By William J. Cromie

Having discovered a gene involved in sleep and a natural hypnotic made in the brain, Harvard scientists are extending these findings to find out what makes us sleepy.

When a gene called c-fos, present in people and mice, is knocked out by genetic engineering, the mice act like human insomniacs. If efforts to determine exactly how this gene works are successful, they could lead not only to a cure for insomnia, but allow us to get along comfortably with considerably less sleep.

This gene is somehow linked to a substance in the brain that produces dreamless sleep in animals. Further studies of that natural chemical are pointing researchers in the direction of creating a sleeping pill that is not addictive, or useless after a few weeks.

"When cats are kept from napping by playing with them, levels of the chemical, called adenosine, build up in their brains," notes Robert McCarley, professor of psychiatry at the Medical School. The longer they stay awake, the higher the levels of adenosine. After they go to sleep, levels progressively drop off. What's true for cats is likely to be true for humans."

McCarley and his team at the Harvard-affiliated Brockton Veterans Administration Medical Center are now trying to figure out how levels of adenosine in the brain can be manipulated to guarantee a good night's sleep, rather than a cat nap.

McCarley's colleague, Priyattam Shiromani, an associate professor of psychology, did the experiments with mice lacking a c-fos gene. The rodents take twice as long to go to sleep and sleep 30 percent less than normal mice.

"C-fos holds instructions for making a protein that is somehow involved in regulating sleep," notes Shiromani. "If we can determine exactly how this works, we may be able to tweak the mechanism to eliminate insomnia, or to counter sleepiness."

The possibility of controlling sleep this way raises an intriguing question. Do humans really need 7 to 8 hours of sleep?

"The mice without c-fos have difficulty getting to sleep and staying asleep," Shiromani notes. "Otherwise, they are active and fit. If we could manipulate the activity of c-fos, perhaps people could get along with, say, three hours less sleep a night without deleterious side effects."

"That's true," agrees McCarley. "If we could figure out what sleep is doing at the gene level, and mimic that in some way, we might be able to get by with less sleep."

Three hours less sleep each day would add more than 45 extra days of wakefulness to a year. If a person lived 70 years, he or she would be awake 8 years and 9 months longer than someone who slept a "normal" 7 or 8 hours a day.

What Makes us Tired

"It's embarrassing," admits McCarley. "We don't know why we need to sleep. During sleep, activity throughout the brain declines. The most straightforward conclusion is that sleep is needed to restore energy."

But what in the brain makes us tired? That's the question that needs to be answered to develop drugs that would allow us to sleep or stay awake without deleterious side effects.

"Sleeping pills are overprescribed for chronic use," McCarley notes. "They become ineffective after a time, and increasing the dosage can lead to addiction. These effects probably contribute to their underprescription for acute use, such as during times of grief."

These drugs put the whole brain to sleep. The key to a successful pill is selectivity, a substance that blocks only brain cells associated with sleep rather than all cells. Adenosine might fill that prescription if researchers can determine exactly how to tailor the way it works.

Adenosine release in the brain may occur when energy-storing molecules containing adensosine triphosphate (ATP) are broken down to provide energy for cell activity. When brain cells burn ATP, McCarley believes, adenosine builds up. The longer cats or humans are awake, the higher the levels of this chemical in their brains.

McCarley and his colleagues speculated that adenosine inhibits the activity of cells in "wakefulness centers" at the front of the brain. To prove this, they infused a chemical that increases adenosine into two areas of cats' brains. Those that received it in the front part of the brain, the basal forebrain, became sleepy; those that got it in another area did not.

"At certain levels of adenosine, sleep becomes irresistible," McCarley notes.

What about giving people adenosine pills to put them into the arms of Morpheus? McCarley explains that this would create undesirable side effects, such as lowered heart rates and blood pressure.

Robert Greene, associate professor of psychiatry and a colleague of McCarley's, is working to find a chemical that will increase the tendency of adenosine to bind to cells in the wakefulness centers, cells called cholinergic neurons. Such a drug would mimic the natural process of sleeping.

A good wakefulness drug would be as popular as a pleasing sleeping pill; presumably, that could be accomplished by a pill that prevented adenosine molecules from docking with the cholinergic cells.

Sleep Gene Signaling

Cells that promote wakefulness have connections to the same area of the brain where the c-fos sleep-gene sits, the hypothalamus. A cherry-sized gland deep in the lower brain, the hypothalamus is involved in regulating sleep, as well as contributing to thirst, appetite, sexual behavior, and emotions.

Without c-fos, mice act like human insomniacs, but the gene's exact contribution to knitting up the 'ravell'd sleave of care' is hard to pin down.

No one believes that sleep (or any other behavior) is controlled by only one gene. C-fos must be part of a complex signaling system whereby some outside stimulus, like a message from the cholinergic neurons, activates other brain cells. The change switches on c-fos, which causes a specific protein to be made. This protein then switches on other genes. The result is a cascade of signals that brings about a response to the original stimulus.

"C-fos is only one part of the puzzle," Shiromani observes. "But when you get one piece in place, the rest of the puzzle becomes easier to solve."

"C-fos doesn't switch on until after sleep begins," McCarley adds. "Therefore, it can't trigger sleep, but it might be responsible for the continuity of sleep." That action might occur by the suppression of wakefulness cells.

Adding to the complexity, adenosine is not the only natural substance that put us to sleep. "A compound called interleukin, present in cells all over the body, may foster the sleepiness associated with infection and inflammation," McCarley points out. "Another brain chemical, histamine, may promote wakefulness with an input into the hypothalamus and possibly to c-fos cells.

"We don't really know what c-fos is doing, so adenosine is a more immediate target for tailoring sleep," he continues. "C-fos works inside cells; adenosine works outside. Drug companies favor the latter because it is so difficult to get a compound into particular cells."

Nevertheless, his team is putting different chemicals into different cells in the hypothalamus to see if they induce sleep in lab animals. "We're looking at everything, from what adenosine does in the brain to the signals going to and from c-fos cells," McCarley says. "We've solved some of the mysteries of sleep, but there's still a great deal we don't know."