Spinal microglial expression and mechanical hypersensitivity in a postoperative pain model: comparison with a neuropathic pain model.
BACKGROUND
Postoperative pain control contributes to quality of life. Activation of spinal cord microglia after peripheral nerve injury contributes to mechanical hypersensitivity. The contribution of spinal cord microglia to hypersensitivity after surgery, however, is not well understood. Here, the authors evaluated whether inhibition of spinal microglia reduced postoperative mechanical hypersensitivity, and if so, whether the effect differed from that in a rat neuropathic pain model.


METHODS
Male Sprague-Dawley rats underwent either unilateral plantar hind paw incision (postoperative pain model) or L5 spinal nerve transection (neuropathic pain model), and the development of mechanical hypersensitivity was assessed using von Frey filaments. The microglial inhibitor minocycline was intraperitoneally administered daily for either 3 or 7 days. Spinal microglial activation was evaluated by OX42 immunohistochemistry. We also tested the effect of intrathecal administration of a p38 mitogen-activated protein kinase inhibitor, SB203580.


RESULTS
In the postoperative pain model, minocycline did not suppress mechanical hypersensitivity, but did inhibit an increase in spinal OX42 expression. In contrast, in the neuropathic pain model, minocycline reduced mechanical hypersensitivity in a dose-related manner and inhibited spinal OX42 expression. SB203580 attenuated hypersensitivity in the neuropathic pain model, but not in the postoperative pain model.


CONCLUSIONS
The results of the present study suggest that spinal OX42 expression has a more important role in the development of neuropathic pain than in postoperative pain, and that an increase in spinal OX42 expression does not contribute to postoperative mechanical hypersensitivity.
Ito
Naomi
N
Department of Anesthesiology, Gunma University Graduate School of Medicine, Showa, Maebashi, Gunma, Japan.
Obata
Hideaki
H
Saito
Shigeru
S
D000818:Animals; D000900:Anti-Bacterial Agents; D001522:Behavior, Animal / Q000187:drug effects; D039481:CD11b Antigen / Q000276:immunology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005455:Fluorescent Antibody Technique; D006930:Hyperalgesia / Q000473:pathology*; D007093:Imidazoles / Q000494:pharmacology; D007150:Immunohistochemistry; D008297:Male; D017628:Microglia / Q000473:pathology*; D008911:Minocycline; D010146:Pain / Q000209:etiology / Q000473:pathology*; D010149:Postoperative Pain / Q000473:pathology*; D010523:Peripheral Nervous System Diseases / Q000150:complications / Q000473:pathology*; D011725:Pyridines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013116:Spinal Cord / Q000473:pathology*; D013127:Spinal Nerves / Q000473:pathology; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism
D000900:Anti-Bacterial Agents; D039481:CD11b Antigen; D004791:Enzyme Inhibitors; D007093:Imidazoles; D011725:Pyridines; D048051:p38 Mitogen-Activated Protein Kinases; D008911:Minocycline; C093642:SB 203580