1. Department of Anatomy; Kawasaki Medical School; Okayama 701-0192 Japan
2. Department of Otolaryngology; Kawasaki Medical School; Okayama 701-0192 Japan
3. Department of Morphological Brain Science; Graduate School of Medicine, Kyoto University; Kyoto 606-8501 Japan
4. Division of Cerebral Circuitry; National Institute for Physiological Sciences; Aichi 444-8787 Japan
5. Research Center for Ultra-High Voltage Electron Microscopy; Osaka University; Osaka 567-0047 Japan