Dopamine modulates male sexual behavior in Japanese quail in part via actions on noradrenergic receptors

In rats, dopamine (DA) facilitates male sexual behavior through its combined action on D1- and D2-like receptors, in the medial preoptic area (MPOA) as well as other brain areas. In Japanese quail, systemic injections of dopaminergic drugs suggested a similar pharmacology but central injections have never been performed. Recent electrophysiological experiments demonstrated that DA effects in the MPOA of quail are mediated mainly through the activation of α2-noradrenergic receptors. Previous studies of DA action on behavior used specific dopaminergic agonists/antagonists and therefore unintentionally avoided the potential cross-reaction with α2-receptors. The present study was thus designed to investigate directly the effects of DA on male sexual behavior and to test whether the interaction of DA with heterologous receptors affects this behavior. Intracerebroventricular (i.c.v.) injection of DA or NE inhibited copulation in a dose-dependent manner. Systemic injections of yohimbine, an α2-noradrenergic antagonist, modulated copulation in a bimodal manner depending on the dose injected. Interestingly, a behaviorally ineffective dose of yohimbine markedly reduced the inhibitory effects of DA when injected 15 min before. Together, these results show for the first time that i.c.v. injections of DA itself inhibit male sexual behavior in quail and suggest that the interaction of DA with α2-receptors has behavioral significance.