Caffeine and the Brain

Ashley is about to take the final exam for her general biology class. She’s spent many long hours studying, and feels a little tired. On her way to class, she stops by the student center to grab a large cup of coffee. She hopes that the caffeine in the coffee will help her do better on the exam.

Chemically, caffeine (C8H10N4O2) is a purine with two oxygens and three methyl groups attached. When ingested, it is rapidly absorbed and soon reaches all cells of the body, including those of the brain, where it acts as a stimulant. Caffeine is found not only in coffee, but also in tea, chocolate, and many soft drinks, including popular “energy drinks.” In addition, caffeine is present in numerous over-the-counter medications, such as headache remedies, diet pills, diuretics, and alertness aids.

How much can Ashley count on coffee to help her on the exam? Without a doubt, caffeine does fight fatigue, so it will likely help Ashley avoid dozing off during the exam (surely among a student’s worst nightmares). But will it help her recall the information she has learned? Most likely it will, because Ashley will be more alert. On the other hand, taking in too much caffeine could make her feel too “jittery” to think clearly.

The mental effects of caffeine can be unpredictable. The rate at which an individual metabolizes caffeine varies by age and sex, and may be affected by the concurrent use of other drugs, such as alcohol and nicotine. Also, the amount of caffeine an individual ingests in a cup of coffee can vary quite a bit depending on the size of the cup, the variety of coffee beans, and the brewing method.

How does caffeine exert its effects on the brain? Much of caffeine’s stimulant action is thought to be due to its blockade of adenosine receptors located in the membranes of the brain’s neurons. Adenosine is not considered a true neurotransmitter, such as acetylcholine, dopamine, or serotonin, because it is not stored and released at chemical synapses. However, adenosine is an important neuromodulator, a chemical that influences synaptic function. One of adenosine’s prominent roles in the central nervous system (CNS) is to promote sleep. When caffeine reaches the CNS, it binds to and blocks adenosine receptors, preventing adenosine from causing drowsiness.

In 1999, Menahem Segal and Eduard Korkotian of the Department of Neurobiology at the Weizmann Institute in Israel reported an interesting discovery. They had removed the part of the brain called the hippocampus from rat embryos and kept the cells alive, cultured on microscope slides. The researchers then applied caffeine to the hippocampal cells and observed them under a microscope to see if there were any changes. Dosing the cells with caffeine caused a rise in cellular calcium levels—a phenomenon known to be related to learning and memory. Even more interesting was the observation that repeated caffeine exposure caused some of the spines on the neuronal dendrites to grow longer! Dendritic spines are protrusions that may be important in influencing the number of synaptic connections a neuron can receive. Thus, caffeine may influence learning and memory by inducing changes in the brain’s “wiring” at the microscopic level.

Questions

Ashley is standing in line at the coffee counter in the student center. What advice would you offer regarding her impending use of caffeine? Explain your answer.
Track your caffeine intake for one day. Be aware that caffeine may be present in unexpected dietary sources, including certain herbal supplements and teas. Check food, beverage, and medicine labels for caffeine content. Did you take in more or less caffeine than you would have predicted?

Assignments

Review how cells form adenosine. (Hint: What does “ATP” stand for?) Research recent work on adenosine and its role in sleep. What regions of the brain are involved in sleep?
Review the role membrane receptors play at a chemical synapse. How do they produce their effects? What role do dendrites play in transmission at chemical synapses?
Research caffeine’s effects on the body. What does it mean when we say that caffeine is a CNS stimulant drug? What are some other CNS stimulant drugs besides caffeine? Are they equally accessible and socially acceptable? Why or why not? Does caffeine affect other organ systems besides the nervous system? Consider the cardiovascular, respiratory, and urinary systems in particular. Besides the “caffeine jitters,” are there any adverse effects associated with ingesting caffeine? If so, what are they? Is there any evidence to support health benefits from the use of caffeine-containing beverages such as coffee and tea? If so, what?
Find out how much caffeine is present in a typical cup of coffee. How does this compare to the amount in a cup of tea or a can of cola?
Research the role of the hippocampus in learning and memory. Explain why Segal and Korkotian chose this part of the brain for their study of the effects of caffeine.

References

http://web.sfn.org/content/Publications/BrainBriefings/adenosine.html

http://web.sfn.org/content/Publications/BrainFacts/index.html

http://health.howstuffworks.com/caffeine.htm

http://health.howstuffworks.com/sleep.htm

http://my.webmd.com/content/article/46/1826_50681.htm

http://my.webmd.com/content/article/17/1671_52718.htm

http://my.webmd.com/content/article/11/1671_50418.htm

http://my.webmd.com/content/article/11/1671_50455.htm

http://www.weizmann.ac.il/neurobiology/labs/segal/segal.html

http://health.howstuffworks.com/framed.htm?parent=sleep.htm&url=http://www.sciencenews.org/sn_arc97/5_24_97/fob2.htm

Weinberg, B. A., and B. K. Bealer. 2001. The world of caffeine: The science and culture of the world’s most popular drug. Routledge.