Acute third ventricular administration of insulin decreases food intake in two paradigms

The pancreatic hormone, insulin, has been hypothesized to be an important regulator of food intake. Consistent with this hypothesis is the finding that exogenous insulin, in doses that do not affect blood glucose, reliably suppresses food intake and body weight. However, previous experiments have utilized a long-term delivery paradigm, in which insulin is administered via osmotic minipump and changes in body weight and food intake are measured across days. In separate experiments, we report that acute central injections of insulin can reduce food intake. In Experiment 1, injection of insulin (8 mU) into the third cerebral ventricle reliably suppressed intake of pelleted rat chow beginning at onset of the rats' dark phase. In Experiment 2, central insulin reliably and dose dependently suppressed intake of a 1-h 15% sucrose meal in the middle of the light phase. These data suggest that insulin can reduce food intake in acute delivery paradigms and provide another means by which to assess the roles of other central systems in the mediation of insulin's effects on energy homeostasis.