Lily Yan, Dr. differences in Fos expression were due to altered responsivity to light, we next characterized light-induced Fos expression in the SCN and vSPZ of pregnant and diestrous rats in the mid-subjective day and night. We found that the SCN core of the two groups responded in the same way at each time of day, whereas the rhythm of Fos responsivity in the SCN shell and vSPZ differed between diestrous and pregnant rats. These results indicate that this SCN and vSPZ are functionally Rabbit Polyclonal to CAD (phospho-Thr456) re-organized during early pregnancy, particularly in how they respond to the photic environment. These changes may contribute to changes in overt behavioral and physiological rhythms that occur at this time. Keywords:Circadian rhythm, ventral subparaventricular zone, Fos, Per2, diestrous, reproduction Circadian rhythms have a period of roughly RO-9187 24 hours and are generated endogenously. When synchronized to the external environment, these rhythms allow RO-9187 organisms to anticipate predictable daily fluctuations in the environment and appropriately time behavioral and physiological events in relation to those changes RO-9187 (Moore-Ede et al., 1982). The circadian timekeeping system plays an important role in the coordination of a variety of physiological and behavioral processes essential for mammalian reproduction. In some mammals, including many rodents, the timing of ovulation is usually regulated by this system (for review, seede la Iglesia and Schwartz, 2006), and rhythms in mating behavior have been observed in multiple species (Beach and Levinson, 1949;Dobson and Michener, 1995;Gilbert et al., 1985;Hansen et al., 1979;Harlan et al., 1980;Mahoney and Smale, 2005). This probably optimizes the likelihood of successful fertilization. However, in all therian mammals, fertilization is usually followed by gestation (pregnancy) and lactation. Circadian rhythms play important roles during these reproductive says as well, although significantly less work has focused on this RO-9187 issue. The best-characterized animal model of circadian processes operating during pregnancy is the nocturnal lab rat. During early pregnancy in this species, locomotor activity generally decreases and becomes less rhythmic (Rosenwasser et al., 1987), whereas body temperature rhythms show an advance in their rising phase and a reduction in amplitude attributable to increases RO-9187 in the daily heat minimum (Kittrell and Satinoff, 1988). Sleep patterns are altered, and the total amount of time spent in both non-rapid vision movement sleep (NREMS) and quick eye movement sleep (REMS) during the dark phase raises during early pregnancy, as does the number of REMS bouts in the dark phase (Kimura et al., 1996). Rhythms in hormone secretion also change during early pregnancy in the rat. Those of circulating adrenal corticotropin hormone (ACTH) and corticosterone experience decreases in amplitude due to a reduction in the peak values, and the rising phase of the rhythm in ACTH is also advanced (Atkinson and Waddell, 1995). Additionally, a prolactin rhythm, with peaks around dawn and dusk, emerges in early pregnancy and promotes progesterone secretion by the corpora lutea (Butcher et al., 1972;Freeman et al., 2000). While these changes have been known for some time, the neural mechanisms responsible for changes in all but the prolactin rhythm have received scant attention. The neural mechanisms controlling circadian rhythms in mammals have been well-characterized in males and nulliparous females, and it is firmly established that the suprachiasmatic nucleus (SCN), located bilaterally in the anterior hypothalamus, houses the primary pacemaker that generates these rhythms (Moore and Eichler, 1972;Ralph et al., 1990;Rusak, 1977;Stephan and Zucker, 1972). The SCN is functionally and neurochemically heterogeneous, and it may be divided into.