Effects of unilateral hypothalamic manipulations on the sexual behaviors of rats.

Four experiments that assessed the contributions of each side of the hypothalamus to the control of sexual behavior found the following. (a) Exposing the left, but not the right, ventromedial nucleus to estrogen neonatally defeminized sexual behavior in female rats. This asymmetry did not reverse as sexual differentiation progressed. (b) Unilateral cuts lateral to the medial preoptic area disrupted mounting in females that had mounted regularly before surgery, when given testosterone. The deficits were greater when the cuts were on the left side, but a third of the females with unilateral cuts showed severe deficits regardless of the side. (c) Comparable cuts did not impair masculine sexual behavior in gonadally intact males. In fact, left-side cuts seemed to accelerate copulation in males. (d) Unilateral lesions of the ventromedial nucleus disrupted lordosis in female rats in an essentially all-or-none fashion. This effect did not vary with side.