1. From the Departments of Physiology (D.-S.W., K.K., G.L., F.M., J.W., I.L., Y.-F.X., N.K.C., A.F.-E., A.J.R., B.A.O.), Anesthesia (A.S., B.A.O.), Pharmacology and Toxicology (A.J.R.), and Ophthalmology and Vision Science (J.M.S.) and the Leslie Dan Faculty of Pharmacy (Y.-F.X., R.P.B.), University of Toronto, Toronto, Ontario, Canada; the Department of Anesthesia, Sunnybrook Health Sciences Centre