title: Involvement of the Nociceptin/Orphanin FQ-NOP receptor system in the ventrolateral periaqueductal gray following mechanical allodynia in chronic pain.
abstract: OBJECTIVE
  It has been well documented that ventrolateral periaqueductal gray (vlPAG) matter is a crucial component of the descending pain modulatory system in the chronic pain condition. The aim of the present study was to identify the role of the vlPAG Nociceptin/Orphanin FQ/NOP receptor system in allodynia, a nociceptive behavioral response associated with chronic pain.
  
  
  METHODS
  We used two animal models of persistent pain: chronic constriction injury (CCI) and inflammation induced by carrageenan. In each, Nociceptin/Orphanin FQ transmission was abolished using UFP-101, a selective NOP receptor antagonist, which was injected into the vlPAG at a dose of 18 microg/1 microl/rat.
  
  
  RESULTS
  We found that treatment with the NOP antagonist reversed the decrease in allodynic threshold in CCI rats fourteen days after the ligature, which was the timepoint of the greatest reduction in threshold. Moreover, UFP-101 administered immediately prior to or 2 h after intra plantar (i.pl.) carrageenan injection prevented or reversed, respectively, allodynic behavior in rats with inflammation.
  
  
  CONCLUSIONS
  Our findings support the hypothesis that the endogenous Nociceptin/Orphanin FQ/NOP receptor system is tonically active at the vlPAG level during neuropathic states or carrageenan inflammation.
authors.affiliation: Department of Pharmaceutical Sciences, University of Catania, v.le A. Doria 6, 95125 Catania, Italy. scotog@unict.it
authors.forename: Giovanna M
authors.initials: GM
authors.lastname: Scoto
authors.forename: Giuseppina
authors.initials: G
authors.lastname: Aricò
authors.forename: Attilio
authors.initials: A
authors.lastname: Iemolo
authors.forename: Simone
authors.initials: S
authors.lastname: Ronsisvalle
authors.forename: Carmela
authors.initials: C
authors.lastname: Parenti
mesh_terms: D000818:Animals; D002351:Carrageenan / Q000633:toxicity; D004195:Disease Models, Animal; D006614:Hindlimb / Q000294:innervation; D006930:Hyperalgesia / Q000139:chemically induced / Q000188:drug therapy / Q000378:metabolism*; D008026:Ligation; D008297:Male; D009292:Narcotic Antagonists; D018847:Opioid Peptides / Q000494:pharmacology; D010146:Pain / Q000139:chemically induced / Q000378:metabolism*; D017288:Pain Threshold; D010487:Periaqueductal Gray / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011957:Receptors, Opioid / Q000187:drug effects / Q000378:metabolism*; D012584:Sciatic Nerve / Q000293:injuries; D014110:Touch; D000094942:Nociceptin Receptor
chemical_list: D002351:Carrageenan; D009292:Narcotic Antagonists; D018847:Opioid Peptides; D011957:Receptors, Opioid; D000094942:Nociceptin Receptor; C479838:(Nphe(1),Arg(14),Lys(15))N-OFQ NH(2); C000722285:Oprl1 protein, rat