Cerebellar pathways to ventral midbrain and nigra

This study on cat and rat indicates that the cerebellar nuclei connect with a continuum of cells located on either side of midline in the ventral tegmentum of the midbrain. The following nuclei are located within this region: nigra, ruber, interpeduncularis, ventral tegmental (Tsai), and linearis rostralis. The nucleus fastigii projection is primarily ipsilateral to this region by way of a mediaal and dorsal pathway (accessory brachium conjunctivum). A greater number of these fibers terminates in medial as contrasted to lateral structures. The projections of nuclei interpositus-dentatus are primarily contralateral and become part of a lateral and ventral pathway through the brachium conjunctivum. Reduced-silver methods and horseradish peroxidase-treated materials furnish some evidence for a small Purkinje cell connection directly to the ventral tegmental area. Biochemical studies on dopamine levels in the forebrain indicate there is an increase ipsilateral to the cerebellar cortical lesion whereas a lesion in nucleus fastigii results in a decrease of dopamine levels in ipsilateral forebrain. Some cerebellar influences on catecholamine systems are discussed.