Senior Note 6 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_TenPercentNotesMember" xlink:label="VSTA_TenPercentNotesMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_TenPercentNotesMember" xlink:to="VSTA_TenPercentNotesMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_TenPercentNotesMember_lbl" xml:lang="en-US">Ten Percent Note [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_AutilionAGMember" xlink:label="VSTA_AutilionAGMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AutilionAGMember" xlink:to="VSTA_AutilionAGMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AutilionAGMember_lbl" xml:lang="en-US">Autilion AG [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_PlatinumModificationSeriesAMember" xlink:label="VSTA_PlatinumModificationSeriesAMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PlatinumModificationSeriesAMember" xlink:to="VSTA_PlatinumModificationSeriesAMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PlatinumModificationSeriesAMember_lbl" xml:lang="en-US">Platinum Mod Series A [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_PlatinumModificationRangeHighMember" xlink:label="VSTA_PlatinumModificationRangeHighMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PlatinumModificationRangeHighMember" xlink:to="VSTA_PlatinumModificationRangeHighMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PlatinumModificationRangeHighMember_lbl" xml:lang="en-US">Range High [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_PlatinumModificationRangeLowMember" xlink:label="VSTA_PlatinumModificationRangeLowMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PlatinumModificationRangeLowMember" xlink:to="VSTA_PlatinumModificationRangeLowMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PlatinumModificationRangeLowMember_lbl" xml:lang="en-US">Range Low [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ConvertibleNoteJulyMember" xlink:label="VSTA_ConvertibleNoteJulyMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConvertibleNoteJulyMember" xlink:to="VSTA_ConvertibleNoteJulyMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConvertibleNoteJulyMember_lbl" xml:lang="en-US">ConvertibleNoteJuly [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_PreMod2Member" xlink:label="VSTA_PreMod2Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PreMod2Member" xlink:to="VSTA_PreMod2Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PreMod2Member_lbl" xml:lang="en-US">PreModification 2 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_PostMod2Member" xlink:label="VSTA_PostMod2Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PostMod2Member" xlink:to="VSTA_PostMod2Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PostMod2Member_lbl" xml:lang="en-US">PostModification 2 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_PreMod3Member" xlink:label="VSTA_PreMod3Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PreMod3Member" xlink:to="VSTA_PreMod3Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PreMod3Member_lbl" xml:lang="en-US">PreModification 3 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_PostMod3Member" xlink:label="VSTA_PostMod3Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PostMod3Member" xlink:to="VSTA_PostMod3Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PostMod3Member_lbl" xml:lang="en-US">PostModification 3 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PreferredStockMember" xlink:label="us-gaap_PreferredStockMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PreferredStockMember" xlink:to="us-gaap_PreferredStockMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PreferredStockMember_lbl" xml:lang="en-US">Preferred Stock [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CommonStockMember" xlink:label="us-gaap_CommonStockMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockMember" xlink:to="us-gaap_CommonStockMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CommonStockMember_lbl" xml:lang="en-US">Common Stock</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AdditionalPaidInCapitalMember" xlink:label="us-gaap_AdditionalPaidInCapitalMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AdditionalPaidInCapitalMember" xlink:to="us-gaap_AdditionalPaidInCapitalMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AdditionalPaidInCapitalMember_lbl" xml:lang="en-US">Additional Paid-In Capital</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_TreasuryStockMember" xlink:label="us-gaap_TreasuryStockMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TreasuryStockMember" xlink:to="us-gaap_TreasuryStockMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_TreasuryStockMember_lbl" xml:lang="en-US">Treasury Stock</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NotesReceivableMember" xlink:label="us-gaap_NotesReceivableMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NotesReceivableMember" xlink:to="us-gaap_NotesReceivableMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NotesReceivableMember_lbl" xml:lang="en-US">Notes Receivable for Sale of Stock</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccumulatedDeficitDuringDevelopmentStageMember" xlink:label="us-gaap_AccumulatedDeficitDuringDevelopmentStageMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccumulatedDeficitDuringDevelopmentStageMember" xlink:to="us-gaap_AccumulatedDeficitDuringDevelopmentStageMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AccumulatedDeficitDuringDevelopmentStageMember_lbl" xml:lang="en-US">Deficit Accumulated During the Development Stage</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_PlatinumExchangeNotesMember" xlink:label="VSTA_PlatinumExchangeNotesMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PlatinumExchangeNotesMember" xlink:to="VSTA_PlatinumExchangeNotesMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PlatinumExchangeNotesMember_lbl" xml:lang="en-US">PlatinumExchangeNotes [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_PlatinumJuly2013NoteMember" xlink:label="VSTA_PlatinumJuly2013NoteMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PlatinumJuly2013NoteMember" xlink:to="VSTA_PlatinumJuly2013NoteMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PlatinumJuly2013NoteMember_lbl" xml:lang="en-US">PlatinumJuly2013Note [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_PrivatePlacementNotesMember" xlink:label="VSTA_PrivatePlacementNotesMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PrivatePlacementNotesMember" xlink:to="VSTA_PrivatePlacementNotesMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PrivatePlacementNotesMember_lbl" xml:lang="en-US">PrivatePlacementNotes [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_AntidilutiveNotes1Member" xlink:label="VSTA_AntidilutiveNotes1Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AntidilutiveNotes1Member" xlink:to="VSTA_AntidilutiveNotes1Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AntidilutiveNotes1Member_lbl" xml:lang="en-US">AntidilutiveNotes1 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_AntidilutiveNotes2Member" xlink:label="VSTA_AntidilutiveNotes2Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AntidilutiveNotes2Member" xlink:to="VSTA_AntidilutiveNotes2Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AntidilutiveNotes2Member_lbl" xml:lang="en-US">AntidilutiveNotes2 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_AntidilutiveNotes3Member" xlink:label="VSTA_AntidilutiveNotes3Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AntidilutiveNotes3Member" xlink:to="VSTA_AntidilutiveNotes3Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AntidilutiveNotes3Member_lbl" xml:lang="en-US">AntidilutiveNotes3 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_AV101Member" xlink:label="VSTA_AV101Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AV101Member" xlink:to="VSTA_AV101Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AV101Member_lbl" xml:lang="en-US">AV 101 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis" xlink:label="us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis" xlink:to="us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis_lbl" xml:lang="en-US">Significant Acquisitions and Disposals by Transaction [Axis]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_DiscountNote1Member" xlink:label="VSTA_DiscountNote1Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_DiscountNote1Member" xlink:to="VSTA_DiscountNote1Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_DiscountNote1Member_lbl" xml:lang="en-US">DiscountNote1 [Member]</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentAxis" xlink:to="us-gaap_DebtInstrumentAxis_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_DebtInstrumentAxis_2_lbl" xml:lang="en-US">Schedule of Receivables with Imputed Interest, Name of Receivable with Imputed Interest [Axis]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_DiscountNote2Member" xlink:label="VSTA_DiscountNote2Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_DiscountNote2Member" xlink:to="VSTA_DiscountNote2Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_DiscountNote2Member_lbl" xml:lang="en-US">DiscountNote2 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_DiscountNote3Member" xlink:label="VSTA_DiscountNote3Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_DiscountNote3Member" xlink:to="VSTA_DiscountNote3Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_DiscountNote3Member_lbl" xml:lang="en-US">DiscountNote3 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_DiscountNote4Member" xlink:label="VSTA_DiscountNote4Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_DiscountNote4Member" xlink:to="VSTA_DiscountNote4Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_DiscountNote4Member_lbl" xml:lang="en-US">DiscountNote4 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_DiscountNote5Member" xlink:label="VSTA_DiscountNote5Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_DiscountNote5Member" xlink:to="VSTA_DiscountNote5Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_DiscountNote5Member_lbl" xml:lang="en-US">DiscountNote5 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_DiscountNote6Member" xlink:label="VSTA_DiscountNote6Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_DiscountNote6Member" xlink:to="VSTA_DiscountNote6Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_DiscountNote6Member_lbl" xml:lang="en-US">DiscountNote6 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_PreModification4Member" xlink:label="VSTA_PreModification4Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PreModification4Member" xlink:to="VSTA_PreModification4Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PreModification4Member_lbl" xml:lang="en-US">PreModification4 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_PostModification4Member" xlink:label="VSTA_PostModification4Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PostModification4Member" xlink:to="VSTA_PostModification4Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PostModification4Member_lbl" xml:lang="en-US">PostModification4 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_PreModification5Member" xlink:label="VSTA_PreModification5Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PreModification5Member" xlink:to="VSTA_PreModification5Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PreModification5Member_lbl" xml:lang="en-US">PreModification5Member</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_PostModification5Member" xlink:label="VSTA_PostModification5Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PostModification5Member" xlink:to="VSTA_PostModification5Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PostModification5Member_lbl" xml:lang="en-US">PostModification5Member</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_StockPlan2008Member" xlink:label="VSTA_StockPlan2008Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockPlan2008Member" xlink:to="VSTA_StockPlan2008Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_StockPlan2008Member_lbl" xml:lang="en-US">Stock Plan 2008 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ShareBasedCompensationAxis" xlink:label="VSTA_ShareBasedCompensationAxis" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationAxis" xlink:to="VSTA_ShareBasedCompensationAxis_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ShareBasedCompensationAxis_lbl" xml:lang="en-US">Share Based Compensation [Axis]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_StockPlan1999Member" xlink:label="VSTA_StockPlan1999Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockPlan1999Member" xlink:to="VSTA_StockPlan1999Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_StockPlan1999Member_lbl" xml:lang="en-US">Stock Plan 1999 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_Plan401kMember" xlink:label="VSTA_Plan401kMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_Plan401kMember" xlink:to="VSTA_Plan401kMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_Plan401kMember_lbl" xml:lang="en-US">Plan 401k [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_Price0.40Member" xlink:label="VSTA_Price0.40Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_Price0.40Member" xlink:to="VSTA_Price0.40Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_Price0.40Member_lbl" xml:lang="en-US">$0.40 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis" xlink:label="us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis" xlink:to="us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis_lbl" xml:lang="en-US">Exercise Price Range [Axis]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_Price0.50Member" xlink:label="VSTA_Price0.50Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_Price0.50Member" xlink:to="VSTA_Price0.50Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_Price0.50Member_lbl" xml:lang="en-US">$0.50 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_Price.721.8Member" xlink:label="VSTA_Price.721.8Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_Price.721.8Member" xlink:to="VSTA_Price.721.8Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_Price.721.8Member_lbl" xml:lang="en-US">$0.72 - $1.80 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_Price.721.80Member" xlink:label="VSTA_Price.721.80Member" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_Price.721.80Member" xlink:to="VSTA_Price.721.80Member_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="VSTA_Price.721.80Member_lbl" xml:lang="en-US">$0.72 - $1.80 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SeriesBPreferredStockMember" xlink:label="us-gaap_SeriesBPreferredStockMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SeriesBPreferredStockMember" xlink:to="us-gaap_SeriesBPreferredStockMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_SeriesBPreferredStockMember_lbl" xml:lang="en-US">Series B Preferred</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_SeriesB1PreferredStockMember" xlink:label="VSTA_SeriesB1PreferredStockMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SeriesB1PreferredStockMember" xlink:to="VSTA_SeriesB1PreferredStockMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SeriesB1PreferredStockMember_lbl" xml:lang="en-US">Series B-1 Preferred</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SeriesCPreferredStockMember" xlink:label="us-gaap_SeriesCPreferredStockMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SeriesCPreferredStockMember" xlink:to="us-gaap_SeriesCPreferredStockMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_SeriesCPreferredStockMember_lbl" xml:lang="en-US">Series C Preferred</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PreferredStockMember" xlink:to="us-gaap_PreferredStockMember_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_PreferredStockMember_2_lbl" xml:lang="en-US">Preferred Stock</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_NotesReceivableSaleStockMember" xlink:label="VSTA_NotesReceivableSaleStockMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesReceivableSaleStockMember" xlink:to="VSTA_NotesReceivableSaleStockMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NotesReceivableSaleStockMember_lbl" xml:lang="en-US">Notes Receivable from Sale of Stock</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_SeniorNoteSixMember" xlink:label="VSTA_SeniorNoteSixMember" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SeniorNoteSixMember" xlink:to="VSTA_SeniorNoteSixMember_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="VSTA_SeniorNoteSixMember_lbl" xml:lang="en-US">Senior Note 6 [Member]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_DocumentAndEntityInformationAbstract" xlink:label="VSTA_DocumentAndEntityInformationAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_DocumentAndEntityInformationAbstract" xlink:to="VSTA_DocumentAndEntityInformationAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_DocumentAndEntityInformationAbstract_lbl" xml:lang="en-US">Document And Entity Information</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_EntityRegistrantName" xlink:label="dei_EntityRegistrantName" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityRegistrantName" xlink:to="dei_EntityRegistrantName_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_EntityRegistrantName_lbl" xml:lang="en-US">Entity Registrant Name</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_EntityCentralIndexKey" xlink:label="dei_EntityCentralIndexKey" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityCentralIndexKey" xlink:to="dei_EntityCentralIndexKey_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_EntityCentralIndexKey_lbl" xml:lang="en-US">Entity Central Index Key</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_DocumentType" xlink:label="dei_DocumentType" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_DocumentType" xlink:to="dei_DocumentType_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_DocumentType_lbl" xml:lang="en-US">Document Type</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_DocumentPeriodEndDate" xlink:label="dei_DocumentPeriodEndDate" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_DocumentPeriodEndDate" xlink:to="dei_DocumentPeriodEndDate_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_DocumentPeriodEndDate_lbl" xml:lang="en-US">Document Period End Date</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_AmendmentFlag" xlink:label="dei_AmendmentFlag" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_AmendmentFlag" xlink:to="dei_AmendmentFlag_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_AmendmentFlag_lbl" xml:lang="en-US">Amendment Flag</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_CurrentFiscalYearEndDate" xlink:label="dei_CurrentFiscalYearEndDate" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_CurrentFiscalYearEndDate" xlink:to="dei_CurrentFiscalYearEndDate_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_CurrentFiscalYearEndDate_lbl" xml:lang="en-US">Current Fiscal Year End Date</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_EntityWellKnownSeasonedIssuer" xlink:label="dei_EntityWellKnownSeasonedIssuer" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityWellKnownSeasonedIssuer" xlink:to="dei_EntityWellKnownSeasonedIssuer_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_EntityWellKnownSeasonedIssuer_lbl" xml:lang="en-US">Is Entity a Well-known Seasoned Issuer?</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_EntityVoluntaryFilers" xlink:label="dei_EntityVoluntaryFilers" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityVoluntaryFilers" xlink:to="dei_EntityVoluntaryFilers_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_EntityVoluntaryFilers_lbl" xml:lang="en-US">Is Entity a Voluntary Filer?</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_EntityCurrentReportingStatus" xlink:label="dei_EntityCurrentReportingStatus" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityCurrentReportingStatus" xlink:to="dei_EntityCurrentReportingStatus_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_EntityCurrentReportingStatus_lbl" xml:lang="en-US">Is Entity's Reporting Status Current?</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_EntityFilerCategory" xlink:label="dei_EntityFilerCategory" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityFilerCategory" xlink:to="dei_EntityFilerCategory_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_EntityFilerCategory_lbl" xml:lang="en-US">Entity Filer Category</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_EntityPublicFloat" xlink:label="dei_EntityPublicFloat" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityPublicFloat" xlink:to="dei_EntityPublicFloat_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_EntityPublicFloat_lbl" xml:lang="en-US">Entity Public Float</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_EntityCommonStockSharesOutstanding" xlink:label="dei_EntityCommonStockSharesOutstanding" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityCommonStockSharesOutstanding" xlink:to="dei_EntityCommonStockSharesOutstanding_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_EntityCommonStockSharesOutstanding_lbl" xml:lang="en-US">Entity Common Stock, Shares Outstanding</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_DocumentFiscalPeriodFocus" xlink:label="dei_DocumentFiscalPeriodFocus" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_DocumentFiscalPeriodFocus" xlink:to="dei_DocumentFiscalPeriodFocus_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_DocumentFiscalPeriodFocus_lbl" xml:lang="en-US">Document Fiscal Period Focus</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2013/dei-2013-01-31.xsd#dei_DocumentFiscalYearFocus" xlink:label="dei_DocumentFiscalYearFocus" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_DocumentFiscalYearFocus" xlink:to="dei_DocumentFiscalYearFocus_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_DocumentFiscalYearFocus_lbl" xml:lang="en-US">Document Fiscal Year Focus</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementOfFinancialPositionAbstract" xlink:label="us-gaap_StatementOfFinancialPositionAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementOfFinancialPositionAbstract" xlink:to="us-gaap_StatementOfFinancialPositionAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_StatementOfFinancialPositionAbstract_lbl" xml:lang="en-US">Statement of Financial Position [Abstract]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AssetsAbstract" xlink:label="us-gaap_AssetsAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AssetsAbstract" xlink:to="us-gaap_AssetsAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AssetsAbstract_lbl" xml:lang="en-US">ASSETS</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AssetsCurrentAbstract" xlink:label="us-gaap_AssetsCurrentAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AssetsCurrentAbstract" xlink:to="us-gaap_AssetsCurrentAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AssetsCurrentAbstract_lbl" xml:lang="en-US">Current assets:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:to="us-gaap_CashAndCashEquivalentsAtCarryingValue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue_lbl" xml:lang="en-US">Cash and cash equivalents</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PrepaidExpenseCurrent" xlink:label="us-gaap_PrepaidExpenseCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PrepaidExpenseCurrent" xlink:to="us-gaap_PrepaidExpenseCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PrepaidExpenseCurrent_lbl" xml:lang="en-US">Prepaid expenses and other current assets</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AssetsCurrent" xlink:label="us-gaap_AssetsCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AssetsCurrent" xlink:to="us-gaap_AssetsCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_AssetsCurrent_lbl" xml:lang="en-US">Total current assets</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="us-gaap_PropertyPlantAndEquipmentNet" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PropertyPlantAndEquipmentNet" xlink:to="us-gaap_PropertyPlantAndEquipmentNet_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PropertyPlantAndEquipmentNet_lbl" xml:lang="en-US">Property and equipment, net</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherAssetsNoncurrent" xlink:label="us-gaap_OtherAssetsNoncurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherAssetsNoncurrent" xlink:to="us-gaap_OtherAssetsNoncurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OtherAssetsNoncurrent_lbl" xml:lang="en-US">Security deposits and other assets</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_Assets" xlink:label="us-gaap_Assets" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_Assets" xlink:to="us-gaap_Assets_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_Assets_lbl" xml:lang="en-US">Total assets</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:label="us-gaap_LiabilitiesAndStockholdersEquityAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:to="us-gaap_LiabilitiesAndStockholdersEquityAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LiabilitiesAndStockholdersEquityAbstract_lbl" xml:lang="en-US">LIABILITIES AND STOCKHOLDERS' DEFICIT</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LiabilitiesCurrentAbstract" xlink:label="us-gaap_LiabilitiesCurrentAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesCurrentAbstract" xlink:to="us-gaap_LiabilitiesCurrentAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LiabilitiesCurrentAbstract_lbl" xml:lang="en-US">Current liabilities:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccountsPayableCurrent" xlink:label="us-gaap_AccountsPayableCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccountsPayableCurrent" xlink:to="us-gaap_AccountsPayableCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AccountsPayableCurrent_lbl" xml:lang="en-US">Accounts payable</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccruedLiabilitiesCurrent" xlink:label="us-gaap_AccruedLiabilitiesCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccruedLiabilitiesCurrent" xlink:to="us-gaap_AccruedLiabilitiesCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AccruedLiabilitiesCurrent_lbl" xml:lang="en-US">Accrued expenses</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DueToRelatedPartiesCurrent" xlink:label="us-gaap_DueToRelatedPartiesCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DueToRelatedPartiesCurrent" xlink:to="us-gaap_DueToRelatedPartiesCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DueToRelatedPartiesCurrent_lbl" xml:lang="en-US">Advance from officer</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NotesAndLoansPayableCurrent" xlink:label="us-gaap_NotesAndLoansPayableCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NotesAndLoansPayableCurrent" xlink:to="us-gaap_NotesAndLoansPayableCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NotesAndLoansPayableCurrent_lbl" xml:lang="en-US">Current portion of notes payable and accrued interest</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_NotesPayableAndAccruedInterestToRelatedParties" xlink:label="VSTA_NotesPayableAndAccruedInterestToRelatedParties" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesPayableAndAccruedInterestToRelatedParties" xlink:to="VSTA_NotesPayableAndAccruedInterestToRelatedParties_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NotesPayableAndAccruedInterestToRelatedParties_lbl" xml:lang="en-US">Current portion of notes payable to related parties and accrued interest</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ConvertibleNotesPayableCurrent" xlink:label="us-gaap_ConvertibleNotesPayableCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ConvertibleNotesPayableCurrent" xlink:to="us-gaap_ConvertibleNotesPayableCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ConvertibleNotesPayableCurrent_lbl" xml:lang="en-US">Convertible promissory notes and accrued interest, net of discount of $697,400 at March 31, 2014</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CapitalLeaseObligationsCurrent" xlink:label="us-gaap_CapitalLeaseObligationsCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalLeaseObligationsCurrent" xlink:to="us-gaap_CapitalLeaseObligationsCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CapitalLeaseObligationsCurrent_lbl" xml:lang="en-US">Capital lease obligations</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LiabilitiesCurrent" xlink:label="us-gaap_LiabilitiesCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesCurrent" xlink:to="us-gaap_LiabilitiesCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_LiabilitiesCurrent_lbl" xml:lang="en-US">Total current liabilities</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LiabilitiesNoncurrentAbstract" xlink:label="us-gaap_LiabilitiesNoncurrentAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesNoncurrentAbstract" xlink:to="us-gaap_LiabilitiesNoncurrentAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LiabilitiesNoncurrentAbstract_lbl" xml:lang="en-US">Non-current liabilities:</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_SeniorSecuredConvertiblePromisoryNotesAndAccruedInterest" xlink:label="VSTA_SeniorSecuredConvertiblePromisoryNotesAndAccruedInterest" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SeniorSecuredConvertiblePromisoryNotesAndAccruedInterest" xlink:to="VSTA_SeniorSecuredConvertiblePromisoryNotesAndAccruedInterest_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SeniorSecuredConvertiblePromisoryNotesAndAccruedInterest_lbl" xml:lang="en-US">Senior secured convertible promissory notes, net of discount of $2,085,900 at March 31, 2014 and $1,963,100 at March 31, 2013 and accrued interest</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_NotesPayableAndAccruedInterest" xlink:label="VSTA_NotesPayableAndAccruedInterest" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesPayableAndAccruedInterest" xlink:to="VSTA_NotesPayableAndAccruedInterest_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NotesPayableAndAccruedInterest_lbl" xml:lang="en-US">Notes payable, net of discount of $848,100 at March 31, 2014 and $1,142,600 at March 31, 2013 and accrued interest</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_NotesPayableAndAccruedInterestToRelatedPartiesNonCurrent" xlink:label="VSTA_NotesPayableAndAccruedInterestToRelatedPartiesNonCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesPayableAndAccruedInterestToRelatedPartiesNonCurrent" xlink:to="VSTA_NotesPayableAndAccruedInterestToRelatedPartiesNonCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NotesPayableAndAccruedInterestToRelatedPartiesNonCurrent_lbl" xml:lang="en-US">Notes payable to related parties, net of discount of $103,200 at March 31, 2014 and $147,200 at March 31, 2013 and accrued interest</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccountsPayableAndAccruedLiabilitiesNoncurrent" xlink:label="us-gaap_AccountsPayableAndAccruedLiabilitiesNoncurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccountsPayableAndAccruedLiabilitiesNoncurrent" xlink:to="us-gaap_AccountsPayableAndAccruedLiabilitiesNoncurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AccountsPayableAndAccruedLiabilitiesNoncurrent_lbl" xml:lang="en-US">Warrant liability</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredRentCredit" xlink:label="us-gaap_DeferredRentCredit" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredRentCredit" xlink:to="us-gaap_DeferredRentCredit_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DeferredRentCredit_lbl" xml:lang="en-US">Deferred rent liability</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CapitalLeaseObligationsNoncurrent" xlink:label="us-gaap_CapitalLeaseObligationsNoncurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalLeaseObligationsNoncurrent" xlink:to="us-gaap_CapitalLeaseObligationsNoncurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_CapitalLeaseObligationsNoncurrent_lbl" xml:lang="en-US">Capital lease obligations</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LiabilitiesNoncurrent" xlink:label="us-gaap_LiabilitiesNoncurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesNoncurrent" xlink:to="us-gaap_LiabilitiesNoncurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_LiabilitiesNoncurrent_lbl" xml:lang="en-US">Total non-current liabilities</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_Liabilities" xlink:label="us-gaap_Liabilities" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_Liabilities" xlink:to="us-gaap_Liabilities_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_Liabilities_lbl" xml:lang="en-US">Total liabilities</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CommitmentsAndContingencies" xlink:label="us-gaap_CommitmentsAndContingencies" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommitmentsAndContingencies" xlink:to="us-gaap_CommitmentsAndContingencies_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CommitmentsAndContingencies_lbl" xml:lang="en-US">Commitments and contingencies</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockholdersEquityAbstract" xlink:label="us-gaap_StockholdersEquityAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockholdersEquityAbstract" xlink:to="us-gaap_StockholdersEquityAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_StockholdersEquityAbstract_lbl" xml:lang="en-US">Stockholders' deficit:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PreferredStockValue" xlink:label="us-gaap_PreferredStockValue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PreferredStockValue" xlink:to="us-gaap_PreferredStockValue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PreferredStockValue_lbl" xml:lang="en-US">Preferred stock, $0.001 par value; 10,000,000 shares, including 500,000 Series A shares, authorized at March 31, 2014 and 2013; 500,000 Series A shares issued and outstanding at March 31, 2014 and 2013, respectively</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CommonStockValue" xlink:label="us-gaap_CommonStockValue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockValue" xlink:to="us-gaap_CommonStockValue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CommonStockValue_lbl" xml:lang="en-US">Common stock, $0.001 par value; 200,000,000 shares authorized at March 31, 2014 and 2013; 26,200,185 and 23,480,169 shares issued at March 31, 2014 and 2013, respectively</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AdditionalPaidInCapital" xlink:label="us-gaap_AdditionalPaidInCapital" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AdditionalPaidInCapital" xlink:to="us-gaap_AdditionalPaidInCapital_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AdditionalPaidInCapital_lbl" xml:lang="en-US">Additional paid-in capital</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_TreasuryStockValue" xlink:label="us-gaap_TreasuryStockValue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TreasuryStockValue" xlink:to="us-gaap_TreasuryStockValue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="us-gaap_TreasuryStockValue_lbl" xml:lang="en-US">Treasury stock, at cost, 2,713,308 shares of common stock held at March 31, 2014 and 2013</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_NotesReceivableFromSaleOfCommonStockToOthers" xlink:label="VSTA_NotesReceivableFromSaleOfCommonStockToOthers" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesReceivableFromSaleOfCommonStockToOthers" xlink:to="VSTA_NotesReceivableFromSaleOfCommonStockToOthers_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NotesReceivableFromSaleOfCommonStockToOthers_lbl" xml:lang="en-US">Notes receivable from sale of common stock</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RetainedEarningsAccumulatedDeficit" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RetainedEarningsAccumulatedDeficit" xlink:to="us-gaap_RetainedEarningsAccumulatedDeficit_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit_lbl" xml:lang="en-US">Deficit accumulated during development stage</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockholdersEquity" xlink:label="us-gaap_StockholdersEquity" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockholdersEquity" xlink:to="us-gaap_StockholdersEquity_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_StockholdersEquity_lbl" xml:lang="en-US">Total stockholders' deficit</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquity" xlink:label="us-gaap_LiabilitiesAndStockholdersEquity" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesAndStockholdersEquity" xlink:to="us-gaap_LiabilitiesAndStockholdersEquity_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_LiabilitiesAndStockholdersEquity_lbl" xml:lang="en-US">Total liabilities and stockholders' deficit</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ConvertiblePromissoryNotesAndAccruedInterestNetOfDiscount" xlink:label="VSTA_ConvertiblePromissoryNotesAndAccruedInterestNetOfDiscount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConvertiblePromissoryNotesAndAccruedInterestNetOfDiscount" xlink:to="VSTA_ConvertiblePromissoryNotesAndAccruedInterestNetOfDiscount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConvertiblePromissoryNotesAndAccruedInterestNetOfDiscount_lbl" xml:lang="en-US">Convertible promissory notes and accrued interest, net of discount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_SeniorSecuredConvertibleNotesPayableDiscount" xlink:label="VSTA_SeniorSecuredConvertibleNotesPayableDiscount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SeniorSecuredConvertibleNotesPayableDiscount" xlink:to="VSTA_SeniorSecuredConvertibleNotesPayableDiscount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SeniorSecuredConvertibleNotesPayableDiscount_lbl" xml:lang="en-US">Senior secured convertible promissory notes, net of discount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_NotesPayableDiscount" xlink:label="VSTA_NotesPayableDiscount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesPayableDiscount" xlink:to="VSTA_NotesPayableDiscount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NotesPayableDiscount_lbl" xml:lang="en-US">Notes payable, net of discount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_NotesPayableDiscountRelatedParties" xlink:label="VSTA_NotesPayableDiscountRelatedParties" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesPayableDiscountRelatedParties" xlink:to="VSTA_NotesPayableDiscountRelatedParties_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NotesPayableDiscountRelatedParties_lbl" xml:lang="en-US">Notes payable to related parties, net of discount</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockholdersEquityAbstract" xlink:to="us-gaap_StockholdersEquityAbstract_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_StockholdersEquityAbstract_2_lbl" xml:lang="en-US">Stockholders deficit:</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_PreferredStockSeriesPerValue1" xlink:label="VSTA_PreferredStockSeriesPerValue1" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PreferredStockSeriesPerValue1" xlink:to="VSTA_PreferredStockSeriesPerValue1_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PreferredStockSeriesPerValue1_lbl" xml:lang="en-US">Preferred Stock, par value</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_PreferredStockSeriesASharesAuthorized" xlink:label="VSTA_PreferredStockSeriesASharesAuthorized" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PreferredStockSeriesASharesAuthorized" xlink:to="VSTA_PreferredStockSeriesASharesAuthorized_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PreferredStockSeriesASharesAuthorized_lbl" xml:lang="en-US">Preferred Stock, Authorized</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_PreferredStockSeriesASharesIssued" xlink:label="VSTA_PreferredStockSeriesASharesIssued" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PreferredStockSeriesASharesIssued" xlink:to="VSTA_PreferredStockSeriesASharesIssued_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PreferredStockSeriesASharesIssued_lbl" xml:lang="en-US">PreferredStockSeriesASharesIssued</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_PreferredStockSeriesASharesOutstanding" xlink:label="VSTA_PreferredStockSeriesASharesOutstanding" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PreferredStockSeriesASharesOutstanding" xlink:to="VSTA_PreferredStockSeriesASharesOutstanding_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PreferredStockSeriesASharesOutstanding_lbl" xml:lang="en-US">PreferredStockSeriesASharesOutstanding</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CommonStockParOrStatedValuePerShare" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockParOrStatedValuePerShare" xlink:to="us-gaap_CommonStockParOrStatedValuePerShare_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare_lbl" xml:lang="en-US">Common Stock, Par Value Par Share</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CommonStockSharesAuthorized" xlink:label="us-gaap_CommonStockSharesAuthorized" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockSharesAuthorized" xlink:to="us-gaap_CommonStockSharesAuthorized_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CommonStockSharesAuthorized_lbl" xml:lang="en-US">Common Stock, Shares Authorized</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CommonStockSharesIssued" xlink:label="us-gaap_CommonStockSharesIssued" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockSharesIssued" xlink:to="us-gaap_CommonStockSharesIssued_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CommonStockSharesIssued_lbl" xml:lang="en-US">Common Stock, Shares, Issued</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_TreasuryStockShares" xlink:label="us-gaap_TreasuryStockShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TreasuryStockShares" xlink:to="us-gaap_TreasuryStockShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_TreasuryStockShares_lbl" xml:lang="en-US">Treasury Stock, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeStatementAbstract" xlink:label="us-gaap_IncomeStatementAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeStatementAbstract" xlink:to="us-gaap_IncomeStatementAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_IncomeStatementAbstract_lbl" xml:lang="en-US">Income Statement [Abstract]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RevenuesAbstract" xlink:label="us-gaap_RevenuesAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RevenuesAbstract" xlink:to="us-gaap_RevenuesAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_RevenuesAbstract_lbl" xml:lang="en-US">Revenues:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RevenueFromGrants" xlink:label="us-gaap_RevenueFromGrants" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RevenueFromGrants" xlink:to="us-gaap_RevenueFromGrants_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_RevenueFromGrants_lbl" xml:lang="en-US">Grant revenue</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_RevenueFromExternalCustomers" xlink:label="VSTA_RevenueFromExternalCustomers" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_RevenueFromExternalCustomers" xlink:to="VSTA_RevenueFromExternalCustomers_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_RevenueFromExternalCustomers_lbl" xml:lang="en-US">Collaboration revenue</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherSalesRevenueNet" xlink:label="us-gaap_OtherSalesRevenueNet" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherSalesRevenueNet" xlink:to="us-gaap_OtherSalesRevenueNet_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OtherSalesRevenueNet_lbl" xml:lang="en-US">Other</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_Revenues" xlink:label="us-gaap_Revenues" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_Revenues" xlink:to="us-gaap_Revenues_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_Revenues_lbl" xml:lang="en-US">Total revenues</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OperatingExpensesAbstract" xlink:label="us-gaap_OperatingExpensesAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingExpensesAbstract" xlink:to="us-gaap_OperatingExpensesAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OperatingExpensesAbstract_lbl" xml:lang="en-US">Operating expenses:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ResearchAndDevelopmentExpenseExcludingAcquiredInProcessCost" xlink:label="us-gaap_ResearchAndDevelopmentExpenseExcludingAcquiredInProcessCost" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ResearchAndDevelopmentExpenseExcludingAcquiredInProcessCost" xlink:to="us-gaap_ResearchAndDevelopmentExpenseExcludingAcquiredInProcessCost_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ResearchAndDevelopmentExpenseExcludingAcquiredInProcessCost_lbl" xml:lang="en-US">Research and development</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ResearchAndDevelopmentInProcess" xlink:label="us-gaap_ResearchAndDevelopmentInProcess" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ResearchAndDevelopmentInProcess" xlink:to="us-gaap_ResearchAndDevelopmentInProcess_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ResearchAndDevelopmentInProcess_lbl" xml:lang="en-US">Acquired in-process research and development</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_GeneralAndAdministrativeExpense" xlink:label="us-gaap_GeneralAndAdministrativeExpense" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_GeneralAndAdministrativeExpense" xlink:to="us-gaap_GeneralAndAdministrativeExpense_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_GeneralAndAdministrativeExpense_lbl" xml:lang="en-US">General and administrative</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OperatingExpenses" xlink:label="us-gaap_OperatingExpenses" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingExpenses" xlink:to="us-gaap_OperatingExpenses_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_OperatingExpenses_lbl" xml:lang="en-US">Total operating expenses</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OperatingIncomeLoss" xlink:label="us-gaap_OperatingIncomeLoss" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingIncomeLoss" xlink:to="us-gaap_OperatingIncomeLoss_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_OperatingIncomeLoss_lbl" xml:lang="en-US">Loss from operations</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NonoperatingIncomeExpenseAbstract" xlink:label="us-gaap_NonoperatingIncomeExpenseAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NonoperatingIncomeExpenseAbstract" xlink:to="us-gaap_NonoperatingIncomeExpenseAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NonoperatingIncomeExpenseAbstract_lbl" xml:lang="en-US">Other expenses, net:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_InterestExpense" xlink:label="us-gaap_InterestExpense" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_InterestExpense" xlink:to="us-gaap_InterestExpense_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_InterestExpense_lbl" xml:lang="en-US">Interest expense, net</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ChangeInPutAndNoteExtensionOptionAndWarrantLiabilities" xlink:label="VSTA_ChangeInPutAndNoteExtensionOptionAndWarrantLiabilities" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ChangeInPutAndNoteExtensionOptionAndWarrantLiabilities" xlink:to="VSTA_ChangeInPutAndNoteExtensionOptionAndWarrantLiabilities_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="VSTA_ChangeInPutAndNoteExtensionOptionAndWarrantLiabilities_lbl" xml:lang="en-US">Change in warrant and put and note extension option liabilities</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_GainsLossesOnExtinguishmentOfDebt" xlink:label="us-gaap_GainsLossesOnExtinguishmentOfDebt" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_GainsLossesOnExtinguishmentOfDebt" xlink:to="us-gaap_GainsLossesOnExtinguishmentOfDebt_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_GainsLossesOnExtinguishmentOfDebt_lbl" xml:lang="en-US">Loss on early extinguishment of debt</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherIncome" xlink:label="us-gaap_OtherIncome" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherIncome" xlink:to="us-gaap_OtherIncome_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OtherIncome_lbl" xml:lang="en-US">Other income</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments" xlink:label="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments" xlink:to="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_lbl" xml:lang="en-US">Loss before income taxes</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeTaxExpenseBenefit" xlink:label="us-gaap_IncomeTaxExpenseBenefit" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeTaxExpenseBenefit" xlink:to="us-gaap_IncomeTaxExpenseBenefit_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="us-gaap_IncomeTaxExpenseBenefit_lbl" xml:lang="en-US">Income taxes</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetIncomeLoss" xlink:label="us-gaap_NetIncomeLoss" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetIncomeLoss" xlink:to="us-gaap_NetIncomeLoss_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_NetIncomeLoss_lbl" xml:lang="en-US">Net loss</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_Dividends" xlink:label="us-gaap_Dividends" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_Dividends" xlink:to="us-gaap_Dividends_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_Dividends_lbl" xml:lang="en-US">Deemed dividend on Series A Preferred stock</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic" xlink:label="us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic" xlink:to="us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_lbl" xml:lang="en-US">Net loss attributable to common stockholders</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EarningsPerShareBasic" xlink:label="us-gaap_EarningsPerShareBasic" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EarningsPerShareBasic" xlink:to="us-gaap_EarningsPerShareBasic_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_EarningsPerShareBasic_lbl" xml:lang="en-US">Basic net loss attributable to common stockholders per common share</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EarningsPerShareDiluted" xlink:label="us-gaap_EarningsPerShareDiluted" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EarningsPerShareDiluted" xlink:to="us-gaap_EarningsPerShareDiluted_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_EarningsPerShareDiluted_lbl" xml:lang="en-US">Diluted net loss attributable to common stockholders per common share</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic" xlink:to="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_lbl" xml:lang="en-US">Weighted average shares used in computing basic net loss attributable to common stockholders per common share</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" xlink:label="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" xlink:to="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_lbl" xml:lang="en-US">Weighted average shares used in computing diluted net loss attributable to common stockholders per common share</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ComprehensiveIncomeNetOfTax" xlink:label="us-gaap_ComprehensiveIncomeNetOfTax" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ComprehensiveIncomeNetOfTax" xlink:to="us-gaap_ComprehensiveIncomeNetOfTax_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ComprehensiveIncomeNetOfTax_lbl" xml:lang="en-US">Comprehensive loss</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementOfCashFlowsAbstract" xlink:label="us-gaap_StatementOfCashFlowsAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementOfCashFlowsAbstract" xlink:to="us-gaap_StatementOfCashFlowsAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_StatementOfCashFlowsAbstract_lbl" xml:lang="en-US">Statement of Cash Flows [Abstract]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xml:lang="en-US">Cash flows from operating activities:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProfitLoss" xlink:label="us-gaap_ProfitLoss" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProfitLoss" xlink:to="us-gaap_ProfitLoss_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ProfitLoss_lbl" xml:lang="en-US">Net loss</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:label="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xml:lang="en-US">Adjustments to reconcile net loss to net cash used in operating activities:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DepreciationAndAmortization" xlink:label="us-gaap_DepreciationAndAmortization" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DepreciationAndAmortization" xlink:to="us-gaap_DepreciationAndAmortization_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DepreciationAndAmortization_lbl" xml:lang="en-US">Depreciation and amortization</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AmortizationOfDebtDiscountPremium" xlink:label="us-gaap_AmortizationOfDebtDiscountPremium" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AmortizationOfDebtDiscountPremium" xlink:to="us-gaap_AmortizationOfDebtDiscountPremium_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AmortizationOfDebtDiscountPremium_lbl" xml:lang="en-US">Amortization of discounts on convertible and promissory notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ChangeInPutAndNoteTermExtensionOptionAndWarrantLiabilities" xlink:label="VSTA_ChangeInPutAndNoteTermExtensionOptionAndWarrantLiabilities" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ChangeInPutAndNoteTermExtensionOptionAndWarrantLiabilities" xlink:to="VSTA_ChangeInPutAndNoteTermExtensionOptionAndWarrantLiabilities_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ChangeInPutAndNoteTermExtensionOptionAndWarrantLiabilities_lbl" xml:lang="en-US">Change in warrant and put and note term extension option liabilities</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensation" xlink:label="us-gaap_ShareBasedCompensation" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensation" xlink:to="us-gaap_ShareBasedCompensation_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensation_lbl" xml:lang="en-US">Stock-based compensation</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ExpenseRelatedToModificationOfWarrants" xlink:label="VSTA_ExpenseRelatedToModificationOfWarrants" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExpenseRelatedToModificationOfWarrants" xlink:to="VSTA_ExpenseRelatedToModificationOfWarrants_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ExpenseRelatedToModificationOfWarrants_lbl" xml:lang="en-US">Expense related to modification of warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PaymentsForRestructuring" xlink:label="us-gaap_PaymentsForRestructuring" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PaymentsForRestructuring" xlink:to="us-gaap_PaymentsForRestructuring_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PaymentsForRestructuring_lbl" xml:lang="en-US">Non-cash rent and relocation expense</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_InterestIncomeOnNoteReceivableForStockPurchase" xlink:label="VSTA_InterestIncomeOnNoteReceivableForStockPurchase" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_InterestIncomeOnNoteReceivableForStockPurchase" xlink:to="VSTA_InterestIncomeOnNoteReceivableForStockPurchase_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_InterestIncomeOnNoteReceivableForStockPurchase_lbl" xml:lang="en-US">Interest income on note receivable for stock purchase</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_FairValueOfCommonStockGrantedForServicesFollowingMerger" xlink:label="VSTA_FairValueOfCommonStockGrantedForServicesFollowingMerger" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfCommonStockGrantedForServicesFollowingMerger" xlink:to="VSTA_FairValueOfCommonStockGrantedForServicesFollowingMerger_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfCommonStockGrantedForServicesFollowingMerger_lbl" xml:lang="en-US">Fair value of common stock granted for services following the Merger</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_FairValueOfWarrantsGrantedForServicesFollowingMerger" xlink:label="VSTA_FairValueOfWarrantsGrantedForServicesFollowingMerger" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfWarrantsGrantedForServicesFollowingMerger" xlink:to="VSTA_FairValueOfWarrantsGrantedForServicesFollowingMerger_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfWarrantsGrantedForServicesFollowingMerger_lbl" xml:lang="en-US">Fair value of warrants granted for services and interest following the Merger</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_LossGainOnCurrencyFluctuation" xlink:label="VSTA_LossGainOnCurrencyFluctuation" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_LossGainOnCurrencyFluctuation" xlink:to="VSTA_LossGainOnCurrencyFluctuation_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_LossGainOnCurrencyFluctuation_lbl" xml:lang="en-US">Gain on currency fluctuation</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_FairValueOfAdditionalWarrantsGrantedUnderDiscountedWarrantExerciseProgram" xlink:label="VSTA_FairValueOfAdditionalWarrantsGrantedUnderDiscountedWarrantExerciseProgram" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfAdditionalWarrantsGrantedUnderDiscountedWarrantExerciseProgram" xlink:to="VSTA_FairValueOfAdditionalWarrantsGrantedUnderDiscountedWarrantExerciseProgram_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfAdditionalWarrantsGrantedUnderDiscountedWarrantExerciseProgram_lbl" xml:lang="en-US">Fair value of additional warrants granted pursuant to exercises of modified warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_LossOnSettlementsOfAccountsPayable" xlink:label="VSTA_LossOnSettlementsOfAccountsPayable" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_LossOnSettlementsOfAccountsPayable" xlink:to="VSTA_LossOnSettlementsOfAccountsPayable_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_LossOnSettlementsOfAccountsPayable_lbl" xml:lang="en-US">Loss on settlements of accounts payable</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_LossOnEarlyExtinguishmentOfDebt" xlink:label="VSTA_LossOnEarlyExtinguishmentOfDebt" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_LossOnEarlyExtinguishmentOfDebt" xlink:to="VSTA_LossOnEarlyExtinguishmentOfDebt_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="VSTA_LossOnEarlyExtinguishmentOfDebt_lbl" xml:lang="en-US">Loss on early extinguishment of debt</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IssuanceOfStockAndWarrantsForServicesOrClaims" xlink:label="us-gaap_IssuanceOfStockAndWarrantsForServicesOrClaims" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IssuanceOfStockAndWarrantsForServicesOrClaims" xlink:to="us-gaap_IssuanceOfStockAndWarrantsForServicesOrClaims_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_IssuanceOfStockAndWarrantsForServicesOrClaims_lbl" xml:lang="en-US">Fair value of Series C preferred stock, common stock, and warrants granted for services prior to the Merger</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_FairValueOfCommonStockIssuedForNoteTermModification" xlink:label="VSTA_FairValueOfCommonStockIssuedForNoteTermModification" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfCommonStockIssuedForNoteTermModification" xlink:to="VSTA_FairValueOfCommonStockIssuedForNoteTermModification_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfCommonStockIssuedForNoteTermModification_lbl" xml:lang="en-US">Fair value of common stock issued for note term modification</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ConsultingServicesByRelatedPartiesSettledByIssuingPromissoryNotes" xlink:label="VSTA_ConsultingServicesByRelatedPartiesSettledByIssuingPromissoryNotes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConsultingServicesByRelatedPartiesSettledByIssuingPromissoryNotes" xlink:to="VSTA_ConsultingServicesByRelatedPartiesSettledByIssuingPromissoryNotes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConsultingServicesByRelatedPartiesSettledByIssuingPromissoryNotes_lbl" xml:lang="en-US">Consulting services by related parties settled by issuing promissory notes</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_GainLossOnSaleOfPropertyPlantEquipment" xlink:label="us-gaap_GainLossOnSaleOfPropertyPlantEquipment" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_GainLossOnSaleOfPropertyPlantEquipment" xlink:to="us-gaap_GainLossOnSaleOfPropertyPlantEquipment_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_GainLossOnSaleOfPropertyPlantEquipment_lbl" xml:lang="en-US">Gain on sale of assets</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:label="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract" xlink:to="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_IncreaseDecreaseInOperatingCapitalAbstract_lbl" xml:lang="en-US">Changes in operating assets and liabilities:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncreaseDecreaseInAccountsReceivable" xlink:label="us-gaap_IncreaseDecreaseInAccountsReceivable" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInAccountsReceivable" xlink:to="us-gaap_IncreaseDecreaseInAccountsReceivable_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_IncreaseDecreaseInAccountsReceivable_lbl" xml:lang="en-US">Unbilled contract payments receivable</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets" xlink:label="us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets" xlink:to="us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_lbl" xml:lang="en-US">Prepaid expenses and other current assets</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncreaseDecreaseInDepositOtherAssets" xlink:label="us-gaap_IncreaseDecreaseInDepositOtherAssets" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInDepositOtherAssets" xlink:to="us-gaap_IncreaseDecreaseInDepositOtherAssets_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_IncreaseDecreaseInDepositOtherAssets_lbl" xml:lang="en-US">Security deposits and other assets</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities" xlink:label="us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities" xlink:to="us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_IncreaseDecreaseInAccountsPayableAndAccruedLiabilities_lbl" xml:lang="en-US">Accounts payable and accrued expenses, including accrued interest</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncreaseDecreaseInDeferredRevenue" xlink:label="us-gaap_IncreaseDecreaseInDeferredRevenue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInDeferredRevenue" xlink:to="us-gaap_IncreaseDecreaseInDeferredRevenue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_IncreaseDecreaseInDeferredRevenue_lbl" xml:lang="en-US">Deferred revenues</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivities" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:to="us-gaap_NetCashProvidedByUsedInOperatingActivities_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivities_lbl" xml:lang="en-US">Net cash used in operating activities</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivitiesAbstract_lbl" xml:lang="en-US">Cash flows from investing activities:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PaymentsToAcquireMachineryAndEquipment" xlink:label="us-gaap_PaymentsToAcquireMachineryAndEquipment" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PaymentsToAcquireMachineryAndEquipment" xlink:to="us-gaap_PaymentsToAcquireMachineryAndEquipment_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="us-gaap_PaymentsToAcquireMachineryAndEquipment_lbl" xml:lang="en-US">Purchases of equipment, net</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivities" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivities" xlink:to="us-gaap_NetCashProvidedByUsedInInvestingActivities_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivities_lbl" xml:lang="en-US">Net cash used in investing activities</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesAbstract_lbl" xml:lang="en-US">Cash flows from financing activities:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProceedsFromIssuanceOfCommonStock" xlink:label="us-gaap_ProceedsFromIssuanceOfCommonStock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProceedsFromIssuanceOfCommonStock" xlink:to="us-gaap_ProceedsFromIssuanceOfCommonStock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ProceedsFromIssuanceOfCommonStock_lbl" xml:lang="en-US">Net proceeds from issuance of common stock and warrants, including Units</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ProceedsFromExerciseOfModifiedWarrantsMayjune2012AndUnderDiscountedWarrantExerciseProgram2011" xlink:label="VSTA_ProceedsFromExerciseOfModifiedWarrantsMayjune2012AndUnderDiscountedWarrantExerciseProgram2011" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProceedsFromExerciseOfModifiedWarrantsMayjune2012AndUnderDiscountedWarrantExerciseProgram2011" xlink:to="VSTA_ProceedsFromExerciseOfModifiedWarrantsMayjune2012AndUnderDiscountedWarrantExerciseProgram2011_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ProceedsFromExerciseOfModifiedWarrantsMayjune2012AndUnderDiscountedWarrantExerciseProgram2011_lbl" xml:lang="en-US">Proceeds from exercise of modified warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProceedsFromIssuanceOfDebt" xlink:label="us-gaap_ProceedsFromIssuanceOfDebt" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProceedsFromIssuanceOfDebt" xlink:to="us-gaap_ProceedsFromIssuanceOfDebt_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ProceedsFromIssuanceOfDebt_lbl" xml:lang="en-US">Proceeds from issuance of Platinum notes and warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProceedsFromRelatedPartyDebt" xlink:label="us-gaap_ProceedsFromRelatedPartyDebt" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProceedsFromRelatedPartyDebt" xlink:to="us-gaap_ProceedsFromRelatedPartyDebt_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_ProceedsFromRelatedPartyDebt_lbl" xml:lang="en-US">Advance from officer</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProceedsFromUnsecuredLinesOfCredit" xlink:label="us-gaap_ProceedsFromUnsecuredLinesOfCredit" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProceedsFromUnsecuredLinesOfCredit" xlink:to="us-gaap_ProceedsFromUnsecuredLinesOfCredit_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ProceedsFromUnsecuredLinesOfCredit_lbl" xml:lang="en-US">Proceeds from issuance of notes under line of credit</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ProceedsFromIssuanceOf7NotePayableToFoundingStockholder" xlink:label="VSTA_ProceedsFromIssuanceOf7NotePayableToFoundingStockholder" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProceedsFromIssuanceOf7NotePayableToFoundingStockholder" xlink:to="VSTA_ProceedsFromIssuanceOf7NotePayableToFoundingStockholder_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ProceedsFromIssuanceOf7NotePayableToFoundingStockholder_lbl" xml:lang="en-US">Proceeds from issuance of 7% note payable to founding stockholder</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_NetProceedsFromIssuanceOf7ConvertibleNotes" xlink:label="VSTA_NetProceedsFromIssuanceOf7ConvertibleNotes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NetProceedsFromIssuanceOf7ConvertibleNotes" xlink:to="VSTA_NetProceedsFromIssuanceOf7ConvertibleNotes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NetProceedsFromIssuanceOf7ConvertibleNotes_lbl" xml:lang="en-US">Net proceeds from issuance of 7% convertible notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_NetProceedsFromIssuanceOf10ConvertibleNotesAndWarrants" xlink:label="VSTA_NetProceedsFromIssuanceOf10ConvertibleNotesAndWarrants" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NetProceedsFromIssuanceOf10ConvertibleNotesAndWarrants" xlink:to="VSTA_NetProceedsFromIssuanceOf10ConvertibleNotesAndWarrants_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NetProceedsFromIssuanceOf10ConvertibleNotesAndWarrants_lbl" xml:lang="en-US">Net proceeds from issuance of 10% convertible notes and warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_NetProceedsFromIssuanceOfPlatinumNotesAndWarrants" xlink:label="VSTA_NetProceedsFromIssuanceOfPlatinumNotesAndWarrants" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NetProceedsFromIssuanceOfPlatinumNotesAndWarrants" xlink:to="VSTA_NetProceedsFromIssuanceOfPlatinumNotesAndWarrants_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NetProceedsFromIssuanceOfPlatinumNotesAndWarrants_lbl" xml:lang="en-US">Net proceeds from issuance of preferred stock and warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_NetProceedsFromIssuanceOf20062007NotesAndWarrants" xlink:label="VSTA_NetProceedsFromIssuanceOf20062007NotesAndWarrants" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NetProceedsFromIssuanceOf20062007NotesAndWarrants" xlink:to="VSTA_NetProceedsFromIssuanceOf20062007NotesAndWarrants_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NetProceedsFromIssuanceOf20062007NotesAndWarrants_lbl" xml:lang="en-US">Net proceeds from issuance of notes and warrants from 2006 to 2010</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_NetProceedsFromIssuanceOfFebruary201212ConvertibleNotesAndWarrants" xlink:label="VSTA_NetProceedsFromIssuanceOfFebruary201212ConvertibleNotesAndWarrants" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NetProceedsFromIssuanceOfFebruary201212ConvertibleNotesAndWarrants" xlink:to="VSTA_NetProceedsFromIssuanceOfFebruary201212ConvertibleNotesAndWarrants_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NetProceedsFromIssuanceOfFebruary201212ConvertibleNotesAndWarrants_lbl" xml:lang="en-US">Net proceeds from issuance of February 2012 12% convertible notes and warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RepaymentsOfLongTermCapitalLeaseObligations" xlink:label="us-gaap_RepaymentsOfLongTermCapitalLeaseObligations" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RepaymentsOfLongTermCapitalLeaseObligations" xlink:to="us-gaap_RepaymentsOfLongTermCapitalLeaseObligations_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_RepaymentsOfLongTermCapitalLeaseObligations_lbl" xml:lang="en-US">Repayment of capital lease obligations</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_RepaymentsOfNotesPayable" xlink:label="us-gaap_RepaymentsOfNotesPayable" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RepaymentsOfNotesPayable" xlink:to="us-gaap_RepaymentsOfNotesPayable_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_RepaymentsOfNotesPayable_lbl" xml:lang="en-US">Repayment of notes</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivities" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:to="us-gaap_NetCashProvidedByUsedInFinancingActivities_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivities_lbl" xml:lang="en-US">Net cash provided by financing activities</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease" xlink:label="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease" xlink:to="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease_lbl" xml:lang="en-US">Net (decrease) increase in cash and cash equivalents</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:to="us-gaap_CashAndCashEquivalentsAtCarryingValue_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue_2_lbl" xml:lang="en-US">Cash and cash equivalents at beginning of period</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:to="us-gaap_CashAndCashEquivalentsAtCarryingValue_3_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue_3_lbl" xml:lang="en-US">Cash and cash equivalents at end of period</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SupplementalCashFlowInformationAbstract" xlink:label="us-gaap_SupplementalCashFlowInformationAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SupplementalCashFlowInformationAbstract" xlink:to="us-gaap_SupplementalCashFlowInformationAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_SupplementalCashFlowInformationAbstract_lbl" xml:lang="en-US">Supplemental disclosure of cash flow activities:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_InterestPaid" xlink:label="us-gaap_InterestPaid" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_InterestPaid" xlink:to="us-gaap_InterestPaid_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_InterestPaid_lbl" xml:lang="en-US">Cash paid for interest</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeTaxesPaid" xlink:label="us-gaap_IncomeTaxesPaid" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeTaxesPaid" xlink:to="us-gaap_IncomeTaxesPaid_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_IncomeTaxesPaid_lbl" xml:lang="en-US">Cash paid for income taxes</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract" xlink:label="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract" xlink:to="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_lbl" xml:lang="en-US">Supplemental disclosure of noncash activities:</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ForgivenessOfAccruedCompensationAndAccruedInterestPayableToOfficersTransferredToEquity" xlink:label="VSTA_ForgivenessOfAccruedCompensationAndAccruedInterestPayableToOfficersTransferredToEquity" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ForgivenessOfAccruedCompensationAndAccruedInterestPayableToOfficersTransferredToEquity" xlink:to="VSTA_ForgivenessOfAccruedCompensationAndAccruedInterestPayableToOfficersTransferredToEquity_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ForgivenessOfAccruedCompensationAndAccruedInterestPayableToOfficersTransferredToEquity_lbl" xml:lang="en-US">Forgiveness of accrued compensation and accrued interest payable to officers transferred to equity</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ExerciseOfWarrantsAndOptionsInExchangeForDebtCancellation" xlink:label="VSTA_ExerciseOfWarrantsAndOptionsInExchangeForDebtCancellation" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExerciseOfWarrantsAndOptionsInExchangeForDebtCancellation" xlink:to="VSTA_ExerciseOfWarrantsAndOptionsInExchangeForDebtCancellation_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ExerciseOfWarrantsAndOptionsInExchangeForDebtCancellation_lbl" xml:lang="en-US">Exercise of warrants and options in exchange for debt cancellation</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_SettlementOfAccruedAndPrepaidInterestByIssuanceOfSeriesCPreferredStock" xlink:label="VSTA_SettlementOfAccruedAndPrepaidInterestByIssuanceOfSeriesCPreferredStock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SettlementOfAccruedAndPrepaidInterestByIssuanceOfSeriesCPreferredStock" xlink:to="VSTA_SettlementOfAccruedAndPrepaidInterestByIssuanceOfSeriesCPreferredStock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SettlementOfAccruedAndPrepaidInterestByIssuanceOfSeriesCPreferredStock_lbl" xml:lang="en-US">Settlement of accrued and prepaid interest by issuance of Series C Preferred Stock</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ConversionOf10NotesPayableNetOfDiscountAndRelatedAccruedInterestOf408600IntoSeriesCPreferredStock" xlink:label="VSTA_ConversionOf10NotesPayableNetOfDiscountAndRelatedAccruedInterestOf408600IntoSeriesCPreferredStock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConversionOf10NotesPayableNetOfDiscountAndRelatedAccruedInterestOf408600IntoSeriesCPreferredStock" xlink:to="VSTA_ConversionOf10NotesPayableNetOfDiscountAndRelatedAccruedInterestOf408600IntoSeriesCPreferredStock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConversionOf10NotesPayableNetOfDiscountAndRelatedAccruedInterestOf408600IntoSeriesCPreferredStock_lbl" xml:lang="en-US">Conversion of 10% notes payable, net of discount, and related accrued interest of $408,600 into Series C Preferred stock</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_IssuanceOfSeriesB1PreferredStockForAcquiredInprocessResearchAndDevelopment" xlink:label="VSTA_IssuanceOfSeriesB1PreferredStockForAcquiredInprocessResearchAndDevelopment" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesB1PreferredStockForAcquiredInprocessResearchAndDevelopment" xlink:to="VSTA_IssuanceOfSeriesB1PreferredStockForAcquiredInprocessResearchAndDevelopment_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IssuanceOfSeriesB1PreferredStockForAcquiredInprocessResearchAndDevelopment_lbl" xml:lang="en-US">Issuance of Series B-1 Preferred stock for acquired in-process research and development</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities" xlink:label="us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities" xlink:to="us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_StockIssuedDuringPeriodValueConversionOfConvertibleSecurities_lbl" xml:lang="en-US">Conversion of 7% notes payable, net of discount, and related accrued interest of $3,800 into Series B Preferred stock</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DebtConversionOriginalDebtAmount1" xlink:label="us-gaap_DebtConversionOriginalDebtAmount1" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtConversionOriginalDebtAmount1" xlink:to="us-gaap_DebtConversionOriginalDebtAmount1_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DebtConversionOriginalDebtAmount1_lbl" xml:lang="en-US">Conversion of accounts payable into convertible promissory notes</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DebtConversionConvertedInstrumentAmount1" xlink:label="us-gaap_DebtConversionConvertedInstrumentAmount1" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtConversionConvertedInstrumentAmount1" xlink:to="us-gaap_DebtConversionConvertedInstrumentAmount1_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DebtConversionConvertedInstrumentAmount1_lbl" xml:lang="en-US">Conversion of accounts payable into note payable</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ConversionOfAccountsPayableIntoCommonStock" xlink:label="VSTA_ConversionOfAccountsPayableIntoCommonStock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConversionOfAccountsPayableIntoCommonStock" xlink:to="VSTA_ConversionOfAccountsPayableIntoCommonStock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConversionOfAccountsPayableIntoCommonStock_lbl" xml:lang="en-US">Conversion of accounts payable into common stock</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ConversionOfAccruedInterestOnConvertiblePromissoryNotesIntoCommonStock" xlink:label="VSTA_ConversionOfAccruedInterestOnConvertiblePromissoryNotesIntoCommonStock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConversionOfAccruedInterestOnConvertiblePromissoryNotesIntoCommonStock" xlink:to="VSTA_ConversionOfAccruedInterestOnConvertiblePromissoryNotesIntoCommonStock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConversionOfAccruedInterestOnConvertiblePromissoryNotesIntoCommonStock_lbl" xml:lang="en-US">Conversion of accrued interest on convertible promissory notes into common stock</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_NotesReceivableFromSaleOfCommonStockToRelatedPartiesUponExerciseOfOptionsAndWarrants" xlink:label="VSTA_NotesReceivableFromSaleOfCommonStockToRelatedPartiesUponExerciseOfOptionsAndWarrants" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesReceivableFromSaleOfCommonStockToRelatedPartiesUponExerciseOfOptionsAndWarrants" xlink:to="VSTA_NotesReceivableFromSaleOfCommonStockToRelatedPartiesUponExerciseOfOptionsAndWarrants_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NotesReceivableFromSaleOfCommonStockToRelatedPartiesUponExerciseOfOptionsAndWarrants_lbl" xml:lang="en-US">Notes receivable from sale of common stock to related parties upon exercise of options and warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CapitalLeaseObligationsIncurred" xlink:label="us-gaap_CapitalLeaseObligationsIncurred" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalLeaseObligationsIncurred" xlink:to="us-gaap_CapitalLeaseObligationsIncurred_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_CapitalLeaseObligationsIncurred_lbl" xml:lang="en-US">Capital lease obligations</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_RecognitionOfPutOptionAndNoteTermExtensionOptionLiabilitiesUponIssuanceOfOriginalPlatinumNotes" xlink:label="VSTA_RecognitionOfPutOptionAndNoteTermExtensionOptionLiabilitiesUponIssuanceOfOriginalPlatinumNotes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_RecognitionOfPutOptionAndNoteTermExtensionOptionLiabilitiesUponIssuanceOfOriginalPlatinumNotes" xlink:to="VSTA_RecognitionOfPutOptionAndNoteTermExtensionOptionLiabilitiesUponIssuanceOfOriginalPlatinumNotes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_RecognitionOfPutOptionAndNoteTermExtensionOptionLiabilitiesUponIssuanceOfOriginalPlatinumNotes_lbl" xml:lang="en-US">Recognition of put option and note term extension option liabilities upon issuance of Original Platinum Notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_IncrementalFairValueOfPutOptionAndNoteTermExtensionOptionLiabilitiesFromDebtModifications" xlink:label="VSTA_IncrementalFairValueOfPutOptionAndNoteTermExtensionOptionLiabilitiesFromDebtModifications" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IncrementalFairValueOfPutOptionAndNoteTermExtensionOptionLiabilitiesFromDebtModifications" xlink:to="VSTA_IncrementalFairValueOfPutOptionAndNoteTermExtensionOptionLiabilitiesFromDebtModifications_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IncrementalFairValueOfPutOptionAndNoteTermExtensionOptionLiabilitiesFromDebtModifications_lbl" xml:lang="en-US">Incremental fair value of put option and note term extension option liabilities from debt modifications</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_IncrementalFairValueOfNoteConversionOptionFromDebtModification" xlink:label="VSTA_IncrementalFairValueOfNoteConversionOptionFromDebtModification" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IncrementalFairValueOfNoteConversionOptionFromDebtModification" xlink:to="VSTA_IncrementalFairValueOfNoteConversionOptionFromDebtModification_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IncrementalFairValueOfNoteConversionOptionFromDebtModification_lbl" xml:lang="en-US">Incremental fair value of note conversion option from debt modification</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_IncrementalFairValueOfWarrantFromDebtModifications" xlink:label="VSTA_IncrementalFairValueOfWarrantFromDebtModifications" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IncrementalFairValueOfWarrantFromDebtModifications" xlink:to="VSTA_IncrementalFairValueOfWarrantFromDebtModifications_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IncrementalFairValueOfWarrantFromDebtModifications_lbl" xml:lang="en-US">Incremental fair value of warrant from debt modifications</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_RecognitionOfWarrantLiabilityUponAdoptionOfNewAccountingStandard" xlink:label="VSTA_RecognitionOfWarrantLiabilityUponAdoptionOfNewAccountingStandard" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_RecognitionOfWarrantLiabilityUponAdoptionOfNewAccountingStandard" xlink:to="VSTA_RecognitionOfWarrantLiabilityUponAdoptionOfNewAccountingStandard_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_RecognitionOfWarrantLiabilityUponAdoptionOfNewAccountingStandard_lbl" xml:lang="en-US">Recognition of warrant liability upon adoption of new accounting standard</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_FairValueOfWarrantsIssuedWithAugust2010ShortTermNotes" xlink:label="VSTA_FairValueOfWarrantsIssuedWithAugust2010ShortTermNotes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfWarrantsIssuedWithAugust2010ShortTermNotes" xlink:to="VSTA_FairValueOfWarrantsIssuedWithAugust2010ShortTermNotes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfWarrantsIssuedWithAugust2010ShortTermNotes_lbl" xml:lang="en-US">Fair value of warrants issued with August 2010 short term notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_NoteDiscountUponIssuanceOfAugust2010ShortTermNotes" xlink:label="VSTA_NoteDiscountUponIssuanceOfAugust2010ShortTermNotes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NoteDiscountUponIssuanceOfAugust2010ShortTermNotes" xlink:to="VSTA_NoteDiscountUponIssuanceOfAugust2010ShortTermNotes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NoteDiscountUponIssuanceOfAugust2010ShortTermNotes_lbl" xml:lang="en-US">Note discount upon issuance of August 2010 short term notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_FairValueOfWarrantsIssuedWithFebruary201212ConvertibleNotes" xlink:label="VSTA_FairValueOfWarrantsIssuedWithFebruary201212ConvertibleNotes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfWarrantsIssuedWithFebruary201212ConvertibleNotes" xlink:to="VSTA_FairValueOfWarrantsIssuedWithFebruary201212ConvertibleNotes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfWarrantsIssuedWithFebruary201212ConvertibleNotes_lbl" xml:lang="en-US">Fair value of warrants issued with February 2012 12 % convertible notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_NoteDiscountUponIssuanceOfFebruary201212ConvertibleNotes" xlink:label="VSTA_NoteDiscountUponIssuanceOfFebruary201212ConvertibleNotes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NoteDiscountUponIssuanceOfFebruary201212ConvertibleNotes" xlink:to="VSTA_NoteDiscountUponIssuanceOfFebruary201212ConvertibleNotes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NoteDiscountUponIssuanceOfFebruary201212ConvertibleNotes_lbl" xml:lang="en-US">Note discount upon issuance of February 2012 12% convertible notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ConversionOf20062007And20082010NotesIntoUnitsIncludingAccruedInterestOf1365600" xlink:label="VSTA_ConversionOf20062007And20082010NotesIntoUnitsIncludingAccruedInterestOf1365600" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConversionOf20062007And20082010NotesIntoUnitsIncludingAccruedInterestOf1365600" xlink:to="VSTA_ConversionOf20062007And20082010NotesIntoUnitsIncludingAccruedInterestOf1365600_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConversionOf20062007And20082010NotesIntoUnitsIncludingAccruedInterestOf1365600_lbl" xml:lang="en-US">Conversion of 2006/2007 and 2008/2010 Notes into Units, including accrued interest of $1,365,600</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ConversionOfAllSeriesOfPremergerPreferredStockIntoUnits" xlink:label="VSTA_ConversionOfAllSeriesOfPremergerPreferredStockIntoUnits" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConversionOfAllSeriesOfPremergerPreferredStockIntoUnits" xlink:to="VSTA_ConversionOfAllSeriesOfPremergerPreferredStockIntoUnits_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConversionOfAllSeriesOfPremergerPreferredStockIntoUnits_lbl" xml:lang="en-US">Conversion of all series of pre-Merger preferred stock into Units</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ConversionOf2011PlatinumNoteIntoSeriesPreferredStockIncludingAccruedInterestOf611100AndConversionPremium" xlink:label="VSTA_ConversionOf2011PlatinumNoteIntoSeriesPreferredStockIncludingAccruedInterestOf611100AndConversionPremium" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConversionOf2011PlatinumNoteIntoSeriesPreferredStockIncludingAccruedInterestOf611100AndConversionPremium" xlink:to="VSTA_ConversionOf2011PlatinumNoteIntoSeriesPreferredStockIncludingAccruedInterestOf611100AndConversionPremium_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConversionOf2011PlatinumNoteIntoSeriesPreferredStockIncludingAccruedInterestOf611100AndConversionPremium_lbl" xml:lang="en-US">Conversion of 2011 Platinum Note into Series A Preferred Stock, including accrued interest of $611,100 and conversion premium</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ConversionOf7NotePayableAndAccruedInterestOf11500IntoCommonStockAndWarrants" xlink:label="VSTA_ConversionOf7NotePayableAndAccruedInterestOf11500IntoCommonStockAndWarrants" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConversionOf7NotePayableAndAccruedInterestOf11500IntoCommonStockAndWarrants" xlink:to="VSTA_ConversionOf7NotePayableAndAccruedInterestOf11500IntoCommonStockAndWarrants_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConversionOf7NotePayableAndAccruedInterestOf11500IntoCommonStockAndWarrants_lbl" xml:lang="en-US">Conversion of 7% note payable and accrued interest of $11,500 into common stock and warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ConversionOfAccountsPayableToMorrisonFoersterMccarthyTetraultAndDesjardinsIntoNotesPayable" xlink:label="VSTA_ConversionOfAccountsPayableToMorrisonFoersterMccarthyTetraultAndDesjardinsIntoNotesPayable" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConversionOfAccountsPayableToMorrisonFoersterMccarthyTetraultAndDesjardinsIntoNotesPayable" xlink:to="VSTA_ConversionOfAccountsPayableToMorrisonFoersterMccarthyTetraultAndDesjardinsIntoNotesPayable_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConversionOfAccountsPayableToMorrisonFoersterMccarthyTetraultAndDesjardinsIntoNotesPayable_lbl" xml:lang="en-US">Conversion of accounts payable to Morrison &amp; Foerster, McCarthy Tetrault and Desjardins into notes payable</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_AccountsPayableAndCancellationPremiumConvertedInto2011PrivatePlacementUnits" xlink:label="VSTA_AccountsPayableAndCancellationPremiumConvertedInto2011PrivatePlacementUnits" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AccountsPayableAndCancellationPremiumConvertedInto2011PrivatePlacementUnits" xlink:to="VSTA_AccountsPayableAndCancellationPremiumConvertedInto2011PrivatePlacementUnits_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AccountsPayableAndCancellationPremiumConvertedInto2011PrivatePlacementUnits_lbl" xml:lang="en-US">Accounts payable and cancellation premium converted into 2011 Private Placement Units</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_AccruedInterestOnCatoHoldingCompanyNoteConvertedToNotePayable" xlink:label="VSTA_AccruedInterestOnCatoHoldingCompanyNoteConvertedToNotePayable" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AccruedInterestOnCatoHoldingCompanyNoteConvertedToNotePayable" xlink:to="VSTA_AccruedInterestOnCatoHoldingCompanyNoteConvertedToNotePayable_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AccruedInterestOnCatoHoldingCompanyNoteConvertedToNotePayable_lbl" xml:lang="en-US">Accrued interest on Cato Holding Company note converted to note payable</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_AccountsPayableSettledInDecember2011AndMayjune2012WarrantExercises" xlink:label="VSTA_AccountsPayableSettledInDecember2011AndMayjune2012WarrantExercises" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AccountsPayableSettledInDecember2011AndMayjune2012WarrantExercises" xlink:to="VSTA_AccountsPayableSettledInDecember2011AndMayjune2012WarrantExercises_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AccountsPayableSettledInDecember2011AndMayjune2012WarrantExercises_lbl" xml:lang="en-US">Accounts payable settled in December 2011 and May/June 2012 warrant exercises</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_InsurancePremiumsSettledByIssuingNotePayable" xlink:label="VSTA_InsurancePremiumsSettledByIssuingNotePayable" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_InsurancePremiumsSettledByIssuingNotePayable" xlink:to="VSTA_InsurancePremiumsSettledByIssuingNotePayable_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_InsurancePremiumsSettledByIssuingNotePayable_lbl" xml:lang="en-US">Insurance premiums settled by issuing note payable</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ConversionOfAccruedInterestAndFeesOnFebruary2012NotesInto2012PrivatePlacementUnits" xlink:label="VSTA_ConversionOfAccruedInterestAndFeesOnFebruary2012NotesInto2012PrivatePlacementUnits" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConversionOfAccruedInterestAndFeesOnFebruary2012NotesInto2012PrivatePlacementUnits" xlink:to="VSTA_ConversionOfAccruedInterestAndFeesOnFebruary2012NotesInto2012PrivatePlacementUnits_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConversionOfAccruedInterestAndFeesOnFebruary2012NotesInto2012PrivatePlacementUnits_lbl" xml:lang="en-US">Conversion of accrued interest and fees on February 2012 Notes into 2012 Private Placement Units</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_AccruedInterestOnJulyAndAugust2012NotesToPlatinumConvertedIntoExchangeNote" xlink:label="VSTA_AccruedInterestOnJulyAndAugust2012NotesToPlatinumConvertedIntoExchangeNote" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AccruedInterestOnJulyAndAugust2012NotesToPlatinumConvertedIntoExchangeNote" xlink:to="VSTA_AccruedInterestOnJulyAndAugust2012NotesToPlatinumConvertedIntoExchangeNote_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AccruedInterestOnJulyAndAugust2012NotesToPlatinumConvertedIntoExchangeNote_lbl" xml:lang="en-US">Accrued interest on July and August 2012 Notes to Platinum converted into Exchange Note</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_AccountsPayableSettledByIssuanceOfStockOrNotesPayableAndStock" xlink:label="VSTA_AccountsPayableSettledByIssuanceOfStockOrNotesPayableAndStock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AccountsPayableSettledByIssuanceOfStockOrNotesPayableAndStock" xlink:to="VSTA_AccountsPayableSettledByIssuanceOfStockOrNotesPayableAndStock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AccountsPayableSettledByIssuanceOfStockOrNotesPayableAndStock_lbl" xml:lang="en-US">Accounts payable settled by issuance of stock or notes payable and stock</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_AccountsPayableConvertedInto2012PrivatePlacementUnits" xlink:label="VSTA_AccountsPayableConvertedInto2012PrivatePlacementUnits" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AccountsPayableConvertedInto2012PrivatePlacementUnits" xlink:to="VSTA_AccountsPayableConvertedInto2012PrivatePlacementUnits_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AccountsPayableConvertedInto2012PrivatePlacementUnits_lbl" xml:lang="en-US">Accounts payable converted into 2012 Private Placement Units</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_RecognitionOfWarrantLiabilityUponIssuanceToPlatinumOfOctober2012" xlink:label="VSTA_RecognitionOfWarrantLiabilityUponIssuanceToPlatinumOfOctober2012" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_RecognitionOfWarrantLiabilityUponIssuanceToPlatinumOfOctober2012" xlink:to="VSTA_RecognitionOfWarrantLiabilityUponIssuanceToPlatinumOfOctober2012_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_RecognitionOfWarrantLiabilityUponIssuanceToPlatinumOfOctober2012_lbl" xml:lang="en-US">Recognition of warrant liability upon issuance to Platinum of October 2012 Exchange Note and October 2012, February 2013 and March 2013 Investment Notes and July 2013 Convertible Note</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_RecognitionOfWarrantLiabilityForPotentialIssuanceToPlatinumOfSeries" xlink:label="VSTA_RecognitionOfWarrantLiabilityForPotentialIssuanceToPlatinumOfSeries" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_RecognitionOfWarrantLiabilityForPotentialIssuanceToPlatinumOfSeries" xlink:to="VSTA_RecognitionOfWarrantLiabilityForPotentialIssuanceToPlatinumOfSeries_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_RecognitionOfWarrantLiabilityForPotentialIssuanceToPlatinumOfSeries_lbl" xml:lang="en-US">Recognition of warrant liability for potential issuance to Platinum of Series A Exchange Warrant under the terms of the October 2012 Agreement</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_StatementTable_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_StatementTable_lbl" xml:lang="en-US">Statement [Table]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementLineItems_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_StatementLineItems_lbl" xml:lang="en-US">Statement [Line Items]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_StockholdersEquityForPreferredStock" xlink:label="VSTA_StockholdersEquityForPreferredStock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockholdersEquityForPreferredStock" xlink:to="VSTA_StockholdersEquityForPreferredStock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel" xlink:label="VSTA_StockholdersEquityForPreferredStock_lbl" xml:lang="en-US">Beginning Balance, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_SharesIssuedForPreferredStock" xlink:label="VSTA_SharesIssuedForPreferredStock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SharesIssuedForPreferredStock" xlink:to="VSTA_SharesIssuedForPreferredStock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel" xlink:label="VSTA_SharesIssuedForPreferredStock_lbl" xml:lang="en-US">Beginning Balance, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf24000Amount" xlink:label="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf24000Amount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf24000Amount" xlink:to="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf24000Amount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf24000Amount_lbl" xml:lang="en-US">Issuance of Series A preferred stock at $2.302 per share for cash, net of issuance costs of $29,500, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf24000Shares" xlink:label="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf24000Shares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf24000Shares" xlink:to="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf24000Shares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf24000Shares_lbl" xml:lang="en-US">Issuance of Series A preferred stock at $2.302 per share for cash, net of issuance costs of $29,500, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_IssuanceOfSeriesBPreferredStockat5.545PerShareForCashIncludingConversionOf575000FaceValueOf7ConvertibleNotesPlusAccruedInterestOf3800NetOfUnamortizedDiscountOf70800AndIssuanceCostsOf39800Amount" xlink:label="VSTA_IssuanceOfSeriesBPreferredStockat5.545PerShareForCashIncludingConversionOf575000FaceValueOf7ConvertibleNotesPlusAccruedInterestOf3800NetOfUnamortizedDiscountOf70800AndIssuanceCostsOf39800Amount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesBPreferredStockat5.545PerShareForCashIncludingConversionOf575000FaceValueOf7ConvertibleNotesPlusAccruedInterestOf3800NetOfUnamortizedDiscountOf70800AndIssuanceCostsOf39800Amount" xlink:to="VSTA_IssuanceOfSeriesBPreferredStockat5.545PerShareForCashIncludingConversionOf575000FaceValueOf7ConvertibleNotesPlusAccruedInterestOf3800NetOfUnamortizedDiscountOf70800AndIssuanceCostsOf39800Amount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IssuanceOfSeriesBPreferredStockat5.545PerShareForCashIncludingConversionOf575000FaceValueOf7ConvertibleNotesPlusAccruedInterestOf3800NetOfUnamortizedDiscountOf70800AndIssuanceCostsOf39800Amount_lbl" xml:lang="en-US">Issuance of Series B preferred stock at $5.545 per share for cash, including conversion of $575,000 face value of 7% convertible notes plus accrued interest of $3,800, net of unamortized discount of $70,800 and issuance costs of $137,000, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_IssuanceOfSeriesBPreferredStockat5.545PerShareForCashIncludingConversionOf575000FaceValueOf7ConvertibleNotesPlusAccruedInterestOf3800NetOfUnamortizedDiscountOf70800AndIssuanceCostsOf39800Shares" xlink:label="VSTA_IssuanceOfSeriesBPreferredStockat5.545PerShareForCashIncludingConversionOf575000FaceValueOf7ConvertibleNotesPlusAccruedInterestOf3800NetOfUnamortizedDiscountOf70800AndIssuanceCostsOf39800Shares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesBPreferredStockat5.545PerShareForCashIncludingConversionOf575000FaceValueOf7ConvertibleNotesPlusAccruedInterestOf3800NetOfUnamortizedDiscountOf70800AndIssuanceCostsOf39800Shares" xlink:to="VSTA_IssuanceOfSeriesBPreferredStockat5.545PerShareForCashIncludingConversionOf575000FaceValueOf7ConvertibleNotesPlusAccruedInterestOf3800NetOfUnamortizedDiscountOf70800AndIssuanceCostsOf39800Shares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IssuanceOfSeriesBPreferredStockat5.545PerShareForCashIncludingConversionOf575000FaceValueOf7ConvertibleNotesPlusAccruedInterestOf3800NetOfUnamortizedDiscountOf70800AndIssuanceCostsOf39800Shares_lbl" xml:lang="en-US">Issuance of Series B preferred stock at $5.545 per share for cash, including conversion of $575,000 face value of 7% convertible notes plus accrued interest of $3,800, net of unamortized discount of $70,800 and issuance costs of $137,000, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_IssuanceOfSeriesb1PreferredStockat5.545ForAcquiredInprocessresearchAndDevelopmentAmount" xlink:label="VSTA_IssuanceOfSeriesb1PreferredStockat5.545ForAcquiredInprocessresearchAndDevelopmentAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesb1PreferredStockat5.545ForAcquiredInprocessresearchAndDevelopmentAmount" xlink:to="VSTA_IssuanceOfSeriesb1PreferredStockat5.545ForAcquiredInprocessresearchAndDevelopmentAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IssuanceOfSeriesb1PreferredStockat5.545ForAcquiredInprocessresearchAndDevelopmentAmount_lbl" xml:lang="en-US">Issuance of Series B-1 preferred stock at $5.545 for acquired in-process research and development, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_IssuanceOfSeriesb1PreferredStockat5.545ForAcquiredInprocessresearchAndDevelopmentShares" xlink:label="VSTA_IssuanceOfSeriesb1PreferredStockat5.545ForAcquiredInprocessresearchAndDevelopmentShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesb1PreferredStockat5.545ForAcquiredInprocessresearchAndDevelopmentShares" xlink:to="VSTA_IssuanceOfSeriesb1PreferredStockat5.545ForAcquiredInprocessresearchAndDevelopmentShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IssuanceOfSeriesb1PreferredStockat5.545ForAcquiredInprocessresearchAndDevelopmentShares_lbl" xml:lang="en-US">Issuance of Series B-1 preferred stock at $5.545 for acquired in-process research and development, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_IssuanceOfSeriesCPreferredStockAt6.00PerShareForCashIncludingConversionOf1655000FaceValueOf10ConvertibleNotesPlusAccruedInterestOf408600NetOfUnamortizedNote" xlink:label="VSTA_IssuanceOfSeriesCPreferredStockAt6.00PerShareForCashIncludingConversionOf1655000FaceValueOf10ConvertibleNotesPlusAccruedInterestOf408600NetOfUnamortizedNote" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesCPreferredStockAt6.00PerShareForCashIncludingConversionOf1655000FaceValueOf10ConvertibleNotesPlusAccruedInterestOf408600NetOfUnamortizedNote" xlink:to="VSTA_IssuanceOfSeriesCPreferredStockAt6.00PerShareForCashIncludingConversionOf1655000FaceValueOf10ConvertibleNotesPlusAccruedInterestOf408600NetOfUnamortizedNote_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IssuanceOfSeriesCPreferredStockAt6.00PerShareForCashIncludingConversionOf1655000FaceValueOf10ConvertibleNotesPlusAccruedInterestOf408600NetOfUnamortizedNote_lbl" xml:lang="en-US">Issuance of Series C preferred stock at $6.00 per share for cash, including conversion of $1,655,000 face value of 10% convertible notes plus accrued interest of $408,600, net of unamortized note discount of $13,200 and issuance costs of $47,200, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_IssuanceOfSeriesCPreferredStockAt6.00PerShareForCashIncludingConversionOf1655000FaceValueOf10ConvertibleNotesPlusAccruedInterestOf408600NetOfUnamortizedShares" xlink:label="VSTA_IssuanceOfSeriesCPreferredStockAt6.00PerShareForCashIncludingConversionOf1655000FaceValueOf10ConvertibleNotesPlusAccruedInterestOf408600NetOfUnamortizedShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesCPreferredStockAt6.00PerShareForCashIncludingConversionOf1655000FaceValueOf10ConvertibleNotesPlusAccruedInterestOf408600NetOfUnamortizedShares" xlink:to="VSTA_IssuanceOfSeriesCPreferredStockAt6.00PerShareForCashIncludingConversionOf1655000FaceValueOf10ConvertibleNotesPlusAccruedInterestOf408600NetOfUnamortizedShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IssuanceOfSeriesCPreferredStockAt6.00PerShareForCashIncludingConversionOf1655000FaceValueOf10ConvertibleNotesPlusAccruedInterestOf408600NetOfUnamortizedShares_lbl" xml:lang="en-US">Issuance of Series C preferred stock at $6.00 per share for cash, including conversion of $1,655,000 face value of 10% convertible notes plus accrued interest of $408,600, net of unamortized note discount of $13,200 and issuance costs of $47,200, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithSeriesCPreferredstockAmount" xlink:label="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithSeriesCPreferredstockAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithSeriesCPreferredstockAmount" xlink:to="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithSeriesCPreferredstockAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithSeriesCPreferredstockAmount_lbl" xml:lang="en-US">Proceeds allocated to warrants issued in connection with Series C preferred stock, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_IssuanceOfSeriescPreferredStockAt6.00PerShareForServicesAndInPaymentOfInterestOnLineOfCreditAmount" xlink:label="VSTA_IssuanceOfSeriescPreferredStockAt6.00PerShareForServicesAndInPaymentOfInterestOnLineOfCreditAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriescPreferredStockAt6.00PerShareForServicesAndInPaymentOfInterestOnLineOfCreditAmount" xlink:to="VSTA_IssuanceOfSeriescPreferredStockAt6.00PerShareForServicesAndInPaymentOfInterestOnLineOfCreditAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IssuanceOfSeriescPreferredStockAt6.00PerShareForServicesAndInPaymentOfInterestOnLineOfCreditAmount_lbl" xml:lang="en-US">Issuance of Series C preferred stock at $6.00 per share for services and in payment of interest on line of credit, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_IssuanceOfSeriescPreferredStockAt6.00PerShareForServicesAndInPaymentOfInterestOnLineOfCreditShares" xlink:label="VSTA_IssuanceOfSeriescPreferredStockAt6.00PerShareForServicesAndInPaymentOfInterestOnLineOfCreditShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriescPreferredStockAt6.00PerShareForServicesAndInPaymentOfInterestOnLineOfCreditShares" xlink:to="VSTA_IssuanceOfSeriescPreferredStockAt6.00PerShareForServicesAndInPaymentOfInterestOnLineOfCreditShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IssuanceOfSeriescPreferredStockAt6.00PerShareForServicesAndInPaymentOfInterestOnLineOfCreditShares_lbl" xml:lang="en-US">Issuance of Series C preferred stock at $6.00 per share for services and in payment of interest on line of credit, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ConversionOfAllSeriesOfPreferredStockIntoVistagenCommonStockInConnectionWithMergerAmount" xlink:label="VSTA_ConversionOfAllSeriesOfPreferredStockIntoVistagenCommonStockInConnectionWithMergerAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConversionOfAllSeriesOfPreferredStockIntoVistagenCommonStockInConnectionWithMergerAmount" xlink:to="VSTA_ConversionOfAllSeriesOfPreferredStockIntoVistagenCommonStockInConnectionWithMergerAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConversionOfAllSeriesOfPreferredStockIntoVistagenCommonStockInConnectionWithMergerAmount_lbl" xml:lang="en-US">Conversion of all series of preferred stock into VistaGen common stock in connection with the Merger, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ConversionOfAllSeriesOfPreferredStockIntoVistagenCommonStockInConnectionWithMergerShares" xlink:label="VSTA_ConversionOfAllSeriesOfPreferredStockIntoVistagenCommonStockInConnectionWithMergerShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConversionOfAllSeriesOfPreferredStockIntoVistagenCommonStockInConnectionWithMergerShares" xlink:to="VSTA_ConversionOfAllSeriesOfPreferredStockIntoVistagenCommonStockInConnectionWithMergerShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConversionOfAllSeriesOfPreferredStockIntoVistagenCommonStockInConnectionWithMergerShares_lbl" xml:lang="en-US">Conversion of all series of preferred stock into VistaGen common stock in connection with the Merger, Shares</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockholdersEquityForPreferredStock" xlink:to="VSTA_StockholdersEquityForPreferredStock_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel" xlink:label="VSTA_StockholdersEquityForPreferredStock_2_lbl" xml:lang="en-US">Ending Balance, Amount</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SharesIssuedForPreferredStock" xlink:to="VSTA_SharesIssuedForPreferredStock_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel" xlink:label="VSTA_SharesIssuedForPreferredStock_2_lbl" xml:lang="en-US">Ending Balance, Shares</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockholdersEquity" xlink:to="us-gaap_StockholdersEquity_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel" xlink:label="us-gaap_StockholdersEquity_2_lbl" xml:lang="en-US">Beginning Balance, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SharesIssued" xlink:label="us-gaap_SharesIssued" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SharesIssued" xlink:to="us-gaap_SharesIssued_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel" xlink:label="us-gaap_SharesIssued_lbl" xml:lang="en-US">Beginning Balance, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueIssuedForServices" xlink:label="us-gaap_StockIssuedDuringPeriodValueIssuedForServices" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockIssuedDuringPeriodValueIssuedForServices" xlink:to="us-gaap_StockIssuedDuringPeriodValueIssuedForServices_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_StockIssuedDuringPeriodValueIssuedForServices_lbl" xml:lang="en-US">Fair value of common stock issued for services, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesIssuedForServices" xlink:label="us-gaap_StockIssuedDuringPeriodSharesIssuedForServices" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockIssuedDuringPeriodSharesIssuedForServices" xlink:to="us-gaap_StockIssuedDuringPeriodSharesIssuedForServices_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_StockIssuedDuringPeriodSharesIssuedForServices_lbl" xml:lang="en-US">Fair value of common stock issued for services, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_EffectOfMergerAmount" xlink:label="VSTA_EffectOfMergerAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_EffectOfMergerAmount" xlink:to="VSTA_EffectOfMergerAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_EffectOfMergerAmount_lbl" xml:lang="en-US">Effect of the Merger, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_EffectOfMergerShares" xlink:label="VSTA_EffectOfMergerShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_EffectOfMergerShares" xlink:to="VSTA_EffectOfMergerShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_EffectOfMergerShares_lbl" xml:lang="en-US">Effect of the Merger, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_SaleOfCommonStockForCashAmount" xlink:label="VSTA_SaleOfCommonStockForCashAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SaleOfCommonStockForCashAmount" xlink:to="VSTA_SaleOfCommonStockForCashAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SaleOfCommonStockForCashAmount_lbl" xml:lang="en-US">Sale of common stock for cash, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_SaleOfCommonStockForCashShares" xlink:label="VSTA_SaleOfCommonStockForCashShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SaleOfCommonStockForCashShares" xlink:to="VSTA_SaleOfCommonStockForCashShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SaleOfCommonStockForCashShares_lbl" xml:lang="en-US">Sale of common stock for cash, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalConvertibleDebtWithConversionFeature" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalConvertibleDebtWithConversionFeature" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AdjustmentsToAdditionalPaidInCapitalConvertibleDebtWithConversionFeature" xlink:to="us-gaap_AdjustmentsToAdditionalPaidInCapitalConvertibleDebtWithConversionFeature_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalConvertibleDebtWithConversionFeature_lbl" xml:lang="en-US">Beneficial conversion feature on note</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_FairValueOfWarrantsIssuedForServices" xlink:label="VSTA_FairValueOfWarrantsIssuedForServices" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfWarrantsIssuedForServices" xlink:to="VSTA_FairValueOfWarrantsIssuedForServices_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfWarrantsIssuedForServices_lbl" xml:lang="en-US">Fair value of warrants issued for services</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAmount" xlink:label="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAmount" xlink:to="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAmount_lbl" xml:lang="en-US">Common stock issued upon exercise of options from 1999 Stock Incentive Plan, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanShares" xlink:label="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanShares" xlink:to="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanShares_lbl" xml:lang="en-US">Common stock issued upon exercise of options from 1999 Stock Incentive Plan, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_SharebasedCompensationExpense" xlink:label="VSTA_SharebasedCompensationExpense" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SharebasedCompensationExpense" xlink:to="VSTA_SharebasedCompensationExpense_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SharebasedCompensationExpense_lbl" xml:lang="en-US">Share-based compensation expense</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ForgivenessOfAccruedCompensationAndAccruedInterestPayableToOfficers" xlink:label="VSTA_ForgivenessOfAccruedCompensationAndAccruedInterestPayableToOfficers" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ForgivenessOfAccruedCompensationAndAccruedInterestPayableToOfficers" xlink:to="VSTA_ForgivenessOfAccruedCompensationAndAccruedInterestPayableToOfficers_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ForgivenessOfAccruedCompensationAndAccruedInterestPayableToOfficers_lbl" xml:lang="en-US">Forgiveness of accrued compensation and accrued interest payable to officers</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithPlatinumNotes" xlink:label="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithPlatinumNotes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithPlatinumNotes" xlink:to="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithPlatinumNotes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithPlatinumNotes_lbl" xml:lang="en-US">Proceeds allocated to warrants issued in connection with Platinum Notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_AccruedInterestOnNotesReceivable" xlink:label="VSTA_AccruedInterestOnNotesReceivable" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AccruedInterestOnNotesReceivable" xlink:to="VSTA_AccruedInterestOnNotesReceivable_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AccruedInterestOnNotesReceivable_lbl" xml:lang="en-US">Accrued interest on notes receivable</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithPlatinumNotesAndIncrementalFairValueOfWarrantModification" xlink:label="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithPlatinumNotesAndIncrementalFairValueOfWarrantModification" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithPlatinumNotesAndIncrementalFairValueOfWarrantModification" xlink:to="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithPlatinumNotesAndIncrementalFairValueOfWarrantModification_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithPlatinumNotesAndIncrementalFairValueOfWarrantModification_lbl" xml:lang="en-US">Proceeds allocated to warrants issued in connection with Platinum Notes and incremental fair value of warrant modification</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_EffectOfReverseStockSplit" xlink:label="VSTA_EffectOfReverseStockSplit" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_EffectOfReverseStockSplit" xlink:to="VSTA_EffectOfReverseStockSplit_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_EffectOfReverseStockSplit_lbl" xml:lang="en-US">Effect of reverse stock split</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_CumulativeEffectOfAdoptingNewAccountingStandard" xlink:label="VSTA_CumulativeEffectOfAdoptingNewAccountingStandard" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CumulativeEffectOfAdoptingNewAccountingStandard" xlink:to="VSTA_CumulativeEffectOfAdoptingNewAccountingStandard_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CumulativeEffectOfAdoptingNewAccountingStandard_lbl" xml:lang="en-US">Cumulative effect of adopting new accounting standard</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_CommonStockIssuedForCancellationOfAccountsPayableAndAccruedInterestAmount" xlink:label="VSTA_CommonStockIssuedForCancellationOfAccountsPayableAndAccruedInterestAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedForCancellationOfAccountsPayableAndAccruedInterestAmount" xlink:to="VSTA_CommonStockIssuedForCancellationOfAccountsPayableAndAccruedInterestAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommonStockIssuedForCancellationOfAccountsPayableAndAccruedInterestAmount_lbl" xml:lang="en-US">Common stock issued for cancellation of accounts payable and accrued interest, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_CommonStockIssuedForCancellationOfAccountsPayableAndAccruedInterestShares" xlink:label="VSTA_CommonStockIssuedForCancellationOfAccountsPayableAndAccruedInterestShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedForCancellationOfAccountsPayableAndAccruedInterestShares" xlink:to="VSTA_CommonStockIssuedForCancellationOfAccountsPayableAndAccruedInterestShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommonStockIssuedForCancellationOfAccountsPayableAndAccruedInterestShares_lbl" xml:lang="en-US">Common stock issued for cancellation of accounts payable and accrued interest, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_IncrementalFairValueOfNoteConversionOptionsFromDebtModification" xlink:label="VSTA_IncrementalFairValueOfNoteConversionOptionsFromDebtModification" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IncrementalFairValueOfNoteConversionOptionsFromDebtModification" xlink:to="VSTA_IncrementalFairValueOfNoteConversionOptionsFromDebtModification_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IncrementalFairValueOfNoteConversionOptionsFromDebtModification_lbl" xml:lang="en-US">Incremental fair value of note conversion options from debt modification</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ReclassificationOfWarrantLiabilityToEquity" xlink:label="VSTA_ReclassificationOfWarrantLiabilityToEquity" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ReclassificationOfWarrantLiabilityToEquity" xlink:to="VSTA_ReclassificationOfWarrantLiabilityToEquity_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ReclassificationOfWarrantLiabilityToEquity_lbl" xml:lang="en-US">Reclassification of warrant liability to equity</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_IncrementalValueOfPlatinumNoteModification" xlink:label="VSTA_IncrementalValueOfPlatinumNoteModification" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IncrementalValueOfPlatinumNoteModification" xlink:to="VSTA_IncrementalValueOfPlatinumNoteModification_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IncrementalValueOfPlatinumNoteModification_lbl" xml:lang="en-US">Incremental value of Platinum note modification</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_IncrementalValueOfMorrisonFoersterWarrantModification" xlink:label="VSTA_IncrementalValueOfMorrisonFoersterWarrantModification" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IncrementalValueOfMorrisonFoersterWarrantModification" xlink:to="VSTA_IncrementalValueOfMorrisonFoersterWarrantModification_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IncrementalValueOfMorrisonFoersterWarrantModification_lbl" xml:lang="en-US">Incremental value of Morrison Foerster warrant modification</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_StockIssuedInMay2011PrivatePlacementNetOf202000PlacementFeesAmount" xlink:label="VSTA_StockIssuedInMay2011PrivatePlacementNetOf202000PlacementFeesAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedInMay2011PrivatePlacementNetOf202000PlacementFeesAmount" xlink:to="VSTA_StockIssuedInMay2011PrivatePlacementNetOf202000PlacementFeesAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_StockIssuedInMay2011PrivatePlacementNetOf202000PlacementFeesAmount_lbl" xml:lang="en-US">Stock issued in May 2011 Private Placement, net of $202,000 placement fees, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_StockIssuedInMay2011PrivatePlacementNetOf202000PlacementFeesShares" xlink:label="VSTA_StockIssuedInMay2011PrivatePlacementNetOf202000PlacementFeesShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedInMay2011PrivatePlacementNetOf202000PlacementFeesShares" xlink:to="VSTA_StockIssuedInMay2011PrivatePlacementNetOf202000PlacementFeesShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_StockIssuedInMay2011PrivatePlacementNetOf202000PlacementFeesShares_lbl" xml:lang="en-US">Stock issued in May 2011 Private Placement, net of $202,000 placement fees, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_PaymentsOnNoteReceivableForSaleOfStock" xlink:label="VSTA_PaymentsOnNoteReceivableForSaleOfStock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PaymentsOnNoteReceivableForSaleOfStock" xlink:to="VSTA_PaymentsOnNoteReceivableForSaleOfStock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PaymentsOnNoteReceivableForSaleOfStock_lbl" xml:lang="en-US">Payments on note receivable for sale of stock</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ProceedsFromSaleOfUnits" xlink:label="VSTA_ProceedsFromSaleOfUnits" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProceedsFromSaleOfUnits" xlink:to="VSTA_ProceedsFromSaleOfUnits_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ProceedsFromSaleOfUnits_lbl" xml:lang="en-US">Allocated proceeds from Sale of Units, amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_AllocatedProceedsFromSaleOfUnitsShares" xlink:label="VSTA_AllocatedProceedsFromSaleOfUnitsShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AllocatedProceedsFromSaleOfUnitsShares" xlink:to="VSTA_AllocatedProceedsFromSaleOfUnitsShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AllocatedProceedsFromSaleOfUnitsShares_lbl" xml:lang="en-US">Allocated proceeds from Sale of Units, shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_StockIssuedUponConversionOfConvertiblePromissoryNotesAmount" xlink:label="VSTA_StockIssuedUponConversionOfConvertiblePromissoryNotesAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedUponConversionOfConvertiblePromissoryNotesAmount" xlink:to="VSTA_StockIssuedUponConversionOfConvertiblePromissoryNotesAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_StockIssuedUponConversionOfConvertiblePromissoryNotesAmount_lbl" xml:lang="en-US">Stock issued upon conversion of convertible promissory notes, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_StockIssuedUponConversionOfConvertiblePromissoryNotesShares" xlink:label="VSTA_StockIssuedUponConversionOfConvertiblePromissoryNotesShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedUponConversionOfConvertiblePromissoryNotesShares" xlink:to="VSTA_StockIssuedUponConversionOfConvertiblePromissoryNotesShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_StockIssuedUponConversionOfConvertiblePromissoryNotesShares_lbl" xml:lang="en-US">Stock issued upon conversion of convertible promissory notes, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_StockIssuedUponConversionOfAllSeriesOfPreferredStockAmount" xlink:label="VSTA_StockIssuedUponConversionOfAllSeriesOfPreferredStockAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedUponConversionOfAllSeriesOfPreferredStockAmount" xlink:to="VSTA_StockIssuedUponConversionOfAllSeriesOfPreferredStockAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_StockIssuedUponConversionOfAllSeriesOfPreferredStockAmount_lbl" xml:lang="en-US">Stock issued upon conversion of all series of preferred stock, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_StockIssuedUponConversionOfAllSeriesOfPreferredStockShares" xlink:label="VSTA_StockIssuedUponConversionOfAllSeriesOfPreferredStockShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedUponConversionOfAllSeriesOfPreferredStockShares" xlink:to="VSTA_StockIssuedUponConversionOfAllSeriesOfPreferredStockShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_StockIssuedUponConversionOfAllSeriesOfPreferredStockShares_lbl" xml:lang="en-US">Stock issued upon conversion of all series of preferred stock, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_FairValueOfStockIssuedForServicesPriorToMergerAmount" xlink:label="VSTA_FairValueOfStockIssuedForServicesPriorToMergerAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfStockIssuedForServicesPriorToMergerAmount" xlink:to="VSTA_FairValueOfStockIssuedForServicesPriorToMergerAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfStockIssuedForServicesPriorToMergerAmount_lbl" xml:lang="en-US">Fair value of stock issued for services prior to the Merger, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_FairValueOfStockIssuedForServicesPriorToMergerShares" xlink:label="VSTA_FairValueOfStockIssuedForServicesPriorToMergerShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfStockIssuedForServicesPriorToMergerShares" xlink:to="VSTA_FairValueOfStockIssuedForServicesPriorToMergerShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfStockIssuedForServicesPriorToMergerShares_lbl" xml:lang="en-US">Fair value of stock issued for services prior to the Merger, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ForgivenessOfNotesAtTheMergerAmount" xlink:label="VSTA_ForgivenessOfNotesAtTheMergerAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ForgivenessOfNotesAtTheMergerAmount" xlink:to="VSTA_ForgivenessOfNotesAtTheMergerAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ForgivenessOfNotesAtTheMergerAmount_lbl" xml:lang="en-US">Forgiveness of notes at the Merger, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_StockIssuedUponExerciseOfModifiedWarrantsIncludesPlatinumExercisesAmount" xlink:label="VSTA_StockIssuedUponExerciseOfModifiedWarrantsIncludesPlatinumExercisesAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedUponExerciseOfModifiedWarrantsIncludesPlatinumExercisesAmount" xlink:to="VSTA_StockIssuedUponExerciseOfModifiedWarrantsIncludesPlatinumExercisesAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_StockIssuedUponExerciseOfModifiedWarrantsIncludesPlatinumExercisesAmount_lbl" xml:lang="en-US">Stock issued upon exercise of modified warrants (includes Platinum exercises), Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_StockIssuedUponExerciseOfModifiedWarrantsIncludesPlatinumExercisesShares" xlink:label="VSTA_StockIssuedUponExerciseOfModifiedWarrantsIncludesPlatinumExercisesShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedUponExerciseOfModifiedWarrantsIncludesPlatinumExercisesShares" xlink:to="VSTA_StockIssuedUponExerciseOfModifiedWarrantsIncludesPlatinumExercisesShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_StockIssuedUponExerciseOfModifiedWarrantsIncludesPlatinumExercisesShares_lbl" xml:lang="en-US">Stock issued upon exercise of modified warrants (includes Platinum exercises), Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_IncrementalValueOfWarrantModificationsIncludingModificationOfPlatinumWarrants" xlink:label="VSTA_IncrementalValueOfWarrantModificationsIncludingModificationOfPlatinumWarrants" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IncrementalValueOfWarrantModificationsIncludingModificationOfPlatinumWarrants" xlink:to="VSTA_IncrementalValueOfWarrantModificationsIncludingModificationOfPlatinumWarrants_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IncrementalValueOfWarrantModificationsIncludingModificationOfPlatinumWarrants_lbl" xml:lang="en-US">Incremental value of warrant modifications (including modification of Platinum warrants)</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_FairValueOfBonusWarrantsUnderDiscountedWarrantExerciseProgram" xlink:label="VSTA_FairValueOfBonusWarrantsUnderDiscountedWarrantExerciseProgram" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfBonusWarrantsUnderDiscountedWarrantExerciseProgram" xlink:to="VSTA_FairValueOfBonusWarrantsUnderDiscountedWarrantExerciseProgram_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfBonusWarrantsUnderDiscountedWarrantExerciseProgram_lbl" xml:lang="en-US">Fair value of bonus warrants under Discounted Warrant Exercise Program</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_StockIssuedInFall2011FollowonOfferingAmount" xlink:label="VSTA_StockIssuedInFall2011FollowonOfferingAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedInFall2011FollowonOfferingAmount" xlink:to="VSTA_StockIssuedInFall2011FollowonOfferingAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_StockIssuedInFall2011FollowonOfferingAmount_lbl" xml:lang="en-US">Stock issued in Fall 2011 Follow-on Offering, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_StockIssuedInFall2011FollowonOfferingShares" xlink:label="VSTA_StockIssuedInFall2011FollowonOfferingShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedInFall2011FollowonOfferingShares" xlink:to="VSTA_StockIssuedInFall2011FollowonOfferingShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_StockIssuedInFall2011FollowonOfferingShares_lbl" xml:lang="en-US">Stock issued in Fall 2011 Follow-on Offering, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_StockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAmount" xlink:label="VSTA_StockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAmount" xlink:to="VSTA_StockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_StockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAmount_lbl" xml:lang="en-US">Stock issued upon exercise of options from 1999 Stock Incentive Plan, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_StockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanShares" xlink:label="VSTA_StockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanShares" xlink:to="VSTA_StockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_StockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanShares_lbl" xml:lang="en-US">Stock issued upon exercise of options from 1999 Stock Incentive Plan, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_FairValueOfStockIssuedForServicesFollowingMergerAmount" xlink:label="VSTA_FairValueOfStockIssuedForServicesFollowingMergerAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfStockIssuedForServicesFollowingMergerAmount" xlink:to="VSTA_FairValueOfStockIssuedForServicesFollowingMergerAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfStockIssuedForServicesFollowingMergerAmount_lbl" xml:lang="en-US">Fair value of stock issued for services following the Merger, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_FairValueOfStockIssuedForServicesFollowingMergerShares" xlink:label="VSTA_FairValueOfStockIssuedForServicesFollowingMergerShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfStockIssuedForServicesFollowingMergerShares" xlink:to="VSTA_FairValueOfStockIssuedForServicesFollowingMergerShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfStockIssuedForServicesFollowingMergerShares_lbl" xml:lang="en-US">Fair value of stock issued for services following the Merger, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ProceedsAllocatedToWarrantsIssuedAndBeneficialConversionFeatureInConnectionWith12ConvertibleNotes" xlink:label="VSTA_ProceedsAllocatedToWarrantsIssuedAndBeneficialConversionFeatureInConnectionWith12ConvertibleNotes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProceedsAllocatedToWarrantsIssuedAndBeneficialConversionFeatureInConnectionWith12ConvertibleNotes" xlink:to="VSTA_ProceedsAllocatedToWarrantsIssuedAndBeneficialConversionFeatureInConnectionWith12ConvertibleNotes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ProceedsAllocatedToWarrantsIssuedAndBeneficialConversionFeatureInConnectionWith12ConvertibleNotes_lbl" xml:lang="en-US">Proceeds allocated to warrants issued and beneficial conversion feature in connection with 12% convertible notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_StockIssuedInConnectionWithNoteTermExtensionAmount" xlink:label="VSTA_StockIssuedInConnectionWithNoteTermExtensionAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedInConnectionWithNoteTermExtensionAmount" xlink:to="VSTA_StockIssuedInConnectionWithNoteTermExtensionAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_StockIssuedInConnectionWithNoteTermExtensionAmount_lbl" xml:lang="en-US">Stock issued in connection with note term extension, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_StockIssuedInConnectionWithNoteTermExtensionShares" xlink:label="VSTA_StockIssuedInConnectionWithNoteTermExtensionShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedInConnectionWithNoteTermExtensionShares" xlink:to="VSTA_StockIssuedInConnectionWithNoteTermExtensionShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_StockIssuedInConnectionWithNoteTermExtensionShares_lbl" xml:lang="en-US">Stock issued in connection with note term extension, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_StockIssuedUponConversionOfPlatinumNoteToEquityNetOfPlatinumWarrantExerciseReflectedAboveAmount" xlink:label="VSTA_StockIssuedUponConversionOfPlatinumNoteToEquityNetOfPlatinumWarrantExerciseReflectedAboveAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedUponConversionOfPlatinumNoteToEquityNetOfPlatinumWarrantExerciseReflectedAboveAmount" xlink:to="VSTA_StockIssuedUponConversionOfPlatinumNoteToEquityNetOfPlatinumWarrantExerciseReflectedAboveAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_StockIssuedUponConversionOfPlatinumNoteToEquityNetOfPlatinumWarrantExerciseReflectedAboveAmount_lbl" xml:lang="en-US">Stock issued upon conversion of Platinum Note to equity (net of Platinum warrant exercise reflected above), Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_StockIssuedUponConversionOfPlatinumNoteToEquityNetOfPlatinumWarrantExerciseReflectedAboveShares" xlink:label="VSTA_StockIssuedUponConversionOfPlatinumNoteToEquityNetOfPlatinumWarrantExerciseReflectedAboveShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedUponConversionOfPlatinumNoteToEquityNetOfPlatinumWarrantExerciseReflectedAboveShares" xlink:to="VSTA_StockIssuedUponConversionOfPlatinumNoteToEquityNetOfPlatinumWarrantExerciseReflectedAboveShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_StockIssuedUponConversionOfPlatinumNoteToEquityNetOfPlatinumWarrantExerciseReflectedAboveShares_lbl" xml:lang="en-US">Stock issued upon conversion of Platinum Note to equity (net of Platinum warrant exercise reflected above), Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumCommonStockExchangeAgreementAmount" xlink:label="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumCommonStockExchangeAgreementAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumCommonStockExchangeAgreementAmount" xlink:to="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumCommonStockExchangeAgreementAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumCommonStockExchangeAgreementAmount_lbl" xml:lang="en-US">Common stock exchanged for Series A Preferred under agreements with Platinum: Common Stock Exchange Agreement, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumCommonStockExchangeAgreementShares" xlink:label="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumCommonStockExchangeAgreementShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumCommonStockExchangeAgreementShares" xlink:to="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumCommonStockExchangeAgreementShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumCommonStockExchangeAgreementShares_lbl" xml:lang="en-US">Common stock exchanged for Series A Preferred under agreements with Platinum: Common Stock Exchange Agreement, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumNoteAndWarrantExchangeAgreementAmount" xlink:label="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumNoteAndWarrantExchangeAgreementAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumNoteAndWarrantExchangeAgreementAmount" xlink:to="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumNoteAndWarrantExchangeAgreementAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumNoteAndWarrantExchangeAgreementAmount_lbl" xml:lang="en-US">Common stock exchanged for Series A Preferred under agreements with Platinum: Note and Warrant Exchange Agreement, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumNoteAndWarrantExchangeAgreementShares" xlink:label="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumNoteAndWarrantExchangeAgreementShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumNoteAndWarrantExchangeAgreementShares" xlink:to="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumNoteAndWarrantExchangeAgreementShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumNoteAndWarrantExchangeAgreementShares_lbl" xml:lang="en-US">Common stock exchanged for Series A Preferred under agreements with Platinum: Note and Warrant Exchange Agreement, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_FairValueOfWarrantsIssuedUponExerciseOfModifiedWarrants" xlink:label="VSTA_FairValueOfWarrantsIssuedUponExerciseOfModifiedWarrants" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfWarrantsIssuedUponExerciseOfModifiedWarrants" xlink:to="VSTA_FairValueOfWarrantsIssuedUponExerciseOfModifiedWarrants_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfWarrantsIssuedUponExerciseOfModifiedWarrants_lbl" xml:lang="en-US">Fair value of warrants issued upon exercise of modified warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_FairValueOfSharesIssuedInSettlementOfAccountsPayable" xlink:label="VSTA_FairValueOfSharesIssuedInSettlementOfAccountsPayable" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfSharesIssuedInSettlementOfAccountsPayable" xlink:to="VSTA_FairValueOfSharesIssuedInSettlementOfAccountsPayable_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfSharesIssuedInSettlementOfAccountsPayable_lbl" xml:lang="en-US">Fair value of shares issued in settlement of accounts payable, amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_FairValueOfSharesIssuedInSettlementOfAccountsPayableShares" xlink:label="VSTA_FairValueOfSharesIssuedInSettlementOfAccountsPayableShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfSharesIssuedInSettlementOfAccountsPayableShares" xlink:to="VSTA_FairValueOfSharesIssuedInSettlementOfAccountsPayableShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfSharesIssuedInSettlementOfAccountsPayableShares_lbl" xml:lang="en-US">Fair value of shares issued in settlement of accounts payable, shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ModificationOfNoteReceivableFromSaleOfStock" xlink:label="VSTA_ModificationOfNoteReceivableFromSaleOfStock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ModificationOfNoteReceivableFromSaleOfStock" xlink:to="VSTA_ModificationOfNoteReceivableFromSaleOfStock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ModificationOfNoteReceivableFromSaleOfStock_lbl" xml:lang="en-US">Modification of note receivable from sale of stock</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_FairValueOfWarrantIssuedToCatoHoldingCompanyInConnectionWithNotePayableRestructure" xlink:label="VSTA_FairValueOfWarrantIssuedToCatoHoldingCompanyInConnectionWithNotePayableRestructure" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfWarrantIssuedToCatoHoldingCompanyInConnectionWithNotePayableRestructure" xlink:to="VSTA_FairValueOfWarrantIssuedToCatoHoldingCompanyInConnectionWithNotePayableRestructure_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfWarrantIssuedToCatoHoldingCompanyInConnectionWithNotePayableRestructure_lbl" xml:lang="en-US">Fair value of warrant issued to Cato Holding Company in connection with note payable restructure</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_FairValueOfWarrantIssuedInConnectionWithAccountsPayableRestructure" xlink:label="VSTA_FairValueOfWarrantIssuedInConnectionWithAccountsPayableRestructure" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfWarrantIssuedInConnectionWithAccountsPayableRestructure" xlink:to="VSTA_FairValueOfWarrantIssuedInConnectionWithAccountsPayableRestructure_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfWarrantIssuedInConnectionWithAccountsPayableRestructure_lbl" xml:lang="en-US">Fair value of warrant issued to Cato Holding Company in connection with accounts payable restructure</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_FairValueOfWarrantIssued2InConnectionWithAccountsPayableRestructure" xlink:label="VSTA_FairValueOfWarrantIssued2InConnectionWithAccountsPayableRestructure" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfWarrantIssued2InConnectionWithAccountsPayableRestructure" xlink:to="VSTA_FairValueOfWarrantIssued2InConnectionWithAccountsPayableRestructure_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfWarrantIssued2InConnectionWithAccountsPayableRestructure_lbl" xml:lang="en-US">Fair value of warrant issued to University Health Network in connection with accounts payable restructure</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_FairValueOfWarrantsIssuedInConnectionWithAccruedInterestOnUnderlyingNotes" xlink:label="VSTA_FairValueOfWarrantsIssuedInConnectionWithAccruedInterestOnUnderlyingNotes" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfWarrantsIssuedInConnectionWithAccruedInterestOnUnderlyingNotes" xlink:to="VSTA_FairValueOfWarrantsIssuedInConnectionWithAccruedInterestOnUnderlyingNotes_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfWarrantsIssuedInConnectionWithAccruedInterestOnUnderlyingNotes_lbl" xml:lang="en-US">Fair value of warrants issued to Morrison &amp; Foerster, Cato Reearch Ltd. and University Health Network in connection with accrued interest on underlying notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_SaleOfUnitsInWinter2012PrivatePlacementNetAmount" xlink:label="VSTA_SaleOfUnitsInWinter2012PrivatePlacementNetAmount" />
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SaleOfUnitsInWinter2012PrivatePlacementNetAmount_lbl" xml:lang="en-US">Sale of Units in Winter 2012 Private Placement, net, Amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_SaleOfUnitsInWinter2012PrivatePlacementNetShares" xlink:label="VSTA_SaleOfUnitsInWinter2012PrivatePlacementNetShares" />
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      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_FairValueOfWarrantsIssuedToBankerInConnectionWithExchangeOfFebruary2012ConvertibleNotes" xlink:label="VSTA_FairValueOfWarrantsIssuedToBankerInConnectionWithExchangeOfFebruary2012ConvertibleNotes" />
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueOfWarrantsIssuedToBankerInConnectionWithExchangeOfFebruary2012ConvertibleNotes_lbl" xml:lang="en-US">Fair value of warrants issued to banker in connection with exchange of February 2012 convertible notes</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_PremiumOfFairValueOverFaceValueOfExchangeNoteIssuedToPlatinum" xlink:label="VSTA_PremiumOfFairValueOverFaceValueOfExchangeNoteIssuedToPlatinum" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PremiumOfFairValueOverFaceValueOfExchangeNoteIssuedToPlatinum" xlink:to="VSTA_PremiumOfFairValueOverFaceValueOfExchangeNoteIssuedToPlatinum_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PremiumOfFairValueOverFaceValueOfExchangeNoteIssuedToPlatinum_lbl" xml:lang="en-US">Premium of fair value over face value of Exchange Note issued to Platinum</link:label>
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      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInDerivativeLiabilities" xlink:to="us-gaap_IncreaseDecreaseInDerivativeLiabilities_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_IncreaseDecreaseInDerivativeLiabilities_lbl" xml:lang="en-US">Fair value of Series A Exchange Warrant issuable to Platinum recorded as a Warrant Liability</link:label>
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ProceedsAllocatedToBeneficialConversionFeatureOfInvestmentNotesIssuedToPlatinumInOctober2012February2013AndMarch2013_lbl" xml:lang="en-US">Proceeds allocated to beneficial conversion feature of Investment Notes issued to Platinum in October 2012, February 2013 and March 2013</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_IncrementalFairValueOfWarrantModificationsInFeburary2013" xlink:label="VSTA_IncrementalFairValueOfWarrantModificationsInFeburary2013" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IncrementalFairValueOfWarrantModificationsInFeburary2013" xlink:to="VSTA_IncrementalFairValueOfWarrantModificationsInFeburary2013_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IncrementalFairValueOfWarrantModificationsInFeburary2013_lbl" xml:lang="en-US">Incremental fair value of warrant modifications in Feburary 2013</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetIncomeLoss" xlink:to="us-gaap_NetIncomeLoss_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NetIncomeLoss_2_lbl" xml:lang="en-US">Net Loss</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockholdersEquity" xlink:to="us-gaap_StockholdersEquity_3_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel" xlink:label="us-gaap_StockholdersEquity_3_lbl" xml:lang="en-US">Ending Balance, Amount</link:label>
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel" xlink:label="us-gaap_SharesIssued_2_lbl" xml:lang="en-US">Ending Balance, Shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_NotesToFinancialStatementsAbstract" xlink:label="VSTA_NotesToFinancialStatementsAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesToFinancialStatementsAbstract" xlink:to="VSTA_NotesToFinancialStatementsAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NotesToFinancialStatementsAbstract_lbl" xml:lang="en-US">Notes to Financial Statements</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_HistoryAndOrganizationTextBlock" xlink:label="VSTA_HistoryAndOrganizationTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_HistoryAndOrganizationTextBlock" xlink:to="VSTA_HistoryAndOrganizationTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_HistoryAndOrganizationTextBlock_lbl" xml:lang="en-US">Description of Business</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LiquidityDisclosureTextBlock" xlink:label="us-gaap_LiquidityDisclosureTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiquidityDisclosureTextBlock" xlink:to="us-gaap_LiquidityDisclosureTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LiquidityDisclosureTextBlock_lbl" xml:lang="en-US">Basis of Presentation and Going Concern</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SignificantAccountingPoliciesTextBlock" xlink:label="us-gaap_SignificantAccountingPoliciesTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SignificantAccountingPoliciesTextBlock" xlink:to="us-gaap_SignificantAccountingPoliciesTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_SignificantAccountingPoliciesTextBlock_lbl" xml:lang="en-US">Summary of Significant Accounting Policies</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueDisclosuresTextBlock" xlink:label="us-gaap_FairValueDisclosuresTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueDisclosuresTextBlock" xlink:to="us-gaap_FairValueDisclosuresTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FairValueDisclosuresTextBlock_lbl" xml:lang="en-US">Fair Value Measurements</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_PrepaidExpensesTextBlock" xlink:label="VSTA_PrepaidExpensesTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PrepaidExpensesTextBlock" xlink:to="VSTA_PrepaidExpensesTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PrepaidExpensesTextBlock_lbl" xml:lang="en-US">Prepaid Expenses and Other Current Assets</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PropertyPlantAndEquipmentAbstract" xlink:label="us-gaap_PropertyPlantAndEquipmentAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PropertyPlantAndEquipmentAbstract" xlink:to="us-gaap_PropertyPlantAndEquipmentAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PropertyPlantAndEquipmentAbstract_lbl" xml:lang="en-US">Property, Plant and Equipment [Abstract]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PropertyPlantAndEquipmentDisclosureTextBlock" xlink:label="us-gaap_PropertyPlantAndEquipmentDisclosureTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PropertyPlantAndEquipmentDisclosureTextBlock" xlink:to="us-gaap_PropertyPlantAndEquipmentDisclosureTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PropertyPlantAndEquipmentDisclosureTextBlock_lbl" xml:lang="en-US">Property and Equipment</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BusinessCombinationsAbstract" xlink:label="us-gaap_BusinessCombinationsAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_BusinessCombinationsAbstract" xlink:to="us-gaap_BusinessCombinationsAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_BusinessCombinationsAbstract_lbl" xml:lang="en-US">Business Combinations [Abstract]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_BusinessAcquisitionIntegrationRestructuringAndOtherRelatedCostsTextBlock" xlink:label="us-gaap_BusinessAcquisitionIntegrationRestructuringAndOtherRelatedCostsTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_BusinessAcquisitionIntegrationRestructuringAndOtherRelatedCostsTextBlock" xlink:to="us-gaap_BusinessAcquisitionIntegrationRestructuringAndOtherRelatedCostsTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_BusinessAcquisitionIntegrationRestructuringAndOtherRelatedCostsTextBlock_lbl" xml:lang="en-US">AV-101 Acquisition</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccountsPayableAndAccruedLiabilitiesDisclosureTextBlock" xlink:label="us-gaap_AccountsPayableAndAccruedLiabilitiesDisclosureTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccountsPayableAndAccruedLiabilitiesDisclosureTextBlock" xlink:to="us-gaap_AccountsPayableAndAccruedLiabilitiesDisclosureTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AccountsPayableAndAccruedLiabilitiesDisclosureTextBlock_lbl" xml:lang="en-US">Accrued Expenses</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DebtDisclosureTextBlock" xlink:label="us-gaap_DebtDisclosureTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtDisclosureTextBlock" xlink:to="us-gaap_DebtDisclosureTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DebtDisclosureTextBlock_lbl" xml:lang="en-US">Convertible Promissory Notes and Other Notes Payable</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockholdersEquityNoteDisclosureTextBlock" xlink:label="us-gaap_StockholdersEquityNoteDisclosureTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockholdersEquityNoteDisclosureTextBlock" xlink:to="us-gaap_StockholdersEquityNoteDisclosureTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_StockholdersEquityNoteDisclosureTextBlock_lbl" xml:lang="en-US">Capital Stock</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ResearchAndDevelopmentAbstract" xlink:label="us-gaap_ResearchAndDevelopmentAbstract" />
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ResearchAndDevelopmentAbstract_lbl" xml:lang="en-US">Research and Development [Abstract]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ResearchDevelopmentAndComputerSoftwareDisclosureTextBlock" xlink:label="us-gaap_ResearchDevelopmentAndComputerSoftwareDisclosureTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ResearchDevelopmentAndComputerSoftwareDisclosureTextBlock" xlink:to="us-gaap_ResearchDevelopmentAndComputerSoftwareDisclosureTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ResearchDevelopmentAndComputerSoftwareDisclosureTextBlock_lbl" xml:lang="en-US">Research and Development Expenses</link:label>
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      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeTaxDisclosureAbstract" xlink:to="us-gaap_IncomeTaxDisclosureAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_IncomeTaxDisclosureAbstract_lbl" xml:lang="en-US">Income Tax Disclosure [Abstract]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_IncomeTaxDisclosureTextBlock" xlink:label="us-gaap_IncomeTaxDisclosureTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeTaxDisclosureTextBlock" xlink:to="us-gaap_IncomeTaxDisclosureTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_IncomeTaxDisclosureTextBlock_lbl" xml:lang="en-US">Income Taxes</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CollaborativeArrangementDisclosureTextBlock" xlink:label="us-gaap_CollaborativeArrangementDisclosureTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CollaborativeArrangementDisclosureTextBlock" xlink:to="us-gaap_CollaborativeArrangementDisclosureTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CollaborativeArrangementDisclosureTextBlock_lbl" xml:lang="en-US">Licensing and Collaborative Agreements</link:label>
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      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TextBlockAbstract" xlink:to="us-gaap_TextBlockAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_TextBlockAbstract_lbl" xml:lang="en-US">Text Block [Abstract]</link:label>
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      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ConvertiblePromissoryNotesAndOtherNotesPayableTablesAbstract" xlink:label="VSTA_ConvertiblePromissoryNotesAndOtherNotesPayableTablesAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConvertiblePromissoryNotesAndOtherNotesPayableTablesAbstract" xlink:to="VSTA_ConvertiblePromissoryNotesAndOtherNotesPayableTablesAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConvertiblePromissoryNotesAndOtherNotesPayableTablesAbstract_lbl" xml:lang="en-US">Convertible Promissory Notes And Other Notes Payable Tables</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfDebtTableTextBlock" xlink:label="us-gaap_ScheduleOfDebtTableTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfDebtTableTextBlock" xlink:to="us-gaap_ScheduleOfDebtTableTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_ScheduleOfDebtTableTextBlock_lbl" xml:lang="en-US">Convertible Promissory Notes and Other Notes Payable</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfAssumptionsUsedTableTextBlock" xlink:label="us-gaap_ScheduleOfAssumptionsUsedTableTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfAssumptionsUsedTableTextBlock" xlink:to="us-gaap_ScheduleOfAssumptionsUsedTableTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ScheduleOfAssumptionsUsedTableTextBlock_lbl" xml:lang="en-US">Assumptions</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ComponentsOfDiscountAndInterestRatesTableTextBlock" xlink:label="VSTA_ComponentsOfDiscountAndInterestRatesTableTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ComponentsOfDiscountAndInterestRatesTableTextBlock" xlink:to="VSTA_ComponentsOfDiscountAndInterestRatesTableTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ComponentsOfDiscountAndInterestRatesTableTextBlock_lbl" xml:lang="en-US">Components of the discount and interest rates</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfShareBasedPaymentAwardStockOptionsValuationAssumptionsTableTextBlock" xlink:label="us-gaap_ScheduleOfShareBasedPaymentAwardStockOptionsValuationAssumptionsTableTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfShareBasedPaymentAwardStockOptionsValuationAssumptionsTableTextBlock" xlink:to="us-gaap_ScheduleOfShareBasedPaymentAwardStockOptionsValuationAssumptionsTableTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ScheduleOfShareBasedPaymentAwardStockOptionsValuationAssumptionsTableTextBlock_lbl" xml:lang="en-US">Black-Scholes assumptions</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_CapitalStockTablesAbstract" xlink:label="VSTA_CapitalStockTablesAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CapitalStockTablesAbstract" xlink:to="VSTA_CapitalStockTablesAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CapitalStockTablesAbstract_lbl" xml:lang="en-US">Capital Stock Tables</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationStockOptionsActivityTableTextBlock" xlink:label="us-gaap_ScheduleOfShareBasedCompensationStockOptionsActivityTableTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfShareBasedCompensationStockOptionsActivityTableTextBlock" xlink:to="us-gaap_ScheduleOfShareBasedCompensationStockOptionsActivityTableTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ScheduleOfShareBasedCompensationStockOptionsActivityTableTextBlock_lbl" xml:lang="en-US">Unit Warrant grants and allocation of Proceeds</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_BlackscholesOptionPricingModelTableTextBlock" xlink:label="VSTA_BlackscholesOptionPricingModelTableTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_BlackscholesOptionPricingModelTableTextBlock" xlink:to="VSTA_BlackscholesOptionPricingModelTableTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_BlackscholesOptionPricingModelTableTextBlock_lbl" xml:lang="en-US">Black-Scholes Option Pricing Model</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ScheduleDescriptionOfUnits" xlink:label="VSTA_ScheduleDescriptionOfUnits" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ScheduleDescriptionOfUnits" xlink:to="VSTA_ScheduleDescriptionOfUnits_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ScheduleDescriptionOfUnits_lbl" xml:lang="en-US">Description of units</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ScheduleOfSharesReservedForFutureIssuance" xlink:label="VSTA_ScheduleOfSharesReservedForFutureIssuance" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ScheduleOfSharesReservedForFutureIssuance" xlink:to="VSTA_ScheduleOfSharesReservedForFutureIssuance_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ScheduleOfSharesReservedForFutureIssuance_lbl" xml:lang="en-US">Shares reserved for future issuance</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfComponentsOfIncomeTaxExpenseBenefitTableTextBlock" xlink:label="us-gaap_ScheduleOfComponentsOfIncomeTaxExpenseBenefitTableTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfComponentsOfIncomeTaxExpenseBenefitTableTextBlock" xlink:to="us-gaap_ScheduleOfComponentsOfIncomeTaxExpenseBenefitTableTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ScheduleOfComponentsOfIncomeTaxExpenseBenefitTableTextBlock_lbl" xml:lang="en-US">Provision/benefit computed for income taxes</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfDeferredTaxAssetsAndLiabilitiesTableTextBlock" xlink:label="us-gaap_ScheduleOfDeferredTaxAssetsAndLiabilitiesTableTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfDeferredTaxAssetsAndLiabilitiesTableTextBlock" xlink:to="us-gaap_ScheduleOfDeferredTaxAssetsAndLiabilitiesTableTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ScheduleOfDeferredTaxAssetsAndLiabilitiesTableTextBlock_lbl" xml:lang="en-US">Components of deferred tax assets</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ScheduleofSharebasedCompensationExpenseTextBlock" xlink:label="VSTA_ScheduleofSharebasedCompensationExpenseTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ScheduleofSharebasedCompensationExpenseTextBlock" xlink:to="VSTA_ScheduleofSharebasedCompensationExpenseTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="VSTA_ScheduleofSharebasedCompensationExpenseTextBlock_lbl" xml:lang="en-US">Share-based compensation expense</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_BlackscholesOptionPricingModelTableAssumptionsTextBlock" xlink:label="VSTA_BlackscholesOptionPricingModelTableAssumptionsTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_BlackscholesOptionPricingModelTableAssumptionsTextBlock" xlink:to="VSTA_BlackscholesOptionPricingModelTableAssumptionsTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_BlackscholesOptionPricingModelTableAssumptionsTextBlock_lbl" xml:lang="en-US">Black-Scholes option valuation model assumptions for share-based compensation expense</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_StockOptionActivitySummaryTextBlock" xlink:label="VSTA_StockOptionActivitySummaryTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockOptionActivitySummaryTextBlock" xlink:to="VSTA_StockOptionActivitySummaryTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_StockOptionActivitySummaryTextBlock_lbl" xml:lang="en-US">Summary of stock option plan activity</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_StockOptionsOutstandingAndExercisableUnderCompanysOptionPlanTextBlock" xlink:label="VSTA_StockOptionsOutstandingAndExercisableUnderCompanysOptionPlanTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockOptionsOutstandingAndExercisableUnderCompanysOptionPlanTextBlock" xlink:to="VSTA_StockOptionsOutstandingAndExercisableUnderCompanysOptionPlanTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_StockOptionsOutstandingAndExercisableUnderCompanysOptionPlanTextBlock_lbl" xml:lang="en-US">Stock options outstanding and exercisable under Company's option plan</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfCapitalLeasedAsssetsTableTextBlock" xlink:label="us-gaap_ScheduleOfCapitalLeasedAsssetsTableTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfCapitalLeasedAsssetsTableTextBlock" xlink:to="us-gaap_ScheduleOfCapitalLeasedAsssetsTableTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ScheduleOfCapitalLeasedAsssetsTableTextBlock_lbl" xml:lang="en-US">Assets under capital lease obligations</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ScheduleOfFutureMinimumLeasePaymentsForCapitalLeasesTableTextBlock" xlink:label="us-gaap_ScheduleOfFutureMinimumLeasePaymentsForCapitalLeasesTableTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfFutureMinimumLeasePaymentsForCapitalLeasesTableTextBlock" xlink:to="us-gaap_ScheduleOfFutureMinimumLeasePaymentsForCapitalLeasesTableTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ScheduleOfFutureMinimumLeasePaymentsForCapitalLeasesTableTextBlock_lbl" xml:lang="en-US">Future minimum payments required under Capital Leases</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ScheduleOfFutureMinimumLeasePaymentsForLongTermDebtTableTextBlock" xlink:label="VSTA_ScheduleOfFutureMinimumLeasePaymentsForLongTermDebtTableTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ScheduleOfFutureMinimumLeasePaymentsForLongTermDebtTableTextBlock" xlink:to="VSTA_ScheduleOfFutureMinimumLeasePaymentsForLongTermDebtTableTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ScheduleOfFutureMinimumLeasePaymentsForLongTermDebtTableTextBlock_lbl" xml:lang="en-US">Future minimum principal payments related to Long-Term Debt</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_QuarterlyFinancialInformationTableTextBlock" xlink:label="VSTA_QuarterlyFinancialInformationTableTextBlock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_QuarterlyFinancialInformationTableTextBlock" xlink:to="VSTA_QuarterlyFinancialInformationTableTextBlock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_QuarterlyFinancialInformationTableTextBlock_lbl" xml:lang="en-US">Unaudited Quarterly Results of Operations</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_HistoryAndOrganizationDetailsTextualsAbstract" xlink:label="VSTA_HistoryAndOrganizationDetailsTextualsAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_HistoryAndOrganizationDetailsTextualsAbstract" xlink:to="VSTA_HistoryAndOrganizationDetailsTextualsAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_HistoryAndOrganizationDetailsTextualsAbstract_lbl" xml:lang="en-US">Description Of Business Details Narrative</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersCompensationEarned" xlink:label="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersCompensationEarned" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersCompensationEarned" xlink:to="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersCompensationEarned_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ResearchAndDevelopmentArrangementContractToPerformForOthersCompensationEarned_lbl" xml:lang="en-US">NIH awarded the Company aggregate support</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_OutstandingShares" xlink:label="VSTA_OutstandingShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_OutstandingShares" xlink:to="VSTA_OutstandingShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_OutstandingShares_lbl" xml:lang="en-US">Merger shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_SharesOutstandingAtMerger" xlink:label="VSTA_SharesOutstandingAtMerger" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SharesOutstandingAtMerger" xlink:to="VSTA_SharesOutstandingAtMerger_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SharesOutstandingAtMerger_lbl" xml:lang="en-US">Shares outstanding at merger</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_OutstandingShareRepresentation" xlink:label="VSTA_OutstandingShareRepresentation" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_OutstandingShareRepresentation" xlink:to="VSTA_OutstandingShareRepresentation_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_OutstandingShareRepresentation_lbl" xml:lang="en-US">Outstanding share representation</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_NumberOfSharesAuthorizedFollowingAmendment" xlink:label="VSTA_NumberOfSharesAuthorizedFollowingAmendment" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NumberOfSharesAuthorizedFollowingAmendment" xlink:to="VSTA_NumberOfSharesAuthorizedFollowingAmendment_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NumberOfSharesAuthorizedFollowingAmendment_lbl" xml:lang="en-US">Number of shares authorized following amendment</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_NumberOfPreferredSharesAuthorizedFollowingAmendment" xlink:label="VSTA_NumberOfPreferredSharesAuthorizedFollowingAmendment" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NumberOfPreferredSharesAuthorizedFollowingAmendment" xlink:to="VSTA_NumberOfPreferredSharesAuthorizedFollowingAmendment_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NumberOfPreferredSharesAuthorizedFollowingAmendment_lbl" xml:lang="en-US">Number of Preferred shares authorized following amendment</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_SeriesPreferredStockShares" xlink:label="VSTA_SeriesPreferredStockShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SeriesPreferredStockShares" xlink:to="VSTA_SeriesPreferredStockShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SeriesPreferredStockShares_lbl" xml:lang="en-US">Series A Preferred Stock shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_SeriesPreferredShareParValue" xlink:label="VSTA_SeriesPreferredShareParValue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SeriesPreferredShareParValue" xlink:to="VSTA_SeriesPreferredShareParValue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SeriesPreferredShareParValue_lbl" xml:lang="en-US">Series A Preferred share par value</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ConversionRateSeriesPreferredShares" xlink:label="VSTA_ConversionRateSeriesPreferredShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConversionRateSeriesPreferredShares" xlink:to="VSTA_ConversionRateSeriesPreferredShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConversionRateSeriesPreferredShares_lbl" xml:lang="en-US">Conversion Rate, Series A Preferred shares</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ConversionTotalSeriesPreferredToCommonStock" xlink:label="VSTA_ConversionTotalSeriesPreferredToCommonStock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConversionTotalSeriesPreferredToCommonStock" xlink:to="VSTA_ConversionTotalSeriesPreferredToCommonStock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConversionTotalSeriesPreferredToCommonStock_lbl" xml:lang="en-US">Conversion total, Series A Preferred to Common</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ConversionToWarrantWarrantValue" xlink:label="VSTA_ConversionToWarrantWarrantValue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConversionToWarrantWarrantValue" xlink:to="VSTA_ConversionToWarrantWarrantValue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ConversionToWarrantWarrantValue_lbl" xml:lang="en-US">Conversion to warrant, warrant value</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_WarrantsExercisePrice" xlink:label="VSTA_WarrantsExercisePrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_WarrantsExercisePrice" xlink:to="VSTA_WarrantsExercisePrice_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_WarrantsExercisePrice_lbl" xml:lang="en-US">Warrant exercise price</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_BasisOfPresentationAndGoingConcernDetailsTextualsAbstract" xlink:label="VSTA_BasisOfPresentationAndGoingConcernDetailsTextualsAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_BasisOfPresentationAndGoingConcernDetailsTextualsAbstract" xlink:to="VSTA_BasisOfPresentationAndGoingConcernDetailsTextualsAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_BasisOfPresentationAndGoingConcernDetailsTextualsAbstract_lbl" xml:lang="en-US">Basis Of Presentation And Going Concern Details Narrative</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RetainedEarningsAccumulatedDeficit" xlink:to="us-gaap_RetainedEarningsAccumulatedDeficit_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit_2_lbl" xml:lang="en-US">Accumulated Deficit during its development stage</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProceedsFromConvertibleDebt" xlink:label="us-gaap_ProceedsFromConvertibleDebt" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProceedsFromConvertibleDebt" xlink:to="us-gaap_ProceedsFromConvertibleDebt_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ProceedsFromConvertibleDebt_lbl" xml:lang="en-US">Cash proceeds from convertible and short-term notes</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProceedsFromGrantors" xlink:label="us-gaap_ProceedsFromGrantors" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProceedsFromGrantors" xlink:to="us-gaap_ProceedsFromGrantors_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ProceedsFromGrantors_lbl" xml:lang="en-US">Cash proceeds from grant awards and other events</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_CashProceedsFromAutilionPurchaseAgreement" xlink:label="VSTA_CashProceedsFromAutilionPurchaseAgreement" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CashProceedsFromAutilionPurchaseAgreement" xlink:to="VSTA_CashProceedsFromAutilionPurchaseAgreement_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CashProceedsFromAutilionPurchaseAgreement_lbl" xml:lang="en-US">Cash proceeds from Autilion purchase agreement</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProceedsFromIssuanceOrSaleOfEquity" xlink:label="us-gaap_ProceedsFromIssuanceOrSaleOfEquity" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProceedsFromIssuanceOrSaleOfEquity" xlink:to="us-gaap_ProceedsFromIssuanceOrSaleOfEquity_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ProceedsFromIssuanceOrSaleOfEquity_lbl" xml:lang="en-US">Equity issuance</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_CashExpenditureMaximum" xlink:label="VSTA_CashExpenditureMaximum" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CashExpenditureMaximum" xlink:to="VSTA_CashExpenditureMaximum_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CashExpenditureMaximum_lbl" xml:lang="en-US">Cash expenditure</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_SharePurchaseObligation" xlink:label="VSTA_SharePurchaseObligation" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SharePurchaseObligation" xlink:to="VSTA_SharePurchaseObligation_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SharePurchaseObligation_lbl" xml:lang="en-US">Share purchase obligation</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_SharePurchaseObligationCashConsideration" xlink:label="VSTA_SharePurchaseObligationCashConsideration" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SharePurchaseObligationCashConsideration" xlink:to="VSTA_SharePurchaseObligationCashConsideration_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SharePurchaseObligationCashConsideration_lbl" xml:lang="en-US">Share purchase obligation cash consideration</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_InitialShareIssuance" xlink:label="VSTA_InitialShareIssuance" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_InitialShareIssuance" xlink:to="VSTA_InitialShareIssuance_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_InitialShareIssuance_lbl" xml:lang="en-US">initial share issuance</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage" xlink:label="us-gaap_DebtInstrumentInterestRateStatedPercentage" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentInterestRateStatedPercentage" xlink:to="us-gaap_DebtInstrumentInterestRateStatedPercentage_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DebtInstrumentInterestRateStatedPercentage_lbl" xml:lang="en-US">Note interest rate</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NoncashOrPartNoncashAcquisitionNoncashFinancialOrEquityInstrumentConsiderationWarrantsIssued1" xlink:label="us-gaap_NoncashOrPartNoncashAcquisitionNoncashFinancialOrEquityInstrumentConsiderationWarrantsIssued1" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NoncashOrPartNoncashAcquisitionNoncashFinancialOrEquityInstrumentConsiderationWarrantsIssued1" xlink:to="us-gaap_NoncashOrPartNoncashAcquisitionNoncashFinancialOrEquityInstrumentConsiderationWarrantsIssued1_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NoncashOrPartNoncashAcquisitionNoncashFinancialOrEquityInstrumentConsiderationWarrantsIssued1_lbl" xml:lang="en-US">Warrants issued</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_WarrantExercisePrice" xlink:label="VSTA_WarrantExercisePrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_WarrantExercisePrice" xlink:to="VSTA_WarrantExercisePrice_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="VSTA_WarrantExercisePrice_lbl" xml:lang="en-US">Warrant exercise price</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProceedsFromIssuanceOfPrivatePlacement" xlink:label="us-gaap_ProceedsFromIssuanceOfPrivatePlacement" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProceedsFromIssuanceOfPrivatePlacement" xlink:to="us-gaap_ProceedsFromIssuanceOfPrivatePlacement_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ProceedsFromIssuanceOfPrivatePlacement_lbl" xml:lang="en-US">Private placement proceeds</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_AlternativeFinancingMinimum" xlink:label="VSTA_AlternativeFinancingMinimum" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AlternativeFinancingMinimum" xlink:to="VSTA_AlternativeFinancingMinimum_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AlternativeFinancingMinimum_lbl" xml:lang="en-US">Alternative financing, minimum</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_AlternativeFinancingMaximum" xlink:label="VSTA_AlternativeFinancingMaximum" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AlternativeFinancingMaximum" xlink:to="VSTA_AlternativeFinancingMaximum_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AlternativeFinancingMaximum_lbl" xml:lang="en-US">Alternative financing, maximum</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_SummaryOfSignificantAccountingPoliciesDetails2Abstract" xlink:label="VSTA_SummaryOfSignificantAccountingPoliciesDetails2Abstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SummaryOfSignificantAccountingPoliciesDetails2Abstract" xlink:to="VSTA_SummaryOfSignificantAccountingPoliciesDetails2Abstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SummaryOfSignificantAccountingPoliciesDetails2Abstract_lbl" xml:lang="en-US">Summary Of Significant Accounting Policies Details 1</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_NumeratorAbstract" xlink:label="VSTA_NumeratorAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NumeratorAbstract" xlink:to="VSTA_NumeratorAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NumeratorAbstract_lbl" xml:lang="en-US">Numerator:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LiabilitiesFairValueAdjustment" xlink:label="us-gaap_LiabilitiesFairValueAdjustment" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesFairValueAdjustment" xlink:to="us-gaap_LiabilitiesFairValueAdjustment_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LiabilitiesFairValueAdjustment_lbl" xml:lang="en-US">less: change in fair value of warrant liability attributable to Exchange, Investment and July 2013 Warrants issued to Platinum</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted" xlink:label="us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted" xlink:to="us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted_lbl" xml:lang="en-US">Net loss for diluted earnings per share attributable to common stockholders</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_DenominatorAbstract" xlink:label="VSTA_DenominatorAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_DenominatorAbstract" xlink:to="VSTA_DenominatorAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_DenominatorAbstract_lbl" xml:lang="en-US">Denominator:</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic" xlink:to="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_2_lbl" xml:lang="en-US">Weighted average basic common shares outstanding</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DilutiveSecuritiesAbstract" xlink:label="us-gaap_DilutiveSecuritiesAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DilutiveSecuritiesAbstract" xlink:to="us-gaap_DilutiveSecuritiesAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DilutiveSecuritiesAbstract_lbl" xml:lang="en-US">Assumed conversion of dilutive securities:</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_WarrantsExcludedFromComputationOfEarningsPerShareAmount" xlink:label="VSTA_WarrantsExcludedFromComputationOfEarningsPerShareAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_WarrantsExcludedFromComputationOfEarningsPerShareAmount" xlink:to="VSTA_WarrantsExcludedFromComputationOfEarningsPerShareAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_WarrantsExcludedFromComputationOfEarningsPerShareAmount_lbl" xml:lang="en-US">Warrants to purchase common stock</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" xlink:to="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_lbl" xml:lang="en-US">Potentially dilutive common shares assumed converted</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" xlink:to="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_2_lbl" xml:lang="en-US">Denominator for diluted earnings per share - adjusted&#160;weighted average shares</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EarningsPerShareAbstract" xlink:label="us-gaap_EarningsPerShareAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EarningsPerShareAbstract" xlink:to="us-gaap_EarningsPerShareAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_EarningsPerShareAbstract_lbl" xml:lang="en-US">Loss per Common Share</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PreferredStockSharesIssued" xlink:label="us-gaap_PreferredStockSharesIssued" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PreferredStockSharesIssued" xlink:to="us-gaap_PreferredStockSharesIssued_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PreferredStockSharesIssued_lbl" xml:lang="en-US">Series A preferred stock issued and outstanding</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_WarrantSharesIssuableUponExerciseNotePurchaseAndExchangeAgreement" xlink:label="VSTA_WarrantSharesIssuableUponExerciseNotePurchaseAndExchangeAgreement" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_WarrantSharesIssuableUponExerciseNotePurchaseAndExchangeAgreement" xlink:to="VSTA_WarrantSharesIssuableUponExerciseNotePurchaseAndExchangeAgreement_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_WarrantSharesIssuableUponExerciseNotePurchaseAndExchangeAgreement_lbl" xml:lang="en-US">Warrant shares issuable to Platinum upon exercise of common stock warrants by Platinum upon exchange of Series A preferred stock under the terms of the October 11, 2012 Note Purchase and Exchange Agreement</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_lbl" xml:lang="en-US">Outstanding options under the 2008 and 1999 Stock Incentive Plans</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_OutstandingWarrantsToPurchaseCommonStock" xlink:label="VSTA_OutstandingWarrantsToPurchaseCommonStock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_OutstandingWarrantsToPurchaseCommonStock" xlink:to="VSTA_OutstandingWarrantsToPurchaseCommonStock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_OutstandingWarrantsToPurchaseCommonStock_lbl" xml:lang="en-US">Outstanding warrants to purchase common stock</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ConvertibleNotesPayableCurrent" xlink:to="us-gaap_ConvertibleNotesPayableCurrent_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_ConvertibleNotesPayableCurrent_2_lbl" xml:lang="en-US">Convertible promissory notes and accrued interest</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_Total" xlink:label="VSTA_Total" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_Total" xlink:to="VSTA_Total_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_Total_lbl" xml:lang="en-US">Total</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LiabilitiesFairValueDisclosureAbstract" xlink:label="us-gaap_LiabilitiesFairValueDisclosureAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesFairValueDisclosureAbstract" xlink:to="us-gaap_LiabilitiesFairValueDisclosureAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LiabilitiesFairValueDisclosureAbstract_lbl" xml:lang="en-US">Liabilities, Fair Value Disclosure</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue" xlink:to="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_lbl" xml:lang="en-US">Warrant liability</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue" xlink:to="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_2_lbl" xml:lang="en-US">Warrant liability, beginning of period</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityTransfersNet" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityTransfersNet" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityTransfersNet" xlink:to="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityTransfersNet_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityTransfersNet_lbl" xml:lang="en-US">Recognition of warrant liability during period</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityTransfersNet2" xlink:label="VSTA_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityTransfersNet2" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityTransfersNet2" xlink:to="VSTA_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityTransfersNet2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityTransfersNet2_lbl" xml:lang="en-US">Subsequent recognition of warrant liability during period</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisGainLossIncludedInEarnings" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisGainLossIncludedInEarnings" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisGainLossIncludedInEarnings" xlink:to="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisGainLossIncludedInEarnings_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringBasisGainLossIncludedInEarnings_lbl" xml:lang="en-US">Mark to Market gain included in net income</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue" xlink:to="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_3_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_3_lbl" xml:lang="en-US">Warrant liability, end of period</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_PrepaidExpensesDetailsAbstract" xlink:label="VSTA_PrepaidExpensesDetailsAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PrepaidExpensesDetailsAbstract" xlink:to="VSTA_PrepaidExpensesDetailsAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PrepaidExpensesDetailsAbstract_lbl" xml:lang="en-US">Prepaid Expenses And Other Current Assets Details</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PrepaidExpenseCurrentAbstract" xlink:label="us-gaap_PrepaidExpenseCurrentAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PrepaidExpenseCurrentAbstract" xlink:to="us-gaap_PrepaidExpenseCurrentAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_PrepaidExpenseCurrentAbstract_lbl" xml:lang="en-US">Prepaid Expenses</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PrepaidInsurance" xlink:label="us-gaap_PrepaidInsurance" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PrepaidInsurance" xlink:to="us-gaap_PrepaidInsurance_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PrepaidInsurance_lbl" xml:lang="en-US">Insurance</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_LegalFees1" xlink:label="VSTA_LegalFees1" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_LegalFees1" xlink:to="VSTA_LegalFees1_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_LegalFees1_lbl" xml:lang="en-US">Legal fees</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_InterestReceivable" xlink:label="us-gaap_InterestReceivable" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_InterestReceivable" xlink:to="us-gaap_InterestReceivable_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_InterestReceivable_lbl" xml:lang="en-US">Interest receivable on note receivable from sale of common stock</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherPrepaidExpenseCurrent" xlink:label="us-gaap_OtherPrepaidExpenseCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherPrepaidExpenseCurrent" xlink:to="us-gaap_OtherPrepaidExpenseCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OtherPrepaidExpenseCurrent_lbl" xml:lang="en-US">Technology license fees and all other</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent" xlink:label="us-gaap_PrepaidExpenseAndOtherAssetsCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PrepaidExpenseAndOtherAssetsCurrent" xlink:to="us-gaap_PrepaidExpenseAndOtherAssetsCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_PrepaidExpenseAndOtherAssetsCurrent_lbl" xml:lang="en-US">Total</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_MachineryAndEquipmentGross" xlink:label="us-gaap_MachineryAndEquipmentGross" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_MachineryAndEquipmentGross" xlink:to="us-gaap_MachineryAndEquipmentGross_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_MachineryAndEquipmentGross_lbl" xml:lang="en-US">Laboratory equipment</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_TenantImprovements" xlink:label="us-gaap_TenantImprovements" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TenantImprovements" xlink:to="us-gaap_TenantImprovements_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_TenantImprovements_lbl" xml:lang="en-US">Tenant improvements</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ComputersAndNetworkEquipment" xlink:label="VSTA_ComputersAndNetworkEquipment" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ComputersAndNetworkEquipment" xlink:to="VSTA_ComputersAndNetworkEquipment_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ComputersAndNetworkEquipment_lbl" xml:lang="en-US">Computers and network equipment</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_OfficeFurnitureAndEquipment" xlink:label="VSTA_OfficeFurnitureAndEquipment" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_OfficeFurnitureAndEquipment" xlink:to="VSTA_OfficeFurnitureAndEquipment_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_OfficeFurnitureAndEquipment_lbl" xml:lang="en-US">Office furniture and equipment</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_PropertyPlantAndEquipmentGross" xlink:label="us-gaap_PropertyPlantAndEquipmentGross" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PropertyPlantAndEquipmentGross" xlink:to="us-gaap_PropertyPlantAndEquipmentGross_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PropertyPlantAndEquipmentGross_lbl" xml:lang="en-US">Property and equipment gross</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:label="us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:to="us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_lbl" xml:lang="en-US">Accumulated depreciation and amortization</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesAcquisitions" xlink:label="us-gaap_StockIssuedDuringPeriodSharesAcquisitions" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockIssuedDuringPeriodSharesAcquisitions" xlink:to="us-gaap_StockIssuedDuringPeriodSharesAcquisitions_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_StockIssuedDuringPeriodSharesAcquisitions_lbl" xml:lang="en-US">Series B-1 Shares issued</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EquityIssuancePerShareAmount" xlink:label="us-gaap_EquityIssuancePerShareAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EquityIssuancePerShareAmount" xlink:to="us-gaap_EquityIssuancePerShareAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_EquityIssuancePerShareAmount_lbl" xml:lang="en-US">Series B-1 value per share</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueAcquisitions" xlink:label="us-gaap_StockIssuedDuringPeriodValueAcquisitions" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockIssuedDuringPeriodValueAcquisitions" xlink:to="us-gaap_StockIssuedDuringPeriodValueAcquisitions_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_StockIssuedDuringPeriodValueAcquisitions_lbl" xml:lang="en-US">Pre-Merger purchase price</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_AccruedExpensesDetailsAbstract" xlink:label="VSTA_AccruedExpensesDetailsAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AccruedExpensesDetailsAbstract" xlink:to="VSTA_AccruedExpensesDetailsAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AccruedExpensesDetailsAbstract_lbl" xml:lang="en-US">Accrued Expenses Details</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccruedLiabilitiesCurrentAbstract" xlink:label="us-gaap_AccruedLiabilitiesCurrentAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccruedLiabilitiesCurrentAbstract" xlink:to="us-gaap_AccruedLiabilitiesCurrentAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_AccruedLiabilitiesCurrentAbstract_lbl" xml:lang="en-US">Accrued Expenses</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccruedProfessionalFeesCurrent" xlink:label="us-gaap_AccruedProfessionalFeesCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccruedProfessionalFeesCurrent" xlink:to="us-gaap_AccruedProfessionalFeesCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AccruedProfessionalFeesCurrent_lbl" xml:lang="en-US">Accrued professional services</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccruedVacationCurrent" xlink:label="us-gaap_AccruedVacationCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccruedVacationCurrent" xlink:to="us-gaap_AccruedVacationCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AccruedVacationCurrent_lbl" xml:lang="en-US">Accrued compensation</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_AccruedRoyaltiesCurrentAndNoncurrent" xlink:label="us-gaap_AccruedRoyaltiesCurrentAndNoncurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccruedRoyaltiesCurrentAndNoncurrent" xlink:to="us-gaap_AccruedRoyaltiesCurrentAndNoncurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AccruedRoyaltiesCurrentAndNoncurrent_lbl" xml:lang="en-US">Accrued royalties and license fees</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OtherAccruedLiabilitiesCurrent" xlink:label="us-gaap_OtherAccruedLiabilitiesCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherAccruedLiabilitiesCurrent" xlink:to="us-gaap_OtherAccruedLiabilitiesCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OtherAccruedLiabilitiesCurrent_lbl" xml:lang="en-US">All other</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccruedLiabilitiesCurrent" xlink:to="us-gaap_AccruedLiabilitiesCurrent_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_AccruedLiabilitiesCurrent_2_lbl" xml:lang="en-US">Total</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DebtInstrumentFaceAmount" xlink:label="us-gaap_DebtInstrumentFaceAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentFaceAmount" xlink:to="us-gaap_DebtInstrumentFaceAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DebtInstrumentFaceAmount_lbl" xml:lang="en-US">Principal Balance</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_InterestPayableCurrentAndNoncurrent" xlink:label="us-gaap_InterestPayableCurrentAndNoncurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_InterestPayableCurrentAndNoncurrent" xlink:to="us-gaap_InterestPayableCurrentAndNoncurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_InterestPayableCurrentAndNoncurrent_lbl" xml:lang="en-US">Accrued Interest</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DebtInstrumentCarryingAmount" xlink:label="us-gaap_DebtInstrumentCarryingAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentCarryingAmount" xlink:to="us-gaap_DebtInstrumentCarryingAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_DebtInstrumentCarryingAmount_lbl" xml:lang="en-US">Total</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ReceivableWithImputedInterestDiscount" xlink:label="us-gaap_ReceivableWithImputedInterestDiscount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ReceivableWithImputedInterestDiscount" xlink:to="us-gaap_ReceivableWithImputedInterestDiscount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ReceivableWithImputedInterestDiscount_lbl" xml:lang="en-US">Note discount on principal</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ReceivableWithImputedInterestDiscountOnAccruedInterest" xlink:label="VSTA_ReceivableWithImputedInterestDiscountOnAccruedInterest" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ReceivableWithImputedInterestDiscountOnAccruedInterest" xlink:to="VSTA_ReceivableWithImputedInterestDiscountOnAccruedInterest_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ReceivableWithImputedInterestDiscountOnAccruedInterest_lbl" xml:lang="en-US">Note discount on accrued interest</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ReceivableWithImputedInterestDiscountOnPrincipalAndAccruedInterest" xlink:label="VSTA_ReceivableWithImputedInterestDiscountOnPrincipalAndAccruedInterest" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ReceivableWithImputedInterestDiscountOnPrincipalAndAccruedInterest" xlink:to="VSTA_ReceivableWithImputedInterestDiscountOnPrincipalAndAccruedInterest_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ReceivableWithImputedInterestDiscountOnPrincipalAndAccruedInterest_lbl" xml:lang="en-US">Note discount, total</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentFaceAmount" xlink:to="us-gaap_DebtInstrumentFaceAmount_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_DebtInstrumentFaceAmount_2_lbl" xml:lang="en-US">Face value</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_DiscountAttributableToFairValueOfWarrant" xlink:label="VSTA_DiscountAttributableToFairValueOfWarrant" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_DiscountAttributableToFairValueOfWarrant" xlink:to="VSTA_DiscountAttributableToFairValueOfWarrant_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_DiscountAttributableToFairValueOfWarrant_lbl" xml:lang="en-US">Discount attributable to fair value of the warrant</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_DiscountAttributableToBeneficialConversionFeature" xlink:label="VSTA_DiscountAttributableToBeneficialConversionFeature" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_DiscountAttributableToBeneficialConversionFeature" xlink:to="VSTA_DiscountAttributableToBeneficialConversionFeature_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_DiscountAttributableToBeneficialConversionFeature_lbl" xml:lang="en-US">Discount attributable to beneficial conversion feature</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_InceptionDateCarryingValue" xlink:label="VSTA_InceptionDateCarryingValue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_InceptionDateCarryingValue" xlink:to="VSTA_InceptionDateCarryingValue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_InceptionDateCarryingValue_lbl" xml:lang="en-US">Inception date carrying value</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DebtInstrumentInterestRateEffectivePercentage" xlink:label="us-gaap_DebtInstrumentInterestRateEffectivePercentage" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentInterestRateEffectivePercentage" xlink:to="us-gaap_DebtInstrumentInterestRateEffectivePercentage_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DebtInstrumentInterestRateEffectivePercentage_lbl" xml:lang="en-US">Effective Interest Rate</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EquityIssuancePerShareAmount" xlink:to="us-gaap_EquityIssuancePerShareAmount_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_EquityIssuancePerShareAmount_2_lbl" xml:lang="en-US">Market price of common stock</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ExercisePrice" xlink:label="VSTA_ExercisePrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExercisePrice" xlink:to="VSTA_ExercisePrice_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ExercisePrice_lbl" xml:lang="en-US">Exercise price</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueAssumptionsRiskFreeInterestRate" xlink:label="us-gaap_FairValueAssumptionsRiskFreeInterestRate" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueAssumptionsRiskFreeInterestRate" xlink:to="us-gaap_FairValueAssumptionsRiskFreeInterestRate_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FairValueAssumptionsRiskFreeInterestRate_lbl" xml:lang="en-US">Risk-free interest rate</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueAssumptionsExpectedVolatilityRate" xlink:label="us-gaap_FairValueAssumptionsExpectedVolatilityRate" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueAssumptionsExpectedVolatilityRate" xlink:to="us-gaap_FairValueAssumptionsExpectedVolatilityRate_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FairValueAssumptionsExpectedVolatilityRate_lbl" xml:lang="en-US">Volatility</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueAssumptionsExpectedTerm" xlink:label="us-gaap_FairValueAssumptionsExpectedTerm" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueAssumptionsExpectedTerm" xlink:to="us-gaap_FairValueAssumptionsExpectedTerm_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FairValueAssumptionsExpectedTerm_lbl" xml:lang="en-US">Term (years)</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueAssumptionsExpectedDividendRate" xlink:label="us-gaap_FairValueAssumptionsExpectedDividendRate" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueAssumptionsExpectedDividendRate" xlink:to="us-gaap_FairValueAssumptionsExpectedDividendRate_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FairValueAssumptionsExpectedDividendRate_lbl" xml:lang="en-US">Dividend rate</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_FairValuePerShare" xlink:label="VSTA_FairValuePerShare" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValuePerShare" xlink:to="VSTA_FairValuePerShare_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValuePerShare_lbl" xml:lang="en-US">Fair value per share</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DebtConversionConvertedInstrumentWarrantsOrOptionsIssued1" xlink:label="us-gaap_DebtConversionConvertedInstrumentWarrantsOrOptionsIssued1" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtConversionConvertedInstrumentWarrantsOrOptionsIssued1" xlink:to="us-gaap_DebtConversionConvertedInstrumentWarrantsOrOptionsIssued1_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DebtConversionConvertedInstrumentWarrantsOrOptionsIssued1_lbl" xml:lang="en-US">Number of shares</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockAndWarrantsIssuedDuringPeriodValuePreferredStockAndWarrants" xlink:label="us-gaap_StockAndWarrantsIssuedDuringPeriodValuePreferredStockAndWarrants" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockAndWarrantsIssuedDuringPeriodValuePreferredStockAndWarrants" xlink:to="us-gaap_StockAndWarrantsIssuedDuringPeriodValuePreferredStockAndWarrants_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_StockAndWarrantsIssuedDuringPeriodValuePreferredStockAndWarrants_lbl" xml:lang="en-US">Fair value at date of issuance</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_MarketPricePerShare" xlink:label="VSTA_MarketPricePerShare" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_MarketPricePerShare" xlink:to="VSTA_MarketPricePerShare_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_MarketPricePerShare_lbl" xml:lang="en-US">Market price per share</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_FairValueAssumptionsExercisePrice1" xlink:label="VSTA_FairValueAssumptionsExercisePrice1" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueAssumptionsExercisePrice1" xlink:to="VSTA_FairValueAssumptionsExercisePrice1_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValueAssumptionsExercisePrice1_lbl" xml:lang="en-US">Exercise price per share</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueAssumptionsExpectedTerm" xlink:to="us-gaap_FairValueAssumptionsExpectedTerm_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_FairValueAssumptionsExpectedTerm_2_lbl" xml:lang="en-US">Expected term (years)</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValuePerShare" xlink:to="VSTA_FairValuePerShare_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="VSTA_FairValuePerShare_2_lbl" xml:lang="en-US">Fair Value per share</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis" xlink:to="us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_2_lbl" xml:lang="en-US">Investment, Name [Axis]</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DerivativeLiabilities" xlink:label="us-gaap_DerivativeLiabilities" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DerivativeLiabilities" xlink:to="us-gaap_DerivativeLiabilities_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DerivativeLiabilities_lbl" xml:lang="en-US">Fair value warrant</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_DecreaseinDerivativeLiabilitiesQuarter" xlink:label="VSTA_DecreaseinDerivativeLiabilitiesQuarter" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_DecreaseinDerivativeLiabilitiesQuarter" xlink:to="VSTA_DecreaseinDerivativeLiabilitiesQuarter_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_DecreaseinDerivativeLiabilitiesQuarter_lbl" xml:lang="en-US">Decrease in fair value warrant quarter end</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_DecreaseinDerivativeLiabilitiesThreeMonth" xlink:label="VSTA_DecreaseinDerivativeLiabilitiesThreeMonth" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_DecreaseinDerivativeLiabilitiesThreeMonth" xlink:to="VSTA_DecreaseinDerivativeLiabilitiesThreeMonth_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_DecreaseinDerivativeLiabilitiesThreeMonth_lbl" xml:lang="en-US">Decrease in fair value warrant three months end</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SharePrice" xlink:label="us-gaap_SharePrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SharePrice" xlink:to="us-gaap_SharePrice_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_SharePrice_lbl" xml:lang="en-US">Market price per share</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_FairValueAssumptionsExercisePrice" xlink:label="us-gaap_FairValueAssumptionsExercisePrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueAssumptionsExercisePrice" xlink:to="us-gaap_FairValueAssumptionsExercisePrice_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_FairValueAssumptionsExercisePrice_lbl" xml:lang="en-US">Exercise price per share</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentInterestRateEffectivePercentage" xlink:to="us-gaap_DebtInstrumentInterestRateEffectivePercentage_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_DebtInstrumentInterestRateEffectivePercentage_2_lbl" xml:lang="en-US">Risk-free interest rate</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ExpectedTermYear" xlink:label="VSTA_ExpectedTermYear" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExpectedTermYear" xlink:to="VSTA_ExpectedTermYear_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ExpectedTermYear_lbl" xml:lang="en-US">Expected term (years)</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongDurationContractsAssumptionsByProductAndGuaranteeVolatilityRate" xlink:label="us-gaap_LongDurationContractsAssumptionsByProductAndGuaranteeVolatilityRate" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LongDurationContractsAssumptionsByProductAndGuaranteeVolatilityRate" xlink:to="us-gaap_LongDurationContractsAssumptionsByProductAndGuaranteeVolatilityRate_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_LongDurationContractsAssumptionsByProductAndGuaranteeVolatilityRate_lbl" xml:lang="en-US">Volatility</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_DividendRate" xlink:label="VSTA_DividendRate" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_DividendRate" xlink:to="VSTA_DividendRate_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="VSTA_DividendRate_lbl" xml:lang="en-US">Dividend rate</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ChangeInWarrantPutAndNoteExtensionOptionAndWarrantLiabilities" xlink:label="VSTA_ChangeInWarrantPutAndNoteExtensionOptionAndWarrantLiabilities" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ChangeInWarrantPutAndNoteExtensionOptionAndWarrantLiabilities" xlink:to="VSTA_ChangeInWarrantPutAndNoteExtensionOptionAndWarrantLiabilities_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ChangeInWarrantPutAndNoteExtensionOptionAndWarrantLiabilities_lbl" xml:lang="en-US">Change in warrant put and note extension option and warrant liabilities</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongTermDebtPercentageBearingFixedInterestRate" xlink:label="us-gaap_LongTermDebtPercentageBearingFixedInterestRate" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LongTermDebtPercentageBearingFixedInterestRate" xlink:to="us-gaap_LongTermDebtPercentageBearingFixedInterestRate_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LongTermDebtPercentageBearingFixedInterestRate_lbl" xml:lang="en-US">Interest rate</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_GrossProceedsConversionNote" xlink:label="VSTA_GrossProceedsConversionNote" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_GrossProceedsConversionNote" xlink:to="VSTA_GrossProceedsConversionNote_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_GrossProceedsConversionNote_lbl" xml:lang="en-US">Gross proceeds</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_AccruedInterestRatePerShare" xlink:label="VSTA_AccruedInterestRatePerShare" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AccruedInterestRatePerShare" xlink:to="VSTA_AccruedInterestRatePerShare_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AccruedInterestRatePerShare_lbl" xml:lang="en-US">Accrued interest rate per share</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" xlink:label="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" xlink:to="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_lbl" xml:lang="en-US">Warrants to purchase shares</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_TemporaryEquityParOrStatedValuePerShare" xlink:label="us-gaap_TemporaryEquityParOrStatedValuePerShare" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TemporaryEquityParOrStatedValuePerShare" xlink:to="us-gaap_TemporaryEquityParOrStatedValuePerShare_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_TemporaryEquityParOrStatedValuePerShare_lbl" xml:lang="en-US">Investment Warrant exercise price</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsOtherShareIncreaseDecreaseInPeriodWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsOtherShareIncreaseDecreaseInPeriodWeightedAverageExercisePrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsOtherShareIncreaseDecreaseInPeriodWeightedAverageExercisePrice" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsOtherShareIncreaseDecreaseInPeriodWeightedAverageExercisePrice_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsOtherShareIncreaseDecreaseInPeriodWeightedAverageExercisePrice_lbl" xml:lang="en-US">Market price per share</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingPeriodIncreaseDecreaseWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingPeriodIncreaseDecreaseWeightedAverageExercisePrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingPeriodIncreaseDecreaseWeightedAverageExercisePrice" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingPeriodIncreaseDecreaseWeightedAverageExercisePrice_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingPeriodIncreaseDecreaseWeightedAverageExercisePrice_lbl" xml:lang="en-US">Exercise price per share</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ShareBasedCompensationArrangementsByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsWeightedAverageGrantDateFairValuePeriodIncreaseDecrease" xlink:label="VSTA_ShareBasedCompensationArrangementsByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsWeightedAverageGrantDateFairValuePeriodIncreaseDecrease" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationArrangementsByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsWeightedAverageGrantDateFairValuePeriodIncreaseDecrease" xlink:to="VSTA_ShareBasedCompensationArrangementsByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsWeightedAverageGrantDateFairValuePeriodIncreaseDecrease_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ShareBasedCompensationArrangementsByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsWeightedAverageGrantDateFairValuePeriodIncreaseDecrease_lbl" xml:lang="en-US">Fair Value per share</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_WarrantsOutstanding" xlink:label="VSTA_WarrantsOutstanding" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_WarrantsOutstanding" xlink:to="VSTA_WarrantsOutstanding_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_WarrantsOutstanding_lbl" xml:lang="en-US">Warrants outstanding</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExercisePrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExercisePrice" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExercisePrice_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExercisePrice_lbl" xml:lang="en-US">Exercise price per share</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ExpirateDateRange" xlink:label="VSTA_ExpirateDateRange" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExpirateDateRange" xlink:to="VSTA_ExpirateDateRange_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ExpirateDateRange_lbl" xml:lang="en-US">Expirate date range</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_WeightedAverageYearsToExpiration" xlink:label="VSTA_WeightedAverageYearsToExpiration" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_WeightedAverageYearsToExpiration" xlink:to="VSTA_WeightedAverageYearsToExpiration_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_WeightedAverageYearsToExpiration_lbl" xml:lang="en-US">Weighted average years to expiration</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ClassOfWarrantOrRightOutstanding" xlink:label="us-gaap_ClassOfWarrantOrRightOutstanding" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ClassOfWarrantOrRightOutstanding" xlink:to="us-gaap_ClassOfWarrantOrRightOutstanding_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ClassOfWarrantOrRightOutstanding_lbl" xml:lang="en-US">Shares subject to purchase</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_CapitalStockDetails2Abstract" xlink:label="VSTA_CapitalStockDetails2Abstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CapitalStockDetails2Abstract" xlink:to="VSTA_CapitalStockDetails2Abstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CapitalStockDetails2Abstract_lbl" xml:lang="en-US">Capital Stock Details 2</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion" xlink:label="us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion" xlink:to="us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ConvertiblePreferredStockSharesIssuedUponConversion_lbl" xml:lang="en-US">Upon exchange of all shares of Series A Preferred Stock currently issued and outstanding</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_WarrantSharesIssuableToPlatinumUponExerciseOfCommonStockWarrantUponExchangeOfSeriesPreferredStockUnderTermsOfOctober112012NotePurchaseAndExchangeAgreement" xlink:label="VSTA_WarrantSharesIssuableToPlatinumUponExerciseOfCommonStockWarrantUponExchangeOfSeriesPreferredStockUnderTermsOfOctober112012NotePurchaseAndExchangeAgreement" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_WarrantSharesIssuableToPlatinumUponExerciseOfCommonStockWarrantUponExchangeOfSeriesPreferredStockUnderTermsOfOctober112012NotePurchaseAndExchangeAgreement" xlink:to="VSTA_WarrantSharesIssuableToPlatinumUponExerciseOfCommonStockWarrantUponExchangeOfSeriesPreferredStockUnderTermsOfOctober112012NotePurchaseAndExchangeAgreement_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_WarrantSharesIssuableToPlatinumUponExerciseOfCommonStockWarrantUponExchangeOfSeriesPreferredStockUnderTermsOfOctober112012NotePurchaseAndExchangeAgreement_lbl" xml:lang="en-US">Warrant shares issuable to Platinum upon exercise of common stock warrant upon exchange of Series A preferred stock under the terms of the October 11, 2012 Note Purchase and Exchange Agreement</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_OfSharesIssuableUponConversionOf10ConvertibleExchangeNoteAndInvestmentNotesIssuedToPlatinumInOctober2012February2013AndMarch2013IncludingInterestAccruedThroughMaturity2" xlink:label="VSTA_OfSharesIssuableUponConversionOf10ConvertibleExchangeNoteAndInvestmentNotesIssuedToPlatinumInOctober2012February2013AndMarch2013IncludingInterestAccruedThroughMaturity2" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_OfSharesIssuableUponConversionOf10ConvertibleExchangeNoteAndInvestmentNotesIssuedToPlatinumInOctober2012February2013AndMarch2013IncludingInterestAccruedThroughMaturity2" xlink:to="VSTA_OfSharesIssuableUponConversionOf10ConvertibleExchangeNoteAndInvestmentNotesIssuedToPlatinumInOctober2012February2013AndMarch2013IncludingInterestAccruedThroughMaturity2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_OfSharesIssuableUponConversionOf10ConvertibleExchangeNoteAndInvestmentNotesIssuedToPlatinumInOctober2012February2013AndMarch2013IncludingInterestAccruedThroughMaturity2_lbl" xml:lang="en-US">110% of shares issuable upon conversion of 10% convertible Exchange Note and Investment Notes issued to Platinum in October 2012, February 2013 and March 2013, including interest accrued through maturity (2)</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_PursuantToWarrantsToPurchaseCommonStock" xlink:label="VSTA_PursuantToWarrantsToPurchaseCommonStock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PursuantToWarrantsToPurchaseCommonStock" xlink:to="VSTA_PursuantToWarrantsToPurchaseCommonStock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PursuantToWarrantsToPurchaseCommonStock_lbl" xml:lang="en-US">Pursuant to warrants to purchase common stock:</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" xlink:to="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights_2_lbl" xml:lang="en-US">Subject to outstanding warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_IssuablePursuantToAccruedInterestThroughMaturityOnOutstandingPromissoryNotesIssuedToMorrisonFoersterCatoResearchLtd.AndUniversityHealthNetwork" xlink:label="VSTA_IssuablePursuantToAccruedInterestThroughMaturityOnOutstandingPromissoryNotesIssuedToMorrisonFoersterCatoResearchLtd.AndUniversityHealthNetwork" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuablePursuantToAccruedInterestThroughMaturityOnOutstandingPromissoryNotesIssuedToMorrisonFoersterCatoResearchLtd.AndUniversityHealthNetwork" xlink:to="VSTA_IssuablePursuantToAccruedInterestThroughMaturityOnOutstandingPromissoryNotesIssuedToMorrisonFoersterCatoResearchLtd.AndUniversityHealthNetwork_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IssuablePursuantToAccruedInterestThroughMaturityOnOutstandingPromissoryNotesIssuedToMorrisonFoersterCatoResearchLtd.AndUniversityHealthNetwork_lbl" xml:lang="en-US">Issuable pursuant to accrued interest through maturity on outstanding promissory notes issued to Morrison &amp; Foerster, Cato Research Ltd., and University Health Network</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_PursuantToWarrantsToPurchaseCommonStockTotal" xlink:label="VSTA_PursuantToWarrantsToPurchaseCommonStockTotal" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PursuantToWarrantsToPurchaseCommonStockTotal" xlink:to="VSTA_PursuantToWarrantsToPurchaseCommonStockTotal_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PursuantToWarrantsToPurchaseCommonStockTotal_lbl" xml:lang="en-US">Pursuant to warrants to purchase common stock, total</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_PursuantToStockIncentivePlans" xlink:label="VSTA_PursuantToStockIncentivePlans" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PursuantToStockIncentivePlans" xlink:to="VSTA_PursuantToStockIncentivePlans_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PursuantToStockIncentivePlans_lbl" xml:lang="en-US">Pursuant to stock incentive plans:</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_SubjectToOutstandingOptionsUnder2008And1999StockIncentivePlans" xlink:label="VSTA_SubjectToOutstandingOptionsUnder2008And1999StockIncentivePlans" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SubjectToOutstandingOptionsUnder2008And1999StockIncentivePlans" xlink:to="VSTA_SubjectToOutstandingOptionsUnder2008And1999StockIncentivePlans_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SubjectToOutstandingOptionsUnder2008And1999StockIncentivePlans_lbl" xml:lang="en-US">Subject to outstanding options under the 2008 and 1999 Stock Incentive Plans</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_lbl" xml:lang="en-US">Available for future grants</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EmployeeStockOwnershipPlanESOPNumberOfCommittedToBeReleasedShares" xlink:label="us-gaap_EmployeeStockOwnershipPlanESOPNumberOfCommittedToBeReleasedShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EmployeeStockOwnershipPlanESOPNumberOfCommittedToBeReleasedShares" xlink:to="us-gaap_EmployeeStockOwnershipPlanESOPNumberOfCommittedToBeReleasedShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_EmployeeStockOwnershipPlanESOPNumberOfCommittedToBeReleasedShares_lbl" xml:lang="en-US">Pursuant to stock incentive plans, total</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_UponConversionOfNotesAndAccruedInterestIssuedPursuantToWinter20132014PrivatePlacementOfUnits" xlink:label="VSTA_UponConversionOfNotesAndAccruedInterestIssuedPursuantToWinter20132014PrivatePlacementOfUnits" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_UponConversionOfNotesAndAccruedInterestIssuedPursuantToWinter20132014PrivatePlacementOfUnits" xlink:to="VSTA_UponConversionOfNotesAndAccruedInterestIssuedPursuantToWinter20132014PrivatePlacementOfUnits_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_UponConversionOfNotesAndAccruedInterestIssuedPursuantToWinter20132014PrivatePlacementOfUnits_lbl" xml:lang="en-US">Upon conversion of notes and accrued interest issued pursuant to the Winter 2013/2014 Private Placement of Units</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_UponSalesOfAdditionalUnitsPursuantTo2012PrivatePlacementOfUnits" xlink:label="VSTA_UponSalesOfAdditionalUnitsPursuantTo2012PrivatePlacementOfUnits" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_UponSalesOfAdditionalUnitsPursuantTo2012PrivatePlacementOfUnits" xlink:to="VSTA_UponSalesOfAdditionalUnitsPursuantTo2012PrivatePlacementOfUnits_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_UponSalesOfAdditionalUnitsPursuantTo2012PrivatePlacementOfUnits_lbl" xml:lang="en-US">Upon further sales of Units pursuant to the 2012 Private Placement of Units</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_UponFurtherSaleOfSharesToAutilionUnderAmendedSecuritiesPurchaseAgreement" xlink:label="VSTA_UponFurtherSaleOfSharesToAutilionUnderAmendedSecuritiesPurchaseAgreement" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_UponFurtherSaleOfSharesToAutilionUnderAmendedSecuritiesPurchaseAgreement" xlink:to="VSTA_UponFurtherSaleOfSharesToAutilionUnderAmendedSecuritiesPurchaseAgreement_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_UponFurtherSaleOfSharesToAutilionUnderAmendedSecuritiesPurchaseAgreement_lbl" xml:lang="en-US">Upon further sale of shares to Autilion under the amended Securities Purchase Agreement</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance" xlink:label="us-gaap_CommonStockCapitalSharesReservedForFutureIssuance" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockCapitalSharesReservedForFutureIssuance" xlink:to="us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_CommonStockCapitalSharesReservedForFutureIssuance_lbl" xml:lang="en-US">Total</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_OwnshareLendingArrangementSharesCommitment" xlink:label="VSTA_OwnshareLendingArrangementSharesCommitment" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_OwnshareLendingArrangementSharesCommitment" xlink:to="VSTA_OwnshareLendingArrangementSharesCommitment_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_OwnshareLendingArrangementSharesCommitment_lbl" xml:lang="en-US">Purchase obligation</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_OwnshareLendingArrangementPerSharePrice" xlink:label="VSTA_OwnshareLendingArrangementPerSharePrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_OwnshareLendingArrangementPerSharePrice" xlink:to="VSTA_OwnshareLendingArrangementPerSharePrice_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_OwnshareLendingArrangementPerSharePrice_lbl" xml:lang="en-US">Purchase obligation, per share price</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_OwnshareLendingArrangementSharesOutstandingCommitmentValue" xlink:label="VSTA_OwnshareLendingArrangementSharesOutstandingCommitmentValue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_OwnshareLendingArrangementSharesOutstandingCommitmentValue" xlink:to="VSTA_OwnshareLendingArrangementSharesOutstandingCommitmentValue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_OwnshareLendingArrangementSharesOutstandingCommitmentValue_lbl" xml:lang="en-US">Purchase obligation, aggregate cash consideration</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OwnshareLendingArrangementSharesOutstandingValue" xlink:label="us-gaap_OwnshareLendingArrangementSharesOutstandingValue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OwnshareLendingArrangementSharesOutstandingValue" xlink:to="us-gaap_OwnshareLendingArrangementSharesOutstandingValue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OwnshareLendingArrangementSharesOutstandingValue_lbl" xml:lang="en-US">Initial closing of financing</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OwnshareLendingArrangementSharesIssued" xlink:label="us-gaap_OwnshareLendingArrangementSharesIssued" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OwnshareLendingArrangementSharesIssued" xlink:to="us-gaap_OwnshareLendingArrangementSharesIssued_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OwnshareLendingArrangementSharesIssued_lbl" xml:lang="en-US">Initial issuance of shares under puchase agreement</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ConvertibleDebtNoncurrent" xlink:label="us-gaap_ConvertibleDebtNoncurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ConvertibleDebtNoncurrent" xlink:to="us-gaap_ConvertibleDebtNoncurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ConvertibleDebtNoncurrent_lbl" xml:lang="en-US">Note issued</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DebtInstrumentConvertibleConversionPrice1" xlink:label="us-gaap_DebtInstrumentConvertibleConversionPrice1" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentConvertibleConversionPrice1" xlink:to="us-gaap_DebtInstrumentConvertibleConversionPrice1_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DebtInstrumentConvertibleConversionPrice1_lbl" xml:lang="en-US">Note conversion price</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_TemporaryEquitySharesIssued" xlink:label="us-gaap_TemporaryEquitySharesIssued" />
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_TemporaryEquitySharesIssued_lbl" xml:lang="en-US">Warrant issued</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_PreviousAdvancesToOfficers" xlink:label="VSTA_PreviousAdvancesToOfficers" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PreviousAdvancesToOfficers" xlink:to="VSTA_PreviousAdvancesToOfficers_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PreviousAdvancesToOfficers_lbl" xml:lang="en-US">Repayment of previous advances to officers</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_RestrictedCommonStock" xlink:label="VSTA_RestrictedCommonStock" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_RestrictedCommonStock" xlink:to="VSTA_RestrictedCommonStock_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_RestrictedCommonStock_lbl" xml:lang="en-US">Restricted common stock</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TemporaryEquityParOrStatedValuePerShare" xlink:to="us-gaap_TemporaryEquityParOrStatedValuePerShare_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_TemporaryEquityParOrStatedValuePerShare_2_lbl" xml:lang="en-US">Exercise price</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ExercisePriceAtGrantDate" xlink:label="VSTA_ExercisePriceAtGrantDate" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExercisePriceAtGrantDate" xlink:to="VSTA_ExercisePriceAtGrantDate_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ExercisePriceAtGrantDate_lbl" xml:lang="en-US">Exercise price at grant date</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ProbabilityOfIssuance" xlink:label="VSTA_ProbabilityOfIssuance" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProbabilityOfIssuance" xlink:to="VSTA_ProbabilityOfIssuance_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ProbabilityOfIssuance_lbl" xml:lang="en-US">Probability of issuance</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercised" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercised" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercised" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercised_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNonOptionEquityInstrumentsExercised_lbl" xml:lang="en-US">Exercised warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ProceedsFromWarrantExercises" xlink:label="us-gaap_ProceedsFromWarrantExercises" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProceedsFromWarrantExercises" xlink:to="us-gaap_ProceedsFromWarrantExercises_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ProceedsFromWarrantExercises_lbl" xml:lang="en-US">Cash proceeds from exercise of warrants</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardModifiedNonOptionEquityInstrumentsExercised" xlink:label="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardModifiedNonOptionEquityInstrumentsExercised" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardModifiedNonOptionEquityInstrumentsExercised" xlink:to="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardModifiedNonOptionEquityInstrumentsExercised_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardModifiedNonOptionEquityInstrumentsExercised_lbl" xml:lang="en-US">Modified warrants exercised</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised" xlink:label="us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised" xlink:to="us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_lbl" xml:lang="en-US">Noncash share compensation paid for professional services</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ResearchAndDevelopmentExpense" xlink:label="us-gaap_ResearchAndDevelopmentExpense" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ResearchAndDevelopmentExpense" xlink:to="us-gaap_ResearchAndDevelopmentExpense_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ResearchAndDevelopmentExpense_lbl" xml:lang="en-US">Research and development expenses</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_IncomeTaxesDetailsAbstract" xlink:label="VSTA_IncomeTaxesDetailsAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IncomeTaxesDetailsAbstract" xlink:to="VSTA_IncomeTaxesDetailsAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IncomeTaxesDetailsAbstract_lbl" xml:lang="en-US">Income Taxes Details</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate" xlink:to="us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_lbl" xml:lang="en-US">Computed expected tax benefit</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_TaxEffectOfWarrantLiabilitiyMarkToMarket" xlink:label="VSTA_TaxEffectOfWarrantLiabilitiyMarkToMarket" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_TaxEffectOfWarrantLiabilitiyMarkToMarket" xlink:to="VSTA_TaxEffectOfWarrantLiabilitiyMarkToMarket_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_TaxEffectOfWarrantLiabilitiyMarkToMarket_lbl" xml:lang="en-US">Tax effect of Warrant Liabilitiy mark to market</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_LossesNotBenefitted" xlink:label="VSTA_LossesNotBenefitted" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_LossesNotBenefitted" xlink:to="VSTA_LossesNotBenefitted_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_LossesNotBenefitted_lbl" xml:lang="en-US">Losses not benefitted</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_EffectiveIncomeTaxRateReconciliationOther" xlink:label="VSTA_EffectiveIncomeTaxRateReconciliationOther" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_EffectiveIncomeTaxRateReconciliationOther" xlink:to="VSTA_EffectiveIncomeTaxRateReconciliationOther_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="VSTA_EffectiveIncomeTaxRateReconciliationOther_lbl" xml:lang="en-US">Other</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EffectiveIncomeTaxRateContinuingOperations" xlink:label="us-gaap_EffectiveIncomeTaxRateContinuingOperations" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EffectiveIncomeTaxRateContinuingOperations" xlink:to="us-gaap_EffectiveIncomeTaxRateContinuingOperations_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_EffectiveIncomeTaxRateContinuingOperations_lbl" xml:lang="en-US">Income tax expense</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_IncomeTaxesDetails1Abstract" xlink:label="VSTA_IncomeTaxesDetails1Abstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IncomeTaxesDetails1Abstract" xlink:to="VSTA_IncomeTaxesDetails1Abstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_IncomeTaxesDetails1Abstract_lbl" xml:lang="en-US">Income Taxes Details 1</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredTaxAssetsOperatingLossCarryforwards" xlink:label="us-gaap_DeferredTaxAssetsOperatingLossCarryforwards" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredTaxAssetsOperatingLossCarryforwards" xlink:to="us-gaap_DeferredTaxAssetsOperatingLossCarryforwards_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DeferredTaxAssetsOperatingLossCarryforwards_lbl" xml:lang="en-US">Net operating loss carry-forwards</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_BasisDifferencesInFixedAssets" xlink:label="VSTA_BasisDifferencesInFixedAssets" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_BasisDifferencesInFixedAssets" xlink:to="VSTA_BasisDifferencesInFixedAssets_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_BasisDifferencesInFixedAssets_lbl" xml:lang="en-US">Basis differences in fixed assets</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccruals" xlink:label="us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccruals" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccruals" xlink:to="us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccruals_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccruals_lbl" xml:lang="en-US">Accruals and reserves</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredTaxAssetsGross" xlink:label="us-gaap_DeferredTaxAssetsGross" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredTaxAssetsGross" xlink:to="us-gaap_DeferredTaxAssetsGross_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DeferredTaxAssetsGross_lbl" xml:lang="en-US">Total deferred tax assets, net</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredTaxAssetsValuationAllowance" xlink:label="us-gaap_DeferredTaxAssetsValuationAllowance" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredTaxAssetsValuationAllowance" xlink:to="us-gaap_DeferredTaxAssetsValuationAllowance_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DeferredTaxAssetsValuationAllowance_lbl" xml:lang="en-US">Valuation allowance</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredTaxAssetsNet" xlink:label="us-gaap_DeferredTaxAssetsNet" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredTaxAssetsNet" xlink:to="us-gaap_DeferredTaxAssetsNet_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DeferredTaxAssetsNet_lbl" xml:lang="en-US">Net deferred tax asset</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ValuationAllowancesAndReservesPeriodIncreaseDecrease" xlink:label="us-gaap_ValuationAllowancesAndReservesPeriodIncreaseDecrease" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ValuationAllowancesAndReservesPeriodIncreaseDecrease" xlink:to="us-gaap_ValuationAllowancesAndReservesPeriodIncreaseDecrease_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ValuationAllowancesAndReservesPeriodIncreaseDecrease_lbl" xml:lang="en-US">Valuation allowance increase</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsDomestic" xlink:label="us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsDomestic" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsDomestic" xlink:to="us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsDomestic_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsDomestic_lbl" xml:lang="en-US">U.S. federal net operating loss carryforwards</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsStateAndLocal" xlink:label="us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsStateAndLocal" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsStateAndLocal" xlink:to="us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsStateAndLocal_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsStateAndLocal_lbl" xml:lang="en-US">state net operating loss carryforwards</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_PeriodicResearchAndDevelopmentArrangementWithFederalGovernmentCustomerFundingToOffsetCostsIncurred" xlink:label="VSTA_PeriodicResearchAndDevelopmentArrangementWithFederalGovernmentCustomerFundingToOffsetCostsIncurred" />
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_PeriodicResearchAndDevelopmentArrangementWithFederalGovernmentCustomerFundingToOffsetCostsIncurred_lbl" xml:lang="en-US">Monthly research funding payments</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_NotesIssued1" xlink:label="us-gaap_NotesIssued1" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NotesIssued1" xlink:to="us-gaap_NotesIssued1_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NotesIssued1_lbl" xml:lang="en-US">Promissory note issuance</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtConversionConvertedInstrumentWarrantsOrOptionsIssued1" xlink:to="us-gaap_DebtConversionConvertedInstrumentWarrantsOrOptionsIssued1_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_DebtConversionConvertedInstrumentWarrantsOrOptionsIssued1_2_lbl" xml:lang="en-US">Warrant issued with promissory note</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ResearchAndDevelopmentArrangementWithFederalGovernmentCustomerFundingToOffsetCostsIncurred" xlink:label="us-gaap_ResearchAndDevelopmentArrangementWithFederalGovernmentCustomerFundingToOffsetCostsIncurred" />
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      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_AwardUponAgreedMilestones" xlink:label="VSTA_AwardUponAgreedMilestones" />
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      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AwardUponAgreedMilestones_lbl" xml:lang="en-US">Award upon agreed milestones</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ChemicalsRevenue" xlink:label="us-gaap_ChemicalsRevenue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ChemicalsRevenue" xlink:to="us-gaap_ChemicalsRevenue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_ChemicalsRevenue_lbl" xml:lang="en-US">Grant revenue</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ResearchAndDevelopmentExpenseExcludingAcquiredInProcessCost" xlink:to="us-gaap_ResearchAndDevelopmentExpenseExcludingAcquiredInProcessCost_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_ResearchAndDevelopmentExpenseExcludingAcquiredInProcessCost_2_lbl" xml:lang="en-US">Research and development expenses</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_SummaryOfSignificantAccountingPoliciesDetailsAbstract" xlink:label="VSTA_SummaryOfSignificantAccountingPoliciesDetailsAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SummaryOfSignificantAccountingPoliciesDetailsAbstract" xlink:to="VSTA_SummaryOfSignificantAccountingPoliciesDetailsAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SummaryOfSignificantAccountingPoliciesDetailsAbstract_lbl" xml:lang="en-US">Stock Option Plans And 401K Plan Details</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ResearchAndDevelopmentExpenseAbstract" xlink:label="us-gaap_ResearchAndDevelopmentExpenseAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ResearchAndDevelopmentExpenseAbstract" xlink:to="us-gaap_ResearchAndDevelopmentExpenseAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ResearchAndDevelopmentExpenseAbstract_lbl" xml:lang="en-US">Research and development expense:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockOptionPlanExpense" xlink:label="us-gaap_StockOptionPlanExpense" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockOptionPlanExpense" xlink:to="us-gaap_StockOptionPlanExpense_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_StockOptionPlanExpense_lbl" xml:lang="en-US">Stock option grants, including expense related to modifications</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_WarrantsGrantedToOfficerInMarch2014" xlink:label="VSTA_WarrantsGrantedToOfficerInMarch2014" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_WarrantsGrantedToOfficerInMarch2014" xlink:to="VSTA_WarrantsGrantedToOfficerInMarch2014_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_WarrantsGrantedToOfficerInMarch2014_lbl" xml:lang="en-US">Warrants granted to officer in March 2014</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ExpenseWarrantsGrantedToOfficer" xlink:label="VSTA_ExpenseWarrantsGrantedToOfficer" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExpenseWarrantsGrantedToOfficer" xlink:to="VSTA_ExpenseWarrantsGrantedToOfficer_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ExpenseWarrantsGrantedToOfficer_lbl" xml:lang="en-US">Warrants granted to officer in March 2013</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_TotalResearchAndDevelopmentExpenseRelatedToStockbasedCompensationExpense" xlink:label="VSTA_TotalResearchAndDevelopmentExpenseRelatedToStockbasedCompensationExpense" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_TotalResearchAndDevelopmentExpenseRelatedToStockbasedCompensationExpense" xlink:to="VSTA_TotalResearchAndDevelopmentExpenseRelatedToStockbasedCompensationExpense_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_TotalResearchAndDevelopmentExpenseRelatedToStockbasedCompensationExpense_lbl" xml:lang="en-US">Total research and development expense related to stock-based compensation expense</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_GeneralAndAdministrativeExpenseAbstract" xlink:label="us-gaap_GeneralAndAdministrativeExpenseAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_GeneralAndAdministrativeExpenseAbstract" xlink:to="us-gaap_GeneralAndAdministrativeExpenseAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_GeneralAndAdministrativeExpenseAbstract_lbl" xml:lang="en-US">General and administrative expense:</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_RelatedToStockOptionGrantsIncludingExpenserelatedToModifications" xlink:label="VSTA_RelatedToStockOptionGrantsIncludingExpenserelatedToModifications" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_RelatedToStockOptionGrantsIncludingExpenserelatedToModifications" xlink:to="VSTA_RelatedToStockOptionGrantsIncludingExpenserelatedToModifications_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="VSTA_RelatedToStockOptionGrantsIncludingExpenserelatedToModifications_lbl" xml:lang="en-US">Stock option grants, including expense related to modifications</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_WarrantsGrantedToOfficerAndDirectorsInMarch2014" xlink:label="VSTA_WarrantsGrantedToOfficerAndDirectorsInMarch2014" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_WarrantsGrantedToOfficerAndDirectorsInMarch2014" xlink:to="VSTA_WarrantsGrantedToOfficerAndDirectorsInMarch2014_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_WarrantsGrantedToOfficerAndDirectorsInMarch2014_lbl" xml:lang="en-US">Warrants granted to officer and directors in March 2014</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_WarrantsGrantedToOfficersAndDirectorExpense" xlink:label="VSTA_WarrantsGrantedToOfficersAndDirectorExpense" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_WarrantsGrantedToOfficersAndDirectorExpense" xlink:to="VSTA_WarrantsGrantedToOfficersAndDirectorExpense_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_WarrantsGrantedToOfficersAndDirectorExpense_lbl" xml:lang="en-US">Warrants granted to officers and directors in March 2013</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_TotalGeneralAndAdministrativeExpenseRelatedToStockbasedCompensationExpense" xlink:label="VSTA_TotalGeneralAndAdministrativeExpenseRelatedToStockbasedCompensationExpense" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_TotalGeneralAndAdministrativeExpenseRelatedToStockbasedCompensationExpense" xlink:to="VSTA_TotalGeneralAndAdministrativeExpenseRelatedToStockbasedCompensationExpense_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_TotalGeneralAndAdministrativeExpenseRelatedToStockbasedCompensationExpense_lbl" xml:lang="en-US">Total General and administrative expense related to stock-based compensation expense</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensation" xlink:to="us-gaap_ShareBasedCompensation_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_ShareBasedCompensation_2_lbl" xml:lang="en-US">Total stock-based compensation expense</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ExpectedDividendYield" xlink:label="VSTA_ExpectedDividendYield" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExpectedDividendYield" xlink:to="VSTA_ExpectedDividendYield_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ExpectedDividendYield_lbl" xml:lang="en-US">Expected dividend yield</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_TemporaryEquityRedemptionPricePerShare" xlink:label="us-gaap_TemporaryEquityRedemptionPricePerShare" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TemporaryEquityRedemptionPricePerShare" xlink:to="us-gaap_TemporaryEquityRedemptionPricePerShare_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_TemporaryEquityRedemptionPricePerShare_lbl" xml:lang="en-US">Exercise price</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SharePrice" xlink:to="us-gaap_SharePrice_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_SharePrice_2_lbl" xml:lang="en-US">Market price on date of grant</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_FairValueAssumptionsRiskFreeInterestRates" xlink:label="VSTA_FairValueAssumptionsRiskFreeInterestRates" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueAssumptionsRiskFreeInterestRates" xlink:to="VSTA_FairValueAssumptionsRiskFreeInterestRates_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="VSTA_FairValueAssumptionsRiskFreeInterestRates_lbl" xml:lang="en-US">Risk-free interest rate</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ExpectedYears" xlink:label="VSTA_ExpectedYears" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExpectedYears" xlink:to="VSTA_ExpectedYears_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ExpectedYears_lbl" xml:lang="en-US">Expected (years)</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardVolatilityRate" xlink:label="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardVolatilityRate" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardVolatilityRate" xlink:to="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardVolatilityRate_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardVolatilityRate_lbl" xml:lang="en-US">Volatility</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_FairValuePerShareAtGrantDate" xlink:label="VSTA_FairValuePerShareAtGrantDate" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValuePerShareAtGrantDate" xlink:to="VSTA_FairValuePerShareAtGrantDate_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FairValuePerShareAtGrantDate_lbl" xml:lang="en-US">Fair value per share at grant date</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_NumberOfShares" xlink:label="VSTA_NumberOfShares" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NumberOfShares" xlink:to="VSTA_NumberOfShares_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NumberOfShares_lbl" xml:lang="en-US">Number of Shares</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_2_lbl" xml:lang="en-US">Options outstanding at beginning of period</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod_lbl" xml:lang="en-US">Options granted</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOtherIncreasesDecreasesInPeriod" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOtherIncreasesDecreasesInPeriod" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOtherIncreasesDecreasesInPeriod" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOtherIncreasesDecreasesInPeriod_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOtherIncreasesDecreasesInPeriod_lbl" xml:lang="en-US">Options exercised</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOtherIncreasesDecreasesInPeriod2" xlink:label="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOtherIncreasesDecreasesInPeriod2" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOtherIncreasesDecreasesInPeriod2" xlink:to="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOtherIncreasesDecreasesInPeriod2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOtherIncreasesDecreasesInPeriod2_lbl" xml:lang="en-US">Options cancelled</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_lbl" xml:lang="en-US">Options forfeited</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod_lbl" xml:lang="en-US">Options expired</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_3_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_3_lbl" xml:lang="en-US">Options outstanding at end of period</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber_lbl" xml:lang="en-US">Options exercisable at end of period</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_WeightedAverageExercisePrice" xlink:label="VSTA_WeightedAverageExercisePrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_WeightedAverageExercisePrice" xlink:to="VSTA_WeightedAverageExercisePrice_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_WeightedAverageExercisePrice_lbl" xml:lang="en-US">Weighted Average Exercise Price</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_lbl" xml:lang="en-US">Weighted average exercise price, Options outstanding at beginning of period</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_lbl" xml:lang="en-US">Options granted</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingPeriodIncreaseDecreaseWeightedAverageExercisePrice2" xlink:label="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingPeriodIncreaseDecreaseWeightedAverageExercisePrice2" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingPeriodIncreaseDecreaseWeightedAverageExercisePrice2" xlink:to="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingPeriodIncreaseDecreaseWeightedAverageExercisePrice2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="VSTA_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingPeriodIncreaseDecreaseWeightedAverageExercisePrice2_lbl" xml:lang="en-US">Options exercised</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsOtherShareIncreaseDecreaseInPeriodWeightedAverageExercisePrice" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsOtherShareIncreaseDecreaseInPeriodWeightedAverageExercisePrice_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsOtherShareIncreaseDecreaseInPeriodWeightedAverageExercisePrice_2_lbl" xml:lang="en-US">Options cancelled</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice_lbl" xml:lang="en-US">Options forfeited</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationsInPeriodWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationsInPeriodWeightedAverageExercisePrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationsInPeriodWeightedAverageExercisePrice" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationsInPeriodWeightedAverageExercisePrice_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationsInPeriodWeightedAverageExercisePrice_lbl" xml:lang="en-US">Options expired</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_2_lbl" xml:lang="en-US">Weighted average exercise price, Options outstanding at end of period</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableWeightedAverageExercisePrice_lbl" xml:lang="en-US">Weighted average exercise price, Options exercisable at end of period</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_lbl" xml:lang="en-US">Weighted average grant-date fair value of options granted during the period</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/invest/2013/invest-2013-01-31.xsd#invest_InvestmentOptionsExercisePrice" xlink:label="invest_InvestmentOptionsExercisePrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="invest_InvestmentOptionsExercisePrice" xlink:to="invest_InvestmentOptionsExercisePrice_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="invest_InvestmentOptionsExercisePrice_lbl" xml:lang="en-US">Option exercise price</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2_lbl" xml:lang="en-US">Weighted Average Remaining Years until Expiration</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationAxis" xlink:to="VSTA_ShareBasedCompensationAxis_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="VSTA_ShareBasedCompensationAxis_2_lbl" xml:lang="en-US">ShareBasedCompensationAxis [Axis]</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ShareBasedCompensationArrangementNumberOfSharesAuthorized" xlink:label="VSTA_ShareBasedCompensationArrangementNumberOfSharesAuthorized" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationArrangementNumberOfSharesAuthorized" xlink:to="VSTA_ShareBasedCompensationArrangementNumberOfSharesAuthorized_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ShareBasedCompensationArrangementNumberOfSharesAuthorized_lbl" xml:lang="en-US">Maximum number of shares granted</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_MaximumTermOf10OrMoreOwners" xlink:label="VSTA_MaximumTermOf10OrMoreOwners" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_MaximumTermOf10OrMoreOwners" xlink:to="VSTA_MaximumTermOf10OrMoreOwners_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_MaximumTermOf10OrMoreOwners_lbl" xml:lang="en-US">Maximum term of 10% or more owners</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_MaximumTermOfAnyOtherOwner" xlink:label="VSTA_MaximumTermOfAnyOtherOwner" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_MaximumTermOfAnyOtherOwner" xlink:to="VSTA_MaximumTermOfAnyOtherOwner_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_MaximumTermOfAnyOtherOwner_lbl" xml:lang="en-US">Maximum term of any other owner</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_lbl" xml:lang="en-US">Cancelled options</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_NewOptionsGrantedToCancelledHolders" xlink:label="VSTA_NewOptionsGrantedToCancelledHolders" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NewOptionsGrantedToCancelledHolders" xlink:to="VSTA_NewOptionsGrantedToCancelledHolders_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NewOptionsGrantedToCancelledHolders_lbl" xml:lang="en-US">New options granted to cancelled holders</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ExercisePriceToNewOptionsGranted" xlink:label="VSTA_ExercisePriceToNewOptionsGranted" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExercisePriceToNewOptionsGranted" xlink:to="VSTA_ExercisePriceToNewOptionsGranted_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ExercisePriceToNewOptionsGranted_lbl" xml:lang="en-US">Exercise price to new options granted</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ModificationOptionsGranted" xlink:label="VSTA_ModificationOptionsGranted" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ModificationOptionsGranted" xlink:to="VSTA_ModificationOptionsGranted_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ModificationOptionsGranted_lbl" xml:lang="en-US">Modification options granted</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExpenseRelatedToModificationOfWarrants" xlink:to="VSTA_ExpenseRelatedToModificationOfWarrants_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="VSTA_ExpenseRelatedToModificationOfWarrants_2_lbl" xml:lang="en-US">Modification charge</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_SharesWithReducedExercisePrice" xlink:label="VSTA_SharesWithReducedExercisePrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SharesWithReducedExercisePrice" xlink:to="VSTA_SharesWithReducedExercisePrice_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SharesWithReducedExercisePrice_lbl" xml:lang="en-US">Shares with reduced exercise price</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_ModificationChargeOfOptionsToCertainEmployees" xlink:label="VSTA_ModificationChargeOfOptionsToCertainEmployees" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ModificationChargeOfOptionsToCertainEmployees" xlink:to="VSTA_ModificationChargeOfOptionsToCertainEmployees_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ModificationChargeOfOptionsToCertainEmployees_lbl" xml:lang="en-US">Modification charge of options to certain employees</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_SharesRemainingForGrantUnder2008Plan" xlink:label="VSTA_SharesRemainingForGrantUnder2008Plan" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SharesRemainingForGrantUnder2008Plan" xlink:to="VSTA_SharesRemainingForGrantUnder2008Plan_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SharesRemainingForGrantUnder2008Plan_lbl" xml:lang="en-US">Shares remaining for grant under 2008 Plan</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_QuotedMarketSharePrice" xlink:label="VSTA_QuotedMarketSharePrice" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_QuotedMarketSharePrice" xlink:to="VSTA_QuotedMarketSharePrice_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_QuotedMarketSharePrice_lbl" xml:lang="en-US">Quoted market price of common stock</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_AggregateIntrinsicValueOfOutstandingOptions" xlink:label="VSTA_AggregateIntrinsicValueOfOutstandingOptions" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AggregateIntrinsicValueOfOutstandingOptions" xlink:to="VSTA_AggregateIntrinsicValueOfOutstandingOptions_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AggregateIntrinsicValueOfOutstandingOptions_lbl" xml:lang="en-US">Aggregate intrinsic value of outstanding options</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_AggregateIntrinsicValueRelatedToExercisableOptions" xlink:label="VSTA_AggregateIntrinsicValueRelatedToExercisableOptions" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AggregateIntrinsicValueRelatedToExercisableOptions" xlink:to="VSTA_AggregateIntrinsicValueRelatedToExercisableOptions_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_AggregateIntrinsicValueRelatedToExercisableOptions_lbl" xml:lang="en-US">Aggregate intrinsic value related to exercisable options</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized" xlink:to="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_lbl" xml:lang="en-US">Unrecognized compensation cost</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedUnvestedWarrants" xlink:label="VSTA_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedUnvestedWarrants" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedUnvestedWarrants" xlink:to="VSTA_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedUnvestedWarrants_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedUnvestedWarrants_lbl" xml:lang="en-US">Unrecognized compensation cost related to unvested warrant grants</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProceedsFromRelatedPartyDebt" xlink:to="us-gaap_ProceedsFromRelatedPartyDebt_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ProceedsFromRelatedPartyDebt_2_lbl" xml:lang="en-US">Proceeds from short-term loan</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_DebtInstrumentInterestRateDuringPeriod" xlink:label="us-gaap_DebtInstrumentInterestRateDuringPeriod" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentInterestRateDuringPeriod" xlink:to="us-gaap_DebtInstrumentInterestRateDuringPeriod_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DebtInstrumentInterestRateDuringPeriod_lbl" xml:lang="en-US">Interest rate on note</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_InterestIncomeExpenseNet" xlink:label="us-gaap_InterestIncomeExpenseNet" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_InterestIncomeExpenseNet" xlink:to="us-gaap_InterestIncomeExpenseNet_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_InterestIncomeExpenseNet_lbl" xml:lang="en-US">Total interest expense</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ResearchAndDevelopmentExpenseExcludingAcquiredInProcessCost" xlink:to="us-gaap_ResearchAndDevelopmentExpenseExcludingAcquiredInProcessCost_3_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ResearchAndDevelopmentExpenseExcludingAcquiredInProcessCost_3_lbl" xml:lang="en-US">Incurred expenses on research and subsequent other projects</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_EstimateAccruedOfGrossupAmount" xlink:label="VSTA_EstimateAccruedOfGrossupAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_EstimateAccruedOfGrossupAmount" xlink:to="VSTA_EstimateAccruedOfGrossupAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_EstimateAccruedOfGrossupAmount_lbl" xml:lang="en-US">Estimate accrued of gross-up amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_CommitmentsContingenciesGuaranteesAndIndemnificationsDetailsAbstract" xlink:label="VSTA_CommitmentsContingenciesGuaranteesAndIndemnificationsDetailsAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommitmentsContingenciesGuaranteesAndIndemnificationsDetailsAbstract" xlink:to="VSTA_CommitmentsContingenciesGuaranteesAndIndemnificationsDetailsAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommitmentsContingenciesGuaranteesAndIndemnificationsDetailsAbstract_lbl" xml:lang="en-US">Commitments Contingencies Guarantees And Indemnifications Details</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CapitalLeaseObligationsAbstract" xlink:label="us-gaap_CapitalLeaseObligationsAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalLeaseObligationsAbstract" xlink:to="us-gaap_CapitalLeaseObligationsAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_CapitalLeaseObligationsAbstract_lbl" xml:lang="en-US">Capital lease obligations</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CapitalLeasesLesseeBalanceSheetAssetsByMajorClassOtherPropertyPlantAndEquipment" xlink:label="us-gaap_CapitalLeasesLesseeBalanceSheetAssetsByMajorClassOtherPropertyPlantAndEquipment" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalLeasesLesseeBalanceSheetAssetsByMajorClassOtherPropertyPlantAndEquipment" xlink:to="us-gaap_CapitalLeasesLesseeBalanceSheetAssetsByMajorClassOtherPropertyPlantAndEquipment_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CapitalLeasesLesseeBalanceSheetAssetsByMajorClassOtherPropertyPlantAndEquipment_lbl" xml:lang="en-US">Leased laboratory equipment</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CapitalLeasesLesseeBalanceSheetAssetsByMajorClassOtherPropertyPlantAndEquipmentNet" xlink:label="us-gaap_CapitalLeasesLesseeBalanceSheetAssetsByMajorClassOtherPropertyPlantAndEquipmentNet" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalLeasesLesseeBalanceSheetAssetsByMajorClassOtherPropertyPlantAndEquipmentNet" xlink:to="us-gaap_CapitalLeasesLesseeBalanceSheetAssetsByMajorClassOtherPropertyPlantAndEquipmentNet_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CapitalLeasesLesseeBalanceSheetAssetsByMajorClassOtherPropertyPlantAndEquipmentNet_lbl" xml:lang="en-US">Leased office equipment</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CapitalLeaseObligations" xlink:label="us-gaap_CapitalLeaseObligations" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalLeaseObligations" xlink:to="us-gaap_CapitalLeaseObligations_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CapitalLeaseObligations_lbl" xml:lang="en-US">Total lease obligations</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CapitalLeasesLesseeBalanceSheetAssetsByMajorClassPropertyPlantAndEquipmentOtherAccumulatedDepreciation" xlink:label="us-gaap_CapitalLeasesLesseeBalanceSheetAssetsByMajorClassPropertyPlantAndEquipmentOtherAccumulatedDepreciation" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalLeasesLesseeBalanceSheetAssetsByMajorClassPropertyPlantAndEquipmentOtherAccumulatedDepreciation" xlink:to="us-gaap_CapitalLeasesLesseeBalanceSheetAssetsByMajorClassPropertyPlantAndEquipmentOtherAccumulatedDepreciation_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CapitalLeasesLesseeBalanceSheetAssetsByMajorClassPropertyPlantAndEquipmentOtherAccumulatedDepreciation_lbl" xml:lang="en-US">Accumulated amortization</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_LeasedLaboratoryAndComputerEquipmentNet" xlink:label="VSTA_LeasedLaboratoryAndComputerEquipmentNet" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_LeasedLaboratoryAndComputerEquipmentNet" xlink:to="VSTA_LeasedLaboratoryAndComputerEquipmentNet_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_LeasedLaboratoryAndComputerEquipmentNet_lbl" xml:lang="en-US">Leased laboratory and computer equipment, net</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_CommitmentsContingenciesGuaranteesAndIndemnificationsDetails1Abstract" xlink:label="VSTA_CommitmentsContingenciesGuaranteesAndIndemnificationsDetails1Abstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommitmentsContingenciesGuaranteesAndIndemnificationsDetails1Abstract" xlink:to="VSTA_CommitmentsContingenciesGuaranteesAndIndemnificationsDetails1Abstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommitmentsContingenciesGuaranteesAndIndemnificationsDetails1Abstract_lbl" xml:lang="en-US">Commitments Contingencies Guarantees And Indemnifications Details 1</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CapitalLeasesFutureMinimumPaymentsDueAbstract" xlink:label="us-gaap_CapitalLeasesFutureMinimumPaymentsDueAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalLeasesFutureMinimumPaymentsDueAbstract" xlink:to="us-gaap_CapitalLeasesFutureMinimumPaymentsDueAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CapitalLeasesFutureMinimumPaymentsDueAbstract_lbl" xml:lang="en-US">Future minimum payment, capital leases, Equipment</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CapitalLeasesFutureMinimumPaymentsDueInTwoYears" xlink:label="us-gaap_CapitalLeasesFutureMinimumPaymentsDueInTwoYears" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalLeasesFutureMinimumPaymentsDueInTwoYears" xlink:to="us-gaap_CapitalLeasesFutureMinimumPaymentsDueInTwoYears_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CapitalLeasesFutureMinimumPaymentsDueInTwoYears_lbl" xml:lang="en-US">Lease payment 2015</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CapitalLeasesFutureMinimumPaymentsDueInThreeYears" xlink:label="us-gaap_CapitalLeasesFutureMinimumPaymentsDueInThreeYears" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalLeasesFutureMinimumPaymentsDueInThreeYears" xlink:to="us-gaap_CapitalLeasesFutureMinimumPaymentsDueInThreeYears_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CapitalLeasesFutureMinimumPaymentsDueInThreeYears_lbl" xml:lang="en-US">Lease payment 2016</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CapitalLeasesFutureMinimumPaymentsDueInFourYears" xlink:label="us-gaap_CapitalLeasesFutureMinimumPaymentsDueInFourYears" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalLeasesFutureMinimumPaymentsDueInFourYears" xlink:to="us-gaap_CapitalLeasesFutureMinimumPaymentsDueInFourYears_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CapitalLeasesFutureMinimumPaymentsDueInFourYears_lbl" xml:lang="en-US">Lease payment 2017</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CapitalLeasesFutureMinimumPaymentsDueInFiveYears" xlink:label="us-gaap_CapitalLeasesFutureMinimumPaymentsDueInFiveYears" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalLeasesFutureMinimumPaymentsDueInFiveYears" xlink:to="us-gaap_CapitalLeasesFutureMinimumPaymentsDueInFiveYears_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CapitalLeasesFutureMinimumPaymentsDueInFiveYears_lbl" xml:lang="en-US">Lease payment 2018</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CapitalLeasesFutureMinimumPaymentsDue" xlink:label="us-gaap_CapitalLeasesFutureMinimumPaymentsDue" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalLeasesFutureMinimumPaymentsDue" xlink:to="us-gaap_CapitalLeasesFutureMinimumPaymentsDue_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CapitalLeasesFutureMinimumPaymentsDue_lbl" xml:lang="en-US">Future minimum lease payments</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CapitalLeasesFutureMinimumPaymentsInterestIncludedInPayments" xlink:label="us-gaap_CapitalLeasesFutureMinimumPaymentsInterestIncludedInPayments" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalLeasesFutureMinimumPaymentsInterestIncludedInPayments" xlink:to="us-gaap_CapitalLeasesFutureMinimumPaymentsInterestIncludedInPayments_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CapitalLeasesFutureMinimumPaymentsInterestIncludedInPayments_lbl" xml:lang="en-US">Less imputed interest included in minimum lease payments</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_CapitalLeasesFutureMinimumPaymentsPresentValueOfNetMinimumPayments" xlink:label="us-gaap_CapitalLeasesFutureMinimumPaymentsPresentValueOfNetMinimumPayments" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalLeasesFutureMinimumPaymentsPresentValueOfNetMinimumPayments" xlink:to="us-gaap_CapitalLeasesFutureMinimumPaymentsPresentValueOfNetMinimumPayments_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CapitalLeasesFutureMinimumPaymentsPresentValueOfNetMinimumPayments_lbl" xml:lang="en-US">Present value of minimum lease payments</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_CapitalLeaseObligationsEquipmentCurrent" xlink:label="VSTA_CapitalLeaseObligationsEquipmentCurrent" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CapitalLeaseObligationsEquipmentCurrent" xlink:to="VSTA_CapitalLeaseObligationsEquipmentCurrent_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CapitalLeaseObligationsEquipmentCurrent_lbl" xml:lang="en-US">Less current portion</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_NoncurrentCapitalLeaseObligation" xlink:label="VSTA_NoncurrentCapitalLeaseObligation" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NoncurrentCapitalLeaseObligation" xlink:to="VSTA_NoncurrentCapitalLeaseObligation_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_NoncurrentCapitalLeaseObligation_lbl" xml:lang="en-US">Non-current capital lease obligation</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_CommitmentsContingenciesGuaranteesAndIndemnificationsDetails2Abstract" xlink:label="VSTA_CommitmentsContingenciesGuaranteesAndIndemnificationsDetails2Abstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommitmentsContingenciesGuaranteesAndIndemnificationsDetails2Abstract" xlink:to="VSTA_CommitmentsContingenciesGuaranteesAndIndemnificationsDetails2Abstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommitmentsContingenciesGuaranteesAndIndemnificationsDetails2Abstract_lbl" xml:lang="en-US">Commitments Contingencies Guarantees And Indemnifications Details 2</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_FutureMinimumPaymentsPrincipal" xlink:label="VSTA_FutureMinimumPaymentsPrincipal" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FutureMinimumPaymentsPrincipal" xlink:to="VSTA_FutureMinimumPaymentsPrincipal_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_FutureMinimumPaymentsPrincipal_lbl" xml:lang="en-US">Future minimum payments, principal</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo" xlink:label="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo" xlink:to="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearTwo_lbl" xml:lang="en-US">2015</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree" xlink:label="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree" xlink:to="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearThree_lbl" xml:lang="en-US">2016</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour" xlink:label="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour" xlink:to="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFour_lbl" xml:lang="en-US">2017</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive" xlink:label="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive" xlink:to="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInYearFive_lbl" xml:lang="en-US">2018</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_FutureMinimumPrincipalPayments" xlink:label="VSTA_FutureMinimumPrincipalPayments" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FutureMinimumPrincipalPayments" xlink:to="VSTA_FutureMinimumPrincipalPayments_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="VSTA_FutureMinimumPrincipalPayments_lbl" xml:lang="en-US">Total</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_CommitmentsContingenciesGuaranteesAndIndemnificationsDetails3Abstract" xlink:label="VSTA_CommitmentsContingenciesGuaranteesAndIndemnificationsDetails3Abstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommitmentsContingenciesGuaranteesAndIndemnificationsDetails3Abstract" xlink:to="VSTA_CommitmentsContingenciesGuaranteesAndIndemnificationsDetails3Abstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_CommitmentsContingenciesGuaranteesAndIndemnificationsDetails3Abstract_lbl" xml:lang="en-US">Commitments Contingencies Guarantees And Indemnifications Details 3</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongTermDebtRollingMaturityAbstract" xlink:label="us-gaap_LongTermDebtRollingMaturityAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LongTermDebtRollingMaturityAbstract" xlink:to="us-gaap_LongTermDebtRollingMaturityAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LongTermDebtRollingMaturityAbstract_lbl" xml:lang="en-US">Future minimum principal payments related to long-term debt:</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextRollingTwelveMonths" xlink:label="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextRollingTwelveMonths" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextRollingTwelveMonths" xlink:to="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextRollingTwelveMonths_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInNextRollingTwelveMonths_lbl" xml:lang="en-US">2015</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingYearTwo" xlink:label="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingYearTwo" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingYearTwo" xlink:to="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingYearTwo_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingYearTwo_lbl" xml:lang="en-US">2016</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingYearThree" xlink:label="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingYearThree" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingYearThree" xlink:to="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingYearThree_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingYearThree_lbl" xml:lang="en-US">2017</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingYearFour" xlink:label="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingYearFour" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingYearFour" xlink:to="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingYearFour_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingYearFour_lbl" xml:lang="en-US">2018</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingAfterYearFour" xlink:label="VSTA_LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingAfterYearFour" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingAfterYearFour" xlink:to="VSTA_LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingAfterYearFour_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_LongTermDebtMaturitiesRepaymentsOfPrincipalInRollingAfterYearFour_lbl" xml:lang="en-US">Thereafter through June 2019</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_LongTermDebt" xlink:label="us-gaap_LongTermDebt" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LongTermDebt" xlink:to="us-gaap_LongTermDebt_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_LongTermDebt_lbl" xml:lang="en-US">Total</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_OperatingLeasesRentExpenseNet" xlink:label="us-gaap_OperatingLeasesRentExpenseNet" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeasesRentExpenseNet" xlink:to="us-gaap_OperatingLeasesRentExpenseNet_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OperatingLeasesRentExpenseNet_lbl" xml:lang="en-US">Facility rent expense</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_SubsequentEventsDetailsTextualsAbstract" xlink:label="VSTA_SubsequentEventsDetailsTextualsAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SubsequentEventsDetailsTextualsAbstract" xlink:to="VSTA_SubsequentEventsDetailsTextualsAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SubsequentEventsDetailsTextualsAbstract_lbl" xml:lang="en-US">Subsequent Events Details Narrative</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NotesIssued1" xlink:to="us-gaap_NotesIssued1_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_NotesIssued1_2_lbl" xml:lang="en-US">Note issued</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentInterestRateDuringPeriod" xlink:to="us-gaap_DebtInstrumentInterestRateDuringPeriod_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_DebtInstrumentInterestRateDuringPeriod_2_lbl" xml:lang="en-US">Interest rate</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesIssuedForCash" xlink:label="us-gaap_StockIssuedDuringPeriodSharesIssuedForCash" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockIssuedDuringPeriodSharesIssuedForCash" xlink:to="us-gaap_StockIssuedDuringPeriodSharesIssuedForCash_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_StockIssuedDuringPeriodSharesIssuedForCash_lbl" xml:lang="en-US">Shares issued</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_WarrantExercisePrice" xlink:to="VSTA_WarrantExercisePrice_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="VSTA_WarrantExercisePrice_2_lbl" xml:lang="en-US">Exercise price</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_TechnologyPromissoryNote" xlink:label="VSTA_TechnologyPromissoryNote" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_TechnologyPromissoryNote" xlink:to="VSTA_TechnologyPromissoryNote_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_TechnologyPromissoryNote_lbl" xml:lang="en-US">Technology promissory note</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_RestrictedSharesOfCommonStockIssuedTechnologyPromissoryNote" xlink:label="VSTA_RestrictedSharesOfCommonStockIssuedTechnologyPromissoryNote" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_RestrictedSharesOfCommonStockIssuedTechnologyPromissoryNote" xlink:to="VSTA_RestrictedSharesOfCommonStockIssuedTechnologyPromissoryNote_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_RestrictedSharesOfCommonStockIssuedTechnologyPromissoryNote_lbl" xml:lang="en-US">Restricted shares of common stock issued, technology promissory note</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_LicenseMaintenanceFeesAndReimbursablePatentProsecutionCosts" xlink:label="VSTA_LicenseMaintenanceFeesAndReimbursablePatentProsecutionCosts" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_LicenseMaintenanceFeesAndReimbursablePatentProsecutionCosts" xlink:to="VSTA_LicenseMaintenanceFeesAndReimbursablePatentProsecutionCosts_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_LicenseMaintenanceFeesAndReimbursablePatentProsecutionCosts_lbl" xml:lang="en-US">License maintenance fees and reimbursable patent prosecution costs</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_UnitNotesAggregateFaceAmount" xlink:label="VSTA_UnitNotesAggregateFaceAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_UnitNotesAggregateFaceAmount" xlink:to="VSTA_UnitNotesAggregateFaceAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_UnitNotesAggregateFaceAmount_lbl" xml:lang="en-US">2013 Unit Notes aggregate face amount</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_UnitNotesPaidAmount" xlink:label="VSTA_UnitNotesPaidAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_UnitNotesPaidAmount" xlink:to="VSTA_UnitNotesPaidAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_UnitNotesPaidAmount_lbl" xml:lang="en-US">2013 Unit Notes paid amount</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProceedsFromIssuanceOfCommonStock" xlink:to="us-gaap_ProceedsFromIssuanceOfCommonStock_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_ProceedsFromIssuanceOfCommonStock_2_lbl" xml:lang="en-US">Gross proceeds</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_SupplementalFinancialInformationDetails2Abstract" xlink:label="VSTA_SupplementalFinancialInformationDetails2Abstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SupplementalFinancialInformationDetails2Abstract" xlink:to="VSTA_SupplementalFinancialInformationDetails2Abstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SupplementalFinancialInformationDetails2Abstract_lbl" xml:lang="en-US">Supplemental Financial Information Details</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_Revenues" xlink:to="us-gaap_Revenues_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_Revenues_2_lbl" xml:lang="en-US">Total revenues</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ResearchAndDevelopmentExpense" xlink:to="us-gaap_ResearchAndDevelopmentExpense_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_ResearchAndDevelopmentExpense_2_lbl" xml:lang="en-US">Research and development</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingExpenses" xlink:to="us-gaap_OperatingExpenses_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OperatingExpenses_2_lbl" xml:lang="en-US">Total operating expenses</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingIncomeLoss" xlink:to="us-gaap_OperatingIncomeLoss_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OperatingIncomeLoss_2_lbl" xml:lang="en-US">Loss from operations</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ChangeInPutAndNoteExtensionOptionAndWarrantLiabilities" xlink:to="VSTA_ChangeInPutAndNoteExtensionOptionAndWarrantLiabilities_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedTerseLabel" xlink:label="VSTA_ChangeInPutAndNoteExtensionOptionAndWarrantLiabilities_2_lbl" xml:lang="en-US">Change in warrant liabilities</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_OtherIncomeLoss" xlink:label="VSTA_OtherIncomeLoss" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_OtherIncomeLoss" xlink:to="VSTA_OtherIncomeLoss_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="VSTA_OtherIncomeLoss_lbl" xml:lang="en-US">Other income</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments" xlink:to="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_2_lbl" xml:lang="en-US">Income (loss) before income taxes</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncomeTaxExpenseBenefit" xlink:to="us-gaap_IncomeTaxExpenseBenefit_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_IncomeTaxExpenseBenefit_2_lbl" xml:lang="en-US">Income taxes</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetIncomeLoss" xlink:to="us-gaap_NetIncomeLoss_3_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_NetIncomeLoss_3_lbl" xml:lang="en-US">Net income (loss)</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EarningsPerShareBasic" xlink:to="us-gaap_EarningsPerShareBasic_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_EarningsPerShareBasic_2_lbl" xml:lang="en-US">Basic net income (loss) per common share</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EarningsPerShareDiluted" xlink:to="us-gaap_EarningsPerShareDiluted_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_EarningsPerShareDiluted_2_lbl" xml:lang="en-US">Diluted net loss per common share</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_EarningsPerShareBasicAndDilutedOtherDisclosuresAbstract" xlink:label="us-gaap_EarningsPerShareBasicAndDilutedOtherDisclosuresAbstract" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EarningsPerShareBasicAndDilutedOtherDisclosuresAbstract" xlink:to="us-gaap_EarningsPerShareBasicAndDilutedOtherDisclosuresAbstract_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_EarningsPerShareBasicAndDilutedOtherDisclosuresAbstract_lbl" xml:lang="en-US">Weighted average shares used in computing:</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_WeightedAverageNumberSharesOutstandingBasic" xlink:label="VSTA_WeightedAverageNumberSharesOutstandingBasic" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_WeightedAverageNumberSharesOutstandingBasic" xlink:to="VSTA_WeightedAverageNumberSharesOutstandingBasic_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_WeightedAverageNumberSharesOutstandingBasic_lbl" xml:lang="en-US">Basic net income (loss) per common share</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding" xlink:to="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_3_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_3_lbl" xml:lang="en-US">Diluted net loss per common share</link:label>
      <link:loc xlink:type="locator" xlink:href="vsta-20140331.xsd#VSTA_SharesOfCommonStockRetroactivelyReflectedAsOutstanding" xlink:label="VSTA_SharesOfCommonStockRetroactivelyReflectedAsOutstanding" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SharesOfCommonStockRetroactivelyReflectedAsOutstanding" xlink:to="VSTA_SharesOfCommonStockRetroactivelyReflectedAsOutstanding_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SharesOfCommonStockRetroactivelyReflectedAsOutstanding_lbl" xml:lang="en-US">Shares of common stock retroactively reflected as outstanding</link:label>
      <link:loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2013/elts/us-gaap-2013-01-31.xsd#us-gaap_UnitsOfPartnershipInterestAmount" xlink:label="us-gaap_UnitsOfPartnershipInterestAmount" />
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_UnitsOfPartnershipInterestAmount" xlink:to="us-gaap_UnitsOfPartnershipInterestAmount_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_UnitsOfPartnershipInterestAmount_lbl" xml:lang="en-US">Shares held by stockholders, pre-merger</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AccruedInterestOnNotesReceivable" xlink:to="VSTA_AccruedInterestOnNotesReceivable_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_AccruedInterestOnNotesReceivable_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_AdditionalInvestorRelationsServicesMember" xlink:to="VSTA_AdditionalInvestorRelationsServicesMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_AdditionalInvestorRelationsServicesMember_doc" xml:lang="en-US">Additional Investor Relations Services Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_BlackscholesOptionPricingModelTableTextBlock" xlink:to="VSTA_BlackscholesOptionPricingModelTableTextBlock_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_BlackscholesOptionPricingModelTableTextBlock_doc" xml:lang="en-US">Blackscholes Option Pricing Model Table Text Block.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_BurrPilgerMayerMember" xlink:to="VSTA_BurrPilgerMayerMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_BurrPilgerMayerMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CatoBioVenturesMember" xlink:to="VSTA_CatoBioVenturesMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CatoBioVenturesMember_doc" xml:lang="en-US">Custom element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CatoHoldingCompanyMember" xlink:to="VSTA_CatoHoldingCompanyMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CatoHoldingCompanyMember_doc" xml:lang="en-US">Cato Holding Company Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ChangeInPutAndNoteExtensionOptionAndWarrantLiabilities" xlink:to="VSTA_ChangeInPutAndNoteExtensionOptionAndWarrantLiabilities_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ChangeInPutAndNoteExtensionOptionAndWarrantLiabilities_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ChangeInPutAndNoteTermExtensionOptionAndWarrantLiabilities" xlink:to="VSTA_ChangeInPutAndNoteTermExtensionOptionAndWarrantLiabilities_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ChangeInPutAndNoteTermExtensionOptionAndWarrantLiabilities_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumCommonStockExchangeAgreementAmount" xlink:to="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumCommonStockExchangeAgreementAmount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumCommonStockExchangeAgreementAmount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumCommonStockExchangeAgreementShares" xlink:to="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumCommonStockExchangeAgreementShares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumCommonStockExchangeAgreementShares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumNoteAndWarrantExchangeAgreementAmount" xlink:to="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumNoteAndWarrantExchangeAgreementAmount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumNoteAndWarrantExchangeAgreementAmount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumNoteAndWarrantExchangeAgreementShares" xlink:to="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumNoteAndWarrantExchangeAgreementShares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CommonStockExchangedForSeriesPreferredUnderAgreementsWithPlatinumNoteAndWarrantExchangeAgreementShares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedForCancellationOfAccountsPayableAndAccruedInterestAmount" xlink:to="VSTA_CommonStockIssuedForCancellationOfAccountsPayableAndAccruedInterestAmount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CommonStockIssuedForCancellationOfAccountsPayableAndAccruedInterestAmount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedForCancellationOfAccountsPayableAndAccruedInterestShares" xlink:to="VSTA_CommonStockIssuedForCancellationOfAccountsPayableAndAccruedInterestShares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CommonStockIssuedForCancellationOfAccountsPayableAndAccruedInterestShares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAmount" xlink:to="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAmount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAmount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanShares" xlink:to="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanShares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CommonStockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanShares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConsultingServicesByRelatedPartiesSettledByIssuingPromissoryNotes" xlink:to="VSTA_ConsultingServicesByRelatedPartiesSettledByIssuingPromissoryNotes_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ConsultingServicesByRelatedPartiesSettledByIssuingPromissoryNotes_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConversionOfAllSeriesOfPreferredStockIntoVistagenCommonStockInConnectionWithMergerAmount" xlink:to="VSTA_ConversionOfAllSeriesOfPreferredStockIntoVistagenCommonStockInConnectionWithMergerAmount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ConversionOfAllSeriesOfPreferredStockIntoVistagenCommonStockInConnectionWithMergerAmount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ConversionOfAllSeriesOfPreferredStockIntoVistagenCommonStockInConnectionWithMergerShares" xlink:to="VSTA_ConversionOfAllSeriesOfPreferredStockIntoVistagenCommonStockInConnectionWithMergerShares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ConversionOfAllSeriesOfPreferredStockIntoVistagenCommonStockInConnectionWithMergerShares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CumulativeEffectOfAdoptingNewAccountingStandard" xlink:to="VSTA_CumulativeEffectOfAdoptingNewAccountingStandard_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CumulativeEffectOfAdoptingNewAccountingStandard_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_CurrentPortionFourMember" xlink:to="VSTA_CurrentPortionFourMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_CurrentPortionFourMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_DesjardinsMember" xlink:to="VSTA_DesjardinsMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_DesjardinsMember_doc" xml:lang="en-US">Desjardins Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_EffectOfMergerAmount" xlink:to="VSTA_EffectOfMergerAmount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_EffectOfMergerAmount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_EffectOfMergerShares" xlink:to="VSTA_EffectOfMergerShares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_EffectOfMergerShares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_EffectOfReverseStockSplit" xlink:to="VSTA_EffectOfReverseStockSplit_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_EffectOfReverseStockSplit_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ExpenseRelatedToModificationOfWarrants" xlink:to="VSTA_ExpenseRelatedToModificationOfWarrants_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ExpenseRelatedToModificationOfWarrants_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueAssumptionsExercisePrice1" xlink:to="VSTA_FairValueAssumptionsExercisePrice1_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_FairValueAssumptionsExercisePrice1_doc" xml:lang="en-US">Custom element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfAdditionalWarrantsGrantedUnderDiscountedWarrantExerciseProgram" xlink:to="VSTA_FairValueOfAdditionalWarrantsGrantedUnderDiscountedWarrantExerciseProgram_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_FairValueOfAdditionalWarrantsGrantedUnderDiscountedWarrantExerciseProgram_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfBonusWarrantsUnderDiscountedWarrantExerciseProgram" xlink:to="VSTA_FairValueOfBonusWarrantsUnderDiscountedWarrantExerciseProgram_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_FairValueOfBonusWarrantsUnderDiscountedWarrantExerciseProgram_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfCommonStockGrantedForServicesFollowingMerger" xlink:to="VSTA_FairValueOfCommonStockGrantedForServicesFollowingMerger_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_FairValueOfCommonStockGrantedForServicesFollowingMerger_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfCommonStockIssuedForNoteTermModification" xlink:to="VSTA_FairValueOfCommonStockIssuedForNoteTermModification_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_FairValueOfCommonStockIssuedForNoteTermModification_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfStockIssuedForServicesFollowingMergerAmount" xlink:to="VSTA_FairValueOfStockIssuedForServicesFollowingMergerAmount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_FairValueOfStockIssuedForServicesFollowingMergerAmount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfStockIssuedForServicesFollowingMergerShares" xlink:to="VSTA_FairValueOfStockIssuedForServicesFollowingMergerShares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_FairValueOfStockIssuedForServicesFollowingMergerShares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfStockIssuedForServicesPriorToMergerAmount" xlink:to="VSTA_FairValueOfStockIssuedForServicesPriorToMergerAmount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_FairValueOfStockIssuedForServicesPriorToMergerAmount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfStockIssuedForServicesPriorToMergerShares" xlink:to="VSTA_FairValueOfStockIssuedForServicesPriorToMergerShares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_FairValueOfStockIssuedForServicesPriorToMergerShares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfWarrantsGrantedForServicesFollowingMerger" xlink:to="VSTA_FairValueOfWarrantsGrantedForServicesFollowingMerger_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_FairValueOfWarrantsGrantedForServicesFollowingMerger_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_FairValueOfWarrantsIssuedForServices" xlink:to="VSTA_FairValueOfWarrantsIssuedForServices_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_FairValueOfWarrantsIssuedForServices_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_February2012ConvertibleNotes12PercentMember" xlink:to="VSTA_February2012ConvertibleNotes12PercentMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_February2012ConvertibleNotes12PercentMember_doc" xml:lang="en-US">February 2012 Convertible Notes 12 Percent Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ForegoingExercisesMember" xlink:to="VSTA_ForegoingExercisesMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ForegoingExercisesMember_doc" xml:lang="en-US">Foregoing Exercises Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ForgivenessOfAccruedCompensationAndAccruedInterestPayableToOfficers" xlink:to="VSTA_ForgivenessOfAccruedCompensationAndAccruedInterestPayableToOfficers_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ForgivenessOfAccruedCompensationAndAccruedInterestPayableToOfficers_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ForgivenessOfNotesAtTheMergerAmount" xlink:to="VSTA_ForgivenessOfNotesAtTheMergerAmount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ForgivenessOfNotesAtTheMergerAmount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_HistoryAndOrganizationTextBlock" xlink:to="VSTA_HistoryAndOrganizationTextBlock_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_HistoryAndOrganizationTextBlock_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IncrementalFairValueOfNoteConversionOptionsFromDebtModification" xlink:to="VSTA_IncrementalFairValueOfNoteConversionOptionsFromDebtModification_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IncrementalFairValueOfNoteConversionOptionsFromDebtModification_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IncrementalValueOfMorrisonFoersterWarrantModification" xlink:to="VSTA_IncrementalValueOfMorrisonFoersterWarrantModification_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IncrementalValueOfMorrisonFoersterWarrantModification_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IncrementalValueOfPlatinumNoteModification" xlink:to="VSTA_IncrementalValueOfPlatinumNoteModification_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IncrementalValueOfPlatinumNoteModification_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IncrementalValueOfWarrantModificationsIncludingModificationOfPlatinumWarrants" xlink:to="VSTA_IncrementalValueOfWarrantModificationsIncludingModificationOfPlatinumWarrants_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IncrementalValueOfWarrantModificationsIncludingModificationOfPlatinumWarrants_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_InvestorRelationServicesMember" xlink:to="VSTA_InvestorRelationServicesMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_InvestorRelationServicesMember_doc" xml:lang="en-US">Investor Relation Services Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_InvestorRelationsAndPublicCompanyServicesMember" xlink:to="VSTA_InvestorRelationsAndPublicCompanyServicesMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_InvestorRelationsAndPublicCompanyServicesMember_doc" xml:lang="en-US">Investor Relations And Public Company Services Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesBPreferredStockat5.545PerShareForCashIncludingConversionOf575000FaceValueOf7ConvertibleNotesPlusAccruedInterestOf3800NetOfUnamortizedDiscountOf70800AndIssuanceCostsOf39800Amount" xlink:to="VSTA_IssuanceOfSeriesBPreferredStockat5.545PerShareForCashIncludingConversionOf575000FaceValueOf7ConvertibleNotesPlusAccruedInterestOf3800NetOfUnamortizedDiscountOf70800AndIssuanceCostsOf39800Amount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IssuanceOfSeriesBPreferredStockat5.545PerShareForCashIncludingConversionOf575000FaceValueOf7ConvertibleNotesPlusAccruedInterestOf3800NetOfUnamortizedDiscountOf70800AndIssuanceCostsOf39800Amount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesBPreferredStockat5.545PerShareForCashIncludingConversionOf575000FaceValueOf7ConvertibleNotesPlusAccruedInterestOf3800NetOfUnamortizedDiscountOf70800AndIssuanceCostsOf39800Shares" xlink:to="VSTA_IssuanceOfSeriesBPreferredStockat5.545PerShareForCashIncludingConversionOf575000FaceValueOf7ConvertibleNotesPlusAccruedInterestOf3800NetOfUnamortizedDiscountOf70800AndIssuanceCostsOf39800Shares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IssuanceOfSeriesBPreferredStockat5.545PerShareForCashIncludingConversionOf575000FaceValueOf7ConvertibleNotesPlusAccruedInterestOf3800NetOfUnamortizedDiscountOf70800AndIssuanceCostsOf39800Shares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesCPreferredStockAt6.00PerShareForCashIncludingConversionOf1655000FaceValueOf10ConvertibleNotesPlusAccruedInterestOf408600NetOfUnamortizedNote" xlink:to="VSTA_IssuanceOfSeriesCPreferredStockAt6.00PerShareForCashIncludingConversionOf1655000FaceValueOf10ConvertibleNotesPlusAccruedInterestOf408600NetOfUnamortizedNote_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IssuanceOfSeriesCPreferredStockAt6.00PerShareForCashIncludingConversionOf1655000FaceValueOf10ConvertibleNotesPlusAccruedInterestOf408600NetOfUnamortizedNote_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesCPreferredStockAt6.00PerShareForCashIncludingConversionOf1655000FaceValueOf10ConvertibleNotesPlusAccruedInterestOf408600NetOfUnamortizedShares" xlink:to="VSTA_IssuanceOfSeriesCPreferredStockAt6.00PerShareForCashIncludingConversionOf1655000FaceValueOf10ConvertibleNotesPlusAccruedInterestOf408600NetOfUnamortizedShares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IssuanceOfSeriesCPreferredStockAt6.00PerShareForCashIncludingConversionOf1655000FaceValueOf10ConvertibleNotesPlusAccruedInterestOf408600NetOfUnamortizedShares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf24000Amount" xlink:to="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf24000Amount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf24000Amount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf24000Shares" xlink:to="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf24000Shares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IssuanceOfSeriesaPreferredStockAt2.302PerShareForCashNetOfIssuanceCostsOf24000Shares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesb1PreferredStockat5.545ForAcquiredInprocessresearchAndDevelopmentAmount" xlink:to="VSTA_IssuanceOfSeriesb1PreferredStockat5.545ForAcquiredInprocessresearchAndDevelopmentAmount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IssuanceOfSeriesb1PreferredStockat5.545ForAcquiredInprocessresearchAndDevelopmentAmount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriesb1PreferredStockat5.545ForAcquiredInprocessresearchAndDevelopmentShares" xlink:to="VSTA_IssuanceOfSeriesb1PreferredStockat5.545ForAcquiredInprocessresearchAndDevelopmentShares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IssuanceOfSeriesb1PreferredStockat5.545ForAcquiredInprocessresearchAndDevelopmentShares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriescPreferredStockAt6.00PerShareForServicesAndInPaymentOfInterestOnLineOfCreditAmount" xlink:to="VSTA_IssuanceOfSeriescPreferredStockAt6.00PerShareForServicesAndInPaymentOfInterestOnLineOfCreditAmount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IssuanceOfSeriescPreferredStockAt6.00PerShareForServicesAndInPaymentOfInterestOnLineOfCreditAmount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_IssuanceOfSeriescPreferredStockAt6.00PerShareForServicesAndInPaymentOfInterestOnLineOfCreditShares" xlink:to="VSTA_IssuanceOfSeriescPreferredStockAt6.00PerShareForServicesAndInPaymentOfInterestOnLineOfCreditShares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_IssuanceOfSeriescPreferredStockAt6.00PerShareForServicesAndInPaymentOfInterestOnLineOfCreditShares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_LegalFees1" xlink:to="VSTA_LegalFees1_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_LegalFees1_doc" xml:lang="en-US">Legal Fees1.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_LossOnEarlyExtinguishmentOfDebt" xlink:to="VSTA_LossOnEarlyExtinguishmentOfDebt_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_LossOnEarlyExtinguishmentOfDebt_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_LossOnSettlementsOfAccountsPayable" xlink:to="VSTA_LossOnSettlementsOfAccountsPayable_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_LossOnSettlementsOfAccountsPayable_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_MarketPricePerShare" xlink:to="VSTA_MarketPricePerShare_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_MarketPricePerShare_doc" xml:lang="en-US">Market Price Per Share.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_MayTwoThousandElevenMorrisonFoersterMember" xlink:to="VSTA_MayTwoThousandElevenMorrisonFoersterMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_MayTwoThousandElevenMorrisonFoersterMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_McCarthyTetraultMember" xlink:to="VSTA_McCarthyTetraultMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_McCarthyTetraultMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NetProceedsFromIssuanceOf10ConvertibleNotesAndWarrants" xlink:to="VSTA_NetProceedsFromIssuanceOf10ConvertibleNotesAndWarrants_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NetProceedsFromIssuanceOf10ConvertibleNotesAndWarrants_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NetProceedsFromIssuanceOf20062007NotesAndWarrants" xlink:to="VSTA_NetProceedsFromIssuanceOf20062007NotesAndWarrants_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NetProceedsFromIssuanceOf20062007NotesAndWarrants_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NetProceedsFromIssuanceOf7ConvertibleNotes" xlink:to="VSTA_NetProceedsFromIssuanceOf7ConvertibleNotes_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NetProceedsFromIssuanceOf7ConvertibleNotes_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NetProceedsFromIssuanceOfFebruary201212ConvertibleNotesAndWarrants" xlink:to="VSTA_NetProceedsFromIssuanceOfFebruary201212ConvertibleNotesAndWarrants_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NetProceedsFromIssuanceOfFebruary201212ConvertibleNotesAndWarrants_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NetProceedsFromIssuanceOfPlatinumNotesAndWarrants" xlink:to="VSTA_NetProceedsFromIssuanceOfPlatinumNotesAndWarrants_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NetProceedsFromIssuanceOfPlatinumNotesAndWarrants_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesPayableAndAccruedInterest" xlink:to="VSTA_NotesPayableAndAccruedInterest_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NotesPayableAndAccruedInterest_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesPayableAndAccruedInterestToRelatedParties" xlink:to="VSTA_NotesPayableAndAccruedInterestToRelatedParties_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NotesPayableAndAccruedInterestToRelatedParties_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesPayableAndAccruedInterestToRelatedPartiesNonCurrent" xlink:to="VSTA_NotesPayableAndAccruedInterestToRelatedPartiesNonCurrent_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NotesPayableAndAccruedInterestToRelatedPartiesNonCurrent_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesPayableDiscount" xlink:to="VSTA_NotesPayableDiscount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NotesPayableDiscount_doc" xml:lang="en-US">Notes Payable Discount.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesPayableDiscountRelatedParties" xlink:to="VSTA_NotesPayableDiscountRelatedParties_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NotesPayableDiscountRelatedParties_doc" xml:lang="en-US">Notes Payable Discount Related Parties.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesPayableToRelatedPartiesMember" xlink:to="VSTA_NotesPayableToRelatedPartiesMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NotesPayableToRelatedPartiesMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_NotesReceivableFromSaleOfCommonStockToOthers" xlink:to="VSTA_NotesReceivableFromSaleOfCommonStockToOthers_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_NotesReceivableFromSaleOfCommonStockToOthers_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_OutstandingShares" xlink:to="VSTA_OutstandingShares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_OutstandingShares_doc" xml:lang="en-US">Outstanding Shares.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_OutstandingWarrantsToPurchaseCommonStock" xlink:to="VSTA_OutstandingWarrantsToPurchaseCommonStock_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_OutstandingWarrantsToPurchaseCommonStock_doc" xml:lang="en-US">Outstanding Warrants To Purchase Common Stock.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PaymentsOnNoteReceivableForSaleOfStock" xlink:to="VSTA_PaymentsOnNoteReceivableForSaleOfStock_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_PaymentsOnNoteReceivableForSaleOfStock_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PlatinumMember" xlink:to="VSTA_PlatinumMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_PlatinumMember_doc" xml:lang="en-US">Platinum Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PostModificationMember" xlink:to="VSTA_PostModificationMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_PostModificationMember_doc" xml:lang="en-US">Custom element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PostModificationWarrantsMember" xlink:to="VSTA_PostModificationWarrantsMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_PostModificationWarrantsMember_doc" xml:lang="en-US">Post Modification Warrants Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PreModificationMember" xlink:to="VSTA_PreModificationMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_PreModificationMember_doc" xml:lang="en-US">Custom element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PreModificationWarrantsMember" xlink:to="VSTA_PreModificationWarrantsMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_PreModificationWarrantsMember_doc" xml:lang="en-US">Pre Modification Warrants Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PreferredStockSeriesASharesAuthorized" xlink:to="VSTA_PreferredStockSeriesASharesAuthorized_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_PreferredStockSeriesASharesAuthorized_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PreferredStockSeriesASharesIssued" xlink:to="VSTA_PreferredStockSeriesASharesIssued_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_PreferredStockSeriesASharesIssued_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PreferredStockSeriesASharesOutstanding" xlink:to="VSTA_PreferredStockSeriesASharesOutstanding_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_PreferredStockSeriesASharesOutstanding_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PreferredStockSeriesPerValue1" xlink:to="VSTA_PreferredStockSeriesPerValue1_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_PreferredStockSeriesPerValue1_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PrepaidExpensesTableTextBlock" xlink:to="VSTA_PrepaidExpensesTableTextBlock_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_PrepaidExpensesTableTextBlock_doc" xml:lang="en-US">Prepaid Expenses TableText Block.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_PrepaidExpensesTextBlock" xlink:to="VSTA_PrepaidExpensesTextBlock_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_PrepaidExpensesTextBlock_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProceedsAllocatedToWarrantsIssuedAndBeneficialConversionFeatureInConnectionWith12ConvertibleNotes" xlink:to="VSTA_ProceedsAllocatedToWarrantsIssuedAndBeneficialConversionFeatureInConnectionWith12ConvertibleNotes_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ProceedsAllocatedToWarrantsIssuedAndBeneficialConversionFeatureInConnectionWith12ConvertibleNotes_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithPlatinumNotes" xlink:to="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithPlatinumNotes_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithPlatinumNotes_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithPlatinumNotesAndIncrementalFairValueOfWarrantModification" xlink:to="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithPlatinumNotesAndIncrementalFairValueOfWarrantModification_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithPlatinumNotesAndIncrementalFairValueOfWarrantModification_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithSeriesCPreferredstockAmount" xlink:to="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithSeriesCPreferredstockAmount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ProceedsAllocatedToWarrantsIssuedInConnectionWithSeriesCPreferredstockAmount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProceedsFromExerciseOfModifiedWarrantsMayjune2012AndUnderDiscountedWarrantExerciseProgram2011" xlink:to="VSTA_ProceedsFromExerciseOfModifiedWarrantsMayjune2012AndUnderDiscountedWarrantExerciseProgram2011_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ProceedsFromExerciseOfModifiedWarrantsMayjune2012AndUnderDiscountedWarrantExerciseProgram2011_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ProceedsFromIssuanceOf7NotePayableToFoundingStockholder" xlink:to="VSTA_ProceedsFromIssuanceOf7NotePayableToFoundingStockholder_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ProceedsFromIssuanceOf7NotePayableToFoundingStockholder_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_QualifiedFinancingMember" xlink:to="VSTA_QualifiedFinancingMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_QualifiedFinancingMember_doc" xml:lang="en-US">Qualified Financing Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ReclassificationOfWarrantLiabilityToEquity" xlink:to="VSTA_ReclassificationOfWarrantLiabilityToEquity_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ReclassificationOfWarrantLiabilityToEquity_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_RevenueFromExternalCustomers" xlink:to="VSTA_RevenueFromExternalCustomers_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_RevenueFromExternalCustomers_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SaleOfCommonStockForCashAmount" xlink:to="VSTA_SaleOfCommonStockForCashAmount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_SaleOfCommonStockForCashAmount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SaleOfCommonStockForCashShares" xlink:to="VSTA_SaleOfCommonStockForCashShares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_SaleOfCommonStockForCashShares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SeniorSecuredConvertiblePromisoryNotesAndAccruedInterest" xlink:to="VSTA_SeniorSecuredConvertiblePromisoryNotesAndAccruedInterest_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_SeniorSecuredConvertiblePromisoryNotesAndAccruedInterest_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SevenPercentNotesPayableAprilTwoThousandElevenMember" xlink:to="VSTA_SevenPercentNotesPayableAprilTwoThousandElevenMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_SevenPercentNotesPayableAprilTwoThousandElevenMember_doc" xml:lang="en-US">Custom Element.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsEightMember" xlink:to="VSTA_ShareBasedCompensationWarrantsEightMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ShareBasedCompensationWarrantsEightMember_doc" xml:lang="en-US">Share Based Compensation Warrants Eight Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsElevenMember" xlink:to="VSTA_ShareBasedCompensationWarrantsElevenMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ShareBasedCompensationWarrantsElevenMember_doc" xml:lang="en-US">Share Based Compensation Warrants Eleven Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsFiveMember" xlink:to="VSTA_ShareBasedCompensationWarrantsFiveMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ShareBasedCompensationWarrantsFiveMember_doc" xml:lang="en-US">Share Based Compensation Warrants Five Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsFourMember" xlink:to="VSTA_ShareBasedCompensationWarrantsFourMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ShareBasedCompensationWarrantsFourMember_doc" xml:lang="en-US">Share Based Compensation Warrants Four Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsNineMember" xlink:to="VSTA_ShareBasedCompensationWarrantsNineMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ShareBasedCompensationWarrantsNineMember_doc" xml:lang="en-US">Share Based Compensation Warrants Nine Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsOneMember" xlink:to="VSTA_ShareBasedCompensationWarrantsOneMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ShareBasedCompensationWarrantsOneMember_doc" xml:lang="en-US">Share Based Compensation Warrants One Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsSevenMember" xlink:to="VSTA_ShareBasedCompensationWarrantsSevenMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ShareBasedCompensationWarrantsSevenMember_doc" xml:lang="en-US">Share Based Compensation Warrants Seven Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsSixMember" xlink:to="VSTA_ShareBasedCompensationWarrantsSixMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ShareBasedCompensationWarrantsSixMember_doc" xml:lang="en-US">Share Based Compensation Warrants Six Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsTenMember" xlink:to="VSTA_ShareBasedCompensationWarrantsTenMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ShareBasedCompensationWarrantsTenMember_doc" xml:lang="en-US">Share Based Compensation Warrants Ten Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsTwelveMember" xlink:to="VSTA_ShareBasedCompensationWarrantsTwelveMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ShareBasedCompensationWarrantsTwelveMember_doc" xml:lang="en-US">Share Based Compensation Warrants Twelve Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ShareBasedCompensationWarrantsTwoMember" xlink:to="VSTA_ShareBasedCompensationWarrantsTwoMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_ShareBasedCompensationWarrantsTwoMember_doc" xml:lang="en-US">Share Based Compensation Warrants Two Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SharebasedCompensationExpense" xlink:to="VSTA_SharebasedCompensationExpense_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_SharebasedCompensationExpense_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SharesIssuedForPreferredStock" xlink:to="VSTA_SharesIssuedForPreferredStock_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_SharesIssuedForPreferredStock_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedInConnectionWithNoteTermExtensionAmount" xlink:to="VSTA_StockIssuedInConnectionWithNoteTermExtensionAmount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_StockIssuedInConnectionWithNoteTermExtensionAmount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedInConnectionWithNoteTermExtensionShares" xlink:to="VSTA_StockIssuedInConnectionWithNoteTermExtensionShares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_StockIssuedInConnectionWithNoteTermExtensionShares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedInFall2011FollowonOfferingAmount" xlink:to="VSTA_StockIssuedInFall2011FollowonOfferingAmount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_StockIssuedInFall2011FollowonOfferingAmount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedInFall2011FollowonOfferingShares" xlink:to="VSTA_StockIssuedInFall2011FollowonOfferingShares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_StockIssuedInFall2011FollowonOfferingShares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedInMay2011PrivatePlacementNetOf202000PlacementFeesAmount" xlink:to="VSTA_StockIssuedInMay2011PrivatePlacementNetOf202000PlacementFeesAmount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_StockIssuedInMay2011PrivatePlacementNetOf202000PlacementFeesAmount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedInMay2011PrivatePlacementNetOf202000PlacementFeesShares" xlink:to="VSTA_StockIssuedInMay2011PrivatePlacementNetOf202000PlacementFeesShares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_StockIssuedInMay2011PrivatePlacementNetOf202000PlacementFeesShares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedUponConversionOfAllSeriesOfPreferredStockAmount" xlink:to="VSTA_StockIssuedUponConversionOfAllSeriesOfPreferredStockAmount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_StockIssuedUponConversionOfAllSeriesOfPreferredStockAmount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedUponConversionOfAllSeriesOfPreferredStockShares" xlink:to="VSTA_StockIssuedUponConversionOfAllSeriesOfPreferredStockShares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_StockIssuedUponConversionOfAllSeriesOfPreferredStockShares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedUponConversionOfConvertiblePromissoryNotesAmount" xlink:to="VSTA_StockIssuedUponConversionOfConvertiblePromissoryNotesAmount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_StockIssuedUponConversionOfConvertiblePromissoryNotesAmount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedUponConversionOfConvertiblePromissoryNotesShares" xlink:to="VSTA_StockIssuedUponConversionOfConvertiblePromissoryNotesShares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_StockIssuedUponConversionOfConvertiblePromissoryNotesShares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedUponConversionOfPlatinumNoteToEquityNetOfPlatinumWarrantExerciseReflectedAboveAmount" xlink:to="VSTA_StockIssuedUponConversionOfPlatinumNoteToEquityNetOfPlatinumWarrantExerciseReflectedAboveAmount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_StockIssuedUponConversionOfPlatinumNoteToEquityNetOfPlatinumWarrantExerciseReflectedAboveAmount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedUponConversionOfPlatinumNoteToEquityNetOfPlatinumWarrantExerciseReflectedAboveShares" xlink:to="VSTA_StockIssuedUponConversionOfPlatinumNoteToEquityNetOfPlatinumWarrantExerciseReflectedAboveShares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_StockIssuedUponConversionOfPlatinumNoteToEquityNetOfPlatinumWarrantExerciseReflectedAboveShares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedUponExerciseOfModifiedWarrantsIncludesPlatinumExercisesAmount" xlink:to="VSTA_StockIssuedUponExerciseOfModifiedWarrantsIncludesPlatinumExercisesAmount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_StockIssuedUponExerciseOfModifiedWarrantsIncludesPlatinumExercisesAmount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedUponExerciseOfModifiedWarrantsIncludesPlatinumExercisesShares" xlink:to="VSTA_StockIssuedUponExerciseOfModifiedWarrantsIncludesPlatinumExercisesShares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_StockIssuedUponExerciseOfModifiedWarrantsIncludesPlatinumExercisesShares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAmount" xlink:to="VSTA_StockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAmount_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_StockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanAmount_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanShares" xlink:to="VSTA_StockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanShares_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_StockIssuedUponExerciseOfOptionsFrom1999StockIncentivePlanShares_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockholdersEquityForPreferredStock" xlink:to="VSTA_StockholdersEquityForPreferredStock_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_StockholdersEquityForPreferredStock_doc" xml:lang="en-US">Custom Element</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_Total" xlink:to="VSTA_Total_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_Total_doc" xml:lang="en-US">Total.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_UnrelatedPartiesMember" xlink:to="VSTA_UnrelatedPartiesMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_UnrelatedPartiesMember_doc" xml:lang="en-US">Unrelated Parties Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_WarrantExercisePrice" xlink:to="VSTA_WarrantExercisePrice_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_WarrantExercisePrice_doc" xml:lang="en-US">Warrant exercise price.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_WarrantModificationsMember" xlink:to="VSTA_WarrantModificationsMember_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_WarrantModificationsMember_doc" xml:lang="en-US">Warrant Modifications Member.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_WarrantsExercisePrice" xlink:to="VSTA_WarrantsExercisePrice_doc" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="VSTA_WarrantsExercisePrice_doc" xml:lang="en-US">WarrantsExercisePrice.</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_Price.721.80Member" xlink:to="VSTA_Price.721.80Member_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_Price.721.80Member_2_lbl" xml:lang="en-US">Price.721.80Member</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SeniorNoteSixMember" xlink:to="VSTA_SeniorNoteSixMember_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SeniorNoteSixMember_2_lbl" xml:lang="en-US">SeniorNoteSixMember</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AssetsCurrent" xlink:to="us-gaap_AssetsCurrent_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AssetsCurrent_2_lbl" xml:lang="en-US">Assets, Current</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_Assets" xlink:to="us-gaap_Assets_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_Assets_2_lbl" xml:lang="en-US">Assets</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesCurrent" xlink:to="us-gaap_LiabilitiesCurrent_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LiabilitiesCurrent_2_lbl" xml:lang="en-US">Liabilities, Current</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalLeaseObligationsNoncurrent" xlink:to="us-gaap_CapitalLeaseObligationsNoncurrent_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CapitalLeaseObligationsNoncurrent_2_lbl" xml:lang="en-US">Capital Lease Obligations, Noncurrent</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesNoncurrent" xlink:to="us-gaap_LiabilitiesNoncurrent_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LiabilitiesNoncurrent_2_lbl" xml:lang="en-US">Liabilities, Noncurrent</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_Liabilities" xlink:to="us-gaap_Liabilities_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_Liabilities_2_lbl" xml:lang="en-US">Liabilities</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TreasuryStockValue" xlink:to="us-gaap_TreasuryStockValue_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_TreasuryStockValue_2_lbl" xml:lang="en-US">Treasury Stock, Value</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StockholdersEquity" xlink:to="us-gaap_StockholdersEquity_4_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_StockholdersEquity_4_lbl" xml:lang="en-US">Stockholders' Equity Attributable to Parent</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesAndStockholdersEquity" xlink:to="us-gaap_LiabilitiesAndStockholdersEquity_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LiabilitiesAndStockholdersEquity_2_lbl" xml:lang="en-US">Liabilities and Equity</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_ChangeInPutAndNoteExtensionOptionAndWarrantLiabilities" xlink:to="VSTA_ChangeInPutAndNoteExtensionOptionAndWarrantLiabilities_4_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_ChangeInPutAndNoteExtensionOptionAndWarrantLiabilities_4_lbl" xml:lang="en-US">ChangeInPutAndNoteExtensionOptionAndWarrantLiabilities</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_LossOnEarlyExtinguishmentOfDebt" xlink:to="VSTA_LossOnEarlyExtinguishmentOfDebt_3_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_LossOnEarlyExtinguishmentOfDebt_3_lbl" xml:lang="en-US">LossOnEarlyExtinguishmentOfDebt</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets" xlink:to="us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_2_lbl" xml:lang="en-US">Increase (Decrease) in Prepaid Expense and Other Assets</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_IncreaseDecreaseInDepositOtherAssets" xlink:to="us-gaap_IncreaseDecreaseInDepositOtherAssets_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_IncreaseDecreaseInDepositOtherAssets_2_lbl" xml:lang="en-US">Increase (Decrease) in Deposit Assets</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:to="us-gaap_NetCashProvidedByUsedInOperatingActivities_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivities_2_lbl" xml:lang="en-US">Net Cash Provided by (Used in) Operating Activities</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PaymentsToAcquireMachineryAndEquipment" xlink:to="us-gaap_PaymentsToAcquireMachineryAndEquipment_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PaymentsToAcquireMachineryAndEquipment_2_lbl" xml:lang="en-US">Payments to Acquire Machinery and Equipment</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivities" xlink:to="us-gaap_NetCashProvidedByUsedInInvestingActivities_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivities_2_lbl" xml:lang="en-US">Net Cash Provided by (Used in) Investing Activities</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivities" xlink:to="us-gaap_NetCashProvidedByUsedInFinancingActivities_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivities_2_lbl" xml:lang="en-US">Net Cash Provided by (Used in) Financing Activities</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease" xlink:to="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease_2_lbl" xml:lang="en-US">Cash and Cash Equivalents, Period Increase (Decrease)</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalLeaseObligationsIncurred" xlink:to="us-gaap_CapitalLeaseObligationsIncurred_2_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CapitalLeaseObligationsIncurred_2_lbl" xml:lang="en-US">Capital Lease Obligations Incurred</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_StockholdersEquityForPreferredStock" xlink:to="VSTA_StockholdersEquityForPreferredStock_4_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_StockholdersEquityForPreferredStock_4_lbl" xml:lang="en-US">StockholdersEquityForPreferredStock</link:label>
      <link:labelArc xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="VSTA_SharesIssuedForPreferredStock" xlink:to="VSTA_SharesIssuedForPreferredStock_4_lbl" xlink:type="arc" />
      <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="VSTA_SharesIssuedForPreferredStock_4_lbl" xml:lang="en-US">SharesIssuedForPreferredStock</link:label>
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