Sleepless in Latin America: Blind cavefish, extreme environments and insomnia

A new study published in eLife by neuroscientists in the Charles E. Schmidt College of Science at Florida Atlantic University is providing new insight into the evolution of sleep.

For the study, the researchers found that the neuropeptide Hypocretin, previously implicated in human narcolepsy, is expressed at higher levels in the cavefish brain. While loss of Hypocretin has been shown to cause narcolepsy in human and animal models, cavefish evolved to have higher levels of Hypocretin resulting in sleeplessness.

"These findings suggest that differences in Hypocretin production may explain variation in sleep between animal species, or even between individual people," said Alex Keene, Ph.D., senior author and an associate professor in the Department of Biological Sciences and a member of the FAU Brain Institute. "It may also provide important insight into how we might build a brain that does not need to sleep."

The team of scientists, led by Keene, set out to uncover the mechanics behind sleep loss in A. mexicanus to find out more about how deficiencies in Hypocretin signaling are associated with altered sleep and narcolepsy, a chronic sleep disorder that causes overwhelming daytime drowsiness, in diverse vertebrate organisms.

To accomplish that, Keene and his team conducted a comparative study among A. mexicanus surface and cavefish brain cells. Their results show that the number of Hypocretin cells in cavefish is significantly higher than that of their surface-dwelling relatives.

Next, they showed that inhibiting Hypocretin signaling, genetically or pharmacologically, increased sleep in cavefish, while it had very little effect on surface fish.

"A central question moving forward is why Hypocretin functions differently in cavefish," said Keene. "We want to understand what advantage sleep loss provides these fish in the cave environment."