EFFECTS OF PVN LESIONS ON THE RESPONSIVENESS OF FEMALE RATS TO ESTRADIOL

Previous research has shown that the paraventricular nucleus of the hypothalamus (PVN) is an important site of action for the effects of estradiol on feeding behavior6.20. The recent finding that estrogenic stimulation of the PVN lowers food intake without inducing lordosis suggests that the effects of estradiol on feeding and sexual behaviors are organized separately within the brain5. Whether the effects of estradiol on food intake can be attenuated by PVN lesions is therefore a question of practical and theoretical interest. In this experiment we examined the behavioral responsiveness of females with PVN lesions to peripheral treatment with estradiol. 32 adult, female rats received either bilateral or sham lesions of the PVN. All subjects were ovariectomized 2 weeks after the lesion. 2 Weeks following ovariectomy, half of the animals were injected with 2-mu-g of estradiol benzoate (EB) for 3 days, and half were injected with the oil vehicle. 10 days later, the treatment conditions for each subject (oil or EB) were reversed. Histological analysis indicated that 9 females had bilateral lesions of the PVN and 4 had bilateral lesions of the dorsomedial nucleus of the hypothalamus (DMN); 11 animals received sham lesions. Compared with oil treatment, EB injections significantly lowered water intake and body weight gain in all groups. However, food intake was suppressed in the DMN and sham but not in PVN-lesioned females. In addition, statistical analyses indicated that EB treatment induced similar levels of female sexual behavior in all groups. Thus, PVN lesions did not interfere with the ability of estradiol to stimulate lordosis. These findings indicate that the effects of estradiol on food intake, but not body weight or lordosis, are attenuated by bilateral lesions of the PVN. Together with those from studies using PVN implants of estradiol, these results support the hypothesis that the effects of estradiol on feeding and reproductive behaviors are organized separately within the brain. The recent report indicating that estrogen-sensitive PVN neurons project to the brainstem suggests a potential neural pathway involved in hormonal effects on eating. It is hypothesized that estradiol influences feeding behavior by altering the biochemical activity of efferent projections from the PVN to the dorsal vagal complex in the medulla.