Spinocerebellar neurons projecting to copula pyramidis, studied by retrograde labeling in the rat.

Spinal neurons project to the vermis and the intermediate part of the hemisphere of the anterior lobe. In the posterior lobe, neurons projecting to the intermediate part, the copular part (copula pyramidis) of the paramedian lobule, differ from those projecting to the vermis in the cat. The present study by the retrograde labeling reveals that the projection patterns in copula pyramidis in the rat are similar to those identified in the cat. The projections through uncrossed ascending axons originate from (1) neurons in the medial part of laminae V and VI of the C2-T1 segments, (2) neurons in lamina V of the C7-L3 segments, (3) the marginal neurons of Clarke's column, and (4) neurons of Clarke's column of the lower thoracic and the lumbar segments. The projections through crossed ascending axons originate from (5) the lateral group of the ventral spinocerebellar tract neurons in the T12-L3 segments, (6) Stilling's sacral nuclei, and (7) the central cervical nucleus. The present findings suggest that the spinal inputs from the specific neuronal groups define the functions of copula pyramidis.