Figure 2. Continuous lighting enhances cocaine-induced locomotor activity. A) Experiment timeline. B-E) Effect of continuous lighting on locomotor activity induced by cocaine at Zeitgeber time (ZT)4, ZT10, ZT16, and ZT22. White bars correspond to the administration of saline (SAL) and black bars correspond to the administration of cocaine (COC). The zero time point corresponds to the basal locomotor activity (BLA). F) Mean (10 days) locomotor activity (± standard error of the mean [SEM]) by group (n=8 animals per group) at different times of day. *Significant (p < 0.01) effects of COC on locomotor activity compared to the SAL group, determined by a two-way analysis of variance (ANOVA) followed by Tukey’s tests. Inset shows the effect of continuous light (L/L) on the mean concentration ± SEM of serum melatonin. ^† Significant (p < 0.01) effects induced by L/L on serum melatonin levels in the SAL and COC groups determined by one-way ANOVA followed by Tukey’s tests (not observed).