Fig 2. Voluntary running-wheel behavior in virgin and lactating mice.

A-D. Reduced activity during lactation, under light-dark conditions. Representative actograms from virgin (A) and lactating (B) female mice. Quantification of wheel counts during daytime (C) and night-time (D). Differences were considered significant for p < 0.05, two-tailed unpaired t-test. E-H. Noticeable rhythmic organization of behavior under constant darkness. Representative actograms (E and F) and corresponding periodograms (G and H) showing a major power peak in the circadian range for both virgin (E and G) and lactating (F and H) females (the calculated free-running period was 23.72±0.01 hr and 23.77±0.14 hr, for virgin and lactating females, respectively, p>0.71 two-tailed unpaired t-test, n = 4 mice for each condition). Note that low levels in wheel counts and the presence of pups in the cage prevent the measurement of a reliable free-running period for lactating mice.