Neurohormonal determinants of sex differences in the hypothalamic regulation of feeding behavior and body weight in the rat.

Abstract

Androgens produce a permanent organizational effect on the brain of rats during a postnatal period of sexual differentiation. In male rats, this process occurs as a consequence of the endogenous release of androgens; however, exposing female rats to exogenous androgens during this critical period initiates the same process, such that early exposure to androgens results in a dose-dependent increase in body weight. Sex-specific gonadal hormones further modulate this basic organizational difference in that androgens and estrogens have facilitatory and inhibitory effects, respectively, on the regulation of food intake (FI) and body weight (BWt). While the biochemical or anatomical basis of this sexual dimorphism in energy regulation has not been defined, the data presented here support the idea of a functional sex difference in the hypothalamic regulation of FI and BWt. In general, the same kinds of behavioral tests which differentiate between normal animals and rats with lesions of the ventromedial hypothalamus (VMH) or lateral hypothalamus (LH) also differentiate between male and female rats. Male rats respond to regulatory challenges more similar to VMH lesioned animals than do female rats. In addition, it has been shown that the VMH may be a primary neural site for the organizational effects of androgens on the brain. Based upon these data and the fact that rats show a sex difference in exactly those regulatory behaviors which are presumably controlled by the VMH, a model is proposed to account for sex differences in energy regulation.