[1] Univ Manchester, Fac Life Sci, Manchester M13 9PT, Lancs, England
[2] Royal Free & Univ Coll Med Sch, Auton Neurosci Ctr, London NW3 2PF, England
[3] Univ Milan, Dept Pharmacol Sci, Lab Mol & Cellular Pharmacol Purinerg Transmiss, I-20133 Milan, Italy
[4] JW Goethe Univ, Inst Zellbiol & Neurowissensch, Biozentrum, D-60438 Frankfurt, Germany