An investigation of the cerebellar cortico-nuclear projections in the rat using an autoradiographic tracing method. I. Projections from the vermis.

The topography of the projections from the vermis of the cerebellar cortex to the intracerebellar nuclei (excluding the vestibular complex) was newly investigated in the rat using an autoradiographic technique. The projection were strictly ipsilateral and the majority terminated in nucleus fastigus although there were small projections to the medial pole of nucleus interpositus. The only portion of fastigius which was never heavily labelled was the dorsolateral protuberance. Some rostrocaudal localisation was evident with lobules II-V projecting to rostral fastigius (Fm), lobules VI-VIII projecting mainly more caudally (Fcm and Fm) and lobule IX projecting to the caudoventral tip of fastigius. Nevertheless, even the densest portions of the terminal fields often overlapped heavily, suggesting that, in the rat, in contrast to some other species, the rostrocaudal localisation is such that individual lobules do not possess private termination fields of any extent. Such an arrangement should provide ample opportunity for integration by individual nuclear neurones of input from extensive areas of cortex. In the mediolateral plane, localisation was more evident, with the medial vermis projecting to the medial pole of fastigius and the lateral portion to lateral fastigus and less heavily to medial interpositus.