Researchers Find Master Switch for Slumber
WASHINGTON (AP) _ A ``slumber switch″ buried in the brain slips an alert mind into deep and restful sleep, according to Harvard researchers, who believe the discovery may lead to drugs to end insomnia.
In experiments with rats, brain researchers found that during sleep most of the nerve cells of the brain are turned off by some signal sent out by a group of cells in the hypothalamus.
By tracing the signals, the researchers found that a neuron group called the ventrolateral preoptic area, or VLPO, acts as a ``slumber switch,″ said Dr. Clifford Saper, chief neurologist at Beth Israel Hospital in Boston and a professor at Harvard Medical School.
``This little subgroup of cells essentially turns out the lights in the brain and lets it go to sleep,″ said Saper. ``It’s like turning a master switch. A slumber switch.″
A report on the sleep research was being published Friday in Science, the journal of the American Association for the Advancement of Science.
The discovery puts scientists on track to find the specific natural chemicals that cause the VLPO to command the brain to sleep.
``To produce a natural sleep, you need to turn on these cells,″ said Saper. If drugs could be found to activate the VLPO, he said, then normal sleep, at last, could be prompted with pills that have no hangover effects.
``Most sleeping pills produce a drugged sleep,″ he said. ``Basically, they hit the brain with a hammer and turn everything off. They don’t work in a normal way that produces a refreshing sleep so that you feel well when you wake up.″
Dr. Mark Mahowald of the Minnesota Regional Sleep Disorder Center in Minneapolis said the study ``is a very important finding, but it should be viewed with some caution.″
Mahowald said that sleep has different phases involving different parts of the brain and that Saper and his colleagues may have found only one element of the complex process.
``They may have found the sleep switch,″ he said, ``but it probably is not that simple. There is probably far more involved.″
The Harvard studies used biological markers to track the activity of rat brain cells during sleep. It was found that the VLPO was the only neuron structure in the brain that becomes very active during sleep.
``As soon as the animal goes to sleep, everything turns off in the brain except for this one little cell group, and it turns on,″ said Saper.
He said researchers found connections between the VLPO and centers of the brain that work through the action of three chemicals that stimulate wakefulness.
Somehow, he said, the VLPO blocks the action of those chemicals.
``Inputs from the VLPO wrap around the arousal nerve cells and turn them off simultaneously,″ said Saper. The result is sleep.
The VLPO is just a small cluster of cells, about the size of a small grape. It is located in the hypothalamus, a structure at the core of the brain that is responsible for such basic drives as eating, drinking and sex.
Now, sleep can be added to the vital functions performed in the hypothalamus.
Saper said the hypothalamus functions basically the same in rodent and human. Also, some clinical experience supports the idea that the VLPO promotes sleep, he said. Insomnia is a major symptom among patients who have experienced injuries in that part of the brain, he said.
The precise chemistry of what prompts the VLPO to act and how the brain overcomes this effect when it awakens are still not known, but Saper said additional experiments with laboratory animals may provide the answers.