Plasma prolactin concentrations and copulatory behavior after salsolinol injection in male rats

Abstract

Purpose: The dopamine-derived endogenous compound, R-salsolinol (SAL), was recently identified as a putative endogenous prolactin (PRL)-releasing factor. However, how SAL influences copulatory behavior is unknown. In this study, we examined the relationship between SAL and copulatory behavior in male rats. Methods: Male Sprague-Dawley rats administered SAL were exposed to female rats in estrus, the plasma PRL concentration was measured, and the behavioral frequency and time during copulatory behavior were noted. Results: In the control and SAL groups, plasma PRL concentrations at 15 min before exposure to the female were 7.3 ± 2.0 and 8.0 ± 1.5 ng/ml, respectively. Moreover, plasma PRL concentrations in males immediately after exposure to the female were 7.4 ± 1.2 and 68.0 ± 5.9 ng/ml, respectively (P < 0.05). All (8/8) of the control animals ejaculated in the presence of the female, whereas only 33% (2/6) of the SAL group ejaculated. An increasing tendency for mount latency and intromission latency and a decreasing tendency for intromission frequency were observed in the SAL group. Conclusions: Copulatory behavior was inhibited in male rats after SAL injection, suggesting that SAL is a copulatory behavior inhibiting factor. © 2010 Japan Society for Reproductive Medicine.