Pisces sleep changes the understanding of human sleep

Certain fish sleep differently than previously thought. They lack the messenger substance orexin, which was previously considered essential for sleeping and waking. Researchers from the University of Basel showed this in a new study in the journal ‘Current Biology’.

The fish are changing the understanding of how sleep is regulated, as the University of Basel said on Thursday. Previously, researchers assumed that all vertebrates – from humans to fish – regulate their sleep-wake rhythm via the orexin signaling pathway.

In humans, a defect in the orexin signaling pathway leads to narcolepsy. Typical symptoms include sudden and unpredictable sleep attacks from which those affected may find it difficult to wake up, sudden loss of muscle control and excessive sleepiness during the day.

Studies on black loaches (C. macracanthus), a type of doughnut, have now shown that they function without the orexin signaling pathway – and can still be easily woken up.

The South Asian fish species stops swimming and lies on its side to sleep. “This remarkable resting behavior is known to aquarium owners and local fishermen, who exploit it to catch C. macracanthus,” the authors led by Alexander Schier wrote in the study. The researchers also wanted to take advantage of this behavior because it makes it easier to observe the sleeping fish.

For more detailed analyses, the researchers then examined the fish’s brains. They were surprised to find that the orexin signaling pathway was missing. “To our knowledge, these results represent the first vertebrates without a functioning orexin system,” they wrote in the study. The researchers also discovered that not only black loaches can control their sleep-wake rhythm without orexin, but also zebrafish.

“It would now be interesting to find out when and why different control systems evolved in vertebrates,” says Schier, according to the announcement from the University of Basel. (sda/lyn)