Catecholaminergic influences on induced hippocampal paroxysmal activity in rats.

Brain catecholamines (noradrenaline and dopamine) seem to suppress certain forms of epileptic activity. In this paper we report the catecholaminergic influences on hippocampal paroxysmal activity in rats induced through hippocampal electrical stimulation via stereotaxic electrode placements. The experiments included: (1) systemic injections of clonidine (0.10 mg/kg); phenoxybenzamine (10 mg/kg); propranolol (10 mg/kg); apomorphine (1 mg/kg) and haloperidol (1 mg/kg) and (2) electrolytic lesions of the locus coeruleus ipsilateral to the stimulated hippocampus. The clonidine group showed a great reduction, while animals which received phenoxybenzamine showed a significant increase in the electrographic seizure activity. Propranolol produced only a transient reduction of epileptic activity. We did not observe any significant change in the epileptic discharges following apomorphine and haloperidol injections. Electrolytic lesions of the locus coeruleus induced a clear enhancement of the epileptiform activity. The results presented here support the view that noradrenergic, but not dopaminergic systems, may exert a tonic inhibitor effect on hippocampal epileptic activity.