Alterations of neocortical development and maturation in autism: insight from valproic acid exposure and animal models of autism

Repurposing SGLT2 Inhibitors for Neurological Disorders: A Focus on the Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a neurodevelopmental disorder with a substantially increasing incidence rate. It is characterized by repetitive behavior, learning difficulties, deficits in social communication, and interactions. Numerous medications, dietary supplements, and behavioral treatments have been recommended for the management of this condition, however, there is no cure yet. Recent studies have examined the therapeutic potential of the sodium-glucose cotransporter 2 (SGLT2) inhibitors in neurodevelopmental diseases, based on their proved anti-inflammatory effects, such as downregulating the expression of several proteins, including the transforming growth factor beta (TGF-β), interleukin-6 (IL-6), C-reactive protein (CRP), nuclear factor κB (NF-κB), tumor necrosis factor alpha (TNF-α), and the monocyte chemoattractant protein (MCP-1). Furthermore, numerous previous studies revealed the potential of the SGLT2 inhibitors to provide antioxidant effects, due to their ability to reduce the generation of free radicals and upregulating the antioxidant systems, such as glutathione (GSH) and superoxide dismutase (SOD), while crossing the blood brain barrier (BBB). These properties have led to significant improvements in the neurologic outcomes of multiple experimental disease models, including cerebral oxidative stress in diabetes mellitus and ischemic stroke, Alzheimer's disease (AD), Parkinson's disease (PD), and epilepsy. Such diseases have mutual biomarkers with ASD, which potentially could be a link to fill the gap of the literature studying the potential of repurposing the SGLT2 inhibitors' use in ameliorating the symptoms of ASD. This review will look at the impact of the SGLT2 inhibitors on neurodevelopmental disorders on the various models, including humans, rats, and mice, with a focus on the SGLT2 inhibitor canagliflozin. Furthermore, this review will discuss how SGLT2 inhibitors regulate the ASD biomarkers, based on the clinical evidence supporting their functions as antioxidant and anti-inflammatory agents capable of crossing the blood-brain barrier (BBB).

Autism-associated CHD8 keeps proliferation of human neural progenitors in check by lengthening the G1 phase of the cell cycle

De novo mutations (DNMs) in chromodomain helicase DNA binding protein 8 (CHD8) are associated with a specific subtype of autism characterized by enlarged heads and distinct cranial features. The vast majority of these DNMs are heterozygous loss-of-function mutations with high penetrance for autism. CHD8 is a chromatin remodeler that preferentially regulates expression of genes implicated in early development of the cerebral cortex. How CHD8 haploinsufficiency alters the normal developmental trajectory of the brain is poorly understood and debated. Using long-term single-cell imaging, we show that disruption of a single copy of CHD8 in human neural precursor cells (NPCs) markedly shortens the G1 phase of the cell cycle. Consistent with faster progression of CHD8+/− NPCs through G1 and the G1/S checkpoint, we observed increased expression of E cyclins and elevated phosphorylation of Erk in these mutant cells – two central signaling pathways involved in S phase entry. Thus, CHD8 keeps proliferation of NPCs in check by lengthening G1, and mono-allelic disruption of this gene alters cell-cycle timing in a way that favors self-renewing over neurogenic cell divisions. Our findings further predict enlargement of the neural progenitor pool in CHD8+/− developing brains, providing a mechanistic basis for macrocephaly in this autism subtype.

Sparse Hierarchical Representation Learning on Functional Brain Networks for Prediction of Autism Severity Levels

Machine learning algorithms have been widely applied in diagnostic tools for autism spectrum disorder (ASD), revealing an altered brain connectivity. However, little is known about whether an magnetic resonance imaging (MRI)-based brain network is related to the severity of ASD symptoms in a large-scale cohort. We propose a graph convolution neural network-based framework that can generate sparse hierarchical graph representations for functional brain connectivity. Instead of assigning initial features for each node, we utilized a feature extractor to derive node features and the extracted representations can be fed to a hierarchical graph self-attention framework to effectively represent the entire graph. By incorporating connectivity embeddings in the feature extractor, we propose adjacency embedding networks to characterize the heterogeneous representations of the brain connectivity. Our proposed model variants outperform the benchmarking model with different configurations of adjacency embedding networks and types of functional connectivity matrices. Using this approach with the best configuration (SHEN atlas for node definition, Tikhonov correlation for connectivity estimation, and identity-adjacency embedding), we were able to predict individual ASD severity levels with a meaningful accuracy: the mean absolute error (MAE) and correlation between predicted and observed ASD severity scores resulted in 0.96, and r = 0.61 (P < 0.0001), respectively. To obtain a better understanding on how to generate better representations, we investigate the relationships between the extracted feature embeddings and the graph theory-based nodal measurements using canonical correlation analysis. Finally, we visualized the model to identify the most contributive functional connections for predicting ASD severity scores.

Valproic Acid-Induced Anxiety and Depression Behaviors are Ameliorated in p39 Cdk5 Activator-Deficient Mice

Valproic acid (VPA) is a drug used for the treatment of epilepsy, seizures, migraines, and bipolar disorders. Cyclin-dependent kinase 5 (Cdk5) is a Ser/Thr kinase activated by p35 or p39 in neurons and plays a role in a variety of neuronal functions, including psychiatric behaviors. We previously reported that VPA suppressed Cdk5 activity by reducing the expression of p35 in cultured cortical neurons, leaving p39 unchanged. In this study, we asked for the role of Cdk5 in VPA-induced anxiety and depression behaviors. Wild-type (WT) mice displayed increased anxiety and depression after chronic administration of VPA for 14 days, when the expression of p35 was decreased. To clarify their relationship, we used p39 knockout (KO) mice, in which p35 is the only Cdk5 activator. When p39 KO mice were treated chronically with VPA, unexpectedly, they exhibited fewer anxiety and depression behaviors than WT mice. The effects were p39 cdk5r2 gene-dosage dependent. Together, these results indicate that Cdk5-p39 plays a specific role in VPA-induced anxiety and depression behaviors.

Pathophysiological Studies of Monoaminergic Neurotransmission Systems in Valproic Acid-Induced Model of Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a neurodevelopmental disorder with complex etiology. The core syndromes of ASD are deficits in social communication and self-restricted interests and repetitive behaviors. Social communication relies on the proper integration of sensory and motor functions, which is tightly interwoven with the limbic function of reward, motivation, and emotion in the brain. Monoamine neurotransmitters, including serotonin, dopamine, and norepinephrine, are key players in the modulation of neuronal activity. Owing to their broad distribution, the monoamine neurotransmitter systems are well suited to modulate social communication by coordinating sensory, motor, and limbic systems in different brain regions. The complex and diverse functions of monoamine neurotransmission thus render themselves as primary targets of pathophysiological investigation of the etiology of ASD. Clinical studies have reported that children with maternal exposure to valproic acid (VPA) have an increased risk of developing ASD. Extensive animal studies have confirmed that maternal treatments of VPA include ASD-like phenotypes, including impaired social communication and repetitive behavior. Here, given that ASD is a neurodevelopmental disorder, we begin with an overview of the neural development of monoaminergic systems with their neurochemical properties in the brain. We then review and discuss the evidence of human clinical and animal model studies of ASD with a focus on the VPA-induced pathophysiology of monoamine neurotransmitter systems. We also review the potential interactions of microbiota and monoamine neurotransmitter systems in ASD pathophysiology. Widespread and complex changes in monoamine neurotransmitters are detected in the brains of human patients with ASD and validated in animal models. ASD animal models are not only essential to the characterization of pathogenic mechanisms, but also provide a preclinical platform for developing therapeutic approaches to ASD.

Refinement of Active and Passive Membrane Properties of Layer V Pyramidal Neurons in Rat Primary Motor Cortex During Postnatal Development

Achieving the distinctive complex behaviors of adult mammals requires the development of a great variety of specialized neural circuits. Although the development of these circuits begins during the embryonic stage, they remain immature at birth, requiring a postnatal maturation process to achieve these complex tasks. Understanding how the neuronal membrane properties and circuits change during development is the first step to understand their transition into efficient ones. Thus, using whole cell patch clamp recordings, we have studied the changes in the electrophysiological properties of layer V pyramidal neurons of the rat primary motor cortex during postnatal development. Among all the parameters studied, only the voltage threshold was established at birth and, although some of the changes occurred mainly during the second postnatal week, other properties such as membrane potential, capacitance, duration of the post-hyperpolarization phase or the maximum firing rate were not defined until the beginning of adulthood. Those modifications lead to a decrease in neuronal excitability and to an increase in the working range in young adult neurons, allowing more sensitive and accurate responses. This maturation process, that involves an increase in neuronal size and changes in ionic conductances, seems to be influenced by the neuronal type and by the task that neurons perform as inferred from the comparison with other pyramidal and motor neuron populations.

Brain and plasma amino acid concentration in infant rats prenatally exposed to valproic acid

Autism spectrum disorder is associated with alterations in GABAergic and glutamatergic neurotransmission. Here, we aimed to determine the concentration of GABA, glutamate, glutamine, aspartate, taurine, and glycine in brain tissue and plasma of rats prenatally exposed to valproic acid (VPA), a well-characterized experimental model of autism. Pregnant rats were injected with VPA (600mg/Kg) during the twelfth-embryonic-day. Control rats were injected with saline. On the fourteen-postnatal-day, rats from both groups (males and females) were anesthetized, euthanized by decapitation and their brain dissected out. The frontal cortex, hippocampus, amygdala, brain stem and cerebellum were dissected and homogenized. Homogenates were centrifuged and supernatants were used to quantify amino acid concentrations by HPLC coupled with fluorometric detection. Blood samples were obtained by a cardiac puncture; plasma was separated and deproteinized to quantify amino acid concentration by HPLC. We found that, in VPA rats, glutamate and glutamine concentrations were increased in hippocampus and glycine concentration was increased in cortex. We did not find changes in other regions or in plasma amino acid concentration in the VPA group with respect to control group. Our results suggest that VPA exposure in utero may impair inhibitory and excitatory amino acid transmission in the infant brain.

The early overgrowth theory of autism spectrum disorder: Insight into convergent mechanisms from valproic acid exposure and translational models

The development of new approaches for the clinical management of autism spectrum disorder (ASD) can only be realized through a better understanding of the neurobiological changes associated with ASD. One strategy for gaining deeper insight into the neurobiological mechanisms associated with ASD is to identify converging pathogenic processes associated with human idiopathic clinicopathology that are conserved in translational models of ASD. In this chapter, we first present the early overgrowth theory of ASD. Second, we introduce valproic acid (VPA), one of the most robust and well-known environmental risk factors associated with ASD, and we summarize the rapidly growing body of animal research literature using VPA as an ASD translational model. Lastly, we will detail the mechanisms of action of VPA and its impact on functional neural systems, as well as discuss future research directions that could have a lasting impact on the field.

Valproic acid induces nuclear factor erythroid 2-related factor 2 expression in fetal and neonatal brains but not in adult brain: evidence of the gamma-aminobutyric acid-shift hypothesis

The gamma-aminobutyric acid (GABA)-shift hypothesis proposes that GABA agonist action is excitatory early in development and transitions to an inhibitory role later in life. In experiment 1, the nonspecific GABA agonist, valproic acid (VPA), was administered to pregnant C57BL/6 mice on embryonic day 13. Fetal and maternal brains were harvested 2 h post-VPA exposure and assayed for nuclear factor erythroid 2-related factor 2 (NRF2) and H3 expression through western blot analysis. In experiment 2, VPA was administered to neonatal pups on P14 and adult mice on P60. In both experiments, it was observed that NRF2 expression was increased in fetal and neonatal brains, but not in the adult brain. Because NRF2 expression is activated by oxidative stress, these results imply support of the GABA-shift hypothesis in that VPA may exert its developmental damage in the fetal and neonatal periods through excitotoxicity.

Alterations of functional connectivities associated with autism spectrum disorder symptom severity: a multi-site study using multivariate pattern analysis

Autism spectrum disorder (ASD) is a highly heterogeneous neurodevelopmental disorder. The estimation of ASD severity is very important in clinical practice due to providing a more elaborate diagnosis. Although several studies have revealed some resting-state functional connectivities (RSFCs) that are related to the ASD severity, they have all been based on small-sample data and local RSFCs. The aim of the present study is to adopt multivariate pattern analysis to investigate a subset of connectivities among whole-brain RSFCs that are more contributive to ASD severity estimation based on large-sample data. Regression estimation shows a Pearson correlation value of 0.5 between the estimated and observed severity, with a mean absolute error of 1.41. The results provide obvious evidence that some RSFCs undergo notable alterations with the severity of ASD. More importantly, these selected RSFCs have an abnormality in the connection modes of the inter-network and intra-network connections. In addition, these selected abnormal RSFCs are mainly associated with the sensorimotor network, the default mode network, and inter-hemispheric connectivities, while exhibiting significant left hemisphere lateralization. Overall, this study indicates that some RSFCs suffer from abnormal alterations in patients with ASD, providing additional evidence of large-scale functional network alterations in ASD.

Developmental nicotine exposure engenders intergenerational downregulation and aberrant posttranslational modification of cardinal epigenetic factors in the frontal cortices, striata, and hippocampi of adolescent mice

BACKGROUND

Maternal smoking of traditional or electronic cigarettes during pregnancy, which constitutes developmental nicotine exposure (DNE), heightens the risk of neurodevelopmental disorders including ADHD, autism, and schizophrenia in children. Modeling the intergenerationally transmissible impacts of smoking during pregnancy, we previously demonstrated that both the first- and second-generation adolescent offspring of nicotine-exposed female mice exhibit enhanced nicotine preference, hyperactivity and risk-taking behaviors, aberrant rhythmicity of home cage activity, nicotinic acetylcholine receptor and dopamine transporter dysfunction, impaired furin-mediated proBDNF proteolysis, hypocorticosteronemia-related glucocorticoid receptor hypoactivity, and global DNA hypomethylation in the frontal cortices and striata. This ensemble of multigenerational DNE-induced behavioral, neuropharmacological, neurotrophic, neuroendocrine, and DNA methylomic anomalies recapitulates the pathosymptomatology of neurodevelopmental disorders such as ADHD, autism, and schizophrenia. Further probing the epigenetic bases of DNE-induced multigenerational phenotypic aberrations, the present study examined the expression and phosphorylation of key epigenetic factors via an array of immunoblot experiments.

RESULTS

Data indicate that DNE confers intergenerational deficits in corticostriatal DNA methyltransferase 3A (DNMT3A) expression accompanied by downregulation of methyl-CpG-binding protein 2 (MeCP2) and histone deacetylase 2 (HDAC2) in the frontal cortices and hippocampi, while the expression of ten-eleven translocase methylcytosine dioxygenase 2 (TET2) is unaltered. Moreover, DNE evokes multigenerational abnormalities in HDAC2 (Ser394) but not MeCP2 (Ser421) phosphorylation in the frontal cortices, striata, and hippocampi.

CONCLUSIONS

In light of the extensive gene regulatory roles of DNMT3A, MeCP2, and HDAC2, the findings of this study that DNE elicits downregulation and aberrant posttranslational modification of these factors in both first- and second-generation DNE mice suggest that epigenetic perturbations may constitute a mechanistic hub for the intergenerational transmission of DNE-induced neurodevelopmental disorder-like phenotypes.

Developmental nicotine exposure elicits multigenerational disequilibria in proBDNF proteolysis and glucocorticoid signaling in the frontal cortices, striata, and hippocampi of adolescent mice

Maternal smoking of conventional or vapor cigarettes during pregnancy, a form of developmental nicotine exposure (DNE), enhances the risk of neurodevelopmental disorders such as ADHD, autism, and schizophrenia in children. Modeling the multigenerational effects of smoking during pregnancy and nursing in the first- (F1) and second- (F2) generation adolescent offspring of oral nicotine-treated female C57BL/6J mice, we have previously reported that DNE precipitates intergenerational transmission of nicotine preference, hyperactivity and impulsivity-like behaviors, altered rhythmicity of home cage activity, corticostriatal nicotinic acetylcholine receptor and dopamine transporter dysfunction, and corticostriatal global DNA methylome deficits. In aggregate, these DNE-evoked behavioral, neuropharmacological, and epigenomic anomalies mirror fundamental etiological aspects of neurodevelopmental disorders including ADHD, autism, and schizophrenia. Expanding this line of research, the current study profiled the multigenerational neurotrophic and neuroendocrine consequences of DNE. Results reveal impaired proBDNF proteolysis as indicated by proBDNF-BDNF imbalance, downregulation of the proBDNF processing enzyme furin, atypical glucocorticoid receptor (GR) activity as implied by decreased relative nuclear GR localization, and deficient basal plasma corticosterone (CORT) levels in adolescent DNE offspring and grandoffspring. Collectively, these data recapitulate the BDNF deficits and HPA axis dysregulation characteristic of neurodevelopmental disorders such as ADHD, autism, and schizophrenia as well as the children of maternal smokers. Notably, as BDNF is a quintessential mediator of neurodevelopment, our prior findings of multigenerational DNE-induced behavioral and neuropharmacological abnormalities may stem from neurodevelopmental insults conferred by the proBDNF-BDNF imbalance detected in DNE mice. Similarly, our findings of multigenerational GR hypoactivity may contribute to the increased risk-taking behaviors and aberrant circadian rhythmicity of home cage activity that we previously documented in first- and second-generation DNE mice.

Maternal Interleukin-6 concentration during pregnancy is associated with variation in frontolimbic white matter and cognitive development in early life

Maternal inflammation during pregnancy can alter the trajectory of fetal brain development and increase risk for offspring psychiatric disorders. However, the majority of relevant research to date has been conducted in animal models. Here, in humans, we focus on the structural connectivity of frontolimbic circuitry as it is both critical for socioemotional and cognitive development, and commonly altered in a range of psychiatric disorders associated with intrauterine inflammation. Specifically, we test the hypothesis that elevated maternal concentration of the proinflammatory cytokine interleukin-6 (IL-6) during pregnancy will be associated with variation in microstructural properties of this circuitry in the neonatal period and across the first year of life. Pregnant mothers were recruited in early pregnancy and maternal blood samples were obtained for assessment of maternal IL-6 concentrations in early (12.6 ± 2.8 weeks [S.D.]), mid (20.4 ± 1.5 weeks [S.D.]) and late (30.3 ± 1.3 weeks [S.D.]) gestation. Offspring brain MRI scans were acquired shortly after birth (N = 86, scan age = 3.7 ± 1.7 weeks [S.D.]) and again at 12-mo age (N = 32, scan age = 54.0 ± 3.1 weeks [S.D.]). Diffusion Tensor Imaging (DTI) was used to characterize fractional anisotropy (FA) along the left and right uncinate fasciculus (UF), representing the main frontolimbic fiber tract. In N = 30 of the infants with serial MRI data at birth and 12-mo age, cognitive and socioemotional developmental status was characterized using the Bayley Scales of Infant Development. All analyses tested for potentially confounding influences of household income, prepregnancy Body-Mass-Index, obstetric risk, smoking during pregnancy, and infant sex, and outcomes at 12-mo age were additionally adjusted for the quality of the postnatal caregiving environment. Maternal IL-6 concentration (averaged across pregnancy) was prospectively and inversely associated with FA (suggestive of reduced integrity under high inflammatory conditions) in the newborn offspring (bi-lateral, p < 0.01) in the central portion of the UF proximal to the amygdala. Furthermore, maternal IL-6 concentration was positively associated with rate of FA increase across the first year of life (bi-lateral, p < 0.05), resulting in a null association between maternal IL-6 and UF FA at 12-mo age. Maternal IL-6 was also inversely associated with offspring cognition at 12-mo age, and this association was mediated by FA growth across the first year of postnatal life. Findings from the current study support the premise that susceptibility for cognitive impairment and potentially psychiatric disorders may be affected in utero, and that maternal inflammation may constitute an intrauterine condition of particular importance in this context.

Transcriptional and splicing dysregulation in the prefrontal cortex in valproic acid rat model of autism

Gene-environmental interaction could be the major cause of autism. The aim of the current study is to detect the effects of valproic acid on gene expression profiles and alternatively spliced genes in the prefrontal cortex in rat models of autism. Female rats received a single intraperitoneal injection of 600 mg/kg valproic acid at day 12.5 post-conception, and controls were injected with saline. Only male offspring were employed in the current study. RNA sequencing was used to investigate transcriptome in the prefrontal cortex of VPA-exposed rats. There were 3228 differently expressed genes and 637 alternative spliced genes, in VPA rats compared to controls. Pathways enrichment among the differently expressed genes and alternatively spliced genes were associated with neurological diseases and neural system development. The results implied VPA affected transcriptional and splicing events genome-wide and the transcriptional and splicing events may be associated with the autistic behaviors of VPA rats.

Neuroimmune and Inflammatory Signals in Complex Disorders of the Central Nervous System

An extensive microglial-astrocyte-monocyte-neuronal cross talk seems to be crucial for normal brain function, development, and recovery. However, under certain conditions neuroinflammatory interactions between brain cells and neuroimmune cells influence disease outcome and brain pathology. Microglial cells express a range of functional states with dynamically pleomorphic profiles from a surveilling status of synaptic transmission to an active player in major events of development such as synaptic elimination, regeneration, and repair. Also, inflammation mediates a series of neurotoxic roles in neuropsychiatric conditions and neurodegenerative diseases. The present review discusses data on the involvement of neuroinflammatory conditions that alter neuroimmune interactions in four different pathologies. In the first section of this review, we discuss the ability of the early developing brain to respond to a focal lesion with a rapid compensatory plasticity of intact axons and the role of microglial activation and proinflammatory cytokines in brain repair. In the second section, we present data of neuroinflammation and neurodegenerative disorders and discuss the role of reactive astrocytes in motor neuron toxicity and the progression of amyotrophic lateral sclerosis. In the third section, we discuss major depressive disorders as the consequence of dysfunctional interactions between neural and immune signals that result in increased peripheral immune responses and increase proinflammatory cytokines. In the last section, we discuss autism spectrum disorders and altered brain circuitries that emerge from abnormal long-term responses of innate inflammatory cytokines and microglial phenotypic dysfunctions.

Mechanisms of Hierarchical Cortical Maturation

Cortical information processing is structurally and functionally organized into hierarchical pathways, with primary sensory cortical regions providing modality specific information and associative cortical regions playing a more integrative role. Historically, there has been debate as to whether primary cortical regions mature earlier than associative cortical regions, or whether both primary and associative cortical regions mature simultaneously. Identifying whether primary and associative cortical regions mature hierarchically or simultaneously will not only deepen our understanding of the mechanisms that regulate brain maturation, but it will also provide fundamental insight into aspects of adolescent behavior, learning, neurodevelopmental disorders and computational models of neural processing. This mini-review article summarizes the current evidence supporting the sequential and hierarchical nature of cortical maturation, and then proposes a new cellular model underlying this process. Finally, unresolved issues associated with hierarchical cortical maturation are also addressed.

Intrinsic functional connectivity variance and state-specific under-connectivity in autism

Autism spectrum disorder (ASD) is a neurodevelopmental condition associated with altered brain connectivity. Previous neuroimaging research demonstrates inconsistent results, particularly in studies of functional connectivity in ASD. Typically, these inconsistent findings are results of studies using static measures of resting-state functional connectivity. Recent work has demonstrated that functional brain connections are dynamic, suggesting that static connectivity metrics fail to capture nuanced time-varying properties of functional connections in the brain. Here we used a dynamic functional connectivity approach to examine the differences in the strength and variance of dynamic functional connections between individuals with ASD and healthy controls (HCs). The variance of dynamic functional connections was defined as the respective standard deviations of the dynamic functional connectivity strength across time. We utilized a large multicenter dataset of 507 male subjects (209 with ASD and 298 HC, from 6 to 36 years old) from the Autism Brain Imaging Data Exchange (ABIDE) to identify six distinct whole-brain dynamic functional connectivity states. Analyses demonstrated greater variance of widespread long-range dynamic functional connections in ASD (P < 0.05, NBS method) and weaker dynamic functional connections in ASD (P < 0.05, NBS method) within specific whole-brain connectivity states. Hypervariant dynamic connections were also characterized by weaker connectivity strength in ASD compared with HC. Increased variance of dynamic functional connections was also related to ASD symptom severity (ADOS total score) (P < 0.05), and was most prominent in connections related to the medial superior frontal gyrus and temporal pole. These results demonstrate that greater intraindividual dynamic variance is a potential biomarker of ASD. Hum Brain Mapp 38:5740-5755, 2017. © 2017 Wiley Periodicals, Inc.

Lysine Acetylation and Deacetylation in Brain Development and Neuropathies

Embryonic development is critical for the final functionality and maintenance of the adult brain. Brain development is tightly regulated by intracellular and extracellular signaling. Lysine acetylation and deacetylation are posttranslational modifications that are able to link extracellular signals to intracellular responses. A wealth of evidence indicates that lysine acetylation and deacetylation are critical for brain development and functionality. Indeed, mutations of the enzymes and cofactors responsible for these processes are often associated with neurodevelopmental and psychiatric disorders. Lysine acetylation and deacetylation are involved in all levels of brain development, starting from neuroprogenitor survival and proliferation, cell fate decisions, neuronal maturation, migration, and synaptogenesis, as well as differentiation and maturation of astrocytes and oligodendrocytes, to the establishment of neuronal circuits. Hence, fluctuations in the balance between lysine acetylation and deacetylation contribute to the final shape and performance of the brain. In this review, we summarize the current basic knowledge on the specific roles of lysine acetyltransferase (KAT) and lysine deacetylase (KDAC) complexes in brain development and the different neurodevelopmental disorders that are associated with dysfunctional lysine (de)acetylation machineries.

Increased expression of fatty acid synthase and acetyl-CoA carboxylase in the prefrontal cortex and cerebellum in the valproic acid model of autism

The primary aim of the present study was to investigate alterations in enzymes associated with fatty acid synthesis, namely fatty acid synthase (FASN) and acetyl-CoA carboxylase (ACC), in the prefrontal cortex and cerebellum of the valproic acid (VPA)-induced animal model of autism. In this model, pregnant rats were given a single intraperitoneal injection of VPA, and prefrontal cortex and cerebellum samples from their pups were analyzed. The results of western blotting and reverse transcription-quantitative polymerase chain reaction analyses demonstrated that the protein and mRNA expression levels of FASN, ACC and phospho-ACC (pACC) were increased in the prefrontal cortex and cerebellum of the VPA model of autism. Furthermore, in the prefrontal cortex and cerebellum of the VPA model of autism, AMPK expression is increased, whereas PI3K and Akt expression are unchanged. This suggests that disorder of the phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K)/Akt/FASN and/or adenosine 5'-monophosphate-activated protein kinase (AMPK)/ACC pathway may be involved in the pathogenesis of autism. It is hypothesized that fatty acid synthesis participates in autism through PI3K/Akt/FASN and AMPK/ACC pathways.

Somato-dendritic decoupling as a novel mechanism for protracted cortical maturation

BACKGROUND

Both human and animal data indicate that disruption of the endogenously slow maturation of temporal association cortical (TeA) networks is associated with abnormal higher order cognitive development. However, the neuronal mechanisms underlying the endogenous maturation delay of the TeA are poorly understood.

RESULTS

Here we report a novel form of developmental plasticity that is present in the TeA. It was found that deep layer TeA neurons, but not hippocampal or primary visual neurons, exist in a protracted 'embryonic-like' state through a mechanism involving reduced somato-dendritic communication and a non-excitable somatic membrane. This mechanism of neural inactivity is present in intact tissue and shows a remarkable transition into an active somato-dendritically coupled state. The quantity of decoupled cells diminishes in a protracted and age-dependent manner, continuing into adolescence.

CONCLUSIONS

Based on our data, we propose a model of neural plasticity through which protracted compartmentalization and decoupling in somato-dendritic signalling plays a key role in controlling how excitable neurons are incorporated into recurrent cortical networks independent of neurogenesis.

Supplementation of Korean Red Ginseng improves behavior deviations in animal models of autism

Background

Autism spectrum disorder (ASD) is heterogeneous neurodevelopmental disorders that primarily display social and communication impairments and restricted/repetitive behaviors. ASD prevalence has increased in recent years, yet very limited therapeutic targets and treatments are available to counteract the incapacitating disorder. Korean Red Ginseng (KRG) is a popular herbal plant in South Korea known for its wide range of therapeutic effects and nutritional benefits and has recently been gaining great scientific attention, particularly for its positive effects in the central nervous system.

Objectives

Thus, in this study, we investigated the therapeutic potential of KRG in alleviating the neurobehavioral deficits found in the valproic acid (VPA)-exposed mice models of ASD.

Design

Starting at 21 days old (P21), VPA-exposed mice were given daily oral administrations of KRG solution (100 or 200 mg/kg) until the termination of all experiments. From P28, mice behaviors were assessed in terms of social interaction capacity (P28–29), locomotor activity (P30), repetitive behaviors (P32), short-term spatial working memory (P34), motor coordination (P36), and seizure susceptibility (P38).

Results

VPA-exposed mice showed sociability and social novelty preference deficits, hyperactivity, increased repetitive behavior, impaired spatial working memory, slightly affected motor coordination, and high seizure susceptibility. Remarkably, long-term KRG treatment in both dosages normalized all the ASD-related behaviors in VPA-exposed mice, except motor coordination ability.

Conclusion

As a food and herbal supplement with various known benefits, KRG demonstrated its therapeutic potential in rescuing abnormal behaviors related to autism caused by prenatal environmental exposure to VPA.

Predictable enriched environment prevents development of hyper-emotionality in the VPA rat model of autism

Understanding the effects of environmental stimulation in autism can improve therapeutic interventions against debilitating sensory overload, social withdrawal, fear and anxiety. Here, we evaluate the role of environmental predictability on behavior and protein expression, and inter-individual differences, in the valproic acid (VPA) model of autism. Male rats embryonically exposed (E11.5) either to VPA, a known autism risk factor in humans, or to saline, were housed from weaning into adulthood in a standard laboratory environment, an unpredictably enriched environment, or a predictably enriched environment. Animals were tested for sociability, nociception, stereotypy, fear conditioning and anxiety, and for tissue content of glutamate signaling proteins in the primary somatosensory cortex, hippocampus and amygdala, and of corticosterone in plasma, amygdala and hippocampus. Standard group analyses on separate measures were complemented with a composite emotionality score, using Cronbach's Alpha analysis, and with multivariate profiling of individual animals, using Hierarchical Cluster Analysis. We found that predictable environmental enrichment prevented the development of hyper-emotionality in the VPA-exposed group, while unpredictable enrichment did not. Individual variation in the severity of the autistic-like symptoms (fear, anxiety, social withdrawal and sensory abnormalities) correlated with neurochemical profiles, and predicted their responsiveness to predictability in the environment. In controls, the association between socio-affective behaviors, neurochemical profiles and environmental predictability was negligible. This study suggests that rearing in a predictable environment prevents the development of hyper-emotional features in animals exposed to an autism risk factor, and demonstrates that unpredictable environments can lead to negative outcomes, even in the presence of environmental enrichment.

Suppression of NMDA receptor function in mice prenatally exposed to valproic acid improves social deficits and repetitive behaviors

Animals prenatally exposed to valproic acid (VPA), an antiepileptic agent, have been used as a model for autism spectrum disorders (ASDs). Previous studies have identified enhanced NMDA receptor (NMDAR) function in the brain of VPA rats, and demonstrated that pharmacological suppression of NMDAR function normalizes social deficits in these animals. However, whether repetitive behavior, another key feature of ASDs, can be rescued by NMDAR inhibition remains unknown. We report here that memantine, an NMDAR antagonist, administered to VPA mice rescues both social deficits and repetitive behaviors such as self-grooming and jumping. These results suggest that suppression of elevated NMDAR function in VPA animals normalizes repetitive behaviors in addition to social deficits.

Recent advances in animal model experimentation in autism research

OBJECTIVE

Autism, a lifelong neuro-developmental disorder is a uniquely human condition. Animal models are not the perfect tools for the full understanding of human development and behavior, but they can be an important place to start. This review focused on the recent updates of animal model research in autism.

METHODS

We have reviewed the publications over the last three decades, which are related to animal model study in autism.

RESULTS

Animal models are important because they allow researchers to study the underlying neurobiology in a way that is not possible in humans. Improving the availability of better animal models will help the field to increase the development of medicines that can relieve disabling symptoms. Results from the therapeutic approaches are encouraging remarkably, since some behavioral alterations could be reversed even when treatment was performed on adult mice. Finding an animal model system with similar behavioral tendencies as humans is thus vital for understanding the brain mechanisms, supporting social motivation and attention, and the manner in which these mechanisms break down in autism. The ongoing studies should therefore increase the understanding of the biological alterations associated with autism as well as the development of knowledge-based treatments therapy for those struggling with autism.

CONCLUSION

In this review, we have presented recent advances in research based on animal models of autism, raising hope for understanding the disease biology for potential therapeutic intervention to improve the quality of life of autism individuals.

An evo-devo approach to thyroid hormones in cerebral and cerebellar cortical development: etiological implications for autism

The morphological alterations of cortical lamination observed in mouse models of developmental hypothyroidism prompted the recognition that these experimental changes resembled the brain lesions of children with autism; this led to recent studies showing that maternal thyroid hormone deficiency increases fourfold the risk of autism spectrum disorders (ASD), offering for the first time the possibility of prevention of some forms of ASD. For ethical reasons, the role of thyroid hormones on brain development is currently studied using animal models, usually mice and rats. Although mammals have in common many basic developmental principles regulating brain development, as well as fundamental basic mechanisms that are controlled by similar metabolic pathway activated genes, there are also important differences. For instance, the rodent cerebral cortex is basically a primary cortex, whereas the primary sensory areas in humans account for a very small surface in the cerebral cortex when compared to the associative and frontal areas that are more extensive. Associative and frontal areas in humans are involved in many neurological disorders, including ASD, attention deficit-hyperactive disorder, and dyslexia, among others. Therefore, an evo-devo approach to neocortical evolution among species is fundamental to understand not only the role of thyroid hormones and environmental thyroid disruptors on evolution, development, and organization of the cerebral cortex in mammals but also their role in neurological diseases associated to thyroid dysfunction.

LMTK1 regulates dendritic formation by regulating movement of Rab11A-positive endosomes

Neurons extend two types of neurites-axons and dendrites-that differ in structure and function. Although it is well understood that the cytoskeleton plays a pivotal role in neurite differentiation and extension, the mechanisms by which membrane components are supplied to growing axons or dendrites is largely unknown. We previously reported that the membrane supply to axons is regulated by lemur kinase 1 (LMTK1) through Rab11A-positive endosomes. Here we investigate the role of LMTK1 in dendrite formation. Down-regulation of LMTK1 increases dendrite growth and branching of cerebral cortical neurons in vitro and in vivo. LMTK1 knockout significantly enhances the prevalence, velocity, and run length of anterograde movement of Rab11A-positive endosomes to levels similar to those expressing constitutively active Rab11A-Q70L. Rab11A-positive endosome dynamics also increases in the cell body and growth cone of LMTK1-deficient neurons. Moreover, a nonphosphorylatable LMTK1 mutant (Ser34Ala, a Cdk5 phosphorylation site) dramatically promotes dendrite growth. Thus LMTK1 negatively controls dendritic formation by regulating Rab11A-positive endosomal trafficking in a Cdk5-dependent manner, indicating the Cdk5-LMTK1-Rab11A pathway as a regulatory mechanism of dendrite development as well as axon outgrowth.

Auditory-cued sensorimotor task reveals disengagement deficits in rats exposed to the autism-associated teratogen valproic acid

Autism Spectrum Disorder (ASD) is often found to co-exist with non-core behavioral manifestations that include difficulties in disengagement of attention to sensory cues. Here we examined whether this behavioral abnormality can be induced in rats prenatally exposed to valproic acid (VPA), a well-established teratogen associated with ASD animal models. We tested rats using an auditory-cued sensorimotor task (ACST) based on the premise that ACST will be more sensitive to developmental changes in temporal association cortex (TeA) of the posterior attention system. We show that VPA rats learned the ACST markedly faster than control animals, but they exhibited a profound preoccupation with cues associated with the expectancy at the reward location such that disengagement was disrupted. Control rats on the other hand were able to disengage and utilize auditory cues for re-engagement. However, both control and VPA-treated rats performed similarly when tested on novel object recognition (NOR) and novel context mismatch (NOCM) behavioral tasks that are known to be sensitive to normal perirhinal and prefrontal network functioning respectively. Consistent with disrupted posterior rather than frontal networks, we also report that VPA can selectively act on deep-layer TeA cortical neurons by showing that VPA increased dendritic density in isolated deep-layer TeA but not frontal neurons. These results describe a useful approach to examine the role of cue-dependent control of attention systems in rodent models of autism and suggest that disengagement impairments may arise from an inability to modify behavior through the appropriate use of sensory cue associations.

Increased BDNF expression in fetal brain in the valproic acid model of autism

Human fetal exposure to valproic acid (VPA), a widely-used anti-epileptic and mood-stabilizing drug, leads to an increased incidence of behavioral and intellectual impairments including autism; VPA administration to pregnant rats and mice at gestational days 12.5 (E12.5) or E13.5 leads to autistic-like symptoms in the offspring and is widely used as an animal model for autism. We report here that this VPA administration protocol transiently increased both BDNF mRNA and BDNF protein levels 5-6-fold in the fetal mouse brain. VPA exposure in utero induced smaller increases in the expression of mRNA encoding the other neurotrophins, NT3 (2.5-fold) and NT4 (2-fold). Expression of the neurotrophin receptors, trkA, trkB and trkC were minimally affected, while levels of the low-affinity neurotrophin receptor, p75(NTR), doubled. Of the nine 5'-untranslated exons of the mouse BDNF gene, only expression of exons I, IV and VI was stimulated by VPA in utero. In light of the well-established role of BDNF in regulating neurogenesis and the laminar fate of postmitotic neurons in the developing cortex, an aberrant increase in BDNF expression in the fetal brain may contribute to VPA-induced cognitive disorders by altering brain development.

Pre-clinical models of neurodevelopmental disorders: focus on the cerebellum

Recent studies have advanced our understanding of the role of the cerebellum in non-motor behaviors. Abnormalities in the cerebellar structure have been demonstrated to produce changes in emotional, cognitive, and social behaviors resembling clinical manifestations observed in patients with autism spectrum disorders (ASD) and schizophrenia. Several animal models have been used to evaluate the effects of relevant environmental and genetic risk factors on the cerebellum development and function. However, very few models of ASD and schizophrenia selectively target the cerebellum and/or specific cell types within this structure. In this review, we critically evaluate the strength and weaknesses of these models. We will propose that the future progress in this field will require time- and cell type-specific manipulations of disease-relevant genes, not only selectively in the cerebellum, but also in frontal brain areas connected with the cerebellum. Such information can advance our knowledge of the cerebellar contribution to non-motor behaviors in mental health and disease.

What We Have Learned about Autism Spectrum Disorder from Valproic Acid

Two recent epidemiological investigations in children exposed to valproic acid (VPA) treatment in utero have reported a significant risk associated with neurodevelopmental disorders and autism spectrum disorder (ASD) in particular. Parallel to this work, there is a growing body of animal research literature using VPA as an animal model of ASD. In this focused review we first summarize the epidemiological evidence linking VPA to ASD and then comment on two important neurobiological findings linking VPA to ASD clinicopathology, namely, accelerated or early brain overgrowth and hyperexcitable networks. Improving our understanding of how the drug VPA can alter early development of neurological systems will ultimately improve our understanding of ASD.

General developmental health in the VPA-rat model of autism

Autism is a neurodevelopmental condition diagnosed by impaired social interaction, abnormal communication and, stereotyped behaviors. While post-mortem and imaging studies have provided good insights into the neurobiological symptomology of autism, animal models can be used to study the neuroanatomical, neurophysiological and molecular mediators in more detail and in a more controlled environment. The valproic acid (VPA) rat model is an environmentally triggered model with strong construct and clinical validity. It is based on VPA teratogenicity in humans, where mothers who are medicated with VPA during early pregnancy show an increased risk for giving birth to an autistic child. In rats, early embryonic exposure, around the time of neural tube closure, leads to autism-like anatomical and behavioral abnormalities in the offspring. Considering the increasing use of the VPA rat model, we present our observations of the general health of Wistar dams treated with a single intraperitoneal injection of 500 or, 600 mg/kg VPA on embryonic day E12.5, as well as their male and female offspring, in comparison to saline-exposed controls. We report increased rates of complete fetal reabsorption after both VPA doses. VPA 500 mg/kg showed no effect on dam body weight during pregnancy or, on litter size. Offspring exposed to VPA 500 mg/kg showed smaller brain mass on postnatal days 1 (P1) and 14 (P14), in addition to abnormal nest seeking behavior at P10 in the olfactory discrimination test, relative to controls. We also report increased rates of physical malformations in the offspring, rare occurrences of chromodacryorrhea and, developmentally similar body mass gain. Further documentation of developmental health may guide sub-grouping of individuals in a way to better predict core symptom severity.