Scrapie as a model for neuroaxonal dystrophy: ultrastructural studies.

Neuritic degeneration is a prominent ultrastructural feature of scrapie in hamsters. To investigate the morphogenesis of neuritic degeneration, we examined brain tissues from hamsters infected with the 263K strain of scrapie virus and from age-matched controls at varying intervals following intracerebral inoculation. Dystrophic neurites--defined as dendrites, axonal preterminals, and myelinated axons containing mitochondria and pleomorphic, electron-dense inclusion bodies--were found as early as 2 weeks postinoculation. Their numbers increased with the incubation period, and their highest density was observed at the terminal stage of disease. Occasionally, small clusters of these structures formed neuritic plaques. Such dystrophic neurites were only rarely seen in brains of uninfected hamsters. Experimental scrapie thus provides an animal model for human neuroaxonal dystrophies. In addition, since this model allows predictable formation of brain amyloid, it may serve as a model for the study of neuronal aging and Alzheimer's disease.