Exercise-induced changes in c-Fos protein levels in skeletal muscle of trained and untrained rats.

We investigated the effect of an acute bout of endurance exercise on c-Fos protein levels in the extensor digitorum longus muscle of trained and untrained rats. Fifty rats were equally divided into a trained and an untrained group. Rats of the trained group ran on a treadmill 45 min/day for 5 days. On the sixth day, 5 rats were killed without exercise, while the remaining 20 ran as above and were killed 0, 3, 6, and 12 h post-exercise (5 rats at each time point). In the untrained group, 5 rats were killed without exercise, while the remaining 20 ran as above only once and were killed at the same time points as the trained group. Western blotting demonstrated no significant changes in c-Fos protein levels in the untrained group. On the contrary, in the trained group, there was a significant increase at 6 and 12 h compared to 3 h post-exercise. The levels of the protein in the trained rats were above the corresponding levels in the untrained ones at all time points, although these differences reached statistical significance only immediately, 6 h and 12 h post-exercise. These results show that trained skeletal muscle exhibits increased levels of c-Fos, probably as a cumulative result of changes occurring during recovery from each exercise bout, and greater c-Fos response after acute endurance exercise compared to untrained skeletal muscle.