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Results for “Biological Clocks”

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At least 73 records · Page 4Linked to original sources
PubMed2006

The GABAergic network in the suprachiasmatic nucleus as a key regulator of the biological clock: does it change during senescence?

GABA is the main neurotransmitter of the hypothalamic suprachiasmatic nucleus (SCN) and plays a key role in the function of this master circadian pacemaker. Despite the evidence that disturbances of biological rhythms are common during aging, little is known about the GABAergic network in the SCN of the aging brain. We here provide a brief overview of the GABAergic structures and the role of GABA in the SCN. We also review some age-related changes of the GABAergic system occurring in the brain outside the SCN. Finally, we present preliminary data on the GABAergic system within the SCN comparing young and aging mice. In particular, our study on age-related changes in the SCN focused on the daily expression of the alpha3 subunit of the GABA(A) receptor and on the density of GABAergic axon terminals. Interestingly, our preliminary findings point to alterations of the GABAergic network in the biological clock during senescence.

Aging↗
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↗
PubMed2000

Possible involvement of light regulated gonadotropin-releasing hormone neurons in biological clock for reproduction in the cerebral ganglion of the ascidian, Halocynthia roretzi.

Since ascidians, a primitive chordate, spawn at a fixed latency after sunrise, light must regulate a biological clock for reproduction in the ascidians. A retinal protein found in the cerebral ganglion of the ascidian is a candidate for the photoreceptor that might drives the change in gonadal activity via the gonadotropin-releasing hormone (GnRH) system. Photoresponses of the cerebral ganglion of ascidian, Halocynthia roretzi, were examined and two light-evoked responses recorded extracellularly, a light-evoked slow potential and light inhibition of high frequency spontaneous discharges. These results suggest that pacemaker signals of GnRH neurons might be regulated by photoreceptor activation. Immunohistochemical studies showed photoreceptor cells located close to the GnRH neurons and thus the photosignal might proceed from photoreceptor cell to GnRH neuron intercellularly.

Animals↗
PubMed2004

Light and diurnal cycle affect autonomic cardiac balance in human; possible role for the biological clock.

The morning shift in cardiac sympatho-vagal balance seems involved in the increased risk of cardiovascular incidents at that time. To investigate the contribution of the biological clock in autonomic cardiac control, we investigated the presence of a diurnal rhythm independent of external factors, and of a circadian phase-dependent effect of moderate light in healthy volunteers. Recordings of heart rate (HR) and vagal and sympathetic cardiac tone were performed at different times over the day-night cycle during supine, awake, resting conditions, during exposure to different light intensities. The similarity between the diurnal rhythm in resting HR and that during previous constant routine conditions, demonstrated that our setup allowed accurate estimation of the endogenous circadian rhythm in HR. The present study suggests that, while a circadian rhythm in vagal cardiac tone is the main cause for the circadian rhythm in resting heart rate, the increase in sympathetic cardiac tone participates in the HR increase caused by early morning light.

Adult↗
PubMed2006

Chronobiology: biological clocks and rhythms of the skin.

The cyclicity of time affects virtually all aspects of our being and is the basis of the underlying rhythmicity which is typical of our lives. To 'tell time', most living organisms use internal timing mechanisms known as 'biological clocks'. These 'clocks' coordinate our physiological and behavioral functions and interactions with our environment. One of the strongest influences on rhythmicity is the solar day. The study of these temporal rhythms in biological systems has been coined chronobiology. With the present article we aim to give an overview on chronobiology. Examples of chronobiological effects on skin will be described. Particular emphasis will be placed on circadian rhythms (including rhythms that take place within a 24-hour period, including so-called infradian and/or diurnal rhythms) but also on seasonal variations (circaannual rhythms).

Biological Clocks↗
PubMed2006

Age-related effects on the biological clock and its behavioral output in a primate.

In humans, activity rhythms become fragmented and attenuated in the elderly. This suggests an alteration of the circadian system per se that could in turn affect the expression of biological rhythms. In primates, very few studies have analyzed the effect of aging on the circadian system. The mouse lemur provides a unique model of aging in non-human primates. To assess the effect of aging on the circadian system of this primate, we recorded the circadian and daily rhythms of locomotor activity of mouse lemurs of various ages. We also examined age-related changes in the daily rhythm of immunoreactivities for vasoactive intestinal polypeptide (VIP) and arginine-vasopressin (AVP) in suprachiasmatic nucleus neurons (SCN), two major peptides of the biological clock. Compared to adult animals, aged mouse lemurs showed a significant increase in daytime activity and an advanced activity onset. Moreover, when maintained in constant dim red light, aged animals exhibited a shortening of the free-running period compared to adult animals. In adults, AVP immunoreactivity (ir) peaked during the second part of the day, and VIP ir peaked during the night. In aged mouse lemurs, the peaks of AVP ir and VIP ir were significantly shifted with no change in amplitude. AVP ir was most intense at the beginning of the night; whereas, VIP ir peaked at the beginning of the daytime. A weakened oscillator could account for the rhythmic disorders often observed in the elderly. Changes in the daily rhythms of AVP ir and VIP ir may affect the ability of the SCN to transmit rhythmic information to other neural target sites, and thereby modify the expression of some biological rhythms.

Aging↗
PubMed2002

Period-2 cycles and 2:1 phase locking in a biological clock driven by temperature pulses.

Crassulacean acid metabolism (CAM) serves as a botanical model system for the investigation of circadian rhythmicity. In a new set of experiments with the obligatory CAM plant Kalanchoë daigremontiana the response to periodic stimulations with temperature pulses has been studied. On the basis of an experimental phase-response curve of net CO(2)-gas exchange the effect of periodic stimulation has been simulated using a finite-difference equation. These simulations revealed the locations of two period-2 cycles in the CO(2) uptake of the CAM plant. In subsequent experiments based upon the simulated bifurcation diagram the position and amplitude of one of these cycles were confirmed, while experimental evidence for the second cycle could be found. Possible roles of such dynamics for the functioning of the biological clock are discussed.

Biological Clocks↗
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↗
PubMedDate not supplied

Task variables determine which biological clock controls circadian rhythms in human performance.

There are circadian (approximately 24 h) rhythms for a wide range of human physiological and psychological functions including mood and performance efficiency. These rhythms are self-sustaining in conditions of temporal isolation, indicating that internal oscillators (or biological clocks) control them. Recent research has proposed an endogenous two-oscillator model of the human circadian system, with one oscillator indicated by the core body temperature rhythm and a second oscillator responsible for the daily cycle of sleep and wakefulness. The present study was designed to produce a desynchronization in period between the two oscillators, to assess directly the behaviour of the rhythms of different performance tasks. The results, reported here, indicate that a simple manual dexterity task is almost entirely under the control of the temperature rhythm oscillator, whereas a more complex cognitive task demonstrates a periodicity which appears to be influenced by those oscillators controlling temperature and the sleep/wake cycle.

Adult↗
PubMed1994

Dysregulation of photic induction of Fos-related protein in the biological clock during experimental trypanosomiasis.

The mammalian suprachiasmatic nuclei of the hypothalamus (SCN) serve as pacemaker for circadian rhythms and the immediate-early gene c-fos is known to be induced by photic stimulation in the SCN of rodents. We studied the induction of Fos-related protein following a light pulse in rats infected with Trypanosoma brucei. This parasite causes in humans African sleeping sickness, a neuropsychiatric syndrome that involves changes of endogenous biological rhythms. Fos-like immunoreactivity after photic stimulation was dramatically reduced in the SCN of trypanosome- infected rats during the subjective night. These findings indicate that the photic entrainment of the biological clock may be altered during the infection.

Animals↗
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↗
PubMed2004

8-OH-DPAT as a 5-HT7 agonist: phase shifts of the circadian biological clock through increases in cAMP production.

Neurons in the suprachiasmatic nucleus (SCN), the site of the endogenous biological clock in mammals, fire spontaneously, peaking in firing rate near ZT6 or at the midpoint of the light phase in a 12:12 light-dark cycle. In rat hypothalamic slices, tissue incubations with drugs can produce a shift in this daily rhythm, the magnitude of which is dependent upon dose and the time of treatment. Previous work with 8-OH-DPAT had noted its ability to produce a phase advance, an earlier occurrence of the peak in neuronal firing, when applied at ZT6. Activation of 5-HT7 receptors was thought to be responsible for the shift, despite the clear preference of 8-OH-DPAT for 5-HT1A sites in terms of receptor binding affinity. In the present work, the actions of 8-OH-DPAT in SCN slices were confirmed and expanded to include additional dose-response and antagonist treatments. By itself, 8-OH-DPAT produced a concentration-dependent phase advance that was sensitive to co-application with 5-HT7 antagonists (ritanserin, mesulergine, SB-269970), but not to 5-HT1A antagonists (WAY-100,635, UH-301). Assignment of the receptor mechanisms for the antagonists employed was accomplished in experiments measuring binding affinities and the generation of cAMP, the latter monitored in a HEK-293 cell line expressing the r5-HT7 receptor and in tissue derived from rat SCN. The results indicate that the increases observed in cAMP levels are small but appear to be sufficient to produce a pharmacological resetting of the clock pacemaker. By aiding in the identification of the 5-HT receptor subtype responsible for the observed phase shifts and cAMP changes, 8-OH-DPAT represents an important pharmacological tool for 5-HT7 receptor activation, essentially broadening its role as the prototypical 5-HT1A agonist to one combining these two receptor activities.

8-Hydroxy-2-(di-n-propylamino)tetralin↗