Figure 3.

Id2 Mutant Mice Show Abnormally Rapid Entrainment to a New Light-Dark Cycle

(A–F) Representative locomotor activity records of wild-type (A and D) and Id2 mutant (B, C, E, and F) exposed to a 10 hr extension of the light phase of the LD cycle. Mice were maintained on a LD cycle for at least 14 days and transferred to a new cycle where ZT12 is delayed by 10 hr by extending the light phase of the LD cycle by 10 hr on day 1 (A–C). In (D)–(F), mice were exposed to the equivalent treatment of 10 hr prolonged light exposure on day 1 and then transferred to DD for the rest of the experiment. The line above DD on the right indicates the transition from LD to DD. The timing of the respective LD cycles is indicated by the white-and-black bars above and below the records. Numbers on the left indicate the number of days following the transition to the new LD cycle or the 10 hr light treatment prior to transfer to DD. The arrow on the left indicates the actual day of treatment (day 1), and the actual midtime of treatment is marked by a green asterisk within the actogram. A red line is fitted to the phase of activity onset for several days before and after the shift of the LD cycle or transfer to DD.

(G) Numbers of days required for stable entrainment to the new photoschedule are shown in the histogram for wild-type (white), heterozygote (pale blue), and mutant (dark blue) mice (mean ± SEM).

(H) Mean ± SEM magnitude of the phase shifts produced by light treatment is shown for wild-type (white), heterozygote (pale blue), and mutant (dark blue) mice. Extrapolated activity onsets of the first day after the 10 hr light treatment were used to determine the size of resultant phase delays. The values marked by asterisks are statistically significant as determined by one-factor ANOVA (Dunnett's post-hoc t tests, ^∗∗p < 0.01, ^∗∗∗p < 0.001).