1. Department of Zoology, University of Nottingham, University Park, Nottingham NG7 2RD; Department of Pharmacology, University of Cambridge, Hills Road, Cambridge CB2 2QD
2. Department of Zoology, University of Nottingham, University Park, Nottingham NG7 2RD; Parke-Davis Research Unit, New Addenbrookes Hospital Site, Cambridge
3. Department of Zoology, University of Nottingham, University Park, Nottingham NG7 2RD
4. Department of Zoology, University of Nottingham, University Park, Nottingham NG7 2RD; The Tokyo Metropolitan Institute of Medical Sciences, Bunkyo-Ku, Tokyo, Japan