Author(s): SUDO, M., ANDO, S., Institution: PHYSICAL FITNESS RESEARCH , Country: JAPAN, Abstract-ID: 1491

INTRODUCTION:
It has been suggested that aerobic exercise is beneficial to brain function. Similarly, environmental enrichment (EE) has a variety of positive effects on brain function by facilitating neuroprotection and enhancing neuroplasticity (Ramirez-Rodriguez et al, 2022). However, the relationship between physical activity and improvements in brain function in an EE environment remains unclear. We hypothesized that physical activity, including wheel running/standing movements, under long-term EE exposure plays a key role in corticosterone level reduction and better emotion. PURPOSE: The purpose of this study was to determine the effects of physical activity on corticosterone level and emotion in the EE.
METHODS:
Wistar rats were housed in four different groups; EE (running wheel and objects: slope, tunnel, and hut), running wheel only (EE-R), objects only (EE-O), and standard environment (SE) (N=6/group), for a period of four weeks. Physical activity (PA) level of each rat was continuously recorded using an embedded three-axis accelerometer. Number of rearing and duration of wheel running were measured during the 12-hour dark period in the last week. After four weeks of exposure to each condition, anxiolytic-like behavior was assessed from the elevated plus maze (EPM) test. Serum corticosterone levels were analyzed using an enzyme-linked immunoassay kit.
RESULTS:
The PA level of the EE, and EE-R groups were higher than the SE group in the dark period (P < 0.0001). Duration of wheel running was higher in the EE (56.3 ± 14.7 min) than EE-R (37.2 ± 9.4 min, P = 0.03) in the dark period. Number of rearing was not different among all groups. The serum corticosterone concentration was lower in the all EE groups than that in the SE group (Ps < 0.01.）In the EPM test, ratio of open and close arms spent time (O/C ratio) was greater in the EE (163.5 ± 63.5) and EE-R (173.1 ± 130.5) groups than the SE group (11.4 ± 7.6, Ps < 0.01). Furthermore, we observed a negative correlation between total PA level and corticosterone level (r2=0.17, P = 0.04). We also observed a positive correlation between total PA level and the O/C ratio (r2=0.37, P = 0.001). In contrast, no correlations were found between duration of wheel running time and the O/C ratio. These results suggest that higher PA level is associated with lower corticosterone levels and better anxiolytic-like behavior in EE.
CONCLUSION:
This study revealed that an enrichment environment reduces corticosterone level and anxiety-like behaviors. Furthermore, reduction of anxiety-like behavior was related to the amount of physical activity, but not to wheel running duration. These results suggest that spontaneous intermittent physical activity may contribute to reductions in corticosterone level and anxiety-like behavior.
Reference: Gerardo Bernab ́e Ramírez-Rodríguez et al., Physiology & Behavior (2022)