1. Department of Pharmacology, University of California, San Diego, La Jolla, California 92093
2. Department of Medicine, University of California, San Diego, La Jolla, California 92093
3. National Institute of Mental Health, Bethesda, Maryland 20892
4. Department of Medicine, Stanford University School of Medicine, Stanford, California 94305
5. Biozentrum, University of Basel, CH-4056 Basel, Switzerland