Circadian Rhythms In Man Research Articles

Psychophysiological effects of early morning bright light exposure in young adults

The effects of bright light on circadian rhythms in man are well documented. Nevertheless the theoretical basis and the rules for the practical utilization of light exposure as therapy need still to be better defined. The present study determined to what extent a 2-hr bright light exposure (0500–0700h) improved the adjustment to an early rising in normal adults. Phase changes were assessed in subjective alertness, performance in several search tasks, time estimation, and a visual discrimination task, as well as in body motility, plasma cortisol concentrations, and body temperature. In comparison with a dim light exposure, the bright light resulted in increased motor activity during waking, in earlier peak of subjective alertness, and an improvement in performance speed in three out of five tasks in the morning. Cortisol and body temperature also were phase-advanced. In summary, light applied to a portion of the circadian cycle sensitive to phase advance shifts influenced rhythms with strong endogenous components (temperature and cortisol), while other rhythms with strong exogenous components were more sensitive to sleep deprivation caused by the early rising time.

A simple method for recording and analysing circadian rhythms in man

We describe a method for recording human rest-activity and body temperature. A small automatic cordless electronic device has been developed in order to record circadian rhythmicity of rest-activity for a period of one week. A comparable device connected to a small temperature transducer by means of a flexible probe was designed to register body temperature. These devices can register human circadian rhythms without interfering with their normal daily activity.

The effect of desynchronization on meal patterns of humans living in time isolation

We analyzed the timing of meals in nine subjects who lived for several weeks in a time isolation environment and whose free-running sleep-wake cycles lengthened markedly and lost synchrony with the body temperature rhythm for part of the study. The long sleep-wake periods (SWP) in free-running desynchrony (mean=34±3 hours) as compared to free-running synchrony (25±1 hours) enabled us to compare meal timing in two distinct temporal frameworks and to relate them to the two major oscillators presumed to underlie circadian rhythms in man. We found that when the SWP lengthened in desynchrony, the intermeal interval (IMI) increased significantly. In half the subjects, the increase in IMI was approximately proportional to the increase in the SWP—the IMI “stretched” along with the SWP. Analysis of prelunch and postlunch IMIs indicated that the lengthening of the IMI during desynchrony was comparable in early and later parts of the subjective day. The increase in meal spacing was not due to increased caloric content of meals. The findings support an interpretation of dual regulation of meal timing. Proportional increases in IMI and SWP suggest that the mechanism governing the timing of the sleep-wake cycle also governs meal timing. The less than proportional increase in some cases suggests that an additional, probably metabolic, mechanism tends to limit the intervals between meals.

Circulating CALLA-positive lymphocytes exhibit circadian rhythms in man

Common acute lymphoblastic leukemia antigen (CALLA) is a polypeptide with a molecular weight of 100,000 daltons (P100). It has been mainly found on the membrane of leukemic lymphoblasts, but not on that of normal circulating lymphocytes. Circadian rhythmicity in circulating CALLA-positive (CALLA+) lymphocytes was investigated in five healthy male subjects. Blood was sampled every 4 h for 24 h in each subject. Seven time series were obtained (three for the same subject). Leukocyte and differential counts were determined, and mononucular cells (>95% lymphocytes) were isolated in Ficoll-Paque gradient. CALLA+ cells were characterized with both J5 and VILA1 monoclonal antibodies. Other T- and B-cell subpopulations were also determined in the same samples. Up to 1160 ± 498 (mean ± 1 S.E.M) J5-labelled CALLA+ lymphocytes per mm 3 were found in peripheral blood at night. At this time, circulating VILA1-labelled CALLA+ lymphocytes also reached their peak although with a much lower number (66 ± 14 cells/mm 3). A circadian rhythm (with a period = 24 h) was statistically validated with several methods for the number of J5-labelled cells, that of VILA1-labelled cells and the J5: VILA1 ratio. The count of J5-labelled CALLA+ cells was correlated with that of total lymphocytes, total T (OKT3+) and inducer T (OKT4+) cells ( p < 0.01), but neither with suppressor/cytotoxic cells (OKT8+) nor with B cells (Sig+, BI+, B2+, or HLA-Dr+). No correlation was found between any of these lymphocyte subpopulation and the count of VILA1-labelled CALLA+ cells. Such results further support the hypothesis that VILA1 and J5 monoclonal antibodies do not bind to the same epitope of the CALLA molecule. The large nocturnal increase in circulating J5-labelled CALLA+ lymphocytes may be accounted for by a release of immature presumably T lymphocytes in the peripheral blood.

Seasonality in freerunning circadian rhythms in man.

Retrospective analysis of data collected over 15 years in normal subjects isolated from time cures showed seasonal rhythms in the circadian period of the core temperature rhythm, in the amount of sleep (both shorter in spring and longer in autumn), and in the incidence of internal desynchronisation (most often in summer). Women slept longer than men at all times of year.

Human brain contains vasopressin and vasoactive intestinal polypeptide neuronal subpopulations in the suprachiasmatic region

The suprachiasmatic nuclei (SCN) and retinohypothalamic tract (RHT) in the anterior hypothalamus have been postulated to play an important role in the timing of daily biological rhythms in mammals. Although physiological studies have described circadian rhythms in man, the presence of an RHT or SCN has not been conclusively demonstrated in the human brain. Immunocytochemical identification of distinct ventral vasoactive intestinal polypeptide (VIP) containing and dorsal vasopressin containing neuronal subpopulations in the human suprachiasmatic region provides correlative evidence of neuronal clusters which are homologous to discrete cell groups in the SCN of other mammalian species. Manipulation of the circadian system has been used to treat some affective illnesses and othe physiological timing disorders. Characterization of the neural substrates underlying human circadian rhythms could be useful in the development of future treatment modalities and is essential for understanding normal human circadian organization.

On reproducibility of circadian rhythms in man (author's transl)

On the basis of our own experimental data and those from the literature, the reproducibility of day-night variations in physiological functions--their 'circadian pattern'--is examined in five sections. They concern the problem of intra- and interindividual variability, demonstrated by the rhythm of deep body temperature, the dependence of the pattern on experimental conditions, and as further examples circadian rhythms in the endocrine system, in blood constituents, in blood pressure and in psychomotor performance. The survey is considered to contribute to the question of how important the circadian temporal structure may be in the search for reference values and hence in diagnosis.

Autonomous circadian rhythms in man. Singly versus collectively isolated subjects.

Autonomous circadian rhythms in man. Singly versus collectively isolated subjects.

The influence of self-controlled changes in ambient temperature on autonomous circadian rhythms in man.

In human experiments under constant conditions where circadian rhythms run autonomously, eight subjects were exposed to a self-controlled cycle of ambient temperature: room temperature had been set 6°C higher during activity-time (wakefulness) than during rest-time (sleep) by the subjects. Under these conditions, the autonomous circadian period was significantly longer than under conditions of constant room temperature of the same mean value. In addition, the change in the period caused by the transition between the two temperature modes was positively correlated to the original period. These results are in agreement with results obtained under the influence of a self-controlled light-dark cycle.

Circadian rhythms in man in the U.S.S.R. and their peculiarities under conditions of industrial work (a review)

Click to increase image sizeClick to decrease image sizeAbstracting key words: Circadian rhythmsindustrial work rhythms

Mutual relations between different physiological functions in circadian rhythms in man

Click to increase image sizeClick to decrease image sizeAbstracting key words: Activity rhythmcircadian rhythmstemperature rhythms

The Arctic as an Environment for Research on Rhythms

MANY hold the view that the Arctic during summer (a time when light is continuous) lacks obvious diel time cues and therefore provides an environment suitable for research on circadian rhythms in man. Several studies based on this assumption have been published1,2; another is now being contemplated3. This communication is designed to correct this assumption. The facts available show the Arctic to be unsuitable for this purpose except perhaps in the exceptional and unpredictable event that uniform heavy overcast persists throughout the experimental period.

Circadian Rhythms in Man

Circadian Rhythms in Man

Effect of Liver Disease Upon Steroid Circadian Rhythms in Man

Summary Steroid circadian variations were studied in 11 patients with biopsy-proven liver disease and compared with observations in eight normal control subjects. Plasma and urinary unconjugated, plasma conjugated, and urinary total 17-hydroxycorticosteroid (17-OHCS) levels were determined in six consecutive 4-hr periods, the plasma levels being measured at the midpoint of each urine collection. In the patients with liver disease, plasma unconjugated as well as conjugated 17-OHCS levels were within the normal range in the morning. Plasma unconjugated 17-OHCS demonstrated a circadian variation within the broad limits of normal in four of eight patients with liver disease studied. In the remaining four, peak levels were maintained longer than normal or else the variation was markedly reduced. Plasma conjugated 17-OHCS showed a slower than normal rise and broader peak resulting in inversion of the normal diurnal rhythm in six of the eight patients investigated. The urinary findings reflected the plasma changes. The 24-hr excretion of free 17-OHCS in the urine was significantly greater than in the normal subjects, whereas total 17-OHCS excretion in contrast was reduced. The observations are in keeping with earlier studies of the effect of liver disease on the disposition of infused cortisol and the response to adrenocorticotropin (ACTH). The findings support the concept of hepatic regulation of pituitary ACTH secretion by the feedback mechanism in that progressive impairment in hepatic degradation of cortisol may lead to a lessened diurnal variation of the unconjugated 17-OHCS, pituitary suppression, and, in turn, reduced adrenocortical cortisol production.

CIRCADIAN RHYTHMS IN MAN.

Like many animals, humans have adjusted to the natural environment so as to be prepared for efficient activity during daytime and to rest at night. As the basis of this program, almost all structures and functions undergo regular changes within 24 hours. Such rhythms have been described in physiological parameters, such as hormone levels in blood plasma, blood pressure and heart rate, body temperature, and sleep propensity, and in behavioral parameters, such as mood, reaction time, computation speed, and performance in learning tasks. These rhythms normally keep distinct phase-relationships with each other, implying a high degree of internal temporal order. In principle, this rhythmicity is maintained when subjects are sleep deprived, when they are starved, or when they receive equal amounts of food at short intervals over the day. The timing of single meals, however, may influence the pattern of some variables, and the sleep-wake cycle can have phase-setting as well as masking effects on the instantaneous value of rhythms as especially known for body temperature and some hormones.

The entrainment of circadian rhythms in man.

The entrainment of circadian rhythms in man.