ASCORBATE AND GLUTAMATE RELEASE IN THE RAT HIPPOCAMPUS AFTER PERFORANT PATH STIMULATION - A DIALYSIS ELECTRODE STUDY

Excitatory amino acids have been proposed to play a critical role in t he development and maintenance of epileptic seizures and in the develo pment of neuronal damage, Previous animal studies of glutamate during seizures, however, have often failed to measure any rise in glutamate. We have overcome many of the problems of these studies by using an an imal model in which epileptic afterdischarges are induced by stimulati on of the perforant path, and glutamate and ascorbate are measured usi ng a newly developed microdialysis electrode that combines the advanta ges of microdialysis and in vivo electrochemistry. We have successfull y shown (1) a rise in glutamate after an epileptic afterdischarge, (2) a concomitant initial fall and then a later rise in ascorbate, and (3 ) progressive dwindling of this effect when afterdischarges are repeat ed within minutes, despite similar electroencephalographic responses. The possible mechanisms of these effects are discussed and include asc orbate/glutamate heteroexchange, reversal of the glutamate uptake mech anism, and augmentation of glutamate uptake after a seizure.