Selective REM sleep deprivation and compensation phenomena in the rat

Adolescent sleep and its disruption in depression and anxiety

Adolescence is a pivotal stage during development when one's personality, emotion, and behavioral traits are shaped to a great extent, and the underlying neural circuits undergo substantial developmental organizations. Dramatic and dynamic changes occur in sleep architecture throughout the postnatal developmental course. Insufficient sleep and disruption of sleep/wake coherence are prevalent among the adolescents worldwide, and even so in young patients with neuropsychiatric conditions. Although accumulating evidence has suggested a tight association between sleep disruption and depression/anxiety, the causal relationship remains largely unclear. More importantly, most of these studies focused on adult subjects, and little is known about the role of sleep during the development of mood and behavior. Here we review recent studies investigating the acute and chronic effects of adolescent sleep disruption on depression and anxiety both in humans and rodent models with focuses on the assessment methodology and age. By discussing the findings and unsolved problems, we hope to achieve a better understanding of the relationship between sleep and mental health in adolescents and provide insights for future research.

Mammalian NREM and REM sleep: Why, when and how

This report proposes that fish use the spinal-rhombencephalic regions of their brain to support their activities while awake. Instead, the brainstem-diencephalic regions support the wakefulness in amphibians and reptiles. Lastly, mammals developed the telencephalic cortex to attain the highest degree of wakefulness, the cortical wakefulness. However, a paralyzed form of spinal-rhombencephalic wakefulness remains in mammals in the form of REMS, whose phasic signs are highly efficient in promoting maternal care to mammalian litter. Therefore, the phasic REMS is highly adaptive. However, their importance is low for singletons, in which it is a neutral trait, devoid of adaptive value for adults, and is mal-adaptive for marine mammals. Therefore, they lost it. The spinal-rhombencephalic and cortical wakeful states disregard the homeostasis: animals only attend their most immediate needs: foraging defense and reproduction. However, these activities generate allostatic loads that must be recovered during NREMS, that is a paralyzed form of the amphibian-reptilian subcortical wakefulness. Regarding the regulation of tonic REMS, it depends on a hypothalamic switch. Instead, the phasic REMS depends on an independent proportional pontine control.

Howard P. Roffwarg: sleep pioneer, legend, and ontogenetic hypothesis author

Narrated in this article are accounts of the many contributions Howard P. Roffwarg, MD, made to the field of sleep research and sleep medicine across his entire professional career as a student, a mentor, a leader in the Sleep Research Society, a sleep medicine clinician, and a scientist who performed experimental investigations in humans and animals. Dr Roffwarg was the originator of what is known as the "Ontogenetic Hypothesis" of sleep. His research over many years on physiology has contributed greatly to much of the experimental support substantiating a role for rapid eye-movement sleep (REMS) in the early development of the brain. Though much is still unknown, the Ontogenetic Hypothesis, still to this day, inspires many neuroscientists in their investigations. These studies have demonstrated roles for both REMS and NREMS in development as well as on brain function throughout his life span. Dr Howard P. Roffwarg, is one of the legends in the field of sleep research.

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.

Activation of brain-derived neurotrophic factor-tropomyosin receptor kinase B signaling in the pedunculopontine tegmental nucleus: a novel mechanism for the homeostatic regulation of rapid eye movement sleep

Rapid eye movement (REM) sleep dysregulation is a symptom of many neuropsychiatric disorders, yet the mechanisms of REM sleep homeostatic regulation are not fully understood. We have shown that, after REM sleep deprivation, the pedunculopontine tegmental nucleus (PPT) plays a critical role in the generation of recovery REM sleep. In this study, we used multidisciplinary techniques to show a causal relationship between brain-derived neurotrophic factor (BDNF)-tropomyosin receptor kinase B (TrkB) signaling in the PPT and the development of REM sleep homeostatic drive. Rats were randomly assigned to conditions of unrestricted sleep or selective REM sleep deprivation (RSD) with PPT microinjections of vehicle control or a dose of a TrkB receptor inhibitor (2, 3, or 4 nmol K252a or 4 nmol ANA-12). On experimental days, rats received PPT microinjections and their sleep-wake physiological signals were recorded for 3 or 6 h, during which selective RSD was performed in the first 3 h. At the end of all 3 h recordings, rats were killed and the PPT was dissected out for BDNF quantification. Our results show that K252a and ANA-12 dose-dependently reduced the homeostatic responses to selective RSD. Specifically, TrkB receptor inhibition reduced REM sleep homeostatic drive and limited REM sleep rebound. There was also a dose-dependent suppression of PPT BDNF up-regulation, and regression analysis revealed a significant positive relationship between REM sleep homeostatic drive and the level of PPT BDNF expression. These data provide the first direct evidence that activation of BDNF-TrkB signaling in the PPT is a critical step for the development of REM sleep homeostatic drive.

Behavioral Effects of Centrally Administered 6-Hydroxydopamine

The effects of intracisternal injection of 6-hydroxydopamine on three behavioral tasks in the rat were measured 8 to 15 wk. after injection. When animals were sacrificed 21 wk. after injection of 6-hydroxydopamine whole brain norepinephrine levels were reduced to 40% of control values. General activity levels were not altered in rats given 6-hydroxydopamine. However, the behavioral stimulation produced by d-amphetamine was much lower in animals treated with 6-hydroxydopamine than in controls. 6-hydroxydopamine-treated rats also exhibited more foot-shock-induced aggression and showed a trend toward slower active avoidance acquisition.

Animal models of bipolar mania: The past, present and future

Bipolar disorder (BD) is the sixth leading cause of disability in the world according to the World Health Organization and affects nearly six million (∼2.5% of the population) adults in the United State alone each year. BD is primarily characterized by mood cycling of depressive (e.g., helplessness, reduced energy and activity, and anhedonia) and manic (e.g., increased energy and hyperactivity, reduced need for sleep, impulsivity, reduced anxiety and depression), episodes. The following review describes several animal models of bipolar mania with a focus on more recent findings using genetically modified mice, including several with the potential of investigating the mechanisms underlying 'mood' cycling (or behavioral switching in rodents). We discuss whether each of these models satisfy criteria of validity (i.e., face, predictive, and construct), while highlighting their strengths and limitations. Animal models are helping to address critical questions related to pathophysiology of bipolar mania, in an effort to more clearly define necessary targets of first-line medications, lithium and valproic acid, and to discover novel mechanisms with the hope of developing more effective therapeutics. Future studies will leverage new technologies and strategies for integrating animal and human data to reveal important insights into the etiology, pathophysiology, and treatment of BD.

Evaluating the Evidence Surrounding Pontine Cholinergic Involvement in REM Sleep Generation

Rapid eye movement (REM) sleep - characterized by vivid dreaming, motor paralysis, and heightened neural activity - is one of the fundamental states of the mammalian central nervous system. Initial theories of REM sleep generation posited that induction of the state required activation of the "pontine REM sleep generator" by cholinergic inputs. Here, we review and evaluate the evidence surrounding cholinergic involvement in REM sleep generation. We submit that: (i) the capacity of pontine cholinergic neurotransmission to generate REM sleep has been firmly established by gain-of-function experiments, (ii) the function of endogenous cholinergic input to REM sleep generating sites cannot be determined by gain-of-function experiments; rather, loss-of-function studies are required, (iii) loss-of-function studies show that endogenous cholinergic input to the PTF is not required for REM sleep generation, and (iv) cholinergic input to the pontine REM sleep generating sites serve an accessory role in REM sleep generation: reinforcing non-REM-to-REM sleep transitions making them quicker and less likely to fail.

The homeostatic regulation of REM sleep: A role for localized expression of brain-derived neurotrophic factor in the brainstem

Homeostatic regulation of REM sleep plays a key role in neural plasticity and deficits in this process are implicated in the development of many neuropsychiatric disorders. Little is known, however, about the molecular mechanisms that underlie this homeostatic regulation process. This study examined the hypothesis that, during selective REM sleep deprivation (RSD), increased brain-derived neurotrophic factor (BDNF) expression in REM sleep regulating areas is critical for the development of homeostatic drive for REM sleep, as measured by an increase in the number of REM sleep transitions. Rats were assigned to RSD, non-sleep deprived (BSL), or total sleep deprivation (TSD) groups. Physiological recordings were obtained from cortical, hippocampal, and pontine EEG electrodes over a 6h period, in which sleep deprivation occurred during the first 3h. In the RSD, but not the other conditions, homeostatic drive for REM sleep increased progressively. BDNF protein expression was significantly greater in the pedunculopontine tegmentum (PPT) and subcoeruleus nucleus (SubCD) in the RSD as compared to the TSD and BSL groups, areas that regulate REM sleep, but not in the medial preoptic area, which regulates non-REM sleep. There was a significant positive correlation between RSD-induced increases in number of REM sleep episodes and increased BDNF expression in the PPT and SubCD. These increases positively correlated with levels of homeostatic drive for REM sleep. These results, for the first time, suggest that selective RSD-induced increased expression of BDNF in the PPT and SubCD are determinant factors in the development of the homeostatic drive for REM sleep.

Acute sleep deprivation enhances avoidance learning and spatial memory and induces delayed alterations in neurochemical expression of GR, TH, DRD1, pCREB and Ki67 in rats

The current study investigated the effects of acute versus repeated periods of sleep deprivation on avoidance learning and spatial memory and on the expression of discrete biochemical brain signals involved in stress regulation, motivation and brain plasticity. Male Long-Evans rats were sleep deprived using the platform-over-water method for a single 4 h period (ASD) or for daily 4h RSD period on five consecutive days (CSD). The Y maze passive avoidance task (YM-PAT) and the Morris water maze (MWM) were used to determine learning and memory 1h following the last SD period. Region-specific changes in glucocorticoid receptors (GR), tyrosine hydroxylase (TH), dopamine 1 receptors (DRD1), phospho-CREB (pCREB) and Ki-67 expression were assessed in the hippocampal formation, hypothalamus and mesolimbic regions 72 h following RSD. Behaviorally, our findings revealed increased latency to re-enter the aversive arm in the YM-PAT and reduced distance traveled and latency to reach the platform in the MWM in ASD rats compared to all other groups, indicative of improved avoidance learning and spatial memory, respectively. Acute SD enhanced TH expression in the ventral tegmental area, nucleus accumbens and A11 neurons of the hypothalamus and DRD1 expression in the lateral hypothalamus. Cell proliferation in the subventricular zone and pCREB expression in the dentate gyrus and CA3 regions was also enhanced following acute SD. In contrast, repeated SD significantly elevated GR-ir at the hypothalamic paraventricular nucleus and CA1 and CA3 layers of the hippocampus compared to all other groups. Our study supports that a brief 4h sleep deprivation period is sufficient to induce delayed neurochemical changes.

Experimental sleep deprivation as a tool to test memory deficits in rodents

Paradigms of sleep deprivation (SD) and memory testing in rodents (laboratory rats and mice) are here reviewed. The vast majority of these studies have been aimed at understanding the contribution of sleep to cognition, and in particular to memory. Relatively little attention, instead, has been devoted to SD as a challenge to induce a transient memory impairment, and therefore as a tool to test cognitive enhancers in drug discovery. Studies that have accurately described methodological aspects of the SD protocol are first reviewed, followed by procedures to investigate SD-induced impairment of learning and memory consolidation in order to propose SD protocols that could be employed as cognitive challenge. Thus, a platform of knowledge is provided for laboratory protocols that could be used to assess the efficacy of drugs designed to improve memory performance in rodents, including rodent models of neurodegenerative diseases that cause cognitive deficits, and Alzheimer's disease in particular. Issues in the interpretation of such preclinical data and their predictive value for clinical translation are also discussed.

Spinal D-amino acid oxidase contributes to mechanical pain hypersensitivity induced by sleep deprivation in the rat

We studied the hypothesis that spinal d-amino acid oxidase (DAAO) that is expressed in astrocytes and that has been reported to promote tonic pain in various pathophysiological conditions plays a role in 'physiological' pain hypersensitivity induced by rapid eye movement sleep deprivation (REMSD). The experiments were performed in healthy rats with a chronic intrathecal (i.t.) catheter. Pain behavior was assessed by determining limb withdrawal response to repetitive stimulation of the hind paw with a calibrated series of monofilaments. REMSD of 48 h duration produced a significant mechanical hypersensitivity. At 48 h of REMSD, the animals were treated i.t. with a DAAO inhibitor or vehicle. Three structurally different DAAO inhibitors were tested in this study: 6-chlorobenzo[d]isoxazol-3-ol (CBIO), sodium benzoate, and 5-methylpyrazole-3-carboxylic acid (AS-057278). CBIO (1-3 μg), sodium benzoate (30-100 μg) and AS-057278 (3-10 μg) produced dose-related antihypersensitivity effects in sleep-deprived animals. In control animals (with no sleep deprivation), the currently used doses of DAAO inhibitors failed to produce significant changes in mechanically evoked pain behavior. The results indicate that among spinal pain facilitatory mechanisms that contribute to the sleep deprivation-induced mechanical pain hypersensitivity is DAAO, presumably due to production of reactive oxygen species, such as hydrogen peroxide, an endogenous agonist of the pronociceptive TRPA1 ion channel.

Arousal state feedback as a potential physiological generator of the ultradian REM/NREM sleep cycle

Human sleep episodes are characterized by an approximately 90-min ultradian oscillation between rapid eye movement (REM) and non-REM (NREM) sleep stages. The source of this oscillation is not known. Pacemaker mechanisms for this rhythm have been proposed, such as a reciprocal interaction network, but these fail to account for documented homeostatic regulation of both sleep stages. Here, two candidate mechanisms are investigated using a simple model that has stable states corresponding to Wake, REM sleep, and NREM sleep. Unlike other models of the ultradian rhythm, this model of sleep dynamics does not include an ultradian pacemaker, nor does it invoke a hypothetical homeostatic process that exists purely to drive ultradian rhythms. Instead, only two inputs are included: the homeostatic drive for Sleep and the circadian drive for Wake. These two inputs have been the basis for the most influential Sleep/Wake models, but have not previously been identified as possible ultradian rhythm generators. Using the model, realistic ultradian rhythms are generated by arousal state feedback to either the homeostatic or circadian drive. For the proposed 'homeostatic mechanism', homeostatic pressure increases in Wake and REM sleep, and decreases in NREM sleep. For the proposed 'circadian mechanism', the circadian drive is up-regulated in Wake and REM sleep, and is down-regulated in NREM sleep. The two mechanisms are complementary in the features they capture. The homeostatic mechanism reproduces experimentally observed rebounds in NREM sleep duration and intensity following total sleep deprivation, and rebounds in both NREM sleep intensity and REM sleep duration following selective REM sleep deprivation. The circadian mechanism does not reproduce sleep state rebounds, but more accurately reproduces the temporal patterns observed in a normal night of sleep. These findings have important implications in terms of sleep physiology and they provide a parsimonious explanation for the observed ultradian rhythm of REM/NREM sleep.

Predictive animal models of mania: hits, misses and future directions

Mania has long been recognized as aberrant behaviour indicative of mental illness. Manic states include a variety of complex and multifaceted symptoms that challenge clear clinical distinctions. Symptoms include over-activity, hypersexuality, irritability and reduced need for sleep, with cognitive deficits recently linked to functional outcome. Current treatments have arisen through serendipity or from other disorders. Hence, treatments are not efficacious for all patients, and there is an urgent need to develop targeted therapeutics. Part of the drug discovery process is the assessment of therapeutics in animal models. Here we review pharmacological, environmental and genetic manipulations developed to test the efficacy of therapeutics in animal models of mania. The merits of these models are discussed in terms of the manipulation used and the facet of mania measured. Moreover, the predictive validity of these models is discussed in the context of differentiating drugs that succeed or fail to meet criteria as approved mania treatments. The multifaceted symptomatology of mania has not been reflected in the majority of animal models, where locomotor activity remains the primary measure. This approach has resulted in numerous false positives for putative treatments. Recent work highlights the need to utilize multivariate strategies to enable comprehensive assessment of affective and cognitive dysfunction. Advances in therapeutic treatment may depend on novel models developed with an integrated approach that includes: (i) a comprehensive battery of tests for different aspects of mania, (ii) utilization of genetic information to establish aetiological validity and (iii) objective quantification of patient behaviour with translational cross-species paradigms.

Intrathecal administration of antioxidants attenuates mechanical pain hypersensitivity induced by REM sleep deprivation in the rat

Background Sleep deprivation as well as peripheral neuropathy and cutaneous neurogenic inflammation has a facilitatory effect on pain perception. Here we studied whether oxidative stress-related mechanisms in the spinal cord that have been shown to contribute to pain facilitation in peripheral neuropathy and cutaneous neurogenic inflammation play a role in sleep deprivation-induced pain hypersensitivity Methods Flower pot method was used to induce rapid eye movement sleep deprivation (REMSD) of 48 h duration in the rat that had a chronic intrathecal (i.t.) catheter for spinal administration of drugs. Pain behavior was assessed by determining the monofilament-induced limb withdrawal response. Results REMSD of 48 h produced mechanical hypersensitivity that was attenuated in a dose-related fashion by i.t. administration of two different antioxidants, phenyl-N-tert-butylnitrone (PBN) or 4-hydroxy-2,2,6,6-tetramethylpiperidine-1 oxyl (TEMPOL). While both antioxidants attenuated mechanical pain behavior also in control animals, their effects were significantly stronger after REMSD than in control conditions. Conversely, i.t. administration of a reactive oxygen species (ROS) donor, tert-butylhydroperoxide (t-BOOH), in control animals produced pain hypersensitivity that was prevented by i.t. pretreatment with an antioxidant, TEMPOL. I.t. treatment with PBN or TEMPOL at the currently used doses failed to influence motor behavior in the Rotarod test. Conclusions The results indicate that among common mechanisms contributing to mechanical pain hypersensitivity following sleep deprivation as well as nerve injury or neurogenic inflammation is oxidative stress in the spinal cord. Implications Compounds with antioxidant properties might prove useful in suppressing the vicious pronociceptive interaction between chronic pain and sleep-deprivation.

Protein kinase A in the pedunculopontine tegmental nucleus of rat contributes to regulation of rapid eye movement sleep

Intracellular signaling mechanisms within the pedunculopontine tegmental (PPT) nucleus for the regulation of recovery rapid eye movement (REM) sleep following REM sleep deprivation remain unknown. This study was designed to determine the role of PPT intracellular cAMP-dependent protein kinase A (cAMP-PKA) in the regulation of recovery REM sleep in freely moving rats. The results show that a brief period (3 h) of selective REM sleep deprivation caused REM sleep rebound associated with increased PKA activity and expression of the PKA catalytic subunit protein (PKA-CU) in the PPT. Local application of a cAMP-PKA-activation-selective inhibitor, RpCAMPS (0.55, 1.1, and 2.2 nmol/100 nl; n = 8 rats/group), bilaterally into the PPT, reduced PKA activity and PKA-CU expression in the PPT, and suppressed the recovery REM sleep, in a dose-dependent manner. Regression analyses revealed significant positive relationships between: PPT levels of PKA activity and the total percentages of REM sleep recovery (Rsqr = 0.944; n = 40 rats); PPT levels of PKA-CU expression and the total percentages of REM sleep recovery (Rsqr = 0.937; n = 40 rats); PPT levels of PKA-CU expression and PKA activity (Rsqr = 0.945; n = 40 rats). Collectively, these results provide evidence that activation of intracellular PKA in the PPT contributes to REM sleep recovery following REM sleep deprivation.

Cross-species assessments of motor and exploratory behavior related to bipolar disorder

Alterations in exploratory behavior are a fundamental feature of bipolar mania, typically characterized as motor hyperactivity and increased goal-directed behavior in response to environmental cues. In contrast, abnormal exploration associated with schizophrenia and depression can manifest as prominent withdrawal, limited motor activity, and inattention to the environment. While motor abnormalities are cited frequently as clinical manifestations of these disorders, relatively few empirical studies have quantified human exploratory behavior. This article reviews the literature characterizing motor and exploratory behavior associated with bipolar disorder and genetic and pharmacological animal models of the illness. Despite sophisticated assessment of exploratory behavior in rodents, objective quantification of human motor activity has been limited primarily to actigraphy studies with poor cross-species translational value. Furthermore, symptoms that reflect the cardinal features of bipolar disorder have proven difficult to establish in putative animal models of this illness. Recently, however, novel tools such as the human behavioral pattern monitor provide multivariate translational measures of motor and exploratory activity, enabling improved understanding of the neurobiology underlying psychiatric disorders.

Growth hormone rescues hippocampal synaptic function after sleep deprivation

Sleep is required for, and sleep loss impairs, normal hippocampal synaptic N-methyl-D-aspartate (NMDA) glutamate receptor function and expression, hippocampal NMDA receptor-dependent synaptic plasticity, and hippocampal-dependent memory function. Although sleep is essential, the signals linking sleep to hippocampal function are not known. One potential signal is growth hormone. Growth hormone is released during sleep, and its release is suppressed during sleep deprivation. If growth hormone links sleep to hippocampal function, then restoration of growth hormone during sleep deprivation should prevent adverse consequences of sleep loss. To test this hypothesis, we examined rat hippocampus for spontaneous excitatory synaptic currents in CA1 pyramidal neurons, long-term potentiation in area CA1, and NMDA receptor subunit proteins in synaptic membranes. Three days of sleep deprivation caused a significant reduction in NMDA receptor-mediated synaptic currents compared with control treatments. When rats were injected with growth hormone once per day during sleep deprivation, the loss of NMDA receptor-mediated synaptic currents was prevented. Growth hormone injections also prevented the impairment of long-term potentiation that normally follows sleep deprivation. In addition, sleep deprivation led to a selective loss of NMDA receptor 2B (NR2B) from hippocampal synaptic membranes, but normal NR2B expression was restored by growth hormone injection. Our results identify growth hormone as a critical mediator linking sleep to normal synaptic function of the hippocampus.

Sleep deprivation in pigeons and rats using motion detection

STUDY OBJECTIVES

Forced sleep deprivation results in substantial behavioral and physiologic effects in mammals. The disk-over-water (DOW) method produces a syndrome characterized by increased energy expenditure and a robust preferentially rapid-eye-movement sleep rebound upon recovery or eventual death after several weeks of sleep deprivation. The DOW has been used successfully only in rats. This paper presents a method to enforce long-term controlled sleep deprivation across species and to compare its effects in rats and pigeons.

DESIGN AND INTERVENTION

A conveyor was substituted for the DOW disk. Behavior rather than electroencephalography was used to trigger arousal stimuli, as in gentle-handling deprivation. Rats and pigeons were deprived using this apparatus, and the results were compared with each other and with published reports.

MEASUREMENTS AND RESULTS

The physiologic consequences and recovery sleep in rats were like those published for DOW rats. Magnitude of sleep loss and recovery patterns in pigeons were similar to those seen in rats, but expected symptoms of the sleep deprivation syndrome were absent in pigeons. The use of a motion trigger allowed us to measure and, thus, to assess the quality and impact of the procedure.

CONCLUSION

Prolonged and controlled sleep deprivation can be enforced using automated motion detection and a conveyor-over-water system. Pigeons and rats, deprived of sleep to the same extent, showed similar patterns of recovery sleep, but pigeons did not exhibit the hyperphagia, weight loss, and debilitation seen in rats.

Paradoxical sleep deprivation: neurochemical, hormonal and behavioral alterations. Evidence from 30 years of research

Sleep comprises approximately one-third of a person's lifetime, but its impact on health and medical conditions remains partially unrecognized. The prevalence of sleep disorders is increasing in modern societies, with significant repercussions on people's well-being. This article reviews past and current literature on the paradoxical sleep deprivation method as well as data on its consequences to animals, ranging from behavioral changes to alterations in the gene expression. More specifically, we highlight relevant experimental studies and our group's contribution over the last three decades.

Compensatory rebound of body movements during sleep, after asphyxia in neonatal rats

PURPOSE: The usefulness of body movements that occur during sleep when assessing perinatal asphyxia and predicting its long-term consequences is contradictory. This study investigated whether neonatal rats manifest these movements in compensatory rebound after asphyxia, and if these alterations play an important role in its pathogenesis. METHODS: Eight neonatal rats (aged 6-48h) were implanted with small EMG and EKG electrodes and sleep movements were recorded over a 30-minute control period. Recordings were continued during asphyxia caused by the enclosure of the animal in a polyvinyl sheet for 60 minutes, followed by a 30-minute recovery period. RESULTS: Heart rate was lowered to bradycardic level during asphyxia causing behavioral agitation and increased waking time during the initial phase (30 minutes). Sleep-related movements were also significantly reduced from 12.5 ± 0.5 (median ± SE/2min) to 9.0 ± 0.44 in the final half of the period (Anova, p<0.05). Movement frequency increased in the recovery period to 15.0 ± 0.49 (Anova, p<0.05). CONCLUSION: These data show that newborn rats present compensatory rebound of body movements during sleep which may help in the diagnosis of asphyxia and other problems related to sleep parameters.

Rapid eye movement (REM) sleep homeostatic regulatory processes in the rat: changes in the sleep-wake stages and electroencephalographic power spectra

The aim of this study was to elucidate physiological processes that are involved in the homeostatic regulation of REM sleep. Adult rats were chronically instrumented with sleep-wake recording electrodes. Following post-surgical recovery, rats were habituated extensively for freely moving polygraphic recording conditions. On the first experimental recording day (baseline day, BLD), polygraphic signs of undisturbed sleep-wake activities were recorded for 4 h (between 11:00 AM and 3:00 PM). During the second experimental recording day (REM sleep deprivation day, RDD), rats were selectively deprived of REM sleep for the first 2 h and then allowed to have normal sleep-wake for the following 2 h. The results demonstrated that during the first 2 h, compared to BLD, RDD recordings exhibited 87.80% less time in REM sleep and 16% more time in non-REM (NREM) sleep. The total percentages of wakefulness remained comparable between the BLD and RDD. During the RDD, the mean number of REM sleep episodes was much higher than in the BLD, indicating increased REM sleep drive. Electroencephalographic (EEG) power spectral analysis revealed that selective REM sleep deprivation increased delta power but decreased theta power during the residual REM sleep. During the last 2 h, after REM sleep deprivation, rats spent 51% more time in REM sleep compared to the BLD. Also during this period, the number of REM sleep episodes with the shortest (5-30 s) and longest (>120 s) duration increased during the RDD. These findings suggest that the REM sleep homeostatic process involves increased delta- and decreased theta-frequency wave activities in the cortical EEG.

Pain-related behavior following REM sleep deprivation in the rat: influence of peripheral nerve injury, spinal glutamatergic receptors and nitric oxide

We assessed whether pain-related behavior in neuropathic or control rats is changed following rapid eye movement sleep deprivation (REMSD). Furthermore, we determined the contribution of spinal glutamatergic receptors and nitric oxide to sensitivity changes following REMSD versus peripheral nerve injury. Pain behavior was assessed in Sprague-Dawley (SD) and Hannover-Wistar (HW) rats with a spinal nerve ligation or a sham operation. Nerve ligation produced mechanical hypersensitivity of the injured dermatome in all animals. Baseline sensitivity to mechanical stimulation was higher in the HW than the SD group, independent of nerve injury. In both strains, mechanical sensitivity of neuropathic and sham-operated animals was increased following 48 h of REMSD. Heat sensitivity of an uninjured dermatome was not different among experimental conditions. Reversal of mechanical hypersensitivity was attempted in HW rats by spinal administration of an antagonist of the metabotropic glutamate receptor 5 (mGluR(5)) or the NMDA receptor and a nitric oxide synthase (NOS) inhibitor. Mechanical hypersensitivity induced by REMSD in unoperated rats was attenuated by all three drugs, while in neuropathic animals the mechanical anti-hypersensitive effect was most pronounced with the antagonist of the mGluR(5) or a NOS inhibitor. The results indicate that the strain of the animals markedly influences baseline withdrawal threshold to mechanical stimulation. Mechanical hypersensitivity following REMSD, however, is similarly increased in HW and SD strains, and the REMSD-associated increase in mechanical sensitivity is independent of nerve injury. Furthermore, mechanical hypersensitivities following REMSD and peripheral nerve injury share common spinal mechanisms involving, at least, the mGluR(5) and nitric oxide.

Selective rapid eye movement sleep deprivation impairs the maintenance of long-term potentiation in the rat hippocampus

Rapid eye movement (REM) sleep deprivation (RSD) is known to impair learning and memory. Previous studies have demonstrated that RSD induces an impairment of hippocampal long-term potentiation (LTP). In most of these studies, RSD was set up prior to LTP induction. In this work, we focused on RSD after LTP induction. We investigated the effect of RSD for 24-48 h after induction of LTP in the dentate gyrus on LTP maintenance and whether a REM rebound after 48 h RSD affected LTP. RSD rats were deprived of REM sleep by stroking their backs using a brush, whereas control rats were allowed to sleep freely. Another control group of rats was awoken during non-REM sleep (NRS) under the same conditions (NRS group). REM-deprived rats displayed a faster decay of population spike amplitudes compared with the control and NRS groups over a 24-h recording time. After 48 h RSD, there was no difference in the population spike amplitudes before or after 4 h of release from RSD. These results suggest that REM sleep after LTP induction in the dentate gyrus plays an essential role in LTP maintenance, whereas a REM rebound does not restore the RSD-induced impairment of LTP.

REM sleep deprivation inhibits LTP in vivo in area CA1 of rat hippocampus

Rapid eye movement (REM) sleep deprivation has previously been shown to interfere with normal learning and memory and to inhibit long-term potentiation (LTP) in vitro. Previous studies on REM sleep deprivation and LTP have relied on in vitro analysis in isolated brain slices taken from animals following several days of sleep deprivation. LTP in the hippocampus in situ may differ from LTP in vitro due to modulatory inputs from other brain regions, which are altered after REM sleep deprivation. Here, we examined LTP in unanesthetized, behaving animals on the first and second recovery days following REM sleep deprivation to determine if similar effects are seen in vivo as previously reported in vitro. We found that LTP was significantly impaired in REM sleep-deprived animals on the second recovery day but not the first recovery day. Our results extend previous findings by showing that REM sleep deprivation continues to affect hippocampal function for more than 24h following the end of deprivation. Our results also suggest the presence of a modulatory process not present in vitro. Our findings are not explained by stress during REM sleep deprivation because equivalent circulating corticosterone levels (an index of stress) were found during both REM sleep deprivation and control treatment.

Sleep homeostasis in rats assessed by a long-term intermittent paradoxical sleep deprivation protocol

Numerous studies have evaluated the sleep homeostasis of rats after short- or long-periods of sleep deprivation, but none has assessed the effects of prolonged sleep restriction on the rat's sleep pattern. The purpose of the present study, therefore, was to evaluate the sleep homeostasis of rats under a protocol of chronic sleep restriction. Male Wistar rats were implanted with electrodes for EEG and EMG recordings. Using the single platform method, the animals were submitted to 18 h of sleep restriction, beginning at 16:00 h (lights on at 07:00 h), followed by a 6 h sleep window (from 10:00 h to 16:00 h) for 21 days. Immediately after this period, rats were allowed to sleep freely for 4 days (recovery period). The sleep-wake cycle was recorded throughout the entire experiment and the results showed that during the 6h sleep window there was an increase on the percentage of sleep time, reflected by augmented time in high amplitude slow wave sleep and in paradoxical sleep, when compared to baseline sleep, whereas bouts of awakening longer than 1.5 min were greatly reduced, with the animals exhibiting a monophasic-type sleep pattern. During the deprivation period, paradoxical sleep was abolished. High amplitude slow wave sleep was also greatly affected by the protocol. Nonetheless, one day of recovery was sufficient to restore the normal sleep pattern. These findings indicate that this protocol was capable to induce many changes in the rat's sleep patterns, suggesting that during the 6h sleep window there is a sleep adaptive homeostatic process.

Nociceptor and age specific effects of REM sleep deprivation induced hyperalgesia

REM sleep deprivation (REMSD) has been shown to increase rates of negatively reinforced operant behavior, but not operant responding maintained by positive reinforcement. The reason for this differential effect is currently unknown. We hypothesize that REMSD can increase sensitivity to noxious stimuli. In the present study, we sought to determine if REMSD was associated with a change in response to noxious heat (i.e., altered nociceptive sensitivity). Two groups of rats, aged 6 and 22 months, were subjected to hotplate algesia testing at two different temperatures (44 and 52 degrees C). Initially, baseline numbers of responses and total response time were obtained at 44 degrees C. Animals then were exposed to 48 h of REMSD or control conditions. The frequency and duration of hindpaw responses (licking and guarding) increased for young animals only after REMSD and none of the control conditions. Old rats showed increased duration of nocifensive responding after REMSD and tank control conditions without a change in the number of responses at 44 degrees C. Latency to first nocifensive response was significantly longer in the 44 degrees C hotplate tests, but decreased to levels observed throughout the 52 degrees C hotplate tests following REMSD and TC conditions. These findings suggest that REMSD increases nociceptive sensitivity under conditions of sustained, selective C nociceptor activation (42 degrees C), but not under conditions of phasic A-delta activation (52 degrees C). The findings also indicate that age can be a significant variable in REMSD studies.

Possible role for the 5-HT1A receptor in the behavioral effects of REM sleep deprivation on free-operant avoidance responding in rat

RATIONALE

REM sleep deprivation (REMSD) has been shown to increase rates of free-operant avoidance responding. Depletion of 5-hydroxytryptamine (5-HT, serotonin) levels produces similar effects on responding.

OBJECTIVE

We studied whether the pharmacological activation of the 5-HT1A receptor would produce effects on avoidance responding similar to REMSD and depleted 5-HT levels.

METHODS

Rats were trained to lever press on a free-operant avoidance task. Dose-effect functions were established for 8-OH-DPAT (a 5-HT1A receptor agonist) (0.1-1.0 mg/kg) and WAY 100635 (a 5-HT1A receptor antagonist) (0.1-1.0 mg/kg). Rats were then exposed to REMSD (48 h) or equivalent control conditions, and then administered 8-OH-DPAT (0.6 mg/kg) and/or WAY 100635 (0.025-0.1 mg/kg).

RESULTS

Injections of 8-OH-DPAT increased rates of avoidance responding in a dose-dependent manner, while WAY 100635 did not alter responding. The effect of 8-OH-DPAT was antagonized by pre-injection of WAY 100635. REMSD and injections of 8-OH-DPAT increased rates of avoidance responding and the effects of both manipulations were reversed by pre-injection of WAY 100635.

CONCLUSIONS

Activation of the 5-HT1A receptor may be a mechanism by which REMSD increases rates of free-operant avoidance responding.

Variable-interval reinforcement schedule value influences responding following REM sleep deprivation

The effects of rapid-eye movement sleep deprivation (REMSD) in rats were studied in relation to variable-interval (VI) reinforcement schedule value. Initially, lever pressing was maintained on a VI 30-s schedule of food pellet delivery. After a baseline was established, rats were repeatedly exposed to 96 hr of REMSD and control conditions of an equivalent duration. Responding decreased following REMSD but not after exposure to control conditions. Lever pressing was then maintained on a VI 15-s schedule of food pellet delivery and exposure to the REMSD and control conditions was repeated. Under this condition following repeated REMSD exposures, rates of lever pressing became similar to baseline responding. A VI 30-s schedule of food pellet delivery was then reinstated and REMSD and control conditions were repeated. Lever pressing following exposure to the REMSD condition decreased for 3 of 4 rats. Results suggest that VI schedule value influences the effects of REMSD on responding.

REM sleep enhancement induced by different procedures improves memory retention in rats

Growing evidence supports the idea that sleep following learning is critically involved in memory formation. Recent studies suggest that information acquired during waking is reactivated and possibly consolidated during subsequent sleep, especially during rapid-eye movement (REM) or paradoxical sleep (PS). Critical reviews, however, have questioned PS and memory relationships, particularly because of shortcomings of the PS deprivation paradigm applied in many studies. Therefore, in the present study we used an opposite strategy, i.e. we investigated the effects of PS enhancement on memory retention. In three experiments, we found that selective PS enhancement, induced by different procedures after discrimination training in rats, results in increased retention tested 24 h later. Moreover, calculated in all animals (n = 61), there was a highly significant correlation between post-training PS values and retention scores. Our results suggest that an experimentally induced increase of PS after learning facilitates memory consolidation.

Rapid eye-movement sleep deprivation does not 'rescue' developmentally regulated long-term potentiation in visual cortex of mature rats

The age at which it is possible to obtain a usually age-limited (developmental) form of long-term potentiation (LTP) in rat visual cortex slices can be extended by suppressing rapid eye movement (REM) sleep. In this study, we examined whether REM sleep deprivation can also 'rescue' this type of LTP in older rats. Rats, 42-59 days of age, were either REM sleep-deprived for 7-10 days (n=8), or not deprived of REM sleep (control group, n=8). Brain slices from visual cortex were tested for the developmental form- and a related, non-developmental form of LTP. Three of the eight REM sleep-deprived animals and four of the eight non-deprived animals met criteria for a valid attempt to induce the developmental form of LTP. Though the non-age-regulated form of LTP could be obtained in all seven of these animals, the developmental form could not be elicited in any, indicating that REM sleep deprivation does not uniformly affect all forms of LTP in adult rats. We conclude that extended periods of REM sleep deprivation do not facilitate induction of developmentally regulated LTP once the animal is beyond a certain age.

Increases in avoidance responding produced by REM sleep deprivation or serotonin depletion are reversed by administration of 5-hydroxytryptophan

Our objective was to directly compare the effects of rapid eye movement (REM) sleep deprivation (REMSD) and serotonin 5-hydroxytryptamine (5-HT) depletion on free-operant avoidance behavior in rats. These experiments were designed to determine if declining 5-HT levels observed during REMSD might mediate the increases in avoidance responding observed in REM sleep deprived rats. Rats were trained on a free-operant avoidance task. Following training, the animals were assigned to one of three sleep conditions (REMSD, tank control, or cage control). Animals in each sleep condition were exposed to four 5-HT manipulations: (a) saline plus saline; (b) p-chlorophenylalanine (PCPA) plus saline; (c) saline plus 5-hydroxytryptophan (5-HTP) and (d) PCPA plus 5-HTP. Both REMSD and 5-HT depletion via PCPA resulted in an increase in avoidance responding that was reversed by administration of 5-HTP. REMSD and 5-HT depletion via PCPA resulted in increased avoidance efficiency and were reversed by 5-HTP administration, but only changes following PCPA injection were statistically significant. Decreases in 5-HT levels that occur during REMSD likely mediate increases in avoidance responding.

The cholinesterase inhibitor DFP facilitates the expression of paradoxical sleep (PS) propensity in rats subjected to short-term PS deprivation

Short-term paradoxical sleep (PS) deprivation was used to examine the effects of chronic exposure to subtoxic doses of the cholinesterase inhibitor diisopropylfluorophosphate (DFP) on PS regulation. Rats were injected once daily with DFP (0.2 mg/kg per day; s.c.) for 11 consecutive days; control rats received a daily injection of oil vehicle. The experiment was conducted on the 10th and 11th days of treatment, when brain cholinesterase inhibition induced by DFP exposure was maximal. On the 10th day, an 8-h baseline recording was carried out. On the 11th day, a 6-h PS deprivation was carried out by manually awaking rats each time they showed polygraphic signs of PS; recordings were then continued for another 2 h to examine recovery sleep. During deprivation, though they slept less than controls, DFP-treated rats made more attempts to enter PS. After deprivation, their PS rebound had an overall amount comparable to that of the controls, but its time course was shortened: whereas PS elevation was manifested through the 2 h of recovery in the control group, it occurred only during the first hour in the DFP group. These results demonstrate that chronic, low-level DFP exposure facilitated the expression of the PS propensity that accumulated as a result of PS deprivation: it enhanced the tendency for PS during deprivation; it accelerated the rate of compensatory PS expression after deprivation. They support the hypothesis that DFP promotes PS initiation by increasing cholinergic transmission.

Effects of short-acting hypnotics on sleep latency in rats placed on grid suspended over water

The present study was performed to develop a new sleep disturbance model for evaluating hypnotic potencies by placing rats on a grid suspended over water up to 1 cm under the grid surface. When rats were placed on the grid, significant increases in sleep latency and amount of wakefulness were observed compared with those of rats placed on sawdust. However, the amounts of non-rapid eye movement (non-REM) sleep and rapid eye movement (REM) sleep of rats placed on the grid were significantly decreased compared with those of rats placed on sawdust. Four short-acting hypnotics (triazolam, zopiclone, brotizolam, lormetazepam) caused significant decreases in sleep latency, and the effects of hypnotics in rats placed on the grid were more potent than those in rats placed on sawdust. In conclusion, the present model can serve as a new sleep disturbance model and may also be useful for evaluating the sleep-inducing effects of short-acting hypnotics.

Is the nonREM-REM sleep cycle reset by forced awakenings from REM sleep?

In selective REM sleep deprivation (SRSD), the occurrence of stage REM is repeatedly interrupted by short awakenings. Typically, the interventions aggregate in clusters resembling the REM episodes in undisturbed sleep. This salient phenomenon can easily be explained if the nonREM-REM sleep process is continued during the periods of forced wakefulness. However, earlier studies have alternatively suggested that awakenings from sleep might rather discontinue and reset the ultradian process. Theoretically, the two explanations predict a different distribution of REM episode duration. We evaluated 117 SRSD treatment nights recorded from 14 depressive inpatients receiving low dosages of Trimipramine. The alarms were triggered by an automatic mechanism for the detection of REM sleep and had to be canceled by the subjects themselves. The REM episodes were determined as in undisturbed sleep-they had to include the remaining REM activity and were separated by 30 min without REM epochs. The frequency histogram of REM episodes declined exponentially with episode duration for each of the first four sleep cycles. The duration of nonREM intervals revealed bimodal distributions. These results were found consistent with the model assuming a reset of the ultradian cycle upon awakening. Whether REM or nonREM activity is resumed on return to sleep can be modeled by a random decision whereby the probability for REM sleep might depend on the momentary REM pressure.

Rapid eye movement sleep deprivation modifies expression of long-term potentiation in visual cortex of immature rats

During rapid eye movement (REM) sleep, activity of non-retinal origin is propagated into central visual-system pathways in a manner similar, in pattern and intensity, to central visual-system activity that is exogenously generated in waking. It has been hypothesized that REM sleep, which is more abundantly represented early in life than later, functions to provide adjunct 'afferent' input for shaping synaptic connectivity during brain maturation. Here we present data that support this proposal. Recent studies have described a developmentally regulated form of in vitro long-term potentiation (LTP) in the visual cortex that is experience- and age-dependent. In immature rats, suppression of retinal activation of the visual system by removal of visual experience (dark rearing) extends the age when the developmentally regulated form of LTP can be produced. This study tests whether suppression of REM-state activation of the visual system also lengthens the developmental period in which this specific form of LTP can be elicited. Young rats were deprived of REM sleep by the multiple-small-platforms-over-water method during the typically latest week for induction of such LTP in slices of visual cortex. After this week, we could still induce LTP in slices from nearly all the REM-sleep-deprived rats (8/9) but not from age-matched rats that had not lost REM sleep (0/5). The control rats had been housed on large platforms that allow the animals to obtain REM sleep. Only body weights and the concentration of thyrotrophin-releasing hormone in the hypothalamus distinguished home-caged, normal-sleeping controls from both groups of platform animals. On all measures, stress levels were not dissimilar in the two platforms groups. After 7 days of behavioral suppression of REM sleep in immature rats, and consequent reduction of the intense, extra-retinal activity endogenously generated during this sleep state, we found that the period was extended in which developmentally regulated synaptic plasticity (LTP) could be elicited in slices of visual neocortex. These studies support the role of REM sleep and its associated neuronal activity in brain maturation.

The effects of the nitric oxide synthase inhibitors on the behaviour of small-platform-stressed mice in the plus-maze test

Effects of the nitric oxide synthase (NOS) inhibitors 7-nitroindazole (7-NI), N(G)-nitro-L-arginine (L-NOARG) and N(G)-nitro-L-arginine methyl ester (L-NAME) on the behaviour of control and small-platform (SP)-stressed mice in the plus-maze test were studied. SP stress was induced by placing mice on SPs (3.5 cm diameter) surrounded by water for 24 h. This model contains several factors of stress like rapid eye movement (REM) sleep deprivation, isolation, immobilization and falling into the water. The plus-maze test was carried out with control and SP-stressed mice. SP stress induced an anxiolytic-like effect that was evidenced by increased percentage of time spent on the open arms of the plus-maze. The administration of NOS inhibitors 7-NI (20.0-120.0 mg/kg) and L-NOARG (20.0 and 40.0 mg/kg) induced an anxiolytic effect and the administration of L-NAME (20.0 and 40.0 mg/kg)--an anxiogenic effect in control mice. In SP-stressed mice, the effects of NOS inhibitors were changed. Contrary to control mice, 7-NI at a dose of 20.0 mg/kg induced an anxiogenic effect in SP-stressed mice and other doses of 7-NI, with exception of 80.0 mg/kg, as well as L-NOARG and L-NAME were without any effect. On the basis of these data, we can propose that SP stress induced changes in the function of L-arginine-NOS-NO pathways. It is also proposed that the behavioural effects of NOS inhibitors can be changed in stressed animals.

Effects of REM sleep deprivation on a multiple schedule of appetitive reinforcement

The effects of rapid eye movement sleep deprivation (REMSD) on appetitively reinforced responding by rats was studied in two experiments. In Experiment 1, a lever press was maintained on a baseline multiple FR 30 FI 60-s schedule of reinforcement that was reestablished after each experimental manipulation. Animals were then repeatedly exposed to 24, 48, or 96 h of REMSD and equivalent periods of tank control and cage control conditions. For all animals responding was reduced only after 96 h of REMSD, but tolerance to REMSD developed following repeated exposures. Experiment 2, replicated the procedures of Experiment 1 except that the apparatus was modified to prevent ad libitum access to REMSD during operant sessions. Animals were repeatedly exposed to 96 h of REMSD and equivalent periods of tank control and cage control conditions. No reduction in responding was observed in Experiment 2. The current findings, in conjunction with previous research, suggest that REMSD may have qualitatively different effects on responding maintained by positive versus negative reinforcement.

Small platform stress increases exploratory activity of mice in staircase test

Small platform (SP) stress was induced by placing mice on small platforms (3.5 cm diameter) surrounded by water for 24 h. This model contains several factors of stress like rapid eye movement (REM) sleep deprivation, isolation, immobilization and falling into the water. The staircase test consisted of placing a mouse in an enclosed staircase with 5 steps and recording (1) the number of steps and (2) rearings made during 3 min. SP stress increased the exploratory activity of mice in the staircase test as evidenced by an increase in the number of steps and rearings made In control mice diazepam (0.25 and 0.5 mg/kg) induced an anxiolytic effect in the staircase test as evidenced by a decrease in the number of rearings without changes in the number of steps. In SP stressed mice the anxiolytic effect of diazepam was not seen and the sedative effect as evidenced by a decrease in the number of steps was more pronounced. Buspirone at a dose of 1.0 mg/kg did not have effect on the behaviour of control or SP stressed mice in the staircase test. To study possible diurnal variations the staircase test was carried out at 3 different times of a day (08:00, 14:00, 20:00) with control and SP stressed mice. The exploratory activity of control mice in the staircase test gradually increased from 08:00 to 20:00 as evidenced by an increased number of steps and rearings made. SP stress increased the exploratory activity of mice irrespective of the time of testing. In conclusion, on the basis of these data the authors can propose that SP stress increases the exploratory activity of mice in the staircase test and induces a hyposensitivity of mice to the anxiolytic effect of diazepam. The effect of SP stress on the behaviour of mice in the staircase test is not caused by the disruptance of diurnal rhythms.