a- Indicates mice that were stereotactically microinjected into the striatum. 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 conditions requiring euthanasia for humane reasons