Enlarged housing space and increased spatial complexity enhance hippocampal neurogenesis but do not increase physical activity in mice.

Introduction: Environmental enrichment (EE) improves various health outcomes, such as hippocampal neurogenesis, in rodents, which is thought to be caused, in part, by increased physical activity. However, the specific effect of each enrichment component, such as enlarged housing spaces and increased spatial complexity with a variety of objects, on physical activity remains unclear because of methodological limitations in measuring physical activity. We aimed to examine whether enlarged housing spaces and increased spatial complexity increase physical activity in mice using a body-implantable actimeter. Methods: Adult male C57BL/6J mice were assigned to either standard housing or EE groups. The housing environment in the EE mice was gradually enriched by enlarging the housing space and the placement of a variety of objects. Physical activity was measured using a body-implanted actimeter. Hippocampal neurogenesis was immunohistochemically examined. Results: Enlarged housing spaces and the placement of a variety of objects did not increase physical activity in mice. In contrast, hippocampal neurogenesis was enhanced in the EE mice, suggesting that environmental interventions successfully provided enriched housing conditions for these mice. Conclusions: These results indicate that enlarged housing spaces and increased spatial complexity do not increase physical activity in mice. Furthermore, we found that EE enhanced hippocampal neurogenesis without increasing activity volume. Besides the current understanding that increasing the amount of physical activity is key to improving hippocampal function, our result suggests that the environment in which physical activity takes place is also a crucial contextual factor in determining the impact of physical activity on hippocampal function.

Exercise type influences the effect of an acute bout of exercise on hippocampal neuronal activation in mice.

The effects of exercise on the hippocampus depend on exercise conditions. Exercise intensity is thought to be a dominant factor that influences the effects of exercise on the hippocampus; however, it is uncertain whether the type of exercise influences its effectiveness. This study investigated whether the effect of an acute bout of exercise on hippocampal neuronal activation differs between two different types of exercise: treadmill and rotarod exercise. The intensities of both exercises were matched at just below the lactate threshold (LT), based on blood lactate concentration. Immunohistochemical examination of c-Fos, a marker of neuronal activation, revealed that treadmill exercise at 15 m/min (T15) significantly increased c-Fos expression in all subfields of the hippocampus (dentate gyrus DG, CA1, CA3), but rotarod exercise at 30 rpm (R30) did not, as compared with the respective control groups. These results demonstrate that moderate treadmill exercise more efficiently evokes hippocampal neuronal activation than does intensity-matched rotarod exercise. This suggests that exercise type is another important factor affecting the effects of exercise on the hippocampus.