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Circadian System (circadian + system)
Selected AbstractsTheoretical and conceptual issues in time,place discriminationEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 9 2009Jonathon D. Crystal Abstract The need to discover resources that are available under specific environmental constraints represents a fundamental environmental pressure on the evolution of behavior. Time,place discrimination refers to the ability to secure resources when they are available under specific temporal and spatial contingencies. This article reviews a number of examples of time,place discrimination. The review highlights theoretical and conceptual issues that are needed to behaviorally identify the mechanisms responsible for time,place performance. Next, limitations on time,place performance that may be imposed by a circadian system are described. Finally, a number of lines of research that broaden these limitations are discussed. These lines of research include studies that suggest that (i) a broad range of long intervals (outside the limited range of circadian entrainment) are timed, (ii) at least some long intervals (16,21 h) are timed with an endogenous self-sustaining oscillator, (iii) short intervals (in the range of 1,3 min) are timed with an endogenous self-sustaining oscillator, and (iv) memory for specific unique events (including when and where they occurred) is based on a circadian representation of time. It is concluded that a unified theory of timing that can retain the times of occurrence of individual events is needed. The time of occurrence of an event may be encoded not only with respect to a circadian oscillator but also with respect to other oscillators in the long-interval and short-interval ranges. [source] Loss of photic entrainment at low illuminances in rats with acute photoreceptor degenerationEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 8 2009Domitille L. Boudard Abstract In several species, an acute injection of N -methyl- N -nitrosourea (MNU) induces a retinal degeneration characterized principally by a rapid loss of the outer nuclear layer, the other layers remaining structurally intact. It has, however, also been reported that down-regulation of melanopsin gene expression is associated with the degeneration and is detectable soon after injection. Melanopsin is expressed by a small subset of intrinsically photosensitive retinal ganglion cells and plays an important role in circadian behaviour photoentrainment. We injected MNU into Long Evans rats and investigated the ability of animals to entrain to three light/dark cycles of different light intensities (300, 15 and 1 lux). Control animals entrained their locomotor activity rhythms to the three cycles. In contrast, MNU-treated animals could only entrain properly to the 300 lux cycle. For the 15 lux cycle, their phase angle was much altered compared with control animals, and for the 1 lux cycle, MNU-injected animals were unable to photoentrain and exhibited an apparent free-run activity pattern with a period of 24.3 h. Subsequent to behavioural studies the animals were killed and rod, cone, melanopsin expression and melanopsin-expressing cells were quantified. Rod and cone loss was almost complete, melanopsin protein was reduced by 83% and melanopsin-expressing cells were reduced by 37%. Our study provides a comprehensive model of photoreceptor degeneration at the adult stage and a simple and versatile method to investigate the relation between retinal photoreceptors and the circadian system. [source] Challenging the omnipotence of the suprachiasmatic timekeeper: are circadian oscillators present throughout the mammalian brain?EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 11 2007Clare Guilding Abstract The suprachiasmatic nucleus of the hypothalamus (SCN) is the master circadian pacemaker or clock in the mammalian brain. Canonical theory holds that the output from this single, dominant clock is responsible for driving most daily rhythms in physiology and behaviour. However, important recent findings challenge this uniclock model and reveal clock-like activities in many neural and non-neural tissues. Thus, in addition to the SCN, a number of areas of the mammalian brain including the olfactory bulb, amygdala, lateral habenula and a variety of nuclei in the hypothalamus, express circadian rhythms in core clock gene expression, hormone output and electrical activity. This review examines the evidence for extra-SCN circadian oscillators in the mammalian brain and highlights some of the essential properties and key differences between brain oscillators. The demonstration of neural pacemakers outside the SCN has wide-ranging implications for models of the circadian system at a whole-organism level. [source] Blockade of the NPY Y5 receptor potentiates circadian responses to light: complementary in vivo and in vitro studiesEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 4 2004P. C. Yannielli Abstract Neuropeptide Y (NPY) is delivered to the suprachiasmatic nuclei (SCN) circadian pacemaker via an input from the thalamic intergeniculate leaflet. NPY can inhibit light-induced responses of the circadian system of Syrian hamsters. Here we studied whether an antagonist to NPY receptors can be used to potentiate photic phase shifts late in the subjective night. First we determined by in situ hybridization that both NPY Y1 and Y5 receptor mRNA are expressed in the SCN of Syrian hamsters. Second, similar to our previous findings at Zeitgeber time 14 (ZT 14, where ZT 12 was the time of lights off), we found that NPY applied at ZT 18.5 onto the SCN region of brain slices maintained in vitro could block NMDA-induced phase advances of the spontaneous firing rate rhythm, and this blocking effect was probably mediated by the Y5 receptor, since co-application of Y5 receptor antagonists completely reversed the effect of NPY, while application of a Y1 receptor antagonist had no effect under the same conditions. Third, we found that co-treatment with a Y5 receptor antagonist in vivo (s.c., 10 mg/kg) not only reversed the effect of NPY applied to the SCN in vivo through a cannula but also significantly potentiated the light-induced phase advance in the absence of NPY. This is the first report of a NPY receptor antagonist having such an effect, and indicates that NPY Y5 receptor antagonists could be clinically useful for potentiating circadian system responses to light. [source] Circadian phase entrainment via nonlinear model predictive controlINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 17 2007N. Bagheri Abstract A nonlinear model predictive control algorithm is developed to investigate the phase-resetting properties of robust nonlinear biological oscillators; in particular, those of the circadian rhythm. This pacemaker is an autonomous biochemical oscillator with a free-running period close to 24 h. Research in chronobiology indicates that light stimuli may delay or advance the phase of the oscillator, allowing it to synchronize physiological processes and entrain to the environment. In this paper, a closed-loop optimal phase tracking control algorithm is developed and applied to a mammalian circadian model. The integration of MPC-based light pulses, coupled with environmental light:dark cycles, allows the circadian system to recover phase differences within 1.5 days,a fraction of the natural open-loop simulated mammalian recovery time. Accelerated phase entrainment may alleviate disorders caused by circadian rhythms that are out of phase with the environment, and improve performance. Copyright © 2007 John Wiley & Sons, Ltd. [source] Rhythm-Dependent Light Induction of the c-fos Gene in the Turkey HypothalamusJOURNAL OF NEUROENDOCRINOLOGY, Issue 6 2007A. Thayananuphat Day length (photoperiod) is a powerful synchroniser of seasonal changes in the reproductive neuroendocrine activity in temperate-zone birds. When exposed to light during the photoinducible phase, reproductive neuroendocrine responses occur. However, the neuroendocrine systems involved in avian reproduction are poorly understood. We investigated the effect of light exposure at different circadian times upon the hypothalamus and components of the circadian system, using c-fos mRNA expression, measured by in situ hybridisation, as an indicator of light-induced neuronal activity. Levels of c-fos mRNA in these areas were compared after turkey hens (on a daily 6-h light period) had been exposed to a 30-min period of light occurring at 8, 14, or 20 h after the onset of first light of the day (subjective dawn). Non-photostimulated control birds were harvested at the same times. In birds, photostimulated within the photoinducibile phase (14 h), in contrast to before or after, c-fos mRNA was significantly increased in the nucleus commissurae pallii (nCPa), nucleus premamillaris (PMM), eminentia mediana (ME), and organum vasculosum lamina terminalis (OVLT). Photostimulation increased c-fos mRNA expression in the pineal gland, nucleus suprachiasmaticus, pars visualis (vSCN) and nucleus inferioris hypothalami compared to that of their corresponding nonphotostimulated controls. However, the magnitudes of the responses in these areas were similar irrespective of where in the dark period the pulses occurred. No c-fos mRNA was induced in the nucleus infundibulari, in response to the 30-min light period at any of the circadian times tested. The lack of c-fos up-regulation in the pineal gland and vSCN following photostimulation during the photoinducible phase lends credence to the hypothesis that these areas are not involved in the photic initiation of avian reproduction. On the other hand, c-fos mRNA increases in the nCPa, ME, and OVLT support other studies showing that these areas are involved in the onset of reproductive behaviour initiated by long day lengths. The present study provides novel data showing that the PMM in the caudal hypothalamus is involved in the neuronally mediated, light-induced initiation of reproductive activity in the turkey hen. [source] Suprachiasmatic astrocytes as an interface for immune-circadian signallingJOURNAL OF NEUROSCIENCE RESEARCH, Issue 7 2006María Juliana Leone Abstract The hypothalamic suprachiasmatic nuclei (SCN), the site of a mammalian circadian clock, exhibit a dense immunoreactivity for glial fibrillary acidic protein (GFAP), a specific marker for astrocytes. Although there is evidence of a circadian variation in GFAP-IR in the hamster SCN and of the participation of glial cells in input and output mechanisms of the clock, the role of these cells within the circadian system is not clearly understood. The fact that astroglia can express and respond to cytokines suggests that they could work as mediators of immune signals to the circadian system. In the present study, we have found a daily variation of GFAP-IR in the mouse SCN, peaking during the light phase. In addition, we have identified GFAP and nuclear factor-,B (NF-,B) in glial cells within the SCN and in primary cultures of the mouse SCN. Moreover, SCN glia cultures were transfected with an NF-,B/luc construct whose transcriptional activity was increased with lipopolysaccharide 2 ,g/ml, tumor necrosis factor-, 20 ng/ml, or interleukin-1, 100 ng/ml, after 12 hr of stimulation. These results suggest that the glial cells of the SCN can mediate input signals to the mouse circadian system coming from the immune system via NF-,B signaling. © 2006 Wiley-Liss, Inc. [source] Daily oscillations in liver function: diurnal vs circadian rhythmicityLIVER INTERNATIONAL, Issue 3 2004Alec J. Davidson Abstract: The rodent suprachiasmatic nucleus (SCN), a site in the brain that contains a light-entrained biological (circadian) clock, has been thought of as the master oscillator, regulating processes as diverse as cell division, reproductive cycles, sleep, and feeding. However, a second circadian system exists that can be entrained by meal feeding and has an influence over metabolism and behavior. Recent advances in the molecular genetics of circadian clocks are revealing clock characteristics such as rhythmic clock gene expression in a variety of non-neural tissues such as liver. Although little is known regarding the function of these clock genes in the liver, there is a large literature that addresses the capabilities of this organ to keep time. This time-keeping capability may be an adaptive function allowing for the prediction of mealtime and therefore improved digestion and energy usage. Consequently, an understanding of these rhythms is of great importance. This review summarizes the results of studies on diurnal and circadian rhythmicity in the rodent liver. We hope to lend support to the hypothesis that there are functionally important circadian clocks outside of the brain that are not light- or SCN-dependent. Rather, these clocks are largely responsive to stimuli involved in nutrient intake. The interaction between these two systems may be very important for the ability of organisms to synchronize their internal physiology. [source] Influence of Temperature on the Liver Circadian Clock in the Ruin Lizard Podarcis siculaMICROSCOPY RESEARCH AND TECHNIQUE, Issue 7 2007Manuela Malatesta Abstract Reptiles represent an interesting animal model to investigate the influence of temperature on molecular circadian clocks. The ruin lizard Podarcis sicula lives in a continental climate and it is subjected to wide range of environmental temperatures during the course of the year. As consequence, ruin lizard daily activity pattern includes either the hibernation or periods of inactivity determined by hypothermia. Here we showed the rhythmic expression of two clock genes, lPer2 and lClock, in the liver of active lizards exposed to summer photo-thermoperiodic conditions. Interestingly, the exposition of lizards to hypothermic conditions, typical of winter season, induced a strong dampening of clock genes mRNA rhythmicity with a coincident decrease of levels. We also examined the qualitative and quantitative distribution of lPER2 and lCLOCK protein in different cellular compartments during the 24-h cycle. In the liver of active lizards both proteins showed a rhythmic expression profile in all cellular compartments. After 3 days at 6°C, some temporal fluctuations of the lCLOCK and lPER2 are still detectable, although, with some marked modifications in respect to the values detected in the liver of active lizards. Besides demonstrating the influence of low temperature on the lizard liver circadian oscillators, present results could provide new essential information for comparative studies on the influence of temperature on the circadian system across vertebrate classes. Microsc. Res. Tech., 2007. © 2007 Wiley-Liss, Inc. [source] Circadian rhythms and the evolution of photoperiodic timing in insectsPHYSIOLOGICAL ENTOMOLOGY, Issue 4 2009DAVID S. SAUNDERS Abstract. This review discusses possible evolutionary trends in insect photoperiodism, mainly from a chronobiological perspective. A crucial step was the forging of a link between the hormones regulating diapause and the systems of biological rhythms, circadian or circannual, which have independently evolved in eukaryotes to synchronize physiology and behaviour to the daily cycles of light and darkness. In many of these responses a central feature is that the circadian system resets to a constant phase at the beginning of the subjective night, and then ,measures' the duration of the next scotophase. In ,external coincidence', one version of such a clock, light now has a dual role. First, it serves to entrain the circadian system to the stream of pulses making up the light/dark cycle and, second, it regulates the nondiapause/diapause switch in development by illuminating/not illuminating a specific light sensitive phase falling at the end of the critical night length. Important work by A. D. Lees on the aphid Megoura viciae using so-called ,night interruption experiments' demonstrates that pulses falling early in the night lead to long-day effects that are reversible by a subsequent dark period longer than the critical night length and also show maximal sensitivity in the blue,green range of the spectrum. Pulses falling in the latter half of the night, however, produce long-day effects that are irreversible by a subsequent long-night and show a spectral sensitivity extending into the red. With movement to higher latitudes, insects develop genetic clines in various parameters, including critical night length, the number of long-night cycles needed for diapause induction, the strength of the response, and the ,depth' or intensity of the diapause thus induced. Evidence for these and other types of photoperiodic response suggests that they provided strong selective advantages for insect survival. [source] Effect of daytime light conditions on sleep habits and morningness,eveningness preference of Japanese students aged 12,15 yearsPSYCHIATRY AND CLINICAL NEUROSCIENCES, Issue 3 2002TETSUO HARADA phd Abstract The effect of daytime light conditions on the sleep habits and morning,evening preference of Japanese junior high school students (415 girls and 411 boys; age range, 12,15 years old) was studied. Students who were outdoors during the short break between classes or their lunch-time break were more morning-type people than those who remained indoors. Students who shut out the light from outside showed longer subjective sleep latency and appealed more shallow sleep rather than those who did not. Sunlight can be an important factor for the timing of sleep based on the circadian system of Japanese young students. [source] Implementation of pigment-dispersing factor-immunoreactive neurons in a standardized atlas of the brain of the cockroach Leucophaea maderaeTHE JOURNAL OF COMPARATIVE NEUROLOGY, Issue 20 2010Hongying Wei Abstract The cockroach Leucophaea maderae is an established model in circadian rhythm research. Its circadian clock is located in the accessory medulla of the brain. Pigment-dispersing factor-immunoreactive (PDF-ir) neurons of the accessory medulla act as circadian pacemakers controlling locomotor activity rhythms. To characterize the neuronal network of the circadian system in L. maderae, the PDF-ir neurons were implemented into a standardized three-dimensional atlas of the cockroach brain. Serial confocal images from 20 wholemount brains were used for the construction of the atlas comprising 21 neuropils. Two different standardization protocols were employed: the iterative shape averaging (ISA) procedure using an affine transformation followed by iterative non-rigid registrations, and the virtual insect brain (VIB) protocol employing local non-rigid transformations after global and local rigid transformations. Quantitative analysis of the 20 brains revealed that volumes of the accessory medulla are directly correlated with the volumes of the medulla, the protocerebral bridge, and the upper division of the central body, suggesting functional connections among these neuropils. For a standardized reconstruction of the circadian pacemaker network, the ISA protocol was used to register PDF-ir neurons in the standard cockroach brain. The registration revealed that two PDF-ir arborization areas in the brain are highly interconnected with other PDF-ir projection sites and appear to be contacted both by fibers in the posterior and the anterior optic commissures. The distances between PDF-ir branching areas show specific numerical relationships that might be physiologically relevant for temporal encoding. J. Comp. Neurol. 518:4113,4133, 2010. © 2010 Wiley-Liss, Inc. [source] Circadian rhythms in plants: a millennial viewPHYSIOLOGIA PLANTARUM, Issue 4 2000C. Robertson McClung Circadian rhythms are endogenous rhythms with periods of approximately 24 h. These rhythms are widespread both within any given organism and among diverse taxa. As genetic and molecular biological studies, primarily in a subset of model organisms, have begun to identify the components of circadian systems, there is optimism that we will soon achieve a detailed molecular understanding of circadian timing mechanisms. Although plants have provided many examples of rhythmic outputs, and our understanding of photoreceptors of circadian input pathways is well-advanced, plants have lagged behind other groups of organisms in the identification of components of the central circadian oscillator. However, there are now a number of promising candidates for components of plant circadian clocks, and it seems probable that we will soon know the details of a plant central oscillator. Moreover, there is also accumulating evidence that plants and other organisms house multiple circadian clocks, both in different tissues and, quite probably, within individual cells. This provides an unanticipated level of complexity with the potential for interaction among these multiple oscillators. [source] Synchronization of the Fungal and the Plant Circadian Clock by LightCHEMBIOCHEM, Issue 16 2008László Kozma-Bognár Abstract Circadian clocks are endogenous time keeping devices that provide temporal control of physiology in accordance with predicted daily changes in the environment. Photoentrainment is the process that synchronizes circadian clocks-and thereby clock-controlled gene expression and physiology-to the environmental day/night cycles. Light is primarily detected by specialized photoreceptors that are coupled,directly or through other signaling components,to the rhythm-generating oscillator. As a consequence, the expression, the activity or the stability of oscillator components are altered, resulting in a change of phase and/or pace of the oscillator. In this review our present knowledge about light absorption/transduction and light-induced modifications of oscillator components in Neurospora crassa and Arabidopsis thaliana is summarized. These systems provide a basis for understanding the molecular mechanisms of entrainment in the fungal and plant circadian systems. [source] | |||||||||||||