[1] Univ Cattolica Sacro Cuore, Dept Anat & Cell Biol, I-00168 Rome, Italy
[2] UCL, Wellcome Lab Mol Pharmacol, London WC1E 6BT, England
[3] Univ Sheffield, Dept Mol Physiol, Sheffield S10 2TN, S Yorkshire, England
[4] Royal Free & Univ Coll Med Sch, Auton Neurosci Inst, London NW3 2PF, England