Brain Chemical May Hold Key to Caffeine’s Kick

That morning cup of coffee perks you up because caffeine blocks a chemical message from being received at a particular site on brain cells, a mouse study suggests.

The message comes from a substance called adenosine, which is produced by the body and has a wide range of effects. Brain cells respond when an adenosine molecule attaches itself to a cell structure called a receptor. Scientists knew caffeine blocked adenosine’s access to receptors, and that might explain why caffeine is stimulating.

In the new study, scientists created mice that lacked one of the four kinds of adenosine receptors. Tests showed these mice weren’t stimulated by caffeine. In fact, caffeine reduced their physical activity.

The result shows that caffeine normally stimulates mice by acting on the missing receptor, researchers said. It probably reduced activity in the special mice by other means, such as blocking adenosine’s access to another kind of receptor, they said.

The work is reported in the Aug. 14 issue of the journal Nature by scientists in Belgium, France, Switzerland and England.

The mice without the receptor also appeared more anxious than normal, which fits with evidence that caffeine makes people edgy, scientist Solomon Snyder of the Johns Hopkins School of Medicine wrote in a Nature commentary.