Adrenalectomy and glucocorticoid inhibition prevent the beneficial effects of voluntary exercise on fear memory and hippocampal neural counting in rats

Several evidences demonstrate the beneficial effects of voluntary exercise on cognitive functions in rodents. It is well established that the glucocorticoid system plays an important role in regulation of learning and memory. In previous study, we have shown that glucocorticoids are involved in mediating the effect of voluntary exercise on spatial learning and memory. Moreover, physical activity enhaces glucocorticoids. This study addressed whether the glucocorticoid system would play a role in the exercise-induced enhancement of fear memory and hippocampal neuronal numbers in rats.
Rats that were either adrenalectomized or daily given the corticosterone-synthesis inhibitor metyrapone were allowed to freely exercise in a running wheel for 10 days. After this period, they were trained and tested on a passive avoidance task, succeeded by a retention test two days later. Immediatley after memory testing, the rats were decapitated, and their hippocampi were removed for the measurement of the neuron conting in the dentate gyrus.
Exercise significantly improved the performance of fear memory retrieval and increased neuronal number in hippocampus whereas this effect was absent in both adrenalectomized and metyrapone-treated rats.
These findings indicate that the glucocorticoids play a crucial role in the beneficial effects of voluntary exercise on fear memory formation and neural counting in the hippocampus