Interactions Between Gut Microbiota and Acute Restraint Stress in Peripheral Structures of the Hypothalamic-Pituitary-Adrenal Axis and the Intestine of Male Mice

Contacts with environmental biodiversity affect human health: links revealed during the initial waves of the COVID-19 pandemic

The gradual decrease in the prevalence of serious infectious diseases over the last century has been followed by increase in so called "modern" diseases, including allergies, chronic inflammatory conditions, psychiatric, and metabolic disorders. Between 2019 and 2022, public awareness of the threat of infectious diseases in humans was renewed by the global pandemic of a new type of a coronavirus, the SARS-COV-2. This public interest opened improved possibilities to test hypotheses on the factors associated with inter-individual variation in susceptibility to infectious and "modern" diseases. Based on the Hygiene hypothesis and Biodiversity hypothesis, we predicted that contacts with natural environment and wildlife in childhood and/or in adulthood can improve general health and decrease the risks of severe COVID-19 progression or prevalence of the "modern" diseases, namely the allergies. Here we report the results of an online, self-evaluating questionnaire survey conducted in the Czech Republic, where we contrasted selected health issues, and linked them to the living environment, including the level of contacts with biodiversity. In a sample of 1188 respondents, we revealed a significant association of time spent in nature or contacts with biodiversity with physical and mental health, or incidence of allergies. This is unlike the COVID-19 progression, which was related to age, physical health, smoking, allergies, and interaction of age with smoking, but not to contacts with the natural environmental diversity. Our findings regarding to physical and mental health and allergies are in agreement with the Biodiversity hypothesis of allergy and, linking human and environmental health, they urge for One Health approach application.

Sex differences in intestinal morphology and increase in diencephalic neuropeptide Y gene expression in female but not male Pekin ducks exposed to chronic heat stress

The impact of heat stress (HS) on production is intricately linked with feed intake. We investigated the effects of HS on intestines and diencephalic genes in Pekin ducks. One hundred and sixty adult ducks were allocated to two treatment rooms. The control room was maintained at 22°C and the HS room at 35°C for the first 10 h of the day then reduced to 29.5°C. After 3 weeks, 10 hens and 5 drakes were euthanized from each room and jejunum and ileum collected for histology. Brains were collected for gene expression analysis using qRT-PCR. Intestinal morphology data were analyzed with two-way ANOVA and diencephalic gene data were analyzed with Kruskal-Wallis test. There was an increase in villi width in the ileum (p = .0136) and jejunum (p = .0019) of HS hens compared to controls. HS drakes showed a higher crypt depth (CD) in the jejunum (p = .0198) compared to controls. There was an increase in crypt goblet cells (GC) count in the ileum (p = .0169) of HS drakes compared to HS hens. There was higher villi GC count (p = .07) in the jejunum of HS drakes compared to controls. There was an increase in the crypt GC density (p = .0054) in the ileum, not jejunum, of HS drakes compared to HS hens. Further, there were no differences in the proopiomelanocortin gene expression in either sex but there was an increase in the expression of neuropeptide Y (NPY) gene in HS hens (p = .031) only and a decrease in the corticotropin releasing hormone gene in the HS drakes (p = .037) compared to controls. These data show that there are sex differences in the effect of HS on gut morphology while the upregulation in NPY gene may suggest a role in mediating response to chronic HS.

Gut microbiota is involved in male reproductive function: a review

Globally, ~8%-12% of couples confront infertility issues, male-related issues being accountable for 50%. This review focuses on the influence of gut microbiota and their metabolites on the male reproductive system from five perspectives: sperm quality, testicular structure, sex hormones, sexual behavior, and probiotic supplementation. To improve sperm quality, gut microbiota can secrete metabolites by themselves or regulate host metabolites. Endotoxemia is a key factor in testicular structure damage that causes orchitis and disrupts the blood-testis barrier (BTB). In addition, the gut microbiota can regulate sex hormone levels by participating in the synthesis of sex hormone-related enzymes directly and participating in the enterohepatic circulation of sex hormones, and affect the hypothalamic-pituitary-testis (HPT) axis. They can also activate areas of the brain that control sexual arousal and behavior through metabolites. Probiotic supplementation can improve male reproductive function. Therefore, the gut microbiota may affect male reproductive function and behavior; however, further research is needed to better understand the mechanisms underlying microbiota-mediated male infertility.

L-Glutamine Substantially Improves 5-Fluorouracil-Induced Intestinal Mucositis by Modulating Gut Microbiota and Maintaining the Integrity of the Gut Barrier in Mice

SCOPE

This study investigates the potential of glutamine to mitigate intestinal mucositis and dysbiosis caused by the chemotherapeutic agent 5-fluorouracil (5-FU).

METHODS AND RESULTS

Over twelve days, Institute of Cancer Research (ICR) mice are given low (0.5 mg kg-1) or high (2 mg kg-1) doses of L-Glutamine daily, with 5-FU (50 mg kg-1) administered between days six and nine. Mice receiving only 5-FU exhibited weight loss, diarrhea, abnormal cell growth, and colonic inflammation, correlated with decreased mucin proteins, increased endotoxins, reduced fecal short-chain fatty acids, and altered gut microbiota. Glutamine supplementation counteracted these effects by inhibiting the Toll-like receptor 4/nuclear factor kappa B (TLR4/NF-κB) pathway, modulating nuclear factor erythroid 2-related factor 2/heme oxygenase 1 (Nrf2/HO-1) oxidative stress proteins, and increasing mammalian target of rapamycin (mTOR) levels, thereby enhancing microbial diversity and protecting intestinal mucosa.

CONCLUSIONS

These findings underscore glutamine's potential in preventing 5-FU-induced mucositis by modulating gut microbiota and inflammation pathways.

Adverse childhood experience and depression: the role of gut microbiota

Depression is the most common psychiatric disorder that burdens modern society heavily. Numerous studies have shown that adverse childhood experiences can increase susceptibility to depression, and depression with adverse childhood experiences has specific clinical-biological features. However, the specific neurobiological mechanisms are not yet precise. Recent studies suggest that the gut microbiota can influence brain function and behavior associated with depression through the "microbe-gut-brain axis" and that the composition and function of the gut microbiota are influenced by early stress. These studies offer a possibility that gut microbiota mediates the relationship between adverse childhood experiences and depression. However, few studies directly link adverse childhood experiences, gut microbiota, and depression. This article reviews recent studies on the relationship among adverse childhood experiences, gut microbiota, and depression, intending to provide insights for new research.

Microbiota modulates the steroid response to acute immune stress in male mice

Microbiota plays a role in shaping the HPA-axis response to psychological stressors. To examine the role of microbiota in response to acute immune stressor, we stimulated the adaptive immune system by anti-CD3 antibody injection and investigated the expression of adrenal steroidogenic enzymes and profiling of plasma corticosteroids and their metabolites in specific pathogen-free (SPF) and germ-free (GF) mice. Using UHPLC-MS/MS, we showed that 4 hours after immune challenge the plasma levels of pregnenolone, progesterone, 11-deoxycorticosterone, corticosterone (CORT), 11-dehydroCORT and their 3α/β-, 5α-, and 20α-reduced metabolites were increased in SPF mice, but in their GF counterparts, only CORT was increased. Neither immune stress nor microbiota changed the mRNA and protein levels of enzymes of adrenal steroidogenesis. In contrast, immune stress resulted in downregulated expression of steroidogenic genes (Star, Cyp11a1, Hsd3b1, Hsd3b6) and upregulated expression of genes of the 3α-hydroxysteroid oxidoreductase pathway (Akr1c21, Dhrs9) in the testes of SPF mice. In the liver, immune stress downregulated the expression of genes encoding enzymes with 3β-hydroxysteroid dehydrogenase (HSD) (Hsd3b2, Hsd3b3, Hsd3b4, Hsd3b5), 3α-HSD (Akr1c14), 20α-HSD (Akr1c6, Hsd17b1, Hsd17b2) and 5α-reductase (Srd5a1) activities, except for Dhrs9, which was upregulated. In the colon, microbiota downregulated Cyp11a1 and modulated the response of Hsd11b1 and Hsd11b2 expression to immune stress. These data underline the role of microbiota in shaping the response to immune stressor. Microbiota modulates the stress-induced increase in C21 steroids, including those that are neuroactive that could play a role in alteration of HPA axis response to stress in GF animals.

The importance of the gut microbiome and its signals for a healthy nervous system and the multifaceted mechanisms of neuropsychiatric disorders

Increasing evidence links the gut microbiome and the nervous system in health and disease. This narrative review discusses current views on the interaction between the gut microbiota, the intestinal epithelium, and the brain, and provides an overview of the communication routes and signals of the bidirectional interactions between gut microbiota and the brain, including circulatory, immunological, neuroanatomical, and neuroendocrine pathways. Similarities and differences in healthy gut microbiota in humans and mice exist that are relevant for the translational gap between non-human model systems and patients. There is an increasing spectrum of metabolites and neurotransmitters that are released and/or modulated by the gut microbiota in both homeostatic and pathological conditions. Dysbiotic disruptions occur as consequences of critical illnesses such as cancer, cardiovascular and chronic kidney disease but also neurological, mental, and pain disorders, as well as ischemic and traumatic brain injury. Changes in the gut microbiota (dysbiosis) and a concomitant imbalance in the release of mediators may be cause or consequence of diseases of the central nervous system and are increasingly emerging as critical links to the disruption of healthy physiological function, alterations in nutrition intake, exposure to hypoxic conditions and others, observed in brain disorders. Despite the generally accepted importance of the gut microbiome, the bidirectional communication routes between brain and gut are not fully understood. Elucidating these routes and signaling pathways in more detail offers novel mechanistic insight into the pathophysiology and multifaceted aspects of brain disorders.

A Review on the Protective Effects of Probiotics against Alzheimer's Disease

This review summarizes the protective effects of probiotics against Alzheimer's disease (AD), one of the most common neurodegenerative disorders affecting older adults. This disease is characterized by the deposition of tau and amyloid β peptide (Aβ) in different parts of the brain. Symptoms observed in patients with AD include struggles with writing, speech, memory, and knowledge. The gut microbiota reportedly plays an important role in brain functioning due to its bidirectional communication with the gut via the gut-brain axis. The emotional and cognitive centers in the brain are linked to the functions of the peripheral intestinal system via this gut-brain axis. Dysbiosis has been linked to neurodegenerative disorders, indicating the significance of gut homeostasis for proper brain function. Probiotics play an important role in protecting against the symptoms of AD as they restore gut-brain homeostasis to a great extent. This review summarizes the characteristics, status of gut-brain axis, and significance of gut microbiota in AD. Review and research articles related to the role of probiotics in the treatment of AD were searched in the PubMed database. Recent studies conducted using animal models were given preference. Recent clinical trials were searched for separately. Several studies conducted on animal and human models clearly explain the benefits of probiotics in improving cognition and memory in experimental subjects. Based on these studies, novel therapeutic approaches can be designed for the treatment of patients with AD.

Butterflies in the gut: the interplay between intestinal microbiota and stress

Psychological stress is a global issue that affects at least one-third of the population worldwide and increases the risk of numerous psychiatric disorders. Accumulating evidence suggests that the gut and its inhabiting microbes may regulate stress and stress-associated behavioral abnormalities. Hence, the objective of this review is to explore the causal relationships between the gut microbiota, stress, and behavior. Dysbiosis of the microbiome after stress exposure indicated microbial adaption to stressors. Strikingly, the hyperactivated stress signaling found in microbiota-deficient rodents can be normalized by microbiota-based treatments, suggesting that gut microbiota can actively modify the stress response. Microbiota can regulate stress response via intestinal glucocorticoids or autonomic nervous system. Several studies suggest that gut bacteria are involved in the direct modulation of steroid synthesis and metabolism. This review provides recent discoveries on the pathways by which gut microbes affect stress signaling and brain circuits and ultimately impact the host's complex behavior.

Dysbiosis and Alzheimer's disease: role of probiotics, prebiotics and synbiotics

Alzheimer's disease (AD) is a neurodegenerative disease characterized by dementia and the accumulation of amyloid beta in the brain. Recently, microbial dysbiosis has been identified as one of the major factors involved in the onset and progression of AD. Imbalance in gut microbiota is known to affect central nervous system (CNS) functions through the gut-brain axis and involves inflammatory, immune, neuroendocrine and metabolic pathways. An altered gut microbiome is known to affect the gut and BBB permeability, resulting in imbalance in levels of neurotransmitters and neuroactive peptides/factors. Restoration of levels of beneficial microorganisms in the gut has demonstrated promising effects in AD in pre-clinical and clinical studies. The current review enlists the important beneficial microbial species present in the gut, the effect of their metabolites on CNS, mechanisms involved in dysbiosis related to AD and the beneficial effects of probiotics on AD. It also highlights challenges involved in large-scale manufacturing and quality control of probiotic formulations.

The Impact of Stress, Microbial Dysbiosis, and Inflammation on Necrotizing Enterocolitis

Necrotizing enterocolitis (NEC) is the leading cause of intestinal morbidity and mortality in neonates. A large body of work exists; however, the pathogenesis of NEC remains poorly understood. Numerous predictors have been implicated in the development of NEC, with relatively less emphasis on maternal factors. Utilizing human tissue plays a crucial role in enhancing our comprehension of the underlying mechanisms accountable for this devastating disease. In this review, we will discuss how maternal stress affects the pathogenesis of NEC and how changes in the intestinal microbiome can influence the development of NEC. We will also discuss the results of transcriptomics-based studies and analyze the gene expression changes in NEC tissues and other molecular targets associated with the pathogenesis of NEC.

Antibiotic-induced microbial depletion enhances murine small intestinal epithelial growth in a serotonin-dependent manner

Regulation of small intestinal epithelial growth by endogenous and environmental factors is critical for intestinal homeostasis and recovery from insults. Depletion of the intestinal microbiome increases epithelial proliferation in small intestinal crypts, similar to the effects observed in animal models of serotonin potentiation. Based on prior evidence that the microbiome modulates serotonin activity, we hypothesized that microbial depletion-induced epithelial proliferation is dependent on host serotonin activity. A mouse model of antibiotic-induced microbial depletion (AIMD) was employed. Serotonin potentiation was achieved through either genetic knockout of the serotonin transporter (SERT) or pharmacological SERT inhibition, and inhibition of serotonin synthesis was achieved with para-chlorophenylalanine. AIMD and serotonin potentiation increased intestinal villus height and crypt proliferation in an additive manner, but the epithelial proliferation observed after AIMD was blocked in the absence of endogenous serotonin. Using Lgr5-EGFP-reporter mice, we evaluated intestinal stem cell (ISC) quantity and proliferation. AIMD increased the number of ISCs per crypt and ISC proliferation compared with controls, and changes in ISC number and proliferation were dependent on the presence of host serotonin. Furthermore, Western blotting demonstrated that AIMD reduced epithelial SERT protein expression compared with controls. In conclusion, host serotonin activity is necessary for microbial depletion-associated changes in villus height and ISC proliferation in crypts, and microbial depletion produces a functional serotonin-potentiated state through reduced SERT protein expression. These findings provide an understanding of how changes to the microbiome contribute to intestinal pathology and can be applied therapeutically.NEW & NOTEWORTHY Antibiotic-induced microbial depletion of the murine small intestine results in a state of potentiated serotonin activity through reduced epithelial expression of the serotonin transporter. Specifically, serotonin-dependent mechanisms lead to increased intestinal surface area and intestinal stem cell proliferation. Furthermore, the absence of endogenous serotonin leads to blunting of small intestinal villi, suggesting that serotonin signaling is required for epithelial homeostasis.

Adaptive remodeling of the stimulus-secretion coupling: Lessons from the 'stressed' adrenal medulla

Stress is part of our daily lives and good health in the modern world is offset by unhealthy lifestyle factors, including the deleterious consequences of stress and associated pathologies. Repeated and/or prolonged stress may disrupt the body homeostasis and thus threatens our lives. Adaptive processes that allow the organism to adapt to new environmental conditions and maintain its homeostasis are therefore crucial. The adrenal glands are major endocrine/neuroendocrine organs involved in the adaptive response of the body facing stressful situations. Upon stress episodes and in response to activation of the sympathetic nervous system, the first adrenal cells to be activated are the neuroendocrine chromaffin cells located in the medullary tissue of the adrenal gland. By releasing catecholamines (mainly epinephrine and to a lesser extent norepinephrine), adrenal chromaffin cells actively contribute to the development of adaptive mechanisms, in particular targeting the cardiovascular system and leading to appropriate adjustments of blood pressure and heart rate, as well as energy metabolism. Specifically, this chapter covers the current knowledge as to how the adrenal medullary tissue remodels in response to stress episodes, with special attention paid to chromaffin cell stimulus-secretion coupling. Adrenal stimulus-secretion coupling encompasses various elements taking place at both the molecular/cellular and tissular levels. Here, I focus on stress-driven changes in catecholamine biosynthesis, chromaffin cell excitability, synaptic neurotransmission and gap junctional communication. These signaling pathways undergo a collective and finely-tuned remodeling, contributing to appropriate catecholamine secretion and maintenance of body homeostasis in response to stress.

Communication of gut microbiota and brain via immune and neuroendocrine signaling

The gastrointestinal tract of the human is inhabited by about 5 × 10¹³ bacteria (of about 1,000 species) as well as archaea, fungi, and viruses. Gut microbiota is known to influence the host organism, but the host may also affect the functioning of the microbiota. This bidirectional cooperation occurs in three main inter-organ signaling: immune, neural, and endocrine. Immune communication relies mostly on the cytokines released by the immune cells into circulation. Also, pathogen-associated or damage-associated molecular patterns (PAMPs or DAMPs) may enter circulation and affect the functioning of the internal organs and gut microbiota. Neural communication relies mostly on the direct anatomical connections made by the vagus nerve, or indirect connections via the enteric nervous system. The third pathway, endocrine communication, is the broadest one and includes the hypothalamic-pituitary-adrenal axis. This review focuses on presenting the latest data on the role of the gut microbiota in inter-organ communication with particular emphasis on the role of neurotransmitters (catecholamines, serotonin, gamma-aminobutyric acid), intestinal peptides (cholecystokinin, peptide YY, and glucagon-like peptide 1), and bacterial metabolites (short-chain fatty acids).

Linking the gut microbiome to microglial activation in opioid use disorder

Substance use disorder (SUD) is a physical and psychological disorder globally prevalent today that has resulted in over 107,000 drug overdose deaths in 2021 in the United States alone. This manuscript reviews the potential relationship between opioid use disorder (OUD), a prevalent subset of SUD, and the microglia, the resident macrophages of the central nervous system (CNS), as they have been found to become significantly more activated during opioid exposure. The inflammatory response mediated by the microglia could contribute to the pathophysiology of SUDs, in particular OUD. Further understanding of the microglia and how they respond to not only signals in the CNS but also signals from other areas of the body, such as the gut microbiome, could explain how the microglia are involved in drug use. Several studies have shown extensive communication between the gut microbiome and the microglia, which may be an important factor in the initiation and development of OUD. Particularly, strategies seeking to manipulate and restore the gut microbiome have been shown to reduce microglial activation and attenuate inflammation. In this review, we discuss the evidence for a link between the microglia and OUD and how the gut microbiome might influence microglial activation to drive the disorder and its associated behaviors. Understanding this connection between microglia and the gut microbiome in the context of drug use may present additional therapeutic targets to treat the different stages of drug use.

Reviewing the role of gut microbiota in the pathogenesis of depression and exploring new therapeutic options

The relationship between gut microbiota (GM) and mental health is one of the focuses of psychobiology research. In recent years, the microbial-gut-brain axis (MGBA) concept has gradually formed about this bidirectional communication between gut and brain. But how the GM is involved in regulating brain function and how they affect emotional disorders these mechanisms are tenuous and limited to animal research, and often controversial. Therefore, in this review, we attempt to summarize and categorize the latest advances in current research on the mechanisms of GM and depression to provide valid information for future diagnoses and therapy of mental disorders. Finally, we introduced some antidepressant regimens that can help restore gut dysbiosis, including classic antidepressants, Chinese materia medica (CMM), diet, and exogenous strains. These studies provide further insight into GM's role and potential pathways in emotion-related diseases, which holds essential possible clinical outcomes for people with depression or related psychiatric disorders. Future research should focus on clarifying the causal role of GM in disease and developing microbial targets, applying these findings to the prevention and treatment of depression.

The gut microbiota in neurodegenerative diseases: revisiting possible therapeutic targets for cannabidiol

Understanding the pathophysiology of Alzheimer's disease (AD) is essential to improve the efficacy of treatments and, consequently, patients' lives. Unfortunately, traditional therapeutic strategies have not been effective. There is therefore an urgent need to discover or develop alternative treatment strategies. Recently, some pieces of the puzzle appear to emerge: on a hand, the gut microbiota (GM) has gained attention since intestinal dysbiosis aggravates and generates some of the pathological processes of AD; on the other hand, cannabidiol (CBD), a phytocannabinoid, attenuates intestinal inflammation and possesses neuroprotective properties. Intestinal dysbiosis (increased population of proinflammatory bacteria) in AD increases plasma lipopolysaccharide and Aβ peptide levels, both responsible for increasing the permeability of the blood-brain barrier (BBB). A leaky BBB may facilitate the entry of peripheral inflammatory mediators into the central nervous system and ultimately aggravate neuroinflammation and neuronal death due to chronic activation of glial cells. Studies investigating the GM reported a strong relationship between intestinal dysbiosis and AD. In this review we conjecture that the GM is a promising therapeutic target for CBD in the context of AD.

Discrete role for maternal stress and gut microbes in shaping maternal and offspring immunity

Psychosocial stress is prevalent during pregnancy, and is associated with immune dysfunction, both for the mother and the child. The gut microbiome has been implicated as a potential mechanism by which stress during pregnancy can impact both maternal and offspring immune function; however, the complex interplay between the gut microbiome and the immune system is not well-understood. Here, we leverage a model of antimicrobial-mediated gut microbiome reduction, in combination with a well-established model of maternal restraint stress, to investigate the independent effects of and interaction between maternal stress and the gut microbiome in shaping maternal and offspring immunity. First, we confirmed that the antimicrobial treatment reduced maternal gut bacterial load and altered fecal alpha and beta diversity, with a reduction in commensal microbes and an increase in the relative abundance of rare taxa. Prenatal stress also disrupted the gut microbiome, according to measures of both alpha and beta diversity. Furthermore, prenatal stress and antimicrobials independently induced systemic and gastrointestinal immune suppression in the dam with a concomitant increase in circulating corticosterone. While stress increased neutrophils in the maternal circulation, lymphoid cells and monocytes were not impacted by either stress or antimicrobial treatment. Although the fetal immune compartment was largely spared, stress increased circulating neutrophils and CD8 T cells, and antibiotics increased neutrophils and reduced T cells in the adult offspring. Altogether, these data indicate similar, but discrete, roles for maternal stress and gut microbes in influencing maternal and offspring immune function.

Metagenomic and Transcriptomic Analyses Reveal the Differences and Associations Between the Gut Microbiome and Muscular Genes in Angus and Chinese Simmental Cattle

Gut microbiome and heredity are two important factors affecting the intramuscular fat (IMF) of cattle, excluding age, sex, and nutrition. This study aimed at deciphering these two differences by analyzing the gut microbiome and intramuscular differentially expressed genes (DEGs) in the Angus and Chinese Simmental cattle. Feces and longissimus dorsi were collected from the two groups of animals (n = 20/group) for multiomics analysis. Angus holds a significantly higher diversity than Chinese Simmental, and the relative abundance of Roseburia, Prevotella, Coprococcus, etc., was obviously higher in Angus. Chinese Simmental had higher levels of isobutyrate, isovalerate, and valerate, although similar levels of acetate, propionate, and butyrate were observed for the two groups. The DEGs upregulated in Chinese Simmental were mainly involved in immune and inflammatory responses, while those in Angus were associated with the regulation of muscle system and myofibril. We finally identified 17 species, including Eubacterium rectale, etc., which were positively correlated to muscle and fat metabolism genes (MSTN, MYLPF, TNNT3, and FABP3/4) and illustrate the associations between them. Our study unveils the gut microbial differences and significant DEGs as well as their associations between the two breeds, providing valuable guidance for future mechanism research and development of intervention strategies to improve meat quality.

Varied Composition and Underlying Mechanisms of Gut Microbiome in Neuroinflammation

The human gut microbiome has been implicated in a host of bodily functions and their regulation, including brain development and cognition. Neuroinflammation is a relatively newer piece of the puzzle and is implicated in the pathogenesis of many neurological disorders. The microbiome of the gut may alter the inflammatory signaling inside the brain through the secretion of short-chain fatty acids, controlling the availability of amino acid tryptophan and altering vagal activation. Studies in Korea and elsewhere highlight a strong link between microbiome dynamics and neurocognitive states, including personality. For these reasons, re-establishing microbial flora of the gut looks critical for keeping neuroinflammation from putting the whole system aflame through probiotics and allotransplantation of the fecal microbiome. However, the numerosity of the microbiome remains a challenge. For this purpose, it is suggested that wherever possible, a fecal microbial auto-transplant may prove more effective. This review summarizes the current knowledge about the role of the microbiome in neuroinflammation and the various mechanism involved in this process. As an example, we have also discussed the autism spectrum disorder and the implication of neuroinflammation and microbiome in its pathogenesis.

Stressor-Induced Reduction in Cognitive Behavior is Associated with Impaired Colonic Mucus Layer Integrity and is Dependent Upon the LPS-Binding Protein Receptor CD14

Purpose

Commensal microbes are impacted by stressor exposure and are known contributors to cognitive and social behaviors, but the pathways through which gut microbes influence stressor-induced behavioral changes are mostly unknown. A murine social stressor was used to determine whether host-microbe interactions are necessary for stressor-induced inflammation, including neuroinflammation, that leads to reduced cognitive and social behavior.

Methods

C57BL/6 male mice were exposed to a paired fighting social stressor over a 1 hr period for 6 consecutive days. Y-maze and social interaction behaviors were tested following the last day of the stressor. Serum cytokines and lipopolysaccharide binding protein (LBP) were measured and the number and morphology of hippocampal microglia determined via immunohistochemistry. Intestinal mucous thickness and antimicrobial peptide expression were determined via fluorescent staining and real-time PCR (respectively) and microbial community composition was assessed using 16S rRNA gene amplicon sequencing. To determine whether the microbiota or the LBP receptor (CD14) are necessary for stressor-induced behavioral changes, experiments were performed in mice treated with a broad-spectrum antibiotic cocktail or in CD14-/- mice.

Results

The stressor reduced Y-maze spontaneous alternations, which was accompanied by increased microglia in the hippocampus, increased circulating cytokines (eg, IL-6, TNF-α) and LBP, and reduced intestinal mucus thickness while increasing antimicrobial peptides and cytokines. These stressor-induced changes were largely prevented in mice given broad-spectrum antibiotics and in CD14-/- mice. In contrast, social stressor-induced alterations of social behavior were not microbe-dependent.

Conclusion

Stressor-induced cognitive deficits involve enhanced bacterial interaction with the intestine, leading to low-grade, CD14-dependent, inflammation.

Defects in NLRP6, autophagy and goblet cell homeostasis are associated with reduced duodenal CRH receptor 2 expression in patients with functional dyspepsia

Functional dyspepsia (FD) affects up to 15% of the population and is characterised by recurring upper gastrointestinal (GI) symptoms occurring in the absence of clinically identifiable pathology. Psychological stress is a key factor associated with the onset of FD and locally acting hypothalamic-pituitary-adrenal (HPA) axis hormones have been implicated in GI motility and barrier dysfunction. Recent pre-clinical work has identified mechanistic pathways linking corticotropin-releasing hormone (CRH) with the innate epithelial immune protein NLRP6, an inflammasome that has been shown to regulate GI mucus secretion. We recruited twelve FD patients and twelve healthy individuals to examine whether dysregulation of hypothalamic-pituitary adrenal (HPA) axis hormones and altered NLRP6 pathways were evident in the duodenal mucosa. Protein expression was assessed by immunoblot and immunohistochemistry in D2 duodenal biopsies. Plasma HPA axis hormones were assayed by ELISA and enteroid and colorectal cancer cell line cultures were used to verify function. FD patients exhibited reduced duodenal CRH-receptor 2, compared to non-GI disease controls, indicating a dysregulation of duodenal HPA signalling. The loss of CRH-receptor 2 correlated with reduced NLRP6 expression and autophagy function, processes critical for maintaining goblet cell homeostasis. In accordance, duodenal goblet cell numbers and mucin exocytosis was reduced in FD patients compared to controls. In vitro studies demonstrated that CRH could reduce NLRP6 in duodenal spheroids and promote mucus secretion in the HT29-MTX-E12 cell line. In conclusion, FD patients exhibit defects in the NLRP6-autophagy axis with decreased goblet cell function that may drive symptoms of disease. These features correlated with loss of CRH receptor 2 and may be driven by dysregulation of HPA signalling in the duodenum of FD patients.

The crosstalk between gut microbiota, intestinal immunological niche and visceral adipose tissue as a new model for the pathogenesis of metabolic and inflammatory diseases: the paradigm of type 2 diabetes mellitus

Gut microbiota (GM) comprises more than one thousand microorganisms between bacterial species, viruses, fungi, and protozoa, and represents the main actor of a wide net of molecular interactions, involving, among others, the endocrine system, immune responses, and metabolism. GM influences many endocrine functions such as adrenal steroidogenesis, thyroid function, sexual hormones, IGF-1 pathway and peptides produced in gastrointestinal system. It is fundamental in glycaemic control and obesity, while also exerting an important function in modulating the immune system and associated inflammatory disease. The result of this crosstalk in gut mucosa is the formation of the intestinal immunological niche. Visceral adipose tissue (VAT) produces about 600 different peptides, it is involved in lipid and glucose metabolism and in some immune reactions through several adipokines. GM and VAT interact in a bidirectional fashion: while gut dysbiosis can modify VAT adipokines and hormone secretion, VAT hyperplasia modifies GM composition. Acquired or genetic factors leading to gut dysbiosis or increasing VAT (i.e., Western diet) induce a proinflammatory condition, which plays a pivotal role in the development of dysmetabolic and immunologic conditions, such as diabetes mellitus. Diabetes is clearly associated with specific patterns of GM alterations, with an abundance or reduction of GM species involved in controlling mucosal barrier status, glycaemic levels and exerting a pro- or anti-inflammatory activity. All these factors could explain the higher incidence of several inflammatory conditions in Western countries; furthermore, besides the specific alterations observed in diabetes, this paradigm could represent a common pathway acting in many metabolic conditions and could pave the way to a new, interesting therapeutic approach.

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

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

Emerging Evidence on the Use of Probiotics and Prebiotics to Improve the Gut Microbiota of Older Adults with Frailty Syndrome: A Narrative Review

BACKGROUND

The gut microbiota can impact older adults' health, especially in patients with frailty syndrome. Understanding the association between the gut microbiota and frailty syndrome will help to explain the etiology of age-related diseases. Low-grade systemic inflammation is a factor leading to geriatric disorders, which is known as "inflammaging". Intestinal dysbiosis has a direct relationship with low-grade systemic inflammation because when the natural gut barrier is altered by age or other factors, some microorganisms or their metabolites can cross this barrier and reach the systemic circulation.

OBJECTIVES

This review had two general goals: first, to describe the characteristics of the gut microbiota associated with age-related diseases, specifically frailty syndrome. The second aim was to identify potential interventions to improve the composition and function of intestinal microbiota, consequently lessening the burden of patients with frailty syndrome.

METHODS

A search of scientific evidence was performed in PubMed, Science Direct, and Redalyc using keywords such as "frailty", "elderly", "nutrient interventions", "probiotics", and "prebiotics". We included studies reporting the effects of nutrient supplementation on frailty syndrome and older adults. These studies were analyzed to identify novel therapeutic alternatives to improve gut microbiota characteristics as well as subclinical signs related to this condition.

RESULTS

The gut microbiota participates in many metabolic processes that have an impact on the brain, muscles, and other organs. These processes integrate feedback mechanisms, comprising their respective axis with the intestine and the gut microbiota. Alterations in these associations can lead to frailty. We report a few interventions that demonstrate that prebiotics and probiotics could modulate the gut microbiota in humans. Furthermore, other nutritional interventions could be used in patients with frailty syndrome.

CONCLUSION

Probiotics and prebiotics may potentially prevent frailty syndrome or improve the quality of life of patients with this disorder. However, there is not enough information about their appropriate doses and periods of administration. Therefore, further investigations are required to determine these factors and improve their efficacy as therapeutic approaches for frailty syndrome.

The Role of the Gut Microbiota in the Development and Progression of Major Depressive and Bipolar Disorder

A growing number of studies in rodents indicate a connection between the intestinal microbiota and the brain, but comprehensive human data is scarce. Here, we systematically reviewed human studies examining the connection between the intestinal microbiota and major depressive and bipolar disorder. In this review we discuss various changes in bacterial abundance, particularly on low taxonomic levels, in terms of a connection with the pathophysiology of major depressive and bipolar disorder, their use as a diagnostic and treatment response parameter, their health-promoting potential, as well as novel adjunctive treatment options. The diversity of the intestinal microbiota is mostly decreased in depressed subjects. A consistent elevation of phylum Actinobacteria, family Bifidobacteriaceae, and genus Bacteroides, and a reduction of family Ruminococcaceae, genus Faecalibacterium, and genus Roseburia was reported. Probiotics containing Bifidobacterium and/or Lactobacillus spp. seemed to improve depressive symptoms, and novel approaches with different probiotics and synbiotics showed promising results. Comparing twin studies, we report here that already with an elevated risk of developing depression, microbial changes towards a “depression-like” microbiota were found. Overall, these findings highlight the importance of the microbiota and the necessity for a better understanding of its changes contributing to depressive symptoms, potentially leading to new approaches to alleviate depressive symptoms via alterations of the gut microbiota.

Psychological intervention to treat distress: An emerging frontier in cancer prevention and therapy

Psychological distress, such as chronic depression and anxiety, is a topical problem. In the context of cancer patients, prevalence rates of psychological distress are four-times higher than in the general population and often confer worse outcomes. In addition to evidence from epidemiological studies confirming the links between psychological distress and cancer progression, a growing body of cellular and molecular studies have also revealed the complex signaling networks which are modulated by psychological distress-derived chronic stress during cancer progression. In this review, aiming to uncover the intertwined networks of chronic stress-driven oncogenesis and progression, we summarize physiological stress response pathways, like the HPA, SNS, and MGB axes, that modulate the release of stress hormones with potential carcinogenic properties. Furthermore, we discuss in detail the mechanisms behind these chronic stimulations contributing to the initiation and progression of cancer through direct regulation of cancer hallmarks-related signaling or indirect promotion of cancer risk factors (including obesity, disordered circadian rhythms, and premature senescence), suggesting a novel research direction into cancer prevention and therapy on the basis of psychological interventions.

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.

Bacteria - derived short chain fatty acids restore sympathoadrenal responsiveness to hypoglycemia after antibiotic-induced gut microbiota depletion

The microbiome co-evolved with their mammalian host over thousands of years. This commensal relationship serves a pivotal role in various metabolic, physiological, and immunological processes. Recently we discovered impaired adrenal catecholamine stress responses in germ-free mice suggesting developmental modification of the reflex arc or absence of an ongoing microbiome signal. To determine whether maturational arrest or an absent bacteria-derived metabolite was the cause, we tested whether depleting gut microbiome in young adult animals could also alter the peripheral stress responses to insulin-induced hypoglycemia. Groups of C57Bl6 male mice were given regular water (control) or a cocktail of non-absorbable broad-spectrum antibiotics (Abx) in the drinking water for two weeks before injection with insulin or saline. Abx mice displayed a profound decrease in microbial diversity and abundance of Bacteroidetes and Firmicutes, plus a markedly enlarged caecum and no detectable by-products of bacterial fermentation (sp. short chain fatty acids, SCFA). Tonic and stress-induced epinephrine levels were attenuated. Recolonization (Abx + R) restored bacterial diversity, but not the sympathoadrenal system responsiveness or caecal acetate, propionate and butyrate levels. In contrast, corticosterone (HPA) and glucagon (parasympathetic) resting values and responses to hypoglycemia remained similar across all conditions. Oral supplementation with SCFA improved epinephrine responses to hypoglycaemia. Whole genome shotgun sequence profiling of fecal samples from control, Abx and Abx + R cohorts identified nine microbes (SCFA producers) absent from both Abx and Abx + R groups. These results implicate gut microbiome depletion plus its attendant reduction in SCFA signalling in adversely affecting the release of epinephrine in response to hypoglycemia. We speculate that regardless of postnatal age, a mutable microbiome messaging system exists throughout life. Unravelling these mechanisms could lead to new therapeutic possibilities through controlled manipulation of the gut microbiota and its ability to alter systemic neurotransmitter responsiveness.

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Gut microbiome depletion affects sympathoadrenal medullary stress axis.

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Recolonization restores bacterial diversity, but not the epinephrine response to hypoglycaemia.

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SCFA supplement during antibiotic treatment improves tonic and stress-induced epinephrine release.

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Delayed recovery of several SCFA producers after recolonization modulates peripheral catecholaminergic pathways.

SRC-1 Deficiency Increases Susceptibility of Mice to Depressive-Like Behavior After Exposure to CUMS

Steroid receptor coactivator 1 (SRC-1) is one of the coactivators recruited by the nuclear receptors (NRs) when NRs are activated by steroid hormones, such as glucocorticoid. SRC-1 is abundant in hippocampus and hypothalamus and is also related to some major risk factors for depression, implicated by its reduced expression after stress and its effect on hypothalamus-pituitary-adrenal gland axis function. However, whether SRC-1 is involved in the formation of depression remains unclear. In this study, we firstly established chronic unpredictable stress (CUS) to induce depressive-like behaviors in mice and found that SRC-1 expression was reduced by CUS. A large number of studies have shown that neuroinflammation is associated with stress-induced depression and lipopolysaccharide (LPS) injection can lead to neuroinflammation and depressive-like behaviors in mice. Our result indicated that LPS treatment also decreased SRC-1 expression in mouse brain, implying the involvement of SRC-1 in the process of inflammation and depression. Next, we showed that the chronic unpredictable mild stress (CUMS) failed to elicit the depressive-like behaviors and dramatically promoted the expression of SRC-1 in brain of wild type mice. What's more, the SRC-1 knockout mice were more susceptible to CUMS to develop depressive-like behaviors and presented the changed expression of glucocorticoid receptor. However, SRC-1 deficiency did not affect the microglia activation induced by CUMS. Altogether, these results indicate a correlation between SRC-1 level and depressive-like behaviors, suggesting that SRC-1 might be involved in the development of depression induced by stress.

Long-lasting effects of prenatal stress on HPA axis and inflammation: A systematic review and multilevel meta-analysis in rodent studies

Exposure to prenatal stress (PNS) can lead to long-lasting neurobiological and behavioral consequences for the offspring, which may enhance the susceptibility for mental disorders. The hypothalamus-pituitary-adrenal (HPA) axis and the immune system are two major factors involved in the stress response. Here, we performed a systematic review and meta-analysis of rodent studies that investigated the effects of PNS exposure on the HPA axis and inflammatory cytokines in adult offspring. Our analysis shows that animals exposed to PNS display a consistent increase in peripheral corticosterone (CORT) levels and central corticotrophin-releasing hormone (CRH), while decreased levels of its receptor 2 (CRHR2). Meta-regression revealed that sex and duration of PNS protocol are covariates that moderate these results. There was no significant effect of PNS in glucocorticoid receptor (GR), CRH receptor 1 (CRHR1), pro- and anti-inflammatory cytokines. Our findings suggest that PNS exposure elicits long-lasting effects on the HPA axis function, providing an important tool to investigate in preclinical settings key pathological aspects related to early-life stress exposure. Furthermore, researchers should be aware of the mixed outcomes of PNS on inflammatory markers in the adult brain.

Dysbiosis and Alzheimer's Disease: A Role for Chronic Stress?

Alzheimer’s disease (AD) is an incurable, neuropsychiatric, pathological condition that deteriorates the worth of geriatric lives. AD is characterized by aggregated senile amyloid plaques, neurofibrillary tangles, neuronal loss, gliosis, oxidative stress, neurotransmitter dysfunction, and bioenergetic deficits. The changes in GIT composition and harmony have been recognized as a decisive and interesting player in neuronal pathologies including AD. Microbiota control and influence the oxidoreductase status, inflammation, immune system, and the endocrine system through which it may have an impact on the cognitive domain. The altered and malfunctioned state of microbiota is associated with minor infections to complicated illnesses that include psychosis and neurodegeneration, and several studies show that microbiota regulates neuronal plasticity and neuronal development. The altered state of microbiota (dysbiosis) may affect behavior, stress response, and cognitive functions. Chronic stress-mediated pathological progression also has a well-defined role that intermingles at various physiological levels and directly impacts the pathological advancement of AD. Chronic stress-modulated alterations affect the well-established pathological markers of AD but also affect the gut–brain axis through the mediation of various downstream signaling mechanisms that modulate the microbial commensals of GIT. The extensive literature reports that chronic stressors affect the composition, metabolic activities, and physiological role of microbiota in various capacities. The present manuscript aims to elucidate mechanistic pathways through which stress induces dysbiosis, which in turn escalates the neuropathological cascade of AD. The stress–dysbiosis axis appears a feasible zone of work in the direction of treatment of AD.

The Gut Microbiota Affects Corticosterone Production in the Murine Small Intestine

Glucocorticoids (GCs) are hormones that are released in response to stressors and exhibit many activities, including immunomodulatory and anti-inflammatory activities. They are primarily synthesized in the adrenal gland but are also produced in peripheral tissues via regeneration of adrenal 11-oxo metabolites or by de novo synthesis from cholesterol. The present study investigated the influence of the microbiota on de novo steroidogenesis and regeneration of corticosterone in the intestine of germ-free (GF) and specific pathogen-free mice challenged with a physical stressor (anti-CD3 antibody i.p. injection). In the small intestine, acute immune stress resulted in increased mRNA levels of the proinflammatory cytokines IL1β, IL6 and Tnfα and genes involved in de novo steroidogenesis (Stard3 and Cyp11a1), as well as in regeneration of active GCs from their 11-oxo metabolites (Hsd11b1). GF mice showed a generally reduced transcriptional response to immune stress, which was accompanied by decreased intestinal corticosterone production and reduced expression of the GC-sensitive marker Fkbp5. In contrast, the interaction between stress and the microbiota was not detected at the level of plasma corticosterone or the transcriptional response of adrenal steroidogenic enzymes. The results indicate a differential immune stress-induced intestinal response to proinflammatory stimuli and local corticosterone production driven by the gut microbiota.

Understanding the role of gut microbiota in the pathogenesis of schizophrenia

Schizophrenia is a chronic mental disorder with marked symptoms of hallucination, delusion, and impaired cognitive behaviors. Although multidimensional factors have been associated with the development of schizophrenia, the principal cause of the disorder remains debatable. Microbiome involvement in the etiology of schizophrenia has been widely researched due to the advancement in sequencing technologies. This review describes the contribution of the gut microbiome in the development of schizophrenia that is facilitated by the gut-brain axis. The gut microbiota is connected to the gut-brain axis via several pathways and mechanisms, that are discussed in this review. The role of the oral microbiota, probiotics and prebiotics in shaping the gut microbiota are also highlighted. Lastly, future perspectives for microbiome research in schizophrenia are addressed.

Restraint Stress in Hypertensive Rats Activates the Intestinal Macrophages and Reduces Intestinal Barrier Accompanied by Intestinal Flora Dysbiosis

Purpose

Hypertension (HTN) is a major risk factor for cardiovascular disease. In recent years, there were numerous studies on the function of stress in HTN. However, the gut dysbiosis linked to hypertension in animal models under stress is still incompletely understood. Purpose of this study is to use multiple determination method to determine the juvenile stage intestinal bacteria, cytokines and changes in hormone levels.

Methods

Four groups of juvenile male spontaneously hypertensive rats (SHRs) and age-matched male Wistar-Kyoto (WKY) rats were randomly selected as control and experimental groups. Rats in the two stress groups were exposed to restraint stress for 3 hours per day for 7 consecutive days. In one day three times in the method of non-invasive type tail-cuff monitoring blood pressure. The detailed mechanism was illuminated based on the intestinal change using immunohistochemical and immunofluorescence staining and the stress-related hormone and inflammation factors were analyzed via ELISA method. The integrity of the epithelial barrier was assessed using FITC/HRP and the expression levels of proteins associated with the tight junction was detected by Western blot. The alteration of stress-related intestinal flora from ileocecal junction and distal colon were also analyzed using its 16S rDNA sequencing.

Results

The results indicate that acute stress rapidly increases mean arterial pressure which is positive correlation to hormone concentration, especially in SHR-stress group. Meanwhile, stress promoted the enhancement of epithelial permeability accompanied with a reduced expression of the tight junction-related protein and the macrophages (Mφ) aggregation to the lamina propria. There were remarkable significant increase of stress-related hormones and pro-inflammatory factor interleukin (IL)-6 along with a decrease in the diversity of intestinal flora and an imbalance in the F/B ratio.

Conclusion

Our results reveal that stress accompanied with HTN could significantly disrupt the domino effect between intestinal flora and homeostasis.

Intestinal mycobiota in health and diseases: from a disrupted equilibrium to clinical opportunities

Bacteria, viruses, protozoa, and fungi establish a complex ecosystem in the gut. Like other microbiota, gut mycobiota plays an indispensable role in modulating intestinal physiology. Notably, the most striking characteristics of intestinal fungi are their extraintestinal functions. Here, we provide a comprehensive review of the importance of gut fungi in the regulation of intestinal, pulmonary, hepatic, renal, pancreatic, and brain functions, and we present possible opportunities for the application of gut mycobiota to alleviate/treat human diseases. Video Abstract.

Regulation of Gut Microbiota Disrupts the Glucocorticoid Receptor Pathway and Inflammation-related Pathways in the Mouse Hippocampus

An increasing number of studies have recently indicated the important effects of gut microbes on various functions of the central nervous system. However, the underlying mechanisms by which gut microbiota regulate brain functions and behavioral phenotypes remain largely unknown. We therefore used isobaric tags for relative and absolute quantitation (iTRAQ)-based quantitative proteomic analysis to obtain proteomic profiles of the hippocampus in germ-free (GF), colonized GF, and specific pathogen-free (SPF) mice. We then integrated the resulting proteomic data with previously reported mRNA microarray data, to further explore the effects of gut microbes on host brain functions. We identified that 61 proteins were upregulated and 242 proteins were downregulated in GF mice compared with SPF mice. Of these, 124 proteins were significantly restored following gut microbiota colonization. Bioinformatic analysis of these significant proteins indicated that the glucocorticoid receptor signaling pathway and inflammation-related pathways were the most enriched disrupted pathways. This study provides new insights into the pathological mechanisms of gut microbiota-regulated diseases.

Microbial memories: Sex-dependent impact of the gut microbiome on hippocampal plasticity

Germ‐free rodents, raised in the absence of a measurable gut microbiome, have been a key model to study the microbiome‐gut‐brain axis. Germ‐free mice exhibit marked behavioural and neurochemical differences to their conventionally raised counterparts. It is as yet unclear how these neurochemical differences lead to the behavioural differences. Here, we test the electrophysiological properties of hippocampal plasticity in adult germ‐free mice and compare them to conventionally raised counterparts. Whilst basal synaptic efficacy and pre‐synaptic short‐term plasticity appear normal, we find a striking alteration of hippocampal long‐term potentiation specifically in male germ‐free slices. However, the spike output of these neurons remains normal along with altered input‐output coupling, potentially indicating homeostatic compensatory mechanisms, or an altered excitation/inhibition balance. To our knowledge this is the first time the electrophysiological properties of the hippocampus have been assessed in a microbiome deficient animal. Our data indicate that the absence of a microbiome alters integration of dendritic signalling in the CA1 region in mice.

Gut-brain axis: A matter of concern in neuropsychiatric disorders…!

The gut microbiota is composed of a large number of microbes, usually regarded as commensal bacteria. It has become gradually clear that gastrointestinal microbiota affects gut pathophysiology and the central nervous system (CNS) function by modulating the signaling pathways of the microbiota-gut-brain (MGB) axis. This bidirectional MGB axis communication primarily acts through neuroendocrine, neuroimmune, and autonomic nervous systems (ANS) mechanisms. Accumulating evidence reveals that gut microbiota interacts with the host brain, and its modulation may play a critical role in the pathology of neuropsychiatric disorders. Recently, neuroscience research has established the significance of gut microbiota in the development of brain systems that are essential to stress-related behaviors, including depression and anxiety. Application of modulators of the MGB, such as psychobiotics (e.g., probiotics), prebiotics, and specific diets, may be a promising therapeutic approach for neuropsychiatric disorders. The present review article primarily focuses on the relevant features of the disturbances of the MGB axis in the pathophysiology of neuropsychiatric disorders and its potential mechanisms.

Prebiotics Regulation of Intestinal Microbiota Attenuates Cognitive Dysfunction Induced by Surgery Stimulation in APP/PS1 Mice

Emerging evidence indicates that the intestinal microbiota could interact with the central nervous system and modulate multiple pathophysiological changes, including the integrity of intestinal barrier and blood-brain barrier, as well as neuroinflammatory response. In the present study, we investigated the potential role of intestinal microbiota in the pathophysiological process of postoperative cognitive dysfunction. Six-month-old APP/PS1 mice were subjected to partial hepatectomy to establish surgery model and exhibited cognitive dysfunction. The expressions of inflammatory mediators increased and tight junction proteins (ZO-1 and Occludin) levels decreased in the intestine and hippocampus. The 16S ribosomal RNA gene sequencing showed altered β diversity and intestinal microbiota richness after surgery, including genus Rodentibacter, Bacteroides, Ruminococcaceae_UCG_014 and Faecalibaculum, as well as family Eggerthellaceae and Muribaculaceae. Furthermore, prebiotics (Xylooligosaccharides, XOS) intervention effectively attenuated surgery-induced cognitive dysfunction and intestinal microbiota alteration, reduced inflammatory responses, and improved the integrity of tight junction barrier in the intestine and hippocampus. In summary, the present study indicates that intestinal microbiota alteration, the related intestinal barrier and blood-brain barrier damage, and inflammatory responses participate the pathophysiological process of postoperative cognitive dysfunction. Prebiotics intervention could be a potential preventative approach.

Gut microbiota modulates stress-induced hypertension through the HPA axis

Stress is associated with an increased risk of hypertension, and the incidence of stress-related hypertension has risen rapidly in recent years; however, the underlying mechanisms remain elusive. Gut dysbiosis has been demonstrated to contribute to hypertension and hyperactivation of the hypothalamus-pituitary-adrenal (HPA) axis. Based on our previous findings showing the altered gut microbiota in the rats of stress-induced hypertension (SIH), the present study aims to investigate whether the stress-induced alteration in gut microbiota can lead to the dysfunction of the HPA axis which contributes to the development of SIH. SIH was developed in rats subjected to electric foot-shock combined with buzzer noise stressors. The gut microbiota of rats were deleted by administering an antibiotic cocktail containing ampicillin (1 g/L), vancomycin (500 mg/L), neomycin (1 g/L), and metronidazole (1 g/L) in drinking water. The serum levels of adrenocorticotropic hormone (ACTH) and corticosterone (CORT) were tested using enzyme-linked immunosorbent assay (ELISA). The mRNA expression of glucocorticoid receptor (GR) and corticotropin-releasing factor (CRF), CRFR1 and CRFR2 was detected by quantitative reverse transcription polymerase chain reaction (qRT-PCR). The cellular protein expressions of corticotropin-releasing hormone (CRH), c-fos, and GR were examined by immunohistochemical staining. In the present study, SIH rats showed a hyperactive HPA axis as indicated by the increased CRH expression in the paraventricular nucleus (PVN) of the hypothalamus, the elevated serum ACTH or CORT concentrations, and increased adrenal gland index. The decreased GR expression and increased CRFR1 in the hypothalamus might underlie the hyperactivation of the HPA axis. The microbial deletion by antibiotics mitigated the hyperactivation of the HPA axis and attenuated the stress-induced elevation of blood pressure, indicating that the causal link of gut microbiota to SIH is mediated, at least in part, by the HPA axis activity. Our findings shed new light on the mechanisms underlying SIH.