Neuronal communication across synapses relies on neurotransmitter release from presynaptic active zones (AZs) followed by postsynaptic transmitter detection. Synaptic plasticity homeostatically maintains functionality during perturbations and enables memory formation. Postsynaptic plasticity targets neurotransmitter receptors, but presynaptic mechanisms regulating the neurotransmitter release apparatus remain largely enigmatic. By studying Drosophila neuromuscular junctions (NMJs) we show that AZs consist of nano-modular release sites and identify a molecular sequence that adds modules within minutes of inducing homeostatic plasticity. This requires cognate transport machinery and specific AZ-scaffolding proteins. Structural remodeling is not required for immediate potentiation of neurotransmitter release, but necessary to sustain potentiation over longer timescales. Finally, mutations in Unc13 disrupting homeostatic plasticity at the NMJ also impair short-term memory when central neurons are targeted, suggesting that both plasticity mechanisms utilize Unc13. Together, while immediate synaptic potentiation capitalizes on available material, it triggers the coincident incorporation of modular release sites to consolidate synaptic potentiation.

Graphical Abstract Highlights d Drosophila R5 network exhibits sleep-regulating compound slow-wave oscillations d Activation of circadian pathways mediates R5 multi-unit synchronization d Synchronization and compound delta oscillations require NMDAR coincidence detection d Eliminating NMDAR coincidence detection in R5 disrupts sleep In Brief Raccuglia et al. discover sleep-regulatory compound delta oscillations within the Drosophila R5 network. NMDAR coincidence detection mediates singleunit synchronization, which is the mechanistic basis for generating compound delta oscillations. Eliminating NMDAR coincidence detection, and thus compound oscillations, disrupts sleep and facilitates wakening. SUMMARYSlow-wave rhythms characteristic of deep sleep oscillate in the delta band (0.5-4 Hz) and can be found across various brain regions in vertebrates. Across phyla, however, an understanding of the mechanisms underlying oscillations and how these link to behavior remains limited. Here, we discover compound delta oscillations in the sleep-regulating R5 network of Drosophila. We find that the power of these slowwave oscillations increases with sleep need and is subject to diurnal variation. Optical multi-unit voltage recordings reveal that single R5 neurons get synchronized by activating circadian input pathways. We show that this synchronization depends on NMDA receptor (NMDAR) coincidence detector function, and that an interplay of cholinergic and glutamatergic inputs regulates oscillatory frequency. Genetically targeting the coincidence detector function of NMDARs in R5, and thus the uncovered mechanism underlying synchronization, abolished network-specific compound slow-wave oscillations. It also disrupted sleep and facilitated light-induced wakening, establishing a role for slow-wave oscillations in regulating sleep and sensory gating. We therefore propose that the synchronization-based increase in oscillatory power likely represents an evolutionarily conserved, potentially ''optimal,'' strategy for constructing sleep-regulating sensory gates.

Highlights d Presynaptic active zone plasticity as a molecular signature of sleep loss d Core active zone scaffold protein BRP drives presynaptic upscaling d Global BRP promotes sleep and arousal threshold in a dosage-dependent manner d BRP-driven synaptic plasticity-encoded sleep need impairs learning via R2 neurons

Highlights d Spermidine supplementation age-protects Drosophila brain mitochondria d Brain hypusination levels decay with age but are boosted by spermidine supplementation d Mitochondrial functionality is defective after genetic attenuation of hypusination d Defective hypusination compromises spermidine effects on locomotion and memory