Easy Catnaps Could Leave Insomniacs Feline Fine
Researchers studying napping cats have discovered a brain chemical that helps them slide into deep slumber, a finding that could eventually lead to a new type of sleeping pill for humans.
Dr. Robert W. McCarley of the Harvard Medical School said that a chemical called adenosine signals the brain when to be alert and when to shut down for sleep.
McCarley, senior author of a study published Friday in the journal Science, said that he and his colleagues identified adenosine by monitoring the chemicals in the blood of cats that were kept awake and then allowed to nap. Their brain waves also were monitored.
Cats were chosen because they are one of nature’s champion sleepers, able to easily slip in and out of slumber. They often take short “cat naps” and then spring instantly awake and alert.
In the study, McCarley said that the cats were first kept awake for six hours, “which is a long time for cats.”
“We petted them to keep them awake,” McCarley said. “Over that time, there was a steady buildup of adenosine” in the animals’ blood.
The cats were then allowed to go to sleep. Immediately the body began breaking down adenosine, and the levels dropped. When the chemical reached a low concentration, the cats became awake and alert. This cycle was repeated several times, said McCarley.
Adenosine, he said, accumulates naturally in some brain cells during wakefulness. When it reaches a certain concentration, it causes drowsiness and sleep, he said, but at low concentrations of adenosine, the brain is alert. “It is probably the major mechanism that causes one to become sleepy after you’ve been awake for a long time,” said McCarley.
Dr. Mark Mahowald, a sleep expert and a professor of neurology at the University of Minnesota, said identifying adenosine as a chemical that contributes to sleepiness “is an important part of the puzzle” but is no complete solution to sleep disorders.
“The wake-sleep cycle is very complex and no one chemical or part of the brain is responsible,” he said. “Adenosine may be an important player in this process, but it is not alone.”
McCarley said adenosine is known to be present in other organs of the body, but the sleep effects seem to concentrate in the basal forebrain. Cells there have special receptors, or openings, that take in the chemical during wakefulness, causing a steady buildup. During sleep, adenosine is reprocessed and released from the cells, he said. When the animal awakes, the cycles start all over again.
“It is almost certain that the mechanism in animals is the same in humans,” he said. This is indicated, said McCarley, because caffeine increases alertness and briefly chases away sleep.
“The stuff you likely drink in the morning--coffee, tea or hot chocolate--blocks the action of adenosine,” he said. “That’s why the universal wake-up beverages are so effective.”
Further research may lead to a sleeping pill based on adenosine. McCarley said it would have the advantage of being a natural sleep inducer, unlike some narcotic drugs that lose effectiveness over long use and can cause addiction or hangover.
Since adenosine is present in many organs, however, McCarley said researchers would have to find ways of limiting its action to the sleep centers of the brain.
And, he said, science needs to learn more about other natural chemicals associated with sleep.
“It has been hard to discover the body’s natural mechanisms for promoting sleep,” McCarley said. “This is just one of the natural mechanisms.”
