(A) Spontaneous AP frequencies (means ± SEM) of Per1::GFP expressing SCN neurons from WT or GSK3-KI mice following exposure to a 15-min light-pulse (LP+) or no light (LP-) at ZT 22. Recordings were made 2–5 hours after onset of photic stimulus (ZT 0–3). Main effect of light, P < 0.001; main effect of genotype, P < 0.005; n = 61, 92 cells, 3–6 slices per group. (B–C) Graph (means ± SEM) of data from (A) divided into 1-hr bins depicting WT and GSK3-KI SFR from LP- (B) or LP+ (C) groups. ***P = 0.001, *P < 0.05; Fisher’s LSD post hoc test.