Elevated GRIA1 mRNA expression in Layer II/III and V pyramidal cells of the DLPFC in schizophrenia

Integrating spatial and single-nucleus transcriptomic data elucidates microglial-specific responses in female cynomolgus macaques with depressive-like behaviors

Major depressive disorder represents a serious public health challenge worldwide; however, the underlying cellular and molecular mechanisms are mostly unknown. Here, we profile the dorsolateral prefrontal cortex of female cynomolgus macaques with social stress-associated depressive-like behaviors using single-nucleus RNA-sequencing and spatial transcriptomics. We find gene expression changes associated with depressive-like behaviors mostly in microglia, and we report a pro-inflammatory microglia subpopulation enriched in the depressive-like condition. Single-nucleus RNA-sequencing data result in the identification of six enriched gene modules associated with depressive-like behaviors, and these modules are further resolved by spatial transcriptomics. Gene modules associated with huddle and sit alone behaviors are expressed in neurons and oligodendrocytes of the superficial cortical layer, while gene modules associated with locomotion and amicable behaviors are enriched in microglia and astrocytes in mid-to-deep cortical layers. The depressive-like behavior associated microglia subpopulation is enriched in deep cortical layers. In summary, our findings show cell-type and cortical layer-specific gene expression changes and identify one microglia subpopulation associated with depressive-like behaviors in female non-human primates.

Identification of rare missense mutations in the glutamate ionotropic receptor AMPA type subunit genes in schizophrenia

OBJECTIVE

The alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptors significantly regulate the synaptic transmission and functions of various synaptic receptors. This study aimed to identify single nucleotide mutations in the glutamate receptor, ionotropic, AMPA type (GRIA) gene family, which is associated with schizophrenia.

METHODS

The exon regions of four genes (GRIA1, GRIA2, GRIA3, and GRIA4) encoding glutamate ionotropic receptor AMPA type proteins were resequenced in 516 patients with schizophrenia. We analyzed the protein function of the identified rare mutants via immunoblotting.

RESULTS

A total of 24 coding variants were detected in the GRIA gene family, including six missense mutations, 17 synonymous mutations, and one frameshift insertion. Notably, three ultra-rare missense mutations (GRIA1p.V182A, GRIA2p.P123Q, and GRIA4p.Y491H) were not documented in the single nucleotide polymorphism database, gnomAD genomes, and 1517 healthy controls available from Taiwan BioBank. Immunoblotting revealed GRIA4p.Y491H mutant with altered protein expressions in cultured cells compared with the wild type.

CONCLUSION

Our findings suggest that, in some patients affected by schizophrenia, the GRIA gene family harbors rare functional mutations, which support rare coding variants that could contribute to the genetic architecture of this illness. The in-vitro impacts of these rare pathological mutations on the pathophysiology of schizophrenia are worthy of future investigation.

Chronic haloperidol administration downregulates select BDNF transcript and protein levels in the dorsolateral prefrontal cortex of rhesus monkeys

Post-mortem studies in the prefrontal cortex and hippocampal formation from schizophrenia patients have revealed significant disruptions in the expression molecules associated with cytoarchitecture, synaptic structure, function, and plasticity, known to be regulated in part by brain derived neurotrophic factor (BDNF). Interestingly, several studies using postmortem brain tissue from individuals diagnosed with schizophrenia have revealed a significant reduction in BDNF mRNA and protein levels in the dorsolateral prefrontal cortex (DLPFC), hippocampus and related areas; however, differentiating the effects of illness from antipsychotic history has remained difficult. We hypothesized that chronic antipsychotic treatment may contribute to the altered BDNF mRNA and protein expression observed in post-mortem brains of individuals diagnosed with schizophrenia. To address the influence of antipsychotic administration on BDNF expression in the primate brain, rhesus monkeys orally administered haloperidol, clozapine, or vehicle twice daily for 180 days. We found BDNF splice variants 4 and 5 in the DLPFC and variant 2 in the EC were significantly down-regulated following chronic administration of haloperidol. In addition, proBDNF and mature BDNF expression in the DLPFC, but not the EC, were significantly reduced. Based on the known regulation of BDNF expression by BDNF-AS, we assessed the expression of this lncRNA and found expression was significantly upregulated in the DLPFC, but not EC. The results of the present study provide evidence of haloperidol-induced regulation of BDNF mRNA and protein expression in the DLFPC and suggest an important role for BDNF-AS in this regulation. Given the role of BDNF in synaptic plasticity, neuronal survival and maintenance, aberrant expression induced by haloperidol likely has significant ramifications for neuronal populations and circuits in primate cortex.

Maternal immune activation induces methylation changes in schizophrenia genes

Susceptibility to schizophrenia is mediated by genetic and environmental risk factors. Infection driven maternal immune activation (MIA) during pregnancy is a key environmental risk factor. However, little is known about how MIA during pregnancy could contribute to adult-onset schizophrenia. In this study, we investigated if maternal immune activation induces changes in methylation of genes linked to schizophrenia. We found that differentially expressed genes in schizophrenia brain were significantly enriched among MIA induced differentially methylated genes in the foetal brain in a cell-type-specific manner. Upregulated genes in layer V pyramidal neurons were enriched among hypomethylated genes at gestational day 9 (fold change = 1.57, FDR = 0.049) and gestational day 17 (fold change = 1.97, FDR = 0.0006). A linear regression analysis, which showed a decrease in gene expression with an increase in methylation in gestational day 17, supported findings from our enrichment analysis. Collectively, our results highlight a connection between MIA driven methylation changes during gestation and schizophrenia gene expression signatures in the adult brain. These findings carry important implications for early preventative strategies in schizophrenia.

Profiling cell-type specific gene expression in post-mortem human brain samples through laser capture microdissection

The transcriptome of a cell constitutes an essential piece of cellular identity and contributes to the multifaceted complexity and heterogeneity of cell-types within the mammalian brain. Thus, while a wealth of studies have investigated transcriptomic alterations underlying the pathophysiology of diseases of the brain, their use of bulk-tissue homogenates makes it difficult to tease apart whether observed differences are explained by disease state or cellular composition. Cell-type-specific enrichment strategies are, therefore, crucial in the context of gene expression profiling. Laser capture microdissection (LCM) is one such strategy that allows for the capture of specific cell-types, or regions of interest, under microscopic visualization. In this review, we focus on using LCM for cell-type specific gene expression profiling in post-mortem human brain samples. We begin with a discussion of various LCM systems, followed by a walk-through of each step in the LCM to gene expression profiling workflow and a description of some of the limitations associated with LCM. Throughout the review, we highlight important considerations when using LCM with post-mortem human brain samples. Whenever applicable, commercially available kits that have proven successful in the context of LCM with post-mortem human brain samples are described.

AMPA receptors in schizophrenia: A systematic review of postmortem studies on receptor subunit expression and binding

BACKGROUND

While altered expression of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) type receptor has been reported in postmortem studies of schizophrenia, these findings are inconsistent. Therefore, we aimed to systematically review postmortem studies that investigated AMPA receptor expressions in schizophrenia.

METHODS

A systematic literature search was conducted for postmortem studies that measured AMPA receptor subunit expressions or receptor bindings in schizophrenia compared to healthy individuals on February 3, 2021, using Medline and Embase.

RESULTS

A total of 39 relevant articles were identified from 1360 initial reports. The dorsolateral prefrontal cortex (DLPFC) was the most investigated region (15 studies), followed by the medial temporal lobe (8 studies). For the DLPFC, 4/15 studies (26.7%) showed increased AMPA receptor binding or subunit expression in patients with schizophrenia compared to that in controls, especially in GRIA1 and GRIA4, 2/15 studies (13.3%) reported a decrease, particularly in GRIA2, and 8/15 studies (56.7%) found no significant differences. A decreased expression or receptor binding was observed in 6/8 studies (75.0%) in the subregions of the hippocampus in patients with schizophrenia compared to that in controls, whereas the other two studies found no significant differences.

CONCLUSION

Published data have reported decreased subunit expression or receptor binding in the hippocampus in schizophrenia. These findings were inconsistent in other brain regions, which might be due to the heterogeneity of this population, various study design, physiological changes after death, and limited number of studies. Future in vivo studies are warranted to examine AMPA receptor expressions in human brains, together with their comprehensive clinical characterization.

Neurodevelopmental Disorders Associated with PSD-95 and Its Interaction Partners

The postsynaptic density (PSD) is a massive protein complex, critical for synaptic strength and plasticity in excitatory neurons. Here, the scaffolding protein PSD-95 plays a crucial role as it organizes key PSD components essential for synaptic signaling, development, and survival. Recently, variants in DLG4 encoding PSD-95 were found to cause a neurodevelopmental disorder with a variety of clinical features including intellectual disability, developmental delay, and epilepsy. Genetic variants in several of the interaction partners of PSD-95 are associated with similar phenotypes, suggesting that deficient PSD-95 may affect the interaction partners, explaining the overlapping symptoms. Here, we review the transmembrane interaction partners of PSD-95 and their association with neurodevelopmental disorders. We assess how the structural changes induced by DLG4 missense variants may disrupt or alter such protein-protein interactions, and we argue that the pathological effect of DLG4 variants is, at least partly, exerted indirectly through interaction partners of PSD-95. This review presents a direction for functional studies to elucidate the pathogenic mechanism of deficient PSD-95, providing clues for therapeutic strategies.

Dysfunction of Glutamatergic Synaptic Transmission in Depression: Focus on AMPA Receptor Trafficking

Pharmacological and anatomical evidence suggests that abnormal glutamatergic neurotransmission may be associated with the pathophysiology of depression. Compounds that act as NMDA receptor antagonists may be a potential treatment for depression, notably the rapid-acting agent ketamine. The rapid-acting and sustained antidepressant effects of ketamine rely on the activation of AMPA receptors (AMPARs). As the key elements of fast excitatory neurotransmission in the brain, AMPARs are crucially involved in synaptic plasticity and memory. Recent efforts have been directed toward investigating the bidirectional dysregulation of AMPAR-mediated synaptic transmission in depression. Here, we summarize the published evidence relevant to the dysfunction of AMPAR in stress conditions and review the recent progress toward the understanding of the involvement of AMPAR trafficking in the pathophysiology of depression, focusing on the roles of AMPAR auxiliary subunits, key AMPAR-interacting proteins, and posttranslational regulation of AMPARs. We also discuss new prospects for the development of improved therapeutics for depression.

Relationships and Interactions between Ionotropic Glutamate Receptors and Nicotinic Receptors in the CNS

Although ionotropic glutamate receptors and nicotinic receptors for acetylcholine (ACh) have usually been studied separately, they are often co-localized and functionally inter-dependent. The objective of this review is to survey the evidence for interactions between the two receptor families and the mechanisms underlying them. These include the mutual regulation of subunit expression, which change the NMDA:AMPA response balance, and the existence of multi-functional receptor complexes which make it difficult to distinguish between individual receptor sites, especially in vivo. This is followed by analysis of the functional relationships between the receptors from work on transmitter release, cellular electrophysiology and aspects of behavior where these can contribute to understanding receptor interactions. It is clear that nicotinic receptors (nAChRs) on axonal terminals directly regulate the release of glutamate and other neurotransmitters, α7-nAChRs generally promoting release. Hence, α7-nAChR responses will be prevented not only by a nicotinic antagonist, but also by compounds blocking the indirectly activated glutamate receptors. This accounts for the apparent anticholinergic activity of some glutamate antagonists, including the endogenous antagonist kynurenic acid. The activation of presynaptic nAChRs is by the ambient levels of ACh released from pre-terminal synapses, varicosities and glial cells, acting as a 'volume neurotransmitter' on synaptic and extrasynaptic sites. In addition, ACh and glutamate are released as CNS co-transmitters, including 'cholinergic' synapses onto spinal Renshaw cells. It is concluded that ACh should be viewed primarily as a modulator of glutamatergic neurotransmission by regulating the release of glutamate presynaptically, and the location, subunit composition, subtype balance and sensitivity of glutamate receptors, and not primarily as a classical fast neurotransmitter. These conclusions and caveats should aid clarification of the sites of action of glutamate and nicotinic receptor ligands in the search for new centrally-acting drugs.

Deciphering the Forebrain Disorder in a Chicken Model of Cerebral Hernia

Cerebral hernia in crested chicken has been characterized as the protrusion of cerebral hemispheres into the unsealed skull for hundreds of years, since Charles Darwin. The development of deformed forebrain (telencephalon) of cerebral hernia remains largely unknown. Here, the unsealed frontal skull combined with misplaced sphenoid bone was observed and potentially associated with brain protuberance. The shifted pallidum, elongated hippocampus, expanded mesopallium and nidopallium, and reduced hyperpallium were observed in seven regions of the malformed telencephalon. The neurons were detected with nuclear pyknosis and decreased density. Astrocytes showed uneven distribution and disordered protuberances in hyperpallium and hippocampus. Transcriptome analyses of chicken telencephalon (cerebral hernia vs. control) revealed 547 differentially expressed genes (DEGs), mainly related to nervous system development, and immune system processes, including astrocyte marker gene GFAP, and neuron and astrocyte developmental gene S100A6. The upregulation of GFAP and S100A6 genes in abnormal telencephalon was correlated with reduced DNA methylation levels in the promoter regions. The morphological, cellular, and molecular variations in the shape, regional specification, and cellular states of malformed telencephalon potentially participate in brain plasticity and previously reported behavior changes. Chickens with cerebral hernia might be an interesting and valuable disease model to further explore the recognition, diagnosis, and therapy of cerebral hernia development of crested chickens and other species.

Evidence for cerebello-thalamo-cortical hyperconnectivity as a heritable trait for schizophrenia

Our recent study has demonstrated that increased connectivity in the cerebello-thalamo-cortical (CTC) circuitry is a state-independent neural trait that can potentially predict the onset of psychosis. One possible cause of such "trait" abnormality would be genetic predisposition. Here, we tested this hypothesis using multi-paradigm functional magnetic resonance imaging (fMRI) data from two independent twin cohorts. In a sample of 85 monozygotic (MZ) and 52 dizygotic (DZ) healthy twin pairs acquired from the Human Connectome Project, we showed that the connectivity pattern of the identified CTC circuitry was more similar in the MZ twins (r = 0.54) compared with that in the DZ twins (r = 0.22). The structural equation modeling analysis revealed a heritability estimate of 0.52 for the CTC connectivity, suggesting a moderately strong genetic effect. Moreover, using an independent schizophrenia cotwin sample (10 discordant MZ cotwins, 30 discordant DZ cotwins, and 32 control cotwins), we observed a significant linear relationship between genetic distance to schizophrenia and the connectivity strength in the CTC circuitry (i.e., schizophrenia MZ cotwins > schizophrenia DZ cotwins > control twins, P = 0.045). The present data provide converging evidence that increased connectivity in the CTC circuitry is likely to be a heritable trait that is associated with the genetic risk of schizophrenia.

Characterization of the Hippocampal Neuroimmune Response to Binge-Like Ethanol Consumption in the Drinking in the Dark Model

OBJECTIVES

Alcohol dependence leads to dysregulation of the neuroimmune system, but the effects of excessive alcohol consumption on key players of the neuroimmune response after episodic binge drinking in nondependence has not been readily assessed. These studies seek to determine how the neuroimmune system within the hippocampus responds to binge-like consumption prior to dependence or evidence of brain damage.

METHODS

C57BL/6J mice underwent the drinking in the dark (DID) paradigm to recapitulate binge consumption. Immunohistochemical techniques were employed to determine the effects of ethanol on cytokine and astrocyte responses within the hippocampus. Astrocyte activation was also assessed using qRT-PCR.

RESULTS

Our results indicated that binge-like ethanol consumption resulted in a 3.6-fold increase in the proinflammatory cytokine interleukin (IL)-1β immunoreactivity in various regions of the hippocampus. The opposite effect was seen in the anti-inflammatory cytokine IL-10. Binge-like consumption resulted in a 67% decrease in IL-10 immunoreactivity but had no effect on IL-4 or IL-6 compared with the water-drinking control group. Moreover, astrocyte activation occurred following ethanol exposure as GFAP immunoreactivity was increased over 120% in mice that experienced 3 cycles of ethanol binges. PCR analyses indicated that the mRNA increased by almost 4-fold after one cycle of DID, but this effect did not persist in abstinence.

CONCLUSIONS

Altogether, these findings suggest that binge-like ethanol drinking prior to dependence causes dysregulation to the neuroimmune system. This altered neuroimmune state may have an impact on behavior but could also result in a heightened neuroimmune response that is exacerbated from further ethanol exposure or other immune-modulating events.

A direct regulatory link between microRNA-137 and SHANK2: implications for neuropsychiatric disorders

BACKGROUND

Mutations in the SHANK genes, which encode postsynaptic scaffolding proteins, have been linked to a spectrum of neurodevelopmental disorders. The SHANK genes and the schizophrenia-associated microRNA-137 show convergence on several levels, as they are both expressed at the synapse, influence neuronal development, and have a strong link to neurodevelopmental and neuropsychiatric disorders like intellectual disability, autism, and schizophrenia. This compiled evidence raised the question if the SHANKs might be targets of miR-137.

METHODS

In silico analysis revealed a putative binding site for microRNA-137 (miR-137) in the SHANK2 3'UTR, while this was not the case for SHANK1 and SHANK3. Luciferase reporter assays were performed by overexpressing wild type and mutated SHANK2-3'UTR and miR-137 in human neuroblastoma cells and mouse primary hippocampal neurons. miR-137 was also overexpressed or inhibited in hippocampal neurons, and Shank2 expression was analyzed by quantitative real-time PCR and Western blot. Additionally, expression levels of experimentally validated miR-137 target genes were analyzed in the dorsolateral prefrontal cortex (DLPFC) of schizophrenia and control individuals using the RNA-Seq data from the CommonMind Consortium.

RESULTS

miR-137 directly targets the 3'UTR of SHANK2 in a site-specific manner. Overexpression of miR-137 in mouse primary hippocampal neurons significantly lowered endogenous Shank2 protein levels without detectable influence on mRNA levels. Conversely, miR-137 inhibition increased Shank2 protein expression, indicating that miR-137 regulates SHANK2 expression by repressing protein translation rather than inducing mRNA degradation. To find out if the miR-137 signaling network is altered in schizophrenia, we compared miR-137 precursor and miR-137 target gene expression in the DLPFC of schizophrenia and control individuals using the CommonMind Consortium RNA sequencing data. Differential expression of 23% (16/69) of known miR-137 target genes was detected in the DLPFC of schizophrenia individuals compared with controls. We propose that in further targets (e.g., SHANK2, as described in this paper) which are not regulated on RNA level, effects may only be detectable on protein level.

CONCLUSION

Our study provides evidence that a direct regulatory link exists between miR-137 and SHANK2 and supports the finding that miR-137 signaling might be altered in schizophrenia.

Adolescent THC exposure in female rats leads to cognitive deficits through a mechanism involving chromatin modifications in the prefrontal cortex

BACKGROUND

Increasing cannabis consumption among adolescents, studies that link its early use with mental illnesses, and the political debate on cannabis legalization together call for an urgent need to study molecular underpinnings of adolescent brain vulnerability. The emerging role of epigenetic mechanisms in psychiatric diseases led us to hypothesize that epigenetic alterations could play a role in causes and subsequent development of the depressive/psychotic-like phenotype induced by adolescent, but not adult, Δ9-tetrahydrocannabinol (THC) exposure in female rats.

METHODS

We performed a time-course analysis of histone modifications, chromatin remodelling enzymes and gene expression in the prefrontal cortex of female rats after adolescent and adult THC exposure. We also administered a specific epigenetic drug (chaetocin) with THC to investigate its impact on THC-induced behavioural alterations.

RESULTS

Adolescent THC exposure induced alterations of selective histone modifications (mainly H3K9me3), impacting the expression of genes closely associated with synaptic plasticity. Changes in both histone modifications and gene expression were more widespread and intense after adolescent treatment, suggesting specific adolescent susceptibility. Adolescent THC exposure significantly increased Suv39H1 levels, which could account for the enhanced H3K9me3. Pharmacological blockade of H3K9me3 during adolescent THC treatment prevented THC-induced cognitive deficits, suggesting the relevant role played by H3K9me3 in THC-induced effects.

LIMITATIONS

Only female rats were investigated, and the expression studies were limited to a specific subset of genes.

CONCLUSION

Through a mechanism involving SUV39H1, THC modifies histone modifications and, thereby, expression of plasticity genes. This pathway appears to be relevant for the development of cognitive deficits.

Genetic variation of GRIA3 gene is associated with vulnerability to methamphetamine dependence and its associated psychosis

Methamphetamine (METH) is an addictive psychostimulant drug commonly leading to schizophrenia-like psychotic symptoms. Disturbances in glutamatergic neurotransmission have been proposed as neurobiological mechanisms and the α-amino-3 hydroxy-5 methyl-4 isoxazole propionic acid (AMPA) glutamate receptor has been implicated in these processes. Moreover, genetic variants in GRIAs, genes encoding AMPA receptor subunits, have been observed in association with both drug dependence and psychosis. We hypothesized that variation of GRIA genes may be associated with METH dependence and METH-induced psychosis. Genotyping of GRIA1 rs1428920, GRIA2 rs3813296, GRIA3 rs3761554, rs502434 and rs989638 was performed in 102 male Thai controls and 100 METH-dependent subjects (53 with METH-dependent psychosis). We observed no evidence of association with METH dependence and METH-dependent psychosis in the GRIA1 and GRIA2 polymorphisms, nor with single polymorphisms rs3761554 and rs989638 in GRIA3. An association of GRIA3 rs502434 was identified with both METH dependence and METH-dependent psychosis, although this did not withstand correction for multiple testing. Combining the analysis of this site with the previously-demonstrated association with BDNF rs6265 resulted in a highly significant effect. These preliminary findings indicate that genetic variability in GRIA3 may interact with a functional BDNF polymorphism to provide a strong risk factor for the development of METH dependence in the Thai population.

Reciprocal Alterations in Regulator of G Protein Signaling 4 and microRNA16 in Schizophrenia

N-methyl-d-aspartate receptor (NMDAR) hypofunction in the dorsolateral prefrontal cortex (DLPFC) has been implicated in the pathology of schizophrenia. NMDAR activity is negatively regulated by some G protein-coupled receptors (GPCRs). Signaling through these GPCRs is reduced by Regulator of G protein Signaling 4 (RGS4). Thus, lower levels of RGS4 would enhance GPCR-mediated reductions in NMDAR activity and could contribute to NMDAR hypofunction in schizophrenia. In this study, we quantified RGS4 mRNA and protein levels at several levels of resolution in the DLPFC from subjects with schizophrenia and matched healthy comparison subjects. To investigate molecular mechanisms that could contribute to altered RGS4 levels, we quantified levels of small noncoding RNAs, known as microRNAs (miRs), which regulate RGS4 mRNA integrity after transcription. RGS4 mRNA and protein levels were significantly lower in schizophrenia subjects and were positively correlated across all subjects. The RGS4 mRNA deficit was present in pyramidal neurons of DLPFC layers 3 and 5 of the schizophrenia subjects. In contrast, levels of miR16 were significantly higher in the DLPFC of schizophrenia subjects, and higher miR16 levels predicted lower RGS4 mRNA levels. These findings provide convergent evidence of lower RGS4 mRNA and protein levels in schizophrenia that may result from increased expression of miR16. Given the role of RGS4 in regulating GPCRs, and consequently the strength of NMDAR signaling, these findings could contribute to the molecular substrate for NMDAR hypofunction in DLPFC pyramidal cells in schizophrenia.

Sex differences in glutamate receptor gene expression in major depression and suicide

Accumulating data indicate that the glutamate system is disrupted in major depressive disorder (MDD), and recent clinical research suggests that ketamine, an antagonist of the N-methyl-d-aspartate (NMDA) glutamate receptor (GluR), has rapid antidepressant efficacy. Here we report findings from gene expression studies of a large cohort of postmortem subjects, including subjects with MDD and controls. Our data reveal higher expression levels of the majority of glutamatergic genes tested in the dorsolateral prefrontal cortex (DLPFC) in MDD (F21,59=2.32, P=0.006). Posthoc data indicate that these gene expression differences occurred mostly in the female subjects. Higher expression levels of GRIN1, GRIN2A-D, GRIA2-4, GRIK1-2, GRM1, GRM4, GRM5 and GRM7 were detected in the female patients with MDD. In contrast, GRM5 expression was lower in male MDD patients relative to male controls. When MDD suicides were compared with MDD non-suicides, GRIN2B, GRIK3 and GRM2 were expressed at higher levels in the suicides. Higher expression levels were detected for several additional genes, but these were not statistically significant after correction for multiple comparisons. In summary, our analyses indicate a generalized disruption of the regulation of the GluRs in the DLPFC of females with MDD, with more specific GluR alterations in the suicides and in the male groups. These data reveal further evidence that, in addition to the NMDA receptor, the AMPA, kainate and the metabotropic GluRs may be targets for the development of rapidly acting antidepressant drugs.

Association analysis of the GRM8 gene with schizophrenia in the Uygur Chinese population

GRM8 is a schizophrenia candidate gene that is also thought to be involved in the glutamate pathway, which is very important in the pathogenesis of schizophrenia. In this study, we aim to investigate the association between GRM8 and schizophrenia in the Uygur Chinese population. Rs2237748 and rs2299472, located in the GRM8 gene, were selected for genotyping in a set of Uygur Chinese case-control samples, which included 723 cases and 561 controls, using TaqMan assays and capillary sequencing. The statistical analysis was carried out using the online software program SHEsis, and a meta-analysis was carried out to identify other relevant studies using Review Manager 5. We found that the rs2299472 genotype was significantly associated with schizophrenia (P = 0.015, P = 0.030, after Bonferroni correction). The frequency of the CC genotype was higher in the schizophrenic patients (P = 0.008), and the frequency of the AC genotype was lower (P = 0.008). Furthermore, the meta-analysis incorporating the previous and current studies also showed that rs2299472 is associated with schizophrenia. This study indicates that the GRM8 gene may play an important role in the pathogenesis of schizophrenia.

The glutamate hypothesis of schizophrenia: evidence from human brain tissue studies

A number of studies have indicated that antagonists of the N-methyl-d-aspartate subtypes of glutamate receptors can cause schizophrenia-like symptoms in healthy individuals and exacerbate symptoms in individuals with schizophrenia. These findings have led to the glutamate hypothesis of schizophrenia. Here we review the evidence for this hypothesis in postmortem studies of brain tissue from individuals affected by schizophrenia, summarizing studies of glutamate neuron morphology, of expression of glutamate receptors and transporters, and of the synthesizing and metabolizing enzymes for glutamate and its co-agonists. We found consistent evidence of morphological alterations of dendrites of glutamatergic neurons in the cerebral cortex of subjects with schizophrenia and of reduced levels of the axon bouton marker synaptophysin. There were no consistent alterations of mRNA expression of glutamate receptors, although there has been limited study of the corresponding proteins. Studies of the glutamate metabolic pathway have been limited, although there is some evidence that excitatory amino acid transporter-2, glutamine synthetase, and glutaminase have altered expression in schizophrenia. Future studies would benefit from additional direct examination of glutamatergic proteins. Further advances, such as selective testing of synaptic microdomains, cortical layers, and neuronal subtypes, may also be required to elucidate the nature of glutamate signaling impairments in schizophrenia.

The role of NMDA receptors in the pathophysiology and treatment of mood disorders

Mood disorders such as major depressive disorder and bipolar disorder are chronic and recurrent illnesses that cause significant disability and affect approximately 350 million people worldwide. Currently available biogenic amine treatments provide relief for many and yet fail to ameliorate symptoms for others, highlighting the need to diversify the search for new therapeutic strategies. Here we present recent evidence implicating the role of N-methyl-D-aspartate receptor (NMDAR) signaling in the pathophysiology of mood disorders. The possible role of NMDARs in mood disorders has been supported by evidence demonstrating that: (i) both BPD and MDD are characterized by altered levels of central excitatory neurotransmitters; (ii) NMDAR expression, distribution, and function are atypical in patients with mood disorders; (iii) NMDAR modulators show positive therapeutic effects in BPD and MDD patients; and (iv) conventional antidepressants/mood stabilizers can modulate NMDAR function. Taken together, this evidence suggests the NMDAR system holds considerable promise as a therapeutic target for developing next generation drugs that may provide more rapid onset relief of symptoms. Identifying the subcircuits involved in mood and elucidating the role of NMDARs subtypes in specific brain circuits would constitute an important step toward the development of more effective therapies with fewer side effects.

The glutamatergic aspects of schizophrenia molecular pathophysiology: role of the postsynaptic density, and implications for treatment

Schizophrenia is one of the most debilitating psychiatric diseases with a lifetime prevalence of approximately 1%. Although the specific molecular underpinnings of schizophrenia are still unknown, evidence has long linked its pathophysiology to postsynaptic abnormalities.

The postsynaptic density (PSD) is among the molecular structures suggested to be potentially involved in schizophrenia. More specifically, the PSD is an electron-dense thickening of glutamatergic synapses, including ionotropic and metabotropic glutamate receptors, cytoskeletal and scaffolding proteins, and adhesion and signaling molecules. Being implicated in the postsynaptic signaling of multiple neurotransmitter systems, mostly dopamine and glutamate, the PSD constitutes an ideal candidate for studying dopamine-glutamate disturbances in schizophrenia. Recent evidence suggests that some PSD proteins, such as PSD-95, Shank, and Homer are implicated in severe behavioral disorders, including schizophrenia. These findings, further corroborated by genetic and animal studies of schizophrenia, offer new insights for the development of pharmacological strategies able to overcome the limitations in terms of efficacy and side effects of current schizophrenia treatment. Indeed, PSD proteins are now being considered as potential molecular targets against this devastating illness.

The current paper reviews the most recent hypotheses on the molecular mechanisms underlying schizophrenia pathophysiology. First, we review glutamatergic dysfunctions in schizophrenia and we provide an update on postsynaptic molecules involvement in schizophrenia pathophysiology by addressing both human and animal studies. Finally, the possibility that PSD proteins may represent potential targets for new molecular interventions in psychosis will be discussed.

Neuropathological and neuromorphometric abnormalities in bipolar disorder: view from the medial prefrontal cortical network

The question of whether BD is primarily a developmental disorder or a progressive, neurodegenerative disorder remains unresolved. Here, we review the morphometric postmortem and neuroimaging literature relevant to the neuropathology of bipolar disorder (BD). We focus on the medial prefrontal cortex (mPFC) network, a key system in the regulation of emotional, behavioral, endocrine, and innate immunological responses to stress. We draw four main conclusions: the mPFC is characterized by (1) a decrease in volume, (2) reductions in neuronal size, and/or changes in neuronal density, (3) reductions in glial cell density, and (4) changes in gene expression. These data suggest the presence of dendritic atrophy of neurons and the loss of oligodendroglial cells in BD, although some data additionally suggest a reduction in the cell counts of specific subpopulations of GABAergic interneurons. Based on the weight of the postmortem and neuroimaging literature discussed herein, we favor a complex hypothesis that BD primarily constitutes a developmental disorder, but that additional, progressive, histopathological processes also are associated with recurrent or chronic illness. Conceivably BD may be best conceptualized as a progressive neurodevelopmental disorder.

Structural basis of PI(4,5)P2-dependent regulation of GluA1 by phosphatidylinositol-5-phosphate 4-kinase, type II, alpha (PIP5K2A)

Ionotropic glutamate receptors are the most important excitatory receptors in the central nervous system, and their impairment can lead to multiple neuronal diseases. Here, we show that glutamate-induced currents in oocytes expressing GluA1 are increased by coexpression of the schizophrenia-associated phosphoinositide kinase PIP5K2A. This effect was due to enhanced membrane abundance and was blunted by a point mutation (N251S) in PIP5K2A. An increase in GluA1 currents was also observed upon acute injection of PI(4,5)P₂, the main product of PIP5K2A. By expression of wild-type and mutant PIP5K2A in human embryonic kidney cells, we were able to provide evidence of impaired kinase activity of the mutant PIP5K2A. We defined the region K813–K823 of GluA1 as critical for the PI(4,5)P₂ effect by performing an alanine scan that suggested PI(4,5)P₂ binding to this area. A PIP strip assay revealed PI(4,5)P₂ binding to the C-terminal GluA1 peptide. The present observations disclose a novel mechanism in the regulation of GluA1.

Group II metabotropic glutamate receptor agonist LY379268 regulates AMPA receptor trafficking in prefrontal cortical neurons

Group II metabotropic glutamate receptor (mGluR) agonists have emerged as potential treatment drugs for schizophrenia and other neurological disorders, whereas the mechanisms involved remain elusive. Here we examined the effects of LY379268 (LY37) on the expression and trafficking of the α-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptor subunits GluA1 and GluA2 in prefrontal neurons. We show that LY37 significantly increased the surface and total expression of both GluA1 and GluA2 subunits in cultured prefrontal neurons and in vivo. This effect was mimicked by the selective mGluR2 agonist LY395756 and was blocked by mGluR2/3 antagonist LY341495. Moreover, we found that both GluA1 and GluA2 subunits were colocalized with PSD95 but not synapsin I, suggesting a postsynaptic localization. Consistently, treatment with LY37 significantly increased the amplitude, but not frequency, of miniature excitatory postsynaptic currents. Further, actinomycin-D blocked LY37's effects, suggesting a transcriptional regulation. In addition, application of glycogen synthase kinase-3beta (GSK-3β) inhibitor completely blocked LY37's effect on GluA2 surface expression, whereas GSK-3β inhibitor itself induced decreases in the surface and total protein levels of GluA1, but not GluA2 subunits. This suggests that GSK-3β differentially mediates GluA1 and GluA2 trafficking. Further, LY37 significantly increased the phosphorylation, but not total protein, of extracellular signal-regulated kinase 1/2 (ERK1/2). Neither ERK1/2 inhibitor PD98059 alone nor PD98059 combined with LY37 treatment induced changes in GluA1 or GluA2 surface expression or total protein levels. Our data thus suggest that mGluR2/3 agonist regulates postsynaptic AMPA receptors by affecting the synaptic trafficking of both GluA1 and GluA2 subunits and that the regulation is likely through ERK1/2 signaling in GluA1 and/or both ERK1/2 and GSK-3β signaling pathways in the GluA2 subunit.

Genetic variants of GRIA1 are associated with susceptibility to schizophrenia in Korean population

The α-amino-3-hydroxy-5-methyl-4-propionic acid (AMPA) receptors are important for glutamate synaptic transmission in the central nervous system. Glutamate receptor, ionotropic, AMPA receptor 1 gene (GRIA1) belongs to the family of AMPA receptors. There is increasing evidence that AMPA receptors dysfunction may be related to an increased susceptibility to schizophrenia. The aim of this study was therefore to investigate whether genetic polymorphisms of GRIA1 are associated with schizophrenia and their clinical symptoms (hallucinations and delusions) in Korean population. Five single nucleotide polymorphisms (rs1428920, rs1552834, rs1422889, rs10035143, and rs2926835) of the GRIA1 were genotyped in 218 schizophrenia patients and 380 healthy controls, using a direct sequencing. All patients were evaluated by the Operational Criteria Checklist for Psychotic Illness. The genotype and allelic frequencies of rs1428920 and rs2926835 showed significant association between schizophrenia and controls (rs1428920, permutation p = 0.008, 0.008; rs2926835, permutation p = 0.038, 0.041, respectively). A significantly increased risk of schizophrenia was associated with the A allele of rs1428920 and rs2926835 of GRIA1. Furthermore, we found that rs1428920 was weakly associated with hallucinations of schizophrenia, but this significance disappeared after multiple testing (permutation p = 0.119). These results suggest that GRIA1 polymorphism may have influence upon the risk of developing schizophrenia.

Case-control association study of GRIA1, GRIA2 and GRIA4 polymorphisms in bipolar disorder

OBJECTIVE

The present study aimed to investigate whether some single nucleotide polymorphisms (SNPs) within GRIA1, GRIA2 and GRIA4 could be associated with bipolar disorder (BD) and they could predict clinical outcomes in in-patients with BD treated with mood stabilizers.

METHODS

One hundred and thirty-two (132) patients with BD and 170 healthy controls were genotyped for 17 SNPs within GRIA1, GRIA2 and GRIA4. Baseline and final clinical measures including Young Mania Rating Scale for patients with BD were recorded. Statistical significance was set at the 0.005 level in order to reduce the likelihood of false positive results.

RESULTS

We failed to show an evidence for a possible association of GRIA1, GRIA2 and GRIA4 with BD patients, in terms of influences on diagnosis and treatment outcomes, although this was the first study to explore the influence of such genes for bipolar disorder.

CONCLUSION

Our results suggest that 17 SNPs within GRIA1, GRIA2 and GRIA4 may not be associated with the development and treatment outcomes in BD. However, taking into account that the several limitations of our study including the moderately small sample size of our study, our findings should be considered with caution and further research is needed to draw more definitive conclusions.

Genome-wide association study of comorbid depressive syndrome and alcohol dependence

OBJECTIVE

Depression and alcohol dependence (AD) are common psychiatric disorders that often co-occur. Both disorders are genetically influenced, with heritability estimates in the range of 35-60%. In addition, evidence from twin studies suggests that AD and depression are genetically correlated. Herein, we report results from a genome-wide association study of a comorbid phenotype, in which cases meet the Diagnostic and Statistical Manual of Mental Disorders-IV symptom threshold for major depressive symptomatology and the Diagnostic and Statistical Manual of Mental Disorders-IV criteria for AD.

METHODS

Samples (N=467 cases and N=407 controls) were of European-American descent and were genotyped using the Illumina Human 1M BeadChip array.

RESULTS

Although no single-nucleotide polymorphism (SNP) meets genome-wide significance criteria, we identified 10 markers with P values less than 1 × 10(-5), seven of which are located in known genes, which have not been previously implicated in either disorder. Genes harboring SNPs yielding P values less than 1 × 10(-5) are functionally enriched for a number of gene ontology categories, notably several related to glutamatergic function. Investigation of expression localization using online resources suggests that these genes are expressed across a variety of tissues, including behaviorally relevant brain regions. Genes that have been previously associated with depression, AD, or other addiction-related phenotypes - such as CDH13, CSMD2, GRID1, and HTR1B - were implicated by nominally significant SNPs. Finally, the degree of overlap of significant SNPs between a comorbid phenotype and an AD-only phenotype is modest.

CONCLUSION

These results underscore the complex genomic influences on psychiatric phenotypes and suggest that a comorbid phenotype is partially influenced by genetic variants that do not affect AD alone.

Expression profiling in neuropsychiatric disorders: emphasis on glutamate receptors in bipolar disorder

Functional genomics and proteomics approaches are being employed to evaluate gene and encoded protein expression changes with the tacit goal to find novel targets for drug discovery. Genome-wide association studies (GWAS) have attempted to identify valid candidate genes through single nucleotide polymorphism (SNP) analysis. Furthermore, microarray analysis of gene expression in brain regions and discrete cell populations has enabled the simultaneous quantitative assessment of relevant genes. The ability to associate gene expression changes with neuropsychiatric disorders, including bipolar disorder (BP), and their response to therapeutic drugs provides a novel means for pharmacotherapeutic interventions. This review summarizes gene and pathway targets that have been identified in GWAS studies and expression profiling of human postmortem brain in BP, with an emphasis on glutamate receptors (GluRs). Although functional genomic assessment of BP is in its infancy, results to date point towards a dysregulation of GluRs that bear some similarity to schizophrenia (SZ), although the pattern is complex, and likely to be more complementary than overlapping. The importance of single population expression profiling of specific neurons and intrinsic circuits is emphasized, as this approach provides informative gene expression profile data that may be underappreciated in regional studies with admixed neuronal and non-neuronal cell types.

Altered levels of glutamatergic receptors and Na+/K+ ATPase-α1 in the prefrontal cortex of subjects with schizophrenia

Evidence has accumulated over the past years that dysregulation of glutamatergic neurotransmission maybe implicated in the pathophysiology of schizophrenia. Glutamate acts on two major classes of receptors: ionotropic receptors, which are ligand-gated ion channels, and metabotropic receptors (mGluRs), coupled to heterotrimeric G-proteins. Although several pharmacological evidences point to abnormal glutamatergic transmission in schizophrenia, changes in the expression of glutamatergic receptors in the prefrontal cortex of patients with schizophrenia remains equivocal. In the present work, we have investigated glutamatergic neurotransmission in schizophrenia by assessing the expression in Brodmann Area 10 of mGluR5, the AMPA receptor subunits GluR1 and GluR2, and Na(+)/K(+) ATPase-α1, a potential modulator of glutamate uptake in the brain. Semiquantitative analysis of the expression of these proteins from postmortem brains revealed a particularly prominent reduction of GluR1 and GluR2 expression in patients with schizophrenia vs the control group. Conversely, we observed an up-regulation in the levels of Na(+)/K(+) ATPase-α1 expression. Finally, no change in the protein levels of mGluR5 was observed in schizophrenia. Our findings support and expand the hypothesis of glutamatergic dysfunction in prefrontal cortex in the pathophysiology of schizophrenia.

The viral theory of schizophrenia revisited: abnormal placental gene expression and structural changes with lack of evidence for H1N1 viral presence in placentae of infected mice or brains of exposed offspring

Researchers have long noted an excess of patients with schizophrenia were born during the months of January and March. This winter birth effect has been hypothesized to result either from various causes such as vitamin D deficiency (McGrath, 1999; McGrath et al., 2010), or from maternal infection during pregnancy. Infection with a number of viruses during pregnancy including influenza, and rubella are known to increase the risk of schizophrenia in the offspring (Brown, 2006). Animal models using influenza virus or Poly I:C, a viral mimic, have been able to replicate many of the brain morphological, genetic, and behavioral deficits of schizophrenia (Meyer et al., 2006, 2008a, 2009; Bitanihirwe et al., 2010; Meyer and Feldon, 2010; Short et al., 2010). Using a murine model of prenatal viral infection, our laboratory has shown that viral infection on embryonic days 9, 16, and 18 leads to abnormal expression of brain genes and brain structural abnormalities in the exposed offspring (Fatemi et al., 2005, 2008a,b, 2009a,b). The purpose of the current study was to examine gene expression and morphological changes in the placenta, hippocampus, and prefrontal cortex as a result of viral infection on embryonic day 7 of pregnancy. Pregnant mice were either infected with influenza virus [A/WSN/33 strain (H1N1)] or sham-infected with vehicle solution. At E16, placentas were harvested and prepared for either microarray analysis or for light microscopy. We observed significant, upregulation of 77 genes and significant downregulation of 93 genes in placentas. In brains of exposed offspring following E7 infection, there were changes in gene expression in prefrontal cortex (6 upregulated and 24 downregulated at P0; 5 upregulated and 14 downregulated at P56) and hippocampus (4 upregulated and 6 downregulated at P0; 6 upregulated and 13 downregulated at P56). QRT-PCR verified the direction and magnitude of change for a number of genes associated with hypoxia, inflammation, schizophrenia, and autism. Placentas from infected mice showed a number of morphological abnormalities including presence of thrombi and increased presence of immune cells. Additionally, we searched for presence of H1N1 viral-specific genes for M1/M2, NA, and NS1 in placentas of infected mice and brains of exposed offspring and found none. Our results demonstrate that prenatal viral infection disrupts structure and gene expression of the placenta, hippocampus, and prefrontal cortex potentially explaining deleterious effects in the exposed offspring without evidence for presence of viral RNAs in the target tissues.

Analyzing schizophrenia by DNA microarrays

To understand the pathological processes of schizophrenia, we must embrace the analysis of the diseased human brain: we will never be able to recapitulate the pathology of uniquely human disorders in an animal model. Based on the outcome of the transcriptome profiling experiments performed to date, it appears that schizophrenia is associated with a global gene expression disturbance across many cortical regions. In addition, transcriptome changes are present in multiple cell types, including specific subclasses of principal neurons, interneurons, and oligodendrocytes. Furthermore, transcripts related to synaptic transmission, energy metabolism, and inhibitory neurotransmission are routinely found underexpressed in the postmortem brain tissue of subjects with schizophrenia. To put these transcriptome data in biological context, we must make our data publicly available and report our findings in a proper, expanded Minimum Information About a Microarray Experiment format. Cell-type specific expression profiling and sequencing-based transcript assessments should be expanded, with particular attention to understanding splice-variant changes in various mental disorders. Deciphering the pathophysiology of mental disorders depends on integrating data from across many research fields and techniques. Leads from postmortem transcriptome profiling will be essential to generate model animals, perform tissue culture experiments, and develop or evaluate novel drugs to treat this devastating disorder.

The cerebral cortex overlying periventricular leukomalacia: analysis of pyramidal neurons

The role of the cerebral cortex in the cognitive deficits in preterm survivors is poorly understood. Periventricular leukomalacia (PVL), the key feature of encephalopathy of prematurity, is characterized by periventricular necrotic foci and diffuse gliosis in the surrounding cerebral white matter. Here, we tested the hypothesis that reductions in the density of layer I neurons and/or pyramidal neurons in layers III and/or V are associated with PVL, indicating cortical pathology potentially associated with cognitive deficits in long-term survivors. In controls (23 gestational weeks to 18 postnatal months) (n = 15), a lack of significant differences in pyramidal density among incipient Brodmann areas suggested that cytoarchitectonic differences across functional areas are not fully mature in the fetal and infant periods. There was a marked reduction (38%) in the density of layer V neurons in all areas sampled in the PVL cases (n = 17) compared to controls (n = 12) adjusted for postconceptional age at or greater than 30 weeks, when the six-layer cortex is visually distinct (P < 0.024). This may reflect a dying-back loss of somata complicating transection of layer V axons projecting through the necrosis in the underlying white matter. This study underscores the potential role of secondary cortical injury in the encephalopathy of prematurity.

Genetic association studies of glutamate, GABA and related genes in schizophrenia and bipolar disorder: a decade of advance

Schizophrenia (SZ) and bipolar disorder (BD) are debilitating neurobehavioural disorders likely influenced by genetic and non-genetic factors and which can be seen as complex disorders of synaptic neurotransmission. The glutamatergic and GABAergic neurotransmission systems have been implicated in both diseases and we have reviewed extensive literature over a decade for evidence to support the association of glutamate and GABA genes in SZ and BD. Candidate-gene based population and family association studies have implicated some ionotrophic glutamate receptor genes (GRIN1, GRIN2A, GRIN2B and GRIK3), metabotropic glutamate receptor genes (such as GRM3), the G72/G30 locus and GABAergic genes (e.g. GAD1 and GABRB2) in both illnesses to varying degrees, but further replication studies are needed to validate these results. There is at present no consensus on specific single nucleotide polymorphisms or haplotypes associated with the particular candidate gene loci in these illnesses. The genetic architecture of glutamate systems in bipolar disorder need to be better studied in view of recent data suggesting an overlap in the genetic aetiology of SZ and BD. There is a pressing need to integrate research platforms in genomics, epistatic models, proteomics, metabolomics, neuroimaging technology and translational studies in order to allow a more integrated understanding of glutamate and GABAergic signalling processes and aberrations in SZ and BD as well as their relationships with clinical presentations and treatment progress over time.

Neuroimaging and neuropathological findings in bipolar disorder

Bipolar disorder (BPD) is increasingly recognized as a neuropathological disorder characterized by reductions in grey matter (GM) volume, as measured by magnetic resonance imaging (MRI) and neuronal and postmortem glial cell changes. Here, we use an anatomical framework to discuss the neurobiology of BPD, focusing on individual components of the "visceromotor network" that regulates bodily homeostasis along with neurophysiological and neuroendocrine responses to stress. MRI-defined reductions in GM volume, combined with neuronal changes, are observed in the perigenual anterior cingulate cortex (ACC) of individuals with BPD, while postmortem glial cell loss is also a characteristic of Brodmann's Area 9. Both postmortem neuronal loss and reduced GM volume have been reported in the amygdala and hippocampus. These structural changes to components of the visceromotor network are associated with increased regional cerebral blood flow (rCBF) or blood oxygenated level-dependent (BOLD) activity in response to affective or rewarding stimuli, raising the possibility that the BPD-associated structural changes are secondary to a glutamate-driven excitotoxic process.

Expression profiles of schizophrenia susceptibility genes during human prefrontal cortical development

BACKGROUND

Disruption in normal development of the human prefrontal cortex (PFC) may lead to cognitive dysfunction that manifests in individuals with schizophrenia. We sought to identify genes associated with age that are implicated in schizophrenia.

METHODS

We generated genome-wide expression profiles for the PFCs of humans ranging in age from 1 month to 49 years using the Affymetrix HG-U133 plus 2.0 microarrays (54 675 transcripts). Based on the criteria of significance (false discovery rate [FDR]-adjusted q < 0.001 and r(2) > 0.6), we identified the genes associated with age in the PFC. We then performed functional annotation analyses of age-associated genes using the Gene Ontology and the Genetic Association Database (GAD).

RESULTS

We found robust age-dependent changes in gene expression in the PFCs of humans (2281 transcripts). The GAD analysis revealed that schizophrenia was an over-represented disease class, with 42 susceptibility genes included (p < 0.001, fold enrichment = 1.66, FDR = 1.5%). Among the 42 genes, glutamate receptor genes (GRIA1, GRIK1, GRIK2, GRIN2D, GRIP1, GRM5, GRM7 and SLC1A6) were consistently downregulated across age. We confirmed microarray gene expression changes by the quantitative polymerase chain reaction experiment.

LIMITATIONS

Although numerous genes undergo robust changes in expression during the PFC development, some of the changes may be confounded by known and unknown factors that are intrinsic to the postmortem brain studies.

CONCLUSION

Multiple schizophrenia susceptibility genes undergo age-dependent expression changes in the human PFC, and any disruption in those genes during the critical period of development may predispose the individuals to schizophrenia.

GLT-1 upregulation impairs prepulse inhibition of the startle reflex in adult rats

We tested the hypothesis that glutamate transporter GLT-1 (also known as EAAT2) plays a role in the regulation of prepulse inhibition (PPI) of the acoustic startle reflex, a simple form of information processing which is reduced in schizophrenia. To do this, we studied PPI in rats treated with ceftriaxone (200 mg/kg/day for 8 days), an antibiotic that selectively enhances GLT-1 expression and activity. We showed that ceftriaxone-induced GLT-1 upregulation is associated with impaired PPI of the startle, that this effect is reversed by dihydrokainate, a GLT-1 antagonist, that GLT-1 expression correlates negatively with PPI, and that PPI normalizes when GLT-1a levels return to baseline. Our data indicate that GLT-1 regulates PPI of the startle reflex.

NMDA receptor subunit expression in GABAergic interneurons in the prefrontal cortex: application of laser microdissection technique

The selective involvement of a subset of neurons in many psychiatric disorders, such as gamma-aminobutyric acid (GABA)-ergic interneurons in schizophrenia, creates a significant need for in-depth analysis of these cells. Here we introduce a combination of techniques to examine the relative gene expression of N-methyl-d-aspartic acid (NMDA) receptor subtypes in GABAergic interneurons from the rat prefrontal cortex. Neurons were identified by immunostaining, isolated by laser microdissection and RNA was prepared for reverse transcription polymerase chain reaction (RT-PCR) and real-time PCR. These experimental procedures have been described individually; however, we found that this combination of techniques is powerful for the analysis of gene expression in individual identified neurons. This approach provides the means to analyze relevant molecular mechanisms that are involved in the neuropathological process of a devastating brain disorder.

Glutamate Neurotransmission in Psychotic Disorders and Substance Abuse

Psychotropic substance abuse and addiction are very prevalent among individuals with major psychiatric disorders world wide. However, this significant association is poorly explained. The dopaminergic circuits have been implemented in addiction as well as in schizophrenia. Recently the important role of glutamatergic neurotransmission has gained attention and current theoretical models of psychosis and substance abuse support the role of interactions between glutamate and other neurotransmitters in the patho-physiology of both disorders. However, the identification of the underlying genetic risk factors remains challenging and not a single genomic variant has been identified with certainty, possibly due to important limitations of the methods used. Clinical trials with glutamatergic neurotransmission modulators, even though still controversial, support the role of glutamate in psychosis and justify further research.

The cerebral microvasculature in schizophrenia: a laser capture microdissection study

Background

Previous studies of brain and peripheral tissues in schizophrenia patients have indicated impaired energy supply to the brain. A number of studies have also demonstrated dysfunction of the microvasculature in schizophrenia patients. Together these findings are consistent with a hypothesis of blood-brain barrier dysfunction in schizophrenia. In this study, we have investigated the cerebral vascular endothelium of schizophrenia patients at the level of transcriptomics.

Methodology/Principal Findings

We used laser capture microdissection to isolate both microvascular endothelial cells and neurons from post mortem brain tissue from schizophrenia patients and healthy controls. RNA was isolated from these cell populations, amplified, and analysed using two independent microarray platforms, Affymetrix HG133plus2.0 GeneChips and CodeLink Whole Human Genome arrays. In the first instance, we used the dataset to compare the neuronal and endothelial data, in order to demonstrate that the predicted differences between cell types could be detected using this methodology. We then compared neuronal and endothelial data separately between schizophrenic subjects and controls. Analysis of the endothelial samples showed differences in gene expression between schizophrenics and controls which were reproducible in a second microarray platform. Functional profiling revealed that these changes were primarily found in genes relating to inflammatory processes.

Conclusions/Significance

This study provides preliminary evidence of molecular alterations of the cerebral microvasculature in schizophrenia patients, suggestive of a hypo-inflammatory state in this tissue type. Further investigation of the blood-brain barrier in schizophrenia is warranted.