Sensitization of the colonic response to novel stress after previous stressful experience

Stressful life events may be important causative or precipitating factors for functional gastrointesti nal disorders such as the irritable bowel syndrome in humans. In the rat, a single session of foot shocks is known to sensitize the behavioral and hormonal responses to subsequent stress, but intestinal responses have not been investigated. Rats were fitted with bipolar electrodes on proximal colon and exposed to a single session of foot shocks (10 x 6 s in 15 min; preshocked) or no shocks (control). Weight gain after foot shocks was identical to that in controls. Two weeks after foot shocks, basal colonic spike burst frequency did not differ from controls or from that recorded before shock treatment. Unlike controls, however, preshocked rats showed a significant increase in colonic spike burst frequency to a novel stressful challenge in the home cage, an electrified prod. Because the behavioral responses to this challenge did not differ, colonic hyperresponsiveness in preshocked rats may represent a form of stress-induced autonomic sensitization. The model should be a useful tool to study mechanisms and pharmacotherapeutic approaches of the gastrointestinal consequences of traumatic stress.