Projections from the lowest lumbar and sacral-caudal segments to the cerebellar nuclei in the rat, studied by anterograde axonal tracing.

Spinocerebellar fibers originate from neurons in the medial part of lamina VII, including Stilling's sacral nucleus, the lateral part of lamina V, and the ventrolateral part of the ventral horn in the lowest lumbar (L6) and sacral-caudal segments. By using the anterograde transport of biotinylated dextran in the rat, this study examined whether these spinocerebellar fibers project to the cerebellar nuclei. Anterogradely labeled axons that originated from the L6-caudal segments ascended contralaterally through the superficial layer of the lateral cord and entered the cerebellum through the superior cerebellar peduncle and the restiform body. Labeled terminals were bilaterally seen in the medial nucleus and the anterior and posterior interpositus nucleus. They were most numerous contralaterally in the anterior interpositus nucleus. In the anterior interpositus nucleus, they were distributed mainly in the most ventral part at rostral levels and in small numbers in the medial part. In the medial nucleus, labeled terminals were seen in limited rostromedial parts of the middle and the caudomedial subdivision. Only a small number of labeled terminals were seen in the caudomedial part of the posterior interpositus nucleus. The present study shows that the spinocerebellar fibers originating from the lowest lumbar and sacral-caudal segments project to specific areas of the anterior interpositus and the medial nucleus. This finding suggests that the neurons of origin convey information from muscles, joints, and integument to the cerebellar cortex and nuclei, in relation to movement of the hindlimbs.