bioRxiv Subject Collection: Neuroscience's Journal

Targeting and anchoring the mechanosensitive ion channel Piezo to facilitate its inhibition of axon regeneration
Mechanical force orchestrates a myriad of cellular events including inhibition of axon regeneration, by locally activating the mechanosensitive ion channel Piezo enriched at the injured axon tip. However, the cellular mechanics underlying Piezo localization and function remains poorly characterized. We show that the RNA repair/splicing enzyme Rtca acts upstream of Piezo to modulate its expression and transport/targeting to the plasma membrane via Rab10 GTPase, whose expression also relies on Rtca. Loss or gain of function of Rab10 promotes or impedes Drosophila sensory neuron axon regeneration, respectively. Rab10 mediates the cell surface expression of integrin beta1 (Itgb1)/mys, which colocalizes and genetically interacts with Piezo, facilitating its anchorage and engagement with the microenvironment, and subsequent activation of mechanotransduction to inhibit regeneration. Importantly, loss of Rtca, Rab10 or Itgb1 promotes CNS axon regeneration after spinal cord injury or optic nerve crush in adult mice, indicating the evolutionary conservation of the machinery.

Random connectivity generates inhibitory microcircuits that decorrelate adaptation in visual cortex
Inhibitory neurons are fundamental to sensory processing in the cortex but the rules governing their connections with excitatory neurons are unclear. Are pyramidal cells with different functions generated through specific or random connections? We used two-photon imaging, optogenetics and modelling to investigate opposing forms of adaptation in layer 2/3 of mouse visual cortex. We find that a slow modulatory drive acts differentially depending on the relative strength of inputs that individual pyramidal cells receive from parvalbumin-positive and somatostatin-positive interneurons. The number of depressing and sensitizing pyramidal cells could be explained quantitatively by the simplest connectivity rule in which all inhbitory synapses are made randomly. The functional heterogeneity of the pyramidal cell population therefore begins with general statistics of the connectome - interneurons are much sparser and connect with probabilities far less than one. The resulting patchwork of inhibitory microcircuits causes modulatory inputs to strongly decorrelate pyramidal cells on the behavioural time-scale of seconds.

Missing what is right under your nose: failed appetitive and aversive audio-olfactory conditioning in humans
The comparison of physiological mechanisms underlying appetitive and aversive conditioning is often challenging due to the involvement of stimuli from different modalities with potentially disparate effective mechanisms (e.g., pain stimuli versus monetary rewards). The olfactory system offers a unique opportunity to examine both types of conditioning in humans, as isointense odors can serve as comparably pleasant and unpleasant stimuli. To study physiological and behavioral responses during appetitive and aversive learning, we employed odors as unconditioned stimuli (US) in a within-subjects design, measuring various conditioned physiological responses including skin conductance, heart rate, pulse wave amplitude, respiration, fear-potentiated startle, postauricular reflex, facial electromyography as well as event-related potentials, and auditory steady-state responses (ASSR) derived from electroencephalography. We conducted four experiments with a total of 95 participants, presenting three neutral sounds paired with either a pleasant odor, unpleasant odor, or odorless air. The first experiment involved uninstructed participants and frequency-modulated conditioned stimuli (CS) for ASSR analysis. In the second experiment, we omitted the frequency modulation and startle probe. The third experiment included pre-experiment instruction on CS-US contingencies, while the fourth employed a delayed conditioning paradigm in contrast to the other three experiments. Our results revealed differences between CS+ and CS- only in the fear-potentiated startle response in Experiment 3. No other effects were found. The minimal or absent learning effects observed across multiple peripheral and neural physiological measures may be attributed to the extra-thalamic nature of olfactory pathways and the subsequent difficulty in forming associations with auditory stimuli.

Image Processing in the Acute to Chronic Pain Signatures (A2CPS) Project
The Acute to Chronic Pain Signatures (A2CPS) project is a large-scale, multi-site initiative aimed at identifying biomarkers and biosignatures that predict the transition from acute to chronic pain. The project is collecting multimodal, longitudinal data from over 2,500 individuals at risk for developing chronic pain after surgery. Here we describe the neuroimaging component of A2CPS, including the acquisition protocols, processing pipelines, and contents of the initial data release. The imaging protocol includes structural, diffusion, resting-state and task-based functional magnetic resonance imaging (MRI) data. Data are collected across multiple clinical sites using different scanner manufacturers, with attention to protocol harmonization and quality control. The processing pipeline integrates several established neuroimaging tools to extract potential biomarkers, including measures of brain structure, connectivity, and pain-related neural signatures. The first data release includes pre-surgical imaging data for 595 participants, with high quality ratings across modalities (98.7% of sMRI, 99.8% of dMRI, and 94.6% of fMRI images were rated as acceptable or better). Initial analyses demonstrate expected relationships between brain-derived measures and clinical variables, such as associations between brain age and psychological factors. This dataset represents a valuable resource for both pain research and neuroimaging methods development, with future releases planned to include additional participants and expanded analysis pipelines and processed data derivatives.

Induction of hemodynamic traveling waves by glial-related vasomotion in a rat model of neuroinflammation: implications for functional neuroimaging
Cerebral hemodynamics are crucial for brain homeostasis and serve as a key proxy for brain activity. Although this process involves coordinated interaction between vessels, neurons and glial cells, its dysregulation in neuroinflammation is not well understood. We used in vivo mesoscopic functional ultrasound imaging to monitor cerebral blood volume changes during neuroinflammation in rats injected with lipopolysaccharide (LPS) in the visual cortex, under resting-state or visual stimulation, combined to advanced ex vivo techniques for glial cell reactivity analysis. Cortical neuroinflammation induced large oscillatory hemodynamic traveling waves in the frequency band of vasomotion (~0.1 Hz) in both anesthetized and awake rats. Vasomotor waves traveled through large distances between adjacent penetrating vessels, spanning the entire cortex thickness, and even extending to subcortical areas. Moreover, vasomotion amplitude correlated with microglial morphology changes and was significantly reduced by astrocytic toxins, suggesting that both microglia and astrocytes are involved in the enhancement of vasomotion during neuroinflammation. Notably, functional connectivity was increased under this oscillatory state and functional hyperemia was exacerbated. These findings reveal new spatiotemporal properties and cellular mechanisms of cerebral vasomotion, and suggest that this is a major component of brain hemodynamics in pathological states. Moreover, reactive microglia and astrocytes are participating to increased vasomotion during neuroinflammation. These results call for a reassessment of vasomotion and traveling waves as primary phenomena when imaging brain hemodynamic activity, particularly in conditions associated with neuroinflammation.

Cross validation coordinate meta-analysis: contrast analysis
Coordinate based meta-analysis (CBMA) can be used to estimate where a future neuroimaging study testing a particular hypothesis might report summary results (activation foci, for example). However, current methods cannot be validated for all possible analyses because of empirical features that might not be appropriate. Furthermore, the use of voxel-wise null hypothesis significance testing (NHST) in the algorithms is not in keeping with meta-analysis, where statistical significance is secondary to the primary aim of effect estimation. Cross-validation coordinate analysis (CVCA) has been described, which can eliminate the need for the empirical use of spatial uncertainty and avoid voxel-wise p values. The result is an estimated effect that is not based on voxel-wise statistical significance, and which allows the uncertainty to reduce with larger numbers of studies as expected. Here an additional function of CVCA is detailed, which uses cross-validation to contrast two different meta-analyses produced using two sets of studies (A & B) to identify differences. Such contrast analysis is common in CBMA. The results are a contrast image with regions that differentiate studies A from studies B. Software to perform CVCA is freely available.

Distinct representational properties of cues and contexts shape fear learning and extinction
Extinction learning does not erase previously established memories but inhibits the expression of fear by the formation of new memory traces that are strongly context-dependent. Previous human neuroimaging studies using representational similarity analysis revealed several core properties of memory traces during fear learning, including their tendency to generalize beyond the initial context - a process described as cue generalization - and their reliance on sensory rather than conceptual representational formats. How fear memories are altered during extinction learning, however, remains largely unknown. To address this question, we used a novel experimental paradigm involving multiple cues and contexts in each experimental phase, which allowed us to disentangle the effect of contingency changes (i.e., reversal learning) from the disappearance of unconditioned stimuli during extinction learning. Our data show that contingency changes during reversal induce memory traces with distinct representational geometries characterized by stable activity patterns across repetitions in the precuneus, which interact with specific context representations in medial and lateral prefrontal cortex. The representational geometries of these traces differ strikingly from the generalized patterns established during initial fear learning and persist in the absence of an unconditioned stimulus during extinction. Interestingly, increased levels of prefrontal context specificity predict the subsequent reinstatement of fear memory traces, providing a possible mechanistic explanation for the clinical phenomenon of fear renewal. Our findings show that contingency changes induce novel memory traces with distinct representational properties that are reminiscent to those observed during episodic memory formation and contrast with the generalized representations of initial fear memories. These results shed new light on the neural mechanisms underlying the malleability of memories that support cognitive flexibility, and contribute to conceptual frameworks of extinction learning during the treatment of anxiety disorders.

The Aging Synapse: An Integrated Proteomic And Transcriptomic Analysis
An important hallmark of aging is the loss of proteostasis, which can lead to the formation of protein aggregates and mitochondrial dysfunction in neurons. Although it is well known that protein synthesis is finely regulated in the brain, especially at synapses, where mRNAs are locally translated in activity-dependent manner, little is known as to the changes in the synaptic proteome and transcriptome during aging. Therefore, this work aims to elucidate the relationship between transcriptome and proteome at soma and synaptic level during aging. Proteomic and transcriptomic data analysis reveal that, in young animals, proteins and transcripts are correlated and synaptic regulation is driven by changes in the soma. During aging, there is a decoupling between transcripts and proteins and between somatic and synaptic compartments. Furthermore, soma-synapse gradient of ribosomal genes changes upon aging, i.e. ribosomal transcripts are less abundant and ribosomal proteins are more abundant in synaptic compartment of old mice with respect to younglings. Additionally, transcriptomics data highlight a difference in the splicing of certain synaptic mRNA with aging. Taken together, our data provide a valuable resource for the study of the aging synapse.

Syngap1 and the development of murine neocortical progenitor cells
SYNGAP1 is a major regulator of synaptic plasticity through its interaction with synaptic scaffold proteins and modulation of Ras and Rap GTPase signaling pathways. SYNGAP1 mutations in humans are often associated with intellectual disability, epilepsy, and autism spectrum disorder. Syngap1 heterozygous loss-of-function results in impaired LTP, premature maturation of dendritic spines, learning disabilities and seizures in mice. More recently, SYNGAP1 was shown to influence cortical neurogenesis and the proliferation of progenitors in human organoids. Here, we show that the absence or haploinsufficiency of Syngap1 does not influence the properties of neocortical progenitors and their cellular output in mice. This discrepancy highlights potential species-specific or methodological differences and raises important questions about the broader applicability of SYNGAP1s role in neurogenesis.

Predicting Future Development of Stress-Induced Anhedonia From Cortical Dynamics and Facial Expression
The current state of mental health treatment for individuals diagnosed with major depressive disorder leaves billions of individuals with first-line therapies that are ineffective or burdened with undesirable side effects. One major obstacle is that distinct pathologies may currently be diagnosed as the same disease and prescribed the same treatments. The key to developing antidepressants with ubiquitous efficacy is to first identify a strategy to differentiate between heterogeneous conditions. Major depression is characterized by hallmark features such as anhedonia and a loss of motivation, and it has been recognized that even among inbred mice raised under identical housing conditions, we observe heterogeneity in their susceptibility and resilience to stress. Anhedonia, a condition identified in multiple neuropsychiatric disorders, is described as the inability to experience pleasure and is linked to anomalous medial prefrontal cortex (mPFC) activity. The mPFC is responsible for higher order functions, such as valence encoding; however, it remains unknown how mPFC valence-specific neuronal population activity is affected during anhedonic conditions. To test this, we implemented the unpredictable chronic mild stress (CMS) protocol in mice and examined hedonic behaviors following stress and ketamine treatment. We used unsupervised clustering to delineate individual variability in hedonic behavior in response to stress. We then performed in vivo 2-photon calcium imaging to longitudinally track mPFC valence-specific neuronal population dynamics during a Pavlovian discrimination task. Chronic mild stress mice exhibited a blunted effect in the ratio of mPFC neural population responses to rewards relative to punishments after stress that rebounds following ketamine treatment. Also, a linear classifier revealed that we can decode susceptibility to chronic mild stress based on mPFC valence-encoding properties prior to stress-exposure and behavioral expression of susceptibility. Lastly, we utilized markerless pose tracking computer vision tools to predict whether a mouse would become resilient or susceptible based on facial expressions during a Pavlovian discrimination task. These results indicate that mPFC valence encoding properties and behavior are predictive of anhedonic states. Altogether, these experiments point to the need for increased granularity in the measurement of both behavior and neural activity, as these factors can predict the predisposition to stress-induced anhedonia.

Host and rabies virus gene expression is shaped by human brain cell type and reveals a preexisting pro-viral transcriptional state in astrocytes
Rabies virus (RABV) proteins play dual roles during the infection of complex neural tissue, the generation and spread of new virions and the active inhibition of cellular innate immune pathways, both contributing to rabies lethality. While spatially-distinct RABV protein residues specializing in virus-centric and immune-inhibitory functions have been identified, how these dual functions interact to shape infection outcomes across diverse types of host brain cells is unknown. To 'unmask' and study how innate immune inhibition affects the transcriptional regulation of the human and viral genome with cellular resolution, we performed single-cell RNA sequencing of co-cultured human brain cell types, comparing infection dynamics of a wild-type RABV isolate virus to a mutant virus in which six critical point mutations in the phosphoprotein (P) and matrix (M) RABV proteins selectively neuter antagonism of interferon- and NF-kB- dependent cellular responses. Our analysis reveals that RABV gene expression is shaped by host cell type and that wild-type RABV infection induces small-scale, cell-type conserved transcriptional programs that may support infection by hijacking transcriptional feedback systems that control pro-viral host cell factors while minimizing anti-viral responses. In contrast to accepted models, disinhibited innate immune signaling increases RABV transcriptional output across infected cell types. Most strikingly, we discovered a subpopulation of astrocytes that supports an average of 6-fold higher viral mRNA expression through a massive host cell transcriptional change involving ~38% of astrocyte expressed genes. Our analysis suggests that these astrocytes we term 'pro-viral' are a rare subtype present in the human brain and are primed to play a protective role during viral infection in concert with interferon-sensitive microglia recalcitrant to infection.

C1q and immunoglobulins mediate activity-dependent synapse loss in the adult brain
C1q, the initiating protein of the classical complement cascade, mediates synapse loss in development and disease. In various mouse models of neurologic diseases, including Alzheimer's disease, C1q, which is secreted by microglia, the brain's resident macrophages, is found deposited on synapses in vulnerable brain regions. However, what underlies C1q deposition on synapses in the adult brain is unclear. Using in vivo chemogenetics, we demonstrate that neuronal hyperactivity acts as a trigger for region-specific deposition of C1q, which is required for activity-dependent synapse loss. Further, using spatial transcriptomics, live cell tracking, super-resolution microscopy and other molecular and cellular tools, we report a role for B lymphocyte lineage cells and immunoglobulins in the activity-dependent C1q deposition and synapse loss. Overall, our work suggests a link between neuronal hyperactivity and C1q-mediated synapse loss in the adult brain and introduces immunoglobulins as players in this process.

Autoimmune mechanisms elucidated through muscle acetylcholine receptor structures
Skeletal muscle contraction is mediated by acetylcholine (ACh) binding to its ionotropic receptors (AChRs) at neuromuscular junctions. In myasthenia gravis (MG), autoantibodies target AChRs, disrupting neurotransmission and causing muscle weakness. Despite available treatments, patient responses vary, suggesting pathogenic heterogeneity. Current information on molecular mechanisms of autoantibodies is limited due to the absence of structures of an intact human muscle AChR. Here, we overcome challenges in receptor purification and present high-resolution cryo-EM structures of the human adult AChR in different functional states. Using a panel of six MG patient-derived monoclonal antibodies, we mapped distinct epitopes involved in diverse pathogenic mechanisms, including receptor blockade, internalization, and complement activation. Electrophysiological and binding assays further defined how these autoantibodies impair AChR function. These findings provide critical insights into MG immunopathology, revealing previously unrecognized antibody epitope diversity and mechanisms of receptor inhibition, offering a foundation for personalized therapies targeting antibody-mediated autoimmune disorders.

Segregated localization of target-SNARE proteins within presynaptic terminals of Munc18-1 deficient photoreceptors
Sec1/Munc18 family proteins are essential for SNARE-mediated vesicular exocytosis. However, where SNARE proteins are localized in Munc18-1 deficient presynaptic terminals remains unclear due to the rapid degeneration of neurons lacking Munc18-1. Here, we found that removing Munc18-1 from photoreceptor cells did not result in major cellular loss until postnatal day 14, which allowed us to investigate the role of Munc18-1 in endogenous presynaptic terminals. In the absence of Munc18-1, even before major photoreceptor cell degeneration, functional impairments were present. While Munc18-1 was not required for the pre-synaptic enrichment of the t-SNARE proteins syntaxin-3 and SNAP-25, it played a critical role in their proper localization. In wild-type conditions, t-SNAREs are highly colocalized. However, in the absence of Munc18-1, their distribution becomes strikingly segregated. Immuno-electron microscopy revealed that without Munc18-1, syntaxin-3 is retained within various organelle membranes rather than being targeted to synaptic plasma membranes. These findings provide the first evidence that Munc18-1 is important to prevent segregation of syntaxin-3 and SNAP-25 within presynaptic terminals.

Common and distinct neural correlates of social interaction perception and theory of mind
Social cognition spans from perceiving agents and their interactions to making inferences based on theory of mind (ToM). Despite their frequent co-occurrence in real life, the commonality and distinction between social interaction perception and ToM at behavioral and neural levels remain unclear. Here, participants (N = 231) provided moment-by-moment ratings of four text and four audio narratives on social interactions and ToM engagement. Social interaction and ToM ratings were reliable (split-half r = .98 and .92, respectively) but only modestly correlated across time (r = .32). In a second sample (N = 90), we analyzed co-variation between normative social interaction and ToM ratings and functional magnetic resonance (fMRI) activity during narrative reading (text) and listening (audio). Social interaction perception and ToM activity maps generalized across text and audio presentation (r = .83 and .57 between unthresholded t maps, respectively). When ToM was held constant, merely perceiving social interactions activated all regions canonically associated with ToM under both modalities (FDR q < .01), including temporoparietal junction, superior temporal sulcus, medial prefrontal cortex, and precuneus. ToM activated these regions as well, indicating a shared, modality-general system for social interaction perception and ToM. Furthermore, ToM uniquely engaged lateral occipitotemporal cortex, left anterior intraparietal sulcus, and right premotor cortex. These results imply that perceiving social interactions automatically engages regions implicated in mental state inferences. In addition, ToM is distinct from social interaction perception in its recruitment of regions associated with higher-level cognitive processes, including action understanding and executive functions.

Single Cell RNAseq to identify subpopulations of glial progenitors in iPSC-derived oligodendroglial lineage cultures
Cellular heterogeneity is a common issue in differentiation protocols of oligodendrocytes (OLs) from human induced pluripotent stem cells. Our previous work described a novel method to generate OLs and highlighted the presence of glial progenitors. Here, we unravel the glial heterogeneity and characterize the response of isolated subpopulations to differentiation. This study provides a novel tool for studying the dynamics of glial development in vitro and on a transcriptomic level.

Neural bidomain model for multidimensional ephaptic coupling of neural spike propagation along myelinated fiber bundles with the nodes of Ranvier
A novel mathematical model is proposed to investigate the effects of ephaptic coupling between general neural fiber bundles in a multidimensional space with anisotropic neural fiber bundles. Ephaptic coupling corresponds to the spatiotemporal interaction between propagating fiber bundles through the extracellular space. Adapted from a well-known model in cardiac electrophysiology, the bidomain model comprises of the nonoverlapping intracellular and extracellular space except the common nodes of Ranvier. The proposed two-variable model, a neural bidomain model, is derived from the classic Frankenhaeuser-Huxley model for neural spike propagation along the general neural fiber bundles. The governing equation is mathematically and computationally validated against existing one-dimensional models of neural fiber bundle propagations with aligned nodes of Ranvier. A high-order continuous Galerkin scheme is employed for efficient two-dimensional computational simulation with moving frames, or orthonormal basis vectors, representing the intracellular and extracellular conductivity and nonoverlapping domains. The proposed model is simulated in various two-dimensional configurations of neural fiber bundles that are little known to the community, such as fiber bundles with misaligned nodes of Ranvier, opposite-traveling fiber bundles, and curved fiber bundles.

Premotor cortex hemodynamics reflect internal auditory category, not reported category
In sensory decision making tasks, animals' decisions are driven by perception, but also by non-perceptual factors. Because of external and internal noise, stimuli may be internally misclassified, leading to perceptual errors. But other, non-sensory factors such as impulsivity or exploratory behavior can lead to non-perceptual errors. Here we exploited the neural traces of these errors in frontal cortex to provide insights into their role in sensory decision making. Using functional ultrasound imaging (fUS), we investigated how the premotor cortex (PMC) in ferrets represents stimuli in a categorization task, varying the difficulty in order to manipulate the rates of perceptual errors. We found that PMC activity reflects the objective (and not the chosen) stimulus category on incorrect Easy trials, when non-perceptual errors are more likely. In contrast, PMC responses correlate with the chosen category (and not objective category) on incorrect Difficult trials, when perceptual errors are more likely. These results suggest that PMC encodes the ferret's perceptual decision but not necessarily the final motor decision. Perceptual errors could be refined further by assessing licking patterns, but licking patterns alone did not explain the effect. This study advances our understanding of the functional role of the frontal cortex in decision making, suggesting that the PMC integrates sensory inputs to guide behavior based on perceptual, rather than motivational, information.

Voice identity invariance by anterior temporal lobe neurons
The ability to recognize speakers by their voice despite acoustical variation plays a significant role in primate social interactions. While neurons in the macaque anterior temporal lobe (ATL) show invariance to face viewpoint, whether they also encode abstract representations of caller identity is not known. Here we show that neurons in the voice-selective ATL of two macaques show invariance to voice identity via dynamic representations that minimize within-caller neuronal distances while maintaining distinct neural trajectories for different individuals. A small proportion of highly identity-selective neurons plays a central role although less selective neurons are also informative. Our findings provide a neural basis for voice identity recognition in primates and highlight the ATL as a key hub for integrating perceptual voice features into higher-level identity representations.

Local Gradients of Functional Connectivity Enable Precise Fingerprinting of Infant Brains During Dynamic Development
Brain functional connectivity patterns exhibit distinctive, individualized characteristics capable of distinguishing one individual from others, like fingerprint. Accurate and reliable depiction of individualized functional connectivity patterns during infancy is crucial for advancing our understanding of individual uniqueness and variability of the intrinsic functional architecture during dynamic early brain development, as well as its role in neurodevelopmental disorders. However, the highly dynamic and rapidly developing nature of the infant brain presents significant challenges in capturing robust and stable functional fingerprint, resulting in low accuracy in individual identification over ages during infancy using functional connectivity. Conventional methods rely on brain parcellations for computing inter-regional functional connections, which are sensitive to the chosen parcellation scheme and completely ignore important fine-grained, spatially detailed patterns in functional connectivity that encodes developmentally-invariant, subject-specific features critical for functional fingerprinting. To solve these issues, for the first time, we propose a novel method to leverage the high-resolution, vertex-level local gradient map of functional connectivity from resting-state functional MRI, which captures sharp changes and subject-specific rich information of functional connectivity patterns, to explore infant functional fingerprint. Leveraging a longitudinal dataset comprising 591 high-resolution resting-state functional MRI scans from 103 infants, our method demonstrates superior performance in infant individual identification across ages. Our method has unprecedentedly achieved 99% individual identification rates across three age-varied sub-datasets, with consistent and robust identification rates across different phase encoding directions, significantly outperforming atlas-based approaches with only around 70% accuracy. Further vertex-wise uniqueness and differential power analyses highlighted the discriminative identifiability of higher-order functional networks. Additionally, the local gradient-based functional fingerprints demonstrated reliable predictive capabilities for cognitive performance during infancy. These findings suggest the existence of unique individualized functional fingerprints during infancy and underscore the potential of local gradients of functional connectivity in capturing neurobiologically meaningful and fine-grained features of individualized characteristics for advancing normal and abnormal early brain development.

Glucocorticoids target postnatal oligodendrocyte precursor cells to modulate adult hippocampal network plasticity and stress-induced behavior
Early life events shape neuronal networks, and prime juvenile and adult behavior. Severely aversive, early experiences can interfere with brain development and enhance the risk for the onset of psychiatric illnesses. Recent evidence has implicated oligodendrocyte precursor cells (OPCs) in the pathophysiology of stress-related mental disorders. Historically classified as precursors of myelinating oligodendrocytes, OPCs are now known to fine-tune neuronal activity and modify their proliferation-maturation dynamics in response to environmental challenges. However, the underlying mechanisms are still elusive. OPCs express the glucocorticoid receptor (GR) for glucocorticoids (GCs), mediating the response to aversive challenges. To decipher the role of early postnatal GCs on OPCs proliferation-maturation dynamics, behavior and neuronal network activity in adulthood, we conditionally deleted GR in postnatal OPCs. Such deletion led to hippocampus-specific reduction of oligodendrocytes, sex-specific alteration of hippocampal activity and impairment in the formation of non-aversive and aversive memories in adulthood. Our findings disclosed a novel OPC-specific role for GRs, establishing the importance of postnatal GCs for modulating OPC maturation, fine-tuning the excitability of neuronal networks in response to a challenge and in adult memory formation. This provides the first evidence for a new dual role of GR-signaling in both the canonical and non-canonical functions of OPCs.

Differential roles of NaV1.2 and NaV1.6 in neocortical pyramidal cell excitability
Mature neocortical pyramidal cells functionally express two sodium channel (NaV) isoforms: NaV1.2 and NaV1.6. These isoforms are differentially localized to pyramidal cell compartments, and as such are thought to contribute to different aspects of neuronal excitability. But determining their precise roles in pyramidal cell excitability has been hampered by a lack of tools that allow for selective, acute block of each isoform individually. Here, we leveraged aryl sulfonamide-based molecule (ASC) inhibitors of NaV channels that exhibit state-dependent block of both NaV1.2 and NaV1.6, along with knockin mice with changes in NaV1.2 or NaV1.6 structure that prevents ASC binding. This allowed for acute, potent, and reversible block of individual isoforms that permitted dissection of the unique contributions of NaV1.2 and NaV1.6 in pyramidal cell excitability. Remarkably, block of each isoform had contrasting--and in some situations, opposing--effects on neuronal action potential output, with NaV1.6 block decreasing and NaV1.2 block increasing output. Thus, NaV isoforms have unique roles in regulating different aspects of pyramidal cell excitability, and our work may help guide development of therapeutics designed to temper hyperexcitability through selective NaV isoform blockade.

Comprehensive Analysis of Human Dendritic Spine Morphology and Density: Exploring Diversity of Human Dendritic Spines
Dendritic spines, small protrusions on neuronal dendrites, play a crucial role in brain function by changing shape and size in response to neural activity. So far, in depth analysis of dendritic spines in human brain tissue is lacking. This study presents a comprehensive analysis of human dendritic spine morphology and density using a unique dataset from human brain tissue from 27 patients (8 females, 19 males, aged 18-71) undergoing tumor or epilepsy surgery at three neurosurgery sites. We used acute slices and organotypic brain slice cultures to examine dendritic spines, classifying them into the three main morphological subtypes: Mushroom, Thin, and Stubby, via 3D reconstruction using ZEISS arivis Pro software. A deep learning model, trained on 39 diverse datasets, automated spine segmentation and 3D reconstruction, achieving a 74% F1-score and reducing processing time by over 50%. We show significant differences in spine density by sex, dendrite type, and tissue condition. Females had higher spine densities than males, and apical dendrites were denser in spines than basal ones. Acute tissue showed higher spine densities compared to cultured human brain tissue. With time in culture, Mushroom spines decreased, while Stubby and Thin spine percentages increased, particularly from 7-9 to 14 days in vitro, reflecting potential synaptic plasticity changes. Our study underscores the importance of using human brain tissue to understand unique synaptic properties and shows that integrating deep learning with traditional methods enables efficient large-scale analysis, revealing key insights into sex- and tissue-specific dendritic spine dynamics relevant to neurological diseases.