Cerebellotectal projections studied in cats with horseradish peroxidase or tritiated amino acids axonal transport.

After injections of horseradish peroxidase (HRP) into various parts of the superior colliculus (SC) in 14 cats, retrogradely labeled neurons were found in parts of all deep cerebellar nuclei. The present study demonstrated that there are three main origins of the cerebellotectal projections in regard to the locations of the cell bodies: (1) the caudal half approximately of the fastigial nucleus (NM) including the subnucleus medialis parvocellularis (SMP), (2) the ventral and lateral parts of the posterior interpositus nucleus (NIP), and (3) the ventral part of the dentate nucleus (NL) including the subnucleus lateralis parvocellularis (SLP). The pathways and terminations of these projections have also been shown autoradiographically. Thus, fibers from NM crossed within the cerebellum and terminated in the intermediate and deep gray layers of the bilateral SC. Fibers from NIP and NL passed within the superior cerebellar peduncle, which crossed in the tegmentum ("decussation" of the peduncle) and ended in the two layers of the contralateral SC. In addition, some cerebellofugal fibers were found to terminate in the nuclei interstitialis of Cajal and Darkschewitsch, as well as in parts of pretectum and thalamus. The tecto-ponto-(and olivo-) cerebellotectal loop (cf. Kawamura 1980) has been established morphologically and it is briefly commented on in correlation with the propagation of the teleceptive (optic and acoustic) impulses.