1. Department of Developmental Physiology, National Institute for Physiological Sciences, Okazaki 444-8585, Japan.
2. Core Research for Evolutional Science and Technology, Japan Science and Technology Agency, Kawaguchi 332-0012, Japan.
3. Functional Probe Research Laboratory, Molecular Imaging Research Program, RIKEN, Kobe 650-0047, Japan.
4. Department of Physiology, University of Göteborg, Post Office Box 432, SE-40530 Göteborg, Sweden.
5. Central Research Institute of Hamamatsu Photonics, Hamamatsu 434-8601, Japan.