Subdivisional involvement of nigrostriatal loop in idiopathic Parkinson's disease and striatonigral degeneration.

A topographical immunocytochemical analysis was performed on the substantia nigra from patients with idiopathic Parkinson's disease and striatonigral degeneration. Antibodies to tyrosine hydroxylase, a marker for nigrostriatal dopaminergic neurons, and to calcineurin, a marker for striatonigral projection fibers, were used in this study. There was a marked depletion of dopaminergic neurons in the substantia nigra of parkinsonian patients compared with control subjects, the reduction being greater in the lateral portion than in the medial portion (p less than 0.001). Calcineurin immunoreactivity was densely distributed throughout the substantia nigra of patients with Parkinson's disease and control subjects. The numbers of dopaminergic neurons and of calcineurin-immunoreactive fibers were markedly reduced in the lateral portion of the substantia nigra in all patients with striatonigral degeneration. Our results suggest that many symptoms of these two diseases may be due to disruption of the functions of the putamen and the lateral portion of the substantia nigra, which have dense reciprocal connections as part of the dopamine-related nigrostriatal loop.