Changes in sleep and wakefulness following 5-HT1A ligands given systemically and locally in different brain regions

Dorsal raphe nucleus to basolateral amygdala 5-HTergic neural circuit modulates restoration of consciousness during sevoflurane anesthesia

The advent of general anesthesia (GA) has significant implications for clinical practice. However, the exact mechanisms underlying GA-induced transitions in consciousness remain elusive. Given some similarities between GA and sleep, the sleep-arousal neural nuclei and circuits involved in sleep-arousal, including the 5-HTergic system, could be implicated in GA. Herein, we utilized pharmacology, optogenetics, chemogenetics, fiber photometry, and retrograde tracing to demonstrate that both endogenous and exogenous activation of the 5-HTergic neural circuit between the dorsal raphe nucleus (DR) and basolateral amygdala (BLA) promotes arousal and facilitates recovery of consciousness from sevoflurane anesthesia. Notably, the 5-HT1A receptor within this pathway holds a pivotal role. Our findings will be conducive to substantially expanding our comprehension of the neural circuit mechanisms underlying sevoflurane anesthesia and provide a potential target for modulating consciousness, ultimately leading to a reduction in anesthetic dose requirements and side effects.

Gα Protein Signaling Bias at Serotonin 1A Receptor

Serotonin 1A receptor (5-HT1AR) is a clinically relevant target because of its involvement in several central and peripheral functions, including sleep, temperature homeostasis, processing of emotions, and response to stress. As a G protein coupled receptor (GPCR) activating numerous Gα i/o/z family members, 5-HT1AR can potentially modulate multiple intracellular signaling pathways in response to different therapeutics. Here, we applied a cell-based bioluminescence resonance energy transfer assay to quantify how ten structurally diverse 5-HT1AR agonists exert biased signaling by differentially stimulating Gα i/o/z family members. Our concentration-response analysis of the activation of each Gα i/o/z protein revealed unique potency and efficacy profiles of selected agonists when compared with the reference 5-hydroxytryptamine, serotonin. Overall, our analysis of signaling bias identified groups of ligands sharing comparable G protein activation selectivity and also drugs with unique selectivity profiles. We observed, for example, a strong bias of F-15599 toward the activation of Gα i3 that was unique among the agonists tested: we found a biased factor of +2.19 when comparing the activation of Gα i3 versus Gα i2 by F-15599, while it was -0.29 for 8-hydroxy-2-(di-n-propylamino) tetralin. Similarly, vortioxetine showed a biased factor of +1.06 for Gα z versus Gα oA, while it was -1.38 for vilazodone. Considering that alternative signaling pathways are regulated downstream of each Gα protein, our data suggest that the unique pharmacological properties of the tested agonists could result in multiple unrelated cellular outcomes. Further investigation is needed to reveal how this type of ligand bias could affect cellular responses and to illuminate the molecular mechanisms underlying therapeutic profile and side effects of each drug. SIGNIFICANCE STATEMENT: Serotonin 1a receptor (5-HT1AR) activates several members of the Gi/o/z protein family. Here, we examined ten structurally diverse and clinically relevant agonists acting on 5-HT1AR and identified distinctive bias patterns among G proteins. Considering the diversity of their intracellular effectors and signaling properties, this data reveal novel mechanisms underlying both therapeutic and undesirable effects.

Network pharmacology and pharmacological evaluation for deciphering novel indication of Sishen Wan in insomnia treatment

BACKGROUND

Insomnia is the most frequent sleep disorder worldwide and is a prominent risk factor for mental and physical health deterioration. The clinical application of common pharmacological treatments for insomnia is far from satisfactory due to their various adverse effects. In recent years, drugs developed from natural herbs have become potential alternative therapies for insomnia. Sishen Wan (SSW), a traditional Chinese medicine (TCM) used for centuries to treat diarrheal disease, consists of multiple neurologically active herbs with sleep-regulating potential that may have therapeutic effects on insomnia. However, its hypnotic and sleep-regulating effects have not been evaluated in clinical practice or laboratory experiments.

PURPOSE

To investigate the anti-insomnia effects of SSW and explore its possible mechanisms using preclinical models.

STUDY DESIGN AND METHODS

The sedative effect of the SSW formula was investigated using network pharmacology analysis that was validated using various pharmacological approaches, including the evaluation of locomotor activity (LMA), pentobarbital-induced sleep time, and electroencephalography/electromyogram (EEG/EMG)-based sleep profiling in normal rats. Several animal models of insomnia, including sleep deprivation, serotonin depletion, and cage-changing models, have been used to further assess the anti-insomnia effects of SSW. Furthermore, the potential underlying mechanisms of action of SSW were predicted using bioinformatics methods and verified using in vivo and in silico experiments.

RESULTS

The results showed that SSW reduced LMA and prolonged pentobarbital-induced sleep time in a dose-dependent manner, which was consistent with the increase in non-rapid eye movement (NREM) sleep in normal rats, indicating a solid sedative effect. In animal models of insomnia, SSW alleviated sleep disturbance by increasing NREM sleep time, shortening NREM sleep latency, and inhibiting sleep fragmentation, suggesting a possible curative effect of SSW on insomnia. Finally, through functional enrichment analysis and in vivo and in silico experiments, 5-HT_1A was identified as the key target of the anti-insomnia effect of SSW. Moreover, (S)-propranolol, nuciferine, zizyphusine, and N,N-dimethyl-5-methoxytryptamine may be the active compounds of SSW responsible for its anti-insomnia effect.

CONCLUSION

This study extended the possible indication scope for SSW, which provides a potential therapeutic TCM that may be used for insomnia treatment, as well as a reference scheme for the discovery of novel indications of TCM.

[Slow-wave sleep and the possibilities of modern insomnia therapy]

Effective therapy of insomnia, especially chronic insomnia, is one of the most pressing neuropsychiatric problems. Unfortunately, at present in the Russian Federation, as in most other countries of the world, there are no officially approved drugs for long-term treatment of insomnia. In this regard, the use of medical sedation agents that do not have restrictions on the duration of use is of considerable interest. This review considers drugs of various psychopharmacological classes, one way or another used in practice for the correction of sleep disorders, especially in patients with underlying comorbid pathology.

Effective Components and Molecular Mechanism of Agarwood Essential Oil Inhalation and the Sedative and Hypnotic Effects Based on GC-MS-Qtof and Molecular Docking

Agarwood has been used for the administration of hypnotic therapy. Its aromatic scent induces a relaxed state. However, its aromatic constituents and the underlying molecular effect are still unclear. This study aims to determine the active substance and molecular mechanism of the hypnotic effect of agarwood essential oil (AEO) incense inhalation in insomniac mice. Insomnia models were induced by para-chlorophenylalanine (PCPA, 300 mg/kg) in mice. The sleep-promoting effect was evaluated. Neurotransmitter levels and its receptor were detected to explore the molecular mechanism. The effective components were analyzed by GC-Q/TOF-MS of AEO. The binding mechanisms of the core compounds and core targets were verified by molecular docking. These results showed that AEO inhalation could significantly shorten sleep latency and prolong sleep time, inhibit autonomous activity and exert good sedative and sleep-promoting effects. A mechanistic study showed that AEO inhalation increased the levels of γ-aminobutyric acid (GABA_A), the GABA_A/glutamic acid (Glu) ratio, 5-hydroxytryptamine (5-HT) and adenosine (AD), upregulated the expression levels of GluR1, VGluT1 and 5-HT1A and downregulated 5-HT2A levels. Component analysis showed that the most abundant medicinal compounds were eremophilanes, cadinanes and eudesmanes. Moreover, the docking results showed that the core components stably bind to various receptors. The study demonstrated the bioactive constituents and mechanisms of AEO in its sedative and hypnotic effects and its multicomponent, multitarget and multipathway treatment characteristics in PCPA-induced insomniac mice. These results provide theoretical evidence for insomnia treatment and pharmaceutical product development with AEO.

A Novel Theanine Complex, Mg-L-Theanine Improves Sleep Quality via Regulating Brain Electrochemical Activity

L-Theanine is commonly used to improve sleep quality through inhibitory neurotransmitters. On the other hand, Mg²⁺, a natural NMDA antagonist and GABA agonist, has a critical role in sleep regulation. Using the caffeine-induced brain electrical activity model, here we investigated the potency of L-theanine and two novel Mg-L-theanine compounds with different magnesium concentrations on electrocorticography (ECoG) patterns, GABAergic and serotonergic receptor expressions, dopamine, serotonin, and melatonin levels. Furthermore, we evaluated the sleep latency and duration in the pentobarbital induced sleep model. We herein showed that L-theanine, particularly its various complexes with magnesium increases the expression of GABAergic, serotonergic, and glutamatergic receptors, which were associated with decreased ECoG frequency, increased amplitude, and enhanced delta wave powers. Besides increased dopamine, serotonin, and melatonin; decreased MDA and increased antioxidant enzyme levels were also observed particularly with Mg-complexes. Protein expression analyses also showed that Mg-L-theanine complexes decrease inducible nitric oxide synthase (iNOS) and endothelial nitric oxide synthase (eNOS) levels significantly. In accordance with these results, Mg complexes improved the sleep latency and duration even after caffeine administration. As a result, our data indicate that Mg-L-theanine compounds potentiate the effect of L-theanine on sleep by boosting slow-brain waves, regulating brain electrical activity, and increasing neurotransmitter and GABA receptor levels.

Utilizing network pharmacology and experimental validation to explore the potential molecular mechanisms of BanXia-YiYiRen in treating insomnia

BanXia-YiYiRen (Pinellia Ternata and Coix Seed, BX-YYR) has been clinically proven to be an effective Chinese medicine compatible with the treatment of insomnia. However, the underlying mechanism of BX-YYR against insomnia remains unclear. This study aimed to explore the pharmacological mechanisms of BX-YYR in treating insomnia based on network pharmacology and experimental validation. The drug-disease targets were obtained using publicly available databases. The analysis revealed 21 active compounds and 101 potential targets of BX-YYR from the pharmacological database of Chinese medicine system and analysis platform (TCMSP) and 1020 related targets of insomnia from the GeneCards and Online Mendelian Inheritance in Man (OMIM) databases. Furthermore, 38 common targets of BX-YYR against insomnia were identified, and these common targets were used to construct a protein–protein interaction (PPI) network. The visual PPI network was constructed by Cytoscape software. The top three genes from PPI according to degree value are FOS, AKT1, and CASP3. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment were applied to reveal the potential targets and signaling pathways involved in BX-YYR against insomnia, especially the serotonergic pathway. In addition, molecular docking revealed that baicalein, beta-sitosterol, and stigmasterol displayed strong binding to AKT1, FOS, PRKCA, and VEGFA. Experimental study found that BX-YYR against insomnia might play a role in improving sleep by modulating the serotonergic pathway. In summary, our findings revealed the underlying mechanism of BX-YYR against insomnia and provided an objective basis for further experimental study and clinical application.

Why It Is Important to Consider the Effects of Analgesics on Sleep: A Critical Review

We review the known physiological mechanisms underpinning all of pain processing, sleep regulation, and pharmacology of analgesics prescribed for chronic pain. In particular, we describe how commonly prescribed analgesics act in sleep-wake neural pathways, with potential unintended impact on sleep and/or wake function. Sleep disruption, whether pain- or drug-induced, negatively impacts quality of life, mental and physical health. In the context of chronic pain, poor sleep quality heightens pain sensitivity and may affect analgesic function, potentially resulting in further analgesic need. Clinicians already have to consider factors including efficacy, abuse potential, and likely side effects when making analgesic prescribing choices. We propose that analgesic-related sleep disruption should also be considered. The neurochemical mechanisms underlying the reciprocal relationship between pain and sleep are poorly understood, and studies investigating sleep in those with specific chronic pain conditions (including those with comorbidities) are lacking. We emphasize the importance of further work to clarify the effects (intended and unintended) of each analgesic class to inform personalized treatment decisions in patients with chronic pain. © 2021 American Physiological Society. Compr Physiol 11:1-31, 2021.

Polygonatum sibiricum rhizome promotes sleep by regulating non-rapid eye movement and GABAergic/serotonergic receptors in rodent models

The aim of this study is to investigate the sleep-promoting effect of a water extract of the Polygonatum sibiricum rhizome (PSE) in rodent models. PSE contained oleamide (0.10 mg/g extract) and glyceryl monolinoleate (0.17 mg/g extract), which are recognized as sleep-promoting substances. In pentobarbital-induced sleep model at hypnotic level, PSE (160 mg/kg) administration significantly decreased sleep latency time by 29% (2.7 min) and increased sleep duration time by 70% (68.4 min) compared with the normal control (3.8 min and 40.7 min, respectively). In the electroencephalography (EEG) analysis of rats, PSE-mediated sleep promotion accompanied the change of sleep architecture including increase of non-rapid eye movement (NREM) and decrease of REM. This sleep promoting effect was more obvious in caffeine-induced awakening model; total sleep time was increased by 40% along with increased NREM by PSE treatment at 160 mg/kg. In addition, PSE significantly increased the protein and mRNA levels of GABA_A-R2 and 5-HT1A receptor, the major sleep-related neurotransmitter receptors. Furthermore, glyceryl monolinoleate and oleamide effectively bound to GABA_A receptor in a competitive binding assay. These results indicate that PSE-mediated sleep-promoting effect is associated with the extension of NREM and upregulation of GABA_A-R2 and 5-HT1A, and is mediated by binding to the GABA_A receptor in vertebrate models.

Astrocyte-Dependent Slow Inward Currents (SICs) Participate in Neuromodulatory Mechanisms in the Pedunculopontine Nucleus (PPN)

Slow inward currents (SICs) are known as excitatory events of neurons caused by astrocytic glutamate release and consequential activation of neuronal extrasynaptic NMDA receptors. In the present article we investigate the role of these astrocyte-dependent excitatory events on a cholinergic nucleus of the reticular activating system (RAS), the pedunculopontine nucleus (PPN). It is well known about this and other elements of the RAS, that they do not only give rise to neuromodulatory innervation of several areas, but also targets neuromodulatory actions from other members of the RAS or factors providing the homeostatic drive for sleep. Using slice electrophysiology, optogenetics and morphological reconstruction, we revealed that SICs are present in a population of PPN neurons. The frequency of SICs recorded on PPN neurons was higher when the soma of the given neuron was close to an astrocytic soma. SICs do not appear simultaneously on neighboring neurons, thus it is unlikely that they synchronize neuronal activity in this structure. Occurrence of SICs is regulated by cannabinoid, muscarinic and serotonergic neuromodulatory mechanisms. In most cases, SICs occurred independently from tonic neuronal currents. SICs were affected by different neuromodulatory agents in a rather uniform way: if control SIC activity was low, the applied drugs increased it, but if SIC activity was increased in control, the same drugs lowered it. SICs of PPN neurons possibly represent a mechanism which elicits network-independent spikes on certain PPN neurons; forming an alternative, astrocyte-dependent pathway of neuromodulatory mechanisms.

Serotonin's role in piglet mortality and thriftiness

Improving piglet survivability rates is of high priority for swine production as well as for piglet well-being. Dysfunction in the serotonin (5-HT) system has been associated with growth deficiencies, infant mortalities, or failure to thrive in human infants. The aim of this research was to determine if a relationship exists between infant mortality and failure to thrive (or unthriftiness), and umbilical 5-HT concentration in piglets. Umbilical blood was collected from a total of 60 piglets from 15 litters for analysis of 5-HT and tryptophan (Trp; the AA precursor to 5-HT) concentrations. Behavior was scan sampled for the first 2 days after birth. Brain samples were also taken at 8 h after birth from healthy and unthrifty piglets (n = 4/group). The raphe nucleus was dissected out and analyzed for 5-HT and dopamine concentrations as well as their major metabolites 5-hydroxyindoleacetic acid (5-HIAA) and homovanillic acid (HVA), respectively. Data were analyzed by ANOVA. Piglets that died within 48 h of birth (n = 14) had significantly lower umbilical blood 5-HT concentrations at the time of their birth compared to their healthy counterparts (n = 46, P = 0.003). However, no difference in Trp was detected (P 0.38). Time spent under the heat lamp and sleeping were positively correlated with umbilical 5-HT levels (P = 0.004 and P = 0.02, respectively), while inactivity had a negative correlation with 5-HT levels (P = 0.04). In the raphe nucleus, the center for brain 5-HT biosynthesis, unthrifty piglets had a greater concentration of 5-HIAA (P = 0.02) and a trend for higher concentrations of 5-HT (P = 0.07) compared with healthy piglets. Dopamine levels did not differ between thrifty and unthrifty piglets (P = 0.45); however, its metabolite HVA tended to be greater in unthrifty piglets (P = 0.05). Our results show evidence of serotonergic dysfunction, at both the central and peripheral levels, accompanying early piglet mortalities. These data suggest a possible route for intervention, via the 5-HT system, to improve piglet survivability. However, further research is required to validate this hypothesis.

Differentiated effects of the multimodal antidepressant vortioxetine on sleep architecture: Part 2, pharmacological interactions in rodents suggest a role of serotonin-3 receptor antagonism

Antidepressants often disrupt sleep. Vortioxetine, a multimodal antidepressant acting through serotonin (5-HT) transporter (SERT) inhibition, 5-HT3, 5-HT7 and 5-HT1D receptor antagonism, 5-HT1B receptor partial agonism, and 5-HT1A receptor agonism, had fewer incidences of sleep-related adverse events reported in depressed patients. In the accompanying paper a polysomnographic electroencephalography (sleep-EEG) study of vortioxetine and paroxetine in healthy subjects indicated that at low/intermediate levels of SERT occupancy, vortioxetine affected rapid eye movement (REM) sleep differently than paroxetine. Here we investigated clinically meaningful doses (80-90% SERT occupancy) of vortioxetine and paroxetine on sleep-EEG in rats to further elucidate the serotoninergic receptor mechanisms mediating this difference. Cortical EEG, electromyography (EMG), and locomotion were recorded telemetrically for 10 days, following an acute dose, from rats receiving vortioxetine-infused chow or paroxetine-infused water and respective controls. Sleep stages were manually scored into active wake, quiet wake, and non-REM or REM sleep. Acute paroxetine or vortioxetine delayed REM onset latency (ROL) and decreased REM episodes. After repeated administration, vortioxetine yielded normal sleep-wake rhythms while paroxetine continued to suppress REM. Paroxetine, unlike vortioxetine, increased transitions from non-REM to wake, suggesting fragmented sleep. Next, we investigated the role of 5-HT3 receptors in eliciting these differences. The 5-HT3 receptor antagonist ondansetron significantly reduced paroxetine's acute effects on ROL, while the 5-HT3 receptor agonist SR57227A significantly increased vortioxetine's acute effect on ROL. Overall, our data are consistent with the clinical findings that vortioxetine impacts REM sleep differently than paroxetine, and suggests a role for 5-HT3 receptor antagonism in mitigating these differences.

Sleep, its regulation and possible mechanisms of sleep disturbances

The state of sleep consists of different phases that proceed in successive, tightly regulated order through the night forming a physiological program, which for each individual is different but stabile from one night to another. Failure to accomplish this program results in feeling of unrefreshing sleep and tiredness in the morning. The program core is constructed by genetic factors but regulated by circadian rhythm and duration and intensity of day time brain activity. Many environmental factors modulate sleep, including stress, health status and ingestion of vigilance-affecting nutrients or medicines (e.g. caffeine). Acute sleep loss results in compromised cognitive performance, memory deficits, depressive mood and involuntary sleep episodes during the day. Moreover, prolonged sleep curtailment has many adverse health effects, as evidenced by both epidemiological and experimental studies. These effects include increased risk for depression, type II diabetes, obesity and cardiovascular diseases. In addition to voluntary restriction of sleep, shift work, irregular working hours, jet lag and stress are important factors that induce curtailed or bad quality sleep and/or insomnia. This review covers the current theories on the function of normal sleep and describes current knowledge on the physiologic effects of sleep loss. It provides insights into the basic mechanisms of the regulation of wakefulness and sleep creating a theoretical background for understanding different disturbances of sleep.

Augmentative effect of spinosin on pentobarbital-induced loss of righting reflex in mice associated with presynaptic 5-HT1A receptor

Objectives

This study investigated whether spinosin potentiates pentobarbital-induced loss of righting reflex (LORR) in mice via 5-HT1A receptors.

Methods

Our primary endpoint for sedation was LORR. In addition, the basal rectal temperature was measured.

Key findings

The results demonstrated that the 5-HT1A agonist 8-OH-DPAT (s.c.) induced reductions in duration of LORR at 0.1, 0.5 and 1.0 mg/kg (P < 0.01), and prolongation of LORR latency at 0.5 and 1.0 mg/kg (s.c., P < 0.01) in pentobarbital (45 mg/kg, i.p.)-treated mice. This effect of 8-OH-DPAT was antagonized either by 5-HT1A antagonist p-MPPI (5 mg/kg, i.p.) or by spinosin (15 mg/kg, i.g.) with significance, respectively. Co-administration of spinosin and p-MPPI both at ineffective doses (spinosin at 5.0 mg/kg, i.g. and p-MPPI at 1.0 mg/kg, i.p.) showed significant augmentative effects in reducing latency to LORR, and increasing LORR duration (P < 0.01) in pentobarbital-treated mice. On the other hand, spinosin inhibited 8-OH-DPAT-induced hypothermia, which has been generally attributed to the activation of somatodendritic 5-HT1A autoreceptors in mice.

Conclusions

Based on our previous results and the present data, it should be presumed that presynaptic 5-HT1A autoreceptor mechanisms may be involved in the inhibitory effect of spinosin on 8-OH-DPAT-induced hypothermia and also in the potentiating effect of spinosin on pentobarbital-induced LORR in mice.

Potentiating effect of spinosin, a C-glycoside flavonoid of Semen Ziziphi spinosae, on pentobarbital-induced sleep may be related to postsynaptic 5-HT(1A) receptors

Previous results have suggested that spinosin, a C-glycoside flavonoid of Semen Ziziphi spinosae, potentiates pentobarbital-induced sleep via the serotonergic system. The present study investigated whether spinosin potentiates pentobarbital-induced sleep via serotonin-1A (5-hydroxytryptamine, 5-HT(1A)) receptors. The results demonstrated that spinosin significantly augmented pentobarbital (35 mg/kg, i.p.)-induced sleep in rats, reflected by reduced sleep latency and increased total sleep time, non-rapid eye movement (NREM) sleep time, and REM sleep time. With regard to NREM sleep duration, spinosin mainly increased slow-wave sleep (SWS). Additionally, spinosin (15mg/kg, i.g.) significantly antagonized 5-HT(1A) agonist 8-OH-DPAT (0.1mg/kg, i.p.)-induced reductions in total sleep time, NREM sleep, REM sleep, and SWS in pentobarbital-treated rats. These results suggest that spinosin may be an antagonist at postsynaptic 5-HT(1A) receptors because these effects of 8-OH-DPAT were considered to be mediated via postsynaptic 5-HT(1A) receptors. Moreover, co-administration of spinosin and the 5-HT(1A) antagonist 4-iodo-N-{2-[4-(methoxyphenyl)-1-piperazinyl]ethyl}-N-2-pyridinylbenzamide (p-MPPI), at doses that are ineffective when administered alone (spinosin 5mg/kg, p-MPPI 1mg/kg), had significant augmentative effects on pentobarbital-induced sleep, reflected by reduced sleep latency and increased total sleep time, NREM sleep, and REM sleep. In contrast to the attenuating effects of p-MPPI on REM sleep via presynaptic 5-HT(1A) autoreceptors, 15mg/kg spinosin significantly increased REM sleep. These results suggest that the effect of spinosin on REM sleep in pentobarbital-treated rats may be related to postsynaptic 5-HT(1A) receptors.

Identification of serotonin 5-HT1A receptor partial agonists in ginger

Animal studies suggest that ginger (Zingiber officinale Roscoe) reduces anxiety. In this study, bioactivity-guided fractionation of a ginger extract identified nine compounds that interact with the human serotonin 5-HT(1A) receptor with significant to moderate binding affinities (K(i)=3-20 microM). [(35)S]-GTP gamma S assays indicated that 10-shogaol, 1-dehydro-6-gingerdione, and particularly the whole lipophilic ginger extract (K(i)=11.6 microg/ml) partially activate the 5-HT(1A) receptor (20-60% of maximal activation). In addition, the intestinal absorption of gingerols and shogaols was simulated and their interactions with P-glycoprotein were measured, suggesting a favourable pharmacokinetic profile for the 5-HT(1A) active compounds.

Time- and dose-related effects of three 5-HT receptor ligands on the genioglossus activity in anesthetized and conscious rats

Clinical trials in obstructive sleep apnea syndrome patients reported moderate effects of serotoninergic drugs on oropharyngeal apneas, although numerous specific 5-HT ligands highly modulate the genioglossus muscle (GG) activity in experiments performed in anesthetized animals. The purpose of this study was to investigate time- and dose-related effects of central and systemic injections of 8-OHDPAT (5-HT1A agonist), SB224289 (5-HT1B antagonist), and DOI (5-HT2A/2C agonist) on the GG activity in anesthetized and conscious rats. Electromyographic recordings of the GG activity (GGemg) were analyzed after central and systemic injections of each drug in ketamine-xylazine anesthetized rats. Electroencephalograms (EEG), as well as neck and GG muscle activities (Nemg and GGemg), were recorded in 15 additional rats to analyze changes in sleep-wake states before and after systemic injection of the drugs. Central injections of 8-OHDPAT and DOI in anesthetized rats induced clear dose-related increases in phasic and tonic GGemg activities, respectively. The time-responses were inferior to 30 min with 8-OHDPAT and over 50 min with DOI. Moderate increases in phasic GGemg activity were also observed after central, but not peripheral injection of SB and DOI. The total sleep time measured in conscious rats significantly decreased after systemic injections of DOI and 8-OHDPAT, although no change was observed in phasic or tonic GGemg activity. The dose- and time-responses of the DOI in anesthetized rat partly explain the lack of GGemg tonic change in conscious rat. The moderate effect on the GGemg phasic activity of peripheral 5-HT1A ligand injection easily explains the lack of change in conscious rat. The serotonergic modulation of the respiratory component of the GGemg remains complex, but is highly sensitive to 5-HT1A receptors after central injection in rats under anesthesia. Forthcoming therapy in OSAS should be made of mixed profiled neurotransmitters and different routes of administration.

Activity of the serotonergic system during isoflurane anesthesia

BACKGROUND

Microdialysis studies have demonstrated that the release of serotonin (5-hydroxytryptamine, 5-HT) in the serotonergic projection areas increases during waking and decreases during sleep in rat and cat, suggesting that 5-HT plays an important role in modulation of sleep. Although it might be expected that 5-HT release is also decreased during general anesthesia, the functional contribution of serotonergic neurons in pharmacological effects of volatile anesthetics has not been fully investigated.

METHODS

Using an in vivo microdialysis technique, we measured extracellular 5-HT in rat frontal cortex during waking, slow-wave sleep, and isoflurane anesthesia. To assess the involvement of the serotonergic system in the hypnotic action of isoflurane, the concentration of isoflurane required for loss of righting reflex was determined with or without pretreatment of fluoxetine hydrochloride, a selective 5-HT reuptake inhibitor.

RESULTS

During slow-wave sleep and isoflurane anesthesia (0.1-1.5 MAC), 5-HT release decreased to 21%-44% of that during the waking state. Loss of righting reflex occurred at significantly higher isoflurane concentrations in fluoxetine-treated rats (0.76% +/- 0.03% [n = 8]) than in control rats (0.60% +/- 0.01% [n = 8]).

CONCLUSIONS

It is suggested that a change in the activity of the serotonergic system in the brain is involved in the hypnotic action of isoflurane.

Sleep quality varies as a function of 5-HTTLPR genotype and stress

OBJECTIVE

To test the hypothesis that allelic variation in 5HTT gene-linked polymorphic region (5-HTTLPR) genotype was associated with sleep quality (Pittsburgh Sleep Quality Index, PSQI) as a main effect and as moderated by the chronic stress of caregiving. Serotonin (5HT) is involved in sleep regulation and the 5HT transporter (5HTT) regulates 5HT function. A common 44-base pair deletion (s allele) polymorphism in the 5-HTTLPR is associated with reduced 5HTT transcription efficiency and 5HT uptake in vitro.

METHODS

Subjects were 142 adult primary caregivers for a spouse or parent with dementia and 146 noncaregiver controls. Subjects underwent genotyping and completed the PSQI.

RESULTS

Variation in 5-HTTLPR genotype was not related to sleep quality as a main effect (p > .36). However, there was a caregiver X 5-HTTLPR interaction (p < .009), such that the s allele was associated with poorer sleep quality in caregivers as compared with controls.

CONCLUSIONS

Findings suggest that the s allele may moderate sleep disturbance in response to chronic stress.

5-hydroxytryptamine 1A (5-HT1A) but not 5-HT3 receptor is involved in mediating the nucleus submedius 5-HT-evoked antinociception in the rat

Our previous studies have indicated that the thalamic nucleus submedius (Sm) is involved in modulation of nociception as part of an ascending component of an endogenous analgesic system consisting of spinal cord-Sm-ventrolateral orbital cortex (VLO)-periaqueductal gray (PAG)-spinal cord loop. Microinjection of 5-hydroxytryptamine (5-HT) into Sm produces antinociception and this effect is blocked by 5-HT(2) receptor antagonist. The aim of the present study was to examine whether the 5-HT(1) and 5-HT(3) receptors were also involved in the Sm 5-HT-evoked antinociception. Nociception was assessed in lightly anesthetized rats with radiant-heat-evoked tail flick (TF). 5-HT(1A) and 5-HT(3) receptor antagonists were microinjected into the Sm alone or in combination with a microinjection of 5-HT into the same Sm site. 5-HT(1A) receptor antagonist p-MPPI (0.87 nmol) facilitated the TF reflex; a lower dose (0.43 nmol) of p-MPPI significantly attenuated the Sm 5-HT-evoked inhibition of TF reflex. Microinjection of the 5-HT(3) receptor antagonist LY-278,584 (12 nmol) had no effect either on the TF reflex or on the Sm 5-HT-evoked inhibition. These results suggest that 5-HT(1A) receptor but not 5-HT(3) receptor is involved in mediating the 5-HT-evoked antinociception. Possible mechanisms of Sm 5-HT-induced descending antinociception are discussed.

5-HT 1A/1B receptor-mediated effects of the selective serotonin reuptake inhibitor, citalopram, on sleep: studies in 5-HT 1A and 5-HT 1B knockout mice

Selective serotonin reuptake inhibitors (SSRIs) are extensively used for the treatment of depression. Aside from their antidepressant properties, they provoke a deficit in paradoxical sleep (PS) that is most probably mediated by the transporter blockade-induced increase in serotonin concentration in the extracellular space. Such an effect can be accounted for by the action of serotonin at various types of serotonergic receptors involved in PS regulation, among which the 5-HT(1A) and 5-HT(1B) types are the best candidates. According to this hypothesis, we examined the effects of citalopram, the most selective SSRI available to date, on sleep in the mouse after inactivation of 5-HT(1A) or 5-HT(1B) receptors, either by homologous recombination of their encoding genes, or pharmacological blockade with selective antagonists. For this purpose, sleep parameters of knockout mice that do not express these receptors and their wild-type counterparts were monitored during 8 h after injection of citalopram alone or in association with 5-HT(1A) or 5-HT(1B) receptor antagonists. Citalopram induced mainly a dose-dependent inhibition of PS during 2-6 h after injection, which was observed in wild-type and 5-HT(1B)-/- mice, but not in 5-HT(1A)-/- mutants. This PS inhibition was fully antagonized by pretreatment with the 5-HT(1A) antagonist WAY 100635, but only partially with the 5-HT(1B) antagonist GR 127935. These data indicate that the action of the SSRI citalopram on sleep in the mouse is essentially mediated by 5-HT(1A) receptors. Such a mechanism of action provides further support to the clinical strategy of antidepressant augmentation by 5-HT(1A) antagonists, because the latter would also counteract the direct sleep-inhibitory side-effects of SSRIs.

Serotonin and sleep

For 50 years, serotonin has been in the centre of the search for the mechanisms and control of sleep. Serotonergic neurotransmission is related to the behavioural state of the animal and plays an important role in modulation of the behavioural state, by interacting with other brain areas modulating circadian rhythm, sleep and waking. Serotonergic activity may be accompanied by waking or sleep depending on the brain area and receptor type involved in the response, on the current behavioural state and on the concomitant agonism/antagonism of other neurotransmitter systems.

The selective 5-HT(1A) receptor antagonist p-MPPI antagonizes sleep--waking and behavioural effects of 8-OH-DPAT in rats

Systemic administration of the selective 5-HT(1A) receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin HBr (8-OH-DPAT) increases waking and reduces slow wave sleep (SWS) and rapid eye movement (REM) sleep in the freely moving rat. The selective 5-HT(1A) antagonist 4-(2'-methoxy-phenyl)-1-[2'-(n-2"-pyridinyl)-p-iodobenzamido]-ethyl-piperazine (p-MPPI) induces a dose-related decrease in REM sleep. The present study examined p-MPPI's potential as an antagonist of the sleep and waking responses elicited by 8-OH-DPAT. Also, the experiments explored the ability of p-MPPI to block behavioural reactions of the 5-HT syndrome induced by 8-OH-DPAT, and whether p-MPPI induced any behavioural effects of its own. This study demonstrated that pre-treatment with p-MPPI (5 mg/kg intraperitoneal (i.p.)) 30 min before 8-OH-DPAT (0.375 mg/kg subcutaneously (s.c.)) reduced the effect of 8-OH-DPAT on waking and REM sleep. Also, p-MPPI (5 and 10 mg/kg i.p.) reduced the effect of 8-OH-DPAT on locomotion and partially or completely antagonized hindlimb abduction and flat body posture. No overt behavioural change was produced by p-MPPI alone. Thus, p-MPPI behaved as a true 5-HT(1A) antagonist.

Sleep and waking following microdialysis perfusion of the selective 5-HT1A receptor antagonist p-MPPI into the dorsal raphe nucleus in the freely moving rat

The aim of this study was to examine the involvement of the dorsal raphe nucleus (DRN) presynaptic serotonergic 5-HT1A autoreceptors on sleep and waking parameters, in particular rapid eye movement (REM) sleep. In a previous study, the systemic administration of the selective 5-HT1A receptor antagonist p-MPPI reduced REM sleep in a dose-dependent manner suggesting a blockade of the 5-HT1A autoreceptors. In the present study, a blockade by microdialysis perfusion of 10 microM and 100 microM of p-MPPI for 7 h into the DRN in freely behaving rats influenced vigilance state only to a small extent. The administration of 10 microM of p-MPPI induced a reduction of total REM sleep mainly due to a suppression of REM sleep during the third 2 h period of the recording of sleep and waking. Perfusion of 100 microM of p-MPPI decreased total transition type sleep (TRANS) but the effect on REM sleep did not reach significance. There was no change in waking or slow wave sleep (SWS) following any of the doses. The data suggest that 5-HT1A receptor-mediated mechanisms in the DRN may be only moderately important in the serotonergic modulation of REM sleep.

Sleep-wake effects following the selective 5-HT(1A) receptor antagonist p-MPPI in the freely moving rat

The 5-HT(1A) receptors appear to play an important role in the serotonergic modulation of sleep and waking. Both presynaptic somatodendritic 5-HT(1A) autoreceptors and postsynaptic 5-HT(1A) heteroreceptors may be involved. The present study addressed the question of whether the selective 5-HT(1A) receptor antagonist 4-(2'-methoxy-phenyl)-1-[2'-(n-2"-pyridinyl)-p-iodobenzamido]-ethy l-p iperazine (p-MPPI) affected sleep and waking and whether such an effect would be dose-related. Polygraphic recording of sleep and waking in freely moving rats was employed following control injection and three doses of p-MPPI (1, 5 and 10 mg/kg i.p. in a balanced order design. Waking was increased and deep slow wave sleep decreased, while rapid eye movement (REM) sleep was suppressed over the first 6 h following injection, compared to after control injection. REM sleep was also suppressed following 10 mg/kg i.p. of p-MPPI as compared to following 1 mg/kg i.p. of p-MPPI. The interpretation of the effects is complex and the effects are not easily compatible with a simple model for serotonergic sleep-waking modulation. However, the REM sleep reduction probably reflects p-MPPIs ability to block the presynaptic 5-HT(1A) autoreceptors, increasing the firing activity in the serotonergic neurones and possibly inhibiting serotonin sensitive REM sleep active neurones.

Discharge modulation of rat dorsal raphe neurons during sleep and waking: effects of preoptic/basal forebrain warming

In cats, putative serotonergic neurons (PSNs) recorded from the dorsal raphe nucleus (DRN) across the sleep-wake cycle exhibit the so-called rapid eye movement sleep-off (REM-off) discharge pattern. Since, the sleep-wake discharge patterns of DRN neurons in behaving rats is poorly known, the present study examined this neuronal populations. The PSNs recorded in this study exhibited: (1) progressive decrease in discharge rate from waking to NREM to REM sleep; (2) long action potential duration, and (3) reduction of discharge rate after systemic administration of a selective 5-HT(1A) agonist, (+/-)-8-hydroxy-2-(di-n-propylamino) tetralin hydrobromide (8-OH-DPAT). Evidence supports the hypothesis that NREM sleep is modulated by thermoregulatory mechanisms localized in the preoptic area and adjacent basal forebrain (POA/BF). We previously reported that POA/BF warming suppresses the discharge of wake-promoting neurons in the posterior hypothalamus and the basal forebrain. Since the DRN is one component of the brainstem arousal system and receives projections from POA/BF, we examined the effects of local POA/BF warming by 1.5-2.0 degrees C during waking on the discharge of DRN neurons. POA/BF warming reduced the discharge in 14 of 19 PSNs and in 12 of 17 other wake-related neurons in the DRN. DRN neuronal discharge reduction occurred without accompanying EEG frequency or behavioral changes. These results suggest that PSNs recorded in DRN in unrestrained and unanesthetized rats exhibit a "wake-active REM-off" discharge pattern and further support the hypothesis that the POA/BF warm-sensitive hypnogenic system induces sleep by a coordinated inhibition of multiple arousal systems including that modulated by the DRN.