Opioid receptor mu 1 (MOR) (MOR)

The Opioid receptor mu 1 (MOR), encoded by the OPRM1 gene, is a G protein-coupled receptor (GPCR) that serves as the primary site of action for most clinically used opioid analgesics, including morphine. It is predominantly expressed in the central and peripheral nervous systems, where it plays a critical role in modulating pain perception, reward pathways, and autonomic functions like respiration and gastric motility (StatPearls, 2023). Upon activation by endogenous ligands like endorphins or exogenous drugs, MOR initiates signaling through Gi/o proteins to inhibit neuronal excitability by decreasing cAMP levels and modulating ion channel activity (UniProt, P35372). While MOR is the gold standard target for managing severe pain, its activation in the brainstem can lead to life-threatening respiratory depression, and its role in the mesolimbic reward system underlies the high potential for addiction and abuse (PubMed, PMC3272204). Chronic stimulation of the receptor often leads to tolerance and physical dependence, presenting significant therapeutic challenges in long-term pain management.

Other names

OPRM1Opioid receptor mu 1MOPMOR1Mu-type opioid receptor

Agonists bind to the receptor, triggering Gi/o protein coupling which inhibits adenylate cyclase, decreases cAMP levels, closes voltage-gated calcium channels, and opens G protein-coupled inwardly rectifying potassium (GIRK) channels, leading to hyperpolarization and reduced neurotransmitter release.