The Tissue Core will play a central role in this Program Project by providing well-characterized human and animal brain tissue as well as other tissues and body fluids to the Research Projects. In addition, the Tissue Core will continue to examine novel and atypical cases. These activities are carried out through three Specific Aims. In Specific Aim 1. the Tissue Core will determine the presence, type, severity and anatomic distribution of structural lesions in tissues from several lines of transgenic mice and Syrian Hamsters. Brains other tissues as needed will be processed for histological and immunohistochemical examinations, and profiles of the histological lesions and maps of scrapie prion protein distribution will be developed as necessary. They will be constructed in a way to be comparable to similar data obtained from the human prion diseases that the animal models may match. Specific Aim 2 deals with human tissues. Well- characterized human brain tissues will be distributed-to the Animal Core for inoculation to receptive animals and will be provided to Research Projects to validate to ability of PMCA to faithfully reproduce the characteristics of in vitro amplified PrPSc and overcome the species barrier. Human brains carryingdiseases modeled in animals will be examined comparatively with the brains from the animal models. In addition, the Tissue Core will continue detailed study of individual cases that carry atypical or novel forms of prion disease as well as groups of cases of particular interest. An important asset of the Tissue Core is its close interaction with the National Prion Disease Pathology Surveillance Center, which collects tissues and body fluids from approximately two hundred cases of human prion disease per year. As a result, the Tissue Core is uniquely situated to examine rare and novel cases of prion disease. In Specific Aim 3. the Tissue Core will continue to collect cases of human and animal prion diseases from other countries as well as the United States including variant Creutzfeldt-Jakob disease, bovine spongiform encephalopathy and bovine amyloidotic spongiform encephalopathy. These tissues are catalogued in a custom-made database and will be available to all research laboratories in the United States and around the world.