Role of aromatase in distinct brain nuclei of the social behavior network in the expression of sexual behavior in male Japanese quail

In male Japanese quail, brain aromatase is crucial for the hormonal activation of sexual behavior, but the sites producing neuro-estrogens critical for these behaviors have not been completely identified. This study examined the function of aromatase expressed in several nuclei of the social behavior network on a measure of sexual motivation known as the frequency of rhythmic cloacal sphincter movements (RCSM) and on copulatory behavior. Sexually experienced castrated males chronically treated with testosterone were stereotaxically implanted with the aromatase inhibitor vorozole (VOR), or cholesterol as control, and tested for sexual behavior. In experiment 1, males were implanted in the medial preoptic nucleus (POM) with VOR, a manipulation known to reduce the expression of copulatory behavior. This experiment served as positive control, but also showed that VOR implanted in the dorsomedial or lateral portions of the POM similarly inhibits male copulatory behavior compared to control implants. In experiments 2 to 4, males received stereotaxic implants of VOR in the periaqueductal gray (PAG), the nucleus taeniae of the amygdala (TnA) and the ventromedial nucleus of the hypothalamus (VMN), respectively. Sexual behavior was affected only in individuals where VOR was implanted in the PAG: these males displayed significantly lower frequencies of cloacal contact movements, the last step of the copulatory sequence. Inhibition of aromatase in the TnA and VMN did not alter copulatory ability. Overall, RCSM frequency remained unaffected by VOR regardless of implantation site. Together, these results suggest that neuro-estrogens produced in the POM contribute the most to the control of male copulatory behavior, while aromatase expressed in the PAG might also participate to premotor aspects of male copulatory behavior.