The effect of real and simulated time-zone shifts upon the circadian rhythms of body temperature, plasma 11-hydroxycorticosteroids, and renal excretion in human subjects

The influence of circadian rhythms on CD8+ T cell activation upon vaccination: A mathematical modeling perspective

Circadian rhythms have been implicated in the modulation of many physiological processes, including those associated with the immune system. For example, these rhythms influence CD8+ T cell responses within the adaptive immune system. The mechanism underlying this immune-circadian interaction, however, remains unclear, particularly in the context of vaccination. Here, we devise a molecularly-explicit gene regulatory network model of early signaling in the naïve CD8+ T cell activation pathway, comprised of three axes (or subsystems) labeled ZAP70, LAT and CD28, to elucidate the molecular details of this immune-circadian mechanism and its relation to vaccination. This is done by coupling the model to a periodic forcing function to identify the molecular players targeted by circadian rhythms, and analyzing how these rhythms subsequently affect CD8+ T cell activation under differing levels of T cell receptor (TCR) phosphorylation, which we designate as vaccine load. By performing both bifurcation and parameter sensitivity analyses on the model at the single cell and ensemble levels, we find that applying periodic forcing on molecular targets within the ZAP70 axis is sufficient to create a day-night discrepancy in CD8+ T cell activation in a manner that is dependent on the bistable switch inherent in CD8+ T cell early signaling. We also demonstrate that the resulting CD8+ T cell activation is dependent on the strength of the periodic coupling as well as on the level of TCR phosphorylation. Our results show that this day-night discrepancy is not transmitted to certain downstream molecules within the LAT subsystem, such as mTORC1, suggesting a secondary, independent circadian regulation on that protein complex. We also corroborate experimental results by showing that the circadian regulation of CD8+ T cell primarily acts at a baseline, pre-vaccination state, playing a facilitating role in priming CD8+ T cells to vaccine inputs according to the time of day. By applying an ensemble level analysis using bifurcation theory and by including several hypothesized molecular targets of this circadian rhythm, we further demonstrate an increased variability between CD8+ T cells (due to heterogeneity) induced by its circadian regulation, which may allow an ensemble of CD8+ T cells to activate at a lower vaccine load, improving its sensitivity. This modeling study thus provides insights into the immune targets of the circadian clock, and proposes an interaction between vaccine load and the influence of circadian rhythms on CD8+ T cell activation.

Effect of naive and cancer-educated fibroblasts on colon cancer cell circadian growth rhythm

Opportunistic modification of the tumour microenvironment by cancer cells enhances tumour expansion and consequently eliminates tumour suppressor components. We studied the effect of fibroblasts on the circadian rhythm of growth and protein expression in colon cancer HCT116 cells and found diminished oscillation in the proliferation of HCT116 cells co-cultured with naive fibroblasts, compared with those co-cultured with tumour-associated fibroblasts (TAFs) or those cultured alone, suggesting that TAFs may have lost or gained factors that regulate circadian phenotypes. Based on the fibroblast paracrine factor analysis, we tested IL6, which diminished HCT116 cell growth oscillation, inhibited early phase cell proliferation, increased early phase expression of the differentiation markers CEA and CDX2, and decreased early phase ERK5 phosphorylation. In conclusion, our data demonstrate how the cancer education of naive fibroblasts influences the circadian parameters of neighbouring cancer cells and highlights a putative role for IL6 as a novel candidate for preoperative treatments.

Circadian rhythmicity of body temperature and metabolism

This article reviews the literature on the circadian rhythms of body temperature and whole-organism metabolism. The two rhythms are first described separately, each description preceded by a review of research methods. Both rhythms are generated endogenously but can be affected by exogenous factors. The relationship between the two rhythms is discussed next. In endothermic animals, modulation of metabolic activity can affect body temperature, but the rhythm of body temperature is not a mere side effect of the rhythm of metabolic thermogenesis associated with general activity. The circadian system modulates metabolic heat production to generate the body temperature rhythm, which challenges homeothermy but does not abolish it. Individual cells do not regulate their own temperature, but the relationship between circadian rhythms and metabolism at the cellular level is also discussed. Metabolism is both an output of and an input to the circadian clock, meaning that circadian rhythmicity and metabolism are intertwined in the cell.

Integration of biological clocks and rhythms

Animals, plants, and microorganisms exhibit numerous biological rhythms that are generated by numerous biological clocks. This article summarizes experimental data pertinent to the often-ignored issue of integration of multiple rhythms. Five contexts of integration are discussed: (i) integration of circadian rhythms of multiple processes within an individual organism, (ii) integration of biological rhythms operating in different time scales (such as tidal, daily, and seasonal), (iii) integration of rhythms across multiple species, (iv) integration of rhythms of different members of a species, and (v) integration of rhythmicity and physiological homeostasis. Understanding of these multiple rhythmic interactions is an important first step in the eventual thorough understanding of how organisms arrange their vital functions temporally within and without their bodies.

The effect of light on the human circadian pacemaker

The periodic light-dark cycle provides the primary signal by which the human circadian pacemaker is synchronized to the 24 h day. Earlier reports that social contacts were more effective than light in the entrainment of human circadian rhythms have not been supported by more recent studies. In fact, we have found that exposure to a cyclic light stimulus can induce strong (type 0) resetting of the human circadian pacemaker, indicating that exposure to light affects the pacemaker's amplitude of oscillation as well as its phase. These findings support Winfree's long-standing prediction, based on his pioneering recognition of the importance of amplitude in the analysis of circadian clocks, that strong (type 0) resetting would prove to be a common property of circadian resetting responses to light across a wide array of species, from algae to humans. Research on humans has shown, for the first time, that the response of the circadian pacemaker to light depends not only on the timing, intensity and duration of light exposure, but also on the number of consecutive daily light exposures. Exposure to light of a critical strength at a critical phase can even drive the human circadian pacemaker to its region of singularity, akin to temporarily 'stopping' the human circadian clock. These findings have important implications for the treatment of circadian rhythm sleep disorders, because properly timed exposure to light can reset the human clock to any desired hour within one to three days.

Temperature rhythm reentrains faster than locomotor rhythm after a light phase shift

Mammalian endogenous circadian rhythms are entrained to the environmental light-dark (LD) cycle. Although the circadian rhythms of core body temperature (Tb) and spontaneous locomotor activity (LA) are well synchronized under stable LD conditions, it is thought that these two parameters are regulated by distinct mechanisms. The purpose of the present study was to examine the adaptability of these two rhythms to an abrupt change in the environmental light phase. Tb and LA were simultaneously recorded in individual mice kept under 12:12-h LD cycle conditions before and after an 8-h photic phase advance. The onset of LA required 8 days to reentrain to the new LD cycle, whereas 6 days were required for reentrainment of the acrophase of Tb. Resting Tb, i.e., the Tb level independent of LA, was extracted from the same data source. The resting Tb level exhibited a robust daily rhythm with a difference of 1.0 degrees C between LD phases. After the photic phase advance, the resting Tb rapidly reached a stable level within 4 days, whereas the uncorrected Tb required 6 days for reentrainment. Based on these findings, we revealed that, independent of LA, the adaptability of the Tb rhythm to a new light cycle is half as rapid as that of LA. These results therefore suggest that the circadian rhythms of Tb and LA are intrinsically regulated by different pacemaker or effector mechanisms.

The timing of the human circadian clock is accurately represented by the core body temperature rhythm following phase shifts to a three-cycle light stimulus near the critical zone

A double-stimulus experiment was conducted to evaluate the phase of the underlying circadian clock following light-induced phase shifts of the human circadian system. Circadian phase was assayed by constant routine from the rhythm in core body temperature before and after a three-cycle bright-light stimulus applied near the estimated minimum of the core body temperature rhythm. An identical, consecutive three-cycle light stimulus was then applied, and phase was reassessed. Phase shifts to these consecutive stimuli were no different from those obtained in a previous study following light stimuli applied under steady-state conditions over a range of circadian phases similar to those at which the consecutive stimuli were applied. These data suggest that circadian phase shifts of the core body temperature rhythm in response to a three-cycle stimulus occur within 24 h following the end of the 3-day light stimulus and that this poststimulus temperature rhythm accurately reflects the timing of the underlying circadian clock.

Extraocular circadian phototransduction in humans

Physiological and behavioral rhythms are governed by an endogenous circadian clock. The response of the human circadian clock to extraocular light exposure was monitored by measurement of body temperature and melatonin concentrations throughout the circadian cycle before and after light pulses presented to the popliteal region (behind the knee). A systematic relation was found between the timing of the light pulse and the magnitude and direction of phase shifts, resulting in the generation of a phase response curve. These findings challenge the belief that mammals are incapable of extraretinal circadian phototransduction and have implications for the development of more effective treatments for sleep and circadian rhythm disorders.

Light treatment for sleep disorders: consensus report. VII. Jet lag

Sleep disturbances are an all-too-familiar symptom of jet lag and a prime source of complaints for transmeridian travelers and flight crews alike. They are the result of a temporary loss of synchrony between an abruptly shifted sleep period, timed in accordance with the new local day-night cycle, and a gradually reentraining circadian system. Scheduled exposure to bright light can, in principle, alleviate the symptoms of jet lag by accelerating circadian reentrainment to new time zones. Laboratory simulations, in which sleep time is advanced by 6 to 8 h and the subjects exposed to bright light for 3 to 4 h during late subjective night on 2 to 4 successive days, have not all been successful. The few field studies conducted to date have had encouraging results, but their applicability to the population at large remains uncertain due to very limited sample sizes. Unresolved issues include optimal times for light exposure on the first as well as on subsequent treatment days, whether a given, fixed, light exposure time is likely to benefit a majority of travelers or whether light treatment should be scheduled instead according to some individual circadian phase marker, and if so, can such a phase marker be found that is both practical and reliable.

Deriving a "phase response curve" from adjustment to simulated time zone transitions

Thirty-eight subjects in groups of two to four have been subjected to simulated time zone transitions of 8 hr eastward, 8 hr westward, or 12 hr; all experiments have taken place in a temporal isolation unit, in which the light intensity during the waking periods was 250-300 lux. Circadian rhythms of rectal temperature have been used as a marker of the process of adjustment, the data being analyzed before (raw) and after "purification." Conventional results have been obtained, but when the data have been treated appropriately, they have produced a relationship between shift of the sleep-activity cycle and shift of the temperature rhythms that shows many characteristics of a phase response curve. Even though the factor or factors causing such adjustment are unknown, the results confirm that changes of a consonant set of "weak" zeitgebers is sufficient for entrainment to a new time zone to occur.

The effect of four-day round trip flights over 10 time zones on the circadian variation of salivary melatonin and cortisol in airline flight attendants

The effects of four-day round flights (Helsinki-Los Angeles-Seattle-Helsinki) were studied on the circadian rhythms of salivary melatonin (MT) and cortisol (COR) in 35 flight attendants. The mean age of the subjects was 33 +/- 7 years (median 34, range 21-50). Five 24 h profiles of unstimulated saliva were collected at 2 h intervals (except at 04:00) before, during, and after the four day flight. Salivary MT and COR were determined by radioimmunoassay. Both MT and COR exhibited a clear circadian rhythm with acrophases before the flight at 03:03 (MT) and 09:08 (COR). Two days after the westward flight from Helsinki to Los Angeles, the MT rhythm (circadian acrophase) had delayed 4 h 51 min and the COR rhythm 3 h 55 min compared to the control day before the flight. Two days later, during the last day in the USA, the MT rhythm had delayed 5 h 59 min and the COR rhythm 5 h 29 min as compared to the situation before the flight. After four days of the eastward flight from Seattle to Helsinki, the circadian acrophase of MT was still 1 h 35 min delayed compared to the control day before the westward flight. The results indicate that the restitution time of five days at the home base is on the average proper for recovery, if a four day round flight over 10 time zones takes four days or less. The resynchronization rate of salivary hormones after westward, outgoing flights is faster than the resynchronization rate after the eastward return flights.

The circadian rhythm of body temperature

This paper reviews the literature on the circadian rhythm of body temperature (CRT). The review starts with a brief discussion of methodological procedures followed by the description of known patterns of oscillation in body temperature, including ultradian and infradian rhythms. Special sections are devoted to issues of species differences, development and aging, and the relationships between the CRT and the circadian rhythm of locomotor activity, between the CRT and the thermoregulatory system, and between the CRT and states of disease. A section on the nervous control of the CRT is followed by summary and conclusions.

Sleep on a shortening day/night schedule

In 2 experiments subjects were exposed for 3.5 weeks to a gradually (0.2 h/day initially) shortening day/night cycle, ending at 22.8 h and 22.0 h, respectively. Shortening of the cycle led to an initial but temporary increase of sleep latency. When the reduction ceased at 22.8 h and this length was maintained, sleep parameters were not further affected and the temperature rhythm in most subjects remained entrained to the 22.8 h period, although some instability occurred towards the end. In the 22.0 h experiment the continued reduction beyond 22.8 h led to disturbed sleep on day 15, at a day length of 22.4 h. Total sleep time, stage 2 and sleep efficiency were then markedly reduced. At this point sleep coincided with the peak of the body temperature rhythm and the amplitude of the latter was extremely small. This was also the point when the body temperature rhythm 'broke out' from the sleep/wake rhythm and showed a large 6 h phase jump (delay). Towards the end of the experiment, when sleep was initiated in the circadian temperature trough, REM propensity was increased. It was concluded that several sleep parameters were affected by the reduction of the day/night cycle although the specific effects depended on the amount of phase advance and on whether desynchronization occurred. Within the range of entrainment, however, most sleep parameters were remarkably unperturbed by the considerable changes of circadian parameters.

A human phase-response curve to light

Using 'classical' experimental protocols, a human phase-response curve (PRC) to a single 3-h bright light pulse has been established. When the light pulse was centred slightly before the time of body temperature minimum, the circadian system delayed, whilst a pulse slightly after the minimum advanced it. Maximum phase shifts were about 2 h. When light pulses over 3 successive cycles were used, larger shifts (4-7 h) were produced. It is concluded that the human PRC does not differ in principle from that found in other species, except with respect to the light intensity required.

"Demasking" the temperature rhythm after simulated time zone transitions

Simulated time zone transitions were performed in an isolation unit upon groups of one to four human subjects. In the first series of experiments, the adjustment of the circadian rhythm of body temperature, measured in the presence of sleep and other masking factors, was assessed by cosinor analysis and by cross-correlation methods. These methods modeled the circadian timing system either as a single component or as the sum of two components, those due to exogenous and endogenous influences. The one-component models described a more rapid adjustment of the temperature rhythm to the time zone transition than did the two-component models; we attribute this difference to the masking effects of the exogenous component. In a second series of experiments, we showed that the shift of the endogenous component, as assessed by the two-component models, was not significantly different from that measured during constant routines. The results also showed that, if the zeitgebers were phased in advance of the endogenous component, then advances of the endogenous component were produced only if this mismatch was less than about 10 hr. Mismatches greater than this, and cases where the zeitgebers were delayed with respect to the endogenous component, both produced delays of the endogenous component. We conclude that the two-component cross-correlation methods can be used to estimate shifts of the endogenous component of a circadian rhythm in the presence of masking factors. They are therefore an alternative to constant routines when these latter are impracticable to carry out.

Removing masking factors from urinary rhythm data in humans

We have previously developed simple models that enable the exogenous and endogenous components of the circadian rhythm of body temperature to be separated. The present paper extends the method to urinary data. First, we have shown that the basic superiority of the two-component model over the one-component model persists when temperature data are converted into a format that is appropriate for urine sampling (that is, a single overnight sample and two-hourly samples during waking). Second, we provide normative endogenous data for urinary sodium, potassium and urate, data obtained from about 80 constant routines. These data are required for the two-component model. Third, we have compared the rate of adjustment to a simulated eastward time-zone transition of 8 hr in 8 subjects. This showed that the rate of adjustment assessed by the two-component model was significantly less than that assessed by the one-component model and much closer to that assessed in separate experiments (n = 15 subjects) using constant routines. We conclude that the two-component model can be used upon urinary data to give a closer approximation to the shift of the endogenous component, as assessed by constant routines, than can estimates that do not take into account the problem of masking caused by exogenous factors.

Effects upon circadian rhythmicity of an alteration to the sleep-wake cycle: problems of assessment resulting from measurement in the presence of sleep and analysis in terms of a single shifted component

Experiments were performed upon groups of three or four human subjects in an isolation chamber (total n = 14). Subjects lived initially on a conventional lifestyle and then delayed their hours of sleep by 8 hr (so mimicking some aspects of nightwork) for 2 or 5 days. They also performed two constant routines--protocols designed to minimize any effects due to the environment, mealtimes, and activity. Regular samples of urine were taken when subjects were awake, and were analyzed for sodium, potassium, and chloride; rectal temperature was measured and logged at 6-min intervals throughout. Shifts in circadian rhythms produced by the change in sleep time were assessed by cosinor and cross-correlation techniques. The protocol enabled these assessments to be made on days when sleep was allowed and under constant-routine conditions, so that masking and behavioral effects could be investigated also. The results confirmed that adjustment to the change in sleep time was slow and only partial, and that assessments made on days when sleep was allowed overestimated this adjustment. Furthermore, it was concluded that, whereas cosinor and cross-correlation techniques using only one shifting component were equally useful in describing the observed changes, both were inferior to a cross-correlation technique that made use of two shifting components. Some practical and theoretical implications of these results are discussed.

Sleep and circadian rhythms of temperature and urinary excretion on a 22.8 hr "day"

Two groups of subjects (total N = 6) were studied in an isolation chamber for a period of 3 weeks whilst living on a 22.8 hr "day". Regular samples of urine were taken when the subjects were awake, deep body temperature was recorded continuously and polygraphic EEG recordings were made of alternate sleeps. The excretion in the urine of potassium, sodium, phosphate, calcium and a metabolite of melatonin were estimated. Measurements of the quantity and quality of sleep were made together with assessments of the temperature profiles associated with sleep. In addition, cosinor analysis of circadian rhythmicity in urinary variables and temperature was performed. The 22.8 hr "days" affected variables and subjects differently. These differences were interpreted as indicating that the endogenous component of half the subjects adjusted to the 22.8 hr "days" but that, for the other three, adjustment did not occur. When the behaviour of different variables was considered then some (including urinary potassium and melatonin, sleep length and REM sleep) appeared to possess a larger endogenous component than others (for example, urinary sodium, phosphate and calcium), with rectal temperature behaving in an intermediate manner. In addition, a comparison between different rhythms in any subject enabled inferences to be drawn regarding any links (or lack of them) that might exist between the rhythms. In this respect also, there was a considerable range in the results and no links between any of the rhythms appeared to exist in the group of subjects as a whole. Two further groups (total N = 8) were treated similarly except that the chamber clock ran at the correct rate. In these subjects, circadian rhythms of urinary excretion and deep body temperature (sleep stages and urinary melatonin were not measured) gave no evidence for deterioration. We conclude, therefore, that the results on the 22.8 hr "day" were directly due to the abnormal "day" length rather than to a prolonged stay in the isolation chamber.

Irregularity of rest and activity: studies on circadian rhythmicity in man

1. Rectal temperature, electrolyte excretion and performance were studied in young adults who followed an irregular pattern of work and rest for 9 days in an isolation unit. 2. In the analysis, effects evoked by the pattern of work and rest were separated from the oscillatory component, and rhythms for individual days were examined by the cosinor method. 3. During the schedule, rhythms no longer showed a period of exactly 24 h, and this effect was confirmed by studies using a repeated cycle of irregular work and rest and by studies using constant routines. 4. Temperature and urinary constituents differed in the strength and phase of their rhythms when corrected for evoked effects, as well as in the strength of the evoked effects themselves. 5. There was evidence of deterioration in performance during work periods which exceeded 9 h, but there was no evidence of progressive deterioration in performance over the 9 day schedule.

Independence of the circadian rhythm in alertness from the sleep/wake cycle

It is common knowledge that our feelings of alertness or drowsiness vary throughout the day. Indeed, this diurnal variation is so widely accepted that it has been used to validate the drowsy/alert component of activation obtained from mood adjective checklists. There is, however, some evidence from sleep deprivation and shiftwork studies that this variation is not simply a reflection of our sleep/wake cycle, as might be expected, but is at least partially dependent on an endogenous circadian (approximately 24 h) oscillator such as that proposed to account for the circadian rhythm in body temperature and other physiological variables. Here we have tested this suggestion by separating the body-temperature rhythm from the sleep/wake cycle by progressively shortening artificial time cues (zeitgebers). Our results indicate that the circadian rhythm in alertness can become independent of both the sleep/wake cycle and the rhythm in body temperature. Further, and contrary to our expectations, the results suggest that the sleep/wake cycle exerts less influence on the alertness rhythm than it does on that of temperature.

Is there more than one circadian clock in humans? Evidence from fractional desynchronization studies

Three groups of four healthy volunteers lived in an isolation unit for 24 days. During this time they lived by a clock which, unknown to themselves, ran progressively faster so that, by real time, the 'day' decreased from 24.0 to 22.0 h in length. Throughout this protocol, the subjects lived a regular regimen of sleep, waking and meals based upon their 'local' time clock. They collected regular urine samples that were analysed for a variety of constituents. Rectal temperature was also recorded automatically throughout. The effects of such a protocol upon circadian rhythmicity in these variables were investigated by a variety of techniques including cosinor analysis. The results showed that the temperature rhythm was less able to adjust to a shortening 'day' than were the urinary variables, with the possible exception of potassium; that is, the protocol forced an internal desynchronization to exist between different variables. These results are discussed in terms of both the possibility that more than one internal circadian clock might exist and the direct effect that sleep exerts upon the expression of circadian rhythms.

The use of constant routines in unmasking the endogenous component of human circadian rhythms

A major problem in the study of the internal clock(s) that drives human circadian rhythms is that due to the effect produced by rhythmicity of habits and external influences ('masking'). A particularly potent factor in this respect is the sleep-wake cycle. It is anomalous that, even though this masking influence is widely accepted, most studies of circadian rhythmicity have been performed in the presence of such interferences. A protocol is described, the constant routine, by which these exogenous influences can be minimized, thereby enabling a closer scrutiny of the internal clock(s) to be made. An account is given of the different circumstances in which the constant routines have been used together with the results derived from such studies. Briefly, they indicate that nychthemeral studies can give misleading information about the rate of adjustment of the internal clock to various manipulations, e.g. time-zone transition, shift work. In addition, future studies making use of constant routines are described, in particular those which might enable the presence of more than one internal clock to be established.

Does 'anchor sleep' entrain circadian rhythms? Evidence from constant routine studies

Experiments have been performed in an isolation unit to investigate the effects of abnormal sleep-waking schedules upon circadian rhythms of renal excretion and deep-body temperature. In confirmation of previous work, nychthemeral rhythms appeared to be 'anchored' to a 24 h period if 4 h sleep was taken regularly each day, even though another 4 h was taken irregularly. The endogenous components were investigated by assessing circadian rhythmicity under constant routine conditions, that is, when rhythmic influences in the environment and sleep-waking pattern had been minimized. Analysis of the constant routine data indicated the presence of a rhythmic component which had been stabilized to a period of 24 h by the 'anchor sleep'. In addition, a delayed component was also present. The starting time of the constant routines produced a direct effect upon the rhythms, which was presumed to result from removing the 'masking' effect that sleep normally exerts upon rhythms. There was some evidence that the relative importance of the masking effect and the delayed component depended upon the variable under consideration. The implications of these findings, in terms of the effects of anchor sleep, the presence of more than one internal clock and the usefulness of constant routines, are discussed.

Circadian rhythms of urinary excretion: the relationship between the amount excreted and the circadian changes

1. The circadian rhythms of urinary excretion of water, sodium, chloride, potassium, urate, calcium and phosphate have been studied in several groups of volunteers. 2. These rhythms have been measured: under nychthemeral and constant routine regimens; while subjects were in an Isolation Unit or allowed free egress into society; with spontaneous changes in dietary intake; or after potassium-loading. 3. A direct relationship between 24 h mean rate of excretion and range of excretion was found in all circumstances and for all variables; this relationship was found also when the mesor and amplitude of the cosine curve best describing each 24 h of data were considered. 4. These relationships derive from the observation that, with increases in 24 h mean rates of excretion, nocturnal rates increased less than diurnal rates. 5. This differential sensitivity as between the night and day times has both endogenous and exogenous components. 6. It is suggested that circadian rhythms of urinary excretion result at least partially from this differential sensitivity of the kidney to homeostatic control mechanisms.

Adaptation to abrupt time shifts of the oscillator(s) controlling human circadian rhythms

1. Thirty-six subjects in an isolation unit were subjected to time shifts of 12 hr, or of 8 hr in either direction. 2. The rhythms of body temperature and excretion of eight urinary constituents were studied before and after the shift, both on a usual nychthemeral routine and during 24 hr when they remained under constant conditions, awake, engaged in light, mainly sedentary activity, and consuming identical food and fluid every hour. 3. The rhythms on nychthemeral routine were defined by fitting cosine curves. On constant routine the rhythm after the shift was cross-correlated with the original rhythm, either with variable delay (or advance) or with an additive mixture between this variably shifted rhythm and the unshifted or a fully shifted rhythm. The process yielding the highest correlation coefficient was accepted as the best descriptor of the nature of adaptation. 4. A combination of two rhythms was observed more often for urinary sodium, chloride and phosphate than for other variables. 5. Adaptation appeared to have proceeded further after westward than eastward shifts, and this difference was particularly noticeable for urinary potassium, sodium and chloride. 6. Partial adaptation usually involved a phase delay, even after an eastward shift when a cumulative delay of 16 hr would be needed to achieve full adaptation and re-entrainment. 7. Observations under nychthemeral conditions often gave a false idea of the degree of adaptation. In particular, after an eastward shift the phase of the rhythms appeared to shift in the appropriate direction when studied under nychthemeral conditions whereas the endogenous oscillator either showed no consistent behaviour or, in the control of urate excretion, a shift in the wrong direction. 8. The implications for people undergoing time shifts, in the course of shift work or transmeridional flights, are indicated.

Three weeks in isolation with two chronic schizophrenic patients

An account is given of impressions and observations collected during three weeks in November 1975 which the writer spent with two of his chronic schizophrenic patients in a purpose-built isolation unit inside which it was impossible to have any idea of the real time. This experience gave the observer an unusually close view of schizophrenic and institutional behaviour and some insight into the natural outcome of staff-patient interaction.

Direct evidence for the location of kallikrein in the striated ducts of the cat's submandibular gland by the use of specific antibody

Kallikrein was located in the apical portion of the striated duct cells of the cat's submandibular gland by an immunohistochemical technique. This portion only of these cells showed an intense band of specific fluorescence. There was no evidence of specific fluorescence in the acinar and demilune cells nor in the interstitial tissue or blood besells. In some sections the collecting ducts showed a very fine fluorescent luminal rim.

The physiological rhythms of subjects living on a day of abnormal length

1. Fourteen subjects, singly or in groups, have been observed while living on a 21 hr day for 8 or 16 experimental 'days' and fifteen other subjects similarly on a 27 hr day. 2. Rhythmic components of body temperature and excretion of various urinary constituents were calculated. 3. On a 21 hr day, for most components and most subjects, two periods were present, one of 21 hr and one of around or somewhat over 24 hr. 4. On a 27 hr day two periods were less often present and a larger number of observed rhythms could be satisfactorily described by a single period, usually between 23 and 28 hr. 5. In subjects spending a second week on a 21 hr day the circadian component was no less prominent than during the first week. 6. When, after life on a 21 hr day, subjects were deprived of knowledge of time, there was evidence that the 21 hr component did not persist. 7. The results are interpreted as evidence of the continuing existance of an influence with a period of around 24 hr, simultaneously rhythmic influences resulting from the subjects' habits. On a 27 hr day there was sometimes evidence of entrainment, yielding an intermediate period. 8. An attempt is made to compare the relative potency of the exogenous and of the persistent circadian influences on the several variables.

The circadian rhythms of human subjects without timepieces or indication of the alternation of day and night

1. Seven solitary subjects, and two groups of four, spent from 5 to 13 days in an isolation unit without knowledge of time. Three solitary subjects and one group of four adopted fairly regular activity habits with a period of 25-27 h; one subject adopted a period of 30 h, and one of 27 h initially, decreasing to 24-25 h after a few days. One group of four awoke roughly every 24 h, after a sleep which was alternately about 8 h, or about 4 h and believed by the subjects to be an afternoon siesta. Two solitary subjects alternated sleeps of about 8 or 16 h, separated by 24 h of activity.2. Deep temperature in all subjects oscillated with a period of 24-26 h, which was thus commonly distinct from their activity habits.3. Urinary potassium followed a rhythm whose period, though usually close to, was sometimes distinct from, that of temperature. A secondary period corresponding to that of activity was also sometimes present.4. Urinary sodium and chloride usually gave evidence of two periodic components, one corresponding to activity and the other to the rhythm of either temperature or of urinary potassium.5. Urinary creatinine and phosphate usually followed the subject's routine of activity.6. Plasma samples were collected on a few occasions and analysed for phosphate and 11-hydroxycorticosteroids. Changes in plasma phosphate were usually, but not always, associated with similar changes in urinary phosphate, and changes in plasma corticosteroids were often, but not always, associated with similar changes in urinary potassium shortly afterwards.7. Observations are recorded on a subject alone in a cave for 127 days. His activity habits, though wildly variable, gave evidence of a period of 25.1 h and his urinary electrolyte excretion indicated a shorter period, of 24.6 h. During the following 3 days, when he remained in the cave but was visited frequently, his plasma corticosteroids and urinary potassium oscillated with a period of 16 h.8. The possible mechanisms controlling these rhythms are discussed.