The opioid receptors belong to the G protein-coupled receptor (GPCR) superfamily whose members share a common structure of seven putative transmembrane domains, an extracellular amino terminus, a cytoplasmic carboxyl terminus, and a third intracellular loop important for binding G proteins.All three classic opioid receptors mediate opioid-induced analgesia. Supraspinal analgesia is mainly mediated by the u-opioid receptor, whereas u-, δ-, and κ-receptors participate in the control of pain at the spinal level. The opioid receptors also mediate the mood-altering properties of opioids.κ-Opioid Receptor is activated by the endogenous peptide dynorphin. Malfunction of their signaling may be involved in epilepsy, addiction, depression, schizophrenia, and chronic pain.n nκ-Opioid Receptor is localized to a number of regions in the brain, as well as the spinal cord, the enteric nervous system and the digestive system