Protection by rapid chemical preconditioning of stressed hippocampal slice: A study of cellular swelling using optical scatter imaging

It has been demonstrated that anoxic preconditioning protects against a subsequent 'lethal' injury in the hippocampal slice. The goal of this paper was to test the hypothesis that chemical preconditioning could help reduce the cellular swelling observed in excitotoxically injured hippocampal slices. The control slice was given a 10-min insult of 100 μM N-methyl-D-aspartate (NMDA) to simulate ischemic injury, followed by 30-min perfusion of standard Ringers solution. Cellular swelling was observed with a microscope designed to image light scatter changes resulting from cellular swelling. After the control NMDA injury, the average peak scatter change for CA1, CA3 and DG regions was 31.0±3.4, 22.4±4.8 and 27.6±4.6%, respectively. The peak scatter change of the overall slice was 26.0±3.6%. The experimental slices were preconditioned by three short 100 μM NMDA insults of 15 s each separated by 10 min of standard Ringers solution perfusion. The slices then received 10 min of 'lethal' injury by 100 μM NMDA. It was observed that the overall scatter signal, as a measure of cellular swelling, was reduced by 8.0% (P<0.05, n=11) after preconditioning. A regional heterogeneity in the responses was also observed. Cellular swelling in CA1, CA3 and DG were reduced by 9.8% (P<0.001, n=11), 9.2% (P<0.005, n=11) and 7.7% (P<0.05, n=11), respectively, when compared to the control. This study presents experimental evidence that short episodes of preconditioning may protect against acute cellular swelling under ischemic conditions.