Experience of exercising in a noisy environment disrupts hippocampal biochemical responses to light intensity exercise

The hippocampus is a brain region susceptible to the deleterious effects of stressors. Therefore, it is crucial to comprehend the adverse consequences of various stressors on the hippocampus. Previous studies have proposed that hippocampal brain-derived neurotrophic factor (BDNF) and vascular endothelial growth factor (VEGF) are upregulated as protective mechanisms in response to stressors. The present study investigated whether the experience of exercising in an environment with a stressor could convert stress-free light intensity exercise to a stressor based on the biochemical responses in the hippocampus.

In the experiment 1, C57BL/6J mice were subjected to 3 weeks of stress-free light intensity exercise (7.0 m/min, 30 min/day, 5 days/week) with or without a 110 dB noise stressor; then their plasma corticosterone levels were measured. Furthermore, in the experiment 2, the mice performed 3 weeks of light intensity exercise with or without a 110 dB noise stressor were subjected 30 min of acute light intensity exercise test (7.0 m/min) without noise. These mice were different from the mice used in Experiment 1. The hippocampi of mice were collected before or immediately after an acute exercise and were used to detect mRNA levels of Bdnf and Vegf.

The findings indicate that the 3-week intervention of light intensity exercise with or without a noise environment did not alter plasma corticosterone levels. However, the experience of exercising in a noisy environment disrupted the hippocampal Bdnf mRNA expression, which was further aggravated by subsequent acute exercise. A higher percentage of change in hippocampal Bdnf expression was shown in mice exposed to noise than those not. Moreover, hippocampal Vegf mRNA expression was upregulated in mice that performed regular exercise in a noisy environment but not in those that performed regular exercise without noise.

Our findings suggest that performing regular exercise at light intensity with environmental noisy stressors transforms the exercise into a threat cue, implying the role of environmental factors in hippocampal health.