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  • 1
    Electronic Resource
    Electronic Resource
    On the development of the spinal cord of the clawed frog, Xenopus laevis (1982)
    Springer
    Anatomy and embryology 164 (1982), S. 443-454 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF00315764
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  • 2
    Electronic Resource
    Electronic Resource
    A quantitative analysis of the development of the pyramidal tract in the cervical spinal cord in the rat (1989)
    Springer
    Anatomy and embryology 179 (1989), S. 377-385 
    Details
    ISSN: 1432-0568
    Keywords: Pyramidal tract ; Rat ; Development ; Axon loss ; Myelination
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary A quantitative electron microscopic analysis was undertaken of the development of the pyramidal tract, at the level of the third cervical spinal segment, in rats ranging in age from the day of birth to three months old. The axon number was calculated as the product of axon density, determined in a systematic random sample of electron micrographs, and tract area. During the first postnatal week the tract contains thin unmyelinated axons and growth cones. Growth cones are abundant in neonatal rats, but can still be observed occasionally at the end of the first postnatal week, indicating a continuous addition of pyramidal tract axons during the first postnatal week. Myelination starts around P10. By the end of the first postnatal month approximately 50% of the axons have already been myelinated. Myelination proceeds during further maturation, but in the three month old rat 28% of the axons are still unmyelinated. The total number of axons increases rapidly after birth up to 153 000 at the fourth postnatal day. Subsequently, the number of axons is reduced by nearly 50% to 79 000 in the adult rat. The axon loss is most prominent during the second postnatal week, when 32 000 axons are climinated, but continues for several weeks at a slower rate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00305064
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    On the development of the spinal cord of the clawed frog, Xenopus laevis (1982)
    Springer
    Anatomy and embryology 164 (1982), S. 427-441 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF00315763
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    On the development of the pyramidal tract in the rat (1985)
    Springer
    Anatomy and embryology 172 (1985), S. 195-204 
    Details
    ISSN: 1432-0568
    Keywords: Pyramidal tract ; Growth cones ; Electron microscopy ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary An electron microscopic study has been made of the tip of the growing pyramidal tract in the rat. This part of the developing bundle, designated as the growthzone, has been examined at the levels of the medulla oblongata and the third spinal segment at embryonic day 20 and on the day of birth, respectively. The tip of the pyramidal tract contains, apart from axons, numerous larger profiles. An analysis of serial sections revealed that these represent either growth cones or preterminal periodic varicosities. In the growth cones of the corticospinal axons three zones can be distinguished: a proximal “tubular”, an intermediate ”vesicular-reticular” and a distal “fine-granular” zone. As distinct from the classical descriptions the corticospinal growth cones end in a single or, less frequently, in two more or less parallel filopodia. None of the growth cones analyzed in this study showed multiple filopodia radiating from the terminal expansion as observed at the end of growing axons in tissue cultures and in developing spinal fibre tracts of nonmammalian vertebrates. As regards the varicosities, most of these structures are characterized by a light cytoplasmic density. Others, however, contain a denser cytoplasm, closely resembling that of the vesiculo-reticular part of growth cones.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00319602
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    Paper (German National Licenses)
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