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Biomedical subjects

G Nicolas

Publications and source records attributed to G Nicolas.

At least 19 recordsLinked to original sources
PubMed1992

[Efficacy of antihypertensive treatment in the French population. A multicenter survey].

In order to assess the efficacy of antihypertensive treatment in the population, a study was undertaken in 5 French cities during the commercial fairs of Grenoble, Marseilles, Nice, Toulouse and Lille. The blood pressure was measured according to the WHO recommendations in volunteers. The study included a total of 7107 subjects of both sexes, with 4064 subjects in the 35-64 year age group. The therapeutic efficacy was evaluated in the 791 hypertensive patients who knew their antihypertensive therapy. Taking < 160/95 mmHg as the criterion of efficacy, 52 to 73% of the hypertensive patients were well controlled. However, if the therapeutic objective of normalisation of the blood pressure (BP < 140/90 mmHg) is taken as the criterion of efficacy, only 23 to 29% of the hypertensive patients were controlled whilst their BP remained significantly higher than that of normotensive controls of the same age. The difference in efficacy of antihypertensive therapy between the cities may be explained by the heterogenicity of the populations whereas the treatment did not differ significantly. After adjustment analysis with respect to sex showed that women were better controlled than men whatever the criterion chosen. The group controlled at BP < 160/95 mmHg only differed from the group < 140/90 with respect to the average BP value which was higher before treatment and decreased less with treatment; though this did not achieve statistical significance. In matters of public health, if the ideal blood pressure is taken as < 140/90 mmHg, this study shows that the objective is only attained in one out of four patients in the population studied.

Adult↗
PubMed1991

Advantages of fast-freeze fixation followed by freeze-substitution for the preservation of cell integrity.

The use of fast-freeze fixation (FFF) followed by freeze-substitution (FS) has supplied new data in a variety of domains due to the rapidity of this fixation compared to the slow process of the conventional chemical fixation. FFF completely arrests all the cell's biological reactions, and physically immobilizes most molecules within a few milliseconds. This review deals with the main results we obtained concerning the preservation of organelles particularly sensitive to osmotic shock, the maintenance in situ of soluble or depolymerizable cell components, the visualization of brief transient events, and the opening up of new prospects in the field of immunocytochemical labeling.

Amoeba↗
PubMed1991

Cryo-electron microscopy of vitrified specimens: an approach to the study of bulk specimens.

We are using and developing cryo-electron microscopy of vitrified specimens. Our main interests concern the structure of muscle and muscular components. Micrographs which generally contain periodic features are analyzed by numerical image processing methods. To detect artifacts induced by the electron microscopy techniques, we correlate our results to those obtained by X-ray diffraction. In this paper, we describe our approach to the study of bulk specimens. Vitrification of such specimens is assessed by cryo-X-ray diffraction. Microscopy is done on cryo-substituted specimens.

Animals↗
PubMed1991

Time-resolved cryo-electron microscopy of vitrified muscular components.

Biological objects may be arrested in defined stages of their activity by fast freezing and may then be structurally examined. If the time between the start of activity and freezing is controlled, structural rearrangements due to biological function can be determined. Cryo-electron microscopy shows great potential for the study of such time-dependent phenomena. This study examines the actin polymerization process using cryo-electron microscopy of vitrified specimens. Actin filaments are shown to undergo a structural change during polymerization. In the early stages of the polymerization process (t less than 2 min), filaments exhibit a pronounced structural variation and frequently show a central low-density area. In the later stages of the polymerization, F-actin-ADP filaments have a more uniform appearance and rarely display a central low-density area. These findings, analysed on the basis of a previously proposed polymerization model, suggest that polymerization intermediates (F-actin-ATP and more probably F-actin-ADP-Pi) and filaments at steady state (F-actin-ADP) have different structures. To investigate the physiological relevance of these results at the cellular level, the potential of cryo-substitution in preserving the structure of muscular fibre was assessed. Optical diffraction patterns of relaxed and contracted frog cutaneous muscle are similar to the corresponding X-ray diffraction patterns. The resolution of the images extends to about 7 nm. These results show that dynamic study of muscle contraction is possible using cryo-substitution.

Actins↗
PubMed1991

[Structure of arterial intima in children and adolescents. A pathological study of 101 cases].

This was a macroscopic and histological study of the arteries of 101 unselected subjects from 0 to 20 years of age without cardiovascular pathology, autopsied to determine the cause of death at the medico-legal Institute of Paris. Stary's classification was used as a reference. Multiple Biopsies were taken from throughout the arterial system: initial aorta, carotid artery and its bifurcation, descending supra and infra renal aorta, iliac artery and left anterior descending artery. In this population, we found arterial lesions in 63% of subjects in the 15 to 20 year age range and this confirms previously reported data, especially by Stary. The lesions were identical irrespective of the site of biopsy and predominated at the bifurcations. No difference was observed with regards to sex and the lesions progressed after puberty.

Adolescent↗
PubMed1989

Organization of actin microfilaments in the apical border of oviduct ciliated cells.

Actin microfilaments were localized in quail oviduct ciliated cells using decoration with myosin subfragment S1 and immunogold labeling. These polarized epithelial cells show a well developed cytoskeleton due to the presence of numerous cilia and microvilli at their apical pole. Most S1-decorated microfilaments extend from the microvilli downward towards the upper part of the ciliary striated rootlets with which they are connected. From the microvillous roots, a few microfilaments connect the proximal part of the basal body or the basal foot associated with the basal body. Microfilament polarity is shown by S1 arrowheads pointing away from the microvillous tip to the cell body. Furthermore, short microfilaments are attached to the plasma membrane at the anchoring sites of basal bodies and run along the basal body. The polarity of these short microfilaments is directed from the basal body anchoring fibers downward to the cytoplasm. At the cell periphery, microfilaments from microvillous roots and ciliary apparatus are connected with those of the circumferential actin belt which is associated with the apical zonula adhaerens. Together with the other cytoskeletal elements, the microfilaments increase ciliary anchorage and could be involved in the coordination of ciliary beating. Moreover, microvilli surrounding the cilia probably modify ciliary beating by offering resistance to cilium bending. The presence of microvilli could explain the fact that mainly the upper part of the cilia appanars to be involved in the axonemal bending in metazoan ciliated cells.

Actin Cytoskeleton↗
PubMed1989

Immunogold labeling of luciferase in the luminous bacterium Vibrio harveyi after fast-freeze fixation and different freeze-substitution and embedding procedures.

We studied the ultrastructural localization of luciferase on sections of the bioluminescent bacterium Vibrio harveyi by indirect immunogold staining, using a polyclonal antiluciferase antibody and the usual control tests, after chemical fixation or fast-freeze fixation (FFF) followed by different freeze-substitution (FS) procedures and embedding in either Epon or LR White. After liquid fixation with glutaraldehyde and paraformaldehyde and LR White embedding, labeling occurred over the cytoplasm but not over the condensed nucleoid. Epon embedding almost abolished it. FFF-FS considerably improved the morphological preservation and revealed cytoplasmic "patches" with a complex ultrastructure in Epon sections. The preservation was always less good in LR White. The patches were densely labeled, even in Epon sections, after FS in acetone. However, labeling intensity was 3.7 times greater in LR White than in Epon. With both resins, labeling diminished similarly when fixative agents were present in the FS medium. The localization of luciferase in the cytoplasm and particularly in the patches is discussed.

Freezing↗
PubMed1987

Characterization of the bioluminescent organelles in Gonyaulax polyedra (dinoflagellates) after fast-freeze fixation and antiluciferase immunogold staining.

To characterize the microsources of bioluminescent activity in the dinoflagellate Gonyaulax polyedra, an immunogold labeling method using a polyclonal antiluciferase was combined with fast-freeze fixation and freeze substitution. The quality of the preservation and the specificity of the labeling were greatly improved compared to earlier results with chemical fixation. Two organelles were specifically labeled: cytoplasmic dense bodies with a finely vermiculate texture, and mature trichocysts, labeled in the space between the shaft and the membrane. The available evidence indicates that the dense bodies are the light-emitting microsources observed in vivo. The dense bodies appear to originate in the Golgi area as cytoplasmic densifications and, while migrating peripherally, come into contact with the vacuolar membrane. Mature organelles protrude and hang like drops in the vacuolar space, linked by narrow necks to the cytoplasm. These structural relationships, not previously apparent with glutaraldehyde fixation, suggest how bioluminescent flashes can be elicited by a proton influx from a triggering action potential propagated along the vacuolar membrane. Similar dense bodies were labeled in the active particulate biochemical fraction (the scintillons), where they were completely membrane bound, as expected if their necks were broken and resealed during extraction. The significance of the trichocyst reactivity remains enigmatic. Both organelles were labeled with affinity-purified antibody, which makes it unlikely that the trichocyst labeling is due to a second antibody of different specificity. But trichocysts are not bioluminescent; the cross-reacting material could be luciferase present in this compartment for some other reason, or a different protein carrying similar antigenic epitopes.

Animals↗
PubMed1979

[Is the process of localized lysosomal exocytosis responsible for the cytolytic action of killer T-lymphocytes?].

In this paper, we formulate the hypothesis that in the process of target cell lysis a lysosomal enzyme regurgitation, performed by killer cells at the level of the target effector junction, accounts for the target lesion which precedes the lysis (lethal hit). This process of exocytosis, similar to the one described previously in polymorphonuclear neutrophils is supported by cytological studies performed directly on identified killers isolated by micromanipulation. Light and electron microscopy observations confirm a previous report which describes the effector cells rich in lysosomal bodies. In addition, when a killer cell is associated with a target cell to form a conjugate, lysosomes are concentrated near the cell junction and, after incubation at 37 degrees C, acid phosphatases may be detected at the junction. Lysosomal enzyme exocytosis explains why target lysis needs an effector target binding to occur and also the other conditions required for any exocytosis process such as Ca++ in the medium, integrity of the microtubular apparatus, a low level of cyclic AMP and energy dependancy.

Acid Phosphatase↗
PubMed1979

[Coronary lesions due to aortic valve disease. I -- Occurrence and clinical prognosis].

A multicentre retrospective study of 467 cases of operated aortic valve disease was undertaken to define the indications of coronary arteriography in the pre-operative work-up. Significant coronary artery disease was present in 15% of all cases or, more precisely, in 17% of cases with angina and in 8% when investigation was only routine. Coronary artery disease was more frequent in males, in patients with clinical or electrical evidence of previous myocardial infarction, in patients with ST-T wave changes, and when angina was severe (more than one attack per day). None of these factors was specific. It is therefore difficult to limit coronary arteriography to these patients or there would be a risk of missing significant lesions in a small number of cases. It is important to give the surgeon all the necessary information before aortic valve replacement and so coronary arteriography should be widely practiced in this context. However exceptions may be made for young patients and also those in congestive cardiac failure in whom coronary arteriography represents an unnecessary risk before surgery.

Aortic Valve Insufficiency↗