INVOLVEMENT OF DOPAMINE D-2 RECEPTORS IN THE EFFECT OF COCAINE ON SEXUAL-BEHAVIOR AND STRETCHING-YAWNING OF MALE-RATS

The effect of cocaine (7.5, 15 and 30 mg/kg) administered in acute or subchronic mode, on the mating behaviour of sexually active male rats varied in a dose- and mode-dependent manner. Regardless of mode of tre atment, 30 mg/kg markedly impaired the rats' copulatory ability and im pairment continued for a week after suspension of subchronic treatment . An acute dose of 15 mg/kg reduced intromission frequency, while in s ubchronic mode it also reduced ejaculation latency. Mount frequency wa s increased by 7.5 and 15 mg/kg, but only on first injection. In the c ase of sexually-naive male rats, acute administration of cocaine (3-30 mg/kg) stimulated penile erections at 7.5 mg/kg and motor hyperactivi ty at all doses. (-) Eticlopride (0.025 and 0.05 mg/kg), a DA D-2 anta gonist, counteracted cocaine-induced motor hyperactivity but not penil e erection, which it enhanced. (-)Eticlopride at the same doses also a ntagonized cocaine potentiation of lisuride (0.2 mg/kg)-induced behavi oural effects. When male rats treated with subchronic cocaine (15 mg/k g) were injected with the DA D-2 agonist SND 919 (0.1 mg/kg), they dis played a more marked stretching-yawning behaviour than control animals receiving SND 919 at the same dose. The involvement of DA D-2 recepto rs in cocaine-induced effects is suggested. (C) 1997 Elsevier Science Ltd.