1. Department of Physiological Sciences, Lund University, Sölvegatan 19, SE-223 62 Lund, Sweden
2. University of Chicago, Department of Neurobiology, Pharmacology and Physiology, 947 E. 58th Street, MC 0926, Chicago, IL 60637, USA
3. Physiologisches Institut, Universität des Saarlandes, D-66421 Homburg/Saar, Germany