L’invasion d 'Arvicanthis niloticus dans le Sahel sénégalais en 1975-1976 et ses conséquences pour la strate ligneuse

Dans le contexte de pullulation généralisée des rongeurs sahéliens en 1975-1976, les auteurs ont recueilli des informations sur l’installation, puis le maintien d’une population d’ Arvicanthis niloticus dans le milieu naturel du Sahel sénégalais. L’invasion consécutive à la phase d’expansion maximale des populations a eu lieu durant la saison des pluies 1975. Les Arvi canthis se sont installés dans les formations arbustives des dépres sions interdunaires. Pour faire face aux rigueurs de la saison sèche, les Arvican this ont modifié leur comportement diurne, qui de terrestre est devenu arboricole : les arbres leur offrant par leurs écorces, les ressources hydriques indispensables à leur survie. Cette exploi tation inhabituelle de la strate arborée aboutit à une dégradation empêchant la régénération d’espèces comme Commiphora afri- cana et Acacia senegal. Les caractéristiques de la dynamique de population des Arvi canthis suggèrent que le maintien dans le milieu naturel est dif ficile : la longueur de la saison de reproduction est suffisante pour permettre l’apparition d’une deuxième génération issue des premiers nés, mais la durée de vie, qui ne dépasse pas 9 mois en raison des difficultés alimentaires et de la pression de prédation, réd.uit considérablement les possibilités de maintien à long terme.A rodent outbreak, involving several species, took place in 1975-1976 in the sahelian zone of Senegal. This first paper des cribes the population movements and fluctuations of the Nile rat, Arvicanthis niloticus in the Ferlo, particularly on the IRP quadrat of Fété-Olé. In Northern Senegal the Nile rat lives permanently only in the more humid and cultivated areas, and around human settle ments. Here, their numbers most likely began to increase after the 1974 rains, following the severe 1972-1973 drought. As in the other species of rodents, this situation led to a lengthening of the breeding season and an increased fecundity among the Nile rats which started invading the sahelian savanna in June-July 1975. During the 1975 rains the rat invaders started to breed again and the subsequent population increase led to the 1975-1976 outbreak. The Nile rat pullulation came to its end at the close of the next dry season, in April-May 1977. The living conditions of Arvicanthis niloticus in the sahelian savanna are described. The rats settled mostly in the more den sely wooded depressions between fossil dunes, where temporary pools occur after the rains. Here they became active by day and foraged in trees and bushes. They ate shoots and bark, mostly from Acacia Senegal and Commiphora africana, and shoots, leaves, flowers, fruits and bark of Balanites aegyptiaca. The highest densities were estimated to be close to 100 Nile rats/ha in February 1976, and the lowest 17.5 rats/ha in June 1976. Population numbers, early in 1977, did not exceed 35.1 Nile rats/ha. The study of Arvicanthis niloticus population structure and dynamics suggests that the species’ prospects of settling perma nently in the sahelian savanna are poor. The breeding season of the species is short (5 months) and the population turnover rapid (average life expectancy : 9 months). A high predation pressure and a shortage of food and water may be held responsible for the inability of the species to colonize permanently the sahelian savanna. The trophic impact of the Nile rat outbreak upon the tree stratum of the Fété-Olé IBP quadrat has been estimated. During the 1975-1976 dry season, 97 % of the Commiphora africana shoots were destroyed. As for Acacia senegal, 80 % of the trees were damaged in 1975-1976, and 33 % in 1976-1977

Sensitivity to CPT-11 of xenografted human colorectal cancers as a function of microsatellite instability and p53 status

Biological parameters influencing the response of human colorectal cancers (CRCs) to CPT-11, a topoisomerase 1 (top1) inhibitor, were investigated using a panel of nine CRCs xenografted into nude mice. CRC xenografts differed in their p53 status (wt or mut) and in their microsatellite instability phenotype (MSI+when altered). Five CRC xenografts were established from clinical samples. All five had a functional p53, two were MSI+and three were MSI–. Tumour-bearing nude mice were treated intraperitonealy (i.p.) with CPT-11. At 10 mg kg–1of CPT-11, four injections at 4-day intervals, four of the five xenografts responded to CPT-11 (growth delay of up to 10 days); the non-responder tumour was MSI−. At 40 mg kg−1of CPT-11, six injections at 4-day intervals, the five CRCs displayed variable but marked responses with complete regressions. In order to assess the role of p53 status in CPT-11 response, four CRC lines were used. HT29 cell line was MSI−/ Ala273-mutp53, its subclone HT29A3 being transfected by wtp53. LoVo cell line was MSI+/ wtp53, its subclone X17LoVo dominantly expressed Ala273-mutp53 after transfection. LoVo tumours (MSI+/ mutp53) were more sensitive than X17LoVo (MSI+/ mutp53. HT 29 tumours (MSI−Imutp53), were refractory to CPT-11 while HT29A3 tumours (MSI−/ wtp53) were sensitive, showing that wtp53 improves the drug-response in these MSI−tumours. Levels of mRNA expression of top1, fasR, TP53 and mdr1 were semi-quantified by reverse transcription polymerase chain reaction. None of these parameters correlated with CPT-11 response. Taken together, these observations indicate that MSI and p53 alterations could be associated with different CPT-11 sensitivities; MSI phenotype moderately influences the CPT-11 sensitivity, MSI+being more sensitive than MSI−CRC freshly obtained from patients, mutp53 status being associated with a poor response to CPT-11. © 2000 Cancer Research Campaig

Comparative study of MRI biomarkers in the substantia nigra to discriminate idiopathic Parkinson disease

BACKGROUND AND PURPOSE: Several new MR imaging techniques have shown promising results in patients with Parkinson disease; however, the comparative diagnostic values of these measures at the individual level remain unclear. Our aim was to compare the diagnostic value of MR imaging biomarkers of substantia nigra damage for distinguishing patients with Parkinson disease from healthy volunteers. MATERIALS AND METHODS: Thirty-six patients and 20 healthy volunteers were prospectively included. The MR imaging protocol at 3T included 3D T2-weighted and T1-weighted neuromelanin-sensitive images, diffusion tensor images, and R2* mapping. T2* high-resolution images were also acquired at 7T to evaluate the dorsal nigral hyperintensity sign. Quantitative analysis was performed using ROIs in the substantia nigra drawn manually around the area of high signal intensity on neuromelanin-sensitive images and T2-weighted images. Visual analysis of the substantia nigra neuromelanin-sensitive signal intensity and the dorsolateral nigral hyperintensity on T2* images was performed. RESULTS: There was a significant decrease in the neuromelanin-sensitive volume and signal intensity in patients with Parkinson disease. There was also a significant decrease in fractional anisotropy and an increase in mean, axial, and radial diffusivity in the neuromelanin-sensitive substantia nigra at 3T and a decrease in substantia nigra volume on T2* images. The combination of substantia nigra volume, signal intensity, and fractional anisotropy in the neuromelanin-sensitive substantia nigra allowed excellent diagnostic accuracy (0.93). Visual assessment of both substantia nigra dorsolateral hyperintensity and neuromelanin-sensitive images had good diagnostic accuracy (0.91 and 0.86, respectively). CONCLUSIONS: The combination of neuromelanin signal and volume changes with fractional anisotropy measurements in the substantia nigra showed excellent diagnostic accuracy. Moreover, the high diagnostic accuracy of visual assessment of substantia nigra changes using dorsolateral hyperintensity analysis or neuromelanin-sensitive signal changes indicates that these techniques are promising for clinical practice

Biliary Bicarbonate Secretion Constitutes a Protective Mechanism against Bile Acid-Induced Injury in Man

Background: Cholangiocytes expose a striking resistance against bile acids: while other cell types, such as hepatocytes, are susceptible to bile acid-induced toxicity and apoptosis already at micromolar concentrations, cholangiocytes are continuously exposed to millimolar concentrations as present in bile. We present a hypothesis suggesting that biliary secretion of HCO(3)(-) in man serves to protect cholangiocytes against bile acid-induced damage by fostering the deprotonation of apolar bile acids to more polar bile salts. Here, we tested if bile acid-induced toxicity is pH-dependent and if anion exchanger 2 (AE2) protects against bile acid-induced damage. Methods: A human cholangiocyte cell line was exposed to chenodeoxycholate (CDC), or its glycine conjugate, from 0.5 mM to 2.0 mM at pH 7.4, 7.1, 6.7 or 6.4, or after knockdown of AE2. Cell viability and apoptosis were determined by WST and caspase-3/-7 assays, respectively. Results: Glycochenodeoxycholate (GCDC) uptake in cholangiocytes is pH-dependent. Furthermore, CDC and GCDC (pK(a) 4-5) induce cholangiocyte toxicity in a pH-dependent manner: 0.5 mM CDC and 1 mM GCDC at pH 7.4 had no effect on cell viability, but at pH 6.4 decreased viability by >80% and increased caspase activity almost 10- and 30-fold, respectively. Acidification alone had no effect. AE2 knockdown led to 3- and 2-fold enhanced apoptosis induced by 0.75 mM CDC or 2 mM GCDC at pH 7.4. Discussion: These data support our hypothesis of a biliary HCO(3)(-) umbrella serving to protect human cholangiocytes against bile acid-induced injury. AE2 is a key contributor to this protective mechanism. The development and progression of cholangiopathies, such as primary biliary cirrhosis, may be a consequence of genetic and acquired functional defects of genes involved in maintaining the biliary HCO(3)(-) umbrella. Copyright (C) 2011 S. Karger AG, Base

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

Disruption of Conscious Access in Psychosis Is Associated with Altered Structural Brain Connectivity

According to global neuronal workspace (GNW) theory, conscious access relies on long-distance cerebral connectivity to allow a global neuronal ignition coding for conscious content. In patients with schizophrenia and bipolar disorder, both alterations in cerebral connectivity and an increased threshold for conscious perception have been reported. The implications of abnormal structural connectivity for disrupted conscious access and the relationship between these two deficits and psychopathology remain unclear. The aim of this study was to determine the extent to which structural connectivity is correlated with consciousness threshold, particularly in psychosis. We used a visual masking paradigm to measure consciousness threshold, and diffusion MRI tractography to assess structural connectivity in 97 humans of either sex with varying degrees of psychosis: healthy control subjects (n = 46), schizophrenia patients (n = 25), and bipolar disorder patients with (n = 17) and without (n = 9) a history of psychosis. Patients with psychosis (schizophrenia and bipolar disorder with psychotic features) had an elevated masking threshold compared with control subjects and bipolar disorder patients without psychotic features. Masking threshold correlated negatively with the mean general fractional anisotropy of white matter tracts exclusively within the GNW network (inferior frontal-occipital fasciculus, cingulum, and corpus callosum). Mediation analysis demonstrated that alterations in long-distance connectivity were associated with an increased masking threshold, which in turn was linked to psychotic symptoms. Our findings support the hypothesis that long-distance structural connectivity within the GNW plays a crucial role in conscious access, and that conscious access may mediate the association between impaired structural connectivity and psychosis

A Collaborative Filtering Approach for Protein-Protein Docking Scoring Functions

A protein-protein docking procedure traditionally consists in two successive tasks: a search algorithm generates a large number of candidate conformations mimicking the complex existing in vivo between two proteins, and a scoring function is used to rank them in order to extract a native-like one. We have already shown that using Voronoi constructions and a well chosen set of parameters, an accurate scoring function could be designed and optimized. However to be able to perform large-scale in silico exploration of the interactome, a near-native solution has to be found in the ten best-ranked solutions. This cannot yet be guaranteed by any of the existing scoring functions