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Biomedical subjects

A Privat

Publications and source records attributed to A Privat.

At least 199 records · Page 11Linked to original sources
PubMed1981

Proliferation of neuroglial cell lines in the degenerating optic nerve of young rats. A radioautographic study.

Wallerian degeneration was investigated in the rat optic nerve after eye enucleation at 2, 5, 8, and 20 D.P.N. (key stages), corresponding to the periods of premyelination, myelination, and postmyelination. The incorporation of tritiated thymidine, and subsequent radioautography of semithin sections, allowed the identification and enumeration of labeled cells, and the computation of labeling indices of the different cell types (glioblasts, astrocytes, oligodendrocytes, and microglia) in the operated as well as the contralateral nerve. The comparison of labeling indices and absolute numbers of labeled cells in each category suggests an increased transformation of glioblasts into astrocytes, and absence of differentiation and stabilization of oligodendrocytes due to the failure of the axonal signal, and a transformation of pericytes into interstitial microglia. The first three key stages (2, 5, and 8 D.P.N.) are characterized by the integration of reactive gliosis and more or less marked failure of myelination gliosis, whereas the last one (20 D.P.N.) shows essentially a reactive gliosis. The modifications of the neural environment interfere with the genetic program of gliogenesis, illustrating the postnatal plasticity of the central nervous system.

Animals↗
PubMed1980

[Evidence of autapses in vitro by electron microscopy combined with iontophoretic intracellular injection of peroxidase].

The existence of autapses, i. e. of synapses between a neuron and its own axon, is demonstrated in vitro by means of Horseradish peroxidase (HRP) iontophoretic filling, combined with electron-microscopic (EM) analysis. After the injection of one single Purkinje cell per explant (Kitten cerebellum), the ultrastructural observation (serial thin sections) reveals the presence of both pre- and post-synaptic labelled structures. Axodendritic autapses are thus illustrated and their significance is discussed in view of earlier morphological and electrophysiological data.

Animals↗
PubMed1979

Jimpy mouse myelin revisited with freeze-fracture.

Corpus callosum, cerebellum, and spinal cord from Jimpy mice, and control littermates, 15 and 21 days old, were prepared for freeze-fracture in a "cryofract" apparatus. The few myelinated axons in the Jimpy exhibited a striking paucity of particles in myelin P faces, though tight junctions were present. In addition, small maculae of particles were found on these P faces. Peripheral myelin appeared normal, both for the quantity and disposition of particles on their P faces.

Animals↗
PubMed1979

In vitro differentiation of hypothalamic magnocellular neurons of guinea pigs.

The development of neurophysin-oxytocin and neurophysin-vasopressin containing neurons of the guinea pig was studied in vitro. Supraoptic (SO) and paraventricular (PV) nuclei were explanted from guinea pig foetuses at the 40th day of gestation and cultured in Maximov slides for nearly fifty days. The cultures were observed daily under a phase-contrast microscope. Explants were fixed every five days for observation with the electron microscope. At the time of explantation, magnocellular neurons were still immature. They acquired the morphologic characteristics of mature neurons, with axosomatic synapses, after about 10 days in vitro. After 15-20 days in vitro, they contained in addition neurosecretory granules (NSG), first in the Golgi region, then also dispersed in the cytoplasm. In the oldest culture (45-50 days), signs of granulolysis were regularly found. It appears that magnocellular neurosecretory neurons are able to differentiate in vitro from a primitive state in the absence of specific stimulation.

Animals↗
PubMed1979

Differential radiosensitivity of neurons and neuroglia of the hippocampus in the adult rabbit.

Adult rabbits were subjected to 4.5 Gy of whole-blody or brain alone gamma-irradiation, and their hippocampus was examined with the light and electron microscope. Pycnotic cells were found at the base of the granular layer of the dentate gyrus in the so-called subgranular zone, as soon as 3 h after irradiation, and were cleared up by active phagocytosis after 48 h. Some of these cells appeared as undifferentiated, whereas others were differentiating granule cells, and possibly immature neuroglia. The extent of cell necrosis was contingent upon the age of the animal, the oldest animal studied (27 months) showing only sparse lesion of that type. Astrocytes and microglia were responsible for the phagocytosis of dead cells. Another type of lesion was found in the nuclei of the mature granule cells and consisted of light spots which appeared 1 h after the irradiation and disappeared almost completely after 48 h. Pyramidal cells did not show any of these two lesions. It is concluded that the laterations in the electrical activity of pyrimidal cells, following irradiation, are at least partly due to lesions affecting the dentate gyrus. Radionecrosis in the subgranular zone is related to the presence of immature cells in this region.

Age Factors↗
PubMed1979

Absence of the major dense line in myelin of the mutant mouse "shiverer".

The myelin of the central nervous system (CNS) of the mutant mouse Shiverer is characterized by the absence of the major dense line (MDL). The intraperiod line, as seen in conventional electron micrographs and in freeze-fractured replicas, appears normal. Peripheral myelin, as seen in ventral and dorsal roots of spinal cord, is unaffected by the mutation. During the period of active myelination, the cytoplasm of most oligodendrocytes (ODs) is packed with electron-lucent vacuoles in continuity with the Golgi apparatus and with bundles of microtubules. It is concluded that a metabolic pathway possibly involving the Golgi apparatus, and contributing to the formation of the MDL is selectively affected in this mutant.

Animals↗
PubMed1979

Immunochemical studies of myelin basic protein in shiverer mouse devoid of major dense line of myelin.

The myelin-deficient mutant Shiverer (Shi/Shi) lacks basic protein (MBP) in the myelin of its central nervous system (CNS). Less than 3% of the normal content in MBP is present in a brain extract of Shi/Shi as determined by radioimmunoassay. Indirect immunofluorescence is negative when using specific anti-MBP serum. The importance of Shi/Shi (as compared to other hypomelinating mutants) stems from the specificity of this genetic lesion, i.e. the lack of basic protein.

Animals↗
PubMed1978

Dendro-dendritic pentalaminar junctions in the Weaver mouse cerebellum.

The cerebellum of weaver mouse is characterized by an extensive reorganization of cell interaction secondary to the absence of mature granule cells. One yet undescribed modality of reorganization found in the hemispheres of 1-month-old animals consisted in the presence of dendro-dendritic pentalaminar junctions. The possible formation of these junctions by fusion of facing post-synaptic densities is discussed.

Animals↗
PubMed1977

Differentiation of chick embryo neuroretina cells in monolayer cultures. An ultrastructural study. I. Seven-day retina.

Neuroretinas from 6--7 day-old chick embryos were cultivated after trypsin dissociation as monolayer cultures in Petri dishes, and examined after various intervals of time with the electron microscope. Soon after plating, cells begin to reaggregate in small clumps, and typical rosettes are formed. During the first week in vitro, cells appear to differentiate as neuroblasts and presumed Müller cells; the latter form a continous sheet on the substrate, upon which neuroblasts migrate and grow their neurites. Differentiated ribbon synapses are found after 8 days in vitro, the time at which they normally appear in situ. After 15 and 21 days in vitro, synapses are still found in large numbers, mimicking their "in vivo" counterparts. Photoreceptor cells were identified on the basis of the presence of typical ribbons in their cytoplasm, but no outer segment was found. It appears then that synaptogenesis in the retina is programmed independently of the tissue environment, which is markedly disturbed in the monolayer culture.

Animals↗
PubMed1977

Infection of cultivated CNS tissue with herpes virus, HSVII. A reappraisal.

Organized cultures of newborn rat and hamster cerebellum were infected with herpes virus type II, after 7 and 14 days "in vitro". 48 h after the infection, electron microscopic examination of the cultures showed that astrocytes contained numerous intranuclear and intracytoplasmic viral particles, while neurons remained apparently intact. The specificity of the infection for a given cell type is discussed.

Animals↗
PubMed1977

Do oculomotor neuroblasts migrate across the midline in the retal rat brain?

Toluidine blue-stained semithin sections and Cajal-Castro preparations are used to study in rat fetuses whether oculomotor neuroblasts migrate across the midline at a certain period of development. In confirmation of previous studies, a group of oculomotor neuroblasts was detected which first grow cytoplasmic processes into the mesencephalic midline, and afterwards translocate their somata towards the midline, between the 12th and the 15th days of gestation. At this moment a midline mass of neuroblasts characterizes the meeting at this landmark of both left and right migrating neuroblastic groups. No crossing oculomotor axons yet are demonstrable with reduced silver techniques. In further stages of development the neuroblasts continue their migration until they arrive at the contralateral nucleus at the 16th and 17th day of gestation. At the midline the mass of neuroblasts disappears gradually and crossed oculomotor axons become visible. The electron microscope was then used to study ultrastructurally the migrating motoneurons. It was discovered that no preexisting structure guides their movement by contact. Their leading processes show no filopodial activity, and contain abundant microtubules and thick bundles of neurofilaments in eccentric position. The neuroblasts carry their axon across the midline as a trailing process.

Animals↗
PubMed1976

Postnatal maturation of rat Purkinje cells cultivated in the absence of two afferent systems: an ultrastructural study.

Organized cultures of newborn rat cerebellum were established in Maximow chambers in order to study the maturation of Purkinje cells in absence of afferent systems. In the first model, standard cultures were devoid of extracerebellar afferents mossy and climbing fibers. Despite this absence, somatic spines appeared upon Purkinje cells during the first week in vitro and maturation proceeded normally except for the almost absence of spiny branchlets. Large dendritic trunks were studded with numerous spines, some of which were naked, a few bearing isolated post-synaptic densities and others occupied by boutons of parallel fibers. Stellate and basket axons made synapses upon the smooth portions of dendrites and soma. In a second model, the cultures were fed the antimitotic drug methylazoxymethanol (MAM) to prevent multiplication of granule cell precursors. Despite the absence of climbing and parallel fibers, the elongation of Purkinje dendrites was not prevented, but again the dendritic arbor consisted of large trunks studded with spines; somatic as well as dendritic spines were contacted by large boutons identified as Purkinje recurrent collaterals (PRC). It is concluded that the Purkinje cell possesses a large autonomy from afferent systems as to the growth of soma and dendrites. Conversely, the geometry of the dendrite and especially the spiny branchlets depend on the presence of both climbing and parallel fibers. One may conclude from the above experiments that specificity of synaptic contacts is maintained as long as postsynaptic sites are not devoid of their normal afferents. Heterologous synapses are formed when postsynaptic sites are present, their normal afferents absent and aberrant ones increasing by collateral sprouting. Such is probably the case in the second model of this study.

Animals↗