High dose administration of methamphetamine (METH) , but not cocaine (COC), causes persistent dopamine (DA) neuronal deficits. METH may effect this loss by causing excess cytoplasmic DA accumulation, and subsequently, neurotoxic reactive oxygen species formation. Accordingly, one explanation for the lack of DA deficits caused by COC may be that it does not cause such an intracellular accumulation. Since the vesicular monoamine and plasmalemmal DA transporters (VMAT and DAT, respectively) effects. Our laboratory has reported that METH and COC treatment differentially affect plasmalemmal and vesicular DA uptake. Hence, this proposal will test the hypothesis that differences in the effect of METH and COC administration on VMAT-2 and DAT contribute to their unique persistent DA consequence. This will be accomplished by completing the following Specific Aims: A. Compare features of the COC- and METH-induced alterations in vesicular and plasmalemmal DA uptake. This will be achieved by: 1) determining dose and temporal effects of these agents on DAT and VMAT-2 function, ligand binding and protein levels; 2) examining the nature of the drug-induced changes in vesicular DA uptake. This will be achieved by: 1) determining dose and temporal effects of these agents on DAT and VMAT-2 function, ligand binding and protein levels; 2) examining the nature of the drug-induced changes in vesicular DA uptake; 3) investigating if other DA agents rapidly alter vesicular DA uptake. B. Elucidate mechanisms whereby COC and METH alter plasmalemmal and/or vesicular DA uptake. This will be accomplished by investigating the role(s) of: 1) DAT phosphorylation and internalization in the METH- induced decrease in plasmalemmal DA uptake; and 2) DA per se, the vesicular ATPase and phosphorylation in the stimulant-induced changes in vesicular DA uptake. C. Determine mechanisms whereby METH- and COC-induced changes in VMAT-2 differentially influence the likelihood of persistent DA deficits. This will be achieved by investigating: 1) the impact of COC treatment on vesicular DA content; 2) if drugs that up-regulate vesicular DA uptake prevent long-term METH-induced deficits; 3) if a tolerance- producing regimen of METH alters vesicular DA uptake thereby preventing long-term DA neuronal deficits; and 4) if kindling alters vesicular DA uptake thereby altering the propensity towards long-term DA neuronal deficits. These studies will elucidate the role of VMAT-2 and DAT in the differential long-term DA effects of METH and COC. This may not only provide insight into mechanisms of psychostimulant-induced toxicity, but also DA-related neurological disorders such as Parkinson's disease. These studies will also provide insight concerning VMAT-2 and DAT regulation that may aid in development of agents useful in substance abuse treatment, and will enhance understanding of the physiological regulation of these transporters.
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