Swedish neurochemist who was the first to show that certain small peptides, produced naturally in the body, act on the brain's opiate receptors in a manner similar to that of other opiates. This discovery helped elucidate the pharmacological effects of opiates and other painkillers, widely used in the practice of medicine. It also gave important insights into the chemistry of the brain, helping researchers to better understand the origins of some mental disorders resulting from chemical imbalances.