title: Effect of superoxide on the development and maintenance of mechanical allodynia in a rat model of chronic post-ischemia pain.
abstract: BACKGROUND
  Reactive oxygen species and inflammatory responses contribute to the development of neuropathic pain. Superoxide serves to mediate cell signaling processes and tissue injury during inflammation. We examined the effects of superoxide on the development and maintenance of mechanical allodynia, as well as its contribution to central sensitization in a superoxide-rich animal model of neuropathic pain.
  
  
  METHODS
  Chronic post-ischemia pain (CPIP) was induced via the left hindpaw ischemia for 3 h, followed by reperfusion. Superoxide dismutase (4,000 U/kg, i.p.) was administered either 5 min before ischemia (BI), 5 min before reperfusion (BR), or 3 days after reperfusion (3AR). Withdrawal thresholds of the four paws were measured to assess the mechanical allodynia and the effects of circulating xanthine oxidase (XO)-mediated superoxide production. In addition, we measured the levels of N-methyl D-aspartate receptor subunit 1 phosphorylation (p-NR1) in the ipsilateral and contralateral spinal cord (L4-6), by Western blotting, to examine the superoxide-mediated central sensitization. Superoxide production was assessed by allopurinol-sensitive, XO-mediated lipid peroxidation of the spinal cord and gastrocnemius muscles.
  
  
  RESULTS
  Withdrawal thresholds of forepaws did not vary across the 7 days of testing. In the hindpaws, both ipsilateral and contralateral mechanical allodynia was most attenuated in the BR group, followed by the BI and 3AR groups. The degree of NR1 activation was in contrast to the changes in the withdrawal thresholds.
  
  
  CONCLUSIONS
  These data suggest that superoxide is involved in the development and maintenance of mechanical allodynia, particularly via central sensitization in the spinal cord.
authors.affiliation: Department of Anesthesiology and Pain Medicine, School of Medicine, Kyungpook National University, Daegu, Korea.
authors.forename: Chang Gyu
authors.initials: CG
authors.lastname: Han
authors.forename: Jae Kyung
authors.initials: JK
authors.lastname: Han
authors.forename: Ki Bum
authors.initials: KB
authors.lastname: Park
authors.forename: Kyung Hwa
authors.initials: KH
authors.lastname: Kwak
authors.forename: Sung Sik
authors.initials: SS
authors.lastname: Park
authors.forename: Dong Gun
authors.initials: DG
authors.lastname: Lim