Time course and localization patterns of interleukin-1β messenger rna expression in brain and pituitary after peripheral administration of lipopolysaccharide

Beyond digestion: Exploring how the gut microbiota modulates human social behaviors

For a long time, traditional medicine has acknowledged the gut's impact on general health. Contemporary science substantiates this association through investigations of the gut microbiota, the extensive community of microorganisms inhabiting our gastrointestinal system. These microscopic residents considerably improve digestive processes, nutritional absorption, immunological function, and pathogen defense. Nevertheless, a variety of gastrointestinal and extra-intestinal disorders can result from dysbiosis, an imbalance of the microbial composition of the gut microbiota. A groundbreaking discovery is the gut-brain axis, a complex communication network that links the enteric and central nervous system (CNS). This bidirectional communication allows the brain to influence gut activities and vice versa, impacting mental health and mood disorders like anxiety and depression. The gut microbiota can influence this communication by creating neurotransmitters and short-chain fatty acids, among other biochemical processes. These factors may affect our mental state, our ability to regulate our emotions, and the hypothalamic-pituitary-adrenal (HPA) axis. This study aimed to explore the complex interrelationships between the brain and the gut microbiota. We also conducted a thorough examination of the existing understanding in the area of how microbiota affects social behaviors, including emotions, stress responses, and cognitive functions. We also explored the potential of interventions that focus on the connection between the gut and the brain, such as using probiotics to treat diseases of the CNS. This research opens up new possibilities for addressing mental health and neurological conditions in an innovative manner.

Exploring the role of galectin-9 and artemin as biomarkers in long COVID with chronic fatigue syndrome: links to inflammation and cognitive function

This study aimed to assess plasma galectin-9 (Gal-9) and artemin (ARTN) concentrations as potential biomarkers to differentiate individuals with Long COVID (LC) patients with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) from SARS-CoV-2 recovered (R) and healthy controls (HCs). Receiver operating characteristic (ROC) curve analysis determined a cut-off value of plasma Gal-9 and ARTN to differentiate LC patients from the R group and HCs in two independent cohorts. Positive correlations were observed between elevated plasma Gal-9 levels and inflammatory markers (e.g. SAA and IP-10), as well as sCD14 and I-FABP in LC patients. Gal-9 also exhibited a positive correlation with cognitive failure scores, suggesting its potential role in cognitive impairment in LC patients with ME/CFS. This study highlights plasma Gal-9 and/or ARTN as sensitive screening biomarkers for discriminating LC patients from controls. Notably, the elevation of LPS-binding protein in LC patients, as has been observed in HIV infected individuals, suggests microbial translocation. However, despite elevated Gal-9, we found a significant decline in ARTN levels in the plasma of people living with HIV (PLWH). Our study provides a novel and important role for Gal-9/ARTN in LC pathogenesis.

JAK1/2 Regulates Synergy Between Interferon Gamma and Lipopolysaccharides in Microglia

Microglia, the resident immune cells of the brain, regulate neuroinflammation which can lead to secondary neuronal damage and cognitive impairment under pathological conditions. Two of the many molecules that can elicit an inflammatory response from microglia are lipopolysaccharide (LPS), a component of gram-negative bacteria, and interferon gamma (IFNγ), an endogenous pro-inflammatory cytokine. We thoroughly examined the concentration-dependent relationship between LPS from multiple bacterial species and IFNγ in cultured microglia and macrophages. We measured the effects that these immunostimulatory molecules have on pro-inflammatory activity of microglia and used a battery of signaling inhibitors to identify the pathways that contribute to the microglial response. We found that LPS and IFNγ interacted synergistically to induce a pro-inflammatory phenotype in microglia, and that inhibition of JAK1/2 completely blunted the response. We determined that this synergistic action of LPS and IFNγ was likely dependent on JNK and Akt signaling rather than typical pro-inflammatory mediators such as NF-κB. Finally, we demonstrated that LPS derived from Escherichia coli, Klebsiella pneumoniae, and Akkermansia muciniphila can elicit different inflammatory responses from microglia and macrophages, but these responses could be consistently prevented using ruxolitinib, a JAK1/2 inhibitor. Collectively, this work reveals a mechanism by which microglia may become hyperactivated in response to the combination of LPS and IFNγ. Given that elevations in circulating LPS and IFNγ occur in a wide variety of pathological conditions, it is critical to understand the pharmacological interactions between these molecules to develop safe and effective treatments to suppress this process.

Systemic inflammation mediates the association between environmental tobacco smoke and depressive symptoms: A cross-sectional study of NHANES 2009-2018

BACKGROUND

Depression is associated with both environmental tobacco smoke (ETS) and inflammation. However, whether systemic inflammation mediates the ETS-depression relationship is unclear.

METHODS

We analyzed 19,612 participants from the 2009-2018 National Health and Nutrition Examination Survey (representing approximately 206,284,711 USA individuals), utilizing data of depressive symptoms (assessed by Patient Health Questionnaire-9), blood cotinine level (an ETS biomarker), dietary inflammatory index (DII, assessed by 24-h dietary recall) and inflammation, represented by immune-inflammation index (SII) and systemic inflammation response index (SIRI).

RESULTS

Weighted multivariable logistic regression showed that a higher blood cotinine level is significantly associated with a higher depressive symptoms risk (OR = 1.79, 1.35-2.38). After adjusting for covariates, the effect in smokers (OR = 1.220, 95 % CI: 1.140-1.309) is larger than that in non-smokers (OR = 1.150, 95 % CI: 1.009-1.318). Compared to the lowest level, depressive symptoms risks in participants with the highest level of SII, SIRI and DII are 19 % (OR = 1.19, 1.05-1.35), 15 % (OR = 1.15, 1.01-1.31) and 88 % (OR = 1.88, 1.48-2.39) higher, respectively. Weighted linear regression demonstrated positive correlations of SII (β = 0.004, 0.001-0.006), SIRI (β = 0.009, 0.005-0.012) and DII (β = 0.213, 0.187-0.240) with blood cotinine level. Restricted cubic splines model showed a linear dose-response relationship between blood cotinine and depressive symptoms (Pnon-linear = 0.410), with decreasing risk for lower DII. And SII and SIRI respectively mediate 0.21 % and 0.1 % of the association between blood cotinine and depressive symptoms.

LIMITATION

Cross-sectional design, and lack of medication data for depression.

CONCLUSIONS

Positive association of ETS (blood cotinine) with depressive symptoms risk is partly mediated by systemic inflammation, and anti-inflammatory diet could be beneficial.

Protective effect of melatonin on blood-brain barrier damage caused by Endotoxemia

OBJECTIVE

Endotoxins, products of Gram-negative bacteria, are the primary cause of blood-brain barrier (BBB) damage. In the present study, we aimed to investigate the possible neuroprotection mechanisms of melatonin on BBB damage induced by endotoxemia.

METHODS

Adult, female Sprague-Dawley rats (n = 42) were separated into four random groups as a control group and three treatment groups. Lipopolysaccharide (7,5 mg/kg/day) was administrated for a single dose to generate a 24-hour sepsis model on rats. Melatonin (10 mg/kg/day) was treated a week before sepsis. Afterward, the dissected brain tissues were examined by histopathological, biochemical, and molecular analyses.

RESULTS

LPS caused weight loss in the groups. As a result, degenerated neurons with cytoplasmic vacuoles and irregular pyknotic nuclei, pale stained necrotic neurons, and vascular congestion were observed in LPS-exposed rats. However, MEL decreased the number of degenerated neurons in treated groups. MEL treatment increased ZO1 and Occludin immunoreactivity while decreasing TLR4 in brain tissues. MEL effect on protein expression was recorded for ZO1 increase and TLR4 decrease in brain tissue compared to LPS groups. MEL also decreased MDA levels in brain tissue.

CONCLUSIONS

MEL recovered the degenerative damage of sepsis by contributing to blood-brain barrier integrity, and by decreasing inflammation, thus the neuroprotective effects of MEL might provide an experimental basis for clinical applications.

Brain structural and functional alterations related to anxiety in allergic asthma

Psychiatric disorders are common in patients with allergic asthma, and they can have a significant impact on their quality of life and disease control. Recent studies have suggested that there may be potential immune-brain communication mechanisms in asthma, which can activate inflammatory responses in different brain areas, leading to structural and functional alterations and behavioral changes. However, the precise mechanisms underlying these alterations remain unclear. In this paper, we comprehensively review the relevant research on asthma-induced brain structural and functional alterations that lead to the initiation and promotion of anxiety. We summarize the possible pathways for peripheral inflammation to affect the brain's structure and function. Our review highlights the importance of addressing neuropsychiatric disorders in the clinical guidelines of asthma, to improve the quality of life of these patients. We suggest that a better understanding of the mechanisms underlying psychiatric comorbidities in asthma could lead to the development of more effective treatments for these patients.

Gut microbes influence the development of central nervous system disorders through epigenetic inheritance

Central nervous system (CNS) disorders, such as depression, anxiety, and Alzheimer's disease (AD), affect quality of life of patients and pose significant economic and social burdens worldwide. Due to their obscure and complex pathogeneses, current therapies for these diseases have limited efficacy. Over the past decade, the gut microbiome has been shown to exhibit direct and indirect influences on the structure and function of the CNS, affecting multiple pathological pathways. In addition to the direct interactions between the gut microbiota and CNS, the gut microbiota and their metabolites can regulate epigenetic processes, including DNA methylation, histone modification, and regulation of non-coding RNAs. In this review, we discuss the tripartite relationship among gut microbiota, epigenetic inheritance, and CNS disorders. We suggest that gut microbes and their metabolites influence the pathogenesis of CNS disorders at the epigenetic level, which may inform the development of effective therapeutic strategies for CNS disorders.

Neutrophil to lymphocyte ratio and platelet to lymphocyte ratio as prognostic predictors for delirium in critically ill patients: a systematic review and meta-analysis

INTRODUCTION

In this systematic review and meta-analysis, we aim to analyze the current literature to evaluate neutrophil to lymphocyte ratio (NLR) and platelet to lymphocyte ratio (PLR) values among critically ill patients who develop delirium as compared to those who do not.

METHODS

PubMed, Web of Science, and Scopus were used to conduct a systematic search for relevant publications published before June 12, 2022. The Newcastle-Ottawa scale was used for quality assessment. Because a significant level of heterogeneity was found, we used the random-effects model to generate pooled effects.

RESULTS

Twenty-four studies including 11,579 critically ill patients, of whom 2439 were diagnosed with delirium, were included in our meta-analysis. Compared with the non-delirious group, the delirious group's NLR levels were significantly higher (WMD = 2.14; CI 95% = 1.48-2.80, p < 0.01). In the subgroup analysis according to the type of critical condition, the NLR levels in patients of delirious group were significantly more than those of non-delirious group in studies on POD, PSD and PCD (WMD = 1.14, CI 95% = 0.38-1.91, p < 0.01, WMD = 1.38, CI 95% = 1.04-1.72, p < 0.001, and WMD = 4.22, CI 95% = 3.47-4.98, p < 0.001, respectively). However, compared with the non-delirious group, the delirious group's PLR levels were not significantly different (WMD = 1.74; CI 95% = -12.39-15.86, p = 0.80).

CONCLUSION

Our findings support NLR to be a promising biomarker that can be readily integrated into clinical settings to aid in the prediction and prevention of delirium.

Association of systemic inflammatory biomarkers with depression risk: Results from National Health and Nutrition Examination Survey 2005-2018 analyses

BACKGROUND/AIM

Depression has become a multiple disease worldwide, and is closely related to the systemic inflammatory response.

METHODS

Based on the data of the National Health and Nutrition Examination Survey (NHANES), this study included 2,514 depressive and 26,487 non-depressive adults. The systemic immune-inflammation index (SII) and systemic inflammation response index (SIRI) were used to quantify systemic inflammation. The multivariate logistic regression and inverse probability weighting methods were used to analyze the effect size of SII and SIRI on the risk of depression.

RESULTS

After adjusting for all confounders, the above associations of SII and SIRI with depression risk remained significant (SII, OR = 1.02, 95% CI = 1.01 to 1.02, p = 0.001; SIRI, OR = 1.06, 95% CI = 1.01 to 1.10, p = 0.016). Each 100-unit increase in SII was associated with a 2% increase in the risk of depression, while each one-unit increase in SIRI was associated with a 6% increase in the risk of depression.

CONCLUSION

Systemic inflammatory biomarkers (SII and SIRI) significantly affected the risk of depression. SII or SIRI can serve as a biomarker of anti-inflammation treatment for depression.

Changes of Dopamine and Tyrosine Hydroxylase Levels in the Brain of Germ-free Mice

Background

Dopamine (DA) is one of the most important catecholamine neurotransmitters in the central nervous system. The degeneration and deletion of dopaminergic neurons are closely linked to Parkinson's disease (PD) and other psychiatric or neurological diseases. Several studies have been suggesting that intestinal microorganisms are associated with the occurrence of central nervous diseases, including diseases that are closely related to dopaminergic neurons. However, the intestinal microorganism's regulation of dopaminergic neurons in the brain is largely unknown.

Objectives

This study aimed to investigate the hypothetical differences of DA and its synthase tyrosine hydroxylase (TH) expression in different parts of the brain of germ free (GF) mice.

Materials and Methods

Several studies in recent years have shown that commensal intestinal microbiota promotes changes in DA receptor expression, DA levels, and affects this monoamine turnover. Germ free (GF) and specific pathogen free (SPF) C57b/L male mice were used to analyze TH mRNA and expression levels, and DA levels in the frontal cortex, hippocampus, striatum, and cerebellum, using real time PCR, western blotting, and ELISA tools.

Results

Compared with SPF mice, the TH mRNA levels were decreased in the cerebellum of GF mice, while the TH protein expression was tended to increase in the hippocampus, and conversely showed significant decrease in the striatum. The average optical density (AOD) of TH immunoreactive nerve fibers and the number of axons in striatum of mice in GF group were significantly lower than that in SPF group. Compared with SPF mice, the DA concentration in the hippocampus, striatum and frontal cortex of GF mice was decreased in GF mice.

Conclusion

The changes of DA and its synthase TH in the brain of GF mice showed that the absence of conventional intestinal microbiota had certain regulatory effects on central dopaminergic nervous system, which is considered helpful for studying the effect of commensal intestinal flora on diseases related to impaired dopaminergic nerve system.

Neural control of the spleen as an effector of immune responses to inflammation: mechanisms and treatments

Immune system responses are a vital defense mechanism against pathogens. Inflammatory mediators finely regulate complex inflammatory responses from initiation to resolution. However, in certain conditions, the inflammation is initiated and amplified, but not resolved. Understanding the biological mechanisms underlying the regulation of the immune response is critical for developing therapeutic alternatives, including pharmaceuticals and bioelectronic tools. The spleen is an important immune effector organ since it orchestrates innate and adaptive immune responses such as pathogen clearance, cytokine production, and differentiation of cells, therefore playing a modulatory role that balances pro- and anti-inflammatory responses. However, modulation of splenic immune activity is a largely unexplored potential therapeutic tool that could be used for the treatment of inflammatory and life-threatening conditions. This review discusses some of the mechanisms controlling neuroimmune communication and the brain-spleen axis.

Neural circuits mediating circulating interleukin-1β-evoked fever in the absence of prostaglandin E2 production

Infectious diseases and inflammatory conditions recruit the immune system to mount an appropriate acute response that includes the production of cytokines. Cytokines evoke neurally-mediated responses to fight pathogens, such as the recruitment of thermoeffectors, thereby increasing body temperature and leading to fever. Studies suggest that the cytokine interleukin-1β (IL-1β) depends upon cyclooxygenase (COX)-mediated prostaglandin E₂ production for the induction of neural mechanisms to elicit fever. However, COX inhibitors do not eliminate IL-1β-induced fever, thus suggesting that COX-dependent and COX-independent mechanisms are recruited for increasing body temperature after peripheral administration of IL-1β. In the present study, we aimed to build a foundation for the neural circuit(s) controlling COX-independent, inflammatory fever by determining the involvement of brain areas that are critical for controlling the sympathetic outflow to brown adipose tissue (BAT) and the cutaneous vasculature. In anesthetized rats, pretreatment with indomethacin, a non-selective COX inhibitor, did not prevent BAT thermogenesis or cutaneous vasoconstriction (CVC) induced by intravenous IL-1β (2 µg/kg). BAT and cutaneous vasculature sympathetic premotor neurons in the rostral raphe pallidus area (rRPa) are required for IL-1β-evoked BAT thermogenesis and CVC, with or without pretreatment with indomethacin. Additionally, activation of glutamate receptors in the dorsomedial hypothalamus (DMH) is required for COX-independent, IL-1β-induced BAT thermogenesis. Therefore, our data suggests that COX-independent mechanisms elicit activation of neurons within the DMH and rRPa, which is sufficient to trigger and mount inflammatory fever. These data provide a foundation for elucidating the brain circuits responsible for COX-independent, IL-1β-elicited fevers.

Microglial Priming in Infections and Its Risk to Neurodegenerative Diseases

Infectious diseases of different etiologies have been associated with acute and long-term neurological consequences. The primary cause of these consequences appears to be an inflammatory process characterized primarily by a pro-inflammatory microglial state. Microglial cells, the local effectors' cells of innate immunity, once faced by a stimulus, alter their morphology, and become a primary source of inflammatory cytokines that increase the inflammatory process of the brain. This inflammatory scenario exerts a critical role in the pathogenesis of neurodegenerative diseases. In recent years, several studies have shown the involvement of the microglial inflammatory response caused by infections in the development of neurodegenerative diseases. This has been associated with a transitory microglial state subsequent to an inflammatory response, known as microglial priming, in which these cells are more responsive to stimuli. Thus, systemic inflammation and infections induce a transitory state in microglia that may lead to changes in their state and function, making priming them for subsequent immune challenges. However, considering that microglia are long-lived cells and are repeatedly exposed to infections during a lifetime, microglial priming may not be beneficial. In this review, we discuss the relationship between infections and neurodegenerative diseases and how this may rely on microglial priming.

What SARS-CoV-2 does to our brains

Neurological symptoms in SARS-CoV-2-infected patients have been reported, but their cause remains unclear. In theory, the neurological symptoms observed after SARS-CoV-2 infection could be (1) directly caused by the virus infecting brain cells, (2) indirectly by our body’s local or systemic immune response toward the virus, (3) by coincidental phenomena, or (4) a combination of these factors. As indisputable evidence of intact and replicating SARS-CoV-2 particles in the central nervous system (CNS) is currently lacking, we suggest focusing on the host’s immune reaction when trying to understand the neurocognitive symptoms associated with SARS-CoV-2 infection. In this perspective, we discuss the possible immune-mediated mechanisms causing functional or structural CNS alterations during acute infection as well as in the post-infectious context. We also review the available literature on CNS affection in the context of COVID-19 infection, as well as observations from animal studies on the molecular pathways involved in sickness behavior.

Neuroinflammation: A Possible Link Between Chronic Vascular Disorders and Neurodegenerative Diseases

Various age-related diseases involve systemic inflammation, i.e. a stereotyped series of acute immune system responses, and aging itself is commonly associated with low-grade inflammation or inflamm’aging. Neuroinflammation is defined as inflammation-like processes inside the central nervous system, which this review discusses as a possible link between cardiovascular disease-related chronic inflammation and neurodegenerative diseases. To this aim, neuroinflammation mechanisms are first summarized, encompassing the cellular effectors and the molecular mediators. A comparative survey of the best-known physiological contexts of neuroinflammation (neurodegenerative diseases and transient ischemia) reveals some common features such as microglia activation. The recently published transcriptomic characterizations of microglia have pointed a marker core signature among neurodegenerative diseases, but also unraveled the discrepancies with neuroinflammations related with acute diseases of vascular origin. We next review the links between systemic inflammation and neuroinflammation, beginning with molecular features of respective pro-inflammatory cells, i.e. macrophages and microglia. Finally, we point out a gap of knowledge concerning the atherosclerosis-related neuroinflammation, which is for the most surprising given that atherosclerosis is established as a major risk factor for neurodegenerative diseases.

Dynamic Interleukin-1 Receptor Type 1 Signaling Mediates Microglia-Vasculature Interactions Following Repeated Systemic LPS

Introduction

Lipopolysaccharide (LPS) preconditioning involves repeated, systemic, and sub-threshold doses of LPS, which induces a neuroprotective state within the CNS, thus preventing neuronal death and functional losses. Recently, proinflammatory cytokine, Interleukin-1 (IL-1), and its primary signaling partner, interleukin-1 receptor type 1 (IL-1R1), have been associated with neuroprotection in the CNS. However, it is still unknown how IL-1/IL-1R1 signaling impacts the processes associated with neuroprotection.

Methods

Using our IL-1R1 restore genetic mouse model, mouse lines were generated to restrict IL-1R1 expression either to endothelia (Tie2-Cre-Il1r1^r/r) or microglia (Cx3Cr1-Cre-Il1r1 ^r/r), in addition to either global ablation (Il1r1 ^r/r) or global restoration of IL-1R1 (Il1r1 ^GR/GR). The LPS preconditioning paradigm consisted of four daily i.p. injections of LPS at 1 mg/kg (4d LPS). 24 hrs following the final i.p. LPS injection, tissue was collected for qPCR analysis, immunohistochemistry, or FAC sorting.

Results

Following 4d LPS, we found multiple phenotypes that are dependent on IL-1R1 signaling such as microglia morphology alterations, increased microglial M2-like gene expression, and clustering of microglia onto the brain vasculature. We determined that 4d LPS induces microglial morphological changes, clustering at the vasculature, and gene expression changes are dependent on endothelial IL-1R1, but not microglial IL-1R1. A novel observation was the induction of microglial IL-1R1 (mIL-1R1) following 4d LPS. The induced mIL-1R1 permits a unique response to central IL-1β: the mIL-1R1 dependent induction of IL-1R1 antagonist (IL-1RA) and IL-1β gene expression. Analysis of RNA sequencing datasets revealed that mIL-1R1 is also induced in neurodegenerative diseases.

Discussion

Here, we have identified cell type-specific IL-1R1 mediated mechanisms, which may contribute to the neuroprotection observed in LPS preconditioning. These findings identify key cellular and molecular contributors in LPS-induced neuroprotection.

The semantics of microglia activation: neuroinflammation, homeostasis, and stress

Microglia are emerging as critical regulators of neuronal function and behavior in nearly every area of neuroscience. Initial reports focused on classical immune functions of microglia in pathological contexts, however, immunological concepts from these studies have been applied to describe neuro-immune interactions in the absence of disease, injury, or infection. Indeed, terms such as 'microglia activation' or 'neuroinflammation' are used ubiquitously to describe changes in neuro-immune function in disparate contexts; particularly in stress research, where these terms prompt undue comparisons to pathological conditions. This creates a barrier for investigators new to neuro-immunology and ultimately hinders our understanding of stress effects on microglia. As more studies seek to understand the role of microglia in neurobiology and behavior, it is increasingly important to develop standard methods to study and define microglial phenotype and function. In this review, we summarize primary research on the role of microglia in pathological and physiological contexts. Further, we propose a framework to better describe changes in microglia1 phenotype and function in chronic stress. This approach will enable more precise characterization of microglia in different contexts, which should facilitate development of microglia-directed therapeutics in psychiatric and neurological disease.

Modulation of Neural Networks by Interleukin-1

Interleukin-1 (IL-1) is an inflammatory cytokine that has been shown to modulate neuronal signaling in homeostasis and diseases. In homeostasis, IL-1 regulates sleep and memory formation, whereas in diseases, IL-1 impairs memory and alters affect. Interestingly, IL-1 can cause long-lasting changes in behavior, suggesting IL-1 can alter neuroplasticity. The neuroplastic effects of IL-1 are mediated via its cognate receptor, Interleukin-1 Type 1 Receptor (IL-1R1), and are dependent on the distribution and cell type(s) of IL-1R1 expression. Recent reports found that IL-1R1 expression is restricted to discrete subpopulations of neurons, astrocytes, and endothelial cells and suggest IL-1 can influence neural circuits directly through neuronal IL-1R1 or indirectly via non-neuronal IL-1R1. In this review, we analyzed multiple mechanisms by which IL-1/IL-1R1 signaling might impact neuroplasticity based upon the most up-to-date literature and provided potential explanations to clarify discrepant and confusing findings reported in the past.

Infectious disease-associated encephalopathies

Infectious diseases may affect brain function and cause encephalopathy even when the pathogen does not directly infect the central nervous system, known as infectious disease-associated encephalopathy. The systemic inflammatory process may result in neuroinflammation, with glial cell activation and increased levels of cytokines, reduced neurotrophic factors, blood-brain barrier dysfunction, neurotransmitter metabolism imbalances, and neurotoxicity, and behavioral and cognitive impairments often occur in the late course. Even though infectious disease-associated encephalopathies may cause devastating neurologic and cognitive deficits, the concept of infectious disease-associated encephalopathies is still under-investigated; knowledge of the underlying mechanisms, which may be distinct from those of encephalopathies of non-infectious cause, is still limited. In this review, we focus on the pathophysiology of encephalopathies associated with peripheral (sepsis, malaria, influenza, and COVID-19), emerging therapeutic strategies, and the role of neuroinflammation.

Swine Inflammation and Necrosis Syndrome (SINS)

Tail biting is a prevalent and undesirable behaviour in pigs and a major source of significant reduction in well-being. However, focusing on biting considers only one part of the solution, because tail damage can be found with a high prevalence without any action by other pigs. The lesions are not limited to the tail but can also be found in the ears, heels, soles, claw coronary bands, teats, navel, vulva, and face. Environmental improvement alone often fails to overcome the problem. This review addresses a new inflammation and necrosis syndrome in swine (SINS). It shows the clinical signs and the frequencies of occurrence in different age groups. It compiles scientific evidence from clinical and histopathological studies in newborn piglets that argue for a primary endogenous aetiology of the disease. Bringing together the findings of a broad body of research, the possible mechanisms leading to the disease are identified and then discussed. This part will especially focus on microbe-associated molecular patterns in the circulation and their role in activating defence mechanisms and inflammation. Finally, the methods are identified to ameliorate the problem by optimizing husbandry and selecting a suitable breeding stock.

Microbiota and Microglia Interactions in ASD

Autism spectrum disorders (ASD) are serious, highly variable neurodevelopmental disorders, commonly characterized by the manifestation of specific behavioral abnormalities, such as stereotypic behaviors and deficits in social skills, including communication. Although the neurobiological basis for ASD has attracted attention in recent decades, the role of microglial cells, which are the main resident myeloid cell population in the brain, is still controversial and underexplored. Microglia play several fundamental roles in orchestrating brain development and homeostasis. As such, alterations in the intrinsic functions of these cells could be one of the driving forces responsible for the development of various neurodevelopmental disorders, including ASD. Microglia are highly sensitive to environmental cues. Amongst the environmental factors known to influence their intrinsic functions, the gut microbiota has emerged as a central player, controlling both microglial maturation and activation. Strikingly, there is now compelling data suggesting that the intestinal microbiota can play a causative role in driving the behavioural changes associated with ASD. Not only is intestinal dysbiosis commonly reported in ASD patients, but therapies targeting the microbiome can markedly alleviate behavioral symptoms. Here we explore the emerging mechanisms by which altered microglial functions could contribute to several major etiological factors of ASD. We then demonstrate how pre- and postnatal environmental stimuli can modulate microglial cell phenotype and function, underpinning the notion that reciprocal interactions between microglia and intestinal microbes could play a crucial role in ASD aetiology.

Increased cytokine expression in the choroid plexus stroma and epithelium in response to endotoxin-induced systemic inflammation in mice

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Brain response to systemic inflammation is initiated by IL-1β from choroid plexus macrophages.

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Choroid plexus stromal cells bear IL-1 receptors and participate in the immediate reaction to systemic inflammation.

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This reaction is followed by elevated gene expression of various cytokines in the choroid plexus stroma and epithelium.

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The choroid plexus immediate responses are relevant to understanding how sepsis-associated encephalopathy is initiated.

Sepsis-associated encephalopathy (SAE) is characterized as diffuse brain dysfunction in patients with excessive systemic inflammatory reaction to an infection. In our previous studies using a mouse model of SAE with intraperitoneal injection of lipopolysaccharide (LPS), tissue concentrations of various cytokines were elevated in the entire brain parenchyma 4 and 24 h following LPS administration. Cytokines elevated at 4 h were produced by the choroid plexus, leptomeninges and vascular endothelium, while those at 24 h were produced by astrocytes. Interleukin (IL)-1β did not increase in the concentration in the brain parenchyma during the period from 1 to 24 h following LPS. In the present study, we hypothesized that the intracranial cells that initially respond to systemic inflammation are situated in the choroid plexus and produce IL-1β to initiate cytokine-mediated reactions. We quantified the transcript levels of related cytokines within the choroid plexus and specified the choroid plexus cells that are involved in the immediate cytokine-mediated responses. Mice received LPS or saline by intraperitoneal injection. Four hours after treatments, the choroid plexuses were isolated and subjected to cytokine gene expression analyses using real-time reverse transcription-polymerase chain reaction. Another group of mice was fixed at 1, 4 and 24 h after treatments and the expression of cytokines and receptors was studied with double immunohistofluorescence staining. The transcript levels of IL-1β, CC-motif ligand (CCL)2, CXC-motif ligand (CXCL)1, CXCL2 and IL-6 in the choroid plexus were significantly increased in mice treated with LPS compared to saline control. The IL-1β expression was remarkable in choroid plexus macrophages at 1 and 4 h but not in the brain parenchyma. Choroid plexus stromal cells expressed IL-1 receptor type 1 (IL-1R1). The IL-1R1-bearing stromal cells produced CCL2, CXCL1, CXCL2 and IL-6 at 4 h. Choroid plexus epithelial cells expressed CXCR2, a common receptor for CXCL1 and CXCL2. Choroid plexus epithelial cells also expressed CCL2, CXCL1 and CXCL2 at 4 h, and IL-1R1-bearing stromal cells expressed CXCR2. Therefore, in response to systemic LPS injection, one of the intracranial reactions was initiated within the choroid plexus using IL-1β derived from macrophages. The choroid plexus stromal cells subsequently had elevated expression of CCL2, CXCL1, CXCL2 and IL-6. The choroid plexus epithelial cells also had elevated expression of CCL2, CXCL1 and CXCL2. The presence of receptors for these cytokines on both epithelial and stromal cells raised the possibility of reciprocal interactions between these cells. The results suggested that the immediate early responses exerted by the choroid plexus are relevant to understanding how SAE is initiated in clinical settings.

Early-life-trauma triggers interferon-β resistance and neurodegeneration in a multiple sclerosis model via downregulated β1-adrenergic signaling

Environmental triggers have important functions in multiple sclerosis (MS) susceptibility, phenotype, and trajectory. Exposure to early life trauma (ELT) has been associated with higher relapse rates in MS patients; however, the underlying mechanisms are not well-defined. Here we show ELT induces mechanistic and phenotypical alterations during experimental autoimmune encephalitis (EAE). ELT sustains downregulation of immune cell adrenergic receptors, which can be attributed to chronic norepinephrine circulation. ELT-subjected mice exhibit interferon-β resistance and neurodegeneration driven by lymphotoxin and CXCR2 involvement. These phenotypic changes are observed in control EAE mice treated with β1 adrenergic receptor antagonist. Conversely, β1 adrenergic receptor agonist treatment to ELT mice abrogates phenotype changes via restoration of immune cell β1 adrenergic receptor function. Our results indicate that ELT alters EAE phenotype via downregulation of β1 adrenergic signaling in immune cells. These results have implications for the effect of environmental factors in provoking disease heterogeneity and might enable prediction of long-term outcomes in MS.

A Proposed Role for Pro-Inflammatory Cytokines in Damaging Behavior in Pigs

Sickness can change our mood for the worse, leaving us sad, lethargic, grumpy and less socially inclined. This mood change is part of a set of behavioral symptoms called sickness behavior and has features in common with core symptoms of depression. Therefore, the physiological changes induced by immune activation, for example following infection, are in the spotlight for explaining mechanisms behind mental health challenges such as depression. While humans may take a day off and isolate themselves until they feel better, farm animals housed in groups have only limited possibilities for social withdrawal. We suggest that immune activation could be a major factor influencing social interactions in pigs, with outbreaks of damaging behavior such as tail biting as a possible result. The hypothesis presented here is that the effects of several known risk factors for tail biting are mediated by pro-inflammatory cytokines, proteins produced by the immune system, and their effect on neurotransmitter systems. We describe the background for and implications of this hypothesis.

Peripheral-to-central immune communication at the area postrema glial-barrier following bleomycin-induced sterile lung injury in adult rats

The pathways for peripheral-to-central immune communication (P → C I-comm) following sterile lung injury (SLI) are unknown. SLI evokes systemic and central inflammation, which alters central respiratory control and viscerosensory transmission in the nucleus tractus solitarii (nTS). These functional changes coincide with increased interleukin-1 beta (IL-1β) in the area postrema, a sensory circumventricular organ that connects P → C I-comm to brainstem circuits that control homeostasis. We hypothesize that IL-1β and its downstream transcriptional target, cyclooxygenase-2 (COX-2), mediate P → C I-comm in the nTS. In a rodent model of SLI induced by intratracheal bleomycin (Bleo), the sigh frequency and duration of post-sigh apnea increased in Bleo- compared to saline- treated rats one week after injury. This SLI-dependent change in respiratory control occurred concurrently with augmented IL-1β and COX-2 immunoreactivity (IR) in the funiculus separans (FS), a barrier between the AP and the brainstem. At this barrier, increases in IL-1β and COX-2 IR were confined to processes that stained for glial fibrillary acidic protein (GFAP) and that projected basolaterally to the nTS. Further, FS radial-glia did not express TNF-α or IL-6 following SLI. To test our hypothesis, we blocked central COX-1/2 activity by intracerebroventricular (ICV) infusion of Indomethacin (Ind). Continuous ICV Ind treatment prevented Bleo-dependent increases in GFAP + and IL-1β + IR, and restored characteristics of sighs that reset the rhythm. These data indicate that changes in sighs following SLI depend partially on activation of a central COX-dependent P → C I-comm via radial-glia of the FS.

Microglia depletion fails to abrogate inflammation-induced sickness in mice and rats

Background

Production of inflammatory mediators by reactive microglial cells in the brain is generally considered the primary mechanism underlying the development of symptoms of sickness in response to systemic inflammation.

Methods

Depletion of microglia was achieved in C57BL/6 mice by chronic oral administration of PLX5622, a specific antagonist of colony stimulating factor-1 receptor, and in rats by a knock-in model in which the diphtheria toxin receptor was expressed under the control of the endogenous fractalkine receptor (CX3CR1) promoter sequence. After successful microglia depletion, mice and rats were injected with a sickness-inducing dose of lipopolysaccharide according to a 2 (depletion vs. control) × 2 (LPS vs. saline) factorial design. Sickness was measured by body weight loss and decreased locomotor activity in rats and mice, and reduced voluntary wheel running in mice.

Results

Chronic administration of PLX5622 in mice and administration of diphtheria toxin to knock-in rats depleted microglia and peripheral tissue macrophages. However, it did not abrogate the inducible expression of proinflammatory cytokines in the brain in response to LPS and even exacerbated it for some of the cytokines. In accordance with these neuroimmune effects, LPS-induced sickness was not abrogated, rather it was exacerbated when measured by running wheel activity in mice.

Conclusions

These findings reveal that the sickness-inducing effects of acute inflammation can develop independently of microglia activation.

A novel role of NLRP3-generated IL-1β in the acute-chronic transition of peripheral lipopolysaccharide-elicited neuroinflammation: implications for sepsis-associated neurodegeneration

BACKGROUND

Sepsis-associated acute brain inflammation, if unresolved, may cause chronic neuroinflammation and resultant neurodegenerative diseases. However, little is known how the transition from acute to chronic neuroinflammation, which is critical for the following progressive neurodegeneration, occurs in sepsis. The goal of this study was to investigate potential immune factors regulating the transition process using a widely used endotoxemia LPS mouse model. This model shows distinct acute and chronic phases of neuroinflammation and recapitulates many cardinal features of Parkinson's disease, thus, providing a unique opportunity for studying phase transition of neuroinflammation.

METHODS

C57BL/6 J, NLRP3-/-, and IL-1R1-/- mice were employed. Mild and severe endotoxemia were produced by LPS ip injection at 1 or 5 mg/kg. Neuroinflammation in vitro and in vivo was assessed with proinflammatory cytokine expression by qPCR or ELISA and microglial activation by immunohistochemical analysis. Neurodegeneration was measured by manual and stereological counts of nigral dopaminergic neurons and immunohistochemical analysis of protein nitrosylation and α-synuclein phosphorylation.

RESULTS

LPS-elicited initial increases in mouse brain mRNA levels of TNFα, IL-6, IL-1β, and MCP-1, and nigral microglial activation were not dose-related. By contrast, the delayed increase in brain mature IL-1β levels was dependent on LPS doses and protracted nigral microglial activation was only observed in high dose of LPS-treated mice. LPS-elicited increase in brain mature IL-1β but not IL-1α level was NLRP3-dependent. After high dose LPS treatment, deficiency of NLRP3 or IL-1R1 did not prevent the initiation of acute neuroinflammation but abolished chronic neuroinflammation. Genetic or pharmacological inhibition of the NLRP3-IL-1β axis repressed LPS-stimulated upregulation of chronic neuroinflammatory mediators including MHC-II, NOX2, and Mac1, and protected dopaminergic neurons. Ten months after LPS-elicited severe endotoxemia, nigral persisted microglial activation, elevated nitrosylated proteins and phosphorylated α-synuclein, and significant neuronal degeneration developed in wild-type mice but not in NLRP3-/- or IL-1R1-/- mice.

CONCLUSIONS

This study uncovers a novel role of the NLRP3-IL-1β signaling pathway in gauging the severity of sepsis-associated inflammation and determining whether acute neuroinflammation will resolve or transition to low grade chronic neuroinflammation. These findings also provide novel targets for developing therapy for severe systemic infection-related neurodegeneration.

Interleukin-1 causes CNS inflammatory cytokine expression via endothelia-microglia bi-cellular signaling

As a major producer of the inflammatory cytokine interleukin-1 (IL-1), peripheral macrophages can augment IL-1 expression via type 1 IL-1 receptor (IL-1R1) mediated autocrine self-amplification. In the CNS, microglial cells are the major producers of inflammatory cytokines, but express negligible levels of IL-1R1. In the present study, we showed CNS IL-1 induced microglial proinflammatory cytokine expression was mediated by endothelial, not microglial, IL-1R1. This paracrine mechanism was further dissected in vitro. IL-1 was unable to stimulate inflammatory cytokine expression directly from the microglial cell line BV-2, but it stimulated the brain endothelial cell line bEnd.3 to produce a factor(s) in the culture supernatant, which was capable of inducing inflammatory cytokine expression in BV-2. We termed this factor IL-1-induced microglial activation factors (IMAF). BV-2 cytokine expression was inducible by extracellular ATP, but IL-1 did not stimulate the release of ATP from bEnd.3 cells. Filtration of IMAF by size-exclusion membranes showed IMAF activity resided in molecules larger than 50 kd and incubation of IMAF at 95 °C for 5 min did not alter its activity. Microglial inhibitor minocycline was unable to block IMAF activity, even though it blocked LPS induced cytokine expression in BV-2 cells. Adding NF-κB inhibitor to the bEnd.3 cells abolished IL-1 induced cytokine expression in this bi-cellular system, but adding NF-κB inhibitor after IMAF is already produced failed to abrogate IMAF induced cytokine expression in BV-2 cells. RNA sequencing of IL-1 stimulated endothelial cells revealed increased expression of genes involved in the production and processing of hyaluronic acid (HA), suggesting HA as a candidate of IMAF. Inhibition of hyaluronidase by ascorbyl palmitate (AP) abolished IMAF-induced cytokine expression in BV-2 cells. AP administration in vivo also inhibited ICV IL-1-induced IL-1 expression in the hippocampus and hypothalamus. In vitro, either TLR2 or TLR4 inhibitors blocked IMAF induced BV-2 cytokine expression. In vivo, however, IL-1 induced cytokine expression persisted in either TLR2 or TLR4 knockouts. These results demonstrate IL-1 induced inflammatory cytokine expression in the CNS requires a bi-cellular system and HA could be a candidate for IMAF.

Ethanol and Cytokines in the Central Nervous System

The innate immune system plays a critical role in the ethanol-induced neuroimmune response in the brain. Ethanol initiates the innate immune response via activation of the innate immune receptors Toll-like receptors (TLRs, e.g., TLR4, TLR3, TLR7) and NOD-like receptors (inflammasome NLRs) leading to a release of a plethora of chemokines and cytokines and development of the innate immune response. Cytokines and chemokines can have pro- or anti-inflammatory properties through which they regulate the immune response. In this chapter, we will focus on key cytokines (e.g., IL-1, IL-6, TNF-α) and chemokines (e.g., MCP-1/CCL2) that mediate the ethanol-induced neuroimmune responses. In this regard, we will use IL-1β, as an example cytokine, to discuss the neuromodulatory properties of cytokines on cellular properties and synaptic transmission. We will discuss their involvement through a set of evidence: (1) changes in gene and protein expression following ethanol exposure, (2) association of gene polymorphisms (humans) and alterations in gene expression (animal models) with increased alcohol intake, and (3) modulation of alcohol-related behaviors by transgenic or pharmacological manipulations of chemokine and cytokine systems. Over the last years, our understanding of the molecular mechanisms mediating cytokine- and chemokine-dependent regulation of immune responses has advanced tremendously, and we review evidence pointing to cytokines and chemokines serving as neuromodulators and regulators of neurotransmission.

Early-life adversity programs long-term cytokine and microglia expression within the HPA axis in female Japanese quail

Stress exposure during prenatal and postnatal development can have persistent and often dysfunctional effects on several physiological systems, including immune function, affecting the ability to combat infection. The neuroimmune response is inextricably linked to the action of the hypothalamic-pituitary-adrenal (HPA) axis. Cytokines released from neuroimmune cells, including microglia, activate the HPA axis, while glucocorticoids in turn regulate cytokine release from microglia. Because of the close links between these two physiological systems, coupled with potential for persistent changes to HPA axis activity following developmental stress, components of the neuroimmune system could be targets for developmental programming. However, little is known of any programming effects of developmental stress on neuroimmune function. We investigated whether developmental stress exposure via elevated prenatal corticosterone (CORT) or postnatal unpredictable food availability had long-term effects on pro- (IL-1β) and anti-inflammatory (IL-10) cytokine and microglia-dependent gene (CSF1R) expression within HPA axis tissues in a precocial bird, the Japanese quail (Coturnix japonica). Following postnatal stress, we observed increased IL-1β expression in the pituitary gland, reduced IL-10 expression in the amygdala and hypothalamus, and reduced CSF1R expression within the hypothalamus and pituitary gland. Postnatal stress disrupted the ratio of IL-1β:IL-10 expression within the hippocampus and hypothalamus. Prenatal stress only increased IL-1β expression in the pituitary gland. We found no evidence for interactive or cumulative effects across life stages on basal cytokine and glia expression in adulthood. We show that postnatal stress may have a larger impact than elevated prenatal CORT on basal immunity in HPA-axis-specific brain regions, with changes in cytokine homeostasis and microglia abundance. These results provide evidence for postnatal programming of a pro-inflammatory neuroimmune phenotype at the expense of reduced microglia, which could have implications for central nervous system health and subsequent neuroimmune responses.

Maternal immune activation in rats blunts brain cytokine and kynurenine pathway responses to a second immune challenge in early adulthood

Maternal immune activation (MIA) with the viral mimic poly I:C provides an established rodent model for studying schizophrenia (SZ) and other human neurodevelopmental disorders. Postnatal infections are additional risk factors in SZ and may cumulatively contribute to the emergence of pathophysiology. Underlying mechanisms may involve metabolites of the kynurenine pathway (KP) of tryptophan degradation, which is readily induced by inflammatory stimuli. Here we compared the expression of selected cytokines and KP enzymes, and the levels of selected KP metabolites, in the brain of MIA offspring following a second, acute immune challenge with lipopolysaccharides (LPS) on postnatal day (PND) 35 (adolescence) or PND 60 (early adulthood). Assessed in adolescence, MIA did not alter the expression of pro-inflammatory cytokines (except TNF-α) or KP metabolite levels compared to controls, but substantially reduced the expression of the anti-inflammatory cytokines IL-4 and IL-10 and influenced the expression of two of the four KP enzymes examined (IDO1 and TDO2). LPS treatment caused distinct changes in the expression of pro- and anti-inflammatory cytokines, as well as KP enzymes in MIA offspring, but had no effect on KP metabolites compared to control rats. Several of these effects were blunted in MIA offspring receiving LPS on PND 60. Notably, LPS caused a significant reduction in brain kynurenine levels in these animals. Of relevance for SZ-related hypotheses, these results indicate that MIA leads to an increasingly defective, rather than an overactive, immune regulation of cerebral KP metabolism during the postnatal period.

A Nationwide Study in Denmark of the Association Between Treated Infections and the Subsequent Risk of Treated Mental Disorders in Children and Adolescents

IMPORTANCE

Infections have been associated with increased risks for mental disorders, such as schizophrenia and depression. However, the association between all infections requiring treatment and the wide range of mental disorders is unknown to date.

OBJECTIVE

To investigate the association between all treated infections since birth and the subsequent risk of development of any treated mental disorder during childhood and adolescence.

DESIGN, SETTING, AND PARTICIPANTS

Population-based cohort study using Danish nationwide registers. Participants were all individuals born in Denmark between January 1, 1995, and June 30, 2012 (N = 1 098 930). Dates of analysis were November 2017 to February 2018.

EXPOSURES

All treated infections were identified in a time-varying manner from birth until June 30, 2013, including severe infections requiring hospitalizations and less severe infection treated with anti-infective agents in the primary care sector.

MAIN OUTCOMES AND MEASURES

This study identified all mental disorders diagnosed in a hospital setting and any redeemed prescription for psychotropic medication. Cox proportional hazards regression was performed reporting hazard rate ratios (HRRs), including 95% CIs, adjusted for age, sex, somatic comorbidity, parental education, and parental mental disorders.

RESULTS

A total of 1 098 930 individuals (51.3% male) were followed up for 9 620 807.7 person-years until a mean (SD) age of 9.76 (4.91) years. Infections requiring hospitalizations were associated with subsequent increased risk of having a diagnosis of any mental disorder (n = 42 462) by an HRR of 1.84 (95% CI, 1.69-1.99) and with increased risk of redeeming a prescription for psychotropic medication (n = 56 847) by an HRR of 1.42 (95% CI, 1.37-1.46). Infection treated with anti-infective agents was associated with increased risk of having a diagnosis of any mental disorder (HRR, 1.40; 95% CI, 1.29-1.51) and with increased risk of redeeming a prescription for psychotropic medication (HRR, 1.22; 95% CI, 1.18-1.26). Antibiotic use was associated with particularly increased risk estimates. The risk of mental disorders after infections increased in a dose-response association and with the temporal proximity of the last infection. In particular, schizophrenia spectrum disorders, obsessive-compulsive disorder, personality and behavior disorders, mental retardation, autistic spectrum disorder, attention-deficit/hyperactivity disorder, oppositional defiant disorder and conduct disorder, and tic disorders were associated with the highest risks after infections.

CONCLUSIONS AND RELEVANCE

Although the results cannot prove causality, these findings provide evidence for the involvement of infections and the immune system in the etiology of a wide range of mental disorders in children and adolescents.

Old Friends, immunoregulation, and stress resilience

There is a considerable body of evidence indicating that chronic adverse experience, especially chronic psychosocial stress/trauma, represents a major risk factor for the development of many somatic and affective disorders, including inflammatory bowel disease (IBD) and posttraumatic stress disorder (PTSD). However, the mechanisms underlying the development of chronic stress-associated disorders are still in large part unknown, and current treatment and prevention strategies lack efficacy and reliability. A greater understanding of mechanisms involved in the development and persistence of chronic stress-induced disorders may lead to novel approaches to prevention and treatment of these disorders. In this review, we provide evidence indicating that increases in immune (re-)activity and inflammation, potentially promoted by a reduced exposure to immunoregulatory microorganisms ("Old Friends") in today's modern society, may be causal factors in mediating the vulnerability to development and persistence of stress-related pathologies. Moreover, we discuss strategies to increase immunoregulatory processes and attenuate inflammation, as for instance contact with immunoregulatory Old Friends, which appears to be a promising strategy to promote stress resilience and to prevent/treat chronic stress-related disorders.

Brain grey matter volume reduction and anxiety-like behavior in lipopolysaccharide-induced chronic pulmonary inflammation rats: A structural MRI study with histological validation

While there have been multiple fMRI studies into the brain functional changes after acutely stimulated peripheral infection, knowledge for the effect of chronic peripheral infection on whole brain morphology is still quite limited. The present study was designed to investigate the brain structural and emotional changes after peripheral local infection initiated chronic systemic inflammation and the relationship between circulating inflammatory markers and brain grey matter. Specifically, in-vivo T2-weighted MRI was performed on rats with lipopolysaccharide (LPS)-induced chronic pulmonary inflammation (CPI) and those without. Grey matter volume was quantified using diffeomorphic anatomical registration through exponentiated lie (DARTEL) enhanced voxel-based morphometry followed by between-group comparison. Open field experiment was conducted to test the potential anxiety-like behaviors after CPI, along with the ELISA estimated inflammatory markers were correlated to grey matter volume. Guided by image findings, we undertook a focused histological investigation with immunefluorescence and Nissl staining. A widespread decrease of grey matter volume in CPI-model rats was revealed. 8 of the 12 measured inflammatory markers presented differential neuroanatomical correlation patterns with three of the pro-inflammatory cytokines (IL-1β, IL-6 and TNF-α) and CRP being the most notable. Lower grey matter volumes in some of the inflammatory markers related regions (amygdala, CA2 and cingulate cortex) were associated with more-severe anxiety-like behaviors. Furthermore, grey matter volumes in amygdala and CA3 were correlated negatively with the expressions of glial proteins (S100β and Nogo-A), while the grey matter volume in hypo-thalamus was changing positively with neural cell area. Overall, the neuroanatomical association patterns and the histopathology underpinning the MRI observations we demonstrated here would probably serve as one explanation for the cerebral and emotional deficits presented in the patients with CPI, which would furthermore yield new insights into the adverse effects the many other systemic inflammation and inflammatory autoimmune diseases would pose on brain morphology.

Microglial Phagocytosis of Neurons: Diminishing Neuronal Loss in Traumatic, Infectious, Inflammatory, and Autoimmune CNS Disorders

Errors in neuron-microglial interaction are known to lead to microglial phagocytosis of live neurons and excessive neuronal loss, potentially yielding poorer clinical outcomes. Factors that affect neuron-microglial interaction have the potential to influence the error rate. Clinical comorbidities that unfavorably impact neuron-microglial interaction may promote a higher rate of neuronal loss, to the detriment of patient outcome. This paper proposes that many common, clinically modifiable comorbidities have a common thread, in that they all influence neuron-microglial interactions. Comorbidities like traumatic brain injury, infection, stress, neuroinflammation, loss of neuronal metabolic integrity, poor growth factor status, and other factors, all have the potential to alter communication between neurons and microglia. When this occurs, microglial phagocytosis of live neurons can increase. In addition, microglia can shift into a morphological form in which they express major histocompatibility complex II (MHC-II), allowing them to function as antigen presenting cells that present neuronal debris as antigen to invading T cells. This can increase risk for the development of CNS autoimmunity, or can exacerbate existing CNS autoimmunity. The detrimental influence of these comorbidities has the potential to contribute to the mosaic of factors that determine patient outcome in some CNS pathologies that have neuropsychiatric involvement, including TBI and CNS disorders with autoimmune components, where excessive neuronal loss can yield poorer clinical outcomes. Recognition of the impact of these comorbidities may contribute to an understanding of the common clinical observation that many seemingly disparate factors contribute to the overall picture of case management and clinical outcome in these complex disorders. In a clinical setting, knowing how these comorbidities can influence neuron-microglial interaction can help focus surveillance and care on a broader group of potential therapeutic targets. Accordingly, an interest in the mechanisms underlying the influence of these factors on neuron-microglial interactions is appropriate. Neuron-microglial interaction is reviewed, and the various mechanisms by which these potential comorbidities influence neuro-microglial interaction are described.

Hypothalamic Inflammation at a Crossroad of Somatic Diseases

Various hypothalamic nuclei function as central parts of regulators that maintain homeostasis of the organism. Recently, findings have shown that inflammation in the hypothalamus may significantly affect activity of these homeostats and consequently participate in the development of various somatic diseases such as obesity, diabetes, hypertension, and cachexia. In addition, hypothalamic inflammation may also affect aging and lifespan. Identification of the causes and mechanisms involved in the development of hypothalamic inflammation creates not only a basis for better understanding of the etiopathogenesis of somatic diseases, but for the development of new therapeutic approaches for their treatment, as well.

Neurobiology and Therapeutic Potential of Cyclooxygenase-2 (COX-2) Inhibitors for Inflammation in Neuropsychiatric Disorders

Neuropsychiatric disorders, such as depression, bipolar disorder, schizophrenia, obsessive-compulsive disorder, and neurodevelopmental disorders such as autism spectrum disorder, are associated with significant illness burden. Accumulating evidence supports an association between these disorders and inflammation. Consequently, anti-inflammatory agents, such as the cyclooxygenase-2 inhibitors, represent a novel avenue to prevent and treat neuropsychiatric illness. In this paper, we first review the role of inflammation in psychiatric pathophysiology including inflammatory cytokines' influence on neurotransmitters, the hypothalamic-pituitary-adrenal axis, and microglial mechanisms. We then discuss how cyclooxygenase-2-inhibitors influence these pathways with potential therapeutic benefit, with a focus on celecoxib, due to its superior safety profile. A search was conducted in PubMed, Embase, and PsychINFO databases, in addition to Clinicaltrials.gov and the Stanley Medical Research Institute trial registries. The results were presented as a narrative review. Currently available outcomes for randomized controlled trials up to November 2017 are also discussed. The evidence reviewed here suggests cyclooxygenase-2 inhibitors, and in particular celecoxib, may indeed assist in treating the symptoms of neuropsychiatric disorders; however, further studies are required to assess appropriate illness stage-related indication.

Sexual activity modulates neuroinflammatory responses in male rats

Immune activity influences reproduction, however, the extent to which mating experience may inversely alter immune pathways is poorly understood. A few studies in humans suggest that mating triggers a circulating immune and hypothalamic-pituitary-adrenal axis response. In male rats, mating experience enhances neuroplasticity and improves cognitive function and affective-like behavior, independent of the physical activity component. Yet, the extent to which mating experience may influence immune responses in the brain remain unexplored. Here, we hypothesized that recent mating experience in male rats increases neuroinflammatory signaling (via lipopolysaccharide [LPS] stimulation, i.p.) and associated sickness behaviors (i.e., food intake, weight loss) relative to sexually-naïve controls. Virgin male rats were exposed to a sexually non-receptive (control) or sexually-receptive female for 30 min for six consecutive days. Immediately following the last mating experience, rats were administered a saline or LPS injection and euthanized four hours later. Mating increased Tnfα responses to LPS in the brain, which positively correlated with LPS-induced weight loss. Mating also increased peripheral corticosterone among saline-treated rats, but this corticosterone response was attenuated in the most proficient copulators (e.g., shortest latencies). Thus, recent mating experience may be a unique modulator of select stimulated inflammatory signals that are relevant to adaptive neuroimmune responses and behavior.

Endotoxin rapidly desensitizes the gonads to kisspeptin-induced luteinizing hormone release in male Siberian hamsters (Phodopus sungorus)

Activation of the immune system induces rapid reductions in hypothalamic-pituitary-gonadal (HPG) axis activity, which in turn decreases secretion of sex steroids. This response is likely adaptive for survival by temporarily inhibiting reproduction to conserve energy; however, the physiological mechanisms controlling this response remain unclear. The neuropeptide kisspeptin is a candidate to mediate the decrease in sex hormones seen during sickness through its key regulation of the HPG axis. In this study, the effects of acute immune activation on the response to kisspeptin were assessed in male Siberian hamsters (Phodopus sungorus). Specifically, an immune response was induced in animals by a single treatment of lipopolysaccharide (LPS), and reproductive hormone concentrations were determined in response to subsequent injections of exogenous kisspeptin. Saline-treated controls showed a robust increase in circulating testosterone in response to kisspeptin; however, this response was blocked in LPS-treated animals. Circulating luteinizing hormone (LH) levels were elevated in response to kisspeptin in both LPS- and saline-treated groups and, thus, were unaffected by LPS treatment, suggesting gonad-level inhibition of testosterone release despite central HPG activation. In addition, blockade of glucocorticoid receptors by mifepristone did not attenuate the LPS-induced inhibition of testosterone release, suggesting that circulating glucocorticoids do not mediate this phenomenon. Collectively, these findings reveal that acute endotoxin exposure rapidly renders the gonads less sensitive to HPG stimulation, thus effectively inhibiting sex hormone release. More broadly, these results shed light on the effects of immune activation on the HPG axis and help elucidate the mechanisms controlling energy allocation and reproduction.

Time and frequency dependent changes in resting state EEG functional connectivity following lipopolysaccharide challenge in rats

Research has shown that inflammatory processes affect brain function and behavior through several neuroimmune pathways. However, high order brain functions affected by inflammation largely remain to be defined. Resting state functional connectivity of synchronized oscillatory activity is a valid approach to understand network processing and high order brain function under different experimental conditions. In the present study multi-electrode EEG recording in awake, freely moving rats was used to study resting state connectivity after administration of lipopolysaccharides (LPS). Male Wistar rats were implanted with 10 cortical surface electrodes and administered with LPS (2 mg/kg) and monitored for symptoms of sickness at 3, 6 and 24 h. Resting state connectivity and power were computed at baseline, 6 and 24 h. Three prominent connectivity bands were identified using a method resistant to spurious correlation: alpha (5–15 Hz), beta-gamma (20–80 Hz), and high frequency oscillation (150–200 Hz). The most prominent connectivity band, alpha, was strongly reduced 6 h after LPS administration, and returned to baseline at 24 h. Beta-gamma connectivity was also reduced at 6 h and remained reduced at 24 h. Interestingly, high frequency oscillation connectivity remained unchanged at 6 h and was impaired 24 h after LPS challenge. Expected elevations in delta and theta power were observed at 6 h after LPS administration, when behavioral symptoms of sickness were maximal. Notably, gamma and high frequency power were reduced 6 h after LPS and returned to baseline by 24 h, when the effects on connectivity were more evident. Finally, increases in cross-frequency coupling elicited by LPS were detected at 6 h for theta-gamma and at 24 h for theta-high frequency oscillations. These studies show that LPS challenge profoundly affects EEG connectivity across all identified bands in a time-dependent manner indicating that inflammatory processes disrupt both bottom-up and top-down communication across the cortex during the peak and resolution of inflammation.

PDGFRβ Cells Rapidly Relay Inflammatory Signal from the Circulatory System to Neurons via Chemokine CCL2

Acute infection, if not kept in check, can lead to systemic inflammatory responses in the brain. Here, we show that within 2 hr of systemic inflammation, PDGFRβ mural cells of blood vessels rapidly secrete chemokine CCL2, which in turn increases total neuronal excitability by promoting excitatory synaptic transmission in glutamatergic neurons of multiple brain regions. By single-cell RNA sequencing, we identified Col1a1 and Rgs5 subgroups of PDGFRβ cells as the main source of CCL2. Lipopolysaccharide (LPS)- or Poly(I:C)-treated pericyte culture medium induced similar effects in a CCL2-dependent manner. Importantly, in Pdgfrb-Cre;Ccl2^fl/fl mice, LPS-induced increase in excitatory synaptic transmission was significantly attenuated. These results demonstrate in vivo that PDGFRβ cells function as initial sensors of external insults by secreting CCL2, which relays the signal to the central nervous system. Through their gateway position in the brain, PDGFRβ cells are ideally positioned to respond rapidly to environmental changes and to coordinate responses.

Kynurenine pathway metabolic balance influences microglia activity: Targeting kynurenine monooxygenase to dampen neuroinflammation

Chronic stress or inflammation increases tryptophan metabolism along the kynurenine pathway (KP), and the generation of neuroactive kynurenine metabolites contributes to subsequent depressive-like behaviors. Microglia regulate KP balance by preferentially producing oxidative metabolites, including quinolinic acid. Research has focused on the interplay between cytokines and HPA axis-derived corticosteroids in regulating microglial activity and effects of KP metabolites directly on neurons; however, the potential role that KP metabolites have directly on microglial activity is unknown. Here, murine microglia were stimulated with lipopolysaccharide(LPS). After 6 h, mRNA expression of interleukin(IL)-1β, IL-6, tumor necrosis factor(TNF)-α and inducible nitric oxide synthase(iNOS) was dose-dependently increased along with the rate-limiting enzymes for oxidative KP metabolism, indoleamine-2,3-dioxygenase(IDO)-1 and kynurenine 3-monooxygenase(KMO). By 24 h post-LPS, kynurenine and quinolinic acid in the media was elevated. Inhibiting KMO with Ro 61-8048 during LPS challenge attenuated extracellular nitrite accumulation and expression of KMO and TNF-α in response to LPS. Similarly, primary microglia isolated from KMO^-/- mice exhibited a significantly reduced pro-inflammatory response to LPS compared to WT controls. To determine whether the substrate (kynurenine) or end product (quinolinic acid) of KMO-dependent metabolism modulates the LPS response, microglia were treated with increasing concentrations of L-kynurenine or quinolinic acid in combination with LPS or saline. Interestingly, quinolinic acid did not impact the microglial LPS response. However, L-kynurenine had dose-dependent inhibitory effect on the LPS response. These data are the first to show an anti-inflammatory effect of KMO inhibition on microglia during immune challenge and suggest that KP metabolic balance may play a direct role in regulating microglia activity.

Neuroimmune Axes of the Blood-Brain Barriers and Blood-Brain Interfaces: Bases for Physiological Regulation, Disease States, and Pharmacological Interventions

Central nervous system (CNS) barriers predominantly mediate the immune-privileged status of the brain, and are also important regulators of neuroimmune communication. It is increasingly appreciated that communication between the brain and immune system contributes to physiologic processes, adaptive responses, and disease states. In this review, we discuss the highly specialized features of brain barriers that regulate neuroimmune communication in health and disease. In section I, we discuss the concept of immune privilege, provide working definitions of brain barriers, and outline the historical work that contributed to the understanding of CNS barrier functions. In section II, we discuss the unique anatomic, cellular, and molecular characteristics of the vascular blood-brain barrier (BBB), blood-cerebrospinal fluid barrier, and tanycytic barriers that confer their functions as neuroimmune interfaces. In section III, we consider BBB-mediated neuroimmune functions and interactions categorized as five neuroimmune axes: disruption, responses to immune stimuli, uptake and transport of immunoactive substances, immune cell trafficking, and secretions of immunoactive substances. In section IV, we discuss neuroimmune functions of CNS barriers in physiologic and disease states, as well as pharmacological interventions for CNS diseases. Throughout this review, we highlight many recent advances that have contributed to the modern understanding of CNS barriers and their interface functions.

Peripheral immune tolerance alleviates the intracranial lipopolysaccharide injection-induced neuroinflammation and protects the dopaminergic neurons from neuroinflammation-related neurotoxicity

BACKGROUND

Neuroinflammation plays a critical role in the onset and development of neurodegeneration disorders such as Parkinson's disease. The immune activities of the central nervous system are profoundly affected by peripheral immune activities. Immune tolerance refers to the unresponsiveness of the immune system to continuous or repeated stimulation to avoid excessive inflammation and unnecessary by-stander injury in the face of continuous antigen threat. It has been proved that the immune tolerance could suppress the development of various peripheral inflammation-related diseases. However, the role of immune tolerance in neuroinflammation and neurodegenerative diseases was not clear.

METHODS

Rats were injected with repeated low-dose lipopolysaccharide (LPS, 0.3 mg/kg) intraperitoneally for 4 days to induce peripheral immune tolerance. Neuroinflammation was produced using intracranial LPS (15 μg) injection. Inflammation cytokines were measured using enzyme-linked immunosorbent assay (ELISA) and quantitative real-time polymerase chain reaction (qRT-PCR). Microglial activation were measured using immunostaining of Iba-1 and ED-1. Dopaminergic neuronal damage was evaluated using immunochemistry staining and stereological counting of TH-positive neurons. Behavioral impairment was evaluated using amphetamine-induced rotational behavioral assessment.

RESULTS

Compared with the non-immune tolerated animals, pre-treatment of peripheral immune tolerance significantly decreased the production of inflammatory cytokines, suppressed the microglial activation, and increased the number of dopaminergic neuronal survival in the substantia nigra.

CONCLUSIONS

Our results indicated that peripheral immune tolerance attenuated neuroinflammation and inhibited neuroinflammation-induced dopaminergic neuronal death.

Interleukin-1β signaling in fenestrated capillaries is sufficient to trigger sickness responses in mice

BACKGROUND

The physiological and behavioral symptoms of sickness, including fever, anorexia, behavioral depression, and weight loss can be both beneficial and detrimental. These sickness responses are triggered by pro-inflammatory cytokines acting on cells within the brain. Previous research demonstrates that the febrile response to peripheral insults depends upon prostaglandin production by vascular endothelial cells, but the mechanisms and specific cell type(s) responsible for other sickness responses remain unknown. The purpose of the present study was to identify which cells within the brain are required for sickness responses triggered by central nervous system inflammation.

METHODS

Intracerebroventricular (ICV) administration of 10 ng of the potent pro-inflammatory cytokine interleukin-1β (IL-1β) was used as an experimental model of central nervous system cytokine production. We examined which cells respond to IL-1β in vivo via fluorescent immunohistochemistry. Using multiple transgenic mouse lines expressing Cre recombinase under the control of cell-specific promoters, we eliminated IL-1β signaling from different populations of cells. Food consumption, body weight, movement, and temperature were recorded in adult male mice and analyzed by two-factor ANOVA to determine where IL-1β signaling is essential for sickness responses.

RESULTS

Endothelial cells, microglia, ependymal cells, and astrocytes exhibit nuclear translocation of NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells) in response to IL-1β. Interfering with IL-1β signaling in microglia, endothelial cells within the parenchyma of the brain, or both did not affect sickness responses. Only mice that lacked IL-1β signaling in all endothelium including fenestrated capillaries lacked sickness responses.

CONCLUSIONS

These experiments show that IL-1β-induced sickness responses depend on intact IL-1β signaling in blood vessels and suggest that fenestrated capillaries act as a critical signaling relay between the immune and nervous systems.

TRIAL REGISTRATION

Not applicable.

Systemic N-terminal fragments of adrenocorticotropin reduce inflammation- and stress-induced anhedonia in rats

Emerging evidence implicates impaired self-regulation of the hypothalamic-pituitary-adrenal (HPA) axis and inflammation as important and closely related components of the pathophysiology of major depression. Antidepressants show anti-inflammatory effects and are suggested to enhance glucocorticoid feedback inhibition of the HPA axis. HPA axis activity is also negatively self-regulated by the adrenocorticotropic hormone (ACTH), a potent anti-inflammatory peptide activating five subtypes of melanocortin receptors (MCRs). There are indications that ACTH-mediated feedback can be activated by noncorticotropic N-terminal ACTH fragments such as a potent anti-inflammatory MC1/3/4/5R agonist α-melanocyte-stimulating hormone (α-MSH), corresponding to ACTH(1-13), and a MC3/5R agonist ACTH(4-10). We investigated whether intraperitoneal administration of rats with these peptides affects anhedonia, which is a core symptom of depression. Inflammation-related anhedonia was induced by a single intraperitoneal administration of a low dose (0.025mg/kg) of lipopolysaccharide (LPS). Stress-related anhedonia was induced by the chronic unpredictable stress (CUS) procedure. The sucrose preference test was used to detect anhedonia. We found that ACTH(4-10) pretreatment decreased LPS-induced increase in serum corticosterone and tumor necrosis factor (TNF)-α, and a MC3/4R antagonist SHU9119 blocked this effect. Both α-MSH and ACTH(4-10) alleviated LPS-induced anhedonia. In the CUS model, these peptides reduced anhedonia and normalized body weight gain. The data indicate that systemic α-MSH and ACTH(4-10) produce an antidepressant-like effect on anhedonia induced by stress or inflammation, the stimuli that trigger the release of ACTH and α-MSH into the bloodstream. The results suggest a counterbalancing role of circulating melanocortins in depression and point to a new approach for antidepressant treatment.