1. Drug Research Center, Laboratory of Medicinal Chemistry, University of Liège, avenue de l'Hôpital, 1 (B36), B-4000 Liège 1, Belgium, and Research Center for Cellular and Molecular Neurobiology, Laboratory of Pharmacology, University of Liège, avenue de l'Hôpital, 1 (B36), B-4000 Liège 1, Belgium