CHANGES IN NEUROPEPTIDE-Y IMMUNOREACTIVITY IN THE ARCUATE NUCLEUS DURING AND AFTER FOOD RESTRICTION IN LACTATING RATS

Previous studies have demonstrated that food restriction during lactat ion extends the length of lactational infertility in rats. In order to determine whether Neuropeptide Y (NPY) plays a role in the increased length of lactational infertility seen in food-restricted rats, NPY im munoreactivity in the arcuate nucleus of lactating rats that were ad l ib fed or food restricted from Day 8 to 14 postpartum was compared. Fo od-restricted rats showed higher numbers of NPY-stained cells at the e nd of the food-restriction period (Day 15 postpartum) than did ad lib- fed rats at the same stage of lactation. This difference persisted unt il Day 25 postpartum although all animals were fed ad libitum from Day 15 onwards. Switching litters between ad lib-fed and food-restricted females from Day 15 until Day 20 postpartum did not eliminate the diff erence in NPY immunoreactivity between the two diet conditions. Given that food restriction during lactation leads to a prolonged suppressio n of LH release that also persists after refeeding and is not affected by the nutritional status of the litter, these data are consistent wi th a role for NPY in the prolonged suppression of reproductive functio n seen in food restricted lactating rats.