1. Department of Nuclear Medicine and Radiobiology, Faculty of Medicine and Health Science, University of Sherbrooke, Quebec, Canada J1H 5N4, Pharmacology Institute, Faculty of Medicine and Health Science, University of Sherbrooke, Quebec, Canada J1H 5N4, and Département de Recherche Fondamentale sur la Matière Condensée, SCIB/LAN, UMR-E n°3 (CEA-UJF), CEA/Grenoble, F-38054 Grenoble Cedex 9, France