QUANTITATIVE-ANALYSIS OF THE VARIABILITY OF SUBSTANTIA-NIGRA PIGMENTED CELL CLUSTERS IN THE HUMAN

At present there is no consensus concerning the internal organization of the human substantia nigra, despite its pivotal role in neurodegene rative conditions. We have quantitatively analysed the variability in the pattern of clusters of melanin-pigmented neurons in the human subs tantia nigra using serial section analysis and computer reconstruction s. The substantia nigra pars compacta showed a bilaminar organization consisting of the pars medialis and pars lateralis, as well as dorsal and ventral tiers as described previously [D. A. McRitchie et al. (199 5) J. comp. Neurol. (in press)]. Both the dorsal and ventral tiers cou ld be further subdivided into three mediolateral cell columns based on position and cell density. The presence and arrangement of these cell clusters was most variable in transverse sections (the plane currentl y used for diagnostic neuropathology). Quantitative assessment of the topographical pattern of cell loss within single transverse sections o f the human substantia nigra should therefore be treated with some cau tion. In contrast, the full rostrocaudal extent of the cell columns co uld be seen in horizontal sections. Thus, consistent samples of larger numbers of pigmented neurons per region were found in this section pl ane, although only two cell columns were found in most sections. Our r esults show that greater quantitative reliability can be achieved with horizontal sections of the substantia nigra.