Role of p38 mitogen-activated protein kinase in spinal cord in development of persistent postoperative pain in rats: the relationship with Toll-like receptor 4 / 中华麻醉学杂志

ABSTRACT

Objective To evaluate the role of p38 mitogen-activated protein kinase (p38MAPK) in the spinal cord in the development of persistent postoperative pain evoked by skin/muscle incision and retraction (SMIR) and the relationship with Toll-like receptor 4 (TLR4).Methods One hundred and twenty male SpragueDawley rats,weighing 200-250 g,aged 2 months,in which intrathecal catheters were successfully implanted,were randomly divided into 5 groups (n =24 each) using a random number tablesham operation group (group S),SMIR group,SMIR + dimethyl sulfoxide (DMSO) group (group DMSO),SMIR + p38MAPK inhibitor SB203580 group (group SB203580) and SMIR + TLR4 small interference RNA (siRNA) group (group TLR4siRNA).The rats were anesthetized with intraperitoneal chloral hydrate 400 mg/kg.The skin and superficial muscle of the medial thigh were incised and a small pair of retractors inserted.This tissue was retracted for 1 h causing potential stretch of the saphenous nerve.2％ DMSO 10 μl and SB203580 5 μg were injected intrathecally at 30 min before operation and 1-12 days after operation in DMSO and SB203580 groups,respectively.TLR4siRNA 2 μg was administered intrathecally at 1 day before operation and 1-12 days after operation once a day in group TLR4siRNA.Mechanical paw withdrawal threshold to von Frey filament stimulation (MWT) was measured at 1 day before operation and 1,3,7,12 and 22 days after operation.Four rats in each group were sacrificed after measurement of MWT at each time point,and the L4-6 segments of the spinal cord were obtained for detection of the expression of phosphorylated p38MAPK (p-p38MAPK) by Western blot analysis.Results Compared with group S,MWT was significantly decreased after operation,and the expression of p-p38MAPK was up-regulated after operation in SMIR and DMSO groups.Compared with group SMIR,MWT was significantly increased after operation,and the expression of p-p38MAPK was down-regulated after operation in SB203580 and TLR4siRNA groups,and no significant changes in MWT and p-p38MAPK expression were found at each time point in group DMSO.Conclusion TLR4-triggered activation of p38MAPK in spinal cord is involved in the development of SMIR-evoked persistent postoperative pain in rats.