title: G protein-coupled receptor kinase 2 mediates mu-opioid receptor desensitization in GABAergic neurons of the nucleus raphe magnus.
abstract: Nucleus raphe magnus (NRM) sends the projection to spinal dorsal horn and inhibits nociceptive transmission. Analgesic effect produced by mu-opioid receptor agonists including morphine partially results from activating the NRM-spinal cord pathway. It is generally believed that mu-opioid receptor agonists disinhibit spinally projecting neurons of the NRM and produce analgesia by hyperpolarizing GABAergic interneurons. In the present study, whole-cell patch-clamp recordings combined with single-cell RT-PCR analysis were used to test the hypothesis that DAMGO ([D-Ala(2),N-methyl-Phe(4),Gly-ol(5)]enkephalin), a specific mu-opioid receptor agonist, selectively hyperpolarizes NRM neurons expressing mRNA of glutamate decarboxylase (GAD(67)). Homologous desensitization of mu-opioid receptors in NRM neurons could result in the development of morphine-induced tolerance. G protein-coupled receptor kinase (GRK) is believed to mediate mu-opioid receptor desensitization in vivo. Therefore, we also investigated the involvement of GRK in mediating homologous desensitization of DAMAMGO-induced electrophysiological effects on NRM neurons by using two experimental strategies. First, single-cell RT-PCR assay was used to study the expression of GRK2 and GRK3 mRNAs in individual DAMGO-responsive NRM neurons. Whole-cell recording was also performed with an internal solution containing the synthetic peptide, which corresponds to G(betagamma)-binding domain of GRK and inhibits G(betagamma) activation of GRK. Our results suggest that DAMGO selectively hyperpolarizes NRM GABAergic neurons by opening inwardly rectifying K(+) channels and that GRK2 mediates short-term homologous desensitization of mu-opioid receptors in NRM GABAergic neurons.
authors: Department of Anesthesiology, Chang Gung Memorial Hospital, Taiwan, China Department of Physiology, Chang Gung University School of Medicine, Kwei-San, Tao-Yuan, Taiwan, China.
authors: A H
authors: AH
authors: Li
authors: H L
authors: HL
authors: Wang
mesh_terms: D000595:Amino Acid Sequence; D000701:Analgesics, Opioid / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites; D017868:Cyclic AMP-Dependent Protein Kinases / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D004361:Drug Tolerance / Q000502:physiology; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000494:pharmacology; D054769:G-Protein-Coupled Receptor Kinase 2; D054770:G-Protein-Coupled Receptor Kinase 3; D005968:Glutamate Decarboxylase / Q000096:biosynthesis; D017136:Ion Transport / Q000187:drug effects; D008564:Membrane Potentials / Q000187:drug effects; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology; D009842:Oligopeptides / Q000138:chemical synthesis / Q000494:pharmacology; D010146:Pain / Q000503:physiopathology; D018408:Patch-Clamp Techniques; D010766:Phosphorylation; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000378:metabolism; D024661:Potassium Channels, Inwardly Rectifying; D011499:Protein Processing, Post-Translational; D017346:Protein Serine-Threonine Kinases / Q000096:biosynthesis / Q000235:genetics; D017434:Protein Structure, Tertiary; D021381:Protein Transport / Q000187:drug effects; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D011903:Raphe Nuclei / Q000187:drug effects / Q000201:enzymology / Q000502:physiology* / Q000503:physiopathology; D051381:Rats; D017207:Rats, Sprague-Dawley; D017450:Receptors, Opioid, mu / Q000819:agonists / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects; D013116:Spinal Cord / Q000503:physiopathology; D051552:beta-Adrenergic Receptor Kinases; D005680:gamma-Aminobutyric Acid / Q000502:physiology*
chemical_list: D000701:Analgesics, Opioid; D009419:Nerve Tissue Proteins; D009842:Oligopeptides; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D012333:RNA, Messenger; D017450:Receptors, Opioid, mu; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D005680:gamma-Aminobutyric Acid; D017346:Protein Serine-Threonine Kinases; D017868:Cyclic AMP-Dependent Protein Kinases; D054770:G-Protein-Coupled Receptor Kinase 3; C496569:Grk2 protein, rat; C517851:Grk3 protein, rat; D051552:beta-Adrenergic Receptor Kinases; D054769:G-Protein-Coupled Receptor Kinase 2; D005968:Glutamate Decarboxylase; D011188:Potassium