Presence of a neural mechanism for the expression of female sexual behaviors in the male rat brain.

Facilitatory and inhibitory neural mechanisms involved in the expression of female sexual behaviors in male rats were examined with a dual operation technique. Male rats were castrated and the preoptic area was dorsally deafferented (anterior roof deafferentation, ARD) in order to remove the forebrain lordosis-inhibitory system. Male rats with ARD displayed not only lordosis but also soliciting behaviors in response to 2 micrograms estradiol benzoate (EB) and 0.5 mg progesterone (P). The ARD male rat then received a second operation involving the hypothalamus or lower brain stem, i.e., the ventromedial nucleus and the adjacent area (ventromedial hypothalamus, VMH) were damaged by a radiofrequency lesion generator; the hypothalamus de-efferented anterolaterally by means of a Halász knife cut posterior to the suprachiasmatic nucleus (ADC) or lesions of the pontine periventricular gray and the adjacent area (dorsomedial tegmental lesion, DMTL). The DMTL effectively suppressed lordosis in EB-P-primed male rats with ARD. Only 1 of 14 ARD-DMTL males showed lordosis. In contrast, the VMH lesions or the ADC failed to interfere with the facilitatory effect of ARD on female sexual behaviors in male rats tested with the same dose of EB-P. Thus, the pontine periventricular gray plays a critical role for lordosis regulation in males. These results suggest that the male rat brain possesses the minimal neural mechanism for the expression of female sexual behaviors associated with the development of the strong forebrain lordosis-inhibiting system.