bioRxiv Subject Collection: Neuroscience's Journal
[Most Recent Entries]
[Calendar View]
Tuesday, February 4th, 2025
| Time |
Event |
| 5:08a |
Active zone maturation state controls synaptic output and release mode and is differentially regulated by neuronal activity
Synapse formation requires the gradual accumulation of cytomatrix proteins and voltage-gated Ca2+ channels (VDCCs) at presynaptic active zones (AZs) to support neurotransmitter release. To correlate AZ maturation with synaptic output, quantal imaging was performed at serially imaged time-stamped Drosophila synapses. Evoked release strength correlated strongly with AZ age and accumulation of late AZ scaffolds, while immature sites lacking VDCC accumulation supported spontaneous release. To examine how neuronal activity regulates AZ maturation and protein accumulation, the effects of disruptions to SV fusion or action potential generation were analyzed. Decreasing neuronal activity reduced AZ seeding and caused hyperaccumulation of presynaptic material at existing AZs. Although enlarged AZs are also observed in rab3 mutants, activity reduction acted through an independent mechanism that required postsynaptic glutamate receptor-dependent signaling. Together, these data indicate AZ maturation state sets distinct presynaptic release modes and output strength, with neuronal activity shaping both AZ number and size across development. | | 5:08a |
Mental exploration of future choices during immobility theta oscillations
Mental exploration enables flexible evaluation of potential future choices, guiding decision-making without requiring direct real-world iterations. Although the hippocampus is known to be active while imagining the future, the precise mechanisms that support mental exploration of future choices remain unclear. In the hippocampus, the theta rhythm (4-12 Hz) is prevalent during movement and supports memory coding during real-world exploration by organizing neuronal activity patterns into short virtual path segments (theta sequences) around the rats location. We observed these theta-related neural activity patterns during movement in a hippocampus-dependent working memory task and also, unexpectedly, theta oscillations and theta-related neural activity during immobility. Compared to standard theta sequences during movement, theta sequences during immobility differed in that they occurred at a shifted theta phase and preferentially represented remote locations, in particular the next choice in the working memory task. Coding for future locations was also observed during awake sharp wave ripple, but these short-lasting events occurred rarely and were biased toward frequently visited locations. Therefore, our findings suggest that recurring bouts of theta oscillations during immobility, which are also observed in primates and humans, support the cognitive demands of mental exploration in the hippocampal network and facilitate ongoing predictions of future choices. | | 5:08a |
Huntingtin inclusion bodies have distinct immunophenotypes and ubiquitination profiles in the Huntington's disease human cerebral cortex
Huntington's disease (HD) is a hereditary neurodegenerative condition caused by a CAG repeat expansion mutation in the gene encoding the huntingtin (Htt) protein. The accumulation of Htt inclusion bodies is a pathological hallmark of HD and a common target for therapeutic strategies. However, the limited efficacy of treatments targeting the Htt protein highlights the need for a better understanding of the role of Htt inclusion bodies in HD pathogenesis. This study examined the heterogeneity of Htt inclusion body composition by co-labelling with three Htt epitope-specific antibodies to characterize Htt inclusion body 'immunophenotype'. We then characterized the size and sub-cellular location of Htt inclusions with distinct immunophenotypes. Using multiplex immunohistochemistry, we also examined the ubiquitination profile of each immunophenotype. Our findings demonstrate that Htt inclusions have a range of immunophenotypes, with some labelled by only one of the three antibodies and others exhibiting co-labelling by several antibodies, thus demonstrating the heterogeneity in inclusion composition and structure. We outline evidence that inclusion bodies exclusively labelled with the EM48 antibody are small, non-nuclear, and more abundant in HD cases with increased CAG repeat length, higher Vonsattel grade, and earlier age of onset. We also find that Htt inclusion bodies labelled by multiple antibodies are more likely to be ubiquitinated, predominantly by K63- rather than K48-linked ubiquitin, suggesting preferential degradation by autophagy. Lastly, we show that ubiquitinated Htt inclusion bodies are more highly immunoreactive for ubiquilin 2 than p62. Our findings highlight the need for multiple antibodies to capture the full spectrum of Htt pathology in HD and imply that future studies should consider the diversity of inclusion body composition and structure when correlating pathology formation to neurodegeneration, clinical symptoms, or disease severity. | | 5:08a |
Inhibition of adenylyl cyclase 1 (AC1) and exchange protein directly activated by cAMP (EPAC) restores ATP-sensitive potassium (KATP) channel activity after chronic opioid exposure
Prolonged exposure to Gi/o receptor agonists such as opioids can lead to a sensitization of adenylyl cyclases (ACs), resulting in heterologous sensitization or cyclic AMP (cAMP) overshoot. The molecular consequences of cAMP overshoot are not well understood, but this adaptive response is suggested to play a critical role in the development of opioid tolerance and withdrawal. We found that genetic reduction of AC1 and simultaneous upregulation of ATP-sensitive potassium (KATP) channel subunits, SUR1 or Kir6.2, significantly attenuated morphine tolerance and reduced naloxone-precipitated withdrawal. In vitro models utilized an EPAC2-GFP-cAMP biosensor to investigate sensitization of adenylyl cyclase in SH-SY5Y neuroblastoma cells and HEK{Delta}AC3/6 knockout cells. Acute application of DAMGO significantly decreased the cAMP signal from the EPAC2-GFP-cAMP biosensor, while chronic DAMGO administration resulted in enhanced cAMP production following AC stimulation. Inhibition of cAMP overshoot was observed with naloxone (NAL), pertussis toxin (PTX), and the neddylation inhibitor, MLN4924 (Pevonedistat), as well as co-expression of {beta}-adrenergic receptor kinase C-terminus ({beta}ARK-CT). After establishment of the AC1-EPAC sensitization in the in vitro models, we found that inhibition of AC1 or EPAC enhanced potassium channel activity after chronic morphine treatment, using a thallium-based assay in SH-SY5Y cells. Similar data were obtained in mouse dorsal root ganglia (DRG) after chronic morphine treatment. This study presents evidence for investigating further AC1 signaling as a target for opioid tolerance and withdrawal, by increasing EPAC activity and affecting potassium channels downstream of opioid receptors.
O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=150 SRC="FIGDIR/small/636278v1_ufig1.gif" ALT="Figure 1">
View larger version (44K):
org.highwire.dtl.DTLVardef@f949f0org.highwire.dtl.DTLVardef@653b73org.highwire.dtl.DTLVardef@21fb38org.highwire.dtl.DTLVardef@f4561f_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOGraphical AbstractC_FLOATNO C_FIG | | 5:37a |
Estradiol promotes habituation learning via an unidentified target, bypassing the suppressive effects of established Estrogen Receptors
Habituating to the constant stimuli in the environment is a critical learning process conserved across species. We use a larval zebrafish visual response to sudden darkness as a model for studying habituation learning, where zebrafish reduce their responses to repeated stimulations. In this paradigm, treatment with estradiol strongly increases learning rate, resulting in more strongly suppressed responses. We used mutant lines for the Estrogen Receptors (esr1, esr2a, esr2b, gper1) in an attempt to identify the receptor(s) mediating these effects. These experiments failed to identify a necessary receptor (or combination of receptors). Surprisingly, esr1, esr2a, and gper1 mutants showed weak but consistent increases in habituation, indicating these receptors suppress habituation learning. These experiments demonstrate that estradiol is a complex modulator of learning in our model, where the learning-promoting effects are mediated by an unidentified estradiol target, and the classical Estrogen Receptors act in competition to subtly suppress learning. | | 7:31a |
Exploring Synergies in Brain-Machine Interfaces: Compression vs. Performance
Individuals with severe neurological injuries often rely on assistive technologies, but current methods have limitations in accurately decoding multi-degree-of-freedom (DoF) movements. Intracortical brain-machine interfaces (iBMIs) use neural signals to provide a more natural control method, but currently struggle with higher-DoF movements--something the brain handles effortlessly. It has been theorized that the brain simplifies high-DoF movement through muscle synergies, which link multiple muscles to function as a single unit. These synergies have been studied using dimensionality reduction techniques like principal component analysis (PCA), non-negative matrix factorization (NMF), and demixed PCA (dPCA) and successfully used to reduce noise and improve offline decoder stability in non-invasive applications. However, their effectiveness in improving decoding and generalizability for implanted recordings across varied tasks is unclear. Here, we evaluated if brain and muscle synergies can enhance iBMI performance in non-human primates performing a two-DoF finger task. Specifically, we tested if PCA, dPCA, and NMF could compress and denoise brain and muscle data and improve decoder generalization across tasks. Our results showed that while all methods effectively compressed data with minimal loss in decoding accuracy, none improved performance through denoising. Additionally, none of the methods enhanced generalization across tasks. These findings suggest that while dimensionality reduction can aid data compression, alone it may not reveal the "true" control space needed to improve decoder performance or generalizability. Further research is required to determine whether synergies are the optimal control framework or if alternative approaches are required to enhance decoder robustness in iBMI applications.
Significance StatementMany researchers believe that brain and muscle synergies represent a fundamental control strategy and could enhance brain-machine interface (BMI) decoding performance. These synergies, extracted through dimensionality reduction techniques, are thought to simplify complex neural data, improving the efficiency and accuracy of BMI systems. In our study, we evaluated brain and muscle synergies in a dexterous finger task. We found that while these synergies effectively compressed high-dimensional data, they did not improve performance through denoising or generalize well across different contexts. Instead, the highest performance was achieved when using all available data, suggesting that synergies, although useful for data compression, may not provide the "true" control space needed to enhance decoder robustness or adaptability in implanted BMI systems. | | 11:47a |
Genes with disrupted connectivity in the architecture of schizophrenia gene co-expression networks highlight atypical neuronal-glial interactions
Dysconnectivity in schizophrenia is a pervasive trait across various levels of systems biology. To better understand disrupted patterns of molecular connectivity distinguishing schizophrenia from control non-clinical populations, we applied novel approaches to gene co-expression networks in large samples of postmortem brains from multiple regions relevant to schizophrenia: the dorso-lateral prefrontal cortex- (DLPFC) (Ndonors=297), hippocampus (Ndonors=250) and caudate (Ndonors=349). We identified differentially connected genes (DCGs) in schizophrenia networks that deviated from architectural relationships characteristic of control gene co-expression networks, by assessing three network metrics - total connectivity (K), clustering coefficient (C), and intra-module degree (kIn) determined by projecting the modular community structure of the control networks onto the schizophrenia co-expression networks. Genes showing significant absolute case-control differences for these metrics (i.e., irrespective of difference directionality) were then tested for their relationships with common genetic variants conferring risk of schizophrenia and their biological significance through post-GWAS analyses (stratified LDSC and MAGMA), gene ontology annotations and enrichment in schizophrenia-relevant gene sets.
We identified multiple DCGs, with case-control differences of connectivity metrics, consistent across brain regions. When parsed by parameter specificity, these genes show shared and specific enrichment in schizophrenia genetic signal, biological ontologies and selected cell-type markers. Notably these findings revealed widespread disturbances in co-expression connectivity affecting both neuronal and glial cells, particularly oligodendrocytes.
Overall, our results highlight disrupted co-expression network architecture in schizophrenia, implicating disrupted neuronal-glial crosstalk and its effect on synaptic transmission. | | 11:47a |
Channel-mediated astrocytic volume transient is required for synaptic plasticity and spatial memory
Astrocytes, known for their support roles, are emerging as active participants in synaptic plasticity and cognitive functions. Astrocytes actively regulate synaptic plasticity and memory through dynamic volume transients. Our previous research identified several key molecules, including TREK-1, TRPA1, and Best1 ion channels, as well as the gliotransmitter BDNF, as critical components of astrocytic volume transients. However, the precise mechanisms by which these volume transients influence synaptic plasticity and memory remain poorly understood. In this study, we investigate the roles of TREK-1 and TRPA1 in astrocytic volume dynamics and their downstream effects. Using intrinsic optical signal imaging, electrophysiology, and behavioral assays, we demonstrate that neuronal stimulation induces astrocytic swelling, initiated by K+ uptake through TREK-1 channels and regulated by Ca2+ influx via TRPA1 channels. This swelling is closely associated short- and long-term potentiation, and is accompanied by the release of BDNF, which restores long-term potentiation under conditions of calcium sequestration during astrocytic calcium clamping experiments. Disruption of astrocytic volume transient associated ion channels results in significant deficits in spatial memory, as evidenced by impairments in object-place recognition and passive avoidance tasks. Furthermore, these channels were found to modulate the synaptic plasticity. These findings reveal astrocytic volume transients and BDNF as pivotal modulators of synaptic plasticity and memory, as well as potential therapeutic targets for addressing memory dysfunctions. | | 12:19p |
An invariant schema emerges within a neural network during hierarchical learning of visual boundaries
Neural circuits must balance plasticity and stability to enable continual learning without catastrophic forgetting, a pervasive feature of artificial neural networks trained using end-to-end learning (e.g. backpropagation). Here, we apply an alternative, hierarchical learning algorithm to the cognitive task of boundary detection in video clips. In contrast to backpropagation, hierarchical training converges to a network executing a fixed schema and generates firing statistics consistent with single-neuron recordings from human subjects performing the same task. The hierarchically trained networks schema circuit remains invariant following training on sparse data, with additional data serving to refine the upstream representation. | | 12:19p |
Challenges in replicating layer-specificity of working memory processes in human dlPFC
Although working memory reliably activates the dorsolateral prefrontal cortex (dlPFC), the functional significance of its distinct cytoarchitectonic layers is not well understood in humans. A recent functional magnetic resonance (fMRI) study at 7T demonstrated for the first time layer-specific responses in the human dlPFC during working memory. Superficial layers were more active during the delay period when working memory items needed to be manipulated compared to mere maintenance. In contrast, deeper layers were more active during the motor response to a probe compared to non-action. Like many current layer fMRI studies, this study relied on several manual and semi-manual processing steps, including the selection of regions of interest. To test the replicability of these findings, we conducted a pre-registered replication of this study in 21 subjects using a fully automated and reproducible analysis pipeline. Our results do not show the same layer-specific effects. Although we observed higher activity in the superficial layers in response to working memory manipulation during the delay period, we did not find any evidence for stronger deep layer involvement during motor response in the probe period. We argue that our results are biologically plausible in light of previous research as well as methodological considerations inherent in layer fMRI acquisition and analysis. Consequently, we conclude that the evidence regarding the functional role of different layers within the human dlPFC during working memory remains inconclusive. A focus on replicability, reproducibility, and a better understanding of the influence of methodological choices will help layer fMRI become a more routine tool in cognitive neuroscience. | | 12:19p |
Reply to: Model mimicry limits conclusions about neural tuning and can mistakenly imply unlikely priors
In Harrison, Bays, and Rideaux (2023), we presented evidence from electroencephalographical recordings of humans that there is an over representation of horizontal orientations in the visual cortex. Wolf and Rademaker (2024) raise concerns about an analysis used in our study and provide an alternative explanation for our results. Here we address their concerns and provide additional magnetencephalography data supporting the conclusions of our original study. | | 2:17p |
A multimodal dataset linking wide-field calcium imaging to behavior changes in mice during an operant lever-pull task
The BraiDyn-BC (Brain Dynamics underlying emergence of Behavioral Change) Database offers an extensive, multimodal dataset that links wide-field calcium imaging of the mouse neocortex to comprehensive behavioral measurements during an operant conditioning task. This dataset includes 15 sessions spanning two weeks of motor skill learning, in which 25 mice were trained to pull a lever to obtain water rewards. Simultaneous high-speed videography captures body, facial, and eye movements, and environmental parameters are monitored. The dataset also features resting-state cortical activity and sensory-evoked responses, enhancing its utility for both learning-related and sensory-driven neural dynamics studies. Data are formatted in accordance with the Neurodata Without Borders (NWB) standard, ensuring compatibility with existing analysis tools and adherence to the FAIR principles. This resource enables in-depth investigations into the neural mechanisms underlying behavior and learning. The platform encourages collaborative research, supporting the exploration of rapid within-session learning effects, long-term behavioral adaptations, and neural circuit dynamics. | | 3:30p |
Separable Dorsal Raphe Dopamine Projections mediate the Facets of Loneliness-like state
Affiliative social connections facilitate well-being and survival in numerous species. Engaging in social interactions requires positive or negative motivational drive, elicited through coordinated activity across neural circuits. However, the identity, interconnectivity, and functional encoding of social information within these circuits remains poorly understood. Here, we focus on downstream projections of dorsal raphe nucleus (DRN) dopamine neurons (DRNDAT), which we previously implicated in social motivation alongside an aversive affective state. We show that three prominent DRNDAT projections - to the bed nucleus of the stria terminalis (BNST), central amygdala (CeA), and posterior basolateral amygdala (BLP) - play separable roles in behavior, despite substantial collateralization. Photoactivation of the DRNDAT-CeA projection promoted social behavior and photostimulation of the DRNDAT-BNST projection promoted exploratory behavior, while the DRNDAT-BLP projection supported place avoidance, suggesting a negative affective state. Downstream regions showed diverse receptor expression, poising DRNDAT neurons to act through dopamine, neuropeptide, and glutamate transmission. Furthermore, we show ex vivo that the effect of DRNDAT photostimulation on downstream neuron excitability depended on region and baseline cell properties, resulting in excitatory responses in BNST cells and diverse responses in CeA and BLP. Finally, in vivo microendoscopic cellular-resolution recordings in the CeA with DRNDAT photostimulation revealed a correlation between social behavior and neurons excited by social stimuli- suggesting that increased dopamine tone may recruit different CeA neurons to social ensembles. Collectively, these circuit features may facilitate a coordinated, but flexible, response in the presence of social stimuli that can be flexibly guided based on the internal social homeostatic need state of the individual. | | 10:49p |
Epidermal Langerhans Cells Drive Painful Diabetic Neuropathy in a Sex-dependent Manner
The interaction between non-neuronal cells and nerve endings in the epidermis significantly influences the development of various diseases, including Painful Diabetic Neuropathy (PDN). PDN is a common and challenging complication of diabetes, characterized by changes in skin innervation accompanied by neuropathic pain. While there is growing evidence that epidermal non-neuronal cells, such as resident immune cells, play a crucial role in the progression of PDN, the underlying mechanisms of this neuropathy remain poorly understood. In our studies, we utilized transgenic methods, pain behavioral assessments, and single-cell RNA sequencing (scRNAseq) in a clinically relevant high-fat diet (HFD) mouse model of PDN and skin biopsy samples from PDN patients, to investigate the role of epidermal Langerhans cells (LCs) in this condition. We observed an increased density of LCs in the skin of PDN male mice coinciding with the onset of mechanical allodynia. Furthermore, we found that LCs density correlated with small fiber degeneration in HFD mice and skin biopsies taken from well-characterized PDN patients compared to healthy controls. Importantly, the selective ablation of LCs using a diphtheria-toxin strategy was found to prevent nociceptive behavior in male mice. This indicates that LCs are both necessary and sufficient for the development of mechanical allodynia and spontaneous pain in HFD male mice. Interestingly, when LCs were ablated in HFD female mice, it did not prevent but rather promoted pain behavior, suggesting the existence of sex-specific mechanisms mediated by LCs. scRNAseq transcriptomic analysis of the paw epidermis from HFD mice, which included both males and females, revealed significant sex-mediated differences in the expression of specific target genes within this PDN model. In male mice, scRNAseq identified differentially expressed genes associated with axonal guidance and immune responses in LCs. Additionally, by integrating single-cell RNA data from the epidermis and dorsal root ganglia (DRG) of male mice, we uncovered altered communication between LCs and cutaneous afferents through Semaphorin-Plexin signaling pathways in PDN. These findings highlight LCs as key contributors to the development of PDN and suggest their potential as therapeutic targets for innovative treatments, particularly topical therapies aimed at modulating immune cell activity and neuroimmune communication in the skin. Our investigations of male and female mice indicate that LCs may play different roles in mechanical sensation under both normal and pathological conditions, such as PDN. This underscores the importance of considering sex differences when developing more effective treatments. |
|