1. Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia 30322, USA
2. Department of Pharmacology and Therapeutics, McGill University, Montreal, Quebec, Canada
3. Department of Molecular Pharmacology, Physiology and Biotechnology, Brown University, Providence, Rhode Island 02912, USA
4. Instrumentation and Computer Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892, USA