1. Stroke Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892-4128, Laboratory of Molecular and Cellular Neuroscience, Rockefeller University, New York, New York 10021, Department of Cellular and Molecular Physiology, The Pennsylvania State University, College of Medicine, Milton S. Hershey Medical Center, Hershey, Pennsylvania 17033, and Division of Neurosurgery, Brigham and Women's Hospital, Boston, Massachusetts 02115