Strength exercise weakens aerobic exercise-induced cognitive improvements in rats

Abstract

Aerobic exercise improves cognitive function and adult hippocampal neurogenesis. However, the effects of aerobic exercise combined with strength exercise on cognitive function and adult hippocampal neurogenesis are still unknown. In this study, we established exercise paradigms in rats to mimic aerobic exercise combined with low- and high-intensity strength exercise. We found that aerobic exercise improved spatial learning and memory as well as adult hippocampal neurogenesis, whereas strength exercise suppressed aerobic exercise-induced cognitive improvements and adult hippocampal neurogenesis in an intensity-dependent manner. Furthermore, the levels of β-hydroxybutyrate (β-HB) and its downstream effector brain-derived neurotrophic factor (BDNF) were increased in the aerobic exercise group, and strength exercise impaired the aerobic exercise-induced increases in β-HB and BDNF mRNA levels. Taken together, these results demonstrated that strength exercise weakened aerobic exercise-induced cognitive improvements and adult hippocampal neurogenesis in rats.

Fig 1. Design of exercise behavior paradigms.

Different exercise strategies were implemented in 8-week-old male Wistar rats. (A, n = 8/group) (B). Paradigms of the familiarization exercise strategies. A detailed outline of the training protocol. (C, n = 8). Detection of lactic acid levels in the blood after physical exercise. ***, p < 0.001, **, p < 0.01; one-way ANOVA; n = 8 for (C). Quantitative analysis of whole body muscle weight/body weight (D) and hind limb muscle weight/body weight (E) after two months of training. Data are shown as the mean ± SEM; ***, p < 0.001; **, p < 0.01; one-way ANOVA; n = 8 for (C and D).

Fig 2. Strength exercise decreases aerobic exercise-induced cognitive function improvements, as indicated by the Morris water maze test.

(A). Outline of the experiment. The Morris water maze test was performed after 8 weeks of training. Each group of rats was trained with the hidden platform for 6 days, and on the seventh day, the platform was removed. Quantitative analysis of the swimming speed on the first day (B), the latency to the platform for six days of training (C), the number of platform crosses in the probe test (D), and the time spent in the target quadrant (E). Data are shown as the mean ± SEM; **, p < 0.01, *, p < 0.05; one-way ANOVA; n = 8.

Fig 3. Strength exercise reduces aerobic exercise-induced adult hippocampal neurogenesis.

(A). Outline of the experiment. BrdU was injected four times into each group of rats within 12 hours after the indicated training. Twelve hours later, the rats were sacrificed, and immunostaining was performed. Coronal brain sections prepared from the indicated training group were stained with an anti-BrdU antibody (green) to label proliferating cells during 4 injections in the dentate gyrus of the hippocampus. (C). Quantitative analysis of BrdU-positive cells in (B). Coronal brain sections were stained with an anti-Ki67 antibody (red) to label proliferating cells in the dentate gyrus. (E). Quantitative analysis of Ki67-positive cells in (D). Data are shown as the mean ± SEM; ***, p < 0.001, **, p < 0.01; one-way ANOVA; n = 8 for (B); ***, p < 0.001, **, p < 0.01, *, p < 0.05; one-way ANOVA; n = 8 for (C, E).

Fig 4. Strength exercise reduces the aerobic exercise-induced increases in the levels of β-HB and BDNF in the hippocampus.

(A). Outline of the experiment. The hippocampus was dissected from each group of rats for analysis after training. (B). The β-HB level of each group of rats was analyzed in the right hippocampus. (C). BDNF mRNA levels in each group of rats were determined in the left hippocampus. Data are shown as the mean ± SEM; ***, p < 0.001, **, p < 0.01, *, p < 0.05, one-way ANOVA; n = 4 for (B, C).