title: Spinal microglia initiate and maintain hyperalgesia in a rat model of chronic pancreatitis.
abstract: OBJECTIVE
  The chronic, persistent pain associated with chronic pancreatitis (CP) has many characteristics of neuropathic pain, initiated and maintained by the activation of spinal microglia. We investigated whether activated microglia in the thoracic spinal cord contribute to chronic pain in a rat model of CP.
  
  
  METHODS
  CP was induced in Sprague-Dawley rats by an intraductal injection of 2% trinitrobenzene sulfonic acid. Hyperalgesia was assessed by the measurement of mechanical sensitivity of the abdomen and nocifensive behavior to electrical stimulation of the pancreas. Three weeks after induction of CP, spinal samples were analyzed by immunostaining and immunoblot analyses for levels of CD11 (a marker of microglia, determined with the antibody OX42) and phosphorylated p38 (P-p38, a marker of activation of p38 mitogen-activated protein kinase signaling). We examined the effects of minocycline (inhibitor of microglia) and fractalkine (microglia-activating factor) on visceral hyperalgesia in rats with CP.
  
  
  RESULTS
  Rats with CP had increased sensitivity and nociceptive behaviors to mechanical probing of the abdomen and electrical stimulation of the pancreas. The dorsal horn of the thoracic spinal cords of rats with CP contained activated microglia (based on increased staining with OX42), with an ameboid appearance. Levels of P-p38 increased in rats with CP and colocalized with OX42-positive cells. Intrathecal injection of minocycline reversed and prevented the increase of nocifensive behaviors and levels of P-p38 in rats with CP. Fractalkine induced hyperalgesia in rats without CP, which was blocked by minocycline.
  
  
  CONCLUSIONS
  Activated spinal microglia have important roles in maintaining and initiating chronic pain in a rat model of CP. Microglia might be a target for treatment of hyperalgesia caused by pancreatic inflammation.
authors.affiliation: Institute of Brain Science, National Yang-Ming University, Taipei, Taiwan.
authors.forename: Pei-Yi
authors.initials: PY
authors.lastname: Liu
authors.forename: Ching-Liang
authors.initials: CL
authors.lastname: Lu
authors.forename: Chia-Chuan
authors.initials: CC
authors.lastname: Wang
authors.forename: I-Hui
authors.initials: IH
authors.lastname: Lee
authors.forename: Jen-Chuen
authors.initials: JC
authors.lastname: Hsieh
authors.forename: Chun-Chia
authors.initials: CC
authors.lastname: Chen
authors.forename: Hsing-Feng
authors.initials: HF
authors.lastname: Lee
authors.forename: Han-Chieh
authors.initials: HC
authors.lastname: Lin
authors.forename: Full-Young
authors.initials: FY
authors.lastname: Chang
authors.forename: Shou-Dong
authors.initials: SD
authors.lastname: Lee
mesh_terms: D000818:Animals; D015153:Blotting, Western; D018845:CD11 Antigens / Q000378:metabolism; D054428:Chemokine CX3CL1 / Q000494:pharmacology; D004195:Disease Models, Animal; D004789:Enzyme Activation; D006930:Hyperalgesia / Q000209:etiology* / Q000378:metabolism / Q000503:physiopathology / Q000517:prevention & control; D007150:Immunohistochemistry; D008297:Male; D017628:Microglia / Q000187:drug effects / Q000378:metabolism; D008911:Minocycline / Q000494:pharmacology; D010147:Pain Measurement; D017288:Pain Threshold / Q000187:drug effects; D050500:Pancreatitis, Chronic / Q000139:chemically induced / Q000150:complications* / Q000188:drug therapy / Q000378:metabolism / Q000503:physiopathology; D010766:Phosphorylation; D051381:Rats; D017207:Rats, Sprague-Dawley; D013116:Spinal Cord / Q000187:drug effects / Q000378:metabolism / Q000503:physiopathology*; D013904:Thoracic Vertebrae; D013997:Time Factors; D014302:Trinitrobenzenesulfonic Acid; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D018845:CD11 Antigens; D054428:Chemokine CX3CL1; D014302:Trinitrobenzenesulfonic Acid; D048051:p38 Mitogen-Activated Protein Kinases; D008911:Minocycline