No abstract available.
Biological Clocks* ; Periodicity*

The animal time structure is a basic fact of life, no matter if one wants to study it or not. The time- dependent, mostly rhythmic, and thus to a certain degree predictable, variations of biochemical and physiological functions and of sensitivity and resistance to many environmental agents are often quite large and offer not only new insight into animal physiology and pathology but also diagnostic possibilities and therapeutic advantages. Chronobiology, chronophysiology and its subspecialities, like chronopharmacology and chronotherapy, will certainly play an important role in the clinical medicine of the future. Successful application of chronobiology to veterinary clinical medicine, however, depends critically on a thorough knowledge of its basic principles.
Animals ; Animals, Domestic/*physiology ; Behavior, Animal/*physiology ; Biological Clocks/*physiology ; Circadian Rhythm/*physiology ; Humans ; Photoperiod ; Seasons

By means of a circadian clock system, all the living organisms on earth including human beings can anticipate the environmental rhythmic changes such as light/dark and warm/cold periods in a daily as well as in a yearly manner. Anticipating such environmental changes provide organisms with survival benefits via manifesting behavior and physiology at an advantageous time of the day and year. Cell-autonomous circadian oscillators, governed by transcriptional feedback loop composed of positive and negative elements, are organized into a hierarchical system throughout the organisms and generate an oscillatory expression of a clock gene by itself as well as clock controlled genes (ccgs) with a 24 hr periodicity. In the feedback loop, hetero-dimeric transcription factor complex induces the expression of negative regulatory proteins, which in turn represses the activity of transcription factors to inhibit their own transcription. Thus, for robust oscillatory rhythms of the expression of clock genes as well as ccgs, the precise control of subcellular localization and/or timely translocation of core clock protein are crucial. Here, we discuss how sub-cellular localization and nuclear translocation are controlled in a time-specific manner focusing on the negative regulatory clock proteins.
Circadian Clocks* ; Circadian Rhythm ; CLOCK Proteins ; Humans ; Periodicity ; Phosphorylation ; Physiology ; Protein Processing, Post-Translational ; Repressor Proteins* ; Transcription Factors

Circadian clocks are the endogenous oscillators that harmonize a variety of physiological processes within the body. Although many urinary functions exhibit clear daily or circadian variation in diurnal humans and nocturnal rodents, the precise mechanisms of these variations are as yet unclear. In this review, we briefly introduce circadian clocks and their organization in mammals. We then summarize known daily or circadian variations in urinary function. Importantly, recent findings by others as well as results obtained by us suggest an active role of circadian clock genes in various urinary functions. Finally, we discuss possible research avenues for the circadian control of urinary function.
Biological Clocks ; Circadian Clocks ; Circadian Rhythm ; Humans ; Mammals ; Physiological Processes ; Rodentia ; Urinary Bladder ; Urination

Mammals synchronize their circadian activity primarily to the cycles of light and darkness in the environment. Circadian rhythm is controlled by the central clock in the hypothalamic suprachiasmatic nucleus (SCN) and the peripheral clocks in various tissues. More importantly, the central clock can integrate photic/nonphotic signals to generate rhythmic outputs, and then drive the slave oscillators in peripheral tissues through neuroendocrine and behavioral signals. Human reproductive activities, as some other physiological functions, are controlled by the biological clocks. Accumulating lines of epidemiological and genetic evidence indicate that disruption of circadian clock can be directly involved in multiple pathological processes, including infertility. In this review, we mainly discuss the presence of a circadian clock in reproductive tissues and its roles in follicles development, ovulation, spermatogenesis, fertilization and embryo implantation, etc. As the increased shift work and assisted reproductive technologies possibly disrupt circadian rhythmicity to impact reproduction, the importance of circadian rhythms should be highlighted in the regulation of reproductive process.
Animals ; Biological Clocks ; Circadian Rhythm ; Hypothalamus ; Light ; Reproduction ; Suprachiasmatic Nucleus

Circadian rhythms are driven by circadian oscillators, and these rhythms result in the biological phenomenon of 24-h oscillations. Previous studies suggest that learning and memory are affected by circadian rhythms. One of the genes responsible for generating the circadian rhythm is Rev-erbα. The REV-ERBα protein is a nuclear receptor that acts as a transcriptional repressor, and is a core component of the circadian clock. However, the role of REV-ERBα in neurophysiological processes in the hippocampus has not been characterized yet. In this study, we examined the time-dependent role of REV-ERBα in hippocampal synaptic plasticity using Rev-erbα KO mice. The KO mice lacking REV-ERBα displayed abnormal NMDAR-dependent synaptic potentiation (E-LTP) at CT12~CT14 (subjective night) when compared to their wild-type littermates. However, Rev-erbα KO mice exhibited normal E-LTP at CT0~CT2 (subjective day). We also found that the Rev-erbα KO mice had intact late LTP (L-LTP) at both subjective day and night. Taken together, these results provide evidence that REV-ERBα is critical for hippocampal E-LTP during the dark period.
Animals ; Biological Phenomena ; Circadian Clocks ; Circadian Rhythm ; Hippocampus ; Learning ; Long-Term Potentiation ; Memory ; Mice ; Neuronal Plasticity

BACKGROUND: Short-term measurement of heart rate variability is known to be a non-invasive technique to examine autonomic nerve system. Heart rate variability exhibits circadian rhythm according to work/sleep cycle and biological clock. In primary practice, short-term measurement of heart rate variability is usually used during the day. Therefore the aims of this study were to investigate the possibility of differences in heart rate variability between morning and afternoon and also to examine the relationship among associated factors. METHODS: Sixty-eight healthy volunteers underwent short- term measurement of heart rate variability on two occasions: in the morning (08:30~11:00) and in the afternoon (13:30~16:00). A structured questionnaire was used to access general characteristics, emotion, fatigue and sleeping hours. RESULTS: The mean heart rate was significantly increased and SDNN, RMSSD, TP, HF and VLF were significantly decreased in the afternoon compared to the morning. LF and LF/HF were not changed. The anxiety group, the depression group and the fatigue group showed significantly greater reduction in TP and RMDDS than the control group. CONCLUSION: In the afternoon, parasympathetic activity and total power were decreased significantly compared to the morning. Short-term heart rate variability should be measured in the same time zone and need to consider food intake effect. Those who complained of anxiety, depression or fatigue were related to much decrease in TP and RMSSD in the afternoon.
Anxiety ; Autonomic Pathways ; Biological Clocks ; Circadian Rhythm ; Depression ; Eating ; Fatigue ; Heart ; Heart Rate ; Surveys and Questionnaires

Developments of chronobiology abroad are forging ahead in elucidating the cellular and molecular basis and the influential factors of circadian clock such as light, jet lag, pharmaceutical. This article also reviews the influence of circadian system on human physiology and disease occurrence. The circadian-based therapy holds promising future and the research emphasis is on prognosis and prevention.
Biological Clocks ; Chronobiology Phenomena ; Circadian Rhythm ; physiology ; Drug Chronotherapy ; Jet Lag Syndrome

Cyclic esotropia is a rare condition, first mentioned by Burian in 1958, in which orthophoria is regularly followed by constant deviation on rhythmic pattern. The periodicity would suggest a biologial clock mechanism. Consecutive cyclic esotropia following strabismus surgery is extremely rare. Only three cases of consecutive cyclic esotropia following surgery for intermittent exotropia have been reported We report one case of consecutive cyclic esotropia in an 8-year-old girl who underwent surgery for intermittent exotropia. The periodic esodeviation was treated with bimedial rectus recession. We suggest the overcorrection after surgery for intermittent exotropia would cause the periodicity by biological clock mechanism when the biorhythm of the patient is in an unstable and dangerous state.
Biological Clocks ; Child ; Esotropia* ; Exotropia* ; Female ; Humans ; Periodicity ; Strabismus

BACKGROUND: The circadian rhythm of circulating melatonin is regulated by the endogenous oscillators, the suprachi-asmatic nuclei, and entrained by the light-dark cycle of the environment, but it seems that the rhythm can be affected by variable lesions outside the retina-pineal pathway. We intended to know how acute cerebral infarction affects on the cir-cadian rhythm of plasma melatonin secretion. METHODS: Plasma melatonin level was measured from 64 patients with acute cerebral infarction. On admission, blood samples were collected by venipuncture at 2AM, 4AM, 10AM, and 2PM and melatonin level was measured by radioimmunoassay. The state of consciousness of each patient was assessed clini-cally and the infarction site and size were evaluated clinically and radiographically. RESULTS: Among 64 patients with acute cerebral infarction, dramatic blunting or obliteration of nocturnal melatonin surge in the blood was found in 29 patients. The circadian rhythm of melatonin secretion was absent in 12 of 35 alert patients, in 10 of 20 drowsy patients, and in 5 of 7 stuporous patients. Melatonin secretion into plasma was markedly decreased in all 2 comatose patients. Of 14 patients with brainstem lesions, 8 patients showed decreased melatonin levels with the absence of a nocturnal rise, although most of them were alert. CONCLUSIONS: This study suggests that brainstem and the initial mental state might contribute to the regulation of the circadian rhythm of plasma melatonin even though the lesion does not involve the retina-pineal pathway, but further extensive study is required to elucidate it. (J Korean Neurol Assoc 19(4):359~363, 2001)
Biological Clocks ; Brain Stem ; Cerebral Infarction* ; Circadian Rhythm* ; Coma ; Consciousness ; Humans ; Infarction ; Melatonin* ; Phlebotomy ; Photoperiod ; Pineal Gland ; Plasma ; Radioimmunoassay ; Stupor