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  • 1
    ISSN: 1432-0568
    Keywords: Conduction system ; HNK-1 ; Rat embryo heart
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract To investigate the origin and development of the cardiac conduction system, the distribution of HNK-1 immunoreactivity in embryonic rat hearts was studied in histological sections and in three-dimensional computer reconstructions. Earliest HNK-1 reactivity was found along the endocardial surface of the fusing tubular heart at 9.5 embryonic days (ED) and subsequently within individual myocytes scattered widely along the looped tubular heart. Immunopositive myocytes appeared along the earliest ventricular trabeculae as they coalesced to form the developing interventricular septum during day 11, spreading to either side to give rise to the right and left bundle branches in the 12.5 ED heart. In the venous pole of the heart, primordia of the sinus node, and of the transient left sinus node, appeared immunopositive from 12.5 ED, coalescing during ED 13 along the anterior wall of the right sinus horn or developing coronary sinus, respectively. In the atria, several distinct tracts of immunoreactive myocytes were defined by 14.5 ED, ramifying from the sinoatrial junction to the atrial appendages or to the atrio-ventricular (AV) junction near the AV node. The timing and distribution of these immunostaining patterns suggest that ventricular conduction tissue develops within the earliest trabecular and septal myocardium, and is distinct from later immunopositive atrial tracts and extracardiac cell populations, such as neural crest, that appear to contribute to formation of the sinus node and autonomic innervation of the heart.
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  • 2
    ISSN: 1432-0827
    Keywords: Epiphyseal chondrocytes ; Freezefracture ; Scanning electron microscopy ; Cell processes ; Membrane particles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Chondrocytes in epiphyseal cartilage were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) using freeze-fracture techniques. Freeze-fracture replicas showed large numbers of fingerlike, 0.11–0.15 μm diameter, projections from the chondrocyte surface, with numerous 95–180 Å diameter intramembranous particles associated with both the cell membrane surface and these projections. With SEM, these cytoplasmic projections were also obvious, but appeared collapsed into clusters of globular-shaped projections on the surface of the chondrocytes. With freeze-fracture techniques, in which shrinkage artifacts were essentially eliminated, the cytoplasmic projections were often seen in intimate contact with the extracapsular matrix. However, with chondrocytes prepared by both SEM and conventional TEM, there was evidence of shrinkage, the cytoplasmic projections having little contact with the extracapsular matrix. These findings show that the cytoplasmic processes are not artifacts of tissue processing and provide morphological evidence in support of the hypothesis that matrix vesicles are of cellular origin.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 0886-1544
    Keywords: myofibrils ; extracellular matrix ; cytoskeleton ; integrins ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The influence of the extracellular matrix (ECM) on cell behavior, myofibrillogenesis and cytoarchitecture was investigated in neonatal rat cardiac myocytes in vitro. Cell behavior was examined by analyzing cell spreading on different ECM components under a variety of experimental conditions. Area measurements were made on digitized images of cells grown for various time intervals on fibronectin (FN), laminin (LN), collagens I and III (C I + III), plastic, and bovine serum albumin (BSA). The amount of spreading was varied on the different matrices and was maximal on FN 〉 LN 〉 C I+III 〉 plastic 〉 BSA. Addition of anti-β1 integrin antibodies to myocytes cultured on FN, LN and C I+III blocked spreading outward on the substrates and altered normal myofibrillogenesis, especially on LN. Concomitantly, the integrin antibodies induced the formation of giant pseudopodial processes which protruded upward from the substrates. These pseudopods contained actin polygonal networks which exhibited a regular geometrical configuration.Effects of the ECM on cytoarchitecture was examined by analyzing the temporal and spatial patterns of fluorescence and immunogold labeling of cytoskeletal and integrin proteins as myocytes spread in culture. The first indication of sarcomeric patterns was the appearance at 4 hours of striations formed by lateral alignment of α-actinin aggregates into Z bands. At later times, vinculin at 8 hours and β integrin at 22 hours became co-localized with α-actinin at the Z bands and focal adhesions. These data indicate that ECM components influence myocyte spreading and that myofibril assembly and/or stability is associated with ECM-integrin-cytoskeleton associations.
    Additional Material: 8 Ill.
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  • 6
    ISSN: 1432-0878
    Keywords: Sensory receptors ; Insects ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The antennae of Scolytus multistriatus were examined with light and scanning and transmitting-electron microscopy to determine the distributions, types and structures of sense organs. Four types of sensilla were found: (1) sensilla chaetica, a singly-innervated receptor; (2) sensilla basiconica, Type A, a short, thin-walled, multiple-innervated receptor; (3) sensilla basiconica, Type B, a long, thin-walled multiple-innervated receptor; and (4) sensilla trichodea, short, thick-walled, multiple-innervated receptors. The positioning of dendrite(s) with regard to pore tubules is elaborated. Evidence for lack of sensory axon fusion is presented.
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  • 7
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The scutate scales are entirely missing in chick embryos homozygous for the gene, “scaleless.” Reticulate scales of this mutant are present; however, they have undergone abnormal morphogenesis into irregular mounds and crevices. The pattern of keratinization seen along the anterior metatarsus of normal embryos differs dramatically from that seen along the anterior metatarsus of scaleless embryos. In contrast, we find that the unique pattern of keratinization seen in the epidermal cells of normal reticulate scales is retained in mutant reticulate scales, even though these scales are morphologically abnormal. We believe that differences in the initial tissue interactions (which establish the inductive ability of the dermis) of these two types of scales are responsible for the differences seen in their responses to the scaleless gene. The pleiotropic nature of the scaleless gene is discussed.
    Additional Material: 5 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    American Journal of Anatomy 165 (1982), S. 435-443 
    ISSN: 0002-9106
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: The formation of the connective tissue network, composed principally of collagen, in the left ventricle of the neonatal hamster heart developed primarily during the first 20 days postpartum. The weave network of the endomysium, which was absent at birth, was visible by 4 days and was similar to that of the adult by 15 days postpartum. Myocyte-myocyte and myocyte-capillary struts formed gradually as the heart underwent physiological hypertrophy. These data were similar to the development of the connective tissue network in the rat except that the myocyte-myocyte struts were more numerous in the hamster. Presumably this is because the hamster has a higher heart rate, which would require more mechanical coupling of the myocytes. Formation of the struts appears to take place at precise areas on the sarcolemma through the interaction of collagenous and noncollagenous components of the extracellular matrix.
    Additional Material: 10 Ill.
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  • 9
    ISSN: 0002-9106
    Keywords: Extracellular matrix ; Matrix mettaloproteinases ; Monoclonal anti-rat collagenase ; Polyclonal anti-human collagenase ; Trabeculation ; Septation ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine
    Notes: During development, extracellular matrix (ECM) molecules are thought to play a major role in regulating the formation of the heart. The change in the heart from a simple tube to a complex, four-chambered organ requires the modification of both the cellular components as well as the surrounding ECM. Matrix metalloproteinases (MMP), which include collagenases, are enzymes present in the ECM that have the potential to modify the existing ECM during the development of the heart. Using both monoclonal and polyclonal antisera against collagenase, specific temporal and spatial patterns have been documented during critial periods of heart development. The cytokine interleukin 1α (IL-1α), a potent inducer of the MMP expression, was also shown to have a similar staining pattern in the developing heart.The monoclonal anti-rat collagenase (Mab) intensely stained the surfaces of the myocytes in the trabeculae and the ventricular and atrial walls of the 11.5 or 12.5 embryonic day (ED) rat hearts. In contrast, the polyclonal anti-human collagenase (Pab) stained not only the cardiomyocytes but also the hypertrophic endocardial cells. Pab appeared to stain the leading edge of the mesenchymal cells that migrate into the cardiac jelly of the 11.5 or 12.5 ED hearts. Immunohistochemical staining showed IL-1α on the endocardial endothelium and the surface of cardiomyocytes near the cardiac jelly just before or coincident with the appearance of migrating cells.IL-1α was detected on the endocardial endothelium, cardiomyocytes in the trabeculae, and the ventricular and atrial walls, as well as in the myocardial basement membrane of the truncal or atrioventricular region. However, no staining could be detected on the migrating cells in the cardiac cushions. These results indicate the presence of collagenase and IL-1α on the surface of cardiomyocytes and mesenchymal cells at times when the heart is undergoing acute remodeling during septation and trabeculation. These data suggest a role for collagenase/cytokine interaction in tissue remodeling during critical stages of cardiac embryogenesis where modification of the ECM is essential to cardiac morphogenesis. © 1992 Wiley Liss, Inc.
    Additional Material: 10 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal of Morphology 161 (1979), S. 111-121 
    ISSN: 0362-2525
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Reticulate scales develop as radial symmetrical anlagen, in contrast to scuttate scales which appear initially as “epidermal placodes.” Unlike scuttate scales whose outer and inner epidermal surfaces elaborate β-and α-type keratins, respectively, reticulate scales elaborate only one type of epidermal surface which has been reported to give an α-type, X-ray diffraction pattern. We find that, histologically and ultrastructurally, this surface differs from either epidermal surface of scuttate scales. The keratinizing cells become filled with long interweaving bundles of α-filaments which aggregate into rather homogeneous α-fibrils. Keratohyalin granules, which have been shown to be associated with other keratinizing regions in the bird, do not form during the keratinization of reticulate scale epidermis.
    Type of Medium: Electronic Resource
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