title: Behavioral and neuropathological changes in animal models of chronic painful scar.
abstract: BACKGROUND
  Long-lasting limb pain or back pain after surgery occasionally develops into chronic pain that leads to lower activity and a poorer quality of life for many patients. To determine the histopathological and neuropathological mechanisms that cause persistent post-operative pain, we developed an original animal model with sustained painful scars and then examined pain-related behavior and the pathological alteration of peripheral tissues and spinal nerves associated with the model.
  
  
  METHODS
  The animal model (Scar group) was prepared in rats by extensively stripping subcutaneous tissue from the plantar in the hind paw followed by subsequent examination of pain-related behavior over the next 12 weeks. Thereafter, we conducted histological staining of the scar tissues, immunohistochemical staining of c-Fos (L5 dorsal horn), and electron microscopic analysis of the L5 spinal nerve fibers/dorsal roots.
  
  
  RESULTS
  The mechanical pain threshold decreased specifically in the ipsilateral plantar in animals with scar. This state was maintained for 12 weeks. A collagen layer developed from fibers derma to the muscular layer in the scar tissue in which many fibroblasts were observed. No statistical differences were found for the areas of the c-Fos-immunoreactive (c-Fos-IR) neurons in the ipsilateral and contralateral sides of the L5 level of the dorsal horn in both the Scar group and Pinhole (sham operation) group. However, myelin sheath fragmentation of the nerve fibers was observed in the ipsilateral dorsal root at the L5 position.
  
  
  CONCLUSIONS
  We created a persistent painful scar model through extensive injury of the peripheral tissues. Fibrotic thickening of the cutaneous tissues, possible sensitization, and partial degradation of the spinal nerve related to the painful scar were observed. This model should enable us to better understand the mechanism of sensitization caused by painful scar and investigate new methods for treating painful scars in humans.
authors: Multidisciplinary Pain Center, Aichi Medical University, Karimata, Yazako, Nagakute, Aichi, 480-1195, Japan.
authors: Yukihiro
authors: Y
authors: Kajita
authors: Katsutoshi
authors: K
authors: Suetomi
authors: Teruhiko
authors: T
authors: Okada
authors: Masahiko
authors: M
authors: Ikeuchi
authors: Young-Chang P
authors: YC
authors: Arai
authors: Keiji
authors: K
authors: Sato
authors: Takahiro
authors: T
authors: Ushida
mesh_terms: D000818:Animals; D001522:Behavior, Animal; D001707:Biopsy, Needle; D059350:Chronic Pain / Q000473:pathology; D002921:Cicatrix / Q000473:pathology*; D004195:Disease Models, Animal; D006930:Hyperalgesia / Q000473:pathology; D007150:Immunohistochemistry; D008297:Male; D008854:Microscopy, Electron; D009412:Nerve Fibers / Q000473:pathology / Q000648:ultrastructure; D010147:Pain Measurement; D017288:Pain Threshold / Q000502:physiology*; D010149:Postoperative Pain / Q000473:pathology*; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D012016:Reference Values; D012720:Severity of Illness Index; D018709:Statistics, Nonparametric
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