ABSTRACT
Objective To observe the different characteristics of spontaneous activitiy after simulated weightlessness 21 days in rats , aimed to provide a evaluation method for space weightlessness induced function change in human beings and to provide a reference for researches on the astronauts protective measures .Methods 30 Wistar male rats were randomly divided into three groups , the control group , the sham tail-suspended hindlimb unloading group ( the sham group ) , the tail-suspended hindlimb unloading group ( the suspending group ) , ten animals in each group .All animals were placed in the simulated space flight environmental equipment which has a real -time monitor system for 21 days.During the 21 days, the intake of water , food and the body weight were measured every week .Meanwhile, five independent activity data were collect every day , for example, morning(8:00am~12:00am), afternoon(2:00pm~6:00pm), daytime(8:00am~8:00pm),night(8:00pm~8:00am),and whole day (8:00am ~8:00am).Results The spontaneous activity of normal rats in the control group between morning and afternoon had no significant difference , but it is significantly between night and daytime .The movement time and distance in night are 2 -3 times than that of the daytime.After 10 days of tail suspending , the circadian rhythm was disordered , and the spontaneous activity in day and night become more similar in rats of the suspending group .Because of the individual difference , the spontaneous activity is not stable at the first 10 days in rats of the sham group , but after 10 days, it become close to the control group .Conclusion Rat is nocturnal animal and sleeps in the daytime , the spontaneous activity in night is 2 -3 times as compared with the daytime.The sham tail-suspended hindlimb unloading 21 days can not influence the circadian rhythm in rats .Tail suspending 21 days will caused to the disappearance in the circadian rhythm in rats .