1. Institut National de la Santé et de la Recherche Médicale U30, Hôpital des Enfants Malades, 75015 Paris, France
2. Department of Anatomy and Cell Biology, McGill University, Montréal H3A 2B2, Québec, Canada
3. Synthélabo Recherche, Central Nervous System Research Department, 92220 Bagneux, France