Apomorphine facilitates male sexual behavior of rhesus monkeys

In the present study, a novel sexual behavior paradigm was used to study the effects of the dopamine agonist, apomorphine, on male sexual behavior of rhesus monkeys. In Experiment 1, the effects of apomorphine treatment were assessed by observing the behavioral responses of male rhesus to a sexually receptive female monkey that they could see, hear, and smell, but could not physically contact. Apomorphine treatment produced a spectrum of behavioral effects that differed depending on the dose of drug administered. Low doses of apomorphine (25-100 micrograms/kg) stimulated yawning, moderate doses (50-200 micrograms/kg) facilitated male sexual responses associated with the genitals including penile erection and masturbation, and high doses (greater than 200 micrograms/kg) elicited stereotypic behavior. Experiment 2 examined whether the behavioral responses of male monkeys to apomorphine treatment were influenced by the stimulus female. Apomorphine treatment facilitated penile erections in tests in which a stimulus female was present, but did not facilitate erections in tests in which she was absent. In sum, these experiments provide preliminary evidence that dopaminergic mechanisms may play a role in the regulation of male sexual behavior of rhesus monkeys.