Infusion of endomorphin-1 (EM-1) in the MPOA and the Me modulate sexual and socio-sexual behavior in the male rat

Abstract

Several neurotransmitters, among them neuropeptides, have been implicated in the control of male sexual behavior. Opioids are involved in mediating the positive affective states generated by the execution of sexual behavior in both males and females. We have previously shown that intracerebroventricular administration of endomorphin-1 (EM-1), the specific ligand for the μ opioid receptor, increased the ejaculation latency and interintromission interval and reduced the number of ejaculations during the test. In the present study we evaluated the effect of EM-1 upon male sexual behavior and socio-sexual interactions when infused in the medial preoptic area (MPOA) or the medial amygdala (Me). The results indicate that the administration of EM-1 in the MPOA increased mount and intromission latencies while infusion in the Me increased the number of mounts before ejaculation as well as the ejaculation latency. With respect to socio-sexual interactions, the duration of pursuit was significantly increased after administration of EM-1 in the MPOA. The effects upon sexual behavior and socio-sexual interactions were blocked by administration of the opioid antagonist naloxone. These results indicate that EM-1 modulates the appetitive aspect of sexual behavior in the MPOA and the consummatory phase in the Me.