bioRxiv Subject Collection: Neuroscience's Journal

The fecal microbiota transplantation from drug-naive schizophrenia patients distinctively changes gut microbiome and metabolic profiles in male and female mice
Background: Emerging evidence suggests a role for the gut microbiome in schizophrenia (SCZ) and antipsychotic-induced metabolic perturbations. Using human fecal microbiota transplantation (FMT) in mice, this study investigated the role of gut microbiome in metabolic changes related to SCZ and antipsychotic (olanzapine) treatment. Methods: 5-6 weeks old germ-free NIH Swiss mice of both sexes received microbiota from either SCZ patients (SCZ-FMT) or healthy controls (HC-FMT) followed by a diet with or without olanzapine for six-weeks. Food intake and body weight were monitored weekly, and an intraperitoneal glucose tolerance test and open field test were performed. Serum glucose, and insulin were measured. Gut microbiome characterization and short-chain fatty acids (SCFAs) quantification were performed in the cecal samples using 16S rRNA gene sequencing and gas chromatography-mass spectrometry, respectively. Results: Olanzapine treatment decreased the locomotor activity in the open field test, irrespective of sex or microbiota. Female SCZ-FMT recipient mice exhibited insulin resistance compared to HC-FMT, irrespective of olanzapine treatment. Female SCZ-FMT mice showed significantly lower alpha-diversity compared to HC-FMT, whereas olanzapine treatment increased alpha-diversity. SCZ-FMT and olanzapine treatment differentially altered the microbial abundances and metabolic pathways in male and female mice. Interestingly, cecal SCFAs, mainly acetate levels, were significantly decreased in female SCZ-FMT mice compared to HC-FMT, while olanzapine treatment increased acetate levels in male mice. Both male and female SCZ-FMT mice showed elevated levels of isovaleric acid compared to HC-FMT. Conclusion: These preliminary findings suggest that the gut microbiome could be a predisposing factor contributing to the intrinsic risk of developing type 2 diabetes associated with SCZ in females.

Whole-brain clearing reveals region- and cell type-specific imbalances in inhibitory neurons in a mouse model for Kleefstra Syndrome
GABAergic inhibition is essential for balanced brain function and is frequently disrupted in neurodevelopmental disorders such as autism spectrum disorder (ASD). The inhibition is generated by a diverse population of GABAergic interneurons, which differ in subtype composition and spatial density across the brain. Here, we applied an unbiased whole-brain clearing and light-sheet imaging approach to systematically map the distribution of the three major GABAergic interneuron subtypes - Parvalbumin-positive (PV+), Somatostatin-positive (SST+), and Vasoactive Intestinal Polypeptide-positive (VIP+) cells - across the mouse brain in a model of Kleefstra Syndrome (Ehmt1+/-), a monogenic intellectual disability disorder with a strong ASD component. Analyzing 895 brain regions we identified widespread, cell type- and region-specific alterations in GABAergic populations. Notably, we observed increased VIP+ neuron density in the Ehmt1+/- cortex and decreased SST+ neuron density in sensory cortical and subcortical regions. In the basolateral amygdala (BLA), PV+ interneurons exhibited precocious maturation already at the juvenile stage, which persisted into adulthood and was associated with enhanced inhibitory input onto BLA principal neurons. We here demonstrate that Ehmt1 haploinsufficiency results in region- and cell-type specific changes throughout the brain. These results underscore the value of whole-brain, high-resolution mapping approaches in uncovering previously unrecognized patterns of neural vulnerability in neurodevelopmental disorders.

Developmental Connectomics of the Mouse Cerebellum
To uncover the developmental processes that establish the precise patterns of synaptic connectivity in the CNS, we employed a connectomic approach in the mouse cerebellar cortex between birth and 2 weeks of age. There were dramatic quantitative and qualitative changes in the structure and connectivity of cerebellar cells. Parallel fiber synapses onto Purkinje cells increased ~500-fold, with the most rapid growth taking place a week after birth. To support this profound synaptogenesis, Purkinje cells generated thousands of transient parallel fiber-oriented filopodia that received nascent synapses from parallel fibers. Importantly, we find that granule cells initiate synaptic output onto Purkinje cells only after receiving mossy fiber input, revealing a sequential, input-dependent logic for circuit assembly. In sharp contrast to the concurrent pruning of climbing fiber inputs, parallel fiber connectivity expanded and became highly individualized during development. Despite anatomical overlap, neighboring Purkinje cells share significantly fewer parallel fiber inputs than expected by chance. Moreover, parallel fibers themselves diverged spatially, further enforcing selective input allocation and resulting in highly specific parallel fiber cohorts for each Purkinje cell. Our findings uncover a mechanistic sequence in which early afferent activity and transient cellular structures guide the selective wiring and expansion of parallel fiber input to Purkinje cells, establishing developmental principles that ensure functional specificity in the mature brain.

Functional Divergence of Axon-Carrying Dendrite (AcD) and NonAcD Cells in Learning and Stability
Axon-carrying dendrite (AcD) cells are a specialized class of hippocampal neurons where the axon initial segment originates from a basal dendrite rather than the soma, creating a privileged pathway for excitatory inputs on AcD branches to bypass perisomatic inhibition. However, their functional role in learning and synaptic stability remains unclear. To address this question, we modeled a CA3-CA1 network to compare the learning dynamics and synaptic stability of AcD and nonAcD cells. The results revealed that, during learning, these cell types employ distinct mechanisms. AcD cells primarily adopt a single-modal strategy, with all dendritic branches converging to encode inputs from a single assembly, whereas nonAcD cells follow a multi-modal approach, with individual branches encoding inputs from distinct assemblies. Additionally, consistent with experimental findings, our results suggest that during periods of high inhibition (such as ripples), AcD cells maintain stable synaptic weights, unlike the synaptic decay observed in nonAcD cells. These results, in line with experimental evidence, suggest that although the morphological distinction between AcD and nonAcD cells was long overlooked, it proves to be important, as it results in functional differences in learning mechanisms and in the capacity for stable information storage, highlighting their key role in learning and memory consolidation.

Hierarchical processing of sensory information across topographically organized thalamocortical-like circuits in the zebrafish brain
Thalamocortical projections contribute to the spatial organization and functional hierarchies of the mammalian cortex. Primary sensory cortices receive topographically segregated information from first-order thalamic nuclei, which process distinct sensory modalities. In contrast, higher-order cortical regions integrate information from multiple information channels. While such hierarchical processing and integration of information is the foundation for neural computations in the mammalian cortex, the fundamental principles of thalamocortical computations in non-mammalian vertebrates remains unexplored. The zebrafish pallium, located in the dorsal telencephalon, is regarded as the homolog of the mammalian cortex. However, it remains unclear how the zebrafish pallium receives and processes sensory information, and how the architecture and function of these processes compare to the thalamocortical circuits in other vertebrates. Using anatomical tracing, electrophysiological circuit mapping, and in vivo Ca2+ imaging, we revealed a thalamocortical-like pathway in the zebrafish brain. We found that the preglomerular nucleus (PG) is the primary source of visual and mechano-vibrational information to the zebrafish pallium. We demonstrated that PG neurons and their pallial projections exhibit sensory-specific and topographically organized responses. In contrast, the sensory responses of pallial neurons display multiple layers of topographically organized hierarchies, ranging from simple sensory-specific responses to multimodal and coincidence-detecting nonlinear responses. Notably, we observed a progressive increase in the complexity of sensory computations, which is organized topographically along the posterior-anterior axis of the zebrafish pallium. Collectively, our results suggest that hierarchical sensory processing across topographically organized pallial regions is a conserved functional feature of the vertebrate pallium.

Distributed and drifting signals for working memory load in human cortex
Increasing working memory (WM) load incurs behavioral costs, and whether the neural constraints on behavioral costs are localized (i.e., emanating from the intraparietal sulcus) or distributed across cortex remains an active area of debate. In a pre-registered fMRI experiment, 12 humans (12 scanner-hours each) performed a visual WM task with varying memory load (0-4 items). We replicated a localized, load-dependent increase in univariate BOLD activity in parietal cortex. However, we also observed both systematic increases and decreases in univariate activity with load across the visual hierarchy. Importantly, multivariate activation patterns encoded WM load regardless of the direction of the univariate effect, arguing against a restricted locus of load signals in parietal cortex. Finally, we observed representational drift in activity patterns encoding memory load across scanning sessions. Our results suggest a distributed code for memory load that may be continually refined over time to support more efficient information storage.

The Hippocampus Rapidly Integrates Sequence Representations During Novel Multistep Predictions
Memories for temporally extended sequences can be used adaptively to predict future events on multiple timescales, a function that relies on the hippocampus. For such predictions to be useful, they should be updated when environments change. We investigated how and when new learning shapes hippocampal representations of temporally extended sequences, and how this updating relates to flexible predictions about future events. Human participants learned sequences of environments in immersive virtual reality. They then learned novel environment transitions connecting previously separate sequences. During subsequent fMRI, participants predicted multiple steps into the future in both the newly connected sequence and control sequences that remained separate. The hippocampus integrated representations of the connected sequence, such that activity patterns became more similar across trials for the connected sequence vs. the unconnected sequences. These integrated sequence representations in the hippocampus emerged soon after learning, incorporated representations of the initial sequences as well as new activity patterns not previously present in either sequence, and predicted participants' ability to update their predictions in behavior. Together, these results advance our understanding of how structured knowledge dynamically emerges in service of adaptive behavior.

Selective genetic targeting of the mouse efferent vestibular nucleus identifies monosynaptic inputs and indicates function as multimodal integrator
The vestibular system is a critical sensory modality required for coordinated movement, balance and our ability to interact with the surrounding environment. Vestibular sensory neurons provide the nervous system with information about head rotation and acceleration. However, the nervous system can also modify the activity of sensory neurons and hair cells via the actions of the efferent vestibular system (EVS). The function of the EVS has remained unknown partly because of an inability to target efferent vestibular neurons in a selective manner to understand their synaptic inputs and function during behaviour. Here, we present a novel method for the selective targeting and expression of flp-recombinase in EVS neurons. We take advantage of the dual expression of choline acetyl transferase (ChAT) and calcitonin gene related peptide (CGRP) in these neurons to develop an adeno-associate virus (AAV) that expresses a gene only in neurons with this intersectional expression. We use this system to map the monosynaptic inputs to EVS neurons and show inputs from distinct populations of brainstem and midbrain regions indicating a functional role as a multimodal processing center and integrator for the vestibular periphery. To demonstrate the applicability of our technology in behavioural assays, we performed a preliminary behaviour analysis in mice with disrupted EVS function. While more bespoke assays are required to ascertain EVS function/s, our viral method presents a novel tool for investigators examining the role of the vestibular system and its central circuits.

Morphological details contribute to neuronal response variability within the same cell type
A large body of literature offers an explanation on how biophysical diversity and variable branching patterns of neurons contribute to degeneracy, and therefore enable multiple solutions for a characteristic neuronal response. The specific influence of finer morphological details, such as diameter and length of dendritic branches, on response variability is yet unclear. In this study, we address this question using a model database approach with spatially extended, conductance-based compartmental models to study variability of response features, such as resting membrane potential, input resistance, spike count, first spike latency, spike height, and spike width. Using 15 reconstructed morphologies of leech touch cells with fixed branching patterns, we identified several thousands of parameter sets that reproduced the experimentally measured response features of all the tested morphologies. Even when the biophysical parameters were kept equal across reconstructed morphologies, variability in response features arose from the morphological details. Systematically varying the distribution of ion channels across the neuronal membrane revealed that all spike response features are influenced by the location of spike initiation zones with higher conductance density. Nevertheless, biologically plausible responses can arise from different locations of spike initiation zones and even homogeneous distribution of ion channels. Furthermore, comparing the simulated spike responses from two morphological subtypes of leech touch cells revealed that the previously published systematic differences cannot be explained by the morphological differences alone. A larger total conductance was required to reproduce the experimental finding of an increased spike count and a larger spike amplitude in a morphological subtype with a larger membrane area. In conclusion, biophysical properties, morphological details, and ion channel distribution across the membrane all interact in their contribution to the functionality and response variability of neurons of the same cell type.

Spontaneous reinstatement of episodic memories in the developing human brain
The hippocampus supports episodic memories in development, and yet how the brain stabilizes these memories determines their long-term accessibility. This study examined how episodic memories formed in development are stabilized and whether early-life experiences influence the neural mechanisms involved. Using fMRI and multivariate analyses, we tracked neural reinstatement of newly learned item-location-context associations in youth (N = 49; mean age = 11.68 years). Hippocampus and visual cortex activity during encoding predicted later memory success. Crucially, spontaneous reinstatement in the medial prefrontal cortex (mPFC) during post-encoding rest also predicted memory. In a second sample (N = 32, mean age = 12.86 years) with early adversity, differential recruitment of the precuneus and visual cortex during encoding, and angular gyrus during reinstatement, was observed. These findings suggest that hippocampus and mPFC contribute to developmental memory stabilization in ways consistent with mature function, while differences in memory accessibility across developmental experiences arise from broader network adaptations.

Encoding of motor sequences in primate globus pallidus and motor cortex: Uniform preference for ordinal position
How the brain organizes discrete actions into fluid sequences is a central problem in motor neuroscience. Competing models of basal ganglia (BG) function propose that BG neurons either signal sequence boundaries or encode movements across ordinal positions. Prior studies have largely examined fixed sequences with end-of-sequence rewards, leaving open whether such findings generalize to more naturalistic conditions. We trained four rhesus macaques to perform a visuomotor sequence task requiring four or five out-and-back joystick movements to peripheral targets. Sequences were completed under two conditions: a random condition, in which target order varied across trials, and a fixed condition, in which order was predictable and consistent. Rewards were delivered after each movement, dissociating reward timing from sequence completion. We recorded single-unit activity in arm-related regions of the globus pallidus (GP; n = 458) and primary motor cortex (M1; n = 306). Regression analyses revealed that many neurons in both GP and M1 encoded ordinal position within a sequence. Order effects were more frequent in the fixed condition, but were also present during random sequences. We found no evidence for preferential encoding of sequence initiation or termination in overlearned sequences, in contrast to prior studies reporting start/stop signals in basal ganglia. Weak effects appeared under the random condition in one animal pair, but these did not generalize across animals or conditions. Instead, neurons exhibited heterogeneous order-related responses spanning the full sequence. These results demonstrate that GP neurons, like those in M1, encode ordinal position throughout a sequence rather than acting solely as sequence initiators or terminators. This challenges boundary-specific models of BG function and highlights a broader role for the BG in representing serial order during motor sequence production.

Hypoplasticity in sensory-driven neocortical circuits of the Fragile X syndrome mouse model
Sensory experience and learning are tightly linked to plasticity in neocortical circuits. Repetitive sensory stimulation, such as rhythmic whisker stimulation (RWS) at behaviourally relevant frequencies (8 Hz), can induce long-term potentiation (LTP) of excitatory synapses in typically developing mice. Fragile X syndrome (FXS), a leading monogenically inherited form of intellectual disability, is associated with altered tactile reactivity, where non-noxious touch can be aversive. To investigate how sensory-evoked plasticity is altered in FXS, we combined ex vivo whole-cell electrophysiology with in vivo two-photon calcium imaging of layer (L) 2/3 pyramidal neurons (PNs) in the Somatosensory (S1) cortex of adult male Fragile X mouse model (Fmr1-/y) mice and typically developing (Fmr1+/y) control littermates. We found that plasticity induced by repetitive sensory stimulation was impaired in Fmr1-/y mice ex and in vivo compared to controls. L4-evoked subthreshold synaptic responses were hyperexcitable in L2/3 PNs, consistent with circuit-level disinhibition. Despite this, baseline intrinsic spiking evoked by current steps remained largely unchanged and whisker-evoked activity appeared diminished in vivo. We observed a shortening of the axon initial segment (AIS) in L2/3 in Fmr1-/y compared to control mice, which may reveal a potential mechanism to explain why subthreshold hyperexcitability did not induce more spiking. We also observed an increase in adaptation to the repetitive stimulation in Fmr1-/y mice compared to controls, which may underlie failure to induce plasticity. Together, these findings suggest that L2/3 PNs of S1 in Fmr1-/y mice are locked in a hypoplastic state, potentially related to disrupted inhibitory control, AIS shortening, and rapid adaptation during repetitive sensory stimulation. As somatosensory processes underly tactile perception, these findings may potentially underly altered tactile reactivity in FXS.

Stimulus-Dependent Dopamine Dynamics from LocusCoeruleus Axons
Arousal is essential for survival, and maladaptive arousal processing leads to an inability to focus, anxiety-like behavior, and dysregulated affective states. Norepinephrine (NE) is known to regulate anxiety, arousal, and learning through locus coeruleus (LC) projections throughout the brain. Evidence for co-release of the NE precursor and neurotransmitter dopamine (DA) from LC neurons has been accumulating for years, yet definitive measures of DA release across regions, stimulus paradigms, and behaviors associated with the LC-NE system remain controversial. Here, we identified the physiological and behavioral properties that evoke DA release from LC axon terminals. Using concomitant approaches, we inhibited the LC and ventral tegmental area (VTA) to selectively isolate the contributions of LC-derived DA release. Together these findings establish the constraints by which LC neurons release DA in a modality-dependent manner.

Encoding visual stimuli by striatal neurons
To move through the world, animals extract visual features from objects. Although visual object encoding is considered a cortical attribute, subcortical areas also contain visual processing circuits. Using electrophysiological recordings of spiny projection neurons (SPNs) located in a target region of the primary visual cortex, we identified striatal modules that process basic visual features. SPNs from the direct and indirect pathways exhibited high orientation selectivity in the absence of behavioral contingencies. SPNs population activity reliably predicted different visual features. Pathway-specific silencing of SPNs revealed that high orientation selectivity depends on intra-striatal connectivity. Thus, specialized striatal modules are active participants in visual feature extraction. These findings indicate parallel visual information processing in basal ganglia circuits, expanding current models of visual perception beyond cortical networks.

Mesoscopic analysis of GABAergic marker expression in acetylcholine neurons in the whole mouse brain
In the central nervous system, acetylcholine (ACh) neurons coordinate neural network activity required for higher brain functions, such as attention, learning, and memory, as well as locomotion. Disturbances in cholinergic signaling have been described in many diseases of the developing and mature brain. Interestingly, ACh neurons can co-transmit GABA to support essential roles in brain function. However, the contributions of ACh/GABA co-transmission to brain function remain unclear. This underscores the need to better understand the heterogeneity of ACh neurons, particularly the sub-population of ACh neurons co-expressing GABAergic markers. We used various combinations of transgenic mouse lines to systematically label ACh neuron populations positive for different GABAergic markers in the brain. We developed a workflow combining tissue clearing, light-sheet fluorescence microscopy, and machine learning to image entire mouse brain hemispheres followed by quantification of ACh neurons throughout the brain. With this approach, we assessed the role of GABA co-transmission in ACh neuron function and quantified ACh and ACh/GABA neuron sub-populations in the brain. Our results suggest that GABA co-transmission from ACh neurons is not required to maintain the regular ACh neuron count in the brain. Furthermore, we report that a large subset of ACh neurons can potentially synthesize GABA by co-expressing the marker Gad2. However, most of these ACh neurons do not express vGAT, which would enable these neurons to release GABA. Taken together, we conclude that GABA co-transmission likely occurs only from a small population of ACh neurons restricted to few brain nuclei.

Spatial transcriptomics of compartmentalised inflammation in a natural disease multiple sclerosis cohort.
Compartmentalised inflammation is a poorly understood aspect of multiple sclerosis (MS) that is associated with worse outcomes and represents an important therapeutic target. To gain deep insight into compartmentalised inflammation, we have taken the approach of digital spatial profiling of the whole human transcriptome in areas of Central Nervous System (CNS) perivascular and meningeal inflammation and tertiary lymphoid-like structures (TLS) in MS. Critically, we had access to rare archival tissue obtained before the era of disease-modifying therapies, representing the natural history of disease. This analysis has identified differentially-expressed genes in TLS compared to meningeal or perivascular inflammation. Pathway analysis highlighted that TLS signalling is dominated by B cell activity including active antibody secretion. Our data demonstrated the diversity of immunoglobulins and the prominence of IgG3- and IgG4-secreting cells in TLS. Intriguingly, our analyses suggest pathways of active viral mRNA translation and associated-cellular responses within TLS immune cells, suggesting TLS may be hubs for viral (re)activation. These findings provide insight into the function of TLS in MS disease pathogenesis, and reveal unique immune signatures that may support biomarker development to predict patients that harbour TLS in life.

Brain Preparedness for Active Forgetting: Cortisol Awakening Response Proacts Prefrontal Control Over Hippocampal-Striatal Circuitry
Stress-related psychiatric pathologies (e.g., rumination in depression, intrusive memories in PTSD) involve impaired inhibitory control over emotional memories and disrupted cortisol circadian rhythms. However, how these mechanisms interact to support adaptive forgetting remains unclear. Here, by integrating multi-modal neuroendocrine profiling with fMRI-based memory suppression in 90 participants, we demonstrate that the cortisol awakening response (CAR)--a circadian surge priming the brain for daily demands--proactively and selectively enhances suppression of recently acquired but not overnight-consolidated emotional memories. This time-dependent facilitation manifests through dual neural mechanisms: Robust CAR broadly amplifies dorsolateral prefrontal cortex (dlPFC) engagement during suppression attempts and specifically strengthens top-down dlPFC control over hippocampal-striatal circuits exclusively for recent traces. Our findings bridge circadian biology, systems neuroscience, and clinical psychopathology to establish CAR as a neuroendocrine preparedness mechanism that proactively configures adaptive forgetting circuits across sleep-wake cycles, thereby informing circadian-based interventions for stress disorders.

VesiclePy: A Machine Learning Vesicle Analysis Toolbox for Volume Electron Microscopy
Vesicles are critical components of neurons that package neurotransmitters and neuropeptides for their release, in order to communicate with other neurons and cells. However, due to their small size, the reconstruction of the full vesicle endowment across an entire neuronal morphology remains challenging. To achieve this, we have used, as a tool to identify and visualize vesicles, Volume Electron Microscopy (vEM), a method that has the nanoscale resolution to detect individual vesicle boundaries, content, and 3D locations. However, the large volume of vEM datasets poses a challenge in the segmentation, classification, and spatial analysis of tens of thousands of vesicles and their target cell in 3D. Here we report the development of VesiclePy, an integrated pipeline for automated segmentation, classification, proofreading, and spatial analysis of vesicles, relative to neuron masks in large-volume electron microscopy data. Our package integrates the efficiency of deep learning and the accuracy of human proofreading and provides a streamlined package in chunked processing and accurate indexing, localization, and visualization of single vesicle resolution in large vEM data. We demonstrate the viability of VesiclePy using high-pressure frozen serial EM data of Hydra vulgaris and quantify the performance of the package using ground truth manual annotations. We show that VesiclePy can process a multiterabyte serial EM dataset, efficiently annotate 53,851 vesicles from 20 complete neurons, and classify vesicles into 5 types. Each vesicle has a unique ID and 3D location for further spatial analysis in relation to neuron or non-neuronal targets nearby. Finally, by combining vesicle data and morphological information of each neuron, we can quantitatively cluster neurons into subtypes. VesiclePy is available at https://github.com/PytorchConnectomics/VesiclePy under an MIT license.

Effects of acute adolescent stress on the acquisition and maintenance of intravenous oxycodone self-administration in male and female rats
Background: The persistent threat of the opioid epidemic warrants investigation into risk factors that predispose individuals to opioid use disorder (OUD). Adolescent stress has been linked to enhanced risk for OUD in humans, however attempts to model this preclinically have yielded mixed results. Additionally, few studies have explored whether adolescent stress modulates the reinforcing effects of prescription opioids. Here we investigate the impact of acute adolescent stress on oxycodone self-administration in male and female rats. Methods: Adolescent male and female rats underwent acute restraint stress during concurrent exposure to predator odor, or control handling. Approximately one week later, subjects were allowed to acquire IV oxycodone self-administration (0.03 mg/kg/inf) over 10 sessions (2 h/day) under a fixed-ratio 1 (FR1) schedule of reinforcement. Following three additional FR1 sessions and seven sessions under FR3, rats underwent two progressive-ratio tests (0.03 mg/kg/inf and 0.06 mg/kg/inf, respectively). Separate groups of adolescent rats underwent similar experimental manipulations but were trained on sucrose reinforcement. Results: Adolescent stress did not affect the rate of acquisition of IV oxycodone self-administration. However, oxycodone self-administration escalated during post-acquisition FR1 sessions and remained elevated during FR3 sessions in stressed rats as compared to unstressed controls. Adolescent stress exposure did not affect responding during progressive-ratio tests, nor did it affect any measure of sucrose pellet reinforcement. Conclusions: The present results are the first to demonstrate adolescent stress-induced enhancement of oxycodone reinforcement in rats and provide a preclinical model for investigating the neurobiological mechanisms by which adolescent stress increases vulnerability for prescription opioid misuse.

Coherent dynamics of thalamic head-direction neurons irrespective of input
While the thalamus is known to relay and modulate sensory signals to the cortex, whether it also participates in active computation and intrinsic signal generation remains unresolved. The anterodorsal nucleus of the thalamus broadcasts the head-direction (HD) signal, which is generated in the brainstem, particularly in the upstream lateral mammillary nucleus, and thalamic HD cells remain coordinated even during sleep. Here, by recording and manipulating neuronal activity along the mammillary-thalamic-cortical pathway, we show that coherence among thalamic HD cells persists even when their upstream inputs are decorrelated, particularly during non-Rapid Eye Movement sleep. These findings suggest that thalamic circuits are sufficient to generate and maintain coherent population dynamics in the absence of structured input.

Arousal-related mediation of perceptual belief updating across auditory domains
Belief updating refers to the integration of prior beliefs with incoming evidence and guides decision-making under uncertainty. In response to surprising events, this process is thought to be modulated by the locus-coeruleus-noradrenaline (LC-NA) arousal system, observable via pupil dilations (PDs). Pertinent literature has mostly focused on conscious, high-level decision-making and estimation processes, while assuming that the same principles apply to low-level sensory perceptual decision-making and generalize across tasks, domains and modalities. To address some of these assumptions, we devised a novel perceptual discrimination paradigm, investigating behavior and PDs across auditory domains. Participants were presented with auditory sequences of randomized length at a rapid pace, changing intermittently between two latent states: acceleration vs. deceleration (temporal group, N = 25) and clockwise vs. counterclockwise movement (spatial group, N = 22). Under high uncertainty, participants continuously inferred latent states to report the final state per sequence. To extract per-stimulus estimates of PDs during sequences, we fitted a deconvolution-based general linear model to the continuous pupil traces with a free amplitude parameter reflecting ongoing PDs. A Bayesian observer model was fitted to participants' responses and used to estimate information gain and surprisal for every stimulus. Participants' performance and PDs showed strong sensitivity to the occurrence of change-points. Both computational variables significantly predicted PDs in both domains, with information gain outperforming surprisal in a model comparison. Further model comparison revealed significant preference for models excluding possible domain-specific effects over models including them, pointing towards a constant effect over domains. We conclude that behavior and associated PDs observed in our purely perceptual auditory task align with Bayesian principles of belief updating. The observed lack of domain specificity supports the assumed generalizability of belief updating.

Spatiotemporal dynamics of alphaherpesviral latency and reactivation in the murine central nervous system
Alphaherpesviruses, including Herpes Simplex Virus 1 (HSV-1) and Pseudorabies Virus (PrV), establish lifelong latency in the nervous system and can cause recurrent disease. While latency has classically been attributed to peripheral sensory ganglia, accumulating evidence indicates that the central nervous system (CNS) also act as a relevant reservoir for viral latency and reactivation. Here, we investigated the CNS as a site of latency using the attenuated mutant PrV-{Delta}UL21/US3{Delta}kin which reproduces key features of herpes simplex encephalitis (HSE) in female CD1 mice. We mapped brain regions permissive to alphaherpesviral latency and analyzed the temporal dynamics of viral transcription, histopathology, and host clinical and immune responses. Following intranasal inoculation, mice were analyzed at 11 to 14, 21, 28, 42, 105, and 190 days post infection (dpi). To assess the potential of reactivation, a subset received cyclophosphamide/dexamethasone at 170 dpi. Viral transcripts were detected by RNAscope in situ hybridization and RT-qPCR targeting the lytic gene UL19 and the latency-associated transcript (LAT). Histopathological analyses included hematoxylin and eosin (H&E) staining and immunohistochemistry for CD3, Iba1, GFAP, and cleaved caspase-3. Major capsid protein (UL19) expression displayed marked regional and temporal heterogeneity, with prominent signals in mesiotemporal structures (piriform cortex, hippocampus, entorhinal cortex), coinciding with pronounced T-cell infiltration. LAT expression remained overall low, with a transient peak during the acute infection (11-14 dpi). RT-qPCR confirmed high viral transcript levels for both UL19 and LAT in mesiotemporal regions during early infection, while LAT expression returned to baseline levels thereafter. Histopathology demonstrated a transition from acute necrotizing meningoencephalitis to prolonged or recurrent low-grade inflammation, accompanied by glial activation and localized apoptosis. Notably, UL19 expression strongly correlated with CD3+ T-cell infiltration, particularly at 42 dpi. These findings define the spatiotemporal interplay between viral transcriptional activity and neuroinflammation and identify selected CNS regions as reservoirs for latent or recurrent alphaherpesvirus infection.

Multitasking Recurrent Networks Utilize CompositionalStrategies for Control of Movement
The brain and body comprise a complex control system that can flexibly perform a diverse range of movements. Despite the high-dimensionality of the musculoskeletal system, both humans and other species are able to quickly adapt their existing repertoire of actions to novel settings. A strategy likely employed by the brain to accomplish such a feat is known as compositionality, or the ability to combine learned computational primitives to perform novel tasks. Previous works have demonstrated that recurrent neural networks (RNNs) are a useful tool to probe compositionality during diverse cognitive tasks. However, the attractor-based computations required for cognition are largely distinct from those required for the generation of movement, and it is unclear whether compositional structure extends to RNNs producing complex movements. To address this question, we train a multitasking RNN in feedback with a musculoskeletal arm model to perform ten distinct types of movements at various speeds and directions, using visual and proprioceptive feedback. The trained network expresses two complementary forms of composition: an algebraic organization that groups tasks by kinematic and rotational structure to enable the flexible creation of novel tasks, and a sequential strategy that stitches learned extension and retraction motifs to produce new compound movements. Across tasks, population activity occupied a shared, low-dimensional manifold, whereas activity across task epochs resides in orthogonal subspaces, indicating a principled separation of computations. Additionally, fixed-point and dynamical-similarity analyses reveal reuse of dynamical motifs across kinematically aligned tasks, linking geometry to mechanism. Finally, we demonstrate rapid transfer to held-out movements via simple input weight updates, as well as the generation of target trajectories from composite rule inputs, without altering recurrent dynamics, highlighting a biologically plausible route to within-manifold generalization. Our framework sheds light on how the brain might flexibly perform a diverse range of movements through the use of shared low-dimensional manifolds and compositional representations.

Frequency-dependent Inhibition during Deep Brain Stimulation of Thalamic Ventral Intermediate Nuclei
Deep brain stimulation (DBS) of the thalamic ventral intermediate nucleus (Vim) has been a standard therapy for essential tremor. It has been shown that high frequency ([≥]100Hz) DBS suppresses Vim neuronal firing and tremor activity, however, the underlying mechanisms are not fully understood. Here, we use in vivo recordings (single-unit) of Vim neurons (n=19, people with essential tremor) during different DBS frequencies to investigate whether neuronal suppression during high-frequency DBS occurs at synaptic/cellular levels (e.g., cell inhibition due to synaptic depression/fatigue during high-frequency DBS) or is influenced by network-level effects (e.g., recurrent inhibition). We propose a theoretical framework that explains DBS effects at both cellular and network levels, i.e., (continuous) high-frequency DBS not only depresses synapses projecting to Vim but also enables the recruitment of inhibitory neurons. A transient burst in the spiking activity of Vim during high-frequency DBS, prior to neuronal suppression, is likely providing sufficient network engagement to recruit inhibitory neurons that are silent during low-frequency DBS. Further, we detected a positive-going evoked-field potential effect, hereafter referred to as quasi-evoked inhibition, during high-frequency (100 Hz and 200 Hz) Vim-DBS in four out of 19 recording sites. Interestingly, it was observed that (i) neuronal suppression is stronger in these four neurons (P < 0.05), implying that inhibitory engagement during high-frequency DBS can further suppress neuronal firing, and (ii) quasi-evoked inhibition emerges after the transient burst (P < 1.00 x 10-7), i.e., the latter may give rise to the former. By removing DBS artifacts with a novel algorithm and characterizing the dynamics of quasi-evoked inhibitory activity, we showed that the likelihood of occurrence of this inhibitory activity negatively correlated with the instantaneous firing rate (P < 1.00 x 10-5). These results suggest that an excitatory-inhibitory balance is likely regulating Vim activities during high-frequency DBS. Our findings shed light on potential network mechanisms underlying Vim-DBS, which can provide insight for optimizing DBS by designing new stimulation patterns.

Novel fat-taste enhancers modulate functional connectivity of the reward system following sustained activation of gustatory pathways in mice
Humans and rodents exhibit an innate preference for dietary fat, and dysfunction of lingual fat-taste receptors CD36 and GPR120 in obesity suggests that impaired oro-sensory lipid detection may contribute to its development. Rodent models with reduced fat-taste sensitivity display increased fat intake, highlighting the role of taste perception in dietary regulation. The newly developed NKS-3 and NKS-5, high-affinity agonists for CD36 and CD36/GPR120 receptors, respectively, induce early fat satiation and reduce both fat-rich food intake and body weight gain in diet-induced obese mice. However, the neural mechanisms underlying these effects remain unclear. Here, we investigated the response of the reward system to a sustained activation of CD36 and GPR120 via fat-taste enhancers NKS-3 and NKS-5 compared to linoleic acid (LA). Male C57BL/6JRj mice (N=88) received oral administration of vehicle, 0.2% LA, 50 uM NKS-3 or 75 uM NKS-5 for 10 days. The immunohistochemical analysis of cerebral FosB neuronal expression revealed a reorganization of the functional network connectivity. Behavioral assessments over an additional 10-day period in a second cohort of animals detected no adverse motivational, compulsive-like, depressive or anxiogenic effect of the treatments. Our findings suggest that our fat-taste enhancers may offer a promising therapeutic strategy against obesity, leveraging the oral-gut-brain axis to regulate fat-rich food intake.

The cellular basis of mitochondrial stress signaling in the brain
Neuronal vulnerability to stress is highly cell-type specific, but the underlying mechanisms are poorly understood. Here we show that the ability to activate endoplasmic reticulum (ER) stress signaling is encoded by the relative mitochondrial metabolic activity of neurons. Genetically inducing mitochondrial dysfunction in the Drosophila brain caused the emergence of a novel cluster of neurons, detected using single nuclear RNA-sequencing, that activated the ER unfolded protein response (UPR). UPR activation occurred only in neurons with high mitochondrial activity. Unexpectedly, mitochondria-ER contacts were also abundant in the neurons that activated the UPR but virtually undetectable in neurons with low mitochondrial activity. In the human brain, strikingly, excitatory neurogranin neurons had the highest mitochondrial activity and triggered the UPR. The selective activation of the UPR only in neurons with high mitochondrial activity is therefore conserved. This study reveals the remarkable dependence on the inherent oxidative metabolic activity of neurons to activate the UPR.

Contributions of superior colliculus and primary visual cortex to visual spatial detection in freely moving mice
Visual spatial detection is a crucial first step in vision to guide decision-making and action. However, its neural basis in freely behaving animals remains unclear due to challenges in controlling visual input and monitoring eye and head position. Studies in head-fixed mice have shown that both the superior colliculus (SC) and primary visual cortex (V1), two key visual processing hubs in mammals, contribute to visual spatial detection. Yet, their relative roles in freely moving animals are poorly understood. Here, we developed a novel approach to study the neural mechanisms of visual spatial detection in unrestrained mice. We combined closed-loop presentation of visual stimuli with neural recordings, optogenetic manipulation, and simultaneous monitoring of eye and head position. Our results show that SC cells are more predictive of reaction times than V1 cells. Furthermore, SC neurons exhibit more sustained activity than V1 neurons during visual spatial detection. Optogenetic SC and V1 silencing causes pervasive and remarkably localized perturbations of visual detection performance. SC silencing has a stronger impact on visual detection than V1 silencing. These results highlight the distinct activity patterns in two principal early visual processing centers, and establish their relative causal contributions to visual spatial detection.

p75 Neurotrophin Receptor Shapes the Dynamics of Adult Hippocampal Neurogenesis in Alzheimer's Disease
Adult hippocampal neurogenesis is essential for cognitive flexibility and emotional resilience, and its disruption is strongly associated with Alzheimer's disease, a disorder marked by cognitive decline and memory impairment. The p75 neurotrophin receptor regulates neuronal survival and plasticity, yet its contribution to adult hippocampal neurogenesis, especially under neurodegeneration, remains unclear. In this study, we investigate the role of p75NTR in Adult Neurogenesis using constitutive and conditional p75NTR knockout mice, the amyloidogenic 5xFAD model, and 5xFAD/p75NTR knockout mutants. We show that p75NTR deletion led to a significant reduction in NSC proliferation and altered neuronal differentiation in the dentate gyrus, acting in a cell non-autonomous function to control neural stem cell fate. Notably, 5xFAD/p75NTR mutants displayed exacerbated neurogenic deficits compared to 5xFAD mice. Transcriptomic profiling confirmed these alterations and supported a disease-relevant regulatory function. Parallel studies in human iPSC-derived neural stem cells exposed to amyloid-? showed p75NTR-dependent mechanisms mirroring findings from the mouse models. Collectively, our findings establish p75NTR as a critical regulator of adult hippocampal neurogenesis, under Alzheimer's Disease and propose it as a therapeutic target.

ALM enables contextual decision-making via dynamic reconfiguration of local circuits
Cognitive operations often require flexible implementation of stimulus-response contingencies, depending on context. We developed an olfactory task in which mice learned to associate a test odor with a directional lick response, conditional on a preceding context odor drawn from a different odor set. Two-photon imaging revealed that anterior lateral motor cortex (ALM) contains distinct populations encoding context, test odors, and choice. Optogenetic silencing during the context and delay periods impaired performance, suggesting that ALM contributes to configuring the appropriate contingency. Although context odors that instructed the same mapping were represented by separate populations, their influence converged at the level of choice-selective neurons. A subpopulation of these neurons exhibited dual selectivity for context and choice, forming what we term "contingency neurons". These findings suggest that ALM supports flexible behavior not by abstracting over context cues, but by dynamically reconfiguring local circuits to route sensory input to the appropriate motor output.

Neuronal HDAC9: A key regulator of cognitive and synaptic aging, rescuing Alzheimer's disease-related phenotypes
Epigenetic regulation is a key determinant of the aging process, and its dysregulation contributes to cognitive aging and increased vulnerability to Alzheimer's disease (AD). As major regulators of epigenetic processes, histone deacetylases (HDACs) have emerged as potential therapeutic targets for cognitive enhancement in neurodegenerative diseases. However, the distinct roles of individual HDAC isoforms remain to be defined. Here, we report that HDAC9 is specifically expressed in neurons of human and mouse brains, and its expression declines with age. HDAC9 deficiency impairs cognitive function and synaptic plasticity in young mice. Selective deletion of HDAC9 in hippocampal CA1 neurons also induces cognitive impairment. In contrast, overexpression of HDAC9 in forebrain glutamatergic neurons preserves cognitive function in aged mice. Moreover, HDAC9 is also downregulated in the brain of AD mouse models, whereas neuronal overexpression of HDAC9 alleviates AD-related cognitive and synaptic deficits and reduces A{beta} deposition. Together, these findings suggest neuronal HDAC9 is necessary and sufficient for maintaining cognitive and synaptic functions in the context of aging and AD.

Lateral hypothalamus CRFR1 regulation of chronic binge drinking: divergence along anterior-posterior axis
Binge alcohol drinking increases the risk of developing an alcohol use disorder (AUD) and comorbid psychopathology. The lateral hypothalamus (LH) is a brain structure that integrates cognitive and sensory information to tightly regulate motivated behavior, including binge drinking. Importantly, LH function is vulnerable to modulation by the pro-stress neuropeptide corticotropin-releasing factor (CRF), and acute antagonism of CRF receptor 1 (CRFR1) in the LH blunts binge drinking. However, the role of LH CRFR1 in chronic binge drinking is unknown. We used genetically targeted knockdown (KD) of CRFR1 in the LH of male and female mice followed by three weeks of binge drinking using the Drinking in the Dark (DID) model. CRFR1 KD in the posterior LH increased alcohol consumption, independent of sex, with no effect of KD in the anterior LH. Consistent with this, total alcohol consumption was negatively correlated with the location of CRFR1 KD in the LH along the anterior-posterior axis. CRFR1 KD did not alter water consumption or body weight, suggesting the effects of CRFR1 KD on alcohol consumption were not due to broad disruption of fluid intake or homeostatic function. In contrast to the observed effects on binge drinking, CRFR1 KD increased anxiety-like behavior and blunted sucrose preference, independent of KD location in the LH. Our findings provide foundational insight into LH function in the context of AUD and prompt further investigation into the divergent roles that distinct circuitry or cell populations along the anterior-posterior axis of the LH may play in binge drinking.

Young adult microglial deletion of C1q reduces engulfment of synapses and prevents cognitive impairment in an aggressive Alzheimer's disease mouse model
C1q is a multifunctional protein, including its role as the initiating protein of the classical complement cascade. While classical pathway activation is involved in synaptic pruning during development of the nervous system, it also contributes to enhanced inflammation and cognitive decline in Alzheimer's disease (AD). Constitutive genetic C1q deficiency has been shown to reduce glial activation and attenuate neuronal loss in AD mouse models, but the specific contributions of microglial C1q to AD pathology while avoiding deficits during post-natal development remain to be determined. To dissect specific role(s) of microglial C1q in AD progression, we crossed the Cx3cr1CreERT2 mouse model that deletes C1q from microglia in young adulthood (8 weeks of age) to the aggressive Arctic48 (Arc) amyloidosis mouse model. At 10 months, young adult microglial C1q deletion (Arc C1q{Delta}MG) rescued cognitive deficits in spatial memory, despite unchanged amyloid plaque burden. Furthermore, Arc C1q{Delta}MG)MG mice exhibited reduced hippocampal C3 protein levels without altering C3 mRNA. No changes were observed in C5aR1, astrocyte GFAP, or microglial Iba1 protein expression. However, Arc C1q{Delta}MG mice demonstrated region specific reductions in microglial synaptic engulfment, alongside decreased phagolysosome-associated amyloid in both microglia and astrocytes, and reduced compaction of amyloid within the hippocampus. These findings support a role for C1q in astrocytic C3 induction and the engulfment of both synapses and amyloid. Importantly, young adult microglial C1q inhibition confers cognitive benefits without exacerbating amyloid pathology, suggesting a therapeutic window in which targeting microglial C1q may mitigate neuroinflammation and synaptic loss during the later stages of AD.

Assessing the digit organisation of focal hand dystonia using 7T functional MRI
Introduction: Focal hand dystonia (FHD) is typically treated with Botulinum Toxin (BTX/BoNT-A/Botox/ Onabotulinum Toxin Type A) injected into digit and wrist muscles to provide temporary symptomatic relief from muscle spasm. We use 7T functional MRI (fMRI) to study 1) differences in somatosensory and motor cortical digit maps between FHD individuals and age and sex-matched healthy volunteers (HV), 2) changes in cortical digit maps of FHD individuals after BTX treatment. Methods: Six FHD patients underwent behavioural measures and 7T fMRI at two timepoints: ~30 days after BTX treatment at peak efficacy (Post-BTX), immediately prior to their next injection ~100 days after treatment when therapeutic effects had declined (Pre-BTX). HVs were scanned at a single time point. Behavioural measures included temporal discrimination (TDT), amplitude thresholding (AMP) and spatial acuity grating orientation tasks. A somatosensory travelling wave (TW) digit-mapping fMRI task was performed on dominant/affected and non-dominant/un-affected hands, and a motor TW digit-mapping task on the dominant/affected hand. Fourier analysis derived digit maps which were compared to a probabilistic digit atlas, and population receptive field (pRF) mapping performed. Structural and resting state fMRI data were acquired. Results: Spatial acuity was lowered in the dominant/affected hand in FHD compared to HVs, while TDT and AMP measures showed no significant differences. Somatosensory and motor TW cortical digit maps in FHD and HV showed clear digit ordering. Somatosensory and motor cortical digit maps were more disordered in the dominant/affected hand than the non-dominant hand for FHD Post and Pre-BTX compared to HVs (DICE coefficient/Figure of Merit). Compared to the atlas, HV maps were in-line for both hands, while in FHD central tendency (CT) was lower in the dominant/affected hand than non-dominant hand. pRF sizes were larger in the FHD Pre-BTX group compared to HV and Post-BTX for the dominant hand. Conclusion: Behaviourally, FHD participants had lower spatial acuity than HVs. FHD digit maps had typical D1-D5 ordering, but DICE coefficients identified a disordered dominant hand in FHDs compared to HVs at both timepoints. The FHD Pre-BTX group had larger pRF sizes than Post-BTX and HVs, suggesting BTX treatment coincides with more localised touch perception.