Cytoskeletal changes in rat cortical neurons induced by long-term intraventricular infusion of leupeptin

Neurofibrillary tangles (NFTs), which are composed of paired helical filament (PHF)-like filaments, were induced by the long-term intraventricular infusion of leupeptin, a potent protease inhibitor. The fibrils composing the NFTs were 20 nm in maximal width and had periodic constrictions at 40-nm intervals. They were identical to the PHF that had been found in aged rat neurons. Dystrophic axons filled with mainly tubular structures were also abundantly found in the parietal and temporal isocortices, which were not affected in the acute or subacute phases of leupeptin treatment. An immunohistochemical study using antibodies related to the neuronal cytoskeleton showed that neuronal cytoskeletal changes accompanying ubiquitination occurred in dystrophic axons distributed widely in the isocortex as well as the hippocampal formation. The present findings suggest that long-term administration of leupeptin accelerates the neuronal ageing process in rats and causes other neuronal changes: NFT formation, such as seen in the aged brain or in neurodegenerative diseases including Alzheimer's disease, in addition to accumulation of lipofuscin granules and degeneration of neuronal processes. In other words, some disturbance of the balance between proteases and their inhibitors may play an important role in the neuronal ageing process, and some regulatory intervention in the intraneuronal protease activity may provide a new therapeutic strategy for the neurodegenerative diseases.