Neuropeptide Y: a physiological orexigen modulated by the feedback action of ghrelin and leptin.

Neuropeptide Y (NPY), a 36-amino-acid neuropeptide is the most potent physiological appetite transducer known. Episodic NPY neurosecretion in hypothalamic target sites is temporally linked with onset of the daily feeding pattern. Upregulation of NPY signaling in the arcuate nucleus-paraventricular nucleus (ARC-PVN) neural axis is responsible for the hyperphagia evoked by dieting, fasting, hormonal and genetic factors, and disruption in intrahypothalamic signaling. Clusters of NPY-producing neurons in the ARC that coexpress gamma- amino butyric acid and agouti-related peptide, and those in the brain stem (BS) that coexpress catecholamines and galanin, participate in disparate manners to regulate appetitive behavior. NPY receptors, Y1, Y2, and Y5, expressed by various components of the NPY network, mediate NPY-induced feeding. Imbalance in NPY signaling due either to high or low abundance of NPY at target sites elicits hyperphagia leading to increased fat accretion and obesity. Recent studies show that intermittent, feedback action of opposing afferent hormonal signals-leptin from adipose tissue and ghrelin from stomach-regulate the episodic secretion of orexigenic NPY in the PVN-ARC. Apparently, the hypothalamic NPY network is the primary common pathway intimately involved in genesis of appetite- stimulating impulses.