Absence of RKIP results in enhanced transcriptional activation of the c-Fos and mPeriod1 genes in the SCN in response to a light pulse. A, Representative micrographs of c-FOS protein expression in the SCN of (top) RKIP+/+ and (bottom) RKIP−/− mice at various times (hours) after a 15 min light pulse (80 lux intensity) at CT 15. B, Quantification of c-FOS expression in the SCN of RKIP+/+ (white bars) and RKIP−/− (black bars) mice at the designated times after a 15 min light pulse at CT 15. Values represent mean ± SEM number of immunoreactive nuclei in the unilateral SCN. n = 4 mice per group. *p < 0.05 vs RKIP+/+ controls. C, Representative micrographs of VENUS expression in the SCN of (top) RKIP+/+ and (bottom) RKIP−/− mice carrying the mPER1::VENUS transgene, 4 h after a 15 min light pulse (LP: 80 lux) at CT 15. Control mice were killed at the same circadian time without receiving a light pulse (DD). Tissues were probed with anti-GFP antibody that recognizes VENUS. D, Quantification of VENUS expression in the SCN of light-pulsed (white bars) and dark control (black bars) mice of both genotypes. Values represent mean ± SEM fluorescence intensity (in arbitrary units) normalized to background staining. n = 4 mice per group. *p < 0.05 vs RKIP+/+ controls.