Neuropeptide Y fails to increase intraoral intake in rats

Neuropeptide Y (NPY) has a potent orexigenic effect when administered either into the third ventricle or directly into hypothalamic nuclei, but the mechanism by which NPY increases intakes is poorly understood. The present study tested the ability of NPY to increase intake of the rat in the intraoral intake test, which focuses on the highly stereotyped consummatory phase of ingestion by introducing a 0.1 M sucrose solution directly into the oral cavity of rats via indwelling intraoral cannulas. Doses of 3, 9.5, and 30 micrograms of NPY, when administered into the third ventricle, all failed to change intraoral intake compared with a saline control. Food deprivation (24 h), however, nearly doubled intraoral intake. Additionally, in separate experiments, 9.5 micrograms of NPY significantly increased both 1-h food intake and 1-h bottle intake of 0.1 M sucrose. These results are consistent with two conclusions. 1) NPY does not affect the consummatory phase of ingestion. 2) NPY administration does not completely mimic the stimulus state associated with food deprivation, since food deprivation but not NPY administration increases intake in the intraoral intake test.