Experimental colitis alters visceromotor response to colorectal distension in awake rats

The influence of intermittent colorectal distension (CRD) on proximal colonic motility and abdominal pain perception was investigated in awake rats equipped with intraparietal electrodes on the cecum, proximal colon, and abdomen, before and three days after rectocolitis induction by trinitrobenzene sulfonic acid (TNB)/ethanol. The normal myoelectrical activities of cecum and proximal colon [5.2 +/- 0.5 and 9.7 +/- 0.7 long spike bursts (LSB) per 5 min, respectively] were significantly (P < 0.05) and gradually decreased by control CRD, at diameters above 9 mm. At the maximum CRD diameter (13.7 mm), 1.6 +/- 0.6 cecal and 3.9 +/- 0.8 colonic spike bursts occurred per 5 min (respectively, 69 and 60% decreases). This upstream inhibition was accompanied by a significant (P < 0.05) and gradual increase in abdominal contractions (0.4 +/- 0.4 per 5 min in control vs 23.4 +/- 1.9 in response to 13.7 mm in diameter). Three days after TNB/ethanol, visceromotor and abdominal responses were significantly (P < 0.05) enhanced at the least CRD diameter of 9 mm (cecum: 3.1 +/- 0.4 after TNB vs 5.0 +/- 0.7 in control; proximal colon: 5.1 +/- 0.9 vs 9.3 +/- 2.2; abdomen: 7.7 +/- 1.5 vs 0.5 +/- 0.4). We conclude that in awake rats, CRD evokes both abdominal contractions in response to pain and inhibition of cecal and proximal colonic motility, which thresholds are both lowered by TNB-induced rectocolitis.