Figure 4. Effect of nitrous oxide, when present only during 4.5 min of hypoxia, on recovery of the evoked population spike recorded in the CA1 region of rat hippocampal slices. Slices were subjected to 50% nitrous oxide (solid line) only during the hypoxic period. This is described as experimental series 3 in Materials and Methods. In nitrogen-treated slices, nitrogen was substituted for nitrous oxide. Control slices, made hypoxic without nitrous oxide (dashed line) did not demonstrate significantly better recovery of the population spike than did the nitrous oxide-treated slices. The oxygen concentration was the same in both groups throughout the experiment and 5% carbon dioxide was present in all gas mixtures. The x axis shows the time after slice preparation and the percentage of oxygen in the gas mixture. Values shown are means +/- SEM; n = 10 animals per group.