1. Department of Organic Pharmaceutical Chemistry, Uppsala Biomedical Centre, Uppsala University, Box 574, S-751 23 Uppsala, Sweden, Department of Pharmacology, Astra Research Centre Montreal, 7171 Frederick-Banting, St-Laurent, Quebec H4S 1Z9, Canada, and Department of Clinical Neuroscience, Experimental Alcohol and Drug Addiction Research Section, Karolinska Hospital, S-171 76 Stockholm, Sweden