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. 2006 Jun 5;103(24):9327–9332. doi: 10.1073/pnas.0603601103

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© 2006 by The National Academy of Sciences of the USA

Freely available online through the PNAS open access option.

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Fig. 3. — Effects of light–pulse duration on the behavioral response (phase shifts) and induction of Per1 and Per2 in the SCN of C57BL/6J coisogenic mice. (A) Behavioral phase shifts (in circadian hours) as a function of light–pulse duration for wild-type (●) and Clock/+ (○) mice. Phase shifts were determined after 15, 30, 60, 180, and 360 min of light exposure that started at CT 17. Clock/+ mice exhibited significantly greater phase shifts than wild types (Tukey–Kramer; P < 0.05) in response to 180 and 360 min light pulses. (B and C) Relative Per1 (B) and Per2 (C) mRNA expression in the SCN of wild-type (● and ○) and Clock/+ (■ and □) mice. Samples were collected at CT 17 or after 60, 180, or 360 min of light exposure beginning at CT 17 (filled symbols). Dark-maintained controls also were sampled at 60, 180, or 360 min after CT 17 (open symbols). Overall, the induction of Per1 and Per2 genes to increase in light–pulse duration did not differ between the genotypes (no significant genotype effect by ANOVA. Per1: F_1,44 = 0.78, P > 0.05 and Per2 F_1,32 = 0.01; P > 0.05). There is significant light induction of both genes (Per1: F_1,44 = 135.65; P < 0.001 and Per2: F_1,32 = 89.23; P < 0.001) as well as a significant effect of light pulse duration on induction (Per1: F_3,44 = 68.38; P < 0.001 and Per2: F_3,32 = 3.96; P < 0.05). For Per1 expression, light-exposed levels are different from dark control levels at 60 and 180 min (Tukey–Kramer; P < 0.05). For Per2 expression, light-exposed levels are different from dark control levels at 60, 180, and 360 min (Tukey–Kramer; P < 0.05). (D and E) Circadian rhythms of Per1 (D) and Per2 (E) mRNA expression in the SCN of wild-type (●) and Clock/+ (○) mice after 3 weeks in constant darkness. The amplitude of circadian rhythms in both Per1 and Per2 genes are significantly reduced in Clock/+ mice (Per1: F_1,71 = 0.6.71; P < 0.05 and Per2 F_1,71 = 5.40; P < 0.05). For both Per1 and Per2, there were significant differences between CTs (Per1: F_5,71 = 8.80; P < 0.001 and Per2: F_5,71 = 46.85; P < 0.001). For Per1, levels are significantly lower at CT18 than CTs 2, 6 and 10, and significantly higher at CT 6 than CTs 14, 18, and 22 (Tukey–Kramer; P < 0.05). For Per2, levels are significantly higher at CT10 than all other times, and CTs 6, 10, and 14 are significantly higher than CTs 18, 22, and 2 (Tukey–Kramer; P < 0.05).