Excitatory Synapses Research Articles

The “don’t eat me” signal CD47 is associated with microglial phagocytosis defects and autism-like behaviors in 16p11.2 deletion mice

Various pathological characteristics of autism spectrum disorder (ASD) stem from abnormalities in brain resident immune cells, specifically microglia, to prune unnecessary synapses or neural connections during early development. Animal models of ASD exhibit an abundance of synapses in different brain regions, which is strongly linked to the appearance of ASD behaviors. Overexpression of CD47 on neurons acts as a "don't eat me" signal, safeguarding synapses from inappropriate pruning by microglia. Indeed, CD47 overexpression occurs in 16p11.2 deletion carriers, causing decreased synaptic phagocytosis and the manifestation of ASD characteristics. However, the role of CD47 in synaptic pruning impairment leading to ASD phenotypes in the 16p11.2 deletion mouse model is unclear. Moreover, whether blocking CD47 can alleviate ASD mice's behavioral deficits remains unknown. Here, we demonstrate a strong link between increased CD47 expression, decreased microglia phagocytosis capacity, and increased impairment in social novelty preference in the 16p11.2 deletion mice. The reduction in microglia phagocytosis caused a rise in excitatory synapses and transmission in the prefrontal cortex of 16p11.2 deletion mice. Importantly, blocking CD47 using a specific CD47 antibody or reducing CD47 expression using a specific short hairpin RNA (shRNA) enhanced the microglia phagocytosis and reduced excitatory transmission. Reduction in CD47 expression improved social novelty preference deficits in 16p11.2 mice. These findings demonstrate that CD47 is associated with the ASD phenotypes in the 16p11.2 deletion mice and could be a promising target for the development of treatment for ASD.

Hypometabolism in Autism Spectrum Disorder: Insights from Brain and Blood Transcriptomics.

Autism spectrum disorder (ASD) is a neurodevelopmental condition characterized by challenges in social communication, repetitive behaviors, and restricted interests. Recent research has emphasized the importance of metabolic dysfunctions in the pathophysiology of ASD. This study investigates metabolic alterations associated with ASD by analyzing transcriptomic data obtained from the prefrontal cortex (bulk tissue and single-nucleus) and data from peripheral blood mononuclear cells (PBMC). We assessed the metabolic activity of each patient based on gene expression profiles, revealing significant downregulation of vital metabolic pathways, including glycolysis, the tricarboxylic acid (TCA) cycle, and oxidative phosphorylation, indicative of hypometabolism. Our analysis also highlighted dysregulation in lipid, vitamin, amino acid, and heme metabolism, which may contribute to the neurodevelopmental delays associated with ASD. Cell-specific metabolic activities in the ASD brain showed altered pathways in astrocytes, oligodendrocytes, excitatory neurons, and interneurons. Furthermore, we identified critical metabolic pathways and genes from PBMC gene expression data that distinguish ASD patients from typically developing individuals. Our findings demonstrate a consistent pattern of metabolic dysfunction across brain and blood samples. This research provides a comprehensive understanding of metabolic alterations in ASD, paving the way for exploring potential therapeutic strategies targeting metabolic dysregulation.

Prefrontal cortex excitatory neurons show distinct response to heroin-associated cue and social stimulus after prolonged heroin abstinence in mice.

Substance use disorder (SUD) has been linked with social impairments. The social cognitive dysfunctions can further increase the risk of the development of SUD or relapse. Therefore, understanding the neural mechanism of substance exposure-associated social impairments is beneficial for the development of novel prevention or treatment strategies for SUD. The prefrontal cortex (PFC) is a key brain region involved in both social cognition and drug addiction. Specifically, the prelimbic part of PFC (PrL) regulates social interaction and heroin-seeking behavior. Therefore, in this study, we explored how PFC excitatory neurons respond to social stimuli after prolonged abstinence from heroin self-administration (SA). Using fiber photometry calcium imaging, we monitored calcium-dependent fluorescent signals in PrL CaMKII-expressing neurons during drug seeking and social interaction tests following 14 days of abstinence from heroin SA. We found that GCaMP6f signals in PrL CaMKII-expressing neurons were increased when heroin-associated cues were presented during drug-seeking tests in both male and female mice after prolonged heroin abstinence, although the baseline neuronal activity in home cage is lower in the heroin group. Conversely, the calcium signals in PrL CaMKII-expressing neurons during social investigation were decreased after heroin abstinence in both sexes, along with reduced total social interaction time. In addition, drug-seeking behavior is partially negatively correlated with social investigation time. These findings provide direct evidence showing that opioid exposure impairs the PFC functional response to social stimuli, which may potentially increase the risk for opioid relapse.

Three-dimensional cell culture technologies in the study of Alzheimer’s disease: a narrative review

Alzheimer’s disease has become a global public health priority, and there is currently no cure. It is characterized by memory loss and cognitive decline, with typical manifestations including amyloid plaques and neurofibrillary tangles. Unfortunately, these features often fail to replicate in conventional models. The emergence of brain organoids, three-dimensional cultures derived from induced pluripotent stem cells, provides a revolutionary approach to studying Alzheimer’s disease. Brain organoid technology is an emerging 3D cell culture method that can mimic the cellular composition and structure of the human brain. Induced pluripotent stem cells from patients can be used to create brain organoids that preserve the patient’s genetic and epigenetic traits, opening up the possibility of personalized medicine. This allows researchers to explore how genetic factors influence the pathogenesis of Alzheimer’s disease while providing an unprecedented platform for modeling the disease and exploring therapeutic exploration. Herein, we aim to highlight the potential of brain organoids in advancing Alzheimer’s disease research. Compared to traditional animal models, brain organoids offer a more accurate and ethical platform for studying Alzheimer’s disease and testing treatments. Brain organoids are generated from induced pluripotent stem cells that are reprogrammed from the patient’s somatic cells. They can differentiate into various nerve cell types, including neurons and glial cells, while retaining the patient’s genetic and epigenetic characteristics. This capability enables personalized disease modeling and drug screening. The review explores methods for generating brain organoids and discusses the direct reprogramming of somatic cells into induced neural progenitor cells and induced neurons, which can autonomously differentiate into complex brain-like structures. Despite thier potential for therapeutic applications in Alzheimer’s disease, brain organoids face challenges, including a lack of proper vascularisation and maturation. The lack of a functional blood-brain barrier in brain organoids limits their ability to mimic neurovascular interactions and the permeability of therapeutic drug. Furthermore, current strategies primarily focus on generating excitatory neurons, while the generation of interneuron phenotypes remains more challenging, posing a significant limitation for modeling complex brain circuits. Innovative solutions have been proposed to address these challenges, such as the use of rotating bioreactors to enhance oxygen and nutrient supply, as well as the integration of gene editing techniques such as CRISPR-Cas9 to correct gene mutations or enhance protective genes within organoids. In this review, we also discuss the potential of bioprinting to create defined neural pathways in organisms. This pioneering approach could revolutionize the modeling and study of neural connections in Alzheimer’s disease. In summary, the review provides an overview of current technologies and future directions for brain organoids, emphasizing the transformative impact of these technologies in Alzheimer’s disease research. This work plays a crucial role in unraveling the complexity of the disease and facilitating the development of targeted therapies.

Multimodal Correspondence Between Optogenetic fMRI, Electrophysiology, and Anatomical Maps of the Secondary Somatosensory Cortex in Nonhuman Primates.

Optogenetic neuromodulation combined with fMRI (opto-fMRI) enables noninvasive monitoring of brain-wide activity and probs causal connections. In this study, we focused on the secondary somatosensory cortex (S2), a hub for integrating tactile and nociceptive information. By selectively stimulating excitatory neurons in the S2 cortex of monkeys using optogenetics, we observed widespread opto-fMRI activity in regions beyond the somatosensory system, as well as a strong spatial correspondence between opto-fMRI activity map and anatomical connections of the S2 cortex. Locally, optogenetically evoked fMRI BOLD signals from putative excitatory neurons exhibited standard hemodynamic response function. At low laser power, graded opto-fMRI signal changes are closely correlated with increases in LFP signals, but not with spiking activity. This indicates that LFP changes in excitatory neurons more accurately reflect the opto-fMRI signals than spikes. In summary, our optogenetic fMRI and anatomical findings provide causal functional and anatomical evidence supporting the role of the S2 cortex as a critical hub connecting sensory regions to higher-order cortical and subcortical regions involved in cognition and emotion. The electrophysiological basis of the opto-fMRI signals uncovered in this study offers novel insights into interpreting opto-fMRI results. Non-human primates are an invaluable intermediate model for translating optogenetic preclinical findings to humans.Significance statement The neocortex consists of excitatory and inhibitory neurons, each playing distinct roles in cognition and contributing to brain disorders. This study marks the first to use optogenetics to selectively stimulate excitatory neurons of the primate somatosensory S2 cortex, establishing a spatial correspondence between brain-wide opto-fMRI activity and anatomical tracer-based connections in the S2 hand region. The differential relationships between laser power and changes in BOLD, local field potentials, and spiking activity suggest that LFP signals better reflect opto-fMRI signals at the excitatory neuron population level. This work has translational potential for developing targeted neuromodulation therapies for neurological and psychiatric disorders. Success in NHPs, along with advances in noninvasive AAV delivery, paves the way for future clinical applications.

An unsupervised map of excitatory neuron dendritic morphology in the mouse visual cortex

Neurons in the neocortex exhibit astonishing morphological diversity, which is critical for properly wiring neural circuits and giving neurons their functional properties. However, the organizational principles underlying this morphological diversity remain an open question. Here, we took a data-driven approach using graph-based machine learning methods to obtain a low-dimensional morphological “bar code” describing more than 30,000 excitatory neurons in mouse visual areas V1, AL, and RL that were reconstructed from the millimeter scale MICrONS serial-section electron microscopy volume. Contrary to previous classifications into discrete morphological types (m-types), our data-driven approach suggests that the morphological landscape of cortical excitatory neurons is better described as a continuum, with a few notable exceptions in layers 5 and 6. Dendritic morphologies in layers 2–3 exhibited a trend towards a decreasing width of the dendritic arbor and a smaller tuft with increasing cortical depth. Inter-area differences were most evident in layer 4, where V1 contained more atufted neurons than higher visual areas. Moreover, we discovered neurons in V1 on the border to layer 5, which avoided deeper layers with their dendrites. In summary, we suggest that excitatory neurons’ morphological diversity is better understood by considering axes of variation than using distinct m-types.

Functional connectomics spanning multiple areas of mouse visual cortex

Understanding the brain requires understanding neurons’ functional responses to the circuit architecture shaping them. Here we introduce the MICrONS functional connectomics dataset with dense calcium imaging of around 75,000 neurons in primary visual cortex (VISp) and higher visual areas (VISrl, VISal and VISlm) in an awake mouse that is viewing natural and synthetic stimuli. These data are co-registered with an electron microscopy reconstruction containing more than 200,000 cells and 0.5 billion synapses. Proofreading of a subset of neurons yielded reconstructions that include complete dendritic trees as well the local and inter-areal axonal projections that map up to thousands of cell-to-cell connections per neuron. Released as an open-access resource, this dataset includes the tools for data retrieval and analysis1,2. Accompanying studies describe its use for comprehensive characterization of cell types3, 4, 5–6, a synaptic level connectivity diagram of a cortical column4, and uncovering cell-type-specific inhibitory connectivity that can be linked to gene expression data4,7. Functionally, we identify new computational principles of how information is integrated across visual space8, characterize novel types of neuronal invariances9 and bring structure and function together to uncover a general principle for connectivity between excitatory neurons within and across areas10,11.

Functional connectomics reveals general wiring rule in mouse visual cortex

Understanding the relationship between circuit connectivity and function is crucial for uncovering how the brain computes. In mouse primary visual cortex, excitatory neurons with similar response properties are more likely to be synaptically connected1, 2, 3, 4, 5, 6, 7–8; however, broader connectivity rules remain unknown. Here we leverage the millimetre-scale MICrONS dataset to analyse synaptic connectivity and functional properties of neurons across cortical layers and areas. Our results reveal that neurons with similar response properties are preferentially connected within and across layers and areas—including feedback connections—supporting the universality of ‘like-to-like’ connectivity across the visual hierarchy. Using a validated digital twin model, we separated neuronal tuning into feature (what neurons respond to) and spatial (receptive field location) components. We found that only the feature component predicts fine-scale synaptic connections beyond what could be explained by the proximity of axons and dendrites. We also discovered a higher-order rule whereby postsynaptic neuron cohorts downstream of presynaptic cells show greater functional similarity than predicted by a pairwise like-to-like rule. Recurrent neural networks trained on a simple classification task develop connectivity patterns that mirror both pairwise and higher-order rules, with magnitudes similar to those in MICrONS data. Ablation studies in these recurrent neural networks reveal that disrupting like-to-like connections impairs performance more than disrupting random connections. These findings suggest that these connectivity principles may have a functional role in sensory processing and learning, highlighting shared principles between biological and artificial systems.

Inhibitory specificity from a connectomic census of mouse visual cortex

Mammalian cortex features a vast diversity of neuronal cell types, each with characteristic anatomical, molecular and functional properties1. Synaptic connectivity shapes how each cell type participates in the cortical circuit, but mapping connectivity rules at the resolution of distinct cell types remains difficult. Here we used millimetre-scale volumetric electron microscopy2 to investigate the connectivity of all inhibitory neurons across a densely segmented neuronal population of 1,352 cells spanning all layers of mouse visual cortex, producing a wiring diagram of inhibition with more than 70,000 synapses. Inspired by classical neuroanatomy, we classified inhibitory neurons based on targeting of dendritic compartments and developed an excitatory neuron classification based on dendritic reconstructions with whole-cell maps of synaptic input. Single-cell connectivity showed a class of disinhibitory specialist that targets basket cells. Analysis of inhibitory connectivity onto excitatory neurons found widespread specificity, with many interneurons exhibiting differential targeting of spatially intermingled subpopulations. Inhibitory targeting was organized into ‘motif groups’, diverse sets of cells that collectively target both perisomatic and dendritic compartments of the same excitatory targets. Collectively, our analysis identified new organizing principles for cortical inhibition and will serve as a foundation for linking contemporary multimodal neuronal atlases with the cortical wiring diagram.

Synaptic dysregulation in a mouse model of GRIN2D developmental and epileptic encephalopathy.

Gain-of-function (GoF) variants in the GRIN2D gene, encoding the GluN2D subunit of the N-methyl-D-aspartate receptor (NMDAR), cause a severe developmental and epileptic encephalopathy (DEE), characterized by intractable seizures, hypotonia, and neurodevelopmental delay. We generated mice carrying the GoF V664I variant, orthologous to V667I, which is present in ∼25% of GRIN2D-DEE patients. Heterozygous mutant mice demonstrate behavioral, neuroanatomical, and electrophysiological abnormalities. Lethal convulsive seizures are observed beginning at postnatal day 17. As adults, heterozygotes display abundant and prolonged runs of spike-wave discharges (SWD) that often persist for minutes. The SWD epochs consist of different populations, differentiated by frequency and association with time-locked behavioral arrest. V664I mutant neurons have enlarged presynaptic terminals and increased synaptic distance. Functional analysis reveals increased inhibitory synaptic activity without changes in NMDAR decay kinetics or presynaptic plasticity in CA1 neurons and analysis of hippocampal local field potentials show a 1.5-fold increase in evoked responses and a 1.7-fold increase in action potential generation. Notably, expression of V664I in GABAergic interneurons, but not excitatory forebrain neurons, is sufficient to recapitulate the severe electroclinical phenotype. Altogether our studies show that altered NMDAR function in inhibitory neurons plays a prominent role in DEE associated with GRIN2D gain-of-function variants and suggests that targeted genetic treatment may represent a path forward to successful therapeutic intervention.

GRAMD1B is a regulator of lipid homeostasis, autophagic flux and phosphorylated tau

Lipid dyshomeostasis and tau pathology are present in frontotemporal lobar degeneration (FTLD) and Alzheimer’s disease (AD). However, the relationship between lipid dyshomeostasis and tau pathology remains unclear. We report that GRAM Domain Containing 1B (GRAMD1B), a nonvesicular cholesterol transporter, is increased in excitatory neurons of human neural organoids (HNOs) with the MAPT R406W mutation. Human FTLD, AD cases, and PS19 tau mice also have increased GRAMD1B expression. We show that overexpression of GRAMD1B increases levels of free cholesterol, lipid droplets, and impairs autophagy flux. Modulating GRAMD1B in iPSC-derived neurons also alters key autophagy-related components such as PI3K, phospho-AKT, and p62, as well as phosphorylated tau, and CDK5R1. Blocking GRAMD1B function decreases free cholesterol and lipid droplets. Knocking down GRAMD1B additionally reduces phosphorylated tau, and CDK5R1 expression. Our findings elucidate the role of GRAMD1B in the nervous system and highlight its relevance to FTLD and AD.

Developmental overproduction of cortical superficial neurons impairs adult auditory cortical processing

While evolutionary cortical expansion is thought to underlie the evolution of human cognitive capabilities, excessive developmental expansion can lead to megalencephaly, often found in neurodevelopmental disorders. Still, little is known about how the overproduction of cortical neurons during development affects cortical processing and behavior in later life. Here we show that developmental overproduction of cortical superficial neurons impairs auditory processing in adult mice. We applied XAV939 to overproduce cortical superficial excitatory neurons during development. XAV939-treated adult mice exhibited auditory behavioral deficits and abnormal auditory cortical processing. Furthermore, we found fewer functional monosynaptic connections between cortical putative excitatory neurons. Altogether, our results suggest that abnormal auditory cortical processing contributes to the atypical auditory detectability in XAV939-treated mice. Although the expansion of cortical size is evolutionarily advantageous, an abnormal expansion during development can result in detrimental effects on cortical processing and perceptual behavior in adulthood.

Activity of spinal RORβ neurons is related to functional improvements following combination treatment after complete SCI

Various strategies targeting spinal locomotor circuitry have been associated with functional improvements after spinal cord injury (SCI). However, the neuronal populations mediating beneficial effects remain largely unknown. Using a combination therapy in a mouse model of complete SCI, we show that virally delivered brain-derived neurotrophic factor (BDNF) (AAV-BDNF) activates hindlimb stepping and causes hyperreflexia, whereas submotor threshold epidural stimulation (ES) reduces BDNF-induced hyperreflexia. Given their role in gating proprioceptive afferents and as a potential convergence point of BDNF and ES, we hypothesized that an enhanced excitability of inhibitory RORβ neurons would be associated with locomotor improvements. Ex vivo spinal slice recordings from mice with a range of locomotor and hyperreflexia scores revealed that the excitability of RORβ neurons was related to functional outcome post-SCI. Mice with poor locomotor function after SCI had less excitable RORβ neurons, but the excitability of RORβ neurons was similar between the uninjured and "best stepping" SCI groups. Further, chemogenetic activation of RORβ neurons reduced BDNF-induced hyperreflexia and improved stepping, similar to ES. Our findings identify inhibitory RORβ neurons as a target population to limit hyperreflexia and enhance locomotor function after SCI.

Cathodal weak direct current decreases epileptic excitability with reduced neuronal activity and enhanced delta oscillations.

Seizures are manifestations of hyperexcitability in the brain. Non-invasive weak current stimulation, delivered through cathodal transcranial direct current stimulation (ctDCS), has emerged to treat refractory epilepsy and seizures, although the cellular-to-populational electrophysiological mechanisms remain unclear. Using the ctDCS in vivo model, we investigate how neural excitability is modulated through weak direct currents by analysing the local field potential (LFP) and extracellular unit spike recordings before, during and after ctDCS versus sham stimulation. In rats with kainic acid (KA)-induced acute hippocampal seizures, ctDCS reduced seizure excitability by decreasing the number and amplitude of epileptic spikes in LFP and enhancing delta (δ) power. We identified unit spikes of putative excitatory neurons in CA1stratum pyramidale based on waveform sorting and validated via optogenetic inhibitions which increased aberrantly in seizure animals. Notably, cathodal stimulation significantly reduced these unit spikes, whereas anodal stimulation exhibited the opposite effect, showing polarity-specific and current strength-dependent responses. The reduced unit spikes after ctDCS coupled to δ oscillations with an increased coupling strength. These effects occurred during stimulation and lasted 90min post-stimulation, accompanied by inhibitory short-term synaptic plasticity changes shown in paired-pulse stimulation after ctDCS. Consistently, neuronal activations measured by c-Fos significantly decreased after ctDCS, particularly in CaMKII+-excitatory neurons while increased in GAD+-inhibitory neurons. In conclusion, epileptic excitability was alleviated with cathodal weak direct current stimulation by diminishing excitatory neuronal activity and enhancing endogenous δ oscillations through strengthened coupling between unit spikes and δ waves, along with inhibitory plasticity changes, highlighting the potential implications to treat brain disorders characterized by hyperexcitability. KEY POINTS: Electric fields generated by transcranial weak electric current stimulation were measured at CA1, showing polarity-specific and current strength-dependent modulation of unit spike activity. Polyspike epileptiform discharges were observed in rats with kainic acid (KA)-induced hippocampal seizures. Cathodal transcranial direct current stimulation (ctDCS) reduced the number and amplitude of the epileptic spikes in local field potentials (LFPs) while increased δ oscillations. Neuronal unit spikes aberrantly increased in seizures and coupled with epileptiform discharges. ctDCS reduced excitatory neuronal firings at CA1 and strengthened the coupling between unit spikes and δ waves. Neuronal activations, measured by c-Fos, decreased in CaMKII+-excitatory neurons while increased in GAD+-inhibitory neurons after ctDCS. These effects on LFP and unit spikes lasted up to 90min post-stimulation. Inhibitory short-term plasticity changes detected through paired-pulse stimulation underpin the enduring effects of ctDCS on seizures.

GRASPs link Reelin to the Golgi during neocortical development to control neuronal migration and dendritogenesis

Reelin serves as a crucial regulator of brain organogenesis, playing a significant role in neuronal positioning and dendritogenesis. At subcellular level, it influences the translocation and remodeling of the Golgi apparatus. Despite its importance, the mechanisms by which Reelin governs the Golgi during neuronal migration and dendrite formation remain largely unknown. This study reveals that Reelin promotes de novo translation of Golgi Re-Assembly Stacking Proteins (GRASPs), which are essential for the functions of Reelin on cortical neurons. Downregulation of GRASPs in migrating excitatory neurons of the embryonic neocortex leads to disoriented cells during the multipolar phase of migration and an aberrant leading process length during locomotion. Postnatally, it results in mislocalized neurons displaying a disorganized Golgi structure and an improperly oriented, underdeveloped apical dendrite. Our findings position GRASPs and their role in Golgi morphology modulation as novel contributors to the Reelin-mediated processes during embryonic development of the mammalian neocortex.

PrP C -induced signaling in human neurons activates phospholipase Cɣ1 and an Arc/Arg3.1 response.

Synaptic dysfunction and loss correlate with cognitive decline in neurodegenerative diseases, including Alzheimer's disease (AD) and prion disease. Neuronal hyperexcitability occurs in the early stages of AD and experimental prion disease, prior to the onset of dementia, yet the underlying drivers are unclear. Here we identify an increase in the immediate early gene, Arc/Arg3.1, in the human prion disease-affected frontal cortex, suggestive of neuronal hyperactivity. To investigate early signaling events initiated by prion aggregates (PrP Sc ) in human neurons, we stimulated PrP C in human iPSC-derived excitatory neurons (iNs) with a known PrP Sc -mimetic antibody (POM1), which recapitulated the Arc/Arg3.1 response within two hours. Proteomics, RNAseq, and a phosphokinase array in iNs revealed alterations in the EGF receptor and increased phosphorylated phospholipase C (PLC)-γ1 (Y783), which was also observed in the cerebral cortex of prion-infected mice. Thus, PrP C ligands can induce a PLC-γ1 intracellular signaling cascade together with an Arc response, suggestive of a neuronal activity response.

Seeding-competent early tau multimers are associated with cell type-specific transcriptional signatures

The initial molecular alterations of Alzheimer’s disease (AD) are unknown. Established AD is characterized by profound structural and transcriptional alterations in the human brain, with the hallmark neuropathological features being beta-amyloid (Aβ) accumulation in senile plaques and hyperphosphorylated fibrillar tau in neurofibrillary tangles (NFTs). Previous evidence indicates that tau multimerization into small aggregates is one of the earliest molecular alterations, anticipating the accumulation of hyperphosphorylated tau in NFTs. In this study, we investigated the seeding capacity of these early small tau multimers and the transcriptional changes associated with them, aiming to unveil early pathogenic processes in AD-type tau pathology. Early tau multimers visualized with tau proximity ligation assay (tau-PLA) in the post-mortem temporal cortex demonstrated high seeding activity detected by real-time quaking-induced conversion (RT-QuIC) assay and induction of aggregates in a tau biosensor cell line. Using single-nucleus transcriptomics, we showed that brain tissue harboring seeding-competent early tau multimers, but without significant NFT pathology, is associated with substantial gene expression alterations across diverse cell types when compared to control tissue lacking either multimers or NFTs. Differentially expressed genes, such as APP, MAPT, and PSEN1, exhibited significant enrichment of AD heritability in up-regulated genes within excitatory neurons, astrocytes, and oligodendrocytes. Pseudotime analysis exposed a positive correlation between the progression of tau pathology and the expression of genes marking reactive astrocytes. In summary, our results support the hypothesis that seeding-competent tau multimerization may initiate AD-type tau pathology cascades before the accumulation of tau in NFTs. This research contributes valuable insights into the early molecular events associated with AD, with implications for future diagnostic and therapeutic strategies.

The Deleterious Influence of Adolescent Alcohol Misuse on the Structural Cohesion of the Tripartite Synapse

Adolescent binge drinking impairs cognitive function in both human and animal models and increases the risk of developing an alcohol use disorder. Recent research indicates that adolescent intermittent ethanol (AIE) exposure, a rat model of binge drinking, disrupts the tripartite synapse. This is composed of a pre- and post-synaptic terminal and an ensheathing peripheral astrocyte process (PAP) that is critical in regulating synaptic function. Tripartite synapses are stabilized by several bridging proteins, e.g., neuroligin and neurexin, that are essential for maintaining synaptic health. Previously, our laboratory has shown that AIE results in a progressive loss of PAP-synaptic coupling at excitatory synapses in the hippocampus. We hypothesize that AIE disrupts the interaction between neurexin-neuroligin, driving a loss of tripartite synapse structural integrity, and subsequent PAP-synaptic decoupling. To conduct this research, Sprague Dawley rats were subjected to AIE or water intermittently over 16 days. After various washout/abstinence periods, brain samples were collected for analysis using techniques such as adeno-associated virus (AAV) to assess astrocyte morphology and immunohistochemistry, western blotting, and co-immunoprecipitation to assess changes in bridge protein expression and interactions. The primary focus was on samples collected at 26 days of washout, as previous studies have shown the most significant uncoupling at this stage. We will show how AIE disrupts PAP-synaptic coupling and how alterations in neurexin and neuroligin interactions contribute to this decoupling. Whether changes in astrocyte morphology contribute to the loss of physical interactions at the synapse remains to be determined and will be the focus of our future investigations.

Preference-independent saliency map in the mouse superior colliculus

Detecting salient stimuli in a visual scene is crucial for animal survival, yet how the brain encodes visual saliency remains unclear. Here, using two-photon calcium imaging, we reveal a preference-independent saliency map in the superficial superior colliculus of awake mice. Salient stimuli evoke stronger responses than uniform stimuli in both excitatory and inhibitory neurons, with similar encoding patterns across both cell types. The strongest response occurs when a salient stimulus is centered within the receptive field, with contextual effects extending approximately 40°. Response amplitude scales with saliency strength but remains independent of neurons’ orientation or motion direction preferences. Notably, saliency-encoding neurons exhibit weak orientation and direction selectivity, indicating a complementary relationship between saliency and feature maps. Importantly, this preference-independent saliency encoding does not require cortical inputs. These findings provide insights into the neural mechanisms underlying visual saliency detection.

Contrasting patterns of extrasynaptic NMDAR-GluN2B expression in macaque subgenual cingulate and dorsolateral prefrontal cortices

Expression of the N-methyl-D-aspartate receptor, particularly when containing the GluN2B subunit (NMDAR-GluN2B), varies across the prefrontal cortex (PFC). In humans, the subgenual cingulate cortex (SGC) contains among the highest levels of NMDAR-GluN2B expression, while the dorsolateral prefrontal cortex (dlPFC) exhibits a more moderate level of NMDAR-GluN2B expression. NMDAR-GluN2B are commonly associated with ionotropic synaptic function and plasticity and are essential to the neurotransmission underlying working memory in the macaque dlPFC in the layer III circuits, which in humans are afflicted in schizophrenia. However, NMDAR-GluN2B can also be found at extrasynaptic sites, where they may trigger distinct events, including some linked to neurodegenerative processes. The SGC is an early site of tau pathology in sporadic Alzheimer’s disease (sAD), which mirrors its high NMDAR-GluN2B expression. Additionally, the SGC is hyperactive in depression, which can be treated with NMDAR antagonists. Given the clinical relevance of NMDAR in the SGC and dlPFC, the current study used immunoelectron microscopy (immunoEM) to quantitatively compare the synaptic and extrasynaptic expression patterns of NMDAR-GluN2B across excitatory and inhibitory neuron dendrites in rhesus macaque layer III SGC and dlPFC. We found a larger population of extrasynaptic NMDAR-GluN2B in dendrites of putative pyramidal neurons in SGC as compared to the dlPFC, while the dlPFC had a higher proportion of synaptic NMDAR-GluN2B. In contrast, in putative inhibitory dendrites from both areas, extrasynaptic expression of NMDAR-GluN2B was far more frequently observed over synaptic expression. These findings may provide insight into varying cortical vulnerability to alterations in excitability and neurodegenerative forces.