1. Laboratory of Toxicology, Department of Environmental Veterinary Science, Graduate School of Veterinary Medicine, Hokkaido University, N18 W9, Kita-ku, Sapporo, Hokkaido 060–0818, Japan
2. Institute for Animal Experimentation, Graduate School of Medicine, Hokkaido University, Sapporo, Hokkaido 060–8638, Japan
3. Maruyama Zoo, 3–1 Miyagaoka,, Chuo-ku, Sapporo, Hokkaido 064–0959, Japan