Projections from the upper lumbar cord to the cerebellar nuclei in the rat, studied by anterograde axonal tracing.

The spinocerebellar tracts arising from the upper lumbar cord consist of the dorsal and the ventral spinocerebellar tracts (DSCT and VSCT), which ascend ipsilaterally and contralaterally, respectively. By using anterograde labeling with biotinylated dextran in the rat, this study examined whether the lumbar DSCT and the VSCT project to the cerebellar nuclei. Injections of the tracer were made unilaterally at levels between the L1 and L3 segments, with diffusion to either a rostral or a caudal segment. The injections resulted in bilateral labeling of axon terminals in the cerebellar nuclei. In the medial nucleus, labeled terminals were distributed in medial, ventral, and ventrolateral parts of the middle subdivision and ventral parts of the caudomedial subdivision. In the anterior interpositus nucleus, they were distributed in medial and dorsomedial parts throughout the rostrocaudal extent. Labeled terminals were seen within the dorsomedial crest region. In the posterior interpositus nucleus, labeled terminals were seen in the rostromedial extension, the caudomedial part, and the caudal pole. Labeled terminals were seen in the hilus and the ventral part of the lateral nucleus. Projections of the DSCT and the VSCT to these regions were confirmed after tracer injections preceded by sectioning of either tract. Both tracts projected bilaterally, but the DSCT projected mainly ipsilaterally. The present study suggests that the spinocerebellar tracts originating from the upper lumbar cord (the lumbar DSCT and the VSCT) project to specific areas of the cerebellar nuclei to transmit information about the peripheral and central events during the movement of hindlimbs.