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How Long Can Degenerating Axons in the Central Nervous System Produce Reactive Changes?

1971; Springer Nature; Linguagem: Inglês

10.1007/978-3-642-47449-1_5

0065-1435

W. Schlote,

Neurogenesis and neuroplasticity mechanisms

The response of previously severed rat optic fibers to a second transection after various time intervals was studied by light and electron microscopy. The optic nerve of adult animals was crushed retrobulbar and, after 6, 12, 28 or 48 h recrushed 2 mm distant from the first lesion. The changes in the axoplasm of myelinated fibers in the stumps distal to the two lesions, in reference to the perikarya of the cells (i.e. on the cerebral side of each lesion) were studied 6 or 12 h after the second lesion. In the nerves that had been severed 6 h after the first retrobulbar lesion, mitochondria, dense bodies, neurofilaments and endoplasmic reticulum accumulated in the axoplasm distal to the second lesion 6–12 h after the operation. These changes were identical to those seen in the corresponding distal stump of the primary lesion; they may represent a peritraumatic reactive change preceeding the process of Wallerian degeneration. In nerves severed for 12 h, the axon stumps distal to the second lesion contained, 12 h after this lesion, enlarged mitochondria with scattered equivalents of cristae, and large empty vacuoles of mitochondrial origin. In addition, focal clear axonal swellings nearly devoid of organelles appeared in fiber portions distal to the second lesion; these were less frequently in the fibers distal to the first lesion. They are probably the result of decreasing energy supply required for the axonal sodium pump. In nerves severed for 28 h the second lesion evoked only a redistribution of axoplasm of distal axon segments towards the stump end indicated by whorls of neurofilaments. These observations demonstrate a gradually decreasing reactivity of the separated axon to a second traumatic lesion during the early phase of Wallerian degeneration.