Beyond the monoaminergic hypothesis: neuroplasticity and epigenetic changes in a transgenic mouse model of depression

Depression unveiled: Insights into etiology and animal models for behavioral assessment, exploring the multifactorial nature and treatment of depression

Over the past century, significant shifts in daily living have led to an increased prevalence of mental disorders, often linked to hormonal imbalances. Among these, anxiety and depression stand out as prevalent diagnoses, particularly in industrialized nations. Depression, according to the DSM-5, is a heterogeneous condition that affects emotional, cognitive, and physical functioning, with symptoms including insomnia, sexual dysfunction, and weight changes. Cognitive theories of depression highlight its impact on judgment, decision-making, thinking, and focus. Depression's multifaceted nature means that no two patients experience identical symptoms, risk factors, or treatment responses. The COVID-19 pandemic has exacerbated mental health issues, with social isolation, restricted contact, and altered daily routines contributing to increased anxiety and depression, especially among adolescents and young adults. The pandemic's psychological toll underscores the need for effective treatment strategies for mental disorders. The physical manifestations of major depressive disorder (MDD) are associated with a heightened risk of developing various medical conditions, including metabolic disorders, cardiovascular disease, stroke, epilepsy, and dementia. This review provides a comprehensive exploration of depression and anxiety, covering their different types, epidemiology, potential causes, diagnostic criteria, and available treatment options. It delves into the role of pharmacological interventions and examines recent advancements to enhance therapeutic outcomes. Additionally, the review assesses the therapeutic potential of drugs, offering insights into their efficacy in treating these complex mental health disorders. By targeting the multifactorial etiology of depression through drug repurposing and new drug development, researchers aim to enhance treatment efficacy and achieve better outcomes for patients with depression.

MiR-184-3p in the paraventricular nucleus participates in the neurobiology of depression via regulation of the hypothalamus-pituitary-adrenal axis

Hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis during chronic stress is essential for the pathogenesis of depression, and increased activity of cAMP response element binding protein (CREB)-regulated transcription co-activator 1 (CRTC1) in the paraventricular nucleus (PVN) plays a critical role. As a well-investigated microRNA (miRNA), miR-184 has two forms, miR-184-3p and miR-184-5p. Recently, miRNAs target genes predictive analysis and dual-luciferase reporter assays identified an inhibitory role of miR-184-3p on CRTC1 expression. Therefore, we speculated that miR-184-3p regulation was responsible for the effects of chronic stress on CRTC1 in the PVN. Various methods, including the chronic social defeat stress (CSDS) model of depression, behavioral tests, Western blotting, co-immunoprecipitation (Co-IP), quantitative real-time reverse transcription PCR (qRT-PCR), immunofluorescence, and adeno-associated virus (AAV)-mediated gene transfer, were used. CSDS evidently downregulated the level of miR-184-3p, but not miR-184-5p, in the PVN. Genetic knockdown and pharmacological inhibition of miR-184-3p in the PVN induced various depressive-like symptoms (e.g., abnormal behaviors, HPA hyperactivity, enhanced CRTC1 function in PVN neurons, downregulation of hippocampal neurogenesis, and decreased brain-derived neurotrophic factor (BDNF) signaling) in naïve male C57BL/6J mice. In contrast, genetic overexpression and pharmacological activation of miR-184-3p in the PVN produced significant beneficial effects against CSDS. MiR-184-3p in the PVN was necessary for the antidepressant actions of two well-known SSRIs, fluoxetine and paroxetine. Collectively. miR-184-3p was also implicated in the neurobiology of depression and may be a viable target for novel antidepressants.

Acupuncture may play a key role in anti-depression through various mechanisms in depression

Depression has emerged as a significant global health concern, exerting a profound impact on individuals, as evidenced by its high prevalence and associated suicide rates. Considering its pervasive nature, the absence of optimal treatment modalities remains a challenge. Acupuncture has garnered substantial clinical and experimental validation for its efficacy in addressing diverse forms of depression, including postpartum, post-stroke, and adolescent depression. This article endeavors to elucidate the distinctive attributes and underlying mechanisms of acupuncture in the contemporary treatment of depression. Research has demonstrated that acupuncture exerts diverse physiological effects in animal models of depression, encompassing modulation of the brain, serum, and brain-gut axis. These effects are attributed to various mechanisms, including anti-inflammatory and anti-oxidative actions, promotion of neuronal plasticity, neuroprotection, neurotrophic effects, modulation of neurotransmitters, regulation of endocrine and immune functions, and modulation of cell signal pathways. Currently, the therapeutic mechanism of acupuncture involves the engagement of multiple targets, pathways, and bidirectional regulation. Hence, acupuncture emerges as a promising alternative medical modality, exhibiting substantial research prospects and meriting comprehensive worth further study and dissemination.

DAPK1 mediates cognitive dysfunction and neuronal apoptosis in PSD rats through the ERK/CREB/BDNF signaling pathway

Post-stroke depression (PSD) is one of the most common mental sequelae after a stroke and can damage the brain. Although PSD has garnered increasing attention in recent years, the precise mechanism remains unclear. Studies have indicated that the expression of DAPK1 is elevated in various neurodegenerative conditions, including depression, ischemic stroke, and Alzheimer's disease. However, the specific molecular mechanism of DAPK1-mediated cognitive dysfunction and neuronal apoptosis in PSD rats is unclear. In this study, we established a rat model of PSD, and then assessed depression-like behaviors and cognitive dysfunction in rats using behavioral tests. In addition, we detected neuronal apoptosis and analyzed the expression of DAPK1 protein and proteins related to the ERK/CREB/BDNF signaling pathway. The findings revealed that MCAO combined with CUMS can induce more severe depression-like behaviors and cognitive dysfunction in rats, while overexpression of DAPK1 may hinder the downstream ERK/CREB/BDNF signaling pathways, resulting in neuronal loss and exacerbation of brain tissue damage. In this study, we will focus on DAPK1 and explore its role in PSD.

Salt-inducible kinase 1-CREB-regulated transcription coactivator 1 signalling in the paraventricular nucleus of the hypothalamus plays a role in depression by regulating the hypothalamic-pituitary-adrenal axis

Elucidating the molecular mechanism underlying the hyperactivity of the hypothalamic-pituitary-adrenal axis during chronic stress is critical for understanding depression and treating depression. The secretion of corticotropin-releasing hormone (CRH) from neurons in the paraventricular nucleus (PVN) of the hypothalamus is controlled by salt-inducible kinases (SIKs) and CREB-regulated transcription co-activators (CRTCs). We hypothesised that the SIK-CRTC system in the PVN might contribute to the pathogenesis of depression. Thus, the present study employed chronic social defeat stress (CSDS) and chronic unpredictable mild stress (CUMS) models of depression, various behavioural tests, virus-mediated gene transfer, enzyme-linked immunosorbent assay, western blotting, co-immunoprecipitation, quantitative real-time reverse transcription polymerase chain reaction, and immunofluorescence to investigate this connection. Our results revealed that both CSDS and CUMS induced significant changes in SIK1-CRTC1 signalling in PVN neurons. Both genetic knockdown of SIK1 and genetic overexpression of CRTC1 in the PVN simulated chronic stress, producing a depression-like phenotype in naive mice, and the CRTC1-CREB-CRH pathway mediates the pro-depressant actions induced by SIK1 knockdown in the PVN. In contrast, both genetic overexpression of SIK1 and genetic knockdown of CRTC1 in the PVN protected against CSDS and CUMS, leading to antidepressant-like effects in mice. Moreover, stereotactic infusion of TAT-SIK1 into the PVN also produced beneficial effects against chronic stress. Furthermore, the SIK1-CRTC1 system in the PVN played a role in the antidepressant actions of fluoxetine, paroxetine, venlafaxine, and duloxetine. Collectively, SIK1 and CRTC1 in PVN neurons are closely involved in depression neurobiology, and they could be viable targets for novel antidepressants.

Global prevalence and factors associated with preoperative depression in women undergoing breast surgery: a meta-analysis and meta-regression

PURPOSE

Depression is one of the main psychological responses experienced by patients with breast cancer perioperatively. Therefore, this review aimed to synthesize the prevalence rate of depression preoperatively among patients with breast cancer.

METHODS

Six databases were searched for published articles, which recruited female patients aged 18 years and above, diagnosed with breast cancer and planned for breast surgery. Grey literatures were searched from ProQuest Theses and Dissertations, Science.gov and CogPrints. Studies published in English from the inception of databases to January 2023 were considered. Two reviewers screened, extracted, and appraised the data independently. Joanna Briggs Institute data collection form was used for data collection. Hoy's Risk of Bias Tool was utilized to assess the individual study's quality. Review Manager 5.4 software was utilized for meta-analysis. Subgroup analyses were conducted to explore the reasons for any heterogeneity. Publication bias was evaluated by Egger's test and funnel plot.

RESULTS

Twenty studies involving 32,143 patients with breast cancer were included. Meta-analyses revealed an overall preoperative prevalence of 30% among all studies. Subgroup analyses showed that studies conducted in the Middle East and North Africa used purposive sampling, with patients undergoing mastectomy and lumpectomy and with moderate risk of bias reported higher prevalence of preoperative depression (54%, 44%, 40%, and 49%, respectively) as compared to other respective subgroups.

CONCLUSION

The high prevalence of preoperative depression among women with breast cancer indicated the need for health care professionals to provide more psychological support to them.

Substance P's Impact on Chronic Pain and Psychiatric Conditions-A Narrative Review

Substance P (SP) plays a crucial role in pain modulation, with significant implications for major depressive disorder (MDD), anxiety disorders, and post-traumatic stress disorder (PTSD). Elevated SP levels are linked to heightened pain sensitivity and various psychiatric conditions, spurring interest in potential therapeutic interventions. In chronic pain, commonly associated with MDD and anxiety disorders, SP emerges as a key mediator in pain and emotional regulation. This review examines SP's impact on pain perception and its contributions to MDD, anxiety disorders, and PTSD. The association of SP with increased pain sensitivity and chronic pain conditions underscores its importance in pain modulation. Additionally, SP influences the pathophysiology of MDD, anxiety disorders, and PTSD, highlighting its potential as a therapeutic target. Understanding SP's diverse effects provides valuable insights into the mechanisms underlying these psychiatric disorders and their treatment. Further research is essential to explore SP modulation in psychiatric disorders and develop more effective treatment strategies.

Myeloid Cell Association with Spinal Cord Injury-Induced Neuropathic Pain and Depressive-like Behaviors in LysM-eGFP Mice

Spinal cord injury (SCI) affects ∼500,000 people worldwide annually, with the majority developing chronic neuropathic pain. Following SCI, approximately 60% of these individuals are diagnosed with comorbid mood disorders, while only ∼21% of the general population will experience a mood disorder in their lifetime. We hypothesize that nociceptive and depressive-like dysregulation occurs after SCI and is associated with aberrant macrophage infiltration in segmental pain centers. We completed moderate unilateral C5 spinal cord contusion on LysM-eGFP reporter mice to visualize infiltrating macrophages. At 6-weeks post-SCI, mice exhibit nociceptive and depressive-like dysfunction compared to naïve and sham groups. There were no differences between the sexes, indicating that sex is not a contributing factor driving nociceptive or depressive-like behaviors after SCI. Utilizing hierarchical cluster analysis, we classified mice based on endpoint nociceptive and depressive-like behavior scores. Approximately 59.3% of the SCI mice clustered based on increased paw withdrawal threshold to mechanical stimuli and immobility time in the forced swim test. SCI mice displayed increased myeloid cell presence in the lesion epicenter, ipsilateral C7-8 dorsal horn, and C7-8 DRGs as evidenced by eGFP, CD68, and Iba1 immunostaining when compared to naïve and sham mice. This was further confirmed by SCI-induced alterations in the expression of genes indicative of myeloid cell activation states and their associated secretome in the dorsal horn and dorsal root ganglia. In conclusion, moderate unilateral cervical SCI caused the development of pain-related and depressive-like behaviors in a subset of mice and these behavioral changes are consistent with immune system activation in the segmental pain pathway. PERSPECTIVE: These experiments characterized pain-related and depressive-like behaviors and correlated these changes with the immune response post-SCI. While humanizing the rodent is impossible, the results from this study inform clinical literature to closely examine sex differences reported in humans to better understand the underlying shared etiologies of pain and depressive-like behaviors following central nervous system trauma.

Efficacy of transcranial photobiomodulation in the treatment for major depressive disorder: A TMS-EEG and pilot study

BACKGROUND

Major depressive disorder (MDD) was a prevalent mental condition that may be accompanied by decreased excitability of left frontal pole (FP) and abnormal brain connections. An 820 nm tPBM can induce an increase in stimulated cortical excitability. The purpose of our study was to establish how clinical symptoms and time-varying brain network connectivity of MDD were affected by transcranial photobiomodulation (tPBM).

METHODS

A total of 11 patients with MDD received 820 nm tPBM targeting the left FP for 14 consecutive days. The severity of symptoms was evaluated by neuropsychological assessments at baseline, after treatment, 4-week and 8-week follow-up; 8-min transcranial magnetic stimulation combined electroencephalography (TMS-EEG) was performed for five healthy controls and five patients with MDD before and after treatment, and time-varying EEG network was analyzed using the adaptive-directed transfer function.

RESULTS

All of scales scores in the 11 patients decreased significantly after 14-day tPBM (p < .01) and remained at 8-week follow-up. The time-varying brain network analysis suggested that the brain regions with enhanced connection information outflow in MDD became gradually more similar to healthy controls after treatment.

CONCLUSIONS

This study showed that tPBM of the left FP could improve symptoms of patients with MDD and normalize the abnormal network connections.

Stress-induced changes in cognitive function and intestinal barrier integrity can be ameliorated by venlafaxine and synbiotic supplementations

Stress profoundly impacts various aspects of both physical and psychological well-being. Our previous study demonstrated that venlafaxine (Vlx) and synbiotic (Syn) treatment attenuated learned fear-like behavior and recognition memory impairment in immobilized-stressed rats. In this study, we further investigated the physical, behavior, and cellular mechanisms underlying the effects of Syn and/or Vlx treatment on brain and intestinal functions in stressed rats. Adult male Wistar rats, aged 8 weeks old were subjected to 14 days of immobilization stress showed a decrease in body weight gain and food intake as well as an increase in water consumption, urinary corticosterone levels, and adrenal gland weight. Supplementation of Syn and/or Vlx in stressed rats resulted in mitigation of weight loss, restoration of normal food and fluid intake, and normalization of corticosterone levels. Behavioral analysis showed that treatment with Syn and/or Vlx enhanced depressive-like behaviors and improved spatial learning-memory impairment in stressed rats. Hippocampal dentate gyrus showed stress-induced neuronal cell death, which was attenuated by Syn and/or Vlx treatment. Stress-induced ileum inflammation and increased intestinal permeability were both effectively reduced by the supplementation of Syn. In addition, Syn and Vlx partly contributed to affecting the expression of the glial cell-derived neurotrophic factor in the hippocampus and intestines of stressed rats, suggesting particularly protective effects on both the gut barrier and the brain. This study highlights the intricate interplay between stress physiological responses in the brain and gut. Syn intervention alleviate stress-induced neuronal cell death and modulate depression- and memory impairment-like behaviors, and improve stress-induced gut barrier dysfunction which were similar to those of Vlx. These findings enhance our understanding of stress-related health conditions and suggest the synbiotic intervention may be a promising approach to ameliorate deleterious effects of stress on the gut-brain axis.

Gut microbiota-derived short-chain fatty acids and depression: deep insight into biological mechanisms and potential applications

The gut microbiota is a complex and dynamic ecosystem known as the 'second brain'. Composing the microbiota-gut-brain axis, the gut microbiota and its metabolites regulate the central nervous system through neural, endocrine and immune pathways to ensure the normal functioning of the organism, tuning individuals' health and disease status. Short-chain fatty acids (SCFAs), the main bioactive metabolites of the gut microbiota, are involved in several neuropsychiatric disorders, including depression. SCFAs have essential effects on each component of the microbiota-gut-brain axis in depression. In the present review, the roles of major SCFAs (acetate, propionate and butyrate) in the pathophysiology of depression are summarised with respect to chronic cerebral hypoperfusion, neuroinflammation, host epigenome and neuroendocrine alterations. Concluding remarks on the biological mechanisms related to gut microbiota will hopefully address the clinical value of microbiota-related treatments for depression.

Anti-inflammatory Drugs in the Treatment of Depression

The last two decades have seen a flourishing of research into the immunobiology of psychiatric phenotypes, in particular major depressive disorder. Both preclinical and clinical data have highlighted pathways and possible mechanisms that might link changes in immunobiology, most especially inflammation, to clinically relevant behaviour. From a therapeutics perspective, a major impetus has been the action of Biologics, often monoclonal antibodies, that target specific cytokines acting as "molecular scalpels" helping to uncover the actions of those proteins. These interventions have been associated with improvements in mood and related symptoms. There are now enough studies and participants to permit meta-analytic analyses of the actions of these and other anti-inflammatory agents.In this chapter, the focus is on the evidence for the role of inflammation biology in depression and the meta-analytic data from trials. The putative mechanisms that might underpin the antidepressant effect of anti-inflammatory drugs are also explored. Lastly, I describe the more stubborn difficulties around heterogeneity, deep phenotyping and stratification as well as improved animal models and greater understanding of the biology that might be addressed by future studies.

Immune mechanisms of depression in rheumatoid arthritis

Depression is a common and disabling comorbidity in rheumatoid arthritis that not only decreases the likelihood of remission and treatment adherence but also increases the risk of disability and mortality in patients with rheumatoid arthritis. Compelling data that link immune mechanisms to major depressive disorder indicate possible common mechanisms that drive the pathology of the two conditions. Preclinical evidence suggests that pro-inflammatory cytokines, which are prevalent in rheumatoid arthritis, have various effects on monoaminergic neurotransmission, neurotrophic factors and measures of synaptic plasticity. Neuroimaging studies provide insight into the consequences of inflammation on the brain (for example, on neural connectivity), and clinical trial data highlight the beneficial effects of immune modulation on comorbid depression. Major depressive disorder occurs more frequently in patients with rheumatoid arthritis than in the general population, and major depressive disorder also increases the risk of a future diagnosis of rheumatoid arthritis, further highlighting the link between rheumatoid arthritis and major depressive disorder. This Review focuses on interactions between peripheral and central immunobiological mechanisms in the context of both rheumatoid arthritis and major depressive disorder. Understanding these mechanisms will provide a basis for future therapeutic development, not least in depression.

Hypericin as a promising natural bioactive naphthodianthrone: A review of its pharmacology, pharmacokinetics, toxicity, and safety

Hypericin can be derived from St. John's wort, which is widely spread around the world. As a natural product, it has been put into clinical practice such as wound healing and depression for a long time. In this article, we review the pharmacology, pharmacokinetics, and safety of hypericin, aiming to introduce the research advances and provide a full evaluation of it. Turns out hypericin, as a natural photosensitizer, exhibits an excellent capacity for anticancer, neuroprotection, and elimination of microorganisms, especially when activated by light, potent anticancer and antimicrobial effects are obtained after photodynamic therapy. The mechanisms of its therapeutic effects involve the induction of cell death, inhibition of cell cycle progression, inhibition of the reuptake of amines, and inhibition of virus replication. The pharmacokinetics properties indicate that hypericin has poor water solubility and bioavailability. The distribution and excretion are fast, and it is metabolized in bile. The toxicity of hypericin is rarely reported and the conventional use of it rarely causes adverse effects except for photosensitization. Therefore, we may conclude that hypericin can be used safely and effectively against a variety of diseases. We hope to provide researchers with detailed guidance and enlighten the development of it.

Neuroprotective astroglial response to neural damage and its relevance to affective disorders

Astrocytes not only support neuronal function with essential roles in synaptic neurotransmission, action potential propagation, metabolic support, or neuroplastic and developmental adaptations. They also respond to damage or dysfunction in surrounding neurons and oligodendrocytes by releasing neurotrophic factors and other molecules that increase the survival of the supported cells or contribute to mechanisms of structural and molecular restoration. The neuroprotective responsiveness of astrocytes is based on their ability to sense signals of degeneration, metabolic jeopardy and structural damage, and on their aptitude to locally deliver specific molecules to remedy threats to the molecular and structural features of their cellular partners. To the extent that neuronal and other glial cell disturbances are known to occur in affective disorders, astrocyte responsiveness to those disturbances may help to better understand the roles astrocytes play in affective disorders. The astrocytic sensing apparatus supporting those responses involves receptors for neurotransmitters, purines, cell adhesion molecules and growth factors. Astrocytes also share with the immune system the capacity of responding to cytokines released upon neuronal damage. In addition, in responses to specific signals astrocytes release unique factors such as clusterin or humanin that have been shown to exert potent neuroprotective effects. Astrocytes integrate the signals above to further deliver structural lipids, removing toxic metabolites, stabilizing the osmotic environment, normalizing neurotransmitters, providing anti-oxidant protection, facilitating synaptogenesis and acting as barriers to contain varied deleterious signals, some of which have been described in brain regions relevant to affective disorders and related animal models. Since various of the injurious signals that activate astrocytes have been implicated in different aspects of the etiopathology of affective disorders, particularly in relation to the diagnosis of depression, potentiating the corresponding astrocyte neuroprotective responses may provide additional opportunities to improve or complement available pharmacological and behavioral therapies for affective disorders.

The role of the circadian system in the etiology of depression

Circadian rhythms have evolved in almost all organisms enabling them to anticipate alternating changes in the environment. As a consequence, the circadian clock controls a broad range of bodily functions including appetite, sleep, activity and cortisol levels. The circadian clock synchronizes itself to the external world mainly by environmental light cues and can be disturbed by a variety of factors, including shift-work, jet-lag, stress, ageing and artificial light at night. Interestingly, mood has also been shown to follow a diurnal rhythm. Moreover, circadian disruption has been associated with various mood disorders and patients suffering from depression have irregular biological rhythms in sleep, appetite, activity and cortisol levels suggesting that circadian rhythmicity is crucially involved in the etiology and pathophysiology of depression. The aim of the present review is to give an overview and discuss recent findings in both humans and rodents linking a disturbed circadian rhythm to depression. Understanding the relation between a disturbed circadian rhythm and the etiology of depression may lead to novel therapeutic and preventative strategies.

Krill oil treatment ameliorates lipid metabolism imbalance in chronic unpredicted mild stress-induced depression-like behavior in mice

The pathology of depression involves various factors including the interaction between genes and the environment. The deficiency of n-3 polyunsaturated fatty acids (n-3 PUFAs) in the brain and depressive symptoms are closely related. Krill oil contains abundant amounts of n-3 PUFAs incorporated in phosphatidylcholine. However, the effect of krill oil treatment on depression-like behaviors induced by chronic stress and its molecular mechanism in the brain remain poorly understood. Here, we used a chronic unpredictable mild stress (CUMS) model to evaluate the effect of krill oil on depression-like behaviors and explored its molecular mechanism through lipid metabolomics and mRNA profiles in the whole brain. We observed that CUMS-induced depression-like behaviors were ameliorated by krill oil supplementation in mice. The metabolism of glycerophospholipids and sphingolipids was disrupted by CUMS treatment, which were ameliorated after krill oil supplementation. Further analysis found that differently expressed genes after krill oil supplementation were mainly enriched in the membrane structures and neuroactive ligand-receptor interaction pathway, which may be responsible for the amelioration of CUMS-induced depression-like behaviors. Altogether, our results uncovered the relationship between lipid metabolism and CUMS, and provided new strategies for the prevention and treatment of depression.

Efficacy, Tolerability, and Safety of Toludesvenlafaxine for the Treatment of Major Depressive Disorder-A Narrative Review

The estimated rate of treatment-resistant major depressive disorder (TRD) remains higher than 30%, even after the discovery of multiple classes of antidepressants in the last 7 decades. Toludesvenlafaxine (ansofaxine, LY03005, or LPM570065) is a first-in-class triple monoaminergic reuptake inhibitor (TRI) that has reached clinical use. The objective of this narrative review was to summarize clinical and preclinical evidence about the efficacy, tolerability, and safety of toludesvenlafaxine. Based on the results of 17 reports retrieved in the literature, the safety and tolerability profiles of toludesvenlafaxine were good in all clinical trials, and the pharmacokinetic parameters were well described in the phase 1 trials. The efficacy of toludesvenlafaxine was demonstrated in one phase 2 and one phase 3 trial, both on primary and secondary outcomes. In conclusion, this review highlights the favorable clinical results of toludesvenlafaxine in only two short-term trials that enrolled patients with major depressive disorder (MDD) (efficacy and tolerability were good for up to eight weeks), indicating the need for more good quality, larger-sample, and longer-term trials. Exploring new antidepressants, such as TRI, can be considered a priority for clinical research due to the high rates of TRD, but also due to the significant percentages of relapse in patients with MDD.

Effects of liraglutide on depressive behavior in a mouse depression model and cognition in the probe trial of Morris water maze test

BACKGROUND

We investigated the effects of liraglutide, a glucagon-like peptide-1 (GLP-1) agonist, on a depression-like phenotype in mice exposed to chronic unpredictable stress (CUS). Learning and memory were also assessed using the Morris water maze (MWM) test.

METHODS

Liraglutide (0.3 mg/kg/day for 21 days) was administered to mice with or without exposure to CUS. After 21 days of CUS, the forced swim test (FST) was performed to assess its antidepressant effect. To evaluate cognitive function, liraglutide was administered to mice under stress-free conditions for 21 days, and then the MWM test was performed on 6 consecutive days.

RESULTS

Chronic liraglutide treatment reduced FST immobility in mice with and without CUS. In the probe trial of the Morris water maze test, the search error rate was reduced and the time spent and path length in the target quadrant and the number of platform crossings were increased.

LIMITATION

Additional animal model experiments and molecular level studies are needed to support the results obtained in this study.

CONCLUSIONS

Liraglutide appears to exert antidepressant effects and could improve cognitive function. Based on these results, GLP-1 agonists could have potential as novel antidepressants.

The effects of physical activity on glutamate neurotransmission in neuropsychiatric disorders

Physical activity (PA) is an effective way of increasing cognitive and emotional health and counteracting many psychiatric conditions. Numerous neurobiological models for depression have emerged in the past 30 years but many struggle to incorporate the effects of exercise. The hippocampus and pre-frontal cortex (PFC) containing predominantly glutamate neurotransmission, are the centres of changes seen in depression. There is therefore increasing interest in glutamatergic systems which offers new paradigms of understanding mechanisms connecting physical activity, stress, inflammation and depression, not explained by the serotonin theories of depression. Similar hippocampal glutamate dysfunction is observed in many other neuropsychiatric conditions. Excitatory glutamate neurones have high functionality, but also high ATP requirements and are therefore vulnerable to glucocorticoid or pro-inflammatory stress that causes mitochondrial dysfunction, with synaptic loss, culminating in depressed mood and cognition. Exercise improves mitochondrial function, angiogenesis and synaptogenesis. Within the glutamate hypothesis of depression, the mechanisms of stress and inflammation have been extensively researched, but PA as a mitigator is less understood. This review examines the glutamatergic mechanisms underlying depression and the evidence of physical activity interventions within this framework. A dynamic glutamate-based homeostatic model is suggested whereby stress, neuroinflammation and PA form counterbalancing influences on hippocampal cell functionality, which manifests as depression and other neuropsychiatric conditions when homeostasis is disrupted.

Genomic-Analysis-Oriented Drug Repurposing in the Search for Novel Antidepressants

From inadequate prior antidepressants that targeted monoamine neurotransmitter systems emerged the discovery of alternative drugs for depression. For instance, drugs targeted interleukin 6 receptor (IL6R) in inflammatory system. Genomic analysis-based drug repurposing using single nucleotide polymorphism (SNP) inclined a promising method for several diseases. However, none of the diseases was depression. Thus, we aimed to identify drug repurposing candidates for depression treatment by adopting a genomic-analysis-based approach. The 5885 SNPs obtained from the machine learning approach were annotated using HaploReg v4.1. Five sets of functional annotations were applied to determine the depression risk genes. The STRING database was used to expand the target genes and identify drug candidates from the DrugBank database. We validated the findings using the ClinicalTrial.gov and PubMed databases. Seven genes were observed to be strongly associated with depression (functional annotation score = 4). Interestingly, IL6R was auspicious as a target gene according to the validation outcome. We identified 20 drugs that were undergoing preclinical studies or clinical trials for depression. In addition, we identified sarilumab and satralizumab as drugs that exhibit strong potential for use in the treatment of depression. Our findings indicate that a genomic-analysis-based approach can facilitate the discovery of drugs that can be repurposed for treating depression.

Carnitine and Depression

Depression has become one of the most common mental diseases in the world, but the understanding of its pathogenesis, diagnosis and treatments remains insufficient. Carnitine is a natural substance that exists in organisms, which can be synthesized in vivo or supplemented by intake. Relationships of carnitine with depression, bipolar disorder and other mental diseases have been reported in different studies. Several studies show that the level of acylcarnitines (ACs) changes significantly in patients with depression compared with healthy controls while the supplementation of acetyl-L-carnitine is beneficial to the treatment of depression. In this review, we aimed to clarify the effects of ACs in depressive patients and to explore whether ACs might be the biomarkers for the diagnosis of depression and provide new ideas to treat depression.

Is (R)-ketamine a Potential Therapeutic Agent for Treatment-Resistant Depression with Less Detrimental Side Effects? A Review of Molecular Mechanisms Underlying Ketamine and its Enantiomers

Approximately one-third of individuals with major depressive disorder are resistant to conventional antidepressants (i.e., monoamine-based therapies), and, even among respondents, a proper therapeutic effect may require weeks of treatment. Ketamine, a racemic mixture of the two enantiomers, (R)-ketamine and (S)-ketamine, is an N-methyl-d-aspartate receptor (NMDAR) antagonist and has been shown to have rapid-acting antidepressant properties in patients with treatment-resistant depression (TRD). Although (R)-ketamine has a lower affinity for NMDAR, it presents greater potency and longer-lasting antidepressant properties, with no major side effects, than racemic ketamine or (S)-ketamine in preclinical findings. Thereby, ketamine and its enantiomers have not only an antagonistic effect on NMDAR but also a strong synaptogenic-modulatory effect, which is impaired in TRD pathophysiology. In this review, we summarize the current evidence regarding the modulation of neurotransmission, neuroplasticity, and neural network activity as putative mechanisms of these rapid-acting antidepressants, highlighting differences on intracellular signaling pathways of synaptic proteins such as mammalian target of rapamycin (mTOR), extracellular signal-regulated kinase (ERK) and brain-derived neurotrophic factor (BDNF). In addition, we discuss probable mechanisms involved in the side effects of ketamine and its enantiomers.

Potential Mechanisms and Clinical Effectiveness of Acupuncture in Depression

Major depressive disorder is the most common mental disorder with significant economic burden and limited treatments. Acupuncture has emerged as a promising non-pharmacological treatment for reducing depressive symptoms. However, the potential mechanisms and clinical effectiveness of acupuncture are not fully understood. This review aimed to: (1) summarize the available evidence on the mechanisms and clinical effectiveness of acupuncture for depression, and then (2) compare with pharmacological interventions, guiding future studies. Studies with animal models of depression and patients have shown that acupuncture could increase hippocampal and network neuroplasticity and decrease brain inflammation, potentially to alleviating depressive disorders. Overall clinical studies indicated that acupuncture could relieve primary depression, particularly milder cases, and was helpful in the management of post-stroke depression, pain-related depression, and postpartum depression both as an isolated and adjunct treatment. It was emphasized that acupuncture combined with antidepressant pharmacological treatment not only enhanced the improvement of primary and secondary depressive symptoms but also reduced the side effects of the medical treatment, which is the main cause for high dropout rates with drug treatment. In summary, substantial evidence from animal and human researches supported the beneficial effect of acupuncture in depression. However, most clinical trials of acupuncture were small, and it is unclear whether their findings can be generalized, so more studies are needed.

Association between the consumption of omega-3-rich fish and depressive symptoms in older adults living in a middle-income country: EpiFloripa Aging cohort study

This study aimed to verify the association between the consumption of omega-3-rich (n-3) fish and depressive symptoms in older adults living in Southern Brazil. This is a cross-sectional analysis with data from the second wave of the EpiFloripa Aging cohort study (2013/2014) including 1,130 individuals aged 60 years or older. The presence of depressive symptoms was measured by the 15-items Geriatric Depression Scale (GDS-15), and the consumption of n-3-rich fish by a question of weekly frequency. The minimum set of variables for adjustment was defined using directed acyclic graph (DAG). Poisson regression with robust error variance was applied (adjusted by Model 1: demographic and socioeconomic variables, Model 2: added behavioral variables, Model 3: added health variables). We identified the prevalence of depressive symptoms in 19% of older adults and 51.8% reported eating n-3-rich fish once a week. Models 1 and 3 showed an inverse association between n-3-rich fish and depressive symptoms. However, the association was reduced when behavioral factors (leisure-time physical activity) were included in Model 2. These findings suggest that n-3-rich fish intake tends to be associated with depressive symptoms in older adults. However, other factors, such as physical exercise, are as pivotal as n-3 fatty acids in preventing the development of depressive symptoms.

Reviewing the Role of the Endocannabinoid System in the Pathophysiology of Depression

Major depressive disorder is a high-impact, debilitating disease and it is currently considered the most prevalent mental illness. It is associated with disability, as well as increased morbidity and mortality. Despite its significant repercussions in our society, its exact pathophysiology remains unclear and therefore, available antidepressant treatment options are limited and, in some cases, ineffective. In the past years, research has focused on the development of a multifactorial theory of depression. Simultaneously, evidence supporting the role of the endocannabinoid system in the neurobiology of neuropsychiatric diseases has emerged. Studies have shown that the endocannabinoid system strongly impacts neurotransmission, and the neuroendocrine and neuroimmune systems, which are known to be dysfunctional in depressive patients. Accordingly, common antidepressants were shown to have a direct impact on the expression of cannabinoid receptors throughout the brain. Therefore, the relationship between the endocannabinoid system and major depressive disorder is worth consideration. Nevertheless, most studies focus on smaller pieces of what is undoubtedly a larger mosaic of interdependent processes. Therefore, the present review summarizes the existing literature regarding the role of the endocannabinoid system in depression aiming to integrate this information into a holistic picture for a better understanding of the relationship between the two.

Identification of 1,2,4-Triazolylthioethanone Scaffold for the Design of New Acetylcholinesterase Inhibitors

Acetylcholinesterase (AChE) inhibitors are the most effective drugs for Alzheimer's disease treatment. However, considering the potential and failure rates of AChE inhibitors, chemical scaffolds targeting cholinesterase specifically are still very limited. Herein, we report a new class of AChE inhibitors identified by employing a virtual screening approach that combines shape similarity with molecular docking calculations. Virtual screening followed by the evaluation of AChE inhibitory activity allowed us to identify 1,2,4-triazolylthioethanones as a novel class of AChE inhibitors. Thirteen compounds with 1,2,4-triazolylthiothanone core and IC₅₀ values in the range of 0.15±0.07 to 3.32±0.92 μM have been reported here. Our findings shed light into a class of AChE inhibitors that could be useful starting point for the development of novel therapeutics to tackle Alzheimer's disease.

Benefits of animal models to understand the pathophysiology of depressive disorders

Major depressive disorder (MDD) is a potentially life-threatening mental disorder imposing severe social and economic burden worldwide. Despite the existence of effective antidepressant treatment strategies the exact pathophysiology of the disease is still unknown. Large number of animal models of MDD have been developed over the years, but all of them suffer from significant shortcomings. Despite their limitations these models have been extensively used in academic research and drug development. The aim of this review is to highlight the benefits of animal models of MDD. We focus here on recent experimental data where animal models were used to examine current theories of this complex disease. We argue, that despite their evident imperfections, these models provide invaluable help to understand cellular and molecular mechanisms contributing to the development of MDD. Furthermore, animal models are utilized in research to find clinically useful biomarkers. We discuss recent neuroimaging and microRNA studies since these investigations yielded promising candidates for biomarkers. Finally, we briefly summarize recent progresses in drug development, i.e. the FDA approval of two novel antidepressant drugs: S-ketamine and brexanolone (allopregnanolone). Deeper understanding of the exact molecular and cellular mechanisms of action responsible for the antidepressant efficacy of these rapid acting drugs could aid us to design further compounds with similar effectiveness, but less side effects. Animal studies are likely to provide valuable help in this endeavor.

On inflammatory hypothesis of depression: what is the role of IL-6 in the middle of the chaos?

Many patients with major depressive disorder (MDD) are reported to have higher levels of multiple inflammatory cytokines including interleukin 6 (IL-6). Recent studies both pre-clinical and clinical have advocated for the functional role of IL-6 in development of MDD and suggested a great potential for targeting this cytokine to open new avenues in pharmacotherapy of depression. The purpose of the present narrative review was to provide an integrated account of how IL-6 may contribute to development of depression. All peer-reviewed journal articles published before July 2020 for each area discussed were searched by WOS, PubMed, MEDLINE, Scopus, Google Scholar, for original research, review articles, and book chapters. Publications between 1980 and July 2020 were included. Alterations in IL-6 levels, both within the periphery and the brain, most probably contribute to depression symptomatology in numerous ways. As IL-6 acts on multiple differing target tissues throughout the body, dysregulation of this particular cytokine can precipitate a multitude of events relevant to depression and blocking its effects can prevent further escalation of inflammatory responses, and potentially pave the way for opening new avenues in diagnosis, treatment, and prevention of this debilitating disorder.

The Selective SIK2 Inhibitor ARN-3236 Produces Strong Antidepressant-Like Efficacy in Mice via the Hippocampal CRTC1-CREB-BDNF Pathway

Depression is a widespread chronic medical illness affecting thoughts, mood, and physical health. However, the limited and delayed therapeutic efficacy of monoaminergic drugs has led to intensive research efforts to develop novel antidepressants. ARN-3236 is the first potent and selective inhibitor of salt-inducible kinase 2 (SIK2). In this study, a multidisciplinary approach was used to explore the antidepressant-like actions of ARN-3236 in mice. Chronic social defeat stress (CSDS) and chronic unpredictable mild stress (CUMS) models of depression, various behavioral tests, high performance liquid chromatography-tandem mass spectrometry, stereotactic infusion, viral-mediated gene transfer, western blotting, co-immunoprecipitation and immunofluorescence were used together. It was found that ARN-3236 could penetrate the blood-brain barrier. Repeated ARN-3236 administration induced significant antidepressant-like effects in both the CSDS and CUMS models of depression, accompanied with fully preventing the stress-enhanced SIK2 expression and cytoplasmic translocation of cyclic adenosine monophosphate response element binding protein (CREB)-regulated transcription coactivator 1 (CRTC1) in the hippocampus. ARN-3236 treatment also completely reversed the down-regulating effects of CSDS and CUMS on the hippocampal brain-derived neurotrophic factor (BDNF) system and neurogenesis. Moreover, we demonstrated that the hippocampal CRTC1-CREB-BDNF pathway mediated the antidepressant-like efficacy of ARN-3236. Collectively, ARN-3236 possesses strong protecting effects against chronic stress, and could be a novel antidepressant beyond monoaminergic drugs.

L-Carnitine and Acetyl-L-Carnitine: Potential Novel Biomarkers for Major Depressive Disorder

The lack of biomarkers greatly limits the diagnosis and treatment of major depressive disorder (MDD). Endogenous L-carnitine (LC) and its derivative acetyl-L-carnitine (ALC) play antidepressant roles by improving brain energy metabolism, regulating neurotransmitters and neural plasticity. The levels of ALC in people and rodents with depression are significantly reduced. It is necessary to determine whether serum LC and ALC might be used as novel biomarkers for the diagnosis of MDD. Here, ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was used to determine the concentration of LC and ALC in the serum of healthy controls and patients with MDD; among the latter, in patients who were responsive (effective group) and non-responsive (ineffective group) after 2 weeks of treatment. The diagnostic value of serum LC and ALC for MDD was assessed. Compared with healthy controls, the serum LC and ALC concentrations in patients with MDD were significantly decreased (P < 0.001). Pearson correlation analysis shows that the HDRS-24 score was negatively associated with serum ALC (r = -0.325, P = 0.007). Receiver operating characteristic (ROC) analysis revealed an area under the curve (AUC) of 0.801 with 83.1% sensitivity and 66.3% specificity for LC, and an AUC of 0.898 with 88.8% sensitivity and 76.4% specificity for ALC, differentiating patients with MDD from healthy controls. Furthermore, the concentration of LC and ALC in patients with depression was significantly increased in the effective treatment group, and no significant change was observed in the ineffective treatment group. These results suggest that serum LC and ALC may be novel biomarkers for the diagnosis of MDD.

Construction and Analysis of a Diagnostic Model Based on Differential Expression Genes in Patients With Major Depressive Disorder

Background: Major depressive disorder (MDD) is a common and severe psychiatric disorder with a heavy burden on the individual and society. However, the prevalence varies significantly owing to the lack of auxiliary diagnostic biomarkers. To identify the shared differential expression genes (DEGs) with potential diagnostic value in both the hippocampus and whole blood, a systematic and integrated bioinformatics analysis was carried out. Methods: Two datasets from the Gene Expression Omnibus database (GSE53987 and GSE98793) were downloaded and analyzed separately. A weighted gene co-expression network analysis was performed to construct the co-expression gene network of DEGs from GSE53987, and the most disease-related module was extracted. The shared DEGs from the module and GSE98793 were identified using a Venn diagram. Functional pathway prediction was used to identify the most disease-related DEGs. Finally, several DEGs were chosen, and their potential diagnostic value was determined by receiver operating characteristic curve analysis. Results: After weighted gene co-expression network analysis, the most MDD-related module (MEgrey) was identified, and 623 DEGs were extracted from this module. The intersection between MEgrey and GSE98793 was calculated, and 163 common DEGs were identified. The co-expression network of 163 DEGs from these was then reconstructed. All hub genes were identified based on the connective degree of the reconstructed co-expression network. Based on the results of functional pathway enrichment, 17 candidate hub genes were identified. Finally, logistic regression and receiver operating characteristic curves showed that three candidate hub genes (CEP350, SMAD5, and HSPG2) had relatively high auxiliary value in the diagnosis of MDD. Conclusion: Our results showed that the combination of CEP350, SMAD5, and HSPG2 has a relatively high diagnostic value for MDD. Pathway enrichment analysis also showed that these genes may play an important role in the pathogenesis of MDD. These results suggest a potentially important role for this gene combination in clinical practice.

Unfolding the Role of BDNF as a Biomarker for Treatment of Depression

Depression is a well-known disabling mental illness characterized by sadness, loss of interest in activities, and decreased energy. The symptoms of depression are usually recurrent in vulnerable individuals, and persistence of symptoms significantly impairs individuals' quality of life. The exact pathophysiology of depression remains ambiguous, though many hypotheses have been proposed. Brain-derived neurotrophic factor (BDNF) has recently been reported to play a vital role in the pathophysiology of depression. BDNF is an important neurotrophic factor found in the human brain and is involved in neuronal growth and proliferation, synaptic neurotransmission, and neuroplasticity. The neurotrophic theory of depression proposes that depression results from reduced BDNF levels in the brain, which can be treated with antidepressants to alleviate depressive behavior and increase BDNF levels. The aim of this review is to provide broad insight into the role of BDNF in the pathogenesis of depression and in antidepressant therapy. The studies mentioned in this review article greatly support the role of BDNF in the pathogenesis of depression and treatment of this disorder with antidepressants. Since abnormalities in BDNF levels lead to the production of diverse insults that amplify the development or progression of depression, it is important to study and explore BDNF impairment in relation to depression, neuroplasticity, and neurogenesis, and increasing BDNF levels through antidepressant therapy, showing positive response in the management of depression.

A UPLC-MS/MS method for determination of endogenous l-carnitine and acetyl-l-carnitine in serum of patients with depression

A simple, rapid, and selective ultra-performance liquid chromatography-tandem mass spectrometry method for determination of l-carnitine (LC) and acetyl-l-carnitine (ALC) in human serum was developed. Acetyl-l-carnitine-d₃ (ALC-d₃ ) was selected as internal standard (IS). After protein precipitation with acetonitrile-water (1 mL, 2:1, v/v), the analytes and IS were separated on a 2.5-μm XSelect HSS T3 C₁₈ column by gradient elution with methanol-water (containing 0.01% ammonia water) as the mobile phase at a flow rate of 0.2 mL/min. Analytes were detected with multiple reaction monitoring using a positive scan mode with electrospray ionization. Good linearity (R²  > 0.999) was observed in the concentration range for LC and ALC. The inter- and intra-day values of relative error were -10.4% to 10.0% with CVs less than 9.84%. The average recoveries of the two analytes were 91.29%-98.23%. Blood samples containing LC and ALC were stable under various storage conditions. Normal, haemolytic, and hyperlipidaemic serum had no significant effect on the quantification of LC and ALC. This method was successfully applied to study the concentrations of endogenous LC and ALC in the serum of patients with first-episode depression.

Targeting Oxidative Stress Reduction and Inhibition of HDAC1, MECP2, and NF-kB Pathways in Rats With Experimentally Induced Hyperglycemia by Administration of Thymus marshallianus Willd. Extracts

The effects of two lyophilized extracts obtained from the aerial parts of Thymus marschallianus Willd. and harvested from wild flora (TMW) and obtained from culture (TMC) were evaluated in Wistar rats with experimentally induced hyperglycemia. The hyperglycemia was induced by streptozotocin (STZ) administration and the obtained results were evaluated in comparison for TMW and TMC. The polyphenolic composition of extracts was evaluated by spectrophotometrical and LC-MS methods. In vitro antioxidant capacity assays (DPPH, FRAP, EPR) were performed in order to preliminary establish the ability of tested samples to protect against free radical induced damage. Afterwards, the effects of these extracts were assessed in vivo on rats with experimental-induced hyperglycemia. Oxidative stress biomarkers (e.g. malondialdehyde-MDA), phosphorylated transcription factor subunit of nuclear kappaB (NF-kB) p65, methyl CpG binding protein (MECP) 2 and histone deacetylase 1 (HDAC1) expressions in hippocampus and frontal lobe were assessed. Open Field Test (OFT) and Elevated Plus Maze (EPM) were conducted on tested animals. Malondialdehyde (MDA) levels and HDAC1and MeCP2 expressions increased significantly in hippocampus (p<0.05) and frontal lobe (p<0.001) of diabetes group compared to the control group in parallel with decreasing of GSH/GSSG ratio. TMW and TMC administration reduced blood glucose levels and diminished lipid peroxidation, HDAC1 expression and enhanced antioxidant capacity in frontal lobe. TMW improved central locomotion of rats, increased phospho-NFkB p65 and diminished MECP2 expressions in hippocampus. Both tested samples exerted a beneficial effect by increasing the antioxidant defense. Our findings indicate that the administration of these extracts might represent a good option in the treatment of diabetes and its complications.

Alleviation of Depression by Glucagon-Like Peptide 1 Through the Regulation of Neuroinflammation, Neurotransmitters, Neurogenesis, and Synaptic Function

Depression has emerged as a major cause of mortality globally. Many studies have reported risk factors and mechanisms associated with depression, but it is as yet unclear how these findings can be applied to the treatment and prevention of this disorder. The onset and recurrence of depression have been linked to diverse metabolic factors, including hyperglycemia, dyslipidemia, and insulin resistance. Recent studies have suggested that depression is accompanied by memory loss as well as depressive mood. Thus, many researchers have highlighted the relationship between depressive behavior and metabolic alterations from various perspectives. Glucagon-like peptide-1 (GLP-1), which is secreted from gut cells and hindbrain areas, has been studied in metabolic diseases such as obesity and diabetes, and was shown to control glucose metabolism and insulin resistance. Recently, GLP-1 was highlighted as a regulator of diverse pathways, but its potential as the therapeutic target of depressive disorder was not described comprehensively. Therefore, in this review, we focused on the potential of GLP-1 modulation in depression.

Stress-Induced Morphological, Cellular and Molecular Changes in the Brain-Lessons Learned from the Chronic Mild Stress Model of Depression

Major depressive disorder (MDD) is a severe illness imposing an increasing social and economic burden worldwide. Numerous rodent models have been developed to investigate the pathophysiology of MDD. One of the best characterized and most widely used models is the chronic mild stress (CMS) model which was developed more than 30 years ago by Paul Willner. More than 2000 published studies used this model, mainly to assess novel compounds with potential antidepressant efficacy. Most of these studies examined the behavioral consequences of stress and concomitant drug intervention. Much fewer studies focused on the CMS-induced neurobiological changes. However, the stress-induced cellular and molecular changes are important as they may serve as potential translational biomarkers and increase our understanding of the pathophysiology of MDD. Here, we summarize current knowledge on the structural and molecular alterations in the brain that have been described using the CMS model. We discuss the latest neuroimaging and postmortem histopathological data as well as molecular changes including recent findings on microRNA levels. Different chronic stress paradigms occasionally deliver dissimilar findings, but the available experimental data provide convincing evidence that the CMS model has a high translational value. Future studies examining the neurobiological changes in the CMS model in combination with clinically effective antidepressant drug intervention will likely deliver further valuable information on the pathophysiology of MDD.

Folic acid ameliorates depression-like behaviour in a rat model of chronic unpredictable mild stress

Background

Depression is characterized by significant and low mood. Classical antidepressants are still not adequate in treating depression because of undesirable side effects. Folic acid, a member of the vitamin B complex, in considered to be strongly associated with the function and development of the central nervous system. Thus, in this study, we established a model of depression through chronic unpredictable mild stress (CUMS) in rats and assessed the antidepressant effects and mechanisms of folic acid.

Methods

Sprague–Dawley rats were randomly divided into four groups: control, chronic unpredictable mild stress (CUMS), CUMS treated with folic acid, and CUMS treated with citalopram. Rats were assessed in terms of weight change, open-field test and sucrose preference. Homocysteine, monoamine neurotransmitters, interleukin-6, brain-derived neurotrophic factor (BDNF), β-endorphin levels in the serum and brains of rats were analysed.

Results

Folic acid exhibited antidepressant-like effects in open-field and sucrose preference tests. Folic acid treatment effectively increased the levels of monoamine neurotransmitters, BDNF and β-endorphin, interleukin-6 and homocysteine levels were also significantly suppressed by folic acid administration.

Conclusions

These findings serve as preclinical evidence that folic acid plays an antidepressant-like role in several pathways involving monoamine neurotransmitters. Thus, folic acid may be used as a potential antidepressant.

The cellular and molecular basis of major depressive disorder: towards a unified model for understanding clinical depression

Major depressive disorder (MDD) is considered a serious public health issue that adversely impacts an individual's quality of life and contributes significantly to the global burden of disease. The clinical heterogeneity that exists among patients limits the ability of MDD to be accurately diagnosed and currently, a symptom-based approach is utilized in many cases. Due to the complex nature of this disorder, and lack of precise knowledge regarding the pathophysiology, effective management is challenging. The aetiology and pathophysiology of MDD remain largely unknown given the complex genetic and environmental interactions that are involved. Nonetheless, the aetiology and pathophysiology of MDD have been the subject of extensive research, and there is a vast body of literature that exists. Here we overview the key hypotheses that have been proposed for the neurobiology of MDD and highlight the need for a unified model, as many of these pathways are integrated. Key pathways discussed include neurotransmission, neuroinflammation, clock gene machinery pathways, oxidative stress, role of neurotrophins, stress response pathways, the endocannabinoid and endovanilloid systems, and the endogenous opioid system. We also describe the current management of MDD, and emerging novel therapies, with particular focus on patients with treatment-resistant depression (TRD).

Association between epigenetic age acceleration and depressive symptoms in a prospective cohort study of urban-dwelling adults

OBJECTIVE

This study tests associations of DNA methylation-based (DNAm) measures of epigenetic age acceleration (EAA) with cross-sectional and longitudinal depressive symptoms in an urban sample of middle-aged adults.

METHODS

White and African-American adult participants in the Healthy Aging in Neighborhoods of Diversity across the Life Span study for whom DNA samples were analyzed (baseline age: 30-65 years) we included. We estimated three DNAm based EAA measures: (1) universal epigenetic age acceleration (AgeAccel); (2) intrinsic epigenetic age acceleration (IEAA); and (3) extrinsic epigenetic age acceleration (EEAA). Depressive symptoms were assessed using the 20-item Center for Epidemiological Studies-Depression scale total and sub-domain scores at baseline (2004-2009) and follow-up visits (2009-2013). Linear mixed-effects regression models were conducted, adjusting potentially confounding covariates, selection bias and multiple testing (N = 329 participants, ∼52% men, k = 1.9 observations/participant, mean follow-up time∼4.7 years).

RESULTS

None of the epigenetic age acceleration measures were associated with total depressive symptom scores at baseline or over time. IEAA - a measure of cellular epigenetic age acceleration irrespective of white blood cell composition - was cross-sectionally associated with decrement in "positive affect" in the total population (γ011± SE = -0.090 ± 0.030, P = 0.003, Cohen's D: -0.16) and among Whites (γ011 ± SE = -0.135 ± 0.048, P = 0.005, Cohen's D: -0.23), after correction for multiple testing. Baseline "positive affect" was similarly associated with AgeAccel.

LIMITATIONS

Limitations included small sample size, weak-moderate effects and measurement error.

CONCLUSIONS

IEAA and AgeAccel, two measures of EAA using Horvath algorithm, were linked to a reduced "positive affect", overall and among Whites. Future studies are needed to replicate our findings and test bi-directional relationships.

Mitochondria: A Connecting Link in the Major Depressive Disorder Jigsaw

Background

Depression is a widespread phenomenon with varying degrees of pathology in different patients. Various hypotheses have been proposed for the cause and continuance of depression. Some of these include, but not limited to, the monoamine hypothesis, the neuroendocrine hypothesis, and the more recent epigenetic and inflammatory hypotheses.

Objective

In this article, we review all the above hypotheses with a focus on the role of mitochondria as the connecting link. Oxidative stress, respiratory activity, mitochondrial dynamics and metabolism are some of the mitochondria-dependent factors which are affected during depression. We also propose exogenous ATP as a contributing factor to depression.

Result

Literature review shows that pro-inflammatory markers are elevated in depressive individuals. The cause for elevated levels of cytokines in depression is not completely understood. We propose exogenous ATP activates purinergic receptors which in turn increase the levels of various pro-inflammatory factors in the pathophysiology of depression.

Conclusion

Mitochondria are integral to the function of neurons and undergo dysfunction in major depressive disorder patients. This dysfunction is reflected in all the various hypotheses that have been proposed for depression. Among the newer targets identified, which also involve mitochondria, includes the role of exogenous ATP. The diversity of purinergic receptors, and their differential expression among various individuals in the population, due to genetic and environmental (prenatal) influences, may influence the susceptibility and severity of depression. Identifying specific receptors involved and using patient-specific purinergic receptor antagonist may be an appropriate therapeutic course in the future.

Cerebral MAO Activity Is Not Altered by a Novel Herbal Antidepressant Treatment

Inhibition of monoamine oxidase (MAO)-A/B can ameliorate depressive- and anxiety-related symptoms via increase of monoamine extracellular levels. However, such inhibition can also instigate hypertensive response following exposure to dietary tyramine (i.e., "the cheese effect"). Novel herbal treatment (NHT) is an herbal formula that has been demonstrated to reduce depressive- and anxiety-like symptoms in pre-clinical studies. The aim of the current study was to examine whether the therapeutic potential of NHT is underlain by inhibition of MAO-A/B and whether NHT poses a risk for tyramine hyper-potentiation. Unpredictable chronic mild stress (UCMS)-exposed mice and naïve mice were treated for 3 weeks with NHT (30 mg/kg; i.p.), the selective serotonin reuptake inhibitor (SSRI) escitalopram (15 mg/kg; i.p.), or saline. Subsequently, MAO-A/B activities in the hypothalamus, striatum, and prefrontal cortex (PFC) were assessed. Exposure to UCMS led to significant increases in both MAO-A and MAO-B activities in the hypothalamus (p < 0.001) and in the PFC (p < 0.01 for MAO-A; p < 0.001 for MAO-B). Neither NHT nor escitalopram had any notable effects. Treatment with NHT was supported as safe in terms of risk for inducing a hypertensive response. The antidepressant- and anxiolytic-like effects of NHT are mediated via pathways other than MAO-A/B inhibition.

5-HTT independent effects of fluoxetine on neuroplasticity

Selective serotonin reuptake inhibitors are among the most prescribed antidepressants. Fluoxetine is the lead molecule which exerts its therapeutic effects, at least in part, by promoting neuroplasticity through increased brain-derived neurotrophic factor (BDNF)/tropomyosin-related receptor kinase B (TrkB) signalling. It is unclear however, to which extent the neuroplastic effects of fluoxetine are solely mediated by the inhibition of the serotonin transporter (5-HTT). To answer this question, the effects of fluoxetine on neuroplasticity were analysed in both wild type (WT) and 5-Htt knock-out (KO) mice. Using Western blotting and RT-qPCR approaches, we showed that fluoxetine 10 µM activated BDNF/TrkB signalling pathways in both CD1 and C57BL/6J mouse primary cortical neurons. Interestingly, effects on BDNF signalling were observed in primary cortical neurons from both 5-Htt WT and KO mice. In addition, a 3-week in vivo fluoxetine treatment (15 mg/kg/d; i.p.) increased the expression of plasticity genes in brains of both 5-Htt WT and KO mice, and tended to equally enhance hippocampal cell proliferation in both genotypes, without reaching significance. Our results further suggest that fluoxetine-induced neuroplasticity does not solely depend on 5-HTT blockade, but might rely, at least in part, on 5-HTT-independent direct activation of TrkB.

Role of inflammation in depression relapse

Major depressive disorder (MDD) is a leading cause of disability worldwide. After the first episode, patients with remitted MDD have a 60% chance of experiencing a second episode. Consideration of therapy continuation should be viewed in terms of the balance between the adverse effects of medication and the need to prevent a possible relapse. Relapse during the early stages of MDD could be prevented more efficiently by conducting individual risk assessments and providing justification for continuing therapy. Our previous work established the neuroimaging markers of relapse by comparing patients with recurrent major depressive disorder (rMDD) in depressive and remitted states. However, it is not known which of these markers are trait markers that present before initial relapse and, consequently, predict disease course. Here, we first describe how inflammation can be translated to subtype-specific clinical features and suggest how this could be used to facilitate clinical diagnosis and treatment. Next, we address the central and peripheral functional state of the immune system in patients with MDD. In addition, we emphasize the important link between the number of depressive episodes and rMDD and use neuroimaging to propose a model for the latter. Last, we address how inflammation can affect brain circuits, providing a possible mechanism for rMDD. Our review suggests a link between inflammatory processes and brain region/circuits in rMDD.

Gestational stress induced differential expression of HDAC2 in male rat offspring hippocampus during development

Accumulating evidence from preclinical and clinical studies indicates prenatal exposure to stress or excess glucocorticoids can affect offspring brain. HDAC2 is an important target of glucocorticoid. Here we detected HDAC2 expression in male offspring hippocampus from gestational restraint stressed rat during development and the relationship between HDAC2 expression and behaviors and neurogenesis in male offspring. Pregnant rats received restrained stress during the last week of pregnancy. Expressions of HDAC2 in offspring hippocampus were detected on postnatal 0 day (P0) and 60 days (P60). Neurogenesis was evaluated by Doublecortin (DCX) staining on P60. Anxiety-like behavior and cognition were detected in open field, elevated plus maze, novel object recognition test, and Barnes maze. We found that HDAC2 expression in the hippocampus of male prenatally stressed offspring (MPSO) was similar to the male control offspring on P0, but significantly lower on P60. Corresponding to the decreased expression of HDAC2 in MPSO hippocampus at P60, neurogenesis in the dentate gyrus of MPSO was significantly lower than the control male offspring. And MPSO also showed greater anxiety and poorer learning and memories abilities than control male offspring. These showed that HDAC2 could partly explain the effects of gestational stress on male offspring behaviors.

Liraglutide Activates mTORC1 Signaling and AMPA Receptors in Rat Hippocampal Neurons Under Toxic Conditions

The aim of the present study was to determine whether treatment with liraglutide, a glucagon-like peptide 1 (GLP-1) receptor agonist, would alter mammalian target of rapamycin complex 1 (mTORC1) signaling and/or α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor activity under dexamethasone-induced toxic conditions. Western blot analyses were performed to assess changes in mTORC1-mediated proteins, brain-derived neurotrophic factor (BDNF), and various synaptic proteins (PSD-95, synapsin I, and GluA1) in rat hippocampal cultures under toxic conditions induced by dexamethasone, which causes hippocampal cell death. Hippocampal dendritic outgrowth and spine formation were measured using immunostaining procedures. Dexamethasone significantly decreased the phosphorylation levels of mTORC1 as well as its downstream proteins. However, treatment with liraglutide prevented these reductions and significantly increased BDNF expression. The increase in BDNF expression was completely blocked by rapamycin and 2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo[f]quinoxaline-7-sulfonamide (NBQX). Liraglutide also recovered dexamethasone-induced decreases in the total length of hippocampal dendrites and reductions in spine density in a concentration-dependent manner. However, the positive effects of liraglutide on neural plasticity were abolished by the blockade of mTORC1 signaling and AMPA receptors. Furthermore, liraglutide significantly increased the expression levels of PSD-95, synapsin I, and GluA1, whereas rapamycin and NBQX blocked these effects. The present study demonstrated that liraglutide activated mTORC1 signaling and AMPA receptor activity as well as increased dendritic outgrowth, spine density, and synaptic proteins under toxic conditions in rat primary hippocampal neurons. These findings suggest that GLP-1 receptor (GLP-1R) activation by liraglutide may affect neuroplasticity through mTORC1 and AMPA receptors.

Resolution of inflammation and mood disorders

Relationship between mood disorders and inflammation is now well-documented, although molecular mechanisms are not understood. Previously mostly pro-inflammatory cytokines of immune system (IL-6, TNF, etc.) were taken into account. However, recent understanding of resolution of inflammation as an active process drew attention to mediators of resolution, which include both proteins and ω-3 and ω-6 polyunsaturated fatty acids derivatives (resolvins, cyclopentenone prostaglandins, etc.). This review takes into account new data on resolution of inflammation and action of mediators of resolution in models of depression. New facts and ideas about mechanisms of chronic inflammation onset are considered in relation to mood disorders. Basic control mechanisms of inflammation at the cellular level and the role of resolution substances in regulation of depression and other mood disorders are discussed. Signaling systems of innate immunity located in non-immune cells and their ability to generate substances that affect an onset of depression are reviewed. A novel hypothesis of depression as a type of abnormal resolution is proposed.

Neurobiology of depression: A neurodevelopmental approach

OBJECTIVES

The main aims of this paper are to review and evaluate the neurobiology of the depressive syndrome from a neurodevelopmental perspective.

METHODS

An English language literature search was performed using PubMed.

RESULTS

Depression is a complex syndrome that involves anatomical and functional changes that have an early origin in brain development. In subjects with genetic risk for depression, early stress factors are able to mediate not only the genetic risk but also gene expression. There is evidence that endocrine and immune interactions have an important impact on monoamine function and that the altered monoamine signalling observed in the depressive syndrome has a neuro-endocrino-immunological origin early in the development.

CONCLUSIONS

Neurodevelopment is a key aspect to understand the whole neurobiology of depression.

Cerebral oxidative metabolism mapping in four genetic mouse models of anxiety and mood disorders

The psychopathology of depression is highly complex and the outcome of studies on animal models is divergent. In order to find brain regions that could be metabolically distinctively active across a variety of mouse depression models and to compare the interconnectivity of brain regions of wild-type and such genetically modified mice, histochemical mapping of oxidative metabolism was performed by the measurement of cytochrome oxidase activity. We included mice with the heterozygous knockout of the vesicular glutamate transporter (VGLUT₁^-/+), full knockout of the cannabinoid 1 receptor (CB1^-/-), an anti-sense knockdown of the glucocorticoid receptor (GRi) and overexpression of the human 5-hydroxytryptamine transporter (h5-HTT). Altogether 76 mouse brains were studied to measure oxidative metabolism in one hundred brain regions, and the obtained dataset was submitted to a variety of machine learning algorithms and multidimensional scaling. Overall, the top brain regions having the largest contribution to classification into depression model were the lateroanterior hypothalamic nucleus, the anterior part of the basomedial amygdaloid nucleus, claustrum, the suprachiasmatic nucleus, the ventromedial hypothalamic nucleus, and the anterior hypothalamic area. In terms of the patterns of inter-regional relationship between wild-type and genetically modified mice there was little overall difference, while the most deviating brain regions were cortical amygdala and ventrolateral and ventral posteromedial thalamic nuclei. The GRi mice that most clearly differed from their controls exhibited deviation of connectivity for a number of brain regions, such as ventrolateral thalamic nucleus, the intermediate part of the lateral septal nucleus, the anteriodorsal part of the medial amygdaloid nucleus, the medial division of the central amygdaloid nucleus, ventral pallidum, nucleus of the vertical limb of the diagonal band, anteroventral parts of the thalamic nucleus and parts of the bed nucleus of the stria terminalis. Conclusively, the GRi mouse model was characterized by changes in the functional connectivity of the extended amygdala and stress response circuits.