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  • 1985-1989  (5)
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Year
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Cell & tissue research 252 (1988), S. 581-587 
    ISSN: 1432-0878
    Keywords: Normal resting breast ; Ultrastructure ; Mitosis ; Cytokinesis ; Human
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The parenchyma of the normal “resting” human breast was examined by electron microscopy to characterize the cells undergoing mitosis and the mechanism by which the normal tissue architecture is maintained during this process. In this study of 112 mitotic cells, it was found that the mitotic cells were luminally positioned, polarised epithelial cells with no evidence of myoepithelial cell division. Ultrastructurally, the nuclear and cytoplasmic changes were consistent with previous reports of mitosis in other tissues. However, unlike all previous reports, two specific orientations of the nuclear spindle and thus the planes of cytokinesis were observed. In a few cases the spindle formed parallel to the lumen and division resulted in two luminally positioned daughter cells. However, in the majority of mitotic cells the spindle was approximately at right angles to the lumen and this orientation resulted in a luminally and a basally positioned daughter cell. It is proposed that the abnormally positioned basal daughter cell could develop into a myoepithelial cell or undergo deletion (apoptosis). Thus the two orientations of mitosis may explain the mechanism by which the epithelial and myoepithelial cell populations were maintained by a single progenitor cell without disrupting the integrity of the tissue architecture.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-6865
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The feasibility of using scanning electron microscopy (SEM) to identify the position of specific DNA sequences was examined using a Y chromosome ‘specific’ probe (pHY2.1). Tests were carried out on chromosome spreads hybridizedin situ with biotinylated pHY2.1. Chromosomal sites of hybridization of the probe were localized by an indirect immunohistochemical procedure which resulted in a gold product which could be amplified by silver precipitation. In the SEM, the specific location of the probe was easily identified due to the enhanced signal produced by the gold—silver complex. The probe was localized both on the long arm of the Y chromosome and within interphase nuclei. It was found that SEM was more sensitive than light microscopy since the probe could be identified without silver amplification. With refinements to the technique, SEM could provide a useful method for high resolution localizing of unique DNA sequences (i.e. single copy genes).
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-1955
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The ultrastructural features of the early development and tissue cyst formation of Toxoplasma gondii were examined in the brains of mice at various intervals from 7 days to 22 months post inoculation (PI). At 11 days PI toxoplasms, with the ultrastructural features of the proliferative (endozoite) form, were identified undergoing multiplication within both inflammatory and neural cells. Early tissue cyst formation was also observed, predominantly within neurons. By 21 days PI the proliferative forms had disappeared and only developing tissue cysts containing densely packed cystozoites were present. The proportion of dividing cystozoites decreased with increasing size and age of the cysts. The wall of the tissue cyst developed as an adaptation of the lining of the parasitophorous vacuole. In the majority of older cysts, numerous tubular structures were present beneath the cyst wall. All the cysts observed were retained within intact host cells. The only morphological change with increasing age was that a proportion of the older cysts contained loosely packed cystozoites in an electron lucent ground substance. There was no evidence of any degenerative changes within the cystozoites.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Parasitology research 75 (1989), S. 599-603 
    ISSN: 1432-1955
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The incidence and effect of tissue cyst rupture in the brains of mice chronically infected withToxoplasma gondii was studied by immunocytochemistry and electron microscopy. Cyst rupture was extremely rare (2 of 750 tissue cysts) irrespective of the interval post-infection. The event was associated with a rapid cell-mediated immune response, giving rise to microglial or inflammatory nodules. Macrophages were observed to engulf and degrade the cystozoites and cyst debris. Initially, the nodules contained large amounts of immunologically reactive material, but this was degraded with the majority (94%) of lesions containing no recognizable parasites orToxoplasma antigens. There was little evidence of parasite multiplication or new cyst formation associated with cyst rupture. This study shows that although intermittent cyst rupture occurs, in immunocompetent individuals the immune response limits the potential damage from the release of large numbers of infective organisms to small microglial/inflammatory nodules.
    Type of Medium: Electronic Resource
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  • 5
    Publication Date: 1987-05-01
    Description: Several species of Mesozoic megaspores that are sculptured with globular, often gemmate elements are sufficiently distinct from most verrucate forms to warrant their inclusion in a genus other than Verrutriletes. Cabochonicus is erected to accommodate them with C. (al. Verrutriletes) carbunculus as the type species. The form of the gemmae, which have a glossy appearance, has been the subject of past debate with one interpretation being that they are the manifestation of fungal attack rather than sculpture. Evidence from ultrastructural studies suggests, however, that they are exinal excrescences. The spores are assumed to be the products of heterosporous lycopods and the structure of the wall layers may indicate selaginellalean affinities. The plants are more likely to have been terrestrial than aquatic or semi-aquatic.
    Print ISSN: 0262-821X
    Electronic ISSN: 2041-4978
    Topics: Geosciences
    Published by Copernicus on behalf of Micropalaeontological Society.
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