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Neural activity in hippocampal slices from hibernating Syrian hamsters (Mesocricetus auratus) is more tolerant to anoxia than slices from nonhibernating hamsters

During arousal from hibernation, when sympathetic signals fully activate brown adipose tissue to generate heat and shivering in muscle adds to oxygen consumption, the brain may, for brief periods, become anoxic. Whether hippocampal neural networks in the hibernating hamster (HH) exhibit greater hypoxic tolerance than do those in the euthermic hamster (EH) is not known. We tested the hypothesis that CA1 pyramidal cell responses in HH hippocampal slices are more tolerant to anoxia than those in EH slices. The HH group was housed in a 6°C cold room on a 8:16 light:dark cycle, and the EH in a 23°C room on a 14:10 L:D cycle. Population spike amplitude (PSA) in both HH and EU groups were measured at 30°C bath temperature each minute throughout the experiment. After a 15 min. control period in oxygenated (95%O2/5%CO2) buffer, oxygen was replaced with nitrogen (95%N2/5%CO2) for 15 min. Slices were then perfused with oxygenated buffer for a 30 min. recovery period. Three minutes after nitrogen exposure, PSA in HH slices dropped 5.0 ± 4.4 % (mean ± SE) from control, compared to a larger drop (20.3 ± 5.3%) in EH slices. Five minutes after nitrogen exposure, PSA in HH slices had dropped 32.2 ± 5.7% (mean ± SE) from control, versus 58.3 ± 8.0% in EH slices. Differences are significant (P<0.05), consistent with our hypothesis that hypoxic tolerance (and thus, neuroprotection) is enhanced in preparation for and/or during the hibernating state.