Fasting activates neuropeptide Y neurons in the arcuate nucleus and the paraventricular nucleus in the rhesus macaque

It is well accepted that neuropeptide Y (NPY) plays a pivotal role in the regulation of food intake and energy homeostasis in the rodent, with NPY neurons in the arcuate nucleus (ARH) being thought of as the major contributor to the complex central feeding circuitry. Recent data from our group also indicate that NPY is important in the regulation of energy homeostasis in the nonhuman primate (NHP); exogenous NPY administration into the 3rd ventricle is a potent stimulator of food intake in the male rhesus macaque. The purpose of this study was to determine if NPY neurons in the rhesus macaque respond to a metabolic challenge, induced by 48 h of fasting, in a manner similar to that seen in the rodent. NPY mRNA was detected in hypothalamic sections from 48-h fasted or fed rhesus monkeys by in situ hybridization, using a [³⁵S]UTP-labeled riboprobe specific for human NPY. Not surprisingly, NPY mRNA was abundant in the ARH of the NHP; however, of great interest was the expression of NPY mRNA in neurons within the paraventricular nucleus of the hypothalamus (PVH) and the supraoptic nucleus (SON). This raised the question as to whether all of these populations of NPY neurons are sensitive to changes in energy availability. Indeed, NPY expression in the ARH and PVH was significantly elevated in response to fasting; however, no significant change was detected in the SON. These data indicate that the NPY neurocircuitry involved in the regulation of food intake is more complex in the NHP than in rodents.