Experimental febrile convulsions in epileptic chickens: the anticonvulsant effect of elevated gamma-aminobutyric acid concentrations.

The high seizure susceptibility in epileptic chickens is due to an autosomal recessive mutation. In 3-day-old chicks homozygous for the epilepsy gene (epileptics), elevation of body temperature using microwave diathermy evoked an initial febrile seizure resembling the clonic seizures evoked in epileptic chicks by photic stimulation. After complete recovery, this was followed by a clonic-tonic seizure. In nonepileptic heterozygote hatchmates (carriers) of the same age, only the latter seizure pattern was observed. In 16- to 17-day-old chicks of either phenotype, both seizure patterns were observed during hyperthermia. In all cases, the temperature at which seizures occurred was significantly lower in epileptic than in nonepileptic chicks, indicating a lower threshold for febrile seizures when there is an inherited predisposition to convulse. The occurrence of seizures was dependent on the body temperature and not on the rate of rise of temperature. Elevation of the brain gamma-aminobutyric acid (GABA) concentrations by administration of the GABA transaminase inhibitor gamma-vinyl GABA reduced the incidence of the initial febrile seizures and increased the latency in those birds that were not fully protected.