Effects of a focal penicillin lesion on responses of rabbit cortical neurones to putative neurotransmitters

Abstract

1 Epileptogenic foci were generated in rabbit cerebral cortex by the topical application of penicillin. 2 Responses to iontophoretically applied putative neurotransmitters were compared in cortical neurones firing spontaneously with those driven by applied excitant substances, both before and after establishing the penicillin focus. 3 In the presence of the spiking focus, currents of γ-aminobutyric acid, which normally produced 100% depression of neuronal firing, were ineffective. 4 In the same situation, currents of (±)-homocysteic acid, glutamate and acetylcholine produced predominantly depolarization block responses, and hence depression of firing. 5 It is concluded that an epileptogenic focus can alter the responses of rabbit cortical neurones to microiontophoretically applied neurotransmitter substances. Possible mechanisms for the spread of seizure activity are discussed.