514 research outputs found
Advances in the neurophysiology of magnocellular neuroendocrine cells
© 2020 British Society for Neuroendocrinology Hypothalamic magnocellular neuroendocrine cells have unique electrical properties and a remarkable capacity for morphological and synaptic plasticity. Their large somatic size, their relatively uniform and dense clustering in the supraoptic and paraventricular nuclei, and their large axon terminals in the neurohypophysis make them an attractive target for direct electrophysiological interrogation. Here, we provide a brief review of significant recent findings in the neuroplasticity and neurophysiological properties of these neurones that were presented at the symposium âElectrophysiology of Magnocellular Neuronsâ during the 13th World Congress on Neurohypophysial Hormones in Ein Gedi, Israel in April 2019. Magnocellular vasopressin (VP) neurones respond directly to hypertonic stimulation with membrane depolarisation, which is triggered by cell shrinkage-induced opening of an N-terminal-truncated variant of transient receptor potential vanilloid type-1 (TRPV1) channels. New findings indicate that this mechanotransduction depends on actin and microtubule cytoskeletal networks, and that direct coupling of the TRPV1 channels to microtubules is responsible for mechanical gating of the channels. Vasopressin neurones also respond to osmostimulation by activation of epithelial Na+ channels (ENaC). It was shown recently that changes in ENaC activity modulate magnocellular neurone basal firing by generating tonic changes in membrane potential. Both oxytocin and VP neurones also undergo robust excitatory synapse plasticity during chronic osmotic stimulation. Recent findings indicate that new glutamate synapses induced during chronic salt loading express highly labile Ca2+-permeable GluA1 receptors requiring continuous dendritic protein synthesis for synapse maintenance. Finally, recordings from the uniquely tractable neurohypophysial terminals recently revealed an unexpected property of activity-dependent neuropeptide release. A significant fraction of the voltage-dependent neurohypophysial neurosecretion was found to be independent of Ca2+ influx through voltage-gated Ca2+ channels. Together, these findings provide a snapshot of significant new advances in the electrophysiological signalling mechanisms and neuroplasticity of the hypothalamic-neurohypophysial system, a system that continues to make important contributions to the field of neurophysiology
Can we avoid high coupling?
It is considered good software design practice to organize source code into modules and to favour within-module connections (cohesion) over between-module connections (coupling), leading to the oft-repeated maxim "low coupling/high cohesion". Prior research into network theory and its application to software systems has found evidence that many important properties in real software systems exhibit approximately scale-free structure, including coupling; researchers have claimed that such scale-free structures are ubiquitous. This implies that high coupling must be unavoidable, statistically speaking, apparently contradicting standard ideas about software structure. We present a model that leads to the simple predictions that approximately scale-free structures ought to arise both for between-module connectivity and overall connectivity, and not as the result of poor design or optimization shortcuts. These predictions are borne out by our large-scale empirical study. Hence we conclude that high coupling is not avoidable--and that this is in fact quite reasonable
Assessing Code Authorship: The Case of the Linux Kernel
Code authorship is a key information in large-scale open source systems.
Among others, it allows maintainers to assess division of work and identify key
collaborators. Interestingly, open-source communities lack guidelines on how to
manage authorship. This could be mitigated by setting to build an empirical
body of knowledge on how authorship-related measures evolve in successful
open-source communities. Towards that direction, we perform a case study on the
Linux kernel. Our results show that: (a) only a small portion of developers (26
%) makes significant contributions to the code base; (b) the distribution of
the number of files per author is highly skewed --- a small group of top
authors (3 %) is responsible for hundreds of files, while most authors (75 %)
are responsible for at most 11 files; (c) most authors (62 %) have a specialist
profile; (d) authors with a high number of co-authorship connections tend to
collaborate with others with less connections.Comment: Accepted at 13th International Conference on Open Source Systems
(OSS). 12 page
A Hypergraph Dictatorship Test with Perfect Completeness
A hypergraph dictatorship test is first introduced by Samorodnitsky and
Trevisan and serves as a key component in their unique games based \PCP
construction. Such a test has oracle access to a collection of functions and
determines whether all the functions are the same dictatorship, or all their
low degree influences are Their test makes queries and has
amortized query complexity but has an inherent loss of
perfect completeness. In this paper we give an adaptive hypergraph dictatorship
test that achieves both perfect completeness and amortized query complexity
.Comment: Some minor correction
An Efficient Partitioning Oracle for Bounded-Treewidth Graphs
Partitioning oracles were introduced by Hassidim et al. (FOCS 2009) as a
generic tool for constant-time algorithms. For any epsilon > 0, a partitioning
oracle provides query access to a fixed partition of the input bounded-degree
minor-free graph, in which every component has size poly(1/epsilon), and the
number of edges removed is at most epsilon*n, where n is the number of vertices
in the graph.
However, the oracle of Hassidimet al. makes an exponential number of queries
to the input graph to answer every query about the partition. In this paper, we
construct an efficient partitioning oracle for graphs with constant treewidth.
The oracle makes only O(poly(1/epsilon)) queries to the input graph to answer
each query about the partition.
Examples of bounded-treewidth graph classes include k-outerplanar graphs for
fixed k, series-parallel graphs, cactus graphs, and pseudoforests. Our oracle
yields poly(1/epsilon)-time property testing algorithms for membership in these
classes of graphs. Another application of the oracle is a poly(1/epsilon)-time
algorithm that approximates the maximum matching size, the minimum vertex cover
size, and the minimum dominating set size up to an additive epsilon*n in graphs
with bounded treewidth. Finally, the oracle can be used to test in
poly(1/epsilon) time whether the input bounded-treewidth graph is k-colorable
or perfect.Comment: Full version of a paper to appear in RANDOM 201
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