At the very end of the curve laid three flies that spontaneously slept an average of 15, 14, and 4 min a day, respectively ( Fig. The distribution of sleep amount in females uncovered a previously undescribed fraction of extreme short sleepers: 50% of female flies slept less than 20% of their time and 6% slept for less than 5% of their time (72 min a day). As expected, in both males and females, sleep amounts were widely distributed, with male flies sleeping for 618.5 (CI 95%, 606.7 to 630.3) min a day and female flies sleeping for 299.2 (CI 95%, 288.8 to 309.6) min a day. 1B) CantonS flies, a commonly used laboratory “wild-type” strain. How much do flies really sleep when, besides their walking activity, we measure their micromovements too? To answer this question, we analyzed sleep for four consecutive days in 881 female ( Fig. To further improve our confidence in sleep estimation, we recently introduced a machine learning approach that uses supervised learning to detect not only walking activity but also micromovements (for example, in-place movements such as grooming, egg laying, and feeding) ( 24). A growing number of laboratories are therefore transitioning to more accurate systems based on computer-assisted video tracking ( 29– 33). This system, however, provides only limited spatial resolution that-unsurprisingly-results in an overestimation of sleep amounts ( 29). In Drosophila too, sleep can be estimated by measuring the absence of walking bouts, generally using a commercially available device to detect whenever an isolated fly crosses the midline of a tube ( 28).
Absence of movement is therefore routinely used as a proxy to measure sleep across a wide range of animals, spanning from jellyfish to elephants ( 17, 26, 27). Prolonged periods of inactivity are an evolutionarily conserved, experimentally convenient behavioral correlate of sleep ( 25). RESULTS Virtually sleepless flies are found in a nonmutant population Here, we report two surprising findings that were uncovered using this system, challenging the notion that sleep is a vital necessity: the discovery of virtually sleepless flies and the finding that chronic sleep restriction in Drosophila melanogaster has notably less pronounced effects on longevity than previously thought. To this end, we recently created a system that allows a faithful high-throughput analysis and manipulation of Drosophila sleep using activity as its behavioral correlate. Therefore, a technological development able to improve the characterization of these correlates may provide a more accurate description of sleep, laying the conditions for a more specific sleep deprivation procedure. Given that we still ignore what sleep does at the cell biological level, in all animals sleep quantification relies exclusively on bona fide macroscopic correlates, either electrophysiological or behavioral. In conclusion, chronic sleep deprivation experiments appear suggestive, but inconclusive, for multiple reasons. In pigeons, chronic sleep deprivation was shown not to be lethal ( 10). The observations in Drosophila are limited in terms of throughput and methodology ( 11). In the cockroach Diploptera punctata, sleep deprivation was achieved by continuously startling the animals ( 9), without, however, accounting for exhaustion-induced stress, a known lethal factor for other species of cockroaches ( 14– 16).
In rats and dog pups, death is associated with a severe systemic syndrome bearing important metabolic changes and clear signs of suffering, making it difficult to ultimately conclude whether lethality is caused by the mere removal of sleep or rather by the very invasive and stressful procedures used to keep the animals awake ( 7, 12, 13). In four of the five tested animal species, sleep deprivation experiments eventually terminated with the premature death of the animals, but the underlying cause of lethality still remains unknown. To date, experiments addressing this question have been reported in a handful of species only: dogs, rats, cockroaches ( 9), pigeons ( 10), and fruit flies ( 11). Unfortunately, the literature on the chronic effects of sleep restriction is not comprehensive, partly dated, and intrinsically complicated by the many confounding factors that correlate with sleep restriction. The study of chronic sleep deprivation could, at least in principle, address this challenge.
0 kommentar(er)
