Dopaminergic influences on male sexual behavior of rhesus monkeys: effects of dopamine agonists.

Previous research has demonstrated that the mixed D1/D2 dopamine receptor agonist, apomorphine, and the specific D2 dopamine receptor agonist, quinelorane, facilitated penile erections and masturbatory behavior of male rhesus monkeys when they were tested in the presence of a female monkey that they could see, hear, and smell but not physically contact. The present study was designed to further examine dopaminergic influences on male sexual behavior of rhesus monkeys by evaluating male copulatory behavior following administration of these dopaminergic agents, as well as a D1 agonist, CY 208-243. Apomorphine and quinelorane treatment produced dose-dependent effects on male sexual responding. Compared to vehicle-based performance, postejaculatory intervals were shortened following treatment with either 100-200 micrograms/kg apomorphine or 2.5-10 micrograms/kg quinelorane. Higher doses of apomorphine or quinelorane did not reliably influence the postejaculatory interval. Ejaculation latency, intromission frequency, and number of thrusts/intromission increased following administration of 200-400 micrograms/kg apomorphine and 25 micrograms/kg quinelorane, indicating that dopaminergic stimulation in this dose range raised the monkeys' ejaculatory threshold. No behavioral effects of the D1 agonist, CY 208-243, were observed in this testing situation. These experiments provide further evidence that dopaminergic mechanisms may play a role in the regulation of male sexual behavior of rhesus monkeys and, in particular, demonstrate that the direction of the effect depends on the dopamine receptor subtype and dosage of the dopamine agonist being administered.