부산대학교 도서관

The circadian pacemaker of the suprachiasmatic nuclei is a complex multioscillator system, which controls circadian and seasonal rhythmicity (Pittendrigh and Daan, 1976; Meijer et al., 1989). A number of clock genes have been identified that play a key role in the generation of circadian rhythms. These clock genes are expressed in a circadian manner as has been shown in mice, rats and hamsters. The time at which their expression reaches peak values differs among the several genes (Lowrey et al., 2000; Daan et al., 2001; Reppert and Weaver, 2001). Expression profiles for a specific gene may also differ among subdivisions of the suprachiasmatic nuclei. It has been shown that mPer1peaks slightly out of phase in the left and right suprachiasmatic nuclei and that the rhythm in c-fosexpression is significantly different between the dorsomedial and ventrolateral regions (Yamazaki et al., 2000; Schwartz et al., 2000). In the special case that the animal shows splitting of its locomotor activity pattern, mPer1in the left and right suprachiasmatic nuclei appeared to oscillate in antiphase (de la Iglesia et al., 2000). Whether the molecular organization within the suprachiasmatic nuclei plays a role in seasonal rhythmicity, allowing animals to track daylength and become reproductive at the proper phase of the annual cycle, receives increasing interest (Daan et al., 2001; Hastings, 2001). The differences in peak expression times that exist between different genes, and the spatial differences in peak time for single genes, are suggestive of a genetic mechanism underlying the multioscillator structure. It is unknown, however, whether phase differences that are observed at the molecular level exist at the level of electrical activity rhythms in the suprachiasmatic nuclei in order to become potentially functional.