1. Torrey Pines Institute for Molecular Studies, San Diego, CA 92121.
2. Laboratory of Chemical Biology and Peptide Research, Clinical Research Institute of Montreal, Montreal H2W 1 R7, Canada.
3. Department of Pharmacology, University of Rochester Medical Center, Rochester, New York 14642, USA.
4. Department of Neurology, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA.
5. Houghten Pharmaceuticals Inc., San Diego, CA 92121, USA.