The Protective Effect Of Oxygen Inhalation Preconditioning On Ischemia-Reperfusion Injury In The Brain And Its Possible Mechanism

BACKGROUNDIschemia / reperfusion injury in central nervous system often leads to neurologic deficits which seriously influence the quality of life and even threaten the life of patients. More and more attentions focus on the prevention and therapy of the central nervous system ischemia-reperfusion injury. Many drugs and measures have proved to be protective to neurons from ischemia-reperfusion damage, but the clinical application of them is hardly accepted because of their toxicity or side effects. The hyperbaric oxygen is also able to mimic ischemic preconditioning to induce neuroprotection against ischemia injury. But, hyperbaric oxygen preconditioning needs hyperbaric oxygen chamber that limits the clinical application. We hypothesized that high concentration of oxygen inhalation for long enough might result in the similar effect with that induced by hyperbaric oxygenation preconditioning. Therefore, we designed the experiments to investigate whether pure oxygen pretreatment induces ischemic tolerance in focal cerebral ischemia and to study the possible mechanism.OBJECTIVE-6-1. To study the protective effect of preconditioning with inhaling 100% oxygen on focal cerebral ischemic injury.2. To study whether the oxygen free radicals play an important role in the ischemia tolerance induced by oxygen inhalation preconditioning.3. To investigate whether oncogene c-fos involved hi the signal transmission of oxygen-inhaling preconditioning and the influence of oxygen-inhaling preconditioning to the functional activity condition on different brain areas.4. To observe the effect of oxygen inhalation preconditioning on the activation of astroglia.METHODS1. To study the protective effect of preconditioning with inhaling 100% oxygen on focal cerebral ischemic injury.Thirty-six male SD rats were randomly allocated to 4 groups (?9 in each group): Group A(control group), the animals inhaled room air for 24 h; Groups B, C and D, the animal inhaled 100% oxygen for 24h, 12h and 6h respectively. 24h after cerebral ischemia, all rats subjected to middle cerebral artery occlusion (MCAO). The MCAO (120min) was induced by introducing a 3-0 nylon mono-filament suture through internal carotid artery based on the Koizumi technique. The neurologic outcome was evaluated until 24 hours after reperfusion. The infarct volume was then assessed by TTC staining.2. To study whether the oxygen free radicals play an important role in the ischemic tolerance induced by oxygen inhalation preconditioning.Thirty-two male Sprague-Dawley rats were randomly assigned to 4 groups (n=8 each): Group A, control, rats received normal saline (5ml/kg) i.p. and theninhaled room air for 24h; Group B, animals received normal saline (5ml/kg) i.p. and then inhaled 100% oxygen for 24 h; Group C, animals received dimethylthiourea (DMTU, 10% solution 500mg/kg) i.p. followed by inhaling 1 00% oxygen for 24 h; Group D, animals received dimethylthiourea (500mg/kg) i.p. and then inhaled room air for 24 h. Twenty-four hours after the treatments, all the animals subjected to transient MCAO. The neurologic outcome and infarct volume were evaluated at 24 h after reperfusion.3 . To investigate whether oncogene c-fos involved in the signal transmission of oxygen-inhaling preconditioning and the influence of oxygen-inhaling preconditioning to the functional activity condition on different brain areas.The SD rats were randomly divided into 2 groups: oxygen-inhaling preconditioning group and control group (?6 each). The rats in oxygen-inhaling preconditioning group inhaled 100% 62 for 24 h, while control animals inhaled 21% OT for 24 h. 24h after the treatment, all the rats were perfused transcardially and the brains were moved out. The Fos protein, which is the production of oncogene c-fos and often used as a marker for the cells under functional activity condition, was observed in rat brain by using ABC immunohistochemistry method.4. To observe the effect of oxygen inhalation preconditioning on the activation of astroglia.