Division of Nuclear Medicine, Department of Pharmacology (R. P. Woods, J. C. Mazziotta, and S. R. Cherry), and Department of Neurology (R. P. Woods and J. C. Mazziotta), Division of Brain Mapping, Neuropsychiatric Institute Laboratory of Nuclear Medicine, University of California at Los Angeles School of Medicine, Los Angeles, CA. Address correspondence and reprint requests to Dr. R. P. Woods at Department of Neurology, Reed Neurologic Institute, University of California at Los Angeles School of Medicine, 10833 LeConte Blvd., Los Angeles, CA 90024–1721, U.S.A.