Interoceptive signals and postingestive consequences produced by regulatory peptides.

Abstract

Regulatory peptides may influence food intake via a variety of mechanisms. For instance, such peptides may produce interoceptive stimulus consequences similar to “hunger” or “satiety”. They may also alter the rewarding after-affects of eating. We examined the first possibility by training rats to use internal cues produced by either 24 h or 1 h food deprivation as discriminative stimuli. After training was completed, we tested the rats for generalization between deprivation-induced cues and cues produced by ghrelin (i3vt and ip), leptin (i3vt and ip), and CCK (ip), respectively. We found that ghrelin (both i3vt and ip) produced cues similar to 24 h food deprivation, whereas leptin (ip, but not i3vt) and CCK produced cues that generalized to 1 h food deprivation. Previous research showed that rats must consume food when food deprived to learn that deprivation enhances the reward value of food; similarly food must be consumed when sated for rats to learn that the value of food reward has been reduced. We examined the extent to which administration of (a) ghrelin in sated rats and (b) leptin in food deprived rats had effects on food reward value like those produced by eating under respective food deprivation and satiation. We found that ghrelin had effects like food deprivation and leptin had effects like food satiation on the rewarding consequences of eating. Collectively, these studies indicate that peptides involved with intake regulation may produce interoceptive cues and postingestive consequences similar to those produced by food-deprivation manipulations.