Jeffrey D Rothstein1
& Evan Y Snyder21
J.D.R. is in the Department of Neurology at Johns Hopkins University, Meyer 6-109, 600 N. Wolfe St., Baltimore, Maryland 21287, USA. jrothste@jhmi.edu
2
E.Y.S. is Director of the Program in Developmental and Regenerative Cell Biology, The Burnham Institute, 10901 North Torrey Pines Road, La Jolla, California 92037, USA. esnyder@burnham.org