title: Suppression of the morphine-induced rewarding effect and G-protein activation in the lower midbrain following nerve injury in the mouse: involvement of G-protein-coupled receptor kinase 2.
abstract: The present study was designed to investigate whether a state of neuropathic pain induced by sciatic nerve ligation could alter the rewarding effect, antinociception, and G-protein activation induced by a prototype of mu-opioid receptor agonist morphine in the mouse. The sciatic nerve ligation caused a long-lasting and profound thermal hyperalgesia. Under this neuropathic pain-like state, an i.c.v. morphine-induced place preference was observed in sham-operated mice but not in sciatic nerve-ligated mice. However, no differences in the antinociceptive effect of i.c.v.-administered morphine were noted between the groups. The increases in the binding of guanosine-5'-o-(3-[(35)S]thio)triphosphate induced by morphine in lower midbrain membranes including the ventral tegmental area, which contributes to the expression of the rewarding effect of opioid, were significantly attenuated in sciatic nerve-ligated mice. On the other hand, there were no differences in the stimulation of guanosine-5'-o-(3-[(35)S]thio)triphosphate binding to pons/medulla membranes, which plays an important role in the antinociception of mu-opioid receptor agonists, between the groups. In addition, no changes in levels of guanosine-5'-o-(3-[(35)S]thio)triphosphate binding by either the selective delta- or kappa-opioid receptor agonists were noted in membrane of the lower midbrain and limbic forebrain membranes obtained from sciatic nerve-ligated mice. Reverse transcription-polymerase chain reaction analysis showed that sciatic nerve ligation did not alter the mRNA product of mu-opioid receptors in the lower midbrain, indicating that a decrease in some mu-opioid receptor functions may result from the uncoupling of mu-opioid receptors from G-proteins. We found a significant increase in protein levels of G-protein-coupled receptor kinase 2, which causes receptor phosphorylation in membranes of the lower midbrain but not in the pons/medulla, obtained from mice with nerve injury, whereas there were no changes in the protein level of phosphorylated-protein kinase C in the lower midbrain. These results suggest that the uncoupling of mu-opioid receptors from G-proteins by G-protein-coupled receptor kinase 2 in the lower midbrain may, at least in part, contribute to the suppression of the rewarding effect of morphine under neuropathic pain.
authors.affiliation: Department of Toxicology, Hoshi University School of Pharmacy and Pharmaceutical Sciences, Tokyo 142-8501, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Ozaki
authors.forename: M
authors.initials: M
authors.lastname: Narita
authors.forename: M
authors.initials: M
authors.lastname: Narita
authors.forename: M
authors.initials: M
authors.lastname: Iino
authors.forename: K
authors.initials: K
authors.lastname: Miyoshi
authors.forename: T
authors.initials: T
authors.lastname: Suzuki
mesh_terms: D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D015153:Blotting, Western; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D054770:G-Protein-Coupled Receptor Kinase 3; D019204:GTP-Binding Proteins / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006930:Hyperalgesia; D008297:Male; D008526:Medulla Oblongata / Q000201:enzymology / Q000378:metabolism*; D008636:Mesencephalon / Q000201:enzymology / Q000378:metabolism*; D051379:Mice; D008813:Mice, Inbred ICR; D009020:Morphine / Q000494:pharmacology*; D010146:Pain / Q000201:enzymology / Q000378:metabolism*; D010147:Pain Measurement; D010766:Phosphorylation; D011149:Pons / Q000378:metabolism; D016548:Prosencephalon / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D017450:Receptors, Opioid, mu / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012201:Reward; D012584:Sciatic Nerve / Q000293:injuries*; D013462:Sulfur Radioisotopes; D051552:beta-Adrenergic Receptor Kinases
chemical_list: D000701:Analgesics, Opioid; D012333:RNA, Messenger; D017450:Receptors, Opioid, mu; D013462:Sulfur Radioisotopes; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D009020:Morphine; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D054770:G-Protein-Coupled Receptor Kinase 3; C517850:GRK3 protein, mouse; D051552:beta-Adrenergic Receptor Kinases; D019204:GTP-Binding Proteins