Diurnal variation in pilocarpine-induced generalized tonic–clonic seizure activity

The efficacy of the cholinergic agonist pilocarpine to evoke generalized seizures in rats was examined over the 24-h photocycle. Both seizure latency and severity during the 24-h period exhibited marked diurnal variation. Seizure activity generalized more rapidly throughout the dark phase and was often characterized by wild running clonus and tonic extensor convulsions. In contrast, electrographic seizures during the light phase were mainly associated with facial/forelimb clonus and rearing typical of pilocarpine-induced seizures. These data suggest that the sensitivity of the rodent brain to pilocarpine exhibits day–night variation and seizure activity induced during the dark phase may generalize via the brainstem.