1. Department of Physiology, Institute of Basic Medical Sciences, University of Oslo, PO Box 1103 Blindern, N0317 Oslo, Norway
2. Department of Cell Physiology at the Max‐Planck‐Institute for Medical Research, Jahnstrasse 29, D‐69120 Heidelberg, Germany
3. Department of Molecular Neurobiology at the Max‐Planck‐Institute for Medical Research, Jahnstrasse 29, D‐69120 Heidelberg, Germany
4. Institute of Anatomy, University of Freiburg, Albertstrasse 17, D‐79104‐Freiburg, Germany