Per2 Rhythms Within and Beyond the Suprachiasmatic Nucleus of Pregnant & Diestrous Rats (Rattus norvegicus)

Jessica Schrader, BS

PhD Candidate
Department of Zoology and Program in Ecology,
Evolutionary Biology, and Behavior
Michigan State University
East Lansing, Michigan

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Secondary pacemakers throughout the brain and body are dependent on the primary pacemaker in the suprachiasmatic nucleus (SCN) for information about the circadian cycle to ensure, for example, hormone secretion at the correct time or appropriate time-dependent changes in blood pressure. Most studies addressing the biology of circadian rhythms use male animal models, which do not take into account hormonal fluctuations that occur at different life stages in females.1 Thus, there is a paucity of information addressing the relationship between sex-specific hormones and circadian rhythms. One approach to investigating these interactions is to look at the relationships between hormones and the expression of clock genes, major regulators of circadian rhythms. For instance, Period 2 (Per2) is a clock gene associated with the SCN and circadian rhythm regulation.2 Per2 has been implicated in several circadian processes, such as the development of advanced and delayed sleep phase syndromes, as well as vulnerability to the effects of sleep deprivation, including cognitive and performance impairment. A recent study examined whether pregnancy-related hormonal changes might affect Per2 expression. The study compared pregnant and nonpregnant rats and found a 4-hour phase advance in the peak Per2 expression in the SCN during early pregnancy. This is consistent with other hormonally regulated circadian changes that occur during pregnancy, including altered body temperature. Thus, the circadian system during pregnancy is reorganized. Findings from this study and others like it will lead to a greater understanding of the relationships between circadian rhythms and hormonal fluctuations.

References

Paul KN, Turek FW, Kryger MH. Influence of sex on sleep regulatory mechanisms. J Womens Health (Larchmt). 2008;17:1201-1208.
Franken P, Dijk DJ. Circadian clock genes and sleep homeostasis. Eur J Neurosci. 2009;29:1820-1829.
Lamont EW, James FO, Boivin DB, Cermakian N. From circadian clock gene expression to pathologies. Sleep Med. 2007;8:547-556.
Lavebratt C, Sjoholm LK, Partonen T, Schalling M, Forsell Y. PER2 variation is associated with depression vulnerability. Am J Med Genet B Neuropsychiatr Genet. August 19, 2009 [epub ahead of print].

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