Long-term exercise is needed to enhance synaptic plasticity in the hippocampus

TLDR

Exercise benefits the brain by boosting neurogenesis, synaptic plasticity, and learning, yet the duration required to achieve these structural and functional gains remains unclear, with prior studies ranging from 3 days to 6 months. This study aimed to determine how different running durations (3, 7, 14, 28, 56 days) affect structural and functional changes in the dentate gyrus of adult male Sprague–Dawley rats. The authors evaluated cell proliferation, maturation, and in vivo long‑term potentiation in the dentate gyrus following voluntary wheel running for each time point. Voluntary running increased cell proliferation even after short periods, but neurogenesis and LTP improvements required longer exposure—neurogenesis appeared after 14 days, while robust LTP emerged only after 56 days, indicating that newly formed neurons must mature before enhancing synaptic plasticity.

Abstract

Exercise can have many benefits for the body, but it also benefits the brain by increasing neurogenesis, synaptic plasticity, and performance on learning and memory tasks. The period of exercise needed to realize the structural and functional benefits for the brain have not been well delineated, and previous studies have used periods of exercise exposure that range from as little as 3 d to up to 6 mo. In this study, we systematically evaluated the effects of differential running periods (3, 7, 14, 28, and 56 d) on both structural (cell proliferation and maturation) and functional (in vivo LTP) changes in the dentate gyrus of adult male Sprague–Dawley rats. We found that voluntary access to a running wheel for both short- and long-term periods can increase cell proliferation in the adult DG; however, increases in neurogenesis required longer term exposure to exercise. Increases in immature neurons were not observed until animals had been running for a minimum of 14 d. Similarly, short-term periods of wheel running did not facilitate LTP in the DG of adult animals, and reliable increases in LTP were only observed with 56 d of running. These results provide us with a greater understanding of the time course of wheel running access needed to enhance DG function. Furthermore, the results indicate that the new neurons produced in response to exercise in rats do not contribute significantly to synaptic plasticity until they mature.