Ultradian light-dark cycles in rodents are a precious tool to study the direct effects of repeated light exposures on sleep, in order to better understand the underlying mechanisms. This study aims to precisely evaluate the effects of light and dark exposures, according to circadian time, on sleep and waking distribution and quality, and to determine if these effects depend on the duration of light and dark pulses. To do this, mice were exposed to 24 h-long ultradian light-dark cycles with different durations of pulses: T2 cycle (1 h of light/1 h of dark) and T7 cycle (3.5 h of light/3.5 h of dark). Exposure to light not only promotes NREM and REM sleep and inhibits wake, but also drastically alters alertness and modifies sleep depth. These effects are modulated by circadian time, appearing especially during early subjective night, and their kinetics is highly dependent on the duration of pulses, suggesting that in the case of pulses of longer duration, the homeostatic process could overtake light direct influence for shaping sleep and waking distribution.
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| http://dx.doi.org/10.3390/clockssleep4020019 | DOI Listing |
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Article Synopsis
- The study highlights that in mice, nearly 40% of the light phase and 80% of the dark phase are marked by periods of increased energy expenditure (EE), known as ultradian bouts.
- These bouts are associated with higher body temperatures and consist of most physical activity and wakefulness, suggesting that they are more indicative of mouse physiology than the traditional light/dark cycles.
- The findings indicate that these ultradian bouts, resulting from brain-driven increases in body temperature, lead to significant energy expenditure from various bodily activities, making mouse metabolic physiology largely episodic rather than solely reliant on circadian rhythms.
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