Pigmented neuron/non-pigmented neuron ratio of the substantia nigra in relation to ageing and pathological conditions

Based on 45 normal cases aged from 32 to 106 years of age, a morphometric study revealed that, despite decrease in the number of both pigmented neurons (PN) and the non-pigmented neurons (NN) with advancing age, the ratio (PN/NN) did not change (4.8). It is well-known that both the substantia nigra and the striatum send fibers to each other. McGee demonstrated that the ratio of the number of large neurons to that of small neurons was constant, irrespective of different ages, although number of both neurons decreased with ageing. It was therefore apparent that this phenomenon in the putamen was the same as in the substantia nigra. It could be considered that "balanced depopulation of different neurons" in the nucleus of the strio-nigral circuit contribute to support normal extrapyramidal functions. Additionally, the centenarian cases showed larger numbers of both PN and NN than younger case. It was likely that they could be classified as so-called "excellent" centenarians. On the other hand, idiopathic Parkinson's disease (15 cases) showed that while the same number of NN remained as in age-matched controls, PN showed marked depopulation. Olivopontocerebellar atrophy of the sporadic type (OPCA, 10 cases) and progressive supranuclear palsy (PSP, 5 cases) showed a decrease in number of both PN and NN. However, NN in PSP showed much more decrease than OPCA. NN sends fibers to the pontine tegmentum as well as the thalamus, and PSP shows marked atrophy of the brainstem tegmentum. In this connection, it was considered that marked decrease of NN in PSP could be related to tegmental atrophy.