Fig. 2.

ClockΔ19 mice exhibit a greater propensity to initiate cocaine use, reduced latency to acquire cocaine self-administration, and increased cocaine intake. a Percent of mice reaching acquisition criteria. Open (ZT2⇒14 group) and closed (ZT14 group) circles denote ClockΔ19 mice, and open (ZT2⇒14 group) and closed (ZT14 group) squares denote WT mice. Dashed vertical line between sessions 10 and 11 denotes the transition ZT2⇒14 (described in the “Materials and methods” section). b Cocaine infusions earned for ZT2 and ZT14 sessions. Open bars denote ClockΔ19 mice and gray bars denote WT mice. c Lever discrimination (mean number of active and inactive lever presses). 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. ***p<0.001; ****p<0.0001. N=7–10/genotype/ZT