Adenylate cyclase activation shifts the phase of a circadian pacemaker

Forskolin, a highly specific activator of adenylate cyclase, produced both delay and advance phase shifts of the circadian rhythm recorded from the isolated eye of the marine mollusk Aplysia. The phase dependence of the response to forskolin was identical to that with serotonin, which also stimulates adenylate cyclase in the eye. The ability of agents to activate adenylate cyclase in homogenates was correlated with their ability to shift the phase of the circadian oscillator. These results along with earlier findings show that adenosine 3',5'-monophosphate mediates the effect of serotonin on the rhythm and regulates the phase of the circadian pacemaker in the eye of Aplysia.     

Extraoptic phase shifting of circadian locomotor rhythm in salamanders

Timing of locomotor rhythm in the slimy ralamander, Plethodon glutinosus, can be shifted in phase by the environmental light cycle, whether the animals have eyes or not. Rhythmicity persists at least for the first day when animals are transferred to constant conditions, with a period of about 24 hours, and is therefore circadian in nature. An extraoptic photoreceptor site in the brain is suggested.     

Photosensitivity of the circadian rhythm and of visual receptors in carotenoid-depleted Drosophila

Drosophila melanogaster was raised on aseptic diets, with and without beta-carotene. The sensitivity of visual receptors in the carotenoid-depleted flies was lowered 3 log units, but the photosensitivity of the circadian rhythm was not affected. This result suggests that the chromophore of the photopigment which mediates light effects on the circadian rhythm is not a carotenoid derivative.     

Action spectra for photoperiodic response in a diapausing mosquito

While 540 nanometers is the most effective wavelength in provoking development, larvae are far more responsive to 540-nanometer light if it is provided immediately preceding rather than followng a white-light photophase which otherwise serves to maintain diapause. This difference in sensitivity is probably due to bleaching and implies that the larvae experience an asymmetric day.     

Selection for circadian eclosion time in Drosophila melanogaster

Early and late eclosion strains were developed from Drosophila melanogaster cultures. The Oregon-R parent strains (isolated in 1925) showed significantly more selectability than the W(2) parent strain collected at the beginning of this study (1971). This is consistent with the hypothesis that the selective advantage of circadian behaviors is reduced in laboratory conditions.     

Persisting circadian rhythm of cell division in a photosynthetic mutant of Euglena

A persisting, free-running, circadian rhythm of cell division in a heterotrophically grown mutant of Euglena gracilis var. bacillaris having impaired photosynthesis is obtained upon placing a culture that has been previously synchronized by a 10,14 light-dark cycle into continuous darkness at 19 degrees C (but not at 25 degrees C). A similar persisting rhythm is initiated in exponentially increasing cultures (growing in darkness at 19 degrees C) by a single "switch-up" in irradiance to continuous bright illumination. The results implicate an endogenous biological clock which "gates" the specific event of cell division in the cell developmental cycle.     

Indole metabolism in the pineal gland: a circadian rhythm in N-acetyltransferase

The activity of N-acetyltransferase in the rat pineal gland is more than 15 times higher at night than during the day. This circadian rhythm persists in complete darkness, or in blinded animals, and is suppressed in constant lighting. The N-acetyltransferase rhythm is 180 degrees out of phase with the serotonin rhythm and is similar to the norepinephrine and melatonin rhythms. Experiments in vitro indicate that norepinephrine, not serotonin, regulates the activity of N-acetyl-transferase through a highly specific receptor.     

昼夜节律对大鼠血液流变学的影响

目的 :观察昼夜节律对大鼠血液流变学的影响。方法 :SD大鼠 2 0只 ,按完全随机化分为两组 :白天组 1 1只 (采血时间在上午 9:0 0～ 1 0 :0 0 ) ;夜间组 9只 (采血时间在晚上 9:0 0～ 1 0 :0 0 )。流变学指标采用 NXE- 1型锥板式粘度计检测 ;检测温度 2 5℃。结果 :夜间组与白天组比较 ,夜间组的ηb(m Pa· s,2 2 5 s- 1 )、ηb(m Pa· s 1 1 .2 5 s- 1 ) ,均比白天组为低 (P<0 .0 5) ,而红细胞压积、ηb(1 1 .2 5 s- 1 ) /ηb(2 2 5 s- 1 )差异无显著性 (P>0 .0 5)。结论 :昼夜节律对 SD大鼠血液流变学有影响     

Controlled phase shifts with a single quantum dot

Optical nonlinearities enable photon-photon interaction and lie at the heart of several proposals for quantum information processing, quantum nondemolition measurements of photons, and optical signal processing. To date, the largest nonlinearities have been realized with single atoms and atomic ensembles. We show that a single quantum dot coupled to a photonic crystal nanocavity can facilitate controlled phase and amplitude modulation between two modes of light at the single-photon level. At larger control powers, we observed phase shifts up to pi/4 and amplitude modulation up to 50%. This was accomplished by varying the photon number in the control beam at a wavelength that was the same as that of the signal, or at a wavelength that was detuned by several quantum dot linewidths from the signal. Our results present a step toward quantum logic devices and quantum nondemolition measurements on a chip.     

Resetting the circadian clock by social experience in Drosophila melanogaster

Circadian clocks are influenced by social interactions in a variety of species, but little is known about the sensory mechanisms underlying these effects. We investigated whether social cues could reset circadian rhythms in Drosophila melanogaster by addressing two questions: Is there a social influence on circadian timing? If so, then how is that influence communicated? The experiments show that in a social context Drosophila transmit and receive cues that influence circadian time and that these cues are likely olfactory.     

高血压脑患者出血手术治疗后心率近日节律的变化

目的研究高血压脑出血手术治疗后心率近日节律的变化特征。方法对100例高血压基底节区脑出血患者进行开颅血肿清除术。术后连续9d监测心率,每小时记录1次。分别用单一和平均群体余弦法进行心率的近日节律分析。结果手术后第1～7天心率的近日节律消失(P>0.05),第8天恢复出现近日节律。结论高血压脑出血手术治疗对心率近日节律的影响严重。脑部手术后近日节律的恢复可能和术后脑水肿的发生、发展有密切的关系。     

Roles of the two Drosophila CRYPTOCHROME structural domains in circadian photoreception

CRYPTOCHROME (CRY) is the primary circadian photoreceptor in Drosophila. We show that CRY binding to TIMELESS (TIM) is light-dependent in flies and irreversibly commits TIM to proteasomal degradation. In contrast, CRY degradation is dependent on continuous light exposure, indicating that the CRY-TIM interaction is transient. A novel cry mutation (cry(m)) reveals that CRY's photolyase homology domain is sufficient for light detection and phototransduction, whereas the carboxyl-terminal domain regulates CRY stability, CRY-TIM interaction, and circadian photosensitivity. This contrasts with the function of Arabidopsis CRY domains and demonstrates that insect and plant cryptochromes use different mechanisms.     

PER-TIM interactions in living Drosophila cells: an interval timer for the circadian clock

In contrast to current models, fluorescence resonance energy transfer measurements using a single-cell imaging assay with fluorescent forms of PER and TIM showed that these proteins bind rapidly and persist in the cytoplasm while gradually accumulating in discrete foci. After approximately 6 hours, complexes abruptly dissociated, as PER and TIM independently moved to the nucleus in a narrow time frame. The per(L) mutation delayed nuclear accumulation in vivo and in our cultured cell system, but without affecting rates of PER/TIM assembly or dissociation. This finding points to a previously unrecognized form of temporal regulation that underlies the periodicity of the circadian clock.     

Catastrophes, phase shifts, and large-scale degradation of a Caribbean coral reef

Many coral reefs have been degraded over the past two to three decades through a combination of human and natural disturbances. In Jamaica, the effects of overfishing, hurricane damage, and disease have combined to destroy most corals, whose abundance has declined from more than 50 percent in the late 1970s to less than 5 percent today. A dramatic phase shift has occurred, producing a system dominated by fleshy macroalgae (more than 90 percent cover). Immediate implementation of management procedures is necessary to avoid further catastrophic damage.     

Changes in mean concentration, phase shifts, and dissipation in a forced oscillatory reaction

Experiments are presented that confirm earlier predictions that the mode of supply of reactants to a nonlinear (bio)chemical reaction determines or controls concentrations at steady states far from equilibrium. The oxidation of nicotinamide adenine dinucleotide (NADH) catalyzed by the enzyme horseradish peroxidase with continuous input of oxygen was studied; NAD+ is continuously recycled to NADH through a glucose-6-phosphate dehydrogenase system. A comparison of steady-state concentrations is made with an oscillatory oxygen input and a constant input at the same average oxygen input for both modes. By varying the frequency and amplitude of the perturbation (O2 influx), the following may be changed: the average concentration of NADH; the Gibbs free energy difference delta G of the reactants and products at steady state; the average rate of the reaction; the phase relation between the oscillatory rate and delta G; and the dissipation. These results confirm the possibility of an "alternating current chemistry," of control and optimization of thermodynamic efficiency and dissipation by means of external variation of constraints in classes of nonlinear reactions and biological pumps, and of improvements of the yield in such reactions (heterogeneous catalysis, for example).     

Melanopsin (Opn4) requirement for normal light-induced circadian phase shifting

The master circadian oscillator in the hypothalamic suprachiasmatic nucleus is entrained to the day/night cycle by retinal photoreceptors. Melanopsin (Opn4), an opsin-based photopigment, is a primary candidate for photoreceptor-mediated entrainment. To investigate the functional role of melanopsin in light resetting of the oscillator, we generated melanopsin-null mice (Opn4-/-). These mice entrain to a light/dark cycle and do not exhibit any overt defect in circadian activity rhythms under constant darkness. However, they display severely attenuated phase resetting in response to brief pulses of monochromatic light, highlighting the critical role of melanopsin in circadian photoentrainment in mammals.     

A circadian output in Drosophila mediated by neurofibromatosis-1 and Ras/MAPK

Output from the circadian clock controls rhythmic behavior through poorly understood mechanisms. In Drosophila, null mutations of the neurofibromatosis-1 (Nf1) gene produce abnormalities of circadian rhythms in locomotor activity. Mutant flies show normal oscillations of the clock genes period (per) and timeless (tim) and of their corresponding proteins, but altered oscillations and levels of a clock-controlled reporter. Mitogen-activated protein kinase (MAPK) activity is increased in Nf1 mutants, and the circadian phenotype is rescued by loss-of-function mutations in the Ras/MAPK pathway. Thus, Nf1 signals through Ras/MAPK in Drosophila. Immunohistochemical staining revealed a circadian oscillation of phospho-MAPK in the vicinity of nerve terminals containing pigment-dispersing factor (PDF), a secreted output from clock cells, suggesting a coupling of PDF to Ras/MAPK signaling.     

JETLAG resets the Drosophila circadian clock by promoting light-induced degradation of TIMELESS

Organisms ranging from bacteria to humans synchronize their internal clocks to daily cycles of light and dark. Photic entrainment of the Drosophila clock is mediated by proteasomal degradation of the clock protein TIMELESS (TIM). We have identified mutations in jetlag-a gene coding for an F-box protein with leucine-rich repeats-that result in reduced light sensitivity of the circadian clock. Mutant flies show rhythmic behavior in constant light, reduced phase shifts in response to light pulses, and reduced light-dependent degradation of TIM. Expression of JET along with the circadian photoreceptor cryptochrome (CRY) in cultured S2R cells confers light-dependent degradation onto TIM, thereby reconstituting the acute response + of the circadian clock to light in a cell culture system. Our results suggest that JET is essential for resetting the clock by transmitting light signals from CRY to TIM.