Conditioning hypoxia causes protection against ischemia in the CA(1)-region of hippocampal slices

Purpose: At present the mechanisms of ischemic or hypoxic tolerance are not fully understood at the cellular level. Methods: In order to further characterize the effects of conditioning hypox ia on the synaptic transmission in the hippocampal area CA1, rats were expo sed to a moderate normobaric hypoxia for 8 h. Transverse hippocampal slices were prepared 1, 7 or 14 days after this conditioning hypoxia and evoked f ield potentials were recorded in the CA1 region upon stimulation of the Sch affer collaterals before, during and up to 4 h after ischemia in vitro (hyp oxia and reduced glucose). Results and Conclusions: The time to disappearance of the evoked potential during ischemia was significantly prolonged after seven, but not after one or 14 days in slices taken from conditioned animals. In addition the input/ output (I/O) curves of evoked potentials were not altered 4 h after the isc hemia. In contrast, the time to disappearance of the evoked potentials was shorter and the I/O curves were diminished in slices from control animals. Possible mechanisms of the protective effect are discussed.