Showing papers by "Aix-Marseille University published in 1997"

Search for neutral heavy leptons produced in Z decays

Abstract: Weak isosinglet Neutral Heavy Leptons (m) have been searched for using data collected by the DELPHI detector corresponding to 3:3 106 hadronic Z0 decays at LEP1. Four separate searches have been performed, for short-lived m production giving monojet or acollinear jet topologies, and for long-lived m giving detectable secondary vertices or calorimeter clusters. No indication of the existence of these particles has been found, leading to an upper limit for the branching ratio BR(Z0 ! m) of about 1:310−6 at 95% confidence level for m masses between 3.5 and 50 GeV/c2. Outside this range the limit weakens rapidly with the m mass. The results are also interpreted in terms of limits for the single production of excited neutrinos.

Neurosteroids: deficient cognitive performance in aged rats depends on low pregnenolone sulfate levels in the hippocampus.

Abstract: Pregnenolone sulfate (PREG S) is synthesized in the nervous system and is a major neurosteroid in the rat brain. Its concentrations were measured in the hippocampus and other brain areas of single adult and aged (22-24 month-old) male Sprague-Dawley rats. Significantly lower levels were found in aged rats, although the values were widely scattered and reached, in about half the animals, the same range as those of young ones. The spatial memory performances of aged rats were investigated in two different spatial memory tasks, the Morris water maze and Y-maze. Performances in both tests were significantly correlated and, accompanied by appropriate controls, likely evaluated genuine memory function. Importantly, individual hippocampal PREG S and distance to reach the platform in the water maze were linked by a significant correlation, i.e., those rats with lower memory deficit had the highest PREG S levels, whereas no relationship was found with the PREG S content in other brain areas (amygdala, prefrontal cortex, parietal cortex, striatum). Moreover, the memory deficit of cognitively impaired aged rats was transiently corrected after either intraperitoneal or bilateral intrahippocampal injection of PREG S. PREG S is both a gamma-aminobutyric acid antagonist and a positive allosteric modulator at the N-methyl-D-aspartate receptor, and may reinforce neurotransmitter system(s) that decline with age. Indeed, intracerebroventricular injection of PREG S was shown to stimulate acetylcholine release in the adult rat hippocampus. In conclusion, it is proposed that the hippocampal content of PREG S plays a physiological role in preserving and/or enhancing cognitive abilities in old animals, possibly via an interaction with central cholinergic systems. Thus, neurosteroids should be further studied in the context of prevention and/or treatment of age-related memory disorders.

Clearance of tissue plasminogen activator (TPA) and TPA/plasminogen activator inhibitor type 1 (PAI-1) complex relationship to elevated TPA antigen in patients with high PAI-1 activity levels

Abstract: Background To evaluate the effect of plasminogen activator inhibitor type 1 (PAI-1) levels on the clearance of total tissue plasminogen activator (TPA) antigen, we studied the clearance of active TPA and TPA/PAI-1 complex in subjects with low (181±109 pmol/L; n=7) and high (1166±322 pmol/L; n=4) baseline active PAI-1. Methods and Results A 5-μg/kg bolus of TPA was infused over a 15-second period followed by measurement of TPA activity, TPA antigen, TPA/PAI-1, TPA/C1 inhibitor, PAI-1 activity, and PAI-1 antigen over a 4-hour period. α-Phase clearance of total TPA antigen was faster in subjects with low PAI-1 (t1/2 of 3.5±0.7 minutes) versus high PAI-1 (t1/2 of 5.3±0.9 minutes) (P=.006). Clearance of all factors was best fit by a two-compartment pharmacokinetic model based on a computer-simulated human circulatory system. The average hepatic clearance fraction in the two-compartment model was greater for active TPA (89±10%, t1/2 of 2.4±0.3 minutes) than for TPA/PAI-1 complex (48±17%, t1/2 of 5.0±1.8 minutes...

On the Use of Banks Balance Sheet Data in Loan Market Studies: A Note

Abstract: Due to the unobservability of the new credit production, most of the empirical loan market studies use, instead, the observable credit stock. This substitution has been pointed out to be likely to generate biases (e.g. see Lown and Peristiani (1996)). In this paper, we show that under quite unrestrictive conditions, this substitution does not lead to biased estimates of any log-log model coefficients, as long as banks panel data is used and fixed effects are included in the estimated equation.

Research Strategies in Dendroecology and Dendroclimatology in Mountain Environments

Abstract: Tree-ring series from living trees near the timberline or timbers buried in the surroundings are exceptionally valuable both for climate reconstruction and investigations of the consequences of climate change to ecosystems. This paper is a critical assessment of the past and potential contributions of dendroecology and dendroclimatology in mountain environments. Problems addressed are the spatial variability of both climate and tree sites, the temporal variability of ecological growth conditions and the reconstruction of signals other than high frequency ones. A synoptic approach appears to be the only way to take into account both the spatial and temporal variability of tree-growth, allowing for a better comparison of spatial climatological patterns with spatial growth patterns.

Microinfusion of the metabotropic glutamate receptor agonist 1S,3R-1-aminocyclopentane-1,3-dicarboxylic acid into the nucleus accumbens induces dopamine-dependent locomotor activation in the rat.

Abstract: Although the striatum has one of the highest densities of metabotropic glutamate receptor (mGluR) binding sites in the brain, little is known about their physiological role. In this study we characterized the contribution of mGluRs located in the ventral part of the striatum (the nucleus accumbens) to the control of extrapyramidal motor function. Activation of mGluRs by local infusion of the selective agonist 1S,3R-1-aminocyclopentane-1,3-dicarboxylic acid (1S,3R-ACPD; 25, 50 and 100 nmol/0.5 microl) into the nucleus accumbens induced a dose-dependent increase in locomotor activity in rats. Intra-accumbens infusion of a selective antagonist of mGluRs, alpha-methyl-4-carboxyphenylglycine (MCPG) did not modify spontaneous locomotion but decreased the locomotor response to 1S,3R-ACPD. This effect appeared to be mediated by dopamine, since blockade of dopamine receptors with haloperidol (0.05 and 0.1 mg/kg i.p.) dose-dependently reduced 1S,3R-ACPD-induced locomotor activation. Furthermore, D-amphetamine (0.5 mg/kg, i.p.) combined with intra-accumbens infusion of 1S,3R-ACPD (100 nmol) potentiated the locomotor hyperactivity response to a higher level than that seen with a single treatment with either drug. In contrast, D-amphetamine-induced hypermotility was abolished by infusion of MCPG (100 nmol) into the nucleus accumbens. These results demonstrate that glutamate may control extrapyramidal motor function through metabotropic receptors. Furthermore, activation of metabotropic glutamate receptors appears to act in synergy with the dopamine system at the level of the nucleus accumbens to produce a motor stimulant response.

Natural killer cell acceptance of H-2 mismatch bone marrow grafts in transgenic mice expressing HLA-Cw3 specific killer cell inhibitory receptor (CD158b)

Abstract: Natural killer (NK) cells express killer cell inhibitory receptors (KIRs) for major histocompatibility complex class I molecules. Engagement of these surface receptors inhibits NK cell cytotoxic programs. KIR can also be expressed on T cell subsets, and their engagement similarly results in inhibition of effector functions initiated by the CD3/T cell receptor complex. KIR genes belong to two distinct families: the immunoglobulin superfamily (IgSF KIRs) and dimeric C2 lectins (lectin-like KIRs). Whereas both IgSF (p58: CD158, p70, and p140) and lectin-like KIRs (CD94/NKG2A heterodimers) have been found in human, only lectin-like KIRs (all members of the Ly-49 family) have been described in the mouse. We have generated transgenic mice expressing an IgSF KIR, CD158b (p58.2), which recognizes HLA-Cw3. Our data show that CD158b is necessary and sufficient to confer specificity to NK cells, as well as to modulate T cell activation programs in vitro. In addition, we did not detect any adaptation of CD158b cell surface expression to that of HLA class I ligands in the CD158b × HLA-Cw3 double transgenic mice, in contrast to observations with Ly-49 in the mouse. Therefore, distinct strategies of selection/calibration appear to be used by IgSF and lectin-like KIRs. Finally, the transgenic expression of CD158b KIR prevents the in vivo rejection of H-2 mismatch bone marrow grafts, which express the cognate major histocompatibility class I HLA-Cw3 allele, demonstrating for the first time the in vivo implication of human IgSF KIRs in the negative regulation of NK cell function.

Three-dimensional modeling of an activated sludge floc

Abstract: A new interpolation method called discrete smooth interpolation was used to construct a 3-D model of an activated sludge floc from digitized microtome sections. This method comprises several advantages: rapidity, almost completely automated, precision, high quality of representation, and, most importantly, availability of specific tools to manipulate the 3-D model. Some parameters of the floc such as the size, the surface area, and the volume were directly measured on the 3-D reconstructed object. The contour and surface are fractal with fractal dimensions of 1.4 and 2.4, respectively. Local curvatures were also calculated and show great deformations of the surface due to anisotropic growth within the floc. Discrete smooth interpolation constitutes a powerful tool to improve the understanding of the floc structure complexity.

Thiocyanatodioxomolybdenum(VI) complexes as eficient oxidizing agents

Abstract: The reaction of [(SCN) 4 Mo VI O 2 ][PPh 4 ] 2 with bipyridine leads to neutralization of the complex by loss of two moles of [SCN][PPh 4 ] and complexation of bipyridine, but was immediately followed by oxo-ligand redistribution resulting in the formation of oligomeric products. The use of 4,4'-di-t-butyl-2,2'-bipyridine slows down significantly this redistribution reaction and allows the isolation of the desired complex dioxodithiocyanato-4,4'-di-t-butyl-2,2'bipyridylmolybdenum(VI) (6). Compound (6) crystallizes in the orthorhombic group PNMA (#32) with a=15.793(2) A. b = 13.914(2) A, C = 10.658(3) A. Full-matrix least-squares refinement converged at R = 4.8% and R w = 5.5%. The reactivity of (6) was studied as an oxygen atom transfer agent towards phosphines, alcohols and arylalkanes under stoichiometric and catalytic conditions, using DMSO as the oxo-donor reactant.

Etude preliminaire des micromammiferes de la Baume Moula-Guercy a Soyons (Ardeche, France). Systematique, biostratigraphie et paleoecologie

Abstract: Les fouilles realisees depuis 1992 dans la Baume Moula-Guercy a Soyons (Ardeche, France) ont livre un tres grand nombre de restes de micromammiferes (insectivores, chiropteres, rongeurs et lagomorphes) se rapportant a plus de 3 000 individus et a 49 especes. L'etude des especes presentant une evolution durant le Quaternaire permet d'attribuer la sequence stratigraphique aux stades 6, 5 et 4 de la chronologie isotopique marine. L'analyse des proportions relatives des rongeurs regroupes en categories climato-ecologiques et l'etude de la communaute mammalienne (methode des cenogrammes) mettent en evidence des variations importantes du climat et des environnements qui individualisent quatre phases climatiques principales. L'abondance de la documentation et la grande variete des taxons identifies, uniques en France, font de la Baume Moula-Guercy un site de reference pour l'etude de la transition entre le Pleistocene moyen et le Pleistocene superieur en Europe occidentale.

Neural crest-like cells originate from the spinal cord during tail regeneration in adult amphibian urodeles.

Abstract: Using in vitro cell-marking experiments and transplantation in tail regenerates, we have recently shown (Benraiss et al., 1996) that clonal cells derived from adult newt spinal cord (SC) cultures could find suitable cues in blastemal mesenchyme to enable them to differentiate into melanocytes or Schwann cells. This led to the question of whether neural crest-like cell derivatives might emerge from the ependymal tube as tail regeneration proceeded. To address this question we used the biolistic method for in situ transfection of caudal SC cells. These cells were transfected with an alkaline phosphatase marker gene. The potentialities of transfected cell derivatives in tail regenerates were analyzed using histochemistry or immunohistochemistry. As early as eight days after transfection, labeled cells were detected in the regenerating SC and around its "terminal vesicle" (TV). Two to four weeks following transfection, most of the labeled cell derivatives could be identified either by dark granules as melanocytes or by galactocerebroside staining as Schwann cells. Electron microscopic investigations revealed the incompletely organized cytoarchitecture of the TV, suggesting that an exit of cells was possible at this level, at least from its "open" dorsal part. Furthermore, the localization of ciliated cells in the blastemal mesenchyme, especially around the TV, supported this view by suggesting that they might be ependymal cells detached from it. Our findings therefore led us to believe that in the newt, during tail regeneration, neural crest-like cells emerging from the TV could participate in the formation of the peripheral nervous system, especially by providing Schwann cells and melanocytes.

Physico-chemistry and cytotoxicity of ceramics: part I: characterization of ceramic powders.

Abstract: The morphology of Al2O3, ZrO2/Y2O3, AIN, B4C, BN, SiC, Si3N4, TiB2, TiC, TiN ceramic, graphite and diamond powders has been studied by scanning electron microscopy (SEM) and the specific area of each powder was determined with the BET method. X-ray diffraction (XRD) investigations have been carried out in order to evaluate the crystallinity and determine the constitutive phases. The chemical composition was assessed by classical chemical analyses and by X-ray microprobe; some powders were studied by the laser micro-Raman technique. Correlations have been established between all these results.

Nutrients limiting the algal growth potential (AGP) in the Po River plume and an adjacent area, northwest Adriatic Sea: enrichment bioassays with the test algae Nitzschia closterium and Thalassiosira pseudonana

Abstract: From April 1993 to March 1994, 135 samples were collected at two sites in the coastal Adriatic Sea, both near (14.5 km) and far (63 km) from the Po River delta. The nutrient(s) limiting algal growth potential (AGP) were estimated by bioassay usingNitzshia closterium (local isolate) andThalassiosira pseudonama (strain 3-H). Estimates were also made by comparing the nutrient molar ratios, ΣN:P and ΣN:Si (whereΣN=NO3 −+NO2 −+NH4 ++urea), to the Redfield Ratio (16∶1, 1∶1). According to the bioassay results, phosphorus was the sole nutrient limiting AGP in 2% of the samples and was the most limiting nutrient in 69% of the samples; nitrogen was sole limiting nutrient in 18% of the samples. In 11% of samples, nitrogen and phosphorus were equally co-limiting. Omission of phosphorus from spike enrichments allowed, on average, only a 1.6-fold increase in biomass over that in the unenriched controls. Similar omission of nitrogen allowed a 4-fold increase, while silicon, iron, and micronutrients resulted in 14-fold, 18-fold, and >20-fold increases, respectively. In most of the samples, ΣN:P was much greater than 16, indicating a marked phosphorus deficiency, while ΣN:Si values suggested that silicon was the third most limiting nutrient in 35% of samples. In water collected for from the Po delta, the yield ofN. closterium was not limited by any nutrients other than the three major ones: P, N and Si. In these same waters,T. pseudonana was also potentially limited by iron and, to a lesser extent, by vitamins. The role of iron varied. In samples collected near the Po delta, iron acted as the third most limiting nutrient forN. closterium in June and September; it appeared 29 times out of 78 on the list of potentially limiting nutrients forT. pseudonana, including 5 times as the most limiting. Altogether, comparison with published results suggests that the roles of iron and silicon in AGP limitation have increased during the past three decades, and could become even more important if eutrophication in the Adriatic Sea continues to increase.

A variational principle for two-fluid models

Abstract: A variational principle for two-fluid homogeneous mixtures is proposed. The Lagrangian is constructed as the difference between the kinetic energy of the mixture and a thermodynamic potential conjugated to the internal energy with respect to the relative velocity of phases. The equations of motion and a set of Rankine-Hugoniot conditions are obtained. It is proved also that the convexity of the internal energy guarantees the hyperbolicity of the one-dimensional equations of motion linearized at rest.

SYNTHESIS AND CYCLIZATION OF PHOSPHORYLATED β-ALLENIC AMINES

Abstract: Phosphorylated β-allenic amines were obtained by aminophosphorylation of β-allenic aldehydes and ketones. When treated by silver tetrafluoroborate in methylene chloride, they generated phosphorylated nitrogen cycles such as 1-pyrrolines and 1,2,3,6-tetrahydropyridines, with dephosphorylation of the latter tetrahydropyridines producing 3,6-dihydropyridines.