Neonatal infection-induced memory impairment after lipopolysaccharide in adulthood is prevented via caspase-1 inhibition

Caspase-1 inhibitor exerts brain-protective effects against sepsis-associated encephalopathy and cognitive impairments in a mouse model of sepsis

Sepsis-associated encephalopathy (SAE) manifested clinically in acute and long-term cognitive impairments and associated with increased morbidity and mortality worldwide. The potential pathological changes of SAE are complex and remain to be elucidated. Pyroptosis, a novel programmed cell death, is executed by caspase-1-cleaved GSDMD N-terminal (GSDMD-NT) and we investigated it in peripheral blood immunocytes of septic patients previously. Here, a caspase-1 inhibitor VX765 was treated with CLP-induced septic mice. Novel object recognition test indicated that VX765 treatment reversed cognitive dysfunction in septic mice. Elevated plus maze, tail suspension test and open field test revealed that depressive-like behaviors of septic mice were relieved. Inhibited caspase-1 suppressed the expressions of GSDMD and its cleavage form GSDMD-NT, and reduced pyroptosis in brain at day 1 and day 7 after sepsis. Meantime, inhibited caspase-1 mitigated the expressions of IL-1β, MCP-1 and TNF-α in serum and brain, diminished microglia activation in septic mice, and reduced sepsis-induced brain-blood barrier disruption and ultrastructure damages in brain as well. Inhibited caspase-1 protected the synapse plasticity and preserved long-term potential, which may be the possible mechanism of cognitive functions protective effects of septic mice. In conclusion, caspase-1 inhibition exerts brain-protective effects against SAE and cognitive impairments in a mouse model of sepsis.

Early Life Inflammation Increases CA1 Pyramidal Neuron Excitability in a Sex and Age Dependent Manner through a Chloride Homeostasis Disruption

Early life, systemic inflammation causes long-lasting changes in behavior. To unmask possible mechanisms associated with this phenomenon, we asked whether the intrinsic membrane properties in hippocampal neurons were altered as a consequence of early life inflammation. C57BL/6 mice were bred in-house and both male and female pups from multiple litters were injected with lipopolysaccharide (LPS; 100 μg/kg, i.p.) or vehicle at postnatal day (P)14, and kept until adolescence (P35-P45) or adulthood (P60-P70), when brain slices were prepared for whole-cell and perforated-patch recordings from CA1 hippocampal pyramidal neurons. In neurons of adult male mice pretreated with LPS, the number of action potentials elicited by depolarizing current pulses was significantly increased compared with control neurons, concomitant with increased input resistance, and a lower action potential threshold. Although these changes were not associated with changes in relevant sodium channel expression or differences in capacitance or dendritic architecture, they were linked to a mechanism involving intracellular chloride overload, revealed through a depolarized GABA reversal potential and increased expression of the chloride transporter, NKCC1. In contrast, no significant changes were observed in neurons of adult female mice pretreated with LPS, nor in adolescent mice of either sex. These data uncover a potential mechanism involving neonatal inflammation-induced plasticity in chloride homeostasis, which may contribute to early life inflammation-induced behavioral alterations.SIGNIFICANCE STATEMENT Early life inflammation results in long-lasting changes in many aspects of adult physiology. In this paper we reveal that a brief exposure to early life peripheral inflammation with LPS increases excitability in hippocampal neurons in a sex- and age-dependent manner through a chloride homeostasis disruption. As this hyperexcitability was only seen in adult males, and not in adult females or adolescent animals of either sex, it raises the possibility of a hormonal interaction with early life inflammation. Furthermore, as neonatal inflammation is a normal feature of early life in most animals, as well as humans, these findings may be very important for the development of animal models of disease that more appropriately resemble the human condition.

Neonatal infection leads to increased susceptibility to Aβ oligomer-induced brain inflammation, synapse loss and cognitive impairment in mice

Harmful environmental stimuli during critical stages of development can profoundly affect behavior and susceptibility to diseases. Alzheimer disease (AD) is the most frequent neurodegenerative disease, and evidence suggest that inflammatory conditions act cumulatively, contributing to disease onset. Here we investigated whether infection early in life can contribute to synapse damage and cognitive impairment induced by amyloid-β oligomers (AβOs), neurotoxins found in AD brains. To this end, wild-type mice were subjected to neonatal (post-natal day 4) infection by Escherichia coli (1 × 10⁴ CFU/g), the main cause of infection in low-birth-weight premature infants in the US. E. coli infection caused a transient inflammatory response in the mouse brain starting shortly after infection. Although infected mice performed normally in behavioral tasks in adulthood, they showed increased susceptibility to synapse damage and memory impairment induced by low doses of AβOs (1 pmol; intracerebroventricular) in the novel object recognition paradigm. Using in vitro and in vivo approaches, we show that microglial cells from E. coli-infected mice undergo exacerbated activation when exposed to low doses of AβOs. In addition, treatment of infected pups with minocycline, an antibiotic that inhibits microglial pro-inflammatory polarization, normalized microglial response to AβOs and restored normal susceptibility of mice to oligomer-induced cognitive impairment. Interestingly, mice infected with by E. coli (1 × 10⁴ CFU/g) during adolescence (post-natal day 21) or adulthood (post-natal day 60) showed normal cognitive performance even in the presence of AβOs (1 pmol), suggesting that only infections at critical stages of development may lead to increased susceptibility to amyloid-β-induced toxicity. Altogether, our findings suggest that neonatal infections can modulate microglial response to AβOs into adulthood, thus contributing to amyloid-β-induced synapse damage and cognitive impairment.

Chorioamnionitis in Rats Precipitates Extended Postnatal Inflammatory Lymphocyte Hyperreactivity

Preterm birth is an important cause of perinatal brain injury (PBI). Neurological injury in extremely preterm infants often begins in utero with chorioamnionitis (CHORIO) or inflammation/infection of the placenta and concomitant placental insufficiency. Studies in humans have shown dysregulated inflammatory signaling throughout the placental-fetal brain axis and altered peripheral immune responses in children born preterm with cerebral palsy (CP). We hypothesized that peripheral immune responses would be altered in our well-established rat model of CP. Specifically, we proposed that isolated peripheral blood mononuclear cells (PBMCs) would be hyperresponsive to a second hit of inflammation throughout an extended postnatal time course. Pregnant Sprague-Dawley dams underwent a laparotomy on embryonic day 18 (E18) with occlusion of the uterine arteries (for 60 min) followed by intra-amniotic injection of lipopolysaccharide (LPS, 4 μg/sac) to induce injury in utero. Shams underwent laparotomy only, with equivalent duration of anesthesia. Laparotomies were then closed, and the rat pups were born at E22. PBMCs were isolated from pups on postnatal day 7 (P7) and P21, and subsequently stimulated in vitro with LPS for 3 or 24 h. A secreted inflammatory profile analysis of conditioned media was performed using multiplex electrochemiluminescent immunoassays, and the composition of inflammatory cells was assayed with flow cytometry (FC). Results indicate that CHORIO PBMCs challenged with LPS are hyperreactive and secrete significantly more tumor necrosis factor α (TNFα) and C-X-C chemokine ligand 1 at P7. FC confirmed increased intracellular TNFα in CHORIO pups at P7 following LPS stimulation, in addition to increased numbers of CD11b/c immunopositive myeloid cells. Notably, TNFα secretion was sustained until P21, with increased interleukin 6, concomitant with increased expression of integrin β1, suggesting both sustained peripheral immune hyperreactivity and a heightened activation state. Taken together, these data indicate that in utero injury primes the immune system and augments enhanced inflammatory signaling. The insidious effects of primed peripheral immune cells may compound PBI secondary to CHORIO and/or placental insufficiency, and thereby render the brain susceptible to future chronic neurological disease. Further understanding of inflammatory mechanisms in PBI may yield clinically important biomarkers and facilitate individualized repair strategies and treatments.

One bout of neonatal inflammation impairs adult respiratory motor plasticity in male and female rats

Neonatal inflammation is common and has lasting consequences for adult health. We investigated the lasting effects of a single bout of neonatal inflammation on adult respiratory control in the form of respiratory motor plasticity induced by acute intermittent hypoxia, which likely compensates and stabilizes breathing during injury or disease and has significant therapeutic potential. Lipopolysaccharide-induced inflammation at postnatal day four induced lasting impairments in two distinct pathways to adult respiratory plasticity in male and female rats. Despite a lack of adult pro-inflammatory gene expression or alterations in glial morphology, one mechanistic pathway to plasticity was restored by acute, adult anti-inflammatory treatment, suggesting ongoing inflammatory signaling after neonatal inflammation. An alternative pathway to plasticity was not restored by anti-inflammatory treatment, but was evoked by exogenous adenosine receptor agonism, suggesting upstream impairment, likely astrocytic-dependent. Thus, the respiratory control network is vulnerable to early-life inflammation, limiting respiratory compensation to adult disease or injury.

Hesperetin, a Citrus Flavonoid, Attenuates LPS-Induced Neuroinflammation, Apoptosis and Memory Impairments by Modulating TLR4/NF-κB Signaling

Glial activation and neuroinflammation play significant roles in apoptosis as well as in the development of cognitive and memory deficits. Neuroinflammation is also a critical feature in the pathogenesis of neurodegenerative disorders such as Alzheimer and Parkinson’s diseases. Previously, hesperetin has been shown to be an effective antioxidant and anti-inflammatory agent. In the present study, in vivo and in vitro analyses were performed to evaluate the neuroprotective effects of hesperetin in lipopolysaccharide (LPS)-induced neuroinflammation, oxidative stress, neuronal apoptosis and memory impairments. Based on our findings, LPS treatment resulted in microglial activation and astrocytosis and elevated the expression of inflammatory mediators such as phosphorylated-Nuclear factor-κB (p-NF-κB), tumor necrosis factor-α (TNF-α), and interleukin-1β (IL-1β) in the cortical and hippocampal regions and in BV2 cells. However, hesperetin cotreatment markedly reduced the expression of inflammatory cytokines by ameliorating Toll-like receptor-4 (TLR4)-mediated ionized calcium-binding adapter molecule 1/glial fibrillary acidic protein (Iba-1/GFAP) expression. Similarly, hesperetin attenuated LPS-induced generation of reactive oxygen species/lipid per oxidation (ROS/LPO) and improved the antioxidant protein level such as nuclear factor erythroid 2-related factor 2 (Nrf2) and Haem-oxygenase (HO-1) in the mouse brain. Additionally, hesperetin ameliorated cytotoxicity and ROS/LPO induced by LPS in HT-22 cells. Moreover, hesperetin rescued LPS-induced neuronal apoptosis by reducing the expression of phosphorylated-c-Jun N-terminal kinases (p-JNK), B-cell lymphoma 2 (Bcl-2)-associated X protein (Bax), and Caspase-3 protein and promoting the Bcl-2 protein level. Furthermore, hesperetin enhanced synaptic integrity, cognition, and memory processes by enhancing the phosphorylated-cAMP response element binding protein (p-CREB), postsynaptic density protein-95 (PSD-95), and Syntaxin. Overall, our preclinical study suggests that hesperetin conferred neuroprotection by regulating the TLR4/NF-κB signaling pathway against the detrimental effects of LPS.

The adaptive immune and stress responses of adult female CD1 mice following exposure to a viral mimetic

Exposure to a bacterial endotoxin during puberty induces long-term changes to reproductive and non-reproductive behaviours. While the underlying mechanisms remain unknown, we have recently shown that there are age and sex differences in acute immune and stress responses following immune challenge. Given that it is unclear whether viral infections result in similar age and sex differences, the objective of this study was to examine the acute immune and stress responses following exposure to polyinosinic:polycytidylic acid (poly(I:C)), a viral mimetic, in CD1 mice and to investigate the role of gonadal hormones in these responses. CD1 male and female mice underwent sham-surgery or gonadectomy at 5 or 9 weeks of age. Following one week of recovery, at 6 (pubertal group) or 10 (adult group) weeks of age, mice were treated with either saline or poly(I:C). Poly(I:C) treatment induced greater sickness behaviour in males compared to females and increased peripheral corticosterone in adult mice relative to their pubertal counterparts. Changes in body temperature and central c-Fos expression were more prominent in adult females. Gonadectomy worsened poly(I:C)-induced sickness behaviour and altered body temperature in both sexes. The results demonstrate that adult females display the most pronounced acute changes in body temperature, corticosterone release, and c-Fos expression but show the fastest recovery in sickness behavior, indicating that, compared to males, females display an adaptive physiological response following immune stress due to higher circulating estradiol and progesterone.

Sex- and region-specific differences in microglia phenotype and characterization of the peripheral immune response following early-life infection in neonatal male and female rats

Early-life infection has been shown to have profound effects on the brain and behavior across the lifespan, a phenomenon termed "early-life programming". Indeed, many neuropsychiatric disorders begin or have their origins early in life and have been linked to early-life immune activation (e.g. autism, ADHD, and schizophrenia). Furthermore, many of these disorders show a robust sex bias, with males having a higher risk of developing early-onset neurodevelopmental disorders. The concept of early-life programming is now well established, however, it is still unclear how such effects are initiated and then maintained across time to produce such a phenomenon. To begin to address this question, we examined changes in microglia, the immune cells of the brain, and peripheral immune cells in the hours immediately following early-life infection in male and female rats. We found that males showed a significant decrease in BDNF expression and females showed a significant increase in IL-6 expression in the cerebellum following E.coli infection on postnatal day 4; however, for most cytokines examined in the brain and in the periphery we were unable to identify any sex differences in the immune response, at least at the time points examined. Instead, neonatal infection with E.coli increased the expression of a number of cytokines in the brain of both males and females similarly including TNF-α, IL-1β, and CD11b (a marker of microglia activation) in the hippocampus and, in the spleen, TNF-α and IL-1β. We also found that protein levels of GRO-KC, MIP-1a, MCP1, IP-10, TNF-α, and IL-10 were elevated 8-hours postinfection, but this response was resolved by 24-hours. Lastly, we found that males have more thin microglia than females on P5, however, neonatal infection had no effect on any of the microglia morphologies we examined. These data show that sex differences in the acute immune response to neonatal infection are likely gene, region, and even time dependent. Future research should consider these factors in order to develop a comprehensive understanding of the immune response in males and females as these changes are likely the initiating agents that lead to the long-term, and often sex-specific, effects of early-life infection.

Prenatal inflammation and risk for schizophrenia: A role for immune proteins in neurodevelopment

Prenatal inflammation is an established risk factor for schizophrenia. However, the specific inflammatory pathways that mediate this association remain unclear. Potential candidate systems include inflammatory markers produced by microglia, such as cytokines and complement. Accumulating evidence suggests that these markers play a role in typical neurodevelopmental processes, such as synapse formation and interneuron migration. Rodent models demonstrate that altered marker levels during the prenatal period can cause lasting deficits in these systems, leading to cognitive deficits that resemble schizophrenia. This review assesses the potential role of prenatal cytokine and complement elevations on the etiology of schizophrenia. The current neurobiological understanding of the development of schizophrenia is reviewed to identify candidate cellular mechanisms that may be influenced by prenatal inflammation. We discuss the functions that cytokines and complement may play in prenatal neurodevelopment, review evidence that links exposure to these factors with risk for schizophrenia, and consider how these markers may interact with genetic vulnerabilities to influence the neurodevelopment of schizophrenia. We consider how prenatal inflammatory exposure may influence childhood and adolescent developmental risk trajectories for schizophrenia. Finally, we identify areas of further research needed to support the development of anti-inflammatory treatments to prevent the development of schizophrenia in at-risk neonates.

Necrotizing enterocolitis is associated with acute brain responses in preterm pigs

Background

Necrotizing enterocolitis (NEC) is an acute gut inflammatory disorder that occurs in preterm infants in the first weeks after birth. Infants surviving NEC often show impaired neurodevelopment. The mechanisms linking NEC lesions with later neurodevelopment are poorly understood but may include proinflammatory signaling in the immature brain. Using preterm pigs as a model for preterm infants, we hypothesized that severe intestinal NEC lesions are associated with acute effects on the developing hippocampus.

Methods

Cesarean-delivered preterm pigs (n = 117) were reared for 8 days and spontaneously developed variable severity of NEC lesions. Neonatal arousal, physical activity, and in vitro neuritogenic effects of cerebrospinal fluid (CSF) were investigated in pigs showing NEC lesions in the colon (Co-NEC) or in the small intestine (Si-NEC). Hippocampal transcriptome analysis and qPCR were used to assess gene expressions and their relation to biological processes, including neuroinflammation, and neural plasticity. Microglia activation was quantified by stereology. The neuritogenic response to selected proteins was investigated in primary cultures of hippocampal neurons.

Results

NEC development rapidly reduced the physical activity of pigs, especially when lesions occurred in the small intestine. Si-NEC and Co-NEC were associated with 27 and 12 hippocampal differentially expressed genes (DEGs), respectively. These included genes related to neuroinflammation (i.e., S100A8, S100A9, IL8, IL6, MMP8, SAA, TAGLN2) and hypoxia (i.e., PDK4, IER3, TXNIP, AGER), and they were all upregulated in Si-NEC pigs. Genes related to protection against oxidative stress (HBB, ALAS2) and oligodendrocytes (OPALIN) were downregulated in Si-NEC pigs. CSF collected from NEC pigs promoted neurite outgrowth in vitro, and the S100A9 and S100A8/S100A9 proteins may mediate the neuritogenic effects of NEC-related CSF on hippocampal neurons. NEC lesions did not affect total microglial cell number but markedly increased the proportion of Iba1-positive amoeboid microglial cells.

Conclusions

NEC lesions, especially when present in the small intestine, are associated with changes to hippocampal gene expression that potentially mediate neuroinflammation and disturbed neural circuit formation via enhanced neuronal differentiation. Early brain-protective interventions may be critical for preterm infants affected by intestinal NEC lesions to reduce their later neurological dysfunctions.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1201-x) contains supplementary material, which is available to authorized users.

Gut-immune-brain dysfunction in Autism: Importance of sex

Autism Spectrum Disorder (ASD) is characterized by social behavior deficits, stereotypies, cognitive rigidity, and in some cases severe intellectual impairment and developmental delay. Although ASD is most widely identified by its neurological deficits, gastrointestinal issues are common in ASD. An intimate and complex relationship exists between the gut, the immune system, and the brain, leading to the hypothesis that ASD may be a systems-level disease affecting the gut and immune systems, in addition to the brain. Despite significant advances in understanding the contribution of the gut and immune systems to the etiology of ASD, there is an intriguing commonality among patients that is not well understood: they are predominantly male. Virtually no attention has been given to the potential role of sex-specific regulation of gut, peripheral, and central immune function in ASD, despite the 4:1 male-to-female bias in this disorder. In this review, we discuss recent revelations regarding the impact of gut-immune-brain relationships on social behavior in rodent models and in ASD patients, placing them in the context of known or putative sex specific mechanisms.

Age-Related Memory Impairment Associated With Decreased Endogenous Estradiol in the Hippocampus of Female Rats

It is widely known that not only the gonadal estradiol (E2) but also hippocampal E2 plays an essential role in memory process. However, the role of hippocampal E2-enhanced memory mechanism during aging is largely unknown. The aim of the present study was to investigate the effect of age on E2 concentration, the expression level of its receptors, and key steroidogenic enzymes in hippocampus. We also investigated the effect of microglia activation on E2 synthesis in hippocampal neurons. The results showed that serum E2 was higher in 19-month-old (aged) rats, which exhibited spatial memory decline in the Morris water maze (MWM) test when compared to the younger rats. Hence, serum E2 may not be associated with the reduced spatial memory performance in aging. In contrast, the level of E2 and the expressions of its receptors were significantly decreased in hippocampus of aged female rat compared to younger females. Furthermore, the expressions of key hippocampal steroidogenic enzymes, steroidogenic acute regulatory protein (StAR), and cytochrome P450 (P450) also significantly decreased with age, which resulted in lower hippocampal E2 levels. In addition, we found that the microglia of aged brain highly expressed interleukin 6 (IL-6), which directly inhibited E2 synthesis in hippocampal neurons via suppression of P450 synthesis. Taken together, we summarized that the microglia-derived IL-6 inhibited hippocampal E2 synthesis in aged rats which, in turn, contributed to the deficit of spatial memory performance.

A gut feeling: Microbiome-brain-immune interactions modulate social and affective behaviors

The expression of a wide range of social and affective behaviors, including aggression and investigation, as well as anxiety- and depressive-like behaviors, involves interactions among many different physiological systems, including the neuroendocrine and immune systems. Recent work suggests that the gut microbiome may also play a critical role in modulating behavior and likely functions as an important integrator across physiological systems. Microbes within the gut may communicate with the brain via both neural and humoral pathways, providing numerous avenues of research in the area of the gut-brain axis. We are now just beginning to understand the intricate relationships among the brain, microbiome, and immune system and how they work in concert to influence behavior. The effects of different forms of experience (e.g., changes in diet, immune challenge, and psychological stress) on the brain, gut microbiome, and the immune system have often been studied independently. Though because these systems do not work in isolation, it is essential to shift our focus to the connections among them as we move forward in our investigations of the gut-brain axis, the shaping of behavioral phenotypes, and the possible clinical implications of these interactions. This review summarizes the recent progress the field has made in understanding the important role the gut microbiome plays in the modulation of social and affective behaviors, as well as some of the intricate mechanisms by which the microbiome may be communicating with the brain and immune system.

Maternal Immune Activation During the Third Trimester Is Associated with Neonatal Functional Connectivity of the Salience Network and Fetal to Toddler Behavior

Prenatal maternal immune activation (MIA) is associated with altered brain development and risk of psychiatric disorders in offspring. Translational human studies of MIA are few in number. Alterations of the salience network have been implicated in the pathogenesis of the same psychiatric disorders associated with MIA. If MIA is pathogenic, then associated abnormalities in the salience network should be detectable in neonates immediately after birth. We tested the hypothesis that third trimester MIA of adolescent women who are at risk for high stress and inflammation is associated with the strength of functional connectivity in the salience network of their neonate. Thirty-six women underwent blood draws to measure interleukin-6 (IL-6) and C-reactive protein (CRP) and electrocardiograms to measure fetal heart rate variability (FHRV) at 34-37 weeks gestation. Resting-state imaging data were acquired in the infants at 40-44 weeks postmenstrual age (PMA). Functional connectivity was measured from seeds placed in the anterior cingulate cortex and insula. Measures of cognitive development were obtained at 14 months PMA using the Bayley Scales of Infant and Toddler Development-Third Edition (BSID-III). Both sexes were studied. Regions in which the strength of the salience network correlated with maternal IL-6 or CRP levels included the medial prefrontal cortex, temporoparietal junction, and basal ganglia. Maternal CRP level correlated inversely with FHRV acquired at the same gestational age. Maternal CRP and IL-6 levels correlated positively with measures of cognitive development on the BSID-III. These results suggest that MIA is associated with short- and long-term influences on offspring brain and behavior.SIGNIFICANCE STATEMENT Preclinical studies in rodents and nonhuman primates and epidemiological studies in humans suggest that maternal immune activation (MIA) alters the development of brain circuitry and associated behaviors, placing offspring at risk for psychiatric illness. Consistent with preclinical findings, we show that maternal third trimester interleukin-6 and C-reactive protein levels are associated with neonatal functional connectivity and with both fetal and toddler behavior. MIA-related functional connectivity was localized to the salience, default mode, and frontoparietal networks, which have been implicated in the pathogenesis of psychiatric disorders. Our results suggest that MIA alters functional connectivity in the neonatal brain, that those alterations have consequences for cognition, and that these findings may provide pathogenetic links between preclinical and epidemiological studies associating MIA with psychiatric risk in offspring.

Sickness-induced changes in physiology do not affect fecundity or same-sex behavior

Previous work in our lab has shown that early-life infection affects female reproductive physiology and function (i.e., smaller ovaries, abnormal estrous cycles) and alters investigation and aggression towards male conspecifics in a reproductive context. Although many studies have investigated the effects of postnatal immune challenge on physiological and behavioral development, fewer studies have examined whether these changes have ultimate effects on reproduction. In the current study, we paired Siberian hamsters (Phodopus sungorus) and simulated a bacterial infection in early life by administering lipopolysaccharide (LPS) to male and female pups on pnd3 and pnd5. In adulthood, hamsters were paired with novel individuals of the same sex, and we scored an array of social behaviors (e.g., investigation, aggression). We then paired animals with individuals of the opposite sex for 5 consecutive nights, providing them with the opportunity to mate. We found that females exhibited impaired reproductive physiology and function in adulthood (i.e., smaller ovaries and abnormal estrous cycles), similar to our previous work. However, both LPS-treated males and females exhibited similar same-sex social behavior when compared with saline-treated controls, they successfully mated, and there were no significant changes in fecundity. These data suggest that the physiological changes in response to neonatal immune challenge may not have long-term effects on reproductive success in a controlled environment. Collectively, the results of this study are particularly important when investigating the relationships between physiology and behavior within an ultimate context. Animals exposed to early-life stress may in fact be capable of compensating for changes in physiology in order to survive and reproduce in some contexts.

Trained innate immunity: a salient factor in the pathogenesis of neuroimmune psychiatric disorders

Historically, only cells of the adaptive immune system have been considered capable of retaining memory for infectious challenges. Recently, however, cells of the innate immune system have been shown to be capable of displaying long-term functional memory following a single immunostimulatory challenge, leading to enhanced production of proinflammatory molecules upon other subsequent, and temporally distant, immunostimulatory challenges. This effect has been termed 'trained innate immunity', and is underwritten by stable epigenetic changes in immune and metabolic pathways. Importantly, the long-term training of innate immune cells can occur as a result of infectious as well as and non-infectious challenges, including stress. Given the role that both stress and an activated immune system have in neuropathology, innate immune training has important implications for our understanding and treatment of neuropsychiatric disorders. This review focuses on the evidence for trained innate immunity and highlights some insights into its relevance for psychiatric diseases.

Glucocorticoid programming of neuroimmune function

Throughout life physiological systems strive to maintain homeostasis and these systems are susceptible to exposure to maternal or environmental perturbations, particularly during embryonic development. In some cases, these perturbations may influence genetic and physiological processes that permanently alter the functioning of these physiological systems; a process known as developmental programming. In recent years, the neuroimmune system has garnered attention for its fundamental interactions with key hormonal systems, such as the hypothalamic pituitary adrenal (HPA) axis. The ultimate product of this axis, the glucocorticoid hormones, play a key role in modulating immune responses within the periphery and the CNS as part of the physiological stress response. It is well-established that elevated glucocorticoids induced by developmental stress exert profound short and long-term physiological effects, yet there is relatively little information of how these effects are manifested within the neuroimmune system. Pre and post-natal periods are prime candidates for manipulation in order to uncover the physiological mechanisms that underlie glucocorticoid programming of neuroimmune responses. Understanding the potential programming role of glucocorticoids may be key in uncovering vulnerable windows of CNS susceptibility to stressful experiences during embryonic development and improve our use of glucocorticoids as therapeutics in the treatment of neurodegenerative diseases.

Protective effects of Nigella sativa L. seed extract on lead induced neurotoxicity during development and early life in mouse models

Lead (Pb), a ubiquitous heavy metal and a known neurotoxicant, produces adverse effects on the brain via increased production of reactive oxygen species (ROS) and causes oxidative stress. In this study we examined the neuroprotective effects of the ethanolic extract of Nigella sativa L. seeds on Pb induced oxidative stress in the developing brain of mice. Mouse pups were exposed to low (0.1%) and high (0.2%) doses of Pb from the first day of pregnancy through their mothers (via drinking water) and lactation until post-natal day (PND) 21. The mRNA expression levels of superoxide dismutase (SOD1), peroxiredoxin (Prdx6), amyloid precursor protein (APP) common, APP695 and APP770 were examined in the cortex and hippocampus of the mouse brain excised on PND 21 by semi-quantitative RT-PCR. The free radical scavenging activity of ethanolic Nigella sativa L. extract was assessed by DPPH assay. The results showed that Pb exposure caused a significant decrease in the expression of SOD1, Prdx6 and APP695 and an increase in APP770 in both cortex and hippocampus in a dose dependent manner as compared to the control group. The expression of APP common remained unaltered. Histological assessment of the cortex and hippocampus demonstrated a decrease in the neuronal number and Nissl bodies. The administration of 250 and 500 mg kg-1 ethanolic Nigella sativa L. extract reversed the adverse effects by significantly increasing the expression of SOD1, Prdx6 and APP695 and decreasing the expression of APP770 in both the regions. These results strongly suggest that Nigella sativa L. supplementation greatly improves Pb-induced neurotoxicity in early life and provides neuroprotective and antioxidant potentials.

Developmental alcohol exposure impairs synaptic plasticity without overtly altering microglial function in mouse visual cortex

Fetal alcohol spectrum disorder (FASD), caused by gestational ethanol (EtOH) exposure, is one of the most common causes of non-heritable and life-long mental disability worldwide, with no standard treatment or therapy available. While EtOH exposure can alter the function of both neurons and glia, it is still unclear how EtOH influences brain development to cause deficits in sensory and cognitive processing later in life. Microglia play an important role in shaping synaptic function and plasticity during neural circuit development and have been shown to mount an acute immunological response to EtOH exposure in certain brain regions. Therefore, we hypothesized that microglial roles in the healthy brain could be permanently altered by early EtOH exposure leading to deficits in experience-dependent plasticity. We used a mouse model of human third trimester high binge EtOH exposure, administering EtOH twice daily by subcutaneous injections from postnatal day 4 through postnatal day 9 (P4-:P9). Using a monocular deprivation model to assess ocular dominance plasticity, we found an EtOH-induced deficit in this type of visually driven experience-dependent plasticity. However, using a combination of immunohistochemistry, confocal microscopy, and in vivo two-photon microscopy to assay microglial morphology and dynamics, as well as fluorescence activated cell sorting (FACS) and RNA-seq to examine the microglial transcriptome, we found no evidence of microglial dysfunction in early adolescence. We also found no evidence of microglial activation in visual cortex acutely after early ethanol exposure, possibly because we also did not observe EtOH-induced neuronal cell death in this brain region. We conclude that early EtOH exposure caused a deficit in experience-dependent synaptic plasticity in the visual cortex that was independent of changes in microglial phenotype or function. This demonstrates that neural plasticity can remain impaired by developmental ethanol exposure even in a brain region where microglia do not acutely assume nor maintain an activated phenotype.

Gene deficiency and pharmacological inhibition of caspase-1 confers resilience to chronic social defeat stress via regulating the stability of surface AMPARs

Both inflammatory processes and glutamatergic systems have been implicated in the pathophysiology of mood-related disorders. However, the role of caspase-1, a classic inflammatory caspase, in behavioral responses to chronic stress remains largely unknown. To address this issue, we examined the effects and underlying mechanisms of caspase-1 on preclinical murine models of depression. We found that loss of caspase-1 expression in Caspase-1^-/- knockout mice alleviated chronic stress-induced depression-like behaviors, whereas overexpression of caspase-1 in the hippocampus of wild-type (WT) mice was sufficient to induce depression- and anxiety-like behaviors. Furthermore, chronic stress reduced glutamatergic neurotransmission and decreased surface expression of glutamate receptors in hippocampal pyramidal neurons of WT mice, but not Caspase-1^-/- mice. Importantly, pharmacological inhibition of caspase-1-interleukin-1β (IL-1β) signaling pathway prevented the depression-like behaviors and the decrease in surface expression of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) in stressed WT mice. Finally, the effects of chronic stress on both depression- and anxiety-like behaviors can be mimicked by exogenous intracerebroventricular (i.c.v.) administration of IL-1β in both WT and Caspase-1^-/- mice. Taken together, our findings demonstrate that an increase in the caspase-1/IL-1β axis facilitates AMPAR internalization in the hippocampus, which dysregulates glutamatergic synaptic transmission, eventually resulting in depression-like behaviors. These results may represent an endophenotype for chronic stress-induced depression.

Early-life immune activation increases song complexity and alters phenotypic associations between sexual ornaments

Early-life adversity can have long-lasting effects on physiological, behavioural, cognitive, and somatic processes. Consequently, these effects may alter an organism's life-history strategy and reproductive tactics.In response to early-life immune activation, we quantified levels of the acute phase protein haptoglobin (Hp) during development in male zebra finches (Taeniopygia guttata). Then, we examined the long-term impacts of early-life immune activation on an important static sexual signal, song complexity, as well as effects of early-life immune activation on the relationship between song complexity and a dynamic sexual signal, beak colouration. Finally, we performed mate-choice trials to determine if male early-life experience impacted female preference.Challenge with keyhole limpet hemocyanin (KLH) resulted in increased song complexity compared to lipopolysaccharide (LPS) treatment or the control. Hp levels were inversely correlated with song complexity. Moreover, KLH-treatment resulted in negative associations between the two sexual signals (beak colouration and song complexity). Females demonstrated some preference for KLH-treated males over controls and for control males over LPS-treated males in mate choice trials.Developmental immune activation has variable effects on the expression of secondary sexual traits in adulthood, including enhancing the expression of some traits. Because developmental levels of Hp and adult song complexity were correlated, future studies should explore a potential role for exposure to inflammation during development on song learning.Early-life adversity may differentially impact static versus dynamic signals. The use of phenotypic correlations can be a powerful tool for examining the impact of early-life experience on the associations among different traits, including sexual signals.

The Cholinergic System Modulates Memory and Hippocampal Plasticity via Its Interactions with Non-Neuronal Cells

Degeneration of central cholinergic neurons impairs memory, and enhancement of cholinergic synapses improves cognitive processes. Cholinergic signaling is also anti-inflammatory, and neuroinflammation is increasingly linked to adverse memory, especially in Alzheimer's disease. Much of the evidence surrounding cholinergic impacts on the neuroimmune system focuses on the α7 nicotinic acetylcholine (ACh) receptor, as stimulation of this receptor prevents many of the effects of immune activation. Microglia and astrocytes both express this receptor, so it is possible that some cholinergic effects may be via these non-neuronal cells. Though the presence of microglia is required for memory, overactivated microglia due to an immune challenge overproduce inflammatory cytokines, which is adverse for memory. Blocking these exaggerated effects, specifically by decreasing the release of tumor necrosis factor α (TNF-α), interleukin 1β (IL-1β), and interleukin 6 (IL-6), has been shown to prevent inflammation-induced memory impairment. While there is considerable evidence that cholinergic signaling improves memory, fewer studies have linked the "cholinergic anti-inflammatory pathway" to memory processes. This review will summarize the current understanding of the cholinergic anti-inflammatory pathway as it relates to memory and will argue that one mechanism by which the cholinergic system modulates hippocampal memory processes is its influence on neuroimmune function via the α7 nicotinic ACh receptor.

Environment matters: microglia function and dysfunction in a changing world

The immune system is our interface with the environment, and immune molecules such as cytokines and chemokines and the cells that produce them within the brain, notably microglia, are critical for normal brain development. This recognition has in recent years led to the working hypothesis that inflammatory events during pregnancy or the early postnatal period, for example, in response to infection, may disrupt the normal developmental trajectory of microglia and consequently their interactions with neurons, thereby contributing to the risk for neurological disorders. The current article outlines recent findings on the impact of diverse, pervasive environmental challenges, beyond infection, including air pollution and maternal stress; and their impact on microglial development and its broad implications for neural pathologies.

A microglia-cytokine axis to modulate synaptic connectivity and function

Microglia have recently been recognized as key regulators of synapse development, function, and plasticity. Critical to progressing the field is the identification of molecular underpinnings necessary for microglia to carry out these important functions within neural circuits. Here, we focus a review specifically on roles for microglial cytokine signaling within developing and mature neural circuits. We review exciting new studies demonstrating essential roles for microglial cytokine signaling in axon outgrowth, synaptogenesis and synapse maturation during development, as well as synaptic transmission and plasticity in adulthood. Together, these studies identify microglia and cytokines as critical modulators of neural circuits within the healthy brain, with implications for a broad range of neurological disorders with disruptions in synaptic structure and function.

Microglia: The Brain's First Responders

New knowledge about microglia is so fresh that it's not even in the textbooks yet. Microglia are cells that help guide brain development and serve as its immune system helpers by gobbling up diseased or damaged cells and discarding cellular debris. Our authors believe that microglia might hold the key to understanding not just normal brain development, but also what causes Alzheimer's disease, Huntington's disease, autism, schizophrenia, and other intractable brain disorders.

Intrauterine inflammation induces sex-specific effects on neuroinflammation, white matter, and behavior

Exposure to inflammation during pregnancy has been linked to adverse neurodevelopmental consequences for the offspring. One common route through which a developing fetus is exposed to inflammation is with intrauterine inflammation. To that end, we utilized an animal model of intrauterine inflammation (IUI; intrauterine lipopolysaccharide (LPS) administration, 50µg, E15) to assess placental and fetal brain inflammatory responses, white matter integrity, anxiety-related behaviors (elevated zero maze, light dark box, open field), microglial counts, and the CNS cytokine response to an acute injection of LPS in both males and females. These studies revealed that for multiple endpoints (fetal brain cytokine levels, cytokine response to adult LPS challenge) male IUI offspring were uniquely affected by intrauterine inflammation, while for other endpoints (behavior, microglial number) both sexes were similarly affected. These data advance our understanding of sex-specific effects of early life exposure to inflammation in a translationally- relevant model.

Modulating Neuroinflammation to Treat Neuropsychiatric Disorders

Neuroinflammation is recognised as one of the potential mechanisms mediating the onset of a broad range of psychiatric disorders and may contribute to nonresponsiveness to current therapies. Both preclinical and clinical studies have indicated that aberrant inflammatory responses can result in altered behavioral responses and cognitive deficits. In this review, we discuss the role of inflammation in the pathogenesis of neuropsychiatric disorders and ask the question if certain genetic copy-number variants (CNVs) associated with psychiatric disorders might play a role in modulating inflammation. Furthermore, we detail some of the potential treatment strategies for psychiatric disorders that may operate by altering inflammatory responses.

Both antenatal and postnatal inflammation contribute information about the risk of brain damage in extremely preterm newborns

BackgroundPreterm newborns exposed to intrauterine inflammation are at an increased risk of neurodevelopmental disorders. We hypothesized that adverse outcomes are more strongly associated with a combination of antenatal and postnatal inflammation than with either of them alone.MethodsWe defined antenatal inflammation as histologic inflammation in the placenta. We measured the concentrations of seven inflammation-related proteins in blood obtained on postnatal days 1, 7, and 14 from 763 infants born before 28 weeks of gestation. We defined postnatal inflammation as a protein concentration in the highest quartile on at least 2 days. We used logistic regression models to evaluate the contribution of antenatal and postnatal inflammation to the risk of neurodevelopmental disorders.ResultsThe risk of white matter damage was increased when placental inflammation was followed by sustained elevation of C-reactive protein or ICAM-1. We found the same for spastic cerebral palsy when placental inflammation was followed by elevation of TNF-α or IL-8. The presence of both placental inflammation and elevated levels of IL-6, TNF-α, or ICAM-1 was associated with an increased risk for microcephaly.ConclusionCompared with a single hit, two inflammatory hits are associated with stronger risk for abnormal cranial ultrasound, spastic cerebral palsy, and microcephaly at 2 years.

Neonatal infection produces significant changes in immune function with no associated learning deficits in juvenile rats

The current experiments examined the impact of early-life immune activation and a subsequent mild immune challenge with lipopolysaccharide (LPS; 25µg/kg) on hippocampal-dependent learning, proinflammatory cytokine expression in the brain, and peripheral immune function in juvenile male and female rats at P24, an age when hippocampal-dependent learning and memory first emerges. Our results indicate that neonatal infection did not produce learning deficits in the hippocampal-dependent context pre-exposure facilitation effect paradigm in juvenile males and females, contrary to what has been observed in adults. Neonatal infection produced an increase in baseline IL-1β expression in the hippocampus (HP) and medial prefrontal cortex (mPFC) of juvenile rats. Furthermore, neonatally infected rats showed exaggerated IL-1β expression in the HP following LPS treatment as juveniles; and juvenile females, but not males, showed exaggerated IL-1β expression in the mPFC following LPS treatment. Neonatal infection attenuated the production of IL-6 expression following LPS treatment in both the brain and the spleen, and neonatal infection decreased the numbers of circulating white blood cells in juvenile males and females, an effect that was further exacerbated by subsequent LPS treatment. Together, our data indicate that the consequences of neonatal infection are detectable even early in juvenile development, though we found no concomitant hippocampal-dependent learning deficits at this young age. These findings underscore the need to consider age and associated on-going neurodevelopmental processes as important factors contributing to the emergence of cognitive and behavioral disorders linked to early-life immune activation. © 2017 Wiley Periodicals, Inc. Develop Neurobiol 77: 1221-1236, 2017.

Effect of Neuroinflammation on Synaptic Organization and Function in the Developing Brain: Implications for Neurodevelopmental and Neurodegenerative Disorders

The brain is a plastic organ where both the intrinsic CNS milieu and extrinsic cues play important roles in shaping and wiring neural connections. The perinatal period constitutes a critical time in central nervous system development with extensive refinement of neural connections, which are highly sensitive to fetal and neonatal compromise, such as inflammatory challenges. Emerging evidence suggests that inflammatory cells in the brain such as microglia and astrocytes are pivotal in regulating synaptic structure and function. In this article, we will review the role of glia cells in synaptic physiology and pathophysiology, including microglia-mediated elimination of synapses. We propose that activation of the immune system dynamically affects synaptic organization and function in the developing brain. We will discuss the role of neuroinflammation in altered synaptic plasticity following perinatal inflammatory challenges and potential implications for neurodevelopmental and neurodegenerative disorders.

Beyond infection - Maternal immune activation by environmental factors, microglial development, and relevance for autism spectrum disorders

Immune molecules such as cytokines and chemokines and the cells that produce them within the brain, notably microglia, are critical for normal brain development. This recognition has in recent years led to the working hypothesis that inflammatory events during pregnancy, e.g. in response to infection, may disrupt the normal expression of immune molecules during critical stages of neural development and thereby contribute to the risk for neurodevelopmental disorders such as autism spectrum disorder (ASD). This hypothesis has in large part been shepherded by the work of Dr. Paul Patterson and colleagues, which has elegantly demonstrated that a single viral infection or injection of a viral mimetic to pregnant mice significantly and persistently impacts offspring immune and nervous system function, changes that underlie ASD-like behavioral dysfunction including social and communication deficits. Subsequent studies by many labs - in humans and in non-human animal models - have supported the hypothesis that ongoing disrupted immune molecule expression and/or neuroinflammation contributes to at least a significant subset of ASD. The heterogeneous clinical and biological phenotypes observed in ASD strongly suggest that in genetically susceptible individuals, environmental risk factors combine or synergize to create a tipping or threshold point for dysfunction. Importantly, animal studies showing a link between maternal immune activation (MIA) and ASD-like outcomes in offspring involve different species and diverse environmental factors associated with ASD in humans, beyond infection, including toxin exposures, maternal stress, and maternal obesity, all of which impact inflammatory or immune pathways. The goal of this review is to highlight the broader implications of Dr. Patterson's work for the field of autism, with a focus on the impact that MIA by diverse environmental factors has on fetal brain development, immune system development, and the pathophysiology of ASD.

Function and Dysfunction of Microglia during Brain Development: Consequences for Synapses and Neural Circuits

Many diverse factors, ranging from stress to infections, can perturb brain homeostasis and alter the physiological activity of microglia, the immune cells of the central nervous system. Microglia play critical roles in the process of synaptic maturation and brain wiring during development. Any perturbation affecting microglial physiological function during critical developmental periods could result in defective maturation of synaptic circuits. In this review, we critically appraise the recent literature on the alterations of microglial activity induced by environmental and genetic factors occurring at pre- and early post-natal stages. Furthermore, we discuss the long-lasting consequences of early-life microglial perturbation on synaptic function and on vulnerability to neurodevelopmental and psychiatric disorders.

Protective Effect of N-Acetyl-Cysteine (NAC) in Lipopolysaccharide (LPS)-Associated Inflammatory Response in Rat Neonates

OBJECTIVE

Increased inflammatory response may be associated with adverse clinical outcomes, especially in the neonatal period. The aims of this study were to determine whether N-acetyl-cysteine (NAC), an anti-inflammatory agent, attenuates the inflammatory response in young rats and to determine the most effective route of administration.

METHODS

Four groups of Sprague-Dawley rats (in each group four rats) were studied at 30 days of age. One hour following intraperitoneal (IP) injection of lipopolysaccharide 50 μg/kg, the rats were randomized to subcutaneous (SC), per os (PO), or intraperitoneal (IP) injection of NAC 300 mg/kg, or saline. The control group received saline injection (IP). Three hours following the N-acetyl-cysteine injection the rats were sacrificed, then serum tumor necrosis factor-α (TNF-α) and IL-6 levels were determined by ELISA.

RESULTS

Lipopolysaccharide significantly increased the neonatal serum IL-6 and TNF-α (2051.0±349 and 147.0±25.8 pg/mL, respectively; P<0.01) levels compared to 10 pg/mL in the controls. N-acetyl-cysteine administered one hour following lipopolysaccharide injection significantly attenuated the inflammatory response. Intraperitoneal administration of NAC decreased IL-6 and TNF-α concentration to 294.6 and 17.1 pg/mL, respectively, and was more effective than SC or PO administration.

CONCLUSIONS

N-acetyl-cysteine attenuated the inflammatory response in the neonatal rats, and IP was the most effective administration route.

Combined effect of BCG vaccination and enriched environment promote neurogenesis and spatial cognition via a shift in meningeal macrophage M2 polarization

Background

The spatial learning abilities of developing mice benefit from extrinsic cues, such as an enriched environment, with concomitant enhancement in cognitive functions. Interestingly, such enhancements can be further increased through intrinsic Bacillus Calmette-Guérin (BCG) vaccination.

Results

Here, we first report that combined neonatal BCG vaccination and exposure to an enriched environment (Enr) induced combined neurobeneficial effects, including hippocampal long-term potentiation, and increased neurogenesis and spatial learning and memory, in mice exposed to the Enr and vaccinated with BCG relative to those in the Enr that did not receive BCG vaccination. Neonatal BCG vaccination markedly induced anti-inflammatory meningeal macrophage polarization both in regular and Enr breeding mice. The meninges are composed of the pia mater, dura mater, and choroid plexus. Alternatively, this anti-inflammatory activity of the meninges occurred simultaneously with increased expression of the neurotrophic factors BDNF/IGF-1 and the M2 microglial phenotype in the hippocampus. Our results reveal a critical role for BCG vaccination in the regulation of neurogenesis and spatial cognition through meningeal macrophage M2 polarization and neurotrophic factor expression; these effects were completely or partially prevented by minocycline or anti-IL-10 antibody treatment, respectively.

Conclusions

Together, we first claim that immunological factor and environmental factor induce a combined effect on neurogenesis and cognition via a common pathway-meningeal macrophage M2 polarization. We also present a novel functional association between peripheral T lymphocytes and meningeal macrophages after evoking adaptive immune responses in the periphery whereby T lymphocytes are recruited to the meninges in response to systemic IFN-γ signaling. This leads to meningeal macrophage M2 polarization, subsequent to microglial M2 activation and neurotrophic factor expression, and eventually promotes a positive behavior.

Electronic supplementary material

The online version of this article (doi:10.1186/s12974-017-0808-7) contains supplementary material, which is available to authorized users.

Developmental time course and effects of immunostressors that alter hormone-responsive behavior on microglia in the peripubertal and adult female mouse brain

In female mice, the experience of being shipped from the breeder facility or a single injection of the bacterial endotoxin, lipopolysaccharide (LPS), during pubertal development alters the behavioral response to estradiol in adulthood as demonstrated by perturbations of estradiol's effects on sexual behavior, cognitive function, as well as its anxiolytic and anti-depressive properties. Microglia, the primary type of immunocompetent cell within the brain, contribute to brain development and respond to stressors with marked and long-lasting morphological and functional changes. Here, we describe the morphology of microglia and their response to shipping and LPS in peripubertal and adult female mice. Peripubertal mice have more microglia with long, thick processes in the hippocampus, amygdala and hypothalamus as compared with adult mice in the absence of an immune challenge. An immune challenge also increases immunoreactivity (IR) of ionized calcium binding adaptor molecule 1 (Iba1), which is constitutively expressed in microglia. In the hippocampus, the age of animal was without effect on the increase in Iba1- IR following shipping from the breeder facility or LPS exposure. In the amygdala, we observed more Iba1-IR following shipping or LPS treatment in peripubertal mice, compared to adult mice. In the hypothalamus, there was a disassociation of the effects of shipping and LPS treatment as LPS treatment, but not shipping, induced an increase in Iba1-IR. Taken together these data indicate that microglial morphologies differ between pubertal and adult mice; moreover, the microglial response to complex stressors is greater in pubertal mice as compared to adult mice.

Inflammation and the neural diathesis-stress hypothesis of schizophrenia: a reconceptualization

An interaction between external stressors and intrinsic vulnerability is one of the longest standing pathoaetiological explanations for schizophrenia. However, novel lines of evidence from genetics, preclinical studies, epidemiology and imaging have shed new light on the mechanisms that may underlie this, implicating microglia as a key potential mediator. Microglia are the primary immune cells of the central nervous system. They have a central role in the inflammatory response, and are also involved in synaptic pruning and neuronal remodeling. In addition to immune and traumatic stimuli, microglial activation occurs in response to psychosocial stress. Activation of microglia perinatally may make them vulnerable to subsequent overactivation by stressors experienced in later life. Recent advances in genetics have shown that variations in the complement system are associated with schizophrenia, and this system has been shown to regulate microglial synaptic pruning. This suggests a mechanism via which genetic and environmental influences may act synergistically and lead to pathological microglial activation. Microglial overactivation may lead to excessive synaptic pruning and loss of cortical gray matter. Microglial mediated damage to stress-sensitive regions such as the prefrontal cortex and hippocampus may lead directly to cognitive and negative symptoms, and account for a number of the structural brain changes associated with the disorder. Loss of cortical control may also lead to disinhibition of subcortical dopamine-thereby leading to positive psychotic symptoms. We review the preclinical and in vivo evidence for this model and consider the implications this has for treatment, and future directions.

Mesenchymal stem cell-derived extracellular vesicles ameliorate inflammation-induced preterm brain injury

OBJECTIVE

Preterm brain injury is a major cause of disability in later life, and may result in motor, cognitive and behavioural impairment for which no treatment is currently available. The aetiology is considered as multifactorial, and one underlying key player is inflammation leading to white and grey matter injury. Extracellular vesicles secreted by mesenchymal stem/stromal cells (MSC-EVs) have shown therapeutic potential in regenerative medicine. Here, we investigated the effects of MSC-EV treatment on brain microstructure and maturation, inflammatory processes and long-time outcome in a rodent model of inflammation-induced brain injury.

METHODS

3-Day-old Wistar rats (P3) were intraperitoneally injected with 0.25mg/kg lipopolysaccharide or saline and treated with two repetitive doses of 1×10⁸ cell equivalents of MSC-EVs per kg bodyweight. Cellular degeneration and reactive gliosis at P5 and myelination at P11 were evaluated by immunohistochemistry and western blot. Long-term cognitive and motor function was assessed by behavioural testing. Diffusion tensor imaging at P125 evaluated long-term microstructural white matter alterations.

RESULTS

MSC-EV treatment significantly ameliorated inflammation-induced neuronal cellular degeneration reduced microgliosis and prevented reactive astrogliosis. Short-term myelination deficits and long-term microstructural abnormalities of the white matter were restored by MSC-EV administration. Morphological effects of MSC-EV treatment resulted in improved long-lasting cognitive functions INTERPRETATION: MSC-EVs ameliorate inflammation-induced cellular damage in a rat model of preterm brain injury. MSC-EVs may serve as a novel therapeutic option by prevention of neuronal cell death, restoration of white matter microstructure, reduction of gliosis and long-term functional improvement.

The impact of inflammation on respiratory plasticity

Breathing is a vital homeostatic behavior and must be precisely regulated throughout life. Clinical conditions commonly associated with inflammation, undermine respiratory function may involve plasticity in respiratory control circuits to compensate and maintain adequate ventilation. Alternatively, other clinical conditions may evoke maladaptive plasticity. Yet, we have only recently begun to understand the effects of inflammation on respiratory plasticity. Here, we review some of common models used to investigate the effects of inflammation and discuss the impact of inflammation on nociception, chemosensory plasticity, medullary respiratory centers, motor plasticity in motor neurons and respiratory frequency, and adaptation to high altitude. We provide new data suggesting glial cells contribute to CNS inflammatory gene expression after 24h of sustained hypoxia and inflammation induced by 8h of intermittent hypoxia inhibits long-term facilitation of respiratory frequency. We also discuss how inflammation can have opposite effects on the capacity for plasticity, whereby it is necessary for increases in the hypoxic ventilatory response with sustained hypoxia, but inhibits phrenic long term facilitation after intermittent hypoxia. This review highlights gaps in our knowledge about the effects of inflammation on respiratory control (development, age, and sex differences). In summary, data to date suggest plasticity can be either adaptive or maladaptive and understanding how inflammation alters the respiratory system is crucial for development of better therapeutic interventions to promote breathing and for utilization of plasticity as a clinical treatment.

Early Life Stress Activates Glial Cells in the Hippocampus but Attenuates Cytokine Secretion in Response to an Immune Challenge in Rat Pups

OBJECTIVE

Early life stress (ELS) increases the vulnerability to developing psychopathological disorders in adulthood that are accompanied by brain inflammatory processes. However, it is not known how a combined double hit (stress and immune) at an early age affects the response of the neuroimmune system. Here we investigated the effect of periodic maternal separation (MS) followed by administration of lipopolysaccharide (LPS) on glial cells in the CA3 region and hilus of the hippocampus and on cytokine release on postnatal day (PN) 15.

METHODS

Male rat pups were subjected to MS (3 h/day, PN1-14). MS and control pups received a single LPS injection (1 mg/kg of body weight) on PN14. They were subjected to an open field test 1 h later. The pups were sacrificed 90 min after LPS injection (PN14) or on PN15 for cytokine or immunohistological analyses, respectively.

RESULTS

LPS reduced the locomotion and induced high corticosterone levels in treated pups. MS or LPS reduced microglial density and activated microglial cells in the hippocampal CA3 and hilus regions. Microglial activation was highest in MS-LPS pups. The astrocyte density was mildly reduced by MS or LPS in the CA3 region and hilus, but the reduction was maximal in MS-LPS pups. LPS increased the secretion of plasmatic interleukin (IL)-1β, tumor necrosis factor-α, and IL-6, and of hippocampal IL-1β protein, but these were attenuated in MS-LPS pups.

CONCLUSION

Although MS and LPS activate neuroimmune cells, stress attenuates the hippocampal and peripheral cytokine response to LPS through an as-yet unidentified adaptive mechanism. These results provide information regarding the neurobiology of stress and inflammation.

Deficient adolescent social behavior following early-life inflammation is ameliorated by augmentation of anandamide signaling

Early-life inflammation has been shown to exert profound effects on brain development and behavior, including altered emotional behavior, stress responsivity and neurochemical/neuropeptide receptor expression and function. The current study extends this research by examining the impact of inflammation, triggered with the bacterial compound lipopolysaccharide (LPS) on postnatal day (P) 14, on social behavior during adolescence. We investigated the role that the endocannabinoid (eCB) system plays in sociability after early-life LPS. To test this, multiple cohorts of Sprague Dawley rats were injected with LPS on P14. In adolescence, rats were subjected to behavioral testing in a reciprocal social interaction paradigm as well as the open field. We quantified eCB levels in the amygdala of P14 and adolescent animals (anandamide and 2-arachidonoylglycerol) as well as adolescent amygdaloid cannabinoid receptor 1 (CB1) binding site density and the hydrolytic activity of the enzyme fatty acid amide hydrolase (FAAH), which metabolizes the eCB anandamide. Additionally, we examined the impact of FAAH inhibition on alterations in social behavior. Our results indicate that P14 LPS decreases adolescent social behavior (play and social non-play) in males and females at P40. This behavioral alteration is accompanied by decreased CB1 binding, increased anandamide levels and increased FAAH activity. Oral administration of the FAAH inhibitor PF-04457845 (1mg/kg) prior to the social interaction task normalizes LPS-induced alterations in social behavior, while not affecting social behavior in the control group. Infusion of 10ng PF-04457845 into the basolateral amygdala normalized social behavior in LPS injected females. These data suggest that alterations in eCB signaling following postnatal inflammation contribute to impairments in social behavior during adolescence and that inhibition of FAAH could be a novel target for disorders involving social deficits such as social anxiety disorders or autism.

Enriched dairy fat matrix diet prevents early life lipopolysaccharide-induced spatial memory impairment at adulthood

Polyunsaturated fatty acids (PUFAs) are essential fatty acids, which are critical for brain development and later life cognitive functions. The main brain PUFAs are docosahexaenoic acid (DHA) for the n-3 family and arachidonic acid (ARA) for the n-6 family, which are provided to the post-natal brain by breast milk or infant formula. Recently, the use of dairy lipids (DL) in replacement of vegetable lipids (VL) was revealed to potently promote the accretion of DHA in the developing brain. Brain DHA, in addition to be a key component of brain development, display potent anti-inflammatory activities, which protect the brain from adverse inflammatory events. In this work, we evaluated the protective effect of partial replacement of VL by DL, supplemented or not with DHA and ARA, on post-natal inflammation and its consequence on memory. Mice were fed with diets poor in vegetal n-3 PUFA (Def VL), balanced in vegetal n-3/n-6 PUFA (Bal VL), balanced in dairy lipids (Bal DL) or enriched in DHA and ARA (Supp VL; Supp DL) from the first day of gestation until adulthood. At post-natal day 14 (PND14), pups received a single administration of the endotoxin lipopolysaccharide (LPS) and brain cytokine expression, microglia phenotype and neurogenesis were measured. In a second set of experiments, memory and neurogenesis were measured at adulthood. Overall, our data showed that lipid quality of the diet modulates early life LPS effect on microglia phenotype, brain cytokine expression and neurogenesis at PND14 and memory at adulthood. In particular, Bal DL diet protects from the adverse effect of early life LPS exposure on PND14 neurogenesis and adult spatial memory.

Neuro-immune interactions across development: A look at glutamate in the prefrontal cortex

Although the primary role for the immune system is to respond to pathogens, more recently, the immune system has been demonstrated to have a critical role in signaling developmental events. Of particular interest for this review is how immunocompetent microglia and astrocytes interact with glutamatergic systems to influence the development of neural circuits in the prefrontal cortex (PFC). Microglia are the resident macrophages of the brain, and astrocytes mediate both glutamatergic uptake and coordinate with microglia to respond to the general excitatory state of the brain. Cross-talk between microglia, astrocytes, and glutamatergic neurons forms a quad-partite synapse, and this review argues that interactions within this synapse have critical implications for the maturation of PFC-dependent cognitive function. Similarly, understanding developmental shifts in immune signaling may help elucidate variations in sensitivities to developmental disruptions.

Computational modeling of cytokine signaling in microglia

Neuroinflammation due to glial activation has been linked to many CNS diseases. We developed a computational model of a microglial cytokine interaction network to study the regulatory mechanisms of microglia-mediated neuroinflammation. We established a literature-based cytokine network, including TNFα, TGFβ, and IL-10, and fitted a mathematical model to published data from LPS-treated microglia. The addition of a previously unreported TGFβ autoregulation loop to our model was required to account for experimental data. Global sensitivity analysis revealed that TGFβ- and IL-10-mediated inhibition of TNFα was critical for regulating network behavior. We assessed the sensitivity of the LPS-induced TNFα response profile to the initial TGFβ and IL-10 levels. The analysis showed two relatively shifted TNFα response profiles within separate domains of initial condition space. Further analysis revealed that TNFα exhibited adaptation to sustained LPS stimulation. We simulated the effects of functionally inhibiting TGFβ and IL-10 on TNFα adaptation. Our analysis showed that TGFβ and IL-10 knockouts (TGFβ KO and IL-10 KO) exert divergent effects on adaptation. TFGβ KO attenuated TNFα adaptation whereas IL-10 KO enhanced TNFα adaptation. We experimentally tested the hypothesis that IL-10 KO enhances TNFα adaptation in murine macrophages and found supporting evidence. These opposing effects could be explained by differential kinetics of negative feedback. Inhibition of IL-10 reduced early negative feedback that results in enhanced TNFα-mediated TGFβ expression. We propose that differential kinetics in parallel negative feedback loops constitute a novel mechanism underlying the complex and non-intuitive pro- versus anti-inflammatory effects of individual cytokine perturbations.

Microglial Priming and Alzheimer's Disease: A Possible Role for (Early) Immune Challenges and Epigenetics?

Neuroinflammation is thought to contribute to Alzheimer's disease (AD) pathogenesis that is, to a large extent, mediated by microglia. Given the tight interaction between the immune system and the brain, peripheral immune challenges can profoundly affect brain function. Indeed, both preclinical and clinical studies have indicated that an aberrant inflammatory response can elicit behavioral impairments and cognitive deficits, especially when the brain is in a vulnerable state, e.g., during early development, as a result of aging, or under disease conditions like AD. However, how exactly peripheral immune challenges affect brain function and whether this is mediated by aberrant microglial functioning remains largely elusive. In this review, we hypothesize that: (1) systemic immune challenges occurring during vulnerable periods of life can increase the propensity to induce later cognitive dysfunction and accelerate AD pathology; and (2) that "priming" of microglial cells is instrumental in mediating this vulnerability. We highlight how microglia can be primed by both neonatal infections as well as by aging, two periods of life during which microglial activity is known to be specifically upregulated. Lasting changes in (the ratios of) specific microglial phenotypes can result in an exaggerated pro-inflammatory cytokine response to subsequent inflammatory challenges. While the resulting changes in brain function are initially transient, a continued and/or excess release of such pro-inflammatory cytokines can activate various downstream cellular cascades known to be relevant for AD. Finally, we discuss microglial priming and the aberrant microglial response as potential target for treatment strategies for AD.

Current understanding and neurobiology of epileptic encephalopathies

Epileptic encephalopathies are a group of diseases in which epileptic activity itself contributes to severe cognitive and behavioral impairments above and beyond what might be expected from the underlying pathology alone. These impairments can worsen over time. This concept has been continually redefined since its introduction. A few syndromes are considered epileptic encephalopathies: early myoclonic encephalopathy and Ohtahara syndrome in the neonatal period, epilepsy of infancy with migrating focal seizures, West syndrome or infantile spasms, Dravet syndrome during infancy, Lennox-Gastaut syndrome, epileptic encephalopathy with continuous spikes-and-waves during sleep, and Landau-Kleffner syndrome during childhood. The inappropriate use of this term to refer to all severe epilepsy syndromes with intractable seizures and severe cognitive dysfunction has led to confusion regarding the concept of epileptic encephalopathy. Here, we review our current understanding of those epilepsy syndromes considered to be epileptic encephalopathies. Genetic studies have provided a better knowledge of neonatal and infantile epilepsy syndromes, while neuroimaging studies have shed light on the underlying causes of childhood-onset epileptic encephalopathies such as Lennox-Gastaut syndrome. Apart from infantile spasm models, we lack animal models to explain the neurobiological mechanisms at work in these conditions. Experimental studies suggest that neuroinflammation may be a common neurobiological pathway that contributes to seizure refractoriness and cognitive involvement in the developing brain.