Maternal immune activation alters glutamic acid decarboxylase-67 expression in the brains of adult rat offspring

Age-related changes in behavior profile in male offspring of rats treated with poly I:C-induced maternal immune activation in early gestation

BACKGROUND

Autism and schizophrenia are environmental risk factors associated with prenatal viral infection during pregnancy. It is still unclear whether behavior phenotypes change at different developmental stages in offspring following the activation of the maternal immune system.

METHODS

Sprague-Dawley rats received a single caudal vein injection of 10 mg/kg polyinosinic:polycytidylic acid (poly I:C) on gestational day 9 and the offspring were comprehensively tested for behaviors in adolescence and adulthood.

RESULTS

Maternal serum levels of interleukin (IL)-6, IL-1β and tumor necrosis factor-α were elevated in poly I:C-treated dams. The offspring of maternal poly I:C-induced rats showed increased anxiety, impaired social approach, and progressive impaired cognitive and sensorimotor gating function.

CONCLUSION

Maternal immune activation led to developmental specificity behavioral impairment in offspring.

Schizophrenia in the genetic era: a review from development history, clinical features and genomic research approaches to insights of susceptibility genes

Schizophrenia is a devastating neuropsychiatric disorder affecting 1% of the world population and ranks as one of the disorders providing the most severe burden for society. Schizophrenia etiology remains obscure involving multi-risk factors, such as genetic, environmental, nutritional, and developmental factors. Complex interactions of genetic and environmental factors have been implicated in the etiology of schizophrenia. This review provides an overview of the historical origins, pathophysiological mechanisms, diagnosis, clinical symptoms and corresponding treatment of schizophrenia. In addition, as schizophrenia is a polygenic, genetic disorder caused by the combined action of multiple micro-effective genes, we further detail several approaches, such as candidate gene association study (CGAS) and genome-wide association study (GWAS), which are commonly used in schizophrenia genomics studies. A number of GWASs about schizophrenia have been performed with the hope to identify novel, consistent and influential risk genetic factors. Finally, some schizophrenia susceptibility genes have been identified and reported in recent years and their biological functions are also listed. This review may serve as a summary of past research on schizophrenia genomics and susceptibility genes (NRG1, DISC1, RELN, BDNF, MSI2), which may point the way to future schizophrenia genetics research. In addition, depending on the above discovery of susceptibility genes and their exact function, the development and application of antipsychotic drugs will be promoted in the future.

The impact of maternal immune activation on GABAergic interneuron development: A systematic review of rodent studies and their translational implications

Mothers exposed to infections during pregnancy disproportionally birth children who develop autism and schizophrenia, disorders associated with altered GABAergic function. The maternal immune activation (MIA) model recapitulates this risk factor, with many studies also reporting disruptions to GABAergic interneuron expression, protein, cellular density and function. However, it is unclear if there are species, sex, age, region, or GABAergic subtype specific vulnerabilities to MIA. Furthermore, to fully comprehend the impact of MIA on the GABAergic system a synthesised account of molecular, cellular, electrophysiological and behavioural findings was required. To this end we conducted a systematic review of GABAergic interneuron changes in the MIA model, focusing on the prefrontal cortex and hippocampus. We reviewed 102 articles that revealed robust changes in a number of GABAergic markers that present as gestationally-specific, region-specific and sometimes sex-specific. Disruptions to GABAergic markers coincided with distinct behavioural phenotypes, including memory, sensorimotor gating, anxiety, and sociability. Findings suggest the MIA model is a valid tool for testing novel therapeutics designed to recover GABAergic function and associated behaviour.

Maternal immune activation and role of placenta in the prenatal programming of neurodevelopmental disorders

Maternal infection during pregnancy, leading to maternal immune activation (mIA) and cytokine release, increases the offspring risk of developing a variety of neurodevelopmental disorders (NDDs), including schizophrenia. Animal models have provided evidence to support these mechanistic links, with placental inflammatory responses and dysregulation of placental function implicated. This leads to changes in fetal brain cytokine balance and altered epigenetic regulation of key neurodevelopmental pathways. The prenatal timing of such mIA-evoked changes, and the accompanying fetal developmental responses to an altered in utero environment, will determine the scope of the impacts on neurodevelopmental processes. Such dysregulation can impart enduring neuropathological changes, which manifest subsequently in the postnatal period as altered neurodevelopmental behaviours in the offspring. Hence, elucidation of the functional changes that occur at the molecular level in the placenta is vital in improving our understanding of the mechanisms that underlie the pathogenesis of NDDs. This has notable relevance to the recent COVID-19 pandemic, where inflammatory responses in the placenta to SARS-CoV-2 infection during pregnancy and NDDs in early childhood have been reported. This review presents an integrated overview of these collective topics and describes the possible contribution of prenatal programming through placental effects as an underlying mechanism that links to NDD risk, underpinned by altered epigenetic regulation of neurodevelopmental pathways.

Maternal immune activation affects socio-communicative behavior in adult rats

A wide body of evidence suggests a relationship between maternal immune activation (MIA) and neurodevelopmental disorders such as autism spectrum disorder (ASD). Since social and communicative deficits are included in the first diagnostic criterion of ASD, we aimed to characterize socio-communicative behaviors in the MIA model based on prenatal exposure to poly(I:C). Our previous studies demonstrated impaired socio-communicative functioning in poly(I:C)-exposed adolescent rats. Therefore, the current study sought to clarify whether these changes would persist beyond adolescence. For this purpose, we analyzed behavior during the social interaction test and recorded ultrasonic vocalizations (USVs) accompanying interactions between adult poly(I:C) rats. The results demonstrated that the altered pattern of social behavior in poly(I:C) males was accompanied by the changes in acoustic parameters of emitted USVs. Poly(I:C) males also demonstrated an impaired olfactory preference for social stimuli. While poly(I:C) females did not differ from controls in socio-positive behaviors, they displayed aggression during the social encounter and were more reactive to somatosensory stimulation. Furthermore, the locomotor pattern of poly(I:C) animals were characterized by repetitive behaviors. Finally, poly(I:C) reduced parvalbumin and GAD67 expression in the cerebellum. The results showed that prenatal poly(I:C) exposure altered the pattern of socio-communicative behaviors of adult rats in a sex-specific manner.

Schizophrenia Hypothesis: Autonomic Nervous System Dysregulation of Fetal and Adult Immune Tolerance

The autonomic nervous system can control immune cell activation via both sympathetic adrenergic and parasympathetic cholinergic nerve release of norepinephrine and acetylcholine. The hypothesis put forward in this paper suggests that autonomic nervous system dysfunction leads to dysregulation of immune tolerance mechanisms in brain-resident and peripheral immune cells leading to excessive production of pro-inflammatory cytokines such as Tumor Necrosis Factor alpha (TNF-α). Inactivation of Glycogen Synthase Kinase-3β (GSK3β) is a process that takes place in macrophages and microglia when a toll-like receptor 4 (TLR4) ligand binds to the TLR4 receptor. When Damage-Associated Molecular Patterns (DAMPS) and Pathogen-Associated Molecular Patterns (PAMPS) bind to TLR4s, the phosphatidylinositol-3-kinase (PI3K)-protein kinase B (Akt) pathway should be activated, leading to inactivation of GSK3β. This switches the macrophage from producing pro-inflammatory cytokines to anti-inflammatory cytokines. Acetylcholine activation of the α7 subunit of the nicotinic acetylcholine receptor (α7 nAChR) on the cell surface of immune cells leads to PI3K/Akt pathway activation and can control immune cell polarization. Dysregulation of this pathway due to dysfunction of the prenatal autonomic nervous system could lead to impaired fetal immune tolerance mechanisms and a greater vulnerability to Maternal Immune Activation (MIA) resulting in neurodevelopmental abnormalities. It could also lead to the adult schizophrenia patient’s immune system being more vulnerable to chronic stress-induced DAMP release. If a schizophrenia patient experiences chronic stress, an increased production of pro-inflammatory cytokines such as TNF-α could cause significant damage. TNF-α could increase the permeability of the intestinal and blood brain barrier, resulting in lipopolysaccharide (LPS) and TNF-α translocation to the brain and consequent increases in glutamate release. MIA has been found to reduce Glutamic Acid Decarboxylase mRNA expression, resulting in reduced Gamma-aminobutyric acid (GABA) synthesis, which combined with an increase of glutamate release could result in an imbalance of glutamate and GABA neurotransmitters. Schizophrenia could be a “two-hit” illness comprised of a genetic “hit” of autonomic nervous system dysfunction and an environmental hit of MIA. This combination of factors could lead to neurotransmitter imbalance and the development of psychotic symptoms.

Disorganization of Oscillatory Activity in Animal Models of Schizophrenia

Schizophrenia is a chronic, debilitating disorder with diverse symptomatology, including disorganized cognition and behavior. Despite considerable research effort, we have only a limited understanding of the underlying brain dysfunction. In this article, we review the potential role of oscillatory circuits in the disorder with a particular focus on the hippocampus, a region that encodes sequential information across time and space, as well as the frontal cortex. Several mechanistic explanations of schizophrenia propose that a loss of oscillatory synchrony between and within these brain regions may underlie some of the symptoms of the disorder. We describe how these oscillations are affected in several animal models of schizophrenia, including models of genetic risk, maternal immune activation (MIA) models, and models of NMDA receptor hypofunction. We then critically discuss the evidence for disorganized oscillatory activity in these models, with a focus on gamma, sharp wave ripple, and theta activity, including the role of cross-frequency coupling as a synchronizing mechanism. Finally, we focus on phase precession, which is an oscillatory phenomenon whereby individual hippocampal place cells systematically advance their firing phase against the background theta oscillation. Phase precession is important because it allows sequential experience to be compressed into a single 120 ms theta cycle (known as a 'theta sequence'). This time window is appropriate for the induction of synaptic plasticity. We describe how disruption of phase precession could disorganize sequential processing, and thereby disrupt the ordered storage of information. A similar dysfunction in schizophrenia may contribute to cognitive symptoms, including deficits in episodic memory, working memory, and future planning.

Maternal immune activation in rodent models: A systematic review of neurodevelopmental changes in gene expression and epigenetic modulation in the offspring brain

Maternal immune activation (mIA) during pregnancy is hypothesised to disrupt offspring neurodevelopment and predispose offspring to neurodevelopmental disorders such as schizophrenia. Rodent models of mIA have explored possible mechanisms underlying this paradigm and provide a vital tool for preclinical research. However, a comprehensive analysis of the molecular changes that occur in mIA-models is lacking, hindering identification of robust clinical targets. This systematic review assesses mIA-driven transcriptomic and epigenomic alterations in specific offspring brain regions. Across 118 studies, we focus on 88 candidate genes and show replicated changes in expression in critical functional areas, including elevated inflammatory markers, and reduced myelin and GABAergic signalling proteins. Further, disturbed epigenetic markers at nine of these genes support mIA-driven epigenetic modulation of transcription. Overall, our results demonstrate that current outcome measures have direct relevance for the hypothesised pathology of schizophrenia and emphasise the importance of mIA-models in contributing to the understanding of biological pathways impacted by mIA and the discovery of new drug targets.

Maternal immune activation generates anxiety in offspring: A translational meta-analysis

Maternal immune activation (MIA) during pregnancy is recognized as an etiological risk factor for various psychiatric disorders, such as schizophrenia, major depressive disorder, and autism. Prenatal immune challenge may serve as a "disease primer" for alteration of the trajectory of fetal brain development that, in combination with other genetic and environmental factors, may ultimately result in the emergence of different psychiatric conditions. However, the association between MIA and an offspring's chance of developing anxiety disorders is less clear. To evaluate the effect of MIA on offspring anxiety, a systematic review and meta-analysis of the preclinical literature was conducted. We performed a systematic search of the PubMed, Web of Science, PsycINFO, and Cochrane Library electronic databases using the PRISMA and World Health Organization (WHO) methodologies for systematic reviews. Studies that investigated whether MIA during pregnancy could cause anxiety symptoms in rodent offspring were included. Overall, the meta-analysis showed that MIA induced anxiety behavior in offspring. The studies provide strong evidence that prenatal immune activation impacts specific molecular targets and synapse formation and function and induces an imbalance in neurotransmission that could be related to the generation of anxiety in offspring. Future research should further explore the role of MIA in anxiety endophenotypes. According to this meta-analysis, MIA plays an important role in the pathophysiological mechanisms of anxiety disorders and is a promising therapeutic target.

Maternal Immune Activation Affects Hippocampal Excitatory and Inhibitory Synaptic Transmission in Offspring From an Early Developmental Period to Adulthood

One of the risk factors for schizophrenia is maternal infection. We have previously shown that Polyriboinosinic-polyribocytidylic acid (poly I:C) induced maternal immune activation in mice caused histological changes in the hippocampal CA1 area of offspring during the developmental period and impaired sensorimotor gating in offspring during adulthood, resulting in behavioral changes. However, it remains unclear how maternal immune activation functionally impacts the hippocampal neuronal activity of offspring. We studied the effect of prenatal poly I:C treatment on synaptic transmission of hippocampal CA1 pyramidal cells in postnatal and adult offspring. Treatment with poly I:C diminished excitatory and enhanced inhibitory (GABAergic) synaptic transmission on pyramidal cells in adult offspring. During the early developmental period, we still observed that treatment with poly I:C decreased excitatory synaptic transmission and potentially increased GABAergic synaptic transmission, which was uncovered under a condition of high extracellular potassium-activated neurons. In conclusion, we demonstrate that maternal immune activation decreased excitatory and increased inhibitory synaptic transmission on hippocampal pyramidal cells from an early developmental period to adulthood, which could result in net inhibition in conjunction with poor functional organization and integration of hippocampal circuits.

Maternal Immune Activation by Poly I:C as a preclinical Model for Neurodevelopmental Disorders: A focus on Autism and Schizophrenia

Maternal immune activation (MIA) in response to a viral infection during early and mid-gestation has been linked through various epidemiological studies to a higher risk for the child to develop autism or schizophrenia-related symptoms.. This has led to the establishment of the pathogen-free poly I:C-induced MIA animal model for neurodevelopmental disorders, which shows relatively high construct and face validity. Depending on the experimental variables, particularly the timing of poly I:C administration, different behavioural and molecular phenotypes have been described that relate to specific symptoms of neurodevelopmental disorders such as autism spectrum disorder and/or schizophrenia. We here review and summarize epidemiological evidence for the effects of maternal infection and immune activation, as well as major findings in different poly I:C MIA models with a focus on poly I:C exposure timing, behavioural and molecular changes in the offspring, and characteristics of the model that relate it to autism spectrum disorder and schizophrenia.

Effect of Immune Activation during Early Gestation or Late Gestation on Inhibitory Markers in Adult Male Rats

People with schizophrenia exhibit deficits in inhibitory neurons and cognition. The timing of maternal immune activation (MIA) may present distinct schizophrenia-like phenotypes in progeny. We investigated whether early gestation [gestational day (GD) 10] or late gestation (GD19) MIA, via viral mimetic polyI:C, produces deficits in inhibitory neuron indices (GAD1, PVALB, SST, SSTR2 mRNAs) within cortical, striatal, and hippocampal subregions of male adult rat offspring. In situ hybridisation revealed that polyI:C offspring had: (1) SST mRNA reductions in the cingulate cortex and nucleus accumbens shell, regardless of MIA timing; (2) SSTR2 mRNA reductions in the cortex and striatum of GD19, but not GD10, MIA; (3) no alterations in cortical or striatal GAD1 mRNA of polyI:C offspring, but an expected reduction of PVALB mRNA in the infralimbic cortex, and; (4) no alterations in inhibitory markers in hippocampus. Maternal IL-6 response negatively correlated with adult offspring SST mRNA in cortex and striatum, but not hippocampus. These results show lasting inhibitory-related deficits in cortex and striatum in adult offspring from MIA. SST downregulation in specific cortical and striatal subregions, with additional deficits in somatostatin-related signalling through SSTR2, may contribute to some of the adult behavioural changes resulting from MIA and its timing.

Reduced cortical somatostatin gene expression in a rat model of maternal immune activation

Alterations in GABAergic interneurons and glutamic acid decarboxylase (GAD) are observed in the brains of people with schizophrenia. Studies also show increased density of interstitial white matter neurons (IWMN), including those containing GAD and somatostatin (SST) in the brain in schizophrenia. Maternal immune activation can be modelled in rodents to investigate the relationship between prenatal exposure to infections and increased risk of developing schizophrenia. We reported that maternal immune activation induced an increase in density of somatostatin-positive IWMN in the adult rat offspring. Here we hypothesised that maternal immune activation induced in pregnant rats by polyinosinic:polycytidylic acid would alter SST and GAD gene expression as well as increase the density of GAD-positive IWMNs in the adult offspring. SST gene expression was significantly reduced in the cingulate cortex of adult offspring exposed to late gestation maternal immune activation. There was no change in cortical GAD gene expression nor GAD-positive IWMN density in adults rats exposed to maternal immune activation at either early or late gestation. This suggests that our model of maternal immune activation induced by prenatal exposure of rats to polyinosinic:polycytidylic acid during late gestation is able to recapitulate changes in SST but not other GABAergic neuropathologies observed in schizophrenia.

JNK signalling mediates aspects of maternal immune activation: importance of maternal genotype in relation to schizophrenia risk

Background

Important insight into the mechanisms through which gene-environmental interactions cause schizophrenia can be achieved through preclinical studies combining prenatal immune stimuli with disease-related genetic risk modifications. Accumulating evidence associates JNK signalling molecules, including MKK7/MAP2K7, with genetic risk. We tested the hypothesis that Map2k7 gene haploinsufficiency in mice would alter the prenatal immune response to the viral mimetic polyriboinosinic-polyribocytidylic acid (polyI:C), specifically investigating the impact of maternal versus foetal genetic variants.

Methods

PolyI:C was administered to dams (E12.5), and cytokine/chemokine levels were measured 6 h later, in maternal plasma, placenta and embryonic brain.

Results

PolyI:C dramatically elevated maternal plasma levels of most cytokines/chemokines. Induction of IL-1β, IL-2, IL-10, IL-12, TNF-α and CXCL3 was enhanced, while CCL5 was suppressed, in Map2k7 hemizygous (Hz) dams relative to controls. Maternal polyI:C administration also increased embryonic brain chemokines, influenced by both maternal and embryonic genotype: CCL5 and CXCL10 levels were higher in embryonic brains from Map2k7 dams versus control dams; for CCL5, this was more pronounced in Map2k7 Hz embryos. Placental CXCL10 and CXCL12 levels were also elevated by polyI:C, the former enhanced and the latter suppressed, in placentae from maternal Map2k7 Hzs relative to control dams receiving polyI:C.

Conclusions

The results demonstrate JNK signalling as a mediator of MIA effects on the foetus. Since both elevated CXCL10 and supressed CXCL12 compromise developing GABAergic interneurons, the results support maternal immune challenge contributing to schizophrenia-associated neurodevelopmental abnormalities. The influence of Map2k7 on cytokine/chemokine induction converges the genetic and environmental aspects of schizophrenia, and the overt influence of maternal genotype offers an intriguing new insight into modulation of embryonic neurodevelopment by genetic risk.

Electronic supplementary material

The online version of this article (10.1186/s12974-019-1408-5) contains supplementary material, which is available to authorized users.

Maternal Inflammation and Neurodevelopmental Programming: A Review of Preclinical Outcomes and Implications for Translational Psychiatry

Early disruptions to neurodevelopment are highly relevant to understanding both psychiatric risk and underlying pathophysiology that can be targeted by new treatments. Much convergent evidence from the human literature associates inflammation during pregnancy with later neuropsychiatric disorders in offspring. Preclinical models of prenatal inflammation have been developed to examine the causal maternal physiological and offspring neural mechanisms underlying these findings. Here we review the strengths and limitations of preclinical models used for these purposes and describe selected studies that have shown maternal immune impacts on the brain and behavior of offspring. Maternal immune activation in mice, rats, nonhuman primates, and other mammalian model species have demonstrated convergent outcomes across methodologies. These outcomes include shifts and/or disruptions in the normal developmental trajectory of molecular and cellular processes in the offspring brain. Prenatal developmental origins are critical to a mechanistic understanding of maternal immune activation-induced alterations to microglia and immune molecules, brain growth and development, synaptic morphology and physiology, and anxiety- and depression-like, sensorimotor, and social behaviors. These phenotypes are relevant to brain functioning across domains and to anxiety and mood disorders, schizophrenia, and autism spectrum disorder, in which they have been identified. By turning a neurodevelopmental lens on this body of work, we emphasize the importance of acute changes to the prenatal offspring brain in fostering a better understanding of potential mechanisms for intervention. Collectively, overlapping results across maternal immune activation studies also highlight the need to examine preclinical offspring neurodevelopment alterations in terms of a multifactorial immune milieu, or immunome, to determine potential mechanisms of psychiatric risk.

Maternal immune activation altered microglial immunoreactivity in the brain of postnatal day 2 rat offspring

Microglia, the resident immune cells of the central nervous system, play critical roles in neurodevelopment, synaptic pruning, and neuronal wiring. Early in development, microglia migrate via the tangential and radial migration pathways to their final destinations and mature gradually, a process that includes morphological changes. Recent research has implicated microglial abnormality in the etiology of schizophrenia. Since prenatal exposure to viral or bacterial infections due to maternal immune activation (MIA) leads to increased risk of schizophrenia in the offspring during adulthood, the present study systematically investigated how MIA induced by polyinosinic:polycytidylic acid (a mimic of viral double-stranded RNA) affected microglial immunoreactivity along the migration and maturation trajectories in the brains of male and female rat offspring on postnatal day (PND) 2. The immunohistochemistry revealed significant changes in the density of IBA-1 immunoreactive cells in the corpus callosum, somatosensory cortex, striatum, and the subregions of the hippocampus of the MIA offspring. The male and female MIA offspring displayed markedly altered microglial immunoreactivity in both the tangential and radial migration, as well as maturation, pathways when compared to their sex- and age-matched controls as evidenced by morphology-based cell counting. Given the important roles of microglia in synaptic pruning and neuronal wiring and survival, these changes may lead to structural and functional neurodevelopmental abnormalities, and so contribute to the functional deficits observed in juvenile and adult MIA offspring. Future research is required to systematically determine how MIA affects microglial migration and maturation in rat offspring.

Effects of maternal immune activation on brain arginine metabolism of postnatal day 2 rat offspring

l-Arginine is a versatile semi-essential amino acid with a number of bioactive metabolites, and altered arginine metabolism has been implicated in the pathogenesis of schizophrenia. Earlier research has demonstrated that maternal immune activation (MIA; a risk factor for schizophrenia) alters arginine metabolism in the prefrontal cortex and hippocampus of the adult offspring. The present study investigated how MIA affected the levels of l-arginine and its downstream metabolites in the whole forebrain, frontal cortex, hippocampus and cerebellum of male and female rat offspring at the age of postnatal day 2. While no effects were evident in the forebrain, MIA significantly increased l-arginine, glutamate, putrescine, spermidine and spermine levels and the glutamate/GABA ratio, but decreased the glutamine/glutamate ratio, in the frontal cortex, hippocampus and/or cerebellum with no marked sex differences. Cluster analyses revealed that l-arginine and its main metabolites formed distinct groups, which changed as a function of MIA or sex in all four brain regions examined. These results demonstrate, for the first time, that MIA alters brain arginine metabolism in the rat offspring during early neonatal development, and further support the involvement of arginine metabolism in the pathogenesis of schizophrenia.

Maternal immune activation leads to increased nNOS immunoreactivity in the brain of postnatal day 2 rat offspring

Neuronal nitric oxide synthase (nNOS) is a key arginine metabolising enzyme in the brain, and nNOS-derived nitric oxide (NO) plays an important role in regulating glutamatergic neurotransmission. NO and its related molecules are involved in the pathogenesis of schizophrenia, and human genetic studies have identified schizophrenia risk genes encoding nNOS. This study systematically investigated how maternal immune activation (MIA; a risk factor for schizophrenia) induced by polyinosinic:polycytidylic acid affected nNOS-immunoreactivity in the brain of the resulting male and female offspring at the age of postnatal day (PND) 2. Immunohistochemistry revealed a markedly increased intensity of nNOS-positive cells in the CA3 and dentate gyrus subregions of the hippocampus, the somatosensory cortex, and the striatum, but not the frontal cortex and hippocampal CA1 region, in the MIA offspring when compared to control group animals. There were no sex differences in the effect. Given the role of nNOS in glutamatergic neurotransmission and its functional relationship with glutamate NMDA receptors, increased nNOS immunoreactivity may indicate the up-regulation of NMDA receptor function in MIA rat offspring at an early postnatal age. Future research is required to determine whether these changes contribute to the neuronal and behavioral dysfunction observed in both juvenile and adult MIA rat offspring.

Prenatal maternal immune activation and brain development with relevance to psychiatric disorders

Growing evidence from epidemiological studies strongly suggests maternal infection as a risk factor for psychiatric disorders including bipolar disorder, schizophrenia, and autism. Animal studies support this association and demonstrate that maternal immune activation (MIA) changes brain morphology and inflammatory cytokines in the adult offspring. Evidence for changes in inflammatory cytokines is also demonstrated in human post-mortem brain and peripheral blood studies from subjects with psychiatric disorders. This perspective briefly highlights convincing evidence from epidemiological, preclinical and human pathological studies to support the role of MIA in major psychiatric disorders. A better understanding of the link between MIA and brain development in psychiatric disorders will lead to the development of novel immunomodulatory interventions for individuals at risk for psychiatric disorders.

Morphology of Human Nucleus Accumbens Neurons Based on the Immunohistochemical Expression of Gad67

The nucleus accumbens is a part of the ventral striatum along with the caudate nucleus and putamen. The role of the human nucleus accumbens in drug addiction and other psychiatric disorders is of great importance. The aim of this study was to characterize medium spiny neurons in the nucleus accumbens according to the immunohistochemical expression of GAD67.

This study was conducted on twenty human brains of both sexes between the ages of 20 and 75. The expression of GAD67 was assessed immunohistochemically, and the characterization of the neurons was based on the shape and size of the soma and the number of impregnated primary dendrites.

We showed that neurons of the human nucleus accumbens expressed GAD67 in the neuron soma and in the primary dendrites. An analysis of the cell body morphology revealed the following four different types of neurons: fusiform neurons, fusiform neurons with lateral dendrites, pyramidal neurons and multipolar neurons.

An immunohistochemical analysis showed a strong GAD67 expression in GABAergic medium spiny neurons, which could be classifi ed into four different types, and these neurons morphologically correlated with those described by the Golgi study.

Developmental disruption of perineuronal nets in the medial prefrontal cortex after maternal immune activation

Maternal infection during pregnancy increases the risk of offspring developing schizophrenia later in life. Similarly, animal models of maternal immune activation (MIA) induce behavioural and anatomical disturbances consistent with a schizophrenia-like phenotype in offspring. Notably, cognitive impairments in tasks dependent on the prefrontal cortex (PFC) are observed in humans with schizophrenia and in offspring after MIA during pregnancy. Recent studies of post-mortem tissue from individuals with schizophrenia revealed deficits in extracellular matrix structures called perineuronal nets (PNNs), particularly in PFC. Given these findings, we examined PNNs over the course of development in a well-characterized rat model of MIA using polyinosinic-polycytidylic acid (polyI:C). We found selective reductions of PNNs in the PFC of polyI:C offspring which did not manifest until early adulthood. These deficits were not associated with changes in parvalbumin cell density, but a decrease in the percentage of parvalbumin cells surrounded by a PNN. Developmental expression of PNNs was also significantly altered in the amygdala of polyI:C offspring. Our results indicate MIA causes region specific developmental abnormalities in PNNs in the PFC of offspring. These findings confirm the polyI:C model replicates neuropathological alterations associated with schizophrenia and may identify novel mechanisms for cognitive and emotional dysfunction in the disorder.

Caloric restriction selectively reduces the GABAergic phenotype of mouse hypothalamic proopiomelanocortin neurons

KEY POINTS

Hypothalamic proopiomelanocortin (POMC) neurons release peptide products that potently inhibit food intake and reduce body weight. These neurons also release the amino acid transmitter GABA, which can inhibit downstream neurons. Although the release of peptide transmitters from POMC neurons is regulated by energy state, whether similar regulation of GABA release might occur had not been examined. The present results show that the GABAergic phenotype of POMC neurons is decreased selectively by caloric deficit and not altered by high-fat diet or stress. The fact the GABAergic phenotype of POMC neurons is sensitive to energy state suggests a dynamic physiological role for this transmitter and highlights the importance of determining the functional consequence of GABA released from POMC neurons in terms of the regulation of normal energy balance.

ABSTRACT

In addition to peptide transmitters, hypothalamic neurons, including proopiomelanocortin (POMC) and agouti-related peptide (AgRP) neurons, also release amino acid transmitters that can alter energy balance regulation. While recent studies show that the GABAergic nature of AgRP neurons is increased by caloric restriction, whether the GABAergic phenotype of POMC neurons is also regulated in an energy-state-dependent manner has not been previously examined. The present studies used fluorescence in situ hybridization to detect Gad1 and Gad2 mRNA in POMC neurons, as these encode the glutamate decarboxylase enzymes GAD67 and GAD65, respectively. The results show that both short-term fasting and chronic caloric restriction significantly reduce the percentage of POMC neurons expressing Gad1 mRNA in both male and female mice, with less of an effect on Gad2 expression. Neither acute nor chronic intermittent restraint stress altered Gad1 expression in POMC neurons. Maintenance on a high-fat diet also did not affect the portion POMC neurons expressing Gad1, suggesting that the GABAergic phenotype of POMC neurons is particularly sensitive to energy deficit. Because changes in Gad1 expression have been previously shown to correlate with altered terminal GABA release, fasting is likely to cause a decrease in GABA release from POMC neurons. Altogether, the present results show that the GABAergic nature of POMC neurons can be dynamically regulated by energy state in a manner opposite to that in AgRP neurons and suggest the importance of considering the functional role of GABA release in addition to the peptide transmitters from POMC neurons.