Zonal organization of the floccular Purkinje cells projecting to the vestibular nucleus in cats.

Injections of horseradish peroxidase (HRP) were made iontophoretically in the vestibular nuclear complex and the prepositus hypoglossal nucleus (PH) in cats. Differential localization of labeled Purkinje cells due to the retrograde axonal transport of HRP was studied in the flocculus. It was found that there existed three-dimensional zones which were perpendicular to the long axis of the folia in the ipsilateral flocculus; Purkinje cells projecting to the superior vestibular nucleus were distributed in the rostral zone, those to the medial vestibular nucleus in the middle zone. Specific projection-zones to the inferior vestibular nucleus, lateral vestibular nucleus and the PH were not found. Only a small number of labeled Purkinje cells were scattered in the flocculus after injection of HRP in them.