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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

Circadian rhythms in human performance and mood under constant conditions

This study explored the relationship between circadian performance rhythms and rhythms in rectal temperature, plasma cortisol, plasma melatonin, subjective alertness and well-being. Seventeen healthy young adults were studied under 36 h of 'unmasking' conditions (constant wakeful bedrest, temporal isolation, homogenized 'meals') during which rectal temperatures were measured every minute, and plasma cortisol and plasma melatonin measured every 20 min. Hourly subjective ratings of global vigour (alertness) and affect (well-being) were obtained followed by one of two performance batteries. On odd-numbered hours performance (speed and accuracy) of serial search, verbal reasoning and manual dexterity tasks was assessed. On even-numbered hours, performance (% hits, response speed) was measured at a 25-30 min visual vigilance task. Performance of all tasks (except search accuracy) showed a significant time of day variation usually with a nocturnal trough close to the trough in rectal temperature. Performance rhythms appeared not to reliably differ with working memory load. Within subjects, predominantly positive correlations emerged between good performance and higher temperatures and better subjective alertness; predominantly negative correlations between good performance and higher plasma levels of cortisol and melatonin. Temperature and cortisol rhythms correlated with slightly more performance measures (5/7) than did melatonin rhythms (4/7). Global vigour correlated about as well with performance (5/7) as did temperature, and considerably better than global affect (1/7). In conclusion: (1) between-task heterogeneity in circadian performance rhythms appeared to be absent when the sleep/wake cycle was suspended; (2) temperature (positively), cortisol and melatonin (negatively) appeared equally good as circadian correlates of performance, and (3) subjective alertness correlated with performance rhythms as well as (but not better than) body temperature, suggesting that performance rhythms were not directly mediated by rhythms in subjective alertness.

NASA Discipline Regulatory Physiology↗
NASA NTRS1987

[Circadian rhythms and temperature homeostasis in monkeys during a flight on the Kosmos 1514 biosatellite]

In the course of a 5-day space flight of two rhesus-monkeys the following parameters were recorded at an interval of 16 min: core body temperature (Tc), skin temperature (Ts), and motor activity (MA). The telemetric Tc sensor was implanted subcutaneously in the right axilla, Ts thermistor was attached to the right ankle, and the MA piezotape was fixed to the inner side of the vest. Circadian rhythms of Tc varied with a period of 24 hours in one monkey and 25 hours in the other. The daily Tc decreased on the average by 0.5 degrees C, Ts fell immediately after launch and remained close to the lower limit throughout the flight. The Ts amplitude decreased 5-fold. Phases of the circadian rhythms of Ts changed and circadian rhythms of MA remained unchanged and equal to 24 hours.

Cosmos 1514 Project↗
NASA NTRS1989

Effects of restricted feeding schedules on circadian organization in squirrel monkeys

Free running circadian rhythms of motor activity, food-motivated lever-pressing, and either drinking (N = 7) or body temperature (N = 3) were recorded from 10 squirrel monkeys maintained in constant illumination with unlimited access to food. Food availability was then restricted to a single unsignaled 3-hour interval each day. The feeding schedule failed to entrain the activity rhythms of 8 monkeys, which continued to free-run. Drinking was almost completely synchronized by the schedule, while body temperature showed a feeding-induced rise superimposed on a free-running rhythm. Nonreinforced lever-pressing showed both a free-running component and a 24-hour component that anticipated the time of feeding. At the termination of the schedule, all recorded variables showed free-running rhythms, but in 3 animals the initial phase of the postschedule rhythms was advanced by several hours, suggesting relative coordination. Of the remaining 2 animals, one exhibited stable entrainment of all 3 recorded rhythms, while the other appeared to entrain temporarily to the feeding schedule. These results indicate that restricted feeding schedules are only a weak zeitgeber for the circadian pacemaker generating free-running rhythms in the squirrel monkey. Such schedules, however, may entrain a separate circadian system responsible for the timing of food-anticipatory changes in behavior and physiology.

Non-NASA Center↗
NASA NTRS2005

Cardiovascular tissues contain independent circadian clocks

Acute cardiovascular events exhibit a circadian rhythm in the frequency of occurrence. The mechanisms underlying these phenomena are not yet fully understood, but they may be due to rhythmicity inherent in the cardiovascular system. We have begun to characterize rhythmicity of the clock gene mPer1 in the rat cardiovascular system. Luciferase activity driven by the mPer1 gene promoter is rhythmic in vitro in heart tissue explants and a wide variety of veins and arteries cultured from the transgenic Per1-luc rat. The tissues showed between 3 and 12 circadian cycles of gene expression in vitro before damping. Whereas peak per1-driven bioluminescence consistently occurred during the late night in the heart and all arteries sampled, the phases of the rhythms in veins varied significantly by anatomical location. Varying the time of the culture procedure relative to the donor animal's light:dark cycle revealed that, unlike some other rat tissues such as liver, the phases of in vitro rhythms of arteries, veins, and heart explants were affected by culture time. However, phase relationships among tissues were consistent across culture times; this suggests diversity in circadian regulation among components of the cardiovascular system.

Non-NASA Center↗
DOE OSTI2024

A Corrected Score Function Framework for Modelling Circadian Gene Expression

Many biological processes display oscillatory behaviour based on an approximately 24 h internal timing system specific to each individual. One process of particular interest is gene expression, for which several circadian transcriptomic studies have identified associations between gene expression during a 24 h period and an individual's health. A challenge with analysing data from these studies is that each individual's internal timing system is offset relative to the 24 h day-night cycle, where day–night cycle time is recorded for each collected sample. Laboratory procedures can accurately determine each individual's offset and determine the internal time of sample collection. However, these laboratory procedures are labour-intensive and expensive. Here, in this paper, we propose a corrected score function framework to obtain a regression model of gene expression given internal time when the offset of each individual is too burdensome to determine. A feature of this framework is that it does not require the probability distribution generating offsets to be symmetric with a mean of zero. Simulation studies validate the use of this corrected score function framework for cosinor regression, which is prevalent in circadian transcriptomic studies. Illustrations with data from three circadian transcriptomic studies further demonstrate that the proposed framework consistently mitigates bias relative to using a score function that does not account for this offset.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

From primordial clocks to circadian oscillators

Circadian rhythms play an essential part in many biological processes, and only three prokaryotic proteins are required to constitute a true post-translational circadian oscillator1. The evolutionary history of the three Kai proteins indicates that KaiC is the oldest member and a central component of the clock. Subsequent additions of KaiB and KaiA regulate the phosphorylation state of KaiC for time synchronization. The canonical KaiABC system in cyanobacteria is well understood but little is known about more ancient systems that only possess KaiBC. However, there are reports that they might exhibit a basic, hourglass-like timekeeping mechanism. Here we investigate the primordial circadian clock in Rhodobacter sphaeroides , which contains only KaiBC, to elucidate its inner workings despite missing KaiA. Using a combination of X-ray crystallography and cryogenic electron microscopy, we find a new dodecameric fold for KaiC, in which two hexamers are held together by a coiled-coil bundle of 12 helices. This interaction is formed by the carboxy-terminal extension of KaiC and serves as an ancient regulatory moiety that is later superseded by KaiA. A coiled-coil register shift between daytime and night-time conformations is connected to phosphorylation sites through a long-range allosteric network that spans over 140 Å. Our kinetic data identify the difference in the ATP-to-ADP ratio between day and night as the environmental cue that drives the clock. They also unravel mechanistic details that shed light on the evolution of self-sustained oscillators.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

CACNA1D is a circadian gene and causes familial advanced sleep phase

Familial advanced sleep phase (FASP) is a heritable human sleep trait characterized by early sleep onset and offset times. We have identified five variants in five different families in the human voltage-gated calcium channel subunit alpha1 D (CACNA1D) that cosegregate with FASP. The variants inCACNA1Dlead to altered channel dynamics in vitro. A mouse model of the E427K variant has a normal circadian period under constant darkness but displays altered phase shifts in response to light in the subjective night at circadian time (CT) 16 and CT22. Overall, these experiments establishCACNA1Das an FASP gene with altered entrainment, highlighting the ability of human genetics to uncover novel aspects of human circadian regulation.

Science & Technology - Other Topics↗
DOE OSTI2021

Naturalistic Intensities of Light at Night: A Review of the Potent Effects of Very Dim Light on Circadian Responses and Considerations for Translational Research

In this review, we discuss the remarkable potency and potential applications of a form of light that is often overlooked in a circadian context: naturalistic levels of dim light at night (nLAN), equivalent to intensities produced by the moon and stars. It is often assumed that such low levels of light do not produce circadian responses typically associated with brighter light levels. A solid understanding of the impacts of very low light levels is complicated further by the broad use of the somewhat ambiguous term “dim light,” which has been used to describe light levels ranging seven orders of magnitude. Here, we lay out the argument that nLAN exerts potent circadian effects on numerous mammalian species, and that given conservation of anatomy and function, the efficacy of light in this range in humans warrants further investigation. We also provide recommendations for the field of chronobiological research, including minimum requirements for the measurement and reporting of light, standardization of terminology (specifically as it pertains to “dim” light), and ideas for reconsidering old data and designing new studies.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Casein kinase 1 dynamics underlie substrate selectivity and the PER2 circadian phosphoswitch

Post-translational control of PERIOD stability by Casein Kinase 1δ and ε (CK1) plays a key regulatory role in metazoan circadian rhythms. Despite the deep evolutionary conservation of CK1 in eukaryotes, little is known about its regulation and the factors that influence substrate selectivity on functionally antagonistic sites in PERIOD that directly control circadian period. Here we describe a molecular switch involving a highly conserved anion binding site in CK1. This switch controls conformation of the kinase activation loop and determines which sites on mammalian PER2 are preferentially phosphorylated, thereby directly regulating PER2 stability. Integrated experimental and computational studies shed light on the allosteric linkage between two anion binding sites that dynamically regulate kinase activity. We show that period-altering kinase mutations from humans to Drosophila differentially modulate this activation loop switch to elicit predictable changes in PER2 stability, providing a foundation to understand and further manipulate CK1 regulation of circadian rhythms.

59 BASIC BIOLOGICAL SCIENCES↗
NASA NTRS1971

A circadian rhythm in optic nerve impulses from an isolated eye in darkness.

Study of the circadian rhythm of optic nerve potentials recorded from the isolated eye of the sea hare Aplysia. The optic nerve activity in constant conditions is found to be clearly circadian and to obey the circadian rule for diurnal animals. In addition, the period length depends on the in vitro culturing solution. In seawater it is about 22 hr, but in culture medium it is 27 hr. The rhythm can be completely phase-shifted in one trial if the phase of the LD 12:12 Zeitgeber is advanced or delayed 4 hr. The rhythm in one eye can be phase-shifted in vivo independently of the other eye and in vitro independently of the rest of the animal. Thus, in the animal, the eye oscillators are, at most, only slightly influenced by each other or by other oscillators in the animal.

Jacklet, J. W.↗
NASA NTRS1976

The effect of low light intensity on the maintenance of circadian synchrony in human subjects

Experiments were conducted on six healthy male subjects aged 20-23 yr and exposed for 21 days in a confined regulated environment to 16L:8D light:dark cycle with a view toward determining whether the light environment of 16L:8D at the relatively low light intensity of 15 ft.c. is adequate for the maintenance of circadian synchrony in man. The light intensity was 100 ft.c. during the first seven days, reduced to 15 ft.c. during the next seven days, and increased again to 100 ft.c. during the last seven days. Rectal temperature (RT) and heart rate (HR) were recorded throughout the three phases. In the 100 ft.c. regime, the RT and HR rhythms remained stable and circadian throughout. It is shown that 15 ft.c. light intensity is at or below threshold for maintaining circadian synchrony of human physiologic rhythms marked by instability and internal desynchronization with degradation of performance and well-being.

Winget, C. M.↗
NASA NTRS1977

Environmental synchronizers of squirrel monkey circadian rhythms

Various temporal signals in the environment were tested to determine if they could synchronize the circadian timing system of the squirrel monkey (Saimiri sciureus). The influence of cycles of light and dark, eating and fasting, water availability and deprivation, warm and cool temperature, sound and quiet, and social interaction and isolation on the drinking and activity rhythms of unrestrained monkeys was examined. In the absence of other time cues, 24-hr cycles of each of these potential synchronizers were applied for up to 3 wk, and the periods of the monkey's circadian rhythms were examined. Only light-dark cycles and cycles of food availability were shown to be entraining agents, since they were effective in determining the period and phase of the rhythmic variables. In the presence of each of the other environmental cycles, the monkey's circadian rhythms exhibited free-running periods which were significantly different from 24 hr with all possible phase relationships between the rhythms and the environmental cycles being examined.

Sulzman, F. M.↗
NASA NTRS1977

Comparison of hormone and electrolyte circadian rhythms in male and female humans

Circadian rhythm characteristics in healthy male and female humans were studied at 4-hour intervals for urine volume, cortisol, 5-hydroxyindoleacetic acid (5-HIAA), Na, K, Na/K ratios in the urine, as well as plasma cortisol. While plasma and urinary cortisol rhythms were very similar in both sexes, the described rhythms in urine volume, electrolyte, and 5-HIAA excretion differ for the two sexes. The results suggest that sex differences exist in the circadian patterns of important hormone and metabolic functions and that the internal synchrony of circadian rhythms differs for the two sexes. The results seem to indicate that the rhythmical secretion of cortisol does not account for the pattern of Na and K excretion.

Vernikos-Danellis, J.↗
NASA NTRS1986

Resynchronization of circadian sleep-wake and temperature cycles in the squirrel monkey following phase shifts of the environmental light-dark cycle

Circadian rhythms in physiological and behavioral functions gradually resynchronize after phase shifts in environmental time cues. In order to characterize the rate of circadian resynchronization in a diurnal primate model, the temperature, locomotor activity, and polygraphically determined sleep-wake states were monitored in squirrel monkeys before and after 8-h phase shifts of an environmental light-dark cycle of 12 h light and 12 h dark (LD 12:12). For the temperature rhythm, resynchronization took 4 d after phase delay shift and 5 d after phase advance shift; for the rest-activity cycle, resynchronization times were 3 d and 6 d, respectively. The activity acrophase shifted more rapidly than the temperature acrophase early in the post-delay shift interval, but this internal desynchronization between rhythms disappeared during the course of resynchronization. Further study of the early resynchronization process requires emphasis on identifying evoked effects and measuring circadian pacemaker function.

Wexler, D. B.↗
NASA NTRS1986

Masking of the circadian rhythms of heart rate and core temperature by the rest-activity cycle in man

Experiments were conducted to estimate the magnitude of the masking effect produced in humans by alternate periods of physical activity and rest or sleep on the circadian rhythms of heart rate and core temperature. The heart rate, rectal temperature, and nondominant wrist activity were monitored in 12 male subjects during 6 days of normal routine at home and during 6 days of controlled bed-rest regimen. The comparisons of averaged waveforms for the activity, heart rate, and temperature indicated that about 45 percent of the range of the circadian heart rate rhythm during normal routine and about 14 percent of the range of the circadian temperature rhythm were attributable to the effects of activity. The smaller effect of activity on the temperature rhythm may be partially attributable to the fact that core temperature is being more rigorously conserved than heart rate, at least during moderate exercise.

Gander, Philippa H.↗
NASA NTRS1991

Light-induced suppression of endogenous circadian amplitude in humans

A recent demonstration that the phase of the human circadian pacemaker could be inverted using an unconventional three-cycle stimulus has led to an investigation of whether critically timed exposure to a more moderate stimulus could drive that oscillator toward its singularity, a phaseless position at which the amplitude of circadian oscillation is zero. It is reported here that exposure of humans to fewer cycles of bright light, centered around the time at which the human circadian pacemaker is most sensitive to light-induced phase shifts, can markedly attenuate endogenous cicadian amplitude. In some cases this results in an apparent loss of rhythmicity, as expected to occur in the region of singularity.

Jewett, Megan↗
NASA NTRS1991

Adaptation of sleep and circadian rhythms to the Antarctic summer - A question of zeitgeber strength

Adaptation of sleep and circadian rhythms was examined in three temperate zone dwellers arriving in Antarctica during summer. Rectal temperature, wrist activity, and heart rate were monitored continuously, sleep timing and quality noted on awakening, and mood and fatigue rated every 2 h while awake. Sleep was poorer in 2/3 subjects in Antarctica, where all subjects reported more difficulty rising. Sleep occurred at the same clock times in New Zealand and Antarctica, however, the rhythms of temperature, activity, and heart rate underwent a delay of about of 2 h. The subject with the most Antarctic experience had the least difficulty adapting to sleeping during constant daylight. The subject with the most delayed circadian rhythms had the most difficulty. The delay in the circadian system with respect to sleep and clock time is hypothesized to be due to differences in zeitgeber strength and/or zeitgeber exposure between Antarctica and New Zealand.

Gander, Philippa H.↗