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In wholemounts of the very early developing nervous system of Xenopus, HNK-1 specifically labeled cell bodies, axons, and growth cones of identifiable CNS neurons during the period of axonal outgrowth. The unique overview provided by these preparations showed that individual growth cones navigate their routes independently rather than by fasciculation and,(More)
In our previous studies on studies on spinal cord regeneration in the adult lizard and the newt, we observed that the radial processes of the regenerating ependyma form between them channels which are subsequently invaded by growing neurites. In the present study we compare embryogenesis of the newt spinal cord with regeneration in the adult. Except for(More)
The HNK-1 antigen, a carbohydrate moiety bound to many cell adhesion and recognition molecules, is implicated in cell-cell and cell-substrate interactions during neural development. HNK-1 immunoreactivity (HNK1-IR) appears on neurons of the Xenopus neural tube very early in their development (Nordlander, Devel. Brain Res., 50:147-153, 1989). The(More)
Axonal growth cones in the spinal cord of embryonic and larval Xenopus (stages 24-48) were filled with the anatomical tracer horseradish peroxidase (HRP). Growth cones of lateral and ventral marginal zones, including those of descending spinal and supraspinal pathways, were labeled by application of tracer to the caudal medulla or to one of several levels(More)
Axonal growth cones in longitudinal fiber tracts of the developing spinal cord of Xenopus were examined using electron microscopy. Fiber tracts of the spinal cord develop by the ingrowth of fibers, into pre-existing longitudinally oriented spaces between adjacent neuroepithelial cells of the neural tube. Growth cones seen among the neurites of the tracts(More)
The epidermis of early Xenopus embryos is innervated by the Rohon-Beard (RB) neurons lying within the spinal cord and by extramedullary (EM) neurons lying outside of the cord. We have examined the innervation patterns of the three epidermal cell types using wholemount preparations of skin double-labelled with the HNK-1 antibody as a marker for neurons and(More)
The enzyme horseradish peroxidase (HRP) was used to describe and identify neurons, axons of which initiate the earliest descending pathways of the tail spinal cord of Xenopus embryos and larvae. Spinal cords were pierced at different rostrocaudal levels with fine insect pins coated with HRP. The resulting pattern of cellular labeling indicated that(More)
The new spinal cord formed during tail regeneration in the newt first develops as a caudal extension of the ependymal tube. Neuroblasts and neuroglia subsequently differentiate from cells of the ependymal tube in a proximal-caudal sweep. Descending axons from the cord rostral to the lesion and from newly differentiating neurons travel in channels which are(More)
Horseradish peroxidase (HRP) was used to determine the sequence in which axons from different brain neurons reach the tail spinal cord during embryonic and early larval development of Xenopus laevis. Brainstem cells of several classes project to the tail at these stages: mesencephalic reticulospinal neurons of the nucleus of the medial longitudinal(More)
The morphology of early interactions between neural tube and myotome in the amphibian embryo and tail regenerate was examined using the electron microscope. Two types of contacts were observed. At the most primitive level where the myotome was yet unsegmented, multiple adhesive-type contacts linked neural tube and myotome. In newly segmented areas early(More)