Chronobiology

The field of chronobiology, the study of the rhythms in plants and animals, was restricted to botanists for centuries. Only recently during the last decades could research be broadened to include animals and later even human beings. Rhythms have been documented and related to the alternation of day and night and to the succession of the seasons. Nowadays, chronobiology has developed into a multidisciplinary field in which scientists are involved in basic research as well as in applied topics. This paper gives an introduction to the field, especially dealing with the aspect of rhythm development, and the way in which the different 24-hour rhythms in children become apparent.     

Chronobiology in Asia

Sleep and Biological Rhythms -     

Chronobiology by moonlight

Most studies in chronobiology focus on solar cycles (daily and annual). Moonlight and the lunar cycle received considerably less attention by chronobiologists. An exception are rhythms in intertidal species. Terrestrial ecologists long ago acknowledged the effects of moonlight on predation success, and consequently on predation risk, foraging behaviour and habitat use, while marine biologists have focused more on the behaviour and mainly on reproduction synchronization with relation to the Moon phase. Lately, several studies in different animal taxa addressed the role of moonlight in determining activity and studied the underlying mechanisms. In this paper, we review the ecological and behavioural evidence showing the effect of moonlight on activity, discuss the adaptive value of these changes, and describe possible mechanisms underlying this effect. We will also refer to other sources of night-time light (‘light pollution’) and highlight open questions that demand further studies.     

Chronobiology in mammalian health

Circadian rhythms are daily cycles of physiology and behavior that are driven by an endogenous oscillator with a period of approximately one day. In mammals, the hypothalamic suprachiasmatic nuclei are our principal circadian oscillators which influences peripheral tissue clocks via endocrine, autonomic and behavioral cues, and other brain regions and most peripheral tissues contain circadian clocks as well. The circadian molecular machinery comprises a group of circadian genes, namely Clock, Bmal1, Per1, Per2, Per3, Cry1 and Cry2. These circadian genes drive endogenous oscillations which promote rhythmically expression of downstream genes and thereby physiological and behavioral processes. Disruptions in circadian homeostasis have pronounced impact on physiological functioning, overall health and disease susceptibility. This review introduces the general profile of circadian gene expression and tissue-specific circadian regulation, highlights the connection between the circadian rhythms and physiological processes, and discusses the role of circadian rhythms in human disease.     

Chronobiology in the diagnosis and treatment of mesor-hypertension.

An elevation of systolic and diastolic bloodpressure to values regarded as abnormal ones on the basis of conventional criteria was recognized by self-measurement. For both systolic and diastolic blood pressure, the overall means adjusted for rhythms, the so-called mesors, also were elevated in the light of their response to treatment: these mesors were found to be lowered with statistical significance when values during treatment were compared by an objective test with values measured before treatment. Individualized rhythmometry quantitatively characterizes a predictalbe portion of the variability in human blood pressure and tests for the statistical significance of changes in blood pressure as a function of the treatment and also as a function of the circadian timing of such treatment. The case report thus illustrates an individualized chronotherapy of systolic and diastolic mesor-hypertension, diagnosed retrospectively from the tested effect of hydrochlorothiazide. In the case reported, and perhaps routinely, computer-analyzed self-measurements can serve 1) to prescribe the right kind and amount with the right timing, for a given therapy, and 2) for diagnosis and prevention as well (Meyer et al.; Halberg et al.).     

Chronobiology in the clinical laboratory

'When to sample?' is a basic question in the clinical laboratory. After some considerations on the concept of biological time in laboratory medicine, the author discusses the implications of sampling time in laboratory tests, either they are performed for diagnosis and prognosis, monitoring therapy, prevention, assessment of risk or for legal reasons.     

Chronobiology: anatomy in time

Chronobiology is that branch of science that objectively explores and quantifies mechanisms of biological time structure, including the important rhythmic manifestations of life. It is the study of biological rhythms. This paper introduces chronobiology and some of its vocabulary, principles, and techniques. A circadian rhythm is a regularly repetitive, quantitative physiological change with a period of about 24 hr (20-28), but the spectrum of rhythms includes those with periods less than 20 hr (ultradian) and longer than 28 hr (infradian). These rhythms are ubiquitous among the eukaryotes, innate and endogenous; their periods are precisely controlled by synchronizers in the environment. Rhythms can be manipulated by altering their synchronizers or by introducing more dominant ones. When organisms are removed from their environment and placed in constant conditions, rhythms revert to their natural frequencies and free-run. All of an organism's rhythms operate simultaneously, but their peaks and troughs do not necessarily occur at the same time. There are rhythms in susceptibility to drugs; a fixed dose may have a therapeutic effect at one point along the 24 hr time scale and a harmful one at another. Knowledge of these rhythms can be important when designing experimental or treatment protocols and interpreting results. Examples are provided to show that single-time-point sampling can lead to erroneous results, unless biological periodicity is taken into consideration.     

Chronobiology in hematology and immunology

The hematopoietic and the immune systems in all their components are characterized by a multifrequency time structure with prominent rhythms in cell proliferation and cell function in the circadian, infradian, and rhythms in cell proliferation and cell function in the circadian, infradian, and circannual frequency ranges. The circulating formed elements in the peripheral blood show highly reproducible circadian rhythms. The timing and the extent of these rhythms were established in a clinically healthy human population and are shown as chronograms, cosinor summaries and, for some high-amplitude rhythms, as time-qualified reference ranges (chronodesms). Not only the number but also the reactivity of circulating blood cells varies predictably as a function of time as shown for the circadian rhythm in responsiveness of human and murine lymphocytes in vitro to lectin mitogens (phytohemagglutinin and pokeweed mitogen). Some circadian rhythms of hematologic functions appear to be innate and are presumably genetically determined but are modulated and adjusted in their timing by environmental factors, so-called synchronizers. Phase alterations in the circadian rhythms of hematologic parameters of human subjects and of mice by manipulation of the activity-rest or light-dark schedule and/or of the time of food uptake are presented. Characteristically these functions do not change their timing immediately after a shift in synchronizer phase but adapt over several and in some instances over many transient cycles. The circadian rhythm of cell proliferation in the mammalian bone marrow and lymphoid system as shown in mice in vivo and in vitro may lend itself to timed treatment with cell-cycle-specific and nonspecific agents in an attempt to maximize the desired and to minimize the undesired treatment effects upon the marrow. Differences in response, and susceptibility of cells and tissues at different stages of their circadian and circaseptan (about 7-day) rhythms and presumably of cyclic variations in other frequencies are expected to lead to the development of a chronopharmacology of the hematopoietic and immune system. Infradian rhythms of several frequencies have been described for numerous hematologic and immune functions. Some of these, i.e., in the circaseptan frequency range, seem to be of importance for humoral and for cell mediated immune functions including allograft rejection. Infradian rhythms with periods of 19 to 22 days seem to occur in some hematologic functions and are very prominent in cyclic neutropenia and (with shorter periods) in its animal model, the grey collie syndrome.(ABSTRACT TRUNCATED AT 400 WORDS)     

Chronobiology in mental retardation research: progress and prospects.

The premise of this review is that chronobiology, the science of biologic time structure and rhythms, is important in investigations concerning the etiology, mechanisms and effects of deficient mental adaptive development. Chronobiology is also shown to have potential importance in therapeutics and rehabilitation. Most of the information available now and supporting this wide-spread relevance of chronobiology relates to circadian rhythms, but physiological and behavioral rhythms having other cycle lengths also contribute. Recent findings in seven topic areas of chronobiology are reviewed with emphasis on facts and relationships actually or potentially important for consideration in mental retardation research. These are: 1) development of sleep and EEG patterns; 2) rhythmic susceptibility to seizures; 3) adrenocortical and dependent rhythms; 4) circadian rhythms in amino acids and biogenic amines; 5) rhythmic behaviors; 6) circadian rhythms in susceptibility and responses to drugs; and 7) circadian rhythms in human perception and performance.