The Mechanism Of Lipopolysaccharide Upregulating Trigeminal Ganglionic Sodium Channel 1.7 Expression In Temporomandibular Joint Inflammatory Pain In Rats

Objective: To investigate whether and how lipopolysaccharide(LPS)can upregulate the expression of sodium channel 1.7(Nav1.7)in trigeminal ganglion(TG),and then participate in temporomandibular joint(TMJ)inflammatory pain in rats;To investigate the effect and mechanism of LPS regulating the expression of Nav1.7 in TG on TMJ inflammatory pain in rats.Methods: Through microinjecting LPS into the TG in adult male Sprague-Dawley(SD)rats,we observed the rats’ head withdrawal threshold.Western blot and Real-time quantitative PCR(Real-time PCR,q PCR)were used to detect the expression of Nav1.7protein and m RNA in TG.After culturing rats’ TG explants in vitro,we treated rats TG explants with LPS of 1ug/m L for 24 h.Western blot and Real-time PCR were used to detect the expression of GFAP,Nav1.7 protein and m RNA in TG.After the combined application of LPS and SGC activation inhibitor fluorocitrate(FC),the expressions of Nav1.7,GFAP and p-p65 protein and m RNA in TG in vitro were detected by Western blot and Real-time PCR.After the combined application of LPS and NF-κB inhibitor pyrrolidine dithiocarbamate(PDTC),the expression of Nav1.7,GFAP and p-p65 m RNA and protein in TG was detected by Real-time PCR and Western blot.Data were collected using SPSS 22.0 software package.Results: After microinjection of LPS into the trigeminal ganglion of living rats for24 h,the results of Western blot and Real-time PCR showed that the protein and m RNA expressions of Nav1.7 in TG were obviously increased in TG.The threshold test of the swinging head in rats showed that the TMJ area was hyperalgesia,and the threshold of swing head in temporomandibular joint area was obviously declined.We cultured the adult male SD rats’ TG in vitro.and LPS of 1ug/m L was applied for 24 h.The results of Western blot and Real-time PCR showed that the protein and m RNA expressions of GFAP and Nav1.7 in TG were obviously increased after TG was treated with LPS of1ug/m L for 24 h.After the combined application of LPS and SGC activation inhibitor FC,the results of Real-time PCR and Western blot showed that the SGC activation inhibitor FC blocked LPS-induced upregulation of the m RNA and protein expressions of Nav1.7,GFAP and p-p65 in TG.After the combined application of LPS and NF-κB inhibitor PDTC,the results of Real-time PCR and Western blot showed that NF-κB inhibitor PDTC blocked LPS-induced upregulation of the m RNA and protein expressions of Nav1.7,GFAP and p-p65 in TG.Conclusion: LPS upregulates the expression of Nav1.7 through the NF-κB signaling pathway(p-p65)activating satellite glial cells(SGC)of trigeminal ganglion,and then participates in TMJ inflammatory pain in rats.Main conclusion:(1)Intra-articular injection of LPS upregulated Nav1.7 expressions and induced the TMJ region hyperalgesia.(2)LPS upregulated expression of Nav1.7 in trigeminal ganglion.(3)LPS can activate SGC in trigeminal ganglion,and then upregulate the expression of Nav1.7 in neurons.(4)NF-κB inhibitor PDTC blocked LPS-activated SGC in TG,and then blocked LPS-induced upregulation of Nav1.7 expressions in neurons.