Abstract
This study aimed to investigate alterations in the activity and sleep of Drosophila melanogaster under simulated microgravity, which was implemented through the random positioning machine, while different light conditions (normal photoperiod and constant dark) were set. Fruit flies of different strains and sexes were treated for 3 days, and activity and sleep were monitored using the Drosophila Activity Monitoring System. After 3 days of treatment, fruit flies were sampled to detect the relative expression levels of the major clock genes and some neurotransmitter-related genes. The results showed that for the normal photoperiod (LD) condition, the activity increased and sleep decreased under simulated microgravity, while for the constant dark (DD) condition, the activity and sleep rhythms appeared disordered and the activity increased, thus decreasing the likelihood of waking up during the day. Light conditions, strains, and sexes, individually or in combination, had impacts on the simulated microgravity effects on behaviors. The clock genes and neurotransmitter-related genes had different degrees of response among sexes and strains, although the overall changes were slight. The results indicated that the normal photoperiod could ease the effects of simulated microgravity on fruit flies’ activity and sleep and possible unidentified pathways involved in the regulatory mechanism need further exploration. This study is expected to provide ideas and references for studying the effects of microgravity on space life science.
Highlights
Gravity is a relatively constant physical factor on Earth, and all living organisms are affected and well adapted to the gravitational field[1,2]
On the basis of our previous study that adopted random positioning machine (RPM) for simulated microgravity to investigate the alterations of activity and sleep of fruit fly[36], this study considered the roles of light conditions, fruit fly strains (Canton-S and w1118), and sexes play in the effects of simulated microgravity on sleep of fruit fly, through real-time activity and sleep behavior monitoring and detection of relative expression levels of target genes, including major clock genes and some neurotransmitter-related genes
Under normal photoperiod (LD) and constant dark (DD) conditions, the data monitored continuously for 3 days under simulated microgravity were selected for a statistical analysis of activity and microgravity during the day, and long sleep increased, which might because it was not easy for fruit flies to wake up when lack of light, or additional sleep was needed to supplement consumption or the energy to remain awake because of the high unit activity level
Summary
Gravity is a relatively constant physical factor on Earth, and all living organisms are affected and well adapted to the gravitational field[1,2]. Several studies have shown that astronauts have sleep disturbances during orbit, such as short sleep times, poor sleep quality and disruption of sleep[5,6,7,8,9,10,11]. Astronaut log data and actigraphy documents showed that the mean estimated sleep duration during orbit was reduced to ~6 h/night, which is 1.5–2 h less than the recommended 8 h and significantly less than the sleep time at ~3 months prior to and 1 week immediately after flight[5,6,9,12]. Some studies have shown that sleep time fluctuates greatly each night and sleep characteristics change, which might further increase the likelihood of waking neurobehavioral performance deficits[7,10,13,14]. The likelihood and consequence of performance errors due to sleep disturbances are dangerous[6,13,15]
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