14 DAY TRIAL // Sleep is a biological phenomenon, which is very difficult to study.
"Until now, the main way to study sleep deprivation's effects on the brain has been to attach electrodes, which can be a bit awkward when your target is a killer whale." said Paul J. Shaw, Ph.D., assistant professor of neurobiology at the Washington University Sleep Medicine Center.
Now, his team has found the first biochemical marker connected to sleep loss, the saliva enzyme named amylase (this enzyme breaks down starches), which increases in activity with sleep loss.
Amylase could be the first biomarker that will diagnose and treat sleep disorders and may one day be used by the police to assess the risk of drivers to fall asleep while driving. "If you're feeling sleepy on your way over the river and through the woods to grandmother's house, it's much better to pull over and find a place where you can sleep for a while than to continue on and risk a serious accident." said Shaw.
Shaw's team found that flies deprived of sleep one day will intend to recover it by sleeping more the next day, a phenomenon known as increased sleep drive or sleep debt. To identify a marker for sleep loss, the team decided to look into saliva, which is easily accessible. Saliva contains and is influenced by many of the substances found in blood and urine. Also, the brain areas that regulate sleep are known to be connected to the brain areas that regulate salivation.
Flies were subjected to different kinds of sleep deprivation and the researchers used microarrays to look for changes in the activity in many different genes. Amylase levels proved sensitive to sleep loss. The researches investigated after that amylase level after sleep loss in fruit flies genetically mutated to change their sleep drive.
The mutant flies kept awake for extended nine or 12 hour stretches that normally presented increased amylase levels anyway. "This helped prove that the increases in amylase activity level we were seeing weren't just triggered by wakefulness," Shaw says.
The same phenomenon was observed in humans: individuals kept awake for 28 hours also had increased amylase levels versus controls, which slept normally. The team also used caffeine (which inflicts sleep debt) and methamphetamine (which does not inflict sleep debt) to keep flies awake. They discovered that caffeine triggered amylase activity while methamphetamine did not.
Flies exposed to herbicides did not have increased amylase levels, thus amylase the activity was not linked to stress. Mutant flies without amylase had normal sleep and waking cycles, so amylase is not linked to sleep regulation, it just reflects it. "We're very pleased with how tightly amylase levels correlate with sleep debt, but for a good diagnostic test we're likely going to need more than one biomarker," Shaw says.
"So we're going to continue to use the processes that we've developed to look for other substances that change in connection with the level of sleep debt."
"Simple, easily accessible biomarkers for sleep debt in humans would revolutionize our ability to conduct research on the causes and consequences of sleep deprivation and provide clinicians with valuable new tools for diagnosing and assessing treatment efficacy in patients with sleep disorders", said Stephen L. Duntley, M.D., associate professor of neurology.
These biomarkers could be useful to studies of sleep in animals. "Cetaceans like killer whales, for example, are known to go for extended periods of time without sleep, and we'd like to know more about how that works and whether they incur sleep debt," Shaw says.
"Hopefully the markers we develop will make these kinds of phenomena much easier to study."