1. Elan Pharmaceuticals Inc., 3760 Haven Avenue, Menlo Park, California 94025, Department of Physiology, University of Massachusetts Medical Center, Worcester, Massachusetts 01655, Departments of Chemistry and Neuroscience Therapeutics, Parke-Davis Pharmaceutical Research Division of Warner Lambert Company, Ann Arbor, Michigan 48105, and Department of Molecular and Cellular Physiology, Beckman Center, Stanford University, Stanford, California 94305