Role of corticosterone on sleep homeostasis induced by REM sleep deprivation in rats

Sleep disturbance in rodent models and its sex-specific implications

Sleep disturbances, encompassing altered sleep physiology or disorders like insomnia and sleep apnea, profoundly impact physiological functions and elevate disease risk. Despite extensive research, the underlying mechanisms and sex-specific differences in sleep disorders remain elusive. While polysomnography serves as a cornerstone for human sleep studies, animal models provide invaluable insights into sleep mechanisms. However, the availability of animal models of sleep disorders is limited, with each model often representing a specific sleep issue or mechanism. Therefore, selecting appropriate animal models for sleep research is critical. Given the significant sex differences in sleep patterns and disorders, incorporating both male and female subjects in studies is essential for uncovering sex-specific mechanisms with clinical relevance. This review provides a comprehensive overview of various rodent models of sleep disturbance, including sleep deprivation, sleep fragmentation, and circadian rhythm dysfunction. We evaluate the advantages and disadvantages of each model and discuss sex differences in sleep and sleep disorders, along with potential mechanisms. We aim to advance our understanding of sleep disorders and facilitate sex-specific interventions.

Effect of glucocorticoid blockade on inflammatory responses to acute sleep fragmentation in male mice

The association between sleep and the immune-endocrine system is well recognized, but the nature of that relationship is not well understood. Sleep fragmentation induces a pro-inflammatory response in peripheral tissues and brain, but it also activates the hypothalamic-pituitary-adrenal (HPA) axis, releasing glucocorticoids (GCs) (cortisol in humans and corticosterone in mice). It is unclear whether this rapid release of glucocorticoids acts to potentiate or dampen the inflammatory response in the short term. The purpose of this study was to determine whether blocking or suppressing glucocorticoid activity will affect the inflammatory response from acute sleep fragmentation (ASF). Male C57BL/6J mice were injected i.p. with either 0.9% NaCl (vehicle 1), metyrapone (a glucocorticoid synthesis inhibitor, dissolved in vehicle 1), 2% ethanol in polyethylene glycol (vehicle 2), or mifepristone (a glucocorticoid receptor antagonist, dissolved in vehicle 2) 10 min before the start of ASF or no sleep fragmentation (NSF). After 24 h, samples were collected from brain (prefrontal cortex, hypothalamus, hippocampus) and periphery (liver, spleen, heart, and epididymal white adipose tissue (EWAT)). Proinflammatory gene expression (TNF-α and IL-1β) was measured, followed by gene expression analysis. Metyrapone treatment affected pro-inflammatory cytokine gene expression during ASF in some peripheral tissues, but not in the brain. More specifically, metyrapone treatment suppressed IL-1β expression in EWAT during ASF, which implies a pro-inflammatory effect of GCs. However, in cardiac tissue, metyrapone treatment increased TNF-α expression in ASF mice, suggesting an anti-inflammatory effect of GCs. Mifepristone treatment yielded more significant results than metyrapone, reducing TNF-α expression in liver (only NSF mice) and cardiac tissue during ASF, indicating a pro-inflammatory role. Conversely, in the spleen of ASF-mice, mifepristone increased pro-inflammatory cytokines (TNF-α and IL-1β), demonstrating an anti-inflammatory role. Furthermore, irrespective of sleep fragmentation, mifepristone increased pro-inflammatory cytokine gene expression in heart (IL-1β), pre-frontal cortex (IL-1β), and hypothalamus (IL-1β). The results provide mixed evidence for pro- and anti-inflammatory functions of corticosterone to regulate inflammatory responses to acute sleep loss.

Sleep rebound leads to marked recovery of prolonged sleep deprivation-induced adversities in the stress response and hippocampal neuroplasticity of male rats

BACKGROUND

Sleep disturbances are not only frequent symptoms, but also risk factors for major depressive disorder. We previously reported that depressed patients who experienced "Hypersomnia" showed a higher and more rapid response rate under paroxetine treatment, but the underlying mechanism remains unclear. The present study was conducted to clarify the beneficial effects of sleep rebound through an experimental "Hypersomnia" rat model on glucocorticoid and hippocampal neuroplasticity associated with antidepressive potency.

METHODS

Thirty-four male Sprague-Dawley rats were subjected to sham treatment, 72-h sleep deprivation, or sleep deprivation and subsequent follow-up for one week. Approximately half of the animals were sacrificed to evaluate adrenal weight, plasma corticosterone level, hippocampal content of mRNA isoforms, and protein of the brain-derived neurotrophic factor (Bdnf) gene. In the other half of the rats, Ki-67- and doublecortin (DCX)-positive cells in the hippocampus were counted via immunostaining to quantify adult neurogenesis.

RESULTS

Prolonged sleep deprivation led to adrenal hypertrophy and an increase in the plasma corticosterone level, which had returned to normal after one week follow-up. Of note, sleep deprivation-induced decreases in hippocampal Bdnf transcripts containing exons II, IV, VI, and IX and BDNF protein levels, Ki-67-(+)-proliferating cells, and DCX-(+)-newly-born neurons were not merely reversed, but overshot their normal levels with sleep rebound.

LIMITATIONS

The present study did not record electroencephalogram or assess behavioral changes of the sleep-deprived rats.

CONCLUSIONS

The present study demonstrated that prolonged sleep deprivation-induced adversities are reversed or recovered by sleep rebound, which supports "Hypersomnia" in depressed patients as having a beneficial pharmacological effect.

Stress systems exacerbate the inflammatory response after corneal abrasion in sleep-deprived mice via the IL-17 signaling pathway

Sleep deprivation (SD) has a wide range of adverse health effects. However, the mechanisms by which SD influences corneal pathophysiology and its post-wound healing remain unclear. This study aimed to examine the basic physiological characteristics of the cornea in mice subjected to SD and determine the pathophysiological response to injury after corneal abrasion. Using a multi-platform water environment method as an SD model, we found that SD leads to disturbances of corneal proliferative, sensory, and immune homeostasis as well as excessive inflammatory response and delayed repair after corneal abrasion by inducing hyperactivation of the sympathetic nervous system and hypothalamic-pituitary-adrenal axis. Pathophysiological changes in the cornea mainly occurred through the activation of the IL-17 signaling pathway. Blocking both adrenergic and glucocorticoid synthesis and locally neutralizing IL-17A significantly improved corneal homeostasis and the excessive inflammatory response and delay in wound repair following corneal injury in SD-treated mice. These results indicate that optimal sleep quality is essential for the physiological homeostasis of the cornea and its well-established repair process after injury. Additionally, these observations provide potential therapeutic targets to ameliorate SD-induced delays in corneal wound repair by inhibiting or blocking the activation of the stress system and its associated IL-17 signaling pathway.

A wireless and battery-less implant for multimodal closed-loop neuromodulation in small animals

Fully implantable wireless systems for the recording and modulation of neural circuits that do not require physical tethers or batteries allow for studies that demand the use of unconstrained and freely behaving animals in isolation or in social groups. Moreover, feedback-control algorithms that can be executed within such devices without the need for remote computing eliminate virtual tethers and any associated latencies. Here we report a wireless and battery-less technology of this type, implanted subdermally along the back of freely moving small animals, for the autonomous recording of electroencephalograms, electromyograms and body temperature, and for closed-loop neuromodulation via optogenetics and pharmacology. The device incorporates a system-on-a-chip with Bluetooth Low Energy for data transmission and a compressed deep-learning module for autonomous operation, that offers neurorecording capabilities matching those of gold-standard wired systems. We also show the use of the implant in studies of sleep-wake regulation and for the programmable closed-loop pharmacological suppression of epileptic seizures via feedback from electroencephalography. The technology can support a broader range of applications in neuroscience and in biomedical research with small animals.

Sleep Deprivation-Induced Oxidative Stress in Rat Models: A Scoping Systematic Review

Sleep deprivation is highly prevalent in the modern world, possibly reaching epidemic proportions. While multiple theories regarding the roles of sleep exist (inactivity, energy conservation, restoration, brain plasticity and antioxidant), multiple unknowns still remain regarding the proposed antioxidant roles of sleep. The existing experimental evidence is often contradicting, with studies pointing both toward and against the presence of oxidative stress after sleep deprivation. The main goals of this review were to analyze the existing experimental data regarding the relationship between sleep deprivation and oxidative stress, to attempt to further clarify multiple aspects surrounding this relationship and to identify current knowledge gaps. Systematic searches were conducted in three major online databases for experimental studies performed on rat models with oxidative stress measurements, published between 2015 and 2022. A total of 54 studies were included in the review. Most results seem to point to changes in oxidative stress parameters after sleep deprivation, further suggesting an antioxidant role of sleep. Alterations in these parameters were observed in both paradoxical and total sleep deprivation protocols and in multiple rat strains. Furthermore, the effects of sleep deprivation seem to extend beyond the central nervous system, affecting multiple other body sites in the periphery. Sleep recovery seems to be characterized by an increased variability, with the presence of both normalizations in some parameters and long-lasting changes after sleep deprivation. Surprisingly, most studies revealed the presence of a stress response following sleep deprivation. However, the origin and the impact of the stress response during sleep deprivation remain somewhat unclear. While a definitive exclusion of the influence of the sleep deprivation protocol on the stress response is not possible, the available data seem to suggest that the observed stress response may be determined by sleep deprivation itself as opposed to the experimental conditions. Due to this fact, the observed oxidative changes could be attributed directly to sleep deprivation.

The stress of losing sleep: Sex-specific neurobiological outcomes

Sleep is a vital and evolutionarily conserved process, critical to daily functioning and homeostatic balance. Losing sleep is inherently stressful and leads to numerous detrimental physiological outcomes. Despite sleep disturbances affecting everyone, women and female rodents are often excluded or underrepresented in clinical and pre-clinical studies. Advancing our understanding of the role of biological sex in the responses to sleep loss stands to greatly improve our ability to understand and treat health consequences of insufficient sleep. As such, this review discusses sex differences in response to sleep deprivation, with a focus on the sympathetic nervous system stress response and activation of the hypothalamic-pituitary-adrenal (HPA) axis. We review sex differences in several stress-related consequences of sleep loss, including inflammation, learning and memory deficits, and mood related changes. Focusing on women's health, we discuss the effects of sleep deprivation during the peripartum period. In closing, we present neurobiological mechanisms, including the contribution of sex hormones, orexins, circadian timing systems, and astrocytic neuromodulation, that may underlie potential sex differences in sleep deprivation responses.

Loss of sleep when it is needed most - Consequences of persistent developmental sleep disruption: A scoping review of rodent models

Sleep is an essential component of development. Developmental sleep disruption (DSD) impacts brain maturation and has been associated with significant consequences on socio-emotional development. In humans, poor sleep during infancy and adolescence affects neurodevelopmental outcomes and may be a risk factor for the development of autism spectrum disorder (ASD) or other neuropsychiatric illness. Given the wide-reaching and enduring consequences of DSD, identifying underlying mechanisms is critical to best inform interventions with translational capacity. In rodents, studies have identified some mechanisms and neural circuits by which DSD causes later social, emotional, sensorimotor, and cognitive changes. However, these studies spanned methodological differences, including different developmental timepoints for both sleep disruption and testing, different DSD paradigms, and even different rodent species. In this scoping review on DSD in rodents, we synthesize these various studies into a cohesive framework to identify common neural mechanisms underlying DSD-induced dysfunction in brain and behavior. Ultimately, this review serves the goal to inform the generation of novel translational interventions for human developmental disorders featuring sleep disruption.

Alterations in the activation of corticotropin-releasing factor neurons in the paraventricular nucleus following a single or multiple days of sleep restriction

Sleep disturbances are common among disorders associated with hypothalamic pituitary-adrenal (HPA) axis dysfunction, such as depression and anxiety. This comorbidity may partly be the result of the intersection between the role of the HPA axis in mediating the stress response and its involvement in sleep-wake cyclicity. Our previous work has shown that following 20 h of sleep restriction, mice show a blunting of the HPA axis in response to an acute stressor. Furthermore, these responses differ in a sex-dependent manner. This study sought to examine the effect of sleep restriction on corticotropin-releasing factor (CRF)-containing neurons in the paraventricular nucleus (PVN) of the hypothalamus. Male and female Crf-IRES-Cre: Ai14 (Tdtomato) reporter mice were sleep restricted for 20 h daily for either a single or three consecutive days using the modified multiple platform method. These mice allowed the visualization of CRF+ neurons throughout the brain. Animals were subjected to acute restraint stress, and their brains were collected to assess PVN neuronal activation via c-Fos immunohistochemistry. Analyses of cell counts revealed an ablation of the restraint-induced increase in both CRF/c-Fos colocalization and overall c-Fos expression in female mice following both a single day and three days of sleep restriction. Males showed an overall decrease in restraint-induced c-Fos levels following a single day of sleep restriction. However, male mice examined after three days of sleep restriction showed a recovery in PVN-CRF and overall PVN neuronal activation. These data suggest the sex dependent dysregulation in CRF function following sleep restriction.

Paradoxical sleep deprivation induces tissue changes in the parotid gland of rats

PURPOSE

This study aimed to evaluate if paradoxical sleep deprivation induces some tissue changes in the parotid gland of rats.

METHODS

A total of 24 male Wistar rats were distributed into the following groups, as follows: Group 1-Control (CTRL; n = 8); Group 2-Sleep deprivation (PS; n = 8): the animals were submitted to Paradoxical Sleep deprivation for 96 h and Group 3-Recovery (R; n = 8): the animals were submitted to sleep loss for 96 h, followed by a period of 96 h without any intervention. The following parameters were evaluated: microscopic analysis, immunohistochemistry for Caspase-3, Ki-67, and COX-2 and gene expression of cytochrome C, TNF-α, and Interleukins 6, 10.

RESULTS

The results pointed out acinar atrophy, and the presence of cytoplasmic vacuoles in the parenchyma of the experimental groups. In the same groups, there was differential expression of interleukins 6, 10 and TNF-α. Apoptosis was also increased by means of cleaved caspase 3 expression. The cellular proliferation (ki-67 expression) was increased the R group.

CONCLUSION

Taken together, sleep deprivation induces tissue degeneration, inflammatory process, as well as activate apoptosis in the parotid gland of rats.

Interactions between Sleep and Emotions in Humans and Animal Models

Recently, increased interest and efforts were observed in describing the possible interaction between sleep and emotions. Human and animal model studies addressed the implication of both sleep patterns and emotional processing in neurophysiology and neuropathology in suggesting a bidirectional interaction intimately modulated by complex mechanisms and factors. In this context, we aimed to discuss recent evidence and possible mechanisms implicated in this interaction, as provided by both human and animal models in studies. In addition, considering the affective component of brain physiological patterns, we aimed to find reasonable evidence in describing the two-way association between comorbid sleep impairments and psychiatric disorders. The main scientific literature databases (PubMed/Medline, Web of Science) were screened with keyword combinations for relevant content taking into consideration only English written papers and the inclusion and exclusion criteria, according to PRISMA guidelines. We found that a strong modulatory interaction between sleep processes and emotional states resides on the activity of several key brain structures, such as the amygdala, prefrontal cortex, hippocampus, and brainstem nuclei. In addition, evidence suggested that physiologically and behaviorally related mechanisms of sleep are intimately interacting with emotional perception and processing which could advise the key role of sleep in the unconscious character of emotional processes. However, further studies are needed to explain and correlate the functional analysis with causative and protective factors of sleep impairments and negative emotional modulation on neurophysiologic processing, mental health, and clinical contexts.

The Pituitary-Adrenal Response to Paradoxical Sleep Deprivation Is Similar to a Psychological Stressor, Whereas the Hypothalamic Response Is Unique

Stressors of different natures induce activation of the hypothalamic-pituitary-adrenal (HPA) axis at different magnitudes. Moreover, the HPA axis response to repeated exposure is usually distinct from that elicited by a single session. Paradoxical sleep deprivation (PSD) augments ACTH and corticosterone (CORT) levels, but the nature of this stimulus is not yet defined. The purpose of the present study was to qualitatively compare the stress response of animals submitted to PSD to that of rats exposed once or four times to cold, as a physiological stress, movement restraint (RST) as a mixed stressor and predator odour (PRED) as the psychological stressor, whilst animals were submitted for 1 or 4 days to PSD and respective control groups. None of the stressors altered corticotropin releasing factor immunoreactivity in the paraventricular nucleus of the hypothalamus (PVN), median eminence (ME) or central amygdala, compared to control groups, whereas vasopressin immunoreactivity in PSD animals was decreased in the PVN and increased in the ME, indicating augmented activity of this system. ACTH levels were higher after repeated stress or prolonged PSD than after single- or 1 day-exposure and control groups, whereas the CORT response was habituated by repeated stress, but not by 4-days PSD. This dissociation resulted in changes in the CORT : ACTH ratio, with repeated cold and RST decreasing the ratio compared to single exposure, but no change was seen in PRED and PSD groups. Comparing the magnitude and pattern of pituitary-adrenal response to the different stressors, PSD-induced responses were closer to that shown by PRED-exposed rats. In contrast, the hypothalamic response of PSD-exposed rats was unique, inasmuch as this was the only stressor which increased the activity of the vasopressin system. In conclusion, we propose that the pituitary-adrenal response to PSD is similar to that induced by a psychological stressor.

Use of Actigraphy for a Rat Behavioural Sleep Study

Previous studies of animal behavioural sleep is mainly divided into two study types, observation by video recording or counts by sensor, both of which require a complex environment and procedure. An actigraph unit is a commercially available product which can provide non-invasive monitoring human rest/activity cycles. The goal of this study was to evaluate whether actigraphy can be applied for analysing behavioural sleep in rats, since no reports have described utilization of the actigraphy unit for monitoring sleep of small animals. The actigraph unit was held on the chest of eight male rats by a loose elastic belt. The rats spent two days in a normal condition, followed by two days of sleep deprivation. Total counts measured by the actigraph could be clearly divided into two phases, sleep phase and awake phase, when the rats were kept in the normal cage. Next, the rats were moved into the sleep-deviation cage, and the total counts were significantly higher during daytime, indicating the successful induction of sleep deprivation. These results showed that the actigraphy unit monitored rest/activity cycles of rats, which will contribute to making sleep behaviour experiments easier.

Sleep and stress in mother-toddler dyads living in low-income homes

Optimal sleeping behaviors are critical for overall development, yet some evidence suggests stress and living in a low-income environment are associated with disruptions of sleeping behaviors early in life. In this study, we investigated the association of toddler sleeping behaviors, particularly difficulties initiating and/or maintaining sleep (DIMS), and maternal and toddler prolonged stress using hair cortisol from dyads living in low-income homes. Hair cortisol was mainly sampled at the posterior vertex of mothers and toddlers (age 20-24 months) and analyzed with immunoassay (n = 94). Toddler DIMS were assessed at 15-19 and 27-31 months of age through mother-rated reports using the Tayside Children's Sleep Questionnaire. We found no associations between toddler DIMS and maternal stress. Additionally, early DIMS did not predict toddler stress. However, while controlling for early DIMS and sociodemographic factors, we found that higher toddler stress predicted greater DIMS in later toddlerhood (b = -2.28, SE = 0.98, p = .02, d_s  = 0.64). These study findings highlight the importance of understanding the role of early life stress on later sleep patterns.

Sleep Disturbance during Infection Compromises Tfh Differentiation and Impacts Host Immunity

Although the influence of sleep quality on the immune system is well documented, the mechanisms behind its impact on natural host immunity remain unclear. Meanwhile, it has been suggested that neuroimmune interactions play an important role in this phenomenon. To evaluate the impact of stress-induced sleep disturbance on host immunity, we used a murine model of rapid eye movement sleep deprivation (RSD) integrated with a model of malaria blood-stage infection. We demonstrate that sleep disturbance compromises the differentiation of T follicular helper cells, increasing host susceptibility to the parasite. Chemical inhibition of glucocorticoid (Glcs) synthesis showed that abnormal Glcs production compromised the transcription of Tfh-associated genes resulting in impaired germinal center formation and humoral immune response. Our data demonstrate that RSD-induced abnormal activation of the hypothalamic-pituitary-adrenal axis drives host susceptibility to infection. Understanding the impact of sleep quality in natural resistance to infection may provide insights for disease management.

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REM sleep deprivation (RSD) worsens malaria induced by Plasmodium yoelii infection

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RSD decreases germinal center formation and impairs specific antibody production

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Exacerbated glucocorticoid production impairs T lymphocyte differentiation

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The relationship between sleep and immunity is a target for malaria management

Sex differences in the hypothalamic-pituitary-adrenal axis response following a single or multiple days of sleep restriction

One in three adults reports experiencing inadequate or disrupted sleep throughout the night, with the incidence being higher in women than in men. Disturbances in nightly sleep result in physiological alterations that contribute to a number of disorders. Poor sleep quality is believed to contribute to the pathogenesis of these disorders through interactions with the hypothalamic-pituitary-adrenal (HPA) axis. The present study investigated the effect of one and three days of restricted sleep on HPA axis reactivity. Male and female C57BL/6J (n = 8/group) mice were sleep-deprived for a 20 h period for one day or three consecutive days using the modified multiple platform method, and then subjected to acute restraint stress. In response to sleep restriction, males showed blunted restraint-induced rises in CORT relative to controls. After three days of restricted sleep, females showed a similar attenuation in restraint-induced CORT. However, this effect was ablated after a single day of sleep restriction. Analyses of gene expression revealed significant elevations in the expression of pituitary HPA axis regulatory genes proopiomelanocortin and corticotropin releasing factor receptor 1 in both sexes following sleep restriction. In males, but not females, adrenal mRNA expression of 11β-hydroxylase and melanocortin receptor 2 were also increased. Altogether, these data suggest several possible mechanisms are involved in the HPA axis dysregulation following sleep restriction, and that there are sex differences in how the HPA axis responds to sleep loss.Lay summarySleep restriction alters the stress response differently in males and females following varying nights of sleep restriction. These alterations are accompanied by changes in gene expression in the pituitary and adrenal glands.

Transient neonatal sleep fragmentation results in long-term neuroinflammation and cognitive impairment in a rabbit model

Sleep fragmentation is an increase in sleep-wake transitions without an overall decrease in total sleep time. Sleep fragmentation is well documented during acute and chronic hospitalization and can result in delirium and memory problems in children. Sleep fragmentation is also often noted in neurodevelopmental disorders. However, it is unclear how sleep fragmentation independent of disease affects brain development and function. We hypothesized that acute sleep fragmentation during the neonatal period in otherwise healthy animals would result in neuroinflammation and would be associated with abnormalities in cognitive development. The orbital shaker method was used to fragment sleep for 72 h in postnatal day 3 New Zealand white rabbit kits (fragmentation group). To control for maternal separation, the sham group was separated from the dam and maintained in the same conditions without undergoing sleep fragmentation. A naïve control group remained with the dam. Kits underwent behavioral testing with novel object recognition and spontaneous alternation T-maze tests at 2-3 weeks post-fragmentation and were sacrificed 3-50 days after fragmentation. Sleep fragmentation resulted in acute and chronic changes in microglial morphology in the hippocampus and cortex, and regional differences in mRNA expression of pro- and anti-inflammatory cytokines at 3, 7 and 50 days post-fragmentation. Impaired novel object recognition and a longer latency in T-maze task completion were noted in the fragmented kits. This was in spite of normalization of sleep architecture noted at 2 months of age in these kits. The results indicate that transient neonatal sleep fragmentation results in short-term and long-term immune alterations in the brain, along with diminished performance in cognitive tasks long-term.

Sleep deprivation and stress: a reciprocal relationship

Sleep is highly conserved across evolution, suggesting vital biological functions that are yet to be fully understood. Animals and humans experiencing partial sleep restriction usually exhibit detrimental physiological responses, while total and prolonged sleep loss could lead to death. The perturbation of sleep homeostasis is usually accompanied by an increase in hypothalamic–pituitary–adrenal (HPA) axis activity, leading to a rise in circulating levels of stress hormones (e.g. cortisol in humans, corticosterone in rodents). Such hormones follow a circadian release pattern under undisturbed conditions and participate in the regulation of sleep. The investigation of the consequences of sleep deprivation, from molecular changes to behavioural alterations, has been used to study the fundamental functions of sleep. However, the reciprocal relationship between sleep and the activity of the HPA axis is problematic when investigating sleep using traditional sleep-deprivation protocols that can induce stress per se. This is especially true in studies using rodents in which sleep deprivation is achieved by exogenous, and potentially stressful, sensory–motor stimulations that can undoubtedly confuse their conclusions. While more research is needed to explore the mechanisms underlying sleep loss and health, avoiding stress as a confounding factor in sleep-deprivation studies is therefore crucial. This review examines the evidence of the intricate links between sleep and stress in the context of experimental sleep deprivation, and proposes a more sophisticated research framework for sleep-deprivation procedures that could benefit from recent progress in biotechnological tools for precise neuromodulation, such as chemogenetics and optogenetics, as well as improved automated real-time sleep-scoring algorithms.

Disruption of Rapid Eye Movement Sleep Homeostasis in Adolescent Rats after Neonatal Anesthesia

BACKGROUND

Previous studies suggest that rapid eye movement sleep rebound and disruption of rapid eye movement sleep architecture occur during the first 24 h after general anesthesia with volatile anesthetics in adult rats. However, it is unknown whether rapid eye movement sleep alterations persist beyond the anesthetic recovery phase in neonatal rats. This study tested the hypothesis that rapid eye movement sleep disturbances would be present in adolescent rats treated with anesthesia on postnatal day 7.

METHODS

Forty-four neonatal rats were randomly allocated to treatment with anesthesia consisting of midazolam, nitrous oxide, and isoflurane or control conditions for 2 h or 6 h. Electroencephalographic and electromyographic electrodes were implanted and recordings obtained between postnatal days 26 and 34. The primary outcome was time spent in rapid eye movement sleep. Data were analyzed using two-tailed unpaired t tests and two-way repeated measures analysis of variance.

RESULTS

Rats treated with midazolam, nitrous oxide, and isoflurane exhibited a significant increase in rapid eye movement sleep three weeks later when compared with control rats, regardless of whether they were treated for 2 h (174.0 ± 7.2 min in anesthetized, 108.6 ± 5.3 in controls, P < 0.0001) or 6 h (151.6 ± 9.9 min in anesthetized, 108.8 ± 7.1 in controls, P = 0.002).

CONCLUSIONS

Treatment with midazolam, nitrous oxide, and isoflurane on postnatal day 7 increases rapid eye movement sleep three weeks later in rats.

Insights into paradoxical (REM) sleep homeostatic regulation in mice using an innovative automated sleep deprivation method

Identifying the precise neuronal networks activated during paradoxical sleep (PS, also called REM sleep) has been a challenge since its discovery. Similarly, our understanding of the homeostatic mechanisms regulating PS, whether through external modulation by circadian and ultradian drives or via intrinsic homeostatic regulation, is still limited, largely due to interfering factors rendering the investigation difficult. Indeed, none of the studies published so far were able to manipulate PS without significantly altering slow-wave sleep and/or stress level, thus introducing a potential bias in the analyses. With the aim of achieving a better understanding of PS homeostasis, we developed a new method based on automated scoring of vigilance states—using electroencephalogram and electromyogram features—and which involves closed-loop PS deprivation through the induction of cage floor movements when PS is detected. Vigilance states were analyzed during 6 and 48 h of PS deprivation as well as their following recovery periods. Using this new automated methodology, we were able to deprive mice of PS with high efficiency and specificity, for short or longer periods of time, observing no sign of stress (as evaluated by plasma corticosterone level and sleep latency) and requiring no human intervention or environmental changes. We show here that PS can be homeostatically modulated and regulated while no significant changes are induced on slow-wave sleep and wakefulness, with a PS rebound duration depending on the amount of prior PS deficit. We also show that PS interval duration is not correlated with prior PS episode duration in the context of recovery from PS deprivation.

Rat Strain and Housing Conditions Alter Oxidative Stress and Hormone Responses to Chronic Intermittent Hypoxia

Sleep apnea has been associated with elevated risk for metabolic, cognitive, and cardiovascular disorders. Further, the role of hypothalamic–pituitary–adrenal (HPA) activation in sleep apnea has been controversial in human studies. Chronic intermittent hypoxia (CIH) is a rodent model, which mimics the hypoxemia experienced by patients with sleep apnea. Most studies of CIH in rats have been conducted in the Sprague Dawley rat strain. Previously published literature suggests different strains of rats exhibit various responses to disease models, and these effects can be further modulated by the housing conditions experienced by each strain. This variability in response is similar to what has been observed in clinical populations, especially with respect to the HPA system. To investigate if strain or housing (individual or pair-housed) can affect the results of CIH (AHI 8 or 10) treatment, we exposed individual and pair-housed Sprague Dawley and Long-Evans male rats to 7 days of CIH treatment. This was followed by biochemical analysis of circulating hormones, oxidative stress, and neurodegenerative markers. Both strain and housing conditions altered oxidative stress generation, hyperphosphorylated tau protein (tau tangles), circulating corticosterone and adrenocorticotropic hormone (ACTH), and weight metrics. Specifically, pair-housed Long-Evans rats were the most sensitive to CIH, which showed a significant association between oxidative stress generation and HPA activation under conditions of AHI of 8. These results suggest both strain and housing conditions can affect the outcomes of CIH.

Phosphorylated delta sleep inducing peptide restores spatial memory and p-CREB expression by improving sleep architecture at high altitude

AIMS

Sleep loss at high altitude (HA) play major role in worsening of neuropsychological functions, such as attention, memory and decision making. This study investigates the role of phosphorylated delta sleep inducing peptide (p-DSIP) in improving sleep architecture during chronic hypobaric hypoxia (HH) exposure and restoration of spatial navigational memory.

METHODS

Morris water maze (MWM) trained rats were exposed to HH at 7620 m. p-DSIP was injected intra-peritoneally (10 μg/Kg bw) during HH exposure as an intervention against sleep alteration. Sleep architecture was recorded telemetrically before and during HH exposure. Monoamines were estimated by high performance liquid chromatography from brain stem (BS) and hypothalamus. CREB and p-CREB level in hippocampus was studied by western blotting and expression of different monoamine regulatory enzymes in BS was measured by flow cytometry. Naloxone (1 mg/kg bw), a μ opioid receptor antagonist of sleep inducing effect of DSIP was also studied.

KEY FINDINGS

p-DSIP injection daily in circadian active period (18.30 h) during chronic HH enhanced non rapid eye movement sleep, rapid eye movement sleep as well as improved MWM performance of rats. p-DSIP treatment showed lower monoamine level and tyrosine hydroxylase (TH) expression and increased monoamine oxidase A (MAO A), glutamic acid decarboxylase (GAD) and Choline acetyltransferase (ChAT) expression. Further, naloxone altered navigational memory by decreasing the CREB and p-CREB level in hippocampus suggesting suppression of sleep inducing effect of p-DSIP.

SIGNIFICANCE

Our study demonstrates that improvement of sleep quality by p-DSIP restores spatial memory by up regulating CREB phosphorylation during simulated high altitude hypoxia.

Relevance of deprivation studies in understanding rapid eye movement sleep

Rapid eye movement sleep (REMS) is a unique phenomenon essential for maintaining normal physiological processes and is expressed at least in species higher in the evolution. The basic scaffold of the neuronal network responsible for REMS regulation is present in the brainstem, which may be directly or indirectly influenced by most other physiological processes. It is regulated by the neurons in the brainstem. Various manipulations including chemical, elec-trophysiological, lesion, stimulation, behavioral, ontogenic and deprivation studies have been designed to understand REMS genesis, maintenance, physiology and functional significance. Although each of these methods has its significance and limitations, deprivation studies have contributed significantly to the overall understanding of REMS. In this review, we discuss the advantages and limitations of various methods used for REMS deprivation (REMSD) to understand neural regulation and physiological significance of REMS. Among the deprivation strategies, the flowerpot method is by far the method of choice because it is simple and convenient, exploits physiological parameter (muscle atonia) for REMSD and allows conducting adequate controls to overcome experimental limitations as well as to rule out nonspecific effects. Notwithstanding, a major criticism that the flowerpot method faces is that of perceived stress experienced by the experimental animals. Nevertheless, we conclude that like most methods, particularly for in vivo behavioral studies, in spite of a few limitations, given the advantages described above, the flowerpot method is the best method of choice for REMSD studies.

Functions and Mechanisms of Sleep

Sleep is a complex physiological process that is regulated globally, regionally, and locally by both cellular and molecular mechanisms. It occurs to some extent in all animals, although sleep expression in lower animals may be co-extensive with rest. Sleep regulation plays an intrinsic part in many behavioral and physiological functions. Currently, all researchers agree there is no single physiological role sleep serves. Nevertheless, it is quite evident that sleep is essential for many vital functions including development, energy conservation, brain waste clearance, modulation of immune responses, cognition, performance, vigilance, disease, and psychological state. This review details the physiological processes involved in sleep regulation and the possible functions that sleep may serve. This description of the brain circuitry, cell types, and molecules involved in sleep regulation is intended to further the reader's understanding of the functions of sleep.

Renin knockout rat: control of adrenal aldosterone and corticosterone synthesis in vitro and adrenal gene expression

The classic renin-angiotensin system is partly responsible for controlling aldosterone secretion from the adrenal cortex via the peptide angiotensin II (ANG II). In addition, there is a local adrenocortical renin-angiotensin system that may be involved in the control of aldosterone synthesis in the zona glomerulosa (ZG). To characterize the long-term control of adrenal steroidogenesis, we utilized adrenal glands from renin knockout (KO) rats and compared steroidogenesis in vitro and steroidogenic enzyme expression to wild-type (WT) controls (Dahl S rat). Adrenal capsules (ZG; aldosterone production) and subcapsules [zona reticularis/fasciculata (ZFR); corticosterone production] were separately dispersed and studied in vitro. Plasma renin activity and ANG II concentrations were extremely low in the KO rats. Basal and cAMP-stimulated aldosterone production was significantly reduced in renin KO ZG cells, whereas corticosterone production was not different between WT and KO ZFR cells. As expected, adrenal renin mRNA expression was lower in the renin KO compared with the WT rat. Real-time PCR and immunohistochemical analysis showed a significant decrease in P450aldo (Cyp11b2) mRNA and protein expression in the ZG from the renin KO rat. The reduction in aldosterone synthesis in the ZG of the renin KO adrenal seems to be accounted for by a specific decrease in P450aldo and may be due to the absence of chronic stimulation of the ZG by circulating ANG II or to a reduction in locally released ANG II within the adrenal gland.

Effects of sleep deprivation on different phases of memory in the rat: dissociation between contextual and tone fear conditioning tasks

Numerous studies show that sleep deprivation (SD) impacts negatively on cognitive processes, including learning and memory. Memory formation encompasses distinct phases of which acquisition, consolidation and retrieval are better known. Previous studies with pre-training SD induced by the platform method have shown impairment in fear conditioning tasks. Nonetheless, pre-training manipulations do not allow the distinction between effects on acquisition and/or consolidation, interfering, ultimately, on recall of/performance in the task. In the present study, animals were first trained in contextual and tone fear conditioning (TFC) tasks and then submitted to SD with the purpose to evaluate the effect of this manipulation on different stages of the learning process, e.g., in the uptake of (new) information during learning, its encoding and stabilization, and the recall of stored memories. Besides, we also investigated the effect of SD in the extinction of fear memory and a possible state-dependent learning induced by this manipulation. For each task (contextual or TFC), animals were trained and then distributed into control, not sleep-deprived (CTL) and SD groups, the latter being submitted to the modified multiple platform paradigm for 96 h. Subsets of eight rats in each group/experiment were submitted to the test of the tasks, either immediately or at different time intervals after SD. The results indicated that (a) pre- but not post-training SD impaired recall in the contextual and TFC; (b) this impairment was not state-dependent; and (c) in the contextual fear conditioning (CFC), pre-test SD prevented extinction of the learned task. Overall, these results suggest that SD interferes with acquisition, recall and extinction, but not necessarily with consolidation of emotional memory.

Development and pharmacological characterization of a model of sleep disruption-induced hypersensitivity in the rat

BACKGROUND

Sleep disturbance is a commonly reported co-morbidity in chronic pain patients, and conversely, disruption of sleep can cause acute and long-lasting hypersensitivity to painful stimuli. The underlying mechanisms of sleep disruption-induced pain hypersensitivity are poorly understood. Confounding factors of previous studies have been the sleep disruption protocols, such as the 'pedestal over water' or 'inverted flower pot' methods, that can cause large stress responses and therefore may significantly affect pain outcome measures.

METHODS

Sleep disruption was induced by placing rats for 8 h in a slowly rotating cylindrical cage causing arousal via the righting reflex. Mechanical (Von Frey filaments) and thermal (Hargreaves) nociceptive thresholds were assessed, and plasma corticosterone levels were measured (mass spectroscopy). Sleep disruption-induced hypersensitivity was pharmacologically characterized with drugs relevant for pain treatment, including gabapentin (30 mg/kg and 50 mg/kg), Ica-6p (Kv7.2/7.3 potassium channel opener; 10 mg/kg), ibuprofen (30 mg/kg and 100 mg/kg) and amitriptyline (10 mg/kg).

RESULTS

Eight hours of sleep disruption caused robust mechanical and heat hypersensitivity in the absence of a measurable change in plasma corticosterone levels. Gabapentin had no effect on reduced nociceptive thresholds. Ibuprofen attenuated mechanical thresholds, while Ica-6p and amitriptyline attenuated only reduced thermal nociceptive thresholds.

CONCLUSIONS

These results show that acute and low-stress sleep disruption causes mechanical and heat hypersensitivity in rats. Mechanical and heat hypersensitivity exhibited differential sensitivity to pharmacological agents, thus suggesting dissociable mechanisms for those two modalities. Ultimately, this model could help identify underlying mechanisms linking sleep disruption and hypersensitivity.

Extended wakefulness: compromised metabolics in and degeneration of locus ceruleus neurons

Modern society enables a shortening of sleep times, yet long-term consequences of extended wakefulness on the brain are largely unknown. Essential for optimal alertness, locus ceruleus neurons (LCns) are metabolically active neurons that fire at increased rates across sustained wakefulness. We hypothesized that wakefulness is a metabolic stressor to LCns and that, with extended wakefulness, adaptive mitochondrial metabolic responses fail and injury ensues. The nicotinamide adenine dinucleotide-dependent deacetylase sirtuin type 3 (SirT3) coordinates mitochondrial energy production and redox homeostasis. We find that brief wakefulness upregulates SirT3 and antioxidants in LCns, protecting metabolic homeostasis. Strikingly, mice lacking SirT3 lose the adaptive antioxidant response and incur oxidative injury in LCns across brief wakefulness. When wakefulness is extended for longer durations in wild-type mice, SirT3 protein declines in LCns, while oxidative stress and acetylation of mitochondrial proteins, including electron transport chain complex I proteins, increase. In parallel with metabolic dyshomeostasis, apoptosis is activated and LCns are lost. This work identifies mitochondrial stress in LCns upon wakefulness, highlights an essential role for SirT3 activation in maintaining metabolic homeostasis in LCns across wakefulness, and demonstrates that extended wakefulness results in reduced SirT3 activity and, ultimately, degeneration of LCns.