Corticotropin-releasing factor (CRF) increases paradoxical sleep (PS) rebound in PS-deprived rats

Copine-7 is required for REM sleep regulation following cage change or water immersion and restraint stress in mice

Sleep is affected by the environment. In rodents, changes in the amount of rapid eye movement sleep (REMS) can precede those of other sleep/wake stages. The molecular mechanism underlying the dynamic regulation of REMS remains poorly understood. Here, we focused on the sublaterodorsal nucleus (SLD), located in the pontine tegmental area, which plays a crucial role in the regulation of REMS. We searched for genes selectively expressed in the SLD and identified copine-7 (Cpne7), whose involvement in sleep was totally unknown. We generated Cpne7-Cre knock-in mice, which enabled both the knockout (KO) of Cpne7 and the genetic labeling of Cpne7-expressing cells. While Cpne7-KO mice exhibited normal sleep under basal conditions, the amount of REMS in Cpne7-KO mice was larger compared to wildtype mice following cage change or water immersion and restraint stress, both of which are conditions that acutely reduce REMS. Thus, it was suggested that copine-7 is involved in negatively regulating REMS under certain conditions. In addition, chemogenetically activating Cpne7-expressing neurons in the SLD reduced the amount of REMS, suggesting that these neurons negatively regulate REMS. These results identify copine-7 and Cpne7-expressing neurons in the SLD as candidate molecular or neuronal components of the regulatory system that controls REMS.

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.

Corticotropin-releasing hormone induces depression-like changes of sleep electroencephalogram in healthy women

We reported previously that repetitive intravenous injections of corticotropin-releasing hormone (CRH) around sleep onset prompt depression-like changes in certain sleep and endocrine activity parameters (e.g. decrease of slow-wave sleep during the second half of the night, blunted growth hormone peak, elevated cortisol concentration during the first half of the night). Furthermore a sexual dimorphism of the sleep-endocrine effects of the hormones growth hormone-releasing hormone and ghrelin was observed. In the present placebo-controlled study we investigated the effect of pulsatile administration of 4×50μg CRH on sleep electroencephalogram (EEG) and nocturnal cortisol and GH concentration in young healthy women. After CRH compared to placebo, intermittent wakefulness increased during the total night and the sleep efficiency index decreased. During the first third of the night, REM sleep and stage 2 sleep increased and sleep stage 3 decreased. Cortisol concentration was elevated throughout the night and during the first and second third of the night. GH secretion remained unchanged. Our data suggest that after CRH some sleep and endocrine activity parameters show also depression-like changes in healthy women. These changes are more distinct in women than in men.

Effects of corticotropin releasing factor (CRF) on sleep and temperature following predictable controllable and uncontrollable stress in mice

Corticotropin releasing factor (CRF) is a major mediator of central nervous system responses to stressors, including alterations in wakefulness and sleep. However, its role in mediating stress-induced alterations in sleep has not been fully delineated. In this study, we assessed the role of CRF and the non-specific CRF antagonist, astressin (AST), in regulating changes in sleep produced by signaled, escapable shock (SES) and signaled inescapable shock (SIS), two stressors that can increase or decrease sleep, respectively. Male BALB/cJ mice were surgically implanted with transmitters (DataSciences ETA10-F20) for recording EEG, activity and core body temperature by telemetry and a cannula for intracerebroventricular (ICV) microinjections. After baseline (Base) sleep recording, mice were presented tones (90 dB, 2 kHz) that started 5.0 s prior to and co-terminated with footshock (0.5 mA; 5.0 s maximum duration). SES mice (n = 9) always received shock but could terminate it by moving to the non-occupied chamber in a shuttlebox. Yoked SIS mice (n = 9) were treated identically, but could not alter shock duration. Training with SES or SIS was conducted over 2 days to stabilize responses. Afterwards, the mice received saline, CRF [0.4 μg (0.42 mM) or AST (1.0 μg (1.4 mM)] prior to SES or SIS. Sleep was analyzed over 20 h post-stress recordings. After administration of saline, REM was significantly greater in SES mice than in SIS mice whereas after CRF or AST, REM was similar in both groups. Total 20 h NREM did not vary across condition or group. However, after administration of saline and CRF, NREM episode duration was significantly decreased, and NREM episode number significantly increased, in SIS mice compared to SES animals. SES and SIS mice showed similar stress induced hyperthermia (SIH) across all conditions. These data demonstrate that CRF can mediate stress-induced changes in sleep independently of SIH, an index of hypothalamic-pituitary-adrenal axis activation.

Stress, arousal, and sleep

Stress is considered to be an important cause of disrupted sleep and insomnia. However, controlled and experimental studies in rodents indicate that effects of stress on sleep-wake regulation are complex and may strongly depend on the nature of the stressor. While most stressors are associated with at least a brief period of arousal and wakefulness, the subsequent amount and architecture of recovery sleep can vary dramatically across conditions even though classical markers of acute stress such as corticosterone are virtually the same. Sleep after stress appears to be highly influenced by situational variables including whether the stressor was controllable and/or predictable, whether the individual had the possibility to learn and adapt, and by the relative resilience and vulnerability of the individual experiencing stress. There are multiple brain regions and neurochemical systems linking stress and sleep, and the specific balance and interactions between these systems may ultimately determine the alterations in sleep-wake architecture. Factors that appear to play an important role in stress-induced wakefulness and sleep changes include various monominergic neurotransmitters, hypocretins, corticotropin releasing factor, and prolactin. In addition to the brain regions directly involved in stress responses such as the hypothalamus, the locus coeruleus, and the amygdala, differential effects of stressor controllability on behavior and sleep may be mediated by the medial prefrontal cortex. These various brain regions interact and influence each other and in turn affect the activity of sleep-wake controlling centers in the brain. Also, these regions likely play significant roles in memory processes and participate in the way stressful memories may affect arousal and sleep. Finally, stress-induced changes in sleep-architecture may affect sleep-related neuronal plasticity processes and thereby contribute to cognitive dysfunction and psychiatric disorders.

Basolateral amygdala and the regulation of fear-conditioned changes in sleep: role of corticotropin-releasing factor

STUDY OBJECTIVE

To determine whether corticotropin-releasing factor (CRF) in the basolateral amygdala (BLA) modulated sleep and fear-conditioned alterations in sleep.

DESIGN

After 2 days of habituation to recording procedures, baseline sleep recordings were obtained. The animals were then habituated to the handling procedure necessary for microinjections over 2 consecutive days. In experiment 1, rats received microinjections of 0.5 μL antalarmin (1.61 or 4.82 mM), a CRF receptor 1 antagonist, or distilled water once a week for 3 wk. In experiment 2, rats received a microinjection of either antalarmin or vehicle prior to inescapable shock training (ST; 20 shocks; 0.8 mA, 0.5 sec; 1 min interstimulus interval). The animals were placed back in the context 7 days later for 30 min without shock (CR; context re-exposure). Sleep was recorded for 8 h after each manipulation.

SETTING

NA.

SUBJECTS

Outbred Wistar rats.

INTERVENTIONS

The rats were surgically implanted with electrodes for recording the electroencephalogram and electromyogram for determining arousal state and with bilateral guide cannulae directed at BLA.

MEASUREMENTS AND RESULTS

Antalarmin microinjected into BLA did not significantly alter sleep under undisturbed conditions. However, antalarmin microinjected bilaterally into BLA prior to ST blocked reductions in rapid eye movement sleep that ST normally produces. Further, the single microinjection prior to ST blocked the reduction in rapid eye movement typically seen after subsequent CR. Behavioral freezing, an indicator of fear memory, was not altered.

CONCLUSIONS

CRF in BLA is involved in regulating stress-induced alterations in sleep and it plays a role in modulating how stressful memories influence sleep.

R278995/CRA0450, a corticotropin-releasing factor (CRF(1)) receptor antagonist modulates REM sleep measures in rats: Implication for therapeutic indication

Abnormalities in the regulation of the hypothalamic stress hormone corticotropin-releasing factor (CRF) are thought to play a critical role in mood disorders. Consequently, CRF receptor antagonists have been proposed as potential novel therapeutic agents of these conditions. Sleep disturbance is common in depressed patients and changed sleep-wake architecture is considered as potential predictor or surrogate marker of response to treatment. The aim of our study was to characterise the effects of oral administration of the corticotropin-releasing factor CRF(1) receptor antagonist R278995/CRA0450 (3 and 10mg/kg) on sleep-wake organization and electroencephalographic (EEG) components in Sprague-Dawley rats, and to determine whether the changes observed in the sleep-EEG pattern resemble those seen with antidepressants. At 3mg/kg, R278995/CRA0450 produced minor changes in sleep behaviour, while an overall reduction in power spectra was observed during deep slow wave sleep. At 10mg/kg, R278995/CRA0450 consistently reduced rapid eye movement (REM) sleep (-75.4%) and increased the REM sleep onset latency (+67%, 92.1±4.9min for vehicle vs. 153.8±24min for R278995/CRA0450), in the absence of systematic changes in spectral EEG pattern, which are characteristic anti-depressant-like effects. These findings in rats indicate that the corticotropin-releasing factor CRF(1) receptor antagonist R278995/CRA0450 is centrally active under standard conditions as it inhibits REM sleep and promotes wakefulness. The characteristic changes found in the sleep EEG model further support the hypothesis that R278995/CRA0450 could exert a non-sedative, antidepressant-like action.

Effects of corticotropin releasing factor (CRF) on sleep and body temperature following controllable footshock stress in mice

Rapid eye movement sleep (REM) is increased after controllable stress (modeled by escapable footshock, ES) and decreased after uncontrollable stress (modeled by inescapable footshock, IS). Decreases in REM after IS are exacerbated by corticotropin releasing factor (CRF) and attenuated by a CRF antagonist. In this study, we trained mice with ES following injections of CRF, astressin (AST), or saline (SAL) to determine whether CRF would alter REM after ES. Male BALB/cJ mice (n=7) were implanted for recording sleep, activity and body temperature via telemetry and with a guide cannula aimed into a lateral ventricle. After recovery from surgery, sleep following exposure to a novel chamber was recorded as a handling control (HC). The mice received one day of training with ES without injection followed by weekly training sessions in which they received counterbalanced intracerebroventricular (ICV) microinjections of either SAL or CRF (days 7 & 14) or SAL or AST (days 21 & 28) prior to ES. On each experimental day, sleep was recorded for 20 h. Compared to HC, the mice showed significantly increased REM when receiving either SAL or AST prior to ES whereas CRF prior to ES significantly reduced REM. Stress-induced hyperthermia had longer duration after ES compared to HC, and was not significantly altered by CRF or AST compared to SAL. The current results demonstrate that activity in the central CRF system is an important regulator of stress-induced alterations in REM.

Neuromedin U(2) receptor signaling mediates alteration of sleep-wake architecture in rats

Growing evidence indicates that neuromedin U (NmU) neuropeptide system plays an integral role in mediating the stress response through the corticotrophin-releasing factor (CRF) pathways. Stress is often associated with alteration in sleep-wake architecture both in human and laboratory animals. Here, we investigated whether activation of the NmU₂ receptor, a major high affinity receptor for NmU predominantly expressed in the brain, affects sleep behavior in rats. Effects of single (acute) intracebroventricular (icv) infusion of 2.5 nmol of the full agonists porcine NmU8 and rat NmU23 were assessed on sleep-wake architecture in freely moving rats, which were chronically implanted with EEG and EMG electrodes. In addition, repeated once daily administration of NmU8 at 2.5 nmol during 8 consecutive days (sub-chronic) was studied. Acute icv infusion of NmU23 elicited a robust alteration in sleep-wake architecture, namely enhanced wakefulness and suppressed sleep during the first 4h after administration. Acute infusion NmU8 had no effect on spontaneous sleep-wake architecture. However, sub-chronic icv infusion of NmU8 increased the amount of rapid eye movement (REM) sleep and intermediate stage (IS), while decreased light sleep. Additionally, NmU8 increased transitions from sleep states towards wakefulness suggesting a disruption in sleep continuity. The present results show that central-activation of NmU₂ receptor markedly reduced sleep duration and disrupted the mechanisms underlying NREM-REM sleep transitions. Given that sleep-wakefulness cycle is strongly influenced by stress and the role of NmU/NmU₂ receptor signaling in stress response, the disruption in sleep pattern associated with peptides species may support at least some signs of stress.

Wake-promoting effects of orexin: Its independent actions against the background of an impaired corticotropine-releasing hormone receptor system

It is widely accepted that orexin (hypocretin) bears wake-promoting effects. While under normal conditions the circadian rhythm of orexin release has a clear circadian distribution, the amplitude of orexin fluctuation is dampened in depression. Interestingly, clinical symptoms of depression include several sleep disturbances. In this disease, corticotropin-releasing hormone (CRH) seems to be another factor influencing sleep. As neurophysiological interactions and anatomical connections between the orexinergic and the CRH system point to mutual influences of these two neuropeptides, we examined whether a dysfunctional CRH-receptor system in two different CRH receptor knock out models alters general wake-promoting effects of orexin applied exogenously. Orexin was injected intracerebroventricularlly into CNS-restricted CRH-receptor type 1 knockout mice (CRH-R1 KO) and CRH-receptor type 2 knockout mice (CRH-R2 KO) and baseline sleep was recorded from the freely behaving mice. A third experiment included antisauvagine-30 injections (CRH-R2 antagonist) into CRH-R1 KO animals. Orexin had similar wake-promoting effects in CRH-R1KO mice, in CRH-R2 KO animals and in CRH-R1KO mice treated with antisauvagine-30. Consistent results were obtained from all corresponding control littermate experiments. According to our results we conclude that the wake-promoting effects of orexin are not influenced by a possible contribution of CRH.

Conditional corticotropin-releasing hormone overexpression in the mouse forebrain enhances rapid eye movement sleep

Impaired sleep and enhanced stress hormone secretion are the hallmarks of stress-related disorders, including major depression. The central neuropeptide, corticotropin-releasing hormone (CRH), is a key hormone that regulates humoral and behavioral adaptation to stress. Its prolonged hypersecretion is believed to play a key role in the development and course of depressive symptoms, and is associated with sleep impairment. To investigate the specific effects of central CRH overexpression on sleep, we used conditional mouse mutants that overexpress CRH in the entire central nervous system (CRH-COE-Nes) or only in the forebrain, including limbic structures (CRH-COE-Cam). Compared with wild-type or control mice during baseline, both homozygous CRH-COE-Nes and -Cam mice showed constantly increased rapid eye movement (REM) sleep, whereas slightly suppressed non-REM sleep was detected only in CRH-COE-Nes mice during the light period. In response to 6-h sleep deprivation, elevated levels of REM sleep also became evident in heterozygous CRH-COE-Nes and -Cam mice during recovery, which was reversed by treatment with a CRH receptor type 1 (CRHR1) antagonist in heterozygous and homozygous CRH-COE-Nes mice. The peripheral stress hormone levels were not elevated at baseline, and even after sleep deprivation they were indistinguishable across genotypes. As the stress axis was not altered, sleep changes, in particular enhanced REM sleep, occurring in these models are most likely induced by the forebrain CRH through the activation of CRHR1. CRH hypersecretion in the forebrain seems to drive REM sleep, supporting the notion that enhanced REM sleep may serve as biomarker for clinical conditions associated with enhanced CRH secretion.

Modulation of Sleep Homeostasis by Corticotropin Releasing Hormone in REM Sleep-Deprived Rats

Studies have shown that sleep recovery following different protocols of forced waking varies according to the level of stress inherent to each method. Sleep deprivation activates the hypothalamic-pituitary-adrenal axis and increased corticotropin-releasing hormone (CRH) impairs sleep. The purpose of the present study was to evaluate how manipulations of the CRH system during the sleep deprivation period interferes with subsequent sleep rebound. Throughout 96 hours of sleep deprivation, separate groups of rats were treated i.c.v. with vehicle, CRH or with alphahelical CRH(9-41), a CRH receptor blocker, twice/day, at 07:00 h and 19:00 h. Both treatments impaired sleep homeostasis, especially in regards to length of rapid eye movement sleep (REM) and theta/delta ratio and induced a later decrease in NREM and REM sleep and increased waking bouts. These changes suggest that activation of the CRH system impact negatively on the homeostatic sleep response to prolonged forced waking. These results indicate that indeed, activation of the HPA axis-at least at the hypothalamic level-is capable to reduce the sleep rebound induced by sleep deprivation.

Corticotropin releasing factor (CRF) modulates fear-induced alterations in sleep in mice

Contextual fear significantly reduces rapid eye movement sleep (REM) during post-exposure sleep in mice and rats. Corticotropin releasing factor (CRF) plays a major role in CNS responses to stressors. We examined the influence of CRF and astressin (AST), a non-specific CRF antagonist, on sleep after contextual fear in BALB/c mice. Male mice were implanted with transmitters for recording sleep via telemetry and with a guide cannula aimed into the lateral ventricle. Recordings for vehicle and handling control were obtained after ICV microinjection of saline (SAL) followed by exposure to a novel chamber. Afterwards, the mice were subjected to shock training (20 trials, 0.5 mA, 0.5 s duration) for 2 sessions. After training, separate groups of mice received ICV microinjections of SAL (0.2 microl, n=9), CRF (0.4 microg, n=8), or AST (1.0 microg, n=8) prior to exposure to the shock context alone. Sleep was then recorded for 20 h (8-hour light and 12-hour dark period). Compared to handling control, contextual fear significantly decreased REM during the 8-h light period in mice receiving SAL and in mice receiving CRF, but not in the mice receiving AST. Mice receiving CRF exhibited reductions in REM during the 12-h dark period after contextual fear, whereas mice receiving SAL or AST did not. CRF also reduced non-REM (NREM) delta (slow wave) amplitude in the EEG. Only mice receiving SAL prior to contextual fear exhibited significant reductions in NREM and total sleep. These findings demonstrate a role for the central CRF system in regulating alterations in sleep induced by contextual fear.

Ghrelin alone or co-administered with GHRH or CRH increases non-REM sleep and decreases REM sleep in young males

Ghrelin activates the somatotropic and the hypothalamic-pituitary-adrenal axes, being crucially involved in sleep regulation. Simplified, growth hormone releasing hormone (GHRH) increases slow-wave sleep and REM sleep in males, whilst corticotropin-releasing hormone (CRH) increases wakefulness and decreases REM sleep. Ghrelin's role in sleep regulation and particularly its interactions with GHRH and CRH are not entirely clear. We aimed to elucidate the interactions between ghrelin, GHRH and CRH in sleep regulation and the secretion of cortisol and GH. Nocturnal GH and cortisol secretion and polysomnographies were determined in 10 healthy males (25.7+/-3.0 years) four times, receiving placebo (A), ghrelin (B), ghrelin and GHRH (C), or ghrelin and CRH (D) at 22:00, 23:00, 00:00, and 01:00h, in this single-blind, randomized, cross-over study. Non-REM sleep was significantly (p<0.05) increased in all verum conditions (mean+/-SEM: B: 355.3+/-7.4; C: 365.4+/-8.1; D: 371.4+/-3.9min) compared to placebo (336.3+/-6.8min). REM sleep was decreased (B: 84.3+/-4.2 [p<0.1]; C: 74.2+/-7.0 [p<0.05]; D: 80.4+/-2.7min [p<0.05]) compared to placebo (100.9+/-8.3). CRH+ghrelin decreased the time spent awake and enhanced the sleep efficiency; furthermore, the REM latency was decreased compared to the other treatment conditions. CRH enhanced the ghrelin-induced cortisol secretion but had no relevant effect on GH secretion. In turn, GHRH enhanced the ghrelin-induced GH secretion but had no effect on cortisol secretion. In conclusion, ghrelin exhibited distinct sleep effects, which tended to be enhanced by both GHRH and CRH. CRH had sleep-improving and REM permissive effects when co-administered with ghrelin, being in contrast to the effect of CRH alone in previous studies.

Mouse strain differences in the effects of corticotropin releasing hormone (CRH) on sleep and wakefulness

Corticotropin releasing hormone (CRH) plays a major role in central nervous system responses to stressors and has been implicated in stress-induced alterations in sleep. In the absence of stressors, CRH contributes to the regulation of spontaneous waking. We examined the effects of CRH and astressin (AST), a non-specific CRH antagonist, on wakefulness and sleep in two mouse strains with differential responsiveness to stress to determine whether CRH might also differentially affect undisturbed sleep and activity. Less reactive C57BL/6J (n=7) and high reactive BALB/cJ (n=7) male mice were implanted with a transmitter for determining sleep via telemetry and with a guide cannula aimed into a lateral ventricle. After recovery from surgery and habituation to handling, ICV microinjections of CRH (0.04, 0.2, and 0.4 microg), AST (0.1, 0.4, and 1.0 microg) or vehicle alone (pyrogen-free saline, 0.2 microl) were administered during the fourth hour after lights on and sleep was recorded for the subsequent 8 h. Comparisons of wakefulness and sleep were conducted across conditions and across strains. In C57BL/6J mice, REM was significantly decreased after microinjections of CRH (0.2 microg) and CRH (0.4 microg), and NREM and total sleep were decreased after microinjections of CRH (0.4 microg). CRH (0.04 microg) and AST did not significantly change wakefulness or sleep. In BALB/cJ mice, CRH (0.4 microg) increased wakefulness and decreased NREM, REM and total sleep. AST decreased active wakefulness and significantly increased REM at the low and high dosages. These findings demonstrate that CRH produces changes in arousal when given to otherwise undisturbed mice. Strain differences in the effects of CRH and AST may be linked to the relative responsiveness of C57BL/6J and BALB/cJ mice to stressors and to underlying differences in the CRH system.

Neurochemical regulation of sleep

This review summarizes recent developments in the field of sleep regulation, particularly in the role of hormones, and of synthetic GABA(A) receptor agonists. Certain hormones play a specific role in sleep regulation. A reciprocal interaction of the neuropeptides growth hormone (GH)-releasing hormone (GHRH) and corticotropin-releasing hormone (CRH) plays a key role in sleep regulation. At least in males GHRH is a common stimulus of non-rapid-eye-movement sleep (NREMS) and GH and inhibits the hypothalamo-pituitary adrenocortical (HPA) hormones, whereas CRH exerts opposite effects. Furthermore CRH may enhance rapid-eye-movement sleep (REMS). Changes in the GHRH:CRH ratio in favor of CRH appear to contribute to sleep EEG and endocrine changes during depression and normal ageing. In women, however, CRH-like effects of GHRH were found. Besides CRH somatostatin impairs sleep, whereas ghrelin, galanin and neuropeptide Y promote sleep. Vasoactive intestinal polypeptide appears to be involved in the temporal organization of human sleep. Beside of peptides, steroids participate in sleep regulation. Cortisol appears to promote REMS. Various neuroactive steroids exert specific effects on sleep. The beneficial effect of estrogen replacement therapy in menopausal women suggests a role of estrogen in sleep regulation. The GABA(A) receptor or GABAergic neurons are involved in the action of many of these hormones. Recently synthetic GABA(A) agonists, particularly gaboxadol and the GABA reuptake inhibitor tiagabine were shown to differ distinctly in their action from allosteric modulators of the GABA(A) receptor like benzodiazepines as they promote slow-wave sleep, decrease wakefulness and do not affect REMS.

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.

Roles of peptides and steroids in sleep disorders

A bidirectional interaction exists between the electrophysiological and neuroendocrine components of sleep. The first is represented by the nonrapid eye movement sleep (NREMS) and rapid eye movement sleep (REMS) cycles, the latter by distinct patterns of the secretion of various hormones. Certain hormones (neuropeptides and steroids) play a specific role in sleep regulation. Changes in their activity contribute to the pathophysiology of sleep disorders. A reciprocal interaction of the peptides growth hormone-releasing hormone (GHRH) and corticotropin-releasing hormone (CRH) plays a key role in sleep regulation. GHRH promotes growth hormone secretion and, at least in males, NREMS, whereas CRH impairs NREMS, promotes REMS and stimulates the secretion of adrenocorticotropic hormone and cortisol. Changes in the CRH:GHRH ratio in favor of CRH contribute to impaired sleep, elevated cortisol secretion and blunted GH levels during depression and normal aging. However, in women, GHRH exerts CRH-like effects. Galanin, ghrelin and neuropeptide Y are other sleep-promoting peptides, whereas somatostatin impairs sleep. A decline of orexin activity causes narcolepsy. In addition to CRH overactivity, hypercortisolism appears to be involved in the pathophysiology of sleep- electroencephalogram (EEG) changes in depression. Various neuroactive steroids exert specific effects on sleep. The changes of sleep EEG in women after the menopause are related to the decline of estrogen and progesterone. Furthermore, sleep-EEG changes in dwarfism, acromegaly, Addison's disease, Cushing's disease, brain injury, sleep apnea syndrome, primary insomnia, prolactinoma and dementia appear to be related to changes in the activity of peptides and steroids.

Alpha-helical CRH exerts CRH agonistic effects on sleep-endocrine activity in humans

CRH is known to enhance wakefulness and to reduce SWS. In addition, some but not all, studies suggest that CRH promotes REM sleep. Alpha-helical CRH exerts CRH-antagonistic effects in various studies. We studied its effect on sleep EEG and nocturnal secretion of ACTH, cortisol, GH (n = 7) in young normal male subjects. After administering the substance cortisol and ACTH levels were enhanced during the total night compared to placebo. We found an increase of the time spent awake for the first half. ACTH (2nd half of the night) and cortisol (total night and 1st half of the night) increased. The results of the present study correspond to a mixture of agonistic and antagonistic effects of alpha-helical CRH.

Interaction between the corticotropin-releasing factor system and hypocretins (orexins): a novel circuit mediating stress response

The hypothalamic neuropeptides hypocretins (orexins) play a crucial role in the stability of arousal and alertness. We tested whether the hypocretinergic system is a critical component of the stress response activated by the corticotropin-releasing factor (CRF). Our results show that CRF-immunoreactive terminals make direct contact with hypocretin-expressing neurons in the lateral hypothalamus and that numerous hypocretinergic neurons express the CRF-R1/2 receptors. We also demonstrate that application of CRF to hypothalamic slices containing identified hypocretin neurons depolarizes membrane potential and increases firing rate in a subpopulation of hypocretinergic cells. CRF-induced depolarization was tetrodotoxin insensitive and was blocked by the peptidergic CRF-R1 antagonist astressin. Moreover, activation of hypocretinergic neurons in response to acute stress was severely impaired in CRF-R1 knock-out mice. Together, our data provide evidence of a direct neuroanatomical and physiological input from CRF peptidergic system onto hypocretin neurons. We propose that, after stressor stimuli, CRF stimulates the release of hypocretins and that this circuit contributes to activation and maintenance of arousal associated with the stress response.

Treatment with the CRH1-receptor-antagonist R121919 improves sleep-EEG in patients with depression

Well documented changes of sleep electroencephalogram (EEG) in patients with depression include rapid eye movement (REM) sleep disinhibition, decreases of slow-wave-sleep (SWS) and increase in wakefulness. Twenty-seven inpatients with major depression were admitted subsequently to a clinical trial with the CRH(1)-receptor-antagonist R121919 administered in two different dose escalation panels. A random subgroup of 10 patients underwent three sleep-EEG recordings (baseline before treatment, at the end of the first week and at the end of the fourth week of active treatment). SWS time increased significantly compared with baseline after 1 week and after 4 weeks. The number of awakenings and REM density showed a trend toward a decrease during the same time period. Separate evaluation of these changes for both panels showed no significant effect at lower doses, whereas in the higher doses after R121919 REM density decreased and SWS increased significantly between baseline and week 4. Furthermore positive associations between HAMD scores and SWS at the end of active treatment were found. Although these data might indicate that R121919 has a normalizing influence on the sleep EEG, the design of the study does not allow to differentiate genuine drug effects from those of clinical improvement and habituation to the clinical setting.

Six-hour selective REM sleep deprivation increases the expression of the galanin gene in the hypothalamus of rats

The effect of short-term selective REM sleep deprivation (RSD) on the gene expression of galanin in the rat hypothalamus was examined using in situ hybridization histochemistry. Monitoring an electroencephalogram (EEG) and electromyogram (EMG) on an on-line computer screen, as the RSD rats entered REM sleep, they were gently stroked on their backs using a brush to wake them during the RSD period. Galanin mRNA levels in the preoptic area (POA) were significantly increased by RSD for a period of 6 h. RSD had no significant effect on the mRNA levels of corticotrophin-releasing factor (CRF), arginine vasopressin (AVP), oxytocin (OXT) or orexins. These results suggest that 6-h selective RSD may not be sufficient to induce the activation of the hypothalamo-pituitary adrenal axis, and that the expression of the galanin gene in the hypothalamus reacts more readily against the loss of REM sleep in comparison to other hypothalamic neuropeptides such as arginine vasopressin, oxytocin and orexins.

Sleep and endocrinology

A bidirectional interaction between sleep electroencephalogram and endocrine activity is well established in various species including humans. Various hormones (peptides and steroids) participate in sleep regulation. A key role was shown for the reciprocal interaction between sleep-promoting growth hormone-releasing hormone (GHRH) and sleep-impairing corticotropin-releasing hormone (CRH). Changes in the GHRH : CRH ratio result in changes of sleep-endocrine activity. It is thought that the change of this ratio in favour of CRH contributes to aberrations of sleep during ageing and depression (shallow sleep, blunted GH and elevated cortisol). Besides GHRH, ghrelin and galanin enhance slow wave sleep. Somatostatin is another sleep-impairing factor. Neuropeptide Y acts as a CRH antagonist and induces sleep onset. There are hints that CRH promotes rapid eye movement sleep (REMS). In animals prolactin enhances REMS. In humans vasoactive intestinal polypeptide (VIP) appears to play a role in the temporal organization of sleep as, after VIP, the non-REMS-REMS cycle decelerated. Cortisol appears to enhance REMS. Finally, gonadal hormones participate in sleep regulation. Oestrogen replacement therapy and CRH-1 receptor antagonism in depression are beneficial clinical applications of sleep-endocrine research.

Sleep and the hypothalamo-pituitary-adrenocortical system

The intention of this review is to summarize the current knowledge on the bidirectional interaction between sleep EEG and the secretion of corticotropin (ACTH) and cortisol. The administration of various hypothalamic-pituitary- adrenocortical (HPA) hormones and their antagonists exerts specific sleep-EEG changes in several species including humans. It is well documented that corticotropin releasing hormone (CRH) impairs sleep and enhances vigilance. In addition, it may promote REM sleep. Changes in the growth hormone-releasing hormone (GHRH):CRH ratio in favour of CRH appear to contribute to shallow sleep, elevated cortisol levels and blunted GH in depression and ageing. On the other hand, in women GHRH appears to exert CRH-like effects on sleep. Acute cortisol administration increases slow-wave sleep (SWS) and GH, probably due to feedback inhibition of CRH, and inhibits REM sleep. With the mixed glucocorticoid and progesterone receptor antagonist mifepriston sleep is disrupted. Subchronic administration of the glucocorticoid agonist methylprednisolone desinhibited REM sleep. A synergism of elevated CRH and cortisol activity may contribute to REM disinhibition during depression. Also ACTH and vasopressin modulate sleep specifically but their physiological role remains unclear. For example acute icv vasopressin enhances wakefulness in rats, whereas its long-term administration increases SWS in the elderly. In various studies the interaction of sleep EEG and HPA hormones has been investigated at the baseline, after manipulation of sleep-wake behaviour and after environmental changes. Most studies agree that the circadian pattern of cortisol is relatively independent from sleep and environmental influences. Some data suggest a major effect of light on cortisol secretion. Sleeping is widely associated with blunting and awakenings are linked with increases of HPA hormones.

Restraint increases prolactin and REM sleep in C57BL/6J mice but not in BALB/cJ mice

Sleep is generally considered to be a recovery from prior wakefulness. The architecture of sleep not only depends on the duration of wakefulness but also on its quality in terms of specific experiences. In the present experiment, we studied the effects of restraint stress on sleep architecture and sleep electroencephalography (EEG) in different strains of mice (C57BL/6J and BALB/cJ). One objective was to determine if the rapid eye movement (REM) sleep-promoting effects of restraint stress previously reported for rats would also occur in mice. In addition, we examined whether the effects of restraint stress on sleep are different from effects of social defeat stress, which was found to have a non-REM (NREM) sleep-promoting effect. We further measured corticosterone and prolactin levels as possible mediators of restraint stress-induced changes in sleep. Adult male C57BL/6J and BALB/cJ mice were subjected to 1 h of restraint stress in the middle of the light phase. To control for possible effects of sleep loss per se, the animals were also kept awake for 1 h by gentle handling. Restraint stress resulted in a mild increase in NREM sleep compared with baseline, but, overall, this effect was not significantly different from sleep deprivation by gentle handling. In contrast, restraint stress caused a significant increase in REM sleep compared with handling in the C57BL/6J mice but not in BALB/cJ mice. Corticosterone levels were significantly and similarly elevated after restraint in both strains, but prolactin was increased only in the C57BL/6J mice. In conclusion, this study shows that the restraint stress-induced increase in REM sleep in mice is strongly strain dependent. The concomitant increases in prolactin and REM sleep in the C57BL/6J mice, but not in BALB/cJ mice, suggest prolactin may be involved in the mechanism underlying restraint stress-induced REM sleep. Furthermore, this study confirms that different stressors differentially affect NREM and REM sleep. Whereas restraint stress promotes REM sleep in C57BL/6J mice, we previously found that in the same strain, social defeat stress promotes NREM sleep. As such, studying the consequences of specific stressful stimuli may be an important tool to unravel both the mechanism and function of different sleep stages.

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.

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.

Modelling and exploring human sleep with event history analysis

In this paper we propose the use of statistical models of event history analysis for investigating human sleep. These models provide appropriate tools for statistical evaluation when sleep data are recorded continuously over time or on a fine time grid, and are classified into sleep stages such as REM and nonREM as defined by Rechtschaffen and Kales (1968). In contrast to conventional statistical procedures, event history analysis makes full use of the information contained in sleep data, and can therefore provide new insights into non-stationary properties of sleep. Probabilities of or intensities for transitions between sleep stages are the basic quantities for characterising sleep processes. The statistical methods of event history analysis aim at modelling and estimating these intensities as functions of time, taking into account individual sleep history and assessing the influence of factors of interest, such as hormonal secretion. In this study we suggest the use of non-parametric approaches to reveal unknown functional forms of transition intensities and to explore time-varying and non-stationary effects. We then apply these techniques in a study of 30 healthy male volunteers to assess the mean population intensity and the effects of plasma cortisol concentration on the transition between selected sleep stages as well as the influence of elapsed time in a current REM period on the intensity for a transition to nonREM. The most interesting findings are that (a) the intensity of the nonREM-to-REM transitions after sleep onset in young men shows a periodicity which is similar to that of nonREM/REM cycles; (b) 30-45 min after sleep onset, young men reveal a great propensity to pass from light sleep (stages 1 or 2) into slow-wave sleep (SWS) (stages 3 or 4); (c) high cortisol levels imposed additional impulses on the transition intensity of (i) wake to sleep around 2 h after sleep onset, (ii) nonREM to REM around 6 h later, (iii) stage 1 or stage 2 sleep to SWS around 2, 4 and 6 h later and (iv) SWS to stage 1 or stage 2 sleep about 2 h later. Moreover, high cortisol concentrations at the beginning of REM periods favoured the change to nonREM sleep, whereas later their influence on a nonREM change became weak and weaker. As sleep data are also available as event-oriented data in many studies in sleep research, event history analysis applied additionally to conventional statistical procedures, such as regression analysis or analysis of variance, could help to acquire more information and knowledge about the mechanisms behind the sleep process.

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.

Stress-induced sleep deprivation modifies corticotropin releasing factor (CRF) levels and CRF binding in rat brain and pituitary

Electroencephalographic (EEG) studies have shown that corticotropin-releasing factor (CRF) administration induces EEG activation, decreases sleep time both in rats and humans and modifies the sleep pattern in sleep deprived rats. In the present study we have investigated whether CRF neuronal activity could be altered in a situation of disrupted sleep-wake cycle. Sleep deprivation (SD) was induced by keeping the rat for 72 h on a small platform (7 cm) surrounded by water. Immediately after the SD period rats were killed and CRF levels and CRF receptor binding were evaluated in different brain areas. A marked increase in CRF levels was present in the striatum (+224%), limbic areas (+144%) and pituitary (+42%) whereas the hypothalamic CRF content was reduced (-57%). A significant decrease in CRF binding was found in the striatum (-33%) and pituitary (-38%) of sleep deprived rats. These results indicate that CRF neuronal activity is stimulated by SD, suggesting that CRF might play an important role in the physiological regulation of the sleep-wake cycle and that an altered CRF neuronal activity might be involved in behavioral modifications related to sleep disturbances.

Localization of corticotropin-releasing hormone in the human locus coeruleus and pedunculopontine tegmental nucleus: an immunocytochemical and in situ hybridization study

The present study utilized immunocytochemistry and in situ hybridization histochemistry to examine the localization of corticotropin-releasing hormone immunoreactivity and messenger RNA in neurons of the human brainstem. A large population of corticotropin-releasing hormone-immunoreactive neurons appeared in the lateral region of the pontomesencephalic tegmentum. These corticotropin-releasing hormone-containing neurons are predominantly located in the compact subnucleus of the pedunculopontine tegmental nucleus. Proceeding caudally, corticotropin-releasing hormone-immunoreactive neurons in the pedunculopontine tegmental nucleus travel in a dorsomedial direction approaching the ventral border of the locus coeruleus in a dispersed fashion and cluster in a region ventromedial to the locus coeruleus which corresponds to the ventral aspect of the laterodorsal tegmental nucleus. Dense corticotropin-releasing hormone-immunoreactive fibers are present in the dorsal portion of the locus coeruleus and are most prominent in the middle to rostral levels of the nucleus. The cellular and regional localization of corticotropin-releasing hormone messenger RNA in the human brainstem is identical to the perikaryal distribution visualized by immunocytochemistry. Neurons in the laterodorsal tegmental nucleus and pedunculopontine tegmental nucleus express abundant levels of corticotropin-releasing hormone messenger RNA as revealed by dense silver grains overlying these neurons on the emulsion autoradiograms. Within the locus coeruleus, the cellular expression of corticotropin-releasing hormone-immunoreactive and corticotropin-releasing hormone messenger RNA is exclusively localized to non-pigmented neurons. The present study confirms a previous finding describing dense corticotropin-releasing hormone-immunoreactive fibers innervating the human locus coeruleus and extends these findings by identifying corticotropin-releasing hormone immunoreactive and corticotropin-releasing hormone messenger RNA-containing perikarya in the pedunculopontine tegmental nucleus, in the ventral portion of the laterodorsal tegmental nucleus and in the locus coeruleus proper. From morphological observations, the corticotropin-releasing hormone-containing neurons in human pontomesencephalic tegmentum form a continuous population of neurons that are positioned anatomically to exert a putative neuromodulatory influence on locus coeruleus neurons.

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.

Growth hormone-releasing hormone (GHRH)-induced effects on sleep EEG and nocturnal secretion of growth hormone, cortisol and ACTH in patients with major depression

Studies in normal human subjects and animals suggest that the neuropeptide growth hormone-releasing hormone (GHRH) is a common regulator of the sleep EEG and nocturnal hormone secretion. In healthy volunteers GHRH prompts an increase in the amount of slow wave sleep (SWS) and in growth hormone (GH) secretion and blunting of cortisol release. Inhibition of GHRH may contribute to sleep-endocrine aberrances during depression. We tested the effects of pulsatile application of 4 x 50 micrograms GHRH on the sleep EEG and simultaneously investigated nocturnal hormone secretion in 10 inpatients (four females, six males) with the acute episode of major depression. In contrast to the effects of placebo, GH secretion increased distinctly and rapid-eye-movement (REM) density decreased during the second half of night. No other significant changes in sleep-endocrine activity, including SWS, cortisol and ACTH secretion, could be observed. We assume that hypothalamic-pituitary-adrenocortical system activity and slow wave sleep are inert to the influence of GHRH during acute depression. Cortisol and ACTH remained unchanged even in a subsample of five younger (aged 19-28 years) patients. This observation is in contrast to our recent finding that cortisol secretion is blunted in young normal volunteers after GHRH. But on the other hand, GHRH is capable of stimulating GH and inducing a decrease in REM density in these subjects.