Single Light Pulse Research Articles

Exogenous melatonin fails to counteract the light-induced phase delay of human melatonin rhythm

Salivary melatonin levels were measured in 6 healthy volunteers in order to determine whether the phase shift caused by a single 60-min light pulse of 2000 lux might be inhibited by maintaining high melatonin concentration. In the control sessions, the samples were collected at 60-min intervals under lighting of < 10 lux from 18.00 to 11.00 h. In the light-exposure sessions, placebo or 0.5 mg melatonin was administered orally 60 min prior to the light pulse, timed at the rising phase of the melatonin synthesis. The after-light sessions, one day after the light exposure, were like the control sessions. The average delays of the melatonin half-rise and half-decline times were equal (about 0.7 h) in the placebo and melatonin replacement experiments. The maintenance of high melatonin levels during the light exposure did not counteract the influence of bright light on the melatonin rhythm. Thus, in the adjustment of the melatonin rhythm, light is a stronger regulator than melatonin itself.

Spiral Wave Dynamics under Pulsatory Modulation of Excitability

The dynamics of meandering spiral waves in the photosensitive Belousov−Zhabotinsky reaction is investigated under external forcing by single light pulses, periodic pulses, and feedback-controlled sequences of light pulses. The effect of a single stimulus on the trajectory of the spiral tip is related to the phase of the tip motion on the trajectory at the moment when the stimulus is applied. Periodic stimulation of the medium can produce spiral wave entrainment and resonance. A connection between the phase of the stimuli and the stability of the regime of entrainment is shown. In the feedback-controlled system each stimulus is applied at a moment corresponding to the passage of a wave front through a particular detection point. The introduction of such a feedback results in two new dynamic regimes, the entrainment and resonance attractor. Size and stability of these attractors are determined by the value of a time delay in the feedback loop. The experimental results are corroborated by numerical simulations performed with a modified two-component Oregonator model.

A short red light pulse during dark phase of LD-cycle perturbs the hamster's circadian clock.

In this study we investigated the influence of red light< which naturally occurs during dawn and dusk, on locomotor activity and body temperature rhythms of Djungarian hamsters (Phodopus sungarus). A single weak red light pulse given 2 h before regular lights on had acute as well as long-term effects persisting for several days following exposure. The hamsters immediately stopped their locomotor activity, accompanied by a drop in body temperature. In the following undisturbed nights (ID 16:8) the nocturnal activity stopped earlier than usual. This lasting effect of the light pulse was more pronounced than the acute effect. The activity phase compressed gradually during 3 to 5 days after the light pulse was administered while time of activity onset was almost unaffected. It took 6 to 11 days for complete recovery of the original activity phase. The maximal activity compression and the recovery period depended on the duration of the single red light pulse and its intensity. Red light pulses of 15 min duration were about twice effective as 1 min pulses; and the effect of a red light pulse of 130 mW/m2 was about 1.5 times stronger than a 30 mW/m2 red light pulse. The maximal value of activity phase compression reached in this experiment was 2.5 + 0.2 h with a recovery period of 11.1 +/- 0.3 days following a given red light pulse of 90 mW/m2 and 15 min. The "morning oscillator" seems to be persistently affected. This indicates a very high photosensitivity of the Djungarian hamster's circadian system to red light.

Angularly resolved autocorrelation for single-shot time-frequency imaging of ultrashort light pulse

A novel technique to measure the frequency resolved temporal image of a single ultrashort light pulse without use of a spectrometer is presented and analyzed theoretically. This technique is based on a single-shot nonlinear autocorrelator and utilizes the relation between the angular distribution of light produced in the autocorrelator and the spectrum of initial pulse. We analyze the angular distribution of light produced in the correlators with different nonlinear processes: second-harmonic generation, self-diffraction and Kerr optical gating. The self-diffraction autocorrelator is the most convenient and unambiguous for spectral measurements, while in the optical-gating autocorrelator the spectral information is nearly spoiled. An optical scheme with a slit diaphragm and cylindrical lens is presented where the transverse and angular distributions of the output beam are combined to produce the two-dimensional time-frequency image of initial pulse.

Sustained response of pineal melatonin synthesis to a single one-minute light pulse during night in Djungarian hamsters ( Phodopus sungorus)

Previous experiments have demonstrated that short light pulses during the night suppress pineal melatonin formation almost completely for the remainder of the night. Here, the effects of a single 1 min light pulse during the night on melatonin synthesis during the following night was investigated in Djungarian hamsters ( Phodopus sungorus). It is shown that the melatonin pattern during the consecutive night is suppressed to a greater extent than that caused by acute light exposure, indicating a very effective light memory of the melatonin-generating neuronal network, possibly a key to understanding the reliability of the photoperiod-measuring system.

Time–frequency imaging of a single ultrashort light pulse from angularly resolved autocorrelation

A new technique to measure the frequency-resolved temporal image of a single ultrashort light pulse is presented. This technique is based on a single-shot self-diffraction autocorrelator in which the pulse duration is related to the spatial width of a diffracted beam, the pulse spectrum is related to its divergence, and the pulse chirp appears as a curvature of the diffracted-beam wave front. An analysis of wave-front curvature by means of a slit diaphragm and a cylindrical lens results in a time-frequency image of the initial pulse when a spectrometer is not used. This image gives a simple intuitive picture of the chirp and the phase modulation of a pulse.

Functional spectroscopy of brain activation following a single light pulse: Examinations of the mechanism of the fast initial response

AbstractLocalized proton spectroscopy using the PRESS sequence was performed to measure the free induction decay of the water signal in a 2 × 2 × 2 = ml voxel located in the visual cortex after a short light pulse. The experiment was run continuously with a repetition time of 400 ms; the onset of the light pulse was triggered by the spectrometer. The FIDs were measured as a function of the echo time (TE) and the length of the stimulus (TS). The time course showed three different phases: An initial response was observed 400 ms after the onset of the stimulus, which was demonstrated to be mainly a change in the apparent spin density and/or T1 with a minor contribution of T2*. No significant change in T2 could be measured. Changes in the ionic cell environment and/or the subsequent increase in cell size upon stimulation are discussed as a potential mechanism for the observed signal response.

Circadian regulation of the Cat3 catalase gene in maize (Zea mays L.): entrainment of the circadian rhythm of Cat3 by different light treatments

The Cat3 maize catalase gene is a non‐photosynthetic, non‐chloroplast‐associated gene that exhibits a transcriptionally regulated circadian rhythm. Cat3 transcript accumulation was examined in leaves of maize seedlings grown under different light regimes. Plants grown in a 12 h light/12 h dark photoperiod (LD) show a distinct diurnal pattern with maximal Cat3 transcript accumulation late in the light period (CT 10, circadian time) and low to undetectable levels late in the dark and early light period (CT 22‐02). The Cat3 gene is expressed at high and constant levels without any diurnal fluctuations in leaves of maize seedlings grown post‐imbibition in constant dark (DD) or constant light (LL). The circadian rhythm of Cat3 is inducible by transferring DD‐grown plants and/ or LL‐grown plants to a 12 h (light/dark LD) or 12 h (dark/light DL) cycle. Entrainment of the rhythm requires a cyclic light signal consisting of one DL‐transition (‘light on’‐signal) followed by one LD transition (‘light off’‐signal). When etiolated maize seedlings were treated with single light pulses of white light and different monochromatic light and transferred to constant darkness (DD) a similar induction pattern of the Cat3 circadian rhythm was observed. Cat3 mRNA accumulates to peak levels 4 h after the light pulse; the next peak appeared 24–28 h later. Induction by far red‐light (FR) exhibits characteristics of a very low fluence phytochrome response. Also blue light and ultraviolet light pulses cause induction of the Cat3 circadian rhythm, but do not influence the periodicity of Cat3 expression. In order to demonstrate differences of the Cat3 circadian regulation from photosynthetic genes, the maize cab gene expression was used for comparison.

Circadian Rhythms in Locomotor Activity of the Hagfish, Eptatretus burgeri V. The Effect of Light Pulses on the Free-running Rhythm

Abstract This study examined the effect of light pulses on the free-running rhythm of locomotor activity of the hagfish, Eptatretus burgeri, reared for prolonged periods under constant darkness. The free-running period (τ) of circadian locomotor activity of 55 hagfishes followed a normal distribution with mean 24.1 hr (min.: 22.8 hr; max.: 25.1 hr). After establishing the τ in constant darkness for each specimen, we examined the effect of single light pulses (intensity; 670 lx at the bottom of the aquarium, duration; 15 min) on the free-running rhythm. Light pulses in the early subjective night lengthened τ and caused a slight phase delay, whereas those in the late subjective night shortened τ and provoked a slight phase advance. Thus, the hagfish showed a distinct “period response” to short light pulse, but the “phase response” was not so clear as other organisms.

Circadian expression of the light-harvesting protein of Photosystem II in etiolated bean leaves following a single red light pulse: Coordination with the capacity of the plant to form chlorophyll and the thylakoid-bound protease

The appearance of the light harvesting II (LHC II) protein in etiolated bean leaves, as monitored by immunodetection in LDS-solubilized leaf protein extracts, is under phytochrome control. A single red light pulse induces accumulation of the protein, in leaves kept in the dark thereafter, which follows circadian oscillations similar to those earlier found for Lhcb mRNA (Tavladoraki et al. (1989) Plant Physiol 90: 665-672). These oscillations are closely followed by oscillations in the capacity of the leaf to form Chlorophyll (Chl) in the light, suggesting that the synthesis of the LHC II protein and its chromophore are in close coordination. Experiments with levulinic acid showed that PChl(ide) resynthesis does not affect the LHC II level nor its oscillations, but new Chl a synthesis affects LHC II stabilization in thylakoids, implicating a proteolytic mechanism. A proteolytic activity against exogenously added LHC II was detected in thylakoids of etiolated bean leaves, which was enhanced by the light pulse. The activity, also under phytochrome control, was found to follow circadian oscillations in verse to those in the stabilization of LHC II protein in thylakoids. Such a proteolytic mechanism therefore, may account for the circadian changes observed in LHC II protein level, being implicated in pigment-protein complex assembly/stabilization during thylakoid biogenesis.

Long-Term Reproductive Effects of a Single Long Day in the Siberian Hamster (Phodopus sungorus

Testicular regression was prevented or attenuated in Siberian hamsters exposed to a single 1- to 4-h extension of the 16-h photophase at 18 days of age and subsequently maintained in a short photoperiod (8L:16D) through Day 35. Testicular weights on Day 35 were not correlated with the duration of the active phase of wheel running or with the time of activity onset after transfer to the 8L:16D photoperiod. Wheel-running activity was not stably entrained to the light-dark cycle by 35 days of age. Progonadal effects of a single 33-h light pulse were greatest at 18 days of age, still evident at 30 days, but undetectable in older hamsters. In female hamsters, a single longer day at weaning was associated with increased fecundity several weeks later. Long photoperiods accelerated development of antral ovarian follicles, but exposure to males was necessary to induce ovulation before 60 days of age. The interval beginning shortly after weaning is one of heightened responsiveness to changes in day length (DL); exposure to increasing DL at this time may prolong the breeding season when DL decreases after the summer solstice. We suggest that the long-term effects of acute light treatments on reproduction are mediated by sustained changes in melatonin secretion induced by reprogramming of circadian oscillators.

Nonlinear optical responses of strontium barium niobate

Single laser light pulses were used to induce gratings in nominally undoped and iron-doped Sr 0.60Ba 0.40Nb 2O 6 (SBN:60) using, in separate experiments, both 22 ps ( λ = 532 nm) and 400 fs ( λ = 580 nm) pulses. In both cases the gratings appear to have at least two temporal components outside the cross correlation time scale of the pulses. The first component is shown to be associated with induced absorption at the probe wavelength while a photorefractive grating associated with the displacement of charge carriers explains the second. The two-photon absorption coefficient, β, was measured to be 2.3 cm/GW ( λ = 532 nm) and 2.0 cm/GW ( λ = 580 nm) for the undoped sample and 2.15 cm/GW ( λ = 532 nm) for the iron-doped sample.

Individual Members of the Cab Gene Family Differ Widely in Fluence Response.

Chlorophyll a/b-binding protein genes (Cab genes) can be extremely sensitive to light. Transcript accumulation following a red light pulse increases with fluence over 8 orders of magnitude (L.S. Kaufman, W.F. Thompson, W.R. Briggs [1984] Science 226: 1447-1449). We have constructed fluence-response curves for individual Cab genes. At least two Cab genes (Cab-8 and AB96) show a very low fluence response to a single red light pulse. In contrast, two other Cab genes (AB80 and AB66) fail to produce detectable transcript following a single pulse of either red or blue light but are expressed in continuous red light. Thus, very low fluence responses and high irradiance responses occur in the same gene family.

Optical Oscillations and Their Peculiarities Caused by Internal Switching Delay in Optically Bistable CdS Crystals

AbstractLight oscillations due to internal switching delay in optically bistable CdS platelets are reported using a geometry with two exciting beams. It is shown that in the case when one of the exciting beams has the form of a long thin light strip, an internal delay occurs due to the final propagation speed of the bistable switching front along it (switching wave) which enables one to obtain oscillations using electrooptical feedback without external delay. If an external delay is applied to one of the beams, while the second one appears as a single light pulse peculiarities of the oscillations caused by the interaction of both delay signals are obtained, which are not observed if only one light beam is used.

Rice phytochrome A controls apical hook opening after a single light pulse in transgenic tobacco seedlings

SummaryApical hook opening in tobacco seedlings can be induced by a single red light pulse and this induction can be reverted by a subsequent far‐red light pulse. The slow hook opening kinetics and the reversibility of an inductive light pulse even after 8 h of darkness indicate the involvement of stable phytochrome. Compared with wild‐type, transgenic BN1 seedlings which overexpress rice phytochrome A exhibit a higher sensitivity to low irradiance red light pulses. Moreover, in BN1 seedlings an inductive red light pulse is only partially reversible even after 30 min, whereas wild‐type tobacco seedlings show complete reversibility during the entire hook opening process. The data found show that rice phytochrome A is active in transgenic tobacco seedlings in controlling hook opening and that the introduced rice phytochrome A and the endogenous stable phytochrome behave differently in this response.

Retinally perceived light is not essential for photic regulation of pineal melatonin rhythms in the pigeon: studies with microdialysis

Using in vivo microdialysis, effects of retinally perceived light on pineal melatonin release and its rhythmicity was examined in the pigeon. In the first experiment, light-induced suppression of pineal melatonin release was studied. Although light given to the whole body during the dark strongly suppressed pineal melatonin release to a daytime level, light exclusively delivered to the eyes did not remarkably inhibit melatonin release. In the second experiment, in order to determine whether retinally perceived light has phase-shifting effects on pineal melatonin rhythms, pigeons were given a single light pulse of 2 h at circadian time (CT) 18 and the phases of the second cycle after the light pulse were compared with those of control pigeons without the light pulse. In this experiment, phase advances of pineal melatonin rhythms were observed when the light was given to the whole body but not when only the eyes were illuminated. In a third experiment, after entrainment to light-dark 12:12 (LD 12:12) cycles, birds whose heads were covered with black tapes were transferred into constant light (LL) conditions and only the eyes were exposed to new LD cycles for 7 days (the phase was advanced by 6 h from the previous cycles) using a patching protocol. This procedure, however, could not entrain pineal melatonin rhythms to the retinal LD cycles. These results indicate that the eyes are not essential for photic regulation of pineal melatonin release and its rhythmicity in the pigeon.

Single-pulse, Fourier-transform spectrometer having no moving parts

A Wollaston prism is used in the design of a polarizing Fourier-transform spectrometer with no moving parts. The effective path difference between orthogonally polarized components varies across the aperture of the instrument, forming an interferogram in the spatial rather than temporal domain. The use of a charge-integrating linear detector array permits the entire interferogram to be sampled simultaneously so that a full spectrum is obtained for a single pulse of light.

Synchronization by light of the circadian rhythm of motor activity in the crayfish

Abstract We have studied the pattern for resetting the circadian rhythm in the spontaneous motor activity of the crayfish. Spontaneous motor activity was recorded continously at a constant temperature and under free running conditions in complete darkness. The effect of single light pulses applied at different circadian times, on the circadian rhythm of motor activity was measured in both transient stage and steady state. The results led us to construct a phase‐transition curve and phase‐response curve which were analyzed to obtain information about the oscillators which underlie the circadian rhythm of motor activity.

Kinetic Modelling of Chloroplast Phototranslocations in Lemna trisulca L.: Two Rate Limiting Components?

An experimental model is derived from analytical action spectroscopy, in which total chloroplast translocation response to blue light is a linear combination of independent positive (low-intensity response) and negative (high-intensity response) components. This model explains transmission changes in Lemna trisulca L. leaves under steady-state light conditions and transient displacements after single pulses of strong blue light. The initial rate of chloroplast phototranslocation as measured by the microphotometric method is dependent on the fluence rate of the actinic light in both positive and negative response ranges. In both cases the absolute level of response is proportional to the initial rate of chloroplast translocation. Model considerations and kinetic experiments indicate that positive and negative chloroplast responses to light are controlled by two different rate-limiting processes and consequently may have separate control mechanisms.

Immediate response to light of rat pineal melatonin rhythm: analysis by in vivo microdialysis

Melatonin in the extracellular space of the pineal gland was measured continuously for 4 consecutive days from single, freely moving rats by means of in vivo microdialysis. A robust circadian rhythm was observed in the pineal extracellular melatonin under both light-dark (LD) and continuous dark (DD) conditions, the patterns of which were almost identical for 4 days within individuals but varied substantially among individuals. The offset phase of melatonin rhythm was more stable than the onset phase. Light-induced phase shift of melatonin rhythm was measured in individual rats, which had been entrained to LD and subsequently released into DD. On the 1st day in DD, a 3-min light pulse of 200 lx was applied either at circadian time (CT) of 17 or 22 h (5 and 10 h after the dark onset, respectively). The light pulse rapidly suppressed the nocturnal melatonin level. The rate as well as the level of melatonin suppression was significantly greater by the pulse at CT22 than at CT17. A phase shift of the melatonin rhythm was calculated on the 2nd and 3rd days in DD. Significant phase delay shift was observed after the pulse at CT17 and advance shift after the pulse at CT22 of approximately 1 h in either case. Because the amount of phase shift was not different between the 2nd and 3rd days in DD, the phase shift of pineal melatonin rhythm by single light pulse seems to be completed immediately.