The Serengeti Rules

releasing factor, CRF, to the nearby pituitary gland that triggered it to release a chemical called adrenocorticotropic hormone, ACTH, that traveled to another part of the adrenal gland and triggered the release of another chemical, cortisol, which increased blood pressure and blood flow to my muscles. All these physiological changes are part of what is known as the fight-or-flight response. Coined and described a century ago by Harvard physiologist Walter Cannon, these responses are aroused by both fear and rage and quickly prepare the body for conflict or escape. We opted for escape. Scaredy Cats. Cannon first became interested in the body's response to fear while conducting pioneering studies on digestion. X-rays had just been discovered when Cannon was a medical student. A professor suggested that he try to use the new gadget to watch the mechanics of the process. In December 1896, Cannon and a fellow student successfully obtained their first images of a dog swallowing a pearl button. They soon experimented with other animals, including a chicken, a goose, a frog, and cats. One challenge to observing digestion was that soft tissues, such as the stomach and intestines, did not show up well on X-rays. Cannon found that feeding animals food mixed with bismuth salts made their digestive tracts visible because the element was opaque to the rays. He also explored the use of barium. It was too expensive at the time for research work, but was later adopted by radiologists and still is used in gastroenterology today. In a classic series of studies, Cannon was able to observe for the first time in living, healthy, non-anesthetized animals, as well as in people, how peristaltic contractions move food through the esophagus, stomach, and intestines. During the course of his experiments, Cannon noticed that when a cat became agitated, the contractions promptly stopped. He jotted in his notebook, "...noticed several times very distinctly, so absolutely no doubt, that when cat passed from quiet breathing into a rage with struggling, the movements stopped entirely. After about one half minute, the movements started again." Cannon repeated the experiment again and again, every time the movements resumed once the animal calmed down. The second-year medical student now had another finding to his credit. In what would become the second classic paper of his budding career, he wrote, "...it has long been common knowledge that violent emotions interfere with the digestive process, but that the gastric motor activities should manifest such extreme sensitiveness to nervous conditions is surprising." Cannon's knack for experiments soon derailed his plans to become a practicing physician. His talent, rigor, and work ethic so impressed the distinguished faculty of the Department of Physiology at Harvard that he was offered an instructorship on graduation. The Nervous Stomach In his own laboratory, Cannon aimed to figure out how emotions affected digestion. He observed that emotional distress also ceased digestion in rabbits, dogs, and guinea pigs, and from the medical literature, that also seemed to be true of humans. The connection between emotions and digestion suggested some direct role of the nervous system in controlling the digestive organs. Cannon knew that all the outward signs of emotional stress—the pallor caused by the contraction of blood vessels, cold sweat, dry mouth, dilation of pupils, skin hair standing on end—occurred in structures that are supplied by smooth muscle and innervated by the so-called sympathetic nervous system. The sympathetic system comprises a series of neurons that originate from the thoracic lumbar region of the spinal cord and travel out to clusters of nerve cells called ganglia. From there, a second set of generally much longer neurons extend to and innervate target organs. Most of the body's organs and glands receive sympathetic input, including the skin, arteries and arterioles, the iris of the eyes, the heart, and the digestive organs. These same organs also receive input from nerves originating in the cranial or sacral parts of the spinal cord.