The dentatorubral projection. An autoradiographic study in rats.

Although the dentatorubral projection is known to end specifically in the parvocellular part of the red nucleus, its topographical arrangement has never been elucidated. We therefore selectively injected the lateral cerebellar nucleus (homologous to the dentate nucleus of primates) of adult Wistar rats with tritiated leucine or proline in order to trace the dentatorubral boundaries. In all cases, the projection was found to extend rostrocaudally throughout the parvocellular red nucleus; dorsoventrally as well as mediolaterally, the fibers were distributed according to the location of the injection within the lateral cerebellar nucleus. Hence, caudal regions of the lateral nucleus send fibers dorsally at the rubral level, rostral regions project ventrally. This dorsoventral arrangement matches the segregation of the parvocellular red nucleus into a dorsal 'forelimb' region and a ventral 'hindlimb' region corresponding to its spinal efferents. In addition, only the ventral part of the lateral cerebellar nucleus, particularly the parvocellular region (subnucleus lateralis parvocellularis), projects to the lateral aspect of the parvocellular red nucleus. These results suggest a common pattern of organization of the dentatorubral and the dentatothalamic projections.