Brainstem projections of different branches of the vestibular nerve: an experimental study by transganglionic transport of horseradish peroxidase in the cat. III. The saccular nerve.

The brainstem projection of the saccular nerve was investigated by transganglionic tracing with horseradish peroxidase in the cat. The labeled fibers were located most caudally and laterally (dorsolaterally) in the vestibular nerve root. This was unique when compared with the locations of the fibers from the nerves of the other vestibular-end organs that were studied by the present authors by the same approach previously. In addition, such a comparison revealed a specific location, from lateral to medial, for the fibers from each of the five divisions of the vestibular nerve. In the present study, labeled fibers from the sacculus, of fine caliber, were found close to the restiform body, both medially and laterally, some even penetrating through this structure. Labeled terminals were present in cell group "y". This was unique, compared with the nerves from the other end organs. Such terminals were also found in the four main vestibular nuclei, except for the medial vestibular nucleus, where no labeled terminals could be detected. No labeled terminals were found in the interstitial nucleus of the vestibular nerve. Together with the findings from our previous studies, this suggests that, in contrast to the ampullar nerves, the nerves from the maculae do not project to this structure. This study confirms, but also extends, findings reported from a previous investigation in the cat, using an experimental degeneration technique.