Coffee Sends Wake Up Call to the Brain

People who queue up at Starbucks to buy a $5 cup of coffee do get their bang for those bucks, according to a Texas researcher. He has tracked the “wake-up” effect of coffee to its ability to block a brain chemical that makes people sleepy.

Robert W. Greene, M.D., a professor of psychiatry at the University of Texas Southwestern Medical Center, said the caffeine in coffee blocks the brain’s production of adenosine, a brain chemical that calms the brain’s arousal centers.

“Humans conduct a neuroscience experiment every time they go to Starbucks for a coffee or tea or drink a Coke,” he said. “The caffeine in coffee and Coke and the theophylline in tea acts to block the adenosine effect and they feel more awake.”

Dr. Greene describes the adenosine effect in a paper published in the April 21 issue of Neuron. Adenosine, he said, is the brain’s endogenous sleep inducer, which makes it an ideal therapeutic target for both treatment of insomnia and treatment of narcolepsy. Ideally, future research will be able to find ways to manipulate adenosine production to increase or decrease adenosine levels, he said.

“In previous studies in rats we discovered that adenosine increased with wakefulness and decreased with sleep,” Dr. Greene said. “But we didn’t know why the levels increased or decreased.”

In the latest study he observed rat brain tissue in vitro. “We were able to keep the tissue ‘alive’ so that we recorded from neurons directly,” he said. His group discovered that activity in the brain’s cholinergic arousal centers increases glutamate in the brain.

Glutamate, in turn, activates NMDA receptors on neurons. “And activation of NMDA receptors causes them to increase production of adenosine. Adenosine feeds back onto the excitatory centers and restricts the release of glutamate,” he said. As glutamate levels decrease, so does adenosine.

The net result, said Dr. Greene, is that sleepy feeling—which is wonderful at bedtime, but when it happens at 10 a.m. many people head for Starbucks.

While adenosine is clearly a “front line” sleep inducer, it is not the only drowsy factor to be found in brain chemistry, Dr. Greene said. “Which is why eventually coffee will not keep you awake and you will fall asleep,” he said. Additional research is needed to identify those other factors.

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