title: Role of nucleus accumbens μ opioid receptors in the effects of morphine on ERK1/2 phosphorylation.
abstract: Despite the critical role attributed to phosphorylated extracellular signal regulated kinase (pERK1/2) in the nucleus accumbens (Acb) in the actions of addictive drugs, the effects of morphine on ERK1/2 phosphorylation in this area are still controversial.
  
  
  
  In order to investigate further this issue, we studied (1) the ability of morphine to affect ERK1/2 phosphorylation in the shell (AcbSh) and core (AcbC) of Sprague-Dawley and Wistar rats and of CD-1 and C57BL/6J mice and (2) the role of dopamine D1 and μ-opioid receptors in Sprague-Dawley rats and CD-1 mice.
  
  
  
  The pERK1/2 expression was assessed by immunohistochemistry.
  
  
  
  In rats, morphine decreased AcbSh and AcbC pERK1/2 expression, whereas in mice, increased it preferentially in the AcbSh compared with the AcbC. Systemic SCH 39166 decreased pERK1/2 expression on its own in the AcbSh and AcbC of Sprague-Dawley rats and CD-1 mice; furthermore, in rats, SCH 39166 disclosed the ability of morphine to stimulate pERK1/2 expression. Systemic (rats and mice) and intra-Acb (rats) naltrexone prevented both decreases, in rats, and increases, in mice.
  
  
  
  These findings confirm the differential effects of morphine in rats and mice Acb and that D1 receptors exert a facilitatory role on ERK1/2 phosphorylation; furthermore, they indicate that, in rats, removal of the D1-dependent pERK1/2 expression discloses the stimulatory influence of morphine on ERK1/2 phosphorylation and that the morphine's ability to decrease pERK1/2 expression is mediated by Acb μ-opioid receptors. Future experiments may disentangle the psychopharmacological significance of the effects of morphine on pERK1/2 in the Acb.
authors.affiliation: Department of Life and Environmental Sciences, University of Cagliari, Via Ospedale, 72, I-09124, Cagliari, Italy.
authors.forename: Michela
authors.initials: M
authors.lastname: Rosas
authors.affiliation: Department of Life and Environmental Sciences, University of Cagliari, Via Ospedale, 72, I-09124, Cagliari, Italy.
authors.forename: Simona
authors.initials: S
authors.lastname: Porru
authors.affiliation: Department of Biomedical Sciences, University of Cagliari, Cagliari, Italy.|Centre of Excellence on Neurobiology of Addiction, University of Cagliari, Cagliari, Italy.
authors.forename: Sandro
authors.initials: S
authors.lastname: Fenu
authors.affiliation: Institute of Translational Pharmacology, National Research Council, Pula, Cagliari, Italy.
authors.forename: Stefania
authors.initials: S
authors.lastname: Ruiu
authors.affiliation: Department of Chemistry and Pharmacy, University of Sassari, Sassari, Italy.
authors.forename: Alessandra T
authors.initials: AT
authors.lastname: Peana
authors.affiliation: Neuroscience and Mental Health Research Institute (NMHRI), Neuroscience Division - School of Biosciences, Cardiff University, Cardiff, UK.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Papale
authors.affiliation: Neuroscience and Mental Health Research Institute (NMHRI), Neuroscience Division - School of Biosciences, Cardiff University, Cardiff, UK.
authors.forename: Riccardo
authors.initials: R
authors.lastname: Brambilla
authors.affiliation: Department of Biomedical Sciences, University of Cagliari, Cagliari, Italy.|Centre of Excellence on Neurobiology of Addiction, University of Cagliari, Cagliari, Italy.
authors.forename: Gaetano
authors.initials: G
authors.lastname: Di Chiara
authors.affiliation: Department of Life and Environmental Sciences, University of Cagliari, Via Ospedale, 72, I-09124, Cagliari, Italy. acquas@unica.it.|Centre of Excellence on Neurobiology of Addiction, University of Cagliari, Cagliari, Italy. acquas@unica.it.
authors.forename: Elio
authors.initials: E
authors.lastname: Acquas
mesh_terms: D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D001552:Benzazepines / Q000494:pharmacology; D018492:Dopamine Antagonists / Q000494:pharmacology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D019950:Mitogen-Activated Protein Kinase 1 / Q000187:drug effects* / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000187:drug effects* / Q000378:metabolism; D009020:Morphine / Q000494:pharmacology*; D009714:Nucleus Accumbens / Q000187:drug effects* / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D017208:Rats, Wistar; D017447:Receptors, Dopamine D1 / Q000187:drug effects* / Q000378:metabolism; D017450:Receptors, Opioid, mu / Q000187:drug effects* / Q000378:metabolism
chemical_list: D000701:Analgesics, Opioid; D001552:Benzazepines; D018492:Dopamine Antagonists; D017447:Receptors, Dopamine D1; D017450:Receptors, Opioid, mu; C058081:ecopipam; D009020:Morphine; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3
keywords: Dopamine D1 receptors; Extracellular signal regulated kinase (ERK1/2); Mice; Morphine; Naltrexone; Nucleus accumbens; Rats; SCH 39166; μ-Opioid receptors