Brain opioid receptors (IMAGE) University of Turku Caption Brain opioid receptors measured with positron emission tomography (A) and regions, where opioid receptor density varied seasonally. Credit University of Turku Usage Restrictions Please attribute the photo to the University of Turku 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.