<i>Per1</i> is required for melatonin to alter the phase of SCN neuronal activity rhythms at CT 10.

<p><b>A)</b> The spontaneous electrical activity rhythm in SCN brain slices peaks at CT 6.38 ± 0.13 in controls. The dotted line indicates the mean time-of-peak for untreated slices. Long, vertical boxes represent subjective night, CT 12–14. <b>B)</b> At CT 10, MEL (1 nM, 10 min) advances the electrical activity rhythm by 3.6 h ± 0.10 (<i>n = 3</i>). Arrow = time of melatonin treatment. <b>C)</b> <i>Per1</i> αODN application from CT 8–10 has no significant effect on the time-of-peak electrical activity (<i>n = 3</i>). Small box = duration of ODN exposure. <b>D)</b> The MEL-induced phase advance is completely blocked by <i>Per1</i> αODN (<i>n = 3</i>). <b>E)</b> <i>Per1</i> missense ODN has no effect on the MEL-induced advance in time-of-peak electrical activity (<i>n = 3</i>). <b>F)</b> <i>Per1</i> missense ODN does not block the MEL-induced phase advance at CT 10. <b>G)</b> Summary of the effects of <i>Per1</i> ODN on MEL-induced phase advances at CT 10. **indicates statistically significant difference compared to controls (p ≤ 0.001) as determined by 1-way ANOVA with Tukey’s <i>post-hoc</i> analysis.