Developmental and Regional Differences in the Vulnerability of Rat Hippocampal Slices to Brief and Prolonged Periods of Hypoxia

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Abstract
Population spikes (PS) were recorded in the pyramidal cell layer of the CA1 and CA3 areas in hippocampal slices prepared from 4-, 7- and 10-day-old and adult rats of the Sprague-Dawley strain during brief (< 10 min) and prolonged periods (30–60 min) of oxygen deprivation (hypoxia). In mature rats, PS were depressed by hypoxia in 6.8 min in the CA1 area and 9.8 min in the CA3 area. Subsequent recovery of PS after brief periods of hypoxia was correspondingly quicker and more complete in the CA3 area than in the CA1 area (respective mean recovery rate of PS in CA3 and CA1 regions after 30 min reoxygenation was 96.5 and 29.2% of original amplitude). Furthermore, the recovery rate of PS after prolonged periods of hypoxia in the CA1 area was only 24.6%. In the slices prepared from 4-, 7- and 10-day-old rats, PS in the CA1 area ceased completely in 240, 11.3 and 9.0 min, respectively, and those in the CA3 area ceased completely in 257, 283 and 109 min after oxygen deprivation. In 4-day-old animals, subsequent recovery of PS in the CA1 area after prolonged periods of hypoxia (60 min) was 73% of the original level. These results indicate that the immature brain is extremely resistant to brief and prolonged periods of hypoxia. This higher resistance of the CA1 neurons in the immature rat hippocampus to hypoxia drastically disappeared in the first week after birth, whereas this higher resistance of the CA3 neurons of immature rats gradually disappeared as the animal matured.

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