Twelve years ago, we first demonstrated that intrastriatal injection of the potent excitatory analogue of glutamate, kainic acid (KA), reproduced many of the synaptic neurochemical and histopathologic features of Huntington's Disease (HD) in the rat. Subsequent studies indicated that agonists at all three glutamate receptor subtypes - quisqualic acid (QA), N-methyl-D-aspartic acid (NMDA) and KA - caused specific patterns of selective neuronal degeneration upon intracerebral injection, leading to the proposal that endogenous excitotoxic mechanisms might account for neuronal death in HD and other neurodegenerative disorders. During the last period of support, we have focused on the endogenous processes - both presynaptic and postreceptor - that may contribute to the excitotoxic mechanisms. We have identified an excitatory dipeptide, N-acetyl aspartyl glutamate (NAAG) which has been localized by immunocytochemical staining, to subsets of putative glutamatergic pathways. Using the neuronal-like cell line, N18-RE-105, we have demonstrated that oxidative stress is the proximate cause of Ca++-dependent cell death due to glutamate or QA exposure in this in vitro model for excitotoxicity. In the proposed studies, we will characterize the enzymes that synthesize and catabolize NAAG and determine whether NAAG is subject to Ca++ -dependent depolarization induced release in vivo, an important criterion for a neurotransmitter candidate. We will examine the metabolic events that underlie the oxidative stress in glutamate/QA induced degenemtion of the N18-RE-105 cells. Using primary cultures of the hippocarnpus, we will determine the contribution of oxidative stress to KA, QA and NMDA induced delayed neuronal degeneration. Finally, we will exploit a mammalian cell replica plating method to isolate clones expressing QA, NMDA or KA receptors, in order to further characterize post-receptor mechanisms responsible for excitotoxin-induced neuronal degeneration.
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