It is 8:00am, and you are still groggy from staying up the night before. What do you do? You grab a cup of coffee.
Later, at 3:00pm, you are beginning to lose steam. What do you do? You grab a chai latte from starbucks. At 11:00pm, when you are trying to pull an all-nighter, what do you do? You grab a Red Bull.
With about 90 percent of the United States population regularly consuming caffeine-containing beverages or foods, it is safe to say that modern society runs on caffeine.
Caffeine’s ability to both counter physical fatigue and increase alertness is, in part, the reason why it is the most commonly consumed psychoactive drug in the world.
The drug is ubiquitous: we not only find in at the soda fountain or the coffee shop but in our medicines and food. While we would never give our kids ecstasy, we routinely serve caffeine to children in the form of soda and chocolate bars.
What is the root of caffeine’s mystical powers? How does this simple molecule exert such a powerful force on both our body and mind?
“Caffeine blocks the action of adenosine receptors which are found on cell membranes both in the central nervous system (CNS) and in the peripheral nervous system (PNS),” Linda Gorman, professor in the Department of Psychology and Brain Sciences, wrote in an e-mail to The NewsLetter.
This is the same adenosine that is found as one of the four bases that are the building blocks of DNA. Caffeine exerts such a powerful action on the CNS because adenosine interacts with all the major neurotransmitter systems in the body, particularly the catecholaminergic system.
This group of neurotransmitters includes the hormone adrenaline. Normally, adenosine acts to inhibit the release of catecholamines.
“Depending on where the adenosine receptors are there is either an increase of decrease in concentration of cAMP, a secondary messenger molecule in side the cell,” Gorman wrote.
When caffeine binds to the adenosine receptor, it effectively prevents the binding of an adenosine molecule to that same receptor. Thus, the receptor becomes inhibited. The result is an increased catecholamine release.
“At the cellular level, adenosine uses several mechanisms to produce inhibition of transmitter release,” wrote Gorman. “Adenosine acts postsynaptically to hyperpolarize neurons and inhibit their firing. It also acts presynaptically to inhibit neurotransmitter release from the axon terminal.”
When caffeine is introduced to the system, adenosine is inhibited. Because adenosine is not around to inhibit neurons from firing or from releasing neurotransmitters, brain activity increases.
Caffeine is well-known for its ability to delay sleep.
As you may have already guessed, this property of caffeine is due to its ability to inhibit adenosine receptors.
It appears that adenosine promotes sleep by decreasing the activity of a certain class of neurons called mesopontine cholinergic neurons.
“Caffeine blocks this effect so you get a delay in the onset of sleep. Those that are particularly susceptible to the effects caffeine on sleep may metabolize caffeine more slowly than others,” Gorman said.
