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Results for “Biological Clocks”

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At least 19 recordsLinked to original sources
PubMed1992

Pre-natal development of a hypothalamic biological clock.

The available evidence indicates that a biological clock oscillates in the mammalian fetus and that the fetal clock is entrained by redundant circadian signals from the mother. An entrainable biological clock during fetal life helps the developing mammal more readily prepare for life in the outside world. In humans, the early establishment of maternal-infant synchrony may help the infant maximize its responsiveness to the outside world.

Animals↗
PubMed1990

The quail's eye: a biological clock.

The site (intraocular vs. extraocular) of the biological clock driving a rhythm in melatonin content in the eyes of Japanese quail was investigated by alternately patching the left and right eyes of individual birds, otherwise held in constant light, for 12-hr periods. This patching protocol, therefore, exposed each eye to a light-dark cycle (LD 12:12) 180 degrees (12 hr) out of phase with the LD cycle experienced by the other eye. The optic nerves to both eyes were transected prior to initiating the patching protocol. The ocular melatonin rhythm (OMR) of the left eyes of quail could be entrained by this procedure 180 degrees out of phase with the rhythm expressed by the right eyes. Since optic nerve section would have deprived any putative extraocular clocks of photic entrainment information, the results show conclusively that the clock driving the OMR is located within the eye itself. In addition, the OMR of Japanese quail is remarkably unaffected by removing two potential neural inputs to the eye (sympathetic innervation from the superior cervical ganglia, and input from the isthmo-optic nucleus of the midbrain); this suggests that these inputs are not required to maintain the OMR. Finally, the clock driving the OMR of one eye does not appear to be coupled to the clock driving the OMR in the other eye, since permanently patching one eye abolished the ability of the patched eye to re-entrain to an 8-hr shift in the phase of an LD 12:12 cycle, whereas the exposed eye rapidly re-entrained to the phase-shifted cycle.

Animals↗
PubMed1990

Stopping the biologic clock for globin gene switching.

The developmental switch from production of fetal (gamma) to adult (beta) globin occurs on a normally set biologic clock which proceeds even if expression of the adult (beta) globin genes is defective and produces little or no protein, as in the beta-thalassemias. Preventing or reversing the globin gene switch could provide a way of keeping the abnormal globin genes "silent" and maintaining expression of the fetal globin gene. We have identified a class of agents which, when present in elevated plasma concentrations during gestation, inhibits the gamma----beta-globin gene switch in developing humans. Further investigation has shown that butyric acid and related compounds can increase gamma-globin and decrease beta-globin expression in cultured erythroid cells of patients with beta-thalassemia. Butyrate compounds were therefore infused in an in vivo fetal animal model, and the globin switch was inhibited and even reversed in some fetal lambs. Histone hyperacetylation, which maintains active chromatin structure, and an effect on the gamma-globin promoter appear to be mechanisms of action involved. These data suggest that inhibiting expression of abnormal beta-globin genes by pharmacologic means may in the future be possible for treatment of individuals with beta-globin disorders.

Anemia, Sickle Cell↗
PubMed1976

Biological clocks: endogenous cycles synchronized by subtle geophysical rhythms.

Organismic sensitivity to atmospheric electromagnetic forces, together with usually asymmetrical phase-response systems, have enabled a simple unified explanation of the biological clocks and their timed rhythms. The clocks, endogenous cycles synchronized by subtle geophysical Zeitgeber, are always accurate. The rhythms, freely phase labile, autophase in "constant conditions" to generate a host of overt frequencies.

Atmosphere↗
PubMed1992

A neurophysiological study of a lithium-sensitive phosphoinositide system in the hamster suprachiasmatic (SCN) biological clock in vitro.

Lithium lengthens the period of free-running circadian rhythms in many species. In mammals the hypothalamic suprachiasmatic nucleus (SCN) has been identified as a biological clock which generates circadian rhythms. The effect of lithium-induced depletion of the intracellular pool of inositol, leading to decreased intracellular second messengers IP3 and DAG, was examined neurophysiologically. Extracellular recordings were obtained from spontaneously discharging SCN neurones maintained in vitro. Superfusion of slices with lithium-containing (0.1-30 mM) aCSF, but not rubidium-containing aCSF, suppressed neuronal firing in a dose-dependent manner. Lithium-induced suppressed firing was reversed by myo-inositol, but not by epi-inositol. These studies provide evidence for basal phosphoinositide turnover in neurones and implicate a lithium-sensitive phosphoinositide system in the maintenance of the spontaneous discharge activity of SCN neurones.

Animals↗
PubMed1992

Ontogeny of a biological clock in Drosophila melanogaster.

Drosophila melanogaster born and reared in constant darkness exhibit circadian locomotor activity rhythms as adults. However, the rhythms of the individual flies composing these populations are not synchronized with one another. This lack of synchrony is evident in populations of flies commencing development at the same time, indicating that a biological clock controlling circadian rhythmicity in Drosophila begins to function without a requirement for light and without a developmentally imparted phase. It is possible to synchronize the phases of rhythms produced by dark-reared flies with light treatments ending as early as the developmental transition from embryo to first-instar larva: Light treatments occurring at developmental times preceding hatching of the first-instar larva fail to synchronize adult locomotor activity rhythms, while treatments ending at completion of larval hatching entrain these rhythms. The synchronized rhythmic behavior of adult flies receiving such light treatments suggests that a clock controlling circadian rhythms may function continuously from the time of larval hatching to adulthood.

Age Factors↗
PubMed1992

[New perspectives in hair research: in search of the "biological clock" of the hair cycle].

The hair follicle is not only a clinically and commercially important tissue, but can also serve as a fascinating model for studying epithelial-mesenchymal-neuroectodermal interactions. Recently, this has led to a renaissance of hair research, which this speculative review attempts to outline. The unanswered key questions in hair biology are defined before we focus on the crucial search for the "biological clock" that governs the hair cycle. Specifically, we delineate the clinical importance of understanding the mechanisms of catagen induction and propose an immunological mechanism of catagen induction. New research trends are discussed against the background of their potential significance for improving the still frustrating management of hair diseases.

Animals↗
PubMedDate not supplied

The heart as a biological clock: phase-locking between heart and efferent vagal activity.

Experiments were performed to evaluate whether the negative inotropic effect of efferent vagal stimulation is more strictly related to the number of stimuli falling with each cardiac cycle (St/c) or to the number of stimuli per second (St/s). Therefore, vagal stimulations were performed in anaesthetized dogs either with constant frequency (CONT), or with trains of 3 stimuli triggered by each atrial activation (SYNCHR). An atrial contractility index was measured while increasing heart rate by artificial heart pacing during CONT and SYNCHR vagal stimulations. The negative inotropic parasympathetic effect was reduced in the former protocol (St/s constant, St/c reduced) and did not change in the latter. It was concluded that the effect of vagal stimulation is more strictly related to St/c rather than to St/s. We suggest that the heart cycle operates as a biological clock with respect to cardiac vagal control.

Animals↗
PubMed1992

Biological clocks: mechanisms and developments.

Almost all organisms ranging from unicellular protists to mammals were found to show biological rhythms. Many workers have performed various kinds of experiment to understand the mechanism as well as to find the origin of the clock responsible for these rhythms. However, there is no doubt about the existence of a biologically controlled clock in almost all organisms; yet its origin and mechanism still remain a mystery. Many theories have been put forward to explain the mechanism of these biological clocks and it seems that the cell membrane may play a key role. The existence of a very high electric field of the order of 10(5) V cm-1 across the cell membrane may have some role in the mechanism of the biological clock. Of all the factors which have the effects on biological rhythms, light and temperature are found to be the most common. Also, the study of these biological clocks can help to solve the sleeping problems of international travellers and shift workers as well as to improve diagnosis, cure and prevention from diseases.

Animals↗
PubMed1992

Perinatal development of human circadian rhythms: role of the foetal biological clock.

The development of circadian rhythms and the neuronal mechanisms underlying their generation (particularly the suprachiasmatic nucleus of the hypothalamus) were reviewed. Based on perinatal animal studies and data from human foetuses and/or preterm infants it was concluded that human circadian rhythms are present as early as at 30 weeks of gestation. The significance of the mother and/or the environment regarding the entrainment of the "endogenous" foetal biological clock was emphasized.

Circadian Rhythm↗
PubMed1992

Endogenous synthesis of peptidoglycan in eukaryotic cells; a novel concept involving its essential role in cell division, tumor formation and the biological clock.

Degradation products of peptidoglycan, the universal bacterial cell wall constituent, were previously found in animal tissues and urine. Reassessment and quantitative analysis of available data lead to an original concept, i.e. that eukaryotic cells synthesize peptidoglycan. We present a model in which this endogenously synthesized peptidoglycan is essential for the processes of eukaryotic cell division and sleep induction in animals. Genes for peptidoglycan metabolism, like those for lysine biosynthesis in plants, are probably inherited from endosymbiotic bacteria, the ancestors of mitochondria and chloroplasts. Corollaries of this concept, i.e. roles for peptidoglycan metabolism in tumor formation and in the biological clock, are supported by abundant evidence. We propose that many interactions between bacteria and eukaryotes are conditioned by their common genetic heritage.

Animals↗
PubMed1975

Ontogenesis of a biological clock for serotonin:acetyl coenzyme A N-acetyltransferase in pineal gland of rat.

Serotonin:acetyl coenzyme A N-acetyltransferase (EC 2.3.1.5) Activity in pineal gland was assayed in rats which were born and raised under diurnal lighting conditions, in continuous darkness, or in constant light. N-Acetyltransferase activity in the pups raised under diurnal lighting showed a rhythmic pattern, with high enzyme activity during dark period. The pups raised in continuous darkness also showed a rhythmic pattern, the phase of which was delayed by 8 hr in 7-week-old pups; the rhythmic phase of N-acetyltransferase began in the evening in 12-day-old pups and was regularly delayed by 1 hr every week. The pups raised in constant illumination also showed a rhythmic pattern; the rhythmic phase was delayed by 3 hr every week. When the mother rats were coupled in darkness and maintained in darkness during pregnancy and after the pups were born, their pups again showed a rhythmic pattern. These observations indicate that the biological clock for N-acetyltransferase is generated independently of environmental lighting. When mothers were coupled under reversed lighting conditions and transferred into darkness or light, the rhythmic pattern in their pups was inverted 180 degrees from that of pups born of diurnal mothers. When the pups were raised in darkness, the rhythmic phase of N-acetyltransferase in the pups was similar to that of their mothers. It is suggested that in the absence of light-darkness cycle, the mother rat sets the rhythm of the pups to synchronize with her own rhythm. When pups were reared by a foster mother with a different rhythmic pattern from that of their original mother, the rhythmic phase in the pups was closer to that of the original mother, suggesting that the original mother plays the predominant role setting the rhythm of the pups.

Acetyltransferases↗