Relationship between the cortical and nuclear functional compartmentalizations in the cerebellum and integration of inputs in the cerebellar nuclei

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We have been revealing the presence of functional compartmentalization in the cerebellar cortex and nuclei by double-labeling neuronal connection and expression of aldolase C, a special marker molecule of the cerebellum. However, how the cortical organization, which is characterized by the alternate stripes of aldolase C-positive and negative longitudinal compartments, is reflected in the cerebellar nuclei has not been clarified. Therefore, we aimed at elucidating the compartmental organization of the cerebellar nuclei, which underlies integration of the cerebellar output, by analyzing in detail the topographic relationships in the corticonuclear Purkinje cell projection and the olivocortical and olivonuclear climbing fiber projection.We reconstructed Purkinje cell axons by labeling them anterogradely with a small injection of biotinylated dextran amine in the rat cerebellar cortex. We then identified the cortical compartment in which the labeled Purkinje cells were located by immunost … More aing aldolase C. Then the termination areas of these Purkinje cell axons were mapped in the cerebellar nuclei. We found that Purkinje cells project to the caudal and rostral parts of the cerebellar nuclei from the aldolase C-positive and -negative compartments in the cerebellar cortex, respectively. Concerning the olivary projection, nuclear collaterals of the axons that project to the aldolase C-positive and negative compartments in the cortex projected to the caudal and rostral parts of the cerebellar nuclei, respectively. This well agreed to the above Purkinje cell projection pattern. Corticonuclear topography and olivo-cortico-nuclear topography coincided nearly completely in detail. Thus, precise parallel loop-shaped neuronal circuitry was formed among the inferior olive, cerebellar cortex and cerebellar nuclei. Furthermore, the alternate longitudinal stripe-shaped compartmentalization in the cortex was transformed to the rostro-caudal dichotomous compartmentalization in the cerebellar nuclei. Less