Ubiquitinated filamentous inclusions in spinal cord of patients with motor neuron disease

The ultrastructural localization of ubiquitin (Ubq) in spinal cord of 2 cases of amyotrophic lateral sclerosis was studied, using immunoperoxidase and immunogold labeling on Vibratome sections or on sections cut from paraffin blocks. Two different types of ubiquitinated cytoplasmic inclusions were observed: (1) bundles composed of 10-15 nm filaments; (2) small rounded bodies without a limiting membrane. A panel of antibodies to neurofilaments (NFs) did not stain the ubiquitinated bundles, and decorated only axonal swellings. Ubq-positive filamentous deposits could be identified with inclusions previously described ultrastructurally. The absence of staining with antibodies to NFs might be due to abnormalities of the filaments, possibly because of a dysfunction of the ubq proteolytic system.