D2 receptors in the paraventricular nucleus regulate genital responses and copulation in male rats

Abstract

The D2 dopamine receptor agonist quinelorane (LY-163502), microinjected into the paraventricular nucleus (PVN), affected genital responses of restrained supine male rats in a biphasic dose-dependent fashion. A moderate dose (1 μg) facilitated penile responses (intense erections and penile movements), and decreased the latency to the first response. A high dose of quinelorane (10 μg) facilitated seminal emission while inhibiting penile responses. The addition of the D1 antagonist SCH-23390 to the 1 μg dose of quinelorane potentiated quinelorane's increase in seminal emission. We suggest that D1 receptors in the PVN may be antagonistic to D2 receptor-mediated seminal emission, and possibly also penile responses. In copulation tests 1 μg quinelorane decreased mount latency, whereas 10 μg quinelorane increased mount and intromission latencies and slowed copulatory rate. Both 1 and 10 μg quinelorane, and also 1 and 10 μg of the mixed D1 and D2 agonist apomorphine, decreased the number of intromissions preceding ejaculation.