1. A. Barria, V. Derkach, T. R. Soderling, Vollum Institute, Oregon Health Sciences University, Portland, OR 97201, USA.
2. D. Muller, Department of Neuropharmacology, Centre Medical Universitaire, 1211 Geneva 4, Switzerland.
3. L. C. Griffith, Department of Biology, Brandeis University, Waltham, MA 02254, USA.