Hormonal and social modulation of cloacal muscle activity in female Japanese quail

Japanese quail are an important model for the discovery of neuroendocrine mechanisms of sexual behavior. In common with most birds and many other vertebrates, there are no genitalia of the mammalian kind (no phallus or vagina). Instead, close contact between the cloacal openings of the male and female is critical for successful mating. Prior research has shown that males produce distinctive rhythmic movements of the foam gland portion of the cloacal sphincter muscle (RCSMs) in response to social stimuli (presentation of a conspecific female or male). These RCSMs enhance the male's fertilization success. Females, unlike males, do not show cloacal sphincter movements to social stimuli (Experiment 1) and female cloacal sphincter muscle activity immediately following copulation does not predict fertilization success (Experiment 2). Females implanted with testosterone propionate (TP), however, show large numbers of male-typical RCSMs in response to social stimuli (Experiment 3). The results of Experiment 3 show that rhythmic movements of the cloacal sphincter muscle shown by TP-treated females are regulated by distal (visual) stimuli and therefore by the brain. They also show that the absence of socially modulated RCSMs in normal females is an activational hormone phenomenon (a sex difference produced by adult hormonal dimorphism), rather than a reflection of prior hormonal organization. These results add to an understanding of the hormonal basis of sex differences in motor mechanisms of sexual behavior in non-mammalian species.