Effects of the melatonin MT-1/MT-2 agonist ramelteon on daytime body temperature and sleep

Circadian aspects in nonpharmacologic and pharmacologic treatment of insomnia

Insomnia disorder is a frequent sleep disorder leading to significant health and economic consequences. It has been proposed that individuals with insomnia may experience compromised deactivation systems of arousal, leading to a chronic state of hyperactivation of arousal known as hyperarousal, along with instability in the flip-flop system. Such disruptions may have a primarily impact on the sleep homeostatic drive process. Insomnia may indeed be associated with a disruption in the body's internal clock, known as chronodisruption. Despite the differentiation established in diagnostic nosology between insomnia disorder and circadian rhythm disorders, there is a significant body of evidence suggesting a complex interplay and frequent co-occurrence between these two conditions. In particular, circadian factors can predispose individuals to insomnia disorders, as well as precipitate and perpetuate their symptoms. Accordingly numerous pieces of evidence suggest that both pharmacologic and nonpharmacologic options for treating insomnia can have a resynchronization effect on circadian rhythms. The first-line treatment for chronic insomnia, according to current guidelines, is cognitive behavioral therapy for insomnia while pharmacologic interventions comprise of benzodiazepine receptor agonists also known as Z-drugs and short- to medium-acting benzodiazepines, melatonergic agonists such as ramelteon and melatonin 2mg prolonged release, and dual orexin receptor antagonists such as daridorexant, suvorexant, and lemborexant. At the same time, certain therapies recommended for circadian rhythm disorders can be utilized as adjunctive treatments for insomnia. Therefore, this chapter will discuss the circadian aspects of insomnia disorder and of its therapeutic approach. Furthermore, the effects of chronobiologic interventions, recommended for the treatment of circadian rhythm sleep-wake disorders, will be examined in individuals afflicted with chronic insomnia.

The MT1 receptor as the target of ramelteon neuroprotection in ischemic stroke

Stroke is the leading cause of death and disability worldwide. Novel and effective therapies for ischemic stroke are urgently needed. Here, we report that melatonin receptor 1A (MT1) agonist ramelteon is a neuroprotective drug candidate as demonstrated by comprehensive experimental models of ischemic stroke, including a middle cerebral artery occlusion (MCAO) mouse model of cerebral ischemia in vivo, organotypic hippocampal slice cultures ex vivo, and cultured neurons in vitro; the neuroprotective effects of ramelteon are diminished in MT1-knockout (KO) mice and MT1-KO cultured neurons. For the first time, we report that the MT1 receptor is significantly depleted in the brain of MCAO mice, and ramelteon treatment significantly recovers the brain MT1 losses in MCAO mice, which is further explained by the Connectivity Map L1000 bioinformatic analysis that shows gene-expression signatures of MCAO mice are negatively connected to melatonin receptor agonist like Ramelteon. We demonstrate that ramelteon improves the cerebral blood flow signals in ischemic stroke that is potentially mediated, at least, partly by mechanisms of activating endothelial nitric oxide synthase. Our results also show that the neuroprotection of ramelteon counteracts reactive oxygen species-induced oxidative stress and activates the nuclear factor erythroid 2-related factor 2/heme oxygenase-1 pathway. Ramelteon inhibits the mitochondrial and autophagic death pathways in MCAO mice and cultured neurons, consistent with gene set enrichment analysis from a bioinformatics perspective angle. Our data suggest that Ramelteon is a potential neuroprotective drug candidate, and MT1 is the neuroprotective target for ischemic stroke, which provides new insights into stroke therapy. MT1-KO mice and cultured neurons may provide animal and cellular models of accelerated ischemic damage and neuronal cell death.

Neuroprotective Effect of Melatonin on Sleep Disorders Associated with Parkinson's Disease

Parkinson's disease (PD) is a complex, multisystem disorder with both neurologic and systemic manifestations, which is usually associated with non-motor symptoms, including sleep disorders. Such associated sleep disorders are commonly observed as REM sleep behavior disorder, insomnia, sleep-related breathing disorders, excessive daytime sleepiness, restless legs syndrome and periodic limb movements. Melatonin has a wide range of regulatory effects, such as synchronizing circadian rhythm, and is expected to be a potential new circadian treatment of sleep disorders in PD patients. In fact, ongoing clinical trials with melatonin in PD highlight melatonin's therapeutic effects in this disease. Mechanistically, melatonin plays its antioxidant, anti-inflammatory, anti-excitotoxity, anti-synaptic dysfunction and anti-apoptotic activities. In addition, melatonin attenuates the effects of genetic variation in the clock genes of Baml1 and Per1 to restore the circadian rhythm. Together, melatonin exerts various therapeutic effects in PD but their specific mechanisms require further investigations.

Ramelteon Reduces Oxidative Stress by Maintenance of Lipid Homeostasis in Porcine Oocytes

This study aimed to determine the underlying mechanism of ramelteon on the competence of oocyte and subsequent embryo development in pigs during in vitro maturation (IVM). Our results showed that the cumulus expansion index was significantly lower in the control group compared to the ramelteon groups (p < 0.05). Moreover, supplementation of 10−11 and 10−9 M ramelteon significantly increased the cumulus expansion and development-related genes expression, and reduced apoptosis in cumulus cells (p < 0.05). In oocytes, the nuclear maturation rate was significantly improved in 10−11, 10−9, and 10−7 M ramelteon groups compared to the control (p < 0.05). Additionally, the level of intracellular GSH was significantly increased and ROS was significantly decreased in ramelteon-supplemented groups, and the gene expression of oocyte development and apoptosis were significantly up- and down-regulated by 10−11 and 10−9 M ramelteon (p < 0.05), respectively. The immunofluorescence results showed that the protein levels of GDF9, BMP15, SOD1, CDK1, and PGC1α were significantly increased by 10−11 M ramelteon compared to the control (p < 0.05). Although there was no significant difference in cleavage rate, the blastocyst formation rate, total cell numbers, and hatching/-ed rate were significantly improved in 10−11 M ramelteon group compared to the control (p < 0.05). Furthermore, embryo development, hatching, and mitochondrial biogenesis-related genes were dramatically up-regulated by 10−11 M ramelteon (p < 0.05). In addition, the activities of lipogenesis and lipolysis in oocytes were dramatically increased by 10−11 M ramelteon compared to the control (p < 0.05). In conclusion, supplementation of 10−11 M ramelteon during IVM improved the oocyte maturation and subsequent embryo development by reducing oxidative stress and maintenance of lipid homeostasis.

Melatonergic agents influence the sleep-wake and circadian rhythms in healthy and psychiatric participants: a systematic review and meta-analysis of randomized controlled trials

Exogenous melatonergic agents are widely used to treat insomnia and sleep disturbance. Several studies have shown that they might also modulate circadian rhythms. The purpose of this systematic review and meta-analysis was to summarize current knowledge about the effects of melatonin supplements and melatonin agonists on the sleep-wake cycle as well as on the circadian rhythm of melatonin in healthy participants and in patients with psychiatric disorders. The following electronic databases were searched: EMBASE, PubMed, Web of Science, CINAHL, and Cochrane Library. Of the 12,719 articles, we finally selected 30 studies including 1294 healthy participants and 8 studies including 687 patients with psychiatric disorders. Cochrane risk of bias tool was used to assess the risk of bias. Using meta-ANOVA, studies on healthy participants showed advancing effects of melatonergic supplements and agonists on sleep-wake cycle according to dosing time and dosage, despite the fact that the original individual melatonin rhythm was within a normal range (fixed effect model standardized mean difference [95% Confidence Interval] = -0.639[-0.968 to -0.310]). In a limited number of randomized controlled trials with psychiatric patients, the findings seemed similar to those with healthy participants, despite the psychiatric disorders and treatment related factors affecting circadian rhythms. Given the unmet clinical need for evidence-based treatments to correct circadian rhythms in psychiatric disorders, efficacy of melatonergic agents seen in healthy participants, and similarity of findings among psychiatric patients, large scale, well-designed randomized controlled trials are needed to test efficacy on circadian parameters in psychiatric disorders.

Periocular Skin Warming Promotes Sleep Onset Through Heat Dissipation From Distal Skin in Patients With Insomnia Disorder

STUDY OBJECTIVES

Periocular skin warming before bedtime has been demonstrated to improve subjective sleep initiation in healthy adults with sleep difficulties scored six or higher in the Pittsburgh Sleep Questionnaire Index. This study aimed to investigate the effects of periocular skin warming on sleep initiation and thermoregulation processes in patients with insomnia disorder.

METHODS

Participants included those with sleep difficulty (n = 22) and those with insomnia disorder (n = 16). Individuals from both groups were assessed at baseline (habitual sleep-wake schedule) and after two intervention conditions (use of a warming eye mask or a sham eye mask before habitual bedtime). The subjective and electroencephalographic sleep onset latency, along with proximal and distal skin temperature after periocular skin warming, were evaluated.

RESULTS

Periocular skin warming reduced objective sleep onset latency in independently of the group. Foot temperature and foot-proximal temperature gradient after getting into bed increased with periocular skin warming in independently of the group. However, the increase in hand temperature was observed only in the insomnia disorder group. Periocular skin warming also increased the normalized high frequency component of heart rate variability in independently of the group. The reduction of objective sleep onset latency was strongly associated with heat dissipation from the foot skin region.

CONCLUSION

These results suggest that periocular skin warming promotes sleep initiation by enhancing heat dissipation from the distal skin regions in individuals with sleep difficulty and insomnia disorder. Periocular skin warming could thus be a novel non-pharmacological therapy for insomnia disorder.

The Circadian Rhythm of Thermoregulation Modulates both the Sleep/Wake Cycle and 24 h Pattern of Arterial Blood Pressure

Borbély proposed an interacting two-component model of sleep regulation comprising a homeostatic Process S and a circadian Process C. The model has provided understanding of the association between core body temperature (CBT) as a key element of Process C that is deterministic of sleep onset and offset. However, it additionally provides a new perspective of the importance of the thermoregulatory mechanisms of Process C in modulating the circadian rhythm of arterial blood pressure (ABP). Herein, we examine the circadian physiology of thermoregulation, including at the end of the activity span the profound redistribution of cardiac output from the systemic circulation to the arteriovenous anastomoses of the glabrous skin that markedly enhances convective transfer of heat from the body to the environment to cause (i) decrease of the CBT as a pathway to sleep onset and (ii) attenuation of the asleep ABP mean and augmentation of the ABP decline (dipping) from the wake-time mean, in combination the strongest predictors of the risk for blood vessel and organ pathology and morbid and mortal cardiovascular disease events. We additionally review the means by which blood perfusion to the glabrous skin can be manipulated on demand by selective thermal stimulation, that is, mild warming, on the skin of the cervical spinal cord to intensify Process C as a way to facilitate sleep induction and promote healthy asleep ABP. © 2021 American Physiological Society. Compr Physiol 11:1-14, 2021.

Work-Fitness Evaluation for Shift Work Disorder

Shift work disorder (SWD), which is characterized by insomnia and excessive sleepiness related with shift work, is one of the most common health problems in shift workers. Shift work disorder causes insomnia, fatigue, worse work performance, an increased likelihood of accidents, and a poor quality of life. In addition, SWD is associated with decreased productivity and increased economic costs. The correct management of SWD is important to prevent sleep disturbances and maintain work performance in shift workers. To diagnose and evaluate SWD, it is necessary to take detailed medical histories, assess the severity of sleep disturbances, and evaluate shift workers’ sleep using a sleep diary and actigraphy. The work-fitness evaluation should include recommendations on how shift workers can reduce their sleep disturbances and increase work performance, as well as the assessment of work performance. This paper reviews previous research on the evaluation, diagnosis, and management of SWD and summarizes the work-fitness evaluation of SWD.

Periocular skin warming promotes body heat loss and sleep onset: a randomized placebo-controlled study

Periocular skin warming was reported to have favorable effects on subjective and objective sleep quality. We hypothesized that enhancing body heat loss by periocular skin warming would reduce sleep onset and improve sleep quality. Eighteen healthy volunteers were asked to maintain wakefulness with their eyes closed for 60 min after applying either a warming or sham eye mask, followed by a 60-min sleep period. Compared to the sham, periocular warming increased the distal skin temperature and distal-proximal skin temperature gradient only during the 30-min thermal manipulation period. In the subsequent sleep period, periocular warming facilitated sleep onset, increased stage 2 sleep and electroencephalographic delta activity during the first half of the sleep period relative to the sham. These results suggest that periocular skin warming may accelerate and deepen sleep by enhancing physiological heat loss via the distal skin, mimicking physiological conditions preceding habitual sleep.

Intervention for Reducing Sleep Disturbances After a 12-Time Zone Transition

Hoshikawa, M, Uchida, S, and Dohi, M. Intervention for reducing sleep disturbances after a 12-time zone transition. J Strength Cond Res 34(7): 1803-1807, 2020-The purpose of this study was to examine the effect of an intervention consisting of bright light exposure, sleep schedule shifts, and ramelteon on sleep disturbances after a transition of 12 time zones. Two groups, which flew from Tokyo to Rio, participated in this study. The experimental group received the treatment, whereas the control group did not receive any treatment. The experimental group members were exposed to bright light at night and their sleep-wake schedules were gradually delayed for 4 days before their flight. They also took 8 mg of ramelteon once a day for 5 days from the day of their first flight. Both groups departed Tokyo at 14:05, transiting through Frankfurt and arriving in Rio at 05:05. In Rio, it was recommended that they go to bed earlier than usual if they experienced sleepiness. Nocturnal sleep variables measured by wristwatch actigraphy and subjective morning tiredness were compared between groups. Statistical analysis revealed shorter sleep onset latencies (SOLs) in the experimental group (p < 0.01). The SOLs in Rio were 7.7 ± 2.5 minutes for the experimental group and 16.3 ± 3.7 minutes for the control group (d = 0.89, effect size: large). Sleep efficiency for the first 3 nights in Rio was 88.5 ± 1.2% for the experimental group and 82.9 ± 3.0% for the control group (p < 0.01, d = 1.09, effect size: large). These results suggest that the intervention reduced sleep disturbances in Rio. Our intervention may increase the options for conditioning methods for athletic events requiring time zone transitions.

Periocular skin warming elevates the distal skin temperature without affecting the proximal or core body temperature

Periocular skin warming reportedly improves the objective and subjective sleep quality in adults with mild difficulty in falling asleep. To clarify the effects of periocular warming, we examined the distal skin temperatures (hands and feet), proximal skin temperature (infraclavicular region) and core body temperature as well as the distal-proximal skin temperature gradient (DPG). Nineteen healthy males underwent two experimental sessions, wherein they used a warming or sham eye mask under a semi-constant routine protocol in a crossover manner. Participants were instructed to maintain wakefulness with their eyes closed for 60 minutes after wearing the eye mask. The warming eye mask increased the periocular skin temperature to 38–40 °C for the first 20 minutes, whereas the temperature remained unchanged with the sham mask. Compared to that of the sham eye mask, the warming eye mask significantly increased the temperatures of the hands and feet and the DPG, whereas the proximal skin and core body temperatures were unaffected. Subjective sleepiness and pleasantness were significantly increased by the warming eye mask. These results represent physiological heat loss associated with sleep initiation without affecting the proximal skin or core body temperatures, suggesting that thermal stimulation in certain areas can provoke similar changes in remote areas of the body.

Medications for Sleep Schedule Adjustments in Athletes

Context:

Sleep schedule adjustments are common requirements of modern-day athletes. Many nonpharmacologic and pharmacologic strategies exist to facilitate circadian rhythm shifts to maximize alertness and performance during competition. This review summarizes the evidence for commonly used pharmacologic agents and presents recommendations for the sports medicine provider.

Evidence Acquisition:

MEDLINE searches were performed using the following keywords: sleep aids, circadian rhythm adjustment, athletes and sleep, caffeine and sports, melatonin and athletes, and sleep aids and sports. Pertinent articles were extracted and discussed.

Study Design:

Clinical review.

Level of Evidence:

Level 2.

Results:

There are very few available studies investigating pharmacologic sleep aids in athletes. Data from studies involving shift workers and airline personnel are more abundant and were used to formulate recommendations and conclusions.

Conclusion:

Melatonin, caffeine, and nonbenzodiazepine sleep aids have a role in facilitating sleep schedule changes in athletes and maximizing sports performance through sleep enhancement.

Shift Work and Shift Work Sleep Disorder: Clinical and Organizational Perspectives

Throughout the industrialized world, nearly one in five employees works some form of nontraditional shift. Such shift work is associated with numerous negative health consequences, ranging from cognitive complaints to cancer, as well as diminished quality of life. Furthermore, a substantial percentage of shift workers develop shift work disorder, a circadian rhythm sleep disorder characterized by excessive sleepiness, insomnia, or both as a result of shift work. In addition to adverse health consequences and diminished quality of life at the individual level, shift work disorder incurs significant costs to employers through diminished workplace performance and increased accidents and errors. Nonetheless, shift work will remain a vital component of the modern economy. This article reviews seminal and recent literature regarding shift work, with an eye toward real-world application in clinical and organizational settings.

Effect of oral γ-aminobutyric acid (GABA) administration on sleep and its absorption in humans

The effects of γ-aminobutyric acid (GABA) on sleep and its levels in blood after oral administration were investigated in humans. A randomized, single-blind, placebo-controlled crossover-designed study was conducted to evaluate the effect of GABA on sleep. Sleep was evaluated by electroencephalography (EEG) after oral GABA administration. GABA significantly shortened sleep latency and increased the total non-rapid eye movement (non-REM) sleep time. Questionnaires showed that subjects receiving GABA realized its effects on sleep. In addition, the blood level of GABA after administration was investigated, and the absorption and metabolism rates of GABA were determined. GABA was quickly absorbed, and the blood level of GABA was the highest 30 min after oral administration, with a subsequent decrease in concentration. As GABA strongly affected the early stage of sleep, the effect of GABA on sleep may be connected to its levels in blood.

Melatonin administration alters nicotine preference consumption via signaling through high-affinity melatonin receptors

RATIONALE

While it is known that tobacco use varies across the 24-h day, the time-of-day effects are poorly understood. Findings from several previous studies indicate a potential role for melatonin in these time-of-day effects; however, the specific underlying mechanisms have not been well characterized. Understanding of these mechanisms may lead to potential novel smoking cessation treatments.

OBJECTIVE

The objective of this study is examine the role of melatonin and melatonin receptors in nicotine free-choice consumption

METHODS

A two-bottle oral nicotine choice paradigm was utilized with melatonin supplementation in melatonin-deficient mice (C57BL/6J) or without melatonin supplementation in mice proficient at melatonin synthesis (C3H/Ibg) compared to melatonin-proficient mice lacking both or one of the high-affinity melatonin receptors (MT1 and MT2; double-null mutant DM, or MT1 or MT2). Preference for bitter and sweet tastants also was assessed in wild-type and MT1 and MT2 DM mice. Finally, home cage locomotor monitoring was performed to determine the effect of melatonin administration on activity patterns.

RESULTS

Supplemental melatonin in drinking water significantly reduced free-choice nicotine consumption in C57BL/6J mice, which do not produce endogenous melatonin, while not altering activity patterns. Independently, genetic deletion of both MT1 and MT2 receptors in a melatonin-proficient mouse strain (C3H) resulted in significantly more nicotine consumption than controls. However, single genetic deletion of either the MT1 or MT2 receptor alone did not result in increased nicotine consumption. Deletion of MT1 and MT2 did not impact taste preference.

CONCLUSIONS

This study demonstrates that nicotine consumption can be affected by exogenous or endogenous melatonin and requires at least one of the high-affinity melatonin receptors. The fact that expression of either the MT1 or MT2 melatonin receptor is sufficient to maintain lower nicotine consumption suggests functional overlap and potential mechanistic explanations.

The sleep-promoting and hypothermic effects of glycine are mediated by NMDA receptors in the suprachiasmatic nucleus

The use of glycine as a therapeutic option for improving sleep quality is a novel and safe approach. However, despite clinical evidence of its efficacy, the details of its mechanism remain poorly understood. In this study, we investigated the site of action and sleep-promoting mechanisms of glycine in rats. In acute sleep disturbance, oral administration of glycine-induced non-rapid eye movement (REM) sleep and shortened NREM sleep latency with a simultaneous decrease in core temperature. Oral and intracerebroventricular injection of glycine elevated cutaneous blood flow (CBF) at the plantar surface in a dose-dependent manner, resulting in heat loss. Pretreatment with N-methyl-D-aspartate (NMDA) receptor antagonists AP5 and CGP78608 but not the glycine receptor antagonist strychnine inhibited the CBF increase caused by glycine injection into the brain. Induction of c-Fos expression was observed in the hypothalamic nuclei, including the medial preoptic area (MPO) and the suprachiasmatic nucleus (SCN) shell after glycine administration. Bilateral microinjection of glycine into the SCN elevated CBF in a dose-dependent manner, whereas no effect was observed when glycine was injected into the MPO and dorsal subparaventricular zone. In addition, microinjection of D-serine into the SCN also increased CBF, whereas these effects were blocked in the presence of L-701324. SCN ablation completely abolished the sleep-promoting and hypothermic effects of glycine. These data suggest that exogenous glycine promotes sleep via peripheral vasodilatation through the activation of NMDA receptors in the SCN shell.

Effects of caffeine on skin and core temperatures, alertness, and recovery sleep during circadian misalignment

Caffeine promotes wakefulness during night shift work, although it also disturbs subsequent daytime sleep. Increased alertness by caffeine is associated with a higher core body temperature (CBT). A lower CBT and a narrow distal-to-proximal skin temperature gradient (DPG) have been reported to be associated with improved sleep, yet whether caffeine influences the DPG is unknown. We tested the hypothesis that the use caffeine during nighttime total sleep deprivation would reduce the DPG, increase CBT and alertness, and disturb subsequent daytime recovery sleep. We also expected that a greater widening of the DPG prior to sleep would be associated with a greater degree of sleep disturbance. Thirty healthy adults (9 females) aged 21.6 ± 3.5 years participated in a double-blind, 28-h modified constant routine protocol. At 23 h of wakefulness, participants in the treatment condition (n = 10) were given 2.9 mg/kg caffeine, equivalent to ~200 mg (or 2 espressos) for a 70-kg adult, 5 h before a daytime recovery sleep episode. Throughout the protocol, core and skin body temperatures, DPG, sleep architecture, and subjective alertness and mood were measured. Prior to sleep, caffeine significantly widened the DPG and increased CBT, alertness, and clear-headedness (p < 0.05). Caffeine also disturbed daytime recovery sleep (p < 0.05). Increased CBT and a wider DPG prior to sleep were associated with a longer latency to sleep, and a wider DPG was associated with disturbed recovery sleep (i.e., increased wakefulness after sleep onset, increased stage 1 sleep, decreased sleep efficiency, and decreased slow wave sleep) (p < 0.05). A widening of the DPG following nighttime caffeine may represent a component of the integrated physiological response by which caffeine improves alertness and disturbs subsequent daytime recovery sleep. Furthermore, our findings highlight that sleep disturbances associated with caffeine consumed near the circadian trough of alertness are still present when daytime recovery sleep occurs 5 h or approximately 1 half-life later.

Twisting the night away: a review of the neurobiology, genetics, diagnosis, and treatment of shift work disorder

Although not all individuals who work outside of standard daytime hours develop physical and psychiatric issues, there is a substantial portion of shift workers who develop shift work disorder. Shift work disorder is due to a misalignment between an individual's endogenous circadian rhythms and environmental stimuli, and can have potentially serious consequences to an individual's health and quality of life. This article reviews the neurobiological and genetic underpinnings of shift work disorder, and describes how desynchronization of the molecular clock may lead to both physical and psychiatric illnesses. Diagnostic tools and treatment guidelines to address the circadian misalignment, excessive sleepiness, and insomnia experienced by patients with shift work disorder are also discussed.

Entrainment of the circadian clock by daily ambient temperature cycles in the camel (Camelus dromedarius)

In mammals the light-dark (LD) cycle is known to be the major cue to synchronize the circadian clock. In arid and desert areas, the camel ( Camelus dromedarius) is exposed to extreme environmental conditions. Since wide oscillations of ambient temperature (Ta) are a major factor in this environment, we wondered whether cyclic Ta fluctuations might contribute to synchronization of circadian rhythms. The rhythm of body temperature (Tb) was selected as output of the circadian clock. After having verified that Tb is synchronized by the LD and free runs in continuous darkness (DD), we submitted the animals to daily cycles of Ta in LL and in DD. In both cases, the Tb rhythm was entrained to the cycle of Ta. On a 12-h phase shift of the Ta cycle, the mean phase shift of the Tb cycle ranged from a few hours in LD (1 h by cosinor, 4 h from curve peaks) to 7–8 h in LL and 12 h in DD. These results may reflect either true synchronization of the central clock by Ta daily cycles or possibly a passive effect of Ta on Tb. To resolve the ambiguity, melatonin rhythmicity was used as another output of the clock. In DD melatonin rhythms were also entrained by the Ta cycle, proving that the daily Ta cycle is able to entrain the circadian clock of the camel similar to photoperiod. By contrast, in the presence of a LD cycle the rhythm of melatonin was modified by the Ta cycle in only 2 (or 3) of 7 camels: in these specific conditions a systematic effect of Ta on the clock could not be evidenced. In conclusion, depending on the experimental conditions (DD vs. LD), the daily Ta cycle can either act as a zeitgeber or not.

Ramelteon in the treatment of chronic insomnia: systematic review and meta-analysis

OBJECTIVE

As a melatonin receptor agonist, ramelteon has been approved in the United States as a treatment for insomnia. As a potential alternation, ramelteon should be further evaluated in different doses and populations. This systematic review with meta-analysis aims to determine the efficacy and safety of ramelteon in the treatment of chronic insomnia.

METHODS

We systematically searched and identified in Medline, Embase, PsycINFO and Cochrane Library until September 2011. We only included randomised controlled trials focused on ramelteon, vs. placebo, or any other treatment for patients with chronic insomnia. Data were extracted and evaluated by two independent investigators. If neither clinical nor statistical heterogeneity was found, we pooled results using a fixed-effect model.

RESULTS

Eight studies were selected to include from 175 identified references. There were significant improvements in all the outcomes (subjective and polysomnographic sleep latency, total sleep time and latency to REM), except for the percentage of REM. By subgroup analysis, subjective sleep latency was reduced only in the patients of 18-64 years old, without in the patients over 65 years old. For the safety, ramelteon was not associated with higher risk ratio of any frequent adverse events comparing with control.

CONCLUSION

The efficacy and safety of ramelteon are promising for the chronic insomnia patients. More researches are required for robust conclusions, particularly well-designed; double-blind randomised controlled trials with higher doses of ramelteon (32 or 64 mg) for the older population comparing with other sedative hypnotics.

Shift work and the assessment and management of shift work disorder (SWD)

Nearly 20% of the labor force worldwide, work shifts that include work hours outside 07:00 h to 18:00 h. Shift work is common in many occupations that directly affect the health and safety of others (e.g., protective services, transportation, healthcare), whereas quality of life, health, and safety during shift work and the commute home can affect workers in any field. Increasing evidence indicates that shift-work schedules negatively influence worker physiology, health, and safety. Shift work disrupts circadian sleep and alerting cycles, resulting in disturbed daytime sleep and excessive sleepiness during the work shift. Moreover, shift workers are at risk for shift work disorder (SWD). This review focuses on shift work and the assessment and management of sleepiness and sleep disruption associated with shift work schedules and SWD. Management strategies include approaches to promote sleep, wakefulness, and adaptation of the circadian clock to the imposed work schedule. Additional studies are needed to further our understanding of the mechanisms underlying the health risks of shift work, understanding which shift workers are at most risk of SWD, to investigate treatment options that address the health and safety burdens associated with shift work and SWD, and to further develop and assess the comparative effectiveness of countermeasures and treatment options.

Circadian and wakefulness-sleep modulation of cognition in humans

Cognitive and affective processes vary over the course of the 24 h day. Time of day dependent changes in human cognition are modulated by an internal circadian timekeeping system with a near-24 h period. The human circadian timekeeping system interacts with sleep-wakefulness regulatory processes to modulate brain arousal, neurocognitive and affective function. Brain arousal is regulated by ascending brain stem, basal forebrain (BF) and hypothalamic arousal systems and inhibition or disruption of these systems reduces brain arousal, impairs cognition, and promotes sleep. The internal circadian timekeeping system modulates cognition and affective function by projections from the master circadian clock, located in the hypothalamic suprachiasmatic nuclei (SCN), to arousal and sleep systems and via clock gene oscillations in brain tissues. Understanding the basic principles of circadian and wakefulness-sleep physiology can help to recognize how the circadian system modulates human cognition and influences learning, memory and emotion. Developmental changes in sleep and circadian processes and circadian misalignment in circadian rhythm sleep disorders have important implications for learning, memory and emotion. Overall, when wakefulness occurs at appropriate internal biological times, circadian clockwork benefits human cognitive and emotion function throughout the lifespan. Yet, when wakefulness occurs at inappropriate biological times because of environmental pressures (e.g., early school start times, long work hours that include work at night, shift work, jet lag) or because of circadian rhythm sleep disorders, the resulting misalignment between circadian and wakefulness-sleep physiology leads to impaired cognitive performance, learning, emotion, and safety.

Pharmacotherapy of insomnia with ramelteon: safety, efficacy and clinical applications

Ramelteon is a tricyclic synthetic analog of melatonin that acts specifically on MT₁ and MT₂ melatonin receptors. Ramelteon is the first melatonin receptor agonist approved by the Food and Drug Administration (FDA) for the treatment of insomnia characterized by sleep onset difficulties. Ramelteon is both a chronobiotic and a hypnotic that has been shown to promote sleep initiation and maintenance in various preclinical and in clinical trials. The efficacy and safety of ramelteon in patients with chronic insomnia was initially confirmed in short-term placebo-controlled trials. These showed little evidence of next-day residual effects, withdrawal symptoms or rebound insomnia. Other studies indicated that ramelteon lacked abuse potential and had a minimal risk of producing dependence or adverse effects on cognitive or psychomotor performance. A 6-month placebo-controlled international study and a 1-year open-label study in the USA demonstrated that ramelteon was effective and well tolerated. Other potential off-label uses of ramelteon include circadian rhythm sleep disorders such as shift-work and jet lag. At the present time the drug should be cautiously prescribed for short-term treatment only.