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Forschungszentrum Jülich - Research in Jülich 2_2013

Research in Jülich 2|201314 L egend has it that it was a herd of goats in the Kingdom of Kaffa – in what’s Ethiopia today – that discov- ered the stimulating effect of coffee more than a thousand years ago. In the middle of the night, the animals were still wide awake after having eaten from the red berries of a certain shrub. The shepherds were amazed. They tried the fruits for themselves and then they, too, were able to turn night into day. Roast- ed, ground, and brewed as an aromatic beverage, coffee beans conquered the Coffee helps us to stay awake when we feel overwhelmed by tiredness. A cup of coffee or two cannot make up for lack of sleep, but it does postpone the moment where we surrender to exhaustion. A team headed by Jülich neuroscientist Prof. Andreas Bauer has now discovered the mechanism behind this effect. Prof. Andreas Bauer, director at the Institute of Neuroscience and Medicine (INM), investigates the effect of coffee in the brain by means of imaging techniques. world from the 17th century onwards. Caffeine has long been the world’s most widely consumed psychoactive sub- stance. Why the brew has its energizing effect is only recently coming to light. BLOCKED SLEEP SIGNAL Whether simple filter coffee or Italian es- presso, French café au lait, or Spanish cortado is simply a matter of taste. The way in which they make us feel wide awake, however, is the same for all of them, explains Andreas Bauer, director at the Institute of Neuroscience and Medicine (INM): “The caffeine binds to adenosine receptors in the membrane of neurons in various regions of the brain. In this way, it blocks the receptor for its proper partner, the signal molecule adenosine.” Adenosine accumulates in the body during prolonged phases of sleep deprivation. When it binds to the appropriate receptor, the activity of the neurons is reduced – for the body, this is a sign to fall asleep. “However, if the re- ceptor is already occupied by caffeine, the information that the body is tired does not reach its destination and you stay awake longer,” says Bauer, who en- joys a cup of coffee himself. The Jülich scientists wanted to find out more about where exactly the pick- me-up takes effect in the brain. This is why they administered a radioactively labelled molecule known as 18F-CPFPX to 15 volunteers. It binds to a certain type of adenosine receptor: the A1 re- ceptor. The researchers then determined where the labelled molecule accumu- lates in the brain and in what concentra- tion by means of positron emission tomography (PET). The participants were subsequently given different amounts of caffeine – unfortunately not in the form of a hot drink, but by injection directly into the blood stream. “Only in this way can we adjust a precisely defined con- centration of caffeine in the volunteers’ blood,” says Bauer. The caffeine reached the brain, where it crowded out the radioactive marker molecule from the receptor – and in doing so, it was sur- prisingly efficient. “Even the amount of caffeine contained in four to five cups of coffee is enough to occupy half of the A1 receptors. Drinking even more coffee, however, does not make sense. “This intensifies the side effects, such as nervousness or even an increased heart rate.” The reason is that receptors for caffeine can also be found in the heart. However, a habituation effect will set in after some time: if you regularly drink large amounts of coffee, you will eventu- ally have to drink even more in order to stay awake. The PET examination also revealed the regions of the brain in which the caf-

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