Sexual receptivity increases in synchrony with the ovulatory cycle in female medaka

BACKGROUND: Successful reproduction requires coordinated regulation of gonadal function and sexual behavior. Nonetheless, the mechanisms underlying this coordination in teleosts remain elusive. Here, we aimed to find out the possible involvement of ovulation in the control of female sexual behavior using medaka. METHODS: We analyzed the sexual behavior of medaka with targeted knockouts of genes involved in ovulation. We also examined the actual timing of ovulation and sexual behavior. Furthermore, we investigated the possible contribution of a progesterone derivative through pharmacological treatment and analyzed the localization of the progesterone receptor in the brain using in situ hybridization. RESULTS AND CONCLUSION: Genetically anovulatory female medaka did not show female receptivity, although they were normally courted by males. Consistently, intact females exhibited sexual behavior only after ovulation. Additionally, the administration of progesterone, which is released during ovulation, partially reinstated the sexual receptivity of anovulatory knockout females. Taken together with our result that progesterone receptor is expressed in brain regions that are considered strong candidates for regulation of sexual behavior, we propose that female sexual receptivity is facilitated in synchrony with the ovulatory cycle via progesterone receptor signaling in specific brain regions around the time of ovulation.