The actions of diazepam and phenytoin on a low dose penicillin epileptiform focus in the anaesthetised rat.

1 A technique is described for the induction of an acute short-lived epileptiform focus by the local injection of benzyl penicillin 25 units into the cerebral cortex of rats anaesthetized with urethane. The effects of anticonvulsants on this microfocus have been studied. 2 Phenytoin 20 mg/kg and diazepam 1 mg/kg intravenously significantly reduced the frequency of the normally occurring surface positive electrocorticogram (ECoG) plateaux and caused a greater decrease in the frequency of the epileptiform spikes normally associated with these plateaux. 3 A novel effect was seen in that both anticonvulsant drugs significantly reduced the amplitude of the epileptiform spike within the focus, as well as causing an even larger decrease in the amplitude of the propagated spike. The contribution of the anticonvulsant drug effect on the focal spike to its effect on propagated activity is discussed.