Imaging anoxic depolarization during ischemia-like conditions in the mousehemi-brain slice

Focal ischemia evokes a sudden loss of membrane potential in neurons and gl ia of the ischemic core termed the anoxic depolarization (AD). In metabolic ally compromised regions with partial blood flow, peri-infarct depolarizati ons (PIDs) further drain energy reserves, promoting acute and delayed neuro nal damage. Visualizing and quantifying the AD and PIDs and their acute del eterious effects are difficult in the intact animal. In the present study, we imaged intrinsic optical signals to measure changes in light transmittan ce in the mouse coronal hemi-brain slice during AD generation. The AD was i nduced by oxygen/glucose deprivation (OGD) or by ouabain exposure. Potentia l neuroprotective strategies using glutamate receptor antagonists or reduce d temperature were tested. Eight minutes of OGD (n = 18 slices) or 4 min of 100 muM ouabain (n = 14) induced a focal increase of increased light trans mittance (LT) in neocortical layers II/III that expanded concentrically to form a wave front coursing through neocortex and independently through stri atum. The front was coincident with a negative voltage shift in extracellul ar potential. Wherever the LT front (denoting cell swelling) propagated, a decrease in LT (denoting dendritic beading) followed in its wake. In additi on the evoked field potential was permanently lost, indicating neuronal dam age. Glutamate receptor antagonists did not block the onset and propagation of AD or the extent of irreversible damage post-AD. Lowering temperature t o 25-30 degreesC protected the tissue from OGD damage by inhibiting AD onse t. This study shows that anoxic depolarization evoked by global ischemia-li ke conditions is a spreading process that is focally initiated at multiple sites in cortical and subcortical gray. The combined energy demands of O-2/ glucose deprivation and the AD greatly exacerbate neuronal damage. Glutama te receptor antagonists neither block the AD in the ischemic core nor, we p ropose, block recurrent PID arising close to the core.