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, published in Current Biology, reveals how specific neurons trigger rest by suppressing wakefulness and activating sleep-promoting signals. The findings could lead to new treatments for human sleep disorders like insomnia.
The researchers identified novel neurons in the zebrafish brain that express the Qrfp and Pth4 genes. These neurons, located in the preoptic region, become highly active when the fish stays awake for long periods. Their activity helps measure accumulated sleep pressure, ensuring the brain shifts to rest at critical times.
The Pth4 neuropeptide plays a key role by suppressing neurons that promote wakefulness while activating those that induce sleep. This mechanism safeguards essential functions such as memory, cellular repair, and energy regulation. The neurons communicate with deeper brain regions—like the hindbrain—via neurotransmitters such as norepinephrine and serotonin, enabling smooth transitions between wakefulness and sleep.
Studies, including those by Chowdhury et al. (2023, Nature), showed that optogenetic activation of Pth4 neurons increases norepinephrine and serotonin release in the caudal hindbrain. This alters arousal and social behaviour, with in vivo experiments using GRAB sensors confirming how neurotransmitter dynamics regulate sleep.
The discovery of this sleep-regulating circuit in zebrafish offers potential insights for human sleep research. Scientists from the Marine Research Institute of the Spanish National Research Council (IIM-CSIC), Caltech, California State University, and the University of Exeter suggest that targeting similar pathways could lead to new therapies for insomnia and other sleep disorders. Further studies may explore whether comparable mechanisms exist in mammals.
