Mechanism of mitigation of neuropathic pain by spinal cord stimulation in rats: the relationship with HMGB1/TLR4/NF-κB signaling pathway in the spinal cord

Objective To investigate the relationship between the mechanism of mitigation of neuropathic pain by spinal cord stimulation (SCS) and high mobility group protein box-1 (HMGB1)/Toll-like receptor 4 (TLR4)/NF-κB signaling pathway in the spinal cord of rats.Methods Forty-eight male Sprague-Dawley rats,aged 8 weeks,weighing 250-300 g,were randomly divided into 4 groups (n =12 each) using a random number table:sham operation group (S group),chronic constrictive injury (CCI) group,sham SCS group (S-SCS group),and SCS group.Neuropathic pain was induced by CCI in the animals anesthetized with intraperitoneal chloral hydrate.The sciatic nerve was exposed and 4 loose ligatures were placed on the sciatic nerve at 1 mm intervals with 4-0 silk thread.Electrodes were placed into the epidural space at 5 days after CCI in S-SCS and SCS groups,and in addition SCS was performed at 12-14 days after CCI in SCS group.Paw withdrawal threshold to mechanical stimulation (MWT) were measured at 1 day before operation and 1,4,7,14 days after CCI.After measurement of pain threshold at day 14 after CCI,the animals were sacrificed and the lumbar segments (L4-6) of the spinal cord were obtained for determination of mRNA expression of HMGB1,TLR4,and NF-κB p65 (in the nuclear protein,by real-time fluorescent quantitative PCR),protein expression of TLR4 and NF-κBp65 (by Western blot),and protein expression of HMGB1 (by immunohistochemistry).Results Compared with S group,MWT was significantly decreased after CCI,the mRNA and protein expression of HMGB1 and TLR4 was up-regulated,and the expression of NF-κB p65in the nuclear protein and mRNA was up-regulated in CCI,S-SCS and SCS groups.Compared with CCI group,MWT was significantly increased after spinal cord stimulation,the mRNA and protein expression of HMGB1 and TLR4 was down-regulated,and the expression of NF-κB p65 in the nuclear protein and mRNA was down-regulated in SCS group.Conclusion The mechanism by which SCS mitigates neuropathic pain may be related to inhibition of HMGB1/TLR4/NF-κB signaling pathway in the spinal cord of rats. Key words: Electric stimulation;  Neuralgia;  Spinal cord;  High mobility group proteins;  Toll-like receptor 4;  NF-kappaB