Effects of restricted feeding on the activity of hypothalamic Orexin (OX)-A containing neurons and OX2 receptor mRNA level in the paraventricular nucleus of rats.

We have examined the effects of 3 weeks of food restriction on both the activity of neurons containing hypothalamic orexin (OX)-A and the level of OX receptor type 2 (OX2R) mRNA in the paraventricular nucleus (PVN) of rats. Double immunohistochemistry was used to examine the expression of OX-A and Fos in the lateral hypothalamic area (LHA), and in situ hybridization histochemistry was used to measure levels of OX2R mRNA in the PVN. After the period of restricted feeding, 20-30% of OX-A-containing neurons exhibited Fos-like immunoreactivity (LI). The distribution of OX-A-LI/Fos-LI cells in the food-restricted rats was similar to that observed in glucose-deprived rats after intracerebroventricular (icv) administration of 2-deoxy-D-glucose (2-DG). In addition, 3 weeks of food restriction caused a significant decrease in the expression of the OX2R gene in the parvocellular division of the PVN. These results suggest that the activation of OX-A-containing neurons induced by restricted feeding may be involved in neuroendocrine responses to food restriction.