Sex steroid-induced decrements in wheel running due to reduced early dark period vigor

• Published in: Physiology (Bethesda, Md.) Vol. 40; no. S1
• Main Author: Bowen, Robert S.
• Format: Journal Article
• Language: English
• Published: 01.05.2025
• ISSN: 1548-9213; 1548-9221
• DOI: 10.1152/physiol.2025.40.S1.0419

Abstract only Introduction: Physical activity behaviors affect overall health and quality of life in human and animal subjects. Despite well-intentioned initiatives to remove the socioeconomic barriers that prevent routine participation in physical activity behaviors, improve city and built landscape walkability, and promote monetary or insurance benefits for physically active persons, most individuals fail to meet physical activity recommendations. Evidence suggests that while external environmental factors influence physical activity, it is regulated biologically by mediators such as sex steroids. The purpose of this study was to assess how physical activity patterns change following the loss of sex steroids and with the reintroduction of testosterone or 17β-estradiol. Hypothetically, the loss of the sex steroids drives the decrements in wheel running activity induced in male mice by altering when and how wheel running occurs during the dark active period. Methods: Eight-week-old male C57BL/6J mice (n=18) were divided into four experimental conditions: physiologically intact, sex steroid deficient (bilateral orchiectomy), 17β-estradiol-treated (bilateral orchidectomy + 17β-estradiol containing Silastic implants), and testosterone-treated (bilateral orchidectomy + testosterone containing Silastic implants). All mice were provided sufficient recovery (10 days) following surgical procedures to induce each experimental condition. The mice were housed individually with free access to a solid surface running wheel (circumference: 450 mm), food (Teklad Global 18% Protein Rodent Diet), and water on a 12-hour light:12-hour dark cycle. Mice ran for 10 days to acclimate to running wheel use and then ran an additional 10 days. A turn-by-turn wheel running system monitored daily and night-time hourly distance, duration, and speed. Wheel use during the light period was also quantified. Data were analyzed by ANOVA followed by Tukey's HSD post hoc tests when appropriate. Results: Daily wheel running distance [F 3,14 =10.97, p=0.001], duration [F 3,14 =9.04, p=0.001], and speed [F 3,14 =6.05, p=0.007] decreased in sex steroid deficiency, but recovered to the levels observed in physiologically-intact mice with sex steroid treatment. Distance, duration, and speed decrease incrementally during the dark period from a zenith in the first or second hour of the night in all conditions. The decrement in wheel running distance induced by sex steroid deficiency appears to be driven by slower initial running speeds and shorter initial running durations during the first three hours (p=0.012-0.044 across pairwise comparisons) of the dark period; latter wheel running is unaffected by sex steroid deficiency. Wheel running during the light period remained low (~1.5% or ~62 m) and was not different between the groups [F 3,14 =1.15, p=0.363]. Conclusion: Reduced wheel running following the loss of the sex steroids appears to be driven by decrements accumulated within the initial hours of the dark period. This work was supported by intramural grant funding from Union University and 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.