Muscle Fibers (image) University of California - Berkeley Caption On the left is healthy muscle tissue from a young mouse. The ability of muscle to repair itself decreases with age, as evidenced by the middle image of old muscle tissue, which shows a lower density of muscle fibers, increased scar tissue and inflammation. The addition of oxytocin to the blood of old mice rapidly rejuvenates the old muscle, as shown in the image on the right. Credit Photos by Wendy Cousin and Christian Elabd, UC Berkeley. Usage Restrictions All rights reserved. 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.