Summary
Following transection of the vestibular nerve in cats, the electron microscopical changes occurring in the lateral vestibular nucleus were studied after survival periods of 2–11 days. Material for study was taken from the rostroventral part of the nucleus of Deiters since this is known to receive the primary vestibular fibres.
Degeneration of terminal boutons is evident two days after the lesion. Degenerating boutons show an increased electron optic density, mitochondrial changes and a loss of synaptic vesicles. They are often surrounded by a pericellular space filled with flocculent (probably protein) material. At three days and later this space is occupied by processes of astrocytes or of a type of phagocytic cells which surround or engulf the degenerating boutons. Nine to eleven days after the lesion almost all degenerating boutons have disappeared. There is evidence of phagocytosis of axons and myelin sheaths by astrocytes but mainly by phagocytes of yet undetermined origin. The “filamentous type” of bouton degeneration has not been observed.
Degenerating boutons are found on neuronal perikarya and on proximal as well as on thin distal dendrites and on spines. They are common on small and medium-sized cells, but have also been seen on some giant cells. The degenerating boutons do not form series of synaptic complexes. Degenerating fibres and boutons have so far been found only ipsilateral to the lesion.
The findings confirm and extend those made in corresponding experiments with silver impregnation procedures, but emphasize the limitations of the latter methods as regards conclusions concerning synaptic contacts.
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This investigation has been supported by Grant NB 02215-07 from the National Institute of Neurological Diseases and Blindness, US Public Health Service. This aid is gratefully acknowledged.
A preliminary presentation of some of the findings described in this paper has been made by one of the authors (A. brodal) at a Ciba Foundation Symposium, “Myotatic, Kinaesthetic and Vestibular Mechanisms”, London, Sept. 27.–29., 1966.
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Mugnaini, E., Walberg, F. & Brodal, A. Mode of termination of primary vestibular fibres in the lateral vestibular nucleus an experimental electron microscopical study in the cat. Exp Brain Res 4, 187–211 (1967). https://doi.org/10.1007/BF00248022
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DOI: https://doi.org/10.1007/BF00248022