Sleep: a functional enigma

[Sleep deprivation and the development of oxidative stress in animal models]

OBJECTIVE

To study the features and mechanisms of development of oxidative stress in animal models during sleep deprivation.

MATERIAL AND METHODS

The experiments were carried out on 6-month-old male rats (n=60), which were divided equally into 3 groups. Group 1 included intact animals, groups 2 and 3 were subjected to modeling of chronic sleep deprivation using the method of cyclic sleep restriction. Animals of group 3, in addition to the standard diet, received resveratrol (10 mg/kg, intragastric) daily. On days 0, 1, 3 and 5 of the experiment, the activity of antioxidant enzymes and the concentration of peroxidation products in the blood serum was assessed.

RESULTS

Sleep deprivation in animal models causes an intensification of oxidative processes (increased concentrations of malondialdehyde and diene conjugates) and a decrease in the activity of antioxidant enzymes (catalase, superoxide dismutase, glutathione peroxidase, glutathione reductase).

CONCLUSION

Sleep deprivation contributes to the accumulation of highly toxic products of lipid peroxidation in the body tissues, which is reflected in metabolic disorders, and a decrease in adaptive capabilities. Additional administration of resveratrol helps to reduce the amplitude of fluctuations in redox balance, which can be considered as a possible way to correct oxidative stress and prevent disorders associated with sleep restriction and dysregulation of the sleep-wake cycle.

Hydroalcoholic extract from Abelmoschus manihot (Linn.) Medicus flower reverses sleep deprivation-evoked learning and memory deficit

Previous researches have indicated that sleep plays a vital role in cognitive functions. Sleep deprivation (SD) causes learning and memory damage, which is associated with oxidative stress. This study was performed to investigate the neuroprotective effects of an extract of Abelmoschus manihot flower (EAM) against memory deficit induced by SD in mice. The SD model was evoked by multiple platform method for 5 days, successively. The learning and memory-improving effects of EAM were assessed by behavioral trials and the underlying mechanism was investigated by measuring the oxidative stress alteration. Our findings indicated that the SD-induced memory deficit and the EAM treatment improved the cognitive functions of mice in the object location recognition test and passive avoidance task. In addition, EAM effectively improved the activities of the antioxidant enzyme, decreased the content of malondialdehyde (MDA), and restored the protein expression of the brain-derived neurotrophic factor (BDNF), tyrosine kinase B (TrkB) and glutamate receptor 1 (GluR1) in brain tissues. In conclusion, EAM could improve the SD-evoked learning and memory impairments. The possible underlying mechanisms of EAM may be related to its antioxidant capacity and enhanced BDNF/TrkB/GluR1 levels in the hippocampal memory.

Sleep, brain development, and autism spectrum disorders: Insights from animal models

Sleep is an evolutionarily conserved and powerful drive, although its complete functions are still unknown. One possible function of sleep is that it promotes brain development. The amount of sleep is greatest during ages when the brain is rapidly developing, and sleep has been shown to influence critical period plasticity. This supports a role for sleep in brain development and suggests that abnormal sleep in early life may lead to abnormal development. Autism spectrum disorder (ASD) is the most prevalent neurodevelopmental disorder in the United States. It is estimated that insomnia affects 44%-86% of the ASD population, predicting the severity of ASD core symptoms and associated behavioral problems. Sleep problems impact the quality of life of both ASD individuals and their caregivers, thus it is important to understand why they are so prevalent. In this review, we explore the role of sleep in early life as a causal factor in ASD. First, we review fundamental steps in mammalian sleep ontogeny and regulation and how sleep influences brain development. Next, we summarize current knowledge gained from studying sleep in animal models of ASD. Ultimately, our goal is to highlight the importance of understanding the role of sleep in brain development and the use of animal models to provide mechanistic insight into the origin of sleep problems in ASD.

Neuroendocrine Control of Sleep

Sleep is a phenomenon in animal behavior as enigmatic as it is ubiquitous, and one deeply tied to endocrine function. Though there are still many unanswered questions about the neurochemical basis of sleep and its functions, extensive interactions have been identified between sleep and the endocrine system, in both the endocrine system's effect on sleep and sleep's effect on the endocrine system. Unfortunately, until recent years, much research on sleep behavior largely disregarded its connections with the endocrine system. Use of both clinical studies and rodent models to investigate interactions between neuroendocrine function, including biological sex, and sleep therefore presents a promising area of further exploration. Further investigation of the neurobiological and neuroendocrine basis of sleep could have wide impact on a number of clinical and basic science fields. In this review, we summarize the state of basic sleep biology and its connections to the field of neuroendocrine biology, as well as suggest key future directions for the neuroendocrine regulation of sleep that may significantly impact new therapies for sleep disorders in women and men.

Transcranial near-infrared photobiomodulation attenuates memory impairment and hippocampal oxidative stress in sleep-deprived mice

Sleep deprivation (SD) causes oxidative stress in the hippocampus and subsequent memory impairment. In this study, the effect of near-infrared (NIR) photobiomodulation (PBM) on learning and memory impairment induced by acute SD was investigated. The mice were subjected to an acute SD protocol for 72 h. Simultaneously, NIR PBM using a laser at 810 nm was delivered (once a day for 3 days) transcranially to the head to affect the entire brain of mice. The Barnes maze and the What-Where-Which task were used to assess spatial and episodic-like memories. The hippocampal levels of antioxidant enzymes and oxidative stress biomarkers were evaluated. The results showed that NIR PBM prevented cognitive impairment induced by SD. Moreover, NIR PBM therapy enhanced the antioxidant status and increased mitochondrial activity in the hippocampus of SD mice. Our findings revealed that hippocampus-related mitochondrial damage and extensive oxidative stress contribute to the occurrence of memory impairment. In contrast, NIR PBM reduced hippocampal oxidative damage, supporting the ability of 810 nm laser light to improve the antioxidant defense system and maintain mitochondrial survival. This confirms that non-invasive transcranial NIR PBM therapy ameliorates hippocampal dysfunction, which is reflected in enhanced memory function.

Exploring the Effect of Ginsenoside Rh1 in a Sleep Deprivation-Induced Mouse Memory Impairment Model

Panax ginseng C.A. Meyer (Araliaceae) has been used in traditional Chinese medicine for enhancing cognition for thousands of years. Ginsenoside Rh1, a constituent of ginseng root, as with other constituents, has memory-improving effects in normal mice and scopolamine-induced amnesic mice. Sleep deprivation (SD) is associated with memory impairment through induction of oxidative stress. The present study investigated the effect of Rh1 against SD-induced cognitive impairment and attempted to define the possible mechanisms involved. Ginsenoside Rh1 (20 μmol/kg; 40 μmol/kg) and modafinil (0.42 g/kg) were administered to the mice intraperitoneally for 23 days. After 14-day SD, locomotor activity was examined using the open field test, and the object location recognition and Morris water maze tests were used to evaluate cognitive ability. The cortex and hippocampus were then dissected and homogenized, and levels and activities of antioxidant defense biomarkers were evaluated to determine the level of oxidative stress. The results revealed that Rh1 prevented cognitive impairment induced by SD, and its ability to reduce oxidative stress in cortex and hippocampus may contribute to the mechanism of action. Copyright © 2017 John Wiley & Sons, Ltd.

Sleep as spatiotemporal integration of biological processes that evolved to periodically reinforce neurodynamic and metabolic homeostasis: The 2m3d paradigm of sleep

Sleep continues to perplex scientists and researchers. Despite decades of sleep research, we still lack a clear understanding of the biological functions and evolution of sleep. In this review, we will examine sleep from a functional and phylogenetic perspective and describe some important conceptual gaps in understanding sleep. Classical theories of the biology and evolution of sleep emphasize sensory activation, energy balance, and metabolic homeostasis. Advances in electrophysiology, functional neuroimaging, and neuroplasticity allow us to view sleep within the framework of neural dynamics. With this paradigm shift, we have come to realize the importance of neurodynamic homeostasis in shaping the biology of sleep. Evidently, animals sleep to achieve neurodynamic and metabolic homeostasis. We are not aware of any framework for understanding sleep where neurodynamic, metabolic, homeostatic, chronophasic, and afferent variables are all taken into account. This motivated us to propose the two-mode three-drive (2m3d) paradigm of sleep. In the 2m3d paradigm, local neurodynamic/metabolic (N/M) processes switch between two modes-m0 and m1-in response to three drives-afferent, chronophasic, and homeostatic. The spatiotemporal integration of local m0/m1 operations gives rise to the global states of sleep and wakefulness. As a framework of evolution, the 2m3d paradigm allows us to view sleep as a robust adaptive strategy that evolved so animals can periodically reinforce neurodynamic and metabolic homeostasis while remaining sensitive to their internal and external environment.

Graph Theoretical Analysis of BOLD Functional Connectivity during Human Sleep without EEG Monitoring

BACKGROUND

Functional brain networks of human have been revealed to have small-world properties by both analyzing electroencephalogram (EEG) and functional magnetic resonance imaging (fMRI) time series.

METHODS & RESULTS

In our study, by using graph theoretical analysis, we attempted to investigate the changes of paralimbic-limbic cortex between wake and sleep states. Ten healthy young people were recruited to our experiment. Data from 2 subjects were excluded for the reason that they had not fallen asleep during the experiment. For each subject, blood oxygen level dependency (BOLD) images were acquired to analyze brain network, and peripheral pulse signals were obtained continuously to identify if the subject was in sleep periods. Results of fMRI showed that brain networks exhibited stronger small-world characteristics during sleep state as compared to wake state, which was in consistent with previous studies using EEG synchronization. Moreover, we observed that compared with wake state, paralimbic-limbic cortex had less connectivity with neocortical system and centrencephalic structure in sleep.

CONCLUSIONS

In conclusion, this is the first study, to our knowledge, has observed that small-world properties of brain functional networks altered when human sleeps without EEG synchronization. Moreover, we speculate that paralimbic-limbic cortex organization owns an efficient defense mechanism responsible for suppressing the external environment interference when humans sleep, which is consistent with the hypothesis that the paralimbic-limbic cortex may be functionally disconnected from brain regions which directly mediate their interactions with the external environment. Our findings also provide a reasonable explanation why stable sleep exhibits homeostasis which is far less susceptible to outside world.

Effect of non-alcoholic beer on Subjective Sleep Quality in a university stressed population

Sleep deprivation affects the homeostasis of the physiological functions in the human organism. Beer is the only beverage that contains hops, a plant which has a sedative effect. Our objective is to determine the improvement of subjective sleep quality using the Pittsburgh Sleep Quality Index (PSQI). The sample was conducted among a population of 30 university students. The study took place during a period of 3 weeks, the first 7 days were used for the Control, and during the following 14 days the students ingested beer (were asked to drink non-alcoholic beer) while having dinner. The results revealed that Subjective Sleep Quality improved in the case of those students who drank one beer during dinner compared to the Control, this is corroborated by the fact that Sleep Latency decreased (p < 0.05) compared to their Control. The overall rating Global Score of Quality of Sleep also improved significantly (p < 0.05). These results confirm that the consumption of non-alcoholic beer at dinner time helps to improve the quality of sleep at night.

Evaluation of the effect of pentoxifylline on sleep-deprivation induced memory impairment

In this study, we examined the ability of Pentoxifylline (PTX) to prevent sleep deprivation induced memory impairment probably through decreasing oxidative stress. Sleep deprivation was chronically induced 8 h/day for 6 weeks in rats using modified multiple platform model. Concurrently, PTX (100 mg/kg) was administered to animals on daily basis. After 6 weeks of treatment, behavioral studies were conducted to test the spatial learning and memory using the Radial Arm Water Maze. Additionally, the hippocampus was dissected; and levels/activities of antioxidant defense biomarkers glutathione reduced (GSH), glutathione oxidized (GSSG), GSH/GSSG ratio, glutathione peroxidase (GPx), catalase, and superoxide dismutase (SOD), were assessed. The results show that chronic sleep deprivation impaired short- and long-term memories, which was prevented by chronic treatment with PTX. Additionally, PTX normalized sleep deprivation-induced reduction in the hippocampus GSH/GSSG ratio (P < 0.05), and activities of GPx, catalase, and SOD (P < 0.05). In conclusion, chronic sleep deprivation induces memory impairment, and treatment with PTX prevented this impairment probably through normalizing antioxidant mechanisms in the hippocampus.

Sleep and obesity: a focus on animal models

The rapid rise in obesity prevalence in the modern world parallels a significant reduction in restorative sleep (Agras et al., 2004; Dixon et al., 2007, 2001; Gangwisch and Heymsfield, 2004; Gupta et al., 2002; Sekine et al., 2002; Vioque et al., 2000; Wolk et al., 2003). Reduced sleep time and quality increases the risk for obesity, but the underlying mechanisms remain unclear (Gangwisch et al., 2005; Hicks et al., 1986; Imaki et al., 2002; Jennings et al., 2007; Moreno et al., 2006). A majority of the theories linking human sleep disturbances and obesity rely on self-reported sleep. However, studies with objective measurements of sleep/wake parameters suggest a U-shaped relationship between sleep and obesity. Studies in animal models are needed to improve our understanding of the association between sleep disturbances and obesity. Genetic and experimenter-induced models mimicking characteristics of human obesity are now available and these animal models will be useful in understanding whether sleep disturbances determine propensity for obesity, or result from obesity. These models exhibit weight gain profiles consistently different from control animals. Thus a careful evaluation of animal models will provide insight into the relationship between sleep disturbances and obesity in humans. In this review we first briefly consider the fundamentals of sleep and key sleep disturbances, such as sleep fragmentation and excessive daytime sleepiness (EDS), observed in obese individuals. Then we consider sleep deprivation studies and the role of circadian alterations in obesity. We describe sleep/wake changes in various rodent models of obesity and obesity resistance. Finally, we discuss possible mechanisms linking sleep disturbances with obesity.

Energy expenditure: role of orexin

The orexins/hypocretins are endogenous, modulatory and multifunctional neuropeptides with prominent influence on several physiological processes. The influence of orexins on energy expenditure is highlighted with focus on orexin action on individual components of energy expenditure. As orexin stabilizes and maintains normal states of arousal and the sleep/wake cycle, we also highlight orexin mediation of sleep and how sleep interacts with energy expenditure.

Ciclo vigília/sono e o transtorno de déficit de atenção/hiperatividade

OBJETIVO: Analisar as relações entre ciclo vigília/sono e transtorno de déficit de atenção/hiperatividade. FONTES DE DADOS: Os artigos foram selecionados nas bases de dados SciELO e PubMed, utilizando-se "sono", "transtorno de déficit de atenção/hiperatividade", "atividade motora" e "crianças" como palavras-chave para a busca. SÍNTESE DOS DADOS: Embora os resultados de diferentes estudos sejam inconclusivos e, por vezes, contraditórios, não sendo possível estabelecer relações claras entre sono e transtorno do déficit de atenção/hiperatividade, observa-se que o sono das crianças diagnosticadas difere do sono de crianças que não possuem o transtorno, sugerindo que alterações de sono possam se relacionar ao transtorno do déficit de atenção/hiperatividade. CONCLUSÕES: A falta de marcadores biológicos e de conhecimento a respeito da sua etiologia gera dificuldades na determinação da real prevalência do transtorno do déficit de atenção/hiperatividade, além de limitar sua compreensão e a busca por novas formas de tratamento e prevenção. Embora dificuldades de sono sejam frequentemente relatadas na prática clínica e já tenham sido utilizadas como um dos critérios diagnósticos para o transtorno, pouco se sabe sobre a possível participação da privação de sono na etiologia do transtorno do déficit de atenção/hiperatividade.

Wake-promoting agent modafinil worsened attentional performance following REM sleep deprivation in a young-adult rat model of 5-choice serial reaction time task

RATIONALE

Individuals who experience sleep loss may exhibit certain physiological abnormalities. Central stimulant drugs have been studied in sleep-loss conditions, and some of them might be therapeutically beneficial. Modafinil (diphenyl-methyl-sulfinyl-2-acetamide, MOD) has been increasingly employed for elevating alertness and vigilance in recent years, yet the underlying mechanism of actions for MOD is not fully understood.

OBJECTIVES

To examine the behavioral effect of MOD following rapid eye movement sleep deprivation (REMD) in rats. A five-choice serial reaction time task (5-CSRTT) was employed to investigate animals' attentional performance and impulsive reactivity.

MATERIALS AND METHODS

Rats of different ages were trained to learn the 5-CSRTT. REMD with the water platform method was applied for 96 h. The impacts of REMD on 5-CSRTT in middle-age (32-weeks-old) and young-adult (12-week-old) rats were compared with baseline or a condition with shorter visual stimulus duration.

RESULTS

The results revealed that following REMD, young-adult but not middle-age rats were liable to be affected in their performances of the 5-CSRTT. In young-adult rats, while MOD had no contributions to the effect of REMD, it worsened rats' performance following REMD when the stimulus duration was shortened, as shown by the reduced number of correct responses and prolonged magazine latency.

CONCLUSIONS

These results suggest that aging might be a crucial factor for the physiological impact following REMD. MOD should be used cautiously, particularly, in conditions that require REM sleep.

Elevated sleep quality and orexin receptor mRNA in obesity-resistant rats

OBJECTIVE

To determine if resistance to weight gain is associated with alterations in sleep-wake states and orexin receptor gene expression.

DESIGN

Three-month-old obesity-susceptible Sprague-Dawley (SD) and obesity-resistant (OR) rats were fed standard rodent chow. Sleep-wake cycle was measured by radiotelemetry and orexin receptor profiles in sleep-wake regulatory areas of the brain were quantified by quantitative reverse transcriptase-PCR.

SUBJECTS

Adult male obesity-susceptible SD and selectively bred OR rats.

MEASUREMENTS

Body weight, food intake, energy efficiency, percent time spent in active wake (AW), quiet wake (QW), slow-wave sleep (SWS), rapid eye movement (REM) sleep, number and mean duration of sleep-wake episodes, number of stage transitions, SWS sleep delta power and orexin receptor mRNA levels were measured.

RESULTS

OR rats weighed significantly less and had lower energy efficiency than SD rats. Food intake was not different between SD and OR rats. Time spent in QW was similar between groups, and therefore AW and QW were combined and are referred to as 'wakefulness'. OR rats spent significantly more time in wakefulness and less time in SWS compared with SD rats during the 24-h recording period. Relative to SD rats, OR rats had significantly fewer sleep-wake episodes and the duration of the episodes were prolonged, indicating less fragmented sleep. Furthermore, OR rats had fewer transitions between sleep stages, which indicates that OR rats were behaviorally more stable and had more consolidated sleep than obesity-susceptible SD rats. OR rats showed lower delta power during SWS, indicating a lower sleep drive. Our results showed greater orexin receptor gene expression in sleep regulatory brain areas in OR rats.

CONCLUSION

These results show that prolonged wakefulness, better sleep quality, lower sleep drive and greater orexin signaling may confer protection against obesity.

Slow wave activity during sleep: functional and therapeutic implications

Electroencephalographic slow-wave activity (EEG SWA) is an electrophysiological signature of slow (0.5 to 4.0 Hz), synchronized, oscillatory neocortical activity. In healthy individuals, EEG SWA is maximally expressed during non-rapid-eye-movement (non-REM) sleep, and intensifies as a function of prior wake duration. Many of the cellular and network mechanisms generating EEG SWA have been identified, but a number of questions remain unanswered. For example, although EEG SWA is a marker of sleep need, its precise relationship with sleep homeostasis and its roles in the brain are unknown. In this review, the authors discuss their current understanding of the neural mechanisms and possible functions of EEG SWA.

Cortical hyperexcitability and epileptogenesis: Understanding the mechanisms of epilepsy - part 2

Epilepsy encompasses a diverse group of seizure disorders caused by a variety of structural, cellular and molecular alterations of the brain primarily affecting the cerebral cortex, leading to recurrent unprovoked epileptic seizures. In this two-part review we examine the mechanisms underlying normal neuronal function and those predisposing to recurrent epileptic seizures starting at the most basic cellular derangements (Part 1, Volume 16, Issue 3) and working up to the highly complex epileptic networks and factors that modulate the predisposition to seizures (Part 2). We attempt to show that multiple factors can modify the epileptic process and that different mechanisms underlie different types of epilepsy, and in most situations there is an interplay between multiple genetic and environmental factors.

Control and function of the homeostatic sleep response by adenosine A1 receptors

During sleep, the mammalian CNS undergoes widespread, synchronized slow-wave activity (SWA) that directly varies with previous waking duration (Borbély, 1982; Dijk et al., 1990). When sleep is restricted, an enhanced SWA response follows in the next sleep period. The enhancement of SWA is associated with improved cognitive performance (Huber et al., 2004), but it is unclear either how the SWA is enhanced or whether SWA is needed to maintain normal cognitive performance. A conditional, CNS knock-out of the adenosine receptor, AdoA(1)R gene, shows selective attenuation of the SWA rebound response to restricted sleep, but sleep duration is not affected. During sleep restriction, wild phenotype animals express a rebound SWA response and maintain cognitive performance in a working memory task. However, the knock-out animals not only show a reduced rebound SWA response but they also fail to maintain normal cognitive function, although this function is normal when sleep is not restricted. Thus, AdoA(1)R activation is needed for normal rebound SWA, and when the SWA rebound is reduced, there is a failure to maintain working memory function, suggesting a functional role for SWA homeostasis.

Effects of sleep restriction periods on serum cortisol levels in healthy men

OBJECTIVES

To clarify effects of partial sleep deprivation (SD) on morning (07:00) serum cortisol concentrations in two protocols that restricted sleep to 3h/day in healthy adult men. The study was also designed to delineate the relationship between anxiety levels in the morning and slow wave sleep (SWS) periods at night.

METHODS

Ten young adult Han Chinese males were recruited to participate in an 'earlier-night' sleep restriction (SR) period (sleep from 00:00 to 03:00) and then a 'later-night' SR period (sleep from 03:00 to 06:00). The duration of each SR period was 4 days, followed by a recovery night. The SR periods were separated by 10 days of normal sleep. Blood samples of serum cortisol were drawn at 07:00 during each of two SR periods for six consecutive mornings (for a total of 12 measurements per subject), and anxiety levels were also assessed over the same period by the State portion of the State-Trait Anxiety Inventory (STAI). Sleeping processes were monitored by polysomnogram.

RESULTS

Serum cortisol levels decreased after SR (P<0.05) in both paradigms, with greater decreases evident after later-night sleep loss than after earlier-night sleep loss. Cortisol levels were significantly, negatively correlated to the number of days of earlier-night SR, but not to later-night SR. Anxiety scores increased gradually in both conditions. The time of SWS changed indiscriminately in both paradigms. Cortisol levels returned to baseline after one night of recovery sleep.

CONCLUSIONS

Cortisol decreased in both SR conditions, especially in the earlier-night SR protocol, even though SWS time and anxiety levels changed roughly in the same manner in both conditions. Data suggested that sleep loss at different times of the night affects the hypothalamic-pituitary-adrenal axis (HPA-axis) differentially.

A chronopharmacological diagnostic test and treatment for bipolar disorder and depression: Nitric oxide release during sleep causes it to become depressogenic in a subset of patients

In some patients sleep can have a depressogenic effect and sleep reduction can result in mania. The hypothesis on which this model is based postulates that it is nitric oxide release during sleep that causes it to become depressogenic in a subset of patients. That subset is comprised of patients with genetic polymorphisms in nitric oxide genes and/or in serotonin and melatonin genes. The nature of the dynamic equilibrium between nitric oxide, on the one hand, and serotonin and melatonin, on the other, determines whether or not sleep is likely to have a depressogenic effect. Changes throughout the sleep cycle thereby impart a chronological factor to the dynamic equilibrium. Other writers have postulated, but not defined, a certain so-called "critical period" during the sleep cycle when sleep can become particularly depressogenic. This model assumes that in fact there is such a critical period and that it is stage IV sleep. In addition to the chronological influences on the dynamic equilibrium, the aging process also exerts an influence. The increased sleep fragmentation associated with the aging process causes stage IV sleep to become increasingly more depressogenic because of a concept called delta rebound. Delta rebound results in deeper sleep intensity. It is associated with increased nitric oxide production and the concomitant serotonin suppression that is associated with it. The chronopharmacological test that is proposed challenges the dynamic equilibrium between nitric oxide, on the one hand, and serotonin and melatonin on the other. It consists of melatonin taken at bedtime and the antidepressant moclobemide, taken as close to the onset of stage IV sleep as possible. If there is a noticeable lessening of depressive symptoms the following morning, then drug treatments that increase serotonin and/or melatonin are appropriate and drugs that suppress or block serotonin or melatonin, or that increase nitric oxide, are not.

A chronopharmacological preventive treatment for sleep-related migraine headaches and chronic morning headaches: Nitric oxide supersensitivity can cause sleep-related headaches in a subset of patients

Frequent and recurrent migraine headaches can, over time, pose the additional risks of stroke, brain damage, heart failure and attention deficit. This is why prevention should always be a part of the treatment. Nitric oxide supersensitivity is the hypothesis upon which this model is based. Its role in causing migraine headaches and chronic morning headaches can be triggered by both normal and abnormal characteristics of the sleep cycle and more specifically by the release of nitric oxide that occurs towards the end of the sleep cycle. Stress and the age-related loss of sleep continuity, together with the corresponding increase in cortisol levels, potentiate delta rebound. Delta rebound results in deeper sleep intensity. It is associated with increased nitric oxide production. Increased delta rebound then causes an increase in the amount and duration of nitric oxide release at night. Migraineurs are susceptible to migraine headaches because they are supersensitive to nitric oxide. The diurnal pattern of the incidence of sleep-related headaches in a subset of the general population is caused by the effect of nitric oxide supersensitivity during the sleep cycle. The proposed treatment is for both sleep-related migraine headaches and chronic morning headaches. It consists of melatonin and moclobemide taken during the night, close the end of the sleep cycle so as to achieve the maximum concentrations. Both melatonin and moclobemide affect three important aspects of sleep-related headaches: nitric oxide supersensitivity, stress system dysfunction and sleep pathology. Both melatonin and moclobemide have demonstrated effectiveness in preventing migraine headaches. Additionally, both melatonin and moclobemide are compatible with most of the other therapeutic agents used to prevent migraine headaches and with at least 1 therapeutic agent that is used to treat migraine headaches.

Neuropeptide S as a novel arousal promoting peptide transmitter

Behavioral arousal requires integration of multiple neurotransmitter and neuromodulatory systems. Identifying these systems is the key to not only a better understanding of the neurobiology of sleep/wakefulness but may also lead to the discovery of potential therapeutic targets for various sleep disorders. We review here a novel arousal promoting neuropeptide system, neuropeptide S (NPS) and its receptor. Pharmacologically, NPS activates NPS receptors at low nanomolar concentration to increase concentrations of intracellular Ca(2+). Anatomically, both NPS precursor and receptor mRNAs are found predominately in the central nervous system. NPS precursor mRNA is expressed only in several discrete regions located mainly in the brainstem. In particular, it is highly expressed in a previously undescribed group of neurons localized between locus coeruleus and Barrington's nucleus. NPS receptor mRNA is widely distributed in many brain areas with high expression levels in cortex, hypothalamus, amygdala and multiple midline thalamic nuclei. Functionally, central administration of NPS increases locomotor activity in both naïve and habituated mice. It also significantly increases wakefulness and decreases paradoxical (rapid eye movement) sleep and slow wave sleep in rats. In addition, NPS suppresses anxiety-like behaviors in mice exposed to different behavioral paradigms measuring responses to novelty or stress. These studies indicate that the NPS system is a newly discovered transmitter system that regulates vigilance and emotional states. NPS appears to possess a unique pharmacological profile in producing both anxiolytic-like and hypervigilant effects.

Brain structures and receptors involved in alertness

Transitions between sleep and wakefulness are regulated by complex neurobiological mechanisms, which ultimately can be delineated as oscillations between two opponent processes--one promoting sleep and the other promoting wakefulness. The suprachiasmatic nuclei (SCN) provide temporal organization to the sleep-wake cycle through arousal mechanisms that oppose homeostatic drive or sleep. Assuming that individual cells in the SCN are competent circadian oscillators, it is important to understand how these cells communicate and remain synchronized with each other. Examination of the brain structures and receptors that are involved in alertness and the complex phenomena involved in regulation of the circadian sleep-wake cycle has provided evidence for an important role for the noradrenergic locus coeruleus (LC) system in the circadian regulation of alertness and performance. However, the broad interest in mechanisms underlying alertness is not solely to understand wakefulness but also to gain insight into how to maintain alertness and cognitive performance while awake. Few studies have attempted to link the role of a brain system in sleep-wake regulation with a role in cognitive performance during waking. We hypothesize that the dorsomedial hypothalamic nucleus (DMH) modulates the circadian rhythm of sleep and waking via projections to the LC. We propose a SCN-DMH-LC signalling pathway that may influence the activity of the LC and thereby a variety of central nervous system functions related to noradrenergic innervations, including alertness, vigilance, attention, learning and memory. The influence of sleep drive on the LC system may be important for our understanding of the deleterious effects of sleep loss on performance, and presents a logical target for developing new treatments to counteract impairments in alertness and performance due to poor quality sleep.