Sweetness induces sleep through gustatory signalling independent of nutritional value in a starved fruit fly

Tatsuya Hasegawa,Taro Ueno,Jun Tomita,Kazuhiko Kume,Rina Hashimoto,Shoen Kume

doi:10.1038/s41598-017-14608-1

Tatsuya Hasegawa, Taro Ueno + Show 4 more

Open Access

https://doi.org/10.1038/s41598-017-14608-1

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Abstract

Starvation reduces sleep in various animal species including humans and fruit flies. Immediate hunger and the following insufficient nutritional status resulting from starvation may affect sleep and arousal differently. In order to clarify the mechanism underlying the relationship between diet and sleep, we analysed the sleep behaviour of Drosophila melanogaster that were either starved or fed with different types of sugars. Starved flies showed longer activity bouts, short sleep bouts and a decreased arousal threshold. Non-nutritive sweeteners such as sucralose and arabinose, which are sweet but not nutritive, induced sleep in starved flies, but sleep bout length and the arousal threshold was short and decreased, respectively. On the other hand, sorbitol, which is not sweet but nutritive, did not induce sleep, but slightly increased the lowered arousal threshold. Activation of sweetness receptor expressing neurons induced sleep in starved flies. These results suggest that sweetness alone is sufficient to induce sleep in starved flies and that the nutritional status affects sleep homeostasis by decreasing the arousal threshold, which resulted in short sleep bouts in Drosophila.

Highlights

The dietary regulation of sleep is a universal phenomenon that occurs in a variety of animals
On day 0, flies were kept in tubes with 150 mM sucrose/1% agar food and on day 1 they were transferred to another tube with 1% agar food containing different sugars
Previous studies by Keene et al reported that a low concentration of sucralose (1 mM) could not drive sleep[21]

Summary

Introduction

The dietary regulation of sleep is a universal phenomenon that occurs in a variety of animals. We reported that a high calorie diet decreases sleep[24]. Sugars have both sweet taste and nutritional value, and naturally occurring sugars usually possess both. Flies can assess sweetness and nutritional value separately and they differentially react to them[25,26,27] They sense sweetness through gustatory taste receptors[28,29,30]. Linford et al reported that, in addition to nutritional (metabolic) value, gustatory perception is required for behavioural changes[33]. We examined how sweetness and nutrient value regulate sleep and wake behaviour differently in Drosophila melanogaster

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