Molecular, topographic, and functional organization of the cerebellar cortex: a study with combined aldolase C and olivocerebellar labeling.

Aldolase C (zebrin) expression in Purkinje cells reveals stripe-shaped compartments in the cerebellar cortex. However, it is not clear how these compartments are related to cerebellar functional localization. Therefore, we identified olivocerebellar projections to aldolase C compartments by labeling climbing fibers with biotinylated dextran injected into various small areas within the inferior olive in rats. Specific rostral and caudal aldolase C compartments were linked in an orderly manner by common olivocerebellar projection across the rostrocaudal boundary on lobule VIc-crus Ib. Based on the localization of the olivary origins of projection to similar compartments, the compartments and olivocerebellar projections could be sorted into five groups: group I, positive compartments extending from the posterior lobe to the anterior lobe innervated by the principal olive and some neighboring areas; group II, positive compartments localized within the posterior lobe innervated by several medial subnuclei; group III, vermal and central negative compartments innervated by the centrocaudal medial accessory olive; group IV, negative and lightly positive compartments in the hemisphere and the rostral and caudal pars intermedia innervated by the dorsal accessory olive and some neighboring areas; group V, the flocculus and nodulus. The olivocerebellar topography within each group was simple and suggests an "orientation axis" within the concerned parts of the inferior olive. Furthermore, parts of the inferior olive in each group receive specific afferent inputs, indicating a close relationship between aldolase C compartments and functional localization. Thus, the five-group scheme we propose here may integrate the molecular, topographic, and functional organization of the cerebellum.