Fine structure of the medial and descending vestibular nuclei in normal rats and after unilateral transection of the vestibular nerve.

Cells and neuropil are of similar structure in the descending and medial vestibular nuclei. Two cell types were found: small neurons and larger cells. Three types of axon terminals have been defined: small and large terminals containing spherical vesicles (SV) and terminals with elongated vesicles (EV). Small SV terminals contact perikarya and dendrites, whereas large SV terminals contact fine dendritic branches. EV terminals contact neurons at perikarya and large as well as small dendritic profiles. SV terminals can be presynaptic to EV terminals. Vestibular nerve transection resulted in degeneration of small SV terminals which were found from the first to fifth postoperative day in the ipsilateral nuclei. Glycogen granules were found in various types of axon terminals bilaterally in the vestibular nuclei 3-5 days after right vestibular transection. They were not observed in normal animals or in degenerating vestibular afferent terminals.