Acceleration of mounting behaviors in female rats by ibotenic acid lesions in the ventromedial hypothalamic nucleus.

To clarify the role of the ventromedial (VMH) or dorsomedial (DMH) hypothalamic nucleus in regulating male sexual behavior in female rats, radiofrequency or ibotenic acid lesions were made in ovariectomized rats, and three behavioral tests in total were carried out after implantation of Silastic tubes containing testosterone. As a result, females with radiofrequency or ibotenic acid lesions in the VMH showed higher levels of mounting behavior than those in females with no brain surgery or with sham-operation. The incidence of intromissive pattern in females with ibotenic acid lesions but not in females with radiofrequency lesions was higher than those in other female control groups. In the group of radiofrequency lesions in the DMH, both frequencies of mounting and intromissive pattern were lower than those in control and sham groups. No ejaculatory pattern was seen in any of the female groups. These results indicate that neuronal cell bodies in the VMH, but not in the DMH, exert an inhibitory influence on mounting activity in female rats.