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

Gut microbiome resilience of green-lipped mussels, Perna canaliculus, to starvation

Host gut microbiomes play an important role in animal health and resilience to conditions, such as malnutrition and starvation. These host-microbiome relationships are poorly understood in the marine mussel Perna canaliculus, which experiences significant variations in food quantity and quality in coastal areas. Prolonged starvation may be a contributory factor towards incidences of mass mortalities in farmed mussel populations, resulting in highly variable production costs and unreliable market supplies. Here, we examine the gut microbiota of P. canaliculus in response to starvation and subsequent re-feeding using high-throughput amplicon sequencing of the 16S rRNA gene. Mussels showed no change in bacterial species richness when subjected to a 14-day starvation, followed by re-feeding/recovery. However, beta bacteria diversity revealed significant shifts (PERMANOVA p-value < 0.001) in community structure in the starvation group and no differences in the subsequent recovery group (compared to the control group) once they were re-fed, highlighting their recovery capability and resilience. Phylum-level community profiles revealed an elevation in dominance of Proteobacteria (ANCOM-BC p-value <0.001) and Bacteroidota (ANCOM-BC p-value = 0.04) and lower relative abundance of Cyanobacteria (ANCOM-BC p-value = 0.01) in the starvation group compared to control and recovery groups. The most abundant genus-level shifts revealed relative increases of the heterotroph Halioglobus (p-value < 0.05) and lowered abundances of the autotroph Synechococcus CC9902 in the starvation group. Furthermore, a SparCC correlation network identified co-occurrence of a cluster of genera with elevated relative abundance in the starved mussels that were positively correlated with Synechococcus CC9902. The findings from this work provide the first insights into the effect of starvation on the resilience capacity of Perna canaliculus gut microbiota, which is of central importance to understanding the effect of food variation and limitation in farmed mussels.

Gut Microbiota in Ischemic Stroke: Role of Gut Bacteria-Derived Metabolites

Ischemic stroke (IS) remains a leading cause of death and long-term disability globally. Several mechanisms including glutamate excitotoxicity, calcium overload, neuroinflammation, oxidative stress, mitochondrial damage, and apoptosis are known to be involved in the pathogenesis of IS, but the underlying pathophysiology mechanisms of IS are not fully clarified. During the past decade, gut microbiota were recognized as a key regulator to affect the health of the host either directly or via their metabolites. Recent studies indicate that gut bacterial dysbiosis is closely related to hypertension, diabetes, obesity, dyslipidemia, and metabolic syndrome, which are the main risk factors for cardiovascular diseases. Increasing evidence indicates that IS can lead to perturbation in gut microbiota and increased permeability of the gut mucosa, known as "leaky gut," resulting in endotoxemia and bacterial translocation. In turn, gut dysbiosis and impaired intestinal permeability can alter gut bacterial metabolite signaling profile from the gut to the brain. Microbiota-derived products and metabolites, such as short-chain fatty acids (SCFAs), bile acids (BAs), trimethylamine N-oxide (TMAO), lipopolysaccharides (LPS), and phenylacetylglutamine (PAGln) can exert beneficial or detrimental effects on various extraintestinal organs, including the brain, liver, and heart. These metabolites have been increasingly acknowledged as biomarkers and mediators of IS. However, the specific role of the gut bacterial metabolites in the context of stroke remains incompletely understood. In-depth studies on these products and metabolites may provide new insight for the development of novel therapeutics for IS.

Development programming: Stress during gestation alters offspring development in sheep

Inappropriate management practices of domestic animals during pregnancy can be potential stressors, resulting in complex behavioural, physiological and neurological consequences in the developing offspring. Some of these consequences can last into adulthood or propagate to subsequent generations. We systematically summarized the results of different experimental patterns using artificially increased maternal glucocorticoid levels or prenatal maternal physiological stress paradigms, mediators between prenatal maternal stress (PMS) and programming effects in the offspring and the effects of PMS on offspring phenotypes in sheep. PMS can impair birthweight, regulate the development of the hypothalamic-pituitary-adrenal axis, modify behavioural patterns and cognitive abilities and alter gene expression and brain morphology in offspring. Further research should focus on the effects of programming on gene expression, immune function, gut microbiome, sex-specific effects and maternal behaviour of offspring, especially comparative studies of gestational periods when PMS is applied, continual studies of programming effects on offspring and treatment strategies that effectively reverse the detrimental programming effects of prenatal stress.

The impact of maternal stress on the development of necrotizing enterocolitis: A comprehensive review

Necrotizing Enterocolitis (NEC) is a devastating intestinal inflammatory disease with significant morbidity and mortality. Numerous predictors have been implicated in the development of NEC, with a relatively less emphasis on maternal factors. Pregnancy drives women into a new stage of life that increases their susceptibility to biological and psychological stress. Additionally, maternal stress during pregnancy has been linked to various complications that can negatively impact both the mother and the developing fetus. These detrimental effects are facilitated by various systemic modifications. Similarly, there is evidence from animal studies that suggest a relationship between maternal stress and the occurrence of NEC due to the alterations observed in neonates. In this review, we will (1) discuss the physiological and psychological burden of maternal stress and how it can be linked to NEC, (2) summarize various predictors and risk factors of NEC, and (3) discuss the most widely utilized animal models for assessing the effects of prenatal stress on offspring.

A Review of the Impact of Maternal Prenatal Stress on Offspring Microbiota and Metabolites

Maternal prenatal stress exposure affects the development of offspring. We searched for articles in the PubMed database and reviewed the evidence for how prenatal stress alters the composition of the microbiome, the production of microbial-derived metabolites, and regulates microbiome-induced behavioral changes in the offspring. The gut-brain signaling axis has gained considerable attention in recent years and provides insights into the microbial dysfunction in several metabolic disorders. Here, we reviewed evidence from human studies and animal models to discuss how maternal stress can modulate the offspring microbiome. We will discuss how probiotic supplementation has a profound effect on the stress response, the production of short chain fatty acids (SCFAs), and how psychobiotics are emerging as novel therapeutic targets. Finally, we highlight the potential molecular mechanisms by which the effects of stress are transmitted to the offspring and discuss how the mitigation of early-life stress as a risk factor can improve the birth outcomes.

The effect of occlusal disharmony on a chronic stress-induced animal model of gut microbiota dysbiosis

BACKGROUND AND OBJECTIVES

Chronic stress (CS) is closely related to intestinal health. Occlusal disharmony (OD) is a risk factor for hypersensitivity to novel stress, and the relationship between OD and the intestinal system with or without other chronic stresses remains unclear. Therefore, the purpose of this study was to investigate whether OD affects the gut microbiota and the intestinal barrier in a CS-exposed animal model.

METHODS

OD was induced by making a 0.5-mm-thick incision on the right maxillary molar. CS involved exposure to one stressor per day for 35 days. Sprague-Dawley rats were randomly divided into an untreated control group and OD-, CS- and OD + CS-treated groups. The behavioural tests, serum corticosterone level, gut microbiota composition and tight junction protein expression in colon tissue were measured on the 56th day to elucidate the effect of OD on animals under CS.

RESULTS

Significant differences in performance on behavioural tests and serum corticosterone concentrations were observed on day 56 in the OD + CS group compared with the control group. Exposure to occlusal disharmony or chronic stress resulted in a change in the composition of the gut microbiota of rats. Differences in the expression of the tight junction proteins zonula occludens-1 and junctional adhesion molecule-A were observed in colon tissue from the OD + CS group compared with the control group.

CONCLUSIONS

We concluded that the significant changes in performance on behavioural tests, serum corticosterone concentrations and microbiota dysbiosis and tight junction protein levels induced by OD with CS may indicate that OD is a potential factor promoting gut microbiota dysbiosis.

Antimicrobial Peptides Relieve Transportation Stress in Ragdoll Cats by Regulating the Gut Microbiota

Transportation is common in cats and often causes stress and intestinal disorders. Antimicrobial peptides (AMPs) exhibit a broad spectrum of antibacterial activity, and they may have the capacity for antioxidant and immune regulation. The objective of this study was to investigate the effects of dietary supplementation with AMPs on stress response, gut microbiota and metabolites of cats that have undergone transport stress. A total of 14 Ragdoll cats were randomly allocated into 2 treatments: basal diet (CON) and a basal diet supplemented with 0.3% AMPs. After a 6-week feeding period, all cats were transported for 3 h and, then, fed for another week. The results show that the diarrhea rate of cats was markedly reduced by supplementation with AMPs throughout the trial period (p < 0.05). In addition, AMPs significantly reduced serum cortisol and serum amyloid A (p < 0.05) and increased apolipoprotein 1 after transportation (p < 0.05). Moreover, AMPs reduced the level of inflammatory factors in the serum caused by transportation stress, including tumor necrosis factor-alpha (TNF-α) and interleukin-1 beta (IL-1β) (p < 0.05). The AMPs enhanced the activities of glutathione peroxidase (p < 0.01) and superoxide dismutase (p < 0.05). Furthermore, cats fed AMPs had higher levels of branched chain fatty acids (BCFAs) and a relative abundance of Blautia and a lower relative abundance of Negativibacillus after transportation (p < 0.05). The serum metabolome analysis further revealed that AMPs markedly regulated lipid metabolism by upregulating cholic acid expression. In conclusion, AMP supplementation alleviated oxidative stress and inflammatory response in transportation by regulating the gut microbiota and metabolites, thereby relieving stress-induced diarrhea and supporting gut and host health in cats.

[The regulatory role of gut microbiota in inflammation in depression and anxiety]

Numerous studies have identified the important role of the gut microbiota in maintaining of the CNS normal functioning and in the pathogenesis of mental disorders as one of the systems regulating the bidirectional communication between the gut and the brain. The microbiota has been found to be involved in the modulation of inflammation as well as in the development and function of the immune and nervous systems. It is assumed that in multicellular organisms, the nervous and immune systems have evolved together with the microbiota, being in interaction with it, in order to optimize the body's ability to adapt to a wide range of environmental stresses in order to maintain the constancy of its homeostasis. Normally, microbes live in stable communities, while under conditions of even mild or chronic social stress, significant shifts in the composition of the microbiota occur, which lead to the development of dysbiosis associated with changes in microbiota metabolites, which can lead to the formation of physiology and behavior characteristic of stress and depression. Microbes influence the activation of peripheral immune cells that regulate the response to neuroinflammation, brain damage, autoimmune responses, and neurogenesis. The review provides a brief overview of the normal gut microbiota, describes the factors influencing the state of the microbiota, and also discusses recent discoveries concerning the regulatory effect of the gut microbiota on CNS functions, the immune system, and inflammation in the pathogenesis of depression and anxiety.

Cross Brain-Gut Analysis Highlighted Hub Genes and LncRNA Networks Differentially Modified During Leucine Consumption and Endurance Exercise in Mice with Depression-Like Behaviors

Depression is a frequent mood disorder that might impair the brain-gut axis. In this study, we divided 30 mice into five groups: untreated mice, mice with depression-like behaviors, mice with depression-like behaviors treated with consumed leucine, mice with depression-like behaviors treated with exercise training, mice with depression-like behaviors treated with exercise training along with consumed leucine. According to artificial intelligence biological analysis, we found some mediators such as lncRNAs profile and Kdr/Vegfα/Pten/Bdnf interactions network in the hippocampus region and ileum tissue which could be decisive molecules in the brain-gut axis. Moreover, KDR as a principal cutpoint protein in the network was identified as the pharmaceutical approach for major depressive ameliorating based on pharmacophore modeling and molecular docking outcomes. Furthermore, we indicated that the mRNA and protein level of the Pten enhanced and Vegfα/Kdr/Bdnf mRNAs, as well as the protein level of KDR, decreased in mice with depression-like behaviors. Moreover, exercise and leucine ameliorated the brain-gut axis in mice with depression-like behaviors. Exercise and leucine regulated the lncRNAs network in the hippocampus and ileum of mice with depression-like behaviors. We suggest that the lncRNAs profiles could be considered as diagnosis and prognosis biomarkers, and exercise + leucine might be a practical approach to improve depression.

Changes in intestinal barrier protein expression and intestinal flora in a rat model of visceral hypersensitivity

BACKGROUND

Destruction of the intestinal mucosal barrier and visceral hypersensitivity are main pathogenesis of irritable bowel syndrome (IBS). The study aimed to establish a rat model of visceral hypersensitivity and explore mechanisms involved the changes of the intestinal barrier protein expression and intestinal flora.

METHODS

A rat model of visceral hypersensitivity was established and evaluated using abdominal withdrawal reflex (AWR) scores, colonic paracellular permeability, and gastrointestinal motility. The expression of tight junction proteins, aquaporin proteins (AQPs), phosphorylated ERK, and proteinase-activated receptor-2 (PAR-2) was determined. The intestinal microflora was evaluated by high-throughput sequencing of the 16S rRNA gene.

KEY RESULTS

In model rats, AWR score and fecal water content were significantly increased, gastrointestinal motilities were disorder and characterized by an inhibition of gastric motility and an enhancement of small intestinal and colonic movement. The expressions of colonic occludin, ZO-1, AQP3, and AQP8 were decreased but claudin-2 and claudin-4 were markedly increased. Imbalance of intestinal flora appeared and showed an obvious decrease of Lactobacillus and an increase of Clostridiales_bacterium. Additionally, the total serine protease activity in feces, the expressions of PAR2 and phosphorylated ERK in the colon tissues were increased significantly.

CONCLUSION AND INFERENCES

The model rats of visceral hypersensitivity possess the decreased expression of occludin, ZO-1, AQP3, AQP8, and the increased expression of claudin-2 and claudin-4, meanwhile develop an imbalance of intestinal flora which probably increase serine protease activity, thereby activating the PAR2/ERK signaling and causing the intestinal barrier disorder.

Gallic Acid Alleviates Gut Dysfunction and Boosts Immune and Antioxidant Activities in Puppies Under Environmental Stress Based on Microbiome-Metabolomics Analysis

Early-life exposure to environmental stress disrupts the gut barrier and leads to inflammatory responses and changes in gut microbiota composition. Gallic acid (GA), a natural plant polyphenol, has received significant interest for its antioxidant, anti-inflammatory, and antimicrobial properties that support the maintenance of intestinal health. To assess whether dietary supplementation of GA alleviates environmental stress, a total of 19 puppies were randomly allocated to the following three dietary treatments for 2 weeks: 1) basal diet (control (CON)); 2) basal diet + transportation (TS); and 3) basal diet with the addition of 500 mg/kg of GA + transportation (TS+GA). After a 1-week supplementation period, puppies in the TS and TS+GA groups were transported from a stressful environment to another livable location, and puppies in the CON group were then left in the stressful environment. Results indicated that GA markedly reduced the diarrhea rate in puppies throughout the trial period and caused a moderate decline of serum cortisol and HSP-70 levels after transportation. Also, GA alleviated the oxidative stress and inflammatory response caused by multiple environmental stressors. Meanwhile, puppies fed GA had a higher abundance of fecal Firmicutes and Lactobacillus and lower Proteobacteria, Escherichia–Shigella, and Clostridium_sensu_stricto_1 after transportation. As a result, the TS+GA group had the highest total short-chain fatty acids and acetic acid. Also, the fecal and serum metabolomics analyses revealed that GA markedly reversed the abnormalities of amino acid metabolism, lipid metabolism, carbohydrate metabolism, and nucleotide metabolism caused by stresses. Finally, Spearman’s correlation analysis was carried out to explore the comprehensive microbiota and metabolite relationships. Overall, dietary supplementation of GA alleviates oxidative stress and inflammatory response in stressed puppies by causing beneficial shifts on gut microbiota and metabolites that may support gut and host health.

WORKbiota: A Systematic Review about the Effects of Occupational Exposure on Microbiota and Workers' Health

The characterization of human microbiota and the impact of its modifications on the health of individuals represent a current topic of great interest for the world scientific community. Scientific evidence is emerging regarding the role that microbiota has in the onset of important chronic illnesses. Since individuals spend most of their life at work, occupational exposures may have an impact on the organism’s microbiota. The purpose of this review is to explore the influence that different occupational exposures have on human microbiota in order to set a new basis for workers’ health protection and disease prevention. The literature search was performed in PubMed, Cochrane, and Scopus. A total of 5818 references emerged from the online search, and 31 articles were included in the systematic review (26 original articles and 5 reviews). Exposure to biological agents (in particular direct contact with animals) was the most occupational risk factor studied, and it was found involved in modifications of the microbiota of workers. Changes in microbiota were also found in workers exposed to chemical agents or subjected to work-related stress and altered dietary habits caused by specific microclimate characteristics or long trips. Two studies evaluated the role of microbiota changes on the development of occupational lung diseases. Occupational factors can interface with the biological rhythms of the bacteria of the microbiota and can contribute to its modifications and to the possible development of diseases. Future studies are needed to better understand the role of the microbiota and its connection with occupational exposure to promote projects for the prevention and protection of global health.

Context-dependent effects of glucocorticoids on the lizard gut microbiome

The vertebrate gut microbiota (bacterial, archaeal and fungal communities of the gastrointestinal tract) can have profound effects on the physiological processes of their hosts. Although relatively stable, changes in microbiome structure and composition occur due to changes in the environment, including exposure to stressors and associated increases in glucocorticoid hormones. Although a growing number of studies have linked stressor exposure to microbiome changes, few studies have experimentally explored the specific influence of glucocorticoids on the microbiome in wild animals, or across ecologically important processes (e.g., reproductive stages). Here we tested the response of the gut microbiota of adult female Sceloporus undulatus across gestation to ecologically relevant elevations of a stress-relevant glucocorticoid hormone (CORT) in order to determine (i) how experimentally elevated CORT influenced microbiome characteristics, and (ii) whether this relationship was dependent on reproductive context (i.e., whether females were gravid or not, and, in those that were gravid, gestational stage). We show that the effects of CORT on gut microbiota are complex and depend on both gestational state and stage. CORT treatment altered microbial community membership and resulted in an increase in microbiome diversity in late-gestation females, and microbial community membership varied according to treatment. In nongravid females, CORT treatment decreased interindividual variation in microbial communities, but this effect was not observed in late-gestation females. Our results highlight the need for a more holistic understanding of the downstream physiological effects of glucocorticoids, as well as the importance of context (here, gestational state and stage) in interpreting stress effects in ecology.

Ingestion of Lactobacillus rhamnosus modulates chronic stress-induced feather pecking in chickens

Feather pecking (FP) is a stress-induced neuropsychological disorder of birds. Intestinal dysbiosis and inflammation are common traits of these disorders. FP is, therefore, proposed to be a behavioral consequence of dysregulated communication between the gut and the brain. Probiotic bacteria are known to favorably modulate the gut microbiome and hence the neurochemical and immune components of the gut-brain axis. Consequently, probiotic supplementation represents a promising new therapeutic to mitigate widespread FP in domestic chickens. We monitored FP, gut microbiota composition, immune markers, and amino acids related to the production of neurochemicals in chickens supplemented with Lactobacillus rhamnosus or a placebo. Data demonstrate that, when stressed, the incidence of FP increased significantly; however, L. rhamnosus prevented this increase. L. rhamnosus supplementation showed a strong immunological effect by increasing the regulatory T cell population of the spleen and the cecal tonsils, in addition to limiting cecal microbiota dysbiosis. Despite minimal changes in aromatic amino acid levels, data suggest that catecholaminergic circuits may be an interesting target for further studies. Overall, our findings provide the first data supporting the use of a single-strain probiotic to reduce stress-induced FP in chickens and promise to improve domestic birds' welfare.

A Microbiome-Driven Approach to Combating Depression During the COVID-19 Pandemic

The significant stressors brought about and exacerbated by COVID-19 are associated with startling surges in mental health illnesses, specifically those related to depressive disorders. Given the huge impact of depression on society, and an incomplete understanding of impactful therapeutics, we have examined the current literature surrounding the microbiome and gut-brain axis to advance a potential complementary approach to address depression and depressive disorders that have increased during the COVID-19 pandemic. While we understand that the impact of the human gut microbiome on emotional health is a newly emerging field and more research needs to be conducted, the current evidence is extremely promising and suggests at least part of the answer to understanding depression in more depth may lie within the microbiome. As a result of these findings, we propose that a microbiome-based holistic approach, which involves carefully annotating the microbiome and potential modification through diet, probiotics, and lifestyle changes, may address depression. This paper's primary purpose is to shed light on the link between the gut microbiome and depression, including the gut-brain axis and propose a holistic approach to microbiome modification, with the ultimate goal of assisting individuals to manage their battle with depression through diet, probiotics, and lifestyle changes, in addition to offering a semblance of hope during these challenging times.

Neurobiological approaches of high-fat diet intake in early development and their impact on mood disorders in adulthood: A systematic review

The early stage of development is a vulnerable period for progeny neurodevelopment, altering cytogenetic and correct cerebral functionality. The exposure High-Fat Diet (HFD) is a factor that impacts the future mental health of individuals. This review analyzes possible mechanisms involved in the development of mood disorders in adulthood because of maternal HFD intake during gestation and lactation, considering previously reported findings in the last five years, both in humans and animal models. Maternal HFD could induce alterations in mood regulation, reported as increased stress response, anxiety-like behavior, and depressive-like behavior. These changes were mostly related to HPA axis dysregulations and neuroinflammatory responses. In conclusion, there could be a relationship between HFD consumption during the early stages of life and the development of psychopathologies during adulthood. These findings provide guidelines for the understanding of possible mechanisms involved in mood disorders, however, there is still a need for more human clinical studies that provide evidence to improve the understanding of maternal nutrition and future mental health outcomes in the offspring.

Application of a simple measuring method to evaluate the fecal microflora of dairy cows in the summer season

OBJECTIVE

The effect of seasonality needs to be considered in designing future studies because global warming has caused a rise in ambient temperatures. The objective of the present study is to investigate the effect of high ambient temperatures on fecal score and fecal microflora in dairy cows during summer.

MATERIALS AND METHODS

During the 7 days before the sampling of feces, the daily mean temperatures were 19.9°C in early summer and more than 27.5°C in late summer. Fecal samples were collected from the rectum of cows and the fecal score was evaluated on a 4-point scale. The equalized samples were used to extract the genomic deoxyribonucleic acid (DNA) of the bacteria (Escherichia coli, Salmonella, Lactobacillus, and Bifidobacterium).

RESULTS

There was no significant difference in fecal scores between the sampling times in early and late summer. In the populations of the bacteria, there was no significant difference between sampling days in the DNA level of Salmonella, and E. coli in late summer increased to more than three times the level in early summer. However, both levels of Lactobacillus and Bifidobacterium in early summer significantly decreased after 2 months.

CONCLUSION

These data suggest that the increase in temperature in late summer may adversely affect the populations of bacteria in the intestinal environment of dairy cows. In addition, the method used in the present study was sufficient to evaluate the changes in internal and external environmental conditions of dairy cattle.

Scabies itch: an update on neuroimmune interactions and novel targets

Frequently described as 'the worst itch' one can ever experience scabies itch is the hallmark of Sarcoptes scabiei mite infestation. Notably, the itchiness often persists for weeks despite scabicides therapy. The mechanism of scabies itch is not yet fully understood, and effective treatment modalities are still missing which can severely affect the quality of life. The aim of this review is to provide an overview of the scope of itch in scabies and highlight candidate mechanisms underlying this itch. We herein discuss scabies itch, with a focus on the nature, candidate underlying mechanisms and treatment options. We also synthesize this information with current understanding of the mechanisms contributing to non-histaminergic itch in other conditions. Itch is a major problem in scabies and can lead to grave consequences. We provide the latest insights on host-mite interaction, secondary microbial infection and neural sensitization with special emphasis on keratinocytes and mast cells to better understand the mechanism of itch in scabies. Also, the most relevant current modalities remaining under investigation that possess promising perspectives for scabies itch (i.e. protease-activated receptor-2 (PAR-2) inhibitor, Mas-related G protein-coupled receptor X2 (MRGPRX2) antagonist) are discussed. Greater understanding of these diverse mechanisms may provide a rational basis for the development of improved and targeted approaches to control itch in individuals with scabies.

Septic Stability? Gut Microbiota in Young Adult Mice Maintains Overall Stability After Sepsis Compared to Old Adult Mice

BACKGROUND

Older adults have worse outcomes after sepsis than young adults. Additionally, alterations of the gut microbiota have been demonstrated to contribute to sepsis-related mortality. We sought to determine if there were alterations in the gut microbiota with a novel sepsis model in old adult mice, which enter a state of persistent inflammation, immunosuppression, and catabolism (PICS), as compared with young adult mice, which recover with the sepsis model.

METHODS

Mixed sex old (∼20 mo) and young (∼4 mo) C57Bl/6J mice underwent cecal ligation and puncture with daily chronic stress (CLP+DCS) and were compared with naive age-matched controls. Mice were sacrificed at CLP+DCS day 7 and feces collected for bacterial DNA isolation. The V3-V4 hypervariable region was amplified, 16S rRNA gene sequencing performed, and cohorts compared. α-Diversity was assessed using Chao1 and Shannon indices using rarefied counts, and β-diversity was assessed using Bray-Curtis dissimilarity.

RESULTS

Naive old adult mice had significantly different α and β-diversity compared with naive adult young adult mice. After CLP+DCS, there was a significant shift in the α and β-diversity (FDR = 0.03 for both) of old adult mice (naive vs. CLP+DCS). However, no significant shift was displayed in the microbiota of young mice that underwent CLP+DCS in regards to α-diversity (FDR = 0.052) and β-diversity (FDR = 0.12), demonstrating a greater overall stability of their microbiota at 7 days despite the septic insult. The taxonomic changes in old mice undergoing CLP+DCS were dominated by decreased abundance of the order Clostridiales and genera Oscillospira.

CONCLUSION

Young adult mice maintain an overall microbiome stability 7 days after CLP+DCS after compared with old adult mice. The lack of microbiome stability could contribute to PICS and worse long-term outcomes in older adult sepsis survivors. Further studies are warranted to elucidate mechanistic pathways and potential therapeutics.

Healthy Gut, Healthy Brain: The Gut Microbiome in Neurodegenerative Disorders

BACKGROUND

The central nervous system (CNS) known to regulate the physiological conditions of human body, also itself gets dynamically regulated by both the physiological as well as pathological conditions of the body. These conditions get changed quite often, and often involve changes introduced into the gut microbiota which, as studies are revealing, directly modulate the CNS via a crosstalk. This cross-talk between the gut microbiota and CNS, i.e., the gut-brain axis (GBA), plays a major role in the pathogenesis of many neurodegenerative disorders such as Parkinson's disease (PD), Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), multiple sclerosis (MS) and Huntington's disease (HD).

OBJECTIVE

We aim to discuss how gut microbiota, through GBA, regulate neurodegenerative disorders such as PD, AD, ALS, MS and HD.

METHODS

In this review, we have discussed the present understanding of the role played by the gut microbiota in neurodegenerative disorders and emphasized the probable therapeutic approaches being explored to treat them.

RESULTS

In the first part, we introduce the GBA and its relevance, followed by the changes occurring in the GBA during neurodegenerative disorders and then further discuss its role in the pathogenesis of these diseases. Finally, we discuss its applications in possible therapeutics of these diseases and the current research improvements being made to better investigate this interaction.

CONCLUSION

We concluded that alterations in the intestinal microbiota modulate various activities that could potentially lead to CNS disorders through interactions via the GBA.

Microbiota-gut-brain axis as a regulator of reward processes

Our gut harbours trillions of microorganisms essential for the maintenance of homeostasis and host physiology in health and disease. In the last decade, there has been a growing interest in understanding the bidirectional pathway of communication between our microbiota and the central nervous system. With regard to reward processes there is accumulating evidence from both animal and human studies that this axis may be a key factor in gating reward valence. Focusing on the mesocorticolimbic pathway, we will discuss how the intestinal microbiota is involved in regulating brain reward functions, both in natural (i.e. eating, social or sexual behaviours) and non-natural reinforcers (drug addiction behaviours including those relevant to alcohol, psychostimulants, opioids and cannabinoids). We will integrate preclinical and clinical evidence suggesting that the microbiota-gut-brain axis could be implicated in the development of disorders associated with alterations in the reward system and how it may be targeted as a promising therapeutic strategy. Cover Image for this issue: https://doi.org/10.1111/jnc.15065.

Gut Microbiota: A Perspective for Psychiatrists

There is mounting evidence that the trillions of microbes that inhabit our gut are a substantial contributing factor to mental health and, equally, to the progression of neuropsychiatric disorders. The extraordinary complexity of the gut ecosystem, and how it interacts with the intestinal epithelium to manifest physiological changes in the brain to influence mood and behaviour, has been the subject of intense scientific scrutiny over the last 2 decades. To further complicate matters, we each harbour a unique microbiota community that is subject to change by a number of factors including diet, exercise, stress, health status, genetics, medication, and age, amongst others. The microbiota-gut-brain axis is a dynamic matrix of tissues and organs including the gastrointestinal (GI) microbiota, immune cells, gut tissue, glands, the autonomic nervous system (ANS), and the brain that communicate in a complex multidirectional manner through a number of anatomically and physiologically distinct systems. Long-term perturbations to this homeostatic environment may contribute to the progression of a number of disorders by altering physiological processes including hypothalamic-pituitary-adrenal axis activation, neurotransmitter systems, immune function, and the inflammatory response. While an appropriate, co-ordinated physiological response, such as an immune or stress response, is necessary for survival, a dysfunctional response can be detrimental to the host, contributing to the development of a number of central nervous system disorders.

Prenatal stress increases IgA coating of offspring microbiota and exacerbates necrotizing enterocolitis-like injury in a sex-dependent manner

Necrotizing enterocolitis (NEC) is an intestinal inflammatory disease with high morbidity and mortality that affects almost exclusively premature infants. Breast milk feeding is known to substantially lower NEC incidence, and specific components of breast milk, such as immunoglobulin (Ig) A, have been identified as mediating this protective effect. On the other hand, accumulating evidence suggests dysbiosis of the neonatal intestinal microbiome contributes to NEC pathogenesis. In mice, neonates can inherit a dysbiotic microbiome from dams that experience stress during pregnancy. Here we show that while prenatal stress lowers fecal IgA levels in pregnant mice, it does not result in lower levels of IgA in the breast milk. Nevertheless, coating of female, but not male, offspring microbiota by IgA is increased by prenatal stress. Accordingly, prenatal stress was found to alter the bacterial community composition in female neonates but not male neonates. Furthermore, female, but not male, offspring of prenatally stressed mothers exhibited more severe colonic tissue damage in a NEC-like injury model compared to offspring with non-stressed mothers. Our results point to prenatal stress as a possible novel risk factor for NEC and potentially reveal new avenues in NEC prevention and therapy.

The Skin Microbiota and Itch: Is There a Link?

Itch is an unpleasant sensation that emanates primarily from the skin. The chemical mediators that drive neuronal activity originate from a complex interaction between keratinocytes, inflammatory cells, nerve endings and the skin microbiota, relaying itch signals to the brain. Stress also exacerbates itch via the skin–brain axis. Recently, the microbiota has surfaced as a major player to regulate this axis, notably during stress settings aroused by actual or perceived homeostatic challenge. The routes of communication between the microbiota and brain are slowly being unraveled and involve neurochemicals (i.e., acetylcholine, histamine, catecholamines, corticotropin) that originate from the microbiota itself. By focusing on itch biology and by referring to the more established field of pain research, this review examines the possible means by which the skin microbiota contributes to itch.

Metabolome and microbiome profiling of a stress-sensitive rat model of gut-brain axis dysfunction

Stress negatively impacts gut and brain health. Individual differences in response to stress have been linked to genetic and environmental factors and more recently, a role for the gut microbiota in the regulation of stress-related changes has been demonstrated. However, the mechanisms by which these factors influence each other are poorly understood, and there are currently no established robust biomarkers of stress susceptibility. To determine the metabolic and microbial signatures underpinning physiological stress responses, we compared stress-sensitive Wistar Kyoto (WKY) rats to the normo-anxious Sprague Dawley (SD) strain. Here we report that acute stress-induced strain-specific changes in brain lipid metabolites were a prominent feature in WKY rats. The relative abundance of Lactococcus correlated with the relative proportions of many brain lipids. In contrast, plasma lipids were significantly elevated in response to stress in SD rats, but not in WKY rats. Supporting these findings, we found that the greatest difference between the SD and WKY microbiomes were the predicted relative abundance of microbial genes involved in lipid and energy metabolism. Our results provide potential insights for developing novel biomarkers of stress vulnerability, some of which appear genotype specific.

Study of the impact of long-duration space missions at the International Space Station on the astronaut microbiome

Over the course of a mission to the International Space Station (ISS) crew members are exposed to a number of stressors that can potentially alter the composition of their microbiomes and may have a negative impact on astronauts’ health. Here we investigated the impact of long-term space exploration on the microbiome of nine astronauts that spent six to twelve months in the ISS. We present evidence showing that the microbial communities of the gastrointestinal tract, skin, nose and tongue change during the space mission. The composition of the intestinal microbiota became more similar across astronauts in space, mostly due to a drop in the abundance of a few bacterial taxa, some of which were also correlated with changes in the cytokine profile of crewmembers. Alterations in the skin microbiome that might contribute to the high frequency of skin rashes/hypersensitivity episodes experienced by astronauts in space were also observed. The results from this study demonstrate that the composition of the astronauts’ microbiome is altered during space travel. The impact of those changes on crew health warrants further investigation before humans embark on long-duration voyages into outer space.

Can Gut Microbiota and Lifestyle Help Us in the Handling of Anorexia Nervosa Patients?

Gut microbiota is composed of different microorganisms that play an important role in the host. New research shows that bidirectional communications happen between intestinal microbiota and the brain, which is known as the gut⁻brain axis. This communication is significant and could have a negative or positive effect depending on the state of the gut microbiota. Anorexia nervosa (AN) is a mental illness associated with metabolic, immunologic, biochemical, sensory abnormalities, and extremely low body weight. Different studies have shown a dysbiosis in patients with AN. Due to the gut⁻brain axis, it was observed that some of the symptoms could be improved in these patients by boosting their gut microbiota. This paper highlights some evidence connecting the role of microbiota in the AN onset and disease progress. Finally, a proposal is done to include the microbiota analysis as part of the recovery protocol used to treat AN patients. When conducting clinical studies of gut microbiota in AN patients, dysbiosis is expected to be found. Then the prescription of a personalized treatment rich in prebiotics and probiotics could be proposed to reverse the dysbiosis.

DHA-phospholipids (DHA-PL) and EPA-phospholipids (EPA-PL) prevent intestinal dysfunction induced by chronic stress

DHA-PL and EPA-PL may effectively protect mice against intestinal dysfunction under chronic stress exposure.

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.

Social and population health science approaches to understand the human microbiome

The microbiome is now considered our 'second genome' with potentially comparable importance to the genome in determining human health. There is, however, a relatively limited understanding of the broader environmental factors, particularly social conditions, that shape variation in human microbial communities. Fulfilling the promise of microbiome research - particularly the microbiome's potential for modification - will require collaboration between biologists and social and population scientists. For life scientists, the plasticity and adaptiveness of the microbiome calls for an agenda to understand the sensitivity of the microbiome to broader social environments already known to be powerful predictors of morbidity and mortality. For social and population scientists, attention to the microbiome may help answer nagging questions about the underlying biological mechanisms that link social conditions to health. We outline key substantive and methodological advances that can be made if collaborations between social and population health scientists and life scientists are strategically pursued.

The Neuroendocrinology of the Microbiota-Gut-Brain Axis: A Behavioural Perspective

The human gut harbours trillions of symbiotic bacteria that play a key role in programming different aspects of host physiology in health and disease. These intestinal microbes are also key components of the gut-brain axis, the bidirectional communication pathway between the gut and the central nervous system (CNS). In addition, the CNS is closely interconnected with the endocrine system to regulate many physiological processes. An expanding body of evidence is supporting the notion that gut microbiota modifications and/or manipulations may also play a crucial role in the manifestation of specific behavioural responses regulated by neuroendocrine pathways. In this review, we will focus on how the intestinal microorganisms interact with elements of the host neuroendocrine system to modify behaviours relevant to stress, eating behaviour, sexual behaviour, social behaviour, cognition and addiction.

"Under the Skin" and into the Gut: Social Epidemiology of the Microbiome

PURPOSE OF THE REVIEW

As the science of the microbiome advances, social epidemiologists can contribute to understanding how the broader social environment shapes the microbiome over the life course. This review summarizes current research and describes potential mechanisms of the social epidemiology of the microbiome.

RECENT FINDINGS

Most existing literature linking the social environment and the microbiome comes from animal models, focused on the impact of social interactions and psychosocial stress. Suggestive evidence of the importance of early life exposures, health behaviors, and the built environment also point to the importance of the social environment for the microbiome in humans.

SUMMARY

Social epidemiology as a field is well poised to contribute expertise in theory and measurement of the broader social environment to this new area, and to consider both the upstream and downstream mechanisms by which this environment gets "under the skin" and "into the gut." As population-level microbiome data becomes increasingly available, we encourage investigation of the multi-level determinants of the microbiome and how the microbiome may link the social environment and health.

Enteric Microbiota⁻Gut⁻Brain Axis from the Perspective of Nuclear Receptors

Nuclear receptors (NRs) play a key role in regulating virtually all body functions, thus maintaining a healthy operating body with all its complex systems. Recently, gut microbiota emerged as major factor contributing to the health of the whole organism. Enteric bacteria have multiple ways to influence their host and several of them involve communication with the brain. Mounting evidence of cooperation between gut flora and NRs is already available. However, the full potential of the microbiota interconnection with NRs remains to be uncovered. Herewith, we present the current state of knowledge on the multifaceted roles of NRs in the enteric microbiota–gut–brain axis.

Gut–brain axis biochemical signalling from the gastrointestinal tract to the central nervous system: gut dysbiosis and altered brain function

Background

The gut–brain axis facilitates a critical bidirectional link and communication between the brain and the gut. Recent studies have highlighted the significance of interactions in the gut–brain axis, with a particular focus on intestinal functions, the nervous system and the brain. Furthermore, researchers have examined the effects of the gut microbiome on mental health and psychiatric well-being.

The present study reviewed published evidence to explore the concept of the gut–brain axis.

Aims

This systematic review investigated the relationship between human brain function and the gut–brain axis.

Methods

To achieve these objectives, peer-reviewed articles on the gut–brain axis were identified in various electronic databases, including PubMed, MEDLINE, CIHAHL, Web of Science and PsycINFO.

Results

Data obtained from previous studies showed that the gut–brain axis links various peripheral intestinal functions to brain centres through a broad range of processes and pathways, such as endocrine signalling and immune system activation. Researchers have found that the vagus nerve drives bidirectional communication between the various systems in the gut–brain axis. In humans, the signals are transmitted from the liminal environment to the central nervous system.

Conclusions

The communication that occurs in the gut–brain axis can alter brain function and trigger various psychiatric conditions, such as schizophrenia and depression. Thus, elucidation of the gut–brain axis is critical for the management of certain psychiatric and mental disorders.

Immunity - a significant pathogenic factor as well as an integral part of the psychoneuroendocrine-immune regulations

Immunity plays an important role in the reactivity of the organism and, in this context, is an essential factor in the pathogenesis of many diseases. Basically, there is no system or organ in the body, whose dysfunction is not related to immunity consequences. In addition, there are also multisystem diseases simultaneously involving multiple body systems. They are not always caused by weak immunity, but also often by modified immune reactions known as overshooting. The essence of all these diseases is a change in the reactivity of the organism where immunity plays an important role. The immunity as such is then part of the systems of neuroendocrine-immune regulation, which have common mediators and receptors. The establishment of psychoneuroimmunology, a relatively new discipline in neuroscience, contributed to a detailed understanding of these mechanisms between central and peripheral nervous system, the endocrine system and the immune system. This research enabled the uncovering of the nature of stress-diseases and impact of other regulatory disturbances on the function of various body organs and systems of the organism as a whole. The aim of this short review is to show complex interconnections of these relationships to better understand the human health and disease.

Altered fecal microbiota composition in all male aggressor-exposed rodent model simulating features of post-traumatic stress disorder

The bidirectional role of gut-brain axis that integrates the gut and central nervous system activities has recently been investigated. We studied "cage-within-cage resident-intruder" all-male model, where subject male mice (C57BL/6J) are exposed to aggressor mice (SJL albino), and gut microbiota-derived metabolites were identified in plasma after 10 days of exposure. We assessed 16S ribosomal RNA gene from fecal samples collected daily from these mice during the 10-day study. Alpha diversity using Chao indices indicated no change in diversity in aggressor-exposed samples. The abundance profile showed the top phyla were Firmicutes and Bacteroidetes, Tenericutes, Verrucomicrobia, Actinobacteria and Proteobacteria, respectively. The phyla Firmicutes and Bacteroidetes are vulnerable to PTSD-eliciting stress and the Firmicutes/Bacteroidetes ratio increases with stress. Principal coordinate analysis showed the control and aggressor-exposed samples cluster separately where samples from early time points (day 1-3) clustered together and were distinct from late time points (day 4-9). The genus-based analysis revealed all control time points clustered together and aggressor-exposed samples had multiple clusters. The decrease in proportion of Firmicutes after aggressor exposure persisted throughout the study. The proportion of Verrucomicrobia immediately decreased and was significantly shifted at most of the later time points. The genus Oscillospira, Lactobacillus, Akkermansia and Anaeroplasma are the top four genera that differed between control and stressor-exposed mice. The data showed immediate effect on microbiome composition during a 10 day time period of stress exposure. Studying the longitudinal effects of a stressor is an important step toward an improved mechanistic understanding of the microbiome dynamics.

Impact of the Gut Microbiota on Intestinal Immunity Mediated by Tryptophan Metabolism

The gut microbiota influences the health of the host, especially with regard to gut immune homeostasis and the intestinal immune response. In addition to serving as a nutrient enhancer, L-tryptophan (Trp) plays crucial roles in the balance between intestinal immune tolerance and gut microbiota maintenance. Recent discoveries have underscored that changes in the microbiota modulate the host immune system by modulating Trp metabolism. Moreover, Trp, endogenous Trp metabolites (kynurenines, serotonin, and melatonin), and bacterial Trp metabolites (indole, indolic acid, skatole, and tryptamine) have profound effects on gut microbial composition, microbial metabolism, the host's immune system, the host-microbiome interface, and host immune system-intestinal microbiota interactions. The aryl hydrocarbon receptor (AhR) mediates the regulation of intestinal immunity by Trp metabolites (as ligands of AhR), which is beneficial for immune homeostasis. Among Trp metabolites, AhR ligands consist of endogenous metabolites, including kynurenine, kynurenic acid, xanthurenic acid, and cinnabarinic acid, and bacterial metabolites, including indole, indole propionic acid, indole acetic acid, skatole, and tryptamine. Additional factors, such as aging, stress, probiotics, and diseases (spondyloarthritis, irritable bowel syndrome, inflammatory bowel disease, colorectal cancer), which are associated with variability in Trp metabolism, can influence Trp-microbiome-immune system interactions in the gut and also play roles in regulating gut immunity. This review clarifies how the gut microbiota regulates Trp metabolism and identifies the underlying molecular mechanisms of these interactions. Increased mechanistic insight into how the microbiota modulates the intestinal immune system through Trp metabolism may allow for the identification of innovative microbiota-based diagnostics, as well as appropriate nutritional supplementation of Trp to prevent or alleviate intestinal inflammation. Moreover, this review provides new insight regarding the influence of the gut microbiota on Trp metabolism. Additional comprehensive analyses of targeted Trp metabolites (including endogenous and bacterial metabolites) are essential for experimental preciseness, as the influence of the gut microbiota cannot be neglected, and may explain contradictory results in the literature.

Revisiting Metchnikoff: Age-related alterations in microbiota-gut-brain axis in the mouse

Over the last decade, there has been increased interest in the role of the gut microbiome in health including brain health. This is by no means a new theory; Elie Metchnikoff proposed over a century ago that targeting the gut by consuming lactic acid bacteria such as those in yogurt, could improve or delay the onset of cognitive decline associated with ageing. However, there is limited information characterising the relationship between the behavioural and physiological sequelae of ageing and alterations in the gut microbiome. To this end, we assessed the behavioural, physiological and caecal microbiota profile of aged male mice. Older mice (20-21months old) exhibited deficits in spatial memory and increases in anxiety-like behaviours compared to younger mice (2-3months old). They also exhibited increased gut permeability, which was directly correlated with elevations in peripheral pro-inflammatory cytokines. Furthermore, stress exacerbated the gut permeability of aged mice. Examination of the caecal microbiota revealed significant increases in phylum TM7, family Porphyromonadaceae and genus Odoribacter of aged mice. This represents a shift of aged microbiota towards a profile previously associated with inflammatory disease, particularly gastrointestinal and liver disorders. Furthermore, Porphyromonadaceae, which has also been associated with cognitive decline and affective disorders, was directly correlated with anxiety-like behaviour in aged mice. These changes suggest that changes in the gut microbiota and associated increases in gut permeability and peripheral inflammation may be important mediators of the impairments in behavioural, affective and cognitive functions seen in ageing.

Gender-based differences in host behavior and gut microbiota composition in response to high fat diet and stress in a mouse model

Obesity is associated with a high prevalence of mood disorders such as anxiety and depression. Both stress and high fat diet can alter the gut microbiota and contribute to obesity. To examine the interrelationships between obesity, stress, gut microbiota and mood disorders, obesity was induced in mice using a high fat diet, and the mice were subsequently stressed using a chronic unpredictable mild stress protocol. During the experiment, the composition of the gut microbiota was analyzed by 16 S rRNA gene high-throughput sequencing, and anxiety-like behaviors were measured. The results revealed distinct gender differences in the impacts of obesity and stress on anxiety-like behaviors, activity levels, and composition of the gut microbiota. Male mice were more vulnerable to the anxiogenic effects of the high fat diet, and obese male mice showed decreased locomotion activity in response to stress whereas obese female mice did not. In females, stress caused the gut microbiota of lean mice to more closely resemble that of obese mice. Taken together, these results suggest the importance of considering gender as a biological variable in studies on the role of gut microbiota in obesity-related mood disorders.

肠道菌群与2型糖尿病及并发症

2型糖尿病(type 2 diabetes mellitus, T2DM)是一种由多因素导致的代谢性疾病, 关于其发病机制的研究逐渐深入, 其中肠道菌群与糖尿病的关系成为近年来研究的焦点. 肠道菌群与人体健康息息相关, 越来越多的研究发现肠道菌群的失调可能通过多种机制参与T2DM的发生与发展, 而T2DM病患者体内代谢环境的改变又可能会影响肠道菌群的组成和功能. 在这篇综述中, 我们总结最近的相关研究探讨肠道菌群失调在T2DM发生和发展中的作用、有关的治疗策略以及未来的研究前景.

Stress & the gut-brain axis: Regulation by the microbiome

The importance of the gut–brain axis in regulating stress-related responses has long been appreciated. More recently, the microbiota has emerged as a key player in the control of this axis, especially during conditions of stress provoked by real or perceived homeostatic challenge. Diet is one of the most important modifying factors of the microbiota-gut-brain axis. The routes of communication between the microbiota and brain are slowly being unravelled, and include the vagus nerve, gut hormone signaling, the immune system, tryptophan metabolism, and microbial metabolites such as short chain fatty acids. The importance of the early life gut microbiota in shaping later health outcomes also is emerging. Results from preclinical studies indicate that alterations of the early microbial composition by way of antibiotic exposure, lack of breastfeeding, birth by Caesarean section, infection, stress exposure, and other environmental influences - coupled with the influence of host genetics - can result in long-term modulation of stress-related physiology and behaviour. The gut microbiota has been implicated in a variety of stress-related conditions including anxiety, depression and irritable bowel syndrome, although this is largely based on animal studies or correlative analysis in patient populations. Additional research in humans is sorely needed to reveal the relative impact and causal contribution of the microbiome to stress-related disorders. In this regard, the concept of psychobiotics is being developed and refined to encompass methods of targeting the microbiota in order to positively impact mental health outcomes. At the 2016 Neurobiology of Stress Workshop in Newport Beach, CA, a group of experts presented the symposium “The Microbiome: Development, Stress, and Disease”. This report summarizes and builds upon some of the key concepts in that symposium within the context of how microbiota might influence the neurobiology of stress.

Perceived Stress in Patients with Common Gastrointestinal Disorders: Associations with Quality of Life, Symptoms and Disease Management

OBJECTIVE AND METHODS

Research supports relationships between stress and gastrointestinal (GI) symptoms and disorders. This pilot study assesses relationships between perceived stress, quality of life (QOL), and self-reported pain ratings as an indicator of symptom management in patients who self-reported gastroesophageal reflux disease (GERD), irritable bowel syndrome (IBS), and inflammatory bowel disease (IBD).

RESULTS

In the full sample (n = 402) perceived stress positively correlated with depression (r = 0.76, P < .0001), fatigue (r = 0.38, P < .0001), sleep disturbance (r = 0.40, P < .0001), average pain (r = 0.26, P < .0001), and worst pain (r = 0.25, P < .0001). Higher perceived stress also correlated with lower mental health-related QOL. Similar correlations were found for the participants with GERD (n = 188), IBS (n = 132), and IBD (n = 82). Finally, there were significant correlations in the GERD cohort between perceived stress, and average pain (r = 0.34, P < .0001) and worst pain (r = 0.29, P < .0001), and in the IBD cohort between perceived stress, and average pain (r = 0.32, P < .0001), and worst pain (r = 0.35, P < .01).

CONCLUSIONS

Perceived stress broadly correlated with QOL characteristics in patients with GERD, IBS, and IBD, and their overall QOL was significantly lower than the general population. Perceived stress also appeared to be an indicator of symptom management (self-reported pain ratings) in GERD and IBD, but not IBS. While future research using objective measures of stress and symptom/disease management is needed to confirm these associations, as well as to evaluate the ability of stress reduction interventions to improve perceived stress, QOL and disease management in these GI disorders, integrative medicine treatment programs would be most beneficial to study.

Handling stress may confound murine gut microbiota studies

BACKGROUND

Accumulating evidence indicates interactions between human milk composition, particularly sugars (human milk oligosaccharides or HMO), the gut microbiota of human infants, and behavioral effects. Some HMO secreted in human milk are unable to be endogenously digested by the human infant but are able to be metabolized by certain species of gut microbiota, including Bifidobacterium longum subsp. infantis (B. infantis), a species sensitive to host stress (Bailey & Coe, 2004). Exposure to gut bacteria like B. infantisduring critical neurodevelopment windows in early life appears to have behavioral consequences; however, environmental, physical, and social stress during this period can also have behavioral and microbial consequences. While rodent models are a useful method for determining causal relationships between HMO, gut microbiota, and behavior, murine studies of gut microbiota usually employ oral gavage, a technique stressful to the mouse. Our aim was to develop a less-invasive technique for HMO administration to remove the potential confound of gavage stress. Under the hypothesis that stress affects gut microbiota, particularly B. infantis, we predicted the pups receiving a prebiotic solution in a less-invasive manner would have the highest amount of Bifidobacteria in their gut.

METHODS

This study was designed to test two methods, active and passive, of solution administration to mice and the effects on their gut microbiome. Neonatal C57BL/6J mice housed in a specific-pathogen free facility received increasing doses of fructooligosaccharide (FOS) solution or deionized, distilled water. Gastrointestinal (GI) tracts were collected from five dams, six sires, and 41 pups over four time points. Seven fecal pellets from unhandled pups and two pellets from unhandled dams were also collected. Qualitative real-time polymerase chain reaction (qRT-PCR) was used to quantify and compare the amount of Bifidobacterium, Bacteroides, Bacteroidetes, and Firmicutes.

RESULTS

Our results demonstrate a significant difference between the amount of Firmicutes in pups receiving water passively and those receiving FOS actively (p-value = 0.009). Additionally, we found significant differences between the fecal microbiota from handled and non-handled mouse pups.

DISCUSSION

From our results, we conclude even handling pups for experimental purposes, without gavage, may induce enough stress to alter the murine gut microbiota profile. We suggest further studies to examine potential stress effects on gut microbiota caused by experimental techniques. Stress from experimental techniques may need to be accounted for in future gut microbiota studies.

Omics Studies of the Murine Intestinal Ecosystem Exposed to Subchronic and Mild Social Defeat Stress

The microbiota-gut-brain axis plays an important role in the development of stress-induced mental disorders. We previously established the subchronic and mild social defeat stress (sCSDS) model, a murine experimental model of depression, and investigated the metabolomic profiles of plasma and liver. Here we used omics approaches to identify stress-induced changes in the gastrointestinal tract. Mice exposed to sCSDS for 10 days showed the following changes: (1) elevation of cholic acid and reduction of 5-aminovaleric acid among cecal metabolites; (2) downregulation of genes involved in the immune response in the terminal ileum; (3) a shift in the diversity of the microbiota in cecal contents and feces; and (4) fluctuations in the concentrations of cecal metabolites produced by gut microbiota reflected in plasma and hepatic metabolites. Operational taxonomic units within the family Lachnospiraceae showed an inverse correlation with certain metabolites. The social interaction score correlated with cecal metabolites, IgA, and cecal and fecal microbiota, suggesting that sCSDS suppressed the ileal immune response, altering the balance of microbiota, which together with host cells and host enzymes resulted in a pattern of accumulated metabolites in the intestinal ecosystem distinct from that of control mice.

Irritable bowel syndrome, the microbiota and the gut-brain axis

Irritable bowel syndrome is a common functional gastrointestinal disorder and it is now evident that irritable bowel syndrome is a multi-factorial complex of changes in microbiota and immunology. The bidirectional neurohumoral integrated communication between the microbiota and the autonomous nervous system is called the gut-brain-axis, which integrates brain and GI functions, such as gut motility, appetite and weight. The gut-brain-axis has a central function in the perpetuation of irritable bowel syndrome and the microbiota plays a critical role. The purpose of this article is to review recent research concerning the epidemiology of irritable bowel syndrome, influence of microbiota, probiota, gut-brain-axis, and possible treatment modalities on irritable bowel syndrome.

Integrating neuroimmune systems in the neurobiology of depression

Data from clinical and preclinical studies indicate that immune dysregulation, specifically of inflammatory processes, is associated with symptoms of major depressive disorder (MDD). In particular, increased levels of circulating pro-inflammatory cytokines and concomitant activation of brain-resident microglia can lead to depressive behavioural symptoms. Repeated exposure to psychological stress has a profound impact on peripheral immune responses and perturbs the function of brain microglia, which may contribute to neurobiological changes underlying MDD. Here, we review these findings and discuss ongoing studies examining neuroimmune mechanisms that influence neuronal activity as well as synaptic plasticity. Interventions targeting immune-related cellular and molecular pathways may benefit subsets of MDD patients with immune dysregulation.

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.

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.