Neural Gonadal Steroid Receptors and Actions: Chemical Anatomy of the Ventromedial Hypothalamus in Relation to Sexual Differentiation and Sexual Behavior

Summary

Steroid hormones act upon the brain to reversibly alter structure and function of adult neural tissue and to influence behavior. They also act irreversibly during development to alter the structure and function of the neural substrate upon which these same hormones act reversibly in adult life. These principles are illustrated by feminine mating behavior in the rat, which is governed by estradiol (E) and progesterone (P) action on a small number of neurons within the ventromedial hypothalamic nuclei (VMN) of female rats. Males do not usually show feminine mating behavior, even after priming with E+P, unless they are castrated perinatally; and females given testosterone perinatally become refractory to E+P activation of feminine mating behavior in adulthood. The VMN displays two neurochemical features related to feminine mating behavior, namely, E induction of receptors for P and of receptors for the neuropeptide, oxytocin, and these are the subject of this article. Oxytocin receptors and oxytocin immunoreactivity are significantly induced by E priming prior to P exposure, and P treatment after E priming causes the oxytocin receptors to spread into the zone occupied by oxytocin immunoreactivity. These effects appear to be significant bécause oxytocin is able to increase feminine mating behavior in rats primed with E+P. Progestin receptor induction is higher in female VMN than in male VMN, whereas oxytocin receptor is the same in males and females. This finding is discussed in terms of other evidence regarding sex differences in the VMN.