Altered NMDA receptor expression and behavior following postnatal hypoxia: potential relevance to schizophrenia

Effects of the PAM of mGluR2, JNJ-46356479, on brain apoptotic protein levels in a mouse model of schizophrenia

Current treatment for schizophrenia (SZ) ameliorates the positive symptoms, but is inefficient in treating the negative and cognitive symptoms. The SZ glutamatergic dysfunction hypothesis has opened new avenues in the development of novel drugs targeting the glutamate storm, an inducer of progressive neuropathological changes. Positive allosteric modulators of metabotropic glutamate receptor 2 (mGluR2), such as JNJ-46356479 (JNJ), reduce the presynaptic release of glutamate, which has previously been demonstrated to attenuate glutamate- and dopamine-induced apoptosis in human neuroblastoma cell cultures. We hypothesised that JNJ treatment would modify the brain levels of apoptotic proteins in a mouse model of ketamine (KET)-induced schizophrenia. We analysed the levels of proapoptotic (caspase-3 and Bax) and antiapoptotic (Bcl-2) proteins by western blot in the prefrontal cortex and hippocampus of JNJ-treated mice. JNJ attenuated apoptosis in the brain by partially restoring the levels of the antiapoptotic Bcl-2 protein, which is significantly reduced in animals exposed to KET. Additionally, a significant inverse correlation was observed between proapoptotic protein levels and behavioural deficits in the mice. Our findings suggest that JNJ may attenuate brain apoptosis in vivo, as previously described in cell cultures, providing a link between neuropathological deficits and SZ symptomatology.

14-3-3 proteins at the crossroads of neurodevelopment and schizophrenia

The 14-3-3 family comprises multifunctional proteins that play a role in neurogenesis, neuronal migration, neuronal differentiation, synaptogenesis and dopamine synthesis. 14-3-3 members function as adaptor proteins and impact a wide variety of cellular and physiological processes involved in the pathophysiology of neurological disorders. Schizophrenia is a psychiatric disorder and knowledge about its pathophysiology is still limited. 14-3-3 have been proven to be linked with the dopaminergic, glutamatergic and neurodevelopmental hypotheses of schizophrenia. Further, research using genetic models has demonstrated the role played by 14-3-3 proteins in neurodevelopment and neuronal circuits, however a more integrative and comprehensive approach is needed for a better understanding of their role in schizophrenia. For instance, we still lack an integrated assessment of the processes affected by 14-3-3 proteins in the dopaminergic and glutamatergic systems. In this context, it is also paramount to understand their involvement in the biology of brain cells other than neurons. Here, we present previous and recent research that has led to our current understanding of the roles 14-3-3 proteins play in brain development and schizophrenia, perform an assessment of their functional protein association network and discuss the use of protein-protein interaction modulators to target 14-3-3 as a potential therapeutic strategy.

Application of animal experimental models in the research of schizophrenia

Schizophrenia is a relatively common but serious mental illness that results in a heavy burden to patients, their families, and society. The disease can be triggered by multiple factors, while the specific pathogenesis remains unclear. The development of effective therapeutic drugs for schizophrenia relies on a comprehensive understanding of the basic biology and pathophysiology of the disease. Therefore, effective animal experimental models play a vital role in the study of schizophrenia. Based on different molecular mechanisms and modeling methods, the currently used experimental animal experimental models of schizophrenia can be divided into four categories that can better simulate the clinical symptoms and the interplay between susceptible genes and the environment: neurodevelopmental, drug-induced, genetic-engineering, and genetic-environmental interaction of animal experimental models. Each of these categories contains multiple subtypes, which has its own advantages and disadvantages and therefore requires careful selection in a research application. The emergence and utilization of these models are promising in the prediction of the risk of schizophrenia at the molecular level, which will shed light on effective and targeted treatment at the genetic level.

Functional NMDA receptors are expressed by human pulmonary artery smooth muscle cells

N-methyl-d-aspartate (NMDA) receptors are widely expressed in the central nervous system. However, their presence and function at extraneuronal sites is less well characterized. In the present study, we examined the expression of NMDA receptor subunit mRNA and protein in human pulmonary artery (HPA) by quantitative polymerase chain reaction (PCR), immunohistochemistry and immunoblotting. We demonstrate that both GluN1 and GluN2 subunit mRNAs are expressed in HPA. In addition, GluN1 and GluN2 (A–D) subunit proteins are expressed by human pulmonary artery smooth muscle cells (HPASMCs) in vitro and in vivo. These subunits localize on the surface of HPASMCs and form functional ion channels as evidenced by whole-cell patch-clamp electrophysiology and reduced phenylephrine-induced contractile responsiveness of human pulmonary artery by the NMDA receptor antagonist MK801 under hypoxic condition. HPASMCs also express high levels of serine racemase and vesicular glutamate transporter 1, suggesting a potential source of endogenous agonists for NMDA receptor activation. Our findings show HPASMCs express functional NMDA receptors in line with their effect on pulmonary vasoconstriction, and thereby suggest a novel therapeutic target for pharmacological modulations in settings associated with pulmonary vascular dysfunction.

The origin of NMDA receptor hypofunction in schizophrenia

N-methyl-d-aspartate (NMDA) receptor (NMDAR) hypofunction plays a key role in pathophysiology of schizophrenia. Since NMDAR hypofunction has also been reported in autism, Alzheimer's disease and cognitive dementia, it is crucial to identify the location, timing, and mechanism of NMDAR hypofunction for schizophrenia for better understanding of disease etiology and for novel therapeutic intervention. In this review, we first discuss the shared underlying mechanisms of NMDAR hypofunction in NMDAR antagonist models and the anti-NMDAR autoantibody model of schizophrenia and suggest that NMDAR hypofunction could occur in GABAergic neurons in both models. Preclinical models using transgenic mice have shown that NMDAR hypofunction in cortical GABAergic neurons, in particular parvalbumin-positive fast-spiking interneurons, in the early postnatal period confers schizophrenia-related phenotypes. Recent studies suggest that NMDAR hypofunction can also occur in PV-positive GABAergic neurons with alterations of NMDAR-associated proteins, such as neuregulin/ErbB4, α7nAChR, and serine racemase. Furthermore, several environmental factors, such as oxidative stress, kynurenic acid and hypoxia, may also potentially elicit NMDAR hypofunction in GABAergic neurons in early postnatal period. Altogether, the studies discussed here support a central role for GABAergic abnormalities in the context of NMDAR hypofunction. We conclude by suggesting potential therapeutic strategies to improve the function of fast-spiking neurons.

Maternal stress, prenatal medical illnesses and obstetric complications: Risk factors for schizophrenia spectrum disorder, bipolar disorder and major depressive disorder

Maternal stress and medical illnesses during early life are well-documented environmental indicators of an increased risk of schizophrenia. Few studies, conversely, have confirmed an association with major affective disorders. The present study examined the impact of maternal stress, medical illnesses and obstetric complications on the development of severe mental disorder in 240 patients with a diagnosis of schizophrenia spectrum disorder, bipolar disorder, or major depressive disorder and matched with 85 controls. Mothers of participants were asked about stressful events during pregnancy using the Social Readjustment Scale; information on prenatal/perinatal illnesses were acquired from medical records. Schizophrenia spectrum disorder was positively associated with maternal stress (OR = 2.16), infections (OR = 7.67), inadequate weight gain (OR = 9.52) during pregnancy, and peripartum asphyxia (OR = 4.00). An increased risk of bipolar disorder was associated with head circumference < 32 cm at birth (OR = 5.40) and inversely with inadequate weight gain (OR = 0.29). Major depressive disorder diagnosis was inversely related to inadequate weight gain (OR = 0.22). These results support a role for maternal stress, medical illnesses and obstetric complications as risk factors for subsequent severe mental illness in adulthood. Further research is needed, especially with regard to affective disorders.

Perinatal Hypoxia and Ischemia in Animal Models of Schizophrenia

Intrauterine or perinatal complications constitute a major risk for psychiatric diseases. Infants who suffered from hypoxia-ischemia (HI) are at twofold risk to develop schizophrenia in later life. Several animal models attempt to reproduce these complications to study the yet unknown steps between an insult in early life and outbreak of the disease decades later. However, it is very challenging to find the right type and severity of insult leading to a disease-like phenotype in the animal, but not causing necrosis and focal neurological deficits. By contrast, too mild, repetitive insults may even be protective via conditioning effects. Thus, it is not surprising that animal models of hypoxia lead to mixed results. To achieve clinically translatable findings, better protocols are urgently needed. Therefore, we compare widely used models of hypoxia and HI and propose future directions for the field.

Cellular, synaptic, and circuit effects of antibodies in autoimmune CNS synaptopathies

Recently, clinicians have identified overlapping but distinguishable encephalitides, each associated with antibodies in serum and cerebrospinal fluid directed against specific cell surface proteins. The antibody targets identified to date are proteins that modulate cell physiology, synaptic transmission, and circuit function. Clinical and laboratory evidence suggests that the anti-cell surface antibodies are not simply markers of disease, but are pathogenic. Patient antibodies to N-methyl-d-aspartate (NMDA), α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), or gamma-aminobutyric acid-A (GABAA) receptors cause a loss of cognate receptors from synapses, while recent work has shown that antibodies to GABAB receptors directly antagonize receptor activity. Despite the distinct mechanisms by which patient antibodies abrogate the function of their targets, the resulting pathophysiology leads to abnormal circuit activity and plasticity, which manifests as patient signs and symptoms. Understanding the underlying synaptic and circuit mechanisms of patient autoantibody action may enable clinicians to develop diagnostics and therapies unique to each synaptic autoimmunity subtype, thereby improving patient identification and outcomes.

The impact of environmental factors in severe psychiatric disorders

During the last decades, schizophrenia has been regarded as a developmental disorder. The neurodevelopmental hypothesis proposes schizophrenia to be related to genetic and environmental factors leading to abnormal brain development during the pre- or postnatal period. First disease symptoms appear in early adulthood during the synaptic pruning and myelination process. Meta-analyses of structural MRI studies revealing hippocampal volume deficits in first-episode patients and in the longitudinal disease course confirm this hypothesis. Apart from the influence of risk genes in severe psychiatric disorders, environmental factors may also impact brain development during the perinatal period. Several environmental factors such as antenatal maternal virus infections, obstetric complications entailing hypoxia as common factor or stress during neurodevelopment have been identified to play a role in schizophrenia and bipolar disorder, possibly contributing to smaller hippocampal volumes. In major depression, psychosocial stress during the perinatal period or in adulthood is an important trigger. In animal studies, chronic stress or repeated administration of glucocorticoids have been shown to induce degeneration of glucocorticoid-sensitive hippocampal neurons and may contribute to the pathophysiology of affective disorders. Epigenetic mechanisms altering the chromatin structure such as histone acetylation and DNA methylation may mediate effects of environmental factors to transcriptional regulation of specific genes and be a prominent factor in gene-environmental interaction. In animal models, gene-environmental interaction should be investigated more intensely to unravel pathophysiological mechanisms. These findings may lead to new therapeutic strategies influencing epigenetic targets in severe psychiatric disorders.

Increased cell proliferation in the rat anterior cingulate cortex following neonatal hypoxia: relevance to schizophrenia

As a consequence of obstetric complications, neonatal hypoxia has been discussed as an environmental factor in the pathophysiology of schizophrenia. However, the biological consequences of hypoxia are unclear. The neurodevelopmental hypothesis of schizophrenia suggests that the onset of abnormal brain development and neuropathology occurs perinatally, whereas symptoms of the disease appear in early adulthood. In our animal model of chronic neonatal hypoxia, we have detected behavioral alterations resembling those known from schizophrenia. Disturbances in cell proliferation possibly contribute to the pathophysiology of this disease. In the present study, we used postnatal rats to investigate cell proliferation in several brain areas following neonatal hypoxia. Rats were repeatedly exposed to hypoxia (89 % N₂, 11 % O₂) from postnatal day (PD) 4–8. We then evaluated cell proliferation on PD 13 and 39, respectively. These investigations were performed in the anterior cingulate cortex (ACC), caudate-putamen (CPU), dentate gyrus, and subventricular zone. Rats exposed to hypoxia exhibited increased cell proliferation in the ACC at PD 13, normalizing at PD 39. In other brain regions, no alterations have been detected. Additionally, hypoxia-treated rats showed decreased CPU volume at PD 13. The results of the present study on the one hand support the assumption of chronic hypoxia influencing transient cell proliferation in the ACC, and on the other hand reveal normalization during ageing.

Differential expression of presynaptic genes in a rat model of postnatal hypoxia: relevance to schizophrenia

Obstetric complications play a role in the pathophysiology of schizophrenia. However, the biological consequences during neurodevelopment until adulthood are unknown. Microarrays have been used for expression profiling in four brain regions of a rat model of neonatal hypoxia as a common factor of obstetric complications. Animals were repeatedly exposed to chronic hypoxia from postnatal (PD) day 4 through day 8 and killed at the age of 150 days. Additional groups of rats were treated with clozapine from PD 120-150. Self-spotted chips containing 340 cDNAs related to the glutamate system ("glutamate chips") were used. The data show differential (up and down) regulations of numerous genes in frontal (FR), temporal (TE) and parietal cortex (PAR), and in caudate putamen (CPU), but evidently many more genes are upregulated in frontal and temporal cortex, whereas in parietal cortex the majority of genes are downregulated. Because of their primary presynaptic occurrence, five differentially expressed genes (CPX1, NPY, NRXN1, SNAP-25, and STX1A) have been selected for comparisons with clozapine-treated animals by qRT-PCR. Complexin 1 is upregulated in FR and TE cortex but unchanged in PAR by hypoxic treatment. Clozapine downregulates it in FR but upregulates it in PAR cortex. Similarly, syntaxin 1A was upregulated in FR, but downregulated in TE and unchanged in PAR cortex, whereas clozapine downregulated it in FR but upregulated it in PAR cortex. Hence, hypoxia alters gene expression regionally specific, which is in agreement with reports on differentially expressed presynaptic genes in schizophrenia. Chronic clozapine treatment may contribute to normalize synaptic connectivity.

Mechanisms underlying autoimmune synaptic encephalitis leading to disorders of memory, behavior and cognition: insights from molecular, cellular and synaptic studies

Recently, several novel, potentially lethal and treatment-responsive syndromes that affect hippocampal and cortical function have been shown to be associated with auto-antibodies against synaptic antigens, notably glutamate or GABA-B receptors. Patients with these auto-antibodies, sometimes associated with teratomas and other neoplasms, present with psychiatric symptoms, seizures, memory deficits and decreased levels of consciousness. These symptoms often improve dramatically after immunotherapy or tumor resection. Here we review studies of the cellular and synaptic effects of these antibodies in hippocampal neurons in vitro and preliminary work in rodent models. Our work suggests that patient antibodies lead to rapid and reversible removal of neurotransmitter receptors from synaptic sites, leading to changes in synaptic and circuit function that in turn are likely to lead to behavioral deficits. We also discuss several of the many questions raised by these and related disorders. Determining the mechanisms underlying these novel anti-neurotransmitter receptor encephalopathies will provide insights into the cellular and synaptic bases of the memory and cognitive deficits that are hallmarks of these disorders, and potentially suggest avenues for therapeutic intervention.

Gene-environment interaction and covariation in schizophrenia: the role of obstetric complications

While genetic factors account for a significant proportion of liability to schizophrenia, a body of evidence attests to a significant environmental contribution. Understanding the mechanisms through which genetic and environmental factors coalesce in influencing schizophrenia is critical for elucidating the pathways underlying psychotic illness and for developing primary prevention strategies. Although obstetric complications (OCs) remain among the most well-documented environmental indicators of risk for schizophrenia, the pathogenic role they play in the etiology of schizophrenia continues to remain poorly understood. A question of major importance is do these factors result from a genetic diathesis to schizophrenia (as in gene-environment covariation), act additively or interactively with predisposing genes for the disorder in influencing disease risk, or independently cause disease onset? In this review, we evaluate 3 classes of OCs commonly related to schizophrenia including hypoxia-associated OCs, maternal infection during pregnancy, and maternal stress during pregnancy. In addition, we discuss several mechanisms by which OCs impact on genetically susceptible brain regions, increasing constitutional vulnerability to neuromaturational events and stressors later in life (ie, adolescence), which may in turn contribute to triggering psychosis.

Realistic expectations of prepulse inhibition in translational models for schizophrenia research

INTRODUCTION

Under specific conditions, a weak lead stimulus, or "prepulse", can inhibit the startling effects of a subsequent intense abrupt stimulus. This startle-inhibiting effect of the prepulse, termed "prepulse inhibition" (PPI), is widely used in translational models to understand the biology of brainbased inhibitory mechanisms and their deficiency in neuropsychiatric disorders. In 1981, four published reports with "prepulse inhibition" as an index term were listed on Medline; over the past 5 years, new published Medline reports with "prepulse inhibition" as an index term have appeared at a rate exceeding once every 2.7 days (n=678). Most of these reports focus on the use of PPI in translational models of impaired sensorimotor gating in schizophrenia. This rapid expansion and broad application of PPI as a tool for understanding schizophrenia has, at times, outpaced critical thinking and falsifiable hypotheses about the relative strengths vs. limitations of this measure.

OBJECTIVES

This review enumerates the realistic expectations for PPI in translational models for schizophrenia research, and provides cautionary notes for the future applications of this important research tool.

CONCLUSION

In humans, PPI is not "diagnostic"; levels of PPI do not predict clinical course, specific symptoms, or individual medication responses. In preclinical studies, PPI is valuable for evaluating models or model organisms relevant to schizophrenia, "mapping" neural substrates of deficient PPI in schizophrenia, and advancing the discovery and development of novel therapeutics. Across species, PPI is a reliable, robust quantitative phenotype that is useful for probing the neurobiology and genetics of gating deficits in schizophrenia.

Neurogenesis and schizophrenia: dividing neurons in a divided mind?

Forty years after the initial discovery of neurogenesis in the postnatal brain of the rat, convincing evidence has been accrued that functional neurons are generated throughout the entire lifespan, particularly in the dentate gyrus (DG) and the subventricular zone (SVZ). This phenomenon has been termed adult neurogenesis (AN) and while it was detected in all examined mammalian species including humans, the physiological role of this process remains unknown. Although a plethora of animal studies indicate an involvement of AN in the pathophysiology of depression, this view has recently kindled considerable controversy. Pertinent studies in humans failed to confirm a role of reduced hippocampal neural stem cell proliferation (NSP) in depression but suggest a contribution to the pathophysiology of schizophrenia. The functional relevance of disturbed AN may encompass erroneous temporal encoding of new memory traces, thereby contributing to cognitive deficits observed in schizophrenia. This AN-hypothesis of schizophrenia is supported by neuroimaging, as well as by several genetically modified rodent models, e.g. reelin and NPAS3 knockout mice. Furthermore, several genes impacting on AN, including NPAS3, were also found to be associated with schizophrenia by case-control studies. In conclusion, several lines of evidence suggest that reduced AN may contribute to the etiopathogenesis of schizophrenic disorders, whereas it does not seem to be a critical risk factor for affective disorders.