Evidences for vagus nerve in maintenance of immune balance and transmission of immune information from gut to brain in STM-infected rats

Vagus nerve stimulation (VNS) preventing postoperative cognitive dysfunction (POCD): two potential mechanisms in cognitive function

Postoperative cognitive dysfunction (POCD) impacts a significant number of patients annually, frequently impairing their cognitive abilities and resulting in unfavorable clinical outcomes. Aimed at addressing cognitive impairment, vagus nerve stimulation (VNS) is a therapeutic approach, which was used in many mental disordered diseases, through the modulation of vagus nerve activity. In POCD model, the enhancement of cognition function provided by VNS was shown, demonstrating VNS effect on cognition in POCD. In the present study, we primarily concentrates on elucidating the role of the VNS improving the cognitive function in POCD, via two potential mechanisms: the inflammatory microenvironment and epigenetics. This study provided a theoretical support for the feasibility that VNS can be a potential method to enhance cognition function in POCD.

Acupuncture influences multiple diseases by regulating gut microbiota

Acupuncture, an important green and side effect-free therapy in traditional Chinese medicine, is widely use both domestically and internationally. Acupuncture can interact with the gut microbiota and influence various diseases, including metabolic diseases, gastrointestinal diseases, mental disorders, nervous system diseases, and other diseases. This review presents a thorough analysis of these interactions and their impacts and examines the alterations in the gut microbiota and the potential clinical outcomes following acupuncture intervention to establish a basis for the future utilization of acupuncture in clinical treatments.

Alleviating effect of vagus nerve cutting in Salmonella-induced gut infections and anxiety-like behavior via enhancing microbiota-derived GABA

The vagus nerve, a pivotal link within the gut-brain axis, plays a critical role in maintaining homeostasis and mediating communication between the gastrointestinal tract and the brain. It has been reported that gastrointestinal infection by Salmonella typhimurium (S. typhimurium) triggers gut inflammation and manifests as anxiety-like behaviors, yet the mechanistic involvement of the vagus nerve remains to be elucidated. In this study, we demonstrated that unilateral cervical vagotomy markedly attenuated anxiety-like behaviors induced by S. typhimurium SL1344 infection in C57BL/6 mice, as evidenced by the open field test and marble burying experiment. Furthermore, vagotomy significantly diminished neuronal activation within the nucleus of the solitary tract and amygdala, alongside mitigating aberrant glial cell activation in the hippocampus and amygdala. Additionally, vagotomy notably decreases serum endotoxin levels, counters the increase in splenic Salmonella concentration, and modulates the expression of inflammatory cytokines-including IL-6, IL-1β, and TNF-α-in both the gastrointestinal tract and brain, with a concurrent reduction in IL-22 and CXCL1 expression. This intervention also fostered the enrichment of beneficial gut microbiota, including Alistipes and Lactobacillus species, and augmented the production of gamma-aminobutyric acid (GABA) in the gut. Administration of GABA replicated the vagotomy's beneficial effects on reducing gut inflammation and anxiety-like behavior in infected mice. However, blockade of GABA receptors with picrotoxin abrogated the vagotomy's protective effects against gut inflammation, without influencing its impact on anxiety-like behaviors. Collectively, these findings suggest that vagotomy exerts a protective effect against infection by promoting GABA synthesis in the colon and alleviating anxiety-like behavior. This study underscores the critical role of the vagus nerve in relaying signals of gut infection to the brain and posits that targeting the gut-brain axis may offer a novel and efficacious approach to preventing gastrointestinal infections and associated behavioral abnormalities.

Air pollution accelerates the development of obesity and Alzheimer's disease: the role of leptin and inflammation - a mini-review

Air pollution is an urgent concern linked to numerous health problems in low- and middle-income countries, where 92% of air pollution-related deaths occur. Particulate matter 2.5 (PM2.5) is the most harmful component of air pollutants, increasing inflammation and changing gut microbiota, favoring obesity, type 2 diabetes, and Alzheimer's Disease (AD). PM2.5 contains lipopolysaccharides (LPS), which can activate the Toll-like receptor 4 (TLR4) signaling pathway. This pathway can lead to the release of pro-inflammatory markers, including interleukins, and suppressor of cytokine signaling-3 (SOCS3), which inhibits leptin action, a hormone that keeps the energy homeostasis. Leptin plays a role in preventing amyloid plaque deposition and hyperphosphorylation of tau-protein (p-tau), mechanisms involved in the neurodegeneration in AD. Approximately 50 million people worldwide are affected by dementia, with a significant proportion living in low-and middle-income countries. This number is expected to triple by 2050. This mini-review focuses on the potential impact of PM2.5 exposure on the TLR4 signaling pathway, its contribution to leptin resistance, and dysbiosis that exacerbates the link between obesity and AD.

Vagal sensory pathway for the gut-brain communication

The communication between the gut and brain is crucial for regulating various essential physiological functions, such as energy balance, fluid homeostasis, immune response, and emotion. The vagal sensory pathway plays an indispensable role in connecting the gut to the brain. Recently, our knowledge of the vagal gut-brain axis has significantly advanced through molecular genetic studies, revealing a diverse range of vagal sensory cell types with distinct peripheral innervations, response profiles, and physiological functions. Here, we review the current understanding of how vagal sensory neurons contribute to gut-brain communication. First, we highlight recent transcriptomic and genetic approaches that have characterized different vagal sensory cell types. Then, we focus on discussing how different subtypes encode numerous gut-derived signals and how their activities are translated into physiological and behavioral regulations. The emerging insights into the diverse cell types and functional properties of vagal sensory neurons have paved the way for exciting future directions, which may provide valuable insights into potential therapeutic targets for disorders involving gut-brain communication.

Nutritional Criminology: Why the Emerging Research on Ultra-Processed Food Matters to Health and Justice

There is mounting concern over the potential harms associated with ultra-processed foods, including poor mental health and antisocial behavior. Cutting-edge research provides an enhanced understanding of biophysiological mechanisms, including microbiome pathways, and invites a historical reexamination of earlier work that investigated the relationship between nutrition and criminal behavior. Here, in this perspective article, we explore how this emergent research casts new light and greater significance on previous key observations. Despite expanding interest in the field dubbed 'nutritional psychiatry', there has been relatively little attention paid to its relevancy within criminology and the criminal justice system. Since public health practitioners, allied mental health professionals, and policymakers play key roles throughout criminal justice systems, a holistic perspective on both historical and emergent research is critical. While there are many questions to be resolved, the available evidence suggests that nutrition might be an underappreciated factor in prevention and treatment along the criminal justice spectrum. The intersection of nutrition and biopsychosocial health requires transdisciplinary discussions of power structures, industry influence, and marketing issues associated with widespread food and social inequalities. Some of these discussions are already occurring under the banner of 'food crime'. Given the vast societal implications, it is our contention that the subject of nutrition in the multidisciplinary field of criminology-referred to here as nutritional criminology-deserves increased scrutiny. Through combining historical findings and cutting-edge research, we aim to increase awareness of this topic among the broad readership of the journal, with the hopes of generating new hypotheses and collaborations.

Microbial Reprogramming in Obsessive-Compulsive Disorders: A Review of Gut-Brain Communication and Emerging Evidence

Obsessive-compulsive disorder (OCD) is a debilitating mental health disorder characterized by intrusive thoughts (obsessions) and repetitive behaviors (compulsions). Dysbiosis, an imbalance in the gut microbial composition, has been associated with various health conditions, including mental health disorders, autism, and inflammatory diseases. While the exact mechanisms underlying OCD remain unclear, this review presents a growing body of evidence suggesting a potential link between dysbiosis and the multifaceted etiology of OCD, interacting with genetic, neurobiological, immunological, and environmental factors. This review highlights the emerging evidence implicating the gut microbiota in the pathophysiology of OCD and its potential as a target for novel therapeutic approaches. We propose a model that positions dysbiosis as the central unifying element in the neurochemical, immunological, genetic, and environmental factors leading to OCD. The potential and challenges of microbial reprogramming strategies, such as probiotics and fecal transplants in OCD therapeutics, are discussed. This review raises awareness of the importance of adopting a holistic approach that considers the interplay between the gut and the brain to develop interventions that account for the multifaceted nature of OCD and contribute to the advancement of more personalized approaches.

The contribution of the peripheral immune system to neurodegeneration

Microglial cells are the major immune cells of the central nervous system (CNS), and directly react to neurodegeneration, but other immune cell types are also able to react to pathology and can modify the course of neurodegenerative processes. These mainly include monocytes/macrophages and lymphocytes. While these peripheral immune cells were initially considered to act only after infiltrating the CNS, recent evidence suggests that some of them can also act directly from the periphery. We will review the existing and emerging evidence for a role of peripheral immune cells in neurodegenerative diseases, both with and without CNS infiltration. Our focus will be on amyotrophic lateral sclerosis, but we will also compare to Alzheimer's disease and Parkinson's disease to highlight similarities or differences. Peripheral immune cells are easily accessible, and therefore may be an attractive therapeutic target for neurodegenerative diseases. Thus, understanding how these peripheral immune cells communicate with the CNS deserves deeper investigation.

Effects of common plastic products heat exposure on cognition: Mediated by gut microbiota

Considering plastic exposure patterns in modern society, the effects of exposure to leachate from boiled-water treated plastic products on cognitive function was probed in mice through changes in gut microbiota diversity. In this study, Institute for Cancer Research (ICR) mice were used to establish drinking water exposure models of three popular kinds of plastic products, including non-woven tea bags, food-grade plastic bags and disposable paper cups. 16S rRNA was used to detect changes in the gut microbiota of mice. Behavioral, histopathology, biochemistry, and molecular biology experiments were used to evaluate cognitive function in mice. Our results showed that the diversity and composition of gut microbiota changed at genus level compared to control group. Nonwoven tea bags-treated mice were proved an increase in Lachnospiraceae and a decreased in Muribaculaceae in gut. Alistipes was increased under the intervention of food grade plastic bags. Muribaculaceae decreased and Clostridium increased in disposable paper cups group. The new object recognition index of mice in the non-woven tea bag and disposable paper cup groups decreased, and amyloid β-protein (Aβ) and tau phosphorylation (P-tau) protein deposition. Cell damage and neuroinflammation were observed in the three intervention groups. Totally speaking, oral exposure to leachate from boiled-water treated plastic results in cognitive decline and neuroinflammation in mammals, which is likely related to MGBA and changes in gut microbiota.

Disruption of the lung-gut-brain axis is responsible for cortex damage induced by pulmonary exposure to zinc oxide nanoparticles

Increasing evidence shows that gut microbiota is important for host health in response to metal nanomaterials exposure. However, the effect of gut microbiota on the cortex damage caused by pulmonary exposure to zinc oxide nanoparticles (ZnONPs) remains mainly unknown. In this study, a total of 48 adult C57BL/6J mice were intratracheally instilled with 0.6 mg/kg ZnONPs in the presence or absence of antibiotics (ABX) treatment. Besides, 24 mice were treated with or without fecal microbiota transplantation (FMT) after the intraperitoneal administration of ABX. Our results demonstrated for the first time that dysbiosis induced by ABX treatment significantly aggravated cortex damage induced by pulmonary exposure to ZnONPs. Such damage might highly occur through the induction of oxidative stress, manifested by the enhancement of antioxidative enzymes and products of lipid peroxidation. However, ferroptosis was not involved in this process. Interestingly, our data revealed that ABX treatment exacerbated the alterations of gut-brain peptides (including Sst, Sstr2, and Htr4) induced by ZnONPs in both gut and cortex tissues. Moreover, fecal microbiota transplantation (FMT) was able to alleviate cerebral cortex damage, oxidative stress, and alterations of gut-brain peptides induced by pulmonary exposure to ZnONPs. The results together indicate that pulmonary exposure to ZnONPs causes cerebral cortex damage possibly via the disruption of the lung-gut-brain axis. These findings not only propose valuable insights into the mechanism of ZnONPs neurotoxicity but also provide a potential therapeutic method against brain disorders induced by pulmonary exposure to ZnONPs. AVAILABILITY OF DATA AND MATERIALS: The datasets used and/or analyzed during the current study are available from the The corresponding author on reasonable request.

Advantages and limitations of experimental autoimmune encephalomyelitis in breaking down the role of the gut microbiome in multiple sclerosis

Since the first model of experimental autoimmune encephalomyelitis (EAE) was introduced almost a century ago, there has been an ongoing scientific debate about the risks and benefits of using EAE as a model of multiple sclerosis (MS). While there are notable limitations of translating EAE studies directly to human patients, EAE continues to be the most widely used model of MS, and EAE studies have contributed to multiple key breakthroughs in our understanding of MS pathogenesis and discovery of MS therapeutics. In addition, insights from EAE have led to a better understanding of modifiable environmental factors that can influence MS initiation and progression. In this review, we discuss how MS patient and EAE studies compare in our learning about the role of gut microbiome, diet, alcohol, probiotics, antibiotics, and fecal microbiome transplant in neuroinflammation. Ultimately, the combination of rigorous EAE animal studies, novel bioinformatic approaches, use of human cell lines, and implementation of well-powered, age- and sex-matched randomized controlled MS patient trials will be essential for improving MS patient outcomes and developing novel MS therapeutics to prevent and revert MS disease progression.

Vagus Nerve and Underlying Impact on the Gut Microbiota-Brain Axis in Behavior and Neurodegenerative Diseases

The gut microbiota is the most abundant and diverse microbiota in the human body and the vagus nerve is the most widely distributed and complex nerve in the body, both of them are essential in maintaining homeostasis. The most important phenomenon is how they coordinate to regulate functions, which has attracted the great attention of scientists. The academic literature on the correlation with a host of intestinal diseases and even systemic diseases has revealed the bidirectional communication between the gut microbiota and the brain, which can be carried out via multiple patterns. In the review, firstly, we have a general overview of the gut microbiota and the gut microbiota-brain axis. Secondly, according to the distribution characteristics of the vagus nerve, we analyzed and summarized its function in the intestinal tract. At the same time, we have summarized the underlying mechanism of some behavior changes such as depressive and anxiety-like behaviors and related neurodegenerative diseases caused by the vagus nerve and intestinal microecological environment disorders, and then we also analyzed inconsistency of the experimental evidence in order to propose novel strategies for the clinical practice.

Bi-directional elucidation of Lactiplantibacillus plantarum (RTA 8) intervention on the pathophysiology of gut-brain axis during Salmonella brain infection

BACKGROUND

There have been reports of patients suffering from typhoid fever, particularly those involving infants and immunocompromised patients, which at times present with Salmonella induced brain infection. Although rare, it has frequently been associated with adverse neurological complications and increased mortality. In this context, the gut-brain axis, involving two-way communication between the gut and the brain, holds immense significance as various gut ailments have been associated with psychiatric complications. In turn, several neurodegenerative diseases have been associated with an altered gut microbiota profile. Given the paucity of effective antimicrobials and increasing incidence of multi-drug resistance in pathogens, alternate treatment therapies such as probiotics have gained significant attention in the recent past.

RESULTS

In the current study, prophylactic effect of Lactiplantibacillus plantarum (RTA 8) in preventing neurological complications occurring due to Salmonella brain infection was evaluated in a murine model. Along with a significant reduction in bacterial burden and improved histoarchitecture, L. plantarum (RTA 8) administration resulted in amelioration in the level of neurotransmitters such as serotonin, norepinephrine and dopamine in the gut as well as in the brain tissue. Simultaneously, increased gene expression of physiologically essential molecules such as mucin (MUC1 and MUC3) and brain-derived neurotrophic factor (BDNF) was also observed in this group.

CONCLUSION

Present study highlights the potential benefits of a probiotic supplemented diet in improving various aspects of host health due to their multi-targeted approach, thereby resulting in multi-faceted gains.

Multiple sclerosis and the microbiota

Multiple sclerosis (MS), a neurological autoimmune disorder, has recently been linked to neuro-inflammatory influences from the gut. In this review, we address the idea that evolutionary mismatches could affect the pathogenesis of MS via the gut microbiota. The evolution of symbiosis as well as the recent introduction of evolutionary mismatches is considered, and evidence regarding the impact of diet on the MS-associated microbiota is evaluated. Distinctive microbial community compositions associated with the gut microbiota of MS patients are difficult to identify, and substantial study-to-study variation and even larger variations between individual profiles of MS patients are observed. Furthermore, although some dietary changes impact the progression of MS, MS-associated features of microbiota were found to be not necessarily associated with diet per se. In addition, immune function in MS patients potentially drives changes in microbial composition directly, in at least some individuals. Finally, assessment of evolutionary histories of animals with their gut symbionts suggests that the impact of evolutionary mismatch on the microbiota is less concerning than mismatches affecting helminths and protists. These observations suggest that the benefits of an anti-inflammatory diet for patients with MS may not be mediated by the microbiota per se. Furthermore, any alteration of the microbiota found in association with MS may be an effect rather than a cause. This conclusion is consistent with other studies indicating that a loss of complex eukaryotic symbionts, including helminths and protists, is a pivotal evolutionary mismatch that potentiates the increased prevalence of autoimmunity within a population.

Potential improvements of the cognition of piglets through a synbiotic supplementation from 1 to 28 days via the gut microbiota

The influence of feed supplements on behavior and memory has been recently studied in livestock. The objectives of the study were to evaluate the effects of a synbiotic on: an episodic-like (SOR: Spontaneous Object Recognition), a working (BARR: Fence barrier task), a long-term (TMAZE: Spatial T-maze task) memory test and on gut microbiota composition. Eighteen female piglets were supplemented from 1 to 28 days of age with a synbiotic (SYN), while 17 served as control (CTL). Feces were collected on days 16, 33 and 41 for 16S rRNA gene composition analyses. In the SOR, SYN piglets interacted more quickly with the novel object than CTL piglets. In the BARR, SYN piglets had shorter distances to finish the test in trial 3. In the TMAZE, SYN piglets were quicker to succeed on specific days and tended to try the new rewarded arm earlier during the reversal stage. Difference of microbiota composition between treatments was nonexistent on D16, a tendency on D33 and significant on D41. The synbiotic supplement may confer memory advantages in different cognitive tasks, regardless of the nature of the reward and the memory request. Difference in memory abilities can potentially be explained by differences in microbiota composition.

Gut microbiota in Parkinson’s disease patients: hospital-based study

Background

Parkinson’s disease (PD) is one of the most common neurodegenerative diseases. There is accumulating evidence that link gut microbiota to symptomatology and pathophysiology of PD. The aim of this study was to describe the pattern of gut microbiota and its association with PD and identify the effect of environmental factors on gut microbiota. This case–control study included 46 patients diagnosed as Parkinson’s disease (PD) and 31 healthy volunteers age and sex matched. Detailed history including age of onset, duration of disease, environmental risk factors, diet data, treatment, Unified Parkinson’s Disease Rating Scale (UPDRS), and gastrointestinal tract (GIT) domain of Non‐Motor Symptoms Scale (NMSS) were assessed. After extraction of bacterial DNA from the fecal samples, bacterial abundance was quantified by qPCR using 16S rRNA group-specific primers.

Results

Significant high abundance of Clostridium cluster IV, Akkermansia, Bifidobacterium, and lactic acid bacteria were found in the PD group compared with the control group (P < 0.001, 0.04, 0.02 and < 0.001, respectively), while Firmicutes were significantly less abundant in the PD group (P < 0.001) compared with the control group. The naive PD patients had significant abundance of Bifidobacterium, and lactic acid compared with control group. Interestingly, Akkermansia was more abundant in treated than untreated patients. There were significant associations between pesticide exposure and Bifidobacterium (P = 0.002), while no significant correlations between different gut microbiota and demographic, environment data, different rating scores or dominant type of PD. There was a significant negative correlation between the Bifidobacterium with the duration of illness (P = 0.012).

Conclusion

The present study highlighted a significant connection between PD and levels of certain types of gut microbiota, in support of a possible link between gut microbiota and a neurodegenerative cascade of PD.

Gut microbiota and neuropsychiatric disorders: Implications for neuroendocrine-immune regulation

Recently, increasing evidence has shown gut microbiota dysbiosis might be implicated in the physiological mechanisms of neuropsychiatric disorders. Altered microbial community composition, diversity and distribution traits have been reported in neuropsychiatric disorders. However, the exact pathways by which the intestinal microbiota contribute to neuropsychiatric disorders remain largely unknown. Given that the onset and progression of neuropsychiatric disorders are characterized with complicated alterations of neuroendocrine and immunology, both of which can be continually affected by gut microbiota via "microbiome-gut-brain axis". Thus, we assess the complicated crosstalk between neuroendocrine and immunological regulation might underlie the mechanisms of gut microbiota associated with neuropsychiatric disorders. In this review, we summarized clinical and preclinical evidence on the role of the gut microbiota in neuropsychiatry disorders, especially in mood disorders and neurodevelopmental disorders. This review may elaborate the potential mechanisms of gut microbiota implicating in neuroendocrine-immune regulation and provide a comprehensive understanding of physiological mechanisms for neuropsychiatric disorders.

Neurotransmitter Profiles Are Altered in the Gut and Brain of Mice Mono-Associated with Bifidobacterium dentium

Background: Accumulating evidence indicates that the gut microbiota can synthesize neurotransmitters as well as impact host-derived neurotransmitter levels. In the past, it has been challenging to decipher which microbes influence neurotransmitters due to the complexity of the gut microbiota. Methods: To address whether a single microbe, Bifidobacterium dentium, could regulate important neurotransmitters, we examined Bifidobacteria genomes and explored neurotransmitter pathways in secreted cell-free supernatant using LC-MS/MS. To determine if B. dentium could impact neurotransmitters in vivo, we mono-associated germ-free mice with B. dentium ATCC 27678 and examined fecal and brain neurotransmitter concentrations. Results: We found that B. dentium possessed the enzymatic machinery to generate γ-aminobutyric acid (GABA) from glutamate, glutamine, and succinate. Consistent with the genome analysis, we found that B. dentium secreted GABA in a fully defined microbial media and elevated fecal GABA in B. dentium mono-associated mice compared to germ-free controls. We also examined the tyrosine/dopamine pathway and found that B. dentium could synthesize tyrosine, but could not generate L-dopa, dopamine, norepinephrine, or epinephrine. In vivo, we found that B. dentium mono-associated mice had elevated levels of tyrosine in the feces and brain. Conclusions: These data indicate that B. dentium can contribute to in vivo neurotransmitter regulation.

Stress and the Gut-Brain Axis: Implications for Cancer, Inflammation and Sepsis

BACKGROUND

The gut-brain axis has been discussed, directly or indirectly, for centuries, with the ideas of the gut affecting anything from moods to overall physiology being discussed across the centuries. With a recent explosion in research that looks to the microbiota as a mechanistic link between the gut and the brain, one sees that the gut-brain axis has various means of communication, such as through the vagus nerve and the enteric nervous system and can use the metabolites in the gut to communicate to the brain.

METHODS

The purpose of this review is to view the gut-brain axis through the lens of stress and how stress, from the prenatal period all the way through adulthood can impact the physiology of a human being. Studies have shown multiple mechanisms of measurable change with disruption in the microbiota that lead to behavioral changes. There are also effects of gut inflammation on the brain and the corresponding systemic response observed.

CONCLUSION

The overall literature is encouraging that the more understanding of the gut-brain axis, the greater ability to wield that understanding for therapeutic benefits.

Vagus nerve stimulation in brain diseases: Therapeutic applications and biological mechanisms

Brain diseases, including neurodegenerative, cerebrovascular and neuropsychiatric diseases, have posed a deleterious threat to human health and brought a great burden to society and the healthcare system. With the development of medical technology, vagus nerve stimulation (VNS) has been approved by the Food and Drug Administration (FDA) as an alternative treatment for refractory epilepsy, refractory depression, cluster headaches, and migraines. Furthermore, current evidence showed promising results towards the treatment of more brain diseases, such as Parkinson's disease (PD), autistic spectrum disorder (ASD), traumatic brain injury (TBI), and stroke. Nonetheless, the biological mechanisms underlying the beneficial effects of VNS in brain diseases remain only partially elucidated. This review aims to delve into the relevant preclinical and clinical studies and update the progress of VNS applications and its potential mechanisms underlying the biological effects in brain diseases.

Unravelling the potential of gut microbiota in sustaining brain health and their current prospective towards development of neurotherapeutics

Increasing incidences of neurological disorders, such as Parkinson's disease (PD), multiple sclerosis (MS), Alzheimer's disease (AD) and amyotrophic lateral sclerosis (ALS) are being reported, but an insight into their pathology remains elusive. Findings have suggested that gut microbiota play a major role in regulating brain functions through the gut-brain axis. A unique bidirectional communication between gut microbiota and maintenance of brain health could play a pivotal role in regulating incidences of neurodegenerative diseases. Contrarily, the present life style with changing food habits and disturbed circadian rhythm may contribute to gut homeostatic imbalance and dysbiosis leading to progression of several neurological disorders. Therefore, dysbiosis, as a primary factor behind intestinal disorders, may also augment inflammation, intestinal and blood-brain barrier permeability through microbiota-gut-brain axis. This review primarily focuses on the gut-brain axis functions, specific gut microbial population, metabolites produced by gut microbiota, their role in regulating various metabolic processes and role of gut microbiota towards development of neurodegenerative diseases. However, several studies have reported a decrease in abundance of a specific gut microbial population and a corresponding increase in other microbial family, with few findings revealing some contradictions. Reports also showed that colonization of gut microbiota isolated from patients suffering from neurodegenerative disease leads to the development of enhance pathological outcomes in animal models. Hence, a systematic understanding of the dominant role of specific gut microbiome towards development of different neurodegenerative diseases could possibly provide novel insight into the use of probiotics and microbial transplantation as a substitute approach for treating/preventing such health maladies.

Japanese quail (Coturnix japonica) as a novel model to study the relationship between the avian microbiome and microbial endocrinology-based host-microbe interactions

BACKGROUND

Microbial endocrinology, which is the study of neuroendocrine-based interkingdom signaling, provides a causal mechanistic framework for understanding the bi-directional crosstalk between the host and microbiome, especially as regards the effect of stress on health and disease. The importance of the cecal microbiome in avian health is well-recognized, yet little is understood regarding the mechanisms underpinning the avian host-microbiome relationship. Neuroendocrine plasticity of avian tissues that are focal points of host-microbiome interaction, such as the gut and lung, has likewise received limited attention. Avian in vivo models that enable the study of the neuroendocrine dynamic between host and microbiome are needed. As such, we utilized Japanese quail (Coturnix japonica) that diverge in corticosterone response to stress to examine the relationship between stress-related neurochemical concentrations at sites of host-microbe interaction, such as the gut, and the cecal microbiome.

RESULTS

Our results demonstrate that birds which contrast in corticosterone response to stress show profound separation in cecal microbial community structure as well as exhibit differences in tissue neurochemical concentrations and structural morphologies of the gut. Changes in neurochemicals known to be affected by the microbiome were also identified in tissues outside of the gut, suggesting a potential relationship in birds between the cecal microbiome and overall avian physiology.

CONCLUSIONS

The present study provides the first evidence that the structure of the avian cecal microbial community is shaped by selection pressure on the bird for neuroendocrine response to stress. Identification of unique region-dependent neurochemical changes in the intestinal tract following stress highlights environmental stressors as potential drivers of microbial endocrinology-based mechanisms of avian host-microbiome dialogue. Together, these results demonstrate that tissue neurochemical concentrations in the avian gut may be related to the cecal microbiome and reveal the Japanese quail as a novel avian model in which to further examine the mechanisms underpinning these relationships. Video abstract.

Living Therapeutics: The Next Frontier of Precision Medicine

Modern medicine has long studied the mechanism and impact of pathogenic microbes on human hosts, but has only recently shifted attention toward the complex and vital roles that commensal and probiotic microbes play in both health and dysbiosis. Fueled by an enhanced appreciation of the human-microbe holobiont, the past decade has yielded countless insights and established many new avenues of investigation in this area. In this review, we discuss advances, limitations, and emerging frontiers for microbes as agents of health maintenance, disease prevention, and cure. We highlight the flexibility of microbial therapeutics across disease states, with special consideration for the rational engineering of microbes toward precision medicine outcomes. As the field advances, we anticipate that tools of synthetic biology will be increasingly employed to engineer functional living therapeutics with the potential to address longstanding limitations of traditional drugs.

Significance of vagus nerve function in terms of pathogenesis of psychosocial disorders

The vagus nerve (VN) belongs to the parasympathetic nervous system, which is well known to be involved in the regulation of the functions of organs in the body. The neurotransmitter acetylcholine, released from the cholinergic system including VN, has been known to play an anti-inflammatory role through the efferent pathways in regulating peripheral inflammatory responses profoundly involved in the pathogenesis of diseases. In contrast, anatomically, it connects the central nervous system (CNS) and peripheral organs, including the heart and gastrointestinal (GI) tract. Therefore, it has been recently reported that the VN also plays an important role in the pathogenesis of psychological disorders since it confers varied signals from the GI tract to the CNS, and alteration of microbiota residing in GI definitely influences the condition of neuropsychiatric disorders. Furthermore, the CNS includes microglia, a neuroinflammatory effector in the brain, which is also influenced by the VN to modulate its inflammatory status. Based on significant findings of the VN, the VN stimulation (VNS) has recently drawn attention from many scientific fields. VNS was initially applied to patients with refractory epilepsy, followed by patients with refractory depression. Subsequently, VNS was also attempted to be introduced to other diseases. However, against whichever disease, central or peripheral, detailed underlying mechanisms of VNS involved in neuropsychiatric disorders as well as VNS target molecules in the GI tract and the CNS remains to be studied. In this review, we discuss the mechanisms and predicted responsible factors of VNS in terms of neuropsychiatric disorders.

Bacterial Metabolites of Human Gut Microbiota Correlating with Depression

Depression is a global threat to mental health that affects around 264 million people worldwide. Despite the considerable evolution in our understanding of the pathophysiology of depression, no reliable biomarkers that have contributed to objective diagnoses and clinical therapy currently exist. The discovery of the microbiota-gut-brain axis induced scientists to study the role of gut microbiota (GM) in the pathogenesis of depression. Over the last decade, many of studies were conducted in this field. The productions of metabolites and compounds with neuroactive and immunomodulatory properties among mechanisms such as the mediating effects of the GM on the brain, have been identified. This comprehensive review was focused on low molecular weight compounds implicated in depression as potential products of the GM. The other possible mechanisms of GM involvement in depression were presented, as well as changes in the composition of the microbiota of patients with depression. In conclusion, the therapeutic potential of functional foods and psychobiotics in relieving depression were considered. The described biomarkers associated with GM could potentially enhance the diagnostic criteria for depressive disorders in clinical practice and represent a potential future diagnostic tool based on metagenomic technologies for assessing the development of depressive disorders.

The microbiota-microglia axis in central nervous system disorders

The innate immune system in the central nervous system (CNS) is mainly represented by specialized tissue-resident macrophages, called microglia. In the past years, various species-, host- and tissue-specific as well as environmental factors were recognized that essentially affect microglial properties and functions in the healthy and diseased brain. Host microbiota are mostly residing in the gut and contribute to microglial activation states, for example, via short-chain fatty acids (SCFAs) or aryl hydrocarbon receptor (AhR) ligands. Thereby, the gut microorganisms are deemed to influence numerous CNS diseases mediated by microglia. In this review, we summarize recent findings of the interaction between the host microbiota and the CNS in health and disease, where we specifically highlight the resident gut microbiota as a crucial environmental factor for microglial function as what we coin "the microbiota-microglia axis."

Human-Derived Bifidobacterium dentium Modulates the Mammalian Serotonergic System and Gut-Brain Axis

BACKGROUND & AIMS

The human gut microbiota can regulate production of serotonin (5-hydroxytryptamine [5-HT]) from enterochromaffin cells. However, the mechanisms underlying microbial-induced serotonin signaling are not well understood.

METHODS

Adult germ-free mice were treated with sterile media, live Bifidobacterium dentium, heat-killed B dentium, or live Bacteroides ovatus. Mouse and human enteroids were used to assess the effects of B dentium metabolites on 5-HT release from enterochromaffin cells. In vitro and in vivo short-chain fatty acids and 5-HT levels were assessed by mass spectrometry. Expression of tryptophan hydroxylase, short-chain fatty acid receptor free fatty acid receptor 2, 5-HT receptors, and the 5-HT re-uptake transporter (serotonin transporter) were assessed by quantitative polymerase chain reaction and immunostaining. RNA in situ hybridization assessed 5-HT-receptor expression in the brain, and 5-HT-receptor-dependent behavior was evaluated using the marble burying test.

RESULTS

B dentium mono-associated mice showed increased fecal acetate. This finding corresponded with increased intestinal 5-HT concentrations and increased expression of 5-HT receptors 2a, 4, and serotonin transporter. These effects were absent in B ovatus-treated mice. Application of acetate and B dentium-secreted products stimulated 5-HT release in mouse and human enteroids. In situ hybridization of brain tissue also showed significantly increased hippocampal expression of 5-HT-receptor 2a in B dentium-treated mice relative to germ-free controls. Functionally, B dentium colonization normalized species-typical repetitive and anxiety-like behaviors previously shown to be linked to 5-HT-receptor 2a.

CONCLUSIONS

These data suggest that B dentium, and the bacterial metabolite acetate, are capable of regulating key components of the serotonergic system in multiple host tissues, and are associated with a functional change in adult behavior.

Salmonella Strain Specificity Determines Post-typhoid Central Nervous System Complications: Intervention by Lactiplantibacillus plantarum at Gut-Brain Axis

Neurological complications occurring due to Salmonella infection in some typhoid patients remain a relatively unexplored serious complication. This study firstly aimed to explore whether disseminative ability of Salmonella from gut to brain is strain specific or not and on the basis of bacterial load, histopathology, and behavioral changes, it was observed that Salmonella enterica serovar Typhimurium NCTC 74 did not cause brain infection in murine model in contrast to Salmonella Typhimurium SL1344. Simultaneously, alarming escalation in antimicrobial resistance, making the existing antibiotics treatment inefficacious, prompted us to evaluate other bio-compatible strategies as a potential treatment option. In this context, the role of gut microbiota in influencing behavior, brain neurochemistry, and physiology by modulating key molecules associated with gut-brain axis has captured the interest of the scientific community. Followed by in vitro screening of potential probiotic strains for beneficial attributes, efficacy of the selected strain was systematically evaluated at various levels of gut-brain axis against Salmonella induced brain infection. Analysis of behavioral (depression, anxiety, and locomotor), neurochemical [gamma amino butyric acid and acetylcholinesterase (AChE)], neuropathological (brain and intestinal histology; bacterial burden), and immunohistochemical studies (tight junction proteins expression) revealed its role in preventing serious manifestations and proving its potential as "psychobiotic." To the best of our knowledge, this is the first report elaborating strain specificity of Salmonella in causing post-typhoidal neurological manifestations and simultaneous use of probiotic in managing the same by influencing the pathophysiology at gut-brain axis.

Coprophagy prevention alters microbiome, metabolism, neurochemistry, and cognitive behavior in a small mammal

Many small mammals engage in coprophagy, or the behavior of consuming feces, as a means to meet nutritional requirements when feeding on low-quality foods. In addition to nutritional benefits, coprophagy may also help herbivores retain necessary gut microbial diversity and function, which may have downstream physiological effects, such as maintaining energy balance and cognitive function. Here, we used collars to prevent Brandt's vole (Lasiopodomys brandtii) from engaging in coprophagy and monitored changes in microbial community structure, energy metabolism, and cognitive performance. In this research, we found that coprophagy prevention decreased alpha diversity of the gut microbiota, and altered proportions of microbial taxa such as Bacteroidetes, Firmicutes, and Oscillospira. Preventing coprophagy resulted in a reduced body mass, and increased food intake. Importantly, coprophagy prevention decreased vole cognitive behavior and altered levels of neurotransmitters in brain. Daily acetate administration was able to reverse some of the coprophagy prevention-induced changes in microbiota composition, metabolism, neurochemistry, and cognitive behavior. These findings identify the functional importance of coprophagy behavior and interactions between the gut microbiota, energy metabolism, and neurological function. Our results suggest that coprophagy contributes to stabilizing the gut microbiota, promoting microbial metabolism, maintaining host energy balance and, consequently, altering cognitive performance.

The Role of the Gut Microbiota in Dietary Interventions for Depression and Anxiety

There is emerging evidence that an unhealthy dietary pattern may increase the risk of developing depression or anxiety, whereas a healthy dietary pattern may decrease it. This nascent research suggests that dietary interventions could help prevent, or be an alternative or adjunct therapy for, depression and anxiety. The relation, however, is complex, affected by many confounding variables, and is also likely to be bidirectional, with dietary choices being affected by stress and depression. This complexity is reflected in the data, with sometimes conflicting results among studies. As the research evolves, all characteristics of the relation need to be considered to ensure that we obtain a full understanding, which can potentially be translated into clinical practice. A parallel and fast-growing body of research shows that the gut microbiota is linked with the brain in a bidirectional relation, commonly termed the microbiome-gut-brain axis. Preclinical evidence suggests that this axis plays a key role in the regulation of brain function and behavior. In this review we discuss possible reasons for the conflicting results in diet-mood research, and present examples of areas of the diet-mood relation in which the gut microbiota is likely to be involved, potentially explaining some of the conflicting results from diet and depression studies. We argue that because diet is one of the most significant factors that affects human gut microbiota structure and function, nutritional intervention studies need to consider the gut microbiota as an essential piece of the puzzle.

The Controversial Role of Human Gut Lachnospiraceae

The complex polymicrobial composition of human gut microbiota plays a key role in health and disease. Lachnospiraceae belong to the core of gut microbiota, colonizing the intestinal lumen from birth and increasing, in terms of species richness and their relative abundances during the host's life. Although, members of Lachnospiraceae are among the main producers of short-chain fatty acids, different taxa of Lachnospiraceae are also associated with different intra- and extraintestinal diseases. Their impact on the host physiology is often inconsistent across different studies. Here, we discuss changes in Lachnospiraceae abundances according to health and disease. With the aim of harnessing Lachnospiraceae to promote human health, we also analyze how nutrients from the host diet can influence their growth and how their metabolites can, in turn, influence host physiology.

Effects of Three Distinct 2-Week Long Diet Strategies After Transport on Weaned Pigs' Short and Long-Term Welfare Markers, Behaviors, and Microbiota

Alternative feed supplements have shown promising effects in terms of performance, but their effects on welfare have had little evaluation. In the present study, we aimed at evaluating the effect of diet supplementation on welfare indicators. A total of 246 piglets were weaned and transported for 12 h. After transport, they were assigned to one of 3 diets for a 14-day period: A-an antibiotic diet including chlortetracycline and tiamulin, NA-a control diet without any antibiotic or feed supplement, GLN-a diet including 0.20% L-glutamine. After the 14-day period, all piglets were fed the same diet. Tear staining was measured 11 times post-weaning (from d0 to 147). Skin lesions were counted before and after weaning (d-2, 2, and 36). Novel object tests (NOT) were done in groups 4 times post-weaning (d17, 47, 85, 111). Samples for 16S rRNA gene composition were collected prior to transport (d0), following the 14-day period (d14) and at the conclusion of the nursery phase (d34). The NA pigs appeared less interested in novel objects. On d17, they avoided the object less than A pigs (P < 0.05). They spent less time exploring the object on d85 and took longer to interact with the object on d111 than A and GLN pigs (P < 0.05). NA pigs also appeared more sensitive to environment and management. They had larger tear stains than GLN pigs on d84 and 110 (P < 0.05). On d2, NA pigs had more lesions than A and GLN (P < 0.01). In terms of microbiota composition, GLN had higher α-diversity than A and NA (P < 0.001). Differences between dietary treatments were absent at d0, were demonstrated at d14 and disappeared at d34. Pearson correlations between aggression, stress and anxiety indicators and bacterial populations were medium to high from 0.31 to 0.69. The results demonstrate that short-term feeding strategy can have both short- and long-term effects on behavior and welfare, that may partly be explained by changes in gut microbiota composition. Supplementation with GLN appears to confer similar benefits to dietary antibiotics and thus could be a viable alternative.

The Role of Short-Chain Fatty Acids From Gut Microbiota in Gut-Brain Communication

A substantial body of evidence supports that the gut microbiota plays a pivotal role in the regulation of metabolic, endocrine and immune functions. In recent years, there has been growing recognition of the involvement of the gut microbiota in the modulation of multiple neurochemical pathways through the highly interconnected gut-brain axis. Although amazing scientific breakthroughs over the last few years have expanded our knowledge on the communication between microbes and their hosts, the underpinnings of microbiota-gut-brain crosstalk remain to be determined. Short-chain fatty acids (SCFAs), the main metabolites produced in the colon by bacterial fermentation of dietary fibers and resistant starch, are speculated to play a key role in neuro-immunoendocrine regulation. However, the underlying mechanisms through which SCFAs might influence brain physiology and behavior have not been fully elucidated. In this review, we outline the current knowledge about the involvement of SCFAs in microbiota-gut-brain interactions. We also highlight how the development of future treatments for central nervous system (CNS) disorders can take advantage of the intimate and mutual interactions of the gut microbiota with the brain by exploring the role of SCFAs in the regulation of neuro-immunoendocrine function.

Attribution of Ghrelin to Cancer; Attempts to Unravel an Apparent Controversy

Ghrelin is an endogenous peptide hormone mainly produced in the stomach. It has been known to regulate energy homeostasis, stimulate secretion of growth hormone, and mediate many other physiologic effects. Various effects attributed to ghrelin contribute to many aspects of cancer development and progression. Accordingly, a large body of evidence has emerged about the association of ghrelin with several types of cancer in scales of cell-line, animal, and human studies. However, existing data are controversial. This controversy occurs in two main domains: one is the controversial results in local effects of ghrelin on different types of human cancer cell-lines; the second is the apparent disagreement in the results of in-vitro and clinical studies that investigated ghrelin association to one type of cancer. These inconsistencies have hampered the indications to consider ghrelin as a potential tumor biomarker or therapeutic agent in cancer patients. Previous studies have reviewed different parts of current literature about the ghrelin-cancer relationship. Although they have highlighted these controversial results in various ways, no specific recommendations have been given to address it. In this study, we comprehensively reviewed in-vitro, in-vivo, and clinical studies and attempted to use the following approaches to unravel the inconsistencies detected: (a) to distinguish local and systemic effects of ghrelin in interpreting its summary clinical role in each cancer; (b) scrutinizing factors that regulate local effects of ghrelin and could justify different effects of ghrelin on different cancer cell-lines. These approaches could have notable implications for future in-vitro and clinical studies.

The influence of neuroinflammation in Autism Spectrum Disorder

Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder characterised by deficits in social communication and restricted or repetitive behaviours. The clinical presentation of ASD is highly variable and diagnosis is based on the presence of impaired social communication and repetitive and/or restricted behaviours. Although the precise pathophysiologies underlying ASD are unclear, growing evidence supports a role for dysregulated neuroinflammation. The potential involvement of microglia and astrocytes reactive to inflammatory stimuli in ASD has generated much interest due to their varied roles including in mounting an immune response and regulating synaptic function. Increased numbers of reactive microglial and astrocytes in both ASD postmortem tissue and animal models have been reported. Whether dysregulation of glial subtypes exacerbates alterations in neural connectivity in the brain of autistic patients is not well explored. A role for the gut-brain axis involving microbial-immune-neuronal cross talk is also a growing area of neuroinflammation research. Greater understanding of these interactions under patho/physiological conditions and the identification of consistent immune profile abnormalities can potentially lead to more reliable diagnostic measures and treatments in ASD.

The gut-brain relationship: Investigating the effect of multispecies probiotics on anxiety in a randomized placebo-controlled trial of healthy young adults

INTRO

There has been an increased interest in understanding the therapeutic effect of gut-microbiota on health, particularly in mental health. However, limited research into the connection between gut-microbiota and mental health makes this study an important endeavor in exploring the effect of gut-microbiota, through probiotics intervention, on mental health like anxiety and factors related to anxiety (e.g., anxiety control, affect, negative mood regulation, and worry).

METHOD

Healthy college students (N = 86; 75.6% female), average age of 20.59, participated in a double-blind, placebo-control, and randomization-control study. Eligible participants completed a baseline survey before being assigned to a condition, which consisted of four probiotics conditions and one placebo condition. After 28 days of daily intake, the participants returned to complete their exit survey.

RESULT

Probiotics were observed to improve panic anxiety, neurophysiological anxiety, negative affect, worry, and increase negative mood regulation. Furthermore, post hoc analyses revealed that the CFU (colony-forming unit) level was more effective than species counts in accounting for the number of significant improvements. A ceiling effect was detected in the study, participants with high distress reported higher number of improvements than those with normative distress.

CONCLUSION

Overall, this study is the first to examine the effect of CFU and species count on probiotics' efficacy. The study's finding suggested that probiotics may have the therapeutic potential to treat anxiety, however, further research is necessary to make that determination.

The microbiome and cognitive aging: a review of mechanisms

Gut microbiota plays an intrinsic role in communication between the gut and the brain and is capable of influencing the host brain by producing neurotransmitters and neurotrophins, the modulation of inflammatory processes amongst other key mechanisms. Increased age is also associated with changes in these key biological processes and impairments in a range of cognitive processes. We hypothesise several mechanisms in which gut microbiota may modulate changes in cognitive function with age. In this review, we discuss issues related to the measurement of cognition in the elderly and in particular outline a standardised model of cognition that could be utilised to better understand cognitive outcomes in future studies examining the relationship between gut microbiota and cognition in the elderly. We then review biological processes such as oxidative stress and inflammation which are related to cognitive changes with age and which are also influenced by our gut microbiota. Finally, we outline other potential mechanisms by which the gut microbiota may influence cognition.

Effects of single and combined toxic exposures on the gut microbiome: Current knowledge and future directions

Human populations are chronically exposed to mixtures of toxic chemicals. Predicting the health effects of these mixtures require a large amount of information on the mode of action of their components. Xenobiotic metabolism by bacteria inhabiting the gastrointestinal tract has a major influence on human health. Our review aims to explore the literature for studies looking to characterize the different modes of action and outcomes of major chemical pollutants, and some components of cosmetics and food additives, on gut microbial communities in order to facilitate an estimation of their potential mixture effects. We identified good evidence that exposure to heavy metals, pesticides, nanoparticles, polycyclic aromatic hydrocarbons, dioxins, furans, polychlorinated biphenyls, and non-caloric artificial sweeteners affect the gut microbiome and which is associated with the development of metabolic, malignant, inflammatory, or immune diseases. Answering the question 'Who is there?' is not sufficient to define the mode of action of a toxicant in predictive modeling of mixture effects. Therefore, we recommend that new studies focus to simulate real-life exposure to diverse chemicals (toxicants, cosmetic/food additives), including as mixtures, and which combine metagenomics, metatranscriptomics and metabolomic analytical methods achieving in that way a comprehensive evaluation of effects on human health.

Man and the Microbiome: A New Theory of Everything?

The gut microbiome is implicated in the pathophysiology of a wide range of psychological disorders. Preclinical studies have provided us with key insights into the mechanisms by which the microbiome influences bidirectional gut-brain communication. There are many signaling pathways involved, including the hypothalamic-pituitary-adrenal axis, immune modulation, tryptophan and serotonin metabolism, bile acid transformation, microbial production of neuroactive compounds, and regulation of the endocannabinoid system. The complex and widespread influence of the microbiome on many physiological and psychological processes has generated a keen interest in its therapeutic potential for depression, anxiety, autism, and other psychiatric disorders. It has been shown that the microbiome composition of people suffering with such conditions differs significantly from that of healthy controls, and although the area is in its infancy, interventional studies that alter a person's microbiome through the use of probiotics, prebiotics, or dietary change can alleviate psychopathological symptoms.

Gut microbiota analysis and its significance in vasovagal syncope in children

BACKGROUND

Vasovagal syncope (VVS) is common in children and greatly affect both physical and mental health. But the mechanisms have not been completely explained. This study was designed to analyze the gut microbiota in children with VVS and explore its clinical significance.

METHODS

Fecal samples from 20 VVS children and 20 matched controls were collected, and the microbiota were analyzed by 16S rRNA gene sequencing. The diversity and microbiota compositions of the VVS cases and controls were compared with the independent sample t test or Mann-Whitney U test. The correlation between the predominant bacteria and clinical symptoms was analyzed using Pearson or Spearman correlation test.

RESULTS

No significant differences in diversity were evident between VVS and controls (P > 0.05). At the family level, the relative abundance of Ruminococcaceae was significantly higher in VVS children than in controls (median [Q1, Q3]: 22.10% [16.89%, 27.36%] vs. 13.92% [10.31%, 20.18%], Z = -2.40, P < 0.05), and LEfSe analysis revealed Ruminococcaceae as a discriminative feature (linear discriminant analysis [LDA] score > 4, P < 0.05). The relative abundance of Ruminococcaceae in VVS patients was positively correlated with the frequency of syncope (r = 0.616, P < 0.01). In terms of its correlation with hemodynamics, we showed that relative abundance of Ruminococcaceae was negatively correlated with the systolic and diastolic pressure reduction at the positive response in head-up tilt test (HUTT; r = -0.489 and -0.448, all P < 0.05), but was positively correlated with the mean pressure drop and decline rate (r = 0.489 and 0.467, all P < 0.05) as well as diastolic pressure drop and decline rate at the HUTT positive response (r = 0.579 and 0.589, all P < 0.01) in VVS patients.

CONCLUSION

Ruminococcaceae was the predominant gut bacteria and was associated with the clinical symptoms and hemodynamics of VVS, suggesting that gut microbiota might be involved in the development of VVS.

Mechanisms Underlying Microbial-Mediated Changes in Social Behavior in Mouse Models of Autism Spectrum Disorder

Currently, there are no medications that effectively treat the core symptoms of Autism Spectrum Disorder (ASD). We recently found that the bacterial species Lactobacillus (L.) reuteri reverses social deficits in maternal high-fat-diet offspring. However, whether the effect of L. reuteri on social behavior is generalizable to other ASD models and its mechanism(s) of action remains unknown. Here, we found that treatment with L. reuteri selectively rescues social deficits in genetic, environmental, and idiopathic ASD models. Interestingly, the effects of L. reuteri on social behavior are not mediated by restoring the composition of the host's gut microbiome, which is altered in all of these ASD models. Instead, L. reuteri acts in a vagus nerve-dependent manner and rescues social interaction-induced synaptic plasticity in the ventral tegmental area of ASD mice, but not in oxytocin receptor-deficient mice. Collectively, treatment with L. reuteri emerges as promising non-invasive microbial-based avenue to combat ASD-related social dysfunction.

Microbiome-microglia connections via the gut-brain axis

Microglia, the resident immune cells in the brain, are essential for modulating neurogenesis, influencing synaptic remodeling, and regulating neuroinflammation by surveying the brain microenvironment. Microglial dysfunction has been implicated in the onset and progression of several neurodevelopmental and neurodegenerative diseases; however, the multitude of factors and signals influencing microglial activity have not been fully elucidated. Microglia not only respond to local signals within the brain but also receive input from the periphery, including the gastrointestinal (GI) tract. Recent preclinical findings suggest that the gut microbiome plays a pivotal role in regulating microglial maturation and function, and altered microbial community composition has been reported in neurological disorders with known microglial involvement in humans. Collectively, these findings suggest that bidirectional crosstalk between the gut and the brain may influence disease pathogenesis. Herein, we discuss recent studies showing a role for the gut microbiome in modulating microglial development and function in homeostatic and disease conditions and highlight possible future research to develop novel microbial treatments for disorders of the brain.

Targeting the gut microbiota to influence brain development and function in early life

In the first 2-3 years of life, the gut microbiota of infants quickly becomes diverse and rich. Disruptions in the evolving gut microbiota during this critical developmental period can impact brain development. Communication between the microbiota, gut and brain is driven by hormonal and neural regulation, as well as immune and metabolic pathways, however, our understanding of how the parallel developments that may underlie this communication are limited. In this paper, we review the known associations between the gut microbiota and brain development and brain function in early life, speculate on the potential mechanisms involved in this complex relationship and describe how nutritional intervention can further modulate the microbiota and, ultimately, brain development and function.

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.

Dysbiotic drift and biopsychosocial medicine: how the microbiome links personal, public and planetary health

The emerging concept of planetary health emphasizes that the health of human civilization is intricately connected to the health of natural systems within the Earth’s biosphere; here, we focus on the rapidly progressing microbiome science - the microbiota-mental health research in particular - as a way to illustrate the pathways by which exposure to biodiversity supports health. Microbiome science is illuminating the ways in which stress, socioeconomic disadvantage and social polices interact with lifestyle and behaviour to influence the micro and macro-level biodiversity that otherwise mediates health. Although the unfolding microbiome and mental health research is dominated by optimism in biomedical solutions (e.g. probiotics, prebiotics), we focus on the upstream psychosocial and ecological factors implicated in dysbiosis; we connect grand scale biodiversity in the external environment with differences in human-associated microbiota, and, by extension, differences in immune function and mental outlook. We argue that the success of planetary health as a new concept will be strengthened by a more sophisticated understanding of the ways in which individuals develop emotional connections to nature (nature relatedness) and the social policies and practices which facilitate or inhibit the pro-environmental values that otherwise support personal, public and planetary health.

The microbiota influences cell death and microglial colonization in the perinatal mouse brain

The mammalian fetus develops in a largely sterile environment, and direct exposure to a complex microbiota does not occur until birth. We took advantage of this to examine the effect of the microbiota on brain development during the first few days of life. The expression of anti- and pro-inflammatory cytokines, developmental cell death, and microglial colonization in the brain were compared between newborn conventionally colonized mice and mice born in sterile, germ-free (GF) conditions. Expression of the pro-inflammatory cytokines interleukin 1β and tumor necrosis factor α was markedly suppressed in GF newborns. GF mice also had altered cell death, with some regions exhibiting higher rates (paraventricular nucleus of the hypothalamus and the CA1 oriens layer of the hippocampus) and other regions exhibiting no change or lower rates (arcuate nucleus of the hypothalamus) of cell death. Microglial labeling was elevated in GF mice, due to an increase in both microglial cell size and number. The changes in cytokine expression, cell death and microglial labeling were evident on the day of birth, but were absent on embryonic day 18.5, approximately one-half day prior to expected delivery. Taken together, our results suggest that direct exposure to the microbiota at birth influences key neurodevelopmental events and does so within hours. These findings may help to explain some of the behavioral and neurochemical alterations previously seen in adult GF mice.