Learning ability of mice infected with different strains of scrapie

CD-1 mice were infected intraperitoneally with one of 4 different strains of scrapie and tested simultaneously at or near the end of incubation. There were no differences between any of the scrapie injected groups and controls in spontaneous motor activity, or in the shock thresholds and entry latencies measured during training in a one-trial passive avoidance test. On testing, the avoidance responses were normal for the mice infected with 22C or ME7, but these mice did not show overt clinical signs (e.g., ataxia) at the time. The 139A and 79A infected mice were showing clinical signs when tested and impaired responses were found in the mice trained at a low shock threshold. However the impairment was completely overcome at a higher shock level. These results suggest that only limited reductions in learning ability are associated with some of the shorter incubation models of scrapie. Specific suggestions are made of how a learning deficit might be produced in certain scrapie models which could be useful in studies of some aspects of dementia.