Daily light sensitivity rhythm in a rodent

Single 10-minute light periods can cause a phase shift in the rhythm of the daily locomotor activity of flying squirrels otherwise maintained in constant darkness. A daily rhythm of sensitivity to these standard light periods was found.     

Circadian clock in photoperiodic time measurement: a test of the Bünning hypothesis

A technique has been developed for effectively separating the direct inductive effect of a light signal from its effect on the phase of the rhythm of sensitivity to photoperiodic induction. With this technique it has been shown that a 75-minute pulse of light per day, when appropriately positioned with respect to the circadian activity cycle of the sparrow Passer domesticus, is sufficient to produce a response normally produced only by long days. The results cannot be interpreted in terms of a requirement of an absolute amount of either darkness or light and offer strong confirmation of Bünning's hypothesis concerning the mechanism of photoperiodic time measurement.     

Circadian involvement in termination of the refractory period in two sparrows

Endogenous daily rhythmicity is involved in the short-day photoperiodic response of breaking the refractory period in both white-crowned and golden-crowned sparrows. Under a modified "coincidence model," short-day photoperiodic induction occurs when light is noncoincident with a specific phase of an internal rhythm.     

Circadian rhythm of cell division in Euglena: effects of random illumination regimen

A persisting, "free-running," circadian rhythm of cell division in autotrophically grown Euglena gracilis is obtained upon placing either an exponentially increasing population or a culture that has been synchronized by a 10:14 light-dark cycle in a random illumination regimen that affords a total of 8 hours of light each 24 hours. These results are interpreted as implicating an endogenous biological clock which "gates" the specific event of cell division in the cell developmental cycle.     

Light pulses that shift rhythms induce gene expression in the suprachiasmatic nucleus

Lighting cycles synchronize (entrain) mammalian circadian rhythms by altering activity of cells in the suprachiasmatic nucleus (SCN) of the hypothalamus, a circadian pacemaker. Exposure of hamsters and rats to light pulses at those phases of the circadian rhythm during which light can shift the rhythm caused increased immunoreactivity for the product of the immediate-early gene c-fos in cells in the region of the SCN that receives retinal fibers. Light pulses also increased messenger RNA for the Fos protein and for the immediate-early protein NGFI-A in the rat SCN. Similar increases in mRNA for NGFI-A were seen in the SCN of hamsters. Thus cells in this portion of the SCN undergo alterations in gene expression in response to retinal illumination, but only at times in the circadian cycle when light is capable of influencing entrainment.     

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.     

Antiphase oscillation of the left and right suprachiasmatic nuclei

An unusual property of the circadian timekeeping systems of animals is rhythm "splitting," in which a single daily period of physical activity (usually measured as wheel running) dissociates into two stably coupled components about 12 hours apart; this behavior has been ascribed to a clock composed of two circadian oscillators cycling in antiphase. We analyzed gene expression in the hypothalamic circadian clock, the suprachiasmatic nucleus (SCN), of behaviorally "split" hamsters housed in constant light. The results show that the two oscillators underlying the split condition correspond to the left and right sides of the bilaterally paired SCN.     

Circadian rhythms in human heart homograft

The electrocardiogram and cardiotachogram of a patient with a human heart transplant has been recorded for 72 hours. Within the donor P-QRS-T complex, one can identify the P waves emanating from residual sinoatrial heart tissue of the recipient. The recipient P waves are independent of the donor complexes. A clear circadian rhythm (23.4 hours) in heart rate is maintained for both donor and recipient tissue, the donor complexes preceding by a phase shift of 135 minutes the complexes of the recipient heart tissue. Both tissues display clear morning and evening minimum and maximum rates paralleling activity and lighting cycles.     

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.     

稻飞虱自然种群扑灯行为的初步观察

白背稻虱自然种群扑灯日照阈限为0.91x,其典型的扑灯活动是一个扑灯量呈型的节律性过程。这种扑灯节律是其种群离株起飞节律的一个局部反映。 33米和1.3米两个高度的对照灯诱试验表明,前者灯下稻飞虱诱集量通常大大高于后者灯下诱量。表明稻飞虱种群存在趋光延迟现象,即夜间离株后首先表现强烈的升空飞行习性,在经历一定时间和距离的飞行活动后趋光表现迅速增强。     

Femtosecond resolution of soft mode dynamics in structural phase transitions

The microscopic pathway along which ions or molecules in a crystal move during a structural phase transition can often be described in terms of a collective vibrational mode of the lattice. In many cases, this mode, called a "soft" phonon mode because of its characteristically low frequency near the phase transition temperature, is difficult to characterize through conventional frequency-domain spectroscopies such as light or neutron scattering. A femtosecond time-domain analog of light-scattering spectroscopy called impulsive stimulated Raman scattering (ISRS) has been used to examine the soft modes of two perovskite ferroelectric crystals. The low-frequency lattice dynamics of KNbO(3) and BaTiO(3) are clarified in a manner that permits critical evaluation of microscopic models for their ferroelectric transitions. The results illustrate the advantages of ISRS over conventional Raman spectroscopy of low-frequency, heavily damped soft modes.     

光照周期对尼罗罗非鱼幼鱼昼夜节律调节的作用

为了研究尼罗罗非鱼幼鱼游泳行为在不喂食时是否存在昼夜节律和光照周期的调节作用,设计了光周期为光照(L)∶黑暗(D)=12 h∶12 h,持续的黑暗(DD),持续的光照(LL),光周期为L∶D=6 h∶6 h和光周期为L∶D=2 h∶2 h。结果表明:(1)光周期为L∶D=12 h∶12 h时,尼罗罗非鱼具有明显的昼夜节律,昼夜节律周期为(24. 3±0. 2) h;(2)尼罗罗非鱼的昼夜节律在持续的黑暗和光照下仍然存在,分别为(25. 1±1. 1) h和(25. 6±1. 0) h;(3)光周期为L∶D=6 h∶6 h时,尼罗罗非鱼仍具有明显的昼夜节律(12. 6±0. 5) h;(4)在光周期为L∶D=2 h∶2 h时,尼罗罗非鱼的昼夜游泳行为仍具有明显的昼夜节律,节律周期为(4. 0±2. 0) h。这些结果表明,尼罗罗非鱼具有以24 h为周期的内源性生物钟,但相比与外源性光照调控,内源性的生物钟对罗非鱼的调控较弱,外源性的光照周期才是调节尼罗罗非鱼幼鱼昼夜行为节律的主要因素。     

Localization of a circadian pacemaker in the eye of a mollusc, bulla

The eye of the marine mollusc Bulla contains a circadian pacemaker which, along with critical entrainment pathways, is located among a small group of neurons at the base of the retina. Long-term intracellular recording from cells of the organized photoreceptor layer, which constitutes most of the retinal volume, indicates that these cells are not involved in generating the rhythm since rhythmic changes in membrane potential were not observed. In addition, surgical removal of the entire photoreceptor layer does not alter the period of the circadian rhythm and does not prevent phase shifts by light pulses.     

Cell division: a second circadian clock system in Paramecium multimicronucleatum

Light-dark cycles entrain a pattern of division in a population of individually isolated cells cultured in excess nutrients at 14 degrees C. This pattern persists for at least 8 days in continuous dim light. Both clones which do and which do not express a circadian rhythm of mating-type reversals can be entrained. The phase is a clonal characteristic.     

不同光照条件下蒙古栎物候期及树高生长节律的研究

本文在不同光照（全光、半荫、全荫）条件下,对实生和萌生蒙古栎幼树进行了物候期及全生长季树高生长的观察和测定。结果表明,不同的光照条件通过对光照强度、光照时间及土壤温度的控制而明显地影响蒙古栎的物候期和树高生长节律。观测的同时还发现,全光照下萌生蒙古栎幼树具有次生生长现象。     

Harderian gland: an extraretinal photoreceptor influencing the pineal gland in neonatal rats?

The circadian rhythm of pineal serotonin and the influence of light on that rhythm have been confirmed. Removal of the Harderian gland abolishes the response to light in blinded animals, which suggests that this gland may act as the extraretinal transducer involved in the persistence of the pineal rhythm in blinded suckling rats.     

Entrainment of circadian rhythms by sound in Passer domesticus

The circadian locomotor rhythm of house sparrows was entrained by a sound stimulus. The birds were maintained at a constant temperature in, dim green light. The entraining agent was 4 (1/2) 12 hours of tape-recorded bird song ,played each day. Variations in the response to this stimulus have been correlated with individual variations in free-running period. This is the first clear demonstration that a biological clock can be influenced by sound stimuli.     

Resetting central and peripheral circadian oscillators in transgenic rats

In multicellular organisms, circadian oscillators are organized into multitissue systems which function as biological clocks that regulate the activities of the organism in relation to environmental cycles and provide an internal temporal framework. To investigate the organization of a mammalian circadian system, we constructed a transgenic rat line in which luciferase is rhythmically expressed under the control of the mouse Per1 promoter. Light emission from cultured suprachiasmatic nuclei (SCN) of these rats was invariably and robustly rhythmic and persisted for up to 32 days in vitro. Liver, lung, and skeletal muscle also expressed circadian rhythms, which damped after two to seven cycles in vitro. In response to advances and delays of the environmental light cycle, the circadian rhythm of light emission from the SCN shifted more rapidly than did the rhythm of locomotor behavior or the rhythms in peripheral tissues. We hypothesize that a self-sustained circadian pacemaker in the SCN entrains circadian oscillators in the periphery to maintain adaptive phase control, which is temporarily lost following large, abrupt shifts in the environmental light cycle.     

Biochemical modeling of an autonomously oscillatory circadian clock in Euglena

Eukaryotic microorganisms, as well as higher animals and plants, display many autonomous physiological and biochemical rhythmicities having periods approximating 24 hours. In an attempt to determine the nature of the timing mechanisms that are responsible for these circadian periodicities, two primary operational assumptions were postulated. Both the perturbation of a putative element of a circadian clock within its normal oscillatory range and the direct activation as well as the inhibition of such an element should yield a phase shift of an overt rhythm generated by the underlying oscillator. Results of experiments conducted in the flagellate Euglena suggest that nicotinamide adenine dinucleotide (NAD+), the mitochondrial Ca2+-transport system, Ca2+, calmodulin, NAD+ kinase, and NADP+ phosphatase represent clock "gears" that, in ensemble, might constitute a self-sustained circadian oscillating loop in this and other organisms.     

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.