Researchers have speculated that sleep facilitates synaptic pruning to rebalance neuronal connections formed during waking hours. In a recent Nature study, Suppermpool et al. tracked the effect of sleep on synapse numbers for individual tectal neurons in larval zebrafish. The authors estimated the number of synapses using fluorescently labeled PSD95, a postsynaptic scaffolding protein, and imaged zebrafish at three intervals across a 24-hour light–dark cycle. In general, the number of synapses increased during a light cycle (when fish were likely to be awake) and decreased during a dark cycle (when they were likely to be asleep). However, this pattern varied among tectal neuron subtypes, as type 3 tectal neurons exhibited an average decrease in synapses during the light cycle and gained synapses during the dark cycle. Although the rate of synapse loss was typically correlated with sleep duration, fish that slept more during the day because of melatonin or clonidine treatment did not exhibit significant changes in synapse counts. Additionally, fish that were prevented from falling asleep at the beginning of the dark cycle did not exhibit a correlation between sleep duration and changes in synapse count. Altogether, these results suggest that sleep can trigger synapse loss, although this process is regulated in a cell type-specific manner and influenced by pressures such as sleep deprivation.

Original reference: Nature https://doi.org/10.1038/s41586-024-07367-3 (2024).