Proopiomelanocortin (POMC)-derived peptides and sleep in the rat. Part 1--Hypnogenic properties of ACTH derivatives

Identification of potential drug targets for insomnia by Mendelian randomization analysis based on plasma proteomics

Introduction

Insomnia, a common clinical disorder, significantly impacts the physical and mental well-being of patients. Currently, available hypnotic medications are unsatisfactory due to adverse reactions and dependency, necessitating the identification of new drug targets for the treatment of insomnia.

Methods

In this study, we utilized 734 plasma proteins as genetic instruments obtained from genome-wide association studies to conduct a Mendelian randomization analysis, with insomnia as the outcome variable, to identify potential drug targets for insomnia. Additionally, we validated our results externally using other datasets. Sensitivity analyses entailed reverse Mendelian randomization analysis, Bayesian co-localization analysis, and phenotype scanning. Furthermore, we constructed a protein-protein interaction network to elucidate potential correlations between the identified proteins and existing targets.

Results

Mendelian randomization analysis indicated that elevated levels of TGFBI (OR = 1.01; 95% CI, 1.01-1.02) and PAM ((OR = 1.01; 95% CI, 1.01-1.02) in plasma are associated with an increased risk of insomnia, with external validation supporting these findings. Moreover, there was no evidence of reverse causality for these two proteins. Co-localization analysis confirmed that PAM (coloc.abf-PPH4 = 0.823) shared the same variant with insomnia, further substantiating its potential role as a therapeutic target. There are interactive relationships between the potential proteins and existing targets of insomnia.

Conclusion

Overall, our findings suggested that elevated plasma levels of TGFBI and PAM are connected with an increased risk of insomnia and might be promising therapeutic targets, particularly PAM. However, further exploration is necessary to fully understand the underlying mechanisms involved.

The stress of losing sleep: Sex-specific neurobiological outcomes

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

Roles of Neuropeptides in Sleep-Wake Regulation

Sleep and wakefulness are basic behavioral states that require coordination between several brain regions, and they involve multiple neurochemical systems, including neuropeptides. Neuropeptides are a group of peptides produced by neurons and neuroendocrine cells of the central nervous system. Like traditional neurotransmitters, neuropeptides can bind to specific surface receptors and subsequently regulate neuronal activities. For example, orexin is a crucial component for the maintenance of wakefulness and the suppression of rapid eye movement (REM) sleep. In addition to orexin, melanin-concentrating hormone, and galanin may promote REM sleep. These results suggest that neuropeptides play an important role in sleep–wake regulation. These neuropeptides can be divided into three categories according to their effects on sleep–wake behaviors in rodents and humans. (i) Galanin, melanin-concentrating hormone, and vasoactive intestinal polypeptide are sleep-promoting peptides. It is also noticeable that vasoactive intestinal polypeptide particularly increases REM sleep. (ii) Orexin and neuropeptide S have been shown to induce wakefulness. (iii) Neuropeptide Y and substance P may have a bidirectional function as they can produce both arousal and sleep-inducing effects. This review will introduce the distribution of various neuropeptides in the brain and summarize the roles of different neuropeptides in sleep–wake regulation. We aim to lay the foundation for future studies to uncover the mechanisms that underlie the initiation, maintenance, and end of sleep–wake states.

Concussive head injury exacerbates neuropathology of sleep deprivation: Superior neuroprotection by co-administration of TiO2-nanowired cerebrolysin, alpha-melanocyte-stimulating hormone, and mesenchymal stem cells

Sleep deprivation (SD) is common in military personnel engaged in combat operations leading to brain dysfunction. Military personnel during acute or chronic SD often prone to traumatic brain injury (TBI) indicating the possibility of further exacerbating brain pathology. Several lines of evidence suggest that in both TBI and SD alpha-melanocyte-stimulating hormone (α-MSH) and brain-derived neurotrophic factor (BDNF) levels decreases in plasma and brain. Thus, a possibility exists that exogenous supplement of α-MSH and/or BDNF induces neuroprotection in SD compounded with TBI. In addition, mesenchymal stem cells (MSCs) are very portent in inducing neuroprotection in TBI. We examined the effects of concussive head injury (CHI) in SD on brain pathology. Furthermore, possible neuroprotective effects of α-MSH, MSCs and neurotrophic factors treatment were explored in a rat model of SD and CHI. Rats subjected to 48h SD with CHI exhibited higher leakage of BBB to Evans blue and radioiodine compared to identical SD or CHI alone. Brain pathology was also exacerbated in SD with CHI group as compared to SD or CHI alone together with a significant reduction in α-MSH and BDNF levels in plasma and brain and enhanced level of tumor necrosis factor-alpha (TNF-α). Exogenous administration of α-MSH (250μg/kg) together with MSCs (1×10⁶) and cerebrolysin (a balanced composition of several neurotrophic factors and active peptide fragments) (5mL/kg) significantly induced neuroprotection in SD with CHI. Interestingly, TiO₂ nanowired delivery of α-MSH (100μg), MSCs, and cerebrolysin (2.5mL/kg) induced enhanced neuroprotection with higher levels of α-MSH and BDNF and decreased the TNF-α in SD with CHI. These observations are the first to show that TiO₂ nanowired administration of α-MSH, MSCs and cerebrolysin induces superior neuroprotection following SD in CHI, not reported earlier. The clinical significance of our findings in light of the current literature is discussed.

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.

Metabolic signals in sleep regulation: recent insights

Sleep and energy balance are essential for health. The two processes act in concert to regulate central and peripheral homeostasis. During sleep, energy is conserved due to suspended activity, movement, and sensory responses, and is redirected to restore and replenish proteins and their assemblies into cellular structures. During wakefulness, various energy-demanding activities lead to hunger. Thus, hunger promotes arousal, and subsequent feeding, followed by satiety that promotes sleep via changes in neuroendocrine or neuropeptide signals. These signals overlap with circuits of sleep-wakefulness, feeding, and energy expenditure. Here, we will briefly review the literature that describes the interplay between the circadian system, sleep-wake, and feeding-fasting cycles that are needed to maintain energy balance and a healthy metabolic profile. In doing so, we describe the neuroendocrine, hormonal/peptide signals that integrate sleep and feeding behavior with energy metabolism.

The Neurobiology of Sleep and Wakefulness

Cortical electroencephalographic activity arises from corticothalamocortical interactions, modulated by wake-promoting monoaminergic and cholinergic input. These wake-promoting systems are regulated by hypothalamic hypocretin/orexins, while GABAergic sleep-promoting nuclei are found in the preoptic area, brainstem and lateral hypothalamus. Although pontine acetylcholine is critical for REM sleep, hypothalamic melanin-concentrating hormone/GABAergic cells may "gate" REM sleep. Daily sleep-wake rhythms arise from interactions between a hypothalamic circadian pacemaker and a sleep homeostat whose anatomical locus has yet to be conclusively defined. Control of sleep and wakefulness involves multiple systems, each of which presents vulnerability to sleep/wake dysfunction that may predispose to physical and/or neuropsychiatric disorders.

Neuropeptidergic control of sleep and wakefulness

Sleep and wake are fundamental behavioral states whose molecular regulation remains mysterious. Brain states and body functions change dramatically between sleep and wake, are regulated by circadian and homeostatic processes, and depend on the nutritional and emotional condition of the animal. Sleep-wake transitions require the coordination of several brain regions and engage multiple neurochemical systems, including neuropeptides. Neuropeptides serve two main functions in sleep-wake regulation. First, they represent physiological states such as energy level or stress in response to environmental and internal stimuli. Second, neuropeptides excite or inhibit their target neurons to induce, stabilize, or switch between sleep-wake states. Thus, neuropeptides integrate physiological subsystems such as circadian time, previous neuron usage, energy homeostasis, and stress and growth status to generate appropriate sleep-wake behaviors. We review the roles of more than 20 neuropeptides in sleep and wake to lay the foundation for future studies uncovering the mechanisms that underlie the initiation, maintenance, and exit of sleep and wake states.

REM Sleep Rebound as an Adaptive Response to Stressful Situations

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

Nitric oxide in the regulation of the sleep-wake states

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

Chronic stress during paradoxical sleep deprivation increases paradoxical sleep rebound: association with prolactin plasma levels and brain serotonin content

Previous studies suggest that stress associated to sleep deprivation methods can affect the expression of sleep rebound. In order to examine this association and possible mechanisms, rats were exposed to footshock stress during or immediately after a 96-h period of paradoxical sleep deprivation (PSD) and their sleep and heart rate were recorded. Control rats (maintained in individual home cages) and paradoxical sleep-deprived (PS-deprived) rats were distributed in three conditions (1) no footshock--NF; (2) single footshock--SFS: one single footshock session at the end of the PSD period (6-8 shocks per minute; 100 ms; 2 mA; for 40 min); and (3) multiple footshock--MFS: footshock sessions with the same characteristics as described above, twice a day throughout PSD (at 7:00 h and 19:00 h) and one extra session before the recovery period. After PSD, animals were allowed to sleep freely for 72 h. Additional groups were sacrificed at the end of the sleep deprivation period for blood sampling (ACTH, corticosterone, prolactin and catecholamine levels) and brain harvesting (monoamines and metabolites). Neither SFS nor MFS produced significant alterations in the sleep patterns of control rats. All PS-deprived groups exhibited increased heart rate which could be explained by increased dopaminergic activity in the medulla. As expected, PS deprivation induced rebound of paradoxical sleep in the first day of recovery; however, PSD+MFS group showed the highest rebound (327.3% above the baseline). This group also showed intermediate levels of corticosterone and the highest levels of prolactin, which were positively correlated with the length of PS episodes. Moreover, paradoxical sleep deprivation resulted in elevation of the serotonergic turnover in the hypothalamus, which partly explained the hormonal results, and in the hippocampus, which appears to be related to adaptive responses to stress. The data are discussed in the realm of a prospective importance of paradoxical sleep for processing of traumatic events.

Effects of chloramphenicol on brain energy metabolism using 31P spectroscopy: influences on sleep-wake states in rat

Effects of chloramphenicol (antibiotic inhibiting complex-1 of respiratory chain) and thioamphenicol (TAP, a structural analog of CAP inactive on complex-1) were examined on cerebral energy metabolites and sleep-wake cycle architecture in rat. In the first group, animals were chronically equipped with a cranial surface resonator and (31)P spectroscopic measurements were performed using a 2 T magnetic resonance spectrometer (operating frequency 34.46 MHz). CAP administration (400 mg/kg, tail vein, light period) induced deficits in phosphocreatine (-30%, p < 0.01) and ATP (-40%, p < 0.01), whereas TAP (400 mg/kg) had no effect. In the second group, animals were chronically implanted with polygraphic electrodes for EEG and electromyogram recordings. CAP administered intraperitoneally at light-onset reduced rapid-eye movement (REM) sleep (-60% in the first 6 h of light period, p < 0.01), increased waking state (+65% in the first 6 h of light period, p < 0.01), and slightly affected slow-wave sleep (SWS). During waking state, theta and sigma power bands of the EEG were, respectively, increased and decreased (p < 0.05). During SWS, delta power band was reinforced (p < 0.05), while theta, alpha, and sigma bands were decreased (p < 0.05). No changes occurred during REM sleep. TAP had no effect on sleep-wake states and spectral components of the EEG. Overall, these data indicate that REM sleep occurrence is linked to an aerobic production of ATP.

The hypothalamic peptidergic system, hypocretin/orexin and vigilance control

Using forward and reverse genetics, the genes (hypocretin/orexin ligand and its receptor) involved in the pathogenesis of the sleep disorder, narcolepsy, in animals, have been identified. Mutations in hypocretin related-genes are extremely rare in humans, but hypocretin-ligand deficiency is found in most narcolepsy-cataplexy cases. Hypocretin deficiency in humans can be clinically detected by CSF hypocretin-1 measures, and undetectably low CSF hypocretin-1 is now included in the revised international diagnostic criteria of narcolepsy. Since hypocretin-ligand deficiency is the major pathophysiology in human narcolepsy, hypocretin replacements (using hypocretin agonists or gene therapy) are promising future therapeutic options. New insights into the roles of hypocretin system on sleep physiology have also rapidly increased. Hypocretins are involved in various fundamental hypothalamic functions such as feeding, energy homeostasis and neuroendocrine regulation. Hypocretin neurons project to most ascending arousal systems (including monoaminergic and cholinergic systems), and generally exhibit excitatory inputs. Together with the recent finding of the sleep promoting system in the hypothalamus (especially in the GABA/galanin ventrolateral preoptic area which exhibits inhibitory inputs to these ascending systems), the hypothalamus is now recognized as the most important brain site for the sleep switch, and other peptidergic systems may also participate in this regulation. Meanwhile, narcolepsy now appears to be a more complex condition than previously thought. The pathophysiology of the disease is involved in the abnormalities of sleep and various hypothalamic functions due to hypocretin deficiency, such as the changes in energy homeostasis, stress reactions and rewarding. Narcolepsy is therefore, an important model to study the link between sleep regulation and other fundamental hypothalamic functions.

Neuropeptides as possible targets in sleep disorders

Insomnia and hypersomnia are frequent sleep disorders, and they are most often treated pharmacologically with hypnotics and wake-promoting compounds. These compounds act on classical neurotransmitter systems, such as benzodiazepines on GABA-A receptors, and amfetamine-like stimulants on monoaminergic terminals to modulate neurotransmission. In addition, acetylcholine, amino acids, lipids and proteins (cytokines) and peptides, are known to significantly modulate sleep and are, therefore, possibly involved in the pathophysiology of some sleep disorders. Due to the recent developments of molecular biological techniques, many neuropeptides have been newly identified, and some are found to significantly modulate sleep. It was also discovered that the impairment of the hypocretin/orexin neurotransmission (a recently isolated hypothalamic neuropeptide system) is the major pathophysiology of narcolepsy, and hypocretin replacement therapy is anticipated to treat the disease in humans. In this article, the authors briefly review the history of neuropeptide research, followed by the sleep modulatory effects of various neuropeptides. Finally, general strategies for the pharmacological therapeutics targeting the peptidergic systems for sleep disorders are discussed.

Multi-target strategies for the improved treatment of depressive states: Conceptual foundations and neuronal substrates, drug discovery and therapeutic application

Major depression is a debilitating and recurrent disorder with a substantial lifetime risk and a high social cost. Depressed patients generally display co-morbid symptoms, and depression frequently accompanies other serious disorders. Currently available drugs display limited efficacy and a pronounced delay to onset of action, and all provoke distressing side effects. Cloning of the human genome has fuelled expectations that symptomatic treatment may soon become more rapid and effective, and that depressive states may ultimately be "prevented" or "cured". In pursuing these objectives, in particular for genome-derived, non-monoaminergic targets, "specificity" of drug actions is often emphasized. That is, priority is afforded to agents that interact exclusively with a single site hypothesized as critically involved in the pathogenesis and/or control of depression. Certain highly selective drugs may prove effective, and they remain indispensable in the experimental (and clinical) evaluation of the significance of novel mechanisms. However, by analogy to other multifactorial disorders, "multi-target" agents may be better adapted to the improved treatment of depressive states. Support for this contention is garnered from a broad palette of observations, ranging from mechanisms of action of adjunctive drug combinations and electroconvulsive therapy to "network theory" analysis of the etiology and management of depressive states. The review also outlines opportunities to be exploited, and challenges to be addressed, in the discovery and characterization of drugs recognizing multiple targets. Finally, a diversity of multi-target strategies is proposed for the more efficacious and rapid control of core and co-morbid symptoms of depression, together with improved tolerance relative to currently available agents.

Bidirectional communication between the brain and the immune system: implications for physiological sleep and disorders with disrupted sleep

This review describes mechanisms of immune-to-brain and brain-to-immune signaling involved in mediating physiological sleep and altered sleep with disease. The central nervous system (CNS) modulates immune function by signaling target cells of the immune system through autonomic and neuroendocrine pathways. Neurotransmitters and hormones produced and released by these pathways interact with immune cells to alter immune functions, including cytokine production. Cytokines produced by cells of the immune and nervous systems regulate sleep. Cytokines released by immune cells, particularly interleukin-1beta and tumor necrosis factor-alpha, signal neuroendocrine, autonomic, limbic and cortical areas of the CNS to affect neural activity and modify behaviors (including sleep), hormone release and autonomic function. In this manner, immune cells function as a sense organ, informing the CNS of peripheral events related to infection and injury. Equally important, homeostatic mechanisms, involving all levels of the neuroaxis, are needed, not only to turn off the immune response after a pathogen is cleared or tissue repair is completed, but also to restore and regulate natural diurnal fluctuations in cytokine production and sleep. The immune system's ability to affect behavior has important implications for understanding normal and pathological sleep. Sleep disorders are commonly associated with chronic inflammatory diseases and chronic age- or stress-related disorders. The best studied are rheumatoid arthritis, fibromyalgia and chronic fatigue syndromes. This article reviews our current understanding of neuroimmune interactions in normal sleep and sleep deprivation, and the influence of these interactions on selected disorders characterized by pathological sleep.

Acute administration of the novel serotonin and noradrenaline reuptake inhibitor, S33005, markedly modifies sleep-wake cycle architecture in the rat

RATIONALE

The interrelationship between depressive states and sleep-wake cycle architecture is characterised by a decreased latency to the first paradoxical sleep (PS) episode, together with an enhancement of PS during the first part of the night. Conversely, slow-wave sleep (SWS) is decreased and intermittent awakenings increased. Notably, antidepressant treatment is generally associated with a diminution of PS.

OBJECTIVES

In light of these observations, we examined the influence of acute administration of the novel mixed serotonin-noradrenaline reuptake blocker, (-)1-(1-dimethylaminomethyl 5-methoxybenzocyclobutan-1-yl)-cyclohexanol HCl (S33005), upon sleep-wake architecture in rats.

METHODS

Animals were injected with vehicle or incremental doses of S33005 at the onset of either the dark or light periods. Digitised polygraphic recordings were performed, and changes evoked by S33005 were determined over 24-h recording periods, i.e., number and duration of sleep-wake episodes, latencies to PS and SWS, power band spectra of the electroencephalogram (EEG) and circadian changes.

RESULTS

At 0.04 mg/kg, S33005 was inactive, whereas at 0.63 mg/kg, it modestly increased PS latencies and diminished PS duration during the light period. At 10 mg/kg, S33005 reduced markedly PS duration for about 4-h when injected prior to both light and dark periods. Latency to PS was prolonged, and the circadian acrophase was delayed. These effects are in keeping with previous studies of monoamine reuptake inhibitors, but, notably, SWS duration was increased when S33005 was injected at the onset of the light phase (+4%). These changes occurred without marked modifications in circadian rhythmicity or EEG spectral band power. Finally, even at the highest dose of S33005, only a limited rebound of SWS (+5%) and PS (+10%) was apparent. Amongst antidepressant to date examined, this is an original profile of influence upon sleep patterns.

CONCLUSIONS

These results demonstrate a pattern of influence of S33005 upon sleep-wake architecture in rats which is globally consistent with antidepressant properties, but with a distinctive enhancement of restorative slow-wave sleep.

Chloramphenicol decreases brain glucose utilization and modifies the sleep-wake cycle architecture in rats

We studied the effects of chloramphenicol on brain glucose utilization and sleep-wake cycles in rat. After slightly anaesthetized animals were injected with [18F]fluoro-2-deoxy-D-glucose, we acquired time-concentration curves from three radiosensitive beta microprobes inserted into the right and left frontal cortices and the cerebellum, and applied a three-compartment model to calculate the cerebral metabolic rates for glucose. The sleep-wake cycle architecture was analysed in anaesthetic-free rats by recording electroencephalographic and electromyographic signals. Although chloramphenicol is a well-established inhibitor of oxidative phosphorylation, no compensatory increase in glucose utilization was detected in frontal cortex. Instead, chloramphenicol induced a significant 23% decrease in the regional cerebral metabolic rate for glucose. Such a metabolic response indicates a potential mismatch between energy supply and neuronal activity induced by chloramphenicol administration. Regarding sleep-wake states, chloramphenicol treatment was followed by a 64% increase in waking, a 20% decrease in slow-wave sleep, and a marked 59% loss in paradoxical sleep. Spectral analysis of the electroencephalogram indicates that chloramphenicol induces long-lasting modifications of delta-band power during slow-wave sleep.

Antagonism of corticotropin-releasing hormone alters serotonergic-induced changes in brain temperature, but not sleep, of rats

Serotonin is involved in many physiological processes, including the regulation of sleep and body temperature. Administration into rats of low doses (25, 50 mg/kg) of the 5-HT precursor l-5-hydroxytryptophan (5-HTP) at the beginning of the dark period of the 12:12-h light-dark cycle initially increases wakefulness. Higher doses (75, 100 mg/kg) increase nonrapid eye movement (NREM) sleep. The initial enhancement of wakefulness after low-dose 5-HTP administration may be a direct action of 5-HT in brain or due to 5-HT-induced activation of other arousal-promoting systems. One candidate arousal-promoting system is corticotropin-releasing hormone (CRH) and the hypothalamic-pituitary-adrenal axis. Serotonergic activation by 5-HTP at the beginning of the dark period also induces hypothermia. Because sleep and body temperature are influenced by circadian factors, one aim of this study was to determine responses to 5-HTP when administered at a different circadian time, the beginning of the light period. Results obtained show that all doses of 5-HTP (25-100 mg/kg) administered at light onset initially increase wakefulness; NREM sleep increases only after a long delay, during the subsequent dark period. Serotonergic activation by 5-HTP at light onset induces hypothermia, the time course of which is biphasic after higher doses (75, 100 mg/kg). Intracerebroventricular pretreatment with the CRH receptor antagonist alpha-helical CRH does not alter the impact of 5-HTP on sleep-wake behavior but potentiates the hypothermic response to 50 mg/kg 5-HTP. These data suggest that serotonergic activation by peripheral administration of 5-HTP may modulate sleep-wake behavior by mechanisms in addition to direct actions in brain and that circadian systems are important determinants of the impact of serotonergic activation on sleep and body temperature.

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.

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

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

Brain structures and mechanisms involved in the generation of NREM sleep: focus on the preoptic hypothalamus

Four lines of research have greatly increased our understanding of the hypothalamic preoptic area (POA) sleep-promoting system. First, sleep-active neurons within the POA have been identified using both electrophysiological recording and immediate early gene protein (c-Fos) staining methods. Segregated sleep-active neurons were found in ventrolateral and median POA (VLPO and MnPN). Additional sleep-active neurons may be intermixed with non-sleep specific neurons in other POA regions and the adjacent basal forebrain. Second, the putative sleep factors, adenosine and prostaglandin D2, were found to excite sleep-active neurons. Other sleep factors may also modulate these sleep-active populations. Third, many sleep-active neurons are warm-sensitive neurons (WSNs). WSNs are identified by excitatory responses to small increases in local POA temperature. The same local POA thermal stimuli strongly modulate sleep propensity and EEG delta activity within sleep. Interactions between sleep regulation and thermoregulation are consistent with studies of circadian sleep propensity, prolonged sleep deprivation in rats, and species differences in sleep amounts. Fourth, sleep-active neurons were found to co-localize the inhibitory neurotransmitter, gamma-aminobutyric acid and to have projections to arousal-related neuronal subgroups in the posterior hypothalamus and midbrain. Sleep-active and arousal-related neurons exhibit reciprocal changes in discharge across the wake-NREM-REM cycle, and activation of WSNs suppresses the neuronal activity of some arousal-related neuronal groups. These studies establish mechanisms by which POA hypnogenic neurons can inhibit EEG and behavioral arousal. In addition, there is evidence that arousal-related neurotransmitters inhibit VLPO sleep-active neurons. Mutually inhibitory interactions between sleep-promoting and the arousal system provide a substrate for a <<<<sleep-wake switch>>>>. 2001 Harcourt Publishers Ltd

Corticotropin-releasing hormone (CRH) as a regulator of waking

Corticotropin-releasing hormone (CRH), expressed in widely distributed regions of the central nervous system (CNS), mediates the hypothalamic-pituitary-adrenal (HPA) axis and autonomic components of responses to stressors. Sleep, a fundamental CNS process, is altered in response to a variety of stressors. Although there is an extensive literature on the role of CRH in responses to stressors, there is relatively little information on the role of CRH in normal, spontaneous behavior. We hypothesize that CRH is involved in the regulation of waking in the absence of overt stressors. Some of the early evidence supporting this hypothesis was indirect. We summarize in this review studies from our laboratory and others that provide direct evidence that CRH is involved in the regulation of spontaneous waking. We also suggest on the basis of recent studies that some effects of CRH on waking and sleep may be mediated by actions within the CNS of the immunomodulatory cytokine interleukin (IL)-1. Collectively, these observations suggest that CRH contributes to the regulation of spontaneous waking in the absence of stressors, and also indicate a potential mechanism mediating complex alterations in sleep that occur in response to immune challenge.

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

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

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

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

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

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

Endogenous and exogenous factors on sleep-wake cycle regulation

A number of theories have proposed the involvement of different brain structures and neurotransmitters in order to explain the regulation of the sleep wake cycle. However, there is no clear consensus as to the mechanisms through which the brain structures and their various neurotransmitters interact to produce theses phases. Perhaps the problem is related to the fact sleep is a very fragile state, easily modified or influenced by a variety of substances or experimental manipulations. In this paper, we describe the evidence of two different groups of factors that induce important changes on the sleep wake cycle. The endogenous factors: neurotransmitters; hormone; peptides; and some substances of lipidic nature and exogenous factors: stress, food intake, learning, sleep deprivation, sensorial stimulation, exercise and temperature on the regulation the sleep-wake cycle. Likewise, we propose a hypothesis which attempts to reconcile the fact that endogenous and exogenous factors have similar effects.

Blockade of corticotropin-releasing hormone receptors reduces spontaneous waking in the rat

We have previously hypothesized that corticotropin-releasing hormone (CRH) is involved in the regulation of physiological waking. To further elucidate this role for CRH, we administered intracerebroventricularly into rats two specific CRH-receptor antagonists, alpha-helical CRH-(9-41) (alpha-hCRH) or astressin, and determined changes in electroencephalogram-defined waking and sleep. Our results indicate that both of these receptor antagonists reduce the amount of time spent awake in a dose-related manner when administered before the dark period of the light-dark cycle. However, the time courses for these effects differ between antagonists; effective doses of alpha-hCRH reduce waking during the first 2 h postinjection, whereas effective doses of astressin reduce waking during postinjection hours 7-12. In contrast to dark-onset administrations, the amount of waking is not altered by either CRH-receptor antagonist when administered before the light period. These results support our hypothesis that CRH contributes to the regulation of physiological waking, since interfering with the binding of CRH to its receptor reduces spontaneous waking.

Reaction of sleep-wakefulness cycle to stress is related to differences in hypothalamo-pituitary-adrenal axis reactivity in rat

Acute stress is known to modify sleep-wakefulness cycle, although with considerable interindividual differences. The origin of these individual differences remains unknown. One possibility is an involvement of the hypothalamo-pituitary-adrenal axis (HPA), as its reactivity is correlated with an individual's behavioral reactivity to stress, and it is known to influence the sleep-wakefulness cycle. The present study was designed to analyze relationships between natural differences in behavioral reactivity to stress associated with differential HPA reactivity and stress-induced changes in sleep-wakefulness. Adult rats were classified into two sub-groups according to their locomotor reactivity to a mild stress (novel environment): the 'low responders (LR)' and the 'high responders (HR)' animals exhibited different glucocorticoid secretion in response to stress. We show that immobilization stress induced an increase in wakefulness in LR animals and a decrease in wakefulness in HR animals. On the other hand, paradoxical sleep was increased in both LR and HR animals. Moreover, we observed that LR animals slept more than the HR animals, whereas the two groups had similar levels of paradoxical sleep. These results indicate that the response of the sleep-wakefulness cycle to stress is related to the behavioral reactivity to stress, in turn governed by the individual's reactivity of the HPA axis. The involvement of dopaminergic mechanisms is discussed.

Rat strain differences suggest a role for corticotropin-releasing hormone in modulating sleep

Corticotropin-releasing hormone (CRH) mediates many of the hormonal, behavioral, and autonomic responses to a variety of stressors. There is also evidence suggesting that CRH may be involved in the modulation of physiologic waking. Lewis (LEW) rats possess a hypothalamic gene defect that results in reduced synthesis and secretion of CRH relative to genetically related Fischer 344 (F344) and Sprague-Dawley (Sp-D) rat strains. We therefore hypothesized that LEW rats would spend less time awake, and more time asleep, than either F344 or Sp-D rats. Adult male LEW, F344, and Sp-D rats were surgically provided with electroencephalograph (EEG) recording electrodes, and a thermistor to measure cortical brain temperature [T(cort)]. Additional rats were also provided with a chronic guide cannula directed into a lateral cerebral ventricle. Spontaneous sleep-wake behavior was determined from 48-h recordings of the EEG, T(cort), and body movements from freely behaving, undisturbed rats. Analyses of 48-h recordings from undisturbed animals indicate that LEW rats spend less time awake and more time in slow-wave sleep, relative to the other strains tested. Rapid eye movement sleep did not differ consistently between rat strains. LEW and Sp-D rats exhibit the same degree of waking in response to intracerebroventricular administration of CRH, indicating central mechanisms mediating behavioral responses to exogenously administered CRH are intact in LEW rats. These data provide support for the hypothesis that CRH may be a modulator of waking and sleep.

Determination of NADH in the rat brain during sleep-wake states with an optic fibre sensor and time-resolved fluorescence procedures

The present paper reports a nanosecond time-resolved fluorescence derived from the cortex and the area of the periaqueductal gray including the nucleus raphe dorsalis (PAG-nRD) in unanaesthetized freely moving rats. The measurements were acquired through a single optic fibre transmitting a subnanosecond nitrogen laser pulse (337 nm, 15 Hz) and collecting the brain fluorescence occurring at 460 nm which might depend on mitochondrial NADH (reduced form of nicotinamide adenine dinucleotide). The fluorometric method was combined with polygraphic recordings, and this procedure allowed us to define, for the first time, variations of the 460 nm signal occurring throughout the sleep-wake cycle. In the PAG-nRD, the signal exhibited moderate heterogeneous variation in amplitude during slow-wave as compared to the waking state. Constant increases were observed during paradoxical sleep as compared to the waking state. For this state of sleep the magnitude of the variations depended on the optic fibre location. In the cortex and during either slow-wave sleep or paradoxical sleep, the signal presented moderate increases which were significant during paradoxical sleep. The magnitude of the redox variations observed either in the PAG-nRD or in the cortex might be ascribed to the oxidative energy balance which is related to sleep states.

Inter-individual differences in the effects of acute stress on the sleep-wakefulness cycle in the rat

It has been described that an acute immobilization stress (IS) modifies subsequent paradoxical sleep (PS). However, its effects are complex because some subjects remain unaffected. This discrepancy might result from constitutive inter-individual psychobiological differences. In order to test this hypothesis, an inter-individual analysis of sleep patterns and their modifications after 60 min IS has been performed. Even though global analysis showed a PS increase after IS, inter-individual analysis evidenced different PS reactivity; subjects which had the least PS during control recordings were those with the largest PS increase. Unlike global analysis, an inter-individual study evidenced different modifications of wakefulness and slow wave sleep according to individuals. Subjects presenting the highest amount of wakefulness in control conditions (the lowest amount of slow wave sleep) decreased their wakefulness amount, while subjects with the lowest amount of wakefulness increased it. Thus, individual characteristics of the sleep-wakefulness cycle should be considered while studying its modifications induced by different treatments.

Influence of a 1 h immobilization stress on sleep states and corticotropin-like intermediate lobe peptide (CLIP or ACTH18-39, Ph-ACTH18-39) brain contents in the rat

A 1 h immobilization stress (IS) was imposed to rats at the beginning of the dark period, i.e., when the animals start to be active. The IS was accompanied by an intense polygraphic waking and followed, over 12 h of the dark period, by a significant rebound of slow-wave sleep (SWS, +17%) and paradoxical sleep (PS, +57%). In order to estimate the IS-related changes in the endogenous concentrations of corticotropin-like intermediate lobe peptide (CLIP, ACTH18-39) and related compounds, a specific radioimmunoassay (RIA) was used. Assays performed in cerebral biopsies taken from arcuate (AN) and raphe dorsalis (nRD) nuclei led to the obtention of 2 main immunoreactive peaks, corresponding to CLIP and its phosphorylated form Ph-CLIP. Just after end of the IS and within the nRD. Ph-CLIP immunoreactivity increased by about 95%. Four hours later, i.e., when PS rebound was maximal, a 37% increase in Ph-CLIP immunoreactivity was measured in the AN. These observations have never been described before. In the blood, at the end of the restraint, CLIP/ACTH1-39 total immunoreactivity was increased by 330%. It returned to baseline level 4 h later. Blood concentration of corticosterone was also increased by 56% at the end of the IS and was close to baseline level 4 h later. Data reported here indicate that the IS first triggers an increase in Ph-CLIP within the nRD. Since the nRD contains sleep permissive components, this increase might be determinant for the SWS and PS rebound induction. The changes observed in the blood as regards CLIP/ACTH1-39 total immunoreactivity and corticosterone concentration testify to the efficacy of the IS and are part of the conventional picture accompanying such a situation. Finally, the increase in Ph-CLIP, occurring in the AN 4 h after the end of the restraint, might be part of the restorative processes necessary to compensate the stress overshoot.

Ultrastructural relationships of the pro-opiomelanocortin axons with the serotoninergic neurons in the dorsal raphe nucleus of the rat

The relationships of the corticotropin-like intermediate lobe peptide (CLIP)/ACTH-immunoreactive axons with the serotoninergic and non-serotoninergic neurons in the dorsal raphe nucleus of the rat were examined by means of a double label immunocytochemical method. It is suggested that the rare contacts established by the CLIP/ACTH-immunoreactive fibers with serotoninergic neurons (cell bodies and dendrites) are not under a synaptic from. In contrast, the contacts with non-serotoninergic neurons were predominantly formed with dendrites and showed a substantial number of synapses.

Effects of the CLIP fragment ACTH 20-24 on the duration of REM sleep episodes

Substances acting upon rapid eye movement (REM) sleep or paradoxical sleep (PS) can affect the number and/or the duration of PS episodes. In the present study, we investigated the effects of the proopiomelanocortin-derived peptide CLIP (corticotropin-like intermediate lobe peptide, ACTH 18-39) and its N-terminal fragments ACTH 18-24 and ACTH 20-24 on the duration of PS episodes in rats. Intracerebroventricular injection of ACTH 20-24 caused a pronounced prolongation of PS episodes (up to 7 min duration, never seen under baseline conditions), whereas ACTH 18-24 acted in a similar way but without reaching statistical significance. We suggest that short N-terminal CLIP fragment(s) may represent endogenous hypnogenic factor(s) involved in the regulation of paradoxical sleep.

Role of the locus coeruleus in the sleep rebound following two different sleep deprivation methods in the rat

The aim of the present study was to assess the involvement of the locus coeruleus in the paradoxical sleep rebound following sleep deprivation in the rat. Animals were sleep-deprived for 10 h before, and after, specific N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) lesioning of the noradrenergic-locus coeruleus system. Sleep deprivation was produced using either an instrumental (water tank) or pharmacological (methylamphetamine) method. After lesioning, the rats submitted to the instrumental method showed a significant decrease in the paradoxical and slow-wave sleep rebounds (-54% and -78%, respectively), while animals receiving metamphetamine did not. Our results suggest that the noradrenergic system of the locus coeruleus is a relevant component of the sleep rebound mechanisms. However, the extent of involvement is dependent on the sleep deprivation method used.

State-dependent cellular activity patterns of the cat paraventricular hypothalamus measured by reflectance imaging

Activity within the cat paraventricular hypothalamus (PVH) during sleep and waking states was measured by quantifying intrinsic tissue reflectivity. A fiber optic probe consisting of a 1.0 mm coherent image conduit, surrounded by plastic fibers which conducted 660 nm source light, was attached to a charge-coupled device camera, and positioned over the PVH in five cats. Electrodes for assessing state variables, including electroencephalographic activity, eye movement, and somatic muscle tone were also placed. After surgical recovery, reflected light intensity was measured continuously at 2.5 Hz during spontaneously varying sleep/waking states. Sequential state transitions from active waking to quiet waking, quiet sleep and active sleep were accompanied by progressively increased levels of PVH activity. Overall activity was highest during active sleep, and decreased markedly upon awakening. Moment-to-moment activity oscillated in the 0-0.1 Hz range, especially during active sleep and active waking; this oscillation diminished during quiet sleep. Distinct sub-regions of enhanced or diminished activity emerged within the imaged area in a state-dependent manner. We conclude that PVH activity changes with behavioral state in a regionally specific manner, and that overall activity increases during quiet sleep, and is even more enhanced in active sleep. PVH activation could be expected to stimulate pituitary release of adrenocorticotropic hormone (ACTH) and affect input to autonomic regulatory sites. Since ACTH and corticotropin releasing factor elicit arousal, and since the PVH projects to other brain areas which modulate state, we speculate that the PVH plays a role in shaping characteristics of sleep/waking states.

Sleep increase after immobilization stress: role of the noradrenergic locus coeruleus system in the rat

In a preliminary study we showed that the sleep rebound occurring after sleep deprivation is decreased in rats treated with N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4), a neurotoxic agent specific for the noradrenergic cells of the locus coeruleus (LC). Sleep deprivation methods not only involve sleep loss, but also stress, which per se may induce an increase in sleep duration. Extensive research showed that the locus coeruleus is involved in stress. To evaluate the participation of LC in this mechanism, the effect of DSP-4 treatment was studied on sleep duration following a short intense stress in the absence of sleep loss. The results showed that the augmentation of sleep after 1 h of immobilization stress is lower in DSP-4-treated rats (slow-wave sleep duration, -24%; paradoxical sleep duration, -52%). These findings suggest that the increase in sleep induced by such a stressor is mediated, at least in part, by the noradrenergic LC.

Sleep permissive components within the dorsal raphe nucleus in the rat

Two peptides known for their hypnogenic properties, CLIP (corticotropin-like intermediate lobe peptide or ACTH 18-39) or VIP (vasoactive intestinal polypeptide), were injected locally into the nucleus raphe dorsalis (nRD) of rats pretreated with p-chlorophenylalanine (PCPA). During the dark period, the PCPA insomnia was primarily associated with a reduction in paradoxical sleep (PS), whereas both slow wave sleep (SWS) and PS were decreased during the light period. Immunohistochemistry of serotonin in PCPA-pretreated animals indicated a clear disappearance of 5-HT fibers in the basal hypothalamus and the nRD as compared to control animals. Local injections of CLIP or VIP in the nRD restored PS and SWS. The positive injection sites corresponded to the anatomical distribution of either CLIP or VIP fibers, i.e., the entire nRD for VIP and the antero-dorsal part of this nucleus for CLIP. The sleep effects obtained in PCPA-pretreated rats involve a non-5-HT sleep permissive component within the nRD upon which these injected peptides act.

Acupuncture treatment for insomnia and acupuncture analgesia

Acupuncture is a simple and useful treatment for insomnia, with a success rate of around 90%. The acupuncture points applied vary depending on the doctor and on the case, but the usual points are Shenmen (HT7) and Anmien (extrapoint). The mechanism of this treatment has not been well elucidated. Acupuncture analgesia may be used as a great indicator, because in both practices needles are inserted in deep tissues as the common stimulation. The possible neuronal integration and transmitter effect in the acupuncture treatment for insomnia are discussed.

Altered ACTH and corticosterone responses to interleukin-1 beta in male rats exposed to an alcohol diet: possible role of vasopressin and testosterone

We have previously shown that female rats exposed to an alcohol (ethanol, E) diet exhibited a blunted ACTH response to systemically administered interleukin-1 beta (IL-1 beta). Because of the presence of gender differences in the activity of the hypothalamic-pituitary-adrenal (HPA) axis, and of the possible role played by sex steroids in modulating the inhibitory influence of E in females, we studied the ability of a 10-day E diet to alter ACTH and corticosterone secretion of intact or castrated male rats injected with IL-1 beta or endotoxin, a releaser of endogenous cytokines. Pituitary responsiveness to secretagogues that mediate the endocrine effects of IL-1 beta, namely corticotropin-releasing factor (CRF) and vasopressin (VP), was also investigated. The ACTH responses of animals fed ad libitum (C group) or pair-fed (PF group) to the intravenous administration of IL-1 beta or endotoxin were not statistically different (p > 0.05); therefore, results from these two groups were combined in the initial experiments. Subsequent experiments only used E and C animals. When compared with this latter group, intact E males showed a significant (p < 0.01) decrease in ACTH levels measured 30 and 60 min after the intravenous injection of IL-1 beta or endotoxin. In contrast, E rats released as much corticosterone as C rats in response to IL-1 beta, but significantly (p < 0.05) more following administration of endotoxin (lipopolysaccharide). The stimulatory effect of VP on ACTH release was also measurably blunted by alcohol, whereas that of CRF was not. In none of these experiments were any significant differences observed between C and PF rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Corticotropin-releasing hormone involvement in stressor-induced alterations in sleep and in the regulation of waking

Sleep responds to a variety of stressors, but the precise mechanisms whereby these alterations occur are not known. Ample evidence, however, testifies to corticotropin-releasing hormone (CRH) being uniquely situated to contribute to stressor-induced alterations in sleep. Behavioral responses to most stressors include periods of increased arousal and waking, regardless of whether the stressor is psychological in nature or results in physical insult. Furthermore, a large body of evidence suggests that CRH may also contribute to the regulation and maintenance of physiological waking. In this paper we hypothesize that CRH mediates waking, particularly after periods of exposure to acute stressors. The complex interactions of multiple systems determine the behavioral response to a particular stressor. As such, many factors determine the time course and duration of response, including stressor type, and the status of a particular system at the time of stressor presentation. We briefly review data indicating that CRH mediates physiological and behavioral responses to stressors, and present new data supporting the hypothesis that CRH may also be involved in the physiological regulation of waking.

Evidence for a sleep-promoting influence of stress

In the present review the data supporting the existence at the central level of a stress-sleep relation are reported and discussed. An immobilization stress of 1 or 2 hour(s) is accompanied by a marked polygraphic waking and followed by a significant sleep rebound concerning mainly paradoxical sleep (PS). During the restraint, an important release of 5-hydroxyindoles [5-OHles, a good index of serotonin (5-HT) release] occurs in the basal hypothalamus (BH). This release, produced by the nerve endings originating from the nucleus raphe dorsalis (nRD), might secondarily influence the release and/or the synthesis of hypnogenic substances directly involved in the sleep rebound production. Corticotropin-like intermediate lobe peptide (CLIP, or ACTH18-39) is a peptide possessing hypnogenic properties and derived from proopiomelanocortin (POMC) whose perikarya are contained within the BH (arcuate nucleus). The POMC nerve endings impinge on the nucleus raphe dorsalis, a structure containing sleep permissive components upon which CLIP acts to trigger sleep. It remains to be defined how the activity of the neuronal loop described above is impaired under chronic stress conditions.

Effects of an acute immobilization stress upon proopiomelanocortin (POMC) mRNA levels in the mediobasal hypothalamus: a quantitative in situ hybridization study

The aim of this study was to examine by quantitative in situ hybridization the effects of an acute stress on the expression of the POMC gene in the mediobasal hypothalamus (MBH) of the rat. In control animals, the highest levels of POMC mRNA were observed in the posterior periventricular region of the MBH. Lower levels were found in the anterior and posterior arcuate nucleus. At the end of a one hour immobilization, a small decrease (-8%) was observed in the periventricular region only. Four hours after the end of immobilization, increases in POMC mRNA levels were detected in the anterior part (7%), in the posterior part (25%) and in the periventricular region (13%) of the MBH. These results suggest that MBH POMC-derived peptides might be an important component in the central response to stress.

Effect of postnatal exposure of female rats to an alcohol diet: influence of age and circulating sex steroids

We have previously reported that when compared with animals fed ad libitum, adult ovariectomized (OVX) female rats fed an alcohol diet, but not its isocaloric equivalent control, showed a blunted ACTH response to the intravenous injection of interleukin-1 beta (IL-1 beta). The present work was undertaken to determine whether this finding could be extended to intact rats, and whether the stage of sexual maturation and/or circulating sex steroids of ovarian origin modulated the inhibitory influence of alcohol. Intact female rats were exposed to alcohol or pair-fed between postnatal days 25-35 (group I), 35-45 (group II), or 45-55 (group III). Animals of comparable age and fed ad libitum served as controls. All alcohol-exposed animals had similar blood alcohol levels measured during the eighth night of treatment. Group I lost the most weight following exposure to alcohol, but did not show measurable changes in ACTH released in response to 20 or 100 ng IL-1 beta/kg. Both alcohol and pair-feeding caused a modest decrease in IL-1-stimulated ACTH in rats of group II, but only alcohol significantly blunted corticotrophs' activity in group III. Group III, when fed alcohol, also showed lower CRF content in the median eminence compared with absolute controls or the isocaloric diet. No measurable changes, however, were observed in steady-state CRF mRNA levels in the hypothalamus of animals fed any of the diets. When intact and OVX rats were compared at 55 days of age, alcohol feeding caused a decrease in IL-1-induced ACTH secretion which was slightly, though not significantly, larger in intact animals.(ABSTRACT TRUNCATED AT 250 WORDS)