[1] Univ Bristol, Sch Med Sci, Dept Anat, MRC Ctr Synapt Plast, Bristol BS8 1TD, Avon, England
[2] Univ British Columbia, Brain Res Ctr, Vancouver, BC V6T 1Z3, Canada
[3] Univ British Columbia, Vancouver Hosp, Dept Med, Vancouver, BC V6T 1Z3, Canada
[4] Univ British Columbia, Hlth Sci Ctr, Vancouver, BC V6T 1Z3, Canada
[5] NIH, Bethesda, MD 20892 USA