Laboratory of Neurosciences, National Institute on Aging Gerontology Research Center, 5600 Nathan Shock Drive, Baltimore, MD 21224; Rush Alzheimer's Disease Center, Rush–Presbyterian–St. Luke's Medical Center, 1645 West Jackson Street, Chicago, IL 60612; and Departments of Pathology and Neuroscience, Johns Hopkins University School of Medicine, 725 North Wolfe Street, Baltimore, MD 21205 (At 2004-02-15)