Thalamic reticular impairment underlies attention deficit in Ptchd1(Y/-) mice

Thalamocortical mGlu8 Modulates Dorsal Thalamus Excitatory Transmission and Sensorimotor Activity

Metabotropic glutamate receptor 8 (mGlu8) is a heterogeneously expressed and poorly understood glutamate receptor with potential pharmacological significance. The thalamic reticular nucleus (TRN) is a critical inhibitory modulator of the thalamocortical-corticothalamic (TC-CT) network and plays a crucial role in information processing throughout the brain, is implicated in a variety of psychiatric conditions, and is also a site of significant mGlu8 expression. Using both male and female mice, we determined via fluorescent in situ hybridization that parvalbumin-expressing cells in the TRN core and shell matrices (identified by spp1+ and ecel1+ expression, respectively), as well as the cortical layers involved in CT signaling, express grm8 mRNA. We then assayed the physiological and behavioral impacts of perturbing grm8 signaling in the TC circuit through conditional (adeno-associated virus-CRE mediated) and cell-type-specific constitutive deletion strategies. We show that constitutive parvalbumin grm8 knock-out (PV grm8 knock-out) mice exhibited (1) increased spontaneous excitatory drive onto dorsal thalamus relay cells and (2) impaired sensorimotor gating, measured via paired-pulse inhibition, but observed no differences in locomotion and thigmotaxis in repeated bouts of open field test (OFT). Conversely, we observed hyperlocomotive phenotypes and anxiolytic effects of AAV-mediated conditional knockdown of grm8 in the TRN (TRN grm8 knockdown) in repeated OFT. Our findings underscore a role for mGlu8 in regulating excitatory neurotransmission as well as anxiety-related locomotor behavior and sensorimotor gating, revealing potential therapeutic applications for various neuropsychiatric disorders and guiding future research endeavors into mGlu8 signaling and TRN function.

Sex and mental health are related to subcortical brain microstructure

Some mental health problems such as depression and anxiety are more common in females, while others such as autism and attention deficit/hyperactivity (AD/H) are more common in males. However, the neurobiological origins of these sex differences are poorly understood. Animal studies have shown substantial sex differences in neuronal and glial cell structure, while human brain imaging studies have shown only small differences, which largely reflect overall body and brain size. Advanced diffusion MRI techniques can be used to examine intracellular, extracellular, and free water signal contributions and provide unique insights into microscopic cellular structure. However, the extent to which sex differences exist in these metrics of subcortical gray matter structures implicated in psychiatric disorders is not known. Here, we show large sex-related differences in microstructure in subcortical regions, including the hippocampus, thalamus, and nucleus accumbens in a large sample of young adults. Unlike conventional T1-weighted structural imaging, large sex differences remained after adjustment for age and brain volume. Further, diffusion metrics in the thalamus and amygdala were associated with depression, anxiety, AD/H, and antisocial personality problems. Diffusion MRI may provide mechanistic insights into the origin of sex differences in behavior and mental health over the life course and help to bridge the gap between findings from experimental, epidemiological, and clinical mental health research.

The thalamic reticular nucleus orchestrates social memory

Social memory has been developed in humans and other animals to recognize familiar conspecifics and is essential for their survival and reproduction. Here, we demonstrated that parvalbumin-positive neurons in the sensory thalamic reticular nucleus (sTRNPvalb) are necessary and sufficient for mice to memorize conspecifics. sTRNPvalb neurons receiving glutamatergic projections from the posterior parietal cortex (PPC) transmit individual information by inhibiting the parafascicular thalamic nucleus (PF). Mice in which the PPCCaMKII→sTRNPvalb→PF circuit was inhibited exhibited a disrupted ability to discriminate familiar conspecifics from novel ones. More strikingly, a subset of sTRNPvalb neurons with high electrophysiological excitability and complex dendritic arborizations is involved in the above corticothalamic pathway and stores social memory. Single-cell RNA sequencing revealed the biochemical basis of these subset cells as a robust activation of protein synthesis. These findings elucidate that sTRNPvalb neurons modulate social memory by coordinating a hitherto unknown corticothalamic circuit and inhibitory memory engram.

Local activation of CB1 receptors by synthetic and endogenous cannabinoids dampens burst firing mode of reticular thalamic nucleus neurons in rats under ketamine anesthesia

The reticular thalamic nucleus (RTN) is a thin shell that covers the dorsal thalamus and controls the overall information flow from the thalamus to the cerebral cortex through GABAergic projections that contact thalamo-cortical neurons (TC). RTN neurons receive glutamatergic afferents fibers from neurons of the sixth layer of the cerebral cortex and from TC collaterals. The firing mode of RTN neurons facilitates the generation of sleep-wake cycles; a tonic mode or desynchronized mode occurs during wake and REM sleep and a burst-firing mode or synchronized mode is associated with deep sleep. Despite the presence of cannabinoid receptors CB1 (CB1Rs) and mRNA that encodes these receptors in RTN neurons, there are few works that have analyzed the participation of endocannabinoid-mediated transmission on the electrical activity of RTN. Here, we locally blocked or activated CB1Rs in ketamine anesthetized rats to analyze the spontaneous extracellular spiking activity of RTN neurons. Our results show the presence of a tonic endocannabinoid input, since local infusion of AM 251, an antagonist/inverse agonist, modifies RTN neurons electrical activity; furthermore, local activation of CB1Rs by anandamide or WIN 55212-2 produces heterogeneous effects in the basal spontaneous spiking activity, where the main effect is an increase in the spiking rate accompanied by a decrease in bursting activity in a dose-dependent manner; this effect is inhibited by AM 251. In addition, previous activation of GABA-A receptors suppresses the effects of CB1Rs on reticular neurons. Our results show that local activation of CB1Rs primarily diminishes the burst firing mode of RTn neurons.

Loss-of-function mutation in DDX53 associated with hereditary spastic paraplegia-like disorder

DEAD-box helicase 53 (DDX53) is a member of the DEAD-box protein family of RNA helicases. Unlike other family members that are responsible for RNA metabolism, the biological function of DDX53 and its impact on the human condition are unclear. Herein, we found a full-length DDX53 deletion mutation in a hereditary spastic paraplegia-like (HSP-like) patient with lower extremity spasticity, walking disorder, visual impairment, and lateral ventricular white matter lesions. Bioinformatic analysis revealed that DDX53 was mainly expressed in the cerebellar cortex and may function as a tissue-specific RNA helicase. Transcriptome analysis showed that the expression of multiple brain-associated genes involved in synapse organization, neuron function, and neuromuscular junctions was affected by DDX53 depletion. Moreover, RNA immunoprecipitation sequencing (RIP-seq) analysis showed that DDX53 interacted with 176 genes, and 96 of these genes were associated with the execution of neurofunction, particularly in the regulation of cell projection organization and nervous system development. Collectively, although a more specified cell or animal model is required to fully understand the functional role of DDX53 in the human brain, we report for the first time that the patient with DDX53 defects exhibits HSP-like symptoms and that DDX53 is essential for maintaining neuronal function, with loss-of-function mutation in DDX53 potentially leading to HSP due to impaired RNA metabolism in the nervous system. KEY MESSAGES: DDX53 deficiency was first reported to be associated with HSP disorder. DDX53 exhibited minimal impact on mitochondrial function. DDX53 impaired RNA metabolism in the nervous system.

Development of reciprocal connections between the dorsal lateral geniculate nucleus and the thalamic reticular nucleus

The thalamic reticular nucleus (TRN) serves as an important node between the thalamus and neocortex, regulating thalamocortical rhythms and sensory processing in a state dependent manner. Disruptions in TRN circuitry also figures prominently in several neurodevelopmental disorders including epilepsy, autism, and attentional defects. An understanding of how and when connections between TRN and 1st order thalamic nuclei, such as the dorsal lateral geniculate nucleus (dLGN), develop is lacking. We used the mouse visual thalamus as a model system to study the organization, pattern of innervation and functional responses between TRN and the dLGN. Genetically modified mouse lines were used to visualize and target the feedforward and feedback components of these intra-thalamic circuits and to understand how peripheral input from the retina impacts their development.Retrograde tracing of thalamocortical (TC) afferents through TRN revealed that the modality-specific organization seen in the adult, is present at perinatal ages and seems impervious to the loss of peripheral input. To examine the formation and functional maturation of intrathalamic circuits between the visual sector of TRN and dLGN, we examined when projections from each nuclei arrive, and used an acute thalamic slice preparation along with optogenetic stimulation to assess the maturation of functional synaptic responses. Although thalamocortical projections passed through TRN at birth, feedforward axon collaterals determined by vGluT2 labeling, emerged during the second postnatal week, increasing in density through the third week. Optogenetic stimulation of TC axon collaterals in TRN showed infrequent, weak excitatory responses near the end of week 1. During weeks 2-4, responses became more prevalent, grew larger in amplitude and exhibited synaptic depression during repetitive stimulation. Feedback projections from visual TRN to dLGN began to innervate dLGN as early as postnatal day 2 with weak inhibitory responses emerging during week 1. During week 2-4, inhibitory responses continued to grow larger, showing synaptic depression during repetitive stimulation. During this time TRN inhibition started to suppress TC spiking, having its greatest impact by week 4-6. Using a mutant mouse that lacks retinofugal projections revealed that the absence of retinal input led to an acceleration of TRN innervation of dLGN but had little impact on the development of feedforward projections from dLGN to TRN. Together, these experiments reveal how and when intrathalamic connections emerge during early postnatal ages and provide foundational knowledge to understand the development of thalamocortical network dynamics as well as neurodevelopmental diseases that involve TRN circuitry.

Shared behavioural impairments in visual perception and place avoidance across different autism models are driven by periaqueductal grey hypoexcitability in Setd5 haploinsufficient mice

Despite the diverse genetic origins of autism spectrum disorders (ASDs), affected individuals share strikingly similar and correlated behavioural traits that include perceptual and sensory processing challenges. Notably, the severity of these sensory symptoms is often predictive of the expression of other autistic traits. However, the origin of these perceptual deficits remains largely elusive. Here, we show a recurrent impairment in visual threat perception that is similarly impaired in 3 independent mouse models of ASD with different molecular aetiologies. Interestingly, this deficit is associated with reduced avoidance of threatening environments-a nonperceptual trait. Focusing on a common cause of ASDs, the Setd5 gene mutation, we define the molecular mechanism. We show that the perceptual impairment is caused by a potassium channel (Kv1)-mediated hypoexcitability in a subcortical node essential for the initiation of escape responses, the dorsal periaqueductal grey (dPAG). Targeted pharmacological Kv1 blockade rescued both perceptual and place avoidance deficits, causally linking seemingly unrelated trait deficits to the dPAG. Furthermore, we show that different molecular mechanisms converge on similar behavioural phenotypes by demonstrating that the autism models Cul3 and Ptchd1, despite having similar behavioural phenotypes, differ in their functional and molecular alteration. Our findings reveal a link between rapid perception controlled by subcortical pathways and appropriate learned interactions with the environment and define a nondevelopmental source of such deficits in ASD.

Restoring thalamocortical circuit dysfunction by correcting HCN channelopathy in Shank3 mutant mice

Thalamocortical (TC) circuits are essential for sensory information processing. Clinical and preclinical studies of autism spectrum disorders (ASDs) have highlighted abnormal thalamic development and TC circuit dysfunction. However, mechanistic understanding of how TC dysfunction contributes to behavioral abnormalities in ASDs is limited. Here, our study on a Shank3 mouse model of ASD reveals TC neuron hyperexcitability with excessive burst firing and a temporal mismatch relationship with slow cortical rhythms during sleep. These TC electrophysiological alterations and the consequent sensory hypersensitivity and sleep fragmentation in Shank3 mutant mice are causally linked to HCN2 channelopathy. Restoring HCN2 function early in postnatal development via a viral approach or lamotrigine (LTG) ameliorates sensory and sleep problems. A retrospective case series also supports beneficial effects of LTG treatment on sensory behavior in ASD patients. Our study identifies a clinically relevant circuit mechanism and proposes a targeted molecular intervention for ASD-related behavioral impairments.

Auditory neuroscience: Sounds make the face move

Animals including humans often react to sounds by involuntarily moving their face and body. A new study shows that facial movements provide a simple and reliable readout of a mouse's hearing ability that is more sensitive than traditional measurements.

Sound elicits stereotyped facial movements that provide a sensitive index of hearing abilities in mice

Sound elicits rapid movements of muscles in the face, ears, and eyes that protect the body from injury and trigger brain-wide internal state changes. Here, we performed quantitative facial videography from mice resting atop a piezoelectric force plate and observed that broadband sounds elicited rapid and stereotyped facial twitches. Facial motion energy (FME) adjacent to the whisker array was 30 dB more sensitive than the acoustic startle reflex and offered greater inter-trial and inter-animal reliability than sound-evoked pupil dilations or movement of other facial and body regions. FME tracked the low-frequency envelope of broadband sounds, providing a means to study behavioral discrimination of complex auditory stimuli, such as speech phonemes in noise. Approximately 25% of layer 5-6 units in the auditory cortex (ACtx) exhibited firing rate changes during facial movements. However, FME facilitation during ACtx photoinhibition indicated that sound-evoked facial movements were mediated by a midbrain pathway and modulated by descending corticofugal input. FME and auditory brainstem response (ABR) thresholds were closely aligned after noise-induced sensorineural hearing loss, yet FME growth slopes were disproportionately steep at spared frequencies, reflecting a central plasticity that matched commensurate changes in ABR wave 4. Sound-evoked facial movements were also hypersensitive in Ptchd1 knockout mice, highlighting the use of FME for identifying sensory hyper-reactivity phenotypes after adult-onset hyperacusis and inherited deficiencies in autism risk genes. These findings present a sensitive and integrative measure of hearing while also highlighting that even low-intensity broadband sounds can elicit a complex mixture of auditory, motor, and reafferent somatosensory neural activity.

An updated review on animal models to study attention-deficit hyperactivity disorder

Attention-deficit hyperactivity disorder (ADHD) is a neuropsychiatric disorder affecting both children and adolescents. Individuals with ADHD experience heterogeneous problems, such as difficulty in attention, behavioral hyperactivity, and impulsivity. Recent studies have shown that complex genetic factors play a role in attention-deficit hyperactivity disorders. Animal models with clear hereditary traits are crucial for studying the molecular, biological, and brain circuit mechanisms underlying ADHD. Owing to their well-managed genetic origins and the relative simplicity with which the function of neuronal circuits is clearly established, models of mice can help learn the mechanisms involved in ADHD. Therefore, in this review, we highlighting the important genetic animal models that can be used to study ADHD.

Atypical co-development of the thalamus and cortex in autism: Evidence from age-related white-gray contrast change

Recent studies have shown that white-gray contrast (WGC) of either cortical or subcortical gray matter provides for accurate predictions of age in typically developing (TD) children, and that, at least for the cortex, it changes differently with age in subjects with autism spectrum disorder (ASD) compared to their TD peers. Our previous study showed different patterns of contrast change between ASD and TD in sensorimotor and association cortices. While that study was confined to the cortex, we hypothesized that subcortical structures, particularly the thalamus, were involved in the observed cortical dichotomy between lower and higher processing. The current paper investigates that hypothesis using the WGC measures from the thalamus in addition to those from the cortex. We compared age-related WGC changes in the thalamus to those in the cortex. To capture the simultaneity of this change across the two structures, we devised a metric capturing the co-development of the thalamus and cortex (CoDevTC), proportional to the magnitude of cortical and thalamic age-related WGC change. We calculated this metric for each of the subjects in a large homogeneous sample taken from the Autism Brain Imaging Data Exchange (ABIDE) (N = 434). We used structural MRI data from the largest high-quality cross-sectional sample (NYU) as well as two other large high-quality sites, GU and OHSU, all three using Siemens 3T scanners. We observed that the co-development features in ASD and TD exhibit contrasting patterns; specifically, some higher-order thalamic nuclei, such as the lateral dorsal nucleus, exhibited reduction in codevelopment with most of the cortex in ASD compared to TD. Moreover, this difference in the CoDevTC pattern correlates with a number of behavioral measures across multiple cognitive and physiological domains. The results support previous notions of altered connectivity in autism, but add more specific evidence about the heterogeneity in thalamocortical development that elucidates the mechanisms underlying the clinical features of ASD.

The mediodorsal thalamus in executive control

Executive control, the ability to organize thoughts and action plans in real time, is a defining feature of higher cognition. Classical theories have emphasized cortical contributions to this process, but recent studies have reinvigorated interest in the role of the thalamus. Although it is well established that local thalamic damage diminishes cognitive capacity, such observations have been difficult to inform functional models. Recent progress in experimental techniques is beginning to enrich our understanding of the anatomical, physiological, and computational substrates underlying thalamic engagement in executive control. In this review, we discuss this progress and particularly focus on the mediodorsal thalamus, which regulates the activity within and across frontal cortical areas. We end with a synthesis that highlights frontal thalamocortical interactions in cognitive computations and discusses its functional implications in normal and pathological conditions.

A novel role for phospholamban in the thalamic reticular nucleus

The thalamic reticular nucleus (TRN) is a brain region that influences vital neurobehavioral processes, including executive functioning and the generation of sleep rhythms. TRN dysfunction underlies hyperactivity, attention deficits, and sleep disturbances observed across various neurodevelopmental disorders. A specialized sarco-endoplasmic reticulum calcium (Ca2+) ATPase 2 (SERCA2)-dependent Ca2+ signaling network operates in the dendrites of TRN neurons to regulate their bursting activity. Phospholamban (PLN) is a prominent regulator of SERCA2 with an established role in myocardial Ca2+-cycling. Our findings suggest that the role of PLN extends beyond the cardiovascular system to impact brain function. Specifically, we found PLN to be expressed in TRN neurons of the adult mouse brain, and utilized global constitutive and innovative conditional genetic knockout mouse models in concert with electroencephalography (EEG)-based somnography and the 5-choice serial reaction time task (5-CSRTT) to investigate the role of PLN in sleep and executive functioning, two complex behaviors that map onto thalamic reticular circuits. The results of the present study indicate that perturbed PLN function in the TRN results in aberrant TRN-dependent phenotypes in mice (i.e., hyperactivity, impulsivity and sleep deficits) and support a novel role for PLN as a critical regulator of SERCA2 in the TRN neurocircuitry.

Thalamocortical organoids enable in vitro modeling of 22q11.2 microdeletion associated with neuropsychiatric disorders

Thalamic dysfunction has been implicated in multiple psychiatric disorders. We sought to study the mechanisms by which abnormalities emerge in the context of the 22q11.2 microdeletion, which confers significant genetic risk for psychiatric disorders. We investigated early stages of human thalamus development using human pluripotent stem cell-derived organoids and show that the 22q11.2 microdeletion underlies widespread transcriptional dysregulation associated with psychiatric disorders in thalamic neurons and glia, including elevated expression of FOXP2. Using an organoid co-culture model, we demonstrate that the 22q11.2 microdeletion mediates an overgrowth of thalamic axons in a FOXP2-dependent manner. Finally, we identify ROBO2 as a candidate molecular mediator of the effects of FOXP2 overexpression on thalamic axon overgrowth. Together, our study suggests that early steps in thalamic development are dysregulated in a model of genetic risk for schizophrenia and contribute to neural phenotypes in 22q11.2 deletion syndrome.

Restoring the Function of Thalamocortical Circuit Through Correcting Thalamic Kv3.2 Channelopathy Normalizes Fear Extinction Impairments in a PTSD Mouse Model

Impaired extinction of fear memory is one of the most common symptoms in post-traumatic stress disorder (PTSD), with limited therapeutic strategies due to the poor understanding of its underlying neural substrates. In this study, functional screening is performed and identified hyperactivity in the mediodorsal thalamic nucleus (MD) during fear extinction. Furthermore, the encoding patterns of the hyperactivated MD is investigated during persistent fear responses using multiple machine learning algorithms. The anterior cingulate cortex (ACC) is also identified as a functional downstream region of the MD that mediates the extinction of fear memory. The thalamocortical circuit is comprehensively analyzed and found that the MD-ACC parvalbumin interneurons circuit is preferentially enhanced in PTSD mice, disrupting the local excitatory and inhibitory balance. It is found that decreased phosphorylation of the Kv3.2 channel contributed to the hyperactivated MD, primarily to the malfunctioning thalamocortical circuit. Using a lipid nanoparticle-based RNA therapy strategy, channelopathy is corrected via a methoxylated siRNA targeting the protein phosphatase 6 catalytic subunit and restored fear memory extinction in PTSD mice. These findings highlight the function of the thalamocortical circuit in PTSD-related impaired extinction of fear memory and provide therapeutic insights into Kv3.2-targeted RNA therapy for PTSD.

Site-specific inhibition of the thalamic reticular nucleus induces distinct modulations in sleep architecture

The thalamic reticular nucleus (TRN) is crucial for the modulation of sleep-related oscillations. The caudal and rostral subpopulations of the TRN exert diverse activities, which arise from their interconnectivity with all thalamic nuclei, as well as other brain regions. Despite the recent characterization of the functional and genetic heterogeneity of the TRN, the implications of this heterogeneity for sleep regulation have not been assessed. Here, using a combination of optogenetics and electrophysiology in C57BL/6 mice, we demonstrate that caudal and rostral TRN modulations are associated with changes in cortical alpha and delta oscillations and have distinct effects on sleep stability. Tonic silencing of the rostral TRN elongates sleep episodes, while tonic silencing of the caudal TRN fragments sleep. Overall, we show evidence of distinct roles exerted by the rostral and caudal TRN in sleep regulation and oscillatory activity.

PTCHD1 gene mutation/deletion: the cognitive-behavioral phenotyping of four case reports

Introduction

X-linked PTCHD1 gene has recently been pointed as one of the most interesting candidates for involvement in neurodevelopmental disorders (NDs), such as intellectual disability (ID) and autism spectrum disorder (ASD). PTCHD1 encodes the patched domain-containing protein 1 (PTCHD1), which is mainly expressed in the developing brain and adult brain tissues. To date, major studies have focused on the biological function of the PTCHD1 gene, while the mechanisms underlying neuronal alterations and the cognitive-behavioral phenotype associated with mutations still remain unclear.

Methods

With the aim of incorporating information on the clinical profile of affected individuals and enhancing the characterization of the genotype-phenotype correlation, in this study, we analyze the clinical features of four individuals (two children and two adults) in which array-CGH detected a PTCHD1 deletion or in which panel for screening non-syndromal XLID (X-linked ID) detected a PTCHD1 gene variant. We define the neuropsychological and psychopathological profiles, providing quantitative data from standardized evaluations. The assessment consisted of clinical observations, structured interviews, and parent/self-reported questionnaires.

Results

Our descriptive analysis align with previous findings on the involvement of the PTCHD1 gene in NDs. Specifically, our patients exhibited a clinical phenotype characterized by psychomotor developmental delay- ID of varying severity. Interestingly, while ID during early childhood was associated with autistic-like symptomatology, this interrelation was no longer observed in the adult subjects. Furthermore, our cohort did not display peculiar dysmorphic features, congenital abnormalities or comorbidity with epilepsy.

Discussion

Our analysis shows that the psychopathological and behavioral comorbidities along with cognitive impairment interfere with development, therefore contributing to the severity of disability associated with PTCHD1 gene mutation. Awareness of this profile by professionals and caregivers can promote prompt diagnosis as well as early cognitive and occupational enhancement interventions.

CRISPR-Cas9-generated PTCHD1 2489T>G stem cells recapitulate patient phenotype when undergoing neural induction

An estimated 3.5%-5.9% of the global population live with rare diseases, and approximately 80% of these diseases have a genetic cause. Rare genetic diseases are difficult to diagnose, with some affected individuals experiencing diagnostic delays of 5-30 years. Next-generation sequencing has improved clinical diagnostic rates to 33%-48%. In a majority of cases, novel variants potentially causing the disease are discovered. These variants require functional validation in specialist laboratories, resulting in a diagnostic delay. In the interim, the finding is classified as a genetic variant of uncertain significance (VUS) and the affected individual remains undiagnosed. A VUS (PTCHD1 c. 2489T>G) was identified in a child with autistic behavior, global developmental delay, and hypotonia. Loss of function mutations in PTCHD1 are associated with autism spectrum disorder and intellectual disability; however, the molecular function of PTCHD1 and its role in neurodevelopmental disease is unknown. Here, we apply CRISPR gene editing and induced pluripotent stem cell (iPSC) neural disease modeling to assess the variant. During differentiation from iPSCs to neural progenitors, we detect subtle but significant gene signatures in synaptic transmission and muscle contraction pathways. Our work supports the causal link between the genetic variant and the child's phenotype, providing evidence for the variant to be considered a pathogenic variant according to the American College of Medical Genetics and Genomics guidelines. In addition, our study provides molecular data on the role of PTCHD1 in the context of other neurodevelopmental disorders.

Genetic variants in DDX53 contribute to Autism Spectrum Disorder associated with the Xp22.11 locus

Autism Spectrum Disorder (ASD) exhibits an ~4:1 male-to-female sex bias and is characterized by early-onset impairment of social/communication skills, restricted interests, and stereotyped behaviors. Disruption of the Xp22.11 locus has been associated with ASD in males. This locus includes the three-exon PTCHD1 gene, an adjacent multi-isoform long noncoding RNA (lncRNA) named PTCHD1-AS (spanning ~1Mb), and a poorly characterized single-exon RNA helicase named DDX53 that is intronic to PTCHD1-AS. While the relationship between PTCHD1/PTCHD1-AS and ASD is being studied, the role of DDX53 has not been examined, in part because there is no apparent functional murine orthologue. Through clinical testing, here, we identified 6 males and 1 female with ASD from 6 unrelated families carrying rare, predicted-damaging or loss-of-function variants in DDX53. Then, we examined databases, including the Autism Speaks MSSNG and Simons Foundation Autism Research Initiative, as well as population controls. We identified 24 additional individuals with ASD harboring rare, damaging DDX53 variations, including the same variants detected in two families from the original clinical analysis. In this extended cohort of 31 participants with ASD (28 male, 3 female), we identified 25 mostly maternally-inherited variations in DDX53, including 18 missense changes, 2 truncating variants, 2 in-frame variants, 2 deletions in the 3' UTR and 1 copy number deletion. Our findings in humans support a direct link between DDX53 and ASD, which will be important in clinical genetic testing. These same autism-related findings, coupled with the observation that a functional orthologous gene is not found in mouse, may also influence the design and interpretation of murine-modelling of ASD.

Diencephalic organoids - A key to unraveling development, connectivity, and pathology of the human diencephalon

The diencephalon, an integral component of the forebrain, governs a spectrum of crucial functions, ranging from sensory processing to emotional regulation. Yet, unraveling its unique development, intricate connectivity, and its role in neurodevelopmental disorders has long been hampered by the scarcity of human brain tissue and ethical constraints. Recent advancements in stem cell technology, particularly the emergence of brain organoids, have heralded a new era in neuroscience research. Although most brain organoid methodologies have hitherto concentrated on directing stem cells toward telencephalic fates, novel techniques now permit the generation of region-specific brain organoids that faithfully replicate precise diencephalic identities. These models mirror the complexity of the human diencephalon, providing unprecedented opportunities for investigating diencephalic development, functionality, connectivity, and pathophysiology in vitro. This review summarizes the development, function, and connectivity of diencephalic structures and touches upon developmental brain disorders linked to diencephalic abnormalities. Furthermore, it presents current diencephalic organoid models and their applications in unraveling the intricacies of diencephalic development, function, and pathology in humans. Lastly, it highlights thalamocortical assembloid models, adept at capturing human-specific aspects of thalamocortical connections, along with their relevance in neurodevelopmental disorders.

A Novel Role for Phospholamban in the Thalamic Reticular Nucleus

The thalamic reticular nucleus (TRN) is a critical brain region that greatly influences vital neurobehavioral processes, including executive functioning and the generation of sleep rhythms. Recently, TRN dysfunction was suggested to underlie hyperactivity, attention deficits, and sleep disturbances observed across various devastating neurodevelopmental disorders, including autism, schizophrenia and attention-deficit/hyperactivity disorder (ADHD). Notably, a highly specialized sarco- endoplasmic reticulum calcium (Ca 2+ ) ATPase 2 (SERCA2)-dependent Ca 2+ signaling network operates in the dendrites of TRN neurons to regulate their high-frequency bursting activity. Phospholamban (PLN) is a prominent regulator of the SERCA2 with an established role in maintaining Ca 2+ homeostasis in the heart; although the interaction of PLN with SERCA2 has been largely regarded as cardiac-specific, our findings challenge this view and suggest that the role of PLN extends beyond the cardiovascular system to impact brain function. Specifically, we found PLN to be expressed in the TRN neurons of the adult mouse brain and utilized global constitutive and innovative conditional genetic mouse models, in combination with 5-choice serial reaction time task (5-CSRTT) and electroencephalography (EEG)-based somnography to assess the role of PLN in regulating executive functioning and sleep, two complex behaviors that map onto thalamic reticular circuits. Overall, the results of the present study show that perturbed PLN function in the TRN results in aberrant thalamic reticular behavioral phenotypes in mice (i.e., hyperactivity, impulsivity and sleep deficits) and support a novel role for PLN as a critical regulator of the SERCA2 in the thalamic reticular neurocircuitry.

Neuronal transcription of autism gene PTCHD1 is regulated by a conserved downstream enhancer sequence

Patched domain-containing 1 (PTCHD1) is a well-established susceptibility gene for autism spectrum disorder (ASD) and intellectual disability (ID). Previous studies have suggested that alterations in the dosage of PTCHD1 may contribute to the etiology of both ASD and ID. However, there has not yet been a thorough investigation regarding mechanisms that regulate PTCHD1 expression. We sought to characterize the Ptchd1 promoter in a mouse neuronal model, as well as to identify and validate cis regulatory elements. We defined specific regions of the Ptchd1 promoter essential for robust expression in P19-induced neurons. Evolutionarily-conserved putative transcription factor binding sites within these regions were subsequently identified. Using a pairwise comparison of chromatin accessibility between mouse forebrain and liver tissues, a candidate regulatory region, ~ 9.1 kbp downstream of the Ptchd1 stop codon was defined. This region harbours two ENCODE-predicted enhancer cis-regulatory elements. Further, using DNase footprint analysis, a putative YY1-binding motif was also identified. Genomic deletion of the entire 8 kbp downstream open chromatin region attenuated Ptchd1 transcription by over 60% in our neuronal model, corroborating its predicted regulatory function. This study provides mechanistic insights related to the expression of PTCHD1, and provides important context to interpret genetic and genomic variation at this locus which may influence neurodevelopment.

Thalamic regulation of ocular dominance plasticity in adult visual cortex

Experience-dependent plasticity in the adult visual system is generally thought of as a cortical process. However, several recent studies have shown that perceptual learning or monocular deprivation can also induce plasticity in the adult dorsolateral geniculate nucleus (dLGN) of the thalamus. How plasticity in the thalamus and cortex interact in the adult visual system is ill-understood. To assess the influence of thalamic plasticity on plasticity in primary visual cortex (V1), we made use of our previous finding that during the critical period ocular dominance (OD) plasticity occurs in dLGN and requires thalamic synaptic inhibition. Using multielectrode recordings we find that this is also true in adult mice, and that in the absence of thalamic inhibition and plasticity, OD plasticity in adult V1 is absent. To study the influence of V1 on thalamic plasticity, we silenced V1 and show that during the critical period, but not in adulthood, the OD shift in dLGN is partially caused by feedback from V1. We conclude that during adulthood the thalamus plays an unexpectedly dominant role in experience-dependent plasticity in V1. Our findings highlight the importance of considering the thalamus as a potential source of plasticity in learning events that are typically thought of as cortical processes.

Generation of ventralized human thalamic organoids with thalamic reticular nucleus

Human brain organoids provide unique platforms for modeling several aspects of human brain development and pathology. However, current brain organoid systems mostly lack the resolution to recapitulate the development of finer brain structures with subregional identity, including functionally distinct nuclei in the thalamus. Here, we report a method for converting human embryonic stem cells (hESCs) into ventral thalamic organoids (vThOs) with transcriptionally diverse nuclei identities. Notably, single-cell RNA sequencing revealed previously unachieved thalamic patterning with a thalamic reticular nucleus (TRN) signature, a GABAergic nucleus located in the ventral thalamus. Using vThOs, we explored the functions of TRN-specific, disease-associated genes patched domain containing 1 (PTCHD1) and receptor tyrosine-protein kinase (ERBB4) during human thalamic development. Perturbations in PTCHD1 or ERBB4 impaired neuronal functions in vThOs, albeit not affecting the overall thalamic lineage development. Together, vThOs present an experimental model for understanding nuclei-specific development and pathology in the thalamus of the human brain.

Critical periods and Autism Spectrum Disorders, a role for sleep

Brain development relies on both experience and genetically defined programs. Time windows where certain brain circuits are particularly receptive to external stimuli, resulting in heightened plasticity, are referred to as "critical periods". Sleep is thought to be essential for normal brain development. Importantly, studies have shown that sleep enhances critical period plasticity and promotes experience-dependent synaptic pruning in the developing mammalian brain. Therefore, normal plasticity during critical periods depends on sleep. Problems falling and staying asleep occur at a higher rate in Autism Spectrum Disorder (ASD) relative to typical development. In this review, we explore the potential link between sleep, critical period plasticity, and ASD. First, we review the importance of critical period plasticity in typical development and the role of sleep in this process. Next, we summarize the evidence linking ASD with deficits in synaptic plasticity in rodent models of high-confidence ASD gene candidates. We then show that the high-confidence rodent models of ASD that show sleep deficits also display plasticity deficits. Given how important sleep is for critical period plasticity, it is essential to understand the connections between synaptic plasticity, sleep, and brain development in ASD. However, studies investigating sleep or plasticity during critical periods in ASD mouse models are lacking. Therefore, we highlight an urgent need to consider developmental trajectory in studies of sleep and plasticity in neurodevelopmental disorders.

GluN2D subunit-containing NMDA receptors regulate reticular thalamic neuron function and seizure susceptibility

Thalamic regulation of cortical function is important for several behavioral aspects including attention and sensorimotor control. This region has also been studied for its involvement in seizure activity. Among the NMDA receptor subunits GluN2C and GluN2D are particularly enriched in several thalamic nuclei including nucleus reticularis of the thalamus (nRT). We have previously found that GluN2C deletion does not have a strong influence on the basal excitability and burst firing characteristics of reticular thalamus neurons. Here we find that GluN2D ablation leads to reduced depolarization-induced spike frequency and reduced hyperpolarization-induced rebound burst firing in nRT neurons. Furthermore, reduced inhibitory neurotransmission was observed in the ventrobasal thalamus (VB). A model with preferential downregulation of GluN2D from parvalbumin (PV)-positive neurons was generated. Conditional deletion of GluN2D from PV neurons led to a decrease in excitability and burst firing. In addition, reduced excitability and burst firing was observed in the VB neurons together with reduced inhibitory neurotransmission. Finally, young mice with GluN2D downregulation in PV neurons showed significant resistance to pentylenetetrazol-induced seizure and differences in sensitivity to isoflurane anesthesia but were normal in other behaviors. Conditional deletion of GluN2D from PV neurons also affected expression of other GluN2 subunits and GABA receptor in the nRT. Together, these results identify a unique role of GluN2D-containing receptors in the regulation of thalamic circuitry and seizure susceptibility which is relevant to mutations in GRIN2D gene found to be associated with pediatric epilepsy.

Different Alterations of Hippocampal and Reticulo-Thalamic GABAergic Parvalbumin-Expressing Interneurons Underlie Different States of Unconsciousness

We traced the changes in GABAergic parvalbumin (PV)-expressing interneurons of the hippocampus and reticulo-thalamic nucleus (RT) as possible underlying mechanisms of the different local cortical and hippocampal electroencephalographic (EEG) microstructures during the non-rapid-eye movement (NREM) sleep compared with anesthesia-induced unconsciousness by two anesthetics with different main mechanisms of action (ketamine/diazepam versus propofol). After 3 h of recording their sleep, the rats were divided into two experimental groups: one half received ketamine/diazepam anesthesia and the other half received propofol anesthesia. We simultaneously recorded the EEG of the motor cortex and hippocampus during sleep and during 1 h of surgical anesthesia. We performed immunohistochemistry and analyzed the PV and postsynaptic density protein 95 (PSD-95) expression. PV suppression in the hippocampus and at RT underlies the global theta amplitude attenuation and hippocampal gamma augmentation that is a unique feature of ketamine-induced versus propofol-induced unconsciousness and NREM sleep. While PV suppression resulted in an increase in hippocampal PSD-95 expression, there was no imbalance between inhibition and excitation during ketamine/diazepam anesthesia compared with propofol anesthesia in RT. This increased excitation could be a consequence of a lower GABA interneuronal activity and an additional mechanism underlying the unique local EEG microstructure in the hippocampus during ketamine/diazepam anesthesia.

Top-down control of human motor thalamic neuronal activity during the auditory oddball task

The neurophysiology of selective attention in visual and auditory systems has been studied in animal models but not with single unit recordings in human. Here, we recorded neuronal activity in the ventral intermediate nucleus as well as the ventral oral anterior, and posterior nuclei of the motor thalamus in 25 patients with parkinsonian (n = 6) and non-parkinsonian tremors (n = 19) prior to insertion of deep brain stimulation electrodes while they performed an auditory oddball task. In this task, patients were requested to attend and count the randomly occurring odd or "deviant" tones, ignore the frequent standard tones and report the number of deviant tones at trial completion. The neuronal firing rate decreased compared to baseline during the oddball task. Inhibition was specific to auditory attention as incorrect counting or wrist flicking to the deviant tones did not produce such inhibition. Local field potential analysis showed beta (13-35 Hz) desynchronization in response to deviant tones. Parkinson's disease patients off medications had more beta power than the essential tremor group but less neuronal modulation of beta power to the attended tones, suggesting that dopamine modulates thalamic beta oscillations for selective attention. The current study demonstrated that ascending information to the motor thalamus can be suppressed during auditory attending tasks, providing indirect evidence for the searchlight hypothesis in humans. These results taken together implicate the ventral intermediate nucleus in non-motor cognitive functions, which has implications for the brain circuitry for attention and the pathophysiology of Parkinson's disease.

Post cardiac arrest physical exercise mitigates cell death in the septal and thalamic nuclei and ameliorates contextual fear conditioning deficits in rats

A major concern for cardiac arrest (CA) survivors is the manifestation of long-term cognitive impairments. Physical exercise (PE) is a well-established approach to improve cognitive functions under certain pathological conditions. We previously showed that PE post-CA mitigates cognitive deficits, but the underlying mechanisms remain unknown. To define neuroprotective mechanisms, we analyzed whether PE post-CA protects neurons involved in memory. We first performed a contextual fear conditioning (CFC) test to confirm that PE post-CA preserves memory in rats. We then conducted a cell-count analysis and determined the number of live cells in the hippocampus, and septal and thalamic nuclei, all areas involved in cognitive functions. Lastly, we performed RNA-seq to determine PE post-CA effect on gene expression. Following CA, exercised rats had preserved CFC memory than sham PE animals. Despite this outcome, PE post-CA did not protect hippocampal cells from dying. However, PE ameliorated cell death in septal and thalamic nuclei compared to sham PE animals, suggesting that these nuclei are crucial in mitigating cognitive decline post-CA. Interestingly, PE affected regulation of genes related to neuroinflammation, plasticity, and cell death. These findings reveal potential mechanisms whereby PE post-CA preserves cognitive functions by protecting septal and thalamic cells via gene regulation.

Sapap4 deficiency leads to postsynaptic defects and abnormal behaviors relevant to hyperkinetic neuropsychiatric disorder in mice

Postsynaptic proteins play critical roles in synaptic development, function, and plasticity. Dysfunction of postsynaptic proteins is strongly linked to neurodevelopmental and psychiatric disorders. SAP90/PSD95-associated protein 4 (SAPAP4; also known as DLGAP4) is a key component of the PSD95-SAPAP-SHANK excitatory postsynaptic scaffolding complex, which plays important roles at synapses. However, the exact function of the SAPAP4 protein in the brain is poorly understood. Here, we report that Sapap4 knockout (KO) mice have reduced spine density in the prefrontal cortex and abnormal compositions of key postsynaptic proteins in the postsynaptic density (PSD) including reduced PSD95, GluR1, and GluR2 as well as increased SHANK3. These synaptic defects are accompanied by a cluster of abnormal behaviors including hyperactivity, impulsivity, reduced despair/depression-like behavior, hypersensitivity to low dose of amphetamine, memory deficits, and decreased prepulse inhibition, which are reminiscent of mania. Furthermore, the hyperactivity of Sapap4 KO mice could be partially rescued by valproate, a mood stabilizer used for mania treatment in humans. Together, our findings provide evidence that SAPAP4 plays an important role at synapses and reinforce the view that dysfunction of the postsynaptic scaffolding protein SAPAP4 may contribute to the pathogenesis of hyperkinetic neuropsychiatric disorder.

Reversal of hyperactive higher-order thalamus attenuates defensiveness in a mouse model of PTSD

Posttraumatic stress disorder (PTSD) is a highly prevalent and debilitating psychiatric disease often accompanied by severe defensive behaviors, preventing individuals from integrating into society. However, the neural mechanisms of defensiveness in PTSD remain largely unknown. Here, we identified that the higher-order thalamus, the posteromedial complex of the thalamus (PoM), was overactivated in a mouse model of PTSD, and suppressing PoM activity alleviated excessive defensive behaviors. Moreover, we found that diminished thalamic inhibition derived from the thalamic reticular nucleus was the major cause of thalamic hyperactivity in PTSD mice. Overloaded thalamic innervation to the downstream cortical area, frontal association cortex, drove abnormal defensiveness. Overall, our study revealed that the malfunction of the higher-order thalamus mediates defensive behaviors and highlighted the thalamocortical circuit as a potential target for treating PTSD-related overreactivity symptoms.

PTCHD1 Binds Cholesterol but Not Sonic Hedgehog, Suggesting a Distinct Cellular Function

Deleterious mutations in the X-linked Patched domain-containing 1 (PTCHD1) gene may account for up to 1% of autism cases. Despite this, the PTCHD1 protein remains poorly understood. Structural similarities to Patched family proteins point to a role in sterol transport, but this hypothesis has not been verified experimentally. Additionally, PTCHD1 has been suggested to be involved in Hedgehog signalling, but thus far, the experimental results have been conflicting. To enable a variety of biochemical and structural experiments, we developed a method for expressing PTCHD1 in Spodoptera frugiperda cells, solubilising it in glycol-diosgenin, and purifying it to homogeneity. In vitro and in silico experiments show that PTCHD1 function is not interchangeable with Patched 1 (PTCH1) in canonical Hedgehog signalling, since it does not repress Smoothened in Ptch1^-/- mouse embryonic fibroblasts and does not bind Sonic Hedgehog. However, we found that PTCHD1 binds cholesterol similarly to PTCH1. Furthermore, we identified 13 PTCHD1-specific protein interactors through co-immunoprecipitation and demonstrated a link to cell stress responses and RNA stress granule formation. Thus, our results support the notion that despite structural similarities to other Patched family proteins, PTCHD1 may have a distinct cellular function.

Genetic and Epigenetic Sexual Dimorphism of Brain Cells during Aging

In recent years, much of the attention paid to theoretical and applied biomedicine, as well as neurobiology, has been drawn to various aspects of sexual dimorphism due to the differences that male and female brain cells demonstrate during aging: (a) a dimorphic pattern of response to therapy for neurodegenerative disorders, (b) different age of onset and different degrees of the prevalence of such disorders, and (c) differences in their symptomatic manifestations in men and women. The purpose of this review is to outline the genetic and epigenetic differences in brain cells during aging in males and females. As a result, we hereby show that the presence of brain aging patterns in males and females is due to a complex of factors associated with the effects of sex chromosomes, which subsequently entails a change in signal cascades in somatic cells.

Genetic and neural mechanisms of sleep disorders in children with autism spectrum disorder: a review

Background

The incidence of sleep disorders in children with autism spectrum disorder (ASD) is very high. Sleep disorders can exacerbate the development of ASD and impose a heavy burden on families and society. The pathological mechanism of sleep disorders in autism is complex, but gene mutations and neural abnormalities may be involved.

Methods

In this review, we examined literature addressing the genetic and neural mechanisms of sleep disorders in children with ASD. The databases PubMed and Scopus were searched for eligible studies published between 2013 and 2023.

Results

Prolonged awakenings of children with ASD may be caused by the following processes. Mutations in the MECP2, VGAT and SLC6A1 genes can decrease GABA inhibition on neurons in the locus coeruleus, leading to hyperactivity of noradrenergic neurons and prolonged awakenings in children with ASD. Mutations in the HRH1, HRH2, and HRH3 genes heighten the expression of histamine receptors in the posterior hypothalamus, potentially intensifying histamine's ability to promote arousal. Mutations in the KCNQ3 and PCDH10 genes cause atypical modulation of amygdala impact on orexinergic neurons, potentially causing hyperexcitability of the hypothalamic orexin system. Mutations in the AHI1, ARHGEF10, UBE3A, and SLC6A3 genes affect dopamine synthesis, catabolism, and reuptake processes, which can elevate dopamine concentrations in the midbrain. Secondly, non-rapid eye movement sleep disorder is closely related to the lack of butyric acid, iron deficiency and dysfunction of the thalamic reticular nucleus induced by PTCHD1 gene alterations. Thirdly, mutations in the HTR2A, SLC6A4, MAOA, MAOB, TPH2, VMATs, SHANK3, and CADPS2 genes induce structural and functional abnormalities of the dorsal raphe nucleus (DRN) and amygdala, which may disturb REM sleep. In addition, the decrease in melatonin levels caused by ASMT, MTNR1A, and MTNR1B gene mutations, along with functional abnormalities of basal forebrain cholinergic neurons, may lead to abnormal sleep-wake rhythm transitions.

Conclusion

Our review revealed that the functional and structural abnormalities of sleep-wake related neural circuits induced by gene mutations are strongly correlated with sleep disorders in children with ASD. Exploring the neural mechanisms of sleep disorders and the underlying genetic pathology in children with ASD is significant for further studies of therapy.

Region-selective control of the thalamic reticular nucleus via cortical layer 5 pyramidal cells

Corticothalamic pathways, responsible for the top-down control of the thalamus, have a canonical organization such that every cortical region sends output from both layer 6 (L6) and layer 5 (L5) to the thalamus. Here we demonstrate a qualitative, region-specific difference in the organization of mouse corticothalamic pathways. Specifically, L5 pyramidal cells of the frontal cortex, but not other cortical regions, establish monosynaptic connections with the inhibitory thalamic reticular nucleus (TRN). The frontal L5-TRN pathway parallels the L6-TRN projection but has distinct morphological and physiological features. The exact spike output of the L5-contacted TRN cells correlated with the level of cortical synchrony. Optogenetic perturbation of the L5-TRN connection disrupted the tight link between cortical and TRN activity. L5-driven TRN cells innervated thalamic nuclei involved in the control of frontal cortex activity. Our data show that frontal cortex functions require a highly specialized cortical control over intrathalamic inhibitory processes.

Developmental trajectories of thalamic progenitors revealed by single-cell transcriptome profiling and Shh perturbation

The thalamus is the principal information hub of the vertebrate brain, with essential roles in sensory and motor information processing, attention, and memory. The complex array of thalamic nuclei develops from a restricted pool of neural progenitors. We apply longitudinal single-cell RNA sequencing and regional abrogation of Sonic hedgehog (Shh) to map the developmental trajectories of thalamic progenitors, intermediate progenitors, and post-mitotic neurons as they coalesce into distinct thalamic nuclei. These data reveal that the complex architecture of the thalamus is established early during embryonic brain development through the coordinated action of four cell differentiation lineages derived from Shh-dependent and -independent progenitors. We systematically characterize the gene expression programs that define these thalamic lineages across time and demonstrate how their disruption upon Shh depletion causes pronounced locomotor impairment resembling infantile Parkinson's disease. These results reveal key principles of thalamic development and provide mechanistic insights into neurodevelopmental disorders resulting from thalamic dysfunction.

Mechanisms Underlying Circuit Dysfunction in Neurodevelopmental Disorders

Recent advances in genomics have revealed a wide spectrum of genetic variants associated with neurodevelopmental disorders at an unprecedented scale. An increasing number of studies have consistently identified mutations-both inherited and de novo-impacting the function of specific brain circuits. This suggests that, during brain development, alterations in distinct neural circuits, cell types, or broad regulatory pathways ultimately shaping synapses might be a dysfunctional process underlying these disorders. Here, we review findings from human studies and animal model research to provide a comprehensive description of synaptic and circuit mechanisms implicated in neurodevelopmental disorders. We discuss how specific synaptic connections might be commonly disrupted in different disorders and the alterations in cognition and behaviors emerging from imbalances in neuronal circuits. Moreover, we review new approaches that have been shown to restore or mitigate dysfunctional processes during specific critical windows of brain development. Considering the heterogeneity of neurodevelopmental disorders, we also highlight the recent progress in developing improved clinical biomarkers and strategies that will help to identify novel therapeutic compounds and opportunities for early intervention.

Ptchd1 mediates opioid tolerance via cholesterol-dependent effects on μ-opioid receptor trafficking

Repeated exposure to opioids causes tolerance, which limits their analgesic utility and contributes to overdose and abuse liability. However, the molecular mechanisms underpinning tolerance are not well understood. Here, we used a forward genetic screen in Caenorhabditis elegans for unbiased identification of genes regulating opioid tolerance which revealed a role for PTR-25/Ptchd1. We found that PTR-25/Ptchd1 controls μ-opioid receptor trafficking and that these effects were mediated by the ability of PTR-25/Ptchd1 to control membrane cholesterol content. Electrophysiological studies showed that loss of Ptchd1 in mice reduced opioid-induced desensitization of neurons in several brain regions and the peripheral nervous system. Mice and C. elegans lacking Ptchd1/PTR-25 display similarly augmented responses to opioids. Ptchd1 knockout mice fail to develop analgesic tolerance and have greatly diminished somatic withdrawal. Thus, we propose that Ptchd1 plays an evolutionarily conserved role in protecting the μ-opioid receptor against overstimulation.

Rapid Effects of Vagus Nerve Stimulation on Sensory Processing Through Activation of Neuromodulatory Systems

After sensory information is encoded into neural signals at the periphery, it is processed through multiple brain regions before perception occurs (i.e., sensory processing). Recent work has begun to tease apart how neuromodulatory systems influence sensory processing. Vagus nerve stimulation (VNS) is well-known as an effective and safe method of activating neuromodulatory systems. There is a growing body of studies confirming VNS has immediate effects on sensory processing across multiple sensory modalities. These immediate effects of VNS on sensory processing are distinct from the more well-documented method of inducing lasting neuroplastic changes to the sensory pathways through repeatedly delivering a brief VNS burst paired with a sensory stimulus. Immediate effects occur upon VNS onset, often disappear upon VNS offset, and the modulation is present for all sensory stimuli. Conversely, the neuroplastic effect of pairing sub-second bursts of VNS with a sensory stimulus alters sensory processing only after multiple pairing sessions, this alteration remains after cessation of pairing sessions, and the alteration selectively affects the response properties of neurons encoding the specific paired sensory stimulus. Here, we call attention to the immediate effects VNS has on sensory processing. This review discusses existing studies on this topic, provides an overview of the underlying neuromodulatory systems that likely play a role, and briefly explores the potential translational applications of using VNS to rapidly regulate sensory processing.

Analysing an allelic series of rare missense variants of CACNA1I in a Swedish schizophrenia cohort

CACNA1I is implicated in the susceptibility to schizophrenia by large-scale genetic association studies of single nucleotide polymorphisms. However, the channelopathy of CACNA1I in schizophrenia is unknown. CACNA1I encodes CaV3.3, a neuronal voltage-gated calcium channel that underlies a subtype of T-type current that is important for neuronal excitability in the thalamic reticular nucleus and other regions of the brain. Here, we present an extensive functional characterization of 57 naturally occurring rare and common missense variants of CACNA1I derived from a Swedish schizophrenia cohort of more than 10 000 individuals. Our analysis of this allelic series of coding CACNA1I variants revealed that reduced CaV3.3 channel current density was the dominant phenotype associated with rare CACNA1I coding alleles derived from control subjects, whereas rare CACNA1I alleles from schizophrenia patients encoded CaV3.3 channels with altered responses to voltages. CACNA1I variants associated with altered current density primarily impact the ionic channel pore and those associated with altered responses to voltage impact the voltage-sensing domain. CaV3.3 variants associated with altered voltage dependence of the CaV3.3 channel and those associated with peak current density deficits were significantly segregated across affected and unaffected groups (Fisher's exact test, P = 0.034). Our results, together with recent data from the SCHEMA (Schizophrenia Exome Sequencing Meta-Analysis) cohort, suggest that reduced CaV3.3 function may protect against schizophrenia risk in rare cases. We subsequently modelled the effect of the biophysical properties of CaV3.3 channel variants on thalamic reticular nucleus excitability and found that compared with common variants, ultrarare CaV3.3-coding variants derived from control subjects significantly decreased thalamic reticular nucleus excitability (P = 0.011). When all rare variants were analysed, there was a non-significant trend between variants that reduced thalamic reticular nucleus excitability and variants that either had no effect or increased thalamic reticular nucleus excitability across disease status. Taken together, the results of our functional analysis of an allelic series of >50 CACNA1I variants in a schizophrenia cohort reveal that loss of function of CaV3.3 is a molecular phenotype associated with reduced disease risk burden, and our approach may serve as a template strategy for channelopathies in polygenic disorders.

Cre driver mouse lines for thalamocortical circuit mapping

Subpopulations of neurons and associated neural circuits can be targeted in mice with genetic tools in a highly selective manner for visualization and manipulation. However, there are not well-defined Cre "driver" lines that target the expression of Cre recombinase to thalamocortical (TC) neurons. Here, we characterize three Cre driver lines for the nuclei of the dorsal thalamus: Oligodendrocyte transcription factor 3 (Olig3)-Cre, histidine decarboxylase (HDC)-Cre, and corticotropin-releasing hormone (CRH)-Cre. We examined the postnatal distribution of Cre expression for each of these lines with the Cre-dependent reporter CAG-tdTomato (Ai9). Cre-dependent expression of tdTomato reveals that Olig3-Cre expresses broadly within the thalamus, including TC neurons and interneurons, while HDC-Cre and CRH-Cre each have unique patterns of expression restricted to TC neurons within and across the sensory relay nuclei of the dorsal thalamus. Cre expression is present by the time of natural birth in all three lines, underscoring their utility for developmental studies. To demonstrate the utility of these Cre drivers for studying sensory TC circuitry, we targeted the expression of channelrhodopsin-2 to thalamus from the CAG-COP4*H134R/EYFP (Ai32) allele with either HDC-Cre or CRH-Cre. Optogenetic activation of TC afferents in primary visual cortex was sufficient to measure frequency-dependent depression. Thus, these Cre drivers provide selective Cre-dependent gene expression in thalamus suitable for both anatomical and functional studies.

PTCHD1: Identification and Neurodevelopmental Contributions of an Autism Spectrum Disorder and Intellectual Disability Susceptibility Gene

Over the last one and a half decades, copy number variation and whole-genome sequencing studies have illuminated the considerable genetic heterogeneity that underlies the etiologies of autism spectrum disorder (ASD) and intellectual disability (ID). These investigations support the idea that ASD may result from complex interactions between susceptibility-related genetic variants (single nucleotide variants or copy number variants) and the environment. This review outlines the identification and neurobiological characterization of two such genes located in Xp22.11, Patched domain-containing 1 (PTCHD1), and its antisense lncRNA PTCHD1-AS. Animal models of Ptchd1 disruption have recapitulated a subset of clinical symptoms related to ASD as well as to ID. Furthermore, these Ptchd1 mouse knockout studies implicate the expression of Ptchd1 in both the thalamic and the hippocampal brain regions as being crucial for proper neurodevelopment and cognitive function. Altered kynurenine metabolic signalling has been postulated as a disease mechanism in one of these animal studies. Additionally, ASD patient-derived induced pluripotent stem cells (iPSCs) carrying a copy number loss impacting the antisense non-coding RNA PTCHD1-AS have been used to generate 2D neuronal cultures. While copy number loss of PTCHD1-AS does not affect the transcription of PTCHD1, the neurons exhibit diminished miniature excitatory postsynaptic current frequency, supporting its role in ASD etiology. A more thorough understanding of risk factor genes, such as PTCHD1 and PTCHD1-AS, will help to clarify the intricate genetic and biological mechanisms that underlie ASD and ID, providing a foundation for meaningful therapeutic interventions to enhance the quality of life of individuals who experience these conditions.

Dyscoordination of non-rapid eye movement sleep oscillations in autism spectrum disorder

Study Objectives

Converging evidence from neuroimaging, sleep, and genetic studies suggest that dysregulation of thalamocortical interactions mediated by the thalamic reticular nucleus (TRN) contribute to autism spectrum disorder (ASD). Sleep spindles assay TRN function, and their coordination with cortical slow oscillations (SOs) indexes thalamocortical communication. These oscillations mediate memory consolidation during sleep. In the present study, we comprehensively characterized spindles and their coordination with SOs in relation to memory and age in children with ASD.

Methods

Nineteen children and adolescents with ASD, without intellectual disability, and 18 typically developing (TD) peers, aged 9–17, completed a home polysomnography study with testing on a spatial memory task before and after sleep. Spindles, SOs, and their coordination were characterized during stages 2 (N2) and 3 (N3) non-rapid eye movement sleep.

Results

ASD participants showed disrupted SO-spindle coordination during N2 sleep. Spindles peaked later in SO upstates and their timing was less consistent. They also showed a spindle density (#/min) deficit during N3 sleep. Both groups showed significant sleep-dependent memory consolidation, but their relations with spindle density differed. While TD participants showed the expected positive correlations, ASD participants showed the opposite.

Conclusions

The disrupted SO-spindle coordination and spindle deficit provide further evidence of abnormal thalamocortical interactions and TRN dysfunction in ASD. The inverse relations of spindle density with memory suggest a different function for spindles in ASD than TD. We propose that abnormal sleep oscillations reflect genetically mediated disruptions of TRN-dependent thalamocortical circuit development that contribute to the manifestations of ASD and are potentially treatable.

Behavioral Testing Design for Evaluation of Cognitive Disabilities

Intellectual disabilities (ID) constitute a class of human neurodevelopmental diseases and are a major medical and socioeconomic problem owing to their high incidence and enormous burden to the families of those affected. In the past three decades, mutant mouse technologies have provided powerful tools for elucidating the pathophysiological mechanisms underlying behavioral and developmental alterations related to IDs and for addressing new therapeutic strategies, and major progress has been made revealing previously unidentified genes involved in ID. However, the pathological hallmarks of IDs are very heterogeneous in regard to both the functional deficits observed and the severity of the phenotype, even within the same mutation types. For this reason, an appropriate experimental design is required to reduce the risk of false negatives and positives in animal functional genomic studies. This experimental design should address functions important to evaluate, tests, and the appropriate workflow. Here, we propose an extensive behavioral screen with detailed protocols, which was successfully used in a systematic mouse functional genomic approach to gain pathway-based insights into mechanisms leading to cognitive dysfunction in humans. © 2022 Wiley Periodicals LLC. Basic Protocol 1: Assessment of circadian activity and ingestive behavior Basic Protocol 2: Assessment of neurological reflexes and motor abilities using the grip and rotarod tests Basic Protocol 3: Evaluation of anxiety-related behavior using the elevated plus maze Basic Protocol 4: Evaluation of recognition memory using the object recognition task Basic Protocol 5: Evaluation of social behavior using the social recognition test Basic Protocol 6: Evaluation of working memory using the Y-maze spontaneous alternation test Basic Protocol 7: Evaluation of emotional learning and memory using the fear conditioning test.

Genetically encoded sensors for Chloride concentration

Insights into chloride regulation in neurons have come slowly, but they are likely to be critical for our understanding of how the brain works. The reason is that the intracellular Cl^- level ([Cl^-]_i) is the key determinant of synaptic inhibitory function, and this in turn dictates all manner of neuronal network function. The true impact on the network will only be apparent, however, if Cl^- is measured at many locations at once (multiple neurons, and also across the subcellular compartments of single neurons), which realistically, can only be achieved using imaging. The development of genetically-encoded anion biosensors (GABs) brings the additional benefit that Cl^- imaging may be done in identified cell-classes and hopefully in subcellular compartments. Here, we describe the historical background and motivation behind the development of these sensors and how they have been used so far. There are, however, still major limitations for their use, the most important being the fact that all GABs are sensitive to both pH and Cl^-. Disambiguating the two signals has proved a major challenge, but there are potential solutions; notable among these is ClopHensor, which has now been developed for in vivo measurements of both ion species. We also speculate on how these biosensors may yet be improved, and how this could advance our understanding of Cl^- regulation and its impact on brain function.

OUP accepted manuscript

Spike-and-wave discharges and an accompanying loss of consciousness are hallmarks of absence seizure, which is a childhood generalized epilepsy disorder. In absence seizure, dysfunction of the cortico-thalamo-cortico circuitry is thought to engage in abnormal cortical rhythms. Previous studies demonstrated that the thalamic reticular nucleus has a critical role in the formation of normal cortical rhythms; however, whether thalamic reticular nucleus dysfunction leads directly to abnormal rhythms, such as epilepsy, is largely unknown. We found that expressing the inhibitory opsin, archaerhodopsin, including in the thalamic reticular nucleus, caused abnormal cortical rhythms in Pvalb-tetracycline transactivator::tetO-ArchT (PV-ArchT) double transgenic mice. We validated the PV-ArchT line as a new mouse model of absence seizure through physiological and pharmacological analyses, as well as through examining their behavioural features. We then discovered that archaerhodopsin expression exclusively in thalamic reticular nucleus parvalbumin-positive neurons was sufficient to induce cortical spike-and-wave discharges using adeno-associated virus-mediated thalamic reticular nucleus targeting. Furthermore, we found that archaerhodopsin expression impaired rebound burst firing and T-current in thalamic reticular nucleus parvalbumin-positive cells by slice physiology. Although T-current in the thalamic reticular nucleus was impaired, the T-current blocker ethosuximide still had a therapeutic effect in PV-ArchT mice, suggesting a gain of function of T-type calcium channels in this absence seizure model. However, we did not find any over- or misexpression of T-type calcium channel genes in the thalamus or the cortex. Thus, we demonstrated that thalamic reticular nucleus dysfunction led to an absence seizure-like phenotype in mice. In a final set of experiments, we showed that the archaerhodopsin-mediated absence seizure-like phenotype disappeared after the removal of archaerhodopsin by using a time-controllable transgenic system. These data may provide a hint as to why many absence seizures naturally regress.

Developmental oxidative stress leads to T-type Ca2+ channel hypofunction in thalamic reticular nucleus of mouse models pertinent to schizophrenia

Impairment of parvalbumin interneurons induced by oxidative stress (OxS) is a "hub" on which converge several genetic and environmental risk factors associated with schizophrenia. In patients, this could be a mechanism leading to anomalies of the thalamic reticular nucleus (TRN) whose major neuronal population expresses parvalbumin. The TRN shapes the information flow within thalamo-cortical circuits. The low-threshold voltage-gated T-type Ca²⁺ (T-Ca²⁺) channels (CaV3.2, CaV3.3) contribute to the excitability and rhythmic bursting of TRN neurons which mediates cortical sleep spindles, known to be affected in schizophrenia. Here, we investigated the impact of OxS during postnatal development and adulthood on firing properties and T-Ca²⁺ channels of TRN neurons. In Gclm knock-out (KO) mice, which display GSH deficit and OxS in TRN, we found a reduction of T-Ca²⁺ current density in adulthood, but not at peripuberty. In KO adults, the decreased T-Ca²⁺ currents were accompanied with a decrease of CaV3.3 expression, and a shift towards more hyperpolarized membrane potentials for burst firing leading to less prominent bursting profile. In young KO mice, an early-life oxidative challenge precipitated the hypofunction of T-Ca²⁺ channels. This was prevented by a treatment with N-acetylcysteine. The concomitant presence of OxS and hypofunction of T-Ca²⁺ channels were also observed in TRN of a neurodevelopmental model relevant to psychosis (MAM mice). Collectively, these data indicate that OxS-mediated T-Ca²⁺ hypofunction in TRN begins early in life. This also points to T-Ca²⁺ channels as one target of antioxidant-based treatments aiming to mitigate abnormal thalamo-cortical communication and pathogenesis of schizophrenia.

Types of Consciousness: The Diversity Problem

Consciousness research has a cognitive-diversity problem. Any view that holds that attention is either necessary for consciousness or that attention precedes conscious awareness confronts the difficulty that the theoretical categorization of attention is as diverse as the categorization of intelligent cognition, but consciousness is typically referred to as a single and unified capacity. On the one hand, we have a multiplicity of kinds of attention. On the other hand, we use a monolithic “phenomenal” notion of consciousness to define the dependency of consciousness on all these diverse kinds of attention. Since attention is defined in terms of a diverse variety of functions, a lot more needs to be said with respect to the claim that attention is either necessary for consciousness or that attentional processing precedes conscious awareness. Is this dependency based on the diverse cognitive functions of attention? If so, why conceive of consciousness as a single informationally unified cognitive capacity? What does the multiplicity of kinds of attention entail for consciousness research? This is the “diversity problem.” This article argues that consciousness should be also considered as a diverse set of capacities, based on the diversity of attention. While we have the intuition that consciousness is a unified perspective, the article shows that consistency demands this diverse approach. Since research on attention distinguishes a wide range of functions and levels of cognitive processing, the dependency of consciousness on attention entails diverse conscious capacities and diverse types of awareness beyond the distinctions between being awake, dreaming, and being minimally conscious.