Effects of Antiepileptic Drugs on Absence-Like and Tonic Seizures in the Spontaneously Epileptic Rat, a Double Mutant Rat

Electroencephalographic (EEG) studies were performed to examine the effects of several antiepileptic drugs (AEDS) on absence-like and tonic seizures in the spontaneously epileptic rat (SER: zi(zi), tm/tm,), a double mutant rat, which was obtained by mating the tremor heterozygous animals (tm/ +) with the zitter homozygous animals (zi/zi), and to determine whether the seizures in the SER correspond to human absence and tonic seizures. Spontaneous EEG was continuously recorded from the frontal cortex and hippocampus using implanted electrodes. The SER showed paroxysmal and synchronized 5-7-Hz spike-wave-like complexes in both cortical and hippocampal EEG during the absence-like state, which was characterized by immobility and staring. The animal also exhibited tonic convulsion without external stimulation concomitant with low-voltage fast waves on cortical and hippocampal EEG. In some animals, sporadic low-amplitude spikes appeared in the low-voltage fast waves during tonic convulsion. the absence-like seizures were inhibited by trimethadione (100 mg/kg intraperitoneally, i.p.) and ethosuximide 100 mg/kg i.p.), whereas the tonic convulsion was not affected by these drugs. In contrast, phenytoin (20 mg/kg i.p.) inhibited the tonic seizures without affecting the absence-like seizures. Phenobarbital (10 mg/kg i.p.) and valproate (200 mg/kg i.p.) inhibited both seizures to a similar degree. These results suggest that the SER, with both absence-like and tonic seizures, is a useful model for evaluation of AEDS.