[1] Merck Res Labs, Dept Med Chem, W Point, PA 19486 USA
[2] Merck Sharp & Dohme Res Labs, Dept Med Chem, Ctr Res Neurosci, Harlow CM20 2QR, Essex, England
[3] Merck Res Labs, Dept Mol Pharmacol, W Point, PA 19486 USA
[4] Merck Sharp & Dohme Res Labs, Dept Pharmacol, W Point, PA 19486 USA
[5] Merck Sharp & Dohme Res Labs, Dept Pharmacol, Ctr Res Neurosci, Harlow CM20 2QR, Essex, England