Regionally specific regulation of ERK MAP kinase in a model of antidepressant-sensitive chronic depression

Ginsenoside Re Prevents Depression-like Behaviors via Inhibition of Inflammation, Oxidative Stress, and Activating BDNF/TrkB/ERK/CREB Signaling: An In Vivo and In Vitro Study

Depression is a widespread disease, with high mortality and recurrence rates. Recent studies have shown that elevated cytokine levels are implicated in the molecular mechanisms of depression. Oxidative stress contributes to the stimulation of cytokine production. Growing evidence suggests that ginsenoside Re (Gs-Re) exerts a neuroprotective effect on the hippocampus by suppressing oxidative stress and inflammation. However, the effect and mechanism of Gs-Re in the treatment of depression remain understudied. This study aimed to evaluate the neuroprotective and antidepressant-like effects of Gs-Re and the possible underlying mechanisms. In this article, the antidepressant-like effect of the Gs-Re was studied both in vitro (H2O2-induced oxidative stress in HT-22 cells) and in vivo (reserpine-induced depressive model mice). Our results indicated that, at the cellular level, Gs-Re effectively enhanced cell survival following H2O2 stimulation, inhibited the mass production of oxidative stress markers (MDA and ROS), and prevented the occurrence of apoptosis. Moreover, Gs-Re significantly reduced the levels of proinflammatory cytokines IL-1β, IL-6, and TNF-α and restored the abnormal mitochondrial membrane potential. Subsequently, Gs-Re treatment reversed reserpine-induced neuroinflammation and depressive-like behaviors in vivo and inhibited microglia overactivation. Furthermore, the alterations in the BDNF/TrkB/ERK/CREB signaling pathway induced by H2O2 or reserpine in HT-22 cells or in the mouse hippocampus were significantly reversed by Gs-Re. K252a blocked the improvement of Gs-Re on depression-like behavior and eliminated the inhibition of oxidative stress and neuroinflammation in vivo. This study suggested that Gs-Re produces neuroprotective and depressive effects by inhibiting oxidative stress and inflammation and activating the BDNF/TrkB/ERK/CREB pathway.

Transcriptomic decoding of regional cortical vulnerability to major depressive disorder

Previous studies in small samples have identified inconsistent cortical abnormalities in major depressive disorder (MDD). Despite genetic influences on MDD and the brain, it is unclear how genetic risk for MDD is translated into spatially patterned cortical vulnerability. Here, we initially examined voxel-wise differences in cortical function and structure using the largest multi-modal MRI data from 1660 MDD patients and 1341 controls. Combined with the Allen Human Brain Atlas, we then adopted transcription-neuroimaging spatial correlation and the newly developed ensemble-based gene category enrichment analysis to identify gene categories with expression related to cortical changes in MDD. Results showed that patients had relatively circumscribed impairments in local functional properties and broadly distributed disruptions in global functional connectivity, consistently characterized by hyper-function in associative areas and hypo-function in primary regions. Moreover, the local functional alterations were correlated with genes enriched for biological functions related to MDD in general (e.g., endoplasmic reticulum stress, mitogen-activated protein kinase, histone acetylation, and DNA methylation); and the global functional connectivity changes were associated with not only MDD-general, but also brain-relevant genes (e.g., neuron, synapse, axon, glial cell, and neurotransmitters). Our findings may provide important insights into the transcriptomic signatures of regional cortical vulnerability to MDD.

Cocaine disrupts action flexibility via glucocorticoid receptors

Many addictive drugs increase stress hormone levels. They also alter the propensity of organisms to prospectively select actions based on long-term consequences. We hypothesized that cocaine causes inflexible action by increasing circulating stress hormone levels, activating the glucocorticoid receptor (GR). We trained mice to generate two nose pokes for food and then required them to update action-consequence associations when one response was no longer reinforced. Cocaine delivered in adolescence or adulthood impaired the capacity of mice to update action strategies, and inhibiting CORT synthesis rescued action flexibility. Next, we reduced Nr3c1, encoding GR, in the orbitofrontal cortex (OFC), a region of the brain responsible for interlacing new information into established routines. Nr3c1 silencing preserved action flexibility and dendritic spine abundance on excitatory neurons, despite cocaine. Spines are often considered substrates for learning and memory, leading to the discovery that cocaine degrades the representation of new action memories, obstructing action flexibility.

Chronic mild stress-induced dysregulation of MAPK and PI3K/AKT signaling in the hippocampus and medial prefrontal cortex of WKY female rats

Wistar-Kyoto (WKY) rats subjected to chronic mild stress (CMS) represent a valid model of treatment-resistant depression (TRD). Considering that depression is more prevalent in women than in men, in the present study, female rats were used. We investigated the effect of CMS on behavior and different factors involved in neuroinflammatory processes and neuroplasticity in the hippocampus and medial prefrontal cortex (mPFC) of WKY female rats. The results show that unstressed WKY females exhibited hypolocomotion, decreased exploratory behavior, and an increase in the total grooming time. After exposure to CMS, WKY females displayed intensified grooming. To investigate potential neural mechanisms underlying these behavioral changes, we analyzed signaling and inflammatory pathways in the hippocampus and mPFC. The findings indicate reduced BDNF and elevated levels levels of IL-1β in both brain structures and NLRP3 in the mPFC of unstressed WKY female rats. WKY rats subjected to CMS showed a further decrease in BDNF levels and increased IL-1β and NLRP3 in these brain structures. WKY showed reduced pERK1/2 and increased pp38 levels in both brain structures, while CMS revealed a further increase of pp38 in WKY in these brain structures. Expressions of p110β and pAKT were decreased in the hippocampus and mPFC of WKY rats. The CMS further suppressed p110 and the downstream AKT phosphorylation in the hippocampus, but did not affect the p110 and pAKT in the mPFC. Our findings indicate behavioral and molecular differences in genetically vulnerable WKY female rats and in their response to CMS that may be involved in TRD.

Serotonergic agonism and pharmacologically-induced adolescent stress cause operant-based learning deficits in mice

BACKGROUND

The interplay between environmental stress and genetic factors is thought to play an important role in the pathogenesis and maintenance of obsessive-compulsive disorder (OCD). However, the relative contribution of these causative antecedents in the manifestation of cognitive inflexibility-a phenotype often seen in obsessive-compulsive (OC)- spectrum disorders-is not fully understood.

METHOD

In this study, we treated mice with 50 mg/L corticosterone (CORT, a glucocorticoid stress hormone) in their drinking water during adolescence. In adulthood, we assessed anxiety-like behaviour and locomotor activity; along with operant-based discrimination and reversal learning. RU-24969, a selective serotonin receptor 5-HT1A/1B receptor agonist, was used as an acute pharmacological model of OC-like behaviour. RU-24969 (5 mg/kg) was administered prior to each reversal learning testing session.

RESULTS

We found that acute treatment with 5 mg/kg RU-24969 induced stereotyped hyperlocomotion in vehicle- and CORT-treated mice. Furthermore, pre-treatment with CORT in adolescence produced subtle anxiety-like behaviour in adult mice, and also resulted in an impairment to late-stage discrimination learning and alterations to reversal learning. Finally, acute treatment with 5 mg/kg RU-24969 caused an impairment to early-stage reversal learning.

CONCLUSION

Whilst we revealed dissociable detrimental effects of adolescent CORT treatment and acute 5-HT1A/1B receptor agonism on discrimination and reversal learning, respectively, we did not find evidence of additive deleterious effects of these two treatments. We therefore suggest that while disrupted serotonergic signalling is likely to be involved in the cognitive phenotype of OC-spectrum disorders, distinct neuropathological pathways may be at play in mediating the role of stress as an antecedent in OCD and related illnesses.

Opioid Mechanisms and the Treatment of Depression

Opioid receptors are widely expressed in the brain, and the opioid system has a key role in modulating mood, reward processing and stress responsivity. There is mounting evidence that the endogenous opioid system may be dysregulated in depression and that drug treatments targeting mu, delta and kappa opioid receptors may show antidepressant potential. The mechanisms underlying the therapeutic effects of opioid system engagement are complex and likely multi-factorial. This chapter explores various pathways through which the modulation of the opioid system may influence depression. These include impacts on monoaminergic systems, the regulation of stress and the hypothalamic-pituitary-adrenal axis, the immune system and inflammation, brain-derived neurotrophic factors, neurogenesis and neuroplasticity, social pain and social reward, as well as expectancy and placebo effects. A greater understanding of the diverse mechanisms through which opioid system modulation may improve depressive symptoms could ultimately aid in the development of safe and effective alternative treatments for individuals with difficult-to-treat depression.

Positive correlation between measures of habitual responding and motivated responding in mice

Habit and motivation are thought to be separate processes, with motivated behavior often considered to be goal directed, whereas habits are defined by the absence of goal-directed control over behavior. However, there has been increasing interrogation of the binary nature of habitual versus goal-directed behavior. Furthermore, although drug and alcohol exposure can promote the formation of habits, drug seeking itself can also be highly flexible, pointing toward the need for complex consideration of the parallel processes that drive behavior. The goal of the current study was to determine whether there was a relation between motivation-as measured by progressive ratio-and habit-as measured by contingency degradation-and whether this relation was affected by ethanol exposure history and sex. The results showed that these measures were positively correlated such that greater contingency insensitivity was associated with achieving higher break points on the progressive-ratio task. However, this relation depended on reinforcement schedule history, ethanol exposure history, and sex. These point to potential relations between measures of habit and motivation and stress the importance of carefully parsing behavioral findings and assays. These findings are also expected to inform future substance use research, as drug history may affect these relations.

Anxiolytic and antidepressant like effects of Zamzam water in STZ-induced diabetic rats, targeting oxidative stress, neuroinflammation, BDNF/ERK/CREP pathway with modulation of hypothalamo-pituitary-adrenal axis

Introduction

Recent studies have reported a strong relationship between diabetes and anxiety- and depression-like behaviors; however, there is a lack of information on the underlying pathophysiology. Alkaline Zamzam water (ZW), which is rich in several trace elements, has neuroprotective properties. This study aimed to investigate the anxiolytic and antidepressant effects of ZW against diabetes-induced behavioral changes and shed light on the possible underlying mechanisms.

Methods

Forty-eight rats were divided into four experimental groups (n = 12): group I (control group), group II (Zamzam water group), group III (diabetic group), and group IV (diabetic + Zamzam water group). Diabetes was induced by an intraperitoneal injection of 60 mg/kg streptozotocin (STZ). At the end of the experiment, the forced swimming test (FST) was used to assess depression-like effects. The elevated plus maze test (EPMT) and open field test (OFT) were performed to evaluate anxiety-like behavior. Blood levels of the hypothalamic-pituitary-adrenal (HPA) axis were measured, and prefrontal cortex and hippocampal tissue samples were removed for histological, immunohistochemical, ELISA, and Q-PCR analyses.

Results

ZW significantly decreased the immobility time in the FST, indicating an antidepressant effect (p < 0.001). Additionally, ZW significantly improved the OFT and open field entry (OFE) percentages in the EPMT, increasing center crossing and decreasing grooming and fecal boli in the OFT. This indicated an anxiolytic-like effect in diabetic rats with histological improvement. Interestingly, ZW significantly increased prefrontal cortical and hippocampal levels of antioxidant enzymes and the Nrf2/HO-1 pathway. It also modulated the HPA axis by increasing cortisol and corticotropin-releasing hormone (CRH) levels, with a decrease in ACTH and an increase in monoamine neurotransmitters. Furthermore, diabetic rats that received ZW showed a decrease in the inflammatory markers TNF-α and GFAP by immunohistochemistry and in the mRNA levels of NFκB, IL-1β, and IL6. In addition, ZW downregulated the expression of the BDNF/ERK2/CREP pathway.

Conclusion

Our results suggested a neuroprotective effect of ZW against diabetes-induced anxiety- and depression-like behaviors and explored the underlying mechanisms. These findings suggest a promising therapeutic strategy for patients with diabetes who experience anxiety and depression.

Bidirectional mechanism of comorbidity of depression and insomnia based on synaptic plasticity

Insomnia is one of the most common accompanying symptoms of depression, with both sharing highly overlapping molecular pathways. The same pathological changes can trigger comorbidity of insomnia and depression, which further forms a vicious cycle with the involvement of more mechanisms and disease progression. Thus, understanding the potential interaction mechanisms between insomnia and depression is critical for clinical diagnosis and treatment. Comorbidity genetic factors, the hypothalamic-pituitary-adrenal axis, along with circadian rhythms of cortisol and the brain reward mechanism, are important ways in contributing to the comorbidity occurrence and development. However, owing to lack of pertinent investigational data, intricate molecular mechanisms necessitate further elaboration. Synaptic plasticity is a solid foundation for neural homeostasis. Pathological alterations of depression and insomnia may perturb the production and release of neurotransmitter, dendritic spine remodeling and elimination, which converges and reflects in aberrant synaptic dynamics. Hence, the introduction of synaptic plasticity research route and the construction of a comprehensive model of depression and insomnia comorbidity can provide new ideas for clinical depression insomnia comorbidity treatment plans.

Viral-mediated expression of Erk2 in the nucleus accumbens regulates responses to rewarding and aversive stimuli

Second-messenger signaling within the mesolimbic reward circuit is involved in both the long-lived effects of stress and in the underlying mechanisms that promote drug abuse liability. To determine the direct role of kinase signaling within the nucleus accumbens, specifically mitogen-activated protein kinase 1 (ERK2), in mood- and drug-related behavior, we used a herpes-simplex virus to up- or down-regulate ERK2 in adult male rats. We then exposed rats to a battery of behavioral tasks including the elevated plus-maze, open field test, forced-swim test, conditioned place preference, and finally cocaine self-administration. Herein, we show that viral overexpression or knockdown of ERK2 in the nucleus accumbens induces distinct behavioral phenotypes. Specifically, over expression of ERK2 facilitated depression- and anxiety-like behavior while also increasing sensitivity to cocaine. Conversely, down-regulation of ERK2 attenuated behavioral deficits, while blunting sensitivity to cocaine. Taken together, these data implicate ERK2 signaling, within the nucleus accumbens, in the regulation of affective behaviors and modulating sensitivity to the rewarding properties of cocaine.

Organic cation transporter 2 contributes to SSRI antidepressant efficacy by controlling tryptophan availability in the brain

Selective serotonin reuptake inhibitors (SSRI) are common first-line treatments for major depression. However, a significant number of depressed patients do not respond adequately to these pharmacological treatments. In the present preclinical study, we demonstrate that organic cation transporter 2 (OCT2), an atypical monoamine transporter, contributes to the effects of SSRI by regulating the routing of the essential amino acid tryptophan to the brain. Contrarily to wild-type mice, OCT2-invalidated mice failed to respond to prolonged fluoxetine treatment in a chronic depression model induced by corticosterone exposure recapitulating core symptoms of depression, i.e., anhedonia, social withdrawal, anxiety, and memory impairment. After corticosterone and fluoxetine treatment, the levels of tryptophan and its metabolites serotonin and kynurenine were decreased in the brain of OCT2 mutant mice compared to wild-type mice and reciprocally tryptophan and kynurenine levels were increased in mutants' plasma. OCT2 was detected by immunofluorescence in several structures at the blood-cerebrospinal fluid (CSF) or brain-CSF interface. Tryptophan supplementation during fluoxetine treatment increased brain concentrations of tryptophan and, more discreetly, of 5-HT in wild-type and OCT2 mutant mice. Importantly, tryptophan supplementation improved the sensitivity to fluoxetine treatment of OCT2 mutant mice, impacting chiefly anhedonia and short-term memory. Western blot analysis showed that glycogen synthase kinase-3β (GSK3β) and mammalian/mechanistic target of rapamycin (mTOR) intracellular signaling was impaired in OCT2 mutant mice brain after corticosterone and fluoxetine treatment and, conversely, tryptophan supplementation recruited selectively the mTOR protein complex 2. This study provides the first evidence of the physiological relevance of OCT2-mediated tryptophan transport, and its biological consequences on serotonin homeostasis in the brain and SSRI efficacy.

The Impact of BDNF, NTRK2, NGFR, CREB1, GSK3B, AKT, MAPK1, MTOR, PTEN, ARC, and SYN1 Genetic Polymorphisms in Antidepressant Treatment Response Phenotypes

This study aimed to investigate the influence of genetic variants in neuroplasticity-related genes on antidepressant treatment phenotypes. The BDNF-TrkB signaling pathway, as well as the downstream kinases Akt and ERK and the mTOR pathway, have been implicated in depression and neuroplasticity. However, clinicians still struggle with the unpredictability of antidepressant responses in depressed patients. We genotyped 26 polymorphisms in BDNF, NTRK2, NGFR, CREB1, GSK3B, AKT, MAPK1, MTOR, PTEN, ARC, and SYN1 in 80 patients with major depressive disorder treated according to the Texas Medical Algorithm for 27 months at Hospital Magalhães Lemos, Porto, Portugal. Our results showed that BDNF rs6265, PTEN rs12569998, and SYN1 rs1142636 SNP were associated with treatment-resistant depression (TRD). Additionally, MAPK1 rs6928 and GSK3B rs6438552 gene polymorphisms were associated with relapse. Moreover, we found a link between the rs6928 MAPK1 polymorphism and time to relapse. These findings suggest that the BDNF, PTEN, and SYN1 genes may play a role in the development of TRD, while MAPK1 and GSK3B may be associated with relapse. GO analysis revealed enrichment in synaptic and trans-synaptic transmission pathways and glutamate receptor activity with TRD-associated genes. Genetic variants in these genes could potentially be incorporated into predictive models of antidepressant response.

Sprouty4 at the crossroads of Trk neurotrophin receptor signaling suppression by glucocorticoids

Glucocorticoids (GC) affect neuronal plasticity, development and function of the nervous system by inhibiting neurotrophin-induced Trk signaling. It has been established that pretreatment with dexamethasone (DEX) restricts Neurotrophin-induced neurite outgrowth by inhibiting Trk-dependent activation of Ras-Erk1/2 signaling pathways. However, the precise molecular mechanism through which DEX interferes with neurotrophin signaling and Trk-mediated neurite outgrowth has not been clearly defined yet. Here, we observed that in PC12 cells DEX treatment promotes the transcription of Sprouty4, a regulatory molecule that is part of a negative feedback module that specifically abrogates Ras to Erk1/2 signaling in response to NGF. In line with this, either knockdown of Sprouty4 or overexpression of a dominant negative form of Sprouty4 (Y53A), rescue the inhibition of NGF/TrkA-promoted neurite outgrowth and Erk1/2 phosphorylation induced by DEX. Likewise, treatment of hippocampal neurons with DEX induces the expression of Sprouty4 and its knockdown abrogates the inhibitory effect of DEX on primary neurite formation, dendrite branching and Erk1/2 activation induced by BDNF. Thus, these results suggest that the induction of Sprouty4 mRNA by DEX translates into a significant inhibition of Trk to Erk1/2 signaling pathway. Together, these findings bring new insights into the crosstalk between DEX and neurotrophin signaling and demonstrate that Sprouty4 mediates the inhibitory effects of DEX on neurotrophin function.

Integrating Network Pharmacology, Molecular Docking and Pharmacological Evaluation for Exploring the Polyrhachis vicina Rogers in Ameliorating Depression

Purpose

To investigate the mechanisms of antidepressant action of active fraction of Polyrhachis vicina Rogers (AFPR) through network pharmacology, molecular docking and experimental validation.

Methods

GC-MS was used to predict chemical compounds, corresponding databases were used to predict chemical compound targets and depression targets, Cytoscape software was used to construct and analyze the protein interaction network map, DAVID database was used to analyze gene ontology (GO) and KEGG signaling pathway, and AGFR software was used to perform molecular docking. Subsequently, the underlying action mechanisms of AFPR on depression predicted by network pharmacology analyses were experimentally validated in a CORT-induced depression model in vitro and in vivo.

Results

A total of 52 potential targets of AFPR on antidepressant were obtained. GO is mainly related to chemical synaptic transmission, signal transduction and others. KEGG signaling pathways are mainly related to cAMP signaling pathway and C-type lectin receptor signaling pathway. The experiment results showed that AFPR significantly increased the expression of PRKACA, CREB and BDNF in mouse brain tissue and PC12 cells. Furthermore, after interfered of cAMP in PC12 cells, the decreased expression of PRKACA, CREB and BDNF was reversed by AFPR.

Conclusion

AFPR may exert antidepressant effects through multiple components, targets and pathways. Furthermore, it could improve neuroplasticity via the cAMP signaling pathway to improve depression-like symptoms.

The role of mGlu receptors in susceptibility to stress-induced anhedonia, fear, and anxiety-like behavior

Stress and trauma exposure contribute to the development of psychiatric disorders such as post-traumatic stress disorder (PTSD) and major depressive disorder (MDD) in a subset of people. A large body of preclinical work has found that the metabotropic glutamate (mGlu) family of G protein-coupled receptors regulate several behaviors that are part of the symptom clusters for both PTSD and MDD, including anhedonia, anxiety, and fear. Here, we review this literature, beginning with a summary of the wide variety of preclinical models used to assess these behaviors. We then summarize the involvement of Group I and II mGlu receptors in these behaviors. Bringing together this extensive literature reveals that mGlu5 signaling plays distinct roles in anhedonia, fear, and anxiety-like behavior. mGlu5 promotes susceptibility to stress-induced anhedonia and resilience to stress-induced anxiety-like behavior, while serving a fundamental role in the learning underlying fear conditioning. The medial prefrontal cortex, basolateral amygdala, nucleus accumbens, and ventral hippocampus are key regions where mGlu5, mGlu2, and mGlu3 regulate these behaviors. There is strong support that stress-induced anhedonia arises from decreased glutamate release and post-synaptic mGlu5 signaling. Conversely, decreasing mGlu5 signaling increases resilience to stress-induced anxiety-like behavior. Consistent with opposing roles for mGlu5 and mGlu2/3 in anhedonia, evidence suggests that increased glutamate transmission may be therapeutic for the extinction of fear learning. Thus, a large body of literature supports the targeting of pre- and post-synaptic glutamate signaling to ameliorate post-stress anhedonia, fear, and anxiety-like behavior.

ERK/mTOR signaling may underlying the antidepressant actions of rapastinel in mice

Rapastinel as the allosteric modulator of N-methyl-D-aspartate receptor (NMDAR) produces rapid antidepressant-like effects dependent on brain-derived neurotrophic factor (BDNF) and VGF (nonacryonimic) release. Herein, we further explore the molecular mechanisms of the antidepressant effects of repeated administration with rapastinel in mice. Our results showed that continuous 3-day rapastinel (5 and 10 mg/kg, i.v.) produced antidepressant-like actions dependent on the increase in extracellular regulated protein kinase (ERK)/mammalian target of rapamycin (mTOR) signaling and downstream substrates p70S6 kinase (p70S6k) and the eukaryotic initiation factor 4E-binding protein 1 (4E-BP1), which may induce the expression of VGF and BDNF in the hippocampus and prefrontal cortex of mice. Furthermore, compared with a single treatment, our data indicated that 3-day repeated rapastinel treatment produced antidepressant-like actions accompanied by potentiation of ERK/mTOR/VGF/BDNF/tropomyosin-related kinase receptor B (TrkB) signaling. Based on previous and our supplementary data that showed the pivotal role of on α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) in the rapid release of VGF and BDNF and activation of TrkB by a single dose of rapastinel, we postulate that the antidepressant-like effects of single or repeated administration of rapastinel may result in the rapid release of VGF and BDNF or ERK/mTOR signaling pathway-mediated VGF/BDNF/TrkB autoregulatory feedback loop respectively. Our current work adds new knowledge to the molecular mechanisms that underlie the antidepressant-like actions of rapastinel in mice.

Long noncoding RNA Gm2694 drives depressive-like behaviors in male mice by interacting with GRP78 to disrupt endoplasmic reticulum homeostasis

Long noncoding RNAs (lncRNAs) are involved in various biological processes and implicated in the regulation of neuronal activity, but the potential role of lncRNAs in depression remains largely unknown. Here, we identified that lncRNA Gm2694 was increased in the medial prefrontal cortex (mPFC) of male mice subjected to chronic social defeat stress (CSDS). The down-regulation of Gm2694 in the mPFC alleviated CSDS-induced depressive-like behaviors through enhanced excitatory synaptic transmission. Furthermore, we found that Gm2694 preferentially interacted with the carboxyl-terminal domain of 78-kilodalton glucose-regulated protein (GRP78), which abrogated GRP78 function and disrupted endoplasmic reticulum homeostasis, resulting in a reduction of the surface expression of AMPA receptors (AMPARs). Overexpression of GRP78 in the mPFC promoted the surface expression of AMPARs and attenuated the CSDS-induced depressive-like behaviors of mice. Together, our results unraveled a previously unknown role of Gm2694 in regulating endoplasmic reticulum homeostasis and excitatory synaptic transmission in depression.

The Opioid System in Depression

Opioid receptors are widely distributed throughout the brain and play an essential role in modulating aspects of human mood, reward, and well-being. Accumulating evidence indicates the endogenous opioid system is dysregulated in depression and that pharmacological modulators of mu, delta, and kappa opioid receptors hold potential for the treatment of depression. Here we review animal and clinical data, highlighting evidence to support: dysregulation of the opioid system in depression, evidence for opioidergic modulation of behavioural processes and brain regions associated with depression, and evidence for opioidergic modulation in antidepressant responses. We evaluate clinical trials that have examined the safety and efficacy of opioidergic agents in depression and consider how the opioid system may be involved in the effects of other treatments, including ketamine, that are currently understood to exert antidepressant effects through non-opioidergic actions. Finally, we explore key neurochemical and molecular mechanisms underlying the potential therapeutic effects of opioid system engagement, that together provides a rationale for further investigation into this relevant target in the treatment of depression.

Comparative Severity Assessment of Genetic, Stress-Based, and Pharmacological Mouse Models of Depression

The use of animals in neurosciences is pivotal to gaining insights into complex functions and dysfunctions of behavior. For example, various forms of physical and/or psychological stress are inherent to various animal models for psychiatric disorders, e.g., depression. Regarding animal welfare, it would be mandatory to use models that inflict the least amount of stress necessary to address the underlying scientific question. This study compared the severity of different approaches to induce depression in mice: mutagenesis in GluA1 knockout, immobilization stress, and stress-induction via stress hormone treatment. While genetic alterations potentially represent a lifelong burden, the temporary intervention only affects the animals for a limited time. Therefore, we used home cage-based behavioral and physiological parameters, including nest building, burrowing, body weight, and fecal corticosterone metabolites, to determine the well-being of male and female mice. In addition, we performed an evidence-based estimate of severity using a composite score for relative severity assessment (RELSA) with this data. We found that even though restraint stress and supplementation of corticosterone in the diet both aimed at depression-related precipitating stress effects, the latter affected the well-being much stronger, especially in females. Restraint leads to less noticeable well-being impairments but causes depression-associated anhedonic behavior. Mice of both sexes recovered well from the stress treatment. GluA1 KO and their littermates showed diminished well-being, comparable to the immobilization experiments. However, since this is a lifelong condition, this burden is not reversible and potentially accumulative. In line with the 3Rs (Replacement, Reduction, and Refinement), the process of choosing the most suitable model should ideally include an evidence-based severity assessment to be able to opt for the least severe alternative, which still induces the desired effect. Promoting refinement, in our study, this would be the restraint stress.

Expression of Trace Amine-Associated Receptors in the Murine and Human Hippocampus Based on Public Transcriptomic Data

Hippocampus is one of the neurogenic zones where adult neurogenesis takes place. This process is quite complex and has a multicomponent regulation. A family of G protein-coupled trace amine-associated receptors (TAARs) was discovered only in 2001, and most of them (TAAR2-TAAR9) were primarily considered olfactory. Recent studies have shown, however, that they are also expressed in the mouse brain, particularly in limbic formations, and can play a role in the regulation of emotional behaviors. The observations in knockout mice indicate that at least two members of the family, TAAR2 and TAAR5, have an impact on the regulation of adult neurogenesis. In the present study, we analyzed the expression of TAARs in the murine and human hippocampus using public RNAseq datasets. Our results indicate a low but detectable level of certain TAARs expression in the hippocampal cells in selected high-quality transcriptomic datasets from both mouse and human samples. At the same time, we observed the difference between humans, where TAAR6 expression was the highest, and murine samples, where TAAR1, TAAR2, TAAR3, TAAR4 and TAAR5 are more pronouncedly expressed. These observations provide further support to the data gained in knockout mice, indicating a role of TAARs in the regulation of adult neurogenesis in the hippocampus.

Sulfuretin exerts anti-depressive effects in the lipopolysaccharide-induced depressive mouse models

BACKGROUND

Herb-derived therapeutics is an attractive strategy to treat depression. Here we report the ameliorating effects of Sulfuretin, an anti-inflammatory compound in a depressive mouse model.

METHODS

Immobility times were obtained in the tail suspension test and forced swim test performed from day 14 to day 16. Quantitative real-time PCR (qRT-PCR) and Western blot were used to measure brain-derived neurotrophic factor (BDNF) and the extracellular signal-regulated kinase (ERK) pathway of the hippocampus tissue on day 17. SL327 was used to block the ERK pathway in mice to evaluate the interaction between Sulfuretin and the ERK pathway. Mice were treated with Sulfuretin for 14 days before lipopolysaccharide (LPS) injection (0.83 mg/kg/day, i.p.) for two days.

RESULTS

Behavior tests showed that Sulfuretin dose-dependently decreased immobility times correlated with depression symptoms. BDNF levels and ERK signaling were significantly restored in the Sulfuretin-treated mice, showing the improvement of brain function. Blocking the p-ERK signaling abrogated the effects of Sulfuretin in improving behaviors and levels of BDNF.

CONCLUSION

Our study suggests that Sulfuretin exhibits anti-depressive function in LPS-induced depressive mice, in which the ERK signaling plays an essential role.

Reinforcement History Dependent Effects of Low Dose Ethanol on Reward Motivation in Male and Female Mice

Alcohol use disorders (AUDs) are more prevalent in men than in women, though AUD diagnoses in women are growing rapidly, making an understanding of sex differences in alcohol-related behaviors increasingly important. The development of AUDs involves the transition from casual, low levels of alcohol drinking to higher, maladaptive levels. The ability of low dose alcohol to drive reward and drug seeking may differ in males and females, and this could underlie differences in susceptibility to AUD. In this study we sought to determine whether a history of chronic, low dose ethanol exposure (0.5 g/kg; i.p.) could drive sucrose reward seeking and motivation, and whether this differed between male and female mice. Adult mice were trained to lever press for a liquid sucrose reward on two reinforcement schedules: a random interval (RI) schedule and a variable ratio (VR) schedule. After training, mice were tested on each of these levers for reward motivation using a progressive ratio test. We found that a history of low dose ethanol exposure increased sucrose reward motivation in male mice, but only on the RI lever and only when exposure occurred proximal to learning. Female mice were more motivated for sucrose on the RI lever than the VR lever regardless of ethanol exposure condition. These findings indicate that training on different reinforcement schedules affects reward motivation. Further, we show that males are more susceptible to the effects of low dose ethanol on sucrose reward motivation than females. These data broaden our understanding of sex differences in reward seeking as a result of ethanol exposure.

MiR-129-5p prevents depressive-like behaviors by targeting MAPK1 to suppress inflammation

Depression is a complex etiological disease with limited effective treatments. Previous studies have indicated the involvement of miRNAs in the pathophysiology of mood disorders. In this study, we focused on the role and mechanisms of miR-129-5p in depression by successfully constructing mice models of depressive-like behavior via chronic unpredictable mild stress (CUMS) exposure. Herein, miR-129-5p expression was decreased in the hippocampus of CUMS mice model. Upregulation of miR-129-5p reduced depressive-like behaviors of CUMS mice, as revealed in sucrose preference test, novelty suppressed feeding test, forced swim test, tail suspension test, social interaction test. MiR-129-5p upregulation decreased the concentrations and protein levels of proinflammatory cytokines (IL-6, IL-1β and TNF-α), indicating the inhibitory role of miR-129-5p in inflammation. Furthermore, miR-129-5p was identified to target MAPK1. MAPK1 was negatively regulated by miR-129-5p, and silencing of MAPK1 attenuated depressive-like behaviors in CUMS mice. Moreover, MAPK1 downregulation decreased inflammation in the hippocampus of CUMS mice. Upregulation of MAPK1 reversed the suppressive effects of miR-129-5p upregulation on depressive-like behaviors and inflammation in CUMS mice. In conclusion, the current study identified that miR-129-5p reduces depressive-like behaviors and suppresses inflammation by targeting MAPK1 in CUMS mice, offering a novel molecular interpretation for depression prevention.

Differential response of diurnal and nocturnal mammals to prolonged altered light-dark cycle: a possible role of mood associated endocrine, inflammatory and antioxidant system

The circadian system maintains internal 24 h oscillation of behavior and physiology, and its misalignment with external light-dark (LD) cycle results in negative health outcomes. In order to elucidate the effect of prolonged constant condition and the differences in the response between nocturnal and diurnal species, we studied the effects of constant light (LL) and constant darkness (DD) on a diurnal (squirrel) and a nocturnal (mouse) rodent species, focusing on the endocrine, inflammatory and antioxidant systems associated with depression-like behavior. Squirrels and mice (n = 10/group) were placed in chronocubicle under 12:12 h LD cycle, LL and DD. After 4 weeks, animals were subjected to sucrose preference test and blood and brain tissues were collected for measuring melatonin, corticosterone, proinflammatory cytokine, tumor necrosis factor-α (TNF-α) and the activity of primary antioxidant enzymes, catalase (CAT) and superoxide dismutase (SOD). The results show that in diurnal squirrels, prolonged constant darkness reduced sucrose preference, CAT, and SOD, increased corticosterone and TNF-α levels, but caused no significant change in the melatonin compared to LD condition. In contrast, in nocturnal mice constant darkness caused no significant changes in sucrose preference and corticosterone levels, increased melatonin, CAT and SOD levels but decreased TNF-α levels. Chronic LL caused a similar response in both squirrels and mice: it decreased sucrose preference, melatonin, CAT and SOD levels but increased corticosterone and TNF-α levels. Together, the study demonstrates differential effects of altered light-dark cycle in a diurnal and a nocturnal rodent on interrelated endocrine, inflammatory and antioxidant systems associated with depression-like behavior, with constant light having adverse effects on both species but constant darkness having a negative effect mainly in the diurnal squirrels.

Comparative Analysis of Pathobiochemical Changes in Major Depression and Post-Traumatic Stress Disorder

Comparative analysis of available literature data on the pathogenetic neuroendocrine mechanisms of depression and post-traumatic stress disorder (PTSD) is provided in this review to identify their common features and differences. We discuss the multidirectional modifications of the activity of cortical and subcortical structures of the brain, levels of neurotransmitters and their receptors, and functions of the hypothalamic-pituitary-adrenocortical axis in depression and PTSD. The analysis shows that these disorders are examples of opposite failures in the system of adaptive stress response of the body to stressful psychotraumatic events. On this basis, it is concluded that the currently widespread use of similar approaches to treat these disorders is not justified, despite the significant similarity of their anxiety-depressive symptoms; development of differential therapeutic strategies is required.

Chronic non-discriminatory social defeat stress reduces effort-related motivated behaviors in male and female mice

Reward and motivation deficits are prominent symptoms in many mood disorders, including depression. Similar reward and effort-related choice behavioral tasks can be used to study aspects of motivation in both rodents and humans. Chronic stress can precipitate mood disorders in humans and maladaptive reward and motivation behaviors in male rodents. However, while depression is more prevalent in women, there is relatively little known about whether chronic stress elicits maladaptive behaviors in female rodents in effort-related motivated tasks and whether there are any behavioral sex differences. Chronic nondiscriminatory social defeat stress (CNSDS) is a variation of chronic social defeat stress that is effective in both male and female mice. We hypothesized that CNSDS would reduce effort-related motivated and reward behaviors, including reducing sensitivity to a devalued outcome, reducing breakpoint in progressive ratio, and shifting effort-related choice behavior. Separate cohorts of adult male and female C57BL/6 J mice were divided into Control or CNSDS groups, exposed to the 10-day CNSDS paradigm, and then trained and tested in instrumental reward or effort-related behaviors. CNSDS reduced motivation to lever press in progressive ratio and shifted effort-related choice behavior from a high reward to a more easily attainable low reward in both sexes. CNSDS caused more nuanced impairments in outcome devaluation. Taken together, CNSDS induces maladaptive shifts in effort-related choice and reduces motivated lever pressing in both sexes.

Characterization of glucocorticoid-induced loss of DNA methylation of the stress-response gene Fkbp5 in neuronal cells

Exposure to stress or glucocorticoids (GCs) is associated with epigenetic and transcriptional changes in genes that either mediate or are targets of GC signalling. FKBP5 (FK506 binding protein 5) is one such gene that also plays a central role in negative feedback regulation of GC signalling and several stress-related psychiatric disorders. In this study, we sought to examine how the mouse Fkbp5 gene is regulated in a neuronal context and identify requisite factors that can mediate the epigenetic sequelae of excess GC exposure. Mice treated with GCs were used to establish the widespread changes in DNA methylation (DNAm) and expression of Fkbp5 across four brain regions. Then two cell lines were used to test the persistence, decay, and functional significance of GC-induced methylation changes near two GC response elements (GREs) in the fifth intron of Fkbp5. We also tested the involvement of DNMT1, cell proliferation, and MeCP2 in mediating the effect of GCs on DNAm and gene activation. DNAm changes at some CpGs persist while others decay, and reduced methylation states are associated with a more robust transcriptional response. Importantly, the ability to undergo GC-induced DNAm loss is tied to DNMT1 function during cell division. Further, GC-induced DNAm loss is associated with reduced binding of MeCP2 at intron 5 and a physical interaction between the fifth intron and promoter of Fkbp5. Our results highlight several key factors at the Fkbp5 locus that may have important implications for GC- or stress-exposure during early stages of neurodevelopment.

Dentate gyrus activin signaling mediates the antidepressant response

Antidepressants that target monoaminergic systems, such as selective serotonin reuptake inhibitors (SSRIs), are widely used to treat neuropsychiatric disorders including major depressive disorder, several anxiety disorders, and obsessive-compulsive disorder. However, these treatments are not ideal because only a subset of patients achieve remission. The reasons why some individuals remit to antidepressant treatments while others do not are unknown. Here, we developed a paradigm to assess antidepressant treatment resistance in mice. Exposure of male C57BL/6J mice to either chronic corticosterone administration or chronic social defeat stress induces maladaptive affective behaviors. Subsequent chronic treatment with the SSRI fluoxetine reverses these maladaptive affective behavioral changes in some, but not all, of the mice, permitting stratification into persistent responders and non-responders to fluoxetine. We found several differences in expression of Activin signaling-related genes between responders and non-responders in the dentate gyrus (DG), a region that is critical for the beneficial behavioral effects of fluoxetine. Enhancement of Activin signaling in the DG converted behavioral non-responders into responders to fluoxetine treatment more effectively than commonly used second-line antidepressant treatments, while inhibition of Activin signaling in the DG converted responders into non-responders. Taken together, these results demonstrate that the behavioral response to fluoxetine can be bidirectionally modified via targeted manipulations of the DG and suggest that molecular- and neural circuit-based modulations of DG may provide a new therapeutic avenue for more effective antidepressant treatments.

The Effect of Swimming on Anxiety-Like Behaviors and Corticosterone in Stressed and Unstressed Rats

This study assessed the effect of swimming training on anxiety-like behaviors and corticosterone. Thirty adult male Wistar rats were randomly assigned to five study conditions: swimming training (ST); exposure to chronic mild stress (CS); exposure to chronic mild stress followed by swimming training (CS + ST); exposure to chronic mild stress followed by a recovery period (CS + recovery); control. The exercise training consisted of 60 min of swimming exercise per day, for five days a week, and four consecutive weeks. A chronic mild stress program (CMS) was applied for a period of four weeks. Anxiety-like behaviors were measured by open field test (OFT). The number of excrements and blood corticosterone were used as physiological parameters of anxiety. To assess corticosterone, blood samples were taken 48 h after the last session of experiments. Compared to other study conditions, the lowest anxiety-like behaviors and corticosterone concentrations were observed in the ST condition in unstressed rats. In stressed rats, as in the ST + CS group, swimming training probably reduced some anxiety behaviors, but the results showed increased corticosterone compared to control and CS + Recovery. Anxiety parameters and corticosterone concentrations were greatest in the CS condition. In the ST group, anxiety parameters were less than for the ST + CS group. In the CS + Recovery group, anxiety parameters were less than for the CS group. In summary, self-paced swimming training could attenuate some anxiety parameters in both stressed and non-stressed rats. The effect of swimming training in unstressed rats was more prominent than in stressed rats. In stressed rats, a period of recovery was more effective than swimming training in reducing corticosterone. Mechanisms of anxiety reduction other than cortisol should be investigated in future research.

Morphological Responses of Excitatory Prelimbic and Orbitofrontal Cortical Neurons to Excess Corticosterone in Adolescence and Acute Stress in Adulthood

Considerable evidence indicates that chronic stress and excess glucocorticoids induce neuronal remodeling in prefrontal cortical (PFC) regions. Adolescence is also characterized by a structural reorganization of PFC neurons, yet interactions between stress- and age-related structural plasticity are still being determined. We quantified dendritic spine densities on apical dendrites of excitatory neurons in the medial prefrontal cortex, prelimbic subregion (PL). Densities decreased across adolescent development, as expected, and spine volume increased. Unexpectedly, exposure to excess corticosterone (CORT) throughout adolescence did not cause additional dendritic spine loss detectable in adulthood. As a positive control dendrite population expected to be sensitive to CORT, we imaged neurons in the orbitofrontal cortex (OFC), confirming CORT-induced dendritic spine attrition on basal arbors of layer V neurons. We next assessed the effects of acute, mild stress in adulthood: On PL neurons, an acute stressor increased the density of mature, mushroom-shaped spines. Meanwhile, on OFC neurons, dendritic spine volumes and lengths were lower in mice exposed to both CORT and an acute stressor (also referred to as a "double hit"). In sum, prolonged exposure to excess glucocorticoids during adolescence can have morphological and also metaplastic consequences, but they are not global. Anatomical considerations are discussed.

Chronic Stress Shifts Effort-Related Choice Behavior in a Y-Maze Barrier Task in Mice

Mood disorders, including major depressive disorder, can be precipitated by chronic stress. The Y-maze barrier task is an effort-related choice test that measures motivation to expend effort and obtain reward. In mice, chronic stress exposure significantly impacts motivation to work for a higher value reward when a lesser value reward is freely available compared to unstressed mice. Here we describe the chronic corticosterone administration paradigm, which produces a shift in effortful responding in the Y-maze barrier task. In the Y-maze task, one arm contains 4 food pellets, while the other arm contains only 2 pellets. After mice learn to select the high reward arm, barriers with progressively increasing height are then introduced into the high reward arm over multiple test sessions. Unfortunately, most chronic stress paradigms (including corticosterone and social defeat) were developed in male mice and are less effective in female mice. Therefore, we also discuss chronic non-discriminatory social defeat stress (CNSDS), a stress paradigm we developed that is effective in both male and female mice. Repeating results with multiple distinct chronic stressors in male and female mice combined with increased usage of translationally relevant behavior tasks will help to advance the understanding of how chronic stress can precipitate mood disorders.

New insights into the effects of caffeine on adult hippocampal neurogenesis in stressed mice: Inhibition of CORT-induced microglia activation

Chronic stress-evoked depression has been implied to associate with the decline of adult hippocampal neurogenesis. Caffeine has been known to combat stress-evoked depression. Herein, we aim to investigate whether the protective effect of caffeine on depression is related with improving adult hippocampus neurogenesis and explore the mechanisms. Mouse chronic water immersion restraint stress (CWIRS) model, corticosterone (CORT)-established cell stress model, a coculture system containing CORT-treated BV-2 cells and hippocampal neural stem cells (NSCs) were utilized. Results showed that CWIRS caused obvious depressive-like disorders, abnormal 5-HT signaling, and elevated-plasma CORT levels. Notably, microglia activation-evoked brain inflammation and inhibited neurogenesis were also observed in the hippocampus of stressed mice. In comparison, intragastric administration of caffeine (10 and 20 mg/kg, 28 days) significantly reverted CWIRS-induced depressive behaviors, neurogenesis recession and microglia activation in the hippocampus. Further evidences from both in vivo and in vitro mechanistic experiments demonstrated that caffeine treatment significantly suppressed microglia activation via the A2AR/MEK/ERK/NF-κB signaling pathway. The results suggested that CORT-induced microglia activation contributes to stress-mediated neurogenesis recession. The antidepression effect of caffeine was associated with unlocking microglia activation-induced neurogenesis inhibition.

Forebrain overexpression of type 1 adenylyl cyclase promotes molecular stability and behavioral resilience to physical stress

The ability to cope with stress is essential for emotional stability and mental health. It is also hypothesized that factors promoting resilience to stress may offer treatment strategies for maladaptive disorders such as anxiety and depression. Here, we find that physical restraint reduces the expression of type 1 adenylyl cyclase (Adcy1), a neurospecific synaptic enzyme that positively regulates the cAMP signaling cascade. Conversely, an increase of forebrain Adcy1 expression in transgenic mouse (i.e., Adcy1 ^tg mouse) predisposes individuals to molecular stability and behavioral resilience. Transgenic overexpression of Adcy1 prevents the physical restraint-induced down-regulation of brain-derived neurotrophic factor (BDNF) and neuropeptide Y (NPY). Further, Adcy1 ^tg mice maintain regular locomotive activity in novelty exploration and voluntary wheel running following physical restraint. Adcy1 ^tg mice show higher corticosterone and lower basal glucocorticoid receptor (GR) expression, along with a higher MR (mineralocorticoid receptor) to GR ratio in the hippocampus. Further, Adcy1 ^tg mice show reduced immobility under acute physical stress conditions in the forced swimming test and are more sensitive to the antidepressant desipramine. Our results demonstrate a novel function of Adcy1 in stress coping and suggest Adcy1 as a potential target to antagonize stress vulnerability and promote antidepressant efficacy.

Beneficial Effects of Crocin against Depression via Pituitary Adenylate Cyclase-Activating Polypeptide

Depression is one of the foremost psychological illness, and the exact mechanism is unclear. Recent studies have reported that the pituitary adenylate cyclase-activating polypeptide (PACAP) signaling pathway is involved in the progression of depression. In the present study, we extracted crocin from the traditional Chinese medicine (TCM), Gardenia jasminoides Ellis, to evaluate its antidepressant effect and clarify the underlying mechanism. Here, we established a chronic unpredictable mild stress (CUMS) mouse model to assess whether crocin can improve depression-like behavior in an open field test (OFT), tail suspension test (TST), forced swimming test (FST), and sucrose preference test (SPT). A corticosterone (CORT) model of PC12 was set up to explore the antidepressant mechanism of crocin. We pretreated PC12 cells with crocin for 1 hour and then stimulated the cells with CORT for 24 hours. Cell survival was detected by Hoechst staining and MTT assay. The expression of PACAP, cyclic adenosine monophosphate (cAMP) response element binding protein (CREB), and extracellular regulated protein kinases (ERK) were analyzed by western blotting. PACAP RNAi was used to interfere with PC12 cells to downregulate the content of PACAP. The results showed that crocin (30 mg/kg) significantly reversed the decrease of body weight and elevation of serum CORT, mitigated CUMS induced depression-like behaviors of mice, and crocin (12.5 μmol/L) protected PC12 cells against CORT (200 μmol/L)-induced injury. Furthermore, crocin greatly increased the protein expression of PACAP and phosphorylation of ERK and CREB in the CORT model. PACAP RNAi cancelled the neuroprotective effect of crocin. In conclusion, these results indicated that crocin exerted an antidepressant effect via upregulating PACAP and its downstream ERK and CREB signaling pathways.

Antidepressant efficacy of a selective organic cation transporter blocker in a mouse model of depression

Current antidepressants act principally by blocking monoamine reuptake by high-affinity transporters in the brain. However, these antidepressants show important shortcomings such as slow action onset and limited efficacy in nearly a third of patients with major depression disorder. Here, we report the development of a prodrug targeting organic cation transporters (OCT), atypical monoamine transporters recently implicated in the regulation of mood. Using molecular modeling, we designed a selective OCT2 blocker, which was modified to increase brain penetration. This compound, H2-cyanome, was tested in a rodent model of chronic depression induced by 7-week corticosterone exposure. In male mice, prolonged administration of H2-cyanome induced positive effects on several behaviors mimicking symptoms of depression, including anhedonia, anxiety, social withdrawal, and memory impairment. Importantly, in this validated model, H2-cyanome compared favorably with the classical antidepressant fluoxetine, with a faster action on anhedonia and better anxiolytic effects. Integrated Z-scoring across these depression-like variables revealed a lower depression score for mice treated with H2-cyanome than for mice treated with fluoxetine for 3 weeks. Repeated H2-cyanome administration increased ventral tegmental area dopaminergic neuron firing, which may underlie its rapid action on anhedonia. H2-cyanome, like fluoxetine, also modulated several intracellular signaling pathways previously involved in antidepressant response. Our findings provide proof-of-concept of antidepressant efficacy of an OCT blocker, and a mechanistic framework for the development of new classes of antidepressants and therapeutic alternatives for resistant depression and other psychiatric disturbances such as anxiety.

Roles of Akt and ERK in mTOR-Dependent Antidepressant Effects of Vanillic Acid

Vanillic acid, an oxidized form of vanilla, is a flavoring agent with a creamy odor. Several studies have reported the neuroprotective effects of vanillic acid, which are predominantly associated with anti-inflammatory and antioxidative properties. The anti-inflammatory and antioxidative properties may result from Akt or ERK signaling activation. The activation of the mammalian target of rapamycin (mTOR), a key downstream target of Akt and ERK signaling, is a crucial therapeutic target for treating depression. However, the antidepressant effects of vanillic acid remain unknown. The present study applied the forced swim test (FST) to investigate the antidepressant effects of vanillic acid and its association with Akt, ERK, and mTOR signaling and upstream α-amino-3-hydroxy-5-methyl-4-isoxazolepropionaic acid receptor (AMPAR) in the prefrontal cortex (PFC) of mice. Vanillic acid demonstrated antidepressant effects by significantly reducing behavioral despair in the FST. None of the treatments changed locomotor activity. Additionally, vanillic acid increased AMPAR throughput, Akt, and mTOR signaling but not ERK signaling in the PFC. NBQX (an AMPAR blocker), MK 2206 (an Akt blocker), and rapamycin (an mTOR blocker) used in pretreatment attenuated the antidepressant effects of vanillic acid, but SL327 (an ERK inhibitor) did not. The immunochemical results indicated that the antidepressant effects of vanillic acid depend on the AMPAR-Akt-mTOR signaling transduction pathway. Our findings reveal an Akt-dependent, but ERK-independent, the mechanism underlying the antidepressant effects of vanillic acid, which may be beneficial for some patients with depression.

Simultaneous Fluorescence Imaging Reveals N-Methyl-d-aspartic Acid Receptor Dependent Zn2+/H+ Flux in the Brains of Mice with Depression

Depression is immensely attributed to the overactivation of N-methyl-d-aspartic acid (NMDA) receptor in the brains. As regulatory binding partners of NMDA receptor, both Zn²⁺ and H⁺ are intimately interrelated to NMDA receptor's activity. Therefore, exploring synergistic changes on the levels of Zn²⁺ and H⁺ in brains will promote the knowledge and treatment of depression. However, the lack of efficient, appropriate imaging tools limits simultaneously tracking Zn²⁺ and H⁺ in living mouse brains. Thus, a well-designed dual-color fluorescent probe (DNP) was fabricated for the simultaneous monitoring of Zn²⁺ and H⁺ in the brains of mice with depression. Encountering Zn²⁺, the probe evoked bright blue fluorescence at 460 nm. Meanwhile, the red fluorescence at 680 nm was decreased with H⁺ addition. With blue/red dual fluorescence signal of DNP, we observed the synchronous increased Zn²⁺ and H⁺ in PC12 cells under oxidative stress. Notably, in vivo imaging for the first time revealed the simultaneous reduction of Zn²⁺ and pH in brains of mice with depression-like behaviors. Further results implied that the NMDA receptor might be responsible for the coinstantaneous fluctuation of Zn²⁺ and H⁺ during depression. Altogether, this work is conducive to the knowledge of neural signal transduction mechanisms, advancing our understanding of the pathogenesis in depression.

Chronic corticosterone administration induces negative valence and impairs positive valence behaviors in mice

Behavioral approaches utilizing rodents to study mood disorders have focused primarily on negative valence behaviors associated with potential threat (anxiety-related behaviors). However, for disorders such as depression, positive valence behaviors that assess reward processing may be more translationally valid and predictive of antidepressant treatment outcome. Chronic corticosterone (CORT) administration is a well-validated pharmacological stressor that increases avoidance in negative valence behaviors associated with anxiety1-4. However, whether chronic stress paradigms such as CORT administration also lead to deficits in positive valence behaviors remains unclear. We treated male C57BL/6J mice with chronic CORT and assessed both negative and positive valence behaviors. We found that CORT induced avoidance in the open field and NSF. Interestingly, CORT also impaired instrumental acquisition, reduced sensitivity to a devalued outcome, reduced breakpoint in progressive ratio, and impaired performance in probabilistic reversal learning. Taken together, these results demonstrate that chronic CORT administration at the same dosage both induces avoidance in negative valence behaviors associated with anxiety and impairs positive valence behaviors associated with reward processing. These data suggest that CORT administration is a useful experimental system for preclinical approaches to studying stress-induced mood disorders.

mGlu2 and mGlu3 Negative Allosteric Modulators Divergently Enhance Thalamocortical Transmission and Exert Rapid Antidepressant-like Effects

Non-selective antagonists of metabotropic glutamate receptor subtypes 2 (mGlu₂) and 3 (mGlu₃) exert rapid antidepressant-like effects by enhancing prefrontal cortex (PFC) glutamate transmission; however, the receptor subtype contributions and underlying mechanisms remain unclear. Here, we leveraged newly developed negative allosteric modulators (NAMs), transgenic mice, and viral-assisted optogenetics to test the hypothesis that selective inhibition of mGlu₂ or mGlu₃ potentiates PFC excitatory transmission and confers antidepressant efficacy in preclinical models. We found that systemic treatment with an mGlu₂ or mGlu₃ NAM rapidly activated biophysically unique PFC pyramidal cell ensembles. Mechanistic studies revealed that mGlu₂ and mGlu₃ NAMs enhance thalamocortical transmission and inhibit long-term depression by mechanistically distinct presynaptic and postsynaptic actions. Consistent with these actions, systemic treatment with either NAM decreased passive coping and reversed anhedonia in two independent chronic stress models, suggesting that both mGlu₂ and mGlu₃ NAMs induce antidepressant-like effects through related but divergent mechanisms of action.

Role of nociceptin/orphanin FQ and nociceptin opioid peptide receptor in depression and antidepressant effects of nociceptin opioid peptide receptor antagonists

Nociceptin/orphanin FQ (N/OFQ) and its receptor, nociceptin opioid peptide (NOP) receptor, are localized in brain areas implicated in depression including the amygdala, bed nucleus of the stria terminalis, habenula, and monoaminergic nuclei in the brain stem. N/OFQ inhibits neuronal excitability of monoaminergic neurons and monoamine release from their terminals by activation of G protein-coupled inwardly rectifying K⁺ channels and inhibition of voltage sensitive calcium channels, respectively. Therefore, NOP receptor antagonists have been proposed as a potential antidepressant. Indeed, mounting evidence shows that NOP receptor antagonists have antidepressant-like effects in various preclinical animal models of depression, and recent clinical studies again confirmed the idea that blockade of NOP receptor signaling could provide a novel strategy for the treatment of depression. In this review, we describe the pharmacological effects of N/OFQ in relation to depression and explore the possible mechanism of NOP receptor antagonists as potential antidepressants.

Altered expression of long noncoding RNAs in patients with major depressive disorder

Although major depressive disorder (MDD) is a leading cause of disability worldwide, its pathophysiology is poorly understood. Increasing evidence suggests that aberrant regulation of transcription plays a key role in the pathophysiology of MDD. Recently, long noncoding RNAs (lncRNAs) have been recognized for their important functions in chromatin structure, gene expression, and the subsequent manifestation of various biological processes in the central nervous system. However, it is unclear whether the aberrant expression and function of lncRNAs are associated with the pathophysiology of MDD. In this study, we sought to evaluate the expression of lncRNAs in peripheral blood leukocytes as potential biomarkers for MDD. We measured the expression levels of 83 lncRNAs in the peripheral blood leukocytes of 29 MDD patients and 29 age- and gender-matched healthy controls using quantitative reverse transcription PCR (RT-qPCR) analysis. We found that MDD patients exhibited distinct expression signatures. Specifically, the expression level of one lncRNA (RMRP) was lower while the levels of four (Y5, MER11C, PCAT1, and PCAT29) were higher in MDD patients compared to healthy controls. The expression level of RMRP was correlated with depression severity as measured by the Hamilton Depression Rating Scale (HAM-D). Moreover, RMRP expression was lower in a mouse model of depression, corroborating the observation from MDD patients. Taken together, our data suggest that lower RMRP levels may serve as a potential biomarker for MDD.

Effect of Chronic Corticosterone Treatment on Depression-Like Behavior and Sociability in Female and Male C57BL/6N Mice

Depression is a very common psychiatric disorder affecting approximately 300 million people worldwide with the prevalence being twice as high in women as in men. Despite intense research efforts in recent decades, the neurobiological basis underlying depression remains incompletely understood. However, the exposure to chronic stress is widely accepted to constitute a precipitating factor for the development of this mental disorder. Several animal models for the investigation of the pathogenetic link between chronic stress and depression exist and have yielded important insights. The present study aimed at comparing two published protocols for the induction of depression-like behavior in mice based on chronic oral glucocorticoid application. Given the gender distribution in the prevalence of depression, the second goal of this study was to reveal possible differences in the behavioral responses of female and male mice to corticosterone (CORT) treatment. CORT treatment was found to modulate depression-like behavior in selected behavioral paradigms in a sex- and protocol-specific manner. These data are of relevance for the experimental design and interpretation of future studies in the field and further highlight the relevance of “sex as biological variable” to be considered an important parameter for experimental planning and interpretation of results.

Chronic unpredictable mild stress-induced behavioral changes are coupled with dopaminergic hyperfunction and serotonergic hypofunction in mouse models of depression

Accumulating evidence shows that stressful events evoke molecular alterations in the brain, considered a pathology in major depressive disorder (MDD). However, the abnormalities of neurotransmissions as well as intracellular signaling pathways affected by chronic stress in brain have not been fully explored. We investigated the effect of chronic unpredictable mild stress (CUMS) on the emotional behaviors, dopaminergic and serotoninergic function, and intracellular signaling in the nucleus accumbens, hippocampus and prefrontal cortex. Male C57BL/6J mice were exposed to CUMS for 4 weeks. CUMS was shown to induce hyperactivity in a novel environment, decrease interaction time in the social interaction test, prolong feeding latency in the novelty suppressed feeding test and enhance immobility in the forced swimming test. The levels of dopamine, its metabolites and turnover, and protein level of tyrosine hydroxylase (TH) were increased by CUMS in the nucleus accumbens (NAc). The level of serotonin and protein levels of tryptophan hydroxylase (TPH) and TH were decreased by CUMS in the hippocampus (HPC) and prefrontal cortex (PFC). Accompanying the increase in dopaminergic function, phosphorylation levels of extracellular signal-regulated kinases (ERK), protein kinase B (Akt) and cAMP response element-binding protein (CREB) were increased by CUMS in the NAc. Administration of fluoxetine (selective serotonin re-uptake inhibitor: 20 mg/kg i.p.) and aripiprazole (dopamine D₂ receptor partial agonist: 0.1 mg/kg i.p.) during CUMS, prevented behavioral changes and increase of dopamine level in the NAc. These data suggest that CUMS-induced depression-like behaviors are coupled with dopaminergic hyperfunction in the NAc and serotonergic hypofunction in the HPC and PFC.

Sustained rescue of prefrontal circuit dysfunction by antidepressant-induced spine formation

The neurobiological mechanisms underlying the induction and remission of depressive episodes over time are not well understood. Through repeated longitudinal imaging of medial prefrontal microcircuits in the living brain, we found that prefrontal spinogenesis plays a critical role in sustaining specific antidepressant behavioral effects and maintaining long-term behavioral remission. Depression-related behavior was associated with targeted, branch-specific elimination of postsynaptic dendritic spines on prefrontal projection neurons. Antidepressant-dose ketamine reversed these effects by selectively rescuing eliminated spines and restoring coordinated activity in multicellular ensembles that predict motivated escape behavior. Prefrontal spinogenesis was required for the long-term maintenance of antidepressant effects on motivated escape behavior but not for their initial induction.

Upregulation of hippocampal extracellular signal-regulated kinase (ERK)-2 induces antidepressant-like behavior in the rat forced swim test

The hippocampus mediates responses to affect-related behavior in preclinical models of pharmacological antidepressant efficacy, such as the forced swim test. However, the molecular mechanisms that regulate escape-directed behavior in this preclinical model of despair are not well understood. Here, using viral-mediated gene transfer, we assessed how overexpression of extracellular signal-regulated protein kinase (ERK)-2 within the dorsal hippocampus influenced behavioral reactivity to inescapable swimming stress in adult male Sprague-Dawley rats. When compared to controls, rats overexpressing hippocampal ERK-2 displayed increases in the time to initially adopt a posture of immobility, along with decreases in total time spent immobile, without influencing general locomotor activity. Collectively, the results indicate that hippocampal upregulation of ERK-2 increases escape-directed behavior in the rat forced swim test, thus providing insight into the neurobiological mechanisms that mediate antidepressant efficacy. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Pterostilbene, an active component of the dragon's blood extract, acts as an antidepressant in adult rats

BACKGROUND

Hippocampal neurogenesis has been widely considered as one of the potential biological mechanisms for the treatment of depression caused by chronic stress. Many natural products have been reported to be beneficial for neurogenesis.

OBJECTIVES

The present study is designed to investigate the effect of dragon's blood extract (DBE) and its biologically active compound, pterostilbene (PTE), on hippocampal neurogenesis.

METHODS

The male Sprague-Dawley (SD) rats were used in this study, which were maintained on the normal, DBE and PTE diet groups for 4 weeks before dissection in the normal rat model and behavioral testing in the CUS depression rat model. Meanwhile, DMI-treated rats are subcutaneously injected with DMI (10 mg/kg, i.p.).

RESULTS

Results revealed that DBE and PTE have the ability to promote hippocampal neurogenesis. DBE and PTE also promoted the proliferation of neural stem cells isolated from the brain of suckling rats. Oral administration of DBE and PTE induced the proliferation, migration, and differentiation of neural progenitor cells (NPCs) in chronic unexpected stressed (CUS) model rats, and improved the behavioral ability and alleviated depress-like symptoms of CUS rats. It was also observed that PTE treatment significantly induced the expression of neurogenesis-related factors, including BDNF, pERK, and pCREB.

CONCLUSION

Oral administration of PTE could affect neurogenesis and it is likely to be achieved via BDNF/ERK/CREB-associated signaling pathways.

The ERK Pathway: Molecular Mechanisms and Treatment of Depression

Major depressive disorder is a chronic debilitating mental illness. Its pathophysiology at cellular and molecular levels is incompletely understood. Increasing evidence supports a pivotal role of the mitogen-activated protein kinase (MAPK), in particular the extracellular signal-regulated kinase (ERK) subclass of MAPKs, in the pathogenesis, symptomatology, and treatment of depression. In humans and various chronic animal models of depression, the ERK signaling was significantly downregulated in the prefrontal cortex and hippocampus, two core areas implicated in depression. Inhibiting the ERK pathway in these areas caused depression-like behavior. A variety of antidepressants produced their behavioral effects in part via normalizing the downregulated ERK activity. In addition to ERK, the brain-derived neurotrophic factor (BDNF), an immediate upstream regulator of ERK, the cAMP response element-binding protein (CREB), a transcription factor downstream to ERK, and the MAPK phosphatase (MKP) are equally vulnerable to depression. While BDNF and CREB were reduced in their activity in the prefrontal cortex and hippocampus of depressed animals, MKP activity was enhanced in parallel. Chronic antidepressant treatment readily reversed these neurochemical changes. Thus, ERK signaling in the depression-implicated brain regions was disrupted during the development of depression, which contributes to the long-lasting and transcription-dependent neuroadaptations critical for enduring depression-like behavior and the therapeutic effect of antidepressants.

Activation of the MAPK signaling pathway induces upregulation of pro-apoptotic proteins in the hippocampi of cold stressed adolescent mice

Stress induces many non-specific responses in the hippocampus, especially during adolescence. Low environmental temperature is known to induce stress, but its influence on the hippocampus, especially in adolescent mice is not clear. We compared apoptotic-related protein levels and MAPK signaling pathway activation in hippocampal neurons of adolescent mice under low temperature conditions (4 °C for 12 h) with western blotting and immunohistochemistry. Western bolt results demonstrated that the levels of phospho-JNK, phospho-p38, and cleaved-caspase 3 significantly increased, while the ratio of Bcl-XL/Bax decreased, in the cold stress group. The results of immunohistochemistry (IHC) and Nissl staining demonstrated that the protein optical density of caspase 3 increased and Nissl bodies decreased in the cold stress group compared with controls. Thus, we conclude that cold exposure initiates activation of the MAPK signaling pathway and subsequently induces the upregulation of pro-apoptotic proteins in the hippocampi of adolescent mice. Overall our study reveals the relationship between cold stress and apoptosis in adolescent mice.

Adult mammalian neurogenesis and motivated behaviors

Adult neurogenesis continues to captivate the curiosity of the scientific community; and researchers seem to have a particular interest in identifying the functional implications of such plasticity. While the majority of research focuses on the association between adult neurogenesis and learning and memory (including spatial learning associated with hippocampal neurogenesis and olfactory discrimination associated with neurogenesis in the olfactory system), the following review will explore the link to motivated behaviors. In particular, goal-directed behaviors such as sociosexual, parental, aggressive, as well as depression- and anxiety-like behaviors and their reciprocal association to adult neurogenesis will be evaluated. The review will detail research in humans and other mammalian species. Furthermore, the potential mechanisms underlying these neurogenic alterations will be highlighted. Lastly, the review will conclude with a discussion on the functional significance of these newly generated cells in mediating goal-directed behaviors.