GLUTAMATE, EXCITOTOXINS AND NEURONAL-GLIAL INTERACTIONS

氨基酸（AA）功能或代谢的畸变

Aberrations of function or metabolism of the putative amino acid (AA) neurotransmitters of glutamate (GLU) and GABA, have been implicated in the etiology or sequelae of several neurological disorders, e.g., Huntington's chorea, Parkinson's disease, epilepsy and certain forms of olivopontocerebellar atrophy. In addition, GLU-analogs, e.g., the excitotoxin kainic acid (KA), when injected directly into rat brain areas, cause neuronal death, raising the intriguing possibility that endogenous excitotoxic activity may be involved in such disorders. Studies have shown that an alteration in energy metabolism and the normal neuronal-glial metabolism of GLU may play a role in this neurotoxicity. Two possible antagonists of KA toxicity, acetazolamide (AZ), (a carbonic anhydrase inhibitor) and Alpha-aminopimelate (AP), a glutamate analogue, will be intensively studied as to the exact mechanism by which they attenuate excitotoxic effects in vitro (e.g., receptor antagonists, metabolic interactions) and whether they interact with other depolarizing agents such as veratridine or K+. Metabolism of GLU, aspartate, glutamine and GABA will be studied in vivo in various brain areas and in vitro in cerebellar and hippocampal slices after treatment with these drugs. Data will be evaluated in terms of neuronal and glial contributions to that metabolism and scrutinized for clues as to how they act. Carbonic anhydrase may be associated with CO2 fixation in glial cells. Therefore, 14C-bicarbonate metabolism into amino acids in the presence of AZ will also be investigated. AZ is especially interesting in that it is a clinically useful anticonvulsant whose mode of action is not well understood. In addition, AZ and AP will be administered to rats in vivo to see if they inhibit or attenuate the excitotoxic action of KA and related compounds injected directly into various brain areas. Studies will also be continued on key enzymes of GLU metabolism in CNS. Using inhibitors, drugs and various tissue preparations, glutamate dehydrogenase (GDH), will be studied as to whether it is involved with neurotransmitter AA pools. In addition, the direction of reaction (i.e., oxidative deamination of glutamate or reductive amination of 2-oxoglutarate) and its rate in situ will be ascertained. It is hoped that the experiments described in this proposal will lead to novel ways of studying normal and diseased states in the CNS.