PAIN AND THE WHOLE BODY: OVERALL BODY RESPONSES
The victim of sudden injury cries out. Every species has its version of this call. For some, it is an alarm call and the group scatters; for some it is a distress call for help and others rush to their aid. One-day-old baby mice emit an ultrasonic call far beyond our hearing range, and the mother runs over while the rest of the pack alert. We humans have an ambiguous reaction. 'Good' citizens move to help while others deliberately move away or waver. The entire body switches to an emergency mode. There are obvious changes in blood pressure, heart rate, sweating and breathing. But there are also less obvious changes. A group of elephants browsing at ease on the plains of Kenya can be heard a mile away because of the loud rumbling in their gut as they digest food. Complete silence descends abruptly if they are alarmed because part of their response is that gut movements cease. Gut paralysis and constipation are examples of the widespread consequences of wounding and can even be a serious complication in postoperative patients. Elective surgery offers a particularly fruitful way to study these overall body reactions because the patient can be studied in detail before the operation and during recovery. In addition to the pain-producing nerve impulses generated in the damaged tissue, there are many other factors including anxiety, starvation, sleep disturbance, blood loss and infection, which all disturb the body. In preparation for the emergency and the subsequent repair, the various hormone systems of the body go into high gear. They increase inflammation and mobilize sugar, fat and protein.
A special fraction of this hormone response is surprising. Hans Kosterlitz, of Austrian origin, was one of many refugee scientists to enrich British and American science. He spent a lifetime working in Aberdeen in Scotland on the action of narcotics. He followed the dictum of Claude Bernard in nineteenth-century Paris that plant poisons led us to discover crucial mechanisms already existing in the body. Bernard's triumph started with curare, which he showed interrupted the normal passage of nerve impulses from motor nerves to muscles and which led to the discovery of the natural chemical, acetylcholine, which makes muscles contract. Kosterlitz examined opium and believed that it must be acting on a body mechanism that normally responded in opium-like compounds. Finally, in his late seventies with his student John Hughes, he discovered that the brain did indeed make naturally occurring narcotics, which they named endorphins.
At almost the same time, Sol Snyder and his student Candace Pert at Johns Hopkins University in Baltimore discovered that some of the brain's cells contained highly specific receptor systems on which narcotics attached that changed the cells' properties. It was discovered to everyone's surprise that the body makes its own narcotics, the endorphins, and has receptors to react to them. Amongst other actions, these naturally occurring substances counteract pain. A special version of these endorphins, called enkephalin, increases in the upper part of the dorsal horn among the small cells. Furthermore, receptors for narcotics appear in damaged tissue.
This provides the basis for the most useful treatment for the pain of injury, the administration of narcotics such as morphine. Morphine simply imitates and enhances part of the ongoing process by which the body reacts to injury. Morphine combined with the natural narcotics of the body reduces pain and other reactions, such as anxiety and hormone responses. Even constipation is caused when narcotics are administered, just as it occurs when wounding releases the body's own narcotics. When nerve impulses from the wounded tissue at the site of the operation are prevented from entering the cord by local anaesthetics in a spinal block, not only does the pain not occur but most of the hormone changes are also prevented.
Fainting is an extreme example of the body's overall reaction to an emergency. Nerve and hormonal mechanisms divert blood to the vital deep organs and away from the skin, which turns white. The blood pressure drops suddenly, reducing bleeding. The person is unconscious and still.
Conscious awareness of pain is one part of a massive synchronized series of reactions associated with tissue damage. The reaction is a coordinated whole. It would be very unwise to assume that each component of this overall reaction, including pain, has its own separate and private mechanism. Unfortunately, that is precisely the traditional view which I will attempt to counteract.
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