Circadian rhythm of the grip strength of the right and left hands: desynchronization in some shift workers

38 male shift workers and former shift workers volunteered to self-measure 4 to 8 times/24 hrs. their oral temperature (OT) as well as right and left hand grip strength (HGS) best performance during a 16 to 30 day span. Time series were analyzed individually according to two methods: day by day circadian acrophase drift and power spectrum. Mainly, but not exclusively, subjects with poor tolerance to shift work exhibited an internal desynchronization with a circadian period tau different from 24 hrs. which was the case for OT as well as right and left HGS; each could be different in tau between one another and from 24 hrs. These results suggest that oscillatory systems may be influenced by the neocortex apparently with difference between right and left side.     

Desynchronization of oral temperature, pulse and performance circadian rhythms in shift working Indian nurses.

Circadian time structure in shift working Indian nurses was studied. In shift workers desynchronization between circadian rhythms in different physiological variables was observed. Circadian amplitudes of oral temperature, pulse and random add speed rhythms decreased significantly in shift workers as compared to control subjects. Circadian mesors of performance rhythms increased significantly in shift workers indicating that the time taken by them was more for performing the tasks. It can be concluded that the subjects studied herein are intolerant to shift work and amplitude decrement may be considered as a chronobiologic index to determine the tolerance of individual workers to shift work.     

Blood pressure in night shift workers: circadian rhythms and levels, and their seasonal variation

Average diurnal blood pressure (BP) profiles (DBPP) were studied in persons working at different hours of a day, including night workers. The results obtained in winter and summer seasons were compared. The study consisted of more than 497 000 pre-work BP measurement points for each of 30 566 locomotive drivers. It was found that average DBPP of persons working at different hours of a day is of the marked non-dipper type in spite of night wakefulness. BP was lower at night but not as low as that of night sleeping persons. In the cohort studied, the form of DBPP curve does not differ in winter and summer; however BP in winter is significantly higher.     

Pattern of shift rota modulates oral temperature circadian rhythm and sleep-wakefulness profiles in shift workers

Twenty four shift workers (8 from a steel industry and 16 from a Government hospital) participated in the study. The subjects were instructed to self-measure oral temperature, 4 6 times a day for about three weeks. Sleep quantity and quality for each subject were analysed with the help of an appropriate inventory. The data were analysed by cosinor and power spectrum methods. The frequency of circadian rhythm detection was in the order of 48% in senior nurses, 29% in steel plant workers and 14% in junior nurses. These were also complemented by the results of power spectrum analysis. Present results suggest that rhythms of subjective fatigue and subjective drowsiness are governed neither by oral temperature oscillator nor by the sleep/wake cycle oscillator. The results show that shift rotation pattern chiefly modulates the circadian time structure of shift workers. It is also suggested that the phenomenon of circadian rhythm desynchronization in oral temperature appears to be independent of per day total sleep length.     

Blood pressure in night shift workers: circadian rhythms and levels and their seasonal differences

The average diurnal blood pressure profiles (DBPPs) were studied in subjects working at different hours of the day, including nighttime. The DBPPs and the curve levels in winter and in summer were compared. The study material included more than 497 000 prework blood pressure (BP) measurement points in 30 566 locomotive drivers. It was found that the average DBPP of the subjects working at different hours of the day is of a markedly nondipper type; i.e., despite night wakefulness, the BP was lower at night but not as low as that of those sleeping at night. In the cohort studied, the shapes of the DBPP curve did not differ in winter and in summer; however, the BP levels in winter were significantly higher.     

Internal desynchronization of circadian rhythms and tolerance to shift work

Intolerance to shift work may result from individual susceptibility to an internal desynchronization. Some shift workers (SW) who show desynchronization of their circadian rhythms (e.g., sleep-wake, body temperature, and grip strength of both hands) exhibit symptoms of SW intolerance, such as sleep alteration, persistent fatigue, sleep medication dependence, and mood disturbances, including depression. Existing time series data previously collected from 48 male Caucasian French SW were reanalyzed specifically to test the hypothesis that internal synchronization of circadian rhythms is associated with SW intolerance and symptoms. The entry of the subjects into the study was randomized. Three groups were formed thereafter: SW with good tolerance (n=14); SW with poor tolerance, as evident by medical complaints for at least one year (n=19); and former SW (n=15) with very poor tolerance and who had been discharged from night work for at 1.5 yr span but who were symptom-free at the time of the study. Individual and longitudinal time series of selected variables (self-recorded sleep-wake data using a sleep log, self-measured grip strength of both hands using a Colin Gentile dynamometer, and oral temperature using a clinical thermometer) were gathered for at least 15 days, including during one or two night shifts. Measurements were performed 4-5 times/24 h. Power spectra used to quantify the prominent period (tau) and t-test, chi square, and correlation coefficient were used as statistical tools. The mean (+/-SEM) age of SW with good tolerance was greater than that of SW with poor tolerance (44.9+/-2.1 yrs vs. 40.1+/-2.6 yrs, p<.001) and of former SW discharged from night work (very poor tolerance; 33.4+/-1.7, p<.001). The shift-work duration (yrs) was longer in SW with good than poor tolerance (19.9+/-2.2 yrs vs. 15.7+/-2.2; p<0.002) and former SW (10.7+/-1.2; p<.0001). The correlation between subject age and shift-work duration was stronger in tolerant SW (r=0.97, p<.0001) than in non-tolerant SW (r=0.80, p<0.001) and greater than that of former SW (r=0.72, p<.01). The mean sleep-wake rhythm tau was 24 h for all 48 subjects. The number of desynchronized circadian rhythms (tau differing from 24 h) was greater in non-tolerant than in tolerant SW (chi square=38.9, p<.0001). In Former SW (i.e., 15 individuals assessed in follow-up studies done 1.5 to 20 yrs after return to day work), both symptoms of intolerance and internal desynchronization were reduced or absent. The results suggest that non-tolerant SW are particularly sensitive to the internal desynchronization of their circadian time organization.     

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.     

The strength and periodicity of D. melanogaster circadian rhythms are differentially affected by alterations in period gene expression

The per gene of D. melanogaster influences or participates in the generation of biological rhythms. Previous experiments have identified the head as the location from which per exerts its effect on circadian rhythms. To localize further this region and to examine the effects of altered levels and altered spatial expression patterns of the per gene on circadian rhythms of locomotor activity, we have characterized transformed lines containing per gene constructs missing substantial cis-acting regulatory information. The data suggest that wild-type levels of per gene expression are necessary in only a small fraction of the nervous system for near wild-type periods, whereas a larger fraction of per-expressing cells in the brain contributes to the strength of the circadian rhythms.     

Alteration of PHYA expression change circadian rhythms and timing of bud set in Populus

In many temperate woody species, dormancy is induced by short photoperiods. Earlier studies have shown that the photoreceptor phytochrome A (phyA) promotes growth. Specifically, Populus plants that over-express the oat PHYA gene (oatPHYAox) show daylength-independent growth and do not become dormant. However, we show that oatPHYAox plants could be induced to set bud and become cold hardy by exposure to a shorter, non-24 h diurnal cycle that significantly alters the relative position between endogenous rhythms and perceived light/dark cycles. Furthermore, we describe studies in which the expression of endogenous Populus tremula × P. tremuloides PHYTOCHROME A (PttPHYA) was reduced in Populus trees by antisense inhibition. The antisense plants showed altered photoperiodic requirements, resulting in earlier growth cessation and bud formation in response to daylength shortening, an effect that was explained by an altered innate period that leads to phase changes of clock-associated genes such as PttCO2. Moreover, gene expression studies following far-red light pulses show a phyA-mediated repression of PttLHY1 and an induction of PttFKF1 and PttFT. We conclude that the level of PttPHYA expression strongly influences seasonally regulated growth in Populus and is central to co-ordination between internal clock-regulated rhythms and external light/dark cycles through its dual effect on the pace of clock rhythms and in light signaling.     

Relationships between the circadian rhythms of finger temperature, core temperature, sleep latency, and subjective sleepiness

Skin temperature circadian rhythms have been explored relatively recently. It has been suggested that distal and proximal skin temperature changes play a role in the regulation of the core temperature circadian rhythm and sleepiness. The authors investigated the circadian finger and core temperature rhythms in conjunction with the circadian rhythms of subjective and objective sleepiness. Fourteen healthy, young, good sleepers participated in a modified constant-routine procedure in which palmar finger temperature, rectal temperature, subjective sleepiness, and objective sleep latency were measured half-hourly across a 48-h period of enforced wakeful bed rest. Individual curves were adjusted to the group mean temperature minimum time of 0500 h and averaged to create the 4 mean curves. The 5 possible cross-correlation curves between these 4 measures were calculated for half-hourly phase lags from 12 h before to 12 h after the group mean core temperature minimum time. Maximum cross-correlations for each curve suggested that finger temperature preceded core temperature by 3 h (r = -0.22), and subjective sleepiness followed core temperature by 0.5 h (r = -0.33) and objective sleepiness by 2 h (r = 0.29). Although these data are correlational, they are consistent with the notion that finger temperature changes drive core temperature changes, which determine changes of subjective and objective sleepiness.     

Effects of three-hour restricted food access during the light period on circadian rhythms of temperature, locomotor activity, and heart rate in rats

The effects of food on biological rhythms may influence the findings of chronopharmacological studies. The present study evaluated the influence of a restricted food access during the rest (light) span of nocturnally active Wistar rats on the 24 h time organization of biological functions in terms of the circadian rhythms of temperature (T), heart rate (HR), and locomotor activity (LA) in preparation for subsequent studies aimed at evaluating the influence of timed food access on the pharmacokinetics and pharmacodynamics of medications. Ten-wk-old male Wistar rats were housed under controlled 12:12 h light:dark (LD) environmental conditions. Food and water were available ad libitum, excepted during a 3 wk period of restriction. Radiotelemetry transmitters were implanted to record daily rhythms in T, HR, and LA. The study lasted 7 wk and began after a 21-d recovery span following surgery. Control baseline data were collected during the first wk (W1). The second span of 3 wk duration (W2 to W4) consisted of the restricted feeding regimen (only 3 h access to food between 11:00 and 14:00 h daily) during the L (rest span) under 12:12 h LD conditions. The third period of 3 wk duration (W5 to W7) consisted of the recovery span with ad libitium normal feeding. Weight loss in the amount of 5% of baseline was observed during W1 with stabilization of body weight thereafter during the remaining 2 wk of food restriction. The 3 h restricted food access during the L rest span induced a partial loss of circadian rhythmicity and the emergence of 12 h rhythms in T, HR, and LA. Return to ad libitum feeding conditions restored circadian rhythmicity in the manner evidenced during the baseline control span. Moreover, the MESORS and amplitudes of the T, HR, and LA 24 h patterns were significantly attenuated during food restriction (p < 0.001) and then returned to initial values during recovery. These changes may be interpreted as a masking effect, since T, HR, and LA are known to directly react to food intake. The consequences of such findings on the methods used to conduct chronokinetic studies, such as the fasting of animals the day before testing, are important since they may alter the temporal structure of the organism receiving the drug and thereby compromise findings.     

Hibernation and circadian rhythms of body temperature in free-living Arctic ground squirrels

In mammals, the circadian master clock generates daily rhythms of body temperature (T(b)) that act to entrain rhythms in peripheral circadian oscillators. The persistence and function of circadian rhythms during mammalian hibernation is contentious, and the factors that contribute to the reestablishment of rhythms after hibernation are unclear. We collected regular measures of core T(b) (every 34 min) and ambient light conditions (every 30 s) before, during, and following hibernation in free-living male arctic ground squirrels. Free-running circadian T(b) rhythms at euthermic levels of T(b) persisted for up to 10 d in constant darkness after animals became sequestered in their hibernacula in fall. During steady state torpor, T(b) was constant and arrhythmic for up to 13 d (within the 0.19°C resolution of loggers). In spring, males ended heterothermy but remained in their burrows at euthermic levels of T(b) for 22-26 d; patterns of T(b) were arrhythmic for the first 10 d of euthermia. One of four squirrels exhibited a significant free-running T(b) rhythm (τ = 22.1 h) before emergence; this squirrel had been briefly exposed to low-amplitude light before emergence. In all animals, diurnal T(b) rhythms were immediately reestablished coincident with emergence to the surface and the resumption of surface activity. Our results support the hypothesis that clock function is inhibited during hibernation and reactivated by exposure to light, although resumption of extended surface activity does not appear to be necessary to reinitiate T(b) cycles.     

Come together, right...now: synchronization of rhythms in a mammalian circadian clock

In mammals, the suprachiasmatic nuclei (SCN) of the hypothalamus act as a dominant circadian pacemaker, coordinating rhythms throughout the body and regulating daily and seasonal changes in physiology and behavior. This review focuses on the mechanisms that mediate synchronization of circadian rhythms between SCN neurons. Understanding how these neurons communicate as a network of circadian oscillators has begun to shed light on the adaptability and dysfunction of the brain's master clock.     

The amplitude of circadian oscillations: temperature dependence, latitudinal clines, and the photoperiodic time measurement.

This paper develops several propositions concerning the lability of the amplitude of Drosophila circadian pacemakers. The first is that the amplitude of the pacemaker's motion, unlike its period, is markedly temperature-dependent. The second is that latitudinal variation in pacemaker amplitude (higher in the north) is responsible for two very different sets of observations on Drosophila circadian systems at successively higher latitudes. One of these is a cline in D. auraria's phase-shifting response to light, which steadily weakens in a succession of more northerly strains. The other, concerning D. littoralis in the very far north, is a cline in the rate at which eclosion activity becomes arrhythmic (the circadian rhythm damps out) in constant darkness; damping is faster in the north. The third proposition concerns a plausible selection pressure for the cline in pacemaker amplitude that we propose underlies the two directly observed clines. Two points are emphasized: (1) The amplitude of the pacemaker's daily oscillation declines as the duration of the entraining light pulse (photoperiod) is increased; and (2) the duration of the daily photoperiods throughout the breeding season is steadily increased as one moves toward the poles. Selection for conservation of pacemaker amplitude (during the breeding season) would produce the latitudinal cline we propose. The fourth, and final proposition is that since the amplitude of the pacemaker's daily motion responds systematically to change in photoperiod, amplitude is clearly one way--and a temperature-dependent way--in which insect circadian systems may sense seasonal change. These propositions concerning the temperature and latitude dependence of pacemaker amplitude may be relevant to a wider array of circadian pacemakers than Drosophila.     

Comparative study on circadian rhythms of body temperature, heart rate, and locomotor activity in three species hamsters.

Circadian rhythms of body temperature, heart rate, and locomotor activity were observed in the unanesthetized and unrestrained Syrian hamsters, Djungarian hamsters and Chinese hamsters, and the differences in these biological characters among the three species of hamster were investigated. In each species, body temperature, heart rate, and locomotor activity in the dark period were higher than those in the light period. Heart rate of Chinese hamsters was higher than that of the others in both the light and dark periods. In addition, it was found that the body temperature of Djungarian hamsters decreased rapidly one time a day. These results show species differences in body temperature, heart rate and locomotor activity of Syrian, Djungarian and Chinese hamsters.