The Study On Simulated Spaceflight Environment Induced Depression And Cognitive Decline In Rats

In the medium-term and long-term mission,the astronauts were constantly exposed to complex spaceflight environments such as microgravity,high-load extravehicular operations,boring and lonely narrow space,which greatly challenge the astronauts’ health,and could causephysiological stress effects in central nerve system,circulation system and immune system,and may lead to anxiety,depression,and even cognitive decline.This study aimed to discusssimulated spaceflight environments induced depression and cognitive function in rats.Objective: To study the effects of simulated spaceflight environment including simulated weightlessness in combination with behavioural constraints on depression and cognitive function in rats and the possible mechanisms.Methods: The rats were divided randomly into seven groups,the control group,the isolation group(I),the behavior constraints group(6h daily,BC),the tail suspension group(the sham group),the simulated weightlessness group(hindlimb suspension by tail and isolation,HLSI),the sham + BC group,the HLSI + BC group,eight rats in every group.The rats were encountered these seven different treatments,14 days later,the behavior tests performed to evaluate the depressive-like and cognitive behavior in rats.1.The effects of simulated spaceflight environment induced depressive-like behavior in rats: the sucrose preference test,the locomotor activity test and the novelty exploration test were carried out to evaluate the depressive-like behavior in rats.2.The effects of simulated spaceflight environment on cognitive function in rats:the rewarding conditioned reflex and the shuttle box active avoidance test were performed to evaluate the cognitive function in rats.3.Mechanisms studies:(1)The concentration of serum corticosterone(CORT)and adrenocorticotropic(ACTH)were measured using enzyme-linked immunosorbent assay(ELISA)kits.(2)The MDA and SOD activities in the cerebral cortex of rats were determined bybiochemical methods.(3)Brain neurotransmitters including 5-HT,DA,NE,E,ACh,GABA and Glu were determined by HPLC analysis.Results: 1.The effects of simulated spaceflight environment induced depressive-like behavior in rats: Behavioral constraintsfor 6hevery day for 14 d led to the decrease of the body weight in the rats of the BC group.HLSI+ BC for 6hevery dayfor 14 d led toreduce of the body weight,decrease locomotor activity level in the open field test and novel objects exploration.2.The effects of simulated spaceflight environment on cognitive function in rats: HLSI+BC for 6hevery dayfor 14 d severely damaged the ability of conditioned reflex formation,and led to decrease the number of CNPs,INPs and TNPs in rewarding conditional reflex test,while had no effect in the shuttle box passive avoidance test.3.Mechanisms studies:(1)HLSI 14 d led to the secretion of serum CORT and ACTH in rats.(2)The MDA and SODactivity in the cortex wasno significantly changes in theBCgroup,the HLSI group and the HLSI + BC group.(3)The levels ofneurotransmitter such as GABA and Glu inthe cerebral cortex were significantly reduced in the HLSI group and the HLSI + BC group.Conclusion: 1.HLSI or HLSI + BC for 6hevery dayfor 14 d could induce the depressive-like behavior and lead to the cognitive ability decline in rats in the rewarding conditioned reflex test,but had no effect on the shuttle box active avoidance test.2.The possible mechanisms of the simulated spaceflight environment induced behavior changes may related to the increase the CORT and ACTH level in the serum in rats,as well as the decrease of GABA and Glu level in cerebral cortex in rats.