Recherches écologiques sur une savane sahélienne du Ferlo septentrional, Sénégal : la régénération de la strate herbacée

La production de diaspores a été calculée sur la zone de référence de Fété Olé en 1970 et 1971 à partir de la structure des trois formations herbacées les plus importantes et des productions unitaires des espèces qui les constituent. Cette production s’établit aux environs de 30,6 kg/ha. Lorsque les graines ont été libérées, elles sont soumises à des déplacements par les agents atmosphé riques et éventuellement les animaux, cependant qu’une fraction est consommée (10,3 kg/ha). Des études de germination en préci sent les conditions et l’importance : 3,3 kg/ha. En ce qui concerne les graines résiduelles, les mesures démontrent qu’une fraction seulement de la production est détruite chaque année et que des graines reliques des années précédentes (environ 17 kg/ha) se retrouvent au sol à l’issue de la saison de production.The production of seeds by the grass layer of a dry thornbush savana has been estimated for 1970 and 1971, at the IBP site of Fété-Olé, Sénégal. The total seed production averages 30.6 kg/ha, dry weight. A third of this yearly production (10.3 kg/ha) is consumed locally by various animals, whereas another part is dispersed by wind, rain and animals. However the major part of the seed production of a year remains on the ground and can last for over one year. Most of these seeds are later destroyed by decomposers. Those surviving (3.3 kg/ha) are sufficient to ensure the perenniality of the grass cover. Most of the seeds are able to retain their germinative power for two years at least

Recherches écologiques sur une savane sahélienne du Ferlo septentrional, Sénégal : influence de la sécheresse de l’année 1972-1973 sur la strate ligneuse

L’action de l’exceptionnelle sécheresse sévissant dans la zone sahélienne en 1972-1973 fut particulièrement marquée au niveau de la strate ligneuse. Si la feuillaison des ligneux fut retardée et écourtée, si la production foliaire a été fortement réduite, les effets du manque d’eau sur la floraison et la fructification furent encore plus nets : peu d’arbres fructifièrent, et quand la fructifi cation eut lieu, la production de fruits apparut bien plus faible que celle des années précédentes. La mortalité fut élevée ; en classant les espèces de la plus résistante à la plus sensible, nous trouvons : Boscia senegalensis, Grewia bicolor, Balanites aegyp tiaca, Commiphora africana, Acacia senegal et Guiera senegalensis.The effects of the 1972 drought were particularly marked upon the tree layer on the IBP study site of Fété Olé, Sénégal. The period at which trees normally come into leaf was delayed, leaf produc tion was strongly decreased, and the trees kept their leaves for a shorter time than usual. Few trees bore fruits or seeds and fruit and seed production was also very much smaller than it is usually the case. Many trees died, but mortality rates varied widely accor ding to species, location and age. The commonest species can be classed as follows, according to their decreasing resistance to drought : Boscia senegalensis, Grewia bicolor, Balanites aegyp tiaca, Commiphora africana, Acacia senegal and Guiera sene galensis

Description de la végétation

The vegetation of the Fété Olé study area is typical of the sahelo-soudanian floristic domain, as conceived by Aubréville (1949). The number of species is low. Some 101 phanerogams have been recorded on the 1 Km2 reference quadrat. Most of these species are annual therophytes which complete their vegetation cycle within a 2-3 month period. Using the Roux and Roux (1957) technique of processing the quantitative data gathered in the field, 8 different types of vege tation (« ecological groupings ») are recognized within this apparently homogenous savana. The density of trees averages 133/ha, most of them belonging to only four species : Guiera senegalensis, Balanites aeggptiaca, Grewia bicolor and Commiphora africana. For each of these species, data are given on the frequency of the various age- categories. Young Commiphora are conspicously scarce, probably owing to recent human interference. The existence of shallow depressions where water temporarily accumulates during the rains exerts a major influence upon vegetation structure and particularly upon the density of trees

Neuroprotective Effects of Diabetes Drugs for the Treatment of Neonatal Hypoxia-Ischemia Encephalopathy

The perinatal period represents a time of great vulnerability for the developing brain. A variety of injuries can result in death or devastating injury causing profound neurocognitive deficits. Hypoxic-ischemic neonatal encephalopathy (HIE) remains the leading cause of brain injury in term infants during the perinatal period with limited options available to aid in recovery. It can result in long-term devastating consequences with neurologic complications varying from mild behavioral deficits to severe seizure, intellectual disability, and/or cerebral palsy in the newborn. Despite medical advances, the only viable option is therapeutic hypothermia which is classified as the gold standard but is not used, or may not be as effective in preterm cases, infection-associated cases or low resource settings. Therefore, alternatives or adjunct therapies are urgently needed. Ongoing research continues to advance our understanding of the mechanisms contributing to perinatal brain injury and identify new targets and treatments. Drugs used for the treatment of patients with type 2 diabetes mellitus (T2DM) have demonstrated neuroprotective properties and therapeutic efficacy from neurological sequelae following HIE insults in preclinical models, both alone, or in combination with induced hypothermia. In this short review, we have focused on recent findings on the use of diabetes drugs that provide a neuroprotective effect using in vitro and in vivo models of HIE that could be considered for clinical translation as a promising treatment

Merkel cell polyomavirus large T antigen disrupts lysosome clustering by translocating human Vam6p from the cytoplasm to the nucleus

Merkel cell polyomavirus (MCV) has been recently described as the cause for most human Merkel cell carcinomas. MCV is similar to simian virus 40 (SV40) and encodes a nuclear large T (LT) oncoprotein that is usually mutated to eliminate viral replication among tumor-derived MCV. We identified the hVam6p cytoplasmic protein involved in lysosomal processing as a novel interactor with MCV LT but not SV40 LT. hVam6p binds through its clathrin heavy chain homology domain to a unique region of MCV LT adjacent to the retinoblastoma binding site. MCV LT translocates hVam6p to the nucleus, sequestering it from involvement in lysosomal trafficking. A naturally occurring, tumor-derived mutant LT (MCV350) lacking a nuclear localization signal binds hVam6p but fails to inhibit hVam6p-induced lysosomal clustering. MCV has evolved a novel mechanism to target hVam6p that may contribute to viral uncoating or egress through lysosomal processing during virus replication

Random noise in Diffusion Tensor Imaging, its Destructive Impact and Some Corrections

The empirical origin of random noise is described, its influence on DTI variables is illustrated by a review of numerical and in vivo studies supplemented by new simulations investigating high noise levels. A stochastic model of noise propagation is presented to structure noise impact in DTI. Finally, basics of voxelwise and spatial denoising procedures are presented. Recent denoising procedures are reviewed and consequences of the stochastic model for convenient denoising strategies are discussed