Sensitization Of P2X3 Receptors By Cystathionine β-synthetase Contributes To Persistent Pain Hypersensitivity In A Rat Model Of Lumbar Disc Herniation

Objective: Lumbar disc herniation(LDH) is a major cause of discogenic low back pain and sciatica, but the underlying mechanisms remain largely unknown. Hydrogen sulfide(H2S) is becoming appreciated that it may be involved in a wide variety of processes including inflammation and nociception. The present study was designed to investigate roles for H2 S signal pathway in regulation of expression and function of purinergic receptors(P2XRs) in dorsal root ganglion(DRG) neurons from rats with LDH.Methods: LDH was induced by implantation of autologous nucleus pulposus(NP) harvested from rat tail to lumbar 5 and 6 spinal nerve roots. Mechanical pain withdrawal threshold and body weight bearing difference of the rat hindpaw were determined. P2XR-mediated responses of L5-6 DRG neurons were measured using calcium-imaging techniques. Western blotting analysis was carried out to measure protein expression in L5-6 DRGs.Results: Implantation of autologous NP induced persistent pain hypersensitivity, which was partially reversed by intrathecal injection of A317491, a potent inhibitor for P2X3 and P2X2/3 receptors. The NP induced persistent pain hypersensitivity was associated with increased expression of P2X3 but not P2X1 and P2X2 receptors in L5-6 DRGs. NP implantation also produced a 2-fold increase in ATP-induced intracellular calcium signals of DRG neurons when compared with those of controls(P<0.05). Interestingly, NP implantation significantly enhanced expression of the endogenous hydrogen sulfide producing enzyme cystathionine-synthetase(CBS). Systematic administration of O-(Carboxymethyl) hydroxylamine hemihydrochloride(AOAA), an inhibitor for CBS, suppressed the upregulation of P2X3 receptor expression and the potentiation of ATP-induced intracellular calcium signals of DRG neurons(P<0.05). Intrathecal injection of AOAA markedly attenuated NP induced persistent pain hypersensitivity.Conclusion: Our results suggest that sensitization of P2X3 receptors, which was likely mediated by CBS-H2 S signaling in primary sensory neurons, contributes to discogenic pain. Targeting CBS-H2S-P2X3 receptor signaling may represent a potential treatment for neuropathic pain caused by LDH.