Three scrapie prion isolates exhibit different accumulation patterns of the prion protein scrapie isoform

To investigate the molecular basis of prion diversity, we inoculated transgenic mice expressing the Syrian hamster prion protein (PrP) with three distinct prion isolates. We compared the three isolates designated Sc237, 139H, and Me7H in Tg(SHaPrP)7 mice with clinical signs of scrapie because the incubation times with these mice are considerably shorter than the times found with hamsters. Each prion isolate produced a distinctive pattern of the scrapie isoform of PrP (PrP^Sc) accumulation, as determined by histoblotting, a technique developed for the regional mapping of PrP^Sc deposition. The PrP^Sc pattern with the Me7H isolate was particularly interesting because it appeared to be confined to the hypothalamus and related structures - including the interstitial nucleus of the stria terminalis, the paraventricular nucleus of the thalamus, and periaqueductal grey. Additionally, the regions of PrP^Sc accumulation remained highly restricted, even though the incubation time for Me7H scrapie was significantly longer than with Sc237 and 139H isolates. Neuropathological changes characterized by neuronal vacuolation and astrocytic gliosis were confined to those regions where PrP^Sc accumulated. These findings argue that the cell-specific propagation of prion isolates may be responsible for different properties exhibited by each of the isolates.