1. Department of Physiology; Keio University School of Medicine; 35 Shinanomachi Shinjuku-ku Tokyo 160-8582 Japan
2. RIKEN-Keio University Joint Research Laboratory; RIKEN Brain Science Institute; 2-1 Hirosawa Wako-shi Saitama 351-0198 Japan
3. Central Institute for Experimental Animals; 3-25-12 Tonomachi Kawasaki-ku Kawasaki-shi Kanagawa 210-0821 Japan