Abstract
Background: Our studies demonstrated that the space environment has an impact on the brain function of astronauts. Numerous ground-based microgravity and social isolation showed that the space environment can induce brain function damages in humans and animals. Dammarane sapogenins (DS), an active fraction from oriental ginseng, possesses neuropsychic protective effects and has been shown to improve depression and memory. This study aimed to explore the effects and mechanisms of DS in attenuating depressive-like behaviors and cognitive deficiency induced by simulated weightlessness and isolation [hindlimb suspension and isolation (HLSI)] in rats.Methods: Male rats were orally administered with two different doses of DS (37.5, 75 mg/kg) for 14 days, and huperzine-A (1 mg/kg) served as positive control. Rats were subjected to HLSI for 14 days except the control group during drug administration. The depressive-like behaviors were then evaluated by the open-field test, the novel object recognition test, and the forced swimming test. The spatial memory and working memory were evaluated by the Morris water maze (MWM) test, and the related mechanism was further explored by analyzing the activity of choline acetyltransferase (ChAT), acetylcholinesterase (AChE), and superoxide dismutase (SOD) in the hippocampus of rats.Results: The results showed that DS treatment significantly reversed the HLSI-induced depressive-like behaviors in the open-field test, the novel object recognition test, and the forced swimming test and improved the HLSI-induced cognitive impairment in the MWM test. Furthermore, after DS treatment, the ChAT and SOD activities of HLSI rats were increased while AChE activity was significantly suppressed.Conclusions: These findings clearly demonstrated that DS might exert a significant neuropsychic protective effect induced by spaceflight environment, driven in part by the modulation of cholinergic system and anti-oxidation in the hippocampus.
Highlights
In long-term space missions, astronauts are exposed to complex and extreme environmental conditions which can negatively affect their physiological and psychological state and performance [1]
In the open-field test (Figure 4), rats of the hindlimb suspension and isolation (HLSI) group covered less total movement distance, accompanied by less duration of movement and slower average speed compared with the control group (Figures 4A–C, p < 0.05 or p < 0.01)
In the center area of the open-field test, rats in the HLSI group covered shorter total movement distance, less duration of movement, and with slower average speed compared with the control group (p < 0.01) (Figures 5A–C)
Summary
In long-term space missions, astronauts are exposed to complex and extreme environmental conditions (microgravity, circadian dys-synchrony, isolation, and confinement) which can negatively affect their physiological and psychological state and performance [1]. A human study of simulated weightlessness with 15◦ head-down tilt and 45◦ head-up tilt profoundly affects the brain function and mental arithmetic with impairment of memory processes [5]. Simulated weightlessness increased cognitive impairment in rats [6]. Our studies demonstrated that the space environment has an impact on the brain function of astronauts. Numerous ground-based microgravity and social isolation showed that the space environment can induce brain function damages in humans and animals. This study aimed to explore the effects and mechanisms of DS in attenuating depressive-like behaviors and cognitive deficiency induced by simulated weightlessness and isolation [hindlimb suspension and isolation (HLSI)] in rats
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