TRIGEMINOCEREBELLAR AND TRIGEMINO-OLIVARY PROJECTIONS IN RATS

Retrograde and anterograde neuronal tracers (HRP, biocytin, biotinylat ed dextran-amine) were used to study the organisation of trigeminocere bellar and trigemino-olivary connections, focusing on the connectivity between trigeminal nuclear regions and the sagittal zones of the rat cerebellar cortex. Trigeminocerebellar projections were bilateral, but mostly ipsilateral. Direct trigeminocerebellar fibres originated most ly in the principal trigeminal nucleus (VP) and pars oralis (Vo), pars interpolaris (Vi), and to a lesser extent in pars caudalis (Vc) of th e spinal trigeminal nucleus. Consistent projections were found from th e Vc to cerebellar lobules IX and X. The trigeminal fibres terminated in the cerebellum in an organised fashion. The ventral part of the VP, Vo and Vi projected to the medial A zone and the C3 and D2 subzones, whereas the dorsal part of the nuclei projected to the lateral A zone and the C2, D0 and D1 subzones. In lobules IX and X, the organisation was different. The medial half of the VP, Vo, Vi and Vc projected to t he lateral aspects of these lobules whereas their lateral part project ed to their medial aspects. Trigeminal projections to the deep cerebel lar nuclei were also present. Projections to a given sagittal zone con comitantly reached its corresponding nuclear target. Trigemino-olivary projections were principally contralateral. The Vo, Vi and Vc project ed to the rostromedial dorsal accessory olive, the adjacent dorsal lea f and the dorsomedial part of the ventral leaf of the principal olive, which are known to project subzones C3, D0 and D1 of the rat cerebell ar cortex.