1. Department of Biology, University of Teacher Education Fukuoka, Akamabunkyo-machi 1-1, Munakata, Fukuoka 811-4192, Japan
2. Brain Functions and Neuroscience Unit, Department of Oral Science, Graduate School of Dentistry, Kanagawa Dental University, Inaoka-cho 82, Yokosuka, Kanagawa 238-8580, Japan