Fetal exposure to teratogens: Evidence of genes involved in autism

Psychoactive pharmaceuticals as environmental contaminants may disrupt highly inter-connected nodes in an Autism-associated protein-protein interaction network

Background

Most cases of idiopathic autism spectrum disorder (ASD) likely result from unknown environmental triggers in genetically susceptible individuals. These triggers may include maternal exposure of a fetus to minute concentrations of pharmaceuticals, such as carbamazepine (CBZ), venlafaxine (VNX) and fluoxetine (FLX). Unmetabolized pharmaceuticals reach drinking water through a variety of routes, including ineffectively treated sewage. Previous studies in our laboratory examined the extent to which gene sets were enriched in minnow brains treated with pharmaceuticals. Here, we tested the hypothesis that genes in fish brains and human cell cultures, significantly enriched by pharmaceuticals, would have distinct characteristics in an ASD-associated protein interaction network. We accomplished this by comparing these groups using 10 network indices.

Results

A network of 7212 proteins and 33,461 interactions was generated. We found that network characteristics for enriched gene sets for particular pharmaceuticals were distinct from each other, and were different from non-enriched ASD gene sets. In particular, genes in fish brains, enriched by CBZ and VNX 1) had higher network importance than that in the overall network, and those enriched by FLX, and 2) were distinct from FLX and non-enriched ASD genes in multivariate network space. Similarly, genes in human cell cultures enriched by pharmaceutical mixtures (at environmental concentrations) and valproate (at clinical dosages) had similar network signatures, and had greater network importance than genes in the overall ASD network.

Conclusions

The results indicate that important gene sets in the ASD network are particularly susceptible to perturbation by pharmaceuticals at environmental concentrations.

Corpus callosum in cognitive and sensory processing: insights into autism

ABSTRACT 

Atypical corpus callosum size and functional connectivity have been repeatedly implicated in autism spectrum disorders (ASDs). Conversely, individuals with agenesis of the corpus callosum often present with diagnostic features characteristic of autism. An emerging literature has identified genetic and environmental factors which may contribute to both ASD symptomatology and the neuroanatomic finding of altered white matter in the corpus callosum. In this review, we consider what is known about the structure and function of the corpus callosum and provide an update on research identifying corpus callosum abnormalities in individuals with ASD. We also review the literature on behaviors characteristic of autism that are observed in individuals with agenesis of the corpus callosum in an effort to identify some of the neuropathology that is likely to be associated with these behaviors. Finally, we suggest a conceptual model of ‘sensory processing inefficiency’ for future research aimed at elucidating some of the phenotypic variation in individuals with social communication challenges.

Zebrafish as a systems toxicology model for developmental neurotoxicity testing

The developing brain is extremely sensitive to many chemicals. Exposure to neurotoxicants during development has been implicated in various neuropsychiatric and neurological disorders, including autism spectrum disorder, attention deficit hyperactive disorder, schizophrenia, Parkinson's disease, and Alzheimer's disease. Although rodents have been widely used for developmental neurotoxicity testing, experiments using large numbers of rodents are time-consuming, expensive, and raise ethical concerns. Using alternative non-mammalian animal models may relieve some of these pressures by allowing testing of large numbers of subjects while reducing expenses and minimizing the use of mammalian subjects. In this review, we discuss some of the advantages of using zebrafish in developmental neurotoxicity testing, focusing on central nervous system development, neurobehavior, toxicokinetics, and toxicodynamics in this species. We also describe some important examples of developmental neurotoxicity testing using zebrafish combined with gene expression profiling, neuroimaging, or neurobehavioral assessment. Zebrafish may be a systems toxicology model that has the potential to reveal the pathways of developmental neurotoxicity and to provide a sound basis for human risk assessments.

Treatment Approaches in Rodent Models for Autism Spectrum Disorder

Recent years have seen an impressive amount of research devoted to the developing of therapies to treat autism spectrum disorder (ASD). This work has been largely based on rodent models, employing a multitude of genetic and environmental manipulations. Unfortunately, the task of identifying suitable treatments for ASD is extremely challenging, due to a variety of problems specific to the research in this field. Here, we first discuss these problems, including (I) the presence of a large variety of rodent models (often without universal consensus on their validity), (II) the difficulties in choosing the most appropriate behavioural markers to assess the efficacy of possible treatments, (III) the limited knowledge we still have of the neurobiological bases of ASD pathology and of its aetiology, and (IV) the complexity of ASD itself, including a highly heterogeneous group of disorders sometimes with markedly different symptoms (therefore unlikely to be treated with the same approaches). Second, we give a critical overview of the most relevant advances in designing treatments for ASD, focusing on the most commonly used animal model, the laboratory mouse. We include pharmacological and non-pharmacological approaches, underlining their specific advantages, but also their current limitations especially in relation to the problems discussed before. Finally, we highlight the theoretical (e.g. the combination of multiple rather than single treatments) and methodological (e.g. use of single-gene mouse models) approaches that seem more promising to us, suggesting various strategies that can be adopted to simplify the complex field of research on treatments for ASD.

Perinatal Influences of Valproate on Brain and Behaviour: An Animal Model for Autism

Valproic acid or valproate (VPA) is an anti-convulsant and mood stabiliser effective in treating epilepsy and bipolar disorders. Although in adults VPA is well tolerated and safe, there is convincing evidence that it has teratogenic properties, ranging from mild neurodevelopmental changes to severe congenital malformations. In particular, studies involving humans and other animals have shown that prenatal exposure to VPA can induce developmental abnormalities reminiscent of autism spectrum disorder (ASD). In this chapter, we discuss the connection between VPA and ASD, evaluate the VPA animal model of ASD, and describe the possible molecular mechanisms underlying VPA's teratogenic properties.

Tactile stimulation improves neuroanatomical pathology but not behavior in rats prenatally exposed to valproic acid

Autism is a severe neurodevelopmental disorder with a population prevalence of 1 in 68, and dramatically increasing. While no single pharmacologic intervention has successfully targeted the core symptoms of autism, emerging evidence suggests that postnatal environmental manipulations may offer greater therapeutic efficacy. Massage therapy, or tactile stimulation (TS), early in life has repeatedly been shown to be an effective, low-cost, therapeutic approach in ameliorating the cognitive, social, and emotional symptoms of autism. While early TS treatment attenuates many of the behavioral aberrations among children with autism, the neuroanatomical correlates driving such changes are unknown. The present study assessed the therapeutic effects of early TS treatment on behavior and neuroanatomy using the valproic acid (VPA) rodent model of autism. Rats were prenatally exposed to VPA on gestational day 12.5 and received TS shortly following birth. Whereas TS reversed almost all the VPA-induced alterations in neuroanatomy, it failed to do so behaviorally. The TS VPA animals, when compared to VPA animals, did not exhibit altered or improved behavior in the delayed non-match-to-sample T-maze, Whishaw tray reaching, activity box, or elevated plus maze tasks. Anatomically, however, there were significant increases in dendritic branching and spine density in the medial prefrontal cortex, orbital frontal cortex, and amygdala in VPA animals following early TS treatment, suggesting a complete reversal or remediation of the VPA-induced effects in these regions. The results suggest that postnatal TS, during a critical period in development, acts as a powerful reorganization tool that can ameliorate the neuroanatomical consequences of prenatal VPA exposure.

5-HT7 receptors as modulators of neuronal excitability, synaptic transmission and plasticity: physiological role and possible implications in autism spectrum disorders

Serotonin type 7 receptors (5-HT7) are expressed in several brain areas, regulate brain development, synaptic transmission and plasticity, and therefore are involved in various brain functions such as learning and memory. A number of studies suggest that 5-HT7 receptors could be potential pharmacotherapeutic target for cognitive disorders. Several abnormalities of serotonergic system have been described in patients with autism spectrum disorder (ASD), including abnormal activity of 5-HT transporter, altered blood and brain 5-HT levels, reduced 5-HT synthesis and altered expression of 5-HT receptors in the brain. A specific role for 5-HT7 receptors in ASD has not yet been demonstrated but some evidence implicates their possible involvement. We have recently shown that 5-HT7 receptor activation rescues hippocampal synaptic plasticity in a mouse model of Fragile X Syndrome, a monogenic cause of autism. Several other studies have shown that 5-HT7 receptors modulate behavioral flexibility, exploratory behavior, mood disorders and epilepsy, which include core and co-morbid symptoms of ASD. These findings further suggest an involvement of 5-HT7 receptors in ASD. Here, we review the physiological roles of 5-HT7 receptors and their implications in Fragile X Syndrome and other ASD.

Intestinal inflammation in a murine model of autism spectrum disorders

Autism spectrum disorder (ASD) is a cluster of neurodevelopmental disorders characterized by impairments in communication, social interest and stereotypical behaviour. Dysfunction of the intestinal tract is reported in patients with ASD and implicated in the development and severity of ASD symptoms. However, more research is required to investigate the association of intestinal problems with ASD and the potential underlying mechanisms. The purpose of this study was to investigate comorbid symptoms of intestinal inflammation in a murine model of ASD induced by prenatal exposure to valproic acid (VPA). Pregnant BALB/c females were treated subcutaneously with 600 mg/kg VPA or phosphate buffered saline on gestational day 11. Offspring were housed with their mother until weaning on postnatal day 21 (P21). All pups were exposed to a social behaviour test on P28. Inflammatory correlates and activity of the serotonergic system were measured in brain and intestinal tissue. Here we demonstrate, in addition to reduced social behaviour and increased expression of neuroinflammatory markers in the brain, that VPA in utero- exposed male offspring showed epithelial cell loss and neutrophil infiltration in the intestinal tract. Furthermore, reduced levels of serotonin were not only observed the prefrontal cortex and amygdala of VPA in utero- exposed males, but also in the small intestine. Overall, we demonstrate that gender-specific inflammatory conditions are present in the small intestines of VPA in utero- exposed mice and are accompanied by a disturbed serotonergic system in the brain as well as in the intestinal tract.

Altered gut microbiota and activity in a murine model of autism spectrum disorders

Autism spectrum disorder (ASD) is a heterogeneous group of complex neurodevelopmental disorders with evidence of genetic predisposition. Intestinal disturbances are reported in ASD patients and compositional changes in gut microbiota are described. However, the role of microbiota in brain disorders is poorly documented. Here, we used a murine model of ASD to investigate the relation between gut microbiota and autism-like behaviour. Using next generation sequencing technology, microbiota composition was investigated in mice in utero exposed to valproic acid (VPA). Moreover, levels of short chain fatty acids (SCFA) and lactic acid in caecal content were determined. Our data demonstrate a transgenerational impact of in utero VPA exposure on gut microbiota in the offspring. Prenatal VPA exposure affected operational taxonomic units (OTUs) assigned to genera within the main phyla of Bacteroidetes and Firmicutes and the order of Desulfovibrionales, corroborating human ASD studies. In addition, OTUs assigned to genera of Alistipes, Enterorhabdus, Mollicutes and Erysipelotrichalis were especially associated with male VPA-exposed offspring. The microbial differences of VPA in utero-exposed males deviated from those observed in females and was (i) positively associated with increased levels of caecal butyrate as well as ileal neutrophil infiltration and (ii) inversely associated with intestinal levels of serotonin and social behaviour scores. These findings show that autism-like behaviour and its intestinal phenotype is associated with altered microbial colonization and activity in a murine model for ASD, with preponderance in male offspring. These results open new avenues in the scientific trajectory of managing neurodevelopmental disorders by gut microbiome modulation.

Developmental regulation of neuroligin genes in Japanese ricefish (Oryzias latipes) embryogenesis maintains the rhythm during ethanol-induced fetal alcohol spectrum disorder

Although prenatal alcohol exposure is the potential cause of fetal alcohol spectrum disorder (FASD) in humans, the molecular mechanism(s) of FASD is yet unknown. We have used Japanese ricefish (Oryzias latipes) embryogenesis as an animal model of FASD and reported that this model has effectively generated several phenotypic features in the cardiovasculature and neurocranial cartilages by developmental ethanol exposure which is analogous to human FASD phenotypes. As FASD is a neurobehavioral disorder, we are searching for a molecular target of ethanol that alters neurological functions. In this communication, we have focused on neuroligin genes (nlgn) which are known to be active at the postsynaptic side of both excitatory and inhibitory synapses of the central nervous system. There are six human NLGN homologs of Japanese ricefish reported in public data bases. We have partially cloned these genes and analyzed their expression pattern during normal development and also after exposing the embryos to ethanol. Our data indicate that the expression of all six nlgn genes in Japanese ricefish embryos is developmentally regulated. Although ethanol is able to induce developmental abnormalities in Japanese ricefish embryogenesis comparable to the FASD phenotypes, quantitative real-time PCR (qPCR) analysis of nlgn mRNAs indicate unresponsiveness of these genes to ethanol. We conclude that the disruption of the developmental rhythm of Japanese ricefish embryogenesis by ethanol that leads to FASD may not affect the nlgn gene expression at the message level.

What We Have Learned about Autism Spectrum Disorder from Valproic Acid

Two recent epidemiological investigations in children exposed to valproic acid (VPA) treatment in utero have reported a significant risk associated with neurodevelopmental disorders and autism spectrum disorder (ASD) in particular. Parallel to this work, there is a growing body of animal research literature using VPA as an animal model of ASD. In this focused review we first summarize the epidemiological evidence linking VPA to ASD and then comment on two important neurobiological findings linking VPA to ASD clinicopathology, namely, accelerated or early brain overgrowth and hyperexcitable networks. Improving our understanding of how the drug VPA can alter early development of neurological systems will ultimately improve our understanding of ASD.

Transcriptomic analysis of genetically defined autism candidate genes reveals common mechanisms of action

Background

Austism spectrum disorder (ASD) is a heterogeneous behavioral disorder or condition characterized by severe impairment of social engagement and the presence of repetitive activities. The molecular etiology of ASD is still largely unknown despite a strong genetic component. Part of the difficulty in turning genetics into disease mechanisms and potentially new therapeutics is the sheer number and diversity of the genes that have been associated with ASD and ASD symptoms. The goal of this work is to use shRNA-generated models of genetic defects proposed as causative for ASD to identify the common pathways that might explain how they produce a core clinical disability.

Methods

Transcript levels of Mecp2, Mef2a, Mef2d, Fmr1, Nlgn1, Nlgn3, Pten, and Shank3 were knocked-down in mouse primary neuron cultures using shRNA constructs. Whole genome expression analysis was conducted for each of the knockdown cultures as well as a mock-transduced culture and a culture exposed to a lentivirus expressing an anti-luciferase shRNA. Gene set enrichment and a causal reasoning engine was employed to identify pathway level perturbations generated by the transcript knockdown.

Results

Quantification of the shRNA targets confirmed the successful knockdown at the transcript and protein levels of at least 75% for each of the genes. After subtracting out potential artifacts caused by viral infection, gene set enrichment and causal reasoning engine analysis showed that a significant number of gene expression changes mapped to pathways associated with neurogenesis, long-term potentiation, and synaptic activity.

Conclusions

This work demonstrates that despite the complex genetic nature of ASD, there are common molecular mechanisms that connect many of the best established autism candidate genes. By identifying the key regulatory checkpoints in the interlinking transcriptional networks underlying autism, we are better able to discover the ideal points of intervention that provide the broadest efficacy across the diverse population of autism patients.

A nationwide study of the association between celiac disease and the risk of autistic spectrum disorders

IMPORTANCE

Most case reports suggest an association between autistic spectrum disorders (ASDs) and celiac disease (CD) or positive CD serologic test results, but larger studies are contradictory.

OBJECTIVE

To examine the association between ASDs and CD according to small intestinal histopathologic findings.

DESIGN AND SETTING

Nationwide case-control study in Sweden.

MAIN OUTCOMES AND MEASURES

Through 28 Swedish biopsy registers, we collected data about 26,995 individuals with CD (equal to villous atrophy, Marsh stage 3), 12,304 individuals with inflammation (Marsh stages 1-2), and 3719 individuals with normal mucosa (Marsh stage 0) but positive CD serologic test results (IgA/IgG gliadin, endomysium, or tissue transglutaminase) and compared them with 213,208 age- and sex-matched controls. Conditional logistic regression estimated odds ratios (ORs) for having a prior diagnosis of an ASD according to the Swedish National Patient Register. In another analysis, we used the Cox proportional hazards regression model to estimate hazard ratios (HRs) for future ASDs in individuals undergoing small intestinal biopsy.

RESULTS

A prior ASD was not associated with CD (OR, 0.93; 95% CI, 0.51-1.68) or inflammation (OR 1.03; 95% CI, 0.40-2.64) but was associated with a markedly increased risk of having a normal mucosa but a positive CD serologic test result (OR, 4.57; 95% CI, 1.58-13.22). Restricting our data to individuals without a diagnosis of an ASD at the time of biopsy, CD (HR, 1.39; 95% CI, 1.13-1.71) and inflammation (HR, 2.01; 95% CI, 1.29-3.13) were both associated with moderate excess risks of later ASDs, whereas the HR for later ASDs in individuals with normal mucosa but positive CD serologic test results was 3.09 (95% CI, 1.99-4.80).

CONCLUSIONS AND RELEVANCE

Although this study found no association between CD or inflammation and earlier ASDs, there was a markedly increased risk of ASDs in individuals with normal mucosa but a positive CD serologic test result.

Valproic acid silencing of ascl1b/Ascl1 results in the failure of serotonergic differentiation in a zebrafish model of fetal valproate syndrome

Fetal valproate syndrome (FVS) is caused by in utero exposure to the drug sodium valproate. Valproate is used worldwide for the treatment of epilepsy, as a mood stabiliser and for its pain-relieving properties. In addition to birth defects, FVS is associated with an increased risk of autism spectrum disorder (ASD), which is characterised by abnormal behaviours. Valproate perturbs multiple biochemical pathways and alters gene expression through its inhibition of histone deacetylases. Which, if any, of these mechanisms is relevant to the genesis of its behavioural side effects is unclear. Neuroanatomical changes associated with FVS have been reported and, among these, altered serotonergic neuronal differentiation is a consistent finding. Altered serotonin homeostasis is also associated with autism. Here we have used a chemical-genetics approach to investigate the underlying molecular defect in a zebrafish FVS model. Valproate causes the selective failure of zebrafish central serotonin expression. It does so by downregulating the proneural gene ascl1b, an ortholog of mammalian Ascl1, which is a known determinant of serotonergic identity in the mammalian brainstem. ascl1b is sufficient to rescue serotonin expression in valproate-treated embryos. Chemical and genetic blockade of the histone deacetylase Hdac1 downregulates ascl1b, consistent with the Hdac1-mediated silencing of ascl1b expression by valproate. Moreover, tonic Notch signalling is crucial for ascl1b repression by valproate. Concomitant blockade of Notch signalling restores ascl1b expression and serotonin expression in both valproate-exposed and hdac1 mutant embryos. Together, these data provide a molecular explanation for serotonergic defects in FVS and highlight an epigenetic mechanism for genome-environment interaction in disease.

Infantile cerebellar pilocytic astrocytoma with autism spectrum disorder

The etiology of autism remains unclear, but relationships to cerebellar factors have been reported. We report 2 cases of infantile cerebellar pilocytic astrocytoma in children with autism spectrum disorder. Cerebellar tumors may be related to the pathogenesis of autism.

Increasing exposure to antibody-stimulating proteins and polysaccharides in vaccines is not associated with risk of autism

OBJECTIVE

To evaluate the association between autism and the level of immunologic stimulation received from vaccines administered during the first 2 years of life.

STUDY DESIGN

We analyzed data from a case-control study conducted in 3 managed care organizations (MCOs) of 256 children with autism spectrum disorder (ASD) and 752 control children matched on birth year, sex, and MCO. In addition to the broader category of ASD, we also evaluated autistic disorder and ASD with regression. ASD diagnoses were validated through standardized in-person evaluations. Exposure to total antibody-stimulating proteins and polysaccharides from vaccines was determined by summing the antigen content of each vaccine received, as obtained from immunization registries and medical records. Potential confounding factors were ascertained from parent interviews and medical charts. Conditional logistic regression was used to assess associations between ASD outcomes and exposure to antigens in selected time periods.

RESULTS

The aOR (95% CI) of ASD associated with each 25-unit increase in total antigen exposure was 0.999 (0.994-1.003) for cumulative exposure to age 3 months, 0.999 (0.997-1.001) for cumulative exposure to age 7 months, and 0.999 (0.998-1.001) for cumulative exposure to age 2 years. Similarly, no increased risk was found for autistic disorder or ASD with regression.

CONCLUSION

In this study of MCO members, increasing exposure to antibody-stimulating proteins and polysaccharides in vaccines during the first 2 years of life was not related to the risk of developing an ASD.

Adverse drug reactions induced by valproic acid

Valproic acid is a widely-used first-generation antiepileptic drug, prescribed predominantly in epilepsy and psychiatric disorders. VPA has good efficacy and pharmacoeconomic profiles, as well as a relatively favorable safety profile. However, adverse drug reactions have been reported in relation with valproic acid use, either as monotherapy or polytherapy with other antiepileptic drugs or antipsychotic drugs. This systematic review discusses valproic acid adverse drug reactions, in terms of hepatotoxicity, mitochondrial toxicity, hyperammonemic encephalopathy, hypersensitivity syndrome reactions, neurological toxicity, metabolic and endocrine adverse events, and teratogenicity.

Etiopathogenesis of autism spectrum disorders: fitting the pieces of the puzzle together

Autism spectrum disorders (ASD) are disorders of the central nervous system characterized by impairments in communication and social reciprocity. Despite thousands of studies on this topic, the etiopathogenesis of these disorders remains unclear, apart from a general belief that they derive from an interaction between several genes and the environment. Given the mystery surrounding the etiopathogenesis of ASD it is impossible to plan effective preventive and treatment measures. This is of particular concern due to the progressive increase in the prevalence of ASD, which has reached a figure as high as 1:88 children in the USA. Here we present data corroborating a novel unifying hypothesis of the etiopathogenesis of ASD. We suggest that ASD are disorders of the immune system that occur in a very early phase of embryonic development. In a background of genetic predisposition and environmental predisposition (probably vitamin D deficiency), an infection (notably a viral infection) could trigger a deranged immune response which, in turn, results in damage to specific areas of the central nervous system. If proven, this hypothesis would have dramatic consequences for strategies aimed at preventing and treating ASD. To confirm or refute this hypothesis, we need a novel research approach, which unlike former approaches in this field, examine the major factors implicated in ASD (genetic, infections, vitamin D deficiency, immune system deregulation) not separately, but collectively and simultaneously.

Neurodevelopmental alcohol exposure elicits long-term changes to gene expression that alter distinct molecular pathways dependent on timing of exposure

BACKGROUND

Maternal alcohol consumption is known to adversely affect fetal neurodevelopment. While it is known that alcohol dose and timing play a role in the cognitive and behavioral changes associated with prenatal alcohol exposure, it is unclear what developmental processes are disrupted that may lead to these phenotypes.

METHODS

Mice (n=6 per treatment per developmental time) were exposed to two acute doses of alcohol (5 g/kg) at neurodevelopmental times representing the human first, second, or third trimester equivalent. Mice were reared to adulthood and changes to their adult brain transcriptome were assessed using expression arrays. These were then categorized based on Gene Ontology annotations, canonical pathway associations, and relationships to interacting molecules.

RESULTS

The results suggest that ethanol disrupts biological processes that are actively occurring at the time of exposure. These include cell proliferation during trimester one, cell migration and differentiation during trimester two, and cellular communication and neurotransmission during trimester three. Further, although ethanol altered a distinct set of genes depending on developmental timing, many of these show interrelatedness and can be associated with one another via 'hub' molecules and pathways such as those related to huntingtin and brain-derived neurotrophic factor.

CONCLUSIONS

These changes to brain gene expression represent a 'molecular footprint' of neurodevelopmental alcohol exposure that is long-lasting and correlates with active processes disrupted at the time of exposure. This study provides further support that there is no neurodevelopmental time when alcohol cannot adversely affect the developing brain.

Maternal immune activation and strain specific interactions in the development of autism-like behaviors in mice

It is becoming increasingly apparent that the causes of autism spectrum disorders (ASD) are due to both genetic and environmental factors. Animal studies provide important translational models for elucidating specific genetic or environmental factors that contribute to ASD-related behavioral deficits. For example, mouse research has demonstrated a link between maternal immune activation and the expression of ASD-like behaviors. Although these studies have provided insights into the potential causes of ASD, they are limited in their ability to model the important interactions between genetic variability and environmental insults. This is of particular concern given the broad spectrum of severity observed in the human population, suggesting that subpopulations may be more susceptible to the adverse effects of particular environmental insults. It is hypothesized that the severity of effects of maternal immune activation on ASD-like phenotypes is influenced by the genetic background in mice. To test this, pregnant dams of two inbred strains (that is, C57BL/6J and BTBR T(+)tf/J) were exposed to the viral mimic polyinosinic-polycytidylic acid (polyI:C), and their offspring were tested for the presence and severity of ASD-like behaviors. To identify differences in immune system regulation, spleens were processed and measured for alterations in induced cytokine responses. Strain-treatment interactions were observed in social approach, ultrasonic vocalization, repetitive grooming and marble burying behaviors. Interestingly, persistent dysregulation of adaptive immune system function was only observed in BTBR mice. Data suggest that behavioral and immunological effects of maternal immune activation are strain-dependent in mice.

Animal model of autism induced by prenatal exposure to valproate: altered glutamate metabolism in the hippocampus

Autism spectrum disorders (ASD) are characterized by deficits in social interaction, language and communication impairments and repetitive and stereotyped behaviors, with involvement of several areas of the central nervous system (CNS), including hippocampus. Although neurons have been the target of most studies reported in the literature, recently, considerable attention has been centered upon the functionality and plasticity of glial cells, particularly astrocytes. These cells participate in normal brain development and also in neuropathological processes. The present work investigated hippocampi from 15 (P15) and 120 (P120) days old male rats prenatally exposed to valproic acid (VPA) as an animal model of autism. Herein, we analyzed astrocytic parameters such as glutamate transporters and glutamate uptake, glutamine synthetase (GS) activity and glutathione (GSH) content. In the VPA group glutamate uptake was unchanged at P15 and increased 160% at P120; the protein expression of GLAST did not change neither in P15 nor in P120, while GLT1 decreased 40% at P15 and increased 92% at P120; GS activity increased 43% at P15 and decreased 28% at P120; GSH content was unaltered at P15 and had a 27% increase at P120. These data highlight that the astrocytic clearance and destination of glutamate in the synaptic cleft might be altered in autism, pointing out important aspects to be considered from both pathophysiologic and pharmacological approaches in ASD.

Modifiable risk factors for schizophrenia and autism--shared risk factors impacting on brain development

Schizophrenia and autism are two poorly understood clinical syndromes that differ in age of onset and clinical profile. However, recent genetic and epidemiological research suggests that these two neurodevelopmental disorders share certain risk factors. The aims of this review are to describe modifiable risk factors that have been identified in both disorders, and, where available, collate salient systematic reviews and meta-analyses that have examined shared risk factors. Based on searches of Medline, Embase and PsycINFO, inspection of review articles and expert opinion, we first compiled a set of candidate modifiable risk factors associated with autism. Where available, we next collated systematic-reviews (with or without meta-analyses) related to modifiable risk factors associated with both autism and schizophrenia. We identified three modifiable risk factors that have been examined in systematic reviews for both autism and schizophrenia. Advanced paternal age was reported as a risk factor for schizophrenia in a single meta-analysis and as a risk factor in two meta-analyses for autism. With respect to pregnancy and birth complications, for autism one meta-analysis identified maternal diabetes and bleeding during pregnancy as risks factors for autism whilst a meta-analysis of eight studies identified obstetric complications as a risk factor for schizophrenia. Migrant status was identified as a risk factor for both autism and schizophrenia. Two separate meta-analyses were identified for each disorder. Despite distinct clinical phenotypes, the evidence suggests that at least some non-genetic risk factors are shared between these two syndromes. In particular, exposure to drugs, nutritional excesses or deficiencies and infectious agents lend themselves to public health interventions. Studies are now needed to quantify any increase in risk of either autism or schizophrenia that is associated with these modifiable environmental factors.

Ultrasound and autism: association, link, or coincidence?

Autism spectrum disorders (ASDs) affect an estimated 1% of children in the United States. The etiology is probably multifactorial, including genetic components and exposure to infections, toxins, and other environmental factors, particularly unfavorable perinatal and neonatal conditions. There has been an increase in the frequency of diagnosis of ASDs over the last 20 years with a parallel increase in the use of obstetric diagnostic ultrasound, with prenatal ultrasound exposure mentioned as the possible main etiology for autism "epidemics." Central nervous system alterations have been described in ASDs, and certain similar changes have been described in animals after exposure to ultrasound. However, analysis of in utero exposure in humans has failed to show harmful effects in neonates or children, particularly in school performance, attention disorders, and behavioral changes. There is no independently confirmed peer-reviewed published evidence that a cause-effect relationship exists between in utero exposure to clinical ultrasound and development of ASDs in childhood. Ultrasound is a form of energy with effects in the tissues it traverses, and its use should be restricted to medical indications, by trained professionals, for as short a period and as low an intensity as compatible with accurate diagnosis.

GABA system dysfunction in autism and related disorders: from synapse to symptoms

Autism spectrum disorders (ASDs) are neurodevelopmental syndromes characterised by repetitive behaviours and restricted interests, impairments in social behaviour and relations, and in language and communication. These symptoms are also observed in a number of developmental disorders of known origin, including Fragile X Syndrome, Rett Syndrome, and Foetal Anticonvulsant Syndrome. While these conditions have diverse etiologies, and poorly understood pathologies, emerging evidence suggests that they may all be linked to dysfunction in particular aspects of GABAergic inhibitory signalling in the brain. We review evidence from genetics, molecular neurobiology and systems neuroscience relating to the role of GABA in these conditions. We conclude by discussing how these deficits may relate to the specific symptoms observed.

Lack of evidence for neonatal misoprostol neurodevelopmental toxicity in C57BL6/J mice

Misoprostol is a synthetic analogue of prostaglandin E1 that is administered to women at high doses to induce uterine contractions for early pregnancy termination and at low doses to aid in cervical priming during labor. Because of the known teratogenic effects of misoprostol when given during gestation and its effects on axonal growth in vitro, we examined misoprostol for its potential as a neurodevelopmental toxicant when administered to neonatal C57BL6/J mice. Mice were injected subcutaneously (s.c.) with 0.4, 4 or 40 µg/kg misoprostol on postnatal day 7, the approximate developmental stage in mice of human birth, after which neonatal somatic growth, and sensory and motor system development were assessed. These doses were selected to span the range of human exposure used to induce labor. In addition, adult mice underwent a battery of behavioral tests relevant to neurodevelopmental disorders such as autism including tests for anxiety, stereotyped behaviors, social communication and interactions, and learning and memory. No significant effects of exposure were found for any measure of development or behavioral endpoints. In conclusion, the results of the present study in C57BL/6J mice do not provide support for neurodevelopmental toxicity after misoprostol administration approximating human doses and timed to coincide with the developmental stage of human birth.

Psychoactive pharmaceuticals induce fish gene expression profiles associated with human idiopathic autism

Idiopathic autism, caused by genetic susceptibility interacting with unknown environmental triggers, has increased dramatically in the past 25 years. Identifying environmental triggers has been difficult due to poorly understood pathophysiology and subjective definitions of autism. The use of antidepressants by pregnant women has been associated with autism. These and other unmetabolized psychoactive pharmaceuticals (UPPs) have also been found in drinking water from surface sources, providing another possible exposure route and raising questions about human health consequences. Here, we examined gene expression patterns of fathead minnows treated with a mixture of three psychoactive pharmaceuticals (fluoxetine, venlafaxine & carbamazepine) in dosages intended to be similar to the highest observed conservative estimates of environmental concentrations. We conducted microarray experiments examining brain tissue of fish exposed to individual pharmaceuticals and a mixture of all three. We used gene-class analysis to test for enrichment of gene sets involved with ten human neurological disorders. Only sets associated with idiopathic autism were unambiguously enriched. We found that UPPs induce autism-like gene expression patterns in fish. Our findings suggest a new potential trigger for idiopathic autism in genetically susceptible individuals involving an overlooked source of environmental contamination.

Developmental sub-chronic exposure to chlorpyrifos reduces anxiety-related behavior in zebrafish larvae

Neurobehavioral disorders such as anxiety, autism, and attention deficit hyperactivity disorders are typically influenced by genetic and environmental factors. Although several genetic risk factors have been identified in recent years, little is known about the environmental factors that either cause neurobehavioral disorders or contribute to their progression in genetically predisposed individuals. One environmental factor that has raised concerns is chlorpyrifos, an organophosphate pesticide that is widely used in agriculture and is found ubiquitously in the environment. In the present study, we examined the effects of sub-chronic chlorpyrifos exposure on anxiety-related behavior during development using zebrafish larvae. We found that sub-chronic exposure to 0.01 or 0.1 μM chlorpyrifos during development induces specific behavioral defects in 7-day-old zebrafish larvae. The larvae displayed decreases in swim speed and thigmotaxis, yet no changes in avoidance behavior were seen. Exposure to 0.001 μM chlorpyrifos did not affect swimming, thigmotaxis, or avoidance behavior and exposure to 1 μM chlorpyrifos induced behavioral defects, but also induced defects in larval morphology. Since thigmotaxis, a preference for the edge, is an anxiety-related behavior in zebrafish larvae, we propose that sub-chronic chlorpyrifos exposure interferes with the development of anxiety-related behaviors. The results of this study provide a good starting point for examination of the molecular, cellular, developmental, and neural mechanisms that are affected by environmentally relevant concentrations of organophosphate pesticides. A more detailed understanding of these mechanisms is important for the development of predictive models and refined health policies to prevent toxicant-induced neurobehavioral disorders.

Long-term alterations to the brain transcriptome in a maternal voluntary consumption model of fetal alcohol spectrum disorders

Many women continue to consume low to moderate quantities of alcohol during pregnancy, which can result in the variable neurobehavioural effects in the absence of physiological abnormalities that characterize fetal alcohol spectrum disorders (FASD). Previously, we reported that a mouse model for FASD based on voluntary maternal ethanol consumption throughout gestation resulted in offspring that showed mild developmental delay, anxiety-related traits, and deficits in spatial learning. Here, we extend this model by evaluating the gene expression changes that occur in the adult brain of C57BL/6J mice prenatally exposed to ethanol via maternal preference drinking. The results of two independent expression array experiments indicate that ethanol induces subtle but consistent changes to global gene expression. Gene enrichment analysis showed over-represented gene ontology classifications of cellular, embryonic, and nervous system development. Molecular network analysis supported these classifications, with significant networks related to cellular and tissue development, free radical scavenging, and small molecule metabolism. Further, a number of genes identified have previously been implicated in FASD-relevant neurobehavioural phenotypes such as cognitive function (Ache, Bcl2, Cul4b, Dkc1, Ebp, Lcat, Nsdh1, Sstr3), anxiety (Bcl2), attention deficit hyperactivity disorder (Nsdh1), and mood disorders (Bcl2, Otx2, Sstr3). The results suggest a complex residual "footprint" of neurodevelopmental ethanol exposure that may provide a new perspective for identifying mechanisms that underlie the life-long persistence of FASD-related cognitive and behavioural alterations, including potential targets for treatment.

Fractone-associated N-sulfated heparan sulfate shows reduced quantity in BTBR T+tf/J mice: a strong model of autism

BTBR T+tf/J (BTBR) mice show abnormal social, communicatory, and repetitive/stereotyped behaviors paralleling many of the symptoms of autism spectrum disorders. BTBR also show agenesis of the corpus callosum (CC) suggesting major perturbations of growth or guidance factors in the dorsal forebrain [1]. Heparan sulfate (HS) is a polysaccaride found in the brain and other animal tissues. It binds to a wide variety of ligands and through these ligands modulates a number of biological processes, including cell proliferation and differentiation, migration and guidance. It is aggregated on fractal-like structures (fractones) in the subventricular zone (SVZ), that may be visualized by laminin immunoreactivity (LAM-ir), as well as by HS immunoreactivity (HS-ir). We report that the lateral ventricles of BTBR mice were drastically reduced in area compared to C57BL/6J (B6) mice while the BTBR SVZ was significantly shorter than that of B6. In addition to much smaller fractones for BTBR, both HS and LAM-ir associated with fractones were significantly reduced in BTBR, and their anterior-posterior distributions were also altered. Finally, the ratio of HS to LAM in individual fractones was significantly higher in BTBR than in B6 mice. These data, in agreement with other findings linking HS to callosal development, suggest that variations in the quantity and distribution of HS in the SVZ of the lateral ventricles may be important modulators of the brain structural abnormalities of BTBR mice, and, potentially, contribute to the behavioral pathologies of these animals.

Oxytocin receptor and Mecp2 308/Y knockout mice exhibit altered expression of autism-related social behaviors

The development of tasks measuring behaviors specific to the three major symptom categories for autism makes it possible to differentiate mouse models of autism spectrum disorders (ASD) in terms of changes in these specific categories. Prior studies indicate that BTBR T+tf/J mice, the strain that has been evaluated most extensively, show autism-relevant changes in all three symptom categories; reciprocal social interactions; communication; and repetitive, ritualized behaviors. This report reviews the behaviors of oxytocin receptor (Oxtr) and Mecp2(308/Y) wild-type (WT) and knockout (KO) mice, in a number of tests specifically designed to provide information on behaviors that may show functional parallels to the core symptoms of ASD. Oxtr KO mice show robust decreases in reciprocal social interactions, and reduced levels of communication, but no changes in repetitive, ritualized behaviors; whereas Mecp2(308/Y) KO mice show a slight but consistent enhancement of social behavior and communication, and no changes in repetitive, ritualized behaviors. This data base, although small, strongly indicates that mouse models can sort the diagnostic symptoms of autism, and suggests that biological and physiological analyses of these strains may be capable of providing differential information on the brain systems involved in particular symptoms of this disorder. Profiles of behavioral changes in other mouse models of ASD should provide additional specificity in the search for biomarkers associated with particular ASD symptoms and symptom clusters.

Epidemiology of autism spectrum disorders

Epidemiologic data gathered over the last 40 years report that the conservative estimate of autistic spectrum disorder prevalence is 27.5 per 10,000 individuals; however, the prevalence estimate based on newer surveys is 60 per 10,000 individuals. Several factors are considered in various epidemiologic surveys of autism, especially the evolution of the concept of autism and changing criteria for diagnosis. This article reviews the incidence, prevalence, and risk factors for autism.

Gene-class analysis of expression patterns induced by psychoactive pharmaceutical exposure in fathead minnow (Pimephales promelas) indicates induction of neuronal systems

Psychoactive pharmaceuticals are among the most frequently prescribed drugs, contributing to persistent measurable concentrations in aquatic systems. Typically, it is assumed that such contaminants have no human health implications because they exist in extremely low concentrations. We exposed juvenile fathead minnows (Pimephales promelas) to three pharmaceuticals, fluoxetine, venlafaxine and carbamazepine, individually and in a mixture, and measured their effect on the induction of gene expression in fish brains using microarray analysis. Gene expression changes were accompanied by behavioral changes and validated by qPCR analysis. Gene Set Enrichment Analysis was used to perform gene-class analysis of gene expression, testing for enrichment of gene sets known to be involved in human neuronal development, regulation and growth. We found significant enrichment of gene sets for each of the treatments, with the largest induction of expression by the mixture treatment. These results suggest that the psychoactive pharmaceuticals are able to alter expression of fish genes associated with development, regulation and differentiation of synapses, neurons and neurotransmitters. The results provide a new perspective for the consideration of potential consequence for human health due to environmental exposure to unmetabolized psychoactive pharmaceuticals.