Observation of Wheel Running Activity Based on Sex and Exogenous Sex Steroid Treatment

Introduction: Physical inactivity is a predominant underlying cause of many major chronic diseases. The sex steroids, including testosterone and 17β-estradiol, are known regulators of physical activity. Understanding the mechanisms by which each sex steroid drives physical activity is a critical step toward better strategies to promote routine participation in this healthy and important behavior. The current consensus regarding the mechanisms by which the sex steroids drive physical activity heavily involves the aromatization of testosterone into 17β-estradiol. Therefore, it is thought that 17β-estradiol is the primary driver in both males and females. However, there is evidence to suggest that testosterone acts on physical activity more quickly than 17β-estradiol, which would indicate a pathway independent of aromatization. We hypothesized that exposure to testosterone versus 17β-estradiol would result in physical activity patterns distinct from each other immediately following reintroduction of the sex steroids to physiologically deficient orchidectomized male and ovariectomized female mice via implantation of sex steroid releasing capsules. Methods: The study utilized 4 experimental groups with 4 mice per group (orchidectomized males treated with testosterone, orchidectomized males treated with 17β-estradiol, ovariectomized females treated with testosterone, and ovariectomized females treated with 17β-estradiol). It consisted of 3 activity measurement phases: baseline, post-gonadectomy, and post-replacement. During baseline measurement, the mice were given unrestricted access to running wheels (circumference of 450 mm) for 7 days following an acclimation period. Following gonadectomy surgeries, the mice were given a 10-day recovery period before wheel running resumed with another 7-day phase of unrestricted access. At the end of this phase, Silastic implants containing either testosterone or 17β-estradiol were introduced via a small incision. Mice were immediately given unrestricted access to running wheels for a 7-day phase following implantation to observe the immediate effects of each of the sex steroids on wheel running reinvigoration. Two-way mixed factorial ANOVAs were used to analyze wheel running distance (km), duration (min), and speed (m·min -1 ) based on sex and the replacement treatment received. Tukey’s HSD post hoc tests were computed when appropriate. Results: Statistically significant differences between the phases of the study were found for distance (F=20.226, p<0.001), duration (F=25.376, p<0.001), and speed (F=34.880, p<0.001). Distance dropped following gonadectomies (p=0.002) and was not restored following replacement (p=0.005). Duration dropped following gonadectomies (p<0.001) and was not restored following replacement (p<0.001). Speed dropped following gonadectomies (p<0.001) and was not restored following replacement (p=0.005). Day-by-day analysis showed a more precise picture of activity recovery and revealed that baseline distance levels dropped significantly following gonadectomies (p=0.012) and were restored on the 5 th day following steroid replacement (p=0.111). Conclusion: While baseline measurements for distance, duration, and speed were very low in the current study compared to values reported elsewhere in the scientific literature, these data suggest that the loss of the sex steroids induced significant decrements in wheel running. The decrease in activity is corrected in both male and female mice treated with either sex steroids but without notable differences in the recovery patterns induced by sex steroid reintroduction. All funding for this project was provided by the Union University Department of Biology. This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.