NPY and galanin in a hibernator: hypothalamic gene expression and effects on feeding.

Neuropeptides such as neuropeptide Y (NPY) and galanin may play a role in regulating the pronounced seasonal changes in food intake shown by golden-mantled ground squirrels (Spermophilus saturatus). We used in situ hybridization histochemistry to localize the expression of NPY and galanin mRNA in the hypothalamus of normally feeding animals. NPY mRNA was abundantly expressed in the arcuate nucleus, while galanin mRNA was concentrated in both the arcuate nucleus and the dorsomedial nuclei. When NPY (0.1, 0.5, 2, and 8 micrograms) or galanin (0.1, 0.5, 2, and 8 micrograms) were injected into the third cerebral ventricle, food intake was significantly and dose-dependently increased over the subsequent 30 min. NPY stimulated significant increases in food intake for up to 2 h whereas galanin's effect did not extend beyond 30 min. Our results suggest that hibernating and nonhibernating rodents share common neural substrates for the regulation of food intake. Seasonal modulation of these neural pathways may contribute to annual cycles of food intake in hibernating mammals.