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Biomedical subjects

G Nicolas

Publications and source records attributed to G Nicolas.

At least 55 records · Page 3Linked to original sources
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↗
PubMed1990

Influence of Endogenous Cytokinins on Reverse Mobilization in Cotyledons of Cicer arietinum L: Reproduction of Endogenous Levels of Total Cytokinins, Zeatin, Zeatin Riboside, and Their Corresponding Glucosides.

The embryonic axis plays an essential role in the mobilization of the main reserves of the cotyledons of seeds of Cicer arietinum L. cv Castellana. This control by the axis of the metabolism of the storage products of the cotyledons largely takes place through the cytokinins, which are transported from the embryonic axis to the cotyledons where the mobilization of reserves begins. The principal regulatory role of the endogenous cytokinins concerns the metabolism of carbohydrates and proteins; there is less influence on lipid metabolism. However, each cytokinin seems to have a different role in the mobilization processes. The glucosides, glucosyl zeatin riboside, and glucosyl zeatin act only as storage forms of the hormones. Zeatin riboside affects mainly the mobilization of carbohydrates and has less effect on protein mobilization. Zeatin regulates both the mobilization of carbohydrates and that of proteins and is more marked in the latter case.

Journal Article↗
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↗
PubMed1988

Changes in magnesium, zinc, calcium, potassium, cholesterol, and creatine kinase concentrations in patients from pre-infarction syndrome to fatal myocardial infarction.

We measured changes in concentrations of magnesium, zinc, calcium, potassium, cholesterol [total and high-density lipoproteins (HDL)], total creatine kinase (CK), and CK isoenzyme-MB in plasma (PI) and/or erythrocytes (Erc) from apparently healthy subjects and from patients with either pre-infarction syndrome (PIS) or myocardial infarction (MI) with a favorable (MI1) or fatal (MI2) outcome, to assess the relationship of these changes to the increasing severity of ischemic disease. Significant sex-related differences led us to study men and women separately. In MI1 and MI2 patients, concentrations of Mg in PI and Erc were increased as a function of time since the infarct, confirming the cardiac Mg leaves the heart and enters the circulatory compartment. Compared with concentrations in MI2 patients, Zn concentrations in PI were lower in MI2 patients in the days before death. Significant negative correlations between Zn in PI in MI1 men or Zn in Erc in MI2 men and CK or CK isoenzyme MB suggest that circulating Zn is taken up by non-necrotic myocardial tissue as part of the repair process. MI2 patients had gradually decreasing Ca concentrations in PI even more marked than those observed in PIS and MI1 patients. We also noted a marked decrease in total and HDL cholesterol concentrations in both MI2 men and MI2 women shortly before death.

Adult↗
PubMed1987

Changes in magnesium, zinc and calcium in men and women after an acute myocardial infarction.

The relations between different elements in acute myocardial infarction (MI) led us to determine erythrocyte (Erc) and/or plasma (Pl) concentrations of magnesium (Erc-Mg; Pl-Mg), zinc (Erc-Zn; Pl-Zn) and calcium (Pl-Ca) in 34 men and 8 women upon admission to hospital and then on days 2, 3, 6, 10 and 12. On day 1, these two groups were compared with 58 reference men or 53 reference women. The changes in the different variables from day 1 to day 12 were analyzed by one-way ANOVA. In MI men, from day 1 to day 12, all cations were significantly modified. In MI women, only Erc-Zn and Pl-Ca remained unchanged. In both populations, Pl-Mg, Erc-Mg and Pl-Zn increased significantly between day 1 and day 12.

Acute Disease↗
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↗
PubMed1987

An optional dyadic junctional complex revealed by fast-freeze fixation in the bioluminescent system of the scale worm.

In the bioluminescent system of the scale worm, the facilitation of the successive flashes is correlated with the progressive recruitment, in each photogenic cell, of new units of activity, the photosomes. To characterize morphologically the coupled state of the photosomes, known to decouple within seconds at rest, fast-freeze fixation was applied to stimulated and nonstimulated elytra and followed by substitution with OsO4 in acetone. The results showed striking differences. Photosomes were surrounded by a new type of smooth endoplasmic reticulum (ER) called intermediate endoplasmic reticulum (IER). In nonstimulated elytra, the IER was most often unattached in the cytoplasm. After stimulation, the IER was connected to large terminal saccules that formed dyad junctions with the plasma membrane. Most of these junctional complexes were symmetrical (triads) and occurred in front of narrow extracellular spaces. These spaces were either constitutive, like invaginations or clefts along adjacent cells and adjacent pouches, or resulted from the pairing of long pseudopods which expanded into a wide extracellular compartment and twisted together in a dynamic process. In that the junctional complexes developed progressively under repeated stimulation and coupled more and more photosomes, they must represent a route constituted by the ER for the propagation of internal conduction. The dynamics of coupling involve membrane growth, recognition, and transformation on a surprisingly large scale and in a surprisingly short time.

Animals↗
PubMed1987

[Gamma-angiography in the diagnosis of akinesia and dyskinesia after myocardial infarction].

A one year prospective double blind trial included all patients with myocardial infarction and clinical, electrocardiographic or radiographic signs of left ventricular aneurysm. All 36 patients underwent ventriculography and radionuclide angiocardiography in the same projections: right anterior oblique, antero-posterior, left anterior oblique and left lateral. The angiographic diagnosis of left ventricular aneurysm was based on the finding of a deformation of the ventricular contour persisting in diastole; 22 patients were classified as having a left ventricular aneurysm and the 14 others had akinesia alone. The radionuclide diagnosis of left ventricular dyskinesia was based on the finding of the following 3 criteria in at least one projection: crossing of the systolic and diastolic isocontours; over 4 p. 100 of LV pixels having a negative ejection fraction; the dephased infarcted region having a movement separate from that of the remaining healthy myocardium. None of the clinical criteria of inclusion allowed diagnosis of LV aneurysm when compared with the results of ventriculography. The results of radionuclide and conventional ventriculography correlated 100 p. 100 in the diagnosis of severe contractile abnormalities. When compared with ventriculography, radionuclide angiocardiography had a specificity of 95 p. 100 and a sensitivity of 86 p. 100 for the diagnosis of aneurysm. The only false negative was a non-surgical septal aneurysm. The multiplication of the incidences of examination increases the sensitivity of the results of radionuclide angiography.

Adult↗
PubMed1987

Se, Zn, Mg, Ca, K, cholesterol, and creatine kinase concentrations in men during the 12 days after an acute myocardial infarction.

We determined concentrations of selenium, zinc, magnesium, calcium, potassium, total and high-density lipoprotein cholesterol, and total creatine kinase (EC 2.7.3.2) in plasma (P) and (or) erythrocytes (E) of 32 men at the time of hospital admission for acute myocardial infarction and then on subsequent days 2, 3, 6, 10, and 12. During these 12 days, only P-selenium and high-density lipoprotein cholesterol concentrations remained unchanged. For the other variables, individual comparison of means indicated the dates of significant changes in concentration (p less than 0.05).

Adult↗
PubMed1986

[Treatment of unstable angina. A randomized double-blind study of propranolol, diltiazem and molsidomine].

A randomized, multicentric, double blind study attempted to compare in 41 patients hospitalized for unstable angina, the efficacy of diltiazem (D) 240 mg/day, propranolol (P) 160 mg/day and molsidomine (M) 8 mg/day. The patients included in the study presented one or several spontaneous angina episodes accompanied by a transient and significant lowering of ST and/or an inverted T wave without necrosis. The evaluation criteria were the occurrence of new angina pain and electrical alterations on a continuous Holter for 5 days. 11 patients received diltiazem, 13 patients received propranolol and 15 patients received molsidomine (including an early death). Clinically, the number of painful episodes per day and per patient goes, in an average, from 1.2 to 0.23 diltiazem, from 2.2 to 0.44 for propranolol and from 2.2 to 0.45 for molsidomine. Pain disappeared on the 5th day in 54.5 per cent of patients under diltiazem, 58.8 per cent of patients under propranolol and 53.5 per cent of patients under molsidomine. Electrically, the number of ischemic accidents per day and per patient was 0.45 under diltiazem, 2.12 under propranolol (0.53 in excluding one patient with latent angina) and 0.81 under molsidomine. The number of patients without any ischemic accident was 63.6 per cent under diltiazem, 53.8 per cent under propranolol and 40 per cent under molsidomine. In conclusion, diltiazem, propranolol, and molsidomine have a comparable efficacy in unstable angina. The association of these medications could have a synergistic effect.

Angina Pectoris↗