Numbers of neurones, synapses and axon terminals were quantified in a murine scrapie model with severe hippocampal pyramidal cell loss, in which definite clinical scrapie is evident from 226 days post-infection (dpi) and death occurs around 250 dpi. Disease-specific PrP accumulations were first seen at 70 dpi (28% of the incubation period (IP)) in thalamus and as sparse foci within the stratum pyramidale of CA1. By 98 dpi (39% IP), PrP was seen in the stratum radiatum and was found at later stages throughout all levels of the hippocampus. At the ultrastructural level in the stratum radiatum of CA1, a decrease in the numbers of simple synapses from 84 dpi (34% IP) and in perforated synapses from 98 dpi (42% IP) was found using an unbiased stereological method, the disector analysis. Degeneration of axon terminals was found from 98 dpi (39% IP) onwards. Neuronal loss was detected in CA1 from 180 dpi (72% IP). The results suggest that the fundamental lesion in the hippocampus of ME7-infected mice is associated with PrP release from CA1 pyramidal neurones, which perturbs synaptic function and leads to degeneration of preterminal axons, and that subsequent pathological changes including neurone loss are sequelae to this initial insult.

Macerates of bovine brain infected with bovine spongiform encephalopathy (BSE) agent, and rodent brain infected with the 263K or ME7 strains of scrapie agent, were subjected to porous-load autoclaving at temperatures between 134 and 138 degrees C for < or = 60 min. Bioassay in rodents showed that none of the regimens produced complete inactivation. Homogenates of BSE-infected bovine brain were exposed for < or = 120 min to solutions of sodium hypochlorite or sodium dichloroisocyanurate containing < or = 16,500 ppm available chlorine. There was no detectable survival of infectivity after the hypochlorite treatments but none of the dichloroisocyanurate solutions produced complete inactivation. Homogenates of BSE-infected bovine brain, and rodent brain infected with the 263K and ME7 strains of scrapie agent, were exposed for < or = 120 min to 1M or 2M sodium hydroxide but no procedure produced complete inactivation of all agents tested.

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