| dc.description.abstract | The suprachiasmatic nucleus (SCN) of the hypothalamus serves as a central circadian oscillator that receives direct retinal light input and synchronizes (or entrains) endogenous daily rhythms in behavior and physiology to environmental light cycles. At the molecular level, nearly all mammalian cells have a circadian clock based on autoregulatory transcription-translation feedback loops of clock genes and their circadian rhythms are coordinated by the SCN. The work presented in this dissertation focuses on how the central SCN clock achieves light entrainment and expresses clock plasticity at the molecular and network levels. SCN clock gene rhythms under light entrainment change their waveforms from sinusoids to asymmetric shapes with accelerated synthetic phases following dawn and prolonged degradative phases following dusk. The SCN shows canonical forms of circadian clock plasticity at the fundamental level of core clock gene rhythms. The SCN has a particular spatial organization of phase resetting and after-effects on circadian period at the network levels: phase resetting is more pronounced in the ventrolateral region, while after-effects are greater in the dorsomedial region. Also, the molecular mechanisms of after-effects were examined, and it was uncovered that DNA methylation is involved in after-effects of photoperiods and that at the level of single clock-resetting cues the SCN clock involves DNA methylation to produce after-effects. Taken together, this work advances the understanding of SCN entrainment and plasticity to environmental lighting conditions. | |
