Brain Advance Access originally published online on August 25, 2005
Brain 2005 128(10):2408-2420; doi:10.1093/brain/awh619
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The electrical response of cerebellar Purkinje neurons to simulated ischaemia
1 Department of Physiology, University College London, London, UK 2 Present address: Department of Cell Physiology, University of Leicester, Leicester, UK 3 Present address: Neurological Sciences Institute, Oregon Health and Science University, Beaverton, USA
Correspondence to: David Attwell, Department of Physiology, University College London, Gower Street, London WC1E 6BT, UK E-mail: D.Attwell{at}ucl.ac.uk
Despite lacking N-methyl-D-aspartate receptors, cerebellar Purkinje cells are highly vulnerable to ischaemic insults, which lead them to die necrotically in an 
-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid (AMPA) receptor-dependent manner. To investigate the electrical events leading to this cell death, we whole-cell clamped Purkinje cells in cerebellar slices. Simulated ischaemia evoked an initial hyperpolarization of Purkinje cells by 8.5 mV, followed by a regenerative ‘anoxic depolarization’ (AD) to –14 mV. The AD was prevented by glutamate receptor blockers. In voltage-clamp mode, we used the cells' glutamate receptors to sense the rise of extracellular glutamate concentration induced by ischaemia, with GABAA and GABAB receptors blocked and Cs+ as the main pipette cation. Ischaemia induced a small (<500 pA) slowly developing inward current in Purkinje cells, followed by a sudden large inward ‘AD current’ (
6 nA) which was largely prevented by blocking AMPA receptors. Removing extracellular calcium reduced the large glutamate-mediated current by 70% at early times (after 10 min ischaemia), but had no effect at later times (15 min). Blocking the operation of glutamate transporters, by preloading cells with the slowly transported glutamate analogue PDC (L-trans-pyrrolidine-2,4-dicarboxylate), reduced the current by 88% at early and 83% at later times. In Purkinje cells in slices from mice lacking the glial glutamate transporters GLAST or GLT-1, the ischaemia-evoked AD current was indistinguishable from that in wild-type slices. These data suggest that, in cerebellar ischaemia, the dominant cause of the electrophysiological dysfunction of Purkinje cells is an activation of Purkinje cell AMPA receptors. The glutamate activating these receptors is released both by exocytosis (at early times) and by reversal of a glutamate transporter, apparently in neurons.
Key Words: glutamate transporter; exocytosis; ischaemia; anoxia; cerebellum
Abbreviations:
AD = anoxic depolarization; NMDA = N-methyl-D-aspartate; AMPA = -amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid; EPSC = excitatory postsynaptic current; PDC = L-trans-pyrrolidine-2,4-dicarboxylic acid
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Received February 6, 2005. Revised June 7, 2005. Accepted July 19, 2005.
* These authors contributed equally to this work