[1] Yamaguchi Univ, Fac Agr, Dept Vet Pharmacol, Yamaguchi 7538515, Japan
[2] Univ Tokyo, Grad Sch Agr & Life Sci, Dept Vet Pharmacol, Tokyo 113, Japan
[3] Yamaguchi Univ, Sch Med, Dept Mol Physiol, Ube, Yamaguchi 755, Japan
[4] Yamaguchi Univ, Fac Agr, Dept Vet Pathol, Ube, Yamaguchi 755, Japan