Cerebellar afferents to paramedian lobule from the trigeminal complex in Tupaia glis: a horseradish peroxidase (HRP) study.

Projections from the trigeminal complex to paramedian lobule (PML) were studied in the tree shrew (Tupaia glis) by means of retrograde transport of horseradish peroxidase (HRP). Neurons which project to both dorsal and ventral folia of PML are located primarily in those areas of the trigeminal nuclear complex interpreted as nucleus interpolaris (Vi) and caudal areas of the nucleus oralis (Vo). The majority of HRP-labeled neurons lie in ventral and ventrolateral regions of Vi/Vo. No HRP-reactive cells are present in the principal (Vp), mesencephalic, or motor nuclei nor in nucleus caudalis or rostral portions of oralis. The majority of trigeminocerebellar (TC) cells are found in ipsilateral Vi; however, sparse numbers of labeled somata are present in this subnucleus on the contralateral side. Within Vi/Vo, small fusiform and medium-and large-sized multipolar neurons contain HRP-reaction product. Large multipolar cells are found primarily in ventrolateral portions of Vi/Vo, while medium and small neurons are scattered throughout the ventral half of the nucleus. Small-sized neurons are also present dorsally within Vi/Vo. Axons of labeled TC cells course laterally through the spinal trigeminal tract, enter medial aspects of the restiform body, and arch dorsally into the cerebellum.