Prenatal stress disrupts social behavior, cortical neurobiology and commensal microbes in adult male offspring

Postweaning sodium citrate exposure induces long-lasting and sex-dependent effects on social behaviours in mice

BACKGROUND

Postweaning is a pivotal period for brain development and individual growth. As an important chemical used in medicines, foods and beverages, sodium citrate (SC) is commonly available. Although some effects of SC exposure on individual physiology have been demonstrated, the potential long-lasting effects of postweaning dietary SC exposure on social behaviours are still elusive.

METHODS

Both postweaning male and female C57BL/6 mice were exposed to SC through drinking water for a total of 3 weeks. A series of behavioural tests, including social dominance test (SDT), social interaction test (SIT), bedding preference test (BPT) and sexual preference test (SPT), were performed in adolescence and adulthood. After these tests, serum oxytocin (OT) levels and gut microbiota were detected.

RESULTS

The behavioural results revealed that postweaning SC exposure decreased the social dominance of male mice in adulthood and female mice in both adolescence and adulthood. SC exposure also reduced the sexual preference rates of both males and females, while it had no effect on social interaction behaviour. ELISA results indicated that SC exposure decreased the serum OT levels of females but not males. 16S rRNA sequencing analysis revealed a significant difference in β-diversity after SC exposure in both males and females. The correlation coefficient indicated the correlation between social behaviours, OT levels and dominant genera of gut microbiota.

CONCLUSION

Our findings suggest that postweaning SC exposure may have enduring and sex-dependent effects on social behaviours, which may be correlated with altered serum OT levels and gut microbiota composition.

Prenatal stress alters transcription of NMDA-type glutamate receptors in the hippocampus

Prenatal stress increases the risk of neurodevelopmental disorders. NMDA-type glutamate receptor (NMDAR) activity plays an important pathophysiological role in the cortico-hippocampal circuit in these disorders. We tested the hypothesis that transcription of NMDAR subunits is modified in the frontal cortex (FCx) and hippocampus after exposure to prenatal restraint stress (PRS) in mice. At 10 weeks of age, male PRS offspring (n = 20) and non-stressed controls (NS, n = 20) were treated with haloperidol (1 mg/kg), clozapine (5 mg/kg) or saline twice daily for 5 days, before measuring social approach (SOC). Saline-treated and haloperidol-treated PRS mice had reduced SOC relative to NS (P < 0.01), but clozapine-treated PRS mice had similar SOC to NS mice. These effects of PRS were associated with increased transcription of NMDAR subunits encoded by GRIN2A and GRIN2B genes in the hippocampus but not FCx. GRIN transcription in FCx correlated positively with SOC, but hippocampal GRIN transcription had negative correlation with SOC. The ratio of GRIN2A/GRIN2B transcription is known to increase during development but was lower in PRS mice. These results suggest that GRIN2A and GRIN2B transcript levels are modified in the hippocampus by PRS, leading to life-long deficits in social behavior. These data have some overlap with the molecular pathophysiology of schizophrenia. Similar to PRS in mice, schizophrenia, has been associated with social withdrawal, with increased GRIN2 expression in the hippocampus, and reduced GRIN2A/GRIN2B expression ratios in the hippocampus. These findings suggest that PRS in mice may have construct validity as a preclinical model for antipsychotic drug development.

Prenatal stress impacts foetal neurodevelopment: Temporal windows of gestational vulnerability

Prenatal maternal stressors ranging in severity from everyday occurrences/hassles to the experience of traumatic events negatively impact neurodevelopment, increasing the risk for the onset of psychopathology in the offspring. Notably, the timing of prenatal stress exposure plays a critical role in determining the nature and severity of subsequent neurodevelopmental outcomes. In this review, we evaluate the empirical evidence regarding temporal windows of heightened vulnerability to prenatal stress with respect to motor, cognitive, language, and behavioural development in both human and animal studies. We also explore potential temporal windows whereby several mechanisms may mediate prenatal stress-induced neurodevelopmental effects, namely, excessive hypothalamic-pituitary-adrenal axis activity, altered serotonin signalling and sympathetic-adrenal-medullary system, changes in placental function, immune system dysregulation, and alterations of the gut microbiota. While broadly defined developmental windows are apparent for specific psychopathological outcomes, inconsistencies arise when more complex cognitive and behavioural outcomes are considered. Novel approaches to track molecular markers reflective of the underlying aetiologies throughout gestation to identify tractable biomolecular signatures corresponding to critical vulnerability periods are urgently required.

Stress and depression-associated shifts in gut microbiota: A pilot study of human pregnancy

Background

Psychosocial stress and mood-related disorders, such as depression, are prevalent and vulnerability to these conditions is heightened during pregnancy. Psychosocial stress induces consequences via several mechanisms including the gut microbiota-brain axis and associated signaling pathways. Previous preclinical work indicates that prenatal stress alters maternal gut microbial composition and impairs offspring development. Importantly, although the fecal and vaginal microenvironments undergo alterations across pregnancy, we lack consensus regarding which shifts are adaptive or maladaptive in the presence of prenatal stress and depression. Clinical studies interrogating these relationships have identified unique taxa but have been limited in study design.

Methods

We conducted a prospective cohort study of pregnant individuals consisting of repeated administration of psychometrics (Perceived Stress Scale (PSS) and Center for Epidemiological Studies Depression Scale (CES-D)) and collection of fecal and vaginal microbiome samples. Fecal and vaginal microbial community composition across psychometric responses were interrogated using full-length 16S rRNA sequencing followed by α and β-diversity metrics and taxonomic abundance.

Results

Early pregnancy stress was associated with increased abundance of fecal taxa not previously identified in related studies, and stress from late pregnancy through postpartum was associated with increased abundance of typical vaginal taxa and opportunistic pathogens in the fecal microenvironment. Additionally, in late pregnancy, maternal stress and depression scores were associated with each other and with elevated maternal C-C motif chemokine ligand 2 (CCL2) concentrations. At delivery, concordant with previous literature, umbilical CCL2 concentration was negatively correlated with relative abundance of maternal fecal Lactobacilli. Lastly, participants with more severe depressive symptoms experienced steeper decreases in prenatal vaginal α-diversity.

Conclusion

These findings a) underscore previous preclinical and clinical research demonstrating the effects of prenatal stress on maternal microbiome composition, b) suggest distinct biological pathways for the consequences of stress versus depression and c) extend the literature by identifying several taxa which may serve critical roles in mediating this relationship. Thus, further interrogation of the role of specific maternal microbial taxa in relation to psychosocial stress and its sequelae is warranted.

The Maternal Microbiome as a Map to Understanding the Impact of Prenatal Stress on Offspring Psychiatric Health

Stress and psychiatric disorders have been independently associated with disruption of the maternal and offspring microbiome and with increased risk of the offspring developing psychiatric disorders, both in clinical studies and in preclinical studies. However, the role of the microbiome in mediating the effect of prenatal stress on offspring behavior is unclear. While preclinical studies have identified several key mechanisms, clinical studies focusing on mechanisms are limited. In this review, we discuss 3 specific mechanisms by which the microbiome could mediate the effects of prenatal stress: 1) altered production of short-chain fatty acids; 2) disruptions in TH17 (T helper 17) cell differentiation, leading to maternal and fetal immune activation; and 3) perturbation of intestinal and microbial tryptophan metabolism and serotonergic signaling. Finally, we review the existing clinical literature focusing on these mechanisms and highlight the need for additional mechanistic clinical research to better understand the role of the microbiome in the context of prenatal stress.

Stressed to the Core: Inflammation and Intestinal Permeability Link Stress-Related Gut Microbiota Shifts to Mental Health Outcomes

Stress levels are surging, alongside the incidence of stress-related psychiatric disorders. Perhaps a related phenomenon, especially in urban areas, the human gut contains fewer bacterial species than ever before. Although the functional implications of this absence are unclear, one consequence may be reduced stress resilience. Preclinical and clinical evidence has shown how stress exposure can alter the gut microbiota and their metabolites, affecting host physiology. Also, stress-related shifts in the gut microbiota jeopardize tight junctions of the gut barrier. In this context, bacteria and bacterial products can translocate from the gut to the bloodstream, lymph nodes, and other organs, thereby modifying systemic inflammatory responses. Heightened circulating inflammation can be an etiological factor in stress-related psychiatric disorders, including some cases of depression. In this review, we detail preclinical and clinical evidence that traces these brain-to-gut-to-brain pathways that underlie stress-related psychiatric disorders and potentially affect their responsivity to conventional psychiatric medications. We also review evidence for interventions that modulate the gut microbiota (e.g., antibiotics, probiotics, prebiotics) to reduce stress responses and psychiatric symptoms. Lastly, we discuss challenges to translation and opportunities for innovations that could impact future psychiatric clinical practice.

Behavioral and Molecular Characterization of Prenatal Stress Effects on the C57BL/6J Genetic Background for the Study of Autism Spectrum Disorder

Stress-inducing events during pregnancy are associated with aberrant neurodevelopment resulting in adverse psychiatric outcomes, including autism spectrum disorder (ASD). While numerous preclinical models for the study of ASD are frequently generated using C57BL/6J mice, few studies have investigated the effects of prenatal stress on this genetic background. In the current manuscript, we stressed C57BL/6 dams during gestation and examined numerous behavioral and molecular endophenotypes in the adult male and female offspring to characterize the resultant phenotype as compared with offspring born from nonstressed (NS) dams. Adult mice born from prenatal restraint stressed (PRS) dams demonstrated reduced sociability and reciprocal social interaction along with increased marble burying behaviors relative to mice born from nonstressed control dams. Differential expression of genes related to excitatory and inhibitory neurotransmission was evaluated in the medial prefrontal cortex, amygdala, hippocampus, nucleus accumbens and caudate putamen via qRT-PCR. The male PRS mouse behavioral phenotype coincided with aberrant expression of glutamate and GABA marker genes (e.g., Grin1, Grin2b, Gls, Gat1, Reln) in neural substrates of social behavior. Rescue of the male PRS sociability deficit by a known antipsychotic with epigenetic properties (i.e., clozapine (5 mg/kg) + 18 hr washout) indicated possible epigenetic regulation of genes that govern sociability. Clozapine treatment increased the expression levels of genes involved in DNA methylation, histone methylation, and histone acetylation in the nucleus accumbens. Identification of etiology-specific mechanisms underlying clinically relevant behavioral phenotypes may ultimately provide novel therapeutic interventions for the treatment of psychiatric disorders including ASD.

Fetal CCL2 signaling mediates offspring social behavior and recapitulates effects of prenatal stress

Maternal stress during pregnancy is prevalent and associated with increased risk of neurodevelopmental disorders in the offspring. Maternal and offspring immune dysfunction has been implicated as a potential mechanism by which prenatal stress shapes offspring neurodevelopment; however, the impact of prenatal stress on the developing immune system has yet to be elucidated. Furthermore, there is evidence that the chemokine C-C motif chemokine ligand 2 (CCL2) plays a key role in mediating the behavioral sequelae of prenatal stress. Here, we use an established model of prenatal restraint stress in mice to investigate alterations in the fetal immune system, with a focus on CCL2. In the placenta, stress led to a reduction in CCL2 and Ccr2 expression with a concomitant decrease in leukocyte number. However, the fetal liver exhibited an inflammatory phenotype, with upregulation of Ccl2, Il6, and Lbp expression, along with an increase in pro-inflammatory Ly6CHi monocytes. Prenatal stress also disrupted chemokine signaling and increased the number of monocytes and microglia in the fetal brain. Furthermore, stress increased Il1b expression by fetal brain CD11b+ microglia and monocytes. Finally, intra-amniotic injections of recombinant mouse CCL2 partially recapitulated the social behavioral deficits in the adult offspring previously observed in the prenatal restraint stress model. Altogether, these data suggest that prenatal stress led to fetal inflammation, and that fetal CCL2 plays a role in shaping offspring social behavior.

Maternal stress during the third trimester of pregnancy and the neonatal microbiome

OBJECTIVES

Preliminary research suggests that maternal prenatal stress may alter the development of the fetal microbiome and resulting microbial composition after birth. However, the findings of existing studies are mixed and inconclusive. The purpose of this exploratory study was to assess whether maternal stress during pregnancy is associated with the overall number and diversity of various microbial species in the infant gut microbiome or the abundance of specific bacterial taxa.

METHODS

Fifty-one women were recruited during their third trimester of pregnancy. The women completed a demographic questionnaire and Cohen's Perceived Stress Scale at recruitment. A stool sample was collected from their neonate at one month of age. Data on potential confounders, such as gestational age and mode of delivery, were extracted from medical records to control for their effects. 16s rRNA gene sequencing was used to identify the diversity and abundance of microbial species, along with multiple linear regression models to examine the effects of prenatal stress on microbial diversity. We employed negative binomial generalized linear models to test for differential expression of various microbial taxa among infants exposed to prenatal stress and those not exposed to prenatal stress.

RESULTS

More severe symptoms of prenatal stress were associated with a greater diversity of microbial species in the gut microbiome of neonates (β = .30, p = .025). Certain microbial taxa, such as Lactobacillus and Bifidobacterium, were enriched among infants exposed to greater maternal stress in utero, while others, such as Bacteroides and Enterobacteriaceae, were depleted in contrast to infants exposed to less stress.

CONCLUSIONS

Findings suggest that mild to moderate stress exposure in utero could be associated with a microbial environment in early life that is more optimally prepared to thrive in a stressful postnatal environment. Adaptation of gut microbiota under conditions of stress may involve upregulation of bacterial species, including certain protective microorganisms (e.g. Bifidobacterium), as well as downregulation of potential pathogens (e.g. Bacteroides) via epigenetic or other processes within the fetal/neonatal gut-brain axis. However, further research is needed to understand the trajectory of microbial diversity and composition as infant development proceeds and the ways in which both the structure and function of the neonatal microbiome may mediate the relationship between prenatal stress and health outcomes over time. These studies may eventually yield microbial markers and gene pathways that are biosignatures of risk or resilience and inform targets for probiotics or other therapies in utero or during the postnatal period.

Ultrasound-Induced Prenatal Stress: New Possibilities for Modeling Mental Disorders

The development of animal models of mental disorders is an important task, since such models are useful for studying the neurobiological mechanisms of psychopathologies and for trial of new therapeutic drugs. One way to model pathologies of the nervous system is to impair fetal neurodevelopment through stress of the pregnant future mother, or prenatal stress. The use of variable frequency ultrasound in rodents is a promising method of imitating psychological stress, to which women in modern society are most often subjected. The aim of our study was to investigate the effect of prenatal stress induced by exposure to variable frequency ultrasound (US PS) throughout the gestational period on the adult rat offspring, namely to identify features of behavioral alterations and neurochemical brain parameters that can be associated with certain mental disorders in humans, to determine the possibility of creating a new model of psychopathology. Our study included a study of some behavioral characteristics of male and female rats in the elevated plus maze, open field test, object recognition test, social interaction test, sucrose preference test, latent inhibition test, Morris water maze, forced swimming test, acoustic startle reflex and prepulse inhibition tests. We also determined the activity of the serotonergic, dopaminergic, and noradrenergic neurotransmitter systems in the hippocampus and frontal cortex by HPLC-ED. Concentration of norepinephrine, dopamine, DOPAC, serotonin, and HIAA, as well as DOPAC/dopamine and HIAA/serotonin ratios were determined. A correlation analysis of behavioral and neurochemical parameters in male and female rats was performed based on the data obtained. The results of the study showed that US PS altered the behavioral phenotype of the rat offspring. US PS increased the level of anxious behavior, impaired orientation-research behavior, increased grooming activity, decreased the desire for social contacts, shifted behavioral reactions from social interaction to interaction with inanimate objects, impaired latent inhibition, and decreased the startle reflex. US PS activated the serotonergic, dopaminergic, and noradrenergic neurotransmitter systems of the rat frontal cortex and hippocampus. A correlation between neurochemical and behavioral parameters was revealed. Our study showed that US PS leads to a certain dysfunction on behavioral and neurochemical levels in rats that is most closely associated with symptoms of schizophrenia or autism. We hypothesize that this could potentially be an indicator of face validity for a model of psychopathology based on neurodevelopmental impairment.

The impact of acute and chronic stress on gastrointestinal physiology and function: a microbiota-gut-brain axis perspective

The physiological consequences of stress often manifest in the gastrointestinal tract. Traumatic or chronic stress is associated with widespread maladaptive changes throughout the gut, although comparatively little is known about the effects of acute stress. Furthermore, these stress-induced changes in the gut may increase susceptibility to gastrointestinal disorders and infection, and impact critical features of the neural and behavioural consequences of the stress response by impairing gut-brain axis communication. Understanding the mechanisms behind changes in enteric nervous system circuitry, visceral sensitivity, gut barrier function, permeability, and the gut microbiota following stress is an important research objective with pathophysiological implications in both neurogastroenterology and psychiatry. Moreover, the gut microbiota has emerged as a key aspect of physiology sensitive to the effects of stress. In this review, we focus on different aspects of the gastrointestinal tract including gut barrier function as well as the immune, humoral and neuronal elements involved in gut-brain communication. Furthermore, we discuss the evidence for a role of stress in gastrointestinal disorders. Existing gaps in the current literature are highlighted, and possible avenues for future research with an integrated physiological perspective have been suggested. A more complete understanding of the spatial and temporal dynamics of the integrated host and microbial response to different kinds of stressors in the gastrointestinal tract will enable full exploitation of the diagnostic and therapeutic potential in the fast-evolving field of host-microbiome interactions.

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.

Risks of adverse perinatal outcomes in relation to maternal depressive symptoms: A prospective cohort study in Kenya

BACKGROUND

Evidence gaps remain regarding the influence of prenatal psychosocial factors on adverse pregnancy outcomes.

OBJECTIVE

The objective of this study is to evaluate relationships between psychosocial factors and adverse perinatal outcomes among Kenyan women.

METHODS

We analysed data from a prospective cohort study enrolling HIV-negative women in pregnancy (NCT03070600) in 20 antenatal clinics in Western Kenya. Study nurses assessed depressive symptoms using the Center for Epidemiologic Studies Depression Scale (CESD-10), social support using the Medical Outcomes Survey scale (MOS-SSS), intimate partner violence (IPV) with the Hurt, Insult, Threaten, Scream scale (HITS), and pregnancy outcomes at 6 weeks postpartum. Cox proportional hazards models were used to evaluate relationships between depressive symptoms (moderate-to-severe [MSD, CESD-10 ≥10] and mild-to-severe [Mild-SD, CESD-10 ≥5]), low social support (MOS-SSS <72), and IPV (HITS ≥10) with adverse perinatal outcomes of pregnancy loss, stillbirth, preterm birth (PTB), small for gestational age, and neonatal mortality. We also estimated the population attributable risk.

RESULTS

Among 4153 women, 23.9% (n = 994) had MSD, 54.7% (n = 2273) mild-SD, 37.3% (n = 1550) low social support, and 7.8% (n = 323) experienced IPV. Pregnancy loss was 5-fold higher among women with MSD (adjusted hazard ratio [HR] 5.04, 95% confidence interval [CI] 2.44, 10.42); 37.4% of losses were attributable to MSD. Mild-SD was associated with PTB (HR 1.39, 95% CI 1.03, 1.87). Stillbirth risk more than doubled among women reporting low social support (HR 2.37, 95% CI 1.14, 4.94).

CONCLUSIONS

Adverse perinatal outcomes were common and associated with prenatal depressive symptoms and low social support in this large cohort of Kenyan mother-infant pairs.

The long-term gut bacterial signature of a wild primate is associated with a timing effect of pre- and postnatal maternal glucocorticoid levels

BACKGROUND

During development, elevated levels of maternal glucocorticoids (GCs) can have detrimental effects on offspring morphology, cognition, and behavior as well as physiology and metabolism. Depending on the timing of exposure, such effects may vary in strength or even reverse in direction, may alleviate with age, or may concern more stable and long-term programming of phenotypic traits. Maternal effects on gut bacterial diversity, composition, and function, and the persistence of such effects into adulthood of long-lived model species in the natural habitats remain underexplored.

RESULTS

In a cross-sectional sample of infant, juvenile, and adult Assamese macaques, the timing of exposure to elevated maternal GCs during ontogeny was associated with the gut bacterial community of the offspring. Specifically, naturally varying maternal GC levels during early but not late gestation or lactation were associated with reduced bacterial richness. The overall effect of maternal GCs during early gestation on the gut bacterial composition and function exacerbated with offspring age and was 10 times stronger than the effect associated with exposure during late prenatal or postnatal periods. Instead, variation in maternal GCs during the late prenatal or postnatal period had less pronounced or less stable statistical effects and therefore a weaker effect on the entire bacterial community composition, particularly in adult individuals. Finally, higher early prenatal GCs were associated with an increase in the relative abundance of several potential pro-inflammatory bacteria and a decrease in the abundance of Bifidobacterium and other anti-inflammatory taxa, an effect that exacerbated with age.

CONCLUSIONS

In primates, the gut microbiota can be shaped by developmental effects with strong timing effects on plasticity and potentially detrimental consequences for adult health. Together with results on other macaque species, this study suggests potential detrimental developmental effects similar to rapid inflammaging, suggesting that prenatal exposure to high maternal GC concentrations is a common cause underlying both phenomena. Our findings await confirmation by metagenomic functional and causal analyses and by longitudinal studies of long-lived, ecologically flexible primates in their natural habitat, including developmental effects that originate before birth. Video Abstract.

Current Understanding of the Roles of Gut-Brain Axis in the Cognitive Deficits Caused by Perinatal Stress Exposure

The term 'perinatal environment' refers to the period surrounding birth, which plays a crucial role in brain development. It has been suggested that dynamic communication between the neuro-immune system and gut microbiota is essential in maintaining adequate brain function. This interaction depends on the mother's status during pregnancy and/or the newborn environment. Here, we show experimental and clinical evidence that indicates that the perinatal period is a critical window in which stress-induced immune activation and altered microbiota compositions produce lasting behavioral consequences, although a clear causative relationship has not yet been established. In addition, we discuss potential early treatments for preventing the deleterious effect of perinatal stress exposure. In this sense, early environmental enrichment exposure (including exercise) and melatonin use in the perinatal period could be valuable in improving the negative consequences of early adversities. The evidence presented in this review encourages the realization of studies investigating the beneficial role of melatonin administration and environmental enrichment exposure in mitigating cognitive alteration in offspring under perinatal stress exposure. On the other hand, direct evidence of microbiota restoration as the main mechanism behind the beneficial effects of this treatment has not been fully demonstrated and should be explored in future studies.

Signalling cognition: the gut microbiota and hypothalamic-pituitary-adrenal axis

Cognitive function in humans depends on the complex and interplay between multiple body systems, including the hypothalamic-pituitary-adrenal (HPA) axis. The gut microbiota, which vastly outnumbers human cells and has a genetic potential that exceeds that of the human genome, plays a crucial role in this interplay. The microbiota-gut-brain (MGB) axis is a bidirectional signalling pathway that operates through neural, endocrine, immune, and metabolic pathways. One of the major neuroendocrine systems responding to stress is the HPA axis which produces glucocorticoids such as cortisol in humans and corticosterone in rodents. Appropriate concentrations of cortisol are essential for normal neurodevelopment and function, as well as cognitive processes such as learning and memory, and studies have shown that microbes modulate the HPA axis throughout life. Stress can significantly impact the MGB axis via the HPA axis and other pathways. Animal research has advanced our understanding of these mechanisms and pathways, leading to a paradigm shift in conceptual thinking about the influence of the microbiota on human health and disease. Preclinical and human trials are currently underway to determine how these animal models translate to humans. In this review article, we summarize the current knowledge of the relationship between the gut microbiota, HPA axis, and cognition, and provide an overview of the main findings and conclusions in this broad field.

Sex difference in prebiotics on gut and blood-brain barrier dysfunction underlying stress-induced anxiety and depression

BACKGROUND

Most of the previous studies have demonstrated the potential antidepressive and anxiolytic role of prebiotic supplement in male subjects, yet few have females enrolled. Herein, we explored whether prebiotics administration during chronic stress prevented depression-like and anxiety-like behavior in a sex-specific manner and the mechanism of behavioral differences caused by sex.

METHODS

Female and male C57 BL/J mice on normal diet were supplemented with or without a combination of fructo-oligosaccharides (FOS) and galacto-oligosaccharides (GOS) during 3- and 4-week chronic restraint stress (CRS) treatment, respectively. C57 BL/J mice on normal diet without CRS were used as controls. Behavior consequences, gut microbiota, dysfunction of gut and brain-blood barriers, and inflammatory profiles were measured.

RESULTS

In the 3rd week, FOS + GOS administration attenuated stress-induced anxiety-like behavior in female, but not in male mice, and the anxiolytic effects in males were observed until the 4th week. However, protective effects of prebiotics on CRS-induced depression were not observed. Changes in the gene expression of tight junction proteins in the distal colon and hippocampus, and decreased number of colon goblet cells following CRS were restored by prebiotics only in females. In both female and male mice, prebiotics alleviated stress-induced BBB dysfunction and elevation in pro-inflammatory cytokines levels, and modulated gut microbiota caused by stress. Furthermore, correlation analysis revealed that anxiety-like behaviors were significantly correlated with levels of pro-inflammatory cytokines and gene expression of tight junction proteins in the hippocampus of female mice, and the abundance of specific gut microbes was also correlated with anxiety-like behaviors, pro-inflammatory cytokines, and gene expression of tight junction proteins in the hippocampus of female mice.

CONCLUSION

Female mice were more vulnerable to stress and prebiotics than males. The gut microbiota, gut and blood-brain barrier, and inflammatory response may mediate the protective effects of prebiotics on anxiety-like behaviors in female mice.

Perturbation of maternal gut microbiota in mice during a critical perinatal window influences early neurobehavioral outcomes in offspring

The gut microbiota is increasingly recognized as a key environmental factor that shapes host development and physiology, including neural circuits formation and function. Concurrently, there has been growing concern that early-life antibiotic exposure may alter brain developmental trajectories, increasing the risk for neurodevelopmental disorders such as autism spectrum disorder (ASD). Here, we assessed whether perturbation of the maternal gut microbiota in mice during a narrow critical perinatal window (last week of pregnancy and first three postnatal days), induced by exposure to a commonly used broad-spectrum oral antibiotic (ampicillin), influences offspring neurobehavioral outcomes relevant to ASD. Our results demonstrate that neonatal offspring from antibiotic-treated dams display an altered pattern of ultrasonic communication, which was more pronounced in males. Moreover, juvenile male, but not female, offspring from antibiotic-treated dams showed reduced social motivation and social interaction, as well as context-dependent anxiety-like behavior. However, no changes were observed in locomotor or exploratory activity. This behavioral phenotype of exposed juvenile males was associated with reduced gene expression of the oxytocin receptor (OXTR) and several tight-junction proteins in the prefrontal cortex, a key region involved in the regulation of social and emotional behaviors, as well as a mild inflammatory response in the colon. Further, juvenile offspring from exposed dams also showed distinct alterations in several gut bacterial species, including, Lactobacillus murinus, and Parabacteroides goldsteinii. Overall, this study highlights the importance of the maternal microbiome in early-life, and how its perturbation by a widely used antibiotic could contribute to atypical social and emotional development of offspring in a sex-dependent manner.

Developmental Brain Injury and Social Determinants of Health: Opportunities to Combine Preclinical Models for Mechanistic Insights into Recovery

Epidemiological studies show that social determinants of health are among the strongest factors associated with developmental outcomes after prenatal and perinatal brain injuries, even when controlling for the severity of the initial injury. Elevated socioeconomic status and a higher level of parental education correlate with improved neurologic function after premature birth. Conversely, children experiencing early life adversity have worse outcomes after developmental brain injuries. Animal models have provided vital insight into mechanisms perturbed by developmental brain injuries, which have indicated directions for novel therapeutics or interventions. Animal models have also been used to learn how social environments affect brain maturation through enriched environments and early adverse conditions. We recognize animal models cannot fully recapitulate human social circumstances. However, we posit that mechanistic studies combining models of developmental brain injuries and early life social environments will provide insight into pathways important for recovery. Some studies combining enriched environments with neonatal hypoxic injury models have shown improvements in developmental outcomes, but further studies are needed to understand the mechanisms underlying these improvements. By contrast, there have been more limited studies of the effects of adverse conditions on developmental brain injury extent and recovery. Uncovering the biological underpinnings for early life social experiences has translational relevance, enabling the development of novel strategies to improve outcomes through lifelong treatment. With the emergence of new technologies to analyze subtle molecular and behavioral phenotypes, here we discuss the opportunities for combining animal models of developmental brain injury with social construct models to deconvolute the complex interactions between injury, recovery, and social inequity.

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

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

Transcriptomic profiling of the developing brain revealed cell-type and brain-region specificity in a mouse model of prenatal stress

BACKGROUND

Prenatal stress (PS) is considered as a risk factor for many mental disorders. PS-induced transcriptomic alterations may contribute to the functional dysregulation during brain development. Here, we used RNA-seq to explore changes of gene expression in the mouse fetal brain after prenatal exposure to chronic unpredictable mild stress (CUMS).

RESULTS

We compared the stressed brains to the controls and identified groups of significantly differentially expressed genes (DEGs). GO analysis on up-regulated DEGs revealed enrichment for the cell cycle pathways, while down-regulated DEGs were mostly enriched in the neuronal pathways related to synaptic transmission. We further performed cell-type enrichment analysis using published scRNA-seq data from the fetal mouse brain and revealed cell-type-specificity for up- and down-regulated DEGs, respectively. The up-regulated DEGs were highly enriched in the radial glia, while down-regulated DEGs were enriched in different types of neurons. Cell deconvolution analysis further showed altered cell fractions in the stressed brain, indicating accumulation of neuroblast and impaired neurogenesis. Moreover, we also observed distinct brain-region expression pattern when mapping DEGs onto the developing Allen brain atlas. The up-regulated DEGs were primarily enriched in the dorsal forebrain regions including the cortical plate and hippocampal formation. Surprisingly, down-regulated DEGs were found excluded from the cortical region, but highly expressed on various regions in the ventral forebrain, midbrain and hindbrain.

CONCLUSION

Taken together, we provided an unbiased data source for transcriptomic alterations of the whole fetal brain after chronic PS, and reported differential cell-type and brain-region vulnerability of the developing brain in response to environmental insults during the pregnancy.

Maternal anxiety, depression and stress affects offspring gut microbiome diversity and bifidobacterial abundances

Uncovering mechanisms underlying fetal programming during pregnancy is of critical importance. Atypical neurodevelopment during the pre- and immediate postnatal period has been associated with long-term adverse health outcomes, including mood disorders and aberrant cognitive ability in offspring. Maternal factors that have been implicated in anomalous offspring development include maternal inflammation and tress, anxiety, and depression. One potential mechanism through which these factors perturb normal offspring postnatal development is through microbiome disruption. The mother is a primary source of early postnatal microbiome seeding for the offspring, and the transference of a healthy microbiome is key in normal neurodevelopment. Since psychological stress, mood disorders, and inflammation have all been implicated in altering maternal microbiome community structure, passing on aberrant microbial communities to the offspring that may then affect developmental outcomes. Therefore, we examined how maternal stress, anxiety and depression assessed with standardized instruments, and maternal inflammatory cytokine levels in the pre- and postnatal period are associated with the offspring microbiome within the first 13 months of life, utilizing full length 16S sequencing on infant stool samples, that allowed for species-level resolution. Results revealed that infants of mothers who reported higher anxiety and perceived stress had reduced alpha diversity. Additionally, the relative taxonomic quantitative abundances of Bifidobacterium dentium and other species that have been associated with either modulation of the gut-brain axis, or other beneficial health outcomes, were reduced in the offspring of mothers with higher anxiety, perceived stress, and depression. We also found associations between bifidobacteria and prenatal maternal pro-inflammatory cytokines IL-6, IL-8, and IL-10. In summary, specific microbial taxa involved in maintaining proper brain and immune function are lower in offspring born to mothers with anxiety, depression, or stress, providing strong evidence for a mechanism by which maternal factors may affect offspring health through microbiota dysregulation.

Mapping trends and hotspot regarding gastrointestinal microbiome and neuroscience: A bibliometric analysis of global research (2002-2022)

BACKGROUND

Scholars have long understood that gastrointestinal microorganisms are intimately related to human disorders. The literature on research involving the gut microbiome and neuroscience is emerging. This study exposed the connections between gut microbiota and neuroscience methodically and intuitively using bibliometrics and visualization. This study's objectives were to summarize the knowledge structure and identify emerging trends and potential hotspots in this field.

MATERIALS AND METHODS

On October 18, 2022, a literature search was conducted utilizing the Web of Science Core Collection (WoSCC) database for studies on gut microbiota and neuroscience studies from 2002 to 2022 (August 20, 2022). VOSviewer and CiteSpace V software was used to conduct the bibliometrics and visualization analysis.

RESULTS

From 2002 to 2022 (August 20, 2022), 2,275 publications in the WoSCC database satisfied the criteria. The annual volume of publications has rapidly emerged in recent years (2016-2022). The most productive nation (n = 732, 32.18%) and the hub of inter-country cooperation (links: 38) were the United States. University College Cork had the most research papers published in this area, followed by McMaster University and Harvard Medical School. Cryan JF, Dinan TG, and Clarke G were key researchers with considerable academic influence. The journals with the most publications are "Neurogastroenterology and Motility" and "Brain Behavior and Immunity." The most cited article and co-cited reference was Cryan JF's 2012 article on the impact of gut microbiota on the brain and behavior. The current research hotspot includes gastrointestinal microbiome, inflammation, gut-brain axis, Parkinson's disease (PD), and Alzheimer's disease (AD). The research focus would be on the "gastrointestinal microbiome, inflammation: a link between obesity, insulin resistance, and cognition" and "the role of two important theories of the gut-brain axis and microbial-gut-brain axis in diseases." Burst detection analysis showed that schizophrenia, pathology, and psychiatric disorder may continue to be the research frontiers.

CONCLUSION

Research on "gastrointestinal microbiome, inflammation: a link between obesity, insulin resistance, and cognition" and "the role of two important theories of the gut-brain axis and microbial-gut-brain axis in diseases" will continue to be the hotspot. Schizophrenia and psychiatric disorder will be the key research diseases in the field of gut microbiota and neuroscience, and pathology is the key research content, which is worthy of scholars' attention.

Beyond the three-chamber test: toward a multimodal and objective assessment of social behavior in rodents

MAIN: In recent years, substantial advances in social neuroscience have been realized, including the generation of numerous rodent models of autism spectrum disorder. Still, it can be argued that those methods currently being used to analyze animal social behavior create a bottleneck that significantly slows down progress in this field. Indeed, the bulk of research still relies on a small number of simple behavioral paradigms, the results of which are assessed without considering behavioral dynamics. Moreover, only few variables are examined in each paradigm, thus overlooking a significant portion of the complexity that characterizes social interaction between two conspecifics, subsequently hindering our understanding of the neural mechanisms governing different aspects of social behavior. We further demonstrate these constraints by discussing the most commonly used paradigm for assessing rodent social behavior, the three-chamber test. We also point to the fact that although emotions greatly influence human social behavior, we lack reliable means for assessing the emotional state of animals during social tasks. As such, we also discuss current evidence supporting the existence of pro-social emotions and emotional cognition in animal models. We further suggest that adequate social behavior analysis requires a novel multimodal approach that employs automated and simultaneous measurements of multiple behavioral and physiological variables at high temporal resolution in socially interacting animals. We accordingly describe several computerized systems and computational tools for acquiring and analyzing such measurements. Finally, we address several behavioral and physiological variables that can be used to assess socio-emotional states in animal models and thus elucidate intricacies of social behavior so as to attain deeper insight into the brain mechanisms that mediate such behaviors. CONCLUSIONS: In summary, we suggest that combining automated multimodal measurements with machine-learning algorithms will help define socio-emotional states and determine their dynamics during various types of social tasks, thus enabling a more thorough understanding of the complexity of social behavior.

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.

The Neurobiology of Infant Attachment-Trauma and Disruption of Parent-Infant Interactions

Current clinical literature and supporting animal literature have shown that repeated and profound early-life adversity, especially when experienced within the caregiver-infant dyad, disrupts the trajectory of brain development to induce later-life expression of maladaptive behavior and pathology. What is less well understood is the immediate impact of repeated adversity during early life with the caregiver, especially since attachment to the caregiver occurs regardless of the quality of care the infant received including experiences of trauma. The focus of the present manuscript is to review the current literature on infant trauma within attachment, with an emphasis on animal research to define mechanisms and translate developmental child research. Across species, the effects of repeated trauma with the attachment figure, are subtle in early life, but the presence of acute stress can uncover some pathology, as was highlighted by Bowlby and Ainsworth in the 1950s. Through rodent neurobehavioral literature we discuss the important role of repeated elevations in stress hormone corticosterone (CORT) in infancy, especially if paired with the mother (not when pups are alone) as targeting the amygdala and causal in infant pathology. We also show that following induced alterations, at baseline infants appear stable, although acute stress hormone elevation uncovers pathology in brain circuits important in emotion, social behavior, and fear. We suggest that a comprehensive understanding of the role of stress hormones during infant typical development and elevated CORT disruption of this typical development will provide insight into age-specific identification of trauma effects, as well as a better understanding of early markers of later-life pathology.

The role of maternal exercise on placental, behavioral and genetic alterations induced by prenatal stress

The present study aimed to evaluate the effects of treadmill maternal exercise on alterations induced by prenatal stress in neonatal mice. Female and male Balb/c mice were divided into five groups: control (CON), prenatal restraint stress (PNS), prenatal restraint stress and physical exercise before pregnancy (PNS + EX1), prenatal restraint stress and physical exercise during pregnancy (PNS + EX2), and prenatal restraint stress and physical exercise before and during pregnancy (PNS + EX3). Exercise was performed using a treadmill, at a speed of 10 m/min, for 60 minutes, 5 days a week. Maternal behavior was assessed on days 3, 4 and 5 postpartum (PPD). Placental gene expression of glucocorticoid receptor (GR), 11-β-hydroxysteroid dehydrogenase 2 (11β-HSD2), 5-hydroxytryptamine receptor 1A (5HT_1AR), and corticotropin releasing hormone receptor 1 (CRHR1) were analyzed. In neonatal mice, the gene expression of GR, mineralocorticoid receptor (MR), CRHR1, 5HTr1, oxytocin Receptor 1 (OXTr1), tropomyosin related kinase B (TRκB), brain-derived neurotrophic factor exon I (BDNF I), and BDNF IV was analyzed in the brain (PND0) and hippocampus (PND10). Maternal exercise improved (p < 0.05) maternal care. In the placenta, maternal exercise prevented (p < 0.01) the increase in GR expression caused by PNS. In the brain from PND0, exercise before pregnancy prevented (p = 0.002) the decreased CRHR1 expression promoted by PNS. In the hippocampus of PND10 males, PNS decreased (p = 0.0005) GR expression, and exercise before pregnancy prevented (p = 0.003) this effect. In PND10 females, maternal exercise prevented (p < 0.05) the PNS-induced increase in MR expression. PNS + EX2 males showed increased (p < 0.01) BDNF I gene expression and PNS + EX1 females demonstrated increased (p = 0.03) BDNF IV expression. In conclusion, maternal physical exercise may play a role in modulating maternal-fetal health and may contribute to preventing neurodevelopmental changes induced by prenatal stress.

An Updated Narrative Mini-Review on the Microbiota Changes in Antenatal and Post-Partum Depression

Background: Antenatal depression (AND) and post-partum depression (PPD) are long-term debilitating psychiatric disorders that significantly influence the composition of the gut flora of mothers and infants that starts from the intrauterine life. Not only does bacterial ratio shift impact the immune system, but it also increases the risk of potentially life-threatening disorders. Material and Methods: Therefore, we conducted a narrative mini-review aiming to gather all evidence published between 2018–2022 regarding microflora changes in all three stages of pregnancy. Results: We initially identified 47 potentially eligible studies, from which only 7 strictly report translocations; 3 were conducted on rodent models and 4 on human patients. The remaining studies were divided based on their topic, precisely focused on how probiotics, breastfeeding, diet, antidepressants, exogenous stressors, and plant-derived compounds modulate in a bidirectional way upon behavior and microbiota. Almost imperatively, dysbacteriosis cause cognitive impairments, reflected by abnormal temperament and personality traits that last up until 2 years old. Thankfully, a distinct technique that involves fecal matter transfer between individuals has been perfected over the years and was successfully translated into clinical practice. It proved to be a reliable approach in diminishing functional non- and gastrointestinal deficiencies, but a clear link between depressive women’s gastrointestinal/vaginal microbiota and clinical outcomes following reproductive procedures is yet to be established. Another gut-dysbiosis-driving factor is antibiotics, known for their potential to trigger inflammation. Fortunately, the studies conducted on mice that lack microbiota offer, without a shadow of a doubt, insight. Conclusions: It can be concluded that the microbiota is a powerful organ, and its optimum functionality is crucial, likely being the missing puzzle piece in the etiopathogenesis of psychiatric disorders.

The Microbiome and Gut Endocannabinoid System in the Regulation of Stress Responses and Metabolism

The endocannabinoid system, with its receptors and ligands, is present in the gut epithelium and enteroendocrine cells, and is able to modulate brain functions, both indirectly through circulating gut-derived factors and directly through the vagus nerve, finally acting on the brain’s mechanisms regarding metabolism and behavior. The gut endocannabinoid system also regulates gut motility, permeability, and inflammatory responses. Furthermore, microbiota composition has been shown to influence the activity of the endocannabinoid system. This review examines the interaction between microbiota, intestinal endocannabinoid system, metabolism, and stress responses. We hypothesize that the crosstalk between microbiota and intestinal endocannabinoid system has a prominent role in stress-induced changes in the gut-brain axis affecting metabolic and mental health. Inter-individual differences are commonly observed in stress responses, but mechanisms underlying resilience and vulnerability to stress are far from understood. Both gut microbiota and the endocannabinoid system have been implicated in stress resilience. We also discuss interventions targeting the microbiota and the endocannabinoid system to mitigate metabolic and stress-related disorders.

Maternal stress and the maternal microbiome have sex-specific effects on offspring development and aggressive behavior in Siberian hamsters (Phodopus sungorus)

The gut microbiome, a community of commensal, symbiotic and pathogenic bacteria, fungi, and viruses, interacts with many physiological systems to affect behavior. Prenatal experiences, including exposure to maternal stress and different maternal microbiomes, are important sources of organismal variation that can affect offspring development. These physiological systems do not act in isolation and can have long-term effects on offspring development and behavior. Here we investigated the interactive effects of maternal stress and manipulations of the maternal microbiome on offspring development and social behavior using Siberian hamsters, Phodopus sungorus. We exposed pregnant females to either a social stressor, antibiotics, both the social stressor and antibiotics, or no treatment (i.e., control) over the duration of their pregnancy and quantified male and female offspring growth, gut microbiome composition and diversity, stress-induced cortisol concentrations, and social behavior. Maternal antibiotic exposure altered the gut microbial communities of male and female offspring. Maternal treatment also had sex-specific effects on aspects of offspring development and aggressive behavior. Female offspring produced by stressed mothers were more aggressive than other female offspring. Female, but not male, offspring produced by mothers exposed to the combined treatment displayed low levels of aggression, suggesting that alteration of the maternal microbiome attenuated the effects of prenatal stress in a sex-specific manner. Maternal treatment did not affect non-aggressive behavior in offspring. Collectively, our study offers insight into how maternal systems can interact to affect offspring in sex-specific ways and highlights the important role of the maternal microbiome in mediating offspring development and behavior.

Prenatal Stress and Adaptive Behavior of Offspring: The Role of Placental Serotonin

The effect of mild prenatal stress in mice, leading to an increase in the placental serotonin level, on the formation of adaptive behavior in male offspring at the age of 35 days was studied. It was shown that, in BalbC mice, daily immobilization for 1 h during the period from 11 to 14 days of pregnancy led to an increase in placental and fetal serotonin levels on the 15th day of prenatal development. According to "resident-intruder" behavioral test, the prenatally stressed mice showed more reactive behavior in adulthood and low tendency to defend their territory. Thus, placental serotonin, formed under the stress condition, may act as a mediator between the environment and the fetuses and determine the adaptive behavior of offspring.

The relationship between human milk, a functional nutrient, and microbiota

The intestinal microbiota begins to take shape in the mother's womb, changes depending on many factors. It is known that the intestinal microbiota has an important role in the maturation of the immune system, also in the prevention of diseases that occur in newborn, childhood, adulthood. Nutrition is the main factor on the development of microbiota in infants after birth. The microbiota compositions of breastfed infants are different from formula-fed infants. Breast milk oligosaccharides play an important role in the development of infants' microbiota. The higher number of Bifidobacterium species and lower α and β diversity in breastfed infants are considered protective. A dysbiosis occurring in the microbiota can cause adverse effects on health. Human milk oligosaccharides also have protective effects on the microbiota. These protective effects are to promote the growth of intestinal microbiota, prevent the adhesion of viruses to the colon, promote the growth of Bifidobacterium with its prebiotic effect. Short-chain fatty acids resulting from their digestion, also have protective effects. Another component that shapes the gut microbiota is HM glycoproteins. The aim of this study is to examine the effect of breast milk on the development of microbiota, to present the results by scanning the literature.

Links Between Gut Dysbiosis and Neurotransmitter Disturbance in Chronic Restraint Stress-Induced Depressive Behaviours: the Role of Inflammation

Accumulating evidence has shown that inflammation, the gut microbiota, and neurotransmitters are closely associated with the pathophysiology of depression. However, the links between the gut microbiota and neurotransmitter metabolism remain poorly understood. The present study aimed to investigate the neuroinflammatory reactions in chronic restraint stress (CRS)-induced depression and to delineate the potential links between the gut microbiota and neurotransmitter metabolism. C57BL/6 mice were subjected to chronic restraint stress for 5 weeks, followed by behavioural tests (the sucrose preference test, forced swim test, open field test, and elevated plus maze) and analysis. The results showed that CRS significantly increased interleukin-1 beta (IL-1β), interleukin-2 (IL-2), interleukin-6 (IL-6), and tumour necrosis factor α (TNFα) levels and decreased brain-derived neurotrophic factor (BDNF) expression, accompanied by the activation of IkappaB-alpha-phosphorylation-nuclear factor kappa-B (IκBα-p-NF-κB) signalling in the mouse hippocampus. In addition, the neurotransmitter metabolomics results showed that CRS resulted in decreased levels of plasma 5-hydroxytryptamine (5-HT), dopamine (DA), and noradrenaline (NE) and their corresponding metabolites, and gut microbiota faecal metabolites with the 16S rRNA gene sequencing indicated that CRS caused marked microbiota dysbiosis in mice, with a significant increase in Helicobacter, Lactobacillus, and Oscillibacter and a decrease in Parabacteroides, Ruminococcus, and Prevotella. Notably, CRS-induced depressive behaviours and the disturbance of neurotransmitter metabolism and microbiota dysbiosis can be substantially restored by dexamethasone (DXMS) administration. Furthermore, a Pearson heatmap focusing on correlations between the microbiota, behaviours, and neurotransmitters showed that Helicobacter, Lactobacillus, and Oscillibacter were positively correlated with depressive behaviours but were negatively correlated with neurotransmitter metabolism, and Parabacteroides and Ruminococcus were negatively correlated with depressive behaviours but were positively correlated with neurotransmitter metabolism. Taken together, the results suggest that inflammation is involved in microbiota dysbiosis and the disturbance of neurotransmitter metabolism in CRS-induced depressive changes, and the delineation of the potential links between the microbiota and neurotransmitter metabolism will provide novel strategies for depression treatment.

Jie-Yu-He-Huan Capsule Ameliorates Anxiety-Like Behaviours in Rats Exposed to Chronic Restraint Stress via the cAMP/PKA/CREB/BDNF Signalling Pathway

Chronic stress is a critical factor in the aetiology of anxiety disorders; however, in the clinic, enduring and preventive measures are not available, and therapeutic drugs are associated with inevitable side effects. Our study established an anxiety rat model using chronic restraint stress (CRS) and assessed these animals using the open-field test, elevated plus-maze test, and light-dark box test. Jie-Yu-He-Huan capsule (JYHH), a Chinese medicine formula, was used as a preventative drug. The HPA axis-mediated release of corticotropin-releasing hormone, adrenocorticotropic hormone, and corticosterone from the hypothalamus was tested. In the hippocampus and prefrontal cortex, concentrations of 5-HT and its metabolite 5-hydroxyindoleacetic acid, as well as monoamine oxidase A, glucocorticoid receptor, and 5-HT1A receptor expression levels, were measured. Furthermore, we examined protein and mRNA expression of cAMP-PKA-CREB-BDNF pathway components. The results showed that JYHH had a significant preventative effect on the anxiety-like behaviour induced by CRS and prevented abnormal changes in the HPA axis and 5-HT system. Furthermore, CRS inhibited the cAMP-PKA-CREB-BDNF pathway, which returned to normal levels following JYHH treatment. This might be the underlying molecular mechanism of the antianxiety effect of JYHH, which could provide a new clinical target for preventative anxiolytic drugs for chronic stress.

Multiplexed functional metagenomic analysis of the infant microbiome identifies effectors of NF-κB, autophagy, and cellular redox state

The human microbiota plays a critical role in host health. Proper development of the infant microbiome is particularly important. Its dysbiosis leads to both short-term health issues and long-term disorders lasting into adulthood. A central way in which the microbiome interacts with the host is through the production of effector molecules, such as proteins and small molecules. Here, a metagenomic library constructed from 14 infant stool microbiomes is analyzed for the production of effectors that modulate three distinct host pathways: immune response (nuclear factor κB [NF-κB] activation), autophagy (LC3-B puncta formation), and redox potential (NADH:NAD ratio). We identify microbiome-encoded bioactive metabolites, including commendamide and hydrogen sulfide and their associated biosynthetic genes, as well as a previously uncharacterized autophagy-inducing operon from Klebsiella spp. This work extends our understanding of microbial effector molecules that are known to influence host pathways. Parallel functional screening of metagenomic libraries can be easily expanded to investigate additional host processes.

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Construction of a metagenomic library from stool of infants

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A multiplexed screen for bacterial effectors of host cellular processes

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Identification of microbiome-encoded effectors hydrogen sulfide and commendamide

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The products of a Klebsiella pneumoniae operon induce autophagy

Moderately pathogenic maternal influenza A virus infection disrupts placental integrity but spares the fetal brain

Maternal infection during pregnancy is a known risk factor for offspring mental health disorders. Animal models of maternal immune activation (MIA) have implicated specific cellular and molecular etiologies of psychiatric illness, but most rely on pathogen mimetics. Here, we developed a mouse model of live H3N2 influenza A virus (IAV) infection during pregnancy that induces a robust inflammatory response but is sublethal to both dams and offspring. We observed classic indicators of lung inflammation and severely diminished weight gain in IAV-infected dams. This was accompanied by immune cell infiltration in the placenta and partial breakdown of placental integrity. However, indications of fetal neuroinflammation were absent. Further hallmarks of mimetic-induced MIA, including enhanced circulating maternal IL-17A, were also absent. Respiratory IAV infection did result in an upregulation in intestinal expression of transcription factor RORγt, master regulator of a subset of T lymphocytes, TH17 cells, which are heavily implicated in MIA-induced etiologies. Nonetheless, subsequent augmentation in IL-17A production and concomitant overt intestinal injury was not evident. Our results suggest that mild or moderately pathogenic IAV infection during pregnancy does not inflame the developing fetal brain, and highlight the importance of live pathogen infection models for the study of MIA.

Stress gets into the belly: Early life stress and the gut microbiome

Research has established that stress "gets under the skin," impacting neuroendocrine and neuroimmune pathways to influence risk for physical and mental health outcomes. These effects can be particularly significant for early life stress (ELS), or adverse childhood experiences (ACEs). In this review, we explore whether stress gets "into the belly," that is, whether psychosocial stress affects the gut microbiome. We review animal and human research utilizing a variety of stress paradigms (acute laboratory stressors, chronic stress, stressful life events, perceived stress, ELS, in utero stress) and their impacts on the gut microbiota, with a particular focus on ELS. We also review data on dietary interventions to moderate impact of stress on the gut microbiome. Our review suggests strong evidence that acute laboratory stress, chronic stress, and ELS affect the gut microbiota in rodents, and growing evidence that perceived stress and ELS may impact the gut microbiota in humans. Emerging data also suggests, particularly in rodents, that dietary interventions such as omega-3 fatty acids and pre- and pro-biotics may buffer against the effects of stress on the gut microbiome, but more research is needed. In sum, growing evidence suggests that stress impacts not only the neuroendocrine and neuroimmune axes, but also the microbiota-gut-brain-axis, providing a pathway by which stress may get "into the belly" to influence health risk.

Prenatal stress-induced disruptions in microbial and host tryptophan metabolism and transport

The aromatic amino acid tryptophan (Trp) is a precursor for multiple metabolites that can steer proper immune and neurodevelopment as well as social behavior in later life. Dysregulation in the Trp metabolic pathways and abundance of Trp or its derivatives, including indoles, kynurenine (Kyn), and particularly serotonin, has been associated with behavioral deficits and neuropsychiatric disorders including autism spectrum disorders (ASD) and schizophrenia. Previously, we have shown that prenatal stress (PNS) alters placental Trp and serotonin, and reduces Trp-metabolizing members of the maternal colonic microbiota. Given that PNS also results in alterations in offspring neurodevelopment, behavior and immune function, we hypothesized that PNS affects Trp metabolism and transport in both the maternal and fetal compartments, and that these alterations continue into adolescence. We surmised that this is due to reductions in Trp-metabolizing microbes that would otherwise reduce the Trp pool under normal metabolic conditions. To test this, pregnant mice were exposed to a restraint stressor and gene expression of enzymes involved in Trp and serotonin metabolism were measured. Specifically, tryptophan 2,3-dioxygenase, aryl hydrocarbon receptor, and solute carrier proteins, were altered due to PNS both prenatally and postnatally. Additionally, Parasutterella and Bifidobacterium, which metabolize Trp in the gut, were reduced in both the dam and the offspring. Together, the reductions of Trp-associated microbes and concomitant dysregulation in Trp metabolic machinery in dam and offspring suggest that PNS-induced Trp metabolic dysfunction may mediate aberrant fetal neurodevelopment.

Maternal effects in mammals: Broadening our understanding of offspring programming

The perinatal period is a sensitive time in mammalian development that can have long-lasting consequences on offspring phenotype via maternal effects. Maternal effects have been most intensively studied with respect to two major conditions: maternal diet and maternal stress. In this review, we shift the focus by discussing five major additional maternal cues and their influence on offspring phenotype: maternal androgen levels, photoperiod (melatonin), microbiome, immune regulation, and milk composition. We present the key findings for each of these topics in mammals, their mechanisms of action, and how they interact with each other and with the maternal influences of diet and stress. We explore their impacts in the contexts of both predictive adaptive responses and the developmental origins of disease, identify knowledge gaps and research opportunities in the field, and place a particular emphasis on the application and consideration of these effects in non-model species and natural ecological systems.

Prenatal stress and KCl-induced depolarization modulate cell death, hypothalamic-pituitary-adrenal axis genes, oxidative and inflammatory response in primary cortical neurons

Maternal stress has been described as an important component in the offspring's cerebral development, altering the susceptibility to diseases in later life. Moreover, the postnatal period is essential for the development and integration of several peripheral and central systems related to the control of homeostasis. Thus, this study aimed to evaluate the effects of prenatal stress on the activation of cortical neurons, by performing experiments both under basal conditions and after KCl-induced depolarization. Female mice were divided in two groups: control and prenatal restraint stress. Cortical neurons from the offspring were obtained at gestational day 18. The effects of prenatal stress and KCl stimulations on cellular mortality, autophagy, gene expression, oxidative stress, and inflammation were evaluated. We found that neurons from PNS mice have decreased necrosis and autophagy after depolarization. Moreover, prenatal stress modulated the HPA axis, as observed by the increased GR and decreased 5HTr1 mRNA expression. The BDNF is an important factor for neuronal function and results demonstrated that KCl-induced depolarization increased the gene expression of BDNF I, BDNF IV, and TRκB. Furthermore, prenatal stress and KCl treatment induced significant alterations in oxidative and inflammatory markers. In conclusion, prenatal stress and stimulation with KCl may influence several markers related to neurodevelopment in cortical neurons from neonate mice, supporting the well-known long-term effects of maternal 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.

Evolutionary Significance of the Neuroendocrine Stress Axis on Vertebrate Immunity and the Influence of the Microbiome on Early-Life Stress Regulation and Health Outcomes

Stress is broadly defined as the non-specific biological response to changes in homeostatic demands and is mediated by the evolutionarily conserved neuroendocrine networks of the hypothalamus-pituitary-adrenal (HPA) axis and the sympathetic nervous system. Activation of these networks results in transient release of glucocorticoids (cortisol) and catecholamines (epinephrine) into circulation, as well as activation of sympathetic fibers innervating end organs. These interventions thus regulate numerous physiological processes, including energy metabolism, cardiovascular physiology, and immunity, thereby adapting to cope with the perceived stressors. The developmental trajectory of the stress-axis is influenced by a number of factors, including the gut microbiome, which is the community of microbes that colonizes the gastrointestinal tract immediately following birth. The gut microbiome communicates with the brain through the production of metabolites and microbially derived signals, which are essential to human stress response network development. Ecological perturbations to the gut microbiome during early life may result in the alteration of signals implicated in developmental programming during this critical window, predisposing individuals to numerous diseases later in life. The vulnerability of stress response networks to maladaptive development has been exemplified through animal models determining a causal role for gut microbial ecosystems in HPA axis activity, stress reactivity, and brain development. In this review, we explore the evolutionary significance of the stress-axis system for health maintenance and review recent findings that connect early-life microbiome disturbances to alterations in the development of stress response networks.

Maternal Distress and Offspring Neurodevelopment: Challenges and Opportunities for Pre-clinical Research Models

Pre-natal exposure to acute maternal trauma or chronic maternal distress can confer increased risk for psychiatric disorders in later life. Acute maternal trauma is the result of unforeseen environmental or personal catastrophes, while chronic maternal distress is associated with anxiety or depression. Animal studies investigating the effects of pre-natal stress have largely used brief stress exposures during pregnancy to identify critical periods of fetal vulnerability, a paradigm which holds face validity to acute maternal trauma in humans. While understanding these effects is undoubtably important, the literature suggests maternal stress in humans is typically chronic and persistent from pre-conception through gestation. In this review, we provide evidence to this effect and suggest a realignment of current animal models to recapitulate this chronicity. We also consider candidate mediators, moderators and mechanisms of maternal distress, and suggest a wider breadth of research is needed, along with the incorporation of advanced -omics technologies, in order to understand the neurodevelopmental etiology of psychiatric risk.

Alterations in 'inflammatory' pathways in the rat prefrontal cortex as early biological predictors of the long-term negative consequences of exposure to stress early in life

Early life stress, especially when experienced during the first period of life, affects the brain developmental trajectories leading to an enhanced vulnerability for stress-related psychiatric disorders later in life. Although both clinical and preclinical studies clearly support this association, the biological pathways deregulated by such exposure, and the effects in shaping the neurodevelopmental trajectories, have so far been poorly investigated. By using the prenatal stress (PNS) model, a well-established rat model of early life stress, we performed transcriptomic analyses in the prefrontal cortex of rats exposed or not to PNS and sacrificed at different postnatal days (PNDs 21, 40, 62). We first investigated the long-lasting mechanisms and pathways affected in the PFC. We have decided to focus on the prefrontal cortex because we have previously shown that this brain region is highly sensitive to PNS exposure. We found that adult animals exposed to PNS show alterations in 389 genes, mainly involved in stress and inflammatory signalling. We then wanted to establish whether PNS exposure could also affect the neurodevelopmental trajectories in order to identify the most critical temporal window. We found that PNS rats show the most significant changes during adolescence (between PND 40 versus PND 21), with alterations of several pathways related to stress, inflammation and metabolism, which were maintained until adulthood.

Identifying a biological signature of prenatal maternal stress

Psychological stress affects maternal gastrointestinal (GI) permeability, leading to low-grade inflammation, which can negatively affect fetal development. We investigated a panel of circulating markers as a biological signature of this stress exposure in pregnant women with and without the stress-related GI disorder irritable bowel syndrome (IBS). Markers of GI permeability and inflammation were measured in plasma from healthy and IBS cohorts of women at 15 and 20 weeks’ gestation. Biomarkers were evaluated with respect to their degree of association to levels of stress, anxiety, and depression as indicated by responses from the Perceived Stress Scale, State-Trait Anxiety Inventory, and Edinburgh Postnatal Depression Scale. High levels of stress were associated with elevations of soluble CD14, lipopolysaccharide binding protein (LBP), and tumor necrosis factor–α, while anxiety was associated with elevated concentrations of C-reactive protein (CRP) in otherwise healthy pregnancies. Prenatal depression was associated with higher levels of soluble CD14, LBP, and CRP in the healthy cohort. High levels of prenatal anxiety and depression were also associated with lower concentrations of tryptophan and kynurenine, respectively, in the IBS cohort. These markers may represent a core maternal biological signature of active prenatal stress, which can be used to inform intervention strategies via stress reduction techniques or other lifestyle approaches. Such interventions may need to be tailored to reflect underlying GI conditions, such as IBS.

Bacteroidota and Lachnospiraceae integration into the gut microbiome at key time points in early life are linked to infant neurodevelopment

The early life microbiome plays critical roles in host development, shaping long-term outcomes including brain functioning. It is not known which initial infant colonizers elicit optimal neurodevelopment; thus, this study investigated the association between gut microbiome succession from the first week of life and head circumference growth (HCG), the earliest validated marker for neurodevelopment. Fecal samples were collected weekly from a preterm infant cohort during their neonatal intensive care unit stay and subjected to 16S rRNA gene sequencing for evaluating gut microbiome composition, in conjunction with clinical data and head circumference measurements. Preterm infants with suboptimal HCG trajectories had a depletion in the abundance/prevalence of Bacteroidota and Lachnospiraceae, independent of morbidity and caloric restriction. The severity of gut microbiome depletion matched the timing of significant HCG pattern separation between study groups at 30-week postmenstrual age demonstrating a potential mediating relationship resultant from clinical practices. Consideration of the clinical variables indicated that optimal infant microbiome succession is primarily driven by dispersal limitation (i.e., delivery mode) and secondarily by habitat filtering (i.e., antibiotics and enteral feeding). Bacteroidota and Lachnospiraceae are known core taxa of the adult microbiome, with roles in dietary glycan foraging, beneficial metabolite production and immunity, and our work provides evidence that their integration into the gut microbiome needs to occur early for optimal neurodevelopment.