Developmental regulation of GABAergic signalling in the hippocampus of neuroligin 3 R451C knock-in mice: an animal model of Autism

From synapses to circuits: What mouse models have taught us about how autism spectrum disorder impacts hippocampal function

Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder that impacts a variety of cognitive and behavioral domains. While a genetic component of ASD has been well-established, none of the numerous syndromic genes identified in humans accounts for more than 1% of the clinical patients. Due to this large number of target genes, numerous mouse models of the disorder have been generated. However, the focus on distinct brain circuits, behavioral phenotypes and diverse experimental approaches has made it difficult to synthesize the overwhelming number of model animal studies into concrete throughlines that connect the data across levels of investigation. Here we chose to focus on one circuit, the hippocampus, and one hypothesis, a shift in excitatory/inhibitory balance, to examine, from the level of the tripartite synapse up to the level of in vivo circuit activity, the key commonalities across disparate models that can illustrate a path towards a better mechanistic understanding of ASD's impact on hippocampal circuit function.

Insulin-like growth factor 2 (IGF-2) rescues social deficits in NLG3-/y mouse model of ASDs

Autism spectrum disorders (ASDs) comprise developmental disabilities characterized by impairments of social interaction and repetitive behavior, often associated with cognitive deficits. There is no current treatment that can ameliorate most of the ASDs symptomatology; thus, identifying novel therapies is urgently needed. Here, we used the Neuroligin 3 knockout mouse (NLG3-/y), a model that recapitulates the social deficits reported in ASDs patients, to test the effects of systemic administration of IGF-2, a polypeptide that crosses the blood-brain barrier and acts as a cognitive enhancer. We show that systemic IGF-2 treatment reverses the typical defects in social interaction and social novelty discrimination reflective of ASDs-like phenotypes. This effect was not accompanied by any change in spontaneous glutamatergic synaptic transmission in CA2 hippocampal region, a mechanism found to be crucial for social novelty discrimination. However, in both NLG3+/y and NLG3-/y mice IGF-2 increased cell excitability. Although further investigation is needed to clarify the cellular and molecular mechanisms underpinning IGF-2 effect on social behavior, our findings highlight IGF-2 as a potential pharmacological tool for the treatment of social dysfunctions associated with ASDs.

Unraveling the Role of Neuroligin3 in Autism Spectrum Disorders: Pathophysiological Insights and Targeted Therapies

Autism Spectrum Disorder is a neurodevelopmental disorder characterized by impaired social and communication skills, repetitive behaviors, and/or restricted interests with a prevalence of as high as 1% of children. Autism spectrum has strongly associated with genetic factors and exhibits wide clinical and heterogeneous genetic architecture. Most genes associated with Autism are involved in neuronal and synaptic development. The neuroligin3, the sex-linked gene on the X chromosome, was the first gene to be associated with a monogenic form of Autism. Neuroligin3 is a postsynaptic cell adhesion protein involved in synapse transmission, brain formation, and neuronal development. In this review, we provide recent findings on different mutations in the Neuroligin3 gene linked to Autism spectrum disorder and their molecular pathway effect. We also give the behavioral, and synaptic alterations reported in the Neuroligin3 animal model of Autism and the potential therapeutic strategies targeting the biological processes and the main symptoms of autism spectrum disorder. In addition, we discuss the use of novel technologies like induced pluripotent stem cells from Autistic patients that have the potential to differentiate in human neurons and therefore have a variety of applications in therapy and biomedical studies to search specific biomarkers, and develop systems for screening chemical molecules in human cells to discover target therapies.

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.

Structural filtering of functional data offered discriminative features for autism spectrum disorder

This study attempted to answer the question, "Can filtering the functional data through the frequency bands of the structural graph provide data with valuable features which are not valuable in unfiltered data"?. The valuable features discriminate between autism spectrum disorder (ASD) and typically control (TC) groups. The resting-state fMRI data was passed through the structural graph's low, middle, and high-frequency band (LFB, MFB, and HFB) filters to answer the posed question. The structural graph was computed using the diffusion tensor imaging data. Then, the global metrics of functional graphs and metrics of functional triadic interactions were computed for filtered and unfiltered rfMRI data. Compared to TCs, ASDs had significantly higher clustering coefficients in the MFB, higher efficiencies and strengths in the MFB and HFB, and lower small-world propensity in the HFB. These results show over-connectivity, more global integration, and decreased local specialization in ASDs compared to TCs. Triadic analysis showed that the numbers of unbalanced triads were significantly lower for ASDs in the MFB. This finding may indicate the reason for restricted and repetitive behavior in ASDs. Also, in the MFB and HFB, the numbers of balanced triads and the energies of triadic interactions were significantly higher and lower for ASDs, respectively. These findings may reflect the disruption of the optimum balance between functional integration and specialization. There was no significant difference between ASDs and TCs when using the unfiltered data. All of these results demonstrated that significant differences between ASDs and TCs existed in the MFB and HFB of the structural graph when analyzing the global metrics of the functional graph and triadic interaction metrics. Also, these results demonstrated that frequency bands of the structural graph could offer significant findings which were not found in the unfiltered data. In conclusion, the results demonstrated the promising perspective of using structural graph frequency bands for attaining discriminative features and new knowledge, especially in the case of ASD.

Impaired synaptic plasticity in an animal model of autism exhibiting early hippocampal GABAergic-BDNF/TrkB signaling alterations

In Neurodevelopmental Disorders, alterations of synaptic plasticity may trigger structural changes in neuronal circuits involved in cognitive functions. This hypothesis was tested in mice carrying the human R451C mutation of Nlgn3 gene (NLG3^R451C KI), found in some families with autistic children. To this aim, the spike time dependent plasticity (STDP) protocol was applied to immature GABAergic Mossy Fibers (MF)-CA3 connections in hippocampal slices from NLG3^R451C KI mice. These animals failed to exhibit STD-LTP, an effect that persisted in adulthood when these synapses became glutamatergic. Similar results were obtained in mice lacking the Nlgn3 gene (NLG3 KO mice), suggesting a loss of function. The loss of STD-LTP was associated with a premature shift of GABA from the depolarizing to the hyperpolarizing direction, a reduced BDNF availability and TrkB phosphorylation at potentiated synapses. These effects may constitute a general mechanism underlying cognitive deficits in those forms of Autism caused by synaptic dysfunctions.

Topological analysis of brain dynamics in autism based on graph and persistent homology

Autism spectrum disorder (ASD) is a heterogeneous disorder with a rapidly growing prevalence. In recent years, the dynamic functional connectivity (DFC) technique has been used to reveal the transient connectivity behavior of ASDs' brains by clustering connectivity matrices in different states. However, the states of DFC have not been yet studied from a topological point of view. In this paper, this study was performed using global metrics of the graph and persistent homology (PH) and resting-state functional magnetic resonance imaging (fMRI) data. The PH has been recently developed in topological data analysis and deals with persistent structures of data. The structural connectivity (SC) and static FC (SFC) were also studied to know which one of the SC, SFC, and DFC could provide more discriminative topological features when comparing ASDs with typical controls (TCs). Significant discriminative features were only found in states of DFC. Moreover, the best classification performance was offered by persistent homology-based metrics and in two out of four states. In these two states, some networks of ASDs compared to TCs were more segregated and isolated (showing the disruption of network integration in ASDs). The results of this study demonstrated that topological analysis of DFC states could offer discriminative features which were not discriminative in SFC and SC. Also, PH metrics can provide a promising perspective for studying ASD and finding candidate biomarkers.

A perspective on molecular signalling dysfunction, its clinical relevance and therapeutics in autism spectrum disorder

Intellectual disability (ID) and autism spectrum disorder (ASD) are neurodevelopmental disorders that have become a primary clinical and social concern, with a prevalence of 2-3% in the population. Neuronal function and behaviour undergo significant malleability during the critical period of development that is found to be impaired in ID/ASD. Human genome sequencing studies have revealed many genetic variations associated with ASD/ID that are further verified by many approaches, including many mouse and other models. These models have facilitated the identification of fundamental mechanisms underlying the pathogenesis of ASD/ID, and several studies have proposed converging molecular pathways in ASD/ID. However, linking the mechanisms of the pathogenic genes and their molecular characteristics that lead to ID/ASD has progressed slowly, hampering the development of potential therapeutic strategies. This review discusses the possibility of recognising the common molecular causes for most ASD/ID based on studies from the available models that may enable a better therapeutic strategy to treat ID/ASD. We also reviewed the potential biomarkers to detect ASD/ID at early stages that may aid in diagnosis and initiating medical treatment, the concerns with drug failure in clinical trials, and developing therapeutic strategies that can be applied beyond a particular mutation associated with ASD/ID.

GABAergic System Dysfunction in Autism Spectrum Disorders

Autism spectrum disorder (ASD) refers to a series of neurodevelopmental diseases characterized by two hallmark symptoms, social communication deficits and repetitive behaviors. Gamma-aminobutyric acid (GABA) is one of the most important inhibitory neurotransmitters in the central nervous system (CNS). GABAergic inhibitory neurotransmission is critical for the regulation of brain rhythm and spontaneous neuronal activities during neurodevelopment. Genetic evidence has identified some variations of genes associated with the GABA system, indicating an abnormal excitatory/inhibitory (E/I) neurotransmission ratio implicated in the pathogenesis of ASD. However, the specific molecular mechanism by which GABA and GABAergic synaptic transmission affect ASD remains unclear. Transgenic technology enables translating genetic variations into rodent models to further investigate the structural and functional synaptic dysregulation related to ASD. In this review, we summarized evidence from human neuroimaging, postmortem, and genetic and pharmacological studies, and put emphasis on the GABAergic synaptic dysregulation and consequent E/I imbalance. We attempt to illuminate the pathophysiological role of structural and functional synaptic dysregulation in ASD and provide insights for future investigation.

Neuroligin-3: A Circuit-Specific Synapse Organizer That Shapes Normal Function and Autism Spectrum Disorder-Associated Dysfunction

Chemical synapses provide a vital foundation for neuron-neuron communication and overall brain function. By tethering closely apposed molecular machinery for presynaptic neurotransmitter release and postsynaptic signal transduction, circuit- and context- specific synaptic properties can drive neuronal computations for animal behavior. Trans-synaptic signaling via synaptic cell adhesion molecules (CAMs) serves as a promising mechanism to generate the molecular diversity of chemical synapses. Neuroligins (Nlgns) were discovered as postsynaptic CAMs that can bind to presynaptic CAMs like Neurexins (Nrxns) at the synaptic cleft. Among the four (Nlgn1-4) or five (Nlgn1-3, Nlgn4X, and Nlgn4Y) isoforms in rodents or humans, respectively, Nlgn3 has a heterogeneous expression and function at particular subsets of chemical synapses and strong association with non-syndromic autism spectrum disorder (ASD). Several lines of evidence have suggested that the unique expression and function of Nlgn3 protein underlie circuit-specific dysfunction characteristic of non-syndromic ASD caused by the disruption of Nlgn3 gene. Furthermore, recent studies have uncovered the molecular mechanism underlying input cell-dependent expression of Nlgn3 protein at hippocampal inhibitory synapses, in which trans-synaptic signaling of specific alternatively spliced isoforms of Nlgn3 and Nrxn plays a critical role. In this review article, we overview the molecular, anatomical, and physiological knowledge about Nlgn3, focusing on the circuit-specific function of mammalian Nlgn3 and its underlying molecular mechanism. This will provide not only new insight into specific Nlgn3-mediated trans-synaptic interactions as molecular codes for synapse specification but also a better understanding of the pathophysiological basis for non-syndromic ASD associated with functional impairment in Nlgn3 gene.

The neuroligins and the synaptic pathway in Autism Spectrum Disorder

The genetics underlying autism spectrum disorder (ASD) is complex and heterogeneous, and de novo variants are found in genes converging in functional biological processes. Neuronal communication, including trans-synaptic signaling involving two families of cell-adhesion proteins, the presynaptic neurexins and the postsynaptic neuroligins, is one of the most recurrently affected pathways in ASD. Given the role of these proteins in determining synaptic function, abnormal synaptic plasticity and failure to establish proper synaptic contacts might represent mechanisms underlying risk of ASD. More than 30 mutations have been found in the neuroligin genes. Most of the resulting residue substitutions map in the extracellular, cholinesterase-like domain of the protein, and impair protein folding and trafficking. Conversely, the stalk and intracellular domains are less affected. Accordingly, several genetic animal models of ASD have been generated, showing behavioral and synaptic alterations. The aim of this review is to discuss the current knowledge on ASD-linked mutations in the neuroligin proteins and their effect on synaptic function, in various brain areas and circuits.

An altered glial phenotype in the NL3R451C mouse model of autism

Autism Spectrum Disorder (ASD; autism) is a neurodevelopmental disorder characterised by deficits in social communication, and restricted and/or repetitive behaviours. While the precise pathophysiologies are unclear, increasing evidence supports a role for dysregulated neuroinflammation in the brain with potential effects on synapse function. Here, we studied characteristics of microglia and astrocytes in the Neuroligin-3 (NL3^R451C) mouse model of autism since these cell types are involved in regulating both immune and synapse function. We observed increased microglial density in the dentate gyrus (DG) of NL3^R451C mice without morphological differences. In contrast, WT and NL3^R451C mice had similar astrocyte density but astrocyte branch length, the number of branch points, as well as cell radius and area were reduced in the DG of NL3^R451C mice. Because retraction of astrocytic processes has been linked to altered synaptic transmission and dendrite formation, we assessed for regional changes in pre- and postsynaptic protein expression in the cortex, striatum and cerebellum in NL3^R451C mice. NL3^R451C mice showed increased striatal postsynaptic density 95 (PSD-95) protein levels and decreased cortical expression of synaptosomal-associated protein 25 (SNAP-25). These changes could contribute to dysregulated neurotransmission and cognition deficits previously reported in these mice.

Autism-associated synaptic mutations impact the gut-brain axis in mice

Interactions between the gut microbiome and the brain affect mood and behaviour in health and disease. Using preclinical animal models, recent discoveries begin to explain how bacteria in the gut influence our mood as well as highlighting new findings relevant to autism. Autism-associated gene mutations known to alter synapse function in the CNS also affect inflammatory response and modify the enteric nervous system resulting in abnormal gastrointestinal motility and structure. Strikingly, these mutations additionally affect the gut microbiome in mice. This review describes the changes in gut physiology and microbiota in mouse models of autism with modified synapse function. The rationale for different regions of the gastrointestinal tract having variable susceptibility to dysfunction is also discussed. To dissect underlying biological mechanisms involving gut-brain axis dysfunction in preclinical models, a range of multidisciplinary approaches are required. This research will provide insights into the role of the gut-brain axis in health and neurodevelopmental disorders including autism.

Understanding intellectual disability and autism spectrum disorders from common mouse models: synapses to behaviour

Normal brain development is highly dependent on the timely coordinated actions of genetic and environmental processes, and an aberration can lead to neurodevelopmental disorders (NDDs). Intellectual disability (ID) and autism spectrum disorders (ASDs) are a group of co-occurring NDDs that affect between 3% and 5% of the world population, thus presenting a great challenge to society. This problem calls for the need to understand the pathobiology of these disorders and to design new therapeutic strategies. One approach towards this has been the development of multiple analogous mouse models. This review discusses studies conducted in the mouse models of five major monogenic causes of ID and ASDs: Fmr1, Syngap1, Mecp2, Shank2/3 and Neuroligins/Neurnexins. These studies reveal that, despite having a diverse molecular origin, the effects of these mutations converge onto similar or related aetiological pathways, consequently giving rise to the typical phenotype of cognitive, social and emotional deficits that are characteristic of ID and ASDs. This convergence, therefore, highlights common pathological nodes that can be targeted for therapy. Other than conventional therapeutic strategies such as non-pharmacological corrective methods and symptomatic alleviation, multiple studies in mouse models have successfully proved the possibility of pharmacological and genetic therapy enabling functional recovery.

Gastrointestinal dysfunction in patients and mice expressing the autism-associated R451C mutation in neuroligin-3

Gastrointestinal (GI) problems constitute an important comorbidity in many patients with autism. Multiple mutations in the neuroligin family of synaptic adhesion molecules are implicated in autism, however whether they are expressed and impact GI function via changes in the enteric nervous system is unknown. We report the GI symptoms of two brothers with autism and an R451C mutation in Nlgn3 encoding the synaptic adhesion protein, neuroligin-3. We confirm the presence of an array of synaptic genes in the murine GI tract and investigate the impact of impaired synaptic protein expression in mice carrying the human neuroligin-3 R451C missense mutation (NL3^R451C ). Assessing in vivo gut dysfunction, we report faster small intestinal transit in NL3^R451C compared to wild-type mice. Using an ex vivo colonic motility assay, we show increased sensitivity to GABA_A receptor modulation in NL3^R451C mice, a well-established Central Nervous System (CNS) feature associated with this mutation. We further show increased numbers of small intestine myenteric neurons in NL3^R451C mice. Although we observed altered sensitivity to GABA_A receptor modulators in the colon, there was no change in colonic neuronal numbers including the number of GABA-immunoreactive myenteric neurons. We further identified altered fecal microbial communities in NL3^R451C mice. These results suggest that the R451C mutation affects small intestinal and colonic function and alter neuronal numbers in the small intestine as well as impact fecal microbes. Our findings identify a novel GI phenotype associated with the R451C mutation and highlight NL3^R451C mice as a useful preclinical model of GI dysfunction in autism. Autism Res 2019, 12: 1043-1056. © 2019 International Society for Autism Research, Wiley Periodicals, Inc. LAY SUMMARY: People with autism commonly experience gastrointestinal problems, however the cause is unknown. We report gut symptoms in patients with the autism-associated R451C mutation encoding the neuroligin-3 protein. We show that many of the genes implicated in autism are expressed in mouse gut. The neuroligin-3 R451C mutation alters the enteric nervous system, causes gastrointestinal dysfunction, and disrupts gut microbe populations in mice. Gut dysfunction in autism could be due to mutations that affect neuronal communication.

Synaptic dysfunction in neurodegenerative and neurodevelopmental diseases: an overview of induced pluripotent stem-cell-based disease models

Synaptic dysfunction in CNS disorders is the outcome of perturbations in physiological synapse structure and function, and can be either the cause or the consequence in specific pathologies. Accumulating data in the field of neuropsychiatric disorders, including autism spectrum disorders, schizophrenia and bipolar disorder, point to a neurodevelopmental origin of these pathologies. Due to a relatively early onset of behavioural and cognitive symptoms, it is generally acknowledged that mental illness initiates at the synapse level. On the other hand, synaptic dysfunction has been considered as an endpoint incident in neurodegenerative diseases, such as Alzheimer's, Parkinson's and Huntington's, mainly due to the considerably later onset of clinical symptoms and progressive appearance of cognitive deficits. This dichotomy has recently been challenged, particularly since the discovery of cell reprogramming technologies and the generation of induced pluripotent stem cells from patient somatic cells. The creation of 'disease-in-a-dish' models for multiple CNS pathologies has revealed unexpected commonalities in the molecular and cellular mechanisms operating in both developmental and degenerative conditions, most of which meet at the synapse level. In this review we discuss synaptic dysfunction in prototype neurodevelopmental and neurodegenerative diseases, emphasizing overlapping features of synaptopathy that have been suggested by studies using induced pluripotent stem-cell-based systems. These valuable disease models have highlighted a potential neurodevelopmental component in classical neurodegenerative diseases that is worth pursuing and investigating further. Moving from demonstration of correlation to understanding mechanistic causality forms the basis for developing novel therapeutics.

Role of CX3CR1 Signaling on the Maturation of GABAergic Transmission and Neuronal Network Activity in the Neonate Hippocampus

In the developing brain, microglial cells play an important role in shaping neuronal circuits. These immune cells communicate with neurons through fractalkine (CX3CL1), a neuronal cytokine that acts on microglial CX3CR1 receptor. Among various functions, this signaling pathway has been implicated in the postnatal maturation of glutamatergic synapses. Although microglial cells are present in the neonate hippocampus when GABA receptor-mediated synaptic transmission and synchronized oscillatory events take place, it remains unknown whether microglial cells tune the establishment of these activities. Using CX3CR1-deficient mice and electrophysiological means, we investigated in CA3 pyramidal neurons the role of the fractalkine signaling in the maturation of GABA_A receptor-mediated synaptic currents and giant depolarizing potentials (GDPs), a network activity important for shaping synaptic connections. In CX3CR1-deficient mice, GABAergic currents were slightly altered, whereas the developmental changes of these currents were comparable with wild-type animals. Despite these minor changes in GABAergic transmission, the GDP frequency was strikingly reduced in CX3CR1-deficient mice compared to wild-type, with no change in the GDP shape and ending period. Collectively, it emerges that, in the neonate hippocampus, the fractalkine signaling pathway tunes GDP activities and is marginally involved in the maturation of GABAergic synapses, suggesting that microglial cells have distinct impact on maturing GABAergic, glutamatergic, and network functions.

Possible Implication of the CA2 Hippocampal Circuit in Social Cognition Deficits Observed in the Neuroligin 3 Knock-Out Mouse, a Non-Syndromic Animal Model of Autism

Autism spectrum disorders (ASDs) comprise a heterogeneous group of neuro-developmental abnormalities with a strong genetic component, characterized by deficits in verbal and non-verbal communication, impaired social interactions, and stereotyped behaviors. In a small percentage of cases, ASDs are associated with alterations of genes involved in synaptic function. Among these, relatively frequent are mutations/deletions of genes encoding for neuroligins (NLGs). NLGs are postsynaptic adhesion molecules that, interacting with their presynaptic partners neurexins, ensure the cross talk between pre- and postsynaptic specializations and synaptic stabilization, a condition needed for maintaining a proper excitatory/inhibitory balance within local neuronal circuits. We have focused on mice lacking NLG3 (NLG3 knock-out mice), animal models of a non-syndromic form of autism, which exhibit deficits in social behavior reminiscent of those found in ASDs. Among different brain areas involved in social cognition, the CA2 region of the hippocampus has recently emerged as a central structure for social memory processing. Here, in vivo recordings from anesthetized animals and ex vivo recordings from hippocampal slices have been used to assess the dynamics of neuronal signaling in the CA2 hippocampal area. In vivo experiments from NLG3-deficient mice revealed a selective impairment of spike-related slow wave activity in the CA2 area and a significant reduction in oscillatory activity in the theta and gamma frequencies range in both CA2 and CA3 regions of the hippocampus. These network effects were associated with an increased neuronal excitability in the CA2 hippocampal area. Ex vivo recordings from CA2 principal cells in slices obtained from NLG3 knock-out animals unveiled a strong excitatory/inhibitory imbalance in this region accompanied by a strong reduction of perisomatic inhibition mediated by CCK-containing GABAergic interneurons. These data clearly suggest that the selective alterations in network dynamics and GABAergic signaling observed in the CA2 hippocampal region of NLG3 knock-out mice may account for deficits in social memory reminiscent of those observed in autistic patients.

[A review on the role of γ-aminobutyric acid signaling pathway in autism spectrum disorder]

The etiology and pathogenesis of autism spectrum disorder (ASD) are not yet clear. Studies have shown that there are many neurotransmitter abnormalities in children with ASD, mainly involving in glutamate, γ-aminobutyric acid (GABA), dopamine, 5-HT and oxytocin. The imbalance of excitatory glutamatergic neurotransmitters and inhibitory GABAergic neurotransmitters is closely related to the pathogenesis of ASD. Both animal model studies and clinical studies on ASD suggest that GABA signaling pathway may play an important role in the pathogenesis of ASD. This article reviews the research on the association between GABA signaling pathway and the pathogenesis of ASD to further explore the pathogenesis of ASD and provide theoretical basis for the treatment of ASD.

Altered Amygdala Excitation and CB1 Receptor Modulation of Aggressive Behavior in the Neuroligin-3R451C Mouse Model of Autism

Understanding neuronal mechanisms underlying aggression in patients with autism spectrum disorder (ASD) could lead to better treatments and prognosis. The Neuroligin-3 (NL3)^R451C mouse model of ASD has a heightened aggressive phenotype, however the biological mechanisms underlying this behavior are unknown. It is well established that NL3^R451C mice have imbalanced excitatory and inhibitory synaptic activity in the hippocampus and somatosensory cortex. The amygdala plays a role in modulating aggressive behavior, however potential changes in synaptic activity in this region have not previously been assessed in this model. We investigated whether aggressive behavior is robustly present in mice expressing the R451C mutation, following back-crossing onto a congenic background strain. Endocannabinoids influence social interaction and aggressive behavior, therefore we also studied the effects of cannabinoid receptor 1 (CB1) agonist on NL3^R451C mice. We report that NL3^R451C mice have increased amplitude of miniature excitatory postsynaptic currents (EPSCs) with a concomitant decrease in the amplitude of inhibitory postsynaptic currents (IPSCs) in the basolateral amygdala. Importantly, we demonstrated that NL3^R451C mice bred on a C57Bl/6 background strain exhibit an aggressive phenotype. Following non-sedating doses (0.3 and 1.0 mg/kg) of the CB1 receptor agonist WIN55,212-2 (WIN), we observed a significant reduction in aggressive behavior in NL3^R451C mice. These findings demonstrate altered synaptic activity in the basolateral amygdala and suggest that the NL3^R451C mouse model is a useful preclinical tool to understand the role of CB1 receptor function in aggressive behavior.

Gamma Oscillation Dysfunction in mPFC Leads to Social Deficits in Neuroligin 3 R451C Knockin Mice

Neuroligins (NLs) are critical for synapse formation and function. NL3 R451C is an autism-associated mutation. NL3 R451C knockin (KI) mice exhibit autistic behavioral abnormalities, including social novelty deficits. However, neither the brain regions involved in social novelty nor the underlying mechanisms are clearly understood. Here, we found decreased excitability of fast-spiking interneurons and dysfunction of gamma oscillation in the medial prefrontal cortex (mPFC), which contributed to the social novelty deficit in the KI mice. Neuronal firing rates and phase-coding abnormalities were also detected in the KI mice during social interactions. Interestingly, optogenetic stimulation of parvalbumin interneurons in the mPFC at 40 Hz nested at 8 Hz positively modulated the social behaviors of mice and rescued the social novelty deficit in the KI mice. Our findings suggest that gamma oscillation dysfunction in the mPFC leads to social deficits in autism, and manipulating mPFC PV interneurons may reverse the deficits in adulthood.

Low-Frequency rTMS Ameliorates Autistic-Like Behaviors in Rats Induced by Neonatal Isolation Through Regulating the Synaptic GABA Transmission

Patients with autism spectrum disorder (ASD) display abnormalities in neuronal development, synaptic function and neural circuits. The imbalance of excitatory and inhibitory (E/I) synaptic transmission has been proposed to cause the main behavioral characteristics of ASD. Repetitive transcranial magnetic stimulation (rTMS) can directly or indirectly induce excitability and synaptic plasticity changes in the brain noninvasively. However, whether rTMS can ameliorate autistic-like behaviors in animal model via regulating the balance of E/I synaptic transmission is unknown. By using our recent reported animal model with autistic-like behaviors induced by neonatal isolation (postnatal days 1-9), we found that low-frequency rTMS (LF-rTMS, 1 Hz) treatment for 2 weeks effectively alleviated the acquired autistic-like symptoms, as reflected by an increase in social interaction and decrease in self-grooming, anxiety- and depressive-like behaviors in young adult rats compared to those in untreated animals. Furthermore, the amelioration in autistic-like behavior was accompanied by a restoration of the balance between E/I activity, especially at the level of synaptic transmission and receptors in synaptosomes. These findings indicated that LF-rTMS may alleviate the symptoms of ASD-like behaviors caused by neonatal isolation through regulating the synaptic GABA transmission, suggesting that LF-rTMS may be a potential therapeutic technique to treat ASD.

Modulation of Neocortical Development by Early Neuronal Activity: Physiology and Pathophysiology

Animal and human studies revealed that patterned neuronal activity is an inherent feature of developing nervous systems. This review summarizes our current knowledge about the mechanisms generating early electrical activity patterns and their impact on structural and functional development of the cerebral cortex. All neocortical areas display distinct spontaneous and sensory-driven neuronal activity patterns already at early phases of development. At embryonic stages, intermittent spontaneous activity is synchronized within small neuronal networks, becoming more complex with further development. This transition is accompanied by a gradual shift from electrical to chemical synaptic transmission, with a particular role of non-synaptic tonic currents before the onset of phasic synaptic activity. In this review article we first describe functional impacts of classical neurotransmitters (GABA, glutamate) and modulatory systems (e.g., acetylcholine, ACh) on early neuronal activities in the neocortex with special emphasis on electrical synapses, nonsynaptic and synaptic currents. Early neuronal activity influences probably all developmental processes and is crucial for the proper formation of neuronal circuits. In the second part of our review, we illustrate how specific activity patterns might interfere with distinct neurodevelopmental processes like proliferation, migration, axonal and dendritic sprouting, synapse formation and neurotransmitter specification. Finally, we present evidence that transient alterations in neuronal activity during restricted perinatal periods can lead to persistent changes in functional connectivity and therefore might underlie the manifestation of neurological and neuropsychiatric diseases.

Synaptic Neurexin Complexes: A Molecular Code for the Logic of Neural Circuits

Synapses are specialized junctions between neurons in brain that transmit and compute information, thereby connecting neurons into millions of overlapping and interdigitated neural circuits. Here, we posit that the establishment, properties, and dynamics of synapses are governed by a molecular logic that is controlled by diverse trans-synaptic signaling molecules. Neurexins, expressed in thousands of alternatively spliced isoforms, are central components of this dynamic code. Presynaptic neurexins regulate synapse properties via differential binding to multifarious postsynaptic ligands, such as neuroligins, cerebellin/GluD complexes, and latrophilins, thereby shaping the input/output relations of their resident neural circuits. Mutations in genes encoding neurexins and their ligands are associated with diverse neuropsychiatric disorders, especially schizophrenia, autism, and Tourette syndrome. Thus, neurexins nucleate an overall trans-synaptic signaling network that controls synapse properties, which thereby determines the precise responses of synapses to spike patterns in a neuron and circuit and which is vulnerable to impairments in neuropsychiatric disorders.

The neurobiological bases of autism spectrum disorders: the R451C-neuroligin 3 mutation hampers the expression of long-term synaptic depression in the dorsal striatum

Autism spectrum disorders (ASDs) comprise a heterogeneous group of disorders with a complex genetic etiology. Current theories on the pathogenesis of ASDs suggest that they might arise from an aberrant synaptic transmission affecting specific brain circuits and synapses. The striatum, which is part of the basal ganglia circuit, is one of the brain regions involved in ASDs. Mouse models of ASDs have provided evidence for an imbalance between excitatory and inhibitory neurotransmission. Here, we investigated the expression of long-term synaptic plasticity at corticostriatal glutamatergic synapses in the dorsal striatum of the R451C-NL3 phenotypic mouse model of autism. This mouse model carries the human R451C mutation in the neuroligin 3 (NL3) gene that has been associated with highly penetrant autism in a Swedish family. The R451C-NL3 mouse has been shown to exhibit autistic-like behaviors and alterations of synaptic transmission in different brain areas. However, excitatory glutamatergic transmission and its long-term plasticity have not been investigated in the dorsal striatum so far. Our results indicate that the expression of long-term synaptic depression (LTD) at corticostriatal glutamatergic synapses in the dorsal striatum is impaired by the R451C-NL3 mutation. A partial rescue of LTD was obtained by exogenous activation of cannabinoid CB1 receptors or enhancement of the endocannabinoid tone, suggesting that an altered cannabinoid drive might underlie the deficit of synaptic plasticity in the dorsal striatum of R451C-NL3 mice.

Early Correlated Network Activity in the Hippocampus: Its Putative Role in Shaping Neuronal Circuits

Synchronized neuronal activity occurring at different developmental stages in various brain structures represents a hallmark of developmental circuits. This activity, which differs in its specific patterns among animal species may play a crucial role in de novo formation and in shaping neuronal networks. In the rodent hippocampus in vitro, the so-called giant depolarizing potentials (GDPs) constitute a primordial form of neuronal synchrony preceding more organized forms of activity such as oscillations in the theta and gamma frequency range. GDPs are generated at the network level by the interaction of the neurotransmitters glutamate and GABA which, immediately after birth, exert both a depolarizing and excitatory action on their targets. GDPs are triggered by GABAergic interneurons, which in virtue of their extensive axonal branching operate as functional hubs to synchronize large ensembles of cells. Intrinsic bursting activity, driven by a persistent sodium conductance and facilitated by the low expression of Kv7.2 and Kv7.3 channel subunits, responsible for I_M, exerts a permissive role in GDP generation. Here, we discuss how GDPs are generated in a probabilistic way when neuronal excitability within a local circuit reaches a certain threshold and how GDP-associated calcium transients act as coincident detectors for enhancing synaptic strength at emerging GABAergic and glutamatergic synapses. We discuss the possible in vivo correlate of this activity. Finally, we debate recent data showing how, in several animal models of neuropsychiatric disorders including autism, a GDPs dysfunction is associated to morphological alterations of neuronal circuits and behavioral deficits reminiscent of those observed in patients.

Emerging Synaptic Molecules as Candidates in the Etiology of Neurological Disorders

Synapses are complex structures that allow communication between neurons in the central nervous system. Studies conducted in vertebrate and invertebrate models have contributed to the knowledge of the function of synaptic proteins. The functional synapse requires numerous protein complexes with specialized functions that are regulated in space and time to allow synaptic plasticity. However, their interplay during neuronal development, learning, and memory is poorly understood. Accumulating evidence links synapse proteins to neurodevelopmental, neuropsychiatric, and neurodegenerative diseases. In this review, we describe the way in which several proteins that participate in cell adhesion, scaffolding, exocytosis, and neurotransmitter reception from presynaptic and postsynaptic compartments, mainly from excitatory synapses, have been associated with several synaptopathies, and we relate their functions to the disease phenotype.

Distortion of the normal function of synaptic cell adhesion molecules by genetic variants as a risk for autism spectrum disorders

Synaptic cell adhesion molecules (SCAMs) are a functional category of cell adhesion molecules that connect pre- and postsynapses by the protein-protein interaction via their extracellular cell adhesion domains. Countless numbers of common genetic variants and rare mutations in SCAMs have been identified in the patients with autism spectrum disorders (ASDs). Among these, NRXN and NLGN family proteins cooperatively function at synaptic terminals both of which genes are strongly implicated as risk genes for ASDs. Knock-in mice carrying a single rare point mutation of NLGN3 (NLGN3 R451C) discovered in the patients with ASDs display a deficit in social interaction and an enhancement of spatial learning and memory ability reminiscent of the clinical phenotype of ASDs. NLGN4 knockout (KO) and NRXN2α KO mice also show a deficit in sociability as well as some specific neuropsychiatric behaviors. In this review, we selected NRXNs/NLGNs, CNTNAP2/CNTNAP4, CNTN4, ITGB3, and KIRREL3 as strong ASD risk genes based on SFARI score and summarize the protein structures, functions at synapses, representative discoveries in human genetic studies, and phenotypes of the mutant model mice in light of the pathophysiology of ASDs.

Pharmacological Modulation of GABA Function in Autism Spectrum Disorders: A Systematic Review of Human Studies

Autism spectrum disorders are an emerging health problem worldwide, but little is known about their pathogenesis. It has been hypothesized that autism may result from an imbalance between excitatory glutamatergic and inhibitory GABAergic pathways. Commonly used medications such as valproate, acamprosate, and arbaclofen may act on the GABAergic system and be a potential treatment for people with ASD. The present systematic review aimed at evaluating the state-of-the-art of clinical trials of GABA modulators in autism. To date there is insufficient evidence to suggest the use of these drugs in autistic subjects, even if data are promising. Of note, short-term use of all the reviewed medications appears to be safe. Future well designed trials are needed to elucidate these preliminary findings.

Premature changes in neuronal excitability account for hippocampal network impairment and autistic-like behavior in neonatal BTBR T+tf/J mice

Coherent network oscillations (GDPs), generated in the immature hippocampus by the synergistic action of GABA and glutamate, both depolarizing and excitatory, play a key role in the construction of neuronal circuits. In particular, GDPs-associated calcium transients act as coincident detectors for enhancing synaptic efficacy at emerging GABAergic and glutamatergic synapses. Here, we show that, immediately after birth, in the CA3 hippocampal region of the BTBR T+tf/J mouse, an animal model of idiopathic autism, GDPs are severely impaired. This effect was associated with an increased GABAergic neurotransmission and a reduced neuronal excitability. In spite its depolarizing action on CA3 pyramidal cells (in single channel experiments E_GABA was positive to E_m), GABA exerted at the network level an inhibitory effect as demonstrated by isoguvacine-induced reduction of neuronal firing. We implemented a computational model in which experimental findings could be interpreted as the result of two competing effects: a reduction of the intrinsic excitability of CA3 principal cells and a reduction of the shunting activity in GABAergic interneurons projecting to principal cells. It is therefore likely that premature changes in neuronal excitability within selective hippocampal circuits of BTBR mice lead to GDPs dysfunction and behavioral deficits reminiscent of those found in autistic patients.

Monogenic mouse models of autism spectrum disorders: Common mechanisms and missing links

Autism spectrum disorders (ASDs) present unique challenges in the fields of genetics and neurobiology because of the clinical and molecular heterogeneity underlying these disorders. Genetic mutations found in ASD patients provide opportunities to dissect the molecular and circuit mechanisms underlying autistic behaviors using animal models. Ongoing studies of genetically modified models have offered critical insight into possible common mechanisms arising from different mutations, but links between molecular abnormalities and behavioral phenotypes remain elusive. The challenges encountered in modeling autism in mice demand a new analytic paradigm that integrates behavioral assessment with circuit-level analysis in genetically modified models with strong construct validity.

FOXG1-Dependent Dysregulation of GABA/Glutamate Neuron Differentiation in Autism Spectrum Disorders

Autism spectrum disorder (ASD) is a disorder of brain development. Most cases lack a clear etiology or genetic basis, and the difficulty of re-enacting human brain development has precluded understanding of ASD pathophysiology. Here we use three-dimensional neural cultures (organoids) derived from induced pluripotent stem cells (iPSCs) to investigate neurodevelopmental alterations in individuals with severe idiopathic ASD. While no known underlying genomic mutation could be identified, transcriptome and gene network analyses revealed upregulation of genes involved in cell proliferation, neuronal differentiation, and synaptic assembly. ASD-derived organoids exhibit an accelerated cell cycle and overproduction of GABAergic inhibitory neurons. Using RNA interference, we show that overexpression of the transcription factor FOXG1 is responsible for the overproduction of GABAergic neurons. Altered expression of gene network modules and FOXG1 are positively correlated with symptom severity. Our data suggest that a shift toward GABAergic neuron fate caused by FOXG1 is a developmental precursor of ASD.

Default mode network segregation and social deficits in autism spectrum disorder: Evidence from non-medicated children

Functional pathology of the default mode network is posited to be central to social-cognitive impairment in autism spectrum disorders (ASD). Altered functional connectivity of the default mode network's midline core may be a potential endophenotype for social deficits in ASD. Generalizability from prior studies is limited by inclusion of medicated participants and by methods favoring restricted examination of network function. This study measured resting-state functional connectivity in 22 8–13 year-old non-medicated children with ASD and 22 typically developing controls using seed-based and network segregation functional connectivity methods. Relative to controls the ASD group showed both under- and over-functional connectivity within default mode and non-default mode regions, respectively. ASD symptoms correlated negatively with the connection strength of the default mode midline core—medial prefrontal cortex–posterior cingulate cortex. Network segregation analysis with the participation coefficient showed a higher area under the curve for the ASD group. Our findings demonstrate that the default mode network in ASD shows a pattern of poor segregation with both functional connectivity metrics. This study confirms the potential for the functional connection of the midline core as an endophenotype for social deficits. Poor segregation of the default mode network is consistent with an excitation/inhibition imbalance model of ASD.

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The DMN is a potential endophenotype for social deficits in ASD.

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This study used resting state functional MRI to probe the default mode network.

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MPFC–PCC connection was reduced in strength in ASD and correlated with ASD severity.

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Graph theory analysis showed that DMN had greater cross-network connectivity in ASD.

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Findings support DMN as an ASD endophenotype and align with a GABA theory of ASD.

Axo-glial communication through neurexin-neuroligin signaling regulates myelination and oligodendrocyte differentiation

Axonal transsynaptic signaling between presynaptic neurexin (NX) and postsynaptic neuroligin (NL) is essential for many properties of synaptic connectivity. Here, we demonstrate the existence of a parallel axo-glial signaling pathway between axonal NX and oligodendritic (OL) NL3. We show that this pathway contributes to the regulation of myelinogenesis, the maintenance of established myelination, and the differentiation state of the OL using in vitro models. We first confirm that NL3 mRNA and protein are expressed in OLs and in OL precursors. We then show that OLs in culture form contacts with non-neuronal cells exogenously expressing NL3's binding partners NX1α or NX1β. Conversely, blocking axo-glial NX-NL3 signaling by saturating NX with exogenous soluble NL protein (NL-ECD) disrupts interactions between OLs and axons in both in vitro and ex vivo assays. Myelination by OLs is tied to their differentiation state, and we find that blocking NX-NL signaling with soluble NL protein also caused OL differentiation to stall at an immature stage. Moreover, in vitro knockdown of NL3 in OLs with siRNAs stalls their development and reduces branching complexity. Interestingly, inclusion of an autism related mutation in the NL blocking protein attenuates these effects; OLs differentiate and the dynamics of OL-axon signaling occur normally as this peptide does not disrupt NX-NL3 axo-glial interactions. Our findings provide evidence not only for a new pathway in axo-glial communication, they also potentially explain the correlation between altered white matter and autism. GLIA 2015;63:2023-2039.

The interplay between synaptic activity and neuroligin function in the CNS

Neuroligins (NLs) are postsynaptic transmembrane cell-adhesion proteins that play a key role in the regulation of excitatory and inhibitory synapses. Previous in vitro and in vivo studies have suggested that NLs contribute to synapse formation and synaptic transmission. Consistent with their localization, NL1 and NL3 selectively affect excitatory synapses, whereas NL2 specifically affects inhibitory synapses. Deletions or mutations in NL genes have been found in patients with autism spectrum disorders or mental retardations, and mice harboring the reported NL deletions or mutations exhibit autism-related behaviors and synapse dysfunction. Conversely, synaptic activity can regulate the phosphorylation, expression, and cleavage of NLs, which, in turn, can influence synaptic activity. Thus, in clinical research, identifying the relationship between NLs and synapse function is critical. In this review, we primarily discuss how NLs and synaptic activity influence each other.

Reduced susceptibility to induced seizures in the Neuroligin-3(R451C) mouse model of autism

Epilepsy is a common comorbidity in patients with autism spectrum disorder (ASD) and several gene mutations are associated with both of these disorders. In order to determine whether a point mutation in the gene for the synaptic protein, Neuroligin-3 (Nlgn3, R451C), identified in patients with ASD alters seizure susceptibility, we administered the proconvulsant pentylenetetrazole (PTZ) to adult male Neuroligin-3(R451C) (NL3(R451C)) and wild type (WT) mice. It has previously been reported that NL3(R451C) mice show altered inhibitory GABAergic activity in brain regions relevant to epilepsy, including the hippocampus and somatosensory cortex. PTZ administration induces absence-seizures at low dose, and generalised convulsive seizures at higher dose. Susceptibility to absence seizures was examined by analysing the frequency and duration of spike-and-wave discharge (SWD) events and accompanying motor seizure activity induced by subcutaneous administration of low dosage (20 or 30mg/kg) PTZ. Susceptibility to generalised convulsive seizures was tested by measuring the response to high dosage (60mg/kg) PTZ using a modified Racine scale. There was no change in the number of SWD events exhibited by NL3(R451C) compared to WT mice following administration of both 20mg/kg PTZ (1.17±0.31 compared to 16.0±11.16 events/30min, NL3(R451C) versus WT, respectively) and 30mg/kg PTZ (7.5±6.54 compared with 27.8±19.9 events/30min, NL3(R451C) versus WT, respectively). NL3(R451C) mice were seizure resistant to generalised convulsive seizures induced by high dose PTZ compared to WT littermates (median latency to first >3s duration clonic seizure; 14.5min versus 7.25min, 95% CI: 1.625-2.375, p=0.0009, NL3(R451C) versus WT, respectively). These results indicate that the R451C mutation in the Nlgn3 gene, associated with ASD in humans, confers resistance to induced seizures, suggesting dysfunction of PTZ-sensitive GABAergic signalling in this mouse model of ASD.

Reduced inhibitory gate in the barrel cortex of Neuroligin3R451C knock-in mice, an animal model of autism spectrum disorders

Neuroligins are postsynaptic adhesion molecules that interacting with presynaptic neurexins ensure the cross‐talk between pre‐ and postsynaptic specializations. Rare mutations in neurexin–neuroligin genes have been linked to autism spectrum disorders (ASDs). One of these, the R451C mutation of the gene encoding for Neuroligin3 (Nlgn3), has been found in patients with familial forms of ASDs. Animals carrying this mutation (NL3^R451C knock‐in mice) exhibit impaired social behaviors, reminiscent of those observed in ASD patients, associated with major alterations in both GABAergic and glutamatergic transmission, which vary among different brain regions and at different developmental stages. Here, pair recordings from parvalbumin‐ (PV) expressing basket cells and spiny neurons were used to study GABAergic synaptic signaling in layer IV barrel cortex of NL3^R451C mutant mice. We found that the R451C mutation severely affects the probability of GABA release from PV‐expressing basket cells, responsible for controlling via thalamo‐cortical inputs the feed‐forward inhibition. No changes in excitatory inputs to parvalbumin‐positive basket cells or spiny neurons were detected. These data clearly show that primary targets of the NL3 mutation are PV‐expressing basket cells, independently of the brain region where they are localized. Changes in the inhibitory gate of layer IV somatosensory cortex may alter sensory processing in ASD patients leading to misleading sensory representations with difficulties to combine pieces of information into a unified perceptual whole.

Autism spectrum disorders (ASDs) comprise a heterogeneous group of neurodevelopmental abnormalities, characterized by impaired social interactions. Here, using mice carrying the R451C mutation of the Nlgn3 gene (found in few familial cases of ASDs), and exhibiting behavioral deficits reminiscent of those present in ASD patients, we found that, in layer IV barrel cortex microcircuit, parvalbumin‐expressing basket cells display a reduced probability of GABA release into spiny neurons. Alterations of GABAergic signaling in layer IV somatosensory cortex of NL3R451C knock‐in mice may alter sensory processing leading to misleading sensory representations with difficulties to combine pieces of information into a unified perceptual whole.

Lithium ameliorates autistic-like behaviors induced by neonatal isolation in rats

Neonatal isolation is a widely accepted model to study the long-term behavioral changes produced by the early life events. However, it remains unknown whether neonatal isolation can induce autistic-like behaviors, and if so, whether pharmacological treatment can overcome it. Here, we reported that newborn rats subjected to individual isolations from their mother and nest for 1 h per day from postnatal days 1–9 displayed apparent autistic-like symptoms including social deficits, excessive repetitive self-grooming behavior, and increased anxiety- and depressive-like behaviors tested in young adult (postnatal days 42–56) compared to normal reared controls. Furthermore, these behavioral changes were accompanied by impaired adult hippocampal neurogenesis and reduced the ratio of excitatory/inhibitory synaptic transmissions, as reflected by an increase in spontaneous inhibitory postsynaptic current (sIPSC) and normal spontaneous excitatory postsynaptic current (sEPSC) in the hippocampal CA1 pyramidal neuron. More importantly, chronic administration of lithium, a clinically used mood stabilizer, completely overcame neonatal isolation-induced autistic-like behaviors, and restored adult hippocampal neurogenesis as well as the balance between excitatory and inhibitory activities to physiological levels. These findings indicate that neonatal isolation may produce autistic-like behaviors, and lithium may be a potential therapeutic agent against autism spectrum disorders (ASD) during development.

GABAergic signaling as therapeutic target for autism spectrum disorders

γ-Aminobutyric acid (GABA), the main inhibitory neurotransmitter in the adult brain, early in postnatal life exerts a depolarizing and excitatory action. This depends on accumulation of chloride inside the cell via the cation-chloride importer NKCC1, being the expression of the chloride exporter KCC2 very low at birth. The developmentally regulated expression of KCC2 results in extrusion of chloride with age and a shift of GABA from the depolarizing to the hyperpolarizing direction. The depolarizing action of GABA leads to intracellular calcium rise through voltage-dependent calcium channels and/or N-methyl-d-aspartate receptors. GABA-mediated calcium signals regulate a variety of developmental processes from cell proliferation migration, differentiation, synapse maturation, and neuronal wiring. Therefore, it is not surprising that some forms of neuro-developmental disorders such as autism spectrum disorders (ASDs) are associated with alterations of GABAergic signaling and impairment of the excitatory/inhibitory balance in selective neuronal circuits. In this review, we will discuss how changes of GABAA-mediated neurotransmission affect several forms of ASDs including the Fragile X, the Angelman, and Rett syndromes. Then, we will describe various animal models of ASDs with GABAergic dysfunctions, highlighting their behavioral deficits and the possibility to rescue them by targeting selective components of the GABAergic synapse. In particular, we will discuss how in some cases, reverting the polarity of GABA responses from the depolarizing to the hyperpolarizing direction with the diuretic bumetanide, a selective blocker of NKCC1, may have beneficial effects on ASDs, thus opening new therapeutic perspectives for the treatment of these devastating disorders.