Inhibition of nitric oxide synthesis inhibits rat sleep

Connecting the dots: An updated review of the role of autoimmunity in narcolepsy and emerging immunotherapeutic approaches

BACKGROUND

Narcolepsy type 1 (NT1) is a chronic disorder characterized by pathological daytime sleepiness and cataplexy due to the disappearance of orexin immunoreactive neurons in the hypothalamus. Genetic and environmental factors point towards a potential role for inflammation and autoimmunity in the pathogenesis of the disease. This study aims to comprehensively review the latest evidence on the autoinflammatory mechanisms and immunomodulatory treatments aimed at suspected autoimmune pathways in NT1.

METHODS

Recent relevant literature in the field of narcolepsy, its autoimmune hypothesis, and purposed immunomodulatory treatments were reviewed.

RESULTS

Narcolepsy is strongly linked to specific HLA alleles and T-cell receptor polymorphisms. Furthermore, animal studies and autopsies have found infiltration of T cells in the hypothalamus, supporting T cell-mediated immunity. However, the role of autoantibodies has yet to be definitively established. Increased risk of NT1 after H1N1 infection and vaccination supports the autoimmune hypothesis, and the potential role of coronavirus disease 2019 and vaccination in triggering autoimmune neurodegeneration is a recent finding. Alterations in cytokine levels, gut microbiota, and microglial activation indicate a potential role for inflammation in the disease's development. Reports of using immunotherapies in NT1 patients are limited and inconsistent. Early treatment with IVIg, corticosteroids, plasmapheresis, and monoclonal antibodies has seldomly shown some potential benefits in some studies.

CONCLUSION

The current body of literature supports that narcolepsy is an autoimmune disorder most likely caused by T-cell involvement. However, the potential for immunomodulatory treatments to reverse the autoinflammatory process remains understudied. Further clinical controlled trials may provide valuable insights into this area.

Urinary polycyclic aromatic hydrocarbon metabolites were associated with short sleep duration and self-reported trouble sleeping in US adults: data from NHANES 2005-2016 study population

Background

The aim of the current study was to investigate the link between human exposure to PAHs with short sleep duration (SSD) and self-reported trouble sleeping.

Methods

A total of 9,754 participants and 9,777 participants obtained from NHANES 2005-2016 were included in this cross-sectional study about SSD and self-reported trouble sleeping, respectively. The association between urinary PAHs metabolites with the prevalence of SSD and self-reported trouble sleeping by the weighted multivariate logistic regression model, restricted cubic spline (RCS) curves, and weighted quantile sum (WQS) regression.

Results

After adjusting for all covariates, 1-hydroxynapthalene, 2-hydroxynapthalene, 3-hydroxyfluorene, 2-hydroxyfluorene, 1-hydroxyphenanthrene, and 1-hydroxyphenanthrene demonstrated positive associations with SSD prevalence. Besides, 1-hydroxynapthalene, 2-hydroxynapthalene, 3-hydroxyfluorene, 2-hydroxyfluorene, 1-hydroxyphenanthrene, and 1-hydroxyphenanthrene exhibited positive associations with the prevalence of self-reported trouble sleeping following the adjustment for all covariates. RCS curves confirmed the non-linear associations between 1-hydroxynapthalene, 2-hydroxynapthalene, 3-hydroxyfluorene, 2-hydroxyfluorene, and 1-hydroxyphenanthrene with the prevalence of SSD, and 1-hydroxynapthalene, 3-hydroxyfluorene, and 2-hydroxyfluorene with the prevalence of self-reported trouble sleeping. The WQS results showed that mixed exposure to PAH metabolites had a significant positive association with the prevalence of SSD (OR: 1.087, 95% CI: 1.026, 1.152, p = 0.004) and self-reported trouble sleeping (OR: 1.190, 95% CI: 1.108, 1.278, p < 0.001).

Conclusion

Urinary concentrations of PAH metabolites exhibited a close association with the prevalence of SSD and self-reported trouble sleeping in US adults. More emphasis should be placed on the importance of environmental effects on sleep health.

Neuroinflammation, Sleep, and Circadian Rhythms

Molecules involved in innate immunity affect sleep and circadian oscillators and vice versa. Sleep-inducing inflammatory molecules are activated by increased waking activity and pathogens. Pathologies that alter inflammatory molecules, such as traumatic brain injury, cancer, cardiovascular disease, and stroke often are associated with disturbed sleep and electroencephalogram power spectra. Moreover, sleep disorders, such as insomnia and sleep disordered breathing, are associated with increased dysregulation of inflammatory processes. Inflammatory molecules in both the central nervous system and periphery can alter sleep. Inflammation can also modulate cerebral vascular hemodynamics which is associated with alterations in electroencephalogram power spectra. However, further research is needed to determine the interactions of sleep regulatory inflammatory molecules and circadian clocks. The purpose of this review is to: 1) describe the role of the inflammatory cytokines interleukin-1 beta and tumor necrosis factor-alpha and nucleotide-binding domain and leucine-rich repeat protein-3 inflammasomes in sleep regulation, 2) to discuss the relationship between the vagus nerve in translating inflammatory signals between the periphery and central nervous system to alter sleep, and 3) to present information about the relationship between cerebral vascular hemodynamics and the electroencephalogram during sleep.

Cellular Effects of Rhynchophylline and Relevance to Sleep Regulation

Uncaria rhynchophylla is a plant highly used in the traditional Chinese and Japanese medicines. It has numerous health benefits, which are often attributed to its alkaloid components. Recent studies in humans show that drugs containing Uncaria ameliorate sleep quality and increase sleep time, both in physiological and pathological conditions. Rhynchophylline (Rhy) is one of the principal alkaloids in Uncaria species. Although treatment with Rhy alone has not been tested in humans, observations in rodents show that Rhy increases sleep time. However, the mechanisms by which Rhy could modulate sleep have not been comprehensively described. In this review, we are highlighting cellular pathways that are shown to be targeted by Rhy and which are also known for their implications in the regulation of wakefulness and sleep. We conclude that Rhy can impact sleep through mechanisms involving ion channels, N-methyl-d-aspartate (NMDA) receptors, tyrosine kinase receptors, extracellular signal-regulated kinases (ERK)/mitogen-activated protein kinases (MAPK), phosphoinositide 3-kinase (PI3K)/RAC serine/threonine-protein kinase (AKT), and nuclear factor-kappa B (NF-κB) pathways. In modulating multiple cellular responses, Rhy impacts neuronal communication in a way that could have substantial effects on sleep phenotypes. Thus, understanding the mechanisms of action of Rhy will have implications for sleep pharmacology.

Targets and underlying mechanisms related to the sedative and hypnotic activities of saponin extracts from semen Ziziphus jujube

Semen Ziziphus jujube (SZJ) has been widely consumed because it is recognized as edible in China to treat insomnia disorders. However, the underlying mechanisms and potential therapeutic targets remain obscure. SZJ-I and SZJ-II with a saponin content of 52.10% and 75.20%, respectively, were extracted from SZJ. LC-MS analysis presented quite different chemical profiles of SZJ-I and SZJ-II. Mice with p-chlorophenylalanine (PCPA)-induced insomnia were used to comparatively and systematically test the sedative-hypnotic activities of SZJ-I and SZJ-II. In vivo behavioral tests revealed that SZJ-I and SZJ-II significantly shortened the immobility time and potentiated sodium pentobarbital-induced sleep. SZJ-II with a higher saponin content showed greater potency than SZJ-I. SZJ-I and SZJ-II also protected against PCPA-triggered neuropathological damages in the brain. Concentrations of 5-hydroxytryptamine (5-HT), dopamine (DA), noradrenaline (NE), glutamate (Glu), interleukin-6 (IL-6), interleukin-1β (IL-1β), nitric oxide (NO) and prostaglandin D₂ (PGD₂) in plasma were significantly affected by SZJ-I and SZJ-II application. SZJ-I and SZJ-II also exhibited differential modulation of 5-hydroxytryptamine 1A (5-HT_1A), 5-hydroxytryptamine 2A (5-HT_2A), GABA_A receptor α2 (GABA_ARα2), GABA_A receptor α3 (GABA_ARα3), glutamic acid decarboxylase (GAD) 65/67, IL-6 and IL-1β expression in the hypothalamus and hippocampus. SZJ-I and SZJ-II might exert excellent sedative-hypnotic effects through multiple mechanisms that worked simultaneously. SZJ-I and especially SZJ-II are promising candidates for relieving insomnia.

Role of the L-PGDS-PGD2-DP1 receptor axis in sleep regulation and neurologic outcomes

To meet the new challenges of modern lifestyles, we often compromise a good night's sleep. In preclinical models as well as in humans, a chronic lack of sleep is reported to be among the leading causes of various physiologic, psychologic, and neurocognitive deficits. Thus far, various endogenous mediators have been implicated in inter-regulatory networks that collectively influence the sleep-wake cycle. One such mediator is the lipocalin-type prostaglandin D2 synthase (L-PGDS)-Prostaglandin D2 (PGD2)-DP1 receptor (L-PGDS-PGD2-DP1R) axis. Findings in preclinical models confirm that DP1R are predominantly expressed in the sleep-regulating centers. This finding led to the discovery that the L-PGDS-PGD2-DP1R axis is involved in sleep regulation. Furthermore, we showed that the L-PGDS-PGD2-DP1R axis is beneficial in protecting the brain from ischemic stroke. Protein sequence homology was also performed, and it was found that L-PGDS and DP1R share a high degree of homology between humans and rodents. Based on the preclinical and clinical data thus far pertaining to the role of the L-PGDS-PGD2-DP1R axis in sleep regulation and neurologic conditions, there is optimism that this axis may have a high translational potential in human therapeutics. Therefore, here the focus is to review the regulation of the homeostatic component of the sleep process with a special focus on the L-PGDS-PGD2-DP1R axis and the consequences of sleep deprivation on health outcomes. Furthermore, we discuss whether the pharmacological regulation of this axis could represent a tool to prevent sleep disturbances and potentially improve outcomes, especially in patients with acute brain injuries.

Functions and Mechanisms of Sleep

Sleep is a complex physiological process that is regulated globally, regionally, and locally by both cellular and molecular mechanisms. It occurs to some extent in all animals, although sleep expression in lower animals may be co-extensive with rest. Sleep regulation plays an intrinsic part in many behavioral and physiological functions. Currently, all researchers agree there is no single physiological role sleep serves. Nevertheless, it is quite evident that sleep is essential for many vital functions including development, energy conservation, brain waste clearance, modulation of immune responses, cognition, performance, vigilance, disease, and psychological state. This review details the physiological processes involved in sleep regulation and the possible functions that sleep may serve. This description of the brain circuitry, cell types, and molecules involved in sleep regulation is intended to further the reader's understanding of the functions of sleep.

Sleep: a synchrony of cell activity-driven small network states

We posit a bottom-up sleep-regulatory paradigm in which state changes are initiated within small networks as a consequence of local cell activity. Bottom-up regulatory mechanisms are prevalent throughout nature, occurring in vastly different systems and levels of organization. Synchronization of state without top-down regulation is a fundamental property of large collections of small semi-autonomous entities. We posit that such synchronization mechanisms are sufficient and necessary for whole-organism sleep onset. Within the brain we posit that small networks of highly interconnected neurons and glia, for example cortical columns, are semi-autonomous units oscillating between sleep-like and wake-like states. We review evidence showing that cells, small networks and regional areas of the brain share sleep-like properties with whole-animal sleep. A testable hypothesis focused on how sleep is initiated within local networks is presented. We posit that the release of cell activity-dependent molecules, such as ATP and nitric oxide, into the extracellular space initiates state changes within the local networks where they are produced. We review mechanisms of ATP induction of sleep-regulatory substances and their actions on receptor trafficking. Finally, we provide an example of how such local metabolic and state changes provide mechanistic explanations for clinical conditions, such as insomnia.

Control of sleep and wakefulness

This review summarizes the brain mechanisms controlling sleep and wakefulness. Wakefulness promoting systems cause low-voltage, fast activity in the electroencephalogram (EEG). Multiple interacting neurotransmitter systems in the brain stem, hypothalamus, and basal forebrain converge onto common effector systems in the thalamus and cortex. Sleep results from the inhibition of wake-promoting systems by homeostatic sleep factors such as adenosine and nitric oxide and GABAergic neurons in the preoptic area of the hypothalamus, resulting in large-amplitude, slow EEG oscillations. Local, activity-dependent factors modulate the amplitude and frequency of cortical slow oscillations. Non-rapid-eye-movement (NREM) sleep results in conservation of brain energy and facilitates memory consolidation through the modulation of synaptic weights. Rapid-eye-movement (REM) sleep results from the interaction of brain stem cholinergic, aminergic, and GABAergic neurons which control the activity of glutamatergic reticular formation neurons leading to REM sleep phenomena such as muscle atonia, REMs, dreaming, and cortical activation. Strong activation of limbic regions during REM sleep suggests a role in regulation of emotion. Genetic studies suggest that brain mechanisms controlling waking and NREM sleep are strongly conserved throughout evolution, underscoring their enormous importance for brain function. Sleep disruption interferes with the normal restorative functions of NREM and REM sleep, resulting in disruptions of breathing and cardiovascular function, changes in emotional reactivity, and cognitive impairments in attention, memory, and decision making.

Refeeding after a 24-hour fasting deepens NREM sleep in a time-dependent manner

Sleep/wake cycle is regulated by a variety of neuropeptides in the hypothalamus, a brain region that also regulates energy homeostasis and feeding behavior. Since circadian rhythms are affected by energy metabolism and feeding condition, we investigated whether changes in feeding regimen would influence sleep/wake parameters and body temperature. We monitored sleep and body temperature across three days of baseline (day 1), fasting (day 2), and refeeding (day 3) conditions under ordinary ambient temperature and employed different refeeding schedules. Refeeding at ZT1 following the 24-h fasting enhanced EEG delta power in NREM sleep. However, when the time of refeeding was set at either ZT7 or ZT12, the enhancement of EEG delta power was attenuated. The amount of NREM sleep was not largely affected by a 24-h fasting started at ZT1, although fasting that started at ZT12 changed the temporal distribution of NREM sleep. Hypothalamic nNOS mRNA level was increased both before and after refeeding at ZT1 compared with control condition, while there was no significant change in mice refed at ZT7. Level of NPY mRNA in the arcuate nucleus was increased before the refeeding only at ZT1. These results suggest that refeeding after a 24-h fasting makes NREM sleep deeper in a time-dependent manner.

The time course of adenosine, nitric oxide (NO) and inducible NO synthase changes in the brain with sleep loss and their role in the non-rapid eye movement sleep homeostatic cascade

Both adenosine and nitric oxide (NO) are known for their role in sleep homeostasis, with the basal forebrain (BF) wakefulness center as an important site of action. Previously, we reported a cascade of homeostatic events, wherein sleep deprivation (SD) induces the production of inducible nitric oxide synthase (iNOS)-dependent NO in BF, leading to enhanced release of extracellular adenosine. In turn, increased BF adenosine leads to enhanced sleep intensity, as measured by increased non-rapid eye movement sleep EEG delta activity. However, the presence and time course of similar events in cortex has not been studied, although a frontal cortical role for the increase in non-rapid eye movement recovery sleep EEG delta power is known. Accordingly, we performed simultaneous hourly microdialysis sample collection from BF and frontal cortex (FC) during 11 h SD. We observed that both areas showed sequential increases in iNOS and NO, followed by increases in adenosine. BF increases began at 1 h SD, whereas FC increases began at 5 h SD. iNOS and Fos-double labeling indicated that iNOS induction occurred in BF and FC wake-active neurons. These data support the role of BF adenosine and NO in sleep homeostasis and indicate the temporal and spatial sequence of sleep homeostatic cascade for NO and adenosine.

Activation of cortical interneurons during sleep: an anatomical link to homeostatic sleep regulation?

Although slow wave activity in the EEG has been linked to homeostatic sleep regulation, the neurobiological substrate of sleep homeostasis is not well understood. Whereas cortical neurons typically exhibit reduced discharge rates during slow wave sleep (SWS), a subpopulation of GABAergic interneurons, which express the enzyme neuronal nitric oxide synthase (nNOS), has recently been found to be activated during SWS. The extent of activation of these nNOS neurons is proportional to homeostatic sleep 'drive'. These cells are an exception among cortical interneurons in that they are projection neurons. We propose that cortical nNOS neurons are positioned to influence neuronal activity across widespread brain areas. They could thus provide a long-sought anatomical link for understanding homeostatic sleep regulation.

Sleep deprivation triggers inducible nitric oxide-dependent nitric oxide production in wake-active basal forebrain neurons

Sleep loss negatively impacts performance, mood, memory, and immune function, but the homeostatic factors that impel sleep after sleep loss are imperfectly understood. Pharmacological studies had implicated the basal forebrain (BF) inducible nitric oxide (NO) synthase (iNOS)-dependent NO as a key homeostatic factor, but its cellular source was obscure. To obtain direct evidence about the cellular source of iNOS-generated NO during sleep deprivation (SD), we used intracerebroventricular perfusion in rats of the cell membrane-permeable dye diaminofluorescein-2/diacetate (DAF-2/DA) that, once intracellular, bound NO and fluoresced. To circumvent the effects of neuronal NOS (nNOS), DAF-2/DA was perfused in the presence of an nNOS inhibitor. SD led to DAF-positive fluorescence only in the BF neurons, not glia. SD increased expression of iNOS, which colocalized with NO in neurons and, more specifically, in prolonged wakefulness-active neurons labeled by Fos. SD-induced iNOS expression in wakefulness-active neurons positively correlated with sleep pressure, as measured by the number of attempts to enter sleep. Importantly, SD did not induce Fos or iNOS in stress-responsive central amygdala and paraventricular hypothalamic neurons, nor did SD elevate corticosterone, suggesting that the SD protocol did not provoke iNOS expression through stress. We conclude that iNOS-produced neuronal NO is an important homeostatic factor promoting recovery sleep after SD.

Further characterization of sleep-active neuronal nitric oxide synthase neurons in the mouse brain

We recently demonstrated that Fos is induced in a subpopulation of cortical neuronal nitric oxide synthase (nNOS)-immunoreactive neurons in three rodent species both during spontaneous sleep (SS) and recovery sleep (RS) after a period of sleep deprivation (SD); the proportion of cortical Fos(+)/nNOS neurons was significantly correlated with non-REM (NREM) sleep delta energy. The present study was undertaken to evaluate the specificity of this state-dependent activation of cortical nNOS cells. The percentage of nNOS neurons that expressed Fos during SD and RS was determined in nine subcortical brain regions and the cortex of the mouse brain; a significantly greater proportion of Fos(+)/nNOS neurons was observed during RS only in the cortex and in none of the nine subcortical regions. The proportion of calretinin-, calbindin- and parvalbumin-immunoreactive cortical interneurons that expressed Fos during SD and RS was also determined. In contrast to cortical nNOS neurons, a higher percentage of Fos(+)/calbindin neurons was found during SD than RS; there were no differences in the proportions of Fos-expressing parvalbumin or calretinin neurons between these conditions. Since the nNOS and calretinin cortical interneuron populations overlap extensively in the mouse brain, triple-labeling with these two phenotypic markers and Fos was undertaken in mice from the RS group to determine which combination of markers could best identify the rare "sleep-active" cortical interneuron population. The proportions of both Fos(+)/nNOS neurons and Fos(+)/nNOS/calretinin neurons far exceeded the proportion of Fos(+)/calretinin neurons during RS, but the proportions of these two cell types were not significantly different during RS. Thus, functional activation of nNOS neurons during sleep appears to be restricted to the cerebral cortex and cortical nNOS cells and nNOS/calretinin cells collectively define a cortical interneuron population that is activated during sleep.

cGMP-dependent protein kinase type I is implicated in the regulation of the timing and quality of sleep and wakefulness

Many effects of nitric oxide (NO) are mediated by the activation of guanylyl cyclases and subsequent production of the second messenger cyclic guanosine-3′,5′-monophosphate (cGMP). cGMP activates cGMP-dependent protein kinases (PRKGs), which can therefore be considered downstream effectors of NO signaling. Since NO is thought to be involved in the regulation of both sleep and circadian rhythms, we analyzed these two processes in mice deficient for cGMP-dependent protein kinase type I (PRKG1) in the brain. Prkg1 mutant mice showed a strikingly altered distribution of sleep and wakefulness over the 24 hours of a day as well as reductions in rapid-eye-movement sleep (REMS) duration and in non-REM sleep (NREMS) consolidation, and their ability to sustain waking episodes was compromised. Furthermore, they displayed a drastic decrease in electroencephalogram (EEG) power in the delta frequency range (1–4 Hz) under baseline conditions, which could be normalized after sleep deprivation. In line with the re-distribution of sleep and wakefulness, the analysis of wheel-running and drinking activity revealed more rest bouts during the activity phase and a higher percentage of daytime activity in mutant animals. No changes were observed in internal period length and phase-shifting properties of the circadian clock while chi-squared periodogram amplitude was significantly reduced, hinting at a less robust oscillator. These results indicate that PRKG1 might be involved in the stabilization and output strength of the circadian oscillator in mice. Moreover, PRKG1 deficiency results in an aberrant pattern, and consequently a reduced quality, of sleep and wakefulness, possibly due to a decreased wake-promoting output of the circadian system impinging upon sleep.

Sleep as a fundamental property of neuronal assemblies

Sleep is vital to cognitive performance, productivity, health and well-being. Earlier theories of sleep presumed that it occurred at the level of the whole organism and that it was governed by central control mechanisms. However, evidence now indicates that sleep might be regulated at a more local level in the brain: it seems to be a fundamental property of neuronal networks and is dependent on prior activity in each network. Such local-network sleep might be initiated by metabolically driven changes in the production of sleep-regulatory substances. We discuss a mathematical model which illustrates that the sleep-like states of individual cortical columns can be synchronized through humoral and electrical connections, and that whole-organism sleep occurs as an emergent property of local-network interactions.

Nitric oxide modulates the discharge rate of basal forebrain neurons

RATIONALE

During prolonged wakefulness, the concentrations of nitric oxide (NO) and adenosine (AD) increase in the basal forebrain (BF). AD inhibits neuronal activity via adenosine (A1) receptors, thus providing a potential mechanism for sleep facilitation. Although NO in the BF increases adenosine and promotes sleep, it is not clear whether the sleep promotion by NO is mediated through adenosine increase, or NO independently of adenosine could modulate sleep.

OBJECTIVE

The objective of the study was to clarify whether NO modulates the discharge rate of BF neurons and whether this effect is mediated via AD.

MATERIALS AND METHODS

We measured the discharge rates of BF neurons in anesthetized rats during microdialysis infusion of NO donor alone or in combination with A1 receptor antagonist, 8-cyclopentyl-1,3-dimethylxanthine.

RESULTS

NO dose dependently modulated the discharge rate of BF neurons. NO donor (0.5 mM) increased the discharge rates in 48% of neurons and decreased it in 22%. A 1-mM dose decreased it in 55% and increased in 18%. Tactile stimulus affected the discharge rates of most neurons: 60% increased (stimulus-on) it and 14% decreased it (stimulus-off). A 1-mM NO donor predominantly inhibited neurons of both stimulus related types. A small proportion of stimulus-on (23%) neurons but none of the stimulus-off neurons were activated by NO donor. The blockade of A1 receptors partly prevented the inhibitory effect of NO on most of the neurons. This response was more prominent in stimulus-on than in stimulus-off neurons.

CONCLUSION

NO modulates the BF neuronal discharge rates in a dose-dependent manner. The inhibitory effect is partly mediated via adenosine A1 receptors.

A role of nitric oxide mechanism involved in the protective effects of venlafaxine in sleep deprivation

The present study was designed to explore the possible nitric oxide mechanism in protective effect of venlafaxine in sleep deprivation in mice. Laca mice were sleep deprived for period of 72 h using grid suspended over water method. Venlafaxine (2.5, 5 and 10mg/kg, ip), l-arginine (50mg/kg, ip), l-NAME (10mg/kg, ip) and methylene blue (10mg/kg, ip) were administered for 5 days, starting 2 days before 72-h sleep deprivation. Various behavioral tests (plus maze, zero maze, mirror chamber tests for anxiety, and actophotometer test) followed by oxidative stress parameters (malondialdehyde level, glutathione, catalase, nitrite and protein) were assessed. The present study showed that venlafaxine (5 and 10mg/kg, ip) drug treatment significantly reversed 72-h sleep deprivation caused anxiety like behavior, impairment in locomotor activity and oxidative damage (increased lipid peroxidation and nitrite levels and depleted reduced glutathione and catalase activity) as compared to control. l-NAME (10mg/kg) and methylene blue (10mg/kg) pretreatment with lower dose of venlafaxine (5mg/kg) potentiated the protective effect of venlafaxine (5mg/kg). However, l-arginine (50mg/kg) pretreatment with venlafaxine (5mg/kg) reversed the protective effect of venlafaxine. Results of present study suggest that nitric oxide mechanism is involved in the protective effect of venlafaxine against sleep-deprivation-induced behavior alteration and oxidative damage in mice.

Effects of ibotenate and 192IgG-saporin lesions of the nucleus basalis magnocellularis/substantia innominata on spontaneous sleep and wake states and on recovery sleep after sleep deprivation in rats

The basal forebrain (BF) is known for its role in cortical and behavioral activation, and has been postulated to have a role in compensatory mechanisms after sleep loss. However, specific neuronal phenotypes responsible for these roles are unclear. We investigated the effects of ibotenate (IBO) and 192IgG-saporin (SAP) lesions of the caudal BF on spontaneous sleep-waking and electroencephalogram (EEG), and recovery sleep and EEG after 6 h of sleep deprivation (SD). Relative to artificial CSF (ACSF) controls, IBO injections decreased parvalbumin and cholinergic neurons in the caudal BF by 43 and 21%, respectively, and cortical acetylcholinesterase staining by 41%. SAP injections nonsignificantly decreased parvalbumin neurons by 11%, but significantly decreased cholinergic neurons by 69% and cortical acetylcholinesterase by 84%. IBO lesions had no effect on sleep-wake states but increased baseline delta power in all states [up to 62% increase during non-rapid eye movement (NREM) sleep]. SAP lesions transiently increased NREM sleep by 13%, predominantly during the dark phase, with no effect on EEG. During the first 12 h after SD, animals with IBO and SAP lesions showed lesser rebound NREM sleep (32 and 77% less, respectively) and delta power (78 and 53% less) relative to ACSF controls. These results suggest that noncholinergic BF neurons promote cortical activation by inhibiting delta waves, whereas cholinergic BF neurons play a nonexclusive role in promoting wake. Intriguingly, these results also suggest that both types of BF neurons play important roles, probably through different mechanisms, in increased NREM sleep and EEG delta power after sleep loss.

Baseline temperature in an animal model of schizophrenia: long-term effects of perinatal phencyclidine administration

Phencyclidine (PCP), a dissociative anaesthetic, acts as a noncompetitive N-methyl-d-aspartate (NMDA) receptor antagonist. PCP is a psychostimulant capable of producing both positive and negative symptoms of schizophrenia, including cognitive dysfunction in normal humans. Perinatal phencyclidine administration to rats has been widely accepted as an animal model of schizophrenia. It has been known for a long time that schizophrenia patients may develop various thermoregulatory disturbances. The aim of this study was to assess the acute effects of phencyclidine administration on the temperature of newborn rats, the long-term effects on the baseline temperature of perinatal phencyclidine administration and the effects of a PCP challenge on the temperature of adult perinatally treated rats. The animals were treated on the 2nd, 6th, 9th and 12th postnatal (PN) days with either phencyclidine (10 mg/kg) or saline. The interscapular skin temperature was measured during the first 40 postnatal days and subsequently the colonic temperature until PN day 62. The immediate effect of phencyclidine administration to pups was a significant decrease of the body temperature, while the application of PCP to adult rats perinatally treated with either saline or PCP caused a significant increase of the baseline temperature. Perinatal phencyclidine administration to rat pups produced a long lasting effect on the baseline temperature. It can be concluded that the nature of the response to acute phencyclidine administration differs between newborn and adult rats. Further experiments are necessary in order to clarify the role of specific neurotransmitter systems in the changes of temperature regulation provoked by phencyclidine administration.

Nitric oxide-induced adenosine inhibition of hippocampal synaptic transmission depends on adenosine kinase inhibition and is cyclic GMP independent

Adenosine is an important inhibitory neuromodulator that regulates neuronal excitability. Several studies have shown that nitric oxide induces release of adenosine. Here we investigated the mechanism of this release. We studied the effects of nitric oxide on evoked field excitatory postsynaptic potentials (fEPSPs) recorded in the CA1 area of rat hippocampal slices. The nitric oxide donor 1,1-diethyl-2-hydroxy-2-nitroso-hydrazine sodium (DEA/NO; 100 microm) depressed the fEPSP by 77.6 +/- 4.1%. This effect was abolished by the adenosine A1 antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX; 400 nm), indicating that the nitric oxide effect was mediated by adenosine accumulation. The DEA/NO effect was unaltered by the 5'-ectonucleotidase inhibitor alpha,beta-methylene-adenosine 5'-diphosphate (AMP-CP; 100 microm), indicating that extracellular adenosine did not derive from ATP or cAMP release. The guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazole[4,3-a]quinoxaline-1-one (ODQ; 5 microm) did not affect nitric oxide depression of the fEPSPs, indicating that nitric oxide-mediated adenosine release was not mediated through a cGMP signaling cascade. This conclusion was confirmed by the observation that 8-(4-chlorophenylthio)-guanosine-3',5'-cyclic monophosphate (8-pCPT-cGMP; 1 mm) reversibly depressed the fEPSP by 24.9 +/- 4.5%, but this effect was not blocked by adenosine antagonists. Adenosine kinase inhibitor 5-iodotubercidin (ITU; 7 microm) occluded the nitric oxide effects by 74%, suggesting that inhibition of adenosine kinase activity contributes to adenosine release. In conclusion, exogenous nitric oxide evokes adenosine release by a cGMP-independent pathway. Intracellular cGMP elevation partially inhibits the fEPSP but not through adenosine release. Although a direct block of adenosine kinase by nitric oxide can not be excluded, the depression of adenosine kinase activity may be due to inhibition by its own substrate adenosine.

Nitric oxide production in the basal forebrain is required for recovery sleep

Sleep homeostasis is the process by which recovery sleep is generated by prolonged wakefulness. The molecular mechanisms underlying this important phenomenon are poorly understood. Here, we assessed the role of the intercellular gaseous signaling agent NO in sleep homeostasis. We measured the concentration of nitrite and nitrate, indicative of NO production, in the basal forebrain (BF) of rats during sleep deprivation (SD), and found the level increased by 100 +/- 51%. To test whether an increase in NO production might play a causal role in recovery sleep, we administered compounds into the BF that increase or decrease concentrations of NO. Infusion of either a NO scavenger, 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, or a NO synthase inhibitor, N(omega)-nitro-L-arginine methyl ester (L-NAME), completely abolished non-rapid eye movement (NREM) recovery sleep. Infusion of a NO donor, (Z)-1-[N-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2diolate (DETA/NO), produced an increase in NREM that closely resembled NREM recovery after prolonged wakefulness. The effects of inhibition of NO synthesis and the pharmacological induction of sleep were effective only in the BF area. Indicators of energy metabolism, adenosine, lactate and pyruvate increased during prolonged wakefulness and DETA/NO infusion, whereas L-NAME infusion during SD prevented the increases. We conclude that an increase in NO production in the BF is a causal event in the induction of recovery sleep.

Platelet activating factor and its metabolite promote sleep in rabbits

Platelet activating factor (PAF) is a key inflammatory mediator. PAF and its receptor are found in brain and PAF affects or is affected by the production of sleep promoting cytokines such as interleukin-1. PAF also interacts with several other sleep-regulatory substances such as nerve growth factor, brain-derived neurotrophic factor, neurotrophin-3, nitric oxide, prostaglandins, and prolactin. We thus hypothesized that PAF would increase sleep. In these experiments, each rabbit received an injection of 25 microl of 2% DMSO to obtain control values, and on a separate day received PAF or lyso-PAF, a metabolite of PAF. Ten, 100 and 500 nmol for each substance was injected intracerebroventricularly. Both PAF and lyso-PAF enhanced non-rapid eye movement (NREM) sleep but not REM sleep. Lyso-PAF, but not PAF, induced hyperthermia. Results are consistent with the hypothesis that the brain cytokine network is involved in physiological sleep regulation.

Evidence that brain nitric oxide inhibition increases metabolic cost of exercise, reducing running performance in rats

To assess the role of nitric oxide (NO) in the metabolic rate and running performance of rats submitted to exercise on a treadmill, 1.43 micromol (2 microL) of Nomega-nitro-L-arginine methyl ester (L-NAME, n=6), a NO synthase inhibitor, or 2 microL of 0.15M NaCl (SAL, n=6) was injected into the lateral cerebral ventricle of male Wistar rats immediately before the animals started running (18m min(-1), 5% inclination). Oxygen consumption (VO2) was measured at rest, during the exercise until fatigue and thereafter during the 30 min of recovery using the indirect calorimetry system. Mechanical efficiency (ME) was also calculated during the running period. During the first 11 min of exercise, there was a similar increase in VO2 while ME remained the same in both groups. Thereafter, VO2 remained stable in the SAL group but continued to increase and remained higher in the L-NAME group until fatigue. The L-NAME-treated rats also showed a sharper decrease in ME than controls. In addition, there was a significant reduction in workload performance by L-NAME-treated animals compared to SAL-treated animals. This suggests that central blockage of nitric oxide increases metabolic cost during exercise, reduces mechanical efficiency and decreases running performance in rats.

Effects of selective neuronal nitric oxide synthase inhibition on sleep and wakefulness in the rat

The role played by the unconventional messenger Nitric Oxide (NO) upon the sleep-wake cycle remains controversial. Evidence suggests a positive role of NO on Slow Wave Sleep (SWS) and Paradoxical Sleep (PS) regulation, favoring sleep. However, other studies have found a role of NO upon wakefulness and alertness, inhibiting sleep. Divergences have been explained in part because of the use of different inhibitors of nitric oxide synthases (NOS). The aim of this study is to analyse the effects of a highly selective neuronal NOS inhibitor (3-Bromo7-Nitroindazole) on sleep-wake states in rats. Male Wistar rats were stereotaxically prepared for polysomnography. 3-Bromo-7-Nitroindazole (10, 20, 40 mg/kg, i.p.) dissolved in DMSO 10% filled with saline, or vehicle (DMSO 10% in saline) was administered at the beginning of the light period. Three hours of polygraphic recordings were evaluated for stages of vigilance. Results show dose-dependent effects of 3-Bromo7-Nitroindazole upon sleep: 10 mg/kg decreases duration and number of episodes of deep SWS, increasing duration of light SWS. 20 mg/kg decreased duration of light and deep SWS, while active and quiet wake increased. Deep SWS and PS latency increased. Number of episodes of PS decreased, as well as number of cycles of sleep and time spent asleep. 40 mg/kg reduced duration of deep SWS and increased mean episode duration of light SWS. Therefore, sleep states are affected by selective inhibition of nNOS, reducing in all cases deep SWS. These results support the hypothesis that nitric oxide, produced by nNOS, is involved in sleep processes, favoring sleep.

Nitric oxide and its modulators in chronic constriction injury-induced neuropathic pain in rats

This study was conducted to examine the role of nitric oxide (NO) in peripheral neuropathy induced by chronic constriction injury of sciatic nerve of rats by using NO precursor, NO donors and nitric oxide synthase (NOS) inhibitors. Chronic constriction injury of sciatic nerve of rats resulted in peripheral neuropathy as confirmed by nociceptive behavioural tests using mechanical, thermal and cold allodynia. NO precursor, L-arginine and NO donors sodium nitroprusside, S-nitroso-N-acetylpenicillamine potentiated the hyperalgesia and allodynia significantly suggesting proalgesic effect in neuropathic rats. Intracerebroventricular (i.c.v.) administration of rats with NOS inhibitors such as L-N(G)-nitroarginine methyl ester, N-iminoethyl lysine and 7-nitroindazole did not show any effect but i.p. administration of NOS inhibitors aminoguanidine, L-N(G)-nitroarginine methyl ester and 7-nitroindazole caused alleviation of pain. The study confirms the involvement of endogenously synthesized and exogenously administered NO in chronic constriction injury-induced neuropathy in rats. Significant increase in the levels of nitrate and nitrite in ligated sciatic nerve suggest that local up regulation of NO in the production and maintenance of neuropathic pain. In conclusion, initial attempt to manipulate L-arginine: NO pathway is indicative of therapeutic potential of these interventions in the management of neuropathic pain.

The effects of intracerebroventricular application of 8-Br-cGMP and LY-83,583, a guanylyl cyclase inhibitor, on sleep-wake activity in rats

Cyclic GMP is the second messenger that mediates most of the neuronal effects of nitric oxide (NO). Several lines of evidence suggest that NO-ergic mechanisms play an integral role in the regulation of vigilance. In the present study, we tested the effects of the activation of cGMP-receptive mechanisms and the inhibitor of guanylyl cyclase (GC), LY-83,583, on sleep in rats. Rats were injected intracerebroventricularly (icv) with 0.16, 4, 100, and 500 microg or 2.5 mg 8-Br-cGMP, a membrane-permeable analogue of cGMP, or 1 and 100 microg LY-83,583. Administration of 4 microg-2.5 mg 8-Br-cGMP increased wakefulness and suppressed rapid-eye-movement sleep (REMS) and non-REMS (NREMS) in rats when given before dark onset but not when given before the light period. The GC inhibitor LY-83,583 strongly promoted NREMS and suppressed REMS during the light period of the day. Furthermore, LY-83,583 induced striking increases in the delta-wave activity of the electroencephalogram (EEG) during NREMS, whereas EEG activity above the 4.5 Hz wave range was suppressed in all vigilance states. Our finding that cGMP has an arousal-promoting activity is in line with the hypothesis that NO/cGMP signaling pathway is involved in the regulation of vigilance.

REM sleep control during aging in SAM mice: a role for inducible nitric oxide synthase

Evidence that nitric oxide (NO) is involved in the regulation of rapid-eye-movement sleep (REMS) is supported by recent studies. During aging, NO generation encounters marked changes mainly related to the activation of the inducible NO-synthase (iNOS). To investigate links existing between iNOS and REMS impairments related to aging, we examine the age-related variations occurring in: mRNA and activity of iNOS in brainstem and frontal cortex; sleep parameters under baseline and after treatment by a selective iNOS inhibitor (AMT) in Senescence Accelerated Mice (SAM). SAMR1 (control) mice are a model of aging while SAMP8 are adequate to study neurodegenerative processes. RT-PCR analysis does not reveal significant variation in iNOS mRNA expression in both strains. However, significant age-related increases in iNOS activity occur in SAMR1 but such variation is not observed in SAMP8. In baseline conditions, aging induces a slight increase in slow-wave sleep (SWS) amounts in both groups and deteriorates greatly REMS architecture in SAMP8 compared to SAMR1. AMT reduces REMS amounts for 4-6h after treatment in a dose and age-dependent manner in SAMR1. Almost no changes occur in SAMP8. Data reported suggest that NO derived from iNOS contributes to trigger and maintain REMS during aging.

Nitric oxide pathway is an important modulator of heat loss in rats during exercise

To assess the role of nitric oxide (NO) in central thermoregulatory mechanisms during exercise, 1.43 micromol (2 microL) of N(omega)-nitro-L-arginine methyl ester (L-NAME, n=6), a NO synthase inhibitor, or 2 microL of 0.15M NaCl (SAL, n=6) was injected into the lateral cerebral ventricle of male Wistar rats immediately before the animals started running (18 m min(-1), 5% inclination). Core (Tb) and skin tail (Ttail) temperatures were measured. Body heating rate (BHR), threshold Tb for tail vasodilation (TTbV), and workload (W) were calculated. During the first 11 min of exercise, there was a greater increase in Tb in the L-NAME group than in the SAL group (BRH=0.17+/-0.02 degrees C min(-1), L-NAME, versus 0.09+/-0.01 degrees C min(-1), SAL, p<0.05). Following the first 11 min until approximately 40 min of exercise, Tb levels remained stable in both groups, but levels remained higher in the L-NAME group than in the SAL group (39.16+/-0.04 degrees C, L-NAME, versus 38.33+/-0.02 degrees C, SAL, p<0.01). However, exercise went on to induce an additional rise in Tb in the SAL group prior to fatigue. These results suggest that the reduced W observed in L-NAME-treated rats (10.8+/-2.0 kg m, L-NAME, versus 25.0+/-2.1 kg m, SAL, p<0.01) was related to the increased BHR in L-NAME-treated animals observed during the first 11 min of exercise (r=0.74, p<0.01) due to the change in TTbV (39.12+/-0.24 degrees C, L-NAME, versus 38.27+/-0.10 degrees C, SAL, p<0.05). Finally, our data suggest that the central nitric oxide pathway modulates mechanisms of heat dissipation during exercise through an inhibitory mechanism.

Day- and nighttime injection of a nitric oxide synthase inhibitor elicits opposite sleep responses in rats

Previous studies suggest that nitric oxide (NO) may play a role in sleep regulation, particularly in the homeostatic process. The present studies were undertaken to compare the sleep effects of injecting a NO synthase (NOS) inhibitor when homeostatic sleep pressure is naturally highest (light onset) or when it is at its nadir (dark onset) in rats. Sleep, electroencephalogram delta-wave activity during nonrapid eye movement sleep (NREMS), also known as slow-wave activity (SWA), and brain temperature responses to three doses of the NOS inhibitor Nω-nitro-l-arginine methyl ester (l-NAME; 5, 50, and 100 mg/kg) injected intraperitoneally at light or dark onset were examined in rats ( n = 6 to 8). The effects of 5 mg/kg l-NAME were determined in both normal and vagotomized (VX) rats. Light onset administration of 50 mg/kg l-NAME decreased NREMS amounts and suppressed SWA and increased rapid eye movement sleep (REMS) amounts. At dark onset, l-NAME injection also dose dependently suppressed SWA; however, unlike light onset injections, both NREMS and REMS amounts were increased after all three doses. Sleep responses to 5 mg/kg l-NAME were not different in control and VX rats, suggesting that the sleep effects of l-NAME are not mediated through the activation of sensory vagal mechanisms. The present findings suggest that timing of the injection is a major determinant of the sleep responses observed after systemic l-NAME injection in rats.

Nitric oxide and sleep

Nitric oxide (NO) is a biological messenger synthesized by three main isoforms of NO synthase (NOS): neuronal (nNOS, constitutive calcium dependent), endothelial (eNOS, constitutive, calcium dependent) and inducible (iNOS, calcium independent). NOS is distributed in the brain either in circumscribed neuronal sets or in sparse interneurons. Within the laterodorsal tegmentum (LDT), pedunculopontine tegmentum and dorsal raphe nucleus, NOS-containing neurons overlap neurons grouped according to their contribution to sleep mechanisms. The main target for NO is the soluble guanylate cyclase that triggers an overproduction of cyclic guanosine monophosphate. NO in neurons of the pontine tegmentum facilitates sleep (particularly rapid-eye-movement sleep), and NO contained within the LDT intervenes in modulating the discharge of the neurons through an auto-inhibitory process involving the co-synthesized neurotransmitters. Moreover, NO synthesized within cholinergic neurons of the basal forebrain, while under control of the LDT, may modulate the spectral components of the EEG instead of the amounts of different sleep states. Finally, impairment of NO production (e.g. neurodegeneration, iNOS induction) has identifiable effects, including ageing, neuropathologies and parasitaemia.

Potential role of inducible nitric oxide synthase in the sleep–wake states occurrence in old rats

Extensive evidences now suggest that an association between inducible nitric oxide synthase and oxidative stress takes place during aging. Since the part played by inducible nitric oxide synthase in the sleep impairments associated with aging still remains unexplored, we compared its involvement in old rats (20-24 months) versus adult ones (3-5 months) using polygraphic, biochemical, voltammetric and immunohistochemical techniques. The experiments were conducted either in basal condition or after a systemic injection of selected inducible nitric oxide synthase inhibitors. We found that 2-amino-5,6-dihydro-6-methyl-4H-1,3-thiazine (10 mg/kg, i.p.) or aminoguanidine (400 mg/kg, i.p.) was capable to suppress rapid-eye-movement sleep and induce a delayed enhancement in slow-wave sleep in old rats. These effects did not occur in adult animals. Within the frontal cortex, the laterodorsal tegmentum and dorsal raphe nuclei, the basal inducible nitric oxide synthase activity was 85-200% higher in old rats than in adult ones. In contrast, the neuronal nitric oxide synthase activity did not vary in both groups. 2-Amino-5,6-dihydro-6-methyl-4H-1,3-thiazine administration significantly reduced inducible nitric oxide synthase activity (70-80% according to the brain areas) independently of age, but significantly decreased the cortical nitric oxide release in old rats. Finally, in frontal cortex and dorsal raphe immunohistochemical analysis showed inducible nitric oxide synthase-positive cells again only in old animals. These data support the idea that nitric oxide produced by inducible nitric oxide synthase plays a role in the triggering and maintenance of rapid-eye-movement sleep during aging.

Influence of temporomandibular joint pain on sleep patterns: role of nitric oxide

Since nitric oxide is related to nociception and the sleep-wake cycle, this study sought to determine its involvement in the altered sleep pattern in a temporomandibular joint pain model by investigating the effect of the inhibitor of nitric oxide synthase (L-NAME) and that of its precursor (L-arginine). The temporomandibular joints of test animals were injected with Freund's adjuvant or saline, and their sleep was recorded. The procedure was repeated after the administration of L-NAME and L-arginine. L-NAME increased rapid eye movement (REM) sleep in the control group. The orofacial pain group showed a reduction in total sleep time and an increase in sleep latency compared with the SHAM group. L-NAME increased sleep time, non-rapid eye movement (NREM), and REM sleep and reduced sleep latency in the orofacial pain group. L-arginine did not alter sleep parameters. Thus, L-NAME improved sleep efficiency, whereas L-arginine did not modify it, suggesting the involvement of nitric oxide in painful temporomandibular joint conditions.

Sleep-wake architecture in mouse models for Down syndrome

Sleep-wake homeostasis is crucial for behavioral performances and memory both in the general population and in patients with learning disability, among whom were Down syndrome (DS) patients. We investigated, in mouse models of DS, cortical EEG and sleep-wake architecture under baseline conditions and after a 4-h sleep deprivation (SD). Young hemizygous mice (hSODwt/+) transgenic for the human CuZn superoxide dismutase (hSOD1) or for the human amyloid precursor protein (HuAPP(695); hAPPwt/+) were obtained on the same FVB/N inbred background. Baseline records for slow wave sleep (SWS) and wake (W) parameters were unchanged, whereas paradoxical sleep (PS) episode numbers were decreased and PS latency increased after lights off in hSODwt/+ mice versus controls. hSODwt/+ mice did not experience SWS or PS rebounds after SD but EEG activity in the delta-SWS activity (SWA) was enhanced. hAPPwt/+ mice exhibited no change in PS but an increase in W and a decrease in SWS before light transition as well as an increase in theta-power in PS and W. After SD, hAPPwt/+ mice exhibited SWS and PS rebounds as well as enhancement of SWA. We investigated also the nitrite/nitrate levels in all mice and found an increase in the brainstem of hSODwt/+ mice only versus control ones. These preliminary data provide useful results to investigate other genetically manipulated mice and to better understand the biochemical basis of sleep disorders in DS patients.

Why Trypanosomes Cause Sleeping Sickness

African trypanosomiasis or sleeping sickness is hallmarked by sleep and wakefulness disturbances. In contrast to other infections, there is no hypersomnia, but the sleep pattern is fragmented. This overview discusses that the causative agents, the parasites Trypanosoma brucei, target circumventricular organs in the brain, causing inflammatory responses in hypothalamic structures that may lead to dysfunctions in the circadian-timing and sleep-regulatory systems.

Adenosine and sleep–wake regulation

This review addresses three principal questions about adenosine and sleep-wake regulation: (1) Is adenosine an endogenous sleep factor? (2) Are there specific brain regions/neuroanatomical targets and receptor subtypes through which adenosine mediates sleepiness? (3) What are the molecular mechanisms by which adenosine may mediate the long-term effects of sleep loss? Data suggest that adenosine is indeed an important endogenous, homeostatic sleep factor, likely mediating the sleepiness that follows prolonged wakefulness. The cholinergic basal forebrain is reviewed in detail as an essential area for mediating the sleep-inducing effects of adenosine by inhibition of wake-promoting neurons via the A1 receptor. The A2A receptor in the subarachnoid space below the rostral forebrain may play a role in the prostaglandin D2-mediated somnogenic effects of adenosine. Recent evidence indicates that a cascade of signal transduction induced by basal forebrain adenosine A1 receptor activation in cholinergic neurons leads to increased transcription of the A1 receptor; this may play a role in mediating the longer-term effects of sleep deprivation, often called sleep debt.

Influenza virus-induced sleep responses in mice with targeted disruptions in neuronal or inducible nitric oxide synthases

Influenza viral infection induces increases in non-rapid eye movement sleep and decreases in rapid eye movement sleep in normal mice. An array of cytokines is produced during the infection, and some of them, such as IL-1β and TNF-α, are well-defined somnogenic substances. It is suggested that nitric oxide (NO) may mediate the sleep-promoting effects of these cytokines. In this study, we use mice with targeted disruptions of either the neuronal NO synthase (nNOS) or the inducible NO synthase (iNOS) gene, commonly referred to as nNOS or iNOS knockouts (KOs), to investigate sleep changes after influenza viral challenge. We report that the magnitude of viral-induced non-rapid eye movement sleep responses in both nNOS KOs and iNOS KOs was less than that of their respective controls. In addition, the duration of rapid eye movement sleep in nNOS KO mice did not decrease compared with baseline values. All strains of mice had similar viral titers and cytokine gene expression profiles in the lungs. Virus was not isolated from the brains of any strain. However, gene expression in the brain stem differed between nNOS KOs and their controls: mRNA for the interferon-induced gene 2′,5′-oligoadenylate synthase 1a was elevated in nNOS KOs relative to their controls at 15 h, and IL-1β mRNA was elevated in nNOS KOs relative to their controls at 48 h. Our results suggest that NO synthesized by both nNOS and iNOS plays a role in virus-induced sleep changes and that nNOS may modulate cytokine expression in the brain.

The role of nitric oxide synthases in the sleep responses to tumor necrosis factor-alpha

It is well established that cytokines such as tumor necrosis factor-alpha (TNFalpha) and interleukin-1beta (IL-1beta) are involved in physiological sleep regulation, yet their downstream somnogenic mechanisms remain largely uninvestigated. Nitric oxide (NO) is an effector molecule for some TNFalpha actions. Neuronal nitric oxide synthase (nNOS) and inducible nitric oxide synthase (iNOS) gene knockout (KO) mice sleep differently than their respective controls. In this study, we tested the hypothesis that NO mediates TNFalpha-induced sleep using iNOS and nNOS KO mice and their corresponding wild-type controls. Systemic administration of TNFalpha increased non-rapid eye movement sleep (NREMS) in the two control strains and in the iNOS KO mice during the first 4 h post-injection but failed to increase NREMS in nNOS KO mice. Rapid eye movement sleep (REMS) was suppressed by TNFalpha in nNOS controls but not in the other strains examined. The results suggest that TNFalpha affects sleep, in part, through nNOS.

Interleukin-8 promotes non-rapid eye movement sleep in rabbits and rats

Interleukin-8 (IL-8) is a cytokine found in the brain. In this study, the ability of IL-8 to induce sleep in rabbits and rats was investigated. Twenty-seven Sprague-Dawley rats and 16 male New Zealand White rabbits were provided electroencephalographic (EEG) electrodes, a brain thermistor, and a lateral intracerebroventricular cannula. The animals were injected intracerebroventricularly (i.c.v.) with pyrogen-free saline and, one of the following doses of IL-8 on a separate day: 1.25 or 12.5 ng in rabbits and 10, 50, or 100 ng in rats. EEG, brain temperature, and motor activity were recorded for 23 h after the i.c.v. injections. IL-8 increased time spent in non-rapid eye movement sleep (NREMS) without affecting rapid eye movement sleep (REMS). In rabbits, both doses of IL-8 promoted NREMS. In rats, the 10 and 50 ng doses of IL-8 failed to affect sleep, but the 100 ng dose of IL-8 enhanced NREMS. EEG slow-wave activity during NREMS was increased after the high dose of IL-8 in rabbits. IL-8 also induced fever in rabbits but not rats. Heat inactivated IL-8 did not alter any of the parameters measured. Current results support the notion that the brain cytokine network plays a role in sleep regulation.

Sleep deprivation inhibits expression of NADPH-d and NOS while activating microglia and astroglia in the rat hippocampus

This study investigated the expression of nitric oxide (NO)-synthesizing enzymes and the glial reaction in the rat hippocampal formation following sleep deprivation for 5 days. Nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) reactivity was markedly reduced in the hippocampal CA1, CA2 and CA3 sectors as well as in the dentate gyrus, suggesting a suppression of NO production in these areas. Microglial cells were hypertrophic and showed an up-regulation of complement type 3 receptors as determined by antibody OX-42. However, expression of major histocompatibility complex class I and II antigens, and antigen of monocyte/macrophage lineage marked by OX-18, OX-6 and ED1, respectively, was undetected. Astrocytes also displayed hypertrophied processes with enhanced glial fibrillary acidic protein (GFAP) immunoreactivity. Western blots of hippocampal tissues corroborated the above-mentioned morphological findings in that expression of NO-synthase (NOS) was decreased while that of OX-42 and GFAP was increased in the sleep-deprived rats. Since NO is thought to be involved in memory consolidation processes in the hippocampus during sleep, the inhibition of NADPH-d and NOS reactivities may account for the memory decline after long-term sleep deprivation. The concomitant reactions in microglia and astrocytes suggest the involvement of these cells in the deleterious effect of prolonged sleep deprivation.

Role of nitric oxide in ethanol-induced ascorbic acid release in striatum of freely moving mice

In the present study, in vivo brain microdialysis coupled with high performance liquid chromatography (HPLC) and electrochemical detection were used to evaluate the effects of either L-arginine (L-Arg), the substrate of nitric oxide synthase (NOS), Nomega-nitro-L-arginine methyl ester hydrochloride (L-NAME), a non-selective NOS inhibitor, or sodium nitroprusside (SNP), a donor of NO, on the ethanol-induced release of ascorbic acid (AA) in the striatum of freely moving mice. Drugs were administered intrastriatally via the microdialysis probe and ethanol (2-4 g/kg) was administered intraperitoneally. The results showed that L-arginine (1-10 mg/ml) had no effect on either the basal AA contents in striatal extracellular fluid or the ethanol-induced release of AA. L-NAME (10(-4) to 10(-3) mg/ml) and SNP (10(-4) to 10(-3) mg/ml) both reduced the basal AA concentrations in striatal extracellular fluid. L-NAME significantly inhibited ethanol-induced release of AA, while SNP only had a transient inhibitory effect on the ethanol-induced release of AA. SNP significantly increased dehydroascorbic acid (DHAA) contents and DHAA/AA ratio but had no effect on the total AA contents (AA and DHAA contents) in striatal extracellular fluid, while L-NAME had no effect on DHAA contents but decreased the total AA contents in striatal extracellular fluid. Only high concentration L-NAME induced a transient increase in DHAA/AA ratio. Our results suggest that nitric oxide (NO) might not directly be involved in the mechanism of ethanol-induced release of AA in mouse striatum.

A cyclooxygenase-2 inhibitor attenuates spontaneous and TNF-alpha-induced non-rapid eye movement sleep in rabbits

Sleep is regulated in part by the brain cytokine network, including tumor necrosis factor-alpha (TNF-alpha). TNF-alpha activates the transcription factor nuclear factor-kappaB, which in turn promotes transcription of many genes, including cyclooxygenase-2 (COX-2). COX-2 is in the brain and is an enzyme responsible for production of prostaglandin D2. The hypothesis that central COX-2 plays a role in the regulation of spontaneous and TNF-alpha-induced sleep was investigated. Three doses (0.5, 5, and 50 microg) of NS-398, a highly selective COX-2 inhibitor, were injected intracerebroventricularly. The highest dose decreased non-rapid eye movement sleep. The intermediate and highest doses decreased electroencephalographic slow-wave activity; the greatest reduction occurred after 50 microg of NS-398 during the first 3-h postinjection period. Rapid eye movement sleep and brain temperature were not altered by any dose of NS-398. Pretreatment of rabbits with 5 or 50 microg of NS-398 blocked the TNF-alpha-induced increases in non-rapid eye movement sleep, electroencephalographic slow-wave activity, and brain temperature. These data suggest that COX-2 is involved in the regulation of spontaneous and TNF-alpha-induced sleep.

Spontaneous sleep in mice with targeted disruptions of neuronal or inducible nitric oxide synthase genes

Nitric oxide (NO) affects almost every physiological process, including the regulation of sleep. There is strong evidence that NO plays an important role in rapid eye movement sleep (REMS) regulation. To further investigate the role of NO in sleep, we characterized spontaneous sleep in mice with targeted disruptions (knockout; KO) in the neuronal nitric oxide synthase (nNOS) or inducible (i)NOS genes. REMS in nNOS KO mice was substantially lower than that of their control mice. In contrast, the iNOS KO mice had significantly more REMS than their controls. Inducible NOS KO mice also had less non-REMS (NREMS) during the dark period. Results suggest that nNOS and iNOS play opposite roles in REMS regulation.

The nitric oxide synthase inhibitor NG-Nitro-L-arginine increases basal forebrain acetylcholine release during sleep and wakefulness

Cholinergic neurotransmission in the basal forebrain changes across the sleep/wake cycle, and considerable data show cortical activation by ACh originating from basal forebrain neurons. These findings have stimulated efforts to elucidate molecular modulators of ACh release within the basal forebrain. Basal forebrain cholinergic neurons contain nitric oxide synthase (NOS), the enzyme that produces the gaseous neuromodulator nitric oxide. This study tested the hypothesis that administration of an NOS inhibitor to the basal forebrain would alter basal forebrain ACh release, sleep, and respiratory rate. Seven cats were instrumented for recording sleep and wakefulness and for in vivo microdialysis and microinjection. Compared with Ringer's solution (control), microdialysis delivery of the NOS inhibitor N(G)-nitro-l-arginine (NLA; 10 mm) increased ACh release during wakefulness (33%), non-rapid eye movement (NREM) sleep (70%), and rapid eye movement (REM) sleep (16%). Mean +/- SEM ACh levels (pmol/10 min) during control and NLA dialysis, respectively, were 0.58 +/- 0.03 and 0.77 +/- 0.06 in wakefulness, 0.36 +/- 0.01 and 0.61 +/- 0.06 in NREM sleep, and 0.68 +/- 0.06 and 0.79 +/- 0.09 in REM sleep. Increases in ACh release were not evoked by dialysis delivery of the less active enantiomer N(G)-nitro-d-arginine. Dialysis administration of NLA did not alter respiratory rate. Sleep-dependent changes in basal forebrain ACh release were localized specifically to lateral basal forebrain regions and did not occur in medial basal forebrain sites. Microinjection of NLA into the lateral basal forebrain did not significantly alter the sleep/wake cycle. In contrast to NLA-induced depression of REM sleep and ACh release in the cat pons, the present results demonstrate that NLA increased ACh release in the cat basal forebrain and had no effect on sleep. The different effects of NLA on ACh release in the cat pons and cat basal forebrain may prove relevant for developing compounds that differentially alter cholinergic neurotransmission in specific brain regions.

Intrapreoptic microinjection of TNF-alpha enhances non-REM sleep in rats

Tumor necrosis factor-alpha (TNFalpha) is involved in sleep regulation. Peripheral or central administration of TNFalpha induces non-rapid eye movement sleep (NREMS) in many species. However, the brain site responsible for TNF-enhanced NREMS remains unclear. Thus, we tested the hypothesis that the preoptic area (POA) of the anterior hypothalamus, a crucial site for sleep regulation, is involved in TNF-induced sleep responses in rats. Unilateral microinjection of TNFalpha (2, 20 and 100 ng) or a TNF receptor fragment (TNFRF; 1.25, 5.0 and 12.5 microg) into the POA was performed at dark onset and light onset, respectively. The two higher doses of TNFalpha increased NREMS and brain temperature with little effect on REMS and EEG slow wave activity. These effects were lost after the heat-treatment of TNFalpha. The two higher doses of the TNFRF decreased NREMS without affecting the other parameters measured. Combined with previous results showing diurnal variations of TNFalpha in the hypothalamus, the present data suggest that POA TNFalpha is involved, in part, in the regulation of physiological sleep.

Expression of cGMP-specific phosphodiesterase 9A mRNA in the rat brain

cGMP has been implicated in the regulation of many essential functions in the brain, such as synaptic plasticity, phototransduction, olfaction, and behavioral state. Cyclic nucleotide phosphodiesterase (PDE) hydrolysis of cGMP is the major mechanism underlying the clearance of cGMP and is likely to be important in any process that depends on intracellular cGMP. PDE9A has the highest affinity for cGMP of any PDE, and here we studied the localization of this enzyme in the rat brain using in situ hybridization. PDE9A mRNA is widely distributed throughout the brain with varying regional expression. The pattern of PDE9A mRNA expression closely resembles that of soluble guanylyl cyclase (sGC) in the rat brain, suggesting a possible functional association or coupling of these two enzymes in the regulation of cGMP levels. Most of the brain areas expressing PDE9A mRNA also contain neuronal nitric oxide synthase (NOS), the enzymatic source of NO and the principal activator of sGC. PDE9A is the only cGMP-specific PDE with significant expression in the forebrain, and as such is likely to play an important role in NO-cGMP signaling.

Interleukin-15 and interleukin-2 enhance non-REM sleep in rabbits

Interleukin (IL)-15 and -2 share receptor- and signal-transduction pathway (Jak-STAT pathway) components. IL-2 is somnogenic in rats but has not been tested in other species. Furthermore, the effects of IL-15 on sleep have not heretofore been described. We investigated the somnogenic actions of IL-15 in rabbits and compared them with those of IL-2. Three doses of IL-15 or -2 (10, 100, and 500 ng) were injected intracerebroventriculary at the onset of the dark period. In addition, 500 ng of IL-15 and -2 were injected 3 h after the beginning of the light period. IL-15 dose dependently increased non-rapid eye movement sleep (NREMS) and induced fever. IL-15 inhibited rapid eye movement sleep (REMS) after its administration during the light period; however, all doses of IL-15 failed to affect REMS if given at dark onset. IL-2 also dose dependently increased NREMS and fever. IL-2 inhibited REMS, and this effect was observed only in the light period. IL-15 and -2 enhanced electroencephalographic (EEG) slow waves during the initial 9-h postinjection period, then, during hours 10-23 postinjection, reduced EEG slow-wave activity. Current data support the notion that the brain cytokine network is involved in the regulation of sleep.