The dopaminergic nigropallidal projection in primates: distinct cellular origin and relative sparing in MPTP-treated monkeys.

In summary, our findings revealed the existence in primates of a dopaminergic pallidal projection that arises from neurons of the substantia nigra-ventral tegmental area complex and terminates preferentially in the internal pallidum. This projection is largely distinct from the nigrostriatal dopaminergic pathway and appears to be relatively spared in parkinsonian monkeys. Thus, in addition to their potent influence at striatal levels, the midbrain dopaminergic neurons may directly modulate the activity of basal ganglia output neurons at pallidal levels.