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 lactation 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 immunoreactivity in the arcuate nucleus of lactating rats that were ad lib fed or food restricted from Day 8 to 14 postpartum was compared. Food-restricted rats showed higher numbers of NPY-stained cells at the end of the food-restriction period (Day 15 postpartum) than did ad lib-fed rats at the same stage of lactation. This difference persisted until 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 difference in NPY immunoreactivity between the two diet conditions. Given that food restriction during lactation leads to a prolonged suppression of LH release that also persists after refeeding and is not affected by the nutritional status of the litter, these data are consistent with a role for NPY in the prolonged suppression of reproductive function seen in food restricted lactating rats.