GLUTAMATE, EXCITOTOXINS AND NEURONAL-GLIAL INTERACTIONS

氨基酸的功能或代谢失常

Aberrations of function or metabolism of the putative amino acid (AA) neurotransmitters, glutmate (GLU) and GABA, have been implicated in the etiology or sequelae of several neurological disorders. GLU or GLU-analogs, e.g., the excitotoxins kainate (KA) and quisqualate (QUIS), when injected directly into CNS structures cause neuronal death, raising the intriguing possibility that endogenous excitotoxicity activity may be involved in such disorders. Studies have shown that an alteration in energy metabolism and normal neuronal-glial metabolism of GLU may play a role in this neurotoxicity. This application is a continuation of those efforts. Recent work has shown that C1- transport, perhaps via the C1-/HCO3- antiport, may play a major role in basic mechanisms underlying the sequelae of excitotoxicity. This proposal will focus on the use of C1- transport inhibitors on excitotoxicity-induced effects in our test systems. C1- uptake will be measured in rat brain cerebellar slices using radioactive Na36C1 in the presence of excitotoxins, and other depolarizing agents such as K+ and veratridine. Known inhibitors of C1- transport will be added to the incubations to see which type of carrier system is activated by the treatments. Chick embryonic retina is also exquisitely sensitive to excitotoxicity. Developmental aspects of toxicity will be examined by using retina of ages E6 to E21, which correspond to specific stages of development. Results will be correlated with alterations in AA metabolism, both in terms of dynamic measurements using radioactive precursors, the development of enzymes as measured by direct assay and immunohistochemistry. The various inhibitors of C1- transport used in the tissue slice studies will be studied to see which, if any, protect against neurotoxicity. The C1-/HCO3- system also regulates intracellular pH in some cell types. Intracellular pH will be measured in the retinas following treatment with excitotoxins with a method which utilizes radioactive benzoic acid. Studies will also be done with glial cultures from neonatal rat brain and embryonic chick retina. Direct effects of excitotoxins, in the presence and absence of high levels of K+ will be examined, including alterations in C1- uptake and intracellular pH changes. These studies should give positive or negative answers to hypotheses concerning mechanisms underlying excitotoxic sequelae and the role of glia. More importantly, they may give novel directions to studying the interactions of neurons and glia.