The Dim Light Melatonin Onset as a Marker for Orcadian Phase Position

Masking is known to affect a variety of circadian rhythms, making it difficult to use them as reliable markers of circadian phase position. Melatonin may be unique in that it appears to be masked only by (bright) light. Sleep and activity do not appear to influence the melatonin rhythm. By measuring the onset of melatonin production, a clearly demarcated event, we can reliably assess circadian phase position, provided blood is sampled under dim light (the dim light melatonin onset, or DL.MO). The DLMO has been useful in assessing the phase-shifting properties of bright light and in phase typing patients with chronobiologic disorders, such as winter depression.     

Characteristics of Food-Entrained Orcadian Rhythms in Rats During Long-Term Exposure to Constant Light

Rats possess a system of circadian oscillators that permit entrainment of circadian activity rhythms independently to 24 hr cycles of light-dark and food access. The nature of interactions between food- and light-entrainable oscillators was examined by observing the generation and persistence of food-entrained circadian rhythms in rats whose light-entrainable rhythms were eliminated by long-term exposure to constant light. Most of these rats showed a delayed generation of food-entrained rhythms and only one of eight animals showed persistence of food associated rhythms during a 4-day food deprivation test. Rats whose light-entrainable rhythms are eliminated by suprachiasmatic nuclei ablation show, in contrast, normal generation and persistence of food-entrained rhythms. The results suggested a disruptive influence of constant light on non-photic entrainment, possibly due to coupling forces between damped light-entrainable oscillators and the food-entrainable oscillators.     

Characteristics of Food-Entrained Orcadian Rhythms in Rats During Long-Term Exposure to Constant Light

Rats possess a system of circadian oscillators that permit entrainment of circadian activity rhythms independently to 24 hr cycles of light-dark and food access. The nature of interactions between food- and light-entrainable oscillators was examined by observing the generation and persistence of food-entrained circadian rhythms in rats whose light-entrainable rhythms were eliminated by long-term exposure to constant light. Most of these rats showed a delayed generation of food-entrained rhythms and only one of eight animals showed persistence of food associated rhythms during a 4-day food deprivation test. Rats whose light-entrainable rhythms are eliminated by suprachiasmatic nuclei ablation show, in contrast, normal generation and persistence of food-entrained rhythms. The results suggested a disruptive influence of constant light on non-photic entrainment, possibly due to coupling forces between damped light-entrainable oscillators and the food-entrainable oscillators.     

Lighting requirements of nocturnal primates in captivity: A chronobiological approach

From the results of chronobiological studies in 11 Aotus lemurinus (trivirgatus) griseimembra, 3 Galago garnettii, 5 Galago senegalensis, and 6 Microcebus murinus, inferences can be made on the most suitable lighting conditions for nocturnal primates kept in captivity. In each species studied light controls the daily periodic course of activity in a dual way. First, the light-dark (LD) cycle acts as the main Zeitgeber, entraining the endogenous circadian timing system (CTS) to the environmental periodicity. Second, the prevailing light intensity has a direct species-specific inhibiting or enhancing effect, masking the level of activity predetermined by the CTS. Marked inhibition of activity is caused especially by low light intensities during dark-time (D-time), which can also lead to drastically reduced food intake (e.g., in Aotus). Therefore, high-amplitude LD cycles should be applied which guarantee a stable external and internal synchronization of the various circadian rhythms of the organism, with a D-illumination intensity high enough to prevent light-induced impairments of the behavior of the animals. Up to now LD cycles of 12:12 h (100–1,000:0.5–0.01 lx; ≥5,000°K) have proved to be most suitable. Only in Microcebus should the D-illumination be reduced to about 10^?4 lx. Moreover, it must be considered that species with a photoperiodically controlled reproduction cycle require specific alterations of the L-time:D-time ratio.     

Circadian and ultradian activity rhythms in male long‐evans rats: Relationship to feeding

Abstract

Rats exhibit ultradian as well as circadian rhythms in activity. Short‐term activity rhythms appear to result from bouts of feeding‐related behavior interspersed with periods of quiescence. We examined the relationship of activity to feeding in 12 male Long‐Evans derived rats during ad lib and restricted feeding (RF) conditions to determine the effect of RF on both circadian and ultradian activity rhythms. By the end of 20 days of RF all animals exhibited an ultradian periodicity of approximately 12 hours. A twenty‐four hour rhythm in feeding persisted, apparently due to the rats adapting to the diurnal feeding period. General findings were that RF resulted in anticipatory activity prior to feeding and that short‐term activity fluctuations and investigations of the food bin continued during RF even though overall nocturnal activity decreased. The results suggest that male rats of this strain exhibit ultradian activity rhythms that appear to be strongly related to feeding.     

Diurnality and nocturnality in nonhuman primates: comparative chronobiological studies in laboratory and nature

Looking for differences in circadian clock characteristics of diurnal and nocturnal nonhuman primates, this article summarizes results of chronobiological studies carried out in various nocturnal, diurnal, and cathemeral prosimian and anthropoid primate species under controlled laboratory conditions, under seminatural conditions, and in the wild. In almost all circadian parameters investigated, no differences were discernible between the two main chrono-ecotypes, either in circadian period length and the influence upon it of after-effects, of light intensity, and ambient temperature, or in the PRC, re-entrainment behavior, rhythm splitting, and internal desynchronization. Diurnal and nocturnal or cathemeral species differed only in the phase of artificial or natural LDs to which their circadian activity phase was adjusted as well as in the characteristics of masking activity upon the rhythms produced by the direct inhibiting or enhancing effects of light. Pronounced lunar periodicity—observed in the activity rhythm of nocturnal neotropical owl monkeys, genus Aotus, in seminatural and natural environments as well as in wild cathemeral Malagasy lemurs, genus Eulemur—is shown to result from masking effects of moonlight. In captive Eulemur fulvus albifrons, a change from dark-active over cathemeral to light-active behavior, without concurrently changing the circadian phase-setting of activity to D, was produced by direct masking effects of a stepwise reduction of darktime luminosity on an LD 12:12 cycle. Long-term activity recordings carried out in wild diurnal Malagasy sifakas (Propithecus verreauxi) and cathemeral redfronted lemurs (Eulemur fulvus rufus), as well as in wild nocturnal owl monkeys (Aotus a. azarai) of the North Argentinean Chaco, yielded in all species distinct bimodal long- and short-day activity patterns with pronounced peaks during dusk and dawn. Applying Pittendrigh's two-oscillator concept to these results, it is hypothesized that the differences in chrono-ecotype behavior may result from variations in internal coupling and external phase-setting of morning and evening oscillators (m, e) to dawn and dusk, interacting with direct masking effects of light.     

生物钟机制研究进展

由生物体内源性生物钟所产生的昼夜节律是近年来生命科学的研究热点之一。几种模型生物（蓝细菌、脉孢菌、拟南芥、果蝇、小鼠）的生物钟相关基因相继被克隆和鉴定,为理解昼夜节律的分子机制奠定了基础。振荡器蛋白对其编码基因的负反馈调控可能是不同生物的生物运作普遍机制,在此基础上,不同生物有不尽相同的调控方式;隐色素可能是高等生物的共同生物钟光受体。     

The effects of feedback lighting on the circadian drinking rhythm in the diurnal new world primate Saimiri sciureus

Feedback lighting provides illumination primarily during the subjective night (i.e., the photosensitive portion of the circadian cycle) in response to a given behavior. This technique has previously been used to test the nonparametric model of entrainment in nocturnal rodents. In three species (Rattus norvegicus, Mesocricetus auratus, and Mus musculus), the free-running period of the locomotor activity rhythm was similar whether the animals were exposed to continuous light or discrete light pulses occurring essentially only during the subjective night (i.e., feedback lighting). In the current experiments, feedback lighting was presented to squirrel monkeys so that light fell predominantly during the subjective night. Feedback lighting was linked to the drinking behavior in this diurnal primate so that when the animal drank, the lights went out. Despite the seemingly adverse predicament, the monkeys maintained regular circadian drinking rhythms. Furthermore, just as the period of the free-running activity rhythms of nocturnal rodents exposed to continuous light or feedback lighting were similar, the period of the drinking rhythms of the squirrel monkeys in continuous light and feedback lighting were comparable (25.6 +/- 0.1 and 25.9 +/- 0.1 hours, respectively), despite a substantial decrease in the total amount of light exposure associated with feedback lighting. The free-running period of monkeys exposed to continuous dark (24.5 +/- 0.1 hours) was significantly shorter than either of the two lighting conditions (P < 0.001). The results presented for the drinking rhythm were confirmed by examination of the temperature and activity rhythms. Therefore, discrete light pulses given predominately during the subjective night are capable of simulating the effects of continuous light on the free-running period of the circadian rhythms of a diurnal primate. The response of squirrel monkeys to feedback lighting thus lends further support for the model and suggests that the major entrainment mechanisms are similar in nocturnal rodents and diurnal primates.     

The effects of chronic marijuana use on circadian entrainment

Animal literature suggests a connection between marijuana use and altered circadian rhythms. However, the effect has not yet been demonstrated in humans. The present study examined the effect of chronic marijuana use on human circadian function. Participants consisted of current users who reported smoking marijuana daily for at least a year and non-marijuana user controls. Participants took a neurocognitive assessment, wore actigraphs and maintained sleep diaries for three weeks. While no significant cognitive changes were found between groups, data revealed that chronic marijuana use may act as an additional zeitgeber and lead to increased entrainment in human users.     

A circadian rhythm of thermal preference in the ant Camponotus mus: masking and entrainment by temperature cycles

Abstract. Along a stable temperature gradient and under a LD 12:12 h cycle, nurse workers of the ant Camponotus mus Roger 1863 (Hymenoptera: Formicidae) select for the brood two different temperatures daily: 30.8°C at the middle of the light period (circadian phase = 90°), and 27.5°C 8 h later, during the dark period (circadian phase = 210°), this rhythm being of endogenous nature.When a 24 h temperature cycle was superimposed along the thermal gradient, so that the immobile brood experienced a temperature transition as they receive when translocated by nurses (8 h at 30.8°C and 16 h at 27.5°C), no brood translocations occurred.The thermal cycle masked the rhythm of brood translocation when temperature fitted the daily pattern expected by nurses.When the same temperature cycle was presented with a phase-advance, nurses did not tolerate the early thermal increase and removed the brood as temperature rose.However, when workers experienced this new phase relationship between light and temperature cycles for more than 10 days, brood translocations were suppressed.Records under constant conditions of light and temperature indicated that the overt rhythm was locked-on to the expected early increase in temperature, so that the temperature cycle dominated over the LD cycle in resetting brood-carrying activity.     

Circadian locomotor rhythms in individual honeybees

ABSTRACT. The circadian locomotor (walking) rhythms of individual forager honeybees ( Apis mellifera ligustica L.) were measured under a variety of conditions. In constant dark the rhythms exhibited endogenous periodicities that were less than 24 h, whereas under constant light the periods tended to be greater than 24 h. Individual honeybees readily entrained to photoperiods, displaying a diurnal pattern of entrainment with most of the activity occurring in late photophase. Evidence is presented which suggests that foraging behaviour and general locomotor behaviour may be governed by two different circadian clock systems.     

Life's 24-hour clock: molecular control of circadian rhythms in animal cells

Our sleep–wake cycles and many other 24-hour rhythms of behavior and physiology persist in the absence of environmental cues. Genetic and biochemical studies have shown that such rhythms are controlled by internal molecular clocks. These are assembled from the cycling RNA and protein products of a small group of genes that are conserved throughout the animal kingdom.     

哺乳动物昼夜节律调节的神经基础——昼夜光感受器

哺乳动物昼夜光感受器为一组具有直接感光功能的特殊视网膜神经节细胞 ,其基本感光色素为黑视素 .昼夜光感受器具有直接、广谱和稳定感受昼夜光变化的功能特点 .昼夜光感受器的功能是通过导引作用 ,使下丘脑视交叉上核内的昼夜节律活动与外界明 暗周期变化同步     

The effect of neonatal administration of monosodium glutamate on the circadian control of food intake in the rat

Abstract

Neonatal treatment with monosodium glutamate (MSG) results in a substantial degeneration of the inner layer of the retina and a decreased diameter of the optic nerves. Nevertheless, MSG‐treated animals entrain and re‐entrain to a light dark cycle. The question arises whether MSG selectively destroys the optic pathways which are involved in vision but not the retinohypothalamic trart that mediates entrainment. In these experiments not only entrainment and re‐entrainment of the circadian food intake rhythm of MSG‐treated rats was investigated but also the freerunning period under continuous bright and dim light It appears that MSG‐treated rats have shorter freerunning periods under continuous illumination than controls. Therefore, these results suggest that also those pathways involved in entrainment of the circadian food intake rhythm are affected by neonatal treatment with MSG.     

运动介导的心脏代谢与生物钟相互调节作用研究

在哺乳动物中,昼夜节律主要由生物钟基因的转录翻译反馈回路产生,生物钟基因通过转录翻译反馈回路调控下游的时钟控制基因,从而影响体内的各种生理活动。心脏作为人体外周组织中的重要器官,其生物钟系统受到运动和营养等授时因子的调控。当心肌细胞的生物钟基因被遗传性破坏或表达异常时,会严重影响心脏的代谢活动,导致心脏生理功能减退,增加心脏不良事件的发生风险,因此心脏生物钟在维持心脏代谢活动和生理功能方面发挥着重要作用。运动作为授时因子,可以独立于中枢生物钟对心脏生物钟进行调节。同时运动作为改善心血管功能的重要手段,可能通过激活下丘脑-垂体-肾上腺轴（HPA）和交感-肾上腺-髓质轴（SAM）、调节能量代谢等途径影响心脏的代谢活动和生物钟基因的转录,维持心脏生物钟的稳定,促进心脏健康。对运动调控心脏生物钟的机制研究,可以为倒班、熬夜人群以及心血管疾病患者提供新的预防和治疗思路。未来需要更多研究来探索运动调节心脏代谢活动和生物钟的机制、运动对光周期诱导的昼夜节律紊乱心脏生物钟的影响及机制以及运动调节心脏生物钟对其他外周器官代谢活动和昼夜节律的影响。