EPILEPTIFORM ACTIVITY-INDUCED BY 4-AMINOPYRIDINE IN GUINEA-PIG AND RAT NEOCORTICES

Extracellular field recordings were performed in guinea-pig and rat ne ocortical slice preparations maintained in vitro. Bath application of the convulsant drug 4-aminopyridine (4-AP, 100 muM) induced spontaneou s epileptiform potentials in 80% of the guinea-pig neocortical slices and only in 6% of the neocortical slices from rat. In both species spo ntaneous epileptiform activity consisted of a 4-16 s long ictal-like d ischarge that recurred with a frequency range of 0.01-0.02 Hz. In rat neocortical slices stimulus-induced responses resembled the spontaneou s occurring epileptiform events. Ictal-like discharges in guinea-pig n eocortical slices were blocked by the N-methyl-D-aspartate (NMDA) rece ptor antagonist ((+/--2-carboxypiperazine-4-yl)propyl-1-phosphonic aci d (5 muM), while those in the rat desappeared during perfusion with th e non-NMDA excitatory amino acid receptor antagonist 6-cyano-7-nitroqu inoxaline-2,3-dione (1-3 muM). These results indicate that the neocort ex of guinea-pig has a higher propensity to generate 4-AP-induced spon taneous epileptiform activity than that of rat. Furthermore the epilep tiform activity in these two species requires a different involvement of excitatory amino acid receptors.