Quinelorane (LY163502), a D2 dopamine receptor agonist, facilitates seminal emission, but inhibits penile erection in the rat

Dopaminergic compounds have been shown to facilitate male sexual responses in various contexts. We investigated the effects of a specific D2 Dopamine Receptor Agonist, quinelorane (LY163502), on sexual responses elicited in the restrained supine male rat (i.e., ex copula reflex tests). Penile erections, evoked by retraction of the penile sheath, were inhibited by systemic administration of 10 micrograms/kg quinelorane; however, the occurrence of seminal emission was dramatically increased. A smaller dose of 0.25 ng/kg was without effect. In a second experiment, intracranial microinjection of quinelorane was followed by ex copula reflex tests. The medial preoptic area (MPOA) has been previously implicated in the dopaminergic regulation of male copulatory behavior. The effects of an intra-MPOA injection of quinelorane on seminal emission and erectile responses were similar to those observed following systemic administration. These results are consistent with the hypothesis that DA receptors in the MPOA are important in the regulation of male sexual behavior and suggest that D2 receptors in the MPOA may decrease ejaculatory threshold while inhibiting erectile mechanisms.