Multi-Stability and Pattern-Selection in Oscillatory Networks with Fast Inhibition and Electrical Synapses

A model or hybrid network consisting of oscillatory cells interconnected by inhibitory and electrical synapses may express different stable activity patterns without any change of network topology or parameters, and switching between the patterns can be induced by specific transient signals. However, little is known of properties of such signals. In the present study, we employ numerical simulations of neural networks of different size composed of relaxation oscillators, to investigate switching between in-phase (IP) and anti-phase (AP) activity patterns. We show that the time windows of susceptibility to switching between the patterns are similar in 2-, 4- and 6-cell fully-connected networks. Moreover, in a network (N = 4, 6) expressing a given AP pattern, a stimulus with a given profile consisting of depolarizing and hyperpolarizing signals sent to different subpopulations of cells can evoke switching to another AP pattern. Interestingly, the resulting pattern encodes the profile of the switching stimulus. These results can be extended to different network architectures. Indeed, relaxation oscillators are not only models of cellular pacemakers, bursting or spiking, but are also analogous to firing-rate models of neural activity. We show that rules of switching similar to those found for relaxation oscillators apply to oscillating circuits of excitatory cells interconnected by electrical synapses and cross-inhibition. Our results suggest that incoming information, arriving in a proper time window, may be stored in an oscillatory network in the form of a specific spatio-temporal activity pattern which is expressed until new pertinent information arrives

Cyclotrivératrylènes fluorescents pour la détection d'ammoniums d'intérêt biologique

Le développement de sondes moléculaires fluorescentes pour le suivi ex vivo de phénomènes biologiques (communication nerveuse, par exemple) est en plein essor. Dans cette optique, des dérivés fluorescents de cyclotrivératrylènes (CTV), cavitands propices à la complexation de petites molécules organiques, ont été synthétisés. La stratégie utilisée consiste à introduire des groupements électro-donneurs et électro-attracteurs conjugués sur chaque unité aromatique du CTV afin d avoir des systèmes de type push-pull . L extension de la conjugaison entre les groupements électro-attracteurs et électro-donneurs a été envisagée afin d améliorer les propriétés spectroscopiques des sondes. Des réactions de couplage organométallique de Sonogashira, ainsi que des cycloadditions alcynes-azotures catalysées par le cuivre (CuAAc), ont été conduites sur le squelette CTV dans ce but. La caractérisation spectroscopique des différentes sondes fluorescentes développées a été réalisée en milieu organique et en conditions physiologiques, pour celles dont la solubilité le permettait. L étude des propriétés de reconnaissance de ces dernières, pour des ammoniums d intérêt biologique (tels que les neurotransmetteurs, acétylcholine, dopamine et dérivés) en conditions physiologiques, a également été menée par spectrofluorimétrie, ainsi que par d autres techniques (RMN, calorimétrie). La formation d assemblages moléculaires en milieu aqueux a également été mise en évidence (expériences de diffusion dynamique de la lumière, microscopie électronique en transmission), pour certaines sondes lors de ce travail.The development of fluorescent probes for the ex vivo detection of biological phenomena (neuronal communication, for example) presents a growing interest. In this context, fluorescent cyclotriveratrylene (CTV) derivatives have been developed, as these cavitands are known to complex small organic molecules. The strategy used to get interesting spectroscopic properties, was to introduce conjugated electron-donating and electron-withdrawing groups on each aromatic unit of the CTV (leading to push-pull systems). To improve the spectroscopic properties of the probes, the conjugation between the electron-donating and the electron-withdrawing groups was extended. Hence, the Sonogashira organometalic coupling reaction and the copper catalyzed cycloaddition directly on CTV skeleton were used. The spectroscopic characterization of the new fluorescent probes synthesized was done, in organic solvent but also in physiological conditions when the solubility permits it. The recognition studies for biological ammoniums, such as neurotransmitters (acetylcholine, dopamine, and derivatives) were performed in physiological conditions by spectrofluorimetry but also other methods (like MNR or micro-calorimetry). The formation of molecular assemblies was also observed (by dynamic light scattering and transmission electron microscopy) during this work with some of the probes.BORDEAUX1-Bib.electronique (335229901) / SudocSudocFranceF

Maturation of the GABAergic Transmission in Normal and Pathologic Motoneurons

γ-aminobutyric acid (GABA) acting on Cl−-permeable ionotropic type A (GABAA) receptors (GABAAR) is the major inhibitory neurotransmitter in the adult central nervous system of vertebrates. In immature brain structures, GABA exerts depolarizing effects mostly contributing to the expression of spontaneous activities that are instructive for the construction of neural networks but GABA also acts as a potent trophic factor. In the present paper, we concentrate on brainstem and spinal motoneurons that are largely targeted by GABAergic interneurons, and we bring together data on the switch from excitatory to inhibitory effects of GABA, on the maturation of the GABAergic system and GABAAR subunits. We finally discuss the role of GABA and its GABAAR in immature hypoglossal motoneurons of the spastic (SPA) mouse, a model of human hyperekplexic syndrome

Analysis of the Peptidoglycan Hydrolase Complement of Lactobacillus casei and Characterization of the Major γ-D-Glutamyl-L-Lysyl-Endopeptidase

Peptidoglycan (PG) is the major component of Gram positive bacteria cell wall and is essential for bacterial integrity and shape. Bacteria synthesize PG hydrolases (PGHs) which are able to cleave bonds in their own PG and play major roles in PG remodelling required for bacterial growth and division. Our aim was to identify the main PGHs in Lactobacillus casei BL23, a lactic acid bacterium with probiotic properties

Plasticite phylogenetique d'un reseau paucineuronique generateur de rythme moteur : comparaison des reseaux pyloriques de la crevette et des grands crustaces

SIGLECNRS T 59004 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Variety of alternative stable phase-locking in networks of electrically coupled relaxation oscillators.

We studied the dynamics of a large-scale model network comprised of oscillating electrically coupled neurons. Cells are modeled as relaxation oscillators with short duty cycle, so they can be considered either as models of pacemaker cells, spiking cells with fast regenerative and slow recovery variables or firing rate models of excitatory cells with synaptic depression or cellular adaptation. It was already shown that electrically coupled relaxation oscillators exhibit not only synchrony but also anti-phase behavior if electrical coupling is weak. We show that a much wider spectrum of spatiotemporal patterns of activity can emerge in a network of electrically coupled cells as a result of switching from synchrony, produced by short external signals of different spatial profiles. The variety of patterns increases with decreasing rate of neuronal firing (or duty cycle) and with decreasing strength of electrical coupling. We study also the effect of network topology--from all-to-all--to pure ring connectivity, where only the closest neighbors are coupled. We show that the ring topology promotes anti-phase behavior as compared to all-to-all coupling. It also gives rise to a hierarchical organization of activity: during each of the main phases of a given pattern cells fire in a particular sequence determined by the local connectivity. We have analyzed the behavior of the network using geometric phase plane methods and we give heuristic explanations of our findings. Our results show that complex spatiotemporal activity patterns can emerge due to the action of stochastic or sensory stimuli in neural networks without chemical synapses, where each cell is equally coupled to others via gap junctions. This suggests that in developing nervous systems where only electrical coupling is present such a mechanism can lead to the establishment of proto-networks generating premature multiphase oscillations whereas the subsequent emergence of chemical synapses would later stabilize generated patterns

Do Altruists Like Equity?

Altruism and inequity aversion are often conceptually interrelated, which implies that altruistic and selfish humans may respond differently to disadvantageous inequity conditions. However, a correlation between altruism and inequity responses has thus far not been directly tested experimentally. We have addressed this question using an experimental paradigm inspired by animal experiments in which adult humans work for real food rewards. We have studied whether subjects' responses to different reward distributions were altered by being exposed to equitable or non-equitable situations. In the control conditions, subjects expressed either a strong altruistic attitude, choosing to work for their partner's welfare in the majority of trials, or mostly rejected this course of action. These purely altruistic and selfish behaviors were also expressed after being exposed to disadvantageous inequity, but priming with equitable conditions significantly reduced their occurrence. This implies an important role of inequity pressure, which is presumably present in modern society, in shaping human-helping attitudes

Maximal number of phases in the activity pattern.

<p>A. A general shape of a multiphase pattern trajectory. The trajectory (dark blue curve) is placed between limit values of <i>W</i> (<i>W^up</i> and <i>W^down</i>) (horizontal lines) at which jumps take place. During the silent phase (dotted green curve) a number of deflection may occur (not shown), equal to number of phases in the pattern - 1. The free nullcline is shown as a reference curve (black solid curve). B. Trajectories of cells belonging to different groups expressing 4-phase pattern (B1-2) or 6-phase pattern (B3) during a full active phase of a single cell. For the 4-phase pattern shown are trajectories of cell 1, 7, 13, 19 (black, red, yellow and blue curves, respectively, B1-2). For the 6-phase pattern shown are trajectories of cell 1, 5, 9, 13, 17, 21, (black, dark blue, green, light green and light blue curves, respectively, B3). Notice the effect of shortening the cells' duty cycle (cf. length of trajectories in the silent phase, see color curves in B1 and B2). C. Voltage traces of cells expressing the 6-phase pattern. Only cells connected with a more advanced group are shown. Parameters: N = 24, N^cc = 2, g^el = 0.08. Phase plane coordinates: <i>V</i> (abscissa), <i>W</i> (ordinate). Cells numbers as in Fig. 7B (insert).</p

Contribution à l'étude de l'usage du brouillard d'eau dans la lutte contre les incendies en tunnels ventilés longitudinalement

Cette étude s'inscrit dans la recherche d'une meilleure maîtrise des feux en tunnel à partir d'installations fixes type brouillard d eau. Ce travail essentiellement expérimental s'est appuyé sur des essais réalisés en réduction d échelle. Les paramètres d'étude sont : le type de foyer (feu de nappe, bûchers et empilements de palettes), la vitesse de ventilation longitudinale (inférieure ou supérieure à la vitesse critique), le déclenchement ou non d'un système de brouillard d'eau ainsi que la sectorisation de celui-ci. A son terme, cette étude a permis d'analyser les effets de l'aspersion sur la puissance intrinsèque du foyer, la stratification des fumées et la tenabilité thermique dans l'ouvrage. Une discussion sur les stratégies d'application de la ventilation en cas d'incendie en tunnel et son couplage avec l'aspersion a également été menée, montrant une nette amélioration de l'efficacité du brouillard lorsque la vitesse de ventilation est faible, et ce en dépit de l'augmentation de puissance du foyer due à l'effet de confinement de l'ouvrage. De plus, un travail de réflexion et de synthèse sur les relations de similitude à respecter lors d'une étude de ce type en réduction d'échelle a été conduit, que ce soit concernant l'aéraulique, la puissance du foyer ou les caractéristiques du brouillard d'eau. Enfin, une étude annexe sur l'influence d'un brouillard d'eau sur l'opacité des fumées a été réalisée, quantifiant l'extinction optique des fumées chargées en gouttelettes d eau.This mostly experimental study is based on tests conducted in small scale. The study parameters are : the type of fuel (pool fire, wood crib and pallet stacks), the ventilation velocity (below and above the critical velocity), the triggering or not of the water mist system and it s dividing in sectors. In the end, this study provided information on the effect of sprinkling on the intrinsic heat release rate of the fire, the smoke stratification and the thermal tolerable zones in the tunnel. By analysing the ventilation strategy and it s linkage with the sprinkling, a clear improvement of the efficiency of the water mist at low ventilation speed has been demonstrated, and this despite the increase of heat release rate due to the confinement. Moreover, a part of this work has been devoted to reasoning on a synthesis of the scale relations for the gas flow, fire s heat release rate and water mist characteristics, relations that have to be respected when using a small scale apparatus. Eventually a research has been conducted on the influence of a water mist on the opacity of smoke, quantifying the optical extinction of the smokes loaded with water droplets.POITIERS-BU Sciences (861942102) / SudocSudocFranceF

Synthèse de sondes fluorescentes pour la détection de l'acétylcholine

L'acétylcholine (ACh) est un neurotransmetteur intervenant au niveau des jonctions neuromusculaires et dans le système nerveux central. Dans celui-ci, la transmission cholinergique est impliquée dans des fonctions majeures comme l'apprentissage , la mémoire, l'attention. La maladie d'Alzheimer, maladie neurodégénérative , entraîne un déficit en ACh et le rôle de cette molécule reste à ce jour peu compris. Par conséquent, il est primordial de pouvoir suivre la présence et la diffusion de cette molécule dans l'espace synaptique lors de la communication neuronale. L'objectif de ce travail consiste à synthétiser des sondes moléculaires fluorescentes et d'étudier leurs propriétés complexantes vis-à-vis de l'ACh par RMN et par fluorescence. Les cyclotrivératrylènes (CTV), macrocycles de forme conique présentant une cavité hydrophobe, sont des molécules de choix pour la reconnaissance moléculaire notamment celles des ammoniums. Trois voies de synthèse ont été envisagées pour rendre ces CTV fluorescents : greffer des groupements polycycliques fluorescents sur un CTV, incorporer le groupement polycyclique fluorescent directement dans la structure de la cage et, troisième voie, générer un transfert de charge intramoléculaire en introduisant des groupements électroattracteurs et électrodonneurs conjugués sur le CTV. Au terme de ce travail, une sonde permettant la détection de l'ACh en milieu physiologique, en mesure d'être testée in-vitro et in-vivo sur des réseaux neuronaux, a été élabirée.BORDEAUX1-BU Sciences-Talence (335222101) / SudocSudocFranceF