81 research outputs found

    Développement d'une méthode de quantification des varicosités synaptiques et asynaptiques établies par les neurones dopaminergiques

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    Les neurones dopaminergiques (DA) de la substance noire compacte (SNc) et de l’aire tegmentaire ventrale (ATV) dĂ©veloppent des contacts de type synaptique et non synaptique. MalgrĂ© de nombreux travaux sur la synaptogĂ©nĂšse en gĂ©nĂ©ral, aucune mĂ©thode autre que la microscopie Ă©lectronique, n’a Ă©tĂ© dĂ©veloppĂ©e pour quantifier les varicositĂ©s synaptiques et asynaptiques issues des neurones DA. L’objectif principal de ce projet Ă©tait de dĂ©velopper une mĂ©thode d’analyse et de quantification des varicositĂ©s synaptiques et asynaptiques des neurones DA. L’hypothĂšse proposĂ©e est qu’il devait ĂȘtre possible de dĂ©tecter la prĂ©sence de synapses en visualisant la colocalisation d’une protĂ©ine prĂ©synaptique telle que synaptotagmine 1 (SYT1) avec un marqueur post-synaptique tel que la postsynaptic density protein 95 (PSD95). Pour ce faire, nous avons prĂ©parĂ© des cultures primaires de neurones DA Ă  l’aide d’une lignĂ©e de souris transgĂ©niques exprimant la protĂ©ine fluorescente verte (GFP) sous le contrĂŽle du promoteur de la tyrosine hydroxyalse (TH). Nous avons ensuite visualisĂ© les terminaisons axonales Ă  l'aide de marquages immunocytochimiques de protĂ©ines prĂ© et post-synaptiques. L’analyse quantitative des images a Ă©tĂ© effectuĂ©e avec le logiciel de traitement d’image Image-J. Nos rĂ©sultats montrent que, via l’association d’un marqueur prĂ©synaptique tel que SYT1 avec un marqueur postsynaptique tel que PSD95, seule une minoritĂ© des terminaisons Ă©tablies par les neurones DA sont de type synaptique. En contraste, des neurones glutamatergiques du cortex, Ă©tablissent une majoritĂ© de terminaisons associĂ©es Ă  un marqueur postsynaptique. Nos rĂ©sultats valident donc la mise en place d'une technique d'analyse permettant de quantifier la proportion de terminaisons synaptiques et asynaptiques Ă©tablies par les neurones DA.Dopamine neurons (DA) of the Substantia Nigra compacta (SNc) and Ventral Tegmental Area (VTA) are able to develop axon terminals that are either synaptic or non-synaptic in terms of their structure. No method other than electron microscopy was previously developed to quantify synaptic and non-synaptic axonal varicosities established by DA neurons. The main objective of this project was to develop a method for the quantification and analysis of synaptic and non-synaptic terminals established by cultured DA neurons. We hypothesized that synapses should be visualized by the colocalisation of presynaptic proteins such as synaptotagmin 1 (SYT1) and postsynaptic markers like the postsynaptic density protein 95 (PSD95). To perform this, we prepared primary DA neurons cultures from neurons obtained from the ventral mesencephalon of TH-GFP transgenic mice. We then used immunocytochemistry and confocal microscopy to localize markers of the pre and postsynaptic compartments. Images were quantified using the Image-J software. Our results show that the majority of axon terminals established by DA neurons contain the presynaptic marker SYT1. However, only a minority are associated with the postsynaptic marker PSD95, compatible with previous in vivo results. In comparison, glutamatergic neurons from the cortex establish a majority of terminals associated with a postsynaptic marker. Our results validate the establishment of an experimental strategy allowing quantification of the proportion of synaptic and non-synaptic contacts established by DA neurons, a technique that we plan to use to explore the molecular mechanisms of synapse formation by these neurons

    Histamine H-3 Receptors Decrease Dopamine Release in the Ventral Striatum by Reducing the Activity of Striatal Cholinergic Interneurons

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    Histamine H-3 receptors are widely distributed Gi-coupled receptors whose activation reduces neuronal activity and inhibits release of numerous neurotransmitters. Although these receptors are abundantly expressed in the striatum, their modulatory role on activity-dependent dopamine release is not well understood. Here, we observed that histamine H-3 receptor activation indirectly diminishes dopamine overflow in the ventral striatum by reducing cholinergic interneuron activity. Acute brain slices from C57BL/6 or channelrhodopsin-2-transfected DAT-cre mice were obtained, and dopamine transients evoked either electrically or optogenetically were measured by fast-scan cyclic voltammetry. The H-3 agonist alpha-methylhistamine significantly reduced electrically-evoked dopamine overflow, an effect blocked by the nicotinic acetylcholine receptor antagonist dihydro-beta-erythroidine, suggesting involvement of cholinergic interneurons. None of the drug treatments targeting H-3 receptors affected optogenetically evoked dopamine overflow, indicating that direct H-3-modulation of dopaminergic axons is unlikely. Next, we used qPCR and confirmed the expression of histamine H-3 receptor mRNA in cholinergic interneurons, both in ventral and dorsal striatum. Activation of H-3 receptors by alpha-methylhistamine reduced spontaneous firing of cholinergic interneurons in the ventral, but not in the dorsal striatum. Resting membrane potential and number of spontaneous action potentials in ventral-striatal cholinergic interneurons were significantly reduced by alpha-methylhistamine. Acetylcholine release from isolated striatal synaptosomes, however, was not altered by alpha-methylhistamine. Together, these results indicate that histamine H-3 receptors are important modulators of dopamine release, specifically in the ventral striatum, and that they do so by decreasing the firing rate of cholinergic neurons and, consequently, reducing cholinergic tone on dopaminergic axons. (C) 2018 IBRO. Published by Elsevier Ltd. All rights reserved.Peer reviewe

    A roadmap to the efficient and robust characterization of temperate terrestrial planet atmospheres with JWST

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    Ultra-cool dwarf stars are abundant, long-lived, and uniquely suited to enable the atmospheric study of transiting terrestrial companions with JWST. Amongst them, the most prominent is the M8.5V star TRAPPIST-1 and its seven planets, which have been the favored targets of eight JWST Cycle 1 programs. While Cycle 1 observations have started to yield preliminary insights into the planets, they have also revealed that their atmospheric exploration requires a better understanding of their host star. Here, we propose a roadmap to characterize the TRAPPIST-1 system -- and others like it -- in an efficient and robust manner. We notably recommend that -- although more challenging to schedule -- multi-transit windows be prioritized to constrain stellar heterogeneities and gather up to 2×\times more transits per JWST hour spent. We conclude that in such systems planets cannot be studied in isolation by small programs, thus large-scale community-supported programs should be supported to enable the efficient and robust exploration of terrestrial exoplanets in the JWST era

    Negation and the functional sequence

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    There exists a general restriction on admissible functional sequences which prevents adjacent identical heads. We investigate a particular instantiation of this restriction in the domain of negation. Empirically, it manifests itself as a restriction the stacking of multiple negative morphemes. We propose a principled account of this restriction in terms of the general ban on immediately consecutive identical heads in the functional sequence on the one hand, and the presence of a Neg feature inside negative morphemes on the other hand. The account predicts that the stacking of multiple negative morphemes should be possible provided they are separated by intervening levels of structure. We show that this prediction is borne out

    The L 98-59 System: Three Transiting, Terrestrial-size Planets Orbiting a Nearby M Dwarf

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    We report the Transiting Exoplanet Survey Satellite (TESS) discovery of three terrestrial-size planets transiting L 98-59 (TOI-175, TIC 307210830)—a bright M dwarf at a distance of 10.6 pc. Using the Gaia-measured distance and broadband photometry, we find that the host star is an M3 dwarf. Combined with the TESS transits from three sectors, the corresponding stellar parameters yield planet radii ranging from 0.8 R ⊕ to 1.6 R ⊕. All three planets have short orbital periods, ranging from 2.25 to 7.45 days with the outer pair just wide of a 2:1 period resonance. Diagnostic tests produced by the TESS Data Validation Report and the vetting package DAVE rule out common false-positive sources. These analyses, along with dedicated follow-up and the multiplicity of the system, lend confidence that the observed signals are caused by planets transiting L 98-59 and are not associated with other sources in the field. The L 98-59 system is interesting for a number of reasons: the host star is bright (V = 11.7 mag, K = 7.1 mag) and the planets are prime targets for further follow-up observations including precision radial-velocity mass measurements and future transit spectroscopy with the James Webb Space Telescope; the near-resonant configuration makes the system a laboratory to study planetary system dynamical evolution; and three planets of relatively similar size in the same system present an opportunity to study terrestrial planets where other variables (age, metallicity, etc.) can be held constant. L 98-59 will be observed in four more TESS sectors, which will provide a wealth of information on the three currently known planets and have the potential to reveal additional planets in the system

    Reconstructing Metaphorical Meaning

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    Your article is protected by copyright and all rights are held exclusively by Springer Science +Business Media Dordrecht. This e-offprint is for personal use only and shall not be self-archived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com”

    Validation of the OECD reproduction test guideline with the New Zealand mudsnail Potamopyrgus antipodarum using trenbolone and prochloraz

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    The Organisation for Economic Cooperation and Development (OECD) provides several standard test methods for the environmental hazard assessment of chemicals, mainly based on primary producers, arthropods, and fish. In April 2016, two new test guidelines with two mollusc species representing different reproductive strategies were approved by OECD member countries. One test guideline describes a 28-day reproduction test with the parthenogenetic New Zealand mudsnail Potamopyrgus antipodarum. The main endpoint of the test is reproduction, reflected by the embryo number in the brood pouch per female. The development of a new OECD test guideline involves several phases including inter-laboratory validation studies to demonstrate the robustness of the proposed test design and the reproducibility of the test results. Therefore, a ring test of the reproduction test with P. antipodarum was conducted including eight laboratories with the test substances trenbolone and prochloraz and results are presented here. Most laboratories could meet test validity criteria, thus demonstrating the robustness of the proposed test protocol. Trenbolone did not have an effect on the reproduction of the snails at the tested concentration range (nominal: 10-1000 ng/L). For prochloraz, laboratories produced similar EC10 and NOEC values, showing the inter-laboratory reproducibility of results. The average EC10 and NOEC values for reproduction (with coefficient of variation) were 26.2 ”g/L (61.7%) and 29.7 ”g/L (32.9%), respectively. This ring test shows that the mudsnail reproduction test is a well-suited tool for use in the chronic aquatic hazard and risk assessment of chemicals

    Supplement: "Localization and broadband follow-up of the gravitational-wave transient GW150914" (2016, ApJL, 826, L13)

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    This Supplement provides supporting material for Abbott et al. (2016a). We briefly summarize past electromagnetic (EM) follow-up efforts as well as the organization and policy of the current EM follow-up program. We compare the four probability sky maps produced for the gravitational-wave transient GW150914, and provide additional details of the EM follow-up observations that were performed in the different bands

    Localization and broadband follow-up of the gravitational-wave transient GW150914

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    © 2016. The American Astronomical Society. All rights reserved. A gravitational-wave (GW) transient was identified in data recorded by the Advanced Laser Interferometer Gravitational-wave Observatory (LIGO) detectors on 2015 September 14. The event, initially designated G184098 and later given the name GW150914, is described in detail elsewhere. By prior arrangement, preliminary estimates of the time, significance, and sky location of the event were shared with 63 teams of observers covering radio, optical, near-infrared, X-ray, and gamma-ray wavelengths with ground- and space-based facilities. In this Letter we describe the low-latency analysis of the GW data and present the sky localization of the first observed compact binary merger. We summarize the follow-up observations reported by 25 teams via private Gamma-ray Coordinates Network circulars, giving an overview of the participating facilities, the GW sky localization coverage, the timeline, and depth of the observations. As this event turned out to be a binary black hole merger, there is little expectation of a detectable electromagnetic (EM) signature. Nevertheless, this first broadband campaign to search for a counterpart of an Advanced LIGO source represents a milestone and highlights the broad capabilities of the transient astronomy community and the observing strategies that have been developed to pursue neutron star binary merger events. Detailed investigations of the EM data and results of the EM follow-up campaign are being disseminated in papers by the individual teams
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