Evidence for a sleep-promoting influence of stress

Regulation of stress-induced sleep perturbations by dorsal raphe VGLUT3 neurons in male mice

Exposure to stressors has profound effects on sleep that have been linked to serotonin (5-HT) neurons of the dorsal raphe nucleus (DR). However, the DR also comprises glutamatergic neurons expressing vesicular glutamate transporter type 3 (DRVGLUT3), leading us to examine their role. Cell-type-specific tracing revealed that DRVGLUT3 neurons project to brain areas regulating arousal and stress. We found that chemogenetic activation of DRVGLUT3 neurons mimics stress-induced sleep perturbations. Furthermore, deleting VGLUT3 in the DR attenuated stress-induced sleep perturbations, especially after social defeat stress. In the DR, VGLUT3 is found in subsets of 5-HT and non-5-HT neurons. We observed that both populations are activated by acute stress, including those projecting to the ventral tegmental area. However, deleting VGLUT3 in 5-HT neurons minimally affected sleep regulation. These findings suggest that VGLUT3 expression in the DR drives stress-induced sleep perturbations, possibly involving non-5-HT DRVGLUT3 neurons.

Bifidobacterium adolescentis SBT2786 Improves Sleep Quality in Japanese Adults with Relatively High Levels of Stress: A Randomized, Double-Blind, Placebo-Controlled Study

Sleep disorders associated with lifestyle changes and unhealthy habits are major public health concerns. Our previous study showed that Bifidobacterium adolescentis SBT2786 has a potent sleep-promoting effect on fruit flies. Fruit flies share many similarities with mammals, making them suitable model organisms for studying sleep. Thus, in the present study, we conducted a randomized, double-blind, placebo-controlled clinical trial to test whether SBT2786 has sleep-enhancing effects in humans. In this study, 61 participants in the SBT2786 group and 65 participants in the placebo group were analyzed. The results showed that SBT2786 increased sleep time; however, it predominantly increased light sleep and did not improve subjective sleep quality. Interestingly, mood improvement was observed. A subgroup analysis was conducted on participants with high stress levels, and results showed that these participants experienced an increase in sleep duration and an improvement in sleepiness upon waking up and reported feeling well-rested during the day. We concluded that SBT2786 may improve sleep quality, particularly in individuals experiencing high levels of stress, and that SBT2786 can be used as a dietary supplement to improve sleep and mood.

Heatwaves and human sleep: Stress response versus adaptation

The World Meteorological Organization considers a heatwave as "a period of statistically unusual hot weather persisting for a number of days and nights". Accompanying the ongoing global climate change, sharp heatwave bouts occur worldwide, growing in frequency and intensity, and beginning earlier in the season. Heatwaves exacerbate the risk of heat-related illnesses, hence human morbidity and mortality, particularly in vulnerable elderly and children. Heat-related illnesses present a continuum from normothermic (prickly heat, heat edema, heat cramps, heat tetany) to hyperthermic syndromes (from heat syncope and heat exhaustion to lethal heat stroke). Heat stroke may occur through passive heating and/or exertional exercise. "Normal sleep", such as observed in temperate conditions, is altered during heatwaves. Brisk excessive heat bouts shorten and fragment human sleep. Particularly, deep N3 sleep (formerly slow-wave sleep) and REM sleep are depleted, such as in other stressful situations. The resultant sleep loss is deleterious to cognitive performance, emotional brain function, behavior, and susceptibility to chronic health conditions and infectious diseases. Our group has previously demonstrated that sleep constitutes an adaptive mechanism during climatic heat acclimatization. In parallel, artificial heat acclimation procedures have been proposed in sports and military activities, and for the elderly. Other preventive actions should be considered, such as education and urban heat island cooling (vegetation, white paint), thus avoiding energy-hungry air conditioning.

Identification of salivary microRNA profiles in male mouse model of chronic sleep disorder

Chronic sleep disorders (CSD) comprise a potential risk factor for metabolic and cardiovascular diseases, obesity and stroke. Thus, the identification of biomarkers for CSD is an important step in the early prevention of metabolic dysfunctions induced by sleep dysfunction. Diagnostic saliva samples can be easily and noninvasively collected. Thus, we aimed to identify whole microRNA (miRNA) profiles of saliva in control and psychophysiologically stressed CSD mouse models and compare them at Zeitgeber time (ZT) 0 (lights on) and ZT12 (lights off). The findings of two-way ANOVA revealed that the expression of 342 and 109 salivary miRNAs was affected by CSD and the time of day, respectively. Interactions were found in 122 miRNAs among which, we identified 197 (ZT0) and 62 (ZT12) upregulated, and 40 (ZT0) and seven (ZT12) downregulated miRNAs in CSD mice. We showed that miR-30c-5p, which is elevated in the plasma of patients with hypersomnia, was upregulated in the saliva of CSD mice collected at ZT0. The miRNAs, miR-10a-5p, miR-146b-5p, miR-150-5p, and miR-25-3p are upregulated in the serum of humans with poor sleep quality, and these were also upregulated in the saliva of CSD mice collected at ZT0. The miRNAs miR-30c, miR146b-5p, miR150, and miR-25-5p are associated with cardiovascular diseases, and we found that plasma concentrations of brain natriuretic peptides were significantly increased in CSD mice. The present findings showed that salivary miRNA profiles could serve as useful biomarkers for predicting CSD.

Chronic restraint stress impairs voluntary wheel running but has no effect on food-motivated behavior in mice

Chronic restraint stress is known to cause significant alterations of mitochondrial biology. However, its effects on effort-based behavior and the sensitivity of these effects to treatments that restore mitochondrial function have not been assessed. Based on the hypothesis that the behavioral consequences of this stressor should be more severe for an energy demanding activity than for an energy procuring activity, we compared the effects of chronic restraint stress on the performance of male mice trained to use a running wheel or to nose poke for a food reward in an operant conditioning cage. In accordance with our hypothesis, we observed that exposure of mice to 2-hour daily restraint sessions for 14 to 16 days during the light phase of the cycle reliably decreased voluntary wheel running but had no effect on working for food in a fixed ratio 10 schedule of food reinforcement or in a progressive ratio schedule of food reinforcement. This dissociation between the two types of behavioral activities could reflect an adaptive response to the constraint imposed by chronic restraint stress on mitochondria function and its negative consequences on energy metabolism. To determine whether it is the case, we administered mesenchymal stem cells intranasally to chronically restrained mice to repair the putative mitochondrial dysfunction induced by chronic restraint stress. This intervention had no effect on wheel running deficits. Assessment of mitochondrial gene expression in the brain of mice submitted to chronic restraint stress revealed an increase in the expression of genes involved in mitochondrial biology that showed habituation with repetition of daily sessions of restraint stress. These original findings can be interpreted to indicate that chronic restraint stress induces behavioral and mitochondrial adjustments that contribute to metabolic adaptation to this stressor and maintain metabolic flexibility.

Pre-exposure via wire-mesh partition reduces intraspecific aggression in male, wild-type Norway rats

There are instances when animals are introduced and expected to live alongside unfamiliar conspecifics within zoos, laboratories and wildlife sanctuaries. These pairings of unfamiliar animals may result in stress, trauma, or even death, in addition to reduced confidence in data resulting from these subjects. For species that communicate relatedness, sex, social status, and emotional state through olfactory cues (eg pheromones), one means of counteracting aggression may involve a period of partial separation — where animals are close enough to become acquainted — while a permeable barrier maintains separation. For our study, we evaluated the use of a novel, autoclavable, wire-mesh partition to separate potential aggressors. We tested different pairs of 24 wild-type male Norway rats (Rattus norvegicus), previously kept in social isolation for seven days. Each control pair were merged directly into one cage, while pairs from the experimental groups underwent three pre-exposure sessions that lasted two to four days. We used continuous video recordings to assess five common threat displays: lateral threat, keep down, upright posture, chase, and clinch attack. We used two types of bedding: new (unscented) bedding and recently used bedding that conveyed scents from both merged rats. We found that rats subjected to pre-exposure demonstrated lower aggression levels across three of the five metrics (lateral threats, upright postures, and keep downs). We conclude that permeable partitions show promise as a humane mechanism to mix new individuals into preexisting colonies. Further research may explore whether partitions could be helpful with other species that communicate social information by pheromones or direct visual inspection.

Challenging sleep homeostasis

In this commentary, I play the Devil’s advocate and assume the title of High Contrarian. I intend to be provocative to challenge long-standing ideas about sleep. I blame all on Professor Craig Heller, who taught me to think this way as a graduate student in his laboratory. Scientists should fearlessly jump into the foaming edge of what we know, but also consider how safe are their intellectual harbors. There are many ideas we accept as ‘known’: that sleep is ubiquitous in the animal kingdom, that it serves vital functions, that it plays an essential role in brain plasticity. All of this could be wrong. As one example, I reexamine the idea that sleep is regulated by a mysterious ‘homeostat’ that determines sleep need based on prior wake time.

Sleep in honey bees is affected by the herbicide glyphosate

Sleep plays an essential role in both neural and energetic homeostasis of animals. Honey bees (Apis mellifera) manifest the sleep state as a reduction in muscle tone and antennal movements, which is susceptible to physical or chemical disturbances. This social insect is one of the most important pollinators in agricultural ecosystems, being exposed to a great variety of agrochemicals, which might affect its sleep behaviour. The intake of glyphosate (GLY), the herbicide most widely used worldwide, impairs learning, gustatory responsiveness and navigation in honey bees. In general, these cognitive abilities are linked with the amount and quality of sleep. Furthermore, it has been reported that animals exposed to sleep disturbances show impairments in both metabolism and memory consolidation. Consequently, we assessed the sleep pattern of bees fed with a sugar solution containing GLY (0, 25, 50 and 100 ng) by quantifying their antennal activity during the scotophase. We found that the ingestion of 50 ng of GLY decreased both antennal activity and sleep bout frequency. This sleep deepening after GLY intake could be explained as a consequence of the regenerative function of sleep and the metabolic stress induced by the herbicide.

Heart Rate and Heart Rate Variability during Sleep in Family Dogs (Canis familiaris). Moderate Effect of Pre-Sleep Emotions

Simple Summary

It is common knowledge that negative emotions in humans are accompanied by both impaired subjective experience as well as maladaptive changes in behavior and physiology. The present paper investigates heart rate—one of the most commonly used emotion-related physiology measures—in the family dog, with the aim of uncovering its potential relationship with emotions. Sleep recordings were conducted following a positive versus a negative social interaction, as sleep alternations are one of the most conspicuous changes in response to negative affect. We observed differences in heart rate following the positive versus negative interactions, however these were only apparent during wakefulness, but not during sleep.

Abstract

The domestic dog (Canis familiaris) has been shown to both excel in recognising human emotions and produce emotion-related vocalisations and postures that humans can easily recognise. However, little is known about the effect of emotional experiences on subsequent sleep physiology, a set of phenomena heavily interrelated with emotions in the case of humans. The present paper examines heart rate (HR) and heart rate variability (HRV) during dogs’ sleep, measures that are influenced by both positive and negative emotions in awake dogs. In Study I, descriptive HR and HRV data is provided on N = 12 dogs about the different sleep stages (wake, drowsiness, non-rapid eye movement (non-REM), REM; scoring based on electroencephalogram (EEG) data). We conclude that wakefulness is characterised by higher HR and lower HRV compared to all sleep stages. Furthermore, drowsiness is characterised by higher HR and lower HRV than non-REM and REM, but only if the electrocardiogram (ECG) samples are taken from the first occurrence of a given sleep stage, not when the longest periods of each sleep stage are analysed. Non-REM and REM sleep were not found to be different from each other in either HR or HRV parameters. In Study II, sleep HR and HRV measures are compared in N = 16 dogs after a positive versus negative social interaction (within-subject design). The positive social interaction consisted of petting and ball play, while the negative social interaction was a mixture of separation, threatening approach and still face test. Results are consistent with the two-dimensional emotion hypothesis in that following the intense positive interaction more elevated HR and decreased HRV is found compared to the mildly negative (lower intensity) interaction. However, although this trend can be observed in all sleep stages except for REM, the results only reach significance in the wake stage. In sum, the present findings suggest that HR and HRV are possible to measure during dogs’ sleep, and can potentially be used to study the effect of emotions not only during but also after such interactions.

Social partnering alters sleep in fear-conditioned Wistar rats

Social support, when provided following a traumatic experience, is associated with a lower incidence of stress-related psychiatric disorders. Our hypothesis was that providing a social interaction period with a naive conspecific would improve sleep architecture in response to cued fear conditioning in Wistar rats. Rats were randomly assigned to either the socially isolated or socially partnered groups. Rats assigned to the socially isolated group were individually housed following electrode implantation and fear conditioning. Rats assigned to the socially partnered group were initially paired-housed, and then one rat from each pair was randomly chosen for sleep electrode implantation and fear conditioning. Rats from both groups were habituated to a recording chamber, and baseline sleep was recorded over 22 hours. One day later (Training Day), they were fear-conditioned to 10 presentations of a tone (800 Hz, 90 dB, 5 sec) co-terminating with a mild electric foot shock (1.0 mA, 0.5 sec), at 30-sec intervals. While rats in the socially isolated group were left undisturbed in their home cage for 30-min, socially partnered rats interacted for 30 minutes with their non-stressed rat partner immediately after fear conditioning and while the auditory tones were presented on Days 1 and 14. The results indicated that social interaction increased sleep efficiency in partnered rats compared to isolated rats following the fear conditioning procedure. This was due to an increase in the amount of rapid eye movement sleep (REMS) during the light phase. Evaluation of REMS microarchitecture revealed that the increase in REMS was due to an increase in the number of single REMS episodes (siREMS), which represented a more consolidated REMS pattern. A surprising finding was that partnered rats had a greater number of sequential REMS episodes (seqREMS) at Baseline, on the Training Day and on Day 1 when compared to isolated rats. The greater number of seqREMS episodes in partnered rats may be due to the partnering procedure and not fear conditioning, as the effect was also seen at Baseline. Thus it appears that while the partnering procedure may have given rise to a fragmented REMS pattern, social partnering promoted a greater consolidation of REMS in response to the fear conditioning procedure.

Neuroendocrine and Peptidergic Regulation of Stress-Induced REM Sleep Rebound

Sleep homeostasis depends on the length and quality (occurrence of stressful events, for instance) of the preceding waking time. Forced wakefulness (sleep deprivation or sleep restriction) is one of the main tools used for the understanding of mechanisms that play a role in homeostatic processes involved in sleep regulation and their interrelations. Interestingly, forced wakefulness for periods longer than 24 h activates stress response systems, whereas stressful events impact on sleep pattern. Hypothalamic peptides (corticotropin-releasing hormone, prolactin, and the CLIP/ACTH18-39) play an important role in the expression of stress-induced sleep effects, essentially by modulating rapid eye movement sleep, which has been claimed to affect the organism resilience to the deleterious effects of stress. Some of the mechanisms involved in the generation and regulation of sleep and the main peptides/hypothalamic hormones involved in these responses will be discussed in this review.

Dicholine succinate, the neuronal insulin sensitizer, normalizes behavior, REM sleep, hippocampal pGSK3 beta and mRNAs of NMDA receptor subunits in mouse models of depression

Central insulin receptor-mediated signaling is attracting the growing attention of researchers because of rapidly accumulating evidence implicating it in the mechanisms of plasticity, stress response, and neuropsychiatric disorders including depression. Dicholine succinate (DS), a mitochondrial complex II substrate, was shown to enhance insulin-receptor mediated signaling in neurons and is regarded as a sensitizer of the neuronal insulin receptor. Compounds enhancing neuronal insulin receptor-mediated transmission exert an antidepressant-like effect in several pre-clinical paradigms of depression; similarly, such properties for DS were found with a stress-induced anhedonia model. Here, we additionally studied the effects of DS on several variables which were ameliorated by other insulin receptor sensitizers in mice. Pre-treatment with DS of chronically stressed C57BL6 mice rescued normal contextual fear conditioning, hippocampal gene expression of NMDA receptor subunit NR2A, the NR2A/NR2B ratio and increased REM sleep rebound after acute predation. In 18-month-old C57BL6 mice, a model of elderly depression, DS restored normal sucrose preference and activated the expression of neural plasticity factors in the hippocampus as shown by Illumina microarray. Finally, young naïve DS-treated C57BL6 mice had reduced depressive- and anxiety-like behaviors and, similarly to imipramine-treated mice, preserved hippocampal levels of the phosphorylated (inactive) form of GSK3 beta that was lowered by forced swimming in pharmacologically naïve animals. Thus, DS can ameliorate behavioral and molecular outcomes under a variety of stress- and depression-related conditions. This further highlights neuronal insulin signaling as a new factor of pathogenesis and a potential pharmacotherapy of affective pathologies.

Deuterium content of water increases depression susceptibility: the potential role of a serotonin-related mechanism

Environmental factors can significantly affect disease prevalence, including neuropsychiatric disorders such as depression. The ratio of deuterium to protium in water shows substantial geographical variation, which could affect disease susceptibility. Thus the link between deuterium content of water and depression was investigated, both epidemiologically, and in a mouse model of chronic mild stress. We performed a correlation analysis between deuterium content of tap water and rates of depression in regions of the USA. Next, we used a 10-day chronic stress paradigm to test whether 2-week deuterium-depleted water treatment (91 ppm) affects depressive-like behavior and hippocampal SERT. The effect of deuterium-depletion on sleep electrophysiology was also evaluated in naïve mice. There was a geographic correlation between a content of deuterium and the prevalence of depression across the USA. In the chronic stress model, depressive-like features were reduced in mice fed with deuterium-depleted water, and SERT expression was decreased in mice treated with deuterium-treated water compared with regular water. Five days of predator stress also suppressed proliferation in the dentate gyrus; this effect was attenuated in mice fed with deuterium-depleted water. Finally, in naïve mice, deuterium-depleted water treatment increased EEG indices of wakefulness, and decreased duration of REM sleep, phenomena that have been shown to result from the administration of selective serotonin reuptake inhibitors (SSRI). Our data suggest that the deuterium content of water may influence the incidence of affective disorder-related pathophysiology and major depression, which might be mediated by the serotoninergic mechanisms.

Aged rats are hypo-responsive to acute restraint: implications for psychosocial stress in aging

Cognitive processes associated with prefrontal cortex and hippocampus decline with age and are vulnerable to disruption by stress. The stress/stress hormone/allostatic load hypotheses of brain aging posit that brain aging, at least in part, is the manifestation of life-long stress exposure. In addition, as humans age, there is a profound increase in the incidence of new onset stressors, many of which are psychosocial (e.g., loss of job, death of spouse, social isolation), and aged humans are well-understood to be more vulnerable to the negative consequences of such new-onset chronic psychosocial stress events. However, the mechanistic underpinnings of this age-related shift in chronic psychosocial stress response, or the initial acute phase of that chronic response, have been less well-studied. Here, we separated young (3 month) and aged (21 month) male F344 rats into control and acute restraint (an animal model of psychosocial stress) groups (n = 9–12/group). We then assessed hippocampus-associated behavioral, electrophysiological, and transcriptional outcomes, as well as blood glucocorticoid and sleep architecture changes. Aged rats showed characteristic water maze, deep sleep, transcriptome, and synaptic sensitivity changes compared to young. Young and aged rats showed similar levels of distress during the 3 h restraint, as well as highly significant increases in blood glucocorticoid levels 21 h after restraint. However, young, but not aged, animals responded to stress exposure with water maze deficits, loss of deep sleep and hyperthermia. These results demonstrate that aged subjects are hypo-responsive to new-onset acute psychosocial stress, which may have negative consequences for long-term stress adaptation and suggest that age itself may act as a stressor occluding the influence of new onset stressors.

Sleep and protein synthesis-dependent synaptic plasticity: impacts of sleep loss and stress

Sleep has been ascribed a critical role in cognitive functioning. Several lines of evidence implicate sleep in the consolidation of synaptic plasticity and long-term memory. Stress disrupts sleep while impairing synaptic plasticity and cognitive performance. Here, we discuss evidence linking sleep to mechanisms of protein synthesis-dependent synaptic plasticity and synaptic scaling. We then consider how disruption of sleep by acute and chronic stress may impair these mechanisms and degrade sleep function.

REM Sleep Rebound as an Adaptive Response to Stressful Situations

Stress and sleep are related to each other in a bidirectional way. If on one hand poor or inadequate sleep exacerbates emotional, behavioral, and stress-related responses, on the other hand acute stress induces sleep rebound, most likely as a way to cope with the adverse stimuli. Chronic, as opposed to acute, stress impairs sleep and has been claimed to be one of the triggering factors of emotional-related sleep disorders, such as insomnia, depressive- and anxiety-disorders. These outcomes are dependent on individual psychobiological characteristics, conferring even more complexity to the stress-sleep relationship. Its neurobiology has only recently begun to be explored, through animal models, which are also valuable for the development of potential therapeutic agents and preventive actions. This review seeks to present data on the effects of stress on sleep and the different approaches used to study this relationship as well as possible neurobiological underpinnings and mechanisms involved. The results of numerous studies in humans and animals indicate that increased sleep, especially the rapid eye movement phase, following a stressful situation is an important adaptive behavior for recovery. However, this endogenous advantage appears to be impaired in human beings and rodent strains that exhibit high levels of anxiety and anxiety-like behavior.

Nitric oxide in the regulation of the sleep-wake states

Nitric oxide (NO) production involves four different NO-synthases (NOSs) that are either constitutive (neuronal, nNOS; endothelial, eNOS; mitochondrial, mNOS) or inducible (iNOS) in nature. Three main processes regulate NO/NOSs output, i.e., the L-arginine/arginase substrate-competing system, the L-citrulline/arginosuccinate-recycling system and the asymmetric dimethyl-/monomethyl-L-arginine-inhibiting system. In adult animals, nNOS exhibits a dense innervation intermingled with pontine sleep structures. It is well established that the NO/nNOS production makes a key contribution to daily homeostatic sleep (slow-wave sleep, SWS; rapid eye movement sleep, REM sleep). In the basal hypothalamus, the NO/nNOS production further contributes to the REM sleep rebound that takes place after a sleep deprivation (SD). This production may also contribute to the sleep rebound that is associated with an immobilization stress (IS). In adult animals, throughout the SD time-course, an additional NO/iNOS production takes place in neurons. Such production mediates a transitory SD-related SWS rebound. A transitory NO/iNOS production is also part of the immune system. Such a production contributes to the SWS increase that accompanies inflammatory events and is ensured by microglial cells and astrocytes. Finally, with aging, the iNOS expression becomes permanent and the corresponding NO/iNOS production is important to ensure an adequate maintenance of REM sleep and, to a lesser extent, SWS. Despite such maintenance, aged animals, however, are not able to elicit a sleep rebound to deal with the challenge of SD or IS. Sleep regulatory processes in adult animals thus become impaired with age. Reduced iNOS expression during aging may contribute to accelerated senescence, as observed in senescence-accelerated mice (SAMP-8 mice).

Influence of the novel antidepressant and melatonin agonist/serotonin2C receptor antagonist, agomelatine, on the rat sleep-wake cycle architecture

RATIONALE

The novel antidepressant, agomelatine, behaves as an agonist at melatonin MT(1) and MT(2) receptors and as an antagonist at serotonin (5-HT)(2C) receptors. In animal models and clinical trials, agomelatine displays antidepressant properties and re-synchronizes disrupted circadian rhythms.

OBJECTIVES

The objectives of this study were to compare the influence of agomelatine upon sleep-wake states to the selective melatonin agonists, melatonin and ramelteon, and to the selective 5-HT(2C) receptor antagonist, S32006.

METHODS

Rats were administered with vehicle, agomelatine, ramelteon, melatonin, or S32006, at the onset of either dark or light periods. Polygraphic recordings were performed and changes determined over 24 h, i.e., number and duration of sleep-wake episodes, latencies to rapid eye movement (REM) and slow-wave (SWS) sleep, power band spectra of the electroencephalogram (EEG), and circadian changes.

RESULTS

Administered at light phase onset, no changes were induced by agomelatine. In contrast, administered shortly before dark phase, agomelatine (10 and 40 mg/kg, per os) enhanced duration of REM and SWS sleep and decreased wake state for 3 h. Melatonin (10 mg/kg, per os) induced a transient enhancement in REM sleep followed by a reduction in REM and SWS sleep and an increase in waking. Ramelteon (10 mg/kg, per os) provoked a transient increase in REM sleep. Finally, S32006 (10 mg/kg, intraperitoneally), administered at dark phase onset, mimicked the increased SWS provoked by agomelatine, yet diminished REM sleep.

CONCLUSIONS

Agomelatine possesses a distinctive EEG profile compared with melatonin, ramelteon, and S32006, possibly reflecting co-joint agonist and antagonist properties at MT(1)/MT(2) and 5-HT(2C) receptors, respectively.

Prenatal malnutrition and sleep states in adult rats: effects of restraint stress

Independently, prenatal malnutrition and psychological/physical stress have been shown to affect sleep architecture in adult rats. As malnutrition and stress commonly co-exist in malnourished human populations, the objective of the present study was to ascertain the combined effects of these two insults by examining sleep-wake parameters following a brief restraint stress in prenatally protein malnourished rats. The male offspring of rats provided with a protein deficient diet (6% casein) for 5 weeks prior to mating and throughout pregnancy were implanted with recording electrodes beginning at postnatal day 90. Polygraph recordings were obtained to quantify sleep states during the first 4 h of the dark phase of the cycle on 2 consecutive days. The first followed a 24-h habituation session to the recording chamber (baseline). The second occurred at the same time of day but followed 20 min of restraint stress in a Plexiglas tube. During baseline, prenatally malnourished rats spent more time in rapid eye movement sleep (REMS) in the first 2 h after "lights off" (block 1), and greater amounts of wakefulness (W) with a corresponding reduction in slow wave sleep (SWS) in the second two hours (block 2), as compared with controls. Following stress, the sleep architecture of both groups of rats remained unaltered in block 1 relative to their baseline day. In block 2, both groups exhibited significant reductions in SWS and REMS with significantly greater reductions being expressed in the prenatally malnourished group (most dramatically, REMS was completely eliminated). These findings suggest that sleep disturbances may be more severe in those malnourished human populations subjected to acutely stressful experiences.

Sleep disturbances in Ube3a maternal-deficient mice modeling Angelman syndrome

BACKGROUND

Angelman syndrome (AS) is a severe neurodevelopmental disorder with electroencephalographic (EEG) abnormalities and sleep disturbances. It results from lack of the functional maternal allele of UBE3A, which encodes a ubiquitin-protein ligase. Different mechanisms of UBE3A inactivation correlate with clinical phenotypes of varying severity; the majority of cases of AS are due to a de novo maternal deletion of the 15q11-q13 region.

METHODS

Ube3a maternal-deficient mice (Ube3a m-/p+) were generated in a C57Bl/6J background. This study compares cortical EEG and architecture of the sleep-waking cycle in adult Ube3a m-/p+ mice compared with those of age-matched WT (m+/p+) mice, under baseline conditions or after 4-h sleep deprivation (SD).

RESULTS

Ube3a m-/p+ mice exhibited: reduced slow-wave sleep (SWS) amount with increase waking (W) at the dark/light transitions; increased SWS and W episode numbers; and deterioration of paradoxical sleep (PS) over 24 h [amount: -44%; episode duration: -46%; episode number: -40%; theta peak frequency (TPF) acceleration: 7.6 Hz vs. 7.0 Hz in WT mice]. Characteristic paroxysmal EEG discharges are observed during W and SWS associated with synchronous muscle bursting activity during hypoactive W. During the recovery period following SD, Ube3a m-/p+ mice exhibited no rebound either in slow-wave activity (+89% in WT) or in delta-power spectra but a slight rebound in PS amount (+20%).

CONCLUSIONS

These data validate the mouse model produced by null mutation of the maternal Ube3a gene and provide useful results to investigate and better understand the molecular basis of sleep disturbances in AS patients.

Sleep pattern in rats under different stress modalities

The present study was designed to evaluate the sleep pattern of rats submitted to chronic stressors (restraint, electrical footshock, swimming and cold) applied to male rats. After 48 h-baseline recording, rats were submitted to 4 days of chronic stress, and electrocorticogram recordings were carried out continuously. The stressors (footshock, swimming and cold) were applied twice a day for periods of 1 h at 9:00 and 16:00 h. Restrained animals were maintained in plastic cylinders for 22 h/day. The findings indicated that sleep efficiency, slow wave sleep (SWS) and paradoxical sleep (PS) were decreased on the third and fourth days of unpredictable shocks compared to baseline while immobilization and swimming presented reduced sleep efficiency in all 4-day recordings. Swimming led to decreased SWS, whereas augmented PS was observed on the first day compared to baseline. Immobilization produced drastic alterations in sleep patterns since it reduced SWS during the 4 days and PS at days 1 to 4 in relation to baseline. Of all stressors, cold was the only one that did not result in any statistical differences in sleep pattern during the light periods. Regarding the effect of stress compared to baseline on the dark recordings, PS was higher during cold stress periods, whereas footshock increased PS on days 2 to 4 and swimming only on day 2. Immobilization decreased PS throughout the 4 days of the stress sessions. Thus, the data suggest that different stress modalities result in distinct sleep responses, with immobilization producing the most dramatic alterations.

Nitric oxide and sleep

Nitric oxide (NO) is a biological messenger synthesized by three main isoforms of NO synthase (NOS): neuronal (nNOS, constitutive calcium dependent), endothelial (eNOS, constitutive, calcium dependent) and inducible (iNOS, calcium independent). NOS is distributed in the brain either in circumscribed neuronal sets or in sparse interneurons. Within the laterodorsal tegmentum (LDT), pedunculopontine tegmentum and dorsal raphe nucleus, NOS-containing neurons overlap neurons grouped according to their contribution to sleep mechanisms. The main target for NO is the soluble guanylate cyclase that triggers an overproduction of cyclic guanosine monophosphate. NO in neurons of the pontine tegmentum facilitates sleep (particularly rapid-eye-movement sleep), and NO contained within the LDT intervenes in modulating the discharge of the neurons through an auto-inhibitory process involving the co-synthesized neurotransmitters. Moreover, NO synthesized within cholinergic neurons of the basal forebrain, while under control of the LDT, may modulate the spectral components of the EEG instead of the amounts of different sleep states. Finally, impairment of NO production (e.g. neurodegeneration, iNOS induction) has identifiable effects, including ageing, neuropathologies and parasitaemia.

Potential role of inducible nitric oxide synthase in the sleep–wake states occurrence in old rats

Extensive evidences now suggest that an association between inducible nitric oxide synthase and oxidative stress takes place during aging. Since the part played by inducible nitric oxide synthase in the sleep impairments associated with aging still remains unexplored, we compared its involvement in old rats (20-24 months) versus adult ones (3-5 months) using polygraphic, biochemical, voltammetric and immunohistochemical techniques. The experiments were conducted either in basal condition or after a systemic injection of selected inducible nitric oxide synthase inhibitors. We found that 2-amino-5,6-dihydro-6-methyl-4H-1,3-thiazine (10 mg/kg, i.p.) or aminoguanidine (400 mg/kg, i.p.) was capable to suppress rapid-eye-movement sleep and induce a delayed enhancement in slow-wave sleep in old rats. These effects did not occur in adult animals. Within the frontal cortex, the laterodorsal tegmentum and dorsal raphe nuclei, the basal inducible nitric oxide synthase activity was 85-200% higher in old rats than in adult ones. In contrast, the neuronal nitric oxide synthase activity did not vary in both groups. 2-Amino-5,6-dihydro-6-methyl-4H-1,3-thiazine administration significantly reduced inducible nitric oxide synthase activity (70-80% according to the brain areas) independently of age, but significantly decreased the cortical nitric oxide release in old rats. Finally, in frontal cortex and dorsal raphe immunohistochemical analysis showed inducible nitric oxide synthase-positive cells again only in old animals. These data support the idea that nitric oxide produced by inducible nitric oxide synthase plays a role in the triggering and maintenance of rapid-eye-movement sleep during aging.

Sleep deprivation in honey bees

Rest at night in forager honey bees (Apis mellifera) meets essential criteria of sleep. This paper reports the effect of a 12-h total sleep deprivation (SD) by forced activity on the behaviour of these animals. The behaviour of sleep-deprived animals is compared with that of control animals under LD [periodic alternation between light (L) and darkness (D)] 12 : 12 hours. SD for 12 h during the first D period resulted in a significant difference with respect to the parameter 'hourly amount of antennal immobility' between sleep-deprived and control animals during the remaining L and D periods. This difference did not occur in the L period following the deprivation night, but rather it became obvious at the beginning of the following D period. The increase of the amount of antennal immobility in sleep-deprived bees was accompanied by an increase of the duration of episodes of antennal immobility. Moreover, the latency from 'lights off' to the first episode of antennal immobility lasting 20 s or longer ('deep sleep latency') tended to be shorter in sleep-deprived than in control animals. Disturbing the bees during the day (L period) did not result in such differences between disturbed and control animals. Highest reaction thresholds in sleeping honey bees occur during long episodes of antennal immobility. We therefore conclude that honey bees compensate a sleep deficit by intensification (deepening) of the sleep process and thus that sleep in honey bees, like that in other arthropods and mammals, is controlled by regulatory mechanisms.

Sleep deprivation induced by the modified multiple platform technique: quantification of sleep loss and recovery

Vigilance status was continually monitored in socially stable groups of rats exposed to the modified multiple platform (MMP) technique for sleep deprivation. For comparison, sleep parameters were also monitored in socially isolated rats deprived of sleep by the single platform (SP) method. In all cases, sleep was continuously recorded during baseline, during 96 h of sleep deprivation and during 4 days of recovery. Both multiple- and single-platform techniques completely abolished paradoxical sleep (PS) during the deprivation period, but also resulted in significant decreases in slow wave sleep (SWS) (-31% and -37%, respectively). Unexpectedly, animals on large platforms, which are normally intended as controls, also showed significant reductions in PS and SWS, and these effects were more pronounced in rats deprived in groups than in animals deprived in isolation. Another control preparation, rats placed on wire-mesh grids in the deprivation tank, also showed PS reduction (-39%) but no loss of SWS during the 4 test days. Paradoxical sleep rebound was observed in the first 24 h in all groups, except for grid controls. Overall, no significant differences were found between single- and multiple-platform procedures during the 4 days of deprivation. However, sleep rebound was more pronounced in MMP-deprived rats than in SP-deprived rats. Sleep loss in both control groups may reflect residual effect of stress that remain in the platform technique. These findings indicate that the MMP technique is effective in inducing PS deprivation (PSD). However, the fact that SWS is also affected may have implications for conclusions on paradoxical sleep function based upon paradoxical sleep deprivation.

Pattern of rapid-eye movement sleep episode occurrence after an immobilization stress in the rat

Rapid-eye movement sleep (REMS) in the rat occurs in the form of episodes separated by long (>3 min: isolated REMS episodes, IREMSEs) and short (<3 min: sequential REMS episodes, SREMSEs) intervals. The mechanism clustering SREMSEs is thought to be better suited to increase the amount of REMS when its drive is high. We tested this hypothesis in a new situation by transiently augmenting this drive with a moderate psychogenic stress. After a 90-min immobilization stress, REMS increased by 54% over the rest of the dark phase. This increase was associated with a modest increase in IREMSEs (+40%), but a massive increase in SREMSEs (+300%). Thus, the mechanism that clusters REMS episodes operates in response to a moderate psychogenic stress imposed in standard laboratory conditions and not preceded by sleep deprivation.

Effects of early handling on basal and stress-induced sleep parameters in rats

Exposure of humans and animals to stressful events early in life leads to significant and often permanent behavioural, neuroendocrine and central alterations. Early handling consists of removing the litter from the nest for 15 min/day, from post-natal days 2 to 14 and results in lowered ACTH and corticosterone stress response and reduced anxiety-like and fear behaviours. Stress-induced sleep alterations usually consists of increased sleep time, known as sleep rebound. In the present study, basal and stress-induced sleep pattern of control non-manipulated (CTL) and early handled (EH) adult male rats was investigated. Sleep was evaluated by 21-h polysomnographic recordings (from 10:00 to 07:00 h of the next day) before and after a 1-h session of restraint stress. The results showed that in the first 3 h following stress, both CTL and EH animals exhibited an impairment of sleep, with a reduction of sleep efficiency, duration of slow wave sleep and of paradoxical sleep. On the contrary, time awake and awakening bouts were augmented in this period. Sleep rebound was observed mainly in the dark period of the light-dark cycle. Stress-induced sleep changes were similar between CTL and EH animals for most sleep parameters. However, EH animals exhibited more bouts of paradoxical sleep on the night following stress exposure and longer bouts of paradoxical sleep in the light period that followed restraint stress. These data indicate that stress-induced alterations of sleep in early handled animals are similar to that observed in control animals, except for some parameters related to paradoxical sleep.

Changes in the sleep-wake cycle architecture and cortical nitric oxide release during ageing in the rat

Changes in sleep-wake states and nitric oxide release were examined in aged rats versus young-adult ones. Sleep-wake recordings and nitric oxide measurements were taken from animals chronically equipped with polygraphic and voltametric electrodes. Animals were examined in baseline conditions and in response to a 24-hour paradoxical sleep deprivation. In aged rats, basal amount of paradoxical sleep is decreased during the light phase versus young-adult animals. After paradoxical sleep deprivation, a paradoxical sleep rebound occurs with an amount and intensity that are less marked in aged animals than in young-adult rats. The amplitude of the circadian distribution for wakefulness, slow-wave sleep and paradoxical sleep amounts is reduced with age. Finally, delta-slow-wave sleep and theta-paradoxical sleep power spectra are attenuated either in baseline conditions or after paradoxical sleep deprivation in aged animals. It is also reported that cortical nitric oxide release exhibits a circadian rhythm with higher amplitude in aged rats than in young-adult ones. However, after paradoxical sleep deprivation, a limited overproduction of nitric oxide is obtained compared with young-adult ones. These results, evidencing the dynamics of the nitric oxide changes occurring in relation to the sleep-wake cycle, point out the homeostatic paradoxical sleep regulation as an age-dependent process in which the nitric oxide molecule is possibly involved.

Copulatory activity increases slow-wave sleep in the male rat

It is believed that sexual activity increases the need to sleep in many species. However, the relationship between copulatory activity and sleep has been poorly studied. Several studies have observed variations in the sleep of female rats and women as a function of their reproductive state. These effects have been correlated with the effects of female steroid hormones, but not with sexual activity. The aim of the present study was to evaluate the sleep-wake pattern of male rats immediately after different conditions of copulatory activity. Sexually experienced male rats were chronically implanted with a standard set of electrodes for sleep recording. After a control sleep recording of 8 h, the males were randomly assigned to one of the following experimental conditions: 30 min in the presence of an ovariectomized (OVX) rat; 30 min in the presence of an intact non-receptive female (NRF); with a receptive female until reaching one ejaculation (1E); and with a receptive female until reaching three ejaculations (3E). In addition, after 10 days, males were randomly exposed to one of the following copulatory conditions during 4 h: to remain in the presence of an OVX rat; to remain in the presence of an NRF female, and with receptive females until reaching sexual satiety (SS). Male sexual behavior was assessed just after the onset of the dark period, and sleep recordings were obtained during 8 h immediately after experimental testing. Both the three ejaculations group (3E) in the first experiment and the sexual satiety group (SS) in the second experiment showed enhanced percentages of time spent in slow wave sleep (SWS) II and a shorter latency to the first SWS II episode than in the control group or under basal conditions. In addition, neither the presence of a non-receptive female or an OVX female, nor sexual behavior until reaching one ejaculation induced any effect on the sleep stages. These findings suggest that the increase in SWS II induced by both 3E and SS may be governed by some specific mechanism that is essentially independent of physical exercise or stress. Copulatory activity might be the source of neurohormonal processes that induce sleep and may involve the participation of gamma-aminobutyric acid, serotonin or other endogenous regulators of sleep and wakefulness. Nevertheless, the precise mechanism by which the sexual behavior increases SWS is still to be determined.

Role of corticotropin-releasing hormone in stressor-induced alterations of sleep in rat

Corticotropin-releasing hormone (CRH) mediates responses to a variety of stressors. We subjected rats to a 1-h period of an acute stressor, physical restraint, and determined the impact on subsequent sleep-wake behavior. Restraint at the beginning of the light period, but not the dark period, increased waking and reduced rapid eye movement sleep without dramatically altering slow-wave sleep (SWS). Electroencephalogram (EEG) slow-wave activity during SWS and brain temperature were increased by this manipulation. Central administration of the CRH receptor antagonist astressin blocked the increase in waking after physical restraint, but not during the period of restraint itself. Blockade of CRH receptors with astressin attenuated the restraint-induced elevation of brain temperature, but not the increase of EEG slow-wave activity during subsequent SWS. Although corticosterone increased after restraint in naive animals, it was not altered by this manipulation in rats well habituated to handling and injection procedures. These results suggest that under these conditions central CRH, but not the hypothalamic-pituitary-adrenal axis, is involved in the alterations in sleep-wake behavior and the modulation of brain temperature of rats exposed to physical restraint.

Involvement of 5-HT1A receptors in homeostatic and stress-induced adaptive regulations of paradoxical sleep: studies in 5-HT1A knock-out mice

For the last two decades, the involvement of 5-HT(1A) receptors in the regulation of vigilance states has been studied extensively thanks to pharmacological tools, but clear-cut conclusion has not been reached yet. By studying mutant mice that do not express this receptor type (5-HT(1A)-/-) and their wild-type 129/Sv counterparts, we herein demonstrate that 5-HT(1A) receptors play key roles in the control of spontaneous sleep-wakefulness cycles, as well as in homeostatic regulation and stress-induced adaptive changes of paradoxical sleep. Both strains of mice exhibited a diurnal sleep-wakefulness rhythm, but 5-HT(1A)-/- animals expressed higher amounts of paradoxical sleep than wild-type mice during both the light and the dark phases. In wild-type mice, pharmacological blockade of 5-HT(1A) receptors by WAY 100635 (0.5 mg/kg, i.p.) promoted paradoxical sleep, whereas the 5-HT(1A) agonist 8-OH-DPAT (0.25-1 mg/kg, s.c.) had an opposite effect. In contrast, none of the 5-HT(1A) receptor ligands affected sleep significantly in 5-HT(1A)-/- mice. However, 5-HT(1B) receptor stimulation by CP 94253 (1-3 mg/kg, i.p.) induced a reduction in paradoxical sleep in both strains, this effect being more pronounced in 5-HT(1A)-/- mutants. Finally, in contrast to wild-type mice, 5-HT(1A)-/- mutants did not exhibit any rebound of paradoxical sleep after either a 9 hr instrumental paradoxical sleep deprivation or a 90 min immobilization stress. Altogether, these data indicate that, in the mouse, 5-HT(1A) receptors participate in the spontaneous and homeostatic regulation, as well as in stress-induced adaptive changes of paradoxical sleep.

The effect of restraint stress on paradoxical sleep is influenced by the circadian cycle

It is well known that the physiological impact imposed by events or behaviors displayed during the waking period determines the way organisms sleep. Among the situations known to affect sleep both in its duration and quality, stress has been widely studied and it is now admitted that its effects on sleep architecture depend on several factors specific to the stressor or the individual itself. Although numerous reports have highlighted the prominent role of the circadian cycle in the physiological, endocrine and behavioral consequences of restraint stress, a possible circadian influence in the effects of stress on the sleep-wake cycle has never been studied. Thus the present study was designed to compare the effects on sleep of a 1 h-lasting restraint stress applied at light onset to those observed after the same stressor was applied at light offset. We report that in both conditions stress induced a marked paradoxical sleep increase, whereas wakefulness displayed a moderate decrease and slow wave sleep a moderate augmentation. Although the effects of stress at lights on were of similar magnitude than those of stress at lights off, important differences in the sleep rebound latencies were observed: whatever the time of day the stress was applied, its effects on sleep always occurred during the dark period. This result thus shows that restraint stress could be efficiently used to study the interaction between the circadian and homeostatic components of sleep regulation.

Effect of noradrenergic denervation of medial prefrontal cortex and dentate gyrus on recovery after sleep deprivation in the rat

The noradrenergic-locus coeruleus (LC) system has a regulatory influence on forebrain neuronal networks. We have previously shown that the amygdala is strongly implicated in the mechanism of rebound seen after a 10 h sleep deprivation (SD). In the present study, our objective was to determine whether the medial prefrontal cortex and dentate gyrus (DG) which receive an important innervation from the LC, play a role in the rebound mechanisms. We found that microinjection of the specific noradrenergic neurotoxin, N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine, into these regions had no effect on the increase in paradoxical sleep duration seen after SD, suggesting that noradrenergic (NA) innervation of the prefrontal cortex and DG are not involved in sleep rebound regulation.

Hormonal and behavioural abnormalities induced by stress in utero: an animal model for depression

Prenatal stress in rats can exert profound influence on the off spring's development, inducing abnormalities such as increased "anxiety", "emotionality" or "depression-like" behaviours.Prenatal stress has long-term effects on the development of the hypothalamo-pituitary-adrenal(HPA) axis and forebrain cholinergic systems. These long-term neuroendocrinological effects are mediated, at least in part, by stress-induced maternal corticosterone increase during pregnancy and stress-induced maternal anxiety during the postnatal period. We have shown a significant phase advance in the circadian rhythms of corticosterone secretion and locomotor activity in prenatally-stressed (PNS) rats. When subjected to an abrupt shift in the light-dark(LD) cycle, PNS rats resynchronized their activity rhythm more slowly than control rats. In view of the data suggesting abnormalities in the circadian timing system in these animals, we have investigated the effects of prenatal stress on the sleep-wake cycle in adult male rats. PNS rats exhibited various changes in sleep-wake parameters, including a dramatic increase in the amount of paradoxical sleep. Taken together, our results indicate that prenatal stress can induce increased responses to stress and abnormal circadian rhythms and sleep in adult rats.Various clinical observations in humans suggest a possible pathophysiological link between depression and disturbances in circadian rhythmicity. Circadian abnormalities in depression can be related to those found in PNS rats. Interestingly, we have recently shown that the increased immobility in the forced swimming test observed in PNS rats can be corrected by chronic treatment with the antidepressant tianeptine, or with melatonin or S23478, a melatonin agonist. Those results reinforce the idea of the usefulness of PNS rats as an appropriate animal model to study human depression and support a new antidepressant-like effect of melatonin and the melatonin agonist S23478.

The effect of high ambient temperature on the adjustment of operators to fast rotating 12-hour shiftwork

The aim of the investigation was to study the effect of high ambient temperature (HAT) on the adjustment to fast rotating 12-h shifts by following the time-of-day variations of certain circadian and stress indicators. We investigated 12 male HAT operators and 21 individuals working in normal ambient temperature (NAT) in a thermoelectric power plant. The shift system of both groups comprised an 8-day cycle of 2 shifts per day (day shift: 0700 to 1900; night shift: 1900 to 0700), with 2 successive days of the same shift followed by 2 days off. We followed variations in oral temperature, 11-oxycorticoids, as well as catecholamines adrenaline and noradrenaline excretion at 4-h intervals during 2 day and 2 night shifts. Our data show daily oriented circadian rhythms of operators working on fast rotating 12-h shifts in conditions of HAT and NAT. Reduced general activation was observed in the second half of the prolonged 12-h night shifts, more pronounced in HAT operators. The stress indicators investigated here showed a stress reaction in HAT operators at the beginning of the first day shift. Both prolonged 12-h shifts and high ambient temperature impose extra demands and may have an impact on the performance and work safety of the operators.

Effect of electric foot shocks, immobilization, and corticosterone administration on the sleep-wake pattern in the rat

Knowledge concerning the impact of stressful situations on the sleep-wake pattern has been growing rapidly in the last decade. Immobilization (IMB) in rats elicits a significant increase of rapid eye movement (REM) sleep during the following 10 h. Participation of the adrenergic system has been clearly shown in this effect. On the other hand, it is well known that the time of the circadian cycle in which the stressor is applied could influence the results. It is also well known that the activation of the hypothalamic-pituitary-adrenal (HPA) axis, the release of corticosterone (COR), and the activation of the adrenergic and of the opioidergic systems are the most evident effects of stress. In the present study, we analyzed the effects of two stressors, IMB and electric foot shocks (EFS), on 24 h of continuous sleep recordings. These stressors were applied immediately before the onset of the light period. COR was also administered in an attempt to replicate the stressor-induced effects. Adult, male Wistar rats were chronically implanted for sleep recording, and after a recovery period and a 24-h basal sleep recording, they were submitted to EFS, COR, and IMB. A 10-day period elapsed between each treatment, and all of them were applied during the last moments of the dark phase of the light cycle. Results showed that IMB increased the percentage of REM sleep (83.7%) and slow-wave sleep II (SWS II; 17.3%) mainly during the dark phase (i.e., after 12 h), while EFS and COR administration elicited only slight and transient changes in the sleep-wake pattern. These data suggest that IMB applied to rats at the end of the dark cycle is effective in producing a sleep-elevating response, although this effect is enhanced during the dark phase. It seems, however, that not all the stressful situations are capable of eliciting this sleep-promoting effect, and also that COR release does not mediate this response.

Sleep rebound in animals deprived of paradoxical sleep by the modified multiple platform method

The objective of the present study was to assess the sleep rebound of animals exposed to the modified multiple platform method (MMPM), in which cage-mate rats were placed onto narrow platforms (NP=6.5 cm in diameter), onto wide platforms (WP=14 cm in diameter) or onto a grid (GR). The last two groups were included as environmental controls for the deprivation method. Animals were implanted with bipolar electrodes in the cortex, hippocampus and neck muscle. Baseline sleep was recorded for 6 h, after which the animals were placed in one of the above-mentioned settings for 90 h and their sleep was again recorded. Comparison between baseline and post-GR recordings revealed no sleep differences in these animals. Placement of animals onto WP resulted in augmented sleep time (16%), time spent in PS (+99%), duration of PS episodes (+77%), sleep efficiency (+16%), and in reduced latency to PS (-84.8%). Finally, NP animals exhibited a dramatic increase in sleep time (+34.3%), time spent in PS (+184.7%), duration of PS episodes (+106%), and in sleep efficiency (+34.4%). Moreover, sleep latency (-52.2%) and time spent in SWS (-12.2%) were reduced. Based on the results of sleep rebound, the data indicated that placement of animals onto narrow platforms in the MMPM was an effective PS deprivation method and the grid should be considered as an adequate environmental control.

Effect of noradrenergic denervation of the amygdala upon recovery after sleep deprivation in the rat

We previously showed that the noradrenergic locus coeruleus (NA-LC) was involved in the regulatory mechanisms of the paradoxical sleep rebound following a 10 h sleep deprivation by using a systemic injection of a specific neurotoxin, N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4). Given that rebound mechanisms are mainly located in the forebrain, we planned to study the role of the forebrain structures receiving LC afferences. In this study we evaluated the involvement of noradrenergic afferences to the central nucleus of the amygdala in the sleep rebound by DSP-4 microinjections into the central nucleus of the rat amygdala. The results showed that during the first recovery day, the paradoxical sleep rebound is lower in DSP-4 treated rats (-67.28%). These findings indicate that the amygdala, through its NA afferents, contributes to the sleep rebound mechanisms.

Influence of a 1-h immobilization stress on sleep and CLIP (ACTH(18-39)) brain contents in adrenalectomized rats

Basal sleep amounts in adrenalectomized rats (AdX), as compared to intact animals, exhibit a significant increase in slow-wave sleep (SWS), a tendency towards an increase in paradoxical sleep (PS), and circadian rhythms (SWS and PS) flattened in amplitude. An immobilization stress (IS) of 1 h, imposed on AdX rats at the beginning of the dark period, is accompanied by an intense polygraphic waking. Just after the IS, SWS amount become significantly higher than in control rats (+44%/11 h of darkness) whereas significant increases of PS occur only 5-10 h after the IS (+24%/11 h of darkness). A specific radioimmunoassay for CLIP (corticotropin-like intermediate lobe peptide or ACTH(18-39)) was performed in biopsies taken either from the nucleus raphe dorsalis (nRD) or the arcuate nucleus (AN). In the nRD, just after the IS, phosphorylated CLIP (Ph-CLIP) concentration exhibits a decreasing tendency, but 4 h later, it increases significantly (+22%, p<0.05). In the AN, Ph-CLIP concentration remains unchanged after the IS as well as 4 h later. These results differ from those previously reported in intact animals also submitted to a 1-h IS, that is, a SWS rebound less marked (+27%/11 h of darkness), a PS rebound more important starting immediately after the IS (+46%/11 h of darkness) and a significant increase in Ph-CLIP occurring just after the end of the restraint. In conclusion, data obtained after a restraint stress either in AdX or in control rats point out the dependence of the PS rebound on the nRD Ph-CLIP concentration.