Fig. 2.

The circadian expression of clock genes in the SCN is abolished under deep hibernation. In situ hybridization was used to examine gene expression in euthermic and hibernating hamsters during daytime, nighttime, or during the subjective day. For all genes, the upper panel displays representative autoradiograms for each condition, and the lower panel shows the relative mRNA levels. (A–C) The expression of the clock genes Per1 (A), Per2 (B), and Bmal1 (C) exhibits circadian fluctuations in euthermic hamsters but not in hibernating animals. During hibernation, Per1 expression is elevated (A), Per2 expression remains low (B), and Bmal1 expression is intermediate between daytime and nighttime levels in euthermic hamsters (C). (D) Similarly, the expression of the clock-controlled gene Avp is rhythmic in euthermic but not in hibernating hamsters, in which its expression remains low. (E) The expression of the immediate early gene c-fos is dramatically increased in hibernating relative to euthermic hamsters, without significant day/night fluctuations. Data are shown as a percentage of the maximum and represent the means ± SEM (n = 4–7). Bars labeled with different characters (a, b, c) are significantly different from each other (P < 0.05).