Thermal environment and light exposure shape sleep-associated metabolic and thermoregulatory rhythms.

Sleep, metabolism, and thermoregulation are coordinated physiological processes that are modulated by the external environment. This study investigated how sleep-wake state is associated with metabolic substrate utilization and thermoregulatory rhythms, and how these relationships are modified by thermal and light-dark conditions. Using continuous electroencephalography, electromyography, indirect calorimetry, and body temperature monitoring in freely moving mice, we examined the baseline metabolic and thermoregulatory fluctuations across sleep-wake states, the impact of ambient temperature, and the influence of light exposure. Our results demonstrate that sleep onset is associated with reduced energy expenditure, increased relative fat oxidation (lower respiratory exchange ratio, RER), and decreased body temperature in a cold (21°C) environment. These effects were attenuated under thermoneutral conditions (30°C). Short-term restricted-light/extended-dark exposure (18 h dark:6 h light) had limited effects on total sleep duration and thermoregulatory rhythms under the conditions tested, but altered sleep-wake state-linked RER at thermoneutrality. These findings indicate that environmental temperature and short-term changes in light exposure conditions interact to modulate sleep-associated metabolic and thermoregulatory rhythms in mice. Our results thus support a model in which environmental context shapes energy-homeostatic adaptations during sleep and underscore the need for studies that directly test causal mechanisms.NEW & NOTEWORTHY Sleep onset in freely moving mice is associated with a shift toward lower RER and reduced body temperature. Thermoneutral temperatures blunt sleep-linked metabolic and thermal signatures while increasing total sleep duration. Short-term restricted light exposure (18 h dark:6 h light) produced limited effects on sleep duration and thermoregulatory rhythms under the conditions tested, yet altered RER at thermoneutrality, suggesting that light exposure and ambient temperature can jointly tune sleep-associated energy metabolism.