1 The Solomon H. Snyder Department of Neuroscience, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
2 Department of Neurobiology, Stanford University, Stanford, CA 94305, USA.
3 Department of Neurobiology, Stanford University, Stanford, CA 94305, USA; Department of Ophthalmology, Stanford University, Stanford, CA 94305, USA.
4 The Solomon H. Snyder Department of Neuroscience, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA. Electronic address: kolodkin@jhmi.edu.