On the origin of the climbing fibers of the cerebellum. An experimental study in the cat with an autoradiographic tracing method

Abstract

An autoradiographic fiber tracing method was used to determine the contribution of climbing fibers to the cerebellar cortex from the olive and other brainstem precerebellar structures. The morphological characteristics of silver grain accumulations and their location in the molecular or granular layer made it possible to distinguish clearly between climbing fibers and mossy fibers. Three injections of l-leucine were made in the olive to obtain extensive labeling. The projection thus demonstrated is completely crossed and covers large portions of all cerebellar lobules. The course of olivocerebellar fibers was described and it was stressed that some of these fibers make a long rostral loop close to the superior and middle cerebellar peduncles. Injections in the pons, including the nucleus reticularis tegmenti pontis, the lateral reticular nucleus, the spinal nucleus of the fifth nerve, the cuneate and external cuneate nuclei, the descending vestibular nucleus and the nucleus reticularis ventralis, labeled only mossy fibers. It is concluded that, in the cat, the large majority and probably all the climbing fibers originate from the inferior olive. Evidence suggesting that the inferior olive sends a collateral projection to the nucleus reticularis tegmenti pontis was also obtained.