1. Fraser Laboratories, Departments of Medicine, Pharmacology, Therapeutics, Neurology, and Neurosurgery, McGill University and Royal Victoria Hospital, Montreal, Quebec H3A 1A1, Canada.
2. Departments of Physics and Chemistry, Clarkson University, Potsdam, NY 13699, USA.
3. VA Connecticut Healthcare System and New England Biomedical Research Center, Newington, CT 06111, USA.