Mode of Termination of Vestibular Primary Afferent Fibers from the Horizontal Semicircular Canals in the Cat Vestibular Nucleus

Physiologically identified single vestibular primary fibers originating from the horizontal semicircular canal were stained by intraaxonal injection of horseradish peroxidase and three-dimensionally reconstructed under the light microscope.In the vestibular root bundle, each fiber had one collateral and distributed terminals in the vestibular interstitial nucleus. The stem axon bifurcated into ascending and descending branches in the lateral vestibular nucleus. The ascending branch distributed terminals in the superior vestibular nucleus. The descending branch sent several collaterals to the ventrolateral region of the lateral and inferior vestibular nucleus.These collaterals ran medially and reached the medial vestibular nucleus. Terminals were observed mainly in the boundaries between the medial nucleus and the lateral or inferior nucleus. Few terminals could be observed in the dorsal part of the lateral vestibular nucleus.