Endorphin and Enkephalin
When a person is injured, pain impulses travel up the spinal cord to the brain, which then releases endorphins and enkephalins, the body 's natural painkillers. Enkephalins block pain signals in the spinal cord, while endorphins are thought to alleviate pain principally at the brainstem. Both are morphine-like substances whose functions are similar to those of opiate drugs.
Today, the word endorphin—a combination of "endo" from endogenously manufactured (i.e. manufactured within the human body) and "orphin" from morphine-like substances--is used generically to describe both groups of painkillers. These endogenous opiates include enkaphalins (methionine and leucine), endorphins (alpha, beta, gamma, and sigma) and a growing number of synthetic compounds.
The discovery of these neurochemicals occurred after several bodies of research were conducted and compared. In 1965, at the University of California, San Francisco, Chinese-born biochemist Choh Hao Li and David Chung reported the discovery of beta-endorphin, the first endorphin to be isolated and announced in scientific journals. Although they had isolated and sequenced the most potent natural opioid, Li and Chung were unable to determine the exact function of beta-endorphin. Their discovery was soon followed in 1967 by theories that proposed that the opiate narcotics mimic the actions of naturally occurring chemicals within the brain and provide analgesia by manipulating the receivers, or opioid receptors, for those naturally occurring substances.
The existence of opioid receptors was conclusively demonstrated in 1973 by Candace Pert and Solomon Snyder, who discovered the receivers in rat brains and guinea pig intestines. This discovery enabled researchers to study the way morphine works with these opioid receptors to diminish pain, as well as providing the opportunity to study the effect of morphine on the brain.
In 1974 John Hughes and Hans Kosterlitz of Scotland discovered that enkephalins are produced in the brains of vertebrates, serving as a kind of opioid receptor and regulating pain pathways leading from peripheral nerves to the brain. Brain chemistry investigations were given added impetus by the discovery in the late 1970s that there are specific sites in the brain to which opiate drugs--morphine and heroin, for example--attach themselves and perform their functions. When such drugs are given, they occupy the pain receptors of the brain, and the brain itself lowers its natural production of endorphins. When the drugs leave the system, the brain is not producing its natural level of endorphins, causing a craving for these painkillers and withdrawal symptoms.
Researchers subsequently identified the two naturally occurring chemicals—endorphins and enkephalins--as producing morphine-like effects. This offered opportunities for developing drugs similar in structure to the natural pain-killing substances. The power of mind-producing pain killers and their psychological effects on the body were revealed in 1978, when researcher Jon Levine and oral surgeon Newton Gordon of the University of California's Fields School of Medicine and School of Dentistry discovered that the endorphin system can also be activated by placebos (sugar pills) administered during studies to patients in a control group. This discovery served as proof that psychological stimuli can trigger the release of endorphins.
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