Five strains of scrapie agent were used as intracerebral inocula for 2 inbred mouse strains, C57BL and VM, and their F1 cross. The degree of vacuolation in specified regions of the brain, and the relative distribution of this damage in 9 regions represented as a “lesion profile”, was different for each agent. Any of the 5 scrapie agents could be distinguished from the others with a very high degree of reliability solely on the basis of these histological parameters, using either strain of mouse. The lesion profile was unaffected by the dose of the agent, using doses of ME7 agent ranging over 6 orders of magnitude in C57BL mice.     The genotype of mouse had a marked effect on the overall degree of vacuolation and on the shape of the lesion profile: these effects were more profound with some agents than others. In certain areas of the brain, depending upon the strain of agent used, the (C57BL × VM)F1 cross was found to have either significantly more or significantly less vacuolation than either parental genotype. The genetic control of the lesion profile was found to be too complex for more detailed analysis in these data.
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