The long-term abnormalities in circadian expression of Period 1 and Period 2 genes in response to stress is normalized by agomelatine administered immediately after exposure

Agomelatine: A Potential Multitarget Compound for Neurodevelopmental Disorders

Agomelatine (AGM) is one of the latest atypical antidepressants, prescribed exclusively for the treatment of depression in adults. AGM belongs to the pharmaceutical class of melatonin agonist and selective serotonin antagonist ("MASS"), as it acts both as a selective agonist of melatonin receptors MT1 and MT2, and as a selective antagonist of 5-HT2C/5-HT2B receptors. AGM is involved in the resynchronization of interrupted circadian rhythms, with beneficial effects on sleep patterns, while antagonism on serotonin receptors increases the availability of norepinephrine and dopamine in the prefrontal cortex, with an antidepressant and nootropic effect. The use of AGM in the pediatric population is limited by the scarcity of data. In addition, few studies and case reports have been published on the use of AGM in patients with attention deficit and hyperactivity disorder (ADHD) and autism spectrum disorder (ASD). Considering this evidence, the purpose of this review is to report the potential role of AGM in neurological developmental disorders. AGM would increase the expression of the cytoskeleton-associated protein (ARC) in the prefrontal cortex, with optimization of learning, long-term memory consolidation, and improved survival of neurons. Another important feature of AGM is the ability to modulate glutamatergic neurotransmission in regions associated with mood and cognition. With its synergistic activity a melatoninergic agonist and an antagonist of 5-HT2C, AGM acts as an antidepressant, psychostimulant, and promoter of neuronal plasticity, regulating cognitive symptoms, resynchronizing circadian rhythms in patients with autism, ADHD, anxiety, and depression. Given its good tolerability and good compliance, it could potentially be administered to adolescents and children.

Agomelatine for the treatment of generalized anxiety disorder: focus on its distinctive mechanism of action

Generalized anxiety disorder (GAD), the most frequently diagnosed form of anxiety, is usually treated by cognitive-behavioural approaches or medication; in particular, benzodiazepines (acutely) and serotonin or serotonin/noradrenaline reuptake inhibitors (long term). Efficacy, compliance, and acceptability are, however, far from ideal, reinforcing interest in alternative options. Agomelatine, clinically employed in the treatment of major depression, expresses anxiolytic properties in rodents and was effective in the treatment of GAD (including severely ill patients) in several double-blind, short-term (12 weeks) and relapse-prevention (6 months) studies. At active doses, the incidence of adverse effects was no higher than for placebo. Agomelatine possesses a unique binding profile, behaving as a melatonin (MT₁/MT₂) receptor agonist and 5-HT_2C receptor antagonist, yet recognizing neither monoamine transporters nor GABA_A receptors. Extensive evidence supports a role for 5-HT_2C receptors in the induction of anxious states, and their blockade likely plays a primary role in mediating the anxiolytic actions of agomelatine, including populations in the amygdala and bed nucleus of stria terminalis, as well as the hippocampus. Recruitment of MT receptors in the suprachiasmatic nucleus, thalamic reticular nucleus, and hippocampus appears to fulfil a complimentary role. Downstream of 5-HT_2C and MT receptors, modulation of stress-sensitive glutamatergic circuits and altered release of the anxiogenic neuropeptides, corticotrophin-releasing factor, and vasopressin, may be implicated in the actions of agomelatine. To summarize, agomelatine exerts its anxiolytic actions by mechanisms clearly distinct from those of other agents currently employed for the management of GAD.

PLAIN LANGUAGE SUMMARY

How agomelatine helps in the treatment of anxiety disorders.

INTRODUCTION

• Anxiety disorders have a significant negative impact on quality of life.• The most common type of anxiety disorder, called generalized anxiety disorder (GAD), is associated with nervousness and excessive worry.• These symptoms can lead to additional symptoms like tiredness, sleeplessness, irritability, and poor attention.• GAD is generally treated through either cognitive-behavioural therapy or medication. However, widely used drugs like benzodiazepines and serotonin reuptake inhibitors have adverse effects.• Agomelatine, a well-established antidepressant drug, has shown anxiety-lowering ('anxiolytic') properties in rats and has been shown to effectively treat GAD with minimal side effects.• However, exactly how it acts on the brain to manage GAD is not yet clear.• Thus, this review aims to shed light on agomelatine's mechanism of action in treating GAD.

METHODS

• The authors reviewed studies on how agomelatine treats anxiety in animals.• They also looked at clinical studies on the effects of agomelatine in people with GAD.

RESULTS

• The study showed that agomelatine 'blocks' a receptor in nerve cells, which plays a role in causing anxiety, called the 5-HT_2C receptor.• Blocking this receptor, especially in specific brain regions such as nerve cells of the amygdala, bed nucleus of stria terminalis, and hippocampus, produced the anxiety reduction seen during agomelatine treatment.• Agomelatine also activates the melatonin (MT) receptor, which is known to keep anxiety in check, promote sleep, and maintain the sleep cycle.• Agomelatine should thus tackle sleep disturbances commonly seen in patients with GAD.• Beyond 5-HT_2C and MT receptors, signalling molecules in nerve cells that are known to be involved in anxiety disorders (called 'neurotransmitters' and 'neuropeptides') are also affected by agomelatine.

CONCLUSION

• Agomelatine's anxiolytic effects are caused by mechanisms that are distinct from those of other medications currently used to treat GAD.• This explains its therapeutic success and minimal adverse side effects.

Agomelatine: An astounding sui-generis antidepressant?

Major depressive disorder (MDD) is one of the foremost causes of disability and premature death worldwide. Although the available antidepressants are effective and well tolerated, they also have many limitations. Therapeutic advances in developing a new drug's ultimate relation between MDD and chronobiology, which targets the circadian rhythm, have led to a renewed focus on psychiatric disorders. In order to provide a critical analysis about antidepressant properties of agomelatine, a detailed PubMed (Medline), Scopus (Embase), Web of Science (Web of Knowledge), Cochrane Library, Google Scholar, and PsycInfo search was performed using the following keywords: melatonin analog, agomelatine, safety, efficacy, adverse effects, pharmacokinetics, pharmacodynamics, circadian rhythm, sleep disorders, neuroplasticity, MDD, bipolar disorder, anhedonia, anxiety, generalized anxiety disorder (GAD), and mood disorders. Agomelatine is a unique melatonin analog with antidepressant properties and a large therapeutic index that improves clinical safety. It is a melatonin receptor agonist (MT1 and MT2) and a 5-HT2C receptor antagonist. The effects on melatonin receptors enable the resynchronization of irregular circadian rhythms with beneficial effects on sleep architectures. In this way, agomelatine is accredited for its unique mode of action, which helps to exert antidepressant effects and resynchronize the sleep-wake cycle. To sum up, an agomelatine has not only antidepressant properties but also has anxiolytic effects.

The impact of stress and stress hormones on endogenous clocks and circadian rhythms

In mammals, daily rhythms in physiology and behavior are under control of a circadian pacemaker situated in the suprachiasmatic nucleus (SCN). This master clock receives photic input from the retina and coordinates peripheral oscillators present in other tissues, maintaining all rhythms in the body synchronized to the environmental light-dark cycle. In line with its function as a master clock, the SCN appears to be well protected against unpredictable stressful stimuli. However, available data indicate that stress and stress hormones at certain times of day are capable of shifting peripheral oscillators in, e.g., liver, kidney and heart, which are normally under control of the SCN. Such shifts of peripheral oscillators may represent a temporary change in circadian organization that facilitates adaptation to repeated stress. Alternatively, these shifts of internal rhythms may represent an imbalance between precisely orchestrated physiological and behavioral processes that may have severe consequences for health and well-being.

Traumatic stress and the circadian system: neurobiology, timing and treatment of posttraumatic chronodisruption

Background: Humans have an evolutionary need for a well-preserved internal 'clock', adjusted to the 24-hour rotation period of our planet. This intrinsic circadian timing system enables the temporal organization of numerous physiologic processes, from gene expression to behaviour. The human circadian system is tightly and bidirectionally interconnected to the human stress system, as both systems regulate each other's activity along the anticipated diurnal challenges. The understanding of the temporal relationship between stressors and stress responses is critical in the molecular pathophysiology of stress-and trauma-related diseases, such as posttraumatic stress disorder (PTSD). Objectives/Methods: In this narrative review, we present the functional components of the stress and circadian system and their multilevel interactions and discuss how traumatic stress can affect the harmonious interplay between the two systems. Results: Circadian dysregulation after trauma exposure (posttraumatic chronodisruption) may represent a core feature of trauma-related disorders mediating enduring neurobiological correlates of traumatic stress through a loss of the temporal order at different organizational levels. Posttraumatic chronodisruption may, thus, affect fundamental properties of neuroendocrine, immune and autonomic systems, leading to a breakdown of biobehavioral adaptive mechanisms with increased stress sensitivity and vulnerability. Given that many traumatic events occur in the late evening or night hours, we also describe how the time of day of trauma exposure can differentially affect the stress system and, finally, discuss potential chronotherapeutic interventions. Conclusion: Understanding the stress-related mechanisms susceptible to chronodisruption and their role in PTSD could deliver new insights into stress pathophysiology, provide better psychochronobiological treatment alternatives and enhance preventive strategies in stress-exposed populations.

The preclinical discovery and development of agomelatine for the treatment of depression

INTRODUCTION

Under the treatment of commonly used antidepressants, many patients with major depressive disorder (MDD) do not achieve remission. All previous first-line treatments for depression have focused on the enhancement of monoaminergic activity. Agomelatine was the first antidepressant with a mechanism of action extending beyond monoaminergic neurotransmission.

AREAS COVERED

The aim of this case history is to describe the discovery strategy and development of agomelatine. The pharmacodynamic profile of the drug is briefly presented. The article summarizes (a) the preclinical behavioral data on agomelatine's effects on depressive-like behavior, anxiety, and circadian rhythmicity disruptions, and (b) the results of early preclinical studies on safety, efficacy in MDD, and the risk-benefit pharmacological profile. Furthermore, the article examines findings of post-marketing research on safety, efficacy, and cost-effectiveness of the drug.

EXPERT OPINION

There is now evidence supporting the clinical efficacy and safety profile of agomelatine in the acute-phase treatment of MDD. Agomelatine may be more effective in specific subgroups of MDD patients, those with severe anxiety symptoms or disturbed circadian profiles. Its antidepressant and anxiolytic activities are due to synergy between its melatonergic and 5-hydroxytryptaminergic effects. Since its discovery, novel compounds acting on the melatonergic system have been under investigation for the treatment of MDD.

Vulnerability to helpless behavior is regulated by the circadian clock component CRYPTOCHROME in the mouse nucleus accumbens

The nucleus accumbens (NAc), a central component of the midbrain dopamine reward circuit, exhibits disturbed circadian rhythms in the postmortem brains of depressed patients. We hypothesized that normal mood regulation requires proper circadian timing in the NAc, and that mood disorders are associated with dysfunctions of the NAc cellular circadian clock. In mice exhibiting stress-induced depression-like behavior (helplessness), we found altered circadian clock function and high nighttime expression of the core circadian clock component CRYPTOCHROME (CRY) in the NAc. In the NAc of helpless mice, we found that higher expression of CRY is associated with decreased activation of dopamine 1 receptor-expressing medium spiny neurons (D1R-MSNs). Furthermore, D1R-MSN-specific CRY-knockdown in the NAc reduced susceptibility to stress-induced helplessness and increased NAc neuronal activation at night. Finally, we show that CRY inhibits D1R-induced G protein activation, likely by interacting with the Gs protein. Altered circadian rhythms and CRY expression were also observed in human fibroblasts from major depressive disorder patients. Our data reveal a causal role for CRY in regulating the midbrain dopamine reward system, and provide a mechanistic link between the NAc circadian clock and vulnerability to depression.

Effects of agomelatine on behaviour, circadian expression of period 1 and period 2 clock genes and neuroplastic markers in the predator scent stress rat model of PTSD

Objectives: The therapeutic value of the antidepressant agomelatine in the aftermath of traumatic experience and early post-reminder has been questioned. Herein, agomelatine, its vehicle or melatonin agonist were administered either acutely 1 h post-stressor or repeatedly (7 days) after early post-reminder in a post-traumatic stress rat model (PSS) using the scent of predator urine.Methods: Behavioural responses, and brain molecular and morphological changes were evaluated after each treatment procedure in PSS-exposed and unexposed rats.Results: When administered immediately after PSS, agomelatine induced a significant reduction of anxiety-like behaviour as assessed in the elevated-plus-maze and acoustic startle response at 8 days post-administration. Concomitantly, agomelatine significantly decreased Per1/Per2 expression in the CA1/CA3 areas, suprachiasmatic nucleus and basolateral amygdala, thereby partially restoring genes expression overregulated by PSS. Agomelatine further significantly increased cell growth and facilitated dendritic growth and arbour in dentate gyrus (DG) granule and apical CA1 cells and upregulated brain-derived neurotrophic factor protein in the DG and cortex III versus vehicle. When administered early post-reminder over 7 days before testing, agomelatine was ineffective on behavioural responses pattern, molecular and morphological changes induced by PSS.Conclusions: These findings suggest that agomelatine may be a potential agent in the acute aftermath of traumatic stress exposure.

Social isolation rearing-induced anxiety and response to agomelatine in male and female rats: Role of corticosterone, oxytocin, and vasopressin

BACKGROUND

The chronobiotic antidepressant, agomelatine, acts via re-entrainment of circadian rhythms. Earlier work has demonstrated late-life anxiety and reduced corticosterone in post-weaning social isolation reared (SIR) rats. Agomelatine was anxiolytic in this model but did not reverse hypocortisolemia. Reduced corticosterone or cortisol (in humans) is well-described in anxiety states, although the anxiolytic-like actions of agomelatine may involve targeting another mechanism. Central oxytocin and vasopressin exert anxiolytic and anxiogenic effects, respectively, and are subject to circadian fluctuation, while also showing sex-dependent differences in response to various challenges.

AIMS AND METHODS

If corticosterone is less involved in the anxiolytic-like actions of agomelatine in SIR rats, we wondered whether effects on vasopressin and oxytocin may mediate these actions, and whether sex-dependent effects are evident. Anxiety as assessed in the elevated plus maze, as well as plasma vasopressin, oxytocin, and corticosterone were analyzed in social vs SIR animals receiving sub-chronic treatment with vehicle or agomelatine (40 mg/kg/day intraperitoneally at 16:00) for 16 days.

RESULTS

Social isolation rearing induced significant anxiety together with increased plasma vasopressin levels, but decreased corticosterone and oxytocin. While corticosterone displayed sex-dependent changes, vasopressin, and oxytocin changes were independent of sex. Agomelatine suppressed anxiety as well as reversed elevated vasopressin in both male and female rats and partially reversed reduced oxytocin in female but not male rats.

CONCLUSION

SIR-associated anxiety later in life involves reduced corticosterone and oxytocin, and elevated vasopressin. The anxiolytic-like effects of agomelatine in SIR rats predominantly involve targeting of elevated vasopressin.

Developmental Trajectories of Early Life Stress and Trauma: A Narrative Review on Neurobiological Aspects Beyond Stress System Dysregulation

Early life stressors display a high universal prevalence and constitute a major public health problem. Prolonged psychoneurobiological alterations as sequelae of early life stress (ELS) could represent a developmental risk factor and mediate risk for disease, leading to higher physical and mental morbidity rates in later life. ELS could exert a programming effect on sensitive neuronal brain networks related to the stress response during critical periods of development and thus lead to enduring hyper- or hypo-activation of the stress system and altered glucocorticoid signaling. In addition, alterations in emotional and autonomic reactivity, circadian rhythm disruption, functional and structural changes in the brain, as well as immune and metabolic dysregulation have been lately identified as important risk factors for a chronically impaired homeostatic balance after ELS. Furthermore, human genetic background and epigenetic modifications through stress-related gene expression could interact with these alterations and explain inter-individual variation in vulnerability or resilience to stress. This narrative review presents relevant evidence from mainly human research on the ten most acknowledged neurobiological allostatic pathways exerting enduring adverse effects of ELS even decades later (hypothalamic-pituitary-adrenal axis, autonomic nervous system, immune system and inflammation, oxidative stress, cardiovascular system, gut microbiome, sleep and circadian system, genetics, epigenetics, structural, and functional brain correlates). Although most findings back a causal relation between ELS and psychobiological maladjustment in later life, the precise developmental trajectories and their temporal coincidence has not been elucidated as yet. Future studies should prospectively investigate putative mediators and their temporal sequence, while considering the potentially delayed time-frame for their phenotypical expression. Better screening strategies for ELS are needed for a better individual prevention and treatment.

Multilevel Interactions of Stress and Circadian System: Implications for Traumatic Stress

The dramatic fluctuations in energy demands by the rhythmic succession of night and day on our planet has prompted a geophysical evolutionary need for biological temporal organization across phylogeny. The intrinsic circadian timing system (CS) represents a highly conserved and sophisticated internal "clock," adjusted to the 24-h rotation period of the earth, enabling a nyctohemeral coordination of numerous physiologic processes, from gene expression to behavior. The human CS is tightly and bidirectionally interconnected to the stress system (SS). Both systems are fundamental for survival and regulate each other's activity in order to prepare the organism for the anticipated cyclic challenges. Thereby, the understanding of the temporal relationship between stressors and stress responses is critical for the comprehension of the molecular basis of physiology and pathogenesis of disease. A critical loss of the harmonious timed order at different organizational levels may affect the fundamental properties of neuroendocrine, immune, and autonomic systems, leading to a breakdown of biobehavioral adaptative mechanisms with increased stress sensitivity and vulnerability. In this review, following an overview of the functional components of the SS and CS, we present their multilevel interactions and discuss how traumatic stress can alter the interplay between the two systems. Circadian dysregulation after traumatic stress exposure may represent a core feature of trauma-related disorders mediating enduring neurobiological correlates of trauma through maladaptive stress regulation. Understanding the mechanisms susceptible to circadian dysregulation and their role in stress-related disorders could provide new insights into disease mechanisms, advancing psychochronobiological treatment possibilities and preventive strategies in stress-exposed populations.

Stress affects expression of the clock gene Bmal1 in the suprachiasmatic nucleus of neonatal rats via glucocorticoid-dependent mechanism

AIM

The reactivity of the circadian clock in the suprachiasmatic nuclei (SCN) to stressful stimuli has been controversial but most studies have confirmed the resilience of the SCN to stress. We tested the hypothesis that during a critical period shortly after birth, the developing SCN clock is affected by glucocorticoids.

METHODS

Mothers of 2 rat strains with different sensitivities to stress, that is Wistar rats and spontaneously hypertensive rats (SHR), and their pups were exposed to stressful stimuli every day from delivery, and clock gene expression profiles were detected in the 4-day-old pups' SCN. Levels of glucocorticoids in plasma were measured by LC-MS/MS. The glucocorticoid receptors antagonist mifepristone was administered to pups to block the effect of the glucocorticoids.

RESULTS

The glucocorticoid receptors were detected at the mRNA and protein levels in the SCN of 4-day-old pups. The exposure of mothers to stressful stimuli elevated their plasma glucocorticoid levels. In Wistar rat pups, combination of daily maternal stress with their manipulation increased the plasma glucocorticoid levels and shifted the Bmal1 rhythm in the SCN which was completely blocked by mifepristone. In contrast, in SHR pups, maternal stress on its own caused phase shift of the Bmal1 expression rhythm in the SCN but the effect was mediated via glucocorticoid-independent mechanism. The Per1 and Per2 expression profiles remained phase-locked to the light/dark cycle.

CONCLUSION

The results demonstrate that the SCN is sensitive to stressful stimuli early after birth in pups maintained under light/dark conditions and the effect is mediated via glucocorticoid-dependent pathways.

The Circadian Oscillator of the Cerebral Cortex: Molecular, Biochemical and Behavioral Effects of Deleting the Arntl Clock Gene in Cortical Neurons

A molecular circadian oscillator resides in neurons of the cerebral cortex, but its role is unknown. Using the Cre-LoxP method, we have here abolished the core clock gene Arntl in those neurons. This mouse represents the first model carrying a deletion of a circadian clock component specifically in an extrahypothalamic cell type of the brain. Molecular analyses of clock gene expression in the cerebral cortex of the Arntl conditional knockout mouse revealed disrupted circadian expression profiles, whereas clock gene expression in the suprachiasmatic nucleus was still rhythmic, thus showing that Arntl is required for normal function of the cortical circadian oscillator. Daily rhythms in running activity and temperature were not influenced, whereas the resynchronization response to experimental jet-lag exhibited minor though significant differences between genotypes. The tail-suspension test revealed significantly prolonged immobility periods in the knockout mouse indicative of a depressive-like behavioral state. This phenotype was accompanied by reduced norepinephrine levels in the cerebral cortex. Our data show that Arntl is required for normal cortical clock function and further give reason to suspect that the circadian oscillator of the cerebral cortex is involved in regulating both circadian biology and mood-related behavior and biochemistry.

Studies into the anxiolytic actions of agomelatine in social isolation reared rats: Role of corticosterone and sex

Anxiety disorders are severely disabling, while current pharmacological treatments are complicated by delayed onset, low remission rates and side-effects. Sex is also noted to contribute towards illness severity and treatment response. Agomelatine is a melatonin (MT₁/MT₂) agonist and serotonin (5-HT_2C) antagonist purported to be anxiolytic in clinical and some pre-clinical studies. We undertook a detailed analysis of agomelatine's anxiolytic activity in a neurodevelopmental model of anxiety, the social isolation reared rat. Rats received sub-chronic treatment with vehicle or agomelatine (40 mg/kg per day intraperitoneally at 16:00 h for 16 days), with behaviour analysed in the open field test, social interaction test and elevated plus maze. The contribution of corticosterone and sex was also studied. Social isolation rearing increased locomotor activity and reduced social interaction in the social interaction test, and was anxiogenic in the elevated plus maze in males and females. Agomelatine reversed these behaviours. Male and female social isolation reared rats developed anxiety-like behaviours to a similar degree, although response to agomelatine was superior in male rats. Social isolation rearing decreased plasma corticosterone in both sexes and tended to higher levels in females, although agomelatine did not affect corticosterone in either sex. Concluding, agomelatine is anxiolytic in SIR rats, although correcting altered corticosterone could not be implicated. Sex-related differences in the response to agomelatine are evident.

[A profile of antidepressive effects of agomelatine and a current view on the mechanism of its action]

Agomelatine is one of the latest antidepressants (melatoninergic agonists) with a new mechanism of action. From the positions of classical monoaminoergic theory, tts mechanism of action is difficult to understand, because the drug increases the levels of monoamines and neurotrophic factors, while not affecting their reuptake and negative feedback, which control neurotransmission level. Besides the effect on suprachiasmatic nucleus, a relevant role in the mechanism of action of agomelatine plays its special functionally selective (with regard to intracellular signaling pathways) interaction with heteromeric complexes of serotonin 5-НТ2С and melatonin MT2 receptors in the hippocampus and cerebral cortex. Agomelatine is competitive to other modern antidepressants in the efficacy assessed by the percentage of complete responders and superior in the total frequency of remissions. Compared to other SSRI antidepressants, agomelatine is more effective for anhedonia. In these cases, agomelatine increases the level of brain-derived neurotrophic factor (BDNF) in the blood of responders.

Potential pleiotropic beneficial effects of adjuvant melatonergic treatment in posttraumatic stress disorder

Loss of circadian rhythmicity fundamentally affects the neuroendocrine, immune, and autonomic system, similar to chronic stress and may play a central role in the development of stress-related disorders. Recent articles have focused on the role of sleep and circadian disruption in the pathophysiology of posttraumatic stress disorder (PTSD), suggesting that chronodisruption plays a causal role in PTSD development. Direct and indirect human and animal PTSD research suggests circadian system-linked neuroendocrine, immune, metabolic and autonomic dysregulation, linking circadian misalignment to PTSD pathophysiology. Recent experimental findings also support a specific role of the fundamental synchronizing pineal hormone melatonin in mechanisms of sleep, cognition and memory, metabolism, pain, neuroimmunomodulation, stress endocrinology and physiology, circadian gene expression, oxidative stress and epigenetics, all processes affected in PTSD. In the current paper, we review available literature underpinning a potentially beneficiary role of an add-on melatonergic treatment in PTSD pathophysiology and PTSD-related symptoms. The literature is presented as a narrative review, providing an overview on the most important and clinically relevant publications. We conclude that adjuvant melatonergic treatment could provide a potentially promising treatment strategy in the management of PTSD and especially PTSD-related syndromes and comorbidities. Rigorous preclinical and clinical studies are needed to validate this hypothesis.

Altered Expression Pattern of Clock Genes in a Rat Model of Depression

BACKGROUND

Abnormalities in circadian rhythms may be causal factors in development of major depressive disorder. The biology underlying a causal relationship between circadian rhythm disturbances and depression is slowly being unraveled. Although there is no direct evidence of dysregulation of clock gene expression in depressive patients, many studies have reported single-nucleotide polymorphisms in clock genes in these patients.

METHODS

In the present study we investigated whether a depression-like state in rats is associated with alternations of the diurnal expression of clock genes. The validated chronic mild stress (CMS) animal model of depression was used to investigate rhythmic expression of three clock genes: period genes 1 and 2 (Per1 and Per2) and Bmal1. Brain and liver tissue was collected from 96 animals after 3.5 weeks of CMS (48 control and 48 depression-like rats) at a 4h sampling interval within 24h. We quantified expression of clock genes on brain sections in the prefrontal cortex, nucleus accumbens, pineal gland, suprachiasmatic nucleus, substantia nigra, amygdala, ventral tegmental area, subfields of the hippocampus, and the lateral habenula using in situ hybridization histochemistry. Expression of clock genes in the liver was monitored by real-time quantitative polymerase chain reaction (PCR).

RESULTS

We found that the effect of CMS on clock gene expression was selective and region specific. Per1 exhibits a robust diurnal rhythm in most regions of interest, whereas Bmal1 and in particular Per2 were susceptible to CMS.

CONCLUSION

The present results suggest that altered expression of investigated clock genes is likely associated with the induction of a depression-like state in the CMS model.

Long-term effects of cognitive therapy on biological rhythms and depressive symptoms: A randomized clinical trial

OBJECTIVE

To evaluate the effect of cognitive therapy on biological rhythm and depressive and anxious symptoms in a twelve-month follow-up period. In addition, correlations between the reduction of depression and anxiety symptoms and the regulation of biological rhythm were observed.

METHODS

This was a randomized clinical trial with young adults from 18 to 29 years of age who were diagnosed with depression. Two models of psychotherapy were used: Cognitive Behavioral Therapy (CBT) and Narrative Cognitive Therapy (NCT). Biological rhythm was assessed with the Biological Rhythm Interview of Assessment in Neuropsychiatry (BRIAN). Severity of depressive and anxious symptoms was assessed by the Hamilton Depression Rating Scale (HDRS) and the Hamilton Anxiety Rating Scale (HARS), respectively. The sample included 97 patients who were divided within the protocols of psychotherapy.

RESULTS

There was a significant reduction in depressive and anxious symptoms (p<0.001) and an increase on regulation of biological rhythm (p<0.05) at the twelve-month follow-up. Moreover, we showed a positive correlation between the reduction of depressive symptoms and regulation of biological rhythm (r=0.638; p<0.001) and between the reduction of anxious symptoms and regulation of biological rhythm (r=0.438; p<0.001).

CONCLUSION

Both models showed that cognitive therapy was effective on the reduction of depressive and anxious symptoms and on the regulation of biological rhythm at a twelve-month follow-up evaluation. This study highlights the association between biological rhythm and symptoms of depression and anxiety.

LIMITATION

We did not assess genetic, hormonal or neurochemical factors and we did not include patients under pharmaceutical treatment or those with severe symptomatology.

Glutamatergic synapse protein composition of wild-type mice is sensitive to in utero MTHFR genotype and the timing of neonatal vigabatrin exposure

The enzyme methylenetetrahydrofolate-reductase (MTHFR) is part of the homocysteine and folate metabolic pathways. In utero, Mthfr-deficient environment has been reported as a risk factor for neurodevelopmental disorders such as autism and neural tube defects. Neonatal disruption of the GABAergic system is also associated with behavioral outcomes. The interaction between Mthfr deficiency and neonatal exposure to the GABA-potentiating drug vigabatrin (GVG) in mice alters anxiety, memory, and social behavior in a gender-dependent manner. In addition, a gender-dependent enhancement of proteins implicated in excitatory synapse plasticity in the cerebral cortex was shown. Here we show that in utero MTHFR deficiency is sufficient to alter the levels of glutamate receptor subunits GluR1, GluR2, and NR2B in the cerebral cortex and hippocampus of adult offspring with a WT genotype. In addition, FMRP1, CAMKII α and γ, and NLG1 levels in WT offspring were vulnerable to the in utero genotype. These effects depend on brain region and the cellular compartment tested. The effect of in utero MTHFR deficiency varies with the age of neonatal GVG exposure to modify GluR1, NR2A, reelin, CAMKII α, and NLG1 levels. These changes in molecular composition of the glutamatergic synapse were associated with increased anxiety-like behavior. Complex, multifactorial disorders of the nervous system show significant association with several genetic and environmental factors. Our data exemplify the contribution of an in utero MTHFR-deficient environment and early exposure to an antiepileptic drug to the basal composition of the glutamatergic synapses. The robust effect is expected to alter synapse function and plasticity and the cortico-hippocampal circuitry.

Glucocorticoids and Stress-Induced Changes in the Expression of PERIOD1 in the Rat Forebrain

The secretion of glucocorticoids in mammals is under circadian control, but glucocorticoids themselves are also implicated in modulating circadian clock gene expression. We have shown that the expression of the circadian clock protein PER1 in the forebrain is modulated by stress, and that this effect is associated with changes in plasma corticosterone levels, suggesting a possible role for glucocorticoids in the mediation of stress-induced changes in the expression of PER1 in the brain. To study this, we assessed the effects of adrenalectomy and of pretreatment with the glucocorticoid receptor antagonist, mifepristone, on the expression of PER1 in select limbic and hypothalamic regions following acute exposure to a neurogenic stressor, restraint, or a systemic stressor, 2-Deoxy-D-glucose (2DG) in rats. Acute restraint suppressed PER1 expression in the oval nucleus of the bed nucleus of the stria terminalis (BNSTov) and the central nucleus of the amygdala (CEAl), whereas 2DG increased PER1 in both regions. Both stressors increased PER1 expression in the paraventricular (PVN) and dorsomedial (DMH) nuclei of the hypothalamus, and the piriform cortex (Pi). Adrenalectomy and pretreatment with mifepristone reversed the effects of both stressors on PER1 expression in the BNSTov and CEAl, and blocked their effects in the DMH. In contrast, both treatments enhanced the effects of restraint and 2DG on PER1 levels in the PVN. Stress-induced PER1 expression in the Pi was unaffected by either treatment. PER1 expression in the suprachiasmatic nucleus, the master circadian clock, was not altered by either exposure to stress or by the glucocorticoid manipulations. Together, the results demonstrate a key role for glucocorticoid signaling in stress-induced changes in PER1 expression in the brain.

Repeated Psychosocial Stress at Night Affects the Circadian Activity Rhythm of Male Mice

We have recently shown that molecular rhythms in the murine suprachiasmatic nucleus (SCN) are affected by repeated social defeat (SD) during the dark/active phase (social defeat dark [SDD]), while repeated SD during the light/inactive phase (social defeat light [SDL]) had no influence on PERIOD2::LUCIFERASE explant rhythms in the SCN. Here we assessed the effects of the same stress paradigm by in vivo biotelemetry on 2 output rhythms of the circadian clock (i.e., activity and core body temperature) in wild-type (WT) and clock-deficient Period (Per)1/2 double -mutant mice during and following repeated SDL and SDD. In general, stress had more pronounced effects on activity compared to body temperature rhythms. Throughout the SD procedure, activity and body temperature were markedly increased during the 2 h of stressor exposure at zeitgeber time (ZT) 1 to ZT3 (SDL mice) and ZT13 to ZT15 (SDD mice), which was compensated by decreased activity during the remaining dark phase (SDL and SDD mice) and light phase (SDL mice) in both genotypes. Considerable differences in the activity between SDL and SDD mice were seen in the poststress period. SDD mice exhibited a reduced first activity bout at ZT13, delayed activity onset, and, consequently, a more narrow activity bandwidth compared with single-housed control (SHC) and SDL mice. Given that this effect was absent in Per1/2 mutant SDD mice and persisted under constant darkness conditions in SDD WT mice, it suggests an involvement of the endogenous clock. Taken together, the present findings demonstrate that SDD has long-lasting consequences for the functional output of the biological clock that, at least in part, appear to depend on the clock genes Per1 and Per2.

Stress-induced changes in the expression of the clock protein PERIOD1 in the rat limbic forebrain and hypothalamus: role of stress type, time of day, and predictability

Stressful events can disrupt circadian rhythms in mammals but mechanisms underlying this disruption remain largely unknown. One hypothesis is that stress alters circadian protein expression in the forebrain, leading to functional dysregulation of the brain circadian network and consequent disruption of circadian physiological and behavioral rhythms. Here we characterized the effects of several different stressors on the expression of the core clock protein, PER1 and the activity marker, FOS in select forebrain and hypothalamic nuclei in rats. We found that acute exposure to processive stressors, restraint and forced swim, elevated PER1 and FOS expression in the paraventricular and dorsomedial hypothalamic nuclei and piriform cortex but suppressed PER1 and FOS levels exclusively in the central nucleus of the amygdala (CEAl) and oval nucleus of the bed nucleus of the stria terminalis (BNSTov). Conversely, systemic stressors, interleukin-1β and 2-Deoxy-D-glucose, increased PER1 and FOS levels in all regions studied, including the CEAl and BNSTov. PER1 levels in the suprachiasmatic nucleus (SCN), the master pacemaker, were unaffected by any of the stress manipulations. The effect of stress on PER1 and FOS was modulated by time of day and, in the case of daily restraint, by predictability. These results demonstrate that the expression of PER1 in the forebrain is modulated by stress, consistent with the hypothesis that PER1 serves as a link between stress and the brain circadian network. Furthermore, the results show that the mechanisms that control PER1 and FOS expression in CEAl and BNSTov are uniquely sensitive to differences in the type of stressor. Finally, the finding that the effect of stress on PER1 parallels its effect on FOS supports the idea that Per1 functions as an immediate-early gene. Our observations point to a novel role for PER1 as a key player in the interface between stress and circadian rhythms.

When time stands still: an integrative review on the role of chronodisruption in posttraumatic stress disorder

PURPOSE OF REVIEW

The human circadian system creates and maintains cellular and systemic rhythmicity essential to homeostasis. Loss of circadian rhythmicity fundamentally affects the neuroendocrine, immune and autonomic system, similar to chronic stress and, thus, may play a central role in the development of stress-related disorders. This article focuses on the role of circadian misalignment in the pathophysiology of posttraumatic stress disorder (PTSD).

RECENT FINDINGS

Sleep disruption is a core feature of PTSD supporting the important supraordinate pathophysiological role of circadian system in PTSD. Furthermore, direct and indirect human and animal PTSD research suggests circadian system linked neuroendocrine, immune, metabolic and autonomic dysregulation with blunted diurnal rhythms, specific sleep pattern pathologies and cognitive deficits, as well as endocannabinoid and neuropeptide Y system alterations and altered circadian gene expression, linking circadian misalignment to PTSD pathophysiology.

SUMMARY

PTSD development is associated with chronodisruption findings. Evaluation and treatment of sleep and circadian disruption should be the first steps in PTSD management. State-of-the-art methods of circadian rhythm assessment should be applied to bridge the gap between clinical significance and limited understanding of the relationship between traumatic stress, sleep and circadian system.

Agomelatine: mechanism of action and pharmacological profile in relation to antidepressant properties

Agomelatine behaves both as a potent agonist at melatonin MT1 and MT2 receptors and as a neutral antagonist at 5-HT2C receptors. Accumulating evidence in a broad range of experimental procedures supports the notion that the psychotropic effects of agomelatine are due to the synergy between its melatonergic and 5-hydroxytryptaminergic effects. The recent demonstration of the existence of heteromeric complexes of MT1 and MT2 with 5-HT2C receptors at the cellular level may explain how these two properties of agomelatine translate into a synergistic action that, for example, leads to increases in hippocampal proliferation, maturation and survival through modulation of multiple cellular pathways (increase in trophic factors, synaptic remodelling, glutamate signalling) and key targets (early genes, kinases). The present review focuses on the pharmacological properties of this novel antidepressant. Its mechanism of action, strikingly different from that of conventional classes of antidepressants, opens perspectives towards a better understanding of the physiopathological bases underlying depression.

Repeated fear-induced diurnal rhythm disruptions predict PTSD-like sensitized physiological acute stress responses in F344 rats

AIM

To identify objective factors that can predict future sensitized stress responses, thus allowing for effective intervention prior to developing sensitization and subsequent stress-related disorders, including post-traumatic stress disorder (PTSD).

METHODS

Adult male F344 rats implanted with biotelemetry devices were exposed to repeated conditioned fear or control conditions for 22 days followed by exposure to either no, mild or severe acute stress on day 23. Diurnal rhythms of locomotor activity (LA), heart rate (HR) and core body temperature (CBT) were biotelemetrically monitored throughout the study. In a subset of rat not implanted, corticosterone and indices of chronic stress were measured immediately following stress.

RESULTS

Rats exposed to repeated fear had fear-evoked increases in behavioural freezing and HR/CBT during exposure to the fear environment and displayed indices of chronic stress. Repeated fear produced flattening of diurnal rhythms in LA, HR and CBT. Repeated fear did not sensitize the corticosterone response to acute stress, but produced sensitized HR/CBT responses following acute stress, relative to the effect of acute stress in the absence of a history of repeated fear. Greater diurnal rhythm disruptions during repeated fear predicted sensitized acute stress-induced physiological responses. Rats exposed to repeated fear also displayed flattened diurnal LA and basal increases in HR.

CONCLUSIONS

Exposure to repeated fear produces outcomes consistent with those observed in PTSD. The results suggest that diurnal rhythm disruptions during chronic stressors may help predict sensitized physiological stress responses following traumatic events. Monitoring diurnal disruptions during repeated stress may thus help predict susceptibility to PTSD.

Links between Circadian Rhythms and Psychiatric Disease

Determining the cause of psychiatric disorders is a goal of modern neuroscience, and will hopefully lead to the discovery of treatments to either prevent or alleviate the suffering caused by these diseases. One roadblock to attaining this goal is the realization that neuropsychiatric diseases are rarely due to a single gene polymorphism, environmental exposure, or developmental insult. Rather, it is a complex interaction between these various influences that likely leads to the development of clinically relevant syndromes. Our lab is exploring the links between environmental exposures and neurobehavioral function by investigating how disruption of the circadian (daily) clock alters the structure and function of neural circuits, with the hypothesis that disrupting this crucial homeostatic system can directly contribute to altered vulnerability of the organism to other factors that interact to produce psychiatric illness. This review explores some historical and more recent findings that link disrupted circadian clocks to neuropsychiatric disorders, particularly depression, mania, and schizophrenia. We take a comparative approach by exploring the effects observed in human populations, as well as some experimental models used in the laboratory to unravel mechanistic and causal relationships between disruption of the circadian clock and behavioral abnormalities. This is a rich area of research that we predict will contribute greatly to our understanding of how genes, environment, and development interact to modulate an individual’s vulnerability to psychiatric disorders.

Agomelatine in the tree shrew model of depression: effects on stress-induced nocturnal hyperthermia and hormonal status

The antidepressive drug agomelatine combines the properties of an agonist of melatonergic receptors 1 and 2 with an antagonist of the 5-HT2C receptor. We analyzed the effects of agomelatine in psychosocially stressed male tree shrews, an established preclinical model of depression. Tree shrews experienced daily social stress for a period of 5 weeks and were concomitantly treated with different drugs daily for 4 weeks. The effects of agomelatine (40 mg/kg/day) were compared with those of the agonist melatonin (40 mg/kg/day), the inverse 5-HT2C antagonist S32006 (10mg/kg/day), and the SSRI fluoxetine (15 mg/kg/day). Nocturnal core body temperature (CBT) was recorded by telemetry, and urinary norepinephrine and cortisol concentrations were measured. Chronic social stress induced nocturnal hyperthermia. Agomelatine normalized the CBT in the fourth week of the treatment (T4), whereas the other drugs did not significantly counteract the stress-induced hyperthermia. Agomelatine also reversed the stress-induced reduction in locomotor activity. Norepinephrine concentration was elevated by the stress indicating sympathetic hyperactivity, and was normalized in the stressed animals treated with agomelatine or fluoxetine but not in those treated with melatonin or S32006. Cortisol concentration was elevated by stress but returned to basal levels by T4 in all animals, irrespective of the treatment. These observations show that agomelatine has positive effects to counteract stress-induced physiological processes and to restore the normal rhythm of nocturnal CBT. The data underpin the antidepressant properties of agomelatine and are consistent with a distinctive profile compared to its constituent pharmacological components and other conventional agents.

Animal models in translational studies of PTSD

Understanding the neurobiological mechanisms of post-traumatic stress disorder (PTSD) is of vital importance for developing biomarkers and more effective pharmacotherapy for this disorder. The design of bidirectional translational studies addressing all facets of PTSD is needed. Animal models of PTSD are needed not only to capture the complexity of PTSD behavioral characteristics, but also to address experimentally the influence of variety of factors which might determine an individual's vulnerability or resilience to trauma, e.g., genetic predisposition, early-life experience and social support. The current review covers recent translational approaches to bridge the gap between human and animal PTSD research and to create a framework for discovery of biomarkers and novel therapeutics.

Agomelatine: Its Role in the Management of Major Depressive Disorder

Circadian rhythm abnormalities, as shown by sleep/wake cycle disturbances, constitute one the most prevalent signs of depressive illness; advances or delays in the circadian phase are documented in patients with major depressive disorder (MDD), bipolar disorder, and seasonal affective disorder (SAD). The disturbances in the amplitude and phase of rhythm in melatonin secretion that occur in patients with depression resemble those seen in chronobiological disorders, thus suggesting a link between disturbed melatonin secretion and depressed mood. Based on this, agomelatine, the first MT1/MT2 melatonergic agonist displaying also 5-HT2C serotonergic antagonism, has been introduced as an antidepressant. Agomelatine has been shown to be effective in several animal models of depression and anxiety and it has beneficial effects in patients with MDD, bipolar disorder, or SAD. Among agomelatine's characteristics are a rapid onset of action and a pronounced effectiveness for correcting circadian rhythm abnormalities and improving the sleep/wake cycle. Agomelatine also improves the 3 functional dimensions of depression—emotional, cognitive, and social—thus aiding in the full recovery of patients to a normal life.

Circadian genes Period 1 and Period 2 in the nucleus accumbens regulate anxiety-related behavior

It has been suggested for some time that circadian rhythm abnormalities underlie the development of multiple psychiatric disorders. However, it is unclear how disruptions in individual circadian genes might regulate mood and anxiety. Here we found that mice lacking functional mPeriod 1 (mPer1) or mPeriod 2 (mPer2) individually did not have consistent behavioral abnormalities in measures of anxiety-related behavior. However, mice deficient in both mPer1 and mPer2 had an increase in levels of anxiety-like behavior in multiple measures. Moreover, we found that mPer1 and mPer2 expression was reduced in the nucleus accumbens (NAc) after exposure to chronic social defeat stress, a paradigm that led to increased anxiety-related behavior. Following social defeat, chronic treatment with fluoxetine normalized Per gene expression towards wild-type levels. Knockdown of both mPer1 and mPer2 expression via RNA interference specifically in the NAc led to a similar increase in anxiety-like behavior as seen in the mutant animals. Taken together, these results implicate the Per genes in the NAc in response to stress and the development of anxiety.

Physiological consequences of repeated exposures to conditioned fear

Activation of the stress response evokes a cascade of physiological reactions that may be detrimental when repeated or chronic, and when triggered after exposure to psychological/emotional stressors. Investigation of the physiological mechanisms responsible for the health damaging effects requires animal paradigms that repeatedly evoke a response to psychological/emotional stressors. To this end, adult male Sprague Dawley rats were repeatedly exposed (2X per day for 20 days) to a context that they were conditioned to fear (conditioned fear test, CFT). Repeated exposure to CFT produced body weight loss, adrenal hypertrophy, thymic involution, and basal corticosterone elevation. In vivo biotelemetry measures revealed that CFT evokes sympathetic nervous system driven increases in heart rate (HR), mean arterial pressure (MAP), and core body temperature. Extinction of behavioral (freezing) and physiological responses to CFT was prevented using minimal reinstatement footshock. MAP responses to the CFT did not diminish across 20 days of exposure. In contrast, HR and cardiac contractility responses declined by day 15, suggesting a shift toward vascular-dominated MAP (a pre-clinical marker of CV dysfunction). Flattened diurnal rhythms, common to stress-related mood/anxiety disorders, were found for most physiological measures. Thus, repeated CFT produces adaptations indicative of the health damaging effects of psychological/emotional stress.