Clinical Neuroscience

[Mechanism of the “dark” axonal degeneration in the central nervous system]

PÁL József, GALLYAS Ferenc

SEPTEMBER 30, 2014

Clinical Neuroscience - 2014;67(09-10)

[Background and purpose - In the central nervous tissue, two types of transsection-resulted axonal degeneration are generally accepted: “watery” and “dark”. The present paper deals with the assumption that the mechanism of this kind of “dark” axonal degeneration has a relationship with that of the “dark” neuronal degeneration. Methods - A minute stab wound is inflicted in the parietal cortex of the rat brain. From 1 h to 3 months postinjury, the resulted ultrastructural events in two distant regions of the corticospinal tract (internal capsule and C3 region of the corticospinal tract) are studied. Results - As a novel finding, the first morphological process of “dark” axonal degeneration was found to consists in a striking reduction of the distances between neighboring neurofilaments, which were readily distinguishable and apparently undamaged. This pattern (compacted ultrastructure) persisted for hours. By day 1 postinjury, the compacted axoplasmic elements aggregated into a homogenous and dense (“dark”) mass in which hardly any ultrastructural elements could be distinguished. Surrounded by apparently normal or mildly abnormal myelin sheat, this mass underwent a non-isotropic shrinkage during the next three months. Morphological signs of phagocytosis were insignificant. Conclusion - The ultrastructural events during the first day post-injury suggest a non-enzymatic mechanism as an alternative to the prevailing molecular-biological mechanism.]

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