title: Reduced spinal microglial activation and neuropathic pain after nerve injury in mice lacking all three nitric oxide synthases.
abstract: BACKGROUND
  Several studies have investigated the involvement of nitric oxide (NO) in acute and chronic pain using mice lacking a single NO synthase (NOS) gene among the three isoforms: neuronal (nNOS), inducible (iNOS) and endothelial (eNOS). However, the precise role of NOS/NO in pain states remains to be determined owing to the substantial compensatory interactions among the NOS isoforms. Therefore, in this study, we used mice lacking all three NOS genes (n/i/eNOS-/-mice) and investigated the behavioral phenotypes in a series of acute and chronic pain assays.
  
  
  RESULTS
  In a model of tissue injury-induced pain, evoked by intraplantar injection of formalin, both iNOS-/-and n/i/eNOS-/-mice exhibited attenuations of pain behaviors in the second phase compared with that in wild-type mice. In a model of neuropathic pain, nerve injury-induced behavioral and cellular responses (tactile allodynia, spinal microglial activation and Src-family kinase phosphorylation) were reduced in n/i/eNOS-/-but not iNOS-/-mice. Tactile allodynia after nerve injury was improved by acute pharmacological inhibition of all NOSs and nNOS. Furthermore, in MG-5 cells (a microglial cell-line), interferon-γ enhanced NOSs and Mac-1 mRNA expression, and the Mac-1 mRNA increase was suppressed by L-NAME co-treatment. Conversely, the NO donor, sodium nitroprusside, markedly increased mRNA expression of Mac-1, interleukin-6, toll-like receptor 4 and P2X4 receptor.
  
  
  CONCLUSIONS
  Our results provide evidence that the NOS/NO pathway contributes to behavioral pain responses evoked by tissue injury and nerve injury. In particular, nNOS may be important for spinal microglial activation and tactile allodynia after nerve injury.
authors.affiliation: Department of Molecular and System Pharmacology, Graduate School of Pharmaceutical Sciences, University of Kyushu, Fukuoka, Japan.
authors.forename: Kazuya
authors.initials: K
authors.lastname: Kuboyama
authors.forename: Makoto
authors.initials: M
authors.lastname: Tsuda
authors.forename: Masato
authors.initials: M
authors.lastname: Tsutsui
authors.forename: Yumiko
authors.initials: Y
authors.lastname: Toyohara
authors.forename: Hidetoshi
authors.initials: H
authors.lastname: Tozaki-Saitoh
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Shimokawa
authors.forename: Nobuyuki
authors.initials: N
authors.lastname: Yanagihara
authors.forename: Kazuhide
authors.initials: K
authors.lastname: Inoue
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D005786:Gene Expression Regulation / Q000187:drug effects; D055786:Gene Knockout Techniques; D006930:Hyperalgesia / Q000150:complications / Q000473:pathology; D007249:Inflammation / Q000150:complications / Q000473:pathology; D007371:Interferon-gamma / Q000494:pharmacology; D015850:Interleukin-6 / Q000235:genetics / Q000378:metabolism; D016177:Macrophage-1 Antigen / Q000235:genetics / Q000378:metabolism; D008297:Male; D051379:Mice; D017628:Microglia / Q000187:drug effects / Q000473:pathology*; D009437:Neuralgia / Q000150:complications / Q000201:enzymology* / Q000473:pathology*; D009569:Nitric Oxide / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D058848:Receptors, Purinergic P2X4 / Q000235:genetics / Q000378:metabolism; D013116:Spinal Cord / Q000187:drug effects / Q000473:pathology*; D013127:Spinal Nerves / Q000187:drug effects / Q000201:enzymology / Q000293:injuries* / Q000473:pathology*; D013696:Temperature; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000378:metabolism; D019061:src-Family Kinases / Q000378:metabolism
chemical_list: D015850:Interleukin-6; D016177:Macrophage-1 Antigen; D012333:RNA, Messenger; D058848:Receptors, Purinergic P2X4; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; D009569:Nitric Oxide; D007371:Interferon-gamma; D019001:Nitric Oxide Synthase; D019061:src-Family Kinases