Abstract
The present study aimed to investigate the effect of microglia on simulated microgravity-induced hippocampal neurogenesis reduction and the possible mechanism underlying. Adult rats were treated with tail suspension for different times and the changes of neural stem cells (NSCs) were examined by immunohistochemistry. Then, minocycline was used to inhibit the activation of microglia, and the numbers of microglia and NSCs were detected after microgravity. Additionally, liquid protein chip analysis was applied to detect proinflammatory factors in hippocampus in order to find out the cytokines responsible for microglia activation after microgravity. The results revealed that microgravity increased the numbers of Iba1+ cells and decreased the numbers of BrdU+ and DCX+ cells in hippocampus but did not affect the ratio of NeuN+/BrdU+ cells to the total number of BrdU+ cells. After treated with minocycline, activated microglia were suppressed and the reduction of NSCs induced by microgravity recovered. Besides, compared with the control, higher concentrations of INF-γ and TNF-α were detected in the rats treated with microgravity. Our study provides the first evidence that microglia-mediated inflammation plays an important part in microgravity-induced neurogenesis reduction in hippocampus, and INF-γ and TNF-α secreted by microglia might be the key factors in this process.
Highlights
With the extent of space exploration, the health and safety of space explorers exposed to a microgravity environment is drawing more and more attention
In the TS groups, compared with the control group (Figures 2(a)–2(c)), the numbers of BrdU+ cells significantly decreased in the dentate gyrus after 7 d, 14 d, and 28 d tail suspension (Figures 2(d)–2(f ))
As hippocampal neurogenesis is closely related to animals’ ability to learn and memorize, in the present study, we firstly demonstrated that microgravity inhibited the proliferation of adult hippocampal neural stem cells (NSCs) in rats, which may tentatively explain the detrimental effects of microgravity on learning and memory
Summary
With the extent of space exploration, the health and safety of space explorers exposed to a microgravity environment is drawing more and more attention. Learning and memory ability in adult mammals has great relation to the neurogenesis of the dentate gyrus in the brain, where granule neurons are generated throughout life from a population of neural stem cells (NSCs) [5]. NSCs in the subgranular zone (SGZ) of the dentate gyrus differentiate into newborn neurons, integrate into the existing circuitry, and receive functional input [6]. Erefore, we wonder whether the hippocampal neurogenesis decreases after exposure to microgravity, resulting in the impairment of learning and memory ability. To test this hypothesis, in the present study, we exposed adult rats to microgravity and observed the changes in proliferation, migration, and differentiation of NSCs and tried to uncover the possible underlying mechanism
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