The overall aim of this laboratory has been the elaboration of mechanisms underlying several models of neurodegeneration. In this proposal we shall continue our studies of the interaction of neuronal-glial amino acid metabolism as it relates to the phenomenon of excitotoxicity. These studies shall make use primarily of the embryonic chick retina and tissue culture of rat cortical astrocytes and retinal Muller cells. All of these proposed studies are the direct outcome of experiments done during previous grant periods. As a model of ischemia/hypoxia, chick retina will be incubated in glucose-free medium or glucose-containing medium with various metabolic inhibitors (iodoacetate or deoxyglucose to inhibit glycolysis, KCN to inhibit mitochondrial electron transport, dinitrophenol to uncouple oxidative phosphorylation). Our previous work has shown that metabolic inhibition causes an excitotoxic lesion which is prevented by inhibitors of the NMDA receptor. These findings will be pursued in depth in an attempt to understand the connection between metabolic inhibition and apparent activation of the NMDA receptor. Parameters such as the temporal relationship of ATP depletion and acute neurotoxicity, the role of free radical generation, extracellular Mg2+ levels, the possible potentiation of the excitotoxicity by intracellular alkalinosis and the effects of extracellular pH and temperature changes will also be assessed. The ontogeny of this effect will be examined and correlated with the development of glycolysis and aerobic metabolism. The role of polyamines in NMDA-mediated toxicity will also be examined using various polyamines as well the anti-ischemic agents ifenprodil and SL82.0715 which have been reported to interact with a """"""""polyamine"""""""" site on the NMDA receptor. In our hands ifenprodil protects against NMDA toxicity in chick retina, however, a subset of neurons is not protected. This will be further examined and attempts made to identify the neurotransmitter phenotype of the unprotected neurons. Studies on astrocyte amino acid metabolism will be continued focusing on direct effects of exciatory amino acids and metabolic inhibition on various parameters such as glycolytic and amino acid metabolism, energy charge and cellular swelling. Similar studies will then be done with the primary glial cell of the retina, the Muller cell. These studies should answer some basic questions concerning the mechanism of excitotoxicity in neurodegenerative disorders and the special role glia might play in that toxicity.
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