Electron microscopy has made important contributions to the study of scrapie over the past decade. Scrapie is a transmissible, neurodegenerative disease of sheep and goats. The scrapie agent is neither a virus nor a viroid and the term """"""""prion"""""""" has been suggested for this class of novel infectious pathogens. Initially, the electron microscope was used to identify components of partially purified fractions of scrapie prions and define the ultrastructure of the particles found in these fractions. Rod- shaped particles were found in some fractions with high prion titers. Ultrastructural analyses of purified rods led to the discovery that scrapie prion proteins can form amyloid filaments which coalesce to amyloid plaques. Antisera raised against the scrapie prion protein, the only identifiable component of the prion was used to demonstrate the immunoreactivity of the prion rods and to identify extracellular collections of amyloid filaments composed of prion proteins in the brains of scrapie-infected hamsters. Ultrastructural analyses showed that the rods were formed as a consequence of detergent extraction of the microsomal membranes. The nature of the scrapie prion was further revealed by studies in which Purified rods were transformed into detergent-lipid-protein complexes (DLPC) by a mixture of cholate and phosphatidylcholine. Dialysis of the DLPC to remove detergent resulted in the formation of closed liposomes. Throughout the transformations from rods to DLPC to liposomes and back to rods, high levels of prion infectivity were maintained. No filamentous or rod-shaped particles were found amongst prion liposomes by electron microscopy. We anticipate that electron microscopy will continue to be an important technique in studies focused on: 1) prion structure, 2) the cell biology of prion proteins, and 3) pathogenic mechanisms of scrapie and CJD. The history of important discoveries in prion research emanating from ultrastructural studies provides excellent support for our view that electron microscopy will continue to be a necessary and important technique for future investigations. Because the scrapie and CJD agents are extremely difficult to inactivate and the CJD agent is a human pathogen, we were forced to set up our own electron microscopy suite 10 years ago. Because our JEOL 100B electron microscope was built in 1970, its useful lifetime is approaching an end. The instrument contains numerous vacuum tubes and other parts which are no longer manufactured. We no seek funds to replace our 18 year old electron microscope with a comprobable, new instrument.
