Food deprivation increases the expression of neuropeptide Y (NPY) in the arcuate nucleus of adult rats and refeeding reverses the increased expression. The NPY response to deprivation occurs as early as postnatal (P) day 2 (Kowalski et al., Am J. Physiol, 1998) and preliminary results showed that this could be reversed by intragastric nutrient infusions on P12 (Kowalski et al., SFN, 1998). To investigate whether nutrient infusions would reverse the NPY response on P2 and whether the nutrients or the water in the infusions was sufficient for the reversal, three groups (n=4-12) of lean Zucker rats (+/+ and +/fa) were removed from the dam for 24 hours on P1, had gastric catheters implanted for infusions, and were housed individually. One group was not infused; the second group received continuous intragastric infusion of milk; the third group received an equivolumetric intragastric infusion of water. A fourth group was not deprived and had free access to the dam for 24h. At the end of the 24h, all pups were p...