1. Laboratory of Molecular Neurobiology, Addiction Research Center, National Institute on Drug Abuse, Baltimore, MD 21224.
2. Laboratory of Molecular Pharmacology, Addiction Research Center, National Institute on Drug Abuse, Baltimore, MD 21224.
3. Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21224.
4. Departments of Neurology and Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21224