Gene × Environment Interactions in Schizophrenia: Evidence from Genetic Mouse Models

The study of gene × environment, as well as epistatic interactions in schizophrenia, has provided important insight into the complex etiopathologic basis of schizophrenia. It has also increased our understanding of the role of susceptibility genes in the disorder and is an important consideration as we seek to translate genetic advances into novel antipsychotic treatment targets. This review summarises data arising from research involving the modelling of gene × environment interactions in schizophrenia using preclinical genetic models. Evidence for synergistic effects on the expression of schizophrenia-relevant endophenotypes will be discussed. It is proposed that valid and multifactorial preclinical models are important tools for identifying critical areas, as well as underlying mechanisms, of convergence of genetic and environmental risk factors, and their interaction in schizophrenia.

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title: The environment and susceptibility to schizophrenia
abstract: In the present article the putative role of environmental factors in schizophrenia is reviewed and synthesized. Accumulating evidence from recent studies suggests that environmental exposures may play a more significant role in the etiopathogenesis of this disorder than previously thought. This expanding knowledge base is largely a consequence of refinements in the methodology of epidemiologic studies, including birth cohort investigations, and in preclinical research that has been inspired by the evolving literature on animal models of environmental exposures. This paper is divided into four sections. In the first, the descriptive epidemiology of schizophrenia is reviewed. This includes general studies on incidence, prevalence, and differences in these measures by urban-rural, neighborhood, migrant, and season of birth status, as well as time trends. In the second section, we discuss the contribution of environmental risk factors acting during fetal and perinatal life; these include infections [e.g. rubella, influenza, Toxoplasma gondii (T. gondii), herpes simplex virus type 2 (HSV-2)], nutritional deficiencies (e.g., famine, folic acid, iron, vitamin D), paternal age, fetal/neonatal hypoxic and other obstetric insults and complications, maternal stress and other exposures [e.g. lead, rhesus (Rh) incompatibility, maternal stress]. Other putative neurodevelopmental determinants, including cannabis, socioeconomic status, trauma, and infections during childhood and adolescence are also covered. In the third section, these findings are synthesized and their implications for prevention and uncovering biological mechanisms, including oxidative stress, apoptosis, and inflammation, are discussed. Animal models, including maternal immune activation, have yielded evidence suggesting that these exposures cause brain and behavioral phenotypes that are analogous to findings observed in patients with schizophrenia. In the final section, future studies including new, larger, and more rigorous epidemiologic investigations, and research on translational and clinical neuroscience, gene-environment interactions, epigenetics, developmental trajectories and windows of vulnerability, are elaborated upon. These studies are aimed at confirming observed risk factors, identifying new environmental exposures, elucidating developmental mechanisms, and shedding further light on genes and exposures that may not be identified in the absence of these integrated approaches. The study of environmental factors in schizophrenia may have important implications for the identification of causes and prevention of this disorder, and offers the potential to complement, and refine, existing efforts on explanatory neurodevelopmental models.

title: Cognition and disability in bipolar disorder: lessons from schizophrenia research.
abstract: Cognitive and functional impairments occur in patients diagnosed with bipolar disorder (BPD), although they are usually less severe and far less studied than in schizophrenia. There may be value in applying approaches developed in schizophrenia research to study cognitive functioning among BPD patients in areas including performance-based disability assessment, cognitive remediation treatments, enhancement of the accuracy of real-world functioning, and studying cognition and disability in relatives.



We reviewed current research on cognitive and functional disability in BPD, noted areas of similarity and discrepancy to research on schizophrenia, and highlighted methods and approaches used to study schizophrenia that can be applied to study unmet needs of BPD patients.



Research in schizophrenia increasingly separates potential functional capacity from real-world outcome status, and has assessed contributions of cognitive impairment and other illness factors to functional outcomes. For schizophrenia, various behavioral and pharmacological treatments aimed at cognitive enhancement have been attempted, with moderate success, compared to rare studies of treatment effects on cognitive impairment in BPD. Very little research has been performed in the occurrence of cognitive impairments in first-degree relatives of people with BPD, despite evidence that cognitive impairments may be stable traits across symptomatic status in people with BPD.



Research and treatment approaches developed for schizophrenia can productively be applied to the study and treatment of patients diagnosed with BPD, notably including studies of the characteristics of and treatments for functional impairment related to cognitive deficits.

title: Cost of disorders of the brain in Europe 2010
abstract: The spectrum of disorders of the brain is large, covering hundreds of disorders that are listed in either the mental or neurological disorder chapters of the established international diagnostic classification systems. These disorders have a high prevalence as well as short- and long-term impairments and disabilities. Therefore they are an emotional, financial and social burden to the patients, their families and their social network. In a 2005 landmark study, we estimated for the first time the annual cost of 12 major groups of disorders of the brain in Europe and gave a conservative estimate of €386 billion for the year 2004. This estimate was limited in scope and conservative due to the lack of sufficiently comprehensive epidemiological and/or economic data on several important diagnostic groups. We are now in a position to substantially improve and revise the 2004 estimates. In the present report we cover 19 major groups of disorders, 7 more than previously, of an increased range of age groups and more cost items. We therefore present much improved cost estimates. Our revised estimates also now include the new EU member states, and hence a population of 514 million people.



To estimate the number of persons with defined disorders of the brain in Europe in 2010, the total cost per person related to each disease in terms of direct and indirect costs, and an estimate of the total cost per disorder and country.



The best available estimates of the prevalence and cost per person for 19 groups of disorders of the brain (covering well over 100 specific disorders) were identified via a systematic review of the published literature. Together with the twelve disorders included in 2004, the following range of mental and neurologic groups of disorders is covered: addictive disorders, affective disorders, anxiety disorders, brain tumor, childhood and adolescent disorders (developmental disorders), dementia, eating disorders, epilepsy, mental retardation, migraine, multiple sclerosis, neuromuscular disorders, Parkinson's disease, personality disorders, psychotic disorders, sleep disorders, somatoform disorders, stroke, and traumatic brain injury. Epidemiologic panels were charged to complete the literature review for each disorder in order to estimate the 12-month prevalence, and health economic panels were charged to estimate best cost-estimates. A cost model was developed to combine the epidemiologic and economic data and estimate the total cost of each disorder in each of 30 European countries (EU27+Iceland, Norway and Switzerland). The cost model was populated with national statistics from Eurostat to adjust all costs to 2010 values, converting all local currencies to Euro, imputing costs for countries where no data were available, and aggregating country estimates to purchasing power parity adjusted estimates for the total cost of disorders of the brain in Europe 2010.



The total cost of disorders of the brain was estimated at €798 billion in 2010. Direct costs constitute the majority of costs (37% direct healthcare costs and 23% direct non-medical costs) whereas the remaining 40% were indirect costs associated with patients' production losses. On average, the estimated cost per person with a disorder of the brain in Europe ranged between €285 for headache and €30,000 for neuromuscular disorders. The European per capita cost of disorders of the brain was €1550 on average but varied by country. The cost (in billion €PPP 2010) of the disorders of the brain included in this study was as follows: addiction: €65.7; anxiety disorders: €74.4; brain tumor: €5.2; child/adolescent disorders: €21.3; dementia: €105.2; eating disorders: €0.8; epilepsy: €13.8; headache: €43.5; mental retardation: €43.3; mood disorders: €113.4; multiple sclerosis: €14.6; neuromuscular disorders: €7.7; Parkinson's disease: €13.9; personality disorders: €27.3; psychotic disorders: €93.9; sleep disorders: €35.4; somatoform disorder: €21.2; stroke: €64.1; traumatic brain injury: €33.0. It should be noted that the revised estimate of those disorders included in the previous 2004 report constituted €477 billion, by and large confirming our previous study results after considering the inflation and population increase since 2004. Further, our results were consistent with administrative data on the health care expenditure in Europe, and comparable to previous studies on the cost of specific disorders in Europe. Our estimates were lower than comparable estimates from the US.



This study was based on the best currently available data in Europe and our model enabled extrapolation to countries where no data could be found. Still, the scarcity of data is an important source of uncertainty in our estimates and may imply over- or underestimations in some disorders and countries. Even though this review included many disorders, diagnoses, age groups and cost items that were omitted in 2004, there are still remaining disorders that could not be included due to limitations in the available data. We therefore consider our estimate of the total cost of the disorders of the brain in Europe to be conservative. In terms of the health economic burden outlined in this report, disorders of the brain likely constitute the number one economic challenge for European health care, now and in the future. Data presented in this report should be considered by all stakeholder groups, including policy makers, industry and patient advocacy groups, to reconsider the current science, research and public health agenda and define a coordinated plan of action of various levels to address the associated challenges.


RECOMMENDATIONS
Political action is required in light of the present high cost of disorders of the brain. Funding of brain research must be increased; care for patients with brain disorders as well as teaching at medical schools and other health related educations must be quantitatively and qualitatively improved, including psychological treatments. The current move of the pharmaceutical industry away from brain related indications must be halted and reversed. Continued research into the cost of the many disorders not included in the present study is warranted. It is essential that not only the EU but also the national governments forcefully support these initiatives.

title: The size and burden of mental disorders and other disorders of the brain in Europe 2010
abstract: To provide 12-month prevalence and disability burden estimates of a broad range of mental and neurological disorders in the European Union (EU) and to compare these findings to previous estimates. Referring to our previous 2005 review, improved up-to-date data for the enlarged EU on a broader range of disorders than previously covered are needed for basic, clinical and public health research and policy decisions and to inform about the estimated number of persons affected in the EU.



Stepwise multi-method approach, consisting of systematic literature reviews, reanalyses of existing data sets, national surveys and expert consultations. Studies and data from all member states of the European Union (EU-27) plus Switzerland, Iceland and Norway were included. Supplementary information about neurological disorders is provided, although methodological constraints prohibited the derivation of overall prevalence estimates for mental and neurological disorders. Disease burden was measured by disability adjusted life years (DALY).



Prevalence: It is estimated that each year 38.2% of the EU population suffers from a mental disorder. Adjusted for age and comorbidity, this corresponds to 164.8million persons affected. Compared to 2005 (27.4%) this higher estimate is entirely due to the inclusion of 14 new disorders also covering childhood/adolescence as well as the elderly. The estimated higher number of persons affected (2011: 165m vs. 2005: 82m) is due to coverage of childhood and old age populations, new disorders and of new EU membership states. The most frequent disorders are anxiety disorders (14.0%), insomnia (7.0%), major depression (6.9%), somatoform (6.3%), alcohol and drug dependence (>4%), ADHD (5%) in the young, and dementia (1-30%, depending on age). Except for substance use disorders and mental retardation, there were no substantial cultural or country variations. Although many sources, including national health insurance programs, reveal increases in sick leave, early retirement and treatment rates due to mental disorders, rates in the community have not increased with a few exceptions (i.e. dementia). There were also no consistent indications of improvements with regard to low treatment rates, delayed treatment provision and grossly inadequate treatment.  Disorders of the brain and mental disorders in particular, contribute 26.6% of the total all cause burden, thus a greater proportion as compared to other regions of the world. The rank order of the most disabling diseases differs markedly by gender and age group; overall, the four most disabling single conditions were: depression, dementias, alcohol use disorders and stroke.



In every year over a third of the total EU population suffers from mental disorders. The true size of "disorders of the brain" including neurological disorders is even considerably larger. Disorders of the brain are the largest contributor to the all cause morbidity burden as measured by DALY in the EU. No indications for increasing overall rates of mental disorders were found nor of improved care and treatment since 2005; less than one third of all cases receive any treatment, suggesting a considerable level of unmet needs. We conclude that the true size and burden of disorders of the brain in the EU was significantly underestimated in the past. Concerted priority action is needed at all levels, including substantially increased funding for basic, clinical and public health research in order to identify better strategies for improved prevention and treatment for disorders of the brain as the core health challenge of the 21st century.

title: Epidemiology, clinical consequences, and psychosocial treatment of nonadherence in schizophrenia.
abstract: Partial adherence and nonadherence to medication continue to be problems in the treatment of patients with schizophrenia. Nonadherence to medication has a negative impact on the course of illness for these patients as is shown by data on relapse, rehospitalization, time to remission, and attempted suicide. Several factors that contribute to poor adherence have been identified and need to be taken into account when attempting to address the problem of nonadherence. These risk factors relate to the patient, his or her illness and social situation, and the physician. Among the measures that have the potential to improve adherence to medication are psychosocial interventions, psychoeducation in the form of professional, peer-to-peer or family-to-family interventions, and shared decision making.

title: Neurodevelopmental model of schizophrenia: update 2012
abstract: The neurodevelopmental model of schizophrenia, which posits that the illness is the end state of abnormal neurodevelopmental processes that started years before the illness onset, is widely accepted, and has long been dominant for childhood-onset neuropsychiatric disorders. This selective review updates our 2005 review of recent studies that have impacted, or have the greatest potential to modify or extend, the neurodevelopmental model of schizophrenia. Longitudinal whole-population studies support a dimensional, rather than categorical, concept of psychosis. New studies suggest that placental pathology could be a key measure in future prenatal high-risk studies. Both common and rare genetic variants have proved surprisingly diagnostically nonspecific, and copy number variants (CNVs) associated with schizophrenia are often also associated with autism, epilepsy and intellectual deficiency. Large post-mortem gene expression studies and prospective developmental multi-modal brain imaging studies are providing critical data for future clinical and high-risk developmental brain studies. Whether there can be greater molecular specificity for phenotypic characterization is a subject of current intense study and debate, as is the possibility of neuronal phenotyping using human pluripotent-inducible stem cells. Biological nonspecificity, such as in timing or nature of early brain development, carries the possibility of new targets for broad preventive treatments.

title: Large-scale genomics unveils the genetic architecture of psychiatric disorders
abstract: Family study results are consistent with genetic effects making substantial contributions to risk of psychiatric disorders such as schizophrenia, yet robust identification of specific genetic variants that explain variation in population risk had been disappointing until the advent of technologies that assay the entire genome in large samples. We highlight recent progress that has led to a better understanding of the number of risk variants in the population and the interaction of allele frequency and effect size. The emerging genetic architecture implies a large number of contributing loci (that is, a high genome-wide mutational target) and suggests that genetic risk of psychiatric disorders involves the combined effects of many common variants of small effect, as well as rare and de novo variants of large effect. The capture of a substantial proportion of genetic risk facilitates new study designs to investigate the combined effects of genes and the environment.

title: Psychiatric genetics: progress amid controversy
abstract: Several psychiatric disorders — such as bipolar disorder, schizophrenia and autism — are highly heritable, yet identifying their genetic basis has been challenging, with most discoveries failing to be replicated. However, inroads have been made by the incorporation of intermediate traits (endophenotypes) and of environmental factors into genetic analyses, and through the identification of rare inherited variants and novel structural mutations. Current efforts aim to increase sample sizes by gathering larger samples for case–control studies or through meta-analyses of such studies. More attention on unique families, rare variants, and on incorporating environment and the emerging knowledge of biological function and pathways into genetic analysis is warranted.

title: Misconceptions about gene-environment interactions in psychiatry.
abstract: Misunderstandings surrounding the study of gene-environment interactions are very common. Given the large increase in the number of studies examining interactions in recent years, this raises serious concerns about the value of time and resources spent in these endeavours. In this article we discuss why, despite frequent claims to the contrary, studies of gene-environment interactions are very unlikely to enhance our understanding of disease aetiology or prevention.

title: Practitioner review: A critical perspective on gene-environment interaction models--what impact should they have on clinical perceptions and practice?
abstract: Psychiatric disorders run in families, and early twin, family and adoption studies confirmed that this was due in part to shared genetic inheritance. While candidate gene studies largely failed to reliably identify genetic variants associated with psychiatric disorders, genome-wide association studies are beginning to do so. However, the proportion of phenotypic variance explained remains well below what would be expected from previous heritability estimates.



We review possible reasons for this 'missing heritability', and whether incorporating gene by environment interactions into our models will substantially improve our understanding of the aetiology of psychiatric disorders, and inform clinical perceptions and practice.



We discuss potential limitations of the gene by environment interaction approach. In particular, we discuss whether these are likely to be a major contributor to psychiatric disorders at the level of the specific interaction (as opposed to at an aggregate level).



Gene by environment interaction studies offered initial promise that a far greater proportion of phenotypic variance could be explained by incorporating measures of environmental exposures into genetic studies. However, in our opinion, there are few (if any) clear examples of gene by environment interactions in psychiatry, and their scope for informing either our understanding of disease pathology or clinical practice remains limited at present.

title: A review of the evidence from family, twin and adoption studies for a genetic contribution to adult psychiatric disorders
abstract: Family, twin and adoption studies have provided major evidence for the role of genetics in numerous psychiatric disorders including obsessive-compulsive disorder, panic disorder, major depressive disorder, bipolar disorder, schizophrenia and Alzheimer's disease. As the search for patterns of inheritance and candidate genes of these complex disorders continues, we review relevant findings from quantitative genetic studies and outline the main challenges for the field of psychiatric genetics to focus on in order to more definitively establish the underpinnings of genetic and environmental influences of adult psychopathology.

title: Genetically mediated vulnerability to schizophrenia.
abstract: Family, twin, and adoption studies have firmly established the genetic basis for a majority of cases of schizophrenia. Several other psychiatric disorders probably represent alternative manifestations of this genetic liability. The underlying genetic mechanisms are not yet well understood, but the development of schizophrenia appears to involve a system of genes that interact with pre- and postnatal stressors. Recent reports of genetic linkage in schizophrenia have not been replicated, but the potential of molecular genetic technology makes us optimistic that the bases of this complex disorder will be uncovered in the near future.

title: Development, disease and degeneration in schizophrenia: a unitary pathophysiological model.
abstract: In recent years, several pathophysiological models of schizophrenia, i.e. the early and late brain neurodevelopmental and post-illness onset neurodegenerative models, have been proposed and theorists have often argued as if these explanations are mutually exclusive. We propose that all these mechanisms may interact cumulatively during successive critical 'windows of vulnerability' during brain development and during the early course of the illness to lead to the clinical manifestations of the illness. Early brain insults may lead to dysplasia of selective neural networks that account for the premorbid cognitive and psychosocial dysfunction seen in many patients. The onset of psychosis in adolescence may be related to an excessive elimination of synapses and secondarily, phasic dopaminergic overactivity. Following illness onset, these neurochemical alterations in relation to continuing untreated psychosis may lead to further neurodegenerative processes. A reduction in tonic glutamatergic neurotransmission and a phasic glutamatergic excess can potentially predispose to these processes and may have considerable explanatory power. This hypothesis is consistent with central characteristics of schizophrenia such as premorbid manifestations, adolescent onset, functional decline early in this illness, cognitive impairments, the role of dopamine and the role of genes and environment in pathophysiology. This 'three hit' model extends similar integrative conceptualization by other investigators and generates testable predictions of relevance to future pathophysiology and treatment research in schizophrenia.

title: Association between the neuregulin 1 gene and schizophrenia: a systematic review.
abstract: Chromosome 8p22-p11 has been identified as a locus for schizophrenia in several genome-wide scans, which has been confirmed by meta-analysis of published linkage data. It appears to be 1 of the most robust linkage findings in psychosis. Several attempts have been made to identify the underlying genetic variation that gives rise to this linkage peak, including systematic fine mapping using extended Icelandic pedigrees that have identified an associated haplotype (HAP(ICE)) in the gene neuregulin 1, also known as heuregulin, glial growth factor, NDF43, and ARIA. Neuregulin 1 (NRG1) is a plausible susceptibility gene because of its involvement in neurodevelopment, regulation of glutamate and other neurotransmitter receptor expression, and synaptic plasticity. Encouragingly, this finding was quickly and directly replicated in a Scottish case-control sample by the same investigators with the same approximately 300 kb associated haplotype. Although in Caucasian populations subsequent attempts at replication of this finding have been difficult to interpret, and no individual functional or causative genetic variants have yet been identified, a summary of HAP(ICE) association results in about 4,500 subjects is consistent with a small (odds ratio approximately 1.5) but significant effect of this haplotype on schizophrenia risk. In Chinese Han populations, where HAP(ICE) is not found, there is good evidence from several studies of association with other markers in the same region. Overall, there is convincing but not yet compelling evidence for a role for NRG1 in susceptibility to schizophrenia. Other genes from this region have also been implicated in schizophrenia, not by systematic mapping but by positional candidate gene analysis; these include MSTP131, frizzled-3, and the calcineurin A gamma subunit gene. Not only are these alternative explanations for the linkage seen between chromosome 8p and schizophrenia, but it is equally possible that there is more than 1 susceptibility gene at this locus.

title: Neurobiology of Schizophrenia
abstract: With its hallucinations, delusions, thought disorder, and cognitive deficits, schizophrenia affects the most basic human processes of perception, emotion, and judgment. Evidence increasingly suggests that schizophrenia is a subtle disorder of brain development and plasticity. Genetic studies are beginning to identify proteins of candidate genetic risk factors for schizophrenia, including dysbindin, neuregulin 1, DAOA, COMT, and DISC1, and neurobiological studies of the normal and variant forms of these genes are now well justified. We suggest that DISC1 may offer especially valuable insights. Mechanistic studies of the properties of these candidate genes and their protein products should clarify the molecular, cellular, and systems-level pathogenesis of schizophrenia. This can help redefine the schizophrenia phenotype and shed light on the relationship between schizophrenia and other major psychiatric disorders. Understanding these basic pathologic processes may yield novel targets for the development of more effective treatments.

title: Genetics of psychosis; insights from views across the genome
abstract: The major psychotic illnesses, schizophrenia and bipolar disorder (BD), are among the most heritable common disorders, but finding specific susceptibility genes for them has not been straightforward. The reasons are widely assumed to include lack of valid phenotypic definition, absence of good theories of pathophysiology for candidate gene studies, and the involvement of many genes, each making small contributions to population risk. Within the last year or so, a number of genome wide association (GWAS) of schizophrenia and BD have been published. These have produced stronger evidence for association to specific risk loci than have earlier studies, specifically for the zinc finger binding protein 804A (ZNF804A) locus in schizophrenia and for the calcium channel, voltage-dependent, L type, alpha 1C subunit (CACNA1C) and ankyrin 3, node of Ranvier (ANK3) loci in bipolar disorder. The ZNF804A and CACNA1C loci appear to influence risk for both disorders, a finding that supports the hypothesis that schizophrenia and BD are not aetiologically distinct. In the case of schizophrenia, a number of rare copy number variants have also been detected that have fairly large effect sizes on disease risk, and that additionally influence risk of autism, mental retardation, and other neurodevelopmental disorders. The existing findings point to some likely pathophysiological mechanisms but also challenge current concepts of disease classification. They also provide grounds for optimism that larger studies will reveal more about the origins of these disorders, although currently, very little of the genetic risk of either disorder is explained.

title: A genome‐wide CNV analysis of schizophrenia reveals a potential role for a multiple‐hit model
abstract: Schizophrenia is a chronic and severe psychiatric disorder that is highly heritable. While both common and rare genetic variants contribute to disease risk, many questions still remain about disease etiology. We performed a genome‐wide analysis of copy number variants (CNVs) in 166 schizophrenia subjects and 52 psychiatrically healthy controls. First, overall CNV characteristics were compared between cases and controls. The only statistically significant finding was that deletions comprised a greater proportion of CNVs in cases. High interest CNVs were then identified as conservative using the following filtering criteria: (i) known deleterious CNVs; (ii) CNVs >1 Mb that were novel (not found in a database of control individuals); and (iii) CNVs <1 Mb that were novel and that overlapped the coding region of a gene of interest. Cases did not harbor a higher proportion of conservative CNVs in comparison to controls. However, similar to previous reports, cases had a slightly higher proportion of individuals with clinically significant CNVs (known deleterious or conservative CNVs >1 Mb) or with multiple conservative CNVs. Two case individuals with the highest burden of conservative CNVs also share a recurrent 15q11.2 BP1‐2 deletion, indicating a role for a potential multiple‐hit CNV model for schizophrenia. In total, we report three 15q11.2 BP1‐2 deletion individuals with schizophrenia, adding to a growing body of evidence that this CNV is involved in disease etiology.

title: Neuregulin 1: a prime candidate for research into gene-environment interactions in schizophrenia? Insights from genetic rodent models
abstract: Schizophrenia is a multi-factorial disease characterized by a high heritability and environmental risk factors. In recent years, an increasing number of researchers worldwide have started investigating the “two-hit hypothesis” of schizophrenia predicting that genetic and environmental risk factors (GxE) interactively cause the development of the disorder. This work is starting to produce valuable new animal models and reveal novel insights into the pathophysiology of schizophrenia. This mini review will focus on recent advancements in the field made by challenging mutant and transgenic rodent models for the schizophrenia candidate gene neuregulin 1 (NRG1) with particular environmental factors. It will outline results obtained from mouse and rat models for various Nrg1 isoforms/isoform types (e.g., transmembrane domain Nrg1, Type II Nrg1), which have been exposed to different forms of stress (acute versus chronic, restraint versus social) and housing conditions (standard laboratory versus minimally enriched housing). These studies suggest Nrg1 as a prime candidate for GxE interactions in schizophrenia rodent models and that the use of rodent models will enable a better understanding of GxE interactions and the underlying mechanisms.

title: Mouse models of gene–environment interactions in schizophrenia
abstract: Gene-environment interactions (GEIs) likely play significant roles in the pathogenesis of schizophrenia and underlie differences in pathological, behavioral, and clinical presentations of the disease. Findings from epidemiology and psychiatric genetics have assisted in the generation of animal models of GEI relevant to schizophrenia. These models may provide a foundation for elucidating the molecular, cellular, and circuitry mechanisms that mediate GEI in schizophrenia. Here we critically review current mouse models of GEI related to schizophrenia, describe directions for their improvement, and propose endophenotypes to provide a more tangible basis for molecular studies of pathways of GEI and facilitate the identification of novel therapeutic targets.

title: Closing the translational gap between mutant mouse models and the clinical reality of psychotic illness
abstract: As animal models of psychotic illness become more refined, mutant mouse models have become increasingly prominent through their ability to inform on the structural, cellular and behavioural roles of genes associated with risk for psychosis via the phenotypic consequences of disruption of those genes. This review will consider recent advances in the field whereby mutant mouse models seek to reflect increasing knowledge of psychotic illness, focusing on four main themes. Firstly, recent GWAS and rare variant analyses have identified that disease-associated targets have not been previously implicated, thereby representing novel biological pathways in the illness, and this has implications for the modelling field. Secondly, the psychosis is disrespectful to conventional diagnostic boundaries, both clinically and in terms of pathobiology: it extends beyond schizophrenia to include several diagnostic categories and may be best captured in terms of psychopathological dimensions rather than/additional to such categories. Thirdly, a given risk gene (G) does not operate in isolation but, rather, appears to participate in complex interactions with environmental (E) risk factors, i.e., G×E interactions. Lastly, a given risk gene is likely to participate in complex, epistatic interactions with other risk genes, i.e., G×G interactions. Such studies constitute important steps in closing the translational gap between mutant mouse models and the clinical reality of psychotic illness.

title: Epigenetics of major psychosis: progress, problems and perspectives.
abstract: Understanding the origins of normal and pathological behavior is one of the most exciting opportunities in contemporary biomedical research. There is increasing evidence that, in addition to DNA sequence and the environment, epigenetic modifications of DNA and histone proteins may contribute to complex phenotypes. Inherited and/or acquired epigenetic factors are partially stable and have regulatory roles in numerous genomic activities, thus making epigenetics a promising research path in etiological studies of psychiatric disease. In this article, we review recent epigenetic studies examining the brain and other tissues, including those from individuals with schizophrenia (SCZ) and bipolar disorder (BPD). We also highlight heuristic aspects of the epigenetic theory of psychiatric disease and discuss the future directions of psychiatric epigenetics.

title: Animal models of gene–environment interaction in schizophrenia: A dimensional perspective
abstract: Schizophrenia has long been considered as a disorder with multifactorial origins. Recent discoveries have advanced our understanding of the genetic architecture of the disease. However, even with the increase of identified risk variants, heritability estimates suggest an important contribution of non-genetic factors. Various environmental risk factors have been proposed to play a role in the etiopathogenesis of schizophrenia. These include season of birth, maternal infections, obstetric complications, adverse events at early childhood, and drug abuse. Despite the progress in identification of genetic and environmental risk factors, we still have a limited understanding of the mechanisms whereby gene-environment interactions (G × E) operate in schizophrenia and psychoses at large. In this review we provide a critical analysis of current animal models of G × E relevant to psychotic disorders and propose that dimensional perspective will advance our understanding of the complex mechanisms of these disorders.

title: Paternal factors and schizophrenia risk: de novo mutations and imprinting.
abstract: There is a strong genetic component for schizophrenia risk, but it is unclear how the illness is maintained in the population given the significantly reduced fertility of those with the disorder. One possibility is that new mutations occur in schizophrenia vulnerability genes. If so, then those with schizophrenia may have older fathers, because advancing paternal age is the major source of new mutations in humans. This review describes several neurodevelopmental disorders that have been associated with de novo mutations in the paternal germ line and reviews data linking increased schizophrenia risk with older fathers. Several genetic mechanisms that could explain this association are proposed, including paternal germ line mutations, trinucleotide repeat expansions, and alterations in genetic imprinting in one or several genes involved in neurodevelopment. Animal models may be useful in exploring these and other explanations for the paternal age effect and they may provide a novel approach for gene identification. Finally, it is proposed that environmental exposures of the father, as well as those of the mother and developing fetus, may be relevant to the etiology of schizophrenia.

title: Advancing paternal and maternal age are both important for autism risk.
abstract: King et al.1 addressed 2 questions using data from the California Department of Developmental Services. The first concerned possible bias in estimating the association between parental age and autism as a result of pooling data across birth years. In their analysis, pooling caused a “reversal paradox” for paternal age—that is, the association between paternal age and autism was substantially inflated in pooled data. On this basis, they argued that the relation between paternal age and autism has been overestimated in previous research. 
 
 
We, however, do not agree with this conclusion. Previous studies have considered birth years and the effects of pooling data. Birth year is often included as a confounder in the statistical models, and data by birth year are often inspected by researchers to check for such possible pooling artifacts.2–6 In fact, a recent study by Grether et al.5 used the same California data source as King et al. and found no evidence for an inflated paternal-age effect when pooling data. For every 10-year increase in paternal age the pooled odds ratio (OR) for autism was 1.22 (95% confidence interval [CI]=1.18, 1.26). The equivalent OR for individual years was lower than was the pooled OR in 7 of the 14 individual years and higher in 6 (Table 2 in Grether et al.5). These results suggested that bias, if it exists, is only minimal. Furthermore, the research clearly indicated that an association between paternal age and autism in offspring can be detected in most populations and is not an artifact of confounding by maternal age or of pooling across birth cohorts. 
 
 
 
 
 
 
 
The Maneki Neko (literally “Beckoning Cat”) is a common Asian sculpture, often made of ceramic, which is believed to bring good luck to the owner. The sculpture depicts a cat (traditionally a Japenese Bobtail) beckoning with an upright paw, and is usually displayed—many times at the entrance—in shops, restaurants, pachinko parlors, and other businesses. In the design of the sculptures, a raised right paw supposedly attracts money, while a raised left paw attracts customers. Image from Punchstock.com. Printed with permission. 
 
 
 
 
The second question that King et al. addressed is the relative importance of paternal or maternal age. The authors used a statistical method of decomposition—about which we have some qualms—to examine this. However, is it really important whether the association with autism is stronger for paternal or for maternal age? Is there a “competition” between the two? At this point, an abundance of large and well-designed studies have demonstrated that advancing maternal and paternal age are associated with autism. One can draw different conclusions about their relative importance depending upon the perspective adopted. For example, men can and often do conceive at much later ages than can women, broadening the paternal age range. So, even if 10 years of maternal age confers greater risk than does 10 years of paternal age, the oldest men carry greater risk than do the oldest women (Table 1 in Grether et al.5). 
 
Regardless of the relative importance of paternal and maternal age, it is noteworthy that so many credible epidemiologic studies (including that conducted by King et al.) have now confirmed that paternal and maternal age at birth are related to autism risk. The evidence is substantial enough to justify a search for the underlying mechanisms. Genomic alterations could be involved in either the case of men or of women,7 as could other factors. All possible mechanisms can and should be studied in both human and animal

title: Rate of de novo mutations and the importance of father’s age to disease risk
abstract: Mutations generate sequence diversity and provide a substrate for selection. The rate of de novo mutations is therefore of major importance to evolution. Here we conduct a study of genome-wide mutation rates by sequencing the entire genomes of 78 Icelandic parent–offspring trios at high coverage. We show that in our samples, with an average father’s age of 29.7, the average de novo mutation rate is 1.20 × 10−8 per nucleotide per generation. Most notably, the diversity in mutation rate of single nucleotide polymorphisms is dominated by the age of the father at conception of the child. The effect is an increase of about two mutations per year. An exponential model estimates paternal mutations doubling every 16.5 years. After accounting for random Poisson variation, father’s age is estimated to explain nearly all of the remaining variation in the de novo mutation counts. These observations shed light on the importance of the father’s age on the risk of diseases such as schizophrenia and autism.

title: Aberrant epigenetic regulation could explain the relationship of paternal age to schizophrenia.
abstract: The causal mechanism underlying the well-established relation between advancing paternal age and schizophrenia is hypothesized to involve mutational errors during spermatogenesis that occur with increasing frequency as males age. Point mutations are well known to increase with advancing paternal age while other errors such as altered copy number in repeat DNA and chromosome breakage have in some cases also been associated with advancing paternal age. Dysregulation of epigenetic processes may also be an important mechanism underlying the association between paternal age and schizophrenia. Evidence suggests that advancing age as well as environmental exposures alter epigenetic regulation. Errors in epigenetic processes, such as parental imprinting can have serious effects on the offspring both pre- and postnatally and into adulthood. This article will discuss parental imprinting on the autosomal and X chromosomes and the alterations in epigenetic regulation that may lead to such errors.

title: Advanced paternal age is associated with altered DNA methylation at brain-expressed imprinted loci in inbred mice: implications for neuropsychiatric disease
abstract: Advanced paternal age is associated with altered DNA methylation at brain-expressed imprinted loci in inbred mice: implications for neuropsychiatric disease

title: Schizophrenia as a complex trait: evidence from a meta-analysis of twin studies.
abstract: There are many published twin studies of schizophrenia. Although these studies have been reviewed previously, to our knowledge, no review has provided quantitative summary estimates of the impact of genes and environment on liability to schizophrenia that also accounted for the different ascertainment strategies used.



To calculate meta-analytic estimates of heritability in liability and shared and individual-specific environmental effects from the pooled twin data.



We used a structured literature search to identify all published twin studies of schizophrenia, including MEDLINE, dissertation, and books-in-print searches.



Of the 14 identified studies, 12 met the minimal inclusion criteria of systematic ascertainment.



By using a multigroup twin model, we found evidence for substantial additive genetic effects-the point estimate of heritability in liability to schizophrenia was 81% (95% confidence interval, 73%-90%). Notably, there was consistent evidence across these studies for common or shared environmental influences on liability to schizophrenia-joint estimate, 11% (95% confidence interval, 3%-19%).



Despite evidence of heterogeneity across studies, these meta-analytic results from 12 published twin studies of schizophrenia are consistent with a view of schizophrenia as a complex trait that results from genetic and environmental etiological influences. These results are broadly informative in that they provide no information about the specific identity of these etiological influences, but they do provide a component of a unifying empirical basis supporting the rationality of searches for underlying genetic and common environmental etiological factors.

title: Rare chromosomal deletions and duplications increase risk of schizophrenia
abstract: Schizophrenia is a severe mental disorder marked by hallucinations, delusions, cognitive deficits and apathy, with a heritability estimated at 73–90% (ref. 1). Inheritance patterns are complex, and the number and type of genetic variants involved are not understood. Copy number variants (CNVs) have been identified in individual patients with schizophrenia and also in neurodevelopmental disorders, but large-scale genome-wide surveys have not been performed. Here we report a genome-wide survey of rare CNVs in 3,391 patients with schizophrenia and 3,181 ancestrally matched controls, using high-density microarrays. For CNVs that were observed in less than 1% of the sample and were more than 100 kilobases in length, the total burden is increased 1.15-fold in patients with schizophrenia in comparison with controls. This effect was more pronounced for rarer, single-occurrence CNVs and for those that involved genes as opposed to those that did not. As expected, deletions were found within the region critical for velo-cardio-facial syndrome, which includes psychotic symptoms in 30% of patients. Associations with schizophrenia were also found for large deletions on chromosome 15q13.3 and 1q21.1. These associations have not previously been reported, and they remained significant after genome-wide correction. Our results provide strong support for a model of schizophrenia pathogenesis that includes the effects of multiple rare structural variants, both genome-wide and at specific loci.

title: Large recurrent microdeletions associated with schizophrenia
abstract: Reduced fecundity, associated with severe mental disorders, places negative selection pressure on risk alleles and may explain, in part, why common variants have not been found that confer risk of disorders such as autism, schizophrenia and mental retardation. Thus, rare variants may account for a larger fraction of the overall genetic risk than previously assumed. In contrast to rare single nucleotide mutations, rare copy number variations (CNVs) can be detected using genome-wide single nucleotide polymorphism arrays. This has led to the identification of CNVs associated with mental retardation and autism. In a genome-wide search for CNVs associating with schizophrenia, we used a population-based sample to identify de novo CNVs by analysing 9,878 transmissions from parents to offspring. The 66 de novo CNVs identified were tested for association in a sample of 1,433 schizophrenia cases and 33,250 controls. Three deletions at 1q21.1, 15q11.2 and 15q13.3 showing nominal association with schizophrenia in the first sample (phase I) were followed up in a second sample of 3,285 cases and 7,951 controls (phase II). All three deletions significantly associate with schizophrenia and related psychoses in the combined sample. The identification of these rare, recurrent risk variants, having occurred independently in multiple founders and being subject to negative selection, is important in itself. CNV analysis may also point the way to the identification of additional and more prevalent risk variants in genes and pathways involved in schizophrenia.

title: Neurexin 1 (NRXN1) deletions in schizophrenia.
abstract: Over the last 2 years, several reports have suggested that submicroscopic chromosomal deletions that disrupt the gene neurexin 1 (NRXN1) increase the risk of developing schizophrenia. In this article, we will review the evidence for this association. 
 
NRXN1 encodes NRXN1, a synaptic neuronal adhesion molecule. NRXNs are found presynaptically and are believed to interact with postsynaptic neuroligins (NLGNs) in excitatory and inhibitory synapses in the brain. The structure and possible function of NRXNs and NLGNs have recently been comprehensively reviewed.1 
 
Vertebrate NRXNs and NLGNs are the only adhesion molecules for which a specifically synaptic function has been demonstrated.1 Current evidence suggests that NRXNs and NLGNs act transsynaptically to mediate essential signaling between presynaptic and postsynaptic specializations. Evidence from cell culture experiments and the study of mouse knockouts suggest that these molecules are required for synapse function but not for synapse formation, that they influence transsynaptic activation of synaptic transmission; and that their dysfunction impairs the properties of synapses and disrupts neural networks without completely abolishing synaptic transmission. NRXNs and NLGNs probably function by binding to each other and by interacting with intracellular proteins (most notably those with PDZ domain), but the precise mechanisms involved remain unknown.1 Whatever the mechanism and their relationship to synaptic function, it is clear that mice lacking NRXNs or NLGNs show marked deficits in synaptic  
 
There are 5 NLGN genes and 3 NRXN genes in humans (NRXN1 [2p16.3], NRXN2 [11q13], NRXN3 [14q31]). The 3 NRXN genes each encode an α protein and a β protein from independent promoters. NRXNs have a striking molecular diversity: the messenger RNA can be processed by alternative splicing, giving potentially thousands of distinct protein

title: Genetics of schizophrenia: new findings and challenges.
abstract: The work conducted using genome-wide approaches during the past several years has invigorated the field, and represents the dawn of molecular genetics of schizophrenia. The aggregate data increasingly support a combination of rare and common genetic variation in schizophrenia, a major role for polygenic inheritance, and a genetic overlap of schizophrenia and other psychiatric disorders, such as bipolar disorder and autism. The current and upcoming resequencing programs (full exomes to full genomes), in combination with the use of more informative genotyping arrays, will allow a more thorough dissection of the molecular genetics of the disorder. A main challenge for the field is the translation of established genetic associations into a better pathophysiological understanding of schizophrenia.

title: Biological Insights From 108 Schizophrenia-Associated Genetic Loci
abstract: Schizophrenia is a highly heritable disorder. Genetic risk is conferred by a large number of alleles, including common alleles of small effect that might be detected by genome-wide association studies. Here we report a multi-stage schizophrenia genome-wide association study of up to 36,989 cases and 113,075 controls. We identify 128 independent associations spanning 108 conservatively defined loci that meet genome-wide significance, 83 of which have not been previously reported. Associations were enriched among genes expressed in brain, providing biological plausibility for the findings. Many findings have the potential to provide entirely new insights into aetiology, but associations at DRD2 and several genes involved in glutamatergic neurotransmission highlight molecules of known and potential therapeutic relevance to schizophrenia, and are consistent with leading pathophysiological hypotheses. Independent of genes expressed in brain, associations were enriched among genes expressed in tissues that have important roles in immunity, providing support for the speculated link between the immune system and schizophrenia.

title: Risk genes for schizophrenia: translational opportunities for drug discovery.
abstract: Despite intensive research over many years, the treatment of schizophrenia remains a major health issue. Current and emerging treatments for schizophrenia are based upon the classical dopamine and glutamate hypotheses of disease. Existing first and second generation antipsychotic drugs based upon the dopamine hypothesis are limited by their inability to treat all symptom domains and their undesirable side effect profiles. Third generation drugs based upon the glutamate hypothesis of disease are currently under evaluation but are more likely to be used as add on treatments. Hence there is a large unmet clinical need. A major challenge in neuropsychiatric disease research is the relatively limited knowledge of disease mechanisms. However, as our understanding of the genetic causes of the disease evolves, novel strategies for the development of improved therapeutic agents will become apparent. In this review we consider the current status of knowledge of the genetic basis of schizophrenia, including methods for identifying genetic variants associated with the disorder and how they impact on gene function. Although the genetic architecture of schizophrenia is complex, some targets amenable to pharmacological intervention can be discerned. We conclude that many challenges lie ahead but the stratification of patients according to biobehavioural constructs that cross existing disease classifications but with common genetic and neurobiological bases, offer opportunities for new approaches to effective drug discovery.

title: A polygenic burden of rare disruptive mutations in schizophrenia
abstract: Schizophrenia is a common disease with a complex aetiology, probably involving multiple and heterogeneous genetic factors. Here, by analysing the exome sequences of 2,536 schizophrenia cases and 2,543 controls, we demonstrate a polygenic burden primarily arising from rare (less than 1 in 10,000), disruptive mutations distributed across many genes. Particularly enriched gene sets include the voltage-gated calcium ion channel and the signalling complex formed by the activity-regulated cytoskeleton-associated scaffold protein (ARC) of the postsynaptic density, sets previously implicated by genome-wide association and copy-number variation studies. Similar to reports in autism, targets of the fragile X mental retardation protein (FMRP, product of FMR1) are enriched for case mutations. No individual gene-based test achieves significance after correction for multiple testing and we do not detect any alleles of moderately low frequency (approximately 0.5 to 1 per cent) and moderately large effect. Taken together, these data suggest that population-based exome sequencing can discover risk alleles and complements established gene-mapping paradigms in neuropsychiatric disease.

title: Genetic Risk for Schizophrenia: Convergence on Synaptic Pathways Involved in Plasticity
abstract: Recent large-scale genomic studies have revealed two broad classes of risk alleles for schizophrenia: a polygenic component of risk mediated through multiple common risk variants and rarer more highly penetrant submicroscopic chromosomal deletions and duplications, known as copy number variants. The focus of this review is on the emerging findings from the latter and subsequent exome sequencing data of smaller, deleterious single nucleotide variants and indels. In these studies, schizophrenia patients were found to have enriched de novo mutations in genes belonging to the postsynaptic density at glutamatergic synapses, particularly components of the N-methyl-D-aspartate receptor signaling complex, including the PSD-95 complex, activity-regulated cytoskeleton-associated protein interactors, the fragile X mental retardation protein complex, voltage-gated calcium channels, and genes implicated in actin cytoskeletal dynamics. The convergence of these implicated genes onto a coherent biological pathway at the synapse, with a specific role in plasticity, provides a significant advance in understanding pathogenesis and points to new targets for biological investigation. We consider the implications of these studies in the context of existing genetic data and the potential need to reassess diagnostic boundaries of neuropsychiatric disorders before discussing ways forward for more directed mechanistic studies to develop stratified, novel therapeutic approaches in the future.

title: Genetic relationship between five psychiatric disorders estimated from genome-wide SNPs
abstract: Most psychiatric disorders are moderately to highly heritable. The degree to which genetic variation is unique to individual disorders or shared across disorders is unclear. To examine shared genetic etiology, we use genome-wide genotype data from the Psychiatric Genomics Consortium (PGC) for cases and controls in schizophrenia, bipolar disorder, major depressive disorder, autism spectrum disorders (ASD) and attention-deficit/hyperactivity disorder (ADHD). We apply univariate and bivariate methods for the estimation of genetic variation within and covariation between disorders. SNPs explained 17–29% of the variance in liability. The genetic correlation calculated using common SNPs was high between schizophrenia and bipolar disorder (0.68 ± 0.04 s.e.), moderate between schizophrenia and major depressive disorder (0.43 ± 0.06 s.e.), bipolar disorder and major depressive disorder (0.47 ± 0.06 s.e.), and ADHD and major depressive disorder (0.32 ± 0.07 s.e.), low between schizophrenia and ASD (0.16 ± 0.06 s.e.) and non-significant for other pairs of disorders as well as between psychiatric disorders and the negative control of Crohn's disease. This empirical evidence of shared genetic etiology for psychiatric disorders can inform nosology and encourages the investigation of common pathophysiologies for related disorders.

title: Polygenic dissection of diagnosis and clinical dimensions of bipolar disorder and schizophrenia
abstract: Bipolar disorder and schizophrenia are two often severe disorders with high heritabilities. Recent studies have demonstrated a large overlap of genetic risk loci between these disorders but diagnostic and molecular distinctions still remain. Here, we perform a combined genome-wide association study (GWAS) of 19 779 bipolar disorder (BP) and schizophrenia (SCZ) cases versus 19 423 controls, in addition to a direct comparison GWAS of 7129 SCZ cases versus 9252 BP cases. In our case–control analysis, we identify five previously identified regions reaching genome-wide significance (CACNA1C, IFI44L, MHC, TRANK1 and MAD1L1) and a novel locus near PIK3C2A. We create a polygenic risk score that is significantly different between BP and SCZ and show a significant correlation between a BP polygenic risk score and the clinical dimension of mania in SCZ patients. Our results indicate that first, combining diseases with similar genetic risk profiles improves power to detect shared risk loci and second, that future direct comparisons of BP and SCZ are likely to identify loci with significant differential effects. Identifying these loci should aid in the fundamental understanding of how these diseases differ biologically. These findings also indicate that combining clinical symptom dimensions and polygenic signatures could provide additional information that may someday be used clinically.

title: Genome-scale neurogenetics: methodology and meaning
abstract: Genetic analysis is currently offering glimpses into molecular mechanisms underlying such neuropsychiatric disorders as schizophrenia, bipolar disorder and autism. After years of frustration, success in identifying disease-associated DNA sequence variation has followed from new genomic technologies, new genome data resources, and global collaborations that could achieve the scale necessary to find the genes underlying highly polygenic disorders. Here we describe early results from genome-scale studies of large numbers of subjects and the emerging significance of these results for neurobiology.

title: Early life stress as a risk factor for mental health: Role of neurotrophins from rodents to non-human primates
abstract: Early adverse events can enhance stress responsiveness and lead to greater susceptibility for psychopathology at adulthood. The epigenetic factors involved in transducing specific features of the rearing environment into stable changes in brain and behavioural plasticity have only begun to be elucidated. Neurotrophic factors, such as nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF), are affected by stress and play a major role in brain development and in the trophism of specific neuronal networks involved in cognitive function and in mood disorders. In addition to the central nervous system, these effectors are produced by peripheral tissues, thus being in a position to integrate the response to external challenges. In this paper we will review data, obtained from animal models, indicating that early maternal deprivation stress can affect neurotrophin levels. Maladaptive or repeated activation of NGF and BDNF, early during postnatal life, may influence stress sensitivity at adulthood and increase vulnerability for stress-related psychopathology.

title: Animal models of neuropsychiatric disorders
abstract: Modeling of human neuropsychiatric disorders in animals is extremely challenging given the subjective nature of many symptoms, the lack of biomarkers and objective diagnostic tests, and the early state of the relevant neurobiology and genetics. Nonetheless, progress in understanding pathophysiology and in treatment development would benefit greatly from improved animal models. Here we review the current state of animal models of mental illness, with a focus on schizophrenia, depression and bipolar disorder. We argue for areas of focus that might increase the likelihood of creating more useful models, at least for some disorders, and for explicit guidelines when animal models are reported.

title: The environment and schizophrenia
abstract: Psychotic syndromes can be understood as disorders of adaptation to social context. Although heritability is often emphasized, onset is associated with environmental factors such as early life adversity, growing up in an urban environment, minority group position and cannabis use, suggesting that exposure may have an impact on the developing ‘social’ brain during sensitive periods. Therefore heritability, as an index of genetic influence, may be of limited explanatory power unless viewed in the context of interaction with social effects. Longitudinal research is needed to uncover gene–environment interplay that determines how expression of vulnerability in the general population may give rise to more severe psychopathology.

title: Dissecting cause and effect in the pathogenesis of psychiatric disorders: genes, environment and behaviour.
abstract: It has long been established that the development of psychiatric illness results from a complex interplay between genetic and environmental factors. Postmortem and genetic linkage studies have identified a number of promising candidate genes which have been reinforced by replication and functional studies. However, the fact that concordance rates for monozygotic twins rarely approach 100% highlights the involvement of environmental factors. Whilst epidemiological studies of psychiatric cohorts have demonstrated potential risk factors, such studies are clearly limited and in many cases the potential mechanism linking a given risk factor with pathogenesis remains unclear. A very powerful method of elucidating the mechanisms underlying gene-environment interactions is the use of appropriate animal models of psychiatric pathology. Whilst animals cannot be used to map the entire complexity of diseases such as schizophrenia, dissecting the symptom profile into more simply encapsulated traits or endophenotypes has proved to be a successful approach. Such endophenotypes provide a measurable link between aetiological factors and phenotypic outcome. Given the potential for the careful control and modification of an experimental animal's environment, the combination of studies of candidate genes with investigations of environmental factors is an effective heuristic tool, allowing examination of behavioural endophenotypes in conjunction with cellular and molecular outcomes. This review will consider the extant genetic, molecular, pharmacological and lesion-based models of psychiatric disorders, and the relevant methods of environmental manipulation appearing in the literature. We will discuss studies where such models have been combined, and the potential for future experimentation in this area.

title: Prenatal Interaction of Mutant DISC1 and Immune Activation Produces Adult Psychopathology
abstract: Gene-environment interactions (GEI) are involved in the pathogenesis of mental diseases. We evaluated interaction between mutant human disrupted-in-schizophrenia 1 (mhDISC1) and maternal immune activation implicated in schizophrenia and mood disorders.



Pregnant mice were treated with saline or polyinosinic:polycytidylic acid at gestation day 9. Levels of inflammatory cytokines were measured in fetal and adult brains; expression of mhDISC1, endogenous DISC1, lissencephaly type 1, nuclear distribution protein nudE-like 1, glycoprotein 130, growth factor receptor-bound protein 2, and glycogen synthase kinase-3beta were assessed in cortical samples of newborn mice. Tissue content of monoamines, volumetric brain abnormalities, dendritic spine density in the hippocampus, and various domains of the mouse behavior repertoire were evaluated in adult male mice.



Prenatal interaction produced anxiety, depression-like responses, and altered social behavior that were accompanied by decreased reactivity of the hypothalamic-pituitary-adrenal axis, attenuated serotonin neurotransmission in the hippocampus, reduced enlargement of lateral ventricles, decreased volumes of amygdala and periaqueductal gray matter and density of spines on dendrites of granule cells of the hippocampus. Prenatal interaction modulated secretion of inflammatory cytokines in fetal brains, levels of mhDISC1, endogenous mouse DISC1, and glycogen synthase kinase-3beta. The behavioral effects of GEI were observed only if mhDISC1 was expressed throughout the life span.



Prenatal immune activation interacted with mhDISC1 to produce the neurobehavioral phenotypes that were not seen in untreated mhDISC1 mice and that resemble aspects of major mental illnesses. Our DISC1 mouse model is a valuable system to study GEI relevant to mental illnesses.

title: Susceptibility genes for schizophrenia: mutant models, endophenotypes and psychobiology.
abstract: Schizophrenia is characterised by a multifactorial aetiology that involves genetic liability interacting with epigenetic and environmental factors to increase risk for developing the disorder. A consensus view is that the genetic component involves several common risk alleles of small effect and/or rare but penetrant copy number variations. Furthermore, there is increasing evidence for broader, overlapping genetic-phenotypic relationships in psychosis; for example, the same susceptibility genes also confer risk for bipolar disorder. Phenotypic characterisation of genetic models of candidate risk genes and/or putative pathophysiological processes implicated in schizophrenia, as well as examination of epidemiologically relevant gene × environment interactions in these models, can illuminate molecular and pathobiological mechanisms involved in schizophrenia. The present chapter outlines both the evidence from phenotypic studies in mutant mouse models related to schizophrenia and recently described mutant models addressing such gene × environment interactions. Emphasis is placed on evaluating the extent to which mutant phenotypes recapitulate the totality of the disease phenotype or model selective endophenotypes. We also discuss new developments and trends in relation to the functional genomics of psychosis which might help to inform on the construct validity of mutant models of schizophrenia and highlight methodological challenges in phenotypic evaluation that relate to such models.

title: Toward the future of psychiatric diagnosis: the seven pillars of RDoC
abstract: BackgroundCurrent diagnostic systems for mental disorders rely upon presenting signs and symptoms, with the result that current definitions do not adequately reflect relevant neurobiological and behavioral systems - impeding not only research on etiology and pathophysiology but also the development of new treatments.DiscussionThe National Institute of Mental Health began the Research Domain Criteria (RDoC) project in 2009 to develop a research classification system for mental disorders based upon dimensions of neurobiology and observable behavior. RDoC supports research to explicate fundamental biobehavioral dimensions that cut across current heterogeneous disorder categories. We summarize the rationale, status and long-term goals of RDoC, outline challenges in developing a research classification system (such as construct validity and a suitable process for updating the framework) and discuss seven distinct differences in conception and emphasis from current psychiatric nosologies.SummaryFuture diagnostic systems cannot reflect ongoing advances in genetics, neuroscience and cognitive science until a literature organized around these disciplines is available to inform the revision efforts. The goal of the RDoC project is to provide a framework for research to transform the approach to the nosology of mental disorders.

title: Schizophrenia and the city: A review of literature and prospective study of psychosis and urbanicity in Ireland
abstract: Urbanicity has been repeatedly associated with increased incidence of schizophrenia. This article (a) presents results of a prospective study of urbanicity and schizophrenia in Ireland and (b) reviews the literature relating to urbanicity and schizophrenia. We prospectively compared incidence of schizophrenia and other psychoses in urban and rural catchment areas (over 4years and 7years, respectively) using face-to-face, DSM-III-R diagnostic interviews. Incidence of schizophrenia in males was higher in urban compared to rural areas, with an age-adjusted incidence rate ratio (IRR) of 1.92 (1.52-2.44) for males and 1.34 (1.00-1.80) for females. Incidence of affective psychosis was lower in urban compared to rural areas for males (IRR 0.48; 0.34-0.67) and females (IRR 0.60; 0.43-0.83). These findings are consistent with the literature, which provides persuasive evidence that risk for schizophrenia increases with urban birth and/or upbringing, especially among males. Register-based studies support this conclusion more consistently than studies using face-to-face diagnostic interviews, the difference being related to power. The mechanism of association is unclear but may relate to biological or social/environmental factors or both, acting considerably before psychotic symptoms manifest. There is a diversity of potential candidates, including air pollution, cannabis and social exclusion. Urbanicity may have a synergistic effect with genetic vulnerability. Future research is likely to focus on the relationship between urbanicity and neural maldevelopment, the possibility of rural protective factors (e.g. social capital, low social fragmentation), urbanicity in developing countries, cultural variables and geographical location, and associations between urbanicity and other disorders (e.g. affective psychosis).

title: Cannabis use in young people: The risk for schizophrenia
abstract: Cannabis is one of the most commonly used illicit drugs, and despite the widely held belief that it is a safe drug, its long-term use has potentially harmful consequences. To date, the research on the impact of its use has largely been epidemiological in nature and has consistently found that cannabis use is associated with schizophrenia outcomes later in life, even after controlling for several confounding factors. While the majority of users can continue their use without adverse effects, it is clear from studies of psychosis that some individuals are more vulnerable to its effects than others. In addiction, evidence from both epidemiological and animal studies indicates that cannabis use during adolescence carries particular risk. Further studies are warranted given the increase in the concentration of the main active ingredient (Δ(9)-tetrahydrocannabinol) in street preparations of cannabis and a decreasing age of first-time exposure to cannabis.

title: Schizophrenia and the influenza epidemics of 1954, 1957 and 1959: A southern hemisphere study
abstract: The dates of birth of patients who were admitted with schizophrenia to public hospitals in Queensland between the years 1972 and 1988 were examined for associations between risk of schizophrenia and influenza epidemics. The hypothesis that infants born between four and six months after an influenza epidemic onset have increased risk of schizophrenia was examined for the 1954, 1957 and 1959 epidemics. After the 1954 epidemic there was a significant excess of male schizophrenia births four months after the onset of the epidemic. In 1957, there was a significant excess of female schizophrenia births in the fifth month after the onset of the epidemic. The 1959 epidemic was not associated with any significant excess.

title: Prenatal exposure to the 1957 influenza epidemic and adult schizophrenia: a follow-up study.
abstract: We investigated the hypothesis that prenatal exposure to the 1957 A2 influenza increases the risk of schizophrenia in adulthood.



We traced a cohort of individuals known to have been exposed to the 1957 influenza epidemic during gestation and an unexposed cohort matched for period of gestation and hospital of birth. Follow-up information on psychiatric illness in subjects was sought from two sources: maternal interview and psychiatric hospital admission data.



Follow-up information was obtained on 54% of the sample: 238 subjects from the influenza-exposed group and 287 subjects from the unexposed group. There was no increased risk of schizophrenia among the exposed cohort compared to the unexposed cohort (relative risk 1.1; 95% Cl 0.41-2.95), although there was an increase in depressive illness (relative risk 1.59; 95% Cl 1.15-2.19).



The association between prenatal influenza and an increased risk of schizophrenia in adulthood has thus far been found only in population-based data and is not supported by the present observational study which has information about exposure and outcome in individuals.

title: Effects of Family History and Place and Season of Birth on the Risk of Schizophrenia
abstract: A BSTRACT Background Although a family history of schizophrenia is the best-established risk factor for schizophrenia, environmental factors such as the place and season of birth may also be important.  Using data from the Civil Registration System in Denmark, we established a populationbased cohort of 1.75 million persons whose mothers were Danish women born between 1935 and 1978. We linked this cohort to the Danish Psychiatric Central Register and identified 2669 cases of schizophrenia among cohort members and additional cases among their parents.  The respective relative risks of schizophrenia for persons with a mother, father, or sibling who had schizophrenia were 9.31 (95 percent confidence interval, 7.24 to 11.96), 7.20 (95 percent confidence interval, 5.10 to 10.16), and 6.99 (95 percent confidence interval, 5.38 to 9.09), as compared with persons with no affected parents or siblings. The risk of schizophrenia was associated with the degree of urbanization of the place of birth (relative risk for the capital vs. rural areas, 2.40; 95 percent confidence interval, 2.13 to 2.70). The risk was also significantly associated with the season of birth; it was highest for births in February and March and lowest for births in August and September. The population attributable risk was 5.5 percent for a history of schizophrenia in a parent or sibling, 34.6 percent for urban place of birth, and 10.5 percent for the season of birth.  Although a history of schizophrenia in a parent or sibling is associated with the highest relative risk of having the disease, the place and season of birth account for many more cases on a population basis. ( 1999;340:603-8.

title: Maternal Exposure to Herpes Simplex Virus and Risk of Psychosis Among Adult Offspring
abstract: Viral exposure during gestation is thought to be a risk factor for schizophrenia. Previous studies have indicated that prenatal exposure to herpes simplex virus type 2 (HSV-2) may be a risk for the subsequent development of schizophrenia in some populations. In this investigation, we tested a large and diverse population to assess the risk of psychoses among offspring of mothers with serological evidence of HSV-2 infection.



We conducted a nested case-control study of 200 adults with psychoses and 554 matched control subjects (matched for city and date of birth, race/ethnicity, gender, and parent history of treatment for mental disorder) from three cohorts of the Collaborative Perinatal Project (Boston, Providence, and Philadelphia). We analyzed stored serum samples that had been obtained from these mothers at the end of pregnancy for antibodies directed at HSV-2, using type-specific solid-phase enzyme immunoassay techniques.



Offspring of mothers with serologic evidence of HSV-2 infection were at significantly increased risk for the development of psychoses (odds ratio [OR] = 1.6; 95% confidence interval [CI] = 1.1-2.3). This risk was particularly elevated among women with high rates of sexual activity during pregnancy (OR = 2.6; 95% CI = 1.4-4.6).



Maternal exposure to herpes simplex virus type 2 is associated with an increased risk for psychoses among adult offspring. These results are consistent with a general model of risk resulting from enhanced maternal immune activation during pregnancy.

title: Prenatal infection and schizophrenia: a review of epidemiologic and translational studies.
abstract: An emerging literature from epidemiologic, clinical, and preclinical investigations has provided evidence that gestational exposure to infection contributes to the etiology of schizophrenia. In recent years, these studies have moved from ecologic designs, which ascertain infection based on epidemics in populations, to investigations that have capitalized on reliable biomarkers in individual pregnancies. These studies have documented specific candidate infections that appear to be associated with an elevated risk of schizophrenia. Animal models of maternal immune activation inspired by this work have revealed intriguing findings indicating behavioral, neurochemical, and neurophysiologic abnormalities consistent with observations in schizophrenia. In parallel studies in humans and animals, investigators are working to uncover the cellular and molecular mechanisms by which in utero exposure to infection contributes to schizophrenia risk. In this review, the authors discuss and critically evaluate the epidemiologic literature on in utero exposure to infection and schizophrenia, summarize emerging animal models of maternal immune activation, and discuss putative unique and common mechanisms by which in utero exposure to infection alters neurodevelopment, potentially increasing susceptibility to schizophrenia. The promise of this work for facilitating the identification of susceptibility loci in genetic studies of schizophrenia is illustrated by examples of interaction between in utero exposure to infection and genetic variants. The authors then elaborate on possible implications of this work, including the use of preventive measures for reducing the incidence of schizophrenia. Finally, they discuss new approaches aimed at addressing current challenges in this area of research.

title: Towards an immuno-precipitated neurodevelopmental animal model of schizophrenia
abstract: Epidemiological studies have indicated an association between maternal bacterial and viral infections during pregnancy and the higher incidence of schizophrenia in the resultant offspring post-puberty. One hypothesis asserts that the reported epidemiological link is mediated by prenatal activation of the foetal immune system in response to the elevation of maternal cytokine level due to infection. Here, we report that pregnant mouse dams receiving a single exposure to the cytokine-releasing agent, polyriboinosinic-polyribocytidilic acid C; at 2.5, 5.0, or 10.0 mg/kg) on gestation day 9 produced offspring that subsequently exhibited multiple schizophrenia-related behavioural deficits in adulthood, in comparison to offspring from vehicle injected or non-injected control dams. The efficacy of the PolyI:C challenge to induce cytokine responses in naïve non-pregnant adult female mice and in foetal brain tissue when injected to pregnant mice were further ascertained in separate subjects: (i) a dose-dependent elevation of interleukin-10 was detected in the adult female mice at 1 and 6h post-injection, (ii) 12 h following prenatal PolyI:C challenge, the foetal levels of interleukin-1beta were elevated. The spectrum of abnormalities included impairments in exploratory behaviour, prepulse inhibition, latent inhibition, the US-pre-exposure effect, spatial working memory; and enhancement in the locomotor response to systemic amphetamine (2.5 mg/kg, i.p.) as well as in discrimination reversal learning. The neuropsychological parallels between prenatal PolyI:C treatment in mice and psychosis in humans, demonstrated here, leads us to conclude that prenatal PolyI:C treatment represents one of the most powerful environmental-developmental models of schizophrenia to date. The uniqueness of this model lies in its epidemiological and immunological relevance. It is, sui generis, ideally suited for the investigation of the neuropsychoimmunological mechanisms implicated in the developmental aetiology and disease processes of schizophrenia.

title: Immunological stress at the maternal–foetal interface: A link between neurodevelopment and adult psychopathology
abstract: Maternal infection during pregnancy is associated with a higher incidence of mental disorders, including schizophrenia, in the offspring in later life. Our recent attempt to study this link between prenatal immunological challenge and subsequent psychopathology has led to the establishment of a mouse model demonstrating the emergence of multiple psychotic-like phenotypes following immunological challenge on gestation day (GD) 9. However, little is known about the impact of similar in utero challenge at different times of pregnancy. Here, we compare the efficacy of identical maternal immune stimulation induced by the exposure to polyriboinosinic-polyribocytidilic acid (Poly(I:C)) at a dose of 5mg/kg (i.v.) on distinct days of gestation (GD 6, 9, 13 or 17). The offspring derived were then compared to those collected from vehicle- and non-treated dams in two paradigms of selective associative learning: latent inhibition (LI) and the US-pre-exposure effect (USPEE). LI deficiency was observed in animals born to dams treated with Poly(I:C) on GD 6, 9 or 13, but not in those on GD17. In contrast, a loss of the USPEE was equivalently seen in all Poly(I:C) treatment groups, regardless of treatment times. Evaluation of the acute cytokine response in a separate cohort of pregnant dams receiving Poly(I:C) challenge on either GD9 or GD17 revealed that the ratio of interleukin-10/tumor necrosis factor-alpha was elevated in the GD17 relative to the GD9 group. The present report thus provides evidence that the acute cytokine reaction as well as the long-term pattern of behavioural sequelae of maternal immune challenge can be affected by its precise timing during pregnancy. The present study provides further support to the use of the prenatal Poly(I:C) model in the elucidation of mechanisms involved in the aetiology and disease process of immuno-precipitated neurodevelopmental mental diseases, including but not limited to, schizophrenia.

title: Adult behavioral and pharmacological dysfunctions following disruption of the fetal brain balance between pro-inflammatory and IL-10-mediated anti-inflammatory signaling
abstract: Maternal infections during pregnancy increase the risk for schizophrenia and related disorders of putative neurodevelopmental origin in the offspring. This association has been attributed to enhanced expression of pro-inflammatory cytokines in the fetal environment in response to maternal immunological stimulation. In contrast, the specific roles of anti-inflammatory cytokines are virtually unknown in this context. Here, we demonstrate that genetically enforced expression of the anti-inflammatory cytokine interleukin (IL)-10 by macrophages attenuates the long-term behavioral and pharmacological consequences of prenatal immune activation in a mouse model of prenatal viral-like infection by polyriboinosinic–polyribocytidilic acid C; 2 mg/kg, intravenously). In the absence of a discrete prenatal inflammatory stimulus, however, enhanced levels of IL-10 at the maternal–fetal interface by itself also precipitates specific behavioral abnormalities in the grown offspring. This highlights that in addition to the disruptive effects of excess pro-inflammatory molecules, a shift toward enhanced anti-inflammatory signaling in prenatal life can similarly affect cognitive and behavioral development. Hence, shifts of the balance between pro- and anti-inflammatory cytokine classes may be a critical determinant of the final impact on neurodevelopment following early life infection or innate immune imbalances.

title: Late Prenatal Immune Activation in Mice Leads to Behavioral and Neurochemical Abnormalities Relevant to the Negative Symptoms of Schizophrenia
abstract: Based on the human epidemiological association between prenatal infection and higher risk of schizophrenia, a number of animal models have been established to explore the long-term brain and behavioral consequences of prenatal immune challenge. Accumulating evidence suggests that the vulnerability to specific forms of schizophrenia-related abnormalities is critically influenced by the precise timing of the prenatal immunological insult. In the present study, we tested the hypothesis whether late prenatal immune challenge in mice may induce long-term behavioral and neurochemical dysfunctions primarily associated with the negative symptoms of schizophrenia. We found that prenatal exposure to the viral mimic polyriboinosinic-polyribocytidilic acid (Poly-I:C; 5 mg/kg, i.v.) on gestation day (GD) 17 led to significant deficits in social interaction, anhedonic behavior, and alterations in the locomotor and stereotyped behavioral responses to acute apomorphine (APO) treatment in both male and female offspring. In addition, male but not female offspring born to immune challenged mothers displayed behavioral/cognitive inflexibility as indexed by the presence of an abnormally enhanced latent inhibition (LI) effect. Prenatal immune activation in late gestation also led to numerous, partly sex-specific changes in basal neurotransmitter levels, including reduced dopamine (DA) and glutamate contents in the prefrontal cortex and hippocampus, as well as reduced γ-aminobutyric acid (GABA) and glycine contents in the hippocampus and prefrontal cortex, respectively. The constellation of behavioral and neurochemical abnormalities emerging after late prenatal Poly-I:C exposure in mice leads us to conclude that this immune-based experimental model provides a powerful neurodevelopmental animal model especially for (but not limited to) the negative symptoms of schizophrenia.

title: Maternal Influenza Infection Causes Marked Behavioral and Pharmacological Changes in the Offspring
abstract: Maternal viral infection is known to increase the risk for schizophrenia and autism in the offspring. Using this observation in an animal model, we find that respiratory infection of pregnant mice (both BALB/c and C57BL/6 strains) with the human influenza virus yields offspring that display highly abnormal behavioral responses as adults. As in schizophrenia and autism, these offspring display deficits in prepulse inhibition (PPI) in the acoustic startle response. Compared with control mice, the infected mice also display striking responses to the acute administration of antipsychotic (clozapine and chlorpromazine) and psychomimetic (ketamine) drugs. Moreover, these mice are deficient in exploratory behavior in both open-field and novel-object tests, and they are deficient in social interaction. At least some of these behavioral changes likely are attributable to the maternal immune response itself. That is, maternal injection of the synthetic double-stranded RNA polyinosinic-polycytidylic acid causes a PPI deficit in the offspring in the absence of virus. Therefore, maternal viral infection has a profound effect on the behavior of adult offspring, probably via an effect of the maternal immune response on the fetus.

title: The Time of Prenatal Immune Challenge Determines the Specificity of Inflammation-Mediated Brain and Behavioral Pathology
abstract: Disturbance to early brain development is implicated in several neuropsychiatric disorders including autism, schizophrenia, and mental retardation. Epidemiological studies have indicated that the risk of developing these disorders is enhanced by prenatal maternal infection, presumably as a result of neurodevelopmental defects triggered by cytokine-related inflammatory events. Here, we demonstrate that the effects of maternal immune challenge between middle and late gestation periods in mice are dissociable in terms of fetal brain cytokine responses to maternal inflammation and the pathological consequences in brain and behavior. Specifically, the relative expression of pro- and anti-inflammatory cytokines in the fetal brains in response to maternal immune challenge may be an important determinant among other developmental factors for the precise pathological profile emerging in later life. Thus, the middle and late gestation periods correspond to two windows with differing vulnerability to adult behavioral dysfunction, brain neuropathology in early adolescence, and of the acute cytokine responses in the fetal brain.

title: Immune Activation During Pregnancy in Rats Leads to a PostPubertal Emergence of Disrupted Latent Inhibition, Dopaminergic Hyperfunction, and Altered Limbic Morphology in the Offspring: A Novel Neurodevelopmental Model of Schizophrenia
abstract: Prenatal exposure to infection is associated with increased liability to schizophrenia, and it is believed that such an association is mediated by the maternal immune response, in particular, the proinflammatory cytokines released by the maternal immune system, which may disrupt fetal brain development. Impaired capacity to ignore irrelevant stimuli is one of the central deficits in schizophrenia, and is manifested, among others, in loss of latent inhibition (LI), a phenomenon whereby repeated inconsequential pre-exposure to a stimulus impairs its subsequent capacity to signal significant consequences. We tested the effects of prenatal immune activation induced by peripheral administration of the synthetic cytokine releaser polyriboinosinic–polyribocytidilic acid (poly I : C) to pregnant dams, on LI in juvenile and adult offspring. Consistent with the characteristic maturational delay of schizophrenia, prenatal immune activation did not affect LI in the juvenile offspring, but led to LI disruption in adulthood. Both haloperidol (0.1 mg/kg) and clozapine (5 mg/kg) reinstated LI in the adult offspring. In addition, prenatal immune activation led to a postpubertal emergence of increased sensitivity to the locomotor-stimulating effects of amphetamine and increased in vitro striatal dopamine release, as well as to morphological alterations in the hippocampus and the entorhinal cortex in the adult offspring, consistent with the well-documented mesolimbic dopaminergic and temporolimbic pathology in schizophrenia. These results suggest that prenatal poly I : C administration may provide a neurodevelopmental model of schizophrenia that reproduces a putative inducing factor; mimics the temporal course as well as some central abnormalities of the disorder; and predicts responsiveness to antipsychotic drugs.

title: Maternal Immune Activation Alters Fetal Brain Development through Interleukin-6
abstract: Schizophrenia and autism are thought to result from the interaction between a susceptibility genotype and environmental risk factors. The offspring of women who experience infection while pregnant have an increased risk for these disorders. Maternal immune activation (MIA) in pregnant rodents produces offspring with abnormalities in behavior, histology, and gene expression that are reminiscent of schizophrenia and autism, making MIA a useful model of the disorders. However, the mechanism by which MIA causes long-term behavioral deficits in the offspring is unknown. Here we show that the cytokine interleukin-6 (IL-6) is critical for mediating the behavioral and transcriptional changes in the offspring. A single maternal injection of IL-6 on day 12.5 of mouse pregnancy causes prepulse inhibition (PPI) and latent inhibition (LI) deficits in the adult offspring. Moreover, coadministration of an anti-IL-6 antibody in the poly(I:C) model of MIA prevents the PPI, LI, and exploratory and social deficits caused by poly(I:C) and normalizes the associated changes in gene expression in the brains of adult offspring. Finally, MIA in IL-6 knock-out mice does not result in several of the behavioral changes seen in the offspring of wild-type mice after MIA. The identification of IL-6 as a key intermediary should aid in the molecular dissection of the pathways whereby MIA alters fetal brain development, which can shed new light on the pathophysiological mechanisms that predispose to schizophrenia and autism.

title: Maternal immune activation yields offspring displaying mouse versions of the three core symptoms of autism
abstract: The core symptoms of autism are deficits in social interaction and language, and the presence of repetitive/stereotyped behaviors. We demonstrate that behaviors related to these symptoms are present in a mouse model of an environmental risk factor for autism, maternal infection. We stimulate the maternal immune system by injecting the viral mimic poly(I:C) during pregnancy, and analyze the social and communicative behaviors of the offspring. In one test, young pups respond to a brief separation from the mother with ultrasonic vocalizations (USVs). We find that, compared to pups born to saline-injected mothers, pups born to maternal immune activation (MIA) mothers produce a lower rate of USVs in the isolation test starting at day 8. The quality of the vocalizations is also different; analysis of sound spectrograms of 10 day-old pups shows that male pups from MIA mothers emit significantly fewer harmonic and more complex and short syllables. These communication differences are also apparent in adult offspring. Compared to controls, adult MIA males emit significantly fewer USVs in response to social encounters with females or males, and display reduced scent marking in response to female urine. Regarding a second autism symptom, MIA males display decreased sociability. In a third test of characteristic autism behaviors, MIA offspring exhibit increased repetitive/stereotyped behavior in both marble burying and self-grooming tests. In sum, these results indicate that MIA yields male offspring with deficient social and communicative behavior, as well as high levels of repetitive behaviors, all of which are hallmarks of autism.

title: Post-pubertal emergence of disrupted latent inhibition following prenatal immune activation
abstract: RationaleThere is evidence pointing to an association between prenatal exposure to infection and increased liability to schizophrenia, and it has been suggested that the maternal immune response, in particular, the release of pro-inflammatory cytokines, may interfere with normal fetal brain development. Impaired capacity to ignore irrelevant stimuli is considered one of the central deficits in schizophrenia, and is manifested, among others, in disrupted latent inhibition (LI).ObjectivesTo test the effects of prenatal immune activation on LI in juvenile and adult offspring.MethodsPregnant rats were injected with the synthetic cytokine releaser polyriboinosinic-polyribocytidilic acid (poly I:C, 4 mg/kg) on gestational day 15. LI was assessed in 35-day and 3-month-old offspring using a thirst motivated conditioned emotional response procedure.ResultsConsistent with the characteristic maturational delay of schizophrenia, prenatal immune activation did not affect LI in the juvenile offspring but led to a post-pubertal emergence of LI disruption. In addition, pronounced alterations in hippocampal morphology resembling those found in schizophrenia, were evident in the adult offspring.ConclusionsThese results support the hypothesis that immune activation during pregnancy may lead to long-term abnormalities mimicking those observed in schizophrenia.

title: Effect of maternal immune activation on the kynurenine pathway in preadolescent rat offspring and on MK801-induced hyperlocomotion in adulthood: Amelioration by COX-2 inhibition
abstract: Infections during pregnancy and subsequent maternal immune activation (MIA) increase risk for schizophrenia in offspring. The progeny of rodents injected with the viral infection mimic polyI:C during gestation display brain and behavioural abnormalities but the underlying mechanisms are unknown. Since the blood kynurenine pathway (KP) of tryptophan degradation impacts brain function and is strongly regulated by the immune system, we tested if KP changes occur in polyI:C offspring at preadolescence. We also tested whether MK801-induced hyperlocomotion, a behaviour characteristic of adult polyI:C offspring, is prevented by adolescent treatment with celecoxib, a COX-2 inhibitor that impacts the KP. Pregnant rats were treated with polyI:C (4mg/kg, i.v.) or vehicle on gestational day 19. Serum levels of KP metabolites were measured in offspring of polyI:C or vehicle treated dams at postnatal day (PND) 31-33 using HPLC/GCMS. C or vehicle exposed offspring were given celecoxib or vehicle between PND 35 and 46 and tested with MK801 (0.3mg/kg) in adulthood (PND>90). C resulted in increases in the serum KP neurotoxic metabolite quinolinic acid at PND 31-33 (105%, p=0.014). In contrast, the neuroprotective kynurenic acid and its precursor kynurenine were significantly decreased (28% p=0.027, and 31% p=0.033, respectively). Picolinic acid, another neuroprotective KP metabolite, was increased (31%, p=0.014). Adolescent treatment with celecoxib (2.5 and 5mg/kg/day, i.p.) prevented the development of MK801-induced hyperlocomotion in adult polyI:C offspring. Our study reveals the blood KP as a potential mechanism by which MIA interferes with postnatal brain maturation and associated behavioural disturbances and emphasises the preventative potential of inflammation targeting drugs.

title: Abnormal Trajectories of Neurodevelopment and Behavior Following In Utero Insult in the Rat
abstract: Environmental or genetic disturbances of early brain development are suggested to underlie the pathophysiology of several adult-onset neuropsychiatric disorders. We traced the developmental trajectories of brain structural and behavioral abnormalities from adolescence to young adulthood in rats born to mothers exposed to the viral mimic polyriboinosinic-polyribocytidylic acid (poly-I:C) in pregnancy.



Pregnant rats were injected on gestational day 15 with poly-I:C (4 mg/kg) or saline. Volumes of lateral ventricles, hippocampus, striatum, and prefrontal cortex in male and female offspring were assessed longitudinally at postnatal days 35, 46, 56, 70, and 90 using in vivo magnetic resonance imaging. At parallel time windows, groups of offspring from the same litters underwent behavioral testing (latent inhibition and amphetamine-induced activity) and magnetic resonance imaging (cross-sectional assessment).



The specific developmental trajectories of volumetric changes in both control and poly-I:C offspring were region-, age-, and sex-specific, but overall, poly-I:C offspring had smaller volumes of the hippocampus, striatum and prefrontal cortex, and larger ventricular volume. Structural pathology in different regions had different times of onset and was gradually accompanied by behavioral deficits, disrupted latent inhibition, and excessive amphetamine-induced activity. The onset of structural frontocortical and ventricular abnormalities and behavioral abnormalities was delayed in females. In both sexes, hippocampal and striatal volume reduction predated the appearance of behavioral abnormalities.



Prenatal insult interferes with postnatal brain maturation, which in turn may result in behavioral abnormalities.

title: The poly(I:C)-induced maternal immune activation model in preclinical neuropsychiatric drug discovery.
abstract: Increasing epidemiological and experimental evidence implicates gestational infections as one important factor involved in the pathogenesis of several neuropsychiatric disorders. Corresponding preclinical model systems based upon maternal immune activation (MIA) by treatment of the pregnant female have been developed. These MIA animal model systems have been successfully used in basic and translational research approaches, contributing to the investigation of the underlying pathophysiological mechanisms at the molecular, cellular and behavioral levels. The present article focuses on the application of a specific MIA rodent paradigm, based upon treatment of the gestating dam with the viral mimic polyinosinic-polycytidilic acid (Poly(I:C)), a synthetic analog of double-stranded RNA (dsRNA) which activates the Toll-like receptor 3 (TLR3) pathway. Important advantages and constraints of this animal model will be discussed, specifically in light of gestational infection as one vulnerability factor contributing to the complex etiology of mood and psychotic disorders, which are likely the result of intricate multi-level gene×environment interactions. Improving our currently incomplete understanding of the molecular pathomechanistic principles underlying these disorders is a prerequisite for the development of alternative therapeutic approaches which are critically needed in light of the important drawbacks and limitations of currently available pharmacological treatment options regarding efficacy and side effects. The particular relevance of the Poly(I:C) MIA model for the discovery of novel drug targets for symptomatic and preventive therapeutic strategies in mood and psychotic disorders is highlighted in this review article.

title: Neuregulin 1 and susceptibility to schizophrenia.
abstract: The cause of schizophrenia is unknown, but it has a significant genetic component. Pharmacologic studies, studies of gene expression in man, and studies of mouse mutants suggest involvement of glutamate and dopamine neurotransmitter systems. However, so far, strong association has not been found between schizophrenia and variants of the genes encoding components of these systems. Here, we report the results of a genomewide scan of schizophrenia families in Iceland; these results support previous work, done in five populations, showing that schizophrenia maps to chromosome 8p. Extensive fine-mapping of the 8p locus and haplotype-association analysis, supplemented by a transmission/disequilibrium test, identifies neuregulin 1 (NRG1) as a candidate gene for schizophrenia. NRG1 is expressed at central nervous system synapses and has a clear role in the expression and activation of neurotransmitter receptors, including glutamate receptors. Mutant mice heterozygous for either NRG1 or its receptor, ErbB4, show a behavioral phenotype that overlaps with mouse models for schizophrenia. Furthermore, NRG1 hypomorphs have fewer functional NMDA receptors than wild-type mice. We also demonstrate that the behavioral phenotypes of the NRG1 hypomorphs are partially reversible with clozapine, an atypical antipsychotic drug used to treat schizophrenia.

title: A two-method meta-analysis of Neuregulin 1(NRG1) association and heterogeneity in schizophrenia
abstract: NRG1 is one of the most researched genes associated with schizophrenia. Although three meta-analyses in this area have been published, the results have been inconclusive and even conflicting. Family based studies can be problematical due to the difficulty of synthesizing them with case-control studies. Heterogeneity is another persistently difficult problem which tends to be side-stepped in genetic studies. To deal with these points, we performed a meta-analysis of 26 published case-control and family-based association studies up to September 2008 covering 8049 cases, 8869 controls and 1515 families. The matrix of coancestry coefficient was also calculated using population genetics. Across these studies, the conclusions are as follows: Firstly, only SNP8NRG221132, 420M9-1395(0) and 478B14-848(0) showed significant association in the relatively small sample size. Secondly, we applied both Kazeem's and Lohmueller's methods for synthesizing family and case control studies and there was no statistically significant difference between the results from the two methods, suggesting that either method can be used. In addition, the association analysis of case-control studies was statistically consistent with that of family studies. Finally, the matrix of coancestry coefficient suggested obvious population stratification. The study reveals that one SNP of the NRG1 gene does not contribute significantly to schizophrenia and that population stratification is evident. In future genetic association analysis on complex psychic diseases, haplotype blocks and population structure should be given greater consideration.

title: 
 Neuregulin-1 (NRG-1) and its susceptibility to schizophrenia: a case–control study and meta-analysis
abstract: Neuregulin-1 is widely investigated due to its hypothesised association with schizophrenia. Single-nucleotide polymorphisms rs764059, rs2954041 and rs3924999 were investigated (417 patients with schizophrenia and 429 controls). We failed to demonstrate a significant association between rs2954041 and rs3924999 with schizophrenia in the three ethnic groups studied (Malay, Chinese, and Indian), while rs764059 was found to be monomorphic.

title: Neuregulin 1 and Schizophrenia: Genetics, Gene Expression, and Neurobiology
abstract: Neuregulin 1 (NRG1) is a leading schizophrenia susceptibility gene. The NRG1 locus on chromosome 8p shows linkage to the disorder, and genetic association has been found between schizophrenia and various non-coding polymorphisms and haplotypes, especially at the 5' end of the NRG1 gene, in many but not all case-control and family studies. NRG1 is a pleiotropic growth factor, important in nervous system development and functioning; roles include the modulation of neuronal migration, synaptogenesis, gliogenesis, neuron-glia communication, myelination, and neurotransmission. Understanding the neurobiology of NRG1 and its involvement in schizophrenia is challenged by the complexity of the gene, which gives rise to multiple functionally distinct isoforms, including six "types" of NRG1 defined by 5' exon usage. Type IV and type I NRG1 may be particularly relevant to schizophrenia, with initial data showing altered expression of these isoforms in the disorder or in association with NRG1 risk alleles. We review the structure and functions of NRG1, consider the evidence for and against it being a schizophrenia susceptibility gene, and discuss mechanisms that might underlie the contribution of NRG1 to disease pathophysiology.

title: Neuregulin 1 in neural development, synaptic plasticity and schizophrenia
abstract: Schizophrenia is a highly debilitating mental disorder that affects ∼1% of the general population, yet it continues to be poorly understood. Recent studies have identified variations in several genes that are associated with this disorder in diverse populations, including those that encode neuregulin 1 (NRG1) and its receptor ErbB4. The past few years have witnessed exciting progress in our knowledge of NRG1 and ErbB4 functions and the biological basis of the increased risk for schizophrenia that is potentially conferred by polymorphisms in the two genes. An improved understanding of the mechanisms by which altered function of NRG1 and ErbB4 contributes to schizophrenia might eventually lead to the development of more effective therapeutics.

title: Interleukin-1 beta gene polymorphism and its interactions with neuregulin-1 gene polymorphism are associated with schizophrenia
abstract: Interleukin-1β (IL-1β) and neuregulin-1 (NRG-1) have an important role in development of the central nervous system. Several recent studies suggest that their genetic polymorphisms are associated with schizophrenia. We studied the effects of the IL-1β gene (IL-1B) -511 and NRG-1 SNP8NRG221533 polymorphisms and their interactions on the risk and age of onset of schizophrenia in 113 Finnish schizophrenic patients and 393 healthy controls. The allele and genotype frequencies of IL-1B and NRG-1 did not differ between schizophrenic patients and healthy controls, but the risk of schizophrenia was more than 10 times higher (odds ratio 10.20, 95% CI 2.53–41.09, p = 0.001) among subjects with the IL-1B 2.2, NRG-1 CC genotypes compared to subjects with the IL-1B 2.2, NRG-1 T-allele carriage. There was also a trend for an association between the interaction between IL-1B and NRG-1 polymorphisms and the age at onset of schizophrenia (χ2 = 2.80; df  = 1; p = 0.09, log rank test). IL-1B-511 allele 1 homozygotes had a significantly higher age of onset than allele 2 carriers (mean age of onset 25.9 ± 7.7 and 22.7 ± 5.4 years, t-test: t = 2.46; p = 0.032). Our results suggest that there is an interaction between the IL-1B and NRG-1 genes in schizophrenia. In addition, the IL-1B-511 polymorphism seems to be associated with the age at onset of schizophrenia.

title: In vivo and in vitro genetic evidence of involvement of neuregulin 1 in immune system dysregulation
abstract: Neuregulin 1 (NRG1) has been implicated in several disorders including breast cancer, multiple sclerosis, and schizophrenia. Also, recent evidence suggests that NRG1 may play a role in regulation of inflammation and immune system response. We therefore hypothesized that a schizophrenia-associated missense mutation (valine to leucine) we identified within the transmembrane region of NRG1 would also be linked to immune dysregulation. We used plasma samples from families carrying the mutation to measure levels of antibodies to 41 autoimmune markers and six cytokines (IL-1b, IL-6, IL-10, IL-8, IL-12p70, and TNF-α) and used these levels as quantitative traits to evaluate association with the NRG1 mutation, using FBAT. Next, we used Epstein–Barr virus-transformed B cells from heterozygous mutation carriers and wild-type individuals to evaluate protein and mRNA cytokine expression in vitro using quantitative PCR and ELISA assays. In vivo, increased levels of 25 autoimmune markers as well as elevated levels of cytokines were significantly associated with the NRG1 mutation. In vitro, we observed a significant increase in protein secretion levels of IL-6, TNF-α, and IL-8 in mutation carriers compared with controls. At the mRNA level, we observed a significant increase in IL-6 expression, while IL-4 levels appeared to be down-regulated in heterozygous individuals compared with wild-type controls. This is the first report of association of a NRG1 mutation with immune dysregulation. This study could contribute towards understanding the role of NRG1 in the pathogenesis of schizophrenia and other disorders in which inflammation plays an important role.

title: Phenotypic Characterization of Transgenic Mice Overexpressing Neuregulin-1
abstract: (NRG1) is one of the susceptibility genes for schizophrenia and implicated in the neurotrophic regulation of GABAergic and dopaminergic neurons, myelination, and NMDA receptor function. Postmortem studies often indicate a pathologic association of increased NRG1 expression or signaling with this illness. However, the psychobehavioral implication of NRG1 signaling has mainly been investigated using hypomorphic mutant mice for individual NRG1 splice variants.  To assess the behavioral impact of hyper NRG1 signaling, we generated and analyzed two independent mouse transgenic (Tg) lines carrying the transgene of green fluorescent protein (GFP)-tagged type-1 NRG1 cDNA. The promoter of elongation-factor 1α gene drove ubiquitous expression of GFP-tagged NRG1 in the whole brain. As compared to control littermates, both heterozygous NRG1-Tg lines showed increased locomotor activity, a nonsignificant trend toward decreasing prepulse inhibition, and decreased context-dependent fear learning but exhibited normal levels of tone-dependent learning. In addition, social interaction scores in both Tg lines were reduced in an isolation-induced resident-intruder test. There were also phenotypic increases in a GABAergic marker (parvalbumin) as well as in myelination markers (myelin basic protein and 2′,3′-cyclic nucleotide 3′-phosphodiesterase) in their frontal cortex, indicating the authenticity of NRG1 hyper-signaling, although there were marked decreases in tyrosine hydroxylase levels and dopamine content in the hippocampus.  These findings suggest that aberrant hyper-signals of NRG1 also disrupt various cognitive and behavioral processes. Thus, neuropathological implication of hyper NRG1 signaling in psychiatric diseases should be evaluated with further experimentation.

title: Altered motor activity, exploration and anxiety in heterozygous neuregulin 1 mutant mice: implications for understanding schizophrenia
abstract: Human genetic studies have shown that neuregulin 1 (NRG1) is a potential susceptibility gene for schizophrenia. Nrg1 influences various neurodevelopmental processes, which are potentially related to schizophrenia. The neurodevelopmental theory of schizophrenia suggests that interactions between genetic and environmental factors are responsible for biochemical alterations leading to schizophrenia. To investigate these interactions and to match experimental design with the pathophysiology of schizophrenia, we applied a comprehensive behavioural phenotyping strategy for motor activity, exploration and anxiety in a heterozygous Nrg1 transmembrane domain mutant mouse model (Nrg1 HET) using different housing conditions and age groups. We observed a locomotion‐ and exploration‐related hyperactive phenotype in Nrg1 HETs. Increased age had a locomotion‐ and exploration‐inhibiting effect, which was significantly attenuated in mutant mice. Environmental enrichment (EE) had a stimulating influence on locomotion and exploration. The impact of EE was more pronounced in Nrg1 hypomorphs. Our study also showed a moderate task‐specific anxiolytic‐like phenotype for Nrg1 HETs, which was influenced by external factors. The behavioural phenotype detected in heterozygous Nrg1 mutant mice is not specific to schizophrenia per se, but the increased sensitivity of mutant mice to exogenous factors is consistent with the pathophysiology of schizophrenia and the neurodevelopmental theory. Our findings reinforce the importance of carefully controlling experimental designs for external factors and of comprehensive, integrative phenotyping strategies. Thus, Nrg1 HETs may, in combination with other genetic and drug models, help to clarify pathophysiological mechanisms behind schizophrenia.

title: Phenotypic effects of repeated psychosocial stress during adolescence in mice mutant for the schizophrenia risk gene neuregulin-1: A putative model of gene×environment interaction
abstract: There is a paucity of animal models by which the contributions of environmental and genetic factors to the pathobiology of psychosis can be investigated. This study examined the individual and combined effects of chronic social stress during adolescence and deletion of the schizophrenia risk gene neuregulin-1 (NRG1) on adult mouse phenotype. Mice were exposed to repeated social defeat stress during adolescence and assessed for exploratory behaviour, working memory, sucrose preference, social behaviour and prepulse inhibition in adulthood. Thereafter, in vitro cytokine responses to mitogen stimulation and corticosterone inhibition were assayed in spleen cells, with measurement of cytokine and brain-derived neurotrophic factor (BDNF) mRNA in frontal cortex, hippocampus and striatum. NRG1 mutants exhibited hyperactivity, decreased anxiety, impaired sensorimotor gating and reduced preference for social novelty. The effects of stress on exploratory/anxiety-related parameters, spatial working memory, sucrose preference and basal cytokine levels were modified by NRG1 deletion. Stress also exerted varied effect on spleen cytokine response to concanavalin A and brain cytokine and BDNF mRNA expression in NRG1 mutants. The experience of psychosocial stress during adolescence may trigger further pathobiological features that contribute to the development of schizophrenia, particularly in those with underlying NRG1 gene abnormalities. This model elaborates the importance of gene × environment interactions in the etiology of schizophrenia.

title: Neuregulin 1 hypomorphic mutant mice: enhanced baseline locomotor activity but normal psychotropic drug-induced hyperlocomotion and prepulse inhibition regulation.
abstract: Neuregulin 1 (Nrg1) has been widely recognized as a candidate gene for schizophrenia. This study therefore investigated mice heterozygous for a mutation in the transmembrane domain of this trophic factor (Nrg1+/- mice) in a number of behavioural test systems with relevance to schizophrenia, including psychotropic drug-induced locomotor hyperactivity and prepulse inhibition (PPI) of startle. Baseline locomotor activity in the open field or in photocell cages was slightly, but significantly enhanced in Nrg1+/- mice compared to wild-type littermate controls at age 12-16 wk, but not at age 6 months. The ability of amphetamine, phencyclidine (PCP) or MK-801 to induce locomotor hyperactivity was not significantly different between the genotypes. There was no difference in baseline PPI, startle or startle habituation and there was no difference in the effect of apomorphine, amphetamine or MK-801 on any of these parameters. Only treatment with the 5-HT1A receptor agonist 8-hydroxy-dipropylaminotetralin (8-OH-DPAT) showed a differential effect between genotypes, with a disruption of PPI occurring in Nrg1+/- mice compared to no effect in wild-type controls. This treatment also induced a significant reduction of startle which could have influenced the result. The density of dopamine D2 receptors in the forebrain and of 5-HT1A receptors in the hippocampus and raphe nuclei was not different between Nrg1+/- mice and controls. These studies add to the knowledge about behavioural effects in this mouse model of impaired Nrg1 function and suggest that a number of the behavioural tests with relevance to schizophrenia are normal in these mice.

title: Do transmembrane domain neuregulin 1 mutant mice exhibit a reliable sensorimotor gating deficit?
abstract: Evidence suggests that the heterozygous transmembrane domain mutant mouse model for the schizophrenia candidate gene neuregulin 1 (Nrg1 HET) exhibits a deficit in prepulse inhibition (PPI). However, not all mouse models for Nrg1 exhibit PPI deficits. Thus, our study intended to clarify the severity of the initially described PPI deficit in Nrg1 HET mice. For this, Nrg1 mutant mice and wild type-like littermates of one breeding colony were tested for PPI in four different phenotyping facilities in Australia employing a variety of different PPI protocols with fixed and variable interstimulus intervals (ISIs). Testing mutant and wild type-like mice in three Australian phenotyping facilities using PPI protocols with variable ISIs revealed no effect of mutant transmembrane domain Nrg1 on sensorimotor gating. Changes to the startle response and startle response habituation were site/protocol-specific. The employment of two different PPI protocols at the same phenotyping facility revealed a protocol-dependent and site-specific facilitation of PPI in Nrg1 mutant mice compared to wild type-like mice. In conclusion, the often-noted PPI phenotype of the transmembrane domain Nrg1 mutant mouse model is highly PPI protocol-specific and appears sensitive to the particular conditions of the test laboratory. Our study describes wild type-like PPI under most test conditions and across three different laboratories. The research suggests that analysing one of the alleged hallmarks of animal models for schizophrenia must be done carefully: to obtain reliable PPI data it seems necessary to use more than one particular PPI protocol.

title: Neuregulin-1 immunoglobulin-like domain mutant mice: clozapine sensitivity and impaired latent inhibition
abstract: Genetic and behavioral studies in humans and mouse mutants have implicated the gene encoding neuregulin-1 (Nrg-1) as a candidate susceptibility gene for schizophrenia. We examined the behavior of mice heterozygous for a mutation in neuregulin-1's immunoglobulin (Ig)-like domain (Ig-nrg-1+/− mice). We found that these animals displayed behaviors related to a schizophrenia-like phenotype, such as clozapine suppression of open-field and running wheel activity and impaired latent inhibition. Contrary to findings with other nrg-1 mutants, Ig-nrg-1+/− mice did not exhibit significantly elevated locomotion relative to littermate controls. These results suggest that Ig-Nrg-1's contribute to some – but not all – aspects of the schizophrenia-like phenotype of nrg-1 mutants, and further support nrg-1 as a candidate gene for schizophrenia.

title: Type III Neuregulin-1 Is Required for Normal Sensorimotor Gating, Memory-Related Behaviors, and Corticostriatal Circuit Components
abstract: Neuregulin-1 (Nrg1)/erbB signaling regulates neuronal development, migration, myelination, and synaptic maintenance. The Nrg1 gene is a schizophrenia susceptibility gene. To understand the contribution of Nrg1 signaling to adult brain structure and behaviors, we studied the regulation of type III Nrg1 expression and evaluated the effect of decreased expression of the type III Nrg1 isoforms. Type III Nrg1 is transcribed by a promoter distinct from those for other Nrg1 isoforms and, in the adult brain, is expressed in the medial prefrontal cortex, ventral hippocampus, and ventral subiculum, regions involved in the regulation of sensorimotor gating and short-term memory. Adult heterozygous mutant mice with a targeted disruption for type III Nrg1 (Nrg1tm1.1Lwr+/−) have enlarged lateral ventricles and decreased dendritic spine density on subicular pyramidal neurons. Magnetic resonance imaging of type III Nrg1 heterozygous mice revealed hypofunction in the medial prefrontal cortex and the hippocampal CA1 and subiculum regions. Type III Nrg1 heterozygous mice also have impaired performance on delayed alternation memory tasks, and deficits in prepulse inhibition (PPI). Chronic nicotine treatment eliminated differences in PPI between type III Nrg1 heterozygous mice and their wild-type littermates. Our findings demonstrate a role of type III Nrg1 signaling in the maintenance of corticostriatal components and in the neural circuits involved in sensorimotor gating and short-term memory.

title: Distinct phenotypes of new transmembrane-domain neuregulin 1 mutant mice and the rescue effects of valproate on the observed schizophrenia-related cognitive deficits
abstract: Accumulating evidence suggests that neuregulin 1 (NRG1) might be involved in the neurodevelopment, neural plasticity, GABAergic neurotransmission, and pathogenesis of schizophrenia. NRG1 is abundantly expressed in the hippocampus, and emerging studies have begun to reveal the link between NRG1 signaling and cognitive deficits in schizophrenic patients. Because the transmembrane domain of NRG1 is vital for both forward and reverse signaling cascades, new Nrg1-deficient mice that carry a truncation of the transmembrane domain of the Nrg1 gene were characterized and used in this study to test a NRG1 loss-of-function hypothesis for schizophrenia. Both male and female Nrg1 heterozygous mutant mice and their wild-type littermates were used in a series of 4 experiments to characterize the impact of Nrg1 on behavioral phenotypes and to determine the importance of Nrg1 in the regulation of hippocampal neuromorphology and local GABAergic interneurons. First, a comprehensive battery of behavioral tasks indicated that male Nrg1-deficient mice exhibited significant impairments in cognitive functions. Second, pharmacological challenges were conducted and revealed that Nrg1 haploinsufficiency altered GABAergic activity in males. Third, although no genotype-specific neuromorphological alterations were found in the hippocampal CA1 pyramidal neurons, significant reductions in the hippocampal expressions of GAD67 and parvalbumin were revealed in the Nrg1-deficient males. Fourth, chronic treatment with valproate rescued the observed behavioral deficits and hippocampal GAD67 reduction in Nrg1-deficient males. Collectively, these results indicate the potential therapeutic effect of valproate and the importance of Nrg1 in the regulation of cognitive functions and hippocampal GABAergic interneurons, especially in males.

title: Phenotypic effects of maternal immune activation and early postnatal milieu in mice mutant for the schizophrenia risk gene neuregulin-1
abstract: Risk of schizophrenia is likely to involve gene × environment (G × E) interactions. Neuregulin 1 (NRG1) is a schizophrenia risk gene, hence any interaction with environmental adversity, such as maternal infection, may provide further insights into the basis of the disease. This study examined the individual and combined effects of prenatal immune activation with polyriboinosinic-polyribocytidilic acid (Poly I:C) and disruption of the schizophrenia risk gene NRG1 on the expression of behavioral phenotypes related to schizophrenia. NRG1 heterozygous (NRG1 HET) mutant breeding pairs were time-mated. Pregnant dams received a single injection (5mg/kg i.p.) of Poly I:C or vehicle on gestation day 9 (GD9). Offspring were then cross-fostered to vehicle-treated or Poly I:C-treated dams. Expression of schizophrenia-related behavioral endophenotypes was assessed at adolescence and in adulthood. Combining NRG1 disruption and prenatal environmental insult (Poly I:C) caused developmental stage-specific deficits in social behavior, spatial working memory and prepulse inhibition (PPI). However, combining Poly I:C and cross-fostering produced a number of behavioral deficits in the open field, social behavior and PPI. This became more complex by combining NRG1 deletion with both Poly I:C exposure and cross-fostering, which had a robust effect on PPI. These findings suggest that concepts of G × E interaction in risk of schizophrenia should be elaborated to multiple interactions that involve individual genes interacting with diverse biological and psychosocial environmental factors over early life, to differentially influence particular domains of psychopathology, sometimes over specific stages of development.

title: Schizophrenia and affective disorders--cosegregation with a translocation at chromosome 1q42 that directly disrupts brain-expressed genes: clinical and P300 findings in a family.
abstract: A family with a (1;11)(q42;q14.3) translocation significantly linked to a clinical phenotype that includes schizophrenia and affective disorders is described. This translocation generates a LOD score of 3.6 when the disease phenotype is restricted to schizophrenia, of 4.5 when the disease phenotype is restricted to affective disorders, of 7.1 when relatives with recurrent major depression, with bipolar disorder, or with schizophrenia are all classed as affected. This evidence for linkage is among the strongest reported for a psychiatric disorder. Family members showed no distinctive features by which the psychiatric phenotype could be distinguished from unrelated cases of either schizophrenia or affective disorders, and no physical, neurological, or dysmorphic conditions co-occurred with psychiatric symptoms. Translocation carriers and noncarriers had the same mean intelligence quotient. Translocation carriers were similar to subjects with schizophrenia and different from noncarriers and controls, in showing a significant reduction in the amplitude of the P300 event-related potential (ERP). Furthermore, P300 amplitude reduction and latency prolongation were measured in some carriers of the translocation who had no psychiatric symptoms-a pattern found in other families with multiple members with schizophrenia, in which amplitude of and latency of P300 appear to be trait markers of risk. The results of karyotypic, clinical, and ERP investigations of this family suggest that the recently described genes DISC1 and DISC2, which are directly disrupted by the breakpoint on chromosome 1, may have a role in the development of a disease phenotype that includes schizophrenia as well as unipolar and bipolar affective disorders.

title: A frameshift mutation in Disrupted in Schizophrenia 1 in an American family with schizophrenia and schizoaffective disorder
abstract: In a large Scottish pedigree, a balanced translocation t(1;11)(q42.1;q14.3) segregates with major mental illness, including schizophrenia, bipolar disorder, and recurrent major depression. The translocation is predicted to result in the loss of the C-terminal region of the protein product of Disrupted In SChizophrenia 1 (DISC1), a gene located on 1q42.1. Since this initial discovery, DISC1 has been functionally implicated in several processes, including neurodevelopment. Based on the genetic and functional evidence that DISC1 may be associated with schizophrenia, we sequenced portions of DISC1 in 28 unrelated probands with schizophrenia and six unrelated probands with schizoaffective disorder, ascertained as part of a large sibpair study. We detected a 4 bp deletion at the extreme 3′ end of exon 12 in a proband with schizophrenia. The mutation was also present in a sib with schizophrenia, a sib with schizoaffective disorder, and the unaffected father, while the mutation was not detected in 424 control individuals. The mutation is predicted to cause a frameshift and encode a truncated protein with nine abnormal C-terminal amino acids. The truncated transcript is detectable, but at a reduced level, in lymphoblastoid cell lines from three of four mutation carriers. These findings are consistent with the possibility that mutations in the DISC1 gene can increase the risk for schizophrenia and related disorders.

title: DISC1-binding proteins in neural development, signalling and schizophrenia
abstract: In the decade since Disrupted in Schizophrenia 1 (DISC1) was first identified it has become one of the most convincing risk genes for major mental illness. As a multi-functional scaffold protein, DISC1 has multiple identified protein interaction partners that highlight pathologically relevant molecular pathways with potential for pharmaceutical intervention. Amongst these are proteins involved in neuronal migration (e.g. APP, Dixdc1, LIS1, NDE1, NDEL1), neural progenitor proliferation (GSK3β), neurosignalling (Girdin, GSK3β, PDE4) and synaptic function (Kal7, TNIK). Furthermore, emerging evidence of genetic association (NDEL1, PCM1, PDE4B) and copy number variation (NDE1) implicate several DISC1-binding partners as risk factors for schizophrenia in their own right. Thus, a picture begins to emerge of DISC1 as a key hub for multiple critical developmental pathways within the brain, disruption of which can lead to a variety of psychiatric illness phenotypes. This article is part of a Special Issue entitled ‘Schizophrenia’.

title: Linking neurodevelopmental and synaptic theories of mental illness through DISC1
abstract: Recent advances in our understanding of the underlying genetic architecture of psychiatric disorders has blown away the diagnostic boundaries that are defined by currently used diagnostic manuals. The disrupted in schizophrenia 1 (DISC1) gene was originally discovered at the breakpoint of an inherited chromosomal translocation, which segregates with major mental illnesses. In addition, many biological studies have indicated a role for DISC1 in early neurodevelopment and synaptic regulation. Given that DISC1 is thought to drive a range of endophenotypes that underlie major mental conditions, elucidating the biology of DISC1 may enable the construction of new diagnostic categories for mental illnesses with a more meaningful biological foundation.

title: Behavioral Phenotypes of Disc1 Missense Mutations in Mice
abstract: To support the role of DISC1 in human psychiatric disorders, we identified and analyzed two independently derived ENU-induced mutations in Exon 2 of mouse Disc1. Mice with mutation Q31L showed depressive-like behavior with deficits in the forced swim test and other measures that were reversed by the antidepressant bupropion, but not by rolipram, a phosphodiesterase-4 (PDE4) inhibitor. In contrast, L100P mutant mice exhibited schizophrenic-like behavior, with profound deficits in prepulse inhibition and latent inhibition that were reversed by antipsychotic treatment. Both mutant DISC1 proteins exhibited reduced binding to the known DISC1 binding partner PDE4B. Q31L mutants had lower PDE4B activity, consistent with their resistance to rolipram, suggesting decreased PDE4 activity as a contributory factor in depression. This study demonstrates that Disc1 missense mutations in mice give rise to phenotypes related to depression and schizophrenia, thus supporting the role of DISC1 in major mental illness.

title: Dominant-negative DISC1 transgenic mice display schizophrenia-associated phenotypes detected by measures translatable to humans
abstract: Here, we report generation and characterization of Disrupted-In-Schizophrenia-1 (DISC1) genetically engineered mice as a potential model for major mental illnesses, such as schizophrenia. DISC1 is a promising genetic risk factor for major mental illnesses. In this transgenic model, a dominant-negative form of DISC1 (DN-DISC1) is expressed under the αCaMKII promoter. In vivo MRI of the DN-DISC1 mice detected enlarged lateral ventricles particularly on the left side, suggesting a link to the asymmetrical change in anatomy found in brains of patients with schizophrenia. Furthermore, selective reduction in the immunoreactivity of parvalbumin in the cortex, a marker for an interneuron deficit that may underlie cortical asynchrony, is observed in the DN-DISC1 mice. These results suggest that these transgenic mice may be used as a model for schizophrenia. DN-DISC1 mice also display several behavioral abnormalities, including hyperactivity, disturbance in sensorimotor gating and olfactory-associated behavior, and an anhedonia/depression-like deficit.

title: Specific developmental disruption of disrupted-in-schizophrenia-1 function results in schizophrenia-related phenotypes in mice
abstract: Disrupted-in-schizophrenia 1 (DISC1) was initially discovered through a balanced translocation (1;11)(q42.1;q14.3) that results in loss of the C terminus of the DISC1 protein, a region that is thought to play an important role in brain development. Here, we use an inducible and reversible transgenic system to demonstrate that early postnatal, but not adult induction, of a C-terminal portion of DISC1 in mice results in a cluster of schizophrenia-related phenotypes, including reduced hippocampal dendritic complexity, depressive-like traits, abnormal spatial working memory, and reduced sociability. Accordingly, we report that individuals in a discordant twin sample with a DISC1 haplotype, associating with schizophrenia as well as working memory impairments and reduced gray matter density, were more likely to show deficits in sociability than those without the haplotype. Our findings demonstrate that alterations in DISC1 function during brain development contribute to schizophrenia pathogenesis.

title: A mutation in mouse Disc1 that models a schizophrenia risk allele leads to specific alterations in neuronal architecture and cognition
abstract: DISC1 is a strong candidate susceptibility gene for schizophrenia, bipolar disorder, and depression. Using a mouse strain carrying an endogenous Disc1 orthologue engineered to model the putative effects of the disease-associated chromosomal translocation we demonstrate that impaired Disc1 function results in region-specific morphological alterations, including alterations in the organization of newly born and mature neurons of the dentate gyrus. Field recordings at CA3/CA1 synapses revealed a deficit in short-term plasticity. Using a battery of cognitive tests we found a selective impairment in working memory (WM), which may relate to deficits in WM and executive function observed in individuals with schizophrenia. Our results implicate malfunction of neural circuits within the hippocampus and medial prefrontal cortex and selective deficits in WM as contributing to the genetic risk conferred by this gene.

title: Inducible expression of mutant human DISC1 in mice is associated with brain and behavioral abnormalities reminiscent of schizophrenia
abstract: A strong candidate gene for schizophrenia and major mental disorders, disrupted-in-schizophrenia 1 (DISC1) was first described in a large Scottish family in which a balanced chromosomal translocation segregates with schizophrenia and other psychiatric illnesses. The translocation mutation may result in loss of DISC1 function via haploinsufficiency or dominant-negative effects of a predicted mutant DISC1 truncated protein product. DISC1 has been implicated in neurodevelopment, including maturation of the cerebral cortex. To evaluate the neuronal and behavioral effects of mutant DISC1, the Tet-off system under the regulation of the CAMKII promoter was used to generate transgenic mice with inducible expression of mutant human DISC1 (hDISC1) limited to forebrain regions, including cerebral cortex, hippocampus and striatum. Expression of mutant hDISC1 was not associated with gross neurodevelopmental abnormalities, but led to a mild enlargement of the lateral ventricles and attenuation of neurite outgrowth in primary cortical neurons. These morphological changes were associated with decreased protein levels of endogenous mouse DISC1, LIS1 and SNAP-25. Compared to their sex-matched littermate controls, mutant hDISC1 transgenic male mice exhibited spontaneous hyperactivity in the open field and alterations in social interaction, and transgenic female mice showed deficient spatial memory. The results show that the neuronal and behavioral effects of mutant hDISC1 are consistent with a dominant-negative mechanism, and are similar to some features of schizophrenia. The present mouse model may facilitate the study of aspects of the pathogenesis of schizophrenia.

title: Schizophrenia-Related Neural and Behavioral Phenotypes in Transgenic Mice Expressing Truncated Disc1
abstract: Disrupted-in-Schizophrenia-1 (DISC1), identified by positional cloning of a balanced translocation (1;11) with the breakpoint in intron 8 of a large Scottish pedigree, is associated with a range of neuropsychiatric disorders including schizophrenia. To model this mutation in mice, we have generated Disc1tr transgenic mice expressing 2 copies of truncated Disc1 encoding the first 8 exons using a bacterial artificial chromosome (BAC). With this partial simulation of the human situation, we have discovered a range of phenotypes including a series of novel features not previously reported. Disc1tr transgenic mice display enlarged lateral ventricles, reduced cerebral cortex, partial agenesis of the corpus callosum, and thinning of layers II/III with reduced neural proliferation at midneurogenesis. Parvalbumin GABAergic neurons are reduced in the hippocampus and medial prefrontal cortex, and displaced in the dorsolateral frontal cortex. In culture, transgenic neurons grow fewer and shorter neurites. Behaviorally, transgenic mice exhibit increased immobility and reduced vocalization in depression-related tests, and impairment in conditioning of latent inhibition. These abnormalities in Disc1tr transgenic mice are consistent with findings in severe schizophrenia.

title: Disrupted in Schizophrenia 1 Regulates Neuronal Progenitor Proliferation via Modulation of GSK3β/β-Catenin Signaling
abstract: The Disrupted in Schizophrenia 1 (DISC1) gene is disrupted by a balanced chromosomal translocation (1; 11) (q42; q14.3) in a Scottish family with a high incidence of major depression, schizophrenia, and bipolar disorder. Subsequent studies provided indications that DISC1 plays a role in brain development. Here, we demonstrate that suppression of DISC1 expression reduces neural progenitor proliferation, leading to premature cell cycle exit and differentiation. Several lines of evidence suggest that DISC1 mediates this function by regulating GSK3beta. First, DISC1 inhibits GSK3beta activity through direct physical interaction, which reduces beta-catenin phosphorylation and stabilizes beta-catenin. Importantly, expression of stabilized beta-catenin overrides the impairment of progenitor proliferation caused by DISC1 loss of function. Furthermore, GSK3 inhibitors normalize progenitor proliferation and behavioral defects caused by DISC1 loss of function. Together, these results implicate DISC1 in GSK3beta/beta-catenin signaling pathways and provide a framework for understanding how alterations in this pathway may contribute to the etiology of psychiatric disorders.

title: Maternal Immune Activation during Gestation Interacts with Disc1 Point Mutation to Exacerbate Schizophrenia-Related Behaviors in Mice
abstract: Schizophrenia is thought to result from interactions between susceptible genotypes and environmental risk factors. DISC1 is an important gene for schizophrenia and mood disorders based on both human and animal studies. In the present study we sought to investigate interactions between two distinct point mutations in the mouse Disc1 gene (L100P and Q31L) and maternal immune activation (MIA) during pregnancy with polyinosinic:polycytidylic acid (polyI:C). C given at 5 mg/kg impaired cognitive and social behavior in both wild-type (WT) and Disc1-Q31L+/− offspring, and reduced prepulse inhibition at 16 but not 8 weeks of age. Disc1-L100P+/− mutants were more sensitive to MIA than WT or Disc1-Q31L+/− mice. Interleukin-6 (IL-6) is a critical cytokine for mediating the behavioral and transcriptional effects of polyI:C. We found a more pronounced increase of IL-6 in response to polyI:C in fetal brain in Disc1-L100P+/− mice compared with WT or Disc1-Q31L+/− mice. Coadministration of an anti-IL-6 antibody with polyI:C reversed schizophrenia-related behavioral phenotypes in Disc1-L100P+/− mice. In summary, we found specific interactions between discrete genetic (Disc1-L100P+/−) and environmental factors (MIA) that exacerbate schizophrenia-related phenotypes. IL-6 may be important in the pathophysiology of this interaction.

title: Neonatal polyI:C treatment in mice results in schizophrenia-like behavioral and neurochemical abnormalities in adulthood
abstract: It has been reported that viral infection in the first and second trimesters of pregnancy in humans increases the risk of subsequently developing schizophrenia. To develop a mouse model of immune activation during the early postnatal period, neonatal ICR mice were repeatedly injected with polyriboinosinic-polyribocytidilic acid (polyI:C; an inducer of strong innate immune responses) for 5 days (postnatal day 2-6) which may correspond, in terms of brain development, to the early second trimester in human. Cognitive and emotional behavior as well as the extracellular level of glutamate in the hippocampus were analyzed at the age of 10-12 weeks old. C-treated mice showed anxiety-like behavior, impairment of object recognition memory and social behavior, and sensorimotor gating deficits, as compared to the saline-treated control group. Depolarization-evoked glutamate release in the hippocampus was impaired in polyI:C-treated mice compared to saline-treated control mice. Furthermore, to investigate the effect of neonatal immune activation on the expression levels of schizophrenia-related genes, we analyzed mRNA levels in the hippocampus 2 and 24h after polyI:C treatment. No significant differences or only transient and marginal changes were observed between polyI:C-treated and saline-treated control mice in the expression levels of schizophrenia-related genes in the hippocampus.

title: Effects of antipsychotics on the behavioral deficits in human dominant-negative DISC1 transgenic mice with neonatal polyI:C treatment
abstract: Interactions of environmental and genetic factors may play a role in the pathoetiology of schizophrenia. We have recently developed a novel animal model of mental disorders such as schizophrenia by inducing abnormal immune response during the perinatal period in mice with overexpression of the human dominant-negative form of disrupted-in-schizophrenia 1 (DN-DISC1). In the present study, we investigated the effects of antipsychotics on the behavioral deficits in this animal model for mental disorders with gene-environment interaction. Neonatal DN-DISC1 transgenic (DN-DISC1 tg) mice were repeatedly injected with polyriboinosinic-polyribocytidylic acid (polyI:C) for 5 days from postnatal days 2 to 6. The behavioral analyses were performed in adulthood. Clozapine (3mg/kg) or haloperidol (1mg/kg) was administered orally once a day from 1 week before starting a series of behavioral experiments and continued until the end of the study. Cognitive impairment in polyI:C-treated DN-DISC1 tg mice was improved by repeated administration of clozapine while haloperidol had no effect. Both antipsychotics suppressed the augmentation of MK-801-induced hyperactivity in the model mice. Neither clozapine nor haloperidol ameliorated the impairments of social behaviors in polyI:C-treated DN-DISC1 tg mice. These results suggest that the polyI:C-treated DN-DISC tg mice are quite unique as an animal model for mental disorders. Furthermore, this mouse model may be useful for the screening of potential antipsychotic compounds that could be more effective than clozapine in ameliorating negative symptoms and cognitive impairment in schizophrenia.

title: Chronic exposure of mutant DISC1 mice to lead produces sex-dependent abnormalities consistent with schizophrenia and related mental disorders: a gene-environment interaction study.
abstract: The glutamatergic hypothesis of schizophrenia suggests that hypoactivity of the N-methyl-D-aspartate receptor (NMDAR) is an important factor in the pathophysiology of schizophrenia and related mental disorders. The environmental neurotoxicant, lead (Pb(2+)), is a potent and selective antagonist of the NMDAR. Recent human studies have suggested an association between prenatal Pb(2+) exposure and the increased likelihood of schizophrenia later in life, possibly via interacting with genetic risk factors. In order to test this hypothesis, we examined the neurobehavioral consequences of interaction between Pb(2+) exposure and mutant disrupted in schizophrenia 1 (mDISC1), a risk factor for major psychiatric disorders. Mutant DISC1 and control mice born by the same dams were raised and maintained on a regular diet or a diet containing moderate levels of Pb(2+). Chronic, lifelong exposure of mDISC1 mice to Pb(2+) was not associated with gross developmental abnormalities but produced sex-dependent hyperactivity, exaggerated responses to the NMDAR antagonist, MK-801, mildly impaired prepulse inhibition of the acoustic startle, and enlarged lateral ventricles. Together, these findings support the hypothesis that environmental toxins could contribute to the pathogenesis of mental disease in susceptible individuals.

title: Nurr1 Is Required for Maintenance of Maturing and Adult Midbrain Dopamine Neurons
abstract: Transcription factors involved in the specification and differentiation of neurons often continue to be expressed in the adult brain, but remarkably little is known about their late functions. Nurr1, one such transcription factor, is essential for early differentiation of midbrain dopamine (mDA) neurons but continues to be expressed into adulthood. In Parkinson's disease, Nurr1 expression is diminished and mutations in the Nurr1 gene have been identified in rare cases of disease; however, the significance of these observations remains unclear. Here, a mouse strain for conditional targeting of the Nurr1 gene was generated, and Nurr1 was ablated either at late stages of mDA neuron development by crossing with mice carrying Cre under control of the dopamine transporter locus or in the adult brain by transduction of adeno-associated virus Cre-encoding vectors. Nurr1 deficiency in maturing mDA neurons resulted in rapid loss of striatal DA, loss of mDA neuron markers, and neuron degeneration. In contrast, a more slowly progressing loss of striatal DA and mDA neuron markers was observed after ablation in the adult brain. As in Parkinson's disease, neurons of the substantia nigra compacta were more vulnerable than cells in the ventral tegmental area when Nurr1 was ablated at late embryogenesis. The results show that developmental pathways play key roles for the maintenance of terminally differentiated neurons and suggest that disrupted function of Nurr1 and other developmental transcription factors may contribute to neurodegenerative disease.

title: Prenatal Immune Activation Interacts with Genetic Nurr1 Deficiency in the Development of Attentional Impairments
abstract: Prenatal exposure to infection has been linked to increased risk of neurodevelopmental brain disorders, and recent evidence implicates altered dopaminergic development in this association. However, since the relative risk size of prenatal infection appears relatively small with respect to long-term neuropsychiatric outcomes, it is likely that this prenatal insult interacts with other factors in shaping the risk of postnatal brain dysfunctions. In the present study, we show that the neuropathological consequences of prenatal viral-like immune activation are exacerbated in offspring with genetic predisposition to dopaminergic abnormalities induced by mutations in Nurr1, a transcription factor highly essential for normal dopaminergic development. We combined a mouse model of heterozygous genetic deletion of Nurr1 with a model of prenatal immune challenge by the viral mimetic poly(I:C) (polyriboinosinic polyribocytidilic acid). In our gene–environment interaction model, we demonstrate that the combination of the genetic and environmental factors not only exerts additive effects on locomotor hyperactivity and sensorimotor gating deficits, but further produces synergistic effects in the development of impaired attentional shifting and sustained attention. We further demonstrate that the combination of the two factors is necessary to trigger maldevelopment of prefrontal cortical and ventral striatal dopamine systems. Our findings provide evidence for specific gene–environment interactions in the emergence of enduring attentional impairments and neuronal abnormalities pertinent to dopamine-associated brain disorders such as schizophrenia and attention deficit/hyperactivity disorder, and further emphasize a critical role of abnormal dopaminergic development in these etiopathological processes.

title: Monitoring the Future Survey Methodology and Definitions of Terms Note: the following Information Was Excerpt- Ed From
abstract: Note: The following information was excerpted from Jerald G. Bachman, Lloyd D. Johnston, and Patrick M. O'Malley, Monitoring the Future 2000 ), pp. 2-11, 13, 14; Lloyd D. Johnston et al., Monitoring the Future National Survey Results on Drug Use, 1975-2003, Volumes I and II (Bethesda, MD: U.S. Department of Health and Human Services, 2004); and information provided by the Monitoring the Future Project. Non-substantive editorial adaptations have been made.

title: Cannabis and psychosis: an update on course and biological plausible mechanisms
abstract: Cannabis use is the most commonly abused illicit substance. Its relation with psychosis remains a topic of debate. Epidemiological studies suggest that cannabis is a component cause accounting for approximately 10% of cases. An increasing number of studies have been published on neurobiological effects of cannabis and vulnerability of psychosis.  Acute cannabis administration can induce memory impairments, sometimes persisting months following abstinence. There is no evidence that residual effects on cognition remain after years of abstinence. The scarce literature on neuro-imaging mainly done in nonpsychotic populations, show little evidence that cannabis has effects on brain anatomy. Acute effects of cannabis include increases of cerebral blood flow, whereas long-term effects of cannabis include attenuation of cerebral blood flow. In animals Δ9-tetrahydrocannabinol enhances dopaminergic neurotransmission in brain regions known to be implicated in psychosis. Studies in humans show that genetic vulnerability may add to increased risk of developing psychosis and cognitive impairments following cannabis consumption. Δ9-tetrahydrocannabinol induces psychotic like states and memory impairments in healthy volunteers.  Simultaneously with increasing understanding of neurobiological cannabis effects, there is a lack of studies in people with psychosis. There are plausible mechanisms that might explain the psychotogenic effects of cannabis.

title: Cannabis dependence and psychotic symptoms in young people
abstract: The aims of this research were to use data gathered over the course of a 21 year longitudinal study to examine the linkages between cannabis dependence at ages 18 and 21 and rates of psychotic symptoms taking into account previous symptom levels and other confounding factors.  Data were gathered during the course of the Christchurch Health and Development Study (CHDS). The CHDS is a longitudinal study of a birth cohort of 1265 children who have been studied from birth to age 21. As part of this study, data were gathered on cannabis dependence and psychotic symptoms at ages 18 and 21.  Young people meeting DSM-IV criteria for cannabis dependence had elevated rates of psychotic symptoms at ages 18 (rate ratio = 3.7; 95% CI 2.8–5.0; P<0.0001) and 21 (rate ratio = 2.3; 95% CI 1.7–3.2; P<0.0001). These associations were adjusted for previous psychotic symptoms and a range of other confounding factors using a generalized estimating equation model. This analysis showed that after adjustment for confounding factors, those meeting criteria for cannabis dependence still had an increased rate of psychotic symptoms (rate ratio = 1.8; 95% CI 1.2–2.6; P<0.005).  The results show that the development of cannabis dependence is associated with increased rates of psychotic symptoms in young people even when pre-existing symptoms and other background factors are taken into account.

title: Cannabis use in adolescence and risk for adult psychosis: longitudinal prospective study
abstract: Papers pp 1195, 1199

The strongest evidence that cannabis use may be a risk factor for later psychosis comes from a Swedish cohort study which found that heavy cannabis use at age 18 increased the risk of later schizophrenia sixfold. 1 2 This study could not establish whether adolescent cannabis use was a consequence of pre-existing psychotic symptoms rather than a cause. We present the first prospective longitudinal study of adolescent cannabis use as a risk factor for adult schizophreniform disorder, taking into account childhood psychotic symptoms3 antedating cannabis use.

View this table:

Association between cannabis use in adolescence and schizophrenia and depressive symptoms and disorders at age 26 (n=759), controlling for childhood psychotic symptoms and use of other drugs in adolescence



The Dunedin multidisciplinary health and development study (a study of a general population birth cohort of 1037 individuals born in Dunedin, New Zealand, in 1972-3)4 has a 96% follow up rate at age 26. It obtained information on psychotic symptoms at age 11 and drug use at ages 15 and 18 from self reports and assessed …

title: Causal association between cannabis and psychosis: examination of the evidence
abstract: Causal association between cannabis and psychosis: examination of the evidence . Arseneault L, Cannon M, Witton J & Murray RM . ( 2004 ) British Journal of Psychiatry , 184 , 110 – 117 . 
 
 
 
Background  Controversy remains as to whether cannabis acts as a causal risk factor for schizophrenia or other functional psychotic illnesses. 
 
 
 
To examine critically the evidence that cannabis causes psychosis using established criteria of causality. 
 
 
 
We identified five studies that included a well-defined sample drawn from population-based registers or cohorts and used prospective measures of cannabis use and adult psychosis. 
 
 
 
Results  On an individual level, cannabis use confers an overall twofold increase in the relative risk for later schizophrenia. At the population level, elimination of cannabis use would reduce the incidence of schizophrenia by approximately 8%, assuming a causal relationship. Cannabis use appears to be neither a sufficient nor a necessary cause for psychosis. It is a component cause, part of a complex constellation of factors leading to psychosis. 
 
 
 
Conclusions  Cases of psychotic disorder could be prevented by discouraging cannabis use among vulnerable youths. Research is needed to understand the mechanisms by which cannabis causes psychosis.

title: Association between cannabis use and psychosis-related outcomes using sibling pair analysis in a cohort of young adults.
abstract: Prospective cohort studies have identified an association between cannabis use and later psychosis-related outcomes, but concerns remain about unmeasured confounding variables. The use of sibling pair analysis reduces the influence of unmeasured residual confounding.



To explore the association between cannabis use and psychosis-related outcomes.



A sibling pair analysis nested within a prospective birth cohort.



Births at a Brisbane, Australia, hospital.



Three thousand eight hundred one young adults born between 1981 and 1984 as part of the Mater-University Study of Pregnancy.



Cannabis use and 3 psychosis-related outcomes (nonaffective psychosis, hallucinations, and Peters et al Delusions Inventory score) were assessed at the 21-year follow-up. Associations between duration since first cannabis use and psychosis-related outcomes were examined using logistic regression adjusted for sex, age, parental mental illness, and hallucinations at the 14-year follow-up. Within 228 sibling pairs, the association between within-pair differences in duration since first cannabis use and Peters et al Delusions Inventory score was examined with general linear modeling. The potential impact of attrition was examined.



Duration since first cannabis use was associated with all 3 psychosis-related outcomes. For those with duration since first cannabis use of 6 or more years, there was a significantly increased risk of (1) nonaffective psychosis (adjusted odds ratio, 2.2; 95% confidence interval, 1.1-4.5), (2) being in the highest quartile of Peters et al Delusions Inventory score (adjusted odds ratio, 4.2; 95% confidence interval, 4.2-5.8), and (3) hallucinations (adjusted odds ratio, 2.8; 95% confidence interval, 1.9-4.1). Within sibling pairs, duration since first cannabis use and higher scores on the Peters et al Delusions Inventory remained significantly associated.



Early cannabis use is associated with psychosis-related outcomes in young adults. The use of sibling pairs reduces the likelihood that unmeasured confounding explains these findings. This study provides further support for the hypothesis that early cannabis use is a risk-modifying factor for psychosis-related outcomes in young adults.

title: Genetic variation underlying psychosis-inducing effects of cannabis: critical review and future directions.
abstract: Cannabis use is associated with an increased risk for psychotic disorder, yet most cannabis users do not develop psychosis, suggesting that other factors are also involved. This paper reviews the available evidence suggesting that differential sensitivity to the psychosis-inducing effects of cannabis may be related to underlying genetic liability. There is robust evidence that persons at psychometric risk for psychosis are most vulnerable to display psychotic symptoms subsequent to the use of cannabis. Multiple studies have also found that persons at familial risk for psychosis have an increased sensitivity to the effects of cannabis. Together, these findings support the concept of a biological interaction between cannabis use and one's underlying genetic vulnerability. At the molecular-genetic level, however, few (if any) interactions have been consistently replicated, although a reported interaction with variation in AKT1 is promising and deserves further follow-up. The apparent lack of consistent replication can be ascribed to problems of initial gene selection, statistical power, a bias towards positive results and insufficient attempts at true replication, leading to the conclusion that increased sample sizes, greater density of genetic markers and a stronger focus on true replication are necessary. The major challenge for molecular-genetic gene-environment interaction research will be to combine the agnostic detection of disorder-associated genetic variants from genome-wide studies with the hypothesis-based approach from epidemiological and neurobiological studies. Possible strategies for future cannabis interaction studies are discussed.

title: Early Cannabis Use, Polygenic Risk Score for Schizophrenia and Brain Maturation in Adolescence.
abstract: Cannabis use during adolescence is known to increase the risk for schizophrenia in men. Sex differences in the dynamics of brain maturation during adolescence may be of particular importance with regard to vulnerability of the male brain to cannabis exposure.



To evaluate whether the association between cannabis use and cortical maturation in adolescents is moderated by a polygenic risk score for schizophrenia.



Observation of 3 population-based samples included initial analysis in 1024 adolescents of both sexes from the Canadian Saguenay Youth Study (SYS) and follow-up in 426 adolescents of both sexes from the IMAGEN Study from 8 European cities and 504 male youth from the Avon Longitudinal Study of Parents and Children (ALSPAC) based in England. A total of 1577 participants (aged 12-21 years; 899 [57.0%] male) had (1) information about cannabis use; (2) imaging studies of the brain; and (3) a polygenic risk score for schizophrenia across 108 genetic loci identified by the Psychiatric Genomics Consortium. Data analysis was performed from March 1 through December 31, 2014.



Cortical thickness derived from T1-weighted magnetic resonance images. Linear regression tests were used to assess the relationships between cannabis use, cortical thickness, and risk score.



Across the 3 samples of 1574 participants, a negative association was observed between cannabis use in early adolescence and cortical thickness in male participants with a high polygenic risk score. This observation was not the case for low-risk male participants or for the low- or high-risk female participants. Thus, in SYS male participants, cannabis use interacted with risk score vis-à-vis cortical thickness (P = .009); higher scores were associated with lower thickness only in males who used cannabis. Similarly, in the IMAGEN male participants, cannabis use interacted with increased risk score vis-à-vis a change in decreasing cortical thickness from 14.5 to 18.5 years of age (t137 = -2.36; P = .02). Finally, in the ALSPAC high-risk group of male participants, those who used cannabis most frequently (≥61 occasions) had lower cortical thickness than those who never used cannabis (difference in cortical thickness, 0.07 [95% CI, 0.01-0.12]; P = .02) and those with light use (<5 occasions) (difference in cortical thickness, 0.11 [95% CI, 0.03-0.18]; P = .004).



Cannabis use in early adolescence moderates the association between the genetic risk for schizophrenia and cortical maturation among male individuals. This finding implicates processes underlying cortical maturation in mediating the link between cannabis use and liability to schizophrenia.

title: Chronic Adolescent Exposure to Δ-9-Tetrahydrocannabinol in COMT Mutant Mice: Impact on Psychosis-Related and Other Phenotypes
abstract: Cannabis use confers a two-fold increase in the risk for psychosis, with adolescent use conferring even greater risk. A high–low activity catechol-O-methyltransferase (COMT) polymorphism may modulate the effects of adolescent Δ-9-tetrahydrocannabinol (THC) exposure on the risk for adult psychosis. Mice with knockout of the COMT gene were treated chronically with THC (4.0 and 8.0 mg/kg over 20 days) during either adolescence (postnatal days (PDs) 32–52) or adulthood (PDs 70–90). The effects of THC exposure were then assessed in adulthood across behavioral phenotypes relevant for psychosis: exploratory activity, spatial working memory (spontaneous and delayed alternation), object recognition memory, social interaction (sociability and social novelty preference), and anxiety (elevated plus maze). Adolescent THC administration induced a larger increase in exploratory activity, greater impairment in spatial working memory, and a stronger anti-anxiety effect in COMT knockouts than in wild types, primarily among males. No such effects of selective adolescent THC administration were evident for other behaviors. Both object recognition memory and social novelty preference were disrupted by either adolescent or adult THC administration, independent of genotype. The COMT genotype exerts specific modulation of responsivity to chronic THC administration during adolescence in terms of exploratory activity, spatial working memory, and anxiety. These findings illuminate the interaction between genes and adverse environmental exposures over a particular stage of development in the expression of the psychosis phenotype.

title: Chronic Pubertal, but not Adult Chronic Cannabinoid Treatment Impairs Sensorimotor Gating, Recognition Memory, and the Performance in a Progressive Ratio Task in Adult Rats
abstract: There is evidence from studies in humans and animals that a vulnerable period for chronic cannabinoid administration exists during certain phases of development. The present study tested the hypothesis that long-lasting interference of cannabinoids with the developing endogenous cannabinoid system during puberty causes persistent behavioral alterations in adult rats. Chronic treatment with the synthetic cannabinoid agonist WIN 55,212-2 (WIN) (1.2 mg/kg) or vehicle was extended over 25 days either throughout the rats' puberty or for a similar time period in adult rats. The rats received 20 injections intraperitoneally (i.p.), which were not delivered regularly. Adult rats were tested for object recognition memory, performance in a progressive ratio (PR) operant behavior task, locomotor activity, and prepulse inhibition (PPI) of the acoustic startle response (ASR). PPI was significantly disrupted only by chronic peripubertal cannabinoid treatment. This long-lasting PPI deficit was reversed by the acute administration of the dopamine antagonist haloperidol. Furthermore, we found deficits in recognition memory of pubertal-treated rats and these animals showed lower break points in a PR schedule, whereas food preference and locomotion were not affected. Adult chronic cannabinoid treatment had no effect on the behaviors tested. Therefore, we conclude that puberty in rats is a vulnerable period with respect to the adverse effects of cannabinoid treatment. Since PPI deficits, object recognition memory impairments, and anhedonia/avolition are among the endophenotypes of schizophrenia, we propose chronic cannabinoid administration during pubertal development as an animal model for some aspects of the etiology of schizophrenia.

title: Adolescent Cannabinoid Exposure Induces a Persistent Sub‐Cortical Hyper‐Dopaminergic State and Associated Molecular Adaptations in the Prefrontal Cortex
abstract: Considerable evidence suggests that adolescent exposure to delta‐9‐tetrahydrocanabinol (THC), the psychoactive component in marijuana, increases the risk of developing schizophrenia‐related symptoms in early adulthood. In the present study, we used a combination of behavioral and molecular analyses with in vivo neuronal electrophysiology to compare the long‐term effects of adolescent versus adulthood THC exposure in rats. We report that adolescent, but not adult, THC exposure induces long‐term neuropsychiatric‐like phenotypes similar to those observed in clinical populations. Thus, adolescent THC exposure induced behavioral abnormalities resembling positive and negative schizophrenia‐related endophenotypes and a state of neuronal hyperactivity in the mesocorticolimbic dopamine (DA) pathway. Furthermore, we observed profound alterations in several prefrontal cortical molecular pathways consistent with sub‐cortical DAergic dysregulation. Our findings demonstrate a profound dissociation in relative risk profiles for adolescent versus adulthood exposure to THC in terms of neuronal, behavioral, and molecular markers resembling neuropsychiatric pathology.

title: From real-world events to psychosis: the emerging neuropharmacology of delusions.
abstract: The earliest stages of delusion are characterized by an overabundance of meaningful coincidences impinging on the sufferer's existing worldview. Successive events are seen by him as pointing to, and then confirming, a fundamentally new reality that takes him over and engulfs his everyday life. Research over the last 4 decades has revealed the importance of dopamine (DA), D2 receptors, and the basal ganglia in psychotic thinking. Recent work has implicated the aberrant reward learning initiated by the excess release of striatal DA in the attribution of excessive importance or "salience" to insignificant stimuli and events. But our knowledge of what is happening beyond D2 receptors has remained scant. The gap is especially apparent at the cellular and microcircuit levels, encompassing the plastic changes, which are believed to be essential for new learning, and whose processes may go awry in major mental illness. Now new pharmacological findings are advancing our understanding of information processing and learning within the striatum. DA has an important role in setting the strength of individual striatal connections, but it does not act in isolation. Two other modulator systems are critical, the endocannabinoids and adenosine. Thus, at medium spiny neurons belonging to the indirect pathway, D2 stimulation evokes endocannabinoid-mediated depression of cortical inputs. Adenosine acting at A2A receptors elicits the opposite effect. Remarkably, drugs that target the endocannabinoid and purinergic systems also have pro- or antipsychotic properties. Here, we discuss how the 3 modulators regulate learning within the striatum and how their dysfunction may lead to delusional thinking.

title: Linkage Analysis Followed by Association Show NRG1 Associated with Cannabis Dependence in African Americans
abstract: A genetic contribution to cannabis dependence (CaD) has been established but susceptibility genes for CaD remain largely unknown.



We employed a multistage design to identify genetic variants underlying CaD. We first performed a genome-wide linkage scan for CaD in 384 African American (AA) and 354 European American families ascertained for genetic studies of cocaine and opioid dependence. We then conducted association analysis under the linkage peak, first using data from a genome-wide association study from the Study of Addiction: Genetics and Environment, followed by replication studies of prioritized single nucleotide polymorphisms (SNPs) in independent samples.



We identified the strongest linkage evidence with CaD (logarithm of odds = 2.9) on chromosome 8p21.1 in AAs. In the association analysis of the Study of Addiction: Genetics and Environment sample under the linkage peak, we identified one SNP (rs17664708) associated with CaD in both AAs (odds ratio [OR] = 2.93, p = .0022) and European Americans (OR = 1.38, p = .02). This SNP, located at NRG1, a susceptibility gene for schizophrenia, was prioritized for further study. We replicated the association of rs17664708 with CaD in an independent AAs sample (OR = 2.81, p = .0068). The joint analysis of the two AA samples demonstrated highly significant association between rs17664708 and CaD with adjustment for either global (p = .00044) or local ancestry (p = .00075).



Our study shows that NRG1 is probably a susceptibility gene for CaD, based on convergent evidence of linkage and replicated associations in two independent AA samples.

title: Heterozygous neuregulin 1 mice display greater baseline and Δ9-tetrahydrocannabinol-induced c-Fos expression
abstract: Cannabis use may increase the risk of developing schizophrenia by precipitating the disorder in genetically vulnerable individuals. Neuregulin 1 (NRG1) is a schizophrenia susceptibility gene and mutant mice heterozygous for the transmembrane domain of this gene (Nrg1 HET mice) exhibit a schizophrenia-related phenotype. We have recently shown that Nrg1 HET mice are more sensitive to the behavioral effects of the main psychoactive constituent of cannabis, Delta(9)-tetrahydrocannabinol (THC). In the present study, we examined the effects of THC (10 mg/kg i.p.) on neuronal activity in Nrg1 HET mice and wild type-like (WT) mice using c-Fos immunohistochemistry. In the lateral septum, THC selectively increased c-Fos expression in Nrg1 HET mice with no corresponding effect being observed in WT mice. In addition, THC promoted a greater increase in c-Fos expression in Nrg1 HET mice than WT mice in the central nucleus of the amygdala, the bed nucleus of the stria terminalis and the paraventricular nucleus of the hypothalamus. Consistent with Nrg1 HET mice exhibiting a schizophrenia-related phenotype, these mice expressed greater drug-free levels of c-Fos in two regions thought to be involved in schizophrenia, the shell of the nucleus accumbens and the lateral septum. Interestingly, the effects of genotype on c-Fos expression, drug-free or following THC exposure, were only observed when animals experienced behavioral testing prior to perfusion. This suggests an interaction with stress was necessary for the promotion of these effects. These data provide neurobiological correlates for the enhanced behavioral sensitivity of Nrg1 HET mice to THC and reinforce the existence of cannabinoid-neuregulin 1 interactions in the CNS. This research may enhance our understanding of how genetic factors increase individual vulnerability to schizophrenia and cannabis-induced psychosis.

title: Heterozygous neuregulin 1 mice are more sensitive to the behavioural effects of Δ9-tetrahydrocannabinol
abstract: RationaleCannabis use may precipitate schizophrenia especially if the individual has a genetic vulnerability to this mental disorder. Human and animal research indicates that neuregulin 1 (Nrg1) is a susceptibility gene for schizophrenia.ObjectivesThe aim of this study was to investigate whether dysfunction in the Nrg1 gene modulates the behavioural effects of Δ9-tetrahydrocannabinol (THC), the major psychotropic component of cannabis.Materials and methodsHeterozygous Nrg1 transmembrane-domain knockout mice (Nrg1 HET) were treated with acute THC (0, 5 or 10 mg/kg i.p.) 30 min before being tested using open field (OF), hole board (HB), light-dark (LD), elevated plus maze (EPM), social interaction (SI) and prepulse inhibition (PPI) tests.ResultsNrg1 HET mice showed differences in baseline behaviour with regard to locomotor activity, exploration and anxiety. More importantly, they were more sensitive to the locomotor suppressant actions of THC compared to wild type-like (WT) mice. In addition, Nrg1 HET mice expressed a greater THC-induced enhancement in % PPI than WT mice. The effects of THC on anxiety-related behaviour were task-dependent, with Nrg1 HET mice being more susceptible than WT mice to the anxiogenic effects of THC in LD, but not in the EPM, SI and OF tests.ConclusionsNrg1 HET mice were more sensitive to the acute effects of THC in an array of different behaviours including those that model symptoms of schizophrenia. It appears that variation in the schizophrenia-related neuregulin 1 gene alters the sensitivity to the behavioural effects of cannabinoids.

title: A follow-up study: acute behavioural effects of Δ9-THC in female heterozygous Neuregulin 1 transmembrane domain mutant mice
abstract: RationaleHeavy cannabis use is linked with an increased risk for schizophrenia. We showed previously that male heterozygous neuregulin 1 transmembrane domain (Nrg1 HET) mice are more sensitive to some effects of the psychotropic cannabis constituent Δ9-tetrahydrocannabinol (THC). We report data from a follow-up study in female Nrg1 HET mice, investigating THC effects on behaviours with some relevance to schizophrenia.MethodsMice were injected with THC (0, 5 or 10 mg/kg i.p.) 30 min before a test battery: open field, elevated plus maze, novel object recognition (set 1) or light–dark, social interaction (SI) and prepulse inhibition (PPI 1: variable interstimulus interval (ISI); set 2). Another set (set 3) was injected with the same doses of THC before a fixed interstimulus interval PPI test (PPI 2).ResultsFemale Nrg1 HETs displayed the hallmark increased locomotor activity at 5 months and anxiolytic-like behaviour in the open field at 3 and 5 months. THC decreased locomotor activity in both genotypes. THC selectively reduced some SI behaviours in WT mice. Baseline PPI was enhanced in mutants under a variable ISI, while THC had no effect on PPI using either protocol.ConclusionsThis study reports novel findings on the baseline PPI profile and resistance to THC-induced social withdrawal in female Nrg1 HET mice. This is the first description of THC effects in females of this mouse model and suggests that the transmembrane domain Nrg1 mutation does not appear to have a severe impact on the behavioural sensitivity to THC in female mice.

title: The schizophrenia susceptibility gene neuregulin 1 modulates tolerance to the effects of cannabinoids.
abstract: Cannabis increases the risk of schizophrenia in genetically vulnerable individuals. In this study we aim to show that the schizophrenia susceptibility gene neuregulin 1 (Nrg1) modulates the development of tolerance to cannabinoids in mice. Nrg1 heterozygous (HET) and wild-type (WT) mice were treated daily for 15 d with the synthetic analogue of Δ9-tetrahydrocannabinol, CP55,940 (0.4 mg/kg). We measured the impact of this exposure on locomotor activity, anxiety, prepulse inhibition (PPI), body temperature and FosB/ΔFosB immunohistochemistry. Tolerance to CP55,940-induced hypothermia and locomotor suppression developed more rapidly in Nrg1 HET mice than WT mice. Conversely in the light-dark test, while tolerance to the anxiogenic effect of CP55,940 developed in WT mice over days of testing, Nrg1 hypomorphs maintained marked anxiety even after 15 d of treatment. Repeated cannabinoid exposure selectively increased FosB/ΔFosB expression in the lateral septum, ventral part (LSV) of Nrg1 HET but not WT mice. On day 1 of exposure opposite effects of CP55,940 treatment were observed on PPI, i.e. it was facilitated in Nrg1 hypomorphs and impaired in WT mice, despite the drug significantly impairing the acoustic startle reflex equally in both genotypes. These effects of CP55,940 on PPI were not maintained as both genotypes became tolerant to cannabinoid action with repeated exposure. Our results highlight that Nrg1 modulates the development of cannabinoid tolerance dependent on the parameter being measured. Furthermore, these data reinforce the notion that the VLS is an important brain region involved in Nrg1-cannabinoid interactions.

title: Transmembrane domain Nrg1 mutant mice show altered susceptibility to the neurobehavioural actions of repeated THC exposure in adolescence.
abstract: Heavy cannabis abuse increases the risk of developing schizophrenia. Adolescents appear particularly vulnerable to the development of psychosis-like symptoms after cannabis use. To test whether the schizophrenia candidate gene neuregulin 1 (NRG1) modulates the effects of cannabinoids in adolescence, we tested male adolescent heterozygous transmembrane domain Nrg1 mutant (Nrg1 TM HET) mice and wild type-like littermates (WT) for their neurobehavioural response to repeated Δ(9)-tetrahydrocannabinol (THC, 10 mg/kg i.p. for 21 d starting on post-natal day 31). During treatment and 48 h after treatment withdrawal, we assessed several behavioural parameters relevant to schizophrenia. After behavioural testing we measured autoradiographic CB(1), 5-HT(2A) and NMDA receptor binding. The hyperlocomotor phenotype typical of Nrg1 mutants emerged after drug withdrawal and was more pronounced in vehicle than THC-treated Nrg1 TM HET mice. All mice were equally sensitive to THC-induced suppression of locomotion. However, mutant mice appeared protected against inhibiting effects of repeated THC on investigative social behaviours. Neither THC nor Nrg1 genotype altered prepulse inhibition. Repeated adolescent THC promoted differential effects on CB(1) and 5-HT(2A) receptor binding in the substantia nigra and insular cortex respectively, decreasing binding in WT while increasing it in Nrg1 TM HET mice. THC also selectively affected 5-HT(2A) receptor binding in several other regions in WT mice, whereas NMDA receptor binding was only affected in mutant mice. Overall, Nrg1 mutation does not appear to increase the induction of psychotomimetic symptoms by repeated adolescent THC exposure but may attenuate some of its actions on social behaviour and schizophrenia-relevant neurotransmitter receptor profiles.

title: Novel molecular changes induced by Nrg1 hypomorphism and Nrg1-cannabinoid interaction in adolescence: a hippocampal proteomic study in mice
abstract: Neuregulin 1 (NRG1) is linked to an increased risk of developing schizophrenia and cannabis dependence. Mice that are hypomorphic for Nrg1 (Nrg1 HET mice) display schizophrenia-relevant behavioral phenotypes and aberrant expression of serotonin and glutamate receptors.  HET mice also display idiosyncratic responses to the main psychoactive constituent of cannabis, Δ9-tetrahydrocannabinol (THC). To gain traction on the molecular pathways disrupted by Nrg1 hypomorphism and Nrg1-cannabinoid interactions we conducted a proteomic study. Adolescent wildtype (WT) and Nrg1 HET mice were exposed to repeated injections of vehicle or THC and their hippocampi were submitted to 2D gel proteomics. Comparison of WT and Nrg1 HET mice identified proteins linked to molecular changes in schizophrenia that have not been previously associated with Nrg1. These proteins are involved in vesicular release of neurotransmitters such as SNARE proteins; enzymes impacting serotonergic neurotransmission, and proteins affecting growth factor expression.  HET mice treated with THC expressed a distinct protein expression signature compared to WT mice. Replicating prior findings, THC caused proteomic changes in WT mice suggestive of greater oxidative stress and neurodegeneration. We have previously observed that THC selectively increased hippocampal NMDA receptor binding of adolescent Nrg1 HET mice. Here we observed outcomes consistent with heightened NMDA-mediated glutamatergic neurotransmission. This included differential expression of proteins involved in NMDA receptor trafficking to the synaptic membrane; lipid raft stabilization of synaptic NMDA receptors; and homeostatic responses to dampen excitotoxicity. These findings uncover novel proteins altered in response to Nrg1 hypomorphism and Nrg1-cannabinoid interactions that improves our molecular understanding of Nrg1 signaling and Nrg1-mediated genetic vulnerability to the neurobehavioral effects of cannabinoids.

title: Neural basis of anxiolytic effects of cannabidiol (CBD) in generalized social anxiety disorder: a preliminary report
abstract: Animal and human studies indicate that cannabidiol (CBD), a major constituent of cannabis, has anxiolytic properties. However, no study to date has investigated the effects of this compound on human pathological anxiety and its underlying brain mechanisms. The aim of the present study was to investigate this in patients with generalized social anxiety disorder (SAD) using functional neuroimaging. Regional cerebral blood flow (rCBF) at rest was measured twice using (99m)Tc-ECD SPECT in 10 treatment-naïve patients with SAD. In the first session, subjects were given an oral dose of CBD (400 mg) or placebo, in a double-blind procedure. In the second session, the same procedure was performed using the drug that had not been administered in the previous session. Within-subject between-condition rCBF comparisons were performed using statistical parametric mapping. Relative to placebo, CBD was associated with significantly decreased subjective anxiety (p < 0.001), reduced ECD uptake in the left parahippocampal gyrus, hippocampus, and inferior temporal gyrus (p < 0.001, uncorrected), and increased ECD uptake in the right posterior cingulate gyrus (p < 0.001, uncorrected). These results suggest that CBD reduces anxiety in SAD and that this is related to its effects on activity in limbic and paralimbic brain areas.

title: Therapeutic Potential of Cannabinoids in Psychosis
abstract: Over recent years, the interest in the endocannabinoid system (ECS) as a new target for the treatment of schizophrenia has evolved. The ECS represents one of the most relevant neurotransmitter systems in the brain and mainly fulfills a homeostatic role in terms of neurotransmission but also with respect to inflammatory processes. Two main approaches to the modulation of endocannabinoid functioning have been chosen so far. First, the selective blockade or inverse agonism of the type 1 cannabinoid receptor has been tested for the improvement of acute psychotic symptoms, as well as for the improvement of cognitive functions in schizophrenia. This was not effective in either case. Second, the modulation of endocannabinoid levels by use of the phytocannabinoid cannabidiol and selective fatty acid amide hydrolase inhibitors has been proposed, and the antipsychotic properties of cannabidiol are currently being investigated in humans. Unfortunately, for most of these trials that have focused on psychopathological and cognitive effects of cannabidiol, no published data are available. However, there is first evidence that cannabidiol may ameliorate psychotic symptoms with a superior side-effect profile compared with established antipsychotics. In conclusion, several clinical trials targeting the ECS in acute schizophrenia have either been completed or are underway. Although publicly available results are currently limited, preliminary data indicate that selected compounds modulating the ECS may be effective in acute schizophrenia. Nevertheless, so far, sample sizes of patients investigated are not sufficient to come to a final judgment, and no maintenance studies are available to ensure long-term efficacy and safety.

title: Distinct Neurobehavioural Effects of Cannabidiol in Transmembrane Domain Neuregulin 1 Mutant Mice
abstract: The cannabis constituent cannabidiol (CBD) possesses anxiolytic and antipsychotic properties. We have previously shown that transmembrane domain neuregulin 1 mutant (Nrg1 TM HET) mice display altered neurobehavioural responses to the main psychoactive constituent of cannabis, Δ9-tetrahydrocannabinol. Here we investigated whether Nrg1 TM HET mice respond differently to CBD and whether CBD reverses schizophrenia-related phenotypes expressed by these mice. Adult male Nrg1 TM HET and wild type-like littermates (WT) received vehicle or CBD (1, 50 or 100 mg/kg i.p.) for 21 days. During treatment and 48 h after withdrawal we measured behaviour, whole blood CBD concentrations and autoradiographic receptor binding. Nrg1 HET mice displayed locomotor hyperactivity, PPI deficits and reduced 5-HT2A receptor binding density in the substantia nigra, but these phenotypes were not reversed by CBD. However, long-term CBD (50 and 100 mg/kg) selectively enhanced social interaction in Nrg1 TM HET mice. Furthermore, acute CBD (100 mg/kg) selectively increased PPI in Nrg1 TM HET mice, although tolerance to this effect was manifest upon repeated CBD administration. Long-term CBD (50 mg/kg) also selectively increased GABAA receptor binding in the granular retrosplenial cortex in Nrg1 TM HET mice and reduced 5-HT2A binding in the substantia nigra in WT mice. Nrg1 appears necessary for CBD-induced anxiolysis since only WT mice developed decreased anxiety-related behaviour with repeated CBD treatment. Altered pharmacokinetics in mutant mice could not explain our findings since no genotype differences existed in CBD blood concentrations. Here we demonstrate that Nrg1 modulates acute and long-term neurobehavioural effects of CBD, which does not reverse the schizophrenia-relevant phenotypes.

title: Adolescent cannabis exposure interacts with mutant DISC1 to produce impaired adult emotional memory
abstract: Cannabis is an increasingly popular and controversial drug used worldwide. Cannabis use often begins during adolescence, a highly susceptible period for environmental stimuli to alter functional and structural organization of the developing brain. Given that adolescence is a critical time for the emergence of mental illnesses before full-onset in early adulthood, it is particularly important to investigate how genetic insults and adolescent cannabis exposure interact to affect brain development and function. Here we show for the first time that a perturbation in disrupted in schizophrenia 1 (DISC1) exacerbates the response to adolescent exposure to delta-9-tetrahydrocannabinol (Δ(9)-THC), a major psychoactive ingredient of cannabis, consistent with the concept that gene-environment interaction may contribute to the pathophysiology of psychiatric conditions. We found that chronic adolescent treatment with Δ(9)-THC exacerbates deficits in fear-associated memory in adult mice that express a putative dominant-negative mutant of DISC1 (DN-DISC1). Synaptic expression of cannabinoid receptor 1 (CB1R) is down-regulated in the prefrontal cortex, hippocampus, and amygdala, critical brain regions for fear-associated memory, by either expression of DN-DISC1 or adolescent Δ(9)-THC treatment. Notably, elevation of c-Fos expression evoked by context-dependent fear memory retrieval is impaired in these brain regions in DN-DISC1 mice. We also found a synergistic reduction of c-Fos expression induced by cue-dependent fear memory retrieval in DN-DISC1 with adolescent Δ(9)-THC exposure. These results suggest that alteration of CB1R-mediated signaling in DN-DISC1 mice may underlie susceptibility to detrimental effects of adolescent cannabis exposure on adult behaviors.

title: A novel protein isoform of catechol O-methyltransferase (COMT): brain expression analysis in schizophrenia and bipolar disorder and effect of Val158Met genotype
abstract: A novel protein isoform of catechol O -methyltransferase (COMT): brain expression analysis in schizophrenia and bipolar disorder and effect of Val 158 Met genotype

title: COMT Val158Met–Stress Interaction in Psychosis: Role of Background Psychosis Risk
abstract: The interplay between the catechol‐O‐methyltransferase (COMT) Val158Met polymorphism and environmental stress may have etiological relevance for psychosis, but differential effects have been reported in healthy control and patient groups, suggesting that COMT Val158Met interactions with stress may be conditional on background genetic risk for psychotic disorder.  Patients with a nonaffective psychotic disorder (n = 86) and control participants (n = 109) were studied with the experience sampling method (a structured diary technique) in order to assess stress, negative affect and momentary psychotic symptoms in the flow of daily life.  Multilevel analyses revealed significant three‐way interactions between group status (patient or control), COMT genotype and stress in the model of negative affect (χ2(2) = 13.26, P < 0.01) as well as in the model of momentary psychotic symptoms (χ2(2) = 6.92, P < 0.05). Exploration of the three‐way interaction revealed that in patients, COMT genotype moderated the association between stress and negative affect (χ2(4) = 11.50, P < 0.005), as well as the association between stress and momentary psychosis (χ2(4) = 12.79, P < 0.005). Met/Met genotype patients showed significantly increased psychotic and affective reactivity to stress in comparison to the Val/Met and Val/Val genotypes. In contrast, healthy controls did not display large or significant COMT Val158Met X stress interactions.  Important differences exist in the effect of COMT Val158Met on stress reactivity, which may depend on background risk for psychotic disorder. Differential sensitivity to environmental stress occasioned by COMT Val158Met may be contingent on higher order interactions with genetic variation underlying psychotic disorder.

title: Gene-environment interaction on cognition: a twin study of childhood maltreatment and COMT variability.
abstract: The functional variant Val(158)Met in the coding sequence of COMT gene is involved in the modulation of dopamine availability in the prefrontal cortex in both clinical and general population samples. It has been suggested that the interplay between this genotype and early environmental factors could be used to predict the observed variation in cognitive flexibility. However, other genetic variants and environmental factors may confound the association and produce the inconsistent results commonly found in the literature. In the present study we aimed at testing putative interaction mechanisms between childhood maltreatment and COMT genotypic variability that might explain a proportion of the observed variability of cognitive flexibility in the population. Our design was based on a sample of adult monozygotic twins, which allowed us to test these effects free from potential genetic and shared-environmental confounding factors. Results showed that unique environmental effects of childhood maltreatment significantly impacted cognitive performance among Met/Met subjects. Interestingly, the direction of the association indicated that exposure to early stressful experiences was associated with enhanced cognitive flexibility in this genotype group. These results suggest that COMT may operate as a plasticity gene that provides differential cognitive capacity to respond to environmental stressors.

title: Psychosis‐inducing effects of cannabis are related to both childhood abuse and COMT genotypes
abstract: To test whether the association between childhood abuse, cannabis use and psychotic experiences (PEs) was moderated by the COMT (catechol‐O‐methyltransferase) gene.

title: Moderation of the Effect of Adolescent-Onset Cannabis Use on Adult Psychosis by a Functional Polymorphism in the Catechol-O-Methyltransferase Gene: Longitudinal Evidence of a Gene X Environment Interaction
abstract: Recent evidence documents that cannabis use by young people is a modest statistical risk factor for psychotic symptoms in adulthood, such as hallucinations and delusions, as well as clinically significant schizophrenia. The vast majority of cannabis users do not develop psychosis, however, prompting us to hypothesize that some people are genetically vulnerable to the deleterious effects of cannabis.



In a longitudinal study of a representative birth cohort followed to adulthood, we tested why cannabis use is associated with the emergence of psychosis in a minority of users, but not in others.



A functional polymorphism in the catechol-O-methyltransferase (COMT) gene moderated the influence of adolescent cannabis use on developing adult psychosis. Carriers of the COMT valine158 allele were most likely to exhibit psychotic symptoms and to develop schizophreniform disorder if they used cannabis. Cannabis use had no such adverse influence on individuals with two copies of the methionine allele.



These findings provide evidence of a gene x environment interaction and suggest that a role of some susceptibility genes is to influence vulnerability to environmental pathogens.

title: Genetic vs. pharmacological inactivation of COMT influences cannabinoid-induced expression of schizophrenia-related phenotypes.
abstract: Catechol-O-methyltransferase (COMT) is an important enzyme in the metabolism of dopamine and disturbance in dopamine function is proposed to be central to the pathogenesis of schizophrenia. Clinical epidemiological studies have indicated cannabis use to confer a 2-fold increase in risk for subsequent onset of psychosis, with adolescent-onset use conveying even higher risk. There is evidence that a high activity COMT polymorphism moderates the effects of adolescent exposure to cannabis on risk for adult psychosis. In this paper we compared the effect of chronic adolescent exposure to the cannabinoid WIN 55212 on sensorimotor gating, behaviours related to the negative symptoms of schizophrenia, anxiety- and stress-related behaviours, as well as ex-vivo brain dopamine and serotonin levels, in COMT KO vs. wild-type (WT) mice. Additionally, we examined the effect of pretreatment with the COMT inhibitor tolcapone on acute effects of this cannabinoid on sensorimotor gating in C57BL/6 mice. COMT KO mice were shown to be more vulnerable than WT to the disruptive effects of adolescent cannabinoid treatment on prepulse inhibition (PPI). Acute pharmacological inhibition of COMT in C57BL/6 mice also modified acute cannabinoid effects on startle reactivity, as well as PPI, indicating that chronic and acute loss of COMT can produce dissociable effects on the behavioural effects of cannabinoids. COMT KO mice also demonstrated differential effects of adolescent cannabinoid administration on sociability and anxiety-related behaviour, both confirming and extending earlier reports of COMT×cannabinoid effects on the expression of schizophrenia-related endophenotypes.

title: Chronic Adolescent Exposure to Delta-9-Tetrahydrocannabinol in COMT Mutant Mice: Impact on Indices of Dopaminergic, Endocannabinoid and GABAergic Pathways
abstract: Cannabis use confers a two-fold increase in risk for psychosis, with adolescent use conferring an even greater risk. A high-low activity polymorphism in catechol-O-methyltransferase (COMT), a gene encoding the COMT enzyme involved in dopamine clearance in the brain, may interact with adolescent cannabis exposure to increase risk for schizophrenia. The impact of such an interaction on central neurotransmitter pathways implicated in schizophrenia is unknown. Male mice with knockout of the COMT gene were treated chronically with delta-9-tetrahydrocannabinol (THC) during adolescence (postnatal day 32–52). We measured the size and density of GABAergic cells and the protein expression of cannabinoid receptor 1 (CB1R) in the prefrontal cortex (PFC) and hippocampus (HPC) in knockout mice relative to heterozygous mutants and wild-type controls. Size and density of dopaminergic neurons was also assessed in the ventral tegmental area (VTA) across the genotypes. COMT genotype × THC treatment interactions were observed for: (1) dopaminergic cell size in the VTA, (2) CB1R protein expression in the HPC, and (3) parvalbumin (PV) cell size in the PFC. No effects of adolescent THC treatment were observed for PV and dopaminergic cell density across the COMT genotypes. COMT genotype modulates the effects of chronic THC administration during adolescence on indices of neurotransmitter function in the brain. These findings illuminate how COMT deletion and adolescent cannabis use can interact to modulate the function of neurotransmitters systems implicated in schizophrenia.

title: Stress, the Hippocampus and the Hypothalamic-Pituitary-Adrenal Axis: Implications for the Development of Psychotic Disorders
abstract: The experience of stress is commonly implicated in models of the onset of psychotic disorders. However, prospective studies investigating associations between biological markers of stress and the emergence of psychotic disorders are limited and inconclusive. One biological system proposed as the link between the psychological experience of stress and the development of psychosis is the Hypothalamic-Pituitary-Adrenal (HPA) axis. This paper summarizes and discusses evidence supporting a role for HPA-axis dysfunction in the early phase of schizophrenia and related disorders.  A selective review of psychiatric and psychological research on stress, coping, HPA-axis, the hippocampus and psychotic disorders was performed, with a particular focus on the relationship between HPA-axis dysfunction and the onset of psychotic disorders.  Individual strands of past research have suggested that the HPA-axis is dysfunctional in at least some individuals with established psychotic disorders; that the hippocampus is an area of the brain that appears to be implicated in the onset and maintenance of psychotic disorders; and that an increase in the experience of stress precedes the onset of a psychotic episode in some individuals. Models of the onset and maintenance of psychotic disorders that link these individual strands of research and strategies for examining these models are proposed in this paper.  The current literature provides some evidence that the onset of psychotic disorders may be associated with a higher rate of stress and changes to the hippocampus. It is suggested that future research should investigate whether a relationship exists between psychological stress, HPA-axis functioning and the hippocampus in the onset of these disorders. Longitudinal assessment of these factors in young people at ‘ultra’ high risk of psychosis and first-episode psychosis cohorts may enhance understanding of the possible interaction between them in the early phases of illness.

title: Longitudinal study of stressful life events and daily stressors among adolescents at high risk for psychotic disorders.
abstract: Psychosocial stress preceding the onset or recurrence of psychotic symptoms has been identified in patients with schizophrenia; yet there is limited understanding of the effects of stress in typically developing adolescents or those who show behavioral signs of risk for schizophrenia spectrum disorders. This study examined the developmental course of symptom progression as a function of stressful life events and daily hassles in adolescents with schizotypal personality disorder (SPD), other personality disorders, or no Axis II disorder. In this prospective longitudinal study, life events and daily stressors were assessed in adolescents aged 12 to 18 years. Results revealed that adolescents with SPD and other personality disorders reported significantly greater total, independent, and undesirable life events than individuals with no Axis II disorders. Youth with SPD report daily hassles to cause more distress compared to peers. Correlational analyses and hierarchal linear regression was used to evaluate the relationship of life events and daily stressors with psychiatric symptoms measured concurrently and 1 year later. Across diagnostic groups, the incidence of independent and undesirable life events were associated with current prodromal symptoms, while the frequency of daily stressors predicted a significant increment in positive, but not negative, prodromal symptoms over time. Therefore, adolescents who report greater daily stressors exhibit an increase in prodromal symptoms over a 1 year period. Psychosocial stress has been implicated in the etiology of schizophrenia, and these findings suggest the importance of life events and daily hassles as potential risk factors in the onset of psychotic symptoms during adolescence.

title: Dissociation mediates the relationship between childhood trauma and hallucination-proneness
abstract: It has been proposed that the relationship between childhood trauma and hallucinations can be explained by dissociative processes. The present study examined whether the effect of childhood trauma on hallucination-proneness is mediated by dissociative tendencies. In addition, the influence of dissociative symptoms on a cognitive process believed to underlie hallucinatory experiences (i.e. reality discrimination; the capacity to discriminate between internal and external cognitive events) was also investigated.  Patients with schizophrenia spectrum disorders (n=45) and healthy controls (with no history of hallucinations; n=20) completed questionnaire measures of hallucination-proneness, dissociative tendencies and childhood trauma, as well as performing an auditory signal detection task.  Compared to both healthy and non-hallucinating clinical controls, hallucinating patients reported both significantly higher dissociative tendencies and childhood sexual abuse. Dissociation positively mediated the effect of childhood trauma on hallucination-proneness. This mediational role was particularly robust for sexual abuse over other types of trauma. Signal detection abnormalities were evident in hallucinating patients and patients with a history of hallucinations, but were not associated with pathological dissociative symptoms.  These results are consistent with dissociative accounts of the trauma-hallucinations link. Dissociation, however, does not affect reality discrimination. Future research should examine whether other cognitive processes associated with both dissociative states and hallucinations (e.g. deficits in cognitive inhibition) may explain the relationship between dissociation and hallucinatory experiences.

title: Hypothesis: social defeat is a risk factor for schizophrenia?
abstract: The increased schizophrenia risks for residents of cities with high levels of competition and for members of disadvantaged groups (for example migrants from low- and middle-income countries, people with low IQ, hearing impairments or a history of abuse) suggest that social factors are important for aetiology. Dopaminergic dysfunctioning is a key mechanism in pathogenesis. This editorial is a selective literature review to delineate a mechanism whereby social factors can disturb dopamine function in the brain. Experiments with rodents have shown that social defeat leads to dopaminergic hyperactivity and to behavioural sensitisation, whereby the animal displays an enhanced behavioural and dopamine response to dopamine agonists. Neuroreceptor imaging studies have demonstrated the same phenomena in patients with schizophrenia who had never received antipsychotics. In humans, the chronic experience of social defeat may lead to sensitisation (and/or increased baseline activity) of the mesolimbic dopamine system and thereby increase the risk for schizophrenia.

title: The social defeat hypothesis of schizophrenia: an update
abstract: Research provides strong evidence of an elevated risk for developing psychotic symptoms and psychotic disorder among various ethnic and other minority groups. Furthermore, ethnicity may modify the risk for autism-spectrum disorder, but the evidence of this is still thin. Misdiagnosis, selective migration and other methodological artefacts are implausible explanations for the findings on psychotic disorder. Instead, we propose that ‘social defeat’, defined as the chronic experience of being excluded from the majority group, may increase the risk for psychotic disorder by sensitizing the mesolimbic dopamine system. Future challenges lie in connecting the underlying biological mechanisms to behavioral expression in socially excluded groups, as well as in bridging the gap with the clinical field and the wider society by stimulating the implementation of strategies that strengthen the position of minority populations.

title: Defeat stress in rodents: From behavior to molecules
abstract: Mood and anxiety disorders are prevalent conditions affecting one out of four people during lifetime. The development of high validity animal models to study these disorders has been a major challenge in the past. When considering experimental approaches for studying affective disorders, the social defeat paradigm has been shown to have etiological, predictive and face validity. Here, we explain the general principle of social defeat stress paradigms, with a strong focus on the resident-intruder model and compare different experimental settings as published to date. We discuss behavioral changes described in defeated animals as well as changes in the animal's physiological parameters. In addition, we provide an overview of the molecular adaptations that are found in animals subjected to defeat stress, with special attention to neural circuits and neuroendocrine signaling. Defeat produces specific behaviors resembling the signs and symptoms of humans with affective disorders, such as anhedonia, social avoidance, despair and anxiety. These can be linked to a wide range of physiological changes-ranging from cardiovascular changes to alterations in the immune system- or by disturbances in specific neurotransmitter systems, in particular serotonin and dopamine. The defeat stress model thus impacts on several functional domains of behavior and may mimic cardinal features of a multitude of psychiatric disorders including depression, post-traumatic stress disorder and schizophrenia. This manuscript critically reviews the core findings, strengths and limitations of the range of animal studies in this field and provides future perspectives.

title: Essential Role of BDNF in the Mesolimbic Dopamine Pathway in Social Defeat Stress
abstract: Mice experiencing repeated aggression develop a long-lasting aversion to social contact, which can be normalized by chronic, but not acute, administration of antidepressant. Using viral-mediated, mesolimbic dopamine pathway–specific knockdown of brain-derived neurotrophic factor (BDNF), we showed that BDNF is required for the development of this experience-dependent social aversion. Gene profiling in the nucleus accumbens indicates that local knockdown of BDNF obliterates most of the effects of repeated aggression on gene expression within this circuit, with similar effects being produced by chronic treatment with antidepressant. These results establish an essential role for BDNF in mediating long-term neural and behavioral plasticity in response to aversive social experiences.

title: Molecular Adaptations Underlying Susceptibility and Resistance to Social Defeat in Brain Reward Regions
abstract: While stressful life events are an important cause of psychopathology, most individuals exposed to adversity maintain normal psychological functioning. The molecular mechanisms underlying such resilience are poorly understood. Here, we demonstrate that an inbred population of mice subjected to social defeat can be separated into susceptible and unsusceptible subpopulations that differ along several behavioral and physiological domains. By a combination of molecular and electrophysiological techniques, we identify signature adaptations within the mesolimbic dopamine circuit that are uniquely associated with vulnerability or insusceptibility. We show that molecular recapitulations of three prototypical adaptations associated with the unsusceptible phenotype are each sufficient to promote resistant behavior. Our results validate a multidisciplinary approach to examine the neurobiological mechanisms of variations in stress resistance, and illustrate the importance of plasticity within the brain's reward circuits in actively maintaining an emotional homeostasis.

title: Partial genetic deletion of neuregulin 1 modulates the effects of stress on sensorimotor gating, dendritic morphology, and HPA axis activity in adolescent mice.
abstract: Stress has been linked to the pathogenesis of schizophrenia. Genetic variation in neuregulin 1 (NRG1) increases the risk of developing schizophrenia and may help predict which high-risk individuals will transition to psychosis. NRG1 also modulates sensorimotor gating, a schizophrenia endophenotype. We used an animal model to demonstrate that partial genetic deletion of Nrg1 interacts with stress to promote neurobehavioral deficits of relevance to schizophrenia. Nrg1 heterozygous (HET) mice displayed greater acute stress-induced anxiety-related behavior than wild-type (WT) mice. Repeated stress in adolescence disrupted the normal development of higher prepulse inhibition of startle selectively in Nrg1 HET mice but not in WT mice. Further, repeated stress increased dendritic spine density in pyramidal neurons of the medial prefrontal cortex (mPFC) selectively in Nrg1 HET mice. Partial genetic deletion of Nrg1 also modulated the adaptive response of the hypothalamic-pituitary-adrenal axis to repeated stress, with Nrg1 HET displaying a reduced repeated stress-induced level of plasma corticosterone than WT mice. Our results demonstrate that Nrg1 confers vulnerability to repeated stress-induced sensorimotor gating deficits, dendritic spine growth in the mPFC, and an abberant endocrine response in adolescence.

title: Social defeat interacts with Disc1 mutations in the mouse to affect behavior
abstract: DISC1 (Disrupted-in-schizophrenia 1) is a strong candidate susceptibility gene for psychiatric disease that was originally discovered in a family with a chromosomal translocation severing this gene. Although the family members with the translocation had an identical genetic mutation, their clinical diagnosis and presentation varied significantly. Gene-environment interactions have been proposed as a mechanism underlying the complex heritability and variable phenotype of psychiatric disorders such as major depressive disorder and schizophrenia. We hypothesized that gene-environment interactions would affect behavior in a mutant Disc1 mouse model. We examined the effect of chronic social defeat (CSD) as an environmental stressor in two lines of mice carrying different Disc1 point mutations, on behaviors relevant to psychiatric illness: locomotion in a novel open field (OF), pre-pulse inhibition (PPI) of the acoustic startle response, latent inhibition (LI), elevated plus maze (EPM), forced swim test (FST), sucrose consumption (SC), and the social interaction task for sociability and social novelty (SSN). We found that Disc1-L100P +/- and wild-type mice have similar anxiety responses to CSD, while Q31L +/- mice had a very different response. We also found evidence of significant gene-environment interactions in the OF, EPM and SSN.

title: Adolescent Stress–Induced Epigenetic Control of Dopaminergic Neurons via Glucocorticoids
abstract: Defeat, Distress, and Glucocorticoids Understanding how individuals control emotions and cope with stressful events is a major clinical concern and of importance for the treatment of psychiatric illnesses (see the Perspective by McEwen). Barik et al. (p. 332) discovered that aggressive defeat stress in mice caused glucocortioid release and increased activity in the dopamine system. Deleting the glucocorticoid receptors in dopaminoceptive neurons completely prevented the social avoidance that usually follows aggressive defeat. How the combination of genetic factors and environmental stressors during adolescence determines adult behavior and how their disturbance results in neuropsychiatric disorders is poorly understood. Niwa et al. (p. 335) found that isolation stress during adolescence, which does not cause any long-lasting changes in wild-type mice, induced significant neurochemical and behavioral alterations in mutant mice expressing a dominant-negative variant of the disrupted in schizophrenia 1 gene under the control of the prion protein promoter. These deficits could be reversed by a glucocorticoid receptor antagonist. Genetically susceptible mice isolated during adolescence can subsequently present schizophrenia-like symptoms.

title: Genetic variation in the 6p22.3 gene DTNBP1, the human ortholog of the mouse dysbindin gene, is associated with schizophrenia.
abstract: Prior evidence has supported the existence of multiple susceptibility genes for schizophrenia. Multipoint linkage analysis of the 270 Irish high-density pedigrees that we have studied, as well as results from several other samples, suggest that at least one such gene is located in region 6p24-21. In the present study, family-based association analysis of 36 simple sequence-length-polymorphism markers and of 17 SNP markers implicated two regions, separated by approximately 7 Mb. The first region, and the focus of this report, is 6p22.3. In this region, single-nucleotide polymorphisms within the 140-kb gene DTNBP1 (dystrobrevin-binding protein 1, or dysbindin) are strongly associated with schizophrenia. Uncorrected, empirical P values produced by the program TRANSMIT were significant (P<.01) for a number of individual SNP markers, and most remained significant when the data were restricted to include only one affected offspring per nuclear family per extended pedigree; multiple three-marker haplotypes were highly significant (P=.008-.0001) under the restricted conditions. The pattern of linkage disequilibrium is consistent with the presence of more than one susceptibility allele, but this important issue is unresolved. The number of markers tested in the adjacent genes, all of which are negative, is not sufficient to rule out the possibility that the dysbindin gene is not the actual susceptibility gene, but this possibility appears to be very unlikely. We conclude that further investigation of dysbindin is warranted.

title: The dystrobrevin binding protein 1 (DTNBP1) gene is associated with schizophrenia in the Irish Case Control Study of Schizophrenia (ICCSS) sample
abstract: DTNBP1 is associated with schizophrenia in many studies, but the associated alleles and haplotypes vary between samples.



We assessed nine single nucleotide polymorphisms (SNPs) in this gene for association with schizophrenia in a new sample of 1021 cases and 626 controls from Ireland.



Four SNPs give evidence of association (0.000018<p<0.045), most strongly with the common allele at rs760761. A haplotype of the common alleles of five markers (including rs760761) and the minor allele of rs2619538 overlapping the 5' end of the DTNBP1 gene also gives evidence for association (p=0.0002). Secondary analyses showed no difference in the association signal based on sex or family history. These results are in agreement with the most consistently observed association with common alleles and common-allele haplotypes, reported in a previous study of Irish cases and controls but not in an Irish high-density family sample. Our results do not support the prior report from a Swedish sample of increased association in cases with a family history of psychotic illness. Comparison of human, chimpanzee and rhesus sequence suggest that rs760761 is a particularly variable position in the primate lineage.



This study provides further evidence from a large case/control sample for association of common DTNBP1 alleles and haplotypes with schizophrenia.

title: Convergent functional genomics of schizophrenia: from comprehensive understanding to genetic risk prediction
abstract: We have used a translational convergent functional genomics (CFG) approach to identify and prioritize genes involved in schizophrenia, by gene-level integration of genome-wide association study data with other genetic and gene expression studies in humans and animal models. Using this polyevidence scoring and pathway analyses, we identify top genes (DISC1, TCF4, MBP, MOBP, NCAM1, NRCAM, NDUFV2, RAB18, as well as ADCYAP1, BDNF, CNR1, COMT, DRD2, DTNBP1, GAD1, GRIA1, GRIN2B, HTR2A, NRG1, RELN, SNAP-25, TNIK), brain development, myelination, cell adhesion, glutamate receptor signaling, G-protein–coupled receptor signaling and cAMP-mediated signaling as key to pathophysiology and as targets for therapeutic intervention. Overall, the data are consistent with a model of disrupted connectivity in schizophrenia, resulting from the effects of neurodevelopmental environmental stress on a background of genetic vulnerability. In addition, we show how the top candidate genes identified by CFG can be used to generate a genetic risk prediction score (GRPS) to aid schizophrenia diagnostics, with predictive ability in independent cohorts. The GRPS also differentiates classic age of onset schizophrenia from early onset and late-onset disease. We also show, in three independent cohorts, two European American and one African American, increasing overlap, reproducibility and consistency of findings from single-nucleotide polymorphisms to genes, then genes prioritized by CFG, and ultimately at the level of biological pathways and mechanisms. Finally, we compared our top candidate genes for schizophrenia from this analysis with top candidate genes for bipolar disorder and anxiety disorders from previous CFG analyses conducted by us, as well as findings from the fields of autism and Alzheimer. Overall, our work maps the genomic and biological landscape for schizophrenia, providing leads towards a better understanding of illness, diagnostics and therapeutics. It also reveals the significant genetic overlap with other major psychiatric disorder domains, suggesting the need for improved nosology.

title: 
 DTNBP1 genotype influences cognitive decline in schizophrenia
abstract: Intellectual decline is common in schizophrenia and predicts functional outcome. While many patients undergo intellectual decline that typically predates the onset of symptoms, few studies have investigated the underlying mechanism through which this occurs. The current study assessed the relationship between intellectual decline in schizophrenia and genetic variation in dysbindin-1 (DTNBP1).



We assessed cognitive decline in 183 Caucasian patients with schizophrenia using a proxy measure of premorbid IQ with which current general cognitive ability (g) was compared. We then tested for a relationship between the risk haplotype identified in previous work (CTCTAC) and intellectual decline.



We found that carriers of the CTCTAC haplotype, demonstrated a significantly greater decline in IQ as compared with non-carriers (p=0.05).



These data suggest that DTNBP1 influences the severity of intellectual decline in schizophrenia and may represent one underlying cause for heterogeneity in cognitive course.

title: DTNBP1 (dysbindin) gene variants modulate prefrontal brain function in schizophrenic patients – support for the glutamate hypothesis of schizophrenias
abstract: Dysbindin (DTNBP1) is a recently characterized protein that seems to be involved in the modulation of glutamatergic neurotransmission in the human brain, thereby influencing prefrontal cortex function and associated cognitive processes. While association, neuroanatomical and cellular studies indicate that DTNBP1 might be one of several susceptibility genes for schizophrenia, the effect of dysbindin on prefrontal brain function at an underlying neurophysiological level has not yet been explored for these patients. The NoGo‐anteriorization (NGA) is a topographical event‐related potential measure, which has been established as a valid neurophysiological marker of prefrontal brain function. In the present study, we investigated the influence of seven dysbindin gene variants on the NGA in a group of 44 schizophrenic patients. In line with our a priori hypothesis, one DTNBP1 polymorphism previously linked to schizophrenia (rs2619528) was found to be associated with changes in the NGA; however, the direction of this association directly contrasts with our previous findings in a healthy control sample. This differential impact of DTNBP1 gene variation on prefrontal functioning in schizophrenic patients vs. healthy controls is discussed in terms of abnormal glutamatergic baseline levels in patients suffering from schizophrenic illnesses. This is the first report on a role of DTNBP1 gene variation for prefrontal functioning at a basic neurophysiological level in schizophrenic patients. An impact on fundamental processes of cognitive response control may be one mechanism by which DTNBP1 gene variants via glutamatergic transmission contribute to the pathophysiology underlying schizophrenic illnesses.

title: Meta-Analysis of Genetic Variation in DTNBP1 and General Cognitive Ability
abstract: The human dystrobrevin binding protein 1 (DTNBP1) gene has been linked to risk for schizophrenia. Recent studies indicate that several single nucleotide polymorphisms (SNPs) in the DTNBP1 gene may also influence general cognitive ability in both schizophrenic patients and healthy control subjects. We examined the relationship between DTNBP1 SNPs and general cognitive ability in nonpsychiatric healthy samples via meta-analysis.



MEDLINE search (12/31/09) yielded 11 articles examining DTNBP1 variation and general cognitive ability, of which 8 studies had data available encompassing 10 independent cohorts (total n = 7592). The phenotype was defined as either the first principal component score from multiple neuropsychological tests (Spearman's g) or full-scale IQ. Meta-analyses were conducted for nine SNPs for which cognitive data were available from at least three cohorts. For each SNP in each cohort, effect size was computed between major allele homozygotes and minor allele carriers; effect size was then pooled across studies using a random effect model.



Pooled effect sizes from two of the nine SNPs (rs1018381 and rs2619522) were -.123 and -.083, ps < .01, respectively, suggesting that the minor allele carriers of these SNPs had lower cognitive ability scores than the major allele homozygotes. Results remained significant after examining heterogeneity among samples and potential publication biases. Other SNPs did not show significant effects on general cognitive ability.



Genetic variation in DTNBP1 modestly influences general cognitive ability. Further studies are needed to elucidate the biological mechanisms that may account for this relationship.

title: Reduced DTNBP1 (dysbindin-1) mRNA in the hippocampal formation of schizophrenia patients
abstract: Genetic and molecular studies indicate that dysbindin-1 plays a role in the pathophysiology of schizophrenia. We examined dysbindin-1 mRNA in the hippocampal formation of patients with schizophrenia and found reduced expression in dentate granule and polymorph cells and in hippocampal field CA3, but not in CA1. Furthermore, there were positive correlations between dysbindin-1 mRNA and expression of synaptic markers known to be reduced in schizophrenia. Our results indicate that previously reported dysbindin-1 protein reductions may be due in part to decreased dysbindin-1 mRNA and that reduced dysbindin-1 may contribute to hippocampal formation synaptic pathology in schizophrenia.

title: Dysbindin-1 in dorsolateral prefrontal cortex of schizophrenia cases is reduced in an isoform-specific manner unrelated to dysbindin-1 mRNA expression.
abstract: DTNBP1 (dystrobrevin binding protein 1) remains a top candidate gene in schizophrenia. Reduced expression of this gene and of its encoded protein, dysbindin-1, have been reported in the brains of schizophrenia cases. It has not been established, however, if the protein reductions encompass all dysbindin-1 isoforms or if they are associated with decreased DTNBP1 gene expression. Using a matched pairs design in which each of 28 Caucasian schizophrenia cases was matched in age and sex to a normal Caucasian control, Western blotting of whole-tissue lysates of dorsolateral prefrontal cortex (DLPFC) revealed significant reductions in dysbindin-1C (but not in dysbindin-1A or -1B) in schizophrenia (P = 0.022). These reductions occurred without any significant change in levels of the encoding transcript in the same tissue samples and in the absence of the only DTNBP1 risk haplotype for schizophrenia reported in the USA. Indeed, no significant correlations were found between case-control differences in any dysbindin-1 isoform and the case-control differences in its encoding mRNA. Consequently, the mean 60% decrease in dysbindin-1C observed in 71% of our case-control pairs appears to reflect abnormalities in mRNA translation and/or processes promoting dysbindin-1C degradation (e.g. oxidative stress, phosphorylation and/or ubiquitination). Given the predominantly post-synaptic localization of dysbindin-1C and known post-synaptic effects of dysbindin-1 reductions in the rodent equivalent of the DLPFC, the present findings suggest that decreased dysbindin-1C in the DLPFC may contribute to the cognitive deficits of schizophrenia by promoting NMDA receptor hypofunction in fast-spiking interneurons.

title: The Schizophrenia-Related Protein Dysbindin-1A Is Degraded and Facilitates NF-Kappa B Activity in the Nucleus
abstract: Dystrobrevin-binding protein 1 (DTNBP1), a gene encoding dysbindin-1, has been identified as a susceptibility gene for schizophrenia. Functioning with partners in synapses or the cytoplasm, this gene regulates neurite outgrowth and neurotransmitter release. Loss of dysbindin-1 affects schizophrenia pathology. Dysbindin-1 is also found in the nucleus, however, the characteristics of dysbindin in the nucleus are not fully understood. Here, we found that dysbindin-1A is degraded in the nucleus via the ubiquitin-proteasome system and that amino acids 2-41 at the N-terminus are required for this process. By interacting with p65, dysbindin-1A promotes the transcriptional activity of NF-kappa B in the nucleus and positively regulates MMP-9 expression. Taken together, the data obtained in this study demonstrate that dysbindin-1A protein levels are highly regulated in the nucleus and that dysbindin-1A regulates transcription factor NF-kappa B activity to promote the expression of MMP-9 and TNF-α.

title: Sandy: a new mouse model for platelet storage pool deficiency.
abstract: Sandy (sdy) is a mouse mutant with diluted pigmentation which recently arose in the DBA/2J strain. Genetic tests indicate it is caused by an autosomal recessive mutation on mouse Chromosome 13 near the cr and Xt genetic loci. This mutation is different genetically and hematologically from previously described mouse pigment mutations with storage pool deficiency (SPD). The sandy mutant has diluted pigmentation in both eyes and fur, is fully viable and has prolonged bleeding times. Platelet serotonin levels are extremely low although ATP dependent acidification activity of platelet organelles appears normal. Also, platelet dense granules are extremely reduced in number when analysed by electron microscopy of unfixed platelets. Platelets have abnormal uptake and flashing of the fluorescent dye mepacrine. Secretion of lysosomal enzymes from kidney and from thrombin-stimulated platelets is depressed 2- and 3-fold, and ceroid pigment is present in kidney. Sandy platelets have a reduced rate of aggregation induced by collagen. The sandy mutant has an unusually severe dense granule defect and thus may be an appropriate model for cases of human Hermansky-Pudlak syndrome with similarly extreme types of SPD. It represents the tenth example of a mouse mutant with simultaneous defects in melanosomes, lysosomes and/or platelet dense granules.

title: Impaired long-term memory retention and working memory in sdy mutant mice with a deletion in Dtnbp1, a susceptibility gene for schizophrenia
abstract: BackgroundSchizophrenia is a complex genetic disorder caused by multiple genetic and environmental factors. The dystrobrevin-binding protein 1 (DTNBP1: dysbindin-1) gene is a major susceptibility gene for schizophrenia. Genetic variations in DTNBP1 are associated with cognitive functions, general cognitive ability and memory function, and clinical features of patients with schizophrenia including negative symptoms and cognitive decline. Since reduced expression of dysbindin-1 has been observed in postmortem brains of patients with schizophrenia, the sandy (sdy) mouse, which has a deletion in the Dtnbp1 gene and expresses no dysbindin-1 protein, could be an animal model of schizophrenia. To address this issue, we have carried out a comprehensive behavioral analysis of the sdy mouse in this study.ResultsIn a rotarod test, sdy mice did not exhibit motor learning whilst the wild type mice did. In a Barnes circular maze test both sdy mice and wild type mice learned to selectively locate the escape hole during the course of the training period and in the probe trial conducted 24 hours after last training. However, sdy mice did not locate the correct hole in the retention probe tests 7 days after the last training trial, whereas wild type mice did, indicating impaired long-term memory retention. A T-maze forced alternation task, a task of working memory, revealed no effect of training in sdy mice despite the obvious effect of training in wild type mice, suggesting a working memory deficit.ConclusionSdy mouse showed impaired long-term memory retention and working memory. Since genetic variation in DTNBP1 is associated with both schizophrenia and memory function, and memory function is compromised in patients with schizophrenia, the sdy mouse may represent a useful animal model to investigate the mechanisms of memory dysfunction in the disorder.

title: Dysbindin Modulates Prefrontal Cortical Glutamatergic Circuits and Working Memory Function in Mice
abstract: Behavioral genetic studies of humans have associated variation in the DTNBP1 gene with schizophrenia and its cognitive deficit phenotypes. The protein coded for by DTNBP1, dysbindin, is expressed within forebrain glutamatergic neurons, in which it interacts with proteins involved in vesicular trafficking and exocytosis. In order to further delineate the cellular, physiological, and behavioral phenotypes associated with reduced dysbindin expression, we conducted studies in mice carrying a null mutation within the dtnbp1 gene. Dysbindin mutants showed impairments of spatial working memory compared with wild-type controls; heterozygous mice showed intermediate levels of cognitive dysfunction. Deep-layer pyramidal neurons recorded in the prefrontal cortex of mutant mice showed reductions in paired-pulse facilitation, and evoked and miniature excitatory post-synaptic currents, indicating a difference in the function of pre-synaptic glutamatergic terminals as well as elevated spike thresholds. Taken together, these data indicate that dysbindin potently regulates excitatory transmission in the prefrontal cortex, potentially through a pre-synaptic mechanism, and consequently modulates cognitive functions depending on this brain region, providing new insights into the molecular mechanisms underlying cortical dysfunction in schizophrenia.

title: Reduced Dysbindin Expression Mediates N-Methyl-D-Aspartate Receptor Hypofunction and Impaired Working Memory Performance
abstract: Schizophrenia is a heritable disorder associated with disrupted neural transmission and dysfunction of brain systems involved in higher cognition. The gene encoding dystrobrevin-binding-protein-1 (dysbindin) is a putative candidate gene associated with cognitive impairments, including memory deficits, in both schizophrenia patients and unaffected individuals. The underlying mechanism is thought to be based in changes in glutamatergic and dopaminergic function within the corticostriatal networks known to be critical for schizophrenia. This hypothesis derives support from studies of mice with a null mutation in the dysbindin gene that exhibit memory dysfunction and excitatory neurotransmission abnormalities in prefrontal and hippocampal networks. At a cellular level, dysbindin is thought to mediate presynaptic glutamatergic transmission.



We investigated the relationship between glutamate receptor dynamics and memory performance in dysbindin mutant mice. We assessed N-methyl-D-aspartate (NMDA) and α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor function in prefrontal cortex pyramidal neurons in vitro with whole-cell recordings, molecular quantitative analyses (reverse transcription-polymerase chain reaction) of the mandatory NMDA receptor subunit NR1, and cognitive function with a spatial working memory task.



Decreases in dysbindin are associated with specific decreases in NMDA-evoked currents in prefrontal pyramidal neurons, as well as decreases in NR1 expression. Furthermore, the degree of NR1 expression correlates with spatial working memory performance, providing a mechanistic explanation for cognitive changes previously associated with dysbindin expression.



These data show a significant downregulation of NMDA receptors due to dysbindin deficiency and illuminate molecular mechanisms mediating the association between dysbindin insufficiency and cognitive impairments associated with schizophrenia, encouraging study of the dysbindin/NR1 expression association in humans with schizophrenia.

title: Dysbindin-1 modulates prefrontal cortical activity and schizophrenia-like behaviors via dopamine/D2 pathways
abstract: Dysbindin-1 regulates D2-receptor trafficking and is implicated in schizophrenia and related cognitive abnormalities, but whether this molecular effect mediates the clinical manifestations of the disorder is unknown. We explored in dysbindin-1-deficient mice (dys−/−) (1) schizophrenia-related behaviors, (2) molecular and electrophysiological changes in medial prefrontal cortex (mPFC) and (3) the dependence of these on D2-receptor stimulation. Dysbindin-1 disruption altered dopamine-related behaviors and impaired working memory under challenging/stressful conditions. Dys−/− pyramidal neurons in mPFC layers II/III were hyperexcitable at baseline but hypoexcitable following D2 stimulation. Dys−/− were also respectively more and less sensitive to D2 agonist- and antagonist-induced behavioral effects. Dys−/− had reduced expression of Ca2+/calmodulin-dependent protein kinase II (CaMKII) and CaMKKβ in mPFC. Chronic D2 agonist treatment reproduced these changes in protein expression, and some of the dys−/− behavioral effects. These results elucidate dysbindin's modulation of D2-related behavior, cortical activity and mPFC CaMK components, implicating cellular and molecular mechanisms of the association of dysbindin with psychosis.

title: Dysbindin‐1 loss compromises NMDAR‐dependent synaptic plasticity and contextual fear conditioning
abstract: Genetic variants in DTNBP1 encoding the protein dysbindin‐1 have often been associated with schizophrenia and with the cognitive deficits prominent in that disorder. Because impaired function of the hippocampus is thought to play a role in these memory deficits and because NMDAR‐dependent synaptic plasticity in this region is a proposed biological substrate for some hippocampal‐dependent memory functions in schizophrenia, we hypothesized that reduced dysbindin‐1 expression would lead to impairments in NMDAR‐dependent synaptic plasticity and in contextual fear conditioning. Acute slices from male mice carrying 0, 1, or 2 null mutant alleles of the Dtnbp1 gene were prepared, and field recordings from the CA1 striatum radiatum were obtained before and after tetanization of Schaffer collaterals of CA3 pyramidal cells. Mice homozygous for the null mutation in Dtnbp1 exhibited significantly reduced NMDAR‐dependent synaptic potentiation compared to wild type mice, an effect that could be rescued by bath application of the NMDA receptor coagonist glycine (10 μM). Behavioral testing in adult mice revealed deficits in hippocampal memory processes. Homozygous null mice exhibited lower conditional freezing, without a change in the response to shock itself, indicative of a learning and memory deficit. Taken together, these results indicate that a loss of dysbindin‐1 impairs hippocampal plasticity which may, in part, explain the role dysbindin‐1 plays in the cognitive impairments of schizophrenia.

title: Dysbindin and Schizophrenia: It's Dopamine and Glutamate All Over Again
abstract: Dysbindin-1 is encoded by the dystrobrevin-binding protein 1 gene (DTNBP1) and is located in synaptic sites throughout human and mouse brain (1). Genetic variations in DTNBP1 impact human cognitive abilities (2-3) and have been associated with risk for schizophrenia (4). Moreover, reduced dysbindin gene and protein expression have been reported in the hippocampus and prefrontal cortex (PFC) of schizophrenic patients (5-8). This latter finding suggests that a molecular phenotype associated with schizophrenia is reduced expression of dysbindin, perhaps of a specific isoform (8), but the role of secondary factors (e.g. drugs, smoking, etc.) and whether altered expression of any dysbindin transcript is the molecular mechanism of genetic risk have not been determined. These uncertainties notwithstanding, mutant mice with diminished DTNBP1 expression have become an informative animal model of reduced dysbindin protein (1, 5-8). 
 
While the statistical evidence for association of DTNBP1 and schizophrenia across diverse population samples is variable, the molecular evidence for a role of dysbindin in dopamine and glutamate signaling, two neurotransmitters at the core of neurochemical hypotheses of psychosis, is fairly consistent. Early speculation that the molecular mechanism of dysbindin's role in psychiatric illness had to do with the dystrophin protein complex, from which its name is derived, has been eclipsed by current data that implicate a pathogenic role of dysbindin as a partner in the biogenesis of lysosome-related organelles complex (BLOC-1). Dysbindin is involved in intracellular protein trafficking involving lysosomes and related organelles and it is important for synaptic homeostasis (1, 9). A number of receptor proteins, including D2 receptors and NR2A receptor subunits, are trafficked after internalization via lysosomal-mediated degradation and dysbindin has been shown to impact these trafficking events. Mice with disrupted dysbindin show selective alterations in internal trafficking of these specific components of dopamine and glutamate signaling, and not of other receptor components that are not trafficked through the lysosomal degradation pathway (e.g. D1 receptors, NR2B components [10-12]). Thus, dysbindin reductions may represent a direct genetic bridge between these two schizophrenia related signaling systems, and the molecular mechanism of DTNBP1 as a psychosis risk gene may involve this bridge. 
 
The report by Karlsgodt and colleagues in this issue of Biological Psychiatry identifies a novel effect of dysbindin reduction in mice, a decrease in NMDA excitation and NR1 mRNA expression in the PFC (13). This finding extends earlier evidence that dysbindin impacts on both pre- and post-synaptic dopamine and glutamate signaling (10-12;14-15). What are the consequences of reduced dysbindin function in the glutamate system? In the hippocampus, dysbindin reduction has been shown to result in increased neuronal surface expression of NR2A, but not NR2B; while total levels of NR2A, NR2B, NR1 and GluR1 are not altered compared to wild-type mice. These modifications result in increased NMDA- but not AMPA-mediated synaptic currents and increased LTP, but not LTD (12). In the PFC of these dysbindin mutant mice, different modifications of the glutamate system have been found, but as in the hippocampus, NR2A surface expression is increased in the PFC, consistent with a defect in BLOC-1 trafficking of internalized NR2A. However, in contrast to the hippocampus, dysbindin reduction in the PFC leads to a decrease in NR2B surface expression (12) and, as now reported by Karlsgodt et al. (13), decreased NR1 mRNA. Moreover, in contrast to that previously found in the hippocampus (12), Karlsgodt and colleagues further report reduced NMDA-mediated current in the PFC of dysbindin mutant mice.  Thus, it seems that dysbindin reductions might differentially affect the glutamate system in the PFC compared with the hippocampus, but it is unclear how dysbindin's predictable role in the BLOC-1 system would have differential ramifications in these cortical regions. It is tempting to speculate that the consistent effect of dysbindin on NR2A trafficking impacts differently on these cortical regions due to their differing connectivity and developmental trajectories. 
 
What are the consequences of reduced dysbindin function in the dopamine system? Quite analogous to its impact on lysosomal trafficking of NR2A but not NR2B subunits, dysbindin reduction increases expression of surface D2 receptors, but not D1, on cortical neurons (10-11). This is due to an enhanced reinsertion of D2 to the neuronal membrane, presumably because the lysosomal trafficking pathway is altered (11). It is interesting to note that the total levels of D2 and D1 receptors are not changed in the cortex of dysbindin mutant mice compared to wild-type mice. Only the levels of D2 receptors on the cell surface are increased (11). The increase in surface D2 receptors results in enhanced sensitivity to D2 agonists, both behaviorally and in terms of the excitability of layer V interneurons and layers II/III pyramidal neurons (11, 16). This may have important consequences in the clinical setting because genetic variations that result in decreased dysbindin functioning might predict important differences in the efficacy and dosing of D2-related drugs (e.g. several antipsychotics). 
 
The effect of increased D2 receptors on the cell surface of dysbindin disrupted mice has rather specific physiologic effects, both regional and cellular. In layer V of the PFC, there is reduced excitability of interneurons but not of pyramidal neurons (11). In contrast, in the more superficial layers II/III of the PFC, dysbindin disruption increases neuron excitability in pyramidal neurons but not interneurons (16). These results implicate potential microcircuit pathophysiological alterations in the PFC following dysbindin reduction. Thus, dysbindin reduction results in a D2-dominated state and alters the pattern of excitability in PFC microcircuits, both mechanisms implicated in schizophrenia and especially in its cognitive deficits (17). 
 
These molecular and physiologic effects of reduced dysbindin on cortical glutamate and dopamine systems directly and the GABA system indirectly would be expected to impact on cortically mediated cognition. Indeed, there are several studies showing an effect of genetic variation in DTNBP1 on human cognition (2-3) and dysbindin altered mice also show abnormalities in cognitive performance. As reported by us (16) and by Karlsgodt et al.(13), dysbindin reductions in C57BL/6J (B6) background mice produce spatial working memory deficits. These working memory deficits seem to depend on the experimental condition and are possibly dependent on altered dopamine/D2 pathways (16), glutamate/NR1 pathways (13) or most likely both. Interestingly, dysbindin seems to have a stronger effect on prefrontally-relevant cognition (e.g. working memory) in comparison to more hippocampal-related cognitive functions (e.g. reference memory) (16). However, further investigation of other executive functions and hippocampal-dependent tasks is required to fully address this question. 
 
In the interpretation of the present and future investigations, it is important to note that dysbindin genetic variations likely interact with the genetic background. In particular, the dysbindin genetic mutation in mice originally occurred spontaneously in the inbred DBA/2J strain (the so called “sandy mice”). On this genetic background, dysbindin reduction produces dramatic locomotor and coordination deficits which might make cognitive investigation more difficult. Moreover, DBA/2J mice per se are impaired in theta burst long-term potentiation, in aspects of learning and memory, and are homozygous for other mutations related to cognitive behavior, and have higher dopaminergic activity in the forebrain compared to the B6 background. This has encouraged backcrossing of the “sandy mouse” with a B6 background strain to limit these confounders (16, 18, and 13), though it is not clear in the Karlsgodt et al., study to what degree the B6 backcrossing has been carried out. Furthermore, a direct comparison of working memory performance between the dysbindin mutation on different genetic backgrounds between (19) and the present work by Karlsgodt et al. (13), is problematic because the test parameters have not been uniformly analyzed. 
 
Dysbindin has substantial value as a genetic link to neurochemical systems strongly implicated in psychosis, particularly dopamine, glutamate and GABA. It illustrates, at least in principle, a mechanism for genetic susceptibility that makes intuitive sense in terms of what we already suspect is important in the pathophysiology of schizophrenia. The debate will surely continue about whether the statistical evidence for genetic association is strong enough and whether altered DTNBP1 expression in schizophrenic brain is a primary phenomenon driven by the clinical risk SNPs. Nevertheless, the compelling biological evidence for a role of dysbindin in modulating neuronal signaling implicated in psychosis should encourage research to follow dysbindin in the search for strategies to individualize outcome with available therapeutic agents and to find new ones.

title: Neurobehavioral abnormalities in the dysbindin‐1 mutant, sandy, on a C57BL/6J genetic background
abstract: Sandy mice have a deletion mutation in the gene encoding dysbindin‐1, Dtnbp1, with consequent reduction of the protein in heterozygotes and its loss in homozygotes. The sandy mouse thus serves as an animal model of dysbindin‐1 function. As this protein is concentrated in synaptic tissue and affects transmitter release, it may affect neuronal processes that mediate behavior. To investigate the neurobehavioral effects of the Dtnbp1 mutation, we studied littermate sandy and wild‐type controls on a C57BL/6J genetic background. The three animal groups were indistinguishable in their external physical characteristics, sensorimotor skills and indices of anxiety‐like behaviors. In the open field, however, homozygous animals were hyperactive and appeared to show less habituation to the initially novel environment. In the Morris water maze, homozygous animals displayed clear deficits in spatial learning and memory with marginal deficits in visual association learning. Apart from the last mentioned deficits, these abnormalities are consistent with hippocampal dysfunction and in some cases with elevated dopaminergic transmission via D2 dopamine receptors. As similar deficits in spatial learning and memory have been found in schizophrenia, where decreased dysbindin‐1 has been found in the hippocampus, the sandy mouse may also model certain aspects of cognition and behavior relevant to schizophrenia.

title: Serious obstetric complications interact with hypoxia-regulated/vascular-expression genes to influence schizophrenia risk
abstract: The etiology of schizophrenia is thought to include both epistasis and gene-environment interactions. We sought to test whether a set of schizophrenia candidate genes regulated by hypoxia or involved in vascular function in the brain (AKT1, BDNF, CAPON, CHRNA7, COMT, DTNBP1, GAD1, GRM3, NOTCH4, NRG1, PRODH, RGS4, TNF-α) interacted with serious obstetric complications to influence risk for schizophrenia. A family-based study of transmission disequilibrium was conducted in 116 trios. Twenty-nine probands had at least one serious obstetric complication (OC) using the McNeil-Sjostrom Scale, and many of the OCs reported were associated with the potential for fetal hypoxia. Analyses were conducted using conditional logistic regression and a likelihood ratio test (LRT) between nested models was performed to assess significance. Of the 13 genes examined, four (AKT1 (three SNPs), BDNF (two SNPs), DTNBP1 (one SNP) and GRM3 (one SNP)) showed significant evidence for gene-by-environment interaction (LRT P-values ranged from 0.011 to 0.037). Although our sample size was modest and the power to detect interactions was limited, we report significant evidence for genes involved in neurovascular function or regulated by hypoxia interacting with the presence of serious obstetric complications to increase risk for schizophrenia.

title: A polymorphism in the dysbindin gene (DTNBP1) associated with multiple psychiatric disorders including schizophrenia
abstract: BackgroundA number of studies have found associations between dysbindin (DTNBP1) polymorphisms and schizophrenia. Recently we identified a DTNBP1 SNP (rs9370822) that is strongly associated with schizophrenia. Individuals diagnosed with schizophrenia were nearly three times as likely to carry the CC genotype compared to the AA genotype.MethodsTo investigate the importance of this SNP in the function of DTNBP1, a number of psychiatric conditions including addictive behaviours and anxiety disorders were analysed for association with rs9370822.ResultsThe DTNBP1 polymorphism was significantly associated with post-traumatic stress disorder (PTSD) as well as nicotine and opiate dependence but not alcohol dependence. Individuals suffering PTSD were more than three times as likely to carry the CC genotype compared to the AA genotype. Individuals with nicotine or opiate dependence were more than twice as likely to carry the CC genotype compared to the AA genotype.ConclusionsThis study provides further support for the importance of DTNBP1 in psychiatric conditions and suggests that there is a common underlying molecular defect involving DTNBP1 that contributes to the development of several anxiety and addictive disorders that are generally recognised as separate clinical conditions. These disorders may actually be different expressions of a single metabolic pathway perturbation. As our participant numbers are limited our observations should be viewed with caution until they are independently replicated.

title: Behavioral abnormalities and dopamine reductions in sdy mutant mice with a deletion in Dtnbp1, a susceptibility gene for schizophrenia.
abstract: Genetic susceptibility plays an important role in the pathogenesis of schizophrenia. Genetic evidence for an association between the dysbindin-1 gene (DTNBP1: dystrobrevin binding protein 1) and schizophrenia has been repeatedly reported in various populations worldwide. Thus, we performed behavioral analyses on homozygous sandy (sdy) mice, which lack dysbindin-1 owing to a deletion in the Dtnbp1 gene. Our results showed that sdy mice were less active and spent less time in the center of an open field apparatus. Consistent with the latter observation, sdy mice also displayed evidence of heightened anxiety-like response and deficits in social interaction. Compared to wild-type mice, sdy mice displayed lower levels of dopamine, but not glutamate, in the cerebral cortex, hippocampus, and hypothalamus. These findings indicate that sdy mice display a number of behavioral abnormalities associated with schizophrenia and suggest that these abnormalities may be mediated by reductions in forebrain dopamine transmission.

title: The dysbindin-containing complex (BLOC-1) in brain: developmental regulation, interaction with SNARE proteins, and role in neurite outgrowth
abstract: Previous studies have implicated DTNBP1 as a schizophrenia susceptibility gene and its encoded protein, dysbindin, as a potential regulator of synaptic vesicle physiology. In this study, we found that endogenous levels of the dysbindin protein in the mouse brain are developmentally regulated, with higher levels observed during embryonic and early postnatal ages than in young adulthood. We obtained biochemical evidence indicating that the bulk of dysbindin from brain exists as a stable component of biogenesis of lysosome-related organelles complex-1 (BLOC-1), a multi-subunit protein complex involved in intracellular membrane trafficking and organelle biogenesis. Selective biochemical interaction between brain BLOC-1 and a few members of the SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) superfamily of proteins that control membrane fusion, including SNAP-25 and syntaxin 13, was demonstrated. Furthermore, primary hippocampal neurons deficient in BLOC-1 displayed neurite outgrowth defects. Taken together, these observations suggest a novel role for the dysbindin-containing complex, BLOC-1, in neurodevelopment, and provide a framework for considering potential effects of allelic variants in DTNBP1—or in other genes encoding BLOC-1 subunits—in the context of the developmental model of schizophrenia pathogenesis.

title: Membrane Fusion: Grappling with SNARE and SM Proteins
abstract: The two universally required components of the intracellular membrane fusion machinery, SNARE and SM (Sec1/Munc18-like) proteins, play complementary roles in fusion. Vesicular and target membrane–localized SNARE proteins zipper up into an α-helical bundle that pulls the two membranes tightly together to exert the force required for fusion. SM proteins, shaped like clasps, bind to trans-SNARE complexes to direct their fusogenic action. Individual fusion reactions are executed by distinct combinations of SNARE and SM proteins to ensure specificity, and are controlled by regulators that embed the SM-SNARE fusion machinery into a physiological context. This regulation is spectacularly apparent in the exquisite speed and precision of synaptic exocytosis, where synaptotagmin (the calcium-ion sensor for fusion) cooperates with complexin (the clamp activator) to control the precisely timed release of neurotransmitters that initiates synaptic transmission and underlies brain function.

title: Genome scan meta-analysis of schizophrenia and bipolar disorder, part II: Schizophrenia.
abstract: Schizophrenia is a common disorder with high heritability and a 10-fold increase in risk to siblings of probands. Replication has been inconsistent for reports of significant genetic linkage. To assess evidence for linkage across studies, rank-based genome scan meta-analysis (GSMA) was applied to data from 20 schizophrenia genome scans. Each marker for each scan was assigned to 1 of 120 30-cM bins, with the bins ranked by linkage scores (1 = most significant) and the ranks averaged across studies (R(avg)) and then weighted for sample size (N(sqrt)[affected casess]). A permutation test was used to compute the probability of observing, by chance, each bin's average rank (P(AvgRnk)) or of observing it for a bin with the same place (first, second, etc.) in the order of average ranks in each permutation (P(ord)). The GSMA produced significant genomewide evidence for linkage on chromosome 2q (PAvgRnk<.000417). Two aggregate criteria for linkage were also met (clusters of nominally significant P values that did not occur in 1,000 replicates of the entire data set with no linkage present): 12 consecutive bins with both P(AvgRnk) and P(ord)<.05, including regions of chromosomes 5q, 3p, 11q, 6p, 1q, 22q, 8p, 20q, and 14p, and 19 consecutive bins with P(ord)<.05, additionally including regions of chromosomes 16q, 18q, 10p, 15q, 6q, and 17q. There is greater consistency of linkage results across studies than has been previously recognized. The results suggest that some or all of these regions contain loci that increase susceptibility to schizophrenia in diverse populations.

title: Preliminary evidence for association between schizophrenia and polymorphisms in the regulatory Regions of the ADRA2A, DRD3 and SNAP-25 Genes
abstract: The results of linkage and candidate gene association studies have led to a range of hypotheses about the pathogenesis of schizophrenia. We limited our study to polymorphisms in candidate genes involved in dopaminergic and noradrenergic systems, and in the 25KDa synaptosomal-associated protein (SNAP-25) gene that is related to neurotransmitter exocytosis. Eight single nucleotide polymorphisms (SNPs) in regulating or coding regions of genes for the alpha-2A adrenergic receptor (ADRA2A), dopamine receptors D1 and D3 (DRD1 and DRD3), dopamine β-hydroxylase (DBH) and SNAP-25 were genotyped in male patients with schizophrenia (n=192) and in healthy controls (n=213). These polymorphisms were previously associated with schizophrenia. The allelic association between schizophrenia and ADRA2A rs1800544 polymorphism, SNAP-25 rs1503112 polymorphism, and DRD3 rs6280 polymorphism was found in our study. However, only observations for rs1503112 survived correction for multiple testing. Association was also evaluated by considering the polymorphisms as interactions; in this case, a likelihood ratio test (LRT) revealed evidence for association with schizophrenia in four polymorphism combinations: two DRD3*SNAP-25 combinations (rs6280*rs3746544 and rs6280*rs3746544, P=0.02), one ADRA2A*SNAP25 combination (rs1800544*rs3746544) and one ADRA2A*DBH combination (rs1800544*rs2519152). Our results are in agreement with the previously proposed role of DNA polymorphisms involved in dopaminergic, noradrenergic and synaptic functions in the pathogenesis of schizophrenia. Further relevant studies including larger sample size and more markers are needed to confirm our results.

title: D2-like dopamine receptors mediate the response to amphetamine in a mouse model of ADHD
abstract: The mechanisms underlying the effects of psychostimulants in attention deficit hyperactivity disorder (ADHD) are not well understood, but indirect evidence implicates D2 dopamine receptors. Here we dissect the components of dopaminergic neurotransmission in the hyperactive mouse mutant coloboma to identify pre- and postsynaptic elements essential for the effects of amphetamine in these mice. Amphetamine treatment reduced locomotor activity in coloboma mice, but induced a robust increase in dopamine overflow suggesting that abnormal regulation of dopamine efflux does not account for the behavioral effect. However, the D2-like dopamine receptor antagonists haloperidol and raclopride, but not the D1-like dopamine receptor antagonist SCH23390, blocked the amphetamine-induced reduction in locomotor activity in coloboma mice, providing direct evidence that D2-like dopamine receptors mediate the effect of amphetamine in these mice. With the precedent established that it is possible to directly antagonize this response, this strategy should prove useful for identifying novel therapeutics in ADHD.

title: D2 dopamine receptor subtype-mediated hyperactivity and amphetamine responses in a model of ADHD
abstract: Low doses of psychostimulants produce beneficial behavioral effects in ADHD patients but the mechanisms underlying the response are not understood. Here we use the hyperactive mouse mutant coloboma to identify D2-like dopamine receptor subtypes that mediate the hyperactivity and response to amphetamine; we have previously demonstrated that D1-like dopamine receptors are not involved. Targeted deletion of the D2, but not the D3 or the D4, dopamine receptor in coloboma mice eliminated the hyperactivity; depleting D2 dopamine receptors also restored the excess dopamine overflow that may drive the hyperactivity to normal concentrations. Similar to its effects on ADHD patients, amphetamine reduced the hyperactivity of coloboma mice. The D2 dopamine receptor-selective antagonist L-741,626, but not D3 or D4 dopamine receptor-selective antagonists, blocked the amphetamine-induced reduction in locomotor activity. Thus, the D2 dopamine receptor subtype mediates both the hyperactivity and response to amphetamine, suggesting a specific target for novel therapeutics in ADHD.

title: Gene-environment interactions affect long-term depression (LTD) through changes in dopamine receptor affinity in Snap25 deficient mice
abstract: Genes and environmental conditions interact in the development of cognitive capacities and each plays an important role in neuropsychiatric disorders such as attention deficit/hyperactivity disorder (ADHD) and schizophrenia. Multiple studies have indicated that the gene for the SNARE protein SNAP-25 is a candidate susceptibility gene for ADHD, as well as schizophrenia, while maternal smoking is a candidate environmental risk factor for ADHD. We utilized mice heterozygous for a Snap25 null allele and deficient in SNAP-25 expression to model genetic effects in combination with prenatal exposure to nicotine to explore genetic and environmental interactions in synaptic plasticity and behavior. We show that SNAP-25 deficient mice exposed to prenatal nicotine exhibit hyperactivity and deficits in social interaction. Using a high frequency stimulus electrophysiological paradigm for long-term depression (LTD) induction, we examined the roles of dopaminergic D2 receptors (D2Rs) and cannabinoid CB1 receptors (CB1Rs), both critical for LTD induction in the striatum. We found that prenatal exposure to nicotine in Snap25 heterozygote null mice produced a deficit in the D2R-dependent induction of LTD, although CB1R regulation of plasticity was not impaired. We also show that prenatal nicotine exposure altered the affinity and/or receptor coupling of D2Rs, but not the number of these receptors in heterozygote null Snap25 mutants. These results refine the observations made in the coloboma mouse mutant, a proposed mouse model of ADHD, and illustrate how gene×environmental influences can interact to perturb neural functions that regulate behavior.

title: A positive correlation between serum levels of mature brain-derived neurotrophic factor and negative symptoms in schizophrenia
abstract: A meta-analysis study reported serum brain-derived neurotrophic factor (BDNF) levels as a potential biomarker for schizophrenia. However, at the time, commercially available human ELISA kits were unable to distinguish between pro-BDNF (precursor BDNF) and mature BDNF, because of limited antibody specificity. Here, we used new ELISA kits, to examine serum levels of mature BDNF and matrix metalloproteinase-9 (MMP-9), which converts pro-BDNF to mature BDNF in schizophrenia. Sixty-three patients with chronic schizophrenia and 52 age- and sex-matched healthy controls were enrolled. Patients were evaluated using the Brief Psychiatry Rating Scale, the Scale for the Assessment of Negative Symptoms (SANS) and neuropsychological tests. Neither serum mature BDNF nor MMP-9 levels differed between patients and controls. In male subgroups, serum MMP-9 levels of smoking patients were higher than those of non-smoking patients, but this was not observed in male controls or the female subgroup. In patients, serum mature BDNF levels were associated with SANS total scores and the Information subtest scores of the Wechsler Adult Intelligence Scale Revised (WAIS-R), while serum MMP-9 levels were associated with smoking and category fluency scores. These findings suggest that neither mature BDNF nor MMP-9 is a suitable biomarker for schizophrenia, although further studies using large samples are needed.

title: Brain derived neurotropic factor (BDNF) is associated with childhood abuse but not cognitive domains in first episode psychosis
abstract: The Brain-derived Neurotrophic Factor (BDNF) modulates cognitive processes and is associated with increased risk of schizophrenia. Childhood trauma (CT) is frequent in patients with psychosis and severely affects course and outcome.



We investigated the hypothesis that BDNF is associated with both CT and cognitive deficits in a sample of first-episode psychosis (FEP) cases and unaffected controls.



Participants with FEP and healthy controls were recruited between August 2008 and July 2011 from South London, UK. Childhood traumatic events were detected using the Childhood Experience of Care and Abuse Questionnaire (CECA-Q). Neuropsychological data were also collected. BDNF plasma levels were measured from fasting blood samples.



Data were available on 87 FEP patients and 152 controls. Our results showed a significant effect of separation ( p=.02), physical (F=4.7; df=1, 118; p=.03) and sexual abuse (F=5.4;  p=.02) on BDNF levels with lower levels among those who experienced the traumatic event compared to those who did not. Physical abuse predicted lower plasma levels of BDNF (β=-.30; p=.03) whereas sexual and/or physical abuse showed a trend (β=-.26; p=.06) in FEP patients but not in unaffected controls. No association between BDNF plasma levels and cognitive functions was found among patients with FEP and controls.



Our findings suggest the possible involvement of BDNF in the onset of first-episode psychosis in individuals exposed to early trauma and propose BDNF as a potential clinical biomarker to detect the detrimental effects of CT on human brain plasticity.

title: Behavioral and molecular neuroepigenetic alterations in prenatally stressed mice: relevance for the study of chromatin remodeling properties of antipsychotic drugs
abstract: We have recently reported that mice born from dams stressed during pregnancy (PRS mice), in adulthood, have behavioral deficits reminiscent of behaviors observed in schizophrenia (SZ) and bipolar (BP) disorder patients. Furthermore, we have shown that the frontal cortex (FC) and hippocampus of adult PRS mice, like that of postmortem chronic SZ patients, are characterized by increases in DNA-methyltransferase 1 (DNMT1), ten-eleven methylcytosine dioxygenase 1 (TET1) and exhibit an enrichment of 5-methylcytosine (5MC) and 5-hydroxymethylcytosine (5HMC) at neocortical GABAergic and glutamatergic gene promoters. Here, we show that the behavioral deficits and the increased 5MC and 5HMC at glutamic acid decarboxylase 67 (Gad1), reelin (Reln) and brain-derived neurotrophic factor (Bdnf) promoters and the reduced expression of the messenger RNAs (mRNAs) and proteins corresponding to these genes in FC of adult PRS mice is reversed by treatment with clozapine (5 mg kg−1 twice a day for 5 days) but not by haloperidol (1 mg kg−1 twice a day for 5 days). Interestingly, clozapine had no effect on either the behavior, promoter methylation or the expression of these mRNAs and proteins when administered to offspring of nonstressed pregnant mice. Clozapine, but not haloperidol, reduced the elevated levels of DNMT1 and TET1, as well as the elevated levels of DNMT1 binding to Gad1, Reln and Bdnf promoters in PRS mice suggesting that clozapine, unlike haloperidol, may limit DNA methylation by interfering with DNA methylation dynamics. We conclude that the PRS mouse model may be useful preclinically in screening for the potential efficacy of antipsychotic drugs acting on altered epigenetic mechanisms. Furthermore, PRS mice may be invaluable for understanding the etiopathogenesis of SZ and BP disorder and for predicting treatment responses at early stages of the illness allowing for early detection and remedial intervention.

title: BDNF-Deficient Mice Show Reduced Psychosis-Related Behaviors Following Chronic Methamphetamine
abstract: One of the most devastating consequences of methamphetamine abuse is increased risk of psychosis. Brain-derived neurotrophic factor has been implicated in both psychosis and neuronal responses to methamphetamine. We therefore examined persistent psychosis-like behavioral effects of methamphetamine in brain-derived neurotrophic factor heterozygous mice.  Mice were chronically treated with methamphetamine from 6 to 9 weeks of age, and locomotor hyperactivity to an acute D-amphetamine challenge was tested in photocell cages after a 2-week withdrawal period.  Methamphetamine-treated wild-type mice, but not brain-derived neurotrophic factor heterozygous mice, showed locomotor sensitization to acute 3mg/kg D-amphetamine. Qualitative analysis of exploration revealed tolerance to D-amphetamine effects on entropy in methamphetamine-treated brain-derived neurotrophic factor heterozygous mice, but not wild-type mice.  Chronic methamphetamine exposure induces contrasting profiles of behavioral changes in wild-type and brain-derived neurotrophic factor heterozygous mice, with attenuation of behaviors relevant to psychosis in methamphetamine-treated brain-derived neurotrophic factor heterozygous mice. This suggests that brain-derived neurotrophic factor signalling changes may contribute to development of psychosis in methamphetamine users.

title: BDNF deficiency and young-adult methamphetamine induce sex-specific effects on prepulse inhibition regulation
abstract: Brain-derived neurotrophic factor (BDNF) has been implicated in the pathophysiology of schizophrenia, yet its role in the development of specific symptoms is unclear. Methamphetamine (METH) users have an increased risk of psychosis and schizophrenia, and METH-treated animals have been used extensively as a model to study the positive symptoms of schizophrenia. We investigated whether METH treatment in BDNF heterozygous (HET) mutant mice has cumulative effects on sensorimotor gating, including the disruptive effects of psychotropic drugs. BDNF HETs and wildtype (WT) littermates were treated during young adulthood with METH and, following a 2-week break, prepulse inhibition (PPI) was examined. At baseline, BDNF HETs showed reduced PPI compared to WT mice irrespective of METH pre-treatment. An acute challenge with amphetamine (AMPH) disrupted PPI but male BDNF HETs were more sensitive to this effect, irrespective of METH pre-treatment. In contrast, female mice treated with METH were less sensitive to the disruptive effects of AMPH, and there were no effects of BDNF genotype. Similar changes were not observed in the response to an acute apomorphine (APO) or MK-801 challenge. These results show that genetically-induced reduction of BDNF caused changes in a behavioral endophenotype relevant to the positive symptoms of schizophrenia. However, major sex differences were observed in the effects of a psychotropic drug challenge on this behavior. These findings suggest sex differences in the effects of BDNF depletion and METH treatment on the monoamine signaling pathways that regulate PPI. Given that these same pathways are thought to contribute to the expression of positive symptoms in schizophrenia, this work suggests that there may be significant sex differences in the pathophysiology underlying these symptoms. Elucidating these sex differences may be important for our understanding of the neurobiology of schizophrenia and developing better treatments strategies for the disorder.

title: Reduction in Reelin immunoreactivity in hippocampus of subjects with schizophrenia, bipolar disorder and major depression
abstract: Accumulation of neurobiological knowledge points to neurodevelopmental origins for certain psychotic and mood disorders. Recent landmark postmortem reports implicate Reelin, a secretory glycoprotein responsible for normal lamination of brain, in the pathology of schizophrenia and bipolar disorders. We employed quantitative immunocytochemistry to measure levels of Reelin protein in various compartments of hippocampal formation in subjects diagnosed with schizophrenia, bipolar disorder and major depression compared to normal controls. Significant reductions were observed in Reelin-positive adjusted cell densities in the dentate molecular layer (ANOVA, P < 0.001), CA4 area (ANOVA, P < 0.001), total hippocampal area (ANOVA, P < 0.038) and in Reelin-positive cell counts in CA4 (ANOVA, P < 0.042) of schizophrenics vs controls. Adjusted Reelin-positive cell densities were also reduced in CA4 areas of subjects with bipolar disorder (ANOVA, P < 0.001) and nonsignificantly in those with major depression. CA4 areas were also significantly reduced in schizophrenic (ANOVA, P < 0.009) patients. No significant effects of confounding variables were found. The exception was that family history of psychiatric illness correlated strongly with Reelin reductions in several areas of hippocampus (CA4, adjusted cell density, F = 13.77, P = 0.001). We present new immunocytochemical evidence showing reductions in Reelin expression in hippocampus of subjects with schizophrenia, bipolar disorder and major depression and confirm recent reports documenting a similar deficit involving Reelin expression in brains of subjects with schizophrenia and bipolar disorder.

title: Reelin-mediated signaling in neuropsychiatric and neurodegenerative diseases
abstract: Reelin is a conserved extracellular glycoprotein crucial for neurodevelopment. In adulthood, Reelin is an important modulator of NMDA receptor-mediated neurotransmission, required for synaptic plasticity, learning and memory. Consequently, abnormal Reelin-mediated signaling has been associated with many human brain disorders involving directly or indirectly altered NMDA receptor function. For most neurological and neuropsychiatric disorders, abnormalities during brain development appear central in the disease etiology. However, a similar causative relationship for neurodegenerative diseases, like Alzheimer's disease (AD), has not been investigated yet. The findings reviewed here center around the hypothesis that dysfunctional Reelin-mediated signaling converges overlapping molecular pathogenic pathways in schizophrenia and AD; highlighting a surprising interaction between prenatal inflammation and developmental abnormalities that appear to play a common role in aging-related neuropathology and cognitive decline. I hypothesize that the progression from normal aging to AD possibly results from late-gestational misregulations of inflammatory cytokines, resulting in immediate neuronal loss of Reelin-expressing neurons, facilitation of protein aggregation and concomitant impairments in proteolytical degradation during adulthood and aging, accompanied by chronic inflammation, expected to induce neurodegenerative processes. Conversely, a developmental immune challenge during mid-gestation, shown to preferentially mimic schizophrenia-like behavioural and neurochemical abnormalities, including impaired Reelin-mediated signaling, prevents progressive neurodegeneration, potentially linked to the immature embryonic immune system at the time of insult, which occludes long-term changes and sub-chronic elevations of inflammatory cytokines. Thus, the findings presented in this review suggest that schizophrenia can indeed be described as a form of accelerated aging or "dementia praecox" as first described by Emil Kraepelin in 1906.

title: Gene–environment interaction during early development in the heterozygous reeler mouse: Clues for modelling of major neurobehavioral syndromes
abstract: Autism and schizophrenia are multifactorial disorders with increasing prevalence in the young population. Among candidate molecules, reelin (RELN) is a protein of the extracellular matrix playing a key role in brain development and synaptic plasticity. The heterozygous (HZ) reeler mouse provides a model for studying the role of reelin deficiency for the onset of these syndromes. We investigated whether early indices of neurobehavioral disorders can be identified in the infant reeler, and whether the consequences of ontogenetic adverse experiences may question or support the suitability of this model. A first study focused on the link between early exposure to Chlorpyryfos and its enduring neurobehavioral consequences. Our data are interesting in view of recently discovered cholinergic abnormalities in autism and schizophrenia, and may suggest new avenues for early pharmacological intervention. In a second study, we analyzed the consequences of repeated maternal separation early in ontogeny. The results provide evidence of how unusual stress early in development are converted into altered behavior in some, but not all, individuals depending on gender and genetic background. A third study aimed to verify the reliability of the model at critical age windows. Data suggest reduced anxiety, increased impulsivity and disinhibition, and altered pain threshold in response to morphine for HZ, supporting a differential organization of brain dopaminergic, serotonergic and opioid systems in this genotype. In conclusion, HZ exhibited a complex behavioral and psycho-pharmacological phenotype, and differential responsivity to ontogenetic adverse conditions. HZ may be used to disentangle interactions between genetic vulnerability and environmental factors. Such an approach could help to model the pathogenesis of neurodevelopmental psychiatric diseases.

title: Neurobehavioural disorders in the infant reeler mouse model: Interaction of genetic vulnerability and consequences of maternal separation
abstract: Studies on heterozygous (HZ) reeler mice suggest a relationship between reelin (a protein of extra cellular matrix) haploinsufficiency and the presence of altered neural networks and behaviour. Neonatal adverse and/or stimulating experiences might interfere with the emergence of this genetic-dependent phenotype. Repeated episodes of maternal separation early in ontogeny result in enduring neuroendocrine, neurochemical and behavioural alterations in the offspring. Therefore, in order to investigate whether developmental indexes of neurobehavioural disorders can be studied in the infant reeler mouse model, and whether ontogenetic adverse experiences may question or improve its suitability, homozygous reeler (RL), heterozygous (HZ) and wild-type (WT) mouse pups underwent maternal separation (SEP, 5h/day) or handling (H, 3min/day) on PND 2-6. As expected, a sex difference appeared, for measure of emotional and communicative behaviour in infant mice. On PND 7, compared to other genotypes, RL mouse pups from the H control group, showed reduced levels of ultrasound (USV) production and of locomotion. Surprisingly, this deficit in RL mice was fully reverted by maternal separation. Maternal separation per se reduced social motivation in the homing test at PND 9 in WT mice, with no effects on HZ and RL ones. Additionally, female pups emitted much lower levels of ultrasound production than males within the H control group. Such a baseline sex difference, however, disappeared in the SEP group. The present results provide evidence that unusual stress and related hormonal stimulation early in development may (i) independently shape individual phenotype and (ii) interact with a genetic make-up to substantially modify its "natural" developmental trajectories.

title: Effects of prenatal hypoxia on schizophrenia-related phenotypes in heterozygous reeler mice: A gene×environment interaction study
abstract: Both genetic and environmental factors play important roles in the pathophysiology of schizophrenia. Although prenatal hypoxia is a potential environmental factor implicated in schizophrenia, very little is known about the consequences of combining models of genetic risk factor with prenatal hypoxia. Heterozygous reeler (haploinsufficient for reelin; HRM) and wild-type (WT) mice were exposed to prenatal hypoxia (9% oxygen for two hour) or normoxia at embryonic day 17 (E17). Behavioral (Prepulse inhibition, Y-maze and Open field) and functional (regional volume in frontal cortex and hippocampus as well as hippocampal blood flow) tests were performed at 3 months of age. The levels of hypoxia and stress-related molecules such as hypoxia-inducible factor-1 α (HIF-1α), vascular endothelial factor (VEGF), VEGF receptor-2 (VEGFR2/Flk1) and glucocorticoid receptor (GR) were examined in frontal cortex and hippocampus at E18, 1 month and 3 months of age. In addition, serum VEGF and corticosterone levels were also examined. Prenatal hypoxia induced anxiety-like behavior in both HRM and WT mice. A significant reduction in hippocampal blood flow, but no change in brain regional volume was observed following prenatal hypoxia. Significant age and region-dependent changes in HIF-1α, VEGF, Flk1 and GR were found following prenatal hypoxia. Serum VEGF and corticosterone levels were found decreased following prenatal hypoxia. None of the above prenatal hypoxia-induced changes were either diminished or exacerbated due to reelin deficiency. These results argue against any gene-environment interaction between hypoxia and reelin deficiency.

title: Animal models of gene–environment interactions in schizophrenia
abstract: The pathogenesis of schizophrenia and related mental illnesses likely involves multiple interactions between susceptibility genes of small effects and environmental factors. Gene-environment interactions occur across different stages of neurodevelopment to produce heterogeneous clinical and pathological manifestations of the disease. The main obstacle for mechanistic studies of gene-environment interplay has been the paucity of appropriate experimental systems for elucidating the molecular pathways that mediate gene-environment interactions relevant to schizophrenia. Recent advances in psychiatric genetics and a plethora of experimental data from animal studies allow us to suggest a new approach to gene-environment interactions in schizophrenia. We propose that animal models based on identified genetic mutations and measurable environment factors will help advance studies of the molecular mechanisms of gene-environment interplay.

title: Gene–environment interactions and construct validity in preclinical models of psychiatric disorders
abstract: The contributions of genetic risk factors to susceptibility for brain disorders are often so closely intertwined with environmental factors that studying genes in isolation cannot provide the full picture of pathogenesis. With recent advances in our understanding of psychiatric genetics and environmental modifiers we are now in a position to develop more accurate animal models of psychiatric disorders which exemplify the complex interaction of genes and environment. Here, we consider some of the insights that have emerged from studying the relationship between defined genetic alterations and environmental factors in rodent models. A key issue in such animal models is the optimization of construct validity, at both genetic and environmental levels. Standard housing of laboratory mice and rats generally includes ad libitum food access and limited opportunity for physical exercise, leading to metabolic dysfunction under control conditions, and thus reducing validity of animal models with respect to clinical populations. A related issue, of specific relevance to neuroscientists, is that most standard-housed rodents have limited opportunity for sensory and cognitive stimulation, which in turn provides reduced incentive for complex motor activity. Decades of research using environmental enrichment has demonstrated beneficial effects on brain and behavior in both wild-type and genetically modified rodent models, relative to standard-housed littermate controls. One interpretation of such studies is that environmentally enriched animals more closely approximate average human levels of cognitive and sensorimotor stimulation, whereas the standard housing currently used in most laboratories models a more sedentary state of reduced mental and physical activity and abnormal stress levels. The use of such standard housing as a single environmental variable may limit the capacity for preclinical models to translate into successful clinical trials. Therefore, there is a need to optimize 'environmental construct validity' in animal models, while maintaining comparability between laboratories, so as to ensure optimal scientific and medical outcomes. Utilizing more sophisticated models to elucidate the relative contributions of genetic and environmental factors will allow for improved construct, face and predictive validity, thus facilitating the identification of novel therapeutic targets.

title: Behavioural sensitization to daily life stress in psychosis
abstract: Recent neurobiological models provide a possible mechanism of daily life stress directly affecting the intensity of psychotic experiences in vulnerable individuals. In order to validate such a mechanism, the impact of daily life stress on psychosis intensity was investigated in two groups at increased risk of onset (relatives) and relapse (patients) of psychosis.  Patients with psychosis in a clinical state of remission (n=42), first-degree relatives (n=47), and control subjects (n=49) were studied with the Experiencing Sampling Method (ESM is a structured diary technique assessing current context and psychopathology in daily life) to assess (1) appraised subjective stress related to daily activities and events, and (2) intensity of subtle psychotic experiences in daily life.  Multilevel regression analyses revealed significant increases in psychosis intensity associated with increases in subjective activity – and event-related stress in patients. First-degree relatives reported increases in psychosis intensity in relation to activity-related stress but not event-related stress. No association was found in control subjects.  Subjects at increased risk for psychosis show continuous variation in the intensity of subtle psychotic experiences associated with minor stresses in the flow of daily life. Behavioural sensitization to environmental stress may therefore be a vulnerability marker for schizophrenia, reflecting dopaminergic hyper-responsivity in response to environmental stimuli.

title: Anxiety and substance use comorbidity among inpatients with schizophrenia
abstract: To determine the association between lifetime anxiety symptoms and anxiety disorders and substance use disorders among patients with schizophrenia.



Participants were 184 inpatients with schizophrenia at the Schizophrenia Research Unit (SRU) at the New York State Psychiatric Institute (NYSPI). Multivariate logistic regression analyses were used to determine the relationship between specific anxiety symptoms and anxiety disorders and substance use disorders among inpatients with schizophrenia.



Anxiety symptoms and anxiety disorders were prevalent among 31.5% of the sample. Panic attacks were associated with a significantly increased odds (OR=7.4 (1.2, 47.1)) of comorbid alcohol or substance use disorders (lifetime). This association was specific to panic attacks and persisted after adjusting for differences in sociodemographic characteristics and comorbid anxiety symptoms and anxiety disorders.



These findings are consistent with and extend previous data by providing evidence of an association between panic attacks and increased likelihood of substance use disorders among inpatients with schizophrenia. Future studies that determine the nature of this relationship, the sequence of symptom onsets, and examine whether treatment of anxiety can influence the onset or outcome associated with substance use are needed.

title: Experience sampling research in psychopathology: opening the black box of daily life
abstract: A growing body of research suggests that momentary assessment technologies that sample experiences in the context of daily life constitute a useful and productive approach in the study of behavioural phenotypes and a powerful addition to mainstream cross-sectional research paradigms. Momentary assessment strategies for psychopathology are described, together with a comprehensive review of research findings illustrating the added value of daily life research for the study of (1) phenomenology, (2) aetiology, (3) psychological models, (4) biological mechanisms, (5) treatment and (6) gene–environment interactions in psychopathology. Overall, this review shows that variability over time and dynamic patterns of reactivity to the environment are essential features of psychopathological experiences that need to be captured for a better understanding of their phenomenology and underlying mechanisms. The Experience Sampling Method (ESM) allows us to capture the film rather than a snapshot of daily life reality of patients, fuelling new research into the gene–environment–experience interplay underlying psychopathology and its treatment.

title: Are there sex differences in neuropsychological functions among patients with schizophrenia?
abstract: Studies of sex differences in neuropsychological performance in schizophrenia report inconsistent results, due in part to methodological artifacts. The study presented here was specifically designed to examine sex differences in neuropsychological performance. It was hypothesized that schizophrenic women would exhibit fewer neuropsychological deficits than schizophrenic men and that their performance would be more similar to that of normal women than schizophrenic men's performance would be to that of normal men.



Thirty-one outpatients with DSM-III-R-defined schizophrenia were systematically sampled from an extensive service network serving a large urban catchment area for seriously mentally ill persons. Twenty-seven normal comparison subjects were matched within sex on the basis of age, parental socioeconomic status, ethnicity, and handedness. An extensive neuropsychological test battery was administered, and multivariate analysis of variance was used to test for the effects of sex and group and sex-by-group interactions.



Male patients were significantly impaired across all functions in comparison with normal male subjects and on tests of attention, verbal memory, and executive functions in comparison with female patients. Female patients performed significantly worse than female normal comparison subjects only on tests of attention, executive functions, visual memory, and motor functions.



The findings suggest that women with schizophrenia may be less vulnerable to particular cognitive deficits, especially those involving verbal processing, than schizophrenic men.

title: Gender differences in cognitive function of patients with chronic schizophrenia
abstract: Schizophrenic patients have cognitive impairments, but gender differences in these cognitive deficits have had limited study. This study assessed cognitive functioning in 471 subjects including 122 male and 78 female schizophrenic patients and 141 male and 130 female healthy controls. We found that immediate memory, language, delayed memory and total RBANS scores were significantly decreased in schizophrenia compared with healthy controls for both genders. Male patients had significant lower immediate memory, delayed memory and total RBANS scores than female patients, and healthy controls showed a similar gender difference. The RBANS showed modest correlations with PANSS scores, duration of illness and antipsychotic dose (chlorpromazine equivalents). Almost all RBANS scores in the schizophrenics and healthy controls showed significant positive correlations with education. Thus, patients of both sexes with schizophrenia experienced more deteriorated performance than healthy controls on cognitive domains of immediate memory, language and delayed memory. Furthermore, male schizophrenic patients had more serious cognitive deficits than female patients in immediate and delayed memory, but not in language, visuospatial and attention indices.

title: Cortical parvalbumin interneurons and cognitive dysfunction in schizophrenia
abstract: Deficits in cognitive control, a core disturbance of schizophrenia, appear to emerge from impaired prefrontal gamma oscillations. Cortical gamma oscillations require strong inhibitory inputs to pyramidal neurons from the parvalbumin basket cell (PVBC) class of GABAergic neurons. Recent findings indicate that schizophrenia is associated with multiple pre- and postsynaptic abnormalities in PVBCs, each of which weakens their inhibitory control of pyramidal cells. These findings suggest a new model of cortical dysfunction in schizophrenia in which PVBC inhibition is decreased to compensate for an upstream deficit in pyramidal cell excitation. This compensation is thought to rebalance cortical excitation and inhibition, but at a level insufficient to generate the gamma oscillation power required for high levels of cognitive control.

title: Maternal Immune Activation Leads to Selective Functional Deficits in Offspring Parvalbumin Interneurons
abstract: Abnormalities in prefrontal gamma aminobutyric acid (GABA)ergic transmission, particularly in fast-spiking interneurons that express parvalbumin (PV), are hypothesized to contribute to the pathophysiology of multiple psychiatric disorders, including schizophrenia, bipolar disorder, anxiety disorders and depression. While primarily histological abnormalities have been observed in patients and in animal models of psychiatric disease, evidence for abnormalities in functional neurotransmission at the level of specific interneuron populations has been lacking in animal models and is difficult to establish in human patients. Using an animal model of a psychiatric disease risk factor, prenatal maternal immune activation (MIA), we found reduced functional GABAergic transmission in the medial prefrontal cortex (mPFC) of adult MIA offspring. Decreased transmission was selective for interneurons expressing PV, resulted from a decrease in release probability and was not observed in calretinin-expressing neurons. This deficit in PV function in MIA offspring was associated with increased anxiety-like behavior and impairments in attentional set shifting, but did not affect working memory. Furthermore, cell-type specific optogenetic inhibition of mPFC PV interneurons was sufficient to impair attentional set shifting and enhance anxiety levels. Finally, we found that in vivo mPFC gamma oscillations, which are supported by PV interneuron function, were linearly correlated with the degree of anxiety displayed in adult mice, and that this correlation was disrupted in MIA offspring. These results demonstrate a selective functional vulnerability of PV interneurons to MIA, leading to affective and cognitive symptoms that have high relevance for schizophrenia and other psychiatric disorders.

title: Pathways to schizophrenia: the impact of environmental factors.
abstract: Schizophrenia is an aetiologically complex disorder arising from the interaction of a range of factors acting at various stages of life. Schizophrenic individuals inherit genes that cause structural brain deviations which may be compounded by early environmental insults. As a result some pre-schizophrenic children exhibit subtle developmental delays, cognitive problems, or poor interpersonal relationships. They are susceptible to dysregulation of dopamine, the final pathway leading to the onset of a psychotic illness. Dopamine dysregulation may arise through a process of sensitization, which, in animals, can be caused by repeated administration of dopamine-releasing drugs. It is clear that the same process occurs in humans, and that some individuals are particularly sensitive to the effects of such drugs for either genetic reasons or through early environmental damage. Stress has also been shown to induce dopamine release in animal studies, and epidemiological studies have demonstrated that social stresses can precipitate schizophrenia. Thus, stresses, such as drug use and social adversity, in adolescence or early adult life may propel the neurodevelopmentally impaired individual over a threshold into frank psychosis.

title: Schizophrenia genes, gene expression, and neuropathology: on the matter of their convergence
abstract: Molecular Psychiatry (2005) 10, 420. doi: 10.1038/sj.mp.4001630 Following the publication of the above corrigendum, the authors found it necessary to further clarify the correction from Molecular Psychiatry (2005), 10, 40–68: on the sixth page, in the left hand column, 10 lines from the bottom, the sentence should read: ‘… such that Met-COMT has significantly lower enzyme activity than val-COMT’.