title: Descending mechanisms activated by the anterior pretectal nucleus initiate but do not maintain neuropathic pain in rats.
abstract: BACKGROUND
  The anterior pretectal nucleus (APtN) activates descending mechanisms of pain control. This study evaluated whether the APtN also controls neuropathic pain in rats.
  
  
  METHODS
  The hypersensitivity to mechanical stimulation with an electronic von Frey apparatus and the number of Fos-immunoreactive (Fos-ir) neurons in the APtN were evaluated in rats before and after chronic constriction injury of the sciatic nerve.
  
  
  RESULTS
  The tactile hypersensitivity was characterized by an initial phase (the 2 days following the injury) and a maintenance phase (the subsequent 7 days). The injection of 2% lidocaine (0.25 μL) or N-methyl-D-aspartate (2.5 μg/0.25 μL) into the APtN intensified the tactile hypersensitivity observed 2 days after injury but did not alter the tactile hypersensitivity observed 7 and 14 days after injury. The injection of naloxone (10 ng/0.25 μL) or methysergide (40 pg/0.25 μL) but not atropine (100 ng/0.25 μL) into the APtN also intensified the tactile hypersensitivity observed 2 days after the injury. A significant increase in the number of Fos-ir cells was found in the contralateral APtN 2 days but not 7 or 14 days after the injury. Electrical stimulation of the APtN reduced the tactile hypersensitivity at 2, 7 and 14 days after the nerve ligation.
  
  
  CONCLUSIONS
  APtN exerts a tonic inhibitory influence on persistent pain. The results point out to an important role of opioid and serotonergic mediation into the APtN to inhibit hyperalgesia during the initial phase of neuropathic pain.
authors.affiliation: Department of Pharmacology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, Brazil.
authors.forename: A C
authors.initials: AC
authors.lastname: Rossaneis
authors.affiliation: Department of Pharmacology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, Brazil.
authors.forename: K
authors.initials: K
authors.lastname: Genaro
authors.affiliation: Oswaldo Cruz Foundation, Fiocruz Rondônia, Brazil.
authors.forename: Q M
authors.initials: QM
authors.lastname: Dias
authors.affiliation: Department of Pharmacology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, Brazil.
authors.forename: L M
authors.initials: LM
authors.lastname: Guethe
authors.affiliation: Department of Pharmacology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, Brazil.
authors.forename: R S
authors.initials: RS
authors.lastname: Fais
authors.affiliation: Department of Morphology, Estomatology and Physiology, Faculty of Odontology of Ribeirão Preto, University of São Paulo, Ribeirão Preto, Brazil.
authors.forename: E A
authors.initials: EA
authors.lastname: Del Bel
authors.affiliation: Department of Pharmacology, Ribeirão Preto Medical School, University of São Paulo, Ribeirão Preto, Brazil.
authors.forename: W A
authors.initials: WA
authors.lastname: Prado
mesh_terms: D000779:Anesthetics, Local / Q000008:administration & dosage / Q000494:pharmacology; D000818:Animals; D003251:Constriction, Pathologic / Q000150:complications / Q000473:pathology; D006930:Hyperalgesia / Q000503:physiopathology; D008012:Lidocaine / Q000008:administration & dosage / Q000494:pharmacology; D008297:Male; D008784:Methysergide / Q000494:pharmacology; D016202:N-Methylaspartate / Q000008:administration & dosage / Q000494:pharmacology; D009270:Naloxone / Q000494:pharmacology; D009292:Narcotic Antagonists / Q000494:pharmacology; D009434:Neural Pathways / Q000473:pathology*; D009437:Neuralgia / Q000473:pathology*; D009474:Neurons / Q000473:pathology; D010147:Pain Measurement / Q000187:drug effects; D010812:Physical Stimulation; D066250:Pretectal Region / Q000473:pathology*; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D020426:Sciatic Neuropathy / Q000473:pathology
chemical_list: D000779:Anesthetics, Local; D009292:Narcotic Antagonists; D016760:Proto-Oncogene Proteins c-fos; D009270:Naloxone; D016202:N-Methylaspartate; D008012:Lidocaine; D008784:Methysergide