Rat Brains (IMAGE) Washington University School of Medicine Caption Pain researchers at Washington University School of Medicine in St. Louis have shown in rodents that they can block receptors on brain cells that are responsible for the negative emotions associated with pain, such as sadness, depression and lethargy. The findings could lead to new, less addictive approaches to pain treatment. In these PET images of rat brains, kappa opioid receptors (dark blue) are active in response to pain (right) in a part of the brain linked to emotion, but are relatively inactive when pain-free (left). Credit Washington University School of Medicine Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.