St John's wort and imipramine-induced gene expression profiles identify cellular functions relevant to antidepressant action and novel pharmacogenetic candidates for the phenotype of antidepressant treatment response

Inhalation Aromatherapy via Brain-Targeted Nasal Delivery: Natural Volatiles or Essential Oils on Mood Disorders

Mood disorders, also often referred to as affective disorders, are a group of psychiatric illnesses that severely impact mood and its related functions. The high medical expenditures have placed a significant financial burden on patients and their families. Aromatherapy is an alternative and complementary treatment that utilizes essential oils (EOs) or volatile oils (VOs) to achieve major therapeutic goals. In general, EOs are volatile chemicals that enter the body primarily through skin absorption and/or nasal inhalation. In addition, they can work through oral administration. Inhalation aromatherapy has shown unique advantages for treating mood disorders, especially depression, anxiety and mental disorders such as sleep disorder, which have been validated over the last decade through clinical and animal studies. Accumulating evidence has shown that EOs or VOs can bypass the blood-brain barrier to target brain tissue through the nasal-brain pathway. Subsequently, they act on the cerebral cortex, thalamus, and limbic system in the brain to improve symptoms of anxiety, depression and improve sleep quality. Here, we review the natural aromatic plants’ volatiles or essential oils used commonly as adjuncts to manage mood disorders and illustrate the mechanisms of inhalation aromatherapy, and mainly summarized the application of transnasal inhalation aromatherapy in depression, anxiety, and sleep disorders. We conclude that aromatherapy does not cause side-effects, which is vastly different from commonly used psychotropic drugs. Inhalation aromatherapy via brain-targeted nasal delivery offers potentially efficacious treatment for mental disorders and merits further study.

The Use of Larval Zebrafish (Danio rerio) Model for Identifying New Anxiolytic Drugs from Herbal Medicine

Anxiety is a widespread psychiatric disorder. The search for a cure is still continuing since many of the synthetic drugs were inefficient in completely treating anxiety, yet caused some dangerous side effects until many of the drugs were withdrawn from the market. One promising source of new anxiolytics could be herbal medicines. The challenge is to screen plant extracts. Rodent models can be used for this purpose but are expensive. Moreover, rodent tests are costly and consume relatively large quantities of sample. For this reason, alternative animal models may be useful. Zebrafish larvae have many advantages for screening natural products. The main advantage is that they can be produced cheaply and in large numbers. Several studies have shown that the zebrafish is a good model for studying drugs that affect anxiety. This review focuses on the use of animal models, including zebrafish larvae, for studying anxiety and screening for herbal medicines that modulate anxiety. Finally, future prospects of the zebrafish larva as an alternative model in this field are also discussed.

Delineation of molecular pathway activities of the chronic antidepressant treatment response suggests important roles for glutamatergic and ubiquitin-proteasome systems

The aim of this study was to identify molecular pathways related to antidepressant response. We administered paroxetine to the DBA/2J mice for 28 days. Following the treatment, the mice were grouped into responders or non-responders depending on the time they spent immobile in the forced swim test. Hippocampal metabolomics and proteomics analyses revealed that chronic paroxetine treatment affects glutamate-related metabolite and protein levels differentially in the two groups. We found significant differences in the expression of N-methyl-d-aspartate receptor and neuronal nitric oxide synthase proteins between the two groups, without any significant alterations in the respective transcript levels. In addition, we found that chronic paroxetine treatment altered the levels of proteins associated with the ubiquitin-proteasome system (UPS). The soluble guanylate cyclase-β1, proteasome subunit α type-2 and ubiquitination levels were also affected in peripheral blood mononuclear cells from antidepressant responder and non-responder patients suffering from major depressive disorder. We submit that the glutamatergic system and UPS have a crucial role in the antidepressant treatment response in both mice and humans.

DNA Microarray-Based Screening and Characterization of Traditional Chinese Medicine

The application of DNA microarray assay (DMA) has entered a new era owing to recent innovations in omics technologies. This review summarizes recent applications of DMA-based gene expression profiling by focusing on the screening and characterizationof traditional Chinese medicine. First, herbs, mushrooms, and dietary plants analyzed by DMA along with their effective components and their biological/physiological effects are summarized and discussed by examining their comprehensive list and a list of representative effective chemicals. Second, the mechanisms of action of traditional Chinese medicine are summarized by examining the genes and pathways responsible for the action, the cell functions involved in the action, and the activities found by DMA (silent estrogens). Third, applications of DMA for traditional Chinese medicine are discussed by examining reported examples and new protocols for its use in quality control. Further innovations in the signaling pathway based evaluation of beneficial effects and the assessment of potential risks of traditional Chinese medicine are expected, just as are observed in other closely related fields, such as the therapeutic, environmental, nutritional, and pharmacological fields.

The contribution of regional gray/white matter volume in preclinical depression assessed by the Automatic Thoughts Questionnaire: a voxel-based morphometry study

Negative automatic thought is a characteristic of depression that contributes toward the risk for episodes of depression. Evidence suggests that gray and white matter abnormalities are linked with depression, but little is known about the association between the negative cognitive experience and brain structure in preclinical depression. We examined the correlation between negative thought and gray (GMV)/white matter volume (WMV) in healthy individuals with preclinical depression. The participants were 309 university students with preclinical depression, as measured by their Automatic Thoughts Questionnaire (ATQ) scores. We collected brain MRIs and used voxel-based morphometry to analyze the correlation of regional GMV/WMV with the ATQ scores. The voxel-based morphometry results showed that the GMV of the right parahippocampal gyrus and fusiform gyrus and the WMV of the right superior temporal pole increased with the severity of depression. Furthermore, the corpus callosum volume decreased with the ATQ scores. This study implied that GMV increase and corpus callosum volume reduction may be associated with negative thought in nonclinical individuals, even at a preclinical depressed level.

Brain glucose metabolism in an animal model of depression

An increasing number of data support the involvement of disturbances in glucose metabolism in the pathogenesis of depression. We previously reported that glucose and glycogen concentrations in brain structures important for depression are higher in a prenatal stress model of depression when compared with control animals. A marked rise in the concentrations of these carbohydrates and glucose transporters were evident in prenatally stressed animals subjected to acute stress and glucose loading in adulthood. To determine whether elevated levels of brain glucose are associated with a change in its metabolism in this model, we assessed key glycolytic enzymes (hexokinase, phosphofructokinase and pyruvate kinase), products of glycolysis, i.e., pyruvate and lactate, and two selected enzymes of the tricarboxylic acid cycle (pyruvate dehydrogenase and α-ketoglutarate dehydrogenase) in the hippocampus and frontal cortex. Additionally, we assessed glucose-6-phosphate dehydrogenase activity, a key enzyme in the pentose phosphate pathway (PPP). Prenatal stress increased the levels of phosphofructokinase, an important glycolytic enzyme, in the hippocampus and frontal cortex. However, prenatal stress had no effect on hexokinase or pyruvate kinase levels. The lactate concentration was elevated in prenatally stressed rats in the frontal cortex, and pyruvate levels remained unchanged. Among the tricarboxylic acid cycle enzymes, prenatal stress decreased the level of pyruvate dehydrogenase in the hippocampus, but it had no effect on α-ketoglutarate dehydrogenase. Like in the case of glucose and its transporters, also in the present study, differences in markers of glucose metabolism between control animals and those subjected to prenatal stress were not observed under basal conditions but in rats subjected to acute stress and glucose load in adulthood. Glucose-6-phosphate dehydrogenase activity was not reduced by prenatal stress but was found to be even higher in animals exposed to all experimental conditions, i.e., prenatal stress, acute stress, and glucose administration. Our data indicate that glycolysis is increased and the Krebs cycle is decreased in the brain of a prenatal stress animal model of depression.

Antidepressant-like effect of ethanol extract from Zuojin Pill, containing two herbal drugs of Rhizoma Coptidis and Fructus Evodiae, is explained by modulating the monoaminergic neurotransmitter system in mice

ETHNOPHARMACOLOGICAL RELEVANCE

Zuojin Pill (ZJP), a traditional Chinese medicinal decoction, contains two herbal drugs: Coptis chinensis Franch. and Evodia rutaecarpa (Juss.) Benth. in the ratio of 6:1 (w/w). Previous pharmacological studies have shown that two herbs in ZJP have the antagonistic effects on catecholamine secretion in bovine adrenal medullary cells. Furthermore, the alkaloids from the two herbs in ZJP may provide a protective effect for depression in individuals with a low expressing 5-HTT allele by increasing receptor concentration in serotonergic neurons. However, antidepressant effect has not been reported before and has not been fully clarified.

AIM OF THE STUDY

The present study aimed to investigate the antidepressant potential of ethanol extract from ZJP and its monoaminergic mechanism in mice.

MATERIALS AND METHODS

Seven alkaloids were determined from the ethanol extract of ZJP using High Performance Liquid Chromatography (HPLC) with the gradient mobile phase. The ethanol extract from ZJP was used to evaluate the antidepressant potential in mice. Mouse models of depression including the tail suspension test (TST) and the forced swim test (FST) were used to evaluate the effects of the ethanol extract from ZJP. A possible mechanism was explored in the tests of antagonism of reserpine-induced ptosis and hypothermia, and 5-HTP induced head twitch response in mice. The contents of monoamine neurotransmitters including norepinephrine (NE), serotonin (5-hydroxytryptamine or 5-HT) in hippocampus of mice and NE, 5-HT, dopamine (DA) in striatum of mice were determined by HPLC system with Electrochemical Detector (ECD).

RESULTS

The results showed that intragastric administration of the ethanol extract from ZJP (5, 10, 20mg/kg) or fluoxetine (7.5mg/kg) significantly reduced the duration of immobility in TST and FST. However, the effect was not dose-dependent. Ethanol extract from ZJP (5, 10, 20mg/kg) also increased the accumulative number of the 5-HTP-induced head twitch response in mice. The mice were treated with the ethanol extract from ZJP (5, 10, 20mg/kg) or fluoxetine (7.5mg/kg), which could antagonize reserpine-induced ptosis and hypothermia, moreover, both of them could elevate the contents of NE, 5-HT in hippocampus as well as NE, 5-HT, DA in striatum significantly.

CONCLUSION

These results indicate that the ethanol extract from ZJP produced antidepressant-like effect and the possible mechanism, at least in part, is via the central monoaminergic neurotransmitter system and 5-HT plays a major role.

St. John's wort for the treatment of psychiatric disorders

St. John's wort (Hypericum perforatum) has been extensively studied and reviewed for its use in depression; however, there is less salient discussion on its clinical application for a range of other psychiatric disorders. This article outlines the current evidence of the efficacy of St John's wort in common psychiatric disorders, including major depression, bipolar depression, attention-deficit hyperactivity disorder, obsessive-compulsive disorder, social phobia, and somatization disorder. Mechanisms of action, including emerging pharmacogenetic data, safety, and clinical considerations are also detailed.

Mitochondrial plasticity of the hippocampus in a genetic rat model of depression after antidepressant treatment

Depressive disorders and the treatment thereof have been associated with a number of neuroplastic events, such as neurogenesis and synaptic remodeling in discrete areas of the brain. The associations of these events in changes regarding the energy supply have not been investigated. Here, we investigated the changes in mitochondrial plasticity and its correlation to morphological alterations of neuroplasticity in the hippocampus, both associated with a depressive phenotype, and after treatment, with antidepressant imipramine. Design-based stereological methods were used to estimate the number and volume of mitochondria in CA1 of the hippocampus in two different strains of rats, the Sprague-Dawley (SD) and Flinders rats, which display a genetic susceptibility to depressive behavior, the Flinders-sensitive line (FSL) and their corresponding controls, the Flinders-resistant line (FRL). Results showed a significantly reduced number of mitochondria in CA1, which was significantly smaller in the untreated FSL saline group compared to the FRL group. However, the mean volume of mitochondria was significantly larger in the FSL saline group compared to the FRL saline group. Following treatment, the FSL imipramine group showed a significant increase in the number of mitochondria compared to the FSL saline group. Treatment with imipramine in the SD rats did not induce significant differences in the number of mitochondria. Our results indicate that depression may be related to impairments of mitochondrial plasticity in the hippocampus and antidepressant treatment may counteract with the structural impairments. Moreover, the changes in mitochondrial morphology and number are a consistent feature of neuroplasticity.

Analysis of region-specific changes in gene expression upon treatment with citalopram and desipramine reveals temporal dynamics in response to antidepressant drugs at the transcriptome level

RATIONALE

The notion that the onset of action of antidepressant drugs (ADs) takes weeks is widely accepted; however, the sequence of events necessary for therapeutic effects still remains obscure.

OBJECTIVE

We aimed to evaluate a time-course of ADs-induced alterations in the expression of 95 selected genes in 4 regions of the rat brain: the prefrontal and cingulate cortices, the dentate gyrus of the hippocampus, and the amygdala.

METHODS

We employed RT-PCR array to evaluate changes during a time-course (1, 3, 7, 14, and 21 days) of treatments with desipramine (DMI) and citalopram (CIT). In addition to repeated treatment, we also conducted acute treatment (a single dose of drug followed by the same time intervals as the repeated doses).

RESULTS

Time-dependent and structure-specific changes in gene expression patterns allowed us to identify spatiotemporal differences in the molecular action of two ADs. Singular value decomposition analysis revealed differences in the global gene expression profiles between treatment types. The numbers of characteristic modes were generally smaller after CIT treatment than after DMI treatment. Analysis of the dynamics of gene expression revealed that the most significant changes concerned immediate early genes, whose expression was also visualized by in situ hybridization. Transcription factor binding site analysis revealed an over-representation of serum response factor binding sites in the promoters of genes that changed upon treatment with both ADs.

CONCLUSIONS

The observed gene expression patterns were highly dynamic, with oscillations and peaks at various time points of treatment. Our study also revealed novel potential targets of antidepressant action, i.e., Dbp and Id1 genes.

Antidepressant-like effect of the extracted of Kai Xin San, a traditional Chinese herbal prescription, is explained by modulation of the central monoaminergic neurotransmitter system in mouse

ETHNOPHARMACOLOGICAL RELEVANCE

Kai Xin San (KXS) is a traditional Chinese herbal prescription for the treatment of depression-like disorders, anxiety, and impairment in learning and memory, however, there is very little scientific data concerning the efficacy of this.

AIM OF THE STUDY

The present study aimed to investigate the antidepressant potential of Kai Xin San and its possible mechanisms.

MATERIALS AND METHODS

Mouse models of depression including the tail suspension test (TST) and the forced swim test (FST) were used to evaluate the effects of KXS. A possible mechanism was explored in the tests of antagonism of reserpine-induced ptosis, akinesia and hypothermia and 5-HTP induced head-twitch response in mice. The contents of monoamine neurotransmitters including epinephrine (NE), 5-hydroxytryptamine (5-HT) and dopamine (DA) in mice brain were determined by Elisa. Spontaneous motor activities of mice and rotarod test were performed to find whether KXS has excitatory or inhibitory actions on the central nervous system.

RESULTS

The results showed that intragastric administration of KXS at 175, 350, 700, 1400 mg/kg/day or fluoxetine at 28 mg/kg/day for 3 days significantly reduced the duration of immobility in TST and FST, while it showed no effect on the spontaneous motor activity and rotarod performance in mice. However, the effect was not dose-dependent. The pre-treatment with KXS or fluoxetine for 3 days could elevate the contents of NE, 5-HT and DA in mice brain significantly. When the mice were treated with KXS (350 mg/kg, p.o) or desipramine (30 mg/kg, p.o) for 7 days, both of them could antagonize reserpine-induced ptosis, akinesia and hypothermia. The KXS (350 mg/kg) also increased the accumulative number of the 5-HTP-induced head twitch response in mice in 20 min when KXS at dosages of 175, 350, 700 and 1400 mg/kg/day were performed per os (p.o.) during a 1-day, 3-day or 7-day period.

CONCLUSIONS

Our results suggested that KXS exerts antidepressant-like effect. A possible mechanism, at least in part, is via the central monoaminergic neurotransmitter system and 5-HT plays a major role.

Should pharmacogenetics be incorporated in major depression treatment? Economic evaluation in high- and middle-income European countries

The serotonin transporter 5-HTTLPR polymorphism moderates response to SSRIs and side-effect burden. The aim of this study is to quantify the cost-utility of incorporating 5-HTTLPR genotyping in drug treatment of major depressive disorder (MDD). We previously reported a theoretical model to simulate antidepressant treatment with citalopram or bupropion for 12 weeks. The drugs were alternatively selected according to an 'as usual' algorithm or based on response and tolerability predicted by 5-HTTLPR profile. Here we apply this model to conduct a cost-utility analysis in three European regions with high GDP (Euro A), middle GDP (Euro B) and middle-high GDP (Euro C). In addition we test a verification scenario in which citalopram+bupropion augmentation is administered to individuals with the least favorable 5-HTTLPR genotype. Treatment outcomes are remission and Quality Adjusted-Life Weeks (QALW). Cost data (international $, year 2009) are retrieved from the World Health Organization (WHO) and national official sources. In base-case scenario incremental cost-effectiveness ratio (ICER) values are $1147 (Euro A), $1185 (Euro B) and $1178 (Euro C). From cost-effectiveness acceptability curve (CEAC), the probability of having an ICER value below WHO recommended cost-utility threshold (3 GDP per capita=$1926) is >90% in high-income countries (Euro A). In middle- income regions, these probabilities are <30% (Euro B) and <55% (Euro C) respectively. All estimates are robust against variations in treatment parameters, but if genetic test cost decreases to $100, pharmacogenetic approach becomes cost-effective in middle-income countries (Euro B). This simulation using data from 27 European states suggests that choosing antidepressant treatment from the results of 5-HTTLPR might be a cost-effective solution in high income countries. Its feasibility in middle income countries needs further research.

Herbal medicine for depression, anxiety and insomnia: a review of psychopharmacology and clinical evidence

Research in the area of herbal psychopharmacology has increased markedly over the past decades. To date however, a comprehensive review of herbal antidepressant, anxiolytic and hypnotic psychopharmacology and applications in depression, anxiety and insomnia has been absent. A search of MEDLINE (PubMed), CINAHL, PsycINFO, and the Cochrane Library databases was conducted (up to February 21st 2011) on commonly used psychotropic herbal medicines. A review of the literature was conducted to ascertain mechanisms of action of these botanicals, in addition to a systematic review of controlled clinical trials for treatment of mood, anxiety and sleep disorders, which are common comorbid psychiatric disorders. Specific emphasis was given to emerging phytomedicines. Analysis of evidence levels was conducted, as were effect sizes (Cohen's d) where data were available. Results provided evidence of a range of neurochemical, endocrinological, and epigenetic effects for 21 individual phytomedicines, which are detailed in this paper. Sixty six controlled studies were located involving eleven phytomedicines. Several of these provide a high level of evidence, such as Hypericum perforatum for major depression, and Piper methysticum for anxiety disorders. Several human clinical trials provide preliminary positive evidence of antidepressant effects (Echium amoenum, Crocus sativus, and Rhodiola rosea) and anxiolytic activity (Matricaria recutita, Ginkgo biloba, Passiflora incanata, E. amoenum, and Scutellaria lateriflora). Caution should however be taken when interpreting the results as many studies have not been replicated. Several herbal medicines with in vitro and in vivo evidence are currently unexplored in human studies, and along with use of emerging genetic technologies "herbomics", are areas of potential future research.

Biomarkers of anhedonic-like behavior, antidepressant drug refraction, and stress resilience in a rat model of depression

The aim of the present study was to identify potential biomarkers for depression in the search for novel disease targets and treatment regimens. Furthermore, the study includes a search for biomarkers involved in treatment resistance and stress resilience in order to investigate mechanisms underlying antidepressant drug refraction and stress-coping strategies. Depression-related transcriptomic changes in gene expression profiles were investigated in laser-captured microdissected (LCM) rat hippocampal granular cell layers (GCL) using the chronic mild stress (CMS) rat model of depression and chronic administration of two selective serotonin reuptake inhibitors (SSRIs), escitalopram and sertraline. CMS rats were segregated into diverging groups according to behavioral readouts, and under stringent constraints, the associated differential gene regulations were analyzed. Accordingly, we identified four genes associated with recovery, two genes implicated in treatment resistance, and three genes involved in stress resilience. The identified genes associated with mechanisms of cellular plasticity, including signal transduction, cell proliferation, cell differentiation, and synaptic release. Hierarchical clustering analysis confirmed the subgroup segregation pattern in the CMS model. Thus antidepressant treatment refractors cluster with anhedonic-like rats, and, interestingly, stress-resilient rats cluster with rats undergoing antidepressant-mediated recovery from anhedonia, suggesting antidepressant mechanisms of action to emulate endogenous stress-coping strategies.

Escitalopram modulates neuron-remodelling proteins in a rat gene-environment interaction model of depression as revealed by proteomics. Part I: genetic background

The wide-scale analysis of protein expression provides a powerful strategy for the molecular exploration of complex pathophysiological mechanisms, such as the response to antidepressants. Using a 2D proteomic approach we investigated the Flinders Sensitive Line (FSL), a genetically selected rat model of depression, and the control Flinders Resistant Line (FRL). To evaluate gene-environment interactions, FSL and FRL pups were separated from their mothers for 3 h (maternal separation, MS), as early-life trauma is considered an important antecedent of depression. All groups were treated with either escitalopram (Esc) admixed to food (25 mg/kg.d) or vehicle for 1 month. At the week 3, forced swim tests were performed. Protein extracts from prefrontal/frontal cortex and hippocampus were separated by 2D electrophoresis. Proteins displaying statistically significant differences in expression levels were identified by mass spectrometry. Immobility time values in the forced swim test were higher in FSL rats and reduced by antidepressant treatment. Moreover, the Esc-induced reduction in immobility time was not detected in MS rats. The impact of genetic background in response to Esc was specifically investigated here. Bioinformatics analyses highlighted gene ontology terms showing tighter associations with the modulated proteins. Esc modulated protein belonging to cytoskeleton organization in FSL; carbohydrate metabolism and intracellular transport in FRL. Proteins differently modulated in the two strains after MS and Esc play a role in cytoskeleton organization, vesicle-mediated transport, apoptosis regulation and macromolecule catabolism. These findings suggest pathways involved in neuronal remodelling as molecular correlates of response to antidepressants in a model of vulnerability.

Profiling of hypothalamic and hippocampal gene expression in chronically stressed rats treated with St. John's wort extract (STW 3-VI) and fluoxetine

RATIONALE

Hypericum perforatum L., known as St. John's wort (SJW), is used as a phytotherapeutic agent for the treatment of mild to moderate forms of depression.

OBJECTIVES

The aim of the present study was to evaluate the effect of SJW extract (STW 3-VI; 250 and 500 mg/kg; p.o.) and fluoxetine (10 mg/kg, p.o.) on genes involved in the pathogenesis of depression using a chronic restraint stress (CRS) model in rats. Of particular interest was the assessment of similarities and differences between SJW extract and fluoxetine on the gene expression level in two different brain regions.

RESULTS

Hypothalamic and hippocampal tissues were analyzed using the Affymetrix gene chip Rat Genome 230 2.0 Array, which comprises more than 30,000 rat transcripts. Limma program and PANTHER database were used to evaluate the microarray data. Genes involved in the pathways of inflammatory processes (Mapk8), oxidative stress (Gpx3, Gstm3, Sod3) or Alzheimer's disease (Sncb, Apbb1ip) were altered by both fluoxetine and SJW extract. For all groups, several signaling pathways were identified which could provide a link between the various hypotheses of depression.

CONCLUSION

In conclusion, microarray analysis proved to be a valuable tool to identify a large number of genes and resulting pathways that may serve as novel drug targets or predict drug responsiveness for SJW or fluoxetine. Based on our comprehensive analysis, it was possible to identify similarities and differences between SJW and fluoxetine which may help to better understand their molecular action and, in addition, help to find novel treatment strategies for stress-related depression.

Proteomic analysis of rat hippocampus exposed to the antidepressant paroxetine

Antidepressant drugs can exert significant effects on the mood of a patient suffering major depression and other disorders. These drugs generally have pharmacological actions on the uptake or metabolism of the neurotransmitters serotonin, noradrenaline and, to a lesser extent, dopamine. However, there are many aspects of antidepressant action we do not understand. We have applied proteomic analysis in a rat hippocampal model in an attempt to identify relevant molecules that operate in pathways functionally relevant to antidepressant action. Rats were administered either 5 mg/kg daily of the antidepressant paroxetine or vehicle for 12 days, then hippocampal protein was recovered and resolved by 2-D gel electrophoresis. After antidepressant exposure, we observed increased expression or modification of cytochrome c oxidase, subunit Va, cyclin-dependent kinase inhibitor 2A interacting protein, dynein, axonemal, heavy polypeptide 3 and RHO GDP-dissociation inhibitor alpha. Decreased expression or modification was observed for complexin 1 (CPLX1), alpha-synuclein, parvalbumin, ribosomal protein large P2, prohibitin, nerve growth factor, beta subunit (NGFB), peroxiredoxin 6 (PRDX6), 1-acylglycerol-3-phosphate O-acyltransferase 2_predicted, cystatin B (CYTB) and lysosomal membrane glycoprotein 1. CPLX1, the most strongly regulated protein observed, mediates the fusion of cellular transport vesicles with their target membranes and has been implicated in the pathophysiology of mood disorders, as well as antidepressant action. CPLX1 and the other proteins identified may represent links into molecular processes of importance to mood dysregulation and control, and their respective genes may represent novel candidates for studies of antidepressant pharmacogenetics.

A proteomic investigation of similarities between conventional and herbal antidepressant treatments

Increasing clinical evidence for the effectiveness of herbal antidepressants has led to investigations at the molecular level. Using two-dimensional gel electrophoresis, this study investigated similarities in protein expression between clomipramine, St John's wort and a Chinese herbal formula, xiao-yao-san, often used in mood disorder treatment. HT22 cells, derived from a mouse hippocampal cell line, were treated for 24 h, and protein expression was compared with that of the untreated cells (n = 4/group). Forty-three protein spots were found to be significantly differentially expressed (P < 0.05) in more than one of the treatment groups. Twenty-nine of these were identified using mass spectrometry. The most affected proteins were those involved in the cytoskeleton and energy metabolism, and an up-regulation of vimentin by all three treatments was confirmed by Western blotting. This study provides preliminary evidence for multiple common molecular targets between conventional and alternative antidepressants, which appear to collectively affect neuronal plasticity.

Corpus callosum size and shape in individuals with current and past depression

BACKGROUND

The corpus callosum enables the efficient linking of the two cerebral hemispheres. Reductions in the size of the anterior callosum have been described in geriatric depression, although findings in young adults have been much more equivocal.

METHODS

Data was acquired in 26 currently depressed (mean age 32.15 years, 5/26 male) and 28 remitted non-geriatric adults (mean age 36.36 years, 7/28 male), and 32 control subjects (mean age 34.41 years, 11/32 male). The total area, length and curvature of the callosum, and regional thickness along 39 points, from a mid-sagittal T1-weighted magnetic resonance image were compared across the groups.

RESULTS

Total area, length and curvature did not differ between the groups. The currently-depressed group showed expansions in the thickness of the posterior body and isthmus when compared to controls; this was not seen in remitted patients. Similar expansions were seen when comorbidly anxious patients were compared to depressed patients without anxiety. There was no difference between melancholic and non-melancholic patients, and medication status did not affect the results.

LIMITATIONS

Currently-depressed patients showed higher rates of co-morbid anxiety and medication usage than remitted patients, although in the depression group as a whole there was no difference between medicated and unmedicated patients.

DISCUSSION

The corpus callosum shows expansions in regions connecting frontal, temporal and parietal regions in currently depressed patients only, suggestive of state-related changes in white matter in major depression that may reflect the effects of state-related factors on white matter structure.

Influence of antidepressant drugs on Ecto-nucleotide pyrophosphatase/phosphodiesterases (E-NPPs) from salivary glands of rats

Xerostomia is commonly caused by antidepressant drugs and ATP can influence the saliva production. Adenosine is the product of extracellular hydrolysis of adenine nucleotides in submandibular gland cells, which occurs by the action of ectonucleotidases. In this study, we have evaluated the effect of three different antidepressants in ecto-nucleotide pyrophosphatase/phosphodiesterase (E-NPP1-3) activities in cultured cells from salivary glands. Rats received imipramine (10mg/ml), fluoxetine (20mg/ml) or moclobemide (30mg/ml) by oral gavage. The drugs were administered once a day for 14 days. Our results have shown that the hydrolysis of p-nitrophenyl-5'-thymidine monophosphate increased in all treatments. These effects were not consequence of transcriptional control of E-NPP1-3 genes. The results reported here can highlight the importance of ectonucleotidases in the most common side effect caused by antidepressant therapy.

Corticolimbic transcriptome changes are state-dependent and region-specific in a rodent model of depression and of antidepressant reversal

Gene microarrays may enable the elucidation of neurobiological changes underlying the pathophysiology and treatment of major depression. However, previous studies of antidepressant treatments were performed in healthy normal rather than 'depressed' animals. Since antidepressants are devoid of mood-changing effects in normal individuals, the clinically relevant rodent transcriptional changes could remain undetected. We investigated antidepressant-related transcriptome changes in a corticolimbic network of mood regulation in the context of the unpredictable chronic mild stress (UCMS), a naturalistic model of depression based on socio-environmental stressors. Mice subjected to a 7-week UCMS displayed a progressive coat state deterioration, reduced weight gain, and increased agonistic and emotion-related behaviors. Chronic administration of an effective (fluoxetine) or putative antidepressant (corticotropin-releasing factor-1 (CRF1) antagonist, SSR125543) reversed all physical and behavioral effects. Changes in gene expression differed among cingulate cortex (CC), amygdala (AMY) and dentate gyrus (DG) and were extensively reversed by both drugs in CC and AMY, and to a lesser extent in DG. Fluoxetine and SSR125543 also induced additional and very similar molecular profiles in UCMS-treated mice, but the effects of the same drug differed considerably between control and UCMS states. These studies established on a large-scale that the molecular impacts of antidepressants are region-specific and state-dependent, revealed common transcriptional changes downstream from different antidepressant treatments and supported CRF1 targeting as an effective therapeutic strategy. Correlations between UCMS, drug treatments, and gene expression suggest distinct AMY neuronal and oligodendrocyte molecular phenotypes as candidate systems for mood regulation and therapeutic interventions.

Improving the prediction of treatment response in depression: integration of clinical, cognitive, psychophysiological, neuroimaging, and genetic measures

Antidepressants are important in the treatment of depression, and selective serotonin reuptake inhibitors are first-line pharmacologic options. However, only 50% to 70% of patients respond to first treatment and <40% remit. Since depression is associated with substantial morbidity, mortality, and family burden, it is unfortunate and demanding on health resources that patients must remain on their prescribed medications for at least 4 weeks without knowing whether the particular antidepressant will be effective. Studies have suggested a number of predictors of treatment response, including clinical, psychophysiological, neuroimaging, and genetics, each with varying degrees of success and nearly all with poor prognostic sensitivity and specificity. Studies are yet to be conducted that use multiple measures from these different domains to determine whether sensitivity and specificity can be improved to predict individual treatment response. It is proposed that a focus on standardized testing methodologies across multiple testing modalities and their integration will be crucial for translation of research findings into clinical practice.

Downregulation of Ccnd1 and Hes6 in rat hippocampus after chronic exposure to the antidepressant paroxetine

OBJECTIVE

The mechanism of action of antidepressant drugs is not fully understood. Application of genomic methods enables the identification of biochemical pathways that are regulated by antidepressants, and this may provide novel clues to the molecular and cellular actions of these drugs. The present study examined gene expression profiles in the hippocampus of rats exposed to chronic antidepressant treatment.

METHODS

Animals were treated for 12 days with the selective serotonin reuptake inhibitor paroxetine; then, hippocampal ribonucleic acid was recovered, and changes in gene expression were assessed by microarray analysis.

RESULTS

A total of 160 genes that showed differential expression after paroxetine exposure were identified. Using functional relevance and observed fold change as selection criteria, the expression changes in a subset of these genes were confirmed by quantitative polymerase chain reaction.

CONCLUSION

Of this subset, only two genes, cyclin D1 (Ccnd1) and hairy and enhancer of split 6 (Hes6), showed robust and consistent changes in expression. Both genes were downregulated by paroxetine, and both have been previously implicated in neurogenesis. Further investigation of these two genes may provide new insight into the mechanism of action of antidepressants.

Polymorphisms in inflammation-related genes are associated with susceptibility to major depression and antidepressant response

There are clinical parallels between the nature and course of depressive symptoms in major depressive disorder (MDD) and those of inflammatory disorders. However, the characterization of a possible immune system dysregulation in MDD has been challenging. Emerging data support the role of T-cell dysfunction. Here we report the association of MDD and antidepressant response to genes important in the modulation of the hypothalamic-pituitary-adrenal axis and immune functions in Mexican Americans with major depression. Specifically, single nucleotide polymorphisms (SNPs) in two genes critical for T-cell function are associated with susceptibility to MDD: PSMB4 (proteasome beta4 subunit), important for antigen processing, and TBX21 (T bet), critical for differentiation. Our analyses revealed a significant combined allele dose-effect: individuals who had one, two and three risk alleles were 2.3, 3.2 and 9.8 times more likely to have the diagnosis of MDD, respectively. We found associations of several SNPs and antidepressant response; those genes support the role of T cell (CD3E, PRKCH, PSMD9 and STAT3) and hypothalamic-pituitary-adrenal axis (UCN3) functions in treatment response. We also describe in MDD increased levels of CXCL10/IP-10, which decreased in response to antidepressants. This further suggests predominance of type 1 T-cell activity in MDD. T-cell function variations that we describe here may account for 47.8% of the attributable risk in Mexican Americans with moderate MDD. Immune function genes are highly variable; therefore, different genes might be implicated in distinct population groups.

Merger of ayurveda and tissue culture-based functional genomics: inspirations from systems biology

Ayurveda is one of the ancient systems of health care of Indian origin. Roughly translated into "Knowledge of life", it is based on the use of natural herbs and herb products for therapeutic measures to boost physical, mental, social and spiritual harmony and improve quality of life. Although sheltered with long history and high trust, ayurveda principles have not entered laboratories and only a handful of studies have identified pure components and molecular pathways for its life-enhancing effects. In the post-genomic era, genome-wide functional screenings for targets for diseases is the most recent and practical approach. We illustrate here the merger of ayurveda and functional genomics in a systems biology scenario that reveals the pathway analysis of crude and active components and inspire ayurveda practice for health benefits, disease prevention and therapeutics.

Effect of chronic citalopram on serotonin-related and stress-regulated genes in the dorsal raphe nucleus of the rat

Using a model of depression in which chronic social stress induces depressive-like symptoms, we investigated effects of the selective serotonin-reuptake inhibitor (SSRI) citalopram on gene expression in the dorsal raphe nucleus of male rats. Expression of tryptophan hydroxylase (TPH) protein was found to be upregulated by the stress and normalized by citalopram, while mRNAs for genes TPH 1 and 2 were differentially affected. Citalopram had no effect on serotonin transporter mRNA but reduced serotonin-1A autoreceptor mRNA in stressed animals. The SSRI prevented the stress-induced upregulation of mRNA for CREB binding protein, synaptic vesicle glycoprotein 2b and the glial N-myc downstream-regulated gene 2, but increased mRNA for neuron-specific enolase (NSE) in both stressed and unstressed animals having no effect on stress-induced upregulation of NSE protein. These findings demonstrate that in the dorsal raphe nucleus of chronically stressed rats, citalopram normalizes TPH expression and blocks stress effects on distinct genes related to neurotransmitter release and neuroplasticity.

Towards understanding the schizophrenia code: an expanded convergent functional genomics approach

Identifying genes for schizophrenia through classical genetic approaches has proven arduous. Here, we present a comprehensive convergent analysis that translationally integrates brain gene expression data from a relevant pharmacogenomic mouse model (involving treatments with a psychomimetic agent - phencyclidine (PCP), and an anti-psychotic - clozapine), with human genetic linkage data and human postmortem brain data, as a Bayesian strategy of cross validating findings. Topping the list of candidate genes, we have three genes involved in GABA neurotransmission (GABRA1, GABBR1, and GAD2), one gene involved in glutamate neurotransmission (GRIA2), one gene involved in neuropeptide signaling (TAC1), two genes involved in synaptic function (SYN2 and KCNJ4), six genes involved in myelin/glial function (CNP, MAL, MBP, PLP1, MOBP and GFAP), and one gene involved in lipid metabolism (LPL). These data suggest that schizophrenia is primarily a disorder of brain functional and structural connectivity, with GABA neurotransmission playing a prominent role. These findings may explain the EEG gamma band abnormalities detected in schizophrenia. The analysis also revealed other high probability candidates genes (neurotransmitter signaling, other structural proteins, ion channels, signal transduction, regulatory enzymes, neuronal migration/neurite outgrowth, clock genes, transcription factors, RNA regulatory genes), pathways and mechanisms of likely importance in pathophysiology. Some of the pathways identified suggest possible avenues for augmentation pharmacotherapy of schizophrenia with other existing agents, such as benzodiazepines, anticonvulsants and lipid modulating agents. Other pathways are new potential targets for drug development. Lastly, a comparison with our earlier work on bipolar disorder illuminates the significant molecular overlap between schizophrenia and bipolar disorder.

The application of DNA micro-arrays (gene arrays) to the study of herbal medicines

DNA micro-arrays (gene arrays) have become a popular and useful tool with which to study the effects of various agents and treatments on gene expression in cells and tissues. In theory one can simultaneously evaluate, in a single experiment, changes in gene expression (at the level of transcription) of the entire genome of the organism under study. Consequently these techniques have been used by many investigators interested in cancer research, differentiation and development, toxicology, and the effects of pharmaceuticals on cells and animals. In addition, recent studies have shown the capacity of the technique for revealing the importance of genes not previously implicated in a given response. However, relatively few attempts have been made so far to evaluate herbal medicines, although the potential to answer a number of relevant questions is there. In this review we first discuss the fundamental principles of the gene array technology, focusing on the individual steps in the process and their problems and pitfalls, and we discuss the analysis and interpretation of the data, the discipline of bio-informatics, without which meaningful evaluation of gene expression changes would be impossible. We next analyze specific studies, which utilized gene array technology, aimed at evaluating the effects of certain herbal medicine formulas and bioactive ingredients in animal tissues and in cell cultures. We also include a brief description of our own evaluation of Echinacea, which we have been studying for several years, to indicate possible mechanisms of action of this herbal, and also to illustrate how the techniques, especially the bio-informatics, continue to evolve. We believe, on the basis of experience acquired by us and other investigators to date, that the technology of gene array analysis can make significant contributions to understanding how herbal medicines work, and therefore can validate their applications in medicine.

DNA microarrays in herbal drug research

Natural products are gaining increased applications in drug discovery and development. Being chemically diverse they are able to modulate several targets simultaneously in a complex system. Analysis of gene expression becomes necessary for better understanding of molecular mechanisms. Conventional strategies for expression profiling are optimized for single gene analysis. DNA microarrays serve as suitable high throughput tool for simultaneous analysis of multiple genes. Major practical applicability of DNA microarrays remains in DNA mutation and polymorphism analysis. This review highlights applications of DNA microarrays in pharmacodynamics, pharmacogenomics, toxicogenomics and quality control of herbal drugs and extracts.

Proteomic analysis identifies alterations in cellular morphology and cell death pathways in mouse brain after chronic corticosterone treatment

Some patients with Major Depression and other neurological afflictions display hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis. HPA hyperactivity may be due to impaired feedback inhibition and manifested as increased levels of circulating cortisol. Subcutaneous implants of corticosterone pellets were used to mimic this situation in mice to gain insight into any effects on brain function by comparative proteomic analysis using two-dimensional Differential In-Gel Electrophoresis. A total of 150 different protein spots were altered by corticosterone treatment in the hypothalamus, hippocampus and cerebral cortex. Of these, 117 spots were identified by matrix-assisted laser desorption/ionization-time of flight mass fingerprinting equating to 51 different proteins. Association of these corticosterone-modulated proteins with biological functions using the Ingenuity Pathways Analysis tool showed that cell morphology was significantly altered in the hippocampus and cerebral cortex, whereas the hypothalamus showed significant changes in cell death. Ingenuity Pathways Analysis of the canonical signaling pathways showed that glycolysis and gluconeogenesis were altered in the hypothalamus and the hippocampus and all three brain regions showed changes in phenylalanine, glutamate and nitrogen metabolism. Further elucidation of these pathways could lead to identification of biomarkers for the development of pharmacological therapies targeted at neuropsychiatric disorders.

A 40-basepair VNTR polymorphism in the dopamine transporter (DAT1) gene and the rapid response to antidepressant treatment

Finding predictors of the response to antidepressant therapy is a major goal of molecular psychiatry. The genes encoding the serotonin (SERT) and dopamine (DAT1) transporters are among the possible candidate genes modulating an individual's antidepressant response. In a naturalistic prospective cohort study with a total of 190 fully assessed patients, improvement of depression symptoms during the 3 weeks following initiation of antidepressant therapy was recorded using the 21-item Hamilton Depression Rating Scale (HDRS). The SLC6A3 3' UTR 40-bp variable number of tandem repeats (VNTR) and the SLC6A4 5' 44-bp insertion/deletion polymorphism were analyzed by polymerase chain reaction. There was a significantly smaller number of rapid responders among homozygous carriers of the DAT1 9-repeat allele (9/9) than among heterozygous (9/10) and homozygous (10/10) carriers of the 10-repeat allele (19 versus 37 versus 52%, respectively, P=0.0037). Median decline in HDRS score was 35, 40, and 52% in patients with the 9/9, 9/10, and 10/10 genotypes, respectively (P=0.013). The effect was found in all classes of medications (selective serotonin reuptake inhibitors (SSRIs), tricyclics, mirtazapine, venlafaxine) and statistically significant also within the subgroup of patients having received SSRIs. The serotonin promoter insertion/deletion genotype had no effect in the entire study group, but there was an insignificant trend of better response in the l/l and l/s carriers who received SSRIs or mirtazapine. In conclusion, the dopamine transporter VNTR polymorphism influenced rapid response to antidepressant therapy. Compared with homozygous carriers of the 10-repeat allele, carriers of the 9/10 genotype had an odds ratio (OR) calculated by logistic regression analysis of 1.6 (95% CI 0.8-3.2) and carriers of the 9/9 genotype had an OR of 6.0 (1.5-24.4) for no or poor response. Further studies are required to confirm this clinical association and to elucidate the underlying mechanisms.

Identification of genes regulated by chronic social stress in the rat dorsal raphe nucleus

1. Changes in the serotonergic (5-HT) system are suspected to play a role in stress-induced neuropathologies and neurochemical measures indicate that serotonergic neurons in the dorsal raphe nucleus (DRN) are activated during stress. In the present study we analyzed gene expression in the DRN after chronic social stress using subtractive cDNA hybridization. 2. In the resident intruder paradigm, male Wistar rats were chronically stressed by daily social defeat during 5 weeks, RNA was isolated from their DRN, cDNA was generated, and subtractive hybridization was performed to clone sequences that are differentially expressed in the stressed animals. 3. From the cDNA libraries that were obtained, we selected the following genes for quantitative Real-time PCR: Two genes related to neurotransmission (synaptosomal associated protein 25 and synaptic vesicle glycoprotein 2b), a glial gene presumptively supporting neuroplasticity (N-myc downstream-regulated gene 2), and a gene possibly related to stress-induced regulation of transcription (CREB binding protein). These four genes were upregulated after the chronic social stress. Quantitative Western blotting revealed increased expression of synaptosomal associated protein 25 and synaptic vesicle glycoprotein 2b. 4. Genes directly related to 5-HT neurotransmission were not contained in the cDNA libraries and quantitative Real-time PCR for the serotonin transporter, tryptophan hydroxylase 2 and the 5-HT(1A) autoreceptor confirmed that these genes are not differentially expressed after 5-weeks of daily social stress. 5. These data show that 5 weeks of daily social defeat lead to significant changes in expression of genes related to neurotransmission and neuroplasticity in the DRN, whereas expression of genes directly related to 5-HT neurotransmission is apparently normal after this period of chronic stress.

St. John's wort and its constituent hyperforin concordantly regulate expression of genes encoding enzymes involved in basic cellular pathways

OBJECTIVES AND METHODS

The effects of St. John's wort and hyperforin on gene expression were analysed in HepG2 cells by Affymetrix microarray hybridization and real time reverse transcription-PCR.

RESULTS

Both compounds increased mRNAs of the drug metabolizing enzymes CYP3A4, CYP1A1, CYP1A2 and the flavin containing monooxygenase FMO5, and of the multidrug resistance protein MRP2. CYP4F2 and the reduced nicotinamide adenine dinucleotide dehydrogenase NQO1 were downregulated. Expression of genes mediating cholesterol biosynthesis was decreased, while facilitated glucose transporters and glycolysis genes were induced, indicating increased glucose metabolism. Changes of a considerable number of additional transcripts corresponded to reports on gene regulation by hypoxia. Endoplasmic reticulum stress-regulated genes involved in unfolded protein response and in protection of cells from apoptosis were downregulated. Other calcium binding proteins were affected by both treatments, suggesting an increase in intracellular calcium.

CONCLUSIONS

St. John's wort and hyperforin concordantly affected expression of genes not only mediating metabolism and transport of exogenous and endogenous compounds, but also involved in energy metabolism, intracellular calcium regulation, cell proliferation and apoptosis.

St. John's Wort modulates the toxicities and pharmacokinetics of CPT-11 (irinotecan) in rats

CPT-11 is a DNA topoisomerase I inhibitor for the therapy of colorectal cancer, whereas St. John's Wort (Hypericum perforatum, SJW) is a widely used herbal anti-depressant. This study aimed to investigate the effects of co-administered SJW on the toxicities and pharmacokinetics of CPT-11 and the underlying mechanisms. The body weight loss, gastrointestinal and hematological toxicities induced by CPT-11, and the pharmacokinetic parameters of CPT-11 were evaluated in rats pretreated with SJW or vehicle. Rats treated with CPT-11 alone experienced rapid decrease in body weight, whereas co-administration of SJW with CPT-11 resulted in lesser body weight loss. The gastrointestinal and hematological toxicities following CPT-11 injection were both alleviated in the presence of SJW. The rat pharmacokinetics of both CPT-11 and its metabolite SN-38 were significantly altered in presence of SJW. In conclusion, co-administered SJW significantly ameliorated the toxicities induced by CPT-11. The protective effect of SJW may be partially due to pharmacokinetic interaction between CPT-11 and SJW.

Transcriptional profiling reveals evidence for signaling and oligodendroglial abnormalities in the temporal cortex from patients with major depressive disorder

Major depressive disorder is one of the most common and devastating psychiatric disorders. To identify candidate mechanisms for major depressive disorder, we compared gene expression in the temporal cortex from 12 patients with major depressive disorder and 14 matched controls using Affymetrix HgU95A microarrays. Significant expression changes were revealed in families of genes involved in neurodevelopment, signal transduction and cell communication. Among these, the expression of 17 genes related to oligodendrocyte function was significantly (P < 0.05, fold change > 1.4) decreased in patients with major depressive disorder. Eight of these 17 genes encode structural components of myelin (CNP, MAG, MAL, MOG, MOBP, PMP22, PLLP, PLP1). Five other genes encode enzymes involved in the synthesis of myelin constituents (ASPA, UGT8), or are essential in regulation of myelin formation (ENPP2, EDG2, TF, KLK6). One gene, that is, SOX10, encodes a transcription factor regulating other myelination-related genes. OLIG2 is a transcription factor present exclusively in oligodendrocytes and oligodendrocyte precursors. Another gene, ERBB3, is involved in oligodendrocyte differentiation. In addition to myelination-related genes, there were significant changes in multiple genes involved in axonal growth/synaptic function. These findings suggest that major depressive disorder may be associated with changes in cell communication and signal transduction mechanisms that contribute to abnormalities in oligodendroglia and synaptic function. Taken together with other studies, these findings indicate that major depressive disorder may share common oligodendroglial abnormalities with schizophrenia and bipolar disorder.

Candidate genes, pathways and mechanisms for bipolar (manic-depressive) and related disorders: an expanded convergent functional genomics approach

Identifying genes for bipolar mood disorders through classic genetics has proven difficult. Here, we present a comprehensive convergent approach that translationally integrates brain gene expression data from a relevant pharmacogenomic mouse model (involving treatments with a stimulant--methamphetamine, and a mood stabilizer--valproate), with human data (linkage loci from human genetic studies, changes in postmortem brains from patients), as a bayesian strategy of crossvalidating findings. Topping the list of candidate genes, we have DARPP-32 (dopamine- and cAMP-regulated phosphoprotein of 32 kDa) located at 17q12, PENK (preproenkephalin) located at 8q12.1, and TAC1 (tachykinin 1, substance P) located at 7q21.3. These data suggest that more primitive molecular mechanisms involved in pleasure and pain may have been recruited by evolution to play a role in higher mental functions such as mood. The analysis also revealed other high-probability candidates genes (neurogenesis, neurotrophic, neurotransmitter, signal transduction, circadian, synaptic, and myelin related), pathways and mechanisms of likely importance in pathophysiology.

From monoamines to genomic targets: a paradigm shift for drug discovery in depression

Depression, a complex psychiatric disorder that affects approximately 15% of the population, has an enormous social cost. Although the disorder is thought to be the outcome of gene-environmental interactions, the causative genes and environmental factors underlying depression remain to be identified. All the antidepressant drugs now in use--the forerunner of which was discovered serendipitously 50 years ago--modulate monoamine neurotransmission, and take six to eight weeks to exert their effects, but each drug is efficacious in only 60-70% of patients. A conceptually novel antidepressant that acted rapidly and safely in a high proportion of patients would almost certainly become the world's bestselling drug. Yet such a drug is not on the horizon. Here, we cover the different phases of antidepressant drug discovery in the past, present and future, and comment on the challenges and opportunities for antidepressant research.