Polyphasic Wake/Sleep Episodes in the Fire Ant, Solenopsis Invicta

Sleep is a well-studied biological process in vertebrates, particularly birds and mammals. Less is know about sleep in solitary and social invertebrates, particularly the ants. This paper reports a study of light/dark periods on worker activity as well as sleep location, posture and the wake/sleep cycles of fire ant workers and queens located in an artificial nest chamber. Workers slept in one of three locations: on the ceiling, against the chamber wall or in the center of the chamber floor. Workers on the ceiling or against the chamber wall slept for longer periods than those at the center of the chamber floor where most grooming and feeding activity occurred. When sleeping, queens huddled together. Their close contact generated synchronized wake/sleep cycles with each other. Sleep posture was distinctly different than wake posture. During deep sleep, queens and workers folded their antennae and were non-responsive to contact by other ants. Another indicator of deep sleep was rapid antennal movement (RAM sleep). Sleep episodes were polyphasic. Queens averaged ~92 sleep episodes per day, each episode lasting ~6 min, for a total of ~9.4 h of sleep per day. Workers averaged ~253 sleep episodes lasting 1.1 min each for a total of ~4.8 h of sleep per day. Activity episodes were unaffected by light/dark periods. Workers were hypervigilant with an average of 80% of the labor force completing grooming, feeding or excavation tasks at any given time. These findings reinforce the parental exploitation hypothesis—sterile workers are a caste of disposable, short-lived helpers whose vigilance and hyperactivty increases the queen’s fitness by buffering her and her fertile offspring from environmental stresses.     

The effect of cataract surgery on salivary melatonin and sleep quality in aging people

Blue light plays an important role in circadian photoentrainment by stimulating the melanopsin-expressing photosensitive retinal ganglion cells. Age-related cataract causes progressive loss of blue light transmission, which may lead to changes in circadian rhythm and sleep quality. In theory, increased light transmission by cataract surgery may improve circadian misalignment and sleep quality, while the effect of cataract surgery on circadian rhythm is not well understood. In this study, we assessed 30 binocular age-related nuclear cataract patients (aged 72.5 ± 7.2, 16 female) who were eligible for cataract surgery. All the patients underwent phacoemulsification cataract extraction and neutral ultraviolet-only blocking intraocular lens (IOLs) implantation. Visual functions including best-corrected visual acuity (BCVA), color perception and dark adaptation were assessed. Salivary samples were collected at 1-hour interval from 19:00 to 23:00 48 hours before and after surgery. Salivary melatonin concentration was measured and dim light melatonin onset (DLMO) was calculated subsequently. Sleep quality and daytime alertness were assessed before and a month after surgery using Pittsburgh Sleep Quality Index (PSQI) and Epworth Sleepiness Scale (ESS). All the operated eyes demonstrated significant improvements in BCVA, color perception and dark adaptation after cataract surgery. Salivary melatonin concentration at 23:00 was significantly increased after surgery (P < 0.001). However, the average DLMO did not change significantly after surgery. In addition, PSQI and ESS scores were significantly decreased a month after surgery (P = 0.027, P < 0.001, respectively). In conclusion, cataract surgery promotes blue-light transmission; consequently, it may lead to the increase in nighttime melatonin concentration and improvement in sleep quality as well as daytime alertness.     

Clocks for the city: circadian differences between forest and city songbirds

To keep pace with progressing urbanization organisms must cope with extensive habitat change. Anthropogenic light and noise have modified differences between day and night, and may thereby interfere with circadian clocks. Urbanized species, such as birds, are known to advance their activity to early morning and night hours. We hypothesized that such modified activity patterns are reflected by properties of the endogenous circadian clock. Using automatic radio-telemetry, we tested this idea by comparing activity patterns of free-living forest and city European blackbirds (Turdus merula). We then recaptured the same individuals and recorded their activity under constant conditions. City birds started their activity earlier and had faster but less robust circadian oscillation of locomotor activity than forest conspecifics. Circadian period length predicted start of activity in the field, and this relationship was mainly explained by fast-paced and early-rising city birds. Although based on only two populations, our findings point to links between city life, chronotype and circadian phenotype in songbirds, and potentially in other organisms that colonize urban habitats, and highlight that urban environments can significantly modify biologically important rhythms in wild organisms.     

Light at night,clocks and health: from humans to wild organisms

The increasing use of electric lights has modified the natural light environment dramatically, posing novel challenges to both humans and wildlife. Indeed, several biomedical studies have linked artificial light at night to the disruption of circadian rhythms, with important consequences for human health, such as the increasing occurrence of metabolic syndromes, cancer and reduced immunity. In wild animals, light pollution is associated with changes in circadian behaviour, reproduction and predator–prey interactions, but we know little about the underlying physiological mechanisms and whether wild species suffer the same health problems as humans. In order to fill this gap, we advocate the need for integrating ecological studies in the field, with chronobiological approaches to identify and characterize pathways that may link temporal disruption caused by light at night and potential health and fitness consequences.     

Entrainment of A Free-Running Human with Bright Light?

The case of a 40-year-old sighted woman with free-running sleep-wake and melatonin rhythms is presented. The subject was studied for 102 days. During the pre-treatment period, both the sleep-wake and melatonin rhythms had a period of 25.1 hr, similar to the average period of humans living in temporal isolation. Treatment consisted of bright artifical light exposure (2500 lx Vita-Lite) for 2 hr each day upon awakening. Clock time of light exposure was held constant for 6 days and then slowly advanced until the subject was arising at her desired time of day. The subject continued the light treatment at home and was able to live on a 24-hr day for the 30-day follow-up study. While other factors may be operating in this situation, it is possible that the light treatment caused the stabilization of the free-running rhythms, advancement to a normal phase and entrainment to the 24-hr day. We suspect that the tendency to free-run was related to sleep onsets that were abnormally delayed relative to the circadian phase response curve for light. By scheduling a 2-hr pulse of bright light each morning, this tendency to delay would be counteracted by light-induced advances, resulting in normal entrainment.     

Circannual Variation of Cell Proliferation in Lymphoid Organs and Bone Marrow of Dbf1 Male Mice on Three Lighting Regimens

The case of a 40-year-old sighted woman with free-running sleep-wake and melatonin rhythms is presented. The subject was studied for 102 days. During the pre-treatment period, both the sleep-wake and melatonin rhythms had a period of 25.1 hr, similar to the average period of humans living in temporal isolation. Treatment consisted of bright artifical light exposure (2500 lx Vita-Lite) for 2 hr each day upon awakening. Clock time of light exposure was held constant for 6 days and then slowly advanced until the subject was arising at her desired time of day. The subject continued the light treatment at home and was able to live on a 24-hr day for the 30-day follow-up study. While other factors may be operating in this situation, it is possible that the light treatment caused the stabilization of the free-running rhythms, advancement to a normal phase and entrainment to the 24-hr day. We suspect that the tendency to free-run was related to sleep onsets that were abnormally delayed relative to the circadian phase response curve for light. By scheduling a 2-hr pulse of bright light each morning, this tendency to delay would be counteracted by light-induced advances, resulting in normal entrainment.     

Association between light exposure at night and insomnia in the general elderly population: The HEIJO-KYO cohort

Chronic circadian misalignment between the internal and environmental rhythms, which is typically related to night-shift work and clock-gene variants, is associated with disruption of suprachiasmatic nucleus function and increased risk of insomnia. Under controlled laboratory conditions, light at night (LAN) suppresses melatonin secretion, delays the internal biological rhythm, and reduces sleepiness. Therefore, LAN exposure may cause circadian misalignment and insomnia, though it remains unclear in real-life situations whether LAN exposure is associated with insomnia. To evaluate an association between LAN exposure and sleep quality in home settings, we conducted a cross-sectional community-based study in 857 elderly individuals (mean age, 72.2 years). We evaluated bedroom light intensity using a light meter and subjectively and objectively measured sleep quality using the Pittsburgh Sleep Quality Index and an actigraph, respectively, along with urinary 6-sulfatoxymelatonin excretion. Compared with the lowest quartile group of LAN intensity, the highest quartile group revealed a significantly higher odds ratio (OR) for subjective insomnia in a multivariate model adjusted for age, gender, body mass index, daytime physical activity, urinary 6-sulfatoxymelatonin excretion, bedtime, rising time, and day length (adjusted OR, 1.61, 95% confidence interval, 1.05–2.45, p?=?0.029). In addition, higher OR for subjective insomnia was significantly associated with the increase in quartiles of LAN intensity (p_trend?=?0.043). Consistently, we observed significant association trends between the increase in quartiles of LAN intensity and poorer actigraphic sleep quality, including decreased sleep efficiency, prolonged sleep-onset latency, increased wake-after-sleep onset, shortened total sleep time, and delayed sleep-mid time in multivariate models adjusted for the covariates mentioned above (all p_trend?<?0.001). In conclusion, we demonstrated that LAN exposure in home settings is significantly associated with both subjectively and objectively measured sleep quality in a community-based elderly population.     

A prospective study of delayed sleep phase syndrome in patients with severe resistant obsessive-compulsive disorder

There have been relatively few studies examining sleep in patients withobsessive-compulsive disorder (OCD) and these have produced contradictoryfindings. A recent retrospective study identified a possible association betweenOCD and a circadian rhythm sleep disorder known as delayed sleep phase syndrome(DSPS). Patients with this pattern of sleeping go to bed and get up much laterthan normal. They are unable to shift their sleep to an earlier time and,as a result, suffer considerable disruption to social and occupational functioning.In this study, we examined the sleep of patients with OCD prospectively. Weaimed to establish the frequency of DSPS in this population and any associatedclinical or demographic factors which might be implicated in its aetiology.     

Effects of a chronic reduction of short-wavelength light input on melatonin and sleep patterns in humans: Evidence for adaptation

Light is an important environmental stimulus for the entrainment of the circadian clock and for increasing alertness. The intrinsically photosensitive ganglion cells in the retina play an important role in transferring this light information to the circadian system and they are elicited in particular by short-wavelength light. Exposure to short wavelengths is reduced, for instance, in elderly people due to yellowing of the ocular lenses. This reduction may be involved in the disrupted circadian rhythms observed in aged subjects. Here, we tested the effects of reduced blue light exposure in young healthy subjects (n?=?15) by using soft orange contact lenses (SOCL). We showed (as expected) that a reduction in the melatonin suppressing effect of light is observed when subjects wear the SOCL. However, after chronic exposure to reduced (short wavelength) light for two consecutive weeks we observed an increase in sensitivity of the melatonin suppression response. The response normalized as if it took place under a polychromatic light pulse. No differences were found in the dim light melatonin onset or in the amplitude of the melatonin rhythms after chronic reduced blue light exposure. The effects on sleep parameters were limited. Our results demonstrate that the non-visual light system of healthy young subjects is capable of adapting to changes in the spectral composition of environmental light exposure. The present results emphasize the importance of considering not only the short-term effects of changes in environmental light characteristics.     

时间生物学—2017年诺贝尔生理或医学奖解读

时间生物学主要研究生物节律的产生及生物钟的运行机制,2017年诺贝尔生理或医学奖的颁布再次引发人们对该领域诸多科学问题的高度关注。生物钟与日月运行引起的环境信号周期性保持同步,有利于生物节律的相位和组织稳态的精确维持。本文介绍了生物节律现象的早期研究及随后生物钟理论体系建立的发展简史,并结合2017年诺贝尔生理或医学奖的解读阐述了果蝇生物钟基因的发现与分子调控机理,进而简单归纳当前时间生物学领域的前沿科学问题,阐明生物钟研究的意义。     

Plasticity of diel and circadian activity rhythms in fishes

In many fish species, some individuals arediurnal while others are nocturnal. Sometimes,the same individual can be diurnal at first andthen switch to nocturnalism, or vice-versa.This review examines the factors that areassociated with such plasticity. It covers thebreakdown of activity rhythms during migration,spawning, and the parental phase; reversals ofactivity patterns during ontogeny or from oneseason to the next; effects of light intensity,temperature, predation risk, shoal size, foodavailability, and intraspecific competition.Case studies featuring goldfish (Carassiusauratus), golden shiner (Notemigonuscrysoleucas), lake chub (Couesiusplumbeus), salmonids, sea bass (Dicentrarchus labrax), and parentalsticklebacks and cichlids illustrate some ofthese influences. It is argued that mostspecies have a circadian system but that havingsuch a system does not necessarily imply strictdiurnalism or nocturnalism. Rigidity ofactivity phase seems more common in species,mostly marine, that display behavioral sleep,and for these animals the circadian clock canhelp maintain the integrity of the sleepperiod and ensure that its occurrence takes place atthat time of day to which the animal's sensoryequipment is not as well adapted. However, inother fishes, mostly from freshwater habitats,the circadian clock seems to be used mainly foranticipation of daily events such as thearrival of day, night, or food, and possiblyfor other abilities such as time-place learningand sun compass orientation, rather than forstrict control of activity phase. In thesespecies, various considerations relating toforaging success and predation risk maydetermine whether the animal is diurnal ornocturnal at any particular time and place.     

Animal activity around the clock with no overt circadian rhythms: patterns,mechanisms and adaptive value

Circadian rhythms are ubiquitous in many organisms. Animals that are forced to be active around the clock typically show reduced performance, health and survival. Nevertheless, we review evidence of animals showing prolonged intervals of activity with attenuated or nil overt circadian rhythms and no apparent ill effects. We show that around-the-clock and ultradian activity patterns are more common than is generally appreciated, particularly in herbivores, in animals inhabiting polar regions and habitats with constant physical environments, in animals during specific life-history stages (such as migration or reproduction), and in highly social animals. The underlying mechanisms are diverse, but studies suggest that some circadian pacemakers continue to measure time in animals active around the clock. The prevalence of around-the-clock activity in diverse animals and habitats, and an apparent diversity of underlying mechanisms, are consistent with convergent evolution. We suggest that the basic organizational principles of the circadian system and its complexity encompass the potential for chronobiological plasticity. There may be trade-offs between benefits of persistent daily rhythms versus plasticity, which for reasons still poorly understood make overt daily arrhythmicity functionally adaptive only in selected habitats and for selected lifestyles.     

Phenotypic effects of genetic variability in human clock genes on circadian and sleep parameters

Circadian rhythms and sleep are two separate but intimately related processes. Circadian rhythms are generated through the precisely controlled, cyclic expression of a number of genes designated clock genes. Genetic variability in these genes has been associated with a number of phenotypic differences in circadian as well as sleep parameters, both in mouse models and in humans. Diurnal preferences as determined by the selfreported Horne-Östberg (HÖ) questionnaire, has been associated with polymorphisms in the human genes CLOCK, PER1, PER2 and PER3. Circadian rhythm-related sleep disorders have also been associated with mutations and polymorphisms in clock genes, with the advanced type cosegrating in an autosomal dominant inheritance pattern with mutations in the genes PER2 and CSNK1D, and the delayed type associating without discernible Mendelian inheritance with polymorphisms in CLOCK and PER3. Several mouse models of clock gene null alleles have been demonstrated to have affected sleep homeostasis. Recent findings have shown that the variable number tandem polymorphism in PER3, previously linked to diurnal preference, has profound effects on sleep homeostasis and cognitive performance following sleep loss, confirming the close association between the processes of circadian rhythms and sleep at the genetic level.