Determination of the role of serotonergic and cholinergic systems in apomorphine--induced aggressiveness in rats.

Aggressive behavior was produced in rats by administration of apomorphine (APO) 20 mg/kg ip. Serotonin (5-HT) agonists, L-tryptophan or 5-hydroxytryptophan and a MAO inhibitor, pargyline, suppressed the APO-induced aggressiveness. However, cyproheptadine was the only one of four 5-HT antagonists used which potentiated the aggressive behavior. Cyproheptadine, metergoline and PCPA released aggressiveness in rats pretreated with a subthreshold dose of APO. Cholinomimetics (pilocarpine, oxytremorine and physostigmine) completely blocked APO induced aggressiveness while cholinolytics (atropine and scopolamine) partially suppressed the inhibiting effect of pilocarpine on aggressive behavior. The results obtained suggest the existence of an interaction between serotonergic, cholinergic systems and dopaminergic system in apomorphine-induced aggressiveness in rats.