Mu, kappa, and delta opioid receptor (MOR, KOR, DOR)

Mu, kappa, and delta opioid receptors are class A G protein-coupled receptors primarily expressed in the central and peripheral nervous system, as well as other tissues. They bind endogenous opioid peptides (endorphins, enkephalins, dynorphins) and exogenous opioids (morphine, fentanyl, etc.), mediating analgesic effects as well as side effects such as euphoria, addiction, and respiratory depression. Each receptor subtype has distinct tissue distribution, endogenous ligand preference, and physiological roles: - Mu opioid receptor (MOR): Most widely expressed, vital for analgesia, respiratory depression, euphoria, dependence, and gastrointestinal effects. - Kappa opioid receptor (KOR): Mediates analgesia, diuresis, and dysphoria, and may have lower abuse potential for agonists. - Delta opioid receptor (DOR): Contributes to analgesia and mood regulation, with potential roles in inflammatory pain and psychiatric disorders. Opioid receptors remain critical therapeutic targets for pain and addiction, but clinical use is complicated by serious adverse effects and misuse potential. Recent research seeks biased ligands to enhance therapeutic benefit while minimizing harm

Other names

Mu opioid receptor (MOR)mu-type opioid receptorμ opioid receptorKappa opioid receptor (KOR)kappa-type opioid receptorκ opioid receptorDelta opioid receptor (DOR)delta-type opioid receptorδ opioid receptorOpioid receptor familyopioid receptors

Agonists: Bind and activate the receptor, leading to Gi/o protein signaling, inhibition of adenylyl cyclase, decreased cAMP, opening of potassium channels, closing of calcium channels, inhibition of neurotransmitter release (presynaptic), reduced neuronal excitability, and promotion of analgesia and other opioid effects Antagonists: Block receptor activation, preventing endogenous or exogenous ligand effects Biased agonists: Preferentially activate G protein- or β-arrestin–mediated pathways, potentially reducing side effects such as respiratory depression or dependence