Relationship between dim light melatonin onset and the timing of sleep in sleep onset insomniacs

Sleep and Biological Rhythms - Dim light melatonin onset (DLMO), a phase marker of the circadian system can be estimated from sleep diaries of good sleepers. Previous studies have shown a strong...     

The dim light melatonin onset, melatonin assays and biological rhythm research in humans

The most useful marker for human circadian phase position is the dim light melatonin onset (DLMO). This is optimally obtained by sampling blood or saliva in the evening at intervals of 30 min or less. Ambient light intensity should not exceed 30-50 lx. For many years, the DLMO was determined mainly with the 'gold standard' GCMS technique for measuring melatonin in human plasma. However, new and improved RIAs now provide the requisite sensitivity and accuracy (specificity) for detecting the time that low daytime levels begin to increase in the evening: the lower the operational threshold for the DLMO, the more reliable it is as a phase marker.     

Preliminary evidence that light through the eyelids can suppress melatonin and phase shift dim light melatonin onset

ABSTRACT: BACKGROUND: A previous study reported a method for measuring the spectral transmittance of individual human eyelids. A prototype light mask using narrow-band "green" light (lambdamax = 527 nm) was used to deliver light through closed eyelids in two within-subjects studies. The first study investigated whether an individual-specific light dose could suppress melatonin by 40% through the closed eyelid without disrupting sleep. The light doses were delivered at three times during the night: 1) beginning (while subjects were awake), 2) middle (during rapid eye movement (REM) sleep), and 3) end (during non-REM sleep). The second study investigated whether two individual-specific light doses expected to suppress melatonin by 30% and 60% and delivered through subjects' closed eyelids before the time of their predicted minimum core body temperature would phase delay the timing of their dim light melatonin onset (DLMO). FINDINGS: Compared to a dark control night, light delivered through eyelids suppressed melatonin by 36% (p = 0.01) after 60-minute light exposure at the beginning, 45% (p = 0.01) at the middle, and 56% (p < 0.0001) at the end of the night. In the second study, compared to a dark control night, melatonin was suppressed by 25% (p = 0.03) and by 45% (p = 0.009) and circadian phase, as measured by DLMO, was delayed by 17 minutes (p = 0.03) and 71 minutes (ns) after 60-minute exposures to light levels 1 and 2, respectively. CONCLUSIONS: These studies demonstrate that individual-specific doses of light delivered through closed eyelids can suppress melatonin and phase shift DLMO and may be used to treat circadian sleep disorders.     

Calculating the dim light melatonin onset: the impact of threshold and sampling rate

The dim light melatonin onset (DLMO) is the most reliable circadian phase marker in humans, but the cost of assaying samples is relatively high. Therefore, the authors examined differences between DLMOs calculated from hourly versus half-hourly sampling and differences between DLMOs calculated with two recommended thresholds (a fixed threshold of 3 pg/mL and a variable "3k" threshold equal to the mean plus two standard deviations of the first three low daytime points). The authors calculated these DLMOs from salivary dim light melatonin profiles collected from 122 individuals (64 women) at baseline. DLMOs derived from hourly sampling occurred on average only 6-8?min earlier than the DLMOs derived from half-hourly saliva sampling, and they were highly correlated with each other (r?≥?0.89, p?30?min from the DLMO derived from half-hourly sampling. The 3 pg/mL threshold produced significantly less variable DLMOs than the 3k threshold. However, the 3k threshold was significantly lower than the 3 pg/mL threshold (p?相似文献   

Effects of day-time exposure to different light intensities on light-induced melatonin suppression at night

Background

Bright nocturnal light has been known to suppress melatonin secretion. However, bright light exposure during the day-time might reduce light-induced melatonin suppression (LIMS) at night. The effective proportion of day-time light to night-time light is unclear; however, only a few studies on accurately controlling both day- and night-time conditions have been conducted. This study aims to evaluate the effect of different day-time light intensities on LIMS.

Methods

Twelve male subjects between the ages of 19 and 23 years (mean ± S.D., 20.8 ± 1.1) gave informed consent to participate in this study. They were exposed to various light conditions (<10, 100, 300, 900 and 2700 lx) between the hours of 09:00 and 12:00 (day-time light conditions). They were then exposed to bright light (300 lx) again between 01:00 and 02:30 (night-time light exposure). They provided saliva samples before (00:55) and after night-time light exposure (02:30).

Results

A one-tailed paired t test yielded significant decrements of melatonin concentration after night-time light exposure under day-time dim, 100- and 300-lx light conditions. No significant differences exist in melatonin concentration between pre- and post-night-time light exposure under day-time 900- and 2700-lx light conditions.

Conclusions

Present findings suggest the amount of light exposure needed to prevent LIMS caused by ordinary nocturnal light in individuals who have a general life rhythm (sleep/wake schedule). These findings may be useful in implementing artificial light environments for humans in, for example, hospitals and underground shopping malls.     

Sleep logs of young adults with self-selected sleep times predict the dim light melatonin onset

The purpose of this study was to determine whether a sleep log parameter could be used to estimate the circadian phase of normal, healthy, young adults who sleep at their normal times, and thus naturally have day-to-day variability in their times of sleep. Thus, we did not impose any restrictions on the sleep schedules of our subjects (n = 26). For 14 d, they completed daily sleep logs that were verified with wrist activity monitors. On day 14, salivary melatonin was sampled every 30 min in dim light from 19:00 to 07:30 h to determine the dim light melatonin onset (DLMO). Daily sleep parameters (onset, midpoint, and wake) were taken from sleep logs and averaged over the last 5, 7, and 14 d before determination of the DLMO. The mean DLMO was 22:48 +/- 01:30 h. Sleep onset and wake time averaged over the last 5 d were 01:44 +/- 01:41 and 08:44 +/- 01:26 h, respectively. The DLMO was significantly correlated with sleep onset, midpoint, and wake time, but was most strongly correlated with the mean midpoint of sleep from the last 5 d (r = 0.89). The DLMO predicted using the mean midpoint of sleep from the last 5 d was within 1 h of the DLMO determined from salivary melatonin for 92% of the subjects; in no case did the difference exceed 1.5 h. The correlation between the DLMO and the score on the morningness-eveningness questionnaire was significant but comparatively weak (r = -0.48). We conclude that the circadian phase of normal, healthy day-active young adults can be accurately predicted using sleep times recorded on sleep logs (and verified by actigraphy), even when the sleep schedules are irregular.     

The hockey-stick method to estimate evening dim light melatonin onset (DLMO) in humans

The onset of melatonin secretion in the evening is the most reliable and most widely used index of circadian timing in humans. Saliva (or plasma) is usually sampled every 0.5–1 hours under dim-light conditions in the evening 5–6 hours before usual bedtime to assess the dim-light melatonin onset (DLMO). For many years, attempts have been made to find a reliable objective determination of melatonin onset time either by fixed or dynamic threshold approaches. The here-developed hockey-stick algorithm, used as an interactive computer-based approach, fits the evening melatonin profile by a piecewise linear-parabolic function represented as a straight line switching to the branch of a parabola. The switch point is considered to reliably estimate melatonin rise time. We applied the hockey-stick method to 109 half-hourly melatonin profiles to assess the DLMOs and compared these estimates to visual ratings from three experts in the field. The DLMOs of 103 profiles were considered to be clearly quantifiable. The hockey-stick DLMO estimates were on average 4 minutes earlier than the experts' estimates, with a range of ?27 to +13 minutes; in 47% of the cases the difference fell within ±5 minutes, in 98% within ?20 to +13 minutes. The raters' and hockey-stick estimates showed poor accordance with DLMOs defined by threshold methods. Thus, the hockey-stick algorithm is a reliable objective method to estimate melatonin rise time, which does not depend on a threshold value and is free from errors arising from differences in subjective circadian phase estimates. The method is available as a computerized program that can be easily used in research settings and clinical practice either for salivary or plasma melatonin values.     

Acute phase proteins, body temperature and urinary melatonin under the influence of bright and dim light intensities during the daytime

Concentrations of five acute phase proteins: C-reactive protein (CRP), alpha 1-antichymotrypsin (ACT), transferin (Tf), alpha 2-macroglobulin (alpha 2-M) and haptoglobin (Hp) as well as glycosylation profiles of alpha 1-antichymotrypsin (ACT) were studied in sera samples with 7 healthy volunteers under the influence of two different light intensities during the daytime dim (100 lx) and bright (3000 lx) light. Concentration of transferin (negative proteins) under the influence of bright light during the daytime decreased significantly. Other proteins have the tendency to increase (positive proteins) under the influence of daytime bright light. The microheterogeneity of ACT did not change under the influence of different light intensities. Melatonin and rectal temperature were also measured simultaneously. Rectal temperature decreased to be lower during the first half of the night and urinary melatonin secretion rate increased to be higher during the night when the subjects spent time under the bright light during the day. Thus, it is concluded that the diurnal bright light exposure may activate some parameters of acute phase proteins, increase nocturnal melatonin secretion and accelerate a fall of rectal temperature during first half period of night sleep.     

Daily exercise facilitates phase delays of circadian melatonin rhythm in very dim light

Shift workers and transmeridian travelers are exposed to abnormal work-rest cycles, inducing a change in the phase relationship between the sleep-wake cycle and the endogenous circadian timing system. Misalignment of circadian phase is associated with sleep disruption and deterioration of alertness and cognitive performance. Exercise has been investigated as a behavioral countermeasure to facilitate circadian adaptation. In contrast to previous studies where results might have been confounded by ambient light exposure, this investigation was conducted under strictly controlled very dim light (standing approximately 0.65 lux; angle of gaze) conditions to minimize the phase-resetting effects of light. Eighteen young, fit males completed a 15-day randomized clinical trial in which circadian phase was measured in a constant routine before and after exposure to a week of nightly bouts of exercise or a nonexercise control condition after a 9-h delay in the sleep-wake schedule. Plasma samples collected every 30-60 min were analyzed for melatonin to determine circadian phase. Subjects who completed three 45-min bouts of cycle ergometry each night showed a significantly greater shift in the dim light melatonin onset (DLMO(25%)), dim light melatonin offset, and midpoint of the melatonin profile compared with nonexercising controls (Student t-test; P < 0.05). The magnitude of phase delay induced by the exercise intervention was significantly dependent on the relative timing of the exercise after the preintervention DLMO(25%) (r = -0.73, P < 0.05) such that the closer to the DLMO(25%), the greater the phase shift. These data suggest that exercise may help to facilitate circadian adaptation to schedules requiring a delay in the sleep-wake cycle.     

Effects of different light intensities during the forenoon on the afternoon thermal sensation in mild cold

1. 1. The study aimed at knowing whether thermal sensation during afternoon cool exposure could be influenced by bright light (4000 lx) or dim light (200 lx) in the forenoon.

2. 2. The subjects felt cooler after exposure to dim light than to bright light.

3. 3. Melatonin in the urine was significantly higher in bright light than in dim light at 10:30 h and at noon.

     

Suppression of nocturnal plasma melatonin and 6-sulphatoxymelatonin by bright and dim light in man

Previous studies have shown that bright light (2500 lux) suppresses nocturnal secretion of melatonin, while dim light (500 lux) has little or no effect. We have studied the effect of varying intensities of light on 5 normal male volunteers (age 18-28). The experiment was divided into 3 parts which took place at weekly intervals. Subjects remained under artificial light (fluorescent strip 150-250 lux) between 2000 h-2300 h, they then retired to bed in darkness. On each occasion, between 0030 h and 0100 h, the subjects were required to get up and were treated with light of different intensities; (a) less than 1 lux, (b) 300 lux and (c) 2500 lux respectively. Subjects returned to bed in darkness until 0700 h. Blood was sampled hourly from 2000 h-1000 h with additional samples at 2330 h, 0015 h, 0030 h, 0045 h, 0115 h and 0130 h. Plasma melatonin and 6-sulphatoxymelatonin (aMT6s), the major melatonin metabolite, were measured by radioimmunoassay. Dim (300 lux) and bright (2500 lux) light, both significantly suppressed melatonin levels compared to less than 1 lux (P less than 0.05 and P less than 0.01 respectively) at the following time points 0100 h, 0115 h and 0130 h. One subject did not show suppression with 300 lux. There was also a significant suppression of aMT6s levels, compared to less than 1 lux, after both 300 lux and 2500 lux at 0115 h (P less than 0.05, P less than 0.01), 0130 h (P less than 0.01, P less than 0.01) and 0200 h (P less than 0.01, P less than 0.001) respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

不同光照强度对兴安落叶松几种主要防御蛋白活力的影响

林木组成抗性对抵御害虫危害发挥着重要作用。为了研究环境因子对其组成抗虫性的影响,以兴安落叶松幼苗为试验材料,通过搭建遮阳棚设置3个光照强度(自然光照作为对照、50%和25%自然光照强度),模拟森林幼苗生长的林缘、林窗和林下3种不同的光环境,分析不同光照强度对其针叶内与植物抗虫性有关的几种主要防御蛋白活力的影响。研究结果表明,不同光照强度对针叶内主要防御蛋白活力有显著影响(P<0.05)。50%和25%光照强度下,POD、SOD、PAL、PPO和CI的活性显著高于自然光照下的(P<0.05),POD和CI的活性在50%光照强度下最高,SOD、PAL和PPO的活性在25%光照强度下最高;自然光照条件下CAT的活性显著高于50%和25%光照强度下的(P<0.05);遮荫处理对TI的活性有显著影响(P<0.05),但在不同月份中波动较大,规律性不明显。相同的光照强度条件下,主要防御蛋白活力在3个月中也有显著变化(P<0.05)。7月和8月份保护性酶POD和CAT的活性显著高于6月(P<0.05);防御性酶PAL、PPO以及蛋白酶抑制剂CI的活性在6月份最高。综合以上研究结果,光照可影响兴安落叶松针叶中几种主要防御蛋白活力,这也说明在较荫蔽的光照环境下,兴安落叶松有较强的抗性。其中SOD、CAT、PAL、PPO和POD是植物次生物质生成过程中的关键酶,其活性的改变在一定程度上表征着植物防御体系在变化。研究环境因子与植物防御之间的关系具有重要的理论和实际应用价值。     

不同光强下细胞外三磷酸腺苷对菜豆叶片光化学反应特性的影响

三磷酸腺苷(ATP)不但分布在细胞内部, 而且广泛存在于动物和植物细胞的细胞外基质中。细胞外ATP (eATP)可与细胞膜表面相应的受体结合并激发细胞内的第二信使, 从而调节细胞的多种生理学功能。但目前对于eATP是否也能对植物的光合作用产生影响则研究较少。该文以菜豆(Phaseolus vulgaris)叶片为实验材料, 研究了在不同光强下eATP对菜豆叶片叶绿素荧光特性和光合放氧速率的影响。结果显示, 随着光强的增加, 叶片的光适应下最大光化学效率(F_v′/F_m′)、光系统II (PSII)实际光化学效率(Y(II))、光化学猝灭系数(q_P)均呈现下降趋势, 而电子传递速率(ETR)、非光化学猝灭系数(q_N)以及调节性能量耗散的量子产量(Y(NPQ))随着光强的增加呈上升趋势。与对照相比, eATP的处理可以显著提高菜豆叶片PSII的潜在最大光化学效率(F_v/F_m)、Y(II)、q_P、ETR和光合放氧速率; 但eATP的处理对F_v′/F_m′、q_N以及Y(NPQ)没有显著影响。AMP-PCP (β,γ-亚甲基三磷酸腺苷, eATP细胞外受体的抑制剂)的处理显著降低了F_v/F_m、F_v′/F_m′、Y(II)、ETR和光合放氧速率, 同时也显著增加了q_N以及Y(NPQ)的水平。以上结果显示, 植物eATP水平的变化对植物光合作用的光化学反应有着重要的影响。     

Dim light melatonin onset in alcohol-dependent men and women compared with healthy controls

Sleep disturbances in alcohol-dependent (AD) individuals may persist despite abstinence from alcohol and can influence the course of the disorder. Although the mechanisms of sleep disturbances of AD are not well understood and some evidence suggests dysregulation of circadian rhythms, dim light melatonin onset (DLMO) has not previously been assessed in AD versus healthy control (HC) individuals in a sample that varied by sex and race. The authors assessed 52 AD participants (mean?±?SD age: 36.0?±?11.0 yrs of age, 10 women) who were 3-12 wks since their last drink (abstinence: 57.9?±?19.3 d) and 19 age- and sex-matched HCs (34.4?±?10.6 yrs, 5 women). Following a 23:00-06:00?h at-home sleep schedule for at least 5 d and screening/baseline nights in the sleep laboratory, participants underwent a 3-h extension of wakefulness (02:00?h bedtime) during which salivary melatonin samples were collected every 30?min beginning at 19:30?h. The time of DLMO was the primary measure of circadian physiology and was assessed with two commonly used methodologies. There was a slower rate of rise and lower maximal amplitude of the melatonin rhythm in the AD group. DLMO varied by the method used to derive it. Using 3 pg/mL as threshold, no significant differences were found between the AD and HC groups. Using 2 standard deviations above the mean of the first three samples, the DLMO in AD occurred significantly later, 21:02?±?00:41?h, than in HC, 20:44?±?00:21?h (t?=?-2.4, p?=?.02). Although melatonin in the AD group appears to have a slower rate of rise, using well-established criteria to assess the salivary DLMO did not reveal differences between AD and HC participants. Only when capturing melatonin when it is already rising was DLMO found to be significantly delayed by a mean 18?min in AD participants. Future circadian analyses on alcoholics should account for these methodological caveats.     

Photoacclimation characteristics of Sargassum thunbergii germlings under different light intensities

The photosynthesis and growth responses of Sargassum thunbergii germlings to different light intensities (10, 60, and 300 μmol photons m^?2 s^?1) were investigated. Maximum photochemical efficiency (F _v/F _m), rapid light curves (RLCs), and photochemical and non-photochemical quenching (qP and NPQ) were estimated by a pulse amplitude-modulated fluorometer. The photosynthesis of S. thunbergii germlings exhibited different properties to optimize light capture and utilization. The excitation pressure (1???qP) was rapidly increased to approximately 0.27 showing that germlings responded to high light by chronic photoinhibition with an accumulation of closed reaction centers, which ultimately resulted in a slow growth. This was accompanied by a reduced F _v/F _m with time and a development of high capacity for NPQ. Although F _v/F _m in moderate-light germlings did not fully recover overnight, germlings demonstrated a less severe chronic photoinhibition considering the reduced degree of excitation pressure accumulation of approximately 0.15. The relative stability of photosynthetic capacity (rETR_max, E _k, and α) could endow germlings with the highest relative growth rate (RGR) of approximately 9.3 % day^?1 in moderate light. By contrast, low-light germlings demonstrated high F _v/F _m and F _o, corresponding high α collectively suggested greater efficiency of light absorption and energy transformation. Sustained increases in electron transport capacity (rETR_max and E _k) occurred in low-light germlings, which resulted in a stable RGR of over 8.2 % day^?1. Consequently, S. thunbergii germlings are considered to prefer low light regimes and have a relative capacity of moderate and high light tolerance. However, the light acclimation to oversaturating conditions is at the cost of slow growth to maintain survival.     

Simulation of a nonphotochemical quenching in plant leaf under different light intensities

An analysis of photosynthetic response on action of stressors is an important problem, which can be solved by experimental and theoretical methods, including mathematical modeling of photosynthetic processes. The aim of our work was elaboration of a mathematical model, which simulated development of a nonphotochemical quenching under different light conditions. We analyzed two variants of the model: the first variant included a light-induced activation of the electron transport chain; in contrast, the second variant did not describe this activation. Both variants of the model described interactions between transitions from open reaction centers to closed ones (and vice versa) and development of the nonphotochemical quenching. Investigation of both variants of the model showed well qualitative and quantitative accordance between simulated and experimental changes in coefficient of the nophotochemical quenching which were analyzed under different light regimes: (i) the stepped increase of the light intensity without dark intervals between steps, (ii) periodical illuminations by different light intensities with constant durations which were separated by constant dark intervals, and (iii) periodical illuminations by the constant light intensity with different durations which were separated by different dark intervals. Thus, the model can be used for theoretical prediction of stress changes in photosynthesis under fluctuations in light intensity and search of optimal regimes of plant illumination.     

不同放牧强度对赛罕乌拉草原蜘蛛多样性的影响

蜘蛛作为草原生态系统中的主要消费者, 对维系草原生物多样性和生态系统功能具有重大意义。放牧是人类利用草原最普遍的方式, 了解放牧对蜘蛛多样性的影响具有重要生态学意义。本研究调查了内蒙古赛罕乌拉草原上5个不同放牧强度样地中的蜘蛛多样性, 通过单因素方差分析(one-way analysis of variance)比较各样地中的蜘蛛多样性, 非度量多维标度分析(non-metric multidimensional scale, NMDS)和相似性分析(analysis of similarities, ANOSIM)比较各样地间的蜘蛛物种组成相似性, 再结合相关性分析探讨了植被高度对蜘蛛多样性的影响。结果表明: 重度放牧强度样地的蜘蛛多样性显著低于其他未放牧及轻度放牧样地; 具体到常见科上, 放牧强度对织网型的园蛛物种数和个体数影响显著, 而对游猎型的狼蛛、跳蛛却不明显; 织网型蜘蛛主要受植被结构影响, 而游猎型蜘蛛更可能受潜在猎物可得性的影响。NMDS分析表明不同放牧强度下, 蜘蛛类群的物种组成呈现明显的梯度变化, 放牧强度越低, 物种组成和未放牧样地越相近。相关性分析表明草原植被高度与蜘蛛多样性总体上呈正相关关系, 即植被高度越高, 蜘蛛多样性越高。其中依靠植物构建蛛网的园蛛科和在植物上层伏击猎物的蟹蛛科、逍遥蛛科等与植被高度显著相关。这说明植物资源及其空间异质性可能对草原蜘蛛多样性起着主导作用。因此, 降低放牧强度有助于保护草原蜘蛛群落的多样性, 特别有利于织网型蜘蛛。     

Influence of different light intensities on the daily grooming distribution of common marmosets Callithrix jacchus

The daily distribution of autogrooming was evaluated in adult marmosets submitted to different illumination intensities in the light phase of the light-dark cycle. Autogrooming and locomotor activity were monitored and the faecal cortisol level assessed as a stress indicator. The distribution of autogrooming showed two distinct tendencies: when the light intensity varied from 500 to 200 lux, a slight increase in frequency and duration was observed, while a significant decrease in both variables occurred at 10 lux. Varying light intensities did not inhibit rhythm synchronization. The daily profile of autogrooming was mainly unimodal with an acrophase in the first half of the light phase. Faecal cortisol levels tended to increase in animals submitted to 100 and 10 lux, but these results are not conclusive. We suggest keeping captive marmosets in light intensities of at least 200 lux in the light phase, allowing animals to maintain autogrooming levels in order to reduce the discomfort caused by captivity and isolation.     

Stoichiometry of proton uptake in isolated pea chloroplasts under different light intensities

The number of protons released inside the chloroplast thylakoids per electron which is transferred through the electron transport chain (H⁺/e^– ratio) was measured in isolated pea chloroplasts at pH 6.0 under continuous illumination and with methyl viologen as an electron acceptor. At saturating light intensity (200 W · m^–2) (strong light) the H⁺/e^– ratio was 3. At low intensity (0.9 W · m^–2) (weak light) the H⁺/e^– ratio was 2 with dark-adapted chloroplasts, but it was close to 3 with chloroplasts that were preilluminated with strong light. It is shown that the presence of azide in the reaction mixture leads to errors in the determination of the H⁺/e^– ratio due to underestimation of the initial rate of H⁺ efflux on switching off the light. To explain the above data, we assume that transformation of the electron transport chain occurs during illumination with strong light, namely, the Q cycle becomes operative.