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Abstract
Nowadays, the delta opioid receptor (DOPr) represents a promising target for the treatment of chronic pain and emotional disorders. Despite the fact that they produce limited antinociceptive effects in healthy animals and in most acute pain models, DOPr agonists have shown efficacy in various chronic pain models. In this chapter, we review the progresses that have been made over the last decades in understanding the role played by DOPr in the control of pain. More specifically, the distribution of DOPr within the central nervous system and along pain pathways is presented. We also summarize the literature supporting a role for DOPr in acute, tonic, and chronic pain models, as well as the mechanisms regulating its activity under specific conditions. Finally, novel compounds that have make their way to clinical trials are discussed.
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Affiliation(s)
- Khaled Abdallah
- Département de pharmacologie-physiologie, Université de Sherbrooke, Sherbrooke, QC, Canada
- Institut de pharmacologie de Sherbrooke, Université de Sherbrooke, Sherbrooke, QC, Canada
- Faculté de médecine et des sciences de la santé, Université de Sherbrooke, Sherbrooke, QC, Canada
- Centre de recherche du CHUS, Sherbrooke, QC, Canada
| | - Louis Gendron
- Département de pharmacologie-physiologie, Université de Sherbrooke, Sherbrooke, QC, Canada.
- Institut de pharmacologie de Sherbrooke, Université de Sherbrooke, Sherbrooke, QC, Canada.
- Faculté de médecine et des sciences de la santé, Université de Sherbrooke, Sherbrooke, QC, Canada.
- Centre de recherche du CHUS, Sherbrooke, QC, Canada.
- Département d'anesthésiologie, Université de Sherbrooke, Sherbrooke, QC, Canada.
- Quebec Pain Research Network, Sherbrooke, QC, Canada.
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Hou Y, Belcheva MM, Clark AL, Zahm DS, Coscia CJ. Increased opioid receptor binding and G protein coupling in the accumbens and ventral tegmental area of postnatal day 2 rats. Neurosci Lett 2006; 395:244-8. [PMID: 16300888 PMCID: PMC1819395 DOI: 10.1016/j.neulet.2005.10.086] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2005] [Revised: 10/27/2005] [Accepted: 10/31/2005] [Indexed: 10/25/2022]
Abstract
In some regions of the developing rat brain such as the nucleus accumbens (Acb), mu opioid (MOP) receptor specific binding in the perinatal period exceeds that in the adult. To investigate the significance of these developmental changes, MOP and nociceptin/orphanin FQ (NOP) receptor binding and G protein coupling as determined by GTPgammaS binding experiments were examined in mesolimbic regions of postnatal day 2 (P2) pups and compared to those of their dams. Acb of the P2 pup exhibited 2-fold greater MOP receptor specific binding than that of the dam. In the ventral tegmental area (VTA), NOP specific binding was about 2-fold higher in the P2 pup. A correlation was found between MOP and NOP binding and their coupling to G protein on dam and P2 pup brain sections. However, the magnitude of increases in MOP and NOP receptor G protein coupling to G protein in P2 pups exceeded the 2-fold differences in binding between pups and dams. Furthermore, the amplitude of the MOP receptor G protein coupling in female P2 Acb was greater than increases in male P2 pup Acb. Differences in MOP and NOP binding and G protein coupling in other mesolimbic regions between P2 pups and dams were rarely observed. The data indicate that greater binding and G protein coupling of MOP and NOP receptors occur in discrete, mesolimbic regions of P2 pups when compared to their dams. It may be of significance that these brain regions, Acb and VTA, are undergoing maturation on P2.
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Affiliation(s)
- Yanning Hou
- Department of Biochemistry & Molecular Biology, St. Louis University School of Medicine, St. Louis, MO 63104, USA
| | - Mariana M. Belcheva
- Department of Biochemistry & Molecular Biology, St. Louis University School of Medicine, St. Louis, MO 63104, USA
| | - Amy L. Clark
- Department of Biochemistry & Molecular Biology, St. Louis University School of Medicine, St. Louis, MO 63104, USA
| | - Daniel S. Zahm
- Department of Pharmacological & Physiological Sciences, St. Louis University School of Medicine, St. Louis, MO 63104, USA
| | - Carmine J. Coscia
- Department of Biochemistry & Molecular Biology, St. Louis University School of Medicine, St. Louis, MO 63104, USA
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Macé G, Miaczynska M, Zerial M, Nebreda AR. Phosphorylation of EEA1 by p38 MAP kinase regulates mu opioid receptor endocytosis. EMBO J 2005; 24:3235-46. [PMID: 16138080 PMCID: PMC1224689 DOI: 10.1038/sj.emboj.7600799] [Citation(s) in RCA: 162] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2005] [Accepted: 08/08/2005] [Indexed: 12/30/2022] Open
Abstract
Morphine analgesic properties and side effects such as tolerance are mediated by the mu opioid receptor (MOR) whose endocytosis is considered of primary importance for opioid pharmacological effects. Here, we show that p38 mitogen-activated protein kinase (MAPK) activation is required for MOR endocytosis and sufficient to trigger its constitutive internalization in the absence of agonist. Further studies established a functional link between p38 MAPK and the small GTPase Rab5, a key regulator of endocytosis. Expression of an activated mutant of Rab5 stimulated endocytosis of MOR ligand-independently in wild-type but not in p38alpha-/- cells. We found that p38alpha can phosphorylate the Rab5 effectors EEA1 and Rabenosyn-5 on Thr-1392 and Ser-215, respectively, and these phosphorylation events regulate the recruitment of EEA1 and Rabenosyn-5 to membranes. Moreover, phosphomimetic mutation of Thr-1392 in EEA1 can bypass the requirement for p38alpha in MOR endocytosis. Our results highlight a novel mechanism whereby p38 MAPK regulates receptor endocytosis under physiological conditions via phosphorylation of Rab5 effectors.
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Affiliation(s)
- Gaëtane Macé
- European Molecular Biology Laboratory, Heidelberg, Germany
- CNIO (Spanish National Cancer Center), Madrid, Spain
| | - Marta Miaczynska
- Max Planck Institute for Molecular Cell Biology and Genetics, Dresden, Germany
| | - Marino Zerial
- Max Planck Institute for Molecular Cell Biology and Genetics, Dresden, Germany
| | - Angel R Nebreda
- European Molecular Biology Laboratory, Heidelberg, Germany
- CNIO (Spanish National Cancer Center), Madrid, Spain
- CNIO (Spanish National Cancer Center), Melchor Fernández Almagro 3, 28029 Madrid, Spain. Tel.: +34 91 7328038; Fax: +34 91 7328033; E-mail:
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Talbot JN, Happe HK, Murrin LC. Mu opioid receptor coupling to Gi/o proteins increases during postnatal development in rat brain. J Pharmacol Exp Ther 2005; 314:596-602. [PMID: 15860573 DOI: 10.1124/jpet.104.082156] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Mu opioid receptors are densely expressed within rat striatum and are concentrated in anatomically discrete patches called striosomes. The density of striosomal mu receptors remains relatively constant during postnatal development, but little is known about their functional maturation. We examined the extent of G protein coupling by mu opioid receptors in rat brain during development, focusing on striosomes within the striatum because of receptor density. The mu receptors were quantified using [(3)H][d-Ala(2),N-Me-Phe(4),Gly(5)-ol]-enkephalin (DAMGO) autoradiography. Adjacent sections were analyzed for DAMGO-stimulated guanosine 5'-O-(3-[(35)S]thio)triphosphate ([(35)S]GTPgammaS) binding to assess mu receptor activation of G(i/o) proteins. Striosomal mu receptor expression increased only slightly between postnatal day 5 and adult. In contrast, mu receptor-stimulated [(35)S]GTPgammaS binding increased from 0.13 to 2.6 fmol/mg tissue over the same period, a 20-fold difference. The ratio of specific DAMGO-stimulated [(35)S]GTPgammaS binding to [(3)H]DAMGO binding, representing the relative number of G proteins activated per receptor, increased 19-fold between postnatal day 5 and adult. Similar patterns were observed throughout the striatum and other brain regions such as the nucleus accumbens, although the extent of change varied from region to region. These data indicate that mu opioid receptors exhibit enhanced function in the adult rat brain compared with the neonate. These data also suggest that this increase in G protein coupling is developmentally regulated and that in the developing rat brain the density of mu opioid receptor expression may not necessarily correlate with receptor activation of G proteins.
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Affiliation(s)
- Jeffery N Talbot
- Depatment of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, 985800 Nebraska Medical Center, Omaha, NE 68198-5800, USA
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Hou Y, Tan Y, Belcheva MM, Clark AL, Zahm DS, Coscia CJ. Differential effects of gestational buprenorphine, naloxone, and methadone on mesolimbic mu opioid and ORL1 receptor G protein coupling. BRAIN RESEARCH. DEVELOPMENTAL BRAIN RESEARCH 2004; 151:149-57. [PMID: 15246701 DOI: 10.1016/j.devbrainres.2004.05.002] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 05/03/2004] [Indexed: 11/20/2022]
Abstract
In addition to its use for heroin addiction pharmacotherapy in general, buprenorphine has advantages in treating maternal heroin abuse. To examine the gestational effects of buprenorphine on opioid receptor signaling, the [(35)S]-GTP gamma S in situ binding induced by the mu agonist [D-Ala(2),MePhe(4),Gly(5)-ol] enkephalin (DAMGO) or the nociceptin/orphanin FQ (N/OFQ) agonist was measured in mesolimbic structures of pup brains from pregnant rats administered with buprenorphine +/- naloxone, naloxone, or methadone by osmotic minipump. Drug- and gender-based changes in DAMGO- and N/OFQ-induced GTP gamma S binding were discovered in mesolimbic regions of dam, P2, and P7 brains. Buprenorphine and/or methadone gestational treatment attenuated DAMGO-induced GTP gamma S binding in some dam and male P2 mesolimbic regions. Methadone diminished DAMGO-induced GTP gamma S binding in almost all monitored brain regions of the dam but had few effects on their N/OFQ-induced GTP gamma S binding. Naloxone used in combination with buprenorphine blocked the inhibition by buprenorphine alone on DAMGO-induced GTP gamma S binding. In contrast to its inhibitory effects on DAMGO-induced GTP gamma S binding, buprenorphine stimulated N/OFQ-induced GTP gamma S binding in male P2 nucleus accumbens and lateral septum. Brain region-dependent gender differences in DAMGO-induced GTP gamma S binding were seen in P2 pups, and males showed greater sensitivity to buprenorphine and methadone than females. Our findings on mu opioid receptor (MOR) GTP-binding regulatory protein (G protein) coupling and its gender dependency are consistent with our earlier studies on mu receptor binding adaptation induced by buprenorphine in dams and neonatal rats after in utero treatment regimens, and they extend the gestational effects of this opiate to mu and N/OFQ receptor functionality.
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Affiliation(s)
- Yanning Hou
- Department of Biochemistry and Molecular Biology, St. Louis University School of Medicine, 1402 S. Grand Boulevard, St. Louis, MO 63104, USA
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