Prenatal influenza infections and adult schizophrenia

Impact of respiratory viral infections during pregnancy on the neurological outcomes of the newborn: current knowledge

Brain development is a complex process that begins during pregnancy, and the events occurring during this sensitive period can affect the offspring's neurodevelopmental outcomes. Respiratory viral infections are frequently reported in pregnant women, and, in the last few decades, they have been related to numerous neuropsychiatric sequelae. Respiratory viruses can disrupt brain development by directly invading the fetal circulation through vertical transmission or inducing neuroinflammation through the maternal immune activation and production of inflammatory cytokines. Influenza virus gestational infection has been consistently associated with psychotic disorders, such as schizophrenia and autism spectrum disorder, while the recent pandemic raised some concerns regarding the effects of severe acute respiratory syndrome coronavirus 2 on neurodevelopmental outcomes of children born to affected mothers. In addition, emerging evidence supports the possible role of respiratory syncytial virus infection as a risk factor for adverse neuropsychiatric consequences. Understanding the mechanisms underlying developmental dysfunction allows for improving preventive strategies, early diagnosis, and prompt interventions.

Infections During Pregnancy and Risks for Adult Psychosis: Findings from the New England Family Study

For the past 40 years, our team has conducted a unique program of research investigating the prenatal risks for schizophrenia and related adult psychiatric disorders. The New England Family Study is a long-term prospective cohort study of over 16,000 individuals followed from the prenatal period for over 50 years. This chapter summarizes several major phases and findings from this work, highlighting recent results on maternal prenatal bacterial infections and brain imaging. Implications regarding the causes and potential prevention of major psychotic disorders are discussed.

Maternal immune activation as an epidemiological risk factor for neurodevelopmental disorders: Considerations of timing, severity, individual differences, and sex in human and rodent studies

Epidemiological evidence suggests that one's risk of being diagnosed with a neurodevelopmental disorder (NDD)-such as autism, ADHD, or schizophrenia-increases significantly if their mother had a viral or bacterial infection during the first or second trimester of pregnancy. Despite this well-known data, little is known about how developing neural systems are perturbed by events such as early-life immune activation. One theory is that the maternal immune response disrupts neural processes important for typical fetal and postnatal development, which can subsequently result in specific and overlapping behavioral phenotypes in offspring, characteristic of NDDs. As such, rodent models of maternal immune activation (MIA) have been useful in elucidating neural mechanisms that may become dysregulated by MIA. This review will start with an up-to-date and in-depth, critical summary of epidemiological data in humans, examining the association between different types of MIA and NDD outcomes in offspring. Thereafter, we will summarize common rodent models of MIA and discuss their relevance to the human epidemiological data. Finally, we will highlight other factors that may interact with or impact MIA and its associated risk for NDDs, and emphasize the importance for researchers to consider these when designing future human and rodent studies. These points to consider include: the sex of the offspring, the developmental timing of the immune challenge, and other factors that may contribute to individual variability in neural and behavioral responses to MIA, such as genetics, parental age, the gut microbiome, prenatal stress, and placental buffering.

Prenatal infection and schizophrenia: A decade of further progress

Epidemiologic studies have provided evidence that prenatal exposure to maternal infection is associated with an increased risk of developing schizophrenia in the offspring. Research over the past decade has added further to our understanding of the role of prenatal infection in schizophrenia risk. These investigations include several well-powered designs, and like some earlier studies, measured maternal antibodies to specific infectious agents in stored serum samples and large registers to identify clinically diagnosed infections during pregnancy. Convergent findings from antibody studies suggest that prenatal maternal infection with Toxoplasma gondii is associated with increased schizophrenia risk in the offspring, while associations with HSV-2 infection are likely attributable to confounding. Maternal influenza infection remains a viable candidate for schizophrenia, based on an early serological study, though there has been only one attempt to replicate this finding, with a differing methodology. A prior association between maternal serologically confirmed cytomegalovirus infections require further study. Clinically diagnosed maternal infection, particularly bacterial infection, also appears to be associated with increased risk of offspring schizophrenia, and heterogeneity in these findings is likely due to methodological differences between studies. Further clarification may be provided by future studies that address the timing, type, and clinical features of infections. Important insight may be gained by examining the long-term offspring outcomes in emerging epidemics such as Zika virus and COVID-19, and by investigating the interaction between exposure to prenatal infection and other risk or protective factors.

Virus-Induced Maternal Immune Activation as an Environmental Factor in the Etiology of Autism and Schizophrenia

Maternal immune activation (MIA) is mediated by activation of inflammatory pathways resulting in increased levels of cytokines and chemokines that cross the placental and blood-brain barriers altering fetal neural development. Maternal viral infection is one of the most well-known causes for immune activation in pregnant women. MIA and immune abnormalities are key players in the etiology of developmental conditions such as autism, schizophrenia, ADHD, and depression. Experimental evidence implicating MIA in with different effects in the offspring is complex. For decades, scientists have relied on either MIA models or human epidemiological data or a combination of both. MIA models are generated using infection/pathogenic agents to induce an immunological reaction in rodents and monitor the effects. Human epidemiological studies investigate a link between maternal infection and/or high levels of cytokines in pregnant mothers and the likelihood of developing conditions. In this review, we discuss the importance of understanding the relationship between virus-mediated MIA and neurodevelopmental conditions, focusing on autism and schizophrenia. We further discuss the different methods of studying MIA and their limitations and focus on the different factors contributing to MIA heterogeneity.

Neuropsychiatric disorders: An immunological perspective

Neuropsychiatric diseases have traditionally been studied from brain, and mind-centric perspectives. However, mounting epidemiological and clinical evidence shows a strong correlation of neuropsychiatric manifestations with immune system activation, suggesting a likely mechanistic interaction between the immune and nervous systems in mediating neuropsychiatric disease. Indeed, immune mediators such as cytokines, antibodies, and complement proteins have been shown to affect various cellular members of the central nervous system in multitudinous ways, such as by modulating neuronal firing rates, inducing cellular apoptosis, or triggering synaptic pruning. These observations have in turn led to the exciting development of clinical therapies aiming to harness this neuro-immune interaction for the treatment of neuropsychiatric disease and symptoms. Besides the clinic, important theoretical fundamentals can be drawn from the immune system and applied to our understanding of the brain and neuropsychiatric disease. These new frameworks could lead to novel insights in the field and further potentiate the development of future therapies to treat neuropsychiatric disease.

Disorganization of Oscillatory Activity in Animal Models of Schizophrenia

Schizophrenia is a chronic, debilitating disorder with diverse symptomatology, including disorganized cognition and behavior. Despite considerable research effort, we have only a limited understanding of the underlying brain dysfunction. In this article, we review the potential role of oscillatory circuits in the disorder with a particular focus on the hippocampus, a region that encodes sequential information across time and space, as well as the frontal cortex. Several mechanistic explanations of schizophrenia propose that a loss of oscillatory synchrony between and within these brain regions may underlie some of the symptoms of the disorder. We describe how these oscillations are affected in several animal models of schizophrenia, including models of genetic risk, maternal immune activation (MIA) models, and models of NMDA receptor hypofunction. We then critically discuss the evidence for disorganized oscillatory activity in these models, with a focus on gamma, sharp wave ripple, and theta activity, including the role of cross-frequency coupling as a synchronizing mechanism. Finally, we focus on phase precession, which is an oscillatory phenomenon whereby individual hippocampal place cells systematically advance their firing phase against the background theta oscillation. Phase precession is important because it allows sequential experience to be compressed into a single 120 ms theta cycle (known as a 'theta sequence'). This time window is appropriate for the induction of synaptic plasticity. We describe how disruption of phase precession could disorganize sequential processing, and thereby disrupt the ordered storage of information. A similar dysfunction in schizophrenia may contribute to cognitive symptoms, including deficits in episodic memory, working memory, and future planning.

Descriptive study of cases of schizophrenia in the Malian population

BACKGROUND

Schizophrenia is a relatively common disease worldwide with a point prevalence of around 5/1000 in the population. The aim of this present work was to assess the demographic, clinical, familial, and environmental factors associated with schizophrenia in Mali.

METHODS

This was a prospective descriptive study on a series of 164 patients aged at least 12 years who came for a follow-up consultation at the psychiatry department of the University Hospital Center (CHU) Point G in Mali between February 2019 and January 2020 for schizophrenia spectrum disorder as defined by DSM-5 diagnostic criteria.

RESULTS

Our results revealed that the male sex was predominant (80.5%). The 25-34 age group was more represented with 44.5%. The place of birth for the majority of our patients was the urban area (52.4%), which also represented the place of the first year of life for the majority of our patients (56.1%). We noted that the unemployed and single people accounted for 56.1 and 61% respectively. More than half of our patients 58.5% reported having reached secondary school level. With the exception of education level, there was a statistically significant difference in the distribution of demographic parameters. Familial schizophrenia cases accounted for 51.7% versus 49.3% for non-familial cases. The different clinical forms were represented by the paranoid form, followed by the undifferentiated form, and the hebephrenic form with respectively 34, 28 and 17.1%. We noted that almost half (48.8%) of patients were born during the cold season. Cannabis use history was not observed in 68.7% of the patients. The proportions of patients with an out-of-school father or an out-of-school mother were 51.2 and 64.2%, respectively.

CONCLUSION

The onset of schizophrenia in the Malian population has been associated with socio-demographic, clinical, genetic and environmental characteristics.

Being Born in Winter-Spring and at Around the Time of an Influenza Pandemic Are Risk Factors for the Development of Schizophrenia: The Apna Study in Navarre, Spain

Background: We analyzed the relationship between the prevalence of schizophrenia and the season of birth and gestation during a period of an influenza pandemic. Methods: Cross-sectional analysis of a prospective population-based cohort of 470,942 adults. We fitted multivariant logistic regression models to determine whether the season of birth and birth in an influenza-pandemic year (1957, 1968, 1977) was associated with schizophrenia. Results: 2077 subjects had been diagnosed with schizophrenia. Logistic regression identified a significantly greater prevalence of schizophrenia in men than in women (OR = 1.516, CI 95% = 1.388–1.665); in those born in the winter or spring than in those born in the summer or autumn (OR = 1.112, CI 95% = 1.020–1.212); and in those born in a period of an influenza pandemic (OR = 1.335, CI 95% = 1.199–1.486). The increase in risk was also significant when each influenza pandemic year was analyzed separately. However, neither month of birth nor season of birth, when each of the four were studied individually, were associated with a statistically significant increase in that risk. Conclusions: The winter–spring period and the influenza pandemics are independent risk factors for developing schizophrenia. This study contradicts many previous studies and thus revitalizes a locked debate in understanding the neurodevelopmental hypothesis of this disorder.

Prenatal exposure to viral infection and neuropsychiatric disorders in offspring: A review of the literature and recommendations for the COVID-19 pandemic

The SARS-CoV-2 virus has emerged as a striking 21st century pandemic. Communities across the globe have experienced significant infection rates and widespread psychosocial stress and trauma, leading to calls for increased allocation of resources for mental health screening and treatment. In addition to the burden of psychosocial stress, there is increasing evidence of direct viral neuroinvasion of the central nervous system through physical contact with the nasal mucosa. In a parallel fashion, there is a significant body of ongoing research related to the risk of in utero viral transmission and the resulting neurodevelopmental impact in the fetus. Aberrant neurodevelopment secondary to viral transmission has previously been related to the later development of psychosis, schizophrenia, and schizophrenia spectrum disorders, generating the hypothesis that this population of individuals exposed to SARS-CoV-2 may see an increased incidence in future decades. We discuss the current understanding of the possible neurotropism and vertical transmission of SARS-CoV-2, and relate this to the history of viral pandemics to better understand the relationship of viral infection, aberrant immune response and neurodevelopment, and the risk for schizophrenia disorder.

The Intergenerational Effects of Intimate Partner Violence in Pregnancy: Mediating Pathways and Implications for Prevention

Prenatal intimate partner violence (P-IPV) can have significant adverse impacts on both mother and fetus. Existing P-IPV interventions focus on the safety of the mother and on reducing revictimization; yet expanding these to address the adverse impact on the fetus has considerable potential for preventing long-term negative developmental outcomes. In this review, we draw together evidence on major pathways linking exposure to P-IPV and child outcomes, arguing that these pathways represent potential targets to improve P-IPV intervention efforts. Using a narrative review of 112 articles, we discuss candidate pathways linking P-IPV to child outcomes, as well as their implications for intervention. Articles were identified via key word searches of social science and medical databases and by inspection of reference lists of the most relevant articles, including recent reviews and meta-analyses. Articles were included if they addressed issues relevant to understanding the effects of P-IPV on child outcomes via six core pathways: maternal stress and mental illness, maternal-fetal attachment, maternal substance use, maternal nutritional intake, maternal antenatal health-care utilization, and infection. We also included articles relevant for linking these pathways to P-IPV interventions. We conclude that developing comprehensive P-IPV interventions that target immediate risk to the mother as well as long-term child outcomes via the candidate mediating pathways identified have significant potential to help reduce the global burden of P-IPV.

Investigating the gut-brain axis in a neurodevelopmental rodent model of schizophrenia

Background

Although the aetiology of schizophrenia remains unknown, it has been suggested that it might occur in response to alterations in the gut-brain axis (GBA), the bi-directional communication system between the gut and the brain. The current study aimed to determine whether the “two-hit” animal model of neuropsychopathology (maternal immune activation combined with adolescent cannabinoid exposure), produced abnormalities in the GBA

Method

Pregnant Wistar rats were administered the viral mimetic polyI:C on gestational day 19 and offspring were administered the synthetic cannabinoid HU210 from postnatal days 35–48. Evidence of GBA activation was assessed in the hypothalamus, colon and fecal samples from male and female offspring at adolescence and adulthood

Results

Findings were sex-specific with adolescent female offspring exhibiting an increased hypothalamic inflammatory profile, increased hypothalamic CRHR1 mRNA, and decreased fecal expression of Bifidobacterium longum, however, no changes were detected in colonic inflammation or integrity.

Conclusion

These results indicate that the rat two-hit model, documented to produce behavioural and neuroanatomical abnormalities, also produces hypothalamic and microbiota abnormalities. The results also demonstrate significant sex differences, suggesting that this model may be useful for investigating the role of the GBA in the aetiology of neurodevelopmental disorders such as schizophrenia.

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Combined MIA and ACE induces sex-specific alterations in hypothalamic inflammation.

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Combined MIA and ACE increases hypothalamic CRHR1 expression.

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Combined MIA and ACE decreases fecal expression of Bifidobacterium longum.

Advances in clinical staging, early intervention, and the prevention of psychosis

The development of effective intervention and prevention strategies among individuals with psychosis risk syndromes may help to reduce symptomatology and conversion to a psychotic disorder. Although strides have been made in this area, more work is needed, particularly given the setbacks that remain (such as heterogeneity among this group). There has been a shift with the introduction of clinical staging models toward expanding current intervention and prevention efforts to a more developmental and transdiagnostic approach. With this, this article seeks to review treatments both recently and currently discussed in the staging literature, introduce advances in psychosis risk syndrome treatments that may be beneficial to consider in clinical staging heuristics, and pinpoint other promising options.

Sex-Dependent Effects of Perinatal Inflammation on the Brain: Implication for Neuro-Psychiatric Disorders

Individuals born preterm have higher rates of neurodevelopmental disorders such as schizophrenia, autistic spectrum, and attention deficit/hyperactivity disorders. These conditions are often sexually dimorphic and with different developmental trajectories. The etiology is likely multifactorial, however, infections both during pregnancy and in childhood have emerged as important risk factors. The association between sex- and age-dependent vulnerability to neuropsychiatric disorders has been suggested to relate to immune activation in the brain, including complex interactions between sex hormones, brain transcriptome, activation of glia cells, and cytokine production. Here, we will review sex-dependent effects on brain development, including glia cells, both under normal physiological conditions and following perinatal inflammation. Emphasis will be given to sex-dependent effects on brain regions which play a role in neuropsychiatric disorders and inflammatory reactions that may underlie early-life programming of neurobehavioral disturbances later in life.

N-3 (Omega-3) Fatty Acids: Effects on Brain Dopamine Systems and Potential Role in the Etiology and Treatment of Neuropsychiatric Disorders

BACKGROUND & OBJECTIVE

A number of neuropsychiatric disorders, including Parkinson's disease, schizophrenia, attention deficit hyperactivity disorder, and, to some extent, depression, involve dysregulation of the brain dopamine systems. The etiology of these diseases is multifactorial, involving genetic and environmental factors. Evidence suggests that inadequate levels of n-3 (omega- 3) polyunsaturated fatty acids (PUFA) in the brain may represent a risk factor for these disorders. These fatty acids, which are derived from the diet, are a major component of neuronal membranes and are of particular importance in brain development and function. Low levels of n-3 PUFAs in the brain affect the brain dopamine systems and, when combined with appropriate genetic and other factors, increase the risk of developing these disorders and/or the severity of the disease. This article reviews the neurobiology of n-3 PUFAs and their effects on dopaminergic function.

CONCLUSION

Clinical studies supporting their role in the etiologies of diseases involving the brain dopamine systems and the potential of n-3 PUFAs in the treatment of these disorders are discussed.

Animal Models of Maternal Immune Activation in Depression Research

Abstract: Background

Depression and schizophrenia are debilitating mental illnesses with significant socio-economic impact. The high degree of comorbidity between the two disorders, and shared symptoms and risk factors, suggest partly common pathogenic mechanisms. Supported by human and animal studies, maternal immune activation (MIA) has been intimately associated with the development of schizophrenia. However, the link between MIA and depression has remained less clear, in part due to the lack of appropriate animal models.

Objective

Here we aim to summarize findings obtained from studies using MIA animal models and discuss their relevance for preclinical depression research.

Methods

Results on molecular, cellular and behavioral phenotypes in MIA animal models were collected by literature search (PubMed) and evaluated for their significance for depression.

Results

Several reports on offspring depression-related behavioral alterations indicate an involvement of MIA in the development of depression later in life. Depression-related behavioral phenotypes were frequently paralleled by neurogenic and neurotrophic deficits and modulated by several genetic and environmental factors.

Conclusion

Literature evidence analyzed in this review supports a relevance of MIA as animal model for a specific early life adversity, which may prime an individual for the development of distinct psychopathologies later life. MIA animal models may present a unique tool for the identification of additional exogenous and endogenous factors, which are required for the manifestation of a specific neuropsychiatric disorder, such as depression, later in life. Hereby, novel insights into the molecular mechanisms involved in the pathophysiology of depression may be obtained, supporting the identification of alternative therapeutic strategies.

Differential expression of the inflammation marker IL12p40 in the at-risk mental state for psychosis: a predictor of transition to psychotic disorder?

BACKGROUND

The identification of biomarkers of transition from the at-risk mental state (ARMS) to psychotic disorder is important because early treatment of psychosis is associated with improved outcome. Increasing evidence points to an inflammatory contribution to psychosis. We questioned whether raised levels of plasma inflammatory markers predict transition from ARMS to psychotic disorder and whether any such predictors could be reduced by omega-3 (ω-3) polyunsaturated fatty acids (PUFAs).

METHODS

We measured the levels of 40 neuroinflammation biomarkers using a commercially available immunoassay kit. Firstly, we compared inflammatory markers in subjects in the ARMS who transitioned to psychotic disorder (n = 11) compared to subjects who did not (n = 28). Then we compared inflammatory markers in all subjects before and after ω-3 PUFA treatment (n = 40).

RESULTS

Our data provides preliminary evidence that elevations in the baseline plasma levels of the inflammatory marker IL12/IL23p40 are associated with transition from ARMS to psychotic disorder. IL12/IL23p40 levels did not change following 12 weeks administration of ω-3 PUFAs. These findings provide evidence that elevated plasma IL12/IL23p40 is a potential biomarker of increased risk for transition to psychotic disorder.

CONCLUSION

Further studies are required to confirm and extend this finding. Our results do not provide support for the possibility that administration of ω-3 PUFAs act to reduced transition to psychotic disorder by reducing blood levels of IL12/IL23p40.

TRIAL REGISTRATION

ClinicalTrials.gov, a service of the U.S. National Institutes of Health, Identifier: NCT00396643 , last updated December 20, 2007. Retrospectively registered.

Prenatal stressors in rodents: Effects on behavior

The current review focuses on studies in rodents published since 2008 and explores possible reasons for any differences they report in the effects of gestational stress on various types of behavior in the offspring. An abundance of experimental data shows that different maternal stressors in rodents can replicate some of the abnormalities in offspring behavior observed in humans. These include, anxiety, in juvenile and adult rats and mice, assessed in the elevated plus maze and open field tests and depression, detected in the forced swim and sucrose-preference tests. Deficits were reported in social interaction that is suggestive of pathology associated with schizophrenia, and in spatial learning and memory in adult rats in the Morris water maze test, but in most studies only males were tested. There were too few studies on the novel object recognition test at different inter-trial intervals to enable a conclusion about the effect of prenatal stress and whether any deficits are more prevalent in males. Among hippocampal glutamate receptors, NR2B was the only subtype consistently reduced in association with learning deficits. However, like in humans with schizophrenia and depression, prenatal stress lowered hippocampal levels of BDNF, which were closely correlated with decreases in hippocampal long-term potentiation. In mice, down-regulation of BDNF appeared to occur through the action of gene-methylating enzymes that are already increased above controls in prenatally-stressed neonates. In conclusion, the data obtained so far from experiments in rodents lend support to a physiological basis for the neurodevelopmental hypothesis of schizophrenia and depression.

Alteration of transcriptional networks in the entorhinal cortex after maternal immune activation and adolescent cannabinoid exposure

Maternal immune activation (MIA) and adolescent cannabinoid exposure (ACE) have both been identified as major environmental risk factors for schizophrenia. We examined the effects of these two risk factors alone, and in combination, on gene expression during late adolescence. Pregnant rats were exposed to the viral infection mimic polyriboinosinic-polyribocytidylic acid (poly I:C) on gestational day (GD) 15. Adolescent offspring received daily injections of the cannabinoid HU210 for 14days starting on postnatal day (PND) 35. Gene expression was examined in the left entorhinal cortex (EC) using mRNA microarrays. We found prenatal treatment with poly I:C alone, or HU210 alone, produced relatively minor changes in gene expression. However, following combined treatments, offspring displayed significant changes in transcription. This dramatic and persistent alteration of transcriptional networks enriched with genes involved in neurotransmission, cellular signalling and schizophrenia, was associated with a corresponding perturbation in the expression of small non-coding microRNA (miRNA). These results suggest that a combination of environmental exposures during development leads to significant genomic remodeling that disrupts maturation of the EC and its associated circuitry with important implications as the potential antecedents of memory and learning deficits in schizophrenia and other neuropsychiatric disorders.

Prenatal Inflammation, Infections and Mental Disorders

BACKGROUND

The objective of this descriptive review is to summarize the current scientific evidence on the effect of prenatal exposure to maternal infection and immune response on the offspring's risk for mental disorders (schizophrenia spectrum disorders, autism spectrum disorders, attention-deficit hyperactivity disorder, anorexia nervosa, and mood disorders).

SAMPLING AND METHODS

Studies were searched from PubMed and Ovid MEDLINE (R) databases with the following keywords: 'prenatal exposure delayed effects' and 'infection', and 'inflammation' and 'mental disorders'. A comprehensive manual search, including a search from the reference list of included articles, was also performed.

RESULTS

Prenatal exposure to maternal influenza appears to increase the offspring's risk for schizophrenia spectrum disorders, although studies are not fully consistent. Prenatal exposure to maternal fever and elevated cytokine levels seems to be related to the elevated risk for autism spectrum disorders in the offspring. No replicated findings of an association between prenatal infectious exposure and other mental disorders exist.

CONCLUSIONS

Evidence for the effect of prenatal exposure to maternal infection on risk for mental disorders exists for several different infections, suggesting that common factors occurring in infections (e.g. elevated cytokine levels and fever), rather than the infectious agent itself, might be the underlying factor in increasing the risk for mental disorders. Additionally, it is likely that genetic liability to these disorders operates in conjunction with the exposure. Therefore, genetically sensitive study designs are needed in future studies.

Schizophrenia: a tale of two critical periods for prefrontal cortical development

Schizophrenia is a disease of abnormal brain development. Considerable evidence now indicates that environmental factors have a causative role in schizophrenia. Elevated incidence of the disease has been linked to a wide range of disturbances in the prenatal environment and to social factors and drug intake during adolescence. Here we examine neurodevelopment of the prefrontal cortex in the first trimester of gestation and during adolescence to gain further insight into the neurodevelopmental processes that may be vulnerable in schizophrenia. Early embryonic development of the prefrontal cortex is characterized by cell proliferation, including renewal of progenitor cells, generation of early transient cell populations and neurogenesis of subcortical populations. Animal models show that curtailing early gestational cell proliferation produces schizophrenia-like pathology in the prefrontal cortex and mimics key behavioral and cognitive symptoms of the disease. At the other end of the spectrum, elimination of excitatory synapses is the fundamental process occurring during adolescent maturation in the prefrontal cortex. Adverse social situations that elevate stress increase dopamine stimulation of the mesocortical pathway and may lead to exaggerated synaptic pruning during adolescence. In a non-human primate model, dopamine hyperstimulation has been shown to decrease prefrontal pyramidal cell spine density and to be associated with profound cognitive dysfunction. Development of the prefrontal cortex in its earliest stage in gestation and in its final stage in adolescence represents two critical periods of vulnerability for schizophrenia in which cell proliferation and synaptic elimination, respectively, may be influenced by environmental factors.

Perinatal Risks and Childhood Premorbid Indicators of Later Psychosis: Next Steps for Early Psychosocial Interventions

Schizophrenia and affective psychoses are debilitating disorders that together affect 2%-3% of the adult population. Approximately 50%-70% of the offspring of parents with schizophrenia manifest a range of observable difficulties including socioemotional, cognitive, neuromotor, speech-language problems, and psychopathology, and roughly 10% will develop psychosis. Despite the voluminous work on premorbid vulnerabilities to psychosis, especially on schizophrenia, the work on premorbid intervention approaches is scarce. While later interventions during the clinical high-risk (CHR) phase of psychosis, characterized primarily by attenuated positive symptoms, are promising, the CHR period is a relatively late phase of developmental derailment. This article reviews and proposes potential targets for psychosocial interventions during the premorbid period, complementing biological interventions described by others in this Special Theme issue. Beginning with pregnancy, parents with psychoses may benefit from enhanced prenatal care, social support, parenting skills, reduction of symptoms, and programs that are family-centered. For children at risk, we propose preemptive early intervention and cognitive remediation. Empirical research is needed to evaluate these interventions for parents and determine whether interventions for parents and children positively influence the developmental course of the offspring.

Schizophrenia: a systemic disorder

The concept of schizophrenia that is most widely taught is that it is a disorder in which psychotic symptoms are the main problem, and a dysregulation of dopamine signaling is the main feature of pathophysiology. However, this concept limits clinical assessment, the treatments offered to patients, research, and the development of therapeutics. A more appropriate conceptual model is that: 1) schizophrenia is not a psychotic disorder, but a disorder of essentially every brain function in which psychosis is present; 2) it is not a brain disease, but a disorder with impairments throughout the body; 3) for many patients, neuropsychiatric problems other than psychosis contribute more to impairment in function and quality of life than does psychosis; and, 4) some conditions that are considered to be comorbid are integral parts of the illness. In conclusion, students, patients, and family members should be taught this model, along with its implications for assessment, research, and therapeutics.

The poly(I:C)-induced maternal immune activation model in preclinical neuropsychiatric drug discovery

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.

Abnormal immune system development and function in schizophrenia helps reconcile diverse findings and suggests new treatment and prevention strategies

Extensive research implicates disturbed immune function and development in the etiology and pathology of schizophrenia. In addition to reviewing evidence for immunological factors in schizophrenia, this paper discusses how an emerging model of atypical immune function and development helps explain a wide variety of well-established - but puzzling - findings about schizophrenia. A number of theorists have presented hypotheses that early immune system programming, disrupted by pre- and perinatal adversity, often combines with abnormal brain development to produce schizophrenia. The present paper focuses on the hypothesis that disruption of early immune system development produces a latent immune vulnerability that manifests more fully after puberty, when changes in immune function and the thymus leave individuals more susceptible to infections and immune dysfunctions that contribute to schizophrenia. Complementing neurodevelopmental models, this hypothesis integrates findings on many contributing factors to schizophrenia, including prenatal adversity, genes, climate, migration, infections, and stress, among others. It helps explain, for example, why (a) schizophrenia onset is typically delayed until years after prenatal adversity, (b) individual risk factors alone often do not lead to schizophrenia, and (c) schizophrenia prevalence rates actually tend to be higher in economically advantaged countries. Here we discuss how the hypothesis explains 10 key findings, and suggests new, potentially highly cost-effective, strategies for treatment and prevention of schizophrenia. Moreover, while most human research linking immune factors to schizophrenia has been correlational, these strategies provide ethical ways to experimentally test in humans theories about immune function and schizophrenia. This article is part of a Special Issue entitled SI: Neuroimmunology in Health And Disease.

Long-term effects of maternal immune activation on depression-like behavior in the mouse

Depression is a debilitating mental disease affecting a large population worldwide, the pathophysiological mechanisms of which remain incompletely understood. Prenatal infection and associated activation of the maternal immune system (MIA) are prominently related to an increased risk for the development of several psychiatric disorders including schizophrenia and autism in the offsprings. However, the role of MIA in the etiology of depression and its neurobiological basis are insufficiently investigated. Here we induced MIA in mice by challenge with polyinosinic:polycytidylic phosphate salt-a synthetic analog of double-stranded RNA, which enhances maternal levels of the cytokine interleukin-6 (IL-6)-and demonstrate a depression-like behavioral phenotype in adult offsprings. Adult offsprings additionally show deficits in cognition and hippocampal long-term potentiation (LTP) accompanied by disturbed proliferation of newborn cells in the dentate gyrus and compromised neuronal maturation and survival. The behavioral, neurogenic and functional deficiencies observed are associated with reduced hippocampal expression of vascular endothelial growth factor (VEGF)A-VEGFR2. IL-6-STAT3-dependent aberrant VEGFA-VEGFR2 signaling is proposed as neurobiological mechanism mediating the effects of MIA on the developing fetal brain and ensuing consequences in adulthood.

Modeling the molecular epigenetic profile of psychosis in prenatally stressed mice

Based on postmortem brain studies, our overarching epigenetic hypothesis is that chronic schizophrenia (SZ) is a psychopathological condition involving dysregulation of the dynamic equilibrium among DNA methylation/demethylation network components and the expression of SZ target genes, including GABAergic and glutamatergic genes. SZ has a natural course, starting with a prodromal phase, a first episode that occurs in adolescents or in young adults, and later deterioration over the adult years. Hence, the epigenetic status at each neurodevelopmental stage of the disease cannot be studied just in postmortem brain of chronic SZ patients, but requires the use of neurodevelopmental animal models. We have directed the focus of our research toward studying the epigenetic signature of the SZ brain in the offspring of dams stressed during pregnancy (PRS mice). Adult PRS mice have behavioral deficits reminiscent of behaviors observed in psychotic patients. The adult PRS brain, like that of postmortem chronic SZ patients, is characterized by a significant increase in DNA methyltransferase 1, Tet methylcytosine dioxygenase 1 (TET1), 5-methylcytosine, and 5-hydroxymethylcytosine at SZ candidate gene promoters and a reduction in the expression of glutamatergic and GABAergic genes. In PRS mice, measurements of epigenetic biomarkers for SZ can be assessed at different stages of development with the goal of further elucidating the pathophysiology of this disease and predicting treatment responses at specific stages of the illness, with particular attention to early detection and possibly early intervention.

Aberrant neural synchrony in the maternal immune activation model: using translatable measures to explore targeted interventions

Maternal exposure to infection occurring mid-gestation produces a three-fold increase in the risk of schizophrenia in the offspring. The critical initiating factor appears to be the maternal immune activation (MIA) that follows infection. This process can be induced in rodents by exposure of pregnant dams to the viral mimic Poly I:C, which triggers an immune response that results in structural, functional, behavioral, and electrophysiological phenotypes in the adult offspring that model those seen in schizophrenia. We used this model to explore the role of synchronization in brain neural networks, a process thought to be dysfunctional in schizophrenia and previously associated with positive, negative, and cognitive symptoms of schizophrenia. Exposure of pregnant dams to Poly I:C on GD15 produced an impairment in long-range neural synchrony in adult offspring between two regions implicated in schizophrenia pathology; the hippocampus and the medial prefrontal cortex (mPFC). This reduction in synchrony was ameliorated by acute doses of the antipsychotic clozapine. MIA animals have previously been shown to have impaired pre-pulse inhibition (PPI), a gold-standard measure of schizophrenia-like deficits in animal models. Our data showed that deficits in synchrony were positively correlated with the impairments in PPI. Subsequent analysis of LFP activity during the PPI response also showed that reduced coupling between the mPFC and the hippocampus following processing of the pre-pulse was associated with reduced PPI. The ability of the MIA intervention to model neurodevelopmental aspects of schizophrenia pathology provides a useful platform from which to investigate the ontogeny of aberrant synchronous processes. Further, the way in which the model expresses translatable deficits such as aberrant synchrony and reduced PPI will allow researchers to explore novel intervention strategies targeted to these changes.

Striatal development involves a switch in gene expression networks, followed by a myelination event: implications for neuropsychiatric disease

Because abnormal development of striatal neurons is thought to be the part of pathology underlying major psychiatric illnesses, we studied the expression pattern of genes involved in striatal development and of genes comprising key striatal-specific pathways, during an active striatal maturation period, the first two postnatal weeks in rat. This period parallels human striatal development during the second trimester, when prenatal stress is though to lead to increased risk for neuropsychiatric disorders. To identify genes involved in this developmental process, we used subtractive hybridization, followed by quantitative real-time PCR, which allowed us to characterize the developmental expression of over 60 genes, many not previously known to play a role in neuromaturation. Of these 12 were novel transcripts, which did not match known genes, but which showed strict developmental expression and may play a role in striatal neurodevelopment. An additional 89 genes were identified as strong candidates for involvement in this neurodevelopmental process. We show that during the first two postnatal weeks in rat, an early gene expression network, still lacking key striatal-specific signaling pathways, is downregulated and replaced by a mature gene expression network, containing key striatal-specific genes including the dopamine D1 and D2 receptors, conferring to these neurons their functional identity. Therefore, before this developmental switch, striatal neurons lack many of their key phenotypic characteristics. This maturation process is followed by a striking rise in expression of myelination genes, indicating a striatal-specific myelination event. Such strictly controlled developmental program has the potential to be a point of susceptibility to disruption by external factors. Indeed, this period is known to be a susceptibility period in both humans and rats.

The disappearing seasonality of autism conceptions in California

BACKGROUND

Autism incidence and prevalence have increased dramatically in the last two decades. The autism caseload in California increased 600% between 1992 and 2006, yet there is little consensus as to the cause. Studying the seasonality of conceptions of children later diagnosed with autism may yield clues to potential etiological drivers.

OBJECTIVE

To assess if the conceptions of children later diagnosed with autism cluster temporally in a systematic manner and whether any pattern of temporal clustering persists over time.

METHOD

We searched for seasonality in conceptions of children later diagnosed with autism by applying a one-dimensional scan statistic with adaptive temporal windows on case and control population data from California for 1992 through 2000. We tested for potential confounding effects from known risk factors using logistic regression models.

RESULTS

There is a consistent but decreasing seasonal pattern in the risk of conceiving a child later diagnosed with autism in November for the first half of the study period. Temporal clustering of autism conceptions is not an artifact of composition with respect to known risk factors for autism such as socio-economic status.

CONCLUSION

There is some evidence of seasonality in the risk of conceiving a child later diagnosed with autism. Searches for environmental factors related to autism should allow for the possibility of risk factors or etiological drivers that are seasonally patterned and that appear and remain salient for a discrete number of years.

Epigenetic modifications of GABAergic interneurons are associated with the schizophrenia-like phenotype induced by prenatal stress in mice

Human studies suggest that a variety of prenatal stressors are related to high risk for cognitive and behavioral abnormalities associated with psychiatric illness (Markham and Koenig, 2011). Recently, a downregulation in the expression of GABAergic genes (i.e., glutamic acid decarboxylase 67 and reelin) associated with DNA methyltransferase (DNMT) overexpression in GABAergic neurons has been regarded as a characteristic phenotypic component of the neuropathology of psychotic disorders (Guidotti et al., 2011). Here, we characterized mice exposed to prenatal restraint stress (PRS) in order to study neurochemical and behavioral abnormalities related to development of schizophrenia in the adult. Offspring born from non-stressed mothers (control mice) showed high levels of DNMT1 and 3a mRNA expression in the frontal cortex at birth, but these levels progressively decreased at post-natal days (PND) 7, 14, and 60. Offspring born from stressed mothers (PRS mice) showed increased levels of DNMTs compared to controls at all time-points studied including at birth and at PND 60. Using GAD67-GFP transgenic mice, we established that, in both control and PRS mice, high levels of DNMT1 and 3a were preferentially expressed in GABAergic neurons of frontal cortex and hippocampus. Importantly, the overexpression of DNMT in GABAergic neurons was associated with a decrease in reelin and GAD67 expression in PRS mice in early and adult life. PRS mice also showed an increased binding of DNMT1 and MeCP2, and an increase in 5-methylcytosine and 5-hydroxymethylcytosine in specific CpG-rich regions of the reelin and GAD67 promoters. Thus, the epigenetic changes in PRS mice are similar to changes observed in the post-mortem brains of psychiatric patients. Behaviorally, adult PRS mice showed hyperactivity and deficits in social interaction, prepulse inhibition, and fear conditioning that were corrected by administration of valproic acid (a histone deacetylase inhibitor) or clozapine (an atypical antipsychotic with DNA-demethylation activity). Taken together, these data show that prenatal stress in mice induces abnormalities in the DNA methylation network and in behaviors indicative of a schizophrenia-like phenotype. Thus, PRS mice may be a valid model for the investigation of new drugs for schizophrenia treatment targeting DNA methylation. This article is part of the Special Issue entitled 'Neurodevelopmental Disorders'.

Tracing the development of psychosis and its prevention: what can be learned from animal models

Schizophrenia (SCZ) is a neurodevelopmental disorder manifested symptomatically after puberty whose pharmacotherapy remains unsatisfactory. In recent years, longitudinal structural neuroimaging studies have revealed that neuroanatomical aberrations occur in this disorder and in fact precede symptom onset, raising the exciting possibility that SCZ can be prevented. There is some evidence that treatment with atypical antipsychotic drugs (APDs) prior to the development of the full clinical phenotype reduces the risk of transition to psychosis, but results remain controversial. It remains unknown whether progressive structural brain aberrations can be halted. Given the diagnostic, ethical, clinical and methodological problems of pharmacological and imaging studies in patients, getting such information remains a major challenge. Animal neurodevelopmental models of SCZ are invaluable for investigating such questions because they capture the notion that the effects of early brain damage are progressive. In recent years, data derived from such models have converged on key neuropathological and behavioral deficits documented in SCZ attesting to their strong validity, and making them ideal tools for evaluating progression of pathology following in-utero insults as well as its prevention. We review here our recent studies that use longitudinal in vivo structural imaging to achieve this aim in the prenatal immune stimulation model that is based on the association of prenatal infection and increased risk for SCZ. Pregnant rats were injected on gestational day 15 with the viral mimic polyriboinosinic-polyribocytidylic acid (poly I:C) or saline. Male and female offspring were imaged and tested behaviorally on postnatal days (PNDs) 35, 46, 56, 70 and 90. In other experiments, offspring of poly I:C- and saline-treated dams received the atypical antipsychotic drugs (APDs) clozapine or risperidone in two developmental windows: PND 34-47 and PND 48-61, and underwent behavioral testing and imaging at adulthood. Prenatal poly I:C-induced interference with fetal brain development led to aberrant postnatal brain development as manifested in structural abnormalities in the hippocampus, the striatum, the prefrontal cortex and lateral ventricles (LV), as seen in SCZ. The specific trajectories were region-, age- and sex-specific, with females having delayed onset of pathology compared to males. Brain pathology was accompanied by development of behavioral abnormalities phenotypic of SCZ, attentional deficit and hypersensitivity to amphetamine, with same sex difference. Hippocampal volume loss and LV volume expansion as well as behavioral abnormalities were prevented in the offspring of poly I:C mothers who received clozapine or risperidone during the asymptomatic period of adolescence (PND 34-47). Administration at a later window, PNDs 48-61, exerted sex-, region- and drug- specific effects. Our data show that prenatal insult leads to progressive postnatal brain pathology, which gradually gives rise to "symptoms"; that treatment with atypical APDs can prevent both brain and behavioral pathology; and that the earlier the intervention, the more pathological outcomes can be prevented.

Strain dependent effects of prenatal stress on gene expression in the rat hippocampus

Multiple animal models have been developed to recapitulate phenotypes of the human disease, schizophrenia. A model that simulates many of the cognitive and sensory deficits of the disorder is the use of random variable prenatal stress (PS) in the rat. These deficits suggest a molecular origin in the hippocampus, a brain region that plays a role in the regulation of stress. To study both hippocampal gene expression changes in offspring of prenatally stressed dams and to address genetic variability, we used a random array of prenatal stressors in three different rat strains with diverse responses to stress: Fischer, Sprague-Dawley, and Lewis rats. Candidate genes involved in stress, schizophrenia, cognition, neurotrophic effects, and immunity were selected for assessment by real-time quantitative PCR under resting conditions and following a brief exposure to restraint stress. PS resulted in significant differences in gene expression in the offspring that were strain dependent. mRNA expression for the N-methyl-D-aspartate receptor subtype 2B (Grin2b) was increased, and tumor necrosis factor-alpha (Tnfα) transcript was decreased in PS Sprague-Dawley and Lewis rats, but not in the Fischer rats. Expression of brain-derived neurotrophic factor (Bdnf) mRNA in the hippocampus was increased after an acute stress in all controls of each strain, yet a decrease was seen after acute stress in the PS Sprague-Dawley and Lewis rats. Expression of the glucocorticoid receptor (Nr3c1) was decreased in the Fischer strain when compared to Lewis or Sprague-Dawley rats, though the Fischer rats had markedly higher α7 nicotinic receptor (Chrna7) expression. The expression differences seen in these animals may be important elements of the phenotypic differences seen due to PS and genetic background.

The timing and specificity of prenatal immune risk factors for autism modeled in the mouse and relevance to schizophrenia

Autism is a highly heritable condition, but there is strong epidemiological evidence that environmental factors, especially prenatal exposure to immune challenge, contribute to it. This evidence is largely indirect, and experimental testing is necessary to directly examine causal mechanisms. Mouse models reveal that prenatal immune perturbation disrupts postnatal brain maturation with alterations in gene and protein expression, neurotransmitter function, brain structure and behavioral indices reminiscent of, but not specific to, autism. This likely reflects a neurodevelopmental spectrum in which autism and schizophrenia share numerous genetic and environmental risk factors for difficulties in social interaction, communication, emotion processing and executive function. Recent epidemiological studies find that early rather than late pregnancy infection confers the greater risk of schizophrenia. The autism literature is more limited, but exposures in the 2nd half of pregnancy may be important. Mouse models of prenatal immune challenge help dissect these observations and show some common consequences of early and late gestational exposures, as well as distinct ramifications potentially relevant to schizophrenia and autism. Although nonspecificity of immune-stimulated mouse models could be considered a disadvantage, we propose a broadened perspective, exploiting the possibility that advances made investigating a target condition can contribute towards the understanding of related conditions.

Effects of prenatal infection on brain development and behavior: a review of findings from animal models

Epidemiological studies with human populations indicate associations between maternal infection during pregnancy and increased risk in offspring for central nervous system (CNS) disorders including schizophrenia, autism and cerebral palsy. Since 2000, a large number of studies have used rodent models of systemic prenatal infection or prenatal immune activation to characterize changes in brain function and behavior caused by the prenatal insult. This review provides a comprehensive summary of these findings, and examines consistencies and trends across studies in an effort to provide a perspective on our current state of understanding from this body of work. Results from these animal modeling studies clearly indicate that prenatal immune activation can cause both acute and lasting changes in behavior and CNS structure and function in offspring. Across laboratories, studies vary with respect to the type, dose and timing of immunogen administration during gestation, species used, postnatal age examined and specific outcome measure quantified. This makes comparison across studies and assessment of replicability difficult. With regard to mechanisms, evidence for roles for several acute mediators of effects of prenatal immune activation has emerged, including circulating interleukin-6, increased placental cytokines and oxidative stress in the fetal brain. However, information required to describe the complete mechanistic pathway responsible for acute effects of prenatal immune activation on fetal brain is lacking, and no studies have yet addressed the issue of how acute prenatal exposure to an immunogen is transduced into a long-term CNS change in the postnatal animal. Directions for further research are discussed.

The maternal immune activation (MIA) model of schizophrenia produces pre-pulse inhibition (PPI) deficits in both juvenile and adult rats but these effects are not associated with maternal weight loss

The developmental onset of deficits in sensorimotor-gating was examined in the maternal immune activation (MIA) animal model of schizophrenia. Pre-pulse inhibition (PPI) deficits were evident in juvenile MIA rats. This parallels the sensorimotor-gating deficits observed in groups at high-risk of schizophrenia. PPI deficits were independent of maternal weight loss following the MIA manipulation, suggesting that this measure may not be a useful marker of treatment efficacy.

A unifying hypothesis of schizophrenia: abnormal immune system development may help explain roles of prenatal hazards, post-pubertal onset, stress, genes, climate, infections, and brain dysfunction

We propose a unifying hypothesis of schizophrenia to help reconcile findings from many different disciplines. This hypothesis proposes that schizophrenia often involves pre- or perinatal exposure to adverse factors that produce a latent immune vulnerability. When this vulnerability is manifested, beginning around puberty with changes in immune function and involution of the thymus, individuals become more susceptible to infections and immune dysfunctions that contribute to schizophrenia. Our hypothesis suggests theoretical bridges between different lines of evidence on schizophrenia and offers explanations for many puzzling findings about schizophrenia. For example, the hypothesis helps account for why schizophrenia patients tend to have had increased exposure to neurotropic infections, but most individuals with such exposure do not develop schizophrenia, and why prenatal hardships increase risk for schizophrenia, but the onset of symptoms typically does not occur until after puberty. The hypothesis also explains another paradox: lower socioeconomic status and poor prenatal care increase risk for schizophrenia at the same geographic site, but international comparisons indicate that countries with higher per capita incomes and better prenatal care actually tend to have higher schizophrenia prevalences. As the hypothesis predicts, (1) prenatal adversity, which increases risk for schizophrenia, also impairs post-pubertal immune competence, (2) schizophrenia patients experience elevated morbidity from infectious and auto-immune diseases, (3) genetic and environmental risk factors for schizophrenia increase vulnerability to these diseases, (4) factors that exacerbate schizophrenic symptoms also tend to impair immune function, (5) many anti-psychotic medications combat infection, (6) effects of early infections may not appear until after puberty, when they can produce neurologic and psychiatric symptoms, and (7) immune dysfunctions, such as imbalances of pro- and anti-inflammatory cytokines, may contribute to the onset of psychotic symptoms and the progressive loss of brain tissue in schizophrenia. The disruptive effects of prenatal adversity on the development of the immune system may often combine with adverse effects on prenatal brain development to produce schizophrenia. This paper focuses on the adverse immune system effects, because effects on the brain have been extensively discussed in neurodevelopmental theories of schizophrenia. We propose new tests of scientific predictions. We also point out potential clinical implications of the hypothesis; for example, individuals with schizophrenia may often have underlying infections or immune dysfunctions, such as imbalances in inflammatory cytokines, that contribute to the illness. This possibility could be tested experimentally--e.g., by clinical trials in which patients' exposure to infection is reduced or immune function is normalized.

Prenatal infection and schizophrenia: a review of epidemiologic and translational studies

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.

Potential microbial origins of schizophrenia and their treatments

Schizophrenia is a severe brain disease that affects approximately 1% of the world's population. Extensive study into the indication of and causes of this disease has been ongoing for decades. Historical review of research into associated abnormalities and markers common in schizophrenic patients has demonstrated a correlation with potential microbial origins in the development of the disease. While infectious etiologies could be responsible for some cases of schizophrenia, no consistent use of anti-infective agents has been developed for its prevention or treatment. Elucidation of the mechanisms for infectious roots of schizophrenia may open new avenues for effective treatment.

The neurodevelopmental hypothesis of schizophrenia, revisited

While multiple theories have been put forth regarding the origin of schizophrenia, by far the vast majority of evidence points to the neurodevelopmental model in which developmental insults as early as late first or early second trimester lead to the activation of pathologic neural circuits during adolescence or young adulthood leading to the emergence of positive or negative symptoms. In this report, we examine the evidence from brain pathology (enlargement of the cerebroventricular system, changes in gray and white matters, and abnormal laminar organization), genetics (changes in the normal expression of proteins that are involved in early migration of neurons and glia, cell proliferation, axonal outgrowth, synaptogenesis, and apoptosis), environmental factors (increased frequency of obstetric complications and increased rates of schizophrenic births due to prenatal viral or bacterial infections), and gene-environmental interactions (a disproportionate number of schizophrenia candidate genes are regulated by hypoxia, microdeletions and microduplications, the overrepresentation of pathogen-related genes among schizophrenia candidate genes) in support of the neurodevelopmental model. We relate the neurodevelopmental model to a number of findings about schizophrenia. Finally, we also examine alternate explanations of the origin of schizophrenia including the neurodegenerative model.

Relation of schizophrenia prevalence to latitude, climate, fish consumption, infant mortality, and skin color: a role for prenatal vitamin d deficiency and infections?

Previous surveys found a large (>10-fold) variation in schizophrenia prevalence at different geographic sites and a tendency for prevalence to increase with latitude. We conducted meta-analyses of prevalence studies to investigate whether these findings pointed to underlying etiologic factors in schizophrenia or were the result of methodological artifacts or the confounding of sites' latitude with level of healthcare at those sites. We found that these patterns were still present after controlling for an index of healthcare--infant mortality--and focusing on 49 studies that used similar diagnostic and ascertainment methods. The tendencies for schizophrenia prevalence to increase with both latitude and colder climate were still large and significant and present on several continents. The increase in prevalence with latitude was greater for groups with low fish consumption, darker skin, and higher infant mortality--consistent with a role of prenatal vitamin D deficiency in schizophrenia. Previous research indicates that poor prenatal healthcare and nutrition increase risk for schizophrenia within the same region. These adverse conditions are more prevalent in developing countries concentrated near the equator, but schizophrenia prevalence is lowest at sites near the equator. This suggests that schizophrenia-producing environmental factors associated with higher latitude may be so powerful they overwhelm protective effects of better healthcare in industrialized countries. The observed patterns of correlations of risk factors with prevalence are consistent with an etiologic role for prenatal vitamin D deficiency and exposure to certain infectious diseases. Research to elucidate environmental factors that underlie variations in schizophrenia prevalence deserves high priority.

Exogenous nicotine normalises sensory gating in schizophrenia; therapeutic implications

There is a current popular recognition that cigarette smoking is deleterious to health. Although this is very clearly the case for physical health, the situation regarding mental health is, however, rather more complicated. This piece concentrates on the role of smoking in schizophrenia: it is important to consider why schizophrenia, exceptionally amongst the severe and enduring mental illnesses, is associated with increased cigarette consumption. People who suffer from schizophrenia consequently have a greater risk of the complications to physical health caused by this addiction and clearly, it is important to understand why this occurs. Numerous investigators have found that both neuroleptic-naive, first-onset schizophrenics, together with chronic sufferers of the illness, consume more cigarettes and extract a greater amount of nicotine from them. Researchers have further determined that there is deficient endogenous central nicotinic neurotransmission in schizophrenia, which causes a disruption of sensory gating. This disrupted sensory gating is a reasonable explanation for the delusional misinterpretation of consequent cerebral events. This is the principal reason for the markedly increased rate of cigarette smoking in people with schizophrenia: tobacco cigarette smoking represents an attempt at self-medication in schizophrenia, because the additional nicotine so provided alleviates the hypofunctional sensory gating seen in this illness. Nicotine has been proposed to alleviate negative symptoms. The hypothesis here proposes that as nicotine alleviates positive symptoms, it consequently also - ultimately - prevents negative symptoms caused by the apoptotic effects of excitotoxicity. It would be worthwhile to investigate the therapeutic effects, if any, of additional exogenous nicotine delivered in a less toxic form than cigarettes.

The evolutionary social brain: From genes to psychiatric conditions

The commentaries on our target article, “Psychosis and Autism as Diametrical Disorders of the Social Brain,” reflect the multidisciplinary yet highly fragmented state of current studies of human social cognition. Progress in our understanding of the human social brain must come from studies that integrate across diverse analytic levels, using conceptual frameworks grounded in evolutionary biology.

Maternal exposure to herpes simplex virus and risk of psychosis among adult offspring

BACKGROUND

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.

METHODS

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.

RESULTS

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).

CONCLUSIONS

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.

Immune activation during mid-gestation disrupts sensorimotor gating in rat offspring

Maternal immune activation (MIA) is a newly developed animal model of schizophrenia. It has recently been reported that when MIA is induced with the cytokine inducer polyinosinic-polycytidilic acid (poly I:C) rats do not show deficits in prepulse inhibition (PPI), a test that is often considered a validity benchmark. The aim of the current experiment was to determine whether doses of poly I:C that have previously been shown to induce the behavioural features of schizophrenia can disrupt PPI in rats. Pregnant rat dams were given a single injection of poly I:C (4.0 mg/kg) or a saline injection equivalent on gestational day 15. Acoustic startle reactivity, habituation of the startle response and PPI were assessed in juvenile (34-35 day) and adult (>56 day) offspring. Prenatal immune activation did not alter startle reactivity on startle-only or prepulse-only trials. Furthermore, there was no effect of MIA on habituation of the startle response. MIA does however disrupt PPI, as PPI was reduced significantly in adult MIA offspring, and a trend was observed in the juvenile animals. Our finding that prenatal poly I:C can disrupt PPI in MIA rats further validates this procedure as an animal model.

Viral regulation of aquaporin 4, connexin 43, microcephalin and nucleolin

The current study investigated whether human influenza viral infection in midpregnancy leads to alterations in proteins involved in brain development. Human influenza viral infection was administered to E9 pregnant Balb/c mice. Brains of control and virally-exposed littermates were subjected to microarray analysis, SDS-PAGE and western blotting at three postnatal stages. Microarray analysis of virally-exposed mouse brains showed significant, two-fold change in expression of multiple genes in both neocortex and cerebellum when compared to sham-infected controls. Levels of mRNA and protein levels of four selected genes were examined in brains of exposed mice. Nucleolin mRNA was significantly decreased in day 0 and day 35 neocortex and significantly increased in day 35 cerebellum. Protein levels were significantly upregulated at days 35 and 56 in neocortex and at day 56 in cerebellum. Connexin 43 protein levels were significantly decreased at day 56 in neocortex. Aquaporin 4 mRNA was significantly decreased in day 0 neocortex. Aquaporin 4 protein levels decreased in neocortex significantly at day 35. Finally, microcephalin mRNA was significantly decreased in day 56 neocortex and protein levels were significantly decreased at 56 cerebellum. These data suggest that influenza viral infection in midpregnancy in mice leads to long-term changes in brain markers for enhanced ribosome genesis (nucleolin), increased production of immature neurons (microcephalin), and abnormal glial-neuronal communication and neuron migration (connexin 43 and aquaporin 4).

Prenatal influenza exposure and delivery complications: implications for the development of schizophrenia

This study assessed prenatal influenza exposure in relation to pregnancy complications and delivery complications. Participants of this study consisted of a community sample of all mothers of 1,795 children who were a birth cohort recruited at age 3 in a prospective longitudinal project in Mauritius. The onset of the 1968-1972 A2/Hong Kong influenza epidemic in January 1970 was established from officially published death rates and newspaper records. Data on pregnancy and delivery complications were derived from hospital and clinic records. The study found that prenatal exposure to influenza was associated with increased delivery complications, F(1,351) = 12.2, P = 0.001. There was no effect of influenza exposure on pregnancy complications. The findings have implications for theories on both the development of schizophrenia and other behavior processes. From a public health perspective, reducing influenza exposure in young women of childbearing age might be a critically important first step in the prevention of adverse psychiatric outcomes associated with obstetric complications.

Toxoplasma gondii as a risk factor for early-onset schizophrenia: analysis of filter paper blood samples obtained at birth

BACKGROUND

Infections during fetal life or neonatal period, including infections with Toxoplasma gondii, may be associated with a risk for schizophrenia and other mental disorders. The objectives of this study were to study the association between serological markers for maternal and neonatal infection and the risk for schizophrenia, related psychoses, and affective disorders in a national cohort of newborns.

METHODS

This study was a cohort-based, case-control study combining data from national population registers and patient registers and a national neonatal screening biobank in Denmark. Patients included persons born in Denmark in 1981 or later followed up through 1999 with respect to inpatient or outpatient treatment for schizophrenia or related disorders (ICD-10 F2) or affective disorders (ICD-10 F3).

RESULTS

Toxoplasma gondii immunoglobulin G (IgG) levels corresponding to the upper quartile among control subjects were significantly associated with schizophrenia risk (odds ratio [OR] = 1.79, p = .045) after adjustment for urbanicity of place of birth, year of birth, gender, and psychiatric diagnoses among first-degree relatives. There was no significant association between any marker of infection and other schizophrenia-like disorders or affective disorders.

CONCLUSIONS

Our study supports an association between Toxoplasma gondii and early-onset schizophrenia. Further studies are needed to establish if the association is causal and if it generalizes to cases with onset after age 18.