Prenatal stress increases the expression of proinflammatory cytokines and exacerbates the inflammatory response to LPS in the hippocampal formation of adult male mice

Developmental functions of microglia: Impact of psychosocial and physiological early life stress

Microglia play numerous important roles in brain development. From early embryonic stages through adolescence, these immune cells influence neuronal genesis and maturation, guide connectivity, and shape brain circuits. They also interact with other glial cells and structures, influencing the brain's supportive microenvironment. While this central role makes microglia essential, it means that early life perturbations to microglia can have widespread effects on brain development, potentially resulting in long-lasting behavioral impairments. Here, we will focus on the effects of early life psychosocial versus physiological stressors in rodent models. Psychosocial stress refers to perceived threats that lead to stress axes activation, including prenatal stress, or chronic postnatal stress, including maternal separation and resource scarcity. Physiological stress refers to physical threats, including maternal immune activation, postnatal infection, and traumatic brain injury. Differing sources of early life stress have varied impacts on microglia, and these effects are moderated by factors such as developmental age, brain region, and sex. Overall, these stressors appear to either 1) upregulate basal microglia numbers and activity throughout the lifespan, while possibly blunting their responsivity to subsequent stressors, or 2) shift the developmental curve of microglia, resulting in differential timing and function, impacting the critical periods they govern. Either could contribute to behavioral dysfunctions that occur after the resolution of early life stress. Exploring how different stressors impact microglia, as well as how multiple stressors interact to alter microglia's developmental functions, could deepen our understanding of how early life stress changes the brain's developmental trajectory. This article is part of the Special Issue on "Microglia".

Coffee polyphenols ameliorate early-life stress-induced cognitive deficits in male mice

Stress exposure during the sensitive period of early development has been shown to program the brain and increases the risk to develop cognitive deficits later in life. We have shown earlier that early-life stress (ES) leads to cognitive decline at an adult age, associated with changes in adult hippocampal neurogenesis and neuroinflammation. In particular, ES has been shown to affect neurogenesis rate and the survival of newborn cells later in life as well as microglia, modulating their response to immune or metabolic challenges later in life. Both of these processes possibly contribute to the ES-induced cognitive deficits. Emerging evidence by us and others indicates that early nutritional interventions can protect against these ES-induced effects through nutritional programming. Based on human metabolomics studies, we identified various coffee-related metabolites to be part of a protective molecular signature against cognitive decline in humans. Caffeic and chlorogenic acids are coffee-polyphenols and have been described to have potent anti-oxidant and anti-inflammatory actions. Therefore, we here aimed to test whether supplementing caffeic and chlorogenic acids to the early diet could also protect against ES-induced cognitive deficits. We induced ES via the limited nesting and bedding paradigm in mice from postnatal(P) day 2-9. On P2, mice received a diet to which 0.02% chlorogenic acid (5-O-caffeoylquinic acid) + 0.02% caffeic acid (3',4'-dihydroxycinnamic acid) were added, or a control diet up until P42. At 4 months of age, all mice were subjected to a behavioral test battery and their brains were stained for markers for microglia and neurogenesis. We found that coffee polyphenols supplemented early in life protected against ES-induced cognitive deficits, potentially this is mediated by the survival of neurons or microglia, but possibly other mechanisms not studied here are mediating the effects. This study provides additional support for the potential of early nutritional interventions and highlights polyphenols as nutrients that can protect against cognitive decline, in particular for vulnerable populations exposed to ES.

Machine learning analysis with population data for prepregnancy and perinatal risk factors for the neurodevelopmental delay of offspring

Neurodevelopmental disorders (NDD) in offspring are associated with a complex combination of pre-and postnatal factors. This study uses machine learning and population data to evaluate the association between prepregnancy or perinatal risk factors and the NDD of offspring. Population-based retrospective cohort data were obtained from Korea National Health Insurance Service claims data for 209,424 singleton offspring and their mothers who gave birth for the first time in 2007. The dependent variables were motor development disorder (MDD), cognitive development disorder (CDD) and combined overall neurodevelopmental disorder (NDD) from offspring. Seventeen independent variables from 2002 to 2007 were included. Random forest variable importance and Shapley Additive Explanation (SHAP) values were calculated to analyze the directions of its associations with the predictors. The random forest with oversampling registered much higher areas under the receiver-operating-characteristic curves than the logistic regression of interaction and non-linearity terms, 79% versus 50% (MDD), 82% versus 52% (CDD) and 74% versus 50% (NDD). Based on random forest variable importance, low socioeconomic status and age at birth were highly ranked. In SHAP values, there was a positive association between NDD and pre- or perinatal outcomes, especially, fetal male sex with growth restriction associated the development of NDD in offspring.

White blood cells and patients with psychiatric disorders needing seclusion: A retrospective non-interventional study

OBJECTIVE

The objective of this retrospective study was to investigate the peripheral immunological markers using leucocyte count, the neutrophil to lymphocyte ratio (NLR), the platelet to lymphocyte ratio (PLR), and the monocyte to lymphocyte ratio (MLR) in patients with aggressive behavior, during and after seclusion.

METHODS

Ninety-nine inpatients were included in this retrospective study. Leucocyte count was measured, and NLR, PLR and MLR were calculated and compared between a group of patients who required seclusion and a group who did not. A multivariate analysis was performed using binary logistic regression, including confounding factors such as age, gender, medication, BMI, smoking status and diagnosis.

RESULTS

We found the lowest levels of lymphocytes (P=0.01) and basophils (P<0.01) and the highest NLR (P=0.02) and MLR (P=0.04) in the seclusion group. We also found a restoration of these parameters after the end of the seclusion period. Furthermore, we found a positive correlation between the PANSS negative subscore, and PLR (P=0.05), or MLR (P=0.03) after seclusion, and between the MLR variation across the seclusion period and the PANSS general subscore after the end of seclusion (P=0.04).

CONCLUSION

This study shows that NLR and MPR are higher in patients with aggressive symptoms and/or agitation who require seclusion. These immunological markers could be considered as state markers.

Increased markers of inflammation after cannabis cessation and their association with psychotic symptoms

INTRODUCTION

A dysbalance of the immune system in psychotic disorders has been well investigated. However, despite a higher prevalence of cannabis (THC) consumption in patients with psychosis, few studies have investigated the impact of this use on inflammatory markers.

METHODS

One hundred and two inpatients were included in this retrospective study. Leukocytic formula, hsCRP, fibrinogen levels and urinary THC were measured, and comparisons were performed at baseline and after 4 weeks of cannabis cessation between cannabis users (THC+) and non-users (THC-).

RESULTS

After cannabis cessation, we found a greater increase in leucocyte level (p < 0.01), monocyte level (p = 0.05) and a statistical trend to a highest increase of lymphocyte level (p = 0.06) between baseline and 4 weeks in the THC+ group as compared to the THC- group. At 4 weeks, highest leucocyte (p = 0.03), lymphocyte (p = 0.04) and monocyte (p < 0.01) counts were found in the THC+ group, whereas at baseline no difference was found. A positive correlation was found between monocyte count at 4 weeks and baseline Positive and Negative Syndrome Scale (PANSS) negative subscore (p = 0.045) and between the variation of monocyte count between baseline and 4 weeks and the PANSS total score at 4 weeks (p = 0.05).

CONCLUSION

THC cessation is associated with an increase in inflammatory markers, including white blood cell, lymphocyte and monocyte levels, which correlates with symptomatology of patients with psychosis.

The role of SIRT3 in mediating the cognitive deficits and neuroinflammatory changes associated with a developmental animal model of schizophrenia

The neuroinflammatory state may contribute to the pathogenesis of many mental disorders including schizophrenia. Nicotinamide adenine dinucleotide (NAD+) is an essential cofactor for activation of proteins involved in mitochondria quality control, such as Sirtuin3 (SIRT3). Our previous study has found that NAD+ supplement could rescue early life stress (ELS)-induced neuroinflammation and down-regulation of SIRT3 in adult offspring. However, it is unclear whether SIRT3 is the key to the neuroprotective effects of NAD+ supplement in this animal model of schizophrenia. The present study used 24 h maternal separation (MS) as ELS to Wistar rat pups on the postnatal day (PND) 9. Schizophrenia-like behaviors and memory impairments were detected by behavioral tests. Microglial activation, pro-inflammatory cytokine expression, and NAD+/SIRT3 expression were detected in the prefrontal cortex and hippocampus. Meanwhile, NAM (a precursor of NAD+), and the SIRT3 activator Honokiol (HNK), and the SIRT3 inhibitor 3-TYP were used as an intervention in vivo. Our results showed that ELS could induce schizophrenia-like behaviors and M1 microglial activation, NAD+ decline, lower expression of SIRT3, and increased acetylated superoxide dismutase 2 expression at the adult stage. NAD+ supplement or HNK administration could block this process and normalize the behavioral alterations of the MS animals. 3-TYP administration in the control group and the NAM-treated MS rats caused M1 microglial activation and cognitive deficits. Our results demonstrated that SIRT3 mediated the stabilizing effect of NAD+ on normalizing M1 microglial activation and behavioral phenotypes in MS rats.

The role of the placenta-brain axis in psychoneuroimmune programming

Gestational exposures have enduring impacts on brain and neuroimmune development and function. Perturbations of pregnancy leading to placental structure/function deficits, cell stress, immune activation, and endocrine changes (metabolic, growth factors, etc.) all increase neuropsychiatric risk in offspring. The existing literature links obstetric diseases with placental involvement to offspring neuroimmune outcomes and neurodevelopmental risk. Psychoneuroimmune outcomes in offspring brain include changes to microglia, cytokine/chemokine production, cell stress, and long-term immunoreactivity. These outcomes are altered by structural, anti-angiogenic/hypoxic, inflammatory, and metabolic diseases of the placenta. This fetal programming occurs via direct placental passage or production of factors which can act directly on fetal brain substrates, or indirectly via action of circulating factors on intermediates in the placenta. Placental neuroendocrine, vascular/angiogenic, immune, and extracellular vesicular mechanisms are detailed. These mechanisms interact within various placental and pregnancy conditions. An increased understanding of the placental origins of psychoneuroimmunology will yield dividends for human health. Identifying maternal and placental biomarkers for fetal neuroimmune health may also revolutionize early diagnosis and precision psychiatry, empowering patients to make the best healthcare decisions for their families. Targeting placental mechanisms may be a valuable approach for the prevention and mitigation of intergenerational, lifelong neuropathology.

Molecular underpinnings of programming by early-life stress and the protective effects of early dietary ω6/ω3 ratio, basally and in response to LPS: Integrated mRNA-miRNAs approach

Early-life stress (ELS) exposure increases the risk for mental disorders, including cognitive impairments later in life. We have previously demonstrated that an early diet with low ω6/ω3 polyunsaturated fatty acid (PUFA) ratio protects against ELS-induced cognitive impairments. Several studies have implicated the neuroimmune system in the ELS and diet mediated effects, but currently the molecular pathways via which ELS and early diet exert their long-term impact are not yet fully understood. Here we study the effects of ELS and dietary PUFA ratio on hippocampal mRNA and miRNA expression in adulthood, both under basal as well as inflammatory conditions. Male mice were exposed to chronic ELS by the limiting bedding and nesting material paradigm from postnatal day(P)2 to P9, and provided with a diet containing a standard (high (15:1.1)) or protective (low (1.1:1)) ω6 linoleic acid to ω3 alpha-linolenic acid ratio from P2 to P42. At P120, memory was assessed using the object location task. Subsequently, a single lipopolysaccharide (LPS) injection was given and 24 h later hippocampal genome-wide mRNA and microRNA (miRNA) expression was measured using microarray. Spatial learning deficits induced by ELS in mice fed the standard (high ω6/ω3) diet were reversed by the early-life protective (low ω6/ω3) diet. An integrated miRNA - mRNA analysis revealed that ELS and early diet induced miRNA driven mRNA expression changes into adulthood. Under basal conditions both ELS and the diet affected molecular pathways related to hippocampal plasticity, with the protective (low ω6/ω3 ratio) diet leading to activation of molecular pathways associated with improved hippocampal plasticity and learning and memory in mice previously exposed to ELS (e.g., CREB signaling and endocannabinoid neuronal synapse pathway). LPS induced miRNA and mRNA expression was strongly dependent on both ELS and early diet. In mice fed the standard (high ω6/ω3) diet, LPS increased miRNA expression leading to activation of inflammatory pathways. In contrast, in mice fed the protective diet, LPS reduced miRNA expression and altered target mRNA expression inhibiting inflammatory signaling pathways and pathways associated with hippocampal plasticity, which was especially apparent in mice previously exposed to ELS. This data provides molecular insights into how the protective (low ω6/ω3) diet during development could exert its long-lasting beneficial effects on hippocampal plasticity and learning and memory especially in a vulnerable population exposed to stress early in life, providing the basis for the development of intervention strategies.

Characterizing the neuroimmune environment of offspring in a novel model of maternal allergic asthma and particulate matter exposure

Inflammation during pregnancy is associated with an increased risk for neurodevelopmental disorders (NDD). Increased gestational inflammation can be a result of an immune condition/disease, exposure to infection, and/or environmental factors. Epidemiology studies suggest that cases of NDD are on the rise. Similarly, rates of asthma are increasing, and the presence of maternal asthma during pregnancy increases the likelihood of a child being later diagnosed with NDD such as autism spectrum disorders (ASD). Particulate matter (PM), via air pollution, is an environmental factor known to worsen the symptoms of asthma, but also, PM has been associated with increased risk of neuropsychiatric disorders. Despite the links between asthma and PM with neuropsychiatric disorders, there is a lack of laboratory models investigating combined prenatal exposure to asthma and PM on offspring neurodevelopment. Thus, we developed a novel mouse model that combines exposure to maternal allergic asthma (MAA) and ultrafine iron-soot (UIS), a common component of PM. In the current study, female BALB/c mice were sensitized for allergic asthma with ovalbumin (OVA) prior to pregnancy. Following mating and beginning on gestational day 2 (GD2), dams were exposed to either aerosolized OVA to induce allergic asthma or phosphate buffered saline (PBS) for 1 h. Following the 1-h exposure, pregnant females were then exposed to UIS with a size distribution of 55 to 169 nm at an average concentration of 176 ± 45 μg/m3) (SD), or clean air for 4 h, over 8 exposure sessions. Offspring brains were collected at postnatal days (P)15 and (P)35. Cortices and hippocampal regions were then isolated and assessed for changes in cytokines using a Luminex bead-based multiplex assay. Analyses identified changes in many cytokines across treatment groups at both timepoints in the cortex, including interleukin-1 beta (IL-1β), and IL-17, which remained elevated from P15 to P35 in all treatment conditions compared to controls. There was a suppressive effect of the combined MAA plus UIS on the anti-inflammatory cytokine IL-10. Potentially shifting the cytokine balance towards more neuroinflammation. In the hippocampus at P15, elevations in cytokines were also identified across the treatment groups, namely IL-7. The combination of MAA and UIS exposure (MAA-UIS) during pregnancy resulted in an increase in microglia density in the hippocampus of offspring, as identified by IBA-1 staining. Together, these data indicate that exposure to MAA, UIS, and MAA-UIS result in changes in the neuroimmune environment of offspring that persist into adulthood.

Maternal chewing alleviates prenatal stress-related neuroinflammation mediated by microglia in the hippocampus of the mouse offspring

PURPOSE

Prenatal stress affects the hippocampal structure and function in pups. Maternal chewing ameliorates hippocampus-dependent cognitive impairments induced by prenatal stress. In this study, we investigated hippocampal microglia-mediated neuroinflammation in pups of dams exposed to prenatal stress with or without chewing during gestation.

METHODS

Pregnant mice were randomly assigned to control, stress, and stress/chewing groups. Stress and stress/chewing animals were subjected to restraint stress for 45 min three times daily from gestation day 12 to parturition, and were given a wooden stick to chew during the stress period. Four-month-old male pups were intraperitoneally administered with lipopolysaccharide (LPS). Serum corticosterone levels were determined 24 h after administration. The expression levels of hippocampal inflammatory cytokines were measured, and the microglia were analyzed morphologically.

RESULTS

Prenatal stress increased serum corticosterone levels, induced hippocampal microglia priming, and facilitated the release of interleukin-1β and tumor necrosis factor-α in the offspring. LPS treatment significantly increased the effects of prenatal stress on serum corticosterone levels, hippocampal microglial activation, and hippocampal neuroinflammation. Maternal chewing significantly inhibited the increase in serum corticosterone levels, suppressed microglial overactivation, and normalized inflammatory cytokine levels under basal prenatal stress conditions as well as after LPS administration.

CONCLUSIONS

Our findings indicate that maternal chewing can alleviate the increase in corticosterone levels and inhibit hippocampal microglia-mediated neuroinflammation induced by LPS administration and prenatal stress in adult offspring.

Characterizing the Neuroimmune Environment of Offspring in a Novel Model of Maternal Allergic Asthma and Particulate Matter Exposure

Autism spectrum disorders (ASD) are neurodevelopmental disorders characterized by the presence of decreased social interactions and an increase in stereotyped and repetitive behaviors. Epidemiology studies suggest that cases of ASD are on the rise. Similarly, rates of asthma are increasing, and the presence of maternal asthma during pregnancy increases the likelihood of a child being later diagnosed with ASD. Particulate matter (PM), via air pollution, is an environmental factor known to worsen the symptoms of asthma, but also, PM has been associated with increased risk of neuropsychiatric disorders including ASD. Despite the links between asthma and PM with neuropsychiatric disorders, there is a lack of laboratory models investigating combined prenatal exposure to asthma and PM on offspring neurodevelopment. Thus, we developed a novel mouse model that combines exposure to maternal allergic asthma (MAA) and ultrafine iron-soot (UIS), a common component of PM. In the current study, female BALB/c mice were primed for allergic asthma with ovalbumin (OVA) prior to pregnancy. Following mating and beginning on gestational day 2 (GD2), dams were exposed to either aerosolized OVA or phosphate buffered saline (PBS) for 1 hour. Following the 1-hour exposure, pregnant females were then exposed to UIS or clean air for 4 hours. Offspring brains were collected at postnatal days (P)15 and (P)35. Cortices and hippocampal regions were then isolated and assessed for changes in cytokines using a Luminex bead-based multiplex assay. Analyses identified changes in many cytokines across treatment groups at both timepoints in the cortex, including interleukin-1 beta (IL-1β), IL-2, IL-13, and IL-17, which remained elevated from P15 to P35 in all treatment conditions compared to controls. In the hippocampus at P15, elevations in cytokines were also identified across the treatment groups, namely interferon gamma (IFNγ) and IL-7. The combination of MAA and UIS exposure (MAA-UIS) during pregnancy resulted in an increase in microglia density in the hippocampus of offspring, as identified by IBA-1 staining. Together, these data indicate that exposure to MAA, UIS, and MAA-UIS result in changes in the neuroimmune environment of offspring that persist into adulthood.

Gut instinct: Sex differences in the gut microbiome are associated with changes in adolescent nociception following maternal separation in rats

Adolescent chronic pain is a growing public health epidemic. Our understanding of its etiology is limited; however, several factors can increase susceptibility, often developing in response to an acute pain trigger such as a surgical procedure or mild traumatic brain injury (mTBI), or an adverse childhood experience (ACE). Additionally, the prevalence and manifestation of chronic pain is sexually dimorphic, with double the rates in females than males. Despite this, the majority of pre-clinical pain research focuses on males, leaving a gap in mechanistic understanding for females. Given that emerging evidence has linked the gut microbiome and the brain-gut-immune axis to various pain disorders, we aimed to investigate sex-dependent changes in taxonomic and functional gut microbiome features following an ACE and acute injury as chronic pain triggers. Male and female Sprague Dawley rat pups were randomly assigned to either a maternal separation (MS) or no stress paradigm, then further into a sham, mTBI, or surgery condition. Chronically, the von Frey test was used to measure mechanical nociception, and fecal samples were collected for 16S rRNA sequencing. Animals in the surgery group had an increase in pain sensitivity when compared to mTBI and sham groups, and this was complemented by changes to the gut microbiome. In addition, significant sex differences were identified in gut microbiome composition, which were exacerbated in response to MS. Overall, we provide preliminary evidence for sex differences and ACE-induced changes in bacterial composition that, when combined, may be contributing to heterogeneity in pain outcomes.

Systemic Prenatal Stress Exposure through Corticosterone Application Adversely Affects Avian Embryonic Skin Development

Prenatal stress exposure is considered a risk factor for developmental deficits and postnatal behavioral disorders. While the effect of glucocorticoid-associated prenatal stress exposure has been comprehensively studied in many organ systems, there is a lack of in-depth embryological investigations regarding the effects of stress on the integumentary system. To approach this, we employed the avian embryo as a model organism and investigated the effects of systemic pathologically-elevated glucocorticoid exposure on the development of the integumentary system. After standardized corticosterone injections on embryonic day 6, we compared the stress-exposed embryos with a control cohort, using histological and immunohistochemical analyses as well as in situ hybridization. The overarching developmental deficits observed in the stress-exposed embryos were reflected through downregulation of both vimentin as well as fibronectin. In addition, a deficient composition in the different skin layers became apparent, which could be linked to a reduced expression of Dermo-1 along with significantly reduced proliferation rates. An impairment of skin appendage formation could be demonstrated by diminished expression of Sonic hedgehog. These results contribute to a more profound understanding of prenatal stress causing severe deficits in the integumentary system of developing organisms.

Gut Microbiota and Behavioural Issues in Production, Performance, and Companion Animals: A Systematic Review

The literature has identified poor nutrition as the leading factor in the manifestation of many behavioural issues in animals, including aggression, hyperalertness, and stereotypies. Literature focused on all species of interest consistently reported that although there were no significant differences in the richness of specific bacterial taxa in the microbiota of individual subjects with abnormal behaviour (termed alpha diversity), there was variability in species diversity between these subjects compared to controls (termed beta diversity). As seen in humans with mental disorders, animals exhibiting abnormal behaviour often have an enrichment of pro-inflammatory and lactic acid-producing bacteria and a reduction in butyrate-producing bacteria. It is evident from the literature that an association exists between gut microbiota diversity (and by extension, the concurrent production of microbial metabolites) and abnormal behavioural phenotypes across various species, including pigs, dogs, and horses. Similar microbiota population changes are also evident in human mental health patients. However, there are insufficient data to identify this association as a cause or effect. This review provides testable hypotheses for future research to establish causal relationships between gut microbiota and behavioural issues in animals, offering promising potential for the development of novel therapeutic and/or preventative interventions aimed at restoring a healthy gut-brain-immune axis to mitigate behavioural issues and, in turn, improve health, performance, and production in animals.

A consideration of the increased risk of schizophrenia due to prenatal maternal stress, and the possible role of microglia

Schizophrenia is caused by interaction of a combination of genetic and environmental factors. Of the latter, prenatal exposure to maternal stress is reportedly associated with elevated disease risk. The main orchestrators of inflammatory processes within the brain are microglia, and aberrant microglial activation/function has been proposed to contribute to the aetiology of schizophrenia. Here, we evaluate the epidemiological and preclinical evidence connecting prenatal stress to schizophrenia risk, and consider the possible mediating role of microglia in the prenatal stress-schizophrenia relationship. Epidemiological findings are rather consistent in supporting the association, albeit they are mitigated by effects of sex and gestational timing, while the evidence for microglial activation is more variable. Rodent models of prenatal stress generally report lasting effects on offspring neurobiology. However, many uncertainties remain as to the mechanisms underlying the influence of maternal stress on the developing foetal brain. Future studies should aim to characterise the exact processes mediating this aspect of schizophrenia risk, as well as focussing on how prenatal stress may interact with other risk factors.

Emerging role of microglia and astrocyte in the affective-motivational response induced by a rat model of persistent orofacial pain

Few studies are approaching the neural basis underlying the aggregation of emotional disorders in orofacial pain despite the stress, depression, and anxiety are some of the most commonly reported risk factors. Using a persistent orofacial pain rat model induced by complete Freund's adjuvant (CFA) injection into the temporomandibular joint, we have investigated the plasticity astrocytes and microglia key brain regions for the affective-emotional component of pain. We measured the expression and morphologic pattern of reactivation of glial fibrillary acidic protein (GFAP, astrocyte marker) and Iba-1 (microglial marker) by western blotting and immunohistochemistry analysis. The results showed no alterations on motor activity during inflammatory pain, indicating an exclusive effect of nociceptive behavior on the plasticity of limbic regions. CFA-induced temporomandibular inflammation changed GFAP and Iba-1 expression in distinct regions related to emotional behavior in a time-dependent manner. A significant increase in GFAP and Iba-1 expression was observed in the central nucleus of the amygdala, hippocampus and periaqueductal grey matter from day 3 to day 10 post-CFA injection. Moreover, a positive correlation between GFAP and Iba-1 upregulation and an increased mechanical hypersensitivity was observed. Conversely, no change on GFAP and Iba-1 expression was observed in the hypothalamus and colliculus during orofacial inflammatory pain. Our data suggest an important role for glial cells in the affective-motivational dimension of orofacial pain beyond their well-explored role in the traditional nociceptive transmission circuits.

Daytime Light Deficiency Leads to Sex- and Brain Region-Specific Neuroinflammatory Responses in a Diurnal Rodent

Seasonal changes in peripheral inflammation are well documented in both humans and animal models, but seasonal changes in neuroinflammation, especially the impact of seasonal lighting environment on neuroinflammation remain unclear. To address this question, the present study examined the effects of environmental lighting conditions on neuroinflammation in a diurnal rodent model, Nile grass rats (Arvicanthis niloticus). Male and female grass rats were housed in either bright (brLD) or dim (dimLD) light during the day to simulate a summer or winter light condition, respectively. After 4 weeks, microglia markers Iba-1 and CD11b, as well as pro-inflammatory cytokines TNF-α and IL-6, were examined in the anterior cingulate cortex (ACC), basolateral amygdala (BLA), and dorsal hippocampus (dHipp). The results revealed that winter-like dim light during the day leads to indicators of increased neuroinflammation in a brain site- and sex-specific manner. Specifically, relatively few changes in the neuroinflammatory markers were observed in the ACC, while numerous changes were found in the BLA and dHipp. In the BLA, winter-like dimLD resulted in hyper-ramified microglia morphology and increased expression of the pro-inflammatory cytokine IL-6, but only in males. In the dHipp, dimLD led to a higher number and hyper-ramified morphology of microglia as well as increased expression of CD11b and TNF-α, but only in females. Neuroinflammatory state is thus influenced by environmental light, differently in males and females, and could play a role in sex differences in the prevalence and symptoms of psychiatric or neurological disorders that are influenced by season or other environmental light conditions. Diurnal Nile grass rats were housed under bright or dim light during the day for 4 weeks, simulating seasonal fluctuations in daytime lighting environment. Dim light housing resulted in hyper-ramified morphology of microglia (scale bar, 15 μm) and altered expression of pro-inflammatory cytokines (TNF-α) in a sex- and brain region-specific manner.

Fetal hypoxia results in sex- and cell type-specific alterations in neonatal transcription in rat oligodendrocyte precursor cells, microglia, neurons, and oligodendrocytes

BACKGROUND

Fetal hypoxia causes vital, systemic, developmental malformations in the fetus, particularly in the brain, and increases the risk of diseases in later life. We previously demonstrated that fetal hypoxia exposure increases the susceptibility of the neonatal brain to hypoxic-ischemic insult. Herein, we investigate the effect of fetal hypoxia on programming of cell-specific transcriptomes in the brain of neonatal rats.

RESULTS

We obtained RNA sequencing (RNA-seq) data from neurons, microglia, oligodendrocytes, A2B5⁺ oligodendrocyte precursor cells, and astrocytes from male and female neonatal rats subjected either to fetal hypoxia or control conditions. Substantial transcriptomic responses to fetal hypoxia occurred in neurons, microglia, oligodendrocytes, and A2B5⁺ cells. Not only were the transcriptomic responses unique to each cell type, but they also occurred with a great deal of sexual dimorphism. We validated differential expression of several genes related to inflammation and cell death by Real-time Quantitative Polymerase Chain Reaction (qRT-PCR). Pathway and transcription factor motif analyses suggested that the NF-kappa B (NFκB) signaling pathway was enriched in the neonatal male brain due to fetal hypoxia, and we verified this result by transcription factor assay of NFκB-p65 in whole brain.

CONCLUSIONS

Our study reveals a significant impact of fetal hypoxia on the transcriptomes of neonatal brains in a cell-specific and sex-dependent manner, and provides mechanistic insights that may help explain the development of hypoxic-ischemic sensitive phenotypes in the neonatal brain.

Environmental Enrichment Protects against Neurotoxic Effects of Lipopolysaccharide: A Comprehensive Overview

Neuroinflammation is a pathophysiological condition associated with damage to the nervous system. Maternal immune activation and early immune activation have adverse effects on the development of the nervous system and cognitive functions. Neuroinflammation during adulthood leads to neurodegenerative diseases. Lipopolysaccharide (LPS) is used in preclinical research to mimic neurotoxic effects leading to systemic inflammation. Environmental enrichment (EE) has been reported to cause a wide range of beneficial changes in the brain. Based on the above, the purpose of the present review is to describe the effects of exposure to EE paradigms in counteracting LPS-induced neuroinflammation throughout the lifespan. Up to October 2022, a methodical search of studies in the literature, using the PubMed and Scopus databases, was performed, focusing on exposure to LPS, as an inflammatory mediator, and to EE paradigms in preclinical murine models. On the basis of the inclusion criteria, 22 articles were considered and analyzed in the present review. EE exerts sex- and age-dependent neuroprotective and therapeutic effects in animals exposed to the neurotoxic action of LPS. EE’s beneficial effects are present throughout the various ages of life. A healthy lifestyle and stimulating environments are essential to counteract the damages induced by neurotoxic exposure to LPS.

A high-fat high-sugar diet and adversity early in life modulate pain outcomes at the behavioural and molecular level in adolescent rats: The role of sex

Given that adolescence is a significant period of brain plasticity and development, early life factors have the potential to alter long term outcomes. For instance, adversities such as consumption of a high-fat high-sugar (HFHS) diet and adverse childhood experiences (ACEs; e.g., neglect), and their resulting inflammation and microglial activation can influence pain outcomes by priming the neuroimmune system to overrespond to stressors. Chronic pain is highly prevalent amongst the adolescent population, with the prevalence and manifestation being sexually dimorphic. Although clinical studies show that females are twice as likely to report pain problems compared to males, the majority of pre-clinical work uses male rodents. Therefore, our aim was to examine the effects of sex, a HFHS diet, and an ACE on chronic pain outcomes following a stressor in adolescence. Rat dams were randomly assigned to a Standard or HFHS diet, with pups maintained on their respective diets then randomly allocated to a No Stress or ACE paradigm, and a Sham or Injury condition as a stressor. Results showed that early life adversities increased nociceptive sensitivity, inflammation, and microglial activation systemically and within the brain. Behaviourally, pain outcomes were more prominent in females, however the neuroimmune response was exacerbated in males. These results demonstrate the sexual dimorphism of chronic pain outcomes following early life adversities and provide insight into the mechanisms driving these changes, which will inform more targeted and effective treatment strategies for youth living with chronic pain.

Maternal immune activation as an epidemiological risk factor for neurodevelopmental disorders: Considerations of timing, severity, individual differences, and sex in human and rodent studies

Epidemiological evidence suggests that one's risk of being diagnosed with a neurodevelopmental disorder (NDD)-such as autism, ADHD, or schizophrenia-increases significantly if their mother had a viral or bacterial infection during the first or second trimester of pregnancy. Despite this well-known data, little is known about how developing neural systems are perturbed by events such as early-life immune activation. One theory is that the maternal immune response disrupts neural processes important for typical fetal and postnatal development, which can subsequently result in specific and overlapping behavioral phenotypes in offspring, characteristic of NDDs. As such, rodent models of maternal immune activation (MIA) have been useful in elucidating neural mechanisms that may become dysregulated by MIA. This review will start with an up-to-date and in-depth, critical summary of epidemiological data in humans, examining the association between different types of MIA and NDD outcomes in offspring. Thereafter, we will summarize common rodent models of MIA and discuss their relevance to the human epidemiological data. Finally, we will highlight other factors that may interact with or impact MIA and its associated risk for NDDs, and emphasize the importance for researchers to consider these when designing future human and rodent studies. These points to consider include: the sex of the offspring, the developmental timing of the immune challenge, and other factors that may contribute to individual variability in neural and behavioral responses to MIA, such as genetics, parental age, the gut microbiome, prenatal stress, and placental buffering.

Early life stress induces visual dysfunction and retinal structural alterations in adult mice

Early life stress (ELS) is defined as a period of severe and/or chronic trauma, as well as environmental/social deprivation or neglect in the prenatal/early postnatal stage. Presently, the impact of ELS on the retina in the adult stage is unknown. The long-term consequences of ELS at retinal level were analyzed in an animal model of maternal separation with early weaning (MSEW), which mimics early life maternal neglect. For this purpose, mice were separated from the dams for 2 h at postnatal days (PNDs) 4-6, for 3 h at PNDs 7-9, for 4 h at PNDs 10-12, for 6 h at PNDs 13-16, and weaned at PND17. At the end of each separation period, mothers were subjected to movement restriction for 10 min. Control pups were left undisturbed from PND0, and weaned at PND21. Electroretinograms, visual evoked potentials, vision-guided behavioral tests, retinal anterograde transport, and retinal histopathology were examined at PNDs 60-80. MSEW induced long-lasting functional and histological effects at retinal level, including decreased retinal ganglion cell function and alterations in vision-guided behaviors, likely associated to decreased synaptophysin content, retina-superior colliculus communication deficit, increased microglial phagocytic activity, and retinal ganglion cell loss through a corticoid-dependent mechanism. A treatment with mifepristone, injected every 3 days between PNDs 4 and16, prevented functional and structural alterations induced by MSEW. These results suggest that retinal alterations might be included among the childhood adversity-induced threats to life quality, and that an early intervention with mifepristone avoided ELS-induced retinal disturbances.

Early-life stress lastingly impacts microglial transcriptome and function under basal and immune-challenged conditions

Early-life stress (ELS) leads to increased vulnerability to psychiatric disorders including depression later in life. Neuroinflammatory processes have been implicated in ELS-induced negative health outcomes, but how ELS impacts microglia, the main tissue-resident macrophages of the central nervous system, is unknown. Here, we determined the effects of ELS-induced by limited bedding and nesting material during the first week of life (postnatal days [P]2-9) on microglial (i) morphology; (ii) hippocampal gene expression; and (iii) synaptosome phagocytic capacity in male pups (P9) and adult (P200) mice. The hippocampus of ELS-exposed adult mice displayed altered proportions of morphological subtypes of microglia, as well as microglial transcriptomic changes related to the tumor necrosis factor response and protein ubiquitination. ELS exposure leads to distinct gene expression profiles during microglial development from P9 to P200 and in response to an LPS challenge at P200. Functionally, synaptosomes from ELS-exposed mice were phagocytosed less by age-matched microglia. At P200, but not P9, ELS microglia showed reduced synaptosome phagocytic capacity when compared to control microglia. Lastly, we confirmed the ELS-induced increased expression of the phagocytosis-related gene GAS6 that we observed in mice, in the dentate gyrus of individuals with a history of child abuse using in situ hybridization. These findings reveal persistent effects of ELS on microglial function and suggest that altered microglial phagocytic capacity is a key contributor to ELS-induced phenotypes.

Stress- and drug-induced neuroimmune signaling as a therapeutic target for comorbid anxiety and substance use disorders

Stress and substance use disorders remain two of the most highly prevalent psychiatric conditions and are often comorbid. While individually these conditions have a debilitating impact on the patient and a high cost to society, the symptomology and treatment outcomes are further exacerbated when they occur together. As such, there are few effective treatment options for these patients, and recent investigation has sought to determine the neural processes underlying the co-occurrence of these disorders to identify novel treatment targets. One such mechanism that has been linked to stress- and addiction-related conditions is neuroimmune signaling. Increases in inflammatory factors across the brain have been heavily implicated in the etiology of these disorders, and this review seeks to determine the nature of this relationship. According to the "dual-hit" hypothesis, also referred to as neuroimmune priming, prior exposure to either stress or drugs of abuse can sensitize the neuroimmune system to be hyperresponsive when exposed to these insults in the future. This review completes an examination of the literature surrounding stress-induced increases in inflammation across clinical and preclinical studies along with a summarization of the evidence regarding drug-induced alterations in inflammatory factors. These changes in neuroimmune profiles are also discussed within the context of their impact on the neural circuitry responsible for stress responsiveness and addictive behaviors. Further, this review explores the connection between neuroimmune signaling and susceptibility to these conditions and highlights the anti-inflammatory pharmacotherapies that may be used for the treatment of stress and substance use disorders.

Sex differences in the vulnerability of the hippocampus to prenatal stress

Distressing events during pregnancy that engage activity of the body's endocrine stress response have been linked with later life cognitive deficits in offspring and associated with developmental changes in cognitive-controlling neural regions. Interestingly, prenatal stress (PS)-induced alterations have shown some sex specificity. Here, we review the literature of animal studies examining sex-specific effect of physical PS on the function and structure of the hippocampus as hippocampal impairments likely underlie PS-associated deficits in learning and memory. Furthermore, the connectivity between the hypothalamic-pituitary-adrenal (HPA) axis and the hippocampus as well as the heavy presence of glucocorticoid receptors (GRs) in the hippocampus suggests this structure plays an important role in modulation of activity within stress circuitry in a sex-specific pattern. We hope that better understanding of sex-specific, PS-related hippocampal impairment will assist in uncovering the molecular mechanisms behind sex-based risk factors in PS populations across development, and perhaps contribute to greater precision in management of cognitive disturbances in this vulnerable population.

Nicotinamide reverses deficits in puberty-born neurons and cognitive function after maternal separation

Background

Early life stress (ELS) is associated with the development of schizophrenia later in life. The hippocampus develops significantly during childhood and is extremely reactive to stress. In rodent models, ELS can induce neuroinflammation, hippocampal neuronal loss, and schizophrenia-like behavior. While nicotinamide (NAM) can inhibit microglial inflammation, it is unknown whether NAM treatment during adolescence reduces hippocampal neuronal loss and abnormal behaviors induced by ELS.

Methods

Twenty-four hours of maternal separation (MS) of Wistar rat pups on post-natal day (PND)9 was used as an ELS. On PND35, animals received a single intraperitoneal injection of BrdU to label dividing neurons and were given NAM from PND35 to PND65. Behavioral testing was performed. Western blotting and immunofluorescence staining were used to detect nicotinamide adenine dinucleotide (NAD⁺)/Sirtuin3 (Sirt3)/superoxide dismutase 2 (SOD2) pathway-related proteins.

Results

Compared with controls, only MS animals in the adult stage (PND56–65) but not the adolescent stage (PND31–40) exhibited pre-pulse inhibition deficits and cognitive impairments mimicking schizophrenia symptoms. MS decreased the survival and activity of puberty-born neurons and hippocampal NAD⁺ and Sirt3 expression in adulthood. These observations were related to an increase in acetylated SOD2, microglial activation, and significant increases in pro-inflammatory IL-1β, TNF-α, and IL-6 expression. All the effects of MS at PND9 were reversed by administering NAM in adolescence (PND35–65).

Conclusions

MS may lead to schizophrenia-like phenotypes and persistent hippocampal abnormalities. NAM may be a safe and effective treatment in adolescence to restore normal hippocampal function and prevent or ameliorate schizophrenia-like behavior.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02591-y.

Brain-immune interaction mechanisms: Implications for cognitive dysfunction in psychiatric disorders

Objectives

Cognitive dysfunction has been identified as a major symptom of a series of psychiatric disorders. Multidisciplinary studies have shown that cognitive dysfunction is monitored by a two‐way interaction between the neural and immune systems. However, the specific mechanisms of cognitive dysfunction in immune response and brain immune remain unclear.

Materials and methods

In this review, we summarized the relevant research to uncover our comprehension of the brain–immune interaction mechanisms underlying cognitive decline.

Results

The pathophysiological mechanisms of brain‐immune interactions in psychiatric‐based cognitive dysfunction involve several specific immune molecules and their associated signaling pathways, impairments in neural and synaptic plasticity, and the potential neuro‐immunological mechanism of stress.

Conclusions

Therefore, this review may provide a better theoretical basis for integrative therapeutic considerations for psychiatric disorders associated with cognitive dysfunction.

The Role of Microglia in the (Mal)adaptive Response to Traumatic Experience in an Animal Model of PTSD

The present study investigates whether predator scent-stress (PSS) shifts the microglia from a quiescent to a chronically activated state and whether morphological alterations in microglial activation differ between individuals displaying resilient vs. vulnerable phenotypes. In addition, we examined the role that GC receptors play during PSS exposure in the impairment of microglial activation and thus in behavioral response. Adult male Sprague Dawley rats were exposed to PSS or sham-PSS for 15 min. Behaviors were assessed with the elevated plus-maze (EPM) and acoustic startle response (ASR) paradigms 7 days later. Localized brain expression of Iba-1 was assessed, visualized, and classified based on their morphology and stereological counted. Hydrocortisone and RU486 were administered systemically 10 min post PSS exposure and behavioral responses were measured on day 7 and hippocampal expression of Ionized calcium-binding adaptor molecule 1 (Iba-1) was subsequently evaluated. Animals whose behavior was extremely disrupted (PTSD-phenotype) selectively displayed excessive expression of Iba-1 with concomitant downregulation in the expression of CX3C chemokine receptor 1 (CX3CR1) in hippocampal structures as compared with rats whose behavior was minimally or partially disrupted. Changes in microglial morphology have also been related only to the PTSD-phenotype group. These data indicate that PSS-induced microglia activation in the hippocampus serves as a critical mechanistic link between the HPA-axis and PSS-induced impairment in behavioral responses.

Differential expression of placental 11β-HSD2 induced by high maternal glucocorticoid exposure mediates sex differences in placental and fetal development

A variety of adverse environmental factors during pregnancy cause maternal chronic stress. Caffeine is a common stressor, and its consumption during pregnancy is widespread. Our previous study showed that prenatal caffeine exposure (PCE) increased maternal blood glucocorticoid levels and caused abnormal development of offspring. However, the placental mechanism for fetal development inhibition caused by PCE-induced high maternal glucocorticoid has not been reported. This study investigated the effects of PCE-induced high maternal glucocorticoid level on placental and fetal development by regulating placental 11β-hydroxysteroid dehydrogenase 2 (11β-HSD2) expression and its underlying mechanism. First, human placenta and umbilical cord blood samples were collected from women without prenatal use of synthetic glucocorticoids. We found that placental 11β-HSD2 expression was significantly correlated with umbilical cord blood cortisol level and birth weight in male newborns but not in females. Furthermore, we established a rat model of high maternal glucocorticoids induced by PCE (caffeine, 60 mg/kg·d, ig), and found that the expression of 11β-HSD2 in male PCE placenta was decreased and negatively correlated with the maternal/fetal/placental corticosterone levels. Meanwhile, we found abnormal placental structure and nutrient transporter expression. In vitro, BeWo cells were used and confirm that 11β-HSD2 mediated inhibition of placental nutrient transporter expression induced by high levels of glucocorticoid. Finally, combined with the animal and cell experiments, we further confirmed that high maternal glucocorticoid could activate the GR-C/EBPα-Egr1 signaling pathway, leading to decreased expression of 11β-HSD2 in males. However, there was no significant inhibition of placental 11β-HSD2 expression, placental and fetal development in females. In summary, we confirmed that high maternal glucocorticoids could regulate placental 11β-HSD2 expression in a sex-specific manner, leading to differences in placental and fetal development. This study provides the theoretical and experimental basis for analyzing the inhibition of fetoplacental development and its sex difference caused by maternal stress.

Astrocytes and Microglia in Stress-Induced Neuroinflammation: The African Perspective

Background: Africa is laden with a youthful population, vast mineral resources and rich fauna. However, decades of unfortunate historical, sociocultural and leadership challenges make the continent a hotspot for poverty, indoor and outdoor pollutants with attendant stress factors such as violence, malnutrition, infectious outbreaks and psychological perturbations. The burden of these stressors initiate neuroinflammatory responses but the pattern and mechanisms of glial activation in these scenarios are yet to be properly elucidated. Africa is therefore most vulnerable to neurological stressors when placed against a backdrop of demographics that favor explosive childbearing, a vast population of unemployed youths making up a projected 42% of global youth population by 2030, repressive sociocultural policies towards women, poor access to healthcare, malnutrition, rapid urbanization, climate change and pollution. Early life stress, whether physical or psychological, induces neuroinflammatory response in developing nervous system and consequently leads to the emergence of mental health problems during adulthood. Brain inflammatory response is driven largely by inflammatory mediators released by glial cells; namely astrocytes and microglia. These inflammatory mediators alter the developmental trajectory of fetal and neonatal brain and results in long-lasting maladaptive behaviors and cognitive deficits. This review seeks to highlight the patterns and mechanisms of stressors such as poverty, developmental stress, environmental pollutions as well as malnutrition stress on astrocytes and microglia in neuroinflammation within the African context.

Preclinical animal models of mental illnesses to translate findings from the bench to the bedside: Molecular brain mechanisms and peripheral biomarkers associated to early life stress or immune challenges

Animal models are useful preclinical tools for studying the pathogenesis of mental disorders and the effectiveness of their treatment. While it is not possible to mimic all symptoms occurring in humans, it is however possible to investigate the behavioral, physiological and neuroanatomical alterations relevant for these complex disorders in controlled conditions and in genetically homogeneous populations. Stressful and infection-related exposures represent the most employed environmental risk factors able to trigger or to unmask a psychopathological phenotype in animals. Indeed, when occurring during sensitive periods of brain maturation, including pre, postnatal life and adolescence, they can affect the offspring's neurodevelopmental trajectories, increasing the risk for mental disorders. Not all stressed or immune challenged animals, however, develop behavioral alterations and preclinical animal models can explain differences between vulnerable or resilient phenotypes. Our review focuses on different paradigms of stress (prenatal stress, maternal separation, social isolation and social defeat stress) and immune challenges (immune activation in pregnancy) and investigates the subsequent alterations in several biological and behavioral domains at different time points of animals' life. It also discusses the "double-hit" hypothesis where an initial early adverse event can prime the response to a second negative challenge. Interestingly, stress and infections early in life induce the activation of the hypothalamic-pituitary-adrenal (HPA) axis, alter the levels of neurotransmitters, neurotrophins and pro-inflammatory cytokines and affect the functions of microglia and oxidative stress. In conclusion, animal models allow shedding light on the pathophysiology of human mental illnesses and discovering novel molecular drug targets for personalized treatments.

Early Life Events and Maturation of the Dentate Gyrus: Implications for Neurons and Glial Cells

The dentate gyrus (DG), an important part of the hippocampus, plays a significant role in learning, memory, and emotional behavior. Factors potentially influencing normal development of neurons and glial cells in the DG during its maturation can exert long-lasting effects on brain functions. Early life stress may modify maturation of the DG and induce lifelong alterations in its structure and functioning, underlying brain pathologies in adults. In this paper, maturation of neurons and glial cells (microglia and astrocytes) and the effects of early life events on maturation processes in the DG have been comprehensively reviewed. Early postnatal interventions affecting the DG eventually result in an altered number of granule neurons in the DG, ectopic location of neurons and changes in adult neurogenesis. Adverse events in early life provoke proinflammatory changes in hippocampal glia at cellular and molecular levels immediately after stress exposure. Later, the cellular changes may disappear, though alterations in gene expression pattern persist. Additional stressful events later in life contribute to manifestation of glial changes and behavioral deficits. Alterations in the maturation of neuronal and glial cells induced by early life stress are interdependent and influence the development of neural nets, thus predisposing the brain to the development of cognitive and psychiatric disorders.

Exploring Sex-Related Differences in Microglia May Be a Game-Changer in Precision Medicine

One area of microglial biology that has been relatively neglected until recently is sex differences and this is in spite of the fact that sex is a risk factor in several diseases that are characterized by neuroinflammation and, by extension, microglial activation. Why these sex differences exist is not known but the panoply of differences extend to microglial number, genotype and phenotype. Significantly, several of these sex-related differences are also evident in health and change during life emphasizing the dynamic and plastic nature of microglia. This review will consider how age impacts on sex-related differences in microglia and ask whether the advancement of personalized medicine demands that a greater focus is placed on studying sex-related differences in microglia in Alzheimer's disease, Parkinson's disease and models of inflammatory stress and trauma in order to make true progress in dealing with these conditions.

Recent Reports on Redox Stress-Induced Mitochondrial DNA Variations, Neuroglial Interactions, and NMDA Receptor System in Pathophysiology of Schizophrenia

Schizophrenia (SZ) is a chronic psychiatric disorder affecting several people worldwide. Mitochondrial DNA (mtDNA) variations could invoke changes in the OXPHOS system, calcium buffering, and ROS production, which have significant implications for glial cell survival during SZ. Oxidative stress has been implicated in glial cells-mediated pathogenesis of SZ; the brain comparatively more prone to oxidative damage through NMDAR. A confluence of scientific evidence points to mtDNA alterations, Nrf2 signaling, dynamic alterations in dorsolateral prefrontal cortex (DLPFC), and provocation of oxidative stress that enhance pathophysiology of SZ. Furthermore, the alterations in excitatory signaling related to NMDAR signaling were particularly reported for SZ pathophysiology. Current review reported the recent evidence for the role of mtDNA variations and oxidative stress in relation to pathophysiology of SZ, NMDAR hypofunction, and glutathione deficiency. NMDAR system is influenced by redox dysregulation in oxidative stress, inflammation, and antioxidant mediators. Several studies have demonstrated the relationship of these variables on severity of pathophysiology in SZ. An extensive literature search was conducted using Medline, PubMed, PsycINFO, CINAHL PLUS, BIOSIS Preview, Google scholar, and Cochrane databases. We summarize consistent evidence pointing out a plausible model that may elucidate the crosstalk between mtDNA alterations in glial cells and redox dysregulation during oxidative stress and the perturbation of NMDA neurotransmitter system during current therapeutic modalities for the SZ treatment. This review can be beneficial for the development of promising novel diagnostics, and therapeutic modalities by ascertaining the mtDNA variations, redox state, and efficacy of pharmacological agents to mitigate redox dysregulation and augment NMDAR function to treat cognitive and behavioral symptoms in SZ.

Prenatal Environment and Neurodevelopmental Disorders

The internal and external environment of the mother during the developmental stages of the fetus affects the offspring's health. According to the developmental origins of health and disease (DOHaD) theory, environmental factors influence the offspring and also affect health in adulthood. Recently, studies based on this theory have gained attracted attention because of their clinical utility in identifying the risk groups for various diseases. Neurodevelopmental disorders (NDDs) such as autism spectrum disorder (ASD) and attention-deficit hyperactivity disorder (ADHD) can be caused by exposure to certain prenatal environments during pregnancy. This review describes the latest findings on the effect of prenatal environment on the onset mechanism of NDDs based on the DOHaD theory. Unravelling the molecular mechanisms underlying the pathogenesis of NDDs is important, because there are no therapeutic drugs for these disorders. Furthermore, elucidating the relationship between the DOHaD theory and NDDs will contribute to the popularization of preventive medicine.

Developmental Stressors Induce Innate Immune Memory in Microglia and Contribute to Disease Risk

Many types of stressors have an impact on brain development, function, and disease susceptibility including immune stressors, psychosocial stressors, and exposure to drugs of abuse. We propose that these diverse developmental stressors may utilize a common mechanism that underlies impaired cognitive function and neurodevelopmental disorders such as schizophrenia, autism, and mood disorders that can develop in later life as a result of developmental stressors. While these stressors are directed at critical developmental windows, their impacts are long-lasting. Immune activation is a shared pathophysiology across several different developmental stressors and may thus be a targetable treatment to mitigate the later behavioral deficits. In this review, we explore different types of prenatal and perinatal stressors and their contribution to disease risk and underlying molecular mechanisms. We highlight the impact of developmental stressors on microglia biology because of their early infiltration into the brain, their critical role in brain development and function, and their long-lived status in the brain throughout life. Furthermore, we introduce innate immune memory as a potential underlying mechanism for developmental stressors' impact on disease. Finally, we highlight the molecular and epigenetic reprogramming that is known to underlie innate immune memory and explain how similar molecular mechanisms may be at work for cells to retain a long-term perturbation after exposure to developmental stressors.

The dual hit hypothesis of schizophrenia: Evidence from animal models

Schizophrenia is a heterogeneous psychiatric disorder, which can severely impact social and professional functioning. Epidemiological and clinical studies show that schizophrenia has a multifactorial aetiology comprising genetic and environmental risk factors. Although several risk factors have been identified, it is still not clear how they result in schizophrenia. This knowledge gap, however, can be investigated in animal studies. In this review, we summarise animal studies regarding molecular and cellular mechanisms through which genetic and environmental factors may affect brain development, ultimately causing schizophrenia. Preclinical studies suggest that early environmental risk factors can affect the immune, GABAergic, glutamatergic, or dopaminergic system and thus increase the susceptibility to another risk factor later in life. A second insult, like social isolation, stress, or drug abuse, can further disrupt these systems and the interactions between them, leading to behavioural abnormalities. Surprisingly, first insults like maternal infection and early maternal separation can also have protective effects. Single gene mutations associated with schizophrenia did not have a major impact on the susceptibility to subsequent environmental hits.

Adverse Childhood Experiences (ACEs) and Internalizing Mental Health, Pain, and Quality of Life in Youth With Chronic Pain: A Longitudinal Examination

The aims of this longitudinal study were to 1) identify categories of adverse childhood experiences (ACEs) (ie, neglect, abuse, household dysfunction in childhood) that increase risk for internalizing mental health problems, pain-related impairment, and poorer quality of life and 2) examine the moderating role of posttraumatic stress symptoms (PTSS) in these associations, in a clinical sample of youth with chronic pain. At 2 timepoints, youth (N = 155; aged 10-18 years) completed measures of exposure to ACEs, PTSS, depressive and anxiety symptoms, pain intensity, pain interference, and quality of life. Multivariate analyses of variance, linear mixed modeling, and moderation analyses were conducted. Results from cross-sectional and longitudinal analyses were similar; youth with a history of 3+ ACEs reported significantly higher PTSS, depressive and anxiety symptoms, and poorer quality of life than youth with no ACE history. Results also revealed differences in functioning between youth exposed to different types of ACEs (ie, maltreatment only, household dysfunction only, both, none). Finally, PTSS was found to moderate the association between ACEs and anxiety and depressive symptoms. Findings underscore the influence that ACEs can have on the long-term functioning of youth with chronic pain as well as the important role of current PTSS in this association. PERSPECTIVE: This study found that the risk of poorer outcomes imposed by ACEs at baseline remains longitudinally and that posttraumatic stress symptoms (PTSS) moderate the relationship between ACEs and anxiety and depressive symptoms in youth with chronic pain. These results underscore the importance of assessing for ACEs and PTSS alongside chronic pain in youth.

Maternal fluoxetine reduces hippocampal inflammation and neurogenesis in adult offspring with sex-specific effects of periadolescent oxytocin

Untreated perinatal depression can have severe consequences for the mother and her children. However, both the efficacy to mothers and safety to exposed infants of pharmacological antidepressants such as selective serotonin reuptake inhibitors (SSRIs), have been questioned. We previously reported that maternal SSRI exposure increased hippocampal IL-1β levels, which may be tied to limited efficacy of SSRIs during the postpartum to the dam but is not yet known whether maternal postpartum SSRIs affect the neuroinflammatory profile of adult offspring. In addition, although controversial, perinatal SSRI exposure has been linked to increased risk of autism spectrum disorder (ASD) in children. Oxytocin (OT) is under investigation as a treatment for ASD, but OT is a large neuropeptide that has difficulty crossing the blood-brain barrier (BBB). Triozan^TM is a nanoformulation that can facilitate OT to cross the BBB. Thus, we investigated the impact of maternal postpartum SSRIs and offspring preadolescent OT treatment on adult offspring neuroinflammation, social behavior, and neurogenesis in the hippocampus. Using a model of de novo postpartum depression, corticosterone (CORT) was given in the postpartum to the dam with or without treatment with the SSRI, fluoxetine (FLX) for 21 days postpartum. Offspring were then subsequently treated with either OT, OT + Triozan^TM, or vehicle for 10 days prior to adolescence (PD25-34). Maternal FLX decreased hippocampal IL-10 and IL-13 and neurogenesis in both sexes, whereas maternal CORT increased hippocampal IL-13 in both sexes. Maternal CORT treatment shifted the neuroimmune profile towards a more proinflammatory profile in offspring hippocampus, whereas oxytocin, independent of formulation, normalized this profile. OT treatment increased hippocampal neurogenesis in adult males but not in adult females, regardless of maternal treatment. OT treatment increased the time spent with a novel social stimulus animal (social investigation) in both adult male and female offspring, although this effect depended on maternal CORT. These findings underscore that preadolescent exposure to OT can reverse some of the long-lasting effects of postpartum maternal CORT and FLX treatments in the adult offspring. In addition, we found that maternal treatments that reduce (CORT) or increase (FLX) hippocampal inflammation in dams resulted in opposing patterns of hippocampal inflammation in adult offspring.

Maternal separation leads to regional hippocampal microglial activation and alters the behavior in the adolescence in a sex-specific manner

Early life adversities during childhood (such as maltreatment, abuse, neglect, or parental deprivation) may increase the vulnerability to cognitive disturbances and emotional disorders in both, adolescence and adulthood. Maternal separation (MS) is a widely used model to study stress-related changes in brain and behavior in rodents. In this study, we investigated the effect of MS (postnatal day 2–14, 3 ​h/day) in both, female and male adolescent mice. Specifically, we evaluated (i) the spatial working memory, anxiety and depressive-like behavior, (ii) the hippocampal synaptic gene expression, and (iii) the hippocampal neuroinflammatory response.

Our results show that MS significantly increased depressive-like behavior in adolescent female mice and altered the spatial memory in adolescent male mice. In addition, MS led to decreased expression of genes related to synaptic function (5ht6r, Synaptophysin, and Cox-2) and induced an exacerbated microglial activation in dentate gyrus (DG), CA1, and CA3. However, while the levels of hippocampal inflammatory cytokines were not modified by MS, they did follow a sex-specific expression in adolescent mice.

Taken together, our results suggest that MS induces long-term changes in hippocampal microglia and synaptic gene expression, alters the spatial memory, and induces depressive-like behavior in the adolescent mice, in a sex-specific manner.

In wildtype adolescent mice (6 weeks of age):•

Maternal separation alters spatial working memory in males and induces depressive-like behavior in females.

•

Maternal separation changes hippocampal synaptic gene expression.

•

Maternal separation activates microglia in dentate gyrus, CA1, and CA3 but does not affect hippocampal cytokine levels. However, males present higher levels of cytokines compared to females.

Prenatal stress and increased susceptibility to anxiety-like behaviors: role of neuroinflammation and balance between GABAergic and glutamatergic transmission

Neuroplasticity during the prenatal period allows neurons to regenerate anatomically and functionally for re-programming the brain development. During this critical period of fetal programming, the fetus phenotype can change in accordance with environmental stimuli such as stress exposure. Prenatal stress (PS) can exert important effects on brain development and result in permanent alterations with long-lasting consequences on the physiology and behavior of the offspring later in life. Neuroinflammation, as well as GABAergic and glutamatergic dysfunctions, has been implicated as potential mediators of behavioral consequences of PS. Hyperexcitation, due to enhanced excitatory transmission or reduced inhibitory transmission, can promote anxiety. Alterations of the GABAergic and/or glutamatergic signaling during fetal development lead to a severe excitatory/inhibitory imbalance in neuronal circuits, a condition that may account for PS-precipitated anxiety-like behaviors. This review summarizes experimental evidence linking PS to an elevated risk to anxiety-like behaviors and interprets the role of the neuroinflammation and alterations of the brain GABAergic and glutamatergic transmission in this phenomenon. We hypothesize this is an imbalance in GABAergic and glutamatergic circuits (as a direct or indirect consequence of neuroinflammation), which at least partially contributes to PS-precipitated anxiety-like behaviors and primes the brain to be vulnerable to anxiety disorders. Therefore, pharmacological interventions with anti-inflammatory activities and with regulatory effects on the excitatory/inhibitory balance can be attributed to the novel therapeutic target for anxiety disorders.

Insulin-like growth factor 1 gene transfer for sporadic Alzheimer's disease: New evidence for trophic factor mediated hippocampal neuronal and synaptic recovery-based behavior improvement

Sporadic Alzheimer's disease (sAD) is the most prevalent neurodegenerative disorder with no cure. Patients typically suffer from cognitive impairment imprinted by irreversible neocortex and hippocampal degeneration with overt synaptic and neuron dysfunction. Insulin-like growth factor 1 (IGF1) has proven to be a potent neuroprotective molecule in animal models of age-related neurodegeneration. In this regard, adenoviral gene transfer aiming at IGF1 brain overexpression has been hitherto an underexplored approach for the sAD treatment. We postulated enhanced IGF1 signaling in the brain as a restorative means in the diseased brain to revert cognitive deficit and restore hippocampal function. We implemented recombinant adenovirus mediated intracerebroventricular IGF1 gene transfer on the streptozotocin (STZ) induced sAD rat model, using 3-month-old male Sprague Dawley rats. This approach enhanced IGF1 signaling in the hippocampus and dampened sAD phosphorylated Tau. We found a remarkable short-term improvement in species-typical behavior, recognition memory, spatial memory, and depressive-like behavior. Histological analysis revealed a significant recovery of immature hippocampal neurons. We additionally recorded an increase in hippocampal microglial cells, which we suggest to exert anti-inflammatory effects. Finally, we found decreased levels of pre- and postsynaptic proteins in the hippocampus of STZ animals. Interestingly, IGF1 gene transfer increased the levels of PSD95 and GAD65/67 synaptic markers, indicating that the treatment enhanced the synaptic plasticity. We conclude that exogenous activation of IGF1 signaling pathway, 1 week after intracerebroventricular STZ administration, protects hippocampal immature neurons, dampens phosphorylated Tau levels, improves synaptic function and therefore performs therapeutically on the sAD STZ model. Hence, this study provides strong evidence for the use of this trophic factor to treat AD and age-related neurodegeneration.

Regulation of microglia population dynamics throughout development, health, and disease

The dynamic expansions and contractions of the microglia population in the central nervous system (CNS) to achieve homeostasis are likely vital for their function. Microglia respond to injury or disease but also help guide neurodevelopment, modulate neural circuitry throughout life, and direct regeneration. Throughout these processes, microglia density changes, as does the volume of area that each microglia surveys. Given that microglia are responsible for sensing subtle alterations to their environment, a change in their density could affect their capacity to mobilize rapidly. In this review, we attempt to synthesize the current literature on the ligands and conditions that promote microglial proliferation across development, adulthood, and neurodegenerative conditions. Microglia display an impressive proliferative capacity during development and in neurodegenerative diseases that is almost completely absent at homeostasis. However, the appropriate function of microglia in each state is critically dependent on density fluctuations that are primarily induced by proliferation. Proliferation is a natural microglial response to insult and often serves neuroprotective functions. In contrast, inappropriate microglial proliferation, whether too much or too little, often precipitates undesirable consequences for nervous system health. Thus, fluctuations in the microglia population are tightly regulated to ensure these immune cells can execute their diverse functions.

An emerging role for microglia in stress‐effects on memory

Stressful experiences evoke, among others, a rapid increase in brain (nor)epinephrine (NE) levels and a slower increase in glucocorticoid hormones (GCs) in the brain. Microglia are key regulators of neuronal function and contain receptors for NE and GCs. These brain cells may therefore potentially be involved in modulating stress effects on neuronal function and learning and memory. In this review, we discuss that stress induces (1) an increase in microglial numbers as well as (2) a shift toward a pro‐inflammatory profile. These microglia have (3) impaired crosstalk with neurons and (4) disrupted glutamate signaling. Moreover, microglial immune responses after stress (5) alter the kynurenine pathway through metabolites that impair glutamatergic transmission. All these effects could be involved in the impairments in memory and in synaptic plasticity caused by (prolonged) stress, implicating microglia as a potential novel target in stress‐related memory impairments.

A subpopulation of embryonic microglia respond to maternal stress and influence nearby neural progenitors

The interplay between hypothalamic neurons and microglia as they integrate stressors to regulate homeostasis is of growing interest. We asked if microglia in the embryonic hypothalamus were likewise stress responsive and, if so, whether their precocious activation perturbs nearby neural stem cell (NSC) programs. We performed single-cell transcriptomics to define embryonic hypothalamic microglia heterogeneity and identified four microglial subsets, including a subpopulation adjacent to NSCs that was responsive to gestational cold stress. Stress exposure elevated CCL3 and CCL4 secretion, but only in male brains, and ex vivo CCL4 treatment of hypothalamic NSCs altered proliferation and differentiation. Concomitantly, gestational stress decreased PVN oxytocin neurons only in male embryos, which was reversed by microglia depletion. Adult offspring exposed to gestational stress displayed altered social behaviors, which was likewise microglia dependent, but only in males. Collectively, immature hypothalamic microglia play an unappreciated role in translating maternal stressors to sexually dimorphic perturbation of neurodevelopmental programs.

Pain in the Developing Brain: Early Life Factors Alter Nociception and Neurobiological Function in Adolescent Rats

Although adverse early experiences prime individuals to be at increased risk for chronic pain, little research has examined the trauma–pain relationship in early life or the underlying mechanisms that drive pathology over time. Given that early experiences can potentiate the nociceptive response, this study aimed to examine the effects of a high-fat, high-sugar (HFHS) diet and early life stress (maternal separation [MS]) on pain outcomes in male and female adolescent rats. Half of the rats also underwent a plantar-incision surgery to investigate how the pain system responded to a mildly painful stimuli in adolescence. Compared with controls, animals that were on the HFHS diet, experienced MS, or had exposure to both, exhibited increased anxiety-like behavior and altered thermal and mechanical nociception at baseline and following the surgery. Advanced magnetic resonance imaging demonstrated that the HFHS diet and MS altered the maturation of the brain, leading to changes in brain volume and diffusivity within the anterior cingulate, amygdala, corpus callosum, nucleus accumbens, and thalamus, while also modifying the integrity of the corticospinal tracts. The effects of MS and HFHS diet were often cumulative, producing exacerbated pain sensitivity and increased neurobiological change. As early experiences are modifiable, understanding their role in pain may provide targets for early intervention/prevention.

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.