The action of ethosuximide, valproate and clonazepam against pentylenetetrazol-induced epileptic EEG phenomena was studied in acute experiments in rats with intercollicular brainstem transection. Ethosuximide lost its action against both rhythmic metrazol activity (model of human absences) and EEG seizures. On the contrary, the action of valproate and clonazepam in cerveau isolé rats was the same as in intact animals. The site of anticonvulsant action of ethosuximide may be localized in hindbrain structures, whereas the actions of both valproate and clonazepam may be demonstrated even if hindbrain structures had been eliminated.
Epileptic afterdischarges induced by electrical stimulation of the sensorimotor cortex as well as minimal metrazol seizures are characterized by EEG spike-and-wave rhythm and nearly the same motor pattern of clonic seizures. The action of ethosuximide on these two models was tested in adult rats with implanted electrodes. Cortical afterdischarges remained practically uninfluenced by ethosuximide (62.5 or 125 mg/kg i.p.) whereas minimal metrazol seizures were suppressed in a dose-dependent manner (doses of 31.25, 62.5 and 125 mg/kg i.p. were used). Present results in connection with recent data on the abolition of spike-and-wave rhythm elicited by low systemic doses of pentylenetetrazol suggest that spike-and-wave rhythm does not represent a single entity.