Figure 5.

Depolarization preconditioning protection from hypoxia does not depend upon GABA_A receptor modulation, adenosine A1 receptor activation, or extracellular Ca²⁺ influx. A. The non-competitive GABA_A antagonist picrotoxin (PTX ;100 μM), applied during hypoxia (2.5 hr), did not prevent depolarization protection. Summary of the indicated experimental conditions (n=6). “N.S.” indicates lack of significant difference in comparisons of the effect of PTX with the corresponding condition in the absence of PTX. B. The A1 receptor antagonists DPCPX (200 nM) did not block depolarization preconditioning protection. Summary of various 4 hr preconditioning conditions. Hypoxic insult was 2.5 hr (n=5). “N.S.” indicates a lack of difference for the indicated comparisons. C. Summary graph showing protection afforded by KCl depolarization preconditioning (n=5) independent of the addition of 1.8 mM extracellular Ca²⁺ to the Ca²⁺ free conditioning media. For all panels, neuronal survival was assessed 24 hr after insult with trypan blue exclusion. Asterisks denote p < 0.05 comparisons (Bonferroni corrected t-tests).