Decoupling of sleepiness from sleep time and intensity during chronic sleep restriction: evidence for a role of the adenosine system

Sleep Patterns, Eating Behavior and the Risk of Noncommunicable Diseases

Sleep is extremely important for the homeostasis of the organism. In recent years, various studies have been carried out to address factors related to sleep patterns and their influence on food choices, as well as on the onset of chronic noncommunicable diseases. The aim of this article is to provide a scientific literature review on the possible role of sleep patterns on eating behavior and the risk of noncommunicable diseases. A search was performed on Medline (PubMed interface) using several keywords (e.g., "Factors Influencing Sleep" OR "Sleep and Chronic Diseases"). Articles published between 2000 and the present date that relate sleep to cyclic metabolic processes and changes in eating behavior were selected. Changes in sleep patterns are increasingly detected today, and these modifications are mainly caused by work and lifestyle conditions as well as a growing dependence on electronic devices. Sleep deprivation and the resultant short sleep duration lead to an increased appetite via an increase in the hunger hormone (ghrelin) and a decrease in the satiety hormone (leptin). Nowadays, sleep is undervalued, and thus often impaired, with consequences for the performance of various body systems. Sleep deprivation alters physiological homeostasis and influences eating behavior as well as the onset of chronic diseases.

[Chronic sleep restriction in rats leads to a weakening of compensatory reactions in response to acute sleep deprivation]

OBJECTIVE

To identify features in the compensatory mechanisms of sleep regulation in response to acute sleep deprivation after chronic sleep restriction in rats.

MATERIAL AND METHODS

Male Wistar rats 7-8 months old underwent 5-day sleep restriction: 3 h of sleep deprivation and 1 h of sleep opportunity repeating throughout each day. Six-hour acute total sleep deprivation was performed at the beginning of daylight hours on the 3rd day after sleep restriction. Polysomnogramms were recorded throughout the day before chronic sleep restriction, on the 2nd recovery day after chronic sleep restriction and after acute sleep deprivation. The control group was not subjected to chronic sleep restriction.

RESULTS

The animals after chronic sleep restriction had the compensatory increase in total sleep time in response to acute sleep deprivation weaker than in control animals. Animals after sleep restriction had the compensatory increase in the time of slow-wave sleep (SWS) only in the first 6 hours after acute sleep deprivation, whereas in control animals the period of compensation of SWS lasted 12 hours. A compensatory increase in slow-wave activity (SWA) was observed in both groups of animals, but in animals experiencing chronic sleep restriction the amplitude of SWA after acute sleep deprivation was less than in control animals. A compensatory increase in REM sleep in sleep restricted animals occurred immediately after acute sleep deprivation and coincides with a compensatory increase in SWS and SWA, whereas in control conditions these processes are spaced in time.

CONCLUSION

Compensatory reactions in response to acute sleep deprivation (sleep homeostasis) are weakened in animals subjected to chronic sleep restriction, as the reaction time and amplitude are reduced.

Arousal-Mediated Sleep Disturbance Persists During Cocaine Abstinence in Male Mice

Acute cocaine disturbs sleep on a dose-dependent basis; however, the consequences of chronic cocaine remain unclear. While the arousal promotion following cocaine has been well-established, effects of cocaine on sleep after termination of chronic cocaine exposure appear variable in human subjects with few studies in non-human subjects. Here, a within-subjects design (outcomes normalized to baseline, undisturbed behavior) and between-subjects design (repeated experimenter-administered cocaine vs. experimenter-administered saline) was used to investigate sleep homeostasis and sleep/waking under repeated cocaine/saline exposure and prolonged forced abstinence conditions in mice. Overall, during the forced abstinence period increases in arousal, as determined by sleep latency and gamma energy, persisted for 2 weeks. However, the sleep response to externally enforced sleep deprivation was unchanged suggesting that sleep disruptions during the forced abstinence period were driven by enhancement of arousal in the absence of changes in sleep homeostatic responses.

No loss of orexin/hypocretin, melanin-concentrating hormone or locus coeruleus noradrenergic neurons in a rat model of chronic sleep restriction

Chronic sleep restriction (CSR) is common in modern society, adversely affecting cognitive performance and health. Yet how it impacts neurons regulating sleep remains unclear. Several studies using mice reported substantial losses of wake-active orexin/hypocretin and locus coeruleus (LC) noradrenergic neurons, but not rapid eye movement sleep-active melanin-concentrating hormone (MCH) neurons, following CSR. Here, we used immunohistochemistry and stereology to examine orexin, MCH and LC noradrenergic neurons in a rat model of CSR that uses programmed wheel rotation (3 h on/1 h off; '3/1' protocol). Adult male Wistar rats underwent one or four cycles of the 4-day 3/1 CSR protocol, with 2-day recovery between cycles in home cages. Time-matched control rats were housed in locked wheels/home cages. We found no significant differences in the numbers of orexin, MCH and LC noradrenergic neurons following either one- or four-cycle CSR protocol compared to respective controls. Similarly, the four-cycle CSR protocol had no effect on the densities of orexin axon terminals in the LC, noradrenergic dendrites in the LC and noradrenergic axon terminals in the frontal cortex. Body weights, however, decreased after one cycle of CSR and then increased with diminishing slope over the next three cycles. Thus, we found no evidence for loss of orexin or LC noradrenergic neurons following one and four cycles of the 4-day 3/1 CSR protocol in rats. Differences in CSR protocols and/or possible species differences in neuronal vulnerability to sleep loss may account for the discrepancy between the current results in rats and previous findings in mice.

[Modeling of chronic sleep restriction for translational studies]

OBJECTIVE

To develop of a chronic sleep restriction model in rats by repeated sleep deprivation using an orbital shaker and to determine whether this model leads to disturbances in sleep homeostatic mechanisms.

MATERIAL AND METHODS

Male Wistar rats (7-8 months old) underwent sleep restriction for five consecutive days: 3 h of sleep deprivation and 1 h of sleep opportunity repeating throughout each day. Polysomnograms were recorded telemetrically throughout the day before sleep restriction (baseline), on the 1st, 3rd, 5th day of sleep restriction and 2 days after the end of sleep restriction (recovery period).

RESULTS

During the period of sleep restriction, the total amount of slow-wave sleep (SWS) and rapid eye movement (REM) sleep decreased by 61% and 55%, respectively, compared to baseline. On the first day of recovery, amount of SWS increased mainly in the dark (active) phase of the day, while REM sleep increased in both light and dark phases; there was no marked rebound of daily SWS amount, while REM sleep increased by 30% from baseline. On the first day of recovery, an elevation of EEG beta and sigma power in sleep states was observed mainly in the light phase of the day. The loss of deep SWS throughout the sleep restriction period increased from 50% on 1st day to 75% on 5th day. The level of deep SWS remained below the baseline by 15-20% on the two subsequent days of recovery. The findings suggest that homeostatic mechanisms of SWS are persistently impaired after 5-day chronic sleep restriction. Besides, a decline of wakefulness accompanied by an increase of SWS in the active phase of the recovery period indicates a disruption in circadian rhythm.

CONCLUSION

The proposed model leads to the disruption of sleep homeostatic mechanisms, which, in turn, impede compensation of SWS loss caused by chronic insufficient sleep.

Sleep loss disrupts pericyte-brain endothelial cell interactions impairing blood-brain barrier function

Sleep loss in the rat increases blood-brain barrier permeability to circulating molecules by disrupting interendothelial tight junctions. Despite the description of the ultrastructure of cerebral microvessels and the evidence of an apparent pericyte detachment from capillary wall in sleep restricted rats the effect of sleep loss on pericytes is unknown. Here we characterized the interactions between pericytes and brain endothelial cells after sleep loss using male Wistar rats. Animals were sleep-restricted 20 h daily with 4 h sleep recovery for 10 days. At the end of the sleep restriction, brain microvessels (MVs) were isolated from cerebral cortex and hippocampus and processed for Western blot and immunocytochemistry to evaluate markers of pericyte-endothelial cell interaction (connexin 43, PDGFR-β), tight junction proteins, and proinflammatory mediator proteins (MMP9, A_2A adenosine receptor, CD73, NFκB). Sleep restriction reduced PDGFR-β and connexin 43 expression in MVs; in addition, scanning electron microscopy micrographs showed that pericytes were detached from capillary walls, but did not undergo apoptosis (as depicted by a reduced active caspase-3 expression). Sleep restriction also decreased tight junction protein expression in MVs and increased BBB permeability to low- and high-molecular weight tracers in in vivo permeability assays. Those alterations seemed to depend on a low-grade inflammatory status as reflected by the increased expression of phosphorylated NFκB and A_2A adenosine receptor in brain endothelial cells from the sleep-restricted rats. Our data show that pericyte-brain endothelial cell interaction is altered by sleep restriction; this evidence is essential to understand the role of sleep in regulating blood-brain barrier function.

Differential modulation of NREM sleep regulation and EEG topography by chronic sleep restriction in mice

Compensatory elevation in NREM sleep EEG delta power has been typically observed following prolonged wakefulness and widely used as a sleep homeostasis indicator. However, recent evidence in human and rodent chronic sleep restriction (CSR) studies suggests that NREM delta power is not progressively increased despite of accumulated sleep loss over days. In addition, there has been little progress in understanding how sleep EEG in different brain regions responds to CSR. Using novel high-density EEG electrode arrays in the mouse model of CSR where mice underwent 18-h sleep deprivation per day for 5 consecutive days, we performed an extensive analysis of topographical NREM sleep EEG responses to the CSR condition, including period-amplitude analysis of individual slow waves. As previously reported in our analysis of REM sleep responses, we found different patterns of changes: (i) progressive decrease in NREM sleep duration and consolidation, (ii) persistent enhancement in NREM delta power especially in the frontal and parietal regions, and (iii) progressive increases in individual slow wave slope and frontal fast oscillation power. These results suggest that multiple sleep-wake regulatory systems exist in a brain region-specific manner, which can be modulated independently, especially in the CSR condition.

How Can Low-Frequency Noise Exposure Interact with the Well-Being of a Population? Some Results from a Portuguese Municipality

Noise pollution is the second most harmful environmental stressor in Europe. Portugal is the fourth European country most affected by noise pollution, whereby 23.0% of the population is affected. This article aims to analyze the effects of exposure to low frequency noise pollution, emitted by power poles and power lines, on the population’s well-being, based on a study of “exposed” and “unexposed” individuals in two predominantly urban areas in north-western Portugal. To develop the research, we used sound level (n = 62) and sound recording measurements, as well as adapted audiometric test performance (n = 14) and surveys conducted with the resident population (n = 200). The sound levels were measured (frequency range between 10 to 160 Hz) and compared with a criterion curve developed by the Department for Environment, Food and Rural Affairs (DEFRA). The sound recorded was performed 5 m away from the source (400 kV power pole). Surveys were carried out with the “exposed” and “unexposed” populations, and adapted audiometric tests were performed to complement the analysis and to determine the threshold of audibility of “exposed” and “unexposed” volunteers. The “exposed” area has higher sound levels and, consequently, more problems with well-being and health than the “unexposed” population. The audiometric tests also revealed that the “exposed” population appears to be less sensitive to low frequencies than the “unexposed” population.

Sleep deprivation alters the time course but not magnitude of locomotor sensitization to cocaine

Repeated exposure to drugs of abuse progressively increases the response to the same stimuli, a process known as sensitization. Behavioral sensitization to cocaine administration is often measured in non-human subjects via locomotor activity which is easily quantifiable. The effects of four hours of sleep deprivation on repeated cocaine (five daily and one challenge) showed attenuated hyperactivity on the first day only, compared to the non-deprived group. Both groups reached the same final level of sensitization, indicating that sleep deprivation altered the time course, but not magnitude of locomotor sensitization.

Cognitive impairments by alcohol and sleep deprivation indicate trait characteristics and a potential role for adenosine A1 receptors

Trait-like differences in cognitive performance after sleep loss put some individuals more at risk than others, the basis of such disparities remaining largely unknown. Similarly, interindividual differences in impairment in response to alcohol intake have been observed. We tested whether performance impairments due to either acute or chronic sleep loss can be predicted by an individual's vulnerability to acute alcohol intake. Also, we used positron emission tomography (PET) to test whether acute alcohol infusion results in an up-regulation of cerebral A₁ adenosine receptors (A₁ARs), similar to the changes previously observed following sleep deprivation. Sustained attention in the psychomotor vigilance task (PVT) was tested in 49 healthy volunteers (26 ± 5 SD years; 15 females) (i) under baseline conditions: (ii) after ethanol intake, and after either (iii) total sleep deprivation (TSD; 35 hours awake; n = 35) or (iv) partial sleep deprivation (PSD; four nights with 5 hours scheduled sleep; n = 14). Ethanol- versus placebo-induced changes in cerebral A₁AR availability were measured in 10 healthy male volunteers (31 ± 9 years) with [¹⁸F]8-cyclopentyl-3-(3-fluoropropyl)-1-propylxanthine (CPFPX) PET. Highly significant correlations between the performance impairments induced by ethanol and sleep deprivation were found for various PVT parameters, including mean speed (TSD, r = 0.62; PSD, r = 0.84). A₁AR availability increased up to 26% in several brain regions with ethanol infusion. Our studies revealed individual trait characteristics for being either vulnerable or resilient to both alcohol and to sleep deprivation. Both interventions induce gradual increases in cerebral A₁AR availability, pointing to a potential common molecular response mechanism.

Pivotal Role of Adenosine Neurotransmission in Restless Legs Syndrome

The symptomatology of Restless Legs Syndrome (RLS) includes periodic leg movements during sleep (PLMS), dysesthesias, and hyperarousal. Alterations in the dopaminergic system, a presynaptic hyperdopaminergic state, seem to be involved in PLMS, while alterations in glutamatergic neurotransmission, a presynaptic hyperglutamatergic state, seem to be involved in hyperarousal and also PLMS. Brain iron deficiency (BID) is well-recognized as a main initial pathophysiological mechanism of RLS. BID in rodents have provided a pathogenetic model of RLS that recapitulates the biochemical alterations of the dopaminergic system of RLS, although without PLMS-like motor abnormalities. On the other hand, BID in rodents reproduces the circadian sleep architecture of RLS, indicating the model could provide clues for the hyperglutamatergic state in RLS. We recently showed that BID in rodents is associated with changes in adenosinergic transmission, with downregulation of adenosine A₁ receptors (A1R) as the most sensitive biochemical finding. It was hypothesized that A1R downregulation leads to hypersensitive striatal glutamatergic terminals and facilitation of striatal dopamine release. Hypersensitivity of striatal glutamatergic terminals was demonstrated by an optogenetic-microdialysis approach in the rodent with BID, indicating that it could represent a main pathogenetic factor that leads to PLMS in RLS. In fact, the dopaminergic agonists pramipexole and ropinirole and the α₂δ ligand gabapentin, used in the initial symptomatic treatment of RLS, completely counteracted optogenetically-induced glutamate release from both normal and BID-induced hypersensitive corticostriatal glutamatergic terminals. It is a main tenet of this essay that, in RLS, a single alteration in the adenosinergic system, downregulation of A1R, disrupts the adenosine-dopamine-glutamate balance uniquely controlled by adenosine and dopamine receptor heteromers in the striatum and also the A1R-mediated inhibitory control of glutamatergic neurotransmission in the cortex and other non-striatal brain areas, which altogether determine both PLMS and hyperarousal. Since A1R agonists would be associated with severe cardiovascular effects, it was hypothesized that inhibitors of nucleoside equilibrative transporters, such as dipyridamole, by increasing the tonic A1R activation mediated by endogenous adenosine, could represent a new alternative therapeutic strategy for RLS. In fact, preliminary clinical data indicate that dipyridamole can significantly improve the symptomatology of RLS.

Modeling the adenosine system as a modulator of cognitive performance and sleep patterns during sleep restriction and recovery

Sleep loss causes profound cognitive impairments and increases the concentrations of adenosine and adenosine A1 receptors in specific regions of the brain. Time courses for performance impairment and recovery differ between acute and chronic sleep loss, but the physiological basis for these time courses is unknown. Adenosine has been implicated in pathways that generate sleepiness and cognitive impairments, but existing mathematical models of sleep and cognitive performance do not explicitly include adenosine. Here, we developed a novel receptor-ligand model of the adenosine system to test the hypothesis that changes in both adenosine and A1 receptor concentrations can capture changes in cognitive performance during acute sleep deprivation (one prolonged wake episode), chronic sleep restriction (multiple nights with insufficient sleep), and subsequent recovery. Parameter values were estimated using biochemical data and reaction time performance on the psychomotor vigilance test (PVT). The model closely fit group-average PVT data during acute sleep deprivation, chronic sleep restriction, and recovery. We tested the model's ability to reproduce timing and duration of sleep in a separate experiment where individuals were permitted to sleep for up to 14 hours per day for 28 days. The model accurately reproduced these data, and also correctly predicted the possible emergence of a split sleep pattern (two distinct sleep episodes) under these experimental conditions. Our findings provide a physiologically plausible explanation for observed changes in cognitive performance and sleep during sleep loss and recovery, as well as a new approach for predicting sleep and cognitive performance under planned schedules.

Leukocyte Expression of Type 1 and Type 2 Purinergic Receptors and Pro-Inflammatory Cytokines during Total Sleep Deprivation and/or Sleep Extension in Healthy Subjects

The purinergic type P1 (adenosine A₁ and A_2A) receptors and the type P2 (X7) receptor have been suggested to mediate physiological effects of adenosine and adenosine triphosphate on sleep. We aimed to determine gene expression of A₁R (receptor), A_2AR, and P2RX₇ in leukocytes of healthy subjects during total sleep deprivation followed by sleep recovery. Expression of the pro-inflammatory cytokines IL-1β and TNF-α were also determined as they have been characterized as sleep regulatory substances, via P2RX₇ activation. Blood sampling was performed on 14 young men (aged 31.9 ± 3.9) at baseline (B), after 24 h of sleep deprivation (24 h-SD), and after one night of sleep recovery (R). We compared gene expression levels after six nights of habitual (22.30–07.00) or extended (21.00–07.00) bedtimes. Using quantitative real-time PCR, the amount of mRNA for A₁R, A_2AR, P2RX₇, TNF-α, and IL-1β was analyzed. After 24 h-SD compared to B, whatever prior sleep condition, a significant increase of A_2AR expression was observed that returned to basal level after sleep recovery [day main effect, F_{(2, 26)} = 10.8, p < 0.001]. In both sleep condition, a day main effect on P2RX₇ mRNA was observed [F_{(2, 26)} = 6.7, p = 0.005] with significant increases after R compared with 24 h-SD. TNF-α and IL-1β expressions were not significantly altered. Before 24 h-SD (baseline), the A_2AR expression was negatively correlated with the latency of stage 3 sleep during the previous night, while that of the A₁R positively. This was not observed after sleep recovery following 24 h-SD. This is the first study showing increased A_2AR and not A₁ gene expression after 24 h-SD in leukocytes of healthy subjects, and this even if bedtime was initially increased by 1.5 h per night for six nights. In conclusion, prolonged wakefulness induced an up-regulation of the A2A receptor gene expression in leukocytes from healthy subjects. Significant correlations between baseline expression of A₁ and A_2A receptors in peripheral cells and stage 3 sleep suggested their involvement in mediating the effects of adenosine on sleep.

Effects of Sleep Deprivation on Spatial Learning and Memory in Juvenile and Young Adult Rats

Sleepiness is commonly seen in adolescents and can negatively impact school performance. Little research has investigated the impact of sleepiness in juvenile animals on spatial learning. Sprague-Dawley juvenile (<30 days) and young adult (>60 days) rats were sleep deprived for 24 hours and tested, along with controls, in a water maze task. Sleep deprived juveniles were slower to learn the location of the hidden platform than controls; however, adult performance was not impaired. Sleep deprivation did not impair recall during a probe trial for either age group. Sleep deprivation prior to testing slowed spatial learning in juveniles but not adults.

Differential modulation of global and local neural oscillations in REM sleep by homeostatic sleep regulation

Homeostatic rebound in rapid eye movement (REM) sleep normally occurs after acute sleep deprivation, but REM sleep rebound settles on a persistently elevated level despite continued accumulation of REM sleep debt during chronic sleep restriction (CSR). Using high-density EEG in mice, we studied how this pattern of global regulation is implemented in cortical regions with different functions and network architectures. We found that across all areas, slow oscillations repeated the behavioral pattern of persistent enhancement during CSR, whereas high-frequency oscillations showed progressive increases. This pattern followed a common rule despite marked topographic differences. The findings suggest that REM sleep slow oscillations may translate top-down homeostatic control to widely separated brain regions whereas fast oscillations synchronizing local neuronal ensembles escape this global command. These patterns of EEG oscillation changes are interpreted to reconcile two prevailing theories of the function of sleep, synaptic homeostasis and sleep dependent memory consolidation.

A2A Adenosine Receptor Antagonism Reverts the Blood-Brain Barrier Dysfunction Induced by Sleep Restriction

Chronic sleep restriction induces blood-brain barrier disruption and increases pro-inflammatory mediators in rodents. Those inflammatory mediators may modulate the blood-brain barrier and constitute a link between sleep loss and blood-brain barrier physiology. We propose that adenosine action on its A_2A receptor may be modulating the blood-brain barrier dynamics in sleep-restricted rats. We administrated a selective A_2A adenosine receptor antagonist (SCH58261) in sleep-restricted rats at the 10^th day of sleep restriction and evaluated the blood-brain barrier permeability to dextrans coupled to fluorescein (FITC-dextrans) and Evans blue. In addition, we evaluated by western blot the expression of tight junction proteins (claudin-5, occludin, ZO-1), adherens junction protein (E-cadherin), A_2A adenosine receptor, adenosine-synthesizing enzyme (CD73), and neuroinflammatory markers (Iba-1 and GFAP) in the cerebral cortex, hippocampus, basal nuclei and cerebellar vermis. Sleep restriction increased blood-brain barrier permeability to FITC-dextrans and Evans blue, and the effect was reverted by the administration of SCH58261 in almost all brain regions, excluding the cerebellum. Sleep restriction increased the expression of A_2A adenosine receptor only in the hippocampus and basal nuclei without changing the expression of CD73 in all brain regions. Sleep restriction reduced the expression of tight junction proteins in all brain regions, except in the cerebellum; and SCH58261 restored the levels of tight junction proteins in the cortex, hippocampus and basal nuclei. Finally, sleep restriction induced GFAP and Iba-1 overexpression that was attenuated with the administration of SCH58261. These data suggest that the action of adenosine on its A_2A receptor may have a crucial role in blood-brain barrier dysfunction during sleep loss probably by direct modulation of brain endothelial cell permeability or through a mechanism that involves gliosis with subsequent inflammation and increased blood-brain barrier permeability.

Adenosine receptors as markers of brain iron deficiency: Implications for Restless Legs Syndrome

Deficits of sensorimotor integration with periodic limb movements during sleep (PLMS) and hyperarousal and sleep disturbances in Restless Legs Syndrome (RLS) constitute two pathophysiologically distinct but interrelated clinical phenomena, which seem to depend mostly on alterations in dopaminergic and glutamatergic neurotransmission, respectively. Brain iron deficiency is considered as a main pathogenetic mechanism in RLS. Rodents with brain iron deficiency represent a valuable pathophysiological model of RLS, although they do not display motor disturbances. Nevertheless, they develop the main neurochemical dopaminergic changes found in RLS, such as decrease in striatal dopamine D₂ receptor density. On the other hand, brain iron deficient mice exhibit the characteristic pattern of hyperarousal in RLS, providing a tool to find the link between brain iron deficiency and sleep disturbances in RLS. The present study provides evidence for a role of the endogenous sleep-promoting factor adenosine. Three different experimental preparations, long-term (22 weeks) severe or moderate iron-deficient (ID) diets (3- or 7-ppm iron diet) in mice and short-term (3 weeks) severe ID diet (3-ppm iron diet) in rats, demonstrated a significant downregulation (Western blotting in mouse and radioligand binding saturation experiments in rat brain tissue) of adenosine A₁ receptors (A1R) in the cortex and striatum, concomitant to striatal D2R downregulation. On the other hand, the previously reported upregulation of adenosine A_2A receptors (A2AR) was only observed with severe ID in both mice and rats. The results suggest a key role for A1R downregulation in the PLMS and hyperarousal in RLS.

Significance of the zero sum principle for circadian, homeostatic and allostatic regulation of sleep-wake state in the rat

Sleep-wake behavior exhibits diurnal rhythmicity, rebound responses to acute total sleep deprivation (TSD), and attenuated rebounds following chronic sleep restriction (CSR). We investigated how these long-term patterns of behavior emerge from stochastic short-term dynamics of state transition. Male Sprague-Dawley rats were subjected to TSD (1day×24h, N=9), or CSR (10days×18h TSD, N=7) using a rodent walking-wheel apparatus. One baseline day and one recovery day following TSD and CSR were analyzed. The implications of the zero sum principle were evaluated using a Markov model of sleep-wake state transition. Wake bout duration (a combined function of the probability of wake maintenance and proportional representations of brief and long wake) was a key variable mediating the baseline diurnal rhythms and post-TSD responses of all three states, and the attenuation of the post-CSR rebounds. Post-NREM state transition trajectory was an important factor in REM rebounds. The zero sum constraint ensures that a change in any transition probability always affects bout frequency and cumulative time of at least two, and usually all three, of wakefulness, NREM and REM. Neural mechanisms controlling wake maintenance may play a pivotal role in regulation and dysregulation of all three states.

Mechanisms of the psychostimulant effects of caffeine: implications for substance use disorders

BACKGROUND

The psychostimulant properties of caffeine are reviewed and compared with those of prototypical psychostimulants able to cause substance use disorders (SUD). Caffeine produces psychomotor-activating, reinforcing, and arousing effects, which depend on its ability to disinhibit the brake that endogenous adenosine imposes on the ascending dopamine and arousal systems.

OBJECTIVES

A model that considers the striatal adenosine A2A-dopamine D2 receptor heteromer as a key modulator of dopamine-dependent striatal functions (reward-oriented behavior and learning of stimulus-reward and reward-response associations) is introduced, which should explain most of the psychomotor and reinforcing effects of caffeine.

HIGHLIGHTS

The model can explain the caffeine-induced rotational behavior in rats with unilateral striatal dopamine denervation and the ability of caffeine to reverse the adipsic-aphagic syndrome in dopamine-deficient rodents. The model can also explain the weaker reinforcing effects and low abuse liability of caffeine, compared with prototypical psychostimulants. Finally, the model can explain the actual major societal dangers of caffeine: the ability of caffeine to potentiate the addictive and toxic effects of drugs of abuse, with the particularly alarming associations of caffeine (as adulterant) with cocaine, amphetamine derivatives, synthetic cathinones, and energy drinks with alcohol, and the higher sensitivity of children and adolescents to the psychostimulant effects of caffeine and its potential to increase vulnerability to SUD.

CONCLUSIONS

The striatal A2A-D2 receptor heteromer constitutes an unequivocal main pharmacological target of caffeine and provides the main mechanisms by which caffeine potentiates the acute and long-term effects of prototypical psychostimulants.

From unwitnessed fatality to witnessed rescue: Pharmacologic intervention in sudden unexpected death in epilepsy

The mechanisms of sudden unexpected death in epilepsy (SUDEP) have been difficult to define, as most cases occur unwitnessed, and physiologic recordings have been obtained in only a handful of cases. However, recent data obtained from human cases and experimental studies in animal models have brought us closer to identifying potential mechanisms. Theories of SUDEP should be able to explain how a seizure starting in the forebrain can sometimes lead to changes in brainstem cardiorespiratory control mechanisms. Herein we focus on three major themes of work on the causes of SUDEP. First, evidence is reviewed identifying postictal hypoventilation as a major contributor to the cause of death. Second, data are discussed that brainstem serotonin and adenosine pathways may be involved, as well as how they may contribute. Finally, parallels are drawn between SIDS and SUDEP, and we highlight similarities pointing to the possibility of shared pathophysiology involving combined failure of respiratory and cardiovascular control mechanisms. Knowledge about the causes of SUDEP may lead to potential pharmacologic approaches for prevention. We end by describing how translation of this work may result in future applications to clinical care.

Effects of partial sleep deprivation on slow waves during non-rapid eye movement sleep: A high density EEG investigation

OBJECTIVE

Changes in slow waves during non-rapid eye movement (NREM) sleep in response to acute total sleep deprivation are well-established measures of sleep homeostasis. This investigation utilized high-density electroencephalography (hdEEG) to examine topographic changes in slow waves during repeated partial sleep deprivation.

METHODS

Twenty-four participants underwent a 6-day sleep restriction protocol. Spectral and period-amplitude analyses of sleep hdEEG data were used to examine changes in slow wave energy, count, amplitude, and slope relative to baseline.

RESULTS

Changes in slow wave energy were dependent on the quantity of NREM sleep utilized for analysis, with widespread increases during sleep restriction and recovery when comparing data from the first portion of the sleep period, but restricted to recovery sleep if the entire sleep episode was considered. Period-amplitude analysis was less dependent on the quantity of NREM sleep utilized, and demonstrated topographic changes in the count, amplitude, and distribution of slow waves, with frontal increases in slow wave amplitude, numbers of high-amplitude waves, and amplitude/slopes of low amplitude waves resulting from partial sleep deprivation.

CONCLUSIONS

Topographic changes in slow waves occur across the course of partial sleep restriction and recovery.

SIGNIFICANCE

These results demonstrate a homeostatic response to partial sleep loss in humans.

Chronic sleep restriction induces long-lasting changes in adenosine and noradrenaline receptor density in the rat brain

Although chronic sleep restriction frequently produces long-lasting behavioural and physiological impairments in humans, the underlying neural mechanisms are unknown. Here we used a rat model of chronic sleep restriction to investigate the role of brain adenosine and noradrenaline systems, known to regulate sleep and wakefulness, respectively. The density of adenosine A1 and A2a receptors and β-adrenergic receptors before, during and following 5 days of sleep restriction was assessed with autoradiography. Rats (n = 48) were sleep-deprived for 18 h day(-1) for 5 consecutive days (SR1-SR5), followed by 3 unrestricted recovery sleep days (R1-R3). Brains were collected at the beginning of the light period, which was immediately after the end of sleep deprivation on sleep restriction days. Chronic sleep restriction increased adenosine A1 receptor density significantly in nine of the 13 brain areas analysed with elevations also observed on R3 (+18 to +32%). In contrast, chronic sleep restriction reduced adenosine A2a receptor density significantly in one of the three brain areas analysed (olfactory tubercle which declined 26-31% from SR1 to R1). A decrease in β-adrenergic receptors density was seen in substantia innominata and ventral pallidum which remained reduced on R3, but no changes were found in the anterior cingulate cortex. These data suggest that chronic sleep restriction can induce long-term changes in the brain adenosine and noradrenaline receptors, which may underlie the long-lasting neurocognitive impairments observed in chronic sleep restriction.

Behavioral sleep-wake homeostasis and EEG delta power are decoupled by chronic sleep restriction in the rat

STUDY OBJECTIVES

Chronic sleep restriction (CSR) is prevalent in society and is linked to adverse consequences that might be ameliorated by acclimation of homeostatic drive. This study was designed to test the hypothesis that the sleep-wake homeostat will acclimatize to CSR.

DESIGN

A four-parameter model of proportional control was used to quantify sleep homeostasis with and without recourse to a sleep intensity function.

SETTING

Animal laboratory, rodent walking-wheel apparatus.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

Acute total sleep deprivation (TSD, 1 day × 18 or 24 h, N = 12), CSR (10 days × 18 h TSD, N = 5, or 5 days × 20 h TSD, N = 6).

MEASUREMENTS AND RESULTS

Behavioral rebounds were consistent with model predictions for proportional control of cumulative times in wake, nonrapid eye movement (NREM) and rapid eye movement (REM). Delta (D) energy homeostasis was secondary to behavioral homeostasis; a biphasic NREM D power rebound contributed to the dynamics (rapid response) but not to the magnitude of the rebound in D energy. REM behavioral homeostasis was little affected by CSR. NREM behavioral homeostasis was attenuated in proportion to cumulative NREM deficit, whereas the biphasic NREM D power rebound was only slightly suppressed, indicating decoupled regulatory mechanisms following CSR.

CONCLUSIONS

We conclude that sleep homeostasis is achieved through behavioral regulation, that the NREM behavioral homeostat is susceptible to attenuation during CSR and that the concept of sleep intensity is not essential in a model of sleep-wake regulation.

STUDY OBJECTIVES

Chronic sleep restriction (CSR) is prevalent in society and is linked to adverse consequences that might be ameliorated by acclimation of homeostatic drive. This study was designed to test the hypothesis that the sleep-wake homeostat will acclimatize to CSR.

DESIGN

A four-parameter model of proportional control was used to quantify sleep homeostasis with and without recourse to a sleep intensity function.

SETTING

Animal laboratory, rodent walking-wheel apparatus.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

Acute total sleep deprivation (TSD, 1 day × 18 or 24 h, N = 12), CSR (10 days × 18 h TSD, N = 5, or 5 days × 20 h TSD, N = 6).

MEASUREMENTS AND RESULTS

Behavioral rebounds were consistent with model predictions for proportional control of cumulative times in wake, nonrapid eye movement (NREM) and rapid eye movement (REM). Delta (D) energy homeostasis was secondary to behavioral homeostasis; a biphasic NREM D power rebound contributed to the dynamics (rapid response) but not to the magnitude of the rebound in D energy. REM behavioral homeostasis was little affected by CSR. NREM behavioral homeostasis was attenuated in proportion to cumulative NREM deficit, whereas the biphasic NREM D power rebound was only slightly suppressed, indicating decoupled regulatory mechanisms following CSR.

CONCLUSIONS

We conclude that sleep homeostasis is achieved through behavioral regulation, that the NREM behavioral homeostat is susceptible to attenuation during CSR and that the concept of sleep intensity is not essential in a model of sleep-wake regulation.

Chronic sleep restriction elevates brain interleukin-1 beta and tumor necrosis factor-alpha and attenuates brain-derived neurotrophic factor expression

Acute sleep loss increases pro-inflammatory and synaptic plasticity-related molecules in the brain, including interleukin-1 beta (IL-1β), tumor necrosis factor-alpha (TNF-α), and brain-derived neurotrophic factor (BDNF). These molecules enhance non-rapid eye movement sleep slow wave activity (SWA), also known as electroencephalogram delta power, and modulate neurocognitive performance. Evidence suggests that chronic sleep restriction (CSR), a condition prevalent in today's society, does not elicit the enhanced SWA that is seen after acute sleep loss, although it cumulatively impairs neurocognitive functioning. Rats were continuously sleep deprived for 18h per day and allowed 6h of ad libitum sleep opportunity for 1 (SR1), 3 (SR3), or 5 (SR5) successive days (i.e., CSR). IL-1β, TNF-α, and BDNF mRNA levels were determined in the somatosensory cortex, frontal cortex, hippocampus, and basal forebrain. Largely, brain IL-1β and TNF-α expression were significantly enhanced throughout CSR. In contrast, BDNF mRNA levels were similar to baseline values in the cortex after 1 day of SR and significantly lower than baseline values in the hippocampus after 5 days of SR. In the basal forebrain, BDNF expression remained elevated throughout the 5 days of CSR, although IL-1β expression was significantly reduced. The chronic elevations of IL-1β and TNF-α and inhibition of BDNF might contribute to the reported lack of SWA responses reported after CSR. Further, the CSR-induced enhancements in brain inflammatory molecules and attenuations in hippocampal BDNF might contribute to neurocognitive and vigilance detriments that occur from CSR.

Effects of sleep fragmentation on sleep and markers of inflammation in mice

Many people in our society experience curtailment and disruption of sleep due to work responsibilities, care-giving, or life style choice. Delineating the health effect of acute and chronic disruptions in sleep is essential to raising awareness of and creating interventions to manage these prevalent concerns. To provide a platform for studying the health impact and underlying pathophysiologic mechanisms associated with inadequate sleep, we developed and characterized an approach to creating chronic disruption of sleep in laboratory mice. We used this method to evaluate how 3 durations of sleep fragmentation (SF) affect sleep recuperation and blood and lung analyte concentrations in male C57BL/6J mice. Mice housed in environmentally controlled chambers were exposed to automated SF for periods of 6, 12, or 24 h or for 12 h daily during the light (somnolent) phase for 4 sequential days. Sleep time, slow-wave amplitude, or bout lengths were significantly higher when uninterrupted sleep was permitted after each of the 3 SF durations. However, mice did not recover all of the lost slow-wave sleep during the subsequent 12- to 24-h period and maintained a net loss of sleep. Light-phase SF was associated with significant changes in serum and lung levels of some inflammatory substances, but these changes were not consistent or sustained. The data indicate that acute light-phase SF can result in a sustained sleep debt in mice and may disrupt the inflammatory steady-state in serum and lung.

Sleep active cortical neurons expressing neuronal nitric oxide synthase are active after both acute sleep deprivation and chronic sleep restriction

Non-rapid eye movement (NREM) sleep electroencephalographic (EEG) delta power (~0.5-4 Hz), also known as slow wave activity (SWA), is typically enhanced after acute sleep deprivation (SD) but not after chronic sleep restriction (CSR). Recently, sleep-active cortical neurons expressing neuronal nitric oxide synthase (nNOS) were identified and associated with enhanced SWA after short acute bouts of SD (i.e., 6h). However, the relationship between cortical nNOS neuronal activity and SWA during CSR is unknown. We compared the activity of cortical neurons expressing nNOS (via c-Fos and nNOS immuno-reactivity, respectively) and sleep in rats in three conditions: (1) after 18-h of acute SD; (2) after five consecutive days of sleep restriction (SR) (18-h SD per day with 6h ad libitum sleep opportunity per day); (3) and time-of-day matched ad libitum sleep controls. Cortical nNOS neuronal activity was enhanced during sleep after both 18-h SD and 5 days of SR treatments compared to control treatments. SWA and NREM sleep delta energy (the product of NREM sleep duration and SWA) were positively correlated with enhanced cortical nNOS neuronal activity after 18-h SD but not 5days of SR. That neurons expressing nNOS were active after longer amounts of acute SD (18h vs. 6h reported in the literature) and were correlated with SWA further suggest that these cells might regulate SWA. However, since these neurons were active after CSR when SWA was not enhanced, these findings suggest that mechanisms downstream of their activation are altered during CSR.

Sleep allostasis in chronic sleep restriction: the role of the norepinephrine system

Sleep responses to chronic sleep restriction may be very different from those observed after acute total sleep deprivation. Specifically, when sleep restriction is repeated for several consecutive days, animals express attenuated compensatory increases in sleep time and intensity during daily sleep opportunities. The neurobiological mechanisms underlying these adaptive, or more specifically, allostatic, changes in sleep homeostasis are unknown. Several lines of evidence indicate that norepinephrine may play a key role in modulating arousal states and NREM EEG delta power, which is widely recognized as a marker for sleep intensity. Therefore, we investigated time course changes in brain adrenergic receptor mRNA levels in response to chronic sleep restriction using a rat model. Here, we observed that significantly altered mRNA levels of the α1- adrenergic receptor in the basal forebrain as well as α2- and β1-adrenergic receptor in the anterior cingulate cortex only on the first sleep restriction day. On the other hand, the frontal cortex α1-, α2-, and β1-adrenergic receptor mRNA levels were reduced throughout the period of sleep restriction. Combined with our earlier findings on EEG that sleep time and intensity significantly increased only on the first sleep restriction days, these results suggest that alterations in the brain norepinephrine system in the basal forebrain and cingulate cortex may mediate allostatic changes in sleep time and intensity observed during chronic sleep restriction.

Chronic sleep restriction impairs spatial memory in rats

Although numerous experimental investigations have evaluated the neurobehavioral effects of either short periods of total sleep deprivation or selective rapid eye movement sleep deprivation, few studies have examined the effects of chronic sleep restriction (CSR). Long-Evans rats were deprived of sleep by the automated movement of activity wheels for 18 h/day for 5 consecutive days from 16:00 to 10:00 h, and were allowed 6 h/day of sleep opportunity (10:00-16:00 h; lights on from 10:00 to 22:00 h). Activity wheels were intermittently activated on a 3 s on : 12 s off schedule for the CSR condition, whereas a schedule of 36 min of continuous wheel movement in every 3 h was used for a cage movement control condition. A cross-over design was used with rats serving in both the CSR and the movement control conditions with 2 days of rest between conditions. Water maze acquisition training occurred at 16:00 h immediately after the 6-h sleep opportunity on each of the first 4 days, followed by a probe trial on day 5 to assess spatial memory recall. Although the rate of learning/acquisition was not affected by the daily 18 h of CSR, the day 5 recall of the platform location was impaired on three different probe trial measures. Thus, CSR impaired spatial memory, but did not affect the rate of learning/acquisition in the water maze.

Cordycepin Increases Nonrapid Eye Movement Sleep via Adenosine Receptors in Rats

Cordycepin (3′-deoxyadenosine) is a naturally occurring adenosine analogue and one of the bioactive constituents isolated from Cordyceps militaris/Cordyceps sinensis, species of the fungal genus Cordyceps. It has traditionally been a prized Chinese folk medicine for the human well-being. Because of similarity of chemical structure of adenosine, cordycepin has been focused on the diverse effects of the central nervous systems (CNSs), like sleep regulation. Therefore, this study was undertaken to know whether cordycepin increases the natural sleep in rats, and its effect is mediated by adenosine receptors (ARs). Sleep was recorded using electroencephalogram (EEG) for 4 hours after oral administration of cordycepin in rats. Sleep architecture and EEG power spectra were analyzed. Cordycepin reduced sleep-wake cycles and increased nonrapid eye movement (NREM) sleep. Interestingly, cordycepin increased θ (theta) waves power density during NREM sleep. In addition, the protein levels of AR subtypes (A₁, A_2A, and A_2B) were increased after the administration of cordycepin, especially in the rat hypothalamus which plays an important role in sleep regulation. Therefore, we suggest that cordycepin increases theta waves power density during NREM sleep via nonspecific AR in rats. In addition, this experiment can provide basic evidence that cordycepin may be helpful for sleep-disturbed subjects.

A novel telemetric system to measure polysomnographic biopotentials in freely moving animals

Mice are by far the most widely used species for scientific research and have been used in many studies involving biopotentials, such as the electroencephalogram (EEG) and electromyogram (EMG) signals monitored for sleep analysis. Unfortunately, current methods for the analysis of these signals involve either tethered systems that are restrictive and heavy for the animal or wireless systems that use transponders that are large relative to the animal and require invasive surgery for implantation; as a result, natural behavior/activity is altered. Here, we propose a novel and inexpensive system for measuring electroencephalographic signals and other biopotentials in mice that allows for natural movement. We also evaluate the new system for the analysis of sleep architecture and EEG power during both spontaneous sleep and the sleep that follows sleep deprivation in mice. Using our new system, vigilance states including non-rapid eye movement sleep (NREMS), rapid eye movement sleep (REMS), and wakefulness, as well as EEG power and NREMS EEG delta power in the 0.5-4 Hz range (an indicator of sleep intensity) showed the diurnal rhythms typically found in mice. These values were also similar to values obtained in mice using telemetry transponders. Mice that used the new system also demonstrated enhanced NREMS EEG delta power responses that are typical following sleep deprivation and few signal artifacts. Moreover, similar movement activity counts were found when using the new system compared to a wireless system. This novel system for measuring biopotentials can be used for polysomnography, infusion, microdialysis, and optogenetic studies, reduces artifacts, and allows for a more natural moving environment and a more accurate investigation of biological systems and pharmaceutical development.

Sleep and immune function: glial contributions and consequences of aging

The reciprocal interactions between sleep and immune function are well-studied. Insufficient sleep induces innate immune responses as evidenced by increased expression of pro-inflammatory mediators in the brain and periphery. Conversely, immune challenges upregulate immunomodulator expression, which alters central nervous system-mediated processes and behaviors, including sleep. Recent studies indicate that glial cells, namely microglia and astrocytes, are active contributors to sleep and immune system interactions. Evidence suggests glial regulation of these interactions is mediated, in part, by adenosine and adenosine 5'-triphosphate actions at purinergic type 1 and type 2 receptors. Furthermore, microglia and astrocytes may modulate declines in sleep-wake behavior and immunity observed in aging.