Physiopathology of the cerebellum in the monkey. I. Origin of cerebellar afferent nervous fibers from the spinal cord and brain stem

Complete cerebellectomy is associated with almost total cell loss in the reticulotegmental, lateral reticular and pontine nuclei and in the principal and accessory olivary nuclei but not in the perihypoglossal and reticular paramedian nuclei in the monkey. The latter structure which is a prominent structure in the cat is underdeveloped or absent in this species. It also results in important retrograde degenerating changes of the neurons of the lateral cuneate nucleus, the dorsal nucleus of Clarke and the border cells of Cooper and Sherrington as disclosed in 1 monkey with a short-term cerebellectomy. A few neurons of the principal cuneate nucleus also undergo retrograde degeneration in the immediate postoperative period. The present findings suggest that the caudal part of the medial accessory olive and its “dorsal cap” are anatomically related to the contralateral nodulus and flocculus, respectively, whereas the rostral part of the medial accessory olive is more directly related to the neovermis. The dorsal accessory olive appears to be related to the contralateral cerebellar nuclei and more specifically, the fastigial nucleus. These results also favour the existence of cerebellopetal fibers from the principal cuneate nucleus and of a few non-cerebellopetal fibers from the lateral cuneate nucleus. The present findings support the suggestion of Cooper and Sherrington pointing to the existence of spinocerebellar fibers originating in the border cells of the ventral horn at the level of the low thoracic and lumbar segments of the cord. However the possibility that such “spinocerebellar” fibers may distribute collateral endings to the dorsolateral area of the medulla or even terminate in this area cannot be entirely ruled out on the basis of the present material. A similar feature possibly explains the fact that most (if not all) cells of the dorsal nucleus of Clarke resist the interruption of their axons at cerebellar level as suggested by the findings in monkeys with long standing lesions.