Ultrastrukturelle Lokalisation von Mukosubstanzen der Zellhülle im Subcommissuralorgan der Ratte

Cutinsomes of Malus Mill. (Rosaceae) leaf and pericarp: genesis, localization, and transport

New data were obtained on specific bionanostructures, cutinsomes, which are involved in the formation of cuticles on the surface of leaf blades and pericarp of Malus domestica Borkh (Malus Mill., Rosaceae)introduced to the mountains at the altitudes of 1200 and 1700 m above sea level. Cutinsomes, which are electron-dense structures of spherical shape, have been identified by transmission electron microscopy. It was demonstrated that plastids can be involved in the synthesis of their constituent nanocomponents. The greatest number of nanoparticles was observed in the granal thylakoid lumen of the chloroplasts in palisade mesophyll cells and pericarp hypodermal cells. The transmembrane transport of cutinsomes into the cell wall cuticle proper by exocytosis has been visualized for the first time. The plasma membrane is directly involved in the excretion of nanostructures from the cell. Nanoparticles of cutinsomes in the form of necklace-like formations line up in a chain near cell walls, merge into larger conglomerates and are loaded into plasmalemma invaginations, and then, in membrane packing, they move into the cuticle, which covers both outer and inner cell walls of external tissues. The original materials obtained by us supplement the ideas about the non-enzymatic synthesis of cuticle components available in the literature and expand the cell compartment geography involved in this process.

The subcommissural organ

The subcommissural organ (SCO) is a phylogenetically ancient and conserved structure. During ontogeny, it is one of the first brain structures to differentiate. In many species, including the human, it reaches its full development during embryonic life. The SCO is a glandular structure formed by ependymal and hypendymal cells highly specialized in the secretion of proteins. It is located at the entrance of the aqueduct of Sylvius. The ependymal cells secrete into the ventricle core-glycosylated proteins of high molecular mass. The bulk of this secretion is formed by glycoproteins that would derive from two different precursors of 540 and 320 kDa and that, upon release into the ventricle aggregate, form a threadlike structure known as Reissner's fiber (RF). By addition of newly released glycoproteins to its proximal end, RF grows caudally and extends along the aqueduct, fourth ventricle, and the whole length of the central canal of the spinal cord. RF material continuously arrives at the dilated caudal end of the central canal, known as the terminal ventricle or ampulla. When reaching the ampulla, the RF material undergoes chemical modifications, disaggregates, and then escapes through openings in the dorsal wall of the ampulla to finally reach local blood vessels. The SCO also appears to secrete a cerebrospinal fluid (CSF)-soluble material that is different from the RF material that circulates in the ventricular and subarachnoidal CSF. Cell processes of the ependymal and hypendymal cells, containing a secretory material, terminate at the subarachnoidal space and on the very special blood capillaries supplying the SCO. The SCO is sequestered within a double-barrier system, a blood-brain barrier, and a CSF-SCO barrier. The function of the SCO is unknown. Some evidence suggests that the SCO may participate in different processes such as the clearance of certain compounds from the CSF, the circulation of CSF, and morphogenetic mechanisms.

Glycoconjugate histochemistry of the subcommissural organ in the domestic chicken: lectin histochemistry using the avidin-biotin-peroxidase complex (ABC) method

The properties and distribution of the secretory substance in the ependymal cells of the subcommissural organ in the domestic chicken were examined with seven different lectins, using the avidin-biotin-peroxidase complex method. On the ventricular surface of this organ, LFA, PNA, RCA-I and WGA reacted positively. In the apical cytoplasm, Con A, LFA, RCA-I and WGA gave positive reactions. On the other hand, only Con A and WGA gave positive reactions in the basal cytoplasm. In the hypendymal vascular wall, LFA, RCA-I and WGA reacted positively. Neuraminidase digestion completely inhibited reactions with LFA and reduced the WGA reaction within the apical cytoplasm. At the same time, this digestion disclosed a moderately positive reaction with PNA in the apical cytoplasm. The significant findings of this study may be summarized as follows: 1) the ependymal cells of the subcommissural organ in the domestic chicken synthesize a complex oligosaccharide for a secretory product which is discharged into the ventricular cavity; 2) in the basal cytoplasm and basal processes, only oligosaccharides containing large amount of mannose are present.

Ultrastructure of complex carbohydrates of rodent and monkey ependymal glycocalyx and meninges

The surfaces of the brain offer metabolic and mechanical support to the underlying parenchyma. Mouse, rat, and monkey brains were fixed by immersion in a glutaraldehyde fixative or glutaraldehyde with cetylpyridinium chloride, followed by block staining for complex carbohydrates using alcian blue with OsO4 postfixation, or OsO4 postfixative solution containing ruthenium red, or alcian blue and then ruthenium red-OsO4 treatment. The ependyma in these species had a glycocalyx extending into the ventricular fluid as a finely filamentous network when stained with alcian blue or with alcian blue followed by ruthenium red-OsO4. Mice in the middle age range had stained material in this glycocalyx resembling the hyaluronic acid reported in the ocular vitreous body. Similar material was seen in the arachnoidal space of these mice and in the inner connective tissue matrix of the dura mater. Both the mouse and monkey had a cell-free zone, termed the inner dural matrix zone, between the thick fibrous dura and its innermost cellular layer. This zone contained filamentous and globular alcian blue-stained material. The complex carbohydrates of the mouse ependymal glycocalyx and inner dural matrix zone underwent changes developmentally. Aged rats were injected intraventricularly with latex beads, which, along with extravasated erythrocytes, were seen to adhere to the ependymal glycocalyx. A similar adhesion of erythrocytes was seen in the mouse and monkey ependymal glycocalyx and in the filamentous network of the mouse and monkey inner dural matrix zone. The ependymal glycocalyx, formed in part of complex carbohydrates, is much thicker than previously demonstrated. Some activities related to the ependymal lining of the ventricles, including the movement of cells or particles, the penetration of metabolites or serum-protein fractions (e.g., immunoglobulins), and cell-surface hydration, probably depend in part on complex carbohydrates that provide a sticky, electrically negative, hydrophilic environment. The complex carbohydrates in the inner dural matrix zone might provide mechanical buffering. Complex carbohydrates in the arachnoidal space may help to maintain a loose tissue that needs not only to be hydrated, but also to be open enough to provide cerebrospinal fluid circulation.

Intercellular junctions between specialized ependymal cells in the subcommissural organ of the rat

The permeability of intercellular junctions in specialized ependymal cells in the rat subcommissural organ (SCO) has been studied ultrastructurally by freeze-fracturing and tracer experiments with horseradish peroxidase (HRP). In addition to normal smooth membrane, areas which could be classified as a leaky tight junction are found within the ependymal junctional region. This consists of only one or two relatively continuous strands but with interruptions in the apical portion. Some strands are perpendicular to the apical membrane surface and often form hairpin-like bends in the basal portion of the junction. The junctional region also shows areas with no strands but only a rippled membrane structure which may be equivalent to very close appositions without fusion of adjacent ependymal cell membranes. The relative proportions of normal smooth membrane, strands and rippled structure in the junctional region is approximately 3:4:6 including two parts overlapping of the strands and rippled structure. Intraventricularly infused HRP passes through many junctions but is occasionally stopped, leaving unstained intercellular spaces of various lengths between membrane fusions of tight junctions. Even when it is stopped, the intercellular space below the junction is densely stained by the enzyme. Orthogonal arrays of intramembrane particles are found to be distributed on the basal and lateral cell membranes below the junctional region in the SCO ependyma.

Serotoninergic synapses on ependymal and hypendymal cells of the rat subcommissural organ

The nervous input to the subcommissural organ (SCO) of the rat has been investigated with Falck-Hillarp fluorescence histochemistry and electron microscopical techniques. Previous fluorescence histochemical observations of a dense plexus of serotoninergic nerve fibres in relation to the basal SCO were confirmed. Electron microscopically, unmyelinated fine varicose axons ranging in size from 0.1--0.6 micrometer were observed to penetrate into the SCO hypendyma. Boutons and presynaptic varicosities filled with a diversity of round and elongated clear vesicles, and occasional large dense cored vesicles establish asymmetric (Gray's type I) synaptic contacts with the basal processes and somata of the SCO ependymal and hypendymal cells. A typical varicosity in synaptic contact with an SCO cell contains a population of approximately 85% clear, elongated vesicles 45 X 60 nm in diameter, 15% clear, round vesicles 50 nm in diameter, and 1--2% large dense cored vesicles with a vesicle diameter of about 85 nm and a dense core diameter of 50--55 nm. The mean length of the postsynaptic membrane specialization was found to be 0.5 micrometer. Experiments with specific neurotoxic drugs revealed that the nerve terminals in synaptic contact with the SCO cells are identical to the fibres of the serotoninergic plexus identified fluorescence histochemically. Thus, an intraventricular injection of either 5,6-dihydroxytryptamine or 5,7-dihydroxytryptamine induced typical degenerative changes in most of the boutons in synaptic contact with the SCO cells, and also a disappearance of the yellow fluorescent nerve plexus. It is concluded that the SCO of the rat receives a dense plexus of serotonin-containing nerve fibres which form typical synaptic contacts with the specialized ependymal cells of the SCO and that these fibres may constitute the only direct nervous input to the organ. The degeneration of the serotoninergic synapses elicited a long-lasting, pronounced increase in the secretory activity of the SCO. Despite long survival times after the treatment with neurotoxic drugs, we found no evidence of regenerative restitution of the serotoninergic innervation nor normalization of the secretory activity of the SCO. The observed inverse relationship between secretory activity and serotoninergic innervation is in line with previous observations which indicate that the 5-hydroxytryptamine input to the SCO ependymal and hypendymal cells exerts a powerful inhibition on their protein synthetic machinary.