Temporal profiles of PK2 mRNA in the SCN in response to abrupt shifts of light/dark cycles. Animals were entrained to 12L:12D (LD) and subjected to either 6-hour delay of light/dark cycles (6hrD), 6-hour advance (6hrA), 6-hour delay followed by adaptation of 2 additional LD (6hrD+2LD), or 6-hour advance followed by adaptation of 2 additional LD (6hrA+2LD) or 6 additional LD (6hrA+6LD). Open and filled horizontal bars indicate light and dark periods, respectively. The LD data is doubled plotted as dashed line (open square) in all graphs. The zeitgeber time (ZT) on the x-axis reflects the timescale for LD, 6hrD or 6hrA. Please note that the additional LD adaptation groups use the same timescale as the 6hrD or 6hrA. (A) Temporal profiles of PK2 mRNA under 6hrD and LD. Note that PK2 mRNA responds quickly to the 6hrD shift. (B) Temporal profiles of PK2 mRNA rhythm under 6hrA and LD. Note that PK2 mRNA did not adjust to the 6hrA shift. (C) Temporal profiles of PK2 mRNA rhythm under 6hrD, 6hrD+2LD and LD to indicate adaptation of PK2 rhythm under 6hrD. Note that PK2 rhythm is stably entrained to 6hrD after two days. (D) Temporal profiles of PK2 mRNA rhythm under 6hrA, 6hrA+2LD, 6hrA+6LD and LD to illustrate adaptation of PK2 rhythm under 6hrA. Note that PK2 rhythm did not stably entrained to 6hrA until after 6 days. Each value is the mean ± SEM of 3 animals.