Circadian Clues to Sleep Onset Mechanisms

Abstract

Human sleep research is (mostly) carried out during the night. Yet sleep is embedded in the 24-hour day, and its timing, duration, and internal structure is strongly determined by the circadian pacemaker. Thus, in order to investigate mechanisms initiating sleepiness and sleep propensity, measurement needs to begin long before the sun sets. Our chronobiological approach to the physiology underlying sleep onset focuses on the role of melatonin and thermoregulation.In both night-active and diurnal species, the circadian peak of melatonin secretion occurs during the night (for review see: Arendt 1995). In contrast, all species, independent of temporal niche, sleep during the circadian trough of the core body temperature (CBT) rhythm. In rats, melatonin administration enhances norepinephrine-induced vasoconstriction of the tail (Viswanathan et al. 1990); in humans, melatonin induces vasodilation in fingers and toes (Kräuchi et al. 1998), suggesting that transduction of the nocturnal melatonin signal is linked to opposite physiological sequelae appropriate to behavioral niche. To further characterize the functional relationships preceding sleep onset, we have analyzed data from a series of experiments designed to phase-shift the circadian system with different putative zeitgebers, using identical methodology of a constant routine (CR) protocol to permit pooling of data.

Time-of-day-dependent effects of bright light exposure on human psychophysiology: comparison of daytime and nighttime exposure

“…Because of the fact that there is almost no melatonin secreted during daytime (33,42,43), which therefore cannot be suppressed by light, this means that there must be an alternative mechanism or pathway by which light immediately influences alertness in humans. Despite the results of Kräuchi and colleagues (29,30) showing a functional link between the degree of heat loss (distal vasodilatation) and subjective sleepiness (measured by the KSS), we found a reduction of subjective sleepiness in the absence of any effect of daytime light on CBT, indicating again that light affects human alertness in another way besides the mechanisms of melatonin suppression and/or elevation of CBT.…”

Circadian rhythms in glucose and lipid metabolism in nocturnal and diurnal mammals

“…Adapted from Crumbley and Burris (2011) and Mohawk et al (2012). nocturnal rodents show elevated energy expenditure and body temperature in their wake/feeding period in association with behavioral arousal, increased locomotion and food consumption at night (Alberts et al, 2006;Yang et al, 2010). Both core body temperature and energy expenditure display rhythms over the daily 24 h periods that are oppositely phased between diurnal and nocturnal animals (Cuesta et al, 2009;Krauchi and Wirz-Justice, 2001;Piccione et al, 2005;Zulley et al, 1981). The other determinants of energy expenditure are behavioral arousal and physical exercise, two activities that are also in anti-phase between nocturnal and diurnal species.…”

Lower-limb warming improves sleep quality in elderly people living in nursing homes

“…Body temperature and sleep-wake rhythms are highly correlated with the circadian rhythm 8,9 . Based on evidences of relationships among body temperature, thermoregulation, and sleep, Kräuchi & Wirz-Justice 10 suggested that heat loss from the core to the periphery, characterized by an abrupt decrease in proximal skin (infraclavicular, thigh, stomach, and forehead) and an increase in distal skin (hand and feet) temperatures, could predict initiation of sleep.…”