(A) Three of pubescent female F344 or COP rats per group were sacrificed every 4 hour over a 24 hour period, beginning at 6 AM, at days 0 (diamond), 2 (square), or 30 (triangle) post-exposure to NMU. mRNA expression levels were determined with RT-qPCR. The Per2 mRNA expression in F344 rat (right) was previously reported and is licensed under CC BY 2.0. (B) Three pubescent female F344 or COP rats per group were sacrificed every 6 hours over a 24 hour period, beginning at 6 AM, at day 30 post-exposure to NMU. mRNA levels of 84 DDRR genes were determined with RT-qPCR array in total RNA samples pooled from 3 rats per time point per group. (C) DDRR mRNA expression in mammary glands of F344 rats maintained on MSC diet for 30 days following exposure to NMU. The expression level of each gene was normalized with that at ZT0. **Indicates statistically significant difference at p<0.01 compared to control group (one way ANOVA, n=3). X-axis: Zeitgeber time (ZT); Y-axis: relative mRNA level, mean ± SE (n=3).