Effects of LY163502, a D2 dopaminergic agonist, on the sexual behavior of male rats.

LY163502, a selective D2 receptor agonist, has been reported to stimulate sexual behavior in both copulating and noncopulating male rats. Three experiments were conducted to further characterize the role of dopamine on male sexual behavior. In the first experiment, quinelorane (LY163502) was directly infused into the medial preoptic area (MPOA) of castrated males either alone or in combination with subphysiological levels of testosterone (T) exposure. The results showed that male sexual behavior was not affected by infusion of LY163502 alone, subphysiological T levels alone, or the combination of LY163502 and subphysiological T levels. For the second experiment, all animals received physiological levels of T and MPOA infusions of LY163502 or saline. The results showed an earlier restoration of male sexual behavior in the LY163502 group when compared to the T-only group. In the third study, noncopulating, gonadally intact males received SC injections of either LY163502 or saline 30 min prior to copulatory testing. The results showed that LY163502 induced a significant decrease in mount and intromission latencies after 14 days of drug exposure. From these results, we conclude a) that D2 receptors play a role in the facilitation of male sexual behavior and b) that the action of dopamine at D2 receptors requires the presence of T.