Subregional loss of putaminal efferents to the basal ganglia output nuclei may cause parkinsonism in striatonigral degeneration.

In this study, we examined the topographic involvement of the putaminal projection neurons and their axons in the globus pallidus and substantia nigra, which we visualized by calcineurin immunostaining, in the basal ganglia of patients with striatonigral degeneration (SND). In all cases examined, there was a marked decrease in number of calcineurin-immunopositive neurons in the caudal and lateral portion of the putamen. Also, marked depletion of calcineurin-immunoreactive putaminal efferents was consistently present in the posteroventrolateral portions of the globus pallidus interna (GPi) and externa, and in the ventrolateral portion of the substantia nigra pars reticulata (SNr) topographically corresponding to the putaminal lesion. In view of the functional model of the basal ganglia "motor" circuit, these findings suggest that subregional deafferentation of the GPi/SNr (i.e., basal ganglia output nuclei) from putaminal inputs may be responsible for parkinsonism in patients with SND.