title: Sex differences in the development of localized and spread mechanical hypersensitivity in rats after injury to the infraorbital or sciatic nerves to create a model for neuropathic pain.
abstract: BACKGROUND
  Neuropathic pain after injury to the nervous system is a difficult clinical problem. Sex differences in the development of neuropathic pain have not been well established experimentally or clinically.
  
  
  OBJECTIVE
  Rats were used to examine sex differences in localized and spread mechanical hypersensitivity after partial injury to their infraorbital or sciatic nerves in a model of neuropathic pain.
  
  
  METHODS
  In adult female and male rats, partial nerve injury to the infraorbital and sciatic nerves was produced using a photochemical method. Mechanical hypersensitivity (allodynia) was examined and compared in the innervation territories of the nerves on the face or hind paw. The spread of hypersensitivity beyond the innervation territories of the injured nerves was also studied. The female and male rats were randomized to active and sham groups. The rats in the sham group had their sciatic or infraorbital nerve exposed, but not injured.
  
  
  RESULTS
  A total of 67 rats (36 females, 31 males) were used. There was a marked sex difference in the response to infraorbital nerve injury: female rats developed more profound and long-lasting facial hypersensitivity than did male rats (P<0.001). Hypersensitivity of the hind paw after sciatic nerve injury did not, however, significantly differ between female and male rats. Spread mechanical hypersensitivity was noted in body areas outside the innervation territory of the injured nerve. This hypersensitivity was more profound after infraorbital than sciatic nerve injury and also displayed a significant sex difference (female>male, P < 0.001). Sham-group rats did not exhibit localized or spread mechanical hypersensitivity.
  
  
  CONCLUSIONS
  Sex differences in the development of neuropathic painlike behaviors in rats were dependent on site of injury and site of testing, with female rats being more susceptible to the development of spread mechanical hypersensitivity, particularly after facial nerve injury, compared with male rats.
authors.affiliation: Section of Clinical Neurophysiology, Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Cecilia A
authors.initials: CA
authors.lastname: Dominguez
authors.forename: Poli Francois
authors.initials: PF
authors.lastname: Kouya
authors.forename: Wei-Ping
authors.initials: WP
authors.lastname: Wu
authors.forename: Jing-Xia
authors.initials: JX
authors.lastname: Hao
authors.forename: Xiao-Jun
authors.initials: XJ
authors.lastname: Xu
authors.forename: Zsuzsanna
authors.initials: Z
authors.lastname: Wiesenfeld-Hallin
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D020209:Cranial Nerve Injuries / Q000209:etiology*; D005157:Facial Pain / Q000503:physiopathology*; D005260:Female; D006967:Hypersensitivity / Q000209:etiology*; D008297:Male; D008962:Models, Theoretical; D051381:Rats; D012584:Sciatic Nerve / Q000293:injuries*; D020426:Sciatic Neuropathy / Q000209:etiology; D012733:Sex Differentiation; D012737:Sex Factors; D014277:Trigeminal Neuralgia / Q000503:physiopathology*