Topographic organization of the corticonuclear and corticovestibular projections from the pyramis and copula pyramidis in the albino rat. An autoradiographic orthograde tracing study.

The topographic organization of the corticonuclear and corticovestibular fibers from the pyramis and copula pyramidis in the albino rat was investigated by the autoradiographic orthograde tracing technique. Cortical efferent fibers from the medial part of the pyramis project to the caudoventral part of the caudomedial and middle subdivisions of the medial cerebellar nucleus, whereas those arising from the lateral part of the pyramis project to the caudomedial part of the posterior interpositus nucleus and also to the dorsal part of the lateral vestibular nucleus via the juxtarestiform body. Fibers from the medial part of the copula pyramidis project to the medial part of the anterior interpositus nucleus. On the other hand, fibers from the medial portion of the lateral part of the copula pyramidis project to the posterior interpositus nucleus, while those from the lateral portion, including the lateral limit of the copula pyramidis, project to the rostroventral part of the lateral cerebellar nucleus. These results indicate that the cortical efferent projections from the pyramis and the copula pyramidis are clearly oriented mediolaterally in the albino rat.