INCREASED NEUROPEPTIDE-Y CONTENT IN INDIVIDUAL HYPOTHALAMIC NUCLEI, BUT NOT NEUROPEPTIDE-Y MESSENGER-RNA, IN DIET-INDUCED OBESITY IN RATS

Neuropeptide Y (NPY) is the most powerful appetite stimulant known, and chronic administration leads to obesity. The hypothalamic content of NPY varies with nutritional status, suggesting that it is of physiological importance. We measured NPY in specific hypothalamic nuclei and NPY mRNA in the hypothalamus by Northern blotting in rats made obese by feeding a highly palatable diet compared with controls fed standard chow. In animals fed the palatable diet, NPY concentrations were increased in the paraventricular nucleus (mean +/- S.E.M.; 19.5 +/- 2.3 vs 11.1 +/- 1.1 fmol/mu-g protein, P < 0.02), the arcuate nucleus (20.4 +/- 3.3 vs 9.3 +/- 0.6 fmol/mu-g protein, P < 0.01), the medial preoptic area (9.1 +/- 0.9 vs 5.9 +/- 0.7 fmol/mu-g protein, P < 0.02) and the anterior hypothalamus (2.7 +/- 0.2 vs 2.0 +/- 0.1 fmol/mu-g, P < 0.02). Hypothalamic NPY mRNA measured by Northern blot analysis was, however, unchanged. These results suggest that the increase in NPY was due to decreased release rather than increased NPY ergic activity. The findings are in accord with the neuroendocrine disturbance and increased thermogenesis observed in this model of obesity.