Fig. 1.

Younger and older mice display differential wheel revolutions and peak wheel-running activity at light offset and onset. Younger (open columns) and older (black columns) male mice (n = 9/10 per group) were housed in wheel cages individually under a constant 12:12-h light/darkness cycle and 24-h wheel-running activity monitored. The average wheel turn activity (± SD) is displayed for the following periods: left panel the final hour of “lights on” (1800 hours) and the initial hour of “lights off/darkness” (1900 hours); middle panel the hour of peak activity level during the “lights off” period (1900 to 0700 hours); right panel the final hour of “lights off/darkness” (0600 hours) and “lights on” (0700 hours). *p < 0.01 indicates significant differences between younger and older cohorts at the indicated time points