Cerebellar plasticity and motor learning deficits in a copy-number variation mouse model of autism

Neuroactive steroid exposure impacts neurodevelopment: Comparison of human and rodent placental contribution

The placenta is a fetal endocrine organ that secretes many neuroactive factors, including steroids, that play critical roles in brain development. The study of the placenta-brain axis and the links between placental function and brain development represents an emerging research area dubbed "neuroplacentology." The placenta drives many circulating fetal steroids to very high levels during gestation. Recent studies have highlighted the critical role of placental steroids in shaping specific brain structures and behaviors. This review uses a cross-species framework to discuss the genomic factors, in-utero environmental changes, and placental conditions that alter placental steroidogenesis, leading to changes in early developmental trajectories relevant for psychiatric conditions such as autism, in a sex-linked manner.

Aberrant outputs of cerebellar nuclei and targeted rescue of social deficits in an autism mouse model

The cerebellum is heavily connected with other brain regions, sub-serving not only motor but also nonmotor functions. Genetic mutations leading to cerebellar dysfunction are associated with mental diseases, but cerebellar outputs have not been systematically studied in this context. Here, we present three dimensional distributions of 50,168 target neurons of cerebellar nuclei (CN) from wild-type mice and Nlgn3R451C mutant mice, a mouse model for autism. Our results derived from 36 target nuclei show that the projections from CN to thalamus, midbrain and brainstem are differentially affected by Nlgn3R451C mutation. Importantly, Nlgn3R451C mutation altered the innervation power of CN→zona incerta (ZI) pathway, and chemogenetic inhibition of a neuronal subpopulation in the ZI that receives inputs from the CN rescues social defects in Nlgn3R451C mice. Our study highlights potential role of cerebellar outputs in the pathogenesis of autism and provides potential new therapeutic strategy for this disease.

Cerebellar impairments in genetic models of autism spectrum disorders: A neurobiological perspective

Functional and molecular alterations in the cerebellum are among the most widely recognised associates of autism spectrum disorders (ASD). As a critical computational hub of the brain, the cerebellum controls and coordinates a range of motor, affective and cognitive processes. Despite well-described circuits and integrative mechanisms, specific changes that underlie cerebellar impairments in ASD remain elusive. Studies in experimental animals have been critical in uncovering molecular pathology and neuro-behavioural correlates, providing a model for investigating complex disease conditions. Herein, we review commonalities and differences of the most extensively characterised genetic lines of ASD with reference to the cerebellum. We revisit structural, functional, and molecular alterations which may contribute to neurobehavioral phenotypes. The cross-model analysis of this study provides an integrated outlook on the role of cerebellar alterations in pathobiology of ASD that may benefit future translational research and development of therapies.

Accelerating the continuous community sharing of digital neuromorphology data

The tree-like morphology of neurons and glia is a key cellular determinant of circuit connectivity and metabolic function in the nervous system of essentially all animals. To elucidate the contribution of specific cell types to both physiological and pathological brain states, it is important to access detailed neuroanatomy data for quantitative analysis and computational modeling. NeuroMorpho.Org is the largest online collection of freely available digital neural reconstructions and related metadata and is continuously updated with new uploads. Earlier in the project, we released multiple datasets together yearly, but this process caused an average delay of several months in making the data public. Moreover, in the past 5 years, >80% of invited authors agreed to share their data with the community via NeuroMorpho.Org, up from <20% in the first 5 years of the project. In the same period, the average number of reconstructions per publication increased 600%, creating the need for automatic processing to release more reconstructions in less time. The progressive automation of our pipeline enabled the transition to agile releases of individual datasets as soon as they are ready. The overall time from data identification to public sharing decreased by 63.7%; 78% of the datasets are now released in less than 3 months with an average workflow duration below 40 days. Furthermore, the mean processing time per reconstruction dropped from 3 h to 2 min. With these continuous improvements, NeuroMorpho.Org strives to forge a positive culture of open data. Most importantly, the new, original research enabled through reuse of datasets across the world has a multiplicative effect on science discovery, benefiting both authors and users.

Genetic influences on motor learning and performance and superperforming mutants revealed by random mutational survey of the mouse genome

Evolution depends upon genetic variations that influence physiology. As defined in a genetic screen, phenotypic performance may be enhanced or degraded by such mutations. We set out to detect mutations that influence motor function, including motor learning. Thus, we tested the motor effects of 36,444 non-synonymous coding/splicing mutations induced in the germline of C57BL/6J mice with N-ethyl-N-nitrosourea by measuring changes in the performance of repetitive rotarod trials while blinded to genotype. Automated meiotic mapping was used to implicate individual mutations in causation. In total, 32,726 mice bearing all the variant alleles were screened. This was complemented with the simultaneous testing of 1408 normal mice for reference. In total, 16.3% of autosomal genes were thus rendered detectably hypomorphic or nullified by mutations in homozygosity and motor tested in at least three mice. This approach allowed us to identify superperformance mutations in Rif1, Tk1, Fan1 and Mn1. These genes are primarily related, among other less well-characterized functions, to nucleic acid biology. We also associated distinct motor learning patterns with groups of functionally related genes. These functional sets included, preferentially, histone H3 methyltransferase activity for mice that learnt at an accelerated rate relative to the remaining mutant mice. The results allow for an estimation of the fraction of mutations that can modify a behaviour influential for evolution such as locomotion. They may also enable, once the loci are further validated and the mechanisms elucidated, the harnessing of the activity of the newly identified genes to enhance motor ability or to counterbalance disability or disease. KEY POINTS: We studied the effect of chemically induced random mutations on mouse motor performance. An array of mutations influenced the rate of motor learning. DNA regulation genes predominated among these mutant loci. Several mutations in unsuspected genes led to superperformance. Assuming little-biased mutagenicity, the results allow for an estimation of the probability for any spontaneous mutation to influence a behaviour such as motor learning and ultimate performance.

Impaired cerebellar plasticity hypersensitizes sensory reflexes in SCN2A-associated ASD

Children diagnosed with autism spectrum disorder (ASD) commonly present with sensory hypersensitivity or abnormally strong reactions to sensory stimuli. Such hypersensitivity can be overwhelming, causing high levels of distress that contribute markedly to the negative aspects of the disorder. Here, we identify a mechanism that underlies hypersensitivity in a sensorimotor reflex found to be altered in humans and in mice with loss of function in the ASD risk-factor gene SCN2A. The cerebellum-dependent vestibulo-ocular reflex (VOR), which helps maintain one's gaze during movement, was hypersensitized due to deficits in cerebellar synaptic plasticity. Heterozygous loss of SCN2A-encoded NaV1.2 sodium channels in granule cells impaired high-frequency transmission to Purkinje cells and long-term potentiation, a form of synaptic plasticity important for modulating VOR gain. VOR plasticity could be rescued in mice via a CRISPR-activator approach that increases Scn2a expression, demonstrating that evaluation of a simple reflex can be used to assess and quantify successful therapeutic intervention.

Accelerating the continuous community sharing of digital neuromorphology data

The tree-like morphology of neurons and glia is a key cellular determinant of circuit connectivity and metabolic function in the nervous system of essentially all animals. To elucidate the contribution of specific cell types to both physiological and pathological brain states, it is important to access detailed neuroanatomy data for quantitative analysis and computational modeling. NeuroMorpho.Org is the largest online collection of freely available digital neural reconstructions and related metadata and is continuously updated with new uploads. Earlier in the project, we released multiple datasets together yearly, but this process caused an average delay of several months in making the data public. Moreover, in the past 5 years, >80% of invited authors agreed to share their data with the community via NeuroMorpho.Org, up from <20% in the first 5 years of the project. In the same period, the average number of reconstructions per publication increased 600%, creating the need for automatic processing to release more reconstructions in less time. The progressive automation of our pipeline enabled the transition to agile releases of individual datasets as soon as they are ready. The overall time from data identification to public sharing decreased by 63.7%; 78% of the datasets are now released in less than 3 months with an average workflow duration below 40 days. Furthermore, the mean processing time per reconstruction dropped from 3 hours to 2 minutes. With these continuous improvements, NeuroMorpho.Org strives to forge a positive culture of open data. Most importantly, the new, original research enabled through reuse of datasets across the world has a multiplicative effect on science discovery, benefiting both authors and users.

The gut microbiota modulate locomotion via vagus-dependent glucagon-like peptide-1 signaling

Locomotor activity is an innate behavior that can be triggered by gut-motivated conditions, such as appetite and metabolic condition. Various nutrient-sensing receptors distributed in the vagal terminal in the gut are crucial for signal transduction from the gut to the brain. The levels of gut hormones are closely associated with the colonization status of the gut microbiota, suggesting a complicated interaction among gut bacteria, gut hormones, and the brain. However, the detailed mechanism underlying gut microbiota-mediated endocrine signaling in the modulation of locomotion is still unclear. Herein, we show that broad-spectrum antibiotic cocktail (ABX)-treated mice displayed hypolocomotion and elevated levels of the gut hormone glucagon-like peptide-1 (GLP-1). Blockade of the GLP-1 receptor and subdiaphragmatic vagal transmission rescued the deficient locomotor phenotype in ABX-treated mice. Activation of the GLP-1 receptor and vagal projecting brain regions led to hypolocomotion. Finally, selective antibiotic treatment dramatically increased serum GLP-1 levels and decreased locomotion. Colonizing Lactobacillus reuteri and Bacteroides thetaiotaomicron in microbiota-deficient mice suppressed GLP-1 levels and restored the hypolocomotor phenotype. Our findings identify a mechanism by which specific gut microbes mediate host motor behavior via the enteroendocrine and vagal-dependent neural pathways.

Molecular and cellular mechanisms of developmental synapse elimination in the cerebellum: Involvement of autism spectrum disorder-related genes

Neural circuits are initially created with excessive synapse formation until around birth and undergo massive reorganization until they mature. During postnatal development, necessary synapses strengthen and remain, whereas unnecessary ones are weakened and eventually eliminated. These events, collectively called "synapse elimination" or "synapse pruning", are thought to be fundamental for creating functionally mature neural circuits in adult animals. In the cerebellum of neonatal rodents, Purkinje cells (PCs) receive synaptic inputs from multiple climbing fibers (CFs). Then, inputs from a single CF are strengthened and those from the other CFs are eliminated, and most PCs become innervated by single CFs by the end of the third postnatal week. These events are regarded as a representative model of synapse elimination. This review examines the molecular and cellular mechanisms of CF synapse elimination in the developing cerebellum and argues how autism spectrum disorder (ASD)-related genes are involved in CF synapse development. We introduce recent studies to update our knowledge, incorporate new data into the known scheme, and discuss the remaining issues and future directions.

Cerebellar contribution to autism-relevant behaviors in fragile X syndrome models

Cerebellar dysfunction has been linked to autism spectrum disorders (ASDs). Although cerebellar pathology has been observed in individuals with fragile X syndrome (FXS) and in mouse models of the disorder, a cerebellar functional contribution to ASD-relevant behaviors in FXS has yet to be fully characterized. In this study, we demonstrate a critical cerebellar role for Fmr1 (fragile X messenger ribonucleoprotein 1) in ASD-relevant behaviors. First, we identify reduced social behaviors, sensory hypersensitivity, and cerebellar dysfunction, with loss of cerebellar Fmr1. We then demonstrate that cerebellar-specific expression of Fmr1 is sufficient to impact social, sensory, cerebellar dysfunction, and cerebro-cortical hyperexcitability phenotypes observed in global Fmr1 mutants. Moreover, we demonstrate that targeting the ASD-implicated cerebellar region Crus1 ameliorates behaviors in both cerebellar-specific and global Fmr1 mutants. Together, these results demonstrate a critical role for the cerebellar contribution to FXS-related behaviors, with implications for future therapeutic strategies.

Altered motor learning and coordination in mouse models of autism spectrum disorder

Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder with increasing prevalence. Over 1,000 risk genes have now been implicated in ASD, suggesting diverse etiology. However, the diagnostic criteria for the disorder still comprise two major behavioral domains - deficits in social communication and interaction, and the presence of restricted and repetitive patterns of behavior (RRBs). The RRBs associated with ASD include both stereotyped repetitive movements and other motor manifestations including changes in gait, balance, coordination, and motor skill learning. In recent years, the striatum, the primary input center of the basal ganglia, has been implicated in these ASD-associated motor behaviors, due to the striatum's role in action selection, motor learning, and habit formation. Numerous mouse models with mutations in ASD risk genes have been developed and shown to have alterations in ASD-relevant behaviors. One commonly used assay, the accelerating rotarod, allows for assessment of both basic motor coordination and motor skill learning. In this corticostriatal-dependent task, mice walk on a rotating rod that gradually increases in speed. In the extended version of this task, mice engage striatal-dependent learning mechanisms to optimize their motor routine and stay on the rod for longer periods. This review summarizes the findings of studies examining rotarod performance across a range of ASD mouse models, and the resulting implications for the involvement of striatal circuits in ASD-related motor behaviors. While performance in this task is not uniform across mouse models, there is a cohort of models that show increased rotarod performance. A growing number of studies suggest that this increased propensity to learn a fixed motor routine may reflect a common enhancement of corticostriatal drive across a subset of mice with mutations in ASD-risk genes.

Vasopressin as Possible Treatment Option in Autism Spectrum Disorder

Autism spectrum disorder (ASD) is rather common, presenting with prevalent early problems in social communication and accompanied by repetitive behavior. As vasopressin was implicated not only in salt-water homeostasis and stress-axis regulation, but also in social behavior, its role in the development of ASD might be suggested. In this review, we summarized a wide range of problems associated with ASD to which vasopressin might contribute, from social skills to communication, motor function problems, autonomous nervous system alterations as well as sleep disturbances, and altered sensory information processing. Beside functional connections between vasopressin and ASD, we draw attention to the anatomical background, highlighting several brain areas, including the paraventricular nucleus of the hypothalamus, medial preoptic area, lateral septum, bed nucleus of stria terminalis, amygdala, hippocampus, olfactory bulb and even the cerebellum, either producing vasopressin or containing vasopressinergic receptors (presumably V1a). Sex differences in the vasopressinergic system might underline the male prevalence of ASD. Moreover, vasopressin might contribute to the effectiveness of available off-label therapies as well as serve as a possible target for intervention. In this sense, vasopressin, but paradoxically also V1a receptor antagonist, were found to be effective in some clinical trials. We concluded that although vasopressin might be an effective candidate for ASD treatment, we might assume that only a subgroup (e.g., with stress-axis disturbances), a certain sex (most probably males) and a certain brain area (targeting by means of virus vectors) would benefit from this therapy.

Single cell analysis of dup15q syndrome reveals developmental and postnatal molecular changes in autism

Duplication 15q (dup15q) syndrome is the most common genetic cause of autism spectrum disorder (ASD). Due to a higher genetic and phenotypic homogeneity compared to idiopathic autism, dup15q syndrome provides a well-defined setting to investigate ASD mechanisms. Previous bulk gene expression studies identified shared molecular changes in ASD. However, how cell type specific changes compare across different autism subtypes and how they change during development is largely unknown. In this study, we used single cell and single nucleus mRNA sequencing of dup15q cortical organoids from patient iPSCs, as well as post-mortem patient brain samples. We find cell-type specific dysregulated programs that underlie dup15q pathogenesis, which we validate by spatial resolved transcriptomics using brain tissue samples. We find degraded identity and vulnerability of deep-layer neurons in fetal stage organoids and highlight increased molecular burden of postmortem upper-layer neurons implicated in synaptic signaling, a finding shared between idiopathic ASD and dup15q syndrome. Gene co-expression network analysis of organoid and postmortem excitatory neurons uncovers modules enriched with autism risk genes. Organoid developmental modules were involved in transcription regulation via chromatin remodeling, while postmortem modules were associated with synaptic transmission and plasticity. The findings reveal a shifting landscape of ASD cellular vulnerability during brain development.

Ablation of KIF2C in Purkinje cells impairs metabotropic glutamate receptor trafficking and motor coordination in male mice

Kinesin family member 2C (KIF2C)/mitotic centromere-associated kinesin (MCAK), is thought to be oncogenic as it is involved in tumour progression and metastasis. Moreover, it also plays a part in neurodegenerative conditions like Alzheimer's disease and psychiatric disorders such as suicidal schizophrenia. Our previous study conducted on mice demonstrated that KIF2C is widely distributed in various regions of the brain, and is localized in synaptic spines. Additionally, it regulates microtubule dynamic properties through its own microtubule depolymerization activity, thereby affecting AMPA receptor transport and cognitive behaviour in mice. In this study, we show that KIF2C regulates the transport of mGlu1 receptors in Purkinje cells by binding to Rab8. KIF2C deficiency in Purkinje cells results in abnormal gait, reduced balance ability and motor incoordination in male mice. These data suggest that KIF2C is essential for maintaining normal transport and synaptic function of mGlu1 and motor coordination in mice. KEY POINTS: KIF2C is localized in synaptic spines of hippocampus neurons, and regulates excitatory transmission, synaptic plasticity and cognitive behaviour. KIF2C is extensively expressed in the cerebellum, and we investigated its functions in development and synaptic transmission of cerebellar Purkinje cells. KIF2C deficiency in Purkinje cells alters the expression of metabotropic glutamate receptor 1 (mGlu1) and the AMPA receptor GluA2 subunit at Purkinje cell synapses, and changes excitatory synaptic transmission, but not inhibitory transmission. KIF2C regulates the transport of mGlu1 receptors in Purkinje cells by binding to Rab8. KIF2C deficiency in Purkinje cells affects motor coordination, but not social behaviour in male mice.

Molecular layer disinhibition unlocks climbing-fiber-instructed motor learning in the cerebellum

Climbing fibers supervise cerebellar learning by providing signals to Purkinje cells (PCs) that instruct adaptive changes to mistakenly performed movements. Yet, climbing fibers are regularly active, even during well performed movements, suggesting that a mechanism dynamically regulates the ability of climbing fibers to induce corrective plasticity in response to motor errors. We found that molecular layer interneurons (MLIs), whose inhibition of PCs powerfully opposes climbing-fiber-mediated excitation, serve this function. Optogenetically suppressing the activity of floccular MLIs in mice during the vestibulo-ocular reflex (VOR) induces a learned increase in gain despite the absence of performance errors. Suppressing MLIs when the VOR is mistakenly underperformed reveled that their inhibitory output is necessary to orchestrate gain-increase learning by conditionally permitting climbing fibers to instruct plasticity induction during ipsiversive head turns. Ablation of an MLI circuit for PC disinhibition prevents gain-increase learning during VOR performance errors which was rescued by re-imposing PC disinhibition through MLI activity suppression. Our findings point to a decisive role for MLIs in gating climbing-fiber-mediated learning through their context-dependent inhibition of PCs.

Climbing fiber multi-innervation of mouse Purkinje dendrites with arborization common to human

Canonically, each Purkinje cell (PC) in the adult cerebellum receives only one climbing fiber (CF) from the inferior olive. Underlying current theories of cerebellar function is the notion that this highly conserved one-to-one relationship renders Purkinje dendrites into a single computational compartment. However, we discovered that multiple primary dendrites are a near-universal morphological feature in humans. Using tract tracing, immunolabeling, and in vitro electrophysiology, we found that in mice ~25% of mature multibranched cells receive more than one CF input. Two-photon calcium imaging in vivo revealed that separate dendrites can exhibit distinct response properties to sensory stimulation, indicating that some multibranched cells integrate functionally independent CF-receptive fields. These findings indicate that PCs are morphologically and functionally more diverse than previously thought.

Overexpression of the autism candidate gene Cyfip1 pathologically enhances olivo-cerebellar signaling in mice

Cyfip1, the gene encoding cytoplasmic FMR1 interacting protein 1, has been of interest as an autism candidate gene for years. A potential role in autism spectrum disorder (ASD) is suggested by its location on human chromosome 15q11-13, an instable region that gives rise to a variety of copy number variations associated with syndromic autism. In addition, the CYFIP1 protein acts as a binding partner to Fragile X Messenger Ribonucleoprotein (FMRP) in the regulation of translation initiation. Mutation of FMR1, the gene encoding FMRP, causes Fragile X syndrome, another form of syndromic autism. Here, in mice overexpressing CYFIP1, we study response properties of cerebellar Purkinje cells to activity of the climbing fiber input that originates from the inferior olive and provides an instructive signal in sensorimotor input analysis and plasticity. We find that CYFIP1 overexpression results in enhanced localization of the synaptic organizer neurexin 1 (NRXN1) at climbing fiber synaptic input sites on Purkinje cell primary dendrites and concomitant enhanced climbing fiber synaptic transmission (CF-EPSCs) measured using whole-cell patch-clamp recordings from Purkinje cells in vitro. Moreover, using two-photon measurements of GCaMP6f-encoded climbing fiber signals in Purkinje cells of intact mice, we observe enhanced responses to air puff stimuli applied to the whisker field. These findings resemble our previous phenotypic observations in a mouse model for the human 15q11-13 duplication, which does not extend to the Cyfip1 locus. Thus, our study demonstrates that CYFIP1 overexpression shares a limited set of olivo-cerebellar phenotypes as those resulting from an increased number of copies of non-overlapping genes located on chromosome 15q11-13.

Retinoic acid supplementation ameliorates motor incoordination via RARα-CBLN2 in the cerebellum of a prenatal valproic acid-exposed rat autism model

In addition to their core symptoms, most individuals with autism spectrum disorder (ASD) also experience motor impairments. These impairments are often linked to the cerebellum, which is the focus of the current study. Herein, we utilized a prenatal valproic acid (VPA)-induced rat model of autism and performed RNA sequencing in the cerebellum. Relative to control animals, the VPA-treated offspring demonstrated both abnormal motor coordination and impaired dendritic arborization of Purkinje cells (PCs). Concurrently, we observed a decrease in the cerebellar expression of retinoic acid (RA) synthesis enzymes (RDH10, ALDH1A1), metabolic enzyme (CYP26A2), and lower levels of RA, retinoic acid receptor α (RARα), and Cerebellin2 (CBLN2) in the VPA-treated offspring. However, RA supplementation ameliorated these deficits, restoring motor coordination, normalizing PCs dendritic arborization, and increasing the expression of RA, RARα, and CBLN2. Further, ChIP assays confirmed that RA supplementation enhanced RARα's binding capacity to CBLN2 promoters. Collectively, these findings highlight the therapeutic potential of RA for treating motor incoordination in VPA-induced autism, acting through the RARα-CBLN2 pathway.

Genetic influences on motor learning and superperformance mutants revealed by random mutational survey of mouse locomotion

Evolution depends upon genetic variations that influence physiology. As defined in a genetic screen, phenotypic performance may be enhanced or degraded by such mutations. We set out to detect mutations that influence motor function, including motor learning. Thus, we tested the motor effects of 36,444 non-synonymous coding/splicing mutations induced in the germline of C57BL/6J mice with N-ethyl-N-nitrosourea by measuring changes in the performance of repetitive rotarod trials while blinded to genotype. Automated meiotic mapping was used to implicate individual mutations in causation. 32,726 mice bearing all the variant alleles were screened. This was complemented with the simultaneous testing of 1,408 normal mice for reference. 16.3% of autosomal genes were thus rendered detectably hypomorphic or nullified by mutations in homozygosity and motor tested in at least 3 mice. This approach allowed us to identify superperformance mutations in Rif1, Tk1, Fan1 and Mn1. These genes are primarily related, among other less well characterized functions, to nucleic acid biology. We also associated distinct motor learning patterns with groups of functionally related genes. These functional sets included preferentially histone H3 methyltransferase activity for mice that learnt at an accelerated rate relative to the rest of mutant mice. The results allow for an estimation of the fraction of mutations that can modify a behavior influential for evolution such as locomotion. They may also enable, once the loci are further validated and the mechanisms elucidated, the harnessing of the activity of the newly identified genes to enhance motor ability or to counterbalance disability or disease.

CSMD3 Deficiency Leads to Motor Impairments and Autism-Like Behaviors via Dysfunction of Cerebellar Purkinje Cells in Mice

Autism spectrum disorder (ASD) is a neurodevelopmental disorder with highly heritable heterogeneity. Mutations of CUB and sushi multiple domains 3 (CSMD3) gene have been reported in individuals with ASD. However, the underlying mechanisms of CSMD3 for the onset of ASD remain unexplored. Here, using male CSMD3 knock-out (CSMD3 -/-) mice, we found that genetic deletion of CSMD3 produced core autistic-like symptoms (social interaction deficits, restricted interests, and repetitive and stereotyped behaviors) and motor dysfunction in mice, indicating that the CSMD3 gene can be considered as a candidate for ASD. Moreover, we discovered that the ablation of CSMD3 in mice led to abnormal cerebellar Purkinje cell (PC) morphology in Crus I/II lobules, including aberrant developmental dendritogenesis and spinogenesis of PCs. Furthermore, combining in vivo fiber photometry calcium imaging and ex vivo electrophysiological recordings, we showed that the CSMD3 -/- mice exhibited an increased neuronal activity (calcium fluorescence signals) in PCs of Crus I/II lobules in response to movement activity, as well as an enhanced intrinsic excitability of PCs and an increase of excitatory rather than inhibitory synaptic input to the PCs, and an impaired long-term depression at the parallel fiber-PC synapse. These results suggest that CSMD3 plays an important role in the development of cerebellar PCs. Loss of CSMD3 causes abnormal PC morphology and dysfunction in the cerebellum, which may underlie the pathogenesis of motor deficits and core autistic-like symptoms in CSMD3 -/- mice. Our findings provide novel insight into the pathophysiological mechanisms by which CSMD3 mutations cause impairments in cerebellar function that may contribute to ASD.SIGNIFICANCE STATEMENT Autism spectrum disorder (ASD) is a neurodevelopmental disorder with highly heritable heterogeneity. Advances in genomic analysis have contributed to numerous candidate genes for the risk of ASD. Recently, a novel giant gene CSMD3 encoding a protein with CUB and sushi multiple domains (CSMDs) has been identified as a candidate gene for ASD. However, the underlying mechanisms of CSMD3 for the onset of ASD remain largely unknown. Here, we unravel that loss of CSMD3 results in abnormal morphology, increased intrinsic excitabilities, and impaired synaptic plasticity in cerebellar PCs, subsequently leading to motor deficits and ASD-like behaviors in mice. These results provide novel insight into the pathophysiological mechanisms by which CSMD3 mutations cause impairments in cerebellar function that may contribute to ASD.

Critical periods and Autism Spectrum Disorders, a role for sleep

Brain development relies on both experience and genetically defined programs. Time windows where certain brain circuits are particularly receptive to external stimuli, resulting in heightened plasticity, are referred to as "critical periods". Sleep is thought to be essential for normal brain development. Importantly, studies have shown that sleep enhances critical period plasticity and promotes experience-dependent synaptic pruning in the developing mammalian brain. Therefore, normal plasticity during critical periods depends on sleep. Problems falling and staying asleep occur at a higher rate in Autism Spectrum Disorder (ASD) relative to typical development. In this review, we explore the potential link between sleep, critical period plasticity, and ASD. First, we review the importance of critical period plasticity in typical development and the role of sleep in this process. Next, we summarize the evidence linking ASD with deficits in synaptic plasticity in rodent models of high-confidence ASD gene candidates. We then show that the high-confidence rodent models of ASD that show sleep deficits also display plasticity deficits. Given how important sleep is for critical period plasticity, it is essential to understand the connections between synaptic plasticity, sleep, and brain development in ASD. However, studies investigating sleep or plasticity during critical periods in ASD mouse models are lacking. Therefore, we highlight an urgent need to consider developmental trajectory in studies of sleep and plasticity in neurodevelopmental disorders.

Virtual reality-based real-time imaging reveals abnormal cortical dynamics during behavioral transitions in a mouse model of autism

Functional connectivity (FC) can provide insight into cortical circuit dysfunction in neuropsychiatric disorders. However, dynamic changes in FC related to locomotion with sensory feedback remain to be elucidated. To investigate FC dynamics in locomoting mice, we develop mesoscopic Ca2+ imaging with a virtual reality (VR) environment. We find rapid reorganization of cortical FC in response to changing behavioral states. By using machine learning classification, behavioral states are accurately decoded. We then use our VR-based imaging system to study cortical FC in a mouse model of autism and find that locomotion states are associated with altered FC dynamics. Furthermore, we identify FC patterns involving the motor area as the most distinguishing features of the autism mice from wild-type mice during behavioral transitions, which might correlate with motor clumsiness in individuals with autism. Our VR-based real-time imaging system provides crucial information to understand FC dynamics linked to behavioral abnormality of neuropsychiatric disorders.

Baseline Gait and Motor Function Predict Long-Term Severity of Neurological Outcomes of Viral Infection

Neurological dysfunction following viral infection varies among individuals, largely due to differences in their genetic backgrounds. Gait patterns, which can be evaluated using measures of coordination, balance, posture, muscle function, step-to-step variability, and other factors, are also influenced by genetic background. Accordingly, to some extent gait can be characteristic of an individual, even prior to changes in neurological function. Because neuromuscular aspects of gait are under a certain degree of genetic control, the hypothesis tested was that gait parameters could be predictive of neuromuscular dysfunction following viral infection. The Collaborative Cross (CC) mouse resource was utilized to model genetically diverse populations and the DigiGait treadmill system used to provide quantitative and objective measurements of 131 gait parameters in 142 mice from 23 CC and SJL/J strains. DigiGait measurements were taken prior to infection with the neurotropic virus Theiler's Murine Encephalomyelitis Virus (TMEV). Neurological phenotypes were recorded over 90 days post-infection (d.p.i.), and the cumulative frequency of the observation of these phenotypes was statistically associated with discrete baseline DigiGait measurements. These associations represented spatial and postural aspects of gait influenced by the 90 d.p.i. phenotype score. Furthermore, associations were found between these gait parameters with sex and outcomes considered to show resistance, resilience, or susceptibility to severe neurological symptoms after long-term infection. For example, higher pre-infection measurement values for the Paw Drag parameter corresponded with greater disease severity at 90 d.p.i. Quantitative trait loci significantly associated with these DigiGait parameters revealed potential relationships between 28 differentially expressed genes (DEGs) and different aspects of gait influenced by viral infection. Thus, these potential candidate genes and genetic variations may be predictive of long-term neurological dysfunction. Overall, these findings demonstrate the predictive/prognostic value of quantitative and objective pre-infection DigiGait measurements for viral-induced neuromuscular dysfunction.

Transcranial cortex-wide Ca2+ imaging for the functional mapping of cortical dynamics

Visualization and tracking of the information flow in the broader brain area are essential because nerve cells make a vast network in the brain. Fluorescence Ca²⁺ imaging is a simultaneous visualization of brain cell activities in a wide area. Instead of classical chemical indicators, developing various types of transgenic animals that express Ca²⁺-sensitive fluorescent proteins enables us to observe brain activities in living animals at a larger scale for a long time. Multiple kinds of literature have reported that transcranial imaging of such transgenic animals is practical for monitoring the wide-field information flow across the broad brain regions, although it has a lower spatial resolution. Notably, this technique is helpful for the initial evaluation of cortical function in disease models. This review will introduce fully intact transcranial macroscopic imaging and cortex-wide Ca²⁺ imaging as practical applications.

Deficits in Cerebellum-Dependent Learning and Cerebellar Morphology in Male and Female BTBR Autism Model Mice

Recently, there has been increased interest in the role of the cerebellum in autism spectrum disorder (ASD). To better understand the pathophysiological role of the cerebellum in ASD, it is necessary to have a variety of mouse models that have face validity for cerebellar disruption in humans. Here, we add to the literature on the cerebellum in mouse models of autism with the characterization of the cerebellum in the idiopathic BTBR T + Itpr3tf/J (BTBR) inbred mouse strain, which has behavioral phenotypes that are reminiscent of ASD in patients. When we examined both male and female BTBR mice in comparison to C57BL/6J (C57) controls, we noted that both sexes of BTBR mice showed motor coordination deficits characteristic of cerebellar dysfunction, but only the male mice showed differences in delay eyeblink conditioning, a cerebellum-dependent learning task that is known to be disrupted in ASD patients. Both male and female BTBR mice showed considerable expansion of, and abnormal foliation in, the cerebellum vermis—including a significant expansion of specific lobules in the anterior cerebellum. In addition, we found a slight but significant decrease in Purkinje cell density in both male and female BTBR mice, irrespective of the lobule. Finally, there was a marked reduction of Purkinje cell dendritic spine density in both male and female BTBR mice. These findings suggest that, for the most part, the BTBR mouse model phenocopies many of the characteristics of the subpopulation of ASD patients that have a hypertrophic cerebellum. We discuss the significance of strain differences in the cerebellum as well as the importance of this first effort to identify both similarities and differences between male and female BTBR mice with regard to the cerebellum.

Role of cerebellar cortex in associative learning and memory in guinea pigs

Time-related cognitive function refers to the capacity of the brain to store, extract, and process specific information. Previous studies demonstrated that the cerebellar cortex participates in advanced cognitive functions, but the role of the cerebellar cortex in cognitive functions is unclear. We established a behavioral model using classical eyeblink conditioning to study the role of the cerebellar cortex in associative learning and memory and the underlying mechanisms. We performed an investigation to determine whether eyeblink conditioning could be established by placing the stimulating electrode in the middle cerebellar peduncle. Behavior training was performed using a microcurrent pulse as a conditioned stimulus to stimulate the middle cerebellar peduncle and corneal blow as an unconditioned stimulus. After 10 consecutive days of training, a conditioned response was successfully achieved in the Delay, Trace-200-ms, and Trace-300-ms groups of guinea pigs, with acquisition rates of >60%, but the Trace-400-ms and control groups did not achieve a conditioned stimulus-related blink conditioned response. It could be a good model for studying the function of the cerebellum during the establishment of eyeblink conditioning.

Sensory Over-responsivity and Aberrant Plasticity in Cerebellar Cortex in a Mouse Model of Syndromic Autism

Background

Patients with autism spectrum disorder often show altered responses to sensory stimuli as well as motor deficits, including an impairment of delay eyeblink conditioning, which involves integration of sensory signals in the cerebellum. Here, we identify abnormalities in parallel fiber (PF) and climbing fiber (CF) signaling in the mouse cerebellar cortex that may contribute to these pathologies.

Methods

We used a mouse model for the human 15q11-13 duplication (patDp/+) and studied responses to sensory stimuli in Purkinje cells from awake mice using two-photon imaging of GCaMP6f signals. Moreover, we examined synaptic transmission and plasticity using in vitro electrophysiological, immunohistochemical, and confocal microscopic techniques.

Results

We found that spontaneous and sensory-evoked CF-calcium transients are enhanced in patDp/+ Purkinje cells, and aversive movements are more severe across sensory modalities. We observed increased expression of the synaptic organizer NRXN1 at CF synapses and ectopic spread of these synapses to fine dendrites. CF-excitatory postsynaptic currents recorded from Purkinje cells are enlarged in patDp/+ mice, while responses to PF stimulation are reduced. Confocal measurements show reduced PF+CF-evoked spine calcium transients, a key trigger for PF long-term depression, one of several plasticity types required for eyeblink conditioning learning. Long-term depression is impaired in patDp/+ mice but is rescued on pharmacological enhancement of calcium signaling.

Conclusions

Our findings suggest that this genetic abnormality causes a pathological inflation of CF signaling, possibly resulting from enhanced NRXN1 expression, with consequences for the representation of sensory stimuli by the CF input and for PF synaptic organization and plasticity.

Probing the structure and function of locus coeruleus projections to CNS motor centers

The brainstem nucleus locus coeruleus (LC) sends projections to the forebrain, brainstem, cerebellum and spinal cord and is a source of the neurotransmitter norepinephrine (NE) in these areas. For more than 50 years, LC was considered to be homogeneous in structure and function such that NE would be released uniformly and act simultaneously on the cells and circuits that receive LC projections. However, recent studies have provided evidence that LC is modular in design, with segregated output channels and the potential for differential release and action of NE in its projection fields. These new findings have prompted a radical shift in our thinking about LC operations and demand revision of theoretical constructs regarding impact of the LC-NE system on behavioral outcomes in health and disease. Within this context, a major gap in our knowledge is the relationship between the LC-NE system and CNS motor control centers. While we know much about the organization of the LC-NE system with respect to sensory and cognitive circuitries and the impact of LC output on sensory guided behaviors and executive function, much less is known about the role of the LC-NE pathway in motor network operations and movement control. As a starting point for closing this gap in understanding, we propose using an intersectional recombinase-based viral-genetic strategy TrAC (Tracing Axon Collaterals) as well as established ex vivo electrophysiological assays to characterize efferent connectivity and physiological attributes of mouse LC-motor network projection neurons. The novel hypothesis to be tested is that LC cells with projections to CNS motor centers are scattered throughout the rostral-caudal extent of the nucleus but collectively display a common set of electrophysiological properties. Additionally, we expect to find these LC projection neurons maintain an organized network of axon collaterals capable of supporting selective, synchronous release of NE in motor circuitries for the purpose of coordinately regulating operations across networks that are responsible for balance and movement dynamics. Investigation of this hypothesis will advance our knowledge of the role of the LC-NE system in motor control and provide a basis for treating movement disorders resulting from disease, injury, or normal aging.

Immune-Triggered Forms of Plasticity Across Brain Regions

Immune cells play numerous roles in the host defense against the invasion of microorganisms and pathogens, which induces the release of inflammatory mediators (e.g., cytokines and chemokines). In the CNS, microglia is the major resident immune cell. Recent efforts have revealed the diversity of the cell types and the heterogeneity of their functions. The refinement of the synapse structure was a hallmark feature of the microglia, while they are also involved in the myelination and capillary dynamics. Another promising feature is the modulation of the synaptic transmission as synaptic plasticity and the intrinsic excitability of neurons as non-synaptic plasticity. Those modulations of physiological properties of neurons are considered induced by both transient and chronic exposures to inflammatory mediators, which cause behavioral disorders seen in mental illness. It is plausible for astrocytes and pericytes other than microglia and macrophage to induce the immune-triggered plasticity of neurons. However, current understanding has yet achieved to unveil what inflammatory mediators from what immune cells or glia induce a form of plasticity modulating pre-, post-synaptic functions and intrinsic excitability of neurons. It is still unclear what ion channels and intracellular signaling of what types of neurons in which brain regions of the CNS are involved. In this review, we introduce the ubiquitous modulation of the synaptic efficacy and the intrinsic excitability across the brain by immune cells and related inflammatory cytokines with the mechanism for induction. Specifically, we compare neuro-modulation mechanisms by microglia of the intrinsic excitability of cerebellar Purkinje neurons with cerebral pyramidal neurons, stressing the inverted directionality of the plasticity. We also discuss the suppression and augmentation of the extent of plasticity by inflammatory mediators, as the meta-plasticity by immunity. Lastly, we sum up forms of immune-triggered plasticity in the different brain regions with disease relevance. Together, brain immunity influences our cognition, sense, memory, and behavior via immune-triggered plasticity.

The Cerebellar Involvement in Autism Spectrum Disorders: From the Social Brain to Mouse Models

Autism spectrum disorders (ASD) are pervasive neurodevelopmental disorders that include a variety of forms and clinical phenotypes. This heterogeneity complicates the clinical and experimental approaches to ASD etiology and pathophysiology. To date, a unifying theory of these diseases is still missing. Nevertheless, the intense work of researchers and clinicians in the last decades has identified some ASD hallmarks and the primary brain areas involved. Not surprisingly, the areas that are part of the so-called “social brain”, and those strictly connected to them, were found to be crucial, such as the prefrontal cortex, amygdala, hippocampus, limbic system, and dopaminergic pathways. With the recent acknowledgment of the cerebellar contribution to cognitive functions and the social brain, its involvement in ASD has become unmistakable, though its extent is still to be elucidated. In most cases, significant advances were made possible by recent technological developments in structural/functional assessment of the human brain and by using mouse models of ASD. Mouse models are an invaluable tool to get insights into the molecular and cellular counterparts of the disease, acting on the specific genetic background generating ASD-like phenotype. Given the multifaceted nature of ASD and related studies, it is often difficult to navigate the literature and limit the huge content to specific questions. This review fulfills the need for an organized, clear, and state-of-the-art perspective on cerebellar involvement in ASD, from its connections to the social brain areas (which are the primary sites of ASD impairments) to the use of monogenic mouse models.

Cerebellar and Striatal Implications in Autism Spectrum Disorders: From Clinical Observations to Animal Models

Autism spectrum disorders (ASD) are complex conditions that stem from a combination of genetic, epigenetic and environmental influences during early pre- and postnatal childhood. The review focuses on the cerebellum and the striatum, two structures involved in motor, sensory, cognitive and social functions altered in ASD. We summarize clinical and fundamental studies highlighting the importance of these two structures in ASD. We further discuss the relation between cellular and molecular alterations with the observed behavior at the social, cognitive, motor and gait levels. Functional correlates regarding neuronal activity are also detailed wherever possible, and sexual dimorphism is explored pointing to the need to apprehend ASD in both sexes, as findings can be dramatically different at both quantitative and qualitative levels. The review focuses also on a set of three recent papers from our laboratory where we explored motor and gait function in various genetic and environmental ASD animal models. We report that motor and gait behaviors can constitute an early and quantitative window to the disease, as they often correlate with the severity of social impairments and loss of cerebellar Purkinje cells. The review ends with suggestions as to the main obstacles that need to be surpassed before an appropriate management of the disease can be proposed.

Microglia: Synaptic modulator in autism spectrum disorder

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by variable impairment of social communication and repetitive behaviors, highly restricted interests, and/or sensory behaviors beginning early in life. Many individuals with ASD have dysfunction of microglia, which may be closely related to neuroinflammation, making microglia play an important role in the pathogenesis of ASD. Mounting evidence indicates that microglia, the resident immune cells of the brain, are required for proper brain function, especially in the maintenance of neuronal circuitry and control of behavior. Dysfunction of microglia will ultimately affect the neural function in a variety of ways, including the formation of synapses and alteration of excitatory-inhibitory balance. In this review, we provide an overview of how microglia actively interact with neurons in physiological conditions and modulate the fate and functions of synapses. We put a spotlight on the multi-dimensional neurodevelopmental roles of microglia, especially in the essential influence of synapses, and discuss how microglia are currently thought to influence ASD progression.

Social Deficits and Cerebellar Degeneration in Purkinje Cell Scn8a Knockout Mice

Mutations in the SCN8A gene encoding the voltage-gated sodium channel α-subunit Nav1. 6 have been reported in individuals with epilepsy, intellectual disability and features of autism spectrum disorder. SCN8A is widely expressed in the central nervous system, including the cerebellum. Cerebellar dysfunction has been implicated in autism spectrum disorder. We investigated conditional Scn8a knockout mice under C57BL/6J strain background that specifically lack Scn8a expression in cerebellar Purkinje cells (Scn8a ^flox/flox , L7Cre ⁺ mice). Cerebellar morphology was analyzed by immunohistochemistry and MR imaging. Mice were subjected to a battery of behavioral tests including the accelerating rotarod, open field, elevated plus maze, light-dark transition box, three chambers, male-female interaction, social olfaction, and water T-maze tests. Patch clamp recordings were used to evaluate evoked action potentials in Purkinje cells. Behavioral phenotyping demonstrated that Scn8a ^flox/flox , L7Cre ⁺ mice have impaired social interaction, motor learning and reversal learning as well as increased repetitive behavior and anxiety-like behaviors. By 5 months of age, Scn8a ^flox/flox , L7Cre ⁺ mice began to exhibit cerebellar Purkinje cell loss and reduced molecular thickness. At 9 months of age, Scn8a ^flox/flox , L7Cre ⁺ mice exhibited decreased cerebellar size and a reduced number of cerebellar Purkinje cells more profoundly, with evidence of additional neurodegeneration in the molecular layer and deep cerebellar nuclei. Purkinje cells in Scn8a ^flox/flox , L7Cre ⁺ mice exhibited reduced repetitive firing. Taken together, our experiments indicated that loss of Scn8a expression in cerebellar Purkinje cells leads to cerebellar degeneration and several ASD-related behaviors. Our study demonstrated the specific contribution of loss of Scn8a in cerebellar Purkinje cells to behavioral deficits characteristic of ASD. However, it should be noted that our observed effects reported here are specific to the C57BL/6 genome type.

Adenosine A2A receptor modulates microglia-mediated synaptic pruning of the retinogeniculate pathway during postnatal development

Synapse pruning is essential not only for the developmental establishment of synaptic connections in the brain but also for the pathogenesis of neurodevelopmental and neurodegenerative disorders. However, there are no effective pharmacological means to regulate synaptic pruning during early development. Using the eye-specific segregation of the dorsal lateral geniculate nucleus (dLGN) as a model of synaptic pruning coupled with adenosine A2A receptor (A2AR) antagonism and knockout, we demonstrated while genetic deletion of the A2AR throughout the development attenuated eye-specific segregation with the attenuated microglial phagocytosis at postnatal day 5 (P5), selective treatment with the A2AR antagonist KW6002 at P2-P4 facilitated synaptic pruning of visual pathway with microglial activation, increased lysosomal activity in microglia and increased microglial engulfment of retinal ganglion cell (RGC) inputs in the dLGN at P5 (but not P10). Furthermore, KW6002-mediated facilitation of synaptic pruning was activity-dependent since tetrodotoxin (TTX) treatment abolished the KW6002 facilitation. Moreover, the A2AR antagonist also modulated postsynaptic proteins and synaptic density at early postnatal stages as revealed by the reduced immunoreactivity of postsynaptic proteins (Homer1 and metabotropic glutamate receptor 5) and colocalization of presynaptic VGlut2 and postsynaptic Homer1 puncta in the dLGN. These findings suggest that A2AR can control pruning by multiple actions involving the retinal wave, microglia engulfment, and postsynaptic stability. Thus, A2AR antagonists may represent a novel pharmacological strategy to modulate microglia-mediated synaptic pruning and treatment of neurodevelopmental disorders associated with dysfunctional pruning.

Hyperexcitable Phenotypes in Induced Pluripotent Stem Cell-Derived Neurons From Patients With 15q11-q13 Duplication Syndrome, a Genetic Form of Autism

BACKGROUND

Chromosome 15q11-q13 duplication syndrome (Dup15q) is a neurogenetic disorder caused by duplications of the maternal copy of this region. In addition to hypotonia, motor deficits, and language impairments, patients with Dup15q commonly meet the criteria for autism spectrum disorder and have a high prevalence of seizures. It is known from mouse models that synaptic impairments are a strong component of Dup15q pathophysiology; however, cellular phenotypes that relate to seizures are less clear. The development of patient-derived induced pluripotent stem cells provides a unique opportunity to study human neurons with the exact genetic disruptions that cause Dup15q.

METHODS

Here, we explored electrophysiological phenotypes in induced pluripotent stem cell-derived neurons from 4 patients with Dup15q compared with 6 unaffected control subjects, 1 patient with a 15q11-q13 paternal duplication, and 3 patients with Angelman syndrome.

RESULTS

We identified several properties of Dup15q neurons that could contribute to neuronal hyperexcitability and seizure susceptibility. Compared with control neurons, Dup15q neurons had increased excitatory synaptic event frequency and amplitude, increased density of dendritic protrusions, increased action potential firing, and decreased inhibitory synaptic transmission. Dup15q neurons also showed impairments in activity-dependent synaptic plasticity and homeostatic synaptic scaling. Finally, Dup15q neurons showed an increased frequency of spontaneous action potential firing compared with control neurons, in part due to disruption of KCNQ2 potassium channels.

CONCLUSIONS

Together, these data point to multiple electrophysiological mechanisms of hyperexcitability that may provide new targets for the treatment of seizures and other phenotypes associated with Dup15q.

Placental endocrine function shapes cerebellar development and social behavior

Compromised placental function or premature loss has been linked to diverse neurodevelopmental disorders. Here we show that placenta allopregnanolone (ALLO), a progesterone-derived GABA-A receptor (GABA_AR) modulator, reduction alters neurodevelopment in a sex-linked manner. A new conditional mouse model, in which the gene encoding ALLO's synthetic enzyme (akr1c14) is specifically deleted in trophoblasts, directly demonstrated that placental ALLO insufficiency led to cerebellar white matter abnormalities that correlated with autistic-like behavior only in male offspring. A single injection of ALLO or muscimol, a GABA_AR agonist, during late gestation abolished these alterations. Comparison of male and female human preterm infant cerebellum also showed sex-linked myelination marker alteration, suggesting similarities between mouse placental ALLO insufficiency and human preterm brain development. This study reveals a new role for a placental hormone in shaping brain regions and behaviors in a sex-linked manner. Placental hormone replacement might offer novel therapeutic opportunities to prevent later neurobehavioral disorders.

Lack of Sez6 Family Proteins Impairs Motor Functions, Short-Term Memory, and Cognitive Flexibility and Alters Dendritic Spine Properties

Seizure-related gene 6 (Sez6), Sez6-Like (Sez6L), and Sez6-Like 2 (Sez6L2) comprise a family of homologous proteins widely expressed throughout the brain that have been linked to neurodevelopmental and psychiatric disorders. Here, we use Sez6 triple knockout (TKO) mice, which lack all three Sez6 family proteins, to demonstrate that Sez6 family proteins regulate dendritic spine structure and cognitive functions, motor learning, and maintenance of motor functions across the lifespan. Compared to WT controls, we found that Sez6 TKO mice had impaired motor learning and their motor coordination was negatively affected from 6 weeks old and declined more rapidly as they aged. Sez6 TKO mice had reduced spine density in the hippocampus and dendritic spines were shifted to more immature morphologies in the somatosensory cortex. Cognitive testing revealed that they had enhanced stress responsiveness, impaired working, and spatial short-term memory but intact spatial long-term memory in the Morris water maze albeit accompanied by a reversal deficit. Our study demonstrates that the lack of Sez6 family proteins results in phenotypes commonly associated with neuropsychiatric disorders making it likely that Sez6 family proteins contribute to the complex etiologies of these disorders.

Sleep Deprivation Impairs Learning-Induced Increase in Hippocampal Sharp Wave Ripples and Associated Spike Dynamics during Recovery Sleep

Sleep deprivation (SD) causes deficits in off-line memory consolidation, but the underlying network oscillation mechanisms remain unclear. Hippocampal sharp wave ripple (SWR) oscillations play a critical role in off-line memory consolidation. Therefore, we trained mice to learn a hippocampus-dependent trace eyeblink conditioning (tEBC) task and explored the influence of 1.5-h postlearning SD on hippocampal SWRs and related spike dynamics during recovery sleep. We found an increase in hippocampal SWRs during postlearning sleep, which predicted the consolidation of tEBC in conditioned mice. In contrast, sleep-deprived mice showed a loss of tEBC learning-induced increase in hippocampal SWRs during recovery sleep. Moreover, the sleep-deprived mice exhibited weaker reactivation of tEBC learning-associated pyramidal cells in hippocampal SWRs during recovery sleep. In line with these findings, tEBC consolidation was impaired in sleep-deprived mice. Furthermore, sleep-deprived mice showed augmented fast excitation from pyramidal cells to interneurons and enhanced participation of interneurons in hippocampal SWRs during recovery sleep. Among various interneurons, parvalbumin-expressing interneurons specifically exhibited overexcitation during hippocampal SWRs. Our findings suggest that altered hippocampal SWRs and associated spike dynamics during recovery sleep may be candidate network oscillation mechanisms underlying SD-induced memory deficits.

Protein Phosphorylation Signaling Cascades in Autism: The Role of mTOR Pathway

The mammalian target of rapamycin (mTOR) signaling pathway is a central regulator of cell metabolism, growth, and survival in response to hormones, growth factors, nutrients, and stress-induced signals. In this review, we analyzed the studies on the molecular abnormalities of the mTOR-associated signaling cascades in autism spectrum disorders (ASDs) and outlined the prospects for the pathogenicity-targeting pharmacotherapeutic approaches to ASDs, in particular syndromic ASDs. Based on available experimental and clinical data, we suggest that very early detection of molecular abnormalities in the ASD risk groups can be facilitated by using peripheral blood platelets. Also, identification of the time window of critical dysregulations in the described pathways in the ASD risk groups might suggest further research directions leading to more efficacious pharmacotherapeutic interventions in ASDs.

Adaptive Prediction for Social Contexts: The Cerebellar Contribution to Typical and Atypical Social Behaviors

Social interactions involve processes ranging from face recognition to understanding others' intentions. To guide appropriate behavior in a given context, social interactions rely on accurately predicting the outcomes of one's actions and the thoughts of others. Because social interactions are inherently dynamic, these predictions must be continuously adapted. The neural correlates of social processing have largely focused on emotion, mentalizing, and reward networks, without integration of systems involved in prediction. The cerebellum forms predictive models to calibrate movements and adapt them to changing situations, and cerebellar predictive modeling is thought to extend to nonmotor behaviors. Primary cerebellar dysfunction can produce social deficits, and atypical cerebellar structure and function are reported in autism, which is characterized by social communication challenges and atypical predictive processing. We examine the evidence that cerebellar-mediated predictions and adaptation play important roles in social processes and argue that disruptions in these processes contribute to autism.

Inhibition of Elevated Ras-MAPK Signaling Normalizes Enhanced Motor Learning and Excessive Clustered Dendritic Spine Stabilization in the MECP2-Duplication Syndrome Mouse Model of Autism

The inflexible repetitive behaviors and "insistence on sameness" seen in autism imply a defect in neural processes controlling the balance between stability and plasticity of synaptic connections in the brain. It has been proposed that abnormalities in the Ras-ERK/MAPK pathway, a key plasticity-related cell signaling pathway known to drive consolidation of clustered synaptic connections, underlie altered learning phenotypes in autism. However, a link between altered Ras-ERK signaling and clustered dendritic spine plasticity has yet to be explored in an autism animal model in vivo The formation and stabilization of dendritic spine clusters is abnormally increased in the MECP2-duplication syndrome mouse model of syndromic autism, suggesting that ERK signaling may be increased. Here, we show that the Ras-ERK pathway is indeed hyperactive following motor training in MECP2-duplication mouse motor cortex. Pharmacological inhibition of ERK signaling normalizes the excessive clustered spine stabilization and enhanced motor learning behavior in MECP2-duplication mice. We conclude that hyperactive ERK signaling may contribute to abnormal clustered dendritic spine consolidation and motor learning in this model of syndromic autism.

Little cells of the little brain: microglia in cerebellar development and function

Microglia are long-lived resident macrophages of the brain with diverse roles that span development, adulthood, and aging. Once thought to be a relatively homogeneous population, there is a growing recognition that microglia are highly specialized to suit their specific brain region. Cerebellar microglia represent an example of such specialization, exhibiting a dynamical, transcriptional, and immunological profile that differs from that of other microglial populations. Here we review the evidence that cerebellar microglia shape the cerebellar environment and are in turn shaped by it. We examine the roles microglia play in cerebellar function, development, and aging. The emerging findings on cerebellar microglia may also provide insights into disease processes involving cerebellar dysfunction.

Genetic dissection identifies Necdin as a driver gene in a mouse model of paternal 15q duplications

Maternally inherited duplication of chromosome 15q11-q13 (Dup15q) is a pathogenic copy number variation (CNV) associated with autism spectrum disorder (ASD). Recently, paternally derived duplication has also been shown to contribute to the development of ASD. The molecular mechanism underlying paternal Dup15q remains unclear. Here, we conduct genetic and overexpression-based screening and identify Necdin (Ndn) as a driver gene for paternal Dup15q resulting in the development of ASD-like phenotypes in mice. An excess amount of Ndn results in enhanced spine formation and density as well as hyperexcitability of cortical pyramidal neurons. We generate 15q dupΔNdn mice with a normalized copy number of Ndn by excising its one copy from Dup15q mice using a CRISPR-Cas9 system. 15q dupΔNdn mice do not show ASD-like phenotypes and show dendritic spine dynamics and cortical excitatory-inhibitory balance similar to wild type animals. Our study provides an insight into the role of Ndn in paternal 15q duplication and a mouse model of paternal Dup15q syndrome.

An Autism-Associated Neuroligin-3 Mutation Affects Developmental Synapse Elimination in the Cerebellum

Neuroligin is a postsynaptic cell-adhesion molecule that is involved in synapse formation and maturation by interacting with presynaptic neurexin. Mutations in neuroligin genes, including the arginine to cystein substitution at the 451st amino acid residue (R451C) of neuroligin-3 (NLGN3), have been identified in patients with autism spectrum disorder (ASD). Functional magnetic resonance imaging and examination of post-mortem brain in ASD patients implicate alteration of cerebellar morphology and Purkinje cell (PC) loss. In the present study, we examined possible association between the R451C mutation in NLGN3 and synaptic development and function in the mouse cerebellum. In NLGN3-R451C mutant mice, the expression of NLGN3 protein in the cerebellum was reduced to about 10% of the level of wild-type mice. Elimination of redundant climbing fiber (CF) to PC synapses was impaired from postnatal day 10–15 (P10–15) in NLGN3-R451C mutant mice, but majority of PCs became mono-innervated as in wild-type mice after P16. In NLGN3-R451C mutant mice, selective strengthening of a single CF relative to the other CFs in each PC was impaired from P16, which persisted into juvenile stage. Furthermore, the inhibition to excitation (I/E) balance of synaptic inputs to PCs was elevated, and calcium transients in the soma induced by strong and weak CF inputs were reduced in NLGN3-R451C mutant mice. These results suggest that a single point mutation in NLGN3 significantly influences the synapse development and refinement in cerebellar circuitry, which might be related to the pathogenesis of ASD.

Behavioral Tests for Mouse Models of Autism: An Argument for the Inclusion of Cerebellum-Controlled Motor Behaviors

Mouse models of Autism Spectrum Disorder (ASD) have been interrogated using a variety of behavioral tests in order to understand the symptoms of ASD. However, the hallmark behaviors that are classically affected in ASD - deficits in social interaction and communication as well as the occurrence of repetitive behaviors - do not have direct murine equivalents. Thus, it is critical to identify the caveats that come with modeling a human disorder in mice. The most commonly used behavioral tests represent complex cognitive processes based on largely unknown brain circuitry. Motor impairments provide an alternative, scientifically rigorous approach to understanding ASD symptoms. Difficulties with motor coordination and learning - seen in both patients and mice - point to an involvement of the cerebellum in ASD pathology. This brain area supports types of motor learning that are conserved throughout vertebrate evolution, allowing for direct comparisons of functional abnormalities between humans with autism and ASD mouse models. Studying simple motor behaviors provides researchers with clearly interpretable results. We describe and evaluate methods used on mouse behavioral assays designed to test for social, communicative, perseverative, anxious, nociceptive, and motor learning abnormalities. We comment on the effectiveness and validity of each test based on how much information its results give, as well as its relevance to ASD, and will argue for an inclusion of cerebellum-supported motor behaviors in the phenotypic description of ASD mouse models. LAY SUMMARY: Mouse models of Autism Spectrum Disorder help us gain insight about ASD symptoms in human patients. However, there are many differences between mice and humans, which makes interpreting behaviors challenging. Here, we discuss a battery of behavioral tests for specific mouse behaviors to explore whether each test does indeed evaluate the intended measure, and whether these tests are useful in learning about ASD.

Cerebellar Dysfunction in Autism Spectrum Disorders: Deriving Mechanistic Insights from an Internal Model Framework

Autism spectrum disorders (ASD) are highly prevalent neurodevelopmental disorders; however, the neurobiological mechanisms underlying disordered behavior in ASD remain poorly understood. Notably, individuals with ASD have demonstrated difficulties generating implicitly derived behavioral predictions and adaptations. Although many brain regions are involved in these processes, the cerebellum contributes an outsized role to these behavioral functions. Consistent with this prominent role, cerebellar dysfunction has been increasingly implicated in ASD. In this review, we will utilize the foundational, theoretical contributions of the late neuroscientist Masao Ito to establish an internal model framework for the cerebellar contribution to ASD-relevant behavioral predictions and adaptations. Additionally, we will also explore and then apply his key experimental contributions towards an improved, mechanistic understanding of the contribution of cerebellar dysfunction to ASD.

Delayed motor learning in a 16p11.2 deletion mouse model of autism is rescued by locus coeruleus activation

Children with autism spectrum disorder often exhibit delays in achieving motor developmental milestones such as crawling, walking and speech articulation. However, little is known about the neural mechanisms underlying motor-related deficits. Here, we reveal that mice with a syntenic deletion of the chromosome 16p11.2, a common copy number variation associated with autism spectrum disorder, also exhibit delayed motor learning without showing gross motor deficits. Using in vivo two-photon imaging in awake mice, we find that layer 2/3 excitatory neurons in the motor cortex of adult male 16p11.2-deletion mice show abnormally high activity during the initial phase of learning, and the process of learning-induced spine reorganization is prolonged. Pharmacogenetic activation of locus coeruleus noradrenergic neurons was sufficient to rescue the circuit deficits and the delayed motor learning in these mice. Our results unveil an unanticipated role of noradrenergic neuromodulation in improving the delayed motor learning in 16p11.2-deletion male mice.

The autism-associated protein CHD8 is required for cerebellar development and motor function

Mutations in the gene encoding the chromatin remodeler chromodomain helicase DNA-binding protein 8 (CHD8) are a highly penetrant risk factor for autism spectrum disorder (ASD). Although cerebellar abnormalities have long been thought to be related to ASD pathogenesis, it has remained largely unknown whether dysfunction of CHD8 in the cerebellum contributes to ASD phenotypes. We here show that cerebellar granule neuron progenitor (GNP)-specific deletion of Chd8 in mice impairs the proliferation and differentiation of these cells as well as gives rise to cerebellar hypoplasia and a motor coordination defect, but not to ASD-like behavioral abnormalities. CHD8 is found to regulate the expression of neuronal genes in GNPs. It also binds preferentially to promoter regions and modulates local chromatin accessibility of transcriptionally active genes in these cells. Our results have thus uncovered a key role for CHD8 in cerebellar development, with important implications for understanding the contribution of this brain region to ASD pathogenesis.

Sushi domain-containing protein 4 controls synaptic plasticity and motor learning

Fine control of protein stoichiometry at synapses underlies brain function and plasticity. How proteostasis is controlled independently for each type of synaptic protein in a synapse-specific and activity-dependent manner remains unclear. Here, we show that Susd4, a gene coding for a complement-related transmembrane protein, is expressed by many neuronal populations starting at the time of synapse formation. Constitutive loss-of-function of Susd4 in the mouse impairs motor coordination adaptation and learning, prevents long-term depression at cerebellar synapses, and leads to misregulation of activity-dependent AMPA receptor subunit GluA2 degradation. We identified several proteins with known roles in the regulation of AMPA receptor turnover, in particular ubiquitin ligases of the NEDD4 subfamily, as SUSD4 binding partners. Our findings shed light on the potential role of SUSD4 mutations in neurodevelopmental diseases.