1. Department of Neurosciences, University of New Mexico School of Medicine, Albuquerque, NM 87131.
2. Departments of Neurology and Neuroscience, Institute for Cell Engineering, Johns Hopkins University School of Medicine, Baltimore, MD 21205.
3. The Salk Institute for Biological Studies, Laboratory of Genetics, La Jolla, CA 92037.
4. Present address: Laboratory of Molecular Neuroscience, Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma 630-0101, Japan.