Ventral tegmental lesions impair sexual receptivity in female hamsters

The ventral mesencephalon appears to be one of the sites of progesterone action in the control of sexual receptivity in female hamsters. The behavioral response to systemic progesterone was assessed in female hamsters following electrolytic lesions of portions of the ventral mesencephalon. Adult female hamsters were ovariectomized and pretested for sexual receptivity, then were given bilateral lesions aimed at the region of the ventral mesencephalon where progesterone implants have been shown to facilitate receptivity. Lesions were produced by stereotaxically lowering an electrode and applying anodal direct current of 1-2 mA for 5-20 seconds. One week later the hamsters were injected with estrogen followed 44 h later by progesterone. They were then tested for sexual receptivity. After this test, their brains were removed and histologically prepared. Lesion location was determined and lesion size was quantified with a digitizing pad. Lesions which were centered in and destroyed much of the ventral tegmental area produced the greatest lordosis impairments. Mesencephalic lesions which did not bilaterally damage the ventral tegmental area had little effect. These results support the hypothesis that the ventral mesencephalon, particularly the ventral tegmental area, is an important site for the facilitative action of progesterone on sexual receptivity in estrogen-primed female hamsters.