ANALYSIS OF THE INCUBATION PERIODS, INDUCTION OF OBESITY AND HISTOPATHOLOGICAL CHANGES IN SENESCENCE-PRONE AND SENESCENCE-RESISTANT MICE INFECTED WITH VARIOUS SCRAPIE STRAINS

The similarity in histopathological changes seen in scrapie-infected m ice and in an uninfected senescence-accelerated mouse strain led to a study in which the mouse strain that is prone to senescence (SAMP8), a strain that is resistant to senescence (SAMR1) and a progenitor strai n (AKR) of these two strains were infected with three different scrapi e strains, ME7, 139A and 22L, For each scrapie strain, the incubation period was shortest in AKR mice and longest in SAMR1 mice. The inducti on of obesity was a function of scrapie strain and not mouse strain; M E7 caused obesity in all mouse strains, whereas the average weights of mice injected with 139A and 22L did not differ significantly from mic e injected with homogenates of normal mouse brain. The pattern of vacu olation seen in the brain of each mouse strain was primarily dependent on the scrapie strain injected. There were, in general, similarities to the patterns induced in other inbred strains; e.g. ME7 caused exten sive forebrain vacuolation, 22L caused prominent vacuolation in the ce rebellum, and the 139A strain induced characteristic white matter vacu olation, Vacuolation was also seen in the medulla and midbrain of SAMP 8 mice injected with normal mouse brain, which is consistent with the occurrence of accelerated ageing changes in the brain of this strain. Further analysis of the differences among these mouse strains should p rovide information relating to the observed differences in scrapie inc ubation periods.