Sleep deprivation drives brain-wide changes in cholinergic presynapse abundance in Drosophila melanogaster

Abstract

Sleep is an evolutionarily conserved state that supports brain functions, including synaptic plasticity, in species across the animal kingdom. Here, we examine the neuroanatomical and cell-type distribution of presynaptic scaling in the fly brain after sleep loss. We previously found that sleep loss drives accumulation of the active zone scaffolding protein Bruchpilot (BRP) within cholinergic Kenyon cells of the Drosophila melanogaster mushroom body (MB), but not in other classes of MB neurons. To test whether similar cell type–specific trends in plasticity occur broadly across the brain, we used a flp-based genetic reporter to label presynaptic BRP in cholinergic, dopaminergic, GABAergic, or glutamatergic neurons. We then collected whole-brain confocal image stacks of BRP intensity to systematically quantify BRP, a marker of presynapse abundance, across 37 neuropil regions of the central fly brain. Our results indicate that sleep loss, either by overnight (12-h) mechanical stimulation or chronic sleep disruption in insomniac mutants, broadly elevates cholinergic synapse abundance across the brain, while synapse abundance in neurons that produce other neurotransmitters undergoes weaker, if any, changes. Extending sleep deprivation to 24 h drives brain-wide upscaling in glutamatergic, but not other, synapses. Finally, overnight male–male social pairings induce increased BRP in excitatory synapses despite male–female pairings eliciting more waking activity, suggesting experience-specific plasticity. Within neurotransmitter class and waking context, BRP changes are similar across the 37 neuropil domains, indicating that similar synaptic scaling rules may apply across the brain during acute sleep loss and that sleep need may broadly alter excitatory–inhibitory balance in the central brain.

ninna nannalinks circadian and homeostatic sleep drive inDrosophila

“…This pattern almost faithfully reproduces changes in bona fide synaptic strength as previously quantified through the Bruchpilot synaptic protein (Fig. 3B) (17, 45–48) and suggests that expression of nanna encodes sleep pressure rather than circadian rhythm. We confirmed an increase of nanna transcript expression with prolonged time awake in male head extracts from flies collected immediately after sleep (ZT0) in comparison to flies collected after the waking day (ZT12, Fig.…”

“…This pattern almost 167 faithfully reproduces changes in bona fide synaptic strength 168 as previously quantified through the Bruchpilot synaptic pro-169 tein (Fig. 3B) (17,(45)(46)(47)(48) and suggests that expression of 170 nanna encodes sleep pressure rather than circadian rhythm.…”

Socialization causes long-lasting behavioral changes

“…In addition, our results revealed that socialization also induces rut-dependent changes in synaptic plasticity of the previously activated MB neurons. The increased synaptic densities in CREB-positive neurons might be explained by the socialization-induced enhanced sleep, given that sleep loss diminishes pre-synaptic densities in cholinergic neurons, including the MB neurons 41,42 . This is unlikely because despite rut mutant animals do sleep much more (fig 2B), their MB presynaptic densities do not reach levels of socialized wt animals, although they are higher than in isolated flies (fig 5D).…”

Developing forebrain synapses are uniquely vulnerable to sleep loss

“…Neuronal synapses have emerged as a distributed and conserved target for the restorative benefits of sleep and a locus of dysfunction in response to SD 4,5 . A prominent synapse-based model proposes information encoding during wake drives synaptic potentiation, perturbing synapse homeostasis, which is restored during sleep by broad synapse weakening through homeostatic scaling-down 6 .…”

“…However, what is actually being restored by sleep remains mysterious. While behavioral switching between wake/sleep states is controlled by discrete neuronal populations 3 , the need for sleep is broadly expressed across the brain 4,5 . The neuronal synapse has emerged as one major conserved target for the restorative benefits of sleep and a distributed locus for the accumulation of sleep need 6 .…”