1,720,961 research outputs found
SynActive’ – a genetic toolbox to study the connectome and proteome of learning and memory-associated synapses
Full text linkLearning and memory correlate with activity-dependent synaptic plasticity processes at appropriate synaptic circuits. The underlying mechanisms of information storage in the brain are currently investigated at a whole-neuron scale to identify cellular memory engrams i.e., ensembles of neurons whose recruitment and activation are necessary and sufficient for the retrieval of a specific memory. Traditional methods for structural and functional analysis of synapses are not sufficient for investigating which subset of synapses encodes and stores a specific memory in a given neuron. To address this fundamental question, we have developed ‘SynActive’, a genetic toolbox exploiting regulatory sequences from the Arc mRNA and synapse-targeting peptides, that allows the expression of any protein of interest specifically at potentiated synapses. Here I have extended the SynActive toolbox to express the protein of interest, including fluorescent reporters, an affinity purification tag, and an optogenetic actuator specifically at in vitro and in vivo potentiated spines.
In SynActive-eGRASP, which allows input-specific labeling of potentiated synapses, one split-GFP fragment was expressed constitutively by presynaptic neurons, while the postsynaptic half was synthesized in an activity-dependent fashion at potentiated spines. After extensive validation in cultured neurons, SynActive-eGRASP was employed to map CA3-CA1 synapses potentiated during an associative memory task – contextual fear conditioning. Semi-automated analysis using a custom-made algorithm revealed a spatially nonuniform and clustered distribution of SynActive-eGRASP-positive synapses. SynActive controlled expression of fluorescent reporters- mVenus, and DsRED-E5 labeled dendritic spines undergoing potentiation in primary neuronal cultures. These optimized vectors should facilitate large-scale, possibly brain-wide as well as time-dependent, mapping of potentiated spines. For the proteomic profiling of in vivo potentiated spines, SynActive AAVs expressing FLAG-tagged PSD95 was delivered to the mouse hippocampus and the PSD95-interactome was immunoprecipitated from potentiated synapses after contextual fear conditioning. In primary neuronal cultures, photoactivation of channelrhodopsin expressed at potentiated spines via SynActive method induced neuronal spiking. In vivo, this construct can be used to tag memory-specific synapses, and optically activating them might induce memory retrieval. These novel tools and the initial results they produced provide the first step towards a shift in the study of memory engrams from a cellular to a synaptic resolution. In addition, our quantitative maps of synaptic potentiation in whole brain areas or specific synaptic circuits can be used to refine computational models of neural plasticity. Ongoing experiments are aimed at performing a comparative analysis of synaptic maps obtained in different phases of memory encoding and recall, in both physiological conditions and models of neurodegenerative and neurodevelopmental diseases
Formin 2 regulates the stabilization of filopodial tip adhesions in growth cones and affects neuronal outgrowth and pathfinding in vivo
No full textGrowth cone filopodia are actin-based mechanosensory structures that are essential for chemoreception and the generation of contractile forces necessary for directional motility. However, little is known about the influence of filopodial actin structures on substrate adhesion and filopodial contractility. Formin 2 (Fmn2) localizes along filopodial actin bundles and its depletion does not affect filopodia initiation or elongation. However, Fmn2 activity is required for filopodial tip adhesion maturation and the ability of filopodia to generate traction forces. Dysregulation of filopodia in Fmn2-depleted neurons leads to compromised growth cone motility. Additionally, in mouse fibroblasts, Fmn2 regulates ventral stress fiber assembly and affects the stability of focal adhesions. In the developing chick spinal cord, Fmn2 activity is required cellautonomously for the outgrowth and pathfinding of spinal commissural neurons. Our results reveal an unanticipated function for Fmn2 in neural development. Fmn2 regulates structurally diverse bundled actin structures, parallel filopodial bundles in growth cones and anti-parallel stress fibers in fibroblasts, in turn modulating the stability of substrate adhesions. We propose Fmn2 as a mediator of actin bundle integrity, enabling efficient force transmission to the adhesion sites
Distinct spatial distribution of potentiated dendritic spines in encoding- and recall-activated hippocampal neurons
Full text linkExperimental advancements in neuroscience have identified cellular engrams—ensembles of neurons whose activation is necessary and sufficient for memory retrieval. Synaptic plasticity, including long-term potentiation, is fundamental to memory encoding and recall, but the relationship between learning-induced dendritic spine potentiation and neuron-wide activation remains unclear. In this study, we employed a post-synaptic translation-dependent reporter consistent with potentiation (SA-PSDΔVenus) and a neuronal activation reporter (ESARE-dTurquoise) to determine their spatiotemporal correlation in the mouse hippocampal CA1 following contextual fear conditioning (CFC). SA-PSDΔVenus+ spines were enriched in ESARE-dTurquoise+ neurons, with distribution varying across CA1 layers at different phases of memory: SA-PSDΔVenus+ were more frequent in activated neurons in stratum oriens and stratum lacunosum moleculare after CFC (encoding), while recall-activated neurons showed a larger number of SA-PSDΔVenus+ in the stratum radiatum. These findings demonstrate that the relative weight and spatial distribution of potentiated synaptic inputs to hippocampal CA1 pyramidal neurons change between the encoding and retrieval phases of memory
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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