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 focu sed on the ventromedial hypothalamus, and on the decrements in lordosi s caused by lesions of this structure. However, opposed changes of com parable size are produced, at least in rats, by horizontal cuts extend ing forward from the anterior commissure (anterior roof deafferentatio n, or ARD). This suggests the existence of a lordosis-inhibiting syste m of forebrain structures that may include the lateral septum and preo ptic area. To test the generality of this system, ovariectomized hamst ers in hormone-induced estrus were observed for levels of ultrasound p roduction and lordosis during tests with male conspecifics. In additio n, subjects were observed for lordosis responses to light manual stimu lation. 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 u ltrasound 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 c onsistency across species in the effects of ARD. At the same time, how ever, they suggest species differences in the magnitude of these effec ts, in turn, suggesting species differences in the dependence of recep tivity on forebrain lordosis-inhibiting mechanisms.