Effects of anabolic androgenic steroids on the development and expression of running wheel activity and circadian rhythms in male rats

Abstract

In humans, anabolic androgenic steroid (AAS) use has been associated with hyperactivity and disruption of circadian rhythmicity. We used an animal model to determine the impact of AAS on the development and expression of circadian function. Beginning on day 68 gonadally intact male rats received testosterone, nandrolone, or stanozolol via constant release pellets for 60 days; gonadally intact controls received vehicle pellets. Wheel running was recorded in a 12:12 LD cycle and constant dim red light (RR) before and after AAS implants. Post-AAS implant, circadian activity phase, period and mean level of wheel running wheel activity were compared to baseline measures. Post-AAS phase response to a light pulse at circadian time 15 h was also tested. To determine if AAS differentially affects steroid receptor coactivator (SRC) expression we measured SRC-1 and SRC-2 protein in brain. Running wheel activity was significantly elevated by testosterone, significantly depressed by nandrolone, and unaffected by stanozolol. None of the AAS altered measures of circadian rhythmicity or phase response. While SRC-1 was unaffected by AAS exposure, SRC-2 was decreased by testosterone in the hypothalamus. Activity levels, phase of peak activity and circadian period all changed over the course of development from puberty to adulthood. Development of activity was clearly modified by AAS exposure as testosterone significantly elevated activity levels and nandrolone significantly suppressed activity relative to controls. Thus, AAS exposure differentially affects both the magnitude and direction of developmental changes in activity levels depending in part on the chemical composition of the AAS.

Figure 1

Mean (±SEM) running wheel activity in LD and RR showing post-AAS values. Chronic exposure to testosterone significantly increased (** p< 0.05) running wheel activity compared to gonadally intact controls. This occurred in both the LD and RR conditions. In contrast, chronic exposure to nandrolone significantly decreased (* p< 0.05) running wheel activity relative to gonadally intact control levels. N = 12 rats/group

Figure 2

Mean (±SEM) activity levels over time. Compared to baseline (day 32–46) there was a highly significant increase in activity levels in testosterone-treated males (p< 0.001). Controls and stanozolol-treated males were similar and also displayed a significant increase in activity compared to baseline (p< 0.001). In contrast, nandrolone-treated males did not show an increase in activity over the course of development.

Figure 3

Sample actograms for each treatment group showing pre-AAS and post-AAS activity patterns. Pre-AAS treatment activity is shown in the top figure for each group, and post-AAS activity is shown below for the same subject. The dotted line separates the 12:12 LD activity from constant dim red light (RR).

Figure 4

Western blot analysis of SRC-2 expression in the hypothalamus. Testosterone treatment decreased mean SRC-2 protein levels in the hypothalamus compared to control animals (mean + SEM, * p < 0.03). Densitometric analysis of SRC-2 immunoreactive bands and Actin immunoreactive bands expressed as a ratio. N = 6 animals/group.