Cuts between the septum and preoptic area increase ultrasound production, lordosis, and body weight in female hamsters.

Studies of the mechanisms for female-typical mating behavior have focused on the ventromedial hypothalamus, and on the decrements in lordosis caused by lesions of this structure. However, opposed changes of comparable size are produced, at least in rats, by horizontal cuts extending forward from the anterior commissure (anterior roof deafferentation, or ARD). This suggests the existence of a lordosis-inhibiting system of forebrain structures that may include the lateral septum and preoptic area. To test the generality of this system, ovariectomized hamsters in hormone-induced estrus were observed for levels of ultrasound production and lordosis during tests with male conspecifics. In addition, subjects were observed for lordosis responses to light manual stimulation. Upon the completion of these tests, subjects received control treatments or ARD prior to a second round of behavioral observations. These postoperative tests revealed clear ARD-stimulated increases in ultrasound production and body weight. In contrast, the facilitation of lordosis was more subtle, appearing in tests with manual stimulation, but not in response to males. These results, then, demonstrate some consistency across species in the effects of ARD. At the same time, however, they suggest species differences in the magnitude of these effects, in turn, suggesting species differences in the dependence of receptivity on forebrain lordosis-inhibiting mechanisms.