Mu-opioid receptor, Kappa-opioid receptor, Delta-opioid receptor (MOR, KOR, DOR)

The μ-opioid receptor (MOR), κ-opioid receptor (KOR), and δ-opioid receptor (DOR) are members of the opioid receptor family, a subfamily of G protein-coupled receptors (GPCRs) that mediate the action of endogenous peptides (endorphins, enkephalins, dynorphins) and exogenous opioids (morphine, fentanyl, etc.). They are widely distributed in the central and peripheral nervous system, particularly in pain pathways, and play key roles in analgesia, addiction, mood, respiratory regulation, and various autonomic processes. MOR is chiefly responsible for the rewarding and addictive effects as well as the potent analgesic and depressant properties of clinically used opioids; KOR is associated with analgesia, diuresis, and dysphoria but is often less reinforcing; DOR has roles in analgesia and emotional responses and is experimentally linked to mood modulation and chronic pain with a possibly reduced side effect profile. All three receptors mediate their effects mainly by coupling to Gi/o proteins, resulting in inhibition of adenylyl cyclase, decreased cellular excitability, and neurotransmitter release. Drugs targeting these receptors are mainstays in the management of pain, opioid dependence, and overdose but carry significant safety and abuse challenges. Recent therapeutic strategies focus on developing receptor- and pathway-selective ligands to reduce adverse outcomes.

Other names

μ-opioid receptor (MOR)kappa-opioid receptor (KOR)delta-opioid receptor (DOR)opioid receptors

Agonists (activate receptor to mimic endogenous opioid peptides and produce analgesia and other effects); Antagonists (block receptor activity, used in overdose reversal and addiction treatment); Partial agonists (produce submaximal activation, useful in opioid dependence therapy); Biased agonists (preferentially activate certain signaling pathways to separate therapeutic from adverse effects)