Spinal toll-like receptor 4-mediated signalling pathway contributes to visceral hypersensitivity induced by neonatal colonic irritation in rats

BackgroundAlthough visceral hypersensitivity is a major pathophysiological feature of irritable bowel syndrome (IBS), its underlying mechanisms remain elusive. Toll-like receptor 4 (TLR4) is a critical pattern recognition molecule of the innate immune system. In this study, we investigated whether the TLR4/myeloid differentiation factor 88 (MyD88)/nuclear factor-kappa B (NF-B) signalling pathway in the spinal cord contributed to the visceral hypersensitivity induced by neonatal colonic irritation (CI) in rats. MethodsThe Sprague-Dawley rat model of IBS was induced by colon irritation on post-natal day (PND) 8, PND10 and PND12. Experiments were conducted in adult rats. TLR4 mRNA and protein, and its downstream signalling molecules, MyD88, inhibitory nuclear factor-kappa B (IB) and NF-B protein expressions in L2-S4 spinal segments were detected by quantitative real-time reverse transcription-polymerase chain reaction as well as Western blotting. TLR4 co-localization was determined by immunohistochemistry. Levels of tumour necrosis factor-alpha (TNF-) and interleukin 1 (IL-1) were measured with enzyme-linked immunosorbent assay. ResultsWe found that neonatal CI treatment induced long-lasting visceral hypersensitivity without identifiable structural abnormalities in descending colons of adult rats. Neonatal CI treatment evoked a significant up-regulation of the expressions of TLR4 in glia, MyD88, p-IB- and NF-B in adult rats. Neonatal CI treatment also increased the levels of its downstream inflammatory agents TNF- and IL-1 in the L2-S4 regions of the spinal cord of adult rats. ConclusionsThese results suggest that neonatal CI stimulates the production of IL-1 and TNF- through the TLR4/MyD88/NF-B signalling pathway in the spinal cord, which contributed to visceral hypersensitivity induced by neonatal CI in rats.