Weather regimes and related atmospheric composition at a Pyrenean observatory characterized by hierarchical clustering of a 5-year data set

Atmospheric composition measurements taken at many high-altitude stations around the world, aim to collect data representative of the free troposphere and of an intercontinental scale. However, the high-altitude environment favours vertical mixing and the transportation of air masses at local or regional scales, which has a potential influence on the composition of the sampled air masses. Mixing processes, source-receptor pathways, and atmospheric chemistry may strongly depend on local and regional weather regimes, and these should be characterized specifically for each station. The Pic du Midi (PDM) isa mountaintop observatory (2850 m a.s.l.) on the north side of the Pyrenees. PDM is associated with the Centre de Recherches Atmosph{\'e}riques (CRA), a site in the foothills ar 600 m a.s.l. 28 km north-east of the PDM. The two centers make up the Pyrenean Platform for the Observation of the Atmosphere (P2OA). Data measured at PDM and CRA were combined to form a5-year hourly dataset of 23 meteorological variables notably: temperature, humidity, cloud cover, wind at several altitudes. The dataset was classified using hierarchical clustering, with the aim of grouping together the days which had similar meteorological characteristics. To complete the clustering, we computed several diagnostic tools, in order to provide additional information and study specific phenomena (foehn, precipitation, atmospheric vertical structure, and thermally driven circulations). This classification resulted in six clusters: three highly populated clusters which correspond to the most frequent meteorological conditions (fair weather, mixed weather and disturbed weather, respectively); a small cluster evidencing clear characteristics of winter northwesterly windstorms; and two small clusters characteristic of south foehn (south- to southwesterly large-scaleflow, associated with warm and dry downslope flow on the lee side of the chain). The diagnostic tools applied to the six clusters provided results in line with the conclusions tentatively drawn from 23 meteorological variables. This, to some extent,validates the approach of hierarchical clustering of local data to distinguish weather regimes. Then statistics of atmospheric composition at PDM were analysed and discussed for each cluster. Radon measurements, notably, revealed that the regional background in the lower troposphere dominates the influence of diurnal thermal flows when daily averaged concentrations are considered. Differences between clusters were demonstrated by the anomalies of CO, CO$_2$, CH$_4$, O$_3$ and aerosol number concentration, and interpretations in relation with chemical sinks and sources are proposed.Comment: Atmospheric Chemistry and Physics, In pres

Cellular and Behavioral Effects of Cranial Irradiation of the Subventricular Zone in Adult Mice

Background: In mammals, new neurons are added to the olfactory bulb (OB) throughout life. Most of these new neurons, granule and periglomerular cells originate from the subventricular zone (SVZ) lining the lateral ventricles and migrate via the rostral migratory stream toward the OB. Thousands of new neurons appear each day, but the function of this ongoing neurogenesis remains unclear. Methodology/Principal Findings: In this study, we irradiated adult mice to impair constitutive OB neurogenesis, and explored the functional impacts of this irradiation on the sense of smell. We found that focal irradiation of the SVZ greatly decreased the rate of production of new OB neurons, leaving other brain areas intact. This effect persisted for up to seven months after exposure to 15 Gray. Despite this robust impairment, the thresholds for detecting pure odorant molecules and short-term olfactory memory were not affected by irradiation. Similarly, the ability to distinguish between odorant molecules and the odorant-guided social behavior of irradiated mice were not affected by the decrease in the number of new neurons. Only long-term olfactory memory was found to be sensitive to SVZ irradiation. Conclusion/Significance: These findings suggest that the continuous production of adult-generated neurons is involved i

Developpement et specificite des comportements chez la souris (Mus musculus). Influence de l'environnement parental

Available from INIST (FR), Document Supply Service, under shelf-number : T 81423 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueSIGLEFRFranc

Neurogenèse dans le cerveau adulte. Conséquences fonctionnelles

Dans le cerveau adulte des Mammifères, des neuroblastes sont produits en permanence dans la zone subgranulaire de l’hippocampe et la zone subventriculaire (ZSV) du cerveau antérieur. Dans cette revue, nous décrivons le rôle déterminant d’un certain nombre de facteurs physiologiques et environnementaux dans la régulation de la neurogenèse hippocampique. Les neuroblastes issus de la SVZ migrent en direction du bulbe olfactif à l’intérieur duquel ils se différencient en interneurones. Les données présentées ont pour objectif de préciser les processus de production, de survie et les conséquences fonctionnelles de ces neurones nouvellement générés. Nous montrons qu’un environnement olfactif enrichi augmente dans le bulbe olfactif adulte la densité des neurones nouvellement générés. Ces effets ne sont pas la conséquence d’une augmentation du taux de prolifération des neuroblastes mais d’une augmentation de la probabilité de survie des nouveaux interneurones. Parallèlement, ces conditions d’élevage sont à l’origine de plus grandes facultés de mémoire olfactive des animaux. Ainsi la régulation par l’activité bulbaire d’un remplacement constitutif permanent des interneurones semble jouer un rôle majeur dans les processus de mémoire olfactive

Adjusting neurophysiological computations in the adult olfactory bulb.

International audienceThe olfactory bulb receives signals from olfactory sensory neurons and conveys them to higher centers. The mapping of the sensory inputs generates a reproducible spatial pattern in the glomerular layer of the olfactory bulb for each odorant. Then, this restricted activation is transformed into highly distributed patterns by lateral interactions between relay neurons and local interneurons. Thus, odor information processing requires the spatial patterning of both sensory inputs and synaptic interactions. In other words, odor representation is highly dynamic and temporally orchestrated. Here, we describe how the local inhibitory network shapes the global oscillations and the precise synchronization of relay neurons. We discuss how local inhibitory interneurons transpose the spatial dimension into temporal patterning. Remarkably, this transposition is not fixed but highly flexible to continuously optimize olfactory information processing

Control of early events in olfactory processing by adult neurogenesis.

International audienceThe mature brain needs to have flexible control over behavior in the face of ever-changing needs. It achieves this control through morphological and physiological changes at the level of molecules, spines, dendrites, and axons and through processes of adult neurogenesis, entire cells. The functional maturation of newly generated cells in the adult forebrain involves the expression of neurotransmitter receptors before synaptic activity and excitatory gamma-aminobutyric acid (GABAergic) influences prior to glutamatergic input. The production of new cells for incorporation into neural circuits that are already up and running gives rise to a unique situation that may require epigenetic regulation. However, once mature, new neurons must carve out a niche among more established cells to be useful. How do they survive and what are they used for? Recent studies have revealed that adult neurogenesis alters the olfactory bulb at all levels, from single cells to the network and system levels. It has also been suggested that cell turnover may be particularly beneficial for the processing of new information in dynamic networks. However, elucidating the functional meaning of adult neurogenesis must wait for the development of new paradigms to eliminate the pool of newly generated neurons but sparing the preexisting ones. Nevertheless, there is already considerable correlative evidence to indicate that adult neurogenesis is a plastic mechanism by which the performance of the brain can be optimized in a given environment

Neurogenese adulte: aspects fondamentaux et potentiels therapeutiques [Adult neurogenesis: from basic research to clinical applications]

International audienceNeural stem cells have recently been found in the central nervous system of adult rodents and humans. In defined conditions, these multipotent cells can generate the three major cell types of the nervous system (neurons, oligodendrocytes and astrocytes). These findings raise questions on the functional role of neural stem cells in the adult brain, and point to the possibility of novel therapeutic approaches. We have been investigating the functional consequences of neural stem cells for the adult circuits of the olfactory system. We are currently investigating this unexpected juvenile characteristic for cognitive functions. For instance, we are exploring the potential of brain adaptation brought into play by adult neurogenesis. Our most recent studies show that neurogenesis contributes to long-term adjustment of the mature brain. Many questions remain to be answered, however. To what extent can we distinguish and compare neuronal production during embryogenesis and adulthood? How does a newborn cell migrate and find its target? How is cellular fate decided? By showing correlations between the regenerative capacities and cognitive functions of the adult brain, our results have interesting implications for the use of endogenous neuronal stem cells for brain repair in patients with neurodegenerative diseases or brain injury due to stroke or trauma

Métacognition chez le babouin : chercher l'information manquante

Le terme "métacognition" renvoie à la capacité d'un organisme à émettre des jugements sur ses propres connaissances, et à exercer en retour un contrôle sur celles-ci. Longtemps considérés comme l'un des produits les plus sophistiqués de la cognition humaine, les travaux menés en cognition comparée cette dernière décennie ont montré que des animaux non-humains, du pigeon au chimpanzé, étaient capables d'évaluer leur degré d'incertitude dans diverses tâches de catégorisation perceptive et de mémorisation. Dans cette étude, une nouvelle procédure expérimentale a été mise en place pour en étudier les mécanismes sous-jacents : dans une tâche de reproduction de pattern sur écran tactile, une icône a été mise à disposition des sujets, leur permettant de revoir à volonté le pattern à mémoriser avant de le reproduire. Les trois babouins testés ont appris à l'utiliser lorsqu'ils se trouvaient en difficulté, et ont spontanément transféré ce comportement à de nouvelles conditions. Dans une seconde expérience, deux d'entre eux ont appris à choisir entre plusieurs clés pour revoir sélectivement les parties du pattern les plus difficiles à mémoriser. Ces résultats suggèrent que des primates non-humains sont capables non seulement d'une évaluation de leur propre degré d'incertitude, mais également d'identifier précisément la source de cette incertitude, et d'orienter leurs comportements de recherche d'informations en conséquence