The goal of this project is to contribute to an understanding of the chemical and biochemical mechanisms that underlie the dopaminergic and/or serotonergic neurotoxicity of methamphetamine (MA) and 3,4-methylenedioxymethampetamine (MDMA). The project is based on the hypothesis that glutathione (GSH), released from both neurons and glia, and extracellular conditions that influence the activity of gamma-glutamyl transpeptidase (g-GT), are key factors in MA- and MDMA-induced neurotoxicity. It is proposed that extracellular conditions evoked by a MA-induced neuronal energy impairment, notably excessive HO* generation, cause upregulation of g-GT and hydrolysis of GSH to glutamate (Glu), glycine (Gly) and cysteine (CySH). Dopaminergic neuronal damage evoked by MA in the rat is proposed to be dependent on the intraneuronal oxidation of DA by O2-*, generated by NMDA receptor activation by elevated extracellular Glu, in the presence of translocated CySH forming dihydrobenzothiazine (DHBT) and benzothiazine (BT) mitochondrial (mt) toxicants. Similarly, serotonergic neuronal damage may be caused by intraneuronal oxidation of 5-HT by O-2-* in the presence of translocated CySH to give endotoxic metabolites. Mechanisms are proposed by which MDMA, because of its HO* scavenging properties, inhibits g-GT and hence hydrolysis of released GSH. Thus, not only is Glu-mediated NMDA receptor activation and intraneuronal O-2-* generation attenuated, CySH, essential for DHBT/BT formation, is not available and DA neurons are spared. In contrast, the O-2-* mediated oxidation of 5-HT generates tryptamine-4,5-dione that in the absence of CySH inhibits mt enzymes and, hence, MDMA evokes selective serotonergic neurotoxicity.
Specific aims are to: (1) monitor extracellular changes of DA, 5-HT and their metabolites, thiols/disulfides, and Glu, Asp and Gly in rat brain in response to MA and MDMA using microdialysis; (2) search for unusual products of oxidation of extracellular DA/5-HT/metabolites by HO* that might contribute to MA/MDMA toxicity, also using microdialysis; (3) study the influence of hypothermia, astroglial ablation, and the glucose metabolism inhibitor 2-deoxy-D-glucose, on MA/MDMA-induced extracellular neurochemical changes; (4) investigate the effects of MA/MDMA on brain thiol/disulfide concentrations and g-GT activity; (5) study the effects of g-GT inhibition, manipulations of brain GSH, 5-S-cysteinyldopamine (DHBT/BT precursor), and glial ablation on MA/MDMA-induced neurotoxicity; (6) analyze brain tissue for evidence of putative endotoxic metabolites and covalently modified proteins; (7) study interactions of putative endotoxins with mt and other enzymes; (8) assay rat brain for activities of mt and other enzymes, following MA/MDMA administration.
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