Ultrastructural study of Bunina bodies in the anterior horn neurons of patients with amyotrophic lateral sclerosis.

We ultrastructurally investigated Bunina bodies (BB) in the anterior horn neurons of 20 amyotrophic lateral sclerosis patients with BB. As for novel findings, filaments thicker than neurofilaments were not uncommonly observed inside the BB. They were occasionally observed around the periphery of the BB. Some of them were composed of bundles of filaments which appeared constricted at 40-50 nm intervals and were 20-25 nm in maximum width. Others consisted of bundles of unconstricted filaments measuring about 20-25 nm in diameter. The BB occasionally contained bundles of filaments of about 20 nm in diameter that closely resembled those found in ubiquitin-positive skein-like inclusions. It seems that some molecular disturbances such as ubiquitin play a role in the formation of the constricted and unconstricted filaments. Probably cytoskeletal or non-cytoskeletal proteins in anterior horn cells are damaged and accumulate to form aggregation of the filaments associated with BB.