Acute antidepressant treatment differently modulates ERK/MAPK activation in neurons and astrocytes of the adult mouse prefrontal cortex

Opioid-environment interaction: Contrasting effects of morphine administered in a novel versus familiar environment on acute and repeated morphine induced behavioral effects and on acute morphine ERK activation in reward associated brain areas

We report that environmental context can have a major impact on morphine locomotor behavior and ERK effects. We manipulated environmental context in terms of an environmental novelty/ familiarity dimension and measured morphine behavioral effects in both acute and chronic morphine treatment protocols. Wistar rats (n=7 per group) were injected with morphine 10 mg/kg or vehicle (s.c.), and immediately placed into an arena for 5 min, and locomotor activity was measured after one or 5 days. The morphine treatments were initiated either when the environment was novel or began after the rats had been familiarized with the arena by being given 5 daily nondrug tests in the arena. The results showed that acute and chronic morphine effects were strongly modified by whether the environment was novel or familiar. Acute morphine administered in a novel environment increased ERK activity more substantially in several brain areas, particularly in reward-associated areas such as the VTA in comparison to when morphine was given in a familiar environment. Repeated morphine treatments initiated in a novel environment induced a strong locomotor sensitization, whereas repeated morphine treatments initiated in a familiar environment did not induce a locomotor stimulant effect but rather a drug discriminative stimulus dis-habituation effect. The marked differential effects of environmental novelty/familiarity and ongoing dopamine activity on acute and chronic morphine treatments may be of potential clinical relevance for opioid drug addiction.

Neuroplasticity and Mechanisms of Action of Acute and Chronic Treatment with Antidepressants in Preclinical Studies

Pharmacotherapy for depression includes drugs such as monoamine oxidase inhibitors (MAOIs), tricyclic antidepressants (TCAs), selective serotonin reuptake inhibitors (SSRIs), noradrenaline (NA) and serotonin (5-HT) reuptake inhibitors (NaSSAs), and atypical antidepressants; these drugs exert differentially beneficial effects on symptoms of depression after acute and chronic treatment in animal models. Said effects are established through neuroplastic mechanisms involving changes in neurogenesis and synaptogenesis as result of the activation of intracellular signaling pathways associated with neurochemical and behavioral changes. Antidepressants increase the synaptic availability of monoamines (monoaminergic hypothesis) such as 5-HT, NA, and gamma-aminobutyric acid (GABA) by inhibiting their reuptake or degradation and activating intracellular signaling pathways such as the responsive element binding protein (cAMP-CREB) cascade, which regulates the expression of genes related to neuroplasticity and neurogenesis, such as brain-derived neurotrophic factor (BDNF), in various brain structures implicated in depression. The aim of this review is to analyze the mechanisms of action of different antidepressants and to compare the effects of acute and chronic treatment on neuroplasticity in animal models of depression. A thorough search was conducted in PubMed, Scopus, and Web of Science, focusing on studies since 1996 with keywords like antidepressants, acute and chronic treatment, neuroplasticity, and experimental depression. Studies included had to investigate antidepressant effects experimentally, with full-text access, while excluding those that did not. Data extraction focused on study design, findings, and relevance to understanding treatment differences. Only high-quality, peer-reviewed studies were considered to ensure a comprehensive synthesis of current knowledge.

The mechanistic basis for the rapid antidepressant-like effects of ketamine: From neural circuits to molecular pathways

Conventional antidepressants that target monoaminergic receptors require several weeks to be efficacious. This lag represents a significant problem in the currently available treatments for serious depression. Ketamine, acting as an N-methyl-d-aspartate receptor antagonist, was shown to have rapid antidepressant-like effects, marking a significant advancement in the study of mood disorders. However, serious side effects and adverse reactions limit its clinical use. Considering the limitations of ketamine, it is crucial to further define the network targets of ketamine. The rapid action of ketamine an as antidepressant is thought to be mediated by the glutamate system. It is believed that synaptic plasticity is essential for the rapid effects of ketamine as an antidepressant. Other mechanisms include the involvement of the γ-aminobutyric acidergic (GABAergic), 5-HTergic systems, and recent studies have linked astrocytes to ketamine's rapid antidepressant-like effects. The interactions between these systems exert a synergistic rapid antidepressant effect through neural circuits and molecular mechanisms. Here, we discuss the neural circuits and molecular mechanisms underlying the action of ketamine. This work will help explain how molecular and neural targets are responsible for the effects of rapidly acting antidepressants and will aid in the discovery of new therapeutic approaches for major depressive disorder.

Exploring the mechanism of Icariin in the treatment of depression through BDNF-TrkB pathway based on network pharmacology

Depression has increasingly become a disease that seriously harms people's mental health around the world. Icariin is the main active component of Epimedii Herba and effective on protecting the central nervous system. The purpose of this study was to explore the mechanism of icariin against depression based on network pharmacology and molecular docking. The potential targets related to icariin and depression were obtained by accessing network databases. The Metascape database was used for the enrichment analysis of GO function and KEGG pathways. A common target-pathway network was constructed using Cytoscape 3.9.0 software. Schrödinger Maestro 12.8 was adopted to evaluate the binding ability of icariin to core targets. Mice were induced by the chronic unpredictable mild stress (CUMS) model, and the prediction results of this study were verified by in vivo experiments. A total of 109 and 3294 targets were identified in icariin and depression, respectively. The common target-pathway network was constructed, and 7 core target genes were obtained. The molecular docking results of the 7 core target genes with icariin showed good affinity. In a CUMS-induced depression model, we found that icariin could effectively improve depression-like behavior of mice, increase the expression of monoamine neurotransmitters 5-hydroxytryptamine, dopamine, and norepinephrine, decrease the secretion of inflammatory factors tumor necrosis factor-α, interleukin-6, and interleukin-1β, and upregulate the relative expression levels of BDNF, p-TrkB/TrkB, p-Akt/Akt, p-CREB/CREB, MAPK3, MAPK1, Bcl-2, EGFR, and mTOR. The results suggest that icariin has certain antidepressant effects, and may be mediated by the BDNF-TrkB signaling pathway. It provides new ideas for the treatment of depression in the future.

A Pattern to Link Adenosine Signaling, Circadian System, and Potential Final Common Pathway in the Pathogenesis of Major Depressive Disorder

Several studies have reported separate roles of adenosine receptors and circadian clockwork in major depressive disorder. While less evidence exists for regulation of the circadian clock by adenosine signaling, a small number of studies have linked the adenosinergic system, the molecular circadian clock, and mood regulation. In this article, we review relevant advances and propose that adenosine receptor signaling, including canonical and other alternative downstream cellular pathways, regulates circadian gene expression, which in turn may underlie the pathogenesis of mood disorders. Moreover, we summarize the convergent point of these signaling pathways and put forward a pattern by which Homer1a expression, regulated by both cAMP-response element binding protein (CREB) and circadian clock genes, may be the final common pathogenetic mechanism in depression.

Traditional herbal formula Jiao-tai-wan improves chronic restrain stress-induced depression-like behaviors in mice

OBJECTIVES

Jiao-tai-wan (JTW) has been often used to treat insomnia and diabetes mellitus. Recent studies found its antidepressant activity, but the related mechanism is not clear. This study is to evaluate the therapeutic effects of JTW on chronic restraint stress (CRS)-induced depression mice and explore the potential mechanisms.

METHODS

CRS was used to set up a depression model. Mice in different groups were treated with 0.9 % saline, JTW and fluoxetine. After the last day of CRS, the behavioral tests were conducted. The levels of neurotransmitters, inflammatory cytokines and HPA axis index were detected and the protein expressions of NLRP3 inflammasome complex were determined. H&E, NISSL, TUNEL and immunofluorescence staining were used to observe histopathological changes and the activation of microglia and astrocytes. The potential mechanisms were explored via network pharmacology and verified by Western blot.

RESULTS

The assessment of liver and kidney function showed that JTW was non-toxic. Behavioral tests proved that JTW can effectively ameliorate depression-like symptoms in CRS mice, which may be related to the inhibition of NLRP3 inflammasome activation. JTW can also improve the inflammatory state and HPA axis hyperactivity in mice, and has a protective effect on CRS-induced hippocampal neurons damage. The network pharmacology analysis and the results of Western blot suggested that the antidepressant effects of JTW may be related to the MAPK signaling pathway.

CONCLUSION

Our findings indicated that JTW may exert antidepressant effects in CRS-induced mice by inhibiting NLRP3 inflammasome activation and improving inflammatory state, and MAPK signaling pathway may also be involved.

Morphological Features of Astrocytes in Health and Neuropsychiatric Disorders

Astroglial cells actively partner with several cell types to regulate the arrangement of neuronal circuits both in the developing and adult brain. Morphological features of astroglial cells strongly impact their functional interactions, thereby supporting the hypothesis that aberrancies in glial morphology may trigger the onset of neuropsychiatric disorders. Thus, understanding the factors which modulate astroglial shapes and the development of tools to examine them may help to gain valuable insights about the role of astroglia in physiological and pathological brain states.Here, we present a collection of representative review and original articles describing the major morphological features which define different subtypes of glial cells and emphasize a high degree of heterogeneity typical of these cell types, besides neurons. Furthermore, we offer an overview about first in vitro and in vivo evidences, which highlight an altered morphology of glial cells in brains of psychiatric patients and animal models of neuropsychiatric disorders.

Diluted concentrations of methamphetamine in surface water induce behavior disorder, transgenerational toxicity, and ecosystem-level consequences of fish

Methamphetamine (METH) has been recognized as an emerging organic contaminant as it was widely detected in the aquatic environment via wastewater effluent discharge. However, the ecological hazard posed by METH at environmentally relevant concentrations was remained unclear. In this study, adult medaka fish were exposed to METH at environmental levels (0.05, 0.2, 0.5, 5 μg L^-1) and high level (25 and 100 μg L^-1) for 90 days to investigate its effect on ecologically behavioral functions, histopathology, bioconcentration, and transgenerational toxicity. The significant increase of locomotion activity, total distance, and max velocity of adult medaka were observed at low METH levels (0.2-0.5 μg L^-1), while it markedly decreased at high levels (25-100 μg L^-1). This effect may increase the predation risk of the fish. The significant alteration on the relative expressions of the genes (cacna1c, oxtr, erk1, and c-fos), as well as the contents of the proteins (oxytocin (OXT) and protein kinase A (PKA)) involved in Voltage Dependent Calcium Channel (VDCC) and Mitogen-Activated Protein Kinase (MAPK) signaling channel induced by METH could partly elucidate the underlying mechanisms of the changes of the behavioral traits. METH could induce obvious minimal gliosis, neuronal loss, and necrotic in brain tissues. Additionally, the significant increase of hepatic-somatic index (HSI) of male medaka at 0.2-5 μg L^-1 groups, and the decrease of female medaka at 100 μg L^-1 group indicated male fish was more susceptible to METH. Nephric-somatic index (NSI) of medaka markedly declined induced by METH at 0.05-100 μg L^-1. The bioconcentration factor (BCF) (0.4-5.8) in medaka fish revealed the bioconcentration potential of METH in fish. This study for the first time demonstrated METH could induced the development defects of larvae in F1 generation at environmentally relevant concentrations, thereby resulting in a significant decrease in the capacity of fish to produce offspring. Meanwhile, the RQ values (>1) of METH in river in China, USA, and Australia showed a high teratogenic risk level, suggesting the ecosystem-levels consequence posed by METH should be concerned.

Regulation of Circadian Genes by the MAPK Pathway: Implications for Rapid Antidepressant Action

Accumulating evidence suggests that the circadian rhythm plays a critical role in mood regulation, and circadian disturbances are often found in patients with major depressive disorder (MDD). The mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) pathway is involved in mediating entrainment of the circadian system. Furthermore, the MAPK/ERK signaling pathway has been shown to be involved in the pathogenesis of MDD and the rapid onset of action of antidepressant therapies, both pharmaceutical and non-pharmaceutical. This review provides an overview of the involvement of the MAPK/ERK pathway in modulating the circadian system in the rapid action of antidepressant therapies. This pathway holds much promise for the development of novel, rapid-onset-of-action therapeutics for MDD.

Dorsal Hippocampus ERK2 Signaling Mediates Anxiolytic-Related Behavior in Male Rats

Background

Anxiety disorders are the most common neuropathologies worldwide, but the precise neuronal mechanisms that underlie these disorders remain unknown. The hippocampus plays a role in mediating anxiety-related responses, which can be modeled in rodents using behavioral assays, such as the elevated plus maze. Yet, the molecular markers that underlie affect-related behavior on the elevated plus maze are not well understood.

Methods

We used herpes simplex virus vector delivery to overexpress extracellular signal-regulated kinase-2, a signaling molecule known to be involved in depression and anxiety, within the dorsal hippocampus of adult Sprague-Dawley male rats. Three days post virus delivery, we assessed anxiety-like responses on the elevated plus maze or general locomotor activity on the open field test.

Results

When compared to controls, rats overexpressing extracellular signal-regulated kinase-2 in the dorsal hippocampus displayed an anxiolytic-like phenotype, per increases in time spent in the open arms, and less time in the closed arms, of the elevated plus maze. Furthermore, no changes in locomotor activity as a function of virus infusion were observed on the open field test between the experimental groups.

Conclusion

This investigation demonstrates that virus-mediated increases of extracellular signal-regulated kinase-2 signaling, within the hippocampus, plays a critical role in decreasing anxiogenic responses on the rat elevated plus maze. As such, our data provide construct validity, at least in part, to the molecular mechanisms that mediate anxiolytic-like behavior in rodent models for the study of anxiety.

The influence of CaMKII and ERK phosphorylation on BDNF changes observed in mice selectively devoid of CREB in serotonergic or noradrenergic neurons

BACKGROUND

The transcription factor CREB and the neurotrophin BDNF are important mood regulators due to their profound role in controlling the neuronal plasticity. Our previously published results from transgenic mice functionally lacking CREB in chosen neural populations have shown that BDNF upregulation evoked by chronic treatment with fluoxetine seems to be dependent on CREB residing exclusively in serotonergic neurons. To further elucidate this observation, we focused on the representative signaling cascades engaged in the regulation of BDNF production.

METHODS

The study was carried out on mice lacking CREB in noradrenergic (Creb1DBHCre) or serotonergic (Creb1TPH2CreERT2) neurons in CREM deficient background. Animals received fluoxetine (10 mg/kg, ip) or desipramine (20 mg/kg, ip) for 21 days. The expression of following proteins and their phosphorylated forms was assessed by Western blot: CREB, BDNF, CaMKIIα, ERK1/2.

RESULTS

We showed that consistent with previously observed BDNF upregulation, chronic treatment with fluoxetine causes an increase in the pool of active CaMKIIα in w/t males, while in Creb1TPH2CreERT2 mutants, this effect ceased along with the observed decrease in ERK1/2 phosphorylation. These effects were region- and sex-specific. We did not observe a similar pattern of changes regarding the levels of BDNF expression and the CaMKIIα, ERK1/2 kinases in Creb1DBHCre mice exposed to desipramine. However, sex-dependent changes in the regulation of CaMKIIα and ERK1/2 activity were also observed.

CONCLUSIONS

Our study highlights the pivotal role of CREB in response to antidepressants, emphasizing different sex-dependent vulnerabilities to particular drugs and the important impact of CREM on the effects of CREB deletion.

Characterization of the Brain Penetrant Neuropeptide Y Y2 Receptor Antagonist SF-11

This paper discusses the biological and three-dimensional molecular structure of the novel, nonpeptide Y2R antagonist, SF-11 [N-(4-ethoxyphenyl)-4-(hydroxydiphenylmethyl)-1-piperidinecarbothioamide]. Pharmacokinetic studies in a rat model indicated that, following intraperitoneal dosing, SF-11 crossed the blood-brain barrier and was able to penetrate the brain, making it a suitable tool for behavioral studies. We showed for the first time that SF-11 decreased the immobility time in the forced swim test (FST) after acute peripheral administration (10 and 20 mg/kg), indicating that it has antidepressant potential. Inhibitors of the mitogen-activated protein kinase/extracellular signal regulated kinase (MAPK/ERK) and phosphatidylinositol 3-kinase (PI3K) signaling pathways blocked the anti-immobility effect of SF-11, suggesting that these pathways are involved in the antidepressant-like activity of SF-11 in the FST. The results of locomotor activity of rats indicate that the effects observed in the FST are specific and due to the antidepressant-like activity of SF-11. These findings provide further evidence for the antidepressant potential of Y2R antagonists. Also, the application of Fourier transform infrared absorption (FT-IR) and Raman spectroscopy (RS) methods combined with theoretical density functional theory (DFT) calculations allowed us to present the optimized spatial orientation of the investigated drug. Structural characterization of SF-11 based on vibrational spectroscopic data is of great importance and will aid in understanding its biological activity and pave the way for its development as a new antidepressant agent.

Neuronal Activity, TGFβ-Signaling and Unpredictable Chronic Stress Modulate Transcription of Gadd45 Family Members and DNA Methylation in the Hippocampus

Neuronal activity is altered in several neurological and psychiatric diseases. Upon depolarization not only neurotransmitters are released but also cytokines and other activators of signaling cascades. Unraveling their complex implication in transcriptional control in receiving cells will contribute to understand specific central nervous system (CNS) pathologies and will be of therapeutically interest. In this study we depolarized mature hippocampal neurons in vitro using KCl and revealed increased release not only of brain-derived neurotrophic factor (BDNF) but also of transforming growth factor beta (TGFB). Neuronal activity together with BDNF and TGFB controls transcription of DNA modifying enzymes specifically members of the DNA-damage-inducible (Gadd) family, Gadd45a, Gadd45b, and Gadd45g. MeDIP followed by massive parallel sequencing and transcriptome analyses revealed less DNA methylation upon KCl treatment. Psychiatric disorder-related genes, namely Tshz1, Foxn3, Jarid2, Per1, Map3k5, and Arc are transcriptionally activated and demethylated upon neuronal activation. To analyze whether misexpression of Gadd45 family members are associated with psychiatric diseases, we applied unpredictable chronic mild stress (UCMS) as established model for depression to mice. UCMS led to reduced expression of Gadd45 family members. Taken together, our data demonstrate that Gadd45 family members are new putative targets for UCMS treatments.

Association analysis between mitogen-activated protein/extracellular signal-regulated kinase (MEK) gene polymorphisms and depressive disorder in the Han Chinese population

BACKGROUND

Recent research findings suggest that BDNF and BDNF signaling pathways participate in the development of major depressive disorder. Mitogen-activated extracellular signal-regulated kinase (MEK) is the most important kinase in the extracellular signal-regulated kinase pathway, and the extracellular signal-regulated kinase pathway is the key signaling pathway of BDNF, so it may play a role in development of depressive disorder. The aim of this study is to investigate the association between polymorphisms of the MAP2K1 (also known as MEK) gene and depressive disorder.

RESULTS

Three single nucleotide polymorphisms (SNPs), were significantly associated with depressive disorder: rs1549854 (p = 0.006), rs1432441 (p = 0.025), and rs7182853 (p = 0.039). When subdividing the sample by gender, two of the SNPs remained statistically associated with depressive disorder in females: rs1549854 (p = 0.013) and rs1432441 (p = 0.04).

CONCLUSION

The rs1549854 and rs1432441 polymorphisms of the MAP2K1 gene may be associated with major depressive disorder, especially in females. This study is the first to report that the MAP2K1 gene may be a genetic marker for depressive disorder.

Serotonin transporter immunoreactivity is modulated during development and after fluoxetine treatment in the rodent visual system

The serotonin transporter (5-HTT) regulates serotonin homeostasis and has been used as a target for different drugs in depression treatment. Although the serotonergic system has received a lot of attention, little is known about the effects of these drugs over serotonin transporters. In this work, we investigated the expression pattern of 5-HTT during development of the visual system and the influence of fluoxetine on different signaling pathways. Our data showed that the expression of 5-HTT has a gradual increase from postnatal day 0 until 42 and decrease afterwards. Moreover, chronic fluoxetine treatment both in childhood and adolescence induces down regulation of 5-HTT expression and phosphorylation of ERK and AKT signaling pathways. Together these data suggest that the levels of 5-HTT protein could be important for the development of the central nervous system and suggest that the ERK and AKT are involved in the molecular pathways of antidepressants drugs, acting in concert to improve serotonergic signaling.

Antidepressant-like activity of the neuropeptide Y Y5 receptor antagonist Lu AA33810: behavioral, molecular, and immunohistochemical evidence

RATIONALE

It has recently been found that chronic treatment with the highly selective, brain-penetrating Y5 receptor antagonist, Lu AA33810 [N-[[trans-4-[(4,5-dihydro [1] benzothiepino[5,4-d] thiazol-2-yl) amino] cyclohexyl]methyl]-methanesulfonamide], produces antidepressant-like effects in the rat chronic mild stress model.

OBJECTIVE

In the present study, we investigated the possible antidepressant-like activity of Lu AA33810 in rats subjected to glial ablation in the prefrontal cortex (PFC) by the gliotoxin L-AAA, which is an astroglial degeneration model of depression.

RESULTS

We observed that Lu AA33810 administered intraperitoneally at a single dose of 10 mg/kg both reversed depressive-like behavioral changes in the forced swim test (FST) and prevented degeneration of astrocytes in the mPFC. The mechanism of antidepressant and glioprotective effects of Lu AA33810 has not been studied, so far. We demonstrated the contribution of the noradrenergic rather than the serotonergic pathway to the antidepressant-like action of Lu AA33810 in the FST. Moreover, we found that antidepressant-like effect of Lu AA33810 was connected with the influence on brain-derived neurotrophic factor (BDNF) protein expression. We also demonstrated the antidepressant-like effect of Lu AA33810 in the FST in rats which did not receive the gliotoxin. We found that intracerebroventricular injection of the selective MAPK/ERK inhibitor U0126 (5 μg/2 μl) and the selective PI3K inhibitor LY294002 (10 nmol/2 μl) significantly inhibited the anti-immobility effect of Lu AA33810 in the FST in rats, suggesting that MAPK/ERK and PI3K signaling pathways could be involved in the antidepressant-like effect of Lu AA33810.

CONCLUSION

Our results indicate that Lu AA33810 exerts an antidepressant-like effect and suggest the Y5 receptors as a promising target for antidepressant therapy.

PTPRR regulates ERK dephosphorylation in depression mice model

BACKGROUND

The Protein tyrosine phosphatase receptor type R (PTPRR), which regulates the dephosphorylation of the downstream mitogen-activated protein kinase (MAPK) steering cell proliferation, apoptosis and synaptic plasticity, may be involved in the pathogenesis of depression.

METHODS

Lentiviral vectors were utilized to express the PTPRR constitutively in the hippocampal dentate gyrus (DG) of mice before or after chronic mild stress. Behavior tests, MAPK levels, neuronal apoptosis and cell proliferation in the hippocampal DG were examined.

RESULTS

Without chronic mild stress (CMS), the lenti-shPTPRR mice showed shorter immobility time in the tail suspension test than controls, while the lenti-PTPRR mice exhibited significantly less sucrose intake and increased immobility time in the forced swim tests than control mice, indicating increased prodepressant-like effects of PTPRR in lenti-PTPRR mice. Similarly, under CMS, the lenti-shPTPRR mice had more sucrose intake, shorter immobility time in the forced swim test and tail suspension test compared to controls, and lenti-PTPRR mice had less sucrose intake and longer immobility time in forced swim test and tail suspension test, exhibiting increased susceptibility to depressive-like behaviors and greater sensitivity to CMS. Besides, the Phospho-ERK1/2(p-ERK) had significant lower phosphorylation in lenti-PTPRR group and higher expression in lenti-shPTPRR group, both without CMS. The Lenti-PTPRR mice exposed to CMS had significant lower p-ERK, and the lenti-shPTPRR mice exposed to CMS had significant higher p-ERK and lower p-P38. Moreover, there were more cells underwent apoptosis in lenti-PTPRR group ,with and without CMS. In cell proliferation, less BrdU positive cells were observed in lenti-PTPRR mice than controls.

CONCLUSION

The site-specific lentiviral injections resulted in the PTPRR over-expression in the hippocampal DG and subsequent increased ERK dephosphorylation, which leads to more neuron apoptosis, less cell proliferation, depression onset and increased sensitivity to CMS. PTPRR/ERK pathway could be potential target for depression therapy.

Comprehensive gene- and pathway-based analysis of depressive symptoms in older adults

Depressive symptoms are common in older adults and are particularly prevalent in those with or at elevated risk for dementia. Although the heritability of depression is estimated to be substantial, single nucleotide polymorphism-based genome-wide association studies of depressive symptoms have had limited success. In this study, we performed genome-wide gene- and pathway-based analyses of depressive symptom burden. Study participants included non-Hispanic Caucasian subjects (n = 6,884) from three independent cohorts, the Alzheimer's Disease Neuroimaging Initiative (ADNI), the Health and Retirement Study (HRS), and the Indiana Memory and Aging Study (IMAS). Gene-based meta-analysis identified genome-wide significant associations (ANGPT4 and FAM110A, q-value = 0.026; GRM7-AS3 and LRFN5, q-value = 0.042). Pathway analysis revealed enrichment of association in 105 pathways, including multiple pathways related to ERK/MAPK signaling, GSK3 signaling in bipolar disorder, cell development, and immune activation and inflammation. GRM7, ANGPT4, and LRFN5 have been previously implicated in psychiatric disorders, including the GRM7 region displaying association with major depressive disorder. The ERK/MAPK signaling pathway is a known target of antidepressant drugs and has important roles in neuronal plasticity, and GSK3 signaling has been previously implicated in Alzheimer's disease and as a promising therapeutic target for depression. Our results warrant further investigation in independent and larger cohorts and add to the growing understanding of the genetics and pathobiology of depressive symptoms in aging and neurodegenerative disorders. In particular, the genes and pathways demonstrating association with depressive symptoms may be potential therapeutic targets for these symptoms in older adults.

Chronic Fluoxetine Treatment Upregulates the Activity of the ERK1/2-NF-κB Signaling Pathway in the Hippocampus and Prefrontal Cortex of Rats Exposed to Forced-Swimming Stress

OBJECTIVES

The aim of this study was to explore whether or not the antidepressant actions of fluoxetine (FLX) are correlated with extracellular signal-regulated kinase 1 and 2 (ERK1/2) and nuclear factor κ-light chain enhancer of activated B cells (NF-κB) in the hippocampus (HC) and prefrontal cortex (PFC) of rats.

MATERIALS AND METHODS

A total of 108 male Sprague-Dawley rats were randomly divided into 6 groups of 18 rats each. Group 1 was the control group, while group 2 comprised the depressed model in which rats were subjected to 28 days of forced-swimming stress (FST); groups 3-6 were also subjected to 28 days of FST and treated with FLX once a day for 1 day (group 3; F1d), 1 week (group 4; F1w), 2 weeks (group 5; F2w), or 4 weeks (group 6; F4w). The control group was not subjected to FST or treated with FLX. Behavior tests that included the Morris water maze (MWM) and saccharin preference were performed, and ERK1/2 and NF-κB proteins were assayed using Western blot.

RESULTS

The rats in the control group and in groups 5 and 6 (F2w and F4w, respectively) had a significantly shorter average escape latency, needed more attempts in order to successfully cross the platform, and had a greater saccharin preference than those in the depressed group (p < 0.05). In the depressed group, the phosphorylated ERK1/2 (p-ERK1/2) and phosphorylated NF-κB (p-NF-κB) expression in the HC and PFC were lower than in the control group (p < 0.05). Treatment with FLX reversed the changes in the expression of p-ERK1/2 and p-NF-κB in rats in the F2w and F4w groups.

CONCLUSIONS

In this study, FLX treatment for 2 weeks or longer reversed the impaired spatial learning, memory, and anhedonia observed in the depressed model rats and upregulated the activities of the ERK1/2-NF-κB signaling pathway.

Bacterial translocation affects intracellular neuroinflammatory pathways in a depression-like model in rats

Recent studies have suggested that depression is accompanied by an increased intestinal permeability which would be related to the inflammatory pathophysiology of the disease. This study aimed to evaluate whether experimental depression presents with bacterial translocation that in turn can lead to the TLR-4 in the brain affecting the mitogen-activated protein kinases (MAPK) and antioxidant pathways. Male Wistar rats were exposed to chronic mild stress (CMS) and the intestinal integrity, presence of bacteria in tissues and plasma lipopolysaccharide levels were analyzed. We also studied the expression in the prefrontal cortex of activated forms of MAPK and some of their activation controllers and the effects of CMS on the antioxidant Nrf2 pathway. Our results indicate that after exposure to a CMS protocol there is increased intestinal permeability and bacterial translocation. CMS also increases the expression of the activated form of the MAPK p38 while decreasing the expression of the antioxidant transcription factor Nrf2. The actions of antibiotic administration to prevent bacterial translocation on elements of the MAPK and Nrf2 pathways indicate that the translocated bacteria are playing a role in these effects. In effect, our results propose a role of the translocated bacteria in the pathophysiology of depression through the p38 MAPK pathway which could aggravate the neuroinflammation and the oxidative/nitrosative damage present in this pathology. Moreover, our results reveal that the antioxidant factor Nrf2 and its activators may be involved in the consequences of the CMS on the brain.

Effects of doxepin on brain-derived neurotrophic factor, tumor necrosis factor alpha, mitogen-activated protein kinase 14, and AKT1 genes expression in rat hippocampus

BACKGROUND

It has been suggested that doxepin in addition to enhancement of noradrenaline and serotonin levels may have neuroprotective effects. Therefore, this study investigated the effect of doxepin on gene expression of brain-derived neurotrophic factor (BDNF), tumor necrosis factor alpha (TNF-α), mitogen-activated protein kinase 14 (MAPK14), and serine-threonine protein kinase AKT1 in rat hippocampus.

MATERIALS AND METHODS

Male rats were divided randomly into three groups: Control, doxepin 1 mg/kg, and doxepin 5 mg/kg. Rats received an i.p injection of doxepin for 21 days. Then the hippocampi were dissected for the measurement of the expression of BDNF, TNF-α, MAPK14, and AKT1 genes.

RESULTS

Our results showed no significant effects of doxepin on gene expression of BDNF, TNF-α, MAPK14, and AKT1 genes in the hippocampus.

CONCLUSIONS

These results did not show significant effects of doxepin on the genes that affect the neuronal survival in intact animals. However, more studies need to be done, especially in models associated with neuronal damage.

Potential molecular and cellular mechanism of psychotropic drugs

Psychiatric disorders are among the most debilitating of all medical illnesses. Whilst there are drugs that can be used to treat these disorders, they give sub-optimal recovery in many people and a significant number of individuals do not respond to any treatments and remain treatment resistant. Surprisingly, the mechanism by which psychotropic drugs cause their therapeutic benefits remain unknown but likely involves the underlying molecular pathways affected by the drugs. Hence, in this review, we have focused on recent findings on the molecular mechanism affected by antipsychotic, mood stabilizing and antidepressant drugs at the levels of epigenetics, intracellular signalling cascades and microRNAs. We posit that understanding these important interactions will result in a better understanding of how these drugs act which in turn may aid in considering how to develop drugs with better efficacy or increased therapeutic reach.

MAPK signaling correlates with the antidepressant effects of ketamine

Studies have pointed to a relationship between MAPK kinase (MEK) signaling and the behavioral effects of antidepressant drugs. So, in the present study we examined the behavioral and molecular effects of ketamine, an antagonist of the N-methyl-d-aspartate receptor (NMDA), which has been shown to have an antidepressant effect after the inhibition of MEK signaling in Wistar rats. Our results showed that acute administration of the MEK inhibitor PD184161, produced depressive-like behavior and stopped antidepressant-like effects of ketamine in the forced swimming test. The phosphorylation of extracellular signal-regulated kinase 1/2 (pERK 1/2) was decreased by PD184161 in the amygdala and nucleus accumbens, and the effects of ketamine on pERK 1/2 in the prefrontal cortex and hippocampus were inhibited by PD184161. The ERK 2 levels were decreased by PD184161 in the nucleus accumbens; and the effects of ketamine were blocked in this brain area. The p38 protein kinase (p38MAPK) and proBDNF were inhibited by PD184161, and the MEK inhibitor prevented the effects of ketamine in the nucleus accumbens. In addition, ketamine increased pro-BDNF levels in the hippocampus. In conclusion, our findings demonstrated that an acute blockade of MAPK signaling lead to depressive-like behavior and stopped the antidepressant response of ketamine, suggesting that the effects of ketamine could be mediated, at least in part, by the regulation of MAPK signaling in these specific brain areas.

Antidepressant-like effect of the mGluR5 antagonist MTEP in an astroglial degeneration model of depression

The glutamatergic predominance in the excitatory-inhibitory balance is postulated to be involved in the pathogenesis of depression. Such imbalance may be induced by astrocyte ablation which reduces glutamate uptake and increases glutamate level in the synaptic cleft. In the present study, we tried to ascertain whether astroglial degeneration in the prefrontal cortex could serve as an animal model of depression and whether inhibition of glutamatergic transmission by the mGluR5 antagonist MTEP could have antidepressant potential. Astrocytic toxins l-or dl-alpha-aminoadipic acid (AAA), 100μg/2μl, were microinjected, bilaterally into the rat medial prefrontal cortex (PFC) on the first and second day of experiment. MTEP (10mg/kg) or imipramine (30mg/kg) were administered on the fifth day. Following administration of MTEP or imipramine the forced swim test (FST) was performed for assessment of depressive-like behavior. The brains were taken out for analysis on day eight. The astrocytic marker, glial fibrillary acidic protein (GFAP) was quantified in PFC by Western blot method and by stereological counting of immunohistochemically stained sections. Both l-AAA and dl-AAA induced a significant increase in immobility time in the FST. This effect was reversed by imipramine, which indicates depressive-like effects of these toxins. A significant decrease in GFAP (about 50%) was found after l-AAA. Both the behavioral and GFAP level changes were prevented by MTEP injection. The obtained results indicate that the degeneration of astrocytes in the PFC by l-AAA may be a useful animal model of depression and suggest antidepressant potential of MTEP.