Cholinergic and adrenergic agents modify the initiation and termination of epileptic discharges in the dentate gyrus.

A unique type of limbic seizures, maximal dentate activation, was used to examine the effects of cholinergic and adrenergic agents on the processes involved in epileptogenesis. The time to onset of maximal dentate activation was used to monitor the initiation of seizures while the duration of maximal dentate activation monitored termination of seizures. The cholinergic agonist pilocarpine shortened maximal dentate activation at 20 mg/kg and lengthened maximal dentate activation at 50 mg/kg, while both doses delayed the onset of maximal dentate activation. Atropine, a cholinergic antagonist, at 50 mg/kg, slowed the rate of lengthening of maximal dentate activation that occurred with repeated stimulation. The beta-adrenergic antagonist propranolol also slowed the rate of lengthening of maximal dentate activation at 3 mg/kg and shortened maximal dentate activation at 10 mg/kg. The alpha 2-agonist clonidine, at 0.5 mg/kg, shortened maximal dentate activation and increased the time to onset; at 0.1 mg/kg, clonidine did not affect maximal dentate activation. Pretreatment with reserpine had no effect on either the time to onset or duration of maximal dentate activation. These results indicate that both cholinergic and adrenergic mechanisms play important roles in the initiation and termination of limbic seizures.