Gene Symbol: MOR
Description: opioid receptor, mu 1
Alias: MORA, Oprm, Oprrm1, mu-type opioid receptor, M-OR-1, MOR-1, MUOR1, mu opioid receptor splice variant rMOR-1S, mu opioid receptor splice variant rMOR-1Z, opioid receptor B
Species: rat
Products:     MOR

Top Publications

  1. Zimprich A, Simon T, Hollt V. Cloning and expression of an isoform of the rat mu opioid receptor (rMOR1B) which differs in agonist induced desensitization from rMOR1. FEBS Lett. 1995;359:142-6 pubmed
    ..Studies measuring the inhibition of adenylate cyclase in cells that had been pre-exposed to the mu opioid agonist DAMGO indicated that rMOR1B is much more resistant to agonist-induced desensitization than rMOR1. ..
  2. Zastawny R, George S, Nguyen T, Cheng R, Tsatsos J, Briones Urbina R, et al. Cloning, characterization, and distribution of a mu-opioid receptor in rat brain. J Neurochem. 1994;62:2099-105 pubmed
  3. Fukuda K, Kato S, Mori K, Nishi M, Takeshima H. Primary structures and expression from cDNAs of rat opioid receptor delta- and mu-subtypes. FEBS Lett. 1993;327:311-4 pubmed
    ..RNA blot hybridization analysis revealed that cerebrum and brainstem contain both ROR-A and ROR-B mRNAs, whereas neither ROR-A nor ROR-B mRNAs can be detected in cerebellum. ..
  4. Miyoshi K, Narita M, Suzuki T. Functional reduction in mu-opioidergic system in the spinal cord under a neuropathic pain-like state following chronic ethanol consumption in the rat. Neuroscience. 2007;144:777-82 pubmed
    ..35)S]GTPgammaS) binding to membranes of the spinal cord induced by the selective mu-opioid receptor (MOR) agonist, [D-Ala(2),N-MePhe(4),Gly(5)-ol]enkephalin (DAMGO), was significantly decreased under the ethanol-..
  5. Wang H, Zhao B, Zhong Y, Li K, Li Z, Wang Q, et al. Coexpression of delta- and mu-opioid receptors in nociceptive sensory neurons. Proc Natl Acad Sci U S A. 2010;107:13117-22 pubmed publisher
    ..Importantly, both DOR and MOR agonists reduce depolarization-induced Ca(2+) currents in single small DRG neurons and inhibit afferent C-fiber ..
  6. Berg K, Zardeneta G, Hargreaves K, Clarke W, Milam S. Integrins regulate opioid receptor signaling in trigeminal ganglion neurons. Neuroscience. 2007;144:889-97 pubmed
    ..g. Galphai vs. Galphas). Collectively, these data provide the first evidence that specific integrins regulate opioid receptor signaling in sensory neurons. ..
  7. Schroeder J, Fischbach P, Zheng D, McCleskey E. Activation of mu opioid receptors inhibits transient high- and low-threshold Ca2+ currents, but spares a sustained current. Neuron. 1991;6:13-20 pubmed
    ..The kinetic effect on high-threshold current is like that caused by diminished rest potential: the transient component is selectively lost, whereas the sustained component is spared. ..
  8. Wang H, Frankfurt M, Burns L. High-affinity naloxone binding to filamin a prevents mu opioid receptor-Gs coupling underlying opioid tolerance and dependence. PLoS ONE. 2008;3:e1554 pubmed publisher
    ..tolerance and dependence by preventing a G protein coupling switch (Gi/o to Gs) by the mu opioid receptor (MOR), although the binding site of such ultra-low-dose opioid antagonists was previously unknown...
  9. Pasternak D, Pan L, Xu J, Yu R, Xu M, Pasternak G, et al. Identification of three new alternatively spliced variants of the rat mu opioid receptor gene: dissociation of affinity and efficacy. J Neurochem. 2004;91:881-90 pubmed
    ..The mouse and human Oprm genes undergo splicing...

More Information


  1. Soderman A, Unterwald E. Cocaine reward and hyperactivity in the rat: sites of mu opioid receptor modulation. Neuroscience. 2008;154:1506-16 pubmed publisher
  2. Sora I, Takahashi N, Funada M, Ujike H, Revay R, Donovan D, et al. Opiate receptor knockout mice define mu receptor roles in endogenous nociceptive responses and morphine-induced analgesia. Proc Natl Acad Sci U S A. 1997;94:1544-9 pubmed
  3. Chen Y, Mestek A, Liu J, Hurley J, Yu L. Molecular cloning and functional expression of a mu-opioid receptor from rat brain. Mol Pharmacol. 1993;44:8-12 pubmed
    ..profile of this binding site thus suggests that it is a mu-type opioid receptor, which we designated MOR-1...
  4. Thompson R, Mansour A, Akil H, Watson S. Cloning and pharmacological characterization of a rat mu opioid receptor. Neuron. 1993;11:903-13 pubmed
    ..Based upon these observations, we conclude that pRMuR-12 encodes a mu opioid receptor. ..
  5. Wang J, Imai Y, Eppler C, Gregor P, Spivak C, Uhl G. mu opiate receptor: cDNA cloning and expression. Proc Natl Acad Sci U S A. 1993;90:10230-4 pubmed
  6. Wang Y, Wang Y, Liu T, Law P, Loh H, Qiu Y, et al. μ-Opioid receptor attenuates Aβ oligomers-induced neurotoxicity through mTOR signaling. CNS Neurosci Ther. 2015;21:8-14 pubmed publisher
    ..It may provide new insight into the pathological process and useful strategy for therapeutic interventions against Aβ neurotoxicity. ..
  7. Wilson Poe A, Morgan M, Aicher S, Hegarty D. Distribution of CB1 cannabinoid receptors and their relationship with mu-opioid receptors in the rat periaqueductal gray. Neuroscience. 2012;213:191-200 pubmed publisher
    ..These results indicate that behavioral interactions between cannabinoids and opioids may be the result of cellular adaptations within PAG neurons co-expressing CB1 and MOP receptors. ..
  8. Fraga D, Machado R, Fernandes L, Souza G, Zampronio A. Endogenous opioids: role in prostaglandin-dependent and -independent fever. Am J Physiol Regul Integr Comp Physiol. 2008;294:R411-20 pubmed
    ..In conclusion, our results suggest that LPS and endogenous pyrogens (except IL-1beta and prostaglandins) recruit the opioid system to cause a mu-receptor-mediated fever. ..
  9. de Oliveira L, De Luca L, Menani J. Opioid activation in the lateral parabrachial nucleus induces hypertonic sodium intake. Neuroscience. 2008;155:350-8 pubmed publisher
    ..The results suggest that deactivation of inhibitory mechanisms by opioid receptor activation in the LPBN releases sodium intake if excitatory signals were activated (sodium depletion) or not. ..
  10. Xiao C, Ye J. Ethanol dually modulates GABAergic synaptic transmission onto dopaminergic neurons in ventral tegmental area: role of mu-opioid receptors. Neuroscience. 2008;153:240-8 pubmed publisher
    ..This dual modulation of GABAergic transmission by ethanol may be an important mechanism underlying alcohol addiction...
  11. Cheng B, Liu H, Fu X, Sheng Z, Qiu J, Cao R. [Expression of beta-endorphin and micro-opioid receptor during wound healing process in rat with deep partial-thickness scald]. Zhonghua Shao Shang Za Zhi. 2007;23:36-9 pubmed
    To observe the expression of beta-endorphin and micro-opioid receptor (MOR) during wound healing process in rat with deep partial-thickness scald...
  12. Peckham E, Barkley L, Divin M, Cicero T, Traynor J. Comparison of the antinociceptive effect of acute morphine in female and male Sprague-Dawley rats using the long-lasting mu-antagonist methocinnamox. Brain Res. 2005;1058:137-47 pubmed
    ..The results suggest that pathways downstream of the micro-opioid receptor and G protein are more efficient in male rats than in female rats such that there is a larger receptor reserve for morphine-mediated antinociception. ..
  13. Greenwell T, Martin Schild S, Inglis F, Zadina J. Colocalization and shared distribution of endomorphins with substance P, calcitonin gene-related peptide, gamma-aminobutyric acid, and the mu opioid receptor. J Comp Neurol. 2007;503:319-33 pubmed
    The endomorphins are endogenous opioids with high affinity and selectivity for the mu opioid receptor (MOR, MOR-1, MOP)...
  14. Coolen L, Fitzgerald M, Yu L, Lehman M. Activation of mu opioid receptors in the medial preoptic area following copulation in male rats. Neuroscience. 2004;124:11-21 pubmed
    ..In particular, activation of mu opioid receptors (MOR) in the medial preoptic area (MPOA), a key area for regulation of male sexual behavior, was studied in male rats...
  15. Kraus J, Borner C, Giannini E, Hickfang K, Braun H, Mayer P, et al. Regulation of mu-opioid receptor gene transcription by interleukin-4 and influence of an allelic variation within a STAT6 transcription factor binding site. J Biol Chem. 2001;276:43901-8 pubmed
    ..These findings provide a molecular basis for understanding bidirectional interactions between the opioid system and the immune system. ..
  16. Mase H, Sakai A, Sakamoto A, Suzuki H. A subset of ?-opioid receptor-expressing cells in the rostral ventromedial medulla contribute to thermal hyperalgesia in experimental neuropathic pain. Neurosci Res. 2011;70:35-43 pubmed publisher
    ..These results suggest that a subset of RVM neurons expressing ?-opioid receptors contribute to the maintenance of thermal hyperalgesia in neuropathic pain. ..
  17. Xu J, Xu M, Rossi G, Pasternak G, Pan Y. Identification and characterization of seven new exon 11-associated splice variants of the rat ? opioid receptor gene, OPRM1. Mol Pain. 2011;7:9 pubmed publisher
    ..The complexity created by alternative splicing of the rat OPRM1 gene may provide important insights of understanding the diverse responses to the various ? opioids seen in rats. ..
  18. Fattore L, Vigano D, Fadda P, Rubino T, Fratta W, Parolaro D. Bidirectional regulation of mu-opioid and CB1-cannabinoid receptor in rats self-administering heroin or WIN 55,212-2. Eur J Neurosci. 2007;25:2191-200 pubmed
    ..SA) of either heroin or the cannabinoid receptor agonist WIN 55,212-2 on levels and functionality of mu-opioid (MOR) and CB1-cannabinoid receptors (CB1R) in reward-related brain areas, such as the prefrontal cortex (PFC), nucleus ..
  19. Zhao M, Wang J, Jia H, Tang J. Roles of different subtypes of opioid receptors in mediating the ventrolateral orbital cortex opioid-induced inhibition of mirror-neuropathic pain in the rat. Neuroscience. 2007;144:1486-94 pubmed
    ..These results suggest that the VLO is involved in opioid-induced inhibition of the MNP and the effect is mediated by mu- (but not delta- and kappa-) opioid receptors. ..
  20. He L, Whistler J. Chronic ethanol consumption in rats produces opioid antinociceptive tolerance through inhibition of mu opioid receptor endocytosis. PLoS ONE. 2011;6:e19372 pubmed publisher
    It is well known that the mu-opioid receptor (MOR) plays an important role in the rewarding properties of ethanol. However, it is less clear how chronic ethanol consumption affects MOR signaling...
  21. Finnegan T, Chen S, Pan H. Mu opioid receptor activation inhibits GABAergic inputs to basolateral amygdala neurons through Kv1.1/1.2 channels. J Neurophysiol. 2006;95:2032-41 pubmed
    ..This study provides new information that activation of presynaptic mu opioid receptors primarily attenuates GABAergic synaptic inputs to CeA-projecting neurons in the BLA through a signaling mechanism involving Kv1.1 and Kv1.2 channels. ..
  22. Dias M, Nucci T, Branco L, Gargaglioni L. Opioid ?-receptors in the rostral medullary raphe modulate hypoxia-induced hyperpnea in unanesthetized rats. Acta Physiol (Oxf). 2012;204:435-42 pubmed publisher
    ..05). No differences in the Tb were observed between groups during hypoxia. These data suggest that opioids acting on ?-receptors in the rMR exert an excitatory modulation of hyperventilation induced by hypoxia. ..
  23. Ray L. Stress-induced and cue-induced craving for alcohol in heavy drinkers: Preliminary evidence of genetic moderation by the OPRM1 and CRH-BP genes. Alcohol Clin Exp Res. 2011;35:166-74 pubmed publisher
    ..Larger studies are needed to validate these preliminary findings, which should also be extended to clinical samples. ..
  24. Pritchett C, Pardee A, McGuirk S, Will M. The role of nucleus accumbens adenosine-opioid interaction in mediating palatable food intake. Brain Res. 2010;1306:85-92 pubmed publisher
    ..In summary, these results suggest a potential role of striatal adenosine A2(A) receptors in mediating baseline and striatal opioid-mediated intake of a high-fat diet. ..
  25. Treskatsch S, Shaqura M, Dehe L, Roepke T, Shakibaei M, Schäfer M, et al. Evidence for MOR on cell membrane, sarcoplasmatic reticulum and mitochondria in left ventricular myocardium in rats. Heart Vessels. 2016;31:1380-8 pubmed publisher
    ..However, several comments in literature exist doubting the existence of MOR in cardiac tissue...
  26. Morganstern I, Liang S, Ye Z, Karatayev O, Leibowitz S. Disturbances in behavior and cortical enkephalin gene expression during the anticipation of ethanol in rats characterized as high drinkers. Alcohol. 2012;46:559-68 pubmed publisher
    ..05) and the mu-opioid receptor (MOR) (p < 0...
  27. Luo D, Huang J, Dong Y, Wu Z, Wei Y, Lu Y, et al. Connections between EM2- and SP-containing terminals and GABAergic neurons in the mouse spinal dorsal horn. Neurol Sci. 2014;35:1421-7 pubmed publisher
    ..These results suggest that the interactions between EM2- and SP-containing terminals and GABAergic interneurons in the lamina II influence pain transmission and modulation in the spinal dorsal horn...
  28. Johnston C, Herschel D, Lasek A, Hammer R, Nikulina E. Knockdown of ventral tegmental area mu-opioid receptors in rats prevents effects of social defeat stress: implications for amphetamine cross-sensitization, social avoidance, weight regulation and expression of brain-derived neurotrophic factor. Neuropharmacology. 2015;89:325-34 pubmed
    ..Moreover, social stress upregulates VTA mu-opioid receptor (MOR) mRNA...
  29. Bailey A, Yuferov V, Bendor J, Schlussman S, Zhou Y, Ho A, et al. Immediate withdrawal from chronic "binge" cocaine administration increases mu-opioid receptor mRNA levels in rat frontal cortex. Brain Res Mol Brain Res. 2005;137:258-62 pubmed
    ..Naloxone had no effect on the increase of MOP or ppdyn mRNA levels. The results indicate that the opioid system is altered during early withdrawal from chronic cocaine administration. ..
  30. Torres Reveron A, Williams T, Chapleau J, Waters E, McEwen B, Drake C, et al. Ovarian steroids alter mu opioid receptor trafficking in hippocampal parvalbumin GABAergic interneurons. Exp Neurol. 2009;219:319-27 pubmed publisher
    ..c.) administration. Dorsal hippocampal sections were dually immunolabeled for MOR and PARV and examined by light and electron microscopy...
  31. Margas W, Mahmoud S, Ruiz Velasco V. Muscarinic acetylcholine receptor modulation of mu (mu) opioid receptors in adult rat sphenopalatine ganglion neurons. J Neurophysiol. 2010;103:172-82 pubmed publisher
    ..In the present study, we examined the coupling mechanism between mu (mu) opioid receptors (MOR) and muscarinic acetylcholine receptors (mAChR) with Ca(2+) channels in acutely dissociated adult rat SPG neurons...
  32. Schnell S, Wessendorf M. Coexpression of the mu-opioid receptor splice variant MOR1C and the vesicular glutamate transporter 2 (VGLUT2) in rat central nervous system. J Comp Neurol. 2008;508:542-64 pubmed publisher
    ..The purpose of the present study was to examine whether a particular mu-opioid receptor (MOR) splice-variant, MOR(1C), is expressed in rat central nervous system (CNS) by terminals expressing the vesicular ..
  33. Yu Y, Wang X, Cui Y, Fan Y, Liu J, Wang R. Abnormal modulation of cholinergic neurotransmission by endomorphin 1 and endomorphin 2 in isolated bronchus of type 1 diabetic rats. Peptides. 2006;27:2770-7 pubmed
    To assess whether diabetes alters the regulatory effects of mu-opioid receptor (MOR) agonists on the cholinergic bronchoconstriction, we investigated the inhibitory effects of endomorphins (EMs) on the electrical field stimulation (EFS)-..
  34. Lin X, Xue L, Wang R, Zhao Q, Chen Q. Protective effects of endomorphins, endogenous opioid peptides in the brain, on human low density lipoprotein oxidation. FEBS J. 2006;273:1275-84 pubmed
    ..In all assay systems, EM1 was more potent than EM2 and l-glutathione, a major intracellular water-soluble antioxidant. We propose that endomorphins provide protection against free radical-induced neurodegenerative disorders. ..
  35. Chen X, Pitis P, Liu G, Yuan C, Gotchev D, Cowan C, et al. Structure-activity relationships and discovery of a G protein biased ? opioid receptor ligand, [(3-methoxythiophen-2-yl)methyl]({2-[(9R)-9-(pyridin-2-yl)-6-oxaspiro-[4.5]decan-9-yl]ethyl})amine (TRV130), for the treatment of acute severe pain. J Med Chem. 2013;56:8019-31 pubmed publisher
    ..It is currently being evaluated in human clinical trials for the treatment of acute severe pain. ..
  36. Mousa S, Cheppudira B, Shaqura M, Fischer O, Hofmann J, Hellweg R, et al. Nerve growth factor governs the enhanced ability of opioids to suppress inflammatory pain. Brain. 2007;130:502-13 pubmed
    ..Peripheral opioid antinociception is dependent on sensory neuron mu opioid receptor (MOR) expression, coupling and efficacy...
  37. Kaplan T, Skyers P, Tabori N, Drake C, Milner T. Ultrastructural evidence for mu-opioid modulation of cholinergic pathways in rat dentate gyrus. Brain Res. 2004;1019:28-38 pubmed
    ..the overlapping distributions of cholinergic and mu-opioid systems, particularly in the dentate gyrus, suggest that MOR activation is a potential mechanism for endogenous opioid modulation of cholinergic activity...
  38. Rios C, Gomes I, Devi L. mu opioid and CB1 cannabinoid receptor interactions: reciprocal inhibition of receptor signaling and neuritogenesis. Br J Pharmacol. 2006;148:387-95 pubmed
  39. Vassoler F, Wright S, Byrnes E. Exposure to opiates in female adolescents alters mu opiate receptor expression and increases the rewarding effects of morphine in future offspring. Neuropharmacology. 2016;103:112-21 pubmed publisher
    ..Results indicate that F1 females whose mothers were exposed to morphine during adolescence (Mor-F1) demonstrate significantly enhanced CPP to the lowest doses of morphine compared with Sal-F1 females...
  40. Wang H, Hsu C, Huang P, Kuo Y, Li A, Yeh T, et al. Heterodimerization of opioid receptor-like 1 and mu-opioid receptors impairs the potency of micro receptor agonist. J Neurochem. 2005;92:1285-94 pubmed
    ..These results provide the evidence that ORL1/muR heterodimerization and the resulting impairment of mu receptor-activated signaling pathways may contribute to ORL1-mediated antiopioid effects in the brain. ..
  41. Parra Gámez L, García Hidalgo A, Salazar Juárez A, Anton B, Paredes R. Endomorphin-1, effects on male sexual behavior. Physiol Behav. 2009;97:98-101 pubmed publisher
  42. Ruegsegger G, Toedebusch R, Will M, Booth F. Mu opioid receptor modulation in the nucleus accumbens lowers voluntary wheel running in rats bred for high running motivation. Neuropharmacology. 2015;97:171-81 pubmed publisher
  43. Han W, Hata H, Imbe H, Liu Q, Takamatsu Y, Koizumi M, et al. Increased body weight in mice lacking mu-opioid receptors. Neuroreport. 2006;17:941-4 pubmed
    ..Our results suggest that the up-regulated expression of neuropeptide Y mRNA might contribute to the increased weights of adult mu-opioid receptor knockout mice. ..
  44. Hirota K, Okawa H, Appadu B, Grandy D, Devi L, Lambert D. Stereoselective interaction of ketamine with recombinant mu, kappa, and delta opioid receptors expressed in Chinese hamster ovary cells. Anesthesiology. 1999;90:174-82 pubmed
    ..Ketamine (100 microM) reversed DAMGO (mu) and spiradoline (kappa) inhibition of formation of cyclic adenosine monophosphate. Ketamine interacts stereoselectively with recombinant mu and kappa opioid receptors. ..
  45. Yu Y, Cui Y, Wang X, Fan Y, Liu J, Yan X, et al. Endomorphin1 and endomorphin2, endogenous potent inhibitors of electrical field stimulation (EFS)-induced cholinergic contractions of rat isolated bronchus. Peptides. 2006;27:1846-51 pubmed, we determined whether endomorphin1 (EM1) and endomorphin2 (EM2), selective endogenous mu-opioid receptor (MOR) agonists, inhibited the response to EFS in rat isolated bronchus in a concentration- and frequency-dependent ..
  46. Leventhal L, Silva R, Rossi G, Pasternak G, Bodnar R. Morphine-6beta-glucuronide-induced hyperphagia: characterization of opioid action by selective antagonists and antisense mapping in rats. J Pharmacol Exp Ther. 1998;287:538-44 pubmed
    ..morphine analgesia is decreased by antisense oligodeoxynucleotides (AS ODNs) targeting exons 1 and 4 of the MOR-1 clone, M6G analgesia is reduced by probes targeting exons 2 and 3 of the MOR-1 clone...
  47. Kawabe T, Ueyama T, Hano T, Sapru H. Cardiovascular responses to microinjections of endomorphin-2 into the nucleus of the solitary tract are attenuated in the spontaneously hypertensive rat. Clin Exp Hypertens. 2015;37:197-206 pubmed publisher
    ..These results demonstrate that attenuation of EM2-induced responses in the mNTS of SHR may contribute to the excitatory responses elicited by ARCN stimulation in SHR. ..
  48. Normandin A, Luccarini P, Molat J, Gendron L, Dallel R. Spinal ? and ? opioids inhibit both thermal and mechanical pain in rats. J Neurosci. 2013;33:11703-14 pubmed publisher
  49. Zhang Y, Chen S, Laumet G, Chen H, Pan H. Nerve Injury Diminishes Opioid Analgesia through Lysine Methyltransferase-mediated Transcriptional Repression of μ-Opioid Receptors in Primary Sensory Neurons. J Biol Chem. 2016;291:8475-85 pubmed publisher
    The μ-opioid receptor (MOR, encoded by Oprm1) agonists are the mainstay analgesics for treating moderate to severe pain...
  50. Gris P, Gauthier J, Cheng P, Gibson D, Gris D, Laur O, et al. A novel alternatively spliced isoform of the mu-opioid receptor: functional antagonism. Mol Pain. 2010;6:33 pubmed publisher
    ..We recently discovered a new human alternatively spliced isoform of MOR (MOR1K) that is missing the N-terminal extracellular and first transmembrane domains, resulting in a 6TM GPCR ..
  51. Teodorov E, Bernardi M, Ferrari M, Fior Chadi D, Felicio L. Plasticity of opioid receptors in the female periaqueductal gray: multiparity-induced increase in the activity of genes encoding for mu and kappa receptors and a post-translational decrease in delta receptor expression. J Mol Neurosci. 2011;43:175-81 pubmed publisher
    ..and ?-opioid receptor (Oprm1, Oprk1, and Oprd1 respectively) gene activity and ?, ? and ? protein expression (MOR, KOR and DOR respectively) in the PAG of the female rats...
  52. Bailey A, Yoo J, Racz I, Zimmer A, Kitchen I. Preprodynorphin mediates locomotion and D2 dopamine and mu-opioid receptor changes induced by chronic 'binge' cocaine administration. J Neurochem. 2007;102:1817-1830 pubmed publisher
  53. Torres Reverón A, Palermo K, Hernández López A, Hernández S, Cruz M, Thompson K, et al. Endometriosis Is Associated With a Shift in MU Opioid and NMDA Receptor Expression in the Brain Periaqueductal Gray. Reprod Sci. 2016;23:1158-67 pubmed publisher
    ..However, MOR immunoreactivity was significantly decreased in the ventral PAG in the endometriosis group...