1. Department of Physiology, Yonsei University College of Medicine, Seoul 120-752, Republic of Korea
2. Brain Korea 21 PLUS Project for Medical Science, Yonsei University College of Medicine, Seoul 120-752, Republic of Korea
3. Division of Bio and Health Sciences, Mokwon University, Daejeon 302-729, Republic of Korea
4. Department of Anesthesiology and Pain Medicine, Yonsei University College of Medicine, Seoul 120-752, Republic of Korea