Zonal organization of olivo-nodulus projections in albino rabbits.

The organization of inferior olivary projections to the cerebellar nodulus in albino rabbits was assessed by autoradiographic, anterograde degeneration and retrograde transport techniques. These data indicate that the caudal aspect of the dorsal cap of Kooy projects to a band extending 0.5-1 mm lateral to the midline of the nodulus. The medial half of this region receives a projection from beta nucleus over at least the dorsal surface of the nodulus; an extension onto the ventral surface, though, is consistent with the anterograde tracing data. The rostral aspect of the dorsal cap and ventrolateral outgrowth projects to an adjacent 0.5-1 mm wide band in the nodulus. A group of cells spanning the intermediocaudal dorsal cap and the adjacent, dorsomedial margin of the beta nucleus appears to project laterally on the ventral surface of the nodulus. On the dorsal aspect of the nodulus and ventral surface of lobule IXd, though, comparisons of anterograde and retrograde tracing data suggest that this lateral field is innervated by the rostral aspect of the dorsomedial cell column and the rostromedial accessory olive. Finally, the regions of lobules X and IXd lining the posterolateral fissure represent a transition between lobule IX and ventral lobule X patterns of olivary projections. These data provide a basis for investigating the efferent projections of the nodulus to distinct olivo-vestibular terminal fields in the vestibular nuclei.