Effects of Testosterone and 17β‐estradiol on Physical Activity Patterns in Mice

Abstract

Physical inactivity causes an increased risk of chronic diseases and can lead to an early death. Notably, sex steroids have been shown to affect physical activity patterns in both humans and rodents. The purpose of this study was to evaluate the effects 17β‐estradiol and testosterone have on wheel‐running behavior in female and male C57BL/6J mice. Initially, testosterone‐deficiency and estrogen‐deficiency were induced by bilateral orchidectomy (n = 4) and ovariectomy (n = 4) surgeries. Control mice (n = 10; 5 males and 5 females) received sham gonadectomies. Wheel running data were collected for seven days following the surgical procedures. After completion of the first experimental period, surgically manipulated mice received implants containing either testosterone (males) or 17β‐estradiol (females) to elevate sex steroid levels back to physiological levels. Wheel running data were collected for a second week. To accumulate a daily turn‐by‐turn record, each wheel revolution was counted and time‐stamped. Turn‐by‐turn data were used to generate seven‐day averages for speed (m·min−1), distance (km), duration (min), onset of wheel running (minutes before (−) or after (+) lights off), completion of wheel running (minutes before (−) or after (+) lights on) and wheel running bouts (number of contiguous blocks of wheel running). Statistical analyses (three‐way ANOVAs) were run for each variable to determine the effects that sex (male vs. female) and sex steroid levels (deficient vs. reintroduced) had on each wheel running parameter between control and experimentally manipulated animals. Follow‐up post‐hoc testing was completed to determine statistically different pair‐wise comparisons. After gonadectomy, distance [F (1,14) = 10.9, p = 0.005], duration [F (1,14) = 5.5, p = 0.035] and bouts [F (1,14) = 18.769, p = 0.001] dropped significantly due to loss of endogenous steroids for both males and females. Speed, the onset of wheel running, and the completion of wheel running was largely unaffected. Females ran less under low estrogen conditions and exhibited reinvigoration following re‐exposure to 17β‐estradiol. Males ran less under low testosterone levels and exhibited reinvigoration following re‐exposure to the steroid. Interestingly, after reintroduction of 17β‐estradiol, female mice approached the daily wheel running task with a more fragmented pattern (4 or more bouts per night), while males exhibited a more fragmented wheel running pattern under low testosterone conditions (5 or more bouts per night) that resolved back to a normal pattern following reintroduction of testosterone. This study suggests that intact mice run almost constantly overnight in longer bouts, while the compromised mice accumulate their wheel running in much smaller bouts sporadically through the night. The continuous pattern approach to wheel running might be associated with the improved resistance to hypokinetic disease progression associated with physically active individuals.