Mu-opioid receptor (OPRM1) (MOR)

The Mu-opioid receptor (MOR), encoded by the OPRM1 gene, is a G protein-coupled receptor (GPCR) that serves as the primary molecular target for fentanyl and its analogs (UniProt P35372). Located throughout the central and peripheral nervous systems, MOR is the principal mediator of the analgesic and euphoric effects of both endogenous opioids and synthetic ligands (StatPearls, "Opioid Receptors"). Fentanyl and its analogs, such as sufentanil and carfentanil, exhibit exceptionally high affinity and potency at this receptor compared to morphine, leading to rapid activation of inhibitory G-protein signaling (PubChem, "Fentanyl"). This activation inhibits adenylyl cyclase and modulates ion channels to reduce neuronal excitability, effectively blocking pain transmission (NIH, "Fentanyl DrugFacts"). However, the receptor's role in the brainstem's respiratory centers makes it the primary site for opioid-induced respiratory depression, a leading cause of fatal overdose (PubMed, PMID: 30001171). Chronic activation of MOR by these potent analogs often leads to receptor desensitization and downregulation, contributing to the rapid development of tolerance and physical dependence. In clinical settings, MOR is targeted for acute and chronic pain management, but its high abuse potential necessitates strict regulatory oversight.

Other names

OPRM1MOPMu-type opioid receptorMOR-1Opioid receptor mu 1

Agonism of the mu-opioid receptor leads to G-protein mediated inhibition of adenylyl cyclase, reduction of cAMP levels, closure of voltage-gated calcium channels, and activation of inward-rectifying potassium channels, resulting in neuronal hyperpolarization and decreased neurotransmitter release (StatPearls, "Opioid Receptors").