Objective To investigate the role of microglial activation in spinal cord in a rat model of persistent postoperative pain evoked by skin/muscle incision and retraction (SMIR) .Methods Seventy-two male SD rats weighing 200-250 g in which intrathecal (IT) catheter was successfully inserted were randomly divided into 3 groups ( n = 24 each) : group sham operation; group SMIR and group SMIR + FT minocycline (a specific microglia inhibitor) . The rat model of persistent postoperative pain evoked by SMIR was established according to the method described by Flatters. Pain behavior was assessed by paw mechanical withdrawal threshold ( MWT) to von Frey filament stimulation at 1 day before (T0,baseline) and 3, 7, 12, 22 and 32 days after operation (T1-5,) . Four animals were sacrificed at each time point in each group for detection of the expression of Iba-1 (a specific marker of microglia) in the spinal dorsal horn by immunofluorescence and the microglia was counted. Results MWT was significantly decreasedat T1-4, while the expression of Iba-1 and microglia counts in the spinal dorsal horn were significantly increased at T1, 2 by SMIR in group Ⅱ. IT minocycline significantly attenuated the hyperalgesia induced by SMIR at T1-4 and decreased Iba-1 expression and microglia counts at T1,2 in group Ⅲ. Conclusion Microglial activation in the spinal cord plays an important role in the development and maintenance of SMIR-evoked persistent postoperative pain in rats.

ObjectiveTo investigate the role of NF-κB signaling pathway in the spinal cord in persistent postoperative pain evoked by skin/muscle incision and retraction (SMIR) in rats.MethodsNinety male SD rats weighing 200-250 g in which intrathecal (IT) catheter was successfully implanted without complication were randomly divided into 3 groups ( n =30 each):group sham operation ( group S ) ; groups SMIR and group pyrrolidine dithiocarbarnate (a NF-κB inhibitor) (group PDTC).Persistent postoperative pain was evoked by SMIR according to the method described by Flatters in groups SMIR and PDTC.PDTC 10 ng in 10 μl was injected IT over 30 s once a day for 7 consecutive days after operation in group PDTC.Mechanical paw withdrawal threshold to von Frey filament stimulation (MWT) was measured at 1 d before (T0,baseline) and 1,3,7,12 and 22 d after surgery (T1-5).Five animals in each group were sacrificed at each time point after MWT measurement and their lumbar segments of the spinal cord were removed for determination of TNF-α content (by ELISA).ResultsSMIR significantly decreased MWT after operation at T1-5 and increased TNF-α content in the spinal cord at T3-5.PDTC significantly attenuated SMIR-induced hyperalgesia and increase in TNF-α content in the spinal cord.Conclusion NF-κB signaling pathway in the spinal cord plays an important role in the development of SMIR-induced persistent postoperafive pain in rats.