Flare in the Galactic stellar outer disc detected in SDSS-SEGUE data

Aims. We explore the outer Galactic disc up to a Galactocentric distance of 30 kpc to derive its parameters and measure the magnitude of its flare. Methods. We obtained the 3D density of stars of type F8V-G5V with a colour selection from extinction-corrected photometric data of the Sloan Digital Sky Survey - Sloan Extension for Galactic Understanding and Exploration (SDSS-SEGUE) over 1,400 deg^2 in off-plane low Galactic latitude regions and fitted it to a model of flared thin+thick disc. Results. The best-fit parameters are a thin-disc scale length of 2.0 kpc, a thin-disc scale height at solar Galactocentric distance of 0.24 kpc, a thick-disc scale length of 2.5 kpc, and a thick-disc scale height at solar Galactocentric distance of 0.71 kpc. We derive a flaring in both discs that causes the scale height of the average disc to be multiplied with respect to the solar neighbourhood value by a factor of 3.3^{+2.2}_{-1.6} at R=15 kpc and by a factor of 12^{+20}_{-7} at R=25 kpc. Conclusions. The flare is quite prominent at large R and its presence explains the apparent depletion of in-plane stars that are often confused with a cut-off at R>15 kpc. Indeed, our Galactic disc does not present a truncation or abrupt fall-off there, but the stars are spread in off-plane regions, even at z of several kpc for R>20 kpc. Moreover, the smoothness of the observed stellar distribution also suggests that there is a continuous structure and not a combination of a Galactic disc plus some other substructure or extragalactic component: the hypothesis to interpret the Monoceros ring in terms of a tidal stream of a putative accreted dwarf galaxy is not only unnecessary because the observed flare explains the overdensity in the Monoceros ring observed in SDSS fields, but it appears to be inappropriate.Comment: Accepted for publication in A&

Involvement of both sodium influx and potassium efflux in ciguatoxin-induced nodal swelling of frog myelinated axons

Ciguatoxins, mainly produced by benthic dinoflagellate Gambierdiscus species, are responsible for a complex human poisoning known as ciguatera. Previous pharmacological studies revealed that these toxins activate voltage-gated Na+ channels. In frog nodes of Ranvier, ciguatoxins induce spontaneous and repetitive action potentials (APs) and increase axonal volume that may explain alterations of nerve functioning in intoxicated humans. The present study aimed determining the ionic mechanisms involved in Pacific ciguatoxin-1B (P-CTX-1B)-induced membrane hyperexcitability and subsequent volume increase in frog nodes of Ranvier, using electrophysiology and confocal microscopy. The results reveal that P-CTX-1B action is not dependent on external Cl- ions since it was not affected by substituting Cl- by methylsulfate ions. In contrast, substitution of external Na+ by Li+ ions suppressed spontaneous APs and prevented nodal swelling. This suggests that P-CTX-1B-modified Na+ channels are not selective to Li+ ions and/or are blocked by these ions, and that Na+ influx through Na+ channels opened during spontaneous APs is required for axonal swelling. The fact that the K+ channel blocker tetraethylammonium modified, but did not suppress, spontaneous APs and greatly reduced nodal swelling induced by P-CTX-1B indicates that K+ efflux might also be involved. This is supported by the fact that P-CTX-1B, when tested in the presence of both tetraethylammonium and the K+ ionophore valinomycin, produced the characteristic nodal swelling. It is concluded that, during the action of P-CTX-1B, water movements responsible for axonal swelling depend on both Na+ influx and K+ efflux. These results pave the way for further studies regarding ciguatera treatment

Dual action of a dinoflagellate-derived precursor of Pacific ciguatoxins (P-CTX-4B) on voltage-dependent K(+) and Na(+) channels of single myelinated axons

The effects of Pacific ciguatoxin-4B (P-CTX-4B, also named gambiertoxin), extracted from toxic Gambierdiscus dinoflagellates, were assessed on nodal K(+) and Na(+) currents of frog myelinated axons, using a conventional voltage-clamp technique. P-CTX-4B decreased, within a few minutes, both K(+) and Na(+) currents in a dose-dependent manner, without inducing any marked change in current kinetics. The toxin was more effective in blocking K(+) than Na(+) channels. P-CTX-4B shifted the voltage-dependence of Na(+) conductance by about 14 mV towards more negative membrane potentials. This effect was reversed by increasing Ca(2+) in the external solution. A negative shift of about 16 mV in the steady-state Na(+) inactivation-voltage curve was also observed in the presence of the toxin. Unmodified and P-CTX-4B-modified Na(+) currents were similarly affected by the local anaesthetic lidocaine. The decrease of the two currents by lidocaine was dependent on both the concentration and the membrane potential during pre-pulses. In conclusion, P-CTX-4B appears about four times more effective than P-CTX-1B to affect K(+) channels, whereas it is about 50 times less efficient to affect Na(+) channels of axonal membranes. These actions may be related to subtle differences between the two chemical structures of molecules

Trachynilysin mediates SNARE-dependent release of catecholamines from chromaffin cells via external and stored Ca2+

Trachynilysin, a 159 kDa dimeric protein purified from stonefish (Synanceia trachynis) venom, dramatically increases spontaneous quantal transmitter release at the frog neuromuscular junction, depleting small clear synaptic vesicles, whilst not affecting large dense core vesicles. The basis of this insensitivity of large dense core vesicles exocytosis was examined using a fluorimetric assay to determine whether the toxin could elicit catecholamine release from bovine chromaffin cells. Unlike the case of the motor nerve endings, nanomolar concentrations of trachynilysin evoked sustained Soluble N-ethylmaleimide-sensitive fusion protein Attachment Protein REceptor-dependent exocytosis of large dense core vesicles, but only in the presence of extracellular Ca2+. However, this response to trachynilysin does not rely on Ca2+ influx through voltage-activated Ca2+ channels because the secretion was only slightly affected by blockers of L, N and P/Q types. Instead, trachynilysin elicited a localized increase in intracellular fluorescence monitored with fluo-3/AM, that precisely co-localized with the increase of fluorescence resulting from caffeine-induced release of Ca2+ from intracellular stores. Moreover, depletion of the latter stores inhibited trachynilysin-induced egocytosis. Thus, the observed requirement of external Ca2+ for stimulation of large dense core vesicles exocytosis from chromaffin cells implicates plasma membrane channels that signal efflux of Ca2+ from intracellular stores. This study also suggests that the bases of exocytosis of large dense core vesicles from motor nerve terminals and neuroendocrine cells are distinct

The young open cluster NGC 7067 using Stromgren photometry

© The Authors 2016. Published by Oxford University Press on behalf of The Royal Astronomical Society. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. M. Monguio et al, ' The young open cluster NGC 7067 using Stromgren photometry ', MNRAS Vol 466(3): 3636-3647 (2017), first published online 17 December 2016, the version of record is available online via doi: 10.1093/mnras/stw3302NGC 7067 is a young open cluster located in the direction between the first and the second Galactic quadrants and close to the Perseus spiral arm. This makes it useful for studies of the nature of the Milky Way spiral arms. Stromgren photometry taken with the Wide Field Camera at the Isaac Newton Telescope allowed us to compute individual physical parameters for the bserved stars and hence to derive cluster’s physical parameters. Spectra from the 1.93-m telescope at the Observatoire de Haute-Provence helped to check and improve the results. We obtained photometry for 1233 stars, individual physical parameters for 515 and spectra for 9 of them. The 139 selected cluster members lead to a cluster distance of 4.4±0.4 kpc, with an age below log10(t(yr))=7.3 and a present Mass of 1260±160M⊙. The morphology of the data reveals that the centre of the cluster is at (α,δ)=(21: 24: 13.69,+48: 00: 39.2) J2000, with a radius of 6.′1. Stromgren and spectroscopic data allowed us to improve the previous parameters available for the cluster in the literature.Peer reviewedFinal Published versio

Identification de cibles d’insecticides spécifiques du puceron du pois Acyrthosiphon piusm par analyse des relations structure-fonction des récepteurs nicotiniques

Session 1 - Thérapies et résistancesNational audienc

Epithelial-mesenchymal transition, IP3 receptors and ER-PM junctions: translocation of Ca2+ signalling complexes and regulation of migration

Disconnection of a cell from its epithelial neighbours and the formation of a mesenchymal phenotype are associated with profound changes in the distribution of cellular components and the formation of new cellular polarity. We observed a dramatic redistribution of inositol trisphosphate receptors (IP3Rs) and stromal interaction molecule 1 (STIM1)-competent endoplasmic reticulum–plasma membrane junctions (ER–PM junctions) when pancreatic ductal adenocarcinoma (PDAC) cells disconnect from their neighbours and undergo individual migration. In cellular monolayers IP3Rs are juxtaposed with tight junctions. When individual cells migrate away from their neighbours IP3Rs preferentially accumulate at the leading edge where they surround focal adhesions. Uncaging of inositol trisphosphate (IP3) resulted in prominent accumulation of paxillin in focal adhesions, highlighting important functional implications of the observed novel structural relationships. ER–PM junctions and STIM1 proteins also migrate to the leading edge and position closely behind the IP3Rs, creating a stratified distribution of Ca2+ signalling complexes in this region. Importantly, migration of PDAC cells was strongly suppressed by selective inhibition of IP3Rs and store-operated Ca2+ entry (SOCE), indicating that these mechanisms are functionally required for migration

A precise measurement of the magnetic field in the corona of the black hole binary V404 Cygni

Observations of binary stars containing an accreting black hole or neutron star often show x-ray emission extending to high energies (>10 kilo­–electron volts), which is ascribed to an accretion disk corona of energetic particles akin to those seen in the solar corona. Despite their ubiquity, the physical conditions in accretion disk coronae remain poorly constrained. Using simultaneous infrared, optical, x-ray, and radio observations of the Galactic black hole system V404 Cygni, showing a rapid synchrotron cooling event in its 2015 outburst, we present a precise 461 ± 12 gauss magnetic field measurement in the corona. This measurement is substantially lower than previous estimates for such systems, providing constraints on physical models of accretion physics in black hole and neutron star binary systems. This article has a correction. Please see: http://science.sciencemag.org/content/360/6386/eaat927