The overall goal of this research is to determine the mechanisms by which gonadal steroids (estrogens, progestins, and androgens) act to influence energy balance, body weight, and body composition. Gonadal hormones affect nearly every aspect of energy metabolism including energy intake (total caloric intake and dietary self-selection), partitioning of circulating metabolic fuels among various tissues and organs, and energy expenditure (e.g., voluntary exercise and thermogenesis). Gonadal effects on energy balance and body weight are widespread among mammalian species ranging from rodents to primates. One group of experiments will focus on sites and mechanisms of hormone action in rats. Intracerebral hormone implants will be used to determine the neural loci where ovarian and testicular steroids act to affect food intake and energy expenditure. Preliminary data indicate that gonadal steroids may alter energy expenditure via changes in the activity of brown adipose tissue, an important thermogenic tissue. The effects of sex hormones on brown adipose tissue function will be further examined and characterized. Another group of experiments will investigate gonadal effects on behavioral and metabolic controls of body weight in Syrian (Mesocricetus auratus) and Siberian (Phodopus sungorus sungorus) hamsters. These two species of hamsters are of interest, because they are unlike rats in several of their regulatory responses to hormones. The role of gonadal hormones in seasonal body weight changes will be determined in both Syrian and Siberian hamsters. This sort of interdisciplinary approach (taking concepts and techniques from neurobiology, endocrinology, and nutrition) should provide new information about: (a) how gonadal hormones act to influence behaviors, (b) how body weight and composition are determined, and (c) the contribution of gonadal hormones to seasonal changes in body weight and energy metabolism.
