Dissociation of hypothalamic effects on ultrasound production and copulation

Two studies were conducted to compare the brain mechanisms for copulation with those controlling other sexual behaviors, such as the ultrasonic calls that help hamsters and other rodents attract potential mates. Specifically, male and female golden hamsters were castrated and hormone-primed prior to being observed for rates of ultrasound production and levels of sex-typical copulatory behavior (mounts, intromissions and ejaculations in males; lordosis in females). Such tests were conducted before and after subjects received sham operations or bilateral lesions of the preoptic area (POA), anterior hypothalamus (AH) or ventromedial hypothalamus (VMN). The results confirmed previous work in showing the POA lesions decrease rates of intromission, ejaculation and ultrasound production, while VMH lesions decrease lordosis duration. More surprising was the tendency of VMN lesions to increase rates of ultrasonic calling by both males and females. For males, these effects identify differences between the neural circuits controlling copulatory and noncopulatory sexual behaviors. For females, they suggest a mechanism for the behavioral incompatibility of ultrasound production and lordosis. In particular, they raise the possibility that the suspension of ultrasonic calling that normally accompanies lordosis reflects an increase in VMN activity that simultaneously provokes lordosis and inhibits vocalization.