1. Institut de Chimie des Substances Naturelles, Centre National de la Recherche Scientifique, 91198 Gif-sur-Yvette Cedex, France, Department of Pharmacology, University of Bern, Friedbühlstrasse 49, CH-3010 Bern, Switzerland, and Section of Biochemical Psychiatry, Department of Psychiatry and Brain Research Institute, Section of Biochemistry and Molecular Biology, University of Vienna, A-1090, Vienna, Austria