Evaluation of the c-Fos expression in the hippocampus after fatigue caused by one session of endurance exercise in pre-pubertal and adult rats.

Purpose: Central fatigue plays an important role in reducing endurance exercise activity during brain development. c-Fos gene expression in the hippocampus was examined as an indicator of neuronal activation after exhaustion.

Methods: Eighteen pre-pubertal male rats at four weeks old and 18 adult rats at eight weeks were randomly divided into three groups: Control (C), Constant time exercise (CTEx), Endurance Exercise until Exhaustion (ExhEx), which started at two minutes and ended in 20 min, the main swimming test was performed with a weight equal to 5% of the bodyweight attached to the rats' tail as a single session in experimental groups and was recorded at the end of their time, while to evaluate the force loss, the Grip strength was measured before and after the activity. The brain activation rate was examined by c-Fos gene expression and Nissl staining in CA3 and dentate gyrus (DG) in the hippocampus of all groups.

Results: Power grip and Nissl positive neurons in CA3 and DG have been significantly higher in pre-pubertal rats than in adults, both in the CTEx group (p = 0.04) and in the ExhEx group (p < 0.001). Also, real-time exhaustion in the pre-pubertal group was significantly longer than in adults. c-Fos gene expression was significantly reduced in adults' hippocampus in comparison to preadolescence (p < 0.01) and control (p < 0.001).

Conclusion: These findings clarified that increased strength and longer fatigue in pre-puberal rats may lead to c-Fos gene expression and decreased neurons in the hippocampus. Perhaps this is a protective effect to suppress stress hormones.