0078 Proboscis Extensions During Sleep: A Novel Sleep Stage In Drosophila With A Functional Role In Waste Clearance?

• Published in: Sleep (New York, N.Y.) Vol. 41; no. suppl_1; pp. A31 - A32
• Main Authors: van Alphen, B, Allada, R
• Format: Journal Article
• Language: English
• Published: US Oxford University Press 27.04.2018
• Subjects: Insects; Sleep; Traumatic brain injury
• ISSN: 0161-8105; 1550-9109
• DOI: 10.1093/sleep/zsy061.077

Abstract Introduction Although the exact function of sleep remains the topic of a lively debate, its proposed functions include memory consolidation and metabolite clearance. Sleep in Drosophila has many hallmarks of mammalian sleep, including homeostasis, altered brain activity, stages of lighter and deeper sleep and increased arousal thresholds. We observed that sleeping flies repeatedly and spontaneously extend their proboscis in a stereotypical manner, without any apparent stimulus, e.g, food exposure. Drosophila, like other arthropods, does not have a sophisticated vasculature or lymphatic system to transport nutrients and waste products. Instead, its organs are bathed in hemolymph and the fly only has a simple, open circulatory system to cycle this around. Here, we explore whether proboscis extensions (PE) during sleep act as a waste clearance mechanism. Methods To study PE, we tethered single flies and observed their behavior using video tracking, arousal threshold measurements and electrophysiology to test whether this behavior qualifies as a sleep stage. We also subjected the flies to different stressors to test their effect on PE. Results Flies are immobile during PE, their arousal thresholds are greatly increased and brain activity is quiescent. Together, these results are indicative of a deep sleep stage. Also, inducing sleep by administering gaboxadol greatly increases PE. We found that PE increase during physiological stress, such starvation/desiccation, increased ambient temperature or CO2 levels, increased reactive oxygen species, amyloid-beta buildup or after traumatic brain injury (TBI). Preventing PE from occurring by immobilizing the proboscis increases 24 hour post-TBI mortality, suggesting that PE is part of a protective process. Conclusion Our data suggest that a distinct sleep stage exists in Drosophila, where it uses its proboscis as a pump to increase the rate at which hemolymph flows through its body, increasing waste clearance. We are currently investigating whether proboscis extension during sleep accomplishes waste clearance to optimize waking brain function and recovery from injury. Support (If Any) This study is funded by an RO1 from NIMH to RA (R01 MH092273-01A).