Origin of descending afferents to the rostral part of dorsal cap of inferior olive which transfers contralateral optic activities to the flocculus. A horseradish peroxidase study.

Neurons in the ventromedial tegmental area that project to the rostral part of the dorsal cap of the ipsilateral inferior olive were labeled by the technique of retrograde transport of horseradish peroxidase (HRP). Following iontophoresis of HRP into the rostral part of the dorsal cap a cluster of labeled cells are found ipsilaterally in the area ventromedial to the red nucleus as well as in the area between the substantia nigra and the medial lemniscus. Following HRP injections into the medial accessory olive just beneath the dorsal cap, labeled cells are found exclusively contralaterally in the deep layers of the superior colliculus and in the adjacent reticular formation. These findings clearly show that neuronal groups in the ventromedial tegmental area are involved in the pathway which from the contralateral eye via the rostral half of the dorsal cap conveys impulses to the flocculus, recorded as climbing fiber activation.