Methamphetamine (MA) causes damage to nerve cells in the central nervous system contain dopamine (DA) or 5-hydroxytryptamine (5HT). This occurs in several species of animal including non-human primates, rodents, and cats. There is also a loss in the DA or 5HT energy dependent high affinity uptake pump and degeneration of DA never terminal axons. Using HPLC/ED, it has been shown that MA engenders the formation of two neurotoxins 6- hydroxydopamine (6-OHDA) and 5,6-dihydroxytryptamine (5,6-DHT) which we have hypothesized are formed from endogenous DA and 5HT, respectively. This research application proposes experiments which will test the hypothesis that the neurotoxins are formed from neurotransmitters via a Fenton type reaction in which hydrogen peroxide is cleaved into hydroxyl ion and hydroxy radical which subsequently hydroxylates the neurotransmitters into the neurotoxins 6-OHDA and 5,6-DHT. The conditions under which this reaction proceeds may be enzymatically or non-enzymatically catalyzed and we will test this condition including conditions of oxygen saturation, hydrogen peroxide availability, and the presence or absence of protective agents such as ascorbate, cysteine, and glutathione. In addition, we will examine the products of the further catabolism of 6-OHDA. There is evidence that 6-OHDA can be oxidized to form quinones and that these quinones can couple with sulfhydrl groups and form sulfhydrl adducts of 6-OHDA quinone. These adducts are markers of the fact that MA-induced neurotoxicity can proceed in the manner described and we shall set up assays to determine the presence of thiol adducts. Experiments will be done in vitro, ex vivo, and in vivo. These experiments are of interest because they not only may tell us the way in which MA produces toxicity to certain neurons in the CNS but may give indications of how general neuronal death occurs in important neurotransmitter systems with other diseases processes of aging.
