1. Center for Magnetic Resonance Research (CMRR) and Department of Radiology, University of Minnesota Medical School, Minneapolis, MN 55455.
2. Brain Sciences Center, Department of Veterans Affairs Medical Center, Minneapolis, MN 55417, and Department of Neurology, University of Minnesota Medical School, Minneapolis, MN 55455.
3. CMRR and Department of Biochemistry, University of Minnesota Medical School, Minneapolis, MN 55455.
4. CMRR and Departments of Radiology, Biochemistry, and Medicine, University of Minnesota Medical School, Minneapolis, MN 55455.
5. Brain Sciences Center, Department of Veterans Affairs Medical Center, Minneapolis, MN 55417, and Departments of Physiology and Neurology, University of Minnesota Medical School, Minneapolis, MN 55455.