NPY increases food intake in white-crowned sparrows: effect in short and long photoperiods.

To determine if altered sensitivity to neuropeptide Y (NPY) underlies premigratory fattening, white-crowned sparrows held on short day length (9:15-h light-dark) received injections into the third ventricle (ivt) of saline or several doses of NPY. An inverted-U function occurred with food intake increasing 30 and 60 min after doses of 1.0 and 2.0 micrograms NPY. When photostimulated (20:4-h light-dark), birds increased daily caloric intake and gained weight rapidly. Birds maintained on long day lengths significantly increased food intake after 0.25 and 0.5 micrograms of NPY and did not respond to higher doses. The effective dose range for NPY to increase food intake moved to the left, suggesting an increase in sensitivity to the peptide on long day lengths. In summary, white-crowned sparrows consume more food when administered NPY ivt and have increased sensitivity when photostimulated and gaining weight. Hence NPY may be a natural stimulator of food intake in this species.