1. Department of Anesthesia and Stanford Pain and Analgesia Research Center, Stanford University, Stanford, CA 94305-5117.
2. Department of Physiology and Biophysics, University of Colorado Health Sciences Center, Denver, C0 80262.
3. Department of Biology and Hopkins Marine Station of Stanford University, Pacific Grove, CA 93950.
4. Department of Pharmacology, Physiology and Neuroscience, University of South Carolina School of Medicine, Columbia, SC 20208.