Pathology of dendrites in subacute spongiform virus encephalopathies.

The spongiform changes in the cerebral cortex of scrapie mice and of chimpanzees afflicted with experimental kuru and Creutzfeldt-Jakob disease were examined by electron microscopy. The pathognomonic findings consisted of swelling and vacuolation of neurons, particularly of dendrites. Fusion of swollen cells and processes occurred. The changes were associated with alterations of plasma membranes. Curled fragments of membranes accumulated at points of cell fusion and at the margin of vacuoles within dendrites. The abnormal membranes were wider and more osmiophilic than normal plasma membranes. These findings as well as other data on the nature of the atypical viruses of scrapies, kuru, and Creutzfeldt-Jakob disease indicate that the infectious agents are closely associated with membranes and that alterations of neuronal membranes initiate the spongiform degeneration of neurons.