Clarifying the role of sleep in depression: A narrative review

It has been established that 4.4 to 20% of the general population suffers from a major depressive disorder (MDD), which is frequently associated with a dysregulation of normal sleep-wake mechanisms. Disturbances of circadian rhythms are a cardinal feature of psychiatric dysfunctions, including MDD, which tends to indicate that biological clocks may play a role in their pathophysiology. Thus, episodes of depression and mania or hypomania can arise as a consequence of the disruption of zeitgebers (time cues). In addition, the habit of sleeping at a time that is out of phase with the body's other biological rhythms is a common finding in depressed patients. In this review, we have covered a vast area, emerging from human and animal studies, which supports the link between sleep and depression. In doing so, this paper covers a broad range of distinct mechanisms that may underlie the link between sleep and depression. This review further highlights the mechanisms that may underlie such link (e.g. circadian rhythm alterations, melatonin, and neuroinflammatory dysregulation), as well as evidence for a link between sleep and depression (e.g. objective findings of sleep during depressive episodes, effects of pharmacotherapy, chronotherapy, comorbidity of obstructive sleep apnea and depression), are presented.

Pharmacotherapy of Insomnia

Insomnia remains a common clinical concern that is associated with negative daytime consequences for patients and represents a significant public health problem for our society. Although a variety of therapies may be employed to treat insomnia, the use of medications has been a dominant approach. Regulatory agencies have now classified insomnia medications into 4 distinct pharmacodynamics classes. Medications with indications approved for insomnia treatment include benzodiazepine receptor agonists, a melatonin receptor agonist, a selective histamine receptor antagonist, and a dual orexin/hypocretin receptor antagonist. Both pharmacodynamic and pharmacokinetic advances with hypnotic medications in recent years have expanded the pharmacopoeia to allow personalized treatment approaches for different patient populations and individual sleep disturbance patterns.

The effects of local microinjection of selective dopamine D1 and D2 receptor agonists and antagonists into the dorsal raphe nucleus on sleep and wakefulness in the rat

The effects of the dopamine (DA) D1 and D2 receptor agonists SKF38393, bromocriptine and quinpirole, respectively, on spontaneous sleep were analyzed in adult rats prepared for chronic sleep recordings. Local administration of the DAergic agonists into the dorsal raphe nucleus (DRN) during the light phase of the light-dark cycle induced a significant reduction of rapid-eye movement sleep (REMS) and the number of REM periods. Additionally, bromocriptine and quinpirole significantly increased wakefulness (W). Opposite, the microinjection into the DRN of the DA D1 and D2 receptor antagonists SCH23390 and sulpiride, respectively, significantly augmented REMS and the number of REM periods. Pretreatment with SCH23390 and sulpiride prevented the effects of SKF38393 and bromocriptine, respectively, on sleep variables. Our results tend to indicate that DAergic neurons located in the ventral tegmental area (VTA) and substantia nigra pars compacta (SNc) contribute to the regulation of predominantly W and REMS by DRN serotonergic neurons.

The effect of second-generation antipsychotic drugs on sleep parameters in patients with unipolar or bipolar disorder

Sleep disturbances predominantly take the form of insomnia in patients with unipolar disorder, while patients with bipolar disorder show a decreased need for sleep. Sleep impairment in these patients is a risk factor for the development of a major depressive episode and suicidal behavior. Administration of second-generation antipsychotics (SGAs) olanzapine, quetiapine, and ziprasidone as augmentation therapy or monotherapy to unipolar and bipolar disorder patients, respectively, has been shown to improve sleep continuity and sleep architecture. Thus, their use by these patients could ameliorate their sleep disorder.

Underlying sources of cognitive-anatomical variation in multi-modal neuroimaging and cognitive testing

Healthy adults have robust individual differences in neuroanatomy and cognitive ability not captured by demographics or gross morphology (Luders, Narr, Thompson, & Toga, 2009). We used a hierarchical independent component analysis (hICA) to create novel characterizations of individual differences in our participants (N=190). These components fused data across multiple cognitive tests and neuroanatomical variables. The first level contained four independent, underlying sources of phenotypic variance that predominately modeled broad relationships within types of data (e.g., "white matter," or "subcortical gray matter"), but were not reflective of traditional individual difference measures such as sex, age, or intracranial volume. After accounting for the novel individual difference measures, a second level analysis identified two underlying sources of phenotypic variation. One of these made strong, joint contributions to both the anatomical structures associated with the core fronto-parietal "rich club" network (van den Heuvel & Sporns, 2011), and to cognitive factors. These findings suggest that a hierarchical, data-driven approach is able to identify underlying sources of individual difference that contribute to cognitive-anatomical variation in healthy young adults.

Melanin-Concentrating Hormone (MCH): Role in REM Sleep and Depression

The melanin-concentrating hormone (MCH) is a peptidergic neuromodulator synthesized by neurons of the lateral sector of the posterior hypothalamus and zona incerta. MCHergic neurons project throughout the central nervous system, including areas such as the dorsal (DR) and median (MR) raphe nuclei, which are involved in the control of sleep and mood. Major Depression (MD) is a prevalent psychiatric disease diagnosed on the basis of symptomatic criteria such as sadness or melancholia, guilt, irritability, and anhedonia. A short REM sleep latency (i.e., the interval between sleep onset and the first REM sleep period), as well as an increase in the duration of REM sleep and the density of rapid-eye movements during this state, are considered important biological markers of depression. The fact that the greatest firing rate of MCHergic neurons occurs during REM sleep and that optogenetic stimulation of these neurons induces sleep, tends to indicate that MCH plays a critical role in the generation and maintenance of sleep, especially REM sleep. In addition, the acute microinjection of MCH into the DR promotes REM sleep, while immunoneutralization of this peptide within the DR decreases the time spent in this state. Moreover, microinjections of MCH into either the DR or MR promote a depressive-like behavior. In the DR, this effect is prevented by the systemic administration of antidepressant drugs (either fluoxetine or nortriptyline) and blocked by the intra-DR microinjection of a specific MCH receptor antagonist. Using electrophysiological and microdialysis techniques we demonstrated also that MCH decreases the activity of serotonergic DR neurons. Therefore, there are substantive experimental data suggesting that the MCHergic system plays a role in the control of REM sleep and, in addition, in the pathophysiology of depression. Consequently, in the present report, we summarize and evaluate the current data and hypotheses related to the role of MCH in REM sleep and MD.

Water versus DNA: new insights into proton track-structure modelling in radiobiology and radiotherapy

Water is a common surrogate of DNA for modelling the charged particle-induced ionizing processes in living tissue exposed to radiations. The present study aims at scrutinizing the validity of this approximation and then revealing new insights into proton-induced energy transfers by a comparative analysis between water and realistic biological medium. In this context, a self-consistent quantum mechanical modelling of the ionization and electron capture processes is reported within the continuum distorted wave-eikonal initial state framework for both isolated water molecules and DNA components impacted by proton beams. Their respective probability of occurrence-expressed in terms of total cross sections-as well as their energetic signature (potential and kinetic) are assessed in order to clearly emphasize the differences existing between realistic building blocks of living matter and the controverted water-medium surrogate. Consequences in radiobiology and radiotherapy will be discussed in particular in view of treatment planning refinement aiming at better radiotherapy strategies.

Increased REM sleep after intra-locus coeruleus nucleus microinjection of melanin-concentrating hormone (MCH) in the rat

A study was carried out on the effects of unilateral microinjection of melanin-concentrating hormone (MCH) into the right locus coeruleus (LC) on the sleep-wake cycle in rats prepared for chronic sleep recordings. MCH 200 ng significantly augmented rapid-eye-movement sleep (REMS) time during the first, second and third 2-h of recording. Furthermore, MCH 100 ng induced a significant increase of REMS during the first 2-h period after treatment. The increment of the behavioral state was related to a greater number of REMS episodes. It is suggested that MCH deactivation of noradrenergic neurons located in the LC facilitates the occurrence of REMS.

When insomnia is not just insomnia: the deeper correlates of disturbed sleep with reference to DSM-5

Recent scientific evidences have brought a paradigm shift in our approach towards the concepts of insomnia and its management. The differentiation between primary and secondary insomnia was proved more hypothetical than actual and based upon the current evidences insomnia subtypes described in earlier system have been lumped into one-insomnia disorder. Research in this field suggests that insomnia occurring during psychiatric or medical disorders has a bidirectional and interactive relationship with and coexisting medical and psychiatric illnesses. The new approach looks to coexist psychiatric or medical disorders as comorbid conditions and hence specifies two coexisting conditions. Therefore, the management and treatment plans should address both the conditions. A number of sleep disorders may present with insomnia like symptoms and these disorders should be treated efficiently in order to alleviate insomnia symptoms. In such cases, a thorough history from the patient and his/her bed-partner is warranted. Moreover, some patients may need polysomnography or other diagnostic tests like actigraphy to confirm the diagnosis of the underlying sleep disorder. DSM-5 classification system of sleep–wake disorders has several advantages, e.g., it has seen insomnia across different dimensions to make it clinically more useful; it focuses on the assessment of severity and guides the mental health professional when to refer a patient of insomnia to a sleep specialist; lastly, it may encourage the psychiatrists to opt for sleep medicine as a career.

The role of serotonin 5-HT7 receptor in regulating sleep and wakefulness

Different approaches have been followed to characterize the role of 5-hydroxytryptamine (serotonin) receptor 7 (5-HT7) in the regulation of sleep-wake behavior: (1) 5-HT7 receptor knockout mice spend less time in rapid eye movement sleep than their wild-type counterparts, mainly during the light period. In contrast, there is no difference between the genotypes in time spent in wakefulness or slow-wave sleep. (2) Systemic administration of the selective 5-HT7 receptor agonist LP-211 significantly increased wakefulness (time spent awake) and reduced rapid eye movement sleep in the rat. Direct infusion of LP-211 into the dorsal raphe nucleus, locus coeruleus nucleus, basal forebrain (horizontal limb of the diagonal band of Broca), or laterodorsal tegmental nucleus also produced a decrease in rapid eye movement sleep. Additionally, microinjection of the 5-HT7 receptor agonist into the basal forebrain augmented the time animals remained awake. Local injection of the 5-HT7 receptor agonist LP-44 into the dorsal raphe nucleus also suppressed rapid eye movement sleep in the rat. (3) A similar reduction of rapid eye movement sleep has been described following intraperitoneal injection of the selective 5-HT7 receptor antagonists SB-269970 and SB-656104 in the rat and oral administration of the 5-HT7 receptor antagonist NJ-18038683 to rat and man. Local microinjection of SB-269970 into the dorsal raphe nucleus and basal forebrain also induced a decrease in rapid eye movement sleep in the rat. This tends to suggest that the on-off (activation/blockade), two-state ligand-receptor interaction model is not tenable for the 5-HT7 receptor.

Systemic administration and local microinjection into the central nervous system of the 5-HT(7) receptor agonist LP-211 modify the sleep-wake cycle in the rat

The effects of LP-211, a selective serotonin 5-HT7 receptor agonist were studied in adult rats implanted for chronic sleep recordings. Intraperitoneal administration of LP-211 (2.5-10mg/kg) during the light phase of the light-dark cycle significantly increased wakefulness (W) and reduced rapid-eye-movement sleep (REMS) and the number of REM periods during the 6-h recording period. Direct infusion of LP-211 into the dorsal raphe nucleus (DRN) (2-6 mM), locus coeruleus nucleus (LC) (4 mM), basal forebrain (horizontal limb of the diagonal band of Broca) (HDB) (2 mM) or laterodorsal tegmental nucleus (LDT) (4 mM) induced also a decrease of REMS. Additionally, microinjection of the 5-HT7 receptor ligand into the HDB (2 mM) augmented W. Presently, there is no satisfactory explanation for the effect of 5-HT7 receptor activation on W and REMS occurrence. Additional studies are required to characterize the neurotransmitter systems responsible for the actions of LP-211 on the behavioral states.

Sleep and circadian rhythm dysregulation in schizophrenia

Sleep-onset and maintenance insomnia is a common symptom in schizophrenic patients regardless of either their medication status (drug-naive or previously treated) or the phase of the clinical course (acute or chronic). Regarding sleep architecture, the majority of studies indicate that non-rapid eye movement (NREM), N3 sleep and REM sleep onset latency are reduced in schizophrenia, whereas REM sleep duration tends to remain unchanged. Many of these sleep disturbances in schizophrenia appear to be caused by abnormalities of the circadian system as indicated by misalignments of the endogenous circadian cycle and the sleep-wake cycle. Circadian disruption, sleep onset insomnia and difficulties in maintaining sleep in schizophrenic patients could be partly related to a presumed hyperactivity of the dopaminergic system and dysfunction of the GABAergic system, both associated with core features of schizophrenia and with signaling in sleep and wake promoting brain regions. Since multiple neurotransmitter systems within the CNS can be implicated in sleep disturbances in schizophrenia, the characterization of the neurotransmitter systems involved remains a challenging dilemma.

The effects of systemic and local microinjection into the central nervous system of the selective serotonin 5-HT6 receptor agonist WAY-208466 on sleep and wakefulness in the rat

The effects of WAY-208466, a selective 5-HT6 receptor agonist on spontaneous sleep were studied in adult rats implanted for chronic sleep recordings. Systemic administration of WAY-208466 during the light phase of the light-dark cycle significantly increased wakefulness (W) and reduced slow wave sleep (SWS), REM sleep (REMS) and the number of REMS periods. Pretreatment with the selective 5-HT6 receptor antagonist RO-399885 prevented the effects of the 5-HT6 receptor agonist on W, SWS and REMS. Direct infusion of WAY-208466 into the dorsal raphe nucleus, locus coeruleus, basal forebrain (horizontal limb of the diagonal band of Broca) or laterodorsal tegmental nucleus specifically decreased REMS without significantly altering W or SWS. In all instances the REMS suppression was dependent upon the reduction of REMS periods. The finding that WAY-208466 increases extracellular γ-aminobutyric acid (GABA) levels in the rat frontal cortex tends to suggest that the neurotransmitter could be involved in the 5-HT6 receptor agonist-induced disruption of the sleep-wake cycle. However, further studies are needed to resolve this issue.

Microinjection of melanin concentrating hormone into the lateral preoptic area promotes non-REM sleep in the rat

The ventrolateral preoptic area (VLPO) has been recognized as one of the key structures responsible for the generation of non-REM (NREM) sleep. The melanin-concentrating hormone (MCH)-containing neurons, which are located in the lateral hypothalamus and incerto-hypothalamic area, project widely throughout the central nervous system and include projections to the VLPO. The MCH has been associated with the central regulation of feeding and energy homeostasis. In addition, recent findings strongly suggest that the MCHergic system promotes sleep. The aim of the present study was to determine if MCH generates sleep by regulating VLPO neuronal activity. To this purpose, we characterized the effect of unilateral and bilateral microinjections of MCH into the VLPO on sleep and wakefulness in the rat. Unilateral administration of MCH into the VLPO and adjacent dorsal preoptic area did not modify sleep. On the contrary, bilateral microinjections of MCH (100 ng) into these areas significantly increased light sleep (LS, 39.2±4.8 vs. 21.6±2.5 min, P<0.05) and total NREM sleep (142.4±23.2 vs. 86.5±10.5 min, P<0.05) compared to control (saline) microinjections. No effect was observed on REM sleep. We conclude that MCH administration into the VLPO and adjacent dorsal lateral preoptic area promotes the generation of NREM sleep.

Microinjection of the 5-HT7 receptor antagonist SB-269970 into the rat brainstem and basal forebrain: site-dependent effects on REM sleep

The effects of SB-269970, a selective 5-HT7 receptor antagonist, on spontaneous sleep were studied in adult rats implanted for chronic sleep recordings. The 5-HT7 receptor ligand was microinjected into the horizontal limb of the diagonal band of Broca (HDB) and the laterodorsal tegmental nucleus (LDT) during the light period of the 12-h light/12-h dark cycle. For comparative purposes the compound was administered systemically and, in addition, injected directly into the dorsal raphe nucleus (DRN). Microinjection of SB-269970 into the HDB and the DRN induced a significant reduction of rapid-eye-movement sleep (REMS). Similar effects were observed after systemic administration of the 5-HT7 receptor antagonist. On the other hand, local infusion of the compound into the LDT provoked the opposite effect. It is proposed that the deactivation of GABAergic cells located in the HDB, DRN and LDT is responsible for the changes induced by SB-269970 on REM sleep values. It is suggested that the antidepressant effect of the 5-HT7 receptor antagonist could partly depend on the involvement of neuronal systems located in the DRN and the HDB.

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.

Melanin-concentrating hormone: a new sleep factor?

Neurons containing the neuropeptide melanin-concentrating hormone (MCH) are mainly located in the lateral hypothalamus and the incerto-hypothalamic area, and have widespread projections throughout the brain. While the biological functions of this neuropeptide are exerted in humans through two metabotropic receptors, the MCHR1 and MCHR2, only the MCHR1 is present in rodents. Recently, it has been shown that the MCHergic system is involved in the control of sleep. We can summarize the experimental findings as follows: (1) The areas related to the control of sleep and wakefulness have a high density of MCHergic fibers and receptors. (2) MCHergic neurons are active during sleep, especially during rapid eye movement (REM) sleep. (3) MCH knockout mice have less REM sleep, notably under conditions of negative energy balance. Animals with genetically inactivated MCHR1 also exhibit altered vigilance state architecture and sleep homeostasis. (4) Systemically administered MCHR1 antagonists reduce sleep. (5) Intraventricular microinjection of MCH increases both slow wave sleep (SWS) and REM sleep; however, the increment in REM sleep is more pronounced. (6) Microinjection of MCH into the dorsal raphe nucleus increases REM sleep time. REM seep is inhibited by immunoneutralization of MCH within this nucleus. (7) Microinjection of MCH in the nucleus pontis oralis of the cat enhances REM sleep time and reduces REM sleep latency. All these data strongly suggest that MCH has a potent role in the promotion of sleep. Although both SWS and REM sleep are facilitated by MCH, REM sleep seems to be more sensitive to MCH modulation.

Immunoneutralization of melanin-concentrating hormone (MCH) in the dorsal raphe nucleus: effects on sleep and wakefulness

Hypothalamic neurons that utilize melanin-concentrating hormone (MCH) as a neuromodulator exert a positive control over energy homeostasis, inducing feeding and decreasing metabolism. Recent studies have shown also that this system plays a role in the generation and/or maintenance of sleep. MCHergic neurons project to the serotonergic dorsal raphe nucleus (DR), a neuroanatomical structure involved in several functions during wakefulness (W), and in the regulation of rapid-eye movements (REM) sleep. Recently, we determined the effect of MCH microinjected into the DR on sleep variables in the rat. MCH produced a marked increment of REM sleep, whereas slow wave sleep (SWS) showed only a moderate increase. In the present study, we analyze the effect of immunoneutralization of MCH in the DR on sleep and W in the rat. Compared to the control solution, microinjections of anti-MCH antibodies (1/100 solution in 0.2 μl) induced a significant increase in REM sleep latency (31.2±7.1 vs. 84.2±24.8 min, p<0.05) and a decrease of REM sleep time (37.8±5.4 vs. 17.8±2.9 min, p<0.05) that was related to the reduction in the number of REM sleep episodes. In addition, there was an increase of total W time (49.8±4.6 vs. 72.0±5.7 min, p<0.01). Light sleep and SWS remained unchanged. The intra-DR administration of a more diluted solution of anti-MCH antibodies (1/500) or rabbit pre-immune serum did not modify neither W nor REM sleep variables. Our findings strongly suggest that MCH released in the DR facilitates the occurrence of REM sleep.

Serotonin 5-HT(2A) receptor antagonists in the treatment of insomnia: present status and future prospects

Benzodiazepine (BZD) and non-BZD hypnotics improve sleep induction and sleep maintenance. BZD induces a further reduction of slow wave sleep (SWS) and rapid eye movement (REM) sleep, whereas SWS and REM values remain decreased during non-BZD administration. There is evidence indicating that the nonselective serotonin 5-HT(2A/2C) receptor antagonists, ritanserin, ketanserin, seganserin and ICI-169369, the selective 5-HT(2A) receptor antagonist eplivanserin and the 5-HT(2A) receptor inverse agonist pimavanserin, increase SWS in subjects with normal sleep. In addition, it has been shown that prior administration of ritanserin prevents the nitrazepam-induced suppression of SWS in normal subjects. Of note, ritanserin also induced an increase of SWS in poor sleepers, patients with chronic primary insomnia and psychiatric patients with a generalized anxiety disorder or a mood disorder. The 5-HT(2A) receptor inverse agonist APD-125 gave rise to a similar effect in patients with chronic primary insomnia. Thus, presently available evidence tends to indicate that the association of a 5-HT(2A) receptor antagonist or a 5-HT(2A) receptor inverse agonist with a BZD or a non-BZD hypnotic could be a valid alternative to normalize SWS in patients with primary or comorbid insomnia.

The structure of the dorsal raphe nucleus and its relevance to the regulation of sleep and wakefulness

Serotonergic (5-HT) cells in the rat dorsal raphe nucleus (DRN) appear in topographically organized groups. Based on cellular morphology, expression of other neurotransmitters, afferent and efferent connections and functional properties, 5-HT neurons of the DRN have been grouped into six cell clusters. The subdivisions comprise the rostral, ventral, dorsal, lateral, caudal and interfascicular parts of the DRN. In addition to 5-HT cells, neurons containing γ-aminobutyric acid (GABA), glutamate, dopamine, nitric oxide and the neuropeptides corticotropin-releasing factor, substance P, galanin, cholecystokinin, neurotensin, somatostatin, vasoactive intestinal peptide, neuropeptide Y, thyrotropin-releasing hormone, growth hormone, leu-enkephalin, met-enkephalin and gastrin have been characterized in the DRN. Moreover, numerous brain areas have neurons that project to the DRN and express monoamines (norepinephrine, histamine), amino acids (GABA, glutamate), acetylcholine or neuropeptides (orexin, melanin-concentrating hormone, corticotropin-releasing factor and substance P) that directly or indirectly, through local circuits, regulate the activity of 5-HT cells. The 5-HT cells predominate along the midline of the rostral, dorsal and ventral subdivisions of the DRN and outnumber the non-5-HT cells occurring in the raphe nucleus. The GABAergic and glutamatergic neurons are clustered mainly in the lateral and dorsal subdivisions of the DRN, respectively. The 5-HT(1A) receptor is located on the soma and the dendrites of 5-HT neurons and at postsynaptic sites (outside the DRN). It is expressed, in addition, by non-5-HT cells of the DRN. The 5-HT(1B) receptor is located at presynaptic and postsynaptic sites (outside the boundaries of the DRN). It has been described also in the ventromedial DRN where it is expressed by non-5-HT cells. The 5-HT(2A) and 5-HT(2C) receptors are located within postsynaptic structures. At the level of the DRN the 5-HT(2A) and 5-HT(2C) receptor-containing cells are predominantly GABAergic interneurons and projection neurons. Within the boundaries of the DRN the 5-HT(3) receptor is expressed by, among others, glutamatergic interneurons. 5-HT(7) receptors in the DRN are not localized to serotonergic neurons but, at least in part, to GABAergic cells and terminals. The complex structure of the DRN may have important implications for neural mechanisms underlying 5-HT modulation of wakefulness and REM sleep.

Activation of the serotonin 5-HT3 receptor in the dorsal raphe nucleus suppresses REM sleep in the rat

The effects of the selective 5-HT(3) receptor agonist and antagonist m-chlorophenylbiguanide (m-CPBG) and ondansetron, respectively, were studied in adult male Wistar rats implanted for chronic sleep recordings. Microinjection of m-CPBG (2.0 and 4.0 mM) into the dorsal raphe nucleus (DRN) decreased rapid-eye-movement sleep (REMS) and the number of REM periods during the first, second, and third 2-h recording period. On the other hand, direct infusion of ondansetron (0.5-1.0 mM) into the DRN induced no significant changes in sleep variables over the 6 h of recording. Pretreatment with ondansetron (0.5 mM) antagonized the m-CPBG (2.0 mM)-induced reduction of REMS and of the number of REM periods. The data are consistent with the hypothesis that the 5-HT(3) receptor is involved in the effect of DRN serotonergic neurons on brainstem structures that act to promote and induce REMS. It is suggested that the suppression of REMS after the microinjection of m-CPBG into the DRN is related, at least in part, to the stimulation of glutamatergic interneurons that express 5-HT(3) receptors. Activation of these receptors facilitates the release of glutamate, which, in turn, acts on postsynaptic N-methyl-d-aspartate and non-N-methyl-d-aspartate receptors expressed by serotonergic neurons of the DRN and increases the release of 5-HT at postsynaptic sites.

Eszopiclone: its use in the treatment of insomnia

Eszopiclone is the S-isomer of racemic zopiclone, a cyclopyrrolone with sedative-hypnotic activity that has been available in Europe, Canada, and Latin America since 1987. Eszopiclone acts by binding to the GABA(A) receptor. In contrast to the benzodiazepine (BZD) hypnotics, eszopiclone has more selectivity for certain subunits of the GABA(A) receptor. Oral eszopiclone is rapidly absorbed and extensively distributed to body tissues including the brain. Peak plasma concentrations are attained 1.0-1.6 hours after a 3 mg dose, while the mean elimination half-life is 6 hours. The half-life increases with age to about 9.0 hours in patients 65 years or older. Eszopiclone's pharmacokinetic (PK) profile is not substantially modified in patients suffering from renal failure or mild-to-moderate hepatic impairment, although patients with severe hepatic insufficiency should have a reduced dose. The subjective perception of improved sleep following eszopiclone 2 or 3 mg treatment has been demonstrated in randomized, double-blind, placebo-controlled studies of up to 6 months' duration. In these studies the drug significantly reduced sleep onset latency (SOL), the number of awakenings, and wake time after sleep onset (WASO) whereas total sleep time (TST) and quality of sleep were increased in non-elderly and elderly subjects. Sleep laboratory studies of the effects of eszopiclone have confirmed the drug's clinical efficacy in subjects with chronic primary insomnia. Eszopiclone, unlike BZD hypnotics, does not significantly alter values corresponding to slow wave sleep (SWS or stages 3 and 4) and rapid eye movement (REM) sleep. Rebound insomnia following withdrawal of eszopiclone has been examined in only one study. Discontinuation of the active treatment with 2 mg was followed by rebound insomnia in non-elderly subjects. Three-mg doses of eszopiclone administered for a period of up to 12 months was associated with a sustained beneficial effect on sleep induction and maintenance, with no occurrence of tolerance. The most common side-effects were unpleasant or bitter taste, headache, dyspepsia, pain, diarrhea, dry mouth, upper respiratory infection, urinary tract infection, dizziness, and accidental injury. New adverse events (withdrawal symptoms) including anxiety, abnormal dreams, hyperesthesia, nausea, and upset stomach were recorded in one study on the days following eszopiclone 2 or 3 mg discontinuation. Although dependence and abuse potential have not been formally assessed, unpublished data show that eszopiclone at doses of 6 and 12 mg produces euphoria effects similar to those of diazepam 20 mg in BZD drug addicts. In conclusion, available evidence tends to indicate that eszopiclone is effective and safe for the treatment of chronic primary insomnia in non-elderly and elderly subjects. Tolerance did not occur during active drug administration for a 12-month period. Thus eszopiclone can be efficacious not only during short- and intermediate-term administration but also in patients requiring prolonged regular drug usage.

The involvement of dopamine in the modulation of sleep and waking

Dopamine (DA)-containing neurons involved in the regulation of sleep and waking (W) arise in the ventral tegmental area (VTA) and the substantia nigra pars compacta (SNc). The VTA and SNc cells have efferent and afferent connections with the dorsal raphe nucleus (DRN), the pedunculopontine and laterodorsal tegmental nuclei (PPT/LDT), the locus coeruleus (LC), the lateral and posterior hypothalamus (LH), the basal forebrain (BFB), and the thalamus. Molecular cloning techniques have enabled the characterization of two distinct groups of DA receptors, D(1)-like and D(2)-like receptors. The D(1) subfamily includes the D(1) and D(5) receptors, whereas the D(2) subfamily comprises the D(2), D(3), and D(4) receptors. Systemic administration of a selective D(1) receptor agonist induces behavioral arousal, together with an increase of W and a reduction of slow wave sleep (SWS) and REM sleep (REMS). Systemic injection of a DA D(2) receptor agonist induces biphasic effects, such that low doses reduce W and increase SWS and REMS (predominant activation of the D(2) autoreceptor), whereas large doses induce the opposite effect (predominant facilitation of the D(2) postsynaptic receptor). Compounds with DA D(1) or D(2) receptor blocking properties augment non-REMS and reduce W. Preliminary findings tend to indicate that the administration of a DA D(3)-preferring agonist induces somnolence and sleep in laboratory animals and man. DA neurons in the VTA and the SNc do not change their mean firing rate across the sleep-wake cycle. It has been proposed that DA cells in the midbrain show a change in temporal pattern rather than firing rate during the sleep-wake cycle. The available evidence tends to indicate that during W there occurs an increase of burst firing activity of DA neurons, and an enhanced release of DA in the VTA, the nucleus accumbens (NAc), and a number of forebrain structures. A series of structures relevant for the regulation of the behavioral state, including the DRN, LDT/PPT, LC, and LH, could be partly responsible for the changes in the temporal pattern of activity of DA neurons.

Effects of the serotonin 5-HT2A/2C receptor agonist DOI and of the selective 5-HT2A or 5-HT2C receptor antagonists EMD 281014 and SB-243213, respectively, on sleep and waking in the rat

The effects of the serotonin 5-HT(2A/2C) receptor agonist 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) and of the selective 5-HT(2A) or 5-HT(2C) receptor antagonists 7-{4-[2-(4-fluoro-phenyl)-ethyl]-piperazine-1-carbonyl}-1H-indole-3-carbonitrile HCl (EMD 281014) and 5-methyl-1-[[-2-[(2-methyl-3-pyridyl)oxy]-5-pyridyl]carbamoyl]-6-trifluoromethylindoline HCl (SB-243213), respectively, on spontaneous sleep were studied in adult rats implanted for chronic sleep recordings. Subcutaneous administration of DOI (0.35-0.7 mmol/kg) significantly increased waking and light sleep and reduced slow wave sleep, rapid-eye-movement (REM) sleep, and the number of REM periods. With subcutaneous EMD 281014 (1.2-4.8 mmol/kg) or SB-243213 (1.2-4.8 mmol/kg) a significant reduction in time spent in REM sleep was also seen. Pretreatment with EMD 281014 prevented the DOI-induced increase of waking and light sleep and the reduction of slow wave sleep. However, REM sleep remained suppressed. SB-243213 failed to reverse the changes of sleep and waking induced by DOI. Thus, on the basis of these results it appears that serotonin 5-HT(2A) receptor mechanisms might be responsible for the DOI-induced effects on waking and slow wave sleep.

Effects of the 5-HT(7) receptor antagonist SB-269970 microinjected into the dorsal raphe nucleus on REM sleep in the rat

The effects of SB-269970, a selective 5-HT(7) receptor antagonist, on spontaneous sleep were studied in adult rats implanted for chronic sleep recordings. SB-269970 was infused directly into the dorsal raphe nucleus (DRN) during the light phase. The 5-HT(7) receptor antagonist (0.25-1.0 mM) induced a significant reduction of REM sleep and of the number of REM periods whereas REM sleep latency was augmented. Pretreatment with the GABA(A) receptor agonist muscimol (1.0-2.0 mM), which by itself did not affect sleep variables, prevented the decrease of REM sleep induced by SB-269970 (1.0 mM). Our results indicate that the 5-HT(7) receptor is involved in the effect of DRN serotonergic (5-HT) neurons on brainstem structures that act to promote and induce REM sleep. We propose that the SB-269970-induced suppression of REM sleep is dependent upon the inhibition of GABA release in the DRN.

Sleep disturbance in schizophrenia

Insomnia is a common symptom in schizophrenia, although it is seldom the predominant complaint. Sleep-onset and maintenance insomnia is a characteristic feature of schizophrenic patients regardless of either their medication status (drug-naive or previously treated) or the phase of the clinical course (acute or chronic). Regarding sleep architecture, the majority of studies indicate that stage 4 sleep and rapid eye movement (REM) latency are reduced in schizophrenia, whereas REM sleep duration tends to remain unchanged. Insomnia in schizophrenic patients could be partly related to the presumed over-activity of the dopaminergic system. However, there is a possibility that the GABAergic system is also involved in sleep disturbance in schizophrenia. Since many signal transmission systems within the CNS can be implicated in the reduction of REM latency in schizophrenia, the characterization of the neurotransmitter systems involved remains a challenging dilemma.

A study of the brain structures involved in the acute effects of fluoxetine on REM sleep in the rat

The effects of acute administration of fluoxetine, a selective serotonin reuptake inhibitor on spontaneous sleep, were studied in adult rats implanted for chronic sleep recordings. Fluoxetine was administered systemically or infused directly into the dorsal raphe nucleus (DRN), the right laterodorsal tegmental nucleus (LDT) or the medial pontine reticular formation (mPRF). Systemic administration of fluoxetine (3.0-12.0 micromol/kg) significantly reduced rapid-eye-movement sleep (REMS) and the number of REM periods; REMS latency was augmented. Direct infusion of fluoxetine (1.0 nmol) into the DRN induced a significant increment of REMS and of the number of REM periods whereas REMS latency was reduced. Microinjection of fluoxetine into the LDT (1.0 nmol) or the mPRF (0.8 nmol) decreased REMS and the number of REM periods whereas REMS latency was augmented. Pre-treatment with the selective 5-HT1A receptor antagonist WAY 100635 prevented the reduction of REMS induced by the microinjection of fluoxetine into the LDT. Our results indicate that the fluoxetine-induced suppression of REMS is related to the inhibition of brainstem structures involved in the promotion and the induction of REMS. The decrease of REMS would be dependent upon the activation of several 5-HT receptor subtypes, including the 5-HT1A receptor.

Effects of L-arginine and SIN-1 on sleep and waking in the rat during both phases of the light-dark cycle

The effects L-arginine (0.15-0.60 micromol), a nitric oxide precursor, and SIN-1 (3-morpholino-sydnonimine; linsidomine) (0.05-0.2 micromol), a nitric oxide donor, on spontaneous sleep were studied in adult rats implanted for chronic sleep recordings. L-arginine or SIN-1 given intracerebroventricularly during the light phase of the light-dark cycle induced no significant changes in sleep variables. On the other hand, administration of L-arginine or SIN-1 during the dark phase significantly increased slow wave sleep and reduced waking during the first 4 h of the recording period. The time spent in rapid-eye-movement sleep (REMS) was not significantly modified. The increase of slow wave sleep and/or reduction of waking was already evident during the first 2 h of recording. On the other hand, values of these variables were not different from control values during post-injection hours 5 and 6. Our findings confirm the role of nitric oxide, generated from L-arginine or released from SIN-1, in the regulation of sleep variables in the rat.

Sleep in schizophrenia patients and the effects of antipsychotic drugs

Insomnia is a common feature in schizophrenia. However, it seldom is the predominant complaint. Nevertheless, severe insomnia is often seen during exacerbations of schizophrenia, and may actually precede the appearance of other symptoms of relapse. The sleep disturbances of either never-medicated or previously treated schizophrenia patients are characterized by a sleep-onset and maintenance insomnia. In addition, stage 4 sleep, slow wave sleep (stages 3 and 4), non-REM (NREM) sleep in minutes and REM latency are decreased. The atypical antipsychotics olanzapine, risperidone, and clozapine significantly increase total sleep time and stage 2 sleep. Moreover, olanzapine and risperidone enhance slow wave sleep. On the other hand, the typical antipsychotics haloperidol, thiothixene, and flupentixol significantly reduce stage 2 sleep latency and increase sleep efficiency. Future research should address: (1) the sleep patterns in subtypes of schizophrenia patients; (2) the role of neurotransmitters other than dopamine in the disruption of sleep in schizophrenia; (3) the functional alterations in CNS areas related to the pathophysiology of schizophrenia during NREM sleep and REM sleep (brain imaging studies); (4) the short-term, intermediate-term, and long-term effects of atypical antisychotics on sleep variables.

Effects of the 5-HT1A receptor ligands flesinoxan and WAY 100635 given systemically or microinjected into the laterodorsal tegmental nucleus on REM sleep in the rat

The effects of flesinoxan, a selective 5-HT1A receptor agonist, and of WAY 100635, a selective high affinity 5-HT1A receptor antagonist, on spontaneous sleep were studied in adult rats implanted for chronic sleep recordings. Systemic administration of flesinoxan (0.03 and/or 0.06 micromol/kg, s.c.) increased waking (W) and sleep latencies and reduced REM sleep (REMS) and the number of REM periods during the first and/or second 2-h period after treatment. Systemic injection of WAY 100635 (0.46 and/or 0.92 micromol/kg, s.c.) augmented W and REMS latency and reduced REMS and the number of REM periods during the 6-h recording period. Microinjection of flesinoxan (0.03, 0.06 and/or 0.12 nmol) into the laterodorsal tegmental nucleus (LDT) reduced REMS and the number of REM periods, and augmented REMS latency during the first, second, and/or third 2-h recording period. Direct infusion of WAY 100635 (0.06 and/or 0.12 nmol) into the LDT increased REMS and the number of REM periods during the first and/or second 2 h of recording. It is proposed that the activation by flesinoxan of postsynaptic 5-HT1A receptors located in the LDT could be responsible for the REMS suppression. The increase in REMS after the blockade of postsynaptic 5-HT1A receptors in the LDT by WAY 100635 further supports our proposal. The effects of systemic flesinoxan on sleep variables may depend mainly on the activation of postsynaptic 5-HT1A receptors, whereas the effects corresponding to systemic WAY 100635 may be predominantly related to the blockade of presynaptic somatodendritic 5-HT1A autoreceptors.

Microinjection of the nitric oxide synthase inhibitor L-NAME into the lateral basal forebrain alters the sleep/wake cycle of the rat

The effects of N(G)-nitro-L-arginine methyl ester (L-NAME) (0.19-0.74 micromol), a competitive inhibitor of the enzyme nitric oxide synthase (NOS); L-arginine (48.0-191.0 nmol), a nitric oxide (NO) precursor; and molsidomine (0.06-0.24 nmol), an NO donor, on spontaneous sleep were studied in adult rats implanted for chronic sleep recordings. Direct bilateral application of L-NAME into the nucleus of the horizontal limb of the diagonal band of Broca (HDB) increased waking (W) and reduced slow wave sleep (SWS). On the other hand, intra-HDB injection of L-arginine or molsidomine induced slight but inconsistent changes of sleep variables that did not attain significance. Pretreatment with L-arginine (191.0 nmol) or molsidomine (0.24 nmol) prevented the increase of W and the reduction of SWS induced by L-NAME (0.37 micromol), thus indicating that a decrease in the availability of NO may be involved in the effects of L-NAME on sleep variables. An increase in the release of acetylcholine (ACh) and/or a reduction in the output of gamma-aminobutyric acid (GABA) and adenosine could tentatively explain the effects of L-NAME on SWS and W.

Differential effects of the 5-HT1A receptor agonist flesinoxan given locally or systemically on REM sleep in the rat

The effects of flesinoxan, a selective 5-HT1A receptor agonist on spontaneous sleep, were studied in adult rats implanted for chronic sleep recordings. Flesinoxan was administered systemically or infused directly into the dorsal raphe nucleus, the left laterodorsal tegmental nucleus or the medial pontine reticular formation. Systemic administration of flesinoxan (0.03 and/or 0.06 micromol/kg) significantly increased wakefulness and sleep latencies, and reduced rapid eye movement (REM) sleep and the number of REM periods, during the first and/or second 2-h period after treatment. Direct infusion of the 5-HT1A receptor agonist (0.06 and/or 0.12 nmol) into the dorsal raphe nucleus induced a significant increment of REM sleep and augmented the number of REM periods during the second and/or third 2-h period of recording. Microinjection of flesinoxan (0.03, 0.06 and/or 0.12 nmol) into the laterodorsal tegmental nucleus reduced REM sleep and the number of REM periods, and augmented REM sleep latency during the first, second and/or third 2-h recording period. Finally, direct infusion of flesinoxan (0.48 nmol) into the medial pontine reticular formation decreased REM sleep and the number of REM periods, and increased REM sleep latency during the first and second 2 h of recording. Our results indicate that the 5-HT1A receptor is involved in the inhibitory effect of serotonin on brainstem structures that act to promote and to induce REM sleep.

Increased REM sleep after intra-dorsal raphe nucleus injection of flesinoxan or 8-OHDPAT: prevention with WAY 100635

The effects of 8-OHDPAT and flesinoxan, two selective 5-HT(1A) receptor agonists, and of WAY 100635, a selective 5-HT(1A) receptor antagonist, on spontaneous sleep were studied in adult rats implanted for chronic sleep recordings. The serotonergic ligands were microinjected directly into the dorsal raphe nucleus (DRN). Direct administration of flesinoxan (25.0-50.0 ng) into the DRN induced a significant increment of REM sleep (REMS) during the second and third 2 h of recording. Microinjection of 8-OHDPAT (50.0 ng) induced similar effects on REMS during the second 2 h of recording. On the other hand, intra-DRN injection of WAY 100635 (12.5-50.0 ng) significantly reduced REMS during the second 2 h recording period. REM sleep values had also decreased significantly during the first 2 h of recording after the 50 ng dose. Pretreatment with WAY 100635 (25.0 or 50.0 ng) prevented the increase of REMS induced by flesinoxan (25.0 ng) during the second two recording hours. Our findings support the proposal that activation of somatodendritic 5-HT(1A) receptors in the DRN increases REMS, whereas their blockade induces the opposite effect.

Dorsal raphe nucleus administration of 5-HT1A receptor agonist and antagonists: effect on rapid eye movement sleep in the rat

The effect of flesinoxan, a selective 5-HT1A receptor agonist, WAY 100635, a selective 5-HT1A receptor antagonist, and (+/-)pindolol, a mixed beta-adrenoceptor and 5-HT1A/B receptor antagonist, on spontaneous sleep was studied in adult rats implanted for chronic sleep recordings. Drugs were infused directly into the dorsal raphe nucleus (DRN). Direct application of flesinoxan (25.0 and/or 50.0 ng) into the DRN induced a significant increment of REM sleep (REMS) during the second and third 2 h period of recording. On the other hand, microinjection into the DRN of (+/-)pindolol (100.0 and/or 200.0 ng), and WAY 100635 (12.5, 25.0 and 50.0 ng) significantly reduced REMS during the first and/or second 2 h recording period. Our findings support previous studies indicating that microdialysis perfusion of the 5-HT1A receptor agonist 8-OHDPAT into the DRN increases REMS. In addition, they favor the proposal that microinjection of 5-HT1A receptor antagonists into the DRN would suppress 5-HT inhibition and reduce REMS.

Increase of waking and reduction of NREM and REM sleep after nitric oxide synthase inhibition: prevention with GABAA or adenosine A1 receptor agonists

The effect of N(G)-nitro-L-arginine methyl ester (L-NAME), a competitive inhibitor of enzyme nitric oxide synthase (NOS), on spontaneous sleep during the light period, was studied in adult rats implanted for chronic sleep recordings. L-NAME was injected by subcutaneous (s.c.) route or was infused directly into the dorsal raphe nucleus (DRN). Subcutaneous (46.0--185.0 micromol/kg) administration of L-NAME increased waking (W), slow wave sleep (SWS) and rapid-eye-movement sleep (REMS) latency, whereas SWS, REMS and the number of REM periods were reduced. Direct application of L-NAME into the DRN (0.37--1.1 micromol) induced an increment of W and a reduction of SWS and REMS. Values corresponding to SWS and REMS latency, and the number of REM periods remained within control levels. Subcutaneous administration of the GABA(A) receptor agonist muscimol (1.7--3.5 micromol/kg) or the adenosine A(1) receptor agonist L-PIA [L(-)N(6)-(2-phenylisopropyl)adenosine] (0.1--0.3 micromol/kg) induced slight but inconsistent changes of W, light sleep (LS), SWS and REMS that did not attain significance. Pretreatment with muscimol (1.7--3.5 micromol/kg, s.c.) or L-PIA (0.1--0.3 micromol/kg, s.c.) antagonized the increase of W and reduction of SWS and REMS induced by s.c. (92.0 micromol/kg) or intra-DRN (0.74 micromol) administration of L-NAME. However, neither muscimol nor L-PIA prevented the increase of REMS latency induced by L-NAME 92.0 micromol/kg, s.c. Our findings tend to indicate that the change of behavioral state observed after systemic or intra-DRN administration of L-NAME is partly related to the reduction of GABA and adenosine at critical sites in the CNS.

Evidence of melatonin involvement in pindolol-induced suppression of REM sleep

The effects of pindolol, melatonin, and the melatonin receptor agonist agomelatine were studied in rats implanted for chronic sleep procedures. Administration of pindolol (1.0-4.0 mg/kg) during the light phase induced a significant reduction of rapid-eye-movement sleep (REMS) and an increase of waking (W). In the rats recorded after receiving 1.0-6.0 mg/kg melatonin no significant differences were found in sleep or W compared with controls. Agomelatine (1.0-6.0 mg/kg) induced a significant increase of light sleep during the first 3 h of the recording period. Pretreatment with melatonin partly prevented the pindolol-induced suppression of REMS. However, agomelatine was ineffective in this respect. Overall, these data suggest that the decreased production of melatonin could play a role in REMS suppression related to pindolol administration.

Conventional and power spectrum analysis of the effects of zolpidem on sleep EEG in patients with chronic primary insomnia

STUDY OBJECTIVE

The purpose of this study was 1) to assess the effect of zolpidem or a placebo on sleep in two groups of insomniac patients with a diagnosis of moderate-to-severe chronic primary insomnia and 2) to determine the effect of zolpidem on sleep structure using spectral analysis.

DESIGN

A randomized, double-blind, placebo-controlled trial.

SETTING

Sleep laboratory of the Department of Pharmacology and Therapeutics at the Clinics Hospital.

PARTICIPANTS

12 female outpatients with chronic primary insomnia.

INTERVENTIONS

Zolpidem was given at a daily dose of 10 mg for 15 nights.

RESULTS

The hypnotic drug reduced sleep latency and waking time after sleep onset, and increased total sleep time and sleep efficiency. Values corresponding to visually scored slow wave sleep (stage 3 and 4) showed no significant changes. All-night spectral analysis of the EEG revealed that power density in NREM sleep was significantly increased in the low frequency band (0.25-1.0 Hz) in the zolpidem group during the first 2-h interval.

CONCLUSIONS

In agreement with previous findings obtained in patients with chronic primary insomnia, zolpidem significantly improved sleep induction and maintenance. Moreover, zolpidem increased power density in the 0.25-1.0 Hz band during short-term and intermediate-term treatment. Nevertheless, other frequency bands in the delta range showed a relative decrease which was not statistically significant.