Via EurekAlert!: researchers "have found that the age-related impairment of the body's ability to replace protective myelin sheaths, which normally surround nerve fibers and allow them to send signals properly, may be reversible, offering new hope that therapeutic strategies aimed at restoring efficient regeneration can be effective in the central nervous system throughout life. ... Using a surgical technique, the researchers introduced an experimental demyelinating injury in the spinal cord of an old mouse, creating small areas of myelin loss, and then exposed those areas to cells found the blood of a young mouse. By doing so, they found that the influx of certain immune cells, called macrophages, from the young mouse helped resident stem cells restore effective remyelination in the old mouse's spinal cord. This 'rejuvenating' effect of young immune cells was mediated in part by the greater efficiency of the young cells in clearing away myelin debris created by the demyelinating injury. Prior studies have shown that this debris impedes the regeneration of myelin. ... Aging impairs regenerative potential in the central nervous system. This impairment can be reversed, however, suggesting that the eventual development of cell-based or drug-based interventions that mimic the rejuvenation signals found in our study could be used therapeutically."