1. H. Cheng, Department of Neuroscience, Karolinska Institute, S-171 77 Stockholm, Sweden, and Department of Neurosurgery, Neurologic Institute, Veterans General Hospital-Taipei and Division of Surgery, National Yang-Ming University, Taiwan.
2. Y. Cao, Department of Cell and Molecular Biology, Karolinska Institute, S-171 77 Stockholm, Sweden.
3. L. Olson, Department of Neuroscience, Karolinska Institute, S-171 77 Stockholm, Sweden.