Social deficits in BTBR T+tf/J mice are unchanged by cross-fostering with C57BL/6J mothers

Morphological Correlates of Behavioral Variation in Autism Spectrum Disorder Groups in A Maternal Immune Activation Model

Introduction

Clinical heterogeneity is one of the biggest challenges for researchers studying underlying neurobiological mechanisms in Autism Spectrum Disorder (ASD). We aimed to use polyinosinic-polycytidylic acid [Poly (I:C)] induced maternal immune activation mice model to investigate the behavioral variation and the role of brain circuits related to symptom clusters in ASD. For this purpose, behavioral tests were applied to offsprings and regional thickness was measured from histological brain sections in medial prefrontal cortex, hippocampus and striatum.

Methods

Pups of intraperitoneal Poly (I:C)-applied mothers (n: 14) and phosphate buffered saline-applied mothers (n: 6) were used for this study. We used three chamber socialization test and social memory test to evaluate social behavior deficit in mice. Marble burying test was used for assessing stereotypic behavior and new object recognition test for learning and cognitive flexibility. Three subgroups (n: 4 for each) were determined according to behavioral test parameters. Regional thickness was measured in medial prefrontal cortex, hippocampus and striatum and compared between subgroups.

Results

We detected that the behavioral differences were distributed in a spectrum as expected in the clinic and also detected increased hippocampus thickness in the stereotypic behavior dominant Poly (I:C) subgroup.

Conclusion

Poly (I:C) induced maternal immune activation model creates the behavioral variation and cortical development differences that are seen in relation with symptom groups in ASD.

Revisiting sociability: Factors facilitating approach and avoidance during the three-chamber test

The three-chamber test, the so-called sociability test, has been widely used to assess social deficits based on impaired socially oriented investigations in rodent models. An innate motivation for investigating conspecifics is theoretically a prerequisite for gaining sociability scores in this paradigm. However, several relevant factors mediating investigatory motives, such as familiarity, attractiveness, and aggression, may affect sociability scores, which must be verified to obtain an adequate evaluation of the psychiatric phenotypes exhibited by disease-relevant rodent models. We assessed the social and non-social factors that mediate proximity preference by the three-chamber test with standard C57BL/6 J (B6) mice and low sociability BTBR+ltpr3tf/J (BTBR) mice. Strains of the opponents had no effect. Sexual cues (i.e., opposite sex) increased proximity preference in both strains of mice; in contrast, novel objects induced an approach in B6 mice but avoidance in BTBR mice. Single-housing before testing, stimulated social motive, affected BTBR mice but not B6 mice. BTBR females showed increased proximity preference across the sessions, and BTBR males showed increased preference toward a male B6 stimulus, but not a male BTBR stimulus. The male preference was restored when the male BTBR stimulus was anesthetized. In addition, self-grooming was facilitated by social and non-social novelty cues in both strains. B6 mice predominantly exhibited an investigatory approach toward social or non-social stimuli, whereas BTBR mice recognized social cues but tended to show avoidance. The three-chamber test could evaluate approach-avoidance strategies in target mouse strains that comprise innate social distance between mice.

Semi-natural housing rescues social behavior and reduces repetitive exploratory behavior of BTBR autistic-like mice

Environmental enrichment confers numerous benefits when implemented in murine models and can reduce behavioral symptomatology in models of disease, such as autism spectrum disorder (ASD). However, previous work did not examine the impact of early-life environmental enrichment on each core feature of ASD. We thus implemented a social and physical enrichment at birth, modeling a semi-natural housing, and examined its impact on communicative, social, sensory, and repetitive behaviors using BTBR (autistic-like) and C57BL/6 J (B6, wildtype) mice, comparing them to standard housing conditions. We found that environmental enrichment alleviated the social deficit of juvenile BTBR mice and reduced their repetitive exploratory behavior but did not affect their rough versus smooth texture preference nor the number of maternal isolation-induced pup calls. Environmental enrichment only affected the call characteristics of B6 mice. One interpretation of these data is that early-life environmental enrichment has significant therapeutic potential to treat selective core features of ASD. Another interpretation is that reducing environmental complexity causes selective behavioral deficits in ASD-prone mice suggesting that current standard housing may be suboptimal. Overall, our data illustrate the extent to which the environment influences behavior and highlights the importance of considering housing conditions when designing experiments and interpreting behavioral results.

Maturation of nucleus accumbens synaptic transmission signals a critical period for the rescue of social deficits in a mouse model of autism spectrum disorder

Social behavior emerges early in development, a time marked by the onset of neurodevelopmental disorders featuring social deficits, including autism spectrum disorder (ASD). Although social deficits are at the core of the clinical diagnosis of ASD, very little is known about their neural correlates at the time of clinical onset. The nucleus accumbens (NAc), a brain region extensively implicated in social behavior, undergoes synaptic, cellular and molecular alterations in early life, and is particularly affected in ASD mouse models. To explore a link between the maturation of the NAc and neurodevelopmental deficits in social behavior, we compared spontaneous synaptic transmission in NAc shell medium spiny neurons (MSNs) between the highly social C57BL/6J and the idiopathic ASD mouse model BTBR T⁺Itpr3^tf/J at postnatal day (P) 4, P6, P8, P12, P15, P21 and P30. BTBR NAc MSNs display increased spontaneous excitatory transmission during the first postnatal week, and increased inhibition across the first, second and fourth postnatal weeks, suggesting accelerated maturation of excitatory and inhibitory synaptic inputs compared to C57BL/6J mice. BTBR mice also show increased optically evoked medial prefrontal cortex-NAc paired pulse ratios at P15 and P30. These early changes in synaptic transmission are consistent with a potential critical period, which could maximize the efficacy of rescue interventions. To test this, we treated BTBR mice in either early life (P4-P8) or adulthood (P60-P64) with the mTORC1 antagonist rapamycin, a well-established intervention for ASD-like behavior. Rapamycin treatment rescued social interaction deficits in BTBR mice when injected in infancy, but did not affect social interaction in adulthood.

A potent and selective CXCR2 antagonist improves neuroimmune dysregulation through the inhibition of NF-κB and notch inflammatory signaling in the BTBR mouse model of autism

Autism comprises a broad range of neurodevelopmental disorders characterized by social communication deficits and repetitive and stereotyped behaviors. Chemokine receptor CXCR2 is expressed on neurons and is upregulated in neurological disorders. BTBR T+ Itpr3tf/J (BTBR) mice, a model for autism that shows the core features of ASD. Here, we studied the anti-inflammatory effect of a potent and selective CXCR2 antagonist SB332235 in the BTBR mice. The CXCR2 antagonist represents a promising therapeutic agent for several neuroinflammatory disorders. In this study, we investigated the effects of SB332235 administration on NF-κB-, Notch-1-, Notch-3-, GM-CSF-, MCP-1-, IL-6-, and IL-2- and TGF-β1-expressing CD40+ cells in BTBR and C57BL/6 (C57) mice in the spleen cells by flow cytometry. We further assessed the effect of SB332235 treatment on NF-κB, Notch-1, GM-CSF, MCP-1, IL-6, and IL-2 mRNA expression levels in the brain tissue by RT-PCR. We also explored the effect of SB332235 administration on NF-κB, GM-CSF, IL-6, and TGF-β1 protein expression levels in the brain tissue by western blotting. The SB332235-treated BTBR mice significantly decreases in CD40 + NF-κB+, CD40 + Notch-1+, CD40 + Notch-3+, CD40 + GM-CSF+, CD40 + MCP-1+, CD40 + IL-6+, and CD40 + IL-2+, and increases in CD40 + TGF-β1+ in the spleen cells. Our results further demonstrated that BTBR mice treated with SB332235 effectively decreased NF-κB, Notch-1, GM-CSF, MCP-1, IL-6, and IL-2, increasing TGF-β1 mRNA and protein expression levels in the brain tissue. In conclusion, these results indicate that SB332235 elicits an anti-inflammatory response by downregulating the inflammatory mediators and NF-κB/Notch inflammatory signaling in BTBR mice. This could represent a promising novel therapeutic target for autism treatment.

A comparison of stress reactivity between BTBR and C57BL/6J mice: an impact of early-life stress

Early-life stress (ELS) is associated with hypothalamic-pituitary-adrenal (HPA) axis dysregulation and can increase the risk of psychiatric disorders later in life. The aim of this study was to investigate the influence of ELS on baseline HPA axis functioning and on the response to additional stress in adolescent male mice of strains C57BL/6J and BTBR. As a model of ELS, prolonged separation of pups from their mothers (for 3 h once a day: maternal separation [MS]) was implemented. To evaluate HPA axis activity, we assessed serum corticosterone levels and mRNA expression of corticotropin-releasing hormone (Crh) in the hypothalamus, of steroidogenesis genes in adrenal glands, and of an immediate early gene (c-Fos) in both tissues at baseline and immediately after 1 h of restraint stress. HPA axis activity at baseline did not depend on the history of ELS in mice of both strains. After the exposure to the acute restraint stress, C57BL/6J-MS mice showed less pronounced upregulation of Crh and of corticosterone concentration as compared to the control, indicating a decrease in stress reactivity. By contrast, BTBR-MS mice showed stronger upregulation of c-Fos in the hypothalamus and adrenal glands as compared to controls, thus pointing to greater activation of these organs in response to the acute restraint stress. In addition, we noted that BTBR mice are more stress reactive (than C57BL/6J mice) because they exhibited greater upregulation of corticosterone, c-Fos, and Cyp11a1 in response to the acute restraint stress. Taken together, these results indicate strain-specific and situation-dependent effects of ELS on HPA axis functioning and on c-Fos expression.

Neurexins in serotonergic neurons regulate neuronal survival, serotonin transmission, and complex mouse behaviors

Extensive serotonin (5-hydroxytryptamine, 5-HT) innervation throughout the brain corroborates 5-HT's modulatory role in numerous cognitive activities. Volume transmission is the major mode for 5-HT transmission but mechanisms underlying 5-HT signaling are still largely unknown. Abnormal brain 5-HT levels and function have been implicated in autism spectrum disorder (ASD). Neurexin (Nrxn) genes encode presynaptic cell adhesion molecules important for the regulation of synaptic neurotransmitter release, notably glutamatergic and GABAergic transmission. Mutations in Nrxn genes are associated with neurodevelopmental disorders including ASD. However, the role of Nrxn genes in the 5-HT system is poorly understood. Here, we generated a mouse model with all three Nrxn genes disrupted specifically in 5-HT neurons to study how Nrxns affect 5-HT transmission. Loss of Nrxns in 5-HT neurons reduced the number of serotonin neurons in the early postnatal stage, impaired 5-HT release, and decreased 5-HT release sites and serotonin transporter expression. Furthermore, 5-HT neuron-specific Nrxn knockout reduced sociability and increased depressive-like behavior. Our results highlight functional roles for Nrxns in 5-HT neurotransmission, 5-HT neuron survival, and the execution of complex behaviors.

The live biotherapeutic Blautia stercoris MRx0006 attenuates social deficits, repetitive behaviour, and anxiety-like behaviour in a mouse model relevant to autism

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterised by deficits in social behaviour, increased repetitive behaviour, anxiety and gastrointestinal symptoms. The aetiology of ASD is complex and involves an interplay of genetic and environmental factors. Emerging pre-clinical and clinical studies have documented a potential role for the gut microbiome in ASD, and consequently, the microbiota represents a potential target in the development of novel therapeutics for this neurodevelopmental disorder. In this study, we investigate the efficacy of the live biotherapeutic strain, Blautia stercoris MRx0006, in attenuating some of the behavioural deficits in the autism-relevant, genetic mouse model, BTBR T+ Itpr3tf/J (BTBR). We demonstrate that daily oral administration with MRx0006 attenuates social deficits while also decreasing repetitive and anxiety-like behaviour. MRx0006 administration increases the gene expression of oxytocin and its receptor in hypothalamic cells in vitro and increases the expression of hypothalamic arginine vasopressin and oxytocin mRNA in BTBR mice. Additionally at the microbiome level, we observed that MRx0006 administration decreases the abundance of Alistipes putredinis, and modulates the faecal microbial metabolite profile. This alteration in the metabolite profile possibly underlies the observed increase in expression of oxytocin, arginine vasopressin and its receptors, and the consequent improvements in behavioural outcomes. Taken together, these findings suggest that the live biotherapeutic MRx0006 may represent a viable and efficacious treatment option for the management of physiological and behavioural deficits associated with ASD.

Social deficits in BTBR T+ Itpr3tf/J mice vary with ecological validity of the test

Translational value of mouse models of neuropsychiatric disorders depends heavily on the accuracy with which they replicate symptoms observed in the human population. In mouse models of autism spectrum disorder (ASD) these include, among others, social affiliation, and communication deficits as well as impairments in understanding and perception of others. Most studies addressing these issues in the BTBR T+ Itpr3tf/J mouse, an idiopathic model of ASD, were based on short dyadic interactions of often non-familiar partners placed in a novel environment. In such stressful and variable conditions, the reproducibility of the phenotype was low. Here, we compared physical conditions and the degree of habituation of mice at the time of testing in the three chambered social affiliation task, as well as parameters used to measure social deficits and found that both the level of stress and human bias profoundly affect the results of the test. To minimize these effects, we tested social preference and network dynamics in mice group-housed in the Eco-HAB system. This automated recording allowed for long-lasting monitoring of differences in social repertoire (including interest in social stimuli) in BTBR T+ Itpr3tf/J and normosocial c57BL/6J mice. With these observations we further validate the BTBR T+ Itpr3tf/J mouse as a model for ASD, but at the same time emphasize the need for more ecological testing of social behavior within all constructs of the Systems for Social Processes domain (as defined by the Research Domain Criteria framework).

Implication of the social function of excessive self-grooming behavior in BTBR T+ltpr3tf/J mice as an idiopathic model of autism

Autism spectrum disorder (ASD) is defined by two core behavioral characteristics, namely, restricted repetitive behaviors and impaired social-communicative functioning. BTBR T⁺ltpr3^tf/J (BTBR) mice provide a valuable animal model for ASD to elucidate the underlying mechanisms of these two behavioral characteristics of ASD. This study examined the social function of excessive grooming behavior in BTBR mice as a phenotype of restricted repetitive behaviors. Compared to the control C57BL/6 J (B6) strain, BTBR mice showed increased self-grooming when placed alone in a test apparatus, and this behavior was even more evident when confronted with a stimulus mouse (either B6 or BTBR) in a three-chamber test apparatus. While B6 mice tended to groom their face/snout region on the empty side of the chamber, BTBR mice showed excessive grooming with frequent transitions among grooming body regions on the side of the chamber containing a social stimulus. Acute systemic injection of buspirone,a serotonin 1A receptor agonist, as an anxiolytic, facilitated approach behavior toward social stimuli in the three-chamber setting in both B6 and BTBR mice. However, this treatment did not affect grooming behavior in B6 mice and significantly enhanced self-grooming in BTBR mice. These behaviors in BTBR mice suggest a potential signaling function of grooming in response to social stimuli, in which bodywide grooming of BTBR mice expressed in the proximity of social opponents may stimulate the release of olfactory (possibly dismissive) signals. Consequently, the putative neural mechanisms underlying excessive grooming may differ from those regulating social approaches that are associated with anxiolytic mechanisms.

Cholinergic transmission from the basal forebrain modulates social memory in male mice

Disruptions in social behaviour are prevalent in many neuropsychiatric disorders such as schizophrenia, bipolar disorder and autism spectrum disorders. However, the underlying neurochemical regulation of social behaviour is still not well understood. The central cholinergic system has been proposed to contribute to the regulation of social behaviour. For instance, decreased global levels of acetylcholine release in the brain leads to decreased social interaction and an impairment of social memory in mice. Nonetheless, it has been difficult to ascertain the specific brain areas where cholinergic signalling influences social preference and social memory. In this study, we investigated the impact of different forebrain cholinergic regions on social behaviour by examining mouse lines that differ in their regional expression level of the vesicular acetylcholine transporter-the protein that regulates acetylcholine secretion. We found that when cholinergic signalling is highly disrupted in the striatum, hippocampus, cortex and amygdala mice have intact social preference but are impaired in social memory, as they cannot remember a familiar conspecific nor recognize a novel one. A similar pattern emerges when acetylcholine release is disrupted mainly in the striatum, cortex, and amygdala; however, the ability to recognize novel conspecifics is retained. In contrast, cholinergic signalling of the striatum and amygdala does not appear to significantly contribute to the modulation of social memory and social preference. Furthermore, we demonstrated that increasing global cholinergic tone does not increase social behaviours. Together, these data suggest that cholinergic transmission from the hippocampus and cortex are important for regulating social memory.

PlexinA1 deficiency in BALB/cAJ mice leads to excessive self-grooming and reduced prepulse inhibition

PlexinA1 (PlxnA1) is a transmembrane receptor for semaphorins, a large family of proteins that act as axonal guidance cues during nervous system development. However, there are limited studies on PlxnA1 function in neurobehavior. The present study examined if PlxnA1 deficiency leads to behavioral abnormalities in BALB/cAJ mice. PlxnA1 knockout (KO) mice were generated by homologous recombination and compared to wild type (WT) littermates on a comprehensive battery of behavioral tests, including open field assessment of spontaneous ambulation, state anxiety, and grooming, home cage grooming, the wire hang test of muscle strength, motor coordination on the rotarod task, working memory on the Y maze alternation task, cued and contextual fear conditioning, anxiety on the elevated plus maze, sociability to intruders, and sensory processing as measured by prepulse inhibition (PPI). Measures of motor performance, working memory, fear memory, and sociability did not differ significantly between genotypes, while PlxnA1 KO mice displayed excessive self-grooming, impaired PPI, and slightly lower anxiety. These results suggest a crucial role for PlxnA1 in the development and function of brain regions controlling self-grooming and sensory gating. PlxnA1 KO mice may be a valuable model to investigate the repetitive behaviors and information processing deficits characteristic of many neurodevelopmental and psychiatric disorders.

Chromatin Dynamics and Genetic Variation Combine to Regulate Innate Immune Memory

Recent work by Ciernia et al. (2020) identified how genetic and epigenetic mechanisms interact to regulate innate immune memory in bone marrow derived macrophages. The authors examined the BTBR strain, a naturally occurring mouse model of Autism Spectrum Disorder (ASD) that captures the complex genetics, behavioral and immune dysregulation found in the human disorder. Immune cell cultures from the BTBR strain compared to the standard C57 showed hyper-responsive immune gene expression that was linked to altered chromatin accessibility at sites with genetic differences between the strains. Together, findings from this work demonstrated that multiple levels of gene regulation likely dictate the formation of innate immune memory and are likely disrupted in immune cells in ASD. Future work will be needed to extend these findings to immune gene regulation in the brain and how changes in immune function are related to abnormal behaviors in brain disorders.

Early genistein exposure of California mice and effects on the gut microbiota-brain axis

Human offspring encounter high amounts of phytoestrogens, such as genistein (GEN), through maternal diet and soy-based formulas. Such chemicals can exert estrogenic activity and thereby disrupt neurobehavioral programming. Besides inducing direct host effects, GEN might cause gut dysbiosis and alter gut metabolites. To determine whether exposure to GEN affects these parameters, California mice (Peromyscus californicus) dams were placed 2 weeks prior to breeding and throughout gestation and lactation on a diet supplemented with GEN (250 mg/kg feed weight) or AIN93G phytoestrogen-free control diet (AIN). At weaning, offspring socio-communicative behaviors, gut microbiota and metabolite profiles were assayed. Exposure of offspring to GEN-induced sex-dependent changes in gut microbiota and metabolites. GEN exposed females were less likely to investigate a novel female mouse when tested in a three-chamber social test. When isolated, GEN males and females exhibited increased latency to elicit their first call, suggestive of reduced motivation to communicate with other individuals. Correlation analyses revealed interactions between GEN-induced microbiome, metabolome and socio-communicative behaviors. Comparison of GEN males with AIN males revealed the fraction of calls above 20 kHz was associated with daidzein, α-tocopherol, Flexispira spp. and Odoribacter spp. Results suggest early GEN exposure disrupts normal socio-communicative behaviors in California mice, which are otherwise evident in these social rodents. Such effects may be due to GEN disruptions on neural programming but might also be attributed to GEN-induced microbiota shifts and resultant changes in gut metabolites. Findings indicate cause for concern that perinatal exposure to GEN may detrimentally affect the offspring microbiome-gut-brain axis.

Differences in the expression of restricted repetitive behaviors in female and male BTBR T + tf/J mice

Autism spectrum disorder (ASD) is characterized by the expression of restricted repetitive behaviors (RRBs) and impairments in social recognition and communication. Epidemiological studies demonstrate males are three times more likely than females to be affected. Although this is the case, more recent studies suggest females may be underrepresented in these numbers due to standard clinical measures of RRBs and social behaviors. In addition, many studies examining mouse models of ASD exclude females due to the sex disparity in diagnoses. The present study examined how female and male BTBR T + Itpr3tf /J (BTBR) compare to control C57BL/6J mice on tests of RRBs (probabilistic reversal learning, repetitive grooming, spontaneous alternation, and marble burying) and social behaviors (three chambered social approach task). Utilizing a spatial reversal learning test with 80/20 probabilistic feedback, in which ASD individuals have exhibited deficits, we find that female BTBR mice do not show the same impairment found in male BTBR mice. Interestingly, control female C57BL/6J mice required more trials to reach criterion. Female BTBR mice expressed comparable rates of repetitive grooming, marble burying and spontaneous alternation compared to female C57BL/6J mice. Male BTBR mice expressed higher rates of grooming behavior and locomotor activity compared to male C57BL/6J mice, as found in previous studies. Similarly, male BTBR mice showed a reduction in both measures of social approach compared to controls. Both male and female BTBR mice showed a reduction in sniff time for the stranger mouse compared to controls. Together these findings demonstrate how female BTBR mice do not display the RRB profile expressed by male BTBR mice. Testing of repetitive behaviors in ASD needs to better reflect the sex differences in how RRBs manifest in females compared to their extensively researched male counterparts.

Enriched Environments as a Potential Treatment for Developmental Disorders: A Critical Assessment

The beneficial effects of enriched environments have been established through a long history of research. Enrichment of the living conditions of captive animals in the form of larger cages, sensory stimulating objects, and opportunities for social interaction and physical exercise, has been shown to reduce emotional reactivity, ameliorate abnormal behaviors, and enhance cognitive functioning. Recently, environmental enrichment research has been extended to humans, in part due to growing interest in its potential therapeutic benefits for children with neurodevelopmental disorders (NDDs). This paper reviews the history of enriched environment research and the use of enriched environments as a developmental intervention in studies of both NDD animal models and children. We argue that while environmental enrichment may sometimes benefit children with NDDs, several methodological factors need to be more closely considered before the efficacy of this approach can be adequately evaluated, including: (i) operationally defining and standardizing enriched environment treatments across studies; (ii) use of control groups and better control over potentially confounding variables; and (iii) a comprehensive theoretical framework capable of predicting when and how environmental enrichment will alter the trajectory of NDDs.

Hypothesis-driven investigations of diverse pharmacological targets in two mouse models of autism

Autism spectrum disorder is a neurodevelopmental syndrome diagnosed primarily by persistent deficits in social interactions and communication, unusual sensory reactivity, motor stereotypies, repetitive behaviors, and restricted interests. No FDA‐approved medical treatments exist for the diagnostic symptoms of autism. Here we interrogate multiple pharmacological targets in two distinct mouse models that incorporate well‐replicated autism‐relevant behavioral phenotypes. Compounds that modify inhibitory or excitatory neurotransmission were selected to address hypotheses based on previously published biological abnormalities in each model. Shank3B is a genetic model of a mutation found in autism and Phelan‐McDermid syndrome, in which deficits in excitatory neurotransmission and synaptic plasticity have been reported. BTBR is an inbred strain model of forms of idiopathic autism in which reduced inhibitory neurotransmission and excessive mTOR signaling have been reported. The GABA‐A receptor agonist gaboxadol significantly reduced repetitive self‐grooming in three independent cohorts of BTBR. The TrkB receptor agonist 7,8‐DHF improved spatial learning in Shank3B mice, and reversed aspects of social deficits in BTBR. CX546, a positive allosteric modulator of the glutamatergic AMPA receptor, and d‐cycloserine, a partial agonist of the glycine site on the glutamatergic NMDA receptor, did not rescue aberrant behaviors in Shank3B mice. The mTOR inhibitor rapamycin did not ameliorate social deficits or repetitive behavior in BTBR mice. Comparison of positive and negative pharmacological outcomes, on multiple phenotypes, evaluated for replicability across independent cohorts, enhances the translational value of mouse models of autism for therapeutic discovery. GABA agonists present opportunities for personalized interventions to treat components of autism spectrum disorder. Autism Res 2019, 12: 401–421 © 2019 The Authors. Autism Research published by International Society for Autism Research published by Wiley Periodicals, Inc.

Lay Summary

Many of the risk genes for autism impair synapses, the connections between nerve cells in the brain. A drug that reverses the synaptic effects of a mutation could offer a precision therapy. Combining pharmacological and behavioral therapies could reduce symptoms and improve the quality of life for people with autism. Here we report reductions in repetitive behavior by a GABA‐A receptor agonist, gaboxadol, and improvements in social and cognitive behaviors by a TrkB receptor agonist, in mouse models of autism.

Effects of cross-rearing with social peers on myelination in the medial prefrontal cortex of a mouse model with autism spectrum disorder

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by impaired social interaction, poor communication skills, and repetitive/restrictive behaviors. Recent studies have indicated that early rehabilitative intervention can alleviate the symptoms of individuals with ASD. However, it remains unknown whether rehabilitative intervention can restore brain structures such as myelin, which generally shows abnormalities in individuals with ASD. Therefore, in the present study, we used a mouse model of ASD (BTBR mice) that demonstrated asocial behaviors and hypomyelination in the medial prefrontal cortex (mPFC) to investigate whether interaction with social peers (C57BL/6J mice) has an effect on myelination. We found that housing with C57BL/6J mice after weaning through adulthood increased the myelin thickness in mPFC, but not in the motor cortex, of BTBR mice. There was no effect of cross-rearing with C57BL/6J mice on axon diameter in mPFC of BTBR mice. This finding suggests that early rehabilitative intervention may alleviate myelin abnormalities in mPFC as well as clinical symptoms in individuals with ASD.

Deficiency of a brain-specific chemokine-like molecule, SAM3, induces cardinal phenotypes of autism spectrum disorders in mice

Chemokines are small secreted signaling proteins produced by a broad range of cells, including immune cells. Several studies have recently suggested potential roles of chemokines and their receptors in the pathophysiology of autism spectrum disorders (ASDs). SAM3 is a novel brain-specific chemokine-like molecule with an unknown physiological function. We explored the relevance of chemokines in the development of ASD in mice, with a focus on SAM3. We generated Sam3 gene knockout (KO) mice and characterized their behavioral phenotypes, with a focus on those relevant to ASD. Sam3-deficient mice displayed all three core phenotypes of ASD: impaired responses to social novelty, defects in social communication, and increased repetitive behavior. In addition, they showed increased anxiety. Interestingly, gender differences were identified for several behaviors: only male Sam3 KO mice exhibited increased anxiety and increased repetitive behaviors. Sam3 KO mice did not exhibit changes in other behaviors, including locomotor activities, fear learning and memory, and object recognition memory. These findings indicate that a deficiency of SAM3, a novel brain-specific chemokine-like molecule, may lead to the pathogenesis of ASDs and suggest the possibility that SAM3, a soluble factor, could be a novel therapeutic target for ASD treatment.

Animal models for autism in 2017 and the consequential implications to drug discovery

INTRODUCTION

Autism spectrum disorder (ASD) is characterized by deficits in social communication and restricted interests/repetitive behaviors, for which there are currently no approved drug treatments. The core symptoms of ASD vary widely in severity and are often accompanied by other neuropsychiatric disorders. Drug discovery has been challenging because of the lack of understanding of the underlying pathophysiology of ASD as well as the heterogeneity of symptoms and symptom severity. Areas covered: In this review, the author discusses animal models of ASD used as targets for drug discovery, focusing primarily on non-syndromic models, primarily rodents. They highlight the wide range of drug targets examined in animal models. While very little of this work has resulted in drug therapy for the behavioral symptoms of ASD yet, it has increased our knowledge of the biology of ASD that is critical for driving drug discovery and has already provided many new drug targets for investigation. Expert opinion: The information gathered from the animal models of ASD is increasing our understanding of the underlying pathophysiology for ASD and is leading to better therapeutic targets. However, the issue of small sample size, heterogeneity within clinical samples, and a lack of replicable outcome measures must be addressed to move forward.

Altered learning, memory, and social behavior in type 1 taste receptor subunit 3 knock-out mice are associated with neuronal dysfunction

The type 1 taste receptor member 3 (T1R3) is a G protein-coupled receptor involved in sweet-taste perception. Besides the tongue, the T1R3 receptor is highly expressed in brain areas implicated in cognition, including the hippocampus and cortex. As cognitive decline is often preceded by significant metabolic or endocrinological dysfunctions regulated by the sweet-taste perception system, we hypothesized that a disruption of the sweet-taste perception in the brain could have a key role in the development of cognitive dysfunction. To assess the importance of the sweet-taste receptors in the brain, we conducted transcriptomic and proteomic analyses of cortical and hippocampal tissues isolated from T1R3 knock-out (T1R3KO) mice. The effect of an impaired sweet-taste perception system on cognition functions were examined by analyzing synaptic integrity and performing animal behavior on T1R3KO mice. Although T1R3KO mice did not present a metabolically disrupted phenotype, bioinformatic interpretation of the high-dimensionality data indicated a strong neurodegenerative signature associated with significant alterations in pathways involved in neuritogenesis, dendritic growth, and synaptogenesis. Furthermore, a significantly reduced dendritic spine density was observed in T1R3KO mice together with alterations in learning and memory functions as well as sociability deficits. Taken together our data suggest that the sweet-taste receptor system plays an important neurotrophic role in the extralingual central nervous tissue that underpins synaptic function, memory acquisition, and social behavior.

Early motor phenotype detection in a female mouse model of Rett syndrome is improved by cross-fostering

Rett syndrome (RTT) is an X-linked neurodevelopmental disorder caused by mutations in the gene encoding methyl CpG binding protein 2 (MeCP2) that occur sporadically in 1:10,000 female births. RTT is characterized by a period of largely normal development followed by regression in language and motor skills at 6-18 months of age. Mecp2 mutant mice recapitulate many of the clinical features of RTT, but the majority of behavioral assessments have been conducted in male Mecp2 hemizygous null mice as offspring of heterozygous dams. Given that RTT patients are predominantly female, we conducted a systematic analysis of developmental milestones, sensory abilities, and motor deficits, following the longitudinal decline of function from early postnatal to adult ages in female Mecp2 heterozygotes of the conventional Bird line (Mecp2tm1.1bird-/+), as compared to their female wildtype littermate controls. Further, we assessed the impact of postnatal maternal environment on developmental milestones and behavioral phenotypes. Cross-fostering to CD1 dams accelerated several developmental milestones independent of genotype, and induced earlier onset of weight gain in adult female Mecp2tm1.1bird-/+ mice. Cross-fostering improved the sensitivity of a number of motor behaviors that resulted in observable deficits in Mecp2tm1.1bird-/+ mice at much earlier (6-7 weeks) ages than were previously reported (6-9 months). Our findings indicate that female Mecp2tm1.1bird-/+ mice recapitulate many of the motor aspects of RTT syndrome earlier than previously appreciated. In addition, rearing conditions may impact the phenotypic severity and improve the ability to detect genotype differences in female Mecp2 mutant mice.

Assessing mouse behaviour throughout the light/dark cycle using automated in-cage analysis tools

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Automated assessment of mouse home-cage behaviour is robust and reliable.

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Analysis over multiple light/dark cycles improves ability to classify behaviours.

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Combined RFID and video analysis enables home-cage analysis in group housed animals.

An important factor in reducing variability in mouse test outcomes has been to develop assays that can be used for continuous automated home cage assessment. Our experience has shown that this has been most evidenced in long-term assessment of wheel-running activity in mice. Historically, wheel-running in mice and other rodents have been used as a robust assay to determine, with precision, the inherent period of circadian rhythms in mice. Furthermore, this assay has been instrumental in dissecting the molecular genetic basis of mammalian circadian rhythms. In teasing out the elements of this test that have determined its robustness – automated assessment of an unforced behaviour in the home cage over long time intervals – we and others have been investigating whether similar test apparatus could be used to accurately discriminate differences in distinct behavioural parameters in mice. Firstly, using these systems, we explored behaviours in a number of mouse inbred strains to determine whether we could extract biologically meaningful differences. Secondly, we tested a number of relevant mutant lines to determine how discriminative these parameters were. Our findings show that, when compared to conventional out-of-cage phenotyping, a far deeper understanding of mouse mutant phenotype can be established by monitoring behaviour in the home cage over one or more light:dark cycles.

Cross-fostering: Elucidating the effects of gene×environment interactions on phenotypic development

Cross-fostering of litters from soon after birth until weaning is a valuable tool to study the ways in which gene×environment interactions program the development of neural, physiological and behavioral characteristics of mammalian species. In laboratory mice and rats, the primary focus of this review, cross-fostering of litters between mothers of different strains or treatment groups (intraspecific) or between mothers of different species (interspecific) has been conducted over the past 9 decades. Areas of particular interest have included maternal effects on emotionality, social preferences, responses to stressful stimulation, nutrition and growth, blood pressure regulation, and epigenetic effects on brain development and behavior. Results from these areas of research highlight the critical role of the postnatal maternal environment in programming the development of offspring phenotypic characteristics. In addition, experimental paradigms that have included cross-fostering have permitted investigators to tease apart prenatal versus postnatal effects of various treatments on offspring development and behavior.

Genetic modifications associated with ketogenic diet treatment in the BTBRT+Tf/J mouse model of autism spectrum disorder

BACKGROUND

Autism spectrum disorder (ASD) is a prevalent and heterogeneous neurodevelopmental disorder characterized by hallmark behavioral features. The spectrum of disorders that fall within the ASD umbrella encompass a distinct but overlapping symptom complex that likely results from an array of molecular and genetic aberrations rather than a single genetic mutation. The ketogenic diet (KD) is a high-fat low-carbohydrate anti-seizure and neuroprotective diet that has demonstrated efficacy in the treatment of ASD-like behaviors in animal and human studies.

METHODS

We investigated changes in mRNA and gene expression in the BTBR mouse model of ASD that may contribute to the behavioral phenotype. In addition, we sought to examine changes in gene expression following KD treatment in BTBR mice.

RESULTS

Despite significant behavioral abnormalities, expression changes in BTBR mice did not differ substantially from controls; only 33 genes were differentially expressed in the temporal cortex, and 48 in the hippocampus. Examination of these differentially expressed genes suggested deficits in the stress response and in neuronal signaling/communication. After treatment with the KD, both brain regions demonstrated improvements in ASD deficits associated with myelin formation and white matter development.

CONCLUSIONS

Although our study supports many of the previously known impairments associated with ASD, such as excessive myelin formation and impaired GABAergic transmission, the RNAseq data and pathway analysis utilized here identified new therapeutic targets for analysis, such as Vitamin D pathways and cAMP signaling. Autism Res 2017, 10: 456-471. © 2016 International Society for Autism Research, Wiley Periodicals, Inc.

Impaired Pavlovian predictive learning between temporally phasic but not static events in autism-model strain mice

Autism-spectrum disorder (ASD) is a multi-aspect developmental disorder characterised by various social and non-social behavioural abnormalities. Using BTBR T+ tf mouse strain (BTBR), a promising animal model displaying a number of behavioural and neural characteristics associated with ASD, we tested the hypothesis that at the core of various symptoms of ASD lies a fundamental deficit in predictive learning between events. In five experiments, we conducted a variety of Pavlovian conditioning tasks, some requiring the establishment of associations between temporally phasic events and others involving static events. BTBR mice were impaired in the acquisition of conditioned magazine approach responses with an appetitive unconditioned stimulus (US) (Experiment 1) and conditioned freezing with an electric shock US (Experiment 2). Both of these tasks had temporally phasic conditioned stimuli (CSs). Conversely, these mice showed normal acquisition of conditioned place preference (CPP), whether the US was a systemic injection of methamphetamine (Experiment 3A) or the presence of food (Experiment 3B). Experiment 4 showed normal acquisition of conditioned taste aversion (CTA) to a flavour-taste compound CS, although BTBR mice still exhibited an abnormal stimulus selection when learning for each element of the compound CS was assessed separately. Experiment 5 revealed a weaker latent inhibition of CTA in BTBR mice. The BTBR mouse's impaired predictive learning between phasic events and intact associations between static events are discussed in terms of dysfunctional contingency-based, but not contiguity-based learning, which may accompany abnormal selective attention to relevant cues. We propose that such dysfunctional contingency learning mechanisms may underlie the development of various social and non-social symptoms of ASD.

Serotonin neuron abnormalities in the BTBR mouse model of autism

The inbred mouse strain BTBR T⁺ Itpr3^tf /J (BTBR) is studied as a model of idiopathic autism because they are less social and more resistant to change than other strains. Forebrain serotonin receptors and the response to serotonin drugs are altered in BTBR mice, yet it remains unknown if serotonin neurons themselves are abnormal. In this study, we found that serotonin tissue content and the density of serotonin axons is reduced in the hippocampus of BTBR mice in comparison to C57BL/6J (C57) mice. This was accompanied by possible compensatory changes in serotonin neurons that were most pronounced in regions known to provide innervation to the hippocampus: the caudal dorsal raphe (B6) and the median raphe. These changes included increased numbers of serotonin neurons and hyperactivation of Fos expression. Metrics of serotonin neurons in the rostral 2/3 of the dorsal raphe and serotonin content of the prefrontal cortex were less impacted. Thus, serotonin neurons exhibit region-dependent abnormalities in the BTBR mouse that may contribute to their altered behavioral profile. Autism Res 2017, 10: 66-77. © 2016 International Society for Autism Research, Wiley Periodicals, Inc.

Genetic and non-genetic animal models for autism spectrum disorders (ASD)

Autism spectrum disorder (ASD) is associated, in addition to complex genetic factors, with a variety of prenatal, perinatal and postnatal etiologies. We discuss the known animal models, mostly in mice and rats, of ASD that helps us to understand the etiology, pathogenesis and treatment of human ASD. We describe only models where behavioral testing has shown autistic like behaviors. Some genetic models mimic known human syndromes like fragile X where ASD is part of the clinical picture, and others are without defined human syndromes. Among the environmentally induced ASD models in rodents, the most common model is the one induced by valproic acid (VPA) either prenatally or early postnatally. VPA induces autism-like behaviors following single exposure during different phases of brain development, implying that the mechanism of action is via a general biological mechanism like epigenetic changes. Maternal infection and inflammation are also associated with ASD in man and animal models.

Therapeutic Effect of a Synthetic RORα/γ Agonist in an Animal Model of Autism

Autism is a developmental disorder of the nervous system associated with impaired social communication and interactions as well excessive repetitive behaviors. There are no drug therapies that directly target the pathology of this disease. The retinoic acid receptor-related orphan receptor α (RORα) is a nuclear receptor that has been demonstrated to have reduced expression in many individuals with autism spectrum disorder (ASD). Several genes that have been shown to be downregulated in individuals with ASD have also been identified as putative RORα target genes. Utilizing a synthetic RORα/γ agonist, SR1078, that we identified previously, we demonstrate that treatment of BTBR mice (a model of autism) with SR1078 results in reduced repetitive behavior. Furthermore, these mice display increased expression of ASD-associated RORα target genes in both the brains of the BTBR mice and in a human neuroblastoma cell line treated with SR1078. These data suggest that pharmacological activation of RORα may be a method for treatment of autism.

Evaluation of the neuroactive steroid ganaxolone on social and repetitive behaviors in the BTBR mouse model of autism

RATIONALE

Abnormalities in excitatory/inhibitory neurotransmission are hypothesized to contribute to autism spectrum disorder (ASD) etiology. BTBR T (+) Itpr3 (tf) /J (BTBR), an inbred mouse strain, displays social deficits and repetitive self-grooming, offering face validity to ASD diagnostic symptoms. Reduced GABAergic neurotransmission in BTBR suggests that GABAA receptor positive allosteric modulators (PAMs) could improve ASD-relevant BTBR phenotypes. The neuroactive steroid ganaxolone acts as a PAM, displaying anticonvulsant properties in rodent epilepsy models and an anxiolytic-like profile in the elevated plus-maze.

OBJECTIVES

We evaluated ganaxolone in BTBR and C57BL/6J mice in standardized assays for sociability and repetitive behaviors. Open field and anxiety-related behaviors were tested as internal controls and for comparison with the existing neuroactive steroid literature.

RESULTS

Ganaxolone improved aspects of social approach and reciprocal social interactions in BTBR, with no effect on repetitive self-grooming, and no detrimental effects in C57BL/6J. Ganaxolone increased overall exploratory activity in BTBR and C57BL/6J in the open field, social approach, and elevated plus-maze, introducing a confound for the interpretation of social improvements. Allopregnanolone and diazepam similarly increased total entries in the elevated plus-maze, indicating that behavioral activation may be a general property of GABAA receptor PAMs in these strains.

CONCLUSIONS

Ganaxolone shows promise for improving sociability. In addition, ganaxolone, as well as other GABAA receptor PAMs, enhanced overall BTBR activity. The translational implications of specific sociability improvements and nonspecific behavioral activation by ganaxolone in the BTBR model remain to be determined. Future studies to explore whether PAMs provide a novel profile with unique benefits for ASD treatment will be worthwhile.

GABAB Receptor Agonist R-Baclofen Reverses Social Deficits and Reduces Repetitive Behavior in Two Mouse Models of Autism

Autism spectrum disorder (ASD) is diagnosed by two core behavioral criteria, unusual reciprocal social interactions and communication, and stereotyped, repetitive behaviors with restricted interests. Excitatory/inhibitory imbalance is a prominent hypothesis for the etiology of autism. The selective GABAB receptor agonist R-baclofen previously reversed social deficits and reduced repetitive behaviors in a mouse model of Fragile X syndrome, and Arbaclofen improved some clinical symptoms in some Fragile X and ASD patients. To evaluate R-baclofen in a broader range of mouse models of ASD, we tested both the R-baclofen enantiomer and the less potent S-baclofen enantiomer in two inbred strains of mice that display low sociability and/or high repetitive or stereotyped behaviors. R-baclofen treatment reversed social approach deficits in BTBR T+ Itpr3tf/J (BTBR), reduced repetitive self-grooming and high marble burying scores in BTBR, and reduced stereotyped jumping in C58/J (C58), at nonsedating doses. S-baclofen produced minimal effects at the same doses. These findings encourage investigations of R-baclofen in other preclinical model systems. Additional clinical studies may be warranted to further evaluate the hypothesis that the GABAB receptor represents a promising pharmacological target for treating appropriately stratified subsets of individuals with ASD.

NMDA receptor activation regulates sociability by its effect on mTOR signaling activity

Tuberous Sclerosis Complex is one example of a syndromic form of autism spectrum disorder associated with disinhibited activity of mTORC1 in neurons (e.g., cerebellar Purkinje cells). mTORC1 is a complex protein possessing serine/threonine kinase activity and a key downstream molecule in a signaling cascade beginning at the cell surface with the transduction of neurotransmitters (e.g., glutamate and acetylcholine) and nerve growth factors (e.g., Brain-Derived Neurotrophic Factor). Interestingly, the severity of the intellectual disability in Tuberous Sclerosis Complex may relate more to this metabolic disturbance (i.e., overactivity of mTOR signaling) than the density of cortical tubers. Several recent reports showed that rapamycin, an inhibitor of mTORC1, improved sociability and other symptoms in mouse models of Tuberous Sclerosis Complex and autism spectrum disorder, consistent with mTORC1 overactivity playing an important pathogenic role. NMDA receptor activation may also dampen mTORC1 activity by at least two possible mechanisms: regulating intraneuronal accumulation of arginine and the phosphorylation status of a specific extracellular signal regulating kinase (i.e., ERK1/2), both of which are "drivers" of mTORC1 activity. Conceivably, the prosocial effects of targeting the NMDA receptor with agonists in mouse models of autism spectrum disorders result from their ability to dampen mTORC1 activity in neurons. Strategies for dampening mTORC1 overactivity by NMDA receptor activation may be preferred to its direct inhibition in chronic neurodevelopmental disorders, such as autism spectrum disorders.

Targeting dynamic interplay among disordered domains or endophenotypes to understand complex neuropsychiatric disorders: Translational lessons from preclinical models

Contemporary biological psychiatry uses clinical and experimental (animal) models to increase our understanding of brain pathogenesis. Modeling psychiatric disorders is currently performed by targeting various key neurobehavioral clusters of phenotypic traits (domains), including affective, cognitive, social, motor and reward. Analyses of such domains and their 'smaller units' - individual endophenotypes - are critical for the study of complex brain disorders and their neural underpinnings. The spectrum nature of brain disorders and the importance of pathogenetic linkage among various disordered domains or endophenotypes have also been recognized as an important strategic direction of translational research. Here, we discuss cross-domain analyses of animal models, and focus on their value for mimicking the clinical overlap between disordered neurobehavioral domains in humans. Based on recent experimental evidence, we argue that understanding of brain pathogenesis requires modeling the clinically relevant inter-relationships between various individual endophenotypes (or their domains).

Prenatal exposure to a common organophosphate insecticide delays motor development in a mouse model of idiopathic autism

Autism spectrum disorders are characterized by impaired social and communicative skills and repetitive behaviors. Emerging evidence supported the hypothesis that these neurodevelopmental disorders may result from a combination of genetic susceptibility and exposure to environmental toxins in early developmental phases. This study assessed the effects of prenatal exposure to chlorpyrifos (CPF), a widely diffused organophosphate insecticide endowed with developmental neurotoxicity at sub-toxic doses, in the BTBR T+tf/J mouse strain, a validated model of idiopathic autism that displays several behavioral traits relevant to the autism spectrum. To this aim, pregnant BTBR mice were administered from gestational day 14 to 17 with either vehicle or CPF at a dose of 6 mg/kg/bw by oral gavages. Offspring of both sexes underwent assessment of early developmental milestones, including somatic growth, motor behavior and ultrasound vocalization. To evaluate the potential long-term effects of CPF, two different social behavior patterns typically altered in the BTBR strain (free social interaction with a same-sex companion in females, or interaction with a sexually receptive female in males) were also examined in the two sexes at adulthood. Our findings indicate significant effects of CPF on somatic growth and neonatal motor patterns. CPF treated pups showed reduced weight gain, delayed motor maturation (i.e., persistency of immature patterns such as pivoting at the expenses of coordinated locomotion) and a trend to enhanced ultrasound vocalization. At adulthood, CPF associated alterations were found in males only: the altered pattern of investigation of a sexual partner, previously described in BTBR mice, was enhanced in CPF males, and associated to increased ultrasonic vocalization rate. These findings strengthen the need of future studies to evaluate the role of environmental chemicals in the etiology of neurodevelopment disorders.

Effect of social odor context on the emission of isolation-induced ultrasonic vocalizations in the BTBR T+tf/J mouse model for autism

An important diagnostic criterion for social communication deficits in autism spectrum disorders (ASD) are difficulties in adjusting behavior to suit different social contexts. While the BTBR T+tf/J (BTBR) inbred strain of mice is one of the most commonly used mouse models for ASD, little is known about whether BTBR mice display deficits in detecting changes in social context and their ability to adjust to them. Here, it was tested therefore whether the emission of isolation-induced ultrasonic vocalizations (USV) in BTBR mouse pups is affected by the social odor context, in comparison to the standard control strain with high sociability, C57BL/6J (B6). It is known that the presence of odors from mothers and littermates leads to a calming of the isolated mouse pup, and hence to a reduction in isolation-induced USV emission. In accordance with their behavioral phenotypes with relevance to all diagnostic core symptoms of ASD, it was predicted that BTBR mouse pups would not display a calming response when tested under soiled bedding conditions with home cage bedding material containing maternal odors, and that similar isolation-induced USV emission rates would be seen in BTBR mice tested under clean and soiled bedding conditions. Unexpectedly, however, the present findings show that BTBR mouse pups display such a calming response and emit fewer isolation-induced USV when tested under soiled as compared to clean bedding conditions, similar to B6 mouse pups. Yet, in contrast to B6 mouse pups, which emitted isolation-induced USV with shorter call durations and lower levels of frequency modulation under soiled bedding conditions, social odor context had no effect on acoustic call features in BTBR mouse pups. This indicates that the BTBR mouse model for ASD does not display deficits in detecting changes in social context, but has a limited ability and/or reduced motivation to adjust to them.

Inflammatory profiles in the BTBR mouse: how relevant are they to autism spectrum disorders?

Autism spectrum disorders (ASD) are a group of disorders characterized by core behavioral features including stereotyped interests, repetitive behaviors and impairments in communication and social interaction. In addition, widespread changes in the immune systems of individuals with ASD have been identified, in particular increased evidence of inflammation in the periphery and central nervous system. While the etiology of these disorders remains unclear, it appears that multiple gene and environmental factors are involved. The need for animal models paralleling the behavioral and immunological features of ASD is paramount to better understand the link between immune system dysregulation and behavioral deficits observed in these disorders. As such, the asocial BTBR mouse strain displays both ASD relevant behaviors and persistent immune dysregulation, providing a model system that has and continues to be instructive in understanding the complex nature of ASD.

Long-term exposure to intranasal oxytocin in a mouse autism model

Oxytocin (OT) is a neuropeptide involved in mammalian social behavior. It is currently in clinical trials for the treatment of autism spectrum disorder (ASD). Previous studies in healthy rodents (prairie voles and C57BL/6J mice) have shown that there may be detrimental effects of long-term intranasal administration, raising the questions about safety and efficacy. To investigate the effects of OT on the aspects of ASD phenotype, we conducted the first study of chronic intranasal OT in a well-validated mouse model of autism, the BTBR T+ Itpr3tf/J inbred strain (BTBR), which displays low sociability and high repetitive behaviors. BTBR and C57BL/6J (B6) mice (N=94) were administered 0.8  IU/kg of OT intranasally, daily for 30 days, starting on day 21. We ran a well-characterized set of behavioral tasks relevant to diagnostic and associated symptoms of autism, including juvenile reciprocal social interactions, three-chambered social approach, open-field exploratory activity, repetitive self-grooming and fear-conditioned learning and memory, some during and some post treatment. Intranasal OT did not improve autism-relevant behaviors in BTBR, except for female sniffing in the three-chambered social interaction test. Male saline-treated BTBR mice showed increased interest in a novel mouse, both in chamber time and sniffing time, whereas OT-treated male BTBR mice showed a preference for the novel mouse in sniffing time only. No deleterious effects of OT were detected in either B6 or BTBR mice, except possibly for the lack of a preference for the novel mouse's chamber in OT-treated male BTBR mice. These results highlight the complexity inherent in understanding the effects of OT on behavior. Future investigations of chronic intranasal OT should include a wider dose range and early developmental time points in both healthy rodents and ASD models to affirm the efficacy and safety of OT.

Subchronic treatment of donepezil rescues impaired social, hyperactive, and stereotypic behavior in valproic acid-induced animal model of autism

Autism spectrum disorder (ASD) is a group of pervasive developmental disorders with core symptoms such as sociability deficit, language impairment, and repetitive/restricted behaviors. Although worldwide prevalence of ASD has been increased continuously, therapeutic agents to ameliorate the core symptoms especially social deficits, are very limited. In this study, we investigated therapeutic potential of donepezil for ASD using valproic acid-induced autistic animal model (VPA animal model). We found that prenatal exposure of valproic acid (VPA) induced dysregulation of cholinergic neuronal development, most notably the up-regulation of acetylcholinesterase (AChE) in the prefrontal cortex of affected rat and mouse offspring. Similarly, differentiating cortical neural progenitor cell in culture treated with VPA showed increased expression of AChE in vitro. Chromatin precipitation experiments revealed that acetylation of histone H3 bound to AChE promoter region was increased by VPA. In addition, other histone deacetyalse inhibitors (HDACIs) such as trichostatin A and sodium butyrate also increased the expression of AChE in differentiating neural progenitor cells suggesting the essential role of HDACIs in the regulation of AChE expression. For behavioral analysis, we injected PBS or donepezil (0.3 mg/kg) intraperitoneally to control and VPA mice once daily from postnatal day 14 all throughout the experiment. Subchronic treatment of donepezil improved sociability and prevented repetitive behavior and hyperactivity of VPA-treated mice offspring. Taken together, these results provide evidence that dysregulation of ACh system represented by the up-regulation of AChE may serve as an effective pharmacological therapeutic target against autistic behaviors in VPA animal model of ASD, which should be subjected for further investigation to verify the clinical relevance.

Oxotremorine treatment reduces repetitive behaviors in BTBR T+ tf/J mice

Repetitive behaviors with restricted interests is one of the core criteria for the diagnosis of autism spectrum disorder (ASD). Current pharmacotherapies that target the dopaminergic or serotonergic systems have limited effectiveness in treating repetitive behaviors. Previous research has demonstrated that administration of muscarinic cholinergic receptor (mAChR) antagonists can exacerbate motor stereotypies while mAChR agonists reduce stereotypies. The present study determined whether the mAChR agonist, oxotremorine affected repetitive behaviors in the BTBR T+ tf/J (BTBR) mouse model of autism. To test the effects of oxotremorine on repetitive behaviors, marble burying and grooming behavior were measured in BTBR mice and compared to that in C57BL/6J (B6) mice. The effects of oxotremorine on locomotor activity was also measured. Thirty minutes before each test, mice received an intraperitoneal (ip) injection of saline, 0.001 mg or 0.01 mg of oxotremorine methiodide. Saline- treated BTBR mice exhibited increased marble burying and self-grooming behavior compared to that of saline-treated B6 mice. Oxotremorine significantly reduced marble burying and self-grooming behavior in BTBR mice, but had no significant effect in B6 mice. In addition, oxotremorine did not affect locomotor activity in BTBR mice, but significantly reduced locomotor activity in B6 mice at the 0.01 mg dose. These findings demonstrate that activation of mAChRs reduces repetitive behavior in the BTBR mouse and suggest that treatment with a mAChR agonist may be effective in reducing repetitive behaviors in ASD.

Mixed housing with DBA/2 mice induces stress in C57BL/6 mice: implications for interventions based on social enrichment

Several behavioral interventions, based on social enrichment and observational learning are applied in treatment of neuropsychiatric disorders. However, the mechanism of such modulatory effect and the safety of applied methods on individuals involved in social support need further investigation. We took advantage of known differences between inbred mouse strains to reveal the effect of social enrichment on behavior and neurobiology of animals with different behavioral phenotypes. C57BL/6 and DBA/2 female mice displaying multiple differences in cognitive, social, and emotional behavior were group-housed either in same-strain or in mixed-strain conditions. Comprehensive behavioral phenotyping and analysis of expression of several plasticity- and stress-related genes were done to measure the reciprocal effects of social interaction between the strains. Contrary to our expectation, mixed housing did not change the behavior of DBA/2 mice. Nevertheless, the level of serum corticosterone and the expression of glucocorticoid receptor Nr3c1 in the brain were increased in mixed housed DBA/2 as compared with those of separately housed DBA/2 mice. In contrast, socially active C57BL/6 animals were more sensitive to the mixed housing, displaying several signs of stress: alterations in learning, social, and anxiety-like behavior and anhedonia. These behavioral impairments were accompanied by the elevated serum corticosterone and the reduced expression of Nr3c1, as well as the elevated Bdnf levels in the cortex and hippocampus. Our results demonstrate the importance of social factors in modulation of both behavior and the underlying neurobiological mechanisms in stress response, and draw attention to the potential negative impact of social interventions for individuals involved in social support.

Dysfunctional dopaminergic neurotransmission in asocial BTBR mice

Autism spectrum disorders (ASD) are neurodevelopmental conditions characterized by pronounced social and communication deficits and stereotyped behaviours. Recent psychosocial and neuroimaging studies have highlighted reward-processing deficits and reduced dopamine (DA) mesolimbic circuit reactivity in ASD patients. However, the neurobiological and molecular determinants of these deficits remain undetermined. Mouse models recapitulating ASD-like phenotypes could help generate hypotheses about the origin and neurophysiological underpinnings of clinically relevant traits. Here we used functional magnetic resonance imaging (fMRI), behavioural and molecular readouts to probe dopamine neurotransmission responsivity in BTBR T(+) Itpr3(tf)/J mice (BTBR), an inbred mouse line widely used to model ASD-like symptoms owing to its robust social and communication deficits, and high level of repetitive stereotyped behaviours. C57BL/6J (B6) mice were used as normosocial reference comparators. DA reuptake inhibition with GBR 12909 produced significant striatal DA release in both strains, but failed to elicit fMRI activation in widespread forebrain areas of BTBR mice, including mesolimbic reward and striatal terminals. In addition, BTBR mice exhibited no appreciable motor responses to GBR 12909. DA D1 receptor-dependent behavioural and signalling responses were found to be unaltered in BTBR mice, whereas dramatic reductions in pre- and postsynaptic DA D2 and adenosine A2A receptor function was observed in these animals. Overall these results document profoundly compromised DA D2-mediated neurotransmission in BTBR mice, a finding that is likely to have a role in the distinctive social and behavioural deficits exhibited by these mice. Our results call for a deeper investigation of the role of dopaminergic dysfunction in mouse lines exhibiting ASD-like phenotypes, and possibly in ASD patient populations.

Tests of unconditioned anxiety - pitfalls and disappointments

The plus-maze, the light-dark box and the open-field are the main current tests of unconditioned anxiety for mice and rats. Despite their disappointing achievements, they remain as popular as ever and seem to play an important role in an ever-growing demand for behavioral phenotyping and drug screening. Numerous reviews have repeatedly reported their lack of consistency and reliability but they failed to address the core question of whether these tests do provide unequivocal measures of fear-induced anxiety, that these measurements are not confused with measures of fear-induced avoidance or natural preference responses - i.e. discriminant validity. In the present report, I examined numerous issues that undermine the validity of the current tests, and I highlighted various flaws in the aspects of these tests and the methodologies pursued. This report concludes that the evidence in support of the validity of the plus-maze, the light/dark box and the open-field as anxiety tests is poor and methodologically questionable.

Long-term memory deficits are associated with elevated synaptic ERK1/2 activation and reversed by mGluR5 antagonism in an animal model of autism

A significant proportion of patients with autism exhibit some degree of intellectual disability. The BTBR T(+) Itpr3(tf)/J mouse strain exhibits behaviors that align with the major diagnostic criteria of autism. To further evaluate the BTBR strain's cognitive impairments, we quantified hippocampus-dependent object location memory (OLM) and found that one-third of the BTBR mice exhibited robust memory, whereas the remainder did not. Fluorescence deconvolution tomography was used to test whether synaptic levels of activated extracellular signal-regulated kinase 1/2 (ERK1/2), a protein that contributes importantly to plasticity, correlate with OLM scores in individual mice. In hippocampal field CA1, the BTBRs had fewer post-synaptic densities associated with high levels of phosphorylated (p-) ERK1/2 as compared with C57BL/6 mice. Although counts of p-ERK1/2 immunoreactive synapses did not correlate with OLM performance, the intensity of synaptic p-ERK1/2 immunolabeling was negatively correlated with OLM scores across BTBRs. Metabotropic glutamate receptor (mGluR) 5 signaling activates ERK1/2. Therefore, we tested whether treatment with the mGluR5 antagonist MPEP normalizes synaptic and learning measures in BTBR mice: MPEP facilitated OLM and decreased synaptic p-ERK1/2 immunolabeling intensity without affecting numbers of p-ERK1/2+ synapses. In contrast, semi-chronic ampakine treatment, which facilitates memory in other models of cognitive impairment, had no effect on OLM in BTBRs. These results suggest that intellectual disabilities associated with different neurodevelopmental disorders on the autism spectrum require distinct therapeutic strategies based on underlying synaptic pathology.

The developmental pattern of the RAS/RAF/Erk1/2 pathway in the BTBR autism mouse model

BTBR mice exhibit several autistic-like behaviors and are currently used as a model for understanding mechanisms that may be responsible for the pathogenesis of autism. Ras/Raf/ERK1/2 signaling has been suggested to play an important role in neural development, learning, memory, and cognition. Two studies reported that a deletion of a locus on chromosome 16 containing the mitogen-activated protein kinase 3 (MAPK3) gene, which encodes ERK1, is associated with autism. In the present study, Ras/Raf/ERK1/2 signaling was found to be up-regulated in BTBR mice relative to matched control B6 mice, to further suggest involvement in the pathogenesis of autism. To further characterize the developmental pattern of Ras/Raf/ERK1/2 signaling, varying stages during development were sampled to reveal an up-regulation in newborn and 2-week old BTBR mice relative to age-matched B6 mice. By the age of 3-week, Ras/Raf/ERK1/2 signaling in the brain of BTBR mice was unaltered relative to B6 mice, with this trend maintained in 6-week samples. These results suggest that the alteration of Ras/Raf/ERK signaling in the early developmental stages in mice could contribute to the noted autistic phenotype. Furthermore, these findings support the value of BTBR mice to serve as a human analog for autistic etiological research and aid in a better understanding of the developmental mechanisms of autism.

Rapamycin improves sociability in the BTBR T(+)Itpr3(tf)/J mouse model of autism spectrum disorders

Overactivation of the mammalian target of rapamycin (mTOR) has been implicated in the pathogenesis of syndromic forms of autism spectrum disorders (ASDs), such as tuberous sclerosis complex, neurofibromatosis 1, and fragile X syndrome. Administration of mTORC1 (mTOR complex 1) inhibitors (e.g. rapamycin) in syndromic mouse models of ASDs improved behavior, cognition, and neuropathology. However, since only a minority of ASDs are due to the effects of single genes (∼10%), there is a need to explore inhibition of mTOR activity in mouse models that may be more relevant to the majority of nonsyndromic presentations, such as the genetically inbred BTBR T(+)Itpr3(tf)/J (BTBR) mouse model of ASDs. BTBR mice have social impairment and exhibit increased stereotypic behavior. In prior work, d-cycloserine, a partial glycineB site agonist that targets the N-methyl-d-aspartate (NMDA) receptor, was shown to improve sociability in both Balb/c and BTBR mouse models of ASDs. Importantly, NMDA receptor activation regulates mTOR signaling activity. The current study investigated the ability of rapamycin (10mg/kg, i.p.×four days), an mTORC1 inhibitor, to improve sociability and stereotypic behavior in BTBR mice. Using a standard paradigm to assess mouse social behavior, rapamycin improved several measures of sociability in the BTBR mouse, suggesting that mTOR overactivation represents a therapeutic target that mediates or contributes to impaired sociability in the BTBR mouse model of ASDs. Interestingly, there was no effect of rapamycin on stereotypic behaviors in this mouse model.

Neuroimaging evidence of major morpho-anatomical and functional abnormalities in the BTBR T+TF/J mouse model of autism

BTBR T+tf/J (BTBR) mice display prominent behavioural deficits analogous to the defining symptoms of autism, a feature that has prompted a widespread use of the model in preclinical autism research. Because neuro-behavioural traits are described with respect to reference populations, multiple investigators have examined and described the behaviour of BTBR mice against that exhibited by C57BL/6J (B6), a mouse line characterised by high sociability and low self-grooming. In an attempt to probe the translational relevance of this comparison for autism research, we used Magnetic Resonance Imaging (MRI) to map in both strain multiple morpho-anatomical and functional neuroimaging readouts that have been extensively used in patient populations. Diffusion tensor tractography confirmed previous reports of callosal agenesis and lack of hippocampal commissure in BTBR mice, and revealed a concomitant rostro-caudal reorganisation of major cortical white matter bundles. Intact inter-hemispheric tracts were found in the anterior commissure, ventro-medial thalamus, and in a strain-specific white matter formation located above the third ventricle. BTBR also exhibited decreased fronto-cortical, occipital and thalamic gray matter volume and widespread reductions in cortical thickness with respect to control B6 mice. Foci of increased gray matter volume and thickness were observed in the medial prefrontal and insular cortex. Mapping of resting-state brain activity using cerebral blood volume weighted fMRI revealed reduced cortico-thalamic function together with foci of increased activity in the hypothalamus and dorsal hippocampus of BTBR mice. Collectively, our results show pronounced functional and structural abnormalities in the brain of BTBR mice with respect to control B6 mice. The large and widespread white and gray matter abnormalities observed do not appear to be representative of the neuroanatomical alterations typically observed in autistic patients. The presence of reduced fronto-cortical metabolism is of potential translational relevance, as this feature recapitulates previously-reported clinical observations.

Inflammatory macrophage phenotype in BTBR T+tf/J mice

Although autism is a behaviorally defined disorder, many studies report an association with increased pro-inflammatory cytokine production. Recent characterization of the BTBR T+tf/J (BTBR) inbred mouse strain has revealed several behavioral characteristics including social deficits, repetitive behavior, and atypical vocalizations which may be relevant to autism. We therefore hypothesized that, asocial BTBR mice, which exhibit autism-like behaviors, may have an inflammatory immune profile similar to that observed in children with autism. The objectives of this study were to characterize the myeloid immune profile of BTBR mice and to explore their associations with autism-relevant behaviors. C57BL/6J (C57) mice and BTBR mice were tested for social interest and repetitive self-grooming behavior. Cytokine production was measured in bone-marrow derived macrophages incubated for 24 h in either growth media alone, LPS, IL-4/LPS, or IFNγ/LPS to ascertain any M1/M2 skewing. After LPS stimulation, BTBR macrophages produced higher levels of IL-6, MCP-1, and MIP-1α and lower IL-10 (p < 0.01) than C57 mice, suggesting an exaggerated inflammatory profile. After exposure to IL-4/LPS BTBR macrophages produced less IL-10 (p < 0.01) than C57 macrophages and more IL-12p40 (p < 0.01) suggesting poor M2 polarization. Levels of IL-12(p70) (p < 0.05) were higher in BTBR macrophages after IFNγ/LPS stimulation, suggesting enhanced M1 polarization. We further observed a positive correlation between grooming frequency, and production of IL-12(p40), IL-12p70, IL-6, and TNFα (p < 0.05) after treatment with IFNγ/LPS across both strains. Collectively, these data suggest that the asocial BTBR mouse strain exhibits a more inflammatory, or M1, macrophage profile in comparison to the social C57 strain. We have further demonstrated a relationship between this relative increase in inflammation and repetitive grooming behavior, which may have relevance to repetitive and stereotyped behavior of autism.