Neurobiological mechanisms of mood disorders: Stress vulnerability and resilience

Inflammation and metabolic dysfunction underly anhedonia-like behavior in antidepressant resistant male rats

Inflammation and metabolic dysfunction impair dopamine neurotransmission, which is thought to serve as a critical mechanism underpinning motivational deficits such as anhedonia across a range of psychiatric and neurological disorders. This difficult-to-treat transdiagnostic symptom has important implications for treatment resistant depression (TRD), and may warrant more targeted therapeutic approaches that address the underlying pathophysiological mechanisms. Using the adrenocorticotrophic hormone (ACTH) model of antidepressant treatment resistance we characterized the relationship between antidepressant-like and anhedonia-like behavioral responses to bupropion, mesocortical tyrosine hydroxylase (TH) expression, chronic low-grade inflammation, and metabolic changes in male rats. We demonstrate that chronic ACTH elicited both an antidepressant resistant- and anhedonia-like phenotype in forced swim and effort-related choice behavioral tasks, respectively. This was associated with decreased TH expression in the brain, increased central and peripheral markers of inflammation, and peripheral metabolic disturbances, including impairment of immune cell insulin action. Multivariate analysis revealed that peripheral interleukin-6 (IL-6) levels, immune cell glucose uptake and disturbance of nucleotide metabolism were strongly associated with anhedonia-like behavior. Post-hoc analyses further confirmed strong correlations between TH expression, inflammation and behavioral performance. These data suggest that stress hormone-induced upregulation of inflammation concurrent with the impairment of insulin-mediated glucose uptake into immune cells is associated with disruption of nucleotide metabolism, and potential impaired central dopamine synthesis contributing to the behavioral expression of anhedonia. These results suggest that immunometabolic perturbations concomitant with impaired insulin action at the level of the immune cell result in a metabolically deficient state that directly impacts nucleotide precursors essential for dopamine synthesis and effortful behavior. These results highlight the potential for immune and metabolic markers for individualized treatment of refractory depression and anhedonia.

Habits and vulnerability or resilience to stress - Impact on depressive disorders

Major depressive disorder (MDD) is prevalent worldwide and impacts the health and quality of life of millions of people. MDD is a condition influenced by a complex interplay of genetic, psychological and environmental factors. This narrative review examines the roles of stress vulnerability, resilience, and lifestyle habits in shaping the risk of depression, emphasizing holistic approaches that address both biological and environmental factors in mental health management. Vulnerability to stress, influenced by factors such as childhood adversity and personality traits such as neuroticism, increases the probability of MDD. On the other hand, resilience acts as a protective mechanism, reducing stress reactivity and supporting mental health. The main findings suggest that healthy lifestyle habits, including consistent sleep patterns, a balanced diet and regular exercise, play significant roles in increasing resilience and preventing depressive symptoms. Interventions to build resilience, such as emotional skills training and promoting a growth mindset, have been proven effective in reducing depressive symptoms. Overall, the findings suggest that lifestyle modifications combined with psychological strategies to build resilience can significantly reduce depressive disorders. This study advocates for personalized therapeutic strategies that consider the multifactorial nature of depressive disorders, integrating psychological and lifestyle interventions to enhance resilience and mental health.

From Stress to Synapse: The Neuronal Atrophy Pathway to Mood Dysregulation

Mood disorders, including major depressive disorder and bipolar disorder, are among the most prevalent mental health conditions globally, yet their underlying mechanisms remain incompletely understood. This review critically examines the neuronal atrophy hypothesis, which posits that chronic stress and associated neurobiological changes lead to structural and functional deficits in critical brain regions, contributing to mood disorder pathogenesis. Key mechanisms explored include dysregulation of neurotrophic factors such as brain-derived neurotrophic factor (BDNF), elevated glucocorticoids from stress responses, neuroinflammation mediated by cytokines, and mitochondrial dysfunction disrupting neuronal energy metabolism. These processes collectively impair synaptic plasticity, exacerbate structural atrophy, and perpetuate mood dysregulation. Emerging evidence from neuroimaging, genetic, and epigenetic studies underscores the complexity of these interactions and highlights the role of environmental factors such as early-life stress and urbanization. Furthermore, therapeutic strategies targeting neuroplasticity, including novel pharmacological agents, lifestyle interventions, and anti-inflammatory treatments, are discussed as promising avenues for improving patient outcomes. Advancing our understanding of the neuronal atrophy hypothesis could lead to more effective, sustainable interventions for managing mood disorders and mitigating their global health burden.

Neurobiological Relationships Between Neurodevelopmental Disorders and Mood Disorders

According to the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), neurodevelopmental disorders (NDDs) are a group of conditions that arise early in development and are characterized by deficits in personal, social, academic, or occupational functioning. These disorders frequently co-occur and include conditions such as autism spectrum disorder (ASD) and attention-deficit/hyperactivity disorder (ADHD). Mood disorders (MDs), such as major depressive disorder and bipolar disorder, also pose significant global health challenges due to their high prevalence and substantial impact on quality of life. Emerging evidence highlights overlapping neurobiological mechanisms between NDDs and MDs, including shared genetic susceptibilities, neurotransmitter dysregulation (e.g., dopaminergic and serotonergic pathways), neuroinflammation, and hypothalamic-pituitary-adrenal (HPA) axis dysfunction. Environmental factors such as early-life adversity further exacerbate these vulnerabilities, contributing to the complexity of their clinical presentation and comorbidity. Functional neuroimaging studies reveal altered connectivity in brain regions critical for emotional regulation and executive function, such as the prefrontal cortex and amygdala, across these disorders. Despite these advances, integrative diagnostic frameworks and targeted therapeutic strategies remain underexplored, limiting effective intervention. This review synthesizes current knowledge on the shared neurobiological underpinnings of NDDs and MDs, emphasizing the need for multidisciplinary research, including genetic, pharmacological, and psychological approaches, for unified diagnosis and treatment. Addressing these intersections can improve clinical outcomes and enhance the quality of life for individuals affected by these disorders.

Deciphering the epigenetic role of long non-coding RNAs in mood disorders: Focus on human brain studies

Epigenetics plays a central role in neuropsychiatric disorders, contributing significantly to their complexity and manifestation. Major depressive disorder (MDD) and bipolar disorder (BD) have profound impact on mood, affect and cognition. Emerging evidence suggests that epigenetic modification of genes plays a pivotal role in the pathogenesis of both MDD and BD. Long non-coding RNAs (lncRNA) constitute a heterogeneous class of transcripts and have emerged as crucial regulators of epigenetic processes, offering promising insights into the pathophysiology of various diseases. Despite their limited coding potential, lncRNAs are known to play a critical role in achieving global transcriptomic regulation in a spatiotemporal fashion, especially in complex tissue like the brain. This review aims to discuss the specific dysregulation of lncRNAs so far observed in the brains of MDD and BD patients and understand their mechanistic contributions to the disease pathogenesis. KEY POINTS: Brain-centric lncRNAs regulate gene networks, and their disruption is linked to MDD. In MDD, altered lncRNAs disrupt gene regulation by changing chromatin looping or modifying chromatin accessibility. These changes lead to neuronal dysfunction, affecting neural circuitry and synaptic plasticity. The result is impaired brain function, contributing to the symptoms of MDD.

Higher Levels of Multiple Types of Stress Are Associated With Worse State Anxiety and Morning Fatigue Profiles in Patients Receiving Chemotherapy

BACKGROUND

Anxiety and fatigue are common problems in patients receiving chemotherapy. Unrelieved stress is a potential cause for the co-occurrence of these symptoms.

OBJECTIVES

The aims of this study were to identify subgroups of patients with distinct state anxiety and morning fatigue profiles and evaluate for differences among these subgroups in demographic and clinical characteristics, as well as measures of global, cancer-specific, and cumulative life stress and resilience and coping.

METHODS

Patients (n = 1335) completed measures of state anxiety and morning fatigue 6 times over 2 cycles of chemotherapy. All of the other measures were completed prior to the second or third cycle of chemotherapy. Latent profile analysis was used to identify the state anxiety and morning fatigue profiles.

RESULTS

Three distinct joint profiles were identified: Low Anxiety and Low Morning Fatigue (59%), Moderate Anxiety and Moderate Morning Fatigue (33.4%), and High Anxiety and High Morning Fatigue (7.6%). Patients in the 2 highest classes were younger, were less likely to be married/partnered, and had a higher comorbidity burden. All of the stress scores demonstrated a dose-response effect (ie, as anxiety and morning fatigue profiles worsened, stress increased). Patients in the 2 highest classes reported higher rates of emotional abuse, physical neglect, physical abuse, and sexual harassment.

CONCLUSIONS

More than 40% of these patients experienced moderate to high levels of both anxiety and morning fatigue. Higher levels of all 3 types of stress were associated with the 2 highest profiles.

IMPLICATIONS FOR PRACTICE

Clinicians need to perform comprehensive evaluations of patients' levels of stress and recommend referrals to psychosocial services.

Understanding the connection between stress and sleep: From underlying mechanisms to therapeutic solutions

The objective of this chapter is to navigate through the nexus between stress and sleep, highlighting the neurobiological systems that connect them. Starting with an overview of neuroanatomy and physiology of stress and sleep, with a further detailed breakdown of sleep stages and key neuroanatomical centers that are responsible for sleep and wakefulness. Starting with suprachiasmatic nuclei (SCN) in circadian rhythm and sleep regulation overview, with a center point on the molecular systems including the CLOCK/CRY and BMAL1/2/PER1/2 feedback loops. Following this is the neurobiological of stress, specifically the hypothalamic-pituitary-adrenal (HPA) axis and sympathetic-adrenal (SPA) axis and influence on sleep. Vital neural circuits connecting stress and sleep are examined with the attention of the ventral tegmental area (VTA) GABA-somatostatin neurons and the locus coerules in sleep regulation in response to stress. In addition, neuroinflammation's role occurs through the cytokines IL-1β and TNF-α are investigated as a mediator of sleep disturbances caused by stress. It concludes by summarizing the implications of neuroinflammatory modulation in stress-related psychopathologies, emphasizing the opening this provides for interventions that target this inflammation helping to lighten sleep disorder.

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.

Worse Morning Energy Profiles Are Associated with Significant Levels of Stress and Decrements in Resilience in Patients Receiving Chemotherapy

OBJECTIVES

Evidence suggests that lower levels of morning energy are associated with higher levels of stress and lower levels of resilience in patients receiving chemotherapy. Study purposes were to identify subgroups of patients with distinct morning energy profiles; evaluate for differences among the profiles in demographic and clinical characteristics, as well as measures of stress, resilience, and coping.

METHODS

A total of 1,343 outpatients receiving chemotherapy completed a demographic questionnaire and measures of global, cancer-related, and cumulative life stress, and resilience at study enrollment. Morning energy was assessed using the Lee Fatigue Scale at six time points over two cycles of chemotherapy. Latent profile analysis was used to identify subgroups of patients with distinct morning energy profiles. Differences among the subgroups were evaluated using parametric and nonparametric tests.

RESULTS

Three morning energy profiles were identified (i.e., High (17.3%), Low (60.3%), Very Low (22.4%)). Compared to High class, the other two morning energy classes were less likely to be employed; had a lower functional status and a higher comorbidity burden; and were more likely to self-report depression and back pain. For all three types of stress, significant differences were found among the three classes with scores that demonstrated a dose response effect (i.e., High < Low < Very Low; as decrements in morning energy increased, stress scores increased). Compared to High class, Very Low class reported higher rates of physical and sexual abuse. The resilience scores exhibited a dose response effect as well (i.e., High > Low > Very Low). Patients with the two worst energy profiles reported a higher use of disengagement coping strategies.

CONCLUSIONS

Findings highlight the complex relationships among decrements in morning energy, various types of stress, resilience, and coping in patients undergoing chemotherapy.

IMPLICATIONS FOR NURSING PRACTICE

Clinicians need to assess for stress and adverse childhood experiences to develop individualized management plans to increase patients' energy levels.

The Identification of Potential Anti-Depression/Anxiety Drug Targets by Stress-Induced Rat Brain Regional Proteome and Network Analyses

Depression and anxiety disorders are prevalent stress-related neuropsychiatric disorders and involve multiple molecular changes and dysfunctions across various brain regions. However, the specific and shared pathophysiological mechanisms occurring in these regions remain unclear. Previous research used a rat model of chronic mild stress (CMS) to segregate and identify depression-susceptible, anxiety-susceptible, and insusceptible groups; then the proteomes of six distinct brain regions (the hippocampus, prefrontal cortex, hypothalamus, pituitary, olfactory bulb, and striatum) were separately and quantitatively analyzed. To gain a comprehensive and systematic understanding of the molecular abnormalities, this study aimed to investigate and compare differential proteomics data from the six regions. Differentially expressed proteins (DEPs) were identified in between specific regions and across all regions and subjected to a series of bioinformatics analyses. Regional comparisons showed that stress-induced proteomic changes and corresponding gene ontology and pathway enrichments were largely distinct, attributable to differences in cell populations, protein compositions, and brain functions of these areas. Additionally, a notable degree of overlap in the significantly enriched terms was identified, potentially suggesting strong connections in the enrichment across different regions. Furthermore, intra-regional and inter-regional protein-protein interaction networks and drug-target-DEP networks were constructed. Integrated analysis of the three association networks in the six regions, along with the DisGeNET database, identified ten DEPs as potential targets for anti-depression/anxiety drugs. Collectively, these findings revealed commonalities and differences across different brain regions at the protein level induced by CMS, and identified several novel protein targets for the development of new therapeutics for depression and anxiety.

Quercetin reshapes gut microbiota homeostasis and modulates brain metabolic profile to regulate depression-like behaviors induced by CUMS in rats

Quercetin, an abundant flavonoid compound in plants, is considered a novel antidepressant; however, its mechanisms of action are poorly understood. This study aimed to investigate the therapeutic effects of quercetin on chronic unpredictable mild stress (CUMS)-induced depression-like behaviors in rats and explore the underlying mechanisms by combining untargeted metabolomics and 16S rRNA sequencing analysis of brain tissue metabolites and gut microbiota. Gut microbiota analysis revealed that at the phylum level, quercetin reduced Firmicutes and the Firmicutes/Bacteroidetes (F/B) ratio and enhanced Cyanobacteria. At the genus level, quercetin downregulated 6 and upregulated 14 bacterial species. Metabolomics analysis revealed that quercetin regulated multiple metabolic pathways, including glycolysis/gluconeogenesis, sphingolipid metabolism, the pentose phosphate pathway, and coenzyme A biosynthesis. This modulation leads to improvements in depression-like phenotypes, anxiety-like phenotypes, and cognitive function, highlighting the therapeutic potential of quercetin in treating depression.

Effects of a Lacticaseibacillus Mix on Behavioural, Biochemical, and Gut Microbial Outcomes of Male Mice following Chronic Restraint Stress

The effect of supplementation with Lactobacillus strains to prevent the consequences of chronic stress on anxiety in mouse strains sensitive to stress and the consequences on gut microbiota have been relatively unexplored. Thus, we administered a Lacticaseibacillus casei LA205 and Lacticaseibacillus paracasei LA903 mix to male BALB/cByJrj mice two weeks before and during 21-day chronic restraint stress (CRS) (non-stressed/solvent (NS-PBS), non-stressed/probiotics (NS-Probio), CRS/solvent (S-PBS), CRS/probiotics (S-Probio)). CRS resulted in lower body weight and coat state alteration, which were attenuated by the probiotic mix. S-Probio mice showed less stress-associated anxiety-like behaviours than their NS counterpart, while no difference was seen in PBS mice. Serum corticosterone levels were significantly higher in the S-Probio group than in other groups. In the hippocampus, mRNA expression of dopamine and serotonin transporters was lower in S-Probio than in S-PBS mice. Few differences in bacterial genera proportions were detected, with a lower relative abundance of Alistipes in S-Probio vs. S-PBS. CRS was accompanied by a decrease in the proportion of caecal acetate in S-PBS mice vs. NS-PBS, but not in the intervention groups. These data show that the probiotic mix could contribute to better coping with chronic stress, although the precise bacterial mechanism is still under investigation.

Longitudinal early epigenomic signatures inform molecular paths of therapy response and remission in depressed patients

Introduction

The etiology of major depressive disorder (MDD) involves the interaction between genes and environment, including treatment. Early molecular signatures for treatment response and remission are relevant in a context of personalized medicine and stratification and reduce the time-to-decision. Therefore, we focused the analyses on patients that responded or remitted following a cognitive intervention of 8 weeks.

Methods

We used data from a randomized controlled trial (RCT) with MDD patients (N = 112) receiving a cognitive intervention. At baseline and 8 weeks, blood for DNA methylation (Illumina Infinium MethylationEPIC 850k BeadChip) was collected, as well as MADRS. First, responders (N = 24; MADRS-reduction of at least 50%) were compared with non-responders (N = 60). Then, we performed longitudinal within-individual analyses, for response (N = 21) and for remission (N = 18; MADRS smaller or equal to 9 and higher than 9 at baseline), respectively, as well as patients with no change in MADRS over time. At 8 weeks the sample comprised 84 individuals; 73 patients had DNA methylation for both time-points. The RnBeads package (R) was used for data cleaning, quality control, and differential DNA-methylation (limma). The within-individual paired longitudinal analysis was performed using Welch's t-test. Subsequently gene-ontology (GO) pathway analyses were performed.

Results

No CpG was genome-wide significant CpG (p < 5 × 10-8). The most significant CpG in the differential methylation analysis comparing response versus non-response was in the IQSEC1 gene (cg01601845; p = 1.53 × 10-6), linked to neurotransmission. The most significant GO-terms were linked to telomeres. The longitudinal response analysis returned 67 GO pathways with a p < 0.05. Two of the three most significant pathways were linked to sodium transport. The analysis for remission returned 46 GO terms with a p-value smaller than 0.05 with pathways linked to phosphatase regulation and synaptic functioning. The analysis with stable patients returned mainly GO-terms linked to basic cellular processes.

Discussion

Our result suggest that DNA methylation can be suitable to capture early signs of treatment response and remission following a cognitive intervention in depression. Despite not being genome-wide significant, the CpG locations and GO-terms returned by our analysis comparing patients with and without cognitive impairment, are in line with prior knowledge on pathways and genes relevant for depression treatment and cognition. Our analysis provides new hypotheses for the understanding of how treatment for depression can act through DNA methylation and induce response and remission.

Electric foot-shock induces neurobehavioral aberrations due to imbalance in oxidative status, stress hormone, neurochemical profile, and irregular cortical-beta wave pattern in rats: A validated animal model of anxiety

Neuropsychiatric disorders can be modeled on animals to investigate the neural mechanism underlying these disorders. Models of neuropsychiatric disorders, such as anxiety, basically aim to produce the signs and symptoms of human anxiety disorders in laboratory animals. Electric foot-shock is recommended to induce anxiety-like symptoms in rodents. For this purpose, however, a range of current intensities is available in the literature. The present study aims to modify the existing practices of generating anxiety-like symptoms through electric foot-shock by identifying an optimum current intensity and combing it with behavioral paradigms to produce a rat model of anxiety. Furthermore, the validity of the model was confirmed by checking the fulfillment of three validity criteria necessary for the development of any disease model including face validity, construct validity, and predictive validity. In the current study, after pre-testing, 1.0 mA electric intensity was selected to produce the model of anxiety. The results showed that the induction of 1.0 mA electric foot-shock induces abnormal behavioral effects which were similar to anxiety-like effects as evident by social interaction test, light-dark transition test, and open field test. Moreover, aberrations in the levels of the stress hormone, oxidative stress parameters, hippocampal neurotransmitter levels, and cortical-EEG wave pattern were also observed in the rat model of anxiety which were successfully overcome using diazepam. In conclusion, the outcome of our study suggests that electric foot-shock can be an adequate stressor to produce a validated animal model of anxiety and this model can be confidently used to identify and screen new and/or novel anxiolytics.