Long-term intervention at high altitudes can inhibit the expression of IBA-1 in the hippocampus of rats and reduce seizure susceptibility
Authors: Xu YuanHang , Fan Qingli 
Published: December 2022

Abstract
Tens of millions of people around the world are affected by high-altitude hypoxia and epilepsy. Previous studies have shown that high-altitude hypobaric hypoxia can affect the homeostasis of the human central nervous system. However, there are no related studies on the excitability of human neurons and seizure susceptibility to natural high-altitude hypoxia. By using the natural experimental site on the Qinghai-Tibet Plateau, our team studied the pathological changes and seizure susceptibility in the hippocampus of rats under the long-term intervention of hypobaric hypoxia on the natural plateau from the aspects of protein expression, histomorphology, and animal behavior. and the linear correlation between the above changes was confirmed by statistical methods. This study is helpful to explore the mechanism of hypoxia adaptation at high altitudes and further clarifies the pathogenesis of epilepsy and has practical significance to explore the regional characteristics of potential epilepsy, antiepileptic drug therapy, and non-drug treatment of epilepsy.
Objectives: Epilepsy is caused by highly synchronized abnormal discharge of brain neurons. At present, its specific pathogenesis has not been clarified. However, the initial event of most epileptic seizures can be seen as an abnormal increase in neuronal excitability, neuroinflammation, oxidative stress, and damage-related molecular models (such as reactive oxygen species from oxidative stress products, activated M1 proinflammatory microglia, high mobility group box-1, etc.) are involved in neuronal loss, decreased excitation threshold and increased seizure susceptibility. In this study, we explored the changes of glial cell activation markers GFAP and IBA-1, the expression of AQP4 at the end of astrocytes, and the number of neurons in the hippocampus of SD rats under the long-term intervention of natural environment at high altitude, and analyzed the correlation between the above changes and the seizure susceptibility in rats. The aim was to study the linear relationship between the changes of hippocampal glial cell activation markers GFAP, IBA-1, AQP-4, hippocampal CA1, CA3, DG neurons, and seizure susceptibility in rats under the long-term intervention of natural hypobaric hypoxia at high altitude.
Methods: Three-week-old SD rats were exposed to the natural hypobaric hypoxia environment at a high altitude (Maduro County, Tibetan Autonomous Region, Golog Prefecture, Qinghai Province, China, 4260m above sea level) for 25 weeks. The control group rats were raised on the plain (Xi’an, Shanxi Province, China) for 25 weeks, and then epilepsy modeling, seizure susceptibility assessment, brain tissue sampling, immunohistochemical staining, Nissl staining, and other tests. In the first stage of the experiment, we studied the effects of different altitudes on the expression levels of astrocyte marker GFAP, astrocyte terminal foot AQP-4, microglial marker IBA-1, and the number of neurons in hippocampal CA1, CA3, DG regions of SD rats, and evaluated their seizure susceptibility, and analyzed the difference in seizure susceptibility of rats in each group and the linear correlation between them and the number of hippocampal GFAP, IBA-1, AQP4, and neurons. In the second stage of the experiment, we used trehalose and acetazolamide to inhibit the expression of GFAP, IBA-1, and AQP-4 in rats of high altitude hypoxia group for a long time respectively, and compared their seizure susceptibility with rats of high altitude hypoxia group to further clarify the relationship between the expression changes of GFAP, IBA-1, AQP4 and seizure susceptibility.
Results: Compared with the rats in the plain control group, long-term natural hypobaric hypoxia at high altitudes can reduce the expression of GFAP, IBA-1, and AQP4 in the hippocampus of SD rats, increase the number of neurons in the DG area of the hippocampus, prolong the latency of the first seizure of SD rats, reduce the total seizure grade score of SD rats (reduce the seizure susceptibility of SD rats), and the change in the expression of IBA-1 has a linear correlation with the difference in the seizure susceptibility of SD rats. In addition, long-term application of trehalose to the natural plateau environment intervention group can prolong the incubation period of the first attack of SD rats, and further reduce the expression of IBA-1 in the hippocampus of SD rats, but the difference is not statistically significant. Our study shows that long-term intervention in high altitude natural hypobaric hypoxia environment may reduce the expression of GFAP, IBA-1, and AQP-4 in the hippocampus and increase the number of neurons in the hippocampal DG region of SD rats by inhibiting neuroinflammation, oxidative stress, glial proliferation, cell swelling, and neuronal loss, and reduce the seizure susceptibility, in which the change of IBA-1 expression is involved in the process of seizure susceptibility. This study shows that long-term intervention in a natural hypobaric hypoxia environment at high altitudes may have a protective effect on brain tissue.