Cerebellar afferents from the vestibular and perihypoglossal nuclei in sheep studied with retrograde transport of horseradish peroxidase.

Cerebellar afferents from the vestibular and perihypoglossal nuclei have been studied in 25 sheep. Following injections of HRP in all cerebellar lobules, with the exceptions of the ventral part of anterior lobe, the ventral paraflocculus and the flocculus, bilateral cerebellar projections from these nuclei with ipsilateral preponderance are evidenced. Experiments in sheep show a wider field of origin and termination of secondary vestibulocerebellar fibers than reported earlier. For the descending and medial vestibular nuclei a topographical organization in their vestibulocerebellar projections is evidenced. Fibers to lobule X mainly originate from their dorsal parts, those to lobule IX from their ventral portion, and fibers to lobule VIII from their caudal pole and the lateral part of the descending nucleus. Cell group x projects to all the cerebellar lobules studied except crus. I. Labeled cells in the lateral vestibular nucleus are few. The superior vestibular nucleus projects mainly to lobule X. Vestibular cells projecting to the hemisphere are located mainly in the cell group x and in the central parts of the descending and medial vestibular nuclei. The interstitial nucleus of the vestibular nerve, the nucleus prepositus hypoglossi and the nucleus intercalatus project to all lobules.