1. Laboratory of Reproductive Biology, Division of Animal Science, Department of Bioresource Science, Graduate School of Agricultural Science, Kobe University, Kobe 657-8501, Japan
2. Hokubu Agricultural Technology Institute, Hyogo Prefectural Technology Center for Agriculture, Forestry and Fisheries, Hyogo 669-5254, Japan
3. Biosignal Research Center, Kobe University, Kobe 657-8501, Japan