Manipulation of gut microbiota blunts the ventilatory response to hypercapnia in adult rats

Impact of Nutrition on the Gut Microbiota: Implications for Parkinson's Disease

Parkinson's disease (PD) is a multifactorial neurodegenerative disease that is characterized by the degeneration of dopaminergic neurons in the substantia nigra pars compacta and by the anomalous accumulation of α-synuclein aggregates into Lewy bodies and Lewy neurites. Research suggests 2 distinct subtypes of PD: the brain-first subtype if the pathology arises from the brain and then spreads to the peripheral nervous system (PNS) and the body-first subtype, where the pathological process begins in the PNS and then spreads to the central nervous system. This review primarily focuses on the body-first subtype. The influence of the gut microbiota on the development of PD has been the subject of growing interest among researchers. It has been suggested that gut inflammation may be closely associated with pathogenesis in PD, therefore leading to the hypothesis that gut microbiota modulation could play a significant role in this process. Nutrition can influence gut health and alter the risk and progression of PD by altering inflammatory markers. This review provides an overview of recent research that correlates variations in gut microbiota composition between patients with PD and healthy individuals with the impact of certain nutrients and dietary patterns, including the Mediterranean diet, the Western diet, and the ketogenic diet. It explores how these diets influence gut microbiota composition and, consequently, the risk of PD. Last, it examines fecal transplantation and the use of prebiotics, probiotics, or synbiotics as potential therapeutic strategies to balance the gut microbiome, aiming to reduce the risk or delay the progression of PD.

Characteristics and clinical value of intestinal metabolites in 4 to 6-year-old children with OSAHS

OBJECTIVE

This study aims to explore the characteristics and functional changes of intestinal metabolites in children with obstructive sleep apnea hypopnea syndrome (OSAHS) aged 4-6 years old through metabolomic approaches, screen potential biomarkers and analyze their correlation with clinical indicators and preliminary discuss the roles of intestinal metabolites in the occurrence and development of OSAHS.

METHODS

We collected fecal samples from 40 OSAHS children and 40 healthy controls aged 4-6 years and recorded some OSAHS-related clinical indicators. Fecal specimens were used to detect all metabolites through untargeted metabolomics.

RESULTS

This study identified a total of 1164 intestinal metabolites and screened out 254 differential metabolites. In the OSAHS group, the relative content of 96 metabolites were higher than the control group, while the relative content of 158 metabolites were lower. The receiver operating characteristic curve analysis results showed that the area under the curve of 14 differential metabolites was greater than 0.8. The area under the curve of Formononetin is the highest, at 0.9100, with sensitivity and specificity of 82.5% and 90.0%, respectively, and is positively correlated with OAHI. The differential metabolite functions mainly include the metabolism of fatty acids and other lipid substances, cellular signaling, protein and amino acid related metabolism, disease-related functions, glucose metabolism, and vitamin metabolism.

CONCLUSION

The intestinal metabolites and metabolic function of 4-to-6-year-old children with OSAHS altered. There was a correlation between differential metabolites and clinical indicators such as uric acid, hemoglobin, and blood sugar, which has potential diagnostic value for OSAHS screening.

The role of the microbiota-gut-brain axis and artificial intelligence in cognitive health of pediatric obstructive sleep apnea: A narrative review

Pediatric obstructive sleep apnea (OSA) is a prevalent sleep-related breathing disorder associated with significant neurocognitive and behavioral impairments. Recent studies have highlighted the role of gut microbiota and the microbiota-gut-brain axis (MGBA) in influencing cognitive health in children with OSA. This narrative review aims to summarize current knowledge on the relationship between gut microbiota, MGBA, and cognitive function in pediatric OSA. It also explores the potential of artificial intelligence and machine learning in advancing this field and identifying novel therapeutic strategies. Pediatric OSA is associated with gut dysbiosis, reduced microbial diversity, and metabolic disruptions. MGBA mechanisms, such as endocrine, immune, and neural pathways, link gut microbiota to cognitive outcomes. Artificial intelligence and machine learning methodologies offer promising tools to uncover microbial markers and mechanisms associated with cognitive deficits in OSA. Future research should focus on validating these findings through clinical trials and developing personalized therapeutic approaches targeting the gut microbiota.

The microbiome is dispensable for normal respiratory function and chemoreflexes in mice

Increasing evidence indicates an association between microbiome composition and respiratory homeostasis and disease, particularly disordered breathing, such as obstructive sleep apnea. Previous work showing respiratory disruption is limited by the methodology employed to disrupt, eliminate, or remove the microbiome by antibiotic depletion. Our work utilized germ-free mice born without a microbiome and described respiratory alterations. We used whole-body flow through barometric plethysmography to assay conscious and unrestrained C57BL/6J germ-free (GF, n = 24) and specific-pathogen-free (SPF, n = 28) adult mice (with an intact microbiome) in normoxic (21% O2,79% N2) conditions and during challenges in hypercapnic (5% CO2, 21% O2, 74% N2) and hypoxic (10% O2, 90% N2) environments. Following initial plethysmography analysis, we performed fecal transplants to test the ability of gut microbiome establishment to rescue any observed phenotypes. Data were comprehensively analyzed using our newly published respiratory analysis software, Breathe Easy, to identify alterations in respiratory parameters, including ventilatory frequency, tidal volume, ventilation, apnea frequency, and sigh frequency. We also considered possible metabolic changes by analyzing oxygen consumption, carbon dioxide production, and ventilatory equivalents of oxygen. We also assayed GF and SPF neonates in an autoresuscitation assay to understand the effects of the microbiome on cardiorespiratory stressors in early development. We found several differences in baseline and recovery cardiorespiratory parameters in the neonates and differences in body weight at both ages studied. However, there was no difference in the overall survival of the neonates, and in contrast to prior studies utilizing gut microbial depletion, we found no consequential respiratory alterations in GF versus SPF adult mice at baseline or following fecal transplant in any groups. Interestingly, we did see alterations in oxygen consumption in the GF adult mice, which suggests an altered metabolic demand. Results from this study suggest that microbiome alteration in mice may not play as large a role in respiratory outcomes when a less severe methodology to eliminate the microbiome is utilized.

Targeted discovery of gut microbiome-remodeling compounds for the treatment of systemic inflammatory response syndrome

Systemic inflammatory response syndrome (SIRS) is a severe inflammatory response that can lead to organ dysfunction and death. Modulating the gut microbiome is a promising therapeutic approach for managing SIRS. This study assesses the therapeutic potential of the Xuanfei Baidu (XFBD) formula in treating SIRS. The results showed that XFBD administration effectively reduced mortality rates and inflammation in SIRS mice. Using 16S rRNA sequencing and fecal microbiota transplantation (FMT), we substantiated that the therapeutic effects of XFBD are partly attributed to gut microbiota modulation. We conducted in vitro experiments to accurately assess the gut microbiome remodeling effects of 51 compounds isolated from XFBD. These compounds exhibited varying abilities to induce a microbial structure that closely resembles that of the healthy control group. By quantifying their impact on microbial structure and clustering their regulatory patterns, we devised multiple gut microbiome remodeling compound (GMRC) cocktails. GMRC cocktail C, comprising aucubin, gentiopicroside, syringic acid, gallic acid, p-hydroxybenzaldehyde, para-hydroxybenzoic acid, and isoimperatorin, demonstrated superior efficacy in treating SIRS compared to a single compound or to other cocktails. Finally, in vitro experiments showcased that GMRC cocktail C effectively rebalanced bacteria composition in SIRS patients. This study underscores XFBD's therapeutic potential in SIRS and highlights the importance of innovative treatment approaches for this disease by targeting the gut microbiota.IMPORTANCEDeveloping effective treatment strategies for systemic inflammatory response syndrome (SIRS) is crucial due to its severe and often life-threatening nature. While traditional treatments like dexamethasone have shown efficacy, they also come with significant side effects and limitations. This study makes significant strides by demonstrating that the Xuanfei Baidu (XFBD) formula can substantially reduce mortality rates and inflammation in SIRS mice through effective modulation of the gut microbiota. By quantitatively assessing the impact of 51 compounds derived from XFBD on the gut microbiome, we developed a potent gut microbiome remodeling compound cocktail. This cocktail outperformed individual compounds and other mixtures in efficacy against SIRS. These findings highlight the potential of XFBD as a therapeutic solution for SIRS and underscore the critical role of innovative strategies targeting the gut microbiota in addressing this severe inflammatory condition.

SubSol-HIe is an AMPK-dependent hypoxia-responsive subnucleus of the nucleus tractus solitarius that coordinates the hypoxic ventilatory response and protects against apnoea in mice

Functional magnetic resonance imaging (fMRI) suggests that the hypoxic ventilatory response is facilitated by the AMP-activated protein kinase (AMPK), not at the carotid bodies, but within a subnucleus (Bregma -7.5 to -7.1 mm) of the nucleus tractus solitarius that exhibits right-sided bilateral asymmetry. Here, we map this subnucleus using cFos expression as a surrogate for neuronal activation and mice in which the genes encoding the AMPK-α1 (Prkaa1) and AMPK-α2 (Prkaa2) catalytic subunits were deleted in catecholaminergic cells by Cre expression via the tyrosine hydroxylase promoter. Comparative analysis of brainstem sections, relative to controls, revealed that AMPK-α1/α2 deletion inhibited, with right-sided bilateral asymmetry, cFos expression in and thus activation of a neuronal cluster that partially spanned three interconnected anatomical nuclei adjacent to the area postrema: SolDL (Bregma -7.44 mm to -7.48 mm), SolDM (Bregma -7.44 mm to -7.48 mm) and SubP (Bregma -7.48 mm to -7.56 mm). This approximates the volume identified by fMRI. Moreover, these nuclei are known to be in receipt of carotid body afferent inputs, and catecholaminergic neurons of SubP and SolDL innervate aspects of the ventrolateral medulla responsible for respiratory rhythmogenesis. Accordingly, AMPK-α1/α2 deletion attenuated hypoxia-evoked increases in minute ventilation (normalised to metabolism), reductions in expiration time, and increases sigh frequency, but increased apnoea frequency during hypoxia. The metabolic response to hypoxia in AMPK-α1/α2 knockout mice and the brainstem and spinal cord catecholamine levels were equivalent to controls. We conclude that within the brainstem an AMPK-dependent, hypoxia-responsive subnucleus partially spans SubP, SolDM and SolDL, namely SubSol-HIe, and is critical to coordination of active expiration, the hypoxic ventilatory response and defence against apnoea.

Croton tiglium L. seeds ameliorate loperamide-induced constipation via regulating gastrointestinal hormones and gut microbiota before and after processing

ETHNOPHARMACOLOGICAL RELEVANCE

Crotonis Fructus (CF), the seeds of Croton tiglium L., have been commonly used in the treatment of constipation for more than two thousand years in traditional Chinese medicine (TCM). CF needs to be processed before clinical use and Crotonis Semen Pulveratum (CP) is the processed cream of CF, which could reduce the drastic purgative action and gastrointestinal damages. However, the mechanism of CF and CP in the treatment of constipation is still unclear.

AIM OF THE STUDY

This study was to evaluate the effects of CF and CP on loperamide-induced constipation and the underlying mechanism.

MATERIALS AND METHODS

The chemical compositions of CF and CP were analyzed by UPLC-Q-TOF-MS. Constipated mouse model was established by loperamide (9.6 mg/kg, b.w., i.g.) for two weeks. After successful modeling, the mice were treated with CF or CP (45.5 and 136.5 mg/kg, b.w., i.g.) once a day for seven days. The physiological status, defecation indices, defecation time, and intestinal propulsion rate in mice were measured. Histopathologic examination and serum biochemical parameters were further estimated. 16S rDNA gene sequencing was carried out to characterize the effects of CF and CP on intestinal microbiome structure. Spearman correlation analysis was also performed to explore the association between gut microbiotic abundance and serum indices.

RESULTS

The results verified the therapeutic effects of CF and CP on loperamide-induced constipation. CF and CP could significantly ameliorate the reduction of fecal number, fecal weight, fecal water content, and intestinal propulsion rate in mice with constipation, and the first stool defecation time was also obviously reduced. Moreover, CF and CP could regulate the secretion of gastrointestinal hormones and inflammatory factors induced by constipation. Histopathologic examination showed that CP was superior to CF in relieving pathological injury and inflammatory cell infiltration. According to 16S rDNA sequencing, CF and CP treatment could improve gut microbiota disturbance in mice with constipation and the abundance of opportunistic pathogens such as Parabacteroides, Parasutterella and Bacillus remarkably declined, while the levels of beneficial bacterial such as Candidatus_Arthromitus significantly increased. Besides, CP may play a better role in correcting the intestinal flora disorder than CF, which was more obvious in the high-dose group. In addition, phytochemical analysis revealed the presence of diterpenoids and alkaloids in CF and CP.

CONCLUSIONS

CF and CP could ameliorate loperamide-induced constipation by regulating gastrointestinal hormones secretion, reducing the levels of inflammatory cytokines and improving the disturbance of gut microbiota. Moreover, CP was superior to CF in the enrichment of beneficial bacteria and reduction of harmful bacteria and histopathological damage induced by constipation, which may be related to the changes in the species and content of diterpenoids after processing. The study provides new evidence for the processing mechanism and clinical application of CF and CP.

Leveraging the microbiome to understand clinical heterogeneity in depression: findings from the T-RAD study

Alterations in the gut microbiome have been linked to a variety of mental illnesses including anxiety and depression. This study utilized advanced bioinformatics tools that integrated both the compositional and community nature of gut microbiota to investigate how gut microbiota influence clinical symptoms in a sample of participants with depression. Gut microbiota of 179 participants with major depressive disorder (MDD) in the Texas Resilience Against Depression (T-RAD) study were analyzed by 16S rRNA gene sequencing of stool samples. Severity of anxiety, depression, and anhedonia symptoms were assessed with General Anxiety Disorder - 7 item scale, Patient Health 9-item Questionnaire, and Dimensional Anhedonia Rating Scale, respectively. Using weighted correlation network analysis, a data-driven approach, three co-occurrence networks of bacterial taxa were identified. One of these co-occurrence networks was significantly associated with clinical features including depression and anxiety. The hub taxa associated with this co-occurrence module -one Ruminococcaceae family taxon, one Clostridiales vadinBB60 group family taxon, and one Christencenellaceae family taxon- were connected to several additional butyrate-producing bacteria suggesting that deficits in butyrate production may contribute to clinical symptoms. Therefore, by considering the community nature of the gut microbiome in a real world clinical sample, this study identified a gut microbial co-occurrence network that was significantly associated with clinical anxiety in a cohort of depressed individuals.

Repeated early-life exposure to anaesthesia and surgery causes subsequent anxiety-like behaviour and gut microbiota dysbiosis in juvenile rats

BACKGROUND

Early exposure to general anaesthetics for multiple surgeries or procedures might negatively affect brain development. Recent studies indicate the importance of microbiota in the development of stress-related behaviours. We determined whether repeated anaesthesia and surgery in early life cause gut microbiota dysbiosis and anxiety-like behaviours in rats.

METHODS

Sprague Dawley rats received skin incisions under sevoflurane 2.3 vol% three times during the first week of life. After 4 weeks, gut microbiota, anxiety-related behaviours, hippocampal serotonergic activity, and plasma stress hormones were tested. Subsequently, we explored the effect of faecal microbiota transplantation from multiple anaesthesia/surgery exposed rats after administration of a cocktail of antibiotics on anxiety-related behaviours.

RESULTS

Anxiety-like behaviours were observed in rats with repeated anaesthesia/surgery exposures: In the OF test, multiple anaesthesia/surgery exposures induced a decrease in the time spent in the centre compared to the Control group (P<0.05, t=3.05, df=16, Cohen's d=1.44, effect size=0.58). In the EPM test, rats in Multiple AS group travelled less (P<0.05, t=5.09, df=16, Cohen's d=2.40, effective size=0.77) and spent less time (P<0.05, t=3.58, df=16, Cohen's d=1.69, effect size=0.65) in the open arms when compared to the Control group. Repeated exposure caused severe gut microbiota dysbiosis, with exaggerated stress response (P<0.01, t=4.048, df=16, Cohen's d=-1.91, effect size=-0.69), a significant increase in the hippocampal concentration of 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) (P<0.05; for 5-HT: t=3.33, df=18, Cohen's d=-1.49, effect size=-0.60; for 5-HIAA: t=3.12, df=18, Cohen's d=-1.40, effect size=-0.57), and changes in gene expression of serotonergic receptors later in life (for Htr1a: P<0.001, t=4.49, df=16, Cohen's d=2.24, effect size=0.75; for Htr2c: P<0.01, t=3.72, df=16, Cohen's d=1.86, effect size=0.68; for Htr6: P<0.001, t=7.76, df=16, Cohen's d=3.88, effect size=0.89). Faecal microbiota transplantation led to similar anxiety-like behaviours and changes in the levels of 5-hydroxytryptamine and 5-hydroxyindoleacetic acid.

CONCLUSIONS

Gut microbiota dysbiosis caused by early repeated exposure to anaesthesia and surgery affects long-term anxiety emotion behaviours in rats.

The Role of Gut Bacteriome in Asthma, Chronic Obstructive Pulmonary Disease and Obstructive Sleep Apnoea

The human body contains a very complex and dynamic ecosystem of bacteria. The bacteriome interacts with the host bi-directionally, and changes in either factor impact the entire system. It has long been known that chronic airway diseases are associated with disturbances in the lung bacteriome. However, less is known about the role of gut bacteriome in the most common respiratory diseases. Here, we aim to summarise the evidence concerning the role of the intestinal bacteriome in the pathogenesis and disease course of bronchial asthma, chronic obstructive pulmonary disease, and obstructive sleep apnea. Furthermore, we discuss the consequences of an altered gut bacteriome on the most common comorbidities of these lung diseases. Lastly, we also reflect on the therapeutic potential of influencing the gut microbiome to improve disease outcomes.

The gut microbiome and obstructive sleep apnea syndrome in children

Obstructive sleep apnea syndrome (OSAS) in children has become a major public health problem that affects the physical and mental growth of children. OSAS can result in adverse outcomes during growth and development, inhibiting the normal development of the metabolic, cardiovascular, and immune systems. OSAS is characterized by partial or complete obstruction of the upper airway, and prolonged obstruction that causes intermittent hypoxia and sleep fragmentation in children. The human microbiota is a complex community that is in dynamic equilibrium in the human body. Intermittent hypoxia and sleep fragmentation induced by childhood OSAS alter the composition of the gut microbiome. At the same time, changes in the gut microbiome affect sleep patterns in children through immunomodulatory and metabolic mechanisms, and induce further comorbidities, such as obesity, hypertension, and cardiovascular disease. This article discusses recent progress in research into the mechanisms of OSAS-induced changes in the gut microbiota and its pathophysiology in children.

Cardiac vagal activity is associated with gut-microbiome patterns in women-An exploratory pilot study

Introduction

A functional reciprocity between the gut microbiome and vagal nerve activity has been suggested, however, human studies addressing this phenomenon are limited.

Methods

Twenty-four-hour cardiac vagal activity (CVA) was assessed from 73 female participants (aged 24.5 ± 4.3 years). Additionally, stool samples were subjected to 16SrRNA gene analysis (V1–V2). Quantitative Insights Into Microbial Ecology (QIIME) was used to analyse microbiome data. Additionally, inflammatory parameters (such as CRP and IL-6) were derived from serum samples.

Results

Daytime CVA correlated significantly with gut microbiota diversity (r_sp = 0.254, p = 0.030), CRP (r_sp = −0.348, p = 0.003), and IL-6 (r_sp = −0.320, p = 0.006). When the group was divided at the median of 24 h CVA (Mdn = 1.322), the following features were more abundant in the high CVA group: Clostridia (Linear discriminant analysis effect size (LDA) = 4.195, p = 0.029), Clostridiales (LDA = 4.195, p = 0.029), Lachnospira (LDA = 3.489, p = 0.004), Ruminococcaceae (LDA = 4.073, p = 0.010), Faecalibacterium (LDA = 3.982, p = 0.042), Lactobacillales (LDA = 3.317, p = 0.029), Bacilli (LDA = 3.294, p = 0.0350), Streptococcaceae (LDA = 3.353, p = 0.006), Streptococcus (LDA = 3.332, p = 0.011). Based on Dirichlet multinomial mixtures two enterotypes could be detected, which differed significantly in CVA, age, BMI, CRP, IL-6, and diversity.

Conclusions

As an indicator of gut-brain communication, gut microbiome analysis could be extended by measurements of CVA to enhance our understanding of signalling via microbiota-gut-brain-axis and its alterations through psychobiotics.

Alterations in gut microbiota and metabolites associated with altitude-induced cardiac hypertrophy in rats during hypobaric hypoxia challenge

The gut microbiota is involved in host responses to high altitude. However, the dynamics of intestinal microecology and their association with altitude-related illness are poorly understood. Here, we used a rat model of hypobaric hypoxia challenge to mimic plateau exposure and monitored the gut microbiome, short-chain fatty acids (SCFAs), and bile acids (BAs) over 28 d. We identified weight loss, polycythemia, and pathological cardiac hypertrophy in hypoxic rats, accompanied by a large compositional shift in the gut microbiota, which is mainly driven by the bacterial families of Prevotellaceae, Porphyromonadaceae, and Streptococcaceae. The aberrant gut microbiota was characterized by increased abundance of the Parabacteroides, Alistipes, and Lactococcus genera and a larger Bacteroides to Prevotella ratio. Trans-omics analyses showed that the gut microbiome was significantly correlated with the metabolic abnormalities of SCFAs and BAs in feces, suggesting an interaction network remodeling of the microbiome-metabolome after the hypobaric hypoxia challenge. Interestingly, the transplantation of fecal microbiota significantly increased the diversity of the gut microbiota, partially inhibited the increased abundance of the Bacteroides and Alistipes genera, restored the decrease of plasma propionate, and moderately ameliorated cardiac hypertrophy in hypoxic rats. Our results provide an insight into the longitudinal changes in intestinal microecology during the hypobaric hypoxia challenge. Abnormalities in the gut microbiota and microbial metabolites contribute to the development of high-altitude heart disease in rats.

Shen-Ling-Bai-Zhu-San (SL) and SL Derived-Polysaccharide (PL) Ameliorate the Severity of Diarrhea-Induced by High Lactose via Modification of Colonic Fermentation

In our previous study, we demonstrated that Shen-ling-bai-zhu-san (SL), a classical Chinese herbal formula, could alleviate lactose-induced diarrhea. However, little is known about the mechanism underlying SL action or the efficacy of the polysaccharide (PL) derived from SL. In this study, we investigated the effect of SL and PL on improving the dysregulated luminal and mucosal microbiota in rats with high lactose diet using 16S rRNA analysis. The concentrations of lactose, lactic acid in cecum and short-chain fatty acids (SCFAs) in cecum and portal vein were measured, meanwhile the expression of ion transporters were ascertained. Our data suggest that the SL, PL and cecal microbiota transplantation (CMT) significantly decreased fecal water content and water intake. In the luminal microbiota there was a significant increase in Akkermansia, Bifidobacterium and Blautia and a lower abundance of Lactobacillus, Escherichia-Shigella, and Dubosiella, while the mucosal microbiota showed a significant increase in Bifidobacterium, Akkermansia, Albaculum, Bilophila, and Coriobacteriaceae_UCG-002 and a lower abundance of Enterococcus, Helicobacter, Dubosiella, and Collinsella. Furthermore, the treatments enhanced lactose fermentation and SCFA production, which may be related to the modulation of the luminal microbial community. A lower ratio of phosphorylation Na/H exchanger3/Na/H exchanger3 (pNHE3/NHE3) and a higher sodium monocarboxylate1 (sMCT1) expression were found in the treatment group than in the model group, which may be related to the changes in the mucosal microbial community. Also, the treatments may restore the impacted metabolic pathways of gut microbiota. These results provide an important foundation for mechanism of SL action and developing PL-based treatment for lactose-induced diarrhea.

Effects of fecal stream deprivation on human intestinal barrier after loop ileostomy

BACKGROUND AND AIM

Intestinal homeostasis is closely associated with the normal intestinal luminal physiological environment. Temporary loop ileostomy changes the intestinal structure and diverts the fecal stream, thereby disturbing the intestinal environment. This study aimed to clarify the changing situation of the human intestinal mucosa barrier in the absence of a fecal stream after loop ileostomy.

METHODS

We obtained paired samples from the fed (fecal stream maintained) and unfed (no fecal stream) portions of the loop ileostomy and subjected these samples to RNA sequencing. We also determined transepithelial electrical resistance. The mucus layer thickness and content of MUC2, tight junction proteins, and common antimicrobial peptides in ileum mucosa were studied.

RESULTS

Transcriptome data revealed that genes associated with enhancing the intestinal barrier function of the unfed ileum were significantly decreased and genes associated with immune defense response were significantly increased. The transepithelial electrical resistance was lower and the mucus layer thickness was thinner in the unfed ileal mucosa than in the fed ileum. The MUC2, Occludin, and zonula occludens 1 content was lower in the unfed ileum than in the fed ileum. α-Defensin 5, α-defensin 6, and lysozyme content was higher in the unfed ileum than in the enterally fed ileum.

CONCLUSION

Intestinal barrier function is weakened after long-term fecal diversion, but antimicrobiota defense function is strengthened. Thus, the intestinal mucosa barrier adopts an alternative stable state during fecal diversion, which may explain the clinical paucity of cases of enterogenic infection caused by loop ileostomy.

Exogenous lipase administration alters gut microbiota composition and ameliorates Alzheimer's disease-like pathology in APP/PS1 mice

Alzheimer's disease (AD) represents the most common form of dementia in the elderly with no available disease modifying treatments. Altered gut microbial composition has been widely acknowledged as a common feature of AD, which potentially contributes to progression or onset of AD. To assess the hypothesis that Candida rugosa lipase (CRL), which has been shown to enhance gut microbiome and metabolite composition, can rebalance the gut microbiome composition and reduce AD pathology, the treatment effects in APPswe/PS1de9 (APP/PS1) mice were investigated. The analysis revealed an increased abundance of Acetatifactor and Clostridiales vadin BB60 genera in the gut; increased lipid hydrolysis in the gut lumen, normalization of peripheral unsaturated fatty acids, and reduction of neuroinflammation and memory deficits post treatment. Finally, we demonstrated that the evoked benefits on memory could be transferred via fecal matter transplant (FMT) into antibiotic-induced microbiome-depleted (AIMD) wildtype mice, ameliorating their memory deficits. The findings herein contributed to improve our understanding of the role of the gut microbiome in AD's complex networks and suggested that targeted modification of the gut could contribute to amelioration of AD neuropathology.

A Randomized Double-Blind Placebo-Controlled Evaluation of the Safety and Efficacy of Wild Sage Metabolites in Preventing Snoring, Improving Sleep, and Activating Alpha Wave Brain Frequencies in Healthy Adults

Upper airway problems and stress can cause sleep disorders. The present study was designed to evaluate the efficacy and safety of wild sage metabolites (WSM) for snoring treatment and alpha wave activation in healthy men and women. A total of 42 subjects compliant with inclusion criteria were randomly assigned to one of the two groups, viz. Group 1-WSM and Group 2-Placebo, using a simple randomization process. Consumption of WSM by healthy men and women resulted in the decrease of Pittsburgh Sleep Quality Index (PSQI) global score by 29%, improved assessment by their sleep mates, and increased alpha brain wave by 55%. In conclusion, medication with WSM resulted in significant reduced snoring, stress, and improved sleep quality after 30 days, with a good tolerance among subjects. No side effects or adverse events were reported during the study. Hence, WSM at 450 mg/day could be recommended as an effective agent for snoring treatment, improving the quality of sleep, and stress reduction.

Establishment and evaluation of a specific antibiotic-induced inflammatory bowel disease model in rats

Physical and chemical methods for generating rat models of enteritis have been established; however, antibiotic induction has rarely been used for this purpose. The present study aimed to establish and evaluate a rat model of inflammatory bowel disease (IBD) using antibiotics. A total of 84 Sprague-Dawley (SD) rats were divided into the following groups, according to the dosage and method of administration of the antibiotics: A, control; B, low-dose clindamycin; C, medium-dose clindamycin; D, high-dose clindamycin; E, low-dose clindamycin, ampicillin and streptomycin; F, medium-dose clindamycin, ampicillin and streptomycin; and G, high-dose clindamycin, ampicillin and streptomycin. Antibiotic administration was stopped on day 7; the modeling period covered days 1-7, and the recovery period covered days 8-15. Half of the animals were dissected on day 11, with the remaining animals dissected on day 15. Food and water intake, body weight and fecal weight were recorded. Intestinal flora was analyzed via microbial culture and quantitative PCR. The content of TNF-α, IL1-β, IL-6 and C-reactive protein (CRP) was assessed in abdominal aorta blood. Colonic and rectal tissues were examined pathologically via hematoxylin-eosin staining to assess leukocyte infiltration and intestinal mucosal changes as indicators of inflammation. Rat weight, food intake, water intake and 2-h fecal weight were significantly different across the experimental groups (P = 0.040, P = 0.016, P<0.001 and P = 0.009, respectively). Microbial cultures revealed no significant differences between group A and B,C (P = 0.546,0.872) but significant differences betwenn group A and the other experimental groups (all P<0.001). Furthermore, significant differences in the levels of Bacteroides, Faecalibacterium prausnitzii and Dialister invisus on day 4 between groups A, C and F (P = 0.033, P = 0.025 and P = 0.034, respectively). Significant differences were detected in the levels of TNF-α, IL1-β, IL-6 and CRP between the groups (all P<0.001). The colonic and rectal pathological inflammation scores of the experimental groups were significantly different compared with group A (B vs. A, P = 0.002; others, all P<0.001). These findings indicated that an antibiotic-induced IBD model was successfully established in SD rats; this animal model may serve as a useful model for clinical IBD research.

The link between brain acidosis, breathing and seizures: a novel mechanism of action for the ketogenic diet in a model of infantile spasms

Infantile spasms (IS) syndrome is a catastrophic, epileptic encephalopathy of infancy that is often refractory to current antiepileptic therapies. The ketogenic diet (KD) has emerged as an alternative treatment for patients with medically intractable epilepsy, though the prospective validity and mechanism of action for IS remains largely unexplored. We investigated the KD's efficacy as well as its mechanism of action in a rodent model of intractable IS. The spasms were induced using the triple-hit paradigm and the animals were then artificially reared and put on either the KD (4:1 fats: carbohydrate + protein) or a control milk diet (CM; 1.7:1). ³¹Phosphorus magnetic resonance spectroscopy (³¹P MRS) and head-out plethysmography were examined in conjunction with continuous video-EEG behavioural recordings in lesioned animals and sham-operated controls. The KD resulted in a peripheral ketosis observed both in the blood and urine. The KD led to a robust reduction in the frequency of spasms observed, with approximately a 1.5-fold increase in the rate of survival. Intriguingly, the KD resulted in an intracerebral acidosis as measured with ³¹P MRS. In addition, the respiratory profile of the lesioned rats on the KD was significantly altered with slower, deeper and longer breathing, resulting in decreased levels of expired CO₂. Sodium bicarbonate supplementation, acting as a pH buffer, partially reversed the KD's protective effects on spasm frequency. There were no differences in the mitochondrial respiratory profiles in the liver and brain frontal cortex measured between the groups, supporting the notion that the effects of the KD on breathing are not entirely due to changes in intermediary metabolism. Together, our results indicate that the KD produces its anticonvulsant effects through changes in respiration leading to intracerebral acidosis. These findings provide a novel understanding of the mechanisms underlying the anti-seizure effects of the KD in IS. Further research is required to determine whether the effects of the KD on breathing and intracerebral acid-base balance are seen in other paediatric models of epilepsy.

Gut Microbial Changes and their Contribution to Post-Burn Pathology

ABSTRACT

Burn injuries are a common form of traumatic injury that leads to significant morbidity and mortality worldwide. Burn injuries are characterized by inflammatory processes and alterations in numerous organ systems and functions. Recently, it has become apparent that the gastrointestinal bacterial microbiome is a key component of regulating the immune response and recovery from burn and can also contribute to significant detrimental sequelae after injury, such as sepsis and multiple organ failure. Microbial dysbiosis has been linked to multiple disease states; however, its role in exacerbating acute traumatic injuries, such as burn, is poorly understood. In this article, we review studies that document changes in the intestinal microbiome after burn injury, assess the implications in post-burn pathogenesis, and the potential for further discovery and research.

Silent hypoxia in COVID-19: a gut microbiota connection

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection has triggered the COVID-19 pandemic. Several factors induce hypoxia in COVID-19. Despite being hypoxic, some SARS-CoV-2-infected individuals do not experience any respiratory distress, a phenomenon termed ‘silent (or happy) hypoxia’. Prolonged undetected hypoxia could be dangerous, sometimes leading to death. A few studies attempted to unravel what causes silent hypoxia, however, the exact mechanisms are still elusive. Here, we aim to understand how SARS-CoV-2 causes silent hypoxia.

The role of NADPH oxidase in chronic intermittent hypoxia-induced respiratory plasticity in adult male mice

Reactive oxygen species (ROS) are proposed as mediators of chronic intermittent hypoxia (CIH)-induced respiratory plasticity. We sought to determine if NADPH oxidase 2 (NOX2)-derived ROS underpin CIH-induced maladaptive changes in respiratory control. Adult male mice (C57BL/6 J) were assigned to one of three groups: normoxic controls (sham); chronic intermittent hypoxia-exposed (CIH, 12 cycles/hour, 8 h/day for 14 days); and CIH + apocynin (NOX2 inhibitor, 2 mM) given in the drinking water throughout exposure to CIH. In addition, we studied sham and CIH-exposed NOX2-null mice (B6.129S-Cybb^TM1Din/J). Whole-body plethysmography was used to measure breathing and metabolic parameters. Ventilation (V̇_I/V̇CO₂) during normoxia was unaffected by CIH, but apnoea index was increased, which was prevented by apocynin, but not by NOX2 deletion. The ventilatory response to hypercapnia following exposure to CIH was potentiated in NOX2-null mice. Our results reveal ROS-dependent influences on the control of breathing and point to antioxidant intervention as a potential adjunctive therapeutic strategy in respiratory control disorders.

Gutted! Unraveling the Role of the Microbiome in Major Depressive Disorder

Microorganisms can be found in virtually any environment. In humans, the largest collection of microorganisms is found in the gut ecosystem. The adult gut microbiome consists of more genes than its human host and typically spans more than 60 genera from across the taxonomic tree. In addition, the gut contains the largest number of neurons in the body, after the brain. In recent years, it has become clear that the gut microbiome is in communication with the brain, through the gut-brain axis. A growing body of literature shows that the gut microbiome plays a shaping role in a variety of psychiatric disorders, including major depressive disorder (MDD). In this review, the interplay between the microbiome and MDD is discussed in three facets. First, we discuss factors that affect the onset/development of MDD that also greatly impinge on the composition of the gut microbiota-especially diet and stressful life events. We then examine the interplay between the microbiota and MDD. We examine evidence suggesting that the microbiota is altered in MDD, and we discuss why the microbiota should be considered during MDD treatment. Finally, we look toward the future and examine how the microbiota might become a therapeutic target for MDD. This review is intended to introduce those familiar with the neurological and psychiatric aspects of MDD to the microbiome and its potential role in the disorder. Although research is in its very early days, with much yet to be the understood, the microbiome is offering new avenues for developing potentially novel strategies for managing MDD.

Aqueous extracts of Aconite promote thermogenesis in rats with hypothermia via regulating gut microbiota and bile acid metabolism

Background

Intermittent or prolonged exposure to severe cold stress disturbs energy homeostasis and can lead to hypothermia, heart failure, Alzheimer’s disease, and so on. As the typical “hot” traditional Chinese medicine, Aconite has been widely used to treat cold-associated diseases for thousands of years, but its critical mechanisms for the promotion of thermogenesis are not fully resolved. Gut microbiota and its metabolites play a crucial role in maintaining energy homeostasis. Here, we investigated whether the aqueous extracts of Aconite (AA) can enhance thermogenesis through modulation of the composition and metabolism of gut microbiota in hypothermic rats.

Methods

The therapeutic effects of AA on body temperature, energy intake, and the histopathology of white adipose tissue and brown adipose tissue of hypothermic rats were assessed. Microbiota analysis based on 16 S rRNA and targeted metabolomics for bile acids (BAs) were used to evaluate the composition of gut microbiota and BAs pool. The antibiotic cocktail treatment was adopted to further confirm the relationship between the gut microbiota and the thermogenesis-promoting effects of AA.

Results

Our results showed a sharp drop in rectal temperature and body surface temperature in hypothermic rats. Administration of AA can significantly increase core body temperature, surface body temperature, energy intake, browning of white adipose tissue, and thermogenesis of brown adipose tissue. Importantly, these ameliorative effects of AA were accompanied by the shift of the disturbed composition of gut microbiota toward a healthier profile and the increased levels of BAs. In addition, the depletion of gut microbiota and the reduction of BAs caused by antibiotic cocktails reduced the thermogenesis-promoting effect of AA.

Conclusions

Our results demonstrated that AA promoted thermogenesis in rats with hypothermia via regulating gut microbiota and BAs metabolism. Our findings can also provide a novel solution for the treatment of thermogenesis-associated diseases such as rheumatoid arthritis, obesity, and type 2 diabetes.

The Microbiome in Obstructive Sleep Apnea

Recent evidence has highlighted important associations between obstructive sleep apnea and the microbiome. Although the intricacies of the pathophysiologic mechanisms are not well understood, available evidence suggests a bidirectional relationship between OSA and microbiota composition. Sleep fragmentation, intermittent hypoxia, and intermittent hypercapnia all play significant roles in altering the microbiome, and initial evidence has shown that alterations of the microbiota affect sleep patterns. Animal model evidence strongly supports the idea that the microbiome mediates disease states associated with OSA including hypertension, atherosclerosis, and obesity. The majority of evidence focuses on changes in the gut microbiome, which may result from OSA as well as contribute to sleep pattern changes, OSA-related CVD, and obesity. Meanwhile, a developing body of work suggests changes in the upper airway microbiome may be associated with OSA and periodontitis-related oral cavity microbiome changes may have significance in OSA-related CVD. Lastly, while evidence is limited, several studies suggest there may be a role for treatment of OSA and OSA-related comorbidities through alteration of the microbiome with probiotics, prebiotics, and microbiota transplantation. These early animal and human studies begin to characterize the interrelationships of the microbiome and OSA and may lead to new avenues for treatment.

Volatility as a Concept to Understand the Impact of Stress on the Microbiome

The microbiome-gut-brain-axis is a complex phenomenon spanning several dynamic systems in the body which can be parsed at a molecular, cellular, physiological and ecological level. A growing body of evidence indicates that this axis is particularly sensitive to the effects of stress and that it may be relevant to stress resilience and susceptibility. Although stress-induced changes in the composition of the microbiome have been reported, the degree of compositional change over time, which we define as volatility, has not been the subject of in-depth scrutiny. Using a chronic psychosocial stress paradigm in male mice, we report that the volatility of the microbiome significantly correlated with several readouts of the stress response, including behaviour and corticosterone response. We then validated these findings in a second independent group of stressed mice. Additionally, we assessed the relationship between volatility and stress parameters in a cohort of health volunteers who were undergoing academic exams and report similar observations. Finally, we found inter-species similarities in the microbiome stress response on a functional level. Our research highlights the effects of stress on the dynamic microbiome and underscores the informative value of volatility as a parameter that should be considered in all future analyses of the microbiome.

Acute effects of increased gut microbial fermentation on the hypoxic ventilatory response in humans

NEW FINDINGS

What is the central question of this study? Is there a link between gut microbial fermentation and ventilatory responsiveness to hypoxia in humans? What is the main finding and its importance? Increased gut microbial fermentation is associated with augmented ventilatory (but not haemodynamic) responses to transient hypoxia. These findings imply a capacity for gut microbiota to modulate the peripheral chemoreflex response to hypoxia in humans.

ABSTRACT

Recent animal data indicate the presence of a bidirectional link between gut microbial activity and respiratory control. Nevertheless, the presence of a similar association between gut microbiota and peripheral chemoreceptor responsiveness to hypoxia in humans has not been reported to date. Therefore, we performed a within subject, placebo-controlled study in a group of 16 healthy individuals (eight men; mean ± SD age 25.9 ± 5.2 years). Participants underwent two tests (in a random order), receiving lactulose, which stimulates gut fermentation, or placebo. Ventilatory and haemodynamic responses to transient hypoxia were evaluated before and 2 h after the test meal. The magnitude of these responses was related to the net hydrogen content in the exhaled air, reflecting gut fermentation intensity. A lactulose meal, compared to placebo, caused an increase in the minute ventilation (Hyp-VI; l/min/ S p O 2 ) and breathing rate (Hyp-BR; breaths/min/ S p O 2 ) responses to hypoxia (for Hyp-VI, mean ± SD -0.03 ± 0.059 in placebo test vs. 0.05 ± 0.116 in lactulose test, P = 0.03; for Hyp-BR, -0.015 ± 0.046 vs. 0.034 ± 0.054, P = 0.01). The magnitude of these responses was positively correlated with the lactulose-induced hydrogen excretion (for Hyp-VI, r = 0.62, P = 0.01; for Hyp-BR, r = 0.73, P = 0.001). Changes in the resting parameters during normoxia did not differ significantly between the tests. Our results demonstrate that the increased gut microbial fermentation is associated with augmented ventilatory (but not haemodynamic) responses to the transient hypoxia, which implies a capacity for gut microbiota to modulate the peripheral chemoreflex in humans.

Using Cordyceps militaris extracellular polysaccharides to prevent Pb2+-induced liver and kidney toxicity by activating Nrf2 signals and modulating gut microbiota

In this study, we investigated the protective efficacy of extracellular polysaccharide from Cordyceps militaris (CEP-I) in liver and kidney and their regulating effect on gut microbiota against Pb-induced toxicity in vivo. The results indicated that CEP-I could reduce the Pb2+ content and organ index of liver and kidney in mice. Besides, biochemical analysis showed that CEP-I could improve the activity of glutathione peroxidase (GSH-Px), malondialdehyde (MDA) and superoxide dismutase (SOD) in serum and organs, restore the physiological indexes of total protein (TP), albumin (ALB), blood urea nitrogen (BUN) and creatinine (CRE) in serum and decrease the enzyme activity of lactate dehydrogenase (LDH) and aspartate aminotransferase (AST) in the liver and kidney of mice poisoned by Pb2+. This indicated that CEP-I has a protective effect on organs against damage in mice. In addition, CEP-I could regulate the expression of key proteins in the Nrf2 signaling pathway, including NF-E2-related factor 2 (Nrf2), Kelch-like ECH-associated protein-1 (Keap1), Heme oxygenase (HO-1) and NAD(P)H: quinone oxidoreductase 1 (NQO1). Furthermore, the intestinal flora analysis results indicated that CEP-I also has the capacity to regulate the intestinal flora imbalance caused by Pb2+ in poisoned mice. In conclusion, we hope that this study can provide theoretical basis for the treatment of tissue damage induced by Pb2+.

Prebiotic administration modulates gut microbiota and faecal short-chain fatty acid concentrations but does not prevent chronic intermittent hypoxia-induced apnoea and hypertension in adult rats

BACKGROUND

Evidence is accruing to suggest that microbiota-gut-brain signalling plays a regulatory role in cardiorespiratory physiology. Chronic intermittent hypoxia (CIH), modelling human sleep apnoea, affects gut microbiota composition and elicits cardiorespiratory morbidity. We investigated if treatment with prebiotics ameliorates cardiorespiratory dysfunction in CIH-exposed rats.

METHODS

Adult male rats were exposed to CIH (96 cycles/day, 6.0% O2 at nadir) for 14 consecutive days with and without prebiotic supplementation (fructo- and galacto-oligosaccharides) beginning two weeks prior to gas exposures.

FINDINGS

CIH increased apnoea index and caused hypertension. CIH exposure had modest effects on the gut microbiota, decreasing the relative abundance of Lactobacilli species, but had no effect on microbial functional characteristics. Faecal short-chain fatty acid (SCFA) concentrations, plasma and brainstem pro-inflammatory cytokine concentrations and brainstem neurochemistry were unaffected by exposure to CIH. Prebiotic administration modulated gut microbiota composition and diversity, altering gut-metabolic (GMMs) and gut-brain (GBMs) modules and increased faecal acetic and propionic acid concentrations, but did not prevent adverse CIH-induced cardiorespiratory phenotypes.

INTERPRETATION

CIH-induced cardiorespiratory dysfunction is not dependant upon changes in microbial functional characteristics and decreased faecal SCFA concentrations. Prebiotic-related modulation of microbial function and resultant increases in faecal SCFAs were not sufficient to prevent CIH-induced apnoea and hypertension in our model. Our results do not exclude the potential for microbiota-gut-brain axis involvement in OSA-related cardiorespiratory morbidity, but they demonstrate that in a relatively mild model of CIH, sufficient to evoke classic cardiorespiratory dysfunction, such changes are not obligatory for the development of morbidity, but may become relevant in the elaboration and maintenance of cardiorespiratory morbidity with progressive disease.

FUNDING

Department of Physiology and APC Microbiome Ireland, University College Cork, Ireland. APC Microbiome Ireland is funded by Science Foundation Ireland, through the Government's National Development Plan.

Dietary Wheat Amylase Trypsin Inhibitors Impact Alzheimer's Disease Pathology in 5xFAD Model Mice

Wheat amylase trypsin inhibitors (ATIs) represent a common dietary protein component of gluten-containing cereals (wheat, rye, and barley). They act as toll-like receptor 4 ligands, and are largely resistant to intestinal proteases, eliciting a mild inflammatory response within the intestine after oral ingestion. Importantly, nutritional ATIs exacerbated inflammatory bowel disease and features of fatty liver disease and the metabolic syndrome in mice. For Alzheimer’s disease (AD), both inflammation and altered insulin resistance are major contributing factors, impacting onset as well as progression of this devastating brain disorder in patients. In this study, we evaluated the impact of dietary ATIs on a well-known rodent model of AD (5xFAD). We assessed metabolic, behavioral, inflammatory, and microbial changes in mice consuming different dietary regimes with and without ATIs, consumed ad libitum for eight weeks. We demonstrate that ATIs, with or without a gluten matrix, had an impact on the metabolism and gut microbiota of 5xFAD mice, aggravating pathological hallmarks of AD. If these findings can be translated to patients, an ATI-depleted diet might offer an alternative therapeutic option for AD and warrants clinical intervention studies.

Bugs, breathing and blood pressure: microbiota-gut-brain axis signalling in cardiorespiratory control in health and disease

There is clear evidence of physiological effects of the gut microbiota on whole-body function in health and disease. Microbiota-gut-brain axis signalling is recognised as a key player in behavioural disorders such as depression and anxiety. Recent evidence suggests that the gut microbiota affects neurocontrol networks responsible for homeostatic functions that are essential for life. We consider the evidence suggesting the potential for the gut microbiota to shape cardiorespiratory homeostasis. In various animal models of disease, there is an association between cardiorespiratory morbidity and perturbed gut microbiota, with strong evidence in support of a role of the gut microbiota in the control of blood pressure. Interventions that target the gut microbiota or manipulate the gut-brain axis, such as short-chain fatty acid supplementation, prevent hypertension in models of obstructive sleep apnoea. Emerging evidence points to a role for the microbiota-gut-brain axis in the control of breathing and ventilatory responsiveness, relevant to cardiorespiratory disease. There is also evidence for an association between the gut microbiota and disease severity in people with asthma and cystic fibrosis. There are many gaps in the knowledge base and an urgent need to better understand the mechanisms by which gut health and dysbiosis contribute to cardiorespiratory control. Nevertheless, there is a growing consensus that manipulation of the gut microbiota could prove an efficacious adjunctive strategy in the treatment of common cardiorespiratory diseases, which are the leading causes of morbidity and mortality.

AMPK and the Need to Breathe and Feed: What's the Matter with Oxygen?

We live and to do so we must breathe and eat, so are we a combination of what we eat and breathe? Here, we will consider this question, and the role in this respect of the AMP-activated protein kinase (AMPK). Emerging evidence suggests that AMPK facilitates central and peripheral reflexes that coordinate breathing and oxygen supply, and contributes to the central regulation of feeding and food choice. We propose, therefore, that oxygen supply to the body is aligned with not only the quantity we eat, but also nutrient-based diet selection, and that the cell-specific expression pattern of AMPK subunit isoforms is critical to appropriate system alignment in this respect. Currently available information on how oxygen supply may be aligned with feeding and food choice, or vice versa, through our motivation to breathe and select particular nutrients is sparse, fragmented and lacks any integrated understanding. By addressing this, we aim to provide the foundations for a clinical perspective that reveals untapped potential, by highlighting how aberrant cell-specific changes in the expression of AMPK subunit isoforms could give rise, in part, to known associations between metabolic disease, such as obesity and type 2 diabetes, sleep-disordered breathing, pulmonary hypertension and acute respiratory distress syndrome.

The impact of preterm adversity on cardiorespiratory function

NEW FINDINGS

What is the topic of this review? We review the influence of prematurity on the cardiorespiratory system and examine the common sequel of alterations in oxygen tension, and immune activation in preterm infants. What advances does it highlight? The review highlights neonatal animal models of intermittent hypoxia, hyperoxia and infection that contribute to our understanding of the effect of stress on neurodevelopment and cardiorespiratory homeostasis. We also focus on some of the important physiological pathways that have a modulatory role on the cardiorespiratory system in early life.

ABSTRACT

Preterm birth is one of the leading causes of neonatal mortality. Babies that survive early-life stress associated with immaturity have significant prevailing short- and long-term morbidities. Oxygen dysregulation in the first few days and weeks after birth is a primary concern as the cardiorespiratory system slowly adjusts to extrauterine life. Infants exposed to rapid alterations in oxygen tension, including exposures to hypoxia and hyperoxia, have altered redox balance and active immune signalling, leading to altered stress responses that impinge on neurodevelopment and cardiorespiratory homeostasis. In this review, we explore the clinical challenges posed by preterm birth, followed by an examination of the literature on animal models of oxygen dysregulation and immune activation in the context of early-life stress.

The Microbiota-Gut-Brain Axis

The importance of the gut-brain axis in maintaining homeostasis has long been appreciated. However, the past 15 yr have seen the emergence of the microbiota (the trillions of microorganisms within and on our bodies) as one of the key regulators of gut-brain function and has led to the appreciation of the importance of a distinct microbiota-gut-brain axis. This axis is gaining ever more traction in fields investigating the biological and physiological basis of psychiatric, neurodevelopmental, age-related, and neurodegenerative disorders. The microbiota and the brain communicate with each other via various routes including the immune system, tryptophan metabolism, the vagus nerve and the enteric nervous system, involving microbial metabolites such as short-chain fatty acids, branched chain amino acids, and peptidoglycans. Many factors can influence microbiota composition in early life, including infection, mode of birth delivery, use of antibiotic medications, the nature of nutritional provision, environmental stressors, and host genetics. At the other extreme of life, microbial diversity diminishes with aging. Stress, in particular, can significantly impact the microbiota-gut-brain axis at all stages of life. Much recent work has implicated the gut microbiota in many conditions including autism, anxiety, obesity, schizophrenia, Parkinson’s disease, and Alzheimer’s disease. Animal models have been paramount in linking the regulation of fundamental neural processes, such as neurogenesis and myelination, to microbiome activation of microglia. Moreover, translational human studies are ongoing and will greatly enhance the field. Future studies will focus on understanding the mechanisms underlying the microbiota-gut-brain axis and attempt to elucidate microbial-based intervention and therapeutic strategies for neuropsychiatric disorders.