Mucosal immunosuppression and epithelial barrier defects are key events in murine psychosocial stress-induced colitis

Chronic sensory contact with subordinated conspecifics promotes splenic glucocorticoid resistance in experimentally wounded C57BL/6N male mice

Chronic psychosocial stress induced by the chronic subordinate colony housing (CSC, 19 Days) paradigm promotes functional splenic in vitro glucocorticoid (GC) resistance, but only if associated with significant bite wounding or prior abdominal transmitter implantation. Moreover, sensory contact to social defeat of conspecifics represents a social stressor for the observer individual. As the occurence and severity of bite wounding is not adequately controllable, the present study aimed to develop an animal model, allowing a bite wound-independent, more reliable generation of chronically-stressed mice characterized by functional splenic in vitro GC resistance. Therefore, male C57BL/6N mice received a standardized sterile intraperitoneal (i.p.) incision surgery or SHAM treatment one week prior to 19-days of (i) CSC, (ii) witnessing social defeat during CSC exposure in sensory contact (SENS) or (iii) single-housing for control (SHC), before assessing basal and LPS-induced splenic in vitro cell viability and GC resistance. Our results indicate that individually-housed SENS but not CSC mice develop mild signs of splenic in vitro GC resistance, when undergoing prior i.p.-wounding. Taken together and considering that future studies are warranted, our findings support the hypothesis that the combination of repeated standardized i.p.-wounding with chronic sensory stress exposure represents an adequate tool to induce functional splenic in vitro GC resistance independent of the occurrence of uncontrollable bite wounds required in social stress paradigms to induce a comparable phenotype.

Intact GR dimerization is critical for restraining plasma ACTH levels during chronic psychosocial stress

Male C57BL/6N mice exposed to the chronic subordinate colony housing (CSC; 19 days) paradigm, a preclinically validated model of chronic psychosocial stress, are characterized by unaffected basal morning plasma corticosterone (CORT) concentrations despite adrenal and pituitary hyperplasia and increased adrenocorticotropic hormone (ACTH) plasma concentrations, compared with single-housed control (SHC) mice. However, as CSC mice are still able to show an increased CORT secretion towards novel heterotypic stressors, these effects might reflect an adaptation rather than a functional breakdown of general hypothalamus-pituitary-adrenal (HPA) axis functionality. In the present study we used male mice of a genetically modified mouse line, to investigate whether genetically-driven ACTH overexpression compromises adaptational processes occurring at the level of the adrenals during CSC exposure. Experimental mice carried a point mutation in the DNA binding domain of the glucocorticoid (GC) receptor (GR), attenuating dimerization of GR (GR^dim), resulting in a congenially compromised negative feedback inhibition at the level of the pituitary. In line with previous studies, CSC mice in both the wild type (WT; GR^+/+) and GR^dim group developed adrenal enlargement. Moreover, compared with respective SHC and WT mice, CSC GR^dim mice show increased basal morning plasma ACTH and CORT concentrations. Quantitative polymerase chain reaction (qPCR) analysis revealed neither a genotype effect, nor a CSC effect on pituitary mRNA expression of the ACTH precursor proopiomelanocortin (POMC). Finally, CSC increased anxiety-related behavior, active coping and splenocyte in vitro (re)activity in both WT and GR^dim mice, while a CSC-induced increase in adrenal lipid vesicles and splenic GC resistance was detectable only in WT mice. Of note, lipopolysaccharide (LPS)-stimulated splenocytes of GR^dim mice were resistant to the inhibitory effects of CORT. Together our findings support the hypothesis that pituitary ACTH protein concentration is negatively controlled by GR dimerization under conditions of chronic psychosocial stress, while POMC gene transcription is not dependent on intact GR dimerization under both basal and chronic stress conditions. Finally, our data suggest that adrenal adaptations during chronic psychosocial stress (i.e., ACTH desensitization), aiming at the prevention of prolonged hypercorticism, are protective only to a certain threshold of plasma ACTH levels.

Role of intestinal microbiota in regulation of immune reactions of gut-associated lymphoid tissue under stress and following the modulation of its composition by antibiotics and probiotics administration

Over the past two decades, active study of the microbial ecosystem of the host organism gastrointestinal tract has led to the recognition of gut microbiome as a "key player" that carries a significant immune pressure and is responsible both for the course of physiological processes and for the development of pathological conditions in humans and animals. A vast number of bacteria living in the human gastrointestinal tract are considered as an organ functioning in dialogue in formation of immunological tolerance, the regulation of normal functional activity of the immune system and maintaining the intestinal mucosa homeostasis. However, disturbances in interaction between these physiological systems is closely related to the pathogenesis of different immune-mediated diseases. In turn, in a large number of works chronic social stress, along with the use of antibiotics, pre- and probiotics, is recognized as one of the leading factors modulating in the microbiota of the gastrointestinal tract. This review focuses on the role of the gut microbiome in the regulation of immune responses of GALT under stress and modulation of its composition by antibiotics and probiotics administration.

Impacts of breast cancer and chemotherapy on gut microbiome, cognitive functioning, and mood relative to healthy controls

Women diagnosed with breast cancer undergoing chemotherapy experience cognitive impairment, symptoms of anxiety and depression, and physical side effects including disruption in the diversity and community composition of the gut microbiome. To date, there is limited research exploring the associations among these specific challenges. The present cross-sectional study explored the associations of self-reported cognitive functioning, depression, and anxiety symptoms, and gut microbiome diversity and community composition in women who were diagnosed with and undergoing chemotherapy treatment for breast cancer (BC) compared to cancer-free healthy controls (HC). The BC group displayed higher rates of cognitive dysfunction (p < 0.001) and depressive symptoms (p < 0.05) relative to HC. There was a significant difference in microbiome community composition between BC and HC, particularly characterized by a decreased relative abundance of the mucin-degrading genus Akkermansia in BC compared to HC (p < 0.05). Association models identified significant associations among group, cognitive, depression, and microbiome variables (p < 0.001). Overall, the study identified that BC participants experienced significant differences in self-reported cognitive functioning, self-reported depression symptoms, microbiome community composition, and mucin-degrading bacteria of the gut-mucosal barrier, relative to HC. The present study is consistent with the hypothesis that gut microbiome community composition impacts a woman's experience with breast cancer and treatment suggesting that microbiome-based interventions have potential for improving quality of life outcomes in individuals with breast cancer.

Experimental Exposure to Noise Alters Gut Microbiota in a Captive Songbird

Noise pollution is an unprecedented evolutionary pressure on wild animals that can lead to alteration of stress hormone levels and changes in foraging behavior. Both corticosterone and feeding behavior can have direct effects on gut bacteria, as well as indirect effects through changes in gut physiology. Therefore, we hypothesized that exposure to noise will alter gut microbial communities via indirect effects on glucocorticoids and foraging behaviors. We exposed captive white-crowned sparrows to city-like noise and measured each individuals' corticosterone level, food intake, and gut microbial diversity at the end of four treatments (acclimation, noise, recovery, and control) using a balanced repeated measures design. We found evidence that noise acts to increase corticosterone and decrease food intake, adding to a growing body of research indicating noise exposure affects stress hormone levels and foraging behaviors. We also found evidence to support our prediction for a causal, positive relationship between noise exposure and gut microbial diversity, such that birds had higher measures of alpha diversity during noise exposure. These results help to explain previous findings that urban, free-living white-crowned sparrows have higher bacterial richness than rural sparrows. However, noise appeared to act directly on the gut microbiome or, more likely, through an unmeasured variable, rather than through indirect effects via corticosterone and food intake. Altogether, our study indicates that noise affects plasma corticosterone, feeding behavior, and the gut microbiome in a songbird and raises new questions as to the mechanism linking noise exposure to gut microbial diversity.

Glucocorticoid induced group 2 innate lymphoid cell overactivation exacerbates experimental colitis

Abnormal activation of the innate and adaptive immune systems has been observed in inflammatory bowel disease (IBD) patients. Anxiety and depression increase the risk of IBD by activating the adaptive immune system. However, whether anxiety affects innate immunity and its impact on IBD severity remains elusive. This study investigated the mechanism by which anxiety contributes to IBD development in a murine model of acute wrap restraint stress (WRS). Here, we found that anxiety-induced overactivation of group 2 innate lymphoid cells (ILC2) aggravated colonic inflammation. Overactivation of the hypothalamic–pituitary–adrenal (HPA) axis is a hallmark of the physiological change of anxiety. Corticosterone (CORT), a stress hormone, is a marker of HPA axis activation and is mainly secreted by HPA activation. We hypothesized that the overproduction of CORT stimulated by anxiety exacerbated colonic inflammation due to the abnormally elevated function of ILC2. The results showed that ILC2 secreted more IL-5 and IL-13 in the WRS mice than in the control mice. Meanwhile, WRS mice experienced more body weight loss, shorter colon length, higher concentrations of IL-6 and TNF-α, more severely impaired barrier function, and more severe inflammatory cell infiltration. As expected, the serum corticosterone levels were elevated after restraint stress. Dexamethasone (DEX) was then injected to mimic HPA axis activation induced CORT secretion. DEX injection can also stimulate ILC2 to secrete more type II cytokines and exacerbate oxazolone (OXA) induced colitis. Blocking the IL-13/STAT6 signaling pathway alleviated colitis in WRS and DEX-injected mice. In conclusion, the overactivation of ILC2 induced by CORT contributed to the development of OXA-induced colitis in mice.

MODULATION OF INTESTINAL BARRIER FUNCTION BY GLUCOCORTICOIDS: LESSONS FROM PRECLINICAL MODELS

Glucocorticoids (GCs) are widely used drugs for their anti-inflammatory and immunosuppressant effects, but they are associated with multiple adverse effects. Despite their frequent oral administration, relatively little attention has been paid to the effects of GCs on intestinal barrier function. In this review, we present a summary of the published studies on this matter carried out in animal models and cultured cells. In cultured intestinal epithelial cells, GCs have variable effects in basal conditions and generally enhance barrier function in the presence of inflammatory cytokines such as tumor necrosis factor (TNF). In turn, in rodents and other animals, GCs have been shown to weaken barrier function, with increased permeability and lower production of IgA, which may account for some features observed in stress models. When given to animals with experimental colitis, barrier function may be debilitated or strengthened, despite a positive anti-inflammatory activity. In sepsis models, GCs have a barrier-enhancing effect. These effects are probably related to the inhibition of epithelial cell proliferation and wound healing, modulation of the microbiota and mucus production, and interference with the mucosal immune system. The available information on underlying mechanisms is described and discussed.

The Exposome and Immune Health in Times of the COVID-19 Pandemic

Growing evidence supports the importance of lifestyle and environmental exposures-collectively referred to as the 'exposome'-for ensuring immune health. In this narrative review, we summarize and discuss the effects of the different exposome components (physical activity, body weight management, diet, sun exposure, stress, sleep and circadian rhythms, pollution, smoking, and gut microbiome) on immune function and inflammation, particularly in the context of the current coronavirus disease 2019 (COVID-19) pandemic. We highlight the potential role of 'exposome improvements' in the prevention-or amelioration, once established-of this disease as well as their effect on the response to vaccination. In light of the existing evidence, the promotion of a healthy exposome should be a cornerstone in the prevention and management of the COVID-19 pandemic and other eventual pandemics.

Evaluation of the gut microbiome in association with biological signatures of inflammation in murine polytrauma and shock

Severe injuries are frequently accompanied by hemorrhagic shock and harbor an increased risk for complications. Local or systemic inflammation after trauma/hemorrhage may lead to a leaky intestinal epithelial barrier and subsequent translocation of gut microbiota, potentially worsening outcomes. To evaluate the extent with which trauma affects the gut microbiota composition, we performed a post hoc analysis of a murine model of polytrauma and hemorrhage. Four hours after injury, organs and plasma samples were collected, and the diversity and composition of the cecal microbiome were evaluated using 16S rRNA gene sequencing. Although cecal microbial alpha diversity and microbial community composition were not found to be different between experimental groups, norepinephrine support in shock animals resulted in increased alpha diversity, as indicated by higher numbers of distinct microbial features. We observed that the concentrations of proinflammatory mediators in plasma and intestinal tissue were associated with measures of microbial alpha and beta diversity and the presence of specific microbial drivers of inflammation, suggesting that the composition of the gut microbiome at the time of trauma, or shortly after trauma exposure, may play an important role in determining physiological outcomes. In conclusion, we found associations between measures of gut microbial alpha and beta diversity and the severity of systemic and local gut inflammation. Furthermore, our data suggest that four hours following injury is too early for development of global changes in the alpha diversity or community composition of the intestinal microbiome. Future investigations with increased temporal-spatial resolution are needed in order to fully elucidate the effects of trauma and shock on the gut microbiome, biological signatures of inflammation, and proximal and distal outcomes.

Inducing a stressed phenotype in healthy recipient mice by adoptively transferring CD4+ lymphocytes from mice undergoing chronic psychosocial stress

Although chronic stress is an acknowledged risk factor for the development of somatic and affective disorders, the cellular and molecular mechanisms underlying stress-induced pathologies are not fully understood. Interestingly, rodent studies involving immune cell transfer suggest that CD4⁺ T cells might be at least in part involved in reactivation of a chemically-induced colitis by stress. However, until now evidence is lacking that these immune cell types are indeed involved in the development of a "stressed phenotype". The aim of the present study was, therefore, to assess the effects of adoptively transferring total mesenteric lymph node cells (mesLNCs) and CD4⁺ mesLNCs isolated from chronically-stressed mice into healthy recipient mice on various physiological, immunological and behavioral parameters. To induce chronic psychosocial stress in donor mice we employed the chronic subordinate colony housing (CSC) paradigm. Our data indicate that transfer of total or CD4⁺ mesLNCs from CSC mice, compared with respective cells from single-housed control (SHC) mice, promoted splenomegaly and interferon (IFN)-γ secretion from in vitro anti-CD3-stimulated mesLNCs in naïve recipient mice. This effect was independent of recipient mice additionally being administered with dextran sulfate sodium (DSS) or not. Transfer of CD4⁺ mesLNCs additionally increased adrenal weight and secretion of IL-6 from in vitro anti-CD3 stimulated mesLNCs in recipients administered with DSS. Importantly, transfer of neither cell type from CSC vs. SHC donor mice affected anxiety-related behavior of recipient mice in the light-dark box. Taken together, our data demonstrate that typical physiological and immunological, but not behavioral, effects of chronic stress can be induced in naïve recipient mice by adoptively transferring mesLNCs, in particular CD4⁺ mesLNCs, from chronically stressed donor mice.

Changes in adrenal functioning induced by chronic psychosocial stress in male mice: A time course study

BACKGROUND AND AIM

Chronic subordinate colony housing (CSC, 19 days), an established and preclinically-validated mouse model for posttraumatic stress disorder (PTSD), causes evening hypocorticism and a reduced adrenal in vitro ACTH (adrenocorticotropic hormone) sensitivity despite pronounced adrenal hyperplasia. However, until now it remains unclear at what time point during CSC exposure evening hypocorticism and adrenal in vitro ACTH insensitivity develop and whether the repeated change of dominant aggressor mice plays an important role in this context. It is, therefore, the aim of the current study, to explore the detailed time course of these stress-induced adrenal changes.

METHODS

Adrenal weight, plasma corticosterone (CORT) and ACTH were assessed in the morning of days 8 (right before exposure to the 2nd aggressor), 9 (24 h after exposure to the 2nd aggressor), 15 (right before exposure to the 3rd aggressor), 16 (24 h after exposure to the 3rd aggressor) and 20 or in the evening of days 8 (10 h after exposure to the 2nd aggressor), 9 (34 h after exposure to the 2nd aggressor), 15 (10 h after exposure to the 3rd aggressor), 16 (34 h after exposure to the 3rd aggressor) and 20 of CSC exposure. Moreover, we in vitro cultured adrenal explants of all mice euthanized in the morning of days 8, 9, 15, 16 and 20 either in the presence or absence of ACTH to subsequently assess CORT concentration in the supernatants.

RESULTS

Our results indicate that while adrenal mass was increased at all time points assessed, plasma morning CORT only transiently increased in response to the 2nd (on day 8) but not 3rd (on day 15) dominant aggressor mouse. Moreover, although mild signs of adrenal in vitro ACTH insensitivity developed already after one week of CSC exposure, moderate and severe adrenal in vitro ACTH insensitivity required two and three weeks of chronic subordination, respectively.

CONCLUSION

Together with unaffected plasma ACTH levels at all time points assessed, our data suggest that stress-induced adrenal in vitro ACTH insensitivity develops gradually during times of chronic subordination while subordination to different aggressor mice aggravates its severity. Moreover, a mild form of adrenal ACTH insensitivity seems to allow prevention of morning hypercorticism on day 8 of CSC, despite functional adrenal mass being increased, while a moderate and severe form of adrenal ACTH insensitivity in CSC mice seems to promote HPA axis adaptation to repeated homotypic stressor exposure (i.e. dominant aggressor mice) and basal evening hypocorticism in CSC mice, respectively. Our results might, therefore, be the basis for future clinical studies assessing CORT supplementation as novel treatment regimen for somatic and affective pathologies linked to chronic and/or traumatic stress.

Restraint stress increased the permeability of the nasal epithelium in BALB/c mice

Stress seems to affect the onset and evolution of diverse illnesses with an inflammatory substrate. Whether physiological or psychological, stress increases epithelial permeability. In the mucosa of the nasal cavity and upper respiratory tract, the epithelial barrier is regulated in large part by bicellular and tricellular tight junctions (bTJs and tTJs, respectively). The junctional complexes are composed of multiple membrane proteins: claudins, tight-junction-associated MARVEL proteins (TAMs: occludin, tricellulin and marvelD3), and scaffolding proteins such as ZO-1, -2 and -3. The aim of the present study was to examine the possible modification of nasal permeability and TJ protein expression in a mouse model of acute psychological stress (a 4-h immobility session). Serum corticosterone was quantified from plasma samples to verify the onset of stress. Evaluation was made of the relative concentration of key proteins in nasal mucosa by using Western blot, and of changes in permeability by analyzing FITC-Dextran leakage from the nose to the blood. Compared to the control, the stressed group showed a greater epithelial permeability to FITC-Dextran, a reduced expression of occludin and tricellulin, and an elevated expression of ZO-2 and claudin-4. This evidence points to increased paracellular flow of large molecules through an altered structure of tTJs. Apparently, the structure of bTJs remained unchanged. The current findings could provide insights into the relation of stress to the onset/exacerbation of respiratory infections and/or allergies.

Microbial and Host Factors That Affect Bacterial Invasion of the Gingiva

Periodontitis is a chronic inflammation of the periodontium caused by the loss of homeostasis between subgingival biofilms and susceptible hosts. Bacterial invasion into the gingival tissue and persistent infection are major events that lead to chronic inflammation. The intratissue bacterial communities are as complex as the subgingival biofilms and can also form biofilm-like structures, which will serve as a reservoir for local and systemic infections. The epithelium forms physical, chemical, and immunological barriers against invading microbes. Nevertheless, many bacterial species can invade the gingival epithelium through transcellular and paracellular pathways. In addition, both genetic and environmental factors of the hosts can affect epithelial barrier functions and thus bacterial invasion of the gingiva. In this review, current evidence for the bacterial invasion of the gingival tissue in periodontitis has been summarized, and the microbial and host factors that determine bacterial invasion of the gingiva have been reviewed.

Intranasal Mycobacterium vaccae administration prevents stress-induced aggravation of dextran sulfate sodium (DSS) colitis

An increasing body of evidence indicates that immunodysregulation and subsequent chronic low-grade inflammation can promote the development of stress-related somatic and psychiatric pathologies, including inflammatory bowel disease (IBD) and posttraumatic stress disorder (PTSD). Thus, immunoregulatory approaches counterbalancing basal and/or stress-induced immune activation should have stress-protective potential. In support of this hypothesis, we recently demonstrated that repeated s.c. preimmunization with a heat-killed preparation of the immunoregulatory bacterium Mycobacterium vaccae (M. vaccae; National Collection of Type Culture (NCTC) 11659), protects mice against stress-induced general anxiety, spontaneous colitis, and aggravation of dextran sulfate sodium (DSS)-induced colitis in the chronic subordinate colony housing (CSC) paradigm, a validated model for PTSD in male mice. In the current study, we repeatedly administered M. vaccae via the non-invasive intranasal (i.n.; 0.1 mg/mouse/administration) route, prior to or during CSC exposure or single housed control (SHC) conditions, and assessed the effects on general and social anxiety, and on parameters related to the severity of DSS-induced colitis. While administration of M. vaccae prior to the onset of CSC exposure only had minor stress-protective effects, administration of M. vaccae during CSC completely prevented CSC-induced aggravation of DSS colitis. As CSC in the current experimental setting did not reliably increase general anxiety-related behavior, potential stress-protective effects of M.vaccae are difficult to interpret. Taken together, these data broaden the framework for developing bioimmunoregulatory approaches, based on the administration of microorganisms with anti-inflammatory and immunoregulatory properties, for the prevention of stress-related disorders.

Impact of chronic immobilization stress on parameters of colonic homeostasis in BALB/c mice

The intestinal epithelium is a monolayer of cells arranged side‑by‑side and connected by tight junction (TJ) proteins expressed at the apical extreme of the paracellular membrane. This layer prevents stress‑induced inflammatory responses, thus helping to maintain gut barrier function and gut homeostasis. The aim of the present study was to evaluate the effects of chronic immobilization stress on the colonic expression of various parameters of homeostasis. A total of two groups of female BALB/c mice (n=6) were included: A stressed group (short‑term immobilization for 2 h/day for 4 consecutive days) and an unstressed (control) group. Colon samples were obtained to detect neutrophils and goblet cells by optical microscopy, TJ protein expression (occludin, and claudin ‑2, ‑4, ‑7, ‑12 and ‑15) by western blotting, mRNA levels of TJ genes and proinflammatory cytokines [tumor necrosis factor (TNF)‑α, interleukin (IL)‑1β, ‑6 and ‑8] by reverse transcription‑quantitative PCR, fecal lactoferrin by ELISA and the number of colony‑forming units of aerobic bacteria. Compared with goblet cells in control mice, goblet cells were enlarged and reduced in number in stressed mice, whereas neutrophil cellularity was unaltered. Stressed mice exhibited reduced mRNA expression for all evaluated TJ mRNAs, with the exception of claudin‑7, which was upregulated. Protein levels of occludin and all claudins (with the exception of claudin‑12) were decreased in stressed mice. Fecal lactoferrin, proinflammatory cytokine mRNA levels and aerobic bacterial counts were all increased in the stressed group. These results indicated that immobilization stress induced proinflammatory and potential remodeling effects in the colon by decreasing TJ protein expression. The present study may be a useful reference for therapies aiming to regulate the effects of stress on intestinal inflammatory dysfunction.

Social defeat stimulates local glucocorticoid regeneration in lymphoid organs

Stress is an important risk factors for human diseases. It activates the hypothalamic-pituitary-adrenal (HPA) axis and increases plasma glucocorticoids, which are powerful regulators of immune system. The response of the target cells to glucocorticoids depends not only on the plasma concentrations of cortisol and corticosterone but also on their local metabolism. This metabolism is catalyzed by 11β-hydroxysteroid dehydrogenases type 1 and 2, which interconvert glucocorticoid hormones cortisol and corticosterone and their 11-oxo metabolites cortisone and 11-dehydrocorticosterone. The goal of this study was to determine whether stress modulates glucocorticoid metabolism within lymphoid organs - the structures where immune cells undergo development and activation. Using the resident-intruder paradigm, we studied the effect of social stress on glucocorticoid metabolism in primary and secondary lymphoid organs of Fisher 344 (F344) and Lewis (LEW) rats, which exhibit marked differences in their HPA axis response to social stressors and inflammation. We show that repeated social defeat increased the regeneration of corticosterone from 11-dehydrocorticosterone in the thymus, spleen and mesenteric lymphatic nodes (MLN). Compared with the F344 strain, LEW rats showed higher corticosterone regeneration in splenocytes of unstressed rats and in thymic and MLN mobile cells after stress but corticosterone regeneration in the stroma of all lymphoid organs was similar in both strains. Inactivation of corticosterone to 11-dehydrocorticosterone was found only in the stroma of lymphoid organs but not in mobile lymphoid cells and was not upregulated by stress. Together, our findings demonstrate the tissue- and strain-dependent regeneration of glucocorticoids following social stress.

The Role of the Intestinal Microbiome in Chronic Psychosocial Stress-Induced Pathologies in Male Mice

Chronic psychosocial stress is a risk factor for the development of physical and mental disorders accompanied or driven by an activated immune system. Given that chronic stress-induced systemic immune activation is lacking in germ-free and antibiotics-treated mice, a causal role of the gut microbiome in the development of stress-related disorders is likely. To address this hypothesis in the current study we employed the chronic subordinate colony housing (CSC, 19 days) paradigm, a pre-clinically validated mouse model for chronic psychosocial stress, known to alter the gut microbial signature and to induce systemic low-grade inflammation, as well as physical and mental abnormalities. In detail, we investigated if (i) CSC-induced alterations can be prevented by repeated transplantation of feces (FT) from non-stressed single-housed control (SHC) mice during CSC exposure, and (ii) if the transplantation of a “stressed” CSC microbiome is able to induce CSC effects in SHC mice. Therefore, we repeatedly infused SHC and CSC recipient mice rectally with SHC donor feces at days 4 and 11 of the CSC paradigm and assessed anxiety-related behavior on day 19 as well as physiological, immunological, and bone parameters on day 20. Furthermore, SHC and CSC recipient mice were infused with CSC donor feces at respective days. To exclude effects of rectal infusions per se, another set of SHC and CSC mice was infused with saline, respectively. Our results showed that transplantation of SHC feces had mild stress-protective effects, indicated by an amelioration of CSC-induced thymus atrophy, anxiety, systemic low-grade inflammation, and alterations in bone homeostasis. Moreover, transplantation of CSC feces slightly aggravated CSC-induced systemic low-grade inflammation and alterations in bone homeostasis in SHC and/or CSC animals. In conclusion, our data provide evidence for a role of the host’s microbiome in many, but not all, adverse consequences of chronic psychosocial stress. Moreover, our data are consistent with the hypothesis that transplantation of healthy feces might be a useful tool to prevent/treat different adverse outcomes of chronic stress. Finally, our data suggests that stress effects can be transferred to a certain extend via FT, proposing therapeutic approaches using FT to carefully screen fecal donors for their stress/trauma history.

Microbiota affects the expression of genes involved in HPA axis regulation and local metabolism of glucocorticoids in chronic psychosocial stress

The commensal microbiota affects brain functioning, emotional behavior and ACTH and corticosterone responses to acute stress. However, little is known about the role of the microbiota in shaping the chronic stress response in the peripheral components of the hypothalamus-pituitary-adrenocortical (HPA) axis and in the colon. Here, we studied the effects of the chronic stress-microbiota interaction on HPA axis activity and on the expression of colonic corticotropin-releasing hormone (CRH) system, cytokines and 11β-hydroxysteroid dehydrogenase type 1 (11HSD1), an enzyme that determines locally produced glucocorticoids. Using specific pathogen-free (SPF) and germ-free (GF) BALB/c mice, we showed that the microbiota modulates emotional behavior in social conflicts and the response of the HPA axis, colon and mesenteric lymph nodes (MLN) to chronic psychosocial stress. In the pituitary gland, microbiota attenuated the expression of Fkbp5, a gene regulating glucocorticoid receptor sensitivity, while in the adrenal gland, it attenuated the expression of genes encoding steroidogenesis (MC2R, StaR, Cyp11a1) and catecholamine synthesis (TH, PNMT). The pituitary expression of CRH receptor type 1 (CRHR1) and of proopiomelanocortin was not influenced by microbiota. In the colon, the microbiota attenuated the expression of 11HSD1, CRH, urocortin UCN2 and its receptor, CRHR2, but potentiated the expression of cytokines TNFα, IFNγ, IL-4, IL-5, IL-6, IL-10, IL-13 and IL-17, with the exception of IL-1β. Compared to GF mice, chronic stress upregulated in SPF animals the expression of pituitary Fkbp5 and colonic CRH and UCN2 and downregulated the expression of colonic cytokines. Differences in the stress responses of both GF and SPF animals were also observed when immunophenotype of MLN cells and their secretion of cytokines were analyzed. The data suggest that the presence of microbiota/intestinal commensals plays an important role in shaping the response of peripheral tissues to stress and indicates possible pathways by which the environment can interact with glucocorticoid signaling.

Biomarkers for classification and class prediction of stress in a murine model of chronic subordination stress

Selye defined stress as the nonspecific response of the body to any demand and thus an inherent element of all diseases. He reported that rats show adrenal hypertrophy, thymicolymphatic atrophy, and gastrointestinal ulceration, referred to as the stress triad, upon repeated exposure to nocuous agents. However, Selye's stress triad as well as its extended version including reduced body weight gain, increased plasma glucocorticoid (GC) concentrations, and GC resistance of target cells do not represent reliable discriminatory biomarkers for chronic stress. To address this, we collected multivariate biological data from male mice exposed either to the preclinically validated chronic subordinate colony housing (CSC) paradigm or to single-housed control (SHC) condition. We then used principal component analysis (PCA), top scoring pairs (tsp) and support vector machines (SVM) analyses to identify markers that discriminate between chronically stressed and non-stressed mice. PCA segregated stressed and non-stressed mice, with high loading for some of Selye's stress triad parameters. The tsp analysis, a simple and highly interpretable statistical approach, identified left adrenal weight and relative thymus weight as the pair with the highest discrimination score and prediction accuracy validated by a blinded dataset (92% p-value < 0.0001; SVM model = 83% accuracy and p-value < 0.0001). This finding clearly shows that simultaneous consideration of these two parameters can be used as a reliable biomarker of chronic stress status. Furthermore, our analysis highlights that the tsp approach is a very powerful method whose application extends beyond what has previously been reported.

Prolonged restraint stressor exposure in outbred CD-1 mice impacts microbiota, colonic inflammation, and short chain fatty acids

Stressor-exposure has been shown to exacerbate inflammation and change the composition of the gastrointestinal microbiota; however stressor-induced effects on microbiota-derived metabolites and their receptors are unknown. Thus, bacterial-produced short chain fatty acids (SCFAs), as well as microbial community composition, were assessed in the colons of mice exposed to stress during infection with Citrobacter rodentium. Mice were exposed to overnight restraint on 7 consecutive nights, or left undisturbed as a control. After the first exposure of restraint, mice were orally challenged with C. rodentium or with vehicle. Microbial community composition was assessed using 16S rRNA gene sequencing and SCFA levels measured using gas chromatography-mass spectrometry (GC-MS). Pathogen levels and colonic inflammation were also assessed 6 days post-infection. Results demonstrated that the microbial community structure and SCFA production were significantly affected by both stressor exposure and C. rodentium-infection. Exposure to prolonged restraint in the absence of infection significantly reduced SCFAs (acetic acid, butyric acid, and propionic acid). Multiple bacterial taxa were affected by stressor exposure, with the relative abundance of Lactobacillus being significantly reduced and directly correlated with propionic acid. Lactobacillus abundances were inversely correlated with colonic inflammation, supporting the contention that Lactobacillus helps to regulate mucosal inflammatory responses. Our data indicates that restraint stressor can have significant effects on pathogen-induced colonic inflammation and suggest that stressor-induced changes in the microbiota, microbial-produced SCFAs and their receptors may be involved.

Chronic psychosocial stress disturbs long-bone growth in adolescent mice

Although a strong association between psychiatric and somatic disorders is generally accepted, little is known regarding the interrelationship between mental and skeletal health. Although depressive disorders have been shown to be strongly associated with osteoporosis and increased fracture risk, evidence from post-traumatic stress disorder (PTSD) patients is less consistent. Therefore, the present study investigated the influence of chronic psychosocial stress on bone using a well-established murine model for PTSD. C57BL/6N mice (7 weeks old) were subjected to chronic subordinate colony housing (CSC) for 19 days, whereas control mice were singly housed. Anxiety-related behavior was assessed in the open-field/novel-object test, after which the mice were euthanized to assess endocrine and bone parameters. CSC mice exhibited increased anxiety-related behavior in the open-field/novel-object test, increased adrenal and decreased thymus weights, and unaffected plasma morning corticosterone. Microcomputed tomography and histomorphometrical analyses revealed significantly reduced tibia and femur lengths, increased growth-plate thickness and reduced mineral deposition at the growth plate, suggesting disturbed endochondral ossification during long-bone growth. This was associated with reduced Runx2 expression in hypertrophic chondrocytes in the growth plate. Trabecular thicknesses and bone mineral density were significantly increased in CSC compared to singly housed mice. Tyrosine hydroxylase expression was increased in bone marrow cells located at the growth plates of CSC mice, implying that local adrenergic signaling might be involved in the effects of CSC on the skeletal phenotype. In conclusion, chronic psychosocial stress negatively impacts endochondral ossification in the growth plate, affecting both longitudinal and appositional bone growth in adolescent mice.

Visceral Inflammation and Immune Activation Stress the Brain

Stress refers to a dynamic process in which the homeostasis of an organism is challenged, the outcome depending on the type, severity, and duration of stressors involved, the stress responses triggered, and the stress resilience of the organism. Importantly, the relationship between stress and the immune system is bidirectional, as not only stressors have an impact on immune function, but alterations in immune function themselves can elicit stress responses. Such bidirectional interactions have been prominently identified to occur in the gastrointestinal tract in which there is a close cross-talk between the gut microbiota and the local immune system, governed by the permeability of the intestinal mucosa. External stressors disturb the homeostasis between microbiota and gut, these disturbances being signaled to the brain via multiple communication pathways constituting the gut-brain axis, ultimately eliciting stress responses and perturbations of brain function. In view of these relationships, the present article sets out to highlight some of the interactions between peripheral immune activation, especially in the visceral system, and brain function, behavior, and stress coping. These issues are exemplified by the way through which the intestinal microbiota as well as microbe-associated molecular patterns including lipopolysaccharide communicate with the immune system and brain, and the mechanisms whereby overt inflammation in the GI tract impacts on emotional-affective behavior, pain sensitivity, and stress coping. The interactions between the peripheral immune system and the brain take place along the gut-brain axis, the major communication pathways of which comprise microbial metabolites, gut hormones, immune mediators, and sensory neurons. Through these signaling systems, several transmitter and neuropeptide systems within the brain are altered under conditions of peripheral immune stress, enabling adaptive processes related to stress coping and resilience to take place. These aspects of the impact of immune stress on molecular and behavioral processes in the brain have a bearing on several disturbances of mental health and highlight novel opportunities of therapeutic intervention.

Splenic glucocorticoid resistance following psychosocial stress requires physical injury

Mice exposed to chronic subordinate colony housing (CSC) stress show glucocorticoid (GC) resistance of in vitro lipopolysaccharide (LPS)-stimulated splenocytes, increased anxiety and colitis. Similar effects were reported in wounded mice exposed to social disruption (SDR). Here we show that CSC exposure induced GC resistance in isolated and in vitro LPS-stimulated, but not unstimulated, splenocytes, and these effects were absent when CD11b⁺ splenocytes were depleted. Moreover, re-active coping behaviour during CSC correlated with the attacks and bites received by the resident, which in turn highly correlated with the dimension of splenic GC resistance, as with basal and LPS-induced in vitro splenocyte viability. Importantly, social stress promoted spleen cell activation, independent of bite wounds or CD11b⁺/CD11b⁻ cell phenotype, whereas GC resistance was dependent on both bite wounds and the presence of CD11b⁺ cells. Together, our findings indicate that the mechanisms underlying splenic immune activation and GC resistance following social stress in male mice are paradigm independent and, to a large extent, dependent on wounding, which, in turn, is associated with a re-active coping style.

Exosomes, DAMPs and miRNA: Features of Stress Physiology and Immune Homeostasis

Psychological/physical stressors and local tissue damage increase inflammatory proteins in tissues and blood in humans and animals, in the absence of pathogenic disease. Stress-evoked cytokine/chemokine responses, or sterile inflammation, can facilitate host survival and/or negatively affect health, depending on context. Recent evidence supports the hypothesis that systemic stress-evoked sterile inflammation is initiated by the sympathetic nervous system, resulting in the elevation of exosome-associated immunostimulatory endogenous danger/damage associated molecular patterns (DAMPs) and a reduction in immunoinhibitory miRNA, which are carried in the circulation to tissues throughout the body. We propose that sterile inflammation should be considered an elemental feature of the stress response and that circulating exosomes transporting immunomodulatory signals, may play a role fundamental role in immune homeostasis.

Individual differences in stress vulnerability: The role of gut pathobionts in stress-induced colitis

Chronic subordinate colony housing (CSC), an established mouse model for chronic psychosocial stress, promotes a microbial signature of gut inflammation, characterized by expansion of Proteobacteria, specifically Helicobacter spp., in association with colitis development. However, whether the presence of Helicobacter spp. during CSC is critically required for colitis development is unknown. Notably, during previous CSC studies performed at Regensburg University (University 1), male specific-pathogen-free (SPF) CSC mice lived in continuous subordination to a physically present and Helicobacter spp.-positive resident. Therefore, it is likely that CSC mice were colonized, during the CSC procedure, with Helicobacter spp. originating from the dominant resident. In the present study we show that employing SPF CSC mice and Helicobacter spp.-free SPF residents at Ulm University (University 2), results in physiological responses that are typical of chronic psychosocial stress, including increased adrenal and decreased thymus weights, decreased adrenal in vitro adrenocorticotropic hormone (ACTH) responsiveness, and increased anxiety-related behavior. However, in contrast to previous studies that used Helicobacter spp.-positive resident mice, use of Helicobacter spp.-negative resident mice failed to induce spontaneous colitis in SPF CSC mice. Consistent with the hypothesis that the latter is due to a lack of Helicobacter spp. transmission from dominant residents to subordinate mice during the CSC procedure, colonization of SPF residents with Helicobacter typhlonius at University 2, prior to the start of the CSC model, rescued the colitis-inducing potential of CSC exposure. Furthermore, using SPF CSC mice and H. typhlonius-free SPF residents at University 1 prevented CSC-induced colitis. In summary, our data support the hypothesis that the presence or absence of exposure to certain pathobionts contributes to individual variability in susceptibility to stress-/trauma-associated pathologies and to reproducibility of stress-related outcomes between laboratories.

Acoustic stress induces long term severe intestinal inflammation in the mouse

The influence of noise on the presentation and progression of inflammatory bowel diseases has been poorly analyzed. We designed this study to investigate immediate and late effects of acoustic stress (AS) on small intestine. To this aim, CBA/J, BALB/c and DBA/2 mice were divided into AS and control groups. AS mice were exposed to noise (300Hz-70dB) during 24hs and randomized into: A) Acute effects group: mice were killed after AS; L) Late effects group: mice were killed 3 weeks after AS and O) Over-exposed effects group: mice were submitted to AS once a week during a month and killed. Small intestine sections were histologically examined. The expression of cytokines (IL-17, IL-22, TNF-α, INF-ɣ and TGF-β), CCL-25 and Ki67 was studied by immunohistochemistry and immunofluorescence techniques. "A" group displayed short and fragmented villi, diminished number of lamina propria cells, leucocyte infiltration, higher number of goblet cells and predominance of IL-17 expression. "L" group showed epithelial proliferative foci (CCL25+Ki67+) and increased TNFα/TGF-β expression. Tissue damage was aggravated in "O" group. In conclusion, AS is able to trigger a severe intestinal inflammatory process in healthy mice, which spontaneously amplifies and perpetuates. Noise might be harmful to humans by aggravating inflammatory bowel diseases.

Blocking metabotropic glutamate receptor subtype 5 relieves maladaptive chronic stress consequences

Etiology and pharmacotherapy of stress-related psychiatric conditions and somatoform disorders are areas of high unmet medical need. Stressors holding chronic plus psychosocial components thereby bear the highest health risk. Although the metabotropic glutamate receptor subtype 5 (mGlu5) is well studied in the context of acute stress-induced behaviors and physiology, virtually nothing is known about its potential involvement in chronic psychosocial stress. Using the mGlu5 negative allosteric modulator CTEP (2-chloro-4-[2-[2,5-dimethyl-1-[4-(trifluoromethoxy)phenyl]imidazol-4yl]ethynyl]pyridine), a close analogue of the clinically active drug basimglurant - but optimized for rodent studies, as well as mGlu5-deficient mice in combination with a mouse model of male subordination (termed CSC, chronic subordinate colony housing), we demonstrate that mGlu5 mediates multiple physiological, immunological, and behavioral consequences of chronic psychosocial stressor exposure. For instance, CTEP dose-dependently relieved hypothalamo-pituitary-adrenal axis dysfunctions, colonic inflammation as well as the CSC-induced increase in innate anxiety; genetic ablation of mGlu5 in mice largely reproduced the stress-protective effects of CTEP and additionally ameliorated CSC-induced physiological anxiety. Interestingly, CSC also induced an upregulation of mGlu5 in the hippocampus, a stress-regulating brain area. Taken together, our findings provide evidence that mGlu5 is an important mediator for a wide range of chronic psychosocial stress-induced alterations and a potentially valuable drug target for the treatment of chronic stress-related pathologies in man.

Light and water are not simple conditions: fine tuning of animal housing in male C57BL/6 mice

While animal housing conditions are highly controlled and standardized between different laboratories, there are still many subtle differences that unavoidably influence the host organisms and, consequently, interlaboratory reproducibility. Here, we investigated the physiological and immunological consequences between two light/dark cycle (LDC) lengths (14-h/10-h vs. 12-h/12-h LDC) and two commonly used forms of drinking water (acidified drinking water (AW) versus normal tap water (NW)) in single-housed (SH) mice. Our results indicate that SH mice bred under a 12-h/12-h LDC and NW at the supplier's facility showed increased basal morning plasma corticosterone (CORT) levels even 4 weeks after arrival at our animal facility employing a 14-h/10-h LDC and AW. This effect was even more pronounced two weeks after arrival and had abated after 8 weeks. In agreement, increased plasma adrenocorticotropic hormone (ACTH), adrenal in vitro ACTH sensitivity, as well as relative and absolute adrenal weight normalized during this 8-week exposure to the novel and unfamiliar 14-h/10-h LDC and AW. Employment of a 12-h/12-h LDC in our facility completely abrogated the CORT-elevating effects of the 14-h/10-h LDC, despite these animals drinking AW. When both the water and light conditions were matched to those at the supplier's facility, we observed a further reduction in adrenal weight, increased thymus weight, and decreased pro-inflammatory cytokine secretion of isolated and anti-CD3/28-stimulated mesenteric lymph node cells. In summary, our results indicate that prolonged alteration of both the light phase and drinking water represent severe and long-lasting stressors for laboratory rodents. These findings are of general interest for all scientists obtaining their experimental animals from conventional suppliers.

Chronic subordinate colony housing paradigm: A mouse model for mechanisms of PTSD vulnerability, targeted prevention, and treatment-2016 Curt Richter Award Paper

There is considerable individual variability in vulnerability for developing posttraumatic stress disorder (PTSD); evidence suggests that this variability is related in part to genetic and environmental factors, including adverse early life experience. Interestingly, recent studies indicate that induction of chronic low-grade inflammation may be a common mechanism underlying gene and environment interactions that increase the risk for development of PTSD symptoms, and, therefore, may be a target for novel interventions for prevention or treatment of PTSD. Development of murine models with face, construct, and predictive validity would provide opportunities to investigate in detail complex genetic, environmental, endocrine, and immunologic factors that determine vulnerability to PTSD-like syndromes, and furthermore may provide mechanistic insight leading to development of novel interventions for both prevention and treatment of PTSD symptoms. Here we describe the potential use of the chronic subordinate colony housing (CSC) paradigm in mice as an adequate animal model for development of a PTSD-like syndrome and describe recent studies that suggest novel interventions for the prevention and treatment of PTSD.

Exercise and Prebiotics Produce Stress Resistance: Converging Impacts on Stress-Protective and Butyrate-Producing Gut Bacteria

The gut microbial ecosystem can mediate the negative health impacts of stress on the host. Stressor-induced disruptions in microbial ecology (dysbiosis) can lead to maladaptive health effects, while certain probiotic organisms and their metabolites can protect against these negative impacts. Prebiotic diets and exercise are feasible and cost-effective strategies that can increase stress-protective bacteria and produce resistance against the detrimental behavioral and neurobiological impacts of stress. The goal of this review is to describe research demonstrating that both prebiotic diets and exercise produce adaptations in gut ecology and the brain that arm the organism against inescapable stress-induced learned helplessness. The results of this research support the novel hypothesis that some of the stress-protective effects of prebiotics and exercise are due to increases in stress-protective gut microbial species and their metabolites. In addition, new evidence also suggests that prebiotic diet or exercise interventions are most effective if given early in life (juvenile-adolescence) when both the gut microbial ecosystem and the brain are plastic. Based on our new understanding of the mechanistic convergence of these interventions, it is feasible to propose that in adults, both interventions delivered in combination may elevate their efficacy to promote a stress-resistant phenotype.

Induction of Suppressor Cells and Increased Tumor Growth following Chronic Psychosocial Stress in Male Mice

To study the impact of psychosocial stress on the immune system, male mice were subjected to chronic subordinate colony housing (CSC), a preclinically validated mouse model for chronic psychosocial stress. CSC substantially affected the cell composition of the bone marrow, blood, and spleen by inducing myelopoiesis and enhancing the frequency of regulatory T cells in the CD4 population. Expansion of the myeloid cell compartment was due to cells identified as immature inflammatory myeloid cells having the phenotype of myeloid-derived suppressor cells of either the granulocytic or the monocytic type. Catecholaminergic as well as TNF signaling were implicated in these CSC-induced cellular shifts. Although the frequency of regulatory cells was enhanced following CSC, the high capacity for inflammatory cytokine secretion of total splenocytes indicated an inflammatory immune status in CSC mice. Furthermore, CSC enhanced the suppressive activity of bone marrow-derived myeloid-derived suppressor cells towards proliferating T cells. In line with the occurrence of suppressor cell types such as regulatory T cells and myeloid-derived suppressor cells, transplanted syngeneic fibrosarcoma cells grew better in CSC mice than in controls, a process accompanied by pronounced angiogenesis and clustering of immature myeloid cells in the tumor tissue. In addition, tumor implantation after CSC reinforced the CSC-induced increase in myeloid-derived suppressor cells and regulatory T cell frequencies while the CSC-induced cellular changes eased off in mice without tumor. Together, our data suggest a role for suppressor cells such as regulatory T cells and myeloid-derived suppressor cells in the enhanced tumor growth after chronic psychosocial stress.

Immunization with a heat-killed preparation of the environmental bacterium Mycobacterium vaccae promotes stress resilience in mice

The prevalence of inflammatory diseases is increasing in modern urban societies. Inflammation increases risk of stress-related pathology; consequently, immunoregulatory or antiinflammatory approaches may protect against negative stress-related outcomes. We show that stress disrupts the homeostatic relationship between the microbiota and the host, resulting in exaggerated inflammation. Repeated immunization with a heat-killed preparation of Mycobacterium vaccae, an immunoregulatory environmental microorganism, reduced subordinate, flight, and avoiding behavioral responses to a dominant aggressor in a murine model of chronic psychosocial stress when tested 1-2 wk following the final immunization. Furthermore, immunization with M. vaccae prevented stress-induced spontaneous colitis and, in stressed mice, induced anxiolytic or fear-reducing effects as measured on the elevated plus-maze, despite stress-induced gut microbiota changes characteristic of gut infection and colitis. Immunization with M. vaccae also prevented stress-induced aggravation of colitis in a model of inflammatory bowel disease. Depletion of regulatory T cells negated protective effects of immunization with M. vaccae on stress-induced colitis and anxiety-like or fear behaviors. These data provide a framework for developing microbiome- and immunoregulation-based strategies for prevention of stress-related pathologies.

Depletion of Cultivatable Gut Microbiota by Broad-Spectrum Antibiotic Pretreatment Worsens Outcome After Murine Stroke

BACKGROUND AND PURPOSE

Antibiotics disturbing microbiota are often used in treatment of poststroke infections. A bidirectional brain-gut microbiota axis was recently suggested as a modulator of nervous system diseases. We hypothesized that gut microbiota may be an important player in the course of stroke.

METHODS

We investigated the outcome of focal cerebral ischemia in C57BL/6J mice after an 8-week decontamination with quintuple broad-spectrum antibiotic cocktail. These microbiota-depleted animals were subjected to 60 minutes middle cerebral artery occlusion or sham operation. Infarct volume was measured using magnetic resonance imaging, and mice were monitored clinically throughout the whole experiment. At the end point, tissues were preserved for further analysis, comprising histology and immunologic investigations using flow cytometry.

RESULTS

We found significantly decreased survival in the middle cerebral artery occlusion microbiota-depleted mice when the antibiotic cocktail was stopped 3 days before surgery (compared with middle cerebral artery occlusion specific pathogen-free and sham-operated microbiota-depleted mice). Moreover, all microbiota-depleted animals in which antibiotic treatment was terminated developed severe acute colitis. This phenotype was rescued by continuous antibiotic treatment or colonization with specific pathogen-free microbiota before surgery. Further, infarct volumes on day one did not differ between any of the experimental groups.

CONCLUSIONS

Conventional microbiota ensures intestinal protection in the mouse model of experimental stroke and prevents development of acute and severe colitis in microbiota-depleted mice not given antibiotic protection after cerebral ischemia. Our experiments raise the clinically important question as to whether microbial colonization or specific microbiota are crucial for stroke outcome.

The microbiome: A key regulator of stress and neuroinflammation

There is a growing emphasis on the relationship between the complexity and diversity of the microorganisms that inhabit our gut (human gastrointestinal microbiota) and health/disease, including brain health and disorders of the central nervous system. The microbiota-gut-brain axis is a dynamic matrix of tissues and organs including the brain, glands, gut, immune cells and gastrointestinal microbiota that communicate in a complex multidirectional manner to maintain homeostasis. Changes in this environment can lead to a broad spectrum of physiological and behavioural effects including hypothalamic-pituitary-adrenal (HPA) axis activation, and altered activity of neurotransmitter systems and immune function. While an appropriate, co-ordinated physiological response, such as an immune or stress response are necessary for survival, a dysfunctional response can be detrimental to the host contributing to the development of a number of CNS disorders. In this review, the involvement of the gastrointestinal microbiota in stress-mediated and immune-mediated modulation of neuroendocrine, immune and neurotransmitter systems and the consequential behaviour is considered. We also focus on the mechanisms by which commensal gut microbiota can regulate neuroinflammation and further aim to exploit our understanding of their role in stress-related disorders as a consequence of neuroinflammatory processes.

Subacute stress and chronic stress interact to decrease intestinal barrier function in rats

Psychological stress increases intestinal permeability, potentially leading to low-grade inflammation and symptoms in functional gastrointestinal disorders. We assessed the effect of subacute, chronic and combined stress on intestinal barrier function and mast cell density. Male Wistar rats were allocated to four experimental groups (n = 8/group): 1/sham; 2/subacute stress (isolation and limited movement for 24 h); 3/chronic crowding stress for 14 days and 4/combined subacute and chronic stress. Jejunum and colon were collected to measure: transepithelial electrical resistance (TEER; a measure of epithelial barrier function); gene expression of tight junction molecules; mast cell density. Plasma corticosterone concentration was increased in all three stress conditions versus sham, with highest concentrations in the combined stress condition. TEER in the jejunum was decreased in all stress conditions, but was significantly lower in the combined stress condition than in the other groups. TEER in the jejunum correlated negatively with corticosterone concentration. Increased expression of claudin 1, 5 and 8, occludin and zonula occludens 1 mRNAs was detected after subacute stress in the jejunum. In contrast, colonic TEER was decreased only after combined stress, and the expression of tight junction molecules was unaltered. Increased mast cell density was observed in the chronic and combined stress condition in the colon only. In conclusion, our data show that chronic stress sensitizes the gastrointestinal tract to the effects of subacute stress on intestinal barrier function; different underlying cellular and molecular alterations are indicated in the small intestine versus the colon.

Aggravation of Established Colitis in Specific Pathogen-free IL-10 Knockout Mice by Restraint Stress Is Not Mediated by Increased Colonic Permeability

BACKGROUND

Pathogenic mechanisms responsible for the undulating symptom pattern, or indeed causative agents for the development, of inflammatory bowel diseases [IBD] are largely unknown. Many physicians and most patients are convinced that stress affects the course of IBD. As with most factors that contribute to IBD, it is unclear whether stress merely exacerbates established disease or indeed contributes to the development of disease. We designed this study to investigate whether stress induces or aggravates colitis in interkeukin-10 knockout [IL-10 ko] mice and to determine the role of intestinal permeability in this model of stress-related colitis.

METHODS

The study was divided into two experiments depending on the age of the animals. Stress was induced by placing 5-week old disease-free mice or 8-week-old mice (IL-10ko and wild type [wt]) with mild colitis in movement restrainers for 2h twice daily for 7 days. The development of colitis was assessed clinically [weight and faecal pellet production], histologically [haematoxylin and eosin staining], and biochemically [colonic IL-2, IL-4, IL-6, IL-12p40, TNFα, and IFNγ]. Permeability was measured in Ussing chambers.

RESULTS

Faecal pellet production increased significantly in all stressed animals compared with control animals, indicating successful application of stress. Stressed 8-week old mice lost weight [p < 0.001] and stressed IL-10(-/-) mice showed a significantly increased histological score compared with non-stressed or wt mice [p < 0.001]. There was no appreciable difference in cytokine production. Stress did not alter intestinal permeability.

CONCLUSIONS

Restraint stress aggravates experimental colitis in 8-week old IL-10ko mice but cannot induce colitis in disease-free younger mice. This is not mediated by an increased intestinal permeability.

Correlation between anxiety/depression and quality of life in patients with inflammatory bowel disease

AIM: To explore the influence of psychological factors on the quality of life in patients with inflammatory bowel disease (IBD) by analyzing the correlation between anxiety/depression and quality of life.

METHODS: One hundred patients with IBD and 100 healthy volunteers were included. The Self-rating Anxiety Scale, Self-rating Depression Scale, Inflammatory Bowel Disease Questionnaire (IBDQ), and Medical Outcomes Study Short Form 36 (SF-36) were used for evaluation of anxiety, depression, and quality of life. Statistical analysis was then performed to evaluate the correlation between anxiety/depression and quality of life.

RESULTS: IBDQ score and IBD SF-36 quality of life score were significantly lower in IBD patients than in healthy people (P = 0.000, 0.003). Anxiety and depression scores were significantly higher in IBD patients than in healthy people (P = 0.006, 0.004). There was a negative correlation between anxiety/depression and quality of life in IBD patients (P < 0.05).

CONCLUSION: The quality of life of patients with IBD decreases with the increase of anxiety and depression. In order to improve the quality of life of patients, it is necessary to conduct psychological assessment and give psychological intervention and/or anti-anxiety drug treatment.

Effects of experimental housing conditions on recovery of laboratory mice

The beneficial effects of environment and social support during disease recovery in humans are widely accepted. Because laboratory mice are social animals and are highly motivated to interact with each other and with their environment, it is very likely that environmental and social factors are also beneficial to their recovery from experimental interventions or spontaneous diseases. The beneficial effects of enriched environments have been particularly well analyzed in the field of brain disorders, but several studies suggest that positive social contact and a complex and familiar environment may also support recovery from injury, from invasive procedures such as surgery or from spontaneously occurring diseases. The author reviews relevant publications on the effects of environment and social housing on recovery from disease or surgery in laboratory mice and other rodents. She concludes that in addition to promoting animal welfare, provision of optimal experimental housing conditions might also contribute to the clinical relevance of preclinical animal models by more closely simulating the environmental and social characteristics of disease recovery in humans.

Chronic subordinate colony housing paradigm: a mouse model to characterize the consequences of insufficient glucocorticoid signaling

Chronic, in particular chronic psychosocial, stress is a burden of modern societies and known to be a risk factor for numerous somatic and affective disorders (in detail referenced below). However, based on the limited existence of appropriate, and clinically relevant, animal models for studying the effects of chronic stress, the detailed behavioral, physiological, neuronal, and immunological mechanisms linking stress and such disorders are insufficiently understood. To date, most chronic stress studies in animals employ intermittent exposure to the same (homotypic) or to different (heterotypic) stressors of varying duration and intensity. Such models are only of limited value, since they do not adequately reflect the chronic and continuous situation that humans typically experience. Furthermore, application of different physical or psychological stimuli renders comparisons to the mainly psychosocial stressors faced by humans, as well as between the different stress studies almost impossible. In contrast, rodent models of chronic psychosocial stress represent situations more akin to those faced by humans and consequently seem to hold more clinical relevance. Our laboratory has developed a model in which mice are exposed to social stress for 19 continuous days, namely the chronic subordinate colony housing (CSC) paradigm, to help bridge this gap. The main aim of the current review article is to provide a detailed summary of the behavioral, physiological, neuronal, and immunological consequences of the CSC paradigm, and wherever possible relate the findings to other stress models and to the human situation.

Stress and the commensal microbiota: importance in parturition and infant neurodevelopment

The body is colonized by an enormous array of microbes that are collectively called the microbiota. During quiescent periods, microbial communities within the gut are relatively resistant to change. However, several factors that disrupt homeostasis can also significantly change gut microbial community structure. One factor that has been shown to change the composition of the gut microbiota is exposure to psychological stressors. Studies demonstrate that the commensal microbiota are involved in stressor-induced immunomodulation, but other biological effects are not yet known. This review discusses emerging evidence that the microbiota can impact the brain and behavior and indicates that stressor-induced alterations in the composition of gut microbial communities contribute to stressor-induced behavioral changes. This review will also discuss the evidence that such effects are most evident early in life, where both stress and the microbiota have been linked to birth outcomes, such as prematurity, and neurodevelopment. When considered together, a paradigm emerges in which stressor-induced alterations in commensal microbial populations significantly impact parturition and infant neurodevelopment.

Paradoxical benefits of psychological stress in inflammatory dermatoses models are glucocorticoid mediated

Acute psychological stress (PS) mobilizes metabolic responses that are of immediate benefit to the host, but the current medical paradigm holds that PS exacerbates systemic and cutaneous inflammatory disorders. Although the adverse consequences of PS are usually attributed to neuroimmune mechanisms, PS also stimulates an increase in endogenous glucocorticoids (GCs) that compromises permeability barrier homeostasis, stratum corneum cohesion, wound healing, and epidermal innate immunity in normal skin. Yet, if such PS-induced increases in GC were uniformly harmful, natural selection should have eliminated this component of the stress response. Hence, we hypothesized here instead that stress-induced elevations in endogenous GC could benefit, rather than aggravate, cutaneous function and reduce inflammation in three immunologically diverse mouse models of inflammatory diseases. Indeed, superimposed exogenous (motion-restricted) stress reduced, rather than aggravated inflammation and improved epidermal function in all three models, even normalizing serum IgE levels in the atopic dermatitis model. Elevations in endogenous GC accounted for these apparent benefits, because coadministration of mifepristone prevented stress-induced disease amelioration. Thus, exogenous stress can benefit rather than aggravate cutaneous inflammatory dermatoses through the anti-inflammatory activity of increased endogenous GC.

Dose-dependent effects of chronic central infusion of oxytocin on anxiety, oxytocin receptor binding and stress-related parameters in mice

Chronic psychosocial stress is a recognized risk factor for various affective and somatic disorders. In an established murine model of chronic psychosocial stress, exposure to chronic subordinate colony housing (CSC) results in an alteration of physiological, behavioral, neuroendocrine and immunological parameters, including a long-lasting increase in anxiety, adrenal hypertrophy and thymus atrophy. Based on the stress-protective and anxiolytic properties of oxytocin (OXT) after acute administration in rodents and humans, the major aims of our study were to assess whether chronic administration of OXT dose-dependently affects the behavior and physiology of male mice, as for therapeutic use in humans, mostly chronic treatment approaches will be used. Further, we studied, whether chronic administration during CSC prevents stress-induced consequences. Our results indicate that chronic intracerebroventricular (ICV) infusion of OXT (15 days) at high (10ng/h), but not at low (1ng/h) dose, induces an anxiogenic phenotype with a concomitant reduction of OXT receptor (OXTR) binding within the septum, the basolateral and medial amygdala, as well as the median raphe nucleus. Further, we demonstrate that chronic ICV infusion of OXT (1ng/h) during a 19-day CSC exposure prevents the hyper-anxiety, thymus atrophy, adrenal hypertrophy, and decreased in vitro adrenal ACTH sensitivity. Thus, given both negative, but also beneficial effects seen after chronic OXT treatment, which appear to be dose-dependent, a deeper understanding of long-lasting treatment effects is required before OXT can be considered for long-term therapeutic use for the treatment of psychopathologies such as autism, schizophrenia or anxiety-disorders.

Regulation of 11β-hydroxysteroid dehydrogenase type 1 and 7α-hydroxylase CYP7B1 during social stress

11β-hydroxysteroid dehydrogenase type 1 (11HSD1) is an enzyme that amplifies intracellular glucocorticoid concentration by the conversion of inert glucocorticoids to active forms and is involved in the interconversion of 7-oxo- and 7-hydroxy-steroids, which can interfere with the activation of glucocorticoids. The presence of 11HSD1 in the structures of the hypothalamic-pituitary-adrenal (HPA) axis suggests that this enzyme might play a role in the regulation of HPA output. Here we show that the exposure of Fisher 344 rats to mild social stress based on the resident-intruder paradigm increased the expression of 11HSD1 and CYP7B1, an enzyme that catalyzes 7-hydroxylation of steroids. We found that social behavioral profile of intruders was significantly decreased whereas their plasma levels of corticosterone were increased more than in residents. The stress did not modulate 11HSD1 in the HPA axis (paraventricular nucleus, pituitary, adrenal cortex) but selectively upregulated 11HSD1 in some regions of the hippocampus, amygdala and prelimbic cortex. In contrast, CYP7B1 was upregulated not only in the hippocampus and amygdala but also in paraventricular nucleus and pituitary. Furthermore, the stress downregulated 11HSD1 in the thymus and upregulated it in the spleen and mesenteric lymphatic nodes whereas CYP7B1 was upregulated in all of these lymphoid organs. The response of 11HSD1 to stress was more obvious in intruders than in residents and the response of CYP7B1 to stress predominated in residents. We conclude that social stress induces changes in enzymes of local metabolism of glucocorticoids in lymphoid organs and in brain structures associated with the regulation of the HPA axis. In addition, the presented data clearly suggest a role of 11HSD1 in modulation of glucocorticoid feedback of the HPA axis during stress.

Stress resilience: a low-anxiety genotype protects male mice from the consequences of chronic psychosocial stress

Chronic psychosocial stress is a risk factor for the development of affective as well as somatic disorders. However, vulnerability to adverse stress effects varies between individuals, with previous negative life events along with genetic predisposition playing a major role. In support, we previously showed that the consequences of chronic psychosocial stress induced by chronic subordinate colony housing (CSC, 19 days) can be amplified by pre-exposing mice to repeated maternal separation during early life. To test the significance of the genetic predisposition on the effects of CSC, mice selectively bred for high (mHAB) and low (mLAB) anxiety-related behavior and nonselected CD1 mice (mNAB) were exposed to CSC in the present study. In confirmation of our previous results, CSC mice of both mHAB and mNAB lines displayed chronic stress-related symptoms including increased adrenal weight, decreased adrenal in vitro ACTH sensitivity, lower plasma corticosterone to ACTH ratio, and increased interferon-γ secretion from isolated mesenteric lymph node cells compared with single-housed controls of the respective line. However, the CSC-induced anxiogenic effect found in mNAB was not confirmed in mHAB mice, possibly due to a ceiling effect in these highly anxious mice. Interestingly, mHAB were not more vulnerable to CSC than mNAB mice, whereas mLAB mice were resilient to CSC as indicated by all of the above mentioned parameters assessed. Taken together, our findings indicate that the genetic predisposition, in this case the innate anxiety of an individual, affects vulnerability to chronic psychosocial stress, with a low-anxiety phenotype mediating resilience to both affective and somatic consequences of CSC.

Influence of stressor-induced nervous system activation on the intestinal microbiota and the importance for immunomodulation

The body is colonized by a vast population of genetically diverse microbes, the majority of which reside within the intestines to comprise the intestinal microbiota. During periods of homeostasis, these microbes reside within stable climax communities, but exposure to physical, physiological, as well as psychological stressors can significantly impact the structure of the intestinal microbiota. This has been demonstrated in humans and laboratory animals, with the most consistent finding being a reduction in the abundance of bacteria in the genus Lactobacillus. Whether stressor exposure also changes the function of the microbiota, has not been as highly studied. The studies presented in this review suggest that stressor-induced disruption of the intestinal microbiota leads to increased susceptibility to enteric infection and overproduction of inflammatory mediators that can induce behavioral abnormalities, such as anxiety-like behavior. Studies involving germfree mice also demonstrate that the microbiota are necessary for stressor-induced increases in innate immunity to occur. Exposing mice to a social stressor enhances splenic macrophage microbicidal activity, but this effect fails to occur in germfree mice. These studies suggest a paradigm in which stressor exposure alters homeostatic interactions between the intestinal microbiota and mucosal immune system and leads to the translocation of pathogenic, and/or commensal, microbes from the lumen of the intestines to the interior of the body where they trigger systemic inflammatory responses and anxiety-like behavior. Restoring homeostasis in the intestines, either by removing the microbiota or by administering probiotic microorganisms, can ameliorate the stressor effects.

Stress-Derived Corticotropin Releasing Factor Breaches Epithelial Endotoxin Tolerance

BACKGROUND AND AIMS

Loss of the endotoxin tolerance of intestinal epithelium contributes to a number of intestinal diseases. The etiology is not clear. Psychological stress is proposed to compromise the intestinal barrier function. The present study aims to elucidate the role of the stress-derived corticotropin releasing factor (CRF) in breaching the established intestinal epithelial endotoxin tolerance.

METHODS

Epithelial cells of HT-29, T84 and MDCK were exposed to lipopolysaccharide to induce the endotoxin tolerance; the cells were then stimulated with CRF. The epithelial barrier function was determined using as indicators of the endotoxin tolerant status. A water-avoid stress mouse model was employed to test the role of CRF in breaching the established endotoxin tolerance in the intestine.

RESULTS

The established endotoxin tolerance in the epithelial cell monolayers was broken down by a sequent exposure to CRF and LPS manifesting a marked drop of the transepithelial resistance (TER) and an increase in the permeability to a macromolecular tracer, horseradish peroxidase (HRP). The exposure to CRF also increased the expression of Cldn2 in the epithelial cells, which could be mimicked by over expression of TLR4 in epithelial cells. Over expression of Cldn2 resulted in low TER in epithelial monolayers and high permeability to HRP. After treating mice with the 10-day chronic stress, the intestinal epithelial barrier function was markedly compromised, which could be prevented by blocking either CRF, or TLR4, or Cldn2.

CONCLUSIONS

Psychological stress-derived CRF can breach the established endotoxin tolerance in the intestinal mucosa.

Correlation between psychological factors and irritable bowel syndrome

AIM: To investigate the incidence of anxiety and depression and factors associated with the occurrence of anxiety and depression in patients with irritable bowel syndrome (IBS) to provide a theoretical basis for the use of anti-anxiety/depression and psychological treatments in IBS patients with psychological abnormalities.

METHODS: Sixty patients with IBS treated from December 2010 to December 2011 in Department of Gastroenterology of the First Affiliated Hospital of Kunming Medical University and 60 healthy controls were included in this study. The patients were assessed using the ZUNG self-rating anxiety scale, ZUNG self-rating depression scale, life event scale and social support rating scale. All scores were compared using statistical methods.

RESULTS: The incidences of anxiety and depression were significantly higher in IBS patients than in healthy controls (P < 0.05, P < 0.01). The self-rating anxiety scale and self-rating depression scale scores differed significantly between IBS patients and healthy controls (both P < 0.01). Although there was no significant difference in positive event scores and social support total scores between IBS patients and healthy controls (both P > 0.05), a statistical significance was noted in negative event score between the two groups (P < 0.01).

CONCLUSION: The incidences of anxiety and depression are significantly higher in IBS patients than in normal controls. Negative life events have an important mental impact on IBS patients. Life events and social support are closely related to psychological changes in IBS patients. IBS patients' psychological state should be monitored in clinical practice, and appropriate interventions should be given if anxiety and depression develop in these patients.

HPA axis changes during the initial phase of psychosocial stressor exposure in male mice

Chronic subordinate colony (CSC) housing for 19 days results in unaffected basal morning corticosterone (CORT) levels despite a pronounced increase in adrenal mass, likely mediated by an attenuation of adrenal corticotropin (ACTH) responsiveness. Given that the pronounced increase in basal morning plasma CORT levels returns to baseline as early as 48 h after the start of CSC, it is likely that the attenuated ACTH responsiveness develops already during this initial phase. This was tested in the present study. In line with previous findings, basal morning plasma CORT levels were elevated following 10 h, but not 48 h, of CSC exposure. Basal morning plasma ACTH concentrations and relative in vivo adrenal CORT content were increased following 10 h and to a lesser extent following 48 h of CSC exposure, positively correlating. Relative in vitro adrenal CORT secretion in response to ACTH (100 nM) and kidney protein expression of 11β-hydroxysteroid dehydrogenase type 2 (HSD11B2) were unaffected following both time points. Adrenal mRNA expression of key steroidogenic enzymes was unaffected/decreased following 10 h and unaffected/increased following 48 h of CSC exposure. Together, our findings suggest that basal plasma hypercorticism during the initial CSC phase is mainly prevented by an attenuation of pituitary ACTH release. An increased absolute adrenal weight following 10 h, but not 48 h, of CSC exposure indicates that restoration of normal adrenal mass also adds to a lesser extent to prevent basal hypercorticism. A contributing role of alterations in enzymatic CORT degradation and steroidogenic enzyme availability is likely, but has to be further addressed in future studies.