An acute stressor enhances sensitivity to a chemical irritant and increases 51CrEDTA permeability of the colon in adult rats

The impact of acute and chronic stress on gastrointestinal physiology and function: a microbiota-gut-brain axis perspective

The physiological consequences of stress often manifest in the gastrointestinal tract. Traumatic or chronic stress is associated with widespread maladaptive changes throughout the gut, although comparatively little is known about the effects of acute stress. Furthermore, these stress-induced changes in the gut may increase susceptibility to gastrointestinal disorders and infection, and impact critical features of the neural and behavioural consequences of the stress response by impairing gut-brain axis communication. Understanding the mechanisms behind changes in enteric nervous system circuitry, visceral sensitivity, gut barrier function, permeability, and the gut microbiota following stress is an important research objective with pathophysiological implications in both neurogastroenterology and psychiatry. Moreover, the gut microbiota has emerged as a key aspect of physiology sensitive to the effects of stress. In this review, we focus on different aspects of the gastrointestinal tract including gut barrier function as well as the immune, humoral and neuronal elements involved in gut-brain communication. Furthermore, we discuss the evidence for a role of stress in gastrointestinal disorders. Existing gaps in the current literature are highlighted, and possible avenues for future research with an integrated physiological perspective have been suggested. A more complete understanding of the spatial and temporal dynamics of the integrated host and microbial response to different kinds of stressors in the gastrointestinal tract will enable full exploitation of the diagnostic and therapeutic potential in the fast-evolving field of host-microbiome interactions.

Gut-brain actions underlying comorbid anxiety and depression associated with inflammatory bowel disease

IntroductionInflammatory bowel disease (IBD) is a chronic relapsing and remitting disorder characterised by inflammation of the gastrointestinal tract. There is a growing consensus that IBD is associated with anxiety- and depression-related symptoms. Psychological symptoms appear to be more prevalent during active disease states with no difference in prevalence between Crohn's disease and ulcerative colitis. Behavioural disturbances including anxiety- and depression-like symptoms have also been observed in animal models of IBD.

RESULTS

The likely mechanisms underlying the association are discussed with particular reference to communication between the gut and brain. The close bidirectional relationship known as the gut-brain axis includes neural, hormonal and immune communication links. Evidence is provided for a number of interacting factors including activation of the inflammatory response system in the brain, the hypothalamic-pituitary-adrenal axis, and brain areas implicated in altered behaviours, changes in blood brain barrier integrity, and an emerging role for gut microbiota and response to probiotics in IBD.DiscussionThe impact of psychological stress in models of IBD remains somewhat conflicted, however, it is weighted in favour of stress or early stressful life events as risk factors in the development of IBD, stress-induced exacerbation of inflammation and relapse.

CONCLUSION

It is recommended that patients with IBD be screened for psychological disturbance and treated accordingly as intervention can improve quality of life and may reduce relapse rates.

Increased wall thickness using ultrasonography is associated with inflammation in an animal model of experimental colitis

Experimentally induced colitis is used in animals to investigate pathophysiological mechanisms in inflammatory bowel disease. When following disease course and treatment effects, it should be possible to perform repeated measurements without harming the animals. This pilot study was performed to investigate whether transabdominal ultrasound using a clinical scanner could be used on rats to demonstrate bowel inflammation in an experimental colitis model. Colitis was induced by either 5% dextran sodium sulfate (DSS) in drinking water for 7 days or a single dose of intracolonic trinitrobenzene sulfonic acid (TNBS). Using ultrasonography, wall thickness of distal colon, cecum, and small bowel was recorded prior to and after DSS, and prior to, 2, and 7 days after TNBS. Blood (tumor necrosis factor [TNF]-alpha) and fecal samples (HemoFEC occult blood) were taken from each group on the same days as sonography. Thereafter, rats were killed and specimens for histology were taken. Wall thickness of distal colon, not of cecum or small bowel, increased significantly after 7 days of DSS, and wall thickness of both distal colon and small bowel increased on day 2 and 7 after TNBS. TNF-alpha increased after 7 days in the latter group only. There was a significant correlation between ultrasonographic measurements and combined histology score of distal colon in the DSS group. HemoFEC was also positive in accordance with sonographic and histological features. Increased intestinal wall thickness in response to both DSS- and TNBS-induced colitis was able to be visualized by transabdominal sonography. Moreover, ultrasound findings, occult blood sampling, and histological findings supported each other, indicating that ultrasonography can be used to assess inflammation in a rat experimental model.

Neonatal maternal separation in male rats increases intestinal permeability and affects behavior after chronic social stress

Prolonged maternal separation in rats has several effects on health and behavior. Here we investigated how maternal separation might interact with social stress in adulthood on behavior and gastrointenstinal permeability. The effects of either daily 180 min long term pup-dam separation (LMS) during the stress hyporesponsive period or daily 10 min brief maternal separation (BMS) on behavior, corticosterone and intestinal permeability were investigated, compared to a non-handling (NH) condition in male offspring. The animals from each separation condition were then randomly assigned to adult stress and control conditions, where the stress condition was exposure to 14 days of social instability (CSI). Sucrose preference, elevated plus maze behavior and corticosterone were measured. Colitis was experimentally induced by dextran sulfate sodium for 7 days, followed by measurement of intestinal permeability using the (51)CrEDTA method. Granulocyte marker protein was measured in feces and colons were examined histologically for inflammation. Prior to the social stress, the LMS offspring showed elevated corticosterone levels, lower elevated plus maze activity and less fluid consumption. After social stress, corticosterone levels were suppressed in LMS animals and again they showed less fluid consumption. LMS animals had significantly higher intestinal permeability, but only when also exposed to the social stress in adulthood. The current results support a two-hit model, whereby early life events interact with adult life events in altering animals' vulnerability.

Animals' emotions: studies in sheep using appraisal theories

Animal welfare concerns stem from recognition of the fact that animals can experience emotions such as pain or joy. Nevertheless, discussion of animal emotions is often considered anthropomorphic, and there is a clear need to use explanatory frameworks to understand animals' emotions. We borrowed appraisal theories developed in cognitive psychology to study sheep emotions. Emotions are viewed as the result of how an individual evaluates a triggering situation, following a sequence of checks, including the relevance of the situation (its suddenness, familiarity, predictability, and intrinsic pleasantness), its implications for the individual (including consistency with the individual's expectations), the potential for control, and both internal and external standards. We assumed that if the outcome of checks has an impact on the animal's emotional responses, then animals do not only show emotional responses but also feel emotions. We showed that sheep use similar checks to those used by humans to evaluate their environment, ie suddenness, familiarity, predictability, consistency with expectations, and control. Furthermore, this evaluation affects their emotional responses (behavioural responses, such as startle, ear postures, and cardiac activity). It is concluded that sheep are able to experience emotions such as fear, anger, rage, despair, boredom, disgust and happiness because they use the same checks involved in such emotions as humans. For instance, despair is triggered by situations which are evaluated as sudden, unfamiliar, unpredictable, discrepant from expectations, and uncontrollable, whereas boredom results from an overly predictable environment, and all these checks have been found to affect emotional responses in sheep. These results have implications for animal welfare: although a completely invariable and totally predictable environment should be avoided to prevent boredom, sudden events should probably be minimised, the animals should be offered the possibility to control their environment, and care should be taken to ensure a degree of predictability concerning the various events.

Behavioural and physiological responses of lambs to controllable vs. uncontrollable aversive events

The identification of the cognitive processing by which animals evaluate their environment helps to predict situations detrimental to their welfare. Appraisal theories developed in cognitive psychology offer a framework to study such cognitive processing. Here we investigated whether the controllability of an aversive event (an airblast and a sliding grate preventing access to a food reward) affected emotional responses in lambs. The animals could (vs. could not) interrupt the aversive event and thus gain access to food by performing an operant task (placing their muzzle in an aperture). Among lambs trained to perform the operant task, seven learnt it completely and six partially (i.e. they approached their muzzle to the aperture). Each of the 13 lambs that learnt the task completely or partially was paired with a "yoked" partner not taught how to interrupt the aversive event. Behaviour, cortisol and cardiac activity were recorded and the groups were compared with ANOVAs for mixed models. Compared with the lambs unable to interrupt the aversive event, the lambs taught to control it were more inclined to enter and stay in the test arena, and more inclined to eat there. These differences were generally more marked in pairs where the operant task had been fully learnt. An occurrence of the aversive event was followed by a transient backwards-pointing position of the ears and an increased heart rate in all the lambs. These responses were less pronounced in controlling lambs that had completely learnt the operant task. We show that an aversive situation is perceived as less stressful by sheep when they can exert control over it and this effect depends on the degree of control.

Experimental gastritis in mice enhances anxiety in a gender-related manner

There is a gender-related comorbidity of pain-related and inflammatory bowel diseases with psychiatric diseases. Since the impact of experimental gastrointestinal inflammation on the emotional-affective behavior is little known, we examined whether experimental gastritis modifies anxiety, stress coping and circulating corticosterone in male and female Him:OF1 mice. Gastritis was induced by adding iodoacetamide (0.1%) to the drinking water for at least 7 days. Inflammation was assessed by gastric histology and myeloperoxidase activity, circulating corticosterone determined by enzyme immunoassay, anxiety-related behavior evaluated with the elevated plus maze and stress-induced hyperthermia tests, and depression-like behavior estimated with the tail suspension test. Iodoacetamide-induced gastritis was associated with gastric mucosal surface damage and an increase in gastric myeloperoxidase activity, this increase being significantly larger in female mice than in male mice. The rectal temperature of male mice treated with iodoacetamide was enhanced, whereas that of female mice was diminished. The circulating levels of corticosterone were reduced by 65% in female mice treated with iodoacetamide but did not significantly change in male mice. On the behavioral level, iodoacetamide treatment caused a decrease in nocturnal home-cage activity, drinking and feeding. While depression-related behavior remained unaltered following induction of gastritis, behavioral indices of anxiety were significantly enhanced in female but not male mice. There was no correlation between the estrous cycle and anxiety as well as circulating corticosterone. Radiotracer experiments revealed that iodoacetamide did not readily enter the brain, the blood-brain ratio being 20:1. Collectively, these data show that iodoacetamide treatment causes gastritis in a gender-related manner, its severity being significantly greater in female than in male mice. The induction of gastritis in female mice is associated with a reduction of circulating corticosterone and an enforcement of behavioral indices of anxiety. Gastric inflammation thus has a distinct gender-dependent influence on emotional-affective behavior and its neuroendocrine control.

Stress-related peripheral neuroendocrine-immune interactions in women with ulcerative colitis

OBJECTIVES

The mechanisms underlying the interaction of psychological stress with the disease course in inflammatory bowel diseases remain unclear. We analyzed the neuroendocrine and cellular immune responses to public speaking stress, and the in vitro adrenergic and glucocorticoid modulation of cytokine production by peripheral blood cells (PBCs) in women with ulcerative colitis (UC) compared to healthy female controls.

METHODS

In 22 female UC patients with inactive disease or mild disease activity and 24 healthy females we analyzed the neuroendocrine and cellular immune responses to public speaking stress and the vitro beta-adrenergic and glucocorticoid regulation of IL-10 and TNF-alpha production by PBCs.

RESULTS

Public speaking stress-induced neuroendocrine and sympatho-adrenal activation, as well as the redistribution of circulating leukocytes were comparable in UC and controls. Significant but comparable public speaking stress-induced increases in LPS-stimulated TNF-alpha and IL-10, as well as in CD2/CD28-stimulated IFN-gamma were observed in both groups. UC demonstrated significantly reduced baseline IFN-gamma production, as well as significantly lower basal cortisol and prolactin levels. The in vitro beta-adrenergic stimulation of PBCs revealed reduced IL-10 response in UC.

CONCLUSIONS

Psychosocial stress-induced activation of the neuroendocrine and sympatho-adrenal systems remain unaltered in UC, suggesting that the mechanism(s) mediating effects of psychological stress on disease activity are likely operative downstream at the level of the intestine. However, UC patients show disturbances in basal endocrine and cytokine measures. Together with our in vitro evidence of disturbed adrenergic regulation of IL-10 production by stimulated PBCs in UC, these may indicate the existence of subtle disturbance of peripheral cellular neuroendocrine-immune interactions in UC.

The autonomic nervous system and inflammatory bowel disease

Crohn's disease and ulcerative colitis, collectively known as inflammatory bowel disease (IBD), are chronic, recurring, inflammatory conditions of the intestine. The precise mechanisms underlying the pathogenesis of IBD are not yet clear but they are believed to involve a number of precipitating factors, most notably genetic susceptibility and environmental influences. The autonomic nervous system (ANS) has long been known as a critical regulator of intestinal function and much evidence now exists to suggest that it also plays an important role in the development of IBD. Dramatic changes in the ANS in IBD are apparent from the cellular to the molecular level ultimately leading to altered communication between the ANS and effector cells of the intestine. This review aims to synthesize the current understanding of the pathogenesis of IBD with a particular emphasis on the role that the ANS plays in the progression of these diseases.