Schizophrenia associated sensory gating deficits develop after adolescent microglia activation

Microglia and microbiome in schizophrenia: can immunomodulation improve symptoms?

In this overview, influences of microglia activation and disturbances of the microbiome in the devastating disorder schizophrenia are discussed. Despite previous assumptions of a primary neurodegenerative character of this disorder, current research underlines the important autoimmunological and inflammatory processes here. Early disturbances of microglial cells as well as cytokines could lead to weakness of the immunological system in the prodromal phase and then fully manifest in patients with schizophrenia. Measurements of microbiome features might allow identifying the prodromal phase. In conclusion, such thinking would imply several new therapeutic options regulating immune processes by old or new anti-inflammatory agents in patients.

Investigating behavioral phenotypes related to autism spectrum disorder in a gene-environment interaction model of Cntnap2 deficiency and Poly I:C maternal immune activation

Introduction

Autism Spectrum Disorder (ASD) has been associated with a wide variety of genetic and environmental risk factors in both human and preclinical studies. Together, findings support a gene-environment interaction hypothesis whereby different risk factors independently and synergistically impair neurodevelopment and lead to the core symptoms of ASD. To date, this hypothesis has not been commonly investigated in preclinical ASD models. Mutations in the Contactin-associated protein-like 2 (Cntnap2) gene and exposure to maternal immune activation (MIA) during pregnancy have both been linked to ASD in humans, and preclinical rodent models have shown that both MIA and Cntnap2 deficiency lead to similar behavioral deficits.

Methods

In this study, we tested the interaction between these two risk factors by exposing Wildtype, Cntnap2+/–, and Cntnap2–/– rats to Polyinosinic: Polycytidylic acid (Poly I:C) MIA at gestation day 9.5.

Results

Our findings showed that Cntnap2 deficiency and Poly I:C MIA independently and synergistically altered ASD-related behaviors like open field exploration, social behavior, and sensory processing as measured through reactivity, sensitization, and pre-pulse inhibition (PPI) of the acoustic startle response. In support of the double-hit hypothesis, Poly I:C MIA acted synergistically with the Cntnap2–/– genotype to decrease PPI in adolescent offspring. In addition, Poly I:C MIA also interacted with the Cntnap2+/– genotype to produce subtle changes in locomotor hyperactivity and social behavior. On the other hand, Cntnap2 knockout and Poly I:C MIA showed independent effects on acoustic startle reactivity and sensitization.

Discussion

Together, our findings support the gene-environment interaction hypothesis of ASD by showing that different genetic and environmental risk factors could act synergistically to exacerbate behavioral changes. In addition, by showing the independent effects of each risk factor, our findings suggest that ASD phenotypes could be caused by different underlying mechanisms.

MiR-124 Reduced Neuroinflammation after Traumatic Brain Injury by Inhibiting TRAF6

INTRODUCTION

Neuroinflammation contributes to secondary injury after traumatic brain injury (TBI), which has been mainly mediated by the microglia. MiR-124 was reported to play an important role in the polarization of microglia by targeting TLR4 signaling pathway. However, the role and mechanism of miR-124 in neuroinflammation mediated by microglia after TBI is unclear. To clarify this, we performed this research.

METHODS

The expression of miR-124 was first measured by RT-PCR in the injured brain at 1/3/7 days post-TBI. Then, miR-124 mimics or inhibitors administration was used to interfere the expression of miR-124 at 24 h post-TBI. Subsequently, the microglia polarization markers were detected by RT-PCR, the expression of inflammatory cytokines was detected by ELISA, the expression of TLR4/MyD88/IRAK1/TRAF6/NF-κB was measured by WB, and the neurological deficit was evaluated by NSS and MWM test. At last, in vitro experiments were performed to explore the exact target molecule of miR-124 on TLR4 signaling pathway.

RESULTS

Animal research indicated that the expression of miR-124 was downregulated after TBI. Upregulation of miR-124 promoted the M2 polarization of microglia and inhibited the activity of TLR4 pathway, as well as reduced neuroinflammation and neurological deficit after TBI. In vitro experiments indicated that miR-124 promoted the M2 polarization of microglia and reduced neuroinflammation by inhibiting TRAF6.

CONCLUSION

This study demonstrated that upregulation of miR-124 promoted the M2 polarization of microglia and reduced neuroinflammation after TBI by inhibiting TRAF6.

Chemokine Dysregulation and Neuroinflammation in Schizophrenia: A Systematic Review

Chemokines are known to be immunoregulatory proteins involved not only in lymphocyte chemotaxis to the site of inflammation, but also in neuromodulation, neurogenesis, and neurotransmission. Multiple lines of evidence suggest a peripheral proinflammatory state and neuroinflammation in at least a third of patients with schizophrenia. Therefore, chemokines can be active players in these processes. In this systematic review, we analyzed the available data on chemokine dysregulation in schizophrenia and the association of chemokines with neuroinflammation. It has been shown that there is a genetic association of chemokine and chemokine receptor gene polymorphisms in schizophrenia. Besides, the most reliable data confirmed by the results of meta-analyses showed an increase in CXCL8/IL-8, CCL2/MCP-1, CCL4/MIP-1β, CCL11/eotaxin-1 in the blood of patients with schizophrenia. An increase in CXCL8 has been found in cerebrospinal fluid, but other chemokines have been less well studied. Increased/decreased expression of genes of chemokine and their receptors have been found in different areas of the brain and peripheral immune cells. The peripheral proinflammatory state may influence the expression of chemokines since their expression is regulated by pro- and anti-inflammatory cytokines. Mouse models have shown an association of schizophrenia with dysregulation of the CX3CL1-CX3CR1 and CXCL12-CXCR4 axes. Altogether, dysregulation in chemokine expression may contribute to neuroinflammation in schizophrenia. In conclusion, this evidence indicates the involvement of chemokines in the neurobiological processes associated with schizophrenia.

Lipopolysaccharide Exacerbates Ketamine-Induced Psychotic-Like Behavior, Oxidative Stress, and Neuroinflammation in Mice: Ameliorative Effect of Diosmin

Schizophrenia, a neuropsychiatric disorder has been associated with aberrant neurotransmission affecting behaviors, social preference, and cognition. Limitations in understanding its pathogenesis via the dopamine hypothesis have engendered other hypotheses such as the glutamate hypothesis. That antagonism of the N-methyl-D-aspartate receptor (NMDAR) elicits schizophrenia-like behaviors indistinguishable from the disorder in animal and human models. There are growing concerns that redox imbalance and neuro-immuno dysfunction may play role in aggravating the symptomologies of this disorder. This 14-day treatment study was designed to investigate the effect of diosmin on lipopolysaccharide (LPS) plus ketamine (NMDAR antagonist). Mice were divided into 4 groups (n = 6). Group 1 was administered 5% DMSO (10 mL/kg, i.p) while group 2-4 received LPS (0.1 mg/kg, i.p) daily for 14 days. Diosmin (50 mg/kg, i.p) and risperidone (0.5 mg/kg, i.p) were given to groups 3 and 4 respectively. Groups 2-4 were given KET (20 mg/kg, i.p.) daily from days 8-14. Behavioral tests were done 30 min after the last dose, and oxidative stress and neuroinflammatory maker were assayed. LPS plus ketamine-induced hyperlocomotion, stereotypy, decreased social preference, and memory impairment. Furthermore, LPS plus-ketamine-induced oxidative stress (reduced GSH, CAT, SOD, and increased MDA and nitrite levels) and marked pro-inflammatory cytokines TNF-α and IL-6 suggesting neuroinflammation. However, diosmin attenuated behavioral deficits and improved memory. Additionally, diosmin potentiated antioxidant level via increased GSH, CAT, and SOD while reducing MDA and nitrite levels. Finally, diosmin reduced TNF-α and IL-6 suggesting anti-neuro-immuno activity. Conclusively, diosmin attenuated LPS plus ketamine-induced behavioral deficits, oxidative stress, neuroinflammation, and improved memory.

Animal Models of Relevance to the Schizophrenia Prodrome

Patients with schizophrenia often undergo a prodromal phase prior to diagnosis. Given the absence of significant therapeutic improvements, attention has recently shifted to the possibility of intervention during this early stage to delay or diminish symptom severity or even prevent onset. Unfortunately, the 20 or so trials of intervention to date have not been successful in either preventing onset or improving long-term outcomes in subjects who are at risk of developing schizophrenia. One reason may be that the biological pathways an effective intervention must target are not static. The prodromal phase typically occurs during late adolescence, a period during which a number of brain circuits and structures are still maturing. We propose that developing a deeper understanding of which circuits/processes and brain structures are still maturing at this time and which processes drive the transition to schizophrenia will take us a step closer to developing better prophylactic interventions. Fortunately, such knowledge is now emerging from clinical studies, complemented by work in animal models. Our task here is to describe what would constitute an appropriate animal model to study and to potentially intervene in such processes. Such a model would allow invasive analysis of the cellular and molecular substrates of the progressive neurobiology that defines the schizophrenia prodrome and hopefully offer valuable insights into potential prophylactic targets.

New insight in the cross-talk between microglia and schizophrenia: From the perspective of neurodevelopment

Characterized by psychotic symptoms, negative symptoms and cognitive deficits, schizophrenia had a catastrophic effect on patients and their families. Multifaceted reliable evidence indicated that schizophrenia is a neurodevelopmental disorder. Microglia, the immune cells in central nervous system, related to many neurodevelopmental diseases. Microglia could affect neuronal survival, neuronal death and synaptic plasticity during neurodevelopment. Anomalous microglia during neurodevelopment may be associated with schizophrenia. Therefore, a hypothesis proposes that the abnormal function of microglia leads to the occurrence of schizophrenia. Nowadays, accumulating experiments between microglia and schizophrenia could afford unparalleled probability to assess this hypothesis. Herein, this review summarizes the latest supporting evidence in order to shed light on the mystery of microglia in schizophrenia.

Microglia sequelae: brain signature of innate immunity in schizophrenia

Schizophrenia is a psychiatric disorder with significant impact on individuals and society. The current pharmacologic treatment, which principally alleviates psychosis, is focused on neurotransmitters modulation, relying on drugs with severe side effects and ineffectiveness in a significant percentage of cases. Therefore, and due to difficulties inherent to diagnosis and treatment, it is vital to reassess alternative cellular and molecular drug targets. Distinct risk factors - genetic, developmental, epigenetic, and environmental - have been associated with disease onset and progression, giving rise to the proposal of different pathophysiological mechanisms and putative pharmacological targets. Immunity is involved and, particularly microglia - innate immune cells of the central nervous system, critically involved in brain development - have captured attention as cellular players. Microglia undergo marked morphologic and functional alterations in the human disease, as well as in animal models of schizophrenia, as reported in several original papers. We cluster the main findings of clinical studies by groups of patients: (1) at ultra-high risk of psychosis, (2) with a first episode of psychosis or recent-onset schizophrenia, and (3) with chronic schizophrenia; in translational studies, we highlight the time window of appearance of particular microglia alterations in the most well studied animal model in the field (maternal immune activation). The organization of clinical and translational findings based on schizophrenia-associated microglia changes in different phases of the disease course may help defining a temporal pattern of microglia changes and may drive the design of novel therapeutic strategies.

Structural and Functional Deviations of the Hippocampus in Schizophrenia and Schizophrenia Animal Models

Schizophrenia is a grave neuropsychiatric disease which frequently onsets between the end of adolescence and the beginning of adulthood. It is characterized by a variety of neuropsychiatric abnormalities which are categorized into positive, negative and cognitive symptoms. Most therapeutical strategies address the positive symptoms by antagonizing D2-dopamine-receptors (DR). However, negative and cognitive symptoms persist and highly impair the life quality of patients due to their disabling effects. Interestingly, hippocampal deviations are a hallmark of schizophrenia and can be observed in early as well as advanced phases of the disease progression. These alterations are commonly accompanied by a rise in neuronal activity. Therefore, hippocampal formation plays an important role in the manifestation of schizophrenia. Furthermore, studies with animal models revealed a link between environmental risk factors and morphological as well as electrophysiological abnormalities in the hippocampus. Here, we review recent findings on structural and functional hippocampal abnormalities in schizophrenic patients and in schizophrenia animal models, and we give an overview on current experimental approaches that especially target the hippocampus. A better understanding of hippocampal aberrations in schizophrenia might clarify their impact on the manifestation and on the outcome of this severe disease.

New Strategies for the Treatment of Neuropsychiatric Disorders Based on Reelin Dysfunction

Reelin is an extracellular matrix protein that is mainly produced in Cajal-Retzius cells and controls neuronal migration, which is important for the proper formation of cortical layers in the developmental stage of the brain. In the adult brain, Reelin plays a crucial role in the regulation of N-methyl-D-aspartate receptor-dependent synaptic function, and its expression decreases postnatally. Clinical studies showed reductions in Reelin protein and mRNA expression levels in patients with psychiatric disorders; however, the causal relationship remains unclear. Reelin-deficient mice exhibit an abnormal neuronal morphology and behavior, while Reelin supplementation ameliorates learning deficits, synaptic dysfunctions, and spine loss in animal models with Reelin deficiency. These findings suggest that the neuronal deficits and brain dysfunctions associated with the down-regulated expression of Reelin are attenuated by enhancements in its expression and functions in the brain. In this review, we summarize findings on the role of Reelin in neuropsychiatric disorders and discuss potential therapeutic approaches for neuropsychiatric disorders associated with Reelin dysfunctions.

Impact of Poly I:C induced maternal immune activation on offspring's gut microbiome diversity - Implications for schizophrenia

Background Immunopathological concepts have been intensively discussed for schizophrenia. The polyriboinosinic-polyribocytidylic (PolyI:C) mouse model has been well validated to invasively study this disease. The intestinal microbiome exhibits broad immunological and neuronal activities. The relevance of microbiome alterations in the PolyI:C model to human schizophrenia should be explored. Methods Feces of offspring from mice mothers, who were administered to PolyI:C or NaCl (controls) at ED 9, were collected at PND 30 and 180 (PolyI:C and control mice (N = 32 each; half males and females). This was analyzed for bacterial 16S ribosomal DNA (rDNA) using a gut microbiome polymerase chain reaction (PCR) microarray tool. Results Differences were found in species richness of microbiome between animals of different ages (PND 30 and 180), but also between offspring from PolyI:C vs. NaCl treated mothers. In female mice at PND 30, the abundance of Prevotellaceae and Porphyromonadaceae was lower and that of Lactobacillales was higher, whereas in male mice at the same time point the abundance of four families of the Firmicutes phylum (Clostridia vadinBB60 group, Clostridiales Family XIII, Ruminococcaceae and Erysipelotrichaceae) was increased relative to the control group. Limitations No further analyses of cell types or cytokines involved in autoimmune gut and brain processes. Conclusions These finding seem to be similar to microbiome disturbances in patients with schizophrenia. The differential bacterial findings at day 30 (i.e., similar to the prodromal phase in patients with schizophrenia) correspond to the tremendous activation of the immune system with a strong increase in microglial cells which might be responsible for neuroplasticity reduction in cortical areas in patients with schizophrenia.

Shedding light on the role of CX3CR1 in the pathogenesis of schizophrenia

Schizophrenia has a complex and heterogeneous molecular and clinical picture. Over the years of research on this disease, many factors have been suggested to contribute to its pathogenesis. Recently, the inflammatory processes have gained particular interest in the context of schizophrenia due to the increasing evidence from epidemiological, clinical and experimental studies. Within the immunological component, special attention has been brought to chemokines and their receptors. Among them, CX3C chemokine receptor 1 (CX3CR1), which belongs to the family of seven-transmembrane G protein-coupled receptors, and its cognate ligand (CX3CL1) constitute a unique system in the central nervous system. In the view of regulation of the brain homeostasis through immune response, as well as control of microglia reactivity, the CX3CL1–CX3CR1 system may represent an attractive target for further research and schizophrenia treatment. In the review, we described the general characteristics of the CX3CL1–CX3CR1 axis and the involvement of this signaling pathway in the physiological processes whose disruptions are reported to participate in mechanisms underlying schizophrenia. Furthermore, based on the available clinical and experimental data, we presented a guide to understanding the implication of the CX3CL1–CX3CR1 dysfunctions in the course of schizophrenia.

Role of Polyinosinic:Polycytidylic Acid-Induced Maternal Immune Activation and Subsequent Immune Challenge in the Behaviour and Microglial Cell Trajectory in Adult Offspring: A Study of the Neurodevelopmental Model of Schizophrenia

Multiple lines of evidence support the pathogenic role of maternal immune activation (MIA) in the occurrence of the schizophrenia-like disturbances in offspring. While in the brain the homeostatic role of neuron-microglia protein systems is well documented, the participation of the CX3CL1-CX3CR1 and CD200-CD200R dyads in the adverse impact of MIA often goes under-recognized. Therefore, in the present study, we examined the effect of MIA induced by polyinosinic:polycytidylic acid (Poly I:C) on the CX3CL1-CX3CR1 and CD200-CD200R axes, microglial trajectory (MhcII, Cd40, iNos, Il-1β, Tnf-α, Il-6, Arg1, Igf-1, Tgf-β and Il-4), and schizophrenia-like behaviour in adult male offspring of Sprague-Dawley rats. Additionally, according to the “two-hit” hypothesis of schizophrenia, we evaluated the influence of acute challenge with Poly I:C in adult prenatally MIA-exposed animals on the above parameters. In the present study, MIA evoked by Poly I:C injection in the late period of gestation led to the appearance of schizophrenia-like disturbances in adult offspring. Our results revealed the deficits manifested as a diminished number of aggressive interactions, presence of depressive-like episodes, and increase of exploratory activity, as well as a dichotomy in the sensorimotor gating in the prepulse inhibition (PPI) test expressed as two behavioural phenotypes (MIA_PPI-low and MIA_PPI-high). Furthermore, in the offspring rats subjected to a prenatal challenge (i.e., MIA) we noticed the lack of modulation of behavioural changes after the additional acute immune stimulus (Poly I:C) in adulthood. The important finding reported in this article is that MIA affects the expression and levels of the neuron-microglia proteins in the frontal cortex and hippocampus of adult offspring. We found that the changes in the CX3CL1-CX3CR1 axis could affect microglial trajectory, including decreased hippocampal mRNA level of MhcII and elevated cortical expression of Igf-1 in the MIA_PPI-high animals and/or could cause the up-regulation of an inflammatory response (Il-6, Tnf-α, iNos) after the “second hit” in both examined brain regions and, at least in part, might differentiate behavioural disturbances in adult offspring. Consequently, the future effort to identify the biological background of these interactions in the Poly I:C-induced MIA model in Sprague-Dawley rats is desirable to unequivocally clarify this issue.

Behavioral Tasks Evaluating Schizophrenia-like Symptoms in Animal Models: A Recent Update

BACKGROUND

Schizophrenia is a serious mental illness that affects more than 21 million people worldwide. Both genetics and the environment play a role in its etiology and pathogenesis. Symptoms of schizophrenia are mainly categorized into positive, negative, and cognitive. One major approach to identify and understand these diverse symptoms in humans has been to study behavioral phenotypes in a range of animal models of schizophrenia.

OBJECTIVE

We aimed to provide a comprehensive review of the behavioral tasks commonly used for measuring schizophrenia-like behaviors in rodents together with an update of the recent study findings.

METHODS

Articles describing phenotypes of schizophrenia-like behaviors in various animal models were collected through a literature search in Google Scholar, PubMed, Web of Science, and Scopus, with a focus on advances over the last 10 years.

RESULTS

Numerous studies have used a range of animal models and behavioral paradigms of schizophrenia to develop antipsychotic drugs for improved therapeutics. In establishing animal models of schizophrenia, the candidate models were evaluated for schizophrenia-like behaviors using several behavioral tasks for positive, negative, and cognitive symptoms designed to verify human symptoms of schizophrenia. Such validated animal models were provided as rapid preclinical avenues for drug testing and mechanistic studies.

CONCLUSION

Based on the most recent advances in the field, it is apparent that a myriad of behavior tests are needed to confirm and evaluate the congruency of animal models with the numerous behaviors and clinical signs exhibited by patients with schizophrenia.

Modulating microglia activation prevents maternal immune activation induced schizophrenia-relevant behavior phenotypes via arginase 1 in the dentate gyrus

Prenatal infection during pregnancy increases the risk for developing neuropsychiatric disorders such as schizophrenia. This is linked to an inflammatory microglial phenotype in the offspring induced by maternal immune activation (MIA). Microglia are crucial for brain development and maintenance of neuronal niches, however, whether and how their activation is involved in the regulation of neurodevelopment remains unclear. Here, we used a MIA rodent model in which polyinosinic: polycytidylic acid (poly (I:C)) was injected into pregnant mice. We found fewer parvalbumin positive (PV+) cells and impaired GABAergic transmission in the dentate gyrus (DG), accompanied by schizophrenia-like behavior in the adult offspring. Minocycline, a potent inhibitor of microglia activation, successfully prevented the above-mentioned deficits in the offspring. Furthermore, by using microglia-specific arginase 1 (Arg1) ablation as well as overexpression in DG, we identified a critical role of Arg1 in microglia activation to protect against poly (I:C) imparted neuropathology and altered behavior in offspring. Taken together, our results highlight that Arg1-mediated alternative activation of microglia are potential therapeutic targets for psychiatric disorders induced by MIA.

The Role of Microglial CX3CR1 in Schizophrenia-Related Behaviors Induced by Social Isolation

According to the microglial hypothesis of schizophrenia, the hyperactivation of microglia and the release of proinflammatory cytokines lead to neuronal loss, which is highly related to the onset of schizophrenia. Recent studies have demonstrated that fractalkine (CX3CL1) and its receptor CX3CR1 modulate the function of microglia. Thus, the present study aimed to determine whether microglial CX3CR1 plays a role in schizophrenia-related behaviors. A classical animal model of schizophrenia, social isolation (from postnatal days 21–56), was used to induce schizophrenia-related behaviors in C57BL/6J and CX3CR1^−/− mice, and the expression of the microglial CX3CR1 protein was examined in several brain areas of the C57BL/6J mice by Western blot analysis. The results revealed that social isolation caused deficits in the prepulse inhibition (PPI) in the C57BL/6J mice but not in the CX3CR1^−/− mice and increased locomotor activity in both the C57BL/6J mice and the CX3CR1^−/− mice. Moreover, the CX3CR1 protein level was increased in the medial prefrontal cortex, nucleus accumbens, and hippocampus of the isolated C57BL/6J mice. These findings suggested that the function of microglia regulated by CX3CR1 might participate in schizophrenia-related behaviors.

Reelin Supplementation Into the Hippocampus Rescues Abnormal Behavior in a Mouse Model of Neurodevelopmental Disorders

In the majority of schizophrenia patients, chronic atypical antipsychotic administration produces a significant reduction in or even complete remission of psychotic symptoms such as hallucinations and delusions. However, these drugs are not effective in improving cognitive and emotional deficits in patients with schizophrenia. Atypical antipsychotic drugs have a high affinity for the dopamine D₂ receptor, and a modest affinity for the serotonin 5-HT_2A receptor. The cognitive and emotional deficits in schizophrenia are thought to involve neural networks beyond the classical dopaminergic mesolimbic pathway, however, including serotonergic systems. For example, mutations in the RELN gene, which encodes Reelin, an extracellular matrix protein involved in neural development and synaptic plasticity, are associated with neurodevelopmental disorders such as schizophrenia and autism spectrum disorder. Furthermore, hippocampal Reelin levels are down-regulated in the brains of both schizophrenic patients and in rodent models of schizophrenia. In the present study, we investigated the effect of Reelin microinjection into the mouse hippocampus on behavioral phenotypes to evaluate the role of Reelin in neurodevelopmental disorders and to test a therapeutic approach that extends beyond classical monoamine targets. To model the cognitive and emotional deficits, as well as histological decreases in Reelin-positive cell numbers and hippocampal synaptoporin distribution, a synaptic vesicle protein, offspring that were prenatally exposed to maternal immune activation were used. Microinjections of recombinant Reelin protein into the hippocampus rescued impairments in object memory and anxiety-like behavior and recruited synaptoporin in the hippocampus in offspring exposed to antenatal inflammation. These results suggest that Reelin supplementation has the potential to treat cognitive and emotional impairments, as well as synaptic disturbances, in patients with neurodevelopmental disorders such as schizophrenia.

Poly I:C-induced maternal immune challenge reduces perineuronal net area and raises spontaneous network activity of hippocampal neurons in vitro

Activation of the maternal immune system (MIA) during gestation is linked to neuropsychiatric diseases like schizophrenia. While many studies address behavioural aspects, less is known about underlying cellular mechanisms. In the following study, BALB/c mice received intraperitoneal injections of polyinosinic-polycytidylic acid (Poly I:C) (20 µg/ml) or saline (0.9%) at gestation day (GD) 9.5 before hippocampal neurons were isolated and cultured from embryonic mice for further analysis. Interestingly, strongest effects were observed when the perineuronal net (PNN) wearing subpopulation of neurons was analysed. Here, a significant reduction of aggrecan staining intensity, area and soma size could be detected. Alterations of PNNs are often linked to neuropsychiatric diseases, changes in synaptic plasticity and in electrophysiology. Utilizing multielectrode array analysis (MEA), we observed a remarkable increase of the spontaneous network activity in neuronal networks after 21 days in vitro (DIV) when mother mice suffered a prenatal immune challenge. As PNNs are associated with GABAergic interneurons, our data indicate that this neuronal subtype might be stronger affected by a prenatal MIA. Degradation or damage of this subtype might cause the hyperexcitability observed in the whole network. In addition, embryonic neurons of the Poly I:C condition developed significantly shorter axons after five days in culture, while dendritic parameters and apoptosis rate remained unchanged. Structural analysis of synapse numbers revealed an increase of postsynaptic density 95 (PSD-95) puncta after 14 DIV and an increase of presynaptic vesicular glutamate transporter (vGlut) puncta after 21 DIV, while inhibitory synaptic proteins were not altered.

Maternal Type-I interferon signaling adversely affects the microglia and the behavior of the offspring accompanied by increased sensitivity to stress

Viral infection during pregnancy is often associated with neuropsychiatric conditions. In mice, exposure of pregnant dams to the viral mimetic poly(I:C), serves as a model that simulates such pathology in the offspring, through a process known as Maternal Immune Activation (MIA). To investigate the mechanism of such effect, we hypothesized that maternal upregulation of Type-I interferon (IFN-I), as part of the dam's antiviral response, might contribute to the damage imposed on the offspring. Using mRNA sequencing and flow cytometry analyses we found that poly(I:C) treatment during pregnancy caused reduced expression of genes related to proliferation and cell cycle in the offspring's microglia relative to controls. This was found to be associated with an IFN-I signature in the embryonic yolk sac, the origin of microglia in development. Neutralizing IFN-I signaling in dams attenuated the effect of MIA on the newborn's microglia, while systemic maternal administration of IFNβ was sufficient to mimic the effect of poly(I:C), and led to increased vulnerability of offspring's microglia to subsequent stress. Furthermore, maternal elevation of IFNβ resulted in behavioral manifestations reminiscent of neuropsychiatric disorders. In addition, by adopting a "two-hit" experimental paradigm, we show a higher sensitivity of the offspring to postnatal stress subsequent to the maternal IFNβ elevation, demonstrated by behavioral irregularities. Our results suggest that maternal upregulation of IFN-I, in response to MIA, interferes with the offspring's programmed microglial developmental cascade, increases their susceptibility to postnatal stress, and leads to behavioral abnormalities.

The Potential Role of Dysfunctions in Neuron-Microglia Communication in the Pathogenesis of Brain Disorders

The bidirectional communication between neurons and microglia is fundamental for the proper functioning of the central nervous system (CNS). Chemokines and clusters of differentiation (CD) along with their receptors represent ligand-receptor signalling that is uniquely important for neuron - microglia communication. Among these molecules, CX3CL1 (fractalkine) and CD200 (OX-2 membrane glycoprotein) come to the fore because of their cell-type-specific localization. They are principally expressed by neurons when their receptors, CX3CR1 and CD200R, respectively, are predominantly present on the microglia, resulting in the specific axis which maintains the CNS homeostasis. Disruptions to this balance are suggested as contributors or even the basis for many neurological diseases. In this review, we discuss the roles of CX3CL1, CD200 and their receptors in both physiological and pathological processes within the CNS. We want to underline the critical involvement of these molecules in controlling neuron - microglia communication, noting that dysfunctions in their interactions constitute a key factor in severe neurological diseases, such as schizophrenia, depression and neurodegeneration-based conditions.

Prenatal immune activation induces age-related alterations in rat offspring: Effects upon NMDA receptors and behaviors

Prenatal exposure to polyriboinosinic-polyribocytidylic acid (poly I:C) results in psychotic-like behavior in mature rat offspring as well as enduring modifications of glutamatergic excitatory synaptic transmission. However, little is known about the dynamic behavioral and glutamate N-methyl-D-aspartate (NMDA) receptor changes in rat offspring following poly I:C treatment of pregnant dams. In this study, poly I:C was administered to rats intravenously at a dose of 10 mg/kg on gestational day 9 in order to assess changes in behavior and NMDA receptors in offspring over time. Results demonstrate progressive worsening behaviors in adolescents and adults that manifest as increased anxiety, cognitive impairment, and pre-pulse inhibition deficits. Age-related alteration of NMDA receptors in the prefrontal cortex and hippocampus, either total number or distribution, were observed from weaning to adulthood. These results suggest that abnormalities of NMDA receptors occur prior to obvious schizophrenia-like behavioral manifestations. Hence, NMDA receptors may be potential therapeutic targets to prevent disease development during asymptomatic periods of schizophrenia, and may serve as targets for preventive and/or therapeutic strategies for schizophrenia. Further, PSD95, a scaffolding protein that is a component of the NMDA receptor signaling complex, is increased in the hippocampus of adult offspring, when serious behavioral abnormalities emerge. This result suggests that PSD95 may be involved in behavioral abnormalities of schizophrenia.

Morin decreases cortical pyramidal neuron degeneration via inhibition of neuroinflammation in mouse model of schizophrenia

Neuroinflammation plays a prominent role in the pathophysiology and progression of schizophrenia. Thus, suppression of neuroinflammation may retard the progression of the disease. This study was designed to investigate whether morin, a bioactive compound with antipsychotic-like activity could reduce biomarkers of neuroinflammation and neurodegeneration in lipopolysaccharide (LPS)- and ketamine (KET)-induced schizophrenic-like behavior in mice. Animals were treated once daily intraperitoneally with morin (100 mg/kg), haloperidol (1 mg/kg), risperidone (0.5 mg/kg), or saline (10 mL/kg) in combination with LPS (0.1 mg/kg) for 14 consecutive days. However, from days 8-14, overt schizophrenia-like episode was produced with i.p. injection of KET (20 mg/kg) once daily. Schizophrenic-like behaviors: positive (open-field test), negative (social-interaction and social-memory tests) and cognitive (Y-maze test) symptoms were assessed on day 14. Thereafter, the levels and expressions of biomarkers of neuroinflammation were estimated in the striatum (ST), prefrontal cortex (PFC) and hippocampus (HC) using spectrophotometry, ELISA and immunohistochemistry. The effects of morin on cortical pyramidal neurons were estimated using Golgi-impregnation staining technique. LPS in combination with KET significantly (p < 0.05) induced schizophrenia-like behaviors, which was attenuated by morin. Morin significantly (p < 0.05) decreased tumor necrosis factor-α, interleukine-6 levels and myeloperoxidase activity in the ST, PFC and HC of mice treated with LPS + KET. Moreover, morin reduced regional brain expressions of cyclooxygenase-2, inducible nitric oxide synthase and nuclear factor kappa-B, and also rescued loss of pyramidal neurons in the PFC. Taken together, these findings suggest that morin reduces schizophrenic-like symptoms induced by LPS + KET via mechanisms related to inhibition of the release of pro-inflammatory mediators and suppression of degeneration of cortical pyramidal neurons in mice.

Age-related changes in neuroinflammation and prepulse inhibition in offspring of rats treated with Poly I:C in early gestation

Background

Maternal immune activation (MIA) during gestation can increase the later risk of schizophrenia in adult offspring. Neuroinflammation is believed to underlie this process. Postmortem brain studies have found changes in the neuroimmune systems of patients with schizophrenia. However, little is known about the dynamic changes in cerebral inflammation and behavior during the course of the disease.

Methods

Here, the prepulse inhibition (PPI) test was conducted in adolescent and adult Sprague–Dawley rats prenatally challenged with polyriboinosinic–polyribocytidylic acid (Poly I:C) on gestational day 9 to determine the behavioral trajectory triggered by early exposure to Poly I:C. Brain immune changes were determined in the prefrontal cortex (PFC) and hippocampus (HC) at both ages. The status of the microglia and astrocytes was determined with immunohistochemical staining. The levels of IL-6, IL-1β, and TNF-α in both brain regions were evaluated with enzyme-linked immunosorbent assays.

Results

Disrupted PPI, the core phenotype of schizophrenia, only emerged in adulthood. Behavioral changes during puberty and adulthood were both accompanied by the activation of microglia (PFC and HC). Astrocytes were only activated at PN60. The levels of proinflammatory cytokines (IL-1β, IL-6, and TNF-α) in the offspring of the Poly I:C-exposed mothers differed with brain region and time, with more cytokines elevated during periadolescence than during adulthood.

Conclusions

Our findings indicate that immune activation emerged before symptom manifestation in the offspring of MIA rats. We conclude that early prenatal Poly I:C challenge can lead to age-related behavioral and neuroinflammatory changes. These data provide new insight into the neuroinflammatory and neuropathological mechanisms underlying the development of schizophrenia. They also suggest that periadolescence could be more important than adulthood in the prevention and treatment of schizophrenia.

Controversies and prospects about microglia in maternal immune activation models for neurodevelopmental disorders

Activation of the maternal immune system during pregnancy is a well-established risk factor for neuropsychiatric disease in the offspring, yet, the underlying mechanisms leading to altered brain function remain largely undefined. Microglia, the resident immune cells of the brain, are key to adequate development of the central nervous system (CNS), and are prime candidates to mediate maternal immune activation (MIA)-induced brain abnormalities. As such, the effects of MIA on the immunological phenotype of microglia has been widely investigated. However, contradicting results due to differences in read-out and methodological approaches impede final conclusions on MIA-induced microglial alterations. The aim of this review is to critically discuss the evidence for an activated microglial phenotype upon MIA.

Prenatal exposure to environmental insults and enhanced risk of developing Schizophrenia and Autism Spectrum Disorder: focus on biological pathways and epigenetic mechanisms

When considering neurodevelopmental disorders (NDDs), Schizophrenia (SZ) and Autism Spectrum Disorder (ASD) are considered to be among the most severe in term of prevalence, morbidity and impact on the society. Similar features and overlapping symptoms have been observed at multiple levels, suggesting common pathophysiological bases. Indeed, recent genome-wide association studies (GWAS) and epidemiological data report shared vulnerability genes and environmental triggers across the two disorders. In this review, we will discuss the possible biological mechanisms, including glutamatergic and GABAergic neurotransmissions, inflammatory signals and oxidative stress related systems, which are targeted by adverse environmental exposures and that have been associated with the development of SZ and ASD. We will also discuss the emerging role of the gut microbiome as possible interplay between environment, immune system and brain development. Finally, we will describe the involvement of epigenetic mechanisms in the maintenance of long-lasting effects of adverse environments early in life. This will allow us to better understand the pathophysiology of these NDDs, and also to identify novel targets for future treatment strategies.

Embryonic stem cell transplants as a therapeutic strategy in a rodent model of autism

Autism is a neurodevelopmental disorder characterized by disruptions in three core behavioral domains: deficits in social interaction, impairments in communication, and repetitive and stereotyped patterns of behavior or thought. There are currently no drugs available for the treatment of the core symptoms of ASD and drugs that target comorbid symptoms often have serious adverse side effects, suggesting an urgent need for new therapeutic strategies. The neurobiology of autism is complex, but converging evidence suggests that ASD involves disruptions in the inhibitory GABAergic neurotransmitter system. Specifically, people with autism have a reduction in parvalbumin (PV)-containing interneurons in the PFC, leading to the suggestion that restoring interneuron function in this region may be a novel therapeutic approach for ASD. Here we used a dual-reporter embryonic stem cell line to generate enriched populations of PV-positive interneurons, which were transplanted into the medial prefrontal cortex (mPFC) of the Poly I:C rodent model of autism. PV interneuron transplants were able to decrease pyramidal cell firing in the mPFC and alleviated deficits in social interaction and cognitive flexibility. Our results suggest that restoring PV interneuron function in the mPFC may be a novel and effective treatment strategy to reduce the core symptoms of autism.

Maternal viral mimetic administration at the beginning of fetal hypothalamic nuclei development accelerates puberty in female rat offspring

This study aimed to investigate the effects of maternal viral infection during a critical time window of fetal hypothalamic development on timing of puberty in the female offspring. For that purpose, a viral mimetic (i.e., synthetic double-strand RNA, namely, polyinosinic–polycytidylic acid, poly (I:C)) or saline was injected (i.p.) to the pregnant rats during the beginning (day 12 of pregnancy, n = 5 for each group) or at the end of this time window (day 14 of pregnancy, n = 5 for each group). Four study groups were formed from the female pups (n = 9–10 pups/group). Following weaning of pups, vaginal opening and vaginal smearing was studied daily until 2 sequential estrous cycles were observed. During the second diestrus phase, blood samples were taken for progesterone, leptin, corticosterone, follicle-stimulating hormone, and luteinizing hormone. Maternal poly (I:C) injection on day 12 of pregnancy increased body mass and reduced the time to puberty in the female offspring. Neither poly (I:C) nor timing of injection affected other parameters studied (p > 0.05). It has been shown for the first time that maternal viral infection during the beginning of fetal hypothalamic development might hasten puberty by increasing body mass in rat offspring.

Prenatal Immune Challenge in Mice Leads to Partly Sex-Dependent Behavioral, Microglial, and Molecular Abnormalities Associated with Schizophrenia

Epidemiological studies revealed that environmental factors comprising prenatal infection are strongly linked to risk for later development of neuropsychiatric disorders such as schizophrenia. Considering strong sex differences in schizophrenia and its increased prevalence in males, we designed a methodological approach to investigate possible sex differences in pathophysiological mechanisms. Prenatal immune challenge was modeled by systemic administration of the viral mimic polyinosinic-polycytidylic acid (Poly I:C) to C57BL/6 mice at embryonic day 9.5. The consequences on behavior, gene expression, and microglia—brain immune cells that are critical for normal development—were characterized in male vs. female offspring at adulthood. The cerebral cortex, hippocampus, and cerebellum, regions where structural and functional alterations were mainly described in schizophrenia patients, were selected for cellular and molecular analyses. Confocal and electron microscopy revealed most pronounced differences in microglial distribution, arborization, cellular stress, and synaptic interactions in the hippocampus of male vs. female offspring exposed to Poly I:C. Sex differences in microglia were also measured under both steady-state and Poly I:C conditions. These microglial alterations were accompanied by behavioral impairment, affecting for instance sensorimotor gating, in males. Consistent with these results, increased expression of genes related to inflammation was measured in cerebral cortex and hippocampus of males challenged with Poly I:C. Overall, these findings suggest that schizophrenia's higher incidence in males might be associated, among other mechanisms, with an increased microglial reactivity to prenatal immune challenges, hence determining disease outcomes into adulthood.

Evidence of microglial activation following exposure to serum from first-onset drug-naïve schizophrenia patients

Abnormal activation of brain microglial cells is widely implicated in the pathogenesis of schizophrenia. Previously the pathophysiology of microglial activation was considered to be intrinsic to the central nervous system. We hypothesised that due to their perivascular localization, microglia can also be activated by factors present in circulating blood. Through application of high-content functional screening, we show that peripheral blood serum from first-onset drug-naïve schizophrenia patients is sufficient to provoke microglial cell signalling network responses in vitro which are indicative of proinflammatory activation. We further explore the composition of the serum for the presence of analytes, with the potential to activate microglia, and the utility of the resultant microglial cellular phenotype for novel drug discovery.

Animal models for bipolar disorder: from bedside to the cage

Bipolar disorder is characterized by recurrent manic and depressive episodes. Patients suffering from this disorder experience dramatic mood swings with a wide variety of typical behavioral facets, affecting overall activity, energy, sexual behavior, sense of self, self-esteem, circadian rhythm, cognition, and increased risk for suicide. Effective treatment options are limited and diagnosis can be complicated. To overcome these obstacles, a better understanding of the neurobiology underlying bipolar disorder is needed. Animal models can be useful tools in understanding brain mechanisms associated with certain behavior. The following review discusses several pathological aspects of humans suffering from bipolar disorder and compares these findings with insights obtained from several animal models mimicking diverse facets of its symptomatology. Various sections of the review concentrate on specific topics that are relevant in human patients, namely circadian rhythms, neurotransmitters, focusing on the dopaminergic system, stressful environment, and the immune system. We then explain how these areas have been manipulated to create animal models for the disorder. Even though several approaches have been conducted, there is still a lack of adequate animal models for bipolar disorder. Specifically, most animal models mimic only mania or depression and only a few include the cyclical nature of the human condition. Future studies could therefore focus on modeling both episodes in the same animal model to also have the possibility to investigate the switch from mania-like behavior to depressive-like behavior and vice versa. The use of viral tools and a focus on circadian rhythms and the immune system might make the creation of such animal models possible.

Evolution of structural abnormalities in the rat brain following in utero exposure to maternal immune activation: A longitudinal in vivo MRI study

Genetic and environmental risk factors for psychiatric disorders are suggested to disrupt the trajectory of brain maturation during adolescence, leading to the development of psychopathology in adulthood. Rodent models are powerful tools to dissect the specific effects of such risk factors on brain maturational profiles, particularly when combined with Magnetic Resonance Imaging (MRI; clinically comparable technology). We therefore investigated the effect of maternal immune activation (MIA), an epidemiological risk factor for adult-onset psychiatric disorders, on rat brain maturation using atlas and tensor-based morphometry analysis of longitudinal in vivo MR images. Exposure to MIA resulted in decreases in the volume of several cortical regions, the hippocampus, amygdala, striatum, nucleus accumbens and unexpectedly, the lateral ventricles, relative to controls. In contrast, the volumes of the thalamus, ventral mesencephalon, brain stem and major white matter tracts were larger, relative to controls. These volumetric changes were maximal between post-natal day 50 and 100 with no differences between the groups thereafter. These data are consistent with and extend prior studies of brain structure in MIA-exposed rodents. Apart from the ventricular findings, these data have robust face validity to clinical imaging findings reported in studies of individuals at high clinical risk for a psychiatric disorder. Further work is now required to address the relationship of these MRI changes to behavioral dysfunction and to establish thier cellular correlates.

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.

MiR-124 contributes to M2 polarization of microglia and confers brain inflammatory protection via the C/EBP-α pathway in intracerebral hemorrhage

Microglia mediated inflammation contributes to intracerebral hemorrhage (ICH) induced secondary injury. Activated microglia has dual functions as pro-inflammatory (M1) and anti-inflammatory (M2) factors in brain injury and repair. MiR-124 is a potent anti-inflammatory agent which affects microglia after brain injury. However, the potential of modulating the M1/M2 polarization of microglia after ICH has not been reported. In this experiment, we detected the effect of miR-124 on the M1/M2 polarization state. In addition, the ability miR-124 to subsequently impacted neurological deficit and cerebral water content of ICH mice were studied. Furthermore, the relationship between miR-124 and C/EBP-α target was detected. We found that miR-124 significantly increased in M2-polarized microglia. Transduction of miR-124 mimics decreased proinflammatory cytokine levels. A coculture model of microglia and neuron indicated that M2-polarized microglia protected neuron damage. Furthermore, miR-124 banded to the 3-untranslated region of C/EBP-α and downregulated its protein levels. In vivo, infusion of miR-124 decreased brain levels of C/EBP-α and significantly reduced brain injury in ICH mice. Thus, miR-124 ameliorated ICH-induced inflammatory injury by modulating microglia polarization toward the M2 phenotype via C/EBP-α. MiR-124 regulatory mechanisms also might represent new therapeutic strategy in ICH.

The Neuro-endocrinological Role of Microbial Glutamate and GABA Signaling

Gut microbiota provides the host with multiple functions (e.g., by contributing to food digestion, vitamin supplementation, and defense against pathogenic strains) and interacts with the host organism through both direct contact (e.g., through surface antigens) and soluble molecules, which are produced by the microbial metabolism. The existence of the so-called gut–brain axis of bi-directional communication between the gastrointestinal tract and the central nervous system (CNS) also supports a communication pathway between the gut microbiota and neural circuits of the host, including the CNS. An increasing body of evidence has shown that gut microbiota is able to modulate gut and brain functions, including the mood, cognitive functions, and behavior of humans. Nonetheless, given the extreme complexity of this communication network, its comprehension is still at its early stage. The present contribution will attempt to provide a state-of-the art description of the mechanisms by which gut microbiota can affect the gut–brain axis and the multiple cellular and molecular communication circuits (i.e., neural, immune, and humoral). In this context, special attention will be paid to the microbial strains that produce bioactive compounds and display ascertained or potential probiotic activity. Several neuroactive molecules (e.g., catecholamines, histamine, serotonin, and trace amines) will be considered, with special focus on Glu and GABA circuits, receptors, and signaling. From the basic science viewpoint, “microbial endocrinology” deals with those theories in which neurochemicals, produced by both multicellular organisms and prokaryotes (e.g., serotonin, GABA, glutamate), are considered as a common shared language that enables interkingdom communication. With regards to its application, research in this area opens the way toward the possibility of the future use of neuroactive molecule-producing probiotics as therapeutic agents for the treatment of neurogastroenteric and/or psychiatric disorders.