[1] Department of Anatomy and Histology, Faculty of Medicine, Niigata University, 1 Asahimachi-dori, Niigata 951-8510, Japan
[2] Department of Internal Medicine, School of Medicine, Hokkaido University, Kita-15 Nishi-7, Kita-ku, Sapporo 060-863, Japan
[3] Takatsuka Unit, Seiko Instruments Inc., 563 Takatsuka-shinden, Matsudo, Chiba 271-2222, Japan