Altered neural connectivity in excitatory and inhibitory cortical circuits in autism

Cognitive impairment and autistic-like behaviour in SAPAP4-deficient mice

In humans, genetic variants of DLGAP1-4 have been linked with neuropsychiatric conditions, including autism spectrum disorder (ASD). While these findings implicate the encoded postsynaptic proteins, SAPAP1-4, in the etiology of neuropsychiatric conditions, underlying neurobiological mechanisms are unknown. To assess the contribution of SAPAP4 to these disorders, we characterized SAPAP4-deficient mice. Our study reveals that the loss of SAPAP4 triggers profound behavioural abnormalities, including cognitive deficits combined with impaired vocal communication and social interaction, phenotypes reminiscent of ASD in humans. These behavioural alterations of SAPAP4-deficient mice are associated with dramatic changes in synapse morphology, function and plasticity, indicating that SAPAP4 is critical for the development of functional neuronal networks and that mutations in the corresponding human gene, DLGAP4, may cause deficits in social and cognitive functioning relevant to ASD-like neurodevelopmental disorders.

Diffusional kurtosis imaging of the corpus callosum in autism

Background

The corpus callosum is implicated in the pathophysiology of autism spectrum disorder (ASD). However, specific structural deficits and underlying mechanisms are yet to be well defined.

Methods

We employed diffusional kurtosis imaging (DKI) metrics to characterize white matter properties within five discrete segments of the corpus callosum in 17 typically developing (TD) adults and 16 age-matched participants with ASD without co-occurring intellectual disability (ID). The DKI metrics included axonal water fraction (f_axon) and intra-axonal diffusivity (D_axon), which reflect axonal density and caliber, and extra-axonal radial (RD_extra) and axial (AD_extra) diffusivities, which reflect myelination and microstructural organization of the extracellular space. The relationships between DKI metrics and processing speed, a cognitive feature known to be impaired in ASD, were also examined.

Results

ASD group had significantly decreased callosal f_axon and D_axon (p = .01 and p = .045), particularly in the midbody, isthmus, and splenium. Regression analysis showed that variation in DKI metrics, primarily in the mid and posterior callosal regions explained up to 70.7% of the variance in processing speed scores for TD (p = .001) but not for ASD (p > .05).

Conclusion

Decreased DKI metrics suggested that ASD may be associated with axonal deficits such as reduced axonal caliber and density in the corpus callosum, especially in the mid and posterior callosal areas. These data suggest that impaired interhemispheric connectivity may contribute to decreased processing speed in ASD participants.

Electronic supplementary material

The online version of this article (10.1186/s13229-018-0245-1) contains supplementary material, which is available to authorized users.

Transglutaminase 2 Induces Deficits in Social Behavior in Mice

Impairments in social behavior are highly implicated in many neuropsychiatric disorders. Recent studies indicate a role for endoplasmic reticulum (ER) stress in altering social behavior, but the underlying mechanism is not known. In the present study, we examined the role of transglutaminase 2 (TG2), a calcium-dependent enzyme known to be induced following ER stress, in social behavior in mice. ER stress induced by tunicamycin administration increased TG2 protein levels in the mouse prefrontal cortex (PFC). PFC-specific inhibition of TG2 attenuated ER stress-induced deficits in social behavior. Conversely, overexpression of TG2 in the PFC resulted in social behavior impairments in mice. In addition, systemic administration of cysteamine, a TG2 inhibitor, attenuated social behavior deficits. Our preliminary findings using postmortem human brain samples found increases in TG2 mRNA and protein levels in the middle frontal gyrus of subjects with autism spectrum disorder. These findings in mice and human postmortem brain samples identify changes in TG2 activity in the possible dysregulation of social behavior.

Recent advances in branching mechanisms underlying neuronal morphogenesis

Proper neuronal wiring is central to all bodily functions, sensory perception, cognition, memory, and learning. Establishment of a functional neuronal circuit is a highly regulated and dynamic process involving axonal and dendritic branching and navigation toward appropriate targets and connection partners. This intricate circuitry includes axo-dendritic synapse formation, synaptic connections formed with effector cells, and extensive dendritic arborization that function to receive and transmit mechanical and chemical sensory inputs. Such complexity is primarily achieved by extensive axonal and dendritic branch formation and pruning. Fundamental to neuronal branching are cytoskeletal dynamics and plasma membrane expansion, both of which are regulated via numerous extracellular and intracellular signaling mechanisms and molecules. This review focuses on recent advances in understanding the biology of neuronal branching.

Opposite development of short- and long-range anterior cingulate pathways in autism

Autism has been linked with the changes in brain connectivity that disrupt neural communication, especially involving frontal networks. Pathological changes in white matter are evident in adults with autism, particularly affecting axons below the anterior cingulate cortices (ACC). It is still unknown whether axon pathology appears early or late in development and whether it changes or not from childhood through adulthood. To address these questions, we examined typical and pathological development of about 1 million axons in post-mortem brains of children, adolescents, and adults with and without autism (ages 3-67 years). We used high-resolution microscopy to systematically sample and study quantitatively the fine structure of myelinated axons in the white matter below ACC. We provide novel evidence of changes in the density, size and trajectories of ACC axons in typical postnatal development from childhood through adulthood. Against the normal profile of axon development, our data revealed lower density of myelinated axons that connect ACC with neighboring cortices in children with autism. In the course of development the proportion of thin axons, which form short-range pathways, increased significantly in individuals with autism, but remained flat in controls. In contrast, the relative proportion of thick axons, which form long-range pathways, increased from childhood to adulthood in the control group, but decreased in autism. Our findings provide a timeline for profound changes in axon density and thickness below ACC that affect axon physiology in a direction suggesting bias in short over distant neural communication in autism. Importantly, measures of axon density, myelination, and orientation provide white matter anisotropy/diffusivity estimates at the level of single axons. The structural template established can be used to compare with measures obtained from imaging in living subjects, and guide analysis of functional and structural imaging data from humans for comparison with pathological states.

Atypical longitudinal development of functional connectivity in adolescents with autism spectrum disorder

Autism spectrum disorder (ASD) is consistently associated with alterations in brain connectivity, but there are conflicting results as to where and when individuals with ASD display increased or reduced functional connectivity. Such inconsistent findings may be driven by atypical neurodevelopmental trajectories in ASD during adolescence, but no longitudinal studies to date have investigated this hypothesis. We thus examined the functional connectivity of three neurocognitive resting-state networks-the default mode network (DMN), salience network, and central executive network (CEN)-in a longitudinal sample of youth with ASD (n = 16) and without ASD (n = 22) studied during early/mid- and late adolescence. Functional connectivity between the CEN and the DMN displayed significantly altered developmental trajectories in ASD: typically developing (TD) controls-but not youth with ASD-exhibited an increase in negative functional connectivity between these two networks with age. This significant interaction was due to the ASD group displaying less negative functional connectivity than the TD group during late adolescence only, with no significant group differences in early/mid-adolescence. These preliminary findings suggest a localized age-dependency of functional connectivity alterations in ASD and underscore the importance of considering age when examining brain connectivity. Autism Research 2019, 12: 53-65. © 2018 International Society for Autism Research, Wiley Periodicals, Inc. LAY SUMMARY: Brain connectivity may develop differently during adolescence in youth with autism spectrum disorder (ASD). We looked at changes in brain connectivity over time within individuals and found that, for some brain regions, adolescents with ASD did not show the same changes in brain connectivity that typically developing adolescents did. This suggests it is important to consider age when studying brain connectivity in ASD.

Adult Ube3a Gene Reinstatement Restores the Electrophysiological Deficits of Prefrontal Cortex Layer 5 Neurons in a Mouse Model of Angelman Syndrome

E3 ubiquitin ligase (UBE3A) levels in the brain need to be tightly regulated, as loss of functional UBE3A protein is responsible for the severe neurodevelopmental disorder Angelman syndrome (AS), whereas increased activity of UBE3A is associated with nonsyndromic autism. Given the role of mPFC in neurodevelopmental disorders including autism, we aimed to identify the functional changes resulting from loss of UBE3A in infralimbic and prelimbic mPFC areas in a mouse model of AS. Whole-cell recordings from layer 5 mPFC pyramidal neurons obtained in brain slices from adult mice of both sexes revealed that loss of UBE3A results in a strong decrease of spontaneous inhibitory transmission and increase of spontaneous excitatory transmission potentially leading to a marked excitation/inhibition imbalance. Additionally, we found that loss of UBE3A led to decreased excitability and increased threshold for action potential of layer 5 fast spiking interneurons without significantly affecting the excitability of pyramidal neurons. Because we previously showed that AS mouse behavioral phenotypes are reversible upon Ube3a gene reactivation during a restricted period of early postnatal development, we investigated whether Ube3a gene reactivation in a fully mature brain could reverse any of the identified physiological deficits. In contrast to our previously reported behavioral findings, restoring UBE3A levels in adult animals fully rescued all the identified physiological deficits of mPFC neurons. Moreover, the kinetics of reversing these synaptic deficits closely followed the reinstatement of UBE3A protein level. Together, these findings show a striking dissociation between the rescue of behavioral and physiological deficits.SIGNIFICANCE STATEMENT Here we describe significant physiological deficits in the mPFC of an Angelman syndrome mouse model. We found a marked change in excitatory/inhibitory balance, as well as decreased excitability of fast spiking interneurons. A promising treatment strategy for Angelman syndrome is aimed at restoring UBE3A expression by activating the paternal UBE3A gene. Here we find that the physiological changes in the mPFC are fully reversible upon gene reactivation, even when the brain is fully mature. This indicates that there is no critical developmental window for reversing the identified physiological deficits in mPFC.

Estrogen Treatment Reverses Prematurity-Induced Disruption in Cortical Interneuron Population

Development of cortical interneurons continues until the end of human pregnancy. Premature birth deprives the newborns from the supply of maternal estrogen and a secure intrauterine environment. Indeed, preterm infants suffer from neurobehavioral disorders. This can result from both preterm birth and associated postnatal complications, which might disrupt recruitment and maturation of cortical interneurons. We hypothesized that interneuron subtypes, including parvalbumin-positive (PV⁺), somatostatin-positive (SST⁺), calretinin-positive (CalR⁺), and neuropeptide Y-positive (NPY⁺) interneurons, were recruited in the upper and lower cortical layers in a distinct manner with advancing gestational age. In addition, preterm birth would disrupt the heterogeneity of cortical interneurons, which might be reversed by estrogen treatment. These hypotheses were tested by analyzing autopsy samples from premature infants and evaluating the effect of estrogen supplementation in prematurely delivered rabbits. The PV⁺ and CalR⁺ neurons were abundant, whereas SST⁺ and NPY⁺ neurons were few in cortical layers of preterm human infants. Premature birth of infants reduced the density of PV⁺ or GAD67⁺ neurons and increased SST⁺ interneurons in the upper cortical layers. Importantly, 17 β-estradiol treatment in preterm rabbits increased the number of PV⁺ neurons in the upper cortical layers relative to controls at postnatal day 14 (P14) and P21 and transiently reduced SST population at P14. Moreover, protein and mRNA levels of Arx, a key regulator of cortical interneuron maturation and migration, were higher in estrogen-treated rabbits relative to controls. Therefore, deficits in PV⁺ and excess of SST⁺ neurons in premature newborns are ameliorated by estrogen replacement, which can be attributed to elevated Arx levels. Estrogen replacement might enhance neurodevelopmental outcomes in extremely preterm infants.SIGNIFICANCE STATEMENT Premature birth often leads to neurodevelopmental delays and behavioral disorders, which may be ascribed to disturbances in the development and maturation of cortical interneurons. Here, we show that preterm birth in humans is associated with reduced population of parvalbumin-positive (PV⁺) neurons and an excess of somatostatin-expressing interneurons in the cerebral cortex. More importantly, 17 β-estradiol treatment increased the number of PV⁺ neurons in preterm-born rabbits, which appears to be mediated by an elevation in the expression of Arx transcription factor. Hence the present study highlights prematurity-induced reduction in PV⁺ neurons in human infants and reversal in their population by estrogen replacement in preterm rabbits. Because preterm birth drops plasma estrogen level 100-fold, estrogen replacement in extremely preterm infants might improve their developmental outcome and minimize neurobehavioral disorders.

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.

Decreased parvalbumin and somatostatin neurons in medial prefrontal cortex in BRINP1-KO mice

BRINPs (BMP/RA-inducible Neural Specific Protein-1, 2, 3) are family genes expressed mainly in both the central and peripheral nervous system. BRINP1 is abundantly expressed in many of adult brain regions including cerebral cortex and hippocampus, with expression regulated in an activity-dependent manner in the dentate gyrus. Mice with disrupted BRINP1 gene exhibit abnormal behaviors such as increased locomotive activity and poor social activity which are analogous to symptoms of human psychiatric disorders such as schizophrenia (SCZ), autism spectrum disorder (ASD) and attention-deficit hyperactivity disorder (ADHD). In the present study, to clarify the physiological roles of BRINP1 in psychiatric disorders, we examined the numbers of parvalbumin (PV)-expressing neurons and somatostatin (SST)-expressing neurons in the medial prefrontal cortex (mPFC) in BRINP1-KO mice. Immunohistochemical analysis revealed the numbers of PV-expressing neurons and SST-expressing neurons in mPFC of BRINP1-KO mice were, respectively, 50% and 20% fewer than corresponding neurons in mPFC of wild-type mice. These data suggest that the abnormal behaviors related to human psychiatric disorders in BRINP1-KO mice could be derived from the hyperexcitability of pyramidal neurons as a consequence of decreased inhibitory innervation and conceivable dysregulation of the Excitatory/Inhibitory balance in mPFC.

Heterogeneity of Cell Surface Glutamate and GABA Receptor Expression in Shank and CNTN4 Autism Mouse Models

Autism spectrum disorder (ASD) refers to a large set of neurodevelopmental disorders, which have in common both repetitive behavior and abnormalities in social interactions and communication. Interestingly, most forms of ASD have a strong genetic contribution. However, the molecular underpinnings of this disorder remain elusive. The SHANK3 gene (and to a lesser degree SHANK2) which encode for the postsynaptic density (PSD) proteins SHANK3/SHANK2 and the CONTACTIN 4 gene which encodes for the neuronal glycoprotein CONTACTIN4 (CNTN4) exhibit mutated variants which are associated with ASD. Like many of the other genes associated with ASD, both SHANKs and CNTN4 affect synapse formation and function and are therefore related to the proper development and signaling capability of excitatory and inhibitory neuronal networks in the adult mammal brain. In this study, we used mutant/knock-out mice of Shank2 (Shank2^−/−), Shank3 (Shank3αβ^−/−), and Cntn4 (Cntn4^−/−) as ASD-models to explore whether these mice share a molecular signature in glutamatergic and GABAergic synaptic transmission in ASD-related brain regions. Using a biotinylation assay and subsequent western blotting we focused our analysis on cell surface expression of several ionotropic glutamate and GABA receptor subunits: GluA1, GluA2, and GluN1 were analyzed for excitatory synaptic transmission, and the α1 subunit of the GABA_A receptor was analyzed for inhibitory synaptic transmission. We found that both Shank2^−/− and Shank3αβ^−/− mice exhibit reduced levels of several cell surface glutamate receptors in the analyzed brain regions—especially in the striatum and thalamus—when compared to wildtype controls. Interestingly, even though Cntn4^−/− mice also show reduced levels of some cell surface glutamate receptors in the cortex and hippocampus, increased levels of cell surface glutamate receptors were found in the striatum. Moreover, Cntn4^−/− mice do not only show brain region-specific alterations in cell surface glutamate receptors but also a downregulation of cell surface GABA receptors in several of the analyzed brain regions. The results of this study suggest that even though mutations in defined genes can be associated with ASD this does not necessarily result in a common molecular phenotype in surface expression of glutamatergic and GABAergic receptor subunits in defined brain regions.

Resveratrol Prevents Cellular and Behavioral Sensory Alterations in the Animal Model of Autism Induced by Valproic Acid

Autism spectrum disorder (ASD) is characterized by impairments in both social communication and interaction and repetitive or stereotyped behaviors. Although its etiology remains unknown, genetic and environmental risk factors have been associated with this disorder, including the exposure to valproic acid (VPA) during pregnancy. Resveratrol (RSV) is an anti-inflammatory and antioxidant molecule known to prevent social impairments in the VPA animal model of autism. This study aimed to analyze the effects of prenatal exposure to VPA, as well as possible preventive effects of RSV, on sensory behavior, the localization of GABAergic parvalbumin (PV⁺) neurons in sensory brain regions and the expression of proteins of excitatory and inhibitory synapses. Pregnant rats were treated daily with RSV (3.6 mg/kg) from E6.5 to E18.5 and injected with VPA (600 mg/kg) in the E12.5. Male pups were analyzed in Nest Seeking (NS) behavior and in whisker nuisance task (WNT). At P30, the tissues were removed and analyzed by immunofluorescence and western blotting. Our data showed for the first time an altered localization of PV⁺-neurons in primary sensory cortex and amygdala. We also showed a reduced level of gephyrin in the primary somatosensory area (PSSA) of VPA animals. The treatment with RSV prevented all the aforementioned alterations triggered by VPA. Our data shed light on the relevance of sensory component in ASD and highlights the interplay between RSV and VPA animal model as an important tool to investigate the pathophysiology of 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.

Psychiatry in a Dish: Stem Cells and Brain Organoids Modeling Autism Spectrum Disorders

Autism spectrum disorders are a group of pervasive neurodevelopmental conditions with heterogeneous etiology, characterized by deficits in social cognition, communication, and behavioral flexibility. Despite an increasing scientific effort to find the pathophysiological explanations for the disease, the neurobiological links remain unclear. A large amount of evidence suggests that pathological processes taking place in early embryonic neurodevelopment might be responsible for later manifestation of autistic symptoms. This dysfunctional development includes altered maturation/differentiation processes, disturbances in cell-cell communication, and an unbalanced ratio between certain neuronal populations. All those processes are highly dependent on the interconnectivity and three-dimensional organizations of the brain. Moreover, in order to gain a deeper understanding of the complex neurobiology of autism spectrum disorders, valid disease models are pivotal. Induced pluripotent stem cells could potentially help to elucidate the complex mechanisms of the disease and lead to the development of more effective individualized treatment. The induced pluripotent stem cells approach allows comparison between the development of various cellular phenotypes generated from cell lines of patients and healthy individuals. A newly advanced organoid technology makes it possible to create three-dimensional in vitro models of brain development and structural interconnectivity, based on induced pluripotent stem cells derived from the respective individuals. The biggest challenge for modeling psychiatric diseases in vitro is finding and establishing the link between cellular and molecular findings with the clinical symptoms, and this review aims to give an overview over the feasibility and applicability of this new tissue engineering tool in psychiatry.

Evidence of Reduced Global Processing in Autism Spectrum Disorder

Frith's original notion of 'weak central coherence' suggested that increased local processing in autism spectrum disorder (ASD) resulted from reduced global processing. More recent accounts have emphasised superior local perception and suggested intact global integration. However, tasks often place local and global processing in direct trade-off, making it difficult to determine whether group differences reflect reduced global processing, increased local processing, or both. We present two measures of global integration in which poor performance could not reflect increased local processing. ASD participants were slower to identify fragmented figures and less sensitive to global geometric impossibility than IQ-matched controls. These findings suggest that reduced global integration comprises one important facet of weak central coherence in ASD.

17-β estradiol increases parvalbumin levels in Pvalb heterozygous mice and attenuates behavioral phenotypes with relevance to autism core symptoms

Background

Autism spectrum disorder (ASD) is a group of neurodevelopmental disorders characterized by two core symptoms: impaired social interaction and communication, and restricted, repetitive behaviors and interests. The pathophysiology of ASD is not yet fully understood, due to a plethora of genetic and environmental risk factors that might be associated with or causal for ASD. Recent findings suggest that one putative convergent pathway for some forms of ASD might be the downregulation of the calcium-binding protein parvalbumin (PV). PV-deficient mice (PV-/-, PV+/-), as well as Shank1-/-, Shank3-/-, and VPA mice, which show behavioral deficits relevant to all human ASD core symptoms, are all characterized by lower PV expression levels.

Methods

Based on the hypothesis that PV expression might be increased by 17-β estradiol (E2), PV+/- mice were treated with E2 from postnatal days 5-15 and ASD-related behavior was tested between postnatal days 25 and 31.

Results

PV expression levels were significantly increased after E2 treatment and, concomitantly, sociability deficits in PV+/- mice in the direct reciprocal social interaction and the 3-chamber social approach assay, as well as repetitive behaviors, were attenuated. E2 treatment of PV+/+ mice did not increase PV levels and had detrimental effects on sociability and repetitive behavior. In PV-/- mice, E2 obviously did not affect PV levels; tested behaviors were not different from the ones in vehicle-treated PV-/- mice.

Conclusion

Our results suggest that the E2-linked amelioration of ASD-like behaviors is specifically occurring in PV+/- mice, indicating that PV upregulation is required for the E2-mediated rescue of ASD-relevant behavioral impairments.

Development and disease in a dish: the epigenetics of neurodevelopmental disorders

Human neurodevelopmental disorders (NDDs) involve mutations in hundreds of individual genes, with over-representation in genes encoding proteins that alter chromatin structure to modulate gene expression. Here, we highlight efforts to model these NDDs through in vitro differentiation of patient-specific induced pluripotent stem cells into neurons. We discuss how epigenetic regulation controls normal cortical development, how mutations in several classes of epigenetic regulators contribute to NDDs, and approaches for modeling cortical development and function using both directed differentiation and formation of cerebral organoids. We explore successful applications of these models to study both syndromic and nonsyndromic NDDs and to define convergent mechanisms, addressing both the potential and challenges of using this approach to define cellular and molecular mechanisms that underlie NDDs.

Parallel trends in cortical gray and white matter architecture and connections in primates allow fine study of pathways in humans and reveal network disruptions in autism

Noninvasive imaging and tractography methods have yielded information on broad communication networks but lack resolution to delineate intralaminar cortical and subcortical pathways in humans. An important unanswered question is whether we can use the wealth of precise information on pathways from monkeys to understand connections in humans. We addressed this question within a theoretical framework of systematic cortical variation and used identical high-resolution methods to compare the architecture of cortical gray matter and the white matter beneath, which gives rise to short- and long-distance pathways in humans and rhesus monkeys. We used the prefrontal cortex as a model system because of its key role in attention, emotions, and executive function, which are processes often affected in brain diseases. We found striking parallels and consistent trends in the gray and white matter architecture in humans and monkeys and between the architecture and actual connections mapped with neural tracers in rhesus monkeys and, by extension, in humans. Using the novel architectonic portrait as a base, we found significant changes in pathways between nearby prefrontal and distant areas in autism. Our findings reveal that a theoretical framework allows study of normal neural communication in humans at high resolution and specific disruptions in diverse psychiatric and neurodegenerative diseases.

Are We "Motorically" Wired to Others? High-Level Motor Computations and Their Role in Autism

High-level motor computations reflect abstract components far apart from the mere motor performance. Neural correlates of these computations have been explored both in nonhuman and human primates, supporting the idea that our brain recruits complex nodes for motor representations. Of note, these computations have exciting implications for social cognition, and they also entail important challenges in the context of autism. Here, we focus on these challenges benefiting from recent studies addressing motor interference, motor resonance, and high-level motor planning. In addition, we suggest new ideas about how one maps and shares the (motor) space with others. Taken together, these issues inspire intriguing and fascinating questions about the social tendency of our high-level motor computations, and this tendency may indicate that we are "motorically" wired to others. Thus, after furnishing preliminary insights on putative neural nodes involved in these computations, we focus on how the hypothesized social nature of high-level motor computations may be anomalous or limited in autism, and why this represents a critical challenge for the future.

Arid1b haploinsufficiency disrupts cortical interneuron development and mouse behavior

Haploinsufficiency of the AT-rich interactive domain 1B (ARID1B) gene causes autism spectrum disorder (ASD) and intellectual disability, however, the neurobiological basis for this is unknown. Here, we generated Arid1b knockout mice and examined heterozygotes to model human patients. Arid1b heterozygous mice showed a decreased number of cortical GABAergic interneurons and reduced proliferation of interneuron progenitors in the ganglionic eminence. Arid1b haploinsufficiency also led to an imbalance between excitatory and inhibitory synapses in the cerebral cortex. Furthermore, we found that Arid1b haploinsufficiency suppressed histone H3 lysine 9 acetylation (H3K9Ac) overall, and in particular reduced H3K9Ac of the Pvalb promoter, resulting in decreased transcription. Arid1b heterozygous mice exhibited abnormal cognitive and social behavior, which was rescued by treatment with a positive allosteric GABA_A receptor modulator. Our results demonstrate a critical role for the Arid1b gene in interneuron development and behavior, and provide insight into the pathogenesis of ASD and intellectual disability.

Neural Hyperexcitability in Autism Spectrum Disorders

Despite the progress that has been made in research on autism spectrum disorders (ASD), the understanding of the biological basis of ASD to identify targets for novel, effective treatment remains limited. One of the leading biological theories of autism is a model of cortical hyperexcitability. While numerous genetic and epigenetic studies support this model, how this particular biological alteration relates to known phenotypes in ASD is not well established. Using examples of sensory processing alterations, this review illustrates how cortical excitability may affect neural processes to result eventually in some core clinical phenotypes in ASD. Applications of the cortical excitability model for translational research and drug development are also discussed.

Mirror trends of plasticity and stability indicators in primate prefrontal cortex

Research on plasticity markers in the cerebral cortex has largely focused on their timing of expression and role in shaping circuits during critical and normal periods. By contrast, little attention has been focused on the spatial dimension of plasticity-stability across cortical areas. The rationale for this analysis is based on the systematic variation in cortical structure that parallels functional specialization and raises the possibility of varying levels of plasticity. Here, we investigated in adult rhesus monkeys the expression of markers related to synaptic plasticity or stability in prefrontal limbic and eulaminate areas that vary in laminar structure. Our findings revealed that limbic areas are impoverished in three markers of stability: intracortical myelin, the lectin Wisteria floribunda agglutinin, which labels perineuronal nets, and parvalbumin, which is expressed in a class of strong inhibitory neurons. By contrast, prefrontal limbic areas were enriched in the enzyme calcium/calmodulin-dependent protein kinase II (CaMKII), known to enhance plasticity. Eulaminate areas have more elaborate laminar architecture than limbic areas and showed the opposite trend: they were enriched in markers of stability and had lower expression of the plasticity-related marker CaMKII. The expression of glial fibrillary acidic protein (GFAP), a marker of activated astrocytes, was also higher in limbic areas, suggesting that cellular stress correlates with the rate of circuit reshaping. Elevated markers of plasticity may endow limbic areas with flexibility necessary for learning and memory within an affective context, but may also render them vulnerable to abnormal structural changes, as seen in neurologic and psychiatric diseases.

The Default Mode Network in Autism

Autism spectrum disorder (ASD) is characterized by deficits in social communication and interaction. Since its discovery as a major functional brain system, the default mode network (DMN) has been implicated in a number of psychiatric disorders, including ASD. Here we review converging multimodal evidence for DMN dysfunction in the context of specific components of social cognitive dysfunction in ASD: 'self-referential processing' - the ability to process social information relative to oneself and 'theory of mind' or 'mentalizing' - the ability to infer the mental states such as beliefs, intentions, and emotions of others. We show that altered functional and structural organization of the DMN, and its atypical developmental trajectory, are prominent neurobiological features of ASD. We integrate findings on atypical cytoarchitectonic organization and imbalance in excitatory-inhibitory circuits, which alter local and global brain signaling, to scrutinize putative mechanisms underlying DMN dysfunction in ASD. Our synthesis of the extant literature suggests that aberrancies in key nodes of the DMN and their dynamic functional interactions contribute to atypical integration of information about the self in relation to 'other', as well as impairments in the ability to flexibly attend to socially relevant stimuli. We conclude by highlighting open questions for future research.

The Anterior Cingulate Gyrus and Social Cognition: Tracking the Motivation of Others

The anterior cingulate cortex (ACC) is implicated in a broad range of behaviors and cognitive processes, but it has been unclear what contribution, if any, the ACC makes to social behavior. We argue that anatomical and functional evidence suggests that a specific sub-region of ACC-in the gyrus (ACCg)-plays a crucial role in processing social information. We propose that the computational properties of the ACCg support a contribution to social cognition by estimating how motivated other individuals are and dynamically updating those estimates when further evidence suggests they have been erroneous. Notably this model, based on vicarious motivation and error processing, provides a unified account of neurophysiological and neuroimaging evidence that the ACCg is sensitive to costs, benefits, and errors during social interactions. Furthermore, it makes specific, testable predictions about a key mechanism that may underpin variability in socio-cognitive abilities in health and disease.

Altered Expression of Endoplasmic Reticulum Stress-Related Genes in the Middle Frontal Cortex of Subjects with Autism Spectrum Disorder

The endoplasmic reticulum (ER) is an important organelle responsible for the folding and sorting of proteins. Disturbances in ER homeostasis can trigger a cellular response known as the unfolded protein response, leading to accumulation of unfolded or misfolded proteins in the ER lumen called ER stress. A number of recent studies suggest that mutations in autism spectrum disorder (ASD)-susceptible synaptic genes induce ER stress. However, it is not known whether ER stress-related genes are altered in the brain of ASD subjects. In the present study, we investigated the mRNA expression of ER stress-related genes (ATF4, ATF6, PERK, XBP1, sXBP1, CHOP, and IRE1) in the postmortem middle frontal gyrus of ASD and control subjects. RT-PCR analysis showed significant increases in the mRNA levels of ATF4, ATF6, PERK, XBP1, CHOP, and IRE1 in the middle frontal gyrus of ASD subjects. In addition, we found a significant positive association of mRNA levels of ER stress genes with the diagnostic score for stereotyped behavior in ASD subjects. These results, for the first time, provide the evidence of the dysregulation of ER stress genes in the brain of subjects with ASD.

Region-specific impairments in parvalbumin interneurons in social isolation-reared mice

Many neuropsychiatric disorders show localized dysfunction in specific cortical regions. The mechanisms underlying such region-specific vulnerabilities are unknown. Post-mortem analyses have demonstrated a selective reduction in the expression of parvalbumin (PV) in GABAergic interneurons in the frontal rather than the sensory cortex of patients with neuropsychiatric disorders such as schizophrenia, autism spectrum disorders, and bipolar disorders. PV neurons are surrounded by perineuronal nets (PNNs), and are protected from oxidative stress. Previous studies have shown that the characteristics of PNNs are brain region-specific. Therefore, we hypothesized that PV neurons and PNNs may be targeted in region-specific lesions in the brain. Oxidative stress was induced in mice by rearing them in socially isolated conditions. We systemically examined the distribution of PV neurons and PNNs in the brains of these mice as well as a control group. Our results show that the regions frequently affected in neuropsychiatric disorders show significantly lower PV expression and a lower percentage of PV neurons surrounded by PNNs in the brains of socially isolated mice. These results indicate that PV neurons and PNNs exhibit region-specific vulnerabilities. Our findings may be useful for elucidating the mechanisms underlying region-specific disruption of the brain in neuropsychiatric disorders.

Decreased parvalbumin mRNA levels in cerebellar Purkinje cells in autism

Recent neuropathology studies in human brains indicate that several areas of the prefrontal cortex have decreased numbers of parvalbumin interneurons or decreased parvalbumin expression in Autism Spectrum disorders (ASD) [Hashemi, Ariza, Rogers, Noctor, & Martinez-Cerdeno, 2017; Zikopoulos & Barbas, ]. These data suggest that a deficit in parvalbumin may be a key neuropathology of ASD and contribute to altered GABAergic inhibition. However, it is unclear if a deficit in parvalbumin is a phenomenon that occurs in regions other than the cerebral cortex. The cerebellum is a major region where neuropathology was first detected in ASD over three decades ago [Bauman & Kemper, ]. In view of the documented association between parvalbumin-expressing neurons and autism, the objective of the present study was to determine if parvalbumin gene expression is also altered in Purkinje neurons of the cerebellum. Radioisotopic in situ hybridization histochemistry was used on human tissue sections from control and ASD brains in order to detect and measure parvalbumin mRNA levels at the single cell level in Purkinje cells of Crus II of the lateral cerebellar hemispheres. Results indicate that parvalbumin mRNA levels are significantly lower in Purkinje cells in ASD compared to control brains. This decrease was not influenced by post-mortem interval or age at death. This result indicates that decreased parvalbumin expression is a more widespread feature of ASD. We discuss how this decrease may be implicated in altered cerebellar output to the cerebral cortex and in key ASD symptoms. Autism Res 2017, 10: 1787-1796. © 2017 International Society for Autism Research, Wiley Periodicals, Inc.

LAY SUMMARY

The cerebellum of the brain controls movement and cognition, including memory and language. This study investigated mechanisms of cerebellar function in Autism. Our hypothesis is that parvalbumin, a molecule that controls and coordinate many cellular brain functions, contributes to the excitatory/inhibitory imbalance in Autism. We report that parvalbumin expression is depressed in Purkinje cells of the cerebellum in autism. This finding contributes to elucidate the cellular and molecular underpinings of autism and should provide a direction for future therapies.

Oxidative stress-driven parvalbumin interneuron impairment as a common mechanism in models of schizophrenia

Parvalbumin inhibitory interneurons (PVIs) are crucial for maintaining proper excitatory/inhibitory balance and high-frequency neuronal synchronization. Their activity supports critical developmental trajectories, sensory and cognitive processing, and social behavior. Despite heterogeneity in the etiology across schizophrenia and autism spectrum disorder, PVI circuits are altered in these psychiatric disorders. Identifying mechanism(s) underlying PVI deficits is essential to establish treatments targeting in particular cognition. On the basis of published and new data, we propose oxidative stress as a common pathological mechanism leading to PVI impairment in schizophrenia and some forms of autism. A series of animal models carrying genetic and/or environmental risks relevant to diverse etiological aspects of these disorders show PVI deficits to be all accompanied by oxidative stress in the anterior cingulate cortex. Specifically, oxidative stress is negatively correlated with the integrity of PVIs and the extracellular perineuronal net enwrapping these interneurons. Oxidative stress may result from dysregulation of systems typically affected in schizophrenia, including glutamatergic, dopaminergic, immune and antioxidant signaling. As convergent end point, redox dysregulation has successfully been targeted to protect PVIs with antioxidants/redox regulators across several animal models. This opens up new perspectives for the use of antioxidant treatments to be applied to at-risk individuals, in close temporal proximity to environmental impacts known to induce oxidative stress.

Ultrastructural analysis of parvalbumin synapses in human dorsolateral prefrontal cortex

Coordinated activity of neural circuitry in the primate dorsolateral prefrontal cortex (DLPFC) supports a range of cognitive functions. Altered DLPFC activation is implicated in a number of human psychiatric and neurological illnesses. Proper DLPFC activity is, in part, maintained by two populations of neurons containing the calcium-binding protein parvalbumin (PV): local inhibitory interneurons that form Type II synapses, and long-range glutamatergic inputs from the thalamus that form Type I synapses. Understanding the contributions of each PV neuronal population to human DLPFC function requires a detailed examination of their anatomical properties. Consequently, we performed an electron microscopic analysis of (1) the distribution of PV immunoreactivity within the neuropil, (2) the properties of dendritic shafts of PV-IR interneurons, (3) Type II PV-IR synapses from PV interneurons, and (4) Type I PV-IR synapses from long-range projections, within the superficial and middle laminar zones of the human DLPFC. In both laminar zones, Type II PV-IR synapses from interneurons comprised ∼60% of all PV-IR synapses, and Type I PV-IR synapses from putative thalamocortical terminals comprised the remaining ∼40% of PV-IR synapses. Thus, the present study suggests that innervation from PV-containing thalamic nuclei extends across superficial and middle layers of the human DLPFC. These findings contrast with previous ultrastructural studies in monkey DLPFC where Type I PV-IR synapses were not identified in the superficial laminar zone. The presumptive added modulation of DLPFC circuitry by the thalamus in human may contribute to species-specific, higher-order functions.

Altered white matter integrity in adults with autism spectrum disorder and an IQ >100: a diffusion tensor imaging study

OBJECTIVE

White matter (WM) alterations have been reported in children and adults with autism spectrum disorder (ASD). In particular, impaired connectivity of limbic structures may be related to social deficits. Heterogeneous findings could be explained in terms of differences in sample characteristics and methodology. In this context, non-syndromic forms might differ substantially in WM structure from secondary ASD forms.

METHOD

In an attempt to recruit a homogeneous study sample, we included adults with high-functioning ASD and an IQ > 100 to decrease the influence of syndromic forms being often associated with cognitive deficits. Diffusion tensor imaging (DTI) was performed in 30 participants with ASD and 30 pairwise-matched controls. Fractional anisotropy (FA) and mean diffusivity (MD) as surrogate imaging markers for WM integrity were calculated.

RESULTS

We found a significant FA decrease in the ASD group in the genu and body of the corpus callosum (CC). Increased MD was detected in the subgenual anterior cingulate cortex (sACC).

CONCLUSION

The finding of decreased WM integrity in the genu of the CC is in line with earlier studies reporting a decreased number of interhemispheric fibers in the frontal lobe of ASD. Alterations in the sACC might be associated with 'Theory of mind' deficits.

Altered proliferation and networks in neural cells derived from idiopathic autistic individuals

Autism spectrum disorders (ASD) are common, complex and heterogeneous neurodevelopmental disorders. Cellular and molecular mechanisms responsible for ASD pathogenesis have been proposed based on genetic studies, brain pathology and imaging, but a major impediment to testing ASD hypotheses is the lack of human cell models. Here, we reprogrammed fibroblasts to generate induced pluripotent stem cells, neural progenitor cells (NPCs) and neurons from ASD individuals with early brain overgrowth and non-ASD controls with normal brain size. ASD-derived NPCs display increased cell proliferation because of dysregulation of a β-catenin/BRN2 transcriptional cascade. ASD-derived neurons display abnormal neurogenesis and reduced synaptogenesis leading to functional defects in neuronal networks. Interestingly, defects in neuronal networks could be rescued by insulin growth factor 1 (IGF-1), a drug that is currently in clinical trials for ASD. This work demonstrates that selection of ASD subjects based on endophenotypes unraveled biologically relevant pathway disruption and revealed a potential cellular mechanism for the therapeutic effect of IGF-1.

Developmental microglial priming in postmortem autism spectrum disorder temporal cortex

Microglia can shift into different complex morphologies depending on the microenvironment of the central nervous system (CNS). The distinct morphologies correlate with specific functions and can indicate the pathophysiological state of the CNS. Previous postmortem studies of autism spectrum disorder (ASD) showed neuroinflammation in ASD indicated by increased microglial density. These changes in the microglia density can be accompanied by changes in microglia phenotype but the individual contribution of different microglia phenotypes to the pathophysiology of ASD remains unclear. Here, we used an unbiased stereological approach to quantify six structurally and functionally distinct microglia phenotypes in postmortem human temporal cortex, which were immuno-stained with Iba1. The total density of all microglia phenotypes did not differ between ASD donors and typically developing individual donors. However, there was a significant decrease in ramified microglia in both gray matter and white matter of ASD, and a significant increase in primed microglia in gray matter of ASD compared to typically developing individuals. This increase in primed microglia showed a positive correlation with donor age in both gray matter and white of ASD, but not in typically developing individuals. Our results provide evidence of a shift in microglial phenotype that may indicate impaired synaptic plasticity and a chronic vulnerability to exaggerated immune responses.

Animal models in psychiatric research: The RDoC system as a new framework for endophenotype-oriented translational neuroscience

The recently proposed Research Domain Criteria (RDoC) system defines psychopathologies as phenomena of multilevel neurobiological existence and assigns them to 5 behavioural domains characterizing a brain in action. We performed an analysis on this contemporary concept of psychopathologies in respect to a brain phylogeny and biological substrates of psychiatric diseases. We found that the RDoC system uses biological determinism to explain the pathogenesis of distinct psychiatric symptoms and emphasises exploration of endophenotypes but not of complex diseases. Therefore, as a possible framework for experimental studies it allows one to evade a major challenge of translational studies of strict disease-to-model correspondence. The system conforms with the concept of a normality and pathology continuum, therefore, supports basic studies. The units of analysis of the RDoC system appear as a novel matrix for model validation. The general regulation and arousal, positive valence, negative valence, and social interactions behavioural domains of the RDoC system show basic construct, network, and phenomenological homologies between human and experimental animals. The nature and complexity of the cognitive behavioural domain of the RDoC system deserve further clarification. These homologies in the 4 domains justifies the validity, reliably and translatability of animal models appearing as endophenotypes of the negative and positive affect, social interaction and general regulation and arousal systems’ dysfunction.

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The RDoC system encourages endophenotype-oriented experimental studies in human and animals.

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The system conforms with the normality-pathology continuum concept.

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The RDoC system appears to be a suitable framework for basic research.

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Four RDoC domains show construct and phenomenological homology in human and animals.

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Endophenotype-based models of affective psychopathologies appear most reliable.

Autism-like behavior in the BTBR mouse model of autism is improved by propofol

Autism spectrum disorder (ASD) is a developmental disorder that is characterized by symptoms of impaired social interactions, restricted interests and repetitive behaviors. Recent studies in humans and animal-models suggest that reduced GABAergic neurotransmission in the brain may underlie autism-related behavioral symptoms. It has been shown that propofol, a commonly used anesthetic, facilitates γ-aminobutyric acid-mediated inhibitory synaptic transmission. The present study investigated whether propofol improved autistic phenotypes in BTBR T + Itpr3tf/J (BTBR) mice, a model of idiopathic autism. We found that i.p. injection of propofol in BTBR mice significantly improved aspects of social approach and repetitive behaviors without affecting reciprocal social interactions and without any detrimental effects in C57BL/6J mice. The ability of propofol to improve autistic phenotypes in BTBR mice through GABAergic neurotransmission suggests a potential pharmacological target for interventions to treat symptoms of autism.

The Number of Parvalbumin-Expressing Interneurons Is Decreased in the Prefrontal Cortex in Autism

The cognitive phenotype of autism has been correlated with an altered balance of excitation to inhibition in the cerebral cortex, which could result from a change in the number, function, or morphology of GABA-expressing interneurons. The number of GABAergic interneuron subtypes has not been quantified in the autistic cerebral cortex. We classified interneurons into 3 subpopulations based on expression of the calcium-binding proteins parvalbumin, calbindin, or calretinin. We quantified the number of each interneuron subtype in postmortem neocortical tissue from 11 autistic cases and 10 control cases. Prefrontal Brodmann Areas (BA) BA46, BA47, and BA9 in autism and age-matched controls were analyzed by blinded researchers. We show that the number of parvalbumin+ interneurons in these 3 cortical areas-BA46, BA47, and BA9-is significantly reduced in autism compared with controls. The number of calbindin+ and calretinin+ interneurons did not differ in the cortical areas examined. Parvalbumin+ interneurons are fast-spiking cells that synchronize the activity of pyramidal cells through perisomatic and axo-axonic inhibition. The reduced number of parvalbumin+ interneurons could disrupt the balance of excitation/inhibition and alter gamma wave oscillations in the cerebral cortex of autistic subjects. These data will allow development of novel treatments specifically targeting parvalbumin interneurons.

Relationship between Long Chain n-3 Polyunsaturated Fatty Acids and Autism Spectrum Disorder: Systematic Review and Meta-Analysis of Case-Control and Randomised Controlled Trials

Omega-3 long chain polyunsaturated fatty acid supplementation (n-3 LCPUFA) for treatment of Autism Spectrum Disorder (ASD) is popular. The results of previous systematic reviews and meta-analyses of n-3 LCPUFA supplementation on ASD outcomes were inconclusive. Two meta-analyses were conducted; meta-analysis 1 compared blood levels of LCPUFA and their ratios arachidonic acid (ARA) to docosahexaenoic acid (DHA), ARA to eicosapentaenoic acid (EPA), or total n-6 to total n-3 LCPUFA in ASD to those of typically developing individuals (with no neurodevelopmental disorders), and meta-analysis 2 compared the effects of n-3 LCPUFA supplementation to placebo on symptoms of ASD. Case-control studies and randomised controlled trials (RCTs) were identified searching electronic databases up to May, 2016. Mean differences were pooled and analysed using inverse variance models. Heterogeneity was assessed using I² statistic. Fifteen case-control studies (n = 1193) were reviewed. Compared with typically developed, ASD populations had lower DHA (−2.14 [95% CI −3.22 to −1.07]; p < 0.0001; I² = 97%), EPA (−0.72 [95% CI −1.25 to −0.18]; p = 0.008; I² = 88%), and ARA (−0.83 [95% CI, −1.48 to −0.17]; p = 0.01; I² = 96%) and higher total n-6 LCPUFA to n-3 LCPUFA ratio (0.42 [95% CI 0.06 to 0.78]; p = 0.02; I² = 74%). Four RCTs were included in meta-analysis 2 (n = 107). Compared with placebo, n-3 LCPUFA improved social interaction (−1.96 [95% CI −3.5 to −0.34]; p = 0.02; I² = 0) and repetitive and restricted interests and behaviours (−1.08 [95% CI −2.17 to −0.01]; p = 0.05; I² = 0). Populations with ASD have lower n-3 LCPUFA status and n-3 LCPUFA supplementation can potentially improve some ASD symptoms. Further research with large sample size and adequate study duration is warranted to confirm the efficacy of n-3 LCPUFA.

Nucleus accumbens deep brain stimulation for a patient with self-injurious behavior and autism spectrum disorder: functional and structural changes of the brain: report of a case and review of literature

The aim of this report was to investigate the clinical outcome of deep brain stimulation (DBS) for autism spectrum disorder (ASD) and the functional and structural changes in the brain after DBS. We present a 14-year-old boy with ASD and self-injurious behavior (SIB) refractory with medical and behavioral therapy. He was treated by bilateral nucleus accumbens (NAc) DBS. Remarkable clinical improvement was observed following NAc DBS. Brain fluorodeoxyglucose-positron emission tomography (FDG-PET) and magnetic resonance imaging (MRI) volumetric studies revealed that the metabolism in the prefrontal and the frontal cortex as well as the occipital cortex was markedly decreased in association with the decreased cortical volumes in those areas 2 years after NAc DBS. The therapeutic potential of NAc DBS is suggested for the clinical improvement of patients with ASD and SIB with structural and functional changes after DBS.

Neuroanatomy and Neuropathology of Autism Spectrum Disorder in Humans

Autism spectrum disorder (ASD) is a lifelong heterogeneous neurodevelopmental condition that is associated with differences in brain anatomy and connectivity. Yet, the molecular and cellular mechanisms that underpin the atypical developmental of the brain in ASD remain poorly understood. Here, we review the findings of in vivo neuroimaging studies examining the time course of atypical brain development in ASD and relate the different neurodevelopmental stages that are atypical in ASD to the known neurobiological mechanisms that drive the maturation of the typically developing brain. In particular, we focus on the notion of 'early brain overgrowth' in ASD, which may lead to differences in the formation of the brain's micro- and macro-circuitry. Moreover, we attempt to link the in vivo reports describing differences in brain anatomy and connectivity on the macroscopic level to the increasing number of post-mortem studies examining the neural architecture of the brain in ASD on the microscopic level. In addition, we discuss future directions and outstanding questions in this particular field of research and highlight the need for establishing the link between micro- and macro-pathology in the same set of individuals with ASD based on advances in genetic, molecular and imaging techniques. In combination, these may proof to be invaluable for patient stratification and the development of novel pharmacotherapies in the future.

Prenatal Valproate Exposure Differentially Affects Parvalbumin-Expressing Neurons and Related Circuits in the Cortex and Striatum of Mice

Autism spectrum disorders (ASD) comprise a number of heterogeneous neurodevelopmental diseases characterized by core behavioral symptoms in the domains of social interaction, language/communication and repetitive or stereotyped patterns of behavior. In utero exposure to valproic acid (VPA) has evolved as a highly recognized rodent ASD model due to the robust behavioral phenotype observed in the offspring and the proven construct-, face- and predictive validity of the model. The number of parvalbumin-immunoreactive (PV+) GABAergic interneurons has been consistently reported to be decreased in human ASD subjects and in ASD animal models. The presumed loss of this neuron subpopulation hereafter termed Pvalb neurons and/or PV deficits were proposed to result in an excitation/inhibition imbalance often observed in ASD. Importantly, loss of Pvalb neurons and decreased/absent PV protein levels have two fundamentally different consequences. Thus, Pvalb neurons were investigated in in utero VPA-exposed male ("VPA") mice in the striatum, medial prefrontal cortex (mPFC) and somatosensory cortex (SSC), three ASD-associated brain regions. Unbiased stereology of PV+ neurons and Vicia Villosa Agglutinin-positive (VVA+) perineuronal nets, which specifically enwrap Pvalb neurons, was carried out. Analyses of PV protein expression and mRNA levels for Pvalb, Gad67, Kcnc1, Kcnc2, Kcns3, Hcn1, Hcn2, and Hcn4 were performed. We found a ∼15% reduction in the number of PV+ cells and decreased Pvalb mRNA and PV protein levels in the striatum of VPA mice compared to controls, while the number of VVA+ cells was unchanged, indicating that Pvalb neurons were affected at the level of the transcriptome. In selected cortical regions (mPFC, SSC) of VPA mice, no quantitative loss/decrease of PV+ cells was observed. However, expression of Kcnc1, coding for the voltage-gated potassium channel Kv3.1 specifically expressed in Pvalb neurons, was decreased by ∼40% in forebrain lysates of VPA mice. Moreover, hyperpolarization-activated cyclic nucleotide-gated channel (HCN) 1 expression was increased by ∼40% in the same samples from VPA mice. We conclude that VPA leads to alterations that are brain region- and gene-specific including Pvalb, Kcnc1, and Hcn1 possibly linked to homeostatic mechanisms. Striatal PV down-regulation appears as a common feature in a subset of genetic (Shank3B-/-) and environmental ASD models.

Altered nocifensive behavior in animal models of autism spectrum disorder: The role of the nicotinic cholinergic system

Caretakers and clinicians alike have long recognized that individuals with autism spectrum disorder (ASD) can have altered sensory processing, which can contribute to its core symptoms. However, the pathobiology of sensory alterations in ASD is poorly understood. Here we examined nocifensive behavior in ASD mouse models, the BTBR T+Itpr3tf/J (BTBR) and the fragile-X mental retardation-1 knockout (Fmr1-KO) mice. We also examined the effects of nicotine on nocifensive behavior given that nicotine, a nicotinic cholinergic receptor (nAChR) agonist that has antinociceptive effects, was shown to improve social deficits and decrease repetitive behaviors in BTBR mice. Compared to respective controls, both BTBR and Fmr1-KO had hyporesponsiveness to noxious thermal stimuli and electrical stimulation of C-sensory fibers, normal responsiveness to electrical stimulation of Aβ- and Aδ-fiber, and hyperresponsiveness to visceral pain after acetic acid intraperitoneal injection. In BTBR, nicotine at lower doses increased, whereas at higher doses, it decreased hotplate latency compared to vehicle. In a significantly different effect pattern, in control mice, nicotine had antinociceptive effects to noxious heat only at the high dose. Interestingly, these nocifensive behavior alterations and differential responses to nicotine antinociceptive effects in BTBR mice were associated with significant downregulation of α3, α4, α5, α7, β2, β3, and β4 nAChR subunits in several cerebral regions both, during embryonic development and adulthood. Taken together, these findings further implicate nAChRs in behaviors alterations in the BTBR model and lend support to the hypothesis that nAChRs may be a target for treatment of behavior deficits and sensory dysfunction in ASD.

Genetic control of social behavior: Lessons from mutant mice

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

Distinction of Neurons, Glia and Endothelial Cells in the Cerebral Cortex: An Algorithm Based on Cytological Features

The estimation of the number or density of neurons and types of glial cells and their relative proportions in different brain areas are at the core of rigorous quantitative neuroanatomical studies. Unfortunately, the lack of detailed, updated, systematic and well-illustrated descriptions of the cytology of neurons and glial cell types, especially in the primate brain, makes such studies especially demanding, often limiting their scope and broad use. Here, following an extensive analysis of histological materials and the review of current and classical literature, we compile a list of precise morphological criteria that can facilitate and standardize identification of cells in stained sections examined under the microscope. We describe systematically and in detail the cytological features of neurons and glial cell types in the cerebral cortex of the macaque monkey and the human using semithin and thick sections stained for Nissl. We used this classical staining technique because it labels all cells in the brain in distinct ways. In addition, we corroborate key distinguishing characteristics of different cell types in sections immunolabeled for specific markers counterstained for Nissl and in ultrathin sections processed for electron microscopy. Finally, we summarize the core features that distinguish each cell type in easy-to-use tables and sketches, and structure these key features in an algorithm that can be used to systematically distinguish cellular types in the cerebral cortex. Moreover, we report high inter-observer algorithm reliability, which is a crucial test for obtaining consistent and reproducible cell counts in unbiased stereological studies. This protocol establishes a consistent framework that can be used to reliably identify and quantify cells in the cerebral cortex of primates as well as other mammalian species in health and disease.

Altered neurotransmitter metabolism in adolescents with high-functioning autism

Previous studies have suggested that alterations in excitatory/inhibitory neurotransmitters might play a crucial role in autism spectrum disorder (ASD). Proton magnetic resonance spectroscopy (¹H-MRS) can provide valuable information about abnormal brain metabolism and neurotransmitter concentrations. However, few ¹H-MRS studies have been published on the imbalance of the two most abundant neurotransmitters in ASD: glutamate (Glu) and gamma-aminobutyric acid (GABA). Moreover, to our knowledge none of these published studies is performed with a study population consisting purely of high-functioning autism (HFA) adolescents. Selecting only individuals with HFA eliminates factors possibly related to intellectual impairment instead of ASD. This study aims to assess Glu and GABA neurotransmitter concentrations in HFA. Occipital concentrations of Glu and GABA plus macromolecules (GABA+) were obtained using ¹H-MRS relative to creatine (Cr) in adolescents with HFA (n=15 and n=13 respectively) and a healthy control group (n=17). Multiple linear regression revealed significantly higher Glu/Cr and lower GABA+/Glu concentrations in the HFA group compared to the controls. These results imply that imbalanced neurotransmitter levels of excitation and inhibition are associated with HFA in adolescents.

Brain oscillations and connectivity in autism spectrum disorders (ASD): new approaches to methodology, measurement and modelling

Although atypical social behaviour remains a key characterisation of ASD, the presence of sensory and perceptual abnormalities has been given a more central role in recent classification changes. An understanding of the origins of such aberrations could thus prove a fruitful focus for ASD research. Early neurocognitive models of ASD suggested that the study of high frequency activity in the brain as a measure of cortical connectivity might provide the key to understanding the neural correlates of sensory and perceptual deviations in ASD. As our review shows, the findings from subsequent research have been inconsistent, with a lack of agreement about the nature of any high frequency disturbances in ASD brains. Based on the application of new techniques using more sophisticated measures of brain synchronisation, direction of information flow, and invoking the coupling between high and low frequency bands, we propose a framework which could reconcile apparently conflicting findings in this area and would be consistent both with emerging neurocognitive models of autism and with the heterogeneity of the condition.

Exploring the relationship between cortical GABA concentrations, auditory gamma-band responses and development in ASD: Evidence for an altered maturational trajectory in ASD

Autism spectrum disorder (ASD) is hypothesized to arise from imbalances between excitatory and inhibitory neurotransmission (E/I imbalance). Studies have demonstrated E/I imbalance in individuals with ASD and also corresponding rodent models. One neural process thought to be reliant on E/I balance is gamma-band activity (Gamma), with support arising from observed correlations between motor, as well as visual, Gamma and underlying GABA concentrations in healthy adults. Additionally, decreased Gamma has been observed in ASD individuals and relevant animal models, though the direct relationship between Gamma and GABA concentrations in ASD remains unexplored. This study combined magnetoencephalography (MEG) and edited magnetic resonance spectroscopy (MRS) in 27 typically developing individuals (TD) and 30 individuals with ASD. Auditory cortex localized phase-locked Gamma was compared to resting Superior Temporal Gyrus relative cortical GABA concentrations for both children/adolescents and adults. Children/adolescents with ASD exhibited significantly decreased GABA+/Creatine (Cr) levels, though typical Gamma. Additionally, these children/adolescents lacked the typical maturation of GABA+/Cr concentrations and gamma-band coherence. Furthermore, children/adolescents with ASD additionally failed to exhibit the typical GABA+/Cr to gamma-band coherence association. This altered coupling during childhood/adolescence may result in Gamma decreases observed in the adults with ASD. Therefore, individuals with ASD exhibit improper local neuronal circuitry maturation during a childhood/adolescence critical period, when GABA is involved in configuring of such circuit functioning. Provocatively a novel line of treatment is suggested (with a critical time window); by increasing neural GABA levels in children/adolescents with ASD, proper local circuitry maturation may be restored resulting in typical Gamma in adulthood. Autism Res 2017, 10: 593-607. © 2016 International Society for Autism Research, Wiley Periodicals, Inc.

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

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

Selective Localization of Shanks to VGLUT1-Positive Excitatory Synapses in the Mouse Hippocampus

Members of the Shank family of multidomain proteins (Shank1, Shank2, and Shank3) are core components of the postsynaptic density (PSD) of excitatory synapses. At synaptic sites Shanks serve as scaffolding molecules that cluster neurotransmitter receptors as well as cell adhesion molecules attaching them to the actin cytoskeleton. In this study we investigated the synapse specific localization of Shank1-3 and focused on well-defined synaptic contacts within the hippocampal formation. We found that all three family members are present only at VGLUT1-positive synapses, which is particularly visible at mossy fiber contacts. No costaining was found at VGLUT2-positive contacts indicating that the molecular organization of VGLUT2-associated PSDs diverges from classical VGLUT1-positive excitatory contacts in the hippocampus. In light of SHANK mutations in neuropsychiatric disorders, this study indicates which glutamatergic networks within the hippocampus will be primarily affected by shankopathies.