Circadian rhythm disturbances in depression

Inborn differences in environmental reactivity predict divergent diurnal behavioral, endocrine, and gene expression rhythms

Circadian dysfunction has long been implicated in the etiology of mood disorders. The gene Clock and related molecules (e.g. Per1, Per2) represent key regulators of circadian rhythmicity, and their targeted disruption in mutant mice produces potentiated reward drive, novelty-seeking, impulsivity, disrupted sleep, reduced depression and anxiety - a behavioral profile highly reminiscent of our selectively bred high responder (bHR) rats compared to bred low responders (bLRs). The current study evaluated potential diurnal bHR-bLR differences in behavior, gene expression, and neuroendocrinology. Relative to bHRs, bLRs showed diminished homecage locomotion during the dark (but not light) phase and a delayed corticosterone peak. In situ hybridizations in hypothalamus, amygdala, and hippocampus at Zeitgeber Time (ZT)2 and ZT14 revealed distinct bHR-bLR day-night gene expression fluctuations. bHRs exhibited altered day-night patterns of corticotrophin releasing hormone (CRH) and arginine vasopression (AVP) mRNA in the hypothalamus, and perturbed hippocampal MR:GR ratios relative to bLR rats. bHR-bLR rats showed disparate day-night Clock expression in the suprachiasmatic nucleus, a master circadian oscillator, with bHRs showing higher levels at ZT14 versus ZT2 and bLRs showing the opposite pattern. Clock, Per1 and Per2 were assessed in the substantia nigra pars compacta (SNc) and ventral tegmental area (VTA) since disruption of these genes induces "bHR-like" behavior in mutant mice. Clock and Per1 did not differ between strains, but there were robust Per2 differences, with bHRs having reduced Per2 in VTA and SNc. These findings resonate with earlier work demonstrating that perturbation of Clock and related molecules contributes to disturbances of emotional and addictive behaviors.

Circadian disruption leads to loss of homeostasis and disease

The relevance of a synchronized temporal order for adaptation and homeostasis is discussed in this review. We present evidence suggesting that an altered temporal order between the biological clock and external temporal signals leads to disease. Evidence mainly based on a rodent model of “night work” using forced activity during the sleep phase suggests that altered activity and feeding schedules, out of phase from the light/dark cycle, may be the main cause for the loss of circadian synchrony and disease. It is proposed that by avoiding food intake during sleep hours the circadian misalignment and adverse consequences can be prevented. This review does not attempt to present a thorough revision of the literature, but instead it aims to highlight the association between circadian disruption and disease with special emphasis on the contribution of feeding schedules in circadian synchrony.

Complex interaction of circadian and non-circadian effects of light on mood: shedding new light on an old story

In addition to its role in vision, light exerts strong effects on behavior. Its powerful role in the modulation of mood is well established, yet remains poorly understood. Much research has focused on the effects of light on circadian rhythms and subsequent interaction with alertness and depression. The recent discovery of a third photoreceptor, melanopsin, expressed in a subset of retinal ganglion cells, allows major improvement of our understanding of how photic information is processed. Light affects behavior in two ways, either indirectly through the circadian timing system, or directly through mechanisms that are independent of the circadian system. These latter effects have barely been studied in regard to mood, but recent investigations on the direct effects of light on sleep and alertness suggest additional pathways through which light could influence mood. Based on our recent findings, we suggest that light, via melanopsin, may exert its antidepressant effect through a modulation of the homeostatic process of sleep. Further research is needed to understand how these mechanisms interplay and how they contribute to the photic regulation of mood. Such research could improve therapeutic management of affective disorders and influence the management of societal lighting conditions.

Mood disorders, circadian rhythms, melatonin and melatonin agonists

Recent advances in the understanding of circadian rhythms have led to an interest in the treatment of major depressive disorder with chronobiotic agents. Many tissues have autonomous circadian rhythms, which are orchestrated by the master clock, situated in the suprachiasmatic nucleus (SNC). Melatonin (N-acetyl-5-hydroxytryptamine) is secreted from the pineal gland during darkness. Melatonin acts mainly on MT1 and MT2 receptors, which are present in the SNC, regulating physiological and neuroendocrine functions, including circadian entrainment, referred to as the chronobiotic effet. Circadian rhythms has been shown to be either misaligned or phase shifted or decreased in amplitude in both acute episodes and relapse of major depressive disorder (MDD) and bipolar disorder. Manipulation of circadian rhythms either using physical treatments (such as high intensity light) or behavioral therapy has shown promise in improving symptoms. Pharmacotherapy using melatonin and pure melatonin receptor agonists, while improving sleep, has not been shown to improve symptoms of depression. A novel antidepressant, agomelatine, combines 5HT2c antagonist and melatonin agonist action, and has shown promise in both acute treatment of MDD and in preventing relapse.

Circadian dimension and severity of depression

The cyclic nature of depressive illness, disturbance of diurnal mood variations, and disturbed sleep-wake and physiological rhythms all suggest that dysfunction of the circadian time-keeping system may underlie the pathophysiology of depression. Circadian misalignment of the phase-delayed type appears to be the most common shift in unipolar disorder patients and misalignment between the timing of sleep and the pacemaker is correlated with depressive symptom severity. Profiles of diurnal mood variation are associated with risks of depression severity and may predict response to treatments. As circadian disturbances are at the core of depression, normalizing circadian rhythm may be a fruitful avenue for new therapeutic targets in depression. The innovative antidepressant agomelatine possesses resynchronizing properties that may be related to its original profile and offers an opportunity to achieve our goals in treating depressed people.

Neuroimmune endocrine effects of antidepressants

Antidepressant pharmacotherapy is to date the most often used treatment for depression, but the exact mechanism of action underlying its therapeutic effect is still unclear. Many theories have been put forward to account for depression, as well as antidepressant activity, but none of them is exhaustive. Neuroimmune endocrine impairment is found in depressed patients; high levels of circulating corticosteroids along with hyperactivation of the immune system, high levels of proinflammatory cytokines, low levels of melatonin in plasma and urine, and disentrainment of circadian rhythms have been demonstrated. Moreover, antidepressant treatment seems to correct or at least to interfere with these alterations. In this review, we summarize the complex neuroimmune endocrine and chronobiological alterations found in patients with depression and how these systems interact with each other. We also explain how antidepressant therapy can modify these systems, along with some possible mechanisms of action shown in animal and human models.

Higher frontal EEG synchronization in young women with major depression: a marker for increased homeostatic sleep pressure?

STUDY OBJECTIVES

Major depressive disorder (MDD) is often associated with disturbances in circadian and/or sleep-wake dependent processes, which both regulate daytime energy and sleepiness levels.

DESIGN

Analysis of continuous electroencephalographic (EEG) recordings during 40 h of extended wakefulness under constant routine conditions. Artifact-free EEG samples derived from 12 locations were subjected to spectral analysis. Additionally, half-hourly ratings of subjective tension and sleepiness levels and salivary melatonin measurements were collected.

SETTING

Centre for Chronobiology, Psychiatric Hospitals of the University of Basel, Switzerland.

PARTICIPANTS

Eight young healthy women and 8 young untreated women with MDD.

INTERVENTIONS

N/A.

MEASUREMENTS AND RESULTS

MDD women exhibited higher frontal low-frequency (FLA) EEG activity (0.5-5.0 Hz) during extended wakefulness than controls, particularly during the night. Enhanced FLA was paralleled by higher levels of subjective sleepiness and tension. In MDD women, overall FLA levels correlated positively with depression scores. The timing of melatonin onset did not significantly differ between the two groups, but the nocturnal secretion of salivary melatonin was significantly attenuated in MDD women.

CONCLUSIONS

Our data imply that young women with MDD live on a higher homeostatic sleep pressure level, as indexed by enhanced FLA during wakefulness. Its positive correlation with depression scores indicates a possible functional relationship. High FLA could reflect a use-dependent phenomenon in depression (enhanced cognitive rumination or tension) and/or an attenuated circadian arousal signal.

Brain and Psyche in Early Christian Asceticism

This study is an 11-part investigation of the psychology and neuropsychology of early Christian asceticism as represented by Evagrius Ponticus (AD 345–399), the tradition's first ascetical theologian and possibly its most influential. Evagrius's biography is reviewed in the first section. The living circumstances and perceptual consequences of desert asceticism are considered in the second. Penitence, dispassion, and the mysticism of “pure prayer” are discussed in the third. Austerities are addressed in the fourth section, particularly fasting, prostrations, and prolonged standing. Ascetical perspectives on sleep, dreams, and the hypnogogic state are analyzed in the fifth. The depressive syndrome of acedia is discussed in the sixth. Evagrius's reports of auditory, olfactory, and visual hallucinations are analyzed in the seventh. Multiple complementary interpretations of demonic phenomena are developed in the eighth section. Evagrius's psychotherapy for anger is reviewed in the ninth. Interpersonal relations among ascetics are considered in the tenth section. The study concludes with a summary.

Relationship between daylength and suicide in Finland

Background

Many previous studies have documented seasonal variation in suicides globally. We re-assessed the seasonal variation of suicides in Finland and tried to relate it to the seasonal variation in daylength and ambient temperature and in the discrepancy between local time and solar time.

Methods

The daily data of all suicides from 1969 to 2003 in Finland (N = 43,393) were available. The calendar year was divided into twelve periods according to the length of daylight and the routinely changing time difference between sun time and official time. The daily mean of suicide mortality was calculated for each of these periods and the 95% confidence intervals of the daily means were used to evaluate the statistical significance of the means. In addition, daily changes in sunshine hours and mean temperature were compared to the daily means of suicide mortality in two locations during these afore mentioned periods.

Results

A significant peak of the daily mean value of suicide mortality occurred in Finland between May 15th and July 25th, a period that lies symmetrically around the solstice. Concerning the suicide mortality among men in the northern location (Oulu), the peak was postponed as compared with the southern location (Helsinki). The daily variation in temperature or in sunshine did not have significant association with suicide mortality in these two locations.

Conclusions

The period with the longest length of the day associated with the increased suicide mortality. Furthermore, since the peak of suicide mortality seems to manifest later during the year in the north, some other physical or biological signals, besides the variation in daylight, may be involved. In order to have novel means for suicide prevention, the assessment of susceptibility to the circadian misalignment might help.

The keys to improving depression outcomes

The heterogeneity of symptoms within major depressive disorder poses significant challenges for treatment and it is likely that current pharmacotherapies do not target all symptoms equally, although they have similar efficacy rates. While there is still continuing interest in understanding monoamine interactions and consequent downstream effects, the limited efficacy and tolerability achieved with classical antidepressants provides a compelling argument to move beyond the monoamines. Several lines of biological research in depression exploring immune function, neurotrophins, amino acid and neuropeptide neurotransmitters, neuroanatomical function and circadian rhythms, may lead to novel therapeutic targets and enhance depression outcomes. This review will evaluate the evidence for emerging treatments as well as recommendations from current international guidelines regarding antidepressant management.

Circadian rhythms and depression: human psychopathology and animal models

Most organisms (including humans) developed daily rhythms in almost every aspect of their body. It is not surprising that rhythms are also related to affect in health and disease. In the present review we present data that demonstrate the evidence for significant interactions between circadian rhythms and affect from both human studies and animal models research. A number of lines of evidence obtained from human and from animal models research clearly demonstrate relationships between depression and circadian rhythms including (1) daily patterns of depression; (2) seasonal affective disorder; (3) connections between circadian clock genes and depression; (4) relationship between sleep disorders and depression; (5) the antidepressant effect of sleep deprivation; (6) the antidepressant effect of bright light exposure; and (7) the effects of antidepressant drugs on sleep and circadian rhythms. The integration of data suggests that the relationships between the circadian system and depression are well established but the underlying biology of the interactions is far from being understood. We suggest that an important factor hindering research into the underlying mechanisms is the lack of good animal models and we propose that additional efforts in that area should be made. One step in that direction could be the attempt to develop models utilizing diurnal animals which might have a better homology to humans with regard to their circadian rhythms. This article is part of a Special Issue entitled 'Anxiety and Depression'.

Novel melatonin-based therapies: potential advances in the treatment of major depression

Major depression is one of the leading causes of premature death and disability. Although available drugs are effective, they also have substantial limitations. Recent advances in our understanding of the fundamental links between chronobiology and major mood disorders, as well as the development of new drugs that target the circadian system, have led to a renewed focus on this area. In this review, we summarise the associations between disrupted chronobiology and major depression and outline new antidepressant treatment strategies that target the circadian system. In particular, we highlight agomelatine, a melatonin-receptor agonist and selective serotonergic receptor subtype (ie, 5-HT(2C)) antagonist that has chronobiotic, antidepressant, and anxiolytic effects. In the short-term, agomelatine has similar antidepressant efficacy to venlafaxine, fluoxetine, and sertraline and, in the longer term, fewer patients on agomelatine relapse (23·9%) than do those receiving placebo (50·0%). Patients with depression treated with agomelatine report improved sleep quality and reduced waking after sleep onset. As agomelatine does not raise serotonin levels, it has less potential for the common gastrointestinal, sexual, or metabolic side-effects that characterise many other antidepressant compounds.

Disruption of circadian rhythms: a crucial factor in the etiology of depression

Circadian factors might play a crucial role in the etiology of depression. It has been demonstrated that the disruption of circadian rhythms by lighting conditions and lifestyle predisposes individuals to a wide range of mood disorders, including impulsivity, mania and depression. Also, associated with depression, there is the impairment of circadian rhythmicity of behavioral, endocrine, and metabolic functions. Inspite of this close relationship between both processes, the complex relationship between the biological clock and the incidence of depressive symptoms is far from being understood. The efficiency and the timing of treatments based on chronotherapy (e.g., light treatment, sleep deprivation, and scheduled medication) indicate that the circadian system is an essential target in the therapy of depression. The aim of the present review is to analyze the biological and clinical data that link depression with the disruption of circadian rhythms, emphasizing the contribution of circadian desynchrony. Therefore, we examine the conditions that may lead to circadian disruption of physiology and behavior as described in depressive states, and, according to this approach, we discuss therapeutic strategies aimed at treating the circadian system and depression.

Effects of constant daylight exposure during early development on marmoset psychosocial behavior

Due to global industrialization, the light cycle is shifting to longer daytime. Mounting evidence indicates that social developmental disorders may correlate with longer periods of daytime in childhood. However, the exact mechanisms of this link remain unclear. To examine the impact of longer day-time on psychosocial development, we developed a novel non-human primate model, using the common marmoset (Callithrix jacchus) reared under constant daylight from birth. Marmosets were reared individually by human nursing under constant light (LL) during varying periods in juvenile development, and their behaviors were compared with those of normal day-night cycle (LD) marmosets by multivariate analysis based on principal component analysis (PCA). LL marmosets elicited egg-like calls (e-call) less in juvenile period, and displayed side-to-side shakes of the upper body with rapid head rotation through adulthood frequently. Based on the PCA, these behaviors were interpreted as 'alert' or 'hyperactive' states. Additionally, behavioral development of marmosets reared under constant dark (DD) was markedly different from both LD and LL marmosets, suggesting the fundamental importance of daylight-dependent neuronal and endocrine processes and entrainment by a constant 24-hour light/dark cycle on psychosocial behavior development.

Altered sirtuin deacetylase gene expression in patients with a mood disorder

Sirtuins are a family of NAD+-dependent enzymes that regulate cellular functions through deacetylation of various proteins. Although recent reports have suggested an important role of deacetylases (i.e., histone deacetylases) in mood disorders and antidepressant action, the involvement of sirtuins in the pathophysiology of mood disorders is largely unknown. In this study, we aimed to determine whether there are alterations in sirtuin mRNA expression in peripheral white blood cells of patients with a mood disorder. Also, to examine whether the altered sirtuin mRNA expression is state- or trait-dependent, mood disorder patients who were in a remissive state were assessed. We used quantitative real-time polymerase chain reaction to measure the mRNA levels of seven sirtuin isoforms (SIRT1-7) in peripheral white blood cells of patients with major depressive disorder (MDD) or bipolar disorder (BPD) during depressive and remissive states and in normal healthy subjects. The SIRT1, 2 and 6 mRNA levels in MDD and BPD patients decreased significantly in those who were in a depressive state compared to healthy controls, whereas the expression of those mRNAs in both MDD and BPD of patients in a remissive state were comparable to those in healthy controls. Thus, our data suggest that altered SIRT1, 2 and 6 expression is state-dependent and might be associated with the pathogenesis and/or pathophysiology of mood disorders.

Strategies to achieve clinical effectiveness: refining existing therapies and pursuing emerging targets

BACKGROUND

Clinical effectiveness reflects a balance between efficacy and tolerability as well as patient satisfaction and overall improvement in quality of life and function. This is of particular importance when considering the long term use of antidepressant therapies for relapse prevention.

METHODS

The purpose of this review is to explore methods to enhance the modest efficacy and effectiveness outcomes reported with current antidepressant strategies. Two strategies are addressed: a) Doing better with existing treatments and b) pursuing novel targets beyond the monoamine system for new antidepressant drug development.

RESULTS

In the first instance, it is important to consider the balance between antidepressant efficacy and tolerability for individual patients and also be aware of evidence supporting superiority of one agent over others. Both sequential and concurrent combination therapies with existing antidepressants are also reviewed. The second approach involves a review of emerging novel pharmacological treatments based on biomarker research. Unique targets where antidepressant treatments appear effective include the melatonergic, glutamatergic, neurotrophic, cytokine, and neuropeptide systems.

CONCLUSIONS

While agomelatine represents an example of a clinically available antidepressant that targets melatonin receptors, drugs that act on other candidate systems are still in the development phase.

Sleep and circadian functioning: critical mechanisms in the mood disorders?

Evidence for the importance of sleep in the mood disorders has mushroomed over the past decade. Among adolescents and adults with a mood disorder, sleep disturbance is a risk factor for episodes, can contribute to relapse, has an adverse impact on emotion regulation, is critical for cognitive functioning, compromises health, and may contribute to substance use comorbidity and suicidality. This evidence has triggered a shift away from viewing sleep disturbance as an epiphenomenon, toward viewing sleep disturbance as an important but under-recognized mechanism in the multifactorial cause and maintenance of the mood disorders. Because the biology underpinning the sleep and circadian system is an open system, readily influenced by inputs from the environment, sleep in the mood disorders represents a unique and exciting domain for interdisciplinary research across behavioral, social, cognitive, and neurobiological levels of explanation. Together, the accumulated evidence has informed a range of novel, powerful, simple, and inexpensive treatments with potential for massive improvements to public health, including improving quality of life, reducing length and severity of episodes, and reducing the risk of subsequent episodes in the large number of individuals who suffer from mood disorders.

The melatonergic agonist and clinically active antidepressant, agomelatine, is a neutral antagonist at 5-HT(2C) receptors

The novel antidepressant, agomelatine, behaves as an agonist at melatonergic receptors, and as an antagonist at edited, human serotonin2C(VSV) receptors [h5-HT2C(VSV)Rs]. However, its actions at constitutively active 5-HT2CRs have yet to be characterized, an issue addressed herein. At unedited h5-HT2C(INI)Rs expressed in HEK-293 cells, 5-HT enhanced [35S]GTPγS binding to Gαq, whereas the inverse agonists SB206,553 and S32006 inhibited binding and, by analogy to the neutral antagonist, SB242,084, agomelatine exerted no effect alone. Mirroring these observations, 5-HT stimulated, whereas SB206,553 and S32006 inhibited, [3H]inositol phosphate formation. Both the agonist actions of 5-HT and the inverse agonist actions of SB206,553 and S32006 were abolished by agomelatine and SB242,084. As demonstrated by bioluminescence resonance energy transfer, 5-HT enhanced, whereas SB206,553 and S32006 decreased, association of 'h5-HT2C(INI)-Rluc-tagged' receptors with yellow-fluorescence-protein-coupled β-arrestin2. These actions of 5-HT, SB206,553 and S32006 were prevented by agomelatine and SB242,084 were ineffective alone. As shown by ELISA and confocal microscopy, prolonged (18 h) exposure to SB206,553 or S32006 enhanced cell surface expression of N-terminal Flag-tagged h5-HT2C(INI)Rs: these effects were blocked by agomelatine and SB242,084, which were inactive alone. Finally, following pre-exposure to SB206,553 or S32006 for 18 h, 5-HT triggered 5-HT2CR-mediated elevations in cytosolic Ca2+ in primary cultures of mice cortical neurons. Agomelatine and SB242,084, inactive alone, prevented these actions of SB206,553 and S32006. In conclusion, agomelatine behaves as a neutral antagonist at constitutively active h5-HT2C(INI)Rs and native, cortical 5-HT2CRs. It will be of interest to determine whether the neutral antagonist properties of agomelatine are related to its favourable clinical profile of antidepressant properties with few side-effects and no discontinuation syndrome.

The Genetics of Sleep: Insight from Rodent Models

Sleep is a fundamental behavior in higher animals that has been firmly established to be under substantial genetic control. However, the identification of individual genes responsible for primary sleep-wake traits has largely eluded researchers. Genetic studies in animal models have uncovered a variety of genomic loci associated with specific traits, validated the role of key neurotransmitter systems (i.e., monoamines) in sleep-wake regulation, identified novel and unexpected genes responsible for controlling sleep-wake traits, and demonstrated substantial genetic overlap in the regulation of sleep and circadian rhythms. Future studies are expected to reveal additional genes and gene networks underlying certain sleep-wake traits, thereby advancing our understanding of the molecular basis of sleep, which may suggest answers to the ultimate question of why we sleep as well as provide unique insight into the relationship between sleep and chronic diseases.

Circadian rhythms, sleep, and substance abuse

Substance abuse is linked to numerous mental and physical health problems, including disturbed sleep. The association between substance use and sleep appears to be bidirectional, in that substance use may directly cause sleep disturbances, and difficulty sleeping may be a risk factor for relapse to substance use. Growing evidence similarly links substance use to disturbances in circadian rhythms, although many gaps in knowledge persist, particularly regarding whether circadian disturbance leads to substance abuse or dependence. Given the integral role circadian rhythms play in regulating sleep, circadian mechanisms may account in part for sleep-substance abuse interactions. Furthermore, a burgeoning research base supports a role for the circadian system in regulating reward processing, indicating that circadian mechanisms may be directly linked to substance abuse independently of sleep pathways. More work in this area is needed, particularly in elucidating how sleep and circadian disturbance may contribute to initiation of, and/or relapse to, substance use. Sleep and circadian-based interventions could play a critical role in the prevention and treatment of substance use disorders.

Sleep disturbances in highly stress reactive mice: modeling endophenotypes of major depression

Background

Neuronal mechanisms underlying affective disorders such as major depression (MD) are still poorly understood. By selectively breeding mice for high (HR), intermediate (IR), or low (LR) reactivity of the hypothalamic-pituitary-adrenocortical (HPA) axis, we recently established a new genetic animal model of extremes in stress reactivity (SR). Studies characterizing this SR mouse model on the behavioral, endocrine, and neurobiological levels revealed several similarities with key endophenotypes observed in MD patients. HR mice were shown to have changes in rhythmicity and sleep measures such as rapid eye movement sleep (REMS) and non-REM sleep (NREMS) as well as in slow wave activity, indicative of reduced sleep efficacy and increased REMS. In the present study we were interested in how far a detailed spectral analysis of several electroencephalogram (EEG) parameters, including relevant frequency bands, could reveal further alterations of sleep architecture in this animal model. Eight adult males of each of the three breeding lines were equipped with epidural EEG and intramuscular electromyogram (EMG) electrodes. After recovery, EEG and EMG recordings were performed for two days.

Results

Differences in the amount of REMS and wakefulness and in the number of transitions between vigilance states were found in HR mice, when compared with IR and LR animals. Increased frequencies of transitions from NREMS to REMS and from REMS to wakefulness in HR animals were robust across the light-dark cycle. Detailed statistical analyses of spectral EEG parameters showed that especially during NREMS the power of the theta (6-9 Hz), alpha (10-15 Hz) and eta (16-22.75 Hz) bands was significantly different between the three breeding lines. Well defined distributions of significant power differences could be assigned to different times during the light and the dark phase. Especially during NREMS, group differences were robust and could be continuously monitored across the light-dark cycle.

Conclusions

The HR mice, i.e. those animals that have a genetic predisposition to hyper-activating their HPA axis in response to stressors, showed disturbed patterns in sleep architecture, similar to what is known from depressed patients. Significant alterations in several frequency bands of the EEG, which also seem to at least partly mimic clinical observations, suggest the SR mouse lines as a promising animal model for basic research of mechanisms underlying sleep impairments in MD.

Wake-promoting effects of orexin: Its independent actions against the background of an impaired corticotropine-releasing hormone receptor system

It is widely accepted that orexin (hypocretin) bears wake-promoting effects. While under normal conditions the circadian rhythm of orexin release has a clear circadian distribution, the amplitude of orexin fluctuation is dampened in depression. Interestingly, clinical symptoms of depression include several sleep disturbances. In this disease, corticotropin-releasing hormone (CRH) seems to be another factor influencing sleep. As neurophysiological interactions and anatomical connections between the orexinergic and the CRH system point to mutual influences of these two neuropeptides, we examined whether a dysfunctional CRH-receptor system in two different CRH receptor knock out models alters general wake-promoting effects of orexin applied exogenously. Orexin was injected intracerebroventricularlly into CNS-restricted CRH-receptor type 1 knockout mice (CRH-R1 KO) and CRH-receptor type 2 knockout mice (CRH-R2 KO) and baseline sleep was recorded from the freely behaving mice. A third experiment included antisauvagine-30 injections (CRH-R2 antagonist) into CRH-R1 KO animals. Orexin had similar wake-promoting effects in CRH-R1KO mice, in CRH-R2 KO animals and in CRH-R1KO mice treated with antisauvagine-30. Consistent results were obtained from all corresponding control littermate experiments. According to our results we conclude that the wake-promoting effects of orexin are not influenced by a possible contribution of CRH.

Evening preference is related to the incidence of depressive states independent of sleep-wake conditions

Although evening preference has recently been identified as a risk factor for depression, it has not been substantiated whether evening preference is a direct risk factor for depressive states, or if it is associated secondarily through other factors, such as delayed sleep timing and shortened sleep duration. The objective of this study is to investigate associations in Japanese adult subjects between evening preference and incidence of depressive states, adjusting for various sleep parameters related to depressive states. The Morningness-Eveningness Questionnaire (MEQ), the Pittsburgh Sleep Quality Index (PSQI), and the Center for Epidemiologic Studies Depression Scale (CES-D) were administered to 1170 individuals (493 males/677 females; mean and range 38.5 and 20-59 yrs) to assess their diurnal preferences, sleeping states, and presence of depression symptoms. Subjects were classified into five chronotypes based on MEQ scores. Evening preference was associated with delayed sleep timing, shortened sleep duration, deteriorated subjective sleep quality, and worsened daytime sleepiness. Logistic regression analysis demonstrated that the extreme evening type (odds ratio [OR] = 1.926, p = .018) was associated with increased incidence of depressive states and that the extreme morning type (OR = 0.342, p = .038) was associated with the decreased incidence of depressive states, independent of sleep parameters, such as nocturnal awakening (OR = 1.844, p < .001), subjective sleep quality (OR = 2.471, p < .001), and daytime sleepiness (OR = 1.895, p = .001). However, no significant associations were observed between the incidence of depressive states and sleep duration, sleep timing, and sleep debt (levels of insufficient sleep). Although the findings of this study do not demonstrate a causative relationship between evening preference and depression, they do suggest the presence of functional associations between mood adjustment and biological clock systems that regulate diurnal preference. They also suggest that evening preference might increase susceptibility to the induction of mood disorders.

Modafinil reduces microsleep during partial sleep deprivation in depressed patients

OBJECTIVE

Sleep deprivation (SD) can induce a prompt decrease in depressive symptoms within 24h. Following the recovery night, however, a relapse into depression occurs in most patients. Recovery sleep, naps and even very short episodes of sleep (microsleep; MS) during SD have been shown to provoke a rapid relapse into depression. This study tested the hypothesis that modafinil reduces MS during SD and stabilizes the treatment response to PSD compared to placebo.

METHODS

A total of 28 patients (13 men, 15 women; age 45.1+/-12.1 years) with a major depressive episode and a cumulative daytime microsleep of five or more minutes were investigated using a double-blind placebo-controlled study design. All patients were treated with a stable mirtazapine monotherapy. A partial SD (PSD) was performed after one week. Additional morning treatment with modafinil vs. placebo started during PSD and was maintained over two weeks. Sleep-EEG and MS episodes were recorded with a portable EEG. Depression severity was assessed using the Hamilton Depression Rating Scale before, during and after PSD and at follow-ups after one and two weeks.

RESULTS

Patients treated with modafinil showed significantly reduced microsleep during PSD (11.63+/-15.99 min) compared to the placebo group (47.77+/-65.31 min). This suppression of MS was not associated with the antidepressive effect of PSD.

CONCLUSIONS

Compared to placebo, modafinil was efficient in reducing daytime microsleep following partial sleep deprivation but did not enhance the antidepressive effects of PSD and did not stabilize antidepressive effects over two weeks.

Pathophysiology of depression: do we have any solid evidence of interest to clinicians?

Due to the clinical and etiological heterogeneity of major depressive disorder, it has been difficult to elucidate its pathophysiology. Current neurobiological theories with the most valid empirical foundation and the highest clinical relevance are reviewed with respect to their strengths and weaknesses. The selected theories are based on studies investigating psychosocial stress and stress hormones, neurotransmitters such as serotonin, norepinephrine, dopamine, glutamate and gamma-aminobutyric acid (GABA), neurocircuitry, neurotrophic factors, and circadian rhythms. Because all theories of depression apply to only some types of depressed patients but not others, and because depressive pathophysiology may vary considerably across the course of illness, the current extant knowledge argues against a unified hypothesis of depression. As a consequence, antidepressant treatments, including psychological and biological approaches, should be tailored for individual patients and disease states. Individual depression hypotheses based on neurobiological knowledge are discussed in terms of their interest to both clinicians in daily practice and clinical researchers developing novel therapies.

CRY2 is associated with rapid cycling in bipolar disorder patients

Background

Bipolar disorder patients often display abnormalities in circadian rhythm, and they are sensitive to irregular diurnal rhythms. CRY2 participates in the core clock that generates circadian rhythms. CRY2 mRNA expression in blood mononuclear cells was recently shown to display a marked diurnal variation and to respond to total sleep deprivation in healthy human volunteers. It was also shown that bipolar patients in a depressive state had lower CRY2 mRNA levels, nonresponsive to total sleep deprivation, compared to healthy controls, and that CRY2 gene variation was associated with winter depression in both Swedish and Finnish cohorts.

Principal Findings

Four CRY2 SNPs spanning from intron 2 to downstream 3′UTR were analyzed for association to bipolar disorder type 1 (n = 497), bipolar disorder type 2 (n = 60) and bipolar disorder with the feature rapid cycling (n = 155) versus blood donors (n = 1044) in Sweden. Also, the rapid cycling cases were compared with bipolar disorder cases without rapid cycling (n = 422). The haplotype GGAC was underrepresented among rapid cycling cases versus controls and versus bipolar disorder cases without rapid cycling (OR = 0.7, P = 0.006−0.02), whereas overrepresentation among rapid cycling cases was seen for AAAC (OR = 1.3−1.4, P = 0.03−0.04) and AGGA (OR = 1.5, P = 0.05). The risk and protective CRY2 haplotypes and their effect sizes were similar to those recently suggested to be associated with winter depression in Swedes.

Conclusions

We propose that the circadian gene CRY2 is associated with rapid cycling in bipolar disorder. This is the first time a clock gene is implicated in rapid cycling, and one of few findings showing a molecular discrimination between rapid cycling and other forms of bipolar disorder.

Positive and negative modulation of circadian activity rhythms by mGluR5 and mGluR2/3 metabotropic glutamate receptors

Glutamate released from retinal ganglion cells conveys information about the daily light:dark cycle to master circadian pacemaker neurons within the suprachiasmatic nucleus that then synchronize internal circadian rhythms with the external day-length. Glutamate activation of ionotropic glutamate receptors in the suprachiasmatic nucleus is well established, but the function of the metabotropic glutamate receptors that are also located in this nucleus is not known. Therefore, in this study we evaluated agonists and antagonists acting at orthosteric or allosteric sites for mGluR5 and mGluR2/3 metabotropic glutamate receptors for their ability to modulate light-induced phase advances and delays of hamster circadian activity rhythms. mGluR5 allosteric antagonists fenobam, MPEP and MTEP, each 10 mg/kg, potentiated light-induced phase advances of hamster circadian activity rhythms, while the mGluR5 agonists CHPG, (S)-3,5-DHPG or positive allosteric modulator CDPPB had no effect. Neither mGluR5 agonists nor antagonists had any effect on light-induced phase delays of activity rhythms. The competitive mGluR2/3 antagonist LY341495, 10 mg/kg, also potentiated light-induced phase advances, but inhibited light-induced phase delays. The mGluR2/3 agonists LY354740 and LY404039 were without effect on phase advances while a third agonist LY379268, 10 mg/kg, inhibited both light-induced advances and delays. Finally, mGluR2/3 agonists LY379268 and LY404039 also inhibited light-induced phase delays of activity rhythms. These results suggest that during light-induced phase advances, mGluR2/3 and mGluR5 receptors act to negatively modulate the effects of light on the circadian pacemaker or its output(s). mGluR5 receptors do not appear to be involved during light-induced phase delays. In contrast, the role for mGluR2/3 receptors during phase delays is more complicated as both agonists and antagonists inhibit light-induced phase delays. Dysfunctions in human circadian rhythms have been implicated in some forms of depression, and metabotropic glutamate receptor ligands, which are also being evaluated for antidepressant activity, are shown here to be capable of modifying light-induced phase shifts of circadian activity rhythms.

Single-nucleotide polymorphisms and mRNA expression for melatonin synthesis rate-limiting enzyme in recurrent depressive disorder

Depressive disorder (DD) is characterised by disturbances in blood melatonin concentration. It is well known that melatonin is involved in the control of circadian rhythms, sleep included. The use of melatonin and its analogues has been found to be effective in depression therapy. Melatonin synthesis is a multistage process, where the last stage is catalysed by acetylserotonin methyltransferase (ASMT), the reported rate-limiting melatonin synthesis enzyme. Taking into account the significance of genetic factors in depression development, the gene for ASMT may become an interesting focus for studies in patients with recurrent DD. The goal of the study was to evaluate two single-nucleotide polymorphisms (SNPs) (rs4446909; rs5989681) of the ASMT gene, as well as mRNA expression for ASMT in recurrent DD-affected patients. We genotyped two polymorphisms in a group of 181 recurrent DD patients and in 149 control subjects. The study was performed using the polymerase chain reaction/restriction fragment length polymorphism method. The distribution of genotypes in both studied SNPs in the ASMT gene differed significantly between DD and healthy subjects. The presence of AA genotype of rs4446909 polymorphism and of GG genotype of rs5989681 polymorphism was associated with lower risk for having recurrent DD. In turn, patients with depression were characterised by reduced mRNA expression for ASMT. In addition, ASMT transcript level in both recurrent DD patients and in healthy subjects depended significantly on genotype distributions in both polymorphisms. In conclusion, our results suggest the ASMT gene as a susceptibility gene for recurrent DD.

Phase relationships between core body temperature, melatonin, and sleep are associated with depression severity: further evidence for circadian misalignment in non-seasonal depression

Misalignment between the timing of sleep and the circadian pacemaker has been linked to depression symptoms. This study sought to extend earlier findings by comparing sleep and circadian markers in healthy controls and individuals with major depression. Two markers of circadian misalignment correlated with depression severity in the depressed group.

Circadian clock genes: non-circadian roles in sleep, addiction, and psychiatric disorders?

Elucidation of the cellular and molecular mechanisms of the circadian clock, along with the realization that these mechanisms are operative in both central and peripheral tissues, has revolutionized circadian biology. Further, these observations have resulted in an explosion of interest in the health implications of circadian organization and disorganization at both molecular and physiological levels. Thus, recent research has implicated mutations and polymorphisms of circadian clock genes in diabetes and obesity, cardiovascular disease, and cancer. At the neuro-behavioral level, circadian clock genes have also been implicated in sleep disorders, drug and alcohol addiction, and other psychiatric conditions. While such findings are frequently described as revealing "non-circadian" effects of clock genes, it remains possible that most of these non-circadian effects are in fact secondary to the loss of cellular and systemic rhythmicity. This review summarizes the evidence linking circadian clock genes to biobehavioral dysregulation, and considers criteria for defining a pleiotropic clock gene effect as non-circadian.

PER2 variantion is associated with depression vulnerability

The circadian clock is driven by transcription-translation feedback loops and regulates rhythms that approximate the 24-hr day-night cycle or light-dark transitions. Disruptions of the circadian rhythms are common in depressed patients, expressed for example as sleep disturbances. Genetic variations in core circadian genes may in part explain these abnormalities. To investigate whether genetic variation in core circadian genes associates with vulnerability to depression, we genotyped 18 genes in a Swedish population based sample. Genetic variations indicative of association with depression, or with winter depression in our previous study, were tested for association to depression in a second Swedish depression-control sample set. PER2 genetic variation was associated with depression vulnerability, and this genetic risk did not seem to require exposure to potential sleep disturbance factors such as negative life event or financial strain that are known to increase the risk for depression. Polymorphisms in the circadian genes NPAS2, ARNTL, and RORA were also suggested to contribute to depression vulnerability. The findings we report for PER2, ARNTL, and RORA are supported by at least two of the three sample sets. In conclusion, genetic variation in PER2 is associated with depression vulnerability a Swedish population-based sample. More studies are needed to determine if this is the case also for NPAS2, ARNTL, and RORA.

CRY2 is associated with depression

Background

Abnormalities in the circadian clockwork often characterize patients with major depressive and bipolar disorders. Circadian clock genes are targets of interest in these patients. CRY2 is a circadian gene that participates in regulation of the evening oscillator. This is of interest in mood disorders where a lack of switch from evening to morning oscillators has been postulated.

Principal Findings

We observed a marked diurnal variation in human CRY2 mRNA levels from peripheral blood mononuclear cells and a significant up-regulation (P = 0.020) following one-night total sleep deprivation, a known antidepressant. In depressed bipolar patients, levels of CRY2 mRNA were decreased (P = 0.029) and a complete lack of increase was observed following sleep deprivation. To investigate a possible genetic contribution, we undertook SNP genotyping of the CRY2 gene in two independent population-based samples from Sweden (118 cases and 1011 controls) and Finland (86 cases and 1096 controls). The CRY2 gene was significantly associated with winter depression in both samples (haplotype analysis in Swedish and Finnish samples: OR = 1.8, P = 0.0059 and OR = 1.8, P = 0.00044, respectively).

Conclusions

We propose that a CRY2 locus is associated with vulnerability for depression, and that mechanisms of action involve dysregulation of CRY2 expression.

CLOCK is suggested to associate with comorbid alcohol use and depressive disorders

Background

Depression and alcohol abuse or dependence (AUD) co-occur in the general population more frequently than expected by chance. Alcohol use influences the circadian rhythms generated by the central pacemaker in the suprachiasmatic nucleus, and circadian rhythm alterations in turn are common in depressive disorders as well as among persons addicted to alcohol.

Methods

32 SNPs in 19 circadian clockwork related genes were analyzed using DNA from 76 individuals with comorbid depression and AUD, 446 individuals with AUD and 517 healthy controls with no psychiatric diagnosis. The individuals participated in a nationwide health examination study, representative of the general population aged 30 and over in Finland.

Results

The CLOCK haplotype TTGC formed by SNPs rs3805151, rs2412648, rs11240 and rs2412646, was associated with increased risk for comorbidity (OR = 1.65, 95% CI = 1.14-2.28, P = 0.0077). The SNPs of importance for this suggestive association were rs2412646 and rs11240 indicating location of the functional variation in the block downstream rs2412648. There was no indication for association between CLOCK and AUD.

Conclusion

Our findings suggest an association between the CLOCK gene and the comorbid condition of alcohol use and depressive disorders. Together with previous reports it indicates that the CLOCK variations we found here may be a vulnerability factor to depression given the exposure to alcohol in individuals having AUD.

Sleep, Hormones, and Circadian Rhythms throughout the Menstrual Cycle in Healthy Women and Women with Premenstrual Dysphoric Disorder

A relationship exists between the sleep-wake cycle and hormone secretion, which, in women, is further modulated by the menstrual cycle. This interaction can influence sleep across the menstrual cycle in healthy women and in women with premenstrual dysphoric disorder (PMDD), who experience specific alterations of circadian rhythms during their symptomatic luteal phase along with sleep disturbances during this time. This review will address the variation of sleep at different menstrual phases in healthy and PMDD women, as well as changes in circadian rhythms, with an emphasis on their relationship with female sex hormones. It will conclude with a brief discussion on nonpharmacological treatments of PMDD which use chronotherapeutic methods to realign circadian rhythms as a means of improving sleep and mood in these women.

Differential influence of selective 5-HT5A vs 5-HT1A, 5-HT1B, or 5-HT2C receptor blockade upon light-induced phase shifts in circadian activity rhythms: interaction studies with citalopram

Though serotonergic mechanisms modulate circadian rhythms, roles of individual serotonin (5-HT) receptors remain uncertain since data are lacking for antagonists. Herein, both the 5-HT(5A) receptor antagonist, A843277 (10 mg/kg), and the 5-HT(1B) antagonist, SB224289 (1 mg/kg), inhibited light-induced phase advances in hamster circadian wheel-running rhythms. Conversely, though 5-HT(1A) and 5-HT(7) receptors are likewise implicated in circadian scheduling, their blockade by WAY100635 (0.5 mg/kg) and SB269970 (1 mg/kg), respectively, was ineffective. Since actions of 5-HT reuptake inhibitors are modified by antagonists, we evaluated their influence on suppression of phase advances by citalopram (10 mg/kg). Its action was potentiated by WAY100635 and the 5-HT(2C) antagonist, SB242084 (1 mg/kg), but not by A842377, SB224289, SB269970, and antagonists at 5-HT(2A) (MDL100907) and 5-HT(6) (SB399885) receptors. In conclusion, this is the first in vivo evidence for an influence of 5-HT(5A) receptors upon circadian rhythms, but no single class of 5-HT receptor mediates their control by citalopram.

Depressive symptomatology is influenced by chronotypes

BACKGROUND

Rhythm disturbances are a frequent clinical manifestation of depression. In recent years a possible relationship between depression and chronotypes has emerged. Specifically eveningness has been proposed as vulnerability factor. The aim of this study was to describe sleep features of depressed patients according to chronotypes and to explore possible associations with the clinical features of depressive episodes.

METHODS

100 patients diagnosed with Major Depressive Disorder according to the Mini International Neuropsychiatric Interview (MINI) were included (age: 34+/-11.74, range: 18-60 years; female/male:79/21). At admission the Hamilton Rating Scale for Depression (HRSD) was administered. Patients were also administered the Morningness-Eveningness Questionnaire (MEQ), the Epworth Sleepiness Scale, the Athens Insomnia Scale and the Pittsburgh Sleep Quality Index.

RESULTS

According to MEQ scores patients were classified in three groups: a) eveningness (n=18), b) neither (n=61) and c) morningness type (n=21). The age was different among chronotypes, being morningness-type patients older. The eveningness-type group showed higher scores in suicidal thoughts, more impaired work and activities, higher paranoid symptoms, higher scores on the anxiety cluster (HRSD), while the morningness-type group showed lower proportion of melancholic symptoms (MINI). We did not find association between sleep parameters and specific chronotypes.

LIMITATIONS

The relatively small sample size and the concurrent assessment of chronotypes and depression may have biased our findings.

CONCLUSIONS

Our data suggest the idea that chronotypes have an impact on depressive episodes features, with higher severity for the eveningness-type.

Risk markers for depression in adolescents: sleep and HPA measures

Previous work has demonstrated reliable electroencephalographic (EEG) sleep and hypothalamic-pituitary-adrenal (HPA) changes associated with adult major depressive disorder. These changes might be evident before clinical manifestation of the illness in at-risk persons. The aim of the study was to identify depression-related EEG sleep and HPA changes in healthy adolescents at high risk for depression, and to examine the relationship between EEG sleep (or HPA) changes and the onset of depression. Forty-eight adolescent volunteers with no personal history of a psychiatric illness, including depression, but who were at high risk for developing depression by virtue of parental depression (high-risk group), and 48 adolescent volunteers with no personal or family history of a psychiatric disorder (normal controls) were recruited. EEG sleep and HPA measures were collected on three consecutive evenings and nights at baseline. Clinical follow-up evaluations were conducted at regular intervals over a 5-year period. Compared with normal controls, adolescents at high risk for depression had shorter latency to rapid eye movement (REM) sleep, increased phasic REM sleep, more REM sleep and elevated nocturnal urinary-free cortisol (NUFC) excretion at baseline. Shorter REM latency, higher REM density and elevated NUFC (measured at baseline) were associated with the development of depression during follow-up. The findings that REM sleep abnormalities and elevated HPA activity occur before the onset of depression in at-risk adolescents suggest that these variables serve as vulnerability markers for the illness.

Circadian rhythms of basal orexin levels in the hypothalamus are not influenced by an impaired corticotropin-releasing hormone receptor type 1 system

Wake-promoting effects of orexins and corticotropin-releasing hormone (CRH) are well documented. Neuronal interactions between these two systems and anatomical data point to a reciprocal influence of these neuropeptides. We examined in how far an impaired CRH system may influence the circadian rhythm of extracellular orexin levels in mice. The basal levels of orexin were collected unilaterally from the lateral hypothalamus over 24 h in conditional CNS-specific CRH receptor type 1 (CRH-R1) knockout animals and control littermates. No significant differences were obtained between both groups suggesting that under basal conditions the circadian variation of hypothalamic orexin is not mediated by CRH, at least not via CRH-R1.

Ethnic differences in electroencephalographic sleep patterns in adolescents

The purpose of the study was to evaluate ethnic differences in polysomnography measures in adolescents. Ninety-six volunteers from four ethnic groups (13 African-American, 18 Asian-American, 19 Mexican-American, and 46 Non-Hispanic White) were recruited. The subjects were in good physical and psychological health, and were asymptomatic with respect to sleep/wake complaints or sleep disorders. Polysomnography measures were collected on three consecutive nights. African-Americans manifested lower sleep efficiency, spent proportionately more time in stage 2 sleep, and had less stage 4 sleep compared to the other ethnic groups. In contrast to this, Mexican-Americans had more rapid eye movement (REM) sleep than their counterparts. The observed sleep patterns in the different ethnic groups persisted after controlling for specific demographic, clinical and psychosocial variables that are known to influence sleep measures. Gender had a differential effect on sleep patterns in the various ethnic groups. For instance, differences in non-REM sleep were more evident in African-American males, whereas increased REM sleep was most notable in Mexican-American females. At present, the clinical implications of the observed cross-ethnic differences in sleep physiology among adolescents are not clear. In previous studies, reduced sleep efficiency and stage 4 sleep, as well as increased REM sleep, were associated with psychopathology. It is not known whether the traditionally described sleep profiles, based largely on Non-Hispanic White populations, will generalize to other racial or ethnic groups. In addition to a systematic investigation of this issue, future research should attempt to identify the underlying causes for cross-ethnic variations in sleep physiology.

Rhythmicity in mice selected for extremes in stress reactivity: behavioural, endocrine and sleep changes resembling endophenotypes of major depression

BACKGROUND

Dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis, including hyper- or hypo-activity of the stress hormone system, plays a critical role in the pathophysiology of mood disorders such as major depression (MD). Further biological hallmarks of MD are disturbances in circadian rhythms and sleep architecture. Applying a translational approach, an animal model has recently been developed, focusing on the deviation in sensitivity to stressful encounters. This so-called 'stress reactivity' (SR) mouse model consists of three separate breeding lines selected for either high (HR), intermediate (IR), or low (LR) corticosterone increase in response to stressors.

METHODOLOGY/PRINCIPLE FINDINGS

In order to contribute to the validation of the SR mouse model, our study combined the analysis of behavioural and HPA axis rhythmicity with sleep-EEG recordings in the HR/IR/LR mouse lines. We found that hyper-responsiveness to stressors was associated with psychomotor alterations (increased locomotor activity and exploration towards the end of the resting period), resembling symptoms like restlessness, sleep continuity disturbances and early awakenings that are commonly observed in melancholic depression. Additionally, HR mice also showed neuroendocrine abnormalities similar to symptoms of MD patients such as reduced amplitude of the circadian glucocorticoid rhythm and elevated trough levels. The sleep-EEG analyses, furthermore, revealed changes in rapid eye movement (REM) and non-REM sleep as well as slow wave activity, indicative of reduced sleep efficacy and REM sleep disinhibition in HR mice.

CONCLUSION/SIGNIFICANCE

Thus, we could show that by selectively breeding mice for extremes in stress reactivity, clinically relevant endophenotypes of MD can be modelled. Given the importance of rhythmicity and sleep disturbances as biomarkers of MD, both animal and clinical studies on the interaction of behavioural, neuroendocrine and sleep parameters may reveal molecular pathways that ultimately lead to the discovery of new targets for antidepressant drugs tailored to match specific pathologies within MD.