STUDENT NAME: Anastasiya Boutko
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For this assignment I chose the article “Wired to run: exercise-induced endocannabinoid signaling in humans and cursorial mammals with implications for the ‘runner’s high” by David A. Raichlen and company. I have been aware of the term “runner’s high” and the generally known positive post exercise effects such as better mood and decreased anxiety. I even experienced some of them myself. As a university student that regularly engages in moderate level of physical activity at the gym, I wanted to have a better understanding of what causes runner’s high and how it psychoactively affects an individual.
The researchers address the main question of why humans and other cursorial mammals engage in high intensity exercise despite it being energetically demanding and posing a high risk of injuries. Our ancestors engaged in physically demanding activities on a daily basis. Such activities included running to search for food, explore terrain, and avoid predators. Through evolution, humans continued to run as a species, despite the significant tradeoffs. Scientists hypothesized that neurobiological rewards are responsible for the differences in mobility across animals (Raichlen, et al, 2012). Based on the observations, after 30 minutes of running, test groups of both humans and dogs experienced an increase in plasma endocannabinoid (eCB) levels, while in ferrets the eCB levels remained unchanged. Endocannabinoids induce the release of dopamine into the mesolimbic area of the brain responsible for behavioral rewards. Therefore, this suggests that less mobile animals do not experience the neurobiological rewards to stimulate endurance exercising, as cursorial animals would experience.
The results of the experiment were anticipated. This is because humans and dogs are morphologically adapted for high intensity exercise and they are able to withstand challenging aerobic workouts. To encourage this demanding level of activity and allow individuals to run further distances, cursorial animals are rewarded with the “runner’s high”. During this state of euphoria, performance is increases by reduction in pain sensation, feelings of effortlessness, and a sense of wellbeing. However, ferrets are built for less metabolically challenging activities; which explains why they do not need the drive to run. With no neurobiological rewards received during and after demanding aerobic exercise, ferrets are less likely to engage in physically challenging exercise.
The experiment conducted does yield significant results, however many limitations are present throughout the investigation. For example, ferrets were the only test subjects used to investigate the theory of runner’s high for mammals that do not historically run. Therefore for more meaningful results, the study should be conducted with several taxa, comparing the response of eCBs levels across different species. This theory can then be applied to a wider selection of cursorial and non-cursorial animals rather than to just the one or two taxa in this experiment. Also, the number of trials should be increased and recorded for longer periods of time. For instance, the researchers should account for running trials every day for a week, to get a general consensus of how the eCB system responds after repeated activation.
Another limitation of the study was that the human volunteers were more athletic than most modern people. Therefore their ability to withstand high intensity workouts and experience effects of the runner’s high may vary compared to the “typical” human. In the experiment, low levels of exercise (such as walking) resulted in no change of plasma eCB levels. This leads to a hypothesis that inactive people may not be fit enough to tolerate intensity of the workout that leads to the rewarding sensation of runner’s high. Further research is necessary to explain why such a majority of the human population has an inactive lifestyle. To see how eCB plasma levels are affected in non-athletes, similar exercise testing should be performed on people accustomed to moderate, low, very minimum-intensity, and no exercise routine.
A third limitation to the conduction of the research is that the eCB levels in the brain could not be measured directly. Blood samples were taken from the periphery, and plasma levels of eCBs were quantified. Endocannabinoids are highly lipophilic which allows them to easily cross the blood brain barrier. Peripherally produced eCBs can hence activate the CB receptors in the mesolimbic reward area of the brain. Thus, the effects of neurotransmitter on the CNS were based on the plasma levels of eCB, and this may consequence in inaccurate results.
The article states that specific endocannabinoids, which are released within the mesolimbic dopamine system, stimulate an intensified dopamine release into specific areas of the brain such as nucleus accumbens. This area is responsible for behavioral rewards and is linked to addictions, as discussed in lecture. This may explain why running can cause an addictive response, where over exercising leads physical damage, and prevents individuals from having adequate rest. This would explain why athletes often experience withdrawal symptoms when an injury inhibits them from intense workouts.
It is widely known that humans engage in endurance exercises and experience its euphoric effects. However, this was the first study to compare the neurobiological effects of demanding aerobic exercise across species. The investigation suggests that all cursorial mammals experience the same rewards that drive them to run, while less active animals do not. The experiment provides insight for other researchers on how activity-dependent neurotransmitter signaling causes the differences in locomotor behavior among animals. This paper has opened opportunities to investigate further questions that have yet to be answered. For example, are neurobiological effects of the runner’s high is only initiated while running, or can other aerobic activity such as cycling trigger eCB levels to increase. Another question that could be proposed is what threshold of aerobic exercise is required to experience neurobiological rewards and why there appears to be no “reward” for less intense workout. An important topic to now consider after reading this paper is, why is natural selection encouraging higher rather than lower intensity activities in mammals that evolved to engage in enduring aerobic exercise.
In conclusion, this paper states there is an evolutionary drive to exercise, however, modern humans have learned to ignore it. By understanding more about how eCBs work, we can eventually help inactive individuals to strengthen their exercise tolerance until they reach the threshold to become motivated to exercise by eCBs. This would relate to my personal life because with a better understanding as to how runner’s high is initiated, I will try to increase my exercise tolerance, to be able to achieve the neurobiological reward, therefore making exercise more enjoyable and improving my lifestyle. This would also relate to the scientifically inclined world because the expansion of this topic can lead to researchers finding a way for eCBs levels to increase at lower intensity activities so that inactive individuals will be more driven to exercise. The study of aerobic exercise can be an available solution for people with medical conditions, improving the mental state through endocannabinoids and cardiovascular conditions and overall health through exercise.
References
Raichlen, D. A., Foster, A. D., Gerdeman, G. L., Seillier, A., & Giuffrida, A. (2012). Wired to run: exercise-induced endocannabinoid signaling in humans and cursorial mammals with implications for the ‘runner’s high’. The Journal of Experimental Biology, 215, 1331-1336. doi: 10.1242/jeb.063677
