Brainstem projections of different branches of the vestibular nerve: an experimental study by transganglionic transport of horseradish peroxidase in the cat. II. The anterior and posterior ampullar nerves.

The brainstem projections of the ampullar nerves from the vertical semicircular canals, the anterior (AAN) and the posterior ampullar nerve (PAN), were studied in adult cats using the transganglionic horseradish peroxidase (HRP) method. Each nerve was exposed in three experiments. Two animals in each group had labeling which allowed detailed mapping. From the AAN, terminal-type labeling was found in two separate groups, one laterally and one medially, both in the lateral (LV) and in the superior (SV) vestibular nucleus. In addition, such labeling was found in all parts of the medial vestibular nucleus (MV). Labeled structures were found also in the descending vestibular nucleus, (DV) more densely over its lateral part, except for cell group f, where no labeling was found. From the PAN, terminal-type labeling was found medially and laterally in the LV and in the medial part of the SV. In the MV, such labeling was evenly distributed rostrally but concentrated laterally in caudal parts. In the DV, terminal-type labeling was present rostrally, whereas no labeling was seen caudally. In the interstitial nucleus of the vestibular nerve, terminal-type labeling was observed from the AAN but not from the PAN. No labeled fibers from either of the two ampullar nerves were seen outside the vestibular root and nuclei, except for small-caliber fibers from the SV heading towards the brachium conjunctivum. The findings clearly indicate a specific termination for each of the two ampullar nerves.