Effects of intermittent tail shock or water avoidance on proximal colonic motor contractility in rats.

Changes in proximal colonic mechanical activity and defecation during exposure to three different types of experimental stressors were examined in rats chronically implanted with 2 force transducers on the proximal colon. To validate the integrity of the recording system, meal-induced changes in proximal colonic contractility were initially measured in all rats 1-2 days prior to stress induction. Different groups of ad lib fed rats were then exposed to tail shock, re-exposure to the shock chamber or water avoidance for 1 h over the next 1-2 days. Two types of phasic colonic contractions, long (0-3/min) and short (6-8/min) duration, were analyzed separately using a computer. Long duration contractions were significantly elevated 21-71% over fasting basal values from 61-120 min following a meal. No other consistent changes during the prandial or postprandial period were observed. Tail shock significantly suppressed proximal colonic contractility from pre-shock values and increased fecal output and fluid content when compared to ad lib fed rats that were not shocked. Fecal output increased but proximal colonic contractility did not change when previously shocked rats were re-exposed to the tail shock chamber but not shocked. In rats exposed to water avoidance, proximal colonic contractility was minimally suppressed but defecation was significantly greater than home cage control animals. These results indicate that proximal colonic contractile activity is differentially altered by exposure to different environmental stressors and may be a contributing factor in stress-induced bowel dysfunction.