Posthypoxic Moderate Hypothermia Improves Electrophysiological Recovery in the Rat Hippocampal Slice

Abstract

Animal studies have shown that prehypoxic or intrahypoxic hypothermia is protective against hypoxic neuronal injury, whereas posthypoxic hypothermia produced divergent findings. This study examined the protective effects of posthypoxic hypothermia on the electrophysiological recovery in the rat hippocampal slice. Eighty-three male Sprague-Dawley rats were used after approval of the Institutional Animal Care and Use Committee. Hippocampal slices were obtained and electrophysiological recordings from the CA1 pyramidal cell layer were used as an indicator of cell function. Moderate hypothermia (30°C) was used for only 30 minutes after hypoxia in the study group, whereas normothermia was maintained throughout the experiment in the control group. Three different periods of hypoxia were used (3, 3.5, and 4 min). Recovery was measured as the ratio of the amplitude of the population spike at the end of 2 hours of recovery to that of the baseline that was obtained immediately before hypoxia. Posthypoxic hypothermia improved electrophysiological recovery in slices exposed to 3 minutes of hypoxia but not in those exposed to 3.5 or 4 minutes of hypoxia. Moderate hypothermia (30°C) applied after hypoxia is protective against short periods (3 min) of hypoxia but not after slightly longer periods (3.5 or 4 min) of hypoxia.