Effects of the selective 5-HT1B agonist, CGS 12066B, on sleep/waking stages and EEG power spectrum in rats

FPT, a 2-Aminotetralin, Is a Potent Serotonin 5-HT1A, 5-HT1B, and 5-HT1D Receptor Agonist That Modulates Cortical Electroencephalogram Activity in Adult Fmr1 Knockout Mice

There are no approved medicines for fragile X syndrome (FXS), a monogenic, neurodevelopmental disorder. Electroencephalogram (EEG) studies show alterations in resting-state cortical EEG spectra, such as increased gamma-band power, in patients with FXS that are also observed in Fmr1 knockout models of FXS, offering putative biomarkers for drug discovery. Genes encoding serotonin receptors (5-HTRs), including 5-HT1A, 5-HT1B, and 5-HT1DRs, are differentially expressed in FXS, providing a rationale for investigating them as pharmacotherapeutic targets. Previously we reported pharmacological activity and preclinical neurotherapeutic effects in Fmr1 knockout mice of an orally active 2-aminotetralin, (S)-5-(2'-fluorophenyl)-N,N-dimethyl-1,2,3,4-tetrahydronaphthalen-2-amine (FPT). FPT is a potent (low nM), high-efficacy partial agonist at 5-HT1ARs and a potent, low-efficacy partial agonist at 5-HT7Rs. Here we report new observations that FPT also has potent and efficacious agonist activity at human 5-HT1B and 5-HT1DRs. FPT's Ki values at 5-HT1B and 5-HT1DRs were <5 nM, but it had nil activity (>10 μM Ki) at 5-HT1FRs. We tested the effects of FPT (5.6 mg/kg, subcutaneous) on EEG recorded above the somatosensory and auditory cortices in freely moving, adult Fmr1 knockout and control mice. Consistent with previous reports, we observed significantly increased relative gamma power in untreated or vehicle-treated male and female Fmr1 knockout mice from recordings above the left somatosensory cortex (LSSC). In addition, we observed sex effects on EEG power. FPT did not eliminate the genotype difference in relative gamma power from the LSSC. FPT, however, robustly decreased relative alpha power in the LSSC and auditory cortex, with more pronounced effects in Fmr1 KO mice. Similarly, FPT decreased relative alpha power in the right SSC but only in Fmr1 knockout mice. FPT also increased relative delta power, with more pronounced effects in Fmr1 KO mice and caused small but significant increases in relative beta power. Distinct impacts of FPT on cortical EEG were like effects caused by certain FDA-approved psychotropic medications (including baclofen, allopregnanolone, and clozapine). These results advance the understanding of FPT's pharmacological and neurophysiological effects.

Modulating role of serotonergic signaling in sleep and memory

Serotonin is an important neurotransmitter with various receptors and wide-range effects on physiological processes and cognitive functions including sleep, learning, and memory. In this review study, we aimed to discuss the role of serotonergic receptors in modulating sleep-wake cycle, and learning and memory function. Furthermore, we mentioned to sleep deprivation, its effects on memory function, and the potential interaction with serotonin. Although there are thousands of research articles focusing on the relationship between sleep and serotonin; however, the pattern of serotonergic function in sleep deprivation is inconsistent and it seems that serotonin has not a certain role in the effects of sleep deprivation on memory function. Also, we found that the injection type of serotonergic agents (systemic or local), the doses of these drugs (dose-dependent effects), and up- or down-regulation of serotonergic receptors during training with various memory tasks are important issues that can be involved in the effects of serotonergic signaling on sleep-wake cycle, memory function, and sleep deprivation-induced memory impairments. This comprehensive review was conducted in the PubMed, Scopus, and ScienceDirect databases in June and July 2021, by searching keywords sleep, sleep deprivation, memory, and serotonin.

Role of the serotonergic system in ethanol-induced aggression and anxiety: A pharmacological approach using the zebrafish model

Acute ethanol (EtOH) consumption exerts a biphasic effect on behavior and increases serotonin levels in the brain. However, the molecular mechanisms underlying alcohol-mediated behavioral responses still remain to be fully elucidated. Here, we investigate pharmacologically the involvement of the serotonergic pathway on acute EtOH-induced behavioral changes in zebrafish. We exposed zebrafish to 0.25, 0.5, 1.0% (v/v) EtOH for 1 h and analyzed the effects on aggression, anxiety-like behaviors, and locomotion. EtOH concentrations that changed behavioral responses were selected to the subsequent experiments. As a pharmacological approach, we used pCPA (inhibitor of tryptophan hydroxylase), WAY100135 (5-HT_1A antagonist), buspirone (5-HT_1A agonist), CGS12066A and CGS12066B (5-HT_1B antagonist and agonist, respectively), ketanserin (5-HT_2A antagonist) and (±)-DOI hydrochloride (5-HT_2A agonist). All serotonergic receptors tested modulated aggression, with a key role of 5-HT_2A in aggressive behavior following 0.25% EtOH exposure. Because CGS12066B mimicked 0.5% EtOH anxiolysis, which was antagonized by CGS12066A, we hypothesized that anxiolytic-like responses are possibly mediated by 5-HT_1B receptors. Conversely, the depressant effects of EtOH are probably not related with direct changes on serotonergic pathway. Overall, our novel findings demonstrate a role of the serotonergic system in modulating the behavioral effects of EtOH in zebrafish. These data also reinforce the growing utility of zebrafish models in alcohol research and help elucidate the neurobiological mechanisms underlying alcohol abuse and associated complex behavioral phenotypes.

Ablation of Central Serotonergic Neurons Decreased REM Sleep and Attenuated Arousal Response

Sleep/wake behavior is regulated by distinct groups of neurons, such as dopaminergic, noradrenergic, and orexinergic neurons. Although monoaminergic neurons are usually considered to be wake-promoting, the role of serotonergic neurons in sleep/wake behavior remains inconclusive because of the effect of serotonin (5-HT)-deficiency on brain development and the compensation for inborn 5-HT deficiency by other sleep/wake-regulating neurons. Here, we performed selective ablation of central 5-HT neurons in the newly developed Rosa-diphtheria toxin receptor (DTR)-tdTomato mouse line that was crossed with Pet1^Cre/+ mice to examine the role of 5-HT neurons in the sleep/wake behavior of adult mice. Intracerebroventricular administration of diphtheria toxin completely ablated tdTomato-positive cells in Pet1^Cre/+; Rosa-DTR-tdTomato mice. Electroencephalogram/electromyogram-based sleep/wake analysis demonstrated that central 5-HT neuron ablation in adult mice decreased the time spent in rapid eye movement (REM) sleep, which was associated with fewer transitions from non-REM (NREM) sleep to REM sleep than in control mice. Central 5-HT neuron-ablated mice showed attenuated wake response to a novel environment and increased theta power during wakefulness compared to control mice. The current findings indicated that adult 5-HT neurons work to support wakefulness and regulate REM sleep time through a biased transition from NREM sleep to REM sleep.

MDMA self-administration fails to alter the behavioral response to 5-HT(1A) and 5-HT(1B) agonists

RATIONALE

Regular use of the street drug, ecstasy, produces a number of cognitive and behavioral deficits. One possible mechanism for these deficits is functional changes in serotonin (5-HT) receptors as a consequence of prolonged 3,4 methylenedioxymethamphetamine (MDMA)-produced 5-HT release. Of particular interest are the 5-HT(1A) and 5-HT(1B) receptor subtypes since they have been implicated in several of the behaviors that have been shown to be impacted in ecstasy users and in animals exposed to MDMA.

OBJECTIVES

This study aimed to determine the effect of extensive MDMA self-administration on behavioral responses to the 5-HT(1A) agonist, 8-hydroxy-2-(n-dipropylamino)tetralin (8-OH-DPAT), and the 5-HT(1B/1A) agonist, RU 24969.

METHODS

Male Sprague-Dawley rats self-administered a total of 350 mg/kg MDMA, or vehicle, over 20-58 daily self-administration sessions. Two days after the last self-administration session, the hyperactive response to 8-OH-DPAT (0.03-1.0 mg/kg) or the adipsic response to RU 24969 (0.3-3.0 mg/kg) were assessed.

RESULTS

8-OH-DPAT dose dependently increased horizontal activity, but this response was not altered by MDMA self-administration. The dose-response curve for RU 24969-produced adipsia was also not altered by MDMA self-administration.

CONCLUSIONS

Cognitive and behavioral deficits produced by repeated exposure to MDMA self-administration are not likely due to alterations in 5-HT(1A) or 5-HT(1B) receptor mechanisms.

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.

Esmirtazapine in non-elderly adult patients with primary insomnia: efficacy and safety from a randomized, 6-week sleep laboratory trial

OBJECTIVE

Esmirtazapine (Org 50081), a medication that binds with high affinity to serotonin 5-HT2A and histamine-1 receptors, was evaluated as a potential treatment for insomnia.

METHODS

Adults with primary insomnia were treated with esmirtazapine (3.0 or 4.5 mg) or placebo in this 6-week, double-blind, randomized, polysomnography (PSG) study. The end points included wake time after sleep onset (WASO) (primary), latency to persistent sleep, and total sleep time. Patient-reported parameters were also evaluated, including sleep quality and satisfaction with sleep duration. Residual daytime effects and rebound insomnia (sleep parameters during the single-blind placebo run-out week after treatment ended) were also assessed.

RESULTS

Overall, 419 patients were randomized and 366 (87%) completed treatment. The median decrease in PSG WASO (double-blind average) was 20.5 min for placebo, and 52.0 min and 53.6 min for the 3.0- and 4.5-mg esmirtazapine groups, respectively (P < 0.0001 vs. placebo for both doses). Changes in the other PSG parameters and in all patient-reported parameters were also statistically significant with both doses versus placebo. Overall, 35-42% of esmirtazapine-treated patients had adverse events (AEs) versus 29% in the placebo group. AEs were mild or moderate in most esmirtazapine-treated patients. Furthermore, the incidence of AEs leading to discontinuation was low (<8%).

CONCLUSIONS

Six weeks of treatment with esmirtazapine was associated with consistent improvements in objective and patient-reported parameters of sleep onset, maintenance, and duration. It was generally well tolerated, and residual daytime effects were minimal and no rebound insomnia was observed.

A study on fear memory retrieval and REM sleep in maternal separation and isolation stressed rats

As rapid brain development occurs during the neonatal period, environmental manipulation during this period may have a significant impact on sleep and memory functions. Moreover, rapid eye movement (REM) sleep plays an important role in integrating new information with the previously stored emotional experience. Hence, the impact of early maternal separation and isolation stress (MS) during the stress hyporesponsive period (SHRP) on fear memory retention and sleep in rats were studied. The neonatal rats were subjected to maternal separation and isolation stress during postnatal days 5-7 (6h daily/3d). Polysomnographic recordings and differential fear conditioning was carried out in two different sets of rats aged 2 months. The neuronal replay during REM sleep was analyzed using different parameters. MS rats showed increased time in REM stage and total sleep period also increased. MS rats showed fear generalization with increased fear memory retention than normal control (NC). The detailed analysis of the local field potentials across different time periods of REM sleep showed increased theta oscillations in the hippocampus, amygdala and cortical circuits. Our findings suggest that stress during SHRP has sensitized the hippocampus-amygdala-cortical loops which could be due to increased release of corticosterone that generally occurs during REM sleep. These rats when subjected to fear conditioning exhibit increased fear memory and increased fear generalization. The development of helplessness, anxiety and sleep changes in human patients, thus, could be related to the reduced thermal, tactile and social stimulation during SHRP on brain plasticity and fear memory functions.

Effects of social defeat on sleep and behaviour: importance of the confrontational behaviour

We studied the short- and long-term effects of a double social defeat (SD) on sleep parameters, EEG power, behaviour in the open field emergence test, corticosterone responsiveness, and acoustic startle responses. Pre-stress levels of corticosterone were assessed before all rats were surgically implanted with telemetric transmitters for sleep recording, and allowed 3weeks of recovery. Rats in the SD group (n=10) were exposed to 1hour SD on two consecutive days, while control rats (n=10) were left undisturbed. Telemetric sleep recordings were performed before SD (day -1), day 1 post SD, and once weekly for 3weeks thereafter. The open field emergence test was performed on day 9 and weekly for 2weeks thereafter. Blood samples for measures of corticosterone responsiveness were drawn after the last emergence test (day 23). Acoustic startle responses were tested on day 24 post SD. Overall, SD rats as a group were not affected by the social conflict. Effects of SD seemed, however, to vary according to the behaviours that the intruder displayed during the social confrontation with the resident. Compared to those SD rats showing quick submission (SDS, n=5), SD rats fighting the resident during one or both SD confrontations before defeat (SDF, n=5) showed more fragmented slow wave sleep, both in SWS1 and SWS2. They also showed longer latency to leave the start box and spent less time in the open field arena compared to SDS rats. In the startle test, SDF rats failed to show response decrement at the lowest sound level. Our results indicate that how animals behave during a social confrontation is more important than exposure to the SD procedure itself, and that rapid submission during a social confrontation might be more adaptive than fighting back.

Analysis of sleep disorders under pain using an optogenetic tool: possible involvement of the activation of dorsal raphe nucleus-serotonergic neurons

Background

Several etiological reports have shown that chronic pain significantly interferes with sleep. Inadequate sleep due to chronic pain may contribute to the stressful negative consequences of living with pain. However, the neurophysiological mechanism by which chronic pain affects sleep-arousal patterns is as yet unknown. Although serotonin (5-HT) was proposed to be responsible for sleep regulation, whether the activity of 5-HTergic neurons in the dorsal raphe nucleus (DRN) is affected by chronic pain has been studied only infrequently. On the other hand, the recent development of optogenetic tools has provided a valuable opportunity to regulate the activity in genetically targeted neural populations with high spatial and temporal precision. In the present study, we investigated whether chronic pain could induce sleep dysregulation while changing the activity of DRN-5-HTergic neurons. Furthermore, we sought to physiologically activate the DRN with channelrhodopsin-2 (ChR2) to identify a causal role for the DRN-5-HT system in promoting and maintaining wakefulness using optogenetics.

Results

We produced a sciatic nerve ligation model by tying a tight ligature around approximately one-third to one-half the diameter of the sciatic nerve. In mice with nerve ligation, we confirmed an increase in wakefulness and a decrease in non-rapid eye movement (NREM) sleep as monitored by electroencephalogram (EEG). Microinjection of the retrograde tracer fluoro-gold (FG) into the prefrontal cortex (PFC) revealed several retrogradely labeled-cells in the DRN. The key finding of the present study was that the levels of 5-HT released in the PFC by the electrical stimulation of DRN neurons were significantly increased in mice with sciatic nerve ligation. Using optogenetic tools in mice, we found a causal relationship among DRN neuron firing, cortical activity and sleep-to-wake transitions. In particular, the activation of DRN-5-HTergic neurons produced a significant increase in wakefulness and a significant decrease in NREM sleep. The duration of NREM sleep episodes was significantly decreased during photostimulation in these mice.

Conclusions

These results suggest that neuropathic pain accelerates the activity of DRN-5-HTergic neurons. Although further loss-of-function experiments are required, we hypothesize that this activation in DRN neurons may, at least in part, correlate with sleep dysregulation under a neuropathic pain-like state.

Post-transcriptional effects and interactions between chronic mild stress and acute sleep deprivation: regulation of translation factor and cytoplasmic polyadenylation element-binding protein phosphorylation

Stress and restricted or disrupted sleep trigger adaptive responses in the brain at the level of gene transcription. We investigated the possible impact of chronic mild stress (CMS), acute sleep deprivation, and a combination of these in male rats on post-transcriptional mechanisms important for cognitive function and synaptic plasticity. Relationships between sleep architecture and translational regulators were also assessed. After four weeks of CMS, phosphorylation of two key translation factors, eukaryotic initiation factor 4E (eIF4E) and elongation factor 2 (eEF2), was enhanced in the prefrontal cortex, but unchanged in the hippocampus and dentate gyrus. Sleep deprivation decreased phosphorylated eIF4E in the dentate gyrus. In contrast, eEF2 phosphorylation was elevated in all brain regions after sleep deprivation. Thus, CMS and sleep deprivation, when given alone, have distinct region-specific effects. Furthermore, the combined treatment revealed striking interactions with eEF2 phosphorylation in which sleep deprivation counteracts the effect of CMS cortically and CMS modulates the effects of sleep deprivation in the hippocampus proper. Although CMS exposure alone had no effect in the hippocampus, it inhibited the sleep deprivation-induced eIF4E phosphorylation, while inducing phosphorylation of a major regulatory RNA-binding protein, cytoplasmic polyadenylation element-binding protein (CPEB) in the combined treatment. CMS had no effect on plasma corticosterone, but led to disruption of sleep. Sleep quality and sleep quantity in non-stressed animals showed predictive changes in eIF4E and eEF2 phosphorylation cortically. Prior exposure to CMS abolishes this relationship. We conclude that CMS and acute sleep deprivation have interactive and brain region-specific effects on translational regulators of relevance to mechanisms of stress responsiveness and sleep homeostasis.

Serotonin conflict in sleep-feeding

Short sleep duration has been suggested to be a risk factor for weight gain and adiposity. Serotonin (5-HT) substantially contributes to the regulation of sleep and feeding behavior. Although 5-HT predominately promotes waking and satiety, the effects of 5-HT depend on 5-HT receptor function. The 5-HT1A, 5-HT1B, 5-HT2A, 5-HT2C, 5-HT6, and 5-HT7 receptors reportedly contribute to sleep-waking regulation, whereas the 5-HT1B and 5-HT2C receptors contribute to the regulation of satiety. The 5-HT1B and 2C receptors may therefore be involved in the regulation of sleep-feeding. In genetic studies, 5-HT1B receptor mutant mice display greater amounts of rapid eye movement sleep (REMS) than wild-type mice, while displaying no effects on waking or slow wave sleep (SWS). On the other hand, 5-HT2C receptor mutant mice exhibit increased wakefulness and decreased SWS, without any effect on REMS. Moreover, the 5-HT2C receptor mutants display leptin-independent hyperphagia, leading to a middle-aged onset of obesity, whereas 5-HT1B receptor mutants do not display any effect on food intake. Thus, the genetic deletion of 5-HT2C receptors results in sleep loss-associated hyperphagia, leading to the late onset of obesity. This is a quite different pattern of sleep-feeding behavior than is observed in disturbed leptin signaling, which displays an increase in sleep-associated hyperphagia. In pharmacologic studies, 5-HT1B and 5-HT2C receptors upregulate wakefulness and downregulate SWS, REMS, and food intake. These findings suggest that 5-HT1B/2C receptor stimulation induces sleep loss-associated anorexia. Thus, the central 5-HT regulation of sleep-feeding can be dissociated. Functional hypothalamic proopiomelanocortin and orexin activities may contribute to the dissociated 5-HT regulation.

Sleep neurobiology from a clinical perspective

Many neurochemical systems interact to generate wakefulness and sleep. Wakefulness is promoted by neurons in the pons, midbrain, and posterior hypothalamus that produce acetylcholine, norepinephrine, dopamine, serotonin, histamine, and orexin/hypocretin. Most of these ascending arousal systems diffusely activate the cortex and other forebrain targets. NREM sleep is mainly driven by neurons in the preoptic area that inhibit the ascending arousal systems, while REM sleep is regulated primarily by neurons in the pons, with additional influence arising in the hypothalamus. Mutual inhibition between these wake- and sleep-regulating regions likely helps generate full wakefulness and sleep with rapid transitions between states. This up-to-date review of these systems should allow clinicians and researchers to better understand the effects of drugs, lesions, and neurologic disease on sleep and wakefulness.

Serotonin control of sleep-wake behavior

Based on electrophysiological, neurochemical, genetic and neuropharmacological approaches, it is currently accepted that serotonin (5-HT) functions predominantly to promote wakefulness (W) and to inhibit REM (rapid eye movement) sleep (REMS). Yet, under certain circumstances the neurotransmitter contributes to the increase in sleep propensity. Most of the serotonergic innervation of the cerebral cortex, amygdala, basal forebrain (BFB), thalamus, preoptic and hypothalamic areas, raphe nuclei, locus coeruleus and pontine reticular formation comes from the dorsal raphe nucleus (DRN). The 5-HT receptors can be classified into at least seven classes, designated 5-HT(1-7). The 5-HT(1A) and 5-HT(1B) receptor subtypes are linked to the inhibition of adenylate cyclase, and their activation evokes a membrane hyperpolarization. The actions of the 5-HT(2A), 5-HT(2B) and 5-HT(2C) receptor subtypes are mediated by the activation of phospholipase C, with a resulting depolarization of the host cell. The 5-HT(3) receptor directly activates a 5-HT-gated cation channel which leads to the depolarization of monoaminergic, aminoacidergic and cholinergic cells. The primary signal transduction pathway of 5-HT(6) and 5-HT(7) receptors is the stimulation of adenylate cyclase which results in the depolarization of the follower neurons. Mutant mice that do not express 5-HT(1A) or 5-HT(1B) receptor exhibit greater amounts of REMS than their wild-type counterparts, which could be related to the absence of a postsynaptic inhibitory effect on REM-on neurons of the laterodorsal and pedunculopontine tegmental nuclei (LDT/PPT). 5-HT(2A) and 5-HT(2C) receptor knock-out mice show a significant increase of W and a reduction of slow wave sleep (SWS) which has been ascribed to the increase of catecholaminergic neurotransmission involving mainly the noradrenergic and dopaminergic systems. Sleep variables have been characterized, in addition, in 5-HT(7) receptor knock-out mice; the mutants spend less time in REMS that their wild-type counterparts. Direct infusion of the 5-HT(1A) receptor agonists 8-OH-DPAT and flesinoxan into the DRN significantly enhances REMS in the rat. In contrast, microinjection of the 5-HT(1B) (CP-94253), 5-HT(2A/2C) (DOI), 5-HT(3) (m-chlorophenylbiguanide) and 5-HT(7) (LP-44) receptor agonists into the DRN induces a significant reduction of REMS. Systemic injection of full agonists at postsynaptic 5-HT(1A) (8-OH-DPAT, flesinoxan), 5-HT(1B) (CGS 12066B, CP-94235), 5-HT(2C) (RO 60-0175), 5-HT(2A/2C) (DOI, DOM), 5-HT(3) (m-chlorophenylbiguanide) and 5-HT(7) (LP-211) receptors increases W and reduces SWS and REMS. Of note, systemic administration of the 5-HT(2A/2C) receptor antagonists ritanserin, ketanserin, ICI-170,809 or sertindole at the beginning of the light period has been shown to induce a significant increase of SWS and a reduction of REMS in the rat. Wakefulness was also diminished in most of these studies. Similar effects have been described following the injection of the selective 5-HT(2A) receptor antagonists volinanserin and pruvanserin and of the 5-HT(2A) receptor inverse agonist nelotanserin in rodents. In addition, the effects of these compounds have been studied on the sleep electroencephalogram of subjects with normal sleep. Their administration was followed by an increase of SWS and, in most instances, a reduction of REMS. The administration of ritanserin to poor sleepers, patients with chronic primary insomnia and psychiatric patients with a generalized anxiety disorder or a mood disorder caused a significant increase in SWS. The 5-HT(2A) receptor inverse agonist APD-125 induced also an increase of SWS in patients with chronic primary insomnia. It is known that during the administration of benzodiazepine (BZD) hypnotics to patients with insomnia there is a further reduction of SWS and REMS, whereas both variables tend to remain decreased during the use of non-BZD derivatives (zolpidem, zopiclone, eszopiclone, zaleplon). Thus, the association of 5-HT(2A) antagonists or 5-HT(2A) inverse agonists with BZD and non-BZD hypnotics could be a valid alternative to normalize SWS in patients with primary or comorbid insomnia.

A double exposure to social defeat induces sub-chronic effects on sleep and open field behaviour in rats

Social defeat, resulting from the fight for a territory is based on the resident-intruder paradigm. A male rat intruder is placed in the territory of an older, bigger and more aggressive male resident and is defeated. In the present study, a double exposure to social defeat increased sleep fragmentation due to an increased amount of waking and slow-wave-sleep-1 (SWS-1) episodes. Also, social defeat increased the amount of slow-wave-sleep-2 (SWS-2). In repeated exposures to an open field, socially defeated rats showed low central activity and persistent defecation indicating high emotionality. The strongest effects of social defeat on sleep and open field behaviour were seen sub-chronically after stress. Social defeat did not induce changes in rapid eye movement (REM) sleep (e.g. total amount, latency), sleep latency, sexual activity, body weight or adrenal weight. A negative correlation between habituation in open field central activity and total sleep fragmentation indicates a commonality of effects of social defeat on both behaviour and sleep.

MDMA treatment 6 months earlier attenuates the effects of CP-94,253, a 5-HT1B receptor agonist, on motor control but not sleep inhibition

The possible long-term effects of the recreational drug "ecstasy" (3,4-methylenedioxymethamphetamine, MDMA) on the function of 5-hydroxytryptamine-1B (5-HT(1B)) receptor in sleep and motor control were investigated using a selective 5-HT(1B) receptor agonist, 5-propoxy-3-(1,2,3,6-tetrahydro-4-pyrinzidyl)-1H-pyrrolo([3,2-b])pyridine hydrochloride (CP-94,253; 5 mg/kg). CP-94,253 or vehicle was administered to freely moving rats pre-treated with MDMA (15 mg/kg) or vehicle 6 months earlier, and polygraphic recording for 24 h and motor activity measurements were performed. Active wake (AW), passive wake (PW), light slow wave sleep (SWS-1), deep slow wave sleep (SWS-2), paradoxical sleep (PS), and diurnal rhythm were analyzed for the whole period. In additional, the EEG power spectrum was calculated for the second hour after the acute treatment for AW, PW, SWS-1, and SWS-2. 5-HT transporter (5-HTT) immunohistochemistry was measured in brain areas related to sleep and motor control 6 months after MDMA treatment. CP-94,253 increased AW and PW, decreased SWS-2 and PS, and altered parameters of diurnal rhythm in control animals. CP-94,253 decreased the EEG power spectra at higher frequencies. The effects of CP-94,253 on AW and diurnal rhythm were reduced or eliminated in MDMA-treated animals. MDMA treatment decreased 5-HTT fibre density in posterior hypothalamus, tuberomammillary nucleus, caudate putamen and ventrolateral striatum. These data suggest that long-term changes in 5-HT(1B) receptor function occur after serotonergic damage caused by a single dose of MDMA.

Stress-induced changes in sleep and associated neuronal activity in rat hippocampus and amygdala

Stress increases vulnerability to anxiety and depression. We have investigated the effect of acute immobilization stress in amygdalohippocampal circuits by measuring the electroencephalogram (EEG) in male Wistar rats during rapid eye movement (REM) sleep. Electrodes were implanted stereotaxically in the hippocampus (CA1 and CA3 subregions of the hippocampus) and the amygdala (lateral nucleus). Prior to the stress, two baseline recordings were taken. Twenty-four hours later rats were exposed once to acute immobilization stress (AIS) session for 2 h. After the release and on subsequent days, electrophysiological changes that occurred due to stress during REM sleep were analyzed by comparing them with baseline measurements. Our results suggest that acute immobilization stress induced significant increase in REM sleep in the first 24 h after the exposure. In addition to changes in the sleep patterns, we have observed increased theta oscillations in CA1 area of the hippocampus with decreased coherence at theta range (4-8 Hz) between hippocampus and amygdala. These results suggest that single exposure to aversive experience such as immobilization stress can lead to dynamic changes in neuronal activities with altered sleep morphology. The results obtained in the present study are comparable to those seen in human patients suffering from panic, and anxiety due to posttraumatic stress disorder (PTSD).

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.

Effects of the selective activation of 5-HT3 receptors on sleep: a polysomnographic study in healthy volunteers

The respective role of various classes of central serotonin (5-HT) receptors in the regulation of sleep-wakefulness cycles has been the subject of many studies. Notably, it has been reported that 5-HT1A/B receptors are involved in the regulation of rapid eye movement sleep (REMS) and that 5-HT2A/C receptors participate in the control of slow wave sleep (SWS), but the role of 5-HT3 receptors is less well characterised. In this study we investigated the effects of SR 57227A, a potent and selective 5-HT3 agonist, on the sleep EEG of normal young male volunteers. SR 57227A (2.5, 5, 10, 20, 40 mg o.d. and 20 mg b.i.d.) or placebo were administered during 7 consecutive days in seven groups of ten subjects using a parallel group design. Sleep EEG recordings were performed on days 6 and 7 after an habituation session. SR 57227A produced a dose-dependent shift of REMS toward the end of the night without changing REMS and SWS duration nor altering sleep continuity. It suggests a role for the 5-HT3 receptor in the human sleep-wakefulness cycle and particularly in REMS regulation.

Serotonin and the sleep/wake cycle: special emphasis on microdialysis studies

Several areas in the brainstem and forebrain are important for the modulation and expression of the sleep/wake cycle. Even if the first observations of biochemical events in relation to sleep were made only 40 years ago, it is now well established that several neurotransmitters, neuropeptides, and neurohormones are involved in the modulation of the sleep/wake cycle. Serotonin has been known for many years to play a role in the modulation of sleep, however, it is still very controversial how and where serotonin may operate this modulation. Early studies suggested that serotonin is necessary to obtain and maintain behavioral sleep (permissive role on sleep). However, more recent microdialysis experiments provide evidence that the level of serotonin during W is higher in most cortical and subcortical areas receiving serotonergic projections. In this view the level of extracellular serotonin would be consistent with the pattern of discharge of the DRN serotonergic neurons which show the highest firing rate during W, followed by a decrease in slow wave sleep and by virtual electrical silence during REM sleep. This suggests that during waking serotonin may complement the action of noradrenaline and acetylcholine in promoting cortical responsiveness and participate to the inhibition of REM-sleep effector neurons in the brainstem (inhibitory role on REM sleep). The apparent inconsistency between an inhibitory and a facilitatory role played by serotonin on sleep has at least two possible explanations. On the one hand serotonergic modulation on the sleep/wake cycle takes place through a multitude of post-synaptic receptors which mediate different or even opposite responses; on the other hand the achievement of a behavioral state depends on the complex interaction between the serotonergic and other neurotransmitter systems. The main aim of this commentary is to review the role of brain serotonin in relation to the sleep/wake cycle. In particular we highlight the importance of microdialysis for on-line monitoring of the level of serotonin in different areas of the brain across the sleep/wake cycle.

Psychogenetically selected (Roman high- and low-avoidance) rats differ in 24-hour sleep organization

A comparison of sleep organization in Roman high-(RHA/Verh) and low-(RLA/Verh) avoidance rats, which differ in the way they respond to environmental stimuli and in several neuroendocrine and neurochemical parameters, was carried out. EEG-sleep recordings were obtained from adult males over 12:12 light-dark periods to determine how these two psychogenetically selected rat lines might also differ in their sleep-wake cycle. There was no significant difference in total sleep time between the two lines. However, the (hypoemotional) RHA/Verh rats showed an overall increase (percentage of total sleep) in paradoxical sleep (PS) duration, with a concomitant decrease in slow-wave sleep (SWS). During the dark phase, RHA/Verh rats showed a shorter PS latency and a larger number of PS episodes. Hourly sleep scoring also revealed a more discontinuous pattern (total sleep and PS vs. SWS) during the dark phase in RHA/Verh rats. In relation to recognized neurochemical and neuroendocrine differences between them, these rat lines may prove useful in investigations of the neurobiological mechanisms underlying sleep regulation.

Key role of 5-HT1B receptors in the regulation of paradoxical sleep as evidenced in 5-HT1B knock-out mice

The involvement of 5-HT1B receptors in the regulation of vigilance states was assessed by investigating the spontaneous sleep-waking cycles and the effects of 5-HT receptor ligands on sleep in knock-out (5-HT1B-/-) mice that do not express this receptor type. Both 5-HT1B-/- and wild-type 129/Sv mice exhibited a clear-cut diurnal sleep-wakefulness rhythm, but knock-out animals were characterized by higher amounts of paradoxical sleep and lower amounts of slow-wave sleep during the light phase and by a lack of paradoxical sleep rebound after deprivation. In wild-type mice, the 5-HT1B agonists CP 94253 (1-10 mg/kg, i.p.) and RU 24969 (0.25-2.0 mg/kg, i.p.) induced a dose-dependent reduction of paradoxical sleep during the 2-6 hr after injection, whereas the 5-HT1B/1D antagonist GR 127935 (0.1-1.0 mg/kg, i.p.) enhanced paradoxical sleep. In addition, pretreatment with GR 127935, but not with the 5-HT1A antagonist WAY 100635, prevented the effects of both 5-HT1B agonists. In contrast, none of the 5-HT1B receptor ligands, at the same doses as those used in wild-type mice, had any effect on sleep in 5-HT1B-/- mutants. Finally, the 5-HT1A agonist 8-OH-DPAT (0.2-1.2 mg/kg, s.c.) induced in both strains a reduction in the amount of paradoxical sleep. Altogether, these data indicate that 5-HT1B receptors participate in the regulation of paradoxical sleep in the mouse.

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

Serotonin (5-HT) has been implicated in the regulation of vigilance, but whether 5-HT is important for sleep or waking processes remains controversial. This review addresses the role of 5-HT1A receptors in sleep and wakefulness. Systemic administration of 5-HT1A agonists consistently increases wakefulness, whereas slow wave sleep (SWS) and REM (rapid-eye movement) sleep are reduced. However, systemic 5-HT1A agonists also produce a delayed increase in deep slow wave sleep, or an increase in slow wave activity. Intrathecal administration of a selective 5-HT1A agonist produces an increase in SWS, whereas wakefulness is reduced, presumably by stimulating 5-HT1A receptors located presynaptically on primary afferents in the spinal cord. Microinjection of serotonin into the region of the cholinergic basalis neurons produces an increase in slow wave activity, presumably by stimulating 5-HT1A receptors. Microdialysis perfusion of a selective 5-HT1A agonist into the dorsal Raphe nucleus causes an increase in REM sleep, whereas the other sleep/wake stages are unaltered. The REM sleep increase is likely due to a decrease in 5-HT neuronal activity, and thereby reduced 5-HT neurotransmission in projection areas, e.g. the laterodorsal and pedunculopontine tegmental nuclei. Direct injection of a selective 5-HT1A agonist into the pedunculopontine tegmental nuclei reduces REM sleep, consistent with such a hypothesis. These complex sleep/wake data of 5-HT1A ligands suggest that 5-HT1A receptor activation may increase waking, increase slow wave sleep or increase REM sleep depending on where the 5-HT1A receptors are located within the central nervous system.

On-line detection of extracellular levels of serotonin in dorsal raphe nucleus and frontal cortex over the sleep/wake cycle in the freely moving rat

We used in vivo microdialysis coupled with polygraphic recording to monitor 5-hydroxytryptamine levels in the dorsal raphe nucleus and frontal cortex across waking, slow-wave sleep and rapid eye-movement sleep. Male Sprague-Dawley rats were prepared with electroencephalogram and electromyogram electrodes. Microdialysis probes were placed in dorsal raphe nucleus and/or frontal cortex. Dialysate samples were manually collected during polygraphically-defined behavioural states and the level of serotonin was assayed by means of microbore high-performance liquid chromatography separation and electrochemical detection. Samples from microdialysis probes histologically localized to the dorsal raphe nucleus and frontal cortex showed different levels of extracellular 5-hydroxytryptamine in waking, slow-wave sleep and rapid eye-movement sleep. In dorsal raphe nucleus the extracellular level of serotonin was highest in waking, decreased in slow-wave sleep to 69% and in rapid eye-movement sleep to 39% of waking mean level (waking 3.2 +/- 0.9; slow-wave sleep 2.2 +/- 0.8; rapid eye-movement sleep 1.3 +/- 0.4 fmol/sample). Mean extracellular levels of serotonin in frontal cortex displayed a similar pattern (waking 1.7 +/- 0.4; slow-wave sleep 1.0 +/- 0.3; rapid eye-movement 0.5 +/- 0.05 fmol/sample). In frontal cortex, rapid eye-movement sleep samples were only obtained in three animals. Our findings are consistent with previous results in cats, and suggest that in rats also, extracellular 5-hydroxytryptamine levels in dorsal raphe nucleus and frontal cortex across the sleep/wake cycle might reflect serotonergic neuronal activity. The findings stress the importance of controlling for behavioural state when investigating neurochemical correlates of serotonergic function.

EEG power densities (0.5-20 Hz) in different sleep-wake stages in rats

Frontofrontal and frontoparietal EEG power densities (0.5-20 Hz) in waking, light and deep slow-wave sleep, transition-type sleep, and rapid-eye-movement (REM) sleep were investigated for 8 h during the light period in 16 male Wistar rats. The data indicate that as delta activity (0.5-4.5 Hz) increased from light to deep slow-wave sleep, the number of epochs per scoring epoch with high sigma activity (11-16 Hz) as well as power densities in the rest of the spectrum (5-20 Hz) including sigma frequencies also increased. This is in parallel with other rat studies but contrasts findings in humans, where EEG sigma activity is reported to decrease as sleep deepens. During the 8-h recording period, delta activity decreased whereas sigma activity increased.

Sleep/waking effects of a selective 5-HT1A receptor agonist given systemically as well as perfused in the dorsal raphe nucleus in rats

Sleep/waking stages and behavior were studied following the selective 5-HT1A agonist 8-OH-DPAT given subcutaneously (s.c.) (0.010-0.375 mg/kg) as well as perfused continuously (10 microM) for 6 h into the dorsal raphe nucleus (DRN) using microdialysis. Given systemically, 8-OH-DPAT at 0.375 mg/kg s.c. induced 5-HT behavioral syndrome, increased waking to 149% and reduced slow wave sleep (SWS) to 86%, transition to 76% and rapid eye movement (REM) sleep to 73%. The effect on deep SWS (SWS-2) was biphasic, with an increase after 2 h. 8-OH-DPAT at 0.010 mg/kg did not have any vigilance effects. 8-OH-DPAT perfusion in DRN produced a fourfold increase in REM sleep compared to perfusion of artificial cerebrospinal fluid. This is consistent with the hypothesis that reduced 5-HT neurotransmission following 5-HT1A autoreceptor stimulation will disinhibit cholinergic REM-promoting mesopontine neurons and thereby lead to a REM sleep increase. The other sleep/waking stages were not significantly affected by 8-OH-DPAT perfusion in DRN.

Human sleep EEG following the 5-HT1A antagonist pindolol: possible disinhibition of raphe neuron activity

The sleep electroencephalogram (EEG) was used to assay central effects of pindolol (10 and 30 mg p.o.), a mixed beta(1/2)-adrenoceptor/5-hydroxytryptamine (5-HT)(1A/1B) receptor blocker, in humans. Compared to placebo, pindolol produced a dose-related suppression of rapid-eye-movement (REM) sleep, including a prolongation of REM latency, and a decrease of REM time and REM density. At the higher dose, it also reduced EEG spectral power during non-REM sleep in portions of the delta, theta, and alpha frequencies (1.125-5.125 Hz, 7.125-9.625 Hz). By contrast, betaxolol (20 mg p.o.), a selective beta1-antagonist devoid of serotonergic affinity, affected neither REM sleep nor EEG power. REM sleep is, in part, under the inhibitory control of serotonergic neurons projecting from the dorsal raphe nucleus to pontine cholinergic/cholinoceptive cells. The EEG power spectrum induced by pindolol tended to be opposite to what has previously been reported for ipsapirone, a 5-HT1A agonist. Therefore, the present data, tentatively, are consistent with the contention that pindolol inhibits, possibly selectively, somatodendritic 5-HT1A autoreceptors in humans and may antagonize self-inhibition of midbrain raphe nuclei 5-HT neurons.

Citalopram: differential sleep/wake and EEG power spectrum effects after single dose and chronic administration

The sleep/wake effects of the selective serotonin re-uptake inhibitor citalopram were studied in both a single-dose study with three dose levels (0.5, 2.0 and 5.0 mg/kg), and a 5-week chronic administration study (15 mg/kg/24 h). Single doses of citalopram resulted in a dose-dependent inhibition of rapid eye movement (REM) sleep. After chronic citalopram treatment there was a sustained REM sleep inhibition. Single doses of citalopram resulted in only minor changes in non-REM (NREM) sleep as well as in NREM EEG power spectral density. Chronic administration resulted in a major shift from SWS-2 to SWS-1. The observed corresponding changes in EEG power density were regional. A 30 to 40 percent reduction of power density in the 0.5-15 Hz range in the fronto-parietal EEG derivation was seen for the whole 8-h registration period. In the fronto-frontal EEG derivation only minor changes were seen. A decreasing trend in NREM sleep power density between 0.5 and 7 Hz, usually seen during the course of the light period, was not observed in the chronic condition, but was seen in control and single-dose condition, suggesting altered diurnal distribution of slow wave activity in the chronic condition. The data indicate that acute and chronic administration of citalopram shows clear differences in sleep effect, which may be caused by alteration of serotonergic transmission, and may be related to the antidepressant effect.

Sleep and EEG power spectrum effects of the 5-HT1A antagonist NAN-190 alone and in combination with citalopram

The sleep and waking and EEG power spectrum effects of the putative 5-HT1A antagonist NAN-190 (0.5 mg/kg, i.p.) were studied alone and in co-administration with the selective serotonin re-uptake inhibitor citalopram (5.0 mg/kg, i.p.) in the rat. Citalopram, as in a prior dose-response study, reduced REM sleep. In addition, a slight increase in NREM sleep was observed. Citalopram reduced NREM fronto-parietal (FP) EEG power density in the 5-20 Hz range. When administered alone, NAN-190 suppressed REM sleep in the first 2 h, and reduced SWS-2 in the first 4 after administration. NAN-190 also suppressed selectively NREM sleep slow-wave activity in both fronto-frontal (FF) and FP EEG power spectrum. When administered in combination with citalopram, an attenuation of the power density reduction in the 7-15 Hz range in the FF EEG of citalopram alone, was observed. However, the EEG power spectral density and REM sleep suppressive effects of NAN-190 were both augmented. The results are compatible with the notion that serotonin is involved in the modulation of the slow wave activity in the EEG during NREM sleep. The results are cordant with other data suggesting that postsynaptic 5-HT1A stimulation might increase slow wave activity in the NREM EEG, and that serotonergic stimulation of other receptor subtypes (possibly 5-HT2) may decrease slow wave activity in the NREM EEG.

Sleep/waking effects following intrathecal administration of the 5-HT(1A) Agonist 8-OH-DPAT alone and in combination with the putative 5-HT(1A) antagonist NAN-190 in rats

Sleep, waking, and EEG power spectra were investigated in rats after intrathecal (IT) administration of a 5-HT(1A) agonist and a 5-HT(1A) antagonist. Total slow wave sleep (TSWS) was increased and waking was decreased over the 8-h recording period after the 5-HT(1A) agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) (38 nmol). Within TSWS, SWS1 was unchanged while SWS-2 tended to be increased. The 5-HT(1A) antagonist 1-[2-Methoxyphenyl)-4-(4-(2-phthalimido)-butyl]piperazine hydrobromide (NAN-190) did not change any sleep/waking stages. Combined treatment with 8-OH-DPAT and NAN-190 increased variance. Following the combination, sleep and waking were not significantly different from control. SWS-2 tended to be reduced compared to the effect of 8-OH-DPAT alone. There were no systematic changes in neither waking nor TSWS fronto-frontal or fronto-parietal EEG power spectrum after any of the treatments, indicating that sleep quality was not changed. The results confirm earlier data suggesting that in the spinal cord, stimulation of 5-HT(1A) receptors have a dampening effect on transmission of sensory information, leading to deactivation and thereby increased sleep tendency. The reason why the 8-OH-DPAT effect was not clearly antagonized by the putative 5-HT1A antagonist NAN-190, may be due to the generally weak antagonistic and also partial agonistic effect of NAN-190 as reported in the literature.

Effects of selective activation of the 5-HT1B receptor with CP-94,253 on sleep and wakefulness in the rat

The effects of the 5-HT1B receptor agonist CP-94,253 were compared with those of the mixed beta-adrenoceptor and 5-HT1A/B receptor antagonist (+/-)pindolol in rats implanted for chronic sleep recordings. CP-94,253 (5.0-10.0 mg/kg) significantly increased waking and reduced slow wave sleep (SWS) and REM sleep (REMS). At 2.0-4.0 mg/kg (+/-)pindolol reduced REMS. Pretreatment with (+/-)pindolol (2.0-4.0 mg/kg) reversed the effect of CP-94,253 on waking and SWS, while REMS remained suppressed. It is suggested that the 5-HT1B receptor together with other 5-HT receptor subtypes may have a direct regulatory action on sleep and waking in the rat.

Lesion of descending 5-HT pathways increases zimeldine-induced waking in rats

Sleep, waking, and EEG power spectra were investigated in rats with spinal 5,6-dihydroxytryptamine (5,6-DHT) lesions, following 20 mg/kg zimeldine or vehicle IP injections. 5,6-DHT selectively lesioned the descending serotonergic pathways. Lesion alone did not change sleep and waking stages compared to baseline, except for a reduction in REM sleep. Consistent with earlier findings, zimeldine in nonlesioned rats increased waking the first 2 h of recording. Zimeldine treatment in lesioned rats gave a significant additional 50% increase in waking the first 2 h and a corresponding decrease in total slow wave sleep, suggesting a potentiation of these effects. Zimeldine gave no significant changes in waking EEG power spectral density. Lesion gave a tendency to reduction between 4.0 and 15.5 Hz compared with baseline, and between 10.0 and 16.5 compared to the independent control group. In both comparisons, the combined treatment strengthened this effect, again suggesting a potentiating effect of lesion. In sleep, zimeldine reduced power over the whole spectrum (0.5-20.0 Hz), less in the lower frequencies than in the higher frequencies.