title: Chronic morphine treatment reduces recovery from opioid desensitization.
abstract: Tolerance and dependence result from long-term exposure to opioids, and there is growing evidence linking acute receptor desensitization to these more long-term processes. Receptor desensitization encompasses a series of events leading to the loss of receptor function and internalization. This study examines the onset and recovery from desensitization in locus ceruleus neurons recorded in brain slices taken from animals that have been chronically treated with morphine. After chronic morphine treatment, desensitization was altered as follows. First, the rate of desensitization was increased. Second, recovery from desensitization was always incomplete, even after a brief (1-2 min) exposure to agonist. This contrasts with experiments in controls in which recovery from desensitization, after a brief exposure to agonist, was complete within 25 min. Finally, morphine-6-beta-D-glucuronide, a metabolite of morphine that was ineffective at causing desensitization in controls, induced significant desensitization in slices from morphine-treated animals. When brain slices from controls were treated with inhibitors of PKC or monensin, agents known to compromise G-protein-coupled receptor resensitization, desensitization was increased, and recovery was significantly reduced. These results indicate that receptor resensitization maintains signaling during periods of intense and sustained stimulation. After chronic morphine treatment, desensitization is potentiated, and receptor resensitization is compromised.
authors.affiliation: Vollum Institute and Department of Physiology and Pharmacology, Oregon Health Sciences University, Portland, Oregon 97239, USA.
authors.forename: Vu C
authors.initials: VC
authors.lastname: Dang
authors.forename: John T
authors.initials: JT
authors.lastname: Williams
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D000068438:Brimonidine Tartrate; D003042:Cocaine / Q000494:pharmacology; D004361:Drug Tolerance / Q000502:physiology*; D004744:Enkephalin, Methionine / Q000494:pharmacology*; D007930:Leucine / Q000031:analogs & derivatives* / Q000494:pharmacology; D008125:Locus Coeruleus / Q000187:drug effects* / Q000502:physiology / Q000648:ultrastructure; D008297:Male; D008985:Monensin / Q000494:pharmacology; D009020:Morphine / Q000008:administration & dosage / Q000633:toxicity*; D009021:Morphine Dependence / Q000503:physiopathology*; D009022:Morphine Derivatives / Q000494:pharmacology* / Q000627:therapeutic use; D009638:Norepinephrine / Q000032:analysis; D010766:Phosphorylation / Q000187:drug effects; D011224:Prazosin / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D018341:Receptors, Adrenergic, alpha-2 / Q000187:drug effects; D017450:Receptors, Opioid, mu / Q000187:drug effects* / Q000378:metabolism; D019311:Staurosporine / Q000494:pharmacology; D015244:Thiorphan / Q000494:pharmacology; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D000316:Adrenergic alpha-Agonists; D009022:Morphine Derivatives; D011810:Quinoxalines; D018341:Receptors, Adrenergic, alpha-2; D017450:Receptors, Opioid, mu; D015016:Yohimbine; D000068438:Brimonidine Tartrate; D004744:Enkephalin, Methionine; C035349:morphine-6-glucuronide; D009020:Morphine; D008985:Monensin; D015244:Thiorphan; D011493:Protein Kinase C; D007930:Leucine; D019311:Staurosporine; C012211:ubenimex; D003042:Cocaine; D009638:Norepinephrine; D011224:Prazosin