nociceptin/orphanin FQ peptide receptor, member of the class A family of seven-transmembrane G protein-coupled receptors
The nociceptin (NOP) receptor binds nociceptin or orphanin FQ, a 17 amino acid endogenous neuropeptide. The NOP receptor is involved in the modulation of various brain activities including instinctive and emotional behaviors. The opioid receptor family is composed of four major subtypes: mu (MOP), delta (DOP), kappa (KOP) opioid receptors, and the nociceptin/orphanin FQ peptide receptor (NOP). They are distributed widely in the central nervous system and respond to classic alkaloid opiates, such as morphine and heroin, as well as to endogenous peptide ligands, which include dynorphins, enkephalins, endorphins, endomorphins, and nociceptin. Opioid receptors are coupled to inhibitory G proteins of the G(i/o) family and involved in regulating a variety of physiological functions such as pain, addiction, mood, stress, epileptic seizure, and obesity, among many others.