bioRxiv Subject Collection: Neuroscience's Journal

Inter-individual differences in cerebrovascular reactivity are synchronized within functional networks and tissue layers: evidence from healthy older adults and patients with hypertension
Functional-connectivity mapping has primarily relied resting-state functional MRI (rs-fMRI), and resting-state functional networks (RSNs) have been used widely to represent interactions within brain circuits. However, recent work demonstrated that resting-state functional networks (RSNs) may co-exist with vascular networks. In this work, we clarify the nature of these vascular networks by assessing the spatial covariation structure in breath-holding-based CVR amplitude and lag in a group of healthy older adults. We demonstrate a spatial synchrony in CVR amplitude and lag co-variations across participants confined to RSNs. Such a network structure is not seen when looking at the time-variate BOLD signal response to the breathhold. a network structure is also maintained in older adults with clinical hypertension, demonstrating its robustness against vascular pathologies. CVR amplitude is also found to vary with tissue layer in the grey matter and white matter, being most variable in deep WM and least variable in superficial cortex. Conversely, CVR lag appears to be organized by fibre tracts. This work demonstrates the use of cross-participant covariation patterns in CVR as an informative way of mapping the vascular routes in the GM and WM, and also raises questions about the nature and interpretation of RSNs.

Dopamine-driven Increase in IL-1β in Myeloid Cells is Mediated by Differential Dopamine Receptor Expression and Exacerbated by HIV
The catecholamine neurotransmitter dopamine is classically known for regulation of central nervous system (CNS) functions such as reward, movement, and cognition. Increasing evidence also indicates that dopamine regulates critical functions in peripheral organs and is an important immunoregulatory factor. We have previously shown that dopamine increases NF-{kappa}B activity, inflammasome activation, and the production of inflammatory cytokines such as IL-1{beta} in human macrophages. As myeloid lineage cells are central to the initiation and resolution of acute inflammatory responses, dopamine-mediated dysregulation of these functions could both impair the innate immune response and exacerbate chronic inflammation. However, the exact pathways by which dopamine drives myeloid inflammation are not well defined, and studies in both rodent and human systems indicate that dopamine can impact the production of inflammatory mediators through both D1-like dopamine receptors (DRD1, DRD5) and D2-like dopamine receptors (DRD2, DRD3, and DRD4). Therefore, we hypothesized that dopamine-mediated production of IL-1{beta} in myeloid cells is regulated by the ratio of different dopamine receptors that are activated. Our data in primary human monocyte-derived macrophages (hMDM) indicate that DRD1 expression is necessary for dopamine-mediated increases in IL-1{beta}, and that changes in the expression of DRD2 and other dopamine receptors can alter the magnitude of the dopamine-mediated increase in IL-1{beta}. Mature hMDM have a high D1-like to D2-like receptor ratio, which is different relative to monocytes and peripheral blood mononuclear cells (PBMCs). We further confirm in human microglia cell lines that a high ratio of D1-like to D2-like receptors promotes dopamine-induced increases in IL-1{beta} gene and protein expression using pharmacological inhibition or overexpression of dopamine receptors. RNA-sequencing of dopamine-treated microglia shows that genes encoding functions in IL-1{beta} signaling pathways, microglia activation, and neurotransmission increased with dopamine treatment. Finally, using HIV as an example of a chronic inflammatory disease that is substantively worsened by comorbid substance use disorders (SUDs) that impact dopaminergic signaling, we show increased effects of dopamine on inflammasome activation and IL-1{beta} in the presence of HIV in both human macrophages and microglia. These data suggest that use of addictive substances and dopamine-modulating therapeutics could dysregulate the innate inflammatory response and exacerbate chronic neuroimmunological conditions like HIV. Thus, a detailed understanding of dopamine-mediated changes in inflammation, in particular pathways regulating IL-1{beta}, will be critical to effectively tailor medication regimens.

Neural Prioritisation of Past Solutions Supports Generalisation
Generalisation from past experience is an important feature of intelligent systems. When faced with a new task, efficient generalisation can be achieved by evaluating solutions to earlier tasks as candidates for reuse. Consistent with this idea, we found that human participants (n=40) learned optimal solutions to a set of training tasks and continued to reuse them on novel test tasks. Corresponding functional magnetic resonance imaging data showed that optimal solutions from the training tasks were represented on test tasks in occipitotemporal and dorsolateral prefrontal cortex. These findings suggest that humans evaluate and generalise successful past solutions when attempting to solve new tasks.

A minimally invasive thrombotic stroke model to study circadian rhythm in awake mice
Experimental stroke models in rodents are essential for mechanistic studies and therapeutic development. However, these models have several limitations negatively impacting their translational relevance. Here we aimed to develop a minimally invasive thrombotic stroke model through magnetic particle delivery that does not require craniotomy, is amenable to reperfusion therapy, can be combined with in vivo imaging modalities, and can be performed in awake mice. We found that the model results in reproducible cortical infarcts within the middle cerebral artery (MCA) with cytologic and immune changes similar to that observed with more invasive distal MCA occlusion models. Importantly, the injury produced by the model was ameliorated by tissue plasminogen activator (tPA) administration. We also show that MCA occlusion in awake animals results in bigger ischemic lesions independent of day/night cycle. Magnetic particle delivery had no overt effects on physiologic parameters and systemic immune biomarkers. In conclusion, we developed a novel stroke model in mice that fulfills many requirements for modeling human stroke.

Neural correlates of retrieval success and precision: an fMRI study
Prior studies examining the neural mechanisms underlying retrieval success and precision have yielded inconsistent results. Here, their neural correlates were examined using a memory task that assessed precision for spatial location. A sample of healthy young adults underwent fMRI scanning during a single study-test cycle. At study, participants viewed a series of object images, each placed at a randomly selected location on an imaginary circle. At test, studied images were intermixed with new images and presented to the participants. The requirement was to move a cursor to the location of the studied image, guessing if necessary. Participants then signaled whether the presented image as having been studied. Memory precision was quantified as the angle between the studied location and the location selected by the participant. A precision effect was evident in the left angular gyrus, where BOLD activity covaried across trials with location accuracy. Multi-voxel pattern analysis also revealed a significant item-level reinstatement effect for high-precision trials. There was no evidence of a retrieval success effect in the angular gyrus. BOLD activity in the hippocampus was insensitive to both success and precision. These findings are partially consistent with prior evidence that success and precision are dissociable features of memory retrieval.

Wavelet transform of single-trial vestibular short-latency evoked potential reveals temporary reduction in signal detectability and temporal precision following noise exposure
The vestibular short-latency evoked potential (VsEP) reflects the activity of irregular vestibular afferents and their target neurons in the brain stem. Attenuation of trial-averaged VsEP waveforms is widely accepted as an indicator of vestibular dysfunction, however, more quantitative analyses of VsEP waveforms could reveal underlying neural properties of VsEP waveforms. Here, we present a time-frequency analysis of the VsEP with a wavelet transform on a single-trial basis, which allows us to examine trial-by-trial variability in the strength of VsEP waves as well as their temporal coherence across trials. Using this method, we examined changes in the VsEP following 110 dB SPL noise exposure in rats. We found detectability of head jerks based on the power of wavelet transform coefficients was significantly reduced 1 day after noise exposure but recovered nearly to pre-exposure level in 3 - 7 days and completely by 28 days after exposure. Temporal coherence of VsEP waves across trials was also significantly reduced on 1 day after exposure but recovered with a similar time course. Additionally, we found a significant reduction in the number of calretinin-positive calyces in the sacculi collected 28 days after noise exposure. Furthermore, the number of calretinin-positive calyces was significantly correlated with the degree of reduction in temporal coherence and/or signal detectability of the smallest-amplitude jerks. This new analysis of the VsEP provides more quantitative descriptions of noise-induced changes as well as new insights into potential mechanisms underlying noise-induced vestibular dysfunction.

Predictive coding model can detect novelty on different levels of representation hierarchy
Novelty detection, also known as familiarity discrimination or recognition memory, refers to the ability to distinguish whether a stimulus has been seen before. It has been hypothesized that novelty detection can naturally arise within networks that store memory or learn efficient neural representation, because these networks already store information on familiar stimuli. However, computational models instantiating this hypothesis have not been shown to reproduce high capacity of human recognition memory, so it is unclear if this hypothesis is feasible. This paper demonstrates that predictive coding, which is an established model previously shown to effectively support representation learning and memory, can also naturally discriminate novelty with high capacity. Predictive coding model includes neurons encoding prediction errors, and we show that these neurons produce higher activity for novel stimuli, so that the novelty can be decoded from their activity. Moreover, the hierarchical predictive coding networks uniquely perform novelty detection at varying abstraction levels across the hierarchy, i.e., they can detect both novel low-level features, and novel higher-level objects. Overall, we unify novelty detection, associative memory, and representation learning within a single computational framework.

Translational profiling reveals novel gene expression changes in the direct and indirect pathways in a mouse model of LDOPA-induced dyskinesia
The molecular mechanisms underlying L dihydroxyphenylalanine (LDOPA) induced dyskinesia in Parkinson's disease are poorly understood. Here we employ two transgenic mouse lines, combining translating ribosomal affinity purification (TRAP) with bacterial artificial chromosome expression (Bac), to selectively isolate RNA from either DRD1A expressing striatonigral, or DRD2 expressing striatopallidal medium spiny neurons (MSNs) of the direct and indirect pathways respectively, to study changes in translational gene expression following repeated LDOPA treatment. 6-OHDA lesioned DRD1A and DRD2 BacTRAP mice were treated with either saline or LDOPA bi-daily for 21 days over which time they developed abnormal involuntary movements reminiscent of dyskinesia. On day 22, all animals received LDOPA 40 minutes prior to sacrifice. The striatum of the lesioned hemisphere was dissected and subject to TRAP. Extracted ribosomal RNA was amplified, purified and gene expression was quantified using microarray. 195 significantly varying transcripts were identified among the 4 treatment groups. Pathway analysis revealed an overrepresentation of calcium signaling and long-term potentiation in the DRD1A expressing MSNs of the direct pathway, with significant involvement of long-term depression in the DRD2 expressing MSNs of the indirect pathway following chronic treatment with LDOPA. Several MAPK associated genes (NR4A1, GADD45G, STMN1, FOS and DUSP1) differentiated the direct and indirect pathways following both acute and chronic LDOPA treatment. However, the MAPK pathway activator PAK1 was downregulated in the indirect pathway and upregulated in the direct pathway, strongly suggesting a role for PAK1 in regulating the opposing effects of LDOPA on these two pathways in dyskinesia. Future studies will assess the potential of targeting these genes and pathways to prevent the development of LDOPA-induced dyskinesia.

M1 Large-scale Network Dynamics Support Human Motor Resonance and Its Plastic Reshaping
Motor resonance - the activation of the observer's motor system when viewing others' actions - grounds the intertwined nature of action perception and execution, with profound implications for social cognition and action understanding. Despite extensive research, the neural underpinnings supporting motor resonance emergence and rewriting remain unexplored. In this study, we investigated the role of sensorimotor associative learning in motor resonance neural mechanisms. To this aim, we applied cross-systems paired associative stimulation (PAS) to induce novel visuomotor associations in the human brain. This protocol, which repeatedly pairs transcranial magnetic stimulation (TMS) pulses over the primary motor cortex (M1) with visual stimuli of actions, drives the emergence of an atypical, PAS-conditioned motor resonance response. Using TMS and electroencephalography (EEG) co-registration during action observation, we tracked the M1 functional connectivity profile during this process to map the inter-areal connectivity profiles associated with typical and PAS-induced motor resonance phenomena. Besides confirming, at the corticospinal level, the emergence of newly acquired motor resonance responses at the cost of typical ones after PAS administration, our results reveal dissociable aspects of motor resonance in M1 interregional communication. On the one side, typical motor resonance effects acquired through the lifespan are associated with prominent M1 alpha-band and reduced beta-band connectivity, which might facilitate the corticospinal output while integrating visuomotor information. Conversely, the atypical PAS-induced motor resonance is linked to M1 beta-band cortical connectivity modulations, only partially overlapping with interregional communication patterns related to the typical mirroring responses. This evidence suggests that beta-phase synchronization may be the critical mechanism supporting the formation of motor resonance by coordinating the activity of motor regions during action observation, which also involves alpha-band top-down control of frontal areas. These findings provide new insights into the neural dynamics underlying (typical and newly acquired) motor resonance, highlighting the role of large-scale interregional communication in sensorimotor associative learning within the action observation network.

Induction of a Muller glial-specific protective pathway safeguards the retina from diabetes induced damage
Diabetes can lead to cell-type-specific responses in the retina, including vascular lesions, glial dysfunction and neurodegeneration, all of which contribute to retinopathy. However, the molecular mechanisms underlying these cell type-specific responses, and the cell types that are sensitive to diabetes have not been fully elucidated. Employing single cell transcriptomic analyses, we profiled the transcriptional changes induced by diabetes in different retinal cell types in diabetic rat models as the disease progressed. Rod photoreceptors, a subtype of amacrine interneurons, and Muller glial cells exhibited rapid responses to diabetes at the transcript levels. Genes associated with ion regulation were upregulated in all three cell types, suggesting a common response to diabetes. Furthermore, focused studies revealed that while Muller glial cells initially increased the expression of genes playing protective roles, they cannot sustain this beneficial effect as the disease progressed. We explored one of the candidate protective genes, Zinc finger protein 36 homolog (Zfp36), and observed that depleting Zfp36 in rat Muller glial cells in vivo using AAV-based tools exacerbated early diabetes-induced phenotypes, including gliosis, neurodegeneration, and vascular defects. Notably, the over-expression of Zfp36 slowed the development of phenotypes associated with diabetic retinopathy. In summary, this work unveiled retinal cell types that are sensitive to diabetes and demonstrated that Muller glial cells can mount protective responses through Zfp36. The failure to maintain Zfp36 levels contributes to the development of diabetic retinopathy.

Communication subspace dynamics of the canonical olfactory pathway
Understanding how different brain areas communicate is crucial for elucidating the mechanisms underlying cognition. A possible way for neural populations to interact is through a communication subspace, a specific region in the state-space enabling the transmission of behaviorally-relevant spiking patterns. In the olfactory system, it remains unclear if different populations employ such a mechanism. Our study reveals that neuronal ensembles in the main olfactory pathway (olfactory bulb to olfactory cortex) interact through a communication subspace, which is driven by nasal respiration and allows feedforward and feedback transmission to occur segregated along the sniffing cycle. Moreover, our results demonstrate that subspace communication depends causally on the activity of both areas, is hindered during anesthesia, and transmits a low-dimensional representation of odor.

Systemic and targeted activation of Nrf2 reverses doxorubicin-induced cognitive impairments and sensorimotor deficits in mice
While cancer survivorship has increased due to advances in treatments, chemotherapy often carries long-lived neurotoxic side effects which reduce quality of life. Commonly affected domains include memory, executive function, attention, processing speed and sensorimotor function, colloquially known as chemotherapy-induced cognitive impairment (CICI) or chemobrain. Oxidative stress and neuroimmune signaling in the brain have been mechanistically linked to the deleterious effects of chemotherapy on cognition and sensorimotor function. With this in mind, we tested if activation of the master regulator of antioxidant response nuclear factor E2-related factor 2 (Nrf2) alleviates cognitive and sensorimotor impairments induced by doxorubicin. The FDA-approved systemic Nrf2 activator, diroximel fumarate (DRF) was used, along with our recently developed prodrug 1c which has the advantage of specifically releasing monomethyl fumarate at sites of oxidative stress. DRF and 1c both reversed doxorubicin-induced deficits in executive function, spatial and working memory, as well as decrements in fine motor coordination and grip strength, across both male and female mice. Both treatments reversed doxorubicin-induced loss of synaptic proteins and microglia phenotypic transition in the hippocampus. Doxorubicin-induced myelin damage in the corpus callosum was reversed by both Nrf2 activators. These results demonstrate the therapeutic potential of Nrf2 activators to reverse doxorubicin-induced cognitive impairments, motor incoordination, and associated structural and phenotypic changes in the brain. The localized release of monomethyl fumarate by 1c has the potential to diminish unwanted effects of fumarates while retaining efficacy.

Spontaneous emergence of alternating hippocampal theta sequences in a simple 2D adaptation model.
Spatial sequences encoded by cells in the hippocampal-entorhinal region have been observed to spontaneously alternate across the animal's midline during navigation in the open field, but it is unknown how this occurs. We show that sinusoidal sampling patterns emerge rapidly and robustly in a simple model of the hippocampus that makes no assumptions about sequence direction. We corroborate our findings using hippocampal data from rats navigating in the open field.

Dye-based Fluorescent Organic Nanoparticles, New Promising Tools for Optogenetics
Dye-based fluorescent organic nanoparticles are a specific class of nanoparticles obtained by nanoprecipitation in water of pure dyes only. While the photophysical and colloidal properties of the nanoparticles strongly depend on the nature of the aggregated dyes, their excellent brightness in the visible and in the near infrared make these nanoparticles a unique and versatile platform for in vivo application. This article examines the promising utilization of these nanoparticles for in vivo optogenetics applications. Their photophysical properties as well as their biocompatibility and their capacity to activate Chrimson opsin in vivo through fluorescence reabsorption process are demonstrated. Additionally, an illustrative example of employing these nanoparticles in fear reduction in mice through close-loop stimulation is presented. Through an optogenetic methodology, the nanoparticles demonstrate an ability to selectively manipulate neurons implicated in the fear response and diminish the latter. Dye-based fluorescent organic nanoparticles represent a promising and innovative strategy for optogenetic applications, holding substantial potential in the domain of translational neuroscience. This work paves the way for novel therapeutic modalities for neurological and neuropsychiatric disorders.

Activity-Dependent Remodeling of Corticostriatal Axonal Boutons During Motor Learning
Motor skill learning induces long-lasting synaptic plasticity at not only the inputs, such as dendritic spines1-4, but also at the outputs to the striatum of motor cortical neurons5,6. However, very little is known about the activity and structural plasticity of corticostriatal axons during learning in the adult brain. Here, we used longitudinal in vivo two-photon imaging to monitor the activity and structure of thousands of corticostriatal axonal boutons in the dorsolateral striatum in awake mice. We found that learning a new motor skill induces dynamic regulation of axonal boutons. The activities of motor corticostriatal axonal boutons exhibited selectivity for rewarded movements (RM) and un-rewarded movements (UM). Strikingly, boutons on the same axonal branches showed diverse responses during behavior. Motor learning significantly increased the fraction of RM boutons and reduced the heterogeneity of bouton activities. Moreover, motor learning-induced profound structural dynamism in boutons. By combining structural and functional imaging, we identified that newly formed axonal boutons are more likely to exhibit selectivity for RM and are stabilized during motor learning, while UM boutons are selectively eliminated. Our results highlight a novel form of plasticity at corticostriatal axons induced by motor learning, indicating that motor corticostriatal axonal boutons undergo dynamic reorganization that facilitates the acquisition and execution of motor skills.

Anoctamins mediate polymodal sensory perception and larval metamorphosis in a non-vertebrate chordate.
An exceptional feature of most animals is their ability to perceive diverse sensory cues from the environment and integrate this information in their brain to yield ethologically relevant behavioral output. For the myriad of marine species, the ocean represents a complex sensory environment, which acts as a crucible of evolution for polymodal sensory perception. The cellular and molecular bases of polymodal sensory perception in a marine environment remain enigmatic. Here we use Ca2+ imaging and quantitative behavioral analysis to show that in the tunicate Ciona intestinalis two members of the evolutionarily conserved Anoctamin family1-4 (Tmem16E/Ano5 and Tmem16F/Ano6), are required for sensing chemosensory and mechanosensory metamorphic cues. We find that they act by modulating neuronal excitability and Ca2+ response kinetics in the primary sensory neurons and axial columnar cells of the papillae, a widely conserved sensory-adhesive organ across ascidians5-9. Finally, we use electrophysiological recordings and a scramblase assay in tissue culture to demonstrate that Tmem16E/Ano5 acts as a channel, while Tmem16F/Ano6 is a bifunctional ion channel and phospholipid scramblase. Our results establish Ano5 and Ano6 as novel players in the zooplanktonic, pre-vertebrate molecular toolkit that controls polymodal sensory perception in aquatic environments.

Rapid emergence of latent knowledge in the sensory cortex drives learning
Rapid learning confers significant advantages to animals in ecological environments. Despite the need for speed, animals appear to only slowly learn to associate rewarded actions with predictive cues. This slow learning is thought to be supported by a gradual expansion of predictive cue representation in the sensory cortex. However, evidence is growing that animals learn more rapidly than classical performance measures suggest, challenging the prevailing model of sensory cortical plasticity. Here, we investigated the relationship between learning and sensory cortical representations. We trained mice on an auditory go/no-go task that dissociated the rapid acquisition of task contingencies (learning) from its slower expression (performance). Optogenetic silencing demonstrated that the auditory cortex (AC) drives both rapid learning and slower performance gains but becomes dispensable at expert. Rather than enhancement or expansion of cue representations, two-photon calcium imaging of AC excitatory neurons throughout learning revealed two higher-order signals that were causal to learning and performance. First, a reward prediction (RP) signal emerged rapidly within tens of trials, was present after action-related errors only early in training, and faded at expert levels. Strikingly, silencing at the time of the RP signal impaired rapid learning, suggesting it serves an associative and teaching role. Second, a distinct cell ensemble encoded and controlled licking suppression that drove the slower performance improvements. These two ensembles were spatially clustered but uncoupled from underlying sensory representations, indicating a higher-order functional segregation within AC. Our results reveal that the sensory cortex manifests higher-order computations that separably drive rapid learning and slower performance improvements, reshaping our understanding of the fundamental role of the sensory cortex.

Experience-dependent predictions of feedforward and contextual information in mouse visual cortex
Neurons in primary visual cortex are driven by feedforward visual inputs and top-down contextual inputs. The nature of this contextual information is difficult to study, as responses to feedforward and top-down inputs overlap in time and are difficult to disentangle experimentally. To address this issue, we measured responses to natural images and partially occluded versions of these images in the visual cortex of mice. Assessing neuronal responses before and after familiarizing mice with the non-occluded images allowed us to study experience-dependent and stimulus-specific contextual responses in pyramidal cells (PyCs) in cortical layers 2/3 and 5 in the absence of feedforward input. Surprisingly, in the same retinotopic region of cortex, we found that separate populations of PyCs in layer 2/3 responded to occluded and non-occluded images. Responses of PyCs selective for occluded images were strengthened upon familiarization and decoding analysis revealed they contained image-specific information, suggesting that they signaled the absence of predicted visual stimuli. Responses of PyCs selective for non-occluded scenes were weaker for familiarized images but stronger for unfamiliar images, suggesting that these neurons signaled the presence of unpredicted visual stimuli. Layer 5 also contained PyCs preferring either feedforward or contextual inputs, but their responses were more complex and strengthening of responses to occluded images required task engagement. The results show that visual experience decreases the activity of neurons responding to known feedforward inputs but increases the activity of neurons responding to contextual inputs tied to expected stimuli.

Visual neurons recognize complex image transformations
Natural visual scenes are dominated by sequences of transforming images. Spatial visual information is thought to be processed by detection of elemental stimulus features which are recomposed into scenes. How image information is integrated over time is unclear. We explored visual information encoding in the optic tectum. Unbiased stimulus presentation shows that the majority of tectal neurons recognize image sequences. This is achieved by temporally dynamic response properties, which encode complex image transitions over several hundred milliseconds. Calcium imaging reveals that neurons that encode spatiotemporal image sequences fire in spike sequences that predict a logical diagram of spatiotemporal information processing. Furthermore, the temporal scale of visual information is tuned by experience. This study indicates how neurons recognize dynamic visual scenes that transform over time.

Dynamics of pitch perception in the auditory cortex
The ability to perceive pitch allows human listeners to experience music, recognize the identity and emotion conveyed by conversational partners, and make sense of their auditory environment. A pitch percept is formed by weighting different acoustic cues (e.g., signal fundamental frequency and inter-harmonic spacing) and contextual cues (expectation). How and when such cues are neurally encoded and integrated remains debated. In this study, twenty-eight participants listened to tone sequences with different acoustic cues (pure tones, complex missing fundamental tones, and ambiguous mixtures), placed in predictable and less predictable sequences, while magnetoencephalography was recorded. Decoding analyses revealed that pitch was encoded in neural responses to all three tone types, in the low-to-mid auditory cortex, bilaterally, with right-hemisphere dominance. The pattern of activity generalized across cue-types, offset in time: pitch was neurally encoded earlier for harmonic tones (~85ms) than pure tones (~95ms). For ambiguous tones, pitch emerged significantly earlier in predictable contexts, and could be decoded even before tone onset. The results suggest that a unified neural representation of pitch emerges by integrating independent pitch cues, and that context alters the dynamics of pitch generation when acoustic cues are ambiguous.

Amyloid beta oligomers dysregulate oligodendrocyte differentiation and myelination via PKC in the zebrafish spinal cord
Amyloid beta oligomers (Abetao) have been proposed as candidates to induce oligodendrocyte (OL) and myelin dysfunctions in early stages of Alzheimer's disease (AD) pathology. Nevertheless, little is known about how Abetao affect OL differentiation and myelination in vivo, and the underlying molecular mechanisms. In this study, we explored the effects of a brain intraventricular injection of Abetao on OLs and myelin in the developing spinal cord of zebrafish larvae. Using quantitative fluorescent in situ RNA hybridization assays, we demonstrated that Abetao altered myrf and mbp mRNA levels and the regional distribution of mbp during larval development, suggesting an early differentiation of OLs. Through live imaging of Tg(myrf:mScarlet) and Tg(mbp:tagRFP) zebrafish lines, both crossed with Tg(olig2:EGFP), we found that Abetao increased the number of myrf+ and mbp+ OLs in the dorsal spinal cord at 72 hpf and 5 dpf, respectively, without affecting total cell numbers. Furthermore, Abetao also increased the number of myelin sheaths per OL and the number of myelinated axons in the dorsal spinal cord compared to vehicle-injected control animals. Interestingly, the treatment of Abetao-injected zebrafish with the pan-PKC inhibitor Go6983 restored the aforementioned alterations in OLs and myelin to control levels. Altogether, not only do we demonstrate that Abetao induce a precocious oligodendroglial differentiation leading to dysregulated myelination, but we also identified PKC as a key player in Abetao-induced pathology.

Human sensory-like neuron cultivation - an optimized protocol
Introduction: Reprogramming of human induced pluripotent stem cells (iPSC) and their differentiation into specific cell types, such as induced sensory-like neurons (iSN), are critical for disease modeling and drug testing. However, the variability of cell populations challenges reliability and reproducibility. While various protocols for iSN differentiation exist, development of non-iSN cells in these cultures remains an issue. Therefore, standardization of protocols is essential. This study aimed to improve iSN culture conditions by reducing the number of non-iSN cells while preserving survival and quality of iSN. Methods: iSN were differentiated from a healthy control iPSC line using an established protocol. Interventions for protocol optimization included floxuridine (FdU) or 1-{beta}-D-arabinofuranosyl-cytosin-hydrochlorid (AraC) treatment, Magnetic-Activated Cell Sorting (MACS), early cell passaging, and replating. Cell viability and iSN-to-total-cell-count ratio were assessed using a luminescent assay and immunocytochemistry, respectively. Results: Passaging of cells during differentiation did not increase the iSN-to-total-cell-count ratio, and MACS of immature iSN led to neuronal blebbing and reduced the iSN-to-total-cell-count ratio. Treatment with high concentrations and prolonged incubation of FdU or AraC resulted in excessive cell death. However, treatment with 10 M FdU for 24 h post-differentiation showed the most selective targeting of non-iSN cells, leading to an increase in the iSN-to-total-cell count ratio without compromising the viability or functionality of the iSN population. Replating of iSN shortly after seeding also helped to reduce non-iSN cells. Conclusion: In direct comparison to other methods, treatment with 10 M FdU for 24 h after differentiation represents a promising approach to improve iSN culture purity, offering a potential benefit for downstream applications in disease modeling and drug discovery. However, further investigations involving multiple iPSC lines and optimization of protocol parameters are warranted to fully exploit the potential of this method and enhance its reproducibility and applicability. Overall, this study provides valuable insights into optimizing culture conditions for iSN differentiation and highlights the importance of standardized protocols in iPSC-based research.

Retinoid X Receptor as a Novel Drug Target to Treat Neurological Disorders Associated with α-Synucleinopathies.
The pathology of Parkinson Disease (PD) is multifaceted, with chronic neuroinflammation associated with glial cell activation standing out as a hallmark of PD pathophysiology. While a few treatments exist to interfere with inflammation, a breakthrough therapy based on innovative molecular mechanisms and targets is still awaited. The nuclear retinoid X receptor (RXR) is of particular interest for therapeutic intervention due to its ability to bind and activate permissive partners, NURR1 and PPARs, which have been shown to be dysfunctional in PD brains. Therefore, the goal of this study was to validate RXR-based therapy to slow down PD pathogenesis. Adult C57BL6 male mice were used in the study. PD-like pathology was triggered by co-delivery of AAV expressing alpha-synuclein and PFF to the substantia nigra pars compacta. The therapeutic potential of RXR activation was evaluated using AAV-mediated gene transport. Unbiased stereology, immunohistochemical analysis, LC/MS, and western blotting were employed to assess the therapeutic effect. At 8 weeks post-injection, elevated GFAP and Iba1 levels, associated with accumulated LB-like aggregates, pronounced loss of TH neuronal cells, and diminished dopamine (DA) levels were observed in affected brains. Moreover, PPAR and NURR1 protein levels were also reduced in these brains. Conversely, RXR overexpression resulted in an increase in PPAR and NURR1 levels, a reduction in GFAP and Iba1 levels, and a decrease in the number and distribution of LB-like aggregates. These phenomena were also accompanied by the prevention of tyrosine hydroxylase (TH)+ cell loss and the DA deficit in the treated brains. Therefore, our data provide direct evidence of the therapeutic potential of RXR-based therapy and highlight RXR as a novel drug target for PD.

Hierarchical Bayesian inference to model continuous phenotypical progression in Alzheimer's Disease
Throughout an organism's lifespan, a multitude of biological systems transition through complex biophysical processes. These processes serve as indicators of the underlying biological states. Inferring these latent unobserved states is a key problem in modern biology and neuroscience. Unfortunately, in many experimental setups, we can at best obtain snapshots of the system at different times for different individuals, and one major challenge is the one of reconciling those measurements. This formalism is particularly relevant in the study of Alzheimer's Disease (AD) progression, in which we observe in brain donors the aggregation of pathological proteins but the underlying disease state is unknown. The progression of AD can be modeled by assigning a latent score - termed pseudotime - to each pathological state, creating a pseudotemporal ordering of donors based on their pathological burden. This paper proposes a hierarchical Bayesian framework to model AD progression using detailed quantification of multiple AD pathological proteins from the Seattle AD Brain Cell Atlas consortium (SEA-AD). Inspired by biophysical models, we model pathological burden as an exponential process. Theoretical properties of the model are studied, by using linearization to reveal convergence and identifiability properties. We provide Markov chain Monte Carlo estimation algorithms, and show the effectiveness of our approach with multiple simulation studies across data conditions. Applying the methodology to SEA-AD brain data, we infer pseudotime for each donor and order them by pathological burden. Finally, we analyze the information within each pathological feature and utilize it to refine the model by focusing on the most informative pathologies. This lays the groundwork for suggesting future experimental design approaches.

Lack of Oncomodulin Increases ATP-Dependent Calcium Signaling and Susceptibility to Noise in Adult Mice
Tight regulation of Ca2+ is crucial for the function of cochlear outer hair cells (OHCs). Dysregulation of Ca2+ homeostasis in OHCs is associated with impaired hearing function and contributes to increased vulnerability to environmental insults, such as noise exposure. Ca2+ signaling in developing OHCs can be modulated by oncomodulin (OCM), an EF-hand calcium-binding protein. Here, we investigated whether the lack of OCM disrupts the control of intracellular Ca2+ in mature OHCs, and influences vulnerability to noise. Using young adult CBA/CaJ mice, we found that OHCs from Ocm-knockout (Ocm-/-) mice exhibited normal biophysical profiles and electromotile responses compared to littermate control OHCs. Moderate noise exposure (95 dB SPL, 2 hrs) caused temporary hearing threshold shifts in Ocm+/+ and Ocm-/- mice but the loss of hearing was permanent for Ocm-/- mice. However, while Ocm+/+ fully recovered their hearing 2 weeks after noise exposure, Ocm-/- mice showed permanent threshold shifts. Using a genetically encoded Ca2+ sensor (GCaMP6s) expressed in Ocm+/+ and Ocm-/- OHCs, we found that chronic noise exposure (95 dB SPL, 9 hrs) increased ATP-induced Ca2+ signaling in Ocm-/- OHCs compared to Ocm+/+ OHCs. Chronic noise exposures also caused higher hearing threshold shifts in Ocm-/- mice. Prior to noise exposure, P2X2 expression was already upregulated in Ocm-/- mice compared to Ocm+/+ mice. Following chronic noise, P2X2 receptors were upregulated in the Ocm+/+ cochlea but not in the Ocm-/- cochlea, which retains their pre-noise high expression level. We propose that the lack of OCM increases susceptibility to noise. Increased purinergic signaling and dysregulation of cytosolic Ca2+ homeostasis could contribute to early onset hearing loss in the Ocm-/- mice.

NMDA receptor antagonist memantine selectively affects recurrent processing during perceptual inference
Perceptual inference requires the integration of visual features through recurrent processing, the dynamic exchange of information between higher and lower level cortical regions. While animal research has demonstrated a crucial role of NMDA receptors in recurrent processing, establishing a causal link between NMDA-mediated recurrent processing and human perception has remained challenging. Here, we report two pharmacological studies with randomized, double-blind, crossover designs in which we administered the NMDA antagonist memantine, while collecting human electroencephalography (EEG). We trained and tested EEG classifiers to reflect the processing of specific stimulus features with increasing levels of complexity, namely differences in stimulus contrast, collinearity between local line elements, and illusory surfaces of a Kanizsa triangle. In two experiments involving different participants and visual tasks, we found that memantine selectively affected decoding of the Kanizsa illusion, known to depend on recurrent processing, while leaving decoding of contrast and collinearity largely unaffected. Interestingly, the results from an attentional blink (experiment 1) and task-relevance manipulation (experiment 2) showed that memantine was only effective when the stimulus was attended and consciously accessed. These findings demonstrate that NMDA inhibition selectively affects recurrent processing, especially for attended objects, and thereby provide a crucial step toward bridging animal and human research, shedding light on the neural mechanisms underpinning perceptual inference and conscious perception.

Olfactory facilitation of visual categorization in the 4-month-old brain depends on visual demand
To navigate their environment, infants rely on intersensory facilitation when unisensory perceptual demand is high, a principle known as inverse effectiveness. Given that this principle was mainly documented in the context of audiovisual stimulations, here we aim to determine whether it applies to olfactory-to-visual facilitation. We build on previous evidence that the mother's body odor facilitates face categorization in the 4-month-old brain, and investigate whether this effect depends on visual demand. Scalp electroencephalogram (EEG) was recorded in 2 groups of 4-month-old infants while they watched 6-Hz streams of visual stimuli with faces displayed every 6th stimulus to tag a face-selective response at 1 Hz. We used variable natural stimuli in one group (Nat Group), while stimuli were simplified in the other group (Simp Group) to reduce perceptual categorization demand. During visual stimulation, infants were alternatively exposed to their mother's vs. a baseline odor. For both groups, we found an occipito-temporal face-selective response, but with a larger amplitude for the simplified stimuli, reflecting less demanding visual categorization. Importantly, the mother's body odor enhances the response to natural, but not to simplified, face stimuli, indicating that maternal odor improves face categorization when it is most demanding for the 4-month-old brain. Overall, this study demonstrates that the inverse effectiveness of intersensory facilitation applies to the sense of smell during early perceptual development.

Interactive data exploration websites for large-scale electrophysiology
Methodological advances in neuroscience have enabled the collection of massive datasets which demand innovative approaches for scientific communication. Existing platforms for data storage lack intuitive tools for data exploration, limiting our ability to interact effectively with these brain-wide datasets. We introduce two public websites: Data and Atlas developed for the International Brain Laboratory which provide access to millions of behavioral trials and hundreds of thousands of individual neurons. These interfaces allow users to discover both the raw and processed brain-wide data released by the IBL at the scale of the whole brain, individual sessions, trials, and neurons. By hosting these data interfaces as websites they are available cross-platform with no installation. By releasing each site's code as a modular open-source framework, other researchers can easily develop their own web interfaces and explore their own data. As neuroscience datasets continue to expand, customizable web interfaces offer a glimpse into a future of streamlined data exploration and act as blueprints for future tools.

Gangliosides in neural stem cell fate determination and nerve cell specification--preparation and administration
Gangliosides are sialylated glycosphingolipids with essential but enigmatic functions in healthy and disease brains. GD3 is the predominant species in neural stem cells (NSCs) and GD3-synthase (sialyltransferase II; St8Sia1) knockout (GD3S-KO) revealed reduction of postnatal NSC pools with severe behavioral deficits including cognitive impairment, depression-like phenotypes, and olfactory dysfunction. Exogenous administration of GD3 significantly restored the NSC pools and enhanced the stemness of NSCs with multipotency and self-renewal, followed by restored neuronal functions. Our group discovered that GD3 is involved in the maintenance of NSC fate determination by interacting with epidermal growth factor receptors (EGFRs), by modulating expression of cyclin-dependent kinase (CDK) inhibitors p27 and p21, and by regulating mitochondrial dynamics via associating a mitochondrial fission protein, the dynamin-related protein-1 (Drp1). Furthermore, we discovered that nuclear GM1 promotes neuronal differentiation by an epigenetic regulatory mechanism. GM1 binds with acetylated histones on the promoter of N-acetylgalactosaminyltransferase (GalNAcT; GM2 synthase (GM2S); B4galnt1) as well as on the NeuroD1 in differentiated neurons. In addition, epigenetic activation of the GM2S gene was detected as accompanied by an apparent induction of neuronal differentiation in NSCs responding to an exogenous supplement of GM1. Interestingly, GM1 induced epigenetic activation of the tyrosine hydroxylase (TH) gene, with recruitment of Nurr1 and PITX3, dopaminergic neuron-associated transcription factors, to the TH promoter region. In this way, GM1 epigenetically regulates dopaminergic neuron specific gene expression, and it would modify Parkinson's disease. Multifunctional gangliosides significantly modulate lipid microdomains to regulate functions of important molecules on multiple sites: the plasma membrane, mitochondrial membrane, and nuclear membrane. Versatile gangliosides regulate functional neurons as well as sustain NSC functions via modulating protein and gene activities on ganglioside microdomains. Maintaining proper ganglioside microdomains benefits healthy neuronal development and millions of senior citizens with neurodegenerative diseases. Here, we introduce how to isolate GD3 and GM1 and how to administer them into the mouse brain to investigate their functions on NSC fate determination and nerve cell specification.

A versatile correlative light and electron microscopy protocol for human brain and other biological models
Correlative light and electron microscopy (CLEM) combines light microscopy (LM) for target identification using genetic labels, dyes, antibodies, and morphological features with electron microscopy (EM) for high-resolution subcellular structure analysis. We describe an optimized room-temperature CLEM protocol for ultrastructural investigation of post-mortem human brain tissues, which is adaptable to cell lines and animal tissues. This versatile 8-day protocol encompasses sample fixation for optimal ultrastructural preservation, immunofluorescence staining, imaging, and multi-modal image correlation, and is executable within standard EM laboratories. Serving as a critical tool for characterizing human tissue and disease models, room-temperature CLEM facilitates the identification and quantification of subcellular morphological features across brain regions and can act as a preliminary step to assess sample suitability for cryo-EM studies.