Campus Queries is a new Q&A series in which Daily Bruin readers send in science-related questions for UCLA professors and experts to answer. Each week, the Daily Bruin will choose a different question to be explored.
Q. How does coffee (caffeine) work exactly? Why does it wake you up? –Megan N.
A. Caffeine blocks a molecule called adenosine from its receptors on cell surfaces and prevents drowsiness induced by adenosine – a generally accepted hypothesis that comes from a 1970 study using guinea pig brain slices.
Scientists think blocking adenosine signals from outside a cell is an appealing description for several reasons. Adenosine has a large number of effects opposite to those of caffeine in different tissues. The caffeine concentrations required to suppress effects of adenosine match the low levels (of caffeine) people get from drinking one to three cups of coffee.
Adenosine forms from the breakdown of adenosine triphosphate, also called ATP, which carries energy for chemical reactions inside cells. During prolonged wakefulness, adenosine accumulates in the space outside cells and seems to regulate use of noradrenaline, dopamine and serotonin. These hormones signal neurons that influence alertness and mood. In a sleeping brain, the flow of cerebrospinal fluid expands and clears out metabolic wastes more efficiently.
“Adenosine is thought to be released by neurons that are using a lot of energy,” said Jerome Siegel, a professor of psychiatry and director of the Center for Sleep Research. “Most likely this then inhibits neurons that are responsible for waking.”
Siegel said several systems in the brain control sleeping and waking, and the exact group of neurons behind the adenosine-caffeine effect is unknown.