Knockdown of orexin type 1 receptor in rat locus coeruleus increases REM sleep during the dark period

The locus coeruleus (LC) regulates sleep/wakefulness and is densely innervated by orexinergic neurons in the lateral hypothalamus. Here we used small interfering RNAs (siRNAs) to test the role of LC orexin type 1 receptor (OxR1) in sleep–wake control. In sleep studies, bilateral OxR1 siRNA injections led to an increase of time spent in rapid eye movement (REM) sleep, which was selective for the dark (active) period, peaked at approximately 30% of control during the second dark period after injection and then disappeared after 4 days. Cataplexy-like episodes were not observed. The percentage time spent in wakefulness and non-REM (NREM) sleep and the power spectral profile of NREM and REM sleep were unaffected. Control animals, injected with scrambled siRNA, had no sleep changes after injection. Quantification of the knockdown revealed that unilateral microinjection of siRNAs targeting OxR1 into the rat LC on two consecutive days induced a 45.5% reduction of OxR1 mRNA in the LC 2 days following the injections when compared with the contralateral side receiving injections of control (scrambled) siRNAs. This reduction disappeared 4 days after injection. Similarly, unilateral injection of OxR1 siRNA into the LC revealed a marked (33.5%) reduction of OxR1 staining 2 days following injections. In contrast, both the mRNA level and immunohistochemical staining for tyrosine hydroxylase were unaffected. The results indicate that a modest knockdown of OxR1 is sufficient to induce observable sleep changes. Moreover, orexin neurons, by acting on OxR1 in the LC, play a role in the diurnal gating of REM sleep.     

Changes in the thermal characteristics of hypothalamic neurons during sleep and wakefulness

The characteristics of the mammalian thermoregulatory system are dependent upon arousal state. During NREM sleep thermoregulatory mechanisms are intact but body temperature is regulated at a lower level than during wakefulness. In REM sleep thermoregulatory effector mechanisms are inhibited and thermal homeostasis is severely disrupted. Thermosensitivity of neurons in the preoptic/anterior hypothalamus (POAH) was determined for behaving kangaroo rats (Dipodomys deserti) during electrophysiologically defined wakefulness, NREM sleep and REM sleep to elucidate possible neural mechanisms for previous findings of state-dependent changes in thermoregulation. Thirty cells were tested during at least two arousal states. During wakefulness, 70% of the recorded cells were sensitive to changes in local temperature, with the number of warm-sensitive (W) cells outnumbering cold-sensitive (C) cells by 1.6:1. In NREM sleep, 43% of the cells were thermally sensitive, with the ratio of W:C remaining the same as in wakefulness. In REM sleep only two cells were thermosensitive (both W). The decrease in neuronal thermosensitivity of POAH cells during REM sleep parallels findings of inhibition of thermoregulatory effector responses during REM, although further work is necessary to determine the source and nature of the inhibition.     

Glutamatergic Neurons in the Preoptic Hypothalamus Promote Wakefulness,Destabilize NREM Sleep,Suppress REM Sleep,and Regulate Cortical Dynamics

Clinical and experimental data from the last nine decades indicate that the preoptic area of the hypothalamus is a critical node in a brain network that controls sleep onset and homeostasis. By contrast, we recently reported that a group of glutamatergic neurons in the lateral and medial preoptic area increases wakefulness, challenging the long-standing notion in sleep neurobiology that the preoptic area is exclusively somnogenic. However, the precise role of these subcortical neurons in the control of behavioral state transitions and cortical dynamics remains unknown. Therefore, in this study, we used conditional expression of excitatory hM3Dq receptors in these preoptic glutamatergic (Vglut2⁺) neurons and show that their activation initiates wakefulness, decreases non-rapid eye movement (NREM) sleep, and causes a persistent suppression of rapid eye movement (REM) sleep. We also demonstrate, for the first time, that activation of these preoptic glutamatergic neurons causes a high degree of NREM sleep fragmentation, promotes state instability with frequent arousals from sleep, decreases body temperature, and shifts cortical dynamics (including oscillations, connectivity, and complexity) to a more wake-like state. We conclude that a subset of preoptic glutamatergic neurons can initiate, but not maintain, arousals from sleep, and their inactivation may be required for NREM stability and REM sleep generation. Further, these data provide novel empirical evidence supporting the hypothesis that the preoptic area causally contributes to the regulation of both sleep and wakefulness.SIGNIFICANCE STATEMENT Historically, the preoptic area of the hypothalamus has been considered a key site for sleep generation. However, emerging modeling and empirical data suggest that this region might play a dual role in sleep-wake control. We demonstrate that chemogenetic stimulation of preoptic glutamatergic neurons produces brief arousals that fragment sleep, persistently suppresses REM sleep, causes hypothermia, and shifts EEG patterns toward a “lighter” NREM sleep state. We propose that preoptic glutamatergic neurons can initiate, but not maintain, arousal from sleep and gate REM sleep generation, possibly to block REM-like intrusions during NREM-to-wake transitions. In contrast to the long-standing notion in sleep neurobiology that the preoptic area is exclusively somnogenic, we provide further evidence that preoptic neurons also generate wakefulness.     

Effects of H1- and H2-histamine receptor agonists and antagonists on sleep and wakefulness in the rat

Summary The H 1-receptor agonist 2-thiazolylethylamine (2-TEA) given by i.c.v. route dose-dependently increased wakefulness (W) and decreased NREM sleep (NRMS) and REM sleep (REMS) in rats prepared for chronic sleep recordings. The H 1-receptor antagonists pyrilamine and diphenhydramine given by i.p. route decreased W and increased NREMS. Pyrilamine prevented the increase of W and decrease of NREMS produced by 2-TEA. However, REMS reduction was not antagonized, what tends to suggest that two different mechanisms could be involved in the 2-TEA-induced effects on NREMS and REMS.Cimetidine which blocks H 2-receptors, when given by i.p. route showed no significant effects on sleep and W. Administration of the H 2-receptor agonist dimaprit and the H 2-receptor antagonists cimetidine, metiamide and ramtidine by i.c.v. route induced the appearance of high voltage spikes at cortical leads, thus leaving inconclusive the matter of their effects on sleep and wakefulness.Our results tend to support the proposal that the H 1-receptor intervenes in sleep-wakefulness regulation. Limitations in the available H 2-receptor agonists and antagonists presently preclude a more detailed analysis of the role of H 2-receptors on sleep and W.     

Sleep disturbance associated with an enhanced orexinergic system induced by chronic treatment with paroxetine and milnacipran

Recent reports have shown that acute or chronic treatment with selective serotonin reuptake inhibitor (SSRI) or serotonin-noradrenaline reuptake inhibitor (SNRI) causes unpleasant side effects in patients. In the present study, through the use of electroencephalography (EEG) and electromyography (EMG), we found that chronic treatment with the SSRI paroxetine or the SNRI milnacipran significantly induced sleep disturbance, which was characterized by an increase in the total wake time and decreased total nonrapid eye movement (NREM) sleep. Furthermore, RT-PCR analysis demonstrated that chronic treatment with paroxetine or milnacipran significantly increased the mRNA levels of orexin 1 receptor and orexin 2 receptor in the hypothalamus and of histamine 1 receptor and histidine decarboxylase in the frontal cortex of mice. The present findings suggest that chronic treatment with either paroxetine or milnacipran causes sleep disturbance associated with an increase in orexinergic transmission in the hypothalamus and histaminergic transmission in the frontal cortex. Although further studies are needed, these imbalances in the orexinergic and histaminergic systems may be, at least in part, responsible for the pathogenesis of sleep disturbance induced by chronic treatment with SSRI or SNRI in rodents.     

Regulation of sleep and wakefulness through the monoaminergic and cholinergic systems

Sleep and wakefulness are regulated in the brainstem and hypothalamus. Classical brain dissecting or stimulating studies have proposed the concept of an ascending reticular activating system, presently known as the wakefulness center, located in the caudal midbrain/rostral pontine (mesopontine) areas, comprising the serotonergic, noradrenergic and cholinergic neural populations. These neural groups, in association with the histaminergic and orexinergic neurons in the hypothalamus, activate the cerebral the cortex through the thalamus or basal forebrain. This activating (waking) system is controlled by the slow wave sleep (SWS) generating system in the preoptic area, which receives inhibitory signals from the waking center. The mesopontine area is also involved in the regulation of rapid eye movement (REM) sleep. Reciprocal interactions between the cholinergic/glutamatergic excitatory systems and the aminergic/GABAergic inhibitory systems are crucial for the regulation of REM sleep. In the REM activating system, mutual excitatory interactions between cholinergic and glutamatergic neurons serve to maintain the state of REM sleep. The REM activating system in the mesopontine area receives GABAergic inhibitory signals from several neural groups in the periaqueductal gray and the medulla. Thus, sleep and wakefulness are controlled by the interplay of various neural populations located in several areas in the central nervous system.     

Selective stimulation of orexin receptor type 2 promotes wakefulness in freely behaving rats

Orexins A and B are a pair of neuropeptides implicated in the regulation of feeding and arousal behavior mediated through two orexin receptors type 1 and type 2. We have determined the arousal effects of newly developed selective orexin receptor type 2 agonist, [Ala11]orexin-B, on the sleep-wake cycle in rats. The effects of third ventricle intracerebroventricular (ICV) infusion of the novel orexin receptor type 2 selective agonist, [Ala11]orexin-B, on the sleep-wake cycle were investigated. ICV infusion of [Ala11]orexin-B (1, 10 and 40 nmol) during the light period (11:00-16:00) dose-dependently resulted in a significant increase in wake duration by 46.9% (n = 5, P < 0.05), 159.2% (n = 4, P < 0.01) and 163.6% (n = 7, P < 0.01)), respectively, and a significant decrease in rapid eye movement (REM) (P < 0.01) and non-REM sleep (P < 0.01) for all doses. In contrast, ICV infusion of orexin B at the same doses (1, 10 and 40 nmol) caused a 16.6% (n = 6, non-significant), 99.8% (n = 6, P < 0.05) and 72.0% (n = 4, P < 0.05) increase in wakefulness, respectively. Moreover, orexin-A, which exerts its effects through orexin receptor type 1 and orexin receptor type 2 with similar potency, resulted in a significant increase in wakefulness duration by 17.1% (n = 6, P < 0.05), 184.0% (n = 6, P < 0.01) and 228.6% (n = 6, P < 0.01) at doses of 0.1, 1 and 10 nmol, respectively. Further, the enhancement of wakefulness was accompanied by a marked reduction in REM and non-REM sleep. These findings suggest that orexin receptor type 2 plays an important role in the modulation of sleep-wake state and behavioral responses.     

Effects on sleep and wakefulness of the injection of hypocretin-1 (orexin-A) into the laterodorsal tegmental nucleus of the cat

Anatomical data demonstrate a dense projection, in the cat, from hypocretin (orexin) neurons in the hypothalamus to the laterodorsal tegmental nucleus (LDT), which is a critical pontine site that is involved in the regulation of the behavioral states of sleep and wakefulness. The present study was therefore undertaken to explore the hypocretinergic control of neurons in the LDT vis-à-vis these behavioral states. Accordingly, hypocretin-1 was microinjected into the LDT of chronic, unanesthetized cats and its effects on the percentage, latency, frequency and duration of wakefulness, quiet (non-REM) sleep and active (REM) sleep were determined. There was a significant increase in the time spent in wakefulness following the microinjection of hypocretin-1 into the LDT and a significant decrease in the time spent in active sleep. The increase in the percentage of wakefulness was due to an increase in the duration of episodes of wakefulness; the reduction in active sleep was due to a decrease in the frequency of active sleep episodes, but not in their duration. These data indicate that hypocretinergic processes in the LDT play an important role in both of the promotion of wakefulness and the suppression of active sleep.     

Influence of sleep stage and wakefulness on spectral EEG activity and heart rate variations around periodic leg movements.

OBJECTIVE: Typical changes in spectral electroencephalographic (EEG) activity and heart rate (HR) have been described in periodic leg movements (PLM) associated with or without microarousals (MA). We aimed to determine the effects of sleep stage and wakefulness on these responses to ascertain whether a common pattern of EEG and HR activation takes place. METHODS: The time course of EEG spectral activity and HR variability associated with PLM was analysed in 13 patients during light NREM sleep, rapid-eye-movement (REM) sleep and wakefulness. The same analysis was also conducted for PLM without MA occurring in stage 2. RESULTS: A significant EEG and electrocardiogram (ECG) activation was found associated with PLM during sleep, but not during wakefulness. While in light NREM sleep, an increase in delta and theta bands was detected before the PLM onset, in REM sleep the EEG activation occurred simultaneously with the PLM onset. Moreover, during stage 1 and REM sleep, alpha and fast frequencies tended to remain sustained after the PLM onset. In contrast, during wakefulness, a small and not significant increase in cerebral activity was present, starting at the PLM onset and persisting in the post-movement period. A typical pattern of cardiac response was present during NREM and REM sleep, the autonomic activation being lesser and prolonged during wakefulness. CONCLUSIONS: We conclude that the EEG and HR responses to PLM differ between sleep stages and wakefulness with lesser changes found during wakefulness. SIGNIFICANCE: These findings suggest that specific sleep state-dependent mechanisms may underlie the occurrence of PLM.     

Hypothetical neurochemical mechanisms of paradoxical sleep deficiency in Alzheimer’s disease

Based on the known experimental data on the specific morphological and neurochemical changes in the neural circuits involved in the occurrence of paradoxical sleep (REM sleep) that are observed in Alzheimer’s disease (AD) and our analysis of the effects of neuromodulators on the functioning of these circuits we propose that REM sleep deficiency in AD is caused by the following mechanisms: (1) the activity of the lateral geniculate body and occipital cortex is not sufficient to generate the ponto-geniculo-occipital (PGO) waves that are specific for REM sleep due to lower activity of cholinergic cells of the pedunculopontine and laterodorsal tegmental nuclei (PPN and LDTN) and lower density of cholinergic receptors; (2) because of reduced activity of cholinergic neurons of the PPN and LDN on GABAergic interneurons projecting to noradrenergic and serotonergic cells, the activity of the latter cannot be completely inhibited, as should occur during REM sleep; (3) the concentration of melanin-concentrating hormone is not sufficient for sleep due to the decreased activity of cholinergic cells of the basal forebrain nucleus, which excite neurons that produce this hormone; and (4) the activity of histaminergic cells increases and the activity of neurons that release melanin-concentrating hormone decreases due to the increased orexin level. Our analysis shows that common use of drugs that increase the acetylcholine concentration in patients with AD may result in increased activity of orexinergic cells and this must prevent the occurrence of REM sleep. We hypothesize that microstimulation of PPN may improve the occurrence of REM sleep because it should decrease the activity of serotoninergic, noradrenergic, and histaminergic cells and promote the generation of PGO waves and hippocampal theta activity. This treatment may improve the conditions for memory consolidation in patients with AD. Such microstimulation should be applied at night according to a special protocol.     

Knockdown of orexin type 2 receptor in the lateral pontomesencephalic tegmentum of rats increases REM sleep

Dysfunction of the orexin/hypocretin neurotransmitter system causes the sleep disorder narcolepsy, characterized by intrusion of rapid eye movement (REM) sleep‐like events into normal wakefulness. The sites where orexins act to suppress REM sleep are incompletely understood. Previous studies suggested that the lateral pontomesencephalic tegmentum (lPMT) contains an important REM sleep inhibitory area, and proposed that orexins inhibit REM sleep via orexin type 2 receptors (OxR2) in this region. However, this hypothesis has heretofore not been tested. We thus performed bilateral injection of small interfering RNAs (siRNAs) targeting Ox2R into the lPMT on two consecutive days. This led to a approximately 30% increase of time spent in REM sleep in both the dark and light periods for the first 2 days after injection, with a return to baseline over the next two post‐injection days. This increase was mainly due to longer (> 120 s) REM episodes. Cataplexy‐like episodes were not observed. The percentage of time spent in wakefulness and non‐(N)REM sleep, as well as the power spectral profile of NREM and REM sleep, were unaffected. Control animals injected with scrambled siRNA had no sleep changes post‐injection. Quantification of the knockdown revealed that unilateral microinjection of siRNAs targeting OxR2 into the lPMT induced a approximately 40% reduction of OxR2 mRNA 2 days following the injections when compared with the contralateral side receiving control (scrambled) siRNA. Orexin type 1 receptor mRNA level was unaffected. Our results indicate that removal of OxR2 neurotransmission in the lPMT enhances REM sleep by increasing the duration of REM episodes.     

Sleep–waking discharge of neurons in the posterior lateral hypothalamus of the albino rat

The sleep–waking discharge patterns of neurons in the posterior lateral hypothalamus (PLH) were investigated in the rat. Previous studies in the cat demonstrated that this region contained neurons that fired tonically at low rates (2–4 Hz) during waking, decreased firing in non-rapid eye-movement (NREM) sleep and nearly ceased firing during rapid eye-movement (REM) sleep. These “REM-off” neurons were proposed to be histaminergic neurons of the tuberomammillary nucleus (TM). Since many anatomical and physiological studies are performed in the rat, we sought to examine the sleep–waking discharge of these neurons in this animal. We found three main types of discharge patterns among PLH neurons. Waking-related neurons decreased their discharge in NREM sleep, and remained at low rates during REM sleep. A subpopulation of these neurons discharged very little during REM sleep (<0.2 Hz) (REM-off neurons). Waking/REM-related neurons decreased their discharge in NREM sleep and returned to waking rates in REM sleep. REM-related neurons decreased their discharge in NREM sleep and increased their discharge during REM sleep higher than waking rates. No NREM-related discharge patterns were recorded. Waking-related and waking/REM-related neurons were similar in location within the PLH and action potential duration. Some REM-off and other waking-related neurons were recorded within the boundaries of the histaminergic TM, however, not all waking-related and REM-off neurons were found within this region. Furthermore, neurons with waking/REM-related and state-indifferent discharge patterns were localized within the TM. These results suggest that waking-related and/or REM-off neurons may not be exclusively histaminergic in rats.     

REM sleep changes in rats induced by siRNA-mediated orexin knockdown

Short interfering RNAs (siRNA) targeting prepro-orexin mRNA were microinjected into the rat perifornical hypothalamus. Prepro-orexin siRNA-treated rats had a significant (59%) reduction in prepro-orexin mRNA compared to scrambled siRNA-treated rats 2 days postinjection, whereas prodynorphin mRNA was unaffected. The number of orexin-A-positive neurons on the siRNA-treated side decreased significantly (23%) as compared to the contralateral control (scrambled siRNA-treated) side. Neither the colocalized dynorphin nor the neighbouring melanin-concentrating hormone neurons were affected. The number of orexin-A-positive neurons on the siRNA-treated side did not differ from the number on the control side 4 or 6 days postinjection. Behaviourally, there was a persistent (approximately 60%) increase in the amount of time spent in rapid eye movement (REM) sleep during the dark (active) period for 4 nights postinjection, in rats treated with prepro-orexin siRNA bilaterally. This increase occurred mainly because of an increased number of REM episodes and decrease in REM-to-REM interval. Cataplexy-like episodes were also observed in some of these animals. Wakefulness and NREM sleep were unaffected. The siRNA-induced increase in REM sleep during the dark cycle reverted to control values on the 5th day postinjection. In contrast, the scrambled siRNA-treated animals only had a transient increase in REM sleep for the first postinjection night. Our results indicate that siRNA can be usefully employed in behavioural studies to complement other loss-of-function approaches. Moreover, these data suggest that the orexin system plays a role in the diurnal gating of REM sleep.     

Sleep and treatment response in depression: new findings using power spectral analysis

This study examined quantitative measures of sleep electroencephalogram (EEG) and phasic rapid eye movements (REM) as correlates of remission and recovery in depressed patients. To address correlates of remission, pre-treatment EEG sleep studies were examined in 130 women outpatients with major depressive disorder treated with interpersonal psychotherapy (IPT). To address correlates of recovery, baseline and post-treatment EEG sleep studies were examined in 23 women who recovered with IPT alone and 23 women who recovered with IPT+fluoxetine. Outcomes included EEG power spectra during non-rapid eye movement (NREM) sleep and REM sleep and quantitative REMs. IPT non-remitters had increased phasic REM compared with remitters, but no significant differences in EEG power spectra. IPT+fluoxetine recoverers, but not IPT recoverers, showed increases in phasic REM and REM percentage from baseline to recovery. In NREM sleep, the IPT+fluoxetine group showed a decrease in alpha power from baseline to recovery, while the IPT group showed a slight increase. The number of REMs was a more robust correlate of remission and recovery than modeled quantitative EEG spectra during NREM or REM sleep. Quantitative REMs may provide a more direct measure of brainstem function and dysfunction during REM sleep than quantitative sleep EEG measures.     

Contribution of melanin-concentrating hormone (MCH1) receptor to thermoregulation and sleep stabilization: evidence from MCH1 (-/-) mice

Recent studies have explored the implication of melanin-concentrating hormone (MCH) in the process of vigilance states. The current experiments were carried out in mice lacking the MCH(1) receptor (-/-) and wild-type (WT) littermates, to assess the role of MCH(1) receptor in the regulation of sleep architecture, body temperature (BT) and locomotor activity (LMA) under normal condition and following a 1h restraint stress at lights onset. Under baseline conditions, MCH(1) (-/-) mice exhibited consistent changes in waking and sleeping time across the 24-h recording period. We found an increase in the amount of wakefulness (MCH(1) (-/-) 680.1 ± 15.3 min vs. WT, 601.9 ± 18.1, p<0.05) at the expense of total duration of non rapid eye movement (NREM) sleep (MCH(1) (-/-) 664.1 ± 13.9 min vs. WT 750.1 ± 18.5, p<0.05). Additionally, MCH(1) (-/-) mice had a higher mean basal body temperature (MCH(1) (-/-), 36.6 ± 0.1°C vs. WT, 36.0 ± 0.1°C, p<0.05), particularly during the light-resting period. Restraint stress resulted in an immediate increase in wakefulness with a concomitant reduction in NREM sleep and REM sleep in both genotypes, followed by a homeostatic rebound sleep. A concomitant long lasting increase in BT, independently of the behavioural state accompanied those changes in both genotypes. The elevated basal body temperature and reduction in NREM sleep time resulting from shorter NREM episode durations observed in MCH(1) (-/-) suggests that central MCH(1) receptor has a role in thermoregulation and presumably stabilization of NREM sleep.     

Sleep during neuromuscular blockade in cats

The purpose of the experiment was to determine whether normal sleep patterns can occur during neuromuscular blockade. Electrographic variables for determining the states of sleep and wakefulness, the electrocorticogram, lateral geniculate nucleus potentials, and dorsal hippocampal potentials, were recorded before, during and after the administration of gallamine triethiodide to cats with chronically implanted electrodes. When respiratory muscles became paralyzed, artificial ventilation commenced through a chronic tracheal fistula. The electrographic wave forms of the states (wakefulness, NREM sleep and REM sleep) in paralyzed cats were indistinquishable by visual observation from those of freely moving animals. As compared to freely moving cats, paralyzed cats had more wakefulness at the expense of both states of sleep (about 33% NREM and 3% REM compared to 45% NREM and 15% REM respectively). REM sleep wasdemonstrated to occur, albeit increase across repeated session in the same cats nor was the distribution uneven within the average session. Large percentages of REM sleep with respect to total recording time were associated with large percentages of NREM sleep (correlation coefficient = 0.58). The sequence of sleep states was like that of freely behaving animals. The main conclusion is that this preparation, depsite low amounts of REM sleep, is useful in neural studies of sleep and wakefulness.     

Orexin A attenuates the sleep-promoting effect of adenosine in the lateral hypothalamus of rats

Orexin neurons within the lateral hypothalamus play a crucial role in the promotion and maintenance of arousal. Studies have strongly suggested that orexin neurons are an important target in endogenous adenosine-regulated sleep homeostasis. Orexin A induces a robust increase in the firing activity of orexin neurons, while adenosine has an inhibitory effect. Whether the excitatory action of orexins in the lateral hypothalamus actually promotes wakefulness and reverses the sleep-producing effect of adenosine in vivo is less clear. In this study, electroencephalographic and electromyographic recordings were used to investigate the effects of orexin A and adenosine on sleep and wakefulness in rats. We found that microinjection of orexin A into the lateral hypothalamus increased wakefulness with a concomitant reduction of sleep during the first 3 h of post-injection recording, and this was completely blocked by a selective antagonist for orexin receptor 1, SB 334867. The enhancement of wakefulness also occurred after application of the excitatory neurotransmitter glutamate in the first 3 h post-injection. However, in the presence of the NMDA receptor antagonist APV, orexin A did not induce any change of sleep and wakefulness in the first 3 h. Further, exogenous application of adenosine into the lateral hypothalamus induced a marked increase of sleep in the first 3-h post-injection. No significant change in sleep and wakefulness was detected after adenosine application followed by orexin A administration into the same brain area. These findings suggest that the sleep-promoting action of adenosine can be reversed by orexin A applied to the lateral hypothalamus, perhaps by exciting glutamatergic input to orexin neurons via the action of orexin receptor 1.     

Sympathetic and cardiovascular changes during sleep in narcolepsy with cataplexy patients

ObjectiveNeural mechanisms underlying sleep-onset rapid eye movement (REM) periods (SOREMPs) in narcolepsy and the role of hypocretin in driving sympathetic changes during sleep are misunderstood. We aimed to characterize autonomic changes during sleep in narcolepsy with cataplexy (NC) patients to clarify the nature of SOREMP events and the effect of hypocretin deficiency on sympathetic activity during sleep.MethodsWe observed 13 hypocretin-deficient NC patients and five healthy controls who underwent nocturnal video-polysomnography (v-PSG) with blood pressure (BP) recording, heart rate (HR), skin sympathetic activity (SSA), and muscle sympathetic nerve activity (MSNA) from the peroneal nerve by microneurography.ResultsCompared to wake, control participants displayed a progressive significant decrease of BP and sympathetic activities during nonrapid eye movement (NREM) sleep and an increase of autonomic activity during REM sleep, as expected. NC patients showed: (1) a decrease of sympathetic activities during SOREMP comparable to NREM sleep stage 1 (N1) but in contrast to the increased activity typical of REM sleep; and (2) physiologic sympathetic change during the following sleep stages with a progressive decrease during NREM sleep stage 2 (N2) and NREM sleep stage 3 (N3) and a clear increase in REM sleep, though BP did not show the physiologic decrease during sleep (nondipper pattern).ConclusionsSOREMPs in NC patients lack the sympathetic activation occurring during physiologic REM sleep, thus suggesting a dissociated REM sleep condition. In addition, our data indicated that hypocretin plays a limited role in the regulation of sympathetic changes during sleep.     

Automated determination of wakefulness and sleep in rats based on non-invasively acquired measures of movement and respiratory activity

The current standard for monitoring sleep in rats requires labor intensive surgical procedures and the implantation of chronic electrodes which have the potential to impact behavior and sleep. With the goal of developing a non-invasive method to determine sleep and wakefulness, we constructed a non-contact monitoring system to measure movement and respiratory activity using signals acquired with pulse Doppler radar and from digitized video analysis. A set of 23 frequency and time-domain features were derived from these signals and were calculated in 10 s epochs. Based on these features, a classification method for automated scoring of wakefulness, non-rapid eye movement sleep (NREM) and REM in rats was developed using a support vector machine (SVM). We then assessed the utility of the automated scoring system in discriminating wakefulness and sleep by comparing the results to standard scoring of wakefulness and sleep based on concurrently recorded EEG and EMG. Agreement between SVM automated scoring based on selected features and visual scores based on EEG and EMG were approximately 91% for wakefulness, 84% for NREM and 70% for REM. The results indicate that automated scoring based on non-invasively acquired movement and respiratory activity will be useful for studies requiring discrimination of wakefulness and sleep. However, additional information or signals will be needed to improve discrimination of NREM and REM episodes within sleep.     

Locus Coeruleus Acid-Sensing Ion Channels Modulate Sleep–Wakefulness and State Transition from NREM to REM Sleep in the Rat

The locus coeruleus (LC) is one of the essential chemoregulatory and sleep–wake (S–W) modulating centers in the brain. LC neurons remain highly active during wakefulness, and some implicitly become silent during rapid eye movement (REM) sleep. LC neurons are also involved in CO₂-dependent modulation of the respiratory drive. Acid-sensing ion channels (ASICs) are highly expressed in some brainstem chemosensory breathing regulatory areas, but their localization and functions in the LC remain unknown. Mild hypercapnia increases the amount of non-REM (NREM) sleep and the number of REM sleep episodes, but whether ASICs in the LC modulate S–W is unclear. Here, we investigated the presence of ASICs in the LC and their role in S–W modulation and the state transition from NREM to REM sleep. Male Wistar rats were surgically prepared for chronic polysomnographic recordings and drug microinjections into the LC. The presence of ASIC-2 and ASIC-3 in the LC was immunohistochemically characterized. Microinjections of amiloride (an ASIC blocker) and APETx2 (a blocker of ASIC-2 and -3) into the LC significantly decreased wakefulness and REM sleep, but significantly increased NREM sleep. Mild hypercapnia increased the amount of NREM and the number of REM episodes. However, APETx2 microinjection inhibited this increase in REM frequency. These results suggest that the ASICs of LC neurons modulate S–W, indicating that ASICs could play an important role in vigilance-state transition. A mild increase in CO₂ level during NREM sleep sensed by ASICs could be one of the determinants of state transition from NREM to REM sleep.Supplementary InformationThe online version contains supplementary material available at 10.1007/s12264-020-00625-0.