Ulcers in Executive Monkeys
Encyclopedia
Ulcers in Executive Monkeys was a study into the effects of stress, published in 1958 in Scientific American
by Joseph V. Brady
.
s every 20 seconds unless they pressed the lever during the same time period. This study came to an abrupt halt when many of the monkeys died from perforated ulcer
s.
To test this Brady used a yoked control
monkey. He placed an 'Executive Monkey' in the restraining chair, which could press the lever to prevent the electric shock. The yoked monkey had no control over the lever, leaving only the 'Executive' with the psychological stress of pushing the lever.
The greatest danger occurred when the sympathetic arousal
stopped and the stomach was flooded with digestive hormones. This was a parasympathetic
rebound associated with the Hypothalamic-pituitary-adrenal axis
, which lead the development of ulcers in the Executive monkeys.
In all the variations of the experiment, no yoked control monkey ever developed an ulcer. This suggests that the ulcers were a symptom of the excessive stress induced by having control. Hans Selye
's General Adaptation Syndrome
proposes a similar effect in the Exhaustion phase.
, a pathologist at the Royal Perth Hospital in Australia, when examining tissue specimens from patients who had undergone stomach biopsies, noticed that several samples had large numbers of curved and spiral-shaped bacteria. The expectation was that stomach acid would destroy such organisms. But those Warren saw lay underneath the organ's thick mucus layer—a lining that coats the stomach's tissues and protects them from acid. Warren made note that the bacteria were present only in tissue samples that were inflamed. Inquiring if the microbes might somehow be related to the irritation, he researched literature for clues to find that German pathologists had witnessed similar organisms a century earlier. The Germans failed to grow the bacteria in culture, their findings were ignored and then forgotten .
Warren, with the help of an enthusiastic young trainee named Barry J. Marshall, also found it difficult to grow the unknown bacteria in culture. He began his efforts in 1981. By April 1982 the two men had attempted to culture samples from 30- odd patients—all without success. Then the Easter holidays arrived. The hospital laboratory staff accidentally held some of the culture plates for five days instead of the usual two. On the fifth day, colonies emerged. The workers christened them Campylobacter pyloridis because they resembled pathogenic bacteria of the Campylobacter
genus found in the intestinal tract. Early in 1983 Warren and Marshall published their first report, and within months scientists around the world had isolated the bacteria. They found that it did not, in fact, fit into the Campylobacter genus, and so a new genus, Helicobacter
, was created. These researchers also confirmed Warren's initial finding, namely that Helicobacter pylori
infection is strongly associated with persistent stomach inflammation, termed chronic superficial gastritis .
Scientific American
Scientific American is a popular science magazine. It is notable for its long history of presenting science monthly to an educated but not necessarily scientific public, through its careful attention to the clarity of its text as well as the quality of its specially commissioned color graphics...
by Joseph V. Brady
Joseph V. Brady
Joseph Vincent Brady was a behavioral neuroscientist at the Walter Reed Army Institute of Research in the United States. While at the Walter Reed Institute he performed the experiment "Ulcers in Executive Monkeys" that suggested a link between stress and peptic ulcers...
.
Method of the experiment
In an early version of the study, Brady placed monkeys in 'restraining chairs' and conditioned them to press a lever . They were given electric shockElectric shock
Electric Shock of a body with any source of electricity that causes a sufficient current through the skin, muscles or hair. Typically, the expression is used to denote an unwanted exposure to electricity, hence the effects are considered undesirable....
s every 20 seconds unless they pressed the lever during the same time period. This study came to an abrupt halt when many of the monkeys died from perforated ulcer
Perforated ulcer
A perforated ulcer, is a very serious condition where an untreated ulcer can burn through the wall of the stomach , allowing digestive juices and food to leech into the abdominal cavity. Treatment generally requires immediate surgery...
s.
To test this Brady used a yoked control
Scientific control
Scientific control allows for comparisons of concepts. It is a part of the scientific method. Scientific control is often used in discussion of natural experiments. For instance, during drug testing, scientists will try to control two groups to keep them as identical and normal as possible, then...
monkey. He placed an 'Executive Monkey' in the restraining chair, which could press the lever to prevent the electric shock. The yoked monkey had no control over the lever, leaving only the 'Executive' with the psychological stress of pushing the lever.
Results
After 23 days of a 6 hours on, 6 hours off schedule to the electric shocks, the executive monkey died. Brady then tried various schedules, but no monkeys died from this. He then returned to the original 6 on, 6 off, and tested the stomachs of the Executives and found that their stomach acidity was greatest during the rest period.The greatest danger occurred when the sympathetic arousal
Sympathetic nervous system
The sympathetic nervous system is one of the three parts of the autonomic nervous system, along with the enteric and parasympathetic systems. Its general action is to mobilize the body's nervous system fight-or-flight response...
stopped and the stomach was flooded with digestive hormones. This was a parasympathetic
Parasympathetic nervous system
The parasympathetic nervous system is one of the two main divisions of the autonomic nervous system . The ANS is responsible for regulation of internal organs and glands, which occurs unconsciously...
rebound associated with the Hypothalamic-pituitary-adrenal axis
Hypothalamic-pituitary-adrenal axis
The hypothalamic-pituitary-adrenal axis , also known as thelimbic-hypothalamic-pituitary-adrenal axis and, occasionally, as the hypothalamic-pituitary-adrenal-gonadotropic axis, is a complex set of direct influences and feedback interactions among the hypothalamus, the pituitary gland ,...
, which lead the development of ulcers in the Executive monkeys.
In all the variations of the experiment, no yoked control monkey ever developed an ulcer. This suggests that the ulcers were a symptom of the excessive stress induced by having control. Hans Selye
Hans Selye
Hans Hugo Bruno Selye, CC was a pioneering endocrinologist. Selye did much important scientific work on the hypothetical non-specific response of an organism to stressors. While he did not recognize all of the many aspects of glucocorticoids, Selye was aware of their role in the stress response...
's General Adaptation Syndrome
Stress (medicine)
Stress is a term in psychology and biology, borrowed from physics and engineering and first used in the biological context in the 1930s, which has in more recent decades become commonly used in popular parlance...
proposes a similar effect in the Exhaustion phase.
Relevance to humans
In 1979 J. Robin WarrenRobin Warren
John Robin Warren AC is an Australian pathologist, Nobel Laureate and researcher who is credited with the 1979 re-discovery of the bacterium Helicobacter pylori, together with Barry Marshall.- Life and career :...
, a pathologist at the Royal Perth Hospital in Australia, when examining tissue specimens from patients who had undergone stomach biopsies, noticed that several samples had large numbers of curved and spiral-shaped bacteria. The expectation was that stomach acid would destroy such organisms. But those Warren saw lay underneath the organ's thick mucus layer—a lining that coats the stomach's tissues and protects them from acid. Warren made note that the bacteria were present only in tissue samples that were inflamed. Inquiring if the microbes might somehow be related to the irritation, he researched literature for clues to find that German pathologists had witnessed similar organisms a century earlier. The Germans failed to grow the bacteria in culture, their findings were ignored and then forgotten .
Warren, with the help of an enthusiastic young trainee named Barry J. Marshall, also found it difficult to grow the unknown bacteria in culture. He began his efforts in 1981. By April 1982 the two men had attempted to culture samples from 30- odd patients—all without success. Then the Easter holidays arrived. The hospital laboratory staff accidentally held some of the culture plates for five days instead of the usual two. On the fifth day, colonies emerged. The workers christened them Campylobacter pyloridis because they resembled pathogenic bacteria of the Campylobacter
Campylobacter
Campylobacter is a genus of bacteria that are Gram-negative, spiral, and microaerophilic. Motile, with either unipolar or bipolar flagella, the organisms have a characteristic spiral/corkscrew appearance and are oxidase-positive. Campylobacter jejuni is now recognized as one of the main causes...
genus found in the intestinal tract. Early in 1983 Warren and Marshall published their first report, and within months scientists around the world had isolated the bacteria. They found that it did not, in fact, fit into the Campylobacter genus, and so a new genus, Helicobacter
Helicobacter
Helicobacter is a genus of Gram-negative bacteria possessing a characteristic helix shape. They were initially considered to be members of the Campylobacter genus, but since 1989 they have been grouped in their own genus...
, was created. These researchers also confirmed Warren's initial finding, namely that Helicobacter pylori
Helicobacter pylori
Helicobacter pylori , previously named Campylobacter pyloridis, is a Gram-negative, microaerophilic bacterium found in the stomach. It was identified in 1982 by Barry Marshall and Robin Warren, who found that it was present in patients with chronic gastritis and gastric ulcers, conditions that were...
infection is strongly associated with persistent stomach inflammation, termed chronic superficial gastritis .