bioRxiv Subject Collection: Neuroscience's Journal

Tie2-Dependent Mechanisms Promote Leptomeningeal Collateral Remodeling and Reperfusion Following Stroke
Leptomeningeal collaterals are distal pial arterial anastomotic vessels that provide an alternative route for 29 redistributing cerebral blood flow following arterial obstruction, thereby limiting tissue damage. However, 30 the regulatory mechanisms and strategies to enhance this adaptive response remain under investigation. 31 This study explored the pharmacological effects of Tie2 receptor activation, using the peptide agonist 32 Vasculotide, following permanent middle cerebral artery occlusion (pMCAO). Vasculotide improved 33 collateral growth and remodeling, which correlated with reduced infarct volume, enhanced blood flow, and 34 functional recovery within 24hrs post-pMCAO. In contrast, collateral growth was attenuated in Tie2 and 35 EphA4/Tie2 double knockdown mice, while the loss of EphA4 increased Tie2 and Ang-1 expression and 36 mimicked the positive effects of Vasculotide following stroke. Furthermore, bulk RNA sequencing of 37 meningeal tissue identified key transcriptomic changes, including alterations in AJ-associated transcripts, 38 such as Krt5, Krt14, and Col17a1, in the ipsilateral meninges of both endothelial cell-specific EphA4 39 knockout and Vasculotide-treated mice. Krt5 expression was found upregulated on meningeal arterial 40 vascular network in injured KO mice, highlighting a potential new mediator of meningeal vascular 41 remodeling. These findings illustrate that EphA4 and Tie2 play opposing roles in collateral remodeling, 42 including the regulation of Krt5. Modulating their activity could potentially enhance the collateral response 43 to stroke.

The P50 predicts conscious perception under tactile but not electrical somatosensory stimulation in human EEG
Past research has not reached consensus about the neural correlates of conscious somatosensory perception. Different studies have identified ERP components at various latencies as predictors of somatosensory detection, but it is still largely unclear which factors are responsible for this variation. Here, for the first time we directly compare the event-related potential correlates of stimulus detection under tactile versus electrical peri-threshold stimulation in a between-groups design, while controlling for task-relevance and post-perceptual processes with a visual-somatosensory matching task. We show that the P50 component predicts conscious perception under tactile, but not electrical stimulation: while electrical stimulation evokes a P50 already for subliminal stimuli, there is no subliminal P50 for tactile stimulation. In contrast, the P100 and N140 components robustly predict conscious detection in both stimulation groups. Tactile stimulation produced a clearly separable N80 component for detected stimuli, that appeared as part of the N140 under electrical stimulation. The P300 predicted conscious detection even though we controlled for post-perceptual processes, suggesting that it partly reflects aspects of subjective experience. Our results demonstrate that the neural correlates of somatosensory detection depend on the type of stimulation used, limiting the scope of previous results achieved using electrical stimulation.

Patchy Striatonigral Neurons Modulate Locomotor Vigor in Response to Environmental Valence
Spiny projection neurons (SPNs) in the dorsal striatum play crucial roles in locomotion control and value-based decision-making. SPNs, which include both direct-pathway striatonigral and indirect-pathway striatopallidal neurons, can be further classified into subtypes based on distinct transcriptomic profiles and cell body distribution patterns. However, how these SPN subtypes regulate spontaneous locomotion in the context of environmental valence remains unclear. Using Sepw1-Cre transgenic mice, which label a specific SPN subtype characterized by a patchy distribution of cell bodies in the dorsal striatum, we found that these patchy striatonigral neurons constrain motor vigor in response to valence differentials. In a modified light/dark box test, mice exhibited differential walking speeds between the light and dark zones. Genetic ablation of these patchy SPNs disrupted restful slowing in the dark zone and increased transition frequencies between zones. In vivo recordings linked the activity of these neurons to zone occupancy, speed, and deceleration, with a specific role in mediating deceleration. Furthermore, chemogenetic activation of patchy SPNs-and optical activation of striatonigral neurons in particular-reduced locomotion and attenuated speed-based zone discrimination. These findings reveal that a subtype of patchy striatonigral neurons regulates implicit walking speed selection based on innate valence differentials.

Biophysical basis for brain folding and misfolding patterns in ferrets and humans
A mechanistic understanding of neurodevelopment requires us to follow the multiscale processes that connect molecular genetic processes to macroscopic cerebral cortical formations and thence to neurological function. Using magnetic resonance imaging of the brain of the ferret, a model organism for studying cortical morphogenesis, we create in vitro physical gel models and in silico numerical simulations of normal brain gyrification. Using observations of genetically manipulated animal models, we identify cerebral cortical thickness and cortical expansion rate as the primary drivers of dysmorphogenesis and demonstrate that in silico models allow us to examine the causes of aberrations in morphology and developmental processes at various stages of cortical ontogenesis. Finally, we explain analogous cortical malformations in human brains, with comparisons with human phenotypes induced by the same genetic defects, providing a unified perspective on brain morphogenesis that is driven proximally by genetic causes and affected mechanically via variations in the geometry of the brain and differential growth of the cortex.

Cerebellar involvement in self-timing
The cerebellum is well-established in sub-second motor timing, but its role in supra-second interval timing remains unclear. Here, we investigate how cerebellar output influences time estimation over longer timescales. Rats performed an interval timing task, estimating time based on an auditory cue, while chemogenetic inhibition of the lateral cerebellar nucleus assessed its role in both predictable (externally cued) and unpredictable (internally cued) timing conditions. Cerebellar inhibition produced bidirectional effects: delayed action initiation in predictable trials and premature responses in unpredictable trials. Despite slowed movement, overall task success rates remained unchanged, suggesting a specific impairment in temporal estimation rather than motor execution. These findings demonstrate that the cerebellum integrates motor and cognitive processes for supra-second timing, with differential effects on externally guided and self-generated timing. Our results provide evidence that the lateral cerebellum contributes to supra-second interval timing, supporting its role in adaptive behavior across extended timescales.

How and when can environmental influences change cerebral cortex? An experimental training study of twins with birth weight differences
Human cortical morphology is genetically programmed but also influenced by environment both in development and adulthood. Determining the timing of these influences across the lifespan is a key challenge. Here we test what makes genetically identical brains differ and converge. Mono- (MZ) and dizygotic (DZ) twins (n = 206, age 16-79 yrs) with known extent of birth weight (BW) discordance, had MRIs pre- and post- 10 weeks immersive virtual reality navigation training in a train-rest-rest/rest-train-rest-design, or as passive controls. As a measure of between-twin similarity, we calculated "brainprints" from 272 structural cortical features, to assess effects of genetic (MZ/DZ) and environmental variation at early (BW discordance) and later life stages (training status). Baseline brainprint similarity was higher in MZ than DZ twins, but greater BW discordance yielded less similarity in MZ (r = -.54, p < .0001), dominated by cortical area effects (t = -6.748, p < .0001). In contrast, training increased brainprint similarity of MZ relative to DZ twins (zygosity x training; t = -2.864, p =.0046), mostly by cortical curvature (t = -4.401, p<.0001). Follow-up analyses indicated training increased white matter curvature and surface area. The findings demonstrate that in adulthood, early life environmental difference persistently contributes to make the brains of genetically identical twins deviate, while concurrent environmental influence in the form of training still can cause their brainprints to converge at the grey-white-matter boundary. This indicates how these early and later environmental influences on the cortex can be distinguished, and how cortical characteristics can be modified.

Frontal connectivity dynamics encode contextual information during action preparation
The context in which we perform motor acts shapes our behavior, with movement speed and accuracy modulated by contingent factors, such as the occurrence of cues that trigger or inhibit our actions. This flexibility relies on network interactions encompassing premotor and prefrontal regions, including the supplementary motor area (SMA) and the right inferior frontal gyrus (rIFG). However, the dynamic interplay between these regions during action preparation and execution based on contextual demands remains unclear. Here, we demonstrate that contextual information is encoded in SMA and rIFG interareal connectivity before action. Using Transcranial Magnetic Stimulation (TMS) and electroencephalography (EEG) during Go/No-Go tasks with varying target probabilities, we found that, during the preparatory stages of action, -band rIFG connectivity increased in contexts where motor responses were more frequently withheld. In contrast, SMA exhibited a reversed pattern only near the target onset. Finally, {beta}-band connectivity encoded proactive inhibition processes, increasing when action likelihood was low. Accordingly, during response implementation, both areas exhibited greater {beta}-band connectivity when action was withheld compared to when a motor response was required, further supporting its role in inhibitory control. Our results demonstrate that - and {beta}-band oscillatory network dynamics support context-sensitive adaptations, illustrating how premotor and prefrontal regions synergistically modulate their interactions as they transition from preparation to response. These findings advance understanding of how the brain integrates predictive information to dynamically organize motor and cognitive resources before an action unfolds, revealing that connectivity encodes critical information driving behavior.

Motor control processes moderate visual working memory gating
Gating processes that regulate sensory input into visual working memory (WM) and the execution of planned actions share neural mechanisms, suggesting a mutual interaction. In a preregistered study (OSF), we examined how this interaction may result in sensory interference during WM storage using a delayed-match-to-sample task. Participants memorized the color of a target stimulus for later report on a color wheel. The shape of the target indicated which hand they would adjust the color wheel with. During the retention interval, an interference task was presented, requiring a response with either the same or different hand as the main task. In half of the interference trials, the interfering task cue was also colored to introduce visual interference. EEG results showed early motor planning during sensory encoding, evidenced by mu/beta suppression contralateral to the responding hand. The interference task only impaired WM performance when it included an irrelevant color, indicating that the interference effect was primarily driven by the irrelevant sensory information. In addition, color reporting in the WM task was biased toward the irrelevant color. This was more pronounced when both tasks were performed with the same hand, suggesting a selective gating mechanism dependent on motor control processes. This effect was mitigated by a control mechanism, which was evident in frontal theta activity, where higher power predicted lower bias on the single-trial level. Our findings thus reveal that sensory WM updating can be induced by interfering motor actions, which can be compensated by a reactive control mechanism.

Representation of visual sequences in the tuning and topology of neuronal activity in the human hippocampus
The hippocampus plays a critical role in the formation of memories and in the representation of time, yet the coding principles that connect these functions are poorly understood. We hypothesized that hippocampal neurons selective for specific visual stimuli adjust their tuning to encode sequence structure, smoothly combining sensory and temporal codes. In epilepsy patients who underwent intracranial EEG, we recorded neuronal activity from the hippocampus and control brain regions as they viewed looping sequences of visual scenes in structured (repeating) or random orders. The firing rates of hippocampal neurons to individual scenes were modulated by temporal distance from their preferred scene in structured sequences, increasing for nearby scenes and decreasing for distant scenes; this modulation was absent in random sequences and control regions. Analysis of population activity in local field potentials revealed that the looping sequence structure was embedded in a high dimensional ring shape representing the serial order of the scenes. These findings show that human hippocampal neurons encode sequence structure in their representational geometry, extracting topological features of experience to add temporal continuity to sensory memories.

Temperature robustness of the timing network within songbird premotor nucleus HVC
Many neuronal processes are temperature-sensitive. Cooling by 10 {degrees}C typically slows ion channel dynamics by more than a factor of two (Q10 > 2). Nevertheless, behaviors can remain robust despite variations in brain temperature. For instance, cooling the premotor nucleus HVC in zebra finches by 10 {degrees}C slows song production by only a factor of Q10 [~]1.3. Here we examine the temperature robustness of the synaptic chain network within HVC. Burst spike propagation along such a chain network is postulated to control the tempo of the song. We show that the dynamics of this network are resilient to cooling and that the slowing of burst propagation exhibits a Q10 similar to that observed for the song. We identify two key factors underlying this robustness: the reliance on axonal delays, which are more resistant to temperature changes than ion channels, and enhanced synaptic efficacy at lower temperatures. We propose that these mechanisms represent general principles by which neural circuits maintain functional stability despite temperature fluctuations in the brain.

The relationship of white matter tract orientation to vascular geometry in the human brain
The white matter of the human brain exhibits highly ordered anisotropic structures of both axonal nerve fibers and cerebral vasculature. Separately, the anisotropic nature of white matter axons and white matter vasculature have been shown to cause an orientation dependence on various MRI contrasts used to study the structure and function of the brain; however, little is known of the relationship between axonal and vascular orientations. Thus, the aim of this study is to compare the orientation between nerve fibers and vasculature within the white matter. To do this, we use diffusion MRI and susceptibility weighted imaging acquired in the same healthy young adult volunteers and analyze the alignment between white matter fibers and blood vessels in different brain regions, and along different pathways, to determine the degree of alignment between these structures. We first describe vascular orientation throughout the brain and note several regions with consistent orientations across individuals. Next, we find that vasculature does not necessarily align with the dominant direction of white matter in many regions, but, due to the presence of crossing fiber populations, does align with at least some white matter within each MRI voxel. Even though the spatial patterns of blood vessels run in parallel to several white matter tracts, they do not do so along the entire pathway, nor for all pathways, suggesting that vasculature does not supply/drain blood in a tract-specific manner. Overall, these findings suggest that the vascular architecture within the white matter is closely related to, but not the same as, the organization of neural pathways. This study contributes to a better understanding of the microstructural arrangement of the brain and may have implications for interpreting neuroimaging data in health and disease.

Impairment of homeostatic structural plasticity caused by the autism and schizophrenia-associated 16p11.2 duplication
Homeostatic plasticity is essential for information processing and the stability of neuronal circuits, however its relevance to neuropsychiatric disorders remains unclear. The 16p11.2 duplication (BP4-BP5) is a genetic risk factor that strongly predisposes to a range of severe mental illnesses including autism, schizophrenia, intellectual disability, and epilepsy. The duplication consists of a 600 kb region on chromosome 16, including 27 protein-coding genes, with poorly defined effects on neuronal structure and function. Here, we used a mouse model of the 16p11.2 duplication to investigate the impact of this variant on synaptic structure and downstream homeostatic plasticity. We find that 16p11.2 duplication neurons exhibit overly branched dendritic arbors and excessive spine numbers, which host an overabundance of surface AMPA receptor subunit GluA1. Using a homeostatic plasticity paradigm, we show that 16p11.2 duplication neurons fail to undergo synaptic upscaling upon activity deprivation, consistent with disrupted structural plasticity. We also observe that the increased surface abundance of GluA1 occludes further insertion events, a critical mechanism for synaptic plasticity. Finally, we show that genetically correcting the dosage of 16p11.2-encoded Prrt2 to wild-type levels rescues structural spine phenotypes. Our work suggests that aberrant plasticity could contribute to the etiology of neuropsychiatric disorders.

Topographically organized dorsal raphe activity modulates forebrain sensory-motor computations and adaptive behaviors.
The dorsal raphe nucleus (DRN) plays an important role in shaping a wide range of behaviors, including mood, motivation, appetite, sleep, and social interactions. Reflecting these diverse roles, the DRN is composed of molecularly distinct and topographically organized groups of neurons that target specific regions of the forebrain. Despite these insights, fundamental questions remain regarding how DRN neurons process sensory information, what do DRN communicate to forebrain, and the role of DRN inputs in forebrain computations and animal behavior.To address these questions, we investigated the spatiotemporal activity patterns of DRN neurons, along with DRN axons and their targets in the juvenile zebrafish forebrain. Our findings revealed a remarkable topographic organization of ongoing activity and sensory-motor responses within the DRN. We discovered that a large fraction of DRN neurons are primarily driven by animals locomotor activity. We also observed that an anterior group of DRN neurons, marked by Gad1, exhibited distinct activity patterns during rest, locomotor activity and sensory stimulation. DRN axons broadly innervating the forebrain exhibit topographically organized excitation and inhibition in response to sensory stimulation and motor activity. Notably, we observed significant and rapid covariation between the activity of DRN axons and nearby forebrain neurons. Chemogenetic ablation of the DRN led to a marked reduction in the synchrony and sensory-motor responses across forebrain neurons, accompanied by significant deficits in adaptive behaviors. Collectively, our findings revealed the functional diversity of DRN neurons and their role in transmitting sensory and locomotor signals via topographically organized projections, which can regulate forebrain activity and play a crucial role in modulating animal behavior.

GABA mediates experience-dependent regulation of myelination in the mouse visual pathway.
Myelination in the visual pathway is critical for transmitting visual information from retina to the brain. Reducing visual experience shortens myelin sheath length and slows the conduction velocity of the optic nerve. However, the mechanism underlying such experience-dependent myelination is unclear. Here, we found that closing both eyes, binocular deprivation (BD), during the juvenile period less affects the optic nerve myelination than monocular deprivation (MD) via GABA signaling. RNA-seq analysis of optic nerves from MD and BD mice revealed that GABAergic signaling is downregulated on the deprived side of MD compared to the intact side and BD. Inhibition of GABAergic signaling during the juvenile period resulted in myelin sheath shortening and excessive oligodendrocyte generation in normal mice, similar to the changes observed in MD mice. Enhancing GABAergic signaling rescued the myelin sheath shortening and excessive oligodendrocyte generation in the optic nerve of MD mice. Furthermore, we identified novel GABAergic neurons located within the optic nerve, whose neurites form belt-like presynaptic structures with the oligodendrocyte lineage cells, suggesting a potential source of the GABAergic inputs into oligodendrocytes. Our results indicate that the myelination of visual pathway is maintained by binocular visual inputs via intra-nerve GABA signaling.

An ultrastructural map of a spinal sensorimotor circuit reveals the potential of astroglia modulation
Information flow through circuits is dictated by the precise connectivity of neurons and glia. While a single astrocyte can contact many synapses, how glial-synaptic interactions are arranged within a single circuit to impact information flow remains understudied. Here, we use the local spinal sensorimotor circuit in zebrafish as a model to understand how neurons and astroglia are connected in a vertebrate circuit. With semi-automated cellular reconstructions and automated approaches to map all the synaptic connections, we identified the precise synaptic connections of the local sensorimotor circuit, from dorsal root ganglia neurons to spinal interneurons and finally to motor neurons. This revealed a complex network of interneurons that interact in the local sensorimotor circuit. We then mapped the glial processes within tripartite synapses in the circuit. We demonstrate that tripartite synapses are equally distributed across the circuit, supporting the idea that glia can modulate information flow through the circuit at different levels. We show that multiple astroglia, including bona fide astrocytes, contact synapses within a single sensory neuron circuit and that each of these astroglia can contact multiple parts of the circuit. This detailed map reveals an extensive network of connected neurons and astroglia that process sensory stimuli in a vertebrate. We then utilized this ultrastructural map to model how synaptic thresholding and glial modulation could alter information flow in circuits. We validated this circuit map with GCaMP6s imaging of dorsal root ganglia, spinal neurons and astroglia. This work provides a foundational resource detailing the ultrastructural organization of neurons and glia in a vertebrate circuit, offering insights in how glia could influence information flow in complex neural networks.

Bodily perception links memory and self: a case study of an amnesic patient
Episodic autobiographical memory (EAM) is a building block of self-consciousness, involving recollection and subjective re-experiencing of personal past experiences. Any life episode is originally encoded by a subject within a body. This raises the possibility that memory encoding is shaped by bodily self-consciousness (BSC), a basic form of self-consciousness arising from the multisensory and sensorimotor perceptual signals from the body. Recent studies in healthy subjects showed that embodied encoding improves EAM, with the involvement of the hippocampus. However, there are only few imaging studies to date, hippocampal data are not consistent, and the role of hippocampal damage is not understood. We investigated how different BSC states during encoding, modulate later EAM retrieval, in a patient with severe amnesia caused by rare bilateral hippocampal damage. We performed three separate behavioral experiments using immersive virtual reality. The patient showed consistently more difficulties recollecting information encoded in embodied vs. disembodied states, particularly when asked to recall her perspective experienced at encoding. These results contrasted with the usual beneficial effect of BSC on EAM, and significantly differed from controls. These data provide consistent evidence that BSC impacts encoding and later reliving, and shows that the hippocampus is not just a critical structure for EAM, but also for effects of embodiment on memory. Additional fMRI data extend these findings by revealing that hippocampal-parietal connectivity mediates BSC-EAM coupling. Our findings plead for an important role of BSC in EAM, mediated by the hippocampus and its connectivity, leading to embodied memories that are experienced as belonging to the self.

Signaling of trans-saccadic prediction error by foveal neurons of the monkey superior colliculus
Across saccades, neurons in retinotopically organized visual representations experience drastically different images, but visual percepts remain stable. Here we investigated whether such stability can be mediated, in part, via prediction-error signaling by neurons processing post-saccadic visual images. We specifically recorded from foveal superior colliculus (SC) neurons when a visual image only overlapped with their response fields (RF's) after foveating saccades but not pre-saccadically. When we rapidly changed the target features intra-saccadically, the foveal neurons' post-saccadic visual reafferent responses were elevated, even though the neurons did not directly sample the pre-saccadic extrafoveal target features. This effect did not occur in the absence of saccades, and it also scaled with the extent of the introduced intra-saccadic image feature discrepancies. These results suggest that foveal SC neurons may signal a trans-saccadic prediction error when the foveated image stimulating them is inconsistent with that expected from pre-saccadic extrafoveal representations, a potential perceptual stability mechanism.

Parity and APOEε4 genotype contribute distinct changes to functional connectivity across the middle-aged brain
Cognition and its underlying neurobiology change throughout the trajectory of aging, with prominent sex differences and influences of sex-specific factors. Research has shown that parity (pregnancy and parenthood) uniquely altered various biomarkers of brain health in middle age depending on presence of Alzheimers disease (AD) risk. The present study builds on prior work by providing a comprehensive view of functional connectivity changes and elucidating how network-level dynamics contribute to cognitive outcomes depending on primiparity and APOEe4 genotype, the top genetic risk factor for late-onset sporadic AD risk. We assessed neural activation in middle-aged wildtype and hAPOEe4 rats that were either nulliparous (0 litters) or primiparous (1 litter). Activation of the immediate early gene zif268 was quantified across 19 brain regions implicated in memory and AD. Primiparous hAPOEe4 rats exhibited widespread reductions in neural activation, particularly in the dorsal striatum, nucleus accumbens, frontal cortex, and retrosplenial cortex. Network analyses further revealed that primiparous wildtype rats had the most cohesive and efficient functional connectivity networks. Notably, the hierarchy of influence of brain regions within the neural network shifted based on parity and hAPOEe4 genotype. Activation of hippocampal new-born neurons in conjunction with subregions of the dorsal striatum, frontal cortex, and retrosplenial cortex dynamically predicted cognitive performance in a parity- and genotype-dependent manner. These findings underscore the lasting impact of reproductive history on brain health and cognitive aging, highlighting the need to consider sex-specific experiences in aging and AD research.

Designing optimal perturbation inputs for system identification in neuroscience
Investigating the dynamics of neural networks, which are governed by connectivity between neurons, is a fundamental challenge in neuroscience. Perturbation-based approaches allow the precise estimation of neural dynamic models and have been extensively applied in studies of brain functions and neural state transitions. However, the question of how optimal perturbations which most effectively identify dynamical models in neuroscience should be designed remains unclear. To address this, we propose a novel theoretical framework for estimating optimal perturbation inputs for system identification in linear time-invariant systems. The model represents neural dynamics using a connectivity matrix and an input matrix. Our framework derives an objective function to optimize perturbation inputs, which minimizes estimation errors in the model matrices. Building upon this, we further explore the relationship of this function with stimulation patterns commonly used in neuroscience, such as frequency, impulse, and step inputs. We then outline an iterative approach to perturbation input design. Our findings demonstrate that incorporating perturbation inputs significantly improves system identification accuracy as dictated by the objective function. Moreover, perturbation inputs tuned to a parameter related to the eigenvalues and a network structure of the intrinsic model enhance system identification. Through this iterative approach, the estimated model matrix gradually approaches the true matrix. As an application, we confirmed that the framework also contributes to the optimal control theory. This study highlights the potential of designing perturbation inputs to achieve the advanced identification of neural dynamics. By providing a framework for optimizing perturbations, our work facilitates deeper insights into brain functions and advances in the study of complex neural systems.

Gamma frequency neuronal oscillations modulate microglia morphology via colony stimulating factor 1 receptor and NFκB pathway signalling
Within the brain, neurons and glial cells engage in dynamic crosstalk to maintain homeostasis and regulate neuroimmune responses. Recent studies have implicated rhythmic neuronal network activity, most notably at gamma oscillation frequencies (approx. 25-100 Hz), in modulating the morphology and function of microglia, the brain's primary immune cells. Little is known, however, about the cellular mechanisms underlying this form of neuroimmune communication. Using pharmacological and optogenetic models of gamma oscillations in mouse brain slices, we found that gamma oscillations stimulate microglia to adopt a reactive morphological phenotype via activation of colony stimulation factor 1 receptor (CSF1R) and nuclear factor kappa B-mediated signalling. Surprisingly, inhibition of two downstream mediators of CSF1R signalling - phosphoinositide-3-kinase or phospholipase C - did not prevent this effect, suggesting that neuron-microglia interactions in this context may occur via compensatory or alternative CSF1R-linked pathways. These findings provide important insights into how rhythmic brain activity regulates neuroimmune function, with potential implications for neurological health and disease.

NADPH oxidase inhibitor enhances brain resilience in Alzheimer's disease by reducing tauopathy and neuroinflammation
Alzheimer's disease associates closely with activation of NADPH oxidase (Nox) isozymes. We identified that CRB-2131, a novel oxadiazole derivative, potently suppresses Nox isozymes. It inhibits reactive oxygen species production (ROS) by hippocampal neuronal and microglial cells and reduces microglial activation. Prophylactic (starting at 3.5 months of age) and therapeutic (starting at 6 months of age) oral administration with CRB-2131 for 10 weeks in 5XFAD mice reduced hippocampal superoxide levels, lipid peroxidation, Tau phosphorylation, and neuroinflammation. Prophylactic and therapeutic CRB-2131 treatment of 5XFAD mice restored their impaired cognition as shown by the novel-object recognition, Y-maze, and Morris water-maze tests. CRB-2131 treatment increased mature neurons, reduced apoptotic mature neurons, and elevated immature neurons in the hippocampus. Positron-emission tomography/computed-tomography imaging confirmed that CRB-2131 stimulated neuronal regeneration. CRB-2131 suppresses brain oxidation, tauopathy, and neuroinflammation, thereby preventing mature neuron death and promoting neuron regeneration. Ultimately, this fosters a resilient brain and protects cognition.

TBCK-deficiency leads to compartment-specific mRNA and lysosomal trafficking defects in patient-derived neurons
Monogenic pediatric neurodegenerative disorders can reveal fundamental cellular mechanisms that underlie selective neuronal vulnerability. TBCK-Encephaloneuronopathy (TBCKE) is a rare autosomal recessive disorder caused by stop-gain variants in the TBCK gene. Clinically, patients show evidence of profound neurodevelopmental delays, but also symptoms of progressive encephalopathy and motor neuron disease. Yet, the physiological role of TBCK protein remains unclear. We report a human neuronal TBCKE model, derived from iPSCs homozygous for the Boricua variant (p.R126X). Using unbiased proteomic analyses of human neurons, we find TBCK interacts with PPP1R21, C12orf4, and Cryzl1, consistent with TBCK being part of the FERRY mRNA transport complex. Loss of TBCK leads to depletion of C12ORF4 protein levels across multiple cell types, suggesting TBCK may also play a role regulating at least some members of the FERRY complex. We find that TBCK preferentially, but not exclusively, localizes to the surface of endolysosomal vesicles and can colocalize with mRNA in lysosomes. Furthermore, TBCK-deficient neurons have reduced mRNA content in the axonal compartment relative to the soma. TBCK-deficient neurons show reduced levels of the lysosomal dynein/dynactin adapter protein JIP4, which functionally leads to TBCK-deficient neurons exhibiting striking lysosomal axonal retrograde trafficking defects. Hence, our work reveals that TBCK can mediate endolysosomal trafficking of mRNA, particularly along lysosomes in human axonal compartments. TBCK-deficiency leads to compartment-specific mRNA and lysosomal trafficking defects in neurons, which likely contribute to the preferential susceptibility to neurodegeneration.

Breathing-Driven Modulation of Reticulospinal Tract Activity
The reticulospinal tract (RST) plays a pivotal role in motor control, especially during recovery after neurological injuries such as stroke and spinal cord injury (SCI). Understanding how RST activity is modulated offers valuable insights into improving motor function recovery. Recent studies have demonstrated that breathing rhythms influence brain activity. This study explores how respiratory rhythms modulate RST excitability during motor tasks, using the StartReact paradigm to examine reaction times (RTs) across visual (VRT), visual-auditory (VART), and visual-auditory startling (VSRT) conditions. We measured RTs in three muscles (first dorsal interosseous, flexor digitorum superficialis, and biceps) in healthy adult participants (n=13, both sexes) performing multi-joint movements. RTs were longest in the VRT condition and significantly decreased when auditory stimuli were added (VART), with further reductions observed in the VSRT condition. Additionally, respiratory phase transitions, particularly from inspiration to expiration (IE), significantly influenced RTs, with the shortest RTs observed during these transitions in the VSRT condition. These findings suggest that RST excitability is dynamically modulated by respiratory rhythms. This modulation of the RST by respiratory phase transitions could inform future neurorehabilitation strategies, such as respiratory-phase-aligned stimulation, to enhance motor recovery following corticospinal lesions. Ultimately, this approach may optimize the timing of interventions, improving outcomes in conditions such as stroke and SCI.