Caffeine is the most widely-used mind-altering substance in the world. Although it's not completely clear how caffeine causes the stimulant effects it's well-known for, it's thought most of those effects are traceable back to its action as an antagonist at receptors for the neurotransmitter adenosine. In this video, I discuss how that antagonistic action may lead to arousal and wakefulness. TRANSCRIPT: Welcome to 2 minute neuroscience, where I simplistically explain neuroscience topics in 2 minutes or less. In this installment I will discuss caffeine. Caffeine is a stimulant drug and the most widely-consumed mind-altering substance in the world. It belongs to a class of compounds known as the methylxanthines, and is commonly found in a number of natural sources including the seeds of coffee plants and the leaves of tea plants. Most of the effects of caffeine are thought to be traceable back to its action as an antagonist at receptors for a neurotransmitter called adenosine. This means that caffeine binds to adenosine receptors and blocks adenosine from binding there and activating the receptor; thus, it reduces activity at the adenosine receptor. Although there are 4 subtypes of the adenosine receptor, most of caffeine’s effects are thought to be due to its antagonistic actions at the A1 and A2A subtypes. Its ability to promote wakefulness may be especially due to actions at the a2a receptor subtype. How exactly the antagonism of the adenosine receptor translates into the effects of caffeine is not completely clear. Research suggests, however, that adenosine receptors are involved in promoting and regulating sleep. One way this is thought to occur is that adenosine activity can prompt the release of the neurotransmitter GABA, which then inhibits neurons involved in arousal and wakefulness. This promotes sleep, but when caffeine antagonizes adenosine receptors it opposes this action and causes arousal. Adenosine receptors are also thought to be involved in reducing the activity of a number of neurotransmitters, including dopamine and norepinephrine, through methods ranging from inhibiting neurotransmitter release to affecting neurotransmitter binding. Thus, caffeine also blocks these effects, which may contribute to caffeine’s stimulating and reinforcing actions. REFERENCES: Fredholm BB, Bättig K, Holmén J, Nehlig A, Zvartau EE. Actions of caffeine in the brain with special reference to factors that contribute to its widespread use. Pharmacol Rev. 1999 Mar;51(1):83-133. Huang ZL, Urade Y, Hayaishi O. Prostaglandins and adenosine in the regulation of sleep and wakefulness. Curr Opin Pharmacol. 2007 Feb;7(1):33-8. Epub 2006 Nov 28. Huang ZL, Zhang Z, Qu WM. Roles of adenosine and its receptors in sleep-wake regulation. Int Rev Neurobiol. 2014;119:349-71. doi: 10.1016/B978-0-12-801022-8.00014-3.