1. S. H. R. Oliet, Department of Cellular and Molecular Pharmacology, University of California, San Francisco, CA 94143-0450, USA.
2. R. C. Malenka, Departments of Psychiatry and Physiology, University of California, San Francisco, CA 94143-0984, USA.
3. R. A. Nicoll, Departments of Cellular and Molecular Pharmacology and Physiology, University of California, San Francisco, CA 94143-0450, USA.