Effects of anticonvulsants on penicillin-induced bursting in guinea pig hippocampal slices.

The effects of gamma-aminobutyric acid (GABA) and six anticonvulsants on penicillin-induced bursting were compared in guinea pig hippocampal slices. GABA, phenobarbital, pentobarbital, phenytoin, and diazepam slowed and eventually blocked spontaneous bursts. Low-intensity stimulation at concentrations that blocked spontaneous activity still evoked synchronous all-or-none burst responses, although the threshold increased and the bursts were briefer. Sodium valproate had similar effects, but very high concentrations (approximately 10 mM) were required. Ethosuximide paradoxically increased spontaneous burst rate. This model appears to be differentially susceptible to the actions of GABA and the anticonvulsants commonly used to treat tonic-clonic and partial seizures but not to the antiabsence drugs.