Glutamic acid decarboxylase 65 and 67 kDa proteins are reduced in autistic parietal and cerebellar cortices

GABA synaptopathy promotes the elevation of caspases 3 and 9 as pro-apoptotic markers in Egyptian patients with autism spectrum disorder

Autism spectrum disorder (ASD) is classified as a neurodevelopmental disorder characterized by reduced social communication as well as repetitive behaviors. Many studies have proved that defective synapses in ASD influence how neurons in the brain connect and communicate with each other. Synaptopathies arise from alterations that affecting the integrity and/or functionality of synapses and can contribute to synaptic pathologies. This study investigated the GABA levels in plasma being an inhibitory neurotransmitter, caspase 3 and 9 as pro-apoptotic proteins in 20 ASD children and 20 neurotypical controls using the ELISA technique. Analysis of receiver-operating characteristic (ROC) of the data that was obtained to evaluate the diagnostic value of the aforementioned evaluated biomarkers. Pearson's correlations and multiple regressions between the measured variables were also done. While GABA level was reduced in ASD patients, levels of caspases 3 and 9 were significantly higher when compared to neurotypical control participants. ROC and predictiveness curves showed that caspases 3, caspases 9, and GABA might be utilized as predictive markers in autism diagnosis. The present study indicates that the presence of GABAergic dysfunction promotes apoptosis in Egyptian ASD children. The obtained GABA synaptopathies and their connection with apoptosis can both relate to neuronal excitation, and imbalance of the inhibition system, which can be used as reliable predictive biomarkers for ASD.

Age-related parietal GABA alterations in children with autism spectrum disorder

GABA is the primary inhibitory neurotransmitter in the brain, and is essential to the balance of cortical excitation and inhibition. Reductions in GABA are proposed to result in an overly excitatory cortex that may cause, or contribute to, symptoms of autism spectrum disorder (ASD). This study employed a cross-sectional design to explore GABA+ differences in ASD and the impact of age, comparing 4-12 year olds with ASD (N = 24) to typically developing children (N = 35). GABA+ concentration was measured using edited magnetic resonance spectroscopy in the left parietal lobe. This study used a mixed model to investigate group differences between children with ASD and typically developing children. There was a significant difference in GABA+ levels between the groups, a significant effect of age and interaction between age and diagnostic group. The ASD group showed an association between GABA+ and age, with GABA+ levels gradually increasing with age (r = 0.59, p = 0.003). Typically developing children did not show age-related change in GABA+ concentration (r = 0.09, p = 0.60). By the age of 9, children with ASD showed GABA+ levels that were comparable to their typically developing peers. This study suggests that children with ASD have initially lower levels of GABA+ in the left parietal lobe compared to typically developing children, and that these initially lower levels of GABA+ increase with age in ASD within this region. It is suggested that this developmental shift of GABA+ levels within the left parietal lobe provides a possible explanation for the previously found reductions in childhood that does not persist in adults. LAY SUMMARY: This study measured levels of GABA in the left parietal lobe using magnetic resonance spectroscopy in children with ASD and typically developing children. GABA levels were initially lower in the ASD group, and increased with age, while GABA did not change with age in the typically developing group. This suggests that alterations in GABA signaling may be associated with ASD in childhood. Autism Res 2021, 14: 859-872. © 2021 International Society for Autism Research, Wiley Periodicals LLC.

Optogenetic Approaches to Understand the Neural Circuit Mechanism of Social Deficits Seen in Autism Spectrum Disorders

Individuals with neurodevelopmental disorders, such as autism spectrum disorders (ASDs), are diagnosed based on nonquantitative objective parameters such as behavioral phenotypes. It is still unclear how any neural mechanism affects such behavioral phenotypes in these patients. In human genetics, a large number of genetic abnormalities including single nucleotide variation (SNV) and copy number variation (CNV) have been found in individuals with ASDs. It is thought that influence of such variations converges on dysfunction of neural circuit resulting in common behavioral phenotypes of ASDs such as deficits in social communication and interaction. Recent studies suggest that an excitatory/inhibitory (E/I) imbalanced state, which induces disruption of neural circuit activities, is one of the pathophysiological abnormalities in ASD brains. To assess the causal relationship between brain abnormalities and behavioral deficits, we can take advantage of optogenetics with animal models of ASDs that recapitulate human genetic mutations. Here, we review optogenetics studies being utilized to dissect neural circuit mechanisms associated with social deficits in model mice of ASD. Optogenetic manipulation of disrupted neural activities would help us understand how neural circuits affect behavioral deficits observed in ASDs.

Combined the GABA-A and GABA-B receptor agonists attenuates autistic behaviors in a prenatal valproic acid-induced mouse model of autism

Autism spectrum disorder (ASD) is an immensely challenging developmental disorder characterized primarily by two core behavioral symptoms of social communication deficits and restricted/repetitive behaviors. Investigating the etiological process and identifying an appropriate therapeutic target remain as formidable challenges to overcome ASD due to numerous risk factors and complex symptoms associated with the disorder. Among the various mechanisms that contribute to ASD, the maintenance of excitation and inhibition balance emerged as a key factor to regulate proper functioning of neuronal circuitry. In this study, we employed prenatally exposed to valproic acid (VPA) to establish a validated ASD mouse model and found impaired inhibitory gamma-aminobutyric acid (GABAergic) neurotransmission through a presynaptic mechanism in these model mice, which was accompanied with decreased GABA release and GABA-A and GABA-B receptor subunits expression. And acute administration of individual GABA-A or GABA-B receptor agonists partially reversed autistic-like behaviors in the model mice. Furthermore, acute administration of the combined GABA-A and GABA-B receptor agonists palliated sociability deficits, anxiety and repetitive behaviors in the animal model of autistic-like behaviors, demonstrating the therapeutic potential of above cocktail in the treatment of ASD.

Executive Function in High-Functioning Autism Spectrum Disorder: A Meta-analysis of fMRI Studies

Abnormalities in executive function (EF) are clinical markers for autism spectrum disorder (ASD). However, the neural mechanisms underlying abnormal EF in ASD remain unclear. This meta-analysis investigated the construct, abnormalities, and age-related changes of EF in ASD. Thirty-three fMRI studies of inhibition, updating, and switching in individuals with high-functioning ASD were included (n = 1114; age range 7-57 years). The results revealed that the EF construct in ASD could be unitary (i.e., common EF) in children/adolescents, but unitary and diverse (i.e., common EF and inhibition) in adults. Abnormalities in this EF construct were found across development in individuals with ASD in comparison with typically developing individuals. Implications and recommendations are discussed for EF theory and for practice in ASD.

The Auditory Steady-State Response: Electrophysiological Index for Sensory Processing Dysfunction in Psychiatric Disorders

Sensory processing is disrupted in several psychiatric disorders, including schizophrenia, bipolar disorder, and autism spectrum disorder. In this review, we focus on the electrophysiological auditory steady-state response (ASSR) driven by high-frequency stimulus trains as an index for disease-associated sensory processing deficits. The ASSR amplitude is suppressed within the gamma band (≥30 Hz) among these patients, suggesting an imbalance between GABAergic and N-methyl-D-aspartate (NMDA) receptor-mediated neurotransmission. The reduced power and synchronization of the 40-Hz ASSR are robust in patients with schizophrenia. In recent years, similar ASSR deficits at gamma frequencies have also been reported in patients with bipolar disorder and autism spectrum disorder. We summarize ASSR abnormalities in each of these psychiatric disorders and suggest that the observed commonalities reflect shared pathophysiological mechanisms. We reviewed studies on phase resetting in which a salient sensory stimulus affects ASSR. Phase resetting induces the reduction of both the amplitude and phase of ASSR. Moreover, phase resetting is also affected by rare auditory stimulus patterns or superimposed stimuli of other modalities. Thus, sensory memory and multisensory integration can be investigated using phase resetting of ASSR. Here, we propose that ASSR amplitude, phase, and resetting responses are sensitive indices for investigating sensory processing dysfunction in psychiatric disorders.

Functional Changes of Mentalizing Network in SCA2 Patients: Novel Insights into Understanding the Social Cerebellum

In recent years, increasing evidence of the cerebellar role in social cognition has emerged. The cerebellum has been shown to modulate cortical activity of social brain regions serving as a regulator of function-specific mentalizing and mirroring processes. In particular, a mentalizing area in the posterior cerebellum, specifically Crus II, is preferentially recruited for more complex and abstract forms of social processing, together with mentalizing cerebral areas including the dorsal medial prefrontal cortex (dmPFC), the temporo-parietal junction (TPJ), and the precuneus. In the present study, the network-based statistics approach was used to assess functional connectivity (FC) differences within this mentalizing cerebello-cerebral network associated with a specific cerebellar damage. To this aim, patients affected by spinocerebellar ataxia type 2 (SCA2), a neurodegenerative disease specifically affecting regions of the cerebellar cortex, and age-matched healthy subjects have been enrolled. The dmPFC, left and right TPJ, the precuneus, and the cerebellar Crus II were used as regions of interest to construct the mentalizing network to be analyzed and evaluate pairwise functional relations between them. When compared with controls, SCA2 patients showed altered internodal connectivity between dmPFC, left (L-) and right (R-) TPJ, and right posterior cerebellar Crus II.The present results indicate that FC changes affect a function-specific mentalizing network in patients affected by cerebellar damage. In particular, they allow to better clarify functional alteration mechanisms driven by the cerebellar damage associated with SCA2 suggesting that selective cortico-cerebellar functional disconnections may underlie patients' social impairment in domain-specific complex and abstract forms of social functioning.

A de novo frameshift pathogenic variant in TBR1 identified in autism without intellectual disability

BACKGROUND

In order to be able to provide accurate genetic counseling to patients with Autism Spectrum Disorder (ASD), it is crucial to identify correlations between heterogeneous phenotypes and genetic alterations. Among the hundreds of de novo pathogenic variants reported in ASD, single-nucleotide variations and small insertions/deletions were reported in TBR1. This gene encodes a transcription factor that plays a key role in brain development. Pathogenic variants in TBR1 are often associated with severe forms of ASD, including intellectual disability and language impairment.

METHODS

Adults diagnosed with ASD but without intellectual disability (diagnosis of Asperger syndrome, according to the DSM-IV) took part in a genetic consultation encompassing metabolic assessments, a molecular karyotype and the screening of a panel of 268 genes involved in intellectual disability, ASD and epilepsy. In addition, the patient reported here went through a neuropsychological assessment, structural magnetic resonance imaging and magnetic resonance spectroscopy measurements.

RESULTS

Here, we report the case of a young adult male who presents with a typical form of ASD. Importantly, this patient presents with no intellectual disability or language impairment, despite a de novo heterozygous frameshift pathogenic variant in TBR1, leading to an early premature termination codon (c.26del, p.(Pro9Leufs*12)).

CONCLUSION

Based on this case report, we discuss the role of TBR1 in general brain development, language development, intellectual disability and other symptoms of ASD. Providing a detailed clinical description of the individuals with such pathogenic variants should help to understand the genotype-phenotype relationships in ASD.

The Role of Synaptic Cell Adhesion Molecules and Associated Scaffolding Proteins in Social Affiliative Behaviors

Social affiliative behaviors-engagement in positive (i.e., nonaggressive) social approach and reciprocal social interactions with a conspecific-comprise a construct within the National Institute of Mental Health Research Domain Criteria Social Processes Domain. These behaviors are disrupted in multiple human neurodevelopmental and neuropsychiatric disorders, such as autism, schizophrenia, social phobia, and others. Human genetic studies have strongly implicated synaptic cell adhesion molecules (sCAMs) in several such disorders that involve marked reductions, or other dysregulations, of social affiliative behaviors. Here, we review the literature on the role of sCAMs in social affiliative behaviors. We integrate findings pertaining to synapse structure and morphology, neurotransmission, postsynaptic signaling pathways, and neural circuitry to propose a multilevel model that addresses the impact of a diverse group of sCAMs, including neurexins, neuroligins, protocadherins, immunoglobulin superfamily proteins, and leucine-rich repeat proteins, as well as their associated scaffolding proteins, including SHANKs and others, on social affiliative behaviors. This review finds that the disruption of sCAMs often manifests in changes in social affiliative behaviors, likely through alterations in synaptic maturity, pruning, and specificity, leading to excitation/inhibition imbalance in several key regions, namely the medial prefrontal cortex, basolateral amygdala, hippocampus, anterior cingulate cortex, and ventral tegmental area. Unraveling the complex network of interacting sCAMs in glutamatergic synapses will be an important strategy for elucidating the mechanisms of social affiliative behaviors and the alteration of these behaviors in many neuropsychiatric and neurodevelopmental disorders.

Stem Cells for Improving the Treatment of Neurodevelopmental Disorders

Treatment options for neurodevelopmental disorders such as schizophrenia and autism are currently limited. Antipsychotics used to treat schizophrenia are not effective for all patients, do not target all symptoms of the disease, and have serious adverse side effects. There are currently no FDA-approved drugs to treat the core symptoms of autism. In an effort to develop new and more effective treatment strategies, stem cell technologies have been used to reprogram adult somatic cells into induced pluripotent stem cells, which can be differentiated into neuronal cells and even three-dimensional brain organoids. This new technology has the potential to elucidate the complex mechanisms that underlie neurodevelopmental disorders, offer more relevant platforms for drug discovery and personalized medicine, and may even be used to treat the disease.

Sleep in autism: A biomolecular approach to aetiology and treatment

People with autism spectrum disorder (ASD) commonly experience other comorbidities. Studies indicate that between 50% and 83% of individuals with ASD have sleep problems or disorders. The most commonly reported sleep problems are: (a) insomnia symptoms including the inability to get to sleep or stay asleep; and (b) circadian rhythm sleep-wake disorders, defined as a misalignment between the timing of endogenous circadian rhythms and the external environment. The circadian system provides timing information for the sleep-wake cycle that is regulated by the interaction of an endogenous processes (circadian - Process C, and homeostatic - Process S) and synchronizing agents (neurohormones and neurotransmitters), which produce somnogenic activity. A clinical priority in ASD is understanding the cause of these sleep problems in order to improve treatment outcomes. This review approaches sleep in autism from several perspectives: Sleep-wake mechanisms and problems, and brain areas and molecules controlling sleep (e.g., GABA and melatonin) and wake maintenance (e.g., serotonin, acetylcholine and glutamate). Specifically, this review examines how altered sleep structure could be related to neurobiological alterations or genetic mutations and the implications this may have for potential pharmacological treatments in individuals with ASD.

Neurotransmitter, Antioxidant and Anti-neuroinflammatory Mechanistic Potentials of Herbal Medicines in Ameliorating Autism Spectrum Disorder

BACKGROUND

Autism spectrum disorder (ASD) is a neurodevelopmental issue that disrupts behavior, nonverbal communication, and social interaction, impacting all aspects of an individual's social development. The underlying origin of autism is unclear, however, oxidative stress, as well as serotonergic, adrenergic and dopaminergic systems are thought to be implicated in ASD. Despite the fact that there is no effective medication for autism, current pharmacological treatments are utilized to ameliorate some of the symptoms such as selfmutilation, aggression, repetitive and stereotyped behaviors, inattention, hyperactivity, and sleep disorders.

METHODS

In accord with the literature regarding the activity of herbal medicines on neurotransmitter function, we aimed to review the most worthy medicinal herbs possessing neuroprotective effects.

RESULTS

Based on the outcome, medicinal herbs such as Zingiber officinale, Astragalus membranaceu, Ginkgo biloba, Centella asiatica and Acorus calamus, have antioxidant activity, which can influence neurotransmitter systems and are potentially neuroprotective.

CONCLUSION

Consequently, these herbs, in theory at least, appear to be suitable candidates within an overall management strategy for those on the autism spectrum.

Update on Atypicalities of Central Nervous System in Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a heterogeneous, behaviorally defined, neurodevelopmental disorder that has been modeled as a brain-based disease. The behavioral and cognitive features of ASD are associated with pervasive atypicalities in the central nervous system (CNS). To date, the exact mechanisms underlying the pathophysiology of ASD still remain unknown and there is currently no cure or effective treatment for this disorder. Many publications implicated the association of ASD with inflammation, immune dysregulation, neurotransmission dysfunction, mitochondrial impairment and cell signaling dysregulation. This review attempts to highlight evidence of the major pathophysiology of ASD including abnormalities in the brain structure and function, neuroglial activation and neuroinflammation, glutamatergic neurotransmission, mitochondrial dysfunction and mechanistic target of rapamycin (mTOR) signaling pathway dysregulation. Molecular and cellular factors that contributed to the pathogenesis of ASD and how they may affect the development and function of CNS are compiled in this review. However, findings of published studies have been complicated by the fact that autism is a very heterogeneous disorder; hence, we addressed the limitations that led to discrepancies in the reported findings. This review emphasizes the need for future studies to control study variables such as sample size, gender, age range and intelligence quotient (IQ), all of which that could affect the study measurements. Neuroinflammation or immune dysregulation, microglial activation, genetically linked neurotransmission, mitochondrial dysfunctions and mTOR signaling pathway could be the primary targets for treating and preventing ASD. Further research is required to better understand the molecular causes and how they may contribute to the pathophysiology of ASD.

Excitation-inhibition balance and auditory multistable perception are correlated with autistic traits and schizotypy in a non-clinical population

Individuals with autism spectrum disorder and individuals with schizophrenia have impaired social and communication skills. They also have altered auditory perception. This study investigated autistic traits and schizotypy in a non-clinical population as well as the excitation-inhibition (EI) balance in different brain regions and their auditory multistable perception. Thirty-four healthy participants were assessed by the Autism-Spectrum Quotient (AQ) and Schizotypal Personality Questionnaire (SPQ). The EI balance was evaluated by measuring the resting-state concentrations of glutamate-glutamine (Glx) and ϒ-aminobutyric acid (GABA) in vivo by using magnetic resonance spectroscopy. To observe the correlation between their traits and perception, we conducted an auditory streaming task and a verbal transformation task, in which participants reported spontaneous perceptual switching while listening to a sound sequence. Their AQ and SPQ scores were positively correlated with the Glx/GABA ratio in the auditory cortex but not in the frontal areas. These scores were negatively correlated with the number of perceptual switches in the verbal transformation task but not in the auditory streaming task. Our results suggest that the EI balance in the auditory cortex and the perceptual formation of speech are involved in autistic traits and schizotypy.

Enhanced accumulation of N-terminally truncated Aβ with and without pyroglutamate-11 modification in parvalbumin-expressing GABAergic neurons in idiopathic and dup15q11.2-q13 autism

Autism, the most frequent neurodevelopmental disorder of a very complex etiopathology, is associated with dysregulation of cellular homeostatic mechanisms, including processing of amyloid-β precursor protein (APP). Products of APP processing — N-terminally truncated amyloid-β peptide (N-tr-Aβ) species — are accumulated in autism in neurons and glia in the cortex, cerebellum, and subcortical structures of the brain. This process in neurons is correlated with increased oxidative stress. Because abnormally high levels of N-tr-Aβ are detected in only a fraction of neurons in the prefrontal cortex, we applied immunocytochemical staining and confocal microscopy in autopsy brain material from idiopathic and chromosome 15q11.2-q13 duplication (dup-15) autism to measure the load of N-tr-Aβ in the cells and synapses and to identify the subpopulation of neurons affected by these pathophysiological processes. The peptides accumulated in autism are N-terminally truncated; therefore, we produced a new antibody against Aβ truncated at N-terminal amino acid 11 modified to pyroglutamate to evaluate the presence and distribution of this peptide species in autism. We also quantified and characterized the oligomerization patterns of the Aβ-immunoreactive peptides in autism and control frozen brain samples. We provide morphological evidence, that in idiopathic and dup-15 autism, accumulation of N-tr-Aβ with and without pyroglutamate-11 modified N-terminus affects mainly the parvalbumin-expressing subpopulation of GABAergic neurons. N-tr-Aβ peptides are accumulated in neurons’ cytoplasm and nucleus as well as in GABAergic synapses. Aβ peptides with both C-terminus 40 and 42 were detected by immunoblotting in frozen cortex samples, in the form of dimers and complexes of the molecular sizes of 18-24kD and 32-34kD. We propose that deposition of N-tr-Aβ specifically affects the functions of the parvalbumin-expressing GABAergic neurons and results in a dysregulation of brain excitatory–inhibitory homeostasis in autism. This process may be the target of new therapies.

GABAARα2 is Decreased in the Axon Initial Segment of Pyramidal Cells in Specific Areas of the Prefrontal Cortex in Autism

Some forms of Autism Spectrum Disorder, a neurodevelopmental syndrome characterized by impaired communication and social skills as well as repetitive behaviors, are purportedly associated with dysregulation of the excitation/inhibition balance in the cerebral cortex. Through human postmortem tissue analysis, we previously found a significant decrease in the number of a gamma-aminobutyric acid (GABA)ergic interneuron subtype, the chandelier (Ch) cell, in the prefrontal cortex of subjects with autism. Ch cells exclusively target the axon initial segment (AIS) of excitatory pyramidal (Pyr) neurons, and a single Ch cell forms synapses on hundreds of Pyr cells, indicating a possible role in maintaining electrical balance. Thus, we herein investigated this crucial link between Ch and Pyr cells in the anatomy of autism neuropathology by examining GABA receptor protein expression in the Pyr cell AIS in subjects with autism. We collected tissue from the prefrontal cortex (Brodmann Areas (BA) 9, 46, and 47) of 20 subjects with autism and 20 age- and sex-matched control subjects. Immunohistochemical staining with antibodies against the GABA_A receptor subunit α2 (GABA_ARα2) - the subunit most prevalent in the Pyr cell AIS - revealed a significantly decreased GABA_ARα2 protein in the Pyr cell AIS in supragranular layers of prefrontal cortical areas BA9 and BA47 in autism. Downregulated GABA_ARα2 protein in the Pyr cell AIS may result from decreased GABA synthesis in the prefrontal cortex of subjects with autism, and thereby contribute to an excitation/inhibition imbalance. Our findings support the potential for GABA receptor agonists asa therapeutic tool for autism.

The Novel Potential Therapeutic Utility of Montelukast in Alleviating Autistic Behavior Induced by Early Postnatal Administration of Thimerosal in Mice

BACKGROUND AND AIM: Thimerosal (THIM) is a mercury-containing preservative widely used in many biological and medical products including many vaccines. It has been accused of being a possible etiological factor for some neurodevelopmental disorders such as autistic spectrum disorders (ASDs). In our study, the potential therapeutic effect of montelukast, a leukotriene receptor antagonist used to treat seasonal allergies and asthma, on THIM mice model (ASDs model) was examined.

METHODOLOGY

Newborn mice were randomly distributed into three groups: (Group 1) Control (Cont.) group received saline injections. (Group 2) THIM-treated (THIM) group received THIM intramuscular (IM) at a dose of 3000 μg Hg/kg on postnatal days 7, 9, 11, and 15. (Group 3) Montelukast-treated (Monte) group received THIM followed by montelukast sodium (10 mg/kg/day) intraperitoneal (IP) for 3 weeks. Mice were evaluated for growth development, social interactions, anxiety, locomotor activity, and cognitive function. Brain histopathology, alpha 7 nicotinic acetylcholine receptors (α7nAChRs), nuclear factor kappa B p65 (NF-κB p65), apoptotic factor (Bax), and brain injury markers were evaluated as well.

RESULTS

THIIM significantly impaired social activity and growth development. Montelukast mitigated THIM-induced social deficit probably through α7nAChRs upregulation, NF-κB p65, Bax, and brain injury markers downregulation, thus suppressing THIM-induced neuronal toxicity and inflammation.

CONCLUSION

Neonatal exposure to THIM can induce growth retardation and abnormal social interactions similar to those observed in ASDs. Some of these abnormalities could be ameliorated by montelukast via upregulation of α7nAChRs that inhibited NF-κB activation and significant suppression of neuronal injury and the associated apoptosis.

Cortical excitation-inhibition ratio mediates the effect of pre-attentive auditory processing deficits on interpersonal difficulties

Several lines of evidence identify aberrant excitatory-inhibitory neural processes across autism and schizophrenia spectrum disorders, particularly within the psychosocial domain. Such neural processes include increased excitatory glutamate and reduced inhibitory GABA concentrations, which may affect auditory pre-attentive processing as indexed by the mismatch negativity (MMN); thus, an excitation-inhibition imbalance might lead to aberrant MMN, which might in turn drive the relationship between the MMN and psychosocial difficulties. This research has the potential to enhance the neurochemical understanding of the relationship between electrophysiology (MMN) and behavioural/clinical measures (psychosocial difficulties). Thirty-eight adults (18 male, 18-40 years) completed the Schizotypal Personality Questionnaire (SPQ) and Autism-Spectrum Quotient (AQ). Glutamate and GABA concentrations in bilateral superior temporal cortex (STC) were quantified using proton magnetic resonance spectroscopy (1H-MRS) while auditory MMN to a duration deviant was measured with magnetoencephalography. Spearman correlations probed the relationships between STC glutamate/GABA ratios, MMN amplitude and latency, and AQ and SPQ dimensions. Mediation effects of glutamate/GABA ratios on the relationship between MMN and AQ-SPQ dimensions were probed using causal mediation analysis. Only SPQ-interpersonal and AQ-communication were significantly correlated with right hemisphere glutamate/GABA ratios and MMN latency (ps < 0.05), which were themselves correlated (p = .035). Two mediation models were investigated, with right MMN latency as predictor and SPQ-interpersonal and AQ-communication as outcome variables. Right STC glutamate/GABA ratios significantly mediated the relationship between MMN latency and SPQ-interpersonal scores, but only partially mediated the relationship between MMN latency and AQ-communication scores. These findings support the growing body of literature pointing toward an excitation-inhibition imbalance that is central to psychosocial functioning across multi-dimensional spectrum disorders, such as autism and schizophrenia, and provides neurochemical indicators of the processes that underlie psychosocial dysfunction.

Role of Vitamin D in Autism Spectrum Disorder

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Autism spectrum disorder (ASD) is a pervasive developmental disorder with heterogeneous etiology. Vitamin D can function as a fat-soluble vitamin as well as a hormone, and can exert its effect through both genomic and non-genomic mechanisms. In the last decades, several studies have examined the relationship between vitamin D levels and ASD. These studies demonstrated that low vitamin D status in early development has been hypothesized as an environmental risk factor for ASD. Both in vivo and in vitro studies have demonstrated that vitamin D deficiency in early life can alter brain development, dysregulates neurotransmitter balance in the brain, decreases body and brain antioxidant ability, and alters the immune system in ways that resemble pathological features commonly seen in ASD. In this review, we focused on the association between vitamin D and ASD. In addition, the above-mentioned mechanisms of action that link vitamin D deficiency with ASD were also discussed. Finally, clinical trials of vitamin D supplementation treatment of ASD have also been discussed.

Aging and Central Auditory Disinhibition: Is It a Reflection of Homeostatic Downregulation or Metabolic Vulnerability?

Aging-related changes have been identified at virtually every level of the central auditory system. One of the most common findings across these nuclei is a loss of synaptic inhibition with aging, which has been proposed to be at the heart of several aging-related changes in auditory cognition, including diminished speech perception in complex environments and the presence of tinnitus. Some authors have speculated that downregulation of synaptic inhibition is a consequence of peripheral deafferentation and therefore is a homeostatic mechanism to restore excitatory/inhibitory balance. As such, disinhibition would represent a form of maladaptive plasticity. However, clinical data suggest that deafferentation-related disinhibition tends to occur primarily in the aged brain. Therefore, aging-related disinhibition may, in part, be related to the high metabolic demands of inhibitory neurons relative to their excitatory counterparts. These findings suggest that both deafferentation-related maladaptive plastic changes and aging-related metabolic factors combine to produce changes in central auditory function. Here, we explore the arguments that downregulation of inhibition may be due to homeostatic responses to diminished afferent input vs. metabolic vulnerability of inhibitory neurons in the aged brain. Understanding the relative importance of these mechanisms will be critical for the development of treatments for the underlying causes of aging-related central disinhibition.

GABAA receptor availability is not altered in adults with autism spectrum disorder or in mouse models

Preliminary studies have suggested that γ-aminobutyric acid type A (GABA_A) receptors, and potentially the GABA_A α5 subtype, are deficient in autism spectrum disorder (ASD). However, prior studies have been confounded by the effects of medications, and these studies did not compare findings across different species. We measured both total GABA_A and GABA_A α5 receptor availability in two positron emission tomography imaging studies. We used the tracer [¹¹C]flumazenil in 15 adults with ASD and in 15 control individuals without ASD and the tracer [¹¹C]Ro15-4513 in 12 adults with ASD and in 16 control individuals without ASD. All participants were free of medications. We also performed autoradiography, using the same tracers, in three mouse models of ASD: the Cntnap2 knockout mouse, the Shank3 knockout mouse, and mice carrying a 16p11.2 deletion. We found no differences in GABA_A receptor or GABA_A α5 subunit availability in any brain region of adults with ASD compared to those without ASD. There were no differences in GABA_A receptor or GABA_A α5 subunit availability in any of the three mouse models. However, adults with ASD did display altered performance on a GABA-sensitive perceptual task. Our data suggest that GABA_A receptor availability may be normal in adults with ASD, although GABA signaling may be functionally impaired.

Purkinje cell-specific Grip1/2 knockout mice show increased repetitive self-grooming and enhanced mGluR5 signaling in cerebellum

Cerebellar Purkinje cell (PC) loss is a consistent pathological finding in autism. However, neural mechanisms of PC-dysfunction in autism remain poorly characterized. Glutamate receptor interacting proteins 1/2 (Grip1/2) regulate AMPA receptor (AMPAR) trafficking and synaptic strength. To evaluate role of PC-AMPAR signaling in autism, we produced PC-specific Grip1/2 knockout mice by crossing Grip2 conventional and Grip1 conditional KO with L7-Cre driver mice. PCs in the mutant mice showed normal morphology and number, and a lack of Grip1/2 expression. Rodent behavioral testing identified normal ambulation, anxiety, social interaction, and an increase in repetitive self-grooming. Electrophysiology studies revealed normal mEPSCs but an impaired mGluR-LTD at the Parallel Fiber-PC synapses. Immunoblots showed increased expression of mGluR5 and Arc, and enhanced phosphorylation of P38 and AKT in cerebellum of PC-specific Grip1/2 knockout mice. Results indicate that loss of Grip1/2 in PCs contributes to increased repetitive self-grooming, a core autism behavior in mice. Results support a role of AMPAR trafficking defects in PCs and disturbances of mGluR5 signaling in cerebellum in the pathogenesis of repetitive behaviors.

Psychosocial deficits across autism and schizotypal spectra are interactively modulated by excitatory and inhibitory neurotransmission

Continued human and animal research has strengthened evidence for aberrant excitatory-inhibitory neural processes underlying autism and schizophrenia spectrum disorder psychopathology, particularly psychosocial functioning, in clinical and nonclinical populations. We investigated the extent to which autistic traits and schizotypal dimensions were modulated by the interactive relationship between excitatory glutamate and inhibitory GABA neurotransmitter concentrations in the social processing area of the superior temporal cortex using proton magnetic resonance spectroscopy. In total, 38 non-clinical participants (20 females; age range = 18-35 years, mean (standard deviation) = 23.22 (5.52)) completed the autism spectrum quotient and schizotypal personality questionnaire, and underwent proton magnetic resonance spectroscopy to quantify glutamate and GABA concentrations in the right and left superior temporal cortex. Regression analyses revealed that glutamate and GABA interactively modulated autistic social skills and schizotypal interpersonal features (p_corr < 0.05), such that those with high right superior temporal cortex glutamate but low GABA concentrations exhibited poorer social and interpersonal skills. These findings evidence an excitation-inhibition imbalance that is specific to psychosocial features across the autism and schizophrenia spectra.

Microglia as possible therapeutic targets for autism spectrum disorders

Malfunctions of the nervous and immune systems are now recognized to be fundamental causes of autism spectrum disorders (ASDs). Studies have suggested that the brain's resident immune cells, microglia are possible key players in ASDs. Specifically, deficits in synaptic pruning by microglia may underlie the pathogenesis of ASDs, in which excess synapses are occasionally reported. This idea has driven researchers to investigate causal links between microglial dysfunction and ASDs. In this review, we first introduce the characteristics of microglia in ASD brains and discuss their possible roles in the pathogenesis of ASDs. We also refer to immunomodulatory agents that could be potentially used as symptomatic therapies for ASDs in light of their ability to modify microglial functions. Finally, we will mention a possible strategy to radically cure some of the symptoms reported in ASDs through reorganizing neural circuits via microglia-dependent synaptic pruning.

Children with Autism Spectrum Disorder Demonstrate Regionally Specific Altered Resting-State Phase-Amplitude Coupling

Studies suggest that individuals with autism spectrum disorder (ASD) exhibit altered electrophysiological alpha to gamma phase-amplitude coupling (PAC). Preliminary reports with small samples report conflicting findings regarding the directionality of the alpha to gamma PAC alterations in ASD. The present study examined resting-state activity throughout the brain in a relatively large sample of 119 children with ASD and 47 typically developing children. Children with ASD demonstrated regionally specific abnormalities in alpha to low-gamma PAC, with increased alpha to low-gamma PAC for a central midline source and decreased PAC at lateral sources. Group differences in local gamma-band power did not account for the regional group differences in alpha to low-gamma PAC. Moreover, local alpha power did not significantly modulate alpha to low-gamma PAC estimates. Finally, PAC estimates were correlated with Social Responsiveness Scale (SRS) indicating clinical relevance of the PAC metric. In conclusion, alpha to low-gamma PAC alterations in ASD demonstrate a heterogeneous spatial profile consistent with previous studies and were related to symptom severity.

A double-blind, placebo-controlled, randomised-designed GABA tea study in children diagnosed with autism spectrum conditions: a feasibility study clinical trial registration: ISRCTN 72571312

Objective: The research has shown an association with sensorimotor integration and symptomology of Autism Spectrum Conditions (ASC). Specific areas of the brain that are involved in sensorimotor integration, such as the cerebellum and basal ganglia, are pathologically different in individuals with ASC in comparison to typically developing (TD) peers. These brain regions contain GABAergic inhibitory neurons that release an inhibitory neurotransmitter, γ-Aminobutyric acid (GABA). Brain GABA levels are decreased in ASC. This study explored the effect of introducing a non-invasive GABA substitute, in the form of GABA Oolong tea, on sensorimotor skills, ASC profiles, anxieties and sleep of children with ASC. Methods: Nine children took part: (5 male, 4 female). Each child participated in three tea conditions: high GABA, high L-Theanine (a compound that increases GABA), placebo with low GABA. A double-blind, repeated measures design was employed. Measures were taken after each tea condition. Sensory and ASC profiles were scored using parental questionnaires. Motor skills were assessed using a gold standard coordination assessment. Sleep was monitored using an actiwatch and anxiety measured through cortisol assays. Subjective views were sought from parents on 'best' tea. Results: The results showed significant improvement in manual dexterity and some large individual improvements in balance, sensory responsivity, DSM-5 criteria and cortisol levels with GABA tea. Improvements were also seen in the L-Theanine condition although they were more sporadic. Conclusions: These results suggest that sensorimotor abilities, anxiety levels and DSM-5 symptomology of children with ASC can benefit from the administration of GABA in the form of Oolong tea.

How could N-Methyl-D-Aspartate Receptor Antagonists Lead to Excitation Instead of Inhibition?

N-methyl-D-aspartate receptors (NMDARs) are a family of ionotropic glutamate receptors mainly known to mediate excitatory synaptic transmission and plasticity. Interestingly, low-dose NMDAR antagonists lead to increased, instead of decreased, functional connectivity; and they could cause schizophrenia- and/or antidepressant-like behavior in both humans and rodents. In addition, human genetic evidences indicate that NMDAR loss of function mutations underlie certain forms of epilepsy, a disease featured with abnormal brain hyperactivity. Together, they all suggest that under certain conditions, NMDAR activation actually lead to inhibition, but not excitation, of the global neuronal network. Apparently, these phenomena are rather counterintuitive to the receptor's basic role in mediating excitatory synaptic transmission. How could it happen? Recently, this has become a crucial question in order to fully understand the complexity of NMDAR function, particularly in disease. Over the past decades, different theories have been proposed to address this question. These include theories of “NMDARs on inhibitory neurons are more sensitive to antagonism”, or “basal NMDAR activity actually inhibits excitatory synapse”, etc. Our review summarizes these efforts, and also provides an introduction of NMDARs, inhibitory neurons, and their relationships with the related diseases. Advances in the development of novel NMDAR pharmacological tools, particularly positive allosteric modulators, are also included to provide insights into potential intervention strategies.

GABARAPs dysfunction by autophagy deficiency in adolescent brain impairs GABAA receptor trafficking and social behavior

Dysfunctional mTOR signaling is associated with the pathogenesis of neurodevelopmental and neuropsychiatric disorders. However, it is unclear what molecular mechanisms and pathogenic mediators are involved and whether mTOR-regulated autophagy continues to be crucial beyond neurodevelopment. Here, we selectively deleted Atg7 in forebrain GABAergic interneurons in adolescent mice and unexpectedly found that these mice showed a set of behavioral deficits similar to Atg7 deletion in forebrain excitatory neurons. By unbiased quantitative proteomic analysis, we identified γ-aminobutyric acid receptor-associated protein-like 2 (GABARAPL2) to differentially form high-molecular weight species in autophagy-deficient brains. Further functional analyses revealed a novel pathogenic mechanism involving the p62-dependent sequestration of GABARAP family proteins, leading to the reduction of surface GABA_A receptor levels. Our work demonstrates a novel physiological role for autophagy in regulating GABA signaling beyond postnatal neurodevelopment, providing a potential mechanism for the reduced inhibitory inputs observed in neurodevelopmental and neuropsychiatric disorders with mTOR hyperactivation.

Neurodevelopmental Disorders: Functional Role of Ambra1 in Autism and Schizophrenia

The activating molecule in Beclin-1-regulated autophagy (Ambra1) is a highly intrinsically disordered protein best known for its role as a mediator in autophagy, by favoring the formation of autophagosomes. Additional studies have revealed that Ambra1 is able to coordinate cell responses to stress conditions such as starvation, and it actively participates in cell proliferation, cytoskeletal modification, apoptosis, mitochondria removal, and cell cycle downregulation. All these functions highlight the importance of Ambra1 in crucial physiological events, including metabolism, cell death, and cell division. Importantly, Ambra1 is also crucial for proper embryonic development, and its complete absence in knock-out animal models leads to severe brain morphology defects. In line with this, it has recently been implicated in neurodevelopmental disorders affecting humans, particularly autism spectrum disorders and schizophrenia. Here, we discuss the recent links between Ambra1 and neurodevelopment, particularly focusing on its role during the maturation of hippocampal parvalbumin interneurons and its importance for maintaining a proper excitation/inhibition balance in the brain.

The contribution of [1H] magnetic resonance spectroscopy to the study of excitation-inhibition in autism

Autism spectrum disorder (ASD) affects over 1:100 of the population and costs the UK more than £32bn and the USA more than $175bn (£104bn) annually. Its core symptoms are social and communication difficulties, repetitive behaviours and sensory hyper- or hypo-sensitivities. A highly diverse phenotypic presentation likely reflects its etiological heterogeneity and makes finding treatment targets for ASD challenging. In addition, there are no means to identify biologically responsive individuals who may benefit from specific interventions. There is hope however, and in this review we consolidate how findings from magnetic resonance spectroscopy (MRS) add to the evidence that differences in the brain's excitatory glutamate and inhibitory γ-aminobutyric acid (GABA) balance may be both a key biomarker and a tractable treatment target in ASD.

Bypassing Glutamic Acid Decarboxylase 1 (Gad1) Induced Craniofacial Defects with a Photoactivatable Translation Blocker Morpholino

γ-Amino butyric acid (GABA) mediated signaling is critical in the central and enteric nervous systems, pancreas, lungs, and other tissues. It is associated with many neurological disorders and craniofacial development. Glutamic acid decarboxylase (GAD) synthesizes GABA from glutamate, and knockdown of the gad1 gene results in craniofacial defects that are lethal in zebrafish. To bypass this and enable observation of the neurological defects resulting from knocking down gad1 expression, a photoactivatable morpholino oligonucleotide (MO) against gad1 was prepared by cyclization with a photocleavable linker rendering the MO inactive. The cyclized MO was stable in the dark and toward degradative enzymes and was completely linearized upon brief exposure to 405 nm light. In the course of investigating the function of the ccMOs in zebrafish, we discovered that zebrafish possess paralogous gad1 genes, gad1a and gad1b. A gad1b MO injected at the 1–4 cell stage caused severe morphological defects in head development, which could be bypassed, enabling the fish to develop normally, if the fish were injected with a photoactivatable, cyclized gad1b MO and grown in the dark. At 1 day post fertilization (dpf), light activation of the gad1b MO followed by observation at 3 and 7 dpf led to increased and abnormal electrophysiological brain activity compared to wild type animals. The photocleavable linker can be used to cyclize and inactivate any MO, and represents a general strategy to parse the function of developmentally important genes in a spatiotemporal manner.

Tactile hypersensitivity and GABA concentration in the sensorimotor cortex of adults with autism

Sensory hypersensitivity is frequently encountered in autism spectrum disorder (ASD). Gamma-aminobutyric acid (GABA) has been hypothesized to play a role in tactile hypersensitivity. The aim of the present study was twofold. First, as a study showed that children with ASD have decreased GABA concentrations in the sensorimotor cortex, we aimed at determining whether the GABA reduction remained in adults with ASD. For this purpose, we used magnetic resonance spectroscopy to measure GABA concentration in the sensorimotor cortex of neurotypical adults (n = 19) and ASD adults (n = 18). Second, we aimed at characterizing correlations between GABA concentration and tactile hypersensitivity in ASD. GABA concentration in the sensorimotor cortex of adults with ASD was lower than in neurotypical adults (decrease by 17%). Interestingly, GABA concentrations were positively correlated with self-reported tactile hypersensitivity in adults with ASD (r = 0.50, P = 0.01), but not in neurotypical adults. In addition, GABA concentrations were negatively correlated with the intra-individual variation during threshold measurement, both in neurotypical adults (r = -0.47, P = 0.04) and in adults with ASD (r = -0.59, P = 0.01). In other words, in both groups, the higher the GABA level, the more precise the tactile sensation. These results highlight the key role of GABA in tactile sensitivity, and suggest that atypical GABA modulation contributes to tactile hypersensitivity in ASD. We discuss the hypothesis that hypersensitivity in ASD could be due to suboptimal predictions about sensations. Autism Research 2019, 12: 562-575. © 2019 International Society for Autism Research, Wiley Periodicals, Inc. LAY SUMMARY: People with autism spectrum disorder (ASD) often experience tactile hypersensitivity. Here, our goal was to highlight a link between tactile hypersensitivity and the concentration of gamma-aminobutyric acid (GABA) (an inhibitory neurotransmitter) in the brain of adults with ASD. Indeed, self-reported hypersensitivity correlated with reduced GABA levels in brain areas processing touch. Our study suggests that this neurotransmitter may play a key role in tactile hypersensitivity in autism.

The association of excitation and inhibition signaling with the relative symptom expression of autism and psychosis-proneness: Implications for psychopharmacology

The underlying mechanisms of autism and schizophrenia are poorly understood, partly due to a lack of dimension-specific research. Aberrant excitatory and inhibitory neurotransmission are implicated in both conditions, particularly in social dysfunction. This study investigates the extent to which the degree of autistic tendency and psychosis-proneness exclusively and interactively predict excitatory and inhibitory neurotransmitter concentrations in the superior temporal cortex (STC). In 38 adults (18 male, 18-40 years), we obtained autistic tendencies (Autism-Spectrum Quotient [AQ]) and psychosis-proneness scores (Schizotypal Personality Questionnaire [PP]); magnetic resonance spectroscopy (MRS) quantified glutamate and GABA+ concentrations from the STC. Results demonstrated a negative AQ/PP interaction with glutamate concentration for the left STC voxel, where PP increased with glutamate for average AQ, while AQ decreased with glutamate for average-high PP. There was a negative AQ/PP interaction with glutamate/GABA+ ratio for the right STC, AQ increasing with glutamate/GABA+ for low-average PP, while PP decreased with glutamate/GABA+ for high AQ. Consistent with animal studies, we also reveal that overall reduced glutamate/GABA+ ratio might be precipitated by increased right hemisphere GABA+ concentrations. These findings illustrate the importance of considering the concurrent effects of autism and psychosis dimensions on understanding the pathophysiological mechanisms implicated in either condition, and can advance psychopharmacological research into better treatment options for patients.

Modeling Psychiatric Diseases with Induced Pluripotent Stem Cells

Neuropsychiatric disorders are a heterogeneous group of disorders that are challenging to model and treat, due to their underlying complex genetic architecture and clinical variability. Presently, increasingly more studies are making use of induced pluripotent stem cell (iPSC)-derived neurons, reprogrammed from patient somatic cells, to model neuropsychiatric disorders. iPSC-derived neurons offer the possibility to recapitulate relevant disease biology in the context of the individual patient genetic background. In addition to disease modeling, iPSC-derived neurons offer unprecedented opportunities in drug screening. In this chapter, the current status of iPSC disease modeling for neuropsychiatric disorders is presented. Both 2D and 3D disease modeling approaches are discussed as well as the generation of different neuronal cell types that are relevant for studying neuropsychiatric disorders. Moreover, the advantages and limitations are highlighted in addition to the future perspectives of using iPSC-derived neurons in the uncovering of robust cellular phenotypes that consecutively have the potential to lead to clinical developments.

Prenatal Stress and Maternal Immune Dysregulation in Autism Spectrum Disorders: Potential Points for Intervention

BACKGROUND

Genetics is a major etiological contributor to autism spectrum disorder (ASD). Environmental factors, however, also appear to contribute. ASD pathophysiology due to gene x environment is also beginning to be explored. One reason to focus on environmental factors is that they may allow opportunities for intervention or prevention.

METHODS AND RESULTS

Herein, we review two such factors that have been associated with a significant proportion of ASD risk, prenatal stress exposure and maternal immune dysregulation. Maternal stress susceptibility appears to interact with prenatal stress exposure to affect offspring neurodevelopment. We also explore how maternal stress may interact with the microbiome in the neurodevelopmental setting. Additionally, understanding of the impact of maternal immune dysfunction on ASD has recently been advanced by recognition of specific fetal brain proteins targeted by maternal autoantibodies, and identification of unique mid-gestational maternal immune profiles. This might also be interrelated with maternal stress exposure. Animal models have been developed to explore pathophysiology targeting each of these factors.

CONCLUSION

We are beginning to understand the behavioral, pharmacopathological, and epigenetic effects related to these interactions, and we are beginning to explore potential mitigating factors. Continued growth in understanding of these mechanisms may ultimately allow for the identification of multiple potential targets for prevention or intervention for this subset of environmental-associated ASD cases.

Social behavior, neuroimmune markers and glutamic acid decarboxylase levels in a rat model of valproic acid-induced autism

Autism is a complex neurodevelopmental disorder characterized by impaired social communication and social interactions, and repetitive behaviors. The etiology of autism remains unknown and its molecular basis is not yet well understood. Pregnant Sprague-Dawley (SD) rats were administered 600 mg/kg of valproic acid (VPA) by intraperitoneal injection on day 12.5 of gestation. Both 11- to 13-week-old male and female rat models of VPA-induced autism showed impaired sociability and impaired preference for social novelty as compared to the corresponding control SD rats. Significantly reduced mRNA expressions of social behavior-related genes, such as those encoding the serotonin receptor, brain-derived neurotrophic factor and neuroligin3, and significantly increased expression levels of proinflammatory cytokines, such as interleukin-1 β and tumor necrosis factor-α, were noted in the hippocampi of both male and female rats exposed to VPA in utero. The hippocampal expression level of gamma amino butyric acid (GABA) enzyme glutamic acid decarboxylase (GAD) 67 protein was reduced in both male and female VPA-exposed rats as compared to the corresponding control animals. Our results indicate that developmental exposure to VPA affects the social behavior in rats by modulating the expression levels of social behavior-related genes and inflammatory mediators accompanied with changes in GABA enzyme in the hippocampus.

Aberrant Cerebellar-Cerebral Functional Connectivity in Children and Adolescents With Autism Spectrum Disorder

The cerebellum, which forms widespread functional networks with many areas in the cerebral cortices and subcortical structures, is one of the brain regions most consistently reported to exhibit neuropathological features in patients with autism spectrum disorder (ASD). However, cerebellar functional connectivity (FC) studies in patients with ASD have been very sparse. Using resting state functional connectivity (rsFC) analysis, we investigated the FC of the hemispheric/vermal subregions and the dentate nucleus of the cerebellum with the cerebral regions in 36 children and adolescents [16 participants with ASD, 20 typically developing (TD) participants, age: 6–15 years]. Furthermore, an independent larger sample population (42 participants with ASD, 88 TD participants, age: 6–15 years), extracted from the Autism Brain Imaging Data Exchange (ABIDE) II, was included for replication. The ASD group showed significantly increased or decreased FC between “hubs” in the cerebellum and cerebral cortices, when compared with the TD group. Findings of aberrant FCs converged on the posterior hemisphere, right dentate nucleus, and posterior inferior vermis of the cerebellum. Furthermore, these aberrant FCs were found to be related to motor, executive, and socio-communicative functions in children and adolescents with ASD when we examined correlations between FC and behavioral measurements. Results from the original dataset were partially replicated in the independent larger sample population. Our findings suggest that aberrant cerebellar–cerebral FC is associated with motor, socio-communicative, and executive functions in children and adolescents with ASD. These observations improve the current knowledge regarding the neural substrates that underlie the symptoms of ASD.

Developmental protein kinase C hyper-activation results in microcephaly and behavioral abnormalities in zebrafish

Susceptible genetic polymorphisms and altered expression levels of protein kinase C (PKC)-encoding genes suggest overactivation of PKC in autism spectrum disorder (ASD) development. To delineate the pathological role of PKC, we pharmacologically stimulated its activity during the early development of zebrafish. Results demonstrated that PKC hyper-activation perturbs zebrafish development and induces a long-lasting head size deficit. The anatomical and cellular analysis revealed reduced neural precursor proliferation and newborn neuron formation. β-Catenin that is essential for brain growth is dramatically degraded. Stabilization of β-catenin by gsk3β inhibition partially restores the head size deficit. In addition, the neuropathogenic effect of developmental PKC hyper-activation was further supported by the alterations in the behavioral domain including motor abnormalities, heightened stress reactivity and impaired habituation learning. Taken together, by causally connecting early-life PKC hyper-activation to these neuropathological traits and the impaired neurogenesis, these results suggest that PKC could be a critical pathway in ASD pathogenesis.

GABAρ3 expression in lobule X of the cerebellum is reduced in the valproate model of autism

Autism spectrum disorder (ASD) is a group of developmental disorders characterized by social interaction deficits, communication impairments, and stereotyped and repetitive behaviors. Additionally, impairments in the GABAergic circuitry have been associated with ASD. Several studies have shown that dysfunction of the cerebellum is a hallmark of ASD, and postmortem studies in humans reported a reduced density of Purkinje cells (PCs) together with an abnormal expression of GABA_A subunits, among which GABAρ3 is expressed in early postnatal development, forms homomeric receptors with high affinity to the agonist (GABA EC₅₀ ∼ 3 μM) and desensitize very little upon activation. Thus, we tested if the expression of GABAρ3 was modified by prenatal exposure to valproate (VPA), a well-known murine model of autism. The latency to find the nest increased in VPA-treated mice when compared to controls at postnatal day 8 (P8). Immunofluorescence studies showed a reduced expression of GABAρ3 in Purkinje cells (PCs) and ependymal glial cells (EGCs) from lobule X of VPA-treated mice. Finally, the expression of GABAρ3 increases linearly throughout normal development of the cerebellum, but this pattern is disrupted in the VPA model of autism. We conclude that the expression of GABAρ3 is reduced in PCs and EGCs from lobule X of the cerebellum in the VPA model of autism. Thus, GABAρ3 may be a relevant marker for ASD etiology.

Prenatal Stress, Maternal Immune Dysregulation, and Their Association With Autism Spectrum Disorders

PURPOSE OF REVIEW

While genetic factors are a major etiological contributor to autism spectrum disorder (ASD), evidence also supports a role for environmental factors. Herein, we will discuss two such factors that have been associated with a significant proportion of ASD risk: prenatal stress exposure and maternal immune dysregulation, and how sex and gender relate to these factors.

RECENT FINDINGS

Recent evidence suggests that maternal stress susceptibility interacts with prenatal stress exposure to affect offspring neurodevelopment. Additionally, understanding of the impact of maternal immune dysfunction on ASD has recently been advanced by recognition of specific fetal brain proteins targeted by maternal autoantibodies, and identification of unique mid-gestational maternal immune profiles. Animal models have been developed to explore pathophysiology targeting both of these factors, with limited sex-specific effects observed. While prenatal stress and maternal immune dysregulation are associated with ASD, most cases of these prenatal exposures do not result in ASD, suggesting interaction with multiple other risks. We are beginning to understand the behavioral, pharmacopathological, and epigenetic effects related to these interactions, as well as potential mitigating factors. Sex differences of these risks have been understudied but are crucial for understanding the higher prevalence of ASD in boys. Continued growth in understanding of these mechanisms may ultimately allow for the identification of multiple potential points for prevention or intervention, and for a personalized medicine approach for this subset of environmental-associated ASD cases.

Prenatal exposure to environmental insults and enhanced risk of developing Schizophrenia and Autism Spectrum Disorder: focus on biological pathways and epigenetic mechanisms

When considering neurodevelopmental disorders (NDDs), Schizophrenia (SZ) and Autism Spectrum Disorder (ASD) are considered to be among the most severe in term of prevalence, morbidity and impact on the society. Similar features and overlapping symptoms have been observed at multiple levels, suggesting common pathophysiological bases. Indeed, recent genome-wide association studies (GWAS) and epidemiological data report shared vulnerability genes and environmental triggers across the two disorders. In this review, we will discuss the possible biological mechanisms, including glutamatergic and GABAergic neurotransmissions, inflammatory signals and oxidative stress related systems, which are targeted by adverse environmental exposures and that have been associated with the development of SZ and ASD. We will also discuss the emerging role of the gut microbiome as possible interplay between environment, immune system and brain development. Finally, we will describe the involvement of epigenetic mechanisms in the maintenance of long-lasting effects of adverse environments early in life. This will allow us to better understand the pathophysiology of these NDDs, and also to identify novel targets for future treatment strategies.

Embryonic stem cell transplants as a therapeutic strategy in a rodent model of autism

Autism is a neurodevelopmental disorder characterized by disruptions in three core behavioral domains: deficits in social interaction, impairments in communication, and repetitive and stereotyped patterns of behavior or thought. There are currently no drugs available for the treatment of the core symptoms of ASD and drugs that target comorbid symptoms often have serious adverse side effects, suggesting an urgent need for new therapeutic strategies. The neurobiology of autism is complex, but converging evidence suggests that ASD involves disruptions in the inhibitory GABAergic neurotransmitter system. Specifically, people with autism have a reduction in parvalbumin (PV)-containing interneurons in the PFC, leading to the suggestion that restoring interneuron function in this region may be a novel therapeutic approach for ASD. Here we used a dual-reporter embryonic stem cell line to generate enriched populations of PV-positive interneurons, which were transplanted into the medial prefrontal cortex (mPFC) of the Poly I:C rodent model of autism. PV interneuron transplants were able to decrease pyramidal cell firing in the mPFC and alleviated deficits in social interaction and cognitive flexibility. Our results suggest that restoring PV interneuron function in the mPFC may be a novel and effective treatment strategy to reduce the core symptoms of autism.

Strong correlation of downregulated genes related to synaptic transmission and mitochondria in post-mortem autism cerebral cortex

Background

Genetic studies in autism have pinpointed a heterogeneous group of loci and genes. Further, environment may be an additional factor conferring susceptibility to autism. Transcriptome studies investigate quantitative differences in gene expression between patient-derived tissues and control. These studies may pinpoint genes relevant to pathophysiology yet circumvent the need to understand genetic architecture or gene-by-environment interactions leading to disease.

Methods

We conducted alternate gene set enrichment analyses using differentially expressed genes from a previously published RNA-seq study of post-mortem autism cerebral cortex. We used three previously published microarray datasets for validation and one of the microarray datasets for additional differential expression analysis. The RNA-seq study used 26 autism and 33 control brains in differential gene expression analysis, and the largest microarray dataset contained 15 autism and 16 control post-mortem brains.

Results

While performing a gene set enrichment analysis of genes differentially expressed in the RNA-seq study, we discovered that genes associated with mitochondrial function were downregulated in autism cerebral cortex, as compared to control. These genes were correlated with genes related to synaptic function. We validated these findings across the multiple microarray datasets. We also did separate differential expression and gene set enrichment analyses to confirm the importance of the mitochondrial pathway among downregulated genes in post-mortem autism cerebral cortex.

Conclusions

We found that genes related to mitochondrial function were differentially expressed in autism cerebral cortex and correlated with genes related to synaptic transmission. Our principal findings replicate across all datasets investigated. Further, these findings may potentially replicate in other diseases, such as in schizophrenia.

Electronic supplementary material

The online version of this article (10.1186/s11689-018-9237-x) contains supplementary material, which is available to authorized users.

Current Enlightenment About Etiology and Pharmacological Treatment of Autism Spectrum Disorder

Autistic Spectrum Disorder (ASD) is a complex neurodevelopmental brain disorder characterized by two core behavioral symptoms, namely impairments in social communication and restricted/repetitive behavior. The molecular mechanisms underlying ASD are not well understood. Recent genetic as well as non-genetic animal models contributed significantly in understanding the pathophysiology of ASD, as they establish autism-like behavior in mice and rats. Among the genetic causes, several chromosomal mutations including duplications or deletions could be possible causative factors of ASD. In addition, the biochemical basis suggests that several brain neurotransmitters, e.g., dopamine (DA), serotonin (5-HT), gamma-amino butyric acid (GABA), acetylcholine (ACh), glutamate (Glu) and histamine (HA) participate in the onset and progression of ASD. Despite of convincible understanding, risperidone and aripiprazole are the only two drugs available clinically for improving behavioral symptoms of ASD following approval by Food and Drug Administration (FDA). Till date, up to our knowledge there is no other drug approved for clinical usage specifically for ASD symptoms. However, many novel drug candidates and classes of compounds are underway for ASD at different phases of preclinical and clinical drug development. In this review, the diversity of numerous aetiological factors and the alterations in variety of neurotransmitter generation, release and function linked to ASD are discussed with focus on drugs currently used to manage neuropsychiatric symptoms related to ASD. The review also highlights the clinical development of drugs with emphasis on their pharmacological targets aiming at improving core symptoms in ASD.

Understanding the roles of glutamine synthetase, glutaminase, and glutamate decarboxylase autoantibodies in imbalanced excitatory/inhibitory neurotransmission as etiological mechanisms of autism

AIM

Autism is a heterogeneous neurological disorder that is characterized by impairments in communication and social interactions, repetitive behaviors, and sensory abnormalities. The etiology of autism remains unclear. Animal, genetic, and post-mortem studies suggest that an imbalance exists in the neuronal excitation and inhibition system in autism. The aim of this study was to determine whether alterations of the measured parameters in children with autism are significantly associated with the risk of a sensory dysfunction.

METHODS

The glutamine synthetase (GS), kidney-type glutaminase (GLS1), and glutamic acid decarboxylase autoantibody levels were analyzed in 38 autistic children and 33 age- and sex-matched controls using enzyme-linked immunosorbent assays.

RESULTS

The obtained data demonstrated significant alterations in glutamate and glutamine cycle enzymes, as represented by GS and GLS1, respectively. While the glutamic acid decarboxylase autoantibodies levels were remarkably increased, no significant difference was observed compared to the healthy control participants.

CONCLUSION

The obtained data indicate that GS and GLS1 are promising indicators of a neuronal excitation and inhibition system imbalance and that combined measured parameters are good predictive biomarkers of autism.