D1 receptors involved in the acquisition of sexual experience in male rats.

As we found previously, changes in ultrasonic vocalizations in the 50-kHz band emitted before a female is introduced into a copulatory chamber (precontact vocalizations-PVs) and shortening of ejaculation latency (EL) in subsequent copulatory sessions are correlated and reflected acquisition of sexual experience in male rats. In the present experiments, we investigate the role of the D1 receptor in this phenomenon. First, the effects of a D1 antagonist and D1 agonists injected subcutaneously during the first sexual contacts were analyzed. The antagonist (SCH-23390) inhibited changes in PVs and EL as well as rearing (R) and mount latency (ML). Both agonists (SKF-38393 and selective SKF-82957) inhibited PVs also at doses where no effects on EL and ML were observed. Repeated injections of five agonists, with or without socio-sexual contacts, had an effect on later PVs and R (long-term effect) but not on copulatory performance during the subsequent four sessions. In the last experiment, a D1 agonist (SKF-82957, 0.5 microg) was injected bilaterally into nucleus accumbens (N.Acc) before each of the first five sessions. The D1 agonist in N.Acc facilitated initiation of copulation in treatment-naïve rats. Repeated administration of the D1 agonist into the brain had long-lasting effects on PVs, R and ML, probably as a result of long-term changes in neuronal structures involved in acquisition of sexual experience, in this part of the nucleus accumbens. Repeated D1 agonist administration probably inhibits/reverses sensitization processes in dopamine structures. The results indicate a role of D1 receptors in acquisition of socio-sexual experience and suggest independent neuronal pathways for changes in PVs and EL.