Expression of excitatory amino acid transporter transcripts in the thalamus of subjects with schizophrenia

The Thalamocortical Mechanism Underlying the Generation and Regulation of the Auditory Steady-State Responses in Awake Mice

The auditory steady-state response (ASSR) is a cortical oscillation induced by trains of 40 Hz acoustic stimuli. While the ASSR has been widely used in clinic measurement, the underlying neural mechanism remains poorly understood. In this study, we investigated the contribution of different stages of auditory thalamocortical pathway-medial geniculate body (MGB), thalamic reticular nucleus (TRN), and auditory cortex (AC)-to the generation and regulation of 40 Hz ASSR in C57BL/6 mice of both sexes. We found that the neural response synchronizing to 40 Hz sound stimuli was most prominent in the GABAergic neurons in the granular layer of AC and the ventral division of MGB (MGBv), which were regulated by optogenetic manipulation of TRN neurons. Behavioral experiments confirmed that disrupting TRN activity has a detrimental effect on the ability of mice to discriminate 40 Hz sounds. These findings revealed a thalamocortical mechanism helpful to interpret the results of clinical ASSR examinations.Significance Statement Our study contributes to clarifying the thalamocortical mechanisms underlying the generation and regulation of the auditory steady-state response (ASSR), which is commonly used in both clinical and neuroscience research to assess the integrity of auditory function. Combining a series of electrophysiological and optogenetic experiments, we demonstrate that the generation of cortical ASSR is dependent on the lemniscal thalamocortical projections originating from the ventral division of medial geniculate body to the GABAergic interneurons in the granule layer of the auditory cortex. Furthermore, the thalamocortical process for ASSR is strictly regulated by the activity of thalamic reticular nucleus (TRN) neurons. Behavioral experiments confirmed that dysfunction of TRN would cause a disruption of mice's behavioral performance in the auditory discrimination task.

The "molecular soldiers" of the CNS: Astrocytes, a comprehensive review on their roles and molecular signatures

For a long time, neurons held the position of central players in the nervous system. Since there are far more astrocytes than neurons in the brain, it makes us wonder if these cells just take up space and support the neurons or if they are actively participating in central nervous system (CNS) homeostasis. Now, astrocytes' contribution to CNS physiology is appreciated as they are known to regulate ion and neurotransmitter levels, synapse formation and elimination, blood-brain barrier integrity, immune function, cerebral blood flow, and many more. In many neurological and psychiatric disorders, astrocyte functions are altered. Advancements in microscopic and transcriptomic tools revealed populations of astrocytes with varied morphology, electrophysiological properties, and transcriptomic profiles. Neuron-circuit-specific functions and neuron-specific interactions of astroglial subpopulations are found, which suggests that diversity is essential in carrying out diverse region-specific CNS functions. Investigations on heterogeneous astrocyte populations are revealing new astrocyte functions and their role in pathological conditions, opening a new therapeutic avenue for targeting neurological conditions. The true extent of astrocytic heterogeneity and its functional implications are yet to be fully explored. This review summarizes essential astrocytic functions and their relevance in pathological conditions and discusses astrocytic diversity in relation to morphology, function, and gene expression throughout the CNS.

NREM sleep oscillations and their relations with sleep-dependent memory consolidation in early course psychosis and first-degree relatives

Sleep spindles are believed to mediate sleep-dependent memory consolidation, particularly when coupled to neocortical slow oscillations. Schizophrenia is characterized by a deficit in sleep spindles that correlates with reduced overnight memory consolidation. Here, we examined sleep spindle activity, slow oscillation-spindle coupling, and both motor procedural and verbal declarative memory consolidation in early course, minimally medicated psychosis patients and non-psychotic first-degree relatives. Using a four-night experimental procedure, we observed significant deficits in spindle density and amplitude in patients relative to controls that were driven by individuals with schizophrenia. Schizophrenia patients also showed reduced sleep-dependent consolidation of motor procedural memory, which correlated with spindle density. Contrary to expectations, there were no group differences in the consolidation of declarative memory on a word pairs task. Nor did the relatives of patients differ in spindle activity or memory consolidation compared with controls, however increased consistency in the timing of SO-spindle coupling were seen in both patient and relatives. Our results extend prior work by demonstrating correlated deficits in sleep spindles and sleep-dependent motor procedural memory consolidation in early course, minimally medicated patients with schizophrenia, but not in first-degree relatives. This is consistent with other work in suggesting that impaired sleep-dependent memory consolidation has some specificity for schizophrenia and is a core feature rather than reflecting the effects of medication or chronicity.

Behavioral profiling of SLC38A10 knockout mice using the multivariate concentric square fieldTM test

Introduction

SLC38A10 is a gene that encodes the SLC38A10 protein, also known as SNAT10. The SLC38 family is evolutionary old, and SLC38A10 is one of the oldest members of the family. It is ubiquitously expressed, and its substrates are glutamine, glutamate, alanine, aspartate, and serine. However, little is known about its biological importance.

Methods

In the current study, an SLC38A10 knockout mouse was run in the multivariate concentric square field ^TM (MCSF) test. The MCSF test gives the mouse a choice of areas to explore; sheltered areas, elevated and illuminated areas, or open spaces, and a behavioral profile is obtained. The multivariate data obtained were analyzed (i) for each parameter, (ii) parameters grouped into functional categories, and (iii) with a principal component analysis.

Results

In the trend analysis, knockout mice had a decreased exploratory behavior compared to controls but did not show a distinct grouping in the principal component analysis.

Discussion

There was not a pronounced difference in the behavioral profile in SLC38A10 knockout mice compared to their wild-type controls, although subtle alterations in zones associated with exploratory behavior and risk assessment in female and male knockout mice, respectively, could be observed. These results imply that a loss of function of the SLC38A10 protein in mice does not drastically alter behavior in the MSCF test.

SLC38A10 Knockout Mice Display a Decreased Body Weight and an Increased Risk-Taking Behavior in the Open Field Test

The solute carrier 38 family (SLC38) is a family of 11 members. The most common substrate among these are alanine and glutamine, and members are present in a wide range of tissues with important functions for several biological processes, such as liver and brain function. Some of these transporters are better characterized than others and, in this paper, a behavioral characterization of SLC38A10^−/− mice was carried out. A battery of tests for general activity, emotionality, motor function, and spatial memory was used. Among these tests, the elevated plus maze, Y-maze, marble burying and challenging beam walk have not been tested on the SLC38A10^−/− mice previously, while the open field and the rotarod tests have been performed by the International Mouse Phenotyping Consortium (IMPC). Unlike the results from IMPC, the results from this study showed that SLC38A10^−/− mice spend less time in the wall zone in the open field test than WT mice, implying that SLC38A10-deficient mice have an increased explorative behavior, which suggests an important function of SLC38A10 in brain. The present study also confirmed IMPC's data regarding rotarod performance and weight, showing that SLC38A10^−/− mice do not have an affected motor coordination impairment and have a lower body weight than both SLC38A10^+/− and SLC38A10^+/+ mice. These results imply that a complete deficiency of the SLC38A10 protein might affect body weight homeostasis, but the underlying mechanisms needs to be studied further.

Abnormal synaptic plasticity and impaired cognition in schizophrenia

Schizophrenia (SCZ) is a severe mental illness that affects several brain domains with relation to cognition and behaviour. SCZ symptoms are typically classified into three categories, namely, positive, negative, and cognitive. The etiology of SCZ is thought to be multifactorial and poorly understood. Accumulating evidence has indicated abnormal synaptic plasticity and cognitive impairments in SCZ. Synaptic plasticity is thought to be induced at appropriate synapses during memory formation and has a critical role in the cognitive symptoms of SCZ. Many factors, including synaptic structure changes, aberrant expression of plasticity-related genes, and abnormal synaptic transmission, may influence synaptic plasticity and play vital roles in SCZ. In this article, we briefly summarize the morphology of the synapse, the neurobiology of synaptic plasticity, and the role of synaptic plasticity, and review potential mechanisms underlying abnormal synaptic plasticity in SCZ. These abnormalities involve dendritic spines, postsynaptic density, and long-term potentiation-like plasticity. We also focus on cognitive dysfunction, which reflects impaired connectivity in SCZ. Additionally, the potential targets for the treatment of SCZ are discussed in this article. Therefore, understanding abnormal synaptic plasticity and impaired cognition in SCZ has an essential role in drug therapy.

Polymorphism of rs12294045 in EAAT2 gene is potentially associated with schizophrenia in Chinese Han population

BACKGROUND

Recent studies have shown that the excitatory amino acid transporters (EAATs) are associated with schizophrenia. The aim of this study was to investigate the relationship between the polymorphism of EAAT1 and EAAT2 genes and schizophrenia in Chinese Han population.

METHODS

A total of 233 patients with schizophrenia and 342 healthy controls were enrolled. Two SNPs in EAAT1 gene (rs2269272, rs2731880) and four SNPs in EAAT2 gene (rs12360706, rs3088168, rs12294045, rs10836387) were genotyped by SNaPshot. Clinical features were collected using a self-made questionnaire. Psychotic symptoms of patients were measured by the Positive and Negative Syndrome Scale (PANSS), and patients' cognitive function was assessed by Matrics Consensus Cognitive Battery (MCCB).

RESULTS

Significant difference in allelic distributions between cases and controls was confirmed at locus rs12294045 (Ρ = 0.004) of EAAT2 gene. Different genotypes of rs12294045 were associated with family history (P = 0.046), in which patients with CT genotype had higher proportion of family history of psychosis. The polymorphism of rs12294045 was related to working operational memory (LNS: P = 0.016) and verbal learning function (HVLT-R: P = 0.042) in patients in which CT genotype had lower scores. However, these differences were no longer significant after Bonferroni correction.

CONCLUSIONS

Our study showed that the polymorphism of rs12294045 in EAAT2 gene may be associated with schizophrenia in Chinese Han population. CT genotype may be one of the risk factors for family history and cognitive deficits of patients.

Covering the Gap Between Sleep and Cognition – Mechanisms and Clinical Examples

A growing number of studies have shown the strong relationship between sleep and different cognitive processes, especially those that involve memory consolidation. Traditionally, these processes were attributed to mechanisms related to the macroarchitecture of sleep, as sleep cycles or the duration of specific stages, such as the REM stage. More recently, the relationship between different cognitive traits and specific waves (sleep spindles or slow oscillations) has been studied. We here present the most important physiological processes induced by sleep, with particular focus on brain electrophysiology. In addition, recent and classical literature were reviewed to cover the gap between sleep and cognition, while illustrating this relationship by means of clinical examples. Finally, we propose that future studies may focus not only on analyzing specific waves, but also on the relationship between their characteristics as potential biomarkers for multiple diseases.

Long non-coding RNA-associated competing endogenous RNA axes in the olfactory epithelium in schizophrenia: a bioinformatics analysis

The etiology of schizophrenia (SCZ), as a serious mental illness, is unknown. The significance of genetics in SCZ pathophysiology is yet unknown, and newly identified mechanisms involved in the regulation of gene transcription may be helpful in determining how these changes affect SCZ development and progression. In the current work, we used a bioinformatics approach to describe the role of long non-coding RNA (lncRNA)-associated competing endogenous RNAs (ceRNAs) in the olfactory epithelium (OE) samples in order to better understand the molecular regulatory processes implicated in SCZ disorders in living individuals. The Gene Expression Omnibus database was used to obtain the OE microarray dataset (GSE73129) from SCZ sufferers and control subjects, which contained information about both lncRNAs and mRNAs. The limma package of R software was used to identify the differentially expressed lncRNAs (DElncRNAs) and mRNAs (DEmRNAs). RNA interaction pairs were discovered using the Human MicroRNA Disease Database, DIANA-LncBase, and miRTarBase databases. In this study, the Pearson correlation coefficient was utilized to find positive correlations between DEmRNAs and DElncRNAs in the ceRNA network. Eventually, lncRNA-associated ceRNA axes were developed based on co-expression relations and DElncRNA-miRNA-DEmRNA interactions. This work found six potential DElncRNA-miRNA-DEmRNA loops in SCZ pathogenesis, including, SNTG2-AS1/hsa-miR-7-5p/SLC7A5, FLG-AS1/hsa-miR-34a-5p/FOSL1, LINC00960/hsa-miR-34a-5p/FOSL1, AQP4-AS1/hsa-miR-335-5p/FMN2, SOX2-OT/hsa-miR-24-3p/NOS3, and CASC2/hsa-miR-24-3p/NOS3. According to the findings, ceRNAs in OE might be promising research targets for studying SCZ molecular mechanisms. This could be a great opportunity to examine different aspects of neurodevelopment that may have been hampered early in SCZ patients.

The effects of eszopiclone on sleep spindles and memory consolidation in schizophrenia: a randomized clinical trial

Sleep spindles, defining oscillations of stage 2 non-rapid eye movement sleep (N2), mediate memory consolidation. Schizophrenia is characterized by reduced spindle activity that correlates with impaired sleep-dependent memory consolidation. In a small, randomized, placebo-controlled pilot study of schizophrenia, eszopiclone (Lunesta®), a nonbenzodiazepine sedative hypnotic, increased N2 spindle density (number/minute) but did not significantly improve memory. This larger double-blind crossover study that included healthy controls investigated whether eszopiclone could both increase N2 spindle density and improve memory. Twenty-six medicated schizophrenia outpatients and 29 healthy controls were randomly assigned to have a placebo or eszopiclone (3 mg) sleep visit first. Each visit involved two consecutive nights of high density polysomnography with training on the Motor Sequence Task (MST) on the second night and testing the following morning. Patients showed a widespread reduction of spindle density and, in both groups, eszopiclone increased spindle density but failed to enhance sleep-dependent procedural memory consolidation. Follow-up analyses revealed that eszopiclone also affected cortical slow oscillations: it decreased their amplitude, increased their duration, and rendered their phase locking with spindles more variable. Regardless of group or visit, the density of coupled spindle-slow oscillation events predicted memory consolidation significantly better than spindle density alone, suggesting that they are a better biomarker of memory consolidation. In conclusion, sleep oscillations are promising targets for improving memory consolidation in schizophrenia, but enhancing spindles is not enough. Effective therapies also need to preserve or enhance cortical slow oscillations and their coordination with thalamic spindles, an interregional dialog that is necessary for sleep-dependent memory consolidation.

Molecular signature of extracellular matrix pathology in schizophrenia

Growing evidence points to a critical involvement of the extracellular matrix (ECM) in the pathophysiology of schizophrenia (SZ). Decreases of perineuronal nets (PNNs) and altered expression of chondroitin sulphate proteoglycans (CSPGs) in glial cells have been identified in several brain regions. GWAS data have identified several SZ vulnerability variants of genes encoding for ECM molecules. Given the potential relevance of ECM functions to the pathophysiology of this disorder, it is necessary to understand the extent of ECM changes across brain regions, their region‐ and sex‐specificity and which ECM components contribute to these changes. We tested the hypothesis that the expression of genes encoding for ECM molecules may be broadly disrupted in SZ across several cortical and subcortical brain regions and include key ECM components as well as factors such as ECM posttranslational modifications and regulator factors. Gene expression profiling of 14 neocortical brain regions, caudate, putamen and hippocampus from control subjects (n = 14/region) and subjects with SZ (n = 16/region) was conducted using Affymetrix microarray analysis. Analysis across brain regions revealed widespread dysregulation of ECM gene expression in cortical and subcortical brain regions in SZ, impacting several ECM functional key components. SRGN, CD44, ADAMTS1, ADAM10, BCAN, NCAN and SEMA4G showed some of the most robust changes. Region‐, sex‐ and age‐specific gene expression patterns and correlation with cognitive scores were also detected. Taken together, these findings contribute to emerging evidence for large‐scale ECM dysregulation in SZ and point to molecular pathways involved in PNN decreases, glial cell dysfunction and cognitive impairment in SZ.

Targeting sleep oscillations to improve memory in schizophrenia

Although schizophrenia is defined by waking phenomena, a growing literature documents a deficit in sleep spindles, a defining oscillation of stage 2 non-rapid eye movement sleep. Compelling evidence supports an important role for spindles in cognition, and particularly memory. In schizophrenia, although the spindle deficit correlates with impaired sleep-dependent memory consolidation, recent clinical trials find that increasing spindles does not improve memory. This may reflect that sleep-dependent memory consolidation relies not on spindles alone, but also on their precise temporal coordination with cortical slow oscillations and hippocampal sharp-wave ripples. Consequently, interventions to improve memory in schizophrenia must not only increase spindles, but also preserve or enhance slow oscillations, hippocampal ripples and their temporal relations. Because hippocampal ripples and the activity of the thalamic spindle generator are difficult to measure noninvasively, screening potential interventions requires complementary animal and human studies. In this review we (i) propose that sleep oscillations are novel pathophysiological targets for therapy to improve cognition in schizophrenia; (ii) summarize our understanding of how these oscillations interact to consolidate memory; (iii) suggest that a systems neuroscience strategy is essential to selecting and evaluating effective treatments, and illustrate this with findings from clinical trials; and (iv) selectively review the interventional literature relevant to sleep and cognition, covering both pharmacological and noninvasive brain stimulation approaches. We conclude that coordinated sleep oscillations are promising targets for improving cognition in schizophrenia and that effective therapies will need to preserve or enhance sleep oscillatory dynamics and restore function at the network level.

Solute Carrier Family 1 (SLC1A1) Contributes to Susceptibility and Psychopathology Symptoms of Schizophrenia in the Han Chinese Population

OBJECTIVE

Schizophrenia (SZ) is a common and complex psychiatric disorder that has a significant genetic component. The glutamate hypothesis describes one possible pathogenesis of SZ. The solute carrier family 1 gene (SLC1A1) is one of several genes thought to play a critical role in regulating the glutamatergic system and is strongly implicated in the pathophysiology of SZ. In this study, we identify polymorphisms of the SLC1A1 gene that may confer susceptibility to SZ in the Han Chinese population.

METHODS

We genotyped 36 single-nucleotide polymorphisms (SNPs) using Illumina GoldenGate assays on a BeadStation 500G Genotyping System in 528 paranoid SZ patients and 528 healthy controls. Psychopathology was rated by the Positive and Negative Symptom Scale.

RESULTS

Significant associations were found in genotype and allele frequencies for SNPs rs10815017 (p = 0.002, 0.030, respectively) and rs2026828 (p = 0.020, 0.005, respectively) between SZ and healthy controls. There were significant associations in genotype frequency at rs6476875 (p = 0.020) and rs7024664 (p = 0.021) and allele frequency at rs3780412 (p = 0.026) and rs10974573 (p = 0.047) between SZ and healthy controls. Meanwhile, significant differences were found in genotype frequency at rs10815017 (p = 0.015), rs2026828 (p = 0.011), and rs3780411 (p = 0.040) in males, and rs7021569 in females (p = 0.020) between cases and controls when subdivided by gender. Also, significant differences were found in allele frequency at rs2026828 (p = 0.003), and rs7021569 (p = 0.045) in males, and rs10974619 in females (p = 0.044). However, those associations disappeared after Bonferroni's correction (p's > 0.05). Significant associations were found in the frequencies of four haplotypes (AA, CA, AGA, and GG) between SZ and healthy controls (χ ² = 3.974, 7.433, 4.699, 4.526, p = 0.046, 0.006, 0.030, 0.033, respectively). There were significant associations between rs7032326 genotypes and PANSS total, positive symptoms, negative symptoms, and general psychopathology in SZ (p = 0.002, 0.011, 0.028, 0.008, respectively).

CONCLUSION

The present study provides further evidence that SLC1A1 may be not a susceptibility gene for SZ. However, the genetic variations of SLC1A1 may affect psychopathology symptoms.

Effects of P-gp and Bcrp as brain efflux transporters on the uptake of [18 F]FPEB in the murine brain

The purpose of this study was to determine whether the brain uptake of [¹⁸ F]FPEB is influenced by P-glycoprotein (P-gp) and breast cancer resistance protein (Bcrp) as efflux transporters in rodents. To assess this possible modulation, positron emission tomography studies were performed in animal models of pharmacological or genetic ablation of these transporters. Compared with the control conditions, when P-gp was blocked with tariquidar, there was an 8%-12% increase in the brain uptake of [¹⁸ F]FPEB. In P-gp knockout mice, such as Mdr1a/b^(-/-) and Mdr1a/b^(-/-) Bcrp1^(-/-) , genetic ablation models, there was an increment of 8%-53% in [¹⁸ F]FPEB uptake compared with that in the wild-type mice. In contrast, Bcrp knockout mice showed a decrement of 5%-12% uptake and P-gp/Bcrp knockout group displayed an increment of 5%-17% compared with wild type. These results indicate that [¹⁸ F]FPEB is possibly a weak substrate for P-gp.

Commonality in dysregulated expression of gene sets in cortical brains of individuals with autism, schizophrenia, and bipolar disorder

Individuals affected with different neuropsychiatric disorders such as autism (AUT), schizophrenia (SCZ) and bipolar disorder (BPD), may share similar clinical manifestations, suggesting shared genetic influences and common biological mechanisms underlying these disorders. Using brain transcriptome data gathered from postmortem donors affected with AUT, SCZ and BPD, it is now possible to identify shared dysregulated gene sets, i.e., those abnormally expressed in brains of neuropsychiatric patients, compared to non-psychiatric controls. Here, we apply a novel aberrant gene expression analysis method, coupled with consensus co-expression network analysis, to identify gene sets with shared dysregulated expression in cortical brains of individuals affected with AUT, SCZ and BPD. We identify eight gene sets with dysregulated expression shared by AUT, SCZ and BPD, 23 by AUT and SCZ, four by AUT and BPD, and two by SCZ and BPD. The identified genes are enriched with functions relevant to amino acid transport, synapse, neurotransmitter release, oxidative stress, nitric oxide synthase biosynthesis, immune response, protein folding, lysophosphatidic acid-mediated signaling and glycolysis. Our method has been proven to be effective in discovering and revealing multigene sets with dysregulated expression shared by different neuropsychiatric disorders. Our findings provide new insights into the common molecular mechanisms underlying the pathogenesis and progression of AUT, SCZ and BPD, contributing to the study of etiological overlap between these neuropsychiatric disorders.

Increased Thalamocortical Connectivity in Schizophrenia Correlates With Sleep Spindle Deficits: Evidence for a Common Pathophysiology

BACKGROUND

Converging evidence implicates abnormal thalamocortical interactions in the pathophysiology of schizophrenia. This evidence includes consistent findings of increased resting-state functional connectivity of the thalamus with somatosensory and motor cortex during wake and reduced spindle activity during sleep. We hypothesized that these abnormalities would be correlated, reflecting a common mechanism: reduced inhibition of thalamocortical neurons by the thalamic reticular nucleus (TRN). The TRN is the major inhibitory nucleus of the thalamus and is abnormal in schizophrenia. Reduced TRN inhibition would be expected to lead to increased and less filtered thalamic relay of sensory and motor information to the cortex during wake and reduced burst firing necessary for spindle initiation during sleep.

METHODS

Overnight polysomnography and resting-state functional connectivity magnetic resonance imaging were performed in 26 outpatients with schizophrenia and 30 demographically matched healthy individuals. We examined the relations of sleep spindle density during stage 2 non-rapid eye movement sleep with connectivity of the thalamus to the cortex during wakeful rest.

RESULTS

As in prior studies, patients with schizophrenia exhibited increased functional connectivity of the thalamus with bilateral somatosensory and motor cortex and reduced sleep spindle density. Spindle density inversely correlated with thalamocortical connectivity, including in somotosensory and motor cortex, regardless of diagnosis.

CONCLUSIONS

These findings link two biomarkers of schizophrenia-the sleep spindle density deficit and abnormally increased thalamocortical functional connectivity-and point to deficient TRN inhibition as a plausible mechanism. If TRN-mediated thalamocortical dysfunction increases risk for schizophrenia and contributes to its manifestations, understanding its mechanism could guide the development of targeted interventions.

Poly(I:C) alters placental and fetal brain amino acid transport in a rat model of maternal immune activation

PROBLEM

Maternal immune activation (MIA) during pregnancy is associated with increased chances of neurodevelopmental disorders including schizophrenia and autism spectrum disorder (ASD). However, the exact mechanism through which MIA contributes to altered neurodevelopment is unknown. Due to the important role that amino acids play in neurodevelopment, altered amino acid transport could play a role in neurodevelopmental disorders. Indeed, altered plasma concentrations of multiple amino acids have been reported in individuals with ASD or schizophrenia. Therefore, our objective was to determine whether virally mediated MIA induces changes in amino acid transporters in the placenta and fetal brain.

METHOD OF STUDY

Pregnant rats were administered poly(I:C) on gestational day 14, and placental and fetal tissues were collected 6, 24, and 48 hours later. Amino acid transporter expression was measured in the placenta and fetal brain using qPCR, Western blotting, and Simple Western. Free amino acid concentrations in the fetal brain were quantified using HPLC.

RESULTS

Poly(I:C) increased mRNA expression of several amino acid transporters in the placenta and fetal brain over these timepoints. Conversely, poly(I:C) imposed significant decreases in the protein expression of ASCT1 and EAAT2 in placenta and expression of SNAT5, EAAT1, and GLYT1 in fetal brain. Functional consequences of altered transporter expression were demonstrated through widespread changes in the concentrations of free amino acids in the fetal brains.

CONCLUSION

Together, these results represent novel findings with the poly(I:C) MIA model and contribute to the understanding of how MIA during pregnancy potentially leads to neurodevelopmental disorders.

Abnormal Sleep Spindles, Memory Consolidation, and Schizophrenia

There is overwhelming evidence that sleep is crucial for memory consolidation. Patients with schizophrenia and their unaffected relatives have a specific deficit in sleep spindles, a defining oscillation of non-rapid eye movement (NREM) Stage 2 sleep that, in coordination with other NREM oscillations, mediate memory consolidation. In schizophrenia, the spindle deficit correlates with impaired sleep-dependent memory consolidation, positive symptoms, and abnormal thalamocortical connectivity. These relations point to dysfunction of the thalamic reticular nucleus (TRN), which generates spindles, gates the relay of sensory information to the cortex, and modulates thalamocortical communication. Genetic studies are beginning to provide clues to possible neurodevelopmental origins of TRN-mediated thalamocortical circuit dysfunction and to identify novel targets for treating the related memory deficits and symptoms. By forging empirical links in causal chains from risk genes to thalamocortical circuit dysfunction, spindle deficits, memory impairment, symptoms, and diagnosis, future research can advance our mechanistic understanding, treatment, and prevention of schizophrenia.

Variability with Astroglial Glutamate Transport Genetics Is Associated with Increased Risk for Post-Traumatic Seizures

Excitotoxicity contributes to epileptogenesis after severe traumatic brain injury (sTBI). Demographic and clinical risk factors for post-traumatic seizures (PTS) have been identified, but genetic risk remains largely unknown. Thus, we investigated whether genetic variation in astroglial glutamate transporter genes is associated with accelerated epileptogenesis and PTS risk after sTBI. Adults (n = 267) 18-75 years old were assessed over a three-year period post-TBI. Single nucleotide polymorphisms (SNPs) throughout the SLC1A2 and SLC1A3 genes were assayed. Kaplan-Meier estimates and log-rank statistics were used to compare seizure frequencies by genotype. Multivariate Cox proportional hazards regression was used to estimate hazard ratios (HRs) for genotypes significant in Kaplan-Meier analyses. Thirty-nine tagging SNPs were examined (SLC1A2: n = 21, SLC1A3: n = 18). PTS developed in 57 (21.4%) individuals. Of those with PTS, n = 20 (35.7%) had an immediate/early seizure within the first seven days, and n = 36 (64.3%) had a late seizure occurring between eight days and three years post-TBI. When adjusting for multiple comparisons, rs4869682 genotypes (SLC1A3, GG vs. T-carriers) were associated with time to first seizure (p = 0.003). Median time until first seizure was 20.4 days for individuals with a GG genotype and 44.8 days for T-carriers. After adjusting for covariates, rs4869682 GG-homozygotes had a 2.05 times increased PTS risk versus T-carriers (aHR = 2.08, 95% confidence interval: 1.20, 3.62, p = 0.009). Variation within SLC1A3 is associated with accelerated epileptogenesis and clinical PTS development after sTBI. Future studies should validate these findings and examine how genetic variation at rs4869682 may be a target for PTS prevention and treatment.

Astroglial correlates of neuropsychiatric disease: From astrocytopathy to astrogliosis

Complex roles for astrocytes in health and disease continue to emerge, highlighting this class of cells as integral to function and dysfunction of the nervous system. In particular, escalating evidence strongly implicates a range of changes in astrocyte structure and function associated with neuropsychiatric diseases including major depressive disorder, schizophrenia, and addiction. These changes can range from astrocytopathy, degeneration, and loss of function, to astrogliosis and hypertrophy, and can be either adaptive or maladaptive. Evidence from the literature indicates a myriad of changes observed in astrocytes from both human postmortem studies as well as preclinical animal models, including changes in expression of glial fibrillary protein, as well as changes in astrocyte morphology and astrocyte-mediated regulation of synaptic function. In this review, we seek to provide a comprehensive assessment of these findings and consequently evidence for common themes regarding adaptations in astrocytes associated with neuropsychiatric disease. While results are mixed across conditions and models, general findings indicate decreased astrocyte cellular features and gene expression in depression, chronic stress and anxiety, but increased inflammation in schizophrenia. Changes also vary widely in response to different drugs of abuse, with evidence reflective of features of astrocytopathy to astrogliosis, varying across drug classes, route of administration and length of withdrawal.

Neurobiology of cognitive remediation in schizophrenia: Effects of EAAT2 polymorphism

Cognitive deficits represent core features of schizophrenia, affecting quality of life and functioning. The excitatory amino acid transporter 2 (EAAT2) is responsible for the majority of glutamate reuptake and its activity is crucial for glutamatergic neurotransmission, prevention of excitotoxic damage and cerebral metabolism. Different studies reported that EAAT2 rs4354668 (-181 T/G) influences cognitive functions and brain structures in patients with schizophrenia. Specifically, the G allele, linked to lower EAAT2 expression, was associated with impaired prefrontal cognitive performance and reduced grey matter volumes. Cognitive remediation therapy (CRT) is one of the best available tool to treat cognitive deficits in schizophrenia, able to induce a neuroplastic modulation of cognitive functions. The present study aims to investigate the effects of rs4354668 on CRT outcome, also considering possible genotype interaction with antipsychotic (AP) treatment, since EAAT2 expression is negatively influenced by clozapine. We examined rs4354668 in 88 clinically stabilized patients with schizophrenia, treated with CRT and assessed at enrolment, at the end of CRT and after 3 months. We observed greater working memory improvements among patients carrying the T/T genotype, regardless of AP treatment. Moreover, we reported a significant interaction between pharmacological treatment and rs4354668 on executive functions, with greater improvements among T/T patients treated with APs other than clozapine. These observations suggest that impaired EAAT2 expression may attenuate CRT outcome. Moreover, our results indicate the possibility that rs4354668 could also differentially influence the response to CRT depending on the AP treatment.

The thalamic reticular nucleus in schizophrenia and bipolar disorder: role of parvalbumin-expressing neuron networks and oxidative stress

Growing evidence points to a disruption of cortico-thalamo-cortical circuits in schizophrenia (SZ) and bipolar disorder (BD). Clues for a specific involvement of the thalamic reticular nucleus (TRN) come from its unique neuronal characteristics and neural connectivity, allowing it to shape the thalamo-cortical information flow. A direct involvement of the TRN in SZ and BD has not been tested thus far. We used a combination of human postmortem and rodent studies to test the hypothesis that neurons expressing parvalbumin (PV neurons), a main TRN neuronal population, and associated Wisteria floribunda agglutinin-labeled perineuronal nets (WFA/PNNs) are altered in SZ and BD, and that these changes may occur early in the course of the disease as a consequence of oxidative stress. In both disease groups, marked decreases of PV neurons (immunoreactive for PV) and WFA/PNNs were observed in the TRN, with no effects of duration of illness or age at onset. Similarly, in transgenic mice with redox dysregulation, numbers of PV neurons and WFA/PNN+PV neurons were decreased in transgenic compared with wild-type mice; these changes were present at postnatal day (P) 20 for PV neurons and P40 for WFA/PNN+PV neurons, accompanied by alterations of their firing properties. These results show profound abnormalities of PV neurons in the TRN of subjects with SZ and BD, and offer support for the hypothesis that oxidative stress may play a key role in impacting TRN PV neurons at early stages of these disorders. We put forth that these TRN abnormalities may contribute to disruptions of sleep spindles, focused attention and emotion processing in these disorders.

A Glutamate Transporter EAAT1 Gene Variant Influences Amygdala Functional Connectivity in Bipolar Disorder

Bipolar disorder (BD) is a severe illness characterized by recurrent depressive and manic episodes and by emotional dysregulation. Altered cortico-limbic connectivity could account for typical symptoms of the disorder such as mood instability, emotional dysregulation, and cognitive deficits. Functional connectivity positively associated with glutamatergic neurotransmission. The inactivation of glutamate is handled by a series of glutamate transporters, among them, the excitatory amino acid transporter 1 (EAAT1) which is modulated by a SNP rs2731880 (C/T) where the C allele leads to increased EAAT1 expression and glutamate uptake. We hypothesized that rs2731880 would affect cortico-limbic functional connectivity during an implicit affective processing task. Sixty-eight BD patients underwent fMRI scanning during implicit processing of fearful and angry faces. We explored the effect of rs2731880 on the strength of functional connectivity from the amygdalae to the whole brain. A significant activation in response to emotional processing was observed in two main clusters encompassing the right and left amygdala. Amygdalae to whole-brain functional connectivity analyses revealed a significant interaction between rs2731880 and the task (emotional stimuli vs geometric shapes) for the functional connections between the right amygdala and right subgenual anterior cingulate cortex. Post-hoc analyses revealed that T/T patients showed a significant negative connectivity between the amygdala and anterior cingulate cortex compared to C carriers. T/T subjects also performed significantly better in the face-matching task than rs2731880*C carriers. Our findings reveal an EAAT1 genotype-associated difference in cortico-limbic connectivity during affective regulation, possibly identifying a neurobiological underpinning of emotional dysfunction in BD.

Glutamate transporters, EAAT1 and EAAT2, are potentially important in the pathophysiology and treatment of schizophrenia and affective disorders

Glutamate is the predominant excitatory neurotransmitter in the human brain and it has been shown that prolonged activation of the glutamatergic system leads to nerve damage and cell death. Following release from the pre-synaptic neuron and synaptic transmission, glutamate is either taken up into the pre-synaptic neuron or neighbouring glia by transmembrane glutamate transporters. Excitatory amino acid transporter (EAAT) 1 and EAAT2 are Na⁺-dependant glutamate transporters expressed predominantly in glia cells of the central nervous system. As the most abundant glutamate transporters, their primary role is to modulate levels of glutamatergic excitability and prevent spill over of glutamate beyond the synapse. This role is facilitated through the binding and transportation of glutamate into astrocytes and microglia. The function of EAAT1 and EAAT2 is heavily regulated at the levels of gene expression, post-transcriptional splicing, glycosylation states and cell-surface trafficking of the protein. Both glutamatergic dysfunction and glial dysfunction have been proposed to be involved in psychiatric disorder. This review will present an overview of the roles that EAAT1 and EAAT2 play in modulating glutamatergic activity in the human brain, and mount an argument that these two transporters could be involved in the aetiologies of schizophrenia and affective disorders as well as represent potential drug targets for novel therapies for those disorders.

Spindle activity in young children with autism, developmental delay, or typical development

OBJECTIVE

To determine whether spindle activity differs in young children with and without autism.

METHODS

We investigated differences in spindle density, duration, and oscillatory features in 135 young children with autism, developmental delay without autism (DD), or typical development (TD) and secondarily assessed the dimensional relationship between spindle density and both cognitive ability and social functioning.

RESULTS

Compared to TD, both spindle density (Cohen d 0.93, 95% confidence interval [CI] 0.49-1.37) and duration (Cohen d 0.58, 95% CI 0.15-1.01) were significantly decreased in autism. Spindle density was also significantly reduced in autism compared to DD (Cohen d 0.61, 95% CI 0.13-1.09). Decreased spindle frequency in autism compared to both TD (Cohen d 0.47, 95% CI 0.04-0.90) and DD (Cohen d 0.58, 95% CI 0.10-1.06) did not survive correction. The DD group did not differ significantly from the TD group on any spindle parameter. These results, suggesting a relationship between spindle density and autism but not DD, were further illustrated in exploratory analyses, wherein nonverbal ratio IQ (RIQ) and the Vineland Socialization domain standard score were strongly correlated with spindle density in the full sample (r = 0.33, p ≤ 001 and r = 0.41, p ≤ 001, respectively) but not within group. After nonverbal RIQ was accounted for, the relationship between spindle density and Vineland Socialization remained statistically significant (r = 0.23, p < 0.01). However, Vineland Socialization scores accounted for the relationship between spindle density and nonverbal RIQ (r = 0.04, p = 0.67).

CONCLUSION

In a large cohort of young children with autism, spindle density was reduced compared to groups of age-matched children with DD or TD. Alterations in the maturational trajectory of spindles may provide valuable insight into the neurophysiologic differences related to behavior in disorders of neurodevelopment.

Reduced Sleep Spindles in Schizophrenia: A Treatable Endophenotype That Links Risk Genes to Impaired Cognition?

Although schizophrenia (SZ) is defined by waking phenomena, abnormal sleep is a common feature. In particular, there is accumulating evidence of a sleep spindle deficit. Sleep spindles, a defining thalamocortical oscillation of non-rapid eye movement stage 2 sleep, correlate with IQ and are thought to promote long-term potentiation and enhance memory consolidation. We review evidence that reduced spindle activity in SZ is an endophenotype that impairs sleep-dependent memory consolidation, contributes to symptoms, and is a novel treatment biomarker. Studies showing that spindles can be pharmacologically enhanced in SZ and that increasing spindles improves memory in healthy individuals suggest that treating spindle deficits in patients with SZ may improve cognition. Spindle activity is highly heritable, and recent large-scale genome-wide association studies have identified SZ risk genes that may contribute to spindle deficits and illuminate their mechanisms. For example, the SZ risk gene CACNA1I encodes a calcium channel that is abundantly expressed in the thalamic spindle generator and plays a critical role in spindle activity based on a mouse knockout. Future genetic studies of animals and humans can delineate the role of this and other genes in spindles. Such cross-disciplinary research, by forging empirical links in causal chains from risk genes to proteins and cellular functions to endophenotypes, cognitive impairments, symptoms, and diagnosis, has the potential to advance the mechanistic understanding, treatment, and prevention of SZ. This review highlights the importance of deficient sleep-dependent memory consolidation among the cognitive deficits of SZ and implicates reduced sleep spindles as a potentially treatable mechanism.

Cell-specific abnormalities of glutamate transporters in schizophrenia: sick astrocytes and compensating relay neurons?

Excitatory amino-acid transporters (EAATs) bind and transport glutamate, limiting spillover from synapses due to their dense perisynaptic expression primarily on astroglia. Converging evidence suggests that abnormalities in the astroglial glutamate transporter localization and function may underlie a disease mechanism with pathological glutamate spillover as well as alterations in the kinetics of perisynaptic glutamate buffering and uptake contributing to dysfunction of thalamo-cortical circuits in schizophrenia. We explored this hypothesis by performing cell- and region-level studies of EAAT1 and EAAT2 expression in the mediodorsal nucleus of the thalamus in an elderly cohort of subjects with schizophrenia. We found decreased protein expression for the typically astroglial-localized glutamate transporters in the mediodorsal and ventral tier nuclei. We next used laser-capture microdissection and quantitative polymerase chain reaction to assess cell-level expression of the transporters and their splice variants. In the mediodorsal nucleus, we found lower expression of transporter transcripts in a population of cells enriched for astrocytes, and higher expression of transporter transcripts in a population of cells enriched for relay neurons. We confirmed expression of transporter protein in neurons in schizophrenia using dual-label immunofluorescence. Finally, the pattern of transporter mRNA and protein expression in rodents treated for 9 months with antipsychotic medication suggests that our findings are not due to the effects of antipsychotic treatment. We found a compensatory increase in transporter expression in neurons that might be secondary to a loss of transporter expression in astrocytes. These changes suggest a profound abnormality in astrocyte functions that support, nourish and maintain neuronal fidelity and synaptic activity.

The importance of the excitatory amino acid transporter 3 (EAAT3)

The neuronal excitatory amino acid transporter 3 (EAAT3) is fairly ubiquitously expressed in the brain, though it does not necessarily maintain the same function everywhere. It is important in maintaining low local concentrations of glutamate, where its predominant post-synaptic localization can buffer nearby glutamate receptors and modulate excitatory neurotransmission and synaptic plasticity. It is also the main neuronal cysteine uptake system acting as the rate-limiting factor for the synthesis of glutathione, a potent antioxidant, in EAAT3 expressing neurons, while on GABAergic neurons, it is important in supplying glutamate as a precursor for GABA synthesis. Several diseases implicate EAAT3, and modulation of this transporter could prove a useful therapeutic approach. Regulation of EAAT3 could be targeted at several points for functional modulation, including the level of transcription, trafficking and direct pharmacological modulation, and indeed, compounds and experimental treatments have been identified that regulate EAAT3 function at different stages, which together with observations of EAAT3 regulation in patients is giving us insight into the endogenous function of this transporter, as well as the consequences of altered function. This review summarizes work done on elucidating the role and regulation of EAAT3.

Molecular genetic models related to schizophrenia and psychotic illness: heuristics and challenges

Schizophrenia is a heritable disorder that may involve several common genes of small effect and/or rare copy number variation, with phenotypic heterogeneity across patients. Furthermore, any boundaries vis-à-vis other psychotic disorders are far from clear. Consequently, identification of informative animal models for this disorder, which typically relate to pharmacological and putative pathophysiological processes of uncertain validity, faces considerable challenges. In juxtaposition, the majority of mutant models for schizophrenia relate to the functional roles of a diverse set of genes associated with risk for the disorder or with such putative pathophysiological processes. This chapter seeks to outline the evidence from phenotypic studies in mutant models related to schizophrenia. These have commonly assessed the degree to which mutation of a schizophrenia-related gene is associated with the expression of several aspects of the schizophrenia phenotype or more circumscribed, schizophrenia-related endophenotypes; typically, they place specific emphasis on positive and negative symptoms and cognitive deficits, and extend to structural and other pathological features. We first consider the primary technological approaches to the generation of such mutants, to include their relative merits and demerits, and then highlight the diverse phenotypic approaches that have been developed for their assessment. The chapter then considers the application of mutant phenotypes to study pathobiological and pharmacological mechanisms thought to be relevant for schizophrenia, particularly in terms of dopaminergic and glutamatergic dysfunction, and to an increasing range of candidate susceptibility genes and copy number variants. Finally, we discuss several pertinent issues and challenges within the field which relate to both phenotypic evaluation and a growing appreciation of the functional genomics of schizophrenia and the involvement of gene × environment interactions.

Form and Function of Sleep Spindles across the Lifespan

Since the advent of EEG recordings, sleep spindles have been identified as hallmarks of non-REM sleep. Despite a broad general understanding of mechanisms of spindle generation gleaned from animal studies, the mechanisms underlying certain features of spindles in the human brain, such as “global” versus “local” spindles, are largely unknown. Neither the topography nor the morphology of sleep spindles remains constant throughout the lifespan. It is likely that changes in spindle phenomenology during development and aging are the result of dramatic changes in brain structure and function. Across various developmental windows, spindle activity is correlated with general cognitive aptitude, learning, and memory; however, these correlations vary in strength, and even direction, depending on age and metrics used. Understanding these differences across the lifespan should further clarify how these oscillations are generated and their function under a variety of circumstances. We discuss these issues, and their translational implications for human cognitive function. Because sleep spindles are similarly affected in disorders of neurodevelopment (such as schizophrenia) and during aging (such as neurodegenerative conditions), both types of disorders may benefit from therapies based on a better understanding of spindle function.

Astrocytes as new targets to improve cognitive functions

Astrocytes are now viewed as key elements of brain wiring as well as neuronal communication. Indeed, they not only bridge the gap between metabolic supplies by blood vessels and neurons, but also allow fine control of neurotransmission by providing appropriate signaling molecules and insulation through a tight enwrapping of synapses. Recognition that astroglia is essential to neuronal communication is nevertheless fairly recent and the large body of evidence dissecting such role has focused on the synaptic level by identifying neuro- and gliotransmitters uptaken and released at synaptic or extrasynaptic sites. Yet, more integrated research deciphering the impact of astroglial functions on neuronal network activity have led to the reasonable assumption that the role of astrocytes in supervising synaptic activity translates in influencing neuronal processing and cognitive functions. Several investigations using recent genetic tools now support this notion by showing that inactivating or boosting astroglial function directly affects cognitive abilities. Accordingly, brain diseases resulting in impaired cognitive functions have seen their physiopathological mechanisms revisited in light of this primary protagonist of brain processing. We here provide a review of the current knowledge on the role of astrocytes in cognition and in several brain diseases including neurodegenerative disorders, psychiatric illnesses, as well as other conditions such as epilepsy. Potential astroglial therapeutic targets are also discussed.

Common variants in SLC1A2 and schizophrenia: Association and cognitive function in patients with schizophrenia and healthy individuals

SLC1A2 is reported to be responsible for the majority of glutamate uptake, which has a crucial role in neural development and synaptic plasticity, and a disturbance in glutamatergic transmission has been suggested to be involved in the pathophysiology of schizophrenia (SCZ) and cognition. To evaluate the relationship of common variants within SLC1A2 with SCZ and cognition in Han Chinese, 28 tag SNPs were genotyped in the discovery stage, which included 1117 cases and 2289 controls; significantly associated markers were genotyped in the replication stage with 2128 cases and 3865 controls. The rs4354668 SNP was identified to be significantly associated with SCZ in both datasets, and a similar pattern was also observed in the two-stage study on conducting imputation and haplotype association analyses. In addition, significant associations between the rs4354668 SNP and cognition were observed when processing the perseverative error of the Wisconsin Card Sorting Test in patients and controls. Our results provide supportive evidence for an effect of SLC1A2 on the etiology of SCZ, suggesting that genetic variation (rs4354668 and its haplotypes) in SLC1A2 may be involved in impaired executive function, which adds to the current body of knowledge regarding the risk of SCZ and the impairment of cognitive performance.

Deletion of adenosine A2A receptors from astrocytes disrupts glutamate homeostasis leading to psychomotor and cognitive impairment: relevance to schizophrenia

BACKGROUND

Adenosine A2A receptors (A2AR) modulate dopamine and glutamate signaling and thereby may influence some of the psychomotor and cognitive processes associated with schizophrenia. Because astroglial A2AR regulate the availability of glutamate, we hypothesized that they might play an unprecedented role in some of the processes leading to the development of schizophrenia, which we investigated using a mouse line with a selective deletion of A2AR in astrocytes (Gfa2-A2AR knockout [KO] mice].

METHODS

We examined Gfa2-A2AR KO mice for behaviors thought to recapitulate some features of schizophrenia, namely enhanced MK-801 psychomotor response (positive symptoms) and decreased working memory (cognitive symptoms). In addition, we probed for neurochemical alterations in the glutamatergic circuitry, evaluating glutamate uptake and release and the levels of key proteins defining glutamatergic signaling (glutamate transporter-I [GLT-I], N-methyl-D-aspartate receptors [NMDA-R] and α-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors [AMPA-R]) to provide a mechanistic understanding of the phenotype encountered.

RESULTS

We show that Gfa2-A2AR KO mice exhibited enhanced MK-801 psychomotor response and decreased working memory; this was accompanied by a disruption of glutamate homeostasis characterized by aberrant GLT-I activity, increased presynaptic glutamate release, NMDA-R 2B subunit upregulation, and increased internalization of AMPA-R. Accordingly, selective GLT-I inhibition or blockade of GluR1/2 endocytosis prevented the psychomotor and cognitive phenotypes in Gfa2-A2AR KO mice, namely in the nucleus accumbens.

CONCLUSIONS

These results show that the dysfunction of astrocytic A2AR, by controlling GLT-I activity, triggers an astrocyte-to-neuron wave of communication resulting in disrupted glutamate homeostasis, thought to underlie several endophenotypes relevant to schizophrenia.

Purinergic receptors in psychiatric disorders

Psychiatric disorders describe different mental or behavioral patterns, causing suffering or poor coping of ordinary life with manifold presentations. Multifactorial processes can contribute to their development and progression. Purinergic neurotransmission and neuromodulation in the brain have attracted increasing therapeutic interest in the field of psychiatry. Purine nucleotides and nucleosides are well recognized as signaling molecules mediating cell to cell communication. The actions of ATP are mediated by ionotropic P2X and metabotropic P2Y receptor subfamilies, whilst the actions of adenosine are mediated by P1 (A1 or A2) adenosine receptors. Purinergic mechanisms and specific receptor subtypes have been shown to be linked to the regulation of many aspects of behavior and mood and to dysregulation in pathological processes of brain function. In this review the recent knowledge on the role of purinergic receptors in the two most frequent psychiatric diseases, major depression and schizophrenia, as well as on related animal models is summarized. At present the most promising data for therapeutic strategies derive from investigations of the adenosine system emphasizing a unique function of A2A receptors at neurons and astrocytes in these disorders. Among the P2 receptor family, in particular P2X7 and P2Y1 receptors were related to disturbances in major depression and schizophrenia, respectively. This article is part of the Special Issue entitled 'Purines in Neurodegeneration and Neuroregeneration'.

Characterization of a Novel Mutation in SLC1A1 Associated with Schizophrenia

We have recently described a hemi-deletion on chromosome 9p24.2 at the SLC1A1 gene locus and its co-segregation with schizophrenia in an extended Palauan pedigree. This finding represents a point of convergence for several pathophysiological models of schizophrenia. The present report sought to characterize the biological consequences of this hemi-deletion. Dual luciferase assays demonstrated that the partially deleted allele (lacking exon 1 and the native promoter) can drive expression of a 5'-truncated SLC1A1 using sequence upstream of exon 2 as a surrogate promoter. However, confocal microscopy and electrophysiological recordings demonstrate that the 5'-truncated SLC1A1 lacks normal membrane localization and glutamate transport ability. To identify downstream consequences of the hemi-deletion, we first used a themed qRT-PCR array to compare expression of 84 GABA and glutamate genes in RNA from peripheral blood leukocytes in deletion carriers (n = 11) versus noncarriers (n = 8) as well as deletion carriers with psychosis (n = 5) versus those without (n = 3). Then, targeted RNA-Seq (TREx) was used to quantify expression of 375 genes associated with neuropsychiatric disorders in HEK293 cells subjected to either knockdown of SLC1A1 or overexpression of full-length or 5'-truncated SLC1A1. Expression changes of several genes strongly implicated in schizophrenia pathophysiology were detected (e.g. SLC1A2, SLC1A3, SLC1A6, SLC7A11, GRIN2A, GRIA1 and DLX1).

SPAK and OSR1 Sensitivity of Excitatory Amino Acid Transporter EAAT3

BACKGROUND/AIMS

Kinases involved in the regulation of epithelial transport include SPAK (SPS1-related proline/alanine-rich kinase) and OSR1 (oxidative stress-responsive kinase 1). SPAK and OSR1 are both regulated by WNK (with-no-K(Lys)) kinases. The present study explored whether SPAK and/or OSR1 influence the excitatory amino acid transporter EAAT3, which accomplishes glutamate and aspartate transport in kidney, intestine and brain.

METHODS

cRNA encoding EAAT3 was injected into Xenopus laevis oocytes with or without additional injection of cRNA encoding wild-type SPAK, constitutively active (T233E)SPAK, WNK insensitive (T233A)SPAK, catalytically inactive (D212A)SPAK, wild-type OSR1, constitutively active (T185E)OSR1, WNK insensitive (T185A)OSR1 and catalytically inactive (D164A)OSR1. Glutamate-induced current was taken as measure of electrogenic glutamate transport and was quantified utilizing dual electrode voltage clamp. Furthermore, Ussing chamber was employed to determine glutamate transport in the intestine from gene-targeted mice carrying WNK insensitive SPAK (spak(tg/tg)) and from corresponding wild-type mice (spak(+/+)).

RESULTS

EAAT3 activity was significantly decreased by wild-type SPAK and (T233E)SPAK, but not by (T233A)SPAK and (D212A)SPAK. SPAK decreased maximal transport rate without affecting significantly affinity of the carrier. Similarly, EAAT3 activity was significantly downregulated by wild-type OSR1 and (T185E)OSR1, but not by (T185A)OSR1 and (D164A)OSR1. Again OSR1 decreased maximal transport rate without affecting significantly affinity of the carrier. Intestinal electrogenic glutamate transport was significantly lower in spak(+/+) than in spak(tg/tg) mice.

CONCLUSION

Both, SPAK and OSR1 are negative regulators of EAAT3 activity.

Glutamate transporter splice variant expression in an enriched pyramidal cell population in schizophrenia

Dysregulation of the glutamate transporters EAAT1 and EAAT2 and their isoforms have been implicated in schizophrenia. EAAT1 and EAAT2 expression has been studied in different brain regions but the prevalence of astrocytic glutamate transporter expression masks the more subtle changes in excitatory amino acid transporters (EAATs) isoforms in neurons in the cortex. Using laser capture microdissection, pyramidal neurons were cut from the anterior cingulate cortex of postmortem schizophrenia (n = 20) and control (n = 20) subjects. The messenger RNA (mRNA) levels of EAAT1, EAAT2 and the splice variants EAAT1 exon9skipping, EAAT2 exon9skipping and EAAT2b were analyzed by real time PCR (RT-PCR) in an enriched population of neurons. Region-level expression of these transcripts was measured in postmortem schizophrenia (n = 25) and controls (n = 25). The relationship between selected EAAT polymorphisms and EAAT splice variant expression was also explored. Anterior cingulate cortex pyramidal cell expression of EAAT2b mRNA was increased (P < 0.001; 67%) in schizophrenia subjects compared with controls. There was no significant change in other EAAT variants. EAAT2 exon9skipping mRNA was increased (P < 0.05; 38%) at region level in the anterior cingulate cortex with no significant change in other EAAT variants at region level. EAAT2 single-nucleotide polymorphisms were significantly associated with changes in EAAT2 isoform expression. Haloperidol decanoate-treated animals, acting as controls for possible antipsychotic effects, did not have significantly altered neuronal EAAT2b mRNA levels. The novel finding that EAAT2b levels are increased in populations of anterior cingulate cortex pyramidal cells further demonstrates a role for neuronal glutamate transporter splice variant expression in schizophrenia.

The thalamic reticular nucleus: a functional hub for thalamocortical network dysfunction in schizophrenia and a target for drug discovery

The thalamus (comprising many distinct nuclei) plays a key role in facilitating sensory discrimination and cognitive processes through connections with the cortex. Impaired thalamocortical processing has long been considered to be involved in schizophrenia. In this review we focus on the thalamic reticular nucleus (TRN) providing evidence for it being an important communication hub between the thalamus and cortex and how it may play a key role in the pathophysiology of schizophrenia. We first highlight the functional neuroanatomy, neurotransmitter localisation and physiology of the TRN. We then present evidence of the physiological roles of the TRN in relation to oscillatory activity, cognition and behaviour. Next we discuss the role of the TRN in rodent models of risk factors for schizophrenia (genetic and pharmacological) and provide evidence for TRN deficits in schizophrenia. Finally we discuss new drug targets for schizophrenia in relation to restoring TRN circuitry dysfunction.

Synergistic association of PI4KA and GRM3 genetic polymorphisms with poor antipsychotic response in south Indian schizophrenia patients with low severity of illness

Literature indicates key role of glutamatergic pathway genes in antipsychotic response among schizophrenia patients. However, molecular basis of their underlying role in antipsychotic response remained unexplained. Thus, to unravel their molecular underpinnings, we sought to investigate interactions amongst GRM3, SLC1A1, SLC1A2, SLC1A3, SLC1A4 gene polymorphisms with drug response in south Indian schizophrenia patients. We genotyped 48 SNPs from these genes in 423 schizophrenia patients stratified into low and high severity of illness groups. The SNPs and haplotypic combinations of associated SNPs were examined for their association with antipsychotic response. Multifactor-dimensionality-reduction was further used to explore gene-gene interaction among these SNPs and 53 SNPs from previously studied genes (BDNF, RGS4, SLC6A3, PI4KA, and PIP4K2A). Single SNP and haplotype analyses revealed no significant association with drug response irrespective of severity of illness. Gene-gene interaction analyses yielded promising leads, including an observed synergistic effect between PI4KA_rs165854 and GRM3_rs1468412 polymorphisms and incomplete antipsychotic response in schizophrenia patients with low severity of illness (OR = 12.4; 95%CI = 3.69-41.69). Further, this interaction was also observed in atypical monotherapy (n = 355) and risperidone (n = 260) treatment subgroups (OR = 11.21; 95%CI = 3.30-38.12 and OR = 13.5; 95%CI = 3.03-121.61 respectively). PI4KA is known to be involved in the biosynthesis of phosphatidylinositol-4, 5-bisphosphate which regulates exocytotic fusion of synaptic vesicles (glutamate, dopamine) with the plasma membrane and regulates duration of signal transduction of GPCRs. Whereas GRM3 regulates glutamate and dopamine transmission. Present findings indicate that PI4KA and GRM3 polymorphisms have potential to jointly modulate antipsychotic response. These results warrant additional replication studies to shed further light on these interactions.

Antipsychotic treatment modulates glutamate transport and NMDA receptor expression

Schizophrenia patients often suffer from treatment-resistant cognitive and negative symptoms, both of which are influenced by glutamate neurotransmission. Innovative therapeutic strategies such as agonists at metabotropic glutamate receptors or glycin reuptake inhibitors try to modulate the brain's glutamate network. Interactions of amino acids with monoamines have been described on several levels, and first- and second-generation antipsychotic agents (FGAs, SGAs) are known to exert modulatory effects on the glutamatergic system. This review summarizes the current knowledge on effects of FGAs and SGAs on glutamate transport and receptor expression derived from pharmacological studies. Such studies serve as a control for molecular findings in schizophrenia brain tissue and are clinically relevant. Moreover, they may validate animal models for psychosis, foster basic research on antipsychotic substances and finally lead to a better understanding of how monoaminergic and amino acid neurotransmissions are intertwined. In the light of these results, important differences dependent on antipsychotic substances, dosage and duration of treatment became obvious. While some post-mortem findings might be confounded with multifold drug effects, others are unlikely to be influenced by antipsychotic treatment and could represent important markers of schizophrenia pathophysiology. In similarity to the convergence of toxic and psychotomimetic effects of dopaminergic, serotonergic and anti-glutamatergic substances, the therapeutic mechanisms of SGAs might merge on a yet to be defined molecular level. In particular, serotonergic effects of SGAs, such as an agonism at 5HT1A receptors, represent important targets for further clinical research.

Sleep spindle deficits in antipsychotic-naïve early course schizophrenia and in non-psychotic first-degree relatives

INTRODUCTION

Chronic medicated patients with schizophrenia have marked reductions in sleep spindle activity and a correlated deficit in sleep-dependent memory consolidation. Using archival data, we investigated whether antipsychotic-naïve early course patients with schizophrenia and young non-psychotic first-degree relatives of patients with schizophrenia also show reduced sleep spindle activity and whether spindle activity correlates with cognitive function and symptoms.

METHOD

Sleep spindles during Stage 2 sleep were compared in antipsychotic-naïve adults newly diagnosed with psychosis, young non-psychotic first-degree relatives of schizophrenia patients and two samples of healthy controls matched to the patients and relatives. The relations of spindle parameters with cognitive measures and symptom ratings were examined.

RESULTS

Early course schizophrenia patients showed significantly reduced spindle activity relative to healthy controls and to early course patients with other psychotic disorders. Relatives of schizophrenia patients also showed reduced spindle activity compared with controls. Reduced spindle activity correlated with measures of executive function in early course patients, positive symptoms in schizophrenia and IQ estimates across groups.

CONCLUSIONS

Like chronic medicated schizophrenia patients, antipsychotic-naïve early course schizophrenia patients and young non-psychotic relatives of individuals with schizophrenia have reduced sleep spindle activity. These findings indicate that the spindle deficit is not an antipsychotic side-effect or a general feature of psychosis. Instead, the spindle deficit may predate the onset of schizophrenia, persist throughout its course and be an endophenotype that contributes to cognitive dysfunction.

Applications of blood-based protein biomarker strategies in the study of psychiatric disorders

Major psychiatric disorders such as schizophrenia, major depressive and bipolar disorders are severe, chronic and debilitating, and are associated with high disease burden and healthcare costs. Currently, diagnoses of these disorders rely on interview-based assessments of subjective self-reported symptoms. Early diagnosis is difficult, misdiagnosis is a frequent occurrence and there are no objective tests that aid in the prediction of individual responses to treatment. Consequently, validated biomarkers are urgently needed to help address these unmet clinical needs. Historically, psychiatric disorders are viewed as brain disorders and consequently only a few researchers have as yet evaluated systemic changes in psychiatric patients. However, promising research has begun to challenge this concept and there is an increasing awareness that disease-related changes can be traced in the peripheral system which may even be involved in the precipitation of disease onset and course. Converging evidence from molecular profiling analysis of blood serum/plasma have revealed robust molecular changes in psychiatric patients, suggesting that these disorders may be detectable in other systems of the body such as the circulating blood. In this review, we discuss the current clinical needs in psychiatry, highlight the importance of biomarkers in the field, and review a representative selection of biomarker studies to highlight opportunities for the implementation of personalized medicine approaches in the field of psychiatry. It is anticipated that the implementation of validated biomarker tests will not only improve the diagnosis and more effective treatment of psychiatric patients, but also improve prognosis and disease outcome.

Effect of early stress on hippocampal gray matter is influenced by a functional polymorphism in EAAT2 in bipolar disorder

Current views on the pathogenesis of psychiatric disorders focus on the interplay between genetic and environmental factors, with individual variation in vulnerability and resilience to hazards being part of the multifactorial development of illness. The aim of the study is to investigate the effect of glutamate transporter polymorphism SLC1A2-181A>C and exposure to Adverse Childhood Experiences (ACE) on hippocampal gray matter volume of patients with bipolar disorder (BD). Patients exposed to higher levels of ACE reported lower gray matter volume. The effect of SLC1A2-181A>C revealed itself only among patients exposed to lower levels of ACE, with T/T homozygotes showing the lowest, and G/G the highest, gray matter volume. The greatest difference between high and low exposures to ACE was observed in carriers of the G allele. Since the mutant G allele has been associated with a reduced transcriptional activity and expression of the transporter protein, we could hypothesize that after exposure to highest levels of ACE G/G homozygotes are more vulnerable to stress reporting the highest brain damage as a consequence of an excess of free glutamate.

Changes in the expression of the glutamate transporter EAAT3/EAAC1 in health and disease

Excitatory amino acid transporters (EAATs) are high-affinity Na(+)-dependent carriers of major importance in maintaining glutamate homeostasis in the central nervous system. EAAT3, the human counterpart of the rodent excitatory amino acid carrier 1 (EAAC1), is encoded by the SLC1A1 gene. EAAT3/EAAC1 is ubiquitously expressed in the brain, mostly in neurons but also in other cell types, such as oligodendrocyte precursors. While most of the glutamate released in the synapses is taken up by the "glial-type" EAATs, EAAT2 (GLT-1 in rodents) and EAAT1 (GLAST), the functional role of EAAT3/EAAC1 is related to the subtle regulation of glutamatergic transmission. Moreover, because it can also transport cysteine, EAAT3/EAAC1 is believed to be important for the synthesis of intracellular glutathione and subsequent protection from oxidative stress. In contrast to other EAATs, EAAT3/EAAC1 is mostly intracellular, and several mechanisms have been described for the rapid regulation of the membrane trafficking of the transporter. Moreover, the carrier interacts with several proteins, and this interaction modulates transport activity. Much less is known about the slow regulatory mechanisms acting on the expression of the transporter, although several recent reports have identified changes in EAAT3/EAAC1 protein level and activity related to modulation of its expression at the gene level. Moreover, EAAT3/EAAC1 expression is altered in pathological conditions, such as hypoxia/ischemia, multiple sclerosis, schizophrenia, and epilepsy. This review summarizes these results and provides an overall picture of changes in EAAT3/EAAC1 expression in health and disease.

Abnormal partitioning of hexokinase 1 suggests disruption of a glutamate transport protein complex in schizophrenia

Excitatory amino acid transporter 2 (EAAT2) belongs to a family of Na(+) dependent glutamate transporters that maintain a low synaptic concentration of glutamate by removing glutamate from the synaptic cleft into astroglia and neurons. EAAT2 activity depends on Na(+) and K(+) gradients generated by Na(+)/K(+) ATPase and ATP. Hexokinase 1 (HK1), an initial enzyme of glycolysis, binds to mitochondrial outer membrane where it couples cytosolic glycolysis to mitochondrial oxidative phosphorylation, producing ATP utilized by the EAAT2/Na(+)/K(+) ATPase protein complex to facilitate glutamate reuptake. In this study, we hypothesized that the protein complex formed by EAAT2, Na(+)/K(+) ATPase and mitochondrial proteins in human postmortem prefrontal cortex may be disrupted, leading to abnormal glutamate transmission in schizophrenia. We first determined that EAAT2, Na(+)/K(+) ATPase, HK1 and aconitase were found in both EAAT2 and Na(+)/K(+) ATPase interactomes by immunoisolation and mass spectrometry in human postmortem prefrontal cortex. Next, we measured levels of glutamate transport complex proteins in subcellular fractions in the dorsolateral prefrontal cortex and found increases in the EAAT2B isoform of EAAT2 in a fraction containing extrasynaptic membranes and increased aconitase 1 in a mitochondrial fraction. Finally, an increased ratio of HK1 protein in the extrasynaptic membrane/mitochondrial fraction was found in subjects with schizophrenia, suggesting that HK1 protein is abnormally partitioned in this illness. Our findings indicate that the integrity of the glutamate transport protein complex may be disrupted, leading to decreased perisynaptic buffering and reuptake of glutamate, as well as impaired energy metabolism in schizophrenia.

Effect of glutamate transporter EAAT2 gene variants and gray matter deficits on working memory in schizophrenia

Glutamate is the major excitatory neurotransmitter in the brain, with up to 40% of all synapses being glutamatergic. An altered glutamatergic transmission could play a critical role in working memory deficts observed in schizophrenia and could underline progressive changes such as grey matter loss throughout the brain. The aim of the study was to investigate if gray matter volume and working memory could be modulated by a genetic polymorphism related to glutamatergic function. Fifty schizophrenia patients underwent magnetic resonance and working memory testing outside of the scanner and were genotyped for rs4354668 EAAT2 polymorphism. Carriers of the G allele had lower gray matter volumes than T/T homozygote and worse working memory performance. Poor working memory performance was associated with gray matter reduction. Differences between the three genotypes are more relevant among patients showing poor performance at the 2-back task. Since glutamate abnormalities are known to be involved in excitotoxic processes, the decrease in cortical thickness observed in schizophrenia patients could be linked to an excess of extracellular glutamate. The differential effect of EAAT2 observed between good and poor performers suggests that the effect of EEAT2 on gray matter might reveal in the presence of a pathological process affecting gray matter.

Neuropsychiatric autoimmune encephalitis without VGKC-complex, NMDAR, and GAD autoantibodies: case report and literature review

We report a patient with a seronegative autoimmune panencephalitis, adding a subtype to the emerging spectrum of seronegative autoimmune encephalitis, and we review the sparse literature on isolated psychiatric presentations of autoimmune encephalitis. (A PubMed search for "seronegative autoimmune encephalitis," "nonvasculitic autoimmune inflammatory meningoencephalitis," and related terms revealed <25 cases.) A 15-year-old girl developed an acute-onset isolated psychosis with prominent negative symptoms and intermittent encephalopathy. Despite clinical worsening, her brain magnetic resonance imaging (MRI) scans remained normal for 7 years. Serology was negative for voltage-gated potassium channel (VGKC)-complex, N-methyl-D-aspartate receptor (NMDAR), and glutamic acid decarboxylase (GAD) autoantibodies. We excluded genetic, metabolic, paraneoplastic, degenerative, and infectious etiologies. The patient's symptoms remitted fully with immune therapy, but recurred in association with widespread bihemispheric brain lesions. Brain biopsy revealed mild nonvasculitic inflammation and prominent vascular hyalinization. Immune therapy with plasma exchanges cleared the MRI abnormalities but, 10 years after onset, the patient still suffers neuropsychiatric sequelae. We conclude that autoimmune panencephalitis seronegative for VGKC-complex, NMDAR, and GAD autoantibodies is a subtype of autoimmune encephalitis that can present with pure neuropsychiatric features and a normal brain MRI. Immunologic mechanisms may account for psychiatric symptoms in a subset of patients now diagnosed with classical psychotic disorders. Delay in starting immune therapy can lead to permanent neuropsychiatric sequelae. We propose a standardized classification system for the autoimmune encephalitides, integrating earlier pathology-oriented terms with more recently defined serologic and clinical phenotypes.

Gene expression of glutamate transporters SLC1A1, SLC1A3 and SLC1A6 in the cerebellar subregions of elderly schizophrenia patients and effects of antipsychotic treatment

OBJECTIVES

The glutamatergic hypothesis of schizophrenia proposes alterations of excitatory amino acid transporters (solute carrier family, SLCs) expression and cerebellar dysfunctions. The influence of the neuregulin-1 (NRG1) risk genotype or effects of antipsychotics on expression of EAATs are unknown.

METHODS

We compared post-mortem samples from the cerebellar hemispheres and vermis of 10 schizophrenia patients with nine normal subjects by investigating gene expression of SLC1A3, SLC1A1 and SLC1A6 by in-situ hybridization. We further assessed the allelic composition regarding the polymorphism rs35753505 (SNP8NRG221533) near the NRG1 gene. To control for effects due to antipsychotic treatment, we chronically treated rats with the antipsychotics haloperidol or clozapine and assessed gene expression of SLCs.

RESULTS

Schizophrenia patients showed increased expression of SLC1A3 in the molecular layer of the vermis. Individuals carrying at least one C allele of rs35753505 (SNP8NRG221533) showed decreased expression of SLC1A6 in the molecular layer of both hemispheres, compared to individuals homozygous for the T allele. The animal model revealed suppression of SLC1A6 by clozapine.

CONCLUSIONS

Increased SLC1A3 expression indicates facilitated transport and may result in reduced glutamate neurotransmission. Decreased SLC1A6 expression in NRG1 risk variant may be an adaptive effect to restore glutamate signalling, but treatment effects cannot be excluded.