REM sleep, energy balance and ‘optimal foraging’

Starvation-induced sleep suppression requires the Drosophila brain nutrient sensor

Animals increase their locomotion activity and reduce sleep duration under starved conditions. This suggests that sleep and metabolic status are closely interconnected. The nutrient and hunger sensors in the Drosophila brain, including diuretic hormone 44 (DH44)-, CN-, and cupcake-expressing neurons, detect circulating glucose levels in the internal milieu, regulate the insulin and glucagon secretion and promote food consumption. Food deprivation is known to reduce sleep duration, but a potential role mediated by the nutrient and hunger sensors in regulating sleep and locomotion activity remains unclear. Here, we show that DH44 neurons are involved in regulating starvation-induced sleep suppression, but CN neurons or cupcake neurons may not be involved in regulating starvation-induced sleep suppression or baseline sleep patterns. Inactivation of DH44 neurons resulted in normal daily sleep durations and patterns under fed conditions, whereas it ablated sleep reduction under starved conditions. Inactivation of CN neurons or cupcake neurons, which were proposed to be nutrient and hunger sensors in the fly brain, did not affect sleep patterns under both fed and starved conditions. We propose that the glucose-sensing DH44 neurons play an important role in mediating starvation-induced sleep reduction.

The subthalamic corticotropin-releasing hormone neurons mediate adaptive REM-sleep responses to threat

When an animal faces a threatening situation while asleep, rapid arousal is the essential prerequisite for an adequate response. Here, we find that predator stimuli induce immediate arousal from REM sleep compared with NREM sleep. Using in vivo neural activity recording and cell-type-specific manipulations, we identify neurons in the medial subthalamic nucleus (mSTN) expressing corticotropin-releasing hormone (CRH) that mediate arousal and defensive responses to acute predator threats received through multiple sensory modalities across REM sleep and wakefulness. We observe involvement of the same neurons in the normal regulation of REM sleep and the adaptive increase in REM sleep induced by sustained predator stress. Projections to the lateral globus pallidus (LGP) are the effector pathway for the threat-coping responses and REM-sleep expression. Together, our findings suggest adaptive REM-sleep responses could be protective against threats and uncover a critical component of the neural circuitry at their basis.

How REM sleep shapes hypothalamic computations for feeding behavior

The electrical activity of diverse brain cells is modulated across states of vigilance, namely wakefulness, non-rapid eye movement (NREM) sleep, and rapid eye movement (REM) sleep. Enhanced activity of neuronal circuits during NREM sleep impacts on subsequent awake behaviors, yet the significance of their activation, or lack thereof, during REM sleep remains unclear. This review focuses on feeding-promoting cells in the lateral hypothalamus (LH) that express the vesicular GABA and glycine transporter (vgat) as a model to further understand the impact of REM sleep on neural encoding of goal-directed behavior. It emphasizes both spatial and temporal aspects of hypothalamic cell dynamics across awake behaviors and REM sleep, and discusses a role for REM sleep in brain plasticity underlying energy homeostasis and behavioral optimization.

Sleep debt induces skeletal muscle injuries in athletes: A promising hypothesis

Sleep is a physiological state and it is fundamental for physical and cognitive recovery of athletes. Due to strenuous training and competitions, athletes may present sleep complaints compromising good quality and quantity of sleep. Studies have related sleep debt to the occurrence of musculoskeletal injuries in athletes, but the mechanisms that can lead to this are not entirely clear. Studies involving animals and humans have shown that poor sleep quality can cause significant changes in hormones and cytokines. Demonstrating that this hormones changes lead to a decrease of testosterone and growth hormone levels and increased cortisol levels, important hormones in the process of protein synthesis and degradation. In athletes, the sport itself is a risk factor of injuries, and sleep debt may result in overtraining syndrome associated with inflammatory markers and ultimately to immune system dysfunction. Thus, we hypothesize that athletes who have sleep debt are more susceptible to musculoskeletal injuries due to increased catabolic pathway signaling, i.e. protein degradation and decreased anabolic pathway signaling, compromising muscle integrity. In this sense, we indicate the relationship between musculoskeletal injuries and sleep debt involving new targets for immunological signaling pathways that start the reduction of the muscle recovery process.

Sleep debt: the impact of weekday sleep deprivation on cardiovascular health in older women

STUDY OBJECTIVES

Short sleep duration is associated with increased cardiovascular disease (CVD) risk. However, it is uncertain whether sleep debt, a measure of sleep deficiency during the week compared to the weekend, confers increased cardiovascular risk. Because sleep disturbances increase with age particularly in women, we examined the relationship between sleep debt and ideal cardiovascular health (ICH) in older women.

METHODS

Sleep debt is defined as the difference between self-reported total weekday and weekend sleep hours of at least 2 hours among women without apparent CVD and cancer participating in the Women's Health Stress Study follow-up cohort of female health professionals (N = 22 082). The ICH consisted of seven health factors and behaviors as defined by the American Heart Association Strategic 2020 goals including body mass index, smoking, physical activity, diet, blood pressure, total cholesterol, and glucose.

RESULTS

Mean age was 72.1 ± 6.0 years. Compared to women with no sleep debt, women with sleep debt were more likely to be obese and have hypertension (pall < .05). Linear regression models adjusted for age and race/ethnicity revealed that sleep debt was significantly associated with poorer ICH (B = -0.13 [95% CI = -0.18 to -0.08]). The relationship was attenuated but remained significant after adjustment for education, income, depression/anxiety, cumulative stress, and snoring.

CONCLUSION

Sleep debt was associated with poorer ICH, despite taking into account socioeconomic status and psychosocial factors. These results suggest that weekly sleep duration variation, possibly leading to circadian misalignment, may be associated with cardiovascular risk in older women.

What Is REM Sleep?

For many decades, sleep researchers have sought to determine which species 'have' rapid eye movement (REM) sleep. In doing so, they relied predominantly on a template derived from the expression of REM sleep in the adults of a small number of mammalian species. Here, we argue for a different approach that focuses less on a binary decision about haves and have nots, and more on the diverse expression of REM sleep components over development and across species. By focusing on the components of REM sleep and discouraging continued reliance on a restricted template, we aim to promote a richer and more biologically grounded developmental-comparative approach that spans behavioral, physiological, neural, and ecological domains.

Neurotropic and modulatory effects of insulin-like growth factor II in Aplysia

Insulin-like growth factor II (IGF2) enhances memory in rodents via the mannose-6-phosphate receptor (M6PR), but the underlying mechanisms remain poorly understood. We found that human IGF2 produces an enhancement of both synaptic transmission and neurite outgrowth in the marine mollusk Aplysia californica. These findings were unexpected since Aplysia lack the mammal-specific affinity between insulin-like ligands and M6PR. Surprisingly, this effect was observed in parallel with a suppression of neuronal excitability in a well-understood circuit that supports several temporally and mechanistically distinct forms of memory in the defensive withdrawal reflex, suggesting functional coordination between excitability and memory formation. We hypothesize that these effects represent behavioral adaptations to feeding that are mediated by the endogenous Aplysia insulin-like system. Indeed, the exogenous application of a single recombinant insulin-like peptide cloned from the Aplysia CNS cDNA replicated both the enhancement of synaptic transmission, the reduction of excitability, and promoted clearance of glucose from the hemolymph, a hallmark of bona fide insulin action.

Sleeping oxygen saturation, rapid eye movement sleep, and the adaptation of postprandial metabolic function in insulin sensitive and resistant individuals without diabetes

AIMS

Sleeping oxygen saturation (SaO₂) and sleep stage duration have been linked with prediabetic alterations but the pathogenic pathways are not well understood. This study of insulin sensitive and resistant adults examined the effect on postprandial metabolic regulation of repeated mixed-meal challenges of different carbohydrate loading. The aim was to examine whether the relationship between lower sleeping oxygen saturation (SaO₂) and poorer fasting and postprandial metabolic function may be linked with reduced slow wave sleep (SWS) and rapid eye movement (REM) duration, independent of age, sex and total adiposity.

METHODS

The 24 men and women, aged 25-54 years, had no diabetes or other diagnosed conditions, were evaluated with polysomnography to derive indices of SaO₂ and sleep architecture. In addition, an OGTT and two 14-h serial mixed-meal tests were administered over 3 successive in-patient days. The carbohydrate content of the mixed-meals was manipulated to compare a standard-load day with a double-load day (300 vs. 600 kcal/meal). Quantitative modeling was applied to derive β-cell glucose sensitivity (β-GS), early insulin secretion rate sensitivity (ESRS), and total postprandial insulinemia (AUC_INS).

RESULTS

Analyses showed that, for the 14-h tests, the SaO₂ relationship with metabolic outcomes was associated significantly with percent time spent in REM but not SWS, independent of age, sex and total adiposity. Specifically, indirect pathways indicated that lower SaO₂ was related to shorter REM duration, and shorter REM was respectively associated with higher β-GS, ESRS, and AUC_INS for the 300- and 600-load days (300 kcal/meal: β = -8.68, p < .03, β = -8.54, p < .002, and β = -10.06, p < .008; 600 kcal/meal: β = -11.45, p < .003, β = -11.44, p < .001, and β = -11.00, p < .03).

CONCLUSION

Sleeping oxygen desaturation and diminished REM duration are associated with a metabolic pattern that reflects a compensatory adaptation of postprandial insulin metabolism accompanying preclinical diabetic risk.

The lateral line confers evolutionarily derived sleep loss in the Mexican cavefish

Sleep is an essential behavior exhibited by nearly all animals, and disruption of this process is associated with an array of physiological and behavioral deficits. Sleep is defined by changes in sensory gating that reduce sensory input to the brain, but little is known about the neural basis for interactions between sleep and sensory processing. Blind Mexican cavefish comprise an extant surface dwelling form and 29 cave morphs that have independently evolved increased numbers of mechanoreceptive lateral line neuromasts and convergent evolution of sleep loss. Ablation of the lateral line enhanced sleep in the Pachón cavefish population, suggesting that heightened sensory input underlies evolutionarily derived sleep loss. Targeted lateral line ablation and behavioral analysis localized the wake-promoting neuromasts in Pachón cavefish to superficial neuromasts of the trunk and cranial regions. Strikingly, lateral line ablation did not affect sleep in four other cavefish populations, suggesting that distinct neural mechanisms regulate the evolution of sleep loss in independently derived cavefish populations. Cavefish are subject to seasonal changes in food availability, raising the possibility that sensory modulation of sleep is influenced by metabolic state. We found that starvation promotes sleep in Pachón cavefish, and is not enhanced by lateral line ablation, suggesting that functional interactions occur between sensory and metabolic regulation of sleep. Taken together, these findings support a model where sensory processing contributes to evolutionarily derived changes in sleep that are modulated in accordance with food availability.

The enigma of sleep

Sleep has a critical role in promoting and maintaining neurological health and organismal homeostasis. Research over the past 135 years has brought significant understanding on various aspects of sleep biology; however, many questions still remain around the role and function of sleep. Sleep clearly has a powerful influence on infectious disease, cardiovascular health and neurological disorders. During the modern age, the majority of investigation into sleep has focused on identifying the biological factors underlying the effect of sleep on various pathological conditions. Disorders of sleep have the power to affect neuroimmunity, cognition and the development of neurological disorders such as Alzheimer's and autism. This present short review will highlight these factors affecting sleep.

Metabolic disturbances: role of the circadian timing system and sleep

The incidence of metabolic disorders such as obesity and diabetes is on the rise, and food quality is not alone to blame. Sleep disturbances, altered feeding time and circadian disruption are linked to metabolic disturbances in many clinical research studies and cross-sectional analyses. This review tried to summarize the role of the circadian timing system and sleep on energy and metabolic homeostasis. We also tried to explain the molecular and endocrine mechanisms behind circadian misalignment and sleep disorders that lead to metabolic disorders.

Nocturnal Hot Flashes: Relationship to Objective Awakenings and Sleep Stage Transitions

STUDY OBJECTIVES

While women report sleep interruption secondary to nighttime hot flashes, the sleep disrupting impact of nocturnal hot flashes (HF) is not well characterized. We utilized a model of induced HF to investigate the relationship of nighttime HF to sleep architecture and sleep-stage transitions.

METHODS

Twenty-eight healthy, premenopausal volunteers received the depot gonadotropin-releasing hormone agonist (GnRHa) leuprolide to rapidly induce menopause, manifesting with HF. Sleep disruption was measured on 2 polysomnograms conducted before and after 4-5 weeks on leuprolide, when HF had developed.

RESULTS

165 HF episodes were recorded objectively during 48 sleep studies (mean 3.4 HF/night). After standardizing to sleep-stage time distribution, the majority of HF were recorded during wake (51.0%) and stage N1 (18.8%). Sixty-six percent of HF occurred within 5 minutes of an awakening, with 80% occurring just before or during the awakening. Objective HF were not associated with sleep disruption as measured by increased transitions to wake or N1, but self-reported nocturnal HF correlated with an increase from pre- to post-leuprolide in the rate of transitions to wake (p = 0.01), and to N1 (p = 0.008).

CONCLUSIONS

By isolating the effect of HF on sleep in women without the confound of age-related sleep changes associated with natural menopause, this experimental model shows that HF arise most commonly during N1 and wake, typically preceding or occurring simultaneously with wake episodes. Perception of HF, but not objective HF, is linked to increased sleep-stage transitions, suggesting that sleep disruption increases awareness of and memory for nighttime HF events.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT01116401.

Human REM sleep: influence on feeding behaviour, with clinical implications

Rapid eye movement (REM) sleep shares many underlying mechanisms with wakefulness, to a much greater extent than does non-REM, especially those relating to feeding behaviours, appetite, curiosity, exploratory (locomotor) activities, as well as aspects of emotions, particularly 'fear extinction'. REM is most evident in infancy, thereafter declining in what seems to be a dispensable manner that largely reciprocates increasing wakefulness. However, human adults retain more REM than do other mammals, where for us it is most abundant during our usual final REM period (fREMP) of the night, nearing wakefulness. The case is made that our REM is unusual, and that (i) fREMP retains this 'dispensability', acting as a proxy for wakefulness, able to be forfeited (without REM rebound) and substituted by physical activity (locomotion) when pressures of wakefulness increase; (ii) REM's atonia (inhibited motor output) may be a proxy for this locomotion; (iii) our nocturnal sleep typically develops into a physiological fast, especially during fREMP, which is also an appetite suppressant; (iv) REM may have 'anti-obesity' properties, and that the loss of fREMP may well enhance appetite and contribute to weight gain ('overeating') in habitually short sleepers; (v) as we also select foods for their hedonic (emotional) values, REM may be integral to developing food preferences and dislikes; and (vii) REM seems to have wider influences in regulating energy balance in terms of exercise 'substitution' and energy (body heat) retention. Avenues for further research are proposed, linking REM with feeding behaviours, including eating disorders, and effects of REM-suppressant medications.

The impact of sleep disorders on glucose metabolism: endocrine and molecular mechanisms

Modern lifestyle has profoundly modified human sleep habits. Sleep duration has shortened over recent decades from 8 to 6.5 hours resulting in chronic sleep deprivation. Additionally, irregular sleep, shift work and travelling across time zones lead to disruption of circadian rhythms and asynchrony between the master hypothalamic clock and pacemakers in peripheral tissues. Furthermore, obstructive sleep apnea syndrome (OSA), which affects 4 - 15% of the population, is not only characterized by impaired sleep architecture but also by repetitive hemoglobin desaturations during sleep. Epidemiological studies have identified impaired sleep as an independent risk factor for all cause of-, as well as for cardiovascular, mortality/morbidity. More recently, sleep abnormalities were causally linked to impairments in glucose homeostasis, metabolic syndrome and Type 2 Diabetes Mellitus (T2DM). This review summarized current knowledge on the metabolic alterations associated with the most prevalent sleep disturbances, i.e. short sleep duration, shift work and OSA. We have focused on various endocrine and molecular mechanisms underlying the associations between inadequate sleep quality, quantity and timing with impaired glucose tolerance, insulin resistance and pancreatic β-cell dysfunction. Of these mechanisms, the role of the hypothalamic-pituitary-adrenal axis, circadian pacemakers in peripheral tissues, adipose tissue metabolism, sympathetic nervous system activation, oxidative stress and whole-body inflammation are discussed. Additionally, the impact of intermittent hypoxia and sleep fragmentation (key components of OSA) on intracellular signaling and metabolism in muscle, liver, fat and pancreas are also examined. In summary, this review provides endocrine and molecular explanations for the associations between common sleep disturbances and the pathogenesis of T2DM.

A new function of rapid eye movement sleep: improvement of muscular efficiency

Previously I demonstrated that the slow wave sleep (SWS) functioned to adjust the emotional balance disrupted by emotional memories randomly accumulated during waking, while the rapid eye movement (REM) sleep played the opposite role. Many experimental results have unambiguously shown that various emotional memories are processed during REM sleep. In this article, it is attempted to combine this confirmed function of REM sleep with the atonic state unique to REM sleep, and to integrate a new theory suggesting that improvement of muscular efficiency be a new function of REM sleep. This new function of REM sleep is more advantageous than the function of REM sleep in emotional memories and disinhibited drives to account for the phylogenetic variations of REM sleep, especially the absence of REM sleep in dolphins and short duration of REM sleep in birds in contrary to that in humans and rodents, the absence of penile erections in REM sleep in armadillo, as well as the higher voltage in EEG during REM sleep in platypus and ostrich. Besides, this new function of REM sleep is also advantageous to explain the association of REM sleep with the atonic episodes in SWS, the absence of drastic menopausal change in duration of REM sleep, and the effects of ambient temperature on the duration of REM sleep. These comparative and experimental evidences support the improvement of muscular efficiency as a new and major function of REM sleep.

The impact of sleep disorders on glucose metabolism: endocrine and molecular mechanisms

Modern lifestyle has profoundly modified human sleep habits. Sleep duration has shortened over recent decades from 8 to 6.5 hours resulting in chronic sleep deprivation. Additionally, irregular sleep, shift work and travelling across time zones lead to disruption of circadian rhythms and asynchrony between the master hypothalamic clock and pacemakers in peripheral tissues. Furthermore, obstructive sleep apnea syndrome (OSA), which affects 4 - 15% of the population, is not only characterized by impaired sleep architecture but also by repetitive hemoglobin desaturations during sleep. Epidemiological studies have identified impaired sleep as an independent risk factor for all cause of-, as well as for cardiovascular, mortality/morbidity. More recently, sleep abnormalities were causally linked to impairments in glucose homeostasis, metabolic syndrome and Type 2 Diabetes Mellitus (T2DM). This review summarized current knowledge on the metabolic alterations associated with the most prevalent sleep disturbances, i.e. short sleep duration, shift work and OSA. We have focused on various endocrine and molecular mechanisms underlying the associations between inadequate sleep quality, quantity and timing with impaired glucose tolerance, insulin resistance and pancreatic β-cell dysfunction. Of these mechanisms, the role of the hypothalamic-pituitary-adrenal axis, circadian pacemakers in peripheral tissues, adipose tissue metabolism, sympathetic nervous system activation, oxidative stress and whole-body inflammation are discussed. Additionally, the impact of intermittent hypoxia and sleep fragmentation (key components of OSA) on intracellular signaling and metabolism in muscle, liver, fat and pancreas are also examined. In summary, this review provides endocrine and molecular explanations for the associations between common sleep disturbances and the pathogenesis of T2DM.

Sleep, recovery, and metaregulation: explaining the benefits of sleep

A commonly held view is that extended wakefulness is causal for a broad spectrum of deleterious effects at molecular, cellular, network, physiological, psychological, and behavioral levels. Consequently, it is often presumed that sleep plays an active role in providing renormalization of the changes incurred during preceding waking. Not surprisingly, unequivocal empirical evidence supporting such a simple bi-directional interaction between waking and sleep is often limited or controversial. One difficulty is that, invariably, a constellation of many intricately interrelated factors, including the time of day, specific activities or behaviors during preceding waking, metabolic status and stress are present at the time of measurement, shaping the overall effect observed. In addition to this, although insufficient or disrupted sleep is thought to prevent efficient recovery of specific physiological variables, it is also often difficult to attribute specific changes to the lack of sleep proper. Furthermore, sleep is a complex phenomenon characterized by a multitude of processes, whose unique and distinct contributions to the purported functions of sleep are difficult to determine, because they are interrelated. Intensive research effort over the last decades has greatly progressed current understanding of the cellular and physiological processes underlying the regulation of vigilance states. Notably, it also highlighted the infinite complexity within both waking and sleep, and revealed a number of fundamental conceptual and technical obstacles that need to be overcome in order to fully understand these processes. A promising approach could be to view sleep not as an entity, which has specific function(s) and is subject to direct regulation, but as a manifestation of the process of metaregulation, which enables efficient moment-to-moment integration between internal and external factors, preceding history and current homeostatic needs.

Genetic dissection of sleep-metabolism interactions in the fruit fly

Dysregulation of sleep and metabolism has enormous health consequences. Sleep loss is linked to increased appetite and insulin insensitivity, and epidemiological studies link chronic sleep deprivation to obesity-related disorders including type II diabetes and cardiovascular disease. Interactions between sleep and metabolism involve the integration of signaling from brain regions regulating sleep, feeding, and metabolic function. Investigating the relationship between these processes provides a model to address more general questions of how the brain prioritizes homeostatically regulated behaviors. The availability of powerful genetic tools in the fruit fly, Drosophila melanogaster, allows for precise manipulation of neural function in freely behaving animals. There is a strong conservation of genes and neural circuit principles regulating sleep and metabolic function, and genetic screens in fruit flies have been effective in identifying novel regulators of these processes. Here, we review recent findings in the fruit fly that further our understanding of how the brain modulates sleep in accordance with metabolic state.

Altered regulation of sleep and feeding contributes to starvation resistance in Drosophila melanogaster

Animals respond to changes in food availability by adjusting sleep and foraging strategies to optimize their fitness. Wild populations of the fruit fly, Drosophila melanogaster, display highly variable levels of starvation resistance that are dependent on geographic location, food availability and evolutionary history. How behaviors that include sleep and feeding vary in Drosophila with increased starvation resistance is unclear. We have generated starvation-resistant flies through experimental evolution to investigate the relationship between foraging behaviors and starvation resistance. Outbred populations of D. melanogaster were selected for starvation resistance over 60 generations. This selection process resulted in flies with a threefold increase in total lipids that survive up to 18 days without food. We tested starvation-selected (S) flies for sleep and feeding behaviors to determine the effect that selection for starvation resistance has had on foraging behavior. Flies from three replicated starvation-selected populations displayed a dramatic reduction in feeding and prolonged sleep duration compared to fed control (F) populations, suggesting that modified sleep and feeding may contribute to starvation resistance. A prolonged larval developmental period contributes to the elevated energy stores present in starvation-selected flies. By preventing S larvae from feeding longer than F larvae, we were able to reduce energy stores in adult S flies to the levels seen in adult F flies, thus allowing us to control for energy storage levels. However, the reduction of energy stores in S flies fails to generate normal sleep and feeding behavior seen in F flies with similar energy stores. These findings suggest that the behavioral changes observed in S flies are due to genetic regulation of behavior rather than elevated lipid levels. Testing S-F hybrid individuals for both feeding and sleep revealed a lack of correlation between food consumption and sleep duration, indicating further independence in genetic factors underlying the sleep and feeding changes observed in S flies. Taken together, these findings provide evidence that starvation selection results in prolonged sleep and reduced feeding through a mechanism that is independent of elevated energy stores. These findings suggest that changes in both metabolic function and behavior contribute to the increase in starvation resistance seen in flies selected for starvation resistance.

Breakfast consumption and physical activity in adolescents: daily associations and hourly patterns

BACKGROUND

The association between breakfast consumption and physical activity (PA) is inconclusive.

OBJECTIVE

We aimed to investigate daily associations and hourly patterns of PA and breakfast consumption in British adolescents.

DESIGN

Daily PA [accelerometry-derived moderate and vigorous physical activity (MVPA)] and breakfast consumption (diet diary) were measured simultaneously over 4 d in 860 adolescents (boys: 43.4%; mean ± SD age: 14.5 ± 0.5 y). Associations between MVPA and breakfast consumption were assessed by using a multilevel mixed-effects logistic regression separately by sex and for weekends and weekdays. Hourly patterns of MVPA by breakfast consumption status were displayed graphically, and differences were tested by using ANOVA. Multilevel linear regression was used to investigate differences in log MVPA on days when 570 inconsistent breakfast consumers ate or skipped breakfast.

RESULTS

On weekends, boys and girls with higher MVPA were more likely to eat breakfast [OR (95% CI): boys, 1.78 (1.30, 2.45) (P < 0.001); girls, 2.30 (1.66, 3.08) (P < 0.001)] when adjusted for socioeconomic status, percentage of body fat, and total energy intake. Peak hourly MVPA differed for breakfast consumers compared with nonconsumers on weekends (P < 0.001). Inconsistent breakfast consumers did more MVPA on days when they ate breakfast [exponentiated β coefficients (95% CIs): 1.2 (1.0, 1.5) on weekdays and 1.4 (1.1, 1.8) on weekends for boys and 1.6 (1.3, 2.1) on weekends for girls; all P < 0.03].

CONCLUSIONS

Eating breakfast was associated with higher MVPA on weekends. The time of peak MVPA differed between breakfast consumers and nonconsumers on weekends. Breakfast consumption at weekends is worth additional investigation to potentially inform PA promotion in adolescents.

Exercise benefits for the aging brain depend on the accompanying cognitive load: insights from sleep electroencephalogram

Although exercise clearly offsets aging effects on the body, its benefits for the aging brain are likely to depend on the extent that physical activity (especially locomotion) facilitates multisensory encounters, curiosity, and interactions with novel environments; this is especially true for exploratory activity, which occupies much of wakefulness for most mammals in the wild. Cognition is inseparable from physical activity, with both interlinked to promote neuroplasticity and more successful brain aging. In these respects and for humans, exercising in a static, featureless, artificially lit indoor setting contrasts with exploratory outdoor walking within a novel environment during daylight. However, little is known about the comparative benefits for the aging brain of longer-term daily regimens of this latter nature including the role of sleep, to the extent that sleep enhances neuroplasticity as shown in short-term laboratory studies. More discerning analyses of sleep electroencephalogram (EEG) slow-wave activity especially 0.5-2-Hz activity would provide greater insights into use-dependent recovery processes during longer-term tracking of these regimens and complement slower changing waking neuropsychologic and resting functional magnetic resonance imaging (fMRI) measures, including those of the brain's default mode network. Although the limited research only points to ephemeral small sleep EEG effects of pure exercise, more enduring effects seem apparent when physical activity incorporates cognitive challenges. In terms of "use it or lose it," curiosity-driven "getting out and about," encountering, interacting with, and enjoying novel situations may well provide the brain with its real exercise, further reflected in changes to the dynamics of sleep.

Sleep architecture when sleeping at an unusual circadian time and associations with insulin sensitivity

Circadian misalignment affects total sleep time, but it may also affect sleep architecture. The objectives of this study were to examine intra-individual effects of circadian misalignment on sleep architecture and inter-individual relationships between sleep stages, cortisol levels and insulin sensitivity. Thirteen subjects (7 men, 6 women, age: 24.3±2.5 y; BMI: 23.6±1.7 kg/m²) stayed in a time blinded respiration chamber during three light-entrained circadian cycles (3x21h and 3x27h) resulting in a phase advance and a phase delay. Sleep was polysomnographically recorded. Blood and salivary samples were collected to determine glucose, insulin and cortisol concentrations. Intra-individually, a phase advance decreased rapid eye movement (REM) sleep and slow-wave sleep (SWS), increased time awake, decreased sleep and REM sleep latency compared to the 24h cycle. A phase delay increased REM sleep, decreased stage 2 sleep, increased time awake, decreased sleep and REM sleep latency compared to the 24h cycle. Moreover, circadian misalignment changed REM sleep distribution with a relatively shorter REM sleep during the second part of the night. Inter-individually, REM sleep was inversely associated with cortisol levels and HOMA-IR index. Circadian misalignment, both a phase advance and a phase delay, significantly changed sleep architecture and resulted in a shift in rem sleep. Inter-individually, shorter REM sleep during the second part of the night was associated with dysregulation of the HPA-axis and reduced insulin sensitivity.

TRIAL REGISTRATION

International Clinical Trials Registry Platform NTR2926 http://apps.who.int/trialsearch/

REM sleep phase preference in the crepuscular Octodon degus assessed by selective REM sleep deprivation

STUDY OBJECTIVES

To determine rapid eye movement (REM) sleep phase preference in a crepuscular mammal (Octodon degus) by challenging the specific REM sleep homeostatic response during the diurnal and nocturnal anticrepuscular rest phases.

DESIGN

We have investigated REM sleep rebound, recovery, and documented REM sleep propensity measures during and after diurnal and nocturnal selective REM sleep deprivations.

SUBJECTS

Nine male wild-captured O. degus prepared for polysomnographic recordings.

INTERVENTIONS

Animals were recorded during four consecutive baseline and two separate diurnal or nocturnal deprivation days, under a 12:12 light-dark schedule. Three-h selective REM sleep deprivations were performed, starting at midday (zeitgeber time 6) or midnight (zeitgeber time 18).

MEASUREMENTS AND RESULTS

Diurnal and nocturnal REM sleep deprivations provoked equivalent amounts of REM sleep debt, but a consistent REM sleep rebound was found only after nocturnal deprivation. The nocturnal rebound was characterized by a complete recovery of REM sleep associated with an augment in REM/total sleep time ratio and enhancement in REM sleep episode consolidation.

CONCLUSIONS

Our results support the notion that the circadian system actively promotes REM sleep. We propose that the sleep-wake cycle of O. degus is modulated by a chorus of circadian oscillators with a bimodal crepuscular modulation of arousal and a unimodal promotion of nocturnal REM sleep

Chronobiology, endocrinology, and energy- and food-reward homeostasis

Energy- and food-reward homeostasis is the essential component for maintaining energy balance and its disruption may lead to metabolic disorders, including obesity and diabetes. Circadian alignment, quality sleep and sleep architecture in relation to energy- and food-reward homeostasis are crucial. A reduced sleep duration, quality sleep and rapid-eye movement sleep affect substrate oxidation, leptin and ghrelin concentrations, sleeping metabolic rate, appetite, food reward, hypothalamic-pituitary-adrenal (HPA)-axis activity, and gut-peptide concentrations, enhancing a positive energy balance. Circadian misalignment affects sleep architecture and the glucose-insulin metabolism, substrate oxidation, homeostasis model assessment of insulin resistance (HOMA-IR) index, leptin concentrations and HPA-axis activity. Mood disorders such as depression occur; reduced dopaminergic neuronal signaling shows decreased food reward. A good sleep hygiene, together with circadian alignment of food intake, a regular meal frequency, and attention for protein intake or diets, contributes in curing sleep abnormalities and overweight/obesity features by preventing overeating; normalizing substrate oxidation, stress, insulin and glucose metabolism including HOMA-IR index, and leptin, GLP-1 concentrations, lipid metabolism, appetite, energy expenditure and substrate oxidation; and normalizing food reward. Synchrony between circadian and metabolic processes including meal patterns plays an important role in the regulation of energy balance and body-weight control. Additive effects of circadian alignment including meal patterns, sleep restoration, and protein diets in the treatment of overweight and obesity are suggested.

Alterations in sleep architecture in response to experimental sleep curtailment are associated with signs of positive energy balance

Sleep reduction is associated with increased energy intake and weight gain, though few studies have explored the relationship between sleep architecture and energy balance measures in the context of experimental sleep restriction. Fourteen males and 13 females (body mass index: 22-26 kg/m(2)) participated in a crossover sleep curtailment study. Participants were studied under two sleep conditions: short (4 h/night; 0100-0500 h) and habitual (9 h/night; 2200-0700 h), for 5 nights each. Sleep was polysomnographically recorded nightly. Outcome measures included resting metabolic rate (RMR), feelings of appetite-satiety, and ad libitum food intake. Short sleep resulted in reductions in stage 2 sleep and rapid eye movement (REM) sleep duration (P < 0.001), as well as decreased percentage of stage 2 sleep and REM sleep and increased slow wave sleep (SWS) percentage (P < 0.05). Linear mixed model analysis demonstrated a positive association between stage 2 sleep duration and RMR (P = 0.051). Inverse associations were observed between REM sleep duration and hunger (P = 0.031) and between stage 2 sleep duration and appetite for sweet (P = 0.015) and salty (P = 0.046) foods. Stage 2 sleep percentage was inversely related to energy consumed (P = 0.024). Stage 2 sleep (P = 0.005), SWS (P = 0.008), and REM sleep (P = 0.048) percentages were inversely related to fat intake, and SWS (P = 0.040) and REM sleep (P = 0.050) were inversely related to carbohydrate intake. This study demonstrates that changes in sleep architecture are associated with markers of positive energy balance and indicate a means by which exposure to short sleep duration and/or an altered sleep architecture profile may lead to excess weight gain over time.

Mio/dChREBP coordinately increases fat mass by regulating lipid synthesis and feeding behavior in Drosophila

During nutrient excess, triglycerides are synthesized and stored to provide energy during times of famine. The presence of high glucose leads to the activation of carbohydrate response element binding protein (ChREBP), a transcription factor that induces the expression of a number of glycolytic and lipogenic enzymes. ChREBP is expressed in major metabolic tissues and while we have a basic understanding of ChREBP function in liver, in vivo genetic systems to study the function of ChREBP in other tissues are lacking. In this study, we characterized the role of the Drosophila homolog of ChREBP, Mlx interactor (Mio), in controlling fat accumulation in larvae and adult flies. In Mio mutants, high sugar-induced lipogenic enzyme mRNA expression is blunted and lowering Mio levels specifically in the fat body using RNA interference leads to a lean phenotype. A lean phenotype is also observed when the gene bigmax, the fly homolog of ChREBP's binding partner Mlx, is decreased in the larval fat body. Interestingly, depleting Mio in the fat body results in decreased feeding providing a potential cause of the lowered triglycerides observed in these animals. However, Mio does not seem to function as a general regulator of hunger-induced behaviors as decreasing fat body Mio levels has no effect on sleep under fed or starved conditions. Together, these data implicate a role for Mio in controlling fat accumulation in Drosophila and suggests that it may act as a nutrient sensor in the fat body to coordinate feeding behavior with nutrient availability.

Interaction between sleep and metabolism in Drosophila with altered octopamine signaling

Sleep length and metabolic dysfunction are correlated, but the causal relationship between these processes is unclear. Octopamine promotes wakefulness in the fly by acting through the insulin-producing cells (IPCs) in the fly brain. To determine if insulin signaling mediates the effects of octopamine on sleep:wake behavior, we assayed flies in which insulin signaling activity was genetically altered. We found that increasing insulin signaling does not promote wake, nor does insulin appear to mediate the wake-promoting effects of octopamine. Octopamine also affects metabolism in invertebrate species, including, as we show here, Drosophila melanogaster. Triglycerides are decreased in mutants with compromised octopamine signaling and elevated in flies with increased activity of octopaminergic neurons. Interestingly, this effect is mediated at least partially by insulin, suggesting that effects of octopamine on metabolism are independent of its effects on sleep. We further investigated the relative contribution of metabolic and sleep phenotypes to the starvation response of flies with altered octopamine signaling. Hyperactivity (indicative of foraging) induced by starvation was elevated in octopamine receptor mutants, despite their high propensity for sleep, indicating that their metabolic state dictates their behavioral response under these conditions. Moreover, flies with increased octopamine signaling do not suppress sleep in response to starvation, even though they are normally hyper-aroused, most likely because of their high triglyceride levels. Together, these data suggest that observed correlations between sleep and metabolic phenotypes can result from shared molecular pathways rather than causality, and environmental conditions can lead to the dominance of one phenotype over the other.

Effects of sleep fragmentation on appetite and related hormone concentrations over 24 h in healthy men

In addition to short sleep duration, reduced sleep quality is also associated with appetite control. The present study examined the effect of sleep fragmentation, independent of sleep duration, on appetite profiles and 24 h profiles of hormones involved in energy balance regulation. A total of twelve healthy male subjects (age 23 (sd 4) years, BMI 24·4 (sd 1·9) kg/m²) completed a 24 h randomised crossover study in which sleep (23.30-07.30 hours) was either fragmented or non-fragmented. Polysomnography was used to determine rapid-eye movement (REM) sleep, slow-wave sleep (SWS) and total sleep time (TST). Blood samples were taken at baseline and continued hourly for the 24 h period to measure glucose, insulin, ghrelin, leptin, glucagon-like peptide 1 (GLP-1) and melatonin concentrations. In addition, salivary cortisol levels were measured. Visual analogue scales were used to score appetite-related feelings. Sleep fragmentation resulted in reduced REM sleep (69·4 min compared with 83·5 min; P< 0·05) and preservation of SWS without changes in TST. In fragmented v. non-fragmented sleep, glucose concentrations did not change, while insulin secretion was decreased in the morning, and increased in the afternoon (P< 0·05), and GLP-1 concentrations and fullness scores were lower (P< 0·05). After dinner, desire-to-eat ratings were higher after fragmented sleep (P< 0·05). A single night of fragmented sleep, resulting in reduced REM sleep, induced a shift in insulin concentrations, from being lower in the morning and higher in the afternoon, while GLP-1 concentrations and fullness scores were decreased. These results may lead to increased food intake and snacking, thus contributing to a positive energy balance.

Altered rest-activity patterns evolve via circadian independent mechanisms in cave adapted balitorid loaches

Circadian rhythms and rest homeostasis are independent processes, each regulating important components of rest-activity patterns. Evolutionarily, the two are distinct from one another; total rest time is maintained unaffected even when circadian pacemaker cells are ablated. Throughout the animal kingdom, there exists a huge variation in rest-activity patterns, yet it is unclear how these behaviors have evolved. Here we show that four species of balitorid cavefish have greatly reduced rest times in comparison to rest times of their surface relatives. All four cave species retained biological rhythmicity, and in three of the four there is a pronounced 24-hour rhythm; in the fourth there is an altered rhythmicity of 38-40 hours. Thus, consistent changes in total rest have evolved in these species independent of circadian rhythmicity. Taken together, our data suggest that consistent reduction in total rest times were accomplished evolutionarily through alterations in rest homeostasis.

Sleep in the rock hyrax, Procavia capensis

We investigated sleep in therock hyrax, Procavia capensis, a social mammal that typically lives in colonies on rocky outcrops throughout most parts of Southern Africa. The sleep of 5 wild-captured, adult rock hyraxes was recorded continuously for 72 h using telemetric relay of signals and allowing unimpeded movement. In addition to waking, slow wave sleep (SWS) and an unambiguous rapid eye movement (REM) state, a sleep state termed somnus innominatus (SI), characterized by low-voltage, high-frequency electroencephalogram, an electromyogram that stayed at the same amplitude as the preceding SWS episode and a mostly regular heart rate, were identified. If SI can be considered a form of low-voltage non-REM, the implication would be that the rock hyrax exhibits the lowest amount of REM recorded for any terrestrial mammal studied to date. Conversely, if SI is a form of REM sleep, it would lead to the classification of a novel subdivision of this state; however, further investigation would be required. The hyraxes spent on average 15.89 h (66.2%) of the time awake, 6.02 h (25.1%) in SWS, 43 min (3%) in SI and 6 min (0.4%) in REM. The unambiguous REM sleep amounts were on average less than 6 min/day. The most common state transition pathway in these animals was found to be wake → SWS → wake. No significant differences were noted with regard to total sleep time, number of episodes and episode duration for all states between the light and dark periods.Thus, prior classification of the rock hyrax as strongly diurnal does not appear to hold under controlled laboratory conditions.

Obesity and short sleep: unlikely bedfellows?

The link between habitual short sleep and obesity is critically examined from a sleep perspective. Sleep estimates are confounded by 'time in bed', naps; the normal distribution of sleep duration. Wide categorizations of 'short sleep', with claims that <7 h sleep is associated with obesity and morbidity, stem from generalizations from 5 h sleepers (<8% of adults) and acute restriction studies involving unendurable sleepiness. Statistically significant epidemiological findings are of questionable clinical concern, even for 5 h sleepers, as any weight gains accumulate slowly over years; easily redressed by e.g. short exercise exposures, contrasting with huge accumulations of 'lost' sleep. Little evidence supports 'more sleep', alone, as an effective treatment for obesity. Impaired sleep quality and quantity are surrogates for many physical and psychological disorders, as can be obesity. Advocating more sleep, in these respects, could invoke unwarranted use of sleep aids including hypnotics. Inadequate sleep in obese children is usually symptomatic of problems not overcome by increasing sleep alone. Interestingly, neuropeptides regulating interactions between sleep, locomotion and energy balance in normal weight individuals, are an avenue for investigation in some obese short sleepers. The real danger of inadequate sleep lies with excessive daytime sleepiness, not obesity.

Sleep duration and circulating adipokine levels

INTRODUCTION

Short sleep duration is associated with systemic inflammation and diabetes; however the mechanisms by which reduced sleep leads to these complications are unclear. One possibility is sleep may impact secretion of adipocyte derived hormones that regulate inflammation and insulin resistance. In this study we assessed the association between sleep duration and 3 adipokine levels.

METHODS

A total of 561 adults from the Cleveland Family Study underwent standardized laboratory polysomnography followed by a morning fasting blood draw assayed for leptin, visfatin, and retinol binding protein-4 (RBP4) levels.

RESULTS

The cohort had an age of 44.5 (16.1) years and total sleep time (TST) of 6.2 (1.3) hours (mean [SD]). Each hour reduction in TST was associated with a 10% increase in leptin (P = 0.01) and a 14% increase in visfatin levels (P = 0.03) in analyses adjusted for age, gender, and race. After additional adjustment for obesity, sleep apnea severity, hypertension, and diabetes, each hour reduction in TST was associated with a 6% increase in leptin (P = 0.01) and a 14% increase in visfatin levels (P = 0.02). Leptin increased by 15% (P = 0.01) and visfatin increased by 31% (P = 0.05) for every 1-h decrease in REM sleep. In contrast, no association between sleep duration and RBP4 was found.

CONCLUSIONS

Reduced sleep and reduced REM sleep are associated with elevations in leptin and visfatin, 2 adipokines associated with inflammation and insulin resistance. Further investigation of the effect of sleep on adipose tissue function should be pursued.

The end of sleep: 'sleep debt' versus biological adaptation of human sleep to waking needs

It is argued that the latter part of usual human sleep is phenotypically adaptable (without 'sleep debt') to habitual shortening or lengthening, according to environmental influences of light, safety, food availability and socio-economic factors, but without increasing daytime sleepiness. Pluripotent brain mechanisms linking sleep, hunger, foraging, locomotion and alertness, facilitate this time management, with REM acting as a 'buffer' between wakefulness and nonREM ('true') sleep. The adaptive sleep range is approximately 6-9h, although, a timely short (<20 min) nap can equate to 1h 'extra' nighttime sleep. Appraisal of recent epidemiological findings linking habitual sleep duration to mortality and morbidity points to nominal causal effects of sleep within this range. Statistical significance, here, may not equate to real clinical significance. Sleep durations outside 6-9h are usually surrogates of common underlying causes, with sleep associations taking years to develop. Manipulation of sleep, alone, is unlikely to overcome these health effects, and there are effective, rapid, non-sleep, behavioural countermeasures. Sleep can be taken for pleasure, with minimal sleepiness; such 'sleepability' is 'unmasked' by sleep-conducive situations. Sleep is not the only anodyne to sleepiness, but so is wakefulness, inasmuch that some sleepiness disappears when wakefulness becomes more challenging and eventful. A more ecological approach to sleep and sleepiness is advocated.

Clock and cycle limit starvation-induced sleep loss in Drosophila

Neural systems controlling the vital functions of sleep and feeding in mammals are tightly interconnected: sleep deprivation promotes feeding, whereas starvation suppresses sleep. Here we show that starvation in Drosophila potently suppresses sleep, suggesting that these two homeostatically regulated behaviors are also integrated in flies. The sleep-suppressing effect of starvation is independent of the mushroom bodies, a previously identified sleep locus in the fly brain, and therefore is regulated by distinct neural circuitry. The circadian clock genes Clock (Clk) and cycle (cyc) are critical for proper sleep suppression during starvation. However, the sleep suppression is independent of light cues and of circadian rhythms as shown by the fact that starved period mutants sleep like wild-type flies. By selectively targeting subpopulations of Clk-expressing neurons, we localize the observed sleep phenotype to the dorsally located circadian neurons. These findings show that Clk and cyc act during starvation to modulate the conflict of whether flies sleep or search for food.

Sleepiness as a need for sleep: when is enough, enough?

This review considers the relationship between sleep need and sleepiness. In healthy adults, objective measures of sleepiness (e.g. Multiple Sleep Latency Test; Psychomotor Vigilance Test) and subjective indices (e.g. Stanford Sleepiness Scale) often poorly inter-correlate and have been seen as orthogonal dimensions. This is perhaps not surprising as the methodology of these tests is quite different in, for example, their duration, testing environment, whether they are experimenter versus participant-paced, and the understanding and expectancy of participants. It is argued, here, that 'sleepiness', the 'propensity to fall asleep' and the 'need for sleep' are not synonymous, but qualitatively different. They may represent different positions on a dimension ranging from essential to non-essential sleep/sleepiness, and the position on this dimension is detected to varying extents by the different measures. As these tests can detect - and perhaps induce - levels of sleepiness which would be undetectable by, and of little concern to people under everyday situations, they can reveal a sleepiness having the potential to be misinterpreted as sleep debt.