The Impact of Stress and Major Depressive Disorder on Hippocampal and Medial Prefrontal Cortex Morphology

Peripheral mitochondrial DNA as a neuroinflammatory biomarker for major depressive disorder

In the pathogenesis of major depressive disorder, chronic stress-related neuroinflammation hinders favorable prognosis and antidepressant response. Mitochondrial DNA may be an inflammatory trigger, after its release from stress-induced dysfunctional central nervous system mitochondria into peripheral circulation. This evidence supports the potential use of peripheral mitochondrial DNA as a neuroinflammatory biomarker for the diagnosis and treatment of major depressive disorder. Herein, we critically review the neuroinflammation theory in major depressive disorder, providing compelling evidence that mitochondrial DNA release acts as a critical biological substrate, and that it constitutes the neuroinflammatory disease pathway. After its release, mitochondrial DNA can be carried in the exosomes and transported to extracellular spaces in the central nervous system and peripheral circulation. Detectable exosomes render encaged mitochondrial DNA relatively stable. This mitochondrial DNA in peripheral circulation can thus be directly detected in clinical practice. These characteristics illustrate the potential for mitochondrial DNA to serve as an innovative clinical biomarker and molecular treatment target for major depressive disorder. This review also highlights the future potential value of clinical applications combining mitochondrial DNA with a panel of other biomarkers, to improve diagnostic precision in major depressive disorder.

Coenzyme Q10 and vitamin E alleviate heat stress-induced mood disturbances in male mice: Modulation of inflammatory pathways and the HPA axis

Heat stress, as an environmental stressor, can lead to temperature dysregulation and neuroinflammation, causing depression and anxiety by disrupting brain physiology and functional connectivity. This study looked at how co-enzyme Q10 (Q10) and vitamin E (Vit E), alone and together, affected heat stress-caused anxiety and depression symptoms and inflammation in male mice. Five groups were utilized in the study: control, heat stress (NS), Q10, Vit E, and the combination group (Q10+Vit E). The mice were subjected for 15 min/day to a temperature of 43°C for 14 consecutive days, followed by daily treatments for two weeks with either normal saline, Q10 (500 mg/kg), Vit E (250 mg/kg), or their combination. The forced swimming test (FST) and tail suspension test (TST) were employed to evaluate despair behavior, whereas the elevated plus maze (EPM) and open field test (OFT) were used to assess anxious behaviors. Subsequently, the animals were sacrificed, and serum corticosterone levels, protein expression of inflammasome-related proteins, and hsp70 gene expression were evaluated in the prefrontal cortex (PFC). The study revealed that treatment with Vit E and Q10, alone or together, provided anxiolytic and antidepressant effects in the heat-stress-subjected animals. Also, giving Vit E and Q10 alone or together greatly lowered serum corticosterone levels. In the PFC, they also lowered the levels of hsp70 mRNA and NF-κB, caspase 1, NLRP3, and IL-1β proteins. It is speculated that treatment with Q10 and Vit E can attenuate heat stress-associated anxious and depressive responses by inhibiting the inflammatory pathways and modulating the hypothalamus-pituitary-adrenal axis.

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.

Chronic social isolation leads to abnormal behavior in male mice through the hippocampal METTL14 mediated epitranscriptomic RNA m6A modifications

BACKGROUND

Social isolation not only increases the risk of mortality in later life but also causes depressive symptoms, cognitive and physical disabilities. Although RNA m6A modifications are suggested to play key roles in brain development, neuronal signaling and neurological disorders, both the roles of m6A and the enzymes that regulate RNA m6A modification in social isolation induced abnormal behavior is unknown. The present study aims to explore the possible epitranscriptomic role of RNA m6A modifications and its enzymes in social isolation induced impaired behavior.

METHODS

3-4 weeks mice experiencing 8 weeks social isolation stress (SI) were used in the present study. We quantified m6A levels in brain regions related to mood and cognitive behavior. And the expression of hippocampal m6A enzymes was also determined. The role of hippocampal m6A and its enzymes in SI induced abnormal behavior was further verified by the virus tool.

RESULTS

SI led to not only depressive and anxiety-like behaviors but also cognitive impairment, with corresponding decreases in hippocampal m6A and METTL14. Hippocampal over-expression METTL14 with lentivirus not only rescued these behaviors but also enhanced the hippocampal m6A level. Hippocampal over-expression METTL14 resulted in increased synaptic related genes.

CONCLUSIONS

We provide the first evidence that post-weaning social isolation reduces hippocampal m6A level and causes altered expression of m6A enzyme in mice. Importantly, hippocampal METTL14 over-expression alleviated the SI-induced depression/anxiety-like and impaired cognitive behaviors and enhanced m6A level and synaptic related genes expression.

Multimodal Associations of FKBP5 Methylation With Emotion-Regulatory Brain Circuits

BACKGROUND

Understanding the biological processes that underlie individual differences in emotion regulation and stress responsivity is a key challenge for translational neuroscience. The gene FKBP5 is a core regulator in molecular stress signaling that is implicated in the development of psychiatric disorders. However, it remains unclear how FKBP5 DNA methylation in peripheral blood is related to individual differences in measures of neural structure and function and their relevance to daily-life stress responsivity.

METHODS

Here, we characterized multimodal correlates of FKBP5 DNA methylation by combining epigenetic data with neuroimaging and ambulatory assessment in a sample of 395 healthy individuals.

RESULTS

First, we showed that FKBP5 demethylation as a psychiatric risk factor was related to an anxiety-associated reduction of gray matter volume in the ventromedial prefrontal cortex, a brain area that is involved in emotion regulation and mental health risk and resilience. This effect of epigenetic upregulation of FKBP5 on neuronal structure is more pronounced where FKBP5 is epigenetically downregulated at baseline. Leveraging 208 functional magnetic resonance imaging scans during a well-established emotion-processing task, we found that FKBP5 DNA methylation in peripheral blood was associated with functional differences in prefrontal-limbic circuits that modulate affective responsivity to daily stressors, which we measured using ecological momentary assessment in daily life.

CONCLUSIONS

Overall, we demonstrated how FKBP5 contributes to interindividual differences in neural and real-life affect regulation via structural and functional changes in prefrontal-limbic brain circuits.

Faecalibacterium prausnitzii, FOS and GOS loaded synbiotic reverses treatment-resistant depression in rats: Restoration of gut-brain crosstalk

Alterations in commensal gut microbiota, such as butyrate-producing bacteria and its metabolites, have been linked to stress-related brain disorders, including depression. Herein, we investigated the effect of Faecalibacterium prausnitzii (ATCC-27766) administered along with fructooligosaccharides (FOS) and galactooligosaccharides (GOS) in a rat model of treatment-resistant depression (TRD). The behavioral changes related to anxiety-, anhedonia- and despair-like phenotypes were recorded employing elevated plus maze, sucrose-preference test, and forced-swim test, respectively. Rats exposed to unpredictable chronic mild-stress (UCMS) and adrenocorticotropic hormone (ACTH) injections exhibited a TRD-like phenotype. Six-week administration of F. prausnitzii and FOS + GOS ameliorated TRD-like conditions in rats. This synbiotic treatment also restored the decreased levels of short-chain fatty acids (SCFAs) such as acetate, propionate, and butyrate in the fecal samples of TRD rats. Synbiotic-recipient TRD rats displayed an increased abundance of Lactobacillus helveticus, Lactobacillus hamsteri, and Ruminococcus flavefaciens. Moreover, more mucus-producing goblet cells were seen in the colon of synbiotic-treated rats, suggesting improved gut health. The synbiotic treatment effectively modulated neuroinflammation by reducing proinflammatory cytokines (IFN-γ, TNF-α, CRP, and IL-6). It normalized the altered levels of key neurotransmitters such as serotonin, gamma-aminobutyric acid, noradrenaline, and dopamine in the hippocampus and/or frontal cortex. The enhanced expression of brain-derived neurotrophic factor, tryptophan hydroxylase 1, and serotonin transporter-3 (SERT-3), and reduced levels of indoleamine 2,3-dioxygenase 1 (IDO-1) and kynurenine metabolite were observed in the synbiotic-treated group. We suggest that F. prausnitzii and FOS + GOS-loaded synbiotic may reverse the TRD-like symptoms in rats by positively impacting gut health, neuroinflammation, neurotransmitters, and gut microbial composition.

Nervonic acid improves depression like behaviors and demyelination of medial prefrontal cortex in chronic restraint stress mice

Major depressive disorder (MDD) is a psychiatric disorder characterized by depressed mood, behavioral despair and anhedonia. Demyelination in specific brain regions underlies the pathology of MDD, raising the alleviating demyelination as a potential strategy for MDD therapy. Nervonic acid (NA) has the potential to improve brain demyelination, offering benefits for various neurological disorders. However, its effects on depression remain undetermined. Mice were subjected to 14 days of chronic restraint stress (CRS) to induce depression-like behaviors, and were injected with NA (70 mg/kg) daily. The administration of NA significantly improved depressive-like behaviors in CRS mice. CRS led to significant demyelination in the medial prefrontal cortex (mPFC), which were reversed by NA treatment. In addition, NA ameliorated the upregulation of inflammatory cytokines and downregulation of brain-derived neurotrophic factor, improved the alternations in axonal spines observed in the mPFC of CRS mice. Our results highlighted the potential of NA as an antidepressant, with its benefits likely attributed to its effects in alleviating demyelination in the mPFC.

Brain-derived neurotrophic factor modulation in response to oxidative stress and corticosterone: role of scopolamine and mirtazapine

Major Depressive Disorder (MDD) is a very complex disease, challenging to study and manage. The complexities of MDD require extensive research of its mechanisms to develop more effective therapeutic approaches. Crucial in the context of this disease is the role of brain-derived neurotrophic factor (BDNF) signaling pathway.

AIM

This manuscript aims to explore the complex relationship between MDD and BDNF signaling pathway, focusing on how BDNF is modulated in response to oxidative stress and corticosterone, known to be altered in MDD and contributing to the pathology of the disorder, when treated with scopolamine and mirtazapine.

METHODS

To assess BDNF levels after the different treatment conditions, rat hippocampal slices and mice primary hippocampus and cortical cell culture were analyzed by immunofluorescence and Western blot.

KEY FINDINGS

Both mirtazapine and scopolamine under stress conditions induced by hydrogen peroxide (H2O2) and corticosterone, had a significant impact on BDNF levels, and this was distinct in different neuronal models. Mirtazapine, especially when combined with H2O2, altered BDNF expression. Scopolamine when combined with both stressors also altered BDNF levels. However, its effects varied depending on the specific neuronal model and stress condition. In accordance with BDNF results, phosphorylated tropomyosin receptor kinase B (pTrkB) presented increased activation when neuronal cells subjected to stress were treated with mirtazapine or scopolamine.

SIGNIFICANCE

Collectively, this study highlights the complex connection between these compounds, stress conditions, and BDNF/TrkB modulation, supporting the potential therapeutic effects of scopolamine and mirtazapine in modulating BDNF levels, even in stressful conditions.

Association of oxidative balance score with epilepsy and moderate to severe depression: Insights from the NHANES study

BACKGROUND

Depression is a significant public health issue, closely associated with epilepsy and oxidative stress (OS). This study aims to explore the level of OS in patients with epilepsy and its relationship with moderate to severe depression (MSD).

METHODS

This cross-sectional study includes 10,819 participants aged 20-80 from the National Health and Nutrition Examination Survey (NHANES) database (2013-2020 pre-pandemic). Depression symptoms were assessed using the Patient Health Questionnaire-9 (PHQ-9), and epilepsy was diagnosed based on antiepileptic drug use in the past 30 days. The oxidative balance score (OBS) was calculated from dietary recall and lifestyle habits over the previous 24 h.

RESULTS

Compared to non-epileptic subjects, epileptic patients have a significantly higher prevalence of depression. Epileptic patients exhibit lower OBS and Dietary Oxidative Balance Scores (DOBS), while there is no significant difference in Lifestyle Oxidative Balance Scores (LOBS). Depressed patients show lower OBS, DOBS, and LOBS. The mediation model indicates that DOBS mediates 3.44 % of epilepsy-related MSD.

CONCLUSIONS

Epileptic patients exhibit significantly higher levels of OS and consume more pro-oxidant foods compared to the general population. However, their lifestyle habits do not differ significantly from those of the control group. Additionally, epileptic patients are at a higher risk of developing MSD. Although a pro-oxidant diet may be associated with epilepsy-mediated MSD, its mediating effect is relatively weak.

Endocannabinoid concentrations in major depression: effects of childhood maltreatment and relation to hippocampal volume

Evidence from preclinical animal models suggests that the stress-buffering function of the endocannabinoid (eCB) system may help protect against stress-related reductions in hippocampal volume, as is documented in major depressive disorder (MDD). However, stress exposure may also lead to dysregulation of this system. Thus, pathways from marked stress histories, such as childhood maltreatment (CM), to smaller hippocampal volumes and MDD in humans may depend on dysregulated versus intact eCB functioning. We examined whether the relation between MDD and peripheral eCB concentrations would vary as a function of CM history. Further, we examined whether eCBs moderate the relation of CM/MDD and hippocampal volume. Ninety-one adults with MDD and 62 healthy comparison participants (HCs) were recruited for a study from the Canadian Biomarker Integration Network in Depression program (CAN-BIND-04). The eCBs, anandamide (AEA) and 2-arachidonylglycerol (2-AG), were assessed from blood plasma. Severe CM history was assessed retrospectively via contextual interview. MDD was associated with eCBs, though not all associations were moderated by CM or in the direction expected. Specifically, MDD was associated with higher AEA compared to HCs regardless of CM history, a difference that could be attributed to psychotropic medications. MDD was also associated with higher 2-AG, but only for participants with CM. Consistent with hypotheses, we found lower left hippocampal volume in participants with versus without CM, but only for those with lower AEA, and not moderate or high AEA. Our study presents the first evidence in humans implicating eCBs in stress-related mechanisms involving reduced hippocampal volume in MDD.

An overview of major depression disorder: The endocannabinoid system as a potential target for therapy

Major depressive disorder is the psychiatric disease with the highest global prevalence, impacting social functioning and decreasing the quality of life. The partial pathophysiological knowledge of the disease, the economic burden and the low remission rates are sufficient justification to carry out an update on the subject in the search for new therapeutic approaches and targets. The endocannabinoid system has been linked to the development of depression, and its stimulation or antagonism is a promising approach in the treatment of major depressive disorder. Cannabidiol (CBD) and its properties have been widely studied recently; its analgesic, anti-inflammatory, antineoplastic and neuroprotective roles have even been reported in animal models and clinical trials, achieving its approved use for certain neurodegenerative pathologies. The use of CBD in depression biomodels and clinical trials has not been the exception, and here we contrast the current evidence of its administration and pharmacology against the pathological mechanisms of major depressive disorder.

Tryptophan Metabolism Disorder-Triggered Diseases, Mechanisms, and Therapeutic Strategies: A Scientometric Review

BACKGROUND

Tryptophan is widely present in foods such as peanuts, milk, and bananas, playing a crucial role in maintaining metabolic homeostasis in health and disease. Tryptophan metabolism is involved in the development and progression of immune, nervous, and digestive system diseases. Although some excellent reviews on tryptophan metabolism exist, there has been no systematic scientometric study as of yet.

METHODS

This review provides and summarizes research hotspots and potential future directions by analyzing annual publications, topics, keywords, and highly cited papers sourced from Web of Science spanning 1964 to 2022.

RESULTS

This review provides a scientometric overview of tryptophan metabolism disorder-triggered diseases, mechanisms, and therapeutic strategies.

CONCLUSIONS

The gut microbiota regulates gut permeability, inflammation, and host immunity by directly converting tryptophan to indole and its derivatives. Gut microbial metabolites regulate tryptophan metabolism by activating specific receptors or enzymes. Additionally, the kynurenine (KYN) pathway, activated by indoleamine-2, 3-dioxygenase (IDO) and tryptophan 2, 3-dioxygenase, affects the migration and invasion of glioma cells and the development of COVID-19 and depression. The research and development of IDO inhibitors help to improve the effectiveness of immunotherapy. Tryptophan metabolites as potential markers are used for disease therapy, guiding clinical decision-making. Tryptophan metabolites serve as targets to provide a new promising strategy for neuroprotective/neurotoxic imbalance affecting brain structure and function. In summary, this review provides valuable guidance for the basic research and clinical application of tryptophan metabolism.

Elevated allostatic load is associated with poorer response to repetitive transcranial magnetic stimulation in treatment-resistant depression

This cohort study investigated whether allostatic load (AL) is associated with treatment response to repetitive transcranial magnetic stimulation (rTMS) in treatment-resistant depression (TRD). Pre-treatment blood samples measured AL across multiple systems. Pre- and post-treatment mood changes were assessed using the Montgomery-Åsberg Depression Rating Scale (MADRS). Associations between AL and treatment outcomes were explored. Higher pre-treatment AL was significantly associated with poorer post-treatment response status but was not significantly associated with smaller reduction in MADRS score after 4 weeks of treatment. Identifying biomarker profiles informed by the AL model could enhance treatment decisions in TRD, reducing risks associated with prolonged, ineffective rTMS trials and emphasizing the need for reliable predictive biomarkers.

Oral administration of osthole mitigates maladaptive behaviors through PPARα activation in mice subjected to repeated social defeat stress

Psychological stress induces neuroinflammatory responses, which are associated with the pathogenesis of various psychiatric disorders, such as posttraumatic stress disorder and anxiety. Osthole-a natural coumarin isolated from the seeds of the Chinese herb Cnidium monnieri-exerts anti-inflammatory and antioxidative effects on the central nervous system. However, the therapeutic benefits of osthole against psychiatric disorders remain largely unknown. We previously demonstrated that mice subjected to repeated social defeat stress (RSDS) in the presence of aggressor mice exhibited symptoms of posttraumatic stress disorder, such as social avoidance and anxiety-like behaviors. In this study, we investigated the therapeutic effects of osthole and the underlying molecular mechanisms. Osthole exerted therapeutic effects on cognitive behaviors, mitigating anxiety-like behaviors and social avoidance in a mouse model of RSDS. The anti-inflammatory response induced by the oral administration of osthole was strengthened through the upregulation of heme oxygenase-1 expression. The expression of PPARα was inhibited in mice subjected to RSDS. Nonetheless, osthole treatment reversed the inhibition of PPARα expression. We identified a positive correlation between heme oxygenase-1 expression and PPARα expression in osthole-treated mice. In conclusion, osthole has potential as a Chinese herbal medicine for anxiety disorders. When designing novel drugs for psychiatric disorders, researchers should consider targeting the activation of PPARα.

Gypenosides alleviate oxidative stress in the hippocampus, promote mitophagy, and mitigate depressive-like behaviors induced by CUMS via SIRT1

ETHNOPHARMACOLOGICAL RELEVANCE

The use and efficacy of Gynostemma [Gynostemma pentaphyllum (Thunb.) Makino], a versatile traditional Chinese herb, was first documented in the renowned pharmacopoeia, "Compendium of Materia Medica". Gypenosides (Gps), saponin components are the primary constituents responsible for its biological activities and clinical effects, which include antioxidant, immunoregulatory, antitumor, and neuroprotective properties. Pharmacological studies have shown that Gps has the potential to combat depression. However, the exact molecular mechanisms underlying its antidepressant effects remain unclear.

AIM OF THE STUDY

This study aims to elucidate the mechanisms underlying the antidepressant effects of Gps through antioxidative stress, utilizing an integrated approach that includes network pharmacology, molecular simulations, and experimental validation.

MATERIALS AND METHODS

Sprague-Dawley rats were subjected to chronic unpredictable mild stress (CUMS) and were orally administered doses of Gps (50 and 100 mg/kg) and fluoxetine (10 mg/kg). The regulatory effects of Gps on depression-like behaviors in CUMS rats and their impact on oxidative stress levels in the hippocampus region were evaluated. Network pharmacology was used to investigate the mechanisms by which Gps affects oxidative stress in depression, and was accompanied by molecular docking and dynamics simulations. CUMS rats were treated orally with Gps (100 mg/kg) and injected with EX527 for rescue experiments to validate the role of SIRT1 in antioxidative stress and evaluate the impact of Gps on mitophagy.

RESULTS

Gps ameliorated depression-like behaviors induced by CUMS in rats. The improvements observed included an increased sucrose preference, reduced immobility time in the tail suspension and forced swim tests, and an increased movement distance in the open-field test. Additionally, Gps effectively reduced reactive oxygen species, malondialdehyde, and 8-hydroxy-2'-deoxyguanosine levels in the hippocampus, while increasing the contents of ATP, catalase, superoxide dismutase, and glutathione, indicating an increased capacity for antioxidative stress in the hippocampus. Furthermore, Gps increased the number of neuronal cells in the hippocampal CA1 region and the level of mitochondrial autophagy, with SIRT1 as a potential key target. Inhibition of SIRT1 expression by exposure to EX527 reversed the beneficial effects of Gps, further validating the critical role of SIRT1 in the regulation of oxidative stress and improving depression-like behavior.

CONCLUSION

Gps improved the antioxidative stress capacity of the hippocampus and promoted mitophagy in CUMS rats through SIRT1, thus protecting hippocampal neurons and improving depression-like behavior.

Running exercise decreases microglial activation in the medial prefrontal cortex in an animal model of depression

BACKGROUND

Running exercise effectively ameliorates depressive symptoms in humans and depression-like behaviors in animals, but the underlying mechanisms remain unclear. Microglia-mediated neuroinflammation plays a major role in the development of depression. The medial prefrontal cortex (mPFC) is a key brain region involved in depression and is sensitive to physical activity. Whether the antidepressant effect of running exercise involves changes in mPFC microglia is not understood.

METHODS

The animals were subjected to chronic unpredictable stress (CUS) intervention followed by treadmill running. The sucrose preference test and elevated plus maze test or tail suspension test were used for behavioral assessment of the animals. The number of microglia in the mPFC was quantified by immunohistochemistry and stereology. The density and morphology of microglia were analyzed via immunofluorescence staining combined with three-dimensional laser scanning techniques. The mRNA expressions of inflammatory cytokines in the mPFC were examined via quantitative real-time PCR.

RESULTS

Running exercise effectively alleviated depressive-like behaviors in depression model animals. Running exercise reversed the increase in the number of microglia and the density of activated microglia in the mPFC of CUS animals. Running exercise effectively reversed the changes in microglia (reduced cell body area, total branch length and branch complexity) in the mPFC of CUS animals. Furthermore, running exercise regulated the gene expressions of pro-/antiinflammatory cytokines in the mPFC of CUS animals.

CONCLUSIONS

Our results suggested that the antidepressant effects of running exercise may involve decreasing the number of activated microglia, reversing morphological changes in microglia in the mPFC, and reducing inflammatory responses.

Depression, brain structure and socioeconomic status: A UK Biobank study

BACKGROUND

Depression results from interactions between biological, social, and psychological factors. Literature shows that depression is associated with abnormal brain structure, and that socioeconomic status (SES) is associated with depression and brain structure. However, limited research considers the interaction between each of these factors.

METHODS

Multivariate regression analysis was conducted using UK Biobank data on 39,995 participants to examine the relationship between depression and brain volume in 23 cortical regions for the whole sample and then separated by sex. It then examined whether SES affected this relationship.

RESULTS

Eight out of 23 brain areas had significant negative associations with depression in the whole population. However, these relationships were abolished in seven areas when SES was included in the analysis. For females, three regions had significant negative associations with depression when SES was not included, but only one when it was. For males, lower volume in six regions was significantly associated with higher depression without SES, but this relationship was abolished in four regions when SES was included. The precentral gyrus was robustly associated with depression across all analyses.

LIMITATIONS

Participants with conditions that could affect the brain were not excluded. UK Biobank is not representative of the general population which may limit generalisability. SES was made up of education and income which were not considered separately.

CONCLUSIONS

SES affects the relationship between depression and cortical brain volume. Health practitioners and researchers should consider this when working with imaging data in these populations.

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.

Depressive symptoms during the transition to adolescence: Left hippocampal volume as a marker of social context sensitivity

The transition to adolescence is a critical period for mental health development. Socio-experiential environments play an important role in the emergence of depressive symptoms with some adolescents showing more sensitivity to social contexts than others. Drawing on recent developmental neuroscience advances, we examined whether hippocampal volume amplifies social context effects in the transition to adolescence. We analyzed 2-y longitudinal data from the Adolescent Brain Cognitive Development (ABCD®) study in a diverse sample of 11,832 youth (mean age: 9.914 y; range: 8.917 to 11.083 y; 47.8% girls) from 21 sites across the United States. Socio-experiential environments (i.e., family conflict, primary caregiver's depressive symptoms, parental warmth, peer victimization, and prosocial school environment), hippocampal volume, and a wide range of demographic characteristics were measured at baseline. Youth's symptoms of major depressive disorder were assessed at both baseline and 2 y later. Multilevel mixed-effects linear regression analyses showed that negative social environments (i.e., family conflict, primary caregiver's depressive symptoms, and peer victimization) and the absence of positive social environments (i.e., parental warmth and prosocial school environment) predicted greater increases in youth's depressive symptoms over 2 y. Importantly, left hippocampal volume amplified social context effects such that youth with larger left hippocampal volume experienced greater increases in depressive symptoms in more negative and less positive social environments. Consistent with brain-environment interaction models of mental health, these findings underscore the importance of families, peers, and schools in the development of depression during the transition to adolescence and show how neural structure amplifies social context sensitivity.

Increased forebrain EAAT3 expression confers resilience to chronic stress

Depression is a disabling and highly prevalent psychiatric illness. Multiple studies have linked glutamatergic dysfunction with the pathophysiology of depression, but the exact alterations in the glutamatergic system that contribute to depressive-like behaviors are not fully understood. Recent evidence suggests that a decreased level in neuronal glutamate transporter (EAAT3), known to control glutamate levels and limit the activation of glutamate receptors at synaptic sites, may contribute to the manifestation of a depressive phenotype. Here, we tested the possibility that increased EAAT3 expression at excitatory synapses could reduce the susceptibility of mice to develop depressive-like behaviors when challenged to a 5-week unpredictable chronic mild stress (UCMS) protocol. Mice overexpressing EAAT3 in the forebrain (EAAT3glo/CMKII) and control littermates (EAAT3glo) were assessed for depressive-like behaviors and long-term memory performance after being subjected to UCMS conditions. We found that, after UCMS, EAAT3glo/CMKII mice did not exhibit depressive-like behaviors or memory alterations observed in control mice. Moreover, we found that EAAT3glo/CMKII mice did not show alterations in phasic dopamine release in the nucleus accumbens neither in long-term synaptic plasticity in the CA1 region of the hippocampus after UCMS, as observed in control littermates. Altogether these results suggest that forebrain EAAT3 overexpression may be related to a resilient phenotype, both at behavioral and functional level, to the deleterious effect of chronic stress, highlighting the importance of neuronal EAAT3 in the pathophysiology of depressive-like behaviors.

Identification of differentially expressed genes in the medial prefrontal cortex of rats subjected to chronic unpredictable mild stress and treated with electroacupuncture

Major depressive disorder is a chronic mental health condition that seriously impacts afflicted individuals. Although electroacupuncture has proven to be an effective therapy for depression, its underlying biological mechanism remains largely unknown. In this study, we aimed to investigate the effects of electroacupuncture on depression-like behavior and to identify potential target genes related to those effects. To achieve this, we subjected rats to chronic unpredictable mild stress (CUMS) and used sucrose preference, forced swimming, and open-field tests to determine their depression-like behavior in the absence or after receipt of electroacupuncture treatment. RNA sequencing technology was then used to reveal the differentially expressed genes associated with depression and electroacupuncture treatment effects in the medial prefrontal cortex (mPFC). Repeated electroacupuncture treatments at the Baihui (GV20) and Taichong (LR3) acupoints significantly alleviated depression-like behavioral defects in the animals. Genomic RNA sequencing revealed several significant changes in the mPFC transcriptome of rats that received treatment. Through differential gene expression analysis, we found that electroacupuncture reversed the CUMS-induced downregulation of 46 genes and upregulation of 13 genes. Among the differentially expressed genes, Casr, Bdkrb2, Gnb3, and Ccl1 were found to be associated with depression and electroacupuncture treatment effects. In conclusion, we verified that electroacupuncture treatment has an effective antidepressant effect, and the underlying mechanism involves multiple systems and targets.

Brain stars take the lead during critical periods of early postnatal brain development: relevance of astrocytes in health and mental disorders

In the brain, astrocytes regulate shape and functions of the synaptic and vascular compartments through a variety of released factors and membrane-bound proteins. An imbalanced astrocyte activity can therefore have drastic negative impacts on brain development, leading to the onset of severe pathologies. Clinical and pre-clinical studies show alterations in astrocyte cell number, morphology, molecular makeup and astrocyte-dependent processes in different affected brain regions in neurodevelopmental (ND) and neuropsychiatric (NP) disorders. Astrocytes proliferate, differentiate and mature during the critical period of early postnatal brain development, a time window of elevated glia-dependent regulation of a proper balance between synapse formation/elimination, which is pivotal in refining synaptic connectivity. Therefore, any intrinsic and/or extrinsic factors altering these processes during the critical period may result in an aberrant synaptic remodeling and onset of mental disorders. The peculiar bridging position of astrocytes between synaptic and vascular compartments further allows them to "compute" the brain state and consequently secrete factors in the bloodstream, which may serve as diagnostic biomarkers of distinct healthy or disease conditions. Here, we collect recent advancements regarding astrogenesis and astrocyte-mediated regulation of neuronal network remodeling during early postnatal critical periods of brain development, focusing on synapse elimination. We then propose alternative hypotheses for an involvement of aberrancies in these processes in the onset of ND and NP disorders. In light of the well-known differential prevalence of certain brain disorders between males and females, we also discuss putative sex-dependent influences on these neurodevelopmental events. From a translational perspective, understanding age- and sex-dependent astrocyte-specific molecular and functional changes may help to identify biomarkers of distinct cellular (dys)functions in health and disease, favouring the development of diagnostic tools or the selection of tailored treatment options for male/female patients.

Ramelteon protects against social defeat stress-associated abnormal behaviors

Psychological stress affects the neuroendocrine regulation, which modulates mental status and behaviors. Melatonin, a hormone synthesized primarily by the pineal gland, regulates many brain functions, including circadian rhythms, pain, sleep, and mood. Selective pharmacological melatonin agonist ramelteon has been clinically used to treat mood and sleep disorders. Posttraumatic stress disorder (PTSD) is a psychiatric condition associated with severe trauma; it is generally triggered by traumatic events, which lead to severe anxiety and uncontrollable trauma recall. We recently reported that repeated social defeat stress (RSDS) may induce robust anxiety-like behaviors and social avoidance in mice. In the present study, we investigated whether melatonin receptor activation by melatonin and ramelteon regulates RSDS-induced behavioral changes. Melatonin treatment improved social avoidance and anxiety-like behaviors in RSDS mice. Moreover, treatment of the non-selective MT1/MT2 receptor agonist, ramelteon, markedly ameliorated RSDS-induced social avoidance and anxiety-like behaviors. Moreover, activating melatonin receptors also balanced the expression of monoamine oxidases, glucocorticoid receptors, and endogenous antioxidants in the hippocampus. Taken together, our findings indicate that the activation of both melatonin and ramelteon regulates RSDS-induced anxiety-like behaviors and PTSD symptoms. The current study also showed that the regulatory effects of neuroendocrine mechanisms and cognitive behaviors on melatonin receptor activation in repeated social defeat stress.

Acute 2-phenyl-3-(phenylselanyl)benzofuran treatment reverses the neurobehavioral alterations induced by sleep deprivation in mice

Sleep is a fundamental state for maintaining the organism homeostasis. Disruptions in sleep patterns predispose to the appearance of memory impairments and mental disorders, including depression. Recent pre-clinical studies have highlighted the antidepressant-like properties of the synthetic compound 2-phenyl-3-(phenylselanyl)benzofuran (SeBZF1). To further investigate the neuromodulatory effects of SeBZF1, this study aimed to assess its therapeutic efficacy in ameliorating neurobehavioral impairments induced by sleep deprivation (SD) in mice. For this purpose, a method known as multiple platforms over water was used to induce rapid eye movement (REM) SD. Two hours after acute SD (24 h), male Swiss mice received a single treatment of SeBZF1 (5 mg/kg, intragastric route) or fluoxetine (a positive control, 20 mg/kg, intraperitoneal route). Subsequently, behavioral tests were conducted to assess spontaneous motor function (open-field test), depressive-like behavior (tail suspension test), and memory deficits (Y-maze test). Brain structures were utilized to evaluate oxidative stress markers, monoamine oxidase (MAO) and acetylcholinesterase (AChE) activities. Our findings revealed that SD animals displayed depressive-like behavior and memory impairments, which were reverted by SeBZF1 and fluoxetine treatments. SeBZF1 also reverted the increase in lipoperoxidation levels and glutathione peroxidase activity in the pre-frontal cortex in mice exposed to SD. Besides, the increase in hippocampal AChE activity induced by SD was overturned by SeBZF1. Lastly, cortical MAO-B activity was reestablished by SeBZF1 in mice that underwent SD. Based on the main findings of this study, it can be inferred that the compound SeBZF1 reverses the neurobehavioral alterations induced by sleep deprivation in male Swiss mice.

Luteolin promotes neuronogenesis in hippocampus of chronic unpredictable mild stress rats and primary hippocampus of fetal rats

OBJECTIVE

To investigate the effects of luteolin on chronic unpredictable mild stress (CUMS)-induced depressive rats and corticosterone (CORT)-induced depressive primary hippocampal neurons, and to elucidate the mechanism behind the action.

METHODS

The antidepressant mechanism of luteolin was studied by using CUMS rat model and primary hippocampal neurons in fetal rats. In vivo, novelty suppressed feeding, open-field and sucrose preference tests as well as Morris water maze were evaluated. The content of brain derived neurotrophic factor (BDNF), 5-hydroxytryptamine (5-HT), norepinephrine (NE), and dopamine (DA) in serum were detected by enzyme-linked immunosorbent assay. The mechanisms of luteolin were explored based on neurotrophin and hippocampal neurogenesis, and proliferation. Survival of the septo-temporal axis in hippocampus was assayed using the 5-bromo-2-deoxyuridine (BrdU), the expression of BDNF, neurotrophin-3 (NT-3), and nerve growth factor (NGF) in hippocampus dentate gyrus region were measured by Western-blotting. In vitro, BDNF, NT-3, tropomyosin receptor kinase B (TrkB), and phosphorylated cyclic adenosine monophosphate responsive element binding protein (p-CREB) were detected through the high content analysis (HCA) to investigate neurotrophin and apoptosis.

RESULTS

Induction of CUMS in rats induced depressive symptoms, while luteolin significantly enhanced sucrose consumption, decreased feeding latency, increased locomotor activity, escape latency, distance of target quadrant and regulated the content of depressive-like biomarkers. Histology analysis revealed that luteolin increased the abundance of new born neurons that had been labeled with BrdU, BrdU + neuronal nuclear antigen, and BrdU + doublecortin in septo-temporal axis of S2 (mid-septal) and T3 (mid-temporal). Moreover, expression of BDNF, NT-3, and NGF increased significantly in the septo-temporal axis of S2 and T3. HCA showed increased expression of BDNF, NT-3, TrkB and p-CREB in primary hippocampal neurons.

CONCLUSION

The results provided direct evidence that luteolin has an antidepressant effect and could effectively promote the regeneration of the septotemporal axis nerve and hippocampal neuronutrition, which suggested that the antidepressant effect of luteolin may be related to hippocampal neurogenesis.

Hippocampal subfield morphology from first episodes of bipolar disorder type II and major depressive disorder in a drug naïve Chinese cohort

Introduction

Symptoms during the onset of major depressive disorder [MDD] and bipolar disorder type II [BD-II] are similar. The difference of hippocampus subregion could be a biological marker to distinguish MDD from BD-II.

Methods

We recruited 61 drug-naïve patients with a first-episode MDD and BD-II episode and 30 healthy controls (HC) to participate in a magnetic resonance imaging [MRI] study. We built a general linear model (one-way analysis of covariance) with 22 hippocampal subfields and two total hippocampal volumes as dependent variables, and the diagnosis of MDD, BD-II, and HC as independent variables. We performed pair-wise comparisons of hippocampal subfield volumes between MDD and HC, BD-II and MDD, BD-II and HC with post hoc for primary analysis.

Results

We identified three regions that differed significantly in size between patients and controls. The left hippocampal fissure, the hippocampal-amygdaloid transition area (HATA), and the right subiculum body were all significantly larger in patients with MDD compared with the HC. In the onset of first-episode of MDD, the hippocampal volume increased significantly, especially on the left side comparing to HC. However, we found differences between MDD and BD-II were not statistically significant. The volume of the left HATA and right subiculum body in BD-II was larger.

Conclusions

The sample size of this study is relatively small, as it is a cross-sectional comparative study. In both MDD and BD-II groups, the volume of more left subregions appeared to increase. The left subregions were severely injured in the development of depressive disorder.

The Impact of Depression on Detrimental Changes in Bone Microstructure in Female Mice

Background

Several clinical studies have examined the connection between depression and bone loss, but the cause-and-effect relationship between the two conditions, especially in animal models, is not well-studied.

Methods

A total of 32 female mice were, randomly divided into control group (CON, n=19) and depression group (DEP, n=13). The mice in the DEP group were subjected to 21 consecutive days of restraint stress, following depressive-like behaviors were assessment. The femurs were collected using Micro-Computed Tomography (μCT) and histochemical staining. In parallel, levels of serotonin-related proteins in the brain were measured using Western blot analysis, and sex hormone profiles were determined through liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS).

Results

The mice in the DEP group exhibited clear signs of depressive-like behaviors and an increase in serotonin transporter levels (t=-2.435, P< 0.05). In comparison to the CON mice, the DEP mice showed a decrease in bone mineral density (t =3.741, P< 0.05), bone surface area density (t =8.009, P<0.01), percent bone volume (t =4.293, P< 0.05), trabecular number (t =5.844, P<0.01), and connected density (t =11.000, P< 0.05). Additionally, there was an increase in trabecular separation (t =-7.436, P<0.01) in DEP mice. Furthermore, the DEP mice displayed a significant reduction in serum estrogen levels (t =4.340, P< 0.05) and changes in its metabolite (t =-3.325, P< 0.05), while the levels of androgens remained unchanged.

Conclusion

The restraint stress not only led to the development of depressive-like behaviors but also disrupted the estrogen metabolism pathway, resulting in damage to bone mass and microstructure in female mice. These findings suggest that stress-induced depression may pose a risk for bone loss in female mice by altering estrogen metabolism pathways.

The involvement of neuroinflammation in an animal model of dementia and depression

Alzheimer's disease (AD) and depression are inflammatory pathologies, leading to increased inflammatory response and neurotoxicity. Therefore, this study aimed to evaluate the effect of the treatment with fluoxetine and/or galantamine and/or donepezil on the levels of proinflammatory and anti-inflammatory cytokines in a mixed animal model of depression and dementia. Adult male Wistar rats underwent chronic mild stress (CMS) protocol for 40 days and were subjected to stereotaxic surgery for intra-hippocampal administration of amyloid-beta (Aꞵ) peptide or artificial cerebrospinal fluid (ACSF) to mimic the dementia animal model. On the 42nd day, animals were treated with water, galantamine, donepezil, and/or fluoxetine, orally for 17 days. On the 57th and 58th days, the Splash and Y-maze tests for behavior analysis were performed. The frontal cortex and hippocampus were used to analyze the tumor necrosis factor alfa (TNF-α), interleukin 1 beta (IL-1ꞵ), IL-6, and IL-10 levels. The results of this study show that animals subjected to CMS and administration of Aꞵ had anhedonia, cognitive impairment, increased TNF-α and IL-1ꞵ levels in the frontal cortex, and reduced IL-10 levels in the hippocampus. All treatment groups were able to reverse the cognitive impairment. Only donepezil did not decrease the TNF-α levels in the hippocampus. Fluoxetine + galantamine and fluoxetine + donepezil reversed the anhedonia. Fluoxetine reversed the anhedonia and IL-1ꞵ levels in the frontal cortex. In addition, fluoxetine + donepezil reversed the reduction of IL-10 levels in the hippocampus. The results indicate a pathophysiological interaction between AD and depression, and the association of medications in the future may be a possible therapeutic strategy to reduce inflammation, especially the fluoxetine-associated treatments.

Dopamine D1 receptor in medial prefrontal cortex mediates the effects of TAAR1 activation on chronic stress-induced cognitive and social deficits

Trace amine-associated receptor 1 (TAAR1) is an intracellular expressed G-protein-coupled receptor that is widely expressed in major dopaminergic areas and plays a crucial role in modulation of central dopaminergic neurotransmission and function. Pharmacological studies have clarified the roles of dopamine D1 receptor (D1R) in the medial prefrontal cortex (mPFC) in cognitive function and social behaviors, and chronic stress can inhibit D1R expression due to its susceptibility. Recently, we identified TAAR1 in the mPFC as a potential target for treating chronic stress-induced cognitive and social dysfunction, but whether D1R is involved in mediating the effects of TAAR1 agonist remains unclear. Combined genomics and transcriptomic studies revealed downregulation of D1R in the mPFC of TAAR1-/- mice. Molecular dynamics simulation showed that hydrogen bond, salt bridge, and Pi-Pi stacking interactions were formed between TAAR1 and D1R indicating a stable TAAR1-D1R complex structure. Using pharmacological interventions, we found that D1R antagonist disrupted therapeutic effect of TAAR1 partial agonist RO5263397 on stress-related cognitive and social dysfunction. Knockout TAAR1 in D1-type dopamine receptor-expressing neurons reproduced adverse effects of chronic stress, and TAAR1 conditional knockout in the mPFC led to similar deficits, along with downregulation of D1R expression, all of these effects were ameliorated by viral overexpression of D1R in the mPFC, suggesting the functional interaction between TAAR1 and D1R. Collectively, our data elucidate the possible molecular mechanism that D1R in the mPFC mediates the effects of TAAR1 activation on chronic stress-induced cognitive and social deficits.

Regulation of depressive-like behaviours by palmitoylation: Role of AKAP150 in the basolateral amygdala

BACKGROUND AND PURPOSE

Protein palmitoylation is involved in learning and memory, and in emotional disorders. Yet, the underlying mechanisms in these processes remain unclear. Herein, we describe that A-kinase anchoring protein 150 (AKAP150) is essential and sufficient for depressive-like behaviours in mice via a palmitoylation-dependent mechanism.

EXPERIMENTAL APPROACH

Depressive-like behaviours in mice were induced by chronic restraint stress (CRS) and chronic unpredictable mild stress (CUMS). Palmitoylated proteins in the basolateral amygdala (BLA) were assessed by an acyl-biotin exchange assay. Genetic and pharmacological approaches were used to investigate the role of the DHHC2-mediated AKAP150 palmitoylation signalling pathway in depressive-like behaviours. Electrophysiological recording, western blotting and co-immunoprecipitation were performed to define the mechanistic pathway.

KEY RESULTS

Chronic stress successfully induced depressive-like behaviours in mice and enhanced AKAP150 palmitoylation in the BLA, and a palmitoylation inhibitor was enough to reverse these changes. Blocking the AKAP150-PKA interaction with the peptide Ht-31 abolished the CRS-induced AKAP150 palmitoylation signalling pathway. DHHC2 expression and palmitoylation levels were both increased after chronic stress. DHHC2 knockdown prevented CRS-induced depressive-like behaviours, as well as attenuating AKAP150 signalling and synaptic transmission in the BLA in CRS-treated mice.

CONCLUSION AND IMPLICATIONS

These results delineate that DHHC2 modulates chronic stress-induced depressive-like behaviours and synaptic transmission in the BLA via the AKAP150 palmitoylation signalling pathway, and this pathway may be considered as a promising novel therapeutic target for major depressive disorder.

Unraveling the molecular basis of cannabidiolic acid methyl Ester's anti-depressive effects in a rat model of treatment-resistant depression

Major depressive disorder (MDD) stands as a significant cause of disability globally. Cannabidiolic Acid-Methyl Ester (CBDA-ME) (EPM-301, HU-580), a derivative of Cannabidiol, demonstrates immediate antidepressant-like effects, yet it has undergone only minimal evaluation in psychopharmacology. Our goal was to investigate the behavioral and potential molecular mechanisms associated with the chronic oral administration of this compound in the Wistar Kyoto (WKY) genetic model of treatment-resistant depression. Male WKY rats were subjected to behavioral assessments before and after receiving chronic (14-day) oral doses of CBDA-ME (0.5 mg/kg), 15 mg/kg of imipramine or vehicle. At the end of the study, plasma corticosterone levels and mRNA expression of various genes in the medial Prefrontal Cortex and Hippocampus were measured. Behavioral outcomes from CBDA-ME treatment indicated an antidepressant-like effect similar to imipramine, as oral ingestion reduced immobility and increased swimming duration in the Forced Swim Test. Neither treatment influenced locomotion in the Open Field Test nor preference in the Saccharin Preference Test. The behavioral impact in WKY rats coincided with reduced corticosterone serum levels, upregulated mRNA expression of Cannabinoid receptor 1, Fatty Acid Amide Hydrolase, and Corticotropin-Releasing Hormone Receptor 1, alongside downregulation of the Serotonin Transporter in the hippocampus. Additionally, there was an upregulation of CB1 mRNA expression and downregulation of Brain-Derived Neurotrophic Factor in the mPFC. These findings contribute to our limited understanding of the antidepressant effects of CBDA-ME and shed light on its potential psychopharmacological mechanisms. This discovery opens up possibilities for utilizing cannabinoids in the treatment of major depressive disorder and related conditions.

Knocking out Selenium Binding Protein 1 Induces Depressive-Like Behavior in Mice

Selenium binding protein 1 (SELENBP1) is involved in neurologic disorders, such as multiple sclerosis, spinal cord injury, Parkinson's disease, epilepsy, and schizophrenia. However, the role of SELENBP1 in the neurogenesis of depression, which is a neurologic disorder, and the underlying mechanisms of oxidative stress and inflammation in depression remain unknown. In this study, we evaluated the changes in the expression levels of SELENBP1 in the hippocampus of a mouse model of depression and in the serum of human patients with depression using the Gene Expression Omnibus database. These changes were validated using blood samples from human patients with depression and mouse models with chronic unpredictable mild stress (CUMS)-induced depressive-like behavior. We also investigated the effects of SELENBP1 knockout (KO) on inflammation, oxidative stress, and hippocampal neurogenesis in mice with CUMS-induced depression. Our results revealed that SELENBP1 levels was decreased in the blood of human patients with depression and in the hippocampus of mice with CUMS-induced depression. SELENBP1 KO increased CUMS-induced depressive behavior in mice and caused dysregulation of inflammatory cytokines and oxidative stress. This led to a decrease in the numbers of doublecortin- and Ki67-positive cells, which might aggravate CUMS-induced depressive symptoms. These findings suggest that SELENBP1 might be involved in the regulation of neurogenesis in mice with depression and could be served as a potential target for diagnosing and treating depression.

Dynamic Changes of the Infralimbic Cortex and Its Regulation of the Prelimbic Cortex in Rats with Chronic Inflammatory Pain

The prelimbic cortex (PL) is actively engaged in pain modulation. The infralimbic cortex (IL) has been reported to regulate the PL. However, how this regulation affects pain remains unclear. In the present study, we recorded temporary hyper-activity of PL pyramidal neurons responding to nociceptive stimuli, but a temporary hypo-function of the IL by in vivo electrophysiological recording in rats with peripheral inflammation. Manipulation of the PL or IL had opposite effects on thermal hyperalgesia. Furthermore, the functional connectivity and chemogenetic regulation between the subregions indicated an inhibitory influence of the IL on the PL. Activation of the pathway from the IL to the PL alleviated thermal hyperalgesia, whereas its inhibition exacerbated chronic pain. Overall, our results suggest a new mechanism underlying the role of the medial prefrontal cortex in chronic pain: hypo-function of the IL leads to hyperactivity of the PL, which regulates thermal hyperalgesia, and thus contributes to the chronicity of pain.

Chronic restraint stress induces depression-like behaviors and alterations in the afferent projections of medial prefrontal cortex from multiple brain regions in mice

INTRODUCTION

The medial prefrontal cortex (mPFC) forms output pathways through projection neurons, inversely receiving adjacent and long-range inputs from other brain regions. However, how afferent neurons of mPFC are affected by chronic stress needs to be clarified. In this study, the effects of chronic restraint stress (CRS) on the distribution density of mPFC dendrites/dendritic spines and the projections from the cortex and subcortical brain regions to the mPFC were investigated.

METHODS

In the present study, C57BL/6 J transgenic (Thy1-YFP-H) mice were subjected to CRS to establish an animal model of depression. The infralimbic (IL) of mPFC was selected as the injection site of retrograde AAV using stereotactic technique. The effects of CRS on dendrites/dendritic spines and afferent neurons of the mPFC IL were investigaed by quantitatively assessing the distribution density of green fluorescent (YFP) positive dendrites/dendritic spines and red fluorescent (retrograde AAV recombinant protein) positive neurons, respectively.

RESULTS

The results revealed that retrograde tracing virus labeled neurons were widely distributed in ipsilateral and contralateral cingulate cortex (Cg1), second cingulate cortex (Cg2), prelimbic cortex (PrL), infralimbic cortex, medial orbital cortex (MO), and dorsal peduncular cortex (DP). The effects of CRS on the distribution density of mPFC red fluorescence positive neurons exhibited regional differences, ranging from rostral to caudal or from top to bottom. Simultaneously, CRS resulted a decrease in the distribution density of basal, proximal and distal dendrites, as well as an increase in the loss of dendritic spines of the distal dendrites in the IL of mPFC. Furthermore, varying degrees of red retrograde tracing virus fluorescence signals were observed in other cortices, amygdala, hippocampus, septum/basal forebrain, hypothalamus, thalamus, mesencephalon, and brainstem in both ipsilateral and contralateral brain. CRS significantly reduced the distribution density of red fluorescence positive neurons in other cortices, hippocampus, septum/basal forebrain, hypothalamus, and thalamus. Conversely, CRS significantly increased the distribution density of red fluorescence positive neurons in amygdala.

CONCLUSION

Our results suggest a possible mechanism that CRS leads to disturbances in synaptic plasticity by affecting multiple inputs to the mPFC, which is characterized by a decrease in the distribution density of dendrites/dendritic spines in the IL of mPFC and a reduction in input neurons of multiple cortices to the IL of mPFC as well as an increase in input neurons of amygdala to the IL of mPFC, ultimately causing depression-like behaviors.

A clinical study based on bidirectional Mendelian randomization: Correlation between generalized anxiety disorder and weight-bearing joints osteoarthritis

Objectives

Bidirectional Mendelian randomization (MR) combined with clinical case analysis was used to elucidate the relationship between generalized anxiety disorder (GAD) caused by mental overload and the risk of weight-bearing joint (hip/knee) osteoarthritis (OA).

Methods

We performed MR analyses using publicly released genome-wide association study summary statistics to measure the causal effects between mental overload and weight-bearing joint OA risk. The primary MR analysis utilized the inverse-variance weighted (IVW) method, complemented by additional methods, including simple mode, weighted mode, MR-Egger regression, and weighted median. The leave-one-out method was used for sensitivity analysis. Concurrently, data from patients with OA (Kellgren-Lawrence grades III-IV) who needed total knee/hip arthroplasty were collected. Patient assessments were conducted utilizing the Western Ontario and McMaster Universities arthritis index, Penn State worry questionnaire, and visual analogue scale.

Results

Genetically predisposed GAD did not correlate with the risk of weight-bearing joint OA (IVW odds ratio [OR] = 0.840, 95 % confidence interval = 0.128, 5.50, P = 0.855). In reverse MR analyses, we detected no causal effect of weight-bearing OA on GAD (IVW OR = 1.00, 95 % CI = 0.985, 1.03, P = 0.687). In the clinical case evaluation, weight overload joint OA and GAD were highly correlated.

Conclusion

MR analysis indicated no bidirectional causal effect of GAD caused by mental overload on weight-bearing joint (hip or knee) OA. Clinical studies support the finding that GAD is highly correlated with weight-bearing joint OA. However, whether there is a causal relationship between GAD caused by mental overload and weight-overloading joint OA requires further investigation.

Prenatal Maternal Psychological Distress During the COVID-19 Pandemic and Newborn Brain Development

Importance

Elevated maternal psychological distress during pregnancy is associated with altered fetal brain development. During the COVID-19 pandemic, prenatal maternal psychological distress more than doubled.

Objective

To examine the association of the pandemic and rising maternal psychological distress with brain growth in newborns using quantitative 3-dimensional volumetric magnetic resonance imaging (MRI).

Design, Setting, and Participants

This prospective cross-sectional study recruited mother-infant dyads at Children's National Hospital, Washington, DC, during the COVID-19 pandemic (June 1, 2020, to June 30, 2022) into a longitudinal infant brain development study and compared them with an existing normative healthy cohort (recruited March 1, 2014, to December 31, 2019). Exclusion criteria included multiple gestation pregnancy, known or suspected congenital infection, documented chromosomal abnormalities, or any maternal contraindication to MRI, as well as prenatal COVID-19 exposure. Infants with structural brain abnormalities or a postnatal confirmation of a genetic syndrome were excluded.

Exposure

Psychological distress during COVID-19 pandemic.

Main Outcomes and Measures

Prenatal maternal mental health was evaluated using the Spielberger State-Trait Anxiety Inventory and the Perceived Stress Scale. Neonates underwent nonsedated brain MRI. An ordinary least squares linear regression model was used to measure the differences in regional brain volumes of neonates born before vs during the pandemic with and without exposure to elevated prenatal maternal psychological distress after adjustment for neonatal sex and gestational age at MRI and maternal age and educational level.

Results

A total of 159 mother-infant dyads were included in the analysis: 103 before and 56 during the pandemic (median gestational age of infants, 39.6 [IQR, 38.4-40.4] weeks; median maternal age, 34.5 [IQR, 31.0-37.0] years). Eighty-three infants (52.2%) were female. Among the mothers, 130 (81.8%) had a college degree and 87 (54.7%) had a graduate degree. Forty-four mothers (27.7%) identified as Asian, Hispanic, or multiracial; 27 (17.0%), as Black; and 88 (55.3%), as White. Scores on anxiety and stress measures were significantly increased in the pandemic cohort. Infants of mothers with elevated maternal distress showed median reductions in white matter (-0.36 [95% CI, -0.61 to -0.11] cm3; Q < .001), right hippocampal (-0.35 [95% CI, -0.65 to -0.06] cm3; Q = .04), and left amygdala (-0.49 [95% CI, -0.84 to -0.13] cm3; Q = .03) volumes compared with infants of mothers with low distress levels. After adjusting for the cohort effect of the pandemic, elevated trait anxiety remained significantly associated with decreased left amygdalar volumes (-0.71 [95% CI, -1.12 to -0.29]; Q < .001).

Conclusions and Relevance

In this cross-sectional study of maternal-infant dyads prior to and during the COVID-19 pandemic, regional neonatal brain volumes were associated with elevated maternal psychological distress.

Myelin-associated oligodendrocytic basic protein-dependent myelin repair confers the long-lasting antidepressant effect of ketamine

Ketamine exhibits rapid and sustained antidepressant effects. As decreased myelination has been linked to depression pathology, changes in myelination may be a pivotal mechanism underlying ketamine's long-lasting antidepressant effects. Although ketamine has a long-lasting facilitating effect on myelination, the precise roles of myelination in ketamine's sustained antidepressant effects remain unknown. In this study, we employed spatial transcriptomics (ST) to examine ketamine's lasting effects in the medial prefrontal cortex (mPFC) and hippocampus of mice subjected to chronic social defeat stress and identified several differentially expressed myelin-related genes. Ketamine's ability to restore impaired myelination in the brain by promoting the differentiation of oligodendrocyte precursor cells (OPCs) into mature oligodendrocytes was demonstrated. Moreover, we showed that inhibiting the expression of myelin-associated oligodendrocytic basic protein (Mobp) blocked ketamine's long-lasting antidepressant effects. We also illustrated that α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) signaling mediated ketamine's facilitation on myelination. In addition, we found that the (R)-stereoisomer of ketamine showed stronger effects on myelination than (S)-ketamine, which may explain its longer-lasting antidepressant effects. These findings reveal novel mechanisms underlying the sustained antidepressant effects of ketamine and the differences in antidepressant effects between (R)-ketamine and (S)-ketamine, providing new insights into the role of myelination in antidepressant mechanisms.

Beyond the serotonin deficit hypothesis: communicating a neuroplasticity framework of major depressive disorder

The serotonin deficit hypothesis explanation for major depressive disorder (MDD) has persisted among clinicians and the general public alike despite insufficient supporting evidence. To combat rising mental health crises and eroding public trust in science and medicine, researchers and clinicians must be able to communicate to patients and the public an updated framework of MDD: one that is (1) accessible to a general audience, (2) accurately integrates current evidence about the efficacy of conventional serotonergic antidepressants with broader and deeper understandings of pathophysiology and treatment, and (3) capable of accommodating new evidence. In this article, we summarize a framework for the pathophysiology and treatment of MDD that is informed by clinical and preclinical research in psychiatry and neuroscience. First, we discuss how MDD can be understood as inflexibility in cognitive and emotional brain circuits that involves a persistent negativity bias. Second, we discuss how effective treatments for MDD enhance mechanisms of neuroplasticity-including via serotonergic interventions-to restore synaptic, network, and behavioral function in ways that facilitate adaptive cognitive and emotional processing. These treatments include typical monoaminergic antidepressants, novel antidepressants like ketamine and psychedelics, and psychotherapy and neuromodulation techniques. At the end of the article, we discuss this framework from the perspective of effective science communication and provide useful language and metaphors for researchers, clinicians, and other professionals discussing MDD with a general or patient audience.

Bacillus coagulans and Clostridium butyricum synergistically alleviate depression in a chronic unpredictable mild stress mouse model through altering gut microbiota and prefrontal cortex gene expression

Introduction: The prevalence of major depressive disorder (MDD) has gradually increased and has attracted widespread attention. The aim of this study was to investigate the effect of a probiotic compound consisting of Bacillus coagulans and Clostridium butyricum, on a mouse depression model. Methods: Mice were subjected to chronic unpredictable mild stress (CUMS) and then treated with the probiotics at different concentrations. And mice received behavior test such as forced swimming test and tail suspension test. After that, all mice were sacrificed and the samples were collected for analysis. Moreover, prefrontal cortex (PFC) gene expression and the gut microbiota among different groups were also analyzed. Results: Probiotics improved depressive-like behavior in CUMS mice, as indicated by decreased immobility time (p < 0.05) in the forced swimming test and tail suspension test. probiotics intervention also increased the level of 5-hydroxytryptamine (5-HT) in the prefrontal cortex and decreased the adrenocorticotropic hormone (ACTH) level in serum. In addition, by comparing the PFC gene expression among different groups, we found that the genes upregulated by probiotics were enriched in the PI3K-Akt signaling pathway in the prefrontal cortex. Moreover, we found that downregulated genes in prefrontal cortex of CUMS group such as Sfrp5 and Angpt2, which were correlated with depression, were reversed by the probiotics. Furthermore, the probiotics altered the structure of the gut microbiota, and reversed the reduction of cob(II)yrinate a,c-diamide biosynthesis I pathway in CUMS group. Several species like Bacteroides caecimuris and Parabacteroides distasoni, whose abundance was significantly decreased in the CUMS group but reversed after the probiotics intervention, showed significantly positive correlation with depression associated genes such as Tbxas1 and Cldn2. Discussion: These findings suggested that CUMS-induced depression-like behavior can be alleviated by the probiotics, possibly through alterations in the PFC gene expression and gut microbiota.

HMGB1/STAT3/p65 axis drives microglial activation and autophagy exert a crucial role in chronic Stress-Induced major depressive disorder

INTRODUCTION

Neuroinflammation and autophagy are implicated in stress-related major depressive disorder (MDD), but the underlying molecular mechanisms remain largely unknown.

OBJECTIVES

Here, we identified that MDD regulated by HMGB1/STAT3/p65 axis mediated microglial activation and autophagy for the first time. Further investigations were performed to uncover the effects of this axis on MDD in vivo and in vitro.

METHODS

Bioinformatics analyses were used to re-analysis the transcriptome data from the dorsolateral prefrontal cortex (dlPFC) of post-mortem male MDD patients. The expression level of HMGB1 and its correlation with depression symptoms were explored in MDD clinical patients and chronic social defeat stress (CSDS)-induced depression model mice. Specific adeno-associated virus and recombinant (r)HMGB1 injection into the medial PFC (mPFC) of mice, and pharmacological inhibitors with rHMGB1 in two microglial cell lines exposed to lipopolysaccharide were used to analyze the effects of HMGB1/STAT3/p65 axis on MDD.

RESULTS

The differential expression of genes from MDD patients implicated in microglial activation and autophagy regulated by HMGB1/STAT3/p65 axis. Serum HMGB1 level was elevated in MDD patients and positively correlated with symptom severity. CSDS not only induced depression-like states in mice, but also enhanced microglial reactivity, autophagy as well as activation of the HMGB1/STAT3/p65 axis in mPFC. The expression level of HMGB1 was mainly increased in the microglial cells of CSDS-susceptible mice, which also correlated with depressive-like behaviors. Specific HMGB1 knockdown produced a depression-resilient phenotype and suppressed the associated microglial activation and autophagy effects of CSDS-induced. The effects induced by CSDS were mimicked by exogenous administration of rHMGB1 or specific overexpression of HMGB1, while blocked by STAT3 inhibitor or p65 knockdown. In vitro, inhibition of HMGB1/STAT3/p65 axis prevented lipopolysaccharide-induced microglial activation and autophagy, while rHMGB1 reversed these changes.

CONCLUSION

Our study established the role of microglial HMGB1/STAT3/p65 axis in mPFC in mediating microglial activation and autophagy in MDD.

Transcutaneous vagus nerve stimulation modulates depression-like phenotype induced by high-fat diet via P2X7R/NLRP3/IL-1β in the prefrontal cortex

BACKGROUND

Depression is a common psychiatric disorder in diabetic patients. Depressive mood associated with obesity/metabolic disorders is related to the inflammatory response caused by long-term consumption of high-fat diets, but its molecular mechanism is unclear. In this study, we investigated whether the antidepressant effect of transcutaneous auricular vagus nerve stimulation (taVNS) in high-fat diet rats works through the P2X7R/NLRP3/IL-1β pathway.

METHODS

We first used 16S rRNA gene sequencing analysis and LC-MS metabolomics assays in Zucker diabetic fatty (ZDF) rats with long-term high-fat diet (Purina #5008) induced significant depression-like behaviors. Next, the forced swimming test (FST) and open field test (OFT) were measured to evaluate the antidepressive effect of taVNS. Immunofluorescence and western blotting (WB) were used to measure the microglia state and the expression of P2X7R, NLRP3, and IL-1β in PFC.

RESULTS

Purina#5008 diet induced significant depression-like behaviors in ZDF rats and was closely related to purine and inflammatory metabolites. Consecutive taVNS increased plasma insulin concentration, reduced glycated hemoglobin and glucagon content in ZDF rats, significantly improved the depressive-like phenotype in ZDF rats through reducing the microglia activity, and increased the expression of P2X7R, NLRP3, and IL-1β in the prefrontal cortex (PFC).

CONCLUSION

The P2X7R/NLRP3/IL-1β signaling pathway may play an important role in the antidepressant-like behavior of taVNS, which provides a promising mechanism for taVNS clinical treatment of diabetes combined with depression.

Group differences in OXT methylation between patients with Major Depressive Disorder and healthy controls: A pre-registered replication study

Depression is linked to stress which leaves traces in the epigenetic signature of genes. The oxytocin system is implicated in allostatic processes promoting adaption to environmental stressors. Interactions of the oxytocin system with the environment, e.g., methylation of the gene coding for oxytocin (OXT), are candidates for the investigation of the biological underpinnings of depression. Recently, we found hypomethylation of OXT in patients with Major Depressive Disorder (MDD) compared to healthy controls (HC). Since the replicability of findings is a key point of criticism in (epi‑)genetic research, we aimed to confirm our previous findings in a pre-registered study (data was stored in a database prior to pre-registration) within a new sample of n = 85 patients with MDD and n = 85 HC. We investigated OXT DNA-methylation in peripheral blood samples, stressful life events and depression severity. In accordance with our previous study, we found hypomethylation of OXT in patients with MDD compared to HC. Methylation was not associated with stressful life events. Patients reported significantly more stressful life events compared to HC. Our study revealed that hypomethylation of OXT can be demonstrated in a reproducible fashion and provides further evidence for the involvement of the oxytocin system in depression.

Sporoderm-removed Ganoderma lucidum spores ameliorated early depression-like behavior in a rat model of sporadic Alzheimer's disease

Introduction: Ganoderma lucidum: (G. lucidum, Lingzhi) is a medicinal and edible homologous traditional Chinese medicine that is used to treat various diseases, including Alzheimer's disease and mood disorders. We previously reported that the sporoderm-removed G. lucidum spore extract (RGLS) prevented learning and memory impairments in a rat model of sporadic Alzheimer's disease (sAD), but the effect of RGLS on depression-like behaviors in this model and its underlying molecular mechanisms of action remain unclear. Method: The present study investigated protective effects of RGLS against intracerebroventricular streptozotocin (ICV-STZ)-induced depression in a rat model of sAD and its underlying mechanism. Effects of RGLS on depression- and anxiety-like behaviors in ICV-STZ rats were assessed in the forced swim test, sucrose preference test, novelty-suppressed feeding test, and open field test. Results: Behavioral tests demonstrated that RGLS (360 and 720 mg/kg) significantly ameliorated ICV-STZ-induced depression- and anxiety-like behaviors. Immunofluorescence, Western blot and enzyme-linked immunosorbent assay results further demonstrated that ICV-STZ rats exhibited microglia activation and neuroinflammatory response in the medial prefrontal cortex (mPFC), and RGLS treatment reversed these changes, reflected by the normalization of morphological changes in microglia and the expression of NF-κB, NLRP3, ASC, caspase-1 and proinflammatory cytokines. Golgi staining revealed that treatment with RGLS increased the density of mushroom spines in neurons. This increase was associated with elevated expression of brain-derived neurotrophic protein in the mPFC. Discussion: In a rat model of ICV-STZ-induced sAD, RGLS exhibits antidepressant-like effects, the mechanism of which may be related to suppression of the inflammatory response modulated by the NF-κB/NLRP3 pathway and enhancement of synaptic plasticity in the mPFC.

Association of dietary overall antioxidant intake with all-cause and cause-specific mortality among adults with depression: evidence from NHANES 2005-2018

Higher intakes of individual antioxidants such as vitamins A, C, and E have been linked to mortality in the general population, but the association of overall antioxidant intake with mortality especially in depressed adults remains unclear. We aimed to investigate whether the dietary overall antioxidant intake is associated with all-cause and cause-specific mortality among depressed adults. This study included 3051 US adults with depression, who participated in the National Health and Nutrition Examination Survey (NHANES) from 2005 to 2018. Patient Health Questionnaire-9 (PHQ-9) was used to define depression and evaluate depression severity. The dietary antioxidant quality score (DAQS) and dietary antioxidant index (DAI) were calculated based on the intakes of vitamins A, C, and E, zinc, selenium, and magnesium. A higher DAQS and DAI were significantly associated with lower depression scores (PHQ-9) (all P-trend < 0.05). For individual antioxidants, significant negative associations of vitamins A and E with all-cause mortality were observed. For overall antioxidant intake, the DAQS and DAI were inversely associated with all-cause and cancer mortality. Compared with participants in the lowest categories of DAQS and DAI, the corresponding HRs (95% CIs) in the highest categories were 0.63 (0.42-0.93) and 0.70 (0.49-0.98) for all-cause mortality and 0.39 (0.17-0.87) and 0.43 (0.21-0.88) for cancer mortality, respectively. The overall dietary antioxidant intake was beneficially associated with all-cause and cancer mortality in depressed adults. These findings suggest that comprehensive dietary antioxidant intake may improve depressive symptoms and lower mortality risk among adults with depression.

Dietary Galacto-oligosaccharides Ameliorate Atopic Dermatitis-like Skin Inflammation and Behavioral Deficits by Modulating Gut Microbiota-Brain-Skin Axis

Atopic dermatitis (AD), a chronic, highly pruritic, and inflammatory skin disorder, often coexists with psychiatric comorbidities including anxiety and depression, posing considerable challenges for treatment. The current research aims at evaluating the efficacy and potential therapeutic mechanism of galacto-oligosaccharides (GOS) on AD-like skin lesions and comorbid anxiety/depressive disorders. Macroscopical and histopathological examination showed that GOS could markedly relieve skin inflammation by decreasing the production of IgE, IL-4, IL-13, IFN-γ, and TNF-α and regulating the PPAR-γ/NF-κB signaling in DNFB-induced AD mice. Moreover, GOS significantly improved the anxiety- and depressive-like symptoms as mirrored by the behavior tests including FST, TST, OFT, and EZM through normalizing the neurotransmitter levels of 5-HT, DA, NE, and CORT in the brain. Mechanistically, by virtue of the high-throughput 16S rRNA gene sequencing and GC-MS techniques, GOS restructured the gut microbiota and specifically induced the proliferation of Lactobacillus and Alloprevotella, leading to an increase in the total content of fecal SCFAs, in particular acetate and butyrate. Pearson correlation analysis found a marked correlation among the altered gut microbiota/SCFAs, AD-associated skin manifestations, and comorbid behavioral phenotypes. Collectively, this work highlights that GOS is a promising strategy against both AD and associated depressive symptoms by modulating the gut microbiota-brain-skin axis.

Melatonin is a Neuroprotective and Antioxidant Agent against Neurotoxicity Induced by an Intrahippocampal Injection of Nickel in Rats

The investigation into the hippocampal function and its response to heavy metal exposure is crucial for understanding the mechanisms underlying neurotoxicity, this can potentially inform strategies for mitigating the adverse effects associated with heavy metal exposure. Melatonin is an essential neuromodulator known for its efficacy as an antioxidant. In this study, we aimed to determine whether melatonin could protect against Nickel (Ni) neurotoxicity. To achieve this, we performed an intracerebral injection of Ni (300 µM NiCl2) into the right hippocampus of male Wistar rats, followed by melatonin treatment. Based on neurobehavioral and neurobiochemical assessments, our results demonstrate that melatonin efficiently enhances Ni-induced behavioral dysfunction and cognitive impairment. Specifically, melatonin treatment positively influences anxious behavior, significantly reduces immobility time in the forced swim test (FST), and improves learning and spatial memory abilities. Moreover, neurobiochemical assays revealed that melatonin treatment modulates the Ni-induced alterations in oxidative stress balance by increasing antioxidant enzyme activities, such as superoxide dismutase (SOD) and catalase (CAT). Additionally, we observed that melatonin significantly attenuated the increased levels of lipid peroxidation (LPO) and nitric oxide (NO). In conclusion, the data from this study suggests that melatonin attenuates oxidative stress, which is the primary mechanism responsible for Ni-induced neurotoxicity. Considering that the hippocampus is the main structure involved in the pathology associated with heavy metal intoxication, such as Ni, these findings underscore the potential therapeutic efficacy of melatonin in mitigating heavy metal-induced brain damage.

Annual Research Review: Neuroimmune network model of depression: a developmental perspective

Depression is a serious public health problem, and adolescence is an 'age of risk' for the onset of Major Depressive Disorder. Recently, we and others have proposed neuroimmune network models that highlight bidirectional communication between the brain and the immune system in both mental and physical health, including depression. These models draw on research indicating that the cellular actors (particularly monocytes) and signaling molecules (particularly cytokines) that orchestrate inflammation in the periphery can directly modulate the structure and function of the brain. In the brain, inflammatory activity heightens sensitivity to threats in the cortico-amygdala circuit, lowers sensitivity to rewards in the cortico-striatal circuit, and alters executive control and emotion regulation in the prefrontal cortex. When dysregulated, and particularly under conditions of chronic stress, inflammation can generate feelings of dysphoria, distress, and anhedonia. This is proposed to initiate unhealthy, self-medicating behaviors (e.g. substance use, poor diet) to manage the dysphoria, which further heighten inflammation. Over time, dysregulation in these brain circuits and the inflammatory response may compound each other to form a positive feedback loop, whereby dysregulation in one organ system exacerbates the other. We and others suggest that this neuroimmune dysregulation is a dynamic joint vulnerability for depression, particularly during adolescence. We have three goals for the present paper. First, we extend neuroimmune network models of mental and physical health to generate a developmental framework of risk for the onset of depression during adolescence. Second, we examine how a neuroimmune network perspective can help explain the high rates of comorbidity between depression and other psychiatric disorders across development, and multimorbidity between depression and stress-related medical illnesses. Finally, we consider how identifying neuroimmune pathways to depression can facilitate a 'next generation' of behavioral and biological interventions that target neuroimmune signaling to treat, and ideally prevent, depression in youth and adolescents.

Threat experiences moderate the link between hippocampus volume and depression symptoms prospectively in adolescence

Identifying neuroimaging risk markers for depression has been an elusive goal in psychopathology research. Despite this, smaller hippocampal volume has emerged as a potential risk marker for depression, with recent research suggesting this association is moderated by family income. The current pre-registered study aimed to replicate and extend these findings by examining the moderating role of family income and three dimensions of environmental experience on the link between hippocampus volume and later depression. Data were drawn from the Adolescent Brain Cognitive Development (ABCD) study and were comprised of 6693 youth aged 9-10 years at baseline. Results indicated that psychosocial threat moderated the association between right hippocampus volume and depression symptoms two years later, such that a negative association was evident in low-threat environments (std. beta=0.15, 95% CI [0.05, 0.24]). This interaction remained significant when baseline depression symptoms were included as a covariate, though only in youth endorsing 1 or more depression symptoms at baseline (β = 0.13, 95% CI = [0.03, 0.22]). These results suggest that hippocampus volume may not be a consistent correlate of depression symptoms in high risk environments and emphasize the importance of including measures of environmental heterogeneity when seeking risk markers for depression.

Decoding and reconstructing disease relations between dry eye and depression: a multimodal investigation comprising meta-analysis, genetic pathways and Mendelian randomization

INTRODUCTION

The clinical presentations of dry eye disease (DED) and depression (DEP) often comanifest. However, the robustness and the mechanisms underlying this association were undetermined.

OBJECTIVES

To this end, we set up a three-segment study that employed multimodality results (meta-analysis, genome-wide association study [GWAS] and Mendelian randomization [MR]) to elucidate the association, common pathways and causality between DED and DEP.

METHODS

A meta-analysis comprising 26 case-control studies was first conducted to confirm the DED-DEP association. Next, we performed a linkage disequilibrium (LD)-adjusted GWAS and targeted phenotype association study (PheWAS) in East Asian TW Biobank (TWB) and European UK Biobank (UKB) populations. Single-nucleotide polymorphisms (SNPs) were further screened for molecular interactions and common pathways at the functional gene level. To further elucidate the activated pathways in DED and DEP, a systemic transcriptome review was conducted on RNA sequencing samples from the Gene Expression Omnibus. Finally, 48 MR experiments were implemented to examine the bidirectional causation between DED and DEP.

RESULTS

Our meta-analysis showed that DED patients are associated with an increased DEP prevalence (OR = 1.83), while DEP patients have a concurrent higher risk of DED (OR = 2.34). Notably, cross-disease GWAS analysis revealed that similar genetic architecture (rG = 0.19) and pleiotropic functional genes contributed to phenotypes in both diseases. Through protein-protein interaction and ontology convergence, we summarized the pleiotropic functional genes under the ontology of immune activation, which was further validated by a transcriptome systemic review. Importantly, the inverse variance-weighted (IVW)-MR experiments in both TWB and UKB populations (p value <0.001) supported the bidirectional exposure-outcome causation for DED-to-DEP and DEP-to-DED. Despite stringent LD-corrected instrumental variable re-selection, the bidirectional causation between DED and DEP remained.

CONCLUSION

With the multi-modal evidence combined, we consolidated the association and causation between DED and DEP.

Association between abnormal default mode network homogeneity and sleep disturbances in major depressive disorder

Background

Sleep disturbance is a common comorbidity of major depressive disorder (MDD). However, network homogeneity (NH) changes of the default mode network (DMN) in MDD with sleep disturbances are unclear.

Aims

The purpose of this study was to probe the abnormal NH in the DMN in MDD with sleep disturbances and to reveal the differences between MDD with or without sleep disturbances.

Methods

Twenty-four patients with MDD and sleep disturbances (Pa_s), 33 patients with MDD without sleep disturbances (Pa_ns) and 32 healthy controls (HCs) were recruited in this study. Resting-state functional imaging data were analysed using NH.

Results

Compared with Pa_ns and HCs, Pa_s showed decreased NH in the left superior medial prefrontal cortex and increased NH in the right precuneus. There was a negative correlation between NH in the left superior medial prefrontal cortex and sleep disturbances (r=-0.42, p=0.001) as well as a positive correlation between NH in the right precuneus and sleep disturbances (r=0.41, p=0.002) in patients with MDD.

Conclusions

MDD with sleep disturbances is associated with abnormal NH in the DMN, which could differentiate pa_s from pa_ns. The DMN may play a crucial role in the neurobiological mechanisms of MDD with sleep disturbances.