Opioid receptor (OR) (OR)

Opioid receptors are a group of inhibitory G protein-coupled receptors (GPCRs) that play a central role in the modulation of pain, reward, and addictive behaviors within the central and peripheral nervous systems (StatPearls, 2023). There are four primary subtypes: mu (μ), delta (δ), kappa (κ), and the nociceptin receptor, each with distinct anatomical distributions and physiological effects (IUPHAR, 2024). Upon activation by endogenous ligands like endorphins or exogenous drugs like morphine, these receptors initiate signaling cascades that inhibit neurotransmitter release and reduce neuronal excitability (PubMed, 2022). Clinically, they are the primary targets for potent analgesic medications used to manage acute and chronic pain (NIH, 2023). However, their involvement in the brain's reward circuitry makes them significant drivers of opioid use disorder and addiction. Beyond analgesia, opioid receptors influence respiratory rate, gastrointestinal motility, and mood, leading to both therapeutic benefits and significant side effects such as respiratory depression and constipation (UniProt, 2024).

Other names

Opiate receptorMu-type opioid receptorDelta-type opioid receptorKappa-type opioid receptorNociceptin receptorMOPDOPKOPNOP

Opioid receptors primarily function as Gi/Go protein-coupled receptors. Activation leads to the inhibition of adenylate cyclase, decreasing intracellular cAMP levels. It also triggers the opening of G protein-coupled inwardly rectifying potassium (GIRK) channels and the closure of voltage-gated calcium channels, resulting in neuronal hyperpolarization and reduced release of neurotransmitters such as glutamate and substance P (StatPearls, 2023; IUPHAR, 2024).