1. Natural and Synthetic Drugs Research Center, Laboratory of Medicinal Chemistry, University of Liège, avenue de l'Hôpital 1 (B36), B-4000 Liège 1, Belgium, Laboratory of Physiology, University of Liège, place Delcour 17 (L1), B-4020 Liège, Belgium, Department of Psychoneuropharmacology, University of Nijmegen, P.O. Box 9101, 6500 HB Nijmegen, The Netherlands, Faculty of Medicine, University of Namur, rue de Bruxelles 61, B-5000 Namur, Belgium, and Therabel Research, rue Egide Van Ophem 108, B-1180...