Effect of cocaine on sexual behaviour in male stumptail macaques (Macaca arctoides)

The effect of cocaine (0.01-1.0 mg/kg) on sexual behaviour was studied in four male stumptail macaques (Macaca arctoides). Following drug-saline control administration, the behaviour of the male monkey with a female was observed for 30 min in two different behavioural conditions; in one of the conditions the baseline sexual activity was low, and in the other it was high (partial or complete separation of the male and the female between the sessions, respectively). The reversal of the cocaine-induced effects was attempted by haloperidol (0.003-0.01 mg/kg), a dopamine-2-receptor antagonist. Cocaine (0.1-1.0 mg/kg) produced a highly significant dose-dependent suppression in the number of ejaculations. The cocaine-induced suppression of ejaculatory behaviour was completely reversed by haloperidol. Haloperidol at the dose range used did not in itself influence ejaculatory behaviour. The effect of cocaine on grooming, nonejaculatory mounting, aggression, or perineal investigations did not reach statistical significance. The possibility that cocaine at very low doses (0.01-0.1 mg/kg) might increase sexual activity was excluded in the behavioural condition with a low basal sexual activity. The results indicate that cocaine dose-dependently suppresses ejaculatory behaviour as a result of dopamine-2-receptor-mediated mechanisms. The cocaine-induced suppression of ejaculatory behaviour might be explained by the strong rewarding effect of cocaine alone.