Effect of in vivo hypoxic preconditioning on changes in intracellular calcium content induced by long-term anoxia in rat brain slices

Abstract

We studied changes in intracellular calcium content induced by 10-min anoxia in olfactory cortex slices from rats exposed to single or 3-fold moderate hypobaric hypoxia ("ascend" at 5000 m). Repeated preconditioning with moderate hypobaric hypoxia produced a neuroprotective effect. This treatment abolished pathological calcium overload in brain slices induced in vitro by 10-min test anoxia.Much attention is paid to the phenomenon of brain resistance to ischemia/hypoxia [2,3,9,15]. Moderate hypoxia increases the resistance of brain neurons to further exposure to severe hypoxia or ischemia. The methodical procedure initiating tolerance of the brain to hypoxia received the name "hypoxic preconditioning". Our previous studies showed that long-term (10 min) anoxia of slices of the olfactory cortex from rats induces sustained hyperactivation of NMDA receptors and pathological calcium overload of neurons [13]. Preconditioning of slices with short-term anoxia performed 90 min before long-term anoxia mobilizes the immediate mechanisms of tolerance (including NMDA receptor-mediated mechanisms) and prevents pathological changes induced by long-term anoxia [3,14]. In vivo moderate hypoxia is an adequate model of preconditioning. Successful preventive strategy requires estimating the "dose" of in vivo hypoxic preconditioning, i.e., depth and duration of hypoxia and period of the development and persistence of a neuroprotective effect. These studies were previously performed in vitro [2][3][4]15]. Two-step experiment is suitable for the search of optimal regimen of hypoxic preconditioning and study the induced intracellular neuroprotective mechanisms.The animal is subjected to moderate hypobaric hypoxia, and then cultured brain slices are in vitro exposed to long-term anoxia [1].Here we studied whether preconditioning with moderate hypobaric hypoxia can increase the resistance of brain neurons to calcium overload induced by test anoxia in brain slices from experimental animals. We also compared the neuroprotective effects of repeated and single hypobaric preconditioning. We recorded changes in intracellular calcium content induced by test anoxia in brain slices from rats exposed to different regimens of preconditioning with moderate hypobaric hypoxia. MATERIALS AND METHODSExperiments were performed on male Wistar-Kyoto rats weighing 190-210 g. The animals were divided into 2 groups. Group 1 rats were exposed to single preconditioning with hypobaric hypoxia. Pressure in a flow altitude chamber was maintained at a level of 380 mm Hg for 2 h (corresponds to an altitude of 5000 m above see level). In group 2 rats this procedure was repeated 3 times with 24-h intervals. Non-preconditioned animals served as the control.The 2nd stage of the study was performed in vitro on the next day after preconditioning. The rats were decapitated and tangential slices of the olfactory cor-

Effect of hypobaric hypoxia on the development of long-term posttetanic potentiation in slices of rat olfactory cortex: Correction with hypoxic preconditioning

“…These abnormalities were less significant in preconditioned animals [1,9]. Moreover, hypobaric hypoxic preconditioning improves neuronal survival after severe HE [3,9] and contributes to the tolerance of neurons to severe anoxia in brain slices [2,6].…”