Apomorphine-induced aggression in the rat

Spontaneous aggression in male rats was observed following injections of apomorphine, 10-30 mg/kg subcutaneously. The aggressive response could be elicited following smaller doses of apomorphine, 5-10 mg/kg, by pinching the tail 30 min after apomorphine treatment. The occurrence of spontaneous fighting and pain-induced fighting following apomorphine depended upon the age of the animals. Aggression was not observed until animals had attained the age of 49-56 days. Pretreatment with reserpine lowered the threshold for induction of aggressive responses by apomorphine. With reserpine pretreatment, spontaneous aggression was observed following apomorphine in doses of 0.5-2.5 mg/kg subcutaneously. If one assumes that apomorphine is a specific agonist at dopaminergic receptors, then these results suggest that the apomorphine-induced aggressive behaviour as well as the similar mock-fighting behaviour following l-DOPA or dexamphetamine, as reported by other authors, is probably a consequence of enhanced activity at dopaminergic receptors.