Reclassification on the Long Ascending Fibers from the Spinal Cord in the Rabbit, Rat and Cat

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  • Yamada Jinzo
    Department of Anatomy, School of Medicine, Chiba University
  • Otani Katsumi
    Department of Anatomy, School of Medicine, Chiba University

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  • Reclassification on the Long Ascending

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Applying silver impregnatio n methods, the long ascending fibers from the spinal cord were reclassified according to the location of degenerating fibers in the brain stem as a result of lesions in the spinal cord in the rabbit, rat and cat. In the bulb, the long ascending fiber systems ascended in the medial lemniscus and lateral to it, and at the level of the trapezoid body diverged into following fiber system: The lateral thalamic system and ventral thalamic system ran through the medial lemniscus, and the former terminated in the posterior ventral nucleus and the latter terminated in the zona incerta, Forel's H-field and posterior hypothalamic area. The FR-system ascended through the reticular formation and terminated in it, and the GM-system ascended medial to the brachium of the inferior colliculus to reach the medial part of the medial geniculate body. Some fibers of these two system interweaving with each other in the rostral mesencephalic reticular formation made up the medial thalamic system which terminated in the internal medullary lamina and its associated nuclei (parafascicular and lateral central nuclei). The spinotectal system terminated in the superior colliculus and passed through it. Further, there occured the fibers terminating in the periaqueductal gray matter and passing through it.<BR>Terminals in the posterior ventral nucleus were observed following the all spinal lesions in the rabbit and rat, and in the cat numerously after the first two cervical lesions and scarcely after the oth er cervical and upper thoracic ones. In the cat, probably in the rat, some fibers of the lateral thalamic system terminated in the lateral ventral nucleus.<BR>Development of the medial thalamic system was most prominent in the cat and least prominent in the rabbit in three species. Degenerating fibers in the internal medullary lamina and its associated nuclei were scarce in the rabbit following the uppermost thoracic lesion and not so much degeneration was found even after the uppermost cervical lesion. These degenerating fibers in the rat were slightly more following a lower thoracic injury than those in the rabbit with some cervical lesion, and were not found with the uppermost sacral one. On the other hand, in the cat even following the fourth lumbar lesion, preterminals in the lateral central nucleus appeared clearly.

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