The nigro-striatal and nigro-amygdaloid pathways undergo different degeneration processes in brains of dementia with Lewy bodies.

We immunohistochemically investigated the degeneration processes of the nigro-striatal and nigro-amygdaloid pathways and the relationship between the loss of dopaminergic neurons and Lewy bodies (LB) formation in the substantia nigra using 15 autopsied cases of dementia with Lewy bodies (DLB). The number of tyrosine hydroxylase (TH)-positive neurons in the substantia nigra and TH-positive axonal terminals in the putamen decreased with a specific pattern. The substantia nigra possessed alpha-synuclein-positive LB-bearing neurons that were almost evenly distributed, while the putamen exhibited diffuse or granular alpha-synuclein-immunostaining. Most of the granular stains were positive for anti-phosphorylated alpha-synuclein antibody, whereas the diffuse stains were negative. These findings suggest that the axonal terminals in the putamen undergo abnormal alpha-synuclein accumulation, but may not always originate from LB-bearing neurons in the substantia nigra. The central amygdaloid nucleus contained anti-alpha-synuclein- and -phosphorylated alpha-synuclein-positive dystrophic axonal terminals, the degree of which was greater for cases with granular staining in the putamen, and which was proportional to the number of alpha-synuclein-positive neurons in the substantia nigra. Thus, the axonal terminals in the central amygdaloid nucleus may have originated from LB-bearing neurons in the substantia nigra. The results of the present study indicate that the nigro-striatal and nigro-amygdaloid pathways undergo different degeneration processes in DLB, and suggest that the degeneration of the nigro-amygdaloid pathway more strongly reflects LB formation in dopaminergic neurons of the substantia nigra than that of the nigro-striatal pathway. In addition, they indicate that there is no direct relationship between the loss of dopaminergic neurons and LB formation in the substantia nigra.