NPY-leptin: opposing effects on appetitive and consummatory ingestive behavior and sexual behavior

Many studies have indicated that neuropeptide Y (NPY) stimulates and leptin inhibits food intake. In line with this, intracerebroventricular injection of NPY (10 mu g) stimulated and leptin (10 mu g) inhibited intake of a suc rose solution when female rats were required to obtain the solution from a bottle. However, NPY inhibited and leptin stimulated intake if the solution was infused intraorally. Thus NPY stimulates the responses used to obtain food but inhibits those used to consume food, and leptin has the opposite e ffects. To test the specificity of these responses the sexual behavior of m ale rats was examined. NPY-treated males showed minor deficits in sexual be havior but chose to ingest a sucrose solution rather than copulate with a f emale if offered the choice. By contrast, leptin-treated males ingested lit tle sucrose and displayed an increase in ejaculatory frequency if given the same choice. It is suggested that NPY is not merely an orexigenic peptide, but one that directs attention toward food. Similarly, leptin may not be a n anorexic peptide, but one that diverts attention away from food toward al ternate stimuli.