1. Drug Discovery Program, Department of Medicinal Chemistry and Pharmacognosy, 539 College of Pharmacy, University of Illinois at Chicago, 833 South Wood Street, Chicago, Illinois 60612, Department of Pharmacology, Georgetown University Medical Center, 3970 Reservoir Road, N.W., Washington, D.C. 20057, Departments of Anesthesiology and Neurobiology, Graduate School of Medicine, Chiba University, Chiba 260-8670, Japan, and Department of Biology, Georgetown University, Washington, D.C. 20057