Sagittal knife cuts in the far-lateral hypothalamus reduce sexual receptivity in female hamsters

Abstract

We have previously shown that hypothalamic knife cuts confined to the sagittal plane lateral to the medial anterior hypothalamus-ventromedial nucleus can disrupt sexual receptivity in female golden hamsters. In the present study we have compared the effects of varying the lateral position of sagittal cuts located at this same rostral-caudal level. Near-lateral (NL) cuts were placed at or just lateral to the fornix, while far-lateral (FL) cuts were placed at the lateral edge of the medial forebrain bundle. Ovariectomized, estradiol benzoate plus progesterone-treated females were given weekly tests for lodosis before and after hypothalamic cuts. Changes in body weight and agonistic behavior were also recorded. Both NL and FL cuts reduced lordosis in response to both manual stimulation and a sexually active male. Postoperatively, it was more difficult to elicit lordosis from these females, and if elicited, the duration of the response was reduced. NL, but not FL, cuts also increased agonistic behavior, and produced obesity. Since both NL and FL cuts severed axons traveling in the region of the supraoptic commissures (SOC), these data support our hypothesis that these SOC connections are critical for sexual receptivity. The SOC carry both efferents and afferents of the ventromedial hypothalamus. Sagittal-plane cuts which interrupt the SOC may disrupt lordosis by cutting either or both types of connection.