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Biomedical subjects

B Rousseau

Publications and source records attributed to B Rousseau.

At least 19 recordsLinked to original sources
PubMed2005

Quantitative and qualitative evaluation of phytoplankton communities by trichromatic chlorophyll fluorescence excitation with special focus on cyanobacteria.

We present results that were obtained with a newly developed fluorometer, the 'PhytoSensor'. They are based on multi-wavelength excitation of chlorophyll fluorescence to detect the phytoplankton biomass and to identify main taxons (among cyanobacteria, green and brown microalgae). A method to evaluate the photosynthetic potential of the phytoplankton was established. Attention was focused on the measurement of the cyanobacterial biomass. A modelling to distinguish between the two spectral groups (blue and red) of cyanobacteria as a function of their pigments and physiological status is proposed. The main innovation of the device results in the recording of the fluorescence induction kinetics of the phytoplankton to confirm and refine the evaluation of the taxonomic composition. The PhytoSensor abilities were compared with pigment analysis, commercial fluorometers, particle and microscopic counting and identification. The PhytoSensor has been used with success to monitor the dynamics of phytoplankton in drinking-water supply reservoirs in Southeast Asia.

Asia↗
PubMed2004

Dissipative particle dynamics simulations of polymer melts. I. Building potential of mean force for polyethylene and cis-polybutadiene.

We present the derivation of coarse-grained force fields for two types of polymers, polyethylene (PE), and cis-polybutadiene (cis-PB), using the concept of potential of mean force. Coarse-grained force fields were obtained from microscopic simulations for several coarse-graining levels, i.e., different number of monomers lambda per mesoscopic unit called "bead." These force fields are then used in dissipative particle dynamics (DPD) simulations to study structural and dynamical properties of polymer melts of PE and cis-PB. The radial distribution functions g(R), the end-to-end distance R0, the end-to-end vector relaxation time tau, and the chain center of mass self-diffusion D(CM), are computed for different chain lengths at different coarse-graining factor lambda. Scaling laws typical of the Rouse regime are obtained for both polymers for chain lengths ranging from 6 to 50 beads. It is found that the end-to-end distance R0 obtained from DPD simulations agree well with values obtained from both microscopic simulations and experiments. The dependence of the friction coefficient used in DPD simulations versus the coarse-graining level is discussed in view of the overall scaling of the dynamical properties.

Journal Article↗
PubMed2002

Soret coefficient for liquid argon-krypton mixtures via equilibrium and nonequilibrium molecular dynamics: a comparison with experiments.

The Soret and the other transport coefficients, characterizing the heat and mass transport in binary mixtures, have been obtained by equilibrium and nonequilibrium molecular dynamics (EMD and NEMD, respectively). Two state points of the argon-krypton mixture are considered, for which experimental values of the Soret coefficient are available. To attempt a comparison between simulations and experiments the common enthalpy-diffusion-free expression for the heat flux has been chosen. The comparison of the simulations with the experiments shows a remarkable agreement, for all the several utilized EMD and NEMD techniques (dynamical and stationary). The techniques, used over 0.3 micros of total simulation time span, are slow convergent but have comparable performances.

Journal Article↗
PubMed2002

In diatoms, a transthylakoid proton gradient alone is not sufficient to induce a non-photochemical fluorescence quenching.

Non-photochemical fluorescence quenching (NPQ) in diatoms is associated with a xanthophyll cycle involving diadinoxanthin (DD) and its de-epoxidized form, diatoxanthin (DT). In higher plants, an obligatory role of de-epoxidized xanthophylls in NPQ remains controversial and the presence of a transthylakoid proton gradient (DeltapH) alone may induce NPQ. We used inhibitors to alter the amplitude of DeltapH and/or DD de-epoxidation, and coupled NPQ. No DeltapH-dependent quenching was detected in the absence of DT. In diatoms, both DeltapH and DT are required for NPQ. The binding of DT to protonated antenna sites could be obligatory for energy dissipation.

Chlorophyll↗
PubMed2001

Systematic intensity errors caused by spectral truncation: origin and remedy.

The wavelength dispersion of graphite(002)-monochromated X-ray beams has been determined for a Cu, a Mo and an Rh tube. The observed values for Deltalambda/lambda were 0.03, 0.14 and 0.16, respectively. The severe reduction in monochromaticity as a function of wavelength is determined by the absorption coefficient mu of the monochromator. Mu(monochromator) varies with lambda3. For an Si monochromator with its much larger absorption coefficient, Deltalambda/lambda values of 0.03 were found, regardless of the X-ray tube. This value matches a beam divergence defined by the size of the focus and of the crystal. This holds as long as the monochromator acts as a mirror, i.e. mu(monochromator) is large. In addition to monochromaticity, homogeneity of the X-ray beam is also an important factor. For this aspect the mosaicity of the monochromator is vital. In cases like Si, in which mosaicity is practically absent, the reflected X-ray beam shows an intensity distribution equal to the mass projection of the filament on the anode. Smearing by mosaicity generates a homogeneous beam. This makes a graphite monochromator attractive in spite of its poor performance as a monochromator for lambda < 1 A. This choice means that scan-angle-induced spectral truncation errors are here to stay. These systematic intensity errors can be taken into account after measurement by a software correction based on the real beam spectrum and the applied measuring mode. A spectral modeling routine is proposed, which is applied on the graphite-monochromated Mo Kalpha beam. Both elements in that spectrum, i.e. characteristic alpha1 and alpha2 emission lines and the Bremsstrahlung, were analyzed using the 6,3,18 reflection of Al2O3 (s = 1.2 A(-1)). The spectral information obtained was used to calculate the truncation errors for intensities measured in an omega/2theta scan mode. The results underline the correctness of previous work on the structure of NiSO4*6H2O [Rousseau, Maes & Lenstra (2000). Acta Cryst. A56, 300-307].

Journal Article↗
PubMed2001

A Thurstonian model for the dual pair (4IAX) discrimination method.

In the dual pair method, the subject is presented with two stimuli in two pairs: One pair is composed of two samples of the same stimulus; the other pair is composed of two samples of different stimuli, one being the same as that in the identical pair. The task of the judge is to select the most different pair. The psychometric function for the dual pair method is derived and expressed in terms of a singly noncentral beta distribution. A table is provided that connects a measure of the degree of difference, d, to the probability of a correct response. This table assumes an unbiased observer and differencing decision rule. A table is provided to give an estimate of the variance of d , the experimental estimate of d. The power of the dual pair method is also investigated, and a formula to determine the sample size required to meet Type I and Type II error specifications is given. The dual pair method appears to be slightly less powerful than the duo-trio and the triangular methods. Experimental investigation is needed to explore the dual pair in applied research work.

Decision Making↗
PubMed2001

[Rehabilitation after anterior cruciate ligament reconstruction: inpatient or outpatient rehabilitation? A series of 103 patients].

PURPOSE OF THE STUDY: The goal of this work was to evaluate outpatient rehabilitation after anterior curciate ligament reconstruction using the bone-tendon technique. MATERIAL AND METHODS: This was a prospective non-randomized study of 103 consecutive patients participating in the same rehabilitation program, excepting for the first month. During the first postoperative month, 55 patients (group A) attended a physical therapy outpatient clinic near their home and 48 patients (group B) followed the same rehabilitation protocol at an inpatient facility of their choice. We recorded preoperative data for age, sex, weight, height and function (sports, occupational activities). Surgery data concerned delay between severe sprain and surgery, and the exact surgical procedure used (meniscal tear, associated procedure). Clinical assessment (mobility, effusion, clinical and radiological laxity) and functional scores (Tegner, Lysholm, Arpege, IKDC) as well as delay to recovery of gait and to renewed physical activity were recorded at 3 and 6 weeks and 4, 6 and 12 months postoperatively. Two isokinetic tests were done 4 and 6 months postoperatively. RESULTS: There was no statistical difference for the pre and peroperative data between the two groups, with the exception of meniscal tears that were more frequent in group A (p<0.05). Postoperative outcome and complications were not significantly different between the 2 groups except for greater flexion at 3 weeks in group B (related to difference in measurement date). Fifteen complications were observed in each group: 4 reflex dystrophies and 2 cyclope syndromes in each group, 5 patellar syndromes in group A and 1 in group B; 3 painful surgical wound sites in group A and 8 in group B (including one requiring revision). In group A there was one early failure due to a surgical error requiring revision. At 1 year, there were 2 cases of persistent femoropatellar syndromes, one of which occurred after reflex dystrophy. A high percentage of the patients were lost to follow-up (45% in group A and 50% in group B) and lack of randomization should also be considered when interpreting the results. DISCUSSION: This is the first report comparing inpatient and outpatient rehabilitation protocols after anterior cruciate ligament reconstruction. The only reports in the literature have compared different ambulatory rehabilitation programs that appear to be internationally accepted as the routine procedure. The current trend towards short hospital stays for surgery is compatible with outpatient rehabilitation programs if dependent patients receive proper support from an ambulatory medical unit, a physical therapist or a home assistant. Our study demonstrated that the bone-tendon technique for anterior cruciate ligament reconstruction is compatible with an outpatient rehabilitation program if quality medical and surgical follow-up is ensured. This type of rehabilitation program gives results comparable with those obtained after inpatient programs conducted in a rehabilitation facility during the first postoperative month.

Activities of Daily Living↗
PubMed2000

Consequences of affinity in heterogeneous catalytic reactions: highly chemoselective hydrogenolysis of iodoarenes

The catalytic hydrodeiodination reaction using molecular hydrogen and Pd/C has been revisited. It is shown, for the first time, that the chemoselectivity of this reaction is controlled by the high affinity of the iodinated compound for the catalyst. This reaction is compatible with most easily reducible functional groups (nitro, aldehyde, olefin, etc.). Using this reaction, the first general method for tritium labeling of 3-(trifluoromethyl)-3-phenyldiazirine is described.

Journal Article↗
PubMed2000

Uptake of the nitroimidazole drug megazol by African trypanosomes.

Megazol, CL 64,855 (2-amino-5-[1-methyl-5-nitro-2-imidazolyl]-1,3, 4-thiazole) has been shown to be extremely effective in clearing experimental infections of African trypanosomes. An unusual amino-purine transporter termed P2, implicated in the transport of both the diamidine and melaminophenyl arsenical classes of drug in Trypanosoma brucei, recognised chemical groups on compounds which are also present on megazol. Megazol interacted with this carrier protein, as judged by its ability to inhibit P2 adenosine transport and to abrogate in vitro arsenical-induced lysis in a dose-dependent manner. However, parasites resistant to melaminophenyl arsenical and diamidine drugs due to lack of the P2 transporter showed no resistance to megazol. This is because passive diffusion represented the major route of entry. Initial rates of uptake were not saturable within the limit of megazol's solubility and did not conform to thermodynamic precepts compatible with carrier-mediated uptake. Adenosine and other P2 transporter substrates, even at high concentration, had little impact on megazol uptake. Uptake was biphasic, with a very rapid equilibration across the membrane followed by a slower accumulation over time. The equilibration phase represented a simple passive diffusion, with the subsequent uptake probably being due to metabolism of the drug.

Africa↗
PubMed2000

Active-site-directed photolabeling of the melibiose permease of Escherichia coli.

Covalent photolabeling of the melibiose permease (MelB) of Escherichia coli has been undertaken with the sugar analogue [(3)H]-p-azidophenyl alpha-D-galactopyranoside ([(3)H]-alpha-PAPG) with the purpose of identifying the domains forming the MelB sugar-binding site. We show that alpha-PAPG is a high-affinity substrate of MelB (K(d) = 1 x 10(-)(6) M). Its binding to or transport by MelB is Na-dependent and is competitively prevented by melibiose or by the high-affinity ligand p-nitrophenyl alpha-D-galactopyranoside (alpha-NPG). Membrane vesicles containing overexpressed histidine-tagged recombinant MelB were photolabeled in the presence of [(3)H]-alpha-PAPG by irradiation with UV light (lambda = 250 nm). Eighty-five percent of the radioactivity covalently associated with the vesicles was incorporated in a polypeptide corresponding to MelB monomer. MelB labeling was completely prevented by an excess of melibiose or alpha-NPG during the assay. Radioactivity analysis of CNBr cleavage or limited proteolysis products of the purified [(3)H]-alpha-PAPG-labeled transporter suggests that several domains of MelB are targets for labeling. One of the labeled CNBr cleavage products is a peptide with an apparent molecular mass of 5.5 kDa. It is shown that (i) its amino acid sequence is that of the Asp124-Met181 domain of MelB (7.5 kDa), which includes the cytoplasmic loop 4-5 connecting helices IV and V, the hydrophobic helix V, and the outer loop connecting helices V-VI, and (ii) that Arg141 in loop 4-5 is the only labeled amino acid of this peptide. Labeling of loop 4-5 provides independent evidence that this specific domain plays a significant role in MelB transport. Comparison with the well-characterized equivalent domain of LacY suggests that sugar transporters with similar structure and substrate specificity may have conserved domains involved in sugar recognition.

Amino Acid Sequence↗
PubMed2000

Neural and angiogenic defects in eyes of transgenic mice expressing a dominant-negative FGF receptor in the pigmented cells.

Fibroblast growth factors (FGF) are multipotent cytokines with demonstrated mitogenic, neurotrophic and angiogenic properties. There is evidence that they have multiple functions during and after development of the vertebrate eye. Amongst these, the role of FGF receptor mediated signaling in the retinal pigmented epithelium (RPE) is not yet well understood. FGF-2 is produced in RPE cells and may play a role in photoreceptor development and/or survival in vivo. It may also stimulate growth of melanocytes and angiogenesis in the choroid. To address these questions, we have specifically disrupted FGF signaling by generating lines of transgenic mice expressing dominant-negative FGF receptor 1 (FGFR-1) in the pigmented cells. Histological analysis of the eyes were conducted on hemizygous and homozygous mice at different ages. In homozygotes, eye growth is strongly impaired during embryogenesis leading to massive eye degeneration seen in the early post-natal stages. In hemizygotes, the choroid is thinned and the finger-like junctions between RPE cells and photoreceptors are disrupted. Scanning electron microscopy of the choroid vasculature showed that choriocapillary density, diameter and branching are strongly affected. As mice age, they develop progressive retinal degeneration as evidenced by photoreceptor cell loss. Our results are in agreement with the hypothesis that FGF signaling in the RPE participates in photoreceptor survival in vivo. Our model provides evidence that FGF signaling is also involved in choroidal angiogenesis by a process that could relate to induction of terminal branching.

Animals↗
PubMed2000

The light-harvesting antenna of brown algae: highly homologous proteins encoded by a multigene family.

Accessory light-harvesting complexes (LHCFs) were isolated from the brown alga Laminaria saccharina. Complexes specifically associated with photosystem I or II are identical with each other with respect to molecular mass, isoelectric point and behavior on anion-exchange chromatography or non-denaturing isoelectric focusing. The purified complexes also have similar pigment composition and spectroscopic properties. It is concluded that LHC antennae associated with photosystem I or II cannot be distinguished biochemically. After screening of genomic and cDNA libraries produced from L. saccharina sporophytes, six lhcf genes were isolated. Sequence analysis of these lhcf genes showed a high level of homology between the encoded polypeptides. Comparisons with coding sequences of lhcf genes from Macrocystis pyrifera and expressed sequence tags from Laminaria digitata (two other Laminariales) indicated that these proteins are probably very similar in all brown algae. Another feature common to the lhcf genes characterized was the presence of an intron in the coding region corresponding to the plastid-targeting presequence. The sequence similarity extended to the 5' and 3' UTRs of several genes. In spite of the common origin of the chloroplasts, no light-regulating elements involved in the expression of the genes encoding the higher-plant light-harvesting proteins has been found in the UTRs.

Amino Acid Sequence↗
PubMed2000

Systematic intensity errors and model imperfection as the consequence of spectral truncation

The wavelength dispersion delta lambda/lambda in a graphite (002) monochromated Mo K alpha beam was analyzed. A wavelength window was found with 0.68 < lambda < 0.79 A, i.e. delta lambda/lambda = 0.14. The very large dispersion leads to systematic errors in Iobserved(H) caused by scan-angle-induced spectral truncation. A limit on the scan angle during data collection is unavoidable, in order that an omega/2 theta measurement should not encompass neighboring reflections. The systematic intensity errors increase with the Bragg angle. Therefore they influence the refined X-ray structure by adding a truncational component to the temperature factor: B(X-ray) = B(true) + B(truncation). For an Mo tube at 50 kV, we find B(truncation) = 0.05 A2, whereas a value of 0.22 A2 applies to the same tube but operated at 25 kV. The values of B(truncation) are temperature independent. The model bias was verified via a series of experimental data collections on spherical crystals of nickel sulfate hexahydrate and ammonium hydrogen tartrate. Monochromatic reference structures were obtained via a synchrotron experiment and via a 'balanced' tube experiment.

Journal Article↗
PubMed2000

[A case of Leber's neuroretinitis].

BACKGROUND: Described in 1916 by Theodore Leber, this rare syndrome characterized by low visual acuity, papillary edema, and a macular star (dry exsudates) occurs classically in the 30 to 40 year age range but also as frequently in children. The visual prognosis is excellent. An infectious cause is found in almost all cases. Case report A 34-year-old man consulted for declining visual acuity of the right eye which began suddenly without pain and was preceded by a flu-like syndrome lasting two weeks. Visual acuity on the right side was 2/10 P6, there was optic disk edema associated with dry macular exsudate (macular star) and a paleness of the posterior pole progressing to the periphery and readily visualized on the angiography, and a central scotome, but no dyschromatopsy. The left eye was strictly normal. Laboratory tests showed an erythrocyte sedimentation rate at 45, C reactive protein at 61, normal red cell count and minimal transaminase elevation. Spinal tap showed: 3 elements/mm(3), protein 0.28g/l, 18% gammaglobulins. Serology tests were negative. Brain imaging was normal. RESULTS: Corticosteroid flashes for three days were initiated and the patient was seen again two weeks later with clear clinical improvement. Visual acuity was 6/10 P2 with considerable resorption of the edema. DISCUSSION: This case is a typical illustration of acute Leber's neuroretinititis, probably caused by viral infection. The cerebrospinal fluid tests and brain imaging ruled out multiple sclerosis, and serology tests for syphilis, tuberculosis, Lyme disease and possible parasite infection were negative. CONCLUSION: Acute lever's neuroretinitis is an uncommon condition which must be distinguished from inflammatory optic neuropathy, particularly in multiple sclerosis which has a very different prognosis and clinical course.

Adrenal Cortex Hormones↗