Summary:
Scientists at the University of Geneva have identified a specific neural pathway that connects the central circadian clock to the brain circuits controlling sleep and wakefulness. Using targeted genetic mapping, connectomic tracing, and live calcium imaging in Drosophila melanogaster, the team shows that core clock neurons rhythmically inhibit a defined group of dopaminergic neurons. Those dopamine-producing cells, in turn, drive the mushroom body — a key center for learning, memory and arousal — thereby converting 24-hour molecular clock signals into daily patterns of alertness and sleep.
Key Facts:
- The circadian relay pathway: Rather than directly activating global arousal systems, central clock neurons modulate a downstream cluster of dopamine-producing neurons, which then signal to the mushroom body to control wakefulness.
- Inhibitory gating of arousal: Clock neurons apply rhythmic inhibition to these dopaminergic cells. During active phases, inhibition is released, dopamine output increases, and the mushroom body receives excitatory input that sustains daytime alertness.
- Relevance to sleep and neurological disorders: Because core circadian mechanisms and monoaminergic arousal systems are conserved across species, this mapped circuit offers insight into how circadian disruption can drive sleep problems and neurological dysfunction in humans.
Source: Université de Genève
Nearly all life times physiological and behavioral processes to the 24-hour day through an internal circadian clock. In animals, networks of pacemaker neurons generate molecular feedback rhythms that coordinate temperature regulation, metabolism, hormone cycles and the timing of sleep and arousal.
A longstanding question has been how the timing signal produced by a relatively small set of clock neurons is relayed to widespread brain systems that decide whether an animal is awake or asleep. The University of Geneva team has now filled that gap in the fruit fly model.
Published in Current Biology, the study delineates the functional circuit by which clock neurons modulate dopaminergic signaling to gate daytime wakefulness in higher brain centers.
Tracing connections downstream of the master clock
Led by Emi Nagoshi, Ph.D., the laboratory combined cell-specific genetic labeling, connectomic tracing and in vivo neural imaging to follow axonal projections from core clock neurons. These experiments revealed direct functional connections between clock neurons and a specific subset of dopamine-producing neurons.
Monitoring these dopamine neurons across the light–dark cycle showed consistent, time-of-day–dependent fluctuations in their activity. The investigators found that clock neurons rhythmically inhibit the dopaminergic population; when inhibition is reduced during the active phase, dopamine neuron firing increases and the mushroom body becomes more strongly activated.
“Clock neurons inhibit these dopaminergic neurons, and those dopaminergic neurons then stimulate the mushroom body,” said co-authors Blanca Lago Solis, Ph.D., and Rafael Koch, Ph.D., explaining how this multi-step pathway translates circadian timing into behavioral state.
Dopamine as a gated switch for daytime wakefulness
The mushroom body, a central neuropil in the insect brain known for associative learning and sensory processing, also plays a demonstrable role in sleep regulation and arousal. The Geneva study shows that the circadian system controls this wake-promoting network through an inhibitory gate on dopamine neurons:
- Suppression phase: When clock neurons are active in their inhibitory role, dopamine release falls. Reduced dopamine weakens excitatory drive to the mushroom body, facilitating sleep and rest.
- Disinhibition phase: At the appropriate time of day, clock-derived inhibition is relieved. Dopaminergic neurons increase firing, release dopamine into the mushroom body, and promote robust daytime wakefulness and activity.
Through this layered arrangement, a molecular oscillation in a small clock network becomes a dynamic neural switch that gates behavioral arousal on a daily schedule.
Broader implications for circadian and neurological disorders
Although these experiments were conducted in fruit flies, the results have broad translational relevance. Fundamental components of the molecular circadian clock were first discovered in Drosophila and later validated in mammals. Likewise, dopamine functions as a conserved promoter of arousal across species, including roles within the human ascending reticular activating system and basal ganglia.
Circadian disruption—whether from shift work, evening screen exposure, or neurodegenerative disease—commonly produces insomnia, daytime sleepiness and mood problems. By identifying precise synaptic checkpoints that link internal clocks to dopaminergic arousal circuits, this study offers a mechanistic framework for how clock dysfunction can degrade sleep architecture and long-term brain health.
Editorial Notes:
- This article was edited by a Neuroscience News editor.
- Journal paper reviewed in full.
- Additional context added by our staff.
About this neuroscience Research:
- Media Contact: Antoine Guenot
- Source: Université de Genève
- Image Credit: Image credited to Neuroscience News
- Original Research is Open Access: Current Biology (Sept 22, 2026). “Circadian control of dopaminergic signaling to the mushroom body regulates sleep through rhythmic Pka-C1 transcription in Drosophila.” Authors: Blanca Lago Solis, Rafael Koch, and Emi Nagoshi.
- DOI: 10.1016/j.cub.2026.09.014
Abstract
Circadian control of dopaminergic signaling to the mushroom body regulates sleep through rhythmic Pka-C1 transcription in Drosophila
Although the molecular circadian pacemaker is well characterized, the mechanisms that connect clock output to sleep regulation remain incomplete. Previous work showed that many genes in mushroom body Kenyon cells (KCs) are rhythmically expressed, including Pka-C1, which encodes the catalytic subunit of protein kinase A (PKA) and contributes to daytime wakefulness. The precise pathway linking clock timing to Pka-C1 rhythms and wake-promoting activity was not fully understood.
Using a novel in vivo luciferase reporter, the authors localized rhythmic Pka-C1 expression primarily to the γ lobe of the mushroom body. Through computational analyses, CRISPR mutagenesis and chromatin immunoprecipitation, they identified the transcription factor Onecut as a regulator of Pka-C1 transcriptional rhythms in γ-KCs.
Genetic trans-synaptic mapping combined with neuronal activity imaging revealed that dorsal lateral clock neurons (LNds) deliver inhibitory input to a subset of protocerebral anterior medial (PAM) dopaminergic neurons (PAM-γ5). This rhythmic inhibition modulates PAM-γ5 activity, which then drives rhythmic activation of MB γ-KCs via excitatory Dop1R signaling.
Activity rhythms in γ-neurons, in turn, drive Pka-C1 transcriptional rhythms through Onecut. These PKA-C1 rhythms reinforce neuronal activity, creating a feedback loop between transcriptional and neural activity rhythms that promotes daytime wakefulness.
Together, these results clarify how dopaminergic signaling is controlled by circadian inputs and provide a mechanistic framework for how molecular rhythms are translated into neuronal activity patterns that organize complex behaviors such as sleep and arousal.