1. M. Spina, E. Merlo-Pich, A. M. Basso, G. F. Koob, Department of Neuropharmacology, The Scripps Research Institute, 10666 North Torrey Pines Road, La Jolla, CA 92037, USA.
2. R. K. W. Chan, Laboratory of Neuronal Structure and Function, The Salk Institute, La Jolla, CA 92037, USA.
3. J. Rivier and W. Vale, Clayton Foundation Laboratories for Peptide Biology, The Salk Institute, La Jolla, CA 92037, USA.