Abnormal axon guidance signals and reduced interhemispheric connection via anterior commissure in neonates of marmoset ASD model

Design and application of a multimodality-compatible 1Tx/6Rx RF coil for monkey brain MRI at 7T

OBJECTIVE

Blood-oxygen-level-dependent functional MRI allows to investigte neural activities and connectivity. While the non-human primate plays an essential role in neuroscience research, multimodal methods combining functional MRI with other neuroimaging and neuromodulation enable us to understand the brain network at multiple scales.

APPROACH

In this study, a tight-fitting helmet-shape receive array with a single transmit loop for anesthetized macaque brain MRI at 7T was fabricated with four openings constructed in the coil housing to accommodate multimodal devices, and the coil performance was quantitatively evaluated and compared to a commercial knee coil. In addition, experiments over three macaques with infrared neural stimulation (INS), focused ultrasound stimulation (FUS), and transcranial direct current stimulation (tDCS) were conducted.

MAIN RESULTS

The RF coil showed higher transmit efficiency, comparable homogeneity, improved SNR and enlarged signal coverage over the macaque brain. Infrared neural stimulation was applied to the amygdala in deep brain region, and activations in stimulation sites and connected sites were detected, with the connectivity consistent with anatomical information. Focused ultrasound stimulation was applied to the left visual cortex, and activations were acquired along the ultrasound traveling path, with all time course curves consistent with pre-designed paradigms. The existence of transcranial direct current stimulation electrodes brought no interference to the RF system, as evidenced through high-resolution MPRAGE structure images.

SIGNIFICANCE

This pilot study reveals the feasibility for brain investigation at multiple spatiotemporal scales, which may advance our understanding in dynamic brain networks.

A radiofrequency coil to facilitate task-based fMRI of awake marmosets

BACKGROUND

The small common marmoset (Callithrix jacchus) is an ideal nonhuman primate for awake fMRI in ultra-high field small animal MRI scanners. However, it can often be challenging in task-based fMRI experiments to provide a robust stimulus within the MRI environment while using hardware (an RF coil and restraint system) that is compatible with awake imaging.

NEW METHOD

Here we present an RF coil and restraint system that permits unimpeded access to an awake marmoset's head subsequent to immobilization, thereby permitting the setup of peripheral devices and stimuli proximal to the head.

RESULTS

As an example application, an fMRI experiment probing whole-brain activation in response to marmoset vocalizations was conducted-this paradigm showed significant bilateral activation in the inferior colliculus, medial lateral geniculate nucleus, and auditory cortex.

COMPARISON WITH EXISTING METHOD(S)

The coil performance was evaluated and compared to a previously published restraint system with integrated RF coil. The image and temporal SNR were improved by up to 58 % and 27 %, respectively, in the peripheral cortex and by 30 % and 3 % in the centre of the brain. The restraint-system topology limited head motion to less than 100 µm of translation and 0.30° of rotation when measured over a 15-minute acquisition.

CONCLUSIONS

The proposed hardware solution provides a versatile approach to awake-marmoset imaging and, as demonstrated, can facilitate task-based fMRI.

Contribution of the dihydropyrimidinase-like proteins family in synaptic physiology and in neurodevelopmental disorders

The dihydropyrimidinase-like (DPYSL) proteins, also designated as the collapsin response mediators (CRMP) proteins, constitute a family of five cytosolic phosphoproteins abundantly expressed in the developing nervous system but down-regulated in the adult mouse brain. The DPYSL proteins were initially identified as effectors of semaphorin 3A (Sema3A) signaling and consequently involved in regulation of growth cone collapse in young developing neurons. To date, it has been established that DPYSL proteins mediate signals for numerous intracellular/extracellular pathways and play major roles in variety of cellular process including cell migration, neurite extension, axonal guidance, dendritic spine development and synaptic plasticity through their phosphorylation status. The roles of DPYSL proteins at early stages of brain development have been described in the past years, particularly for DPYSL2 and DPYSL5 proteins. The recent characterization of pathogenic genetic variants in DPYSL2 and in DPYSL5 human genes associated with intellectual disability and brain malformations, such as agenesis of the corpus callosum and cerebellar dysplasia, highlighted the pivotal role of these actors in the fundamental processes of brain formation and organization. In this review, we sought to establish a detailed update on the knowledge regarding the functions of DPYSL genes and proteins in brain and to highlight their involvement in synaptic processing in later stages of neurodevelopment, as well as their particular contribution in human neurodevelopmental disorders (NDDs), such as autism spectrum disorders (ASD) and intellectual disability (ID).

Implication of Hippocampal Neurogenesis in Autism Spectrum Disorder: Pathogenesis and Therapeutic Implications

Autism spectrum disorder (ASD) is a cluster of heterogeneous neurodevelopmental conditions with atypical social communication and repetitive sensory-motor behaviors. The formation of new neurons from neural precursors in the hippocampus has been unequivocally demonstrated in the dentate gyrus of rodents and non-human primates. Accumulating evidence sheds light on how the deficits in the hippocampal neurogenesis may underlie some of the abnormal behavioral phenotypes in ASD. In this review, we describe the current evidence concerning pre-clinical and clinical studies supporting the significant role of hippocampal neurogenesis in ASD pathogenesis, discuss the possibility of improving hippocampal neurogenesis as a new strategy for treating ASD, and highlight the prospect of emerging pro-neurogenic therapies for ASD.

Progress in magnetic resonance imaging of autism model mice brain

Autism spectrum disorder (ASD) is a neurodevelopmental disease characterized by social disorder and stereotypical behaviors with an increasing incidence. ASD patients are suffering from varying degrees of mental retardation and language development abnormalities. Magnetic resonance imaging (MRI) is a noninvasive imaging technology to detect brain structural and functional dysfunction in vivo, playing an important role in the early diagnosisbasic research of ASD. High-field, small-animal MRI in basic research of autism model mice has provided a new approach to research the pathogenesis, characteristics, and intervention efficacy in autism. This article reviews MRI studies of mouse models of autism over the past 20 years. Reduced gray matter, abnormal connections of brain networks, and abnormal development of white matter fibers have been demonstrated in these studies, which are present in different proportions in the various mouse models. This provides a more macroscopic view for subsequent research on autism model mice. This article is categorized under: Cognitive Biology > Genes and Environment Neuroscience > Computation Neuroscience > Genes, Molecules, and Cells Neuroscience > Development.

Effects of arginine vasopressin on the transcriptome of prefrontal cortex in autistic rat model

Our previous studies have also demonstrated that AVP can significantly improve social interaction disorders and stereotypical behaviours in rats with VPA‐induced autism model. To further explore the mechanisms of action of AVP, we compared the PFC transcriptome changes before and after AVP treatment in VPA‐induced autism rat model. The autism model was induced by intraperitoneally injected with VPA at embryonic day 12.5 and randomly assigned to two groups: the VPA‐induced autism model group and the AVP treatment group. The AVP treatment group were treated with intranasal AVP at postnatal day 21 and for 3 weeks. The gene expression levels and function changes on the prefrontal cortex were measured by RNA‐seq and bioinformatics analysis at PND42 and the mRNA expression levels of synaptic and myelin development related genes were validated by qPCR. Our results confirmed that AVP could significantly improve synaptic and axon dysplasia and promote oligodendrocyte development in the prefrontal cortex in VPA‐induced autism models by regulating multiple signalling pathways.

The marmoset as a model for investigating the neural basis of social cognition in health and disease

Social-cognitive processes facilitate the use of environmental cues to understand others, and to be understood by others. Animal models provide vital insights into the neural underpinning of social behaviours. To understand social cognition at even deeper behavioural, cognitive, neural, and molecular levels, we need to develop more representative study models, which allow testing of novel hypotheses using human-relevant cognitive tasks. Due to their cooperative breeding system and relatively small size, common marmosets (Callithrix jacchus) offer a promising translational model for such endeavours. In addition to having social behavioural patterns and group dynamics analogous to those of humans, marmosets have cortical brain areas relevant for the mechanistic analysis of human social cognition, albeit in simplified form. Thus, they are likely suitable animal models for deciphering the physiological processes, connectivity and molecular mechanisms supporting advanced cognitive functions. Here, we review findings emerging from marmoset social and behavioural studies, which have already provided significant insights into executive, motivational, social, and emotional dysfunction associated with neurological and psychiatric disorders.

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.

Reduced childhood social attention in autism model marmosets predicts impaired social skills and inflexible behavior in adulthood

Autism spectrum disorder (ASD) is a neurodevelopmental condition characterized by social and communication impairments and restricted and repetitive behavior. Although there is currently no established cure for ASD, early interventions for deficits of attention to other individuals are expected to reduce the progression of ASD symptoms in later life. To confirm this hypothesis and improve early therapeutic interventions, it is desirable to develop an animal model of ASD in which social attention is impaired in childhood and ASD-like social behavior is observed in adulthood. However, rodent models of ASD have difficulty in recapitulating the deficit of gaze-based social attention. In this study, we examined the direction of gaze toward other conspecifics during childhood and puberty in a three-chamber test setting using an ASD marmoset model produced by maternal exposure to valproic acid (VPA). We also conducted a reversal learning test in adult VPA-exposed marmosets as an indicator of perseveration, a core symptom of ASD that has not previously been investigated in this model. The results showed that time spent gazing at other conspecifics was reduced in VPA-exposed marmosets in childhood, and that mature animals persisted with previous strategies that required long days for acquisition to pass the test. In a longitudinal study using the same animals, deficits in social attention in childhood correlated well with ASD-like social disturbance (inequity aversion and third-party reciprocity) and inflexible behavior in adulthood. Since VPA-exposed marmosets exhibit these diverse ASD-like behaviors that are consistent from childhood to adulthood, VPA-exposed marmosets will provide a valuable means of elucidating mechanisms for early intervention and contribute to the development of early therapies.

Simultaneous functional MRI of two awake marmosets

Social cognition is a dynamic process that requires the perception and integration of a complex set of idiosyncratic features between interacting conspecifics. Here we present a method for simultaneously measuring the whole-brain activation of two socially interacting marmoset monkeys using functional magnetic resonance imaging. MRI hardware (a radiofrequency coil and peripheral devices) and image-processing pipelines were developed to assess brain responses to socialization, both on an intra-brain and inter-brain level. Notably, the brain activation of a marmoset when viewing a second marmoset in-person versus when viewing a pre-recorded video of the same marmoset-i.e., when either capable or incapable of socially interacting with a visible conspecific-demonstrates increased activation in the face-patch network. This method enables a wide range of possibilities for potentially studying social function and dysfunction in a non-human primate model.

Functional and molecular characterization of a non-human primate model of autism spectrum disorder shows similarity with the human disease

Autism spectrum disorder (ASD) is a multifactorial disorder with characteristic synaptic and gene expression changes. Early intervention during childhood is thought to benefit prognosis. Here, we examined the changes in cortical synaptogenesis, synaptic function, and gene expression from birth to the juvenile stage in a marmoset model of ASD induced by valproic acid (VPA) treatment. Early postnatally, synaptogenesis was reduced in this model, while juvenile-age VPA-treated marmosets showed increased synaptogenesis, similar to observations in human tissue. During infancy, synaptic plasticity transiently increased and was associated with altered vocalization. Synaptogenesis-related genes were downregulated early postnatally. At three months of age, the differentially expressed genes were associated with circuit remodeling, similar to the expression changes observed in humans. In summary, we provide a functional and molecular characterization of a non-human primate model of ASD, highlighting its similarity to features observed in human ASD.

Cellular-resolution gene expression profiling in the neonatal marmoset brain reveals dynamic species- and region-specific differences

Precise spatiotemporal control of gene expression in the developing brain is critical for neural circuit formation, and comprehensive expression mapping in the developing primate brain is crucial to understand brain function in health and disease. Here, we developed an unbiased, automated, large-scale, cellular-resolution in situ hybridization (ISH)-based gene expression profiling system (GePS) and companion analysis to reveal gene expression patterns in the neonatal New World marmoset cortex, thalamus, and striatum that are distinct from those in mice. Gene-ontology analysis of marmoset-specific genes revealed associations with catalytic activity in the visual cortex and neuropsychiatric disorders in the thalamus. Cortically expressed genes with clear area boundaries were used in a three-dimensional cortical surface mapping algorithm to delineate higher-order cortical areas not evident in two-dimensional ISH data. GePS provides a powerful platform to elucidate the molecular mechanisms underlying primate neurobiology and developmental psychiatric and neurological disorders.

The evolution, formation and connectivity of the anterior commissure

The anterior commissure is the most ancient of the forebrain interhemispheric connections among all vertebrates. Indeed, it is the predominant pallial commissure in all non-eutherian vertebrates, universally subserving basic functions related to olfaction and survival. A key feature of the anterior commissure is its ability to convey connections from diverse brain areas, such as most of the neocortex in non-eutherian mammals, thereby mediating the bilateral integration of diverse functions. Shared developmental mechanisms between the anterior commissure and more evolutionarily recent commissures, such as the corpus callosum in eutherians, have led to the hypothesis that the former may have been a precursor for additional expansion of commissural circuits. However, differences between the formation of the anterior commissure and other telencephalic commissures suggest that independent developmental mechanisms underlie the emergence of these connections in extant species. Here, we review the developmental mechanisms and connectivity of the anterior commissure across evolutionarily distant species, and highlight its potential functional importance in humans, both in the course of normal neurodevelopment, and as a site of plastic axonal rerouting in the absence or damage of other connections.

Association of Reduced Tract Integrity with Social Communication Deficits in Preschool Autism Children: A Tract-Based Spatial Statistics Study

PURPOSE

To analyze the changes in white matter tracts in preschool children with autism spectrum disorder (ASD), and the correlation between these changes and social communication deficits.

METHODS

Diffuse tensor imaging was used to assess white matter integrity using tract-based spatial statistics in a sample of 50 right-handed children with ASD aged 2-6 years vis a reference sample of 46 typically developing children aged 2-6 years. We then correlated these significant different fiber tracts between groups with communication and social interaction scores using the Autism Diagnostic Interview-Revised Assessment (ADI-R) Scale.

RESULTS

We observed decreased fractional anisotropy (FA) in tracts including the left superior longitudinal fasciculus (SLF), the splenium of the corpus callosum (splCC), the left corticospinal tracts, and the left inferior longitudinal fasciculus (ILF) in children with ASD. Specifically, there was reduced white matter integrity of these tracts in the left cerebral hemisphere. In addition, we found that the decreased FA of left SLF and ILF was negatively associated with the ADI-R scores in children with ASD.

CONCLUSION

The structural integrity of some white matter tracts in the five-level anatomical model for the social communication was reduced. The reduced integrity white matter that we observed primarily in the left cerebral hemisphere may be a neural substrate of social communication deficits in preschool children with ASD, and we speculate that the reduction is associated with the severity of social interaction. The reduced FA of the splCC might be a substantial biomarker for children with ASD.

The Complex Structure of the Anterior White Commissure of the Human Brain: Fiber Dissection and Tractography Study

OBJECTIVE

Commissural fibers are necessary for bilateral integration, body coordination, and complex cognitive information flow between the hemispheres. The anterior commissure (AC) has a complex architecture interconnecting areas of the frontal, temporal and occipital lobes. The present study aims to demonstrate the connections and the course of the anterior (ACa) and posterior (ACp) limb of the AC using fiber dissection and diffusion tensor imaging (DTI) of the human brain.

METHODS

Fiber dissection was performed in a stepwise manner from lateral to medial on 6 left hemispheres. The gray matter was decorticated and the ACa-ACp was exposed. The ACa and ACp tracts were demonstrated using a high-spatial-resolution DTI with a 3T magnetic resonance unit in 13 cases.

RESULTS

Using both techniques showed that the AC has complex interconnections with large areas of the frontal (olfactory tubercles, anterior olfactory nucleus, olfactory bulb, and the orbital gyri), temporal (amygdaloidal nuclei, temporal and perirhinal cortex), and occipital (visual cortex) lobes. The ACp makes up the major component of the AC and is composed of temporal and occipital fibers. We observed that these fibers do not make a distinct bundle; the temporal fibers joined the uncinate fasciculus and the occipital fibers joined the sagittal striatum to reach their targets.

CONCLUSIONS

Being aware of the course of the AC is important during transcallosal and interforniceal approaches to the third ventricle tumors and temporal lobe epilepsy surgery. The intermingling fibers of the AC can provide a better understanding of the unexplained deficit that may occur during regional surgery.

Axonal Projections from Middle Temporal Area to the Pulvinar in the Common Marmoset

The pulvinar, the largest thalamic nucleus in the primate brain, has connections with a variety of cortical areas and is involved in many aspects of higher brain functions. Among cortico-pulvino-cortical systems, the connection between the middle temporal area (MT) and the pulvinar has been thought to contribute significantly to complex motion recognition. Recently, the common marmoset (Callithrix jacchus), has become a valuable model for a variety of neuroscience studies, including visual neuroscience and translational research of neurological and psychiatric disorders. However, information on projections from MT to the pulvinar in the marmoset brain is scant. We addressed this deficiency by injecting sensitive anterograde viral tracers into MT to examine the distribution of labeled terminations in the pulvinar. The injection sites were placed retinotopically according to visual field coordinates mapped by optical intrinsic imaging. All injections produced anterograde terminal labeling, which was densest in the medial nucleus of the inferior pulvinar (PIm), sparser in the central nucleus of the inferior pulvinar, and weakest in the lateral pulvinar. Within each subnucleus, terminations formed separate retinotopic fields. Most labeled terminals were small but these comingled with a few large terminals, distributed mainly in the dorsomedial part of the PIm. Our results further delineate the organization of projections from MT to the pulvinar in the marmoset as forming parallel complex networks, which may differentially contribute to motion processing. It is interesting that the densest projections from MT target the PIm, the subnucleus recently reported to preferentially receive direct retinal projections.

Gestational Exposure to Sodium Valproate Disrupts Fasciculation of the Mesotelencephalic Dopaminergic Tract, With a Selective Reduction of Dopaminergic Output From the Ventral Tegmental Area

Gestational exposure to valproic acid (VPA) is known to cause behavioral deficits of sociability, matching similar alterations in human autism spectrum disorder (ASD). Available data are scarce on the neuromorphological changes in VPA-exposed animals. Here, we focused on alterations of the dopaminergic system, which is implicated in motivation and reward, with relevance to social cohesion. Whole brains from 7-day-old mice born to mothers given a single injection of VPA (400 mg/kg b.wt.) on E13.5 were immunostained against tyrosine hydroxylase (TH). They were scanned using the iDISCO method with a laser light-sheet microscope, and the reconstructed images were analyzed in 3D for quantitative morphometry. A marked reduction of mesotelencephalic (MT) axonal fascicles together with a widening of the MT tract were observed in VPA treated mice, while other major brain tracts appeared anatomically intact. We also found a reduction in the abundance of dopaminergic ventral tegmental (VTA) neurons, accompanied by diminished tissue level of DA in ventrobasal telencephalic regions (including the nucleus accumbens (NAc), olfactory tubercle, BST, substantia innominata). Such a reduction of DA was not observed in the non-limbic caudate-putamen. Conversely, the abundance of TH+ cells in the substantia nigra (SN) was increased, presumably due to a compensatory mechanism or to an altered distribution of TH+ neurons occupying the SN and the VTA. The findings suggest that defasciculation of the MT tract and neuronal loss in VTA, followed by diminished dopaminergic input to the ventrobasal telencephalon at a critical time point of embryonic development (E13-E14) may hinder the patterning of certain brain centers underlying decision making and sociability.

Anterior Commissure Regulates Neuronal Activity of Amygdalae and Influences Locomotor Activity, Social Interaction and Fear Memory in Mice

The two hemispheres of the vertebrate brain are connected through several commissures. Although the anterior commissure (AC) is the most conserved white matter structure in the brains of different vertebrates, its complete physiological functionality remains elusive. Since the AC is involved in the connection between two amygdalae and because amygdalae are critical for emotional behaviors and social interaction, we assessed amygdalar activity and function to investigate the physiological role of the AC. We first performed ex vivo electrophysiological recording on mouse brains to demonstrate that the AC delivers a positive signal to facilitate synaptic responses and to recruit basolateral amygdalar neurons via glutamatergic synapses. Transection was then undertaken to investigate the role of the AC in vivo. Results from in vivo optogenetic stimulation suggest that AC transection impairs mutual activation between two basolateral amygdalae. Behavioral analyses were then used to assess if AC surgical lesioning results in hyperactivity, anxiety, social reduction or learning/memory impairment, which are behavioral features associated with neuropsychiatric disorders, such as autism spectrum disorders. We found that AC transection results in higher locomotor activity, aberrant social interaction and reduced associative memory, but not anxiety. Moreover, systemic administration of D-cycloserine, a coagonist of N-methyl-D-aspartate receptor, ameliorated auditory fear memory in AC-transected mice, reinforcing our evidence that the AC potentiates the activity of basolateral amygdalae. Our study suggests that the AC regulates basolateral amygdalar activity and influences neuropsychiatry-related behaviors in mice.

Segmented Iba1-Positive Processes of Microglia in Autism Model Marmosets

Autism spectrum disorder (ASD) is one of the most widespread neurodevelopmental disorders, characterized by impairment in social interactions, and restricted stereotyped behaviors. Using immunohistochemistry and positron emission tomography (PET), several studies have provided evidence of the existence of activated microglia in ASD patients. Recently, we developed an animal model of ASD using the new world monkey common marmoset (Callithrix jacchus) and demonstrated ASD-like social impairment after the in utero administration of valproic acid (VPA). To characterize microglia in this marmoset model of ASD from early toddler to adult, morphological analyses of microglia in VPA marmosets and age-matched unexposed (UE) marmosets were performed using immunohistochemistry for microglia-specific markers, Iba1, and P2RY12. The most robust morphological difference between VPA marmosets and UE marmosets throughout the life span evaluated were the microglia processes in VPA marmosets being frequently segmented by thin and faintly Iba1-positive structures. The segmentation of microglial processes was only rarely observed in UE marmosets. This feature of segmentation of microglial processes in VPA marmosets can also be observed in images from previous studies on ASD conducted in humans and animal models. Apoptotic cells have been shown to have segmented processes. Therefore, our results might suggest that microglia in patients and animals with ASD symptoms could frequently be in the apoptotic phase with high turnover rates of microglia found in some pathological conditions.