a - Tg44+/+ mice were inoculated with RML scrapie by two routes (i.c, intracerebral; i.v., intravenous) as described in the Methods. For some mice, i.v. scrapie inoculation was followed immediately by a needle stab to the brain to break the blood–brain-barrier. Some of these data were presented previously in a different format .
b - Number of mice with PrPres amyloid in brain or extraneural organs (heart, brown fat and colon) detected by immunohistochemistry/total mice inoculated.
c - From 450-600dpi 2 of 4 mice inoculated by the i.v. route had detectable PrPres amyloid in brain. The route of actual CNS invasion in these mice might have been either via slow neural transport or via blood, if the BBB was less efficient at later ages. However, this could not be determined by our experiments.