Progesterone effects on sexual behavior and neuronal ultrastructure in female rats

Treatment of female rats with a low dose of estradiol (5% estradiol in a 5 mm Silastic capsule) and progesterone (0.5 mg) increased the percentage of neurons in the ventromedial nucleus of the hypothalamus that contained stacks of rough endoplasmic reticulum, as compared with female rats receiving either estradiol alone or no treatment. Only females treated with both estradiol and progesterone displayed any sexual behavior, with these females responding at maximal levels. These results support the relationship between stacking of rough endoplasmic reticulum in ventromedial hypothalamic neurons and levels of sexual behavior in female rats, and provide evidence that progesterone can produce rapid changes in the morphology of hypothalamic neurons in estrogen-treated animals.