1,721,553 research outputs found
Ecological Connectivity Through UBC – An Omniscape Approach
No full textHuman activities and rapid urbanization have led to habitat destruction and fragmentation, severely impacting biodiversity and ecosystem services globally. This study focuses on the UBC campus, surrounded by the Pacific Spirit Regional Park, to assess and enhance ecological connectivity through the urban landscape. Using advanced remote sensing techniques, including Planet SkySat satellite imagery and British Columbia 2022 LiDAR data, we classified the landscape and identified key habitats. Keystone species were selected based on habitat dependency, observation density, and conservation status, utilizing datasets from the Global Biodiversity Information Facility (GBIF) between 2010 to 2023. The study employed Omniscape, an implementation of Circuitscape 4.0, to model the randomized movement of animals across a resistance-weighted landscape, providing a nuanced understanding of how
urban features influence ecological flows. Our findings indicate that urban areas, especially the central UBC campus, act as barriers and funnel species movement, particularly affecting those with small movement ranges and unique habitat requirements, such as the Pacific Tree Frog and Douglas's Squirrel. The analysis
highlighted areas of highly channelized flows where predicted movement exceeds landscape capacity, leading from Pacific Spirit Regional Park to UBC's Central core. UBC’s Main Mall was predicted to have highly channelized flow across all species and is a critical corridor for conservation and enhancement. Other recommendations for UBC include creating an East West Ecological Corridor, replicating Main Mall’s design. The existing landscape should be intensified by integrating more water bodies and riparian areas to support amphibian species and interspersing shrub planting between trees to expand habitat availability
A sequential two-step priming scheme reproduces diversity in synaptic strength and short-term plasticity
No full textGlutamatergic synapses display variable strength and diverse short-term plasticity (STP), even for a given type of connection. Using nonnegative tensor factorization and conventional state modeling, we demonstrate that a kinetic scheme consisting of two sequential and reversible steps of release–machinery assembly and a final step of synaptic vesicle (SV) fusion reproduces STP and its diversity among synapses. Analyzing transmission at the calyx of Held synapses reveals that differences in synaptic strength and STP are not primarily caused by variable fusion probability (p(fusion)) but are determined by the fraction of docked synaptic vesicles equipped with a mature release machinery. Our simulations show that traditional quantal analysis methods do not necessarily report p(fusion) of SVs with a mature release machinery but reflect both p(fusion) and the distribution between mature and immature priming states at rest. Thus, the approach holds promise for a better mechanistic dissection of the roles of presynaptic proteins in the sequence of SV docking, two-step priming, and fusion. It suggests a mechanism for activity-induced redistribution of synaptic efficacy
Author response image 1.
Get PDFNeurotransmitter is released at synapses by fusion of synaptic vesicles with the plasma membrane. To sustain synaptic transmission, compensatory retrieval of membranes and vesicular proteins is essential. We combined capacitance measurements and pH-imaging via pH-sensitive vesicular protein marker (anti-synaptotagmin2-cypHer5E), and compared the retrieval kinetics of membranes and vesicular proteins at the calyx of Held synapse. Membrane and Syt2 were retrieved with a similar time course when slow endocytosis was elicited. When fast endocytosis was elicited, Syt2 was still retrieved together with the membrane, but endocytosed organelle re-acidification was slowed down, which provides strong evidence for two distinct endocytotic pathways. Strikingly, CaM inhibitors or the inhibition of the Ca2+-calmodulin-Munc13-1 signaling pathway only impaired the uptake of Syt2 while leaving membrane retrieval intact, indicating different recycling mechanisms for membranes and vesicle proteins. Our data identify a novel mechanism of stimulus-and Ca2+-dependent regulation of coordinated endocytosis of synaptic membranes and vesicle proteins
Presynaptic Ca2+ influx and vesicle exocytosis at the mouse endbulb of Held: A comparison of two auditory nerve terminals.
No full textNon-technical summary The release of neurotransmitter from presynaptic nerve endings is triggered by Ca2+ influx through voltage-gated Ca2+ channels (VGCCs) that open when an action potential (AP) invades the presynaptic terminal. The functional properties of VGCCs expressed in presynaptic terminals remain elusive because most terminals are too small to be accessible to electrophysiological recordings. We performed direct presynaptic recordings to characterize Ca2+ channels and transmitter release in a large mammalian presynaptic terminal, the endbulb of Held. Endbulb terminals are formed by the endings of auditory nerve fibres that contact bushy cells located in the anterior ventral cochlear nucleus. We find that endbulb terminals are endowed with >1000 readily releasable vesicles and express an average number of >6000 VGCCs. About half of the VGCCs open during a single AP. Thus, multiple Ca2+ channels control the release of a single transmitter vesicle at the endbulb of Held
Similar Intracellular Ca2+ Requirements for Inactivation and Facilitation of Voltage-Gated Ca2+ Channels in a Glutamatergic Mammalian Nerve Terminal
Get PDFVoltage-gated Ca (2+) channels (VGCCs) of the P/Q-type, which are expressed at a majority of mammalian nerve terminals, show two types of Ca (2+)-dependent feedback regulation-inactivation (CDI) and facilitation (CDF). Because of the nonlinear relationship between Ca (2+) influx and transmitter release, CDI and CDF are powerful regulators of synaptic strength. To what extent VGCCs inactivate or facilitate during spike trains depends on the dynamics of free Ca (2+) ([Ca2+](i)) and the Ca2+ sensitivity of CDI and CDF, which has not been determined in nerve terminals. In this report, we took advantage of the large size of a rat auditory glutamatergic synapse-the calyx of Held-and combined voltage-clamp recordings of presynaptic Ca (2+) currents (I-Ca(v)) with UV-light flash-induced Ca (2+) uncaging and presynaptic Ca (2+) imaging to study the Ca (2+) requirements for CDI and CDF. We find that nearly half of the presynaptic VGCCs inactivate during 100 ms voltage steps and require several seconds to recover. This inactivation is caused neither by depletion of Ca (2+) ions from the synaptic cleft nor by metabotropic feedback inhibition, because it is resistant to blockade of metabotropic and ionotropic glutamate receptors. Facilitation of I-Ca(V) induced by repetitive depolarizations or preconditioning voltage steps decays within tens of milliseconds. Since Ca (2+) buffers only weakly affect CDI and CDF, we conclude that the Ca (2+) sensors are closely associated with the channel. CDI and CDF can be induced by intracellular photo release of Ca (2+) resulting in (Ca2+](i); elevations in the low micromolar range, implying a surprisingly high affinity of the Ca (2+) sensors
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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
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