Fig. 1.

Entrainment and free-running periods of Rpe65^−/−;Opn4^−/− mice. (A) Wheel-running record of a representative Rpe65^−/−;Opn4^−/− mouse housed for 19 days in a LD12:12 cycle before receiving a 4-h phase delay of the light:dark cycle (the arrow indicates the day of delay). Each horizontal line represents 24 h, with subsequent daily records plotted beneath each other. The original LD12:12 cycle is indicated by black (dark) and white (light) bars at the top of the record, and the light phase is highlighted in yellow within the activity record. Note the slow reentrainment and the immediate positive masking response. (B) Analysis of free-running periods in DD or LL for Rpe65^−/−;Opn4^−/− (Double KO) and Rpe65^+/−;Opn4^+/− (Double HET) mice. The free-running period was calculated over days 1–21 or days 22–42 in DD from animals previously entrained (entrained in LD) or free-running (free-running in LD) for 4 weeks in a LD12:12 cycle. The free-running period in LL was calculated over days 1–21 in LL after transfer from DD ns, not significantly different. **, P < 0.01. ANOVA, Tukey's post hoc comparison. (C) Running-wheel activity record of a representative Rpe65^−/−;Opn4^−/− mouse maintained in a LD12:12 cycle for 40 days before being exposed to a short day photoperiod of 8-h-light:16-h-dark for 100 days. The arrow indicates the day of light cycle change. The record is double plotted so that each horizontal line represents 48 h, and successive days are shown to the right and beneath the previous day. The light:dark cycle is the same as that in A. (D) Histograms showing mean number of minutes (±SEM) by which activity onset preceded lights-on in Rpe65^−/−;Opn4^−/− mice (n = 7) in LD12:12 (open bar) or LD6:18 (filled bar). *, P < 0.05, Student's t test. Activity onsets were calculated over the entire 40-day period in LD12:12 and the 100-day period in LD6:18.