Examining sleep modulation by Drosophila ellipsoid body neurons.

Abstract

Recent work in Drosophila has uncovered several neighboring classes of sleep-regulatory neurons within the central complex. However, the logic of connectivity and network motifs remains limited by the incomplete examination of relevant cell types. Using a recent genetic-anatomical classification of ellipsoid body ring neurons, we conducted a thermogenetic screen in female flies to assess sleep/wake behavior and identified two wake-promoting drivers that label ER3d neurons and two sleep-promoting drivers that express in ER3m cells. We then used intersectional genetics to refine driver expression patterns. Activation of ER3d cells shortened sleep bouts, suggesting a key role in sleep maintenance. While sleep-promoting drivers from our miniscreen label overlapping ER3m neurons, intersectional strategies cannot rule out sleep regulatory roles for additional neurons in their expression patterns. Suppressing GABA synthesis in ER3m neurons prevents post-injury sleep, and GABAergic ER3d cells are required for thermogenetically induced wakefulness. Finally, we use an activity-dependent fluorescent reporter for putative synaptic contacts to embed these neurons within the known sleep-regulatory network. ER3m and ER3d neurons may receive connections from wake-active Helicon/ExR1 cells, and ER3m neurons likely inhibit ER3d neurons. Together, these data suggest a neural mechanism by which previously uncharacterized circuit elements stabilize sleep-wake states.Significance StatementNeural circuits that control sleep must be stable to ensure therapeutic rest but readily adaptable to a variety of experiences. The Drosophila ellipsoid body (EB) regulates many cognitive processes, and recent studies show that certain EB neurons can intensify sleepiness, but the contributions of other EB neuron subclasses in sleep regulation remain unclear. Thus, we searched for sleep-regulatory neurons across the EB to better understand sleep control. Our studies indicate that ER3d neurons promote wakefulness by reducing the persistence of sleep episodes and suggest that ER3m neuron activity may increase sleep. Understanding the stability and flexibility of sleep, then, may emerge from investigating the connectivity and conductivity of sleep-regulatory neurons in the EB.