Immunocytochemical and ultrastructural studies of lower motor neurons in amyotrophic lateral sclerosis

Abstract

Neuronal inclusions in lower motor neurons in 23 cases of adult-onset sporadic amyotrophic lateral sclerosis were studied immunocytochemically and ultrastructurally. Monoclonal and polyclonal antiubiquitin antibodies recognized four structures in the neuronal perikarya: (1) all Lewy body-like inclusions in 6 cases with a relatively short clinical course, (2) a small percentage of Bunina bodies in 4 cases with abundant Bunina bodies, (3) ill-defined structures closely associated with Bunina bodies (Bunina body-related structures) in 15 cases, and (4) a focally aggregated meshwork of fine filamentous structures not associated with Bunina bodies in all cases. These four structures were not recognized by the antibodies raised against cytoskeletal proteins (neurofilament, tubulin, microtubule-associated protein 2, and phosphorylated tau). Electron microscopy revealed Lewy body-like inclusions to be accumulations of randomly oriented filaments, approximately 15 nm in diameter, covered by fine granules. Bundles of coated filaments 12 nm in diameter that sometimes formed Bunina body-like structures were also observed in the perikarya. Immunoelectron microscopy showed the reaction product with antiubiquitin to be on the filaments, 15 nm in diameter, of Lewy body-like inclusions. Our study revealed the existence of two types of filaments in lower motor neurons of patients with amyotrophic lateral sclerosis: (1) ubiquitin-positive, granule-associated filaments, approximately 15 nm in diameter, that form Lewy body-like inclusions; and (2) 12 nm coated filaments that may be a candidate for another ubiquitin-positive structure and possibly a precursor of Bunina bodies. These two types of filaments may represent early pathological changes of lower motor neurons in amyotrophic lateral sclerosis.