Cerebello-olivary projections in the rat. An autoradiographic study

Projections of deep cerebellar nuclei onto the inferior olive have been studied using autoradiographic methods in adult Wistar rats: the distribution of the labelling consequent to injections of tritiated amino acids, limited to one of the cerebellar nuclei, was mapped in the inferior olive. Each of the four cerebellar deep nuclei project to a specific region of the contralateral inferior olive. Only caudal parts of the medial cerebellar nucleus send fibres to the olive, where they reach the caudal half of the medial accessory olive. Anterior and posterior interposed nuclei project to the dorsal accessory and the rostral half to the medial accessory olives, respectively. The lateral, or dentate nucleus projects to the principal olive. This projection discloses a clear-cut topological arrangement. Besides, a few dentato-olivary fibres recross the midline in the interolivary region and end in areas of the ipsilateral principal olive symmetric to the contralateral projection. These results are discussed with special consideration to comparative anatomy.