Secondary trigeminocerebellar projections in sheep studied with the horseradish peroxidase tracing method

Secondary trigeminocerebellar connections have been studied with HRP histochemistry in 25 sheep. The results indicate that almost all of the cerebellar cortex except flocculus, ventral paraflocculus and lobules I-IV receives bilateral (mostly ipsilateral) fibers from the trigeminal nuclei. A topographical organization of trigeminocerebellar fibers is present. The mesencephalic tract nucleus projects to the anterior lobe, the simple lobule (HVI), lobules VI, VIII, and the dorsal paraflocculus. The ventral group of the princeps and spinal tract (mainly IDV) nuclei projects to all lobules studied in vermis and hemispheres. More dorsal parts of these nuclei have a more restricted projection field including the vermal lobules VI, VII, and IX and the hemisphere. Cells within and ventral to the motor nucleus of the trigeminal nerve were found labeled after injections into the anterior lobe, the simple lobule, and lobule IX. Labeled cells in the region of the nucleus ovalis and close to the solitary tract project to the simple and paramedian lobule and lobule IX.