PAP Enzyme in Pain-sensing Neurons (IMAGE) University of North Carolina Health Care Caption Image shows PAP (in red) in pain-sensing neurons. Credit Mark Zylka, Ph.D. 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.