Influence of Age of Exposure to a Running Wheel on Activity in Inbred Mice

Abstract

It is currently unknown whether the age of wheel exposure influences running wheel activity in mice. The purpose of this study was to determine whether the age at which a running wheel was introduced affected running wheel activity for a subsequent 15-wk period. Twenty female C57Bl/6J mice (age 7 wk) were assigned to one of four experimental groups. Group 1 received a running wheel at 7 wk of age. Thereafter, groups 2, 3, and 4 received running wheels at 10, 13, and 16 wk of age, respectively. Daily running wheel activity (duration, distance, and velocity) was recorded from the time of running wheel exposure until 30 wk of age. A repeated-measures MANOVA found significant differences between groups for distance (P = 0.02), duration (P = 0.04), and velocity (P = 0.001) during the 15-wk concurrent running period (age 16-30 wk). Post hoc tests revealed significantly greater distance and duration in group 4 compared with group 2 and significantly greater velocity in group 4 compared with each of the other groups. Significant interactions were found between groups over time for distance (P = 0.01) and duration (P = 0.05). No significant difference between groups was observed for body weight over the 24-wk period (P > 0.05). Although differences were found between groups 2 and 4, these data suggest that the age at which physical activity is introduced has little influence on the subsequent level of physical activity in C57Bl/6J mice. However, it appears that introduction of the running wheel at 16 wk of age results in greater within group variance, suggestive of a greater environmental influence on daily running wheel activity.