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Search Results: 1 - 10 of 5488 matches for " Xavier Leinekugel "
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Recruitment of Perisomatic Inhibition during Spontaneous Hippocampal Activity In Vitro
Anna Beyeler, Aude Retailleau, Colin Molter, Amine Mehidi, Janos Szabadics, Xavier Leinekugel
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0066509
Abstract: It was recently shown that perisomatic GABAergic inhibitory postsynaptic potentials (IPSPs) originating from basket and chandelier cells can be recorded as population IPSPs from the hippocampal pyramidal layer using extracellular electrodes (eIPSPs). Taking advantage of this approach, we have investigated the recruitment of perisomatic inhibition during spontaneous hippocampal activity in vitro. Combining intracellular and extracellular recordings from pyramidal cells and interneurons, we confirm that inhibitory signals generated by basket cells can be recorded extracellularly, but our results suggest that, during spontaneous activity, eIPSPs are mostly confined to the CA3 rather than CA1 region. CA3 eIPSPs produced the powerful time-locked inhibition of multi-unit activity expected from perisomatic inhibition. Analysis of the temporal dynamics of spike discharges relative to eIPSPs suggests significant but moderate recruitment of excitatory and inhibitory neurons within the CA3 network on a 10 ms time scale, within which neurons recruit each other through recurrent collaterals and trigger powerful feedback inhibition. Such quantified parameters of neuronal interactions in the hippocampal network may serve as a basis for future characterisation of pathological conditions potentially affecting the interactions between excitation and inhibition in this circuit.
Computational modeling of the effects of amyloid-beta on release probability at hippocampal synapses
Armando Romani,Cristina Marchetti,Daniela Bianchi,Xavier Leinekugel,Panayiota Poirazi,Michele Migliore,Hélène Marie
Frontiers in Computational Neuroscience , 2013, DOI: 10.3389/fncom.2013.00001
Abstract: The role of amyloid beta (Aβ) in brain function and in the pathogenesis of Alzheimer's disease (AD) remains elusive. Recent publications reported that an increase in Aβ concentration perturbs pre-synaptic release in hippocampal neurons. In particular, it was shown in vitro that Aβ is an endogenous regulator of synaptic transmission at the CA3-CA1 synapse, enhancing its release probability. How this synaptic modulator influences neuronal output during physiological stimulation patterns, such as those elicited in vivo, is still unknown. Using a realistic model of hippocampal CA1 pyramidal neurons, we first implemented this Aβ-induced enhancement of release probability and validated the model by reproducing the experimental findings. We then demonstrated that this synaptic modification can significantly alter synaptic integration properties in a wide range of physiologically relevant input frequencies (from 5 to 200 Hz). Finally, we used natural input patterns, obtained from CA3 pyramidal neurons in vivo during free exploration of rats in an open field, to investigate the effects of enhanced Aβ on synaptic release under physiological conditions. The model shows that the CA1 neuronal response to these natural patterns is altered in the increased-Aβ condition, especially for frequencies in the theta and gamma ranges. These results suggest that the perturbation of release probability induced by increased Aβ can significantly alter the spike probability of CA1 pyramidal neurons and thus contribute to abnormal hippocampal function during AD.
Intensification of Paraxylene Production using a Simulated Moving Bed Reactor Intensification de la production de paraxylène à l’aide du lit mobile simulé réactif
Bergeot G.,Leinekugel-Le-Cocq D.,Wolff L.,Muhr L.
Oil & Gas Science and Technology , 2010, DOI: 10.2516/ogst/2009086
Abstract: Multifunctional reactors, which combine a reaction step and a separation step in one single unit, constitute an important advance in design of sustainable processes to save energy and reduce environmental impact. They allow reductions of recycle flows and size units in order to have more safety and less expansive processes. This paper deals with separation by adsorption and reaction coupled in a Simulated Moving Bed reactor (SMBR) for paraxylene (PX) production. In the current industrial process, the major part of the separation step comes from a recycle flow where the C8 aromatics are isomerized. The SMBR, by decreasing this recycle stream, may reduce the energy needed to treat and convert the raffinate into a rich PX stream. As separation takes place in the liquid phase, the first part of this paper establishes the feasibility of liquid phase isomerization of xylene. Tests in a fixed bed reactor validate the use of a HZSM-5 zeolite catalyst. Paradiethylbenzene (paraDEB), the classical desorbent used in xylene separation, isomerizes into orthodiethylbenzene and metadiethylbenzene so it is replaced by toluene. Experimental data permit one to estimate the parameters used in a simple analytical model implemented in a classical True Moving Bed model. This TMBR model permits to find the various operating regimes of such a SMBR. The conditions found allow a 40% reduction of the recycle flow without any productivity loss. With this lower recycle flow, a reduction of investment and operating costs is expected on the global PX production process thanks to the SMBR process. Les réacteurs multifonctionnels, qui associent une étape de séparation et une étape de réaction dans une seule et même unité, constituent un axe de développement important dans le domaine de l’écoconception des procédés afin de réduire les co ts énergétiques et environnementaux. Ils permettent de réduire, voire d’éliminer, les flux de recyclage et la taille des unités afin d’obtenir des procédés moins co teux et plus s rs. Cet article présente l’étude d’un réacteur multifonctionnel couplant une réaction d’isomérisation et une séparation par adsorption : le Lit Mobile Simulé Réactif (LMSR). Ce procédé est appliqué à la séparation réactive des xylènes. Le procédé actuel permet de produire du paraxylène (PX) pur (à plus de 99,7 %) à partir d’un mélange d’isomères grace à une étape de séparation par Lit Mobile Simulé (LMS) et une étape d’isomérisation en phase gaz. La majeure partie de l’alimentation du LMS provient du recyclage des isomères du paraxylène qui sont transformés dans le réacteur. La
On the Communication Requirements for the Smart Grid  [PDF]
Mohamed Daoud, Xavier Fernando
Energy and Power Engineering (EPE) , 2011, DOI: 10.4236/epe.2011.31008
Abstract: The current power grid is facing many challenges that it was not designed or engineered to handle which range from congestions and major blackouts to the overwhelming increase in demand and security concerns. The current electric grid was established before the 1960’s. It is believed that the electric grid is the most complex and gigantic machine ever made in human history; it consists of wires, cables, towers, transformers and circuit breakers installed together in outdated manner. During the 60’s, computers and sensors were used to monitor and slightly control the grid; however, fifty years later these sensors are considered less than ideal. Presented here is a review of the smart grid communication network in terms of configuration, bandwidth and latency requirements as well as the technology used. We simulate the access layer of the smart grid net-work and show that no single available communication technology can be used for all layers of the smart grid; thus, different technologies for different layers are needed. A new protocol for optimizing the smart grid is recommended.
A Conservative Model for Nonlinear Dynamics in a Stratified, Rotating Fluid  [PDF]
Nicolas Filatoff, Xavier Carton
Open Journal of Marine Science (OJMS) , 2018, DOI: 10.4236/ojms.2018.82013
Abstract:
We present a set of equations describing the nonlinear dynamics of flows constrained by environmental rotation and stratification (Rossby numbers Ro∈[0.1,0.5] and Burger numbers of order unity). The fluid is assumed incompressible, adiabatic, inviscid and in hydrostatic balance. This set of equations is derived from the Navier Stokes equations (with the above properties), using a Rossby number expansion with second order truncation. The resulting model has the following properties: 1) it can represent motions with moderate Rossby numbers and a Burger number of order unity; 2) it filters inertia-gravity waves by assuming that the divergence of horizontal velocity remains small; 3) it is written in terms of a single function of space and time (pressure, generalized streamfunction or Bernoulli function); 4) it conserves total (Ertel) vorticity in a Lagrangian form, and its quadratic norm (potential enstrophy) at the model order in Rossby number; 5) it also conserves total energy at the same order if the work of pressure forces vanishes when integrated over the fluid domain. The layerwise version of the model is finally presented, written in terms of pressure. Integral properties (energy, enstrophy) are conserved by these layerwise equations. The model equations agree with the generalized geostrophy equations in the appropriate parameter regime. Application to vortex dynamics are mentioned.
On the zeros and critical points of a rational map
Xavier Buff
International Journal of Mathematics and Mathematical Sciences , 2001, DOI: 10.1155/s0161171201011589
Abstract: Let f:ℙ1→ℙ1 be a rational map of degree d. It is well known that f has d zeros and 2d−2 critical points counted with multiplicities. In this note, we explain how those zeros and those critical points are related.
How does BAFF activate B cells in patients with autoimmune diseases?
Xavier Mariette
Arthritis Research & Therapy , 2012, DOI: 10.1186/ar3729
Abstract: In a study in a recent issue of Arthritis Research & Therapy, Yoshimoto and colleagues [1] demonstrate that peripheral monocytes from patients with Sj?gren's syndrome (SS) produce significantly higher amounts of the cytokines B cell-activating factor (BAFF) (also called B-lymphocyte stimulator, or BlyS) and interleukin-6 (IL-6) in comparison with normal monocytes. Increased expression of BAFF might explain pathogenic B-cell activation in several systemic autoimmune diseases (reviewed in [2]). Interestingly, autoreactive B cells depend more on BAFF for survival than do alloreactive B cells. BAFF involvement in the pathogenesis of autoimmune diseases is well illustrated in BAFF-transgenic mice, which exhibit an autoimmune disease mimicking systemic lupus erythematosus (SLE) and primary Sj?gren's syndrome (pSS) as well as a twofold increase in frequency of B-cell lymphoma [3]. In humans, an increased serum level of BAFF was reported in different autoimmune diseases, and findings concerning SLE and pSS were more consistent (reviewed in [2]).Recent findings showed that BAFF could be expressed and secreted by resident cell targets of autoimmunity after stimulation with different cytokines: synoviocytes in rheumatoid arthritis, astrocytes in multiple sclerosis, and epithelial cells in pSS [4]. Moreover, in the context of autoimmunity, BAFF could be secreted by T [5] and B [6] lymphocytes. However, the main sources of BAFF are myeloid cells and, especially, blood monocytes, myeloid dendritic cells, and macrophages [7].It has been suggested that monocytes from patients with autoimmune diseases were more susceptible to BAFF expression and secretion after stimulation with type 1 interferon (IFN) than those from healthy controls [8]. Yoshimoto and colleagues [1] add an important point to this discussion by emphasizing the role of monocytes in the overproduction of BAFF in autoimmunity. The authors demonstrate that peripheral pSS monocytes produce significantly higher amounts of
A Phase Space Diagram for Gravity
Xavier Hernandez
Entropy , 2012, DOI: 10.3390/e14050848
Abstract: In modified theories of gravity including a critical acceleration scale a 0, a critical length scale rM = (GM/a 0 )1/2 will naturally arise with the transition from the Newtonian to the dark matter mimicking regime occurring for systems larger than rM. This adds a second critical scale to gravity, in addition to the one introduced by the criterion v < c of the Schwarzschild radius, rS = 2GM/c2. The distinct dependencies of the two above length scales give rise to non-trivial phenomenology in the (mass, length) plane for astrophysical structures, which we explore here. Surprisingly, extrapolation to atomic scales suggests gravity should be at the dark matter mimicking regime there.
Seleno-enzymes and seleno-compounds: the two faces of selenium
Xavier Forceville
Critical Care , 2006, DOI: 10.1186/cc5109
Abstract: Biological and medical advances in the area of selenium provide interest in selenium for both its antioxidant properties through seleno-enzyme incorporation, as illustrated in the previous issue of Critical Care [1], and its direct pro-oxidant toxic effect through seleno-compounds.In intensive care, and especially in septic shock adjunctive therapy, there is a growing interest in the antioxidant role of selenium [2-5]. We know that there is a very low level of selenium in the human (20 mg for the whole body) but that a severe deficiency is lethal [6]. We also know that selenium plays a crucial role in antioxidant defense, as one selenium atom is absolutely required at the active site of all seleno-enzymes in the form of the 21-amino-acid selenocystein [6,7]. Mammals largely use seleno-enzymes for antioxidant purposes, whereas bacteria do not. The seleno-enzymes are ubiquitous in mammal cells and have two main roles. Firstly, the seleno-enzymes protect cell components against oxidation: membranes, enzymes, proteins, and DNA. Secondly, seleno-enzymes inhibit proinflammatory cell metabolisms by reducing the peroxide tone of intracellular water (NF-κB, acid arachidonic and complement cascades, and mitochondria) [6,8]. As a consequence, selenium has been found to improve immunity [6,7]. In septic shock patients there is a dramatic and early decrease of the plasma selenium concentration [9].In the previous issue of Critical Care, Berger and colleagues [1] reported the results of a very interesting aggregative study on a group of 41 severely burnt patients. The authors show a significant reduction of nosocomial pneumonia by intravenous multitrace-element supplements (copper, selenium, and zinc). These results confirm Berger's research on burnt and trauma patients conducted since 1986 [4]. This particular population has lower mortality than septic shock patients [2].The approach of these studies is to increase the antioxidant defense by supplementing patients with multimicr
Bacterial genomics in Spain
Xavier Bosch
Genome Biology , 2003, DOI: 10.1186/gb-spotlight-20040405-01
Abstract: The Network of Bacterial Genomics (RGB), made up of 41 research teams at universities, hospitals, and centers of the Higher Research Council, will allow scientists to share human and technical resources in an effort to understand the genetic roots of bacterial pathogenicity and utility.The network, whose creation was announced last week (March 23), aims to create a critical mass of researchers in the field to allow them, among other things, to apply for joint research projects. Fellows and senior researchers will move freely among the different centers to build their skills not only in the lab but also in bioinformatics. It is planned to organize periodical meetings and congresses of Spanish and foreign researchers.Central to the initiative is the collaboration of five biotech companies - Biomeda, Progenika, Noraybio, Bioalma, and Newbiotech - which will provide the necessary genetic and bioinformatics tools to the scientists.The RGB idea emerged in February in a meeting at the Valencia-based Institute of Cytologic Research. In the meeting, "it became clear that Spain has the capacity to start projects of bacterial genomics," Andrés Moya, head of the University of Valencia's Institute Cavanilles for Biodiversity and Evolutionary Biology, told us. "It's a pity that, given our potential in this area, we can say that our country has contributed to the sequencing of only two microorganisms out of dozens sequenced so far."It was Moya's team that sequenced the genomes of Buchnera aphidicola and Blochmannia floridanus. Moya argues that there is the "wrong perception by managers of national research programs that work in genomics ends with the sequence of a model genome."Comparative genomics analysis, sequencing, and bioinformatics should be added to the "key words already applied to national programs," he adds.Francisco Rodríguez-Valera, at Universidad Miguel Hernández in San Juan de Alicante, notes that in Spain, sparse genomics resources have been almost exclusively devo
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