title: Activation of extracellular signal-regulated kinase in sciatic nerve contributes to neuropathic pain after partial sciatic nerve ligation in mice.
abstract: BACKGROUND
  The mitogen-activated protein kinase family plays an important role in several types of pain. However, the detailed role of phosphorylated extracellular signal-regulated kinase (pERK) in the region of injured peripheral nerve is poorly understood. In this study, we investigated whether pERK in injured sciatic nerve contributes to neuropathic pain induced by partial sciatic nerve ligation (PSL) in mice.
  
  
  METHODS
  Mice received PSL; pERK1/2 (p44/42) in sciatic nerve was measured by both Western blotting and immunohistochemistry. U0126 (an ERK kinase inhibitor) was injected twice, an intraneural injection (20 nmol/2 microL) 30 min before PSL, and a perineural injection (20 nmol/10 microL) on Day 1 after PSL. Thermal hyperalgesia and tactile allodynia induced by PSL were evaluated by the thermal paw withdrawal test and the von Frey test, respectively.
  
  
  RESULTS
  As measured by Western blotting, in sham-operated mice, the levels of pERK1/2 in sciatic nerve were constant and the same as those in naive mice across Days 1-14. In PSL-operated mice, a significant increase in pERK1/2 was observed on Day 1 after PSL and persisted until Day 3. As measured by immunohistochemistry, immunoreactivity of pERK1/2 in PSL-operated sciatic nerve was markedly increased in comparison with that in sham-operated sciatic nerve on Day 1 after PSL. In the sciatic nerve on Day 1 after PSL, as indicated by double immunostaining, the increased immunoreactivity of pERK1/2 was colocalized with glial fibrillary acidic protein (GFAP), a marker of Schwann cells, but not F4/80, a marker of macrophages. PSL-induced thermal hyperalgesia was significantly attenuated by treatment with U0126 on Days 3, 7, and 14 after PSL. The PSL-induced tactile allodynia was also significantly attenuated by treatment with U0126 on Days 7 and 14 after PSL.
  
  
  CONCLUSIONS
  Activation of ERK in Schwann cells of the injured peripheral nervous system may play an important role in the development of neuropathic pain. Our results suggest that pERK itself and ERK-related mediators are potential therapeutic targets for the treatment of neuropathic pain.
authors.affiliation: Department of Pharmacology, Wakayama Medical University, 811-1 Kimiidera, Wakayama City, Wakayama 641-0012, Japan.
authors.forename: Norikazu
authors.initials: N
authors.lastname: Kiguchi
authors.forename: Takehiko
authors.initials: T
authors.lastname: Maeda
authors.forename: Yuka
authors.initials: Y
authors.lastname: Kobayashi
authors.forename: Yohji
authors.initials: Y
authors.lastname: Fukazawa
authors.forename: Shiroh
authors.initials: S
authors.lastname: Kishioka
mesh_terms: D000700:Analgesics / Q000494:pharmacology; D000818:Animals; D001522:Behavior, Animal; D002070:Butadienes / Q000494:pharmacology; D004195:Disease Models, Animal; D004789:Enzyme Activation; D006930:Hyperalgesia / Q000201:enzymology / Q000209:etiology* / Q000503:physiopathology / Q000517:prevention & control; D008026:Ligation; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009570:Nitriles / Q000494:pharmacology; D010147:Pain Measurement; D017288:Pain Threshold; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D012583:Schwann Cells / Q000187:drug effects / Q000201:enzymology*; D012584:Sciatic Nerve / Q000187:drug effects / Q000201:enzymology* / Q000601:surgery; D020426:Sciatic Neuropathy / Q000150:complications / Q000188:drug therapy / Q000201:enzymology* / Q000503:physiopathology; D012585:Sciatica / Q000201:enzymology / Q000209:etiology* / Q000503:physiopathology / Q000517:prevention & control; D013997:Time Factors
chemical_list: D000700:Analgesics; D002070:Butadienes; D009570:Nitriles; D047428:Protein Kinase Inhibitors; C113580:U 0126; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3