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  • 1
    ISSN: 1432-0568
    Keywords: Chick embryo ; Notochord ; Neural tube ; Floor plate ; Proliferation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The role of a notochord fragment on the origin of an additional floor plate area in the neural tube is investigated by quantitative morphological methods. In 1.5 to 2 day chick embryos a notochordal fragment was implanted in close apposition to the lateral wall of the neural groove in the region between prospective wing and leg bud. At 4 days, adjacent to the implant a distinct area of the neural wall was present, which resembled the natural floor plate with respect to its thickness, the abluminal location of elongated nuclei and the absence of neuroblasts. The mitotic density of this area was reduced. This “additional floor plate” was distinct when the experiment was performed at 1.5 days but was hardly recognizable when it was carried out at 2 days. From these results it is concluded that a) the notochord induces floor plate like structures and diminishes proliferation, and b) that the period of floor plate induction by the notochord is very restricted.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Anatomy and embryology 164 (1982), S. 427-441 
    ISSN: 1432-0568
    Keywords: Spinal cord ; Morphogenesis ; Histogenesis ; Amphibia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The morphogenesis and histogenesis of the spinal cord of Xenopus were examined. The study encompasses the developmental period between stage 41 and stage 66 (stages according to Nieuwkoop and Faber 1967). This period can roughly be divided into three phases. From stage 50 up to stage 53 strong proliferation and rapid growth are the most striking features. This developmental phase is preceded and followed by less dynamic periods. From stage 41 up to stage 50 the rate of proliferation is relatively low. The numbers of cells in the matrix and in the mantle layer are very small. In the mantle layer two classes of early differentiated transient neurons can be distinguished: primitive giant sensory or Rohon-Beard cells and primitive motor neurons. From stage 46 onward the originally tube-shaped spinal cord swells at the thoracic level into a thoracic enlargement. After stage 50 the proliferation strongly increases until a maximum at stage 53. Concomitantly a considerable acceleration of growth takes place. The major part of the mitoses are always concentrated in the dorsal part of the matrix. From stage 51 onward the cervical and lumbar regions show much more mitoses than the thoracic part. Distinct cervical and lumbar enlargements develop and are going to mask the thoracic swelling of the cord. From stage 54 on proliferation continues on an increasingly low level. The period between stage 54 and stage 66 is characterized by differentiation of the spinal neuronal elements.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Anatomy and embryology 164 (1982), S. 443-454 
    ISSN: 1432-0568
    Keywords: Spinal cord ; Differentiation ; Migration ; 3H-Thymidine autoradiography ; Amphibia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary in order to determine the time and site of origin and the final location of various cell groups in the spinal cord, tadpoles of Xenopus laevis, ranging from stage 48 to stage 56 were treated with tritiated thymidine and sacrified at various stages from 49 to 66 (stages according to Nieuwkoop and Faber (1967). From the poorly developed matrix at stage 48–49 not only ventral horn cells, but also neuroblasts of the intermediate zone and the dorsal horn arise. Both the matrix and the ventricle expand in a dorsal direction. From the well-developed matrix at stage 54, in which the mitotic activity is almost exclusively confined to its dorsal part, mainly cells of the dorsal horn develop. However, this later-stage matrix also gives rise to a considerable number of neuroblasts, which become located in the central parts of the intermediate zone and the ventral horn. Generally the later-born cells come to lie dorsomedially to the older ones. The neuroblasts of the lateral motor column, however, migrate through and settle ventrolaterally to their predecessors. Our observations do not support the basal plate-alar plate concept of His (1893).
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0012-1606
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology
    Type of Medium: Electronic Resource
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