 Case Study: 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 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 into the blood stream 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 the popular "energy drinks". In addition, caffeine is present in numerous over-the-counter medications, such as headache remedies, diet pills, 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. 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 drink can vary quite a bit. 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, a study at the Weizmann Institute of 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. Assignment:
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