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Synchronization of circadian system during prenatal and early postnatal development
Houdek, Pavel ; Sumová, Alena (advisor) ; Novotná, Růžena (referee)
One of the few attributes common to almost all living organisms is an ability to generate and maintain endogenous rhythms, which are controlled by a biological clock. The processes, which recur with a period of about 24 hours, are known as the circadian rhythms. The circadian clock controls rhythms of molecular, physiological as well as behavioral processes and adapts their activity to regularly appearing changes in day and night or season. In case of mammals, central oscillator is located in the hypothalamic suprachiasmatic nuclei (SCN). The SCN clock entrains rhythms of peripheral oscillators located in cells of other tissues. The central oscillator itself is synchronized with external environment mainly by a light-dark cycle, however, other cues can entrain the SCN clock as well. For example, during prenatal development, entrainment of a fetal clock is entirely dependent on non-photic cues derived from maternal organism. This study aimed to investigate a mechanism of the communication between the maternal and fetal central oscillators. A hypothesis was tested whether maternal melatonin may play a role in entrainment of the circadian clock in the fetal SCN. Furthermore, a mechanism, how melatonin may entrain the fetal clock was investigated at molecular level. The results provided evidence, that...
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Entrainment of the circadian clock within the rat suprachiasmatic nukleus during fetal and early postnatal development
El-Hennamy Essam, Rehab ; Sumová, Alena (advisor) ; Novotná, Růžena (referee) ; Mourek, Jindřich (referee)
All mammals exhibit daily rhythms which persist in non-periodic environment with a period close to 24h. These rhythms are entrained to the 24h day mostly by the light-dark cycle. These circadian rhythms are controlled by a clock (pacemaker) located in the suprachiasmatic nuclei (SCN) of the hypothalamus. In the rat, the circadian clock within the SCN develops gradually from prenatal to postnatal period and is supposed to be synchronized mainly by maternal signals. However, the rat SCN is sensitive to light immediately after birth. The aim of the present work was to investigate the mechanism of entrainment of the circadian clock within the rat SCN during fetal and early postnatal development. The specific questions were whether and when the immature fetal and neonatal molecular SCN clocks can be reset by maternal cues, and whether and when the external light-dark cycle (LD) can affect the developing circadian rhythms. The role of light-dark cycle in the development of the photoperiodic entrainment during early postnatal period was also examined. Experiment no. (1): Pregnant rats were maintained under a light - dark regime with 12 h of light and 12 h of darkness (LD12:12). At gestational day 20 (E20), the fetuses were sampled throughout the day under either LD12:12 or constant darkness (DD). The...
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Maternal entrainment during prenatal ontogenesis of the rat
Nováková, Marta ; Sumová, Alena (advisor) ; Novotná, Růžena (referee)
Under constant conditions, many biological processes repeat regularly with a period about 24 hour, i.e., exhibit circadian rhythms. For example, these rhythms are in sleep/wakefulness, locomotor activity, hormonal secretion and body temperature. In mammals, circadian rhythms are controlled centrally from the hypothalamic suprachiasmatic nuclei (SCN). At the molecular level, the periodicity of these rhythms is due to the rhythmic expression of clock genes within individual neurons of the SCN. The expression of the clock genes is controlled by transcriptional-translational feedback loops. Apart form the SCN, the clock genes are rhytmically transcribed also in various peripheral tissues. The peripheral oscillations are synchronized centrally by the SCN clock that is entrained precisely to the 24 hour day by regular changes of the light and dark period, namely by the light period of the day. The central and peripheral circadian clocks drive rhythmic expression of clock-controlled genes and thus affect many physiological processes. Malfunctions in the circadian system may contribute to development of many diseases, such as malignant growth, obesity or sleep disorders. Circadian clock in the SCN develops gradually during prenatal and early postnatal period. In the rat, this period lasts from around 14th day of...
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