Phosphorylation of neurofilament proteins and localization of axonal swellings in motor neuron disease

Seven lumbosacral spinal cords with motor neuron disease were examined immunocytochemically with monoclonal antibodies (MAb) directed against neurofilament proteins (NFP). Each of the 5 MAbs used in this study was monospecific to one of the triplet of NFP. Two of them were specific to the highly phosphorylated form of high molecular weight peptide of NFP (NFP-H). All 5 MAbs stained all axonal swellings examined. In 2 spinal cords examined, some axonal swellings were found in the anterolateral funiculus and some of these were as far as 1000 μm from the grey matter. This localization of axonal swellings suggests that a high degree of phosphorylation of NFP is not the cause of accumulation of NFP in axonal swellings in motor neuron disease.