1. Medicinal Chemistry and Psychobiology Sections, National Institute on Drug AbuseIntramural Research Program, National Institutes of Health, Department of Health and Human Services, Baltimore, Maryland, University of North Dakota School of Medicine, Grand Forks, North Dakota, University of MissouriColumbia, Departments of Radiology and Medical Pharmacology and Physiology, and Harry S. Truman Veterans Administration Medical Center, Columbia, Missouri