1. Department of New Materials and Biosystems, Max Planck Institute for Metals Research, Stuttgart, Germany, and Department of Biophysical Chemistry, University of Heidelberg, Germany, postal address: Heisenbergstrasse 3, 70569 Stuttgart, Germany
2. Department of Neurobiology, Interdisciplinary Center for Neurosciences (IZN), University of Heidelberg, Im Neuenheimer Feld 364, 69120 Heidelberg, Germany