A comparison of the ultrastructure of synapses in the cerebello-rubral and cerebello-thalamic pathways in the rat.

The aim of this study was to compare the ultrastructure of anterogradely labelled cerebellar terminals in the red nucleus (RN), ventrolateral (VL), parafascicular (PF) and central medial (CM) thalamic nuclei, as well as in the zona incerta (ZI). No differences were found in the morphology of synapses in any of the nuclei. Terminals in RN and VL were larger than those in PF, CM and ZI and synapsed proximally. In contrast, synapses in PF, CM and ZI formed mainly on distal dendrites. These findings indicate that cerebellar output neurones (a) form morphologically similar synapses (Gray's type I) on neurones in functionally different nuclei, and (b) form larger, more proximal synapses in RN and VL than in PF, CM and ZI.