Brainstem mossy fiber projections to lobules VIa, VIb,c, VII and VIII of the cerebellar vermis in the rat.

The brainstem mossy-fiber projections to lobules VIa, VIb,c, VII and VIII of the cerebellar vermis were studied by retrograde transport of horseradish peroxidase in the rat. The distribution of labeled cells indicated that these lobules received major projections from topographically different locations of the basilar pontine nuclei and the nucleus reticularis tegmenti pontis. Lobules VIa and VIII received an additional strong projection from the lateral reticular nucleus. Moderate projections were found to reach lobule VIa from the raphe pontis and external cuneate nucleus; lobules VIb,c from the raphe pontis, lateral reticular nucleus, and a group of cells in the lateral tegmentum; lobule VII from the spinal vestibular nucleus and a lateral tegmental cell group; and lobule VIII from the medial and spinal vestibular nuclei, nucleus intercalatus and Roller of the perihypoglossal nuclei, and the main cuneate nucleus. The quantitative and topographical differences in the origin of mossy fibers suggest that these lobules may subserve slightly different functions.