title: Regulation of RGS proteins by chronic morphine in rat locus coeruleus.
abstract: The present study explored a possible role for RGS (regulators of G protein signalling) proteins in the long term actions of morphine in the locus coeruleus (LC), a brainstem region implicated in opiate physical dependence and withdrawal. Morphine influences LC neurons through activation of micro -opioid receptors, which, being Gi/o-linked, would be expected to be modulated by RGS proteins. We focused on several RGS subtypes that are known to be expressed in this brain region. Levels of mRNAs encoding RGS2, -3, -4, -5, -7, -8 and -11 are unchanged following chronic morphine, but RGS2 and -4 mRNA levels are increased 2-3-fold 6 h following precipitation of opiate withdrawal. The increases in RGS2 and -4 mRNA peak after 6 h of withdrawal and return to control levels by 24 h. Immunoblot analysis of RGS4 revealed a striking divergence between mRNA and protein responses in LC: protein levels are elevated twofold following chronic morphine and decrease to control values by 6 h of withdrawal. In contrast, levels of RGS7 and -11 proteins, the only other subtypes for which antibodies are available, were not altered by these treatments. Intracellular application of wild-type RGS4, but not a GTPase accelerating-deficient mutant of RGS4, into LC neurons diminished electrophysiological responses to morphine. The observed subtype- and time-specific regulation of RGS4 protein and mRNA, and the diminished morphine-induced currents in the presence of elevated RGS4 protein levels, indicate that morphine induction of RGS4 could contribute to aspects of opiate tolerance and dependence displayed by LC neurons.
authors.affiliation: Department of Psychiatry, The University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Blvd, Dallas TX 75390, USA. stephen.gold@utsouthwestern.edu
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Gold
authors.forename: Ming-Hu
authors.initials: MH
authors.lastname: Han
authors.forename: Amy E
authors.initials: AE
authors.lastname: Herman
authors.forename: Yan G
authors.initials: YG
authors.lastname: Ni
authors.forename: Cindy M
authors.initials: CM
authors.lastname: Pudiak
authors.forename: George K
authors.initials: GK
authors.lastname: Aghajanian
authors.forename: Rong-Jian
authors.initials: RJ
authors.lastname: Liu
authors.forename: Bryan W
authors.initials: BW
authors.lastname: Potts
authors.forename: Susanne M
authors.initials: SM
authors.lastname: Mumby
authors.forename: Eric J
authors.initials: EJ
authors.lastname: Nestler
mesh_terms: D000818:Animals; D015153:Blotting, Western; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D008125:Locus Coeruleus / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D009020:Morphine / Q000494:pharmacology*; D009271:Naltrexone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D009294:Narcotics / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects* / Q000378:metabolism; D009924:Organ Culture Techniques; D018408:Patch-Clamp Techniques; D020710:RGS Proteins / Q000187:drug effects* / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D013375:Substance Withdrawal Syndrome / Q000503:physiopathology
chemical_list: D009292:Narcotic Antagonists; D009294:Narcotics; D020710:RGS Proteins; D012333:RNA, Messenger; C098799:RGS4 protein; D009271:Naltrexone; D009020:Morphine