Search PubMed⌕ Search

Biomedical subjects

C Simon

Publications and source records attributed to C Simon.

At least 307 records · Page 17Linked to original sources
PubMed1982

[Facial nerve anatomy in neonates. Second and third parts : Surgical applications].

Anatomy of the second and third parts of the facial nerve in the neonatal period was studied by dissection of 15 cadavers. A particular feature was the shortness of the 3rd portion, due to the absence of development of the mastoid. The facial nerve lies an average of 2.4 mm below the antral floor, close to the vertical portion of its posterior border. The stylomastoid foramen is situated on the external surface of the mastoid rudiment, masked by the anterior border of the digastric muscle. Though surgery is rarely indicated, the characteristic features of facial nerve anatomy in neonates should be known.

Facial Nerve↗
PubMed1981

Mechanism of tubulin assembly: role of rings in the nucleation process and of associated proteins in the stabilization of microtubules.

Several types of experiments were designed to elucidate the mechanism of initiation of tubulin assembly in the presence of microtubule-associated proteins (MAPs): (1) The evolution of the proportion of the double ring species with temperature was examined in the ultracentrifuge, under nonpolymerizing conditions (guanosine diphosphate = 0.5 mM). A net dissociation of rings into dimers occurred when temperature increased. The transition took place above 20 degrees C. (2) The kinetic parameters of the exchange at equilibrium between free tubulin dimers and tubulin in rings were studied at different temperatures, using the technique of isotopic exchange at equilibrium with radioactively labeled tubulin. The values found for the half-time of the exchange reaction varied between or approximately 100 min at 0 degrees C and 10 min at 2 degrees C. (3) The relative participation of unlabeled rings and labeled dimers to microtubules in the time course of assembly was studied at 22 degrees C. The time dependence of microtubule specific radioactivity showed that tubulin incorporated in the initial stages of assembly came predominantly from rings (85-90%). This result indicates that oligomers directly issued from rings are the first intermediates in the assembly process and suggests that at the beginning of polymerization incorporation of isomers or fragments of rings proceeds at a faster rate than their dissociation into dimers. (4) Polymerization experiments in the presence of MAPs with increasing concentrations of tubulin dimers indicated that MAPs are in rapid equilibrium with the microtubules and are distributed along the wall in a more or less loose lattice depending on the relative concentrations of tubulin and MAPs in the solution.

Animals↗
PubMed1981

Antibody decoration of neurofilaments.

We have decorated neurofilaments with antibodies against three polypeptides (designated here as H [mol wt = 195,000], 45[mol wt = 145,000], and 46[mol wt = 73,000]) in an effort to understand the arrangement of these polypeptides within neurofilaments. The three polypeptides were purified and antibodies were raised against each. The cross-reactivity of the antibodies suggested that each polypeptide contains both shared and unique antigenic determinants. The differential reactivities of each antibody preparation were enhanced by adsorption with the two heterologous polypeptides, and the resulting preparations were used to decorate purified neurofilaments, which were then negatively stained and examined in an electron microscope. The appearance of the antibody-decorated structures led to the following conclusions: All three polypeptides are physically associated with the same neurofilament. However, the disposition of H and 46 within a filament is different; 46 antigens appear to be associated with a "central core" of the filament, whereas H antigens compose a structure more loosely and peripherally attached to the central core and periodically arranged along its axis. The antibody-decorated H-containing structure assumes variable configurations; in some cases it appears asa bridge connecting two filaments; in other cases it appears as a helix wrapping the central core with a period of approximately 1,000 A and an apparent unit length of approximately 1.5 periods. These configurations suggest several functional implications, including the possibility that H is a component of the cross-bridges observed between filaments in situ. We also note that the central core-helix relationship could be used in the design of an intracellular transport motor.

Animals↗
PubMed1981

The thyroid lysosomal system: dynamic state of the organelles in relation to iodine release.

Endocytosis and hydrolysis of thyroglobulin (Tg) by the thyroid lysosomal system were studied in vivo in normal rats. By double labelling experiments, with 125I (old label) and 131I (new label), it was found that the well known preferential utilisation of newly labelled iodine by the thyroid follicles did not take place during endocytosis: the specific radioactivity (SRA = 131I/125I) was the same for the soluble Tg, luminal in origin, and the particulate Tg, lysosomal in origin. By contrast, the SRA of the total iodine content of the lysosomes was 2-15 times lower than the SRA of the soluble Tg. When the total lysosomal fraction (LT) was fractionated by size into subpopulations, with L1 less than LII less than LIII (Miquelis et al. [14]), it was found, after kinetics experiments, that SRA(LI) greater than SRA(LII) greater than SRA(LIII) for their iodine content. As observed after ultracentrifugation analysis on a discontinuous Ficoll gradient, only a small portion of the lysosomes is responsible for the difference of the SRA between LI and LT. Moreover, the LI subpopulation, significantly enriched in organelles of 0.03-0.25 micron diameter (Simon et al. [25], exhibits a higher acid phosphatase activity/beta-galactosidase activity ration than LT. It is suggested that 1) endocytosis is not preferential for newly iodinated Tg, 2) the thyroid lysosomes hydrolyse preferentially recently iodinated Tg, 3) Tg enters the cell by micropinocytosis, 4) the micropinocytotic vesicles fuse rapidly with primary lysosomes, 5) progressive release of iodinated compounds occur during the maturation of secondary lysosomes which fuse amongst themselves.

Animals↗