Effect of anticonvulsant drugs on thalamo-cortical and hippocampo-cortical self-sustained after-discharges in the rat.

The action of four antiepileptic drugs was studied in acute experiments in 98 rats. Two types of cortical self-sustained afterdischarges ( SSADs ) induced by rhythmic electrical stimulation of subcortical structures were used as models. SSAD formed by the spike-and-wave rhythm (most frequently induced by stimulation of thalamic somatosensory relay nucleus) was almost completely blocked by dipropylacetate (valproate, 400 mg/kg i.p.) and significantly shortened by ethosuximide (125 mg/kg i.p.). Diphenylhydantoin (60 mg/kg i.p.) tended to prolong this type of SSAD whereas carbamazepine did not influence it. SSAD formed by serrated waves (induced usually by stimulation of the dorsal hippocampus) was augmented by ethosuximide, uninfluenced by dipropylacetate and diphenylhydantoin, and significantly shortened by carbamazepine. The pharmacological profile of the two types of SSADs is in agreement with our hypothesis that the spike-and-wave type of SSAD represents a model of primary generalized seizures of the absence type whereas hippocampo -cortical SSAD could be used as a model of partial seizures with complex symptomatology.