The anxiolytic effect of Bifidobacterium longum NCC3001 involves vagal pathways for gut-brain communication

A Microbial Signature of Psychological Distress in Irritable Bowel Syndrome

OBJECTIVE

Irritable bowel syndrome (IBS) is associated with alterations along the brain-gut-microbiota axis. Previous studies have suggested a parallel segregation of microbial features and psychological burden in IBS. This study aimed at exploring the microbial correlates of psychological distress in patients with IBS.

METHODS

Forty-eight patients with IBS (Rome III criteria, M (SD) age = 42 (15) years, 35 female, 25 diarrhea-dominant, 5 constipation-dominant, and 18 alternating-type IBS) were assessed for psychological and clinical variables with validated questionnaires, fecal samples underwent microbial 16S rRNA analyses (regions V1-2). Microbial analyses comprised examination of alpha and beta diversity, correlational analyses of bacterial abundance and comparisons among subgroups defined by thresholds of psychological and IBS symptom variables, and machine learning to identify bacterial patterns corresponding with psychological distress.

RESULTS

Thirty-one patients (65%) showed elevated psychological distress, 22 (31%) anxiety, and 10 depression (21%). Microbial beta diversity was significantly associated with distress and depression (q = .036 each, q values are p values false discovery rate-corrected for multiple testing). Depression was negatively associated with Lachnospiraceae abundance (Spearman's ρ = -0.58, q = .018). Patients exceeding thresholds of distress, anxiety, depression, and stress perception showed significantly higher abundances of Proteobacteria (q = .020-.036). Patients with anxiety were characterized by elevated Bacteroidaceae (q = .036). A signature of 148 unclassified species accounting for 3.9% of total bacterial abundance co-varied systematically with the presence of psychological distress.

CONCLUSIONS

Psychological variables significantly segregated gut microbial features, underscoring the role of brain-gut-microbiota interaction in IBS. A microbial signature corresponding with psychological distress was identified.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov identifier NCT02536131, retrospectively registered.

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

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

RESULTS

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

CONCLUSION

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

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.

The Gut Microbiota and Dysbiosis in Autism Spectrum Disorders

PURPOSE OF REVIEW

There is a growing body of evidence indicating the gut microbiota influence neurodevelopment and behavior. The purposes of this review are to provide an overview of studies analyzing the microbiota and their metabolites in autism spectrum disorders (ASD) and to discuss the possible mechanisms of action involved in microbial influence on the brain and behavior.

RECENT FINDINGS

The microbiota-gut-brain (MGB) axis has been extensively studied in animal models, and it is clear that alterations in the composition of microbiota alter neurological and behavioral outcomes. However, findings in human studies are less abundant. Although there are several studies so far showing altered microbiota (dysbiosis) in ASD, the results are heterogeneous and often contradictory. Intervention studies such as fecal microbiota transplant therapies show promise and lend credence to the involvement of the microbiota in ASD. A role for the microbiota in ASD is likely; however, further studies elucidating microbial or metabolomic signatures and mechanisms of action are needed. Future research should focus on intervention studies that can identify specific metabolites and immune mediators that improve with treatment to help identify etiologies and pathological mechanisms of ASD.

Immobilization stress-induced Escherichia coli causes anxiety by inducing NF-κB activation through gut microbiota disturbance

The present study aimed to understand the crosstalk between anxiety and gut microbiota. Exposure of mice to immobilization stress (IS) led to anxiety-like behaviors, increased corticosterone and tumor necrosis factor-α levels in the blood, increased nuclear factor (NF)-κB activation and microglia/monocyte populations in the hippocampus, and suppressed brain-derived neurotrophic factor (BDNF) expression in the hippocampus. Furthermore, IS exposure increased NF-κB activation and monocyte population in the colon and increased Proteobacteria and Escherichia coli populations in the gut microbiota and fecal and blood lipopolysaccharide (LPS) levels while decreasing the lactobacilli population. Oral administration of the fecal microbiota of mice treated with IS (FIS) or E. coli led to the increased NF-κB activation and monocyte population in the colon. These treatments increased blood corticosterone and LPS levels and anxiety-like behaviors, decreased BDNF expression, and induced NF-κB activation and microglia/monocyte populations in the hippocampus. Intraperitoneal injection of LPS purified from E. coli also led to anxiety and colitis in mice. Oral administration of commensal lactobacilli, particularly Lactobacillus johnsonii, attenuated IS- or E. coli-induced colitis and anxiety-like behaviors and biomarkers. These findings suggest that exposure to stressors can increase Proteobacteria populations and fecal LPS levels and cause gastrointestinal inflammation, resulting in the deterioration of anxiety through NF-κB activation. However, the amelioration of gastrointestinal inflammation by treatment with probiotics including L. johnsonii can alleviate anxiety.

The Microbiota-Gut-Brain Axis in Neuropsychiatric Disorders: Pathophysiological Mechanisms and Novel Treatments

Background

The human gut microbiome comprise a huge number of microorganisms with co-evolutionary associations with humans. It has been repeatedly revealed that bidirectional communication exists between the brain and the gut and involves neural, hormonal, and immunological pathways. Evidences from neuroscience researches over the past few years suggest that microbiota is essential for the development and maturation of brain systems that are associated to stress responses.

Method

This review provides that the summarization of the communication among microbiota, gut and brain and the results of preclinical and clinical studies on gut microbiota used in treatments for neuropsychiatric disorders.

Result

Recent studies have reported that diverse forms of neuropsychiatric disorders (such as autism, depression, anxiety, and schizophrenia) are associated with or modulated by variations in the microbiome, by microbial substrates, and by exogenous prebiotics, antibiotics, and probiotics.

Conclusion

The microbiota–gut–brain axis might provide novel targets for prevention and treatment of neuropsychiatric disorders. However, further studies are required to substantiate the clinical use of probiotics, prebiotics and FMT.

Gut-Brain Psychology: Rethinking Psychology From the Microbiota-Gut-Brain Axis

Mental disorders and neurological diseases are becoming a rapidly increasing medical burden. Although extensive studies have been conducted, the progress in developing effective therapies for these diseases has still been slow. The current dilemma reminds us that the human being is a superorganism. Only when we take the human self and its partner microbiota into consideration at the same time, can we better understand these diseases. Over the last few centuries, the partner microbiota has experienced tremendous change, much more than human genes, because of the modern transformations in diet, lifestyle, medical care, and so on, parallel to the modern epidemiological transition. Existing research indicates that gut microbiota plays an important role in this transition. According to gut-brain psychology, the gut microbiota is a crucial part of the gut-brain network, and it communicates with the brain via the microbiota-gut-brain axis. The gut microbiota almost develops synchronously with the gut-brain, brain, and mind. The gut microbiota influences various normal mental processes and mental phenomena, and is involved in the pathophysiology of numerous mental and neurological diseases. Targeting the microbiota in therapy for these diseases is a promising approach that is supported by three theories: the gut microbiota hypothesis, the "old friend" hypothesis, and the leaky gut theory. The effects of gut microbiota on the brain and behavior are fulfilled by the microbiota-gut-brain axis, which is mainly composed of the nervous pathway, endocrine pathway, and immune pathway. Undoubtedly, gut-brain psychology will bring great enhancement to psychology, neuroscience, and psychiatry. Various microbiota-improving methods including fecal microbiota transplantation, probiotics, prebiotics, a healthy diet, and healthy lifestyle have shown the capability to promote the function of the gut-brain, microbiota-gut-brain axis, and brain. It will be possible to harness the gut microbiota to improve brain and mental health and prevent and treat related diseases in the future.

Mind the gut: probiotics in paediatric neurogastroenterology

The gut-brain axis has recently emerged as a key modulator of human health and the intestinal microbiome has a well-recognised pivotal role in this strong connection. The aim of this narrative review is to update and summarise the effect and clinical applicability of probiotics in paediatric neurogastroenterology. The Cochrane Database and PubMed were searched using keywords relating to different subtypes of functional gastrointestinal disorders (FGIDs) and their symptoms, those relating to the CNS and related neurological or behavioural dysfunction as well as 'probiotic' OR 'probiotics'. Included papers were limited to those including children (aged 0-18 years) and using English language. Although significant effects of specific strains have been reported in infants with FGIDs, heterogeneity amongst the studies (different products and concentrations used and FGID subtypes), has limited the ability to draw an overall conclusion on the clinical value of probiotics. According to different meta-analyses of randomised controlled trials, the use of Lactobacillus reuteri (DSM 17938) was associated with a significant decrease in average crying time in infantile colic. There is moderate evidence for this strain and LGG and limited evidence (based on one study each) for the beneficial effect of VSL#3 and a three-strain bifidobacteria mix in abdominal pain FGIDs, particularly in the irritable bowel disease subgroup of children, but not in functional dyspepsia. There is currently no clear evidence of positive effects of oral probiotics in autistic spectrum disorder. Efficacy and safety of other strains or beneficial effects in other conditions still need to be proven, as probiotic properties are strain-specific, and data cannot be extrapolated to other brain-gut or mood diseases or to other probiotics of the same or different species. To transform the use of probiotics from a tempting suggestion to a promising treatment modality in neurogastroenterological disorders more accurate differentiation of the efficacy-proven strains, clarification of dose, duration, and outcome and a careful selection of the target patients are still necessary.

Effect of combined bifidobacteria supplementation and resistance training on cognitive function, body composition and bowel habits of healthy elderly subjects

Physical exercise exerts favourable effects on brain health and quality of life of the elderly; some of these positive health effects are induced by the modulation of microbiota composition. We therefore conducted a randomised, double blind, placebo-controlled trial that assessed whether a combination of Bifidobacterium spp. supplementation and moderate resistance training improved the cognitive function and other health-related parameters in healthy elderly subjects. Over a 12-week period, 38 participants (66-78 years) underwent resistance training and were assigned to the probiotic Bifidobacterium supplementation (n=20; 1.25×10¹⁰ cfu each of Bifidobacterium longum subsp. longum BB536, B. longum subsp. infantis M-63, Bifidobacterium breve M-16V and B. breve B-3) or the placebo (n=18) group. At baseline and at 12 weeks, we assessed the cognitive function, using the Japanese version of the Montreal Cognitive Assessment instrument (MoCA-J); modified flanker task scores; depression-anxiety scores; body composition; and bowel habits. At 12 weeks, the MoCA-J scores showed a significant increase in both the groups, while the flanker task scores of the probiotic group increased more significantly than those of the placebo group (0.35±0.9 vs -0.29±1.1, P=0.056). Only the probiotic group showed a significant decrease in the depression-anxiety scores (5.2±6.3 to 3.4±5.5, P=0.012) and body mass index (24.0±2.8 to 23.5±2.8 kg/m², P<0.001), with a significant increase in the defecation frequency (5.3±2.3 to 6.4±2.3 times/5 days, P=0.023) at 12 weeks. Thus, in healthy elderly subjects, combined probiotic bifidobacteria supplementation and moderate resistance training may improve the mental condition, body weight and bowel movement frequency.

Neuropsychiatric Disorders: Influence of Gut Microbe to Brain Signalling

The microbiome gut brain (MGB) axis consists of bidirectional routes of communication between the gut and the brain. It has emerged as a potential therapeutic target for multiple medical specialties including psychiatry. Significant numbers of preclinical trials have taken place with some transitioning to clinical studies in more recent years. Some positive results have been reported secondary to probiotic administration in both healthy populations and specific patient groups. This review aims to summarise the current understanding of the MGB axis and the preclinical and clinical findings relevant to psychiatry. Significant differences have been identified between the microbiome of patients with a diagnosis of depressive disorder and healthy controls. Similar findings have occurred in patients diagnosed with bipolar affective disorder and irritable bowel syndrome. A probiotic containing Lactobacillus acidophilus, Lactobacillus casei, and Bifidobacterium bifidum produced a clinically measurable symptom improvement in patients with depressive disorder. To date, some promising results have suggested that probiotics could play a role in the treatment of stress-related psychiatric disease. However, more well-controlled clinical trials are required to determine which clinical conditions are likely to benefit most significantly from this novel approach.

Oral microbiome activity in children with autism spectrum disorder

Autism spectrum disorder (ASD) is associated with several oropharyngeal abnormalities, including buccal sensory sensitivity, taste and texture aversions, speech apraxia, and salivary transcriptome alterations. Furthermore, the oropharynx represents the sole entry point to the gastrointestinal (GI) tract. GI disturbances and alterations in the GI microbiome are established features of ASD, and may impact behavior through the "microbial-gut-brain axis." Most studies of the ASD microbiome have used fecal samples. Here, we identified changes in the salivary microbiome of children aged 2-6 years across three developmental profiles: ASD (n = 180), nonautistic developmental delay (DD; n = 60), and typically developing (TD; n = 106) children. After RNA extraction and shotgun sequencing, actively transcribing taxa were quantified and tested for differences between groups and within ASD endophenotypes. A total of 12 taxa were altered between the developmental groups and 28 taxa were identified that distinguished ASD patients with and without GI disturbance, providing further evidence for the role of the gut-brain axis in ASD. Group classification accuracy was visualized with receiver operating characteristic curves and validated using a 50/50 hold-out procedure. Five microbial ratios distinguished ASD from TD participants (79.5% accuracy), three distinguished ASD from DD (76.5%), and three distinguished ASD children with/without GI disturbance (85.7%). Taxonomic pathways were assessed using the Kyoto Encyclopedia of Genes and Genomes microbial database and compared with one-way analysis of variance, revealing significant differences within energy metabolism and lysine degradation. Together, these results indicate that GI microbiome disruption in ASD extends to the oropharynx, and suggests oral microbiome profiling as a potential tool to evaluate ASD status. Autism Res 2018, 11: 1286-1299. © 2018 International Society for Autism Research, Wiley Periodicals, Inc. LAY SUMMARY: Previous research suggests that the bacteria living in the human gut may influence autistic behavior. This study examined genetic activity of microbes living in the mouth of over 300 children. The microbes with differences in children with autism were involved in energy processing and showed potential for identifying autism status.

Evidence for interplay among antibacterial-induced gut microbiota disturbance, neuro-inflammation, and anxiety in mice

The aim of the present study was to determine whether there is the mechanistic connection between antibacterial-dependent gut microbiota disturbance and anxiety. First, exposure of mice to ampicillin caused anxiety and colitis and increased the population of Proteobacteria, particularly Klebsiella oxytoca, in gut microbiota and fecal and blood lipopolysaccharide levels, while decreasing lactobacilli population including Lactobacillus reuteri. Next, treatments with fecal microbiota of ampicillin-treated mouse (FAP), K. oxytoca, or lipopolysaccharide isolated from K. oxytoca (KL) induced anxiety and colitis in mice and increased blood corticosterone, IL-6, and lipopolysaccharide levels. Moreover, these treatments also increased the recruitment of microglia (Iba1⁺), monocytes (CD11b⁺/CD45⁺), and dendritic cells (CD11b⁺/CD11c⁺) to the hippocampus, as well as the population of apoptotic neuron cells (caspase-3⁺/NeuN⁺) in the brain. Furthermore, ampicillin, K. oxytoca, and KL induced NF-κB activation and IL-1β and TNF-α expression in the colon and brain as well as increased gut membrane permeability. Finally, oral administration of L. reuteri alleviated ampicillin-induced anxiety and colitis. These results suggest that ampicillin exposure can cause anxiety through neuro-inflammation which can be induced by monocyte/macrophage-activated gastrointestinal inflammation and elevated Proteobacteria population including K. oxytoca, while treatment with lactobacilli suppresses it.

Gut microbiome and depression: what we know and what we need to know

Gut microbiome diversity has been strongly associated with mood-relating behaviours, including major depressive disorder (MDD). This association stems from the recently characterised bi-directional communication system between the gut and the brain, mediated by neuroimmune, neuroendocrine and sensory neural pathways. While the link between gut microbiome and depression is well supported by research, a major question needing to be addressed is the causality in the connection between the two, which will support the understanding of the role that the gut microbiota play in depression. In this article, we address this question by examining a theoretical ‘chronology’, reviewing the evidence supporting two possible sequences of events. First, we discuss that alterations in the gut microbiota populations of specific species might contribute to depression, and secondly, that depressive states might induce modification of specific gut microbiota species and eventually contribute to more severe depression. The feasibility of both sequences is supported by pre-clinical trials. For instance, research in rodents has shown an onset of depressive behaviour following faecal transplantations from patients with MDD. On the other hand, mental induction of stress and depressive behaviour in rodents resulted in reduced gut microbiota richness and diversity. Synthesis of these chronology dynamics raises important research directions to further understand the role that gut microbiota play in mood-relating behaviours, which holds substantial potential clinical outcomes for persons who experience MDD or related depressive disorders.

Microbiota influence the development of the brain and behaviors in C57BL/6J mice

We investigated the contributions of commensal bacteria to brain structural maturation by magnetic resonance imaging and behavioral tests in four and 12 weeks old C57BL/6J specific pathogen free (SPF) and germ free (GF) mice. SPF mice had increased volumes and fractional anisotropy in major gray and white matter areas and higher levels of myelination in total brain, major white and grey matter structures at either four or 12 weeks of age, demonstrating better brain maturation and organization. In open field test, SPF mice had better mobility and were less anxious than GF at four weeks. In Morris water maze, SPF mice demonstrated better spatial and learning memory than GF mice at 12 weeks. In fear conditioning, SPF mice had better contextual memory than GF mice at 12 weeks. In three chamber social test, SPF mice demonstrated better social novelty than GF mice at 12 weeks. Our data demonstrate numerous significant differences in morphological brain organization and behaviors between SPF and GF mice. This suggests that commensal bacteria are necessary for normal morphological development and maturation in the grey and white matter of the brain regions with implications for behavioral outcomes such as locomotion and cognitive functions.

Dysbiosis of gut microbiota and microbial metabolites in Parkinson's Disease

Gut microbial dysbiosis and alteration of microbial metabolites in Parkinson's disease (PD) have been increasingly reported. Dysbiosis in the composition and abundance of gut microbiota can affect both the enteric nervous system and the central nervous system (CNS), indicating the existence of a microbiota-gut-brain axis and thereby causing CNS diseases. Disturbance of the microbiota-gut-brain axis has been linked to specific microbial products that are related to gut inflammation and neuroinflammation. Future directions should therefore focus on the exploration of specific gut microbes or microbial metabolites that contribute to the development of PD. Microbiota-targeted interventions, such as antibiotics, probiotics and fecal microbiota transplantation, have been shown to favorably affect host health. In this review, recent findings regarding alterations and the role of gut microbiota and microbial metabolites in PD are summarized, and potential molecular mechanisms and microbiota-targeted interventions in PD are discussed.

Age-related changes in the gut microbiota influence systemic inflammation and stroke outcome

Objective

Chronic systemic inflammation contributes to the pathogenesis of many age‐related diseases. Although not well understood, alterations in the gut microbiota, or dysbiosis, may be responsible for age‐related inflammation.

Methods

Using stroke as a disease model, we tested the hypothesis that a youthful microbiota, when established in aged mice, produces positive outcomes following ischemic stroke. Conversely, an aged microbiota, when established in young mice, produces negative outcomes after stroke. Young and aged male mice had either a young or an aged microbiota established by fecal transplant gavage (FTG). Mice were subjected to ischemic stroke (middle cerebral artery occlusion; MCAO) or sham surgery. During the subsequent weeks, mice underwent behavioral testing and fecal samples were collected for 16S ribosomal RNA analysis of bacterial content.

Results

We found that the microbiota is altered after experimental stroke in young mice and resembles the biome of uninjured aged mice. In aged mice, the ratio of Firmicutes to Bacteroidetes (F:B), two main bacterial phyla in gut microbiota, increased ∼9‐fold (p < 0.001) compared to young. This increased F:B ratio in aged mice is indicative of dysbiosis. Altering the microbiota in young by fecal gavage to resemble that of aged mice (∼6‐fold increase in F:B ratio, p < 0.001) increased mortality following MCAO, decreased performance in behavioral testing, and increased cytokine levels. Conversely, altering the microbiota in aged to resemble that of young (∼9‐fold decrease in F:B ratio, p < 0.001) increased survival and improved recovery following MCAO.

Interpretation

Aged biome increased the levels of systemic proinflammatory cytokines. We conclude that the gut microbiota can be modified to positively impact outcomes from age‐related diseases. Ann Neurol 2018;83:23–36

Impact of gut microbiota on neurological diseases: Diet composition and novel treatments

Gut microbiota has significant effects on the structure and function of the enteric and central nervous system including human behaviour and brain regulation. Herein, we analyze the role of this intestinal ecosystem, the effects of dietary changes and the administration of nutritional supplements, such as probiotics, prebiotics, or fecal transplantation in neuropsychiatric disorders. Numerous factors have been highlighted to influence gut microbiota composition, including genetics, health status, mode of birth delivery and environment. However, diet composition and nutritional status has been repeatedly shown to be one of the most critical modifiable factors of this ecosystem. A comprehensively analysis of the microbiome-intestine-brain axis has been performed, including the impact of intestinal bacteria in alterations in the nervous, immune and endocrine systems and their metabolites. Finally, we discuss the latest literature examining the effects of diet composition, nutritional status and microbiota alterations in several neuropsychiatric disorders, such as autism, anxiety, depression, Alzheimer's disease and anorexia nervosa.

Lactobacillus paracasei PS23 Delays Progression of Age-Related Cognitive Decline in Senescence Accelerated Mouse Prone 8 (SAMP8) Mice

Probiotic supplements are potential therapeutic agents for age-related disorders due to their antioxidant and anti-inflammatory properties. However, the effect of probiotics on age-related brain dysfunction remains unclear. To investigate the effects of Lactobacillus paracasei PS23 (LPPS23) on the progression of age-related cognitive decline, male and female senescence-accelerated mouse prone 8 (SAMP8) mice were divided into two groups (n = 6 each): the control and PS23 groups. From the age of 16 weeks, these groups were given saline and LPPS23, respectively, because SAMP8 mice start aging rapidly after four months of age. After 12 weeks of treatment, we evaluated the effect of LPPS23 by analyzing their appearance, behavior, neural monoamines, anti-oxidative enzymes, and inflammatory cytokines. The PS23 group showed lower scores of senescence and less serious anxiety-like behaviors and memory impairment compared to the control group. The control mice also showed lower levels of neural monoamines in the striatum, hippocampus, and serum. Moreover, LPPS23 induced the anti-oxidative enzymes superoxide dismutase (SOD) and glutathione peroxidase (GPx). Higher levels of tumor necrosis factor (TNF)-α and monocyte chemotactic protein-1 (MCP1) and lower levels of interleukin (IL)-10 indicated that LPPS23 modulated the inflammation. Our results suggest that LPPS23 supplements could delay age-related cognitive decline, possibly by preventing oxidation and inflammation and modulating gut–brain axis communication.

The gut microbiome and irritable bowel syndrome: State of art review

Irritable bowel syndrome (IBS) is a functional disorder of the gastrointestinal tract, the physiology of which is not very well understood. There are multiple factors and pathways involved in pathogenesis of this entity. Among all, dysmotility, dysregulation of the brain-gut axis, altered intestinal microbiota and visceral hypersensitivity play a major role. Over the last years, research has shown that the type of gut microbiome present in an individual plays a significant role in the pathophysiology of IBS. Multiple studies have consistently shown that subjects diagnosed with IBS have disruption in gut microbiota balance. It has been established that host immune system and its interaction with metabolic products of gut microbiota play an important role in the gastrointestinal tract. Therefore, probiotics, prebiotics and antibiotics have shown some promising results in managing IBS symptoms via modulating the interaction between the above. This paper discusses the various factors involved in pathophysiology of IBS, especially gut microbiota.

The anxiolytic effect of probiotics: A systematic review and meta-analysis of the clinical and preclinical literature

Background

Probiotics have generated intensive research interest in recent years as a novel mode of treatment for physical and mental illness. Nevertheless, the anxiolytic potential of probiotics remains unclear. The present systematic review and meta-analysis aimed to evaluate the clinical and preclinical (animal model) evidence regarding the effect of probiotic administration on anxiety.

Methods

The PubMed, PsycINFO, and Web of Science databases were reviewed for preclinical and clinical studies that met the defined inclusion and exclusion criteria. The effects of probiotics on anxiety-like behavior and symptoms of anxiety were analyzed by meta-analyses. Separate subgroup analyses were conducted on diseased versus healthy animals, specific preclinical probiotic species, and clinical versus healthy human samples.

Results

Data were extracted from 22 preclinical studies (743 animals) and 14 clinical studies (1527 individuals). Overall, probiotics reduced anxiety-like behavior in animals (Hedges’ g = -0.47, 95% CI -0.77 –-0.16, p = 0.004). Subgroup analyses revealed a significant reduction only among diseased animals. Probiotic species-level analyses identified only Lactobacillus (L.) rhamnosus as an anxiolytic species, but these analyses were broadly under-powered. Probiotics did not significantly reduce symptoms of anxiety in humans (Hedges’ g = -0.12, 95% CI -0.29–0.05, p = 0.151), and did not differentially affect clinical and healthy human samples.

Conclusions

While preclinical (animal) studies suggest that probiotics may help reduce anxiety, such findings have not yet translated to clinical research in humans, perhaps due to the dearth of extant research with clinically anxious populations. Further investigation of probiotic treatment for clinically relevant anxiety is warranted, particularly with respect to the probiotic species L. rhamnosus.

Reciprocal Interactions Between Gut Microbiota and Host Social Behavior

Animals harbor an extensive, dynamic microbial ecosystem in their gut. Gut microbiota (GM) supposedly modulate various host functions including fecundity, metabolism, immunity, cognition and behavior. Starting by analyzing the concept of the holobiont as a unit of selection, we highlight recent findings suggesting an intimate link between GM and animal social behavior. We consider two reciprocal emerging themes: (i) that GM influence host social behavior; and (ii) that social behavior and social structure shape the composition of the GM across individuals. We propose that, throughout a long history of coevolution, GM may have become involved in the modulation of their host’s sociality to foster their own transmission, while in turn social organization may have fine-tuned the transmission of beneficial endosymbionts and prevented pathogen infection. We suggest that investigating these reciprocal interactions can advance our understanding of sociality, from healthy and impaired social cognition to the evolution of specific social behaviors and societal structure.

The microbiome as a novel paradigm in studying stress and mental health

At the intersection between neuroscience, microbiology, and psychiatry, the enteric microbiome has potential to become a novel paradigm for studying the psychobiological underpinnings of mental illness. Several studies provide support for the view that the enteric microbiome influences behavior through the microbiota-gut-brain axis. Moreover, recent findings are suggestive of the possibility that dysregulation of the enteric microbiota (i.e., dysbiosis) and associated bacterial translocation across the intestinal epithelium may be involved in the pathophysiology of stress-related psychiatric disorders, particularly depression. The current article reviews preliminary evidence linking the enteric microbiota and its metabolites to psychiatric illness, along with separate lines of empirical inquiry on the potential involvement of psychosocial stressors, proinflammatory cytokines and neuroinflammation, the hypothalamic-pituitary-adrenal axis, and vagal nerve activation, respectively, in this relationship. Finally, and drawing on these independent lines of research, an integrative conceptual model is proposed in which stress-induced enteric dysbiosis and intestinal permeability confer risk for negative mental health outcomes through immunoregulatory, endocrinal, and neural pathways. (PsycINFO Database Record

Microbiota-gut-brain axis: Interaction of gut microbes and their metabolites with host epithelial barriers

The gastrointestinal barrier and the blood brain barrier represent an important line of defense to protect the underlying structures against harmful external stimuli. These host barriers are composed of epithelial and endothelial cells interconnected by tight junction proteins along with several other supporting structures. Disruption in host barrier structures has therefore been implicated in various diseases of the gastrointestinal tract and the central nervous system. While there are several factors that influence host barrier, recently there is an increasing appreciation of the role of gut microbiota and their metabolites in regulating barrier integrity. In the current issue of Neurogastroenterology and Motility, Marungruang et al. describe the effect of gastrointestinal barrier maturation on gut microbiota and the blood brain barrier adding to the growing evidence of microbiota-barrier interactions. In this mini-review I will discuss the effect of gut microbiota on host epithelial barriers and its implications for diseases associated with disrupted gut-brain axis.

The effects of repeated antibiotic administration to juvenile BALB/c mice on the microbiota status and animal behavior at the adult age

Recent studies carried on germ -free (GF) animal models suggest that the gut microbiota (GM) may play a role in the regulation of anxiety, mood, and cognitive abilities such as memory and learning processes. Consistently, any treatment disturbing the gut microbiota, including the overuse of antibiotics, may influence the brain functions and impact behavior. In the present study, to address this issue, two wide-spectrum antibiotics (ampicillin and cefoperazone, 1 g/l) were repeatedly applied throughout a 6-week period to initially 21-day-old male BALB/c mice. Antibiotics were administered separately or in a mixed fashion. On the completion of the antibiotic treatment, all mice were subjected to the behavioral tests. The serum levels of corticosterone and brain-derived neurotropic factor (BDNF) were assessed. Gut microbiota profiles were obtained by using denaturing gradient gel electrophoresis system, DGGE, from fecal samples. Ampicillin had a greater impact on both, gut microbiota composition and mice behavior compared to cefoperazone. All antibiotic-treated groups manifested a decrease in the locomotor activity and reduced recognition memory. However, the ampicillin-treated groups showed a higher anxiety level as assessed by the open field and the elevated plus maze tests and an increased immobility (behavioral despair) in the forced swim test. Obtained results evidently show that in mice, a repeated antibiotic treatment applied during adolescence, parallel to the changes in GM, affects locomotor activity, affective behavior and cognitive skills in young adults with ampicillin specifically enhancing anxiety- and depressive-like responses. Lower levels of serum BDNF were not associated with cognitive impairment but with changes in affective-like behaviors. Repeated administration of neither ampicillin nor cefoperazone affected basal serum corticosterone levels. This is one of the few studies demonstrating changes in a behavioral phenotype of young-adult subjects who were previously exposed to a repeated antibiotic treatment.

Postnatal colonization with human "infant-type" Bifidobacterium species alters behavior of adult gnotobiotic mice

Accumulating studies have defined a role for the intestinal microbiota in modulation of host behavior. Research using gnotobiotic mice emphasizes that early microbial colonization with a complex microbiota (conventionalization) can rescue some of the behavioral abnormalities observed in mice that grow to adulthood completely devoid of bacteria (germ-free mice). However, the human infant and adult microbiomes vary greatly, and effects of the neonatal microbiome on neurodevelopment are currently not well understood. Microbe-mediated modulation of neural circuit patterning in the brain during neurodevelopment may have significant long-term implications that we are only beginning to appreciate. Modulation of the host central nervous system by the early-life microbiota is predicted to have pervasive and lasting effects on brain function and behavior. We sought to replicate this early microbe-host interaction by colonizing gnotobiotic mice at the neonatal stage with a simplified model of the human infant gut microbiota. This model consortium consisted of four “infant-type” Bifidobacterium species known to be commensal members of the human infant microbiota present in high abundance during postnatal development. Germ-free mice and mice neonatally-colonized with a complex, conventional murine microbiota were used for comparison. Motor and non-motor behaviors of the mice were tested at 6–7 weeks of age, and colonization patterns were characterized by 16S ribosomal RNA gene sequencing. Adult germ-free mice were observed to have abnormal memory, sociability, anxiety-like behaviors, and motor performance. Conventionalization at the neonatal stage rescued these behavioral abnormalities, and mice colonized with Bifidobacterium spp. also exhibited important behavioral differences relative to the germ-free controls. The ability of Bifidobacterium spp. to improve the recognition memory of both male and female germ-free mice was a prominent finding. Together, these data demonstrate that the early-life gut microbiome, and human “infant-type” Bifidobacterium species, affect adult behavior in a strongly sex-dependent manner, and can selectively recapitulate the results observed when mice are colonized with a complex microbiota.

Glyphosate based- herbicide exposure affects gut microbiota, anxiety and depression-like behaviors in mice

Recently, a number of studies have demonstrated the profound relationship between gut microbiota (GM) alterations and behavioral changes. Glyphosate-based herbicides (GBH) have been shown to induce behavioral impairments, and it is possible that they mediate the effects through an altered GM. In this study, we investigated the toxic effects of GBH on GM and its subsequent effects on the neurobehavioral functions in mice following acute, subchronic and chronic exposure to 250 or 500 mg/kg/day. The effect of these acute and repeated treatments was assessed at the behavioral level using the open field, the elevated plus maze, the tail suspension and splash tests. Then, mice were sacrificed and the intestinal samples were collected for GM analysis. Subchronic and chronic exposure to GBH induced an increase of anxiety and depression-like behaviors. In addition, GBH significantly altered the GM composition in terms of relative abundance and phylogenic diversity of the key microbes. Indeed, it decreased more specifically, Corynebacterium, Firmicutes, Bacteroidetes and Lactobacillus in treated mice. These data reinforce the essential link between GM and GBH toxicity in mice and suggest that observed intestinal dysbiosis could increase the prevalence of neurobehavioral alterations.

The Brain-Gut-Microbiome Axis

Preclinical and clinical studies have shown bidirectional interactions within the brain-gut-microbiome axis. Gut microbes communicate to the central nervous system through at least 3 parallel and interacting channels involving nervous, endocrine, and immune signaling mechanisms. The brain can affect the community structure and function of the gut microbiota through the autonomic nervous system, by modulating regional gut motility, intestinal transit and secretion, and gut permeability, and potentially through the luminal secretion of hormones that directly modulate microbial gene expression. A systems biological model is proposed that posits circular communication loops amid the brain, gut, and gut microbiome, and in which perturbation at any level can propagate dysregulation throughout the circuit. A series of largely preclinical observations implicates alterations in brain-gut-microbiome communication in the pathogenesis and pathophysiology of irritable bowel syndrome, obesity, and several psychiatric and neurologic disorders. Continued research holds the promise of identifying novel therapeutic targets and developing treatment strategies to address some of the most debilitating, costly, and poorly understood diseases.

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.

Beneficial psychological effects of novel psychobiotics in diabetic rats: the interaction among the gut, blood and amygdala

Type 2 diabetes mellitus (T2DM) can lead to major complications such as psychiatric disorders which include depressive and anxiety-like behaviors. The association of the gut-brain axis in the development of such disorders, especially in T2DM, has been elucidated; however, gut dysbiosis is also reported in patients with T2DM. Hence, the regulation of the gut-brain axis, in particular, the gut-amygdala, as a vital region for the regulation of behavior is essential. Thirty-five male Wistar rats were divided into six groups. To induce T2DM, treatment groups received high-fat diet and 35 mg/kg streptozotocin. Then, supplements of Lactobacillus plantarum, inulin or their combination were administered to each group for 8 weeks. Finally, the rats were sacrificed for measurement of blood and tissue parameters after behavioral testing. The findings demonstrated the favorable effects of the psychobiotics (L. plantarum, inulin or their combination) on oxidative markers of the blood and amygdala (superoxide dismutase, glutathione peroxidase, malondialdehyde and total antioxidant capacity), as well as on concentrations of amygdala serotonin and brain-derived neurotrophic factor, in the diabetic rats. In addition, beneficial effects were observed on the elevated plus maze and forced swimming tests with no change in locomotor activity of the rats. There was a strong correlation between the blood and amygdala oxidative markers, insulin and fasting blood sugar with depressive and anxiety-like behaviors. Our results identified L. plantarum ATCC 8014 and inulin or their combination as novel psychobiotics that could improve the systemic and nervous antioxidant status and improve amygdala performance and beneficial psychotropic effects.

Altered Brain Excitability and Increased Anxiety in Mice With Experimental Colitis: Consideration of Hyperalgesia and Sex Differences

Crohn’s disease (CD) and ulcerative colitis (UC) are incurable lifelong inflammatory bowel diseases (IBD) with a rising worldwide incidence. IBD is characterized by diarrhea, rectal bleeding, severe cramping and weight loss. However, there is a growing evidence that IBD is also associated with anxiety- and depression-related disorders, which further increase the societal burden of these diseases. Given the limited knowledge of central nervous system (CNS) changes in IBD, we investigated CNS-related comorbidities in a mouse model of experimental colitis induced by dextran sulfate sodium (DSS) administration in drinking water for 5 days. In male and female C57BL6J mice, DSS treatment caused increased brain excitability, revealed by a decrease in seizure onset times after intraperitoneal administration of kainic acid. Moreover, both sexes showed increased anxiety-related behavior in the elevated plus-maze (EPM) and open field (OF) paradigms. We assessed somatic pain levels, because they may influence behavioral responses. Only male mice were hyperalgesic when tested with calibrated von Frey hairs and on the hotplate for mechanical and thermal pain sensitivity respectively. Administration of diazepam (DZP; ip, 1 mg/kg) 30 min before EPM rescued the anxious phenotype and improved locomotion, even though it significantly increased thermal sensitivity in both sexes. This indicates that the altered behavioral response is unlikely attributable to an interference with movement due to somatic pain in females. We show that experimental colitis increases CNS excitability in response to administration of kainic acid, and increases anxiety-related behavior as revealed using the EPM and OF tests.

Microbiota in obesity: interactions with enteroendocrine, immune and central nervous systems

Western diets, with high consumption of simple sugars and saturated fats, contribute to the rise in the prevalence of obesity. It now seems clear that high-fat diets cause obesity, at least in part, by modifying the composition and function of the microorganisms that colonize in the gastrointestinal tract, the microbiota. The exact pathways by which intestinal microbiota contribute to obesity remain largely unknown. High-fat diet-induced alterations in intestinal microbiota have been suggested to increase energy extraction, intestinal permeability and systemic inflammation while decreasing the capability to generate obesity-suppressing short-chain fatty acids. Moreover, by increasing systemic inflammation, microglial activation and affecting vagal nerve activity, 'obese microbiota' indirectly influence hypothalamic gene expression and promote overeating. Because the potential of intestinal microbiota to induce obesity has been recognized, multiple ways to modify its composition and function are being investigated to provide novel preventive and therapeutic strategies against diet-induced obesity.

Mechanisms underlying the effects of n-3 polyunsaturated fatty acids on fear memory processing and their hypothetical effects on fear of cancer recurrence in cancer survivors

The relationship of n-3 polyunsaturated fatty acids (PUFAs) and gut microbiota with brain function has been extensively reported. Here, we review how n-3 polyunsaturated fatty acids affect fear memory processing. n-3 PUFAs may improve dysfunctional fear memory processing via immunomodulation/anti-inflammation, increased BDNF, upregulated adult neurogenesis, modulated signal transduction, and microbiota-gut-brain axis normalization. We emphasize how n-3 PUFAs affect this axis and also focus on the hypothetical effects of PUFAs in fear of cancer recurrence (FCR), the primary psychological unmet need of cancer survivors. Its pathophysiology may be similar to that of post-traumatic stress disorder (PTSD), which involves dysfunctional fear memory processing. Due to fewer adverse effects than psychotropic drugs, nutritional interventions involving n-3 PUFAs should be acceptable for physically vulnerable cancer survivors. We are currently studying the relationship of FCR with n-3 PUFAs and gut microbiota in cancer survivors to provide them with a nutritional intervention that protects against FCR.

Targeting the Microbiota, from Irritable Bowel Syndrome to Mood Disorders: Focus on Probiotics and Prebiotics

PURPOSE OF REVIEW

The crosstalk between the gut and the brain has revealed a complex communication system responsible for maintaining a proper gastrointestinal homeostasis as well as affect emotional mood and cognitive functions. Recent research has revealed that beneficial manipulation of the microbiota by probiotics and prebiotics represent an emerging and novel strategy for the treatment of a large spectrum of diseases ranging from visceral pain to mood disorders. The review critically evaluates current knowledge of the effects exerted by both probiotics and prebiotics in irritable bowel syndrome (IBS) and mood disorders such as anxiety and depression.

RECENT FINDINGS

Relevant literature was identified through a search of MEDLINE via PubMed using the following words, "probiotics", "prebiotics", "microbiota", and "gut-brain axis" in combination with "stress", "depression", "IBS", and "anxiety". A number of trials have shown efficacy of probiotics and prebiotics in ameliorating both IBS related symptoms and emotional states. However, limitations have been found especially due to the small number of clinical studies, studies design, patient sample size, and placebo effect.

SUMMARY

Nonetheless, current finding supports the view that beneficial manipulation of the microbiota through both probiotics and prebiotics intake represents a novel attractive strategy to treat gut-brain axis disorders such as IBS and depression.

A meta-analysis of the use of probiotics to alleviate depressive symptoms

INTRODUCTION

Some preclinical and clinical studies have demonstrated the positive impact of probiotic supplementation on depressive symptoms. This paper aims to provide an updated meta-analysis on the topic.

METHODS

Using the keywords [probiotics OR gut OR microflora OR microbiome OR bacteria OR yeast OR yoghurt OR lactobacillus OR bifidobacterium] AND [mood OR depression OR MDD OR suicide], a preliminary search on the PubMed, Ovid, Clinical Trials Register of the Cochrane Collaboration Depression, Anxiety and Neurosis Group (CCDANTR) and Cochrane Field for Complementary Medicine database yielded 917 papers published in English between 1-Jan-1960 and 1-June-2017.

RESULTS

10 clinical trials with a total of 1349 patients were reviewed, comparing the use of probiotics to placebo controls. There was no significant difference in mood between the treatment and placebo group post-intervention as the standardized mean difference (SMD) was -0.128 (95% CI -0.261 to 0.00463, P=0.059). A separate subgroup analysis of studies conducted in healthy versus depressed individuals found significant improvements in the moods of individuals with mild to moderate depressive symptoms (SMD -0.684, 95% CI -1.296 to -0.0712, P=0.029) and non-significant effects in healthy individuals (SMD -0.0999, 95% CI -0.235 to 0.0348, P=0.146).

LIMITATIONS

Inter-study discrepancies with respect to probiotic dosing, bacterial strains and strain combinations limit the comparability of current clinical trials. Furthermore, majority of existing RCTs were conducted in healthy individuals, making it difficult to extrapolate the results to depressed individuals.

CONCLUSION

Probiotic supplementation has an overall insignificant effect on mood. Future studies should be conducted on more patients with clinically diagnosed depression.

Development of an ex Vivo Method for Multi-unit Recording of Microbiota-Colonic-Neural Signaling in Real Time

Background and Objectives: Bidirectional signaling between the gastrointestinal tract and the brain is vital for maintaining whole-body homeostasis. Moreover, emerging evidence implicates vagal afferent signaling in the modulation of host physiology by microbes, which are most abundant in the colon. This study aims to optimize and advance dissection and recording techniques to facilitate real-time recordings of afferent neural signals originating in the distal colon. New Protocol: This paper describes a dissection technique, which facilitates extracellular electrophysiological recordings from visceral pelvic, spinal and vagal afferent neurons in response to stimulation of the distal colon. Examples of Application: Focal application of 75 mM KCl to a section of distal colon with exposed submucosal or myenteric nerve cell bodies and sensory nerve endings evoked activity in the superior mesenteric plexus and the vagal nerve. Noradrenaline stimulated nerve activity in the superior mesenteric plexus, whereas application of carbachol stimulated vagal nerve activity. Exposure of an ex vivo section of distal colon with an intact colonic mucosa to peptidoglycan, but not lipopolysaccharide, evoked vagal nerve firing. Discussion: Previous studies have recorded vagal signaling evoked by bacteria in the small intestine. The technical advances of this dissection and recording technique facilitates recording of afferent nerve signals evoked in extrinsic sensory pathways by neuromodulatory reagents applied to the distal colon. Moreover, we have demonstrated vagal afferent activation evoked by bacterial products applied to the distal colonic mucosa. This protocol may contribute to our understanding of functional bowel disorders where gut-brain communication is dysfunctional, and facilitate real-time interrogation of microbiota-gut-brain signaling.

Impact of food additives on the gut-brain axis

The mammalian intestinal tract is heavily colonized with a complex community of micro-organisms, present at a very high density, and containing an estimated amount of 10¹⁴ bacteria. The microbiota generally benefits the host, as it plays a central role in maturing the immune system, protecting against infection by entero-pathogens such as Clostridium difficile, and favoring nutrient digestion/energy extraction in our intestine. An altered microbiota, however, can become detrimental and lead to inflammation, metabolic disorders, and even altered behavior/neuroinflammation. While there are many factors involved in regulating the intestinal microbiota composition and the way it interacts with its host, this review will focus on the role played by food additives on host/microbiota relationship.

The Vagus Nerve at the Interface of the Microbiota-Gut-Brain Axis

The microbiota, the gut, and the brain communicate through the microbiota-gut-brain axis in a bidirectional way that involves the autonomic nervous system. The vagus nerve (VN), the principal component of the parasympathetic nervous system, is a mixed nerve composed of 80% afferent and 20% efferent fibers. The VN, because of its role in interoceptive awareness, is able to sense the microbiota metabolites through its afferents, to transfer this gut information to the central nervous system where it is integrated in the central autonomic network, and then to generate an adapted or inappropriate response. A cholinergic anti-inflammatory pathway has been described through VN's fibers, which is able to dampen peripheral inflammation and to decrease intestinal permeability, thus very probably modulating microbiota composition. Stress inhibits the VN and has deleterious effects on the gastrointestinal tract and on the microbiota, and is involved in the pathophysiology of gastrointestinal disorders such as irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD) which are both characterized by a dysbiosis. A low vagal tone has been described in IBD and IBS patients thus favoring peripheral inflammation. Targeting the VN, for example through VN stimulation which has anti-inflammatory properties, would be of interest to restore homeostasis in the microbiota-gut-brain axis.

Analysis of microbiota in first episode psychosis identifies preliminary associations with symptom severity and treatment response

The effects of gut microbiota on the central nervous system, along its possible role in mental disorders, have received increasing attention. Here we investigated differences in fecal microbiota between 28 patients with first-episode psychosis (FEP) and 16 healthy matched controls and explored whether such differences were associated with response after up to 12months of treatment. Numbers of Lactobacillus group bacteria were elevated in FEP-patients and significantly correlated with severity along different symptom domains. A subgroup of FEP patients with the strongest microbiota differences also showed poorer response after up to 12months of treatment. The present findings support the involvement of microbiota alterations in psychotic illness and may provide the basis for exploring the benefit of their modulation on treatment response and remission.

The vagus nerve modulates BDNF expression and neurogenesis in the hippocampus

Accumulating evidence suggests that certain gut microbiota have antidepressant-like behavioural effects and that the microbiota can regulate neurogenesis and the expression of brain-derived neurotrophic factor (BDNF) in the hippocampus. The precise mechanisms underlying these effects are not yet clear. However, the vagus nerve is one of the primary bidirectional routes of communication between the gut and the brain and thus may represent a candidate mechanism. Yet, relatively little is known about the direct influence of vagus nerve activity on hippocampal function and plasticity. Thus, the aim of the present study was to determine whether constitutive vagus nerve activity contributes to the regulation of neurogenesis and BDNF mRNA expression in the hippocampus. To this end, we examined the impact of subdiaphragmatic vagotomy in adult mice on these parameters. We found that vagotomy decreased BDNF mRNA in all areas of the hippocampus. Vagotomy also reduced the proliferation and survival of newly born cells and decreased the number of immature neurons, particularly those with a more complex dendritic morphology. Taken together, these findings suggest that vagal nerve activity influences neurogenesis and BDNF mRNA expression in the adult hippocampus.

Abdominal Vagal Afferents Modulate the Brain Transcriptome and Behaviors Relevant to Schizophrenia

Reduced activity of vagal efferents has long been implicated in schizophrenia and appears to be responsible for diminished parasympathetic activity and associated peripheral symptoms such as low heart rate variability and cardiovascular complications in affected individuals. In contrast, only little attention has been paid to the possibility that impaired afferent vagal signaling may be relevant for the disorder's pathophysiology as well. The present study explored this hypothesis using a model of subdiaphragmatic vagal deafferentation (SDA) in male rats. SDA represents the most complete and selective vagal deafferentation method existing to date as it leads to complete disconnection of all abdominal vagal afferents while sparing half of the abdominal vagal efferents. Using next-generation mRNA sequencing, we show that SDA leads to brain transcriptional changes in functional networks annotating with schizophrenia. We further demonstrate that SDA induces a hyperdopaminergic state, which manifests itself as increased sensitivity to acute amphetamine treatment and elevated accumbal levels of dopamine and its major metabolite, 3,4-dihydroxyphenylacetic acid. Our study also shows that SDA impairs sensorimotor gating and the attentional control of associative learning, which were assessed using the paradigms of prepulse inhibition and latent inhibition, respectively. These data provide converging evidence suggesting that the brain transcriptome, dopamine neurochemistry, and behavioral functions implicated in schizophrenia are subject to visceral modulation through abdominal vagal afferents. Our findings may encourage the further establishment and use of therapies for schizophrenia that are based on vagal interventions.SIGNIFICANCE STATEMENT The present work provides a better understanding of how disrupted vagal afferent signaling can contribute to schizophrenia-related brain and behavioral abnormalities. More specifically, it shows that subdiaphragmatic vagal deafferentation (SDA) in rats leads to (1) brain transcriptional changes in functional networks related to schizophrenia, (2) increased sensitivity to dopamine-stimulating drugs and elevated dopamine levels in the nucleus accumbens, and (3) impairments in sensorimotor gating and the attentional control of associative learning. These findings may encourage the further establishment of novel therapies for schizophrenia that are based on vagal interventions.

Decreased microglial activation through gut-brain axis by prebiotics, probiotics, or synbiotics effectively restored cognitive function in obese-insulin resistant rats

BACKGROUND

Chronic high-fat diet (HFD) consumption caused not only obese-insulin resistance, but also cognitive decline and microglial hyperactivity. Modified gut microbiota by prebiotics and probiotics improved obese-insulin resistance. However, the effects of prebiotics, probiotics, and synbiotics on cognition and microglial activity in an obese-insulin resistant condition have not yet been investigated. We aimed to evaluate the effect of prebiotic (Xyloolidosaccharide), probiotic (Lactobacillus paracasei HII01), or synbiotics in male obese-insulin resistant rats induced by a HFD.

METHODS

Male Wistar rats were fed with either a normal diet or a HFD for 12 weeks. At week 13, the rats in each dietary group were randomly divided into four subgroups including vehicle group, prebiotics group, probiotics group, and synbiotics group. Rats received their assigned intervention for an additional 12 weeks. At the end of experimental protocol, the cognitive functioning of each rat was investigated; blood and brain samples were collected to determine metabolic parameters and investigate brain pathology.

RESULTS

We found that chronic HFD consumption leads to gut and systemic inflammation and impaired peripheral insulin sensitivity, which were improved by all treatments. Prebiotics, probiotics, or synbiotics also improved hippocampal plasticity and attenuated brain mitochondrial dysfunction in HFD-fed rats. Interestingly, hippocampal oxidative stress and apoptosis were significantly decreased in HFD-fed rats with all therapies, which also decreased microglial activation, leading to restored cognitive function.

CONCLUSIONS

These findings suggest that consumption of prebiotics, probiotics, and synbiotics restored cognition in obese-insulin resistant subjects through gut-brain axis, leading to improved hippocampal plasticity, brain mitochondrial function, and decreased microglial activation.

Low Cerebral Exposure Cannot Hinder the Neuroprotective Effects of Panax Notoginsenosides

A bidirectional route of communication between the gastrointestinal tract and the central nervous system, termed the "gut-brain axis," is becoming increasingly relevant to treatment of cerebral damage. Panax Notoginsenoside extract (PNE) is popular for prevention and treatment of cardio-cerebrovascular ischemic diseases although plasma and cerebral exposure levels are extremely low. To date, the mechanisms underlying the neuroprotective effects of PNE remain largely unknown. In the present study, the neuroprotective effects of PNE were systematically studied via investigation of the regulation by PNE of the gastrointestinal microbial community and γ aminobutyric acid (GABA) receptors. The results demonstrated that pretreatment with PNE exerted a remarkable neuroprotective effect on focal cerebral ischemia/reperfusion (I/R) injury in rats, and the efficiency was attenuated in germ-free rats. Pretreatment with PNE could significantly prevent downregulation of Bifidobacterium longum (B.L) caused by I/R surgery, and colonization by B.L could also exert neuroprotective effects. More importantly, both PNE and B.L could upregulate the expression of GABA receptors in the hippocampus of I/R rats, and coadministration of a GABA-B receptor antagonist could significantly attenuate the neuroprotective effects of PNE and B.L. The study above suggests that the neuroprotective effects of PNE may be largely attributable to its regulation of intestinal flora, and oral treatment with B.L was also useful in therapy of ischemia/reperfusion injury (I/R) by upregulating GABA-B receptors.

Microbiota Signaling Pathways that Influence Neurologic Disease

Though seemingly distinct and autonomous, emerging evidence suggests there is a bidirectional interaction between the intestinal microbiota and the brain. This crosstalk may play a substantial role in neurologic diseases, including anxiety, depression, autism, multiple sclerosis, Parkinson's disease, and, potentially, Alzheimer's disease. Long hypothesized by Metchnikoff and others well over 100 years ago, investigations into the mind-microbe axis is now seeing a rapid resurgence of research. If specific pathways and mechanisms of interaction are understood, it could have broad therapeutic potential, as the microbiome is environmentally acquired and can be modified to promote health. This review will discuss immune, endocrine, and neural system pathways that interconnect the gut microbiota to central nervous system and discuss how these findings might be applied to neurologic disease.

Targeting gut microbiome: A novel and potential therapy for autism

Autism spectrum disorder (ASD) is a severely neurodevelopmental disorder that impairs a child's ability to communicate and interact with others. Children with neurodevelopmental disorder, including ASD, are regularly affected by gastrointestinal problems and dysbiosis of gut microbiota. On the other hand, humans live in a co-evolutionary association with plenty of microorganisms that resident on the exposed and internal surfaces of our bodies. The microbiome, refers to the collection of microbes and their genetic material, confers a variety of physiologic benefits to the host in many key aspects of life as well as being responsible for some diseases. A large body of preclinical literature indicates that gut microbiome plays an important role in the bidirectional gut-brain axis that communicates between the gut and central nervous system. Moreover, accumulating evidences suggest that the gut microbiome is involved in the pathogenesis of ASD. The present review introduces the increasing evidence suggesting the reciprocal interaction network among microbiome, gut and brain. It also discusses the possible mechanisms by which gut microbiome influences the etiology of ASD via altering gut-brain axis. Most importantly, it highlights the new findings of targeting gut microbiome, including probiotic treatment and fecal microbiota transplant, as novel and potential therapeutics for ASD diseases.