Neonatal colonic inflammation sensitizes voltage-gated Na+ channels via upregulation of cystathionine beta-synthetase expression in rat primary sensory neurons

The pathogenesis of pain in irritable bowel syndrome (IBS) is poorly understood, and treatment remains difficult. We have previously reported that colon-specific dorsal root ganglion (DRG) neurons were hyperactive in a rat model of IBS induced by neonatal colonic inflammation (NCI). This study was designed to examine plasticity of voltage-gated Na+ channel activities and roles for the endogenous hydrogen sulfide-producing enzyme cystathionine beta-synthetase (CBS) in chronic visceral hyperalgesia. Abdominal withdrawal reflex (AWR) scores were recorded in response to graded colorectal distention in adult male rats as a measure of visceral hypersensitivity. Colon-specific DRG neurons were labeled with 1,1'-dioleyl-3,3,3', 3-tetramethylindocarbocyanine methanesulfonate and acutely dissociated for measuring Na+ channel currents. Western blot analysis was employed to detect changes in expressions of voltage-gated Na+ (Na-V) channel subtype 1.7, Na(V)1.8, and CBS. NCI significantly increased AWR scores when compared with age-matched controls. NCI also led to an similar to 2.5-fold increase in Na+ current density in colon-specific DRG neurons. Furthermore, NCI dramatically enhanced expression of Na(V)1.7, Na(V)1.8, and CBS in colon-related DRGs. CBS was colocalized with Na(V)1.7 or -1.8 in colon-specific DRG neurons. Administration of O-(carboxymethyl)-hydroxylamine hemihydrochloride (AOAA), an inhibitor for CBS, remarkably suppressed Na+ current density and reduced expression of Na(V)1.7 and Na(V)1.8. More importantly, intraperitoneal or intrathecal application of AOAA attenuated AWR scores in NCI rats in a dose-dependent manner. These data suggest that NCI enhances Na+ channel activity of colon DRG neurons, which is most likely mediated by upregulation of CBS expression, thus identifying a potential target for treatment for chronic visceral pain in patients with IBS.