μ-opioid receptor
The μ-opioid receptors exist mostly presynaptically in the periaqueductal gray region, and in the superficial dorsal horn of the spinal cord (specifically the substantia gelatinosa of Rolando).Some of these effects, such as analgesia, sedation, euphoria, itching and decreased respiration, tend to lessen with continued use as tolerance develops.This includes downregulation of MOR gene expression, so the number of receptors presented on the cell surface is actually reduced, as opposed to the more short-term desensitisation induced by β-arrestins or RGS proteins.[35][36][37] A potentiation effect occurs when opioids are combined with ethanol, benzodiazepines, barbiturates, or other central depressants which can result in rapid loss of consciousness and an increased risk of fatal overdose.Additional doses of naloxone may be necessary and supportive care should be given to prevent hypoxic brain injury by monitoring vital signs.Tramadol and tapentadol carry additional risks associated with their dual effects as SNRIs and can cause serotonin syndrome and seizures.
AliasesHomoloGeneGeneCardsChromosome 6 (human)RNA expressionGene ontologyOrthologsEntrezEnsemblUniProtPubMedWikidataopioid receptorsenkephalinsbeta-endorphindynorphinspeptideagonistmorphineMorpheusG-protein coupled receptorGi alpha subunitadenylate cyclaseβ-FNAalvimopanβ-endorphinfentanylartifactsstructure-based designfunctional selectivityreverse transcription polymerase chain reactionTRIMU 5alkaloidsopioid peptidespresynapticallyperiaqueductal graydorsal hornspinal cordsubstantia gelatinosa of Rolandoolfactory bulbnucleus accumbenscerebral cortexnucleiamygdalaanalgesiasedationblood pressureitchingnauseaeuphoriadecreased respirationmiosisconstipationgastrin-releasing peptide receptorG protein-coupled receptorstachyphylaxisβ-arrestinsarrestin beta 1arrestin beta 2RGS proteinsRGS9-2opioid overdosebradypneahypoxemiacardiac outputhypotensionvasodilationbradycardiapotentiationethanolbenzodiazepinesbarbituratescentral depressantscirculatory collapseantagonistsnaloxoneTramadoltapentadolserotonin syndromeList of opioidsdynorphin Adynorphin BEndomorphinsendomorphin-1endomorphin-2Endorphinsleu-enkephalinmet-enkephalinadrenorphinCodeineHeroinHydrocodoneHydromorphoneLevorphanolMethadoneOxycodoneOxymorphonePethidineTianeptineBuprenorphineButorphanolDezocineNalbuphineOliceridinePentazocine7-HydroxymitragynineSHR9352SR-17018TegileridineTRV734LoperamideChloroxymorphamineMethoclocinnamoxOxymorphazoneCyclazocineCyprodimeDiprenorphineLevallorphanNalmefeneNalodeineNalorphineNaltrexoneSamidorphansilent antagonists6β-NaltrexolAxelopran