Fig. 2.

Rhythms of melatonin in stool and stool weight diminishes with age. Top: melatonin content in stool taken from young (black lines with circles), middle-aged (dark gray lines with squares), and old-aged (light gray lines with triangles) was assayed by ELISA (n = 3–5 samples per time point per mouse) and reported as % of minimum value. Bottom: stool weights measured from timed collections (20 min for n = 5 mice per time point). Shade-matched asterisks indicate significant difference determined by 2-way ANOVA. x-Axis is plotted as Zeitgeber time (ZT), where ZT0 corresponds to lights on and ZT14 corresponds to lights off in a 14:10 light-dark cycle.