1. Department of Toxicology; Azabu University School of Veterinary Medicine; Kanagawa 252-5201 Japan
2. Drug Safety Testing Center; Saitama 335-0116 Japan
3. Department of Pathology; The Jikei University School of Medicine; Tokyo 105-8461 Japan
4. Department of Pathology; Osaka City University Medical School; Osaka 545-8585 Japan
5. Japan Bioassay Research Center; Japan Industrial Safety and Health Association; Kanagawa 257-0015 Japan