As I wrap up my last week in Paris, I’ve started noticing a peculiar number of coffee shops at just about every corner. Usually filled with people enjoying pastries accompanied with a small coffee, these cafés represent a snapshot of Parisian life. Outside of the café’s, people typically sit at the small but cleverly ornamented tables calmly and almost elegantly sipping on their simple beverage while reading the newspaper or chatting with a friend.
This isn’t anything like back at Emory, though! Unlike the sleep deprived college students at Emory who drink coffee as on-the-go rocket fuel, Parisians especially savor their brewed drinks as a vital part of their day. Nobody’s running around, on the go, fumbling with their food and coffee on the train, or spilling their drinks as they rush among pedestrians. This honor rests almost exclusively with American tourists, and in fact, remains as one of my surefire methods to find and befriend Americans in Paris!
I should mention that I personally don’t enjoy drinking coffee this way, or in any way for that matter. I find it far too bitter and it seems that even if I can gulp it down with heaps of added sugar, caffeine and I don’t get along very well. It all started back in middle school when I drank a giant bottle of Pepsi during a back-yard soccer game (This would be forbidden at Emory, a school renowned for only selling Coke products on campus!). After about 20 minutes I felt a burst of energy as I sprinted down the field, but my heart raced, and my face got incredibly warm. Panicking about my racing heart, I ended up going to the hospital after the game, only to have the doctors tell me I was fine. Of course, by the time I got there, the effects of the caffeine faded. Since that experience though, I try to stray away from caffeinated drinks because of the side effects that come with it.
However, I recently participated in a small group-experiment as part of a project for our class that involved drinking coffee. As a willing participant, I bought coffee from the local café at Cité Internationale, and quickly drank one cup before completing a series of reaction time tests to examine the effects of caffeine on reaction time.
My reaction time increased, but interestingly so did my perceived body temperature and alertness. This got me thinking about the effects of caffeine on the body. How does this drug, available so readily throughout most of the world, affect the brain and body? Once again, equipped with Neuroscience, I turned to the Internet in my search for answers.
It turns out that caffeine works by blocking the activation of brain processes responsible for regulating sleepiness and fatigue. These processes normally activate when a certain neurotransmitter, adenosine, binds to a certain receptor, the adenosine receptor. When awake, adenosine builds up in the body and eventually binds to its receptor, signaling the body to sleep. Caffeine also binds at this site, but it binds without activating fatiguing processes, and just gets in the way of adenosine binding. By doing so, caffeine keeps its users energized (Fredholm et al., 1999). Previous research also indicates that caffeine increases dopamine release in the striatum, and nucleus accumbens, areas of the brain responsible for motivation, reward, and sympathetic nervous system activities typically known as fight or flight systems (Balthazar et al., 2009).
In a recent study, Zheng et al. (2014) tested the effects of caffeine on temperature regulation and neurotransmitter release in the preoptic area and anterior hypothalamus (PO/AH) of the brain, areas responsible for regulating body temperature. According to their study, researchers chose to study these areas because increased dopamine activity here leads to a better tolerance for heat storage in the brain and facilitates an increased metabolic rate (Balthazar et al., 2009). To investigate whether caffeine helps produce these enhancing effects, researchers measured temperature, oxygen consumption, and neurotransmitter presence in rats during rest and exercise states. In a total of 10 male winstar rats, Zheng et al. (2014) measured baseline serotonin (5-HT), dopamine (DA), and noradrenaline (NA) release in PO/AH using a microdyalisis probe or cannula for control. This tiny filter collected neurotransmitters and allowed experimenters to analyze measurements. To further test for temperature and oxygen consumption, researchers measured core and tail skin temperature in the same spot for all rats, and oxygen with an oxygen/carbon dioxide measuring box. One hour before rats were placed in the box to run on a treadmill until fatigue at an 18m/min pace, investigators intraperitoneally injected (injected into the abdomen) rats with saline, 3mg/kg caffeine, or 10mg/kg caffeine. (See Link1 at the bottom for a video of rats running on a treadmill!)
From their data, Zhang et al. (2014) found that at rest, 3mg/kg caffeine levels did not result in any significant changes. However, at 10mg/kg, caffeine caused significantly higher core and tail temperatures, higher oxygen consumption, and extracellular DA and NA in the PO/AH. Data also showed that caffeinated rats showed increased endurance, and could run longer before fatigue set in. The researchers interpreted this to mean that caffeine facilitates dopamine pathways in the brain that lead to physical enhancements, specifically by modulating the PO/AH in a way that allows the brain to work under higher energy levels. I personally think of this as caffeine rearranging the brain’s thresholds for what we consider a state of exhaustion, and increasing energy consumptions by resetting the thermostat so we can function at a higher level. I particularly chose this study because the comprehensive testing used in the methods mimics these same high stress functioning levels I experienced while playing soccer.
I think as a whole the findings are incredibly interesting, and in my opinion, make perfect sense when interpreted this way. However I think that the researchers should definitely have included more details on the effect of caffeine on heart rate, as well as more incremental investigation on the effects of caffeine doses between 3 and 10 mg/kg. I would also like to see a larger sample size, or at least more than one trial per rat, as a sample size of 10 makes it difficult to collect meaningful data. I also wonder though, how long can this high energy state last before burning the body’s metaphorical engines? Perhaps future studies could test the effects of chronic caffeine use on prolonged energy levels.
As I continue my time in Paris, it feels great to see scientific explanations for everyday events. This past spring, I remember seeing a “contains caffeine” label on one of my running snacks when I ran a marathon. At the time, I thought that caffeine simply keeps you more awake, but little did I know that it facilitates increased endurance levels!
I’m glad neuroscience keeps sneaking up on me, pleasantly surprising me with answers. Who would have known that it would answer my childhood questions and help me chill out about coffee’s side effects.
For now, maybe coffee is not all that bad.
Here’s to new experiences and breaking out of my comfort zone!
Until next time,
Balthazar CH, Leite LHR, Rodrigues AG, Coimbra CC (2009) Performance-enhancing and thermoregulatory effects of intracerebroventricular dopamine in running rats. Pharmacol Biochem Behav 93:465–469
Fredholm BB, Bättig K, Holmén J, Nehlig A, Zvartau EE (1999) Actions of Caffeine in the Brain with Special Reference to Factors That Contribute to Its Widespread Use. 51.
Zheng X, Takatsu S, Wang H, Hasegawa H (2014) Pharmacology , Biochemistry and Behavior Acute intraperitoneal injection of caffeine improves endurance exercise performance in association with increasing brain dopamine release during exercise. 122:136–143.