Effet de la buspirone sur le réflexe-H chez la souris adulte décérébrée spinale

La locomotion est générée par un réseau neuronal semi-autonome de la moelle épinière sous l’influence du contrôle supraspinal et des afférences périphériques. Aussi lors d’une lésion de la moelle épinière la perte de stimulation par les voies descendantes rend le réseau locomoteur silencieux. La sérotonine (5HT) étant un neurotransmetteur d’origine supraspinale essentiel à la locomotion, son utilisation chez les rongeurs facilite la réexpression de ce circuit neuronale et la récupération des fonctions motrices suite à une lésion spinale chez le rongeur. Cet effet est accompagné d’une réorganisation neuronale qui devrait être visible au niveau des réponses réflexes. Notre objectif consiste donc à observer la modulation du réflexe induite par l’utilisation de buspirone, un agoniste partiel 5HT1A favorable à la réexpression de la locomotion chez la souris spinale adulte. Un modèle de souris décérébrée non anesthésiée a été développé afin de mesurer la modification de l’excitabilité du réflexe-H par la buspirone suite à une lésion spinale complète sur une durée de 60 minutes postinjection. La comparaison d’un groupe (N=8) traité à la buspirone (8mg/kg) à un groupe contrôle (N=6) montre une diminution significative (69%) du réflexe tôt après l’injection suivi d’une augmentation significative (170%) après 30 minutes. Cette hyperréflexie demeure caractérisée par un niveau d’inhibition postactivation similaire à la condition prédose. Ces résultats nous permettent d’associer une diminution du réflexe lors de la période prolocomotrice observée tôt après l’injection de buspirone. Ceux-ci sous-tendent également un rôle de la buspirone dans le contrôle sensorimoteur.Locomotion is generated by a spinal network which is, under normal conditions, modulated by supraspinal inputs and peripheral feedback. A spinal cord injury induces a loss of descending command and silence the locomotor network. Nevertheless, reexpression of this network can be facilitated by application of serotonin, a neurotransmitter originating supraspinally known to help locomotor recovery in spinal rodents. Such effect is associated with neuronal rearrangement which could be observed on reflex pathway. The aim of our study is to measure reflex modulation induced by buspirone, a 5-HT1A partial agonist that allowed reexpression of locomotion in adult spinal mice. Using a newly developed model of decerebrated unanesthetized mouse we measure the modulation of H-reflex excitability induced by buspirone after an acute spinal transection for 60 minutes post-injection. Comparison between buspirone (8mg/kg) treated (N=8) and control (N=6) groups present a significant decrease in reflex amplitude (69%) at early stages of pharmacological treatment followed by a raise (170%) that become significant 30 minutes postdose. Those results allowed us to associate reflexe decrease during prolocomotor period observed in first minutes after buspirone injection. There also support the involvement of buspirone in sensorimotor control

Optimal Attitude Control Management For A Cubesat

CubeSats have become popular among universities, research organizations, and government agencies due to their low cost, small size, and light weight. Their standardized configurations further reduce the development time and ensure more frequent launch opportunities. Early cubesat missions focused on hardware validation and simple communication missions, with little requirement for pointing accuracy. Most of these used magnetic torque rods or coils for attitude stabilization. However, the intrinsic problems associated with magnetic torque systems, such as the lack of three-axis control and low pointing accuracy, make them unsuitable for more advanced missions such as detailed imaging and on-orbit inspection. Threeaxis control in a cubesat can be achieved by combining magnetic torque coils with other devices such as thrusters, but the lifetime is limited by the fuel source onboard. To maximize the mission lifetime, a fast attitude control management algorithm that could optimally manage the usage of the magnetic and thruster torques is desirable. Therefore, a recently developed method, the BSpline-augmented virtual motion camouflage, is presented in this defense to solve the problem. This approach provides results which are very close to those obtained through other popular nonlinear constrained optimal control methods with a significantly reduced computational time. Simulation results are presented to validate the capabilities of the method in this applicatio

Lipid biomarker (brGDGT)- and pollen-based reconstruction of temperature change during the Middle to Late Holocene transition in the Carpathians

To reconstruct changes in vegetation, temperature, and sediment geochemistry through the last 6.5 cal ka BP, in the Subcarpathian belt of the Eastern Carpathians (Romania), pollen, branched glycerol dialkyl glycerol tetraethers (brGDGTs) and X-ray fluorescence analyses have been integrated. Pollen and brGDGTs (a bacterial lipid biomarker proxy) are used as paleothermometers for reconstructing the mean annual air temperature (MAAT) and mean temperature above freezing (MAF), respectively. Both proxies show roughly consistent records. The highest MAAT and MAF occurs during the oldest part of the record (from 6.5 to 4.2 cal ka BP), and the Middle to the Late Holocene shift is marked by a prominent decrease in temperature between 5.4 and 4.2 cal ka BP, coinciding with Bond event 4 and 3. This transition is coeval with a decrease in summer insolation, shift from consistent NAO-conditions to a predominance of NAO+ phase and coincides with the beginning of the Neoglacial cooling in northern latitudes. The warm bias in the MAF reconstruction during the Late Holocene is explained as a change in the lipid provenance or in the composition of the brGDGT producers after 4.2 cal ka BP.Peer reviewe

Musculoskeletal ultrasound for 3D bone modeling: A preliminary study applied to lumbar vertebra

BACKGROUND: There is no non-invasive in vivo method to assess intervertebral kinematics. Current kinematics models are based on in vitro bone reconstructions from computed tomography (CT)-scan imaging, fluoroscopy and MRIs, which are either expensive or deleterious for human tissues. Musculoskeletal ultrasound is an accessible, easy to use and cost-effective device that allows high-resolution, real-time imaging of bone structure. OBJECTIVE: The aim of this preliminary study was to compare the concordance of 3D bone modeling of lumbar vertebrae between CT-scan and ultrasound imaging and to study the intra and inter-reliability of distances measured on 3D ultrasound bone models. METHODS: CT-scan, ultrasound, and in situ data of five lumbar vertebrae from the same human specimen were used. All vertebrae were scanned by tomography and a new musculoskeletal ultrasound procedure. Then, 3D bone modeling was created from both CT-scan and ultrasound image data set. Distances between anatomical bones landmarks were measured on the 3D models and compared to in situ measurements. © 2021-IOS Press. All rights reserved

Chronologie et spatialisation de retombées de cendres volcaniques tardiglaciaires dans les massifs des Vosges et du Jura, et le plateau suisse

L’établissement d’une chronologie précise des différents événements climatiques du Tardiglaciaire et de l’Holocène nécessite l’emploi de différents moyens de datation. Parmi ceux-ci, la téphrochronologie apparaît comme un outil permettant à la fois une datation précise et une synchronisation à l’échelle inter-régionale de ces événements. Dans le cadre de l’étude de l’enregistrement des variations du climat ayant régné en Europe de l’Ouest durant les 20 000 dernières années, des niveaux de téphras et de « cryptotéphras » ont été détectés dans des remplissages de lacs situés dans les massifs du Jura, des Vosges et sur le Plateau suisse. Certains de ces niveaux étant invisibles à l’œil nu, leur détection a été rendue possible grâce à l’emploi de la mesure de la susceptibilité magnétique à un pas de 5 mm. Nos observations permettent de compléter l’extension géographique de la bordure ouest du nuage de dispersion méridional du Laacher See Tephra (env. 12900 ans, Eifel, Allemagne) déjà observé dans d’autres remplissages lacustres du Jura et de l’Europe de l’Ouest et du Nord. Dans les sites étudiés, les échardes de verre volcanique présentent des compositions chimiques comparables à celles des phases les plus jeunes du Laacher See Tephra. D’autres niveaux de téphras, non répertoriés jusqu’à présent dans cette région, ont été détectés et caractérisés. Deux niveaux, très discrets et uniquement présents dans les sites du massif du Jura et du Plateau suisse, sont caractérisés par des âges et compositions chimiques de phénocristaux compatibles avec les produits émis par le Puy de la Nugère (Chaîne des Puys, France) pendant l’Allerød (autour de 13300 ans). Les sites du massif des Vosges, quant à eux, sont caractérisés par l’occurence d’un téphra rhyolitique, le Vedde Ash (env. 12000 ans), déposé durant le Dryas récent. Actuellement, il s’agit là de l’occurence la plus méridio‑occidentale de ce téphra. Nos résultats complètent la téphrochronologie tardiglaciaire de l’Est de la France et offrent donc un « pont » chronologique supplémentaire entre les séquences sédimentaires nord- et centreeuropéennes et celles situées plus à l’ouest. Ils soulignent l’importance du Laacher See Tephra et du Vedde Ash pour les études paléoenvironnementales dans cette partie de l’Europe puisque ces deux téphras encadrent la limite Allerød - Dryas récent et permettent, pour cet intervalle de temps, de pallier l’absence de données radiochronologiques.Establishment of a precise chronicle of the lateglacial and holocene climatic variations requires the use of various dating methods. Among them, tephrochronology allows high-resolution dating and synchronization of these events at a regional scale and sometimes at a continental scale. Study of the record of the climatic variations occuring in western Europe since twenty thousands years leads to the discovery of tephras levels and “cryptotephras” in sediments cored in lakes from the Jura and Vosges mountains, and the Swiss plateau. Some of these levels are invisible to the naked eye. Their detection was obtained using magnetic susceptibility measurement with a 5 mm step along the cores. Our observations allow to complete the western boundary of the southern distribution of the Laacher See Tephra (ca. 12,900 yr, Eifel, Germany). This tephra has been already described in others lacustrine sequences from the Jura and the western and northern Europe. In the sites we have studied, the volcanic glass shards show geochemical compositions comparable to those of the youngest phases of the Laacher See Tephra eruption. Other tephra levels, never described in this region until then, have been detected and characterized. Two very discrete tephra levels, only observed in sites from the Jura and the Swiss plateau, present ages, mineral assemblages and chemical compositions close to those of tephras that were emitted by the Puy de la Nugère (Chaîne des Puys, France) during the Alleröd (about 13,300 yr). Sites from the Vosges mountains are characterized by the occurrence of the rhyolitic Vedde Ash (ca. 12,000 yr, from the icelandic Katla volcano), deposited during the Younger Dryas. Presently, this is the most southwestern occurrence of the Vedde Ash. Our data make up the Eastern France Lateglacial tephrochrology and offer an additional chronological bridge between sedimentary sequences from northern and central Europe and those situated more westerly. They show the importance of the Laacher See Tephra and the Vedde Ash for palaeoenvironmental studies in western Europe since they are flanking the AllerödYounger Dryas transition and allow to compensate the lack of radiochronological data

New insights on lake sediment DNA from the catchment: importance of taphonomic and analytical issues on the record quality

Over the last decade, an increasing number of studies have used lake sediment DNA to trace past landscape changes, agricultural activities or human presence. However, the processes responsible for lake sediment formation might affect DNA records via taphonomic and analytical processes. It is crucial to understand these processes to ensure reliable interpretations for “palaeo” studies. Here, we combined plant and mammal DNA metabarcoding analyses with sedimentological and geochemical analyses from three lake-catchment systems that are characterised by different erosion dynamics. The new insights derived from this approach elucidate and assess issues relating to DNA sources and transfer processes. The sources of eroded materials strongly affect the “catchment-DNA” concentration in the sediments. For instance, erosion of upper organic and organo-mineral soil horizons provides a higher amount of plant DNA in lake sediments than deep horizons, bare soils or glacial flours. Moreover, high erosion rates, along with a well-developed hydrographic network, are proposed as factors positively affecting the representation of the catchment flora. The development of open and agricultural landscapes, which favour the erosion, could thus bias the reconstructed landscape trajectory but help the record of these human activities. Regarding domestic animals, pastoral practices and animal behaviour might affect their DNA record because they control the type of source of DNA (“point” vs. “diffuse”)

From Experimental psychology to a science of learning

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Commentaire

Develle Michel. Commentaire. In: Revue d'économie financière, n°1, 1987. articles divers. pp. 99-101