1. Medicinal Chemistry and Psychobiology Sections, Intramural Research Program, National Institute on Drug Abuse, 5500 Nathan Shock Drive, Baltimore, Maryland 21224, Department of Radiology, University of MissouriColumbia, and Harry S. Truman Veterans Hospital, 800 Hospital Drive, Columbia, Missouri, 65201, and Department of Chemistry, Emory University, Atlanta, Georgia 30322