Scientists discover a 'biological sleep switch' in zebrafish brains

An international team of scientists has uncovered a previously unknown brain circuit in zebrafish that acts as a 'biological switch' for sleep. The discovery highlights novel neurons expressing the Qrfp and Pth4 genes, which play a key role in regulating sleep by suppressing wakefulness and activating rest-promoting pathways.

The research, published in Current Biology, involved experts from the Marine Research Institute of the Spanish National Research Council (IIM-CSIC), Caltech, California State University, and the University of Exeter. They found that the Pth4 neuropeptide triggers sleep by dampening neurons linked to wakefulness while stimulating those that promote rest. These neurons grow more active when zebrafish stay awake for long periods, helping the brain measure accumulated sleep pressure.

The newly identified circuit communicates with deeper brain regions using neurotransmitters like norepinephrine and serotonin. This interaction ensures smooth transitions between wakefulness and sleep, particularly at critical moments when memory consolidation, cellular repair, and energy balance are needed. Scientists believe this mechanism reflects an ancient evolutionary system shared across species, designed to conserve energy and maintain bodily functions.

While no human clinical trials yet exist for this specific pathway, preclinical studies are underway. Research teams at Stanford University, led by Philippe Mourrain, and the Max Planck Institute are testing PTH/PTHrP receptor agonists in rodent models for insomnia. NeuroSleep Biotech plans to launch Phase I human trials in 2027, exploring potential treatments for sleep disorders.

The findings offer a clearer picture of how sleep is regulated at a fundamental level. By targeting this newly discovered circuit, future therapies could provide relief for conditions like insomnia. The research also underscores the importance of zebrafish as a model for understanding complex brain functions across species.