Fig. 1.

Normal CLOCK function is not required for acquisition of responding for sucrose pellet reinforcers during the early phase of the light or dark cycle. a The percent of mice that reached acquisition criteria for each session (presented as a cumulative percentage). Open (ZT14 group) and closed (ZT2 group) circles denote ClockΔ19 mice, and open (ZT14 group) and closed (ZT2 group) squares denote WT mice. b Latency to acquire sucrose pellet self-administration at ZT2 and ZT14. Open bars denote ClockΔ19 mice and gray bars denote WT mice. c Lever discrimination (mean number of active and inactive lever presses) for the three consecutive sessions that enabled each subject to meet acquisition criteria. Open bars denote ClockΔ19 mice active lever presses, bars with vertical lines denote ClockΔ19 mice inactive lever presses, gray bars denote WT mice active lever presses, and checkered bars denote WT mice inactive lever presses. Open (inactive lever) and closed (active lever) circles denote ClockΔ19 mice, and open (inactive lever) and closed (active lever) squares denote WT mice. N=9–10/genotype/ZT