Experimentally induced active and quiet sleep engage non-overlapping transcriptional programs inDrosophila

Abstract

Sleep in mammals is broadly classified into two different categories: rapid eye movement (REM) sleep and slow wave sleep (SWS), and accordingly REM and SWS are thought to achieve a different set of functions. The fruit flyDrosophila melanogasteris increasingly being used as a model to understand sleep functions, although it remains unclear if the fly brain also engages in different kinds of sleep as well. Here, we compare two commonly used approaches for studying sleep experimentally inDrosophila: optogenetic activation of sleep-promoting neurons and provision of a sleep-promoting drug, Gaboxadol. We find that these different sleep-induction methods have similar effects on increasing sleep duration, but divergent effects on brain activity. Transcriptomic analysis reveals that drug-induced deep sleep (‘quiet’ sleep) mostly downregulates metabolism genes, whereas optogenetic ‘active’ sleep upregulates a wide range of genes relevant to normal waking functions. This suggests that optogenetics and pharmacological induction of sleep inDrosophilapromote different features of sleep, which engage different sets of genes to achieve their respective functions.

Multivariate classification of multichannel long-term electrophysiology data identifies different sleep stages in fruit flies

“…Additionally, the effect observed during induced sleep was only observed in the central channels whereas the spontaneous sleep effects appear to at least cover the entire hemisphere from center to periphery. This shows that genetically-induced sleep in flies can produce strikingly different electrophysiological signatures than spontaneous sleep, consistent with several previous similar observations (Tainton-Heap et al 2021;Yap et al 2017;Anthoney et al 2023;Lin, Panula, and Passani 2015;Troup et al 2018). For the rest of this current study, we focus on spontaneous sleep.…”

“…This suggests that PEs occurring during sleep are qualitatively different from identical PE events occurring during wake. This suggests that the brain activity state (e.g., quiet or deep sleep (Tainton-Heap et al 2021;Anthoney et al 2023)) overrides the neural correlates associated with the same behavior occurring during wake.…”

Homeostatic control of deep sleep and molecular correlates of sleep pressure in Drosophila

“…The fact that lower levels of mechanical stimulation failed to produce rebound over one full cycle, despite having produced similar amounts of sleep deprivation, suggests that high-frequency physical perturbation produces sleep-independent behavioral effects that might mask bona fide homeostatic sleep increases. Alternatively, it is also possible that during lower stimulation frequencies, flies may increase their levels of the recently hypothesized ‘active sleep’ state (inactivity of between 1 and 5 min in duration associated with physiological changes) ( Anthoney et al, 2023 ; Tainton-Heap et al, 2021 ) and that this may prevent the build-up of sleep pressure and rebound. We examined the levels of such sleep during and after deprivation using 220 s stimulation frequencies and found that the flies do display substantial increases in this short sleep state throughout deprivation using 220 s stimulation frequencies ( Figure 1—figure supplement 1 ).…”

“…That is, the mechanical disturbance experienced by the sleep-deprived flies may produce effects on the fly that could obscure sleep-pressure-driven behavioral changes. Second, the 220 s inactivity triggers used to deprive flies of sleep may have allowed brief inactivity bouts recently hypothesized to represent an ‘active sleep’ state ( Anthoney et al, 2023 ; Tainton-Heap et al, 2021 ) and such a state prevented the build-up of sufficient sleep pressure to produce a homeostatic response. This would suggest that the 5 min inactivity criterion for sleep may be too long to capture all forms of homeostatically controlled fly sleep.…”

“…The physiological and metabolic correlates of this deep sleep state are associated with bouts of inactivity that are significantly longer than the 5 min inactivity criterion used to define fly sleep ( Nitz et al, 2002 ; Stahl et al, 2017 ; van Alphen et al, 2021 ). Furthermore, recent studies have suggested that periods of inactivity briefer than the 5 min criterion may represent an ‘active sleep’ state in the fly ( Anthoney et al, 2023 ; Tainton-Heap et al, 2021 ). The existence of multiple sleep states in the fly suggests that treating sleep as a unitary state in this species might obscure homeostatic sleep responses, particularly if, as in mammals, specific states more strongly linked to homeostatic sleep pressure than shallower stages of sleep.…”