Changes in extracellular amino acids during soman- and kainic acid-induced seizures.

Extracellular amino acid levels in the rat piriform cortex, an area highly susceptible to seizure-induced neuropathology, were determined by means of intracranial microdialysis. Seizures were induced by systemic administration of either soman (O-1,2,2-trimethylpropyl methylphosphonofluoridate), a potent inhibitor of acetylcholinesterase, or the excitotoxin kainic acid. Extracellular glutamate levels increased in animals with seizures shortly after administration of either convulsant, but this change was statistically significant only in the case of soman-treated animals. Extracellular taurine levels increased markedly, reaching two- and fourfold baseline levels during the second hour of soman- and kainic acid-induced seizures, respectively. Taurine levels did not increase in the subpopulation of soman-treated animals without seizures, a finding indicating that elevation of extracellular taurine level is seizure related. Thus, we propose that taurine efflux may be a physiological cellular response to neuronal changes produced by excitotoxic chemicals, either directly or as a consequence of seizures.