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

The dorsal spinocerebellar tract (DSCT) of the thoracic cord (the thoracic DSCT) consists of uncrossed ascending axons originating from Clarke's column, marginal neurons of Clarke's column, and lamina V neurons, and crossed ascending axons originating from neurons in lamina VIII and the ventromedial part of lamina VII. The present study has examined, by using anterograde labeling with biotinylated dextran, whether the thoracic DSCT projects to the cerebellar nuclei. The tracer was injected into the thoracic cord, for two to four segments at levels between the T4 and T9 segments in the rat. The distribution of anterogradely labeled axons and terminals was bilateral but predominantly ipsilateral to the injections. Labeled axons entered the medial nucleus from its rostromedial aspect and terminated widely in medial and ventral parts of the middle subdivision. Furthermore, they terminated in the medial and ventral part of the caudomedial subdivision. Labeled terminals were seen in rostromedial parts of the anterior interpositus nucleus and in medial to caudal parts of the posterior interpositus nucleus. A small number of labeled terminals were consistently seen in the ventral part of the lateral nucleus and the dorsolateral hump region. The present study shows that the thoracic DSCT projects bilaterally, but predominantly ipsilaterally, to the medial and the anterior and posterior interpositus nuclei and suggests that it conveys input related to posture and movement of the trunk and respiratory movement of the thorax.