Behavioural and neuroplastic effects of the new-generation antidepressant agomelatine compared to fluoxetine in glucocorticoid receptor-impaired mice

Successful Treatment with Agomelatine in NES: A Series of Five Cases

The NES is an emerging disease in eating behavior that combines eating disorders, sleep, mood and stress. In recent years, the NES is becoming more interested in close association with obesity and depression.

In the present study we have followed for 12 weeks 5 patients (2 males and 3 females) with NES and comorbid depression treated with agomelatine (25 mg / day for the first two weeks, then 50 mg / day), an antidepressant similar of melatonin.

At the end of the three months of treatment, it was found an improvement in symptoms characteristic of the NES, as assessed by a reduction an average of the NEQ (from 31 to 22.8), improved mood, mean values ​​reduced by 23, 2 to 13.2 on the HAM-D, weight reduction, an average of 3.6 kg reduction in average weekly awakenings from 12 to 6.4 and the time of snoring and motion detected polysomnography. The serum chemistry values ​​remained stable and there were no reported adverse events.

The present study showed that the treatment with agomelatine has improved the symptoms of NES and mood, decrease of body weight, reduce, albeit not in an optimal manner, the number of awakenings per night with a reduction of movement time and snoring . Of course, these preliminary data need to be confirmed by controlled trials on a larger sample.

Beyond the monoaminergic hypothesis: neuroplasticity and epigenetic changes in a transgenic mouse model of depression

The monoamine hypothesis of depression has dominated our understanding of both the pathophysiology of depression and the action of pharmacological treatments for the last decades, and it has led to the production of several generations of antidepressant agents. However, there are serious limitations to the current monoamine theory, and additional mechanisms, including hypothalamic-pituitary-adrenal (HPA) axis dysfunctions, as well as neurodegenerative and inflammatory alterations, are potentially associated with the pathogenesis of mood disorders. Moreover, new data have recently indicated that epigenetic mechanisms such as histone modifications and DNA methylation could affect diverse pathways leading to depression-like behaviours in animal models. In a transgenic mouse model of depression, in which a downregulation of glucocorticoid receptors (GR) causes a deficit in the HPA axis feedback control, besides alterations in monoamine neurotransmission and neuroplasticity, we found modifications in the expression of many proteins involved in epigenetic regulation, as well as clock genes, in the hippocampus and the frontal cortex, that might be central in the genesis of depressive-like behaviours.

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.

Single nucleotide polymorphisms of NR3C1 gene and recurrent depressive disorder in population of Poland

Depressive disorder is a disease characterized by disturbances in the hypothalamo-pituitary-adrenal axis. Abnormalities include the increased level of glucocorticoids (GC) and changes in sensitivity to these hormones. The changes are related to glucocorticoid receptors gene (NR3C1) variants. The NR3C1 gene is suggested to be a candidate gene affecting depressive disorder risk and management. The aim of this study was to investigate polymorphisms within the NR3C1 gene and their role in the susceptibility to recurrent depressive disorder (rDD). 181 depressive patients and 149 healthy ethnically matched controls were included in the study. Single nucleotide polymorphisms were assessed using polymerase chain reaction/restriction fragment length polymorphism method. Statistical significance between rDD patients and controls was observed for the allele and genotype frequencies at three loci: BclI, N363S, and ER22/23EK. The presence of C allele, CC, and GC genotype of BclI polymorphism, G allele and GA genotype for N363S and ER22/23EK variants respectively were associated with increased rDD risk. Two haplotypes indicated higher susceptibility for rDD, while haplotype GAG played a protective role with OR(dis) 0.29 [95 % confidence interval (CI) = 0.13-0.64]. Data generated from this study support the earlier results that genetic variants of the NR3C1 gene are associated with rDD and suggest further consideration on the possible involvement of these variants in etiology of the disease.

The genetics of selective serotonin reuptake inhibitors

Selective serotonin reuptake inhibitors (SSRIs) are among the most widely prescribed drugs in psychiatry. Based on the fact that SSRIs increase extracellular monoamine levels in the brain, the monoamine hypothesis of depression was introduced, postulating that depression is associated with too low serotonin, dopamine and noradrenaline levels. However, several lines of evidence indicate that this hypothesis is too simplistic and that depression and the efficacy of SSRIs are dependent on neuroplastic changes mediated by changes in gene expression. Because a coherent view on global gene expression is lacking, we aim to provide an overview of the effects of SSRI treatment on the final targets of 5-HT receptor signal transduction pathways, namely the transcriptional regulation of genes. We address gene polymorphisms in humans that affect SSRI efficacy, as well as in vitro studies employing human-derived cells. We also discuss the molecular targets affected by SSRIs in animal models, both in vivo and in vitro. We conclude that serotonin transporter gene variation in humans affects the efficacy and side-effects of SSRIs, whereas SSRIs generally do not affect serotonin transporter gene expression in animals. Instead, SSRIs alter mRNA levels of genes encoding serotonin receptors, components of non-serotonergic neurotransmitter systems, neurotrophic factors, hypothalamic hormones and inflammatory factors. So far little is known about the epigenetic and age-dependent molecular effects of SSRIs, which might give more insights in the working mechanism(s) of SSRIs.

Psychotropic drug effects on gene transcriptomics relevant to Parkinson's disease

OBJECTIVES

Psychotropic drugs are widely prescribed in Parkinson's disease (PD) without regard to their pathobiological effects, and these drugs affect the transcription of a large number of genes. Effects of these drugs on PD risk gene transcription were therefore surveyed.

METHODS

Results summarize a comprehensive survey of psychotropic effects on messenger ribonucleic acid (mRNA) expression evident in published data for 70 genes linked to PD risk.

RESULTS

Psychotropic drugs can meaningfully affect PD risk gene mRNA transcription, including antipsychotics (upregulate dopamine receptors D2 and D3 (DRD2, DRD3); downregulate low-density lipoprotein receptor-related protein 8 (LRP8), ubiquitin carboxyl-terminal esterase L1 (UCHL1, also known as PARK5)), haloperidol (upregulates DRD3, parkin (PRKN, also known as PARK2), DRD2; downregulates brain-derived neurotrophic factor (BDNF)), risperidone (upregulates monoamine oxidase B (MAOB), DRD2), olanzapine (upregulates transmembrane protein 163 (TMEM163), BDNF, glutathione S-transferase mu 1 (GSTM1), MAOB, DRD2, solute carrier organic anion transporter family, member 3A1 (SLCO3A1)), aripiprazole (upregulates DRD2), quetiapine, paliperidone, lurasidone, carbamazepine, and many antidepressants (upregulate BDNF), lithium and bupropion (downregulate BDNF), amitriptyline (upregulates DRD3, DRD2), imipramine (upregulates BDNF, DRD3, DRD2), desipramine (upregulates BDNF, DRD3), and fluoxetine (upregulates acid beta-glucosidase (GBA), coiled-coil domain containing 62 (CCDC62), BDNF, DRD3, UCHL1, unc-13 homolog B (UNC13B), and perhaps huntingtin interacting protein 1 related (HIP1R); downregulates microtubule-associated protein tau (MAPT), methylcrotonoyl-coenzyme A carboxylase I (MCCC1), GSTM1, 28kDa calbindin 1 (CALB1)). Fluoxetine effects on BDNF and UCHL1 in GEO Profiles were statistically robust.

CONCLUSIONS

This report provides an initial summary and framework to understand the potential impact of psychotropic drugs on PD-relevant genes. Antipsychotics and serotoninergic antidepressants may potentially attenuate PD risk, and lithium and bupropion may augment risk, through MAPT, GBA, CCDC62, HIP1R, BDNF, and DRD2 transcription, with MAPT, GBA, and CCDC62 being strongly associated with PD risk in recent meta-analyses. Limitations of these findings and a research agenda to better relate them to the nigrostriatum and PD are discussed.

Neuroplasticity and major depression, the role of modern antidepressant drugs

The pathophysiology of depression has been traditionally attributed to a chemical imbalance and critical interactions between genetic and environmental risk factors, and antidepressant drugs suggested to act predominantly amplifying monoaminergic neurotransmission. This conceptualization may be currently considered reductive. The current literature about the pathophysiological mechanisms underlying depression, stress-related disorders and antidepressant treatment was examined. In order to provide a critical overview about neuroplasticity, depression and antidepressant drugs, a detailed Pubmed/Medline, Scopus, PsycLit, and PsycInfo search to identify all papers and book chapters during the period between 1980 and 2011 was performed. Pathological stress and depression determine relevant brain changes such as loss of dendritic spines and synapses, dendritic atrophy as well as reduction of glial cells (both in number and size) in specific areas such as the hippocampus and prefrontal cortex. An increased dendritic arborisation and synaptogenesis may instead be observed in the amygdala as a consequence of depression and stress-related disorders. While hippocampal and prefrontal functioning was impaired, amygdala functioning was abnormally amplified. Most of molecular abnormalities and biological changes of aberrant neuroplasticity may be explained by the action of glutamate. Antidepressant treatment is associated with neurogenesis, gliogenesis, dendritic arborisation, new synapse formation and cell survival both in the hippocampus and prefrontal cortex. Antidepressants (ADs) induce neuroplasticity mechanisms reversing the pathological effects of depression and stress-related disorders. The neuroplasticity hypothesis may explain the therapeutic and prophylactic action of ADs representing a new innovative approach to the pathophysiology of depression and stress-related disorders.

Agomelatine (S20098) modulates the expression of cytoskeletal microtubular proteins, synaptic markers and BDNF in the rat hippocampus, amygdala and PFC

RATIONALE

Agomelatine is described as a novel and clinical effective antidepressant drug with melatonergic (MT(1)/MT(2)) agonist and 5-HT(2C) receptor antagonist properties. Previous studies suggest that modulation of neuronal plasticity and microtubule dynamics may be involved in the treatment of depression.

OBJECTIVE

The present study investigated the effects of agomelatine on microtubular, synaptic and brain-derived neurotrophic factor (BDNF) proteins in selected rat brain regions.

METHODS

Adult male rats received agomelatine (40 mg/kg i.p.) once a day for 22 days. The pro-cognitive effect of agomelatine was tested in the novel object recognition task and antidepressant activity in the forced swimming test. Microtubule dynamics markers, microtubule-associated protein type 2 (MAP-2), phosphorylated MAP-2, synaptic markers [synaptophysin, postsynaptic density-95 (PSD-95) and spinophilin] and BDNF were measured by Western blot in the hippocampus, amygdala and prefrontal cortex (PFC).

RESULTS

Agomelatine exerted pro-cognitive and antidepressant activity and induced molecular changes in the brain areas examined. Agomelatine enhanced microtubule dynamics in the hippocampus and to a higher magnitude in the amygdala. By contrast, in the PFC, a decrease in microtubule dynamics was observed. Spinophilin (dendritic spines marker) was decreased, and BDNF increased in the hippocampus. Synaptophysin (presynaptic) and spinophilin were increased in the PFC and amygdala, while PSD-95 (postsynaptic marker) was increased in the amygdala, consistent with the phenomena of synaptic remodelling.

CONCLUSIONS

Agomelatine modulates cytoskeletal microtubule dynamics and synaptic markers. This may play a role in its pharmacological behavioural effects and may result from the melatonergic agonist and 5-HT(2C) antagonist properties of the compound.

Neuroimmunomodulation in unipolar depression: a focus on chronobiology and chronotherapeutics

The rising burden of unipolar depression along with its often related sleep disturbances, as well as increasing rates of sleep restriction in modern society, make the search for an extended understanding of the aetiology and pathophysiology of depression necessary. Accumulating evidence suggests an important role for the immune system in mediating disrupted neurobiological and chronobiological processes in depression. This review aims to provide an overview of the neuroimmunomodulatory processes involved with depression and antidepressant treatments with a special focus on chronobiology, chronotherapeutics and the emerging field of immune-circadian bi-directional crosstalk. Increasing evidence suggests that chronobiological disruption can mediate immune changes in depression, and likewise, immune processes can mediate chronobiological disruption. This may suggest a bi-directional relationship in immune-circadian crosstalk. Furthermore, given the immunomodulatory effects of antidepressants and chronotherapeutics, as well as their associated beneficial effects on circadian disturbance, we--and others--suggest that these therapeutic agents may exert their chronobiotic effects partially via the neuroimmune system. Further research is required to better elucidate the mechanisms of immune involvement in the chronobiology of depression.

Effects of environmental manipulations in genetically targeted animal models of affective disorders

Mental illness is the leading cause of disability worldwide. We are only just beginning to reveal and comprehend the complex interaction that exists between the genetic makeup of an organism and the potential modifying effect of the environment in which it lives, and how this translates into mediating susceptibility to neurological and psychiatric conditions. The capacity to address this issue experimentally has been facilitated by the availability of rodent models which allow the precise manipulation of genetic and environmental factors. In this review, we discuss the valuable nature of animal models in furthering our understanding of the relationship between genetic and environmental factors in affective illnesses, such as anxiety and depressive disorders. We first highlight the behavioral impairments exhibited by genetically targeted animal models of affective disorders, and then provide a discussion of the underlying neurobiology, focusing on animal models that involve exposure to stress. This is followed by a review of recent studies that report of beneficial effects of environmental manipulations such as environmental enrichment and enhanced physical activity and discuss the likely mechanisms that mediate those benefits.

Beneficial behavioural and neurogenic effects of agomelatine in a model of depression/anxiety

Agomelatine (S20098) is a novel antidepressant drug with melatonergic agonist and 5-HT2C receptor antagonist properties, displaying antidepressant/anxiolytic-like properties in animal models and in humans. In a depression/anxiety-like mouse model in which the response of the HPA axis is blunted, we investigated whether agomelatine could reverse behavioural deficits related to depression/anxiety compared to the classical selective serotonin reuptake inhibitor, fluoxetine. Adult mice were treated for 8 wk with either vehicle or corticosterone (35 μg/ml.d) via drinking water. During the final 4 wk, animals were treated with vehicle, agomelatine (10 or 40 mg/kg i.p.) or fluoxetine (18 mg/kg i.p.) and tested in several behavioural paradigms and also evaluated for home-cage activity. Our results showed that the depressive/anxiety-like phenotype induced by corticosterone treatment is reversed by either chronic agomelatine or fluoxetine treatment. Moreover, agomelatine increased the dark/light ratio of home-cage activity in vehicle-treated mice and reversed the alterations in this ratio induced by chronic corticosterone, suggesting a normalization of disturbed circadian rhythms. Finally, we investigated the effects of this new antidepressant on neurogenesis. Agomelatine reversed the decreased cell proliferation in the whole hippocampus in corticosterone-treated mice and increased maturation of newborn neurons in both vehicle- and corticosterone-treated mice. Overall, the present study suggests that agomelatine, with its distinct mechanism of action based on the synergy between the melatonergic agonist and 5-HT2C antagonist properties, provides a distinct antidepressant/anxiolytic spectrum including circadian rhythm normalization.

Efficacy of agomelatine in major depressive disorder: meta-analysis and appraisal

Agomelatine is the first approved antidepressant that mediates its activity through the melatoninergic pathway rather than the monoaminergic system. This meta-analysis aims to summarize an up-to-date report on the efficacy of agomelatine in major depressive disorder. Archives of published results in PubMed, CINAHL, Cochrane Library, EMBASE and PsycINFO databases were searched for randomized double-blind trials comparing agomelatine against placebo or antidepressant in major depressive disorder. Change in severity of depression as a result of intervention was the main outcome measure. Data necessary to compute the standardized mean difference (SMD) of this outcome and additional sample parameters that were likely to influence the main outcome were extracted for each selected studies. Summary effect sizes of various groups and subgroups were computed from SMDs between agomelatine and control (placebo or antidepressants) arms. There were nine trials involving 3943 severe cases of depression on agomelatine (n=2390) and either placebo (n=689) or antidepressants (n=864). Agomelatine (n=1274) stood superior to placebo (n=689) by a small margin (SMD -0.26, p=3.48×10-11) and the superiority of agomelatine (n=834, dose ≥ 25 mg/d) over antidepressants (paroxetine, fluoxetine, sertraline, venlafaxine; n=864) was even smaller (SMD -0.11, p=0.02). Although there is evidence of the superiority of agomelatine over placebo and selected antidepressants, it is questionable whether the magnitude of effect size is clinically significant and sample characteristics are relevant to the general patient population with major depressive disorder.

Partial reduction in neural cell adhesion molecule (NCAM) in heterozygous mice induces depression-related behaviour without cognitive impairment

The neural cell adhesion molecule (NCAM) plays an important role in brain plasticity. Using mice deficient in all isoforms of NCAM we have previously demonstrated that constitutive deficiency in the NCAM gene (NCAM-/-) resulted in cognitive impairment, anhedonic behaviour and a reduced ability to cope with stress. This was accompanied by reduced basal phosphorylation of the fibroblast growth factor receptor 1 (FGFR1) and reduced phosphorylation of calcium-calmodulin kinase (CaMK) II and IV and cAMP response element binding protein (CREB). The present study was aimed to investigate how partial deficiency in NCAM in mice (NCAM+/-) affected phenotype. We found that NCAM+/- mice showed a longer period of immobility in the tail suspension test, increased latency to feed in the novelty-suppressed feeding test and reduced preference for sucrose in sucrose preference test. Both NCAM+/- and NCAM-/- mice showed reduced extinction of contextual fear. In contrast to NCAM-/- mice, NCAM+/- mice did not demonstrate memory impairment in either object recognition or contextual fear conditioning tests. Levels of phosphorylated FGFR1 in the hippocampus and prefrontal/frontal cortex of NCAM+/- mice were partially reduced and no changes in the phosphorylation of CaMKII, CaMKIV or CREB in the hippocampus were found. We conclude that a constitutive partial reduction in NCAM proteins results in a behavioural phenotype related to depression without impairment in cognitive functions, also affecting the level of FGFR1 phosphorylation without major alterations in CaMKII and CaMKIV intracellular signalling. Partial reduction in FGFR1 phosphorylation might explain the observed behavioural phenotype in NCAM+/- mice.

Mode of action of agomelatine: synergy between melatonergic and 5-HT2C receptors

OBJECTIVES

The association between depression and circadian rhythm disturbances is well established and successful treatment of depressed patients is accompanied by restoration of circadian rhythms. The new antidepressant agomelatine is an agonist of melatonergic MT₁/MT₂ receptors as well as an antagonist of serotonergic 5-HT2C receptors. Animal studies showed that agomelatine resynchronizes disturbed circadian rhythms and reduces depression-like behaviour.

METHODS

This review analyzes results from different experimental studies.

RESULTS

Recent data on the effects of agomelatine on cellular processes involved in antidepressant mechanisms have shown that the drug is able to increase the expression of brain-derived neurotrophic factor in prefrontal cortex and hippocampus, as well as the expression of activity-regulated cytoskeleton associated protein (Arc) in the prefrontal cortex. In line with this, prolonged treatment with agomelatine increases neurogenesis within the hippocampus, particularly via enhancement of neuronal cell survival. Agomelatine attenuates stress-induced glutamate release in the prefrontal/frontal cortex. Treatment with 5-HT2C antagonists or melatonin alone failed to reproduce these effects.

CONCLUSIONS

The unique mode of action of agomelatine may improve the management of major depression by counteracting the pathogenesis of depression at cellular level, thereby relieving the symptoms of depression. These effects are suggested to be due to a synergistic action on MT₁/MT₂ and 5-HT2C receptors.

A placebo-controlled study of sertraline's effect on cortisol response to the dexamethasone/corticotropin-releasing hormone test in healthy adults

RATIONALE

The dexamethasone/corticotropin-releasing hormone (Dex/CRH) test is a neuroendocrine probe involving serial blood sampling of cortisol during a standardized pharmacological challenge without inducing psychological distress in humans. Some past studies in depressed patients have shown a "normalization" or decrease in cortisol response to the Dex/CRH test following successful treatment with an antidepressant. Studies in nondepressed healthy adult samples have also shown aberrant cortisol reactivity to be associated with depression risk factors. These findings prompted research into the use of the Dex/CRH test as a tool for developing antidepressant drugs.

OBJECTIVES

In this study, the Dex/CRH test was evaluated with regard to its potential utility for drug development in nonclinical samples.

METHODS

The Dex/CRH test was administered before and after 6 weeks of blinded treatment with either sertraline 100 mg/day or matching placebo in 22 healthy adults (13 women, nine men).

RESULTS

Cortisol response to the Dex/CRH test increased following treatment with standard doses of sertraline, compared to placebo, after controlling for age and sex.

CONCLUSIONS

The observed pattern of change contrasts with results from published studies in depressed patients and with our initial hypothesis.

Long-term effects of neonatal stress on adult conditioned place preference (CPP) and hippocampal neurogenesis

Critically ill preterm infants are often exposed to stressors that may affect neurodevelopment and behavior. We reported that exposure of neonatal mice to stressors or morphine produced impairment of adult morphine-rewarded conditioned place preference (CPP) and altered hippocampal gene expression. We now further this line of inquiry by examining both short- and long-term effects of neonatal stress and morphine treatment. Neonatal C57BL/6 mice were treated twice daily from postnatal day (P) 5 to P9 using different combinations of factors. Subsets received saline or morphine injections (2mg/kgs.c.) or were exposed to our neonatal stress protocol (maternal separation 8h/d × 5d+gavage feedings ± hypoxia/hyperoxia). Short-term measures examined on P9 were neuronal fluorojade B and bromodeoxyuridine staining, along with urine corticosterone concentrations. Long-term measures examined in adult mice (>P60) included CPP learning to cocaine reward (± the kappa opioid receptor (KOR) agonist U50,488 injection), and adult hippocampal neurogenesis (PCNA immunolabeling). Neonatal stress (but not morphine) decreased the cocaine-CPP response and this effect was reversed by KOR stimulation. Both neonatal stress or morphine treatment increased hippocampal neurogenesis in adult mice. We conclude that reduced learning and increased hippocampal neurogenesis are both indicators that neonatal stress desensitized mice and reduced their arousal and stress responsiveness during adult CPP testing. Reconciled with other findings, these data collectively support the stress inoculation hypothesis whereby early life stressors prepare animals to tolerate future stress.

Subchronic peripheral neuregulin-1 increases ventral hippocampal neurogenesis and induces antidepressant-like effects

Background

Adult hippocampal neurogenesis has been implicated in the mechanism of antidepressant action, and neurotrophic factors can mediate the neurogenic changes underlying these effects. The neurotrophic factor neuregulin-1 (NRG1) is involved in many aspects of brain development, from cell fate determination to neuronal maturation. However, nothing is known about the influence of NRG1 on neurodevelopmental processes occurring in the mature hippocampus.

Methods

Adult male mice were given subcutaneous NRG1 or saline to assess dentate gyrus proliferation and neurogenesis, as well as cell fate determination. Mice also underwent behavioral testing. Expression of ErbB3 and ErbB4 NRG1 receptors in newborn dentate gyrus cells was assessed at various time points between birth and maturity. The phenotype of ErbB-expressing progenitor cells was also characterized with cell type-specific markers.

Results

The current study shows that subchronic peripheral NRG1β administration selectively increased cell proliferation (by 71%) and neurogenesis (by 50%) in the caudal dentate gyrus within the ventral hippocampus. This pro-proliferative effect did not alter neuronal fate, and may have been mediated by ErbB3 receptors, which were expressed by newborn dentate gyrus cells from cell division to maturity and colocalized with SOX2 in the subgranular zone. Furthermore, four weeks after cessation of subchronic treatment, animals displayed robust antidepressant-like behavior in the absence of changes in locomotor activity, whereas acute treatment did not produce antidepressant effects.

Conclusions

These results show that neuregulin-1β has pro-proliferative, neurogenic and antidepressant properties, further highlight the importance of peripheral neurotrophic factors in neurogenesis and mood, and support the role of hippocampal neurogenesis in mediating antidepressant effects.

Chronic agomelatine treatment corrects behavioral, cellular, and biochemical abnormalities induced by prenatal stress in rats

RATIONALE AND OBJECTIVES

The rat model of prenatal restraint stress (PRS) replicates factors that are implicated in the etiology of anxious/depressive disorders. We used this model to test the therapeutic efficacy of agomelatine, a novel antidepressant that behaves as a mixed MT1/MT2 melatonin receptor agonist/5-HT(2c) serotonin receptor antagonist.

RESULTS

Adult PRS rats showed behavioral, cellular, and biochemical abnormalities that were consistent with an anxious/depressive phenotype. These included an increased immobility in the forced swim test, an anxiety-like behavior in the elevated plus maze, reduced hippocampal levels of phosphorylated cAMP-responsive element binding protein (p-CREB), reduced hippocampal levels of mGlu2/3 and mGlu5 metabotropic glutamate receptors, and reduced neurogenesis in the ventral hippocampus, the specific portion of the hippocampus that encodes memories related to stress and emotions. All of these changes were reversed by a 3- or 6-week treatment with agomelatine (40-50 mg/kg, i.p., once a day). Remarkably, agomelatine had no effect in age-matched control rats, thereby behaving as a "disease-dependent" drug.

CONCLUSIONS

These data indicate that agomelatine did not act on individual symptoms but corrected all aspects of the pathological epigenetic programming triggered by PRS. Our findings strongly support the antidepressant activity of agomelatine and suggest that the drug impacts mechanisms that lie at the core of anxious/depressive disorders.

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.

Chronic agomelatine and fluoxetine induce antidepressant-like effects in H/Rouen mice, a genetic mouse model of depression

The novel antidepressant agomelatine behaves as an agonist at melatonergic MT(1) and MT(2) receptors and as an antagonist at serotonin 5-HT(2C) receptors. This study investigated the effects of agomelatine and fluoxetine in a genetic model of depression called H/Rouen mice Male and female H/Rouen (helpless line) and NH/Rouen (nonhelpless line) mice, received once daily for 3 weeks agomelatine (10 and 50 mg/kgi.p.), fluoxetine (10 mg/kgi.p.) or vehicle. Immobility duration in the tail suspension test (TST) was assessed on day 1 (D1), day 8 (D8), day 15 (D15) and day 22 (D22). Locomotor activity in a novel environment was assessed on day 18 (D18) and anhedonia (2-bottle sucrose preference test) was considered after the end of chronic treatment, from days 22 to 25. Agomelatine (50 mg/kg) significantly reduced immobility at D15 (p<0.01), and D22 (p<0.001) in treated H/Rouen mice whereas agomelatine at 10 mg/kg did not induce a statistically significant change. Fluoxetine reduced immobility at D8 (p<0.01), D15 (p<0.001) and D22 (p<0.001). Locomotor activity was unchanged in all treated groups as compared to vehicle groups. In the sucrose test, there was a significant decrease in sucrose preference in H/Rouen mice compared with NH/Rouen mice receiving vehicle. Both agomelatine doses (10 mg/kg (p=0.05) and 50 mg/kg (p<0.001) as well as fluoxetine (p<0.001) significantly increased the sucrose preference in H/Rouen mice as compared with H/Rouen mice that had received vehicle. These data indicate that the novel antidepressant agomelatine has antidepressant-like properties in H/Rouen mice, a genetic model of depression.

Lithium-induced effects on adult hippocampal neurogenesis are topographically segregated along the dorso-ventral axis of stressed mice

Adult hippocampal neurogenesis is an important process in the regulation of cognition, stress responsivity, and sensitivity to antidepressant and mood stabiliser drugs. Increasing evidence suggests that the hippocampus is functionally divided along its axis with the ventral hippocampus (vHi) playing a preferential role in stress- and anxiety-related processes, while the dorsal hippocampus (dHi) is crucial for spatial learning and memory. However, it is currently unclear whether stress or the medications used to treat stress-related disorders, preferentially affect neurogenesis in the vHi rather than dHi. The aim of this study was to determine whether the mood stabiliser, lithium, preferentially affects cell proliferation and survival in the vHi rather than dHi under stress conditions. To this end, mice of the stress-sensitive strain, BALB/c, underwent chronic exposure to immobilisation stress plus lithium treatment (0.2% lithium-supplemented diet), and the rates of cell proliferation and survival were compared in the dHi and vHi. Lithium preferentially increased cell proliferation in the vHi under stress conditions only. This increase in cell proliferation was secondary to reductions in the survival of newly-born cells. Moreover, lithium-induced decreases in cell survival in the vHi were only observed under stress conditions. Taken together, the data suggest that the turnover of newly-born cells in response to chronic stress and lithium treatment occurs predominantly in the vHi rather than the dHi. This article is part of a Special Issue entitled 'Anxiety and Depression'.

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.

Chronic stress and antidepressant agomelatine induce region-specific changes in synapsin I expression in the rat brain

The antidepressant agomelatine acts as a melatonergic receptor (MT(1)/MT(2)) agonist and 5-HT(2C) receptor antagonist. Agomelatine has demonstrated efficacy in treating depression, but its neurobiological effects merit further investigation. Preclinical studies reported that agomelatine enhances adult hippocampal neurogenesis and increases expression of several neuroplasticity-associated molecules. Recently, we showed that agomelatine normalizes hippocampal neuronal activity and promotes neurogenesis in the stress-compromised brain. To characterize further the effects of this antidepressant in the stressed brain, here we investigated whether it induces changes in the expression of synapsin I (SynI), a regulator of synaptic transmission and plasticity. Adult male rats were subjected to daily footshock stress and agomelatine treatment for 3 weeks. Their brains were subsequently stained for total and phosphorylated SynI. Chronic footshock and agomelatine induced region-specific changes in SynI expression. Whereas chronic stress increased total SynI expression in all layers of the medial prefrontal cortex, agomelatine treatment abolished some of these effects. Furthermore, chronic agomelatine administration decreased total SynI expression in the hippocampal subregions of both stressed and nonstressed rats. Importantly, chronic stress decreased the fraction of phosphorylated SynI in all layers of the medial prefrontal cortex as well as selectively in the outer and middle molecular layers of the hippocampal dentate gyrus. These stress effects were at least partially abolished by agomelatine. Altogether, our data show that chronic stress and agomelatine treatment induce region-specific changes in SynI expression and its phosphorylation. Moreover, agomelatine partially counteracts the stress effects on SynI, suggesting a modulation of synaptic function by this antidepressant.

Memory facilitating effects of agomelatine in the novel object recognition memory paradigm in the rat

The aim of the present study was to evaluate the effects of agomelatine, an antidepressant with melatonergic agonist and 5-HT(2C) antagonist properties, in the rat novel object recognition (NOR) task, a model of short-term episodic memory. To assess the potential involvement of its chronobiotic activity, single intraperitoneal administration of agomelatine and NOR testing were performed either in the evening or in the morning. In both conditions, using a 24h retention interval, vehicle-treated rats did not discriminate between the novel and the familiar object (recognition index was not different from chance performance) while object memory performance of rats treated with agomelatine either in the evening (10 and 40mg/kg) or in the morning (2.5, 10, and 40mg/kg) was significantly improved. Moreover, the selective 5-HT(2C) antagonist SB 242,084 (0.63, 2.5, and 10mg/kg) and melatonin (2.5, 10, and 40mg/kg) displayed also memory facilitating effects in both administration conditions. Finally, thioperamide used as positive reference compound to validate the experimental conditions, demonstrated a memory facilitating effect. In conclusion, agomelatine was shown to possess memory facilitating effects in the rat NOR task and both melatonergic agonist and 5-HT(2C) antagonist properties could be involved in these effects.

Agomelatine reverses the decrease in hippocampal cell survival induced by chronic mild stress

The antidepressant agomelatine is a MT(1)/MT(2) receptor agonist and 5-HT(2C) antagonist. Its antidepressant activity is proposed to result from the synergy between these sets of receptors. Agomelatine-induced changes in the brain have been reported under basal conditions. Yet, little is known about its effects in the brain exposed to chronic stress as a risk factor for major depressive disorder. Recently, we described agomelatine-induced changes on neuronal activity and adult neurogenesis in the hippocampus of rats subjected to chronic footshock stress. In order to better characterize the actions of agomelatine in the stress-compromised brain, here we investigated its effects on hippocampal neurogenesis in the chronic mild stress (CMS) model. Adult male rats were subjected to various mild stressors for 5 weeks, and treated with agomelatine during the last 3 weeks of the stress period. The sucrose preference test was performed weekly to measure anhedonia, and the marble burying test was carried out at the end of the experiment to assess anxiety-like behavior. In our model, the CMS paradigm did not change sucrose preference; however, it increased marble burying behavior, indicating enhanced anxiety. Interestingly, this stress model differentially affected distinct stages of the neurogenesis process. Whereas CMS did not influence the rate of hippocampal cell proliferation, it significantly decreased the newborn cell survival and doublecortin expression in the dentate gyrus. Importantly, treatment with agomelatine completely normalized stress-affected cell survival and partly reversed reduced doublecortin expression. Taken together, these data show that agomelatine has beneficial effects on hippocampal neurogenesis in the CMS paradigm.

Severe early life stress hampers spatial learning and neurogenesis, but improves hippocampal synaptic plasticity and emotional learning under high-stress conditions in adulthood

Early life stress increases the risk for developing stress-related pathologies later in life. Recent studies in rats suggest that mild early life stress, rather than being overall unfavorable, may program the hippocampus such that it is optimally adapted to a stressful context later in life. Here, we tested whether this principle of "adaptive programming" also holds under severely adverse early life conditions, i.e., 24 h of maternal deprivation (MD), a model for maternal neglect. In young adult male rats subjected to MD on postnatal day 3, we observed reduced levels of adult hippocampal neurogenesis as measured by cell proliferation, cell survival, and neuronal differentiation. Also, mature dentate granule cells showed a change in their dendritic morphology that was most noticeable in the proximal part of the dendritic tree. Lasting structural changes due to MD were paralleled by impaired water maze acquisition but did not affect long-term potentiation in the dentate gyrus. Importantly, in the presence of high levels of the stress hormone corticosterone, even long-term potentiation in the dentate gyrus of MD animals was facilitated. In addition to this, contextual learning in a high-stress environment was enhanced in MD rats. These morphological, electrophysiological, and behavioral observations show that even a severely adverse early life environment does not evolve into overall impaired hippocampal functionality later in life. Rather, adversity early in life can prepare the organism to perform optimally under conditions associated with high corticosteroid levels in adulthood.

Hippocampal adult neurogenesis is enhanced by chronic eszopiclone treatment in rats

The adult hippocampal dentate gyrus (DG) exhibits cell proliferation and neurogenesis throughout life. We examined the effects of daily administration of eszopiclone (Esz), a commonly used hypnotic drug and gamma-aminobutyric acid (GABA) agonist, compared with vehicle, on DG cell proliferation and neurogenesis, and on sleep-wake patterns. Esz was administered during the usual sleep period of rats, to mimic typical use in humans. Esz treatment for 7 days did not affect the rate of cell proliferation, as measured by 5-bromo-2'-deoxyuridine (BrdU) immunostaining. However, twice-daily Esz administration for 2 weeks increased survival of newborn cells by 46%. Most surviving cells exhibited a neuronal phenotype, identified as BrdU-neuronal nuclei (NeuN) double-labeling. NeuN is a marker of neurons. Non-rapid eye movement sleep was increased on day 1, but not on days 7 or 14 of Esz administration. Delta electroencephalogram activity was increased on days 1 and 7 of treatment, but not on day 14. There is evidence that enhancement of DG neurogenesis is a critical component of the effects of antidepressant treatments of major depressive disorder (MDD). Adult-born DG cells are responsive to GABAergic stimulation, which promotes cell maturation. The present study suggests that Esz, presumably acting as a GABA agonist, has pro-neurogenic effects in the adult DG. This result is consistent with evidence that Esz enhances the antidepressant treatment response of patients with MDD with insomnia.

The novel antidepressant agomelatine normalizes hippocampal neuronal activity and promotes neurogenesis in chronically stressed rats

Agomelatine is a novel antidepressant which acts as a melatonergic (MT1/MT2) receptor agonist and serotonergic (5-HT2C) receptor antagonist. The antidepressant properties of agomelatine have been demonstrated in animal models as well as in clinical studies. Several preclinical studies reported agomelatine-induced effects on brain plasticity, mainly under basal conditions in healthy animals. Yet, it is important to unravel agomelatine-mediated changes in the brain affected by psychopathology or exposed to conditions that might predispose to mood disorders. Since stress is implicated in the etiology of depression, it is valid to investigate antidepressant-induced effects in animals subjected to chronic stress. In this context, we sought to determine changes in the brain after agomelatine treatment in chronically stressed rats. Adult male rats were subjected to footshock stress and agomelatine treatment for 21 consecutive days. Rats exposed to footshock showed a robust increase in adrenocorticotropic hormone (ACTH) and corticosterone. Chronic agomelatine treatment did not markedly influence this HPA-axis response. Whereas chronic exposure to daily footshock stress reduced c-Fos expression in the hippocampal dentate gyrus, agomelatine treatment reversed this effect and normalized neuronal activity to basal levels. Moreover, chronic agomelatine administration was associated with enhanced hippocampal cell proliferation and survival in stressed but not in control rats. Furthermore, agomelatine reversed the stress-induced decrease in doublecortin expression in the dentate gyrus. Taken together, these data show a beneficial action of agomelatine in the stress-compromised brain, where it restores stress-affected hippocampal neuronal activity and promotes adult hippocampal neurogenesis.

Marcadores Biológicos da Depressão:

Introdução. A depressão é um dos mais prevalentes transtornos psi­quiátricos e tem sido associada a alterações nas vias de sinalização que regulam a neuroplasticidade e a sobrevivência celular. Objetivo. O objetivo deste estudo foi revisar a relação entre neurotrofinas e mo­delos experimentais de depressão, bem como a forma em que os me­dicamentos antidepressivos podem estar atuando na estimulação da produção dos fatores neurotróficos. Método. Uma revisão de litera­tura através de pesquisa nas bases de dados MEDLINE e SCIELO, utilizando a combinação dos seguintes descritores: modelo animal de depressão, fatores neurotróficos e BDNF, e suas respectivas traduções no idioma inglês. Resultados. Foram apresentados dados que revela­ram que o fator neurotrófico derivado do cérebro apresenta um papel crucial na regulação da atividade sináptica e plasticidade, relacionando a depressão maior com danos nas vias de sinalização celular. Entre­tanto, para a transcrição desta neurotrofina é necessário a ativação de mecanismos de sinalização, incluindo cálcio, CREB, MEK, MeCP2, CaMKII e hormônios. Conclusão. Após esses argumentos foi possível rever o conceito sobre a fisiopatologia e os mecanismos envolvidos para o desenvolvimento da doença e com isso sugerir possíveis estra­tégias a fim de desenvolver novos fármacos para melhorar a eficácia do tratamento.