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Coffee gets many of us through the day. But scientists have only recently figured out why we start to feel tired as the day goes on, and why a coffee break gives us a boost. This ScienCentral News video has more.
Feeling Worn Out
There's no doubt an afternoon coffee break often gives new energy to the weary. But scientists have only recently figured out why we start to feel worn out in the first place. Researchers at University of Texas Southwestern Medical Center in Dallas, identified a chemical change in the brains of rats that causes the transition between being awake and asleep. They say the chemistry is shared by all mammals, including people, and is triggered by prolonged neural (nerve) activity -- being awake for a long period of time. The finding explains why coffee gives us a boost and may also provide more natural treatments for people fighting insomnia.
The researchers focused on the "arousal centers" - the regions scattered through the brain that regulate the smooth transition from being asleep, to waking up, to falling back asleep. Without these regions, our sleep patterns might be completely erratic and we could fall asleep at any moment.
Activity in a rat brain cell.
The research team showed that under normal "awake" conditions these arousal centers release an excitatory chemical called glutamate. Glutamate is a neurotransmitter, a chemical that carries messages between brain cells. In the arousal centers it keeps the cells firing, so they interact and respond effectively to everyday stimuli. Through the course of the day however, these same neurons release a second neurotransmitter called adenosine. Adenosine is a natural sleep chemical that counteracts the effects of glutamate and quiets the cells down, essentially making them, and us, sleepy.
"Adenosine actually is increased when the nerve activity coming into the arousal center is present or active for a long period of time, which is what happens when you're awake for a long period of time," says psychiatrist Robert Greene who led the research team and was senior author on their recent paper in the journal Neuron.
Green and his colleagues found the relationship between continued neural activity, glutamate and adenosine by looking directly at individual rat neurons. They artificially stimulated the neurons with tiny pulses of electricity, creating a type of "activity" in the cells similar to how the brain would normally function. As time went by however, the cells responded less and less to the stimulation, as though they were getting sleepy.
"The stimulus ... remained the same for the whole time, but despite that, the activity level decreased," says Greene.
As the experiment continued, the researchers could see an increase in adenosine and a drop in glutamate. But they reversed the experiment and blocked the release of adenosine with a chemical similar to caffeine (formally known as 8-cyclopentyltheophylline), the activity in the cells and the amount of glutamate released "remained at the same high level straight on through," says Greene.
Greene says coffee and other beverages that contain caffeine or theophylline, which is a comparable component of tea, work because they temporarily obstruct this natural sleep chemistry. "When you have a cup of tea or a cup of coffee, you block the effects of the brain's own fatigue factor, that's adenosine, acting on the arousal center," says Green but adds that there must be other brain mechanisms that make us fall asleep because even with a constant supply of coffee, "You still get tired and you still finally fall asleep. "
Natural Insomnia Relief
But because adenosine is a natural brain chemical, the research team hopes these findings will lead to better and more natural treatments for insomnia.
"If someone is suffering from insomnia, then we can look at the adenosine system to see if something is going wrong there," says Greene.
Joyce Walsleben, coordinator of the insomnia program at the Sleep Disorders Center at the New York University School of Medicine, says some sleeping irregularities are currently treated with adenosine and that this research is "highly promising" and could help to improve treatments. But she warns that because the research was observed at the cellular level and in rats, it is still only a "building block," for future medications.
It's "meaningless to people until a pharmaceutical company makes the next six [or so] moves down the line," says Walsleben. Greene plans to be part of those next moves. "Maybe we can manipulate the adenosine system – that is we can facilitate it in a way that induces us to fall asleep in a more natural way," says Greene.
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