Differential antiepileptic sensitivity between cortical sites in the rat.

The relative efficacies of phenobarbital (PB), phenytoin (PHT), carbamazepine (CBZ), and valproic acid (VPA) in the suppression of focal and generalized seizures produced by electrical stimulation of two different cortical sites (areas 3 and 10) were evaluated in the rat. The two cortical sites were distinguished by significantly different dose-response curve slopes for the suppression of afterdischarge duration by PHT, CBZ and VPA, which suggests more than one mechanism of action for these drugs. The dose-response curve slopes for PB, on the contrary, were not significantly different, although its potency was significantly greater in area 10. For suppression of generalized convulsions, dose-response curve slopes were not significantly different for any of the drugs. Potencies of PHT, CBZ and VPA were equivalent in the two areas, but PB was significantly more potent in the suppression of generalized convulsions triggered from area 10. It is concluded that focal seizures elicited by the stimulation of different cortical sites are differentially refractory to antiepileptic drugs.