Low sociability in BTBR T+tf/J mice is independent of partner strain

Parenting behaviors in mice: Olfactory mechanisms and features in models of autism spectrum disorders

Rodents, along with numerous other mammals, heavily depend on olfactory cues to navigate their social interactions. Processing of olfactory sensory inputs is mediated by conserved brain circuits that ultimately trigger social behaviors, such as social interactions and parental care. Although innate, parenting is influenced by internal states, social experience, genetics, and the environment, and any significant disruption of these factors can impact the social circuits. Here, we review the molecular mechanisms and social circuits from the olfactory epithelium to central processing that initiate parental behaviors and their dysregulations that may contribute to the social impairments in mouse models of autism spectrum disorders (ASD). We discuss recent advances of the crucial role of olfaction in parental care, its consequences for social interactions, and the reciprocal influence on social interaction impairments in mouse models of ASD.

Apigenin Alleviates Autistic-like Stereotyped Repetitive Behaviors and Mitigates Brain Oxidative Stress in Mice

Studying the involvement of nicotinic acetylcholine receptors (nAChRs), specifically α7-nAChRs, in neuropsychiatric brain disorders such as autism spectrum disorder (ASD) has gained a growing interest. The flavonoid apigenin (APG) has been confirmed in its pharmacological action as a positive allosteric modulator of α7-nAChRs. However, there is no research describing the pharmacological potential of APG in ASD. The aim of this study was to evaluate the effects of the subchronic systemic treatment of APG (10-30 mg/kg) on ASD-like repetitive and compulsive-like behaviors and oxidative stress status in the hippocampus and cerebellum in BTBR mice, utilizing the reference drug aripiprazole (ARP, 1 mg/kg, i.p.). BTBR mice pretreated with APG (20 mg/kg) or ARP (1 mg/g, i.p.) displayed significant improvements in the marble-burying test (MBT), cotton-shredding test (CST), and self-grooming test (SGT) (all p < 0.05). However, a lower dose of APG (10 mg/kg, i.p.) failed to modulate behaviors in the MBT or SGT, but significantly attenuated the increased shredding behaviors in the CST of tested mice. Moreover, APG (10-30 mg/kg, i.p.) and ARP (1 mg/kg) moderated the disturbed levels of oxidative stress by mitigating the levels of catalase (CAT) and superoxide dismutase (SOD) in the hippocampus and cerebellum of treated BTBR mice. In patch clamp studies in hippocampal slices, the potency of choline (a selective agonist of α7-nAChRs) in activating fast inward currents was significantly potentiated following incubation with APG. Moreover, APG markedly potentiated the choline-induced enhancement of spontaneous inhibitory postsynaptic currents. The observed results propose the potential therapeutic use of APG in the management of ASD. However, further preclinical investigations in additional models and different rodent species are still needed to confirm the potential relevance of the therapeutic use of APG in ASD.

Social experience in adolescence shapes prefrontal cortex structure and function in adulthood

During adolescence, the prefrontal cortex (PFC) undergoes dramatic reorganization. PFC development is profoundly influenced by the social environment, disruptions to which may prime the emergence of psychopathology across the lifespan. We investigated the neurobehavioral consequences of isolation experienced in adolescence in mice, and in particular, the long-term consequences that were detectable even despite normalization of the social milieu. Isolation produced biases toward habit-like behavior at the expense of flexible goal seeking, plus anhedonic-like reward deficits. Behavioral phenomena were accompanied by neuronal dendritic spine over-abundance and hyper-excitability in the ventromedial PFC (vmPFC), which was necessary for the expression of isolation-induced habits and sufficient to trigger behavioral inflexibility in socially reared controls. Isolation activated cytoskeletal regulatory pathways otherwise suppressed during adolescence, such that repression of constituent elements prevented long-term isolation-induced neurosequelae. Altogether, our findings unveil an adolescent critical period and multi-model mechanism by which social experiences facilitate prefrontal cortical maturation.

Suppression of Cofilin function in the somatosensory cortex alters social contact behavior in the BTBR mouse inbred line

Sensory differences are a core feature of autism spectrum disorders (ASD) and are predictive of other ASD core symptoms such as social difficulties. However, the neurobiological substrate underlying the functional relationship between sensory and social functioning is poorly understood. Here, we examined whether misregulation of structural plasticity in the somatosensory cortex modulates aberrant social functioning in BTBR mice, a mouse model for autism spectrum disorder-like phenotypes. By locally expressing a dominant-negative form of Cofilin (CofilinS3D; a key regulator of synaptic structure) in the somatosensory cortex, we tested whether somatosensory suppression of Cofilin activity alters social functioning in BTBR mice. Somatosensory Cofilin suppression altered social contact and nest-hide behavior of BTBR mice in a social colony, assessed for seven consecutive days. Subsequent behavioral testing revealed that altered social functioning is related to altered tactile sensory perception; CofilinS3D-treated BTBR mice showed a time-dependent difference in the sensory bedding preference task. These findings show that Cofilin suppression in the somatosensory cortex alters social functioning in BTBR mice and that this is associated with tactile sensory processing, a critical indicator of somatosensory functioning.

Shaping the development of complex social behavior

Early life experiences can have an enduring impact on the brain and behavior, with implications for stress reactivity, cognition, and social behavior. In particular, the neural systems that contribute to the expression of social behavior are altered by early life social environments. However, paradigms that have been used to alter the social environment during development have typically focused on exposure to stress, adversity, and deprivation of species-typical social stimulation. Here, we explore whether complex social environments can shape the development of complex social behavior. We describe lab-based paradigms for studying early life social complexity in rodents that are generally focused on enriching the social and sensory experiences of the neonatal and juvenile periods of development. The impact of these experiences on social behavior and neuroplasticity is highlighted. Finally, we discuss the degree to which our current approaches for studying social behavior outcomes give insight into "complex" social behavior and how social complexity can be better integrated into lab-based methodologies.

Neurodevelopmental deficits and cell-type-specific transcriptomic perturbations in a mouse model of HNRNPU haploinsufficiency

Heterozygous de novo loss-of-function mutations in the gene expression regulator HNRNPU cause an early-onset developmental and epileptic encephalopathy. To gain insight into pathological mechanisms and lay the potential groundwork for developing targeted therapies, we characterized the neurophysiologic and cell-type-specific transcriptomic consequences of a mouse model of HNRNPU haploinsufficiency. Heterozygous mutants demonstrated global developmental delay, impaired ultrasonic vocalizations, cognitive dysfunction and increased seizure susceptibility, thus modeling aspects of the human disease. Single-cell RNA-sequencing of hippocampal and neocortical cells revealed widespread, yet modest, dysregulation of gene expression across mutant neuronal subtypes. We observed an increased burden of differentially-expressed genes in mutant excitatory neurons of the subiculum-a region of the hippocampus implicated in temporal lobe epilepsy. Evaluation of transcriptomic signature reversal as a therapeutic strategy highlights the potential importance of generating cell-type-specific signatures. Overall, this work provides insight into HNRNPU-mediated disease mechanisms and provides a framework for using single-cell RNA-sequencing to study transcriptional regulators implicated in disease.

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.

Cannabidiol and cannabis-inspired terpene blends have acute prosocial effects in the BTBR mouse model of autism spectrum disorder

Introduction

Cannabidiol (CBD) is a non-intoxicating phytocannabinoid with increasing popularity due to its purported therapeutic efficacy for numerous off-label conditions including anxiety and autism spectrum disorder (ASD). Those with ASD are commonly deficient in endogenous cannabinoid signaling and GABAergic tone. CBD has a complex pharmacodynamic profile that includes enhancing GABA and endocannabinoid signaling. Thus, there is mechanistic justification for investigating CBD's potential to improve social interaction and related symptoms in ASD. Recent clinical trials in children with ASD support CBD's beneficial effects in numerous comorbid symptoms, but its impact on social behavior is understudied.

Methods

Here, we tested the prosocial and general anxiolytic efficacy of a commercially available CBD-rich broad spectrum hemp oil delivered by repeated puff vaporization and consumed via passive inhalation in the female cohort of the BTBR strain, a common inbred mouse line for preclinical assessment of ASD-like behaviors.

Results

We observed that CBD enhanced prosocial behaviors using the 3-Chamber Test with a different vapor dose-response relationship between prosocial behavior and anxiety-related behavior on the elevated plus maze. We also identified that inhalation of a vaporized terpene blend from the popular OG Kush cannabis strain increased prosocial behavior independently of CBD and acted together with CBD to promote a robust prosocial effect. We observed similar prosocial effects with two additional cannabis terpene blends from the Do-Si-Dos and Blue Dream strains, and further reveal that these prosocial benefits rely on the combination of multiple terpenes that comprise the blends.

Discussion

Our results illustrate the added benefit of cannabis terpene blends for CBD-based treatment of ASD.

Brain-Derived Neurotrophic Factor (BDNF) in Mechanisms of Autistic-like Behavior in BTBR Mice: Crosstalk with the Dopaminergic Brain System

Disturbances in neuroplasticity undoubtedly play an important role in the development of autism spectrum disorders (ASDs). Brain neurotransmitters and brain-derived neurotrophic factor (BDNF) are known as crucial players in cerebral and behavioral plasticity. Such an important neurotransmitter as dopamine (DA) is involved in the behavioral inflexibility of ASD. Additionally, much evidence from human and animal studies implicates BDNF in ASD pathogenesis. Nonetheless, crosstalk between BDNF and the DA system has not been studied in the context of an autistic-like phenotype. For this reason, the aim of our study was to compare the effects of either the acute intracerebroventricular administration of a recombinant BDNF protein or hippocampal adeno-associated-virus-mediated BDNF overexpression on autistic-like behavior and expression of key DA-related and BDNF-related genes in BTBR mice (a widely recognized model of autism). The BDNF administration failed to affect autistic-like behavior but downregulated Comt mRNA in the frontal cortex and hippocampus; however, COMT protein downregulation in the hippocampus and upregulation in the striatum were insignificant. BDNF administration also reduced the receptor TrkB level in the frontal cortex and midbrain and the BDNF/proBDNF ratio in the striatum. In contrast, hippocampal BDNF overexpression significantly diminished stereotypical behavior and anxiety; these alterations were accompanied only by higher hippocampal DA receptor D1 mRNA levels. The results indicate an important role of BDNF in mechanisms underlying anxiety and repetitive behavior in ASDs and implicates BDNF-DA crosstalk in the autistic-like phenotype of BTBR mice.

Faded neural projection from the posterior bed nucleus of the stria terminalis to the lateral habenula contributes to social signaling deficit in male BTBR mice as a mouse model of autism

BTBR T⁺ Itpr3^tf/J (BTBR) mice display several behavioral characteristics, including social deficits resembling the core symptoms of human autism. Atypical social behaviors include sequential processes of assembled cognitive-behavior components, such as recognition, investigatory assessment, and signaling response. This study aimed to elucidate the neural circuits responsible for the regulation of the social signaling response, as shown by scent marking behavior in male mice. We first assessed the recognition and investigatory patterns of male BTBR mice compared to those of C57BL/6 J (B6) mice. Next, we examined their scent-marking behavior as innate social signaling responses adjusted to a confronted feature of social stimuli and situations, along with the expression of c-Fos as a marker of neuronal activity in selected brain areas involved in the regulation of social behavior. The function of the targeted brain area was confirmed by chemogenetic manipulation. We also examined the social peptides, oxytocin and vasopressin neurons of the major brain regions that are associated with the regulation of social behavior. Our data indicate that male BTBR mice are less responsive to the presentation of social stimuli and the expression of social signaling responses, which is paralleled by blunted c-Fos responsivity and vasopressin neurons morphological changes in selected brain areas, including the posterior bed nucleus of the stria terminalis (pBnST) and lateral habenula (LHb) in BTBR mice. Further investigation of LHb function revealed that chemogenetic inhibition and activation of LHb activity can induce a change in scent marking responses in both B6 and BTBR mice. Our elucidation of the downstream LHb circuits controlling scent marking behavior indicates intact function in BTBR mice. The altered morphological characteristics of oxytocin neurons in the paraventricular nucleus of the hypothalamus and vasopressin-positive neurons and axonal projections in the pBnST and LHb appear to underlie the dysfunction of scent marking responses in BTBR mice. (300/300 words).

Twenty years of discoveries emerging from mouse models of autism

More than 100 single gene mutations and copy number variants convey risk for autism spectrum disorder. To understand the extent to which each mutation contributes to the trajectory of individual symptoms of autism, molecular genetics laboratories have introduced analogous mutations into the genomes of laboratory mice and other species. Over the past twenty years, behavioral neuroscientists discovered the consequences of mutations in many risk genes for autism in animal models, using assays with face validity to the diagnostic and associated behavioral symptoms of people with autism. Identified behavioral phenotypes complement electrophysiological, neuroanatomical, and biochemical outcome measures in mutant mouse models of autism. This review describes the history of phenotyping assays in genetic mouse models, to evaluate social and repetitive behaviors relevant to the primary diagnostic criteria for autism. Robust phenotypes are currently employed in translational investigations to discover effective therapeutic interventions, representing the future direction of an intensely challenging research field.

Does the stranger mouse strain matter to female BTBR mice?

Autism spectrum disorder (ASD) is characterized by deficits in social communication and repetitive behaviors/restricted interests. One mouse model of ASD is the BTBR T⁺Itpr^tf/J (BTBR) mice which display low levels of social behavior in several tests. The social approach test is used to examine the preference for social interaction between a stranger mouse or a novel object. While female BTBR mice have been used in the social approach test, no one has examined the degree to which the strain of the stranger mouse will affect social behavior. The current experiment tested female BTBR subject mice in the social approach test with stranger mice from different strains including the BTBR, 129S1/SvImJ (129), and C57BL/6J (B6) mice, of which the B6 mice are most social. The results show that female BTBR mice overall spent significantly more time in the stranger mouse chamber. However, further analysis revealed that the subject mice spent significantly more time in the stranger mouse chamber when the stranger was from the B6 strain, but not the BTBR or 129 strains. The BTBR female mice also sniffed the B6 and 129 stranger mice more than the novel object. This suggests that BTBR females are more social with mice that display high levels of social behavior, but less so with less social mice.

Molecular Abnormalities in BTBR Mice and Their Relevance to Schizophrenia and Autism Spectrum Disorders: An Overview of Transcriptomic and Proteomic Studies

Animal models of psychopathologies are of exceptional interest for neurobiologists because these models allow us to clarify molecular mechanisms underlying the pathologies. One such model is the inbred BTBR strain of mice, which is characterized by behavioral, neuroanatomical, and physiological hallmarks of schizophrenia (SCZ) and autism spectrum disorders (ASDs). Despite the active use of BTBR mice as a model object, the understanding of the molecular features of this strain that cause the observed behavioral phenotype remains insufficient. Here, we analyzed recently published data from independent transcriptomic and proteomic studies on hippocampal and corticostriatal samples from BTBR mice to search for the most consistent aberrations in gene or protein expression. Next, we compared reproducible molecular signatures of BTBR mice with data on postmortem samples from ASD and SCZ patients. Taken together, these data helped us to elucidate brain-region-specific molecular abnormalities in BTBR mice as well as their relevance to the anomalies seen in ASDs or SCZ in humans.

CA2 physiology underlying social memory

In recent years, convergent evidence has emerged in support of the idea of social brain networks, specific brain regions that are interconnected and support social behaviors. One of these regions is the CA2 area of the hippocampus, a small region strongly connected with cortical and subcortical areas implicated in social behaviors. Furthermore, CA2 area is enriched in receptors for several neuromodulators that are related to various aspects of social behaviors, suggesting that this area could be a key component of social information processing in the brain. In this review, recent findings related to the physiological mechanisms underlying the role of CA2 in social memory are discussed.

Atypical perineuronal nets in the CA2 region interfere with social memory in a mouse model of social dysfunction

Social memory dysfunction is an especially devastating symptom of many neuropsychiatric disorders, which makes understanding the cellular and molecular processes that contribute to such abnormalities important. Evidence suggests that the hippocampus, particularly the CA2 region, plays an important role in social memory. We sought to identify potential mechanisms of social memory dysfunction in the hippocampus by investigating features of neurons, glia, and the extracellular matrix (ECM) of BTBR mice, an inbred mouse strain with deficient social memory. The CA2 is known to receive inputs from dentate gyrus adult-born granule cells (abGCs), neurons known to participate in social memory, so we examined this cell population and found fewer abGCs, as well as fewer axons from abGCs in the CA2 of BTBR mice compared to controls. We also found that BTBR mice had fewer pyramidal cell dendritic spines, in addition to fewer microglia and astrocytes, in the CA2 compared to controls. Along with diminished neuronal and glial elements, we found atypical perineuronal nets (PNNs), specialized ECM structures that regulate plasticity, in the CA2 of BTBR mice. By diminishing PNNs in the CA2 of BTBR mice to control levels, we observed a partial restoration of social memory. Our findings suggest that the CA2 region of BTBR mice exhibits multiple cellular and extracellular abnormalities and identify atypical PNNs as one mechanism producing social memory dysfunction, although the contribution of reduced abGC afferents, pyramidal cell dendritic spine, and glial cell numbers remains unexplored.

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).

Sex Differences in Autism Spectrum Disorder: Diagnostic, Neurobiological, and Behavioral Features

Autism Spectrum Disorder (ASD) is a complex neurodevelopmental disorder with a worldwide prevalence of about 1%, characterized by impairments in social interaction, communication, repetitive patterns of behaviors, and can be associated with hyper- or hypo-reactivity of sensory stimulation and cognitive disability. ASD comorbid features include internalizing and externalizing symptoms such as anxiety, depression, hyperactivity, and attention problems. The precise etiology of ASD is still unknown and it is undoubted that the disorder is linked to some extent to both genetic and environmental factors. It is also well-documented and known that one of the most striking and consistent finding in ASD is the higher prevalence in males compared to females, with around 70% of ASD cases described being males. The present review looked into the most significant studies that attempted to investigate differences in ASD males and females thus trying to shade some light on the peculiar characteristics of this prevalence in terms of diagnosis, imaging, major autistic-like behavior and sex-dependent uniqueness. The study also discussed sex differences found in animal models of ASD, to provide a possible explanation of the neurological mechanisms underpinning the different presentation of autistic symptoms in males and females.

Effects of the Partial M1 Muscarinic Cholinergic Receptor Agonist CDD-0102A on Stereotyped Motor Behaviors and Reversal Learning in the BTBR Mouse Model of Autism

BACKGROUND

Autism spectrum disorders (ASD) are a set of neurodevelopmental disorders marked by a lack of social interaction, restrictive interests, and repetitive behaviors. There is a paucity of pharmacological treatments to reduce core ASD symptoms. Various lines of evidence indicate that reduced brain muscarinic cholinergic receptor activity may contribute to an ASD phenotype.

METHODS

The present experiments examined whether the partial M1 muscarinic receptor agonist, 5-(3-ethyl-1,2,4-oxadiazol-5-yl)-1,4,5,6-tetrahydropyrimidine hydrochloride (CDD-0102A), alleviates behavioral flexibility deficits and/or stereotyped motor behaviors in the BTBR mouse model of autism. Behavioral flexibility was tested using a reversal learning test. Stereotyped motor behaviors were measured by eliciting digging behavior after removal of nesting material in a home cage and by measuring repetitive grooming.

RESULTS

CDD-0102A (0.2 and 0.6 mg/kg but not 1.2 mg/kg) injected prior to reversal learning attenuated a deficit in BTBR mice but did not affect performance in B6 mice. Acute CDD-0102A treatment (1.2 and 3 mg/kg) reduced self-grooming in BTBR mice and reduced digging behavior in B6 and BTBR mice. The M1 muscarinic receptor antagonist VU0255035 (3 mg/kg) blocked the effect of CDD-0102A on grooming behavior. Chronic treatment with CDD-0102A (1.2 mg/kg) attenuated self-grooming and digging behavior in BTBR mice. Direct CDD-0102A infusions (1 µg) into the dorsal striatum reduced elevated digging behavior in BTBR mice. In contrast, CDD-0102A injections in the frontal cortex were not effective.

CONCLUSIONS

The results suggest that treatment with a partial M1 muscarinic receptor agonist may reduce repetitive behaviors and restricted interests in autism in part by stimulating striatal M1 muscarinic receptors.

μ-Opioid Receptor (Oprm1) Copy Number Influences Nucleus Accumbens Microcircuitry and Reciprocal Social Behaviors

The μ-opioid receptor regulates reward derived from both drug use and natural experiences, including social interaction, through actions in the nucleus accumbens. Here, we studied nucleus accumbens microcircuitry and social behavior in male and female mice with heterozygous genetic knockout of the μ-opioid receptor (Oprm1+/-). This genetic condition models the partial reduction of μ-opioid receptor signaling reported in several neuropsychiatric disorders. We first analyzed inhibitory synapses in the nucleus accumbens, using methods that differentiate between medium spiny neurons (MSNs) expressing the D1 or D2 dopamine receptor. Inhibitory synaptic transmission was increased in D2-MSNs of male mutants, but not female mutants, while the expression of gephyrin mRNA and the density of inhibitory synaptic puncta at the cell body of D2-MSNs was increased in mutants of both sexes. Some of these changes were more robust in Oprm1+/- mutants than Oprm1-/- mutants, demonstrating that partial reductions of μ-opioid signaling can have large effects. At the behavioral level, social conditioned place preference and reciprocal social interaction were diminished in Oprm1+/- and Oprm1-/- mutants of both sexes. Interaction with Oprm1 mutants also altered the social behavior of wild-type test partners. We corroborated this latter result using a social preference task, in which wild-type mice preferred interactions with another typical mouse over Oprm1 mutants. Surprisingly, Oprm1-/- mice preferred interactions with other Oprm1-/- mutants, although these interactions did not produce a conditioned place preference. Our results support a role for partial dysregulation of μ-opioid signaling in social deficits associated with neuropsychiatric conditions.SIGNIFICANCE STATEMENT Activation of the μ-opioid receptor plays a key role in the expression of normal social behaviors. In this study, we examined brain function and social behavior of female and male mice, with either partial or complete genetic deletion of μ-opioid receptor expression. We observed abnormal social behavior following both genetic manipulations, as well as changes in the structure and function of synaptic input to a specific population of neurons in the nucleus accumbens, which is an important brain region for social behavior. Synaptic changes were most robust when μ-opioid receptor expression was only partially lost, indicating that small reductions in μ-opioid receptor signaling can have a large impact on brain function and behavior.

Criss-crossing autism spectrum disorder and adult neurogenesis

Autism spectrum disorder (ASD) comprises a group of multifactorial neurodevelopmental disorders primarily characterized by deficits in social interaction and repetitive behavior. Although the onset is typically in early childhood, ASD poses a lifelong challenge for both patients and caretakers. Adult neurogenesis (AN) is the process by which new functional neurons are created from neural stem cells existing in the post-natal brain. The entire event is based on a sequence of cellular processes, such as proliferation, specification of cell fate, maturation, and ultimately, synaptic integration into the existing neural circuits. Hence, AN is implicated in structural and functional brain plasticity throughout life. Accumulating evidence shows that impaired AN may underlie some of the abnormal behavioral phenotypes seen in ASD. In this review, we approach the interconnections between the molecular pathways related to AN and ASD. We also discuss existing therapeutic approaches targeting such pathways both in preclinical and clinical studies. A deeper understanding of how ASD and AN reciprocally affect one another could reveal important converging pathways leading to the emergence of psychiatric disorders.

Sex-specific behavioral and structural alterations caused by early-life stress in C57BL/6 and BTBR mice

Lately, the development of various mental illnesses, such as depression, personality disorders, and autism spectrum disorders, is often associated with traumatic events in childhood. Nonetheless, the mechanism giving rise to this predisposition is still unknown. Because the development of a disease often depends on a combination of a genetic background and environment, we decided to evaluate the effect of early-life stress on BTBR mice, which have behavioral, neuroanatomical, and physiological features of autism spectrum disorders. As early-life stress, we used prolonged separation of pups from their mothers in the first 2 weeks of life (3 h once a day). We assessed effects of the early-life stress on juvenile (postnatal day 23) and adolescent (postnatal days 37-38) male and female mice of strains C57BL/6 (B6) and BTBR. We found that in both strains, the early-life stress did not lead to changes in the level of social behavior, which is an important characteristic of autism-related behavior. Nonetheless, the early-life stress resulted in increased locomotor activity in juvenile BTBR mice. In adolescent mice, the stress early in life caused a low level of anxiety in B6 males and BTBR females and increased exploratory activity in adolescent BTBR males and females. In addition, adolescent B6 male and female mice with a history of the early-life stress tended to have a thinner motor cortex as assessed by magnetic resonance imaging. As compared to B6 mice, BTBR mice showed reduced levels of social behavior and exploratory activity but their level of locomotor activity was higher. BTBR mice had smaller whole-brain, cortical, and dorsal hippocampal volumes; decreased motor cortex thickness; and increased ventral-hippocampus volume as compared to B6 mice, and these parameters correlated with the level of exploratory behavior of BTBR mice. Overall, the effects of early postnatal stress are sex- and strain-dependent.

Curcumin Potentiates α7 Nicotinic Acetylcholine Receptors and Alleviates Autistic-Like Social Deficits and Brain Oxidative Stress Status in Mice

Autistic spectrum disorder (ASD) refers to a group of neurodevelopmental disorders characterized by impaired social interaction and cognitive deficit, restricted repetitive behaviors, altered immune responses, and imbalanced oxidative stress status. In recent years, there has been a growing interest in studying the role of nicotinic acetylcholine receptors (nAChRs), specifically α7-nAChRs, in the CNS. Influence of agonists for α7-nAChRs on the cognitive behavior, learning, and memory formation has been demonstrated in neuro-pathological condition such as ASD and attention-deficit hyperactivity disorder (ADHD). Curcumin (CUR), the active compound of the spice turmeric, has been shown to act as a positive allosteric modulator of α7-nAChRs. Here we hypothesize that CUR, acting through α7-nAChRs, influences the neuropathology of ASD. In patch clamp studies, fast inward currents activated by choline, a selective agonist of α7-nAChRs, were significantly potentiated by CUR. Moreover, choline induced enhancement of spontaneous inhibitory postsynaptic currents was markedly increased in the presence of CUR. Furthermore, CUR (25, 50, and 100 mg/kg, i.p.) ameliorated dose-dependent social deficits without affecting locomotor activity or anxiety-like behaviors of tested male Black and Tan BRachyury (BTBR) mice. In addition, CUR (50 and 100 mg/kg, i.p.) mitigated oxidative stress status by restoring the decreased levels of superoxide dismutase (SOD) and catalase (CAT) in the hippocampus and the cerebellum of treated mice. Collectively, the observed results indicate that CUR potentiates α7-nAChRs in native central nervous system neurons, mitigates disturbed oxidative stress, and alleviates ASD-like features in BTBR mice used as an idiopathic rodent model of ASD, and may represent a promising novel pharmacological strategy for ASD treatment.

Altered responsiveness to pups in virgin female mice of the BTBR strain: Insights from pattern of c-Fos expression in brain regions involved in maternal behavior

BTBR is an inbred mouse strain that displays several behavioral alterations resembling the core symptoms of Autism Spectrum Disorder, including deficit in sociability. In the present study, we investigated whether the pup-induced maternal behavior in virgin female mice, a naturally rewarding behavior, is impaired in this strain similarly to social interaction with adult conspecifics. We firstly assessed the maternal responsiveness towards newly born pups expressed by either virgin female mice of the BTBR strain or of the normo-social B6 strain. Next, we examined in both strains the expression of c-Fos as a marker of neuronal activity in selected brain areas involved in the regulation of maternal behavior in rodents including the olfactory bulb, the medial preoptic area and the paraventricular nucleus (PVN). We also examined the effects of pup presentation on oxytocinergic neurons of the PVN, the major brain site of synthesis of oxytocin, which has a pivotal role in facilitation of maternal response and social responsiveness in general. As a final step, we assessed the c-Fos expression pattern comparing the effect of exposure to pups with that induced by exposure to another social stimulus, focusing on other areas implicated in maternal responsiveness as well as in the affective component of social behavior such as pyriform cortex and central and basolateral amygdala. Our data showed that BTBR virgin females are less responsive to presentation of pups in comparison to B6, in parallel with lower activation of brain areas implicated in the maternal and social responsiveness.

Oxytocin and 'social hyperthermia': Interaction with β3-adrenergic receptor-mediated thermogenesis and significance for the expression of social behavior in male and female mice

Oxytocin (OT) is a critical regulator of multiple facets of energy homeostasis, including brown adipose tissue (BAT) thermogenesis. Nevertheless, it is unclear what, if any, consequence the thermoregulatory and metabolic effects of OT have for the display of social behavior in adult rodents. Here, we examine the contribution of the OT receptor (OTR) and β₃ adrenergic receptor (β₃AR) to the increase in body temperature that typically accompanies social interaction (i.e., social hyperthermia; SH) and whether SH relates to the expression of social behavior in adult mice. Specifically, we examined how OTR antagonism via peripheral injection of L-368,899 (10 mg/kg) affects the expression of social behavior in C57BL/6J mice, in the presence of active/agonized versus antagonized β₃AR, the receptor known to mediate stress-induced BAT thermogenesis. After drug treatment and a 30 min delay, mice were provided a 10 min social interaction test with an unfamiliar, same-sex conspecific. We hypothesized that OTR and β₃AR/BAT interact to influence behavior during social interaction, with at least some effects of OT on social behavior dependent upon OT's thermal effects via β₃AR/BAT. We found that OTR-mediated temperature elevation is largely responsible for SH during social interaction in mice-albeit not substantially via β₃AR-dependent BAT thermogenesis. Further, our results reveal a complex relationship between OTR, β₃AR, social hyperthermia and the display of specific social behaviors, with SH most closely associated with anxiety and/or vigilance-related behaviors-that is, behaviors that antagonize or interfere with the initiation of close, non-agonistic social behavior.

Folic Acid Fortification Prevents Morphological and Behavioral Consequences of X-Ray Exposure During Neurulation

Previous studies suggested a causal link between pre-natal exposure to ionizing radiation and birth defects such as microphthalmos and exencephaly. In mice, these defects arise primarily after high-dose X-irradiation during early neurulation. However, the impact of sublethal (low) X-ray doses during this early developmental time window on adult behavior and morphology of central nervous system structures is not known. In addition, the efficacy of folic acid (FA) in preventing radiation-induced birth defects and persistent radiation-induced anomalies has remained unexplored. To assess the efficacy of FA in preventing radiation-induced defects, pregnant C57BL6/J mice were X-irradiated at embryonic day (E)7.5 and were fed FA-fortified food. FA partially prevented radiation-induced (1.0 Gy) anophthalmos, exencephaly and gastroschisis at E18, and reduced the number of pre-natal deaths, fetal weight loss and defects in the cervical vertebrae resulting from irradiation. Furthermore, FA food fortification counteracted radiation-induced impairments in vision and olfaction, which were evidenced after exposure to doses ≥0.1 Gy. These findings coincided with the observation of a reduction in thickness of the retinal ganglion cell and nerve fiber layer, and a decreased axial length of the eye following exposure to 0.5 Gy. Finally, MRI studies revealed a volumetric decrease of the hippocampus, striatum, thalamus, midbrain and pons following 0.5 Gy irradiation, which could be partially ameliorated after FA food fortification. Altogether, our study is the first to offer detailed insights into the long-term consequences of X-ray exposure during neurulation, and supports the use of FA as a radioprotectant and antiteratogen to counter the detrimental effects of X-ray exposure during this crucial period of gestation.

Genetic Differences in Dorsal Hippocampus Acetylcholinesterase Activity Predict Contextual Fear Learning Across Inbred Mouse Strains

Learning is a critical behavioral process that is influenced by many neurobiological systems. We and others have reported that acetylcholinergic signaling plays a vital role in learning capabilities, and it is especially important for contextual fear learning. Since cholinergic signaling is affected by genetic background, we examined the genetic relationship between activity levels of acetylcholinesterase (AChE), the primary enzyme involved in the acetylcholine metabolism, and learning using a panel of 20 inbred mouse strains. We measured conditioned fear behavior and AChE activity in the dorsal hippocampus, ventral hippocampus, and cerebellum. Acetylcholinesterase activity varied among inbred mouse strains in all three brain regions, and there were significant inter-strain differences in contextual and cued fear conditioning. There was an inverse correlation between fear conditioning outcomes and AChE levels in the dorsal hippocampus. In contrast, the ventral hippocampus and cerebellum AChE levels were not correlated with fear conditioning outcomes. These findings strengthen the link between acetylcholine activity in the dorsal hippocampus and learning, and they also support the premise that the dorsal hippocampus and ventral hippocampus are functionally discrete.

The Role of Nicotinic Receptors in the Attenuation of Autism-Related Behaviors in a Murine BTBR T + tf/J Autistic Model

Nicotinic receptors are distributed throughout the central and peripheral nervous system. Postmortem studies have reported that some nicotinic receptor subtypes are altered in the brains of autistic people. Recent studies have demonstrated the importance of nicotinic acetylcholine receptors (nAChRs) in the autistic behavior of BTBR T + tf/J mouse model of autism. This study was undertaken to examine the behavioral effects of targeted nAChRs using pharmacological ligands, including nicotine and mecamylamine in BTBR T + tf/J and C57BL/6J mice in a panel of behavioral tests relating to autism. These behavioral tests included the three-chamber social interaction, self-grooming, marble burying, locomotor activity, and rotarod test. We examined the effect of various oral doses of nicotine (50, 100, and 400 mcg/mL; po) over a period of 2 weeks in BTBR T + tf/J mouse model. The results indicated that the chronic administration of nicotine modulated sociability and repetitive behavior in BTBR T + tf/J mice while no effects observed in C57BL/6J mice. Furthermore, the nonselective nAChR antagonist, mecamylamine, reversed nicotine effects on sociability and increased repetitive behaviors in BTBR T + tf/J mice. Overall, the findings indicate that the pharmacological modulation of nicotinic receptors is involved in modulating core behavioral phenotypes in the BTBR T + tf/J mouse model. LAY SUMMARY: The involvement of brain nicotinic neurotransmission system plays a crucial role in regulating autism-related behavioral features. In addition, the brain of the autistic-like mouse model has a low acetylcholine level. Here, we report that nicotine, at certain doses, improved sociability and reduced repetitive behaviors in a mouse model of autism, implicating the potential therapeutic values of a pharmacological intervention targeting nicotinic receptors for autism therapy. Autism Res 2020, 13: 1311-1334. © 2020 International Society for Autism Research, Wiley Periodicals, Inc.

P-cresol Alters Brain Dopamine Metabolism and Exacerbates Autism-Like Behaviors in the BTBR Mouse

Background: Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder characterized by deficits in social interaction/communication, stereotypic behaviors, restricted interests, and abnormal sensory-processing. Several studies have reported significantly elevated urinary and foecal levels of p-cresol in ASD children, an aromatic compound either of environmental origin or produced by specific gut bacterial strains. Methods: Since p-cresol is a known uremic toxin, able to negatively affect multiple brain functions, the present study was undertaken to assess the effects of a single acute injection of low- or high-dose (1 or 10 mg/kg i.v. respectively) of p-cresol in behavioral and neurochemical phenotypes of BTBR mice, a reliable animal model of human ASD. Results: P-cresol significantly increased anxiety-like behaviors and hyperactivity in the open field, in addition to producing stereotypic behaviors and loss of social preference in BTBR mice. Tissue levels of monoaminergic neurotransmitters and their metabolites unveiled significantly activated dopamine turnover in amygdala as well as in dorsal and ventral striatum after p-cresol administration; no effect was recorded in medial-prefrontal cortex and hippocampus. Conclusion: Our study supports a gene x environment interaction model, whereby p-cresol, acting upon a susceptible genetic background, can acutely induce autism-like behaviors and produce abnormal dopamine metabolism in the reward circuitry.

3Rs-based optimization of mice behavioral testing: The habituation/dishabituation olfactory test

BACKGROUND

There is clear evidence that most of the paradigms that are used in the field of behavioral neuroscience suffer from a lack of reliability mainly because of oversimplification of both testing procedures and interpretations. In the present study we show how an already existing behavioral test, the olfactory habituation / dishabituation task, can be optimized in such a way that animal number and animal distress could be minimized, number/confidence of behavioral outcomes and number of explored behavioral dimensions could be increased.

NEW METHOD

We used ethologically relevant technical and procedural changes associated with videotracking-based automated quantification of sniffing behavior to validate our new setup. Mainly internal and construct validity were challenged through the implementation of a series of simple experiments.

RESULTS

We show that the new version of the test: 1) has very good within and inter laboratory replicability, 2) is sensitive to some environmental / experimental factors while insensitive to others, 3) allows investigating hedonism, both state and trait anxiety, efficacy of anxiolytic molecules, acute stress, mental retardation-related social impairments and learning and memory. 4) We also show that interest for both nonsocial and social odors is stable over time which makes repetitive testing possible.

CONCLUSIONS

This work paves the way for future studies showing how behavioral tests / procedures may be improved by using ethologically relevant changes, in order to question laboratory animals more adequately. Refining behavioral tests may considerably increase predictivity of preclinical tests and, ultimately, help reinforcing translational research.

Inbred strain preference in the BTBR T+ Itpr3tf /J mouse model of autism spectrum disorder: Does the stranger mouse matter in social approach?

BTBR T⁺ Itpr3^tf /J (BTBR) mice have been used as a model of autism spectrum disorder (ASD) due to their low levels of sociability and high levels of repetitive grooming. These experiments explored social behavior in the BTBR and C57BL/6J mice using variations of the three-chambered social approach test. In the first test, the subject mice had a choice between a stranger mouse of the same strain or from a strain with a different level of sociability. The BTBR male mice demonstrated a strong preference for the more social C57BL/6J stranger mouse, as did the C57BL/6J male mice, although more moderately with sniff time only. The C57BL/6J female mice showed a moderate preference, sniff time only, for the BTBR stranger mouse, whereas the BTBR female mice did not show a preference. The second experiment examined whether the subject mouse preferred a stranger mouse or bedding from the stranger mouse home cage. Male BTBR mice always preferred bedding, whereas the C57BL/6J male mice did not show a preference. Both BTBR and C57BL/6J female mice preferred bedding when the stranger mouse was a different strain but not when the stranger mouse was the same strain. Therefore, the stranger mouse strain seems to influence the preference of the female mice more than the male mice. The mice preferred spending time in the chamber with the social smell but not the actual stranger mouse although not always significantly. This suggests that contact with a stranger mouse is more stressful or anxiety provoking than the smell. Autism Res 2019, 12: 1184-1191. © 2019 International Society for Autism Research, Wiley Periodicals, Inc. LAY SUMMARY: BTBR T⁺ Itpr3^tf /J (BTBR) mice have been used as a model of autism spectrum disorder (ASD) due to their low levels of sociability and high levels of repetitive grooming. These experiments explored social behavior in the BTBR and C57BL/6J mice using variations of the three-chambered social approach test. These experiments examined how the sociability level of the stranger mouse affected the subject mouse's preference and if social odor was preferable to a social situation in the BTBR mice. The BTBR male mice demonstrated a strong preference for the more social C57BL/6J stranger mouse, as did the C57BL/6J male mice. The C57BL/6J female mice showed a moderate preference for the BTBR stranger mouse, whereas the BTBR female mice did not show a preference for either stranger mouse. The second modification let the subject mouse have a choice between a stranger mouse or bedding. Male BTBR mice preferred bedding, regardless of the strain of the stranger mouse, whereas the C57BL/6J male mice did not show a preference. Both BTBR and C57BL/6J female mice preferred bedding when the stranger mouse was a different strain but showed no preference when the stranger mouse was from the same strain. The stranger mouse strain seems to influence the female mice more. Male BTBR mice preferred spending time in the chamber with the social smell but not the actual mouse, suggesting that actual contact with a stranger mouse is more stressful or anxiety provoking.

Characterization of behavioral phenotypes in the BTBR T+ Itpr3tf/J mouse model of autism spectrum disorder under social housing conditions using the multiple animal positioning system

The BTBR T⁺ Itpr3^tf/J (BTBR) mouse strain is a widely used model of autism spectrum disorder (ASD). The BTBR mice display behavior consistent with the three diagnostic categories of ASD. However, the behavioral phenotypes of the BTBR mice in a long-term group housing setting are largely unknown because conventional behavioral tests for ASD model mice are designed for use under simplified artificial conditions over a short observation period. In this study, we applied a newly developed assay system, the Multiple Animal Positioning System (MAPS), to quantify behaviors under group housing conditions over four days of continuous observation. Using MAPS, we showed that in a group housing condition, the BTBR mice exhibited lower activity levels in the dark phase and alteration of social behavior in comparison with the C57BL/6J mice. The phenotypes of the BTBR mice were affected by co-housing with the C57BL/6J mice for four days, but the influence was weak and limited. Our results by MAPS differ from those obtained using conventional behavioral tests. The present study demonstrated that MAPS would be useful for evaluating the usual/natural behaviors of various animal models in detail and under more ethological conditions.

Age-related changes in social behaviours in the 5xFAD mouse model of Alzheimer's disease

In addition to memory impairments, patients with Alzheimer's disease (AD) exhibit a number of behavioural and psychological symptoms that can affect social interactions over the course of the disease. While altered social interactions have been demonstrated in a number of mouse models of AD, many models only recapitulate the initial stages of the disease, and these behavioural changes have yet to be examined over the course of disease progression. By performing a longitudinal study using the 5xFAD mouse model, we have demonstrated that transgenic females exhibit progressive alterations in social investigation compared to wild-type controls. Transgenic females exhibited an age-related reduction in interest for social odours, as well as reduced investigative behaviours towards novel conspecifics in a novel environment. However, transgenic mice exhibited no obvious olfactory deficits, nor any changes in scent-marking behaviour compared to wild-type controls, indicating that changes in investigative behaviour were due to motivation to engage with a social stimulus. This evidence suggests that transgenic 5xFAD females exhibit increased social anxiety in novel environments compared to wild-type controls. Overall, transgenic 5xFAD female mice mimic some features of social withdrawal observed in human AD patients suggesting this strain may be suitable for modelling aspects of the social dysfunction observed in human patients.

Sex-specific Behavioral Features of Rodent Models of Autism Spectrum Disorder

Sex is an important factor in understanding the clinical presentation, management, and developmental trajectory of children with neuropsychiatric disorders. While much is known about the clinical and neurobehavioral profiles of males with neuropsychiatric disorders, surprisingly little is known about females in this respect. Animal models may provide detailed mechanistic information about sex differences in autism spectrum disorder (ASD) in terms of manifestation, disease progression, and development of therapeutic options. This review aims to widen our understanding of the role of sex in autism spectrum disorder, by summarizing and comparing behavioral characteristics of animal models. Our current understanding of how differences emerge in boys and girls with neuropsychiatric disorders is limited: Information derived from animal studies will stimulate future research on the role of biological maturation rates, sex hormones, sex-selective protective (or aggravating) factors and psychosocial factors, which are essential to devise sex precision medicine and to improve diagnostic accuracy. Moreover, there is a strong need of novel strategies to elucidate the major mechanisms leading to sex-specific autism features, as well as novel models or methods to examine these sex differences.

MPS-IIIA mice acquire autistic behaviours with age

Mucopolysaccharidosis (MPS) type IIIA is an inherited, neurodegenerative lysosomal storage disorder resulting from mutations in the SGSH gene. Consequently, N-sulphoglucosamine sulphohydrolase enzyme activity is reduced resulting in impaired catabolism of heparan sulphate. After an asymptomatic period, patients typically show a progressive loss of cognitive and motor skills, with death often during the second decade of life. The diagnostic criteria of autism spectrum disorders (ASD) include impaired communication and social interactions, as well as displays of repetitive behaviours and fixed interests. Children with MPS-IIIA have been shown to exhibit decreased social communicative behaviours from approximately 3-4 years of age but behavioural stereotypies are mostly absent. In this study, we investigated whether a mouse model of MPS-IIIA exhibited ASD-like symptoms. The BTBR T⁺Itpr3^tf/J inbred mouse model of autism was used as a positive control. Male MPS-IIIA and BTBR mice were less sociable compared with unaffected C57BL/6 male mice in the reciprocal social approach test administered at 20 weeks of age. Alternations in the frequency of social interactions was not evident at earlier stages of the disease course, suggesting an acquisition of ASD-like social behaviours. Stereotypical behaviours were not evident in male MPS-IIIA mice in the marble-burying test nor was the quality of nest constructed by mice affected. Collectively, these data suggest that MPS-IIIA mice acquire autistic social behaviours similar to the human condition, and thus they may be useful for elucidating symptom generating mechanisms and novel treatments for ASD.

Several behavioral traits relevant for alcoholism are controlled by ɣ2 subunit containing GABAA receptors on dopamine neurons in mice

The risk factors for developing alcohol addiction include impulsivity, high sensitivity to the rewarding action of ethanol, and low sensitivity to its sedative and intoxicating effects. Genetic variation in GABA_A receptor subunits, including the ɣ2 subunit (Gabrg2), affects the risk for developing alcoholism. Alcohol directly potentiates GABA_A receptors and activates the mesolimbic dopamine system. Here, we deleted Gabrg2 selectively in dopamine cells of adult mice. The deletion resulted in elevated firing of dopamine neurons and made them less sensitive to drugs acting at GABA_A receptors. At the behavioral level, the deletion increased exploratory behavior and augmented both correct and incorrect responding in the go/no-go task, a test often used to assay the response inhibition component of impulsivity. In addition, conditioned place preference to alcohol, but not to cocaine or morphine, was increased. Ethanol-induced locomotor activation was enhanced in the mice lacking Gabrg2 on dopaminergic cells, whereas the sedative effect of alcohol was reduced. Finally, the alcohol drinking, but not the alcohol preference, at a high concentration was increased in the mutant mice. In summary, deletion of Gabrg2 on dopamine cells induced several behavioral traits associated with high risk of developing alcoholism. The findings suggest that mice lacking Gabrg2 on dopaminergic cells could be used as models for individuals at high risk for developing alcoholism and that GABA_A receptors on dopamine cells are protective against the development of excessive alcohol drinking.

Prenatal and early-life diesel exhaust exposure causes autism-like behavioral changes in mice

Background

Escalating prevalence of autism spectrum disorders (ASD) in recent decades has triggered increasing efforts in understanding roles played by environmental risk factors as a way to address this widespread public health concern. Several epidemiological studies show associations between developmental exposure to traffic-related air pollution and increased ASD risk. In rodent models, a limited number of studies have shown that developmental exposure to ambient ultrafine particulates or diesel exhaust (DE) can result in behavioral phenotypes consistent with mild ASD. We performed a series of experiments to determine whether developmental DE exposure induces ASD-related behaviors in mice.

Results

C57Bl/6J mice were exposed from embryonic day 0 to postnatal day 21 to 250–300 μg/m³ DE or filtered air (FA) as control. Mice exposed developmentally to DE exhibited deficits in all three of the hallmark categories of ASD behavior: reduced social interaction in the reciprocal interaction and social preference tests, increased repetitive behavior in the T-maze and marble-burying test, and reduced or altered communication as assessed by measuring isolation-induced ultrasonic vocalizations and responses to social odors.

Conclusions

These findings demonstrate that exposure to traffic-related air pollution, in particular that associated with diesel-fuel combustion, can cause ASD-related behavioral changes in mice, and raise concern about air pollution as a contributor to the onset of ASD in humans.

Electronic supplementary material

The online version of this article (10.1186/s12989-018-0254-4) contains supplementary material, which is available to authorized users.

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.

Advances in nonhuman primate models of autism: Integrating neuroscience and behavior

Given the prevalence and societal impact of autism spectrum disorders (ASD), there is an urgent need to develop innovative preventative strategies and treatments to reduce the alarming number of cases and improve core symptoms for afflicted individuals. Translational efforts between clinical and preclinical research are needed to (i) identify and evaluate putative causes of ASD, (ii) determine the underlying neurobiological mechanisms, (iii) develop and test novel therapeutic approaches and (iv) ultimately translate basic research into safe and effective clinical practices. However, modeling a uniquely human brain disorder, such as ASD, will require sophisticated animal models that capitalize on unique advantages of diverse species including drosophila, zebra fish, mice, rats, and ultimately, species more closely related to humans, such as the nonhuman primate. Here we discuss the unique contributions of the rhesus monkey (Macaca mulatta) model to ongoing efforts to understand the neurobiology of the disorder, focusing on the convergence of brain and behavior outcome measures that parallel features of human ASD.

Behavioral Phenotyping for Autism Spectrum Disorders in Mice

Autism spectrum disorder (ASD) represents a heterogeneous group of disorders characterized by alterations in three behavioral symptom domains: Social interactions, verbal and nonverbal communication, and repetitive behaviors. Increasing prevalence of ASD in recent years suggests that exposure to environmental toxicants may be critical in modulating etiology of this disease. As clinical diagnosis of autism still relies on behavioral evaluation, it is important to be able to assess similar behavioral traits in animal models, to provide biological plausibility of associations between environmental exposures and ASD. Rodents naturally exhibit a large number of behaviors that can be linked to similar behaviors in human. In this unit, behavioral tests are described that are relevant to the domains affected in ASD. For the repetitive domain, the T-maze spontaneous alternation test and marble burying test are described. For the communication domain, neonatal ultrasonic vocalization and olfactory habituation test toward social and non-social odor are described. Finally, for the sociability domain, the three-chambered social preference test and the reciprocal interaction test are presented. © 2017 by John Wiley & Sons, Inc.

Perinatal Exposure to Glufosinate Ammonium Herbicide Impairs Neurogenesis and Neuroblast Migration through Cytoskeleton Destabilization

Neurogenesis, a process of generating functional neurons from neural precursors, occurs throughout life in restricted brain regions such as the subventricular zone (SVZ). During this process, newly generated neurons migrate along the rostral migratory stream to the olfactory bulb to replace granule cells and periglomerular neurons. This neuronal migration is pivotal not only for neuronal plasticity but also for adapted olfactory based behaviors. Perturbation of this highly controlled system by exogenous chemicals has been associated with neurodevelopmental disorders. We reported recently that perinatal exposure to low dose herbicide glufosinate ammonium (GLA), leads to long lasting behavioral defects reminiscent of Autism Spectrum Disorder-like phenotype in the offspring (Laugeray et al., 2014). Herein, we demonstrate that perinatal exposure to low dose GLA induces alterations in neuroblast proliferation within the SVZ and abnormal migration from the SVZ to the olfactory bulbs. These disturbances are not only concomitant to changes in cell morphology, proliferation and apoptosis, but are also associated with transcriptomic changes. Therefore, we demonstrate for the first time that perinatal exposure to low dose GLA alters SVZ neurogenesis. Jointly with our previous work, the present results provide new evidence on the link between molecular and cellular consequences of early life exposure to the herbicide GLA and the onset of ASD-like phenotype later in life.

Absence of Prenatal Forebrain Defects in the Dp(16)1Yey/+ Mouse Model of Down Syndrome

Studies in humans with Down syndrome (DS) show that alterations in fetal brain development are followed by postnatal deficits in neuronal numbers, synaptic plasticity, and cognitive and motor function. This same progression is replicated in several mouse models of DS. Dp(16)1Yey/+ (hereafter called Dp16) is a recently developed mouse model of DS in which the entire region of mouse chromosome 16 that is homologous to human chromosome 21 has been triplicated. As such, Dp16 mice may more closely reproduce neurodevelopmental changes occurring in humans with DS. Here, we present the first comprehensive cellular and behavioral study of the Dp16 forebrain from embryonic to adult stages. Unexpectedly, our results demonstrate that Dp16 mice do not have prenatal brain defects previously reported in human fetal neocortex and in the developing forebrains of other mouse models, including microcephaly, reduced neurogenesis, and abnormal cell proliferation. Nevertheless, we found impairments in postnatal developmental milestones, fewer inhibitory forebrain neurons, and deficits in motor and cognitive performance in Dp16 mice. Therefore, although this new model does not express prenatal morphological phenotypes associated with DS, abnormalities in the postnatal period appear sufficient to produce significant cognitive deficits in Dp16.

Behavioral Phenotyping of Juvenile Long-Evans and Sprague-Dawley Rats: Implications for Preclinical Models of Autism Spectrum Disorders

The laboratory rat is emerging as an attractive preclinical animal model of autism spectrum disorder (ASD), allowing investigators to explore genetic, environmental and pharmacological manipulations in a species exhibiting complex, reciprocal social behavior. The present study was carried out to compare two commonly used strains of laboratory rats, Sprague-Dawley (SD) and Long-Evans (LE), between the ages of postnatal day (PND) 26-56 using high-throughput behavioral phenotyping tools commonly used in mouse models of ASD that we have adapted for use in rats. We detected few differences between young SD and LE strains on standard assays of exploration, sensorimotor gating, anxiety, repetitive behaviors, and learning. Both SD and LE strains also demonstrated sociability in the 3-chamber social approach test as indexed by spending more time in the social chamber with a constrained age/strain/sex matched novel partner than in an identical chamber without a partner. Pronounced differences between the two strains were, however, detected when the rats were allowed to freely interact with a novel partner in the social dyad paradigm. The SD rats in this particular testing paradigm engaged in play more frequently and for longer durations than the LE rats at both juvenile and young adult developmental time points. Results from this study that are particularly relevant for developing preclinical ASD models in rats are threefold: (i) commonly utilized strains exhibit unique patterns of social interactions, including strain-specific play behaviors, (ii) the testing environment may profoundly influence the expression of strain-specific social behavior and (iii) simple, automated measures of sociability may not capture the complexities of rat social interactions.

Prenatal exposure to the organophosphate insecticide chlorpyrifos enhances brain oxidative stress and prostaglandin E2 synthesis in a mouse model of idiopathic autism

BACKGROUND

Autism spectrum disorders (ASD) are emerging as polygenic and multifactorial disorders in which complex interactions between defective genes and early exposure to environmental stressors impact on the correct neurodevelopment and brain processes. Organophosphate insecticides, among which chlorpyrifos (CPF), are widely diffused environmental toxicants associated with neurobehavioral deficits and increased risk of ASD occurrence in children. Oxidative stress and dysregulated immune responses are implicated in both organophosphate neurodevelopmental effects and ASD etiopathogenesis. BTBR T+tf/J mice, a well-studied model of idiopathic autism, show several behavioral and immunological alterations found in ASD children, and we recently showed that CPF gestational exposure strengthened some of these autistic-like traits. In the present study, we aimed at investigating whether the behavioral effects of gestational CPF administration are associated with brain increased oxidative stress and altered lipid mediator profile.

METHODS

Brain levels of F2-isoprostanes (15-F2t-IsoP), as index of in vivo oxidative stress, and prostaglandin E2 (PGE2), a major arachidonic acid metabolite released by immune cells and by specific glutamatergic neuron populations mainly in cortex and hippocampus, were assessed by specific enzyme-immuno assays in brain homogenates from BTBR T+tf/J and C57Bl6/J mice, exposed during gestation to either vehicle or CPF. Measures were performed in mice of both sexes, at different postnatal stages (PNDs 1, 21, and 70).

RESULTS

At birth, BTBR T+tf/J mice exhibited higher baseline 15-F2t-IsoP levels as compared to C57Bl6/J mice, suggestive of greater oxidative stress processes. Gestational treatment with CPF-enhanced 15-F2t-IsoP and PGE2 levels in strain- and age-dependent manner, with 15-F2t-IsoP increased in BTBR T+tf/J mice at PNDs 1 and 21, and PGE2 elevated in BTBR T+tf/J mice at PNDs 21 and 70. At PND 21, CPF effects were sex-dependent being the increase of the two metabolites mainly associated with male mice. CPF treatment also induced a reduction of somatic growth, which reached statistical significance at PND 21.

CONCLUSIONS

These findings indicate that the autistic-like BTBR T+tf/J strain is highly vulnerable to environmental stressors during gestational period. The results further support the hypothesis that oxidative stress might be the link between environmental neurotoxicants such as CPF and ASD. The increased levels of oxidative stress during early postnatal life could result in delayed and long-lasting alterations in specific pathways relevant to ASD, of which PGE2 signaling represents an important one.

Sustained lentiviral-mediated overexpression of microRNA124a in the dentate gyrus exacerbates anxiety- and autism-like behaviors associated with neonatal isolation in rats

Autism spectrum disorders (ASD) are highly disabling psychiatric disorders. Despite a strong genetic etiology, there are no efficient therapeutic interventions that target the core symptoms of ASD. Emerging evidence suggests that dysfunction of microRNA (miR) machinery may contribute to the underlying molecular mechanisms involved in ASD. Here, we report a stress model demonstrating that neonatal isolation-induced long-lasting hippocampal elevation of miR124a was associated with reduced expression of its target BDNF mRNA. In addition, we investigated the impact of lentiviral-mediated overexpression of miR124a into the dentate gyrus (DG) on social interaction, repetitive- and anxiety-like behaviors in the neonatal isolation (Iso) model of autism. Rats isolated from the dams on PND 1 to PND 11 were assessed for their social interaction, marble burying test (MBT) and repetitive self-grooming behaviors as adults following miR124a overexpression. Also, anxiety-like behavior and locomotion were evaluated in the elevated plus maze (EPM) and open-field (OF) tests. Results show that, consistent with previously published reports, Iso rats displayed decreased social interaction contacts but increased repetitive- and anxiety-like behaviors. Interestingly, across both autism- and anxiety-like behavioral assays, miR124a overexpression in the DG significantly exacerbated repetitive behaviors, social impairments and anxiety with no effect on locomotor activity. Our novel findings attribute neonatal isolation-inducible cognitive impairments to induction of miR124a and consequently suppressed BDNF mRNA, opening venues for intercepting these miR124a-mediated damages. They also highlight the importance of studying microRNAs in the context of ASD and identify miR124a as a novel potential therapeutic target for improving mood disorders.

Longitudinal measures of cognition in the Ts65Dn mouse: Refining windows and defining modalities for therapeutic intervention in Down syndrome

Mouse models have provided insights into adult changes in learning and memory in Down syndrome, but an in-depth assessment of how these abnormalities develop over time has never been conducted. To address this shortcoming, we conducted a longitudinal behavioral study from birth until late adulthood in the Ts65Dn mouse model to measure the emergence and continuity of learning and memory deficits in individuals with a broad array of tests. Our results demonstrate for the first time that the pace at which neonatal and perinatal milestones are acquired is correlated with later cognitive performance as an adult. In addition, we find that life-long behavioral indexing stratifies mice within each genotype. Our expanded assessment reveals that diminished cognitive flexibility, as measured by reversal learning, is the most robust learning and memory impairment in both young and old Ts65Dn mice. Moreover, we find that reversal learning degrades with age and is therefore a useful biomarker for studying age-related decline in cognitive ability. Altogether, our results indicate that preclinical studies aiming to restore cognitive function in Ts65Dn should target both neonatal milestones and reversal learning in adulthood. Here we provide the quantitative framework for this type of approach.

Variability in empathic fear response among 11 inbred strains of mice

Empathy is an important emotional process that involves the ability to recognize and share emotions with others. We have previously developed an observational fear learning (OFL) behavioral assay to measure empathic fear in mice. In the OFL task, a mouse is conditioned for context-dependent fear when it observes a conspecific demonstrator receiving aversive stimuli. In the present study, by comparing 11 different inbred mouse strains that are commonly used in the laboratory, we found that empathic fear response was highly variable between different strains. Five strains--C57BL/6J, C57BL/6NTac, 129S1/SvImJ, 129S4/SvJae and BTBR T(+) Itpr3(tf) /J--showed observational fear (OF) responses, whereas AKR/J, BALB/cByJ, C3H/HeJ, DBA/2J, FVB/NJ and NOD/ShiLtJ mice exhibited low empathic fear response. Importantly, day 2 OF memory was significantly correlated with contextual memory in the classical fear conditioning among the 11 strains. Innate differences in anxiety, locomotor activity, sociability and preference for social novelty were not significantly correlated with OFL. Interestingly, early adolescent C57BL/6J mice exhibited an increase in acquisition of OF. The level of OFL in C57BL/6J strain was not affected by sex or strains of the demonstrator. Taken together, these data strongly suggest that there are naturally occurring OFL-specific genetic variations modulating empathic fear behaviors in mice. The identification of causal genes may uncover novel genetic pathways and underlying neural mechanisms that modulate empathic fear and, ultimately, provide new targets for therapeutic intervention in human mental disorders associated with impaired empathy.