[1] Johns Hopkins Univ, Sch Med, Solomon H Snyder Dept Neurosci, Baltimore, MD 21205 USA
[2] Kitasato Univ, Sch Med, Dept Anat, Sagamihara, Kanagawa 228, Japan
[3] Johns Hopkins Univ, Sch Med, Dept Neurol, Baltimore, MD 21205 USA
[4] Univ Tokyo, Dept Mol Neurobiol & Pharmacol, Tokyo, Japan