Sleep in amphibians and reptiles: a review and a preliminary analysis of evolutionary patterns

Despite the ubiquitous nature of sleep, its functions remain a mystery. In an attempt to address this, many researchers have studied behavioural and electrophysiological phenomena associated with sleep in a diversity of animals. The great majority of vertebrates and invertebrates display a phase of immobility that could be considered as a sort of sleep. Terrestrial mammals and birds, both homeotherms, show two sleep states with distinct behavioural and electrophysiological features. However, whether these features have evolved independently in each clade or were inherited from a common ancestor remains unknown. Unfortunately, amphibians and reptiles, key taxa in understanding the evolution of sleep given their position at the base of the tetrapod and amniote tree, respectively, remain poorly studied in the context of sleep. This review presents an overview of what is known about sleep in amphibians and reptiles and uses the existing data to provide a preliminary analysis of the evolution of behavioural and electrophysiological features of sleep in amphibians and reptiles. We also discuss the problems associated with analysing existing data, as well as the difficulty in inferring homologies of sleep stages based on limited data in the context of an essentially mammalian‐centric definition of sleep. Finally, we highlight the importance of developing comparative approaches to sleep research that may benefit from the great diversity of species with different ecologies and morphologies in order to understand the evolution and functions of sleep.     

Shared and unique features of mammalian sleep spindles – insights from new and old animal models

Sleep spindles are phasic events observed in mammalian non-rapid eye movement sleep. They are relevant today in the study of memory consolidation, sleep quality, mental health and ageing. We argue that our advanced understanding of their mechanisms has not exhausted the utility and need for animal model work. This is both because some topics, like cognitive ageing, have not yet been addressed sufficiently in comparative efforts and because the evolutionary history of this oscillation is still poorly understood. Comparisons across species often are either limited to referencing the classical cat and rodent models, or are over-inclusive, uncritically including reports of sleep spindles in rarely studied animals. In this review, we discuss the emergence of new (dog and sheep) models for sleep spindles and compare the strengths and shortcomings of new and old models based on the three validation criteria for animal models – face, predictive, and construct validity. We conclude that an emphasis on cognitive ageing might dictate the future of comparative sleep spindle studies, a development that is already becoming visible in studies on dogs. Moreover, reconstructing the evolutionary history of sleep spindles will require more stringent criteria for their identification, across more species. In particular, a stronger emphasis on construct and predictive validity can help verify if spindle-like events in other species are actual sleep spindles. Work in accordance with such stricter validation suggests that sleep spindles display more universally shared features, like defining frequency, than previously thought.     

Solving the mystery of human sleep schedules one mutation at a time

Abstract

Sleep behavior remains one of the most enigmatic areas of life. The unanswered questions range from “why do we sleep?” to “how we can improve sleep in today’s society?” Identification of mutations responsible for altered circadian regulation of human sleep lead to unique opportunities for probing these territories. In this review, we summarize causative circadian mutations found from familial genetic studies to date. We also describe how these mutations mechanistically affect circadian function and lead to altered sleep behaviors, including shifted or shortening of sleep patterns. In addition, we discuss how the investigation of mutations can not only expand our understanding of the molecular mechanisms regulating the circadian clock and sleep duration, but also bridge the pathways between clock/sleep and other human physiological conditions and ailments such as metabolic regulation and migraine headaches.     

Proteomic analysis of the effects and interactions of sleep deprivation and aging in mouse cerebral cortex

The cellular and molecular processes that underlie the drives and functions of sleep have been the topic of many studies in the last few decades. Discovery-based techniques, such as cDNA microarrays, have increasingly been utilized in conjunction with sleep deprivation paradigms to examine the molecular mechanisms and functions of sleep. These studies have helped to validate and expand existing hypotheses, such as those on the roles of sleep in synaptic plasticity and in energy metabolism. The mechanisms underlying the highly prevalent changes in sleep architecture with age are not known, but likely reflect fundamental changes in the molecular basis of circadian timing and sleep homeostatic processes. We decided to explore the effects and interactions of sleep deprivation and aging utilizing the proteomic technique of difference in gel electrophoresis (DIGE). DIGE, which utilizes cyanine dye labeling of samples, allows for the comparison of multiple experimental groups within and across gels. In this study, we compared cerebral cortex tissue from young (2.5 months) and old (24 months) mice that had been sleep deprived for 6 h to tissue from undisturbed young and old control animals. Following DIGE, automatic image matching and spot identification, and statistical analysis, 43 unique proteins were identified. The proteins were grouped into seven functional classes based on published characteristics: cell signaling, cytoskeletal, energy metabolism, exocytosis, heat shock proteins, mRNA processing/trafficking, and serum proteins. The identity and characteristics of these proteins relevant to sleep and aging are discussed.     

Heat tolerance after total and partial acute sleep deprivation

Sleep deprivation (SD) is suggested to be associated with reduced thermo-regulatory functions. This study aimed to quantify the effect of partial (PSD) and total (TSD) 24?h SD using a standard heat tolerance test (HTT). Eleven participants underwent HTT after well-rested state, PSD and TSD. No significant physiological differences were found between the exposures but subjective discomfort was higher after TSD. Evening chronotypes' temperature during HTT was higher after TSD compared with PSD (p = 0.017). After TSD, evening chronotypes compared to intermediate chronotypes' temperature was higher during the first hour of the HTT (p?<?0.05), suggesting that thermo-regulatory function during exercise in the heat is influenced by chronotype.     

Sleep quality and duration following evening intake of alpha-lactalbumin: a pilot study#

Tryptophan loading enhances sleep quality by increasing the ratio of plasma tryptophan to large neutral amino acids (TRP:LNAA) and consequently synthesis and availability of serotonin in the brain. Alpha-lactalbulmin (A-LAC) is rich in tryptophan and has the highest TRP:LNAA of all protein sources. This pilot study investigated the effect of an evening intake of A-LAC on objective and subjective sleep measures in male subjects without sleep complaints. Ten healthy male university students (aged: 26.9 ± 5.3 years; BMI: 21.7 ± 1.9 kg.m^?2) participated in a double-blind, randomized, and placebo-controlled crossover counter-balanced study. Objective (actigraphy) and subjective (sleep log) sleep measures were recorded for two nights after a standardized evening meal supplemented with either A-LAC (20 g) or a placebo of sodium caseinate (20 g) one hour before bedtime. Evening A-LAC intake resulted in increased objective and subjective total sleep time by 12.8% (p = 0.037) and 10.8% (p = 0.013), respectively, compared to placebo. Objective sleep efficiency increased by 7.0% (p = 0.028) following A-LAC with no significant effects for other sleep indices. This pilot study demonstrates the efficacy of evening A-LAC intake on sleep quality in young healthy adults, however further large-scale studies are warranted to confirm the benefit.     

BEHAVIORAL ASPECTS OF SLEEP IN PACIFIC WHITE-SIDED DOLPHINS (LAGENORHYNCHUS OBLIQUIDENS,GILL 1865)1

Dolphin sleep is unlike typical mammalian sleep in that slow wave sleep occurs in one hemisphere at a time and rapid eye movement (REM) sleep is apparently reduced or absent (Mukhametov 1987). Lilly (1964) observed that bottlenose dolphins (Tursiops truncatus) sleep with one eye open and one eye closed and suggested that the open eye monitored the immediate area for predators. Mukhametov (1987) and Supin et al. (1978) found no physiological correlation between the active brain hemisphere and the open eye, and suggested that no sentinel function exists. I describe the behavioral and social aspects of sleep in a captive school of four Pacific white-sided dolphins (Lagenorhynchus obliquidens) at Long Marine Lab at the University of California at Santa Cruz for 32 nights. As the animals swam in formation, I recorded their positions and eye condition. Dolphins did not close their eyes or switch positions in the school randomly. While in formation, dolphins switched positions in bouts while concurrently changing eye condition. This resulted in a sleeping formation in which the dolphins likely had the eye open towards schoolmates, not toward the external environment. I suggest that this allows sleep to proceed while allowing dolphins to maintain visual contact with group members.     

基于Flexible ICA的睡眠EEG及EOG中心电伪差的消除

提出了一种采用自适应非线性函数的ICA学习算法,Flexible ICA算法,并将其应用于睡眠EEG自动分期的前期预处理中,用于消除采集到的各通道信号中的心电伪差.实验结果证明,Flexible ICA算法能够快速有效的消除各通道的心电伪差,为后期的睡眠EEG自动分期打下了良好的基础.     

Dim Light at Night Does Not Disrupt Timing or Quality of Sleep in Mice

Artificial nighttime illumination has recently become commonplace throughout the world; however, in common with other animals, humans have not evolved in the ecological context of chronic light at night. With prevailing evidence linking the circadian, endocrine, immune, and metabolic systems, understanding these relationships is important to understanding the etiology and progression of several diseases. To eliminate the covariate of sleep disruption in light at night studies, researchers often use nocturnal animals. However, the assumption that light at night does not affect sleep in nocturnal animals remains unspecified. To test the effects of light at night on sleep, we maintained Swiss-Webster mice in standard light/dark (LD) or dim light at night (DLAN) conditions for 8–10 wks and then measured electroencephalogram (EEG) and electromyogram (EMG) biopotentials via wireless telemetry over the course of two consecutive days to determine differences in sleep timing and homeostasis. Results show no statistical differences in total percent time, number of episodes, maximum or average episode durations in wake, slow-wave sleep (SWS), or rapid eye movement (REM) sleep. No differences were evident in SWS delta power, an index of sleep drive, between groups. Mice kept in DLAN conditions showed a relative increase in REM sleep during the first few hours after the dark/light transition. Both groups displayed normal 24-h circadian rhythms as measured by voluntary running wheel activity. Groups did not differ in body mass, but a marked negative correlation of body mass with percent time spent awake and a positive correlation of body mass with time spent in SWS was evident. Elevated body mass was also associated with shorter maximum wake episode durations, indicating heavier animals had more trouble remaining in the wake vigilance state for extended periods of time. Body mass did not correlate with activity levels, nor did activity levels correlate with time spent in different sleep states. These data indicate that heavier animals tend to sleep more, potentially contributing to further weight gain. We conclude that chronic DLAN exposure does not significantly affect sleep timing or homeostasis in mice, supporting the use of dim light with nocturnal rodents in chronobiology research to eliminate the possible covariate of sleep disruption.     

Effects of exercise with or without light exposure on sleep quality and hormone reponses

[Purpose]

The objectives of the present study were to determine the effect of sun exposure and aerobic exercise on quality of sleep and investigate sleep-related hormonal responses in college-aged males.

[Methods]

In this study, the cross-over design was utilized. The subjects (N = 10) without any physical problems or sleep disorders participated in the experimental performed 4 protocols in only sun exposure (for 30 minutes, EG1) protocol, only aerobic exercise (walking and jogging for 30 minutes, EG2) protocol, aerobic exercise with sun exposure (EG3) protocol, and control (no exercise and no sun exposure, EG4) protocol. Each protocol was 5 times per week with one-week break (wash-out period) between protocols to prevent the effects of the previous protocol. Total test period was should be 7 weeks (one week of protocol and one week of break). Before and after each aerobic exercise session, the subjects completed stretching to warm up for 5 to 10 minutes. Surveys consisting of (bedtime, wake-up time, sleep onset latency, and (Pittsburgh Sleep Quality Index (PSQI) were obtained before the test and after each protocol. After each protocol, the following sleep-related hormonal responses were measured: blood concentrations of melatonin, cortisol, epinephrine, and norepinephrine. One-way ANOVA was used to determine differences between protocols. Statistical significance was set at p < 0.05.

[Results]

Bedtime of EG4 was significantly later than that of the EG1 or EG3. Wake-up time in the EG4 was significantly later than that of the EG1 or the EG3. Sleep onset latency in the EG4 was longer than that of the EG3. The quality of sleep in the EG4 was lower than that of the EG3. Sleep cycle in the EG4 was significantly shorter than that of the EG1. Blood melatonin concentrations of the EG3 was significantly higher than that of the EG4. There were no significant differences in blood concentrations of cortisol, epinephrine, or norepinephrine among protocols, with the order from the lowest to the highest values of EG1 < EG2 < EG3 < EG4.

[Conclusion]

The present data found that EG1 and EG3 showed positive sleep-related hormonal responses, sleep habits, and quality of sleep, indicating that sun exposure or exercise with sun exposure may improve the physical status and quality of life.     

睡眠研究的科学前沿

关于睡眠机制的研究是一门历史悠久的学科.在过去的几十年中,运用细胞电生理学来研究睡眠取得了可喜的成果.由于种种技术上的困难,近年来该领域的研究多集中于临床和医学范围,例如嗜睡症、抑郁症等.虽说睡眠的节律性较易理解,但作为其本质———睡眠的基因和分子水平的自动平衡调节仍是一个谜.细胞因子(IL-1和TNFα)对睡眠的诱导作用已显示从分子水平上了解睡眠的可能性.到目前为止,关于睡眠的功能已有不少理论和假说,但人类对睡眠的生化机制的认识尚处于起步阶段.     

Bullying,sleep/wake patterns and subjective sleep disorders: Findings from a cross-sectional survey

The aim of this study was to explore: (a) sleep patterns and disorders possibly associated with adolescent bullying profiles (pure bully, pure victim, bully/victim and neutral) and (b) the effect of sleep on psychosocial problems (externalized and internalized) related to bullying. The sample consisted of 1422 students aged 10–18 (mean?=?14.3, SD?=?2.7; 57% male) from five socioeconomically diverse schools in France. Bullying profiles were obtained using the revised Bully–Victim Questionnaire. Subjective sleep disorders were assessed using the Athens Insomnia Scale. School-week and weekend sleep/wake patterns were recorded. Internalizing problems were investigated using a Perceived Social Disintegration Scale and a Psychological Distress Scale. Externalizing behaviors were assessed using a General Aggressiveness Scale and an Antisocial Behavior Scale. These questionnaires were administered during individual interviews at school. After controlling for effects of gender and age, victims of bullying showed significantly more subjective sleep disturbances than the pure-bully or neutral groups (p?<?0.001). Bullies’ sleep schedules were more irregular (p?<?0.001 for bedtime irregularity and p<0.01 for wake-up time irregularity) and their sleep duration was shorter than their schoolmates (p?<?0.001 for the school week and p?<?0.05 for the weekend). There was an effect of sleep on psychosocial problems related to bullying, and our results indicate that sleep has a moderating effect on aggression in bullies (p?<?0.001). This would suggest a higher vulnerability of bullies to sleep deprivation. These results show differences in sleep problems and patterns in school-bullying profiles. Findings of this study open up new perspectives for understanding and preventing bullying in schools, with implications for research and clinical applications.     

Comparison between paper and electronic sleep diary

This study aimed to test the concurrent validity of an electronic version (to run on tablet) of a sleep diary derived from the core Consensus Sleep Diary compared with the traditional paper and pencil version. To this end, 15 healthy volunteers (6 males; mean age 37.20 ± 17.55 years) every morning, for at least 7 consecutive days, filled both paper and electronic sleep diary. Furthermore, sleep was objectively assessed through actigraphy. With reference to all sleep parameters examined, no significant differences were observed between paper and electronic sleep diary. As expected, paper and electronic sleep diary showed the same poor agreement with actigraphic estimates of sleep quantity and sleep quality. On the basis of the present data, we can conclude that electronic sleep diary performs like paper sleep diary. Bearing in mind that electronic sleep diary presents several benefits in comparison to the paper sleep diary (e.g. avoiding of the “parking lot syndrome”, in which patient retrospectively completes more days at the same time; reducing the time for data entry and scoring), we suggest that, if the present findings will be confirmed also in clinical populations, electronic sleep diary should replace paper sleep diary in both research and clinical settings.     

Effects of Filtering Visual Short Wavelengths During Nocturnal Shiftwork on Sleep and Performance

Circadian phase resetting is sensitive to visual short wavelengths (450–480?nm). Selectively filtering this range of wavelengths may reduce circadian misalignment and sleep impairment during irregular light-dark schedules associated with shiftwork. We examined the effects of filtering short wavelengths (<480?nm) during night shifts on sleep and performance in nine nurses (five females and four males; mean age?±?SD: 31.3?±?4.6 yrs). Participants were randomized to receive filtered light (intervention) or standard indoor light (baseline) on night shifts. Nighttime sleep after two night shifts and daytime sleep in between two night shifts was assessed by polysomnography (PSG). In addition, salivary melatonin levels and alertness were assessed every 2?h on the first night shift of each study period and on the middle night of a run of three night shifts in each study period. Sleep and performance under baseline and intervention conditions were compared with daytime performance on the seventh day shift, and nighttime sleep following the seventh daytime shift (comparator). On the baseline night PSG, total sleep time (TST) (p?<?0.01) and sleep efficiency (p?=?0.01) were significantly decreased and intervening wake times (wake after sleep onset [WASO]) (p?=?0.04) were significantly increased in relation to the comparator night sleep. In contrast, under intervention, TST was increased by a mean of 40?min compared with baseline, WASO was reduced and sleep efficiency was increased to levels similar to the comparator night. Daytime sleep was significantly impaired under both baseline and intervention conditions. Salivary melatonin levels were significantly higher on the first (p?<?0.05) and middle (p?<?0.01) night shifts under intervention compared with baseline. Subjective sleepiness increased throughout the night under both conditions (p?<?0.01). However, reaction time and throughput on vigilance tests were similar to daytime performance under intervention but impaired under baseline on the first night shift. By the middle night shift, the difference in performance was no longer significant between day shift and either of the two night shift conditions, suggesting some adaptation to the night shift had occurred under baseline conditions. These results suggest that both daytime and nighttime sleep are adversely affected in rotating-shift workers and that filtering short wavelengths may be an approach to reduce sleep disruption and improve performance in rotating-shift workers. (Author correspondence: casper@lunenfeld.ca)     

Daytime naps can be used to supplement night-time sleep in athletes

ABSTRACT

This study examined the efficacy of daytime napping to supplement night-time sleep in athletes. Twelve well-trained male soccer players completed three conditions in a randomised, counterbalanced order: 9 h in bed overnight with no daytime nap (9 h + 0 h); 8 h in bed overnight with a 1-h daytime nap (8 h + 1 h); and 7 h in bed overnight with a 2-h daytime nap (7 h + 2 h). Sleep was assessed using polysomnography. The total amount of sleep obtained in the three conditions was similar, i.e. 8.1 h (9 h + 0 h), 8.2 h (8 h + 1 h), and 8.0 h (7 h + 2 h). Daytime napping may be an effective strategy to supplement athletes’ night-time sleep.     

Does a change in sleep timing increase testosterone in young adult men?

Men are more evening oriented than women. These sex difference might be a result of gonadal hormones, especially of testosterone. Here, we tested for a causal relationship by shifting the sleep timing of young men to one hour later and assessed the influence on saliva testosterone. 50 men participated in our study (31 experimental, 19 control group). Sleep timing was measured with actigraphy. One week served as baseline and afterwards, participants were randomly assigned to either the control or the experimental group. In the experimental group, men were asked to go to bed about one hour later and to sleep one hour longer in the morning. Participants in the control group experienced no significant changes in sleep timing. In the experimental group, participants went to bed later and woke up later; therefore, mid-point of sleep was shifted to a later time and sleep duration decreased, because he men went to bed about one hour later but woke up only about 30 min later. The control group experienced a decline in testosterone, but the experimental group not. Changes in mid-point of sleep between baseline week and experimental week were correlated with the change in testosterone (r = 0.285).     

Sleeping Dreams, Waking Hallucinations, and the Central Nervous System

Consciousness is now considered a primary function and activity of the brain itself. If so, consciousness is simply the brain's interpretation and integration of all the information made available to it at any given time. On the assumption that the brain is active across all states of being (wakefulness, REM sleep, and NREM sleep), this article proposes that dreaming and hallucinations represent variations on the same theme. Under usual circumstances during wakefulness, the brain ignores internally generated activity and attends to environmental sensory stimulation. During sleep, dreaming occurs because the brain attends to endogenously generated activity. In unusual settings, such as sleep-deprivation, sensory deprivation, or medication or drug ingestion, the brain attends to exogenous and endogenous activities simultaneously, resulting in hallucinations, or wakeful dreaming. This concept is supported by numerous neurologic conditions and syndromes that are associated with hallucinations.     

Toward an integrative theory of sleep and dreaming

Non-rapid-eye-movement sleep (NREMS) is triggered by the accumulation of adenosine, as a result of the perceptual overload of the brain cortex. NREMS starts in the most burdened regions of the cortex first and then eventually, after the released adenosine has reached the ventrolateral pre-optic nucleus area of the hypothalamus, triggers the "general NREMS pattern". This is accompanied by the usual familiar changes in the thalamocortical system. When NREMS reaches the slow-wave sleep (SWS) phase, with its predominant delta activity, brain metabolism drops significantly with the brain temperature, and this is recognized by the alarm system in the pre-optic anterior hypothalamus and/or the other thermostat circuit in the brainstem as a life-threatening situation. This alarm system triggers a reaction similar to abortive or partial awakening called rapid-eye-movement sleep (REMS), which is aimed at restoring the optimal body-core temperature. As soon as this restoration is accomplished by the activation of the brainstem-to-cortex ascending pathways, NREMS may continue, as may the interchange of the two sleep phases during the entire sleep period. During both NREMS and REMS, the same essential pattern occurs in the cortex: the loops "used" during the previous waking period, now deprived of external input, replay their waking activity at a lower frequency, one which enables them to restore the membrane's potential (possibly by means of LTD). During REMS, however, the cholinergic flood originating in the LTD/PPT nuclei of the pons tegmentum, increases in the basal forebrain and, provoking theta activity in the medial septum is extended to the hippocampus, causing the circuits that are active at that particular moment in the cortex, to store the information they carry as memory. This is the explanation of both the memory improvement known to be related to REMS and of dreams. Both phenomena are clearly side effects of REMS.