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  • Electron microscopy  (68)
  • Springer  (68)
  • Cambridge University Press
  • Frontiers Media
  • 2020-2022
  • 1980-1984
  • 1975-1979  (68)
  • 1978  (68)
Collection
Publisher
  • Springer  (68)
  • Cambridge University Press
  • Frontiers Media
Years
  • 2020-2022
  • 1980-1984
  • 1975-1979  (68)
Year
  • 1
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    Calcified tissue international 25 (1978), S. 217-222 
    ISSN: 1432-0827
    Keywords: Bone mineral ; Electron microscopy ; X-ray diffraction ; Dark field
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Electron microscopical observations of the size and shape of bone mineral crystallites have not been in complete agreement with X-ray diffraction findings. The two prevalent viewpoints consider bone mineral crystals to be either rod, or plate like in habit. There appears to be agreement that the smallest dimension of the crystals is about 5 nm, but there is discrepancy in the reported c-axial lengths. The method of dark field imaging is used to obtain a quantitative measurement of the c-axial length distribution in rabbit, ox and human bone: mean c-axial lengths 32.6 nm, 36.2 nm and 32.4 nm, respectively, show no significant difference at the 5% level to the mean c-axial length measured by X-ray line broadening. Both bright and dark field images strongly suggest that bone mineral has a plate like form. Reasons for past discrepancies are discussed.
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  • 2
    ISSN: 1432-041X
    Keywords: Synaptogenesis ; Electron microscopy ; Visual acuity ; Fish development
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The morphogenetic differentiation of synapses of the optic tectum of the rainbow trout was investigated at different stages of development (from hatching to adult) and compared with the improvement in visual discrimination (minimum separable). (1) The main phase of synaptogenesis (increase in number of synapses, length of contact zone and number of vesicles) begins about one week after hatching and continues up to the age of one month, when the larvae start swimming freely. (2) Myelination begins 26 days after hatching and induces the end of the synaptogenesis period. (3) The visual discrimination (minimum separable) of trout larvae improves from 30 degrees of arc on the 10th day after hatching to 1 degree on day 30, then to about 14 to 18 min of arc in the adult. The results are discussed with special reference to previous biochemical investigations on changes in the ganglioside composition of the trout brain during comparable periods of development.
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  • 3
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    Calcified tissue international 26 (1978), S. 181-190 
    ISSN: 1432-0827
    Keywords: Cellular calcium ; Electron microscopy ; Osteoblasts ; Chondrocytes ; Mineralization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The calcium distribution in cartilage and bone cells during beginning ossification of fetal mouse long bones was studied after fixation with 2% K-pyroantimonate in 1% osmium. In the developing periosteum, the future osteoblasts showed a sparse cation-antimonate precipitate over the cytoplasm. In young osteoblasts the precipitate was accumulated on the mitochondrial membranes and the plasmalemma. Both organelles were sharply outlined by precipitate in the mature osteoblasts at the onset of mineralization. X-Ray microprobe analysis of these organelles demonstrated the presence of both Sb and Ca. In the extracellular compartment, a collagen-associated precipitate with 50 to 60 nm periodicity appeared during osteoblastic differentiation. During the initial phase of matrix mineralization, a random gross precipitate appeared in the matrix and seemed to be accumulated by osmiophilic matrix vesicles while the collagen fibrils lost their precipitate. Subsequently, during the confluent phase of matrix mineralization, the precipitate rapidly disappeared from the cells, leaving them devoid of precipitate once they were surrounded by mineralized matrix. Similar changes were found in the chondrocytes of the growth plate, but cartilage collagen, unlike osteoid collagen, did not bind precipitate. The results indicate that both osteoblasts and calcifying cartilage cells bind calcium prior to matrix mineralization. Bone collagen has strong pyroantimonate binding capacity, but it is not directly involved with initial stages of matrix mineralization, which starts in close association with matrix vesicles.
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  • 4
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    Calcified tissue international 25 (1978), S. 179-190 
    ISSN: 1432-0827
    Keywords: Decalcification ; Electron microscopy ; Calcified matrices
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The ultrastructure of calcifying cartilage and bone has been examined under the electron microscope after using three different methods of decalcification. The first was carried out before embedding (by soaking specimens in EDTA or formic acid), the second after embedding (by floating ultrathin sections on formic acid), and the third after embedding (by soaking embedded specimens in EDTA or formic acid), and with later re-embedding. The first procedure invariably induces drastic changes in the fine structure of the cells and calcified matrix, probably as a results of the extraction of organic material along with extraction of mineral. The second and third procedures make it possible to preserve ultrastructural details perfectly in both cells and calcified matrix. Of the two, the third procedure is preferable because of its greater simplicity. In areas that are still calcifying, these post-embedding decalcification techniques reveal the presence of crystal-associated, filamentous organic structures which are not recognizable in specimens decalcified before embedding. These structures, which could have a key role in inducing and regulating crystal formation and growth, are less evident in fully calcified areas (but not at their borders). This may partly be due to the loss of glycan components in the matrix during calcification. The most important determinant, however, seems to be the fact that during calcification the components of the matrix, including collagen fibrils, are involved in an aggregation process which reduces the amounts of free chemical groups available for reaction with the stain solution. Because post-embedding decalcification does not disturb this state of aggregation, the stainability of the matrix and the electron microscopic evidence of its components remain very low.
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  • 5
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    Calcified tissue international 25 (1978), S. 45-51 
    ISSN: 1432-0827
    Keywords: CaCO3 ; Amino acids ; Sheaths ; Ligament ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The aragonite crystals in the molluscan bivalve hinge ligament are surrounded by an organic sheath which is distinct from the remainder of the ligament matrix. Methods have been developed to isolate these sheathed crystals from the ligaments ofSpisula solidissima andMercenaria mercenaria employing a papain digestion of the matrix protein. The sheathed crystals fromSpisula have a CaCO3/protein ratio of 11.1 and those fromMercenaria a ratio of 29.6. The sheathed crystals and the empty crystal sheaths have been examined by electron microscopy for structural integrity. The sheath proteins exhibit much smaller proportions of the amino acids glycine and methionine than the hinge ligaments. These are characteristic amino acids of high concentration in the hinge ligaments of both species. The concentrations of acidic and basic amino acids are increased about two fold in the sheaths over those of the ligaments. Otherwise there is little similarity in the amino acid composition of the sheaths in the two species. However, SDS electrophoresis shows the sheaths of both to contain a major protein component with a molecular weight of about 25,000. The sheath protein from theMercenaria ligament contains about 5% carbohydrate and that ofSpisula sheaths less than 1% carbohydrate.
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  • 6
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    Calcified tissue international 25 (1978), S. 133-143 
    ISSN: 1432-0827
    Keywords: Osteon ; X-Ray diffraction ; Electron microscopy ; Calcification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary To obtain information on the changes in the inorganic bone fraction during calcification, low- and wide-angle X-ray diffraction techniques and electron microscopy have been applied to single osteon samples. The samples were cylindrically shaped and their axes corresponded to the axes of the Haversian canals. The selection was made according to the degree of calcification and the orientation of collagen bundles and inorganic particles. Osteons at both the initial and final stages of calcification were chosen. Arrangements of fiber bundles and inorganic particles in successive lamellae characteristic of three types of osteon were selected, that is, longitudinally structured osteons, transversely structured osteons, and alternately structured osteons. The results indicate that in osteonic lamellar bone there are two types of inorganic particles: (1) granules arranged in linear or needle-shaped entities with maximum width 40–45 Å, which are regularly distributed at the level of the main band of the collagen fibrils where their maximum length reaches the length of the main band itself; that is, about 400 Å; and (2) very long crystallites, with a diameter of 40–45 Å, which grow with their crystallographicc-axis parallel to the collagen fibrils and cover much more than a major collagen period.
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  • 7
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    Archives of microbiology 118 (1978), S. 67-69 
    ISSN: 1432-072X
    Keywords: Corynebacterium autotrophicum ; Outer Membrane ; Lipopolysaccharides ; Biochemical analysis ; Polymyxin B ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Lipopolysaccharides (LPS) from Corynebacterium autotrophicum were isolated and analyzed. Autotrophically grown cells contained 2–5 mg of partly purified LPS per g dry weight of lyophilized cells. Serological cross reaction with Lipid A antigen of Salmonella minnesota confirmed the presence of LPS in C. autotrophicum. Electron microscopy of negatively stained Polymyxin B-treated cells showed formation of blebs on the Outer Membrane indicating an interaction of Polymyxin B specifically with LPS. Up to now, no Gram-positive organisms are known which contain any LPS. Thus, C. autotrophicum, though giving opposite results when the Gram-staining reaction was applied by several authors, has to be classified into the group of Gram-negative bacteria.
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  • 8
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    Archives of microbiology 119 (1978), S. 303-304 
    ISSN: 1432-072X
    Keywords: Vibrio cholera phage group II ; Properties ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The basic physical, chemical and physiological properties of a group II cholera phage belonging to Mukerjee's classification has been described.
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  • 9
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    Archives of microbiology 119 (1978), S. 87-90 
    ISSN: 1432-072X
    Keywords: Salmonella typhimurium strain LT2 (ColIb) ; Cryptic plasmids ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Small cryptic plasmids of molecular weights ranging from 1 to 3 Mdal were detected by electron microscopy in Salmonella typhimurium strain LT2 (ColIb). They were divided into different size classes. Two of the cryptic plasmids were transferred simultaneously with ColIb to Escherichia coli.
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  • 10
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    Archives of microbiology 119 (1978), S. 227-229 
    ISSN: 1432-072X
    Keywords: Cell wall ; Electron microscopy ; Methylomonas albus ; Goblet sub-units
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In surface view, the cell wall complex ofMethylomonas albus possesses a hexagonal pattern of ridges. Thin sections reveal a continuous layer of goblet-shaped elements attached to the outermost surface of the lipopolysaccharide membrane. A possible interpretation of the cell wall complex ofM. albus, based on the fine-structural data is presented.
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  • 11
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    Archives of microbiology 118 (1978), S. 305-308 
    ISSN: 1432-072X
    Keywords: Carotenoid mutant strain R-26-Rhodopseudomonas sphaeroides ; Electron microscopy ; Intracellular membranes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Stained thin-sections and freeze-fractured preparations of the carotenoid-less mutant strain R-26 of Rhodopseudomonas sphaeroides grown photosynthetically revealed 2 morphological kinds of intracellular membrane systems- spherical vesicles distributed throughout the cytoplasm and lamellae confined to the periphery of the cell. The lamellar membranes appeared to be large, flattened vesicles.
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  • 12
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    Archives of microbiology 116 (1978), S. 133-139 
    ISSN: 1432-072X
    Keywords: Lagenisma ; Coscinodiscus ; Infection ; Endosymbiotic bacteria ; Tip growth ; Wall-less thallus ; Host-parasite interface ; Membranes ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Lagenisma coscinodisci is diplanetic and has two different cyst stages. The secondary cyst has a uniform cell wall of fibrillar material. It attaches to a Coscinodiscus frustule and germinates with an infection tube. The cyst becomes filled with an enlarging expulsion vacuole. The infection tube penetrates the diatom cell between the cingula. Inside the host cell the fungus grows as an irregularly branched wall-less thallus. In the hyphae apical vesicles are lacking. The infection tube is plugged by wall material. There are no microtubules which might participate in the morphogenesis of the thallus. The plasmalemma of the diatom is pushed inward but not pierced by the fungus. Along the host-parasite interface it lies closely paralled to the Lagenisma plasmalemma which is extremely straight here and measures about 10 nm instead of about 5–6 nm at the surfaces of other stages. The Coscinodiscus plasmalemma disintegrates at about the same time when the cytoplasm breaks down. The fungus allows bacteria to enter the diatom; there are also endosymbiontic bacteria in unattacked cells — The growth mechanisms are discussed and the host-parasite interface is compared with that of other fungi.
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  • 13
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    Cell & tissue research 186 (1978), S. 121-133 
    ISSN: 1432-0878
    Keywords: Proximal tubule ; Tight junctions ; Ultrastructure ; Electron microscopy ; Freeze fracturing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The morphology of tight junctions of the renal proximal tubule was studied comparing the pars convoluta and pars recta of rat, golden hamster, rabbit, cat, dog and tupaia. Though some interspecies variations were observed, the convoluted portions of the proximal tubules revealed quite uniformly very leaky tight junctions with mainly 1–2 strands. Along the whole proximal tubule of the rabbit kidney including the pars recta only minor differences of the zonulae occludentes were found. By contrast, the tight junctions of the pars recta in other species were much more elaborate, especially in cat and tupaia, having up to 6 strands and an overall depth of more than 150 nm. The implications of these findings are discussed with special regard to the functional differences between the pars convoluta and pars recta of the proximal tubule.
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  • 14
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    Cell & tissue research 187 (1978), S. 457-472 
    ISSN: 1432-0878
    Keywords: Ovarian follicles (sheep) ; Theca interna ; Oestrogen ; Androgen ; Capillaries ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The theca interna of non-atretic ovarian follicles from 2.0 mm in diameter up to the stage shortly following ovulation was studied by light and electron microscopy. In follicles 〈3.0mm in diameter, the theca interna consisted of about 8–12 layers of flattened cells, together with many capillaries and small bundles of collagen. Two main forms of cellular differentiation were seen. These were towards either fibroblast-like cells or presumed steroidogenic cells whose cytoplasm contained large amounts of predominantly smooth tubular endoplasmic reticulum, to which some ribosomes were attached. The majority of cells were of relatively undifferentiated or intermediate structure. In larger follicles up to the early stages of oestrus the theca interna cells became larger and less flattened, and cells rich in tubular endoplasmic reticulum became proportionately more numerous. By 18 h after the onset of oestrus the theca interna was oedematous, and many cells possessed pseudopodia. Many cells also contained numerous lipid droplets, but there were no signs of thecal cell degeneration or death. Shortly after ovulation the basal lamina of the membrana granulosa was incomplete, and it became more difficult to distinguish between theca and granulosa layers. Structural heterogeneity, with two major cell types and cells of intermediate structure, was present at all stages. It was concluded that: (1) the theca interna of 2.0–2.9 mm follicles contained many cells whose structure was compatible with a steroidogenic capacity; (2) changes in the differentiated thecal cells up to the early stages of oestrus were quantitative rather than qualitative, and suggestive of an increased steroidogenic capacity; (3) the accumulation of lipid in many cells of the theca interna by 18 h after the onset of oestrus probably reflected a reduction in steroidogenic activity; and (4) there was no evidence of any structural specialization to facilitate the transport of steroids from the theca interna to the membrana granulosa.
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  • 15
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    Cell & tissue research 188 (1978), S. 75-82 
    ISSN: 1432-0878
    Keywords: Drum muscles ; Piranha ; Degenerative changes ; Fine structure ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary In the posterior drum muscle of the piranha structural alterations are frequently observed. Electron microscopic studies revealed a disordering of the myofibrils in these regions, accompanied by conspicuous changes in the mitochondria. As the degree of disorder increases, the mitochondrial cristae initially swell to form vesicles. Eventually the mitochondria become filled with myelin-like lamellar structures, which in many cases coalesce to form a dense outer wall. A striking concentration of lysosomes into localized masses was also characteristic of these regions.
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  • 16
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    Cell & tissue research 189 (1978), S. 167-177 
    ISSN: 1432-0878
    Keywords: Hypodermis ; Rotifer ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The integument of the rotifer Habrotrocha rosa Donner is provided with pores and formed by an extrasyncytial cuticle and a syncytial hypodermis. The hypodermis peripherally contains 3 layers of dense cytoplasm and borders the cuticle by an asymmetric cell membrane. The wall of the pores is stiffened proximally like an annulus. The pores lead into cytoplasmic invaginations which are surrounded by vesicles. Close to and also beneath the condensed cytoplasmic layers microbodies are found, which are interpreted as microperoxisomes. Subhypodermal layers of muscles are connected with the cytoplasm of the hypodermis by desmosome-like structures.
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  • 17
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    Cell & tissue research 189 (1978), S. 257-266 
    ISSN: 1432-0878
    Keywords: Neuromuscular junction ; Hindgut ; Crustacea ; Catecholamine ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The crustacean species Pacifastacus leniusculus and Gammarus pulex were investigated by electron microscopy in a search for possible neuromuscular junctions in the hindgut, which has a rich supply of catecholaminergic fibres. True neuromuscular synapses were found in both species between nerve terminals containing dense-core vesicles (80–110 nm in diam.) and muscle fibres. We suggest that the dense-core vesicle terminals contain a catecholamine, and this is supported by ultrahistochemical tests for monoamines. Two types of junctions are found: one in which the nerve terminal is embedded in the muscle cell (both species) and one in which protrusions from the muscle cell meet nerve terminals (Pacifastacus). Gammarus pulex, which has only circular muscles in the hindgut, has only catecholaminergic innervation, whereas Pacifastacus leniusculus has circular and longitudinal muscles both with at least two types of innervation.
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  • 18
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    Cell & tissue research 189 (1978), S. 277-286 
    ISSN: 1432-0878
    Keywords: Maternal adrenalectomy ; Rat ; Influence on the adrenals of newborn animals ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Maternal adrenalectomy at 7 or 14 days of gestation produced increased cell necrosis within zona reticularis cells on the day of birth and at 24 or 48 h after birth. Small remnants or large portions of adrenocortical cells were present within macrophages. In otherwise normal adrenocortical cells, lipid droplets were incorporated within some mitochondria. Autophagocytosis of single mitochondria was observed within adrenocortical cells. Undoubtedly ultrastructural changes represent stimulation of adrenocortical cells in neonatal rats in response to maternal adrenalectomy.
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  • 19
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    Cell & tissue research 191 (1978), S. 449-462 
    ISSN: 1432-0878
    Keywords: Ileum (Rat) ; Occluding junctions ; Freeze-fracture ; Ultrastructure ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Two kinds of occluding junctions are found between ileal epithelial cells of suckling rats: apical zonulae occludentes (ZO) and fasciae occludentes (FO) which are associated with the lateral plasma membranes of many epithelial cells. In unfixed preparations, glycerol treatment induces the further proliferation of extensive fasciae occludentes. Both kinds of junction have identical structural elements when visualized in freeze fracture replicas, although the arrangement of these elements differs. Zonulae occludentes consist of networks of branching and anastomosing linear ridges or rows of ∼10 nm particles with 20–30 nm spaces between the rows which form narrow belt-like structures around the apical region of adjacent cells. Fasciae occludentes, on the other hand, consist of similar linear ridges or rows of particles but the junction strands are often discontinuous, open ended and only occasionally intersect with each other. Several different fracture planes through the plasma membrane in the region of the occluding junctions have been observed and these provide further evidence that two components, one from each membrane, fused at the level of the extracellular space, form the junction sealing element. Furthermore, we present evidence which indicates a staggered rather than an in-register arrangement of these two components.
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  • 20
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    Cell & tissue research 192 (1978), S. 39-51 
    ISSN: 1432-0878
    Keywords: Prostate ; Rat-Anti-Androgens ; Nuclear alterations ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The fine structure of the nuclei of epithelial cells of the dorsal lobe of the rat prostate were studied after administration of three different antiandrogenic compounds. The nucleolus appears to undergo a progressive disorganisation with partial fragmentation and dispersion of its normal components. Different types of intranuclear inclusions were found. The various alterations observed were often encountered within the same section. This may indicate that the nuclear alterations occur in the same compartment of the cell, and represent a dysfunction of integrated biochemical events occurring within this compartment. The findings support a view that the stimulatory secretory effect of androgens is mediated via a ‘secretory center’, located within the nucleolusassociated chromatin. Within this ‘secretory center’, the initial steps of the secretory process, the binding of the DHT receptor complex to DNA is assumed to occur.
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  • 21
    ISSN: 1432-0878
    Keywords: T-lymphocytes ; Stereological model system ; Free cells ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Description / Table of Contents: Zusammenfassung Menschliche, in Nylonwolle gereinigte T-Lymphozyten aus dem peripheren Blut dienten als repräsentatives Untersuchungsobjekt zur Schaffung eines neuen stereologischen Modellsystems für freie, sphärische Zellen. Dieses System erlaubt, die Zelle und die darin enthaltenen Strukturkomponenten auf ultrastruktureller Ebene quantitativ zu charakterisieren.
    Notes: Summary T-lymphocytes derived from human peripheral blood and passed through a nylon-wool column, were employed to develop and test a new Stereological model system for free spherical cells, allowing a quantitative characterization of the cell and its components at the ultrastructural level. Electron micrographs were recorded in a hierarchical manner at three different levels of magnification and subjected to point counting procedures. The resulting parameters were expressed in relation to various reference compartments, both absolute and relative. Results indicated that the average volume of a small, non-activated T-lymphocyte was 103.8 μm3, the nuclear volume 47.5 μm3 and the cytoplasmic volume 55.9 μm3. On the average, the cytoplasm contained 30 mitochondria, 0.7 μm3 RER-cisternae, 0.2 μm3 cisternae and vesicles of the Golgi apparatus and about 231,000 free ribosomes (most of them single). The ratio of eu- to heterochromatin volume was 0.5. The design and application of the Stereological model system are discussed with regard to dynamic studies of a variety of free cells, such as macrophages, neutrophilic granulocytes and various lymphocytes.
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  • 22
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    Cell & tissue research 186 (1978), S. 535-540 
    ISSN: 1432-0878
    Keywords: Skeletal muscle ; Satellite cells ; Regeneration ; Electron microscopy ; Autoradiography
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Satellite cells were traced autoradiographically during the regeneration of skeletal muscle in young Sprague-Dawley rats. Approximately 31% of the satellite cells in uninjured muscles appeared labelled after three injections of tritiated thymidine; none of the myonuclei were labelled in the same muscles. Four to six days after transplanting the radioactive muscles to non-radioactive littermates, regenerating myotube nuclei in the host appeared labelled. Thus, this study confirms that satellite cells in young rats can differentiate into multinucleated myotubes following muscle injury.
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  • 23
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    Cell & tissue research 187 (1978), S. 159-165 
    ISSN: 1432-0878
    Keywords: Endocrine cells ; Ascidian (Styela clava) ; Gut epithelium ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Ultrastructural studies have shown the presence of two types of granulated endocrine cell in the gut of Styela clava. Type I, which occurs in the stomach and intestine contains small irregular granules, each with a distinct halo. Type II, found only in the oesophagus contains larger rounded granules, often with little or no halo. The characteristics of these two cell types are compared with those of endocrine cells found in the digestive tracts of other protochordates and discussed with special reference to the evolution of gastrointestinal endocrine cells in vertebrates.
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  • 24
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    Cell & tissue research 187 (1978), S. 439-448 
    ISSN: 1432-0878
    Keywords: Urinary bladder epithelium (Rat) ; Gap junctions ; Tight junctions ; Electron microscopy ; Freeze-fracturing
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The junctional connections between the cells of the urinary bladder epithelium in rat have been studied by freeze-fracturing. Tight junctions and desmosomes are known as structural features of the epithelium. In addition, gap junctions (nexus) have been found to connect the epithelial cells in an irregular distribution pattern. The junction size ranges from few assembled particles up to plaques with irregular forms. This may indicate that the gap junctions are mobile structures. The functional significance of the junctions in comparison with electrophysiological data is discussed.
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  • 25
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    Cell & tissue research 188 (1978), S. 497-508 
    ISSN: 1432-0878
    Keywords: Fertilization ; Domestic fowl ; Acrosome reaction ; Vitelline membrane ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The developing outer layer of the vitelline membrane of the ovum in the posterior part of the infundibulum of the domestic fowl contains many spermatozoa in nearly parallel orientation with its inner layer. When the acrosomal region of a spermatozoon approaches or contacts the inner layer, promptly undergoes the acrosome reaction. The outer acrosomal membrane and overlying plasma membrane fuse together and the apical region of the acrosome opens, so that the acrosomal contents are released. Meanwhile the spermatozoon remains a time in contact with the surface of the inner layer, and the network of the inner layer just under the tip of the sperm head begins to be dissolved. This dissolution extends downward forming a tunnel, approximately 9 μm in diameter. The spermatozoon then passes through the inner layer obliquely via the central region of the tunnel and arrives at the perivitelline space.
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  • 26
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    Cell & tissue research 189 (1978), S. 375-388 
    ISSN: 1432-0878
    Keywords: Lateral line organ ; Pit organ ; Sea eel (Conger myriaster) ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The fine structure of the pit organ of the sea eel has been studied by means of electron microscopy. The sensory epithelium of the pit organ consists of sensory cells and supporting cells. The apical surface of the sensory cell is studded with sensory hairs consisting of a kinocilium and stereocilia. The sensory cells are divided into two groups. In one, the kinocilium points dorsally and in the other the kinocilium points ventrally. The total number of sensory cells in one pit organ is about 100, and the ratio of cells with opposite polarity is about 1∶1. On the basis of these structural features, the pit organ is considered to be a mechano-receptor sensitive to the movement of liquid in a dorso-ventral direction. It may also serve as an ion receptor, sensitive to environmental ion concentration. Efferent nerve terminals make rare synaptic contacts on the afferent nerve fiber.
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  • 27
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    Cell & tissue research 189 (1978), S. 515-523 
    ISSN: 1432-0878
    Keywords: Protonephridium ; Rotifer ; Electron microscopy
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    Topics: Biology , Medicine
    Notes: Summary The excretory system of Habrotrocha rosa consists of two protonephridia. From each of them seven tubules lead to a terminal organ, also called cyrtocyte. Its weir basket contains structures which resemble ciliary rootlets. The lumen of the excretory system is bordered by a syncytial layer of cytoplasm. Cells are only found in the upper region of the trunk, where the channel is twisted several times.
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  • 28
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    Cell & tissue research 189 (1978), S. 525-535 
    ISSN: 1432-0878
    Keywords: Alimentary system ; Rotifer ; Electron microscopy
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    Topics: Biology , Medicine
    Notes: Summary The alimentary system of Habrotrocha rosa is composed of the alimentary channel, five digestive glands and another gland which is in close relation to the intestinal syncytium. After the present investigation, the alimentary channel can be divided into sections which clearly differ from each other, these are: oral cavity, pharynx, oesophagus, mastax, stomach-hose, syncytium of intestine, and terminal intestine.
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  • 29
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    Cell & tissue research 188 (1978), S. 11-18 
    ISSN: 1432-0878
    Keywords: Purkinje fibers (Ox, goat) ; Axons ; Nerve endings ; Electron microscopy
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    Topics: Biology , Medicine
    Notes: Summary The moderator band in the heart of the ox and goat contains bundles of Purkinje fibers and nerve fibers separated by connective tissue. The axons are mostly unmyelinated and embedded in the cytoplasm of Schwann cells. Small bundles of axons run close to the Purkinje fibers. The axons dilate into varicosities 0.5 to 1.6 μ in diameter (mean 0.95 μ), containing three types of vesicles: 1) agranular vesicles with a diameter of 400–500 Å, 2) large dense-cored vesicles with a diameter of 800–1200 Å, 3) small dense-cored vesicles with a diameter of 500 Å. Most varicosities contain agranular vesicles together with a few large dense-cored vesicles. The gap between the varicosities and the nearest Purkinje fiber is unusually wide and normally varies between 0.3 μ and 0.8 μ. No intimate nerve-Purkinje fiber contacts, with a cleft of 200 Å, were observed.
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  • 30
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    Cell & tissue research 188 (1978), S. 265-272 
    ISSN: 1432-0878
    Keywords: Muscles ; T-system ; Fish ; Frog ; Electron microscopy
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    Topics: Biology , Medicine
    Notes: Summary In “white” muscle fibres of a teleost fish T-tubule openings may occur regularly at all Z-disc levels between adjacent peripheral myofibrils, the T-tubule openings thus occurring at a density of ca. 0.9 μm-2. In frog “white” fibres, T-tubule openings are infrequently seen in material fixed like the fish material. In material prepared according to the albumin method of Gray (1975, 1976 a, b) which renders the muscle fibres swollen, straight tubules or sometimes chains of vesicles instead are seen opening at the sarcolemmal surface. Such tubules occur at a higher density than expected from experiments with local activation of contraction. Lability and dynamics within the T-system normally and during fixation are discussed.
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  • 31
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    Cell & tissue research 191 (1978), S. 405-419 
    ISSN: 1432-0878
    Keywords: Subfornical organ ; Japanese quail, Coturnix coturnix japonica ; Monoaminergic innervation ; Electron microscopy
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    Topics: Biology , Medicine
    Notes: Summary The parenchyma of the subfornical organ (SFO) of the Japanese quail was studied by light and electron microscopy. The SFO consists of ependymal, intermediate, and basal (perimeningeal) layers. In the intermediate layer, neurons, glial cells, and their processes are found. Axons containing dense core granules approximately 80 nm in diameter are numerous, some of which make synaptic contact with the neuronal perikarya or dendrites. Synaptic vesicles in some axons contain a dense dot in the interior after treatment with 5-hydroxydopamine. The activity of the SFO, which is probably concerned with elicitation of drinking by angiotensin II, may be regulated at least partly by afferent monoaminergic axons. Capillaries with a non-fenestrated endothelium are occasionally found in the parenchyma. The basal layer is occupied by glial processes abutting on the digitating layer of perivascular connective tissue of meningeal vessels. The endothelium of these vessels is occasionally fenestrated. Trypan blue injected systemically accumulated in the SFO, but not in the deeper areas of the brain. The absence of a blood-brain barrier is suggested in the SFO.
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  • 32
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    Cell & tissue research 192 (1978), S. 267-276 
    ISSN: 1432-0878
    Keywords: Endocrine glands ; Mouse small intestine ; Mouse embryo ; Electron microscopy
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    Topics: Biology , Medicine
    Notes: Summary The duodenum and ileum of 15 to 18-day old Swiss ICR mouse embryos were studied with the electron microscope to follow the differentiation of endocrine cells. Endocrine cells were classified on purely morphological characteristics. EC cells appeared at 16 days of gestation in both segments. At the same stage G cells were seen in the duodenum and K cells in the ileum. ECL, and S cells were identified in the duodenum at 17 days. Finally, D cells were seen at 18 days of gestation in the duodenum and ileum. With the electron microscope, endocrine cells were not identified in the small intestine of the mouse before the formation of villi.
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  • 33
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    Cell & tissue research 188 (1978), S. 509-520 
    ISSN: 1432-0878
    Keywords: Cerebellar cortex (Cat) ; Postnatal development ; Myelination of efferent and afferent fiber systems ; Electron microscopy
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    Notes: Summary The myelination of the cerebellar cortex of the cat was investigated in 61 cats aged from 3 hrs post partum to two and a half years. The first myelinated fibers appear at the time of birth in the central medullary ray. Before the onset of myelination, all fibers reach a critical diameter of about 1 μm. About the 14th day of life the number of oligodendrocytes in the prospective white matter increases markedly. Thereafter, the oligodendrocytes invade the inner granular layer. It therefore seems that the myelination of the cerebellar cortex proceeds from the central medullary ray towards the granular layer. At the 60th day of postnatal life, most of the afferent and efferent fiber systems are myelinated. These findings are discussed in relation to the development of function and the maturation of the electrical activity of the cerebellar circuit.
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  • 34
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    Cell & tissue research 189 (1978), S. 1-18 
    ISSN: 1432-0878
    Keywords: Kidney medulla ; Rat, rabbit, gerbil ; Interstitial cells ; Lipid droplets ; Electron microscopy
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    Notes: Summary The inner zone of the renal medulla of rats, gerbils, and rabbits was investigated to determine whether or not there are any characteristic ultrastructural differences between the interstitial cells of these species. The effects on the interstitial cells of water deprivation and water loading were also investigated. In all three species, the Type 1 interstitial cells, the lipid containing cells, were abundant and their distribution and topographical relations as well as their general ultrastructure were similar. The previously reported significantly higher frequency in desert rats could not be confirmed. Although the lipid droplets of the interstitial cells were smaller in gerbils and rabbits when compared to rats, their fine structure was similar. Their electron dense outer zone was sometimes associated with a granular material and/or a lamellar material with a periodicity of about 40 Å resembling phospholipid “myelin figures”. Water-loaded rats showed a considerable increase in the number of lipid droplets when compared to dehydrated or untreated animals. In contrast, the interstitial cells of waterloaded gerbils and rabbits were depleted of lipid droplets.
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  • 35
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    Plant systematics and evolution 129 (1978), S. 135-142 
    ISSN: 1615-6110
    Keywords: Algae ; Chrysophyceae ; Chrysosphaerella solitaria ; Electron microscopy ; phytoplankton
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    Topics: Biology
    Notes: Abstract A new unicellular species of the genusChrysosphaerella (Chrysophyceae) was found in fresh-water ponds in Switzerland, Japan, and the U.S.A. It is described asC. solitaria. The genus is divided into two subgenera:Chrysosphaerella, comprising the colonial species, andPseudochrysosphaerella, the unicellular ones.
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  • 36
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    Environmental biology of fishes 3 (1978), S. 185-191 
    ISSN: 1573-5133
    Keywords: Euthynnus affinis ; Electron microscopy ; Kawakawa tuna ; Red fibres ; White fibres ; Muscle size ; Activity ; Thermogenesis ; Thermal inertia
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    Topics: Biology
    Notes: Synopsis An electron microscopic study of the red and white muscle fibres in the trunk musculature of the Kawakawa tuna (Euthynnus affinis) was carried out with a view to correlating their structure with metabolic adaptation. The red fibres which are considerably smaller in diameter (34.58 μm ± 6.16 S.D.) are characterized by their high content of myoglobin, mitochondria, lipid droplets and glycogen granules. The white fibres which are relatively larger in diameter (66.03 μm ± 11.59 S.D.) are characterized by their lack of myoglobin, low mitochondria) density, high content of glycogen granules and the conspicuous absence of lipid droplets. The characteristics in fine structure of the two fibre types are discussed in the light of their metabolic adaptation, the red fibres as being adapted for long term cruising movement utilizing lipid as the main source of energy and the white fibres for short bursts of activity metabolizing glycogen as the chief fuel. The tuna, with the acquisition of the counter-current heat exchange system which provides for the retention of the heat generated from high substrate oxidation in the red muscle and an efficient respiratory system, it is postulated, is well adapted for high speed sustained swimming.
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  • 37
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    Keywords: Pancreatic β-cells (mouse) ; Formation and storage of insulin ; Role of zinc and calcium ; Culture of islets ; Electron microscopy
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    Notes: Summary 1. The effects of culture of isolated mouse islets of Langerhans for up to 9 days in media which had been depleted of zinc electrochemically or with the chelating agent Tris-(2-aminoethyl) amine, or of calcium, have been compared. 2. An 83% reduction of extracellular zinc concentration did not adversely affect proinsulin biosynthesis, conversion of proinsulin to insulin, or the ability of cells to store newly formed insulin in granules. When incubation media were depleted of both zinc and calcium the β-cells produced abnormally large electron-lucent granules, consistent with the failure of insulin to crystallise within the granule sac. 3. Very similar results, with formation of large electron lucent granules, were obtained after culture of islets in the absence of calcium but in the presence of normal concentrations of zinc. 4. It is suggested that zinc may play a less critical role in the biosynthesis of proinsulin and its conversion to insulin, while calcium may have a more important function in insulin storage, than has sometimes previously been supposed.
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  • 38
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    Keywords: Fertilization ; Membrane fusion ; Male pronucleus ; Electron microscopy
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    Notes: Summary The apex of the sperm head which has undergone the acrosome reaction comes in contact with the plasma membrane of the ovum. After the entire surface of the inner acrosomal membrane has come into close contact with the plasma membrane of the ovum, the two membranes fuse to form a continuous membrane. All parts of the spermatozoon that are devoid of plasma membrane penetrate into the ooplasm. As the head of the spermatozoon moves deeper into the ooplasm, the chromatin begins to disperse, and the head of spermatozoon is transformed into a large spherical nucleus with low electron density. At a later stage of the transformation, many small vesicles appear around the nucleus and subsequently fuse to form two continuous membranes. These membranes represent the male pronuclear envelope. The condensation of the chromatin occurs in places in the nucleus, so that the male pronucleus is formed. During the course of the formation of the male pronucleus, the subacrosomal rod and tail become detached from the head and disintegrate.
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  • 39
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    Cell & tissue research 190 (1978), S. 357-369 
    ISSN: 1432-0878
    Keywords: Ampullary organs ; Siluroidea ; Sensory cells ; Synaptic junctions ; Electron microscopy
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    Topics: Biology , Medicine
    Notes: Summary Ampullary organs were found in the epidermis of the paddle-fish Sorubim lima; they are distributed all over the skin surface of the fish but are particularly densely grouped in the head region and on the dorsal surface of the paddle. Histological and electron microscopical observations show that their structure is similar to the type of cutaneous ampullary organs characteristic of other Siluroidea. Composed of a relatively large mucus-filled ampulla, the organ possesses a short and narrow canal which leads to the outer epidermal surface. The wall of the ampulla is formed of several layers of flat epidermal cells. In general four sensory cells, each one surrounded by supporting cells, compose the sensory epithelium at the bottom of the ampulla. The inner surface of the sensory cells in contact with the ampullary mucus bears only microvilli. The contact between the nerve endings and the sensory cells show the characteristic structure of an afferent neuro-sensory junction. Two ampullae are innervated in some cases by the same afferent nerve fibre.
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  • 40
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    Cell & tissue research 190 (1978), S. 539-552 
    ISSN: 1432-0878
    Keywords: Prostate ; Praomys natalensis ; Castration ; Changes ; Electron microscopy
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    Topics: Biology , Medicine
    Notes: Summary Male ventral and female prostates of Praomys (Mastomys) natalensis were examined with the electron microscope. The findings support and add to information obtained with the light microscope on tissues from normal, castrated and ovariectomised animals. Our results indicate that although the female prostate may be considered a homologue of the male ventral prostate anatomically and histologically, there are differences in sub-cellular morphology and hormone dependence. Cells of the intact ventral prostate of the male are characterised by prominent dilated Golgi vesicles and electron-dense “mature secretory granules” seen in the apical region of the cell. In the cells of the female prostate these features are absent. These morphological differences reflect the influence of hormones upon the cells, as shown by the reduction of the dilated Golgi vesicles in the castrated male and conversely, their occasional presence in the cells of the oestrous female. Comparison of castrated and ovariectomised animals shows that the male ventral prostate is much more dependent on androgens than the female is on ovarian hormones. There are several modes of secretion in the male ventral and the female prostate. These are by acellular and cellular blebbing, by a variety of secretory vesicles into the acinar lumina, and by a system of “double walled” vesicles not previously described.
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  • 41
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    Keywords: Adrenal medulla ; Dog ; SGC cell ; Histochemistry ; Electron microscopy
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    Notes: Summary Small granule chromaffin cells (SGC cells) were identified in the adrenal medulla of adult dogs. They were small in size and usually showed a high nucleo-cytoplasmic ratio. Cytoplasmic projections were occasionally observed in some of these cells. They contained a variable number of small secretory granules with diameters ranging from 70 to 300 nm, but mostly from 100 to 200 nm. The densities of the secretory granules were variable, ranging from highly dense to less dense. These adrenal SGC cells were rich in free ribosomes and polysomes, but were relatively poor in other cell organelles. Chromaffin cells which were intermediate in their characteristics (IM cells) between the SGC cells and the typical A and N cells were also identified. These IM cells contained both highly electron dense and less dense granules in various proportions. The IM cells were classified into two subgroups, according to the proportions of adrenaline type granules and noradrenaline type granules. One group resembled A cells (IM-A cells) and the other resembled N cells (IM-N cells). Light microscopic histochemical studies of A cells stained with the ammoniacal silver solution demonstrated that they contained a small number of darkly stained granules. Electron microscopic cytochemistry revealed that the electron dense granules in the SGC cells, IM cells and A cells reacted positively with both the potassium dichromate solution at pH 4.1 and the ammoniacal silver solution.
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  • 42
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    Cell & tissue research 191 (1978), S. 27-37 
    ISSN: 1432-0878
    Keywords: Spermatozoon ; Oikopleura dioica ; Electron microscopy
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    Topics: Biology , Medicine
    Notes: Summary The spermatozoon of Oikopleura dioica is about 30 μm long, with a spherical head, about 1 μm wide, a 3 μm long and 1 μm wide midpiece, and a 25 μm long tail with a tapered end piece. The head contains a nucleus with the chromatin volume limited to about 0.1 μm3. A small acrosome is found in an anterior inpocketing, and a flagellar basal body in a posterior inpocketing of the nucleus. The midpiece contains a single mitochondrion with the flagellar axoneme embedded in a groove along its medial surface. The flagellar axoneme has the typical 9 + 2 substructure, and the basal body the typical 9+0 substructure. A second centriole and special anchoring fibres are absent.
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  • 43
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    Keywords: Subfornical organ ; Third ventricle ; 6-Hydroxydopamine ; Electron microscopy ; Primate
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    Notes: Summary The neurotoxin 6-hydroxydopamine (6-OH-DA) has been shown to produces degenerative changes in noradrenergic nerve terminals and preterminals in the CNS following intracisternal, intraventricular, and stereotaxic injection into the brain parenchyma. Systemic injections of this drug are also known to result in degenerative changes in noradrenergic terminals in the peripheral nervous system and in the circumventricular organs (CVO; areas of the CNS which lie outside the blood brain barrier). In the present study eight adult female cynomolgus monkeys were employed. The four experimental animals were injected on two successive days with 150 and 200 mg/kg 6-OH-DA, respectively. The four controls received only the diluent consisting of 0.1% ascorbic acid in normal saline. Two animals from each of the experimental and control groups were sacrificed at 2 h and 24 h after the second injection. Degenerative changes in the SFO neurons were characterized by a generalized increase in electron density of cytoplasmic elements in axonal terminals and preterminals. Multilamellar bodies, and increases in the number of dense core vesicles, dense bodies and secondary lysosomes were also observed after treatment with 6-OH-DA. The neurons showed clumping of mitochondria, which also appeared to be undergoing degenerative changes. The vacuoles in some supraependymal cells were greatly dilated as was the Golgi apparatus in the ependymal cells. The ependymal cell layer appeared to be intact, but there were areas immediately deep to this cell layer that contained large extracellular spaces. This increase in extracellular space was also commonly observed surrounding the perivascular spaces. These phenomena greatly contribute to the “spongy” appearance that the SFO takes on after 6-OH-DA administration.
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  • 44
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    Cell & tissue research 191 (1978), S. 171-182 
    ISSN: 1432-0878
    Keywords: Frontal ganglion ; Periplaneta ; Synaptic contacts ; Immunohistochemistry ; Electron microscopy
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    Topics: Biology , Medicine
    Notes: Summary The frontal ganglion, part of the stomatogastric nervous system, contains about 60 to 80 neurons, 25 to 30 μm in diameter. A well developed Golgi system, producing dense-core vesicles, lysosomes, multivesicular bodies and dense bodies are abundant. Glia elements are sparsely distributed. Many nerve fibres contain granules of different size and electron density. Five groups of fibres can be distinguished: Fibres with granules of about 200 nm (type A), fibres with granules of about 160 to 170 nm (type B), fibres with granules of about 80 to 100 nm (type C) and those with synaptic vesicles of 50 nm (type D) respectively. A fifth very small type contains neither vesicles nor granules. Special attention was paid to synaptic contacts. The divergent dyad seems to be the main type in the frontal ganglion. Frequently, neurosecretory endings are observed in presynaptic position. Immunocytochemical “staining” of neurosecretory material closely corresponds to the distribution of type A fibres, as observed electron microscopically. Immunoelectrophoresis of extracts from frontal ganglia with polyspecific anti-neurosecretion-serum reveals a single precipitation line, indicating that the immunocytochemical localization of neurosecretory material is due to reaction with a specific as well as a crossreagent antibody.
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  • 45
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    Keywords: Osteoblasts (Chick embryo) ; Golgi complex ; Microtubules ; Colchicine ; Electron microscopy
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    Notes: Summary Embryonic chick frontal bones were cultured in the presence of colchicine or vinblastine and subsequently examined by transmission electron microscopy. In control cultures the osteoblasts showed a large Golgi complex consisting of dictyosomes arranged in a well-defined juxtanuclear area. Microtubules were particularly numerous within this Golgi area although they could be observed throughout the cytoplasm. Colchicine and vinblastine caused the disappearance of cytoplasmic microtubules, while bundles of 10nm diameter filaments appeared more frequently. In addition, cell polarity was lost and the Golgi complex became disorganized, with the dictyosomes randomly dispersed in the cytoplasm and showing a decreased number of cisternae and an increased number of vacuoles, the latter generally lacking stainable material. Increased number of autophagosomes were also noted. These findings indicate that microtubules function in the organization of the Golgi complex in osteoblasts. In view of the well documented role of this organelle system in collagen secretion it is suggested that previously observed secretory disturbances produced by antimicrotubular drugs may be due to a defective transfer of material to the dictyosomes and/or a defect in the packaging and transport of such material away from them.
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  • 46
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    Cell & tissue research 194 (1978), S. 79-102 
    ISSN: 1432-0878
    Keywords: Duodenum ; Endocrine cells ; Differentiation ; Immunocytochemistry ; Electron microscopy
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    Topics: Biology , Medicine
    Notes: Summary The development and cytodifferentiation of endocrine cells that produce the gastrointestinal hormones gastrin, cholecystokinin and secretin have been studied by a combined fluorescence-cytochemical, immunocytochemical and ultrastructural approach. The results show that, during development, several ultrastructurally distinct cell types exhibit COOH-terminal gastrin and cholecystokinin immunoreactivity. Furthermore, some cells simultaneously contain both gastrin- and cholecystokinin-specific antigenic determinants. Studies on the time course of development of gastrin and cholecystokinin cells, together with the above-mentioned data, suggest that gastrin cells may be converted into cholecystokinin cells in development. During this period, gastrin, cholecystokinin and secretin cells store the biogenic monoamine, 5-hydroxytryptamine a feature not displayed by the adult counter-parts of these cells. In the adult duodenum, characteristic enterochromaffin (EC) cells store 5-hydroxytryptamin for which, evidence for a possible hormonal role has been presented. Taken together, our data indicate that the differentiation of duodenal endocrine cells occurs in distinct steps, each involving a restriction in the biosynthetic repertoire of the cell.
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  • 47
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    Cell & tissue research 194 (1978), S. 183-205 
    ISSN: 1432-0878
    Keywords: Bone marrow ; Heterophil granulocytes ; Granules ; Guineapig ; Electron microscopy
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    Topics: Biology , Medicine
    Notes: Summary The development of the heterophil granulocytes in the bone marrow of the guinea pig is described. During the maturation of these cells, three types of granule are formed, not only the azurophil and specific granules already described in other mammals but also a third type of granule referred to here as the nucleated granule. During the process of maturation of the cells, these three types of granule are formed successively. On this basis, two steps can be distinguished in the promyelocyte phase in which primary (nucleated and azurophil) granules are formed, i.e. an early and a late stage, nucleated granules being formed in early and azurophil granules in late promyelocytes. Secondary (specific) granules occur first in myelocytes. In mature heterophils of the guinea pig the granule population is composed of about 85% secondary granules, about 10% azurophil granules, and about 5% nucleated granules. The changes in the granule population during the maturation process were quantified. The observations and calculations point to the occurrence of three mitoses: one in the early and one in the late promyelocyte and the third in the myelocyte.
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  • 48
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    Cell & tissue research 194 (1978), S. 279-285 
    ISSN: 1432-0878
    Keywords: 14C-thymidine incorporation ; Autoradiography ; Multinucleated blasts ; Electron microscopy ; Deformities of cellular membranes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Cytochalasin B (CB) administered simultaneously with a mitogenic dose of concanavalin A (Con A) interferes with the activation process. This interference involves structural alterations of cellular membrane which do not include a reduced Con A-binding capacity. This conclusion is supported by the observation of deformities in both nuclear and cytoplasmic membranes in Con A-activated lymphocytes subsequently treated with CB. The high incidence of membrane blebs and pseudomyelin bodies in the cytoplasm points to a general effect of CB on the structural organization of membrane which may secondarily interfere with some specific event such as generation or transfer of signals for activation or cytokinesis.
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  • 49
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    Cell & tissue research 194 (1978), S. 503-511 
    ISSN: 1432-0878
    Keywords: Cell cultures ; Electron microscopy ; Synaptic organelles ; Spinal cord (mouse)
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    Topics: Biology , Medicine
    Notes: Summary This study describes some of the ultrastructural features of presynaptic and postsynaptic organelles at synapses developed in cultures of previously dissociated mouse spinal cord cells. Particular attention was paid to the agranular reticulum which is well developed at many presynaptic and postsynaptic sites, either in the form of simple tubules or cisternae, or more complex networks and often closely associated with mitochondria. In addition, the disposition of microtubules at and close to synaptic specializations is described. These and other features of synaptic zones, such as granular vesicles in presynaptic sites, are discussed in relation to cultures developed on feeder layers and synapses in vivo, and in relations to possible degenerative and regenerative events in the cell cultures.
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  • 50
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    Cell & tissue research 195 (1978), S. 17-27 
    ISSN: 1432-0878
    Keywords: Myosatellite cells ; Muscles ; Atlantic hagfish (Myxine glutinosa, L.) ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The incidence of myosatellite cells associated with “white” and “red” muscle fibres of the parietal muscle and “red” fibres of the craniovelar muscle was estimated by quantitative electron microscopy in the Atlantic hagfish (Myxine glutinosa, L.). Myosatellite cell nuclei constitute 3, 11 and 23 % of the total number of nuclei inside the basal lamina of the three types of muscle fibres, respectively. However, the total number of nuclei is highest in “white” fibres, most of the nuclei belonging to striated muscle cells. Myosatellite cell profiles in transverse sections constitute 23, 41 and 61 % of the number of muscle fibre profiles of the three types, respectively. The intervals between adjacent myosatellite cells are ∼ 135 μm in “white” fibres, ∼ 55 μm in “red” parietal fibres, and only ∼ 25 μm in craniovelar fibres. Since craniovelar fibres are also comparatively thin, myosatellite cells constitute a significant fraction of the volume inside the basal lamina in these fibres. The myosatellite cells are ∼ 30–50 μm long and up to 5 μm thick. Some myosatellite cells possess few organelles, whereas others appear to contain many free ribosomes, granular endoplasmic reticulum, prominent Golgi apparatus and lysosome-like bodies.
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    Cell & tissue research 195 (1978), S. 29-43 
    ISSN: 1432-0878
    Keywords: Endocrine hypothalamus (rat) ; Arcuate nucleus ; L-dopa ; Autoradiography ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Light and electron microscopic autoradiography has been employed to define the neuroanatomical patterns of uptake and binding of radiolabelled L-dopa in the endocrine hypothalamus of the rat. A dorsomedial continuum of arcuate and periventricular neurons selectively sequester 3H L-dopa 20 min following its intraventricular infusion. By 40 and 60 min following the infusion labelling of neurons is minimal and supports the notion of rapid degradation. Other cell compartments such as tanycytes demonstrate uptake of 3H L-dopa. The ultrastructural localization and distribution of radiolabelled L-dopa (or its metabolites) in the rodent hypothalamus is discussed with respect to mechanisms and cell compartments involved in neuroendocrine regulatory processes.
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  • 52
    ISSN: 1432-0878
    Keywords: Guinea pig uterus ; Myometrium, pregnancy ; Sympathetic nerves ; Electron microscopy ; Axon degeneration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary In the guinea pig myometrium, the adrenergic nerves selectively demonstrated at the ultrastructural level after treatment with 5-OH-DA, show varying degree of degeneration during pregnancy. The changes are more extensive in a late gestational stage (40–45 days) than in an early one (20–25 days), and are particularly evident in the uterus overlying the conceptus as compared to the regions between the fetuses. Scattered degenerative changes were also observed in myometrial specimens from virgin animals, but probably reflect the normal continuous turnover of axons.
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  • 53
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    Cell & tissue research 195 (1978), S. 527-533 
    ISSN: 1432-0878
    Keywords: Ciliated neurons ; Habenula ; Interpeduncular nucleus ; Electron microscopy ; Rana esculenta, tadpole
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Cilia of the 9+2 pattern are found electron microscopically in nonependymal cells of the habenulae and the interpeduncular nucleus of the tadpole of Rana esculenta at an early stage of development (8 mm length, head to tip of tail). A comparison is made between these and the ependymal and sensory cilia in the same specimens. The cilia project into the neuropil emerging from a perikaryon rich in free ribosomes and displaying a prominent Golgi apparatus. These perikarya contain dense core vesicles. Synapses with vesicles of the clear spherical type have been observed along the ciliary shaft. On a purely morphologic basis the authors hypothesize that these cilia, at least in this early ontogenetic stage, may extend considerably the conducting surface of the cell and represent a sensory structure which could be stimulated by terminal processes belonging to distantly located cells. In addition, they could also be involved in the trophic exchange of material with the adjacent structures.
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  • 54
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    Cell & tissue research 195 (1978), S. 557-564 
    ISSN: 1432-0878
    Keywords: Osteoclasts ; Osteocytes ; Bone resorption ; Phagocytosis ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The osteoclast-osteocyte relationship at the endosteal surface of femora of two-week old rabbits was studied. Light microscopic observations suggest that during physiological resorption phagocytosis by osteoclasts of osteocytes takes place. Serial sections confirm that the cells are totally engulfed within the cytoplasm of the osteoclasts. Ultrastructural studies support these findings and indicate that the initial stage of phagocytosis of the osteocytes consists of the insinuation of an extension of the ruffled border into the osteocyte lacuna. These extensions are seen to make close contact with the osteocytes prior to their engulfment by the osteoclasts and their final digestion within phagosomes.
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  • 55
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    Cell & tissue research 186 (1978), S. 39-52 
    ISSN: 1432-0878
    Keywords: Muscle spindle ; Nerve endings ; Acetylcholinesterase ; Cytochemistry ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Muscle spindles from lumbricalis muscles of the rat were incubated for acetylcholinesterase with a modified thiocholine-method of Lewis and Shute and examined by light and electron microscopy. All types of motor nerve ending showed heavy deposits of reaction product in the synaptic cleft. The underlying sarcoplasmic reticulum, transverse tubular system, and, when present, the envelope of sole plate nuclei were also stained. In the sensory region, the reaction was negative in the interface between the plasma membranes of the primary sensory terminal and muscle. One of two secondary sensory endings identified showed distinct reaction product in the cleft; the other secondary sensory ending showed no such reaction. Precipitates were present on the sarcolemma of the intrafusal muscle fibers in the polar and adjacent myotube regions, but not at the spindle equator. Extrafusal and intrafusal myelinated γ-nerve fibers and preterminal motor axons showed staining of the axolemma. Fibers with thick myelin sheaths and preterminal sensory axons were free of acetylcholinesterase activity, as were the unmyelinated nerve fibers.
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  • 56
    ISSN: 1432-0878
    Keywords: Serum and pituitary LH ; Rat gonadotrophs ; LH-RH and Granule release, Synthesis and Degradation ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The effects of single and repeated LH-RH injections at 120 min intervals on female rat LH gonadotrophs and on pituitary and serum LH levels were investigated using electronmicroscopy and radioimmunoassay. A temporary stimulation of granule release, of protein and new granule synthesis and of the accumulation of lysosomal structures was found in LH cells after the first LH-RH injection. The temporary stimulations were massively enhanced after the second injection. These consecutive yet in their time-sequence overlapping processes account for the initial depletion of secretory granule content (3–15 min after LH-RH injection), for the subsequent regranulation and accumulation of granules above control levels (60–120 min after injection) and also for the reduction in the number of granules to control levels (150 min after LH-RH injection and thereafter). Increased polymorphic lysosomal structures are believed to be responsible for this reduction of excess granules. The amount of assayable pituitary and serum LH generally corresponds with the morphological changes observed in LH-gonadotrophs, thus further substantiating the above observations. A schema which summarizes the observed morphological and hormonal changes in their time-sequence in response to LH-RH stimulation depicts the short-term regulation of secretory processes in female gonadotrophs.
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  • 57
    ISSN: 1432-0878
    Keywords: Endometrium ; Rabbit ; Reproductive cycle ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Changes occurring on the surface of the uterine luminal epithelium of the rabbit during the estrous and progestational stages of the reproductive cycle were examined by scanning and transmission electron microscopy. The findings demonstrate that the uterine epithelium, or endometrium, contains two cell types: ciliated cells and nonciliated, microvillous cells. In estrous animals, ciliated cells, although not very numerous, were usually observed in small groups. However, at increasing intervals of time following mating, ciliated cells progressively disappeared from the endometrium until approximately eight to ten days post coitum, when they became scare. From several hours to four to five days following mating, extensive changes occurred on the surfaces of microvillous cells. When observed by TEM, these elements contained organelles typical of cells involved in the synthesis and secretion of glycoproteins. Furthermore, microvillous cells during this period displayed numerous apical protrusions of different sizes and shapes and containing material of varying electron density. Parallel SEM examinations of the same material confirmed the presence of these protrusions. Some of the protrusions appeared as spheroidal masses attached to the cytoplasm by means of a cytoplasmic strand. Other surface masses were clearly unattached to the cell surface and were distributed (1) on the surface of microvillous cells, (2) on the cilia of adjacent ciliated cells, and (3) on the surface of spermatozoa. Changes occurring on the luminal surface during the early postcoital period are interpreted as an expression of morphodynamic processes likely involving coupled secretion (exocytosis) and resorption (endocytosis) of luminal material. The observations presented here also demonstrate that between six and ten days post coitum, the rabbit endometrium contained increasing numbers of enlarged, nonciliated cells that probably arose by the fusion of smaller, microvillous elements.
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  • 58
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    Cell & tissue research 190 (1978), S. 301-316 
    ISSN: 1432-0878
    Keywords: Trachea (Guinea-Pig) ; Plexus submucosus ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The ultrastructure of the nerves forming the submucous plexus of cervical and thoracic parts of the trachea was studied in the guinea-pig. Specimens were obtained from 6 animals perfused with warm fixative and from 6 animals in which pieces of trachea were incubated in buffer containing 5-hydroxydopamine before being immersed in cold fixative. Of the two types of axonal terminal identified in the nerves, one contained mainly large dense-cored vesicles, and the second contained numerous small vesicles. In specimens incubated in 5-hydroxydopamine, the small vesicles of the latter terminals exhibited the electron-dense cores which are characteristic of adrenergic axonal terminals. Counts made on perfused specimens showed that, in both the thoracic and cervical parts of the trachea, the density of adrenergic terminals was higher than that of terminals containing mainly large dense-cored vesicles. Overall terminal density was, however, higher in the thoracic than in the cervical part of the trachea, and estimates of nerve size showed that this was associated with the presence in the thoracic plexus of a substantially greater proportion of nerves with less than 6 axons. The possible function of the nerves in the control of the calibre of the submucous blood vessels was discussed.
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  • 59
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    Cell & tissue research 191 (1978), S. 187-203 
    ISSN: 1432-0878
    Keywords: Pituitary ; GTH-cells ; Teleost ; Immunofluorescence ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The gonadotropin-producing cells (GTH-cells) in the Atlantic salmon were studied light and electron microscopically before, during and after spawning, and after injections of luteinizing hormone-releasing hormone (LH-RH). The double immunofluorescent technique was applied using rabbit anti-carp GTH as the first antibody. Numerous immunofluorescent cells were observed throughout the pars distalis, but very few in the pars intermedia. These cells are basophilic and PAS-positive, and ultrastructurally classified as globular gonadotropes. Only one gonadotropic cell type could be identified; its size, morphology and fine structure vary considerably. In the same specimen the GTH-cells can be predominantly globular or vesicular in appearance, depending on the reproductive phase of the fish. At spawning and after LH-RH injection, many GTH-cells reach a vacuolar stage; the content of the vacuoles is not immunofluorescent. Another cell type, which resembles GTH-cells in semithin sections, did not show gonadotropic properties; its nature and functional significance are unknown. In addition, the present study revealed an increase in the synthetic and exocytotic activity of prolactin cells after LH-RH injections. It is suggested that LH-RH mediates this effect via LH and eventually via estradiol.
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  • 60
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    Cell & tissue research 191 (1978), S. 357-362 
    ISSN: 1432-0878
    Keywords: Prothoracic glands ; Insects ; Electron microscopy ; Macromitochondria ; Crystalloid organization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The fine structure of the prothoracic glands of Spodoptera littoralis was investigated during the first half of the last larval instar. The secretory cells have two types of mitochondria, micromitochondria and macromitochondria. The micromitochondria have rounded to elongated profiles and sometimes branch. They contain lamellar, tubular and also tubulo-vesicular cristae. The macromitochondria appear generally rounded or oval and possess tubular cristae. Many regular parallel membranes appear within macromitochondria. Favorable sections show tubular structures packed in honeycomb fashion. The mitochondrial cristae are in connection with the tubular structures. Honeycomb and parallel membranes increase in number as the size of the macromitochondria increases.
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  • 61
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    Cell & tissue research 192 (1978), S. 461-474 
    ISSN: 1432-0878
    Keywords: Cerebral vessels ; Venules ; Pericytes ; Electron microscopy ; Microvasculature
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Intracerebral venules of the cat were examined to establish criteria for a distinct separation between the venous and arterial system, and to characterize, in greater detail, the mural construction of individual venules. The intracerebral venules were compared with those of other organs. Venules do not have a vascular wall composed clearly of endothelium, media, and adventitia, as is characteristic of arteries and arterioles. The venous endothelium has a similar structure to that of capillaries. The periendothelial cells of the venule differ in shape depending on the vascular diameter. The number of periendothelial cell processes in postcapillary venules increases progressively. Segments in which the basal lamina of the endothelium merges with that of the glia cover a smaller portion of the circumference than in venous capillary loops. In collecting venules, the endothelium is almost completely enveloped by periendothelial cells which have a larger number of filaments. There are no typical smooth muscle cells in the intracerebral venules. The perivascular space becomes wider in collecting venules, contains adventitial cells, phagocytes and a great number of collagen fibers.
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  • 62
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    Cell & tissue research 193 (1978), S. 11-23 
    ISSN: 1432-0878
    Keywords: Tectorial membrane ; Organ of Corti ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The tectorial membrane (t.m.) of mammals, which lies over the organ of Corti, is made up of an agglomerate of protofibrils of varying degrees of hydration. Two types of protofibrils are clearly distinguishable in the mouse t.m. While type-A protofibrils are straight and unbranched (thickness: 110Å) demonstrating a periodic structure (period = 70Å), type-B protofibrils are branched and coiled (thickness: 150–200Å). These protofibrils could be systematically ordered according to the different t.m. zones. Type-A protofibrils predominate in the basal layer and in the entire middle zone, where they are interlaced with strongly hydrated type-B protofibrils. Weakly hydrated type-B protofibrils essentially make up the marginal zone (with the marginal net), the covering net, Hensen's stripe and the immediate contact layer with the limbus.
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  • 63
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    Cell & tissue research 193 (1978), S. 41-59 
    ISSN: 1432-0878
    Keywords: Electrical synapse (frog) ; Electrotonic coupling ; Electron microscopy ; Freeze fracture ; Gap junction ; Mixed synapse ; Motoneuron
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Freeze-fracture replicas and ultrathin sections were used to characterize the gap junctions on the somata and large dendrites of frog motoneurons found earlier by Sonnhof et al. (1977). In freeze-fracture replicas one of the specific features of these relatively frequent gap junctions is the presence of circular regions of non-junctional membrane (“fenestrae”) within areas of typical gap junction appearance displaying P-face particles or E-face pits. Such “fenestrated” gap junctions are mostly associated with membrane specializations indicative of the active zone of a chemical synapse (including vesicle attachment sites in non anaesthetized animals) to constitute mixed synapses. These findings could be verified in ultrathin sections, which revealed that the vesicles of the chemical component of the mixed synapses were spherical and agranular. Our results suggest that the mixed synapses are predominantly axo-somatic and axo-dendritic. The existence of dendro-dendritic gap junctions in the ventral horn region as described by Sotelo and Taxi (1970) was verified in ultrathin sections; they were rare, solely electrotonic in character, and probably represent the morphological basis for the VR-EPSP (Katz and Miledi, 1963; Kubota and Brookhart, 1963), i.e. electrotonic coupling between motoneurons of different spinal segments (Washizu, 1960). Electrotonic coupling can also be demonstrated between motoneurons and afferent fibers of the dorsal root and the lateral column. Electrotonic potentials recorded within motoneurons during electrical stimulation of dorsal root or lateral column precede the chemical postsynaptic potentials; after Mn2+ blockade of chemical synaptic transmission, the electrotonic component persists. Some fibers of these afferent pathways are therefore assumed to act monosynaptically on the motoneuron via mixed axo-somatic and axo-dendritic synapses.
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  • 64
    ISSN: 1432-0878
    Keywords: Olfactory epithelium ; Supporting cells ; Protuberances ; Electron microscopy ; Insectivora ; Talpidae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The regio olfactoria of the mole, Talpa europaea, was studied by scanning and transmission electron microscopy. Peculiar structural differentiations, i.e. ovoid-shaped, balloon-like protuberances were found on the surface of the supporting cells. The apical portion of these protuberances contained finely dispersed granular material, whereas in their central part vesicular extensions of the smooth endoplasmic reticulum were observed.
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  • 65
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    Cell & tissue research 193 (1978), S. 543-560 
    ISSN: 1432-0878
    Keywords: Human ; Urinary bladder epithelium ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary An electron microscopic study of normal bladder urothelium of elderly patients ranging in age from 61 to 82 years has shown the occurrence of unusually thin regions consisting of either one or two layers of undifferentiated cells interspersed between 3–4 cell layers thick regions. A morphometric study has confirmed the existence of a pattern of cytodifferentiation in cells of the thick region. The generally microvillous nature of the luminal surface is attributed to incompletely differentiated cells that have come to occupy the superficial layer. The lack of thickened and/or asymmetric membrane plaques in luminal plasma as well as the dearth of characteristic precursor vesicles in the cytoplasm are also explicable in terms of a failure of normal cell differentiation. It is suggested that the unusual features noted are consequences of tissue ageing rather than prognostic of cancer. There are indications that the aged urothelium may be prone to increased leakiness and the bladder tissues may therefore be at greater risk from urine-borne chemicals and carcinogens.
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  • 66
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    Cell & tissue research 195 (1978), S. 227-237 
    ISSN: 1432-0878
    Keywords: Vinblastine ; Lacrimal gland ; Electron microscopy ; Autophagy ; Secretion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The effects of vinblastine treatment on acinar cells of the rat exorbital lacrimal gland were studied by electron microscopy. Experimental animals of both sexes were given single intraperitoneal injections of (1) vinblastine (4mg/kg body weight) at 1 to 24 h before sacrifice; (2) pilocarpine (20 mg/kg b.w.) for 1 h; or (3) vinblastine for l h followed by pilocarpine for 1 h. Vinblastine treatment caused a number of changes including autophagocytosis, formation of intracisternal granules, and alteration of secretory granules. These changes varied in extent and onset between male and female rats. In addition, the Golgi apparatus was reduced in size and dispersed throughout the cytoplasm. Mitotic figures were commonly observed. Moreover, vinblastine inhibited the pilocarpine-stimulated degranulation of the acinar cells. In view of the known anti-microtubular action of vinblastine, these results suggest that microtubules are involved in various aspects of the transport, packaging, and secretion of exportable proteins in the lacrimal gland. Additionally, autophagocytosis and alteration of secretory granules may partially result from the interaction of vinblastine with membranes.
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  • 67
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    Cell & tissue research 186 (1978), S. 507-525 
    ISSN: 1432-0878
    Keywords: Human thymus ; Age involution ; Cellular composition of cortex, medulla and connective tissue ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Age involuted thymus tissue from a middle aged (33 years) and an old (63 years) man have been examined by electron microscopy and compared with thymus tissue from children. Biopsies had been taken during surgical correction of congenital heart defects. The fine structural architecture of cortex, medulla and connective tissue in the remaining lymphatic islands in the adult thymus investigated was not different to the thymus of children. We were surprised to find vigorous lymphocytopoiesis in the cortical regions and to recognize extended areas of medulla with a cellular composition which obviously provides the same microenvironment for T-cell maturation as the medulla of the non involuted thymus. Our findings are discussed in relation to the increasing arguments that the human thymus serves an immunological function throughout life.
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  • 68
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    Cell & tissue research 188 (1978), S. 171-187 
    ISSN: 1432-0878
    Keywords: Embryonic heart ; Crustacea (Homarus americanus) ; Cardiac muscle ; Intercellular junctions ; Electron microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The cellular organization of the embryonic heart of the lobster Homarus americanus was examined in 6-week and 6-month-old animals. The heart wall consists of an outer adventitial layer of fibroblast cells and an inner layer of transversely striated myocardial cells. Present in close association with the myocardium are cardiac neurons, hemocytes and so-called storage cells. Adjacent fibroblasts form fasciae adhaerentes and gap junctions. Adherent junctions also occur between fibroblasts and myocardial cells. Intercalated discs and differentiated membrane regions of close apposition (4 nm) occur between adjacent myocardial cells. The cardiac neurons form a ganglion that contains four small and five large somata. Regions of neuropil are present. Motor axons arising from the cardiac ganglion form neuromuscular synapses with the myocardial cells. The storage cells contain large inclusions and form gap junctions with the myocardial cells. They may supply nutritive material to the developing myocardium. The heart at 6 weeks is about 200 μm long and 160 μm wide. At 6 months, it is about 300 μm long and 250 μm wide. The myocardium at 6 weeks is one cell layer thick, and the cells are from 2–6 μm in maximum width. At 6 months the myocardium is 2–4 cells thick, and the cells are from 6–12 μm in width. Therefore, the myocardium grows by an increase in the number and size of the myocardial cells.
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