A novel social proximity test suggests patterns of social avoidance and gaze aversion-like behavior in BTBR T+ tf/J mice

The BTBR mouse model of idiopathic autism - Current view on mechanisms

Autism spectrum disorder (ASD) is the most commonly diagnosed neurodevelopmental disorder, with current estimates of more than 1% of affected children across nations. The patients form a highly heterogeneous group with only the behavioral phenotype in common. The genetic heterogeneity is reflected in a plethora of animal models representing multiple mutations found in families of affected children. Despite many years of scientific effort, for the majority of cases the genetic cause remains elusive. It is therefore crucial to include well-validated models of idiopathic autism in studies searching for potential therapeutic agents. One of these models is the BTBR T⁺Itpr3^tf/J mouse. The current review summarizes data gathered in recent research on potential molecular mechanisms responsible for the autism-like behavioral phenotype of this strain.

Genetic control of social behavior: Lessons from mutant mice

Social behavior is evolutionary conserved, and is thought to be evolved since it increased reproductive and survival fitness of living species. In humans, disturbances of social behavior are a peculiar pathological trait of neurodevelopmental disorders, namely autism spectrum disorder (ASD). ASD is defined by deficits in two core domains (social interaction/communication and repetitive/restrictive behaviors), which emerge during early postnatal development. ASD has a strong genetic component: copy number variations, de novo and familial mutations, as well as epigenetic modifications have been reported in a huge number of genes. Recent studies in mice demonstrate that mutations in a wide variety of ASD-associated genes can cause neurodevelopmental defects, which subsequently result in social behavior disturbances during early postnatal age and adulthood. From these studies, it clearly emerges that functionally interrelated cellular mechanisms underlie social behavior and its disturbances in ASD. Indeed, most of ASD-associated genes control neuronal differentiation and migration, growth of neuronal connections and synaptic function. Here we will present the recent advances in understanding the genetic determinants of social behavior, as they emerge from the study of ASD mouse models, and discuss the importance of these studies for the development of novel therapeutic approaches to overcome social disturbances in ASD.

Putting the "Biology" Back into "Neurobiology": The Strength of Diversity in Animal Model Systems for Neuroscience Research

Current trends in neuroscience research have moved toward a reliance on rodent animal models to study most aspects of brain function. Such laboratory-reared animals are highly inbred, have been disengaged from their natural environments for generations and appear to be of limited predictive value for successful clinical outcomes. In this Perspective article, we argue that research on a rich diversity of animal model systems is fundamental to new discoveries in evolutionarily conserved core physiological and molecular mechanisms that are the foundation of human brain function. Analysis of neural circuits across phyla will reveal general computational solutions that form the basis for adaptive behavioral responses. Further, we stress that development of ethoexperimental approaches to improve our understanding of behavioral nuance will help to realign our research strategies with therapeutic goals and improve the translational validity of specific animal models. Finally, we suggest that neuroscience has a role in environmental conservation of habitat and fauna that will preserve and protect the ecological settings that drive species-specific behavioral adaptations. A rich biodiversity will enhance our understanding of human brain function and lead in unpredicted directions for development of therapeutic treatments for neurological disorders.

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.

A transgenic mouse expressing CHMP2Bintron5 mutant in neurons develops histological and behavioural features of amyotrophic lateral sclerosis and frontotemporal dementia

Mutations in the charged multivesicular body protein 2B (CHMP2B) are associated with frontotemporal dementia (FTD), amyotrophic lateral sclerosis (ALS), and with a mixed ALS-FTD syndrome. To model this syndrome, we generated a transgenic mouse line expressing the human CHMP2B^intron5 mutant in a neuron-specific manner. These mice developed a dose-dependent disease phenotype. A longitudinal study revealed progressive gait abnormalities, reduced muscle strength and decreased motor coordination. CHMP2B^intron5 mice died due to generalized paralysis. When paralyzed, signs of denervation were present as attested by altered electromyographic profiles, by decreased number of fully innervated neuromuscular junctions, by reduction in size of motor endplates and by a decrease of sciatic nerve axons area. However, spinal motor neurons cell bodies were preserved until death. In addition to the motor dysfunctions, CHMP2B^intron5 mice progressively developed FTD-relevant behavioural modifications such as disinhibition, stereotypies, decrease in social interactions, compulsivity and change in dietary preferences. Furthermore, neurons in the affected spinal cord and brain regions showed accumulation of p62-positive cytoplasmic inclusions associated or not with ubiquitin and CHMP2B^intron5 As observed in FTD3 patients, these inclusions were negative for TDP-43 and FUS. Moreover, astrogliosis and microgliosis developed with age. Altogether, these data indicate that the neuronal expression of human CHMP2B^intron5 in areas involved in motor and cognitive functions induces progressive motor alterations associated with dementia symptoms and with histopathological hallmarks reminiscent of both ALS and FTD.

In tribute to Bob Blanchard: Divergent behavioral phenotypes of 16p11.2 deletion mice reared in same-genotype versus mixed-genotype cages

Mouse models offer indispensable heuristic tools for studying genetic and environmental causes of neuropsychiatric disorders, including autism. Development of useful animal models of complex human behaviors depends not only on extensive knowledge of the human disease, but also on a deep understanding of animal behavior and ethology. Robert and Caroline Blanchard pioneered a number of elegant social paradigms in rodents. Their early work led to systematic delineations of rodent naturalist defensive behaviors,which were proven to be highly useful models of human psychiatric disorders, including fear and anxiety. Their work using the Visible Burrow System to study social stress in rats represented an unprecedented approach to study biological mechanisms of depression. In recent years, their extensive knowledge of mouse behavior and ethology enabled them to quickly become leading figures in the field of behavioral genetics of autism. To commemorate Robert Blanchard's influences on animal models of human psychiatric disorders, here we describe a study conceptualized and led by Mu Yang who was trained as a graduate student in the Blanchard laboratory in the early 2000s. This investigation focuses on social housing in a genetic mouse model of 16p11.2 deletion syndrome. Heterozygous deletions and duplications of a segment containing about 29 genes on human chromosome 16 appear in approximately 0.5–1% of all cases of autism. 16p11.2 deletion syndrome is also associated with intellectual disabilities and speech impairments. Our previous studies showed that a mouse model of 16p11.2 deletion syndrome exhibited deficits in vocalizations and novel object recognition, as compared to wildtype littermate control cagemates. In the spirit of Bob Blanchard's careful attention to the role of social dominance in rodent behaviors, we became interested in the question of whether behavioral outcomes of a mutation differ when mutants are housed in mixed genotype cages, versus housing only mutants together in one group cage, and only wildtype littermates together in another group cage after weaning. 16p11.2 deletion presented a particularly good model organism to investigate this question, because the heterozygotes are smaller than their wildtype littermates, and may therefore become subordinate to their larger cagemates.Wildtype and heterozygotes were housed with cagemates of the same genotype (same-genotype cage) or with cagemates of the opposite genotype (mixed-genotype cage). Current results replicated social vocalization and object recognition deficits that we previously found in heterozygotes living in mixed-genotype cages. In contrast, heterozygotes that lived in same-genotype cages emitted normal numbers of vocalizations during male–female interactions, and displayed normal novel object recognition, indicating that the deletion per se was not sufficient to cause cognitive or social deficits. Social approach, same-sex social interaction, anxiety-related behavior, depression-related behavior, and open field exploration were not different between genotypes, and were not affected by housing in mixed versus in same-genotype cages. These findings suggest that elements of the home cage social environment could interact with genotype to impact aspects of disease phenotypes. Current findings are discussed as potentially reflecting behavioral deficits resulted from social stress, as inspired by a seminal paper by Bob and Caroline Blanchard [1].

Applying the ethoexperimental approach to neurodevelopmental syndrome research reveals exaggerated defensive behavior in Mecp2 mutant mice

Rett syndrome is a Pervasive Developmental Disorder (PDD) associated with de novo mutations of the methyl CpG-binding protein 2 (MECP2) gene. Mecp2 functions as a transcription factor that regulates the expression of hundreds of genes. Identification of the role of Mecp2 in specific neurodevelopmental symptoms remains an important research aim. We previously demonstrated that male mice possessing a truncation mutation in Mecp2 are hyper-social. We predicted that reduced fear or anxiety might underlie this enhanced affiliation. In order to probe risk assessment and anxiety-like behavior, we compared Mecp2 truncation mutants to their wild-type littermates in the elevated plus maze and elevated zero maze. Additionally, subjects were administered the mouse defense test battery to evaluate unconditioned fear- and panic-like behavior to a graded set of threat scenarios and a predator stimulus. Mutant mice showed no significant changes in anxiety-like behavior. Yet, they displayed hyper-reactive escape and defensive behaviors to an animate predatory threat stimulus. Notably, mutant mice engaged in exaggerated active defense responding to threat stimuli at nearly all phases of the fear battery. These results reveal abnormalities in emotion regulation in Mecp2 mutants particularly in response to ecologically relevant threats. This hyper-responsivity suggests that transcriptional targets of Mecp2 are critical to emotion regulation. Moreover, we suggest that detailed analysis of defensive behavior and aggression with ethologically relevant tasks provides an avenue to interrogate gene-behavior mechanisms of neurodevelopmental and other psychiatric conditions.

Nuance and behavioral cogency: How the Visible Burrow System inspired the Stress-Alternatives Model and conceptualization of the continuum of anxiety

By creating the Visible Burrow System (VBS) Bob Blanchard found a way to study the interaction of genetics, physiology, environment, and adaptive significance in a model with broad validity. The VBS changed the way we think about anxiety and affective disorders by allowing the mechanisms which control them to be observed in a dynamic setting. Critically, Blanchard used the VBS and other models to show how behavioral systems like defense are dependent upon context and behavioral elements unique to the individual. Inspired by the VBS, we developed a Stress Alternatives Model (SAM) to further explore the multifaceted dynamics of the stress response with a dichotomous choice condition. Like the VBS, the SAM is a naturalistic model built upon risk assessment and defensive behavior, but with a choice of response: escape or submission to a large conspecific aggressor. The anxiety of novelty during the first escape must be weighed against fear of the aggressor, and a decision must be made. Both outcomes are adaptively significant, evidenced by a 50/50 split in outcome across several study systems. By manipulating the variables of the SAM, we show that a gradient of anxiety exists that spans the contextual settings of escaping an open field, escaping from aggression, and submitting to aggression. These findings correspond with increasing levels of corticosterone and increasing levels of NPS and BDNF in the central amygdala as the context changes.Whereas some anxiolytics were able to reduce the latency to escape for some animals, only with the potent anxiolytic drug antalarmin (CRF1R-blocker) and the anxiogenic drug yohimbine (α2 antagonist) were we able to reverse the outcome for a substantial proportion of individuals. Our findings promote a novel method for modeling anxiety, offering a distinction between low-and-high levels, and accounting for individual variability. The translational value of the VBS is immeasurable, and it guided us and many other researchers to seek potential clinical solutions through a deeper understanding of regional neurochemistry and gene expression in concert with an ecological behavioral model.

α5GABAA receptor deficiency causes autism-like behaviors

The prevalence of autism spectrum disorders (ASDs), which affect over 1% of the population, has increased twofold in recent years. Reduced expression of GABA_A receptors has been observed in postmortem brain tissue and neuroimaging of individuals with ASDs. We found that deletion of the gene for the α5 subunit of the GABA_A receptor caused robust autism‐like behaviors in mice, including reduced social contacts and vocalizations. Screening of human exome sequencing data from 396 ASD subjects revealed potential missense mutations in GABRA5 and in RDX, the gene for the α5GABA_A receptor‐anchoring protein radixin, further supporting a α5GABA_A receptor deficiency in ASDs.

Dietary docosahexaenoic acid alleviates autistic-like behaviors resulting from maternal immune activation in mice

The prevalence of autism spectrum disorders over the last several decades has risen at an alarming rate. Factors such as broadened clinical definitions and increased parental age only partially account for this precipitous increase, suggesting that recent changes in environmental factors may also be responsible. One such factor could be the dramatic decrease in consumption of anti-inflammatory dietary omega-3 (n-3) polyunsaturated fatty acids (PUFAs) relative to the amount of pro-inflammatory omega-6 (n-6) PUFAs and saturated fats in the Western diet. Docosahexaenoic acid (DHA) is the principle n-3 PUFA found in neural tissue and is important for optimal brain development, especially during late gestation when DHA rapidly and preferentially accumulates in the brain. In this study, we tested whether supplementation of a low n-3 PUFA diet with DHA throughout development could improve measures related to autism in a mouse model of maternal immune activation. We found that dietary DHA protected offspring from the deleterious effects of gestational exposure to the viral mimetic polyriboinosinic-polyribocytidilic acid on behavioral measures of autism and subsequent adulthood immune system reactivity. These data suggest that elevated dietary levels of DHA, especially during pregnancy and nursing, may help protect normal neurodevelopment from the potentially adverse consequences of environmental insults like maternal infection.

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.

Hippocampal Transcriptomic and Proteomic Alterations in the BTBR Mouse Model of Autism Spectrum Disorder

Autism spectrum disorders (ASD) are complex heterogeneous neurodevelopmental disorders of an unclear etiology, and no cure currently exists. Prior studies have demonstrated that the black and tan, brachyury (BTBR) T+ Itpr3tf/J mouse strain displays a behavioral phenotype with ASD-like features. BTBR T+ Itpr3tf/J mice (referred to simply as BTBR) display deficits in social functioning, lack of communication ability, and engagement in stereotyped behavior. Despite extensive behavioral phenotypic characterization, little is known about the genes and proteins responsible for the presentation of the ASD-like phenotype in the BTBR mouse model. In this study, we employed bioinformatics techniques to gain a wide-scale understanding of the transcriptomic and proteomic changes associated with the ASD-like phenotype in BTBR mice. We found a number of genes and proteins to be significantly altered in BTBR mice compared to C57BL/6J (B6) control mice controls such as BDNF, Shank3, and ERK1, which are highly relevant to prior investigations of ASD. Furthermore, we identified distinct functional pathways altered in BTBR mice compared to B6 controls that have been previously shown to be altered in both mouse models of ASD, some human clinical populations, and have been suggested as a possible etiological mechanism of ASD, including “axon guidance” and “regulation of actin cytoskeleton.” In addition, our wide-scale bioinformatics approach also discovered several previously unidentified genes and proteins associated with the ASD phenotype in BTBR mice, such as Caskin1, suggesting that bioinformatics could be an avenue by which novel therapeutic targets for ASD are uncovered. As a result, we believe that informed use of synergistic bioinformatics applications represents an invaluable tool for elucidating the etiology of complex disorders like ASD.

Neuronal correlates of asocial behavior in a BTBR T (+) Itpr3(tf)/J mouse model of autism

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized, in part, by an inability to adequately respond to social cues. Patients diagnosed with ASD are often devoid of empathy and impaired in understanding other people's emotional perspective. The neuronal correlates of this impairment are not fully understood. Replicating such a behavioral phenotype in a mouse model of autism would allow us insight into the neuronal background of the problem. Here we tested BTBR T(+)Itpr3(tf)/J (BTBR) and c57BL/6J (B6) mice in two behavioral paradigms: the Transfer of Emotional Information test and the Social Proximity test. In both tests BTBR mice displayed asocial behavior. We analyzed c-Fos protein expression in several brain regions after each of these tests, and found that, unlike B6 mice, BTBR mice react to a stressed cagemate exposure in the Transfer of Emotional Information test with no increase of c-Fos expression in either the prefrontal cortex or the amygdala. However, after Social Proximity exposure we observed a strong increase in c-Fos expression in the CA3 field of the hippocampus and two hypothalamic regions of BTBR brains. This response was accompanied by a strong activation of periaqueductal regions related to defensiveness, which suggests that BTBR mice find unavoidable social interaction highly aversive.

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.

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.

An open-source toolbox for automated phenotyping of mice in behavioral tasks

Classifying behavior patterns in mouse models of neurological, psychiatric and neurodevelopmental disorders is critical for understanding disease causality and treatment. However, complete characterization of behavior is time-intensive, prone to subjective scoring, and often requires specialized equipment. Although several reports describe automated home-cage monitoring and individual task scoring methods, we report the first open source, comprehensive toolbox for automating the scoring of several common behavior tasks used by the neuroscience community. We show this new toolbox is robust and achieves equal or better consistency when compared to manual scoring methods. We use this toolbox to study the alterations in behavior that occur following blast-induced traumatic brain injury (bTBI), and study if these behavior patterns are altered following genetic deletion of the transcription factor Ets-like kinase 1 (Elk-1). Due to the role of Elk-1 in neuronal survival and proposed role in synaptic plasticity, we hypothesized that Elk-1 deletion would improve some neurobehavioral deficits, while impairing others, following blast exposure. In Elk-1 knockout (KO) animals, deficits in open field, spatial object recognition (SOR) and elevated zero maze performance after blast exposure disappeared, while new significant deficits appeared in spatial and associative memory. These are the first data suggesting a molecular mediator of anxiety deficits following bTBI, and represent the utility of the broad screening tool we developed. More broadly, we envision this open-source toolbox will provide a more consistent and rapid analysis of behavior across many neurological diseases, promoting the rapid discovery of novel pathways mediating disease progression and treatment.

The effects of aging on the BTBR mouse model of autism spectrum disorder

Autism spectrum disorder (ASD) is a complex heterogeneous neurodevelopmental disorder characterized by alterations in social functioning, communicative abilities, and engagement in repetitive or restrictive behaviors. The process of aging in individuals with autism and related neurodevelopmental disorders is not well understood, despite the fact that the number of individuals with ASD aged 65 and older is projected to increase by over half a million individuals in the next 20 years. To elucidate the effects of aging in the context of a modified central nervous system, we investigated the effects of age on the BTBR T + tf/j mouse, a well characterized and widely used mouse model that displays an ASD-like phenotype. We found that a reduction in social behavior persists into old age in male BTBR T + tf/j mice. We employed quantitative proteomics to discover potential alterations in signaling systems that could regulate aging in the BTBR mice. Unbiased proteomic analysis of hippocampal and cortical tissue of BTBR mice compared to age-matched wild-type controls revealed a significant decrease in brain derived neurotrophic factor and significant increases in multiple synaptic markers (spinophilin, Synapsin I, PSD 95, NeuN), as well as distinct changes in functional pathways related to these proteins, including “Neural synaptic plasticity regulation” and “Neurotransmitter secretion regulation.” Taken together, these results contribute to our understanding of the effects of aging on an ASD-like mouse model in regards to both behavior and protein alterations, though additional studies are needed to fully understand the complex interplay underlying aging in mouse models displaying an ASD-like phenotype.

Sensory integration in mouse insular cortex reflects GABA circuit maturation

Insular cortex (IC) contributes to a variety of complex brain functions, such as communication, social behavior, and self-awareness through the integration of sensory, emotional, and cognitive content. How the IC acquires its integrative properties remains unexplored. We compared the emergence of multisensory integration (MSI) in the IC of behaviorally distinct mouse strains. While adult C57BL/6 mice exhibited robust MSI, this capacity was impaired in the inbred BTBR T+tf/J mouse model of idiopathic autism. The deficit reflected weakened γ-aminobutyric acid (GABA) circuits and compromised postnatal pruning of cross-modal input. Transient pharmacological enhancement by diazepam in BTBR mice during an early sensitive period rescued inhibition and integration in the adult IC. Moreover, impaired MSI was common across three other monogenic models (GAD65, Shank3, and Mecp2 knockout mice) displaying behavioral phenotypes and parvalbumin-circuit abnormalities. Our findings offer developmental insight into a key neural circuit relevant to neuropsychiatric conditions like schizophrenia and autism.

Sex differences in animal models of psychiatric disorders

Psychiatric disorders are characterized by sex differences in their prevalence, symptomatology and treatment response. Animal models have been widely employed for the investigation of the neurobiology of such disorders and the discovery of new treatments. However, mostly male animals have been used in preclinical pharmacological studies. In this review, we highlight the need for the inclusion of both male and female animals in experimental studies aiming at gender-oriented prevention, diagnosis and treatment of psychiatric disorders. We present behavioural findings on sex differences from animal models of depression, anxiety, post-traumatic stress disorder, substance-related disorders, obsessive-compulsive disorder, schizophrenia, bipolar disorder and autism. Moreover, when available, we include studies conducted across different stages of the oestrous cycle. By inspection of the relevant literature, it is obvious that robust sex differences exist in models of all psychiatric disorders. However, many times results are conflicting, and no clear conclusion regarding the direction of sex differences and the effect of the oestrous cycle is drawn. Moreover, there is a lack of considerable amount of studies using psychiatric drugs in both male and female animals, in order to evaluate the differential response between the two sexes. Notably, while in most cases animal models successfully mimic drug response in both sexes, test parameters and treatment-sensitive behavioural indices are not always the same for male and female rodents. Thus, there is an increasing need to validate animal models for both sexes and use standard procedures across different laboratories.

Enhancing the value of psychiatric mouse models; differential expression of developmental behavioral and cognitive profiles in four inbred strains of mice

The behavioral characterization of animal models of psychiatric disorders is often based upon independent traits measured at adult age. To model the neurodevelopmental aspects of psychiatric pathogenesis, we introduce a novel approach for a developmental behavioral analysis in mice. C57BL/6J (C57) mice were used as a reference strain and compared with 129S1/SvImJ (129Sv), BTBR T+tf/J (BTBR) and A/J (AJ) strains as marker strains for aberrant development. Mice were assessed at pre-adolescence (4 weeks), adolescence (6 weeks), early adulthood (8 weeks) and in adulthood (10-12 weeks) on a series of behavioral tasks measuring general health, neurological reflexes, locomotor activity, anxiety, short- and long-term memory and cognitive flexibility. Developmental delays in short-term object memory were associated with either a hypo-reactive profile in 129Sv mice or a hyper-reactive profile in BTBR mice. Furthermore, BTBR mice showed persistent high levels of repetitive grooming behavior during all developmental stages that was associated with the adult expression of cognitive rigidity. In addition, strain differences in development were observed in puberty onset, touch escape, and body position. These data showed that this longitudinal testing battery provides sufficient behavioral and cognitive resolution during different development stages and offers the opportunity to address the behavioral developmental trajectory in genetic mouse models for neurodevelopmental disorders. Furthermore, the data revealed that the assessment of multiple behavioral and cognitive domains at different developmental stages is critical to determine confounding factors (e.g., impaired motor behavior) that may interfere with the behavioral testing performance in mouse models for brain disorders.

Enhancement of inhibitory neurotransmission by GABAA receptors having α2,3-subunits ameliorates behavioral deficits in a mouse model of autism

Autism spectrum disorder (ASD) may arise from increased ratio of excitatory to inhibitory neurotransmission in the brain. Many pharmacological treatments have been tested in ASD, but only limited success has been achieved. Here we report that BTBR T(+)Itpr3(tf)/J (BTBR) mice, a model of idiopathic autism, have reduced spontaneous GABAergic neurotransmission. Treatment with low nonsedating/nonanxiolytic doses of benzodiazepines, which increase inhibitory neurotransmission through positive allosteric modulation of postsynaptic GABAA receptors, improved deficits in social interaction, repetitive behavior, and spatial learning. Moreover, negative allosteric modulation of GABAA receptors impaired social behavior in C57BL/6J and 129SvJ wild-type mice, suggesting that reduced inhibitory neurotransmission may contribute to social and cognitive deficits. The dramatic behavioral improvement after low-dose benzodiazepine treatment was subunit specific-the α2,3-subunit-selective positive allosteric modulator L-838,417 was effective, but the α1-subunit-selective drug zolpidem exacerbated social deficits. Impaired GABAergic neurotransmission may contribute to ASD, and α2,3-subunit-selective positive GABAA receptor modulation may be an effective treatment.

The role of behavior in translational models for psychopathology: functionality and dysfunctional behaviors

The history of science has frequently included a problem-based impetus toward research that can be translated expeditiously into solutions. A current problem is that psychopathologies, typically chronic, contribute hugely to the economic and social burden of medical care, especially in the United States. For behavioral neuroscientists a psychopathology-aimed translational research emphasis particularly involves animal models to facilitate the experimental and invasive work necessary to an understanding of the biology of normal and aberrant behavior. When the etiology of a particular psychopathology is unknown, and there are no specific biomarkers, behavioral parallels between the focal disorder and its putative models become crucial elements in assessing model validity. Evaluation of these parallels is frequently neglected, reflecting in part the lack of a systematic conceptualization of the organization of behavior and how this may be conserved across species. Recent work specifically attempting to bridge this gap suggests that analysis of behaviors that are functional - adaptive in crucial situations such as danger or social contexts - can facilitate an understanding of the parallels between behaviors of human and nonhuman species, including the dysfunctional behaviors of psycho pathologies. As research with animal models comes to provide a more systematic analysis of particular behaviors and their adaptive functions, cross-talk between model and focal psychopathology may be advantageous to understanding both.

Influence of stimulant-induced hyperactivity on social approach in the BTBR mouse model of autism

Translational research is needed to discover pharmacological targets and treatments for the diagnostic behavioral domains of autism spectrum disorders. Animal models with phenotypic relevance to diagnostic criteria offer clear experimental strategies to test the efficacy and safety of novel treatments. Antagonists of mGluR5 receptors are in clinical trials for Fragile X syndrome and under investigation for the treatment of autism spectrum disorders. However, in preclinical studies of mGluR5 compounds tested in our laboratory and others, increased locomotion following mGluR5 modulation has been observed. Understanding the influence of general activity on sociability and repetitive behaviors will increase the accuracy of interpretations of positive outcomes measured from pharmacological treatment that produces locomotor activating or sedating effects. In the present studies, dose-response curves for d-amphetamine (AMPH)-induced hyperlocomotion were similar in standard B6 mice and in the BTBR mouse model of autism. AMPH produced significant, robust reductions in the high level of repetitive self-grooming that characterizes BTBR, and also reduced the low baseline grooming in B6, indicating that AMPH-induced hyperlocomotion competes with time spent engaged in self-grooming. We then tested AMPH in B6 and BTBR on the 3-chambered social approach task. One component of sociability, the time spent in the chamber with the novel mouse, in B6 mice was reduced, while the sniffing time component of sociability in BTBR mice was enhanced. This finding replicated across multiple cohorts treated with AMPH and saline vehicle. In-depth analysis revealed that AMPH increased the number and decreased the duration of sniffing bouts in BTBR, suggesting BTBR treated with AMPH mostly engaged in brief sniffs rather than true social interactions with the novel mouse during the social approach task. Our data suggest that compounds with stimulant properties may have some direct benefits on reducing repetitive behaviors in autism spectrum disorders, particularly in the subset of autistic individuals with hyperactivity. This article is part of the Special Issue entitled 'Neurodevelopmental Disorders'.

Low home cage social behaviors in BTBR T+tf/J mice during juvenile development

BTBR T+tf/J (BTBR) is a genetically homogenous inbred strain of mice that displays abnormal social behaviors, deficits in vocalizations, and high levels of repetitive behaviors, relevant to the three diagnostic symptoms of autism spectrum disorder, leading to the use of this strain as a mouse model of autism. Comprehensive observations of BTBR social behaviors within the home cage during early stages of development have not been conducted. Here we evaluate the home cage behaviors of BTBR in two laboratory environments (NIMH, Bethesda, Maryland vs. UC Davis, Davis, California), starting from the day of weaning and continuing into adulthood. Extensive ethogram parameters were scored for BTBR in home cages that contained four BTBR conspecifics, versus home cages that contained four C57BL/6J (B6) conspecifics. BTBR were considerably less interactive than B6 in the home cage at both sites, as measured during the early dark stage of their circadian cycle. A novel home cage behavioral measure, frequency of long interactions, was found to be more frequent and of longer duration in B6 versus BTBR home cages across experimental sites. Significant strain differences in the occurrence of investigative and affiliative behaviors were also seen, however these findings were not fully consistent across the two testing sites. At the end of the 30-day home cage observation period, each seven-week old subject mouse was tested in the three-chambered social approach task. BTBR displayed lack of sociability and B6 displayed significant sociability, consistent with previous reports. Our findings reveal that BTBR engaged in lower levels of some components of spontaneous conspecific social interactions in the home cage environment throughout juvenile development, consistent with their deficits in juvenile and adult sociability as measured in specialized social tasks.

The importance of considering all attributes of memory in behavioral endophenotyping of mouse models of genetic disease

In order to overcome difficulties in evaluating cognitive function in mouse models of genetic disorders, it is critical to take into account the background strain of the mouse and reported phenotypes in the clinical population being studied. Recent studies have evaluated cognitive function across a number of background strains and found that spatial memory assayed by the water maze and contextual fear conditioning often does not provide optimal results. The logical extension to these results is to emphasize not only spatial, but all attributes or domains of memory function in behavioral phenotyping experiments. A careful evaluation of spatial, temporal, sensory/perceptual, affective, response, executive, proto-linguistic, and social behaviors designed to specifically evaluate the cognitive function each mouse model can be performed in a rapid, relatively high throughput manner. Such results would not only provide a more comprehensive snapshot of brain function in mouse disease models than the more common approach that approaches nonspecific spatial memory tasks to evaluate cognition, but also would better model the disorders being studied.

Are you real? Visual simulation of social housing by mirror image stimulation in single housed mice

Individual housing of social species is a common phenomenon in laboratory animal facilities. Single housing, however, is known to inflict social deprivation with a number of detrimental consequences. Aiming to improve housing conditions of single housed rodents, we investigated the simulation of social housing by mirrors in a series of behavioural experiments and biochemical parameters in mice. We found that chronic mirror-image stimulation increased exploratory behaviours in the holeboard and novel cage tests, but did not alter anxiety, locomotor, or depression-like behaviours. Moreover, no influence on visual recognition memory was observed. Hippocampal brain-derived neurotrophic factor (BDNF) levels, a biomarker for enrichment effects, were unaltered. In line, mirror-image stimulation did not alter home cage behaviour in mice housed with and without mirrors when left undisturbed. Thus, though we found subtle behavioural effects after long-term mirror exposure, we conclude that the simulation of social housing by mirrors is not sufficient to gain the presumably beneficial outcomes induced by social housing.

AMPAKINE enhancement of social interaction in the BTBR mouse model of autism

Autism is a neurodevelopmental disorder in which the first diagnostic symptom is unusual reciprocal social interactions. Approximately half of the children diagnosed with an autism spectrum disorder also have intellectual impairments. General cognitive abilities may be fundamental to many aspects of social cognition. Cognitive enhancers could conceivably be of significant benefit to children and adults with autism. AMPAKINE compounds are a novel class of pharmacological agents that act as positive modulators of AMPA receptors to enhance excitatory glutamatergic neurotransmission. This class of compounds was reported to improve learning and memory in several rodent and non-human primate tasks, and to normalize respiratory abnormalities in a mouse model of Rett syndrome. Here we evaluate the actions of AMPA compounds in adult male and female BTBR mice, a well characterized mouse model of autism. Acute treatment with CX1837 and CX1739 reversed the deficit in sociability in BTBR mice on the most sensitive parameter, time spent sniffing a novel mouse as compared to time spent sniffing a novel object. The less sensitive parameter, time in the chamber containing the novel mouse versus time in the chamber containing the novel object, was not rescued by CX1837 or CX1739 treatment. Preliminary data with CX546, in which β-cyclodextrin was the vehicle, revealed behavioral effects of the acute intraperitoneal and oral administration of vehicle alone. To circumvent the artifacts introduced by the vehicle administration, we employed a novel treatment regimen using pellets of peanut butter for drug delivery. Absence of vehicle treatment effects when CX1837 and CX1739 were given in the peanut butter pellets, to multiple cohorts of BTBR and B6 control mice, confirmed that the pharmacologically-induced improvements in sociability in BTBR were not confounded by the administration procedures. The highest dose of CX1837 improved the cognitive deficit in novel object recognition in BTBR. No drug effects were detected on the high levels of repetitive self-grooming in BTBR. In open field tests, CX1837 and CX1739 did not induce hyperactivity or sedation in either strain. It is interesting to speculate that the ability of CX1837 and CX1739 to restore aspects of sociability in BTBR mice could utilize synaptic mechanisms regulating social cognition, suggesting a potential pharmacological target for interventions to treat symptoms of autism. This article is part of a Special Issue entitled 'Cognitive Enhancers'.

Neuroanatomical analysis of the BTBR mouse model of autism using magnetic resonance imaging and diffusion tensor imaging

Autism is a neurodevelopmental disorder characterized by abnormal reciprocal social interactions, communication deficits, and repetitive behaviors with restricted interests. Autism-relevant phenotypes in the inbred mouse strain BTBR T+tf/J (BTBR) offer translational tools to discover biological mechanisms underlying unusual mouse behaviors analogous to symptoms of autism. Two of the most consistent findings with BTBR are lack of sociability as measured by the three-chamber social approach task and increased amount of time engaged in self-grooming in an empty cage. Here we evaluated BTBR as compared to two typical inbred strains with high sociability and low self-grooming, C57BL/6J (B6) and FVB/AntJ (FVB), on both the automated three-chambered social approach task and repetitive self-grooming assays. Brains from the behaviorally tested mice were analyzed using magnetic resonance imaging and diffusion tensor imaging to investigate potential neuroanatomical abnormalities throughout the brain; specifically, to discover neuroanatomical mechanisms which could explain the autism-relevant behavioral abnormalities. Significant differences in volume and white matter microstructure were detected in multiple anatomical regions throughout the brain of BTBR compared to B6 and FVB. Further, significant correlations were found between behavioral measures and areas of the brain known to be associated with those behaviors. For example, striatal volume was strongly correlated to time spent in self-grooming across strains. Our findings suggest that neuropathology exists in BTBR beyond the previously reported white matter abnormalities in the corpus callosum and hippocampal commissure and that these brain differences may be related to the behavioral abnormalities seen in BTBR.

Classical and novel approaches to the preclinical testing of anxiolytics: A critical evaluation

Over 80% of current anxiety studies employ one of the tests that were developed earlier than, or concurrently with the elevated plus-maze, i.e. before 1985. Considering 1985 as a historical reference point, we briefly review here 115 new tests and models of anxiety, the development of which was likely prompted by the poor predictive validity of classical tests as shown here by the comparison of preclinical and clinical findings with putative novel anxiolytics. The new approaches comprise major innovations to classical tests, the pre-test application of manipulations that mimic etiological factors of anxiety disorders, and entirely new approaches including anxiety disorder-specific tests. Thus, intensive test development over the last 27 years created a large pool of novel approaches. However, these are infrequently used and as such, their impact on anxiolytic drug development remains low. We suggest here that test/model development should step over the intensive phase when several new methods are proposed each year and should start selecting and establishing the methodologies that would successfully replace or complement classical tests. We propose here a novel strategy for improving the validity of anxiety testing that includes the retrospective analysis of the predictive validity of new procedures (as opposed to classical pharmacological validation), and a call for concerted international efforts at both the conceptual and practical levels. Similar endeavors proved recently successful with other psychiatric disorders.

Differential responses to distinct psychotropic agents of selectively bred dominant and submissive animals

Dominance and submissiveness are two opposite poles of behavior representing important functional elements in the development of social interactions. We previously demonstrated the inheritability of these traits by selective breeding based upon the dominant-submissive relationships (DSR) food competition paradigm. Continued multigenerational behavioral selection of Sabra mice yielded animal populations with strong and stable features of dominance and submissiveness. We found that these animals react differentially to stressogenic triggers, antidepressants and mood stabilizing agents. The anxiolytic compound diazepam (1.5mg/kg, i.p.) reduced anxiety-like behavior of submissive animals, but showed anxiogenic effects among dominant animals. In the Forced Swim test, the antidepressant paroxetine (1, 3 and 10mg/kg, i.p.) markedly reduced immobility of submissive animals, demonstrating antidepressant-like effect. In contrast, when administered to dominant animals, paroxetine caused extreme (frenetic) activity. The mood stabilizer lithium (0.4%, p.o.) selectively influenced dominant mice, without affecting the behavior of submissive animals. In summary, we describe here two distinct animal populations possessing strong dominant and submissive phenotypes. We suggest that these populations hold potential as tools for studying the molecular basis and pharmacogenetics of dominant and submissive behavior.

Development of home cage social behaviors in BALB/cJ vs. C57BL/6J mice

BALB/cJ and C57BL/6J inbred mouse strains have been proposed as useful models of low and high levels of sociability (tendency to seek social interaction), respectively, based primarily on behaviors of ∼30-day-old mice in the Social Approach Test (SAT). In the SAT, approach and sniffing behaviors of a test mouse toward an unfamiliar stimulus mouse are measured in a novel environment. However, it is unclear whether such results generalize to a familiar environment with a familiar social partner, such as with a littermate in a home cage environment. We hypothesized that C57BL/6J mice would show higher levels of social behaviors than BALB/cJ mice in the home cage environment, particularly at 30 days-of-age. We measured active and passive social behaviors in home cages by pairs of BALB/cJ or C57BL/6J littermates at ages 30, 41, and 69 days. The strains did not differ robustly in their active social behaviors. C57BL/6J mice were more passively social than BALB/cJ mice at 30 days, and C57BL/6J levels of passive social behaviors declined to BALB/cJ levels by 69 days. The differences in passive social behaviors at 30 days-of-age were primarily attributable to differences in huddling. These results indicate that different test conditions (SAT conditions vs. home cage conditions) elicit strain differences in distinct types of behaviors (approach/sniffing vs. huddling behaviors, respectively). Assessment of the more naturalistic social interactions in the familiar home cage environment with a familiar littermate will provide a useful component of a comprehensive assessment of social behaviors in mouse models relevant to autism.

The BTBR T+ tf/J mouse model for autism spectrum disorders-in search of biomarkers

Autism spectrum disorders (ASD) form a common group of neurodevelopmental disorders appearing to be under polygenic control, but also strongly influenced by multiple environmental factors. The brain mechanisms responsible for ASD are not understood and animal models paralleling related emotional and cognitive impairments may prove helpful in unraveling them. BTBR T+ tf/J (BTBR) mice display behaviors consistent with the three diagnostic categories for ASD. They show impaired social interaction and communication as well as increased repetitive behaviors. This review covers much of the data available to date on BTBR behavior, neuroanatomy and physiology in search for candidate biomarkers, which could both serve as diagnostic tools and help to design effective treatments for the behavioral symptoms of ASD.

Acetaminophen differentially enhances social behavior and cortical cannabinoid levels in inbred mice

Supratherapeutic doses of the analgesic acetaminophen (paracetomol) are reported to promote social behavior in Swiss mice. However, we hypothesized that it might not promote sociability in other strains due to cannabinoid CB(1) receptor-mediated inhibition of serotonin (5-HT) transmission in the frontal cortex. We examined the effects of acetaminophen on social and repetitive behaviors in comparison to a cannabinoid agonist, WIN 55,212-2, in two strains of socially-deficient mice, BTBR and 129S1/SvImJ (129S). Acetaminophen (100mg/kg) enhanced social interactions in BTBR, and social novelty preference and marble burying in 129S at serum levels of ≥70 ng/ml. Following acetaminophen injection or sociability testing, anandamide (AEA) increased in BTBR frontal cortex, while behavior testing increased 2-arachidonyl glycerol (2-AG) levels in 129S frontal cortex. In contrast, WIN 55,212-2 (0.1mg/kg) did not enhance sociability. Further, we expected CB(1)-deficient (+/-) mice to be less social than wild-type, but instead found similar sociability. Given strain differences in endocannabinoid response to acetaminophen, we compared cortical CB(1) and 5-HT(1A) receptor density and function relative to sociable C57BL/6 mice. CB(1) receptor saturation binding (Bmax=958±117 fmol/mg protein), and affinity for [(3)H] CP55,940 (K(D)=3±0.8 nM) was similar in frontal cortex among strains. CP55,940-stimulated [(35)S] GTPγS binding in cingulate cortex was 136±12, 156±22, and 75±9% above basal in BTBR, 129S and C57BL/6 mice. The acetaminophen metabolite para-aminophenol (1 μM) failed to stimulate [(35)S] GTPγS binding. Hence, it appears that other indirect actions of acetaminophen, including 5-HT receptor agonism, may underlie its sociability promoting properties outweighing any CB(1) mediated suppression by locally-elevated endocannabinoids in these mice.

Co-learning facilitates memory in mice: a new avenue in social neuroscience

Social context affects brain function but our understanding of its neurobiology is at an early stage. The mere presence of one individual can alter the cognitive capacities of another and social learning has been demonstrated in many species, including the mouse. We asked several questions: 1. How can active engagement of two familiar mice in the same learning activity (co-learning) alter their memory? 2. Under which environmental conditions (aversive vs non-aversive) can we expect the memory to be enhanced, impaired, or not affected? 3. Can a genetic factor modify the co-learning effect on memory? More specifically, can co-learning correct memory deficits in autistic-like BTBR inbred mice with deficient sociability? We demonstrated that pairs of familiar inbred mice of the same or different genotypes (C57BL/6J and BTBR) that were habituated to new objects and their spatial location, had enhanced episodic memory in the spatial object recognition test, whereas individually-trained animals failed to solve this task. Notably, the co-learning effect was genotype-dependent. BTBR mice paired with BTBR cage-mates in the habituation session modestly ameliorated their performance in the object recognition test but co-learning with a familiar C57BL/6J mouse completely normalized episodic memory deficit. Next, we explored the co-learning effect on fear memory in these inbred strains. Interestingly, mice of both genotypes displayed significantly enhanced contextual fear memory once they had been conditioned together with BTBR animals. The same influence of BTBR presence was observed on cued fear memory in C57BL/6J mice, whereas a modest co-learning effect was found on cued fear conditioning in the BTBR strain. Taken together, we demonstrated for the first time the co-learning effect on cognitive capacities in mice, which can be modified by genetic background and environmental conditions. The possible implications of this methodological approach in social neuroscience are discussed. This article is part of a Special Issue entitled 'Cognitive Enhancers'.

Negative allosteric modulation of the mGluR5 receptor reduces repetitive behaviors and rescues social deficits in mouse models of autism

Neurodevelopmental disorders such as autism and fragile X syndrome were long thought to be medically untreatable, on the assumption that brain dysfunctions were immutably hardwired before diagnosis. Recent revelations that many cases of autism are caused by mutations in genes that control the ongoing formation and maturation of synapses have challenged this dogma. Antagonists of metabotropic glutamate receptor subtype 5 (mGluR5), which modulate excitatory neurotransmission, are in clinical trials for fragile X syndrome, a major genetic cause of intellectual disabilities. About 30% of patients with fragile X syndrome meet the diagnostic criteria for autism. Reasoning by analogy, we considered the mGluR5 receptor as a potential target for intervention in autism. We used BTBR T+tf/J (BTBR) mice, an established model with robust behavioral phenotypes relevant to the three diagnostic behavioral symptoms of autism--unusual social interactions, impaired communication, and repetitive behaviors--to probe the efficacy of a selective negative allosteric modulator of the mGluR5 receptor, GRN-529. GRN-529 reduced repetitive behaviors in three cohorts of BTBR mice at doses that did not induce sedation in control assays of open field locomotion. In addition, the same nonsedating doses reduced the spontaneous stereotyped jumping that characterizes a second inbred strain of mice, C58/J. Further, GRN-529 partially reversed the striking lack of sociability in BTBR mice on some parameters of social approach and reciprocal social interactions. These findings raise the possibility that a single targeted pharmacological intervention may alleviate multiple diagnostic behavioral symptoms of autism.

Reduced sulfate plasma concentrations in the BTBR T+tf/J mouse model of autism

Clinical studies have shown that children diagnosed with autism show abnormal sulfate chemistry, which is critical for cellular and metabolic processes. To determine if the inbred BTBR T+tf/J mouse shows autism-relevant aberrations in sulfate chemistry, the present study examined plasma sulfate concentrations in BTBR T+tf/J, inbred C57BL/6J, and outbred CD-1 mice. Results showed that the BTBR T+tf/J mouse exhibits significantly lower plasma sulfate concentrations in comparison to both C57BL/6J and CD-1 mice. These results suggest that the BTBR mouse shows autism-relevant abnormalities in sulfate chemistry and may serve additional utility in examining the role of sulfate and sulfate-dependent systems in relation to autism-relevant behavioral aberrations.

Facial expressions of mice in aggressive and fearful contexts

Some animals display a variety of context dependent facial expressions. Previous studies have shown that rodents display a facial grimace while in pain. To determine if the facial expressions of mice extend beyond pain, facial expressions were analyzed in the presence of non-social, social and predator stimuli. In a vibrissae contact test, the whiskers of mice were stroked by the bristles of a brush. In a social proximity test, two mice were placed together in a small chamber where contact was virtually unavoidable. In a resident-intruder test of aggression, an unknown mouse was placed into the homecage of another mouse. In a cat odor exposure test and in a live rat exposure test, mice were presented with the respective stimuli. Results from this study indicated that mice showed two patterns of expression, either a full display of changes in the measured facial components, characterized by tightened eyes, flattened ears, nose swells and cheek swells; or a more limited display of these facial changes. The full display of changes occurred in the vibrissae contact test, the social proximity test, and in resident mice in the resident-intruder test. The more limited display of facial changes occurred in the cat odor exposure test, the rat exposure test and in intruder mice in the resident-intruder test. The differential display of facial changes across conditions indicated that mice showed tightened eyes and flattened ears in situations that provided the immediate potential for contact, suggesting that such changes are involved in protection of sensitive and/or vulnerable body parts. Furthermore, the display of facial expressions by mice indicates that these expressions are widely distributed across evolution.

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

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

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

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

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

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

Mouse females devoid of exposure to males during fetal development exhibit increased maternal behavior

Many sex differences can be found in the expression of aggression and parental nurturing behaviors. It is important to determine if these are modulated by prenatal conditions. Here, using assisted reproduction technologies, we generated females that were (mixed-sex) or were not (same-sex) exposed to males during fetal development, raised them by cross fostering among fosters' own female only pups to control for effects of postnatal environment, and compared their reproductive abilities and behavior. There were no differences between females from the two prenatal conditions in estrus cycle length and length of time spent at individual estrus cycle stages. Both types of females had similar ovulation efficiency and bred equally well yielding comparable litter size and progeny sex ratio. Females from the two prenatal conditions were also indistinguishable in social behavior and exhibited normal social responses towards unfamiliar females in the three-chamber social approach and social proximity tests. When urine was collected from both types of females and used as a point source in a scent-marking paradigm, exposed males showed a similar distribution and extent of urinary scent marking in response to urine from each type of female but tended to engage in higher durations of sniffing the urine from same-sex females. When females were tested in a resident-intruder paradigm 3 days after giving birth, same-sex females exhibited enhancement of pup grooming and an overall decrease of non-pup activity prior to male intruder introduction, and after introduction were more defensive as evidenced by higher rates of burying, open-mouth threat/lunges, and attacks towards the male, and decreased latencies to display these defensive behaviors. Our results suggest that females devoid of male exposure during fetal development have reproductive abilities similar to those of females from mixed-sex pregnancies, and have normal social interactions with other females. However, they exhibit hyper-maternal behavior both in terms of the care and defense of pups in front of a male intruder, and potentially produce a pheromonal milieu that renders them more attractive to males during olfactory investigations.

Long-lived epigenetic interactions between perinatal PBDE exposure and Mecp2308 mutation

The widespread use of persistent organic polybrominated diphenyl ethers (PBDEs) as commercial flame retardants has raised concern about potential long-lived effects on human health. Epigenetic mechanisms, such as DNA methylation, are responsive to environmental influences and have long-lasting consequences. Autism spectrum disorders (ASDs) have complex neurodevelopmental origins whereby both genetic and environmental factors are implicated. Rett syndrome is an X-linked ASD caused by mutations in the epigenetic factor methyl-CpG binding protein 2 (MECP2). In this study, an Mecp2 truncation mutant mouse (Mecp2(308)) with social behavioral defects was used to explore the long-lasting effects of PBDE exposure in a genetically and epigenetically susceptible model. Mecp2(308/+) dams were perinatally exposed daily to 2,2',4,4'-tetrabromodiphenyl ether 47 (BDE-47) and bred to wild-type C57BL/6J males, and the offspring of each sex and genotype were examined for developmental, behavioral and epigenetic outcomes. Perinatal BDE-47 exposure negatively impacted fertility of Mecp2(308/+) dams and preweaning weights of females. Global hypomethylation of adult brain DNA was observed specifically in female offspring perinatally exposed to BDE-47 and it coincided with reduced sociability in a genotype-independent manner. A reversing interaction of Mecp2 genotype on BDE-47 exposure was observed in a short-term memory test of social novelty that corresponded to increased Dnmt3a levels specifically in BDE-47-exposed Mecp2(308/+) offspring. In contrast, learning and long-term memory in the Morris water maze was impaired by BDE-47 exposure in female Mecp2(308/+) offspring. These results demonstrate that a genetic and environmental interaction relevant to social and cognitive behaviors shows sexual dimorphism, epigenetic dysregulation, compensatory molecular mechanisms and specific behavioral deficits.

Comprehensive neurocognitive endophenotyping strategies for mouse models of genetic disorders

There is a need for refinement of the current behavioral phenotyping methods for mouse models of genetic disorders. The current approach is to perform a behavioral screen using standardized tasks to define a broad phenotype of the model. This phenotype is then compared to what is known concerning the disorder being modeled. The weakness inherent in this approach is twofold: First, the tasks that make up these standard behavioral screens do not model specific behaviors associated with a given genetic mutation but rather phenotypes affected in various genetic disorders; secondly, these behavioral tasks are insufficiently sensitive to identify subtle phenotypes. An alternate phenotyping strategy is to determine the core behavioral phenotypes of the genetic disorder being studied and develop behavioral tasks to evaluate specific hypotheses concerning the behavioral consequences of the genetic mutation. This approach emphasizes direct comparisons between the mouse and human that facilitate the development of neurobehavioral biomarkers or quantitative outcome measures for studies of genetic disorders across species.

Sociability and brain development in BALB/cJ and C57BL/6J mice

Sociability--the tendency to seek social interaction--propels the development of social cognition and social skills, but is disrupted in autism spectrum disorders (ASD). BALB/cJ and C57BL/6J inbred mouse strains are useful models of low and high levels of juvenile sociability, respectively, but the neurobiological and developmental factors that account for the strains' contrasting sociability levels are largely unknown. We hypothesized that BALB/cJ mice would show increasing sociability with age but that C57BL/6J mice would show high sociability throughout development. We also hypothesized that littermates would resemble one another in sociability more than non-littermates. Finally, we hypothesized that low sociability would be associated with low corpus callosum size and increased brain size in BALB/cJ mice. Separate cohorts of C57BL/6J and BALB/cJ mice were tested for sociability at 19-, 23-, 31-, 42-, or 70-days-of-age, and brain weights and mid-sagittal corpus callosum area were measured. BALB/cJ sociability increased with age, and a strain by age interaction in sociability between 31 and 42 days of age suggested strong effects of puberty on sociability development. Sociability scores clustered according to litter membership in both strains, and perinatal litter size and sex ratio were identified as factors that contributed to this clustering in C57BL/6J, but not BALB/cJ, litters. There was no association between corpus callosum size and sociability, but smaller brains were associated with lower sociability in BALB/cJ mice. The associations reported here will provide directions for future mechanistic studies of sociability development.

Mecp2 truncation in male mice promotes affiliative social behavior

Mouse models of Rett syndrome, with targeted mutations in the Mecp2 gene, show a high degree of phenotypic consistency with the clinical syndrome. In addition to severe and age-specific regression in motor and cognitive abilities, a variety of studies have demonstrated that Mecp2 mutant mice display impaired social behavior. Conversely, other studies indicate complex enhancements of social behavior in Mecp2 mutant mice. Since social behavior is a complicated accumulation of constructs, we performed a series of classic and refined social behavior tasks and revealed a relatively consistent pattern of enhanced pro-social behavior in hypomorphic Mecp2 (308/Y) mutant mice. Analyses of repetitive motor acts, and cognitive stereotypy did not reveal any profound differences due to genotype. Taken together, these results suggest that the mutations associated with Rett syndrome are not necessarily associated with autism-relevant social impairment in mice. However, this gene may be a valuable candidate for revealing basic mechanisms of affiliative behavior.