bioRxiv Subject Collection: Neuroscience's Journal
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Friday, October 11th, 2024
| Time |
Event |
| 2:17a |
Endogenous tagging of Munc13-1 with a SNAP tag as a tool for monitoring synapse nanoarchitecture
Synaptic function is governed by highly regulated protein machineries, whose abundance and spatial localization change continually. Studies to determine the dynamic changes in synaptic proteins nanoarchitecture typically rely on immunolabeling, or on the expression of fluorescent proteins. The former employs chemical fluorophores and signal amplification, but requires fixation. The latter disturbs the cells minimally, but uses suboptimal fluorophores. Self-labeling tags have been introduced to combine the advantages of these approaches, and here we introduce a knock-in mouse line where the essential synaptic protein Munc13-1 is endogenously fused to the self-labeling SNAP tag. We demonstrate efficient Munc13-1-SNAP labeling in fixed neurons and brain sections by various SNAP dyes, as well as by a novel bright and far-red compound, SBG-SiR-d12, which we introduce here. SBG-SiR-d12 is designed as a membrane impermeable dye, but we repurposed it to stain cytosolic Munc13-1-SNAP in permeabilized, fixed cells and tissue, where we find it outperforms other dyes as evaluated by both conventional and super-resolution microscopy. Finally, we show that Munc13-1-SNAP can also be monitored by live cell imaging. We conclude that the Munc13-1SNAP mouse line is a useful tool for the analysis of Munc13-1 nanoarchitectural dynamics in synapses, with a potential for wide adoption. | | 2:17a |
Sounds and Sights in Sequence Learning: Can Accessory Auditory Cues Enhance Motor Task Performance?
Motor sequence learning, or the ability to learn and remember sequences of actions, such as the sequence of actions required to tie ones shoelaces, is ubiquitous to everyday life. Contemporary research on motor sequence learning has been largely unimodal, ignoring the possibility that our nervous system might benefit from sensory inputs from multiple modalities. In this study, we investigated the properties of motor sequence learning in response to auditory-visual stimuli. We found that sequence learning with auditory-visual stimuli showed a hallmark feature of traditional unimodal sequence learning tasks: sensitivity to stimulus timing, where lengthier interstimulus intervals of 500 ms improved sequence learning compared to briefer interstimulus intervals of 200 ms. Consistent with previous findings, we also found that auditory-visual stimuli improved learning compared to a unimodal visual-only condition. Furthermore, the informativeness of the auditory stimuli was important, as auditory stimuli which predicted the location of visual cues improved sequence learning compared to uninformative auditory stimuli which did not predict the location of the visual cues. Our findings suggest a potential utility of leveraging audio-visual stimuli in sequence learning interventions to enhance skill acquisition in education and rehabilitation contexts. | | 6:46p |
Amygdala Subregion Volumes and Apportionment in Preadolescents -- Associations with Age, Sex, and Body Mass Index
Importance: The amygdala, a key limbic structure, plays a critical role in emotional, social, and appetitive behaviors that develop throughout adolescence. Composed of a heterogeneous group of nuclei, questions remain about potential differences in the maturation of its subregions during development. Objective: To characterize the associations between developmental variables and amygdala subregion volumes during preadolescence. Design, Setting, and Participants: Cross-sectional Adolescent Brain Cognitive Development (ABCD(R)) Study data was collected from 3,953 9- and 10-year-old children between September 1, 2016, and October 15, 2018. Data analysis was conducted between June 1, 2023, and July 30, 2024. Main Outcomes and Measures: Using the CIT168 Amygdala Atlas, nine amygdala subregion volumes were quantified from high-quality MRI scans. Linear mixed-effects models were used to examine the effects of age, sex, pubertal stage, and body mass index z-score (BMIz) on subregion volumes and their relative apportionment within the amygdala. Results: The study population consisted of 3,953 preadolescents (mean [SD] age, 120 [7.41] months; 1,763 [44.6%] female; 57 [1.4%] Asian, 527 [13.3%] Black, 740 [18.7%] Hispanic, 2,279 [57.7%] white, and 350 [8.9%] from other racial/ethnic groups [identified by parents as American Indian/Native American, Alaska Native, Native Hawaiian, Guamanian, Samoan, other Pacific Islander, or other race]). Distinct associations were observed between age, sex, and BMIz and whole amygdala volume, subregion volumes, and subregion apportionment. Pubertal stage was not related to amygdala subregion volumes. Age was associated with near-global expansion of amygdala subregions during this developmental period. Female sex was linked to smaller volumes in most amygdala subregions, with larger relative apportionment in dorsal amygdala subregions and smaller apportionment in the basolateral ventral paralaminar subregion. Higher BMIz was associated with smaller volumes in large laterobasal subregions, with increased relative apportionment in smaller subregions. Conclusions and Relevance: This cross-sectional study suggests that age, but not pubertal stage, is associated with near-global expansion of the amygdala at ages 9 and 10, while sex and BMIz are linked to distinct changes in amygdala subregions that explain observed differences in total volumes. These findings provide a foundational context for understanding how developmental variables influence amygdala structure in preadolescents, with implications for understanding future risk for brain disorders. | | 6:46p |
Fronto-motor circuits linked to subclinical apathy
Apathy is a syndrome characterized by a disruption in effort-reward decision-making, accompanied by structural and functional changes in a related fronto-basal ganglia (BG) network. While activity changes in the primary motor cortex (M1) during effort and reward valuation have been repeatedly observed, previous work on apathy has largely overlooked the connections between the fronto-BG network and M1, potentially missing key circuits in the apathy network. This study addresses this gap by investigating structural and effective connectivity in fronto-M1, fronto-BG-M1, and intra-M1 circuits in relation to subclinical apathy in 45 healthy subjects. Behavior was assessed using a battery of apathy-related questionnaires and computational modeling of effort and reward valuation in a decision-making task. Fronto-motor circuits were examined through a combination of MRI-derived tractography and paired-pulse transcranial magnetic stimulation, which probed structural and effective connectivity, respectively. The data reveal that apathy scores are associated with both structural and effective connectivity in fronto-M1 and fronto-BG-M1 circuits. Circuits originating from the supplementary motor area primarily index effort valuation, while connectivity in intra-M1 GABAergic circuits correlates exclusively with reward valuation. These findings suggest that distinct fronto-motor circuits are linked to different dimensions of motivated behavior and may constitute specific neuromodulation targets for patients suffering from apathy. | | 7:16p |
Multiple neural pathways to successful visual short-term memory across the adult lifespan
Cognitive task performance can be supported through multiple neural pathways, a concept referred to as brain degeneracy. We used a novel approach to consider brain degeneracy during a visual short-term memory task (VSTM) across the adult lifespan in the Cam-CAN study (n = 113, 23-87 years old). Our main goal was to identify subgroups of participants whose VSTM performance was characterized by distinct brain activation patterns. First, we identified seven brain modules that responded similarly to the VSTM task and resembled previously identified functional networks (adjusted mutual information [aMI] = 0.45). Subsequently, latent profile analysis revealed four distinct subgroups of participants. Each subgroup was characterized by different recruitment patterns of these brain modules, predominantly in the frontal control module (FCM), visual module (VM), and default mode module (DMM). Subgroups did not differ in demographics or task performance. However, associations between brain activity and performance varied across subgroups, particularly in the FCM, suggesting that individuals may use different cognitive operations to perform the VSTM task. Further analyses revealed group differences in white matter integrity, mostly in the uncinate fasciculus, suggested that individual differences in structural brain properties may shape the different brain activation patterns. Altogether, our study contributes to our understanding of how multiple neural pathways could underlie cognitive performance. | | 7:16p |
An abstract relational map emerges in the human medial prefrontal cortex with consolidation
Understanding the structure of a problem, such as the relationships between stimuli, supports fast learning and flexible reasoning. Recent theoretical suggestions have highlighted the usefulness of explicit structural representations that are fully divorced from sensory details for generalisation. Rodent work has suggested that abstraction of structure occurs gradually, over time, in cortex. However, direct evidence of such explicit relational representations in humans is scarce, and its relationship to consolidation mechanisms is underexplored. Here, we use a graph-learning paradigm to find such a relational map in the human medial prefrontal cortex. Importantly, this representation was absent early after learning but emerged on the time scale of days. These results shed new light on neural representations underlying the remarkable human ability to draw accurate inferences from little data. | | 7:16p |
Extending mathematical frameworks to investigate neuronal dynamics in the presence of microglial ensheathment
Recent experimental evidence has shown that glial cells, including microglia and astrocytes, can ensheathe synapses, positioning them to disrupt neurotransmitter flow between pre- and post-synaptic terminals. This study extends micro- and network-scale theoretical models to explore how varying degrees of synaptic ensheathment affect synaptic communication and network dynamics. Consistent with previous studies, our microscale model shows that ensheathment accelerates synaptic transmission while reducing its strength and reliability, with the potential to effectively switch off synaptic connections. Building on these findings, we integrate an "effective" glial cell model into a large-scale neuronal network. Specifically, we analyze a network with highly heterogeneous synaptic strengths and time constants, where glial proximity parametrizes synaptic parameters. Unlike previous models that assumed normal parameter distributions, our model uses parameters drawn from distinct distributions. This framework is applied to large networks of exponential integrate-and-fire neurons, extending linear response theory to analyze not only firing rate distributions but also noise correlations across the network. Despite the significant heterogeneity in the system, a mean-field approximation accurately captures network statistics. We demonstrate the utility of our model by reproducing experimental findings, showing that microglial ensheathment leads to post-anesthesia hyperactivity in excitatory neurons of mice. Furthermore, we explore how glial ensheathment may be used in the visual cortex to target specific neuronal subclasses, tuning higher-order network statistics. | | 7:16p |
Effects of oral contraceptive pills on brain networks: A replication and extension
Neuroimaging research has identified significant effects of oral contraceptive pills (OCPs) on brain networks. A wide variety of approaches have been employed, largely in observational samples, with few converging results. This study was designed to replicate and expand this previous work using a randomized, double-blind, placebo-controlled crossover trial to investigate effects of OCPs on brain networks. Using functional MRI, we focused on brain regions identified in prior studies. Our analyses did not strictly replicate previously reported effects of OCPs on functional connectivity. Exploratory analyses suggest that traditional seed-based approaches may miss broader, network-level effects of OCPs on brain circuits. We applied data-driven, multivariate techniques to assess these network-level changes, A deeper understanding of neural effects of OCPs can be important in helping patients make informed decisions regarding contraception, mitigating unwanted side effects, and also in understanding the potentially confounding effects of OCPs in other neuroimaging investigations. | | 7:16p |
Dopamine and cortical iPSC-derived neurons with different Parkinsonian mutations show variation in lysosomal and mitochondrial dysfunction: implications for protein deposition versus selective cell loss
Background: Mutations causing Parkinson's disease (PD) give diverse pathological phenotypes whose cellular correlates remain to be determined. For example, those with PRKN loss of function mutations have significantly earlier selective vulnerability of dopamine neurons, those with SNCA mutations have increased alpha-synuclein deposition, while those with LRRK2 mutations have additional deposition of tau. Yet all three mutation types are implicated in mitochondrial and/or lysosomal dysfunction. Direct comparison of cell models with these mutations would clarify the relative cellular dysfunctions associated with these different pathological phenotypes. Methods: An unbiased high-content imaging platform using orthogonal probes to assess both lysosomal and mitochondrial dysfunction, along with alpha-synuclein and tau protein deposition was established using induced pluripotent stem cell (iPSC) derived cortical and ventral midbrain neurons. Three mutation types, SNCA A53T, LRRK2 R1441G and PRKN loss of function (lof), were selected as exemplars of divergent PD pathological phenotypes and compared to each other, and to control iPSC from subjects without PD. Results: Different PD mutations caused cell type specific dysfunctions, likely to impact on both selective neuronal vulnerability and the pathologies observed in PD. Comparison of dopamine neurons identified that both lysosomal and mitochondrial dysfunction were predominant with PRKN lof mutations, whereas immunofluorescent staining revealed that SNCA A53T and LRRK2 R1441G mutations had increased tau deposition. In contrast, cortical neurons with SNCA and LRRK2 mutations both had mitochondrial and autophagy impairments without protein deposition, with LRRK2 cells additionally showing decreased glucocerebrosidase activity and increased alpha-synuclein phosphorylation. Conclusions: Lysosomal and mitochondrial dysfunction are predominant in dopamine neurons with PRKN lof mutations, and may drive the early selective loss of dopamine neurons in PRKN mutation carriers. More subtle cellular abnormalities in the SNCA A53T cell lines are likely to predispose to alpha-synuclein aggregation and tau protein deposition over time. The LRRK2 R1441G may also predispose to tau deposition, but despite substantial lysosomal dysfunction with increased alpha-synuclein phosphorylation, pathological alpha-synuclein accumulations were not observed. Understanding the mechanistic differences in how lysosomal and mitochondrial dysfunction impact on PD pathogenesis in different disease subtypes may be important for therapeutic development. | | 7:45p |
Isotope Encoded Chemical Imaging Identifies Amyloid Plaque Age Dependent Structural Maturation, Synaptic Loss, and Increased Toxicity
It is of critical importance to our understanding of Alzheimers disease (AD) pathology to determine how key pathological factors are interconnected and implicated in nerve cell death, clinical symptoms, and disease progression. The formation of extracellular beta-amyloid plaques is the major pathological hallmark of AD and beta-amyloid has been suggested to be a critical inducer of AD, driving disease pathogenesis. Exactly how beta-amyloid plaque formation begins and how ongoing plaque deposition proceeds and initiates subsequent neurotoxic mechanisms is not well understood. The primary aim of our research is to elucidate the biochemical processes underlying early beta-amyloid plaque formation in brain tissue. We recently introduced a chemical imaging paradigm based on mass spectrometry imaging (MSI) and metabolic isotope labelling to follow stable isotope labelling kinetics (iSILK) in vivo to track the in vivo build-up and deposition of beta-amyloid. Herein, knock-in beta-amyloid mouse models (AppNL-F) that develop beta-amyloid pathology gradually are metabolically labeled with stable isotopes. This chemical imaging approach timestamps amyloid plaques during the period of initial deposition allowing the fate of aggregating beta-amyloid species from before and during the earliest events of plaque pathology through plaque maturation to be tracked. To identify the molecular and cellular response to plaque maturation, we integrated iSILK with single plaque transcriptomics performed on adjacent tissue sections. This enabled changes in gene expression to be tracked as a function of plaque age (as encoded in the beta-amyloid peptide isotopologue pattern) distinct from changes due to the chronological age or pathological severity. This approach identified that plaque age correlates negatively with gene expression patterns associated with synaptic function as early as in 10-month-old animals but persists into 18 months. Finally, we integrated hyperspectral confocal microscopy into our multiomic approach to image amyloid structural isomers, revealing a positive correlation between plaque age and amyloid structural maturity. This analysis identified three categories of plaques, each with a distinct impact on the surrounding microenvironment. Here, we identified that older, more compact plaques were associated with the most significant synapse loss and toxicity. These data show how isotope-encoded MS imaging can be used to delineate beta-amyloid toxicity dynamics in vivo. Moreover, we show for the first time a functional integration of dynamic MSI, structural plaque imaging and whole genome-wide spatial transcriptomics at the single plaque level. This multiomic approach offers an unprecedented combination of temporal and spatial resolution enabling a description of the earliest events of precipitating amyloid pathology and how beta-amyloid modulates synaptotoxic mechanisms. | | 7:45p |
Longitudinal multi-omics reveals pathogenic TSC2 variants disrupt developmental trajectories of human cortical organoids derived from Tuberous Sclerosis Complex
Tuberous Sclerosis Complex (TSC), an autosomal dominant condition, is caused by heterozygous mutations in either the TSC1 or TSC2 genes, manifesting in systemic growth of benign tumors. In addition to brain lesions, neurologic sequelae represent the greatest morbidity in TSC patients. Investigations utilizing TSC1/2-knockout animal or human stem cell models suggest that TSC deficiency-causing hyper-activation of mTOR signaling might precipitate anomalous neurodevelopmental processes. However, how the pathogenic variants of TSC1/2 genes affect the longitudinal trajectory of human brain development remains largely unexplored. Here, we employed 3-dimensional cortical organoids derived from induced pluripotent stem cells (iPSCs) from TSC patients harboring TSC2 variants, alongside organoids from age- and sex-matched healthy individuals as controls. Through comprehensively longitudinal molecular and cellular analyses of TSC organoids, we found that TSC2 pathogenic variants dysregulate neurogenesis, synaptogenesis, and gliogenesis, particularly for reactive astrogliosis. The altered developmental trajectory of TSC organoids significantly resembles the molecular signatures of neuropsychiatric disorders, including autism spectrum disorders, epilepsy, and intellectual disability. Intriguingly, single cell transcriptomic analyses on TSC organoids revealed that TSC2 pathogenic variants disrupt the neuron/reactive astrocyte crosstalk within the NLGN-NRXN signaling network. Furthermore, cellular and electrophysiological assessments of TSC cortical organoids, along with proteomic analyses of synaptosomes, demonstrated that the TSC2 variants precipitate perturbations in synaptic transmission, neuronal network activity, mitochondrial translational integrity, and neurofilament formation. Notably, similar perturbations were observed in surgically resected cortical specimens from TSC patients. Collectively, our study illustrates that disease-associated TSC2 variants disrupt the neurodevelopmental trajectories through perturbations of gene regulatory networks during early cortical development, leading to mitochondrial dysfunction, aberrant neurofilament formation, impaired synaptic formation and neuronal network activity. | | 7:45p |
Long-Term Effects of Working Memory Retrieval From Prioritized and Deprioritized States
Which factors determine whether information temporarily held in working memory (WM) is transferred to long-term memory (LTM)? Previous work has shown that retrieving ('testing') memories from LTM can benefit their future LTM recall. Here, we examined the extent to which a benefit for subsequent LTM may also occur after retrieval from WM, depending on whether the WM contents were retrieved from a prioritized or deprioritized state. In three experiments, we combined variants of a novel visual WM paradigm with a subsequent surprise LTM recall test. We found a LTM benefit of WM testing both for prioritized and deprioritized WM contents, which, interestingly, was stronger for the deprioritized information. This pattern showed similarly across experiments with different priority manipulations. Subsequent LTM benefits generally occurred after WM testing with a recall-like test format (continuous report), but not after simple WM comparisons against a probe. The surprisingly larger LTM benefit for deprioritized WM contents may reflect enhanced encoding of the participants' own subjective WM report - as opposed to the originally presented sample information - into LTM. | | 7:45p |
T-scope V4: miniaturized microscope for optogenetic tagging in freely behaving animals
A miniaturized microscope (i.e., miniscope) enables the imaging of neuronal activity using calcium sensors while simultaneously manipulating that activity using opsins in freely moving animals. However, many miniscopes use light-emitting diodes with broadband emission, leading to unintentional opsin stimulation by light intended solely for calcium sensor activation (a phenomenon referred to as "biological crosstalk"). To address this issue, we previously developed a miniscope including a port for chosen light sources, such as lasers, by restructuring the open-source UCLA Miniscope v3. However, targeting the same neuronal soma for both excitable opsin stimulation and calcium sensor imaging remained a challenge. Here, we integrated features from the UCLA Miniscope v4 into our new T-scope V4 miniscope. In optogenetic tagging experiments, we demonstrated that a 445-nm blue laser can be used to image neuronal activity with the calcium sensor GCaMP6s without inadvertently stimulating the ChrimsonR opsin, allowing for simultaneous neuronal activity imaging and manipulation in freely moving mice. Thus, the T-scope V4 can serve as a powerful tool for probing causal relationships between neuronal activity and its function in living animals. | | 7:45p |
Activity in the peripheral representation within primate V1 is substantially modulated during running
We recently investigated whether activity in primary visual cortex of a primate (Callithrix jacchus) is modulated during running, and found that the effects were small (and suppressive), a notable difference from the large and positive modulations observed in mice. In that first report, we noted that the majority of our data were collected from the retinotopic representation of the fovea, and surmised that running modulations might be different in the peripheral representation. Here, we report that running-correlated modulations of the peripheral representation in marmoset V1 are positive and substantial, on order of 30%. In light of both the small and negative modulations observed in foveal V1, and the large and positive modulations seen in mouse V1, these results suggest that the foveal representation in primates may be unique. In this domain, non-foveal V1 in primates appears more similar to that of rodents. |
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