The Role Of Nf-kb In The Neuropathic Pain Induced By L5 Spinal Nerve Ligation

BackgroundCentral and peripheral nerve injury or inflammation often leads to neuropathic pain,which is characterized by hyperalgesia,allodynia and spontaneous pain. Although amount of studies have been performed in the past,the underlying mechanism still remain largely unknown.Recent studies indicate that Wallerian degeneration following nerve injury contributed to the development of neuropathic pain via production of cytokins.Among them,tumor necrosis factor-alpha(TNF-α) and interleukin-1(IL-1) appears to play an important role in the induction and maintenance of the neuropathic pain after nerve injury.Previous studies have also shown that the synthesis of these cytokines as well as their action to target cells need the activation of nuclear factor-kappa B(NF-kB) signal pathway.But,the role of NF-kB in the neuropathic pain is still short of a systemic data.ObjectiveIn the present study,we ligated the lumbar 5 spinal nerve(L5 SNL) to induce neuropathic pain,and then observed the role of NF-kB in the development of the neuropathic pain by intrathecal or intraperitoneal injection of PDTC,a potent inhibitor of NF-kB activation.To further confirm the activation of NF-kappa B and the cell type of the activated NF-kB in L5 and L4 dorsal root ganglia(DRG), immunohistochemistry and double immunofluorescence staining were also employed in this study. MethodsAdult male Sprague-Dawley(SD) rats are chosen in the present study.Firstly, using behavioral tests,we systemically observed the role of NF-kB in the development of the neuropathic pain by intrathecal or intraperitonea injection of different doses of PDTC(a potent inhibitor of NF-kB activation) in different time point befor or after L5 SNL.Then,using the methods of immunofluorescent staining,the activation of NF-kappa B in L5 and L4 dorsal root ganglia was examined in different time point after L5 SNL.To further confirm the cell type of the activated NF-kB,double immunofluorescence staining were also employed in this study.The methods of behavioral tests were performed as following:50%Mechanical paw withdrawal threshold are measured through Up-down method and thermal paw withdrawal latency are measured by hot-plate testor.We analyzed quantitively the activation of NF-kB through calculating the percentage of NF-kB-immunoreactivity (NF-kB-IR) positive staining cells in this study.Results1.The behavioral test indicated that L5 SNL could induce allodynia and hyperalgesia.We also found that intrathecal or intraperitoneal injection of PDTC (1ug/10ul or 100mg/kg).started at 0.5h before surgery and once daily for 7 days,could block the development of neuropathic pain induced by L5 SNL completely.Intrathecal injection of PDTC(1ug/10ul),started at 1d after surgery and once daily for 7 days,also blocked the formation of neuropathic pain.But injection of the same dose of PDTC,started at 7d after surgery and once daily for 7 days,had no effect on the stablished neuropathic pain.2.The results of immunohistochemistry revealed that of NF-kB-IR in ipsilateral L4 and L5 DRG was increased following L5 SNL.Compared with sham group,the percentage of NF-kB-IR positive staining cells after L5 SNL significantly incresed on day 1,reached a peak on day 3 and persisited for 2 weeks.Intrathecal injection of PDTC(1ug/10ul),started at 0.5h before surgery and once daily for 3 days,inhibited the activation of NF-kB.3.Double immunofluorescence staining revealed that the increased NF-kB-IR in DRG was in satellite-like glial cells.Conclusions1.L5 SNL induced neuropathic pain and led to NF-kB activation in satellite-like glia cell in ipsilateral L5 and L4 DRG.2.Intrathecal or intraperitoneal injection of PDTC started before surgery significantly alleviated the neuropathic pain induced by L5 SNL.3.Treatment with PDTC started 1 day after operation also reduced the neuropathic pain.But,PDTC treated-rats started at 7 days after L5 SNL had no effect on the established neuropathic pain.The data indicated that NF-kB activation might be involved in the induction but not in the maintenance of the neuropathic pain induced by L5 SNL.