Anticonvulsants in epileptic fowl.

The high seizure susceptibility in epileptic fowl is an autosomal recessive trait characterized in homozygotes by seizures that occur spontaneously and in response to photic stimulation or hyperthermia. Both of the latter stimuli can be used to evoke seizures in drug studies. Epileptic fowl have abnormal inter-ictal EEG activity. When exposed to photic stimulation spiking is apparent on the EEG at seizure onset. Phenobarbital, primidone, phenytoin, and valproic acid reduce seizure susceptibility at plasma concentrations approximating those used to control generalized and focal cortical tonic-clonic seizures in humans. Carbamazepine and the benzodiazepines also reduce seizure susceptibility. These data indicate that epileptic fowl provide a useful model for generalized and focal cortical tonic-clonic epilepsies. Ethosuximide was inactive in epileptic fowl. However, trimethadione had anticonvulsant activity indicating that this model is only relatively specific for the above seizure types. When seizures were evoked by hyperthermia phenobarbital but not phenytoin or valproate reduced seizure susceptibility. GABA (gamma-aminobutyric acid), AOAA (amino-oxyacetic acid) and THPO (4,5,6,7-tetrahydroisoxazolo[4,5-c] pyridin-3-ole, a glial specific inhibitor of GABA uptake) all have anticonvulsant activity against seizures evoked by photic stimulation in young chicks. These data indicate that this model may be particularly useful for studies of the anticonvulsant activity of compounds designed to enhance GABAergic transmission.