Rapid effects of aromatase inhibition on male reproductive behaviors in Japanese quail

Abstract

Non-genomic effects of steroid hormones on cell physiology have been reported in the brain. However, relatively little is known about the behavioral significance of these actions. Male sexual behavior is activated by testosterone partly through its conversion to estradiol via the enzyme aromatase in the preoptic area (POA). Brain aromatase activity (AA) changes rapidly which might in turn be important for the rapid regulation of behavior. Here, acute effects of Vorozole™, an aromatase inhibitor, injected IP at different doses and times before testing (between 15 and 60 min), were assessed on male sexual behavior in quail. To limit the risk of committing both types of statistical errors (I and II), data of all experiments were entered into a meta-analysis. Vorozole™ significantly inhibited mount attempts ( P < 0.05, size effect [ g] = 0.527) and increased the latency to first copulation ( P < 0.05, g = 0.251). The treatment had no effect on the other measures of copulatory behavior. Vorozole™ also inhibited appetitive sexual behavior measured by the social proximity response ( P < 0.05, g = 0.534) or rhythmic cloacal sphincter movements ( P < 0.001, g = 0.408). Behavioral inhibitions always reached a maximum at 30 min. Another aromatase inhibitor, androstatrienedione, induced a similar rapid inhibition of sphincter movements. Radioenzyme assays demonstrated that within 30 min Vorozole™ had reached the POA and completely blocked AA measured in homogenates. When added to the extracellular milieu, Vorozole™ also blocked within 5 min the AA in POA explants maintained in vitro. Together, these data demonstrate that aromatase inhibition rapidly decreases both consummatory and appetitive aspects of male sexual behavior.