1. A. J. Yool, Departments of Physiology and Pharmacology, University of Arizona, Tucson, AZ 85724-5051, USA.
2. W. D. Stamer, Department of Pharmacology and Toxicology, University of Arizona, Tucson, AZ 85721, USA.
3. J. W. Regan, Department of Pharmacology and Toxicology and Department of Physiology, Program in Neuroscience, University of Arizona, Tucson, AZ 85721, USA.