Any of a group of protein s occurring in the brain and having pain-relieving properties typical of opium and related opiates.
Discovered in the 1970s, they include enkephalin, beta-endorphin, and dynorphin. Each is distributed in characteristic patterns throughout the nervous system. Endorphins are released in response to pain or sustained exertion (causing, e.g., the "runner's high"). They are also believed to have a role in appetite control, release of shock . There is strong evidence that they are connected with "pleasure centres" in the brain, and they seem to be activated by acupuncture . Knowledge of their behaviour has implications for treating addictions and chronic pain.