Neuropeptide Y (NPY)
A 36 amino acid neuropeptide that is one of the most abundant peptides in the brain. NPY is a potent appetite stimulant and plays roles in stress response, anxiety, and circadian rhythms. It counterbalances the satiety signals of GLP-1 and PYY, and its biology is relevant to understanding appetite regulation.
Technical Context
NPY (36 aa) acts on Y1-Y5 receptors (GPCRs). In the hypothalamic arcuate nucleus, NPY/AgRP neurons are the primary orexigenic (appetite-stimulating) pathway, counterbalanced by anorexigenic POMC/CART neurons. NPY is the most potent known appetite stimulant — intracerebroventricular injection causes intense feeding behaviour. Y1 and Y5 receptors mediate the appetite-stimulating effect. NPY is also involved in stress response, circadian rhythms, vasoconstriction, and anxiety. The melanocortin agonist setmelanotide works downstream of NPY/AgRP signalling — it activates MC4R on second-order neurons that NPY/AgRP neurons normally inhibit. Ghrelin stimulates NPY neurons, linking peripheral hunger signals to central appetite circuits.