Preferential neurogenesis of nitrergic neurons in the myenteric plexus of the DSS-induced colitis mouse colon causes colonic dysmotility in colitis.

The enteric nervous system (ENS) continues to be exposed to various disturbances throughout life, which causes apoptosis in the ENS. Therefore, it is assumed that neurogenesis is induced to maintain the neuronal network in the adult ENS. However, these underlying mechanisms are largely unknown. We aimed to investigate adult neurogenesis in the dextran sodium sulfate (DSS)-induced colitis mouse colon. Male C57BL/6N mice (12-wk-old) were administered 2% DSS in their drinking water for 8 days. After DSS treatment, cross-sections and longitudinal muscle and myenteric plexus preparations from the colon were used for immunohistochemistry. The segments of colons were mounted in organ baths and then exposed to a voltage-gated sodium channel activator veratridine. In the motility study, veratridine-induced colonic contractions were significantly suppressed in DSS-induced colitis mice compared with normal mice. Immunohistochemical analyses revealed that the proportion of nitrergic neurons per ganglion was significantly increased in the colons of DSS-induced colitis mice compared with normal mice. Furthermore, the proportion of Sox2 (new-born neuron marker)-positive neurons per ganglion was not significantly different between normal mice and DSS-induced colitis mice, whereas the proportion of Sox2-positive nitrergic neurons to Sox2-positive neurons per ganglion was significantly increased in the colons of DSS-induced colitis mice compared with normal mice. In addition, NOS inhibitor significantly enhanced veratridine-induced colonic contractions in DSS-induced colitis mice compared with normal mice. These findings suggested that colitis caused an imbalance in the enteric neural circuit composed of excitatory neurons and inhibitory neurons in the myenteric plexus of the colon, which resulted in colonic dysmotility. ENS continues to be exposed to various disturbances throughout life, which causes adult apoptosis in the ENS. In this study, the frequency of adult neurogenesis was not altered by colitis, whereas colitis selectively induced adult neurogenesis of nNOS-positive inhibitory motor neurons in the myenteric plexus of the colon by preferential adult neurogenesis, indicating that colitis caused an imbalance in the enteric neural circuit composed of excitatory neurons and inhibitory neurons, which resulted in colonic dysmotility.