Discriminative cues produced by NPY do not generalize to the interoceptive cues produced by food deprivation

Exogenous administration of neuropeptide Y (NPY) into the third ventricle causes a rapid and robust feeding response in sated rats. The current experiment was designed to assess whether the interoceptive cues produced by exogenous NPY administration generalize to those produced by another orexigenic treatment: 24-h food deprivation. Rats were placed in a chamber after receiving either NPY or saline infused into the third ventricle for a total of six sessions (three after NPY and three after saline). Half of the rats were given a brief foot shock after NPY and not after saline, while the other half received the opposite contingency. The pattern of behavioral immobility for the two groups differed with the rats "freezing" significantly more to the treatment (NPY or saline) paired with shock. Then rats were tested for generalization by placing them in the chamber either after 0- or 24-h food deprivation with no NPY or saline administration or any foot shock. Behavioral immobility during the generalization test of rats that had been trained with shock following saline was greater than that for rats that had been trained with shock following NPY, independent of whether testing occurred when the rats were 0- or 24-h food deprived. This outcome indicates that interoceptive stimuli produced by NPY are no more similar to internal cues produced by 24-h food deprivation than to the stimulus consequences of ad lib feeding. These and other recent findings suggest that food deprivation activates processes or mechanisms different from those that underlie the orexigenic effects of NPY.