A switch in arousal circuit architecture shapes sleep across the lifespan

Sleep is a continuous behavior across the lifespan, yet its features and functions evolve markedly with development1-4. In Drosophila melanogaster, as in mammals, early life sleep differs from mature sleep5,6, but it is unknown whether disparate sleep regulatory mechanisms underlie these changes. Here, we identify distinct populations of octopaminergic (OA) neurons that promote arousal in larval and adult flies, thus revealing a developmental switch in sleep-wake circuit architecture. Of eight OA neurons present in the sub-esophageal zone (SEZ) of the nervous system at both life stages, dedicated, non-overlapping subsets drive arousal in larvae versus adults. Morphologic and connectomic analyses show that larval OA arousal neurons project primarily to the ventral nerve cord and lack substantial sensory input, suggesting a circuit logic optimized for internally driven arousal during early development. In contrast, adult OA arousal neurons target higher brain regions involved in cognition and receive rich multimodal sensory input, supporting wakefulness in response to environmental cues. These findings highlight a developmental transition in arousal circuitry that mirrors changing ecological demands, with juvenile systems organized to prioritize growth and feeding, insulated from sensory disturbance, and mature systems supporting sensory-guided behavior. Our results support a model of sleep regulation as a developmentally dynamic process, in which shared neuromodulators like OA operate through distinct cellular substrates tailored to life stage- specific behavioral priorities.