bioRxiv Subject Collection: Neuroscience's Journal

Cerebellar Ex Vivo Magnetic Resonance Imaging at its Feasibility Limit: Up to 77-Microns Isotropic Resolution using Low-Bandwidth Balanced Steady State Free Precession (LoBa-bSSFP) Sequences and 3T Standard Equipment
Background: Ultra-high-resolution magnetic resonance imaging of the ex vivo brain is increasingly becoming an indispensable tool for studying the morphology and potential pathology of the brain. Despite the important role of the cerebellum in nervous system functions and motor control, as well as its potential damage in neurological diseases, it remains relatively understudied compared to other brain regions. One major reason is the even finer structures. Methods: A balanced steady state free precession approach with receiver bandwidths as low as 50Hz/pixel and long repetition times of 36ms is suggested and optimized, called "LoBa-bSSFP", which enhances the signal-to-noise ratio and alleviates strain on the gradient system for the ultra-high spatial resolutions. A radiofrequency phase cycle scheme is used to reduce potential artifacts. Only 3T MRI standard equipment is utilized for acquisition and basic image reconstruction of the ex vivo brain immersed in perfluoropolyether. Results: The presented LoBa-bSSFP approach provides images with very good soft tissue contrast and a detailed visualization of cerebellar morphology. It enables isotropic resolutions of 98-microns for the entire cerebellum, a further refinement allows even up to 77-microns isotropic on a purely clinical MR system. The acquisitions preserved the integrity of the ex vivo cerebellum, so maintaining its connection to the cerebrum and brainstem. Conclusions: Our findings demonstrate the feasibility of employing 3T based LoBa-bSSFP for true ultra-high-resolution ex vivo imaging of the cerebellum, reaching resolutions up to 77-microns isotropic and the potential to reveal subtle microscopic abnormalities of the cerebellar cortex. LoBa-bSSFP may be superior to conventional FLASH sequences in terms of acquisition efficiency and - in some cases - even contrast.

Mesolimbic dopamine encodes reward prediction errors independent of learning rates
Biological accounts of reinforcement learning posit that dopamine encodes reward prediction errors (RPEs), which are multiplied by a learning rate to update state or action values. These values are thought to be represented in synaptic weights in the striatum, and updated by dopamine-dependent plasticity, suggesting that dopamine release might reflect the product of the learning rate and RPE. Here, we leveraged the fact that animals learn faster in volatile environments to characterize dopamine encoding of learning rates. We trained rats on a task with semi-observable states offering different rewards, and rats adjusted how quickly they initiated trials across states using RPEs. Computational modeling and behavioral analyses showed that learning rates were higher following state transitions, and scaled with trial-by-trial changes in beliefs about hidden states, approximating normative Bayesian strategies. Notably, dopamine release in the nucleus accumbens encoded RPEs independent of learning rates, suggesting that dopamine-independent mechanisms instantiate dynamic learning rates.

Early-life scarcity adversity biases behavioral development toward a bipolar-like phenotype in mice heterozygous for CNTNAP2
The etiological complexity of psychiatric disorders arises from the dynamic interplay between genetic and environmental vulnerabilities. Among the environmental components, early-life adversities (ELA) are a major risk-factors for developing a psychiatric disorder. Yet, the mechanistic interaction between ELA and genetic vulnerability contributing to psychopathology is poorly understood. To fill this gap, we took advantage of the ideally controlled conditions of a pre-clinical approach. In this study we raised a mouse model with genetic predisposition to multiple psychiatric disorders (autism spectrum, schizophrenia, bipolar disorder), the Cntnap2+/- mouse, with limited bedding and nesting (LBN), a well-established paradigm to induce early-life stress in rodents. These mice were compared to LBN-raised Cntnap2+/+ littermates, as well as parallel groups of Cntnap2+/+ and Cntnap2+/- raised in standard conditions. Using a battery for behavioral phenotyping we show that ELA shapes non-overlapping phenotypic landscapes based on genetic predisposition. Specifically, we found that LBN-raised Cntnap2+/- mice develop a perseverative risk-taking behavior in the elevated plus maze and that this behavior is highly predictive of their success in the social interaction, assessed with the 3-chamber test. This finding suggests that the intrusion of anxiety into the social behavioral domain contributes to extreme gain- or loss-of function in social interaction, resembling a bipolar-like phenotype. Finally, we show that LBN promotes synaptic hypertrophy in the basolateral nucleus of the amygdala, but only in Cntnap2+/- raised in LBN this condition was found in combination with microglia abnormalities. We conclude that the interplay between ELA and Cntnap2 haploinsufficiency exacerbates bipolar-like behaviors in mice, and that this may be consequence of deficient synaptic homeostasis in the basolateral amygdala.

Lateral frontoparietal functional connectivity based on individual sulcal morphology
A salient neuroanatomical feature of the human brain is its pronounced cortical folding, and there is mounting evidence that sulcal morphology is relevant to functional brain architecture and cognition. Recent studies have emphasized putative tertiary sulci (pTS): small, shallow, late-developing, and evolutionarily new sulci that have been posited to serve as functional landmarks in association cortices. A fruitful approach to characterizing brain architecture has been to delineate regions based on transitions in fMRI-based functional connectivity profiles; however, exact regional boundaries can change depending on the data used to generate the parcellation. As sulci are fixed neuroanatomical structures, here, we propose to anchor functional connectivity to individual-level sulcal anatomy. We characterized fine-grained patterns of functional connectivity across 42 sulci in lateral prefrontal (LPFC) and lateral parietal cortices (LPC) in a pediatric sample (N = 43; 20 female; ages 7-18). Further, we test for relationships between pTS morphology and functional network architecture, focusing on depth as a defining characteristic of these shallow sulci, and one that has been linked to variability in cognition. We find that 1) individual sulci have distinct patterns of connectivity, but nonetheless cluster together into groups with similar patterns -- in some cases with distant rather than neighboring sulci, 2) there is moderate agreement in cluster assignments at the group and individual levels, underscoring the need for individual-level analyses, and 3) across individuals, greater depth was associated with higher network centrality for several pTS. These results highlight the importance of considering individual sulcal morphology for understanding functional brain organization.

Frataxin deficiency in proprioceptive neurons is causal to inflammatory and glial responses in dorsal root ganglia
Friedreich ataxia (FA), the most common recessive hereditary ataxia, is an early-onset neurodegenerative disease characterized by pathological changes occurring first in the peripheral dorsal root ganglia (DRG), with loss of the large sensory proprioceptive neurons, leading to ganglionopathy and proprioceptive deficits. FA is caused by a mutation in frataxin gene (Fxn), leading to reduced expression of frataxin protein (FXN), an essential ubiquitous mitochondrial protein. Most research has focused on the pathophysiological involvement of proprioceptors. However, in recent years, neuroinflammation is increasingly recognized as an integral and critical contributor in FA pathogenesis. Furthermore, it has also recently been shown a primary reactivity of satellite glial cells (SGCs; glia tightly enwrapping proprioceptor cell bodies), suggesting a role of inflammation and SGC responses in the destruction of proprioceptors in FA patients' DRGs. It remains unclear to what extent the increase in DRG macrophage response and/or SGC reactivity may contribute to FA phenotype. Therefore, it is important to fully study and understand the mechanism of proprioceptor-macrophages-SGC interactions and their regulations. Exploring relationship between these three cell types has profound implications for breaking through the limitation of treatment of FA. Here we asked whether FXN deficiency selectively in DRG proprioceptive neurons is sufficient to cause inflammatory and glial responses found in patients' DRG. We used RNA profiling, bioinformatics signaling network and pathway analysis, combined with immunohistochemistry and behavioral experiments to reveal some genes, signaling pathways in macrophages and SGCs that may represent potential biomarkers of the disease. Our study revealed that proprioceptor FXN deficiency causes major changes in inflammatory macrophage and SGC gene transcription as well as macrophage and SGC number, highlighting molecular and cellular pathways that were sequentially altered, thus representing temporal signatures of FA ganglionopathy progression.

Astrocyte Contribution to Brain State-Dependent Neurovascular Coupling
The process of neurovascular coupling (NVC) is the regulation of sufficient and targeted blood flow during energy-consuming cerebral processes. Astrocyte participation in NVC has long been debated. The lack of clear answers is likely based on the diversity of astrocyte intracellular Ca2+ activities and the multitude of ways astrocytes may regulate cerebral blood flow. We focused our investigation on NVC responses to sensory input actively reached for by freely behaving mice. To do so, we studied the cellular and vascular activity in the sensory whisker barrel cortex of awake head-fixed mice and aligned this activity to the volitional whisking events. We compared the NVC initiated by the whisking event in the resting mouse to the whisking evoked by the experimenter and the whisking prior to locomotion. We did this comparison because astrocyte signaling is known to be sensitive to brain state transitions. In the NVC response to all three, we found that both neuronal and astrocytic activity corresponded to vascular activity. When we repeated this investigation after depletion of NA release from locus coeruleus projections, we identified that the three NVC responses did not equally depend on NA delivery or astrocytic activity. Though we found the expected effect on astrocytic Ca2+ surges, the whisking-dependent astrocytic Ca2+ activity was only moderately reduced by the reduced NA levels in the resting mouse and only in cells near the vessels. On the vascular side, we found that the dilation of the 1st order capillary to volitional whisking was much reduced. This suggests a disturbance in the precision regulation of the cerebral blood flow that may limit the appropriate delivery of blood to the region of activated neurons. Finally, this disturbance might partially account for the extended period of exploratory whisking prior to the initiation of locomotion that we saw in the NA-depleted mice. Our study reveals an astrocytic contribution to NVC in the natural shifts in the attention directed toward the sensory input received during volitional whisking.

Multiscale Detrended Cross-Correlation Coefficient: Estimating Coupling in Nonstationary Neurophysiological Signals
The brain consists of a vastly interconnected network of regions, the connectome. By estimating the statistical interdependence of neurophysiological time series, we can measure the functional connectivity (FC) of this connectome. Pearsons correlation (rP) is a common metric of coupling in FC studies. Yet rP does not account properly for the non-stationarity of the signals recorded in neuroimaging. In this study, we introduced a novel estimator of coupled dynamics termed multiscale detrended cross-correlation coefficient (MDC3). Firstly, we showed that MDC3 had higher accuracy compared to rP using simulated time series with known coupling, as well as simulated functional magnetic resonance imaging (fMRI) signals with known underlying structural connectivity. Next, we computed functional brain networks based on empirical magnetoencephalography (MEG) and fMRI. We found that by using MDC3 we could construct networks of healthy populations with significantly different properties compared to rP networks. Based on our results, we believe that MDC3 is a valid alternative to rP that should be incorporated in future FC studies.

Moving towards precision TMS? Evaluating individual differences and reproducibility of personalized stimulation targets in UK Biobank
Objective: Personalized transcranial magnetic stimulation (TMS) targeting, guided by functional connectivity (FC), shows potential in treating depression. The present study aims to map individual FC peak location using UK Biobank, to evaluate individual differences and reproducibility of FC-based targets. Methods: We analyzed UK Biobank resting-state fMRI (rfMRI) of 35,423 participants, identifying individual FC peak locations on the dorsolateral prefrontal cortex (DLPFC) that functionally connected to the subcallosal cingulate, amygdala, and ventromedial prefrontal cortex, respectively. Euclidean distance between each participant's individual peak and group-average peak was calculated. With follow-up rfMRI of 1341 participants, within-subject FC peak location changes were calculated. We also compared common TMS targets and random locations for their median distance to individual peaks in a permutation test. Results: Seed-based FC analyses revealed large differences in the individual FC peak location on DLPFC: the mean distance from the individual peaks to group-average peak ranged from 14.24 to 29.92mm; 70% to 94% of participants were >10mm away from the group-average peak and potentially located outside of the TMS effective area with common TMS coils. Similar variability was observed in within-subject peak locations across two fMRI assessments. Common TMS targets and the group-average FC peak showed no significant difference in median distances to individual FC peaks when compared to random locations. Conclusions: FC peak location shows wide inter- and intra- individual variability. We further highlight limited advantage of group-based FC as TMS target. These findings provide insights to help guide neuromodulation techniques for depression.

Hemispheric difference of adaptation lifetime in human auditory cortex measured with MEG
Adaptation is the attenuation of a neuronal response when a stimulus is repeatedly presented. The phenomenon has been linked to sensory memory, but its exact neuronal mechanisms are under debate. One defining feature of adaptation is its lifetime, that is, the timespan over which the attenuating effect of previous stimulation persists. This can be revealed by varying the stimulus-onset interval (SOI) of the repeated stimulus. As SOI is increased, the peak amplitude of the response grows before saturating at large SOIs. The rate of this growth can be quantified and used as an estimate of adaptation lifetime. Here, we studied whether adaptation lifetime varies across the left and the right auditory cortex of the human brain. Event-related fields of whole-head magnetoencephalograms (MEG) were measured in 14 subjects during binaural presentation of pure tone stimuli. To make statistical inferences on the single-subject level, additional event-related fields were generated by resampling the original single-trial data via bootstrapping. For each hemisphere and SOI, the peak amplitude of the N1m response was then derived from both original and bootstrap-based data sets. Finally, the N1m peak amplitudes we used for deriving subject- and hemisphere-specific estimates of adaptation lifetime. Comparing subject-specific adaptation lifetime across hemispheres, we found a significant difference, with longer adaptation lifetimes in the left than in the right auditory cortex (p = 0.004). This difference might have a functional relevance in the context of temporal binding of auditory stimuli, leading to larger integration time windows in the left than in the right hemisphere.

Endothelial and neuronal engagement by AAV-BR1 alleviates neurological symptoms and cholesterol deposition in a mouse model of Niemann-Pick type C2
Background: Patients with the genetic disorder Niemann-Pick type C2 disease (NP-C2) suffer from lysosomal accumulation of cholesterol causing both systemic and severe neurological symptoms. In a murine NP-C2 model, otherwise successful intravenous Niemann-Pick C2 protein (NPC2) replacement therapy fails to alleviate progressive neurodegeneration as infused NPC2 is unable to cross the blood-brain barrier (BBB). Genetic modification of brain endothelial cells (BECs) is thought to enable secretion of recombinant proteins thereby overcoming the restrictions of the BBB. We hypothesized that BBB-directed gene therapy using the AAV-BR1-NPC2 vector would transduce both BECs and neurons in a mouse model of NP-C2 (Npc2-/-). Methods: Six weeks old Npc2-/- mice were intravenously injected with the AAV-BR1-NPC2 vector. Post-mortem analyses included gene expression analyses, determination of NPC2 transduction in the CNS, and co-detection of cholesterol with NPC2 in neurons. Results: The vector exerted tropism for BECs and neurons resulting in a widespread NPC2 distribution in the brain with a concomitant reduction of cholesterol in adjacent neurons, presumably not transduced by the vector. Conclusion: The data suggests cross-correcting gene therapy to the brain via delivery of NPC2 from BECs and neurons.

Enhancing Prosthetic Vision by Upgrade of a Subretinal Photovoltaic Implant in situ
In patients with atrophic age-related macular degeneration, subretinal photovoltaic implant (PRIMA) provided visual acuity up to 20/440, matching its 100 m pixels size. Next-generation implants with smaller pixels should significantly improve the acuity. This study in rats evaluates removal of a subretinal implant, replacement with a newer device, and the resulting grating acuity in-vivo. Six weeks after the initial implantation with planar and 3-dimensional devices, the retina was re-detached, and the devices were successfully removed. Histology demonstrated a preserved inner nuclear layer. Re-implantation of new devices into the same location demonstrated retinal re-attachment to a new implant. New devices with 22 m pixels increased the grating acuity from the 100 m capability of PRIMA implants to 28 m, reaching the limit of natural resolution in rats. Reimplanted devices exhibited the same stimulation threshold as for the first implantation of the same implants in a control group. This study demonstrates the feasibility of safely upgrading the subretinal photovoltaic implants to improve prosthetic visual acuity.

EcoHIV Infection Modulates the Effects of Cocaine Exposure Pattern and Abstinence on Cocaine Seeking and Neuroimmune Protein Expression in Male Mice
Cocaine use disorders (CUDs) and human immunodeficiency virus (HIV) remain persistent public health dilemmas throughout the world. One major hurdle for treating CUD is the increase in cocaine craving and seeking behavior that occurs over a protracted period of abstinence, an effect known as the incubation of craving. Little is known about how HIV may modulate this process. Thus, we sought to examine the impact of chronic HIV infection on the incubation of cocaine craving and associated changes in the central and peripheral immune systems. Here, mice were inoculated with EcoHIV, which is a chimeric HIV-1 construct that produces chronic HIV infection in mice. EcoHIV- and sham-infected mice were conditioned with cocaine daily or intermittently in a conditioned place preference (CPP) paradigm, followed by 1 or 21 days of forced abstinence prior to assessing preference for the cocaine-paired chamber. Under both conditioning regimens, sham mice exhibited incubation of cocaine CPP after 21 days of abstinence. EcoHIV-infected mice conditioned daily with cocaine showed enhanced cocaine seeking at both abstinence timepoints, whereas infected mice conditioned intermittently showed a reversal of the incubation effect, with higher cocaine seeking after 1 day of abstinence compared to 21 days. Analysis of corticolimbic CX3CL1-CX3CR1 and glutamate receptor expression revealed alterations in medial prefrontal cortex (mPFC) CX3CL1 and nucleus accumbens (NAc) GluN2A receptors that correlated with cocaine seeking following daily cocaine exposure. Moreover, examination of peripheral immune markers showed that the effect of abstinence and EcoHIV infection on these measures depended on the cocaine exposure regimen. Altogether, these results highlight the importance of cocaine abstinence and exposure pattern as critical variables that modulate HIV-associated neuroimmune outcomes and relapse vulnerability.

Axon demyelination and degeneration in a zebrafishspastizin model of hereditary spastic paraplegia
Hereditary spastic paraplegias (HSPs) are a diverse set of neurological disorders characterized by progressive spasticity and weakness in the lower limbs caused by damage to the axons of the corticospinal tract. More than 88 genetic mutations have been associated with HSP, yet the mechanisms underlying these disorders are little understood. We studied the pathogenesis of one form of HSP known as spastic paraplegia 15 (SPG15). This disorder is caused by mutations in the ZFYVE26 gene, which codes for a protein called SPASTIZIN. We show that, in zebrafish, the significant reduction of Spastizin caused degeneration of Mauthner (M)-cells. M-cell degeneration is associated with axon demyelination in the spinal cord and impaired locomotion in the spastizin mutants. Our findings reveal that the mutation not only compromises axonal integrity but also affects the structural molecules of the myelin sheath, laying the foundation for degeneration and advancing our understanding of the intricate mechanisms underlying HSPs.

Joint Gray and White Matter Networks Predict Mindfulness and Mind Wandering Traits: A Data Fusion Machine Learning Approach
Mind wandering is a ubiquitous part of our normal cognition and daily lives, with people reporting that their mind wanders during 25-50% of their waking hours. Studies suggest that mind wandering shares an inverse relationship with mindfulness skills. Our aim was to expand this evidence directly by investigating the mediating effect among mindfulness, mind wandering, and brain features. The main goal of our study in particular was to find out which morphometric brain features are associated with mindfulness and mind wandering, and to investigate how mindfulness mediates deliberate and spontaneous mind wandering in terms of these associated brain components. GM and WM MRI scans of 76 individuals and self-reported questionnaires were included in the analysis. We predicted that specific gray matter (GM) and white matter (WM) networks would also influence deliberate and spontaneous mind wandering tendencies with mindfulness as a mediator. We found that GM and WM networks including structures that have been consistently linked to mindfulness, such as the cingulate, the insula, the basal ganglia and fronto-parietal attentive regions, exert direct effects on mindfulness, and deliberate and spontaneous mind wandering. We also found an indirect mediating effect of the FFMQ facet acting with awareness on spontaneous mind wandering in terms of increased and decreased GM volume concentrations. This study elicited the link between mind wandering and mindfulness and expands our knowledge on the neural bases of these two psychological constructs.

Prediction of acoustic tinnitus suppression using resting state EEG: An explainable AI approach
Tinnitus, characterized by the perception of sound without an external source, affects a significant portion of the population and can lead to considerable individual suffering, yet understanding of its suppression remains limited. Understanding neural traits of tinnitus suppression may be crucial for developing accurate predictive models in tinnitus research and treatment. This study aims to classify individuals capable of brief acoustic tinnitus suppression (BATS; also known as residual inhibition) based on their independent resting state EEG (n=102), exploring the classifications robustness on various sample splits, and the relevance of resulting specific EEG features in the spirit of explainable AI. A comprehensive set of EEG features, including band power in standard frequency bands, spectral entropy, aperiodic slope and offset of the power spectrum, and connectivity, was included in both sensor and source space. Binary classification of the BATS status was performed using a comprehensive set of standard classifiers and Pearson correlation for feature selection, which addresses multicollinearity, avoiding complex dimensionality reduction techniques. Feature importance was assessed using Gini impurity metrics, allowing interpretation of the directionality of identified neural features. The Random Forest model showed the most consistent performance, with its majority voting mechanism effectively reducing overfitting and providing reliable predictions, and was therefore chosen for subsequent feature interpretation analysis. Our classification task demonstrated high accuracy across the various BATS split thresholds, suggesting that the choice of threshold does not significantly influence the underlying pattern in the data. We achieved classification accuracies of 98% for sensor and source models and 86% for the connectivity model in the main split. Looking at identified important features, our findings align with and extend existing neuroscience research in tinnitus by discovering highly specific and novel neural features in naive resting-state data predictive of BATS. Gamma power is identified as the most important feature in the sensor model, followed by alpha power, which fits current models of sensory processing, prediction, and updating (gamma) as well as inhibitory (alpha) frameworks. The overall spectral shape of the EEG power spectrum tends to be more normal in +BATS individuals, as reflected in the aperiodic offset and slope features. In the source model, important features are lateralized in that the gamma feature is more prominent in the left core auditory network, whereas the alpha feature is distributed more sparsely over the right hemisphere in line with auditory attention data. Furthermore, we identified several hotspots in the temporal, insular, parietal, parahippocampal, medial prefrontal, and (posterior) cingulate cortex implicated in sensory processing, gating, attention, and memory processes. Relevant network features were found in a hyperconnected bilateral auditory network (within the network), while the full auditory network was hyperconnected to limbic regions (between networks), which may reflect an intact sensory gating mechanism aiding tinnitus suppression. This studys implications extend to improving the understanding and prediction of tinnitus loudness perception and tinnitus distress as well as its (acoustic) suppression. Furthermore, our approach underscores the importance of careful feature selection, model choice, and validation strategies in analyzing complex neurophysiological data.

Stabilizing transglutaminase 2 in the open conformation results in reactive astrocytes being more neurosupportive
Astrocytes play critical roles in supporting structural and metabolic homeostasis in the central nervous system (CNS). Inflammatory conditions bring about a range of poorly understood, heterogeneous, reactive phenotypes in astrocytes. Finding ways to manipulate the phenotype of reactive astrocytes, and leveraging a pro-recovery phenotype, holds promise in treating CNS injury. Previous studies have shown that the protein transglutaminase 2 (TG2) plays a significant role in determining the phenotype of reactive astrocytes. Recently it has been demonstrated that ablation of TG2 from astrocytes improves injury outcomes both in vitro and in vivo. Excitingly, in an in vivo mouse model, pharmacological inhibition of TG2 with the irreversible inhibitor VA4 phenocopies the neurosupportive effects of TG2 deletion in astrocytes. The focus of this study was to provide insights into the mechanisms by which TG2 deletion or inhibition of TG2 with VA4 result in a more neurosupportive astrocytic phenotype. Using a neuron-astrocyte co-culture model of neurite outgrowth, we show that VA4 treatment improves the ability of astrocytes to support neurite outgrowth on an injury-relevant matrix, further validating the ability of VA4 to phenocopy astrocytic TG2 deletion. VA4 treatment of neurons alone had no effect on neurite outgrowth. VA4 covalently binds to active site residues of TG2 that are exposed in its open conformation and are critical for its enzymatic function, and prevents TG2 from taking on a closed conformation, which interferes with its protein scaffolding function. To begin to understand how pharmacologically altering TG2s conformation affects its ability to regulate reactive astrocyte phenotypes, we assayed the impact of VA4 on TG2s interaction with Zbtb7a, a transcription factor that we have previously identified as a TG2 interactor, and whose functional outputs are significantly regulated by TG2. The results of these studies demonstrated that VA4 significantly decreases the interaction of TG2 and Zbtb7a. Further, previous findings indicate that TG2 may act as an epigenetic regulator, through its nuclear protein-protein interactions, to modulate gene expression. Since both TG2 and Zbtb7a interact with members of the Sin3a chromatin repressor complex, we assayed the effect of TG2 deletion and VA4 treatment on histone acetylation and found significantly greater acetylation with TG2 deletion or inhibition with VA4. Overall, this work points toward a possible epigenetic mechanism by which genetic deletion or acute inhibition of TG2 leads to enhanced astrocytic support of neurons.

Enteric glia regulate Paneth cell secretion and intestinal microbial ecology
Glial cells of the enteric nervous system (ENS) interact closely with the intestinal epithelium and secrete signals that influence epithelial cell proliferation and barrier formation in vitro. Whether these interactions are important in vivo, however, is unclear because previous studies reached conflicting conclusions [1]. To better define the roles of enteric glia in steady state regulation of the intestinal epithelium, we characterized the glia in closest proximity to epithelial cells and found that the majority express PLP1 in both mice and humans. To test their functions using an unbiased approach, we genetically depleted PLP1+ cells in mice and transcriptionally profiled the small and large intestines. Surprisingly, glial loss had minimal effects on transcriptional programs and the few identified changes varied along the gastrointestinal tract. In the ileum, where enteric glia had been considered most essential for epithelial integrity, glial depletion did not drastically alter epithelial gene expression but caused a modest enrichment in signatures of Paneth cells, a secretory cell type important for innate immunity. In the absence of PLP1+ glia, Paneth cell number was intact, but a subset appeared abnormal with irregular and heterogenous cytoplasmic granules, suggesting a secretory deficit. Consistent with this possibility, ileal explants from glial-depleted mice secreted less functional lysozyme than controls with corresponding effects on fecal microbial composition. Collectively, these data suggest that enteric glia do not exert broad effects on the intestinal epithelium but have an essential role in regulating Paneth cell function and gut microbial ecology.

Remodeling of the brain angioarchitecture in experimental chronic neurodegeneration
Background: Chronic neurodegenerative diseases are characterized by substantial neuroinflammation with accumulation of macrophages, reactive microglia, and reactive astrocytes. Impairment of the brain vasculature is also commonly seen in chronic neurodegeneration with causal links warranting further investigation. Methods: To address the effects of chronic neurodegeneration on regional vasculature, we performed a unilateral injection of a glutamate receptor agonist ibotenic acid into striatum of adult rats, which caused excitotoxicity in the substantia nigra pars reticulata (SNpr) due to imbalance between inhibitory inputs from the striatum and excitatory signals from the subthalamic nucleus. Brains were examined at 28 days (short-term neurodegeneration) and 91 days (long-term neurodegeneration). Dissected brain samples were analyzed for protein and gene expression using immunohistochemistry and qPCR. Brains were further analyzed for remodeling of vasculature labeled with wheat germ agglutinin (WGA) Alexa Fluor 647 conjugate using 3D deep confocal microscopy of optically cleared samples combined with machine learning-based image analysis. Results: The resulting neurodegeneration was accompanied by neuroinflammation, verified by the expression of inflammatory markers with gradual, regional loss of brain tissue. An in-depth analysis of the angioarchitecture of the degenerating SNpr revealed substantial changes of the vasculature with higher density, increased diameter, and number of tortuous vessels already after 28 days continuing at 91 days. Interestingly, the vascular remodeling changes occurred without changes in the expression of endothelial tight junction proteins, vascular basement membrane proteins, or markers of angiogenesis. Conclusions: These results demonstrate how neurodegeneration causing prominent tissue loss in SNpr also leads to substantial remodeling of the angioarchitecture, while not altering the structural integrity of the vessel wall judged from the continuous expression of hallmarks of brain endothelial cells and the vascular basement membrane. We propose that this remodeling occurs as a consequence of the loss of brain tissue and with the resulting changes leaving the vasculature prone to additional vascular pathologies like vessel occlusion or formation of aneurysms.

A role for astrocytic miR-129-5p in Frontotemporal Dementia
Frontotemporal dementia is a debilitating neurodegenerative disorder characterized by frontal and temporal lobe degeneration, resulting in behavioral changes, language difficulties, and cognitive decline. In this study, smallRNA sequencing was conducted on postmortem brain tissues obtained from FTD patients with GRN, MAPT, or C9ORF72 mutations, focusing on the frontal and temporal lobes. Our analysis identified miR-129-5p as consistently deregulated across all mutation conditions and brain regions. Functional investigations revealed a novel role of miR-129-5p in astrocytes, where its loss led to neuroinflammation and impaired neuronal support functions, including reduced glutamate uptake. Depletion of miR-129-5p in astrocytes resulted in the loss of neuronal spines and altered neuronal network activity. These findings highlight miR-129-5p as a potential therapeutic target in neurodegenerative diseases and also sheds light on the role of astrocytes in Frontotemporal dementia pathogenesis.

An Intra-Hypothalamic Pathway Modulating Body Temperature and Feeding
The intricate interplay between energy metabolism and body temperature regulation underscores the necessity of finely tuned mechanisms to maintain thermo-energetic homeostasis. Hot environments are known to suppress food intake and to reduce energy expenditure. However, the interplay between thermoregulatory and caloric-regulatory hypothalamic areas remains largely unexplored. In this study, we unveil two unconventional pathways originating from a subpopulation of genetically defined excitatory, leptin receptor-expressing POA neurons (VMPO(LepR)) that connect to the paraventricular nucleus of the hypothalamus (PVH) and the dorsomedial hypothalamic nucleus (DMH). Both, VMPO(LepR)[->]PVH and VMPO(LepR)[->]DMH connections, inhibit brown adipose tissue (BAT) thermogenesis and reduce body temperature; surprisingly, the VMPO(LepR)[->]PVH connection additionally exhibits the unique ability to suppress food intake and also promotes tail vasodilation. Our findings suggest that the excitatory VMPO(LepR)[->]PVH loop integrates temperature and caloric information to complement the canonical inhibitory arcuate nucleus (ARC)[->]PVH pathway. We propose that this novel pathway contributes to energy and temperature homeostasis in hot environments, offering new insights into previously unrecognized neuronal circuits orchestrating thermo-metabolic balance in response to environmental challenges.

Systems Neuroscience Computing in Python (SyNCoPy): A Python Package for Large-scale Analysis of Electrophysiological Data
We introduce an open-source Python package for the analysis of large-scale electrophysiological data called SyNCoPy, for Systems Neuroscience Computing in Python. The package includes signal processing analyses across time (e.g. time-lock analysis), frequency (e.g. power spectrum), and connectivity (e.g. coherence) domains. It enables user-friendly data analysis on both laptop-based and high performance computing systems. SyNCoPy is designed to facilitate trial-parallel workflows (parallel processing of trials) making it an ideal tool for large-scale analysis of electrophysiological data. Based on parallel processing of trials, the software can support very large-scale datasets via innovative out-of-core computation techniques. It also provides seamless interoperability with other standard software packages through a range of file format importers and exporters and open file formats. The naming of the user functions closely follows the well-established FieldTrip framework, which is an open-source Matlab toolbox for advanced analysis of electrophysiological data.

Human iPSCs from aged donors retain their mitochondrial aging signature
Aging represents the main risk factor for developing neurodegenerative disorders. One of the hallmarks of aging is mitochondrial dysfunction. Age-related mitochondrial alterations have been shown to affect mitochondrial energy metabolism and redox homeostasis as well as mitochondrial dynamics. In the present study, we addressed the question of whether or not, induced pluripotent stem cells (iPSCs) may be used as a model of aging in a dish to identify therapies at alleviating the aging of mitochondria. Notably, we could demonstrate that compared to human iPSCs from young donors, those from aged donors show impaired mitochondrial bioenergetics and exhibit a rise in reactive oxygen species generation. Furthermore, we demonstrate that iPSCs from aged donors present low mitochondrial mass and alterations of the morphology of the mitochondrial network. This study provides evidence that the aging phenotype is present at the mitochondrial level in iPSCs from aged donors, ranging from bioenergetics to dynamics. Thus, this model can be used for high through put screening to identify drugs that improve mitochondrial function.

Magnetomyography: A novel modality for non-invasive muscle sensing
The measurement of magnetic fields generated by skeletal muscle activity, called magnetomyography (MMG), has seen renewed interest from the academic community in recent years. Although studies have demonstrated complex models of MMG and experiments classifying between different movements using MMG, there has yet to be time frequency analysis of MMG as well as concurrent recordings of MMG and its electrical counterpart, surface electromyography (sEMG). Here, we aim to better understand MMG in the context of sEMG by simultaneously recording both modalities during various muscle contraction tasks. We found that, similar to sEMG, MMG shows highly linearly correlated power to the degree of muscle contraction, has a unimodal distribution in spectral power, and can detect changes in muscle fatigue via changes in the spectral distribution. One main difference we found was that MMG typically has more high frequency content compared to sEMG, even when accounting for the filtering induced by the size of the sEMG electrodes. We additionally demonstrate empirically the decrease in MMG power due to distance from the arm and show MMG decreases slower than the inverse square law and can be measured up to 50 mm from the surface of the skin. Finally, we were able to capture MMG with non-OPM sensors showing that sensor technology has made great strides towards enabling MMG applications.

Assessing visual performance during intense luminance changes in virtual reality
During indoor-outdoor transitions humans encounter luminance changes beyond the functional range of the photoreceptors, leaving the individual at risk of overlooking harmful low-contrast objects until adaptation processes re-enable optimal vision. To study human visual performance during intense luminance changes, we propose a virtual reality based testbed. After linearization of the headset's luminance output, detection times were recorded for ten participants. The small (FWHM = 0.6 degree) low-contrast stimuli appeared randomly in one of four corners ({+/-}10 degree) after luminance changes of three magnitudes within 1 or 3 seconds. Significantly decreased detection times were observed for the conditions with simulated self-tinting lenses compared to lenses with fixed transmission rates after luminance decreases. In cases of luminance increases all detection times were similar. In conclusion, the proposed virtual reality testbed allows for studying vision during or after steep luminance changes and helps to design technical aids like self-tinting lenses.

Opaque Ontology: Neuroimaging Classification of ICD-10 Diagnostic Groups in the UK Biobank
Background: The use of machine learning to classify diagnostic cases versus controls defined based on diagnostic ontologies such as the ICD-10 from neuroimaging features is now commonplace across a wide range of diagnostic fields. However, transdiagnostic comparisons of such classifications are lacking. Such transdiagnostic comparisons are important to establish the specificity of classification models, set benchmarks, and assess the value of diagnostic ontologies. Results: We investigated case-control classification accuracy in 17 different ICD-10 diagnostic groups from Chapter V (mental and behavioral disorders) and Chapter VI (diseases of the nervous system) using data from the UK Biobank. Classification models were trained using either neuroimaging (structural or functional brain MRI feature sets) or socio-demographic features. Random forest classification models were adopted using rigorous shuffle splits to estimate stability as well as accuracy of case-control classifications. Diagnostic classification accuracies were benchmarked against age classification (oldest versus youngest) from the same feature sets and against additional classifier types (K-nearest neighbors and linear support vector machine). In contrast to age classification accuracy, which was high for all feature sets, few ICD-10 diagnostic groups were classified significantly above chance (namely, demyelinating diseases based on structural neuroimaging features, and depression based on socio-demographic and functional neuroimaging features). Conclusion: These findings highlight challenges with the current disease classification system, leading us to recommend caution with the use of ICD-10 diagnostic groups as target labels in brain-based disease prediction studies.

The disappointment centre of the brain gets exciting: A systematic review of habenula dysfunction in depression
Background: The habenula is an epithalamic brain structure that acts as a neuroanatomical hub connecting the limbic forebrain to the major monoamine centres. Abnormal habenula activity is increasingly implicated in depression, with a surge in publications on this topic in the last 5 years. Direct stimulation of the habenula is sufficient to induce a depressive phenotype in rodents, suggesting a causative role in depression. However, the molecular basis of habenula dysfunction in depression remains elusive and it is unclear how the preclinical advancements translate to the clinical field. Methods: A systematic literature search was conducted following the PRISMA guidelines. The two search terms depress* and habenula* were applied across the databases Scopus, Web of Science and PubMed. Studies eligible for inclusion must have examined changes in the habenula in clinical cases of depression or preclinical models of depression. Results: Preclinical studies (n=57) measured markers of habenula activity (n=16) and neuronal firing (n=21), largely implicating habenula hyperactivity in depression. Neurotransmission was briefly explored (n=13), suggesting imbalances within excitatory and inhibitory habenula signalling. Additional preclinical studies reported neuroconnectivity (n=1), inflammatory (n=2), genomic (n=2) and circadian rhythm (n=2) abnormalities. Seven preclinical studies (12.2%) included both males and females. From these, 5 studies (71%) reported a significant difference between the sexes in at least one habenula measure taken. Clinical studies (n=18) reported abnormalities in habenula connectivity (n=11), volume (n=5) and molecular markers (n=2). Clinical studies generally included male and female subjects (n=15), however, few of these studies examined sex as a biological variable (n=5) Conclusions: Both preclinical and clinical evidence suggest the habenula is disrupted in depression. However, there are opportunities for sex-specific analyses across both areas. Preclinical evidence consistently suggests habenula hyperactivity as a primary driver for the development of depressive symptoms. Clinical studies support gross habenula abnormalities such as altered activation, connectivity, and volume, with emerging evidence of blood brain barrier dysfunction, however, progress is limited by a lack of detailed molecular analyses.