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Biomedical subjects

G Géraud

Publications and source records attributed to G Géraud.

At least 19 recordsLinked to original sources
PubMed1992

Revealing nucleolar architecture by low ionic strength treatment.

The internal nucleolar architecture of HeLa cells was revealed after a short hypotonic treatment. The response of nucleoli to a gradual reduction in the ionic strength of incubation buffer was assessed by immunofluorescence, confocal microscopy using human autoimmune sera monospecific for antigens present in different nucleolar components, and electron microscopy. The granular component dispersed first, followed by the dense fibrillar component, leaving distinct fibrillar centers remaining. This demonstrates differential sensitivity to low ionic strength treatment in the transcription and the maturation territories of the nucleoli. The changes described develop in only a few minutes and this approach can reveal momentary in situ intranucleolar arrangements. We suggest that the fibrillar centers provide a structural support for RNA-polymerase I complexes and are possibly also attached to a nuclear skeleton. The evidence presented implicates the fibrillar centers as the core elements of nucleoli and that functional nucleoli arise around them.

Antigens↗
PubMed1992

Cell cycle modification during the transitions between meiotic M-phases in mouse oocytes.

When metaphase II-arrested mouse oocytes (M II) are activated very soon after ovulation, they respond abortively by second polar body extrusion followed by another metaphase arrest (metaphase III, M III; Kubiak, 1989). The M II/M III transition resembles the natural transition between the first and second meiotic metaphases (M I/M II). We observed that a similar sequence of events takes place during these two transitions: after anaphase, a polar body is extruded, the microtubules of the midbody disappear rapidly and a new metaphase spindle forms. The MPM-2 monoclonal antibody (which reacts with phosphorylated proteins associated with the centrosome during M-phase) stains discrete foci of peri-centriolar material only in metaphase arrested oocytes; during both transitional periods, a diffuse staining is observed, suggesting that these centrosomal proteins are dephosphorylated, as in a normal interphase. However, the chromosomes always remain condensed and an interphase network of microtubules is never observed during the transitional periods. Incorporation of 32P into proteins increases specifically during the transitional periods. Pulse-chase experiments, after labeling of the oocytes in M phase with 32P, showed that a 62 kDa phosphoprotein band disappears at the time of polar body extrusion. Histone H1 kinase activity (which reflects the activity of the maturation promoting factor) drops during both transitional periods to the level characteristic of interphase and then increases when the new spindle forms. Both the M I/M II and M II/M III transitions require protein synthesis as demonstrated by the effect of puromycin. These results suggest that the two M-phase/M-phase transitions are probably driven by the same molecular mechanism.

Animals↗
PubMed1992

The small GTP-binding protein rab6p is distributed from medial Golgi to the trans-Golgi network as determined by a confocal microscopic approach.

A key role in the regulation of membrane traffic is played by the rab proteins, members of a family of ras-related small GTP-binding proteins. This family comprises at least 25 identified members, the intracellular localization of only a few of which has been investigated. rab6p has been shown to be distributed along the exocytic pathway in association with the medial and trans regions of the Golgi apparatus. A confocal laser scanning microscopic (CLSM) approach coupled with image analysis was used to compare the localization of rab6p with selected reference Golgi markers by double immunofluorescence on culture cell lines. CLSM analysis shows that, under a set of well-defined conditions, one can investigate the possible colocalization of known markers of Golgi compartments and orientate a couple of labeled Golgi antigens with regard to the polarity of the Golgi apparatus. Thus, having validated the CLSM analysis, the localization of rab6p was studied and compared with some of these markers and the VSV-G protein in VSV (vesicular stomatitis virus)-infected cells blocked at 20 degrees C. rab6p is shown to be associated in all the cell lines used with the last cisternae of the Golgi apparatus and particularly with the trans-Golgi network (TGN), the site of protein sorting at the exit of the Golgi apparatus. These results were supported by an electron microscopic study using double-immunolabeled cryosections: rab6p was found in some flat cisternae of the Golgi stack and colocalized with the VSV-G protein in the TGN. Our results show that the small GTP-binding protein rab6p is distributed from medial Golgi to TGN along the exocytic pathway.

Biological Transport↗
PubMed1989

Three-dimensional organization of micronuclei induced by colchicine in PtK1 cells.

In PtK1 cells micronucleated by colchicine, we previously demonstrated that some micronuclei contain a single chromosome. Here, we investigated interphase chromosome organization in micronucleated PtK1 cells using conventional electron microscopy and three-dimensional computer reconstruction. The distribution of micronuclei was not always polarized, but in some cells they formed a ring. When this occurred, centrioles and Golgi apparatus were located inside the ring. On freeze-fracture replicas, we observed that nuclear pore distribution among the micronuclei was heterogeneous, and on thin sections some micronuclei displayed an incomplete nuclear envelope, with gaps in the double membrane and areas without lamina or condensed chromatin. By autoradiography, we showed that the fibrillar dots were not sites of active transcription. We applied three-dimensional reconstruction to one micronucleated cell containing 22 micronuclei whose size indicated that each micronucleus probably contained one chromosome. In this cell we demonstrated that only the smallest micronuclei had an incomplete nuclear envelope. The presence in micronuclei of either nucleoli or fibrillar dots was found to be mutually exclusive. These dots might constitute stores of nucleolar proteins which migrate into micronuclei possessing no ribosomal genes. In NOR-bearing micronuclei, the structural organization was similar to that of diploid nuclei: the nucleoli were attached to the nuclear membrane and a nucleolar canal was seen, even in single-chromosome spherical micronuclei. Taken together, these findings indicate that in the diploid nuclei of PtK1 cells, the three-dimensional organization of the nucleolar domain seems to be directly controlled by the X-chromosome.

Animals↗
PubMed1986

[Acebutolol and cerebral blood flow of the moderately hypertensive aged subject].

In 17 moderate hypertensive patients (mean age = 67 +/- 8.8) the effects of a chronic oral administration of the beta blocking agent acebutolol on regional cerebral blood flow (rCBF) was studied using the non invasive 133 Xenon inhalation technique. The results was compared to the rCBF obtained in an age matched normal control group. Our study shows that during long term therapy low doses of acebutolol (200 mg/daily) the rCBF is unaffected by a decrease (20 mmHg) of the mean arterial blood pressure. The relative hypofrontality of the elderly hypertensive patients leads to be corrected by acebutolol.

Acebutolol↗
PubMed1986

Pharmacological exploration of dopamine hypersensitivity in migraine patients.

Patients with migraine show a hypersensitivity to dopamine or its agonists. One of these, piribedil, was administered as 0.1 mg/kg intravenously over 30 min to subjects with either migraine or other types of headache. This test provoked in migraine patients an increase of the cerebral blood flow and the peripheral signs of dopamine hypersensitivity:- nausea or vomiting and a rapid fall in blood pressure. In contrast, in those subjects with chronic non-migrainous headache, the administration of piribedil had no effect. The piribedil test appears to possess good specificity vis à vis migraine, enabling a differential diagnosis from atypical periodic headache, a condition difficult to consider as migraine or psychogenic headache on clinical grounds alone.

Cerebrovascular Circulation↗
PubMed1985

[Cerebral blood flow and meningeal hemorrhage. An aid to the surgical decision].

One hundred and eleven measurements of cerebral blood flow (C.B.F.) were performed using the Xenon 133 inhalation method in 80 cases of spontaneous subarachnoid hemorrhage of which 59 were due to ruptured aneurysms. This method is non-traumatic, reproducible and dependable. A correlation was found between clinical condition and C.B.F. values, but in a number of cases which cannot be dismissed, very low mean C.B.F. values or ischemic foci were revealed where clinical state gave no indication. A poor correlation appeared between vasospasm seen by angiography and ischemic foci detected by isotopic technique. Patients' age influenced C.B.F. values but not clinical evolution. No correlation was found between C.B.F. values and cisternal blood seen on CT scan. C.B.F. values, measured in the first two weeks of illness, were significantly higher in those patients having favorable outcome, whatever their clinical state at the time of C.B.F. measurement (comas excluded). The figure of 60 ml/100 g/min for mean cortical flow seemed to be a critical level below which the risk of complication was greater. Below this level or in cases or ischemic foci, surgery was delayed. Thus, C.B.F. measurement promises to be a valuable prognostic tool, playing an important role in the therapeutic strategy for this type of patients.

Adult↗
PubMed1984

[Central pontine myelinolysis with regressive development and x-ray computed tomographic interpretation].

A 68 year-old woman presented after rapid correction of a hyponatremia a clinical picture suggestive of central pontine myelinolysis. Clinical disorders regressed but serial CT scans showed the late development of a central pontine low density area which persisted for several months. Such a lack of correlation between clinical and CT scan data has been previously reported. On the present case the demyelination lesions appeared to have resulted principally from the rapid increase of natremia.

Aged↗
PubMed1983

[Recurrent cerebral ischaemic attacks in young subjects. Arteriolar dysplasia or early atheroma?].

The case of a 33-year old woman with recurrent cerebral and peripheral ischaemic attacks is reported and the difficult nosological problem of juvenile ischaemia is discussed. Thromboangiitis obliterans (Buerger's disease) was excluded by morphological studies of finger tips, temporal artery and dermis, which demonstrated arteriolar dysplasia and premature aging of the connective tissue. A diagnosis of "juvenile atheroma" may be considered in view of the dyslipidaemia and increase in skin cholesterol and apoprotein B concentrations observed. A review of the literature, together with the biochemical and histological findings in this patient, suggests that ischaemic attacks, dysplasia of small vessels and serum dyslipidaemia reflected in the dermis are all manifestations of early atheroma.

Adult↗