Neonatal lipopolysaccharide treatment alters hippocampal neuroinflammation, microglia morphology and anxiety-like behavior in rats selectively bred for an infantile trait

High-intensity interval training ameliorates postnatal immune activation-induced mood disorders through KDM6B-regulated glial activation

Postnatal immune activation (PIA) induces persistent glial activation in the brain and causes various neuropathologies in adults. Exercise training improves stress-related mood disorders; however, the role of exercise in psychiatric disorders induced by early-life immune activation and the association between exercise training and glial activation remain unclear. We compared the effects of different exercise intensities on the PIA model, including high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT). Both HIIT and MICT in adolescent mice inhibited neuroinflammation, remodeled synaptic plasticity, and improved PIA-induced mood disorders in adulthood. Importantly, HIIT was superior to MICT in terms of reducing inflammation and increasing body weight. RNA-seq of prefrontal cortex (PFC) tissues revealed a gene expression pattern, confirming that HIIT was more effective than MICT in improving brain glial cell activation through epigenetic modifications of KDM6B. We investigated the role of KDM6B, a specific histone lysine demethylation enzyme - histone 3 lysine 27 demethylase, in inhibiting glial activation against PIA-induced depression and anxiety by regulating the expression of IL-4 and brain-derived neurotrophic factor (BDNF). Overall, our data support the idea that HIIT improves PIA-induced mood disorders by regulating KDM6B-mediated epigenetic mechanisms and indicate that HIIT might be superior to MICT in improving mood disorders with PIA in mice. Our findings provide new insights into the treatment of anxiety and depression disorders.

Peripheral inflammation triggering central anxiety through the hippocampal glutamate metabolized receptor 1

AIMS

This study aimed to investigate the relationship between ulcerative colitis (UC) and anxiety and explore its central mechanisms using colitis mice.

METHODS

Anxiety-like behavior was assessed in mice induced by 3% dextran sodium sulfate (DSS) using the elevated plus maze and open-field test. The spatial transcriptome of the hippocampus was analyzed to assess the distribution of excitatory and inhibitory synapses, and Toll-like receptor 4 (TLR4) inhibitor TAK-242 (10 mg/kg) and AAV virus interference were used to examine the role of peripheral inflammation and central molecules such as Glutamate Receptor Metabotropic 1 (GRM1) in mediating anxiety behavior in colitis mice.

RESULTS

DSS-induced colitis increased anxiety-like behaviors, which was reduced by TAK-242. Spatial transcriptome analysis of the hippocampus showed an excitatory-inhibitory imbalance mediated by glutamatergic synapses, and GRM1 in hippocampus was identified as a critical mediator of anxiety behavior in colitis mice via differential gene screening and AAV virus interference.

CONCLUSION

Our work suggests that the hippocampus plays an important role in brain anxiety caused by peripheral inflammation, and over-excitation of hippocampal glutamate synapses by GRM1 activation induces anxiety-like behavior in colitis mice. These findings provide new insights into the central mechanisms underlying anxiety in UC and may contribute to the development of novel therapeutic strategies for UC-associated anxiety.

Lipopolysaccharide impairs neurodevelopment and induces changes in astroglial reactivity, antioxidant defenses and bioenergetics in the cerebral cortex of neonatal rats

Neonates have an immature immune system, which increases their vulnerability to infectious agents and inflammatory insults. The administration of the immunostimulatory agent lipopolysaccharide (LPS) has been shown to induce the expression of pro-inflammatory cytokines and cause behavior alterations in rodents at different ages. However, the effects of LPS administration during the neonatal period and its consequences during immune system maturation remain to be elucidated. We showed here that a single intraperitoneal administration of LPS in rats on postnatal day (PND) 7 caused early and variable alterations in TNF-α, S100B and GFAP levels in the cerebral cortex, CSF and serum of the animals, indicating long-term induction of neuroinflammation and astroglial reactivity. However, on PND 21, only GFAP levels were increased by LPS. Additionally, LPS induced oxidative stress and altered energy metabolism enzymes in the cerebral cortex on PND 21, and caused neurodevelopment impairment over time. These data suggest that neuroinflammation induction during the neonatal period induces glial reactivity, oxidative stress and bioenergetic disruption that may lead to neurodevelopment impairment and cognitive deficit in adult life.

Neonatal inflammation increases hippocampal KCC2 expression through methylation-mediated TGF-β1 downregulation leading to impaired hippocampal cognitive function and synaptic plasticity in adult mice

The mechanisms by which neonatal inflammation leads to cognitive deficits in adulthood remain poorly understood. Inhibitory GABAergic synaptic transmission plays a vital role in controlling learning, memory and synaptic plasticity. Since early-life inflammation has been reported to adversely affect the GABAergic synaptic transmission, the aim of this study was to investigate whether and how neonatal inflammation affects GABAergic synaptic transmission resulting in cognitive impairment. Neonatal mice received a daily subcutaneous injection of lipopolysaccharide (LPS, 50 μg/kg) or saline on postnatal days 3-5. It was found that blocking GABAergic synaptic transmission reversed the deficit in hippocampus-dependent memory or the induction failure of long-term potentiation in the dorsal CA1 in adult LPS mice. An increase of mIPSCs amplitude was further detected in adult LPS mice indicative of postsynaptic potentiation of GABAergic transmission. Additionally, neonatal LPS resulted in the increased expression and function of K⁺-Cl^--cotransporter 2 (KCC2) and the decreased expression of transforming growth factor-beta 1 (TGF-β1) in the dorsal CA1 during adulthood. The local TGF-β1 overexpression improved KCC2 expression and function, synaptic plasticity and memory of adult LPS mice. Adult LPS mice show hypermethylation of TGFb1 promoter and negatively correlate with reduced TGF-β1 transcripts. 5-Aza-deoxycytidine restored the changes in TGFb1 promoter methylation and TGF-β1 expression. Altogether, the results suggest that hypermethylation-induced reduction of TGF-β1 leads to enhanced GABAergic synaptic inhibition through increased KCC2 expression, which is a underlying mechanism of neonatal inflammation-induced hippocampus-dependent memory impairment in adult mice.

Neonatal inflammation via persistent TGF-β1 downregulation decreases GABAAR expression in basolateral amygdala leading to the imbalance of the local excitation-inhibition circuits and anxiety-like phenotype in adult mice

Neonatal inflammation can increase the risk of anxiety disorder in adulthood. The balance between glutamatergic excitatory and GABAergic inhibitory transmissions in the basolateral amygdala (BLA) plays a vital role in controlling anxiety state. Based on the reports that early-life inflammation had adverse effects on GABAergic system, the aim of this study was to investigate whether and how neonatal inflammation affects excitatory-inhibitory circuits in the BLA resulting in anxiety disorder. Neonatal mice received a daily subcutaneous injection of lipopolysaccharide (LPS, 50 μg/kg) or saline on postnatal days 3-5. LPS-treated mice developed anxiety behaviors accompanied by the hyperactivity of adrenal axis in adulthood. Electrophysiological study revealed the increase of postsynaptic neuronal excitability in the cortical-BLA excitatory synapses of LPS mice which could be recovered by bath-application of GABA_AR agonist suggesting the impairment of GABAergic system in LPS mice. Compared with controls, GABA_ARα2 subunit expression and density of GABA-evoked current in BLA principal neurons were reduced in LPS mice. Additionally, neonatal LPS treatment resulted in the down-regulation of transforming growth factor-beta 1 (TGF-β1) expression and PKC signaling pathway in the adult BLA. The local TGF-β1 overexpression in the BLA improved GABA_ARα2 expression via up-regulating the activity of PKC signaling, which corrected GABA_AR-mediated inhibition leading to the abolishment of anxiety-like change in adrenal axis regulation and behaviors in LPS mice. These data suggest the persistent TGF-β1deficit induces the down-regulation of GABA_ARα2 expression and subsequent disruption of the excitation-inhibition balance in the BLA circuits, which is the important mechanisms of neonatal inflammation-induced anxiety disorder.

Folic Acid Attenuates Glial Activation in Neonatal Mice and Improves Adult Mood Disorders Through Epigenetic Regulation

Growing evidence indicates that postnatal immune activation (PIA) can adversely increase the lifetime risk for several neuropsychiatric disorders, including anxiety and depression, which involve the activation of glial cells and early neural developmental events. Several glia-targeted agents are required to protect neonates. Folic acid (FA), a clinical medication used during pregnancy, has been reported to have neuroprotective properties. However, the effects and mechanisms of FA in PIA-induced neonatal encephalitis and mood disorders remain unclear. Here, we investigated the roles of FA in a mouse model of PIA, and found that FA treatment improved depressive- and anxiety-like behaviors in adults, accompanied by a decrease in the number of activated microglia and astrocytes, as well as a reduction in the inflammatory response in the cortex and hippocampus of neonatal mice. Furthermore, we offer new evidence describing the functional differences in FA between microglia and astrocytes. Our data show that epigenetic regulation plays an essential role in FA-treated glial cells following PIA stimulation. In astrocytes, FA promoted the expression of IL-10 by decreasing the level of EZH2-mediated H3K27me3 at its promoter, whereas FA promoted the expression of IL-13 by reducing the promoter binding of H3K9me3 mediated by KDM4A in microglia. Importantly, FA specifically regulated the expression level of BDNF in astrocytes through H3K27me3. Overall, our data supported that FA may be an effective treatment for reducing mood disorders induced by PIA, and we also demonstrated significant functional differences in FA between the two cell types following PIA stimulation.

Early Life Painful Procedures: Long-Term Consequences and Implications for Farm Animal Welfare

Farm animals routinely undergo painful husbandry procedures early in life, including disbudding and castration in calves and goat kids, tail docking and castration in piglets and lambs, and beak trimming in chicks. In rodents, inflammatory events soon after birth, when physiological systems are developing and sensitive to perturbation, can profoundly alter phenotypic outcomes later in life. This review summarizes the current state of research on long-term phenotypic consequences of neonatal painful procedures in rodents and farm animals, and discusses the implications for farm animal welfare. Rodents exposed to early life inflammation show a hypo-/hyper-responsive profile to pain-, fear-, and anxiety-inducing stimuli, manifesting as an initial attenuation in responses that transitions into hyperresponsivity with increasing age or cumulative stress. Neonatal inflammation also predisposes rodents to cognitive, social, and reproductive deficits, and there is some evidence that adverse effects may be passed to offspring. The outcomes of neonatal inflammation are modulated by injury etiology, age at the time of injury and time of testing, sex, pain management, and rearing environment. Equivalent research examining long-term phenotypic consequences of early life painful procedures in farm animals is greatly lacking, despite obvious implications for welfare and performance. Improved understanding of how these procedures shape phenotypes will inform efforts to mitigate negative outcomes through reduction, replacement, and refinement of current practices.

Neonatal Proinflammatory Stress and Expression of Neuroinflammation-Associated Genes in the Rat Hippocampus

Differential effect of the neonatal proinflammatory stress (NPS) on the development of neuroinflammation in the hippocampus and induction of the depressive-like behavior in juvenile and adult male and female rats was studied. NPS induction by bacterial lipopolysaccharide in the neonatal period upregulated expression of the Il6 and Tnf mRNAs accompanied by the development of depressive-like behavior in the adult male rats. NPS increased expression of the mRNAs for fractalkine and its receptor in the ventral hippocampus of the juvenile male rats, but did not affect expression of mRNAs for the proinflammatory cytokines and soluble form of fractalkine. NPS downregulated expression of fractalkine mRNA in the dorsal hippocampus of juvenile males. No significant effects of NPS were found in the female rats. Therefore, the NPS induces long-term changes in the expression of neuroinflammation-associated genes in different regions of the hippocampus, which ultimately leads to the induction of neuroinflammation and development of depressive-like behavior in male rats.

Upregulation of KDM6B contributes to lipopolysaccharide-induced anxiety-like behavior via modulation of VGLL4 in mice

Histone H3K27me3 demethylase KDM6B (also known as Jumonji domain-containing protein D3, JMJD3) plays vital roles in the etiology of inflammatory responses; however, little is known about the role of KDM6B in neuroinflammation-induced anxiety-like behavior. The present study aimed to investigate the potential role of KDM6B in lipopolysaccharide (LPS)-induced anxiety-like behavior and to evaluate whether it is associated with the modulation of vestigial-like family member 4 (VGLL4). The elevated plus maze, light-dark box, and open-field test were performed to test the anxiety-like behavior induced by LPS in C57BL/6 J male mice. Levels of relative protein expression in the hippocampus were quantified by western blotting. KDM6B inhibitor GSK-J4 and microglia inhibitor minocycline as well as adeno-associated virus of Vgll4 shRNA were used to explore the underlying mechanisms. We found that KDM6B, VGLL4, interleukin-1β (IL-1β), and ionized calcium-binding adaptor molecule-1 (Iba-1, microglia marker) protein levels were increased in LPS-dose dependent manner in the hippocampus but not in prefrontal cortex. GSK-J4 treatment attenuated LPS-induced VGLL4, the signal transducer and activator of transcription 3 (STAT3), IL-1β and Iba-1 upregulation and anxiety-like behavior. Knockdown VGLL4 with Vgll4 shRNA prevented the increase of anxiety-like behavior and levels of STAT3, IL-1β, and Iba-1 expression in the hippocampus of LPS-treated mice. Moreover, minocycline, an inhibitor of microglia treatment blunted LPS-induced anxiety-like behavior. Collectively, these results demonstrate that the induction of neuroinflammation by LPS promotes KDM6B activation in the hippocampus, and LPS-induced anxiety-like behavior is associated with upregulation of VGLL4 by KDM6B in the hippocampus.

The effect of early life immune challenge on adult forced swim test performance and hippocampal neurogenesis

Many psychiatric diseases can be considered neurodevelopmental in nature and accumulating evidence links immune system dysfunction to disease etiology. Yet, it is currently unknown how the immune system alters brain function through development to increase susceptibility to psychiatric illness. Neonatal immune challenge in rodents is a neurodevelopmental model that has been associated with long-term molecular and behavioural changes in stress-reactivity. As enhanced stress-reactivity is associated with the emergence of depressive-like behaviours concurrent with hippocampal pathology, we measured depressive-like behaviour in the forced swim test and hippocampal neurogenesis in adult mice neonatally exposed to lipopolysaccharide LPS; 0.05 mg/kg, i.p. on postnatal days 3 and 5. As there are important functional differences along the ventral-dorsal hippocampus axis, ventral and dorsal hippocampal neurogenesis were measured separately. Our findings reveal a sexually-dimorphic response to early-life LPS challenge. Male LPS-mice spent less time immobile in the forced swim test, suggesting altered reactivity to swim stress. This was accompanied by an increase in doublecortin-positive cells in the dorsal hippocampus of female mice. These findings demonstrate that exposure to an immune challenge during critical developmental time periods leads to long-term sexually-dimorphic alterations in stress-reactivity that are accompanied by changes to adult hippocampal neurogenesis.

Dexmedetomidine alleviates neurobehavioral impairments and myelination deficits following lipopolysaccharide exposure in early postnatal rats

AIMS

White matter injury (WMI) is the main form of brain injury in preterm neonate survivors, and perinatal inflammation is implicated in the pathogenesis of WMI. It has been demonstrated that dexmedetomidine, an anesthetic adjuvant, possesses neuroprotective effects in both preclinical and clinical trials. The present study was conducted to explore whether dexmedetomidine could protect against neurobehavioral impairments and myelination deficits caused by lipopolysaccharide (LPS) exposure in the early postnatal rat brain.

MAIN METHODS

LPS (2 mg/kg) was intraperitoneally (i.p.) injected in Sprague-Dawley rat pups on postnatal day 2 (P2). Dexmedetomidine (25 μg/kg) or vehicle was given i.p. immediately after LPS injection. STAT3 and p-STAT3 expression were detected by western blot in rat brain 24 h after drug administration. Immunostaining for GFAP to was performed to evaluate astrocytic response at 24 h post-LPS and P14. Neurobehavioral tests (the righting reflex, negative geotaxis, and wire hanging maneuver tests) were performed from P5 to P10. Histological analysis of myelin content was accessed by immunohistochemistry for CNPase and MBP at P14.

KEY FINDINGS

Our results showed that treatment with dexmedetomidine significantly ameliorated LPS-induced neurobehavioral abnormalities and myelin damage, which is accompanied by suppression of STAT3 activation and reactive astrogliosis.

SIGNIFICANCE

Dexmedetomidine can alleviate neurobehavioral impairments and myelination deficits after LPS exposure in early postnatal rats, probably by mitigating STAT3-mediated reactive astrogliosis. Our results suggest that dexmedetomidine might be a promising agent to treat brain injury in neonates.

Amelioration of neurobehavioral and cognitive abilities of F1 progeny following dietary supplementation with Spirulina to protein malnourished mothers

Early life adversities (stress, infection and mal/undernutrition) can affect neurocognitive, hippocampal and immunological functioning of the brain throughout life. Substantial evidence suggests that maternal protein malnutrition contributes to the progression of neurocognitive abnormalities and psychopathologies in adolescence and adulthood in offspring. Maternal malnutrition is prevalent in low and middle resource populations. The present study was therefore undertaken to evaluate the effects of dietary Spirulina supplementation of protein malnourished mothers during pregnancy and lactation on their offspring's reflex, neurobehavioral and cognitive development. Spirulina is a Cyanobacterium and a major source of protein and is being used extensively as a dynamic nutraceutical against aging and neurodegeneration. Sprague Dawley rats were switched to low protein (8% protein) or normal protein (20% protein) diet for 15 days before conception. Spirulina was orally administered (400 mg/kg/b.wt.) to subgroups of pregnant females from the day of conception throughout the lactational period. We examined several parameters including reproductive performance of dams, physical development, postnatal reflex ontogeny, locomotor behavior, neuromuscular strength, anxiety, anhedonic behavior, cognitive abilities and microglia populations in the F1 progeny. The study showed improved reproductive performance of Spirulina supplemented protein malnourished dams, accelerated acquisition of neurological reflexes, better physical appearance, enhanced neuromuscular strength, improved spatial learning and memory and partly normalized PMN induced hyperactivity, anxiolytic and anhedonic behavior in offspring. These beneficial effects of Spirulina consumption were also accompanied by reduced microglial activation which might assist in restoring the behavioral and cognitive skills in protein malnourished F1 rats. Maternal Spirulina supplementation is therefore proposed as an economical nutraceutical/supplement to combat malnutrition associated behavioral and cognitive deficits.

Microglial Function in the Effects of Early-Life Stress on Brain and Behavioral Development

The putative effects of early-life stress (ELS) on later behavior and neurobiology have been widely investigated. Recently, microglia have been implicated in mediating some of the effects of ELS on behavior. In this review, findings from preclinical and clinical literature with a specific focus on microglial alterations induced by the exposure to ELS (i.e., exposure to behavioral stressors or environmental agents and infection) are summarized. These studies were utilized to interpret changes in developmental trajectories based on the time at which the stress occurred, as well as the paradigm used. ELS and microglial alterations were found to be associated with a wide array of deficits including cognitive performance, memory, reward processing, and processing of social stimuli. Four general conclusions emerged: (1) ELS interferes with microglial developmental programs, including their proliferation and death and their phagocytic activity; (2) this can affect neuronal and non-neuronal developmental processes, which are dynamic during development and for which microglial activity is instrumental; (3) the effects are extremely dependent on the time point at which the investigation is carried out; and (4) both pre- and postnatal ELS can prime microglial reactivity, indicating a long-lasting alteration, which has been implicated in behavioral abnormalities later in life.

Microglia cytoarchitecture in the brain of adenosine A2A receptor knockout mice: Brain region and sex specificities

Microglia cells exert a critical role in brain development, mainly supported by their immune functions, which predicts an impact on the genesis of psychiatric disorders. In fact, microglia stress during gestation is, for instance, associated with chronic anxiety and cognitive deficits accompanied by long-lasting, region- and sex-specific changes in microglia morphology. We recently reported that the pattern of microglia morphologic plasticity, which is sex-determined, impacts on anxious-like behaviour and cognition. We also reported that the pharmacologic blockade of adenosine A_2A receptors (A_{2 A} R) is able to reshape microglia morphology, in a sex-specific manner and with behavioural sequelae. In order to better understand the role of A_{2 A} R in the sex differentiation of microglia, we now compared their morphology in wild-type and A_{2 A} R knockout male and female C57BL/6 mice in two cardinal brain regions implicated in anxiety-like behaviour and cognition, the prefrontal cortex (PFC) and the dorsal hippocampus (dHIP). We report interregional differences between PFC and dHIP in a sex-specific manner: while males presented more complex microglia in the dHIP, microglia from females had a more complex morphology in the PFC. Surprisingly, the genetic deletion of A_{2 A} R did not alter these sex differences, but promoted the exclusive remodelling (increase in complexity) in PFC microglia from females. These findings further support the existence of a heterogeneous microglial network, distinct between sexes and brain regions, and help characterizing the role of A_{2 A} R in the sex- and brain region-specific morphologic differentiation of microglia.

Mitochondria: A Connecting Link in the Major Depressive Disorder Jigsaw

Background

Depression is a widespread phenomenon with varying degrees of pathology in different patients. Various hypotheses have been proposed for the cause and continuance of depression. Some of these include, but not limited to, the monoamine hypothesis, the neuroendocrine hypothesis, and the more recent epigenetic and inflammatory hypotheses.

Objective

In this article, we review all the above hypotheses with a focus on the role of mitochondria as the connecting link. Oxidative stress, respiratory activity, mitochondrial dynamics and metabolism are some of the mitochondria-dependent factors which are affected during depression. We also propose exogenous ATP as a contributing factor to depression.

Result

Literature review shows that pro-inflammatory markers are elevated in depressive individuals. The cause for elevated levels of cytokines in depression is not completely understood. We propose exogenous ATP activates purinergic receptors which in turn increase the levels of various pro-inflammatory factors in the pathophysiology of depression.

Conclusion

Mitochondria are integral to the function of neurons and undergo dysfunction in major depressive disorder patients. This dysfunction is reflected in all the various hypotheses that have been proposed for depression. Among the newer targets identified, which also involve mitochondria, includes the role of exogenous ATP. The diversity of purinergic receptors, and their differential expression among various individuals in the population, due to genetic and environmental (prenatal) influences, may influence the susceptibility and severity of depression. Identifying specific receptors involved and using patient-specific purinergic receptor antagonist may be an appropriate therapeutic course in the future.

Effect of Photobiomodulation in Rescuing Lipopolysaccharide-Induced Dopaminergic Cell Loss in the Male Sprague-Dawley Rat

Photobiomodulation (PBM) provides neuroprotection against dopaminergic cell death and associated motor deficits in rodent and primate models of Parkinson’s disease (PD). However, it has not yet been tested in the lipopolysaccharide (LPS) model of PD, which leads to dopaminergic cell death through microglia-evoked neuroinflammation. We investigated whether transcranial PBM could protect against dopaminergic cell death within the substantia nigra in male Sprague–Dawley rats following supranigral LPS injection. PBM fully protected rats from 10 µg LPS which would have otherwise caused 15% cell loss, but there was no significant neuroprotection at a 20 µg dose that led to a 50% lesion. Cell loss at this dose varied according to the precise site of injection and correlated with increased local numbers of highly inflammatory amoeboid microglia. Twenty microgram LPS caused motor deficits in the cylinder, adjusted stepping and rotarod tests that correlated with dopaminergic cell loss. While PBM caused no significant improvement at the group level, motor performance on all three tests no longer correlated with the lesion size caused by 20 µg LPS in PBM-treated rats, suggesting extranigral motor improvements in some animals. These results provide support for PBM as a successful neuroprotective therapy against the inflammatory component of early PD, provided inflammation has not reached a devastating level, as well as potential benefits in other motor circuitries.

Neonatal Lipopolysaccharide Challenge Induces Long-lasting Spatial Cognitive Impairment and Dysregulation of Hippocampal Histone Acetylation in Mice

Neonatal inflammation induces long-term effects on brain function. We investigated the effects of systematic neonatal inflammation using lipopolysaccharide (LPS) injection at postnatal day 3 (P3) and P5 in a mouse model of spatial memory capacity measured using a Morris water maze (MWM) task in adulthood. Subsequently, we assessed histone acetylation and immediate-early response gene expression (c-Fos and brain-derived neurotrophic factor) in the hippocampus in response to MWM acquisition training. The LPS-treated mice exhibited a significant spatial cognitive impairment, which was accompanied by insufficient histone acetylation of the H4K12-specific lysine residue and repressed c-Fos gene expression immediately after acquisition training. Moreover, the enrichment of acetyl-H4K12 on the c-Fos promoter following acquisition training was decreased in LPS-treated mice. Administration of trichostatin A (TSA), a histone deacetylase inhibitor, 2 h before each MWM acquisition training session effectively enhanced hippocampal histone acetylation levels and enrichment of acetyl-H4K12 on the c-Fos promoter following acquisition training in LPS-treated mice. TSA also increased c-Fos gene expression underlying synaptic plasticity and memory formation, and consequently rescued impaired spatial cognitive function. These results indicate that the dysregulation of H4K12 acetylation during the ongoing process of memory formation plays a key role in the spatial cognitive impairment associated with a neonatal LPS challenge. The histone deacetylase inhibitor TSA exhibits therapeutic potential for treating cognitive impairment induced by neonatal inflammation, by means of improving hippocampal histone acetylation and downstream c-Fos gene expression in response to a learning task.

Effect of acupuncture on Lipopolysaccharide-induced anxiety-like behavioral changes: involvement of serotonin system in dorsal Raphe nucleus

Background

Acupuncture has been used as a common therapeutic tool in many disorders including anxiety and depression. Serotonin transporter (SERT) plays an important role in the pathology of anxiety and other mood disorders. The aim of this study was to evaluate the effects of acupuncture on lipopolysaccharide (LPS)-induced anxiety-like behaviors and SERT in the dorsal raphe nuclei (DRN).

Methods

Rats were given acupuncture at ST41 (Jiexi), LI11 (Quchi) or SI3 (Houxi) acupoint in LPS-treated rats. Anxiety-like behaviors of elevated plus maze (EPM) and open field test (OFT) were measured and expressions of SERT and/or c-Fos were also examined in the DRN using immunohistochemistry.

Results

The results showed that 1) acupuncture at ST41 acupoint, but neither LI11 nor SI3, significantly attenuated LPS-induced anxiety-like behaviors in EPM and OFT, 2) acupuncture at ST41 decreased SERT expression increased by LPS in the DRN.

Conclusions

Our results suggest that acupuncture can ameliorate anxiety-like behaviors, possibly through regulation of SERT in the DRN.

Microglia at center stage: a comprehensive review about the versatile and unique residential macrophages of the central nervous system

Microglia cells are the unique residential macrophages of the central nervous system (CNS). They have a special origin, as they derive from the embryonic yolk sac and enter the developing CNS at a very early stage. They play an important role during CNS development and adult homeostasis. They have a major contribution to adult neurogenesis and neuroinflammation. Thus, they participate in the pathogenesis of neurodegenerative diseases and contribute to aging. They play an important role in sustaining and breaking the blood-brain barrier. As innate immune cells, they contribute substantially to the immune response against infectious agents affecting the CNS. They play also a major role in the growth of tumours of the CNS. Microglia are consequently the key cell population linking the nervous and the immune system. This review covers all different aspects of microglia biology and pathology in a comprehensive way.

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.

Live imaging of the innate immune response in neonates reveals differential TLR2 dependent activation patterns in sterile inflammation and infection

Activation of microglial cells in response to brain injury and/or immune stimuli is associated with a marked induction of Toll-like receptors (TLRs). While in adult brain, the contribution of individual TLRs, including TLR2, in pathophysiological cascades has been well established, their role and spatial and temporal induction patterns in immature brain are far less understood. To examine whether infectious stimuli and sterile inflammatory stimuli trigger distinct TLR2-mediated innate immune responses, we used three models in postnatal day 9 (P9) mice, a model of infection induced by systemic endotoxin injection and two models of sterile inflammation, intra-cortical IL-1β injection and transient middle cerebral artery occlusion (tMCAO). We took advantage of a transgenic mouse model bearing the dual reporter system luciferase/GFP under transcriptional control of a murine TLR2 promoter (TLR2-luc-GFP) to visualize the TLR2 response in the living neonatal brain and then determined neuroinflammation, microglial activation and leukocyte infiltration. We show that in physiological postnatal brain development the in vivo TLR2-luc signal undergoes a marked ∼30-fold decline and temporal-spatial changes during the second and third postnatal weeks. We then show that while endotoxin robustly induces the in vivo TLR2-luc signal in the living brain and increases levels of several inflammatory cytokines and chemokines, the in vivo TLR2-luc signal is reduced after both IL-1β and tMCAO and the inflammatory response is muted. Immunofluorescence revealed that microglial cells are the predominant source of TLR2 production during postnatal brain development and in all three neonatal models studied. Flow cytometry revealed developmental changes in CD11b+/CD45+ and CD11b+/Ly6C+ cell populations, involvement of cells of the monocyte lineage, but lack of Ly6G+ neutrophils or CD3+ cells in acutely injured neonatal brains. Cumulatively, our results suggest distinct TLR2 induction patterns following PAMP and DAMP - mediated inflammation in immature brain.

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.