Receptors for neuropeptide Y: multiple subtypes and multiple second messengers.

Neuropeptide Y (NPY) can elicit numerous physiological responses by activating specific pre- and postsynaptic receptors. Different orders of potency for agonists in various model systems suggest that there are multiple subtypes of NPY receptors, described here by Martin Michel, but their pharmacological definition remains tentative, awaiting development of specific antagonists and receptor cloning studies. The coupling of NPY receptors to various signal transduction mechanisms is also reviewed, including inhibition of adenylyl cyclase and stimulation or inhibition of increases in intracellular Ca2+, but a link between individual NPY receptor subtypes and specific signal transduction pathways has not been established.