Neuropeptide Y (NPY) is a 36 amino acid peptide neurotransmitter present in the central and peripheral nervous systems. NPY is involved in the regulation of a broad range of functions such as eating behavior, hypertension, and reproduction. NPY exerts its effects via five receptor subtypes known as the neuropeptide Y receptors (NPYR): Y1 (NPY1R), Y2 (NPY2R), Y4 (NPY4R), Y5 (NPY5R), and Y6 (NPY6R). Four of these (Y1, Y2, Y4, and Y5) are expressed in humans. The NPY receptors belong to the G protein-coupled receptor superfamily. Activation of these receptors by NPY affects [Ca2+]i, adenylate cyclase signalling, and a number of ion channel functions.