A re-examination of the cerebellar projections from the gracile, main and external cuneate nuclei in the cat.

Cerebellar projections from the dorsal column and external cuneate nuclei in the cat have been studied by means of retrograde axonal transport of horseradish peroxidase. Localized injections covering the entire cerebellar cortex and nuclei show that the gracile nucleus has a weak projection only to the cortex of the anterior lobe, but that there is a conspicuous projection from the main cuneate nucleus to the cerebellum. Most of these fibres reach lobule V and the adjacent parts of lobules IV and VI, and there is also a heavy projection to the paramedian lobule. Some fibres reach lobule IX and possibly also lobules II, III and VIIIB, and nuclear afferents also reach the fastigial and interposite nuclei. Three cerebellar cortical regions are the main targets for the fibres from the external cuneate nucleus, viz. lobule V with the adjacent regions of lobules IV and VI, lobules I and II and lobule IX (the anterior part). Other important afferent regions are the paramedian lobule and the cerebellar nuclei, especially the anterior interposite, and some fibres reach the flocculus. The projections are predominantly ipsilateral. The investigation is the first detailed study of the cerebellar projections from the three nuclei and the findings are discussed in relation to previous experimental observations.