1. Departments of Molecular Biology and Pharmacology, Anatomy and Neurobiology, Neurology and Neurosurgery, Washington University School of Medicine, 660 South Euclid Avenue, St. Louis, Missouri 63110, and Division of Pediatric Neurology, St. Louis Children's Hospital, One Children's Place, St. Louis, Missouri 63110, and Department of Neurology, University of Texas Health Science Center, 6431 Fannin Street, Houston, Texas 77030