Structural and biochemical imaging reveals systemic LPS-induced changes in the rat brain

Regional brain structural alterations in reward and salience networks in asthma

INTRODUCTION

Chronic systemic inflammation is highly prevalent and has deleterious effects on the brain, impacting both function and structure, and manifesting in elevations in psychological symptoms transdiagnostically. Asthma is a chronic inflammatory disease of the airway that affects more than 300 million people worldwide and is known to be highly comorbid with psychological and cognitive dysfunction. Though a growing corpus of work has identified functional brain abnormalities associated with asthma, limited research has investigated structural differences which may partially underlie functional changes. Identifying and characterizing asthma-related structural brain changes will shed light on the neurobiology through which asthma impacts mental function and has the potential to inform prophylaxis and treatment.

METHODS

We examined differences in regional brain volume, cortical thickness, and surface area, in 128 individuals with asthma compared to 134 non-asthma healthy controls. Five regions of interest were examined a priori, based on their previous implication in inflammation-related functional consequences (dorsal and ventral striatum, pallidum, and insula), or previous evidence of asthma-related structural impact (hippocampus and thalamus). We supplemented our region of interest approach with a voxel-wise whole-brain analysis. Additionally, we examined the association of brain structure with depression symptoms, asthma severity, degree of inflammation, and plasma biomarkers of neuroinflammation, neurodegeneration, and Alzheimer's disease specific pathology.

RESULTS

Compared to non-asthma control participants, those with asthma had smaller nucleus accumbens volumes, thicker orbitofrontal cortices, larger middle frontal cortex surface areas, and greater diencephalon volumes. Those with more severe asthma had smaller nucleus accumbens and dorsal striatal volumes, reduced anterior cingulate cortex surface area, and greater amygdala volume compared to those with mild asthma. In untreated asthma patients, greater depressive symptoms were associated with smaller striatal volume, suggesting a potential CNS-protective effect of medications that reduce airway inflammation in asthma. In addition, a plasma marker of astrogliosis was associated with larger diencephalon, cerebellum, brainstem, and thalamus volumes, but reduced insula thickness and surface area.

CONCLUSIONS

Patterns of structural brain changes in participants with asthma encompass key regions of reward and salience networks, which may in part give rise to the functional alterations in these networks characteristic of chronic systemic inflammation.

Peripheral inflammatory cytokines are associated with the microstructural characteristics of the corpus callosum and prefrontal cortex as detected by magnetic resonance T1/T2 mapping in the CUMS rat model

Background

Several clinical neuroimaging studies have reported structural and functional brain abnormalities associated with peripheral inflammatory cytokines or kynurenine pathway metabolites in patients with depression. However, it is not clear whether the abnormal findings are changes that are intrinsic to depression or whether they are caused by confounding factors such as age, illness duration, or medication.

Methods

To exclude confounding factors, we used chronic unpredictable mild stress (CUMS) rat model and magnetic resonance T1/T2 mapping to investigate the microstructural characteristics of the prefrontal cortex (PFC), hippocampus and corpus callosum and further explored the association between peripheral blood depression-related indicators and microstructural characteristics.

Results

The results revealed that the T2 relaxation time of the corpus callosum was significantly decreased in the CUMS model compared to the control group. Additionally, positive correlations were found between the levels of inflammatory cytokines (interleukin (IL)-1 and IL-6) and the T1 relaxation time of the corpus callosum and between the level of IL-6 and the T1 relaxation time of the PFC.

Conclusion

Our study demonstrates that the microstructural abnormality of the corpus callosum is an intrinsic change that accompanies depression and also provides robust evidence that the microstructural characteristics of the corpus callosum and PFC associated with inflammatory cytokines in peripheral blood play an important role in the fundamental pathophysiological mechanism of depression.

The telencephalon is a neuronal substrate for systemic inflammatory responses in teleosts via polyamine metabolism

Systemic inflammation elicits sickness behaviors and fever by engaging a complex neuronal circuitry that begins in the preoptic area of the hypothalamus. Ectotherms such as teleost fish display sickness behaviors in response to infection or inflammation, seeking warmer temperatures to enhance survival via behavioral fever responses. To date, the hypothalamus is the only brain region implicated in sickness behaviors and behavioral fever in teleosts. Yet, the complexity of neurobehavioral manifestations underlying sickness responses in teleosts suggests engagement of higher processing areas of the brain. Using in vivo models of systemic inflammation in rainbow trout, we find canonical pyrogenic cytokine responses in the hypothalamus whereas in the telencephalon and the optic tectum il-1b and tnfa expression is decoupled from il-6 expression. Polyamine metabolism changes, characterized by accumulation of putrescine and decreases in spermine and spermidine, are recorded in the telencephalon but not hypothalamus upon systemic injection of bacteria. While systemic inflammation causes canonical behavioral fever in trout, blockade of bacterial polyamine metabolism prior to injection abrogates behavioral fever, polyamine responses, and telencephalic but not hypothalamic cytokine responses. Combined, our work identifies the telencephalon as a neuronal substrate for brain responses to systemic inflammation in teleosts and uncovers the role of polyamines as critical chemical mediators in sickness behaviors.

Unmoving and uninflamed: Characterizing neuroinflammatory dysfunction in the Wistar-Kyoto rat model of depression

Reductionistic research on depressive disorders has been hampered by the limitations of animal models. Recently, it has been hypothesized that neuroinflammation is a key player in depressive disorders. The Wistar-Kyoto (WKY) rat is an often-used animal model of depression, but no information so far exists on its neuroinflammatory profile. As such, we compared male young adult WKY rats to Wistar (WS) controls, with regard to both behavioral performance and brain levels of key neuroinflammatory markers. We first assessed anxiety- and depression-like behaviors in a battery consisting of the Elevated Plus Maze (EPM), the Novelty Suppressed Feeding (NSFT), Open Field (OFT), Social Interaction (SIT), Forced Swim (FST), Sucrose Preference (SPT), and Splash tests (ST). We found that WKY rats displayed increased NSFT feeding latency, decreased OFT center zone permanence, decreased EPM open arm permanence, decreased SIT interaction time, and increased immobility in the FST. However, WKY rats also evidenced marked hypolocomotion, which is likely to confound performance in such tests. Interestingly, WKY rats performed similarly, or even above, to WS levels in the SPT and ST, in which altered locomotion is not a significant confound. In a separate cohort, we assessed prefrontal cortex (PFC), hippocampus and amygdala levels of markers of astrocytic (GFAP, S100A10) and microglial (Iba1, CD86, Ym1) activation status, as well as of three key proinflammatory cytokines (IL-1β, IL-6, TNF-α). There were no significant differences between strains in any of these markers, in any of the regions assessed. Overall, results highlight that behavioral data obtained with WKY rats as a model of depression must be carefully interpreted, considering the marked locomotor activity deficits displayed. Furthermore, our data suggest that, despite WKY rats replicating many depression-associated neurobiological alterations, as shown by others, this is not the case for neuroinflammation-related alterations, thus representing a novel limitation of this model.

Neurodevelopmental and Neuropsychiatric Disorders

This chapter will focus on microglial involvement in neurodevelopmental and neuropsychiatric disorders, particularly autism spectrum disorder (ASD), schizophrenia and major depressive disorder (MDD). We will describe the neuroimmune risk factors that contribute to the etiopathology of these disorders across the lifespan, including both in early life and adulthood. Microglia, being the resident immune cells of the central nervous system, could play a key role in triggering and determining the outcome of these disorders. This chapter will review preclinical and clinical findings where microglial morphology and function were examined in the contexts of ASD, schizophrenia and MDD. Clinical evidence points out to altered microglial morphology and reactivity, as well as increased expression of pro-inflammatory cytokines, supporting the idea that microglial abnormalities are involved in these disorders. Indeed, animal models for these disorders found altered microglial morphology and homeostatic functions which resulted in behaviours related to these disorders. Additionally, as microglia have emerged as promising therapeutic targets, we will also address in this chapter therapies involving microglial mechanisms for the treatment of neurodevelopmental and neuropsychiatric disorders.

Evidence of persistent glial cell dysfunction in the anterior cingulate cortex of juvenile idiopathic arthritis children: a proton MRS study

BACKGROUND

This study aims to investigate whether the neurometabolites of the anterior cingulate cortex (ACC) were distinct in patients with active and inactive juvenile idiopathic arthritis (JIA) using the proton magnetic resonance spectroscopy.

METHODS

We measured the levels of total N-acetylaspartate (tNAA), choline (Cho), myo-inositol (ml), glutamate (Glu) and the complex of glutamate and glutamine (Glx) relative to total creatine (tCr) in ACC of each participant.

RESULTS

Compared with the healthy controls, a significant decrease of total Cho/tCr and Glx/tCr ratio in ACC occurred in active and inactive JIA group. The tCho/Cr level was negatively associated with the serum level of ESR in active JIA patients. There was no difference in NAA/tCr ratio among the three groups, which may imply that no neuron and axonal losses occurred in either active or inactive JIA patients.

CONCLUSIONS

The abnormal neurometabolites in tCho/tCr and Glx/tCr in ACC may indicate that persistent dysfunction of glial cell, while neither neuron nor axonal losses occurred in active and inactive JIA patients.

Moxibustion attenuates inflammation in intestinal mucosal by regulating RAGE-mediated TLR4-NF-κBp65 signaling pathway in vivo and in vitro

This study was performed to investigate the effect of moxibustion on the RAGE/TLR4-NF-κBp65 pathways and mucosal damage in rat model of 5-fluorouracil (5-Fu)-induced intestinal mucositis (IM) and the underlying mechanisms. 5-Fu treatment significantly increased the expression of the receptor for advanced glycation end products (RAGE) and its ligand, thehigh-mobility group box 1 protein (HMGB1), in the rat intestinal tissue. The inhibition of RAGE could induce the repair of intestinal mucosal damage and downregulate the expression of Toll-like receptor (TLR)-4 and nuclear factor kappa-B (NF-κB) p65 in intestinal tissues of 5-Fu-treated rats. Moxibustion treatment significantly improved the physical symptoms and repaired the intestinal mucosal damage of IM rats and increased the expression of tight junction proteins in these rats. The expression of RAGE, HMGB1, TLR4, NF-κBp65, and related downstream inflammatory factors, namely, tumor necrosis factor (TNF)-α, interleukin (IL)-6 and IL-1β, were significantly decreased after moxibustion treatment. A moxibustion dose of 15 min/day exerted a better therapeutic effect than a dose of 30 min/day. The phosphorylation of NF-κBp65 and IκBa is involved in reducing inflammation by regulating the RAGE signaling pathway. Moxibustion can reduce intestinal mucosal damage and inflammation in 5-Fu-induced IM rats via modulation of the RAGE/TLR4-NF-κBp65 signaling pathways.

Systemic Administration of the TLR7/8 Agonist Resiquimod (R848) to Mice Is Associated with Transient, In Vivo-Detectable Brain Swelling

Peripheral administration of the E. coli endotoxin lipopolysaccharide (LPS) to rats promotes secretion of pro-inflammatory cytokines and in previous studies was associated with transient enlargement of cortical volumes. Here, resiquimod (R848) was administered to mice to stimulate peripheral immune activation, and the effects on brain volumes and neurometabolites determined. After baseline scans, 24 male, wild-type C57BL mice were triaged into three groups including R848 at low (50 μg) and high (100 μg) doses and saline controls. Animals were scanned again at 3 h and 24 h following treatment. Sickness indices of elevated temperature and body weight loss were observed in all R848 animals. Animals that received 50 μg R848 exhibited decreases in hippocampal N-acetylaspartate and phosphocreatine at the 3 h time point that returned to baseline levels at 24 h. Animals that received the 100 μg R848 dose demonstrated transient, localized, volume expansion (~5%) detectable at 3 h in motor, somatosensory, and olfactory cortices; and pons. A metabolic response evident at the lower dose and a volumetric change at the higher dose suggests a temporal evolution of the effect wherein the neurochemical change is demonstrable earlier than neurostructural change. Transient volume expansion in response to peripheral immune stimulation corresponds with previous results and is consistent with brain swelling that may reflect CNS edema.

Microglia and BDNF at the crossroads of stressor related disorders: Towards a unique trophic phenotype

Stressors ranging from psychogenic/social to neurogenic/injury to systemic/microbial can impact microglial inflammatory processes, but less is known regarding their effects on trophic properties of microglia. Recent studies do suggest that microglia can modulate neuronal plasticity, possibly through brain derived neurotrophic factor (BDNF). This is particularly important given the link between BDNF and neuropsychiatric and neurodegenerative pathology. We posit that certain activated states of microglia play a role in maintaining the delicate balance of BDNF release onto neuronal synapses. This focused review will address how different "activators" influence the expression and release of microglial BDNF and address the question of tropomyosin receptor kinase B (TrkB) expression on microglia. We will then assess sex-based differences in microglial function and BDNF expression, and how microglia are involved in the stress response and related disorders such as depression. Drawing on research from a variety of other disorders, we will highlight challenges and opportunities for modulators that can shift microglia to a "trophic" phenotype with a view to potential therapeutics relevant for stressor-related disorders.