The Roles Of COX-2 In The Glia Cell Acitvation Following Neuropathic Pain

ObjectiveGlial cells are immune cells involved in the immune response of the central nervous system.It has been reported that glial cells participate in the occurrence and development of neuropathic pain(NP).Cyclooxygenase-2(COX-2)is involved in the synthesis of Prostaglandins,and has long been thought to play key roles in inflammatory process.In order to explore the roles of COX-2 in th NP,the effect of COX-2 on the activation of glial cells was investigated in NP induced by SNL(spinal nerve ligation)model from ethology,morphology to molecular biology.MethodsForty male SD rats(180-220 g)were randomly assigned into four groups,including Normal control group(NC Group),Sham control group(SC Group),Spinal nerve ligation group(SNL Group),SNL+Parecoxib treatment group(SNL+PAR Group).L5 spinal nerve was ligated in SNL group and SNL+PAR group respectively,and L5 spinal nerve was separated but not ligated in SC group.Then The rats in PAR group received intrathecal injection of paroxib sodium saline solution(40 μg/μL)10 μL immediately after operation;SC group and SNL group were given normal saline 10μL,and NC group did not recive any treatment.Paw withdrawal threshold(PWT)was measured by von frey filaments before operation,day of operation,and day 1,3,7 after operation for Sham,SNL,and SNL+PAR group.The spinal expression of Iba-1 protein(specific marker for microglia)and GFAP protein(specific marker for astrocyte)were observed by immunohistochemistry on day 1、3、7 after operation for NC,SC,SNL and SNL+PAR groups.The expression of COX-2,Iba-1 and GFAP protein were detected with fresh spinal tissue by using Western blot on day 1,3 and 7 after operation for NC,SC,SNL and SNL+PAR groups.ResultsThere was no significant difference in PWT between each group before the establishment of SNL model,but on day after operation the PWT of SNL and PAR groups were shorter than group SC(P=0.00).When PAR group were intrathecal injected parecoxib sodium on the 3rd day after operation,the PWT was significantly higher than SNL group(P=0.00).And there was no difference between PAR and SC groups on the 7th day.In addition,it was observed by immunohistochemistry that the glial cells of spinal dorsal horn were activated rapidly after operation in SNL group compared with SC,but the activation of microglia and astrocyte were inhibited in PAR group after administration of paroxib sodium.Moreover,Western blot showed that the expression of Iba-1 protein in spinal cord increased and reached its peak level on 3 day after operation(P=0.0058;P=0.0057;P=0.0160).Then it decreased gradually.While the expression of GFAP protein increased slightly on first 3 days,it increased markedly to its peak on 7 days after operation(P=0.0109).At the same time,the expression of COX-2 protein was significantly up-regulated on the 1st day(P=0.0001;P=0.0004;P=0.0025),and it is also the highest.However,the expression of Iba-1,GFAP and COX-2 protein decreased significantly inSNL+PAR group(P=0.0099;P=0.0109;P=0.0042).ConclusionHyperalgesia induced by SNL in rats can be effectively relieved by intrathecal injection of parecoxib sodium.In the rats treated with SNL,the expression of COX-2 in spinal cord is related to the activation of microglia and astrocytes.The activation of microglia and astrocytes in SNL-induced NP could be significantly inhibited by intrathecal injection of parecoxib sodium,a COX-2 inhibitor.In conclusion,COX-2 may be involved in the occurrence and development of NP by activating microglia and astrocytes in spinal cord.