New views on antidepressant action

The Role of Natural Products in Treatment of Depressive Disorder

Depressive disorder is one of the most common psychiatric syndromes that, if left untreated, can cause many disturbances in a person's life. Numerous factors are involved in depression, including inflammation, brain-derived neurotrophic factor (BDNF), GABAergic system, hypothalamic- pituitary-adrenal (HPA) Axis, monoamine neurotransmitters (serotonin (5-HT), noradrenaline, and dopamine). Common treatments for depression are selective serotonin reuptake inhibitors, tricyclic antidepressants, and monoamine oxidase inhibitors, but these drugs have several side effects such as anxiety, diarrhea, constipation, weight loss, and sexual dysfunctions. These agents only reduce the symptoms and temporarily reduce the rate of cognitive impairment associated with depression. As a result, extensive research has recently been conducted on the potential use of antidepressant and sedative herbs. According to the available data, herbs used in traditional medicine can be significantly effective in reducing depression, depressive symptoms and improving patients' performance. The present study provides a summary of biomarkers and therapeutic goals of depression and shows that natural products such as saffron or genipin have antidepressant effects. Some of the useful natural products and their mechanisms were evaluated. Data on various herbs and natural isolated compounds reported to prevent and reduce depressive symptoms is also discussed.

The rise and fall of MRI studies in major depressive disorder

Structural and functional brain alterations are common in patients with major depressive disorder (MDD). In this review, we assessed the recent literature (1995-2018) on the structural and functional magnetic resonance imaging (MRI) studies of MDD. Despite the growing number of MRI studies on MDD, reverse inference is not possible as MRI scans cannot be used to aid in the diagnosis or treatment planning of patients with MDD. Hence, researchers must develop "bridges" to overcome the reverse inference fallacy in order to build effective tools for MDD diagnostics. From our findings, we proposed that the "bridges" may be built using multidisciplinary technologies, such as artificial intelligence, multimodality imaging, and nanotheranostics, allowing for the further study of MDD at the biological level. In return, the "bridges" will aid in the development of future diagnostics for MDD and other mental disorders.

Time Course of Changes in Peripheral Blood Gene Expression During Medication Treatment for Major Depressive Disorder

Changes in gene expression (GE) during antidepressant treatment may increase understanding of the action of antidepressant medications and serve as biomarkers of efficacy. GE changes in peripheral blood are desirable because they can be assessed easily on multiple occasions during treatment. We report here on GE changes in 68 individuals who were treated for 8 weeks with either escitalopram alone, or escitalopram followed by bupropion. GE changes were assessed after 1, 2, and 8 weeks of treatment, with significant changes observed in 156, 121, and 585 peripheral blood gene transcripts, respectively. Thirty-one transcript changes were shared between the 1- and 8-week time points (seven upregulated, 24 downregulated). Differences were detected between the escitalopram- and bupropion-treated subjects, although there was no significant association between GE changes and clinical outcome. A subset of 18 genes overlapped with those previously identified as differentially expressed in subjects with MDD compared with healthy control subjects. There was statistically significant overlap between genes differentially expressed in the current and previous studies, with 10 genes overlapping in at least two previous studies. There was no enrichment for genes overexpressed in nervous system cell types, but there was a trend toward enrichment for genes in the WNT/β-catenin pathway in the anterior thalamus; three genes in this pathway showed differential expression in the present and in three previous studies. Our dataset and other similar studies will provide an important source of information about potential biomarkers of recovery and for potential dysregulation of GE in MDD.

Genistein Improves the Major Depression through Suppressing the Expression of miR-221/222 by Targeting Connexin 43

OBJECTIVE

Recent studies have indicated the possibility that genistein may improve depression via regulating the expression of miR221/222. This study is to explore whether genistein could improve depression by altering miR-221/222 levels and investigate the possible mechanisms involved in the improvement effect of genistein.

METHODS

The animal model of depression was established through unpredictable chronic mild stress. Nest building test and splash test were adapted to evaluate the effects of genistein on depressive symptoms in mice. qRT-PCR and western blot analysis were used to detect the expression of miR-221/222 and connexin 43 (Cx43) in the prefrontal cortex of the mice. In vitro, U87-MG astrocytes were treated with genistein and the expression of miR-221/222 and Cx43 was measured. The dual-luciferase reporter assay was used to verify whether Cx43 was a direct target of miR-221/222.

RESULTS

The behavioral tests showed that genistein could significantly reduce depression symptoms of mice, and this remission was not affected by gender. Genistein in vivo and in vitro could reduce increased levels of miR-221 and miR-222 in the prefrontal cortex of depressed mice, while upregulate Cx43 expression. Dual-luciferase reporter assay suggested Cx43 was directly regulated by miR-221/222 in astrocytes.

CONCLUSION

Genistein can play its antidepressant effect through down-regulating miR-221/222 by targeting Cx43.

Recent advances in predicting responses to antidepressant treatment

Major depressive disorder is one of the leading causes of disability in the world since depression is highly frequent and causes a strong burden. In order to reduce the duration of depressive episodes, clinicians would need to choose the most effective therapy for each individual right away. A prerequisite for this would be to have biomarkers at hand that would predict which individual would benefit from which kind of therapy (for example, pharmacotherapy or psychotherapy) or even from which kind of antidepressant class. In the past, neuroimaging, electroencephalogram, genetic, proteomic, and inflammation markers have been under investigation for their utility to predict targeted therapies. The present overview demonstrates recent advances in all of these different methodological areas and concludes that these approaches are promising but also that the aim to have such a marker available has not yet been reached. For example, the integration of markers from different systems needs to be achieved. With ongoing advances in the accuracy of sensing techniques and improvement of modelling approaches, this challenge might be achievable.

Theoretical Approaches to Enhancing Motivation for Adherence to Antidepressant Medications

PROBLEM

Adherence to antidepressants is a major challenge in our health care system, with a high percentage of patients discontinuing their medications within six months.

AIMS

The purpose of this position paper is to discuss theoretical frameworks that address the psychological beliefs, benefits and barriers and feelings of autonomy that affect a person's willingness and motivation to take anti-depressant medications within a therapeutic relationship with a nurse practitioner.

METHODS

Three theoretical frameworks were selected to highlight particular perspectives relevant to enhancing patient motivation for medication adherence. The Self-Regulation Model, Health Belief Model, and Self-Determination Theory combined with motivational interviewing all offer guidance on strategies for improving adherence to antidepressants.

CONCLUSIONS

The Self-Regulation Model underscores the importance of illness representations that prompt considering patient perceptions of depression that affect adherence. The Health Belief Model focuses on cost-benefit considerations that affect patient's adherence, along with perceived control. Finally, Self-Determination Theory combined with motivational interviewing offers strategies that enhance autonomy and optimize collaboration and motivation for adherence.

RELEVANCE FOR CLINICAL PRACTICE

These three theoretical models are applied to a vignette for a patient who is having difficulty with adherence to antidepressant medication.

Psychological therapies versus pharmacological interventions for panic disorder with or without agoraphobia in adults

BACKGROUND

Panic disorder is common and deleterious to mental well-being. Psychological therapies and pharmacological interventions are both used as treatments for panic disorder with and without agoraphobia. However, there are no up-to-date reviews on the comparative efficacy and acceptability of the two treatment modalities, and such a review is necessary for improved treatment planning for this disorder.

OBJECTIVES

To assess the efficacy and acceptability of psychological therapies versus pharmacological interventions for panic disorder, with or without agoraphobia, in adults.

SEARCH METHODS

We searched the Cochrane Common Mental Disorders Group Specialised Register on 11 September 2015. This register contains reports of relevant randomised controlled trials from the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (1950 to present), Embase (1974 to present), and PsycINFO (1967 to present). We cross-checked reference lists of relevant papers and systematic reviews. We did not apply any restrictions on date, language, or publication status.

SELECTION CRITERIA

We included all randomised controlled trials comparing psychological therapies with pharmacological interventions for panic disorder with or without agoraphobia as diagnosed by operationalised criteria in adults.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted data and resolved any disagreements in consultation with a third review author. For dichotomous data, we calculated risk ratios (RR) with 95% confidence intervals (CI). We analysed continuous data using standardised mean differences (with 95% CI). We used the random-effects model throughout.

MAIN RESULTS

We included 16 studies with a total of 966 participants in the present review. Eight of the studies were conducted in Europe, four in the USA, two in the Middle East, and one in Southeast Asia.None of the studies reported long-term remission/response (long term being six months or longer from treatment commencement).There was no evidence of a difference between psychological therapies and selective serotonin reuptake inhibitors (SSRIs) in terms of short-term remission (RR 0.85, 95% CI 0.62 to 1.17; 6 studies; 334 participants) or short-term response (RR 0.97, 95% CI 0.51 to 1.86; 5 studies; 277 participants) (very low-quality evidence), and no evidence of a difference between psychological therapies and SSRIs in treatment acceptability as measured using dropouts for any reason (RR 1.33, 95% CI 0.80 to 2.22; 6 studies; 334 participants; low-quality evidence).There was no evidence of a difference between psychological therapies and tricyclic antidepressants in terms of short-term remission (RR 0.82, 95% CI 0.62 to 1.09; 3 studies; 229 participants), short-term response (RR 0.75, 95% CI 0.51 to 1.10; 4 studies; 270 participants), or dropouts for any reason (RR 0.83, 95% CI 0.53 to 1.30; 5 studies; 430 participants) (low-quality evidence).There was no evidence of a difference between psychological therapies and other antidepressants in terms of short-term remission (RR 0.90, 95% CI 0.48 to 1.67; 3 studies; 135 participants; very low-quality evidence) and evidence that psychological therapies did not significantly increase or decrease the short-term response over other antidepressants (RR 0.96, 95% CI 0.67 to 1.37; 3 studies; 128 participants) or dropouts for any reason (RR 1.55, 95% CI 0.91 to 2.65; 3 studies; 180 participants) (low-quality evidence).There was no evidence of a difference between psychological therapies and benzodiazepines in terms of short-term remission (RR 1.08, 95% CI 0.70 to 1.65; 3 studies; 95 participants), short-term response (RR 1.58, 95% CI 0.70 to 3.58; 2 studies; 69 participants), or dropouts for any reason (RR 1.12, 95% CI 0.54 to 2.36; 3 studies; 116 participants) (very low-quality evidence).There was no evidence of a difference between psychological therapies and either antidepressant alone or antidepressants plus benzodiazepines in terms of short-term remission (RR 0.86, 95% CI 0.71 to 1.05; 11 studies; 663 participants) and short-term response (RR 0.95, 95% CI 0.76 to 1.18; 12 studies; 800 participants) (low-quality evidence), and there was no evidence of a difference between psychological therapies and either antidepressants alone or antidepressants plus benzodiazepines in terms of treatment acceptability as measured by dropouts for any reason (RR 1.08, 95% CI 0.77 to 1.51; 13 studies; 909 participants; very low-quality evidence). The risk of selection bias and reporting bias was largely unclear. Preplanned subgroup and sensitivity analyses limited to trials with longer-term, quality-controlled, or individual psychological therapies suggested that antidepressants might be more effective than psychological therapies for some outcomes.There were no data to contribute to a comparison between psychological therapies and serotonin-norepinephrine reuptake inhibitors (SNRIs) and subsequent adverse effects.

AUTHORS' CONCLUSIONS

The evidence in this review was often imprecise. The superiority of either therapy over the other is uncertain due to the low and very low quality of the evidence with regard to short-term efficacy and treatment acceptability, and no data were available regarding adverse effects.The sensitivity analysis and investigation of the sources of heterogeneity indicated three possible influential factors: quality control of psychological therapies, the length of intervention, and the individual modality of psychological therapies.Future studies should examine the long-term effects after intervention or treatment continuation and should provide information on risk of bias, especially with regard to selection and reporting biases.

Predisposition to treatment response in major depressive episode: A peripheral blood gene coexpression network analysis

Antidepressant efficacy is insufficient, unpredictable and poorly understood in major depressive episode (MDE). Gene expression studies allow for the identification of significantly dysregulated genes but can limit the exploration of biological pathways. In the present study, we proposed a gene coexpression analysis to investigate biological pathways associated with treatment response predisposition and their regulation by microRNAs (miRNAs) in peripheral blood samples of MDE and healthy control subjects. We used a discovery cohort that included 34 MDE patients that were given 12-week treatment with citalopram and 33 healthy controls. Two replication cohorts with similar design were also analyzed. Expression-based gene network was built to define clusters of highly correlated sets of genes, called modules. Association between each module's first principal component of the expression data and clinical improvement was tested in the three cohorts. We conducted gene ontology analysis and miRNA prediction based on the module gene list. Nine of the 59 modules from the gene coexpression network were associated with clinical improvement. The association was partially replicated in other cohorts. Gene ontology analysis demonstrated that 4 modules were associated with cytokine production, acute inflammatory response or IL-8 functions. Finally, we found 414 miRNAs that may regulate one or several modules associated with clinical improvement. By contrast, only 12 miRNAs were predicted to specifically regulate modules unrelated to clinical improvement. Our gene coexpression analysis underlines the importance of inflammation-related pathways and the involvement of a large miRNA program as biological processes predisposing associated with antidepressant response.

Rhythms and blues: modulation of oscillatory synchrony and the mechanism of action of antidepressant treatments

Treatments for major depressive disorder (MDD) act at different hierarchical levels of biological complexity, ranging from the individual synapse to the brain as a whole. Theories of antidepressant medication action traditionally have focused on the level of cell-to-cell interaction and synaptic neurotransmission. However, recent evidence suggests that modulation of synchronized electrical activity in neuronal networks is a common effect of antidepressant treatments, including not only medications, but also neuromodulatory treatments such as repetitive transcranial magnetic stimulation. Synchronization of oscillatory network activity in particular frequency bands has been proposed to underlie neurodevelopmental and learning processes, and also may be important in the mechanism of action of antidepressant treatments. Here, we review current research on the relationship between neuroplasticity and oscillatory synchrony, which suggests that oscillatory synchrony may help mediate neuroplastic changes related to neurodevelopment, learning, and memory, as well as medication and neuromodulatory treatment for MDD. We hypothesize that medication and neuromodulation treatments may have related effects on the rate and pattern of neuronal firing, and that these effects underlie antidepressant efficacy. Elucidating the mechanisms through which oscillatory synchrony may be related to neuroplasticity could lead to enhanced treatment strategies for MDD.

Valeriana officinalis root extract suppresses physical stress by electric shock and psychological stress by nociceptive stimulation-evoked responses by decreasing the ratio of monoamine neurotransmitters to their metabolites

Background

In this study, we investigate the effects of valerian root extracts (VE) on physical and psychological stress responses by utilizing a communication box.

Methods

Eight-week-old ICR mice received oral administration of VE (100 mg/kg/0.5 ml) or equal volume of distilled water in every day for 3 weeks prior to being subjected to physical or psychological stress for 3 days, which are induced by communication box developed for physical electric shock and psychological stress by nociceptive stimulation-evoked responses. The stress condition was assessed by forced swimming test and serum corticosterone levels. In addition, norepinephrine (NE), serotonin (5-HT), and their metabolites such as 3-methoxy-4-hydroxyphenylethyleneglycol sulfate (MHPG-SO₄) and 5-hydroxyindoleacetic acid (5-HIAA) were measured in the hippocampus and amygdala at 1 h after final stress condition, respectively.

Results

Immobility time and corticosterone levels were significantly increased in both the physical and psychological stress groups compared to the control group. The administration of VE significantly reduced these parameters in both the physical and psychological stress groups. In addition, compared to the control group, physical and psychological stress groups showed significantly increased levels of MHPG-SO₄ and 5-HIAA in the hippocampus and amygdala, respectively. The administration of VE significantly suppressed the increase of MHPG-SO₄ and 5-HIAA in the two stress groups.

Conclusion

These results suggest that VE can suppress physical and psychological stress responses by modulating the changes in 5-HT and NE turnover in the hippocampus and amygdala.

Genes involved in neuroplasticity and stressful life events act on the short-term response to antidepressant treatment: a complex interplay between genetics and environment

OBJECTIVE

During the last few years, an increasing number of studies have focused on the association between neuroplasticity and affective disorders. The aim of the study is to evaluate the interactive effect of stressful life events (SLEs) and genes involved in neuroplasticity (BDNF and ST8SIA) on the short-term response to antidepressant treatment.

METHODS

A total of 114 patients affected by mood or anxiety disorders under antidepressant treatment were enrolled in the study. We evaluated the interactive effects of three BDNF single-nucleotide polymorphisms (SNPs) and five ST8SIA SNPs and SLEs at different time points (childhood SLEs, SLEs at illness onset, and SLEs reported over the last preceding treatment) over 1-month of antidepressant treatment.

RESULTS

Carriers of some genetic variants in both BDNF and ST8SIA had a slower response to antidepressants if non-exposed to the onset SLEs, whereas they had a similar trend compared with the carriers of the opposite variant if exposed (allelic analysis: BDNF p = 0.00003, p = 0.00609; ST8SIA p = 0.04, p = 0.033). The BDNF haplotype analysis confirmed this trend (p = 0.00016).

CONCLUSIONS

Though our results are limited by the small sample size, variants in BDNF and ST8SIA may slow down the early response to antidepressants in subjects non-exposed to stressors at the illness onset, with a remarkable gene-environment interaction.

Effects of chronic fluoxetine treatment on neurogenesis and tryptophan hydroxylase expression in adolescent and adult rats

The antidepressant drug fluoxetine (Prozac) has been increasingly prescribed to children and adolescents with depressive disorders despite a lack of thorough understanding of its therapeutic effects in the paediatric population and of its putative neurodevelopmental effects. Within the framework of PRIOMEDCHILD ERA-NET, we investigated; a) effects of chronic fluoxetine treatment on adult hippocampal neurogenesis, a structural readout relevant for antidepressant action and hippocampal development; b) effects on tryptophan hydroxylase (TPH) expression, a measure of serotonin synthesis; c) whether treatment effects during adolescence differed from treatment at an adult age, and d) whether they were subregion-specific. Stereological quantification of the number of proliferating (Ki-67+) cells and of the number of young migratory neurons (doublecortin+), revealed a significant age-by-treatment interaction effect, indicating that fluoxetine affects both proliferation and neurogenesis in adolescent-treated rats differently than it does in adult-treated rats. In terms of subregional differences, fluoxetine enhanced proliferation mainly in the dorsal parts of the hippocampus, and neurogenesis in both the suprapyramidal and infrapyramidal blades of the dentate gyrus in adolescent-treated rats, while no such differences were seen in adult-treated rats. Fluoxetine exerted similar age-by-treatment interaction effects on TPH cells mainly in the ventral portion of the dorsal raphe nucleus. We conclude that fluoxetine exerts divergent effects on structural plasticity and serotonin synthesis in adolescent versus adult-treated rats. These preliminary data indicate a differential sensitivity of the adolescent brain to this drug and thus warrant further research into their behavioural and translational aspects. Together with recent related findings, they further call for caution in prescribing these drugs to the adolescent population.

When less is more--microRNAs and psychiatric disorders

OBJECTIVE

MicroRNAs are small non-coding RNA molecules that regulate gene expression, including genes involved in neuronal function and plasticity that have relevance for brain function and mental health. We therefore performed a systematic review of miRNAs in general adult psychiatric disorders.

METHOD

Systematic searches in PubMed/MEDLINE and Web of Science were conducted to identify published clinical articles on microRNAs in general adult psychiatric disorders. We also reviewed references from included articles.

RESULTS

There is mounting evidence of microRNAs' regulatory roles in a number of central nervous system processes, including neurogenesis and synaptic plasticity. The majority of clinical studies of microRNAs in psychiatric disorders are in schizophrenia, where a number of specific microRNAs have been identified in separate studies. There is some evidence of marked downregulation of some microRNAs in affective disorders. Treatment with antidepressants appears to upregulate microRNA levels. There is currently little evidence from human studies in anxiety, addiction or other psychiatric disorders.

CONCLUSION

MicroRNA research in psychiatry is currently in a nascent period, but represents an emerging and exciting area, with the potential to clarify molecular mechanisms of disease and identify novel biomarkers and therapeutic agents.

Peripheral biomarkers in animal models of major depressive disorder

Investigations of preclinical biomarkers for major depressive disorder (MDD) encompass the quantification of proteins, peptides, mRNAs, or small molecules in blood or urine of animal models. Most studies aim at characterising the animal model by including the assessment of analytes or hormones affected in depressive patients. The ultimate objective is to validate the model to better understand the neurobiological basis of MDD. Stress hormones or inflammation-related analytes associated with MDD are frequently measured. In contrast, other investigators evaluate peripheral analytes in preclinical models to translate the results in clinical settings afterwards. Large-scale, hypothesis-free studies are performed in MDD models to identify candidate biomarkers. Other studies wish to propose new targets for drug discovery. Animal models endowed with predictive validity are investigated, and the assessment of peripheral analytes, such as stress hormones or immune molecules, is comprised to increase the confidence in the target. Finally, since the mechanism of action of antidepressants is incompletely understood, studies investigating molecular alterations associated with antidepressant treatment may include peripheral analyte levels. In conclusion, preclinical biomarker studies aid the identification of new candidate analytes to be tested in clinical trials. They also increase our understanding of MDD pathophysiology and help to identify new pharmacological targets.

Neurodegeneration, β-amyloid and mood disorders: state of the art and future perspectives

OBJECTIVE

Depression may increase the risk of developing Alzheimer's disease (AD). Recent studies have shown modifications in blood beta-amyloid (Aβ) levels in depressed patients. This literature review examines the potential relationship between Aβ-mediated neurotoxicity and pathophysiology of mood disorders.

DESIGN

We conducted a review of the literature focusing on recent studies reporting alterations of plasma and serum Aβ peptides levels in patients suffering from mood disorders.

RESULTS

Different data suggest that patients with mood disorders are at great risk of developing cognitive impairment and dementia. In particular, low plasma levels of Aβ42 peptide and a high Aβ40/Aβ42 ratio have been found in depressed patients. In addition, changes in Aβ protein levels in patients with mood disorders have been associated with the severity of cognitive impairment and correlated positively with the number of episodes and severity of illness course.

CONCLUSIONS

Given the intriguing association between change in plasma level of Aβ, depression and cognitive impairment, future work should focus on the relationship between Aβ peripheral level(s), biomarkers of neurodegeneration and development of dementia in patients affected by mood disorders.

Anxiety-associated alternative polyadenylation of the serotonin transporter mRNA confers translational regulation by hnRNPK

The serotonin transporter (SERT) is a major regulator of serotonergic neurotransmission and anxiety-related behaviors. SERT is expressed in two alternative polyadenylation forms that differ by an evolutionarily conserved element in the 3' untranslated region of its mRNA. Expression of SERT mRNA containing the distal polyadenylation element is associated with decreased anxiety-related behaviors in mice and humans, suggesting that this element has behaviorally relevant modulatory effects on SERT expression. We have identified heterogeneous nuclear ribonucleoprotein K (hnRNPK), a protein known to integrate multiple signal transduction pathways with gene expression, as a SERT distal polyadenylation element binding protein. This interaction is functionally meaningful because genetic manipulation of hnRNPK alters expression of the SERT protein. Furthermore, the trophic factor S100β induces Src-family kinase-mediated tyrosine phosphorylation of hnRNPK and increased SERT expression. These results identify a previously unknown mechanism of regulated SERT expression and provide a putative mechanism by which the SERT distal polyadenylation element modulates anxiety-related behaviors.

Psychiatric drugs bind to classical targets within early exocytotic pathways: therapeutic effects

The classical targets for antipsychotic and antidepressant drugs are G protein-coupled receptors and neurotransmitter transporters, respectively. Full therapeutic actions of these drugs require several weeks. We show how therapeutic effects may eventually accrue after existing therapeutic ligands bind to these classical targets, not on the plasma membrane but rather within endoplasmic reticulum (ER) and cis-Golgi. Consequences of such binding may include pharmacological chaperoning: the nascent drug targets are stabilized against degradation and can therefore exit the ER more readily. Another effect may be matchmaking: heterodimers and homodimers of the target form and can more readily exit the ER. Summarizing recent data for nicotinic receptors, we explain how such effects could lead to reduced ER stress and to a decreased unfolded protein response, including changes in gene activation and protein synthesis. In effects not directly related to cellular stress, escorting would allow increased ER exit and trafficking of known associated proteins, as well as other proteins such as growth factors and their receptors, producing both cell-autonomous and non-cell-autonomous effects. Axonal transport of relevant proteins may underlie the several weeks required for full therapy. In contrast, the antidepressant effects of ketamine and other N-methyl-D-aspartate receptor ligands, which occur within <2 hours, could arise from dendritically localized intracellular binding, followed by chaperoning, matchmaking, escorting, and reduced ER stress. Thus, the effects of intracellular binding extend beyond proteostasis of the targets themselves and involve pathways distinct from ion channel and G protein activation. We propose experimental tests and note pathophysiological correlates.

Understanding migraine through the lens of maladaptive stress responses: a model disease of allostatic load

The brain and body respond to potential and actual stressful events by activating hormonal and neural mediators and modifying behaviors to adapt. Such responses help maintain physiological stability ("allostasis"). When behavioral or physiological stressors are frequent and/or severe, allostatic responses can become dysregulated and maladaptive ("allostatic load"). Allostatic load may alter brain networks both functionally and structurally. As a result, the brain's responses to continued/subsequent stressors are abnormal, and behavior and systemic physiology are altered in ways that can, in a vicious cycle, lead to further allostatic load. Migraine patients are continually exposed to such stressors, resulting in changes to central and peripheral physiology and function. Here we review how changes in brain states that occur as a result of repeated migraines may be explained by a maladaptive feedforward allostatic cascade model and how understanding migraine within the context of allostatic load model suggests alternative treatments for this often-debilitating disease.

Little things on which happiness depends: microRNAs as novel therapeutic targets for the treatment of anxiety and depression

Anxiety and depression are devastating mental illnesses that are a significant public health concern. Selective serotonin-reuptake inhibitors are the first-line treatment strategy for these disorders, which despite being a significant advantage over older treatments, are hampered by a limited efficacy in a significant subset of patients, delayed onset of action and side effects that affect compliance. Thus, there is much impetus to develop novel therapeutic strategies. However, this goal can only be rationally realised with a better understanding of the molecular pathophysiology of these disorders. MicroRNAs (miRNAs) are a newly discovered class of gene-expression regulators that may represent a novel class of therapeutic targets to treat a variety of disorders including psychiatric diseases. miRNAs are heavily involved in regulating many physiological processes including those fundamental to the functioning of the central nervous system. Evidence collected to date has already demonstrated that miRNA-expression levels are altered in patients suffering from depression and anxiety and in pre-clinical models of psychological stress. Furthermore, increasing evidence suggests that psychoactive agents including antidepressants and mood stabilisers utilise miRNAs as downstream effectors. Altering miRNA levels has been shown to alter behaviour in a therapeutically desirable manner in pre-clinical models. This review aims to outline the evidence collected to date demonstrating miRNAs role in anxiety and depression, the potential advantages of targeting these small RNA molecules as well as some of the hurdles that will have to be overcome to fully exploit their therapeutic potential.

Raphe-mediated signals control the hippocampal response to SRI antidepressants via miR-16

Serotonin reuptake inhibitor (SRI) antidepressants such as fluoxetine (Prozac), promote hippocampal neurogenesis. They also increase the levels of the bcl-2 protein, whose overexpression in transgenic mice enhances adult hippocampal neurogenesis. However, the mechanisms underlying SRI-mediated neurogenesis are unclear. Recently, we identified the microRNA miR-16 as an important effector of SRI antidepressant action in serotonergic raphe and noradrenergic locus coeruleus (LC). We show here that miR-16 mediates adult neurogenesis in the mouse hippocampus. Fluoxetine, acting on serotonergic raphe neurons, decreases the amount of miR-16 in the hippocampus, which in turn increases the levels of the serotonin transporter (SERT), the target of SRI, and that of bcl-2 and the number of cells positive for Doublecortin, a marker of neuronal maturation. Neutralization of miR-16 in the hippocampus further exerts an antidepressant-like effect in behavioral tests. The fluoxetine-induced hippocampal response is relayed, in part, by the neurotrophic factor S100β, secreted by raphe and acting via the LC. Fluoxetine-exposed serotonergic neurons also secrete brain-derived neurotrophic factor, Wnt2 and 15-Deoxy-delta12,14-prostaglandin J2. These molecules are unable to mimic on their own the action of fluoxetine and we show that they act synergistically to regulate miR-16 at the hippocampus. Of note, these signaling molecules are increased in the cerebrospinal fluid of depressed patients upon fluoxetine treatment. Thus, our results demonstrate that miR-16 mediates the action of fluoxetine by acting as a micromanager of hippocampal neurogenesis. They further clarify the signals and the pathways involved in the hippocampal response to fluoxetine, which may help refine therapeutic strategies to alleviate depressive disorders.