Effect of light on the development of the circadian rhythm of motor activity in the mouse

In previous experiments, we found that rats raised in constant light (LL) manifested a more robust circadian rhythm of motor activity in LL and showed longer phase shifts after a light pulse in constant darkness (DD) than those raised under constant darkness. In addition, we observed that the effects produced by constant light differed depending on the time of postnatal development in which it was given. These results suggest that both sensitivity to light and the functioning of the circadian pacemaker of the rat could be affected by the environmental conditions experienced during postembryonic development. Thus, the present experiment aimed to study whether postnatal exposure to light could also affect the circadian system of the mouse. Three groups of mice were formed: One group was raised under constant darkness during lactation (DD group), the second under constant light (LL group), and the third under light-dark cycles (LD group). After lactation, the three groups were submitted first to constant light of high intensity, then to LD cycles, and finally to constant darkness. In the DD stage, a light pulse was given. Finally, mice were submitted to constant light of low intensity. We observed that the circadian rhythm of the DD group was more disturbed under constant light than the rhythm of the LL group, and that, when light intensity increased, the period of the rhythm of the DD group lengthened more than that of the LL group. No significant differences among the groups were found in the phase shift induced by the light pulse. Therefore, it appears that DD mice are more sensitive to light than their LL counterparts. However, at present there is no evidence to affirm that the light environment experienced by the mouse during postnatal development affects the circadian pacemaker. (Chronobiology International, 18(4), 683-696, 2001)     

Photobiology of the Gonyaulax circadian system. I. Different phase response curves for red and blue light

Phase responses to red and blue light pulses were measured at different times during the circadian cycle (phase response curves, PRC) in the marine unicellular dinoflagellate Gonyaulaxpolyedra Stein. Pulses were given during a 24-h period of darkness; thereafter, cultures were released into constant dim red light for the assessment of phase and period. The results confirmed earlier findings that the Gonyaulax circadian system receives light signals via two distinct input pathways. During the subjective day and for the first 3 h of the subjective night, red and blue light pulses led to identical phase responses. For the rest of the circadian cycle, however, phase responses to pulses of either red or blue light differed drastically both in their amplitude and direction (advances or delays). Thus, the Gonyaulax light PRC is generated by two distinct light responses. One of these represents responses via a light input that is responsive both to red and blue light mainly producing small delays. The other represents responses of a primarily blue-sensitive input system leading to large advances restricted to the subjective night. Via feed-back, the blue-sensitive light input appears to be under the control of the circadian system. Received: 27 November 1996/Accepted: 30 January 1997     

The circadian rhythm controls telomeres and telomerase activity

Circadian clocks are fundamental machinery in organisms ranging from archaea to humans. Disruption of the circadian system is associated with premature aging in mice, but the molecular basis underlying this phenomenon is still unclear. In this study, we found that telomerase activity exhibits endogenous circadian rhythmicity in humans and mice. Human and mouse TERT mRNA expression oscillates with circadian rhythms and are under the control of CLOCK–BMAL1 heterodimers. CLOCK deficiency in mice causes loss of rhythmic telomerase activities, TERT mRNA oscillation, and shortened telomere length. Physicians with regular work schedules have circadian oscillation of telomerase activity while emergency physicians working in shifts lose the circadian rhythms of telomerase activity. These findings identify the circadian rhythm as a mechanism underlying telomere and telomerase activity control that serve as interconnections between circadian systems and aging.     

The circadian rhythm of thermoregulation in Japanese quail

Japanese quail exhibit a robust circadian rhythm in body temperature. This rhythm is readily entrainable by 24 h light-dark (LD) cycles and persists under constant conditions. Because both the pineal organ and the eyes have been implicated as major components of the circadian system of birds, the role of these organs in generating the rhythm of body temperature was investigated. Pinealectomy, when performed alone, had little effect on the body temperature rhythm of quail either under LD or under constant darkness (DD). Most birds subjected to optic nerve section alone remained rhythmic in DD although the robustness of the rhythm was decreased, and 25% became arrhythmic. Birds subjected to both pinealectomy and optic nerve section behaved similarly to birds subjected to optic nerve section alone. However, complete eye removal, when performed alone or in combination with pinealectomy, caused all birds to become arrhythmic in DD. The data support the hypothesis that the eyes are the loci of circadian pacemakers in quail that act, via both neural and hormonal outputs, to preserve the integrity of (self-sustaining or damped) circadian oscillators located elsewhere.     

Photobiology of the Gonyaulax circadian system. II. Allopurinol inhibits blue-light effects

Light is the main environmental signal (zeitgeber) for practically all circadian systems, but little is known about the transduction mechanisms by which light signals reach the circadian oscillator. To identify components involved in the circadian light transduction pathway in the unicellular alga Gonyaulax polyedra Stein, we assayed inhibitors of pigment synthesis and of flavo-enzymes for their effects on circadian properties such as phase and period. We found that allopurinol, an inhibitor of xanthine oxidoreductase, specifically inhibits the period and phase effects mediated by the blue-light-sensitive input pathway, while the other light input of the Gonyaulax circadian system, that is sensitive to both red and blue light, appears to be unaffected. Received: 27 November 1996 / Accepted: 30 January 1997     

Functional diversities of two activity components of circadian rhythm in genetical splitting mice (CS strain)

CS mice, an inbred strain, showed two distinctive characteristics in the circadian rhythm of locomotor activity: (1) large variation in the freerunning period, and (2) spontaneous rhythm splitting under continuous darkness. In the splitting rhythm there was a positive correlation between the freerunning period of the evening component and the activity time of the morning component. The phase-shifting effect of a 15-min light pulse was examined on the two activity components of the splitting rhythm. There were significant differences in the amount of light-induced phase response between the two components. A light pulse during the late subjective night induced a phase advance shift only in the morning component, while a light pulse during the early subjective night induced a phase delay shift only in the evening component. These results indicate functional diversities of the two activity components in the circadian locomotor rhythm of CS mice, and suggest that the circadian system in CS mice consists of two mutually coupled oscillators which have different circadian periods and different responsiveness to light. The CS mouse is a useful model to explore a genetic background of oscillator coupling in the circadian system of nocturnal rodents. Accepted: 19 November 1998     

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 (LD 168) 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.Abbreviations T _b body temperature - DD constant darkness - LD light:dark cycle - LL constant light - duration of activity phase - CT circadian time - PRC phase response curve - SCN suprachiasmatic nuclei     

The effect of repeated pulses of light at the same time on period responses of the rat circadian pacemaker

A consequence of simple velocity-based models is that, in response to light pulses, the circadian period should adjust inversely to phase. In addition, because of the interaction of circadian period and phase response, earlier circadian period changes should modify later circadian period changes. The literature contains few mentions of response curves of circadian period responses following light pulses. Rats were exposed to four pulses of light (60 minutes, 1000 lux) at the same circadian time, a minimum of 26 days apart; we assessed period responses and possible bias in the period-response curve. Modulation of circadian period following light-induced phase responses was examined by assessing the period of running wheel activity onset. Phase and circadian period were not consistently found to share an inverse relationship. Moreover, biases in initial period tended to be increased by the experimental protocol regardless of circadian time of pulse. Rats with a short initial (high-velocity) period had a lengthened period, while rats with a long initial period (low velocity) tended to have a reduce period. However, rats with a long initial period were phase delay biased, not phase advance biased. These results do not support a simple velocity model of the pacemaker. (Chronobiology International, 18(2), 187-201, 2001)     

The circadian system of c-fos deficient mice

We examined the role of c-fos in the synchronization of circadian rhythms to environmental light cycles using a line of gene-targeted mice carrying a null mutation at this locus. Circadian locomotor rhythms in mutants had similar periods as wild-type controls but took significantly longer than controls to entrain to 12:12 light-dark cycles. Light-induced phase shifts of rhythms in constant dark were attenuated in mutants although the circadian timing of phase delays and advances was not changed. A functional retinohypothalamic projection was indicated from behavioral results and light-induced jun-B expression in the SCN. The results indicate that while c-fos activation is not an absolute requirement for rhythm generation nor photic responses, it is required for normal entrainment of the mammalian biological clock.Abbreviations SCN suprachiasmatic nucleus - RHT retinohypothalamic tract - IEG immediate early genes - NGF nerve growth factor - VIP vasoactive intestinal polypeptide - DD constant darkness - CT circadian time     

Phase relations between the circadian leaf movement rhythm and its zeitgeber within the range of entrainment in the cotton plant,Gossypium hirsutum L.

Abstract

The leaf movement rhythm of Gossypium hirsutum L. (cv. Lakshmi) could be entrained to 24 h LD cycles with different photofractions varying from 4 to 20 h such that the night peak position of the rhythm occurred during darkness. The phase angle (ψ) of the rhythm varied in a regular manner with different photoperiods of a 24 h LD cycle. Under 24 h LD cycles with different photoperiods, the leaf movement shows probable evidences for the concurrent participation of a ‘light‐on’ and ‘light‐off rhythm.     

肠道菌群昼夜节律与宿主生物节律相互作用的研究进展

为了适应地球昼夜更替对机体的影响,哺乳动物进化出了一套内在的适应性计时机制,由此形成了生物钟系统（circadian clock）。昼夜节律作为该系统中的重要部分可与机体的代谢过程同步变化[1]。肠道菌群作为与机体共生的生物群落,在肠道功能方面发挥着重要作用。对肠道菌群的昼夜节律性波动以及与宿主生物节律之间的相互作用进行研究有重要意义。本文将着重阐述肠道菌群昼夜节律与宿主生物节律的相互作用,以及这种相互作用对宿主代谢的影响。     

The complex regulation of ferredoxin/thioredoxin-related genes by light and the circadian clock

The biochemical properties of the ferredoxin/thioredoxin transduction pathway regulating the activity of key carbon-fixation enzymes through post-translational modifications are well characterized but little is known about the regulation of the different genes. In the present study, we investigated in Chlamydomonas reinhardtii the regulation of the expression of ferredoxin, thioredoxin m, ferredoxin-NADP reductase, phosphoribulokinase, as well as that of cytosolic thioredoxin h, the function of which is still largely unknown. The effects of light, the circadian clock and active cell division were investigated by northern blotting. The five genes were found to be regulated by light and the circadian clock but with different kinetics and amplitudes. This leads for the first time to the proposal that an extra-chloroplastic thioredoxin is possibly implicated in light and/or circadian-related processes. An interplay between several light-transduction pathways in controlling the expression of the genes is suggested by the expression studies and the theoretical analysis of the promoters. Received: 2 December 1998 / Accepted: 19 March 1999     

Azadirachtin affects the circadian rhythm of locomotion in Leucophaea maderae

Abstract

Azadirachtin shortens the period length of the locomotor activity rhythm in the circadian rhythm of Leucophaea maderae and induces splitting of this rhythm in two components in about 40% of the animals. The phase relationship between the two components is 180°. Both shortening of period and splitting are more pronounced in animals possessing longer periods before the injection of azadirachtin.     

Calcium plays a central role in phase shifting the ocular circadian pacemaker of Aplysia

The eye of the marine mollusk Aplysia californica contains an oscillator that drives a circadian rhythm of spontaneous compound action potentials in the optic nerve. Both light and serotonin are known to influence the phase of this ocular rhythm. The aim of the present study was to evaluate the role of extracellular calcium in both light and serotonin-mediated phase shifts. Low calcium treatments were found to cause phase shifts which resembled those produced by the transmitter serotonin. However, unlike serotonin, low calcium neither increased ocular cAMP levels nor could these phase shifts be prevented by increasing extracellular potassium concentration. Low calcium-induced phase shifts were prevented by the simultaneous application of the translational inhibitor anisomycin and low calcium treatment resulted in changes in [³⁵S]methionine incorporation into several proteins as measured by a two-dimensional electrophoresis gel analysis. Finally, light treatments failed to produce phase shifts in the presence of low calcium or the calcium channel antagonist nickel chloride. These results are consistent with a model in which serotonin phase shifts the ocular pacemaker by decreasing a transmembrane calcium flux through membrane hyperpolarization while light-induced phase shifts are mediated by an increase in calcium flux.Abbreviations ASW artificial seawater - EGTA ethylene glycol-bis(-amino-ethyl ester) N,N,N N-tetraacetic acid - CAP compound action potential - CT circadian time 5-HT serotonin - Ni⁺⁺ nickel     

Expression of circadian rhythmicity in Djungarian hamsters under constant light: Effects of light intensity and the circadian system's state

Summary Djungarian hamsters (Phodopus sungorus), were exposed to constant light with increasing intensities (20, 60, 350 lux), and wheel running activity was recorded. With increasing light intensity the percentage of hamsters showing a split in their daily activity pattern increased and the free running period was lengthened for both the unsplit and the split state. The fact that the free running period of both states depended on the light intensity together with the observation that the highest incidence of acircadian activity occurred under 350 lux, provoked the idea that the emergence of splitting or acircadian rhythmicity is a direct consequence of the light induced lengthening of the free running period. However, analysis of the data failed to support the idea that emergence of a split or acircadian activity is a threshold phenomenon with respect to the free running period.Due to differences in circadian function some Djungarian hamsters do not exhibit photoinduction following short day exposure. In these individuals splitting also occurred but required exposure to a higher light intensity than in photo-responsive hamsters. This observation is in accordance with the idea that the two phenotypes differ in the interaction of the two component oscillators underlying circadian rhythmicity.Abbreviations LD long day photoperiod - LL constant light - SD short day photoperiod - free running period     

Nitrate-reductase expression is under the control of a circadian rhythm and is light inducible in Nicotiana tabacum leaves

Over a 24-h light-dark cycle, the level of mRNA coding for nitrate reductase (NR; EC 1.6.6.1) in the leaves of nitrate-fed Nicotiana tabacum L. plants increased throughout the night and then decreased until it was undetectable during the day. The amount of NR protein and NR activity were two-fold higher during the day than at night. When plants were transferred to continuous light conditions for 32 h, similar variations in NR gene expression, as judged by the above three parameters, still took place in leaf tissues. On the other hand, when plants were transferred to continuous dark conditions for 32 h, the NR-mRNA level continued to display the rhythmic fluctuations, while the amount of NR protein and NR activity decreased constantly, becoming very low, and showed no rhythmic variations. After 56 h of continuous darkness, the levels of NR mRNA, protein and activity in leaves all became negligible, and light reinduced them rapidly. These results indicate the circadian rhythmicity and light dependence of NR expression.