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The Journal of Neurophysiology Vol. 85 No. 1 January 2001, pp. 414-424
Copyright ©2001 by the American Physiological Society
Department of Anatomy and Cell Biology, Queen's University, Kingston, Ontario K7L 3N6, Canada
Joshi, I. and
R. D. Andrew.
Imaging Anoxic Depolarization During Ischemia-Like Conditions in
the Mouse Hemi-Brain Slice. J. Neurophysiol. 85: 414-424, 2001. Focal ischemia evokes a sudden loss of
membrane potential in neurons and glia of the ischemic core termed the
anoxic depolarization (AD). In metabolically compromised regions with
partial blood flow, peri-infarct depolarizations (PIDs) further drain
energy reserves, promoting acute and delayed neuronal damage.
Visualizing and quantifying the AD and PIDs and their acute deleterious
effects are difficult in the intact animal. In the present study, we
imaged intrinsic optical signals to measure changes in light
transmittance in the mouse coronal hemi-brain slice during AD
generation. The AD was induced by oxygen/glucose deprivation (OGD) or
by ouabain exposure. Potential neuroprotective strategies using
glutamate receptor antagonists or reduced temperature were tested.
Eight minutes of OGD (n = 18 slices) or 4 min of 100 µM ouabain (n = 14) induced a focal increase of
increased light transmittance (LT) in neocortical layers II/III that
expanded concentrically to form a wave front coursing through neocortex
and independently through striatum. The front was coincident with a
negative voltage shift in extracellular potential. Wherever the LT
front (denoting cell swelling) propagated, a decrease in LT (denoting
dendritic beading) followed in its wake. In addition the evoked field
potential was permanently lost, indicating neuronal damage. Glutamate
receptor antagonists did not block the onset and propagation of AD or
the extent of irreversible damage post-AD. Lowering temperature to 25-30°C protected the tissue from OGD damage by inhibiting AD onset.
This study shows that anoxic depolarization evoked by global ischemia-like conditions is a spreading process that is focally initiated at multiple sites in cortical and subcortical gray. The
combined energy demands of O2/glucose deprivation
and the AD greatly exacerbate neuronal damage. Glutamate
receptor antagonists neither block the AD in the ischemic core nor, we
propose, block recurrent PID arising close to the core.
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