Upregulation Of Cystathionine-β-synthetase Expression Contributes To Inflammatory Pain In Rat Temporomandibular Joint

Background: Hydrogen sulfide (H2S), an endogenous gaseotransmitter/modulator,is becoming appreciated that it may be involved in a wide variety of processes includinginflammation and nociception. However, the role for H2S in nociceptive processing intrigeminal ganglion (TG) neuron remains unknown. The aim of this study was designedto investigate whether endogenous H2S synthesizing enzyme cystathionine-β-synthetase(CBS) plays a role in inflammatory pain in temporomandibular joint (TMJ) and theunderlying mechanisms.Methods: TMJ inflammatory pain was induced by injection of complete Freund’sadjuvant (CFA) into TMJ of adult male rats. Von Frey filaments were used to examinepain behavioral responses in rats following injection of CFA or normal saline (NS).Trigeminal ganglia (TG) neurons innervating the TMJ were labeled by injection of DiI(1,1’-dioleyl-3,3,3’,3-tetramethylindocarbocyanine methanesulfonate) into the TMJ.Whole cell patch clamp recording techniques were employed to examine excitability,potassium channel currents and ATP currents of TMJ specific TG neurons. Western Blotanalysis was carried out to measure protein expression in TGs. Immunohistochemicalanalysis was employed to determine whether CBS was co-expressed in P2X3-positiveTG neurons.Results:(1) Two days after injection of CFA into TMJ capsule, escape thresholdfor mechanical stimulation in TMJ-infamed rats was remarkably lower than that incontrol rats.(2) In rat TG neurons, CBS was co-expressed in P2X3-positive TG neurons.(3) CBS expression in TGs in rats with TMJ inflammation was greatly enhanced. CFAinjection also markedly upregulated P2X3receptor expression.(4) The excitability ofTG neurons from rats with TMJ inflammation was increased, mainly featured as decreased rhobase and increased repetitive discharge frequency. In addition,ATP-evoked current density was also remarkably increased in CFA injected rats whencompared with that in control rats.(5) The reduced escape threshold was partiallyreversed by injection of O-(Carboxymethyl) hydroxylamine hemihydrochloride(AOAA), an inhibitor for CBS, in a dose-dependent manner.(6) Application of AOAAin TMJ reversed enhanced neural hyperexcitability of TG neurons, and also reversedmean peak current density of ATP currents.(7) NaHS, a donor of H2S, produced asignificant reduction of escape threshold in a dose dependent manner.Conclusion: These data together with our previous report indicate that TMJinflammation may be mediated by upregulation of CBS and P2X3receptor expression inTGs. This and future researches would shed light on identifying a potential therapeutictarget for the treatment of inflammatory pain in temporomandibular joint.