a- Indicates mice that were stereotactically microinjected into the striatum. As described in the methods, this technique was used to facilitate possible early detection of PrPSc replication at the site of the needle track, as was previously demonstrated . Mice injected using this technique were euthanized electively and tissues were processed to directly screen the injection needle track and adjacent brain by IHC for any PrP replication. Mice without asterisks were intracerebrally inoculated with a 30ul volume of brain homogenate and euthanized when they developed neurologic signs consistent with prion infection or when they developed conditions requiring euthanasia for humane reasons. nt = not tested