The findings, published in the journal Nature Communications, suggested boosting hypocretin could elevate both mood and alertness in humans, that might lead to future treatments of psychiatric disorders like depression.
Senior author Jerome Siegel, a professor of psychiatry and director of the Center for Sleep Research at the University of California's Semel Institute for Neuroscience and Human Behavior, said the study measured for the first time the release of another peptide, melanin concentrating hormone, or MCH.
The researchers found MCH's release was minimal in waking but greatly increased during sleep, suggesting a key role for this peptide in making humans sleepy, Siegel said.
"The current findings explain the sleepiness of narcolepsy, as well as the depression that frequently accompanies this disorder," Siegel said in a statement. "The findings also suggest that hypocretin deficiency may underlie depression from other causes."
The researchers obtained their data on both hypocretin and MCH directly from the brains of eight patients who were being treated at Ronald Reagan UCLA Medical Center for intractable epilepsy.
The patients had been implanted with intracranial depth electrodes by Dr. Itzhak Fried, a UCLA professor of neurosurgery and psychiatry and study co-author.