[Light and electron microscopic observations of sheep scrapie]

Two Suffolk sheep diagnosed as scrapie clinically and epidemiologically were investigated light and electron microscopically. They were female and four years four months of age. Spongiform lesions were found in the gray and white matter of midbrain, pons, medulla oblongata, spinal cord and the cerebellar white matter as well as the cerebral gray and white matter. Ultrastructurally, the spongiform lesions were shown to be caused by vacuolation in neuronal perikarya, vacuolation and/or swelling of neuropil, dilatation of the periaxonal space, and splitting of the myelin sheath followed by the intramyelinic vacuolation. Vacuole in neuronal perikaryon was associated with the enlarged endoplasmic reticulum. Adjacent to the vacuole, enlargement of the rough endoplasmic reticulum and cisterns of Golgi apparatus was observed. The cytoplasmic processes found in the intraneuronal vacuoles were formed by the separation of the cytoplasm caused by the continuous dilatation of the endoplasmic reticulum and cisterns of Golgi apparatus. This indicated that the degeneration of the neuronal perikaryon due to such separation contributed to the formation of the intraneuronal vacuole. Vacuolation and swelling with disappearance of the organelles were also found in astro- and oligodendroglial perikarya. Splitting of myelin sheath and the intramyelinic vacuolation were regarded as primary changes. The latter was supported by the degeneration of oligodendroglias found in this study.