Inhibitory effect of oxytocin on accelerated colonic motility induced by water-avoidance stress in rats.

Recent studies have indicated that brain and gut activities are interrelated and exposure to several stressors, such as water-avoidance stress, stimulates the motor function of the gut through corticotropin-releasing factor (CRF)-signalling pathways in the brain. Central oxytocin is known to attenuate stress responses, including CRF expression in the brain. Here, we examined whether central oxytocin attenuated the acceleration of colonic motility induced by water-avoidance stress. A force transducer was attached to the distal colon of male rat, and the colonic motility and faecal pellet output were recorded while the rats were exposed to water-avoidance stress. Intracerebroventricular (i.c.v.) injections of oxytocin (5, 50 and 500 pmol) and the oxytocin receptor antagonist tocinoic acid (25 microg) were administered before exposure to water-avoidance stress, and the effect of oxytocin on colonic motor function was determined. Centrally administered oxytocin inhibited the accelerated colonic motility induced by water-avoidance stress. The effective dose ranged between 5 and 50 pmol on i.c.v. injection. Oxytocin also decreased the number of CRF-positive cells in the paraventricular nucleus and corticosterone release. The inhibitory effect of oxytocin on accelerated colonic motility was blocked by pretreatment with oxytocin receptor antagonist. Furthermore, centrally administered tocinoic acid enhanced the acceleration of colonic motility. These results suggested that endogenous central oxytocin may contribute to the regulation of colonic function and inhibit the brain CRF-signalling pathways targeting the gut, resulting in the inhibition of stress-induced colonic contractions.