The Work of Bruce McEwen

Dr. Bruce McEwen, a luminary in the field of neuroscience, died on January 2, 2020. Despite the role he played in expanding the studies conducted on hormones such as cortisol and adrenaline in the brain, his experiments remain mostly unrecognized. His work began in the 1960s, a time when stress was defined as the body’s alarm system, switching on only when a person faces a drastic situation. Dr. McEwen redefined stress as not only a reaction to an extreme situation, but also the body’s way of responding to the obstacles it faces every day.

An example of his groundbreaking research was a project in which his team discovered the profound effects hormones had on the brain. His experiment consisted of placing four to five male rats as well as two to three female rats in a controlled environment. The male rats quickly established social hierarchies, where the dominant males controlled access to food, water, and to a lesser extent, the females. The subordinate and dominant males were easily identified based on the patterns of offensive or defensive wounding as subordinate rats were attacked when they attempted to access food and water. The stress of trying to survive in a hostile environment was enough for the subordinate rats to experience significant weight loss and after two weeks, death. Analysis of the subordinate rats’ brains revealed that the neurons near the hippocampus, the brain’s memory and learning center, were atrophied, a result of the stress from the hostile environment created by the dominant rats.

One radical idea of Dr. McEwen was that of “good” stress. He categorized stress into three categories: "good stress," a response to an immediate challenge with a burst of energy that focuses the mind; "transient stress," a response to daily frustrations that resolve quickly; and "chronic stress," a response to a toxic, unrelenting barrage of challenges that eventually break down the body.

In his later years, Dr. McEwen became interested in how hormones like insulin and ghrelin, the hunger hormone, affect the brain and explored why people with diabetes and metabolic syndrome (conditions that raise the likelihood of developing heart disease, a stroke, or diabetes) are more likely to suffer from depression. For example, he performed an experiment in which rats predisposed to Type 1 diabetes (an animal model for human Type 1 diabetes) were exposed to chronic stress. Dr. McEwen discovered that exposing the rats to chronic stress made them phenotypically express the Type 1 diabetes gene much more: 80 percent of the male stress and 70 percent of the female stress animals developed diabetes, compared with 50 percent in both control groups. He also explored how factors like nutrition, physical activity, and exposure to early-life trauma can also alter the brain.

Dr. McEwen’s work is extremely meaningful in the context of Stuyvesant, where a stressful school environment can lead to physiological changes. “Good stress” could be redefined as acing a test that you had doubts about, while an example of “transient stress” would be facing the daily subway delays that cause you to be late to school. “Chronic stress” in the context of Stuyvesant could be the sleep deprivation that students face on a daily basis. Changing your breakfast meal from a bowl of cereal to eggs and bacon or eating healthy snacks throughout the day could reduce the allostatic load your body faces. Managing your life in the context of Dr. McEwen’s research may ease the grind of getting through a busy day at Stuyvesant.