The environment and susceptibility to schizophrenia

Animal models of schizophrenia

Developing reliable, predictive animal models for complex psychiatric disorders, such as schizophrenia, is essential to increase our understanding of the neurobiological basis of the disorder and for the development of novel drugs with improved therapeutic efficacy. All available animal models of schizophrenia fit into four different induction categories: developmental, drug-induced, lesion or genetic manipulation, and the best characterized examples of each type are reviewed herein. Most rodent models have behavioural phenotype changes that resemble 'positive-like' symptoms of schizophrenia, probably reflecting altered mesolimbic dopamine function, but fewer models also show altered social interaction, and learning and memory impairment, analogous to negative and cognitive symptoms of schizophrenia respectively. The negative and cognitive impairments in schizophrenia are resistant to treatment with current antipsychotics, even after remission of the psychosis, which limits their therapeutic efficacy. The MATRICS initiative developed a consensus on the core cognitive deficits of schizophrenic patients, and recommended a standardized test battery to evaluate them. More recently, work has begun to identify specific rodent behavioural tasks with translational relevance to specific cognitive domains affected in schizophrenia, and where available this review focuses on reporting the effect of current and potential antipsychotics on these tasks. The review also highlights the need to develop more comprehensive animal models that more adequately replicate deficits in negative and cognitive symptoms. Increasing information on the neurochemical and structural CNS changes accompanying each model will also help assess treatments that prevent the development of schizophrenia rather than treating the symptoms, another pivotal change required to enable new more effective therapeutic strategies to be developed.

Reduced ventricular proliferation in the foetal cortex following maternal inflammation in the mouse

It has been well established that maternal inflammation during pregnancy alters neurological function in the offspring, but its impact on cortical development and long-term consequences on the cytoarchitecture is largely unstudied. Here we report that lipopolysaccharide-induced systemic maternal inflammation in C57Bl/6 mice at embryonic Day 13.5 of pregnancy, as early as 8 h after challenge, caused a significant reduction in cell proliferation in the ventricular zone of the developing cerebral cortex, as revealed by quantification of anti-phospho-Histone H3 immunoreactivity and bromodeoxyuridine pulse labelling. The angle of mitotic cleavage, determined from analysis of haematoxylin and eosin staining, cyclin E1 gene expression and the pattern of β-catenin immunoreactivity were also altered by the challenge, which suggests a change from symmetric to asymmetric division in the radial progenitor cells. Modifications of cortical lamination and gene expression patterns were detected at post-natal Day 8 suggesting prolonged consequences of these alterations during embryonic development. Cellular uptake of proteins from the cerebrospinal fluid was observed in brains from lipopolysaccharide-treated animals in radial progenitor cells. However, the foetal blood–brain barrier to plasma proteins remained intact. Together, these results indicate that maternal inflammation can disrupt the ventricular surface and lead to decreased cellular proliferation. Changes in cell density in Layers IV and V at post-natal Day 8 show that these initial changes have prolonged effects on cortical organization. The possible shift in the fate of progeny and the resulting alterations in the relative cell numbers in the cerebral cortex following a maternal inflammatory response shown here will require further investigation to determine the long-term consequences of inflammation on the development of neuronal circuitry and behaviour.

Translational research approach to biological and modifiable risk factors of psychosis and affective disorders

OBJECTIVES

This review summarizes the literature on (molecular-) biological, medical, environmental and modifiable risk factors for psychosis and mood disorders with the view of their suitability for translational research and mental health practice from preventative and clinical treatment perspectives.

METHODS

This review summarized literature on biological, medical, environmental and modifiable risk factors for psychosis and mood disorders evaluating their potential for translational research and clinical practice.

RESULTS

Based on the concept of the gene - environment interaction in the development of mental disorders, we highlight the numerous risk factors reported to contribute to an increased susceptibility to schizophrenia and mood disorders of young adults to late-life. Special emphasis is placed onto the discussion on the requirement of translational and interdisciplinary research approaches integrating basic and clinical neuroscience approaches that may have important implications for future studies and clinical practice.

CONCLUSIONS

Interdisciplinary research approaches integrating developmental neuroscience and policy makers are encouraged in order to achieve effective prevention and intervention programs addressing environmental, behavioural, biological factors relevant to psychiatric disorders during young ages, adulthood and aging.

Translational epidemiology in psychiatry: linking population to clinical and basic sciences

Translational research generally refers to the application of knowledge generated by advances in basic sciences research translated into new approaches for diagnosis, prevention, and treatment of disease. This direction is called bench-to-bedside. Psychiatry has similarly emphasized the basic sciences as the starting point of translational research. This article introduces the term translational epidemiology for psychiatry research as a bidirectional concept in which the knowledge generated from the bedside or the population can also be translated to the benches of laboratory science. Epidemiologic studies are primarily observational but can generate representative samples, novel designs, and hypotheses that can be translated into more tractable experimental approaches in the clinical and basic sciences. This bedside-to-bench concept has not been explicated in psychiatry, although there are an increasing number of examples in the research literature. This article describes selected epidemiologic designs, providing examples and opportunities for translational research from community surveys and prospective, birth cohort, and family-based designs. Rapid developments in informatics, emphases on large sample collection for genetic and biomarker studies, and interest in personalized medicine--which requires information on relative and absolute risk factors--make this topic timely. The approach described has implications for providing fresh metaphors to communicate complex issues in interdisciplinary collaborations and for training in epidemiology and other sciences in psychiatry.

Impact of early adverse experience on complexity of adult-generated neurons

New neurons continue to be generated in the dentate gyrus (DG) region of the hippocampus throughout adulthood, and abnormal regulation of this process has emerged as an endophenotype common to several psychiatric disorders. Previous research shows that genetic risk factors associated with schizophrenia alter the maturation of adult-generated neurons. Here, we investigate whether early adversity, a potential environmental risk factor, similarly influences adult neurogenesis. During the first 2 weeks of postnatal life, mice were subject to repeated and unpredictable periods of separation from their mothers. When the mice reached adulthood, pharmacological and retroviral labelling techniques were used to assess the generation and maturation of new neurons. We found that adult mice that were repeatedly separated from their mothers early in life had similar rates of proliferation in the DG, but had fewer numbers of cells that survived and differentiated into neurons. Furthermore, neurons generated in adulthood had less complex dendritic arborization and fewer dendritic spines. These findings indicate that early adverse experience has a long-lasting impact on both the number and the complexity of adult-generated neurons in the hippocampus, suggesting that the abnormal regulation of adult neurogenesis associated with psychiatric disorders could arise from environmental influence alone, or from complex interactions of environmental factors with genetic predisposition.

Maternal-fetal blood incompatibility and neuromorphologic anomalies in schizophrenia: Preliminary findings

Prior research has shown that maternal-fetal Rhesus (Rh) and ABO blood incompatibility increase the risk for schizophrenia. In the present study, the relationship between blood incompatibility and volumes of brain structures previously implicated in schizophrenia was assessed in schizophrenia cases and controls from a large birth cohort. Rh/ABO incompatible cases had significantly reduced cortical gray matter volume compared to compatible cases, a finding which appears to be driven by significant volume reductions in the dorsolateral prefrontal cortex and inferior frontal cortex. Larger hippocampal and putamen volumes were also observed in exposed controls compared to unexposed controls. Although the sample size is small and replications are required, these data suggest that maternal-fetal blood incompatibility may increase the risk for altered brain morphology in both schizophrenia and in controls. The findings also suggest that the larger hippocampal volume in exposed controls may indicate a mechanism of adaptive resilience which diminishes the risk that controls will develop schizophrenia.

Schizophrenia and autism: both shared and disorder-specific pathogenesis via perinatal inflammation?

Prenatal exposure to infection and subsequent inflammatory responses have been implicated in the etiology of schizophrenia and autism. In this review, we summarize current evidence from human and animal studies supporting the hypothesis that the pathogenesis of these two disorders is linked via exposure to inflammation at early stages of development. Moreover, we propose a hypothetical model in which inflammatory mechanisms may account for multiple shared and disorder-specific pathological characteristics of both entities. In essence, our model suggests that acute neuroinflammation during early fetal development may be relevant for the induction of psychopathological and neuropathological features shared by schizophrenia and autism, whereas postacute latent and persistent inflammation may contribute to schizophrenia- and autism-specific phenotypes, respectively.

Epigenetic impacts on neurodevelopment: pathophysiological mechanisms and genetic modes of action

Disruptions of genes that are involved in epigenetic functions are known to be causative for several mental retardation/intellectual disability (MR/ID) syndromes. Recent work has highlighted genes with epigenetic functions as being implicated in autism spectrum disorders (ASDs) and schizophrenia (SCZ). The gene-environment interaction is an important factor of pathogenicity for these complex disorders. Epigenetic modifications offer a mechanism by which we can explain how the environment interacts with, and is able to dynamically regulate, the genome. This review aims to provide an overview of the role of epigenetic deregulation in the etiopathology for neurodevelopment disease.

Prenatal exposure to a viral mimetic alters behavioural flexibility in male, but not female, rats

Current understanding of the etiology of neurodevelopmental disorders is limited; however, recent epidemiological studies demonstrate a strong correlation between prenatal infection during pregnancy and the development of schizophrenia in adult offspring. In particular, schizophrenia patients subjected to prenatal infection exhibit impairments in executive functions greater than schizophrenia patients not exposed to an infection while in utero. Acute prenatal treatment of rodents with the viral mimetic polyinosinic-polycytidylic acid (PolyI:C) induces behavioural and neuropathological alterations in the adult offspring similar to schizophrenia. However, impairments on tasks of executive function that involve the prefrontal cortex (PFC) have been rarely examined for the prenatal infection model. Hence, we investigated the effects of acute prenatal injection of PolyI:C (4.0 mg/kg, i.v., gestational day 15) on strategy set-shifting and reversal learning in an operant-based task. Our results show male, but not female, PolyI:C-treated adult offspring require more trials to reach criterion and perseverate during set-shifting. An opposite pattern was seen on the reversal day where the PolyI:C-treated male rats made fewer regressive errors. Females took more pre-training days and were slower to respond during the trials when compared to males regardless of prenatal treatment. The present findings validate the utility of the prenatal infection model for examining alterations of executive function, one of the most prominent cognitive symptoms of schizophrenia.