An electron microscopic study of MPTP-induced inclusion bodies in an old monkey.

Eosinophilic inclusion bodies have recently been found in the nerve cells of the substantia nigra in aged primates with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced parkinsonism. This report describes the ultrastructure of the inclusion-bearing nerve cells in the substantia nigra from one of these animals. By electron microscopy the inclusions were less well demarcated and less conspicuous than those seen in hematoxylin-eosin stained paraffin sections. The bodies corresponded to portions of the nerve cell that were devoid of Nissl substance, but contained an increased number of randomly oriented, thick filamentous or tubular structures with some resemblance to neurotubules. The inclusion bodies were compared to Pick bodies: argentophilic inclusions in Pick's disease, a rare form of dementia, and to Lewy bodies: the inclusions characteristically present in Parkinson's disease. The MPTP-induced inclusions differed from both Pick bodies and Lewy bodies, but could represent immature Lewy bodies, similar to Lewy bodies in the cerebral cortex. The mechanism of formation of these structures, their relationship to Parkinson's disease and the reason why they appear to require the substrate of an aged nervous system, remain to be determined.