Mild stress facilitates learning and exercise improves retention in aged mice.

While chronic or severe stress generally has negative consequences in the brain, moderate stress has been shown to facilitate learning in young animals. It is unknown if stress facilitates or impairs learning in an aged animal. In this study, the effect of mild stress on learning and task retention (1 week later) was assessed in young and aged mice. In addition, because exercise can counteract negative effects of stress and facilitate learning, the effect of 1 week of voluntary exercise on task retention was assessed. Regulation of the learning/memory related genes BDNF exon VI, synapsin, MAPK, and CRFR1 were also examined in the hippocampus using real-time PCR. Results of this study demonstrate that mild stress 24h prior to the learning test improved performance in aged, but not young animals. However, exercise for 1 week between tests improved the performance of both groups of animals in the retention task. In aged, but not young animals, all four genes increased significantly after exercise. Thus, in aged animals mild stress facilitates learning and the retention of this task is improved by voluntary exercise.