Fig. 1.

Effects of testosterone propionate on the circadian rhythms of wheel-running activity in old mice. a Representative double-plotted actograms showing the wheel-running activity of old intact mice implanted with vehicle or testosterone propionate (TP) under light/dark (LD) and constant darkness (DD) conditions. The light schedule is indicated by black and white bars above the record. b The free-running period of wheel running activity in DD is shown. The daily amounts of wheel running activity are shown in c LD and b DD. e, f The weights of the seminal vesicles and testis are shown. The weights were calculated as ratios of body weights. g The concentrations of serum testosterone are shown. Data are presented as mean ± standard error of the mean, n = 7–9 per group, *p < 0.05, **p < 0.01, ***p < 0.001 for vehicle vs TP (Student’s t-test)