Gene expression deficits in pontine locus coeruleus astrocytes in men with major depressive disorder

Possible antidepressant mechanism of acupuncture: targeting neuroplasticity

Major depressive disorder (MDD) is a highly prevalent and severely disabling psychiatric disorder that decreases quality of life and imposes substantial economic burden. Acupuncture has emerged as an effective adjunctive treatment for depression, it regulates neurotransmitters involved in mood regulation and modulates the activity of specific brain regions associated with emotional processing, as evidenced by neuroimaging and biochemical studies. Despite these insights, the precise neuroplastic mechanisms through which acupuncture exerts its antidepressant effects remain not fully elucidated. This review aims to summarize the current knowledge on acupuncture's modulation of neuroplasticity in depression, with a focus on the neuroplasticity-based targets associated with acupuncture's antidepressant effects. We encapsulate two decades of research into the neurobiological mechanisms underpinning the efficacy of acupuncture in treating depression. Additionally, we detail the acupoints and electroacupuncture parameters used in the treatment of depression to better serve clinical application.

An Astroglial Basis of Major Depressive Disorder: Molecular, Cellular, and Circuit Features

Major depressive disorder is a common psychiatric disorder and a leading cause of disability worldwide. Astrocytes play a role in the maintenance of the function of the central nervous system, both physiologically and pathologically. Accumulated evidence indicates that the astrocyte is an important contributor to the pathophysiology of major depressive disorder including blood-brain barrier integrity, gap junctions, gliotransmission, glutamate homeostasis, and energy metabolism. Here, we comprehensively summarize an astroglial basis for major depressive disorder based on molecular, cellular, and circuit properties, suggesting that astrocytes appear to be highly sensitive to stress and are likely to be uniquely positioned to integrate peripheral and central stress responses.

Neuroglia in suicide

Suicide is the worst outcome for many neuropsychiatric disorders having a high social and economic burden. There is a great need to determine the neurobiologic background of the etiopathogenesis and resilience toward suicide and to find novel pharmacologic strategies to treat suicidal behaviors. Neuroglia have been found to actively participate in the regulation of many cerebral functions, but it is debated whether these cells are structurally or functionally involved in the neuropathology of suicide, or merely follow the changes of comorbid psychiatric disorders. The purpose of this chapter is to review the scattered literature on the involvement of neuroglia in suicide and to describe how these cells might be responsive to the current pharmacologic interventions. We describe the different biological features of neuroglia in relation to suicide and the underlying psychiatric disorders, the molecular commonalities of neuroglial alterations in suicide across different psychiatric disorders, and the evidence for morphologic neuroglia changes in relation to the severity and resilience of suicide. Illuminating the mechanisms by which neuroglia are involved in suicide may ultimately lead to the development of suicide-related biomarkers and novel therapies for suicide prevention.

Unraveling the Role of the Blood-Brain Barrier in the Pathophysiology of Depression: Recent Advances and Future Perspectives

Depression is a highly prevalent psychological disorder characterized by persistent dysphoria, psychomotor retardation, insomnia, anhedonia, suicidal ideation, and a remarkable decrease in overall well-being. Despite the prevalence of accessible antidepressant therapies, many individuals do not achieve substantial improvement. Understanding the multifactorial pathophysiology and the heterogeneous nature of the disorder could lead the way toward better outcomes. Recent findings have elucidated the substantial impact of compromised blood-brain barrier (BBB) integrity on the manifestation of depression. BBB functions as an indispensable defense mechanism, tightly overseeing the transport of molecules from the periphery to preserve the integrity of the brain parenchyma. The dysfunction of the BBB has been implicated in a multitude of neurological disorders, and its disruption and consequent brain alterations could potentially serve as important factors in the pathogenesis and progression of depression. In this review, we extensively examine the pathophysiological relevance of the BBB and delve into the specific modifications of its components that underlie the complexities of depression. A particular focus has been placed on examining the effects of peripheral inflammation on the BBB in depression and elucidating the intricate interactions between the gut, BBB, and brain. Furthermore, this review encompasses significant updates on the assessment of BBB integrity and permeability, providing a comprehensive overview of the topic. Finally, we outline the therapeutic relevance and strategies based on BBB in depression, including COVID-19-associated BBB disruption and neuropsychiatric implications. Understanding the comprehensive pathogenic cascade of depression is crucial for shaping the trajectory of future research endeavors.

Identification of Potential Biomarkers for Major Depressive Disorder: Based on Integrated Bioinformatics and Clinical Validation

Major depressive disorder (MDD) is a severe mental illness characterized by a lack of objective biomarkers. Mounting evidence suggests there are extensive transcriptional molecular changes in the prefrontal cortex (PFC) of individuals with MDD. However, it remains unclear whether there are specific genes that are consistently altered and possess diagnostic power. In this study, we conducted a systematic search of PFC datasets of MDD patients from the Gene Expression Omnibus database. We calculated the differential expression of genes (DEGs) and identified robust DEGs using the RRA and MetaDE methods. Furthermore, we validated the consistently altered genes and assessed their diagnostic power through enzyme-linked immunosorbent assay experiments in our clinical blood cohort. Additionally, we evaluated the diagnostic power of hub DEGs in independent public blood datasets. We obtained eight PFC datasets, comprising 158 MDD patients and 263 healthy controls, and identified a total of 1468 unique DEGs. Through integrated analysis, we identified 290 robustly altered DEGs. Among these, seven hub DEGs (SLC1A3, PON2, AQP1, EFEMP1, GJA1, CENPD, HSD11B1) were significantly down-regulated at the protein level in our clinical blood cohort. Moreover, these hub DEGs exhibited a negative correlation with the Hamilton Depression Scale score (P < 0.05). Furthermore, these hub DEGs formed a panel with promising diagnostic power in three independent public blood datasets (average AUCs of 0.85) and our clinical blood cohort (AUC of 0.92). The biomarker panel composed of these genes demonstrated promising diagnostic efficacy for MDD and serves as a useful tool for its diagnosis.

Reactive Astrocytosis-A Potential Contributor to Increased Suicide in Long COVID-19 Patients?

BACKGROUND

Long COVID-19 is an emerging chronic illness of significant public health concern due to a myriad of neuropsychiatric sequelae, including increased suicidal ideation (SI) and behavior (SB).

METHODS

This review provides a concise synthesis of clinical evidence that points toward the dysfunction of astrocytes, the most abundant glial cell type in the central nervous system, as a potential shared pathology between SI/SB and COVID-19.

RESULTS

Depression, a suicide risk factor, and SI/SB were both associated with reduced frequencies of various astrocyte subsets and complex proteomic/transcriptional changes of astrocyte-related markers in a brain-region-specific manner. Astrocyte-related circulating markers were increased in depressed subjects and, to a less consistent extent, in COVID-19 patients. Furthermore, reactive astrocytosis was observed in subjects with SI/SB and those with COVID-19.

CONCLUSIONS

Astrocyte dysfunctions occurred in depression, SI/SB, and COVID-19. Reactive-astrocyte-mediated loss of the blood-brain barrier (BBB) integrity and subsequent neuroinflammation-a factor previously linked to SI/SB development-might contribute to increased suicide in individuals with long COVID-19. As such, the formulation of new therapeutic strategies to restore astrocyte homeostasis, enhance BBB integrity, and mitigate neuroinflammation may reduce SI/SB-associated neuropsychiatric manifestations among long COVID-19 patients.

Unveiling the hidden pathways: Exploring astrocytes as a key target for depression therapy

Depressive disorders are widely debilitating psychiatric disease. Despite the considerable progress in the field of depression therapy, extensive research spanning many decades has failed to uncover pathogenic pathways that might aid in the creation of long-acting and rapid-acting antidepressants. Consequently, it is imperative to reconsider existing approaches and explore other targets to improve this area of study. In contemporary times, several scholarly investigations have unveiled that persons who have received a diagnosis of depression, as well as animal models employed to study depression, demonstrate a decrease in both the quantity as well as density of astrocytes, accompanied by alterations in gene expression and morphological attributes. Astrocytes rely on a diverse array of channels and receptors to facilitate their neurotransmitter transmission inside tripartite synapses. This study aimed to investigate the potential processes behind the development of depression, specifically focusing on astrocyte-associated neuroinflammation and the involvement of several molecular components such as connexin 43, potassium channel Kir4.1, aquaporin 4, glutamatergic aspartic acid transporter protein, SLC1A2 or GLT-1, glucocorticoid receptors, 5-hydroxytryptamine receptor 2B, and autophagy, that localized on the surface of astrocytes. The study also explores novel approaches in the treatment of depression, with a focus on astrocytes, offering innovative perspectives on potential antidepressant medications.

Glial Markers of Suicidal Behavior in the Human Brain-A Systematic Review of Postmortem Studies

Suicide is a major public health priority, and its molecular mechanisms appear to be related to glial abnormalities and specific transcriptional changes. This study aimed to identify and synthesize evidence of the relationship between glial dysfunction and suicidal behavior to understand the neurobiology of suicide. As of 26 January 2024, 46 articles that met the inclusion criteria were identified by searching PubMed and ISI Web of Science. Most postmortem studies, including 30 brain regions, have determined no density or number of total Nissl-glial cell changes in suicidal patients with major psychiatric disorders. There were 17 astrocytic, 14 microglial, and 9 oligodendroglial studies using specific markers of each glial cell and further on their specific gene expression. Those studies suggest that astrocytic and oligodendroglial cells lost but activated microglia in suicides with affective disorder, bipolar disorders, major depression disorders, or schizophrenia in comparison with non-suicided patients and non-psychiatric controls. Although the data from previous studies remain complex and cannot fully explain the effects of glial cell dysfunction related to suicidal behaviors, they provide risk directions potentially leading to suicide prevention.

Neurobiological Underpinnings of Hyperarousal in Depression: A Comprehensive Review

Patients with major depressive disorder (MDD) exhibit an abnormal physiological arousal pattern known as hyperarousal, which may contribute to their depressive symptoms. However, the neurobiological mechanisms linking this abnormal arousal to depressive symptoms are not yet fully understood. In this review, we summarize the physiological and neural features of arousal, and review the literature indicating abnormal arousal in depressed patients. Evidence suggests that a hyperarousal state in depression is characterized by abnormalities in sleep behavior, physiological (e.g., heart rate, skin conductance, pupil diameter) and electroencephalography (EEG) features, and altered activity in subcortical (e.g., hypothalamus and locus coeruleus) and cortical regions. While recent studies highlight the importance of subcortical-cortical interactions in arousal, few have explored the relationship between subcortical-cortical interactions and hyperarousal in depressed patients. This gap limits our understanding of the neural mechanism through which hyperarousal affects depressive symptoms, which involves various cognitive processes and the cerebral cortex. Based on the current literature, we propose that the hyperconnectivity in the thalamocortical circuit may contribute to both the hyperarousal pattern and depressive symptoms. Future research should investigate the relationship between thalamocortical connections and abnormal arousal in depression, and explore its implications for non-invasive treatments for depression.

Does decreased autophagy and dysregulation of LC3A in astrocytes play a role in major depressive disorder?

Astrocytic dysfunction contributes to the molecular pathogenesis of major depressive disorder (MDD). However, the astrocytic subtype that mainly contributes to MDD etiology and whether dysregulated autophagy in astrocytes is associated with MDD remain unknown. Using a single-nucleus RNA sequencing (snRNA-seq) atlas, three astrocyte subtypes were identified in MDD, while C2 State-1Q astrocytes showed aberrant changes in both cell proportion and most differentially expressed genes compared with other subtypes. Moreover, autophagy pathways were commonly inhibited in astrocytes in the prefrontal cortices (PFCs) of patients with MDD, especially in C2 State-1Q astrocytes. Furthermore, by integrating snRNA-seq and bulk transcriptomic data, we found significant reductions in LC3A expression levels in the PFC region of CUMS-induced depressed mice, as well as in postmortem PFC tissues and peripheral blood samples from patients with MDD. These results were further validated by qPCR using whole-blood samples from patients with MDD and healthy controls. Finally, LC3A expression in the whole blood of patients with MDD was negatively associated with the severity of depressive symptoms. Overall, our results underscore autophagy inhibition in PFC astrocytes as a common molecular characteristic in MDD and might reveal a novel potential diagnostic marker LC3A.

Astrocytes in Post-Stroke Depression: Roles in Inflammation, Neurotransmission, and Neurotrophin Signaling

Post-stroke depression (PSD) is a frequent and disabling complication of stroke that affects up to one-third of stroke survivors. The pathophysiology of PSD involves multiple mechanisms, including neurochemical, neuroinflammatory, neurotrophic, and neuroplastic changes. Astrocytes are a type of glial cell that is plentiful and adaptable in the central nervous system. They play key roles in various mechanisms by modulating neurotransmission, inflammation, neurogenesis, and synaptic plasticity. This review summarizes the latest evidence of astrocyte involvement in PSD from human and animal studies, focusing on the alterations of astrocyte markers and functions in relation to monoamine neurotransmitters, inflammatory cytokines, brain-derived neurotrophic factor, and glutamate excitotoxicity. We also discuss the potential therapeutic implications of targeting astrocytes for PSD prevention and treatment. Astrocytes could be new candidates for antidepressant medications and other interventions that aim to restore astrocyte homeostasis and function in PSD. Astrocytes could be new candidates for antidepressant medications and other interventions that aim to restore astrocyte homeostasis and function in PSD.

The physio-affective phenome of major depression is strongly associated with biomarkers of astroglial and neuronal projection toxicity which in turn are associated with peripheral inflammation, insulin resistance and lowered calcium

BACKGROUND

Major depressive disorder (MDD) is characterized by elevated activity of peripheral neuro-immune and neuro-oxidative pathways, which may cause neuro-affective toxicity by disrupting neuronal circuits in the brain. No study has explored peripheral indicators of neuroaxis damage in MDD in relation to serum inflammatory and insulin resistance (IR) biomarkers, calcium, and the physio-affective phenome consisting of depressive, anxious, chronic fatigue, and physiosomatic symptoms.

METHODS

Serum levels of phosphorylated tau protein 217 (P-tau217), platelet-derived growth factor receptor beta (PDGFR), neurofilament light chain (NF-L), glial fibrillary acidic protein (GFAP), C-reactive protein (CRP), calcium and the HOMA2-insulin resistance (IR) index were measured in 94 MDD patients and 47 controls.

RESULTS

61.1 % of the variance in the physio-affective phenome (conceptualized as a factor extracted from depression, anxiety, fatigue and physiosomatic symptoms) is explained by the regression on GFAP, NF-L, P-tau2017, PDGFRβ and HOMA2-IR (all positively associated), and decreased calcium. In addition, CRP and HOMA2-IR predicted 28.9 % of the variance in the neuroaxis index. We observed significant indirect effects of CRP and calcium on the physio-affective phenome which were partly mediated by the four neuroaxis biomarkers. Annotation and enrichment analysis revealed that the enlarged GFAP, P-tau217, PDGFR, and NF-L network was enriched in glial cell and neuronal projections, the cytoskeleton and axonal transport, including a mitochondrion.

CONCLUSIONS

Peripheral inflammation and IR may damage the astroglial and neuronal projections thereby interfering with mitochondrial transport. This neurotoxicity, combined with inflammation, IR and lowered calcium, may, at least in part, induce the phenome of MDD.

Formulating treatment of major psychiatric disorders: algorithm targets the dominantly affected brain cell-types

BACKGROUND

Pharmacotherapy for most psychiatric conditions was developed from serendipitous observations of benefit from drugs prescribed for different reasons. An algorithmic approach to formulating pharmacotherapy is proposed, based upon which combination of changed activities by brain cell-types is dominant for any particular condition, because those cell-types contain and surrogate for genetic, metabolic and environmental information, that has affected their function. The algorithm performs because functions of some or all the affected cell-types benefit from several available drugs: clemastine, dantrolene, erythropoietin, fingolimod, fluoxetine, lithium, memantine, minocycline, pioglitazone, piracetam, and riluzole PROCEDURES/FINDINGS: Bipolar disorder, major depressive disorder, schizophrenia, Alzheimer's disease, and post-traumatic stress disorder, illustrate the algorithm; for them, literature reviews show that no single combination of altered cell-types accounts for all cases; but they identify, for each condition, which combination occurs most frequently, i.e., dominates, as compared with other possible combinations. Knowing the dominant combination of altered cell-types in a particular condition, permits formulation of therapy with combinations of drugs taken from the above list. The percentage of patients who might benefit from that therapy, depends upon the frequency with which the dominant combination occurs in patients with that particular condition.

CONCLUSIONS

Knowing the dominant combination of changed cell types in psychiatric conditions, permits an algorithmically formulated, rationally-based treatment. Different studies of the same condition often produce discrepant results; all might be correct, because identical clinical phenotypes result from different combinations of impaired cell-types, thus producing different results. Clinical trials would validate both the proposed concept and choice of drugs.

Astrocytes as Context for the Involvement of Myelin and Nodes of Ranvier in the Pathophysiology of Depression and Stress-Related Disorders

Astrocytes, despite some shared features as glial cells supporting neuronal function in gray and white matter, participate and adapt their morphology and neurochemistry in a plethora of distinct regulatory tasks in specific neural environments. In the white matter, a large proportion of the processes branching from the astrocytes' cell bodies establish contacts with oligodendrocytes and the myelin they form, while the tips of many astrocyte branches closely associate with nodes of Ranvier. Stability of myelin has been shown to greatly depend on astrocyte-to-oligodendrocyte communication, while the integrity of action potentials that regenerate at nodes of Ranvier has been shown to depend on extracellular matrix components heavily contributed by astrocytes. Several lines of evidence are starting to show that in human subjects with affective disorders and in animal models of chronic stress there are significant changes in myelin components, white matter astrocytes and nodes of Ranvier that have direct relevance to connectivity alterations in those disorders. Some of these changes involve the expression of connexins supporting astrocyte-to-oligodendrocyte gap junctions, extracellular matrix components produced by astrocytes around nodes of Ranvier, specific types of astrocyte glutamate transporters, and neurotrophic factors secreted by astrocytes that are involved in the development and plasticity of myelin. Future studies should further examine the mechanisms responsible for those changes in white matter astrocytes, their putative contribution to pathological connectivity in affective disorders, and the possibility of leveraging that knowledge to design new therapies for psychiatric disorders.

Antidepressant effects of cherry leaf decoction on a chronic unpredictable mild stress rat model based on the Glu/GABA-Gln metabolic loop

Cherry leaves (Prunus pseudocerasus Lindl. [Rosaceae]), a traditional Chinese herbal medicine, can regulate the factors closely related to depression including inflammatory cytokines, oxidative stress and blood glucose level. However, the antidepressant effects of cherry leaves and underlying neuromodulatory mechanisms remain relatively have not been elucidated explicitly. The present study investigated the antidepressant effects of cherry leaf decoction (CLD). The underlying neuromodulatory mechanism was explored by examining the glutamate (Glu)/γ-aminobutyric acid (GABA)-glutamine (Gln) metabolic loop. The chronic unpredictable mild stress (CUMS) rodent model was used in this study. The main flavonoids components of CLD were identified using high-performance liquid chromatography (HPLC). The antidepressant effects of CLD were assessed throughout behavioural tests including the bodyweight, sucrose preference test (SPT), forced swimming test (FPT) and tail suspension test (TST). Moreover, The baseline levels of serum adrenocorticotropic hormone (ACTH) and corticosterone (CORT) were quantified. The expression of proteins integrally involved in the Glu/GABA-Gln metabolic loop were observed and quantified by Western blotting, reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry. This study found that CLD ameliorated depressive-like behaviours induced by CUMS. The increase of serum ACTH and CORT baseline levels induced by CUMS was also reversed after CLD intervention. Furthermore, CUMS reduced the expression of GAD65, GAD67, GLT-1, GS and GABA_A and increased NMDAR1 levels in the rat hippocampus, which was normalized by CLD treatment. The findings demonstrated that CLD could ameliorate the depression-like behaviours induced by CUMS, potentially through the inhibition of hypothalamic-pituitary-adrenal (HPA) axis hyperactivity and the regulation of Glu/GABA-Gln metabolic loop.

Markers of elevated oxidative stress in oligodendrocytes captured from the brainstem and occipital cortex in major depressive disorder and suicide

Major depressive disorder (MDD) and suicide have been associated with elevated indices of oxidative damage in the brain, as well as white matter pathology including reduced myelination by oligodendrocytes. Oligodendrocytes highly populate white matter and are inherently susceptible to oxidative damage. Pathology of white matter oligodendrocytes has been reported to occur in brain regions that process behaviors that are disrupted in MDD and that may contribute to suicidal behavior. The present study was designed to determine whether oligodendrocyte pathology related to oxidative damage extends to brain areas outside of those that are traditionally considered to contribute to the psychopathology of MDD and suicide. Relative telomere lengths and the gene expression of five antioxidant-related genes, SOD1, SOD2, GPX1, CAT, and AGPS were measured in oligodendrocytes laser captured from two non-limbic brain areas: occipital cortical white matter and the brainstem locus coeruleus. Postmortem brain tissues were obtained from brain donors that died by suicide and had an active MDD at the time of death, and from psychiatrically normal control donors. Relative telomere lengths were significantly reduced in oligodendrocytes of both brain regions in MDD donors as compared to control donors. Three antioxidant-related genes (SOD1, SOD2, GPX1) were significantly reduced and one was significantly elevated (AGPS) in oligodendrocytes from both brain regions in MDD as compared to control donors. These findings suggest that oligodendrocyte pathology in MDD and suicide is widespread in the brain and not restricted to brain areas commonly associated with depression psychopathology.

A Selective Histamine H4 Receptor Antagonist, JNJ7777120, Role on Glutamate Transporter Activity in Chronic Depression

Glutamate release and reuptake play a key role in the pathophysiology of depression. glutamatergic nerves in the hippocampus region are modulated by histaminergic afferents. Excessive accumulation of glutamate in the synaptic area causes degeneration of neuron cells. The H4 receptor is defined as the main immune system histamine receptor with a pro-inflammatory role. To understand the role of this receptor, the drug JNJ7777120 was used to reveal the chronic depression-glutamate relationship. We have important findings showing that the H4 antagonist increases the glutamate transporters’ instantaneous activity. In our experiment, it has been shown that blocking the H4 receptor leads to increased neuron cell viability and improvement in behavioral ability due to glutamate. Therefore, JNJ can be used to prevent neurotoxicity, inhibit membrane phospholipase activation and free radical formation, and minimize membrane disruption. In line with our findings, results have been obtained that indicate that JNJ will contribute to the effective prevention and treatment of depression.

Glial Cell Abnormalities in Major Psychiatric Diseases: A Systematic Review of Postmortem Brain Studies

There have been a large number of reports about glial cell dysfunction being related to major psychiatric diseases such as schizophrenia (SCZ), bipolar disorder (BD), and major depressive disorder (MDD). In this review, we provide an overview of postmortem studies analyzing the structural changes of glial cells in these three major psychiatric diseases, including the density, number and size of glial cells, and the expression of related markers. Up to May 1, 2021, 108 articles that met the inclusion criteria were identified by searching PubMed and Web of Science. Although most studies evaluating total glial cells did not show abnormalities in the brains of postmortem patients, astrocytes, microglial cells, and oligodendrocytes seem to have specific patterns of changes in each disease. For example, out of 20 studies that evaluated astrocyte markers in MDD, 11 studies found decreased astrocyte marker expression in MDD patients. Similarly, out of 25 studies evaluating oligodendrocyte markers in SCZ, 15 studies showed decreased expression of oligodendrocyte markers in different brain regions of SCZ patients. In addition, activated microglial cells were observed in patients with SCZ, BD, and MDD, but suicide may be a confounding factor for the observed effects. Although the data from the included studies were heterogeneous and this cannot be fully explained at present, it is likely that there are a variety of contributing factors, including the measured brain regions, methods of measurement, gender, age at time of death, and medications.

Changes in glial gene expression in the prefrontal cortex in relation to major depressive disorder, suicide and psychotic features

BACKGROUND

To establish whether major depressive disorder (MDD), suicidal behaviors and psychotic features contribute to glial alterations in the human prefrontal cortex.

MATERIALS AND METHODS

We compared mRNA expression using real-time qPCR of 17 glia related genes in the dorsolateral prefrontal cortex (DLPFC) and the anterior cingulate cortex (ACC) between 24 patients with MDD and 12 well-matched controls without psychiatric or neurological diseases. The MDD group was subdivided into i) MDD who died of suicide (MDD-S) or natural causes (MDD-NS) and ii) MDD with or without psychotic features (MDD-P and MDD-NP). The results were followed up with confounder factor analysis.

RESULTS

Astrocyte gene aldehyde dehydrogenase-1 L1 (ALDH1L1) showed an increased expression in the DLPFC of MDD-NS and the ACC of MDD-NP. S100 calcium-binding protein B (S100B) was upregulated in the DLPFC of MDD compared to the controls. Microglial markers CD11B and purinergic receptor 12 (P2RY12) both showed decreased expression in the ACC of MDD-NS. CD68 was increased in the DLPFC of MDD in both, MDD-S and MDD-P, compared to the controls. In addition, there was increased translocator protein (TSPO) expression in the DLPFC of MDD, especially MDD-NS. In the ACC, this gene had a lower expression in MDD-P than in MDD-NP. Myelin basic protein (MBP) mRNA in the DLPFC increased in MDD, in relation to psychotic features, but not to suicide.

LIMITATIONS

Sample volumes are relatively small.

CONCLUSIONS

Different glial functions in MDD were related to specific brain area, suicide or psychotic features.

Role of neuroglia in neuropathic pain and depression

Patients with neuropathic pain induced by nerve injury usually present with co-morbid affective changes, such as depression. Neuroglia was reported to play an important role in the development and maintenance of neuropathic pain both centrally and peripherally. Meanwhile, there have been studies showing that neuroglia participated in the development of depression. However, the specific role of neuroglia in neuropathic pain and depression has not been reviewed comprehensively. Therefore, we summarized the recent findings on the role of neuroglia in neuropathic pain and depression. Based on this review, we found a bridge-like role of neuroglia in neuropathic pain co-morbid with depression. This review may provide therapeutic implications in the treatment of neuropathic pain and offer potential help in the studies of mechanisms in the future.

Genome-wide study of key genes and scoring system as potential noninvasive biomarkers for detection of suicide behavior in major depression disorder

Although some progress has been made in the molecular biological detection of major depression disorder (MDD), its specificity and accuracy are still insufficient. This study is aimed to find hub genes, which could contribute to MDD related suicide and provide potential therapeutic targets for diagnosis and treatment. We downloaded RNA expression and clinical information from Gene Expression Omnibus (GEO) Dataset. Then, weighted gene co-expression network analysis (WGCNA) was applied to find core modules. Logistic regression was performed to identify the independent risk factors, and a scoring system was constructed based on these independent risk factors. As a result, a total of 16487 genes were selected to further conducted WGCNA analysis. We found that tan and green functional modules were exhibited high correlation with suicide behavior. 309 genes were identified in tan modules that were the strongest positively correlated with suicide behavior. Functional analysis in tan module indicated that activation of enzymes including nitric-oxide synthase and endoribonuclease, estrogen signaling pathway, glucagon signaling pathway, and legionellosis pathway were most enriched in MDD. Furthermore, we applied protein–protein interaction (PPI) analysis to select the hub genes and 10 genes were found in the core area of network. Then, we identified three-gene base independent risk signature by logistic regression model, including HSPA1A, RASEF, TBC1D8B. In conclusion, our study suggests that the tan module genes are closely related to suicide behaviors, which is mainly caused by multiple signaling pathway activation. The three-genes-based signature could provide a better efficacy to predict suicidal behavior in MDD patients.

The Association Between Antidepressant Effect of SSRIs and Astrocytes: Conceptual Overview and Meta-analysis of the Literature

Major depressive disorders (MDD) a worldwide psychiatric disease, is yet to be adequately controlled by therapies; while the mechanisms of action of antidepressants are yet to be fully characterised. In the last two decades, an increasing number of studies have demonstrated the role of astrocytes in the pathophysiology and therapy of MDD. Selective serotonin reuptake inhibitors (SSRIs) are the most widely used antidepressants. It is generally acknowledged that SSRIs increase serotonin levels in the central nervous system by inhibiting serotonin transporters, although the SSRIs action is not ideal. The SSRIs antidepressant effect develops with considerable delay; their efficacy is low and frequent relapses are common. Neither cellular nor molecular pharmacological mechanisms of SSRIs are fully characterised; in particular their action on astrocytes remain underappreciated. In this paper we overview potential therapeutic mechanisms of SSRIs associated with astroglia and report the results of meta-analysis of studies dedicated to MDD, SSRIs and astrocytes. In particular, we argue that fluoxetine, the representative SSRI, improves depressive-like behaviours in animals treated with chronic mild stress and reverses depression-associated decrease in astrocytic glial fibrillary acidic protein (GFAP) expression. In addition, fluoxetine upregulates astrocytic mRNA expression of 5-hydroxytriptamin/serotonin2B receptors (5-HT2BR). In summary, we infer that SSRIs exert their anti-depressant effect by regulating several molecular and signalling pathways in astrocytes.

N-3 polyunsaturated fatty acids promote astrocyte differentiation and neurotrophin production independent of cAMP in patient-derived neural stem cells

Evidence from epidemiological and laboratory studies, as well as randomized placebo-controlled trials, suggests supplementation with n-3 polyunsaturated fatty acids (PUFAs) may be efficacious for treatment of major depressive disorder (MDD). The mechanisms underlying n-3 PUFAs potential therapeutic properties remain unknown. There are suggestions in the literature that glial hypofunction is associated with depressive symptoms and that antidepressants may normalize glial function. In this study, induced pluripotent stem cells (iPSC)-derived neuronal stem cell lines were generated from individuals with MDD. Astrocytes differentiated from patient-derived neuronal stem cells (iNSCs) were verified by GFAP. Cells were treated with eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA) or stearic acid (SA). During astrocyte differentiation, we found that n-3 PUFAs increased GFAP expression and GFAP positive cell formation. BDNF and GDNF production were increased in the astrocytes derived from patients subsequent to n-3 PUFA treatment. Stearic Acid (SA) treatment did not have this effect. CREB activity (phosphorylated CREB) was also increased by DHA and EPA but not by SA. Furthermore, when these astrocytes were treated with n-3 PUFAs, the cAMP antagonist, RP-cAMPs did not block n-3 PUFA CREB activation. However, the CREB specific inhibitor (666-15) diminished BDNF and GDNF production induced by n-3 PUFA, suggesting CREB dependence. Together, these results suggested that n-3 PUFAs facilitate astrocyte differentiation, and may mimic effects of some antidepressants by increasing production of neurotrophic factors. The CREB-dependence and cAMP independence of this process suggests a manner in which n-3 PUFA could augment antidepressant effects. These data also suggest a role for astrocytes in both MDD and antidepressant action.

Can pharmacotherapy improve treatment outcomes in people with co-occurring major depressive and cocaine use disorders?

Introduction: Major depressive disorder (MDD) and cocaine use disorder (CUD) are prevalent and frequently co-occur. When co-occurring, the presence of one disorder typically negatively impacts the prognosis for the other. Given the clinical relevance, we sought to examine pharmacotherapies for co-occurring CUD and MDD. While multiple treatment options have been examined in the treatment of each condition individually, studies exploring pharmacological options for their comorbidity are fewer and not conclusive.Areas Covered: For this review, the authors searched the literature in PubMed using clinical query options for therapies and keywords relating to each condition. Then, they described potentially promising pharmacologic therapeutic options based on shared mechanisms between the two conditions and/or results from individual clinical trials conducted to date.Expert opinion: Medications like stimulants, dopamine (D3) receptors partial agonists or antagonists, antagonists of kappa opioid receptors, topiramate, and ketamine could be promising as there is significant overlap relating to reward deficiency models, antireward pathways, and altered glutamatergic systems. However, the available clinical literature on any one of these types of agents is mixed. Additionally, for some agents there is possible concern related to abuse potential (e.g. ketamine and stimulants).

Ketamine Alters Functional Plasticity of Astroglia: An Implication for Antidepressant Effect

Ketamine, a non-competitive N–methyl–d–aspartate receptor (NMDAR) antagonist, exerts a rapid, potent and long-lasting antidepressant effect, although the cellular and molecular mechanisms of this action are yet to be clarified. In addition to targeting neuronal NMDARs fundamental for synaptic transmission, ketamine also affects the function of astrocytes, the key homeostatic cells of the central nervous system that contribute to pathophysiology of major depressive disorder. Here, I review studies revealing that (sub)anesthetic doses of ketamine elevate intracellular cAMP concentration ([cAMP]_i) in astrocytes, attenuate stimulus-evoked astrocyte calcium signaling, which regulates exocytotic secretion of gliosignaling molecules, and stabilize the vesicle fusion pore in a narrow configuration, possibly hindering cargo discharge or vesicle recycling. Next, I discuss how ketamine affects astrocyte capacity to control extracellular K⁺ by reducing vesicular delivery of the inward rectifying potassium channel (K_ir4.1) to the plasmalemma that reduces the surface density of Kir4.1. Modified astroglial K⁺ buffering impacts upon neuronal firing pattern as demonstrated in lateral habenula in a rat model of depression. Finally, I highlight the discovery that ketamine rapidly redistributes cholesterol in the astrocyte plasmalemma, which may alter the flux of cholesterol to neurons. This structural modification may further modulate a host of processes that synergistically contribute to ketamine’s rapid antidepressant action.

Gene expression studies in Depression development and treatment: an overview of the underlying molecular mechanisms and biological processes to identify biomarkers

A combination of different risk factors, such as genetic, environmental and psychological factors, together with immune system, stress response, brain neuroplasticity and the regulation of neurotransmitters, is thought to lead to the development of major depressive disorder (MDD). A growing number of studies have tried to investigate the underlying mechanisms of MDD by analysing the expression levels of genes involved in such biological processes. These studies have shown that MDD is not just a brain disorder, but also a body disorder, and this is mainly due to the interplay between the periphery and the Central Nervous System (CNS). To this purpose, most of the studies conducted so far have mainly dedicated to the analysis of the gene expression levels using postmortem brain tissue as well as peripheral blood samples of MDD patients. In this paper, we reviewed the current literature on candidate gene expression alterations and the few existing transcriptomics studies in MDD focusing on inflammation, neuroplasticity, neurotransmitters and stress-related genes. Moreover, we focused our attention on studies, which have investigated mRNA levels as biomarkers to predict therapy outcomes. This is important as many patients do not respond to antidepressant medication or could experience adverse side effects, leading to the interruption of treatment. Unfortunately, the right choice of antidepressant for each individual still remains largely a matter of taking an educated guess.

Implication of cerebral astrocytes in major depression: A review of fine neuroanatomical evidence in humans

Postmortem investigations have implicated astrocytes in many neurological and psychiatric conditions. Multiple brain regions from individuals with major depressive disorder (MDD) have lower expression levels of astrocyte markers and lower densities of astrocytes labeled for these markers, suggesting a loss of astrocytes in this mental illness. This paper reviews the general properties of human astrocytes, the methods to study them, and the postmortem evidence for astrocyte pathology in MDD. When comparing astrocyte density and morphometry studies, astrocytes are more abundant and smaller in human subcortical than cortical brain regions, and immunohistochemical labeling for the astrocyte markers glial fibrillary acidic protein (GFAP) and vimentin (VIM) reveals fewer than 15% of all astrocytes that are present in cortical and subcortical regions, as revealed using other staining techniques. By combining astrocyte densities and morphometry, a model was made to illustrate that domain organization is mostly limited to GFAP-IR astrocytes. Using these markers and others, alterations of astrocyte densities appear more widespread than those for astrocyte morphologies throughout the brain of individuals having died with MDD. This review suggests how reduced astrocyte densities may relate to the association of depressive episodes in MDD with elevated S100 beta (S100B) cerebrospinal fluid serum levels. Finally, a potassium imbalance theory is proposed that integrates the reduced astrocyte densities generated from postmortem studies with a hypothesis for the antidepressant effects of ketamine generated from rodent studies.

Peripheral blood neurotrophic factor levels in children with autism spectrum disorder: a meta-analysis

Increasing evidence suggests that abnormal regulation of neurotrophic factors is involved in the etiology and pathogenesis of Autism Spectrum Disorder (ASD). However, clinical data on neurotrophic factor levels in children with ASD were inconsistent. Therefore, we performed a systematic review of peripheral blood neurotrophic factors levels in children with ASD, and quantitatively summarized the clinical data of peripheral blood neurotrophic factors in ASD children and healthy controls. A systematic search of PubMed and Web of Science identified 31 studies with 2627 ASD children and 4418 healthy controls to be included in the meta-analysis. The results of random effect meta-analysis showed that the peripheral blood levels of brain-derived neurotrophic factor (Hedges’ g = 0.302; 95% CI = 0.014 to 0.591; P = 0.040) , nerve growth factor (Hedges’ g = 0.395; 95% CI = 0.104 to 0.686; P = 0.008) and vascular endothelial growth factor (VEGF) (Hedges’ g = 0.097; 95% CI = 0.018 to 0.175; P = 0.016) in children with ASD were significantly higher than that of healthy controls, whereas blood neurotrophin-3 (Hedges’ g =  − 0.795; 95% CI =  − 1.723 to 0.134; P = 0.093) and neurotrophin-4 (Hedges’ g = 0.182; 95% CI =  − 0.285 to 0.650; P = 0.445) levels did not show significant differences between cases and controls. Taken together, these results clarified circulating neurotrophic factor profile in children with ASD, strengthening clinical evidence of neurotrophic factor aberrations in children with ASD.

Widespread Decrease of Cerebral Vimentin-Immunoreactive Astrocytes in Depressed Suicides

Post-mortem investigations have implicated cerebral astrocytes immunoreactive (-IR) for glial fibrillary acidic protein (GFAP) in the etiopathology of depression and suicide. However, it remains unclear whether astrocytic subpopulations IR for other astrocytic markers are similarly affected. Astrocytes IR to vimentin (VIM) display different regional densities than GFAP-IR astrocytes in the healthy brain, and so may be differently altered in depression and suicide. To investigate this, we compared the densities of GFAP-IR astrocytes and VIM-IR astrocytes in post-mortem brain samples from depressed suicides and matched non-psychiatric controls in three brain regions (dorsomedial prefrontal cortex, dorsal caudate nucleus and mediodorsal thalamus). A quantitative comparison of the fine morphology of VIM-IR astrocytes was also performed in the same regions and subjects. Finally, given the close association between astrocytes and blood vessels, we also assessed densities of CD31-IR blood vessels. Like for GFAP-IR astrocytes, VIM-IR astrocyte densities were found to be globally reduced in depressed suicides relative to controls. By contrast, CD31-IR blood vessel density and VIM-IR astrocyte morphometric features in these regions were similar between groups, except in prefrontal white matter, in which vascularization was increased and astrocytes displayed fewer primary processes. By revealing a widespread reduction of cerebral VIM-IR astrocytes in cases vs. controls, these findings further implicate astrocytic dysfunctions in depression and suicide.

RAGE Signaling pathway in hippocampus dentate gyrus involved in GLT-1 decrease induced by chronic unpredictable stress in rats

A pivotal role of glutamatergic neurotransmission in the pathophysiology of major depressive disorder (MDD) has been supported in preclinical and clinical studies. Glutamate transporters are responsible for rapid uptake of glutamate to maintain glutamate homeostasis. Down-regulation of glutamate transporters has been reported in MDD patients and animal models. However, the mechanism for stress-induced modulation of glutamate transporter expression is poorly understood. Receptor for advanced glycosylation end products (RAGE), a member of immunoglobulin family, is found expressed widely in brain and play important roles in neuronal development, neurite growth, neurogenesis and neuroinflammation. Our study showed chronic unpredictable stress (CUS) induced depressive-like behaviors and reduced RAGE expression in hippocampus DG, CA1 and CA3 areas. The protein levels of GLT-1, p-CREB and p-p65 decreased in hippocampus DG as well. Knockdown of RAGE expression in hippocampus DG with RAGE shRNA lentivirus particles induced depressive-like behaviors. Meanwhile, the protein and mRNA levels of GLT-1 were significantly decreased as well as phosphorylation of CREB and p65. Neither CUS nor RAGE knockdown altered GLAST protein and mRNA levels. These findings suggested that RAGE/CREB-NF-κB signaling pathway in hippocampus DG involved in modulation of GLT-1 expression, which possibly contributed to the depressive-like behavior induced by CUS.

L-Carnosine combination therapy for major depressive disorder: A randomized, double-blind, placebo-controlled trial

BACKGROUND

Evidence for antidepressant effects of L-Carnosine was shown in some experimental studies. In this study we tried to evaluate the efficacy and tolerability of L-Carnosine combination therapy in treatment of patients with major depressive disorder (MDD).

METHODS

Fifty-eight patients with MDD (DSM-V) and Hamilton Depression Rating Scale (HAM-D) score ≥ 19 were randomized to receive either 400 mg twice daily L-Carnosine or placebo in addition to citalopram (maximum dosage of 40 mg/day) for six weeks in a randomized double-blind, and placebo-controlled study. Patients were assessed using the HAM-D scale at baseline and weeks 2, 4, and 6.

RESULTS

Fifty-two patients completed the trial. General linear model repeated measure showed significant difference for time × treatment on HAM-D score [F = 3.17, df = 2.39, p-value = 0.03]. Significantly greater improvement was detected in HAM-D score of the L-Carnosine group compared with the placebo group from baseline to weeks 2, 4 and 6 [Ps = 0.013, 0.028 and 0.023; respectively]. Patients in the L-Carnosine group experienced significantly greater response and remission rate than the placebo group [Ps = 0.023 and 0.012; respectively]. There was no significant difference between the two groups in baseline parameters and frequency of side effects.

LIMITATIONS

Short follow-up period and small population size were two important limitations of this study.

CONCLUSIONS

L-Carnosine combination therapy with citalopram can effectively improve symptoms of patients with major depressive disorder. Rapid-onset antidepressant effects of L-Carnosine were also shown which need further investigation.

EAAT2 as a Research Target in Bipolar Disorder and Unipolar Depression: A Systematic Review

Glutamate is implicated in the neuropathology of both major depressive disorder and bipolar disorder. Excitatory amino acid transporter 2 (EAAT2) is the major glutamate transporter in the mammalian brain, removing glutamate from the synaptic cleft and transporting it into glia for recycling. It is thereby the principal regulator of extracellular glutamate levels and prevents neuronal excitotoxicity. EAAT2 is a promising target for elucidating the mechanisms by which the glutamate-glutamine cycle interacts with neuronal systems in mood disorders. Forty EAAT2 studies (published January 1992-January 2018) were identified via a systematic literature search. The studies demonstrated that chronic stress/steroids were most commonly associated with decreased EAAT2. In rodents, EAAT2 inhibition worsened depressive behaviors. Human EAAT2 expression usually decreased in depression, with some regional brain differences. Fewer data have been collected regarding the roles and regulation of EAAT2 in bipolar disorder. Future directions for research include correlating EAAT2 and glutamate levels in vivo, elucidating genetic variability and epigenetic regulation, clarifying intracellular protein and pharmacologic interactions, and examining EAAT2 in different bipolar mood states. As part of a macromolecular complex within glia, EAAT2 may contribute significantly to intracellular signaling, energy regulation, and cellular homeostasis. An enhanced understanding of this system is needed.

Retinal-glia ischemia and inflammation induced by chronic stress: The SABPA study

Background

Psychobiological processes linking stress and vascular diseases remain poorly understood. The retina and the brain share a common embryonic-diencephalon origin and blood-barrier physiology e.g. ongoing ischemia facilitates S100B release with astrocytic activity and glial-fibrillary-acidic-protein expression (GFAP). However, GFAP decreases revealed astrocyte pathology in the prefrontal cortex of depression/suicide cases; and might be a key mechanism in stress - disease pathways.

Methods

A chronic emotional stress phenotype independent of age, ethnicity or sex was used to stratify the current prospective cohort (N ​= ​359; aged 46 ​± ​9 years) into Stress (N ​= ​236) and no-Stress groups (N ​= ​123). Prospective data for glia ischemia risk markers were obtained, including 24 ​h BP, fasting S100B, GFAP, HbA1C and tumor-necrosis-factor-α (TNF-α). At 3-yr follow-up: diastolic-ocular-perfusion-pressure (indicating hypo-perfusion risk) was measured and retinal vessel calibers were quantified from digital images in the mydriatic eye.

Results

Higher hypertension (75% vs. 16%), diabetes (13% vs. 0%) and retinopathy (57% vs. 45%) prevalence was observed in Stress compared to no-Stress individuals. Stressed individuals had consistently raised S100B, TNF-α, HbA1C and higher diastolic-ocular-perfusion-pressure, but decreases in GFAP and GFAP:S100B. Furthermore stroke risk markers, arterial narrowing and venous widening were associated with consistently raised S100B, GFAP:S100B (p ​= ​0.060), TNF-α and higher diastolic-ocular-perfusion-pressure [Adj. R2 0.39-0.41, p ​≤ ​0.05]. No retinal-glia associations were evident in the no-Stress group.

Conclusions

Retinal-glia ischemia and inflammation was induced by chronic stress. Persistent higher inflammation and S100B with GFAP decreases further reflected stress-induced astrocyte pathology in the human retina. It is recommended to increase awareness on chronic stress and susceptibility for brain ischemia.

Sex differences in stress-related disorders: Major depressive disorder, bipolar disorder, and posttraumatic stress disorder

Stress-related disorders, such as mood disorders and posttraumatic stress disorder (PTSD), are more common in women than in men. This sex difference is at least partly due to the organizing effect of sex steroids during intrauterine development, while activating or inhibiting effects of circulating sex hormones in the postnatal period and adulthood also play a role. Such effects result in structural and functional changes in neuronal networks, neurotransmitters, and neuropeptides, which make the arousal- and stress-related brain systems more vulnerable to environmental stressful events in women. Certain brainstem nuclei, the amygdala, habenula, prefrontal cortex, and hypothalamus are important hubs in the stress-related neuronal network. Various hypothalamic nuclei play a central role in this sexually dimorphic network. This concerns not only the hypothalamus-pituitary-adrenal axis (HPA-axis), which integrates the neuro-endocrine-immune responses to stress, but also other hypothalamic nuclei and systems that play a key role in the symptoms of mood disorders, such as disordered day-night rhythm, lack of reward feelings, disturbed eating and sex, and disturbed cognitive functions. The present chapter focuses on the structural and functional sex differences that are present in the stress-related brain systems in mood disorders and PTSD, placing the HPA-axis in the center. The individual differences in the vulnerability of the discussed systems, caused by genetic and epigenetic developmental factors warrant further research to develop tailor-made therapeutic strategies.

Suicide and suicide risk

Although recent years have seen large decreases in the overall global rate of suicide fatalities, this trend is not reflected everywhere. Suicide and suicidal behaviour continue to present key challenges for public policy and health services, with increasing suicide deaths in some countries such as the USA. The development of suicide risk is complex, involving contributions from biological (including genetics), psychological (such as certain personality traits), clinical (such as comorbid psychiatric illness), social and environmental factors. The involvement of multiple risk factors in conveying risk of suicide means that determining an individual's risk of suicide is challenging. Improving risk assessment, for example, by using computer testing and genetic screening, is an area of ongoing research. Prevention is key to reduce the number of suicide deaths and prevention efforts include universal, selective and indicated interventions, although these interventions are often delivered in combination. These interventions, combined with psychological (such as cognitive behavioural therapy, caring contacts and safety planning) and pharmacological treatments (for example, clozapine and ketamine) along with coordinated social and public health initiatives, should continue to improve the management of individuals who are suicidal and decrease suicide-associated morbidity.

Markers of central inflammation in major depressive disorder: A systematic review and meta-analysis of studies examining cerebrospinal fluid, positron emission tomography and post-mortem brain tissue

BACKGROUND

Increased peripheral inflammation has been consistently reported in patients with major depressive disorder (MDD). However, only few studies have explored markers of central (brain) inflammation in patients with MDD. The aim of this study is to systematically review in vivo and post-mortem markers of central inflammation, including studies examining cerebrospinal fluid (CSF), positron emission tomography, and post-mortem brain tissues in subjects suffering with MDD compared with controls.

METHODS

PubMed and Medline databases were searched up to December 2018. We included studies measuring cerebrospinal fluid (CSF) cytokines and chemokines, positron emission tomography (PET) studies; and post-mortem studies measuring cytokines, chemokines and cell-specific markers of microglia and astrocytes, all in MDD. A meta-analysis was performed only for CSF and PET studies, as studies on post-mortem markers of inflammation had different cell-specific markers and analysed different brain regions.

RESULTS

A total of 69 studies met the inclusion criteria. CSF levels of IL-6 and TNF-α were higher in patients with MDD compared with controls (standardised mean difference SMD 0.37, 95%CI: 0.17-0.57 and SMD 0.58, 95%CI 0.26-0.90, respectively). CSF levels of IL-6 were increased in suicide attempters regardless of their psychiatric diagnosis. Translocator protein, a PET marker of central inflammation, was elevated in the anterior cingulate cortex and temporal cortex of patients with MDD compared with controls (SMD 0.78, 95%CI: 0.41-1.16 and SMD 0.52, 95%CI: 0.19-0.85 respectively). Abnormalities in CSF and PET inflammatory markers were not correlated with those in peripheral blood. In post-mortem studies, two studies found increased markers of microglia in MDD brains, while four studies found no MDD related changes. Of the studies investigating expression of cell-specific marker for astrocytes, thirteen studies reported a decreased expression of astrocytes specific markers, two studies reported increased expression of astrocytes specific markers, and eleven studies did not detect any difference. Four out of six studies reported decreased markers of oligodendrocytes in the prefrontal cortex. Post-mortem brain levels of tumor necrosis alpha (TNF-α) were also found increased in MDD.

CONCLUSIONS

Our review suggests the presence of an increase in IL-6 and TNF-alpha levels in CSF and brain parenchyma, in the context of a possible increased microglia activity and reduction of astrocytes and oligodendrocytes markers in MDD. The reduced number of astrocytes may lead to compromised integrity of blood brain barrier with increased monocyte recruitment and infiltration, which is partly supported by post-mortem studies and by PET studies showing an increased TSPO expression in MDD.

Xiaoyaosan exerts antidepressant-like effects by regulating the functions of astrocytes and EAATs in the prefrontal cortex of mice

BACKGROUND

Mounting evidence indicates that the cerebral cortex is an important physiological system of emotional activity, and its dysfunction may be the main cause of stress. Glutamate is the primary excitatory neurotransmitter in the central nervous system (CNS), which initiates rapid signal transmission in the synapse before its reuptake into the surrounding glia, specifically astrocytes (ASTs). The astrocytic excitatory amino acid transporters 1 (EAAT1) and 2 (EAAT2) are the major transporters that take up synaptic glutamate to maintain optimal extracellular glutamic levels, thus preventing accumulation in the synaptic cleft and ensuing excitotoxicity. Growing evidence has shown that excitotoxicity is associated with depression. Therefore, we hypothesized that the underlying antidepressant-like mechanism of Xiaoyaosan (XYS), a Chinese herbal formula, may be related to the regulation of astrocytic EAATs. Therefore, we studied the antidepressant mechanism of XYS on the basis of EAAT dysfunction in ASTs.

METHODS

Eighty adult C57BL/6 J mice were randomly divided into 4 groups: a control group, a chronic unpredictable mild stress (CUMS) group, a Xiaoyaosan (XYS) treatment group and a fluoxetine hydrochloride (Flu) treatment group. Except for the control group, mice in the other groups all received chronic unpredictable mild stress for 21 days. Mice in the control and CUMS groups received gavage administration with 0.5 mL of normal saline (NS) for 21 days, and mice in the XYS and Flu treatment groups were administered dosages of 0.25 g/kg/d and 2.6 mg/kg/d by gavage. The effects of XYS on the depressive-like behavioral tests, including the open field test (OFT), forced swimming test (FST) and sucrose preference test (SPT), were examined. The glutamate (Glu) concentrations of the prefrontal cortex (PFC) were detected with colorimetry. The morphology of neurons in the PFC was observed by Nissl staining. The expression of glial fibrillary acidic protein (GFAP), NeuN, EAAT1 and EAAT2 proteins in the PFC of mice was detected by using Western blotting and immunohistochemistry. Quantitative real-time PCR (qPCR) was used to detect the expression of the GFAP, NeuN, EAAT1 and EAAT2 genes in the PFC of mice.

RESULTS

The results of behavioral tests showed that CUMS-induced mice exhibited depressive-like behavior, which could be improved in some tests with XYS and Flu treatment. Immunohistochemistry and Western blot analysis showed that the protein levels of GFAP, NeuN, EAAT1 and EAAT2 in the PFC of CUMS mice were significantly lower than those in the control group, and these changes could be reversed by XYS and Flu. The results of qPCR analysis showed that the expression of GFAP, NeuN, EAAT1 and EAAT2 mRNAs in the PFC of CUMS mice was not significantly changed, with the exception of EAAT2, compared with that of the control group, while the expression of the above mRNAs was significantly higher in the XYS and Flu groups than that in the CUMS group.

CONCLUSION

XYS may exert antidepressant-like effects by improving the functions of AST and EAATs and attenuating glutamate-induced neuronal damage in the frontal cortex.

Melanin-concentrating hormone in the Locus Coeruleus aggravates helpless behavior in stressed rats

Animal studies have shown that antagonists of receptor 1 of Melanin-Concentrating Hormone (MCH-R1) elicit antidepressive-like behavior, suggesting that MCH-R1 might be a novel target for the treatment of depression and supports the hypothesis that MCHergic signaling regulates depressive-like behaviors. Consistent with the evidence that MCHergic neurons send projections to dorsal and median raphe nuclei, we have previously demonstrated that MCH microinjections in both nuclei induced a depressive-like behavior. Even though MCH neurons also project to Locus Coeruleus (LC), only a few studies have reported the behavioral and neurochemical effect of MCH into the LC. We studied the effects of MCH (100 and 200 ng) into the LC on coping-stress related behaviors associated with depression, using two different behavioral tests: the forced swimming test (FST) and the learned helplessness (LH). To characterize the functional interaction between MCH and the noradrenergic LC system, we also evaluated the neurochemical effects of MCH (100 ng) on the extracellular levels of noradrenaline (NA) in the medial prefrontal cortex (mPFC), an important LC terminal region involved in emotional processing. MCH administration into the LC elicited a depressive-like behavior evidenced in both paradigms. Interestingly, in the LH, MCH (100) elicited a significant increase in escape failures only in stressed animals. A significant decrease in prefrontal levels of NA was observed after MCH microinjection into the LC. Our results demonstrate that increased MCH signaling into the LC triggers depressive-like behaviors, especially in stressed animals. These data further corroborate the important role of MCH in the neurobiology of depression.

Quinolinic Acid and Nuclear Factor Erythroid 2-Related Factor 2 in Depression: Role in Neuroprogression

Depression is an incapacitating neuropsychiatric disorder. The serotonergic system in the brain plays an important role in the pathophysiology of depression. However, due to delayed and/or poor performance of selective serotonin reuptake inhibitors in treating depressive symptoms, the role of the serotonergic system in depression has been recently questioned further. Evidence from recent studies suggests that increased inflammation and oxidative stress may play significant roles in the pathophysiology of depression. The consequences of these factors can lead to the neuroprogression of depression, involving neurodegeneration, astrocytic apoptosis, reduced neurogenesis, reduced plasticity (neuronal and synaptic), and enhanced immunoreactivity. Specifically, increased proinflammatory cytokine levels have been shown to activate the kynurenine pathway, which causes increased production of quinolinic acid (QA, an N-Methyl-D-aspartate agonist) and decreases the synthesis of serotonin. QA exerts many deleterious effects on the brain via mechanisms including N-methyl-D-aspartate excitotoxicity, increased oxidative stress, astrocyte degeneration, and neuronal apoptosis. QA may also act directly as a pro-oxidant. Additionally, the nuclear translocation of antioxidant defense factors, such as nuclear factor (erythroid-derived 2)-like 2 (Nrf2), is downregulated in depression. Hence, in the present review, we discuss the role of QA in increasing oxidative stress in depression by modulating the nuclear translocation of nuclear factor (erythroid-derived 2)-like 2 and thus affecting the synthesis of antioxidant enzymes.

Localization of the Locus Coeruleus in the Mouse Brain

The locus coeruleus (LC) is a major hub of norepinephrine producing neurons that modulate a number of physiological functions. Structural or functional abnormalities of LC impact several brain regions including cortex, hippocampus, and cerebellum and may contribute to depression, bipolar disorder, anxiety, as well as Parkinson disease and Alzheimer disease. These disorders are often associated with metal misbalance, but the role of metals in LC is only partially understood. Morphologic and functional studies of LC are needed to better understand the human pathologies and contribution of metals. Mice are a widely used experimental model, but the mouse LC is small (~0.3 mm diameter) and hard to identify for a non-expert. Here, we describe a step-by-step immunohistochemistry-based protocol to localize the LC in the mouse brain. Dopamine-β-hydroxylase (DBH), and alternatively, tyrosine hydroxylase (TH), both enzymes highly expressed in the LC, are used as immunohistochemical markers in brain slices. Sections adjacent to LC-containing sections can be used for further analysis, including histology for morphological studies, metabolic testing, as well as metal imaging by X-ray fluorescence microscopy (XFM).

Quantification of Tyrosine Hydroxylase and ErbB4 in the Locus Coeruleus of Mood Disorder Patients Using a Multispectral Method to Prevent Interference with Immunocytochemical Signals by Neuromelanin

The locus coeruleus (LC) has been studied in major depressive disorder (MDD) and bipolar disorder (BD). A major problem of immunocytochemical studies in the human LC is interference with the staining of the immunocytochemical end-product by the omnipresent natural brown pigment neuromelanin. Here, we used a multispectral method to untangle the two colors: blue immunocytochemical staining and brown neuromelanin. We found significantly increased tyrosine hydroxylase (TH) in the LC of MDD patients-thus validating the method-but not in BD patients, and we did not find significant changes in the receptor tyrosine-protein kinase ErbB4 in the LC in MDD or BD patients. We observed clear co-localization of ErbB4, TH, and neuromelanin in the LC neurons. The different stress-related molecular changes in the LC may contribute to the different clinical symptoms in MDD and BD.

Astroglial correlates of neuropsychiatric disease: From astrocytopathy to astrogliosis

Complex roles for astrocytes in health and disease continue to emerge, highlighting this class of cells as integral to function and dysfunction of the nervous system. In particular, escalating evidence strongly implicates a range of changes in astrocyte structure and function associated with neuropsychiatric diseases including major depressive disorder, schizophrenia, and addiction. These changes can range from astrocytopathy, degeneration, and loss of function, to astrogliosis and hypertrophy, and can be either adaptive or maladaptive. Evidence from the literature indicates a myriad of changes observed in astrocytes from both human postmortem studies as well as preclinical animal models, including changes in expression of glial fibrillary protein, as well as changes in astrocyte morphology and astrocyte-mediated regulation of synaptic function. In this review, we seek to provide a comprehensive assessment of these findings and consequently evidence for common themes regarding adaptations in astrocytes associated with neuropsychiatric disease. While results are mixed across conditions and models, general findings indicate decreased astrocyte cellular features and gene expression in depression, chronic stress and anxiety, but increased inflammation in schizophrenia. Changes also vary widely in response to different drugs of abuse, with evidence reflective of features of astrocytopathy to astrogliosis, varying across drug classes, route of administration and length of withdrawal.

Effects of glucocorticoids in depression: Role of astrocytes

Astrocytes or astroglia are heterogeneous cells, similar to neurons, that have different properties in different brain regions. The implications of steroid hormones on glial cells and stress-related pathologies have been studied previously. Glucocorticoids (GCs) that are released in response to stress have been shown to be deleterious to neurons in various brain regions. Further, in the light of the effect of GCs on astrocytes, several reports have shown the crucial role of glia. Still, much remains to be done to understand the stress-astrocytes-glucocorticoid interactions associated with the pathological consequences of various CNS disorders. This review is an attempt to summarize the effects of GCs and stress on astrocytes and its implications in depression.

Hippocampal astrocyte atrophy in a mouse depression model induced by corticosterone is reversed by fluoxetine instead of benzodiazepine diazepam

Astrocytes have become promising new agents against major depressive disorders (MDD) primarily due to the crucial role they play in the pathogenesis of such disorders. However, a simple and reliable animal model that can be used to screen for astrocyte-targeting antidepressants has not yet been developed. In this study, we utilized a repeated corticosterone (CORT) injection paradigm to develop a mouse depression model wherein we examined the occurrence of alterations in hippocampal astrocyte population by using two astrocytic markers, namely, glial fibrillary acidic protein (GFAP) and S100β. Moreover, we determined the effects of fluoxetine and diazepam on CORT-induced astrocytic alterations to assess the predictive validity. Results showed that repeated CORT injections showed no effects on the number of GFAP⁺ and S100β⁺ astrocytes, but they decreased the protrusion length of GFAP⁺ astrocytes and GFAP protein expression in the hippocampus. Furthermore, repeated CORT injections produced a sustained increase of S100β protein levels in the entire hippocampus of male mice. CORT-induced hippocampal astrocyte disruption was antagonized by chronic fluoxetine treatment. By contrast, the anxiolytic drug diazepam was ineffective in the same experimental setting. All these findings suggest that the repeated CORT injection paradigm produces the astrocytic alterations similar to those in MDD and can serve as a useful mouse model to screen antidepressants meant to target astrocytes. These observations can also help in further discussing the underlying mechanisms of CORT-induced astrocytic alterations.

Clinical Findings Documenting Cellular and Molecular Abnormalities of Glia in Depressive Disorders

Depressive disorders are complex, multifactorial mental disorders with unknown neurobiology. Numerous theories aim to explain the pathophysiology. According to the “gliocentric theory”, glial abnormalities are responsible for the development of the disease. The aim of this review article is to summarize the rapidly growing number of cellular and molecular evidences indicating disturbed glial functioning in depressive disorders. We focus here exclusively on the clinical studies and present the in vivo neuroimaging findings together with the postmortem molecular and histopathological data. Postmortem studies demonstrate glial cell loss while the in vivo imaging data reveal disturbed glial functioning and altered white matter microstructure. Molecular studies report on altered gene expression of glial specific genes. In sum, the clinical findings provide ample evidences on glial pathology and demonstrate that all major glial cell types are affected. However, we still lack convincing theories explaining how the glial abnormalities develop and how exactly contribute to the emotional and cognitive disturbances. Abnormal astrocytic functioning may lead to disturbed metabolism affecting ion homeostasis and glutamate clearance, which in turn, affect synaptic communication. Abnormal oligodendrocyte functioning may disrupt the connectivity of neuronal networks, while microglial activation indicates neuroinflammatory processes. These cellular changes may relate to each other or they may indicate different endophenotypes. A theory has been put forward that the stress-induced inflammation—mediated by microglial activation—triggers a cascade of events leading to damaged astrocytes and oligodendroglia and consequently to their dysfunctions. The clinical data support the “gliocentric” theory, but future research should clarify whether these glial changes are truly the cause or simply the consequences of this devastating disorder.

In Silico Preliminary Association of Ammonia Metabolism Genes GLS, CPS1, and GLUL with Risk of Alzheimer's Disease, Major Depressive Disorder, and Type 2 Diabetes

Ammonia is a toxic by-product of protein catabolism and is involved in changes in glutamate metabolism. Therefore, ammonia metabolism genes may link a range of diseases involving glutamate signaling such as Alzheimer's disease (AD), major depressive disorder (MDD), and type 2 diabetes (T2D). We analyzed data from a National Institute on Aging study with a family-based design to determine if 45 single nucleotide polymorphisms (SNPs) in glutaminase (GLS), carbamoyl phosphate synthetase 1 (CPS1), or glutamate-ammonia ligase (GLUL) genes were associated with AD, MDD, or T2D using PLINK software. HAPLOVIEW software was used to calculate linkage disequilibrium measures for the SNPs. Next, we analyzed the associated variations for potential effects on transcriptional control sites to identify possible functional effects of the SNPs. Of the SNPs that passed the quality control tests, four SNPs in the GLS gene were significantly associated with AD, two SNPs in the GLS gene were associated with T2D, and one SNP in the GLUL gene and three SNPs in the CPS1 gene were associated with MDD before Bonferroni correction. The in silico bioinformatic analysis suggested probable functional roles for six associated SNPs. Glutamate signaling pathways have been implicated in all these diseases, and other studies have detected similar brain pathologies such as cortical thinning in AD, MDD, and T2D. Taken together, these data potentially link GLS with AD, GLS with T2D, and CPS1 and GLUL with MDD and stimulate the generation of testable hypotheses that may help explain the molecular basis of pathologies shared by these disorders.

Trigeminal, Visceral and Vestibular Inputs May Improve Cognitive Functions by Acting through the Locus Coeruleus and the Ascending Reticular Activating System: A New Hypothesis

It is known that sensory signals sustain the background discharge of the ascending reticular activating system (ARAS) which includes the noradrenergic locus coeruleus (LC) neurons and controls the level of attention and alertness. Moreover, LC neurons influence brain metabolic activity, gene expression and brain inflammatory processes. As a consequence of the sensory control of ARAS/LC, stimulation of a sensory channel may potential influence neuronal activity and trophic state all over the brain, supporting cognitive functions and exerting a neuroprotective action. On the other hand, an imbalance of the same input on the two sides may lead to an asymmetric hemispheric excitability, leading to an impairment in cognitive functions. Among the inputs that may drive LC neurons and ARAS, those arising from the trigeminal region, from visceral organs and, possibly, from the vestibular system seem to be particularly relevant in regulating their activity. The trigeminal, visceral and vestibular control of ARAS/LC activity may explain why these input signals: (1) affect sensorimotor and cognitive functions which are not directly related to their specific informational content; and (2) are effective in relieving the symptoms of some brain pathologies, thus prompting peripheral activation of these input systems as a complementary approach for the treatment of cognitive impairments and neurodegenerative disorders.

Neuropathology of suicide: recent findings and future directions

Suicide is a major public health concern and a leading cause of death in most societies. Suicidal behaviour is complex and heterogeneous, likely resulting from several causes. It associates with multiple factors, including psychopathology, personality traits, early-life adversity and stressful life events, among others. Over the past decades, studies in fields ranging from neuroanatomy, genetics and molecular psychiatry have led to a model whereby behavioural dysregulation, including suicidal behaviour (SB), develops as a function of biological adaptations in key brain systems. More recently, the unravelling of the unique epigenetic processes that occur in the brain has opened promising avenues in suicide research. The present review explores the various facets of the current knowledge on suicidality and discusses how the rapidly evolving field of neurobehavioural epigenetics may fuel our ability to understand, and potentially prevent, SB.