L’initiative PPTE et la lutte contre la pauvreté.

Ce chapitre vise à présenter l’initiative PPTE originale et renforcée (ainsi que les initiatives annexes qui se sont greffées dessus), de manière à analyser la manière dont les modalités retenues induisent aujourd’hui l’élaboration des programmes de réduction de la pauvreté et leur mise en œuvre.Dettes extérieures; Pays les moins avancés;

Store-Operated Ca2+ Entry (SOCE) Contributes to Normal Skeletal Muscle Contractility in young but not in aged skeletal muscle

Muscle atrophy alone is insufficient to explain the significant decline in contractile force of skeletal muscle during normal aging. One contributing factor to decreased contractile force in aging skeletal muscle could be compromised excitation-contraction (E-C) coupling, without sufficient available Ca2+ to allow for repetitive muscle contractility, skeletal muscles naturally become weaker. Using biophysical approaches, we previously showed that store-operated Ca2+ entry (SOCE) is compromised in aged skeletal muscle but not in young ones. While important, a missing component from previous studies is whether or not SOCE function correlates with contractile function during aging. Here we test the contribution of extracellular Ca2+ to contractile function of skeletal muscle during aging. First, we demonstrate graded coupling between SR Ca2+ release channel-mediated Ca2+ release and activation of SOCE. Inhibition of SOCE produced significant reduction of contractile force in young skeletal muscle, particularly at high frequency stimulation, and such effects were completely absent in aged skeletal muscle. Our data indicate that SOCE contributes to the normal physiological contractile response of young healthy skeletal muscle and that defective extracellular Ca2+ entry through SOCE contributes to the reduced contractile force characteristic of aged skeletal muscle

Challenges in optics for Extremely Large Telescope instrumentation

We describe and summarize the optical challenges for future instrumentation for Extremely Large Telescopes (ELTs). Knowing the complex instrumental requirements is crucial for the successful design of 30-60m aperture telescopes. After all, the success of ELTs will heavily rely on its instrumentation and this, in turn, will depend on the ability to produce large and ultra-precise optical components like light-weight mirrors, aspheric lenses, segmented filters, and large gratings. New materials and manufacturing processes are currently under study, both at research institutes and in industry. In the present paper, we report on its progress with particular emphasize on volume-phase-holographic gratings, photochromic materials, sintered silicon-carbide mirrors, ion-beam figuring, ultra-precision surfaces, and free-form optics. All are promising technologies opening new degrees of freedom to optical designers. New optronic-mechanical systems will enable efficient use of the very large focal planes. We also provide exploratory descriptions of "old" and "new" optical technologies together with suggestions to instrument designers to overcome some of the challenges placed by ELT instrumentation.Comment: (Proc. OPTICON Key Technology Network Workshop, Rome 20-21 October 2005

Turnover rate of cerebrospinal fluid in female sheep: changes related to different light-dark cycles

<p>Abstract</p> <p>Background</p> <p>Sheep are seasonal breeders. The key factor governing seasonal changes in the reproductive activity of the ewe is increased negative feedback of estradiol at the level of the hypothalamus under long-day conditions. It has previously been demonstrated that when gonadotropin secretions are inhibited during long days, there is a higher concentration of estradiol in the cerebrospinal fluid (CSF) than during short days. This suggests an involvement of the CSF and choroid plexus in the neuroendocrine regulatory loop, but the mechanisms underlying this phenomenon remain unknown. One possible explanation of this difference in hormonal content is an effect of concentration or dilution caused by variations in CSF secretion rate. The aim of this study was thus to investigate changes in the CSF turnover rate related to light-dark cycles.</p> <p>Methods</p> <p>The turnover rate of the CSF was estimated by measuring the time taken for the recovery of intraventricular pressure (IVP) after removal of a moderate volume (0.5 to 2 ml) of CSF (slope in mmHg/min). The turnover rate was estimated three times in the same group of sheep: during a natural period of decreasing day-length corresponding to the initial period when gonadotropin activity is stimulated (SG1), during a long-day inhibitory period (IG), and finally during a short-day stimulatory period (SG2).</p> <p>Results</p> <p>The time taken and the speed of recovery of initial IVP differed between groups: 8 min 30 sec, 0.63 ± 0.07 mmHg/min(SG1), 11 min 1 sec, 0.38 ± 0.06 mmHg/min (IG) and 9 min 0 sec, 0.72 ± 0.15 mmHg/min (SG2). Time changes of IVP differed between groups (ANOVA, p < 0.005, SG1 different from IG, <it>p </it>< 0.05). The turnover rate in SG2: 183.16 ± 23.82 μl/min was not significantly different from SG1: 169. 23 ± 51.58 μl/min (Mann-Whitney test, <it>p </it>= 0.41), but was significantly different from IG: 71.33 ± 16.59 μl/min (<it>p </it>= 0.016).</p> <p>Conclusion</p> <p>This study shows that the turnover rate of CSF in ewes changes according to the light-dark cycle; it is increased during short day periods and reduced in long day periods. This phenomenon could account for differences in hormonal concentrations in the CSF in this seasonal species.</p

Implication des plexus choroïdes dans les échanges des stéroïdes entre plasma sanguin et liquide cérébrospinal ; Recherche d'une modulation par la photopériode

Diplôme : Dr. d'Universit

Dualité vasculaire et cardiaque des veines pulmonaires (études fonctionnelles et histologiques chez le rat)

Pulmary veins (VPs) exhibit a particular structure where sleeves of cardiomyocytes are inserted between layers of smooth muscle cells. They can be the source of focal pacemaker activity which may initiate atrial fibrillation inman, the most common cardiac arrythmia. Thereby, VPs are the subject of many electrophysiological and morphological investigations. However, studies devoted to their vasoactive properties and the relationship to their histological structure are very few. Inrat VPs taken from differnt sites, our studies show an heterogeneity of functional responses to pharmacological agents which can be explained by their histological heterogeneity. The endothelium does not seem to play a significantt part in the regulation of the vasomotricity wheras the stimulation of the b -adrenergic receptor induced a relaxation. Finally, electric field and pharmacological stimulations give the possiblity to dissociate the contractile responses of smooth muscle cells tothose of cardiomyocytes.Les veines pulmonaires (VP) constituent une structure vasculaire très particulière par la présence d un manchon de cardiomyocytes qui s insère parmi les cellules musculaires lisses du tissu veineux. Elles peuvent être la source de foyers ectopiques responsables du déclenchement de la fibrillation auriculaire, trouble du rythme le plus fréquent chez l homme. De ce fait, les VP font l objet de nombreuses investigations électrophysiologiques et morphologiques. Toutefois, leurs propriétés vasomotrices ainsi que la relation de celles-ci avec leur structure histologique ont été peu explorées. Nos travaux menés sur des VP de rat montrent ainsi une hétérogénéité au plan des réponses en pharmacologie fonctionnelle qui peut s expliquer par l hétérogénéité histologique. L endothélium ne semble pas jouer un rôle significatif dans la régulation de la vasomotricité alors que la stimulation des récepteurs b -adrénergiques induit une relaxation. Enfin le couplage des stimulations électrique de champ et pharmacologique permet de dissocier les réponses contractiles des cellules musculaires lisses de celles des cardiomyocytes.TOURS-BU Sciences Pharmacie (372612104) / SudocSudocFranceF