Effects of colonic insufflation with CO gas on histological findings in the colon 7 days after trinitrobenzene sulfonic acid (TNBS)-induced injury. Histological appearance of colonic tissue in sham-operated rats (A), rats with TNBS-induced colitis (B), and rats with TNBS-induced colitis treated with colonic insufflation of CO gas (C). Histological examination revealed that TNBS administration induced marked thickening of the colonic wall and colonic ulceration, which was associated with transmural infiltration of inflammatory cells. In contrast, both wall thickening and colonic ulceration were reduced in rats treated with colonic insufflation of CO gas. Hematoxylin and eosin (H&E) staining is shown (40 × magnification).