SLEEPYSYNAPSE · Synapse dynamics across sleep-wake states

Sleep is essential, yet its core functions and regulatory mechanisms are not fully understood. The synaptic homeostasis hypothesis suggests sleep helps normalize synapse strength and number accumulated during wakefulness. We have developed a zebrafish model for directly visualizing dynamic synaptic changes in single neurons across sleep/wake states. Our research indicates that synaptic changes in single neurons vary significantly across similar neuronal types under baseline conditions. Notably, only sleep periods with high sleep pressure—such as at the start of the night, after sleep deprivation, or with artificially elevated adenosine levels—support net synaptic removal. Aim 1 investigates how sleep/wake-dependent changes in synaptic number and strength relate to neuronal activity. We will use single-neuron synapse labeling combined with genetically encoded calcium imaging to observe how activity affects synaptic dynamics during sleep and wakefulness. Chemogenetic tools will help us test if wake activity shapes subsequent synaptic changes during sleep and if single-synapse activity tags synapses for preservation or removal. Aim 2 explores how sleep pressure signals affect single neurons. By mapping adenosine and noradrenaline release with new sensors across the sleep/wake cycle, we will analyze their impact on sleep-dependent synaptic changes, including in zebrafish sleep homeostasis mutants. Aim 3 examines how synaptic dynamics influence behavioral states. Using transgenic zebrafish to track synapses in key sleep/wake-regulating neurons (e.g., galaninergic, serotonergic, orexin/hypocretin, and noradrenaline-producing neurons), we will investigate if changes in synaptic dynamics are related to sleep pressure and how they affect behavioral state transitions. This project advances our understanding of sleep by employing novel imaging and genetic tools in zebrafish to provide insights into the interplay between sleep pressure, neuronal activity, and synaptic dynamics.