Persistent alterations to enteric neural signalling in guinea pig colon following resolution of colitis

Running title: Persistent alterations in colonic function after colitis. Abstract Functional changes induced by inflammation persist following recovery from the inflammatory response, but the mechanisms underlying these changes are not well understood. Our aim was to investigate whether the excitability and synaptic properties of submucosal neurons remained altered eight weeks post trinitrobenzene sulphonic acid (TNBS) treatment, and to determine whether these changes were accompanied by alterations in secretory function in submucosal preparations voltage clamped in Ussing chambers. Mucosal serotonin (5-HT) release measurements and serotonin reuptake transporter (SERT) immunohistochemistry were also performed. Eight weeks after TNBS treatment, colonic inflammation resolved, as assessed macroscopically and by myeloperoxidase assay. However, fast excitatory post synaptic potential (fEPSP) amplitude was significantly increased in submucosal S neurons from previously inflamed colons relative to those in control tissue. In addition, fEPSPs from previously inflamed colons had a hexamethonium-insensitive component that was not evident in age-matched controls. AH-neurons were hyperexcitable, had shorter action potential durations, and a decreased afterhyperpolarisation eight weeks following TNBS adminstration. Neuronally-mediated colonic secretory function was significantly reduced after TNBS treatment, although epithelial cell signalling, as measured by responsiveness to both forskolin and bethanecol in the presence of tetrodotoxin, was comparable to control tissue. 5-HT levels and SERT immunoreactivity were comparable to controls eight weeks after the induction of inflammation, but there was an increase in GLP-2 immunoreactive L cells. In conclusion, sustained alterations in enteric neural signalling occur following the resolution of colitis, which are accompanied by functional changes in the absence of active inflammation.