Endorphins are the body's natural way of toning down specific pain responses by binding with opiate receptors in the brain. Endorphins are polypeptides naturally produced in the brain. Their physiological effect is similar to the analgesia (pain relief) of morphine. Chemically, they are classified as opioid-peptides and have 16-31 amino acids in their polypeptide chain.
The search for endorphins began in the 1970s with the attempts to isolate opiate binding sites in the brain. Vincent Dole of Rockefeller University did the early work in this area in 1970. In 1973, at Johns Hopkins University, Solomon Snyder and his graduate student Candace Pert isolated opiate receptors on nervous tissue. With the discovery of the receptor sites, the search for the molecules that bound to these sites intensified. In 1975, Choh Hao Li of the University of California at Berkeley isolated endorphins from a pituitary hormone that he had originally isolated in 1960. He named the biochemical endorphin, meaning "the morphine within." Endorphin research achieved worldwide recognition in 1977 with the awarding of the Nobel Prize in physiology or medicine to Roger Guillemin and Andrew Schally for their work on peptide hormone production of the brain.
The three main families of opioid-peptides are the endorphins, the enkephalins, and the dynorphins. To date, four groups of endorphins (alpha, beta, gamma, and sigma) have been identified. Beta-endorphins are the most potent endogenous opioid that affects both physiological and mental processes. The effects range from central nervous system and peripheral nervous system analgesia and pain modulation to effects on neuro-endocrine control of reproduction, stress, spontaneous behavior, and motivation. Although endorphins act as neurotransmitters and neurohormones, their role in physiological processes is still not completely understood. For example, a small 2006 study showed that people expecting to see a humorous video released more beta-endorphins than a control group who did not get to watch a video. The group who saw the videos experienced higher beta-endorphin readings before, during, and after the viewing.