Effects Of Oxygen Enrichment Intervention Of Membrane Oxygenerator On Cognitive Function And Hippocampal Structure In Rats Under Acute Hypobaric Hypoxia

The natural environment of the plateau is special.The main climatic features that have great impact on human body include low temperature,strong ultraviolet radiation,low atmospheric pressure,low oxygen partial pressure,etc.with the hypoxia showing the greatest threat to human health.The acclimatization mechanism of the body to the hypoxia environment has not yet been established at the early stage of acute exposure to the plateau,which is prone to induce acute mountain sickness.The central nervous system has the least resistance to hypoxia among all systems in human body.The current studies demonstrated that acute hypoxia exposure in the plateau could affect almost all functional activities of the body.Changes in high-level neurological activities often occur at the early stage under hypoxia stimulation.Slight hypoxia stimulation may cause different degrees of injury of neuronal cells.Irreversible damage or even death of neuronal cells may also induced by severe hypoxia stimulation.Cognitive impairment caused by acute hypoxia is a serious threat to the work efficiency and physical and mental health of people acutely exposed to the plateau,and even worse,is life-threatening.With the development of plateau medicine in China,the research on plateau anti-hypoxia technology and equipment is progressing continuously.Numorous studies have found that the plateau oxygen enrichment intervention could show preventive and protective effects on the cardiopulmonary physiological function and structure of the crowd rapidly exposed to the plateau.Nevertheless,few studies have reported how oxygen-enriched intervention affects the cognitive function and brain structure of the body.Therefore,the preventive and protective effects of oxygen-enriched intervention on cognitive dysfunction and brain structural damage caused by acute hypoxia in the plateau need to be further confirmed.In this study,the diffuse oxygen-enriched environment under plain conditions,the simulated low-pressure hypoxia environment and the simulated oxygen-enriched environment under low-pressure and low-oxygen conditions were established,respectively.Then the environmental parameters(e.g.oxgyen concentration,altitude,temperature,etc.)of the three platforms were tested continuously.We have found that the oxygen concentration and temperature of the three systems could maintain stability after 12-hour continuous operation.Meanwhile,an acute hypoxia rat model was also established.The reliability of the experimental platform was verified by detecting the spontaneous coordination activities,which provided hardware support for subsequent animal experiments.Secondly,effective oxygen-enriched intervention on the acute hypoxia animal model was performed by using a portable membrane oxygenerator.The effect of oxygen-enriched intervention on the spatial learning and memory ability,hippocampus structure and Tau protein phosphorylation expression levels of rats under simulated acute hypobaric hypoxia environment were also studied.Our results indicated that oxygen-enriched intervention can significantly reverse the spatial learning and memory dysfunction and rescue the damage effects of acute hypoxia on the hippocampal formation and neuronal ultrastructure.The research provided a theoretical basis for maintaining the physical and mental health of the people acutely exposed to plateau,and also provided scientific methods and experimental evidence for the further application of the anti-hypoxia series equipment in the plateau region.This study was divided into the following two parts:Part 1: Establishment of diffuse oxygen-enriched environment and acute hypoxiaanimal model under simulated hypobaric hypoxia plateau conditions Background: Numerous studies have demonstrated that the hypoxia environment in the plateau could seriously affect the normal physiological functions of the nervous,respiratory,digestive,urinary and circulatory systems of the people who rapidly access to plateau.Therefore,it is of vital significance to systematically study the mechanism of hypoxia damage on the organism and explore scientific and effective methods of oxygen-enriched intervention to maintain normal physiological functions and health of the human body.Therefore,it is of great economic and scientific value to establish an effective acute hypoxia animal model and construct the corresponding diffuse oxygen-enriched environment for studying the damage mechanism of the organism acutely exposed to the plateau and explore related intervention methods.Methods: Firstly,the diffuse oxygen-enriched environment was created by connecting the the outlet end of the portable membrane oxygenerator and the inlet of the IVC cagea.Secondly,the oxygen-enriched cage was placed in a low-pressure chamber,and the membrane oxygenerator was operated in cooperation to establish the diffuse oxygen-enriched environment under hypobaric hypoxia condition.Then,the oxygen concentration and temperature of the oxygen-enriched cage were tested at various altitudes,followed by the establishment of an acute hypoxia rat model and the detection of its spontaneous coordination activity after oxygen-enriched intervention.Results: Our results showed that the oxygen concentration in the oxygen-enriched cage could reach to 30.72% within 20 minutes under plain condition,and the oxygen concentration was relatively stable.The oxygen concentration in the low-pressure chamber was consistent with the plain but the pressure was significantly reduced,while the oxygen concentration in the oxygen-enriched cage decreased slightly with the increase of altitude(but it could still be maintained at 28.41% with the simulated altitude 6000 m),and the oxygen concentration in the oxygen-enriched cage was basically stable at a fixed altitude.In addition,oxygen-enriched intervention could effectively alleviate the negative effects of hypoxia on body weight and spontaneous activities in rats.Conclusion: Through the establishment of three oxygen environments and an animal model of acute hypoxia,a scientific and effective experimental platform and technology were established for the subsequent study of the effects of oxygen enrichment intervention on the cognitive function and brain structure related to spatial learning and memory in rats.Part 2: Effects of oxygen enrichment intervention of membrane oxygenerator on spatiallearning and memory ability and hippocampal structure in rats under acute hypobarichypoxia Background: At present,studies on the effects of oxygen-enriched environment on the organism were mostly concentrated on cardiopulmonary function.Nevertheless,researches on whether oxygen-enriched intervention could improve brain structure and learning and memory impairment induced by acute hypoxia,especially the mechanism of oxygen enrichment on brain structure and function were seldom studied.Methods: After the navigation training through Morris water maze,the rats were exposed to acute hypoxia environment and oxygen-enriched intervention,respectively.Then their spatial learning and memory abilities were detected.Additionally,the effects of acute hypoxia and oxygen-enriched intervention on the hippocampal structure and the ultrastructure of nerve cells in rats were observed.Meanwhile,the phosphorylation expression levels of Tau protein(which is closely related to cognitive function)at four important sites was analysed via western blotting assays at the molecular level.Results: The results of the space exploration capability test showed that the counts of the rats crossing the underwater platform of the Morris water maze was significantly reduced after acute hypoxia exposure,and this negative effect was dramatically reversed by the oxygen-enriched intervention.The results of HE staining showed that the pyramidal cells in the hippocampal CA1 region were dispersedly arranged after acute hypoxia exposure.The volume of the nucleus was also reduced with the staining deepened,the cytoplasmic boundary unclear,and a large number of vacuole formation.The number of denatured pyramidal cells was also significantly increased after acute hypoxia exposure.However,the structural damage was significantly reduced by oxygen-enriched intervention.The results of transmission electron microscopy scanning showed that neuronal cellular structure and mitochondrial morphology were significantly destroyed by acute hypoxia,while the negative effects was remarkably reversed by oxygen-enriched intervention.The results of western blotting showed that the abnormal phosphorylation of Tau protein at different sites could be detected after acute hypoxia exposure.However,no significant effects on the expression of total Tau protein in the hippocampal was observed under neither hypoxia nor oxygen enrichment treatment.The expression level of phosphorylation of Tau protein could also significantly reduced by the effective oxygen enrichment intervention.Conclusion: Oxygen-enriched intervention with membrane oxygenerator can significantly alleviate the spatial learning and memory dysfunction,abnormal hippocampal structure,nerve cell morphology and mitochondrial structure of rats induced by acute hypobaric hypoxia exposure,which has significantly protective effects on the cognitive function of rats caused by acute hypobaric hypoxia.