Departments of Neurosurgery, Pharmacology, and Biomedical Engineering, The Pennsylvania State University, Hershey, Pennsylvania, United States of America.|Department of Biochemistry & Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States of America.|Departments of Pharmacology, Biochemistry & Molecular Biology, Chemistry, and Biomedical Engineering, The Pennsylvania State University, Hershey, Pennsylvania, United States of America.