Studies on the cerebellar projections from the main and external cuneate nuclei in the cat by means of retrograde axonal transport of horseradish peroxidase.

The cerebellar projections from the main and external cuneate nuclei in the cat have been studied by means of retrograde axonal transport of horseradish peroxidase. The main projection from the external cuneate nucleus (ECN) is to the intermediate and, possibly, the small lateral part of lobule V and to the paramedian lobule on the ipsilateral side. The projection from the ECN to the cerebellar regions mentioned is topographically organized. Cells in the caudal part of the ECN send their axons to the caudal parts of lobule V and to the rostral part of the paramedian lobule. Cells in the rostral part of the ECN project to the rostralmost part of lobule V and to the folia in the caudal part of the paramedian lobule. The experimental study also shows that cells in the main cuneate nucleus (MCN) send their axons to the cerebellum. These axons, like those from the ECN, terminate in the intermediate part of lobule V of the anterior lobe and in the paramedian lobule. However, the axons of the cells in the MCN terminate only in the superficial parts of the folia, whereas those from the ECN terminate in the depth of the folia in these two cerebellar areas. The present study also gives evidence that cells in the ventral part of the gracile nucleus send their axons to lobules I and II of the anterior lobe vermis. The observations referred to here are to our knowledge the first anatomical findings demonstrating a projection from the main cuneate and gracile nuclei onto the cerebellar cortex. The observations confirm previous physiological studies.