Fluid intake and behavioral changes in rats associated with the distension of the small and large intestine

Effects of volumetric distension of the small and the large intestine on rats' behavior were compared. Rats were stimulated by a rubber balloon inserted into chronic isolated intestinal loops prepared from the lower duodenum-upper jejunum and from the upper colon in the same animal. Thresholds of 3 reaction classes (weak, strong, and painful) were not different from each other in the 2 loops. Distension decreased fluid intake in an intensity-dependent way, with weak and painful stimuli being less effective in the large intestine and strong stimuli less effective in the small bowel. Behavioral indexes supported intake data, satiety indexes were similar to each other and changed in time, whereas aversivity indexes differed in the 2 loops and as a function of intensity but not time. The author suggests that mild discomfort is a physiological satiety factor whereas strong and painful stimuli signal danger and induce aversivity.