THE INFLUENCE OF HOST STRESS ON THE GASTROINTESTINAL TRACT AND THE MICROBIOTA

Abstract

<p>Stress is known to play an important role in the natural history of gastrointestinal diseases, and functional disorders in particular. In health, activation of the stress response serves to maintain homeostasis in response to harmful stimuli. However, prolonged activation of the stress response can become maladaptive and contribute to the initiation and maintenance of symptoms in disorders such as irritable bowel syndrome (IBS). The mechanisms underlying this detrimental effect are unclear. This thesis investigates this relationship by examining the influence of 10 days of water avoidance stress on a murine model of acute bacterial gastroenteritis; a known trigger in a subset of IBS patients. Results indicate that stress can increase the level of the stress hormone norepinephrine in the gut. However, the overall influence of host stress during infection proves to be beneficial in this model, with decreased colonic inflammation and earlier clearance of the pathogen. Next, we utilized the olfactory bulbectomy (OBx) model of depression comorbid anxiety, which shows a heightened stress response, to examine mechanism underlying stress-mediated susceptibility in a more chronic setting. OBx resulted in increased neural activity and motility in the gut, and a change in composition of gut microbiota. These responses were not accompanied by changes in gut permeability or immune activation. Thus stress alters the habitat of commensal bacteria via a neurally mediated change in colonic motility. These results have bearing on the ability of stress to alter the microbiota: a feature of functional GI disorders.</p>