A, example bioluminescence waveforms from the SCN of WT mice subjected to wheel-access conditions. B, average timing of PER2::LUCIFERASE (PER2::LUC) peaks in the peripheral tissues of WT mice. Significant delays in timing were detected in the adrenals and livers. C, average timing of PER2::LUC peaks in the SCN of WT mice (larger symbols with error bars) did not significantly differ between wheel-access groups; however, when examining individual samples (smaller grey circles), the variability of the timing was increased when mice were provided with any form of wheel access. The x-axis represents the number of hours after ZT (Zeitgeber) 12 of culture day. D, effects of wheel access on the amplitude of PER2::LUC rhythms in the SCN of WT mice, where early night wheel access significantly dampened the amplitude of PER2::LUC rhythms compared with no-access conditions. Average PER2::LUC timing and amplitude were analysed using a one-way ANOVA. For statistical results, see main text. Error bars are SEM (*P < 0.05).