Exercise-induced Neuroadaptations in Receptor Expression That Predispose to Addiction

- The neuroscience of addiction is complex and involves a variety of responses. Addiction is a chronic, relapsing disorder that involves compulsive seeking of a stimulant to feel euphoria, despite the adverse consequences. It involves functional changes to brain circuits that are involved with reward, stress, and self-control. Anybody can fall into the trap of addiction, even elite athletes. This research addresses certain neuroadaptations in the striatum of the brain that renders elite athletes more vulnerable to addictive behavior, particularly because of an increased tolerance to dopamine and an elongated stress response, leading athletes to seek additional stimulation through risk-taking. The intense exercise of elite athletes can increase D2 receptor expression and binding in the striatum, until tolerance to the elevated levels of dopamine is eventually developed. At the same time, long-term endurance exercise can activate the stress response and stimulate the HPA axis and the SAM pathway, releasing cortisol. Activation of the stress response can push athletes to seek out abusive drugs or behaviors and makes them more vulnerable to the euphoric effects of the stimulant. Rodent studies revealed that reduced function of striatal D2 receptors can lead to diminished sensitivity to negative outcomes, since striatal D2 receptors facilitate avoidance learning. With diminished sensitivity to punishing consequences, athletes are more likely to take part in risky behavior in search of a dopamine rush. Risk-taking behavior can directly lead to a greater vulnerability to addictive behavior. In addition, low striatal D2 receptor expression represents a predisposing factor for risk-taking and subsequent substance abuse. Although athletes' personalities and genetics may predispose them to certain addictive behaviors, their lifestyle can certainly endanger them as well. With the relatively small availability of literature on this topic, this paper will review the literature to test the above hypothesis.