title: Peripheral neuropathy induces cutaneous hypersensitivity in chronically spinalized rats.
abstract: OBJECTIVE
  The present study was aimed at the issue of whether peripheral nerve injury-induced chronic pain is maintained by supraspinal structures governing descending facilitation to the spinal dorsal horn, or whether altered peripheral nociceptive mechanisms sustain central hyperexcitability and, in turn, neuropathic pain. We examined this question by determining the contribution of peripheral/spinal mechanisms, isolated from supraspinal influence(s), in cutaneous hypersensitivity in an animal model of peripheral neuropathy.
  
  
  METHODS
  Adult rats were spinalized at T8-T9; 8 days later, peripheral neuropathy was induced by implanting a 2-mm polyethylene cuff around the left sciatic nerve. Hind paw withdrawal responses to mechanical or thermal plantar stimulation were evaluated using von Frey filaments or a heat lamp, respectively.
  
  
  RESULTS
  Spinalized rats without cuff implantation exhibited a moderate decrease in mechanical withdrawal threshold on ~day 10 (P < 0.05) and in thermal withdrawal threshold on ~day 18 (P < 0.05). However, cuff-implanted spinalized rats developed a more rapid and significant decrease in mechanical (~day 4; P < 0.001) and thermal (~day 10; P < 0.05) withdrawal thresholds that remained significantly decreased through the duration of the study.
  
  
  CONCLUSIONS
  Our findings demonstrate an aberrant peripheral/spinal mechanism that induces and maintains thermal and to a greater degree tactile cutaneous hypersensitivity in the cuff model of neuropathic pain, and raise the prospect that altered peripheral/spinal nociceptive mechanisms in humans with peripheral neuropathy may have a pathologically relevant role in both inducing and sustaining neuropathic pain.
authors.affiliation: Departments of Physiology and Psychiatry, McGill University, Montreal, Quebec, Canada. graham.pitcher@utoronto.ca
authors.forename: Graham M
authors.initials: GM
authors.lastname: Pitcher
authors.forename: Jennifer
authors.initials: J
authors.lastname: Ritchie
authors.forename: James L
authors.initials: JL
authors.lastname: Henry
mesh_terms: D000818:Animals; D003655:Decerebrate State / Q000503:physiopathology*; D006614:Hindlimb / Q000502:physiology; D006358:Hot Temperature; D008297:Male; D009437:Neuralgia / Q000503:physiopathology*; D010147:Pain Measurement; D017288:Pain Threshold; D010523:Peripheral Nervous System Diseases / Q000503:physiopathology*; D010812:Physical Stimulation; D051381:Rats; D017207:Rats, Sprague-Dawley; D020426:Sciatic Neuropathy / Q000209:etiology / Q000503:physiopathology
keywords: Central Sensitization; Dorsal Horn; Mechanical Hypersensitivity; Neuropathic Pain; Peripheral Neuropathy; Primary Afferent; Spinal Cord; Spinal Transection; Supraspinal; Tactile Hypersensitivity