The striatopallidal and striatonigral projections: two distinct fiber systems in primate.

The use of the fluorescence retrograde double-labeling method has revealed that striatal neurons projecting to the globus pallidus in the squirrel monkey are mainly confined to the putamen whereas those projecting to the substantia nigra occur mostly in the caudate nucleus. Only about 10% of the striatal neurons were found to be double-labeled after injections into the globus pallidus and substantia nigra. The segregation of the putaminofugal and caudatofugal projections was further confirmed by the anterograde tracing of WGA-HRP. These findings do not fit in the current unitary concept of the striatofugal fiber system. Instead, they suggest that the striatopallidal and striatonigral projections exist largely as two distinct subsystems in the primate.