1. Laboratory of Laboratory Animal Science and Medicine, School of Veterinary Medicine, Kitasato University, 35-1 Higashi-23, Towada, Aomori 034-8628, Japan
2. Department of Laboratory Animal Medicine, Section of Animal Models, Research Institute, National Center for Global Health and Medicine, 1-21-1 Toyama, Shinjuku, Tokyo 162-8655, Japan
3. Laboratory of Veterinary Anatomy, School of Veterinary Medicine, Kitasato University, 35-1 Higashi-23, Towada, Aomori 034-8628, Japan