Influence de la distance sur le transfert par ruissellement de quelques substances phytosanitaires

Les travaux présentés dans cet article ont pour objet l'étude de l'influence de la distance parcourue par les écoulements de surface sur l'intensité des transferts par ruissellement des produits phytosanitaires. Une première série d'essais réalisée sur des parcelles expérimentales labourées mais non cultivées montre une rapide décroissance des quantités exportées avec l'augmentation de la distance de transfert. La quantité cumulée de matières transférées peut alors être décrite par une fonction exponentielle décroissante de la distance. Une seconde série d'expérimentations sur des parcelles cultivées en blé en hiver puis au printemps en maïs montre que l'intensité de cette réduction dépend pour une large part de la pénétration des molécules dans le sol, qui les soustrait aux entraînements de surface. Cette migration verticale est favorisée par la faible affinité des matières avec les composants du sol en particulier la matière organique. Elle est également plus forte quand la réserve en eau du sol est élevée, ce qui augmente la migration par diffusion des composés et la descente lors des pluies des tranches d'eau les plus contaminées. Par ailleurs des pratiques culturales laissant peu de sol nu limitent le ruissellement au profit de l'infiltration. Ces divers mécanismes expliquent que l'effet distance est moins sensible pour une molécule peu mobile comme le lindane que pour l'atrazine, dont la mobilité conduit à des exportations élevées lors des premières pluies qui suivent les traitements.The aim of this study was to investigate how the distance covered by runoff water containing pesticides influenced the resulting quantity of pesticides liable to enter neighbouring waters courses. We carried out primary experiments on a bare soil, equipped with runoff water collection equipment placed at the following distances from the area to which the pesticide was applied: 1.5 m, 5 m, 9 m and 13 m. Each 10 m2 test surface was treated with several pesticides: atrazine, simazine, cyanazine, 2,4-D and 2,4-DB. Results show that the pesticide quantities found in the water collectors decreased exponentially with distance. Under the experimental conditions, a distance of about 4 m led to a 10-fold reduction in pesticide runoff transfer rates.Further similar experiments were carried out on soil cultivated with wheat and with maize. Two different pesticides, atrazine and lindane, exhibiting different behaviour in soil and different chemical and physical properties, were chosen. Observed results were similar and the total pesticide quantity was again found to be a decreasing exponential function of the distance from the treated plot. Reduction in the amount transferred, as a function of runoff distance, depends mainly on vertical migration, which in turn reduces the quantity of surface pesticide available. This vertical migration is favoured by a low affinity between pesticide and soil. This phenomenon is amplified with increasing soil water reserve. It is due to both pesticide diffusion and vertical displacement of water. The state of the surface due to arable farming practices and vegetation also plays a determining role in the vertical and horizontal displacement of water, and consequently affects pesticide transfer by runoff. Therefore the distance factor was less prominent in spring for soils cultivated with maize than in winter for the same soil cultivated with wheat. However, in all cases, the influence of runoff distance upon the quantities of pesticide transferred to surface waters remains crucial

MicroRNAs targeting oncogenes are down-regulated in pancreatic malignant transformation from benign tumors

BACKGROUND MicroRNA (miRNA) expression profiles have been described in pancreatic ductal adenocarcinoma (PDAC), but these have not been compared with pre-malignant pancreatic tumors. We wished to compare the miRNA expression signatures in pancreatic benign cystic tumors (BCT) of low and high malignant potential with PDAC, in order to identify miRNAs deregulated during PDAC development. The mechanistic consequences of miRNA dysregulation were further evaluated. METHODS Tissue samples were obtained at a tertiary pancreatic unit from individuals with BCT and PDAC. MiRNA profiling was performed using a custom microarray and results were validated using RT-qPCR prior to evaluation of miRNA targets. RESULTS Widespread miRNA down-regulation was observed in PDAC compared to low malignant potential BCT. We show that amongst those miRNAs down-regulated, miR-16, miR-126 and let-7d regulate known PDAC oncogenes (targeting BCL2, CRK and KRAS respectively). Notably, miR-126 also directly targets the KRAS transcript at a "seedless" binding site within its 3'UTR. In clinical specimens, miR-126 was strongly down-regulated in PDAC tissues, with an associated elevation in KRAS and CRK proteins. Furthermore, miR-21, a known oncogenic miRNA in pancreatic and other cancers, was not elevated in PDAC compared to serous microcystic adenoma (SMCA), but in both groups it was up-regulated compared to normal pancreas, implicating early up-regulation during malignant change. CONCLUSIONS Expression profiling revealed 21 miRNAs down-regulated in PDAC compared to SMCA, the most benign lesion that rarely progresses to invasive carcinoma. It appears that miR-21 up-regulation is an early event in the transformation from normal pancreatic tissue. MiRNA expression has the potential to distinguish PDAC from normal pancreas and BCT. Mechanistically the down-regulation of miR-16, miR-126 and let-7d promotes PDAC transformation by post-transcriptional up-regulation of crucial PDAC oncogenes. We show that miR-126 is able to directly target KRAS; re-expression has the potential as a therapeutic strategy against PDAC and other KRAS-driven cancers

Awareness of cognitive decline trajectories in asymptomatic individuals at risk for AD

Background: Lack of awareness of cognitive decline (ACD) is common in late-stage Alzheimer’s disease (AD). Recent studies showed that ACD can also be reduced in the early stages. Methods: We described different trends of evolution of ACD over 3 years in a cohort of memory-complainers and their association to amyloid burden and brain metabolism. We studied the impact of ACD at baseline on cognitive scores’ evolution and the association between longitudinal changes in ACD and in cognitive score. Results: 76.8% of subjects constantly had an accurate ACD (reference class). 18.95% showed a steadily heightened ACD and were comparable to those with accurate ACD in terms of demographic characteristics and AD biomarkers. 4.25% constantly showed low ACD, had significantly higher amyloid burden than the reference class, and were mostly men. We found no overall effect of baseline ACD on cognitive scores’ evolution and no association between longitudinal changes in ACD and in cognitive scores. Conclusions: ACD begins to decrease during the preclinical phase in a group of individuals, who are of great interest and need to be further characterized. Trial registration: The present study was conducted as part of the INSIGHT-PreAD study. The identification number of INSIGHT-PreAD study (ID-RCB) is 2012-A01731-42

Low Cognitive Awareness, but Not Complaint, is a Good Marker of Preclinical Alzheimer's Disease

Subjective cognitive decline (SCD) may result from many conditions, including Alzheimer's disease (AD)

L'effet de deux types d'entrainement sur la vitesse de marche des personnes âgées MCI

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Blood pressure, cognitive functions, and prevention of dementias in older patients with hypertension

The prevalence and incidence of degenerative and vascular dementias increase exponentially with age, from 70 years onward. In view of the increasing longevity of humans, both varieties are bound to evolve into a major problem worldwide. According to several longitudinal studies, hypertension appears to predispose individuals to the development of cognitive impairment and ensuing dementia, after a period varying from a few years to several decades. Antihypertensive drug treatment, according to preliminary evidence, may serve to reduce the rates of such events. Such findings await to be confirmed by formal therapeutic trials against a backdrop of "historical" observational sources