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

Brain region-specific roles of brain-derived neurotrophic factor in social stress-induced depressive-like behavior

Brain-derived neurotrophic factor is a key factor in stress adaptation and avoidance of a social stress behavioral response. Recent studies have shown that brain-derived neurotrophic factor expression in stressed mice is brain region-specific, particularly involving the corticolimbic system, including the ventral tegmental area, nucleus accumbens, prefrontal cortex, amygdala, and hippocampus. Determining how brain-derived neurotrophic factor participates in stress processing in different brain regions will deepen our understanding of social stress psychopathology. In this review, we discuss the expression and regulation of brain-derived neurotrophic factor in stress-sensitive brain regions closely related to the pathophysiology of depression. We focused on associated molecular pathways and neural circuits, with special attention to the brain-derived neurotrophic factor-tropomyosin receptor kinase B signaling pathway and the ventral tegmental area-nucleus accumbens dopamine circuit. We determined that stress-induced alterations in brain-derived neurotrophic factor levels are likely related to the nature, severity, and duration of stress, especially in the above-mentioned brain regions of the corticolimbic system. Therefore, BDNF might be a biological indicator regulating stress-related processes in various brain regions.

Pro-inflammatory cytokines in stress-induced depression: Novel insights into mechanisms and promising therapeutic strategies

Stress-mediated depression is one of the common psychiatric disorders with a high prevalence and suicide rate, there is a lack of effective treatment. Accordingly, effective treatments with few adverse effects are urgently needed. Pro-inflammatory cytokines (PICs) may play a key role in stress-mediated depression. Thereupon, both preclinical and clinical studies have found higher levels of IL-1β, TNF-α and IL-6 in peripheral blood and brain tissue of patients with depression. Recent studies have found PICs cause depression by affecting neuroinflammation, monoamine neurotransmitters, hypothalamic pituitary adrenal axis and neuroplasticity. Moreover, they play an important role in the symptom, development and progression of depression, maybe a potential diagnostic and therapeutic marker of depression. In addition, well-established antidepressant therapies have some relief on high levels of PICs. Importantly, anti-inflammatory drugs relieve depressive symptoms by reducing levels of PICs. Collectively, reducing PICs may represent a promising therapeutic strategy for depression.

Bergamot essential oil improves CUMS-induced depression-like behaviour in rats by protecting the plasticity of hippocampal neurons

Bergamot essential oil (BEO) is an extract of the bergamot fruit with significant neuroprotective effect. This study was to investigate the effects and the underlying mechanism of BEO in mitigating depression. GC-MS were used to identify its constituents. Antidepressive properties of BEO were evaluated by sucrose preference test (SPT), force swimming test (FST) and open field test (OFT). Nissl staining was used to determine the number of Nissl bodies in hippocampus (HIPP) of rats. Changes in HIPP dendritic length and dendritic spine density were detected by Golgi-Cox staining. Immunohistochemistry and Western blot were used to detect the postsynaptic density protein-95 (PSD-95) and synaptophysin (SYP) in the HIPP of rats. The enzyme-linked immunosorbent assay was used to determine the 5-hydroxytryptamine (5-HT), insulin-like growth factor 1 (IGF-1) and interleukin-1β (IL-1β) in the HIPP, serum and cerebrospinal fluid (CSF) of rats. Inhaled BEO significantly improved depressive behaviour in chronic unpredictable mild stress (CUMS) rats. BEO increased Nissl bodies, dendritic length and spine density, PSD-95 and SYP protein in the HIPP. Additionally, BEO upregulated serum 5-HT, serum and CSF IGF-1, while downregulating serum IL-1β. Collectively, inhaled BEO mitigates depression by protecting the plasticity of hippocampal neurons, hence, providing novel insights into treatment of depression.

Developmental perspectives on the origins of psychotic disorders: The need for a transdiagnostic approach

Research on serious mental disorders, particularly psychosis, has revealed highly variable symptom profiles and developmental trajectories prior to illness-onset. As Dante Cicchetti pointed out decades before the term "transdiagnostic" was widely used, the pathways to psychopathology emerge in a system involving equifinality and multifinality. Like most other psychological disorders, psychosis is associated with multiple domains of risk factors, both genetic and environmental, and there are many transdiagnostic developmental pathways that can lead to psychotic syndromes. In this article, we discuss our current understanding of heterogeneity in the etiology of psychosis and its implications for approaches to conceptualizing etiology and research. We highlight the need for examining risk factors at multiple levels and to increase the emphasis on transdiagnostic developmental trajectories as a key variable associated with etiologic subtypes. This will be increasingly feasible now that large, longitudinal datasets are becoming available and researchers have access to more sophisticated analytic tools, such as machine learning, which can identify more homogenous subtypes with the ultimate goal of enhancing options for treatment and preventive intervention.

Supraspinal neuroinflammation and anxio-depressive-like behaviors in young- and older- adult mice with osteoarthritis pain: the effect of morphine

RATIONALE

Asteoarthritis (OA) is a leading cause of chronic pain in the elderly population and is often associated with emotional comorbidities such as anxiety and depression. Despite age is a risk factor for both OA and mood disorders, preclinical studies are mainly conducted in young adult animals.

OBJECTIVES

Here, using young adult (11-week-old) and older adult (20-month-old) mice, we evaluate in a monosodium-iodoacetate-(MIA)-induced OA model the development of anxio-depressive-like behaviors and whether brain neuroinflammation may underlie the observed changes. We also test whether an effective pain treatment may prevent behavioral and biochemical alterations.

METHODS

Mechanical allodynia was monitored throughout the experimental protocol, while at the end of protocol (14 days), anxio-depressive-like behaviors and cognitive dysfunction were assessed. Neuroinflammatory condition was evaluated in prefrontal cortex, hippocampus and hypothalamus. Serum IFNγ levels were also measured. Moreover, we test the efficacy of a 1-week treatment with morphine (2.5 mg/kg) on pain, mood alterations and neuroinflammation.

RESULTS

We observed that young adult and older adult controls (CTRs) mice had comparable allodynic thresholds and developed similar allodynia after MIA injection. Older adult CTRs were characterized by altered behavior in the tests used to assess the presence of depression and cognitive impairment and by elevated neuroinflammatory markers in brain areas compared to younger ones. The presence of pain induced depressive-like behavior and neuroinflammation in adult young mice, anxiety-like behavior in both age groups and worsened neuroinflammation in older adult mice. Morphine treatment counteracted pain, anxio-depressive behaviors and neuroinflammatory activation in both young adult and older adult mice.

CONCLUSIONS

Here, we demonstrated that the presence of chronic pain in young adult mice induces mood alterations and supraspinal biochemical changes and aggravates the alterations already evident in older adult animals. A treatment with morphine, counteracting the pain, prevents the development of anxio-depressive disorders and reduces neuroinflammation.

Prokineticin System Is a Pharmacological Target to Counteract Pain and Its Comorbid Mood Alterations in an Osteoarthritis Murine Model

Osteoarthritis (OA) is the most prevalent joint disease associated with chronic pain. OA pain is often accompanied by mood disorders. We addressed the role of the Prokineticin (PK) system in pain and mood alterations in a mice OA model induced with monosodium iodoacetate (MIA). The effect of a PK antagonist (PC1) was compared to that of diclofenac. C57BL/6J male mice injected with MIA in the knee joint were characterized by allodynia, motor deficits, and fatigue. Twenty-eight days after MIA, in the knee joint, we measured high mRNA of PK2 and its receptor PKR1, pro-inflammatory cytokines, and MMP13. At the same time, in the sciatic nerve and spinal cord, we found increased levels of PK2, PKR1, IL-1β, and IL-6. These changes were in the presence of high GFAP and CD11b mRNA in the sciatic nerve and GFAP in the spinal cord. OA mice were also characterized by anxiety, depression, and neuroinflammation in the prefrontal cortex and hippocampus. In both stations, we found increased pro-inflammatory cytokines. In addition, PK upregulation and reactive astrogliosis in the hippocampus and microglia reactivity in the prefrontal cortex were detected. PC1 reduced joint inflammation and neuroinflammation in PNS and CNS and counteracted OA pain and emotional disturbances.

Stress circuitry: mechanisms behind nervous and immune system communication that influence behavior

Inflammatory processes are increased by stress and contribute to the pathology of mood disorders. Stress is thought to primarily induce inflammation through peripheral and central noradrenergic neurotransmission. In healthy individuals, these pro-inflammatory effects are countered by glucocorticoid signaling, which is also activated by stress. In chronically stressed individuals, the anti-inflammatory effects of glucocorticoids are impaired, allowing pro-inflammatory effects to go unchecked. Mechanisms underlying this glucocorticoid resistance are well understood, but the precise circuits and molecular mechanisms by which stress increases inflammation are not as well known. In this narrative review, we summarize the mechanisms by which chronic stress increases inflammation and contributes to the onset and development of stress-related mood disorders. We focus on the neural substrates and molecular mechanisms, especially those regulated by noradrenergic signaling, that increase inflammatory processes in stressed individuals. We also discuss key knowledge gaps in our understanding of the communication between nervous and immune systems during stress and considerations for future therapeutic strategies. Here we highlight the mechanisms by which noradrenergic signaling contributes to inflammatory processes during stress and how this inflammation can contribute to the pathology of stress-related mood disorders. Understanding the mechanisms underlying crosstalk between the nervous and immune systems may lead to novel therapeutic strategies for mood disorders and/or provide important considerations for treating immune-related diseases in individuals suffering from stress-related disorders.

Changes in Multiple microRNA Levels with Antidepressant Treatment Are Associated with Remission and Interact with Key Pathways: A Comprehensive microRNA Analysis

Individual treatment outcomes to antidepressants varies widely, yet the determinants to this difference remain elusive. MicroRNA (miRNA) gene expression regulation in major depressive disorder (MDD) has attracted interest as a biomarker. This 4-week randomized controlled trial examined changes in the plasma miRNAs that correlated with the treatment outcomes of mirtazapine (MIR) and selective serotonin reuptake inhibitor (SSRI) monotherapy. Pre- and post- treatment, we comprehensively analyzed the miRNA levels in MDD patients, and identified the gene pathways linked to these miRNAs in 46 patients. Overall, 141 miRNA levels significantly demonstrated correlations with treatment remission after 4 weeks of MIR, with miR-1237-5p showing the most robust and significant correlation after Bonferroni correction. These 141 miRNAs displayed a negative correlation with remission, indicating a decreasing trend. These miRNAs were associated with 15 pathways, including TGF-β and MAPK. Through database searches, the genes targeted by these miRNAs with the identified pathways were compared, and it was found that MAPK1, IGF1, IGF1R, and BRAF matched. Alterations in specific miRNAs levels before and after MIR treatment correlated with remission. The miRNAs mentioned in this study have not been previously reported. No other studies have investigated treatment with MIR. The identified miRNAs also correlated with depression-related genes and pathways.

A whole transcriptome profiling analysis for antidepressant mechanism of Xiaoyaosan mediated synapse loss via BDNF/trkB/PI3K signal axis in CUMS rats

BACKGROUND

Depression is a neuropsychiatric disease resulting from deteriorations of molecular networks and synaptic injury induced by stress. Traditional Chinese formula Xiaoyaosan (XYS) exert antidepressant effect, which was demonstrated by a great many of clinical and basic investigation. However, the exact mechanism of XYS has not yet been fully elucidated.

METHODS

In this study, chronic unpredictable mild stress (CUMS) rats were used as a model of depression. Behavioral test and HE staining were used to detect the anti-depressant effects of XYS. Furthermore, whole transcriptome sequencing was employed to establish the microRNA (miRNA), long non-coding RNA (lncRNA), circular RNA (circRNA), and mRNA profiles. The biological functions and potential mechanisms of XYS for depression were gathered from the GO and KEGG pathway. Then, constructed the competing endogenous RNA (ceRNA) networks to illustrate the regulatory relationship between non-coding RNA (ncRNA) and mRNA. Additionally, longest dendrite length, total length of dendrites, number of intersections, and density of dendritic spines were detected by Golgi staining. MAP2, PSD-95, SYN were detected by immunofluorescence respectively. BDNF, TrkB, p-TrkB, PI3K, Akt, p-Akt were measured by Western Blotting.

RESULTS

The results showed that XYS could increase the locomotor activity and sugar preference, decreased swimming immobility time as well as attenuate hippocampal pathological damage. A total of 753 differentially expressed lncRNAs (DElncRNAs), 28 circRNAs (DEcircRNAs), 101 miRNAs (DEmiRNAs), and 477 mRNAs (DEmRNAs) were identified after the treatment of XYS in whole transcriptome sequencing analysis. Enrichment results revealed that XYS could regulate multiple aspects of depression through different synapse or synaptic associated signal, such as neurotrophin signaling and PI3K/Akt signaling pathways. Then, vivo experiments indicated that XYS could promote length, density, intersections of synapses and also increase the expression of MAP2 in hippocampal CA1, CA3 regions. Meanwhile, XYS could increase the expression of PSD-95, SYN in the CA1, CA3 regions of hippocampal by regulating the BDNF/trkB/PI3K signal axis.

CONCLUSION

The possible mechanism on synapse of XYS in depression was successfully predicted. BDNF/trkB/PI3K signal axis were the potential mechanism of XYS on synapse loss for its antidepressant. Collectively, our results provided novel information about the molecular basis of XYS in treating depression.

Role of the mesolimbic dopamine pathway in the antidepressant effects of ketamine

Depression is a complex and highly heterogeneous disorder which diagnosis is based on an exceedingly variable set of clinical symptoms. Current treatments focus almost exclusively on the manipulation of monoamine neurotransmitter systems, but despite considerable efforts, these remain inadequate for a significant proportion of those afflicted by the disorder. The emergence of racemic (R, S)-ketamine as a fast-acting antidepressant has provided an exciting new path for the study of major depressive disorder (MDD) and the search for better therapeutics for its treatment. Previous work suggested that ketamine's mechanism of action is primarily mediated via blockaded of N-methyl-d-aspartate (NMDA) receptors, however, this is an area of active research and clinical and preclinical evidence now indicate that ketamine acts on multiple systems. The last couple of decades have cemented the mesolimbic dopamine reward pathway's involvement in the pathogenesis of MDD and related mood disorders. Exposure to negative stress dysregulates dopamine neuronal activity disrupting reward and motivational processes resulting in anhedonia (lack of pleasure), a hallmark symptom of depression. Although the mechanism(s) underlying ketamine's antidepressant activity continue to be elucidated, current evidence indicate that its therapeutic effects are mediated, at least in part, via long-lasting synaptic changes and subsequent molecular adaptations in brain regions within the mesolimbic dopamine system. Notwithstanding, ketamine is a drug of abuse, and this liability may pose limitations for long term use as an antidepressant. This review outlines the current knowledge of ketamine's actions within the mesolimbic dopamine system and its abuse potential. This article is part of the Special Issue on 'Ketamine and its Metabolites'.

Models of Affective Illness: Chronic Mild Stress in the Rat

This article describes a chronic mild stress (CMS) model for predicting antidepressant response and investigating mechanisms of antidepressant action in rats. Following exposure to a variety of mild stressors for several weeks, the rats' behavior is modified in several ways that parallel symptoms of depression. Among these is a substantial reduction in consumption of a 1% sucrose solution, which models the cardinal symptom of major depression, anhedonia. Our standard procedure employs a battery of behavioral tests, comprising weekly assessment of sucrose intake and, at the end of treatment, the elevated plus-maze and novel object recognition tests to assess the anxiogenic and dyscognitive effects of CMS. Chronic administration of antidepressant drugs reverses the decreased sucrose intake and other behavioral changes in these subjects. Also effective are second-generation antipsychotics. The CMS model can be employed in discovery programs to identify anti-anhedonic drugs (e.g., antidepressants and antipsychotics) that act more quickly than existing agents. While most antidepressants require 3 to 5 weeks to normalize behavior, some treatments provide a faster onset of action. For example, the CMS-induced deficits can be reversed by acute or sub-chronic application of treatments that act rapidly in depressed patients, such as deep brain stimulation (DBS), ketamine, and scopolamine, as well as several compounds that have yet to be tested in humans but have fast-onset antidepressant-like effects in animals, such as the 5-HT-1A biased agonists NLX-101 and GLYX-13. Application of the CMS model in Wistar-Kyoto (WKY) rats causes similar behavioral changes to those seen in Wistars, but these are not reversed by antidepressant treatment. However, WKY rats respond to DBS and ketamine, which are effective in patients who are antidepressant non-responders, establishing CMS in WKY rats as a model of treatment-resistant depression. © 2023 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol: Induction of chronic mild stress in rats as a model of depression and treatment-resistant depression.

StressMatic: A Novel Automated System to Induce Depressive- and Anxiety-like Phenotype in Rats

Major depressive disorder (MDD) is a multidimensional psychiatric disorder that is estimated to affect around 350 million people worldwide. Generating valid and effective animal models of depression is critical and has been challenging for neuroscience researchers. For preclinical studies, models based on stress exposure, such as unpredictable chronic mild stress (uCMS), are amongst the most reliable and used, despite presenting concerns related to the standardization of protocols and time consumption for operators. To overcome these issues, we developed an automated system to expose rodents to a standard uCMS protocol. Here, we compared manual (uCMS) and automated (auCMS) stress-exposure protocols. The data shows that the impact of the uCMS exposure by both methods was similar in terms of behavioral (cognition, mood, and anxiety) and physiological (cell proliferation and endocrine variations) measurements. Given the advantages of time and standardization, this automated method represents a step forward in this field of preclinical research.

Functional comorbidities and brain tissue changes before and after lung transplant in adults

Background

Adults undergoing lung transplant, as a lifesaving treatment for end stage lung disease, exhibit high levels of peri-operative neurocognitive dysfunction in multiple domains, including delirium, cognition, and autonomic deficits. These complications impact healthcare costs, quality of life, and patient outcomes. Post-operative symptoms likely result from loss of brain tissue integrity in sites mediating such regulatory functions. Our aim in this study was to examine peri-operative neurocognitive dysfunction and brain tissue changes after lung transplant in adults.

Methods

We retrospectively examined the UCLA lung transplant database to identify 114 lung transplant patients with pre-operative clinical and neurocognitive data. Of 114 patients, 9 lung transplant patients had pre- and post-transplant brain magnetic resonance imaging. Clinical and neurocognitive data were summarized for all subjects, and brain tissue volume changes, using T1-weighted images, before and after transplant were examined. T1-weighted images were partitioned into gray matter (GM)-tissue type, normalized to a common space, smoothed, and the smoothed GM-volume maps were compared between pre- and post-transplant (paired t-tests; covariate, age; SPM12, p < 0.005).

Results

Increased comorbidities, including the diabetes mellitus (DM), hypertension, kidney disease, and sleep disordered breathing, as well as higher rates of neurocognitive dysfunction were observed in the lung transplant patients, with 41% experiencing post-operative delirium, 49% diagnosed with a mood disorder, and 25% of patients diagnosed with cognitive deficits, despite incomplete documentation. Similarly, high levels of delirium, cognitive dysfunction, and mood disorder were noted in a subset of patients used for brain MRI evaluation. Significantly decreased GM volumes emerged in multiple brain regions, including the frontal and prefrontal, parietal, temporal, bilateral anterior cingulate and insula, putamen, and cerebellar cortices.

Conclusion

Adults undergoing lung transplant often show significant pre-operative comorbidities, including diabetes mellitus, hypertension, and chronic kidney disease, as well as neurocognitive dysfunction. In addition, patients with lung transplant show significant brain tissue changes in regions that mediate cognition, autonomic, and mood functions. The findings indicate a brain structural basis for many enhanced post-operative symptoms and suggest a need for brain tissue protection in adults undergoing lung transplant to improve health outcomes.

Hyperexcitability: From Normal Fear to Pathological Anxiety and Trauma

Hyperexcitability in fear circuits is suggested to be important for development of pathological anxiety and trauma from adaptive mechanisms of fear. Hyperexcitability is proposed to be due to acquired sensitization in fear circuits that progressively becomes more severe over time causing changing symptoms in early and late pathology. We use the metaphor and mechanisms of kindling to examine gains and losses in function of one excitatory and one inhibitory neuropeptide, corticotrophin releasing factor and somatostatin, respectively, to explore this sensitization hypothesis. We suggest amygdala kindling induced hyperexcitability, hyper-inhibition and loss of inhibition provide clues to mechanisms for hyperexcitability and progressive changes in function initiated by stress and trauma.

Activation of liver X receptors protects oligodendrocytes in CA3 of stress-induced mice

Depression is a complex disorder that is associated with various structural abnormalities. Oligodendrocyte (OL) dysfunction is associated with the pathogenesis of depression and the promotion of hippocampal oligodendrocyte maturation and myelination could be a novel therapeutic strategy for ameliorating depressive behaviors. Recent studies have shown that activation of liver X receptors (LXRs) by GW3965 improves depressive phenotypes, but the effects of GW3965 on OL function and myelination in the hippocampus of depression remain relatively unclear. To address this issue, we investigated the effects of GW3965 on mature OL in the hippocampus and on the myelin sheaths of mice subjected to chronic unpredictable stress (CUS). Behavioral tests were performed to assess depressive behaviors. Then, the number of mature OLs (CC1⁺) in each hippocampal subregion was precisely quantified with immunohistochemical and stereological methods, and the density of newborn mature OLs (BrdU⁺/Olig2⁺/CC1⁺ cells) in each hippocampal subregion was quantified with immunofluorescence. In addition, myelin basic protein (MBP) staining intensity in the cornu ammonis 3 (CA3) region was assessed by using immunofluorescence. We found that both the number of CC1⁺ OLs and the density of BrdU⁺/Olig2⁺/CC1⁺ cells were obviously decreased in each hippocampal subregion of mice subjected to CUS, and 4 weeks of GW3965 treatment reversed these effects only in the CA3 region. Furthermore, the decreased MBP expression in the CA3 region of mice subjected to CUS was ameliorated by GW3965 treatment. Collectively, these results suggested that improvement of OL maturation and enhancement of myelination may be structural mechanisms underlying the antidepressant effects of LXR agonists.

Chronic treatment with enhancer drugs modifies the gene expression of selected parameters related to brain plasticity in rats under stress conditions

Selegiline, also known as L-deprenyl, and (2R)-1-(1-benzofuran-2-yl)-N-propylpentane-2-amine (BPAP) were found to induce enhancement of monoamine neurotransmission in low and very low doses. In addition, these enhancers may modify glutamatergic neurotransmission. The aim of the present study was to test the hypothesis that under stress conditions, chronic treatment with enhancer drugs has a positive impact on the glutamatergic system and other parameters related to brain plasticity, stress-related systems, and anxiety behavior. We exposed male Wistar rats to a chronic mild stress procedure combined with chronic treatment with two synthetic enhancer drugs. The gene expression of GluR1, an AMPA receptor subunit was reduced by repeated treatment with deprenyl in the hippocampus and with both BPAP and deprenyl in the prefrontal cortex. A significant reduction of NMDA receptor subunit GluN2B expression was observed in the hippocampus but not in the prefrontal cortex. Deprenyl treatment led to an enhancement of hippocampal BDNFmRNA concentrations in stress-exposed rats. Treatment with enhancer drugs failed to induce significant changes in stress hormone concentrations or anxiety behavior. In conclusion, the present study in chronically stressed rats showed that concomitant treatment with enhancer drugs did not provoke substantial neuroendocrine changes, but modified gene expression of selected parameters associated with brain plasticity. Observed changes may indicate a positive influence of enhancer drugs on brain plasticity, which is important for preventing negative consequences of chronic stress and enhancement of stress resilience. It may be suggested that the changes in glutamate receptor subunits induced by enhancer drugs are brain region-specific and not dose-related.

Antidepressant-like Effects of Polygonum minus Aqueous Extract in Chronic Ultra-Mild Stress-Induced Depressive Mice Model

Depression is the most common behavior disorder that leads to many disabilities. The main aim of this study was to evaluate the effects of a Polygonum minus (P. minus) aqueous extract on chronic ultra-mild stress (CUMS)-induced depressive mice model. Chronic ultra-mild stress can disturb the neurotransmitters levels and plasticity of the hippocampus. Balb/c male mice were used in this study, which consisted of six groups (n = 14). Treatment was given for eight weeks, and chronic ultra-mild stress was applied for six weeks. Commercially available P. minus extract (BioKesum®) was used in this study. The behavior and neurochemical parameters were investigated through behavioral Tests and ELISA assays. P. minus administration significantly (p < 0.05) restored CUMS-induced behavior abnormalities, decreased the immobility time, and increased the sucrose preference and increased the spatial memory. P. minus treatment also showed the decreased level of serum corticosterone and increased the level of hippocampal neurotransmitters (Serotonin and Norepinephrine) significantly (p < 0.05). The brain-derived neurotrophic factor (BDNF) level also increased significantly in both the prefrontal cortex and hippocampus (p < 0.05). P. minus treatment exhibited significant (p < 0.05) reduction of Monoamine Oxidase-A (MAO-A) in the hippocampus. These findings indicate that P. minus aqueous extract exhibits antidepressant effects, including decreased immobility time, increased spatial memory, reduced corticosterone, increased BDNF level, and reduced MAO-A enzyme level with increasing the monoamines (serotonin and norepinephrine) in the hippocampus.

A Preliminary Quantitative Electron Microscopic Analysis Reveals Reduced Number of Mitochondria in the Infralimbic Cortex of Rats Exposed to Chronic Mild Stress

Exposure to severe, uncontrollable and long-lasting stress is a strong risk factor for the development of numerous mental and somatic disorders. Animal studies document that chronic stress can alter neuronal morphology and functioning in limbic brain structures such as the prefrontal cortex. Mitochondria are intracellular powerhouses generating chemical energy for biochemical reactions of the cell. Recent findings document that chronic stress can lead to changes in mitochondrial function and metabolism. Here, we studied putative mitochondrial damage in response to chronic stress in neurons of the medial prefrontal cortex. We performed a systematic quantitative ultrastructural analysis to examine the consequences of 9-weeks of chronic mild stress on mitochondria number and morphology in the infralimbic cortex of adult male rats. In this preliminary study, we analyzed 4,250 electron microscopic images and 67000 mitochondria were counted and examined in the brains of 4 control and 4 stressed rats. We found significantly reduced number of mitochondria in the infralimbic cortex of the stressed animals, but we could not detect any significant alteration in mitochondrial morphology. These data support the concept that prolonged stress can lead to mitochondrial loss. This in turn may result in impaired energy production. Reduced cellular energy may sensitize the neurons to additional injuries and may eventually trigger the development of psychopathologies.

Animal models of postpartum depression revisited

Postpartum depression (PPD) is a heterogeneous mood disorder and the most frequent psychiatric complication of the postnatal period. Given its potential long-lasting repercussions on the well-being of the mother and the infants, it should be a priority in public health. In spite of efforts devoted to clinical investigation and preclinical studies, the underlying neurobiological mechanisms of this disorder remain unknown in detail. Much of the progress in the area has been made from animal models, especially rodent models. The aim of this mini-review is to update the current rodent models in PPD research and their main contributions to the field. Animal models are critical tools to advance understanding of the pathophysiological basis of this disorder and to help the development of new therapeutic strategies. Here, we group PPD models into 2 main categories (Models based on hormone manipulations, Models based on stress exposure), each of which includes different paradigms that reflect risk factors or physiological conditions associated with this disease. Finally, we provide an overview of emerging models that provide new perspectives on the study of possible pathophysiological factors related to PPD, to contribute to tackling potential therapeutic targets.

Mitochondrial transplantation improves anxiety- and depression-like behaviors in aged stress-exposed rats

Impaired mitochondrial function and abnormalities in the tryptophan (Trp)-kynurenine (Kyn) pathway are linked to age-related mood disorders. This study investigated the effect of intracerebroventricular (ICV) injection of the mitochondria isolated from young rat brain on depression-like behaviors of aged rats subjected to chronic mild stress (CMS). Aged (22 months old) male rats were randomly assigned into four groups: Aged, Aged + Mit, Aged + CMS, and Aged + CMS + Mit. Anxiety- and depression-like behaviors were assessed using elevated plus maze (EPM), open field test (OFT), forced swimming test (FST), and sucrose preference test (SPT). Mitochondrial membrane potential (MMP), ATP levels, indoleamine 2, 3-dioxygenase (IDO) levels, and Kyn metabolites were measured in the prefrontal cortex (PFC). Golgi Cox staining was used to investigate the neuronal morphology. Mitotherapy decreased immobility time and anhedonia in the FST; increased open arm time and entries in the EPM; decreased grooming and increased rearing, center time, and the entrance in the OFT. Mitotherapy also reduced IDO and Kyn metabolites, restored MMP and ATP production, and enhanced dendritic length and spine density in the PFC. Overall, mitotherapy improved anxiety-and depression-like behaviors in aged rats and it could be considered as a new therapeutic strategy for age-related depressive disorders.

Brain-body responses to chronic stress: a brief review

In order to survive and thrive, organisms must adapt to constantly changing environmental pressures. When there are significant shifts in the environment, the brain and body engage a set of physiological and behavioral countermeasures collectively known as the "stress response". These responses, which include changes at the cellular, systems, and organismal level, are geared toward protecting homeostasis and adapting physiological operating parameters so as to enable the organism to overcome short-term challenges. It is the shift of these well-organized acute responses to dysregulated chronic responses that leads to pathologies. In a sense, the protective measures become destructive, causing the myriad health problems that are associated with chronic stress. To further complicate the situation, these challenges need not be purely physical in nature. Indeed, psychosocial stressors such as ruminating about challenges at work, resource insecurity, and unstable social environments can engage the very same emergency threat systems and eventually lead to the same types of pathologies that sometimes are described as "burnout" in humans. This short review focuses on very recent empirical work exploring the effects of chronic stress on key brain circuits, metabolism and metabolic function, and immune function.

The miRNome of Depression

Depression is an effect of complex interactions between genetic, epigenetic and environmental factors. It is well established that stress responses are associated with multiple modest and often dynamic molecular changes in the homeostatic balance, rather than with a single genetic factor that has a strong phenotypic penetration. As depression is a multifaceted phenotype, it is important to study biochemical pathways that can regulate the overall allostasis of the brain. One such biological system that has the potential to fine-tune a multitude of diverse molecular processes is RNA interference (RNAi). RNAi is an epigenetic process showing a very low level of evolutionary diversity, and relies on the posttranscriptional regulation of gene expression using, in the case of mammals, primarily short (17–23 nucleotides) noncoding RNA transcripts called microRNAs (miRNA). In this review, our objective was to examine, summarize and discuss recent advances in the field of biomedical and clinical research on the role of miRNA-mediated regulation of gene expression in the development of depression. We focused on studies investigating post-mortem brain tissue of individuals with depression, as well as research aiming to elucidate the biomarker potential of miRNAs in depression and antidepressant response.

P2X7R antagonists in chronic stress-based depression models: a review

Depression affects around 320 million people worldwide. Growing evidence proposes the immune system to be the core interface between psychosocial stress and the neurobiological and behavioural features of depression. Many studies have identified purinergic signalling via the P2X7 receptor (P2X7R) to be of great importance in depression genesis yet only a few have evaluated P2X7R antagonists in chronic stress-based depression models. This review summarizes their findings and analyses their methodology. The four available studies used three to nine weeks of unpredictable, chronic mild stress or unpredictable, chronic stress in male mice or rats. Stress paradigm composition varied moderately, with stimuli being primarily psychophysical rather than psychosocial. Behavioural testing was performed during or after the last week of stress application and resulted in depressive-like behaviours, immune changes (NLRP3 assembly, interleukin-1β level increase, microglia activation) and neuroplasticity impairment. During the second half of each stress paradigm, a P2X7R antagonist (Brilliant Blue G, A-438079, A-804598) was applied. Studies differed with regard to antagonist dosage and application timing. Nonetheless, all treatments attenuated the stress-induced neurobiological changes and depressive-like behaviours. The evidence at hand underpins the importance of P2X7R signalling in chronic stress and depression. However, improvements in study planning and reporting are necessary to minimize experimental bias and increase data purview. To achieve this, we propose adherence to the Research Domain Criteria and the STRANGE framework.

The Antagonism of the Prokineticin System Counteracts Bortezomib Induced Side Effects: Focus on Mood Alterations

The development of neuropathy and of mood alterations is frequent after chemotherapy. These complications, independent from the antitumoral mechanism, are interconnected due to an overlapping in their processing pathways and a common neuroinflammatory condition. This study aims to verify whether in mice the treatment with the proteasome inhibitor bortezomib (BTZ), at a protocol capable of inducing painful neuropathy, is associated with anxiety, depression and supraspinal neuroinflammation. We also verify if the therapeutic treatment with the antagonist of the prokineticin (PK) system PC1, which is known to contrast pain and neuroinflammation, can prevent mood alterations. Mice were treated with BTZ (0.4 mg/kg three times/week for 4 weeks); mechanical allodynia and locomotor activity were evaluated over time while anxiety (dark light and marble burying test), depression (sucrose preference and swimming test) and supraspinal neuroinflammation were checked at the end of the protocol. BTZ treated neuropathic mice develop anxiety and depression. The presence of mood alterations is related to the presence of neuroinflammation and PK system activation in prefrontal cortex, hippocampus and hypothalamus with high levels of PK2 and PKR2 receptor, IL-6 and TNF-α, TLR4 and an upregulation of glial markers. PC1 treatment, counteracting pain, prevented the development of supraspinal inflammation and depression-like behavior in BTZ mice.

Glycogen Synthase Kinase-3: A Focal Point for Advancing Pathogenic Inflammation in Depression

Increasing evidence indicates that the host immune response has a monumental role in the etiology of major depressive disorder (MDD), motivating the development of the inflammatory hypothesis of depression. Central to the involvement of chronic inflammation in MDD is a wide range of signaling deficits induced by the excessive secretion of pro-inflammatory cytokines and imbalanced T cell differentiation. Such signaling deficits include the glutamatergic, cholinergic, insulin, and neurotrophin systems, which work in concert to initiate and advance the neuropathology. Fundamental to the communication between such systems is the protein kinase glycogen synthase kinase-3 (GSK-3), a multifaceted protein critically linked to the etiology of MDD and an emerging target to treat pathogenic inflammation. Here, a consolidated overview of the widespread multi-system involvement of GSK-3 in contributing to the neuropathology of MDD will be discussed, with the feed-forward mechanistic links between all major neuronal signaling pathways highlighted.

Hippocampal overexpression of NOS1AP promotes endophenotypes related to mental disorders

BACKGROUND

Nitric oxide synthase 1 adaptor protein (NOS1AP; previously named CAPON) is linked to the glutamatergic postsynaptic density through interaction with neuronal nitric oxide synthase (nNOS). NOS1AP and its interaction with nNOS have been associated with several mental disorders. Despite the high levels of NOS1AP expression in the hippocampus and the relevance of this brain region in glutamatergic signalling as well as mental disorders, a potential role of hippocampal NOS1AP in the pathophysiology of these disorders has not been investigated yet.

METHODS

To uncover the function of NOS1AP in hippocampus, we made use of recombinant adeno-associated viruses to overexpress murine full-length NOS1AP or the NOS1AP carboxyterminus in the hippocampus of mice. We investigated these mice for changes in gene expression, neuronal morphology, and relevant behavioural phenotypes.

FINDINGS

We found that hippocampal overexpression of NOS1AP markedly increased the interaction of nNOS with PSD-95, reduced dendritic spine density, and changed dendritic spine morphology at CA1 synapses. At the behavioural level, we observed an impairment in social memory and decreased spatial working memory capacity.

INTERPRETATION

Our data provide a mechanistic explanation for a highly selective and specific contribution of hippocampal NOS1AP and its interaction with the glutamatergic postsynaptic density to cross-disorder pathophysiology. Our findings allude to therapeutic relevance due to the druggability of this molecule.

FUNDING

This study was funded in part by the DFG, the BMBF, the Academy of Finland, the NIH, the Japanese Society of Clinical Neuropsychopharmacology, the Ministry of Education of the Russian Federation, and the European Community.

Chronic Stress Alters Astrocyte Morphology in Mouse Prefrontal Cortex

BACKGROUND

Neuromorphological changes are consistently reported in the prefrontal cortex of patients with stress-related disorders and in rodent stress models, but the effects of stress on astrocyte morphology and the potential link to behavioral deficits are relatively unknown.

METHODS

To answer these questions, transgenic mice expressing green fluorescent protein (GFP) under the glial fibrillary acid protein (GFAP) promotor were subjected to 7, 21, or 35 days of chronic restraint stress (CRS). CRS-induced behavioral effects on anhedonia- and anxiety-like behaviors were measured using the sucrose intake and the PhenoTyper tests, respectively. Prefrontal cortex GFP+ or GFAP+ cell morphology was assessed using Sholl analysis, and associations with behavior were determined using correlation analysis.

RESULTS

CRS-exposed male and female mice displayed anxiety-like behavior at 7, 21, and 35 days and anhedonia-like behavior at 35 days. Analysis of GFAP+ cell morphology revealed significant atrophy of distal processes following 21 and 35 days of CRS. CRS induced similar decreases in intersections at distal radii for GFP+ cells accompanied by increased proximal processes. In males, the number of intersections at the most distal radius step significantly correlated with anhedonia-like behavior (r = 0.622, P < .05) for GFP+ cells and with behavioral emotionality calculated by z-scoring all behavioral measured deficits (r = -0.667, P < .05). Similar but not significant correlations were observed in females. No correlation between GFP+ cell atrophy with anxiety-like behavior was found.

CONCLUSION

Chronic stress exposure induces a progressive atrophy of cortical astroglial cells, potentially contributing to maladaptive neuroplastic and behavioral changes associated with stress-related disorders.

Stress-Associated Molecular and Cellular Hippocampal Mechanisms Common for Epilepsy and Comorbid Depressive Disorders

The review discusses molecular and cellular mechanisms common to the temporal lobe epileptogenesis/epilepsy and depressive disorders. Comorbid temporal lobe epilepsy and depression are associated with dysfunction of the hypothalamic-pituitary-adrenocortical axis. Excessive glucocorticoids disrupt the function and impair the structure of the hippocampus, a brain region key to learning, memory, and emotions. Selective vulnerability of the hippocampus to stress, mediated by the reception of glucocorticoid hormones secreted during stress, is the price of the high functional plasticity and pleiotropy of this limbic structure. Common molecular and cellular mechanisms include the dysfunction of glucocorticoid receptors, neurotransmitters, and neurotrophic factors, development of neuroinflammation, leading to neurodegeneration and loss of hippocampal neurons, as well as disturbances in neurogenesis in the subgranular neurogenic niche and formation of aberrant neural networks. These glucocorticoid-dependent processes underlie altered stress response and the development of chronic stress-induced comorbid pathologies, in particular, temporal lobe epilepsy and depressive disorders.

What Do the Animal Studies of Stress Resilience Teach Us?

Long-lasting stress factors, both biological and psychological, are commonly accepted as the main cause of depressive disorders. Several animal models, using various stressful stimuli, have been used to find biochemical and molecular alterations that could help us understand the etiopathogenesis of depression. However, recent sophisticated studies indicate that the most frequently used animal models of stress only capture a portion of the molecular features associated with complex human disorders. On the other hand, some of these models generate groups of animals resilient to stress. Studies of the mechanisms of stress resilience bring us closer to understanding the process of adapting to aversive stimuli and the differences between stress-susceptible vs. resilient phenotypes. Especially interesting in this context is the chronic mild stress (CMS) experimental paradigm, most often using rats. Studies using this animal model have revealed that biochemical (e.g., the dopamine D2 receptor) and molecular (e.g., microRNA) alterations are dynamic (i.e., depend on stress duration, 2 vs. 7 weeks) and much more pronounced in stress-resilient than stress-susceptible groups of animals. We strongly suggest that studies aimed at understanding the molecular and biochemical mechanisms of depression must consider these dynamics. A good candidate to serve as a biomarker in such studies might be serum microRNA, since it can be obtained relatively easily from living individuals at various time points.

Adult neurogenic process in the subventricular zone-olfactory bulb system is regulated by Tau protein under prolonged stress

Objectives

The area of the subventricular zone (SVZ) in the adult brain exhibits the highest number of proliferative cells, which, together with the olfactory bulb (OB), maintains constant brain plasticity through the generation, migration and integration of newly born neurons. Despite Tau and its malfunction is increasingly related to deficits of adult hippocampal neurogenesis and brain plasticity under pathological conditions [e.g. in Alzheimer's disease (AD)], it remains unknown whether Tau plays a role in the neurogenic process of the SVZ and OB system under conditions of chronic stress, a well‐known sculptor of brain and risk factor for AD.

Materials and methods

Different types of newly born cells in SVZ and OB were analysed in animals that lack Tau gene (Tau‐KO) and their wild‐type littermates (WT) under control or chronic stress conditions.

Results

We demonstrate that chronic stress reduced the number of proliferating cells and neuroblasts in the SVZ leading to decreased number of newborn neurons in the OB of adult WT, but not Tau‐KO, mice. Interestingly, while stress‐evoked changes were not detected in OB granular cell layer, Tau‐KO exhibited increased number of mature neurons in this layer indicating altered neuronal migration due to Tau loss.

Conclusions

Our findings suggest the critical involvement of Tau in the neurogenesis suppression of SVZ and OB neurogenic niche under stressful conditions highlighting the role of Tau protein as an essential regulator of stress‐driven plasticity deficits.

Deciphering the links between psychological stress, depression, and neurocognitive decline in patients with Down syndrome

The relationships between psychological stress and cognitive functions are still to be defined despite some recent progress. Clinically, we noticed that patients with Down syndrome (DS) may develop rapid neurocognitive decline and Alzheimer's disease (AD) earlier than expected, often shortly after a traumatic life event (bereavement over the leave of a primary caregiver, an assault, modification of lifestyle, or the loss of parents). Of course, individuals with DS are naturally prone to develop AD, given the triplication of chromosome 21. However, the relatively weak intensity of the stressful event and the rapid pace of cognitive decline after stress in these patients have to be noticed. It seems DS patients react to stress in a similar manner normal persons react to a very intense stress, and thereafter develop a state very much alike post-traumatic stress disorders. Unfortunately, only a few studies have studied stress-induced regression in patients with DS. Thus, we reviewed the biochemical events involved in psychological stress and found some possible links with cognitive impairment and AD. Interestingly, these links could probably be also applied to non-DS persons submitted to an intense stress. We believe these links should be further explored as a better understanding of the relationships between stress and cognition could help in many situations including individuals of the general population.

mRNA and miRNA profiles in the nucleus accumbens are associated with psychological stress-induced susceptible and resilient mice

BACKGROUND

Stress may be one of the main causes of fear and anxiety. Previous studies have shown that the nucleus accumbens is involved in emotional responses. However, in the nucleus accumbens, the mRNA and miRNA profiles of stress susceptibility and resilience of psychological stress still need to be studied.

MATERIALS AND METHODS

In this study, by observing the conspecific being attacked, the witness group experienced psychological stress. After five days of psychological stress, the fear memory of mice was measured by social interaction test, and the degree of anxiety was measured by elevated plus maze. mRNA and miRNA profiles in the nucleus accumbens tissue of control, susceptible and resilient mice were established by high-throughput sequencing.

RESULTS

In susceptible mice versus resilient mice, the Differentially expressed genes (DEGs) may be related to psychological stress-induced susceptibility. DEGs enriched in Cell adhesion molecules, Neuroactive ligand-receptor interaction, Gap junction, PI3K-Akt, VEGF, Jak-STAT, Ras, and Chemokine pathways were up-regulated. DEGs enriched in cGMP-PKG, B cell receptor, and NOD-like receptor pathways were down- regulated. The sequencing results of mRNAs and miRNAs were verified by qRT-PCR and dual luciferase reporter assay.

CONCLUSION

The imbalance of different synapses and pathways in the nucleus accumbens may be related to susceptibility and resilience caused by psychological stress.