A function for REM sleep: regulation of noradrenergic receptor sensitivity

A Narrative Review on REM Sleep Deprivation: A Promising Non-Pharmaceutical Alternative for Treating Endogenous Depression

Endogenous depression represents a severe mental health condition projected to become one of the worldwide leading causes of years lived with disability. The currently available clinical and non-clinical interventions designed to alleviate endogenous depression-associated symptoms encounter a series of inconveniences, from the lack of intervention effectiveness and medication adherence to unpleasant side effects. In addition, depressive individuals tend to be more frequent users of primary care units, which markedly affects the overall treatment costs. In parallel with the growing incidence of endogenous depression, researchers in sleep science have discovered multiple links between rapid eye movement (REM) sleep patterns and endogenous depression. Recent findings suggest that prolonged periods of REM sleep are associated with different psychiatric disorders, including endogenous depression. In addition, a growing body of experimental work confidently describes REM sleep deprivation (REM-D) as the underlying mechanism of most pharmaceutical antidepressants, proving its utility as either an independent or adjuvant approach to alleviating the symptoms of endogenous depression. In this regard, REM-D is currently being explored for its potential value as a sleep intervention-based method for improving the clinical management of endogenous depression. Therefore, this narrative review represents a comprehensive inventory of the currently available evidence supporting the potential use of REM-D as a reliable, non-pharmaceutical approach for treating endogenous depression, or as an adjuvant practice that could improve the effectiveness of currently used medication.

Functional roles of REM sleep

Rapid eye movement (REM) sleep is an enigmatic and intriguing sleep state. REM sleep differs from non-REM sleep by its characteristic brain activity and from wakefulness by a reduced anti-gravity muscle tone. In addition to these key traits, diverse physiological phenomena appear across the whole body during REM sleep. However, it remains unclear whether these phenomena are the causes or the consequences of REM sleep. Experimental approaches using humans and animal models have gradually revealed the functional roles of REM sleep. Extensive efforts have been made to interpret the characteristic brain activity in the context of memory functions. Numerous physical and psychological functions of REM sleep have also been proposed. Moreover, REM sleep has been implicated in aspects of brain development. Here, we review the variety of functional roles of REM sleep, mainly as revealed by animal models. In addition, we discuss controversies regarding the functional roles of REM sleep.

Cognitive Function Decline in the Third Trimester of Pregnancy Is Associated with Sleep Fragmentation

During late pregnancy, sleep deterioration is regularly observed. In concert with these observations, in previous studies by other researchers, a slight objective cognitive decline in pregnant women has been found. Sleep is essential for memory consolidation. The hypothesis of the study was that cognitive impairment could be related to sleep deterioration during pregnancy. The study included 19 pregnant women in their third trimester of pregnancy (28−40 weeks, median 33 weeks (IQR 32−37)) recruited at the Department of Gynecology and Obstetrics, Medical University of Warsaw, and 20 non-pregnant women as controls. The assessment was performed using the vocabulary subtest from the Wechsler Adult Intelligence Scale (WAIS), D2 Test of Attention, OSPAN task (Operational Span Task) to assess cognitive performance, actigraphy to examine sleep parameters, and a set of self-report instruments: Athens Insomnia Scale (AIS), Beck Depression Inventory (BDI), Ford Insomnia Response to Stress (FIRST), Regenstein Hyperarousal Scale (HS), and Epworth Sleepiness Scale (ESS). Although there were no differences between the groups in WAIS (p = 0.18), pregnant women had worse scores in working memory capacity (overall number of remembered letters: p = 0.012, WM span index: p = 0.004) and a significantly lower score in attention (p = 0.03). Pregnant women also had lower sleep efficiency (p = 0.001), more awakenings from sleep (p = 0.001), longer average awakenings (p < 0.0001), longer wake after sleep onset (WASO, p < 0.0001), and longer total time in bed (p < 0.0001). In psychological assessment, pregnant women had only a higher FIRST score (p = 0.02). Using mediation analysis, we found that frequent awakening might be the major factor contributing to deterioration in working memory performance, explaining almost 40% of the total effect. In conclusion, sleep fragmentation in the third trimester of pregnancy may impair working memory consolidation. Pregnant women often complain about poor daily performance as well as non-restorative sleep. In this study, we showed that there is a relationship between lower sleep quality in pregnancy and worse cognitive functioning. We can expect a cognitive decline in women with sleep disturbances in pregnancy. Therefore, we should pay more attention to the treatment of sleep disorders in pregnancy.

Is paradoxical sleep setting up innate and acquired complex sensorimotor and adaptive behaviours?: A proposed function based on literature review

We summarize here the progress in identifying the neuronal network as well as the function of paradoxical sleep and the gaps of knowledge that should be filled in priority. The core system generating paradoxical sleep localized in the brainstem is now well identified, and the next step is to clarify the role of the forebrain in particular that of the hypothalamus including the melanin-concentrating hormone neurons and of the basolateral amygdala. We discuss these two options, and also the discovery that cortical activation during paradoxical sleep is restricted to a few limbic cortices activated by the lateral supramammillary nucleus and the claustrum. Such activation nicely supports the findings recently obtained showing that neuronal reactivation occurs during paradoxical sleep in these structures, and induces both memory consolidation of important memory and forgetting of less relevant ones. The question that still remains to be answered is whether paradoxical sleep is playing more crucial roles in processing emotional and procedural than other types of memories. One attractive hypothesis is that paradoxical sleep is responsible for erasing negative emotional memories, and that this function is not properly functioning in depressed patients. On the other hand, the presence of a muscle atonia during paradoxical sleep is in favour of a role in procedural memory as new types of motor behaviours can be tried without harm during the state. In a way, it also fits with the proposed role of paradoxical sleep in setting up the sensorimotor system during development.

Importance of the locus coeruleus-norepinephrine system in sleep-wake regulation: implications for aging and Alzheimer’s disease

Five decades ago, seminal studies positioned the brainstem locus coeruleus (LC) norepinephrine (NE) system as a key substrate for the regulation of wakefulness and sleep, and this picture has recently been elaborated thanks to methodological advances in the precise investigation and experimental modulation of LC structure and functions. This review presents and discusses findings that support the major role of the LC-NE system at different levels of sleep-wake organization, ranging from its involvement in the overall architecture of the sleep-wake cycle to its associations with sleep microstructure, while accounting for the intricate neuroanatomy surrounding the LC. Given the particular position held by the LC-NE system by being at the intersection of sleep-wake dysregulation and initial pathophysiological processes of Alzheimer's disease (AD), we conclude by examining emerging opportunities to investigate LC-NE mediated relationships between sleep-wake alteration and AD in human aging. We further propose several research perspectives that could support the LC-NE system as a promising target for the identification of at-risk individuals in the preclinical stages of AD, and for the development of novel preventive interventions.

Voluntary exercise ameliorates synaptic pruning deficits in sleep-deprived adolescent mice

Adolescence is a critical period for brain development and adequate sleep during this period is essential for physical function and mental health. Emerging evidence has detailed the neurological impacts of sleep insufficiency on adolescents, as was unveiled by our previous study, microglia, one of the crucial contributors to synaptic pruning, is functionally disrupted by lack of sleep. Here, we provided evidence featuring the protective effect and the underlying mechanisms of voluntary exercise (VE) on microglial functions in an adolescent 72 h sleep deprivation (SD) model. We identified that the aberrant hippocampal neuronal activity and impaired short-term memory performance in sleep-deprived mice were prevented by 11 days of VE. VE significantly normalized the SD-induced dendritic spine increment and maintained the microglial phagocytic ability in sleep-deprived mice. Moreover, we found that the amendment of the noradrenergic signal in the central nervous system may explain the preventative effects of VE on the abnormalities of microglial and neuronal functions caused by SD. These data suggested that VE may confer protection to the microglia-mediated synaptic pruning in the sleep-deprived adolescent brains. Therefore, physical exercise could be a beneficial health practice for the adolescents that copes the adverse influence of inevitable sleep insufficiency.

Sex, Sleep Deprivation, and the Anxious Brain

Insufficient sleep is a known trigger of anxiety. Nevertheless, not everyone experiences these effects to the same extent. One determining factor is sex, wherein women experience a greater anxiogenic impact in response to sleep loss than men. However, the underlying brain mechanism(s) governing this sleep-loss-induced anxiety increase, including the markedly different reaction in women and men, is unclear. Here, we tested the hypothesis that structural brain morphology in a discrete network of emotion-relevant regions represents one such explanatory factor. Healthy participants were assessed across sleep-rested and sleep-deprived conditions, with brain structure quantified using gray matter volume measures. Sleep loss triggered greater levels of anxiety in women compared with men. Reduced gray matter volume in the anterior insula and lateral orbitofrontal cortex predicted the anxiogenic impact of sleep loss in women, yet predicted resilience in men, and did so with high discrimination accuracy. In contrast, gray matter volume in ventromedial prefrontal cortex predicted the anxiogenic impact of sleep loss in both men and women. Structural human brain morphology therefore appears to represent one mechanistic pathway (and possible biomarker) determining anxiety vulnerability to sleep loss-a discovery that may help explain the higher prevalence of sleep disruption and anxiety in women.

Unraveling the Evolutionary Determinants of Sleep

Despite decades of intense study, the functions of sleep are still shrouded in mystery. The difficulty in understanding these functions can be at least partly attributed to the varied manifestations of sleep in different animals. Daily sleep duration can range from 4-20 hrs among mammals, and sleep can manifest throughout the brain, or it can alternate over time between cerebral hemispheres, depending on the species. Ecological factors are likely to have shaped these and other sleep behaviors during evolution by altering the properties of conserved arousal circuits in the brain. Nonetheless, core functions of sleep are likely to have arisen early and to have persisted to the present day in diverse organisms. This review will discuss the evolutionary forces that may be responsible for phylogenetic differences in sleep and the potential core functions that sleep fulfills.

The sleep-deprived human brain

How does a lack of sleep affect our brains? In contrast to the benefits of sleep, frameworks exploring the impact of sleep loss are relatively lacking. Importantly, the effects of sleep deprivation (SD) do not simply reflect the absence of sleep and the benefits attributed to it; rather, they reflect the consequences of several additional factors, including extended wakefulness. With a focus on neuroimaging studies, we review the consequences of SD on attention and working memory, positive and negative emotion, and hippocampal learning. We explore how this evidence informs our mechanistic understanding of the known changes in cognition and emotion associated with SD, and the insights it provides regarding clinical conditions associated with sleep disruption.

Search Activity Concept: Relationship between Behavior, Health and Brain Functions

Search activity concept provides a new classification of the behavior which distinguishes search activity (activity in the uncertain situation with the constant feedback between behavior and its outcome), stereotyped behavior with a definite probability forecast, panic (activity without feedback between activity and its outcome) and renunciation of search. Only search activity which includes fight, flight, orienting behavior and creativity raises the body’s resistance to stress, to natural and experimentally induced pathology whereas renunciation of search which display itself in freezing, helplessness and depression forms a nonspecific predisposition to somatic disturbances (e.g. psychosomatic diseases). Dreams in REM sleep are regarded as a specific form of search activity aimed at compensating for the lack of search in waking. REM sleep deprivation on a small as well as on rotating platform raises the requirement in REM sleep by frustrating search activity. It is suggested that in wakefulness characterized by the prominent search activity the inhibitory alpha-2- adrenoreceptors became less sensitive to stimulation and consequently in this state the activity of the brain monoamine neurons is less limited by the level of brain monoamines. During renunciation of search brain monoamine synthesis is not stimulated by monoamine exhaustion. In REM sleep the critical level of brain monoamines for search activity to start is lower than in wakefulness and alpha-2-adrenoreceptors are less sensitive than in the state of renunciation of search although more sensitive than during search behavior in waking. REM sleep indirectly contributes to memory consolidation by carrying out its main function — restoration of search activity. A functionally sufficient REM sleep contains search activity in dreams (subject is active in his/her own dream scenario) while in functionally insufficient REM sleep dreams are characterized by subject’s passive position and feeling of helplessness. REM sleep insufficiency is an obligate condition for mental and somatic disorders to appear. The difference between normal (adaptive) and pathological (maladaptive) emotional tension is determined by the presence or absence of search activity in the structure of emotional tension. Repression of the unacceptable motive causing neurotic anxiety is a human variant of renunciation of search. Hypochondriac symptoms are in negative relationships with psychosomatic disorders and they, as well as positive symptoms in schizophrenia and anorectic behavior in anorexia nervosa, represent a pathological misdirected search activity.

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.

Neuroscience: A Distributed Neural Network Controls REM Sleep

How does the brain control dreams? New science shows that a small node of cells in the medulla - the most primitive part of the brain - may function to control REM sleep, the brain state that underlies dreaming.

Region-Specific Dissociation between Cortical Noradrenaline Levels and the Sleep/Wake Cycle

STUDY OBJECTIVES

The activity of the noradrenergic system of the locus coeruleus (LC) is high in wake and low in sleep. LC promotes arousal and EEG activation, as well as attention, working memory, and cognitive flexibility. These functions rely on prefrontal cortex and are impaired by sleep deprivation, but the extent to which LC activity changes during wake remains unclear. Moreover, it is unknown whether noradrenergic neurons can sustain elevated firing during extended wake. Recent studies show that relative to LC neurons targeting primary motor cortex (M1), those projecting to medial prefrontal cortex (mPFC) have higher spontaneous firing rates and are more excitable. These results suggest that noradrenaline (NA) levels should be higher in mPFC than M1, and that during prolonged wake LC cells targeting mPFC may fatigue more, but direct evidence is lacking.

METHODS

We performed in vivo microdialysis experiments in adult (9-10 weeks old) C57BL/6 mice implanted for chronic electroencephalographic recordings. Cortical NA levels were measured during spontaneous sleep and wake (n = 8 mice), and in the course of sleep deprivation (n = 6).

RESULTS

We found that absolute NA levels are higher in mPFC than in M1. Moreover, in both areas they decline during sleep and increase during wake, but these changes are faster in M1 than mPFC. Finally, by the end of sleep deprivation NA levels decline only in mPFC.

CONCLUSIONS

Locus coeruleus (LC) neurons targeting prefrontal cortex may fatigue more markedly, or earlier, than other LC cells, suggesting one of the mechanisms underlying the cognitive impairment and the increased sleep presure associated with sleep deprivation.

COMMENTARY

A commentary on this article appears in this issue on page 11.

Sleep Deprivation Impairs the Human Central and Peripheral Nervous System Discrimination of Social Threat

Facial expressions represent one of the most salient cues in our environment. They communicate the affective state and intent of an individual and, if interpreted correctly, adaptively influence the behavior of others in return. Processing of such affective stimuli is known to require reciprocal signaling between central viscerosensory brain regions and peripheral-autonomic body systems, culminating in accurate emotion discrimination. Despite emerging links between sleep and affective regulation, the impact of sleep loss on the discrimination of complex social emotions within and between the CNS and PNS remains unknown. Here, we demonstrate in humans that sleep deprivation impairs both viscerosensory brain (anterior insula, anterior cingulate cortex, amygdala) and autonomic-cardiac discrimination of threatening from affiliative facial cues. Moreover, sleep deprivation significantly degrades the normally reciprocal associations between these central and peripheral emotion-signaling systems, most prominent at the level of cardiac-amygdala coupling. In addition, REM sleep physiology across the sleep-rested night significantly predicts the next-day success of emotional discrimination within this viscerosensory network across individuals, suggesting a role for REM sleep in affective brain recalibration. Together, these findings establish that sleep deprivation compromises the faithful signaling of, and the "embodied" reciprocity between, viscerosensory brain and peripheral autonomic body processing of complex social signals. Such impairments hold ecological relevance in professional contexts in which the need for accurate interpretation of social cues is paramount yet insufficient sleep is pervasive.

Sleep restores behavioral plasticity to Drosophila mutants

Given the role that sleep plays in modulating plasticity, we hypothesized that increasing sleep would restore memory to canonical memory mutants without specifically rescuing the causal molecular lesion. Sleep was increased using three independent strategies: activating the dorsal fan-shaped body, increasing the expression of Fatty acid binding protein (dFabp), or by administering the GABA-A agonist 4,5,6,7-tetrahydroisoxazolo-[5,4-c]pyridine-3-ol (THIP). Short-term memory (STM) or long-term memory (LTM) was evaluated in rutabaga (rut) and dunce (dnc) mutants using aversive phototaxic suppression and courtship conditioning. Each of the three independent strategies increased sleep and restored memory to rut and dnc mutants. Importantly, inducing sleep also reverses memory defects in a Drosophila model of Alzheimer's disease. Together, these data demonstrate that sleep plays a more fundamental role in modulating behavioral plasticity than previously appreciated and suggest that increasing sleep may benefit patients with certain neurological disorders.

Stability of P50 auditory sensory gating during sleep from infancy to 4 years of age

The stability of cerebral inhibition was assessed across early childhood using a paired-click auditory sensory gating paradigm. The P50 ERP was measured during REM (or its infant analogue, active sleep) and NREM sleep in 14 children at approximately 3 months of age and again at approximately 4 years of age. Evoked response amplitudes, latencies, and the S2/S1 ratio of the amplitudes of the evoked responses were compared between the two visits. Significant reliability was found for the S2/S1 ratio (r = .73, p = .003) during REM but not non REM sleep (r = -.05, p = .88). A significant stimulus number by sleep stage interaction (F(1,12) = 17.1, p = .001) demonstrated that the response to the second stimulus decreased during REM but not NREM sleep. These findings suggest that this measure is stable during REM sleep across early childhood, is not affected by age, and is sleep-state dependent. P50 sensory gating is a biomarker which, if used properly, may provide a mechanism to further explore changes in the developing brain or may help with early screening for psychiatric illness vulnerability.

Sleep deprivation therapy for depression

Sleep deprivation (SD) is the most widely documented rapid-onset antidepressant therapy, targeting the broadly defined depressive syndrome. Although SD responses are transient, its effects can be sustained by concomitant medications (e.g., selective serotonin reuptake inhibitors and lithium) and circadian-related interventions (e.g., bright light and sleep phase advance). Thus, considering its safety, this technique can now be considered among the first-line antidepressant treatment strategies for patients affected by mood disorders. SD is a complex intervention and it should be considered multi-target in nature. Thus, the mechanisms explaining its antidepressant effect can be looked for on many levels, involving not only monoaminergic mechanisms but also sleep homeostatic and circadian mechanisms, glutamatergic mechanisms and synaptic plasticity.

Trauma exposure and sleep: using a rodent model to understand sleep function in PTSD

Post-traumatic stress disorder (PTSD) is characterized by intrusive memories of a traumatic event, avoidance behavior related to cues of the trauma, emotional numbing, and hyper-arousal. Sleep abnormalities and nightmares are core symptoms of this disorder. In this review, we propose a model which implicates abnormal activity in the locus coeruleus (LC), an important modifier of sleep-wake regulation, as the source of sleep abnormalities and memory abnormalities seen in PTSD. Abnormal LC activity may be playing a key role in symptom formation in PTSD via sleep dysregulation and suppression of hippocampal bidirectional plasticity.

The role of sleep in emotional brain function

Rapidly emerging evidence continues to describe an intimate and causal relationship between sleep and emotional brain function. These findings are mirrored by long-standing clinical observations demonstrating that nearly all mood and anxiety disorders co-occur with one or more sleep abnormalities. This review aims to (a) provide a synthesis of recent findings describing the emotional brain and behavioral benefits triggered by sleep, and conversely, the detrimental impairments following a lack of sleep; (b) outline a proposed framework in which sleep, and specifically rapid-eye movement (REM) sleep, supports a process of affective brain homeostasis, optimally preparing the organism for next-day social and emotional functioning; and (c) describe how this hypothesized framework can explain the prevalent relationships between sleep and psychiatric disorders, with a particular focus on posttraumatic stress disorder and major depression.

Antidepressant chronotherapeutics for bipolar depression

Chronotherapeutics refers to treatments based on the principles of circadian rhythm organization and sleep physiology, which control the exposure to environmental stimuli that act on biological rhythms, in order to achieve therapeutic effects in the treatment of psychiatric conditions. It includes manipulations of the sleep-wake cycle such as sleep deprivation and sleep phase advance, and controlled exposure to light and dark. The antidepressant effects of chronotherapeutics are evident in difficult-to-treat conditions such as bipolar depression, which has been associated with extremely low success rates of antidepressant drugs in naturalistic settings and with stable antidepressant response to chronotherapeutics in more than half of the patients. Recent advances in the study of the effects of chronotherapeutics on neurotransmitter systems, and on the biological clock machinery, allow us to pinpoint its mechanism of action and to transform it from a neglected or “orphan” treatment to a powerful clinical instrument in everyday psychiatric practice.

Perspectives on the rapid eye movement sleep switch in rapid eye movement sleep behavior disorder

Rapid eye movement (REM) sleep in mammals is associated with wakelike cortical and hippocampal activation and concurrent postural muscle atonia. Research during the past 5 decades has revealed the details of the neural circuitry regulating REM sleep and muscle atonia during this state. REM-active glutamatergic neurons in the sublaterodorsal nucleus (SLD) of the dorsal pons are critical for generation for REM sleep atonia. Descending projections from SLD glutamatergic neurons activate inhibitory premotor neurons in the ventromedial medulla (VMM) and in the spinal cord to antagonize the glutamatergic supraspinal inputs on the motor neurons during REM sleep. REM sleep behavior disorder (RBD) consists of simple behaviors (i.e., twitching, jerking) and complex behaviors (i.e., defensive behavior, talking). Animal research has lead to the hypothesis that complex behaviors in RBD are due to SLD pathology, while simple behaviors of RBD may be due to less severe SLD pathology or dysfunction of the VMM, ventral pons, or spinal cord.

Symmetrical serotonin release during asymmetrical slow-wave sleep: implications for the neurochemistry of sleep-waking states

On land, fur seals predominately display bilaterally synchronized electroencephalogram (EEG) activity during slow-wave sleep (SWS), similar to that observed in all terrestrial mammals. In water, however, fur seals exhibit asymmetric slow-wave sleep (ASWS), resembling the unihemispheric slow-wave sleep of odontocetes (toothed whales). The unique sleeping pattern of fur seals allows us to distinguish neuronal mechanisms mediating EEG changes from those mediating behavioral quiescence. In a prior study we found that cortical acetylcholine release is lateralized during ASWS in the northern fur seal, with greater release in the hemisphere displaying low-voltage (waking) EEG activity, linking acetylcholine release to hemispheric EEG activation (Lapierre et al. 2007). In contrast to acetylcholine, we now report that cortical serotonin release is not lateralized during ASWS. Our data demonstrate that bilaterally symmetric levels of serotonin are compatible with interhemispheric EEG asymmetry in the fur seal. We also find greatly elevated levels during eating and hosing the animals with water, suggesting that serotonin is more closely linked to bilateral variables, such as axial motor and autonomic control, than to the lateralized cortical activation manifested in asymmetrical sleep.

Antidepressant chronotherapeutics for bipolar depression

Chronotherapeutics refers to treatments based on the principles of circadian rhythm organization and sleep physiology, which control the exposure to environmental stimuli that act on biological rhythms, in order to achieve therapeutic effects in the treatment of psychiatric conditions. It includes manipulations of the sleep-wake cycle such as sleep deprivation and sleep phase advance, and controlled exposure to light and dark. The antidepressant effects of chronotherapeutics are evident in difficult-to-treat conditions such as bipolar depression, which has been associated with extremely low success rates of antidepressant drugs in naturalistic settings and with stable antidepressant response to chronotherapeutics in more than half of the patients. Recent advances in the study of the effects of chronotherapeutics on neurotransmitter systems, and on the biological clock machinery, allow us to pinpoint its mechanism of action and to transform it from a neglected or "orphan" treatment to a powerful clinical instrument in everyday psychiatric practice.

Long-term relationships between cholinergic tone, synchronous bursting and synaptic remodeling

Cholinergic neuromodulation plays key roles in the regulation of neuronal excitability, network activity, arousal, and behavior. On longer time scales, cholinergic systems play essential roles in cortical development, maturation, and plasticity. Presumably, these processes are associated with substantial synaptic remodeling, yet to date, long-term relationships between cholinergic tone and synaptic remodeling remain largely unknown. Here we used automated microscopy combined with multielectrode array recordings to study long-term relationships between cholinergic tone, excitatory synapse remodeling, and network activity characteristics in networks of cortical neurons grown on multielectrode array substrates. Experimental elevations of cholinergic tone led to the abrupt suppression of episodic synchronous bursting activity (but not of general activity), followed by a gradual growth of excitatory synapses over hours. Subsequent blockage of cholinergic receptors led to an immediate restoration of synchronous bursting and the gradual reversal of synaptic growth. Neither synaptic growth nor downsizing was governed by multiplicative scaling rules. Instead, these occurred in a subset of synapses, irrespective of initial synaptic size. Synaptic growth seemed to depend on intrinsic network activity, but not on the degree to which bursting was suppressed. Intriguingly, sustained elevations of cholinergic tone were associated with a gradual recovery of synchronous bursting but not with a reversal of synaptic growth. These findings show that cholinergic tone can strongly affect synaptic remodeling and synchronous bursting activity, but do not support a strict coupling between the two. Finally, the reemergence of synchronous bursting in the presence of elevated cholinergic tone indicates that the capacity of cholinergic neuromodulation to indefinitely suppress synchronous bursting might be inherently limited.

The neurobiology of the switch process in bipolar disorder: a review

OBJECTIVE

The singular phenomenon of switching from depression to its opposite state of mania or hypomania, and vice versa, distinguishes bipolar disorder from all other psychiatric disorders. Despite the fact that it is a core aspect of the clinical presentation of bipolar disorder, the neurobiology of the switch process is still poorly understood. In this review, we summarize the clinical evidence regarding somatic interventions associated with switching, with a particular focus on the biologic underpinnings presumably involved in the switch process.

DATA SOURCES

Literature for this review was obtained through a search of the MEDLINE database (1966-2008) using the following keywords and phrases: switch, bipolar disorder, bipolar depression, antidepressant, SSRIs, tricyclic antidepressants, norepinephrine, serotonin, treatment emergent affective switch, mania, hypomania, HPA-axis, glucocorticoids, amphetamine, dopamine, and sleep deprivation.

STUDY SELECTION

All English-language, peer-reviewed, published literature, including randomized controlled studies, naturalistic and open-label studies, and case reports, were eligible for inclusion.

DATA SYNTHESIS

Converging evidence suggests that certain pharmacologic and nonpharmacologic interventions with very different mechanisms of action, such as sleep deprivation, exogenous corticosteroids, and dopaminergic agonists, can trigger mood episode switches in patients with bipolar disorder. The switch-inducing potential of antidepressants is unclear, although tricyclic antidepressants, which confer higher risk of switching than other classes of antidepressants, are a possible exception. Several neurobiological factors appear to be associated with both spontaneous and treatment-emergent mood episode switches; these include abnormalities in catecholamine levels, up-regulation of neurotrophic and neuroplastic factors, hypothalamic-pituitary-adrenal axis hyperactivity, and circadian rhythms.

CONCLUSIONS

There is a clear need to improve our understanding of the neurobiology of the switch process; research in this field would benefit from the systematic and integrated assessment of variables associated with switching.

Comparative anatomy of the locus coeruleus in humans and nonhuman primates

The locus coeruleus (LC) is a dense cluster of neurons that projects axons throughout the neuroaxis and is located in the rostral pontine tegmentum extending from the level of the inferior colliculus to the motor nucleus of the trigeminal nerve. LC neurons are lost in the course of several neurodegenerative disorders, including Alzheimer's and Parkinson's diseases. In this study we used Nissl staining and tyrosine hydroxylase (TH) immunoreactivity to compare the human LC with that of closely related primate species, including great and lesser apes, and macaque monkeys. TH catalyzes the initial and rate-limiting step in catecholamine biosynthesis. The number of TH-immunoreactive (TH-ir) neurons was estimated in each species using stereologic methods. In the LC of humans the mean total number of TH-ir neurons was significantly higher compared to the other primates. Because the total number of TH-ir neurons in the LC was highly correlated with the species mean volume of the medulla oblongata, cerebellum, and neocortical gray matter, we conclude that much of the observed phylogenetic variation can be explained by anatomical scaling. Notably, the total number of LC neurons in humans was most closely predicted by the nonhuman allometric scaling relationship relative to medulla size, whereas the number of LC neurons in humans was considerably lower than predicted according to neocortex and cerebellum volume.

Sleep viewed as a state of adaptive inactivity

Sleep is often viewed as a vulnerable state that is incompatible with behaviours that nourish and propagate species. This has led to the hypothesis that sleep has survived because it fulfills some universal, but as yet unknown, vital function. I propose that sleep is best understood as a variant of dormant states seen throughout the plant and animal kingdoms and that it is itself highly adaptive because it optimizes the timing and duration of behaviour. Current evidence indicates that ecological variables are the main determinants of sleep duration and intensity across species.

Distinct behavioral and neurochemical alterations induced by intermittent hypoxia or paradoxical sleep deprivation in rats

The current study investigated the effects of paradoxical sleep deprivation and intermittent hypoxia by examining whether a combination of the two would induce anxiety-like alterations in behavior. The neurochemical effects of these manipulations were investigated by measuring cortical, striatal and hippocampal monoamine concentrations. Wistar Hannover rats were submitted to subchronic (3 days) intermittent hypoxia exposure (alternating cycles of 2 min room air-2 min 10% O2 from 0700-1900 h) and paradoxical sleep deprivation using the single platform method. Rats were randomly assigned to four different protocols: 1) control, 2) intermittent hypoxia during the light period (12 h/day), 3) paradoxical sleep deprivation (24 h/day), and 4) intermittent hypoxia combined with paradoxical sleep deprivation. Rats subjected to intermittent hypoxia showed no modification in the behavioral or neurochemical parameters assessed. Although paradoxical sleep deprivation did not produce alterations in anxiety-like behavior, the rats did increase exploratory activity in the elevated plus-maze. Moreover, a significant increase in striatal epinephrine and hippocampal homovanilic acid (HVA) concentrations was found in the paradoxical sleep deprivation groups, but not in the intermittent hypoxia/paradoxical sleep deprivation group. Of note, both paradoxical sleep deprivation and intermittent hypoxia/paradoxical sleep deprivation groups showed an increase in plasma corticosterone concentration. These results suggest that paradoxical sleep deprivation induces behavioral alterations, and these abnormalities may reflect altered neurotransmission in the brain. When paradoxical sleep deprivation was combined with intermittent oxygen depletion, the behavioral and biochemical parameters were comparable to those of control rats.

Sleep enhances serum interleukin-7 concentrations in humans

Growing evidence points towards a beneficial effect of sleep on immune function. Human studies indicate that the T cell mediated adaptive immune function including formation of antigen specific antibodies is facilitated by sleep. Along this line, here we aimed to dissociate the effect of sleep and circadian rhythm on circulating interleukin-7 (IL-7) and interleukin-15 (IL-15). These cytokines play a key role in the homeostatic regulation of naïve and memory T cell numbers and are critical for the differentiation of memory T cells. Serum IL-7 concentration and expression of membrane-bound IL-15 (mIL-15) on CD14(+) monocytes were measured in 18 men on two occasions: once during a regular 24-h sleep-wake cycle and another time during a 24-h period of continuous wakefulness. During sleep and especially during late sleep serum IL-7 concentrations were distinctly increased as compared to wakefulness (p<0.05). mIL-15 density on monocytes remained unchanged by sleep. The sleep-dependent increase in IL-7 concentration was associated with increased REM sleep, but did not correlate with concentrations of GH, cortisol or norepinephrine during sleep. The findings concur with the notion of a supportive influence of sleep on T cell function related to formation of T cell memory.

CNS and anticonvulsant activity of a non-protein toxin (KC-MMTx) isolated from King Cobra (Ophiophagus hannah) venom

In the present study, King Cobra (Ophiophagus hannah) venom was subjected to TLC followed by column chromatography/HPLC to isolate and purify a non-protein toxin designated as KC-MMTx. (1)H NMR, IR and EIMS studies showed KC-MMTx likely to be a 282 D unsaturated aliphatic acid having molecular formula C18H34O2. The minimum lethal dose of KC-MMTx was 200 microg/kg (i.v.) and 350 microg/kg (i.p.) in Swiss albino male mice. It significantly increased pentobarbitone induced sleeping time and significantly decreased the body temperature of male albino mice. It provided protection against amphetamine aggregate toxicity in mice but failed to protect amphetamine stereotypy in male albino rats. KC-MMTx provided significant protection against drug (strychnine, pentylenetetrazole, yohimbine) induced convulsions in male albino mice. It increased serum Na+ and decreased serum Ca2+ significantly in male mice. MAO activity and brain neurotransmitter levels in male mice were altered significantly. Further detailed study is warranted on the CNS, anticonvulsant potential of KC-MMTx, which may lead to the development of newer therapeutic tools in the near future.

Clues to the functions of mammalian sleep

The functions of mammalian sleep remain unclear. Most theories suggest a role for non-rapid eye movement (NREM) sleep in energy conservation and in nervous system recuperation. Theories of REM sleep have suggested a role for this state in periodic brain activation during sleep, in localized recuperative processes and in emotional regulation. Across mammals, the amount and nature of sleep are correlated with age, body size and ecological variables, such as whether the animals live in a terrestrial or an aquatic environment, their diet and the safety of their sleeping site. Sleep may be an efficient time for the completion of a number of functions, but variations in sleep expression indicate that these functions may differ across species.

Antiepileptic activity of delta sleep-inducing peptide and its analogue in metaphit-provoked seizures in rats

PROBLEM

Previous studies have shown that humoral, endogenous and somnogenic, delta sleep-inducing peptide (DSIP) has influence on insomnia, pain, adaptation to stress, epilepsy, etc. We investigated the potential of DSIP and its analogue DSIP-12 (a nonapeptide with alanine in position 2 of DSIP molecule substituted by beta-alanine) to antagonize metaphit (1-[1(3-isothiocyanatophenyl)-cyclohexyl]piperidine) induced generalized, reflex audiogenic seizures in adult male Wistar albino rats.

METHODS

The rats divided in four groups received (i.p.): saline; metaphit; metaphit+DSIP; and metaphit+DSIP-12, respectively. Metaphit-treated animals displaying seizure in eight previous tests received DSIP or DSIP-12 and afterwards audiogenic stimuli were applied at hourly intervals for the next 30 h. The animals were exposed to sound stimulation 60 min after metaphit administration and further on at hourly intervals. Incidence and severity of seizures were behaviorally analyzed. Selected EEGs and power spectra were recorded and analyzed.

RESULTS AND CONCLUSIONS

Metaphit led to hypersynchronous epileptiform activity (polyspikes and spike-wave complexes) and increased power spectra 0.5-30 h after the treatment. Severity of metaphit seizures increased with time to reach the peak 7-12 h after injection. DSIP and DSIP-12 significantly (*P<0.05 and **P<0.01) increased in delta and theta frequency bands and decreased the incidence, mean seizure grade and duration of metaphit convulsions. The results suggest that DSIP and DSIP-12 may be considered as potential antiepileptics in the animal model, DSIP-12 being more efficient than DSIP.

Rapid fluctuations in rat barrel cortex plasticity

Neuronal populations in the sensory cortex exhibit fluctuations in excitability, and the present experiments tested the hypothesis that these variations coincide with peaks and troughs in cortical modifiability. The activity of multiunit neuronal clusters under light urethane anesthesia was recorded through 100-microelectrode arrays implanted in the infragranular layers of rat barrel cortex. Spontaneous activity was characterized by "bursts" of spikes, synchronized across the barrel cortex. This allowed activity at one selected electrode to be taken as a reliable monitor of widespread cortical bursts. We used spikes at the selected electrode to trigger stimulation of two pairs of whiskers during a 50 min conditioning procedure: (1) for the "burst-conditioned" whisker pair, each stimulus was delivered 1 msec after the triggering spike, activating cortex coincident with the burst; and (2) for the "interburst-conditioned" whisker pair, each stimulus was delivered 300 msec after the triggering spike, activating cortex during the trough between bursts. The cross-correlation between cortical neurons in the pairs of columns matching the stimulated whisker pairs was estimated after the termination of the conditioning procedure. Conditioning produced a twofold increase in the degree of co-firing between infragranular neurons in columns receiving burst-conditioned costimulation but no significant change in connectivity between infragranular neurons in columns receiving interburst-conditioned costimulation, although the two pairs of columns received an equal number of sensory inputs. These findings suggest that the strength of co-activity between columns in the barrel cortex can be modified by sensory input patterns during discrete, intermittent intervals time-locked to bursts.

Oxidative injury to the locus coeruleus of rat brain: neuroprotection by melatonin

Neurodegeneration in the locus coeruleus (LC) has been documented in several central nervous system (CNS) neurodegenerative diseases. In the present study, iron-induced oxidative injury in the LC was investigated in chloral-hydrate anesthetized rats. Three days after bilateral infusion of iron in the LC, both vertical and horizontal locomotor activities were decreased. Seven days after unilateral infusion of iron, lipid peroxidation was elevated in the infused LC, and the norepinephrine content was depleted in the ipsilateral hippocampus of the brain. Furthermore, the immunohistochemical study demonstrated a reduction in tyrosine hydroxylase-positive neurons in the infused LC. The involvement of programmed cell death (apoptosis) in iron-induced oxidative injury in the LC was investigated. Forty-eight hours after iron infusion, cytosolic cytochrome c was elevated in the infused LC. Moreover, terminal deoxytransferase-mediated dUTP-nick end labeling (TUNEL)-positive cells, an indicative of apoptosis, were detected in the infused LC. In an attempt to prevent oxidative injury in the LC, melatonin was systemically administered. Intraperitoneal injection of melatonin attenuated iron-induced behavioral changes in locomotor activity as well as iron-induced increases in cytosolic cytochrome c and TUNEL-positive cells. Moreover, melatonin diminished iron-induced oxidative injury. At the same time, the level of glial derived neurotrophic factor (GDNF) was elevated in the LC of melatonin-treated rats. Our data suggests that oxidative stress because of iron results in apoptosis in the infused LC and causes degeneration of the coeruleohippocampal noradrenergic system in the rat brain. Furthermore, melatonin, among other mechanisms, may exert its neuroprotection via up-regulation of GDNF levels in CNS.

Effect of Acute Exposure to Loud Occupational Noise during Daytime on the Nocturnal Sleep Architecture, Heart Rate, and Cortisol Secretion in Healthy Volunteers

OBJECTIVES

Noise is one of the commonest physical stressors to which industrial workers are exposed. Many workers complain of symptoms associated with a non-specific generalized stress response, including disturbed sleep. However, industrial workers may be exposed to more than one source of stress and it is not possible to completely attribute the disturbed nocturnal sleep and changes in heart rate to the effects of loud noise alone. This study was done to find out whether acute exposure of healthy individuals to loud occupational noise during the daytime would cause changes in their nocturnal sleep architecture, heart rate during sleep and serum cortisol levels.

METHODS

Baseline polysomnography was done on ten subjects who were exposed for eight hours either to continuous occupational background noise levels of >75dB(A), or a quiet environment. Sleep polysomnography was done on the night prior to and after exposure. Blood was collected for serum cortisol estimation at night prior to sleep and in the morning after waking up. Statistical analysis was done by repeated measures ANOVA with Tukey's post test.

RESULTS

The sleep efficiency was less than 80% and the total time spent in Rapid Eye Movement (REM) sleep, Slow Wave Sleep (SWS) and the REM onset latency were significantly decreased on the night after exposure to noise. There was a significant increase in stage shifts. The percentage fall in heart rate during sleep was decreased compared to the baseline values. The serum cortisol levels in the morning after exposure to noise was significantly increased.

CONCLUSION

Workers exposed to loud background occupational noise react to the stress and show changes in nocturnal sleep architecture and heart rate which may be contributed to the exposure to noise.

Systemic vitamin D3 attenuated oxidative injuries in the locus coeruleus of rat brain

Iron-induced oxidative injuries in locus coeruleus (LC), a major source of noradrenergic projections in the central nervous system (CNS), were investigated in chloral-hydrate anesthetized rats. Local infusion of iron dose-dependently elevated lipid peroxidation of iron-infused LC seven days after infusion. At the same time, norepinephrine content in the hippocampus ipsilateral to the iron-infused LC was decreased in a concentration-dependent manner. Our immunostaining study demonstrated reduced tyrosine hydroxylase-positive neurons in the iron-infused LC, indicating a reduction of neuron number by iron infusion. The involvement of apoptosis in iron-induced oxidative injuries was studied. An abrupt increase in cytosolic cytochrome c content was demonstrated in the infused LC 48 hours after iron infusion. TUNEL-positive cells, an indication of apoptosis, were detected in the iron-infused LC. In an attempt to prevent iron-induced neurotoxicity, vitamin D3, an active metabolite of vitamin D, was systemically administered. Iron-induced increases in cytosolic cytochrome c and TUNEL-positive cells were reduced by this treatment. Furthermore, systemic administration of vitamin D3 attenuated iron-induced oxidative injuries in the infused LC. Our data suggest that local infusion of iron in LC induced oxidative stress and resulted in programmed cell death in the LC-hippocampal noradrenergic system. Furthermore, vitamin D3 may be neuroprotective and therapeutic in attenuating iron-induced neurotoxicity in CNS.

Semantic analysis of auditory input during sleep: studies with event related potentials

This review summarises the results of event-related potentials studies exploring the extent to which the human brain can extract semantic information from external stimuli during sleep. The persistence of a differential response to the subject's own name, relative to any other proper name, during stage 2 (S2) and paradoxical (REM) sleep (PS) suggests that the brain remains able to discriminate an intrinsically relevant word during these sleep stages. The similarities and the differences between these sleep cognitive responses and the waking P300 are stressed, and the functional significance of this component discussed especially in relation with consciousness and memory of the stimulus. Recent studies of the 'N400' potential evoked by semantically incongruous words, have shown that this component may be also elicited during S2 and PS, indicating preserved detection of semantic discordance during these sleep stages. However, linguistic incongruity appears to be processed in a different manner during PS than during waking, since words devoid of meaning (pseudo-words), which are detected as anomalous and evoke N400 during waking, yielded responses similar to those of congruous words in PS. All these data support the view that some semantic analysis of auditory stimuli remains possible in the human sleeping brain, and warrant further studies to elucidate the extent and limits of these capabilities.

Timing is everything: does the robust upregulation of noradrenergically regulated plasticity genes underlie the rapid antidepressant effects of sleep deprivation?

The mechanisms by which sleep deprivation brings about rapid antidepressant effects remain to be elucidated. Biological rhythms have the capacity to temporally dissociate biochemical processes, and imposing a temporal coincidence on normally dissociated events can have striking and unexpected effects. In this context, it is noteworthy that the locus coeruleus (LC) noradrenergic projection is quiescent only during rapid-eye-movement (REM) sleep, when the target tissues display their greatest sensitivity; indeed, the temporal dissociation between the firing of the LC noradrenergic neurons and the sensitivity of its postsynaptic targets in the cortex may have considerable relevance for the antidepressant effects of sleep deprivation. Sleep deprivation rapidly upregulates several plasticity-related genes, effects that are noradrenergically mediated; these are the very same genes that are upregulated by chronic antidepressants. Thus, activating the norepinephrine system during REM sleep (by infusing an alpha(2) antagonist) may allow an interaction with a primed, sensitized postsynaptic milieu, thereby rapidly increasing the expression of plasticity genes and consequently a rapid antidepressant response.

Correlations using the NREM-REM sleep cycle frequency support distinct regulation mechanisms for REM and NREM sleep

Polysomnograms of most homeothermic species distinguish two states, rapid eye movement (REM) and non-REM (NREM) sleep. These alternate several times during the night for reasons and following rules that remain poorly understood. It is unknown whether each state has its own function and regulation or whether they represent two facets of the same process. The present study compared the mean REM/NREM sleep ratio and the mean number of NREM-REM sleep cycles across 3 consecutive nights. The rationale was that, if REM and NREM sleep are tightly associated, their ratio should be comparable whatever the cycle frequency in the night. Twenty-six healthy subjects of both sexes were recorded at their home for 4 consecutive nights. The correlation between the REM/NREM sleep ratio and the number of cycles was highly significant. Of the two sleep components, REM sleep was associated to the number of cycles, whereas NREM sleep was not. This suggests that the relationship between REM sleep and NREM sleep is rather weak within cycles, does not support the concept of NREM-REM sleep cycles as miniature units of the sleep process, and favors the concept of distinct mechanisms of regulation for the two components.