A role for BDNF/TrkB signaling in behavioral and physiological consequences of social defeat stress

Obligatory role of microglia-mobilized hippocampal CREB-BDNF signaling in the prophylactic effect of β-glucan on chronic stress-induced depression-like behaviors in mice

Our previous studies have reported that pre-stimulation of microglia before stress stimulation is a possible strategy to prevent depression-like phenotypes; however, the molecular mechanisms underlying this effect are still unclear. Here, we used β-glucan, a polysaccharide from Saccharomyces cerevisiae with immunomodulatory activities that cannot elicit pro-inflammatory responses in microglia, to address this issue. Our results showed that a single injection of β-glucan one day before stress exposure dose-dependently prevented the depression-like behaviors triggered by chronic unpredictable stress (CUS), which peaked at 20 mg/kg and prevented the impairment of hippocampal brain-derived neurotrophic factor (BDNF) signaling, a pathological process critical for the progression of depression-like phenotypes. Inhibition of BDNF signaling by infusion of an anti-BDNF antibody into the hippocampus, knock-in of the mutant BDNF Val68Met allele, or blockade of the BDNF receptor in the hippocampus abolished the preventive effect of β-glucan on CUS-induced depression-like behaviors. Further analysis showed that cAMP-response element binding protein (CREB)-mediated increase of BDNF expression in the hippocampus was essential for the prevention of depression-like phenotypes by β-glucan. Pretreatment with minocycline or PLX3397 before β-glucan injection to suppress microglia abolished the preventive effect of β-glucan on impaired CREB-BDNF signaling in the hippocampus and depression-like behaviors in CUS mice. These results suggest that an increase in hippocampal BDNF following CREB activation triggered by β-glucan-induced microglia stimulation and subsequent TrkB signaling mediates the preventive effect of β-glucan on depression. β-Glucan may be a more suitable immunostimulant for the prevention of depression due to its inability to promote pro-inflammatory responses in microglia.

An Interaction between Brain-Derived Neurotrophic Factor and Stress-Related Glucocorticoids in the Pathophysiology of Alzheimer's Disease

Both the brain-derived neurotrophic factor (BDNF) and glucocorticoids (GCs) play multiple roles in various aspects of neurons, including cell survival and synaptic function. BDNF and its receptor TrkB are extensively expressed in neurons of the central nervous system (CNS), and the contribution of the BDNF/TrkB system to neuronal function is evident; thus, its downregulation has been considered to be involved in the pathogenesis of Alzheimer's disease (AD). GCs, stress-related molecules, and glucocorticoid receptors (GRs) are also considered to be associated with AD in addition to mental disorders such as depression. Importantly, a growing body of evidence suggests a close relationship between BDNF/TrkB-mediated signaling and the GCs/GR system in the CNS. Here, we introduce the current studies on the interaction between the neurotrophic system and stress in CNS neurons and discuss their involvement in the pathophysiology of AD.

A Truncated Receptor TrkB Isoform (TrkB.T1) in Mechanisms of Genetically Determined Depressive-like Behavior of Mice

Depression is a mental disorder that significantly reduces quality of life, and the discovery of new drug targets is an urgent problem for modern neuroscience. Brain-derived neurotrophic factor (BDNF) and its receptors have been found to participate in mechanisms of depression and antidepressant drugs' action. In this study, we focused on a less-studied truncated isoform of receptor TrkB: TrkB.T1. Initially, we noticed that the level of TrkB.T1 is low in the hippocampus of Antidepressant-Sensitive Cataleptics (ASC) mice, which are characterized by genetically determined depressive-like behavior in contrast to "normal" C57BL/6J mice. Next, overexpression of TrkB.T1 receptor in hippocampal neurons of ACS mice was induced to clarify the role of this receptor in mechanisms of depressive-like behavior. TrkB.T1 overexpression lowered BDNF protein concentration in the hippocampus. On the behavioral level, TrkB.T1 overexpression severely decreased aggression and enhanced social behavior. Additionally, this excess of receptor TrkB.T1 slightly promoted anxiety and depressive-like behavioral traits without affecting learning and memory. Our results show that this TrkB isoform participates in the control of aggression, anxiety, and depressive-like behavior and in the regulation of BDNF system functioning in ASC mice (genetically predisposed to depressive-like behavior). Considering our findings, we believe that hippocampal receptor TrkB.T1 can be a drug target for the correction of behavioral pathologies.

Long-term effects of chronic stress models in adult mice

Neuropsychiatric disorders, such as major depression, anxiety disorders, and post-traumatic stress disorder, tend to be long-term conditions in whose development and maintenance stress are central pathogenic factors. Translational mouse models are widely used in neuropsychiatric research, exploiting social and non-social stressors to investigate the mechanisms underlying their detrimental effects. However, most studies focus on the short-term consequences of chronic stress, whereas only a few are interested in the long-term course. This is counterintuitive given the human conditions that preclinical models are designed to mimic. In this review, we have summarized the limited work to date on long-term effects of chronic stress in mice models. First, the different models are presented and a definition of short- vs. long-term sequelae is proposed. On this basis, behavioral, endocrine, and vegetative effects are addressed before examining data on cellular and molecular alterations in the brain. Finally, future directions for research on the long-term effects of stress are discussed.

Genetic insights into the neurobiology of anxiety

Anxiety and fear are evolutionarily conserved emotions that increase the likelihood of an organism surviving threatening situations. Anxiety and vigilance states are regulated by neural networks involving multiple brain regions. In anxiety disorders, this intricate regulatory system is disturbed, leading to excessive or prolonged anxiety or fear. Anxiety disorders have both genetic and environmental risk factors. Genetic research has the potential to identify specific genetic variants causally associated with specific phenotypes. In recent decades, genome-wide association studies (GWASs) have revealed variants predisposing to neuropsychiatric disorders, suggesting novel neurobiological pathways in the etiology of these disorders. Here, we review recent human GWASs of anxiety disorders, and genetic studies of anxiety-like behavior in rodent models. These studies are paving the way for a better understanding of the neurobiological mechanisms underlying anxiety disorders.

Treadmill exercise promotes retinal astrocyte plasticity and protects against retinal degeneration in a mouse model of light-induced retinal degeneration

Exercise is an effective neuroprotective intervention that preserves retinal function and structure in several animal models of retinal degeneration. However, the retinal cell types governing exercise-induced neuroprotection remain elusive. Previously, we found exercise-induced retinal neuroprotection was associated with increased levels of retinal brain-derived neurotrophic factor (BDNF) and required intact signal transduction with its high-affinity receptor, tropomyosin kinase B (TrkB). Brain studies have shown astrocytes express BDNF and TrkB and that decreased BDNF-TrkB signaling in astrocytes contributes to neurodegeneration. Additionally, exercise has been shown to alter astrocyte morphology. Using a light-induced retinal degeneration (LIRD) model, we investigated how exercise influences retinal astrocytes in adult male BALB/c mice. Treadmill exercise in dim control and LIRD groups had increased astrocyte density, GFAP labeling, branching, dendritic endpoints, and arborization. Meanwhile, inactive LIRD animals had significant reductions in all measured parameters. Additionally, exercised groups had increased astrocytic BDNF expression that was visualized using proximity ligase assay. Isolated retinal astrocytes from exercised LIRD groups had significantly increased expression of a specific isoform of TrkB associated with cell survival, TrkB.FL. Conversely, inactive LIRD isolated retinal astrocytes had significantly increased expression of TrkB.T1, which has been implicated in neuronal cell death. Our data indicate exercise not only alters retinal astrocyte morphology but also promotes specific BDNF-TrkB signaling associated with cell survival and protection during retinal degeneration. These findings provide novel insights into the effects of treadmill exercise on retinal astrocyte morphology and cellular expression, highlighting retinal astrocytes as a potential cell type involved in BDNF-TrkB signaling.

Effect of Qingyangshen glycosides on social defeat mice model

ETHNOPHARMACOLOGICAL RELEVANCE

Qingyangshen (Cynanchum otophyllum C.K.Schneid.PI.Wilson.) is the folk medicine of Yunnan which is renowned for its use in the management of neuropsychiatric diseases. The isolated glycosides from Qingyangshen have demonstrated relief in the social defeat stress, however, mechanism of action has not yet been elucidated.

AIM OF THE STUDY

This study is aimed to elucidate the effect of Qingyangshen glycosides (QYS) on chronic social defeat stress (CSDS)-induced depression-like symptoms and the related mechanism.

MATERIALS AND METHODS

In mice, CSDS model was developed, and the effect of QYS was evaluated by observing the behavioral performance of these mice exposed to tasks related to depression-like activities. Moreover, microscopic pathological examinutesation was also done. Furthermore, the protein expressions related to social defeat stress were also determined to elucidate the possible underlying mechanism.

RESULTS

Our results indicated that QYS treatment reversed the CSDS-induced depressive-like behaviors as measured by the increased sucrose preference, open field activity, and social interactions among mice. The reversal of the morphological changes in the hippocampus of the CSDS mice was also noted. Additionally, QYS treatment also upregulated the silent mating type information regulation 2 homolog 1 (SIRT1), peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α), fibronectin III domain containing protein 5 (FNDC5), brain-derived neurotrophic factor (BDNF), tropomyosin-related kinase B (TrkB), and mitogen-activated protein kinase (MAPK) proteins.

CONCLUSIONS

Our study indicated that QYS had a good anti-social defeat stress effect on CSDS-induced depression in mice, mainly through SIRT1/PGC-1α/FNDC5/BDNF-TrkB signaling pathway activation.

Astroglia in the Vulnerability to and Maintenance of Stress-Mediated Neuropathology and Depression

Significant stress exposure and psychiatric depression are associated with morphological, biochemical, and physiological disturbances of astrocytes in specific brain regions relevant to the pathophysiology of those disorders, suggesting that astrocytes are involved in the mechanisms underlying the vulnerability to or maintenance of stress-related neuropathology and depression. To understand those mechanisms a variety of studies have probed the effect of various modalities of stress exposure on the metabolism, gene expression and plasticity of astrocytes. These studies have uncovered the participation of various cellular pathways, such as those for intracellular calcium regulation, neuroimmune responses, extracellular ionic regulation, gap junctions-based cellular communication, and regulation of neurotransmitter and gliotransmitter release and uptake. More recently epigenetic modifications resulting from exposure to chronic forms of stress or to early life adversity have been suggested to affect not only neuronal mechanisms but also gene expression and physiology of astrocytes and other glial cells. However, much remains to be learned to understand the specific role of those and other modifications in the astroglial contribution to the vulnerability to and maintenance of stress-related disorders and depression, and for leveraging that knowledge to achieve more effective psychiatric therapies.

Chronic Administration of 7,8-DHF Lessens the Depression-like Behavior of Juvenile Mild Traumatic Brain Injury Treated Rats at Their Adult Age

Traumatic brain injury (TBI) is a leading cause of mortality and morbidity among the global youth and commonly results in long-lasting sequelae, including paralysis, epilepsy, and a host of mental disorders such as major depressive disorder. Previous studies were mainly focused on severe TBI as it occurs in adults. This study explored the long-term adverse effect of mild TBI in juvenile animals (mTBI-J). Male Sprague Dawley rats received mTBI-J or sham treatment at six weeks old, then underwent behavioral, biochemical, and histological experiments three weeks later (at nine weeks old). TTC staining, H&E staining, and brain edema measurement were applied to evaluate the mTBI-J induced cerebral damage. The forced swimming test (FST) and sucrose preference test (SPT) were applied for measuring depression-like behavior. The locomotor activity test (LAT) was performed to examine mTBI-J treatment effects on motor function. After the behavioral experiments, the dorsal hippocampus (dHip) and ventral hippocampus (vHip) were dissected out for western blotting to examine the expression of brain-derived neurotrophic factor (BDNF) and tropomyosin receptor kinase B (TrkB). Finally, a TrkB agonist 7,8-DHF was injected intraperitoneally to evaluate its therapeutic effect on the mTBI-J induced behavioral abnormalities at the early adult age. Results showed that a mild brain edema occurred, but no significant neural damage was found in the mTBI-J treated animals. In addition, a significant increase of depression-like behaviors was observed in the mTBI-J treated animals; the FST revealed an increase in immobility, and a decrease in sucrose consumption was found in the mTBI-J treated animals. There were no differences observed in the total distance traveled of the LAT and the fall latency of the rotarod test. The hippocampal BDNF expression, but not the TrkB, were significantly reduced in mTBI-J, and the mTBI-J treatment-induced depression-like behavior was lessened after four weeks of 7,8-DHF administration. Collectively, these results indicate that even a mild juvenile TBI treatment that did not produce motor deficits or significant histological damage could have a long-term adverse effect that could be sustained to adulthood, which raises the depression-like behavior in the adult age. In addition, chronic administration of 7,8-DHF lessens the mTBI-J treatment-induced depression-like behaviors in adult rats. We suggest the potential usage of 7,8-DHF as a therapeutic agent for preventing the long-term adverse effect of mTBI-J.

Emerging Role of Flavonoids as the Treatment of Depression

Depression is one of the most frequently observed psychological disorders, affecting thoughts, feelings, behavior and a sense of well-being in person. As per the WHO, it is projected to be the primitive cause of various other diseases by 2030. Clinically, depression is treated by various types of synthetic medicines that have several limitations such as side-effects, slow-onset action, poor remission and response rates due to complicated pathophysiology involved with depression. Further, clinically, patients cannot be given the treatment unless it affects adversely the job or family. In addition, synthetic drugs are usually single targeted drugs. Unlike synthetic medicaments, there are many plants that have flavonoids and producing action on multiple molecular targets and exhibit anti-depressant action by affecting multiple neuronal transmissions or pathways such as noradrenergic, serotonergic, GABAnergic and dopaminergic; inhibition of monoamine oxidase and tropomyosin receptor kinase B; simultaneous increase in nerve growth and brain-derived neurotrophic factors. Such herbal drugs with flavonoids are likely to be useful in patients with sub-clinical depression. This review is an attempt to analyze pre-clinical studies, structural activity relationship and characteristics of reported isolated flavonoids, which may be considered for clinical trials for the development of therapeutically useful antidepressant.

A Glimpse Into the Sexual Dimorphisms in Major Depressive Disorder Through Epigenetic Studies

Depression is an umbrella term used to describe a mood disorder with a broad spectrum of symptoms including a persistent feeling of sadness, loss of interest, and deficits in social behavior. Epigenetic research bridges the environmental and genetic landscape and has the potential to exponentially improve our understanding of such a complex disorder. Depression is also a sexually dimorphic disorder and variations exist within epigenetic modification sites between sexes. These sex-specific mediators may impact behavioral symptomology and could serve as therapeutic targets for treatments to improve behavioral deficits. This mini review will focus on the social behavior perspective of depression and specifically explore the sexually different epigenetic modifications on depression.

Evolution of stress responses refine mechanisms of social rank

Social rank functions to facilitate coping responses to socially stressful situations and conditions. The evolution of social status appears to be inseparably connected to the evolution of stress. Stress, aggression, reward, and decision-making neurocircuitries overlap and interact to produce status-linked relationships, which are common among both male and female populations. Behavioral consequences stemming from social status and rank relationships are molded by aggressive interactions, which are inherently stressful. It seems likely that the balance of regulatory elements in pro- and anti-stress neurocircuitries results in rapid but brief stress responses that are advantageous to social dominance. These systems further produce, in coordination with reward and aggression circuitries, rapid adaptive responding during opportunities that arise to acquire food, mates, perch sites, territorial space, shelter and other resources. Rapid acquisition of resources and aggressive postures produces dominant individuals, who temporarily have distinct fitness advantages. For these reasons also, change in social status can occur rapidly. Social subordination results in slower and more chronic neural and endocrine reactions, a suite of unique defensive behaviors, and an increased propensity for anxious and depressive behavior and affect. These two behavioral phenotypes are but distinct ends of a spectrum, however, they may give us insights into the troubling mechanisms underlying the myriad of stress-related disorders to which they appear to be evolutionarily linked.

Social defeat stress affects resident's clock gene and bdnf expression in the brain

Social defeat stress affects behavior and changes the expression of the genes underlying neuronal plasticity in the brain. The circadian clock regulates most neuronal processes in the brain, which results in daily variations of complex behavior, and any disturbance in circadian clock oscillations increases the risk of mood and cognitive disbalance. In this study, we assessed the effect of acute and repeated social defeat stress on Per2 and Nr1d1 expression in prefrontal cortexes, hippocampi, pineal glands, olfactory bulbs, cerebella, and pituitary glands. We also evaluated the effect of our experimental setting on levels of Bdnf and plasma corticosterone, two markers widely used to asses the impact of stress on mammalian physiology. Our data show that single and repeated social defeat stress upregulates the expression of both clock genes and Bdnf in all brain structures, and corticosterone in the blood. While the general pattern of Bdnf upregulation suggests higher sensitivity in the intruder group, the clock genes are induced more significantly in residents, especially by repeated stress sessions. Our work thus suggests that the model of stress-induced anxiety and depression should consider a group of residents because, for some parameters, they may respond more distinctively than intruders.LAY SUMMARYThe resident/intruder experimental paradigm affects the expression of clock genes Per2, Nr1d1and Bdnf in the brain structures and plasma corticosterone level. The induction of clock genes is evident in both experimental groups; however, it is more marked in residents. Together with the significant increase in Bdnf levels in the majority of brain structures and plasma corticosterone in residents, our data suggest that in the model of social defeat stress, the utility of an experimental group of residents could be contributive.

Molecular and neurocircuitry mechanisms of social avoidance

Humans and animals live in social relationships shaped by actions of approach and avoidance. Both are crucial for normal physical and mental development, survival, and well-being. Active withdrawal from social interaction is often induced by the perception of threat or unpleasant social experience and relies on adaptive mechanisms within neuronal networks associated with social behavior. In case of confrontation with overly strong or persistent stressors and/or dispositions of the affected individual, maladaptive processes in the neuronal circuitries and its associated transmitters and modulators lead to pathological social avoidance. This review focuses on active, fear-driven social avoidance, affected circuits within the mesocorticolimbic system and associated regions and a selection of molecular modulators that promise translational potential. A comprehensive review of human research in this field is followed by a reflection on animal studies that offer a broader and often more detailed range of analytical methodologies. Finally, we take a critical look at challenges that could be addressed in future translational research on fear-driven social avoidance.

Fluoxetine increases hippocampal neural survival by improving axonal transport in stress-induced model of depression male rats

INTRODUCTION

Axonal transport deficit is a key mechanism involved in neurodegenerative conditions. Fluoxetine, a commonly used antidepressant for treatment of depression, is known to regulate several important structural and neurochemical aspects of hippocampal functions. However, the mechanisms underlying these effects are still poorly understood. This study aimed to investigate the effects of chronic fluoxetine treatment on axonal transport in the hippocampus of rat stress-induced model of depression.

METHODS

We have analyzed the effects of chronic fluoxetine treatment (20 mg/kg/day, 24 days) on immobility behavior (forced swimming test), hippocampal iNOS (inflammatory factor) expression (RT-PCR) as well as hippocampal BDNF, kinesin and dynein expression (RT-PCR) and hippocampal neuronal survival (Nissl staining).

RESULTS

This study provided evidence that fluoxetine could effectively suppress iNOS expression following unpredictable chronic mild stress (P < 0.01), increase hippocampal BDNF (P < 0.01), kinesin (P < 0.05) and dynein (P < 0.01) gene expression, and control neuronal death in CA1 (P < 0.01) and CA3 regions (P < 0.01) of the hippocampus and thereby improve immobility behavior (P < 0.001).

CONCLUSION

Based on the findings of this study, we concluded the neuroprotective effect of fluoxetine may be due to its ability to improve axonal transmission, followed by increased energy supply and neurotrophin concentration and function.

Chronic Psychosocial Stress Causes Increased Anxiety-Like Behavior and Alters Endocannabinoid Levels in the Brain of C57Bl/6J Mice

Introduction: Chronic stress causes a variety of physiological and behavioral alterations, including social impairments, altered endocrine function, and an increased risk for psychiatric disorders. Thereby, social stress is one of the most effective stressful stimuli among mammals and considered to be one of the major risk factors for the onset and progression of neuropsychiatric diseases. For analyzing the effects of social stress in mice, the resident/intruder paradigm of social defeat is a widely used model. Although the chronic social defeat stress model has been extensively studied, little is known about the effects of repeated or chronic social defeat stress on the endocannabinoid system (ECS). The present study aimed to understand the effects of chronic social stress on anxiety behavior and the levels of endocannabinoids (ECs) and two N-acylethanolamines (NAEs) in different brain regions of mice. Materials and Methods: Two-month-old, male C57Bl/6J mice were exposed to chronic psychosocial stress for 3 weeks. The effects of stress on anxiety behavior were measured using the light-dark box and hole board test. The EC levels of 2-arachidonoyl glycerol (2-AG) and anandamide (N-arachidonoylethanolamine [AEA]), as well as the levels of two NAEs (oleoylethanolamide [OEA] and palmitoylethanolamide), were analyzed by liquid chromatography-tandem mass spectrometry in the hippocampus, cerebellum, and cortex. Results: In comparison with control mice (n=12), mice exposed to social defeat stress (n=11) showed increased anxiety behaviors in the light-dark box and hole board test and gained significantly more weight during the experimental period. Additionally, chronic social stress induced differential alterations in the brain levels of 2-AG and AEA. More precisely, 2-AG levels were higher in the cortex and cerebellum, whereas reduced AEA levels were found in the hippocampus. Furthermore, we observed lower OEA levels in the hippocampus. Conclusion: The current study confirms that the ECS plays an essential role in stress responses, whereby its modulation seems to be brain region dependent.

Knockdown of miR-124 Reduces Depression-like Behavior by Targeting CREB1 and BDNF

OBJECTIVE

As a brain-specific microRNA, the mechanism of miR-124 in depression has not been clarified so far. The present study aimed to explore the role of miR-124 in depression and its potential targets.

METHODS

The depression model was first replicated by the chronic unpredictable mild stress (CUMS) method. miR-124 antagomir was injected into the hippocampus of CUMS rats. Sucrose preference test (SPT), open-field test (OFT), elevated-plus maze (EPM), and forced swimming test (FST) were used to analyze the depression-like behavior. The content of norepinephrine (NE), dopamine (DA) and 5-hydroxytryptamine (5-HT) in the hypothalamus was analyzed by ELISA. qRT-PCR and western blot assay were used for functional analysis.

RESULTS

miR-124 expression was up-regulated in the hippocampus of CUMS -induced depression model rats, while CREB1 and BDNF were down-regulated. Administration of miR-124 antagomir in the hippocampus inhibited miR-124 expression in the hippocampus of CUMS rats. Additionally, SPT, OFT, EPM, and FST also showed that miR-124 antagomir can reduce the depression-like behavior of CUMS rats. Furthermore, miR-124 antagomir injection increased the levels of NE, DA and 5-HT in the hypothalamus of CUMS rats. Moreover, miR-124 antagomir injection increased the expression of cyclic AMP-responsive element-binding protein1 (CREB1) and brain-derived neurotrophic factor (BDNF) in the hippocampus. Using the dual-luciferase reporter assay, it was confirmed that miR-124 directly targets 3'UTR of CREB1 and BDNF genes.

CONCLUSION

Knockdown of miR-124 can improve depression-like behavior in CUMS-induced depressive rats, which may be related at least in part to the up-regulation of CREB1 and BDNF expression in the hippocampus.

Multi-omics analysis identifies mitochondrial pathways associated with anxiety-related behavior

Stressful life events are major environmental risk factors for anxiety disorders, although not all individuals exposed to stress develop clinical anxiety. The molecular mechanisms underlying the influence of environmental effects on anxiety are largely unknown. To identify biological pathways mediating stress-related anxiety and resilience to it, we used the chronic social defeat stress (CSDS) paradigm in male mice of two inbred strains, C57BL/6NCrl (B6) and DBA/2NCrl (D2), that differ in their susceptibility to stress. Using a multi-omics approach, we identified differential mRNA, miRNA and protein expression changes in the bed nucleus of the stria terminalis (BNST) and blood cells after chronic stress. Integrative gene set enrichment analysis revealed enrichment of mitochondrial-related genes in the BNST and blood of stressed mice. To translate these results to human anxiety, we investigated blood gene expression changes associated with exposure-induced panic attacks. Remarkably, we found reduced expression of mitochondrial-related genes in D2 stress-susceptible mice and in exposure-induced panic attacks in humans, but increased expression of these genes in B6 stress-susceptible mice. Moreover, stress-susceptible vs. stress-resilient B6 mice displayed more mitochondrial cross-sections in the post-synaptic compartment after CSDS. Our findings demonstrate mitochondrial-related alterations in gene expression as an evolutionarily conserved response in stress-related behaviors and validate the use of cross-species approaches in investigating the biological mechanisms underlying anxiety disorders.

Hippocampal Salt-Inducible Kinase 2 Plays a Role in Depression via the CREB-Regulated Transcription Coactivator 1-cAMP Response Element Binding-Brain-Derived Neurotrophic Factor Pathway

BACKGROUND

Developing novel pharmacological targets beyond monoaminergic systems is now a popular strategy for finding new ways to treat depression. Salt-inducible kinase (SIK) is a kinase that regulates the nuclear translocation of cyclic adenosine monophosphate response element binding protein (CREB)-regulated transcription coactivator (CRTC) by phosphorylation. Here, we hypothesize that dysfunction of the central SIK-CRTC system may contribute to the pathogenesis of depression.

METHODS

Chronic social defeat stress (CSDS) and chronic unpredictable mild stress (CUMS) models of depression, various behavioral tests, viral-mediated gene transfer, Western blotting, coimmunoprecipitation, quantitative real-time reverse transcription polymerase chain reaction, and immunohistochemistry were used in this study (for in vivo studies, n = 10; for in vitro studies, n = 5).

RESULTS

Both CSDS and CUMS markedly increased the expression of hippocampal SIK2, which reduced CRTC1 nuclear translocation and binding of CRTC1 and CREB in the hippocampus. Genetic overexpression of hippocampal SIK2 in naïve mice simulated chronic stress, inducing depressive-like behaviors in the forced swim test, tail suspension test, sucrose preference test, and social interaction test, as well as decreasing the brain-derived neurotrophic factor signaling cascade and neurogenesis in the hippocampus. In contrast, genetic knockdown and knockout of hippocampal SIK2 protected against CSDS and CUMS, exerting significant antidepressant-like effects that were mediated via the downstream CRTC1-CREB-brain-derived neurotrophic factor pathway. Moreover, fluoxetine, venlafaxine, and mirtazapine all significantly restored the effects of CSDS and CUMS on the hippocampal SIK2-CRTC1 pathway, which was necessary for their antidepressant actions.

CONCLUSIONS

The hippocampal SIK2-CRTC1 pathway is involved in the pathogenesis of depression, and hippocampal SIK2 could be a novel target for the development of antidepressants.

Hippocampal PPARα is a novel therapeutic target for depression and mediates the antidepressant actions of fluoxetine in mice

BACKGROUND AND PURPOSE

Developing novel pharmacological targets beyond the monoaminergic system is now a popular strategy for treating depression. PPARα is a nuclear receptor protein that functions as a transcription factor,-regulating gene expression. We have previously reported that both WY14643 and fenofibrate, two pharmacological agonists of PPARα, have antidepressant-like effects in mice, implying that PPARα is a potential antidepressant target.

EXPERIMENTAL APPROACH

We first used various biotechnological methods to evaluate the effects of chronic stress and fluoxetine on hippocampal PPARα. The viral-mediated genetic approach was then employed to explore whether hippocampal PPARα was an antidepressant target. PPARα inhibitors, PPARα-knockout (KO) mice and PPARα-knockdown (KD) mice were further used to determine the role of PPARα in the antidepressant effects of fluoxetine.

KEY RESULTS

Chronic stress significantly decreased mRNA and protein levels of PPARα in the hippocampus, but not other regions, and also fully reduced the recruitment of hippocampal PPARα to the cAMP response element-binding (CREB) promoter. Genetic overexpression of hippocampal PPARα induced significant antidepressant-like actions in mice by promoting CREB-mediated biosynthesis of brain-derived neurotrophic factor. Moreover, fluoxetine notably restored the stress-induced negative effects on hippocampal PPARα. Using PPARα antagonists fully blocked the antidepressant effects of fluoxetine in mice, and similarly, both PPARα-KO and PPARα-KD abolished the effects of fluoxetine. Besides, PPARα-KO and PPARα-KD aggravated depression in mice.

CONCLUSIONS AND IMPLICATIONS

Hippocampal PPARα is a potential novel antidepressant target that mediates the antidepressant actions of fluoxetine in mice.

Histamine-deficient mice do not respond to the antidepressant-like effects of oleoylethanolamide

It has been suggested that the bioactive lipid mediator oleoylethanolamide (OEA), a potent agonist of the peroxisome proliferator-activated receptor-alpha (PPAR-α) possesses anti-depressant-like effects in several preclinical models. We recently demonstrated that several of OEA's behavioural actions require the integrity of the brain histaminergic system, and that an intact histaminergic neurotransmission is specifically required for selective serotonin re-uptake inhibitors to exert their anti-depressant-like effect. The purpose of our study was to test if OEA requires the integrity of the histaminergic neurotransmission to exert its antidepressant-like effects. Immobility time in the tail suspension test was measured to assess OEA's potential (10 mg/kg i.p.) as an antidepressant drug in histidine decarboxylase null (HDC^-/-) mice and HDC^+/+ littermates, as well as in PPAR-α^+/+ and PPAR-α^-/- mice. CREB phosphorylation was evaluated using Western blot analysis in hippocampal and cortical homogenates, as pCREB is considered partially responsible for the efficacy of antidepressants. Serotonin release from ventral hippocampi of HDC^+/+ and HDC^-/- mice was measured with in-vivo microdialysis, following OEA administration. OEA decreased immobility time and increased brain pCREB levels in HDC^+/+ mice, whereas it was ineffective in HDC^-/- mice. Comparable results were obtained in PPAR-α^+/+ and PPAR-α^-/- mice. Microdialysis revealed a dysregulation of serotonin release induced by OEA in HDC^-/- mice. Our observations corroborate our hypothesis that brain histamine and signals transmitted by OEA interact to elaborate appropriate behaviours and may be the basis for the efficacy of OEA as an antidepressant-like compound.

Brain-derived neurotrophic factor signaling plays a role in resilience to stress promoted by isoquinoline in defeated mice

Certain stressful life events have been associated with the onset of depression. This study aims to investigate if 7-fluoro-1,3-diphenylisoquinoline-1-amine (FDPI) is effective against social avoidance induced by social defeat stress model in mice. Furthermore, it was investigated the effects of FDPI in the mouse prefrontal cortical plasticity-related proteins and some parameters of toxicity. Adult Swiss mice were subjected to social defeat stress for 10 days. Two protocols with FDPI were carried out: 1- FDPI (25 mg/kg, intragastric) was administered to mice 24 h after the last social defeat stress episode; 2- FDPI (1-25 mg/kg, intragastric) was administered to mice once a day for 10 days concomitant with the social defeat stress. The mice performed social avoidance and locomotor tests. The prefrontal cortical protein contents of kinase B (Akt), extracellular signal-regulated kinase (ERK), cAMP-response element binding protein (CREB), pro-brain-derived neurotrophic factor (proBDNF), p75^NTR, neuronal nuclear protein (NeuN) and nuclear factor-κB (NF-κB) were determined in mice. A single administration of FDPI (25 mg/kg) partially protected against social avoidance induced by stress in mice. Repeated administration of FDPI (25 mg/kg) protected against social avoidance induced by stress in mice. Social defeat stress decreased the protein contents of p75^NTR, NeuN and the pERK/ERK ratio but increased those of proBDNF and the pCREB/CREB ratio, without changing that of NF-κB. Repeated administration of FDPI modulated signaling pathways altered by social defeat stress in mice. The present findings demonstrate that FDPI promoted resilience to stress in mice.

Regulation of actions and habits by ventral hippocampal trkB and adolescent corticosteroid exposure

In humans and rodents, stress promotes habit-based behaviors that can interfere with action-outcome decision-making. Further, developmental stressor exposure confers long-term habit biases across rodent-primate species. Despite these homologies, mechanisms remain unclear. We first report that exposure to the primary glucocorticoid corticosterone (CORT) in adolescent mice recapitulates multiple neurobehavioral consequences of stressor exposure, including long-lasting biases towards habit-based responding in a food-reinforced operant conditioning task. In both adolescents and adults, CORT also caused a shift in the balance between full-length tyrosine kinase receptor B (trkB) and a truncated form of this neurotrophin receptor, favoring the inactive form throughout multiple corticolimbic brain regions. In adolescents, phosphorylation of the trkB substrate extracellular signal-regulated kinase 42/44 (ERK42/44) in the ventral hippocampus was also diminished, a long-term effect that persisted for at least 12 wk. Administration of the trkB agonist 7,8-dihydroxyflavone (7,8-DHF) during adolescence at doses that stimulated ERK42/44 corrected long-lasting corticosterone-induced behavioral abnormalities. Meanwhile, viral-mediated overexpression of truncated trkB in the ventral hippocampus reduced local ERK42/44 phosphorylation and was sufficient to induce habit-based and depression-like behaviors. Together, our findings indicate that ventral hippocampal trkB is essential to goal-directed action selection, countering habit-based behavior otherwise facilitated by developmental stress hormone exposure. They also reveal an early-life sensitive period during which trkB-ERK42/44 tone determines long-term behavioral outcomes.

Neuropeptide VGF C-Terminal Peptide TLQP-62 Alleviates Lipopolysaccharide-Induced Memory Deficits and Anxiety-like and Depression-like Behaviors in Mice: The Role of BDNF/TrkB Signaling

Peripheral inflammatory responses affect central nervous system (CNS) function, manifesting in symptoms of memory deficits, depression, and anxiety. Previous studies have revealed that neuropeptide VGF (nonacronymic) C-terminal peptide TLQP-62 rapidly reinforces brain-derived neurotrophic factor (BDNF)/tropomyosin receptor kinase B (TrkB) signaling, regulating memory consolidation and antidepressant-like action. However, whether it is beneficial for lipopolysaccharide (LPS)-induced neuropsychiatric dysfunction in mice is unknown. Herein, we explored the involvement of BDNF/TrkB signaling and biochemical alterations in inflammatory or oxidative stress markers in the alleviating effects of TLQP-62 on LPS-induced neuropsychiatric dysfunction. The mice were treated with TLQP-62 (2 μg/side) via intracerebroventricular (i.c.v.) injection 1 h before LPS (0.5 mg/kg, i.p.) administration. Our results showed that a single treatment with LPS (0.5 mg/kg, i.p) is sufficient to produce recognition memory deficits (in the novel object recognition test), depression-like behavior (in the forced swim test and sucrose preference test), and anxiety-like behavior (in the elevated zero maze). However, pretreatment with TLQP-62 prevented LPS-induced behavioral dysfunction, neuroinflammatory, and oxidative responses. In addition, our results further demonstrated that a reduction in BDNF expression mediated by BDNF-shRNA lentivirus significantly blocked the effects of TLQP-62, suggesting the critical role of BDNF/TrkB signaling in the neuroprotective effects of TLQP-62 in the mice. In conclusion, TLQP-62 could be a therapeutic approach for neuropsychiatric disorders, which are closely associated with neuroinflammation and oxidative stress.

Hippocampal BDNF in physiological conditions and social isolation

Exposure of an organism to chronic psychosocial stress may affect brain-derived neurotrophic factor (BDNF) expression that has been implicated in the etiology of psychiatric disorders, such as depression. Given that depression in humans has been linked with social stress, the chronic social stress paradigms for modeling psychiatric disorders in animals have thus been developed. Chronic social isolation in animal models generally causes changes in hypothalamic-pituitary-adrenal axis functioning, associated with anxiety- and depressive-like behaviors. Also, this chronic stress causes downregulation of BDNF protein and mRNA in the hippocampus, a stress-sensitive brain region closely related to the pathophysiology of depression. In this review, we discuss the current knowledge regarding the structure, function, intracellular signaling, inter-individual differences and epigenetic regulation of BDNF in both physiological conditions and depression and changes in corticosterone levels, as a marker of stress response. Since BDNF levels are age dependent in humans and rodents, this review will also highlight the effects of adolescent and adult chronic social isolation models of both genders on the BDNF expression.

Antidepressant-like effects of tetrahydroxystilbene glucoside in mice: Involvement of BDNF signaling cascade in the hippocampus

BACKGROUND AND AIMS

Current antidepressants in clinic need weeks of administration and always have significant limitations. Tetrahydroxystilbene glucoside (TSG) is one of the major bioactive ingredients of Polygonum multiflorum with neuroprotective effects. This study aimed to evaluate the antidepressant effects of TSG in mice.

METHODS

The antidepressant-like effects of TSG in mice were examined in the forced swim test (FST), tail suspension test (TST), and chronic social defeat stress (CSDS) model of depression. The effects of CSDS and TSG on the hippocampal brain-derived neurotrophic factor (BDNF) signaling pathway and neurogenesis were further investigated. Moreover, the pharmacological inhibitors and lentiviral-shRNA were used to explore the antidepressant mechanisms of TSG.

RESULTS

TSG produced antidepressant-like effects in the FST and TST and also reversed the CSDS-induced depressive-like symptoms. Moreover, TSG treatment significantly restored the decreased hippocampal BDNF signaling pathway and neurogenesis in CSDS mice. Importantly, blockade of the hippocampal BDNF system fully abolished the antidepressant-like effects of TSG in mice.

CONCLUSION

In conclusion, TSG produces antidepressant-like effects in mice via enhancement of the hippocampal BDNF system.

Effects of Diet Quality and Psychosocial Stress on the Metabolic Profiles of Mice

There has been an increasing interest in relationship between stress and diet. To address this relationship, we evaluated an animal model of depression: male C57BL/6J mice subjected to subchronic mild social defeat stress (sCSDS) for 10 consecutive days using male ICR mice under two different calorie-adjusted diets conditions-nonpurified (MF) and semipurified (AIN) diets made from natural and chemical ingredients mainly, respectively. Our previous study indicates that diet quality and purity affect stress susceptibility in sCSDS mice. We therefore hypothesized that there are some key peripheral metabolites to change stress-susceptible behavior. GC-MS metabolomics of plasma, liver, and cecal content were performed on four test groups: sCSDS + AIN diet (n = 7), sCSDS + MF diet (n = 6), control (no sCSDS) + AIN diet (n = 8), and control + MF diet (n = 8). Metabolome analyses revealed that the number of metabolites changed by food was larger than the number changed by stress in all tissues. Enrichment analysis of the liver metabolite set altered by food implies that stress-susceptible mice show increased glycolysis-related substrates in the liver. We found metabolites that were affected by stress (e.g., plasma and liver 4-hydroxyproline and plasma beta-alanine are higher in sCSDS than in control) and a stress × food interaction (e.g., plasma GABA is lower in sCSDS + AIN than in sCSDS + MF). Because functional compounds were altered by both stress and food, diet may be able to attenuate various stress-induced symptoms by changing metabolites in peripheral tissues.

Antidepressant-like effects of ginsenoside Rg5 in mice: Involving of hippocampus BDNF signaling pathway

Ginsenoside Rg5 is one of the major bioactive ingredients of Panax ginseng with little toxicity and has been shown to have pharmacological effects on the central nervous system. In this study, we investigated the antidepressant effects of Rg5 in mice models of depression. The effects of Rg5 were first assessed in the forced swimming test (FST) and tail suspension test (TST), and then investigated in the chronic social defeat stress (CSDS) model of depression. The changes in hippocampal brain-derived neurotrophic factor (BDNF) signaling pathway after CSDS and Rg5 treatment were also examined. The tryptophan hydroxylase inhibitor and tyrosine kinase B inhibitor were used to explore the antidepressant mechanisms of Rg5. It was found that Rg5 exhibited antidepressant-like activities in the FST and TST without affecting locomotor activity. Rg5 was also effective in the CSDS model of depression, and restored the CSDS-induced decrease in hippocampal BDNF signaling cascade. Moreover, the usage of the tyrosine kinase B inhibitor blocked the antidepressant effects of Rg5, while the tryptophan hydroxylase inhibitor did not. Collectively, ginsenoside Rg5 has antidepressant activities via the activation of hippocampal BDNF system.

Understanding the epigenetic basis of sex differences in depression

Epigenetics refers to potentially heritable processes that can mediate both lasting and transient changes in gene expression in the absence of genome sequence alterations. The field of epigenetics has introduced a novel understanding of the mechanisms through which the environment can shape an individual and potentially its offspring. This Mini-Review examines the current literature exploring the role of epigenetics in the development of mood disorders such as depression. Depression is twofold more common in females, yet the majority of preclinical research has been conducted exclusively in male subjects. Here we discuss what is known about sex differences in epigenetic regulation and function and how this may contribute to the etiology and onset of mood disorders. © 2016 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.

Elevation of synaptic protein is associated with the antidepressant-like effects of ferulic acid in a chronic model of depression

Ferulic acid is a hydroxycinnamic acid that widely presents in plant cell wall components. It has been demonstrated that ferulic acid can reverse depressive-like behaviors in both forced swimming test and tail suspension test. However, it is unclear whether chronic ferulic acid treatment can ameliorate the depressive-like behaviors in chronic unpredictable mild stress (CUMS). Because of the putative relationship between neurotrophic system and antidepressant-like activity, we also investigated the effects of chronic ferulic acid on the brain-derived neurotrophic factor (BDNF), postsynaptic protein PSD95, presynaptic protein synapsin I in both prefrontal cortex and hippocampus. The results showed that ferulic acid significantly alleviated CUMS-induced depressive-like behaviors in sucrose preference test and forced swimming test. In addition, ferulic acid significantly up-regulated the levels of BDNF, PSD95 and synapsin I in the prefrontal cortex and hippocampus. The present data indicated that ferulic acid exerted the antidepressant-like effects on behaviors by increasing neurotrophin-related synaptic protein levels in CUMS mice.

Antidepressant-Like Effects of GM1 Ganglioside Involving the BDNF Signaling Cascade in Mice

BACKGROUND

Depression is a serious psychiatric disorder that easily causes physical impairments and a high suicide rate. Monosialotetrahexosylganglioside is a crucial ganglioside for the central nervous system and has been reported to affect the function of the brain derived neurotrophic factor system. This study is aimed to evaluate whether monosialotetrahexosylganglioside has antidepressant-like effects.

METHODS

Antidepressant-like effects of monosialotetrahexosylganglioside were assessed in the chronic social defeat stress model of depression, and various behavioral tests were performed. Changes in the brain derived neurotrophic factor signaling pathway after chronic social defeat stress and monosialotetrahexosylganglioside treatment were also investigated. A tryptophan hydroxylase inhibitor and brain derived neurotrophic factor signaling inhibitors were used to determine the antidepressant mechanisms of monosialotetrahexosylganglioside.

RESULTS

Monosialotetrahexosylganglioside administration significantly reversed the chronic social defeat stress-induced reduction of sucrose preference and social interaction in mice and also prevented the increased immobility time in the forced swim test and tail suspension test. In addition, monosialotetrahexosylganglioside completely ameliorated the stress-induced dysfunction of brain derived neurotrophic factor signaling cascade in the hippocampus and medial prefrontal cortex, 2 regions closely involved in the pathophysiology of depression. Furthermore, the usage of brain derived neurotrophic factor signaling cascade inhibitors, K252a and anti-brain derived neurotrophic factor antibody, each abolished the antidepressant-like effects of monosialotetrahexosylganglioside, while the usage of a serotonin system inhibitor did not.

CONCLUSIONS

Taken together, our findings suggest that monosialotetrahexosylganglioside indeed has antidepressant-like effects, and these effects were mediated through the activation of brain derived neurotrophic factor signaling cascade.

The effect of Piper laetispicum extract (EAE-P) during chronic unpredictable mild stress based on interrelationship of inflammatory cytokines, apoptosis cytokines and neurotrophin in the hippocampus

Backgroud

The Piper laetispicum C.DC. (Piperaceae) is a traditionally used herb in China for invigorating circulation and reducing stasis, detumescence and analgesia, which is distributed in the southern part of China and the southeastern part of Asia. Previous studies demonstrated that the ethyl acetate extract (EAE-P) of P. laetispicum possesses a significant antidepressant-like effect at doses higher than 60 mg/kg in Kunming (KM) mice, and this effect was not due to an increase in locomotive activity.

Methods

To research this mechanism, in the present study, the chronic unpredictable mild stress (CUMS) model in Sprague–Dawley rats was used to further elucidate behavioral changes and corresponding changes in inflammatory cytokines (TNF-α, IL-6, IL-10), apoptosis cytokines (P53, Bax, Bcl2, caspase-3) and neurotrophin (BDNF) in the hippocampus of EAE-P treatment animals.

Results and conclusions

The results suggest that EAE-P is beneficial to the behavioral outcome of the CUMS model animals, and decreased amounts of inflammatory cytokine IL-6 contributed to the antidepressant-like activation of EAE-P in every dosage group (15, 30, 60 mg/kg). In the low dosage group, down-regulated apoptosis cytokine p53 is associated with EAE-P effect, but it is inflammatory cytokine TNF-α that is related to the effect of EAE-P in the high dosage group. Meanwhile, the P53-dependent antiapoptotic effect of EAE-P may not be through Bcl-2 and Bax modulation. Furthermore, EAE-P showed up-regulated expression of brain-derived neurotrophic factor (BDNF) mRNA and down-regulated apoptosis cytokine caspase-3 mRNA, which was the same change tendency as with Fluoxetine.

Epigenetic signaling in psychiatric disorders: stress and depression

Psychiatric disorders are complex multifactorial disorders involving chronic alterations in neural circuit structure and function. While genetic factors play a role in the etiology of disorders such as depression, addiction, and schizophrenia, relatively high rates of discordance among identical twins clearly point to the importance of additional factors. Environmental factors, such as stress, play a major role in the psychiatric disorders by inducing stable changes in gene expression, neural circuit function, and ultimately behavior. Insults at the developmental stage and in adulthood appear to induce distinct maladaptations. Increasing evidence indicates that these sustained abnormalities are maintained by epigenetic modifications in specific brain regions. Indeed, transcriptional dysregulation and associated aberrant epigenetic regulation is a unifying theme in psychiatric disorders. Aspects of depression can be modeled in animals by inducing disease-like states through environmental manipulations, and these studies can provide a more general understanding of epigenetic mechanisms in psychiatric disorders. Understanding how environmental factors recruit the epigenetic machinery in animal models is providing new insights into disease mechanisms in humans.

WY14643 produces anti-depressant-like effects in mice via the BDNF signaling pathway

RATIONALE

Current anti-depressants are clinically effective only after several weeks of administration and always produce side effects.

OBJECTIVES

WY14643 is a selective agonist of peroxisome proliferator-activated receptor-α with neuroprotective and neurotrophic effects. Here, we investigated the anti-depressant effects of WY14643 in mice models of depression.

METHODS

We assessed the anti-depressant effects of WY14643 in the forced swim test (FST), tail suspension test (TST) and chronic social defeat stress (CSDS) model. Western blotting and immunohistochemistry studies were further performed to detect the effects of WY14643 on the brain-derived neurotrophic factor (BDNF) signaling pathway and hippocampal neurogenesis. The anti-BDNF antibody, BDNF signaling inhibitor, and tryptophan hydroxylase inhibitor were also used to explore the anti-depressant mechanisms of WY14643.

RESULTS

WY14643 exhibited robust anti-depressant effects in the FST and TST and also protected against the CSDS stress in mice models. Moreover, WY14643 reversed the stress-induced elevation of corticosterone, deficiency of BDNF signaling pathway, and hippocampal neurogenesis. Blockade of BDNF signaling cascade, not the monoaminergic system, abolished all the anti-depressant effects of WY14643.

CONCLUSIONS

These data provide the first evidence that WY14643 exerts anti-depressant-like activity through promoting the BDNF signaling pathway.

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.

SKF83959 produces antidepressant effects in a chronic social defeat stress model of depression through BDNF-TrkB pathway

BACKGROUND

SKF83959 stimulates the phospholipase Cβ/inositol phosphate 3 pathway, resulting in the activation of Ca(2+)/calmodulin-dependent kinase IIα, which affects the synthesis of brain-derived neurotrophic factor, a neurotrophic factor critical for the pathophysiology of depression. Previous reports showed that SKF83959 elicited antidepressant activity in the forced swim test and tail suspension test as a novel triple reuptake inhibitor. However, there are no studies showing the effects of SKF83959 in a chronic stress model of depression and the role of phospholipase C/inositol phosphate 3/calmodulin-dependent kinase IIα/brain-derived neurotrophic factor pathway in SKF83959-mediated antidepressant effects.

METHODS

In this study, SKF83959 was firstly investigated in the chronic social defeat stress model of depression. The changes in hippocampal neurogenesis, dendrite spine density, and brain-derived neurotrophic factor signaling pathway after chronic social defeat stress and SKF83959 treatment were then investigated. Pharmacological inhibitors and small interfering RNA/short hairpin RNA methods were further used to explore the antidepressive mechanisms of SKF83959.

RESULTS

We found that SKF83959 produced antidepressant effects in the chronic social defeat stress model and also restored the chronic social defeat stress-induced decrease in hippocampal brain-derived neurotrophic factor signaling pathway, dendritic spine density, and neurogenesis. By using various inhibitors and siRNA/shRNA methods, we further demonstrated that the hippocampal dopamine D5 receptor, phospholipase C/inositol phosphate 3/ calmodulin-dependent kinase IIα pathway, and brain-derived neurotrophic factor system are all necessary for the SKF83959 effects.

CONCLUSION

These results suggest that SKF83959 can be developed as a novel antidepressant and produces antidepressant effects via the hippocampal D5/ phospholipase C/inositol phosphate 3/calmodulin-dependent kinase IIα/brain-derived neurotrophic factor pathway.

The molecular bases of the suicidal brain

Suicide ranks among the leading causes of death around the world and takes a heavy emotional and public health toll on most societies. Both distal and proximal factors contribute to suicidal behaviour. Distal factors - such as familial and genetic predisposition, as well as early-life adversity - increase the lifetime risk of suicide. They alter responses to stress and other processes through epigenetic modification of genes and associated changes in gene expression, and through the regulation of emotional and behavioural traits. Proximal factors are associated with the precipitation of a suicidal event and include alterations in key neurotransmitter systems, inflammatory changes and glial dysfunction in the brain. This Review explores the key molecular changes that are associated with suicidality and discusses some promising avenues for future research.

Rodent models of depression: neurotrophic and neuroinflammatory biomarkers

Rodent models are an indispensable tool for studying etiology and progress of depression. Since interrelated systems of neurotrophic factors and cytokines comprise major regulatory mechanisms controlling normal brain plasticity, impairments of these systems form the basis for development of cerebral pathologies, including mental diseases. The present review focuses on the numerous experimental rodent models of depression induced by different stress factors (exteroceptive and interoceptive) during early life (including prenatal period) or adulthood, giving emphasis to the data on the changes of neurotrophic factors and neuroinflammatory indices in the brain. These parameters are closely related to behavioral depression-like symptoms and impairments of neuronal plasticity and are both gender- and genotype-dependent. Stress-related changes in expression of neurotrophins and cytokines in rodent brain are region-specific. Some contradictory data reported by different groups may be a consequence of differences of stress paradigms or their realization in different laboratories. Like all experimental models, stress-induced depression-like conditions are experimental simplification of clinical depression states; however, they are suitable for understanding the involvement of neurotrophic factors and cytokines in the pathogenesis of the disease—a goal unachievable in the clinical reality. These major regulatory systems may be important targets for therapeutic measures as well as for development of drugs for treatment of depression states.

Functional DNA methylation in a transcript specific 3'UTR region of TrkB associates with suicide

Previous studies indicate that a subgroup of suicide completers has low cortical brain expression levels of TrkB-T1, a TrkB gene transcript that is highly expressed in astrocytes. Epigenetic modifications, including methylation changes in the TrkB promoter, partially explain TrkB-T1 low expression levels in brain tissue from suicide completers. The aim of this study was to investigate whether methylation changes in other regions of the TrkB gene could also contribute to the significant downregulation of the TrkB-T1 transcript observed in the brain of suicide completers. Methylation levels were assessed on BA8/9 from suicide completers expressing low TrkB-T1 transcript levels and controls, using custom-made Agilent arrays tiling the whole TrkB gene. After statistical correction for multiple testing, five probes located in the TrkB-T1 3'UTR region were found hypermethylated in the frontal cortex of suicide completers. These results were validated for four CpGs spanning a 150 bp sequence by cloning and Sanger sequencing bisulfite treated DNA. We found a significant correlation between the methylation level at these four CpGs and TrkB-T1 expression in BA8/9. Site-specific hypermethylation on this 3'UTR sequence induced decreased luciferase activity in reporter gene cell assays. Site-specific differential methylation in the TrkB-T1 3'UTR region associates with functional changes in TrkB-T1 expression and may play a significant role in the important decrease of cortical TrkB-T1 expression observed among suicide completers.

Mice with altered BDNF signaling as models for mood disorders and antidepressant effects

Brain-derived neurotrophic factor (BDNF) and its receptor tyrosine kinase TrkB support neuronal survival during development and promote connectivity and plasticity in the adult brain. Decreased BDNF signaling is associated with the pathophysiology of depression and the mechanisms underlying the actions of antidepressant drugs (AD). Several transgenic mouse models with decreases or increases in the amount of BDNF or the activity of TrkB signaling have been created. This review summarizes the studies where various mouse models with increased or decreased BDNF levels or TrkB signaling were used to evaluate the role of BDNF signaling in depression-like behavior. Although a large number of models have been employed and several studies have been published, no clear-cut connections between BDNF levels or signaling and depression-like behavior in mice have emerged. However, it is clear that BDNF plays a critical role in the mechanisms underlying the actions of AD.

Neuropeptide S and BDNF gene expression in the amygdala are influenced by social decision-making under stress

In a newly developed conceptual model of stressful social decision-making, the Stress-Alternatives Model (SAM; used for the 1st time in mice) elicits two types of response: escape or remain submissively. Daily (4d) aggressive social interaction in a neutral arena between a C57BL6/N test mouse and a larger, novel aggressive CD1 mouse, begin after an audible tone (conditioned stimulus; CS). Although escape holes (only large enough for smaller test animals) are available, and the aggressor is unremittingly antagonistic, only half of the mice tested utilize the possibility of escape. During training, for mice that choose to leave the arena and social interaction, latency to escape dramatically decreases over time; this is also true for control C57BL6/N mice which experienced no aggression. Therefore, the open field of the SAM apparatus is intrinsically anxiogenic. It also means that submission to the aggressor is chosen despite this anxiety and the high intensity of the aggressive attacks and defeat. While both groups that received aggression displayed stress responsiveness, corticosterone levels were significantly higher in animals that chose submissive coexistence. Although both escaping and non-escaping groups of animals experienced aggression and defeat, submissive animals also exhibited classic fear conditioning, freezing in response to the CS alone, while escaping animals did not. In the basolateral amygdala (BLA), gene expression of brain-derived neurotrophic factor (BDNF) was diminished, at the same time neuropeptide S (NPS) expression was significantly elevated, but only in submissive animals. This increase in submission-evoked NPS mRNA expression was greatest in the central amygdala (CeA), which coincided with decreased BDNF expression. Reduced expression of BDNF was only found in submissive animals that also exhibit elevated NPS expression, despite elevated corticosterone in all socially interacting animals. The results suggest an interwoven relationship, linked by social context, between amygdalar BDNF, NPS and plasma corticosterone.

Epigenetic signaling in psychiatric disorders

Psychiatric disorders are complex multifactorial illnesses involving chronic alterations in neural circuit structure and function. While genetic factors are important in the etiology of disorders such as depression and addiction, relatively high rates of discordance among identical twins clearly indicate the importance of additional mechanisms. Environmental factors such as stress or prior drug exposure are known to play a role in the onset of these illnesses. Such exposure to environmental insults induces stable changes in gene expression, neural circuit function, and ultimately behavior, and these maladaptations appear distinct between developmental and adult exposures. Increasing evidence indicates that these sustained abnormalities are maintained by epigenetic modifications in specific brain regions. Indeed, transcriptional dysregulation and associated aberrant epigenetic regulation is a unifying theme in psychiatric disorders. Aspects of depression and addiction can be modeled in animals by inducing disease-like states through environmental manipulations (e.g., chronic stress, drug administration). Understanding how environmental factors recruit the epigenetic machinery in animal models reveals new insight into disease mechanisms in humans.

Chemokines and chemokine receptors in mood disorders, schizophrenia, and cognitive impairment: a systematic review of biomarker studies

The search for immune biomarkers in psychiatric disorders has primarily focused on pro-inflammatory cytokines. Other immune proteins including chemokines have been relatively neglected in such studies. Recent evidence has implicated chemokines in many neurobiological processes potentially relevant to psychiatric disorders, beyond their classical chemotactic functions. These may include neuromodulator effects, neurotransmitter-like effects, and direct/indirect regulation of neurogenesis. This systematic review presents the existing early evidence which supports an association of many chemokines with the psychiatric disorders: depression, bipolar disorder, schizophrenia, mild cognitive impairment and Alzheimer's disease. The non-specific association of chemokines including CXCL8 (IL-8), CCL2 (MCP-1), CCL3 (MIP-1α) and CCL5 (RANTES) with these disorders across diagnostic categories implies a generalised involvement of many chemokine systemic with psychiatric disease. Additional chemokines with great mechanistic relevance including CXCL12 (SDF-1) and CX3CL1 (fractalkine) have been rarely reported in the existing human literature and should be included in future clinical studies. The potential utility of these proteins as pathologically relevant biomarkers or therapeutic targets should be considered by future clinical and translational research.

Does stress elicit depression? Evidence from clinical and preclinical studies

Exposure to stressful situations may induce or deteriorate an already existing depression. Stress-related depression can be elicited at an adolescent/adult age but evidence also shows that early adverse experiences even at the fetal stage may predispose the offspring for later development of depression. The hypothalamus-pituitary-adrenal axis (HPA-axis) plays a key role in regulating the stress response and dysregulation in the system has been linked to depression both in humans and in animal models. This chapter critically reviews clinical and preclinical findings that may explain how stress can cause depression, including HPA-axis changes and alterations beyond the HPA-axis. As stress does not elicit depression in the majority of the population, this motivated research to focus on understanding the biology underlying resilient versus sensitive subjects. Animal models of depression have contributed to a deeper understanding of these mechanisms. Findings from these models will be presented.

Oxidative/nitrosative stress and antidepressants: targets for novel antidepressants

The brain is an organ predisposed to oxidative/nitrosative stress. This is especially true in the case of aging as well as several neurodegenerative diseases. Under such circumstances, a decline in the normal antioxidant defense mechanisms leads to an increase in the vulnerability of the brain to the deleterious effects of oxidative damage. Highly reactive oxygen/nitrogen species damage lipids, proteins, and mitochondrial and neuronal genes. Unless antioxidant defenses react appropriately to damage inflicted by radicals, neurons may experience microalteration, microdysfunction, and degeneration. We reviewed how oxidative and nitrosative stresses contribute to the pathogenesis of depressive disorders and reviewed the clinical implications of various antioxidants as future targets for antidepressant treatment.