bioRxiv Subject Collection: Neuroscience's Journal

Comparative analysis of building Pearson and Canonical correlation functional connectivity matrices for classification tasks in neuroimaging
Machine learning (ML) methodologies offer significant potential for addressing the intricate challenges inherent in the analysis of neuroimaging data within the realm of neurological research. Nonetheless, the effective application of these techniques is markedly contingent upon the particular task and dataset under examination, and the absence of standardized methodologies poses impediments to cross-study result comparisons. This study contributes substantively to the collective endeavor by conducting a comprehensive evaluation and comparative analysis of ML models in the context of predicting schizophrenia and autism spectrum disorder (ASD) utilizing distinct functional Magnetic Resonance Imaging (fMRI) datasets. In this research, we introduce Canonical Correlation Analysis (CCA) as an innovative modality to augment the classification of these multifaceted neurological conditions. By elucidating the efficacy of CCA in ameliorating classification accuracy within the framework of Support Vector Machines (SVM), our study endeavors to propel the domain of neuroimaging and deepen our understanding of these intricate neurological disorders.

Genetic tuning of intrinsically photosensitive retinal ganglion cell subtype identity to drive visual behavior
The melanopsin-expressing, intrinsically photosensitive retinal ganglion cells (ipRGCs) comprise a subset of the ~40 retinal ganglion cell types in the mouse retina and drive a diverse array of light-evoked behaviors from circadian photoentrainment to pupil constriction to contrast sensitivity for visual perception. Central to the ability of ipRGCs to control this diverse array of behaviors is the distinct complement of morphophysiological features and gene expression patterns found in the M1-M6 ipRGC subtypes. However, the genetic regulatory programs that give rise to subtypes of ipRGCs are unknown. Here, we identify the transcription factor Brn3b (Pou4f2) as a key genetic regulator that shapes the unique functions of ipRGC subtypes and their diverse downstream visual behaviors.

A Dynamic Entropy Approach Reveals Reduced Functional Network Connectivity Trajectory Complexity in Schizophrenia
Over the past decade and a half, dynamic functional imaging has revolutionized the neuroimaging field. Since 2009, it has revealed low dimensional brain connectivity measures, has identified potential common human spatial connectivity states, has tracked the transition patterns of these states, and has demonstrated meaningful alterations in these transition and spatial patterns in neurological disorders, psychiatric disorders, and over the course of development. More recently, researchers have begun to analyze this data from the perspective of dynamic system and information theory in the hopes of understanding the constraints within which these dynamics occur and how they may support less easily quantified processes, such as information processing, cortical hierarchy, and consciousness. Progress has begun to accelerate in this area, particularly around consciousness, which appears to be strongly linked to entropy production in the brain. Outside of disorders of consciousness, however, little attention has been paid to the effects of psychiatric disease on entropy production in the human brain. Even disorders characterized by substantial changes in conscious experience have not been widely analyzed from this perspective. Here, we begin to rectify this gap by examining the complexity of subject trajectories in this state space through the lens of information theory. Specifically, we identify a basis for the dynamic functional connectivity state space and track subject trajectories through this state space over the course of the scan. The dynamic complexity of these trajectories is estimated using a Kozachenko-Leonenko entropy estimator, which assesses the rate of Shannon entropy production along each dimension of the proposed basis space. Using these estimates, we demonstrate that schizophrenia patients display substantially simpler trajectories than demographically matched healthy controls, and that this drop in complexity concentrates along specific dimensions of projected basis space. We also demonstrate that entropy generation in at least one of these dimensions is linked to cognitive performance. Overall, results suggest great value in applying dynamic systems theory to problems of neuroimaging and reveal a substantial drop in the complexity of brain function in schizophrenia patients.

Spatial neglect after subcortical stroke: sometimes a cortico-cortical disconnection syndrome
Background and Objectives: Spatial neglect is commonly attributed to lesions of a predominantly right-hemispheric cortical network. Although spatial neglect was also repeatedly observed after lesions to the basal ganglia and the thalamus, many anatomical network models omit these structures. We investigated if disruption of functional or structural connectivity can explain spatial neglect in subcortical stroke. Methods: We retrospectively investigated data of first-ever, acute stroke patients with right sided lesions of the basal ganglia (n = 27) or the thalamus (n = 16). Based on lesion location, we estimated i) functional connectivity via lesion-network mapping with normative resting state fMRI data, ii) structural white matter disconnection and iii) tract-wise disconnection of association fibres based on normative tractography data to investigate the association of spatial neglect and disconnection measures. Results: Apart from very small clusters of functional disconnection observed in inferior/middle frontal regions in lesion-network symptom mapping for basal ganglia lesions, our analyses found no evidence of functional or structural subcortico-cortical disconnection. Instead, the multivariate consideration of lesion load to several association fibres predicted the occurrence of spatial neglect (p = 0.0048; AUC = 0.76), which were the superior longitudinal fasciculus, inferior occipitofrontal fasciculus, superior occipitofrontal fasciculus, and the uncinate fasciculus. Conclusion: Disconnection of long (cortico-cortical) association fibres can explain spatial neglect in subcortical stroke. Like the competing theory of remote cortical hypoperfusion, this mechanism does not require the assumption of a genuine role for subcortical grey matter structures in spatial neglect.

Neurodegenerative fluid biomarkers are enriched in human cervical lymph nodes
In animal models, brain neurodegeneration biomarkers drain into cervical lymph nodes (CLNs). If this occurred in humans, CLNs may provide a readily accessible source of these biomarkers, draining the site of primary pathology. We tested this hypothesis in discovery and validation cohorts using ultrasound-guided fine needle aspiration (FNA). We measured amyloid-beta 40 and 42, phospho-Tau-181, glial-fibrillary-acidic-protein, and neurofilament-light using single molecule array in CLN aspirates and plasma from: i) a discovery cohort of 25 autoimmune patients, and from ii) plasma, CLNs and capillary blood in four healthy volunteers, an optimisation-validation cohort. FNA was well-tolerated by all participants. In both cohorts, all biomarkers were detected in all plasmas and CLNs, other than neurofilament-light (8/17 of discovery cohort). CLN biomarker concentrations were significantly greater than plasma concentrations for all except neurofilament-light, most markedly for phospho-Tau-181 (266 fold; P<0.02), whose CLN concentrations decreased with age (Spearman r=-0.66, P=0.001). This study presents the first evidence that neurodegenerative biomarkers are detectable in human CLNs. Raised CLN:plasma biomarker ratios suggest their concentration in CLNs, which may offer a sensitive compartment for minimally-invasive sampling in clinical trials. Further, age-associated phospho-Tau-181 reduction with age suggests FNA of CLNs may measure the integrity of brain lymphatic drainage in vivo.

Paranormal believers are more quickly and less accurate in rejecting the presence of the target in conjunction visual search compared to skeptics
Recent studies have shown that paranormal believers may exhibit cognitive dysfunctions, yet their performance in conjunction visual search has not been understood. To address this issue, we examined the performance of both paranormal believers and skeptics in a conjunction visual search task, with particular attention to their search time and accuracy across different set sizes in both target-present (TP) and target-absent (TA) trials. In our study, believers demonstrated a tendency toward fast but also displayed carelessness compared to skeptics when rejecting the presence of the target. Conversely, skeptics exhibited slower search times but showcased greater accuracy both in rejecting the presence of the target and in finding it. Overall, our findings suggest that believers were more quickly and less accurate in rejecting the presence of the target in conjunction visual search compared to skeptics, highlighting potential differences in cognitive processing between the skeptics and believers.

LSD flattens the hierarchy of directed information flow in fast whole-brain dynamics
Psychedelics are serotonergic drugs that profoundly alter consciousness, yet their neural mechanisms are not fully understood. A popular theory, RElaxed Beliefs Under pSychedelics (REBUS), posits that psychedelics flatten the hierarchy of information flow in the brain. Here, we investigate hierarchy based on the imbalance between sending and receiving brain signals, as determined by directed functional connectivity. We measure directed functional hierarchy in a magnetoencephalography (MEG) dataset of 16 healthy human participants who were administered a psychedelic dose (75 micrograms, intravenous) of lysergic acid diethylamide (LSD) under four different conditions. LSD diminishes the asymmetry of directed connectivity when averaged across time. Additionally, we demonstrate that machine learning classifiers distinguish between LSD and placebo more accurately when trained on one of our hierarchy metrics than when trained on traditional measures of functional connectivity. Taken together, these results indicate that LSD weakens the hierarchy of directed connectivity in the brain by increasing the balance between senders and receivers of neural signals.

Effects of Age on Cross-Cultural Differences in the Neural Correlates of Memory Retrieval
Culture can shape memory, but little research investigates age effects. The present study examines the neural correlates of memory retrieval for old, new, and similar lures in younger and older Americans and Taiwanese. Results show that age and culture impact discrimination of old from new items. Taiwanese performed worse than Americans, with age effects more pronounced for Taiwanese. Americans activated the hippocampus for new more than old items, but pattern of activity for the conditions did not differ for Taiwanese, nor did it interact with age. The engagement of left inferior frontal gyrus (LIFG) differed across cultures. Patterns of greater activity for old (for Americans) or new (for Taiwanese) items were eliminated with age, particularly for older Americans. The results are interpreted as reflecting cultural differences in orientation to novelty vs. familiarity for younger, but not older, adults, with the LIFG supporting interference resolution at retrieval. Support is not as strong for cultural differences in pattern separation processes. Although Americans had higher levels of memory discrimination than Taiwanese and engaged the LIFG for correct rejections more than false alarms, the patterns of behavior and neural activity did not interact with culture and age. Neither culture nor age impacted hippocampal activity, which is surprising given the region's role in pattern separation. The findings suggest ways in which cultural life experiences and concomitant information processing strategies can contribute to consistent effects of age across cultures or contribute to different trajectories with age in terms of memory.

Imaging demyelinated axons after spinal cord injuries with PET tracer 3F4AP
Spinal cord injuries (SCI) often lead to lifelong disability. Among the various types of injuries, incomplete and dyscomplete injuries, where some axons remain intact, offer potential for recovery. However, demyelination of these spared axons can worsen disability. Demyelination is a reversible phenomenon, and drugs like 4-aminopyridine (4AP), which target K+ channels in demyelinated axons, show that conduction can be restored. Yet, accurately assessing and monitoring demyelination post-SCI remains challenging due to the lack of suitable imaging methods. In this study, we introduce a novel approach utilizing the positron emission tomography (PET) tracer, [18F]3F4AP, specifically targeting K+ channels in demyelinated axons for SCI imaging. Rats with incomplete contusion injuries were imaged up to one month post-injury, revealing [18F]3F4AP's exceptional sensitivity to injury and its ability to detect temporal changes. Further validation through autoradiography and immunohistochemistry confirmed [18F]3F4AP's targeting of demyelinated axons. In a proof-of-concept study involving human subjects, [18F]3F4AP differentiated between complete and incomplete injuries, indicating axonal loss and demyelination, respectively. Moreover, alterations in tracer delivery were evident on dynamic PET images, suggestive of differences in spinal cord blood flow between complete and incomplete injuries. In conclusion, [18F]3F4AP demonstrates efficacy in detecting incomplete SCI in both animal models and humans. The potential for monitoring post-SCI demyelination changes and response to therapy underscores the utility of [18F]3F4AP in advancing our understanding and management of spinal cord injuries.

The adhesion GPCR ADGRV1 controls glutamate homeostasis in hippocampal astrocytes supporting neuron development: First insights into to pathophysiology of ADGRV1-associated epilepsy
ADGRV1 is the largest member of adhesion G protein-coupled receptor (aGPCR) family. In the cell, aGPCRs have dual roles in cell adhesion and signal transduction. Mutations in ADGRV1 have been linked not only to Usher syndrome (USH), which causes deaf-blindness, but recently also to various forms of epilepsy. While the USH defects are attributed to the loss of fiber links between membranes formed by the extracellular domain of ADGRV1, the pathomechanisms leading to epilepsy remain elusive to date. Here, we study the specific functions of ADGRV1 in astrocytes where it is highest expressed in the nervous system. Affinity proteomics showed the interaction of ADRGV1 with proteins enriched in astrocytes. Dysregulations of cellular processes important in astrocyte function were indicated by the different transcriptomes of patient-derived cells and Adgrv1-deficent mouse hippocampi compared to appropriate controls. Alteration in morphology and reduced numbers of astrocytes in the hippocampus of Adgrv1-deficent mice. Monitoring the glutamate uptake in colorimetric assay and by live cell imaging of a genetic glutamate reporter consistently showed that glutamate uptake from the extracellular environment is significantly reduced in Adgrv1-deficent astrocytes. Expression analyses of key enzymes of the glutamate-glutamine cycle in astrocytes and the glutamate metabolism indicated imbalanced glutamate homeostasis in Adgrv1-deficient astrocytes. Finally, we provide evidence that the supportive function of astrocytes in neuronal development also relies on ADGRV1 expression in astrocytes. Our data collectively provides first insights into the molecular pathophysiology underlying the development of epilepsy associated with mutations in ADGRV1.

CA1i pyramidal neurons mediate the role of NMDA receptor subunit GluN3A in depressive behavior and D-serine anti-depression
Depression is a heterogeneous psychiatric disorder characterized by multiple symptom clusters. N-methyl-d-aspartic acid receptors (NMDARs), consisting of various subunit proteins GluN1-3, are known to be critical molecular bases for the occurrence and treatment of depression. However, the involvement of the NMDAR subunit GluN3A in the heterogeneity of depressive symptoms and antidepressant effects remains unclear. Here, we found that chronic social defeat stress (CSDS) induced a range of depression-related behaviors, including decreased social interest, increased helplessness and anxiety-like behavior, and reduced GluN3A mRNA and protein expression in the hippocampal CA1 intermediate (CA1i) region. Additionally, GluN3A knockout (KO) mice exhibited pronounced helplessness behavior. Increasing GluN3A expression in the CA1i in both models specifically reversed the increased helplessness behavior but not social interest and anxiety-like behavior. Furthermore, the lack of CA1i GluN3A expression reduced the activity of CA1i pyramidal neurons in mice during helplessness behavior, a phenomenon also reversed by upregulating CA1i GluN3A expression. Further bidirectional modulation of CA1i pyramidal neuron activity directly mimicked or reversed CSDS-induced helplessness behavior. Finally, injection of D-serine into the CA1i rapidly improved helplessness behavior in CSDS mice while increasing the activity of CA1i pyramidal neurons, whereas knockout of the GluN3A or inhibition of CA1i neuron activity prevented the effect of D-serine. Our study elucidates the critical role of GluN3A subunit in regulating depression-related helplessness behavior and its mechanisms, as well as its role in the rapid antidepressant effect of D-serine, which deepen the understanding of the complex pathophysiology of depression and develop a potential clinical treatment new target.

Divergent Subregional Information Processing in Mouse Prefrontal Cortex During Working Memory
Working memory (WM) is a critical cognitive function allowing recent information to be temporarily held in mind to inform future action. This process depends on coordination between key subregions in prefrontal cortex (PFC) and other connected brain areas. However, few studies have examined the degree of functional specialization between these subregions throughout the phases of WM using electrophysiological recordings in freely-moving animals, particularly mice. To this end, we recorded single-units in three neighboring medial PFC (mPFC) subregions in mouse -- supplementary motor area (MOs), dorsomedial PFC (dmPFC), and ventromedial (vmPFC) -- during a freely-behaving non-match-to-position WM task. We found divergent patterns of task-related activity across the phases of WM. The MOs is most active around task phase transitions and encodes the starting sample location most selectively. Dorsomedial PFC contains a more stable population code, including persistent sample-location-specific firing during a five second delay period. Finally, the vmPFC responds most strongly to reward-related information during the choice phase. Our results reveal anatomically and temporally segregated computation of WM task information in mPFC and motivate more precise consideration of the dynamic neural activity required for WM.

Plaque-associated endogenous IgG and its impact on immunohistochemical detection of mouse monoclonal IgG antibodies in mouse models of Alzheimer's disease
Experimental studies for Alzheimer's disease (AD) have largely depended on transgenic mice with {beta}-amyloidosis. Here, we report plaque-associated endogenous immunoglobulin G (PA-IgG) and its impact on indirect immunohistochemical detection of mouse monoclonal IgG antibodies (Ms monoclonal IgG Abs) in the brain of AD mouse models. Immunostaining for Ms IgG in AD mouse models demonstrated endogenous IgG in the brain parenchyma accumulated on microglia associated with amyloid {beta} (A{beta}) plaques and/or A{beta} plaques themselves. This PA-IgG caused robust off-target binding of secondary Abs against Ms IgG (H+L) in indirect immunohistochemistry using Ms monoclonal IgG Abs. Blocking with Fab fragments of anti-Ms IgG (H+L) Ab was not effective against off-target binding. Unexpectedly, we found that secondary Abs that specifically recognize Ms IgG1, 2a, 2b, and 3 did not cause off-target binding on frozen brain sections of AppNL-G-F/NL-G-F mice, and enabled specific labeling of Ms monoclonal IgG Abs in the AD mouse model brains. We further demonstrated that indirect detection with a conventional secondary Ab against Ms IgG (H+L) Ab could lead to erroneous conclusions regarding A{beta} plaque burden and phosphorylated tau accumulation in AppNL-G-F/NL-G-F mice, and the use of Ms IgG subclass specific secondary Abs allowed to avoid the inevitable impediment caused by the endogenous IgG accumulation. Specific indirect detection of Ms monoclonal IgG Abs in AD mouse models by the use of secondary Abs against Ms IgG subclass would accelerate AD research by expanding the choice of Abs available for histochemical analysis in AD studies.

Optimal filtering strategies for task-specific functional PET imaging
Functional Positron Emission Tomography (fPET) has advanced as an effective tool for investigating dynamic processes in glucose metabolism and neurotransmitter action, offering potential insights into brain function, disease progression, and treatment development. Despite significant methodological advances, extracting stimulation-specific information presents additional challenges in optimizing signal processing across both spatial and temporal domains, which are essential for obtaining clinically relevant insights. This study aims to provide a systematic evaluation of state-of-the-art filtering techniques for fPET imaging. Forty healthy participants underwent a single [18F]FDG PET/MR scan, engaging in the cognitive task Tetris(R). Twenty thereof also underwent a second PET/MR session. Eight filtering techniques, including 3D and 4D Gaussian smoothing, highly constrained backprojection (hypr), iterative hypr (Ihypr4D), two MRI-Markov Random Field (MRI-MRF) filters (L=10 and 14 mm neighborhood) as well as static and dynamic Non-Local Means (sNLM and dNLM respectively) approaches, were applied to fPET data. Test-retest reliability (intraclass correlation coefficient), the identifiability of the task signal (temporal signal-to-noise ratio (tSNR)), spatial task-based activation (group level t-values), and sample size calculations were assessed. Results indicate distinct performance between filtering techniques. Compared to standard 3D Gaussian smoothing, dNLM, sNLM, MRI-MRF L=10 and Ihypr4D filters exhibited superior tSNR, while only dNLM and hypr showed improved test-retest reliability. Spatial task-based activation was enhanced by both NLM filters and MRI-MRF approaches. The dNLM enabled a minimum reduction of 15.4% in required sample size. The study systematically evaluated filtering techniques in fPET data processing, highlighting their strengths and limitations. The dNLM filter emerges as a promising choice, with improved performance across all metrics. However, filter selection should align with specific study objectives, considering factors like processing time and resource constraints.

Microstructural Mapping of Neural Pathways in Alzheimer's Disease using Macrostructure-Informed Normative Tractometry
Introduction: Diffusion MRI is sensitive to the microstructural properties of brain tissues and shows great promise in detecting the effects of degenerative diseases. However, many approaches analyze single measures averaged over regions of interest, without considering the underlying fiber geometry. Methods: Here, we propose a novel Macrostructure-Informed Normative Tractometry (MINT) framework, to investigate how white matter microstructure and macrostructure are jointly altered in mild cognitive impairment (MCI) and dementia. We compare MINT-derived metrics with univariate metrics from diffusion tensor imaging (DTI), to examine how fiber geometry may impact interpretation of microstructure. Results: In two multi-site cohorts from North America and India, we find consistent patterns of microstructural and macrostructural anomalies implicated in MCI and dementia; we also rank diffusion metrics' sensitivity to dementia. Discussion: We show that MINT, by jointly modeling tract shape and microstructure, has potential to disentangle and better interpret the effects of degenerative disease on the brain's neural pathways.

Working memory as a representational template for reinforcement learning
Working memory (WM) and reinforcement learning (RL) both influence decision-making, but how they interact to affect behaviour remains unclear. We assessed whether RL is influenced by the format of visual stimuli in WM, either feature-based or unified, object-based representations. In a pre-registered paradigm, participants learned stimulus-action combinations, mapping four stimuli onto two feature dimensions to one of two actions through probabilistic feedback. In parallel, participants retained the RL stimulus in WM and were asked to recall this stimulus after each trial. Crucially, the format of representation probed in WM was manipulated, with blocks encouraging either separate features or bound objects to be remembered. Incentivising a feature-based WM representation facilitated feature-based learning, shown by an improved choice strategy. This reveals a role of WM in providing sustained internal representations that are harnessed by RL, providing a framework by which these two cognitive processes cooperate.

Group social dynamics in a semi-natural setup reveal an adaptive value for aggression in male mice
Background: Maladaptive aggression in humans is associated with several psychiatric conditions and lacks effective treatment. Nevertheless, aggression constitutes an essential behavior throughout the animal kingdom as long as it is tightly regulated. Studying how social dominance hierarchies (SDH) regulate aggression and access to resources in an enriched environment (EE) can narrow the translational gap between aggression in animal models and humans normal and pathological behavior. Methods: The social box (SB) is a semi-natural setup for automatic and prolonged monitoring of mouse group dynamics. We utilized the SB to decipher complex tradeoffs between aggression, social avoidance, resource allocation, and dominance in two mouse models of increased aggression: (i) a model of early exposure to EE and (ii) a model of oxytocin receptor deficiency (OxtR-/-). While EE increases aggression as an adaptive response to external stimuli, hyper-aggression in OxtR-/- mice is accompanied by marked abnormalities in social behavior. Results: EE groups exhibited significant social avoidance, and an increased proportion of their encounters developed into aggressive interactions, resulting in lower levels of exploratory activity and overall aggression. The hierarchy in EE was more stable than in control groups, and dominance was correlated with access to resources. In OxtR-/- groups, mice engaged in excessive social encounters and aggressive chasing, accompanied by increased overall activity. In OxtR-/- groups, dominance hierarchies existed but were not correlated with access to resources. Conclusion: Measuring aggression and social dominance hierarchies in a semi-natural setup reveals the adaptive value of aggression in EE and OxtR-/- mice, respectively. This approach can enhance translational research of pathological aggression.

HSD2 neurons are evolutionarily conserved and required for aldosterone-induced salt appetite
Excessive aldosterone production increases the risk of heart disease, stroke, dementia, and death. Aldosterone increases both sodium retention and sodium consumption, and increased sodium consumption predicts end-organ damage in patients with aldosteronism. Preventing this increase may improve outcomes, but the behavioral mechanisms of aldosterone-induced sodium appetite remain unclear. In rodents, we identified aldosterone-sensitive neurons, which express the mineralocorticoid receptor and its pre-receptor regulator, 11-beta-hydroxysteroid dehydrogenase 2 (HSD2). Here, we identify HSD2 neurons in the human brain and use a mouse model to evaluate their role in aldosterone-induced salt intake. First, we confirm that dietary sodium deprivation increases aldosterone production, HSD2 neuron activity, and salt intake. Next, we show that activating HSD2 neurons causes a large and specific increase in salt intake. Finally, we use dose-response studies and genetically targeted ablation of HSD2 neurons to show that aldosterone-induced salt intake requires these neurons. Identifying HSD2 neurons in the human brain and their necessity for aldosterone-induced salt intake in mice improves our understanding of appetitive circuits and highlights this small cell population as a therapeutic target for moderating dietary sodium.

Le Petit Prince Hong Kong (LPPHK): Naturalistic fMRI and EEG data from older Cantonese speakers
Currently, the field of neurobiology of language is based on data from only a few Indo-European languages. The majority of this data comes from younger adults neglecting other age groups. Here we present a multimodal database which consists of task-based and resting state fMRI, structural MRI, and EEG data while participants over 65 years old listened to sections of the story The Little Prince in Cantonese. We also provide data on participants' language history, lifetime experiences, linguistic and cognitive skills. Audio and text annotations, including time-aligned speech segmentation and prosodic information, as well as word-by-word predictors such as frequency and part-of-speech tagging derived from natural language processing (NLP) tools are included in this database. Both MRI and EEG data diagnostics revealed that the data has good quality. This multimodal database could advance our understanding of spatiotemporal dynamics of language comprehension in the older population and help us study the effects of healthy aging on the relationship between brain and behaviour.

High-dimensional proteomic analysis for pathophysiological classification of Traumatic Brain Injury
Pathophysiology and outcomes after Traumatic Brain Injury (TBI) are complex and highly heterogenous. Current classifications are uninformative about pathophysiology, which limits prognostication and treatment. Fluid-based biomarkers can identify pathways and proteins relevant to TBI pathophysiology. Proteomic approaches are well suited to exploring complex mechanisms of disease, as they enable sensitive assessment of an expansive range of proteins. We used novel high-dimensional, multiplex proteomic assays to study changes in plasma protein expression in acute moderate-severe TBI. We analysed samples from 88 participants in the longitudinal BIO-AX-TBI cohort (n=38 TBI within 10 days of injury, n=22 non-TBI trauma, n=28 non-injured controls) on two platforms: Alamar NULISA(TM) CNS Diseases and OLINK(R) Target 96 Inflammation. Participants also had data available from Simoa(R) (neurofilament light, GFAP, total tau, UCHL1) and Millipore (S100B). The Alamar panel assesses 120 proteins, most of which have not been investigated before in TBI, as well as proteins, such as GFAP, which differentiate TBI from non-injured and non-TBI trauma controls. A subset (n=29 TBI, n=24 non-injured controls) also had subacute 3T MRI measures of lesion volume and white matter injury (fractional anisotropy, scanned 10 days to 6 weeks after injury). Differential Expression analysis identified 16 proteins with TBI-specific significantly different plasma expression. These were neuronal markers (calbindin2, UCHL1, visinin-like protein1), astroglial markers (S100B, GFAP), tau and other neurodegenerative disease proteins (total tau, pTau231, PSEN1, amyloid beta42, 14-3-3{gamma}), inflammatory cytokines (IL16, CCL2, ficolin2), cell signalling (SFRP1), cell metabolism (MDH1) and autophagy related (sequestome1) proteins. Acute plasma levels of UCHL1, PSEN1, total tau and pTau231 correlated with subacute lesion volume, while sequestome1 was correlated with whole white matter skeleton fractional anisotropy and CCL2 was inversely correlated with corpus callosum FA. Neuronal, astroglial, tau and neurodegenerative proteins correlated with each other, and IL16, MDH1 and sequestome1. Clustering (k means) by acute protein expression identified 3 TBI subgroups which had differential injury patterns, but did not differ in age or outcome. Proteins that overlapped on two platforms had excellent (r>0.8) correlations between values. We identified TBI-specific changes in acute plasma levels of proteins involved in amyloid processing, inflammatory and cellular processes such as autophagy. These changes were related to patterns of injury, thus demonstrating that processes previously only studied in animal models are also relevant in human TBI pathophysiology. Our study highlights the potential of proteomic analysis to improve the classification and understanding of TBI pathophysiology, with implications for prognostication and treatment development.

Morphology and synapse topography optimize linear encoding of synapse numbers in Drosophila looming responsive descending neurons.
Synapses are often precisely organized on dendritic arbors, yet the role of synaptic topography in dendritic integration remains poorly understood. Utilizing electron microscopy (EM) connectomics we investigate synaptic topography in Drosophila melanogaster looming circuits, focusing on retinotopically tuned visual projection neurons (VPNs) that synapse onto descending neurons (DNs). Synapses of a given VPN type project to non-overlapping regions on DN dendrites. Within these spatially constrained clusters, synapses are not retinotopically organized, but instead adopt near random distributions. To investigate how this organization strategy impacts DN integration, we developed multicompartment models of DNs fitted to experimental data and using precise EM morphologies and synapse locations. We find that DN dendrite morphologies normalize EPSP amplitudes of individual synaptic inputs and that near random distributions of synapses ensure linear encoding of synapse numbers from individual VPNs. These findings illuminate how synaptic topography influences dendritic integration and suggest that linear encoding of synapse numbers may be a default strategy established through connectivity and passive neuron properties, upon which active properties and plasticity can then tune as needed.

Complementary benefits of multivariate and hierarchical models for identifying individual differences in cognitive control
Understanding individual differences in cognitive control is a central goal in psychology and neuroscience. Reliably measuring these differences, however, has proven extremely challenging, at least when using standard measures in cognitive neuroscience such as response times or task-based fMRI activity. While prior work has pinpointed the source of the issue --- the vast amount of cross-trial variability within these measures --- no study has rigorously evaluated potential solutions. Here, we do so with one potential way forward: an analytic framework that combines hierarchical Bayesian modeling with multivariate decoding of trial-level fMRI data. Using this framework and longitudinal data from the Dual Mechanisms of Cognitive Control project, we estimated individuals' neural responses associated with cognitive control within a color-word Stroop task, then assessed the reliability of these individuals' responses across a time interval of several months. We show that in many prefrontal and parietal brain regions, test--retest reliability was near maximal, and that only hierarchical models were able to reveal this state of affairs. Further, when compared to traditional univariate contrasts, multivariate decoding enabled individual-level correlations to be estimated with significantly greater precision. We specifically link these improvements in precision to the optimized suppression of cross-trial variability in decoding. Together, these findings not only indicate that cognitive control-related neural responses individuate people in a highly stable manner across time, but also suggest that integrating hierarchical and multivariate models provides a powerful approach for investigating individual differences in cognitive control, one that can effectively address the issue of high-variability measures.

Common neural mechanisms supporting time judgements in humans and monkeys
There has been an increasing interest in identifying the biological underpinnings of human time perception, for which purpose research in non-human primates (NHP) is common. Although previous work, based on behaviour, suggests that similar mechanisms support time perception across species, the neural correlates of time estimation in humans and NHP have not been directly compared. In this study, we assess whether brain evoked responses during a time categorization task are similar across species. Specifically, we assess putative differences in post-interval evoked potentials as a function of perceived duration in human EEG (N = 24) and local field potential (LFP) and spike recordings in pre-supplementary motor area (pre-SMA) of one monkey. Event-related potentials (ERPs) differed significantly after the presentation of the temporal interval between short and long perceived durations in both species, even when the objective duration of the stimuli was the same. Interestingly, the polarity of the reported ERPs was reversed for incorrect trials (i.e., the ERP of a long stimulus looked like the ERP of a short stimulus when a time categorization error was made). Hence, our results show that post-interval potentials reflect the perceived (rather than the objective) duration of the presented time interval in both NHP and humans. In addition, firing rates in monkey's pre-SMA also differed significantly between short and long perceived durations and were reversed in incorrect trials. Together, our results show that common neural mechanisms support time categorization in NHP and humans, thereby suggesting that NHP are a good model for investigating human time perception

Projection-TAGs enable multiplex projection tracing and multi-modal profiling of projection neurons
Single-cell multiomic techniques have sparked immense interest in developing a comprehensive multi-modal map of diverse neuronal cell types and their brain wide projections. However, investigating the spatial organization, transcriptional and epigenetic landscapes of brain wide projection neurons is hampered by the lack of efficient and easily adoptable tools. Here we introduce Projection-TAGs, a retrograde AAV platform that allows multiplex tagging of projection neurons using RNA barcodes. By using Projection-TAGs, we performed multiplex projection tracing of the mouse cortex and high-throughput single-cell profiling of the transcriptional and epigenetic landscapes of the cortical projection neurons. Projection-TAGs can be leveraged to obtain a snapshot of activity-dependent recruitment of distinct projection neurons and their molecular features in the context of a specific stimulus. Given its flexibility, usability, and compatibility, we envision that Projection-TAGs can be readily applied to build a comprehensive multi-modal map of brain neuronal cell types and their projections.

Angiotensin Converting Enzyme (ACE) expression in microglia reduces amyloid β deposition and neurodegeneration by increasing SYK signaling and endolysosomal trafficking.
Genome-wide association studies (GWAS) have identified many gene polymorphisms associated with an increased risk of developing Late Onset Alzheimer's Disease (LOAD). Many of these LOAD risk-associated alleles alter disease pathogenesis by influencing microglia innate immune responses and lipid metabolism pathways. Angiotensin Converting Enzyme (ACE), a GWAS LOAD risk-associated gene best known for its role in regulating systemic blood pressure, also enhances innate immunity and lipid processing in peripheral myeloid cells, but a role for ACE in modulating the function of myeloid-derived microglia remains unexplored. Using novel mice engineered to express ACE in microglia and CNS associated macrophages (CAMs), we find that ACE expression in microglia reduces A{beta} plaque load, preserves vulnerable neurons and excitatory synapses, and greatly reduces learning and memory abnormalities in the 5xFAD amyloid mouse model of Alzheimer's Disease (AD). ACE-expressing microglia show enhanced A{beta} phagocytosis and endolysosomal trafficking, increased clustering around amyloid plaques, and increased SYK tyrosine kinase activation downstream of the major A{beta} receptors, TREM2 and CLEC7A. Single microglia sequencing and digital spatial profiling identifies downstream SYK signaling modules that are differentially expressed by ACE expression in microglia that mediate endolysosomal biogenesis and trafficking, mTOR and PI3K/AKT signaling, and increased oxidative phosphorylation, while pharmacologic inhibition of SYK activity in ACE-expressing microglia abrogates the potentiated A{beta} engulfment and endolysosomal trafficking. These findings establish a role for ACE in enhancing microglial immune function and they identify potential utility for ACE-expressing microglia as a cell-based therapy to augment endogenous microglial responses to A{beta} in AD.

Amblyopic deficits in monocular processing and binocular interactions revealed by submillimeter 7T fMRI and EEG frequency tagging
Disruption of retinal input early in life can lead to amblyopia, a condition characterized by reduced visual acuity despite corrected optics. Although extensive losses of neural activity have been found in the early visual cortex, it remains unclear whether they reflect deficits in feedforward or feedback processing, or abnormal binocular interactions. Combining submillimeter 7T fMRI and EEG frequency tagging, our study revealed the precise neural deficits in monocular processing and binocular interactions in human adults with unilateral amblyopia. Cortical depth-dependent fMRI revealed monocular response deficits in cortical layers of the primary visual cortex (V1) receiving thalamic input, which carried over to the downstream areas (V2-V4) in feedforward processing. Binocular stimulation produced a greater signal loss in the superficial layers of V1, consistent with suppression from the fellow eye by lateral inhibition. EEG data further demonstrate reduced suppression from the amblyopic eye, weakened binocular integration, and delayed monocular and binocular processing. Our results support attenuated and delayed monocular processing in V1 layers receiving thalamic input in human amblyopia, followed by imbalanced binocular suppression and weakened binocular integration in the superficial layers, further reducing signal strength and processing speed. These precise neural deficits can help developing more targeted and effective treatments for the vision disorder.

Intrinsic diving reflex enhances cognitive performance by alleviating microvascular dysfunction in vascular cognitive impairment
Vascular cognitive impairment (VCI) stands as the second-most prominent contributor to cognitive decline, lacking efficacious interventions. Chronic cerebral hypoperfusion (CCH) triggers microvascular dysfunction, which plays a critical role in VCI pathophysiology, emerging as a pivotal therapeutic target. While interventions addressing facets of microvascular dysfunction like angiogenesis and blood-brain barrier functionality show promise, the evaluation of microvascular constriction, another key component, remains unexplored. The diving reflex (DR) represents an oxygen-conserving response, characterized by robust vasodilation and potentially also inducing angiogenesis. In this investigation, we studied DR's functionality and underlying mechanisms within a rat bilateral common carotid artery occlusion induced CCH model. Remarkably, progressive hippocampal microvascular constriction exhibited strong correlations with short-term memory impairment during both early (R2=0.641) and late phases (R2=0.721) of CCH. Implementation of DR led to a significant reduction in microvascular constriction within the hippocampus (~2.8-fold) and striatum (~1.5-fold), accompanied by enhanced vasodilatory capacity and heightened expression of vasoactive neuropeptides. Furthermore, DR attenuated microvascular degeneration across various brain subregions affected by CCH, concomitant with increased levels of multiple angiogenic factors. The reinforced microvascular integrity facilitated by DR corresponded with significantly improved short-term recognition memory and long-term spatial memory functions observed during the late phase of CCH. The comprehensive and synergistic effects of DR on various aspects of microvascular function and cognitive preservation highlight its potential as a disease-modifying therapeutic strategy in VCI.

Involvement of neurons in the non-human primate anterior striatum in proactive inhibition
Behaving as desired requires selecting the appropriate behavior and inhibiting the selection of inappropriate behavior. This inhibitory function involves multiple processes, such as reactive and proactive inhibition, instead of a single process. In this study, macaque monkeys were required to perform a task in which they had to sequentially select (accept) or refuse (reject) a choice. Neural activity was recorded from the anterior striatum, which is considered to be involved in behavioral inhibition, focusing on the distinction between proactive and reactive inhibitions. We identified neurons with significant activity changes during the rejection of bad objects. Cluster analysis revealed three distinct groups, of which one showed obviously increased activity during object rejection, suggesting its involvement in proactive inhibition. This activity pattern was consistent irrespective of the rejection method, indicating a role beyond mere saccadic suppression. Furthermore, minimal activity changes during the fixation task indicated that these neurons were not primarily involved in reactive inhibition. In conclusion, these findings suggest that the anterior striatum plays a crucial role in cognitive control and orchestrates goal-directed behavior through proactive inhibition, which may be critical in understanding the mechanisms of behavioral inhibition dysfunction that occur in patients with basal ganglia disease.

Self-Assembled Origami Neural Probes for Scalable, Multifunctional, Three-Dimensional Neural Interface
Flexible intracortical neural probes have drawn attention for their enhanced longevity in high-resolution neural recordings due to reduced tissue reaction. However, the conventional monolithic fabrication approach has met significant challenges in: (i) scaling the number of recording sites for electrophysiology; (ii) integrating of other physiological sensing and modulation; and (iii) configuring into three-dimensional (3D) shapes for multi-sided electrode arrays. We report an innovative self-assembly technology that allows for implementing flexible origami neural probes as an effective alternative to overcome these challenges. By using magnetic-field-assisted hybrid self-assembly, multiple probes with various modalities can be stacked on top of each other with precise alignment. Using this approach, we demonstrated a multifunctional device with scalable high-density recording sites, dopamine sensors and a temperature sensor integrated on a single flexible probe. Simultaneous large-scale, high-spatial-resolution electrophysiology was demonstrated along with local temperature sensing and dopamine concentration monitoring. A high-density 3D origami probe was assembled by wrapping planar probes around a thin fiber in a diameter of 80-105 um using optimal foldable design and capillary force. Directional optogenetic modulation could be achieved with illumination from the neuron-sized micro-LEDs (uLEDs) integrated on the surface of 3D origami probes. We could identify angular heterogeneous single-unit signals and neural connectivity 360 degrees surrounding the probe. The probe longevity was validated by chronic recordings of 64-channel stacked probes in behaving mice for up to 140 days. With the modular, customizable assembly technologies presented, we demonstrated a novel and highly flexible solution to accommodate multifunctional integration, channel scaling, and 3D array configuration.

Post-mortem evidence for a reciprocal relationship between genomic DNA damage and alpha-synuclein pathology in dementia with Lewy bodies.
DNA damage and DNA damage repair (DDR) dysfunction are insults with broad implications on cellular physiology, including in proteostasis, and have been recently implicated in many neurodegenerative diseases. Alpha-synuclein (aSyn), a pre-synaptic and nuclear protein associated with neurodegenerative disorders known as synucleinopathies, has been implicated in DNA double strand break (DSB) repair function. Consistently, DSB induction has been demonstrated in cell and animal models of synucleinopathy. Nevertheless, the types of DNA damage and the contribution of DNA damage towards Lewy body (LB) formation in synucleinopathies are unknown. Here, we demonstrate the increase of DSB in neuronal and non-neuronal cellular populations of post-mortem temporal cortex tissue from dementia with Lewy body (DLB) patients and demonstrate increases in DSBs early at a presymptomatic age of aSyn transgenic mice. Strikingly, in postmortem DLB tissue, DNA damage-derived ectopic cytoplasmic genomic material (eCGM) was evident within the majority of LBs examined. The observed cellular pathology was consistent with nucleoproteasomal upregulation of associated DNA damage repair proteins, particularly in base excision repair and DSB repair pathways. Collectively our study demonstrates the early occurrence of DNA damage and associated nucleoproteasomal changes in response to nuclear aSyn pathology. Furthermore, the data suggests a potential involvement for DNA damage derived eCGM for the facilitation of cytoplasmic aSyn aggregates. Ultimately, uncovering pathological mechanisms underlying DNA damage in DLB sheds light into novel disease mechanisms and opens novel possibilities for diagnosing and treating synucleinopathies.

Repix: reliable, reusable, versatile chronic Neuropixels implants using minimal components
Neuropixels probes represent the state-of-the-art for high-yield electrophysiology in neuroscience: the simultaneous recording of hundreds of neurons is now routinely carried out in head-restrained animals. In contrast, neural recording in unrestrained animals, as well as recording and tracking neurons over days, remains challenging, though it is possible using chronic implants. A major challenge is the availability of simple methods that can be implemented with limited or no prior experience with Neuropixels probes, while achieving reliable, reusable, versatile high-density electrophysiology. Here we developed, deployed, and evaluated the real-world performance of Repix, a chronic implantation system that permits the repeated re-use of Neuropixels probes. The lightweight system allows implanted animals to express a full range of natural behaviors, including social behaviors. We show that Repix allows the recording of hundreds of neurons across many months, up to a year, with implants across cortical and subcortical brain regions. Probes can be reused repeatedly with stable yield. Repix has been used by 16 researchers in 10 laboratories to date, and we evaluated the real-world performance of Repix in a variety of chronic recording paradigms in both mice and rats with a combined 202 implantations. We found that the key advantage of Repix is robustness and simplicity. Adopters of Repix became proficient at five procedures on average, regardless of prior experience with in vivo electrophysiology. With the companion protocol alongside this article, the performance and user-friendliness of Repix should facilitate a wide uptake of chronic Neuropixels recordings.

Blind but alive - congenital loss of atoh7 disrupts the visual system of adult zebrafish.
Purpose Vision is the predominant sense in most animal species. Loss of vision can be caused by a multitude of factors resulting in anatomical as well as behavioral changes. In mice and zebrafish, atoh7 mutants are completely blind as they fail to generate retinal ganglion cells during development. In contrast to mice, raising blind zebrafish to adulthood is challenging and this important model is currently missing in the field. Here, we report the phenotype of homozygous mutant adult zebrafish atoh7 mutants that have been raised using adjusted feeding and holding conditions. Methods The phenotype of adult mutants was characterized using classical histology and immunohistochemistry as well as optical coherence tomography. In addition, the optokinetic response was characterized. Results Adult atoh7 mutants display dark body pigmentation and significantly reduced body length. They fail to form retinal ganglion cells, the resulting nerve fiber layer as well as the optic nerve, and consequently behave completely blindly. In contrast, increased amounts of other retinal neurons and Muller glia are formed. In addition, the optic tectum is anatomically reduced in size, presumably due to the missing retinal input. Conlusions Taken together, we provide a comprehensive characterization of a completely blind adult zebrafish mutant with focus on retinal and tectal morphology, as a useful model for glaucoma and optic nerve aplasia.

Nutritional state-dependent modulation of Insulin-Producing Cells in Drosophila
Insulin plays a key role in regulating metabolic homeostasis across vertebrate and invertebrate species. Drosophila Insulin-Producing Cells (IPCs) are functional analogues to mammalian pancreatic beta cells and release insulin directly into circulation. IPC activity is modulated by nutrient availability, circadian time, and the behavioral state of animals. To investigate the in vivo dynamics of IPC activity in the context of metabolic homeostasis, we quantified effects of nutritional and internal state changes on IPCs using electrophysiological recordings. We found that the nutritional state strongly modulates IPC activity. IPCs were less active in starved flies than in fed flies. Refeeding starved flies with glucose significantly increased IPC activity, suggesting that IPCs are regulated by hemolymph sugar levels. In contrast to glucose feeding, glucose perfusion had no effect on IPC activity. This was reminiscent of the mammalian incretin effect, in which ingestion of glucose drives higher insulin release than intravenous glucose application. Contrary to IPCs, Diuretic hormone 44-expressing neurons in the pars intercerebralis (DH44PINs), which are anatomically similar to IPCs, significantly increased their activity during glucose perfusion. Functional connectivity experiments based on optogenetic activation demonstrated that glucose-sensing DH44PINs do not affect IPC activity, while other DH44Ns inhibit IPCs. This suggests that populations of autonomously and systemically glucose-sensing neurons are working in parallel to maintain metabolic homeostasis. Ultimately, metabolic state changes affect animal behavior. For example, hungry flies increase their locomotor activity in search of food to maintain metabolic homeostasis. In support of this idea, activating IPCs had a small, satiety-like effect in starved flies, resulting in reduced walking activity, whereas activating DH44Ns strongly increased walking activity. Taken together, we show that IPCs and DH44Ns are an integral part of a sophisticated modulatory network that orchestrates glucose homeostasis and adaptive behavior in response to shifts in the metabolic state.

Loss of spontaneous vasomotion precedes impaired cerebrovascular reactivity and microbleeds in a mouse model of cerebral amyloid angiopathy
Background: Cerebral amyloid angiopathy (CAA) is a cerebral small vessel disease in which amyloid-{beta} accumulates in vessel walls. CAA is a leading cause of symptomatic lobar intracerebral hemorrhage and an important contributor to age-related cognitive decline. Recent work has suggested that vascular dysfunction may precede symptomatic stages of CAA, and that spontaneous slow oscillations in arteriolar diameter (termed vasomotion), important for amyloid-{beta} clearance, may be impaired in CAA. Methods: To systematically study the progression of vascular dysfunction in CAA, we used the APP23 mouse model of amyloidosis, which is known to develop spontaneous cerebral microbleeds mimicking human CAA. Using in vivo 2-photon microscopy, we longitudinally imaged unanesthetized APP23 transgenic mice and wildtype littermates from 7 to 14 months of age, tracking amyloid-{beta} accumulation and vasomotion in individual pial arterioles over time. MRI was used in separate groups of 12-, 18-, and 24-month-old APP23 transgenic mice and wildtype littermates to detect microbleeds and to assess cerebral blood flow and cerebrovascular reactivity with pseudo-continuous arterial spin labeling. Results: We observed a significant decline in vasomotion with age in APP23 mice, while vasomotion remained unchanged in wildtype mice with age. This decline corresponded in timing to initial vascular amyloid-{beta} deposition (~8-10 months of age), although was more strongly correlated with age than with vascular amyloid-{beta} burden in individual arterioles. Declines in vasomotion preceded the development of MRI-visible microbleeds and the loss of smooth muscle actin in arterioles, both of which were observed in APP23 mice by 18 months of age. Additionally, evoked cerebrovascular reactivity was intact in APP23 mice at 12 months of age, but significantly lower in APP23 mice by 24 months of age. Conclusions: Our findings suggest that a decline in spontaneous vasomotion is an early, potentially pre-symptomatic, manifestation of CAA and vascular dysfunction, and a possible future treatment target.

The aperiodic exponent of pupil fluctuations in the resting state predicts excitation/inhibition balance in attentional processing
The aperiodic exponent of neural signals in different modalities is associated with the excitation/inhibition balance of the neural system. Given that resting pupil fluctuations contain rich temporal dynamics, we hypothesized that the aperiodic exponent of pupil fluctuations could predict the neural excitation/inhibition balance in attentional processing. The present study was the first attempt to investigate the cognitive significance of the aperiodic exponent of pupil responses. We recorded participants' resting pupil fluctuations and measured their visual attention with a Posner cueing task. Significant correlations were found between the aperiodic exponent of pupil fluctuations and microsaccadic and behavioral responses when stimulus uncertainty was high and thus required a neural excitation/inhibition balance. Furthermore, an independent analysis showed that the aperiodic exponent of pupil fluctuations was predictive of an individual's ADHD symptoms of hyperactivity/impulsivity, suggesting its potential to reflect an individual's trait of attentional processing. These findings highlight the rich information contained in pupil fluctuations and open a new avenue for accessing the neural excitation/inhibition balance in cognitive processing.

A comparative analysis of Parkinson's disease and inflammatory bowel disease gut microbiomes highlights shared depletions in key butyrate-producing bacteria
Epidemiological studies reveal that a diagnosis of inflammatory bowel disease (IBD) is associated with an increased risk of developing Parkinson's disease (PD). The presence of gut dysbiosis has been documented in both PD and IBD patients, however it is currently unknown how alterations in the gut microbiome may contribute to the epidemiological link between both diseases. To identify shared and distinct features of the PD and IBD microbiome, we performed the first joint analysis of 54 PD, 26 IBD, and 16 healthy control gut metagenomes recruited from clinics at the University of Florida, and directly compared the gut microbiomes from PD and IBD persons. Larger, publicly available PD and IBD metagenomic datasets were also analyzed to validate and extend our findings. Depletions in short-chain fatty acid (SCFA) producing bacteria, including Roseburia intestinalis, Faecalibacterium prausnitzii, Anaerostipes hadrus, and Eubacterium rectale, as well as depletions in SCFA synthesis pathways, were demonstrated across PD and IBD datasets. We posit that direct comparison of PD and IBD gut microbiomes will be important in identifying features within the IBD gut which may be associated with PD. The data revealed a consistent depletion in SCFA-producing bacteria across both PD and IBD, suggesting that loss of these microbes may influence the pathophysiology of both disease states.

5-HT Neurons Integrate GABA and Dopamine Inputs to Regulate Meal Initiation
Obesity is a growing global health epidemic with limited effective therapeutics. Serotonin (5-HT) is one major neurotransmitter which remains an excellent target for new weight-loss therapies, but there remains a gap in knowledge on the mechanisms involved in 5-HT produced in the dorsal Raphe nucleus (DRN) and its involvement in meal initiation. Using a closed-loop optogenetic feeding paradigm, we showed that the 5-HTDRN[->]arcuate nucleus (ARH) circuit plays an important role in regulating meal initiation. Incorporating electrophysiology and ChannelRhodopsin-2-Assisted Circuit Mapping, we demonstrated that 5-HTDRN neurons receive inhibitory input partially from GABAergic neurons in the DRN, and the 5-HT response to GABAergic inputs can be enhanced by hunger. Additionally, deletion of the GABAA receptor subunit in 5-HT neurons inhibits meal initiation with no effect on the satiation process. Finally, we identified the instrumental role of dopaminergic inputs via dopamine receptor D2 in 5-HTDRN neurons in enhancing the response to GABA-induced feeding. Thus, our results indicate that 5-HTDRN neurons are inhibited by synergistic inhibitory actions of GABA and dopamine, which allows for the initiation of a meal.

GABA and astrocytic cholesterol determine the lipid environment of GABAAR in cultured cortical neurons.
The {gamma}-aminobutyric acid (GABA) type A receptor (GABAAR), a GABA activated pentameric chloride channel, mediates fast inhibitory neurotransmission in the brain. The lipid environment is critical for GABAAR function. How lipids regulate the channel in the cell membrane is not fully understood. Here we employed super resolution imaging of lipids to demonstrate that the agonist GABA induces a rapid and reversible membrane translocation of GABAAR to phosphatidylinositol 4,5-bisphosphate (PIP2) clusters in mouse primary cortical neurons. This translocation relies on nanoscopic separation of PIP2 clusters and lipid rafts (cholesterol-dependent ganglioside clusters). In a resting state, the GABAAR associates with lipid rafts and this colocalization is enhanced by uptake of astrocytic secretions. These astrocytic secretions enhance endocytosis and delay desensitization. Our findings suggest intercellular signaling from astrocytes regulates GABAAR location based on lipid uptake in neurons. The findings have implications for treating mood disorders associated with altered neural excitability.