Early-Age Running Enhances Activity of Adult-Born Dentate Granule Neurons following Learning in Rats

Abstract

Cognitive reserve, the brain's capacity to draw on enriching experiences during youth, is believed to protect against memory loss associated with a decline in hippocampal function, as seen in normal aging and neurodegenerative disease. Adult neurogenesis has been suggested as a specific mechanism involved in cognitive (or neurogenic) reserve. The first objective of this study was to compare learning–related neuronal activity in adult-born vs. developmentally-born hippocampal neurons in juvenile male rats that had engaged in extensive running activity during early development or reared in a standard laboratory environment. The second objective was to investigate the long-term effect of exercise in rats on learning and memory of a contextual fear response later in adulthood. These aims address the important question as to whether exercise in early life is sufficient to build a reserve that protects against the process of cognitive aging. The results reveal a long-term effect of early running on adult-born dentate granule neurons and a special role for adult-born neurons in contextual memory, in a manner that is consistent with the neurogenic reserve hypothesis.

Significance Statement The role of adult neurogenesis in learning and memory is under active investigation, but the underlying mechanisms remain unclear. The present study found that early-age running led to enhanced associative learning and memory in adult rats and increased activity of adult-born granule neurons in the dentate gyrus during memory retrieval. This study demonstrates the long-term effect of early-age physical activity on learning and memory much later in life. The findings emphasize the involvement of adult-born hippocampal neurons in neurogenic and functional cognitive reserve and show that physical activity contributes to memory improvement.