Projections of the basal ganglia to the zona incerta of the dog diencephalon.

Retrograde axonal transport of horseradish peroxidase was used to show that the projections of the globus pallidus, entopeduncular nucleus, substantia nigra, and pedunculopontine tegmental nucleus in dogs are directed to all segments of the zone incerta. The experiments reported here identified no topical features in the organization of these projections in dogs, as application of marker to different areas of the zona incerta yielded similar distributions of labeled neurons in the basal ganglia. No striatal projections to the zone incerta were found.