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  • Articles  (185)
  • Ultrastructure  (185)
  • Springer  (185)
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  • Medicine  (184)
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  • Articles  (185)
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  • 1
    Electronic Resource
    Electronic Resource
    Biology and ultrastructure of the mycophagus, soil testate amoeba, Phryganella acropodia (Rhizopoda, Protozoa) (1990)
    Springer
    Biology and fertility of soils 9 (1990), S. 101-109 
    Details
    ISSN: 1432-0789
    Keywords: Phryganella acropodia ; Testate amoeba ; Growth rate ; Rhizopoda ; Feeding ; Fungal species ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Clones of Phryganella acropodia were cultivated under different trophic conditions with bacteria as the food source. The doubling time was estimated to be 3 days. The edibility of four species of fungi, Aspergillus niger, Cunninghamella echinulata, Penicillium echinulatum and Stilbella bulbicola, was tested, but only Penicillium enchinulatum and Stilbella bulbicola were eaten and digested by the amoeba. An ultrastructure examination showed that there are two contractile vacuoles, many dictyosomes, a single nucleus with several nucleoli, and peroxisomes. The pseudopodia are filiform when attached to the substrate but change to lobose when the animal is floating. A thin organic membrane covers the aperture of resting forms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00335791
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  • 2
    Electronic Resource
    Electronic Resource
    In vitro formation of mineralized nodules by periodontal ligament cells from the rat (1992)
    Springer
    Calcified tissue international 50 (1992), S. 459-467 
    Details
    ISSN: 1432-0827
    Keywords: Periodontal ligament fibroblast ; Mineralized nodule ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The purposes of this study were to determine whether periodontal ligament (PDL) cells are capable of producing mineralized nodules in vitro and to analyze ultrastructural features of the nodules. Rat PDL cells were obtained from coagulum in the socket at 2 days after tooth extraction and cultured at confluence in standard medium containing Dulbecco's Modified Eagle's Medium supplemented with 10% FBS and antibiotics. To test mineralized nodule formation, cells were further cultured for an additional 3 weeks in the standard medium containing (1) ascorbic acid (50 μg/ml) and sodium β-glycerophosphate (10 mM), (2) ascorbic acid, sodium β-glycerophosphate, and dexamethasone (5 μM), or (3) ascorbic acid alone. Cells were then fixed in 2.5% glutaraldehyde, postfixed in 1% OsO4, and prepared for light and electron microscopy. Threedimensional nodules containing mineralized matrices were formed only when the cells were cultured in the presence of ascorbic acid and dexamethasone. They were composed of multilayered fibroblasts (up to 13 layers), and highly organized collagen fibrils with 64 nm cross-banding patterns between the cell layers. The fibroblasts in the nodules exhibited an elongated shape with a high degree of cytoplasmic polarity throughout the nodule, and have the morphological features of PDL fibroblasts as seen in vivo. Mineral deposition with needle-like crystals was initiated on collagen fibrils located in intercellular spaces of the upper cell layers and became increasingly heavier towards the bottom half of the nodules. X-ray microanalysis and electron diffraction analysis confirmed that mineral deposition contained calcium and phosphate in the form of immature hydroxyapatite. These nodules contained neither osteoblasts nor osteocytes, and have their own morphological organization and characteristics which differ from those formed by bone cells in culture. Therefore, these data suggest that PDL cells are capable of forming mineralized tissue in vitro with the morphological characteristics different from bone mineralized nodules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00296778
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  • 3
    Electronic Resource
    Electronic Resource
    Ultrastructural evidence of GABA-ergic inhibition and glutamatergic excitation in the pacemaker nucleus of the gymnotiform electric fish, Hypopomus (1994)
    Springer
    Journal of comparative physiology 174 (1994), S. 267-280 
    Details
    ISSN: 1432-1351
    Keywords: Electric fish ; Pacemaker ; GABA ; Glutamate ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The medullary pacemaker nucleus of Hypopomus triggers each electric organ discharge (EOD) by a single command pulse. It consists of electrotonically coupled ‘pacemaker’ cells, which generate the rhythm, and ‘relay’ cells, which follow the pacemaker cells and excite the spinal motoneurons of the electric organ. The pacemaker cells receive two inputs from the complex of the diencephalic prepacemaker nucleus (PPn), a GABA-ergic inhibition and a glutamatergic excitation. Relay cells, on the other hand, receive two glutamatergic inputs, one from a subnucleus of the PPn, the PPn-C, and a second from the sublemniscal prepacemaker nucleus (SPPn). We have labelled afferents to the pacemaker nucleus by injecting HRP to specific sites of the prepacemaker complex. By using immunogold-labelled antibodies and en-grid staining techniques, we demonstrated GABA and glutamate immunoreactivity in labelled synaptic profiles of ultra-thin sections of the pacemaker nucleus. The two types of synapses were interspersed on the surfaces of pacemaker cells, with GABA-immunoreactive synapses apparently representing the GABA-mediated input of the ‘PPn-I’, an inhibitory subdivision of the PPn, and glutamate-immunoreactive synapses representing the input of the ‘PPn-G’, an excitatory subdivision of the PPn. Only glutamate-immunoreactive synapses were found on relay cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00240210
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  • 4
    Electronic Resource
    Electronic Resource
    Ultrastructural study ofCryptococcus neoformans by quick-freezing and deep-etching method (1993)
    Springer
    Mycopathologia 121 (1993), S. 133-141 
    Details
    ISSN: 1573-0832
    Keywords: Capsule ; Cryptococcus neoformans ; Deep-etching ; Quick-freezing ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The three-dimensional ultrastructure ofCryptococcus neoformans was studied by quick-freezing and deep-etching (QF-DE) method.C. neoformans, strain CDC551, was cultured on agar. The viable yeast cells (107 cells) were inoculated into each mouse from the tail vein. Three weeks after the inoculation, the brains of the mice were perfused with fixatives, quickly frozen, freeze-fractured, deeply etched and rotary shadowed with platinum and carbon. In addition, the viable cells ofC. neoformans on agar were picked up and quickly frozen, and replica membranes were prepared as described above. The ultrastructure ofC. neoformans was three-dimensionally demonstrated by the QF-DE method. The capsule was composed of fine meshworks of microfibrils (10–13 nm in diameter), which were directly attached to the cell walls. The capsule of the in vivo yeasts (yeast cells in the brain lesion) was thicker than that of the in vitro yeasts (yeast cells on agar culture). At the outer part of the cell wall, a particle-accumulating layer was observed. This layer in vivo was thicker than that in vitro. Occasionally, the yeast cells were ingested by phagocytes in the mouse brain. Although the cytoplasm of such yeast cells was destroyed, the capsular meshworks were well preserved. The ultrastructure of the capsule was the same both in cultured and phagocytized yeasts in the cystic lesions of the brains. This lack of morphological changes of the capsular meshworks suggests that they are resistant to the digestion by phagocytes. This stability of capsular structures may provide one of the important pathogenic factors in cystic lesions byC. neoformans.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01104068
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  • 5
    Electronic Resource
    Electronic Resource
    Aflatoxin B1-induced ultrastructural alterations in matureZea mays embryos (1994)
    Springer
    Mycopathologia 128 (1994), S. 181-192 
    Details
    ISSN: 1573-0832
    Keywords: Aflatoxin B1 ; Embryo ; Mature ; Ultrastructure ; Zea mays L.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Mature maize (Zea mays L.) embryos were exposed to aflatoxin B1 (AFB1) concentrations ranging from 0.1 to 25 µg/ml for 9 days. With increasing toxin concentration above 2 µg/ml, primary root elongation of germinated embryos was progressively inhibited, to reach a maximum value of 81% at 25 µ/ml toxin. An ultrastructural investigation of the subcellular alterations induced following toxin exposure provided evidence of deteriorative changes in several compartments of the plant cell. Alteration in membrane integrity (e.g., the tonoplast, plasmalemma and inner mitochondrial membrane) was a frequent feature of many cells. Apparent fusion of vacuoles, incorporation of cytoplasmic components into vacuoles and intravacuolar membrane whorls might be interpreted as deteriorative alterations. The results are discussed in the light of ultrastructural findings for other plant systems exposed to similar AFB1 concentrations, as well as findings for animal systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01138481
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  • 6
    Electronic Resource
    Electronic Resource
    Ultrastructural localization of catalase and D-amino acid oxidase in ‘normal’ fetal mouse liver (1986)
    Springer
    Cellular and molecular life sciences 42 (1986), S. 144-147 
    Details
    ISSN: 1420-9071
    Keywords: Ultrastructure ; catalase ; D-amino acid oxidase ; fetal mouse liver ; hepatocytes ; peroxisomes ; muscular dysgenesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary In the hepatocytes of ‘normal’ fetal mice from mothers which were carriers of muscular dysgenesis, catalase and D-amino acid oxidase (DAAO) positive as well as negative peroxisomes were observed. DAAO reaction product was occasionally localized in patches around cell membranes and DAAO-positive peroxisomes were frequently observed near mitochondria.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01952437
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  • 7
    Electronic Resource
    Electronic Resource
    The loci of mineral in turkey leg tendon as seen by atomic force microscope and electron microscopy (1994)
    Springer
    Calcified tissue international 55 (1994), S. 180-189 
    Details
    ISSN: 1432-0827
    Keywords: Collagen ; Crystal habit ; Ultrastructure ; Turkey leg tendon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract Transmission electron micrographs of fully mineralized turkey leg tendon in cross-section show the ultrastructure to be more complex than has been previously described. The mineral is divided into two regions. Needlelike-appearing crystallites fill the extrafibrillar volume whereas only platelike crystallites are found within the fibrils. When the speciment is tilted through a large angle, some of the needlelike-appearing crystallites are replaced by platelets, suggesting that the needlelike crystallites are platelets viewed on edge. If so, these platelets have their broad face roughly parallel to the fibril surface and thereby the fibril axis, where the intrafibrillar platelets are steeply inclined to the fibril axis. The projection of the intrafibrillar platelets is perpendicular to the fibril axis. The extrafibrillar volume is at least 60% of the total, the fibrils occupying 40%. More of the mineral appears to be extrafibrillar than within the fibrils. Micrographs of the mineralized tendon in thickness show both needlelike-appearing and platelet crystallites. Stereoscopic views show that the needlelike-appearing crystallites do not have a preferred orientation. From the two-dimensional Fourier transform of a selected area of the cross-sectional image, the platelike crystallites have an average dimension of 58 nm. The needlelike-appearing crystallites have an average thickness of 7 nm. The maximum length is at least 90 nm. Atomic force microscopy (AFM) of unstained, unmineralized turkey leg tendon shows collagen fibrils very much like shadow replicas of collagen in electron micrographs. AFM images of the mineralized tendon show only an occasional fibril. Mineral crystallites are not visible. Because the collagen is within the fibrils, the extrafibrillar mineral must be embedded in noncollagenous organic matter. When the tissue is demineralized, the collagen fibrils are exposed. The structure as revealed by the two modalities is a composite material in which each component is itself a composite. Determination of the properties of the mineralized tendon from the properties of its elements is more difficult than considering the tendon to be just mineral-filled collagen.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00425873
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  • 8
    Electronic Resource
    Electronic Resource
    Bioactive glass-ceramic containing crystalline apatite and wollastonite initiates biomineralization in bone cell cultures (1994)
    Springer
    Calcified tissue international 55 (1994), S. 458-466 
    Details
    ISSN: 1432-0827
    Keywords: In vitro ; Bioactive glass ceramic ; Mineralization ; Bone bonding mechanisms ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Abstract Rat bone cells were cultured in the presence of bioactive glass-ceramic containing crystalline apatite and wollaston te. Scanning electron microscopy observations of the surface of the seeded ceramic disks revealed that cells attached, spread, and proliferated on the material surface. Soaking in cell-free culture medium showed that no change occurred in the surface structure. However, when cultured with bone cells and observed under a transmission electron microscope, an electron-dense layer was noted initially at the surface of the material, before bone formation occurred. In addition, energy-dispersive X-ray microanalysis demonstrated the presence of calcium and phosphorus in this layer. Progressively, during the following days of culture, active osteoblasts synthetized and laid down an osteoid matrix composed of numerous collagen fibrils arranged either parallel or perpendicularly to the first-formed electron-dense layer. Mineralization initiated on the ceramic surface dispersed then along the collagenous fibrils, leading to a mineralized matrix which surrounded the ceramic particles. These results demonstrate the capacity of apatite-wollastonite glass ceramic to initiate biomineralization in osteoblast cultures and to achieve a direct bond between the surface apatite layer of the bioactive glass-ceramic and the mineralized bone matrix.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00298560
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  • 9
    Electronic Resource
    Electronic Resource
    Evidence for tight junctions between odontoblasts in the rat incisor (1985)
    Springer
    Cell & tissue research 239 (1985), S. 137-140 
    Details
    ISSN: 1432-0878
    Keywords: Lanthanum ; Odontoblasts ; Tight junctions ; Tooth pulp ; Ultrastructure ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Odontoblasts are known to be involved in the process of dentinogenesis but it is not clear whether substances may also be deposited in predentine and dentine by passing between these cells. Although tight junctions have been described, it is not clear if they are macular or “leaky” as opposed to continuous or “tight”. In this study use has been made of the permeability of fenestrated capillaries amongst the odontoblasts to deposit the penetrative tracer lanthanum in the interodontoblastic space. This was done by perfusion of anaesthetized rats with physiological solutions containing lanthanum nitrate at 37° C. Immersion fixation of transverse segments of mandibular incisors and examination with an electron microscope showed that lanthanum could permeate 40–50 μm between the odontoblasts to reach the peripheral pulp. Towards the predentine, often less than 10 μm from the capillaries, its progress was abruptly and completely halted by the junctions at the apical ends of the odontoblast cell bodies. Lanthanum was not found in the predentine. The mature secretory odontoblasts in the rat incisor have therefore been shown to be joined by continuous tight junctions. In the process of dentinogenesis this means that all substances deposited in predentine and dentine must arrive by passing through the odontoblasts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00214913
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  • 10
    Electronic Resource
    Electronic Resource
    Ultrastructure of corpora allata of known activity during the vitellogenic cycle in the cockroach Diploptera punctata (1985)
    Springer
    Cell & tissue research 239 (1985), S. 317-327 
    Details
    ISSN: 1432-0878
    Keywords: Corpora allata ; Ultrastructure ; Juvenile hormone ; Rates of synthesis ; Reproductive cycle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Ultrastructure was correlated with rates of juvenile hormone synthesis in corpora allata from females of the viviparous cockroach Diploptera punctata at seven daily intervals during the first vitellogenic cycle. Synthetic activity of the glands was determined by in vitro radiochemical assay before the glands were fixed for electron microscopic analysis. The cycle in rates of juvenile hormone synthesis progressed from about 20 pmol h-1 per gland pair (oocytes 0.60 mm long) to a maximum mean rate of 140 pmol h-1 per pair (oocytes 1.40–1.47 mm long) and declined to about 20 pmol h-1 per pair at ovulation (oocytes about 1.65 mm long). Conspicuous ultrastructural changes occurred with changing synthetic rates. In glands with increasing rates of synthesis, mitochondria showed less electron-dense matrix, greater diameter and more irregular shape. Smooth endoplasmic reticulum changed from easily seen to obscure tubules, networks, and vesicles. Rough endoplasmic reticulum appeared in longer, more curved segments. Newly formed autophagic vacuoles appeared in all glands of highest activity rates. In glands with decreasing rates of synthesis, the mitochondrial matrix became denser, width smaller, and shapes less irregular. Smooth endoplasmic reticulum again appeared tubular and distinct. Golgi complexes were more conspicuous. Rough endoplasmic reticulum in whorls and large numbers of autophagic vacuoles continued to be present.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00218010
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