Lipopolysaccharide induces delayed FosB/DeltaFosB immunostaining within the mouse extended amygdala, hippocampus and hypothalamus, that parallel the expression of depressive-like behavior

Exploring environmental exposomes and the gut-brain nexus: Unveiling the impact of pesticide exposure

This review delves into the escalating concern of environmental pollutants and their profound impact on human health in the context of the modern surge in global diseases. The utilisation of chemicals in food production, which results in residues in food, has emerged as a major concern nowadays. By exploring the intricate relationship between environmental pollutants and gut microbiota, the study reveals a dynamic bidirectional interplay, as modifying microbiota profile influences metabolic pathways and subsequent brain functions. This review will first provide an overview of potential exposomes and their effect to gut health. This paper is then emphasis the connection of gut brain function by analysing microbiome markers with neurotoxicity responses. We then take pesticide as example of exposome to elucidate their influence to biomarkers biosynthesis pathways and subsequent brain functions. The interconnection between neuroendocrine and neuromodulators elements and the gut-brain axis emerges as a pivotal factor in regulating mental health and brain development. Thus, manipulation of gut microbiota function at the onset of stress may offer a potential avenue for the prevention and treatment for mental disorder and other neurodegenerative illness.

Review of research progress on intestinal microbiota based on metabolism and inflammation for depression

Depression is a prevalent mental illness, affecting a significant portion of the global population. Recent research has highlighted the crucial role of the gut microbiota in both metabolic and central nervous health. By reviewing literature from various databases, including Pubmed, Science Direct, Web of Science, and Scopus, spanning the years 2005-2023, a comprehensive search was conducted using keywords such as "Depression" and "Gut Microbiota". The gut microbiota acts as a "second brain" in humans and can communicate bidirectionally with the brain through the Brain-gut-microbiota axis pathway. This communication involves the immune and nervous systems. However, there are challenges in detecting and treating depression effectively. To address these limitations, researchers have been exploring the relationship between gut microbiota and depression. Studies have shown that gut microbial metabolites, such as lipopolysaccharides and short-chain fatty acids, can induce pro-inflammatory cytokines that contribute to neuroinflammation and increase the risk of depression. The kynurenine pathway, triggered by gut microbial metabolites, has also been associated with neuroinflammation. Thus, investigating these microbial metabolites can provide insights into depression treatment. This review focuses on analyzing the connection between gut microbial metabolites, inflammation, and depression. It explores novel mechanisms contributing to depression, specifically focusing on the mediation of inflammation through the release of pro-inflammatory cytokines. The objective is to provide valuable insights into the mechanisms underlying depression and to propose potential treatments.

The inflammatory response to birth requires MyD88 and is driven by both mother and offspring

Birth is an inflammatory event for the newborn, characterized by elevations in interleukin (IL)-6, IL-10, and tumor necrosis factor (TNF)-α peripherally and/or centrally, as well as changes in brain microglia. However, the mechanism(s) underlying these responses is unknown. Toll-like receptors (TLRs) play crucial roles in innate immunity and initiate inflammatory cascades upon recognition of endogenous or exogenous antigens. Most TLR signaling depends on the adaptor molecule myeloid differentiation primary response 88 (MyD88). We independently varied MyD88 gene status in mouse dams and their offspring to determine whether the inflammatory response to birth depends on MyD88 signaling and, if so, whether that signaling occurs in the offspring, the mother, or both. We find that the perinatal surges in plasma IL-6 and brain expression of TNF-α depend solely on MyD88 gene status of the offspring, whereas postnatal increases in plasma IL-10 and TNF-α depend on MyD88 in both the pup and dam. Interestingly, MyD88 genotype of the dam primarily drives differences in offspring brain microglial density and has robust effects on developmental neuronal cell death. Milk cytokines were evaluated as a possible source of postnatal maternal influence; although we found high levels of CXCL1/GROα and several other cytokines in ingested post-partum milk, their presence did not require MyD88. Thus, the inflammatory response previously described in the late-term fetus and newborn depends on MyD88 (and, by extension, TLRs), with signaling in both the dam and offspring contributing. Unexpectedly, naturally-occuring neuronal cell death in the newborn is modulated primarily by maternal MyD88 gene status.

Reviewing the neurobiology of electroconvulsive therapy on a micro- meso- and macro-level

BACKGROUND

Electroconvulsive therapy (ECT) remains the one of the most effective of biological antidepressant interventions. However, the exact neurobiological mechanisms underlying the efficacy of ECT remain unclear. A gap in the literature is the lack of multimodal research that attempts to integrate findings at different biological levels of analysis METHODS: We searched the PubMed database for relevant studies. We review biological studies of ECT in depression on a micro- (molecular), meso- (structural) and macro- (network) level.

RESULTS

ECT impacts both peripheral and central inflammatory processes, triggers neuroplastic mechanisms and modulates large scale neural network connectivity.

CONCLUSIONS

Integrating this vast body of existing evidence, we are tempted to speculate that ECT may have neuroplastic effects resulting in the modulation of connectivity between and among specific large-scale networks that are altered in depression. These effects could be mediated by the immunomodulatory properties of the treatment. A better understanding of the complex interactions between the micro-, meso- and macro- level might further specify the mechanisms of action of ECT.

Icilin, a cool/cold-inducing agent, alleviates lipopolysaccharide-induced septic sickness responses in mice

Sepsis is a significant global public health challenge, resulting in millions of human deaths annually. Transient receptor potential melastatin 8 (TRPM8), a non-selective ion channel, is the primary cold sensor in humans; however, its effects on endotoxin-induced inflammation remain unclear. We previously reported that TRPM8 knockout mice exhibited more severe physiological and behavioral endotoxemia responses upon a high-dose injection with lipopolysaccharide (LPS). In the present study, we investigated whether icilin, a TRPM8 agonist, was a target for the suppression of sickness responses using a mouse model of LPS-induced sepsis. A peripheral high-dose injection of LPS at 5 mg/kg showed a maximal body temperature decrease of 5.1 °C in mice subcutaneously pretreated with vehicle and 1.5 °C in icilin-pretreated animals. The decline in locomotor activity was attenuated in icilin-pretreated mice and its recovery was faster; however, the high-dose LPS injection rapidly decreased locomotor activity regardless of the icilin pretreatment. Furthermore, the icilin pretreatment attenuated LPS-induced decreases in body weight and food and water intakes and accelerated recovery from these sickness responses. Therefore, the present results demonstrated that the icilin pretreatment alleviated LPS-induced sickness responses or decreases in body temperature, locomotor activity, body weight loss, and food and water intakes, suggesting its potential as a therapeutic target for sepsis.

Immunoception: the insular cortex perspective

To define the systemic neuroimmune interactions in health and disease, we recently suggested immunoception as a term that refers to the existence of bidirectional functional loops between the brain and the immune system. This concept suggests that the brain constantly monitors changes in immune activity and, in turn, can regulate the immune system to generate a physiologically synchronized response. Therefore, the brain has to represent information regarding the state of the immune system, which can occure in multiple ways. One such representation is an immunengram, a trace that is partially stored by neurons and partially by the local tissue. This review will discuss our current understanding of immunoception and immunengrams, focusing on their manifestation in a specific brain region, the insular cortex (IC).

Endotoxin-Induced Physiological and Psychological Sickness Responses in Healthy Humans: Insights into the Post-Acute Phase

INTRODUCTION

Experimental endotoxemia is a translational model of systemic inflammation that has contributed significantly to our current understanding of sickness behavior and inflammation-associated depression. Previous studies using this model revealed a strong association between cytokine levels, endocrine changes, and psychological sickness symptoms during the acute phase of inflammation. The objective of this randomized, double-blind, placebo-controlled crossover study was to gain insight into potential post-acute physiological and psychological consequences of endotoxin administration that may either persist or newly emerge between 24 and 72 h after injection. The main focus was on associations between serum levels of C-reactive protein (CRP) and affective symptoms as well as alterations in diurnal cortisol profile, the two key features of inflammation-associated depression.

METHODS

Healthy male volunteers (N = 18) received an injection of either endotoxin (0.8 ng/kg) or placebo on two separate but otherwise identical study days, 7 days apart. Blood and saliva samples were collected during acute and post-acute phases after injection to measure blood inflammatory markers (interleukin [IL]-6, IL-1 receptor antagonist [ra], CRP) and salivary cortisol levels. In addition, participants completed a comprehensive battery of questionnaires to assess physical and psychological sickness symptoms.

RESULTS

Endotoxin treatment induced a short-time rise in plasma IL-6 and a longer increase in IL-1ra. The increase in serum CRP was delayed compared to cytokines, peaking at 24 h and gradually decreasing until 72 h after injection. The inflammatory response was accompanied by bodily and psychological sickness symptoms which occurred only in the acute phase, whereas none of the symptoms persisted or recurred in the post-acute phase. Salivary cortisol levels were significantly increased during the acute phase and exhibited pronounced circadian changes. However, no significant differences in diurnal cortisol profiles were observed between placebo and endotoxin conditions on the days after treatment.

CONCLUSION

Our findings suggest that CRP, which is elevated in patients with inflammation-associated depression, does not appear to be responsible for depressive symptomatology. Moreover, a single inflammatory episode is not sufficient to alter diurnal cortisol profiles, as observed in inflammation-associated depression. In addition, the absence of persistent lipopolysaccharide-induced psychological and physiological changes beyond the acute phase further supports the safety of endotoxin administration in humans.

Saffron extract interferes with lipopolysaccharide-induced brain activation of the kynurenine pathway and impairment of monoamine neurotransmission in mice

Background

Although activation of inflammatory processes is essential to fight infections, its prolonged impact on brain function is well known to contribute to the pathophysiology of many medical conditions, including neuropsychiatric disorders. Therefore, identifying novel strategies to selectively counter the harmful effects of neuroinflammation appears as a major health concern. In that context, this study aimed to test the relevance of a nutritional intervention with saffron, a spice known for centuries for its beneficial effect on health.

Methods

For this purpose, the impact of an acute oral administration of a standardized saffron extract, which was previously shown to display neuromodulatory properties and reduce depressive-like behavior, was measured in mice challenged with lipopolysaccharide (LPS, 830 μg/kg, ip).

Results

Pretreatment with saffron extract (6.5 mg/kg, per os) did not reduce LPS-induced sickness behavior, preserving therefore this adaptive behavioral response essential for host defense. However, it interfered with delayed changes of expression of cytokines, chemokines and markers of microglial activation measured 24 h post-LPS treatment in key brain areas for behavior and mood control (frontal cortex, hippocampus, striatum). Importantly, this pretreatment also counteracted by that time the impact of LPS on several neurobiological processes contributing to inflammation-induced emotional alterations, in particular the activation of the kynurenine pathway, assessed through the expression of its main enzymes, as well as concomitant impairment of serotonergic and dopaminergic neurotransmission.

Conclusion

Altogether, this study provides important clues on how saffron extract interferes with brain function in conditions of immune stimulation and supports the relevance of saffron-based nutritional interventions to improve the management of inflammation-related comorbidities.

Antidepressant-like effects of tomatidine and tomatine, steroidal alkaloids from unripe tomatoes, via activation of mTORC1 in the medial prefrontal cortex in lipopolysaccharide-induced depression model mice

ABSTRACTKetamine, an N-methyl-D-aspartate receptor antagonist, produces rapid antidepressant effects in patients with treatment-resistant depression. However, owing to the undesirable adverse effects of ketamine, there is an urgent need for developing safer and more effective prophylactic and therapeutic interventions for depression. Preclinical studies have demonstrated that activation of the mechanistic target of rapamycin complex 1 (mTORC1) in the medial prefrontal cortex (mPFC) mediates the rapid antidepressant effects of ketamine. The steroidal alkaloid tomatidine and its glycoside α-tomatine (tomatine) can activate mTORC1 signaling in peripheral tissues/cells. We examined whether tomatidine and tomatine exerted prophylactic and therapeutic antidepressant-like actions via mPFC mTORC1 activation using a mouse model of lipopolysaccharide (LPS)-induced depression. Male mice were intraperitoneally (i.p.) administered tomatidine/tomatine before and after the LPS challenge to test their prophylactic and therapeutic effects, respectively. LPS-induced depression-like behaviors in the tail suspension test (TST) and forced swim test (FST) were significantly reversed by prophylactic and therapeutic tomatidine/tomatine administration. LPS-induced anhedonia in the female urine sniffing test was reversed by prophylactic, but not therapeutic, injection of tomatidine, and by prophylactic and therapeutic administration of tomatine. Intra-mPFC infusion of rapamycin, an mTORC1 inhibitor, blocked the prophylactic and therapeutic antidepressant-like effects of tomatidine/tomatine in TST and FST. Moreover, both tomatidine and tomatine produced antidepressant-like effects in ovariectomized female mice, a model of menopause-associated depression. These results indicate that tomatidine and tomatine exert prophylactic and therapeutic antidepressant-like effects via mTORC1 activation in the mPFC and suggest these compounds as promising candidates for novel prophylactic and therapeutic agents for depression.

Stress to inflammation and anhedonia: Mechanistic insights from preclinical and clinical models

Anhedonia, as evidenced by impaired pleasurable response to reward, reduced reward motivation, and/or deficits in reward-related learning, is a common feature of depression. Such deficits in reward processing are also an important clinical target as a risk factor for depression onset. Unfortunately, reward-related deficits remain difficult to treat. To address this gap and inform the development of effective prevention and treatment strategies, it is critical to understand the mechanisms that drive impairments in reward function. Stress-induced inflammation is a plausible mechanism of reward deficits. The purpose of this paper is to review evidence for two components of this psychobiological pathway: 1) the effects of stress on reward function; and 2) the effects of inflammation on reward function. Within these two areas, we draw upon preclinical and clinical models, distinguish between acute and chronic effects of stress and inflammation, and address specific domains of reward dysregulation. By addressing these contextual factors, the review reveals a nuanced literature which might be targeted for additional scientific inquiry to inform the development of precise interventions.

Hydrogen Sulfide Prevents LPS-Induced Depression-like Behavior through the Suppression of NLRP3 Inflammasome and Pyroptosis and the Improvement of Mitochondrial Function in the Hippocampus of Mice

Hydrogen sulfide (H2S) has been implicated to have antidepressive effects. We sought to investigate the prevention effects of H2S donor NaHS on depression-like behavior induced by lipopolysaccharide (LPS) in mice and its potential mechanisms. Sucrose preference, force swimming, open field, and elevate zero maze were used to evaluate depression-like behavior. NF-κB and NLRP3 inflammasome activation and mitochondrial function in the hippocampus were determined. It was found that depression-like behavior induced by LPS was prevented by NaHS pretreatment. LPS caused NF-κB and NLRP3 inflammasome activation in the hippocampus as evidenced by increased phosphorylated-p65 levels and increased NLRP3, ASC, caspase-1, and mature IL-1β levels in the hippocampus, which were also blocked by NaHS. LPS increased GSDMD-N levels and TUNEL-positive cells in the hippocampus, which was prevented by NaHS. Abnormal mitochondrial morphology in the hippocampus was found in LPS-treated mice. Mitochondrial membrane potential and ATP production were reduced, and ROS production was increased in the hippocampus of LPS-treated mice. NaHS pretreatment improved impaired mitochondrial morphology and increased membrane potential and ATP production and reduced ROS production in the hippocampus of LPS-treated mice. Our data indicate that H2S prevents LPS-induced depression-like behaviors by inhibiting NLRP3 inflammasome activation and pyroptosis and improving mitochondrial function in the hippocampus.

From Bench to Bedside: Implications of Lipid Nanoparticle Carrier Reactogenicity for Advancing Nucleic Acid Therapeutics

In biomedical applications, nanomaterial-based delivery vehicles, such as lipid nanoparticles, have emerged as promising instruments for improving the solubility, stability, and encapsulation of various payloads. This article provides a formal review focusing on the reactogenicity of empty lipid nanoparticles used as delivery vehicles, specifically emphasizing their application in mRNA-based therapies. Reactogenicity refers to the adverse immune responses triggered by xenobiotics, including administered lipid nanoparticles, which can lead to undesirable therapeutic outcomes. The key components of lipid nanoparticles, which include ionizable lipids and PEG-lipids, have been identified as significant contributors to their reactogenicity. Therefore, understanding the relationship between lipid nanoparticles, their structural constituents, cytokine production, and resultant reactogenic outcomes is essential to ensure the safe and effective application of lipid nanoparticles in mRNA-based therapies. Although efforts have been made to minimize these adverse reactions, further research and standardization are imperative. By closely monitoring cytokine profiles and assessing reactogenic manifestations through preclinical and clinical studies, researchers can gain valuable insights into the reactogenic effects of lipid nanoparticles and develop strategies to mitigate undesirable reactions. This comprehensive review underscores the importance of investigating lipid nanoparticle reactogenicity and its implications for the development of mRNA-lipid nanoparticle therapeutics in various applications beyond vaccine development.

Effects of inhaled corticosteroids on brain volumetry, depression and anxiety-like behaviors in a rat model of asthma

Brain functional deficits have been reported in asthma patients which can result in behavioral disorders like depression and anxiety. These deficits may be associated with factors like resistance to treatment, incorrect self-evaluation, and inadequate self-control. However, changes in the brain volume in allergic asthma and the effects of inhaled corticosteroids, the most common anti-inflammatory agents for asthma treatment, on these alterations remain largely unclear. Here, we evaluated depression and anxiety-like behavior as well as volume changes in different brain area, using magnetic resonance imaging in an animal model of allergic asthma with pretreatment of inhaled fluticasone propionate. Asthma-induced behavioral changes were partially, but not completely, prevented by pretreatment with inhaled fluticasone propionate. Volumetry findings showed that the allergen decreased volumes of the corpus callosum and subcortical white matter, as well as the septal region and hippocampus (especially CA1 and fimbria). However, volumes of neocortex, insular, and anterior cingulate cortex increased in asthmatic rats compared to controls. Namely, pretreatment with inhaled fluticasone propionate partially prevented asthma-induced brain volume changes, but not completely. These findings suggest that asthma is associated with structural alterations in the brain, which may contribute to the induction of psychological disorders. Thus, considering brain changes in the clinical assessments could have important implications for asthma treatment.

Allergen induces depression-like behavior in association with altered prefrontal-hippocampal circuit in male rats

Allergic asthma is a common chronic inflammatory condition associated with psychiatric comorbidities. Notably depression, correlated with adverse outcomes in asthmatic patients. Peripheral inflammation's role in depression has been shown previously. However, evidence regarding the effects of allergic asthma on the medial prefrontal cortex (mPFC)-ventral hippocampus (vHipp) interactions, an important neurocircuitry in affective regulation, is yet to be demonstrated. Herein, we investigated the effects of allergen exposure in sensitized rats on the immunoreactivity of glial cells, depression-like behavior, brain regions volume, as well as activity and connectivity of the mPFC-vHipp circuit. We found that allergen-induced depressive-like behavior was associated with more activated microglia and astrocytes in mPFC and vHipp, as well as reduced hippocampus volume. Intriguingly, depressive-like behavior was negatively correlated with mPFC and hippocampus volumes in the allergen-exposed group. Moreover, mPFC and vHipp activity were altered in asthmatic animals. Allergen disrupted the strength and direction of functional connectivity in the mPFC-vHipp circuit so that, unlike normal conditions, mPFC causes and modulates vHipp activity. Our results provide new insight into the underlying mechanism of allergic inflammation-induced psychiatric disorders, aiming to develop new interventions and therapeutic approaches for improving asthma complications.

The effects of lipopolysaccharide exposure on social interaction, cytokine expression, and alcohol consumption in male and female mice

Much recent research has demonstrated a role of inflammatory pathways in depressive-like behavior and excess alcohol consumption. Lipopolysaccharide (LPS) is a cell wall component of gram-negative bacteria that can be used to trigger a strong inflammatory response in rodents in a preclinical research setting to study the mechanisms behind this relationship. In our study, we exposed male and female mice to LPS and assessed depressive-like behavior using the social interaction (SI) test, alcohol consumption in the two-bottle choice procedure, and expression of inflammatory mediators using quantitative PCR. We found that LPS administration decreased SI in female mice but had no significant impact on male mice when assessed 24 h after injection. LPS resulted in increased proinflammatory cytokine expression in both male and female mice; however, some aspects of the cytokine upregulation observed was greater in female mice as compared to males. A separate cohort of male and female mice underwent drinking for 12 days before receiving a saline or LPS injection, which we found to increase alcohol intake in both males and females. We have previously observed a role of the neurokinin-1 receptor (NK1R) in escalated alcohol intake, and in the inflammatory and behavioral response to LPS. The NK1R is the endogenous target of the neuropeptide SP, and this system has wide ranging roles in depression, anxiety, drug/alcohol seeking, pain, and inflammation. Thus, we administered a NK1R antagonist prior to alcohol access. This treatment reduced escalated alcohol consumption in female mice treated with LPS but did not affect drinking in males. Taken together, these results indicate that females are more sensitive to some physiological and behavioral effects of LPS administration, but that LPS escalates alcohol consumption in both sexes. Furthermore, NK1R antagonism can reduce alcohol consumption that is escalated by LPS treatment, in line with our previous findings.

Quercetin abrogates lipopolysaccharide-induced depressive-like symptoms by inhibiting neuroinflammation via microglial NLRP3/NFκB/iNOS signaling pathway

BACKGROUND

Major depressive disorder is a serious psychiatric illness having serious damaging effect on the quality of life of suffers. Quercetin is a plant flavonoid, mostly used as a constituent in dietary products. This study evaluated antidepressant effect of quercetin on lipopolysaccharide (LPS)-induced depression in rats.

MATERIALS AND METHODS

Twenty-one male rats were randomly assigned into three groups (n= 7): group 1 (vehicle only), group 2 (quercetin), group 3 (LPS). Rats were treated with vehicle (10mL/kg, p.o.) or quercetin (50mg/kg, p.o.) for seven days. Sixty minutes after treatment on day seven, all animals were injected with LPS (0.83mg/kg, i.p.) except group 1 (vehicle only). Twenty-four hours after LPS injection, animals were assessed for depressive symptoms using forced swim, sucrose splash and open field tests. Animals were sacrificed; brain samples collected for bioassay of pro-inflammatory mediators, TNF-α, IL-6 and IL-17 were measured using enzyme-linked immunosorbent assay (ELISA) while expressions of NF-κB, inflammasomes, microglia and iNOS were quantified by immunohistochemistry.

RESULTS

The LPS significantly (p<0.05) decreased mobility of rats in FST and decreased sucrose preference, which is indicative of depressive-like behaviours. These behaviours were significantly (p<0.05) attenuated by quercetin compared to control (vehicle only). Following LPS exposure, the expressions of inflammasomes, NF-κB, iNOS, proinflammatory cytokines and microglia positive cells in the hippocampus and prefrontal cortex were significantly (p<0.05) elevated. All these were attenuated by pretreating animals with quercetin.

CONCLUSION

Quercetin exhibit antidepressant-like property, which may be related to inhibition of neuroinflammatory signaling pathways.

Latroeggtoxin-VI protects nerve cells and prevents depression by inhibiting NF-κB signaling pathway activation and excessive inflammation

Depression has a high incidence and seriously endangers human health. Accumulated evidence indicates that targeting neuroinflammation is a potential avenue for neuroprotection and thus depression prevention. Herein, the effects of latroeggtoxin-VI (LETX-VI), a bioactive protein from the eggs of spider Latrodectus tredecimguttatus, on lipopolysaccharide (LPS)-induced inflammation and depression were systematically investigated using RAW264.7 macrophages and depression mouse model. Pretreatment with LETX-VI suppressed LPS-evoked NF-κB signaling pathway activation, inhibited LPS-induced over-production of NO, iNOS, IL-6 and TNF-α; at the same time LETX-VI mitigated the inhibitory effect of LPS on the expression of anti-inflammatory factors such as Arg-1, thereby suppressing oxidative stress and excessive inflammation. Culture of PC12 cells with the conditioned medium of RAW264.7 cells pretreated with LETX-VI demonstrated the neuroprotective effect of LETX-VI due to its anti-inflammation effect. In the LPS-induced depression mouse model, pretreatment with LETX-VI improved the LPS-induced depression-like behaviors, inhibited the activation of microglia and astrocytes, prevented the down-regulation of Nurr1 expression and alleviated the LPS-caused adverse changes in the brain tissues. Taken together, these in vitro and in vivo findings provide powerful insights into the anti-inflammation-based neuroprotective and antidepressant mechanisms of LETX-VI, which is helpful to deeply reveal the biological effects and potential applications of LETX-VI.

Intranasal Administration of Resolvin E1 Produces Antidepressant-Like Effects via BDNF/VEGF-mTORC1 Signaling in the Medial Prefrontal Cortex

Intracerebroventricular infusion of resolvin E1 (RvE1), a bioactive metabolite derived from eicosapentaenoic acid, exerts antidepressant-like effects in a mouse model of lipopolysaccharide (LPS)-induced depression; these effects are blocked by systemic injection of rapamycin, a mechanistic target of rapamycin complex 1 (mTORC1) inhibitor. Additionally, local infusion of RvE1 into the medial prefrontal cortex (mPFC) or dorsal hippocampal dentate gyrus (DG) produces antidepressant-like effects. To evaluate the potential of RvE1 for clinical use, the present study examined whether treatment with RvE1 via intranasal (i.n.) route, a non-invasive route for effective drug delivery to the brain, produces antidepressant-like effects in LPS-challenged mice using tail suspension and forced swim tests. Intranasal administration of RvE1 significantly attenuated LPS-induced immobility, and these antidepressant-like effects were completely blocked by an AMPA receptor antagonist or L-type voltage-dependent Ca2+ channel blocker. The antidepressant-like effects of both i.n. and intra-mPFC administrations of RvE1 were blocked by intra-mPFC infusion of a neutralizing antibody (nAb) for brain-derived neurotrophic factor (BDNF) or vascular endothelial growth factor (VEGF). Intra-mPFC infusion of rapamycin completely blocked the antidepressant-like effects of both i.n. and intra-mPFC administrations of RvE1 as well as those of intra-mPFC infusion of BDNF and VEGF. Moreover, i.n. RvE1 produced antidepressant-like effects via mTORC1 activation in the mPFC of a mouse model of repeated prednisolone-induced depression. Intra-dorsal DG infusion of BDNF and VEGF nAbs, but not rapamycin, blocked the antidepressant-like effects of i.n. RvE1. These findings suggest that i.n. administration of RvE1 produces antidepressant-like effects through activity-dependent BDNF/VEGF release in the mPFC and dorsal DG, and mTORC1 activation in the mPFC, but not in the dorsal DG. Thus, RvE1 can be a promising candidate for a novel rapid-acting antidepressant.

Blocking osteopontin expression attenuates neuroinflammation and mitigates LPS-induced depressive-like behavior in mice

INTRODUCTION

Neuroinflammation plays an important role in the development of major depressive disorder (MDD). Osteopontin (OPN) is one of the key molecules involved in neuroinflammation. We demonstrate here for the first time a key role of OPN in lipopolysaccharide (LPS)-induced depressive-like behavioral syndrome.

METHODS

Systemic administration of LPS (5 mg/kg) mimics distinct depressive-like behavior, which could significantly upregulate OPN expression in microglia/macrophage in the hippocampus. The neurobehavioral assessments, quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR), Western blot, immunofluorescent staining, flow cytometry cell staining and Golgi staining were performed.

RESULTS

Similar to fluoxetine treatment (the positive control), OPN knockdown with shRNA lentivirus markedly reversed LPS-induced depressive-like behavior. Moreover, knockdown of OPN suppressed LPS-induced proinflammatory cytokine expression, microglial activation, dendritic spines loss, as well as unregulated PSD-95 and BDNF in the hippocampus.

CONCLUSION

We demonstrated that targeting OPN expression in microglia/macrophage might help to rescue LPS-induced depressive-like behavior. The underlying mechanism may relate to the modulation of neuroinflammation, BDNF signaling and synaptic structural complexity.

Time course and mechanistic analysis of human umbilical cord perivascular cell mitigation of lipopolysaccharide-induced systemic and neurological inflammation

BACKGROUND AIMS

Because of their potent immunomodulatory and anti-inflammatory properties, mesenchymal stromal cells are a major focus in the field of stem cell therapy. However, the precise mechanisms underlying this are not entirely understood. Human umbilical cord perivascular cells (HUCPVCs) are a promising cell therapy candidate. This study was designed to evaluate the time course and mechanisms by which HUCPVCs mitigate lipopolysaccharide (LPS)-induced systemic and neurological inflammation in immunocompetent mice. To explore the underlying mechanisms, the authors investigated the biodistribution and fate of HUCPVCs.

METHODS

Male C57BL/6 mice were randomly allocated to four groups: control, LPS, HUCPVCs or LPS + HUCPVCs. Quantitative polymerase chain reaction, enzyme-linked immunosorbent assay and cytokine arrays were used to assess changes in pro-inflammatory mediators systemically and in the brain. Depressive-like behavioral changes were evaluated via a forced swim test. Quantum dot (qDot) labeling and immunohistochemistry were used to assess the biodistribution and fate of HUCPVCs and interactions with recipient innate immune cells.

RESULTS

A single intravenously delivered dose of HUCPVCs significantly reduced the systemic inflammation induced by LPS within the first 24 h after administration. HUCPVC treatment abrogated the upregulated expression of pro-inflammatory genes in the hippocampus and cortex and attenuated depressive-like behavior induced by LPS treatment. Biodistribution analysis revealed that HUCPVC-derived qDots rapidly accumulated in the lungs and demonstrated limited in vivo persistence. Furthermore, qDot signals were associated with major recipient innate immune cells and promoted a shift in macrophages toward a regulatory phenotype in the lungs.

CONCLUSIONS

Overall, this study demonstrates that HUCPVCs can successfully reduce systemic and neurological inflammation induced by LPS within the first 24 h after administration. Biodistribution and fate analyses suggest a critical role for the innate immune system in the HUCPVC-based immunomodulation mechanism.

Prolactin-Releasing Peptide Contributes to Stress-Related Mood Disorders and Inhibits Sleep/Mood Regulatory Melanin-Concentrating Hormone Neurons in Rats

Stress disorders impair sleep and quality of life; however, their pathomechanisms are unknown. Prolactin-releasing peptide (PrRP) is a stress mediator; we therefore hypothesized that PrRP may be involved in the development of stress disorders. PrRP is produced by the medullary A1/A2 noradrenaline (NA) cells, which transmit stress signals to forebrain centers, and by non-NA cells in the hypothalamic dorsomedial nucleus. We found in male rats that both PrRP and PrRP-NA cells innervate melanin-concentrating hormone (MCH) producing neurons in the dorsolateral hypothalamus (DLH). These cells serve as a key hub for regulating sleep and affective states. Ex vivo, PrRP hyperpolarized MCH neurons and further increased the hyperpolarization caused by NA. Following sleep deprivation, intracerebroventricular PrRP injection reduced the number of REM sleep-active MCH cells. PrRP expression in the dorsomedial nucleus was upregulated by sleep deprivation, while downregulated by REM sleep rebound. Both in learned helplessness paradigm and after peripheral inflammation, impaired coping with sustained stress was associated with (1) overactivation of PrRP cells, (2) PrRP protein and receptor depletion in the DLH, and (3) dysregulation of MCH expression. Exposure to stress in the PrRP-insensitive period led to increased passive coping with stress. Normal PrRP signaling, therefore, seems to protect animals against stress-related disorders. PrRP signaling in the DLH is an important component of the PrRP's action, which may be mediated by MCH neurons. Moreover, PrRP receptors were downregulated in the DLH of human suicidal victims. As stress-related mental disorders are the leading cause of suicide, our findings may have particular translational relevance.SIGNIFICANCE STATEMENT Treatment resistance to monoaminergic antidepressants is a major problem. Neuropeptides that modulate the central monoaminergic signaling are promising targets for developing alternative therapeutic strategies. We found that stress-responsive prolactin-releasing peptide (PrRP) cells innervated melanin-concentrating hormone (MCH) neurons that are crucial in the regulation of sleep and mood. PrRP inhibited MCH cell activity and enhanced the inhibitory effect evoked by noradrenaline, a classic monoamine, on MCH neurons. We observed that impaired PrRP signaling led to failure in coping with chronic/repeated stress and was associated with altered MCH expression. We found alterations of the PrRP system also in suicidal human subjects. PrRP dysfunction may underlie stress disorders, and fine-tuning MCH activity by PrRP may be an important part of the mechanism.

Effects of Ozone on Sickness and Depressive-like Behavioral and Biochemical Phenotypes and Their Regulation by Serum Amyloid A in Mice

Ozone (O₃) is an air pollutant that primarily damages the lungs, but growing evidence supports the idea that O₃ also harms the brain; acute exposure to O₃ has been linked to central nervous system (CNS) symptoms such as depressed mood and sickness behaviors. However, the mechanisms by which O₃ inhalation causes neurobehavioral changes are limited. One hypothesis is that factors in the circulation bridge communication between the lungs and brain following O₃ exposure. In this study, our goals were to characterize neurobehavioral endpoints of O₃ exposure as they relate to markers of systemic and pulmonary inflammation, with a particular focus on serum amyloid A (SAA) and kynurenine as candidate mediators of O₃ behavioral effects. We evaluated O₃-induced dose-, time- and sex-dependent changes in pulmonary inflammation, circulating SAA and kynurenine and its metabolic enzymes, and sickness and depressive-like behaviors in Balb/c and CD-1 mice. We found that 3 parts per million (ppm) O₃, but not 2 or 1 ppm O₃, increased circulating SAA and lung inflammation, which were resolved by 48 h and was worse in females. We also found that indoleamine 2,3-dioxygenase (Ido1) mRNA expression was increased in the brain and spleen 24 h after 3 ppm O₃ and that kynurenine was increased in blood. Sickness and depressive-like behaviors were observed at all O₃ doses (1-3 ppm), suggesting that behavioral responses to O₃ can occur independently of increased SAA or neutrophils in the lungs. Using SAA knockout mice, we found that SAA did not contribute to O₃-induced pulmonary damage or inflammation, systemic increases in kynurenine post-O₃, or depressive-like behavior but did contribute to weight loss. Together, these findings indicate that acute O₃ exposure induces transient symptoms of sickness and depressive-like behaviors that may occur in the presence or absence of overt pulmonary neutrophilia and systemic increases of SAA. SAA does not appear to contribute to pulmonary inflammation induced by O₃, although it may contribute to other aspects of sickness behavior, as reflected by a modest effect on weight loss.

Neuroinflammation mechanisms of neuromodulation therapies for anxiety and depression

Mood disorders are associated with elevated inflammation, and the reduction of symptoms after multiple treatments is often accompanied by pro-inflammation restoration. A variety of neuromodulation techniques that regulate regional brain activities have been used to treat refractory mood disorders. However, their efficacy varies from person to person and lack reliable indicator. This review summarizes clinical and animal studies on inflammation in neural circuits related to anxiety and depression and the evidence that neuromodulation therapies regulate neuroinflammation in the treatment of neurological diseases. Neuromodulation therapies, including transcranial magnetic stimulation (TMS), transcranial electrical stimulation (TES), electroconvulsive therapy (ECT), photobiomodulation (PBM), transcranial ultrasound stimulation (TUS), deep brain stimulation (DBS), and vagus nerve stimulation (VNS), all have been reported to attenuate neuroinflammation and reduce the release of pro-inflammatory factors, which may be one of the reasons for mood improvement. This review provides a better understanding of the effective mechanism of neuromodulation therapies and indicates that inflammatory biomarkers may serve as a reference for the assessment of pathological conditions and treatment options in anxiety and depression.

Echinacoside exerts antidepressant-like effects through enhancing BDNF-CREB pathway and inhibiting neuroinflammation via regulating microglia M1/M2 polarization and JAK1/STAT3 pathway

The present study was performed to investigate the antidepressant effect of echinacoside (ECH) using chronic unpredictable mild stress (CUMS) induced depression mice and lipopolysaccharide (LPS)-stimulated N9 microglial cells. CUMS treatment was performed on C57BL/6 mice for 28 days, followed by gavaging with different doses of echinacoside (15 and 60 mg/kg) for 21 consecutive days. Sucrose preference test (SPT), open field test (OFT), tail suspension test (TST), and forced swimming test (FST) were measured to assess the effects of echinacoside on CUMS-Induced Depressive-Like Behaviors. After that, the pathological changes of hippocampus were determined by Hematoxylin and eosin (HE) staining and Nissl staining; the neurotransmitters, pro-inflammatory cytokines and indoleamine 2,3-dioxygenase (IDO) levels, and the hypothalamic-pituitary-adrenal (HPA) axis activity were determined by enzyme linked immunosorbent assay (ELISA); Iba 1were evaluated by Immunofluorescence assay; Key protein expression levels of CREB/BDNF signal pathway were measured by western blotting. Subsequently, N9 cells were stimulated with 1 μg/ml LPS to induce N9 microglia activation, and were treated with 5-20 μM of echinacoside for 24 h. After that, the levels of NO, interleukin (IL)-1β, IL-6, tumor necrosis factor alpha (TNF-α), IL-4, IL-10, and transforming growth factor beta (TGF-β) in N9 cell culture supernatants were measured by enzyme-linked immunosorbent assay (ELISA) kits; morphology and Iba 1 expression level were observed by high-content screening assay; the M1 markers of CD11b, CD86 and M2 markers of CD206 were analyzed by imaging flow cytometry. Results show that treatment with echinacoside reversed CUMS-increased immobility time in OFT, TST, FST and reversed CUMS-reduced sucrose preference in SPT. In addition, echinacoside reduced the levels of pro-inflammatory cytokines and Iba 1. Moreover, echinacoside significantly increased p-CREB/CREB ratio and BDNF level in hippocampus. Furthermore, echinacoside reduced the secretion of inflammatory factors and inhibited microglia M1 polarization in N9 cells. In conclusion, echinacoside may be beneficial for the treatment of depression diseases through regulating the microglia balance by inhibiting the polarization of microglia to M1 phenotype, and improving hippocampal neurogenesis by the CREB-BDNF signaling pathway.

Hippocampal Inflammation and Gene Expression Changes in Peripheral Lipopolysaccharide Challenged Mice Showing Sickness and Anxiety-Like Behaviors

Neuroinflammation is often associated with the development of depressive and anxiety disorders. The hippocampus is one of the brain regions affected by inflammation that is associated with these symptoms. However, the mechanism of hippocampal inflammation-induced emotional behavior remains unknown. The aim of this study was to clarify temporal changes in the neuroinflammatory responses in the hippocampus and the response of dentate gyrus (DG) neurons using peripheral lipopolysaccharide (LPS)-challenged mice. LPS administration induced anxiety-like activity in the elevated plus maze test and social interaction test after 24 h, at which time the mice had recovered from sickness behavior. We examined the hippocampal inflammation-related gene expression changes over time. The expression of interleukin-1β (Il1b) and tumor necrosis factor α (Tnfa) was rapidly enhanced and sustained until 24 h after LPS administration, whereas the expression of Il6 was transiently induced at approx. 6 h. IL-6-dependent downstream signaling of transducer and activator of transcription 3 (STAT3) was also activated approx. 3-6 h after LPS treatment. The expression of innate immune genes including interferon-induced transmembrane proteins such as interferon-induced transmembrane protein 1 (Ifitm1) and Ifitm3 and complement factors such as C1qa and C1qb started to increase approx. 6 h and showed sustained or further increase at 24 h. We also examined changes in the expression of several maturation markers in the DG and found that LPS enhanced the expression of calbindin 1 (Calb1), tryptophan-2,3-dioxigenase 2 (Tdo2), Il1rl, and neurotrophin-3 (Ntf3) at 24 h after LPS treatment. Collectively, these results demonstrate temporal changes of inflammation and gene expression in the hippocampus in LPS-induced sickness and anxiety-like behaviors.

C1473G Polymorphism in Tph2 Gene Affects Activation of Serotonin Metabolism in Mouse Brain 24 h after LPS Administration

We studied the effect of the C1473G polymorphism in the Tph2 gene that reduces the activity of the tryptophan hydroxylase 2 in the brain on the severity of changes in motor activity (23 h after intraperitoneal administration of 0.8 mg/kg LPS or saline) and on the level of serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) in the endings of 5-HT neurons in the cortex, hippocampus, and striatum (24 h after administration) of mature male mice of congenic lines B6-1473CC (high activity) and B6-1473GG (low activity). The state of the immune system in these structures was assessed by the expression of genes for proinflammatory cytokines IL-1β and TNF. LPS caused a decrease in motor and exploratory activities and increased the expression of the Il1b and Tnf genes in the studied brain structures in mice of both genotypes. LPS did not affect the level of 5-HT in any of the studied brain structures, but dramatically increased the level of 5-HIAA in these structures. The influence of the C1473G polymorphism on the intensity of the LPS-dependent increase in the level of 5-HIAA in the cortex and striatum was shown: in B6-1473CC mice this increase was more pronounced than in B6-1473GG mice. Demonstration of the influence of this polymorphism on the response of the 5-HT system after stimulation of the innate immunity is important for understanding of the role of tryptophan hydroxylase 2 in the mechanism of adaptation of the nervous system during infections and for predicting and reducing the risks of mental disorders.

LQFM212, a piperazine derivative, exhibits potential antioxidant effect as well as ameliorates LPS-induced behavioral, inflammatory and oxidative changes

AIMS

Oxidative stress, impaired antioxidant defense and neuroinflammation are often associated with the onset and progression of neuropsychiatric diseases. Conversely, several piperazine compounds presents beneficial neuropharmacological effects as well as antioxidant activity, and some derivatives combine both activities. LQFM212 (2,6-di-tert-butyl-4-((4-(2-hydroxyethyl)piperazin-1-yl)methyl)phenol) was synthesized to produce effects on CNS and to have an additional antioxidant effect. Previous preclinical tests have been shown anxiolytic- and antidepressant-like effects of LQFM212 in mice. Herein, the main objective was to verify the possible antioxidant potential and the effects of LQFM212 against behavioral changes, inflammatory and oxidative markers induced by lipopolysaccharide (LPS).

MAIN METHODS

Initially, antioxidant potential of LQFM212 was evaluated by electrochemical assays. Afterwards, the effects of oral treatment with LQFM212 were evaluated in mice using LPS-induced models of systemic or local inflammation.

KEY FINDINGS

In LPS-induced neuroinflammation, LQFM212 treatment reverted changes caused by LPS, demonstrated by attenuated anxiogenic- and depressive-like behaviors, reduced pro-inflammatory cytokines (TNF-α and IL-1β) and increased anti-inflammatory cytokines (IL-4 and IL-10) on serum, and also improved oxidative stress-related changes (levels of nitrite, malondialdehyde, glutathione and carbonylated protein, and superoxide dismutase, catalase, myeloperoxidase and cholinesterase activities) on brain cortex and hippocampus. However, LQFM212 treatment did not attenuate the inflammatory changes in LPS-induced pleurisy model.

SIGNIFICANCE

LQFM212 presents antioxidant activity and ameliorates behavioral, inflammatory and oxidative changes after LPS-induced neuroinflammation model. These effects do not seem to be secondary to a peripheral anti-inflammatory action of LQFM212, since this compound failed to attenuate the inflammatory changes in LPS-induced pleurisy model.

Resolution of depression: antidepressant actions of resolvins

Major depressive disorder, one of the most widespread mental illnesses, brings about enormous individual and socioeconomic consequences. Conventional monoaminergic antidepressants require weeks to months to produce a therapeutic response, and approximately one-third of the patients fail to respond to these drugs and are considered treatment-resistant. Although recent studies have demonstrated that ketamine, an N-methyl-D-aspartate receptor antagonist, produces rapid antidepressant effects in treatment-resistant patients, it also has undesirable side effects. Hence, rapid-acting antidepressants that have fewer adverse effects than ketamine are urgently required. D-series (RvD1-RvD6) and E-series (RvE1-RvE4) resolvins are endogenous lipid mediators derived from docosahexaenoic and eicosapentaenoic acids, respectively. These mediators reportedly play a pivotal role in the resolution of acute inflammation. In this review, we reveal that intracranial infusions of RvD1, RvD2, RvE1, RvE2, and RvE3 produce antidepressant-like effects in various rodent models of depression. Moreover, the behavioral effects of RvD1, RvD2, and RvE1 are mediated by the activation of the mechanistic target of rapamycin complex 1, which is essential for the antidepressant-like actions of ketamine. Finally, we briefly provide our perspective on the possible role of endogenous resolvins in stress resilience.

Sex differences in inflammation in the hippocampus and amygdala across the lifespan in rats: associations with cognitive bias

Background

Cognitive symptoms of major depressive disorder, such as negative cognitive bias, are more prevalent in women than in men. Cognitive bias involves pattern separation which requires hippocampal neurogenesis and is modulated by inflammation in the brain. Previously, we found sex differences in the activation of the amygdala and the hippocampus in response to negative cognitive bias in rats that varied with age. Given the association of cognitive bias to neurogenesis and inflammation, we examined associations between cognitive bias, neurogenesis in the hippocampus, and cytokine and chemokine levels in the ventral hippocampus (HPC) and basolateral amygdala (BLA) of male and female rats across the lifespan.

Results

After cognitive bias testing, males had more IFN-γ, IL-1β, IL-4, IL-5, and IL-10 in the ventral HPC than females in adolescence. In young adulthood, females had more IFN-γ, IL-1β, IL-6, and IL-10 in the BLA than males. Middle-aged rats had more IL-13, TNF-α, and CXCL1 in both regions than younger groups. Adolescent male rats had higher hippocampal neurogenesis than adolescent females after cognitive bias testing and young rats that underwent cognitive bias testing had higher levels of hippocampal neurogenesis than controls. Neurogenesis in the dorsal hippocampus was negatively associated with negative cognitive bias in young adult males.

Conclusions

Overall, the association between negative cognitive bias, hippocampal neurogenesis, and inflammation in the brain differs by age and sex. Hippocampal neurogenesis and inflammation may play greater role in the cognitive bias of young males compared to a greater role of BLA inflammation in adult females. These findings lay the groundwork for the discovery of sex-specific novel therapeutics that target region-specific inflammation in the brain and hippocampal neurogenesis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12979-022-00299-4.

• Adolescent male rats had more hippocampal inflammation than females after cognitive bias testing.

• Adult female rats had more basolateral amygdalar inflammation than males after cognitive bias testing.

• HPC neurogenesis was negatively associated to cognitive bias in young adult male rats.

Tetrahydrobiopterin modulates the behavioral neuroinflammatory response to an LPS challenge in mice

Tetrahydrobiopterin (BH4) is a necessary cofactor for the synthesis of monoamines from essential amino-acids, phenylalanine, tyrosine and tryptophan. The BH4 synthesis pathway is induced by inflammatory factors but highly regulated processes maintain levels in a physiological range. However, BH4 activity can be durably altered in inflammation-related pathologies, such as certain types of depression, potentially involving impairment of dopaminergic neurotransmission. The purpose of this study was to investigate the response of the brain BH4 pathway to the inflammatory stimulus induced by lipopolysaccharide (LPS) in mice. Brain expression of genes related to BH4 synthesis, levels of BH4, changes in L-aromatic amino acid precursors of monoamines and dopamine levels were determined. As secondary aim, the effect of acute BH4 supply under the inflammatory challenge was tested on these parameters and on the expression of inflammatory cytokines. Mice were also submitted to the sucrose preference test and to the open-field in order to asses hedonic and locomotor responses to LPS, in addition to their modulation by BH4 supply. The LPS challenge resulted in decreased striatal DA levels and increased Phenylalanine/Tyrosine ratio, suggesting reduced BH4 activity. BH4 supply was effective to increase striatal BH4 levels, to restore the LPS-induced decreased in DA levels in striatum and to dampen the LPS-induced expression of inflammatory cytokines. At the behavioral level, BH4 supply was able to restore the loss of locomotor response to amphetamine in the LPS treated mice, suggesting a modulation of the dopaminergic neurotransmission. These data suggest that BH4 can be considered as a potential add-on molecule, helping to maintain or restore dopaminergic neurotransmission in neuroinflammatory conditions..

New Insights into the Pivotal Role of the Amygdala in Inflammation-Related Depression and Anxiety Disorder

Depression and anxiety disorders are the two most prevalent psychiatric diseases that affect hundreds of millions of individuals worldwide. Understanding the etiology and related mechanisms is of great importance and might yield new therapeutic strategies to treat these diseases effectively. During the past decades, a growing number of studies have pointed out the importance of the stress-induced inflammatory response in the amygdala, a kernel region for processing emotional stimuli, as a potentially critical contributor to the pathophysiology of depression and anxiety disorders. In this review, we first summarized the recent progress from both animal and human studies toward understanding the causal link between stress-induced inflammation and depression and anxiety disorders, with particular emphasis on findings showing the effect of inflammation on the functional changes in neurons in the amygdala, at levels ranging from molecular signaling, cellular function, synaptic plasticity, and the neural circuit to behavior, as well as their contributions to the pathology of inflammation-related depression and anxiety disorders. Finally, we concluded by discussing some of the difficulties surrounding the current research and propose some issues worth future study in this field.

LPS-Induced Coagulation and Neuronal Damage in a Mice Model Is Attenuated by Enoxaparin

Background. Due to the interactions between neuroinflammation and coagulation, the neural effects of lipopolysaccharide (LPS)-induced inflammation (1 mg/kg, intraperitoneal (IP), n = 20) and treatment with the anti-thrombotic enoxaparin (1 mg/kg, IP, 15 min, and 12 h following LPS, n = 20) were studied in C57BL/6J mice. Methods. One week after LPS injection, sensory, motor, and cognitive functions were assessed by a hot plate, rotarod, open field test (OFT), and Y-maze. Thrombin activity was measured with a fluorometric assay; hippocampal mRNA expression of coagulation and inflammation factors were measured by real-time-PCR; and serum neurofilament-light-chain (NfL), and tumor necrosis factor-α (TNF-α) were measured by a single-molecule array (Simoa) assay. Results. Reduced crossing center frequency was observed in both LPS groups in the OFT (p = 0.02), along with a minor motor deficit between controls and LPS indicated by the rotarod (p = 0.057). Increased hippocampal thrombin activity (p = 0.038) and protease-activated receptor 1 (PAR1) mRNA (p = 0.01) were measured in LPS compared to controls, but not in enoxaparin LPS-treated mice (p = 0.4, p = 0.9, respectively). Serum NfL and TNF-α levels were elevated in LPS mice (p < 0.05) and normalized by enoxaparin treatment. Conclusions. These results indicate that inflammation, coagulation, neuronal damage, and behavior are linked and may regulate each other, suggesting another pharmacological mechanism for intervention in neuroinflammation.

Birth triggers an inflammatory response in the neonatal periphery and brain

Birth is preceded by inflammation at the fetal/maternal interface. Additionally, the newborn experiences stimuli that under any other circumstance could elicit an immune response. It is unknown, however, whether birth elicits an inflammatory response in the newborn that extends to the brain. Moreover, it is unknown whether birth mode may alter such a response. To study these questions, we first measured corticosterone and pro- and anti-inflammatory cytokines in plasma of mouse offspring at several timepoints spaced closely before and after a vaginal or Cesarean birth. We found highest levels of IL-6 one day before birth and surges in corticosterone and IL-10 just after birth, regardless of birth mode. We next examined the neuroimmune response by measuring cytokine mRNA expression and microglial number and morphology in the paraventricular nucleus of the hypothalamus and hippocampus around the time of birth. We found a marked increase in TNF-α expression in both brain regions a day after birth, and rapid increases in microglial cell number in the first three days postnatal, with subtle differences by birth mode. To test whether the association between birth and cytokine production or expansion of microglia is causal, we manipulated birth timing. Remarkably, advancing birth by a day advanced the increases in all of the markers tested. Thus, birth triggers an immune response in the body and brain of offspring. Our results may provide a mechanism for effects of birth (e.g., acute changes in cell death and neural activation) previously reported in the newborn brain.

IL-1R/C3aR signaling regulates synaptic pruning in the prefrontal cortex of depression

Background

Major depressive disorder is characterized by not only monoamine neurotransmitters deficiencies but also persistent neuroinflammation. The complement system is an attractive therapeutic target for various inflammation-related diseases due to its early activation in inflammatory processes.

Results

In the present study, the dynamic alteration of complement C3 and its receptor C3aR during the occurrence of depression and the mechanism of astrocyte-microglia IL-1R/C3/C3aR on synaptic pruning were investigated. The proteomic analysis firstly showed that chronic stress caused an elevation of C3. GO analysis indicated that complement system-mediated synaptic pruning signaling was involved in depression. The dynamic observation indicated that C3/C3aR was activated in the early onset and throughout the course of depression induced by lipopolysaccharide (LPS) and chronic stress. In contrast, C3aR blockade inhibited the hyperactivation of microglial APT2/DHHC7 palmitoylation cycle, which mediated the translocation of STAT3 and the expression of proinflammatory cytokines. Meanwhile, C3aR blockade also attenuated the synaptic pruning and enhanced the synaptogenesis in the prefrontal cortex of mice. Moreover, the blockade of IL-1R/NF-κB signaling pathway reduced the release of C3 from astrocyte.

Conclusions

The current study demonstrates that astrocyte-microglia IL-1R/C3/C3aR activation causes the abnormal synaptic pruning in depression, and suggests that the activation of complement C3/C3aR may be particularly helpful in predicting the onset stage of depression.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-022-00832-4.

Obesity and the Brain

Innate and adaptive immunity are essential for neurodevelopment and central nervous system (CNS) homeostasis; however, the fragile equilibrium between immune and brain cells can be disturbed by any immune dysregulation and cause detrimental effects. Accumulating evidence indicates that, despite the blood-brain barrier (BBB), overactivation of the immune system leads to brain vulnerability that increases the risk of neuropsychiatric disorders, particularly upon subsequent exposure later in life. Disruption of microglial function in later life can be triggered by various environmental and psychological factors, including obesity-driven chronic low-grade inflammation and gut dysbiosis. Increased visceral adiposity has been recognized as an important risk factor for multiple neuropsychiatric conditions. The review aims to present our current understanding of the topic.

Peripheral NOD-like receptor deficient inflammatory macrophages trigger neutrophil infiltration into the brain disrupting daytime locomotion

Inflammation is known to disrupt normal behavior, yet the underlying neuroimmune interactions remain elusive. Here, we investigated whether inappropriate macrophage-evoked inflammation alters CNS control of daily-life animal locomotion using a set of zebrafish mutants selected for specific macrophage dysfunction and microglia deficiency. Large-scale genetic and computational analyses revealed that NOD-like receptor nlrc3l mutants are capable of normal motility and visuomotor response, but preferentially swim less in the daytime, suggesting possible low motivation rather than physical impairment. Examining their brain activities and structures implicates impaired dopaminergic descending circuits, where neutrophils abnormally infiltrate. Furthermore, neutrophil depletion recovered daytime locomotion. Restoring wild-type macrophages reversed behavioral and neutrophil aberrations, while three other microglia-lacking mutants failed to phenocopy nlrc3l mutants. Overall, we reveal how peripheral inflammatory macrophages with elevated pro-inflammatory cues (including il1β, tnfα, cxcl8a) in the absence of microglia co-opt neutrophils to infiltrate the brain, thereby potentially enabling local circuitry modulation affecting daytime locomotion.

Protective Effect of Portulaca oleracea Extract Against Lipopolysaccharide-Induced Neuroinflammation, Memory Decline, and Oxidative Stress in Mice: Potential Role of miR-146a and miR-let 7

Neuroinflammation is an adaptive immune response to the central nervous system (CNS) injury induced by infection or toxins. MicroRNAs (miRs) showed critical roles in neuroinflammation as either proinflammatory or anti-inflammatory molecules. Interestingly, Portulaca oleracea (purslane) is an edible plant capable of ameliorating several diseases, including headache, burns, and diabetes; however, its effect on the neuroinflammation-associated miRs was not previously investigated. This study aimed to investigate the effect of aqueous purslane extract on the neuroinflammation induced by lipopolysaccharide (LPS) in mice and to identify its effect on animal cognition, oxidative stress, and expressions of miR-146a and miR-let 7. Adult mice were divided into the following groups: Normal group, LPS group, and Purslane+LPS group. Novel target recognition test, brain histopathology, and measurement of oxidative stress and inflammatory markers were performed. The results showed that LPS group exhibited significant decline in the cognitive memory, brain histopathological injury and a decrease in the number of intact neurons compared to the normal group. Furthermore, the LPS group showed a significant increase in malondialdehyde concentration, whereas superoxide dismutase and catalase activities were decreased. The LPS group also showed an increase in the inflammatory markers tumor necrosis factor-α and nuclear factor kappa B and downregulation of miR-146a and miR-let 7 expressions in the brain cells compared to the normal group, P value <.05. Interestingly, all these changes were reversed by administration of the aqueous purslane extract. In conclusion, the aqueous purslane extract protected from LPS-induced neuroinflammation and memory decline in mice through antioxidant and anti-inflammatory effect where upregulation of miR-146a and miR-1et 7 expressions was involved.

Amyloid Beta Pathology Exacerbates Weight Loss and Brain Cytokine Responses following Low-Dose Lipopolysaccharide in Aged Female Tg2576 Mice

Systemic inflammation has been implicated in the progression of Alzheimer’s disease (AD); however, less is understood about how existing AD pathology contributes to adverse outcomes following acute inflammatory insults. In the present study, our goal was to determine how AD-associated amyloid beta (Aβ) pathology influences the acute neuroinflammatory and behavioral responses to a moderate systemic inflammatory insult. We treated 16–18-month-old female Tg2576 (Tg) mice, which overproduce human Aβ and develop plaques, and age-matched wild-type (WT) littermate mice with an intraperitoneal injection of 0.33 mg/kg lipopolysaccharide (LPS) or saline. Mice were then evaluated over the next 28 h for sickness/depressive-like behaviors (food intake, weight loss, locomotion, and sucrose preference), systemic inflammation (serum amyloid A, SAA), blood-brain barrier (BBB) disruption, astrogliosis (glial fibrillary acidic protein/GFAP), Aβ, and cytokine levels in the brain. We found that LPS caused a larger reduction in body weight in Tg vs. WT mice, but that other behavioral responses to LPS did not differ by genotype. BBB disruption was not apparent in either genotype following LPS. Concentrations of the systemic inflammatory marker, SAA, in the blood and brain were significantly increased with LPS but did not significantly differ by genotype. GFAP was increased in Tg mice vs. WT but was not significantly affected by LPS in either genotype. Finally, LPS-induced increases of eight cytokines (IL-1β, IL-6, IL-12 (p40), IL-10, IL-17A, MIP-1α/CCL3, MIP-1β/CCL4, and RANTES/CCL5) were found to be significantly higher in Tg mice vs. WT. In summary, our data show that Aβ pathology exacerbates the neuroinflammatory response to LPS and identifies cytokines that are selectively regulated by Aβ. The association of worse neuroinflammation with greater weight loss in Tg mice suggests that Aβ pathology could contribute to poor outcomes following a systemic inflammatory insult.

Neuroinflammatory transcriptional signatures in the entorhinal cortex based on lipopolysaccharide-induced depression model in mice

The inflammation and immune hypothesis of major depressive disorder (MDD) explains the mechanism of neuroinflammatory response to promote depression-like behaviors and provides targets for immunotherapy. Previous studies revealed that the neuronal function of the entorhinal cortex (EC) was relative to the depression symptoms in MDD. However, it remains largely unknown what role of neuroinflammation plays in the EC. Hence, we used immunofluorescence to determine c-Fos expression in the EC of lipopolysaccharide (LPS)-treated mice. Mice model was constructed of 10-day LPS treatment, and depression-related behaviors were assessed. We used gene expression microarray to determine differentially expressed genes (DEGs) in the EC of LPS group comparing to control group, and molecular verification was performed by quantitative real-time PCR and Western blot. We found that c-Fos expression was significant reduced in the two layers (Lateral 3.25 mm and 3.00 mm) of the EC in LPS-treated mice compared to saline-treated mice. Mice in LPS group exhibited depression- and anxiety-like behaviors in chronic model. Gene expression analyses identified 339 DEGs in the EC between LPS and control group. The molecular verification showed activation of IL-1R1/NF-κB/CCL5 signaling and upregulation of markers of astrocyte (GFAP) and microglia (AIF1 and CD86) in the EC. Our results suggested that LPS-induced neuroinflammation inhibited neuronal activity in the EC of mice, and that activation of IL-1R1/NF-κB/CCL5 signaling could be involved in the neuroinflammation in the EC of LPS-treated depression model.

Brain-derived neurotrophic factor and inflammation in depression: Pathogenic partners in crime?

Major depressive disorder is a debilitating disorder affecting millions of people each year. Brain-derived neurotrophic factor (BDNF) and inflammation are two prominent biologic risk factors in the pathogenesis of depression that have received considerable attention. Many clinical and animal studies have highlighted associations between low levels of BDNF or high levels of inflammatory markers and the development of behavioral symptoms of depression. However, less is known about potential interaction between BDNF and inflammation, particularly within the central nervous system. Emerging evidence suggests that there is bidirectional regulation between these factors with important implications for the development of depressive symptoms and anti-depressant response. Elevated levels of inflammatory mediators have been shown to reduce expression of BDNF, and BDNF may play an important negative regulatory role on inflammation within the brain. Understanding this interaction more fully within the context of neuropsychiatric disease is important for both developing a fuller understanding of biological pathogenesis of depression and for identifying novel therapeutic opportunities. Here we review these two prominent risk factors for depression with a particular focus on pathogenic implications of their interaction.

Evidence for Effects of Extracellular Vesicles on Physical, Inflammatory, Transcriptome and Reward Behaviour Status in Mice

Immune-inflammatory activation impacts extracellular vesicles (EVs), including their miRNA cargo. There is evidence for changes in the EV miRNome in inflammation-associated neuropsychiatric disorders. This mouse study investigated: (1) effects of systemic lipopolysaccharide (LPS) and chronic social stress (CSS) on plasma EV miRNome; and (2) physiological, transcriptional, and behavioural effects of peripheral or central delivered LPS-activated EVs in recipient mice. LPS or CSS effects on the plasma EV miRNome were assessed by using microRNA sequencing. Recipient mice received plasma EVs isolated from LPS-treated or SAL-treated donor mice or vehicle only, either intravenously or into the nucleus accumbens (NAc), on three consecutive days. Bodyweight, spleen or NAc transcriptome and reward (sucrose) motivation were assessed. LPS and CSS increased the expression of 122 and decreased expression of 20 plasma EV miRNAs, respectively. Peripheral LPS-EVs reduced bodyweight, and both LPS-EVs and SAL-EVs increased spleen expression of immune-relevant genes. NAc-infused LPS-EVs increased the expression of 10 immune-inflammatory genes. Whereas motivation increased similarly across test days in all groups, the effect of test days was more pronounced in mice that received peripheral or central LPS-EVs compared with other groups. This study provides causal evidence that increased EV levels impact physiological and behavioural processes and are of potential relevance to neuropsychiatric disorders.

Ultrasound Stimulation of Prefrontal Cortex Improves Lipopolysaccharide-Induced Depressive-Like Behaviors in Mice

Increasing evidence indicates that inflammatory responses may influence brain neurochemical pathways, inducing depressive-like behaviors. Ultrasound stimulation (US) is a promising non-invasive treatment for neuropsychiatric diseases. We investigated whether US can suppress inflammation and improve depressive-like behaviors. Mice were intraperitoneally injected with lipopolysaccharide to induce depressive-like behaviors. Ultrasound wave was delivered into the prefrontal cortex (PFC) for 30 min. Depressive- and anxiety-like behaviors were evaluated through the forced swimming test (FST), tail suspension test (TST), and elevated plus maze (EPM). Biochemical analyses were performed to assess the expression of inflammatory cytokines in the PFC and serum. The results indicated that US of the PFC significantly improved depressive-like behaviors in the TST (p < 0.05) and FST (p < 0.05). Anxiety-like behaviors also improved in the EPM (p < 0.05). Furthermore, the lipopolysaccharide-mediated upregulation of IL-6, IL-1β, and TNF-α in the PFC was significantly reduced (p < 0.05) by US. In addition, no tissue damage was observed. Overall, US of PFC can effectively improve lipopolysaccharide-induced depressive-like behaviors, possibly through the downregulation of inflammatory cytokines in the PFC. US may be a safe and promising tool for improvement of depression.

Microglial glutaminase 1 deficiency mitigates neuroinflammation associated depression

Glutaminase 1 (GLS1) has recently been reported to be expressed in microglia and plays a crucial role in neuroinflamation. Significantly increased level of GLS1 mRNA expression together with neuroinflammation pathway were observed in postmortem prefrontal cortex from depressed patients. To find out the function of microglial GLS1 in depression and neuroinflammation, we generated transgenic mice (GLS1 cKO), postnatally losing GLS1 in microglia, to detect changes in the lipopolysaccharide (LPS)-induced depression model. LPS-induced anxiety/depression-like behavior was attenuated in GLS1 cKO mice, paralleled by a significant reduction in pro-inflammatory cytokines and an abnormal microglia morphological phenotype in the prefrontal cortex. Reduced neuroinflammation by GLS1 deficient microglia was a result of less reactive astrocytes, as GLS1 deficiency enhanced miR-666-3p and miR-7115-3p levels in extracellular vesicles released from microglia, thus suppressing astrocyte activation via inhibiting Serpina3n expression. Together, our data reveal a novel mechanism of GLS1 in neuroinflammation and targeting GLS1 in microglia may be a novel strategy to alleviate neuroinflammation-related depression and other disease.

Towards Modeling Anhedonia and Its Treatment in Zebrafish

Mood disorders, especially depression, are a major cause of human disability. The loss of pleasure (anhedonia) is a common, severely debilitating symptom of clinical depression. Experimental animal models are widely used to better understand depression pathogenesis and to develop novel antidepressant therapies. In rodents, various experimental models of anhedonia have already been developed and extensively validated. Complementing rodent studies, the zebrafish (Danio rerio) is emerging as a powerful model organism to assess pathobiological mechanisms of affective disorders, including depression. Here, we critically discuss the potential of zebrafish for modeling anhedonia and studying its molecular mechanisms and translational implications.

Sickness and the social brain: How the immune system regulates behavior across species

Many instances of sickness critically involve the immune system. The immune system talks to the brain in a bi-directional loop. This discourse affords the immune system immense control, such that it can influence behavior and optimize recovery from illness. These behavioral responses to infection are called sickness behaviors and can manifest in many ways, including changes in mood, motivation, or energy. Fascinatingly, most of these changes are conserved across species, and most organisms demonstrate some form of sickness behaviors. One of the most interesting sickness behaviors, and not immediately obvious, is altered sociability. Here, we discuss how the immune system impacts social behavior, by examining the brain regions and immune mediators involved in this process. We first outline how social behavior changes in response to infection in various species. Next, we explore which brain regions control social behavior and their evolutionary origins. Finally, we describe which immune mediators establish the link between illness and social behavior, in the context of both normal development and infection. Overall, we hope to make clear the striking similarities between the mechanisms that facilitate changes in sociability in derived and ancestral vertebrate, as well as invertebrate, species.

PSD-93 up-regulates the synaptic activity of corticotropin-releasing hormone neurons in the paraventricular nucleus in depression

Since the discovery of ketamine anti-depressant effects in last decade, it has effectively revitalized interest in investigating excitatory synapses hypothesis in the pathogenesis of depression. In the present study, we aimed to reveal the excitatory synaptic regulation of corticotropin-releasing hormone (CRH) neuron in the hypothalamus, which is the driving force in hypothalamic-pituitary-adrenal (HPA) axis regulation. This study constitutes the first observation of an increased density of PSD-93-CRH co-localized neurons in the hypothalamic paraventricular nucleus (PVN) of patients with major depression. PSD-93 overexpression in CRH neurons in the PVN induced depression-like behaviors in mice, accompanied by increased serum corticosterone level. PSD-93 knockdown relieved the depression-like phenotypes in a lipopolysaccharide (LPS)-induced depression model. Electrophysiological data showed that PSD-93 overexpression increased CRH neurons synaptic activity, while PSD-93 knockdown decreased CRH neurons synaptic activity. Furthermore, we found that LPS induced increased the release of glutamate from microglia to CRH neurons resulted in depression-like behaviors using fiber photometry recordings. Together, these results show that PSD-93 is involved in the pathogenesis of depression via increasing the synaptic activity of CRH neurons in the PVN, leading to the hyperactivity of the HPA axis that underlies depression-like behaviors.

Transcriptomic signatures of psychomotor slowing in peripheral blood of depressed patients: evidence for immunometabolic reprogramming

Inflammation impacts basal ganglia motor circuitry in association with psychomotor retardation, a key symptom of major depression (MD). We previously reported associations between circulating protein inflammatory biomarkers and psychomotor slowing as measured by neuropsychological tests probing psychomotor speed in patients with MD. To discover novel transcriptional signatures in peripheral blood immune cells related to psychomotor slowing, microarray data were analyzed in a primary cohort of 88 medically-stable, unmedicated, ambulatory MD patients. Results were confirmed and extended in a second cohort of 57 patients with treatment resistant depression (TRD) before and after anti-inflammatory challenge with the tumor necrosis factor antagonist infliximab versus placebo. Composite scores reflecting pure motor and cognitive-motor processing speed were linearly associated with 403 and 266 gene transcripts in each cohort, respectively (|R| > 0.30, p < 0.01), that were enriched for cytokine signaling and glycolysis-related pathways (p < 0.05). Unsupervised clustering in the primary cohort revealed two psychomotor slowing-associated gene co-expression modules that were enriched for interferon, interleukin-6, aerobic glycolysis, and oxidative phosphorylation pathways (p < 0.05, q < 0.1). Transcripts were predominantly derived from monocytes, plasmacytoid dendritic cells, and natural killer cells (p's < 0.05). In infliximab-treated TRD patients with high plasma C-reactive protein concentrations (>5 mg/L), two differential co-expression modules enriched for oxidative stress and mitochondrial degradation were associated with improvements in psychomotor reaction time (p < 0.05). These results indicate that inflammatory signaling and associated metabolic reprogramming in peripheral blood immune cells are associated with systemic inflammation in depression and may affect relevant brain circuits to promote psychomotor slowing.

Neurobiological effects of a probiotic-supplemented diet in chronically stressed male Long-Evans rats: Evidence of enhanced resilience

Probiotics that regulate the microbiome-gut-brain axis and provide mental health benefits to the host are referred to as psychobiotics. Preclinical studies have demonstrated psychobiotic effects on early life stress-induced anxiety- and depression-related behavior in rodents; however, the specific mechanisms remain ill-defined. In the current study, we investigated the effects of probiotic supplementation on neurobiological responses to chronic stress in adult male Long-Evans rats. Twenty-four rats were randomly assigned to probiotic (PB) or vehicle control (VEH) groups, then to either chronic unpredictable stress (CUS) or no-stress control (CON) conditions within each group (n = 6/subgroup). We hypothesized that PB supplementation would reduce markers of anxiety and enhance emotional resilience, especially in the CUS animals. In the cognitive uncertainty task, a nonsignificant trend was observed indicating that the PB-supplemented animals spent more time oriented toward the food reward than VEH animals. In the open-field task, CUS-PB animals spent more time in the center of the arena than CUS-VEH animals, an effect not observed between the two CON groups. In the swim task, the PB animals, regardless of stress assignment, exhibited increased floating, suggesting a conserved response in a challenging context. Focusing on the endocrine measures, higher dehydroepiandrosterone (DHEA)-to-corticosterone fecal metabolite ratios, a correlate of emotional resilience, were observed in PB animals. Further, PB animals exhibited reduced microglia immunoreactivity in the basolateral amygdala, possibly indicating a neuroprotective effect of PB supplements in this rodent model. These results provide evidence that PB supplementation interacts with stress exposure to influence adaptive responses associated with endocrine, neural, and behavioral indices of anxiety.

Neuronal Mitochondrial Dysfunction and Bioenergetic Failure in Inflammation-Associated Depression

Depression is a leading cause of disability and affects more than 4% of the population worldwide. Even though its pathophysiology remains elusive, it is now well accepted that peripheral inflammation might increase the risk of depressive episodes in a subgroup of patients. However, there is still insufficient knowledge about the mechanisms by which inflammation induces alterations in brain function. In neurodegenerative and neuroinflammatory diseases, extensive studies have reported that inflammation negatively impacts mitochondrial health, contributing to excitotoxicity, oxidative stress, energy deficits, and eventually neuronal death. In addition, damaged mitochondria can release a wide range of damage-associated molecular patterns that are potent activators of the inflammatory response, creating a feed-forward cycle between oxidative stress, mitochondrial impairment, inflammation, and neuronal dysfunction. Surprisingly, the possible involvement of this vicious cycle in the pathophysiology of inflammation-associated depression remains understudied. In this mini-review we summarize the research supporting the association between neuroinflammation, mitochondrial dysfunction, and bioenergetic failure in inflammation-associated depression to highlight the relevance of further studies addressing this crosstalk.