Topography of cerebellar corticonuclear fibers of the albino rat. Vermis of anterior and posterior lobes.

The distribution of cerebellar corticonuclear fibers of the vermis of anterior and posterior lobes was determined for the albino rat using the Fink and Heimer method. Efferent fibers from vermal cortex terminate in the ipsilateral medial cerebellar nucleus (NM) in an organized circumferential manner. Rostral lobules (I--III) project to rostroventral and rostrocentral NM, more central lobules (IV, V, VI) project to rostrodorsal, dorsocentral and caudodorsal areas of the nucleus respectively, while caudal lobules (VII, VIII, IX) send fibers into caudal and ventrocaudal NM. No evidence was seen to corroborate the contention that individual lobules of the vermis may project essentially throughout the rostrocaudal extent of the nucleus. Although species differences are apparent the arrangement of terminal fields in the NM for vermal cortex of rats is similar to that reported for other mammals. Degenerated fibers from medial aspects of each lesion primarily enter the NM while those coursing into the juxtarestiform body originate from more lateral portions of the cortical injury. This suggests that the arrangement of cortical zones in rat is fundamentally similar to that described in other mammals.