Animal models of autism spectrum disorders: information for neurotoxicologists

"Comparative evaluation of different chemical agents induced Autism Spectrum Disorder in experimental Wistar rats"

Autism Spectrum Disorder (ASD) is a complex neurodevelopmental condition with uncertain etiology and pathophysiology. Several studies revealed that the commonly used animal models like Valproic Acid (VPA) and Propionic Acid (PPA) do not precisely represent the disease as the human patient does. The current study was conducted on different chemically (VPA, PPA, Poly I:C, Dioxin (2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD)) & Chlorpyrifos (CPF)) induced ASD-like animal models and validated the best suitable experimental animal model, which would closely resemble with clinical features of the ASD. This validated model might help to explore the pathophysiology of ASD. This study included rat pups prenatally exposed to VPA, PPA, Poly I:C, Dioxin & CPF within GD9 to GD15 doses. The model groups were validated through developmental and behavioral parameters, Gene Expressions, Oxidative Stress, and Pro-inflammatory and Anti-inflammatory cytokines levels. Developmental and neurobehavioral parameters showed significant changes in model groups compared to the control. In oxidative stress parameters and neuro-inflammatory cytokines levels, model groups exhibited high oxidative stress and neuro-inflammation compared to control groups. Gene expression profile of ASD-related genes showed significant downregulation in model groups compared to the control group. Moreover, the Poly I:C group showed more significant results than other model groups. The comparison of available ASD-like experimental animal models showed that the Poly I:C induced model represented the exact pathophysiology of ASD as the human patient does. Poly I:C was reported in the maternal immune system activation via the inflammatory cytokines pathway, altering embryonic development and causing ASD in neonates.

Altered Developmental Trajectory in Male and Female Rats in a Prenatal Valproic Acid Exposure Model of Autism Spectrum Disorder

Early motor and sensory developmental delays precede Autism Spectrum Disorder (ASD) diagnosis and may serve as early indicators of ASD. The literature on sensorimotor development in animal models is sparse, male centered, and has mixed findings. We characterized early development in a prenatal valproic acid (VPA) model of ASD and found sex-specific developmental delays in VPA rats. We created a developmental composite score combining 15 test readouts, yielding a reliable gestalt measure spanning physical, sensory, and motor development, that effectively discriminated between VPA and control groups. Considering the heterogeneity in ASD phenotype, the developmental composite offers a robust metric that can enable comparison across different animal models of ASD and can serve as an outcome measure for early intervention studies.

A Mini-Review Regarding the Modalities to Study Neurodevelopmental Disorders-Like Impairments in Zebrafish—Focussing on Neurobehavioural and Psychological Responses

Neurodevelopmental disorders (NDDs) are complex disorders which can be associated with many comorbidities and exhibit multifactorial-dependent phenotypes. An important characteristic is represented by the early onset of the symptoms, during childhood or young adulthood, with a great impact on the socio-cognitive functioning of the affected individuals. Thus, the aim of our review is to describe and to argue the necessity of early developmental stages zebrafish models, focusing on NDDs, especially autism spectrum disorders (ASD) and also on schizophrenia. The utility of the animal models in NDDs or schizophrenia research remains quite controversial. Relevant discussions can be opened regarding the specific characteristics of the animal models and the relationship with the etiologies, physiopathology, and development of these disorders. The zebrafish models behaviors displayed as early as during the pre-hatching embryo stage (locomotor activity prone to repetitive behavior), and post-hatching embryo stage, such as memory, perception, affective-like, and social behaviors can be relevant in ASD and schizophrenia research. The neurophysiological processes impaired in both ASD and schizophrenia are generally highly conserved across all vertebrates. However, the relatively late individual development and conscious social behavior exhibited later in the larval stage are some of the most important limitations of these model animal species.

Gene-Environment Interactions in Developmental Neurotoxicity: a Case Study of Synergy between Chlorpyrifos and CHD8 Knockout in Human BrainSpheres

BACKGROUND

Autism spectrum disorder (ASD) is a major public health concern caused by complex genetic and environmental components. Mechanisms of gene-environment (G × E ) interactions and reliable biomarkers associated with ASD are mostly unknown or controversial. Induced pluripotent stem cells (iPSCs) from patients or with clustered regularly interspaced short palindromic repeats and CRISPR-associated protein 9 (CRISPR/Cas9)-introduced mutations in candidate ASD genes provide an opportunity to study (G × E ) interactions.

OBJECTIVES

In this study, we aimed to identify a potential synergy between mutation in the high-risk autism gene encoding chromodomain helicase DNA binding protein 8 (CHD8) and environmental exposure to an organophosphate pesticide (chlorpyrifos; CPF) in an iPSC-derived human three-dimensional (3D) brain model.

METHODS

This study employed human iPSC-derived 3D brain organoids (BrainSpheres) carrying a heterozygote CRISPR/Cas9-introduced inactivating mutation in CHD8 and exposed to CPF or its oxon-metabolite (CPO). Neural differentiation, viability, oxidative stress, and neurite outgrowth were assessed, and levels of main neurotransmitters and selected metabolites were validated against human data on ASD metabolic derangements.

RESULTS

Expression of CHD8 protein was significantly lower in CHD8 heterozygous knockout (C H D 8 + / - ) BrainSpheres compared with C H D 8 + / + ones. Exposure to CPF/CPO treatment further reduced CHD8 protein levels, showing the potential (G × E ) interaction synergy. A novel approach for validation of the model was chosen: from the literature, we identified a panel of metabolic biomarkers in patients and assessed them by targeted metabolomics in vitro. A synergistic effect was observed on the cholinergic system, S-adenosylmethionine, S-adenosylhomocysteine, lactic acid, tryptophan, kynurenic acid, and α -hydroxyglutaric acid levels. Neurite outgrowth was perturbed by CPF/CPO exposure. Heterozygous knockout of CHD8 in BrainSpheres led to an imbalance of excitatory/inhibitory neurotransmitters and lower levels of dopamine.

DISCUSSION

This study pioneered (G × E ) interaction in iPSC-derived organoids. The experimental strategy enables biomonitoring and environmental risk assessment for ASD. Our findings reflected some metabolic perturbations and disruption of neurotransmitter systems involved in ASD. The increased susceptibility of CHD 8 + / - BrainSpheres to chemical insult establishes a possibly broader role of (G × E ) interaction in ASD. https://doi.org/10.1289/EHP8580.

Altered Caecal Neuroimmune Interactions in the Neuroligin-3R451C Mouse Model of Autism

The intrinsic nervous system of the gut interacts with the gut-associated lymphoid tissue (GALT) via bidirectional neuroimmune interactions. The caecum is an understudied region of the gastrointestinal (GI) tract that houses a large supply of microbes and is involved in generating immune responses. The caecal patch is a lymphoid aggregate located within the caecum that regulates microbial content and immune responses. People with Autism Spectrum Disorder (ASD; autism) experience serious GI dysfunction, including inflammatory disorders, more frequently than the general population. Autism is a highly prevalent neurodevelopmental disorder defined by the presence of repetitive behavior or restricted interests, language impairment, and social deficits. Mutations in genes encoding synaptic adhesion proteins such as the R451C missense mutation in neuroligin-3 (NL3) are associated with autism and impair synaptic transmission. We previously reported that NL3^R451C mice, a well-established model of autism, have altered enteric neurons and GI dysfunction; however, whether the autism-associated R451C mutation alters the caecal enteric nervous system and immune function is unknown. We assessed for gross anatomical changes in the caecum and quantified the proportions of caecal submucosal and myenteric neurons in wild-type and NL3^R451C mice using immunofluorescence. In the caecal patch, we assessed total cellular density as well as the density and morphology of Iba-1 labeled macrophages to identify whether the R451C mutation affects neuro-immune interactions. NL3^R451C mice have significantly reduced caecal weight compared to wild-type mice, irrespective of background strain. Caecal weight is also reduced in mice lacking Neuroligin-3. NL3^R451C caecal ganglia contain more neurons overall and increased numbers of Nitric Oxide (NO) producing neurons (labeled by Nitric Oxide Synthase; NOS) per ganglion in both the submucosal and myenteric plexus. Overall caecal patch cell density was unchanged however NL3^R451C mice have an increased density of Iba-1 labeled enteric macrophages. Macrophages in NL3^R451C were smaller and more spherical in morphology. Here, we identify changes in both the nervous system and immune system caused by an autism-associated mutation in Nlgn3 encoding the postsynaptic cell adhesion protein, Neuroligin-3. These findings provide further insights into the potential modulation of neural and immune pathways.

Autism in India: a case-control study to understand the association between socio-economic and environmental risk factors

Autism spectrum disorder is a neurodevelopmental disorder and the cause of autism is still unclear. The aim of this study was to investigate the association of socioeconomic, environmental, pregnancy and newborn-related risk factors among children with autism spectrum disorders. This was a population-based case-control study. The study included 55 children with autism spectrum disorder and 55 age and sex matched typically developing normal children (TD) between 3 and 12 years. Several socio-economic factors, environmental factors, pregnancy related, natal, post-natal factors and the first noticed signs by the parents were analyzed. Chi-square test was used to compare nominal variables. For multivariate analysis, forward stepwise logistic regression model was employed to examine the association between autism and the chances that the child develops ASD to assess the odds ratios. Male predominance was observed in the study. Logistic regression model showed statistical significance of the following factors: paternal age greater than 40 years, family history of autism, nutrition during pregnancy, mode of labor, fetal hypoxia, NICU stay and history of breast feeding. In this epidemiological study of autism in Coimbatore city, we found correlation between several environmental factors during fetal development and can be transmitted to succeeding generations, causing atypical behavior phenotypes. The exact exposure magnitude, exposure time in relation to vital developmental periods need to be studied to understand the influence of socioeconomic and environmental factors, which can be improved to prevent ASD-related challenges.

Decreased Expression of Synaptophysin 1 (SYP1 Major Synaptic Vesicle Protein p38) and Contactin 6 (CNTN6/NB3) in the Cerebellar Vermis of reln Haplodeficient Mice

Reeler heterozygous mice (reln^+/-) are seemingly normal but haplodeficient in reln, a gene implicated in autism. Structural/neurochemical alterations in the reln^+/- brain are subtle and difficult to demonstrate. Therefore, the usefulness of these mice in translational research is still debated. As evidence implicated several synapse-related genes in autism and the cerebellar vermis is structurally altered in the condition, we have investigated the expression of synaptophysin 1 (SYP1) and contactin 6 (CNTN6) within the vermis of reln^+/- mice. Semi-thin plastic sections of the vermis from adult mice of both sexes and different genotypes (reln^+/- and reln^+/+) were processed with an indirect immunofluorescence protocol. Immunofluorescence was quantified on binary images and statistically analyzed. Reln^+/- males displayed a statistically significant reduction of 11.89% in the expression of SYP1 compared to sex-matched wild-type animals, whereas no differences were observed between reln^+/+ and reln^+/- females. In reln^+/- male mice, reductions were particularly evident in the molecular layer: 10.23% less SYP1 than reln^+/+ males and 5.84% < reln^+/+ females. In reln^+/- females, decrease was 9.84% versus reln^+/+ males and 5.43% versus reln^+/+ females. Both reln^+/- males and females showed a stronger decrease in CNTN6 expression throughout all the three cortical layers of the vermis: 17-23% in the granular layer, 24-26% in the Purkinje cell layer, and 9-14% in the molecular layer. Altogether, decrease of vermian SYP1 and CNTN6 in reln^+/- mice displayed patterns compatible with the structural modifications of the autistic cerebellum. Therefore, these mice may be a good model in translational studies.

A Review of Oxytocin and Arginine-Vasopressin Receptors and Their Modulation of Autism Spectrum Disorder

Oxytocin (OXT) and arginine-vasopressin (AVP) play a key regulatory part in social and affiliative behaviors; two aspects highly compromised in Autism Spectrum Disorder (ASD). Furthermore, variants in the adjacent oxytocin-vasopressin gene regions have been found to be associated with ASD diagnosis and endophenotypes. This review focuses mainly on common OXTr single nucleotide polymorphisms (SNPs), AVPR1a microsatellites and AVPR1b polymorphisms in relation to the development of autism. Although these genes did not surface in genome-wide association studies, evidence supports the hypothesis that these receptors and their polymorphisms are widely involved in the regulation of social behavior, and in modulating neural and physiological pathways contributing to the etiology of ASD. With a specific focus on variants considered to be among the most prevalent in the development of ASD, these issues will be discussed in-depth and suggestions to approach inconsistencies in the present literature will be provided. Translational implications and future directions are deliberated from a short-term and a forward-looking perspective. While the scientific community has made significant progress in enhancing our understanding of ASD, more research is required for the ontology of this disorder to be fully elucidated. By supplementing information related to genetics, highlighting the differences across male and female sexes, this review provides a wider view of the current state of knowledge of OXTr and AVPr mechanisms of functioning, eventually addressing future research in the identification of further risk factors, to build new strategies for early interventions.

What California sea lions exposed to domoic acid might teach us about autism: lessons for predictive and preventive medicine

Autism spectrum disorder (ASD) shares many biological and behavioral similarities with the deleterious effects of domoic acid (DA) exposure. DA is produced by marine algae and most commonly by species of Pseudo-nitzschia. Humans and marine mammals can be exposed to DA when they consume whole fish or shellfish. The mammalian fetus is highly sensitive to the deleterious effects of DA exposure. Both ASD and exposures to toxic levels of DA feature repetitive behaviors, challenges with social interaction, and seizures. They can also share a commonality in brain anatomy and function, particularly the balance between excitatory and inhibitory mechanisms. The current article is relevant to predictive, preventive, and personalized medicine for three reasons. First, shellfish consumption may be a risk factor for ASD and the regulatory limit for DA should be adjusted to prevent this possibility. Human contributions to increased algal production of DA in coastal waters should be identified and reduced. Second, evaluations of sentinel species wild and free-roaming in the environment, though typically outside the purview of biomedical research, should be much more fully employed to gain insights to risk factors for human disease. To better identify and prevent disease, biomedical researchers should study wild populations. Third, studies of DA exposure highlight the possibility that glutamate additives to processed foods may also have deleterious impacts on human brain development and behavior.

Social Reward and Empathy as Proximal Contributions to Altruism: The Camaraderie Effect

Natural selection favors individuals to act in their own interests, implying that wild animals experience a competitive psychology. Animals in the wild also express helping behaviors, presumably at their own expense and suggestive of a more compassionate psychology. This apparent paradox can be partially explained by ultimate mechanisms that include kin selection, reciprocity, and multilevel selection, yet some theorists argue such ultimate explanations may not be sufficient and that an additional "stake in others" is necessary for altruism's evolution. We suggest this stake is the "camaraderie effect," a by-product of two highly adaptive psychological experiences: social motivation and empathy. Rodents can derive pleasure from access to others and this appetite for social rewards motivates individuals to live together, a valuable psychology when group living is adaptive. Rodents can also experience empathy, the generation of an affective state more appropriate to the situation of another compared to one's own. Empathy is not a compassionate feeling but it has useful predictive value. For instance, empathy allows an individual to feel an unperceived danger from social cues. Empathy of another's stance toward one's self would predict either social acceptance or ostracism and amplify one's physiological sensitivity to social isolation, including impaired immune responses and delayed wound healing. By contrast, altruistic behaviors would promote well-being in others and feelings of camaraderie from others, thereby improving one's own physiological well-being. Together, these affective states engender a stake in others necessary for the expression of altruistic behavior.

Ketogenic diet exposure during the juvenile period increases social behaviors and forebrain neural activation in adult Engrailed 2 null mice

Prolonged consumption of ketogenic diets (KD) has reported neuroprotective benefits. Several studies suggest KD interventions could be useful in the management of neurological and developmental disorders. Alterations in the Engrailed (En) genes, specifically Engrailed 2 (En2), have neurodevelopmental consequences and produce autism-related behaviors. The following studies used En2 knockout (KO; En2(-/-)), and wild-type (WT; En2(+/+)), male mice fed either KD (80% fat, 0.1% carbohydrates) or control diet (CD; 10% fat, 70% carbohydrates). The objective was to determine whether a KD fed from weaning at postnatal day (PND) 21 to adulthood (PND 60) would alter brain monoamines concentrations, previously found dysregulated, and improve social outcomes. In WT animals, there was an increase in hypothalamic norepinephrine content in the KD-fed group. However, regional monoamines were not altered in KO mice in KD-fed compared with CD-fed group. In order to determine the effects of juvenile exposure to KD in mice with normal blood ketone levels, separate experiments were conducted in mice removed from the KD or CD and fed standard chow for 2days (PND 62). In a three-chamber social test with a novel mouse, KO mice previously exposed to the KD displayed similar social and self-grooming behaviors compared with the WT group. Groups previously exposed to a KD, regardless of genotype, had more c-Fos-positive cells in the cingulate cortex, lateral septal nuclei, and anterior bed nucleus of the stria terminalis. In the novel object condition, KO mice previously exposed to KD had similar behavioral responses and pattern of c-Fos immunoreactivity compared with the WT group. Thus, juvenile exposure to KD resulted in short-term consequences of improving social interactions and appropriate exploratory behaviors in a mouse model that displays autism-related behaviors. Such findings further our understanding of metabolic-based therapies for neurological and developmental disorders.

Gestational/perinatal chlorpyrifos exposure is not associated with autistic-like behaviors in rodents

Although animal models cannot exactly replicate human psychiatric disorders, they may be useful to investigate whether the behaviors associated with certain exposures in animals parallel those observed in people. According to the most current version of the Diagnostic and Statistical Manual of Mental Disorders, autism is diagnosed based on (1) persistent deficits in social communication and social interaction; and (2) the presence of restricted, repetitive patterns of behavior, interests and activities. To address whether developmental chlorpyrifos (CPF) exposure was associated with the development of autistic behaviors, a literature search was conducted to identify studies in rats and mice involving gestational or early postnatal exposure to CPF or CPF oxon (CPO, the active metabolite of CPF) and subsequent behavioral testing to assess behaviors related to autism. A total of 13 studies conducted in six different laboratories were identified. Analysis of these studies found that perinatal CPF exposure was generally associated with (1) no effect or increased social communications; (2) no effect or increased social encounters; (3) no effect, reduced stereotypies, or conflicting findings on stereotypic behaviors; and (4) no effect or increased preference for novelty and reduced anxiety in novel environments. These behavioral findings are generally inconsistent with the types of behaviors that would be expected in children with clinical autism. Based on the results of this analysis of rodent model studies involving CPF/CPO exposure, it cannot be concluded that gestational and/or perinatal CPF exposure is likely to be associated with the development of autism-like behaviors in humans.

Molecular Advances Leading to Treatment Implications for Fragile X Premutation Carriers

Fragile X syndrome (FXS) is the most common single gene cause of intellectual disability and it is characterized by a CGG expansion of more than 200 repeats in the FMR1 gene, leading to methylation of the promoter and gene silencing. The fragile X premutation, characterized by a 55 to 200 CGG repeat expansion, causes health problems and developmental difficulties in some, but not all, carriers. The premutation causes primary ovarian insufficiency in approximately 20% of females, psychiatric problems (including depression and/or anxiety) in approximately 50% of carriers and a neurodegenerative disorder, the fragile X-associated tremor ataxia syndrome (FXTAS), in approximately 40% of males and 16% of females later in life. Recent clinical studies in premutation carriers have expanded the health problems that may be seen. Advances in the molecular pathogenesis of the premutation have shown significant mitochondrial dysfunction and oxidative stress in neurons which may be amenable to treatment. Here we review the clinical problems of carriers and treatment recommendations.

Neuronal connectivity as a convergent target of gene × environment interactions that confer risk for Autism Spectrum Disorders

Evidence implicates environmental factors in the pathogenesis of Autism Spectrum Disorders (ASD). However, the identity of specific environmental chemicals that influence ASD risk, severity or treatment outcome remains elusive. The impact of any given environmental exposure likely varies across a population according to individual genetic substrates, and this increases the difficulty of identifying clear associations between exposure and ASD diagnoses. Heritable genetic vulnerabilities may amplify adverse effects triggered by environmental exposures if genetic and environmental factors converge to dysregulate the same signaling systems at critical times of development. Thus, one strategy for identifying environmental risk factors for ASD is to screen for environmental factors that modulate the same signaling pathways as ASD susceptibility genes. Recent advances in defining the molecular and cellular pathology of ASD point to altered patterns of neuronal connectivity in the developing brain as the neurobiological basis of these disorders. Studies of syndromic ASD and rare highly penetrant mutations or CNVs in ASD suggest that ASD risk genes converge on several major signaling pathways linked to altered neuronal connectivity in the developing brain. This review briefly summarizes the evidence implicating dysfunctional signaling via Ca(2+)-dependent mechanisms, extracellular signal-regulated kinases (ERK)/phosphatidylinositol-3-kinases (PI3K) and neuroligin-neurexin-SHANK as convergent molecular mechanisms in ASD, and then discusses examples of environmental chemicals for which there is emerging evidence of their potential to interfere with normal neuronal connectivity via perturbation of these signaling pathways.

Genomic and proteomic advances in autism research

Recent studies suggest that adult neural stem cells (NSCs) may play a role in the pathogenesis of a number of the developmental disorders subsumed under the term autism spectrum disorders (ASD) that have in common impaired social interaction, communication deficits, and stereotypical behavior or interests. Since there is no "unifying hypothesis" about the etiology and pathogenesis of ASD, several factors have been associated with ASD, including genetic factors, physical co-morbidity, disturbances of brain structure and function, biochemical anomalies, cognitive impairment, and disorders of speech and emotional development, mostly the lack of empathy. Most of disturbances of brain interconnectivity are regarded as main problem in autism. Since NSCs have a distinct life cycle in the mammalian brain consisting of proliferation, migration, arborization, integration into existing neuronal circuits, and myelinization, disturbances in NSCs differentiation is thought to be deleterious. In the current review, I will summarize the results of genomic and proteomic studies finding susceptibility genes and proteins for autism with regard to NSCs differentiation and maturation.

Tipping the balance of autism risk: potential mechanisms linking pesticides and autism

BACKGROUND

Autism spectrum disorders (ASDs) have been increasing in many parts of the world and a portion of cases are attributable to environmental exposures. Conclusive replicated findings have yet to appear on any specific exposure; however, mounting evidence suggests gestational pesticides exposures are strong candidates. Because multiple developmental processes are implicated in ASDs during gestation and early life, biological plausibility is more likely if these agents can be shown to affect core pathophysiological features.

OBJECTIVES

Our objectives were to examine shared mechanisms between autism pathophysiology and the effects of pesticide exposures, focusing on neuroexcitability, oxidative stress, and immune functions and to outline the biological correlates between pesticide exposure and autism risk.

METHODS

We review and discuss previous research related to autism risk, developmental effects of early pesticide exposure, and basic biological mechanisms by which pesticides may induce or exacerbate pathophysiological features of autism.

DISCUSSION

On the basis of experimental and observational research, certain pesticides may be capable of inducing core features of autism, but little is known about the timing or dose, or which of various mechanisms is sufficient to induce this condition.

CONCLUSIONS

In animal studies, we encourage more research on gene × environment interactions, as well as experimental exposure to mixtures of compounds. Similarly, epidemiologic studies in humans with exceptionally high exposures can identify which pesticide classes are of greatest concern, and studies focused on gene × environment are needed to determine if there are susceptible subpopulations at greater risk from pesticide exposures.

Etiology of autistic features: the persisting neurotoxic effects of propionic acid

BACKGROUND

Recent clinical observations suggest that certain gut and dietary factors may transiently worsen symptoms in autism. Propionic acid (PA) is a short chain fatty acid and an important intermediate of cellular metabolism. Although PA has several beneficial biological effects, its accumulation is neurotoxic.

METHODS

Two groups of young Western albino male rats weighing about 45 to 60 grams (approximately 21 days old) were used in the present study. The first group consisted of oral buffered PA-treated rats that were given a neurotoxic dose of 250 mg/kg body weight/day for three days, n = eight; the second group of rats were given only phosphate buffered saline and used as a control. Biochemical parameters representing oxidative stress, energy metabolism, neuroinflammation, neurotransmission, and apoptosis were investigated in brain homogenates of both groups.

RESULTS

Biochemical analyses of brain homogenates from PA-treated rats showed an increase in oxidative stress markers (for example, lipid peroxidation), coupled with a decrease in glutathione (GSH) and glutathione peroxidase (GPX) and catalase activities. Impaired energy metabolism was ascertained through the decrease of lactate dehydrogenase and activation of creatine kinase (CK). Elevated IL-6, TNFα, IFNγ and heat shock protein 70 (HSP70) confirmed the neuroinflammatory effect of PA. Moreover, elevation of caspase3 and DNA fragmentation proved the pro-apoptotic and neurotoxic effect of PA to rat pups

CONCLUSION

By comparing the results obtained with those from animal models of autism or with clinical data on the biochemical profile of autistic patients, this study showed that the neurotoxicity of PA as an environmental factor could play a central role in the etiology of autistic biochemical features.

Valproate-induced teratogenesis in Japanese rice fish (Oryzias latipes) embryogenesis

Fertilized eggs of Japanese rice fish (medaka) at three developmental stages (Iwamatsu stages 4-30) were exposed to waterborne valproic acid (VPA) (0-80 mM) in hatching solution for 48 h. The amount of valproate to cause 50% mortality (IC(50)) is found to be developmental stage-specific. The embryos were more sensitive to valproate at early stages of development (Iwamatsu stages 4-10) than in the embryos in late stages (Iwamatsu stages 17-30). Valproate exposed embryos have microcephaly and disrupted cardiovasculature with delayed vessel circulation, thrombus formation, and slow heart rate. The hatching efficiency is also reduced by valproate exposure due to developmental delay. The mRNA analysis of nine genes belong to oxidative stress (catalase, gsr, gst), neurogenesis (iro3, wnt1, shh, otx2, nlgn3b) and cell cycle regulation (ccna2) have been done. It was observed that the genes belong to oxidative stress remained unaltered after valproate exposure. However, some of the genes belong to neurogenesis (wnt1,shh, otx2 and nlgn3b) and cell cycle (ccna2) showed developmental stage-specific alteration after valproate exposure. This study indicates that valproate is able to induce some of the phenotypic features which are analogous to human fetal valproate syndrome (FVS). Modulation of genes expressed in neural tissues indicates that this fish can be used to analyze the mechanisms of many neurobehavioral disorders like Autism spectrum disorder (ASD) in human.

Oxytocin receptor knockout mice display deficits in the expression of autism-related behaviors

A wealth of studies has implicated oxytocin (Oxt) and its receptors (Oxtr) in the mediation of social behaviors and social memory in rodents. It has been suggested that failures in this system contribute to deficits in social interaction that characterize autism spectrum disorders (ASD). In the current analyses, we investigated the expression of autism-related behaviors in mice that lack the ability to synthesize the oxytocin receptor itself, Oxtr knockout (KO) mice, as compared to their wild-type (WT) littermates. In the visible burrow system, Oxtr KO mice showed robust reductions in frontal approach, huddling, allo-grooming, and flight, with more time spent alone, and in self-grooming, as compared to WT. These results were corroborated in the three-chambered test: unlike WT, Oxtr KO mice failed to spend more time in the side of the test box containing an unfamiliar CD-1 mouse. In the social proximity test, Oxtr KO mice showed clear reductions in nose to nose and anogenital sniff behaviors oriented to an unfamiliar C57BL/6J (B6) mouse. In addition, our study revealed no differences between Oxtr WT and KO genotypes in the occurrence of motor and cognitive stereotyped behaviors. A significant genotype effect was found in the scent marking analysis, with Oxtr KO mice showing a decreased number of scent marks, as compared to WT. Overall, the present data indicate that the profile for Oxtr KO mice, including consistent social deficits, and reduced levels of communication, models multiple components of the ASD phenotype. This article is part of a Special Issue entitled Oxytocin, Vasopressin, and Social Behavior.

The autism diagnosis in translation: shared affect in children and mouse models of ASD

In the absence of molecular biomarkers that can be used to diagnose ASD, current diagnostic tools depend upon clinical assessments of behavior. Research efforts with human subjects have successfully utilized standardized diagnostic instruments, which include clinician interviews with parents and direct observation of the children themselves [Risi et al., 2006]. However, because clinical instruments are semi-structured and rely heavily on dynamic social processes and clinical skill, scores from these measures do not necessarily lend themselves directly to experimental investigations into the causes of ASD. Studies of the neurobiology of autism require experimental animal models. Mice are particularly useful for elucidating genetic and toxicological contributions to impairments in social function [Halladay et al., 2009]. Behavioral tests have been developed that are relevant to autism [Crawley, 2004, 2007], including measures of repetitive behaviors [Lewis, Tanimura, Lee, & Bodfish, 2007; Moy et al., 2008], social behavior [Brodkin, 2007; Lijam et al., 1997; Moretti, Bouwknecht, Teague, Paylor, & Zoghbi, 2005], and vocal communication [D'Amato et al., 2005; Panksepp et al., 2007; Scattoni et al., 2008]. Advances also include development of high-throughput measures of mouse sociability that can be used to reliably compare inbred mouse strains [Moy et al., 2008; Nadler et al., 2004], as well as measures of social reward [Panksepp & Lahvis, 2007] and empathy [Chen, Panksepp, & Lahvis, 2009; Langford et al., 2006]. With continued generation of mouse gene-targeted mice that are directly relevant to genetic linkages in ASD, there remains an urgent need to utilize a full suite of mouse behavioral tests that allows for a comprehensive assessment of the spectrum of social difficulties relevant to ASD. Using impairments in shared affect as an example, this paper explores potential avenues for collaboration between clinical and basic scientists, within an amply considered translational framework.

Role for antibodies in altering behavior and movement

At the past meeting of INSAR, the role of autoimmunity was discussed in an educational session. This article summarizes this discussion. In immune-mediated diseases, antibodies can contribute to the pathogenesis of the disease and are sometimes the force that drives the disease process. This concept has not been established for autism. In autoimmune diseases, such as systemic lupus erythematosus (SLE), antibodies are found to react with double-stranded DNA. These antibodies also cross-react with N-methyl-D aspartate receptors. Many SLE patients suffer neurologic syndromes of the central nervous system (CNS). Similarly individuals infected with Group A streptococcus (GAS) have antibodies against the GAS carbohydrate, which cross-react with tubulin and lysoganglioside GM1 on neurons. During the acute stage of infection, GAS-infected patients develop Syndenham chorea where the disease process is driven in part by these cross-reactive antibodies. As the antibody levels decrease, the clinical features of Syndenham chorea resolve. In these two immune-mediated diseases, antibodies clearly play a role in the pathogenesis of the diseases. There are reports that mothers of individuals with autism have antibodies that react with brain proteins and when these antibodies are passively transferred to pregnant non-human primates or rodents the offspring has behavioral and nervous system changes. It is still not clear whether the antibodies found in mothers of individuals with autism actually play a role in the disease. More studies need to be performed to identify the proteins recognized by the antibodies and to determine how these could affect development, behavior and changes within the CNS.

The EL mouse: a natural model of autism and epilepsy

PURPOSE

Autism is a multifactorial disorder that involves impairments in social interactions and communication, as well as restricted and repetitive behaviors. About 30% of individuals with autism develop epilepsy by adulthood. The EL mouse has long been studied as a natural model of multifactorial idiopathic generalized epilepsy with complex partial seizures. Because epilepsy is a comorbid trait of autism, we evaluated the EL mouse for behaviors associated with autism.

METHODS

We compared the behavior of EL mice to age-matched control DDY mice, a genetically related nonepileptic strain. The mice were compared in the open field and in the light-dark compartment tests to measure activity, exploratory behavior, and restricted and repetitive behaviors. The social transmission of food preference test was employed to evaluate social communication. Home-cage behavior was also evaluated in EL and DDY mice as a measure of repetitive activity.

KEY FINDINGS

We found that EL mice displayed several behavioral abnormalities characteristic of autism. Impairments in social interaction and restricted patterns of interest were evident in EL mice. Activity, exploratory behavior, and restricted behavior were significantly greater in EL mice than in DDY mice. EL mice exhibited impairment in the social transmission of food preference assay. In addition, a stereotypic myoclonic jumping behavior was observed in EL mice, but was not seen in DDY mice. It is of interest to note that seizure activity within 24 h of testing exacerbated the autistic behavioral abnormalities found in EL mice.

SIGNIFICANCE

These findings suggest that the EL mouse expresses behavioral abnormalities similar to those seen in persons with autism. We propose that the EL mouse can be utilized as a natural model of autism and epilepsy.

Mouse models of autism: testing hypotheses about molecular mechanisms

Autism is a neurodevelopmental disorder that is currently diagnosed by the presence of three behavioral criteria (1) qualitative impairments in reciprocal social interactions, (2) deficits in communication, including delayed language and noninteractive conversation, and (3) motor stereotypies, repetitive behaviors, insistence on sameness, and restricted interests. This chapter describes analogous behavioral assays that have been developed for mice, including tests for social approach, reciprocal social interactions, olfactory communication, ultrasonic vocalizations, repetitive and perseverative behaviors, and motor stereotypies. Examples of assay applications to genetic mouse models of autism are provided. Robust endophenotypes that are highly relevant to the core symptoms of autism are enabling the search for the genetic and environmental causes of autism, and the discovery of effective treatments.

General and social anxiety in the BTBR T+ tf/J mouse strain

BTBR T+ tf/J (BTBR) is an inbred mouse strain that shows behavioral traits with analogies to the three diagnostic symptoms of autism spectrum disorder (ASD); deficits in social interaction, impaired communication, and repetitive behaviors with restricted interests. Previous findings reveal that when compared to C57BL/6J (B6) and other inbred strains, BTBR exhibit normal to low anxiety-like traits in paradigms designed to assess anxiety-related behaviors. The current study assessed the generality of these anxiety findings. In experiment 1, B6 and BTBR mice were tested in the elevated plus maze (EPM), mouse defense test battery (MDTB) and elevated zero-maze. BTBR mice exhibited an anxiogenic profile in the EPM, with a reduction in open arm time and an increase in risk assessment behaviors, as compared to B6. In the MDTB, BTBR showed enhanced vocalization to the predator, and significantly less locomotor activity than B6 in the pre-threat situation, but significantly more locomotion than B6 following exposure to a predator threat, suggesting enhanced defensiveness to the predator. In the zero-maze, BTBR mice showed a significantly higher number of entries and time spent in the open segments of the apparatus, when compared to B6. In experiment 2, a three-chambered social preference test was used to evaluate effects of the systemic administration of an anxiolytic compound, diazepam, on B6 and BTBR social approach. Diazepam consistently increased time in the compartment containing the social stimulus, for both B6 and BTBR mice. However, in the vehicle treated groups, B6 mice spent significantly more time while BTBR mice spent significantly less time in the social stimulus compartment; after diazepam administration both B6 and BTBR strains significantly preferred the social stimulus chamber. These results suggest that while the anxiety responses of BTBR mice to novel situations (EPM and zero-maze) are inconsistent, BTBR mice appear to be more defensive to animate threat stimuli (predator or another mouse). Reduction of anxiety by diazepam normalized the social preference of BTBR for a mouse stimulus in the three-chambered test.

Expression of social behaviors of C57BL/6J versus BTBR inbred mouse strains in the visible burrow system

The core symptoms of autism spectrum disorder (ASD) include deficits in social interaction, impaired communication, and repetitive behaviors with restricted interests. Mouse models with behavioral phenotypes relevant to these core symptoms offer an experimental approach to advance the investigation of genes associated with ASD. Previous findings demonstrate that BTBR T+ tf/J (BTBR) is an inbred mouse strain that shows robust behavioral phenotypes with analogies to all three of the diagnostic symptoms of ASD. In the present study, we investigated the expression of social behaviors in a semi-natural visible burrow system (VBS), during colony formation and maintenance in groups comprising three adult male mice of the same strain, either C57BL/6J (B6) or BTBR. For comparative purposes, an extensively investigated three-chambered test was subsequently used to assess social approach in both strains. The effects of strain on these two situations were consistent and highly significant. In the VBS, BTBR mice showed reductions in all interactive behaviors: approach (front and back), flight, chase/follow, allo-grooming and huddling, along with increases in self-grooming and alone, as compared to B6. These results were corroborated in the three-chambered test: in contrast to B6, male BTBR mice failed to spend more time in the side of the test box containing the unfamiliar CD-1 mouse. Overall, the present data indicates that the strain profile for BTBR mice, including consistent social deficits and high levels of repetitive self-grooming, models multiple components of the ASD phenotype.