Biochemical changes in scrapie affeced brain.
central rod-like core, has been described. In view of the tendency of scrapie infectivity to be associated firmly (though not exclusively) with mitochondrial fractions these changes deserve further study. Pattison (1965) has emphasized the remarkable symmetrical localization of the changes of scrapie. This is quite striking, but unilateral changes may be seen in the earliest stages (see above). In summary, scrapie changes comprise: (a) Neuronal vacuolation, more marked in some species than others and varying in degree with different strains of scrapie agent. (b) Widespread non-specific nerve-cell degeneration. (c) Myelin sickness, especially in long fibre tracts. (d) Astroglial hypertrophy, regarded by several workers as the earliest and most clear-cut sign of scrapie change. The glial changes are reminiscent of those occurring in a low-grade astrocytoma and suggest the possibility that there has been widespread 'transformation' of glial cells in scrapie. (e) Strict symmetry of histological changes in established disease. (f ) Changes that are usually associated with aging, e.g. amyloid bodies, ordered neuronal tubule formation. (g) Changes much more marked in grey matter than in white.