Individual characteristics and biological rhythms. VI. Circadian variations of body temperature]

It has been reported that body temperature fluctuates differently in evening and morning type subjects. In order to assess this finding in 779 university students the body temperature has been measured between 1986 and 1989. Body temperature exhibits circadian rhythm in 78.6% of subjects, but no differences between morning and evening type crest phases were found. Since this result contradicts literature data, the finding is discussed also on the basis of the difference of the percentage between our grouping and that of the other authors. Further studies are in progress in order to detect if the subjects of the two groups differ for other biological and psychological parameters as well.     

Circadian rhythms of body temperature and activity levels during 63 h of hypoxia in the rat

The hypothermic response of rats to only brief ( approximately 2 h) hypoxia has been described previously. The present study analyzes the hypothermic response in rats, as well as level of activity (L(a)), to prolonged (63 h) hypoxia at rat thermoneutral temperature (29 degrees C). Mini Mitter transmitters were implanted in the abdomens of 10 adult Sprague-Dawley rats to continuously record body temperature (T(b)) and L(a). After habituation for 7 days to 29 degrees C and 12:12-h dark-light cycles, 48 h of baseline data were acquired from six control and four experimental rats. The mean T(b) for the group oscillated from a nocturnal peak of 38.4 +/- 0.18 degrees C (SD) to a diurnal nadir of 36.7 +/- 0.15 degrees C. Then the experimental group was switched to 10% O(2) in N(2). The immediate T(b) response, phase I, was a disappearance of circadian rhythm and a fall in T(b) to 36.3 +/- 0.52 degrees C. In phase II, T(b) increased to a peak of 38.7 +/- 0.64 degrees C. In phase III, T(b) gradually decreased. At reoxygenation at the end of the hypoxic period, phase IV, T(b) increased 1.1 +/- 0.25 degrees C. Before hypoxia, L(a) decreased 70% from its nocturnal peak to its diurnal nadir and was entrained with T(b). With hypoxia L(a) decreased in phase I to essential quiescence by phase II. L(a) had returned, but only to a low level in phase III, and was devoid of any circadian rhythm. L(a) resumed its circadian rhythm on reoxygenation. We conclude that 63 h of sustained hypoxia 1) completely disrupts the circadian rhythms of both T(b) and L(a) throughout the hypoxic exposure, 2) the hypoxia-induced changes in T(b) and L(a) are independent of each other and of the circadian clock, and 3) the T(b) response to hypoxia at thermoneutrality has several phases and includes both hypothermic and hyperthermic components.     

Circadian rhythms of body temperature and motor activity in rodents their relationships with the light-dark cycle

In rodents, the alternation of light and dark is the main synchronizer of circadian rhythms. The entrainment abilities of the LD cycle could be estimated by experimental modifications of the photoperiod and by following the subsequent temporal distribution of a circadian rhythm. The rate of reentrainment of a rhythm is determined by the nature of the studied variable, by the direction (advance or delay) and the magnitude (or value) of the phase shift. In rodents, core body temperature and motor activity are known to be well synchronized with each other under L:D 12:12 and under constant conditions (LL or DD). There are clear evidences that the circadian pattern of motor activity is generated by two oscillators, one from dusk signal and the other from dawn signal. Whether the circadian rhythms of body temperature and motor activity are generated by a common circadian mechanism or controlled by separate ones still remains unknown. The purpose of this review is to summarize the results obtained on the circadian rhythms of body temperature and motor activity throughout the daily cycle in order to clarify the relationships between these two functions.     

Circadian rhythms ofMacaca mulatta: Sleep,EEG, body and eye movement,and temperature

EEG, EOG, EMG, gross activity, and temperature were continuously recorded over 24 hours from 38 maleMacaca mulatta monkeys. EEG, EOG, and EMG were translated into standard Sleep Stages. The EEG also was automatically filtered, rectified, integrated, digitized, and plotted. Results are presented first as 24-hour plots for temperature, Sleep Stages Awake, 1–2, 3–4, and REM, for EMG, gross motion, EOG, and for the occurrence of EEG bands delta, theta, alpha, sigma, and beta.Twenty-four-hour cosine curves were fitted to the data by least squares, demonstrating and quantifying with confidence intervals a circadian rhythm in each function. During the 12-hour dark span the acrophases, or peaks of the cosines fitted to the data, appeared in the following clockwise order: Stage 3–4, delta, Stage 1–2, Stage REM, total EEG, and theta. The clockwise order of acrophases appearing in the light span was: alpha, gross motion, sigma, beta, EMG, EOG, temperature, and Stage Awake. Circadian amplitudes are given for each rhythm.Three of these measures of brain function had circadian rises or falls which appeared to be influenced by the daily times of light-on or -off. Lighting acted as circadian phase-synchronizing stimulus for temperature and the EEG bands beta and sigma.The data demonstrate circadian rhythms for certain parameters associated with sleep—delta, theta, Stage REM, and Stage 3–4 and important differences in phase. This finding constitutes another line of evidence that sleep is not unitary, consisting rather of related but separately controlled rhythmic functions.Considerable phylogenetic constancy appears when these data on circadian phasing are compared with similar data from other primates, including man.The experimental work was part of Aeromedical Research Laboratory Project 6892, Holloman Air Force Base, U.S.A.F. Biochemical assays were supported by the U.S.P.H.S. (MH 15413). Data analysis performed at the University of Minnesota was supported by NASA (NAS 2-2738 and NGR-24-005-006), the U.S. Air Force (F29608-69-C-0011), and by the USPHS (CA 5-K6-GM 13981). Further reproduction of this article is authorized as needed to meet the requirements of the U.S. government. The animals used in this study were handled in accordance with the Guide for Laboratory Animal Facilities and Care published by the National Academy of Science-National Research Council. Drs.Crowley andKripke were on active duty, and Dr.Pegram was a civilian employee with the USAF during part of this project.     

Diurnal rhythms of body temperature, heart rate, and behaviour in the stanchioned adult Shiba goats

Using a data logger system, body temperature (dorsal subcutaneous temperature), heart rate, ingestive or ruminating behaviour and posture in adult Shiba goats tied to a stanchion were recorded automatically during 24 hours, to obtain basic information on the biological rhythms. A 600 g of usual ration mixed with hay cube, hay, beet pulp and wheat bran was fed twice a day (morning; 9:00-9:30, evening; 16:00-16:30). Animals kept under an artificial photoperiod (12L-12D, light period; 5:30-17:30) and about 10 degrees C room temperature. 1) Diurnal patterns of the above-mentioned items were recorded, mutual relationships relationships between these items were revealed. 2) The heart rate was higher after morning feeding, or during a light period and decreased gradually from midnight to early morning. Twice feeding greatly increased the heart rate. 3) The body temperature was lower in the early morning and increased gradually after morning feeding and showed the highest level during 1 to 1.5 hours after evening feeding. After that it decreased gradually till the early morning. 4) The numbers of jaw movement (bites/min) were a 70-90 bites in the ingestive behaviour and a 80-90 bites in the ruminating behaviour at dark period. 5) The total heart rate was a 110000 to 120000 beats/day, the total biting time was a 9.5 hours/day, and the mean standing time was a 9.3 to 11.7 hours/day. The standing time during light period (12 hours) was a 7.3 to 9.9 hours and that during dark period (12 hours) was a 1.8 to 2 hours.     

Circadian rhythms in bed rest: Monitoring core body temperature via heat-flux approach is superior to skin surface temperature

Continuous recordings of core body temperature (CBT) are a well-established approach in describing circadian rhythms. Given the discomfort of invasive CBT measurement techniques, the use of skin temperature recordings has been proposed as a surrogate. More recently, we proposed a heat-flux approach (the so-called Double Sensor) for monitoring CBT. Studies investigating the reliability of the heat-flux approach over a 24-hour period, as well as comparisons with skin temperature recordings, are however lacking. The first aim of the study was therefore to compare rectal, skin, and heat-flux temperature recordings for monitoring circadian rhythm. In addition, to assess the optimal placement of sensor probes, we also investigated the effect of different anatomical measurement sites, i.e. sensor probes positioned at the forehead vs. the sternum. Data were collected as part of the Berlin BedRest study (BBR2-2) under controlled, standardized, and thermoneutral conditions. 24-hours temperature data of seven healthy males were collected after 50 days of -6° head-down tilt bed-rest. Mean Pearson correlation coefficients indicated a high association between rectal and forehead temperature recordings (r > 0.80 for skin and Double Sensor). In contrast, only a poor to moderate relationship was observed for sensors positioned at the sternum (r = -0.02 and r = 0.52 for skin and Double Sensor, respectively). Cross-correlation analyses further confirmed the feasibility of the forehead as a preferred monitoring site. The phase difference between forehead Double Sensor and rectal recordings was not statistically different from zero (p = 0.313), and was significantly smaller than the phase difference between forehead skin and rectal temperatures (p = 0.016). These findings were substantiated by cosinor analyses, revealing significant differences for mesor, amplitude, and acrophase between rectal and forehead skin temperature recordings, but not between forehead Double Sensor and rectal temperature measurements. Finally, Bland-Altman analysis indicated narrower limits of agreement for rhythm parameters between rectal and Double Sensor measurements compared to between rectal and skin recordings, irrespective of the measurement site (i.e. forehead, sternum). Based on these data we conclude that (1) Double Sensor recordings are significantly superior to skin temperature measurements for non-invasively assessing the circadian rhythm of rectal temperature, and (2) temperature rhythms from the sternum are less reliable than from the forehead. We suggest that forehead Double Sensor recordings may provide a surrogate for rectal temperature in circadian rhythm research, where constant routine protocols are applied. Future studies will be needed to assess the sensor’s ecological validity outside the laboratory under changing environmental and physiological conditions.     

Circadian temperature rhythms in rabbit pups and in their does.

Circadian rhythms of mammals are generated endogenously, the master oscillator system residing in the suprachiasmatic nuclei (SCN). Previous experiments have indicated that the rabbit has a feeding entrainable circadian oscillator (FEO) which is supposed to be of greatest importance during the early infancy of the rabbit. Here we report the course of telemetrically monitored core body temperature of rabbit pups and of their does. Temperature increased from 37.6+/-0.3 degrees C on day 2 to 39.5+/-0.1 degrees C on day 28 of life. The pups showed a 24 h temperature rhythm even during their first days of life. Temperature increased 2 1/2-3 h prior to nursing for 0.4-0.8 degrees C and rose for an additional 0.4-0.6 degrees C immediately after milk ingestion. The anticipatory, but not the postprandial component persisted when nursing was skipped twice. The persistence of a rhythm in the absence of any entraining agent is crucial for its endogenous generation. In the doe, the core body temperature gradually decreased during the last 2/3 of pregnancy. During parturition it steeply rose for 1.5-1.7 degrees C and attained a plateau of 39.7+/-0.2 degrees C during lactation. The circadian rhythm persisted during the whole course of pregnancy and lactation. Thus, in the rabbit an endogenous, feeding entrainable circadian oscillator appears to operate from the first days of life. It is of functional significance in that it alerts the pup in time so that it is able to utilize the singular short presence of the doe for maximal milk intake.     

Circadian temperature rhythms in clockwise and counter-clockwise rapidly rotating shift schedules

The purpose of this study was to examine the circadian temperature rhythm in clockwise (CW) and counter-clockwise (CCW) rapidly rotating shift schedules. Arguments against the CCW rotation of shifts are that they result in shortened sleep and promote greater disruption of circadian rhythms. The 3-week study included a week of day shifts (0800-1600) and 2 weeks of shiftwork. The CW 2-2-1 schedule rotated from two early mornings (0600-1400) to two evenings (1400-2200) to one midnight shift (2200-0600) allowing 24 hours off at each shift rotation and a 48-hour weekend. The CCW schedule rotated from two evenings to two early mornings to one midnight shifts allowing only 8 hours off at each shift rotation and an 80-hour weekend. Analysis of the 72-hr periods at the end of each workweek, including the midnight shifts and recovery periods during weeks 2 and 3 were compared to the same 72-hour period at the end of week 1 (baseline). A cosine function that fit the temperature curves by minimizing the sums of squares produced parameters that underwent analysis of covariance procedures. Significant differences were found between rotation conditions for amplitude and acrophase. An attenuation of amplitude and a delay in the acrophase was the found for the counter-clockwise condition. Features inherent in this schedule might explain these effects, particularly, the increased opportunity for "sleeping in" at the beginning of the week and an expanded (2-shift) workday at the end of the week.     

内蒙古草原小毛足鼠的活动性、代谢特征和体温的似昼夜节律

小毛足鼠(Phodopus roborovskii)是分布在内蒙古草原沙地的一种小型哺乳动物,关于其生物学和生态学特征,尤其是生理学特征还知之甚少。似昼夜节律是动物行为学和生理生态学中备受关注的一个领域。在室内条件下通过体内埋置无线电传感器连续监测小毛足鼠的体温、用自动监测系统连续监测活动性和TSE LabMaster呼吸代谢测定系统连续测定了其代谢率的昼夜节律性。结果发现:小毛足鼠在夜间的平均体温是(37.27±0.39)℃,昼间的平均体温是(36.11±0.18)℃;在夜间的平均代谢率是(4.65±1.10)mLO2·g-1·h-1,昼间的平均代谢率是(3.09±0.42)mLO2·g-1·h-1;在夜间的平均活动率为(237±145)次/0.1h,昼间的平均活动率为(38±5)次/0.1h。小毛足鼠的代谢率、活动性和体温的峰值相位主要集中在夜间,属典型的夜行性动物。实验结果从行为学特性和生理学特征等新的角度支持了野外观察小毛足鼠是夜行性动物的推断。综合活动性、代谢率和体温三方面同步变化的特征,为小毛足鼠的似昼夜节律变化提供了新的机理性解释。研究也表明小毛足鼠是研究野生动物似昼夜节律变化机理的好模型。     

Circadian rhythms: per2bations in the liver clock

A master circadian clock resides in the brain and is required to synchronize the clocks in peripheral tissues such as the liver. Until now, it has been unclear how the central clock synchronizes the peripheral ones. New work points to one of the core clock genes, mPer2, as an essential link in this chain.     

Circadian rhythms in cockroaches

Summary The driving oscillator, which mediates circadian locomotor rhythms in cockroaches, appears to reside in the protocerebrum of the brain. The evidence indicates that the optic lobes are crucial elements in this circadian system, and that control of rhythmicity is mediated through electrical, rather than hormonal, channels. Lesions were placed at various sites within the optic lobes in order to localize the areas controlling rhythmicity. It appears that the two innermost synaptic areas (the lobula and the medulla) constitute the crucial optic lobe elements. The outer synaptic area of the optic lobe (the lamina) is not necessary for the expression of rhythmicity, but does function as a coupling through which light cycles, transduced by the compound eyes, entrain the circadian clock.I would like to thank both Dr. Sue Binkley for her helpful comments in the preparation of this report, and Mr. Eli Levine for his assistance in photography. Support for this research was provided by a grant from the National Science Foundation (NS GB-30497).     

Circadian rhythms and insomnia

Sleep and Biological Rhythms - Circadian rhythms strongly influence when we are sleepy and when we are alert. If the timing of these rhythms is later than normal, it can contribute to sleep onset...     

Circadian aspects of body temperature regulation in exercise

Internal and external factors contribute to resting core temperature and affect thermoregulation. Also, a robust circadian rhythm exists, implying that the body is in “heat-gain” or “heat-loss” modes at different times during the 24 h. Moreover, many variables associated with exercise, and the body's capacity for exercise, show circadian variation. All these factors contribute to circadian changes in thermoregulation during exercise. Attention is focused on responses at the onset of exercise, “critical temperature”, and recovery after exercise. Practical implications of circadian changes in thermoregulation during exercise include ergogenic aids and inter-individual differences, including those due to gender, age and acclimatisation.     

Circadian rhythms in the phosphorylation of rat liver histones and similar basic proteins

In the rat liver, the phosphorylation of histones is subject to a circadian rhythm. Most classes of histones, which had been obtained by polyacrylamide gel electrophoresis of nuclear HCl-extracts, exhibited maximum phosphorylation at 21.00 h and at 08.00 h. This is in correlation to maxima of RNA synthesis (23.00 h) and protein synthesis (24.00 h and 12.00 h), reported in the literature. A series of basic proteins, not as yet described, could be separated from the histones. These proteins exhibit a high extent of phosphorylation and a rhythmicity analogous to that of the histones. It is suggested that these proteins are of importance in the expression of genetic information.     

Circadian rhythms and the regulation of metabolic tissue function and energy homeostasis

Circadian oscillators play an indispensable role in the coordination of physiological processes with the cyclic changes in the physical environment. A significant number of recent clinical and molecular studies suggest that circadian biology may play an important role in the regulation of adipose and other metabolic tissue functions. In this discussion, we present the hypothesis that circadian dysfunction may be involved in the pathogenesis of obesity, type 2 diabetes, and the metabolic syndrome.