GONADAL-STEROIDS AND HYPOTHALAMIC GALANIN AND NEUROPEPTIDE-Y - ROLE IN EATING BEHAVIOR AND BODY-WEIGHT CONTROL IN FEMALE RATS

The neuropeptides, galanin (GAL) and neuropeptide Y (NPY), based on st udies in male rodents, are believed to have a role in controlling ener gy balance, both nutrient ingestion and metabolism. Whereas these pept ides are also involved in reproduction, little is known about their sp ecific function in energy balance in females. In rats consuming lab ch ow or macronutrient diets, measurements across the estrous cycle were taken of hypothalamic GAL and NPY, using RIA and immunohistochemistry; of the circulating hormones, estradiol, progesterone, and LH; and als o of food intake and body weight. Levels of GAL and NPY peak during th e proestrous phase of the female cycle when circulating estradiol and progesterone also rise. As previously reported for GAL, this peak is d etected in two areas, the medial preoptic area (MPOA; +110%; P < 0.05) and the external zone of the :median eminence (+ 57%; P < 0.05). In a ddition, this proestrous peak is seen in the paraventricular nucleus ( PVN), specifically the anterior parvocellular portion (+ 35%; P < 0.05 ). Similarly, NPY rises during proestrous in the medial region of the PVN (+21%; P < 0.05) in addition to the MPOA (+78%; P < 0.05) and arcu ate nucleus (+35%; P < 0.05). This peak in peptide levels is accompani ed by an increase in caloric intake in rats receiving the lab chow die t and a specific increase in preference for fat in rats receiving macr onutrient diets. Animals showing a preference for a fat-rich diet exhi bit higher levels of GAL in the MPOA as well as the PVN and median emi nence and also of NPY specifically in the MPOA. These peptides in the MPOA are similarly enhanced in animals with greater body fat, independ ent of diet. This evidence suggests that in the female rat, both GAL a nd NPY in the MPOA may contribute to the overeating and increased weig ht gain that occur during a fat-rich diet.