1. Chemistry and Life Sciences, Research Triangle Institute, 3040 Cornwallis Road, Research Triangle Park, North Carolina 27709, Clinical Psychopharmacology Section, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, 5500 Nathan Shock Drive, Baltimore, Maryland 21224, and Lilly Research Laboratories, Eli Lilly and Company, Lilly Corporate Center, Indianapolis, Indiana 46285