Microstructural analysis of licking behavior following peripheral administration of bombesin or gastrin-releasing peptide.

To determine the effects of bombesin (BN) and gastrin-releasing peptide [GRP(1-27)] on food intake and the microstructure of licking, the rate and pattern of licking were measured by lickometer after intraperitoneal administration of 2, 4, 8, and 16 micrograms/kg of each peptide. Although both peptides inhibited intake significantly, the dose-response functions of the peptides were different. At lower doses (2-4 micrograms/kg) the peptides were equipotent; at higher doses (8-16 micrograms/kg) BN was significantly more potent than GRP(1-27), possibly due to an action of BN on neuromedin B (NMB) receptors. The microstructural results demonstrated that both peptides decreased intake by increasing the rate of decay of licking and decreasing the number of bursts and clusters without changing the initial rate of licking or the size of the bursts and clusters. This combination of microstructural changes is evidence that both peptides increased the postingestive negative feedback effects of the diet without changing the orosensory positive feedback. These results are consistent with, but do not prove, the hypothesis that endogenous GRP(1-27) acts as a postingestive satiety signal in rats.