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Golgi-electron microscopic study of sprouting endothelial cells in the neonatal rat cerebellar cortex.
Intraparenchymal postnatal development of the CNS vasculature proceeds by a process of vascular 'budding' or 'sprouting' from existing endothelial cells and elongation of these immature vessels. A modified Golgi technique combined with gold toning and deimpregnation was used to identify and characterize sprouting endothelial cells in the neonatal rat cerebellar cortex with light and electron microscopy. Sprouting endothelial cells were the terminal endothelial cells of immature, developing blood vessels and they had characteristic morphologic features. The most distinctive feature was an array of tentacular processes (0.1-0.2 micron in diameter and ca. 20 microns in length) which radiated from the apex of these cells in the presumed direction of vessel growth. Cytoskeletal microtubules and microfilaments were the characteristic organelles of these tentacles. Sprouting endothelial cells were thin (1-3 microns in diameter). lacked a vessel lumen and basement membrane, had abundant cytoplasmic organelles and a prominent nucleus and were closely associated with the subterminal endothelial cell without interendothelial gaps. The developing blood vessels had a blood-brain barrier which excluded intravenously injected colloidal carbon from the neuropil.
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Zika virus enhances monocyte adhesion and transmigration favoring viral dissemination to neural cells.
Zika virus (ZIKV) invades and persists in the central nervous system (CNS), causing severe neurological diseases. However the virus journey, from the bloodstream to tissues through a mature endothelium, remains unclear. Here, we show that ZIKV-infected monocytes represent suitable carriers for viral dissemination to the CNS using human primary monocytes, cerebral organoids derived from embryonic stem cells, organotypic mouse cerebellar slices, a xenotypic human-zebrafish model, and human fetus brain samples. We find that ZIKV-exposed monocytes exhibit higher expression of adhesion molecules, and higher abilities to attach onto the vessel wall and transmigrate across endothelia. This phenotype is associated to enhanced monocyte-mediated ZIKV dissemination to neural cells. Together, our data show that ZIKV manipulates the monocyte adhesive properties and enhances monocyte transmigration and viral dissemination to neural cells. Monocyte transmigration may represent an important mechanism required for viral tissue invasion and persistence that could be specifically targeted for therapeutic intervention.
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[Ultrastructure of blood capillaries in several secretory organs].
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The chromodomain protein CDYL confers forebrain identity to human cortical organoids by inhibiting neuronatin.
Fate determination of neural stem cells (NSCs) is crucial for cortex development and is closely linked to neurodevelopmental disorders when gene expression networks are disrupted. The transcriptional corepressor chromodomain Y-like (CDYL) is widely expressed across diverse cell populations within the human embryonic cortex. However, its precise role in cortical development remains unclear. Here, we show that CDYL is critical for human cortical neurogenesis and that its deficiency leads to a substantial increase in gamma-aminobutyric acid (GABA)-ergic neurons in cortical organoids. Subsequently, neuronatin (NNAT) is identified as a significant target of CDYL, and its abnormal expression obviously influences the fate commitment of cortical NSCs. Cross-species comparisons of CDYL targets unravel a distinct developmental trajectory between human cortical organoids and the mouse cortex at an analogous stage. Collectively, our data provide insight into the evolutionary roles of CDYL in human cortex development, emphasizing its critical function in maintaining the fate of human cortical NSCs.
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Cytochemical localization of cyclic 3', 5'-nucleotide phosphodiesterase activity in the neuromuscular junction and skeletal muscle of the newt.
The localization of cyclic 3', 5'-nucleotide phosphodiesterase activity at the neuromuscular junction and in skeletal muscle of the newt was studied cytochemically. In the axon terminal, activity was localized to a site on the membranes of synaptic vesicles. In skeletal muscle, activity occurred in the sarcoplasmic reticulum but was restricted to the longitudinal tubules. Junctional folds of the motor end plate were unreactive. These findings are suggestive of a role of cyclic AMP in the functions of synaptic vesicles and sarcoplasmic reticulum and indicate its effects are terminated at these sites.
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An ultrastructural study of the microfilaments in rat brain by means of E-PTA staining and heavy meromyosin labeling. II. The synapses.
To identify structures involved in the translocation of the synaptic vesicles towards the presynaptic membrane, an ultrastructural study has been undertaken by means of (1) the E-PTA stain and (2) the HMM-labeling procedure. Using serial sections of E-PTA stained nervous tissue, especially those made in transversal and tangential planes, the geometric order of the presynaptic grid and of its constituents has been described in detail. It consisted of dense projections having the shape of small truncated pyramids cut parallel to their hexagonal bases which rested on the electron-lucent presynaptic membrane. The dense projections were arranged at the points of equilateral triangles. Around each dense projection, six asymmetric hexagonal holes were seen to be arrayed in an hexagonal pattern, forming thus the presynaptic sieve. From the spiny tops of the dense projections, which appeared as specialized structures of the dense material coating the inner surface of the plasma membrane at the level of the synaptic cleft, fine filaments, 40--60 A in diameter, radiated and formed a three-dimensional meshwork pervading the presynaptic bag. The dense cytoplasmic coating delineating the plasma membrane served as anchor points for these microfilaments. Upon incubation with rabbit skeletal muscle HMM the microfilaments underwent specific structural changes, consisting of: (1) a striking increase in diameter; (2) the association of periodic and polarized substructures with their surfaces. The synaptic vesicles and mitochondria were seen to be attached to the numerous HMM-decorated filaments or enmeshed in the network formed by these filaments. The actin-like filaments were anchored to the plasma membrane at many points and to the presynaptic dense projections. Following incubation in the buffer alone or in buffer HMM solutions containing Na+ pyrophosphate or ATP, no arrowheaded structures were observed. Thus, a network consisting of actin-like filaments was demonstrated in the presynaptic bag. Of particular interest was the structural relation of the actin-like filaments with the occasional, tapered myosin-like filaments. The role of the presynaptic actin-like network in the transport of synaptic vesicles towards the presynaptic membrane by a mechanism of chemomechanical transduction is discussed. In the postsynaptic dendrite or dendritic spine, a filamentous network was observed to be attached to the subsynaptic web by means of the E-PTA stain and of the HMM-labeling procedure. The occurrence of an actin-like meshwork in the postsynaptic region is suggested to produce changes in the macromolecular configuration of the postsynaptic membrane by a "mechanoenzyme" system similar to that described in the mitochondrial membrane.
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Transsynaptic response of the lateral geniculate nucleus and the pattern of degeneration of the nerve terminals in the rhesus monkey after eye enucleation.
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Complex convolutions in neurons of the dorsal lateral geniculate nucleus of the normal albino rat.
The postnatal development of complex convolutions (CCs) of the dorsal lateral geniculate nucleus (LGNd) in normal rats has been studied quantitatively with light microscopy. We report that immature neurons do not contain these scarcely understood organelles, since they can be seen for the first time in very few, mature neurons of the 30 day rat; their number constantly increases during the following 4 months. These cytoplasmic inclusions can be equally seen in the aged rat. CCs are present in neurons of all sizes, except the smallest, which correspond to the interneuron population. Although, morphologically, CCs of the LGNd of the rat are similar, but not identical, to the cytoplasmic multilaminated bodies of the cat, intermediate forms are described.
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Organization of the neurofilamentous network.
The neurofilamentous network of the normal rabbit brain (lateral vestibular nucleus) and of biopsies of human patients (cerebral cortex, sural nerve) was investigated electron microscopically. Thin sections of samples prepared by standard techniques and unfixed spreads of freshly isolated perikarya were utilized. The neurofilaments are assembled into a three-dimensional network associated with the axolemma, microtubules, mitochondria and polyribosomes. The elements of this network demonstrate helicity at several levels of organization. It is proposed that they are in a dynamic state of equilibrium between ordered lattice and open network paracrystalline states. Reversible phase transitions in the subunit proteins of the neurofilaments may lead to coiling and uncoiling of the filaments and induce alterations in the network structure of the neuroplasm. Giant axonal swellings in biopsies of the sural nerve are interpreted as accumulations of cytoskeletal elements in the absence of the orienting effect of microtubules. In cortical neurons of patients with Alzheimer's disease parts of the neurofilamentous network are in altered paracrystalline states; virus-like particles occur within this modified network. These concepts of cytoskeletal organization - network, helicity, phase transitions, and paracrystallinity - are useful for the interpretation of pathological alterations of the cytoskeleton and for an understanding of cytoskeletal organization in general.
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The role of Müller cells in the formation of the blood-retinal barrier.
We have compared the ability of Müller cells and astrocytes to induce the formation of barrier properties in blood vessels. Müller cells cultured from the rabbit retina, and astrocytes and meningeal cells cultured from the rat cerebral cortex, were injected into the anterior chamber of the rat eye, where they formed aggregates on the iris. We have examined the barrier properties of the vessels in those aggregates and, for comparison, the barrier properties of vessels in the retina, ciliary processes and iris. Two tracers were perfused intravascularly to test barrier properties. The movement of Evans Blue was assessed by light microscopy, and the movement of horseradish peroxidase by light and electron microscopy. Our results indicate that Müller cells share the ability of astrocytes to induce the formation of barrier properties by vascular endothelial cells, and we suggest that Müller cells play a major role in the formation of barrier properties in retinal vessels.