Central implants of diluted estradiol: independent effects on ingestive and reproductive behaviors of ovariectomized rats

Abstract

The present experiment was undertaken to evaluate the hypothesis that the effects of estrogens on feeding and sexual behaviors are organized separately within the brain. Thirty-three ovariectomized rats were implanted with bilateral guide cannulae aimed at either the paraventricular nucleus (PVN), medial preoptic area (MPOA), or posterior hypothalamus (PH). Subjects that received PVN implants were stimulated with either undiluted estradiol, a 3:1, or 10:1 mixture of cholesterol and estradiol. Animals in the other groups were treated with undiluted estradiol. All females were stimulated unilaterally with cholesterol and estradiol, yielding a total of 66 stimulation sites. Histological analysis revealed that, compared to cholesterol implants, undiluted estradiol in the PVN reduced food intake and body weight. More importantly, diluted estradiol implants in the PVN significantly lowered food intake and body weight. In contrast, undiluted estradiol in the MPOA, PH, or ventromedial hypothalamus (VMH) had no significant effects on feeding or body weight. Analyses of variance revealed significant main effects of implant location on female sexual behavior. Newman-Keuls tests indicated that diluted estradiol implants in the PVN produced lordosis quotients and quality scores that were significantly lower than those obtained with VMH implants. The possibility that the behavioral changes observed were due to peripheral rather than central effects of the hormone was evaluated by comparing the results of implants that produced vaginal cell cornification to those that did not. There were no significant differences between these groups on any of the other dependent variables, indicating that peripheral estradiol sufficient to induce vaginal cell cornification was neither necessary nor sufficient to account for the behavioral changes.(ABSTRACT TRUNCATED AT 250 WORDS)