Relationships between behavioral rhythms, plasma corticosterone and hypothalamic circadian rhythms

Circadian rhythms in physiological processes and behaviors were compared with hypothalamic circadian rhythms in norepinephrine (NE) metabolites, adrenergic transmitter receptors, cAMP, cGMP and suprachiasmatic nucleus (SCN) arginine vasopressin (AVP) in a single population of rats under D:D conditions. Eating, drinking and locomotor activity were high during the subjective night (the time when lights were out in L:D) and low during the subjective day (the time when lights were on in L:D). Plasma corticosterone concentration rose at subjective dusk and remained high until subjective dawn. Binding to hypothalamic alpha 1- and beta-adrenergic receptors also peaked during the subjective night. Cyclic cGMP concentration was elevated throughout the 24-hr period except for a trough at dusk, whereas DHPG concentration peaked at dawn. Arginine vasopressin levels in the suprachiasmatic nucleus peaked in the middle of the day. No rhythm was found either in binding to the alpha 2-adrenergic receptor, or in MHPG or cAMP concentration. Behavioral and corticosterone rhythms, therefore, are parallel to rhythms in hypothalamic alpha 1- and beta-receptor binding and NE-release. Cyclic GMP falls only at dusk, suggesting the possibility that cGMP inhibits activity much of the day and that at dusk the inhibition of nocturnal activity is removed. SCN AVP, on the other hand, peaking at 1400 hr, may play a role in the pacemaking function of the SCN that drives these other rhythms.     

The relation of age to the adjustment of the circadian rhythms of oral temperature and sleepiness to shift work

The relation of age to the adjustment of the circadian rhythms of oral temperature (T0) and sleepiness (S) in shift work was studied. 145 healthy female nurses underwent detailed laboratory and field measurements. Self-rated sleepiness, and oral temperature measured with a special extended-scale mercury thermometer, were recorded at 2 hr intervals during a morning (M) and 2 consecutive night (N) shifts. Sleeping times were registered during the same days. The results were analyzed separately in the age-groups of 22-29, 30-39 and 40-49-year-old subjects. From the morning shift to the second night shift day, the oral temperature and sleepiness acrophases shifted significantly (p less than 0.001) forward in all age groups. The amplitude decreased in the youngest and in the 30-39-year old age groups but not in the oldest age group. During the second night shift day, the acrophases and amplitudes of oral temperature rhythms were significantly different (P less than 0.05) between the groups, but there were no significant differences by age in the change of the circadian rhythms from morning to the second night shift days. The results thus fail to corroborate that physiological adjustment to night work would be influenced by age.     

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

Heart rate and core temperature are elevated by physical activity and reduced during rest and/or sleep. These masking effects may confound interpretation of rhythm waveforms, particularly in situations where the rest-activity rhythm has a different period from that of the core temperature rhythm. Such desynchronization often occurs temporarily as an individual adjusts to a new work shift or to a new time zone following rapid transmeridian travel, making it difficult to assess the impact of such schedule changes on the circadian system. The present experiments were designed to estimate the magnitude of these masking effects, by monitoring the heart rate, rectal temperature, and nondominant wrist activity (2-min samples) of 12 male subjects during 6 days of normal routine outside the lab and during 6 days of strict bedrest. Subjects also kept sleep, dietary, and exercise logs throughout the study. Average (20-min) waveforms were computed for each subject and each rhythm, at home and in bedrest. In addition, data were partitioned according to self-reported sleep and wake times and were analyzed separately for each state. Average waveform comparisons indicated that about 45% of the range of the circadian heart rate rhythm during normal routine was attributable to the masking effects of activity during wake, which also produced a 16% elevation in mean heart rate during wake and an 11% increase in mean heart rate overall. (Analysis of variance indicated that mean heart rate during sleep at home was not significantly different from the mean during sleep in bedrest.) On average, about 14% of the range of the circadian temperature rhythm during normal routine was attributable to the effects of activity masking. However, the change in range of the temperature rhythm, from home to bedrest, was very variable between subjects (-41% to +13%). This variability was not accounted for by age or by reported frequency of exercise at home. Normal activity during wake increased the mean temperature during wake by an average of 0.16 degrees C and the overall mean by about 0.12 degrees C. (Analysis of variance indicated that mean temperature during sleep at home was not significantly different from the mean during sleep in bedrest.) A 10-hr "night" (lights-off from 2200 to 0800 hr) was provided during bedrest, within which subjects could select their own sleep times. Times of sleep onset and wake onset were not significantly different between home and bedrest.(ABSTRACT TRUNCATED AT 400 WORDS)     

The effect of sleep upon human circadian rhythms

Subjects who slept for 4 h from 0000, and for a second 4 h variously distributed over the day, have provided values for rectal temperature and for urinary excretion of water, potassium, sodium, chloride, phosphate, creatinine, calcium and urate in the sleeping subject at all hours of the 24. These are compared with similar values in the wakeful subject. Temperature was lower during sleep at all hours except 1000 and 1200, and the difference was maximal shortly before 0000. At all hours potassium excretion was lower and phosphate excretion higher during sleep. Cosinor analysis of the different variables in the sleeping subject is compared with that in subjects following nycthemeral habits, and the interaction between endogenous rhythms and external influences such as sleep is discussed. The phasing of the temperature and urinary rhythms was essentially normal by the end of the observations. By contrast in a subject who slept at irregular hours mimicking the habits of an air pilot a free-running rhythm unrelated to the habits of sleep emerged. When he was finally living again on normal time his temperature and urinary acrophases had moved to the middle of the night. Phosphate excretion was largely exogenous, falling consistently when subjects rose after 8 h, but not after 4 h of sleep.     

Acute dim light at night increases body mass,alters metabolism,and shifts core body temperature circadian rhythms

The circadian system is primarily entrained by the ambient light environment and is fundamentally linked to metabolism. Mounting evidence suggests a causal relationship among aberrant light exposure, shift work, and metabolic disease. Previous research has demonstrated deleterious metabolic phenotypes elicited by chronic (>4 weeks) exposure to dim light at night (DLAN) (～5?lux). However, the metabolic effects of short-term (<2 weeks) exposure to DLAN are unspecified. We hypothesized that metabolic alterations would arise in response to just 2 weeks of DLAN. Specifically, we predicted that mice exposed to dim light would gain more body mass, alter whole body metabolism, and display altered body temperature (T_b) and activity rhythms compared to mice maintained in dark nights. Our data largely support these predictions; DLAN mice gained significantly more mass, reduced whole body energy expenditure, increased carbohydrate over fat oxidation, and altered temperature circadian rhythms. Importantly, these alterations occurred despite similar activity locomotor levels (and rhythms) and total food intake between groups. Peripheral clocks are potently entrained by body temperature rhythms, and the deregulation of body temperature we observed may contribute to metabolic problems due to “internal desynchrony” between the central circadian oscillator and temperature sensitive peripheral clocks. We conclude that even relatively short-term exposure to low levels of nighttime light can influence metabolism to increase mass gain.     

The effects of skin pressure by clothing on circadian rhythms of core temperature and salivary melatonin

The present experiment investigated the effects of skin pressure by foundation garments (girdle and brassiere) on the circadian rhythms of core temperature and salivary melatonin. Ten healthy females (18-23 years) maintained regular sleep-wake cycles for a week prior to participation in the experiment. The experiments were performed from June to August 1999 using a bioclimatic chamber controlled at 26.5 degrees C +/- 0.2 degrees C and 62% +/- 3% RH. Ambient light intensity was controlled at 500 lux from 07:30 to 17:30, 100 lux from 17:30 to 19:30, 20 lux from 19:30 to 23:30; there was total darkness from 23:30 to 07:30. The experiment lasted for 58h over three nights. The participants arose at 07:30 on the first full day and retired at 23:30, adhering to a set schedule for 24h, but without wearing foundation garments. For the final 24h of the second full day, the subjects wore foundation garments. Rectal and leg skin temperatures were measured continuously throughout the experiment. Saliva and urine were collected every 4h for the analysis of melatonin and catecholamines, respectively. Skin pressure applied by the foundation garments was in the range 11-17 gf/cm2 at the regions of the abdomen, hip, chest, and back. The main results were as follows: (1) Rectal temperatures were significantly higher throughout the day and night when wearing foundation garments. (2) The nocturnal level of salivary melatonin measured at 03:30 was 115.2 +/- 40.4 pg/mL (mean +/- SEM, N = 10) without and 51.3 +/- 18.4 pg/mL (mean +/- SEM, N = 10) with foundation garments. (3) Mean urinary noradrenaline excretion was significantly lower throughout the day and night when wearing foundation garments (p < .05), but mean urinary adrenaline excretion was not different. The results suggest that skin pressure by clothing could markedly suppress the nocturnal elevation of salivary melatonin, resulting in an increase of rectal temperature.     

Relationships between daytime sleepiness and sleep quality,duration, and phase among school-aged children: a cross-sectional survey

A cross-sectional survey was conducted to simultaneously evaluate sleep quality, duration, and phase in school-aged children and correlations between each dimension of sleep and daytime sleepiness were comprehensively examined. A cross-sectional survey was conducted with school-aged children enrolled in four public elementary schools in Joetsu city, Niigata prefecture in Japan (n = 1683). Among the collected responses (n = 1290), 1134 valid responses (547 boys and 587 girls) were analyzed (valid response rate was 87.90%). Data on daytime sleepiness, sleep quality (problems in sleeping at night), sleep duration (the average sleeping time during a week), and sleep phase (sleep timing: bedtime and rising time on weekdays, and sleep regularity: differences in bedtime and rising time between on weekdays and weekends) were collected. The results of multivariate logistic regression analysis indicated that the following dimensions were significantly correlated with daytime sleepiness: the decline in sleep quality [adjusted odds ratio (AOR) = 2.62, 95% confidence interval (CI) = 1.71–4.00], bedtime after 21:30 on weekdays (AOR = 1.58, 95% CI = 1.15–2.18), bedtime delay on weekends, compared to weekdays (AOR = 1.75, 95% CI = 1.27–2.41), and bedtime advance on weekends, compared to weekdays (AOR = 3.33, 95% CI = 1.78–6.20). Sleep dimensions that significantly affected daytime sleepiness in school-aged children are sleep quality, bedtime-timing, and regularity of bedtime. It is important to detect problems in night sleep and establish treatments, as well as to provide support for early bedding on weekdays and for a regular bedtime both on weekdays and on weekends to prevent daytime sleepiness in school-aged children.

     

Masking effects of posture and sleep onset on core body temperature have distinct circadian rhythms: results from a 90-min/day protocol

Both recumbency and sleep affect core body temperature (CBT). To characterize their circadian effects and interactions, the authors examined the bedtime temperature drops (TDs) of nine men and eight women (aged 20 to 30) who repeated 90-min sleep-wake cycles over 2.5 days. While awake, subjects were exposed to 50 to 250 lux; while asleep, lights were off. Electroencephalogram-monitored time inbed lasted 30 min during each cycle. Cosinor nonlinear mixed-effects regressions modeled the circadian rhythm of TDs. The circadian maximum of TDs occurred approximately 4 h before the time of circadian CBT minimum, in a model that included the effects of baseline expected CBT, deviations from baseline CBT, time in study, and gender-dependent 24- and 12-h adjustments. Rates of temperature drops were faster during initial periods of lying awake than during periods of initially sleeping. Both rates followed separate circadian rhythms. The circadian maximum of TDs was located near customary nocturnal bedtimes, suggesting its role in fostering sleep during a normal bedtime routine. The apparent deceleration of temperature dropping at sleep onset supports the notion that the sleep onset period has complicated circadian neuroregulatory dynamics. These findings confirm the need for nonlinear models of temperature responses to postural changes and sleep that incorporate circadian variability in these masking effects.     

Pronounced juvenile circadian core temperature rhythms exist in several strains of rats but not in rabbits

Torpor-like circadian variations of core temperature are well documented for suckling-age Zucker rat pups. To determine (1) whether this juvenile circadian rhythm is as strongly expressed in other rat strains, and (2) whether a similar rhythm is expressed in rabbit pups, we recorded core temperature and metabolic rate of artificially reared pups. Wistar, Brown Norway, and Long Evans pups were studied for 30 h under moderate cold loads (ambient temperature=28°C) when 9–11 days old, i.e. at the age and ambient temperature for which the rhythm has been most thoroughly characterized in Zucker rats. Chinchilla bastard rabbit pups were studied under similar conditions when they were 3–8 days old, the youngest age at which the rhythm can be easily detected in rats. Rat pups of each strain showed clear circadian rhythms with sharp decreases of core temperature and metabolic rate in subjective morning. Core temperature amplitudes were in the order Wistar < Brown Norway < Zucker < Long Evans strain. In contrast, the rabbit pups maintained stable high levels of core temperature and metabolic rate throughout the day. A torpor-like decrease of core temperature in the morning is thus not a pecularity of the Zucker rat strain but also occurs in other pigmented rat strains, whereas rabbit pups at a similar developmental stage do not show a circadian core temperature rhythm.     

Entrainment of Drosophila circadian rhythms by temperature cycles

Sleep and Biological Rhythms - The fruit fly, Drosophila melanogaster, has been a good organism for elucidating the molecular and cellular bases of circadian behavioral rhythms. The fly shows a...     

Correlations between objective and subjective sleep and circadian markers in remitted patients with bipolar disorder

Bipolar disorder (BD) is a chronic psychiatric condition characterized by recurrences of depressive and (hypo)manic episodes. Patients in remission report a wide range of sleep and circadian disturbances that correlate with several outcomes measures such as functioning or physical health. The most appropriate way to measure these abnormalities in clinical practice requires further investigation since the external validity of self-reports, as compared to more physiological measures (such as polysomnography or actigraphy), has been questioned. Despite the fact that questionnaires are inexpensive, fast and easy to use, they need to be validated against objective measures. This study aims to validate three sleep and circadian questionnaires, namely the Pittsburgh Sleep Quality Index (PSQI), the Composite Scale of Morningness (CSM) and the Circadian Type Inventory (CTI) – against actigraphy in BD patients in remission. Twenty-six carefully assessed BD patients in remission completed the PSQI, the CTI and the CSM, and wore an actigraph (AW7, Camntech) for 21 consecutive days. Phase preference assessed by the CSM strongly correlated with actigraphic phase markers (M10 onset ρ?=??0.69 and L5 onset ρ?=??0.63). Sleep duration and sleep latency assessed by the PSQI and by actigraphy were also highly correlated (ρ?=??0.76; ρ?=?0.50). Moderate correlation coefficients were observed between questionnaires and actigraphy for markers that explored the stability of rhythms, sleep quality, sleep latency and sleep disturbances (|ρ|?>?0.40) although these were not significant after correcting for multiple testing. No correlation was observed between markers for the amplitude of rhythms. While the external validity of the CTI clearly requires further investigation, this study supported the external validity of the CSM and the PSQI for phase preference, sleep duration and latency. We conclude that the CSM and the PSQI could be useful in routine practice and research when actigraphy is not easily available.     

Sex differences in subjective sleep quality,sleepiness, and health-related quality of life among collegiate soccer players

Sleep and Biological Rhythms - Sleep is an important recovery phase after exercise that should be taken into account by athletes. Females are likely to be dissatisfied with their sleep quality,...     

Prolonged mild hypoxia modifies human circadian core body temperature and may be associated with sleep disturbances

Fatigue is often reported after long-haul airplane flights. Hypobaric hypoxia, observed in pressurized cabins, may play a role in this phenomenon by altering circadian rhythms. In a controlled cross-over study, we assessed the effects of two levels of hypoxia, corresponding to cabin altitudes of 8000 and 12,000 ft, on the rhythm of core body temperature (CBT), a marker of circadian rhythmicity, and on subjective sleep. Twenty healthy young male volunteers were exposed for 8 h (08:00-16:00 h) in a hypobaric chamber to a cabin altitude of 8000 ft and, 4 weeks later, 12,000 ft. Each subject served as his own control. For each exposure, CBT was recorded by telemetry for two 24 h cycles (control and hypoxic exposure). After filtering out nonphysiological values, the individual CBT data were fitted with a five-order moving average before statistical group analysis. Sleep latency, sleep time, and sleep efficiency were studied by sleep logs completed every day in the morning. Our results show that the CBT rhythm expression was altered, mainly at 12,000 ft, with a significant increase of amplitude and a delay in the evening decline in CBT, associated with alterations of sleep latency. Mild hypoxia may therefore alter circadian structure and result in sleep disturbances. These results may explain in part the frequent complaints of prolonged post-flight fatigue after long flights, even when no time zones are crossed.     

Aging of intrinsic circadian rhythms and sleep in a diurnal nonhuman primate, Macaca mulatta

There is growing evidence that alterations in the intrinsic circadian clock and sleep might affect the aging process. The rhesus monkey (Macaca mulatta) provides unique opportunities to explore the role of the clock in successful and unsuccessful physiological and cognitive aging in a diurnal primate with consolidated nighttime sleep, complex cognitive functions, long life span, and phylogenetic proximity to humans. A longitudinal study was conducted to characterize the effects of aging on the entrained and intrinsic circadian rhythms of activity, polysomnographic sleep patterns, and melatonin production in unrestrained male rhesus monkeys [6-9 (n=6) and 24-28 (n=4) years of age]. An age-dependent decline was found in the stability of circadian rhythms of activity and in peak melatonin levels. The range of individual intrinsic circadian periods (τ) is not age-dependent. Aged monkeys do not display clearly defined morningness-eveningness chronotypes and, unlike the young, show no correlation between the chronotype under entrained conditions and the length of intrinsic circadian period. The daily activity period (α) is reduced with age and this is associated with high day-to-day variability in sleep quantity and quality, fragmentation of nighttime sleep and daytime wakefulness, increased daytime sleep time, overall increase in stage 1 sleep, and reduced time spent in rapid-eye movement and slow-wave sleep. In the absence of environmental time cues, age-dependent changes in sleep and circadian rhythms are exacerbated and circadian patterns of sleep in young rhesus monkeys start resembling those in aged animals, together suggesting important role of circadian regulation in aging sleep phenotype. This first characterization of age-dependent changes in the intrinsic rhythms and sleep in rhesus monkeys, demonstrating major similarities to human aging phenotype, should assist in the search for the mechanisms involved and for effective prophylactic and therapeutic strategies.     

Phase shifting the circadian rhythms of nocturnal insects by temperature changes

The behavioural rhythms of three species of nocturnal insects were studied: locomotion in a cockroach, luminescence in a firefly and luminescence in a glow-worm. The behaviour was released at the change from light to dark in all cases. In continuous dim light, a circadian rhythm was apparent with a period of from 22.5 to 27 h in the cockroach, and from 19 to 23.5 h in the glow-worm. In constant dim light, the cockroach shifted the phase of its rhythm when subjected to a change of temperature. A temperature step down some time prior to the expected onset of locomotion generated a phase advance, whereas a temperature step up generated a phase delay; the greater the step up, the greater the phase delay. By advancing the change from light to dark, it was found that glow-worms could synchronize immediately to advances of up to about 6 h only. At greater advances an increasing phase angle difference between onsets of darkness and activity occurred. However, if a temperature step down was applied at the light change, immediate synchronization occurred up to 9–12 h before the normal onset. A theory is propounded which assumes that the onset of rhythmic behaviour is determined by the interaction of a circadian process of sensitization and a threshold for release of the behaviour. The threshold is high at high temperatures and light intensities, and low at low values of these. A temperature step up raises the threshold and delays the activity while a step down lowers the threshold and advances the activity.     

Qualitative similarities between the behavior of coupled oscillators and circadian rhythms

This paper summarizes in a nonmathematical way the major properties of coupled oscillators which relate to circadian rhythms. For certain values of the coupling strength it is far easier to maintain synchrony than to achieve it among the various interacting units. This property not only simulates the free run period lability but also the effects of critical pulses.