The monkeys were deprived of sleep for 30 to 36 hours and then given either orexin A or a saline placebo before taking standard cognitive tests. The monkeys given orexin A in a nasal spray scored about the same as alert monkeys, while the saline-control group was severely impaired.
The study, published in the Dec. 26 edition of The Journal of Neuroscience, found orexin A not only restored monkeys' cognitive abilities but made their brains look "awake" in PET scans.
Siegel said that orexin A is unique in that it only had an impact on sleepy monkeys, not alert ones, and that it is "specific in reversing the effects of sleepiness" without other impacts on the brain.
The research follows the discovery by Siegel that the absence of orexin A appears to cause narcolepsy. That finding pointed to a major role for the peptide's absence in causing sleepiness. It stood to reason that if the deficit of orexin A makes people sleepy, adding it back into the brain would reduce the effects, said Siegel.
"What we've been doing so far is increasing arousal without dealing with the underlying problem," he said. "If the underlying deficit is a loss of orexin, and it clearly is, then the best treatment would be orexin."
Orexin A is a promising candidate to become a "sleep replacement" drug.
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