1. Department of Special Medicine, Basic Medicine College, Qingdao University, Qingdao, Shandong 266071, P. R.China
2. Department of Neurosurgery, The Affiliated Hospital of Qingdao University, Qingdao University, Qingdao, Shandong 266000, P. R.China
3. Department of Natural Sciences, College of Science and Health Professions, Northeastern State University, Broken Arrow, Oklahoma 74014, United States