1. Merck Sharp & Dohme Research Laboratories, The Neuroscience Research Centre, Terlings Park, Harlow, Essex CM20 2QR, United Kingdom, Department of Safety Assessment, Merck Research Laboratories, West Point, Pennsylvania 19486, Division of Biomedical Sciences, Imperial College of Science, Technology and Medicine, Sir Alexander Fleming Building, London SW7 2AZ, United Kingdom, and Department of Medicinal Chemistry, Merck Research Laboratories, Rahway, New Jersey 07065