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Tyrosine hydroxylase was used as an immunocytochemical marker of dopaminergic axons in the cerebral cortex either in fetuses or in postnatal life after lesion of the noradrenergic input. The lesion was controlled by the absence of dopamine-beta-hydroxylase immunoreactivity. Fluorescence histochemistry also allowed the specific visualization of the dopaminergic system following uptake of exogenous amines in tissue sections in presence of selective high affinity transport inhibitors. Two main dopaminergic (DA) subpopulations reach the medial cortex of the rat: 1) a deep one, first detected in the anterior frontal cortex on day 16 of embryonic life, was well developed at birth and extended caudally in layer V and/or layer VI toward the splenium of corpus callosum; 2) a superficial one was detected in layer I of the anterior cingulate cortex (area 24) on postnatal day 3 to 5 and invaded layer III from day 6 to 14. The adult distribution pattern and striking varicose aspect were not reached until day 21 to 30. In addition to these medial fields, a dopaminergic innervation of low density was detected laterally along a dorsal sagittal strip which encompassed several distinct cytoarchitectonic areas in the sensorimotor and visual cortex (medial and lateral agranular field, area 18b) as well as in discrete zones of the retrosplenial granular 29c, b, and agranular 29d areas. Several characteristics of this newly observed DA input were similar to that of the superficial field described in the anterior cingulate cortex; these similarities suggested that the subpopulation of DA neurons which provides projections to the anterior cingulate cortex could also contribute to the motor and visual cortex and thus play a role in sensorimotor integration. A DA terminal field was also demonstrated in the temporal part (ventral and caudal) of the hippocampal formation, the subiculum especially the prosubiculum and the adjacent CA1 hippocampal field being the main targets. This DA terminal field in the hippocampal formation matches with the area which projects toward the accumbens nucleus. Thus, the hippocampo-striatal projections which represent a link of functional importance between the limbic and central motor systems, could be modulated by the dopaminergic meso-cortico-limbic pathway. The predictive values of these data in the ascent of the phylogenetic scale are further considered.

Some rare mitotic Schwann cells (one in about a thousand) were found in normal mature spinal roots of adult lizards. Mitotic cells retained their relationships with unmyelinated axons, a finding consistent with the hypothesis that the stimulation of Schwann cell proliferation requires direct contact between axons and Schwann cells. The observation presented in this paper shows that Schwann cells and the satellite cells of sensory and autonomic ganglia behave in the same way also with regard to their mitotic activity.

An histological study of the peripheral nervous fibres has been performed at various anatomical levels during aging: the spinal ganglion, the dorsal and the ventral nerve roots, the spinal and the sciatic nerves. During aging the various alterations occurring in a peripheral nerve can be summarized as following. In the myelinated fibres, the axoplasm was progressively invaded by several inclusions: glycogen granules, granulo-filamentous bodies and lipofuscins. The crystalloid networks arising from the cytoskeleton were mainly localised in the intraganglionic fibres. Among the axoplasmic organelles, the mitochondria were the most affected. The myelinic sheath split, became dystrophic and then was totally disrupted. The inner schwann cell compartment was invaded by several inclusions like Hirano bodies and dense residual deposits. Further, macrophages phagocytosed the axon and the myelin sheath. In the non-myelinated fibres, the alterations were less important and less precocious. When these results are analysed from a chronological point of view it is established that the alterations appear at the same time in each observed level but their amount differ from each other. In the 24-month-old-rats, the ventral root and the sciatic nerve present many dystrophies whereas in the spinal ganglion and in the dorsal root they are less numerous. From these results, it can be suspected that the motor fibres are more vulnerable during aging. Moreover, the myelinated fibres of large diameter are the first affected. Furthermore, only the ventral root and the sciatic nerve show typical regeneration pictures at 32 months.

INTRODUCTION. Aging--the effect of time--occurs in every living organism. Senescence is the last period of the lifespan, leading to death. It happens in all animals, with the exception of a few didermic species (Hydras) having a stock of embryonic cells and being immortal. The causes of animal senescence are badly known. They depend both on genetic characters (maximal lifespan of a species) and on medium factors (mean expectation of life of the animals of a species). Animal senescence could depend on cell aging: 1) by senescence and death of the differentiated cells, 2) by modified proliferation and differentiation of the stem cells of differentiated tissues, 3) by alterations in the extracellular matrices, 4) by interactions between factors 1) 2) and 3) in each tissue, 5) by interactions between the several tissues of an organism. This complexity badly impedes the experimental study of animal senescence. Normal mammal cells are aging when they are cultivated (in vitro ageing): their phenotype varies and depends on the cell generation (in vitro differentiation); the last cell-generation doesn't divide anymore and declines until death of the culture (in vitro senescence). Analysis of these artificial but well controlled systems allows an experimental approach of the proliferation, differentiation, senescence and death of the cells and of the extracellular matrix functions. Present literature upon in vitro aging of cultivated human cells is essentially made of papers where proliferation and differentiation characteristics are compared between early ("young") and late ("old") cell-generations of the cultures. FIBROBLASTIC CELLS OF THE MOUSE SKIN. This cell type has been studied in our laboratory, using different systems: 1) Primary cultures isolated from peeled skins of 19 day old mouse embryos, 2) Mouse dermis analyzed in the animals, 3) Cultivated explants of skins, 4) Serial sub-cultures of fibroblasts isolated from these explants, 5) Cells cultivated comparably on plane substrates (glass, plastic, collagen films) and on tridimensional matrices (collagen fibres). Systems 2), 3), 4) and 5) have been obtained either from 19 day old embryos or from 6 groups of animals of different ages (from 1/2 till 25 month). In primary cultures (system 1) all the cell generations have been analyzed, including the last one until death of the culture. We have shown that many characters are varying with cell-generation: cell form and cell mass, rate of DNA replication and cell division, rate of RNA transcription, nature of the accumulated and of the synthetized proteins, organization of the cytoskeletal elements, organization of the extracellular matrix, type of cell death.(ABSTRACT TRUNCATED AT 400 WORDS)

In an attempt to define cytophysiological criteria with which to establish whether or not a given neuron is serotoninergic, radioautography was combined with serotonin (5-HT) immunocytochemistry on the same sections from the nucleus raphe dorsalis (NRD) and/or nucleus dorsomedialis hypothalami (NDM) in rats subjected to intraventricular administrations of (3H)-5-HT or (3H)-dopamine (DA). All the (3H)-5-HT-accumulating neurons (cell bodies, dendrites and terminals) were found to be distinct from the (3H)-DA labeled ones and invariably immunostained for 5-HT in both regions studied. However, some immunoreactive neuronal elements within the area of tracer diffusion did not exhibit significant radioautographic labeling. In the NDM where 5-HT immunoreactive nerve cells could be detected only after intraventricular administration of 5-HT, these were found to be definitely distinct from the tyrosine hydroxylase immunoreactive and (3H)-DA labeled neurons of the dopaminergic periventricular-arcuate complex. After immunostaining for GAD at the electron microscopic level, (3H)-5-HT labeled nerve cells and terminals were not found to exhibit any significant immunoreactivity. Associations between (3H)-DA labeled and GAD immunoreactive processes with 5-HT immunoreactive or (3H)-5-HT-accumulating neurons, respectively, could also be observed in the NDM. When considered as a whole along with previous observations by other authors indicating a probable synthesis of 5-HT within NDM neurons, our data suggest that a given neuron can be classified as serotoninergic on the sole basis of its ability to selectively take up exogenous 5-HT under experimental conditions compatible with non interspecific labeling of catecholaminergic neurons. They also provide valuable information on the neurochemical environment and possible control of central serotoninergic neurons.

Isosmotic fluid absorption carried out by many mammalian epithelia appears to be similar to the isosmotic secretion of insect epithelia such as the Malpighian tubules, which are responsible for urine formation and osmoregulation. We have studied by electron microscopy (80 kV) the three-dimensional characteristics of organelles in the Malpighian tubules of Rhodnius prolixus using thick sections (0.3-0.5 microns) and uranyl and lead impregnation. The ER presents a different organization in the upper (distal) and lower (proximal) segments of the Malpighian tubule. In distal secretory segment, the ER forms a network made of chains of vesicles having irregular shapes (ca. 0.06 micron in diameter) connected to each other by canaliculi while in the lower absorptive segment, the ER is made of parallel saccules arranged in stacks or whorls in the central region of the cytoplasm. In both segments, the ER network extends throughout the cytoplasm from the basolateral infoldings to the apex between the many mitochondria present in these two areas. A unique feature of these cells, revealed by thick sections, is the presence in each microvillus of either a mitochondrion or an ER canaliculus in continuity with the ER network. The ER does not seem to have any specific association with mitochondria or other organelles. As in the mammalian nephron, this ER organization is most likely related to specific segmental functions and adds support to its potential role as a transcellular epithelial route.

An electron microscopic study was undertaken of the protein release mechanism within myeloma cells showing a very high degree of protein production. Smooth surfaced vesicles (50 millimicrons) were seen to originate from the outer margin of the perinuclear cistern. Similar vesicles were also associated with distended Golgi sacs. Possible function of these vesicles could not be determined. Coated vesicles (60 millimicrons) originated as evaginations from endoplasmic reticulum in the transitional region. They were present throughout the cytoplasm and were seen to fuse with the cell membrane discharging an electron dense material. These vesicles are, therefore, thought to transport protein from the rough endoplasmic reticulum and discharge it at the cell surface.