Expression of the cAMP response element binding protein (CREB) in hippocampus produces an antidepressant effect

Fluoxetine effects on molecular, cellular and behavioral endophenotypes of depression are driven by the living environment

Selective serotonin reuptake inhibitors (SSRIs) represent the most common treatment for major depression. However, their efficacy is variable and incomplete. In order to elucidate the cause of such incomplete efficacy, we explored the hypothesis positing that SSRIs may not affect mood per se but, by enhancing neural plasticity, render the individual more susceptible to the influence of the environment. Consequently, SSRI administration in a favorable environment promotes a reduction of symptoms, whereas in a stressful environment leads to a worse prognosis. To test such hypothesis, we exposed C57BL/6 mice to chronic stress in order to induce a depression-like phenotype and, subsequently, to fluoxetine treatment (21 days), while being exposed to either an enriched or a stressful condition. We measured the most commonly investigated molecular, cellular and behavioral endophenotypes of depression and SSRI outcome, including depression-like behavior, neurogenesis, brain-derived neurotrophic factor levels, hypothalamic-pituitary-adrenal axis activity and long-term potentiation. Results showed that, in line with our hypothesis, the endophenotypes investigated were affected by the treatment according to the quality of the living environment. In particular, mice treated with fluoxetine in an enriched condition overall improved their depression-like phenotype compared with controls, whereas those treated in a stressful condition showed a distinct worsening. Our findings suggest that the effects of SSRI on the depression- like phenotype is not determined by the drug per se but is induced by the drug and driven by the environment. These findings may be helpful to explain variable effects of SSRI found in clinical practice and to device strategies aimed at enhancing their efficacy by means of controlling environmental conditions.

Highly polygenic architecture of antidepressant treatment response: Comparative analysis of SSRI and NRI treatment in an animal model of depression

Response to antidepressant (AD) treatment may be a more polygenic trait than previously hypothesized, with many genetic variants interacting in yet unclear ways. In this study we used methods that can automatically learn to detect patterns of statistical regularity from a sparsely distributed signal across hippocampal transcriptome measurements in a large-scale animal pharmacogenomic study to uncover genomic variations associated with AD. The study used four inbred mouse strains of both sexes, two drug treatments, and a control group (escitalopram, nortriptyline, and saline). Multi-class and binary classification using Machine Learning (ML) and regularization algorithms using iterative and univariate feature selection methods, including InfoGain, mRMR, ANOVA, and Chi Square, were used to uncover genomic markers associated with AD response. Relevant genes were selected based on Jaccard distance and carried forward for gene-network analysis. Linear association methods uncovered only one gene associated with drug treatment response. The implementation of ML algorithms, together with feature reduction methods, revealed a set of 204 genes associated with SSRI and 241 genes associated with NRI response. Although only 10% of genes overlapped across the two drugs, network analysis shows that both drugs modulated the CREB pathway, through different molecular mechanisms. Through careful implementation and optimisations, the algorithms detected a weak signal used to predict whether an animal was treated with nortriptyline (77%) or escitalopram (67%) on an independent testing set. The results from this study indicate that the molecular signature of AD treatment may include a much broader range of genomic markers than previously hypothesized, suggesting that response to medication may be as complex as the pathology. The search for biomarkers of antidepressant treatment response could therefore consider a higher number of genetic markers and their interactions. Through predominately different molecular targets and mechanisms of action, the two drugs modulate the same Creb1 pathway which plays a key role in neurotrophic responses and in inflammatory processes. © 2016 The Authors. American Journal of Medical Genetics Part B: Neuropsychiatric Genetics Published by Wiley Periodicals, Inc.

Antidepressant-like effects of fenofibrate in mice via the hippocampal brain-derived neurotrophic factor signalling pathway

BACKGROUND AND PURPOSE

Depression is a neuropsychiatric disorder accompanied by a decrease in the brain-derived neurotrophic factor (BDNF) signalling cascade in the hippocampus. Fenofibrate is a selective agonist of PPAR-α. In this study, we investigated the antidepressant-like effects of fenofibrate in C57BL/6J mice.

EXPERIMENTAL APPROACH

The antidepressant-like effects of fenofibrate were first identified in the forced swim test (FST) and tail suspension test (TST), and then assessed in the chronic social defeat stress (CSDS) model. The changes in the hippocampal BDNF signalling pathway and adult hippocampal neurogenesis after CSDS and fenofibrate treatment were further investigated. A PPAR-α inhibitor, cannabinoid system inhibitors and BDNF signalling inhibitors were also used to determine the antidepressant mechanisms of fenofibrate.

KEY RESULTS

Fenofibrate administration exhibited antidepressant-like effects in the FST and TST without affecting the locomotor activity of mice. Chronic fenofibrate treatment also prevented the depressive-like symptoms induced by CSDS. Moreover, fenofibrate restored the CSDS-induced decrease in the hippocampal BDNF signalling cascade and adult hippocampal neurogenesis. The antidepressant-like effects of fenofibrate could be blocked by a PPAR-α inhibitor and BDNF signalling inhibitors.

CONCLUSIONS AND IMPLICATIONS

Taken together, these results suggest that fenofibrate has antidepressant-like effects mediated through the promotion of the hippocampal BDNF signalling cascade.

Kappa-Opioid Antagonists for Psychiatric Disorders: From Bench to Clinical Trials

Kappa-opioid receptor (KOR) antagonists are currently being considered for the treatment of a variety of neuropsychiatric conditions, including depressive, anxiety, and substance abuse disorders. A general ability to mitigate the effects of stress, which can trigger or exacerbate these conditions, may explain their putative efficacy across such a broad array of conditions. The discovery of their potentially therapeutic effects evolved from preclinical research designed to characterize the molecular mechanisms by which experience causes neuroadaptations in the nucleus accumbens (NAc), a key element of brain reward circuitry. This research established that exposure to drugs of abuse or stress increases the activity of the transcription factor CREB (cAMP response element binding protein) in the NAc, which leads to elevated expression of the opioid peptide dynorphin that in turn causes core signs of depressive- and anxiety-related disorders. Disruption of KORs-the endogenous receptors for dynorphin-produces antidepressant- and anxiolytic-like actions in screening procedures that identify standard drugs of these classes, and reduces stress effects in tests used to study addiction and stress-related disorders. Although interest in this target is high, prototypical KOR antagonists have extraordinarily persistent pharmacodynamic effects that complicate clinical trials. The development of shorter acting KOR antagonists together with more rapid designs for clinical trials may soon provide insight on whether these drugs are efficacious as would be predicted by preclinical work. If successful, KOR antagonists would represent a unique example in psychiatry where the therapeutic mechanism of a drug class is understood before it is shown to be efficacious in humans.

Alterations in leukocyte transcriptional control pathway activity associated with major depressive disorder and antidepressant treatment

Major depressive disorder (MDD) is associated with a significantly elevated risk of developing serious medical illnesses such as cardiovascular disease, immune impairments, infection, dementia and premature death. Previous work has demonstrated immune dysregulation in subjects with MDD. Using genome-wide transcriptional profiling and promoter-based bioinformatic strategies, we assessed leukocyte transcription factor (TF) activity in leukocytes from 20 unmedicated MDD subjects versus 20 age-, sex- and ethnicity-matched healthy controls, before initiation of antidepressant therapy, and in 17 of the MDD subjects after 8 weeks of sertraline treatment. In leukocytes from unmedicated MDD subjects, bioinformatic analysis of transcription control pathway activity indicated an increased transcriptional activity of cAMP response element-binding/activating TF (CREB/ATF) and increased activity of TFs associated with cellular responses to oxidative stress (nuclear factor erythroid-derived 2-like 2, NFE2l2 or NRF2). Eight weeks of antidepressant therapy was associated with significant reductions in Hamilton Depression Rating Scale scores and reduced activity of NRF2, but not in CREB/ATF activity. Several other transcriptional regulation pathways, including the glucocorticoid receptor (GR), nuclear factor kappa-B cells (NF-κB), early growth response proteins 1-4 (EGR1-4) and interferon-responsive TFs, showed either no significant differences as a function of disease or treatment, or activities that were opposite to those previously hypothesized to be involved in the etiology of MDD or effective treatment. Our results suggest that CREB/ATF and NRF2 signaling may contribute to MDD by activating immune cell transcriptome dynamics that ultimately influence central nervous system (CNS) motivational and affective processes via circulating mediators.

The HDAC inhibitor SAHA improves depressive-like behavior of CRTC1-deficient mice: Possible relevance for treatment-resistant depression

Major depression is a highly complex disabling psychiatric disorder affecting millions of people worldwide. Despite the availability of several classes of antidepressants, a substantial percentage of patients are unresponsive to these medications. A better understanding of the neurobiology of depression and the mechanisms underlying antidepressant response is thus critically needed. We previously reported that mice lacking CREB-regulated transcription coactivator 1 (CRTC1) exhibit a depressive-like phenotype and a blunted antidepressant response to the selective serotonin reuptake inhibitor fluoxetine. In this study, we similarly show that Crtc1(-/-) mice are resistant to the antidepressant effect of chronic desipramine in a behavioral despair paradigm. Supporting the blunted response to this tricyclic antidepressant, we found that desipramine does not significantly increase the expression of Bdnf and Nr4a1-3 in the hippocampus and prefrontal cortex of Crtc1(-/-) mice. Epigenetic regulation of neuroplasticity gene expression has been associated with depression and antidepressant response, and histone deacetylase (HDAC) inhibitors have been shown to have antidepressant-like properties. Here, we show that unlike conventional antidepressants, chronic systemic administration of the HDAC inhibitor SAHA partially rescues the depressive-like behavior of Crtc1(-/-) mice. This behavioral effect is accompanied by an increased expression of Bdnf, but not Nr4a1-3, in the prefrontal cortex of these mice, suggesting that this epigenetic intervention restores the expression of a subset of genes by acting downstream of CRTC1. These findings suggest that CRTC1 alterations may be associated with treatment-resistant depression, and support the interesting possibility that targeting HDACs may be a useful therapeutic strategy in antidepressant development.

Antidepressant drug action--From rapid changes on network function to network rewiring

There has been significant recent progress in understanding the neurobiological mechanisms of antidepressant treatments. The delayed-onset of action of monoamine-based antidepressant drugs have been associated to their ability to slowly increase synaptic plasticity and neuronal excitability via altering neurotrophic signaling (synthesis of BDNF and activation of its receptor TrkB), dematuration of GABAergic interneurons and inhibition of "breaks of plasticity". On the other hand, antidepressants rapidly regulate emotional processing that - with the help of heightened plasticity and appropriate rehabilitation - gradually lead to significant changes on functional neuronal connectivity and clinical recovery. Moreover, the discovery of rapid-acting antidepressants, most notably ketamine, has inspired interest for novel antidepressant developments with better efficacy and faster onset of action. Therapeutic effects of rapid-acting antidepressants have been linked with their ability to rapidly regulate neuronal excitability and thereby increase synaptic translation and release of BDNF, activation of the TrkB-mTOR-p70S6k signaling pathway and increased synaptogenesis within the prefrontal cortex. Thus, alterations in TrkB signaling, synaptic plasticity and neuronal excitability are shared neurobiological phenomena implicated in antidepressant responses produced by both gradually and rapid acting antidepressants. However, regardless of antidepressant, their therapeutic effects are not permanent which suggests that their effects on neuronal connectivity and network function remain unstable and vulnerable for psychosocial challenges.

Primary phospholipase C and brain disorders

In the brain, the primary phospholipase C (PLC) proteins, PLCβ, and PLCγ, are activated primarily by neurotransmitters, neurotrophic factors, and hormones through G protein-coupled receptors (GPCRs) and receptor tyrosine kinases (RTKs). Among the primary PLC isozymes, PLCβ1, PLCβ4, and PLCγ1 are highly expressed and differentially distributed, suggesting a specific role for each PLC subtype in different regions of the brain. Primary PLCs control neuronal activity, which is important for synapse function and development. In addition, dysregulation of primary PLC signaling is linked to several brain disorders including epilepsy, schizophrenia, bipolar disorder, Huntington's disease, depression and Alzheimer's disease. In this review, we included current knowledge regarding the roles of primary PLC isozymes in brain disorders.

Treadmill exercise alleviates stress-induced impairment of social interaction through 5-hydroxytryptamine 1A receptor activation in rats

Brain-derived neurotrophic factor (BDNF) and its receptors tyrosine kinase B (trkB), and cyclic adenosine monophosphate response element binding protein (CREB) have been suggested as the neurobiological risk factors causing depressive disorder. Serotonin (5-hydroxytryptamine, 5-HT) plays an important role in the pathogenesis of depression. We in-vestigated the effect of treadmill exercise on social interaction in relation with BDNF and 5-HT expressions following stress in rats. Stress was induced by applying inescapable 0.2 mA electric foot shock to the rats for 7 days. The rats in the exercise groups were forced to run on a motorized treadmill for 30 min once a day for 4 weeks. Social interaction test and western blot for BDNF, TrkB, pCREB, and 5-HT1A in the hippocampus were performed. The results indicate that the spend time with unfamiliar partner was decreased by stress, in contrast, treadmill exercise increased the spending time in the stress-induced rats. Expressions of BDNF, TrkB, and pCREB were decreased by stress, in contrast, treadmill exercise enhanced expressions of BDNF, TrkB, and pCREB in the stress-induced rats. In addition, 5-HT1A receptor expression was de-creased by stress, in contrast, treadmill exercise enhanced 5-HT1A expression in the stress-induced rats. In the present study, treadmill exercise alleviated stress-induced social interaction impairment through enhancing hippocampal plasticity and serotonergic function in the hippocampus. These effects of treadmill exercise are achieved through 5-HT1A receptor activation.

Alterations in Gene Expression in Depression: Prospects for Personalize Patient Treatment

The number of people around the world suffering from depression has dramatically increased in last few decades. It has been predicted that by 2020 depression will become the second most common cause of disability. Furthermore, depression is often misdiagnosed and confused with other psychiatric disorders showing similar symptoms, i.e., anxiety and bipolar disorder, due to the fact that diagnosing is often carried out by medical workers who are not psychiatrically trained. These facts prompt us to prepare this review which focuses on alterations in gene expression in depression. We believe that an in-depth knowledge of molecular bases of behavior in depression and other mood disorders would be of a great benefit for the correct diagnosing of these disorders, as well as for prescribing a treatment that best suits each individual depending on expression alterations in depression-related genes. Therefore, the main aim of this review is to promote further translational research on the biochemistry of mood disorders and take the results further for the design of new targeted therapeutics that can be used for personalized treatment with minimal adverse effects.

Drug withdrawal conceptualized as a stressor

Drug withdrawal is often conceptualized as an aversive state that motivates drug-seeking and drug-taking behaviors in humans. Stress is more difficult to define, but is also frequently associated with aversive states. Here we describe evidence for the simple theory that drug withdrawal is a stress-like state, on the basis of common effects on behavioral, neurochemical, and molecular endpoints. We also describe data suggesting a more complex relationship between drug withdrawal and stress. As one example, we will highlight evidence that, depending on drug class, components of withdrawal can produce effects that have characteristics consistent with mood elevation. In addition, some stressors can act as positive reinforcers, defined as having the ability to increase the probability of a behavior that produces it. As such, accumulating evidence supports the general principles of opponent process theory, whereby processes that have an affective valence are followed in time by an opponent process that has the opposite valence. Throughout, we identify gaps in knowledge and propose future directions for research. A better understanding of the similarities, differences, and overlaps between drug withdrawal and stress will lead to the development of improved treatments for addiction, as well as for a vast array of neuropsychiatric conditions that are triggered or exacerbated by stress.

Tetramethylpyrazine Produces Antidepressant-Like Effects in Mice Through Promotion of BDNF Signaling Pathway

BACKGROUND

Current antidepressants are clinically effective only after several weeks of administration. Tetramethylpyrazine (TMP) is an identified component of Ligusticum wallichii with neuroprotective effects. Here, we investigated the antidepressant effects of TMP in mice models of depression.

METHODS

Antidepressant effects of TMP were first detected in the forced swim test (FST) and tail suspension test (TST), and further assessed in the chronic social defeat stress (CSDS) model. Changes in the brain-derived neurotrophic factor (BDNF) signaling pathway and in hippocampal neurogenesis after CSDS and TMP treatment were then investigated. A tryptophan hydroxylase inhibitor and BDNF signaling inhibitors were also used to determine the mechanisms of TMP.

RESULTS

TMP exhibited potent antidepressant effects in the FST and TST without affecting locomotor activity. TMP also prevented the CSDS-induced symptoms. Moreover, TMP completely restored the CSDS-induced decrease of BDNF signaling pathway and hippocampal neurogenesis. Furthermore, a blockade of the BDNF signaling pathway prevented the antidepressant effects of TMP, while TMP produced no influence on the monoaminergic system.

CONCLUSIONS

In conclusion, these data provide the first evidence that TMP has antidepressant effects, and this was mediated by promoting the BDNF signaling pathway.

Icariin upregulates phosphorylated cyclic adenosine monophosphate response element binding protein levels in the hippocampus of the senescence- accelerated mouse

At 8 weeks after intragastric administration of icariin to senescence-accelerated mice (P8 strain), Morris water maze results showed that escape latency was shortened, and the number of platform crossings was increased. Immunohistochemical staining and western blot assay detected significantly increased levels of cyclic adenosine monophosphate response element binding protein. These results suggest that icariin upregulates phosphorylated cyclic adenosine monophosphate response element binding protein levels and improves learning and memory functions in hippocampus of the senescence-accelerated mouse.

The Antidepressant-like Effects of Estrogen-mediated Ghrelin

Ghrelin, one of the brain-gut peptides, stimulates food-intake. Recently, ghrelin has also shown to play an important role in depression treatment. However, the mechanism of ghrelin's antidepressant-like actions is unknown. On the other hand, sex differences in depression, and the fluctuation of estrogens secretion have been proved to play a key role in depression. It has been reported that women have higher level of ghrelin expression, and ghrelin can stimulate estrogen secretion while estrogen acts as a positive feedback mechanism to up-regulate ghrelin level. Ghrelin may be a potential regulator of reproductive function, and estrogen may have additional effect in ghrelin's antidepressantlike actions. In this review, we summarize antidepressant-like effects of ghrelin and estrogen in basic and clinical studies, and provide new insight on ghrelin's effect in depression.

A Review of Biomarkers in Mood and Psychotic Disorders: A Dissection of Clinical vs. Preclinical Correlates

Despite significant research efforts aimed at understanding the neurobiological underpinnings of mood (depression, bipolar disorder) and psychotic disorders, the diagnosis and evaluation of treatment of these disorders are still based solely on relatively subjective assessment of symptoms as well as psychometric evaluations. Therefore, biological markers aimed at improving the current classification of psychotic and mood-related disorders, and that will enable patients to be stratified on a biological basis into more homogeneous clinically distinct subgroups, are urgently needed. The attainment of this goal can be facilitated by identifying biomarkers that accurately reflect pathophysiologic processes in these disorders. This review postulates that the field of psychotic and mood disorder research has advanced sufficiently to develop biochemical hypotheses of the etiopathology of the particular illness and to target the same for more effective disease modifying therapy. This implies that a "one-size fits all" paradigm in the treatment of psychotic and mood disorders is not a viable approach, but that a customized regime based on individual biological abnormalities would pave the way forward to more effective treatment. In reviewing the clinical and preclinical literature, this paper discusses the most highly regarded pathophysiologic processes in mood and psychotic disorders, thereby providing a scaffold for the selection of suitable biomarkers for future studies in this field, to develope biomarker panels, as well as to improve diagnosis and to customize treatment regimens for better therapeutic outcomes.

Rapid-onset antidepressant efficacy of glutamatergic system modulators: the neural plasticity hypothesis of depression

Depression is a devastating psychiatric disorder widely attributed to deficient monoaminergic signaling in the central nervous system. However, most clinical antidepressants enhance monoaminergic neurotransmission with little delay but require 4-8 weeks to reach therapeutic efficacy, a paradox suggesting that the monoaminergic hypothesis of depression is an oversimplification. In contrast to the antidepressants targeting the monoaminergic system, a single dose of the N-methyl-D-aspartate receptor (NMDAR) antagonist ketamine produces rapid (within 2 h) and sustained (over 7 days) antidepressant efficacy in treatment-resistant patients. Glutamatergic transmission mediated by NMDARs is critical for experience-dependent synaptic plasticity and learning, processes that can be modified indirectly by the monoaminergic system. To better understand the mechanisms of action of the new antidepressants like ketamine, we review and compare the monoaminergic and glutamatergic antidepressants, with emphasis on neural plasticity. The pathogenesis of depression may involve maladaptive neural plasticity in glutamatergic circuits that may serve as a new class of targets to produce rapid antidepressant effects.

The role of serotonin in adult hippocampal neurogenesis

Serotonin is probably best known for its role in conveying a sense of contentedness and happiness. It is one of the most unique and pharmacologically complex monoamines in both the peripheral and central nervous system (CNS). Serotonin has become in focus of interest for the treatment of depression with multiple serotonin-mimetic and modulators of adult neurogenesis used clinically. Here we will take a broad view of serotonin from development to its physiological role as a neurotransmitter and its contribution to homeostasis of the adult rodent hippocampus. This chapter reflects the most significant findings on cellular and molecular mechanisms from neuroscientists in the field over the last two decades. We illustrate the action of serotonin by highlighting basic receptor targeting studies, and how receptors impact brain function. We give an overview of recent genetically modified mouse models that differ in serotonin availability and focus on the role of the monoamine in antidepressant response. We conclude with a synthesis of the most recent data surrounding the role of serotonin in activity and hippocampal neurogenesis. This synopsis sheds light on the mechanisms and potential therapeutic model by which serotonin plays a critical role in the maintenance of mood.

Possible additional antidepressant-like mechanism of sodium butyrate: targeting the hippocampus

Chromatin remodeling mediated by histone acetylation might be involved in the pathophysiology and the treatment of depression. Recently, it has been reported that the histone deacetylase (HDAC) inhibitors, such as sodium butyrate (SB), could be a potential therapeutic agent for depression treatment. In the present study, we aimed to clarify the antidepressant mechanism of SB in the hippocampus. The mice were exposed to chronic restraint stress (CRS) for 14 consecutive days (2 h/day) to induce depression-like behaviors. To assess depression-like behaviors, sucrose preference test, light dark test (LD), tail suspension test (TST), and forced swim test (FST) were performed after CRS. We observed that CRS decreased HDAC2 and 5 mRNA and protein levels in the hippocampus. In addition, SB co-treatment decreased the depression-like behaviors that are induced by CRS. SB prevented and normalized the phosphorylation of cAMP response element binding protein (pCREB), acetylation of histone H3 (AceH3), HDAC2, and brain-derived neurotrophic factor (BDNF) expression level that were decreased by CRS in the hippocampus. These results suggest that the decreased HDAC2 and 5 expressions in the hippocampus of CRS may be a type of spontaneous coping response against CRS. However, it seems to be unsuccessful to prevent depression induction since reduction of pCREB, AceH3 and BDNF were accompanied by CRS in the hippocampus. Moreover, the reduced AceH3 level may be associated with the decreased pCREB, which appears to lead to the decreased BDNF.

Serotonergic pharmacology in animal models: from behavioral disorders to dyskinesia

Serotonin (5-HT) dysfunction has been involved in both movement and behavioral disorders. Serotonin pharmacology improves dyskinetic movements as well as depressive, anxious, aggressive and anorexic symptoms. Animal models have been useful to investigate more precisely to what extent 5-HT is involved and whether drugs targeting the 5-HT system can counteract the symptoms exhibited. We review existing rodent and non-human primate (NHP) animal models in which selective 5-HT or dual 5-HT-norepinephrine (NE) transporter inhibitors, as well as specific 5-HT receptors agonists and antagonists, monoamine oxidase A inhibitors (IMAO-A) and MDMA (Ecstasy) have been used. We review overlaps between the various drug classes involved. We confront behavioral paradigms and treatment regimen. Some but not all animal models and associated pharmacological treatments have been extensively studied in the litterature. In particular, the impact of selective serotonin reuptake inhibitors (SSRI) has been extensively investigated using a variety of pharmacological or genetic rodent models of depression, anxiety, aggressiveness. But the validity of these rodent models is questioned. On the contrary, few studies did address the potential impact of targeting the 5-HT system on NHP models of behavioral disorders, despite the fact that those models may match more closely to human pathologies. Further investigations with carefull behavioral analysis will improve our understanding of neural bases underlying the pathophysiology of movement and behavioral disorders.

Regulator of G-protein signaling 6 (RGS6) promotes anxiety and depression by attenuating serotonin-mediated activation of the 5-HT(1A) receptor-adenylyl cyclase axis

Targeting serotonin (5-HT) bioavailability with selective 5-HT reuptake inhibitors (SSRIs) remains the most widely used treatment for mood disorders. However, their limited efficacy, delayed onset of action, and side effects restrict their clinical utility. Endogenous regulator of G-protein signaling (RGS) proteins have been implicated as key inhibitors of 5-HT(1A)Rs, whose activation is believed to underlie the beneficial effects of SSRIs, but the identity of the specific RGS proteins involved remains unknown. We identify RGS6 as the critical negative regulator of 5-HT(1A)R-dependent antidepressant actions. RGS6 is enriched in hippocampal and cortical neurons, 5-HT(1A)R-expressing cells implicated in mood disorders. RGS6(-/-) mice exhibit spontaneous anxiolytic and antidepressant behavior rapidly and completely reversibly by 5-HT(1A)R blockade. Effects of the SSRI fluvoxamine and 5-HT(1A)R agonist 8-OH-DPAT were also potentiated in RGS6(+/-) mice. The phenotype of RGS6(-/-) mice was associated with decreased CREB phosphorylation in the hippocampus and cortex, implicating enhanced Gα(i)-dependent adenylyl cyclase inhibition as a possible causative factor in the behavior observed in RGS6(-/-) animals. Our results demonstrate that by inhibiting serotonergic innervation of the cortical-limbic neuronal circuit, RGS6 exerts powerful anxiogenic and prodepressant actions. These findings indicate that RGS6 inhibition may represent a viable means to treat mood disorders or enhance the efficacy of serotonergic agents.

BDNF and CREB1 genetic variants interact to affect antidepressant treatment outcomes in geriatric depression

AIM

Brain-derived neurotrophic factor (BDNF) is associated with antidepressant response on the cellular level, in animal models, and in clinical studies. A common variant in the BDNF gene results in a substitution of a methionine (Met) for a valine at the amino acid position 66. Previous studies reported that the Met variant results in enhanced response to antidepressant medications. These findings may be at odds with studies indicating that on a cellular level the Met variant impairs the secretion of BDNF.

MATERIALS AND METHODS

We examined the effects of BDNF single nucleotide polymorphisms (SNPs) in response to the antidepressants paroxetine and mirtazapine in a sample of 246 geriatric patients with major depression, treated in a double-blind, randomized, 8-week clinical trial. We also examined the effects of genetic variation at the BDNF-related loci neurotrophic tyrosine kinase receptor 2, cyclic AMP responsive element binding protein 1 (CREB1), and CREB binding protein. A total of 53 SNPs were genotyped.

RESULTS

BDNF genetic variation had a significant effect on the efficacy of paroxetine, with patients carrying the Met allele showing impaired response. SNPs at the CREB1 locus, which encodes a transcription factor important in BDNF signaling, also predicted response to paroxetine. Furthermore, we found a significant gene-gene interaction between BDNF and CREB1 that affected response to paroxetine. Because BDNF has been associated with cognitive function, we tested the effects of BDNF SNPs on change in a wide variety of cognitive tests over the 8-week trial, but there were no significant effects of genotype on cognition.

CONCLUSION

These results provide new evidence for the importance of the BDNF pathway in antidepressant response in geriatric patients. The negative effect of the Met66 allele on antidepressant outcomes is consistent with basic science findings indicating a negative effect of this variant on BDNF activity in the brain. Further, the effect of BDNF genetic variation on antidepressant treatment is modified by variation in the gene encoding the downstream effector CREB1.

Long-term adaptive changes induced by serotonergic antidepressant drugs

The development of conventional antidepressants has been largely based on the hypothesis of monoaminergic dysfunctions and focuses particularly on the serotonin 5-hydroxytryptamine (5-HT) system. Hence, various classes of antidepressant treatments enhance 5-HT neurotransmission with a time course consistent with their delayed therapeutic effect. This delayed onset appears to be associated with the gradual development of specific adaptive changes of functional 5-HT receptors. However, recent theories suggest that major depressive disorders may be associated with impairments of functional plasticity and cellular flexibility. This review discusses several physiological mechanisms by which 5-HT function and hippocampal neuroplasticity are regulated. Knowledge of these long-term adaptations will increase not only our understanding of pathological processes underlying affective disorders, but could also lead to the development of new strategies to treat these devastating illnesses.

Regulation of adult hippocampal neurogenesis: relevance to depression

Recent hypotheses suggest that depression may involve an inability to mount adaptive structural changes in key neuronal networks. In particular, the addition of new neurons within the hippocampus, a limbic region implicated in mood disorders, is compromised in animal models of depression. Adult hippocampal neurogenesis is also a target for chronic antidepressant treatments, and an increase in adult hippocampal neurogenesis is implicated in the behavioral effects of antidepressants in animal models. The 'neurogenic' hypothesis of depression raises the intriguing possibility that hippocampal neurogenesis may contribute to the pathogenesis and treatment of depressive disorders. While there remains substantial debate about the precise relevance of hippocampal neurogenesis to mood disorders, this provocative hypothesis has been the focus of many recent studies. In this review, we discuss the pathways that may mediate the effects of depression models and antidepressants on adult hippocampal neurogenesis, and the promise of these studies in the development of novel antidepressants.

Increased hippocampal neurogenesis and accelerated response to antidepressants in mice with specific deletion of CREB in the hippocampus: role of cAMP response-element modulator τ

The transcription factor cAMP response element-binding protein (CREB) has been implicated in the pathophysiology of depression as well as in the efficacy of antidepressant treatment. However, altering CREB levels appears to have differing effects on anxiety- and depression-related behaviors, depending on which brain region is examined. Furthermore, many manipulations of CREB lead to corresponding changes in other CREB family proteins, and the impact of these changes has been largely ignored. To further investigate the region-specific importance of CREB in depression-related behavior and antidepressant response, we used Creb(loxP/loxP) mice to localize CREB deletion to the hippocampus. In an assay sensitive to chronic antidepressant response, the novelty-induced hypophagia procedure, hippocampal CREB deletion, did not alter the response to chronic antidepressant treatment. In contrast, mice with hippocampal CREB deletion responded to acute antidepressant treatment in this task, and this accelerated response was accompanied by an increase in hippocampal neurogenesis. Upregulation of the CREB-family protein cAMP response-element modulator (CREM) was observed after CREB deletion. Viral overexpression of the activator isoform of CREM, CREMτ, in the hippocampus also resulted in an accelerated response to antidepressants as well as increased hippocampal neurogenesis. This is the first demonstration of CREMτ within the brain playing a role in behavior and specifically in behavioral outcomes following antidepressant treatment. The current results suggest that activation of CREMτ may provide a means to accelerate the therapeutic efficacy of current antidepressant treatment.

Sexual activity counteracts the suppressive effects of chronic stress on adult hippocampal neurogenesis and recognition memory

Adult neurogenesis can be influenced by a variety of factors. Stress is one of the most potent inhibitors of hippocampal neurogenesis. Stress effects on adult hippocampal neurogenesis are affected differently by environmental factors, including social interaction. Sexual behavior between males and females in a social context has been suggested to influence neurogenesis and enhance hippocampal cell proliferation. However, the mechanisms of action of sexual interaction, the possible changes relative to stress state, and its effects on learning and memory remain uncertain. The current study examined the influence of sexual interaction on neurological responses in adult male mice and the function of sexual interaction relative to recognition memory in stress states. Changes in the expression of neurotrophic and transcription factors were assessed in reference to stress and/or sexual behaviors. The survival of newly generated cells and their rate of differentiation into neurons were determined in the hippocampus of chronically stressed and/or sexually experienced mice. Finally, to evaluate whether sexual experience alters adult hippocampal function, we tested learning and memory in a recognition memory task. The results demonstrated that sexual activity increased the expression of brain-derived neurotrophic factor, tyrosine kinase B, and cAMP response element-binding factor. Furthermore, the results supported the view that sexual interaction could be helpful for buffering adult hippocampal neurogenesis and recognition memory function against the suppressive actions of chronic stress.

The involvement of ERK/CREB/Bcl-2 in depression-like behavior in prenatally stressed offspring rats

A number of studies reveal that prenatal stress (PS) may induce an increased vulnerability to depression in offspring. Some evidences indicate that extracellular signal-regulated kinase (ERK)-cyclic AMP responsive element binding protein (CREB) signal system may play an important role in the molecular mechanism of depression. In the present study, we examined the effects of prenatal restraint stress on depression-like behavior in one-month offspring Sprague-Dawley rats and expression of ERK2, CREB, B-cell lymphoma-2 (Bcl-2) mRNA in the hippocampus, prefrontal cortex and striatum to explore the potential role of ERK-CREB pathway in mediating the behavioral effects of PS exposure. Our findings demonstrated that PS increased immobility time in forced swimming test and decreased expression of ERK2, CREB, Bcl-2 mRNA in the hippocampus and prefrontal cortex of juvenile offspring rats except for CREB in hippocampus of male offspring. Changes induced by PS were partly prevented by MK-801, an N-methyl-D-aspartate (NMDA) receptor antagonist. These findings suggested that the ERK-CREB system might be related with the depression-like behavior in juvenile offspring rats subjected to PS, in which NMDA receptors might be involved.

Imipramine treatment increases cell proliferation following fluid percussion brain injury in rats

OBJECTIVE

Researchers have observed unsustainable neurogenesis of the dentate gyrus of the hippocampus, as well as cognitive improvements in short-term imipramine-treated mice following a controlled cortical impact (CCI) model of traumatic brain injury (TBI). But they have yet to investigate the effects of a longer-duration imipramine treatment. In this study, we investigated the effects of a longer treatment regimen on rats following a fluid percussion injury (FPI) model, which creates a brain injury that more closely resembles those incurred by human patients.

METHODS

We administered imipramine to rats for 8 weeks following FPI. Brain histology was performed to measure neurogenesis and cognitive recovery was evaluated using the Morris water maze (MWM).

RESULTS

The Injury+imipramine group demonstrated 172% neurogenesis relative to the injury alone group at 9+ weeks in the dentate gyrus of the hippocampus. Neurogenesis observed here involved both the injured and the uninjured sides of the brain. All four groups (FPI+imipramine, FPI, sham, sham+imipramine) showed a similar performance in the MWM task.

DISCUSSION

Longer duration of treatment with imipramine promotes sustained increase in hippocampal cell proliferation and survival. Global neurogenesis corresponds to the diffuse nature of FPI injury. Cognitive outcome can be due to a delay in our behavior testing as much as an absence of cognitive benefit of imipramine at this stage of neurogenesis. Nevertheless, exploring the potential benefits of prophylactic antidepressant treatment in human TBI patients is worthwhile.

TRPC6 channel-mediated neurite outgrowth in PC12 cells and hippocampal neurons involves activation of RAS/MEK/ERK, PI3K, and CAMKIV signaling

The non-selective cationic transient receptor canonical 6 (TRPC6) channels are involved in synaptic plasticity changes ranging from dendritic growth, spine morphology changes and increase in excitatory synapses. We previously showed that the TRPC6 activator hyperforin, the active antidepressant component of St. John's wort, induces neuritic outgrowth and spine morphology changes in PC12 cells and hippocampal CA1 neurons. However, the signaling cascade that transmits the hyperforin-induced transient rise in intracellular calcium into neuritic outgrowth is not yet fully understood. Several signaling pathways are involved in calcium transient-mediated changes in synaptic plasticity, ranging from calmodulin-mediated Ras-induced signaling cascades comprising the mitogen-activated protein kinase, PI3K signal transduction pathways as well as Ca(2+) /calmodulin-dependent protein kinase II (CAMKII) and CAMKIV. We show that several mechanisms are involved in TRPC6-mediated synaptic plasticity changes in PC12 cells and primary hippocampal neurons. Influx of calcium via TRPC6 channels activates different pathways including Ras/mitogen-activated protein kinase/extracellular signal-regulated kinases, phosphatidylinositide 3-kinase/protein kinase B, and CAMKIV in both cell types, leading to cAMP-response element binding protein phosphorylation. These findings are interesting not only in terms of the downstream targets of TRPC6 channels but also because of their potential to facilitate further understanding of St. John's wort extract-mediated antidepressant activity. Alterations in synaptic plasticity are considered to play an important role in the pathogenesis of depression. Beside several other proteins, TRPC6 channels regulate synaptic plasticity. This study demonstrates that different pathways including Ras/MEK/ERK, PI3K/Akt, and CAMKIV are involved in the improvement of synaptic plasticity by the TRPC6 activator hyperforin, the antidepressant active constituent of St. John's wort extract.

Altered brain-derived neurotrophic factor expression in the ventral tegmental area, but not in the hippocampus, is essential for antidepressant-like effects of electroconvulsive therapy

BACKGROUND

Impaired neuronal plasticity and, specifically, altered expression of brain-derived neurotrophic factor (BDNF) were shown to play a critical role in depressive behavior and the mechanism of various antidepressant treatments including electroconvulsive therapy (ECT). Interestingly, opposing roles were suggested for BDNF in the hippocampus and the ventral tegmental area (VTA), while interactions between these regions were shown on various levels. Here, we evaluated whether BDNF plays an essential role in the antidepressant-like effects of ECT and performed a direct comparison between BDNF manipulations in the VTA and the hippocampus.

METHODS

Knockdown or overexpression of BDNF was induced in hippocampus or VTA of rats by microinjection of specific lentiviral vectors. The effects of these manipulations on antidepressant outcomes of ECT were evaluated by the forced swim test and by sucrose preference measurements, and BDNF expression levels were assessed in other reward-related brain regions.

RESULTS

Here, we show that whereas ECT increased hippocampal BDNF expression, induction of hippocampal BDNF knockdown did not block its antidepressant-like effect. Importantly, we found that ECT caused a robust reduction in VTA BDNF levels. Moreover, VTA BDNF knockdown alone was sufficient to induce an antidepressant-like effect, and VTA BDNF overexpression blocked the antidepressant-like effect of ECT.

CONCLUSIONS

While neuroplastic alterations, as expressed by changes in BDNF expression within different brain regions, are induced by ECT, the antidepressant-like effect of ECT in an animal model depends on reduction of VTA BDNF expression but not on the elevation of hippocampal BDNF expression.

Protective effects of aqueous extract from Acanthopanax senticosus against corticosterone-induced neurotoxicity in PC12 cells

ETHNOPHARMACOLOGICAL RELEVANCE

Acanthopanax senticosus, classified into the family of Araliaceae, has been known for thousands of years as a remedy and is used to treat various diseases in traditional Chinese medicine system including hypertension, ischemic heart disease and hepatitis.

AIM OF THE STUDY

This study aimed to examine the protective effects of aqueous extract from Acanthopanax senticosus (ASE) on corticosterone-induced neurotoxicity and its possible mechanisms, using PC12 cells as a suitable in vitro model of depression.

MATERIALS AND METHODS

In this paper, PC12 cells were treated with 200 μM of corticosterone in the absence or presence of ASE in varying concentrations for 24 h. Then, cell viability was measured by MTT assay. The release amount of lactate dehydrogenase (LDH) was quantified using LDH assay kit. Apoptosis of PC12 cells was measured by Annexin V-FITC and PI labeling. The intracellular Ca(2+) content was tested by fluorescent labeling. The mRNA level of brain-derived neurotrophic factor (BDNF) was examined by real-time RT-PCR, and the expression of cAMP response element binding protein (CREB) was determined by western blotting.

RESULTS

The results showed that treatment with 200 μM of corticosterone could induce cytotoxicity in PC12 cells. However, different concentrations of ASE (50, 100, 200, and 400 μg/mL) significantly increased the cell viability, decreased the LDH release, suppressed the apoptosis of PC12 cells, attenuated the intracellular Ca(2+) overloading, up-regulated the BDNF mRNA level and CREB protein expression compared with the corresponding corticosterone-treated group.

CONCLUSION

The present results suggest that ASE exerts a neuroprotective effect on corticosterone-induced neurotoxicity in PC12 cells, which may be one of the acting mechanisms that accounts for the in vivo antidepressant activity of ASE.

Neural plasticity and proliferation in the generation of antidepressant effects: hippocampal implication

It is widely accepted that changes underlying depression and antidepressant-like effects involve not only alterations in the levels of neurotransmitters as monoamines and their receptors in the brain, but also structural and functional changes far beyond. During the last two decades, emerging theories are providing new explanations about the neurobiology of depression and the mechanism of action of antidepressant strategies based on cellular changes at the CNS level. The neurotrophic/plasticity hypothesis of depression, proposed more than a decade ago, is now supported by multiple basic and clinical studies focused on the role of intracellular-signalling cascades that govern neural proliferation and plasticity. Herein, we review the state-of-the-art of the changes in these signalling pathways which appear to underlie both depressive disorders and antidepressant actions. We will especially focus on the hippocampal cellularity and plasticity modulation by serotonin, trophic factors as brain-derived neurotrophic factor (BDNF), and vascular endothelial growth factor (VEGF) through intracellular signalling pathways—cAMP, Wnt/β-catenin, and mTOR. Connecting the classic monoaminergic hypothesis with proliferation/neuroplasticity-related evidence is an appealing and comprehensive attempt for improving our knowledge about the neurobiological events leading to depression and associated to antidepressant therapies.

Synaptic regulation of affective behaviors; role of BDNF

Brain derived neurotrophic factor (BDNF), a neurotrophin essential for nervous system development and synaptic plasticity, has been found to have a significant influence on affective behaviors. The notion that an impairment in BDNF signaling might be involved in affective disorders is originated primarily from the opposing effects of antidepressants and stress on BDNF signaling. Antidepressants enhance BDNF signaling and synaptic plasticity. On the other hand, negative environmental factors such as severe stress suppress BDNF signaling, impair synaptic activity and increase susceptibility to affective disorders. Postmortem studies provided strong support for decreased BDNF signaling in depressive disorders. Remarkably, studies in humans with a single nucleotide polymorphism in the BDNF gene, the BDNF Val66Met which affects regulated release of BDNF, showed profound deficits in hippocampal and prefrontal cortical (PFC) plasticity and cognitive behaviors. BDNF regulates synaptic mechanisms responsible for various cognitive processes including attenuation of aversive memories, a key process in the regulation of affective behaviors. The unique role of BDNF in cognitive and affective behaviors suggests that cognitive deficits due to altered BDNF signaling might underlie affective disorders. Understanding how BDNF modulates synapses in neural circuits relevant to affective behaviors, particularly the medial prefrontal cortical (mPFC)-hippocampus-amygdala pathway, and its interaction with development, sex, and environmental risk factors might shed light on potential therapeutic targets for affective disorders. This article is part of the Special Issue entitled 'BDNF Regulation of Synaptic Structure, Function, and Plasticity'.

MicroRNA as therapeutic targets for treatment of depression

Depression is a potentially life-threatening mental disorder affecting approximately 300 million people worldwide. Despite much effort, the molecular underpinnings of clinical depression remain poorly defined, and current treatments carry limited therapeutic efficacy and potentially burdensome side effects. Recently, small noncoding RNA molecules known as microRNA (miRNA) have gained prominence as a target for therapeutic intervention, given their capacity to regulate neuronal physiology. Further, mounting evidence suggests a prominent role for miRNA in depressive molecular signaling. Recent studies have demonstrated that dysregulation of miRNA expression occurs in animal models of depression, and in the post-mortem tissue of clinically depressed patients. Investigations into depression-associated miRNA disruption reveals dramatic effects on downstream targets, many of which are thought to contribute to depressive symptoms. Furthermore, selective serotonin reuptake inhibitors, as well as other antidepressant drugs, have the capacity to reverse aberrant depressive miRNA expression and their downstream targets. Given the powerful effects that miRNA have on the central nervous system transcriptome, and the aforementioned studies, there is a compelling rationale to begin to assess the potential contribution of miRNA to depressive etiology. Here, we review the molecular biology of miRNA, our current understanding of miRNA in relation to clinical depression, and the utility of targeting miRNA for antidepressant treatment.

Cellular plasticity and resilience and the pathophysiology of severe mood disorders

Recent advances in the identification of the neural circuits, neurochemicals, and signal transduction mechanisms involved in the pathophysiology and treatment of mood disorders have led to much progress toward understanding the roles of genetic factors and psychosocial stressors. The monoaminergic neurotransmitter systems have received the most attention, partly because of the observation that effective antidepressant drugs exert their primary biochemical effects by regulating intrasynaptic concentrations of serotonin and norepinephrine. Furthermore, the monoaminergic systems are extensively distributed throughout the network of limbic, striatal, and prefrontal cortical neuronal circuits thought to support the behavioral and visceral manifestations of mood disorders. Increasing numbers of neuroimaging, neuropathological, and biochemical studies indicate impairments in cellular plasticity and resilience in patients who suffer from severe, recurrent mood disorders. In this paper, we describe studies identifying possible structural, functional, and cellular abnormalities associated with depressive disorders, which are potentially the cellular underpinnings of these diseases. We suggest that drugs designed to enhance cellular plasticity and resilience, and attenuate the activity of maladaptive stress-responsive systems, may be useful for the treatment of severe mood disorders.

Neural plasticity: consequences of stress and actions of antidepressant treatment

Neural plasticity is emerging as a fundamental and critical mechanism of neuronal function, which allows the brain to receive information and make the appropriate adaptive responses to subsequent related stimuli. Elucidation of the molecular and cellular mechanisms underlying neural plasticity is a major goal of neuroscience research, and significant advances have been made in recent years. These mechanisms include regulation of signal transduction and gene expression, and also structural alterations of neuronal spines and processes, and even the birth of new neurons in the adult brain. Altered plasticity could thereby contribute to psychiatric and neurological disorders. This article revievi/s the literature demonstrating altered plasticity in response to stress, and evidence that chronic antidepressant treatment can reverse or block the effects, and even induce neural piasiicity-iike responses. Continued elucidation of the mechanisms underlying neural plasticity will lead to novel drug targets that could prove to be effective and rapidly acting therapeutic interventions.

Neurotrophins role in depression neurobiology: a review of basic and clinical evidence

Depression is a neuropsychiatric disorder affecting a huge percentage of the active population especially in developed countries. Research has devoted much of its attention to this problematic and many drugs have been developed and are currently prescribed to treat this pathology. Yet, many patients are refractory to the available therapeutic drugs, which mainly act by increasing the levels of the monoamines serotonin and noradrenaline in the synaptic cleft. Even in the cases antidepressants are effective, it is usually observed a delay of a few weeks between the onset of treatment and remission of the clinical symptoms. Additionally, many of these patients who show remission with antidepressant therapy present a relapse of depression upon treatment cessation. Thus research has focused on other possible molecular targets, besides monoamines, underlying depression. Both basic and clinical evidence indicates that depression is associated with several structural and neurochemical changes where the levels of neurotrophins, particularly of brain-derived neurotrophic factor (BDNF), are altered. Antidepressants, as well as other therapeutic strategies, seem to restore these levels. Neuronal atrophy, mostly detected in limbic structures that regulate mood and cognition, like the hippocampus, is observed in depressed patients and in animal behavioural paradigms for depression. Moreover, chronic antidepressant treatment enhances adult hippocampal neurogenesis, supporting the notion that this event underlies antidepressants effects. Here we review some of the preclinical and clinical studies, aimed at disclosing the role of neurotrophins in the pathophysiological mechanisms of depression and the mode of action of antidepressants, which favour the neurotrophic/neurogenic hypothesis.

Increased Cdk5/p35 activity in the dentate gyrus mediates depressive-like behaviour in rats

Depression is one of the most pervasive and debilitating psychiatric diseases, and the molecular mechanisms underlying the pathophysiology of depression have not been elucidated. Cyclin-dependent kinase 5 (Cdk5) has been implicated in synaptic plasticity underlying learning, memory, and neuropsychiatric disorders. However, whether Cdk5 participates in the development of depressive diseases has not been examined. Using the chronic mild stress (CMS) procedure, we examined the effects of Cdk5/p35 activity in the hippocampus on depressive-like behaviour in rats. We found that CMS increased Cdk5 activity in the hippocampus, accompanied by translocation of neuronal-specific activator p35 from the cytosol to the membrane in the dentate gyrus (DG) subregion. Inhibition of Cdk5 in DG but not in the cornu ammonis 1 (CA1) or CA3 hippocampal subregions inhibited the development of depressive-like symptoms. Overexpression of p35 in DG blocked the antidepressant-like effect of venlafaxine in the CMS model. Moreover, the antidepressants venlafaxine and mirtazapine, but not the antipsychotic aripiprazole, reduced Cdk5 activity through the redistribution of p35 from the membrane to the cytosol in DG. Our results showed that the development of depressive-like behaviour is associated with increased Cdk5 activity in the hippocampus and that the Cdk5/p35 complex plays a key role in the regulation of depressive-like behaviour and antidepressant actions.

Regionally selective activation and differential regulation of ERK, JNK and p38 MAP kinase signalling pathway by protein kinase C in mood modulation

A growing body of evidence indicates that the extracellular signal-regulated kinase (ERK) pathway may participate in the neuronal modulation of depression. p38MAPK and c-Jun-N-terminal kinase/stress-activated protein kinase (JNK/SAPK) also belong to the MAPK family which mainly function as mediators of cellular stresses. Since increasing evidence implicates stress as an important factor in vulnerability to depressive illnesses, the involvement of ERK, JNK and p38MAPK pathways in the modulation of mood was investigated in the forced swim test (FST) and tail suspension test (TST). The effect produced by a single acute session of FST and TST on hippocampal and cortical MAPK expression and phosphorylation was investigated by immunoblotting experiments. In the hippocampus of animals exposed to FST and TST, an intensive, PKC-dependent, ERK1, ERK2, JNK, and p38MAPK phosphorylation was observed. In the frontal cortex, the FST and TST produced a PKC-dependent increase of ERK2 and p38MAPK phosphorylation, a PKC-independent activation of JNK and cAMP response element-binding protein (CREB) whereas any involvement of ERK1 was detected. The PKC blocker calphostin C (0.05-0.1 μg i.c.v.), the MEK inhibitor U0126 (10-20 μg i.c.v.), the p38MAPK inhibitor SB203580 (5-20 μg i.c.v.) and the JNK inhibitor II (0.5-5 μg i.c.v.), produced antidepressant-like behaviour without altering locomotor activity. These results illustrate a differentially mediated activation of MAPK in hippocampus and frontal cortex of animals exposed to behavioural despair paradigms. An antidepressant-like phenotype produced by acute blockade of MAPK signalling was also demonstrated.

The relationship between single nucleotide polymorphisms in 5-HT2A signal transduction-related genes and the response efficacy to selective serotonin reuptake inhibitor treatments in Chinese patients with major depressive disorder

OBJECTIVE

To explore the possible relationship between six single nucleotide polymorphisms (SNPs) (rs6311 and rs6305 of 5-HT2A, rs5443 of Gβ3, rs2230739 of ACDY9, rs1549870 of PDE1A and rs255163 of CREB1, which are all related with 5-HT2A the signal transduction pathway) and the response efficacy to selective serotonin reuptake inhibitor (SSRI) treatments in major depressive disorder (MDD) Chinese.

METHODS

This study included 194 depressed patients to investigate the influence of 6 polymorphisms in 5-HT2A signal transduction-related genes on the efficacy of SSRIs assessed over 1 year. The efficacies of SSRIs on 194 MDD patients were evaluated in an 8-week open-trial study. Over 1 year, a follow-up study was completed for 174 of them to observe the long-term efficacy of SSRIs. The optimal-scaling regression analysis was used for testing the relationship between the different genotypes of five SNPs and the efficacy in MDD.

RESULTS

It showed that the patients with rs5443TT and rs2230739GG have a relatively good efficacy in response to short-term SSRIs. We also found that good efficacy appeared in depressed patients with rs2230739GG in response to long-term SSRIs.

CONCLUSIONS

It suggested that different genotypes of rs5443 and rs2230739 might influence the signal transduction pathways of second message and affect therapeutic efficacy.

Analysis of target genes regulated by chronic electroconvulsive therapy reveals role for Fzd6 in depression

BACKGROUND

Chronic electroconvulsive seizure (chr-ECS), one of the most efficacious treatments for depressed patients, increases the levels of transcription factor cyclic adenosine monophosphate response element binding protein (CREB) in rodent models and mediates the effects of chronic antidepressant treatment. The objective of this study was to determine the changes in CREB occupancy at gene promoters and subsequent gene expression changes induced by chr-ECS.

METHODS

We use chromatin immunoprecipitation followed by microarray analysis to identify CREB binding promoters that are influenced by chr-ECS (n = 6/group). Selected genes are confirmed by secondary validation techniques, and the functional significance of one target was tested in behavioral models (n = 8/group) by viral mediated inhibition of gene expression.

RESULTS

The results demonstrate that chr-ECS enhances CREB binding and activity at a select population of genes in the hippocampus, effects that could contribute to the efficacy of chr-ECS. Viral vector-mediated inhibition of one of the CREB-target genes regulated by chr-ECS, Fzd6, produced anxiety and depressive-like effects in behavioral models of depression.

CONCLUSIONS

The results identify multiple gene targets differentially regulated by CREB binding in the hippocampus after chr-ECS and demonstrate the role of Fzd6, a Wnt receptor in behavioral models of depression.

DISC1: Structure, Function, and Therapeutic Potential for Major Mental Illness

Disrupted in schizophrenia 1 (DISC1) is well established as a genetic risk factor across a spectrum of psychiatric disorders, a role supported by a growing body of biological studies, making the DISC1 protein interaction network an attractive therapeutic target. By contrast, there is a relative deficit of structural information to relate to the myriad biological functions of DISC1. Here, we critically appraise the available bioinformatics and biochemical analyses on DISC1 and key interacting proteins, and integrate this with the genetic and biological data. We review, analyze, and make predictions regarding the secondary structure and propensity for disordered regions within DISC1, its protein-interaction domains, subcellular localization motifs, and the structural and functional implications of common and ultrarare DISC1 variants associated with major mental illness. We discuss signaling pathways of high pharmacological potential wherein DISC1 participates, including those involving phosphodiesterase 4 (PDE4) and glycogen synthase kinase 3 (GSK3). These predictions and priority areas can inform future research in the translational and potentially guide the therapeutic processes.