Ulcers in Executive Monkeys

Ulcers in Executive Monkeys was a study into the effects of stress, published in 1958 in "Scientific American" by Joseph V. Brady.

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 shocks 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 ulcers.

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.

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 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.

Relevance to humans

In 1979 J. Robin Warren, 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.