An experimental study of the efferent connections of the superior cerebellar peduncle in the rhesus monkey.

Unilateral electrolytic lesions were made in the right superior cerebellar peduncle immediately lateral of its decussation or in the dentate nucleus of 6 monkeys. The course of the contralateral ascending and descending degenerated fibers and sites of preterminal degenerated fibers were studied in material stained by Fink-Heimer, Nissl and Weil methods. Major thalamic sites of preterminal degeneration were in the rostral part of VPLo, and in VPI, VLo, VApc, CL and PCn. In other thalamic nuclei or subdivisions, no preterminal was observed or was questionable. No degenerated fibers entered the internal capsule or corpus striatum. There was abundant preterminal degeneration in the rostral part of the nucleus ruber and adjacent reticular formation. The descending degenerated fibers of the superior cerebellar peduncle led to massive preterminal degeneration in the central part of the nucleus reticularis tegmentalis and in nuclei raphe pontis and magnus. The most caudal site of preterminal degeneration (minimal) was in the nucleus reticularis gigantocellularis adjacent to the median longitudinal fasciculus.