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R Seïte

Publications and source records attributed to R Seïte.

At least 19 recordsLinked to original sources
PubMed1985

Daily fluctuations of nucleoli in neurosecretory cells of the rat supraoptic nucleus. An ultrastructural and stereological study.

Daily fluctuations of nucleoli and nucleolar fibrillar centres in neurosecretory cells from the supraoptic nucleus (SON) were investigated in rats artificially synchronized for 3 weeks to a set 12 h light/12 h dark cycle with free access to food and water. Group of 3 animals were sacrificed by intracardiac perfusion every 4 h for a 24-h period and every 2 h between 22.00 h and 07.00 h. The SON of each animal was removed, and the mean nucleolar volume and the mean volume of the nucleolar fibrillar centres were estimated by a stereological analysis. The quantitative data showed that the fluctuations in the nucleolar volume of SON neurons depend on the time of sacrifice. A peak value was found in animals sacrificed at 03.00 h which was 1.5 times the value found in animals sacrificed at 19.00 h. The volume of fibrillar centres underwent small, but not significant changes over the 24-h period. None of the large fibrillary centres that can be observed in the superior cervical ganglion were found in the SON. Our results demonstrate that in these neurons the size of the nucleolus under-goes daily fluctuations. These results are discussed in the light of previous studies conducted at our laboratory on the circadian rhythm of nucleolar volume and of nucleolar components in neurons of the superior cervical ganglion.

Animals↗
PubMed1985

Ultrastructure and stereological analysis of nucleoli of rat nodose ganglion neuron during a 24-h period: a comparison with sympathetic neurons of rat superior cervical ganglion.

The nucleoli of rat nodose ganglion were investigated during a 24-h span (light span 07.00-19.00 h). The mean volume of nucleoli and that of their components, especially fibrillar centers considered to be the interphasic counterpart of nucleolus-organizing regions, were determined by stereological analysis. The quantitative data showed that (1) nucleoli volumes of rat nodose ganglion neurons did not oscillate diurnally but that (2) there were diurnal dimensional changes in the volume of their fibrillar centers which strongly suggest an ultradian rhythmicity. These results are different from those obtained in studies of superior cervical ganglion neurons, in which nucleoli and nucleolar components followed a circadian rhythm with peak values during daily periods of darkness. Although the nucleoli of these 2 kinds of neurons involved in autonomic nervous system reactions do not show the same behavioural patterns, the present data bring to light a new example of circadian fluctuation in nucleoli and describes their organization in this respect.

Animals↗
PubMed1985

Changes in nucleoli and nucleolar fibrillar centres of chromaffin cells in rat adrenal medulla over a 24-hour period: an ultrastructural and stereological analysis.

A stereological and ultrastructural study was performed on the nucleoli of the adrenal medulla chromaffin cells of rats exposed to a standardized 12 h light/12 h dark cycle with free access to food and water. The animals were killed three at a time, every 4 h during the 24-h span and fixed by intracardiac perfusion. In these reticulated nucleoli, the stereological analysis over a 24-h period showed a variation dependent on the time of killing for the two parameters investigated, the mean nucleolar volume, Vnu, and the mean volume of the fibrillar centres, Vfc(nu). The minimal value occurred at 0300 h (dark span) and the maximal one at 0700 h (at the onset of the light span). Between these two extreme values, Vnu increased 1.8-fold and Vfc(nu) 5.3-fold. These data are compared with a previous description from our laboratory of circadian rhythm in nucleoli of sympathetic neurons of superior cervical ganglion in the same animals. Analogies and differences are pointed out, but apart from these considerations the present study provides a new example of temporal organization at the cellular level in the organelle involved in ribosomal RNA synthesis and ribosome assembly.

Adrenal Medulla↗
PubMed1985

Chronobiological studies on the nucleolus.

Chronobiological studies on the nucleolus were performed, using stereological analysis at the electron microscopic level, on different cell types in permanent interphasic state, in rats submitted to various lighting regimen. During the dark span (12L/12D): (1) in sympathetic neurons of superior cervical ganglion circadian changes in nucleolar organization were characterized by an increase in volumes of the nucleolus and each of its components, namely, fibrillar centres, dense fibrillar, granular and vacuolar components; (2) concerning the fibrillar centres, regarded as the interphasic counterpart of nucleolar organizing regions (NORs), the most striking fact, only observed in sympathetic neurons, is the occurrence of a single large-type fibrillar centre, accompanied by small-type fibrillar centres which are present throughout the 24-hr period; (3) the overall increase in volume of fibrillar centres was shown to correspond to a marked drop in the number (up to 4 fold) of small-type fibrillar centres, the unit volume of which (0.01 mum3) remaining unchanged over the 24-hr period and to an increase in size of a large-type fibrillar centre, the volume of which is 100 fold greater than the latter and (4) cytochemical studies showed that the Ag-NOR proteins exhibit a marked increase in amount, suggesting a circadian rhythmicity of these nucleolar proteins. These results, discussed in the light of our current understanding of the nucleolus, briefly summarized in this paper, suggest that the circadian rhythm of the nucleolus and of its components is correlated with circadian rhythms in both transcriptional activity and processing of preribosomes. Analogies between sympathetic neurons and the two other cell types studied, namely, chromaffin cells of adrenal medulla and vagal sensory neurons of nodose ganglion, led to the conclusion that rhythmicity is a fundamental characteristic of the nuclear structure devoted to ribosome biogenesis. Attention is focused on the superior cervical ganglion in which amplitude of nucleolar rhythms are greater and in which fibrillar centres exhibit a particular pattern. These results are discussed with regard to the role played by this sympathetic paravertebral ganglion which is known to regulate circadian rhythmic activities of the rat pineal gland. The persistence of these nucleolar rhythms in continuous lighting, as demonstrated in sympathetic superior cervical ganglion neurons, provide evidence that they are endogenously generated. The intrinsic factors underlying these rhythms in morpho-functional organization of the nucleolus are yet unknown.(ABSTRACT TRUNCATED AT 400 WORDS)

Adrenal Medulla↗
PubMed1984

A combined light and electron microscopic method for the visualization of the same in vitro neuron by radioautography and serial sections.

We report here on a technical improvement which makes it possible to study, at the ultrastructural level, a dopaminergic neuron which has been previously identified by light microscopy. Primary cultures of virtually pure mesencephalic neurons from mouse embryos were obtained. These cultures were kept for 6 days, then incubated with tritiated dopamine, fixed and embedded in Epon. The dopaminergic neurons were firstly visualized by radioautography directly through Epon blocks in toto by light microscopy. In a second step, ultrathin sections of the identified dopaminergic cells were prepared and the neurons observed at the electron microscopy level. The dopaminergic nature of these neurons was regularly checked by radioautographic control on some selected ultrathin sections.

Animals↗
PubMed1983

The axon of the giant neuron in the rat neostriatum.

The axon of the giant cells in the rat neostriatum was studied by serial sections on Golgi and electron microscopic preparations and with the combined Golgi-electron microscopic technique (Fairen, Peters and Saldanha, 1977). The ultrastructural characteristics of the initial part are given. It was established that the axon was coated with myelin and gives off myelinated collaterals. The present observations are discussed with regard to the problem of striato-cortical connections.

Animals↗
PubMed1981

Electron microscopic studies of silver-strained proteins in nucleolar organizer regions: location in nucleoli of rat sympathetic neurons during light and dark periods.

Ag-AS staining of nucleolar organizer regions was carried out on interphasic superior cervical ganglia neurons of rats sacrificed during light and dark periods. While the Ag-AS technique has mostly been used monolayer cell lines or cell suspensions, the present study showed that in electron microscopy this technique is also applicable to small pieces of tissues. The finest pictures are obtained when (I) all solutions used for the staining procedure are at pH 4.5-4.7 and (2) the second step of the reaction involving ammoniacal silver and formalin developing solutions does not exceed 3 min. The results indicate that in the 2 time periods studied, a positive reaction took place exclusively in nucleolar fibrillar centres and in the fibrillar centres and in the fibrillar ribonucleoprotein (RNP) component (dense fibrillar component). The other nucleolar components, i.e. granular and vacuolar, were devoid of silver deposits. As previously shown in sympathetic neurons, the fibrillar centres of the nucleoli show a 10-fold increase in volume during the dark period. In this period, silver grains were located on both "giant" and small-sized fibrillar centres. The fibrillar RNP component seen either at the periphery of fibrillar centres or in the form of a well-delimited network showed the strongest reaction. The same distribution of silver grains was observed in the sympathetic neurons of rats sacrificed during the light period. Here again, silver accumulation occurred exclusively in the fibrillar centres and the fibrillar RNP component. The same difference in reactivity was observed as for the dark period, the fibrillar RNP component being the main site of the reaction.

Animals↗
PubMed1981

Diurnal rhythm of nucleolar volume in sympathetic neurons of the rat superior cervical ganglion.

Rhythmic variations of nucleolar volume in neurons from the superior cervical ganglion were studied in rats under artificial synchronization (light: 0700-1900 h; dark: 1900-0700 h) with free access to food and water. Groups of 3 animals were sacrificed by intracardiac perfusion every four hours during the 24-hour period and every two hours between 22 and 07 h. The mean nucleolar volume (Vnu) was estimated in the SCG neurons of each group by measuring the surface area of 450 semi-thin nucleolar sections using a camera lucida and a semi-quantitative analyzer. Stereological analysis demonstrated that variations in Vnu followed a normal curve distribution according to the time of sacrifice, the maximum Vnu being found during the dark between 00 and 01 h. During the 24-hour period, the Vnu (plus or minus SEM) which was low at 14 to 15 h (6.451 plus or minus 0.540 microns(3)), increased two fold to reach a maximum value (13.443 plus or minus 0.705 microns(3)) at 00 to 01 h and then decreased to its nadir at 14 to 15 h on the following day. The results of this study demonstrate that the more or less pronounced variation in the nucleolar volume of these interphase nuclei is related to a diurnal rhythm.

Animals↗
PubMed1979

Effects of various media on tissular and cellular structures of the superior cervical ganglion of the rat.

The superior cervical ganglia of the rat have been incubated in vitro for 1 h in basal medium Eagle (BME) with Hanks' salts, BME with Earle's salts, Kreb's solution and NCTC 109 medium. Comparison of the cell areas, established by a semi-automatic quantitative method, shows that the three former induce a 30--35% neuronal retraction, whereas NCTC 109 has no effect. Thus this latter medium seems the best one for studies using incubation of these cells.

Animals↗
PubMed1979

Frequency and distribution of tubulo-filamentous nuclear inclusions in the celiac ganglion of the cat as revealed by serial sections.

On sections at random of a cat celiac ganglion we counted 68 sections of nuclear inclusions (NI) for 320 sections of neuronal nuclei, i.e. an "apparent' frequency of 0.20. As revealed by serial sections the "actual' frequency is higher since the 5 nuclei entirely explored exhibit 19 NI. Such a study shows that each nucleus may contain at least 3 and up to 5 different tubulo-filamentous NI.

Animals↗