An experimental electron microscopical study on the mode of termination of cerebellar corticovestibular fibres in the cat lateral vestibular nucleus (Deiters' nucleus).

Abstract

The present paper is an experimental study on the mode of termination of cerebellar corticovestibular fibres in the cat. The distribution of degenerating terminal structures as this appears in electron micrographs of eight animals with a survival time from three up to eleven days is described. The early stage of degeneration of Purkinje cell axons is a filamentous reaction during which fibres as well as boutons are enlarged and filled with filaments. The initial reaction is followed by shrinkage, and many fibres and boutons are at the 4 day stage electron dense, and no filaments can be recognized. Other fibres and boutons show intermediate stages of degeneration. Only dark degenerating axons and boutons are present at the 11 day stage. The observations are related to those made in other nuclei and regions where degeneration has been described in electron micrographs. Degenerating terminal myelinated fibres ending with terminal and en passage boutons are found. An attempt is made to correlate the findings with those made in normal animals and in Golgi sections. The mode of termination and the pattern of branching of Purkinje cell axons are discussed. The degenerating terminal structures are in synaptic contact with cells of all sizes and with all parts of the neurons, i. e., soma, proximal and distal dendritic trunks and spine-like projections. Elongated and rounded synaptic vesicles are present in the degenerating boutons. The glial reaction adjacent to degenerating boutons is also described, and brief mentioning is made of findings in the intracerebellar nuclei of the same animals. The findings in these nuclei are essentially the same as those made in the lateral vestibular nucleus.