1. R. H. Zetterström and L. Olson, Department of Neuroscience, Karolinska Institute, S-171 77 Stockholm, Sweden.
2. L. Solomin, L. Jansson, T. Perlmann, The Ludwig Institute for Cancer Research, Stockholm Branch, Post Office Box 240, S-171 77 Stockholm, Sweden.
3. B. J. Hoffer, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, Baltimore, MD 21224, USA.