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Biomedical subjects

G Maret

Publications and source records attributed to G Maret.

At least 19 recordsLinked to original sources
PubMed2000

Dynamic criteria for melting in two dimensions

The two-dimensional (2D) melting transition is analyzed on the basis of the long-time behavior of a modified Lindemann parameter in 2D gamma(L)(t) and the bond-angular correlation function g(6)(t). Using video microscopy complete positional data are obtained over five decades in time for an ensemble of superparamagnetic colloidal particles confined to an air-water interface. We find that each of the three phases (solid/hexatic/isotropic liquid) is uniquely characterized by the long-time behavior of gamma(L)(t), g(6)(t), and the non-Gaussian parameter of the relative neighbor-neighbor displacement.

Journal Article↗
PubMed1998

The susceptibility of pure tubulin to high magnetic fields: a magnetic birefringence and x-ray fiber diffraction study.

The orientational behavior of microtubules assembled in strong magnetic fields has been studied. It is shown that when microtubules are assembled in a magnetic field, they align with their long axis parallel to the magnetic field. The effect of several parameters known to affect the microtubule assembly are investigated with respect to their effect on the final degree of alignment. Aligned samples of hydrated microtubules suitable for low-resolution x-ray fiber diffraction experiments have been produced, and the results obtained from the fiber diffraction experiments have been compared with the magnetic birefringence experiments. Comparisons with earlier fiber diffraction work and small-angle x-ray solution scattering experiments have been made.

Animals↗
PubMed1991

Seventeen years of surgical treatment of thymoma: factors influencing survival.

We report on 17 years experience of the surgical treatment of thymoma in 65 patients, 11 with and 54 without myasthenia gravis. Patients were staged using the French "GETT" classification; 38 were in stage I (no invasive tumor), 6 in stage II, 13 in stage III and 8 in stage IV. In 45 patients, surgical excision was total while the remaining 20 underwent partial resection only. Postoperative radiotherapy was given in 12 cases, and 17 received a combination of radiotherapy and chemotherapy. One patient was lost to follow up, but no operative death occurred in the series. The mean survival for all patients was 70 +/- 7 months, and the 5- and 10-year survival was 91% +/- 4% and 69% +/- 8%, respectively. Follow-up for the 47 patients still alive and 4 patients deceased from unrelated causes ranged from 1.5 to 180 months (mean 142 +/- 10 months). Our data indicate that the prognosis of thymoma relates to radiological discovery (P less than 0.01), total surgical resection (P less than 0.01) and stage of tumor (P less than 0.01). It is not influenced by age, sex, tumor cell type or the presence or absence of myasthenia gravis.

Adult↗
PubMed1991

[Our experience of the surgical treatment of thirty-nine tracheobronchial carcinoid tumors].

Thirty-nine patients were operated for bronchial carcinoid tumour between 1967 and 1988 out of a total of 97 so-called benign bronchial tumours. Based on a clinical, radiological and endoscopic assessment of this series, the authors discuss the modalities of surgical treatment which depend on the site of the tumour. Treatment consisted of enucleation for the two peripheral carcinoid tumours and tracheobronchectomy in 6 cases (15%) and pulmonary resection in 31 cases (79%) for the central tumours. Lung resection was performed alone in 25 cases (64%): 1 pneumonectomy, 2 bilobectomies, 19 lobectomies and 3 segmental resections. The lung resection was associated with bronchial resection-anastomosis in 6 cases (15%). The immediate postoperative course was uneventful. There were two deaths: one from myocardial infarction after one year and one from hepatic metastases (malignant carcinoid) after 7 years.

Adolescent↗
PubMed1990

Toxication of MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) and analogs by monoamine oxidase. A structure-reactivity relationship study.

MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) elicits motor deficits similar to those observed in Parkinson's disease. Before exerting its neurotoxic action, MPTP must be activated by brain monoamine oxidase (MAO) to the neurotoxic metabolite MPP+ (1-methyl-4-phenylpyridinium). MPTP derivatives differ in their reactivity as MAO substrates and in their neurotoxicity. A structure-reactivity relationship study based on literature data was undertaken in order to determine the key features in the structure of MPTP and analogs that are responsible for the reactivity towards MAO. Thirty-three MPTP derivatives (including MPTP itself) were included in the study. To explain the reactivity towards MAO of the 33 MPTP analogs, different statistical methods (principal component analysis, multiple linear regression analysis) as well as the CoMFA (Comparative Molecular Field Analysis) approach, a new tool in structure-activity correlations, were used. Linear regression analysis failed to yield any predictive model, but suggested some trends. In contrast, the CoMFA approach was successful in correlating structural features and MAO reactivity. Coefficient contour maps showed where differences in the steric field (van der Waals' interactions) are most highly associated with differences in MAO reactivity. Several positive (in the ortho- and meta-position of the phenyl group) and negative (in the para-position of the phenyl group; beyond the N-methyl group) interaction regions were identified. Some structural features of the MAO active site could be postulated. First, the N-methyl group has the ideal size and elicits ideal interactions within the MAO active pocket, while smaller or larger groups are less favorable; second, para-substituent on the phenyl ring produce steric hindrances and are unfavorable to reactivity; third, ortho- and meta-substituents may have stabilizing interactions within the active pocket and are favorable to the reactivity. Moreover the model derived by CoMFA allowed us to make successful predictions of reactivity towards MAO for several additional tetrahydropyridines.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1989

[Pulmonary arteriovenous fistula. Apropos of 12 cases].

Arteriovenous fistula of the lung is a relatively rare lesion with various clinical manifestations. It may be clinically silent and discovered by chance on X-ray films of the chest or during evaluation of Rendu-Osler-Weber disease with which it is associated in about one-half of the cases. It may also have loud manifestations when complicated. The fistula is diagnosed in successive steps, mainly by respiratory function tests and pulmonary angiography. Conservative treatment should be the rule, especially in case with multiple fistulae, but it must begin at an early stage to avoid the dramatic complications of this abnormality, such as acute neurological disorders, haemoptysis, haemothorax, etc. Wide and crippling lung resection must be avoided. Aneurysmorrhaphy or embolization is sufficient to cure most of these multiple angiomas. The results obtained are measured by calculating the blood flow rate in the shunt, as it should theoretically disappear after surgery.

Adult↗
PubMed1987

Synthesis and use of peptide substrates for the isolation and characterization of proenkephalin processing enzymes.

Classical methods of peptide synthesis in solution were used for the preparation of the two tetrapeptides alanyl-lysyl-arginyl-tyrosine and acetyl-alanyl-lysyl-arginyl-tyrosine-(N-methylamide). The two compounds were able to be recognized as substrates by proenkephalin processing enzymes and were used for the development of a quantitative assay for these enzymes. The first substrate proved to be convenient, although it was also partially degraded by amino- and carboxypeptidases under the conditions of the assay. The second was found to be hydrolyzed by the endopeptidases at too slow a rate to allow its routine use in the assay.

Adrenal Medulla↗
PubMed1983

Fibrinogen and fibrin structure and fibrin formation measured by using magnetic orientation.

Accurate birefringence measurements show that fibrinogen orients to a small degree in high magnetic fields. This effect can be explained as due to the molecule having about 30% (by weight) alpha-helix oriented relatively parallel to the long axis. Birefringence measurements on fully oriented fibrin suggest that aligned alpha-helical content is less than that estimated for fibrinogen. But because of limitations in the analysis this difference must be viewed with caution. Highly oriented fibrin results when polymerization takes place slowly in a strong magnetic field. Low-angle neutron diffraction patterns from oriented fibrin made in the presence of EDTA, made in the presence of calcium, or stabilized with factor XIIIa are very similar, showing that the packing of the molecules within the fibers is the same or very similar in these different preparations. The induced magnetic birefringence was used to follow fibrin formation under conditions in which thrombin was rate limiting. The fiber network formed by approximately the gelation point constitutes a kind of matrix or frame that is largely built upon during the remaining approximately 85% of the reaction. After gelation the reaction is pseudo-first order.

Animals↗