The Influence of Activity and Age on Endurance in Mice Selected for High Voluntary Wheel Running

Event Center A & B

Voluntary locomotor activity may be affected by a variety of intrinsic factors (e.g., physiology) and environmental factors (e.g., substrate). Voluntary activity is known to decline with age in mammals due to decreases in neurological motivation and musculoskeletal vitality. Because disuse and aging exhibit similar pathologies and / performance deficits, isolating the influences or effects of a single factor is difficult. In this study we used house mice that have been selectively bred for voluntary wheel running over 70 generations in order to determine the effects of varying activity level and age on endurance. A total of 32 mice from four control (C) and four high wheel running (HWR) lines were housed either in cages with monitored wheels (active treatment: AT) or in cages with no wheels (inactive treatment: IT). Endurance was measured as time to exhaustion during an incremental speed test on a treadmill elevated to nearly 30°, and was tested for each mouse at two early stage aging time points (14 and 16 months). For mice with wheel access (N=16 / AT), daily wheel revolutions were recorded at 0.25-0.5 Hz for the month prior to endurance testing. Additionally, the duration and number of pauses during each mouse’s two hour peak activity was recorded to quantify the intermittency of an individual’s wheel activity. HWR lines demonstrated significantly greater endurance times, regardless of treatment or age. However, endurance performance decreased significantly with age in all line x treatment combinations except for the HWR-AT group, which maintained nearly the same mean performance times. Our results suggest that activity level and motivation are both important contributions to agerelated decline in locomotor performance.