Figure 3.

(A) A double-plot actogram showing slow resetting of locomotor activity rhythms in male Wistar rats following a 6 h advance of the LD cycle. Every row illustrates the locomotor activity of the animal on a given day, and consecutive days are stacked below. The initial LD cycle is shown on top, with the shifted cycle shown on the bottom, and light and dark periods are indicated by the white and black bars respectively. The arrow points to the day of the shift. The activity of the animal is shown as black tick marks [15]. (B) The SCN shows internal disorder following a 6 h phase advance shift of the LD cycle. Coronal sections of SCN stained for Per1 mRNA from rats sacrificed every 2 h. The top bar indicates timing of the LD cycle and the lower bars indicate the new LD cycle. Time of day is indicated at the bottom of each column of images. Midline is to the left of each SCN image. On the baseline day (Day 0), ventrolateral SCN and dorsomedial SCN show similar timed Per1 expression. Following the LD advance, the two regions are desynchronized but eventually come together [15]. Note on Day 1, when the lights first interrupt the prior dark phase, Per1 mRNA label is observed for the first 2 samples (3:00 and 5:00) mainly in the ventrolateral SCN. On Day 2, we note that the signal in dorsomedial SCN is high in the sample taken at 11:00, a time that on the prior baseline day showed Per1 signal both in ventrolateral as well as dorsomedial SCN. As the days of the shifted cycle continue, the SCN readjusts to the new phase. Note that in the baseline samples there was little Per1 visible in the SCN in the beginning of the dark period. Following the shift, signal is apparent in the dorsomedial SCN at 15:00 even on Day 9, and is only no longer visible on Day 13 post-shift. The ventrolateral SCN appears shifted to the new LD cycle immediately, but may be reporting direct response to light exposure.