Summary
The neuronal changes were studied in the facial nucleus of mice after crush lesions and complete section of the facial nerve. These lesions were followed by complete nerve cell regeneration and extensive nerve cell disintegration, respectively.
Light microscopical examination showed dispersion of the Nissl substance from the first day after both types of lesion, and the cytoplasmic basophilia increased during the first week. After crush lesions the Nissl substance began to reappear after one week, and after 30 days the neurons again were normal. After section of the nerve the basophilic substance remained dispersed and there was a slow depletion of the basophilia until the majority of the cells disappeared between 14 and 60 days after the lesion.
The ultrastructural changes were identical during the first days after both types of lesion: The Nissl bodies, which consisted of parallel cisterns of granular endoplasmic reticulum and clusters of free ribosomes between the lamellae, were replaced by short segments of granular endoplasmic reticulum and free ribosomal clusters throughout the cytoplasm.
After crush lesions no changes were seen in any of the other cell organelles. New Nissl bodies began to reappear after one week. It is suggested that the dispersion and re-formation of the Nissl substance is not caused by a massive exchange of organelles but rather by a simple spreading of the membranes and ribosomal clusters and a re-arrangement of the same structures during recovery.
After section of the nerve the endoplasmic reticulum remained dispersed without further changes until shortly before disintegration. The cytoplasm then showed extensive degeneration. The neurons were ultimately removed through phagocytosis by microglial cells.
Zusammenfassung
Die Nervenzellveränderungen im Facialiskern von Mäusen wurden nach Quetschung und kompletter Durchtrennung des N. facialis untersucht. Die Läsionen waren von kompletter Nervenzellregeneration bzw. ausgedehnter Nervenzelldesintegration gefolgt.
Lichtoptische Untersuchungen zeigten Zerstreuung der Nissl-Substanz ab dem 1. Tage nach beiden Läsionsformen; Zunahme der Cytoplasmabasophilie in der 1. Woche. Nach Quetschung begann die Nissl-Substanz nach 1 Woche wieder aufzutreten, und nach 30 Tagen waren die Neuronen wieder regelrecht. Nach Nervendurchtrennung blieb die basophile Substanz zerstreut. Es kam zum langsamen Verschwinden der Basophilie und zum Untergang der meisten Zellen 14–60 Tage nach der Läsion.
Die ultrastrukturellen Veränderungen waren in den ersten Tagen nach beiden Läsionen identisch: Die aus parallelen Zisternen des granulären EPR und Haufen freier Ribosomen zwischen Lamellen bestehenden Nissl-Körper wurden durch kurze Segmente granulären EPR und freie Ribosomenhaufen im gesamten Cytoplasma ersetzt.
Nach Quetschung fanden sich keine Veränderungen an anderen Zellorganellen. Die Nissl-Körper traten nach 1 Woche wieder auf. Es wird vermutet, daß die Dispersion und Neubildung der Nissl-Substanz nicht durch einen massiven Austausch von Organellen, sondern eher durch einfache Verteilung der Membranen und Ribosomenhaufen sowie eine Neuordnung dieser Strukturen während der Erholungsperiode beding ist.
Nach Nervendurchtrennung bleibt das EPR verstreut, ohne daß weitere Veränderungen bis kurz vor der Desintegration auftreten. Später zeigt das Cytoplasma eindeutige Degenerationszeichen. Die Neurone werden schließlich durch Phagocytose durch Mikrogliazellen entfernt.
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Torvik, A., Skjörten, F. Electron microscopic observations on nerve cell regeneration and degeneration after axon lesions. Acta Neuropathol 17, 248–264 (1971). https://doi.org/10.1007/BF00685058
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DOI: https://doi.org/10.1007/BF00685058