Abstract
Spongiform lesions were found in the gray matter of cerebrum, midbrain, pons and medulla oblongata, and the white matter of cerebrum in three scrapie sheep aged 4 to 5 years old. Ultrastructural evidence supports that the spongiform lesions were caused by vacuolation in the neuronal and glial perikarya, vacuolation or swelling of the neuronal and glial processes, dilatation of the periaxonal space, and splitting of the myelin sheath followed by the intramyelinic vacuolation. Association of the vacuoles in the neuronal perikarya with the endoplasmic reticulum was supported by enlargement of the rough endoplasmic reticulum and of cisterns of Golgi apparatus adjacent to the vacuoles. The vacuolation and swelling in the neurons or glias were regarded as primary pathologic changes.
