Morphological and Functional Alterations of the Myenteric Plexus in Rats with TNBS-Induced Colitis

The 2,4,6-trinitrobenzenesulfonic acid (TNBS)-induced model of experimental colitis was used to investigate the time-course of alterations in enteric neurotransmission and/or smooth muscle function that occur in chronic inflammation. Myenteric plexus morphology (immunocytochemical markers), functional integrity of cholinergic neurons (3H-choline uptake, acetylcholine release and contractile response to electrical field stimulation) and smooth muscle integrity (contractile response to exogenous acetylcholine) were determined 2, 7, 15, and 30 days after TNBS treatment. In TNBS-treated rats extensive ulcerations of the mucosa and/or the submucosa and increase in colonic weights were accompanied by significant reduction in 3H-choline uptake, acetylcholine release and contractile response to stimulation of enteric nerves. These changes were maximal 7 and 15 days after TNBS treatment. Immunocytochemical marker (PGP 9.5, SNAP 25, synaptophysin and S100 protein) expression was absent in necrotic areas of colons removed 7 days post-injury and partially reduced in colons removed 15 days after TNBS treatment. By contrast, the contractile response to exogenous acetylcholine was significantly increased after 7 days in both inflamed and uninflamed regions and returned to control values by day 30. Likewise, an almost complete recovery of neural cholinergic function and of myenteric plexus morphology was observed 30 days after TNBS treatment. These data suggest that TNBS-induced colitis is associated with progressive and selective alterations in myenteric plexus structure and function, with consequent reduction of cholinergic neurotransmission and abnormality in colonic contractility. The reversibility of myenteric plexus disruption is a clear indication of neuronal plasticity within enteric nervous system as an adaptative mechanism against inflammatory challenges.