Astrocyte plasticity induced by emotional stress: A new partner in psychiatric physiopathology?

Intriguing astrocyte responses in CA1 to reduced and rehabilitated masticatory function: Dorsal and ventral distinct perspectives in adult mice

OBJECTIVE

We sought to investigate the plasticity of diet-induced changes in astrocyte morphology of stratum lacunosum-moleculare (SLM) in CA1.

DESIGN

Three diet regimes were adopted in 15 mice, from the 21st postnatal day to 6 months. The first diet regimen was pellet feed, called Hard Diet (HD). The second, with reduced masticatory, received a pellet-diet followed by a powdered-diet, and it was identified as Hard Diet/Soft Diet (HD/SD). Finally, the group with rehabilitated masticatory was named Hard Diet/Soft Diet/Hard Diet (HD/SD/HD). In the end, euthanasia and brain histological processing were performed, in which astrocytic immunoreactivity to glial-fibrillary-acidic-protein (GFAP) was tested. In reconstructed astrocytes, morphometric analysis was performed.

RESULTS

Astrocyte morphometric revealed that changes in masticatory regimens impact astrocyte morphology. In the dorsal CA1, switching from a hard diet to a soft diet led to reductions in most variables, whereas in the ventral, fewer variables were affected, highlighting regional differences in astrocyte responses. Cluster analysis further showed that diet-induced changes in astrocyte morphology were reversible in the dorsal region, but not in the ventral region, indicating a persistent impact on astrocyte diversity and complexity in the ventral even after rehabilitation. Correlation tests between astrocyte morphology and behavioral performance demonstrated disrupted relationships under masticatory stress, with effects persisting after rehabilitation.

CONCLUSION

Changes in the diet result in significant alterations in astrocyte morphology, suggesting a direct link between dietary modulation and cellular structure. Morphometric analyses revealed distinct alterations in astrocyte morphology in response to changes in the masticatory regimen, with both dorsal/ventral regions displaying notable changes. Moreover, the regional differential effects on astrocytes underscore the complexity of mastication on neuroplasticity and cognitive function.

Understanding stress-induced transmission of peripherally derived factors into the brain and responses in non-neuronal cells

Stress is a significant cause of mental disorders, for which effective treatments remain limited due to an insufficient understanding of its pathogenic mechanisms. Recent research has increasingly focused on non-neuronal cells to elucidate the molecular mechanisms underlying psychopathology. In this review, we summarize the current knowledge on how non-neuronal cells in the central nervous system, including microglia, astrocytes, and oligodendrocytes, respond to peripherally derived stress-related factors and how these responses contribute to the development of mental disorders. A more comprehensive understanding of stress-induced alterations, with careful consideration of the type and timing of stress exposure, will provide fundamental insights into the pathogenesis of diverse stress-related mental disorders.

Dynamic changes of media prefrontal cortex astrocytic activity in response to negative stimuli in male mice

Astrocytes play significant roles in regulating the central stress response. Chronic stress impairs the structure and function of astrocytes in many brain regions such as media prefrontal cortex (mPFC) in multiple neuropsychiatric conditions, but the astrocytic dynamics on the timescale of behavior remains unclear. Here, we recorded mPFC astrocytic activity in freely behaving mice and found that astrocytes are activated immediately by different aversive stimuli. Astrocyte specific GCaMP6s calcium indicator were virally expressed in mPFC astrocytes and fiber photometry experiments revealed that astrocytes are activated by tail-restraint (TRT), foot shock (FS), open arm exploration, stressor of height, predator odor and social defeat (SD) stress. ΔF/F analyses demonstrated that an unpredictable stimulus such as elevated platform stress (EPS) at the initial encounter induced the most intense and rapid changes in astrocytic calcium activity, while a predictable 2,5-dihydro-2,4,5-trimethylthiazoline (TMT) stimulus resulted in the weakest response with a longer peak latency. In TRT, FS or SD test, a somatic stimulus led to higher average calcium activity level and faster average peak latency in repeated trails. Similar to TMT stimulus, astrocytic calcium activity in elevated plus maze (EPM) test exhibited a smaller average change in amplitude and the longest peak latency during open arm exploration. Moreover, astrocytic calcium activity exhibited different changes across behavioral states in SD tests. Our findings show that mPFC astrocytes exhibit distinct patterns of calcium activity in response to various negative stimuli, indicating that the dynamic activity of astrocytes may reflect the stress-related behavioral state under different stimulus conditions.

Persistence of post-stress blood pressure elevation requires activation of astrocytes

The reflexive excitation of the sympathetic nervous system in response to psychological stress leads to elevated blood pressure, a condition that persists even after the stress has been alleviated. This sustained increase in blood pressure, which may contribute to the pathophysiology of hypertension, could be linked to neural plasticity in sympathetic nervous activity. Given the critical role of astrocytes in various forms of neural plasticity, we investigated their involvement in maintaining elevated blood pressure during the post-stress phase. Specifically, we examined the effects of arundic acid, an astrocytic inhibitor, on blood pressure and heart rate responses to air-jet stress. First, we confirmed that the inhibitory effect of arundic acid is specific to astrocytes. Using c-Fos immunohistology, we then observed that psychological stress activates neurons in cardiovascular brain regions, and that this stress-induced neuronal activation was suppressed by arundic acid pre-treatment in rats. By evaluating astrocytic process thickness, we also confirmed that astrocytes in the cardiovascular brain regions were activated by stress, and this activation was blocked by arundic acid pre-treatment. Next, we conducted blood pressure measurements on unanesthetized, unrestrained rats. Air-jet stress elevated blood pressure, which remained high for a significant period during the post-stress phase. However, pre-treatment with arundic acid, which inhibited astrocytic activation, suppressed stress-induced blood pressure elevation both during and after stress. In contrast, arundic acid had no significant impact on heart rate. These findings suggest that both neurons and astrocytes play integral roles in stress-induced blood pressure elevation and its persistence after stress, offering new insights into the pathophysiological mechanisms underlying hypertension.

Sex-dependent astrocyte reactivity: Unveiling chronic stress-induced morphological changes across multiple brain regions

Chronic stress is a major precursor to various neuropsychiatric disorders and is linked with increased inflammation in the brain. However, the bidirectional association between inflammation and chronic stress has yet to be fully understood. Astrocytes are one of the key inflammatory regulators in the brain, and the morphological change in reactive astrocytes serves as an important indicator of inflammation. In this study, we evaluated the sex-specific astrocyte response to chronic stress or systemic inflammation in key brain regions associated with mood disorders. We conducted the unpredictable chronic mild stress (UCMS) paradigm to model chronic stress, or lipopolysaccharide (LPS) injection to model systemic inflammation. To evaluate stress-induced morphological changes in astrocyte complexity, we measured GFAP fluorescent intensity for astrocyte expression, branch bifurcation by quantifying branch points and terminal points, branch arborization by conducting Sholl analysis, and calculated the ramification index. Our analysis indicated that chronic stress-induced morphological changes in astrocytes in all brain regions investigated. The effects of chronic stress were region and sex specific. Notably, females had greater stress or inflammation-induced astrocyte activation in the hypothalamus (HYPO), CA1, CA3, and amygdala (AMY) than males. These findings indicate that chronic stress induces astrocyte activation that may drive sex and region-specific effects in females, potentially contributing to sex-dependent mechanisms of disease.

Role of mitochondria-associated membranes in the hippocampus in the pathogenesis of depression

BACKGROUND

Pathological changes, such as microglia activation in the hippocampus frequently occur in individuals with animal models of depression; however, they may share a common cellular mechanism, such as endoplasmic reticulum (ER) stress and mitochondrial dysfunction. Mitochondria associated membranes (MAMs) are communication platforms between ER and mitochondria. This study aimed to investigate the role of intracellular stress responses, especially structural and functional changes of MAMs in depression.

METHODS

We used chronic social defeat stress (CSDS) to mimic depression in C57 mice to investigate the pathophysiological changes in the hippocampus associated with depression and assess the antidepressant effect of electroacupuncture (EA). Molecular, histological, and electron microscopic techniques were utilized to study intracellular stress responses, including the ER stress pathway reaction, mitochondrial damage, and structural and functional changes in MAMs in the hippocampus after CSDS. Proteomics technology was employed to explore protein-level changes in MAMs caused by CSDS.

RESULTS

CSDS caused mitochondrial dysfunction, ER stress, closer contact between ER and mitochondria, and enrichment of functional protein clusters at MAMs in hippocampus along with depressive-like behaviors. Also, EA showed beneficial effects on intracellular stress responses and depressive-like behaviors in CSDS mice.

LIMITATION

The cellular specificity of MAMs related protein changes in CSDS mice was not explored.

CONCLUSIONS

In the hippocampus, ER stress and mitochondrial damage occur, along with enriched mitochondria-ER interactions and MAM-related protein enrichment, which may contribute to depression's pathophysiology. EA may improve depression by regulating intracellular stress responses.

Chronic activation of a negative engram induces behavioral and cellular abnormalities

Negative memories engage a brain and body-wide stress response in humans that can alter cognition and behavior. Prolonged stress responses induce maladaptive cellular, circuit, and systems-level changes that can lead to pathological brain states and corresponding disorders in which mood and memory are affected. However, it is unclear if repeated activation of cells processing negative memories induces similar phenotypes in mice. In this study, we used an activity-dependent tagging method to access neuronal ensembles and assess their molecular characteristics. Sequencing memory engrams in mice revealed that positive (male-to-female exposure) and negative (foot shock) cells upregulated genes linked to anti- and pro-inflammatory responses, respectively. To investigate the impact of persistent activation of negative engrams, we chemogenetically activated them in the ventral hippocampus over 3 months and conducted anxiety and memory-related tests. Negative engram activation increased anxiety behaviors in both 6- and 14-month-old mice, reduced spatial working memory in older mice, impaired fear extinction in younger mice, and heightened fear generalization in both age groups. Immunohistochemistry revealed changes in microglial and astrocytic structure and number in the hippocampus. In summary, repeated activation of negative memories induces lasting cellular and behavioral abnormalities in mice, offering insights into the negative effects of chronic negative thinking-like behaviors on human health.

Role of amygdala astrocytes in different phases of contextual fear memory

Growing evidence indicates a critical role of astrocytes in learning and memory. However, little is known about the role of basolateral amygdala complex (BLA-C) astrocytes in contextual fear conditioning (CFC), a paradigm relevant to understand and generate treatments for fear- and anxiety-related disorders. To get insights on the involvement of BLA-C astrocytes in fear memory, fluorocitrate (FLC), a reversible astroglial metabolic inhibitor, was applied at critical moments of the memory processing in order to target the acquisition, consolidation, retrieval and reconsolidation process of the fear memory. Adult Wistar male rats were bilaterally cannulated in BLA-C. Ten days later they were infused with different doses of FLC (0.5 or 1 nmol/0.5 µl) or saline before or after CFC and before or after retrieval. FLC impaired fear memory expression when administered before and shortly after CFC, but not one hour later. Infusion of FLC prior and after retrieval did not affect the memory. Our findings suggest that BLA-C astrocytes are critically involved in the acquisition/early consolidation of fear memory but not in the retrieval and reconsolidation. Furthermore, the extinction process was presumably not affected (considering that peri-retrieval administration could also affect this process).

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.

The impact of early life stress and schizophrenia on motor and cognitive functioning: an experimental study

Background

Early life stress (ELS) and parental psychopathology, such as schizophrenia (SZ), have been associated with altered neurobiological and behavioral outcomes later in life. Previous studies have investigated the effects of ELS and parental SZ on various aspects of behavior, however, we have studied the combined effects of these stressors and how they interact, as individuals in real-life situations may experience multiple stressors simultaneously.

Objective

The aim of this study was to investigate the impact of ELS and schizophrenia on locomotor activity, anxiety-like behavior, exploratory tendencies, and spatial memory in Sprague Dawley (SD) rats.

Methods

Male and female SD pups were randomly assigned to eight groups: control, ELS, schizophrenia, and ELS + schizophrenia. ELS was induced by prenatal stress (maternal stress) and maternal separation (MS) during the first 2 weeks of life, while SZ was induced by subcutaneous administration of ketamine. Behavioral tests included an open field test (OFT) for motor abilities and a Morris water maze (MWM) for cognitive abilities. ANOVA and post hoc Tukey tests were utilized to analyze the data.

Results

Our results show that ELS and parental psychopathology had enduring effects on SZ symptoms, particularly psychomotor retardation (p < 0.05). The OFT revealed increased anxiety-like behavior in the ELS group (p = 0.023) and the parental psychopathology group (p = 0.017) compared to controls. The combined ELS and parental psychopathology group exhibited the highest anxiety-like behavior (p = 0.006). The MWM analysis indicated impaired spatial memory in the ELS group (p = 0.012) and the combined ELS and parental psychopathology group (p = 0.003) compared to controls. Significantly, the exposure to ELS resulted in a decrease in the population of glial fibrillary acidic protein-positive (GFAP+) astrocytes. However, this effect was reversed by positive parental mental health.

Conclusion

Our findings highlight the interactive effects of ELS and parental psychopathology on anxiety-like behavior and spatial memory in rats. ELS was linked to increased anxiety-like behavior, while SZ was associated with anhedonia-like behavior. Positive parenting augments neuroplasticity, synaptic function, and overall cognitive capacities.

Putative role of glial cells in treatment resistance depression: An updated critical literation review and evaluation of single-nuclei transcriptomics data

AIMS

Major depressive disorder (MDD) is a prevalent global mental illness with diverse underlying causes. Despite the availability of first-line antidepressants, approximately 10-30 % of MDD patients do not respond to these medications, falling into the category of treatment-resistant depression (TRD). Our study aimed to elucidate the precise molecular mechanisms through which glial cells contribute to depression-like episodes in TRD.

MATERIALS AND METHODS

We conducted a comprehensive literature search using the PubMed and Scopus electronic databases with search terms carefully selected to be specific to our topic. We strictly followed inclusion and exclusion criteria during the article selection process, adhering to PRISMA guidelines. Additionally, we carried out an in-depth analysis of postmortem brain tissue obtained from patients with TRD using single-nucleus transcriptomics (sn-RNAseq).

KEY FINDINGS

Our data confirmed the involvement of multiple glia-specific markers (25 genes) associated with TRD. These differentially expressed genes (DEGs) primarily regulate cytokine signaling, and they are enriched in important pathways such as NFκB and TNF-α. Notably, DEGs showed significant interactions with the transcription factor CREB1. sn-RNAseq analysis confirmed dysregulation of nearly all designated DEGs; however, only Cx30/43, AQP4, S100β, and TNF-αR1 were significantly downregulated in oligodendrocytes (OLGs) of TRD patients. With further exploration, we identified the GLT-1 in OLGs as a hub gene involved in TRD.

SIGNIFICANCE

Our findings suggest that glial dysregulation may hinder the effectiveness of existing therapies for TRD. By targeting specific glial-based genes, we could develop novel interventions with minimal adverse side effects, providing new hope for TRD patients who currently experience limited benefits from invasive treatments.

The role of astrocytes in behaviors related to emotion and motivation

Astrocytes are present throughout the brain and intimately interact with neurons and blood vessels. Three decades of research have shown that astrocytes reciprocally communicate with neurons and other non-neuronal cells in the brain and dynamically regulate cell function. Astrocytes express numerous receptors for neurotransmitters, neuromodulators, and cytokines and receive information from neurons, other astrocytes, and other non-neuronal cells. Among those receptors, the main focus has been G-protein coupled receptors. Activation of G-protein coupled receptors leads to dramatic changes in intracellular signaling (Ca²⁺ and cAMP), which is considered a form of astrocyte activity. Methodological improvements in measurement and manipulation of astrocytes have advanced our understanding of the role of astrocytes in circuits and have begun to reveal unexpected functions of astrocytes in behavior. Recent studies have suggested that astrocytic activity regulates behavior flexibility, such as coping strategies for stress exposure, and plays an important role in behaviors related to emotion and motivation. Preclinical evidence suggests that impairment of astrocytic function contributes to psychiatric diseases, especially major depression. Here, we review recent progress on the role of astrocytes in behaviors related to emotion and motivation.

Human Astrocyte Spheroids as Suitable In Vitro Screening Model to Evaluate Synthetic Cannabinoid MAM2201-Induced Effects on CNS

There is growing concern about the consumption of synthetic cannabinoids (SCs), one of the largest groups of new psychoactive substances, its consequence on human health (general population and workers), and the continuous placing of new SCs on the market. Although drug-induced alterations in neuronal function remain an essential component for theories of drug addiction, accumulating evidence indicates the important role of activated astrocytes, whose essential and pleiotropic role in brain physiology and pathology is well recognized. The study aims to clarify the mechanisms of neurotoxicity induced by one of the most potent SCs, named MAM-2201 (a naphthoyl-indole derivative), by applying a novel three-dimensional (3D) cell culture model, mimicking the physiological and biochemical properties of brain tissues better than traditional two-dimensional in vitro systems. Specifically, human astrocyte spheroids, generated from the D384 astrocyte cell line, were treated with different MAM-2201 concentrations (1-30 µM) and exposure times (24-48 h). MAM-2201 affected, in a concentration- and time-dependent manner, the cell growth and viability, size and morphological structure, E-cadherin and extracellular matrix, CB1-receptors, glial fibrillary acidic protein, and caspase-3/7 activity. The findings demonstrate MAM-2201-induced cytotoxicity to astrocyte spheroids, and support the use of this human 3D cell-based model as species-specific in vitro tool suitable for the evaluation of neurotoxicity induced by other SCs.

Rapid volumetric brain changes after acute psychosocial stress

Stress is an important trigger for brain plasticity: Acute stress can rapidly affect brain activity and functional connectivity, and chronic or pathological stress has been associated with structural brain changes. Measures of structural magnetic resonance imaging (MRI) can be modified by short-term motor learning or visual stimulation, suggesting that they also capture rapid brain changes. Here, we investigated volumetric brain changes (together with changes in T1 relaxation rate and cerebral blood flow) after acute stress in humans as well as their relation to psychophysiological stress measures. Sixty-seven healthy men (25.8±2.7 years) completed a standardized psychosocial laboratory stressor (Trier Social Stress Test) or a control version while blood, saliva, heart rate, and psychometrics were sampled. Structural MRI (T1 mapping / MP2RAGE sequence) at 3T was acquired 45 min before and 90 min after intervention onset. Grey matter volume (GMV) changes were analysed using voxel-based morphometry. Associations with endocrine, autonomic, and subjective stress measures were tested with linear models. We found significant group-by-time interactions in several brain clusters including anterior/mid-cingulate cortices and bilateral insula: GMV was increased in the stress group relative to the control group, in which several clusters showed a GMV decrease. We found a significant group-by-time interaction for cerebral blood flow, and a main effect of time for T1 values (longitudinal relaxation time). In addition, GMV changes were significantly associated with state anxiety and heart rate variability changes. Such rapid GMV changes assessed with VBM may be induced by local tissue adaptations to changes in energy demand following neural activity. Our findings suggest that endogenous brain changes are counteracted by acute psychosocial stress, which emphasizes the importance of considering homeodynamic processes and generally highlights the influence of stress on the brain.

Hippocampal astrocytes modulate anxiety-like behavior

Astrocytes can affect animal behavior by regulating tripartite synaptic transmission, yet their influence on affective behavior remains largely unclear. Here we showed that hippocampal astrocyte calcium activity reflects mouse affective state during virtual elevated plus maze test using two-photon calcium imaging in vivo. Furthermore, optogenetic hippocampal astrocyte activation elevating intracellular calcium induced anxiolytic behaviors in astrocyte-specific channelrhodopsin 2 (ChR2) transgenic mice (hGFAP-ChR2 mice). As underlying mechanisms, we found ATP released from the activated hippocampal astrocytes increased excitatory synaptic transmission in dentate gyrus (DG) granule cells, which exerted anxiolytic effects. Our data uncover a role of hippocampal astrocytes in modulating mice anxiety-like behaviors by regulating ATP-mediated synaptic homeostasis in hippocampal DG granule cells. Thus, manipulating hippocampal astrocytes activity can be a therapeutic strategy to treat anxiety.

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

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

Beyond the neuron: Role of non-neuronal cells in stress disorders

Stress disorders are leading causes of disease burden in the U.S. and worldwide, yet available therapies are fully effective in less than half of all individuals with these disorders. Although to date, much of the focus has been on neuron-intrinsic mechanisms, emerging evidence suggests that chronic stress can affect a wide range of cell types in the brain and periphery, which are linked to maladaptive behavioral outcomes. Here, we synthesize emerging literature and discuss mechanisms of how non-neuronal cells in limbic regions of brain interface at synapses, the neurovascular unit, and other sites of intercellular communication to mediate the deleterious, or adaptive (i.e., pro-resilient), effects of chronic stress in rodent models and in human stress-related disorders. We believe that such an approach may one day allow us to adopt a holistic "whole body" approach to stress disorder research, which could lead to more precise diagnostic tests and personalized treatment strategies. Stress is a major risk factor for many psychiatric disorders. Cathomas et al. review new insight into how non-neuronal cells mediate the deleterious effects, as well as the adaptive, protective effects, of stress in rodent models and human stress-related disorders.

Astroglia Abnormalities in Post-stroke Mood Disorders

Stroke is the leading cause of human death and disability. After a stroke, many patients may have some physical disability, including difficulties in moving, speaking, and seeing, but patients may also exhibit changes in mood manifested by depression, anxiety, and cognitive changes which we call post-stroke mood disorders (PSMDs). Astrocytes are the most diverse and numerous glial cell type in the central nervous system (CNS). They provide structural, nutritional, and metabolic support to neurons and regulate synaptic activity under normal conditions. Astrocytes are also critically involved in focal ischemic stroke (FIS). They undergo many changes after FIS. These changes may affect acute neuronal death and brain damage as well as brain recovery and PSMD in the chronic phase after FIS. Studies using postmortem brain specimens and animal models of FIS suggest that astrocytes/reactive astrocytes are involved in PSMD. This chapter provides an overview of recent advances in the molecular base of astrocyte in PSMD. As astrocytes exhibit high plasticity after FIS, we suggest that targeting local astrocytes may be a promising strategy for PSMD therapy.

Korean red ginseng alleviate depressive disorder by improving astrocyte gap junction function

ETHNOPHARMACOLOGICAL RELEVANCE

Korean red ginseng (KRG), a processed product of Panax ginseng C. A. Mey, show significant anti-depressive effect in clinic. However, its mechanism is still unclear.

AIM OF THE STUDY

Gap junction intercellular communication (GJIC) dysfunction is a potential pathogenesis of depression. Therefore, this study's objective is to investigate whether the antidepressant effect of KRG is related to GJIC.

MATERIALS AND METHODS

Rat were restraint 8 h every day for 28 consecutive days to prepare depression models, and meanwhile, rats were intragastrically administrated with normal saline, KRG solutions (25, 50 or 100 mg/kg) or fluoxetine (10 mg/kg) 1 h before stress. The behavioral performance was determined by forced swimming test, sucrose preference test and open field test. GJIC was determined by the Lucifer yellow (LY) diffusion distance in prelimb cortex (PLC). In addition, the level of Cx43, one of executors of GJIC, was tested by Western blot. To find out the protective effect of KRG against GJIC dysfunction directly, rats were intracranially injected with carbenoxolone (CBX, blocker of GJIC), and meanwhile normal saline, KRG (100 mg/kg) or fluoxetine (10 mg/kg) was administered daily. The behavioral performance of these rats was detected, and the LY localization injection PLC area was used to detect the gap junction function.

RESULTS

Chronic resistant stress (CRS) induced depressive symptoms, as manifested by prolonged immobility time in forced swimming test and decreased sucrose consumption ratio. Administration of KRG alleviated these depressive symptoms significantly. GJIC determination showed that KRG improved the LY diffusion and increased Cx43 level in prefrontal cortex (PFC) significantly, indicated that GJIC dysfunction was alleviated by the treatment of KRG. However, the astrocytes number was also increased by the treatment of KRG, which maybe alleviate depression-like symptoms by increasing the number of astrocytes rather than improving GJIC. Injection of CBX produced depressive symptoms and GJIC dysfunction, as manifested by decreased sucrose consumption ratio and prolonged immobility time in forced swimming test, but no astrocytes number changes, KRG also reversed depressive symptoms and GJIC dysfunction, suggested that the improvement of depressive-like symptoms was improved by GJIC.

CONCLUSIONS

KRG alleviate depressive disorder by improving astrocytic gap junction function.

Tak1 in the astrocytes of mediobasal hypothalamus regulates anxiety-like behavior in mice

Anxiety disorder is characterized by excessive fear, anxiety, and avoidance of perceived threats in internal to oneself or the environment, however, the underlying mechanisms are less well understood. Here, we show that transforming growth factor-β-activated kinase 1 (Tak1) expressed in the astrocytes of mediobasal hypothalamus (MBH) plays a crucial role in anxiety-like behavior in mice. Our data demonstrate that deficiency of Tak1 in astrocytes increased anxiety level, but did not impact locomotor activity in mice. Astrocytic activation of Tak1 in the MBH mitigated the anxiety-like behavior, whereas suppression of Tak1 in MBH astrocytes promoted the anxiety-like behavior in mice. Collectively, these data suggest that Tak1 expressed in the MBH astrocytes could modulate the anxiety-like behavior in mice.

Tetragonia tetragonioides Relieves Depressive-Like Behavior through the Restoration of Glial Loss in the Prefrontal Cortex

Tetragonia tetragonioides, which is a halophyte and grows widely in Asian-Pacific regions, has been used for the treatment of digestive disorders in traditional oriental medicine. This study examined the potential antidepressant effect of Tetragonia tetragonioides in an astroglial degeneration model of depression, which was established based on the postmortem study of depressive patients' brain presenting diminished astrocytes in the prefrontal cortex. C57BL/6 male mice were exposed to glial ablation in the prefrontal cortex by the administration of the gliotoxin, L-alpha-aminoadipic acid (L-AAA) to induce depression. Tetragonia tetragonioides at doses of 100 mg/kg and 300 mg/kg, imipramine at a dose of 15 mg/kg, and distilled water were orally administrated to mice for 18 days. Behavioral tests including the open field test (OFT), sucrose preference test (SPT), forced swimming test (FST), and tail suspension test (TST) were carried out after 2 days of L-AAA injection. The expression levels of GFAP and NeuN in the prefrontal cortex were determined by immunohistochemistry. Mice subjected to glial ablation in the prefrontal cortex displayed decreased sucrose consumption in SPT and increased immobility time in FST and TST. Treatment with imipramine and Tetragonia tetragonioides remarkably ameliorated the behavioral despair induced by L-AAA. In addition, immunohistochemistry analysis showed that treatment with Tetragonia tetragonioides significantly restored the glial loss as indicated by the elevated GFAP expression level. These findings suggest that Tetragonia tetragonioides exerts an antidepressant effect through the restoration of glial loss under conditions of depression and can be a candidate for an antidepressant agent.

Chronic stress followed by social isolation promotes depressive-like behaviour, alters microglial and astrocyte biology and reduces hippocampal neurogenesis in male mice

Unpredictable chronic mild stress (UCMS) is one of the most commonly used, robust and translatable models for studying the neurobiological basis of major depression. Although the model currently has multiple advantages, it does not entirely follow the trajectory of the disorder, whereby depressive symptomology can often present months after exposure to stress. Furthermore, patients with depression are more likely to withdraw in response to their stressful experience, or as a symptom of their depression, and, in turn, this withdrawal/isolation can further exacerbate the stressful experience and the depressive symptomology. Therefore, we investigated the effect(s) of 6 weeks of UCMS followed by another 6 weeks of social isolation (referred to as UCMSI), on behaviour, corticosterone stress responsivity, immune system functioning, and hippocampal neurogenesis, in young adult male mice. We found that UCMSI induced several behavioural changes resembling depression but did not induce peripheral inflammation. However, UCMSI animals showed increased microglial activation in the ventral dentate gyrus (DG) of the hippocampus and astrocyte activation in both the dorsal and ventral DG, with increased GFAP-positive cell immunoreactivity, GFAP-positive cell hypertrophy and process extension, and increased s100β-positive cell density. Moreover, UCMSI animals had significantly reduced neurogenesis in the DG and reduced levels of peripheral vascular endothelial growth factor (VEGF) - a trophic factor produced by astrocytes and that stimulates neurogenesis. Finally, UCMSI mice also had normal baseline corticosterone levels but a smaller increase in corticosterone following acute stress, that is, the Porsolt Swim Test. Our work gives clinically relevant insights into the role that microglial and astrocyte functioning, and hippocampal neurogenesis may play in the context of stress, social isolation and depression, offering a potentially new avenue for therapeutic target.

FKBP5 polymorphisms induce differential glucocorticoid responsiveness in primary CNS cells - First insights from novel humanized mice

The brain is a central hub for integration of internal and external conditions and, thus, a regulator of the stress response. Glucocorticoids are the essential communicators of this response. Aberrations in glucocorticoid signaling are a common symptom in patients with psychiatric disorders. The gene FKBP5 encodes a chaperone protein that functionally inhibits glucocorticoid signaling and, thus, contributes to the regulation of stress. In the context of childhood trauma, differential expression of FKBP5 has been found in psychiatric patients compared to controls. These variations in expression levels of FKBP5 were reported to be associated with differences in stress responsiveness in human carriers of the single nucleotide polymorphism (SNP) rs1360780. Understanding the mechanisms underlying FKBP5 polymorphism‐associated glucocorticoid responsiveness in the CNS will lead to a better understanding of stress regulation or associated pathology. To study these mechanisms, two novel humanized mouse lines were generated. The lines carried either the risk (A/T) allele or the resilient (C/G) allele of rs1360780. Primary cells from CNS (astrocytes, microglia, and neurons) were analyzed for their basal expression levels of FKBP5 and their responsiveness to glucocorticoids. Differential expression of FKBP5 was found for these cell types and negatively correlated with the cellular glucocorticoid responsiveness. Astrocytes revealed the strongest transcriptional response, followed by microglia and neurons. Furthermore, the risk allele (A/T) was associated with greater induction of FKBP5 than the resilience allele. Novel FKBP5‐humanized mice display differential glucocorticoid responsiveness due to a single intronic SNP. The vulnerability to stress signaling in the shape of glucocorticoids in the brain correlated with FKBP5 expression levels. The strong responsiveness of astrocytes to glucocorticoids implies astrocytes play a prominent role in the stress response, and in FKBP5‐related differences in glucocorticoid signaling. The novel humanized mouse lines will allow for further study of the role that FKBP5 SNPs have in risk and resilience to stress pathology.

Cellular mechanisms and molecular signaling pathways in stress-induced anxiety, depression, and blood-brain barrier inflammation and leakage

Depression and anxiety are comorbid conditions in many neurological or psychopathological disorders. Stress is an underlying event that triggers development of anxiety and depressive-like behaviors. Recent experimental data indicate that anxiety and depressive-like behaviors occurring as a result of stressful situations can cause blood-brain barrier (BBB) dysfunction, which is characterized by inflammation and leakage. However, the underlying mechanisms are not completely understood. This paper sought to review recent experimental preclinical and clinical data that suggest possible molecular mechanisms involved in development of stress-induced anxiety and depression with associated BBB inflammation and leakage. Critical therapeutic targets and potential pharmacological candidates for treatment of stress-induced anxiety and depression with associated BBB dysfunctions are also discussed.

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.

Emotional Stress Induces Structural Plasticity in Bergmann Glial Cells via an AC5-CPEB3-GluA1 Pathway

Stress alters brain function by modifying the structure and function of neurons and astrocytes. The fine processes of astrocytes are critical for the clearance of neurotransmitters during synaptic transmission. Thus, experience-dependent remodeling of glial processes is anticipated to alter the output of neural circuits. However, the molecular mechanisms that underlie glial structural plasticity are not known. Here we show that a single exposure of male and female mice to an acute stress produced a long-lasting retraction of the lateral processes of cerebellar Bergmann glial cells. These cells express the GluA1 subunit of AMPA-type glutamate receptors, and GluA1 knockdown is known to shorten the length of glial processes. We found that stress reduced the level of GluA1 protein and AMPA receptor-mediated currents in Bergmann glial cells, and these effects were absent in mice devoid of CPEB3, a protein that binds to GluA1 mRNA and regulates GluA1 protein synthesis. Administration of a β-adrenergic receptor blocker attenuated the reduction in GluA1, and deletion of adenylate cyclase 5 prevented GluA1 suppression. Therefore, stress suppresses GluA1 protein synthesis via an adrenergic/adenylyl cyclase/CPEB3 pathway, and reduces the length of astrocyte lateral processes. Our results identify a novel mechanism for GluA1 subunit plasticity in non-neuronal cells and suggest a previously unappreciated role for AMPA receptors in stress-induced astrocytic remodeling.SIGNIFICANCE STATEMENT Astrocytes play important roles in synaptic transmission by extending fine processes around synapses. In this study, we showed that a single exposure to an acute stress triggered a retraction of lateral/fine processes in mouse cerebellar astrocytes. These astrocytes express GluA1, a glutamate receptor subunit known to lengthen astrocyte processes. We showed that astrocytic structural changes are associated with a reduction of GluA1 protein levels. This requires activation of β-adrenergic receptors and is triggered by noradrenaline released during stress. We identified adenylyl cyclase 5, an enzyme that elevates cAMP levels, as a downstream effector and found that lowering GluA1 levels depends on CPEB3 proteins that bind to GluA1 mRNA. Therefore, stress regulates GluA1 protein synthesis via an adrenergic/adenylyl cyclase/CPEB3 pathway in astrocytes and remodels their fine processes.

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.

Astrocytic plasticity at the dorsal dentate gyrus on an animal model of recurrent depression

Astrocytes are now known to play crucial roles in the central nervous system, supporting and closely interacting with neurons and therefore able to modulate brain function. Both human postmortem studies in brain samples from patients diagnosed with Major Depressive Disorder and from animal models of depression reported numerical and morphological astrocytic changes specifically in the hippocampus. In particular, these studies revealed significant reductions in glial cell density denoted by a decreased number of S100B-positive cells and a decrease in GFAP expression in several brain regions including the hippocampus. To reveal plastic astrocytic changes in the context of recurrent depression, we longitudinally assessed dynamic astrocytic alterations (gene expression, cell densities and morphologic variations) in the hippocampal dentate gyrus under repeated exposure to unpredictable chronic mild stress (uCMS) and upon treatment with two antidepressants, fluoxetine and imipramine. Both antidepressants decreased astrocytic complexity immediately after stress exposure. Moreover, we show that astrocytic alterations, particularly an increased number of S100B-positive cells, are observed after recurrent stress exposure. Interestingly, these alterations were prevented at the long-term by either fluoxetine or imipramine treatment.

Gonadal hormones differentially regulate sex-specific stress effects on glia in the medial prefrontal cortex

Women are more susceptible to various stress-linked psychopathologies, including depression. Dysfunction of the medial prefrontal cortex (mPFC) has been implicated in depression, and studies indicate sex differences in stress effects on mPFC structure and function. For example, chronic stress induces dendritic atrophy in the mPFC in male rats, yet dendritic growth in females. Recent findings suggest glial pathways toward depression. Glia are highly responsive to neuronal activity and function as critical regulators of synaptic plasticity. Preclinical models demonstrate stress-induced microglial activation in mPFC in males, yet deactivation in females. By contrast, stress reduces astrocyte complexity in mPFC in male rats, whereas the effects in females are unknown. Glia possess receptors for most gonadal hormones and gonadal hormones are known to modulate neuronal activity. Thus, gonadal hormones represent a potential mechanism underlying sex differences in glia, as well as divergent stress effects. Therefore, we examined the role of gonadal hormones in sex-specific stress effects on neuronal activity (ie FosB/ ΔFosB induction) and glia in the mPFC. The findings obtained indicate greater microglial activation in mPFC in females and a greater astrocyte area in males. Basal astrocyte morphology is modulated by androgens, whereas androgens or oestrogens dampen the microglial state in males. Astrocyte morphology is associated with neuronal activity in both sexes, regardless of hormonal condition. Chronic stress induced astrocytic atrophy in males, yet hypertrophy in females, with gonadal hormones partly regulating this difference. Stress effects on microglia are oestradiol-dependent in females. Taken together, these data suggest sex-specific, gonadal hormone-dependent stress effects on astrocytes and microglia in the mPFC.

Astrocyte, a Promising Target for Mood Disorder Interventions

Mood disorders have multiple phenotypes and complex underlying biological mechanisms and, as such, there are no effective therapeutic strategies. A review of recent work on the role of astrocytes in mood disorders is thus warranted, which we embark on here. We argue that there is tremendous potential for novel strategies for therapeutic interventions based on the role of astrocytes. Astrocytes are traditionally considered to have supporting roles within the brain, yet emerging evidence has shown that astrocytes have more direct roles in influencing brain function. Notably, evidence from postmortem human brain tissues has highlighted changes in glial cell morphology, density and astrocyte-related biomarkers and genes following mood disorders, indicating astrocyte involvement in mood disorders. Findings from animal models strongly imply that astrocytes not only change astrocyte morphology and physiological characteristics but also influence neural circuits via synapse structure and formation. This review pays particular attention to interactions between astrocytes and neurons and argues that astrocyte dysfunction affects the monoaminergic system, excitatory–inhibitory balance and neurotrophic states of local networks. Together, these studies provide a foundation of knowledge about the exact role of astrocytes in mood disorders. Importantly, we then change the focus from neurons to glial cells and the interactions between the two, so that we can understand newly proposed mechanisms underlying mood disorders, and to identify more diagnostic indicators or effective targets for treatment of these diseases.

The reduction of astrocytes and brain volume loss in anorexia nervosa-the impact of starvation and refeeding in a rodent model

Anorexia nervosa (AN) is an often chronic, difficult to treat illness that leads to brain volume reductions in gray and white matter. The underlying pathophysiology is poorly understood, despite its potential importance in explaining the neuropsychological deficits and clinical symptoms associated with the illness. We used the activity-based anorexia model (ABA), which includes food reduction and running wheel access in female rats to study brain changes after starvation and refeeding. Longitudinal animal MRI and post-mortem brain sections confirmed a reduction in the mean brain volumes of ABA animals compared to controls. In addition, the mean number of astrocytes was reduced by over 50% in the cerebral cortex and corpus callosum, while the mean number of neurons was unchanged. Furthermore, mean astrocytic GFAP mRNA expression was similarly reduced in the ABA animals, as was the mean cell proliferation rate, whereas the mean apoptosis rate did not increase. After refeeding, the starvation-induced effects were almost completely reversed. The observation of the astrocyte reduction in our AN animal model is an important new finding that could help explain starvation-induced neuropsychological changes in patients with AN. Astrocyte-targeted research and interventions could become a new focus for both AN research and therapy.

Stress Elicits Contrasting Effects on the Structure and Number of Astrocytes in the Amygdala versus Hippocampus

Stress causes divergent patterns of structural and physiological plasticity in the hippocampus versus amygdala. However, a majority of earlier studies focused primarily on neurons. Despite growing evidence for the importance of glia in health and disease, relatively little is known about how stress affects astrocytes. Further, previous work focused on hippocampal astrocytes. Hence, we examined the impact of chronic immobilization stress (2 h/d, 10 d), on the number and structure of astrocytes in the rat hippocampus and amygdala. We observed a reduction in the number of glial fibrillary acidic protein (GFAP)-positive astrocytes in the basal amygdala (BA), 1 d after the end of 10 d of chronic stress. Detailed morphometric analysis of individual dye-filled astrocytes also revealed a decrease in the neuropil volume occupied by these astrocytes in the BA, alongside a reduction in the volume fraction of fine astrocytic protrusions rather than larger dendrite-like processes. By contrast, the same chronic stress had no effect on the number or morphology of astrocytes in hippocampal area CA3. We also confirmed previous reports that chronic stress triggers dendritic hypertrophy in dye-filled BA principal neurons that were located adjacent to astrocytes that had undergone atrophy. Thus, building on earlier evidence for contrasting patterns of stress-induced plasticity in neurons across brain areas, our findings offer new evidence that the same stress can also elicit divergent morphological effects in astrocytes in the hippocampus versus the amygdala.

Norepinephrine stimulates glycogenolysis in astrocytes to fuel neurons with lactate

The mechanism of rapid energy supply to the brain, especially to accommodate the heightened metabolic activity of excited states, is not well-understood. We explored the role of glycogen as a fuel source for neuromodulation using the noradrenergic stimulation of glia in a computational model of the neural-glial-vasculature ensemble (NGV). The detection of norepinephrine (NE) by the astrocyte and the coupled cAMP signal are rapid and largely insensitive to the distance of the locus coeruleus projection release sites from the glia, implying a diminished impact for volume transmission in high affinity receptor transduction systems. Glucosyl-conjugated units liberated from glial glycogen by NE-elicited cAMP second messenger transduction winds sequentially through the glycolytic cascade, generating robust increases in NADH and ATP before pyruvate is finally transformed into lactate. This astrocytic lactate is rapidly exported by monocarboxylate transporters to the associated neuron, demonstrating that the astrocyte-to-neuron lactate shuttle activated by glycogenolysis is a likely fuel source for neuromodulation and enhanced neural activity. Altogether, the energy supply for both astrocytes and neurons can be supplied rapidly by glycogenolysis upon neuromodulatory stimulus.

Although efficient compared to computers, the human brain utilizes energy at 10-fold the rate of other organs by mass. How the brain is supplied with sufficient on-demand energy to support its activity in the absence of neuronal storage capacity remains unknown. Neurons are not capable of meeting their own energy requirements, instead energy supply in the brain is managed by an oligocellular cartel composed of neurons, glia and the local vasculature (NGV), wherein glia can provide the ergogenic metabolite lactate to the neuron in a process called the astrocyte-to-neuron shuttle (ANLS). The only means of energy storage in the brain is glycogen, a polymerized form of glucose that is localized largely to astrocytes, but its exact role and conditions of use are not clear. In this computational model we show that neuromodulatory stimulation by norepinephrine induces astrocytes to recover glucosyl subunits from glycogen for use in a glycolytic process that favors the production of lactate. The ATP and NADH produced support metabolism in the astrocyte while the lactate is exported to feed the neuron. Thus, rapid energy demands by both neurons and glia in a stimulated brain can be met by glycogen mobilization.

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.

Prior stress promotes the generalization of contextual fear memories: Involvement of the gabaergic signaling within the basolateral amygdala complex

Fear generalization occurs when a response, previously acquired with a threatening stimulus, is transferred to a similar one. However, it could be maladaptive when stimuli that do not represent a real threat are appraised as dangerous, which is a hallmark of several anxiety disorders. Stress exposure is a major risk factor for the occurrence of anxiety disorders and it is well established that it influences different phases of fear memory; nevertheless, its impact on the generalization of contextual fear memories has been less studied. In the present work, we have characterized the impact of acute restraint stress prior to contextual fear conditioning on the generalization of this fear memory, and the role of the GABAergic signaling within the basolateral amygdala complex (BLA) on the stress modulatory effects. We have found that a single stress exposure promoted the generalization of this memory trace to a different context that was well discriminated in unstressed conditioned animals. Moreover, this effect was dependent on the formation of a contextual associative memory and on the testing order (i.e., conditioning context first vs generalization context first). Furthermore, we observed that increasing GABA-A signaling by intra-BLA midazolam administration prior to the stressful session exposure prevented the generalization of fear memory, whereas intra-BLA administration of the GABA-A antagonist (Bicuculline), prior to fear conditioning, induced the generalization of fear memory in unstressed rats. We concluded that stress exposure, prior to contextual fear conditioning, promotes the generalization of fear memory and that the GABAergic transmission within the BLA has a critical role in this phenomenon.

Integrating Genetic and Gene Co-expression Analysis Identifies Gene Networks Involved in Alcohol and Stress Responses

Although the link between stress and alcohol is well recognized, the underlying mechanisms of how they interplay at the molecular level remain unclear. The purpose of this study is to identify molecular networks underlying the effects of alcohol and stress responses, as well as their interaction on anxiety behaviors in the hippocampus of mice using a systems genetics approach. Here, we applied a gene co-expression network approach to transcriptomes of 41 BXD mouse strains under four conditions: stress, alcohol, stress-induced alcohol and control. The co-expression analysis identified 14 modules and characterized four expression patterns across the four conditions. The four expression patterns include up-regulation in no restraint stress and given an ethanol injection (NOE) but restoration in restraint stress followed by an ethanol injection (RSE; pattern 1), down-regulation in NOE but rescue in RSE (pattern 2), up-regulation in both restraint stress followed by a saline injection (RSS) and NOE, and further amplification in RSE (pattern 3), and up-regulation in RSS but reduction in both NOE and RSE (pattern 4). We further identified four functional subnetworks by superimposing protein-protein interactions (PPIs) to the 14 co-expression modules, including γ-aminobutyric acid receptor (GABA) signaling, glutamate signaling, neuropeptide signaling, cAMP-dependent signaling. We further performed module specificity analysis to identify modules that are specific to stress, alcohol, or stress-induced alcohol responses. Finally, we conducted causality analysis to link genetic variation to these identified modules, and anxiety behaviors after stress and alcohol treatments. This study underscores the importance of integrative analysis and offers new insights into the molecular networks underlying stress and alcohol responses.

Reduced astrocyte density underlying brain volume reduction in activity-based anorexia rats

OBJECTIVES

Severe grey and white matter volume reductions were found in patients with anorexia nervosa (AN) that were linked to neuropsychological deficits while their underlying pathophysiology remains unclear. For the first time, we analysed the cellular basis of brain volume changes in an animal model (activity-based anorexia, ABA).

METHODS

Female rats had 24 h/day running wheel access and received reduced food intake until a 25% weight reduction was reached and maintained for 2 weeks.

RESULTS

In ABA rats, the volumes of the cerebral cortex and corpus callosum were significantly reduced compared to controls by 6% and 9%, respectively. The number of GFAP-positive astrocytes in these regions decreased by 39% and 23%, total astrocyte-covered area by 83% and 63%. In neurons no changes were observed. The findings were complemented by a 60% and 49% reduction in astrocyte (GFAP) mRNA expression.

CONCLUSIONS

Volumetric brain changes in ABA animals mirror those in human AN patients. These alterations are associated with a reduction of GFAP-positive astrocytes as well as GFAP expression. Reduced astrocyte functioning could help explain neuronal dysfunctions leading to symptoms of rigidity and impaired learning. Astrocyte loss could constitute a new research target for understanding and treating semi-starvation and AN.

Cerebrovascular dysfunction with stress and depression

Maintenance of adequate tissue perfusion through a dense network of cerebral microvessels is critical for the perseveration of normal brain function. Regulation of the cerebral blood flow has to ensure adequate delivery of nutrients and oxygen with moment-to-moment adjustments to avoid both hypo- and hyper-perfusion of the brain tissue. Even mild impairments of cerebral blood flow regulation can have significant implications on brain function. Evidence suggests that chronic stress and depression elicits multifaceted functional impairments to the cerebral microcirculation, which plays a critical role in brain health and the pathogenesis of stress-related cognitive impairment and cerebrovascular events. Identifying the functional and structural changes to the brain that are induced by stress is crucial for achieving a realistic understanding of how related illnesses, which are highly disabling and with a large economic cost, can be managed or reversed. This overview discusses the stress-induced alterations in neurovascular coupling with specific attention to cerebrovascular regulation (endothelial dependent and independent vasomotor function, microvessel density). The pathophysiological consequences of cerebral microvascular dysfunction with stress and depression are explored.

Modulation of Astrocyte Activity by Cannabidiol, a Nonpsychoactive Cannabinoid

The astrocytes have gained in recent decades an enormous interest as a potential target for neurotherapies, due to their essential and pleiotropic roles in brain physiology and pathology. Their precise regulation is still far from understood, although several candidate molecules/systems arise as promising targets for astrocyte-mediated neuroregulation and/or neuroprotection. The cannabinoid system and its ligands have been shown to interact and affect activities of astrocytes. Cannabidiol (CBD) is the main non-psychotomimetic cannabinoid derived from Cannabis. CBD is devoid of direct CB1 and CB2 receptor activity, but exerts a number of important effects in the brain. Here, we attempt to sum up the current findings on the effects of CBD on astrocyte activity, and in this way on central nervous system (CNS) functions, across various tested models and neuropathologies. The collected data shows that increased astrocyte activity is suppressed in the presence of CBD in models of ischemia, Alzheimer-like and Multiple-Sclerosis-like neurodegenerations, sciatic nerve injury, epilepsy, and schizophrenia. Moreover, CBD has been shown to decrease proinflammatory functions and signaling in astrocytes.

Preventive Effects of Ginseng Total Saponins on Chronic Corticosterone-Induced Impairment in Astrocyte Structural Plasticity and Hippocampal Atrophy

To further explore the underlying antidepressant mechanism of ginseng total saponins (GTS), this study observed the effects on hippocampal astrocyte structural plasticity and hippocampal volume in the corticosterone-induced mouse depression model. Corticosterone (20 mg/kg/day) was administered subcutaneously for 5 weeks, and GTS (12.5, 25, and 50 mg/kg/day; namely GTSL, GTSM, and GTSH) or fluoxetine (10 mg/kg/day) were given intragastrically during the last 3 weeks. On day 33 and day 34, depression-like behavior was observed via a forced swimming test and a tail suspension test, respectively. At 6 h after the last dose of corticosterone (day 35), all mice were sacrificed followed by serum corticosterone assays, stereological analysis of hippocampal glial fibrillary acidic protein-positive (GFAP⁺ ) astroctyes and hippocampal volume, and hippocampal glycogen tests. Results showed that all doses of GTS ameliorated depression-like behavior and the decrease in hippocampal glycogen without normalizing hypercortisolism. Moreover, GTSH and GTSM reversed the corticosterone-induced reduction in the total number of hippocampal GFAP⁺ astrocytes and hippocampal volume. Additionally, GTSH alleviated the diminished protrusion length and somal volume of GFAP⁺ astrocytes induced by corticosterone. These findings imply that the effects of GTS on corticosterone-induced depression-like behavior may be mediated partly through the protection to hippocampal astrocyte structural plasticity. Copyright © 2017 John Wiley & Sons, Ltd.

Decreased Glycogen Content Might Contribute to Chronic Stress-Induced Atrophy of Hippocampal Astrocyte volume and Depression-like Behavior in Rats

The involvement of brain glycogen in the progress of chronic stress-induced impairment of hippocampal astrocyte structural plasticity and depression-like behavior is yet to be clarified. The present study designed three experiments to determine the role of brain glycogen in the plasticity and behavioral consequences of chronic stress. Time course studies on brain glycogen, astrocytes, and behavioral responses to stress were conducted in Experiment 1. Chronic stress decreased the hippocampal glycogen levels, reduced astrocytic size and protrusion length in the hippocampus, and induced depression-like behavior. Glycogen synthase 1 mRNA in the hippocampus was silenced by lentiviral vector-based RNA interference (RNAi) in Experiment 2. This RNAi produced a lack of glycogen in the hippocampus, decreased the hippocampal astrocyte size, and induced depressive behavior in rats. The mechanisms of chronic stress-induced brain glycogen decrease were investigated in Experiment 3. Chronic stress promoted hippocampal glycogen breakdown and increased hippocampal glycogen synthesis. Results suggest that decreased glycogen content was associated with chronic stress-induced atrophy of hippocampal astrocyte size and depression-like behavior. Furthermore, the decrease of glycogen content in the hippocampus might be due to the compensation of glycogen synthesis for breakdown in an insufficient manner.