1. Department of Bio-Pharmaceutical Analysis, TNO Pharma, P.O. Box 360, 3700 AJ Zeist, The Netherlands, Institute of Laser Medicine and Biologisch-Medizinisches, Forschungs-zentrum, Heinrich Heine University Düsseldorf, P.O. Box 101007, D40001 Düsseldorf, Germany, Department of Animal Physiology, Institute for Neurosciences, Subfaculty of Biology, University of Nijmegen, Toernooiveld 1, 6525 ED Nijmegen, The Netherlands