L-glutamate released from activated microglia downregulates astrocytic L-glutamate transporter expression in neuroinflammation: the 'collusion' hypothesis for increased extracellular L-glutamate concentration in neuroinflammation

The dual role of microglia in intracerebral hemorrhage

Intracerebral hemorrhage has the characteristics of high morbidity, disability and mortality, which has caused a heavy burden to families and society. Microglia are resident immune cells in the central nervous system, and their activation plays a dual role in tissue damage after intracerebral hemorrhage. The damage in cerebral hemorrhage is embodied in the following aspects: releasing inflammatory factors and inflammatory mediators, triggering programmed cell death, producing glutamate induced excitotoxicity, and destroying blood-brain barrier; The protective effect is reflected in the phagocytosis and clearance of harmful substances by microglia, and the secretion of anti-inflammatory and neurotrophic factors. This article summarizes the function of microglia and its dual regulatory mechanism in intracerebral hemorrhage. In the future, drugs, acupuncture and other clinical treatments can be used to intervene in the activation state of microglia, so as to reduce the harm of microglia.

Exploring neuroglial signaling: diversity of molecules implicated in microglia-to-astrocyte neuroimmune communication

Effective communication between different cell types is essential for brain health, and dysregulation of this process leads to neuropathologies. Brain glial cells, including microglia and astrocytes, orchestrate immune defense and neuroimmune responses under pathological conditions during which interglial communication is indispensable. Our appreciation of the complexity of these processes is rapidly increasing due to recent advances in molecular biology techniques, which have identified numerous phenotypic states of both microglia and astrocytes. This review focuses on microglia-to-astrocyte communication facilitated by secreted neuroimmune modulators. The combinations of interleukin (IL)-1α, tumor necrosis factor (TNF), plus complement component C1q as well as IL-1β plus TNF are already well-established microglia-derived stimuli that induce reactive phenotypes in astrocytes. However, given the large number of inflammatory mediators secreted by microglia and the rapidly increasing number of distinct functional states recognized in astrocytes, it can be hypothesized that many more intercellular signaling molecules exist. This review identifies the following group of cytokines and gliotransmitters that, while not established as interglial mediators yet, are known to be released by microglia and elicit functional responses in astrocytes: IL-10, IL-12, IL-18, transforming growth factor (TGF)-β, interferon (IFN)-γ, C-C motif chemokine ligand (CCL)5, adenosine triphosphate (ATP), l-glutamate, and prostaglandin E2 (PGE2). The review of molecular mechanisms engaged by these mediators reveals complex, partially overlapping signaling pathways implicated in numerous neuropathologies. Additionally, lack of human-specific studies is identified as a significant knowledge gap. Further research on microglia-to-astrocyte communication is warranted, as it could discover novel interglial signaling-targeted therapies for diverse neurological disorders.

N-methyl-d-aspartate receptors: Structure, function, and role in organophosphorus compound poisoning

Acute organophosphorus compound (OP) poisoning induces symptoms of the cholinergic crises with the occurrence of severe epileptic seizures. Seizures are induced by hyperstimulation of the cholinergic system, but are enhanced by hyperactivation of the glutamatergic system. Overstimulation of muscarinic cholinergic receptors by the elevated acetylcholine causes glutamatergic hyperexcitation and an increased influx of Ca2+ into neurons through a type of ionotropic glutamate receptors, N-methyl-d-aspartate (NMDA) receptors (NMDAR). These excitotoxic signaling processes generate reactive oxygen species, oxidative stress, and activation of the neuroinflammatory response, which can lead to recurrent epileptic seizures, neuronal cell death, and long-term neurological damage. In this review, we illustrate the NMDAR structure, complexity of subunit composition, and the various receptor properties that change accordingly. Although NMDARs are in normal physiological conditions important for controlling synaptic plasticity and mediating learning and memory functions, we elaborate the detrimental role NMDARs play in neurotoxicity of OPs and focus on the central role NMDAR inhibition plays in suppressing neurotoxicity and modulating the inflammatory response. The limited efficacy of current medical therapies for OP poisoning concerning the development of pharmacoresistance and mitigating proinflammatory response highlights the importance of NMDAR inhibitors in preventing neurotoxic processes and points to new avenues for exploring therapeutics for OP poisoning.

Glutamate uptake is transiently compromised in the perilesional cortex following controlled cortical impact

Glutamate, the primary excitatory neurotransmitter in the CNS, is regulated by the excitatory amino acid transporters (EAATs) GLT-1 and GLAST. Following traumatic brain injury (TBI), extracellular glutamate levels increase, contributing to excitotoxicity, circuit dysfunction, and morbidity. Increased neuronal glutamate release and compromised astrocyte-mediated uptake contribute to elevated glutamate, but the mechanistic and spatiotemporal underpinnings of these changes are not well established. Using the controlled cortical impact (CCI) model of TBI and iGluSnFR glutamate imaging, we quantified extracellular glutamate dynamics after injury. Three days post-injury, glutamate release was increased, and glutamate uptake and GLT-1 expression were reduced. 7- and 14-days post-injury, glutamate dynamics were comparable between sham and CCI animals. Changes in peak glutamate response were unique to specific cortical layers and proximity to injury. This was likely driven by increases in glutamate release, which was spatially heterogenous, rather than reduced uptake, which was spatially uniform. The astrocyte K + channel, Kir4.1, regulates activity-dependent slowing of glutamate uptake. Surprisingly, Kir4.1 was unchanged after CCI and accordingly, activity-dependent slowing of glutamate uptake was unaltered. This dynamic glutamate dysregulation after TBI underscores a brief period in which disrupted glutamate uptake may contribute to dysfunction and highlights a potential therapeutic window to restore glutamate homeostasis.

An Expanded Narrative Review of Neurotransmitters on Alzheimer's Disease: The Role of Therapeutic Interventions on Neurotransmission

Alzheimer's disease (AD) is a progressive neurodegenerative disease. The accumulation of amyloid-β (Aβ) plaques and tau neurofibrillary tangles are the key players responsible for the pathogenesis of the disease. The accumulation of Aβ plaques and tau affect the balance in chemical neurotransmitters in the brain. Thus, the current review examined the role of neurotransmitters in the pathogenesis of Alzheimer's disease and discusses the alterations in the neurochemical activity and cross talk with their receptors and transporters. In the presence of Aβ plaques and neurofibrillary tangles, changes may occur in the expression of neuronal receptors which in turn triggers excessive release of glutamate into the synaptic cleft contributing to cell death and neuronal damage. The GABAergic system may also be affected by AD pathology in a similar way. In addition, decreased receptors in the cholinergic system and dysfunction in the dopamine neurotransmission of AD pathology may also contribute to the damage to cognitive function. Moreover, the presence of deficiencies in noradrenergic neurons within the locus coeruleus in AD suggests that noradrenergic stimulation could be useful in addressing its pathophysiology. The regulation of melatonin, known for its effectiveness in enhancing cognitive function and preventing Aβ accumulation, along with the involvement of the serotonergic system and histaminergic system in cognition and memory, becomes remarkable for promoting neurotransmission in AD. Additionally, nitric oxide and adenosine-based therapeutic approaches play a protective role in AD by preventing neuroinflammation. Overall, neurotransmitter-based therapeutic strategies emerge as pivotal for addressing neurotransmitter homeostasis and neurotransmission in the context of AD. This review discussed the potential for neurotransmitter-based drugs to be effective in slowing and correcting the neurodegenerative processes in AD by targeting the neurochemical imbalance in the brain. Therefore, neurotransmitter-based drugs could serve as a future therapeutic strategy to tackle AD.

Neurodegenerative Etiology of Aromatic L-Amino Acid Decarboxylase Deficiency: a Novel Concept for Expanding Treatment Strategies

Aromatic l-amino acid decarboxylase deficiency (AADC-DY) is caused by one or more mutations in the DDC gene, resulting in the deficit in catecholamines and serotonin neurotransmitters. The disease has limited therapeutic options with relatively poor clinical outcomes. Accumulated evidence suggests the involvement of neurodegenerative mechanisms in the etiology of AADC-DY. In the absence of neurotransmitters' neuroprotective effects, the accumulation and the chronic presence of several neurotoxic metabolites including 4-dihydroxy-L-phenylalanine, 3-methyldopa, and homocysteine, in the brain of subjects with AADC-DY, promote oxidative stress and reduce the cellular antioxidant and methylation capacities, leading to glial activation and mitochondrial dysfunction, culminating to neuronal injury and death. These pathophysiological processes have the potential to hinder the clinical efficacy of treatments aimed at increasing neurotransmitters' synthesis and or function. This review describes in detail the mechanisms involved in AADC-DY neurodegenerative etiology, highlighting the close similarities with those involved in other neurodegenerative diseases. We then offer novel strategies for the treatment of the disease with the objective to either reduce the level of the metabolites or counteract their prooxidant and neurotoxic effects. These treatment modalities used singly or in combination, early in the course of the disease, will minimize neuronal injury, preserving the functional integrity of neurons, hence improving the clinical outcomes of both conventional and unconventional interventions in AADC-DY. These modalities may not be limited to AADC-DY but also to other metabolic disorders where a specific mutation leads to the accumulation of prooxidant and neurotoxic metabolites.

The Conventional and Breakthrough Tool for the Study of L-Glutamate Transporters

In our recent report, we clarified the direct interaction between the excitatory amino acid transporter (EAAT) 1/2 and polyunsaturated fatty acids (PUFAs) by applying electrophysiological and molecular biological techniques to Xenopus oocytes. Xenopus oocytes have a long history of use in the scientific field, but they are still attractive experimental systems for neuropharmacological studies. We will therefore summarize the pharmacological significance, advantages (especially in the study of EAAT2), and experimental techniques that can be applied to Xenopus oocytes; our new findings concerning L-glutamate (L-Glu) transporters and PUFAs; and the significant outcomes of our data. The data obtained from electrophysiological and molecular biological studies of Xenopus oocytes have provided us with further important questions, such as whether or not some PUFAs can modulate EAATs as allosteric modulators and to what extent docosahexaenoic acid (DHA) affects neurotransmission and thereby affects brain functions. Xenopus oocytes have great advantages in the studies about the interactions between molecules and functional proteins, especially in the case when the expression levels of the proteins are small in cell culture systems without transfections. These are also proper to study the mechanisms underlying the interactions. Based on the data collected in Xenopus oocyte experiments, we can proceed to the next step, i.e., the physiological roles of the compounds and their significances. In the case of EAAT2, the effects on the neurotransmission should be examined by electrophysiological approach using acute brain slices. For new drug development, pharmacokinetics pharmacodynamics (PKPD) data and blood brain barrier (BBB) penetration data are also necessary. In order not to miss the promising candidate compounds at the primary stages of drug development, we should reconsider using Xenopus oocytes in the early phase of drug development.

Deplete and repeat: microglial CSF1R inhibition and traumatic brain injury

Traumatic brain injury (TBI) is a public health burden affecting millions of people. Sustained neuroinflammation after TBI is often associated with poor outcome. As a result, increased attention has been placed on the role of immune cells in post-injury recovery. Microglia are highly dynamic after TBI and play a key role in the post-injury neuroinflammatory response. Therefore, microglia represent a malleable post-injury target that could substantially influence long-term outcome after TBI. This review highlights the cell specific role of microglia in TBI pathophysiology. Microglia have been manipulated via genetic deletion, drug inhibition, and pharmacological depletion in various pre-clinical TBI models. Notably, colony stimulating factor 1 (CSF1) and its receptor (CSF1R) have gained much traction in recent years as a pharmacological target on microglia. CSF1R is a transmembrane tyrosine kinase receptor that is essential for microglia proliferation, differentiation, and survival. Small molecule inhibitors targeting CSF1R result in a swift and effective depletion of microglia in rodents. Moreover, discontinuation of the inhibitors is sufficient for microglia repopulation. Attention is placed on summarizing studies that incorporate CSF1R inhibition of microglia. Indeed, microglia depletion affects multiple aspects of TBI pathophysiology, including neuroinflammation, oxidative stress, and functional recovery with measurable influence on astrocytes, peripheral immune cells, and neurons. Taken together, the data highlight an important role for microglia in sustaining neuroinflammation and increasing risk of oxidative stress, which lends to neuronal damage and behavioral deficits chronically after TBI. Ultimately, the insights gained from CSF1R depletion of microglia are critical for understanding the temporospatial role that microglia develop in mediating TBI pathophysiology and recovery.

Ursolic acid inhibits the synaptic release of glutamate and prevents glutamate excitotoxicity in rats

The present study evaluated the effect of ursolic acid, a natural pentacyclic triterpenoid, on glutamate release in rat cortical nerve terminals (synaptosomes) and its neuroprotection in a kainic acid-induced excitotoxicity rat model. In cortical synaptosomes, ursolic acid produced a concentration-dependent inhibition of evoked glutamate release with a half-maximum inhibition of release value of 9.5 μM, and calcium-free medium and the P/Q -type Ca2+ channel blocker, ω-agatoxin IVA, but not ω-conotoxin GVIA, an N-type Ca2+ channel blocker, prevented the ursoloic acid effect. The molecular docking study indicated that ursolic acid interacted with P/Q-type Ca2+ channels. Ursolic acid also significantly decreased the depolarization-induced activation of Ca2+/calmodulin-dependent protein kinase II (CaMKII) and the subsequent phosphorylation of synapsin I, and the ursolic acid effect on evoked glutamate release was inhibited by the CaMKII inhibitor KN 62 in synaptosomes. In addition, in rats that were intraperitoneally injected with ursolic acid 30 min before kainic acid intraperitoneal injection, cortical neuronal degeneration was attenuated. This effect of ursolic acid in the improvement of kainic acid-induced neuronal damage was associated with the reduction of kainic acid-induced glutamate increase in the cortex of rats; this was characterized by the reduction of glutamate and glutaminase levels and elevation of glutamate dehydrogenase, glutamate transporter 1, glutamate-aspartate transporter, and glutamine synthetase protein levels. These results suggest that ursolic acid inhibits glutamate release from cortical synaptosomes by decreasing P/Q-type Ca2+ channel activity and subsequently suppressing CaMKII and exerts a preventive effect against glutamate neurotoxicity by controlling glutamate levels.

A systematic review for the development of Alzheimer's disease in in vitro models: a focus on different inducing agents

Alzheimer's disease (AD) is the most common progressive neurodegenerative disease and is associated with dementia. Presently, various chemical and environmental agents are used to induce in-vitro models of Alzheimer disease to investigate the efficacy of different therapeutic drugs. We screened literature from databases such as PubMed, ScienceDirect, and Google scholar, emphasizing the diverse targeting mechanisms of neuro degeneration explored in in-vitro models. The results revealed studies in which different types of chemicals and environmental agents were used for in-vitro development of Alzheimer-targeting mechanisms of neurodegeneration. Studies using chemically induced in-vitro AD models included in this systematic review will contribute to a deeper understanding of AD. However, none of these models can reproduce all the characteristics of disease progression seen in the majority of Alzheimer's disease subtypes. Additional modifications would be required to replicate the complex conditions of human AD in an exact manner. In-vitro models of Alzheimer's disease developed using chemicals and environmental agents are instrumental in providing insights into the disease's pathophysiology; therefore, chemical-induced in-vitro AD models will continue to play vital role in future AD research. This systematic screening revealed the pivotal role of chemical-induced in-vitro AD models in advancing our understanding of AD pathophysiology and is therefore important to understand the potential of these chemicals in AD pathogenesis.

Correlation Between Systemic Immune-Inflammation Index and Suicide Attempts in Children and Adolescents with First-Episode, Drug-Naïve Major Depressive Disorder During the COVID-19 Pandemic

Objective

This study aims to investigate the association between the systemic immune-inflammatory index (SII) and suicide attempt (SA) in children and adolescents with first-episode, drug-naïve Major Depressive Disorder (MDD) during the COVID-19 pandemic.

Methods

A retrospective study was conducted on 263 MDD patients hospitalized at the Third Hospital of Fuyang City between 2020 and 2022. Patients were categorized into two groups based on the presence of previous SA. The study compared the differences in SII and clinical characteristics between the two groups and used the receiver operating characteristic (ROC) curve to determine the optimal critical value of SII and the area under the curve. Binary logistic regression was used to analyze the independent risk factors for SA.

Results

Compared with the patients without SA history, the patients with a personal history of SA had a higher mean HDRS scores (Z=-2.369, p=0.018), higher mean neutrophil count (Z=-2.870, p=0.004), higher mean platelet count (Z=-2.155, p=0.031), and higher mean SII (Z=-3.170, p=0.002). The optimal critical SII determined by the ROC curve was 548.15 (sensitivity = 63.2%, specificity = 83.1%), and the area under the curve was 0.661. After adjusting for gender, age, BMI, illness duration and HDRS score, the risk of total SA in patients with high SII was 8.296 times higher than in those with low SII (OR = 8.296, 95% CI: 3.803-18.095, P < 0.001), The risk of recent SA was 13.922 times higher in patients with high SII than in those with low SII (OR = 13.922, 95% CI: 5.587-34.693, p < 0.001). However, high SII was not a risk factor for past SA (OR = 0.547, 95% CI: 0.062-4.842, P=0.587).

Conclusion

SII may be an inexpensive, easily accessible strategy that can assist in determining suicide risk in adolescents with MDD.

Levodopa-induced dyskinesia: interplay between the N-methyl-D-aspartic acid receptor and neuroinflammation

Parkinson's disease (PD) is a common neurodegenerative disorder of middle-aged and elderly people, clinically characterized by resting tremor, myotonia, reduced movement, and impaired postural balance. Clinically, patients with PD are often administered levodopa (L-DOPA) to improve their symptoms. However, after years of L-DOPA treatment, most patients experience complications of varying severity, including the "on-off phenomenon", decreased efficacy, and levodopa-induced dyskinesia (LID). The development of LID can seriously affect the quality of life of patients, but its pathogenesis is unclear and effective treatments are lacking. Glutamic acid (Glu)-mediated changes in synaptic plasticity play a major role in LID. The N-methyl-D-aspartic acid receptor (NMDAR), an ionotropic glutamate receptor, is closely associated with synaptic plasticity, and neuroinflammation can modulate NMDAR activation or expression; in addition, neuroinflammation may be involved in the development of LID. However, it is not clear whether NMDA receptors are co-regulated with neuroinflammation during LID formation. Here we review how neuroinflammation mediates the development of LID through the regulation of NMDA receptors, and assess whether common anti-inflammatory drugs and NMDA receptor antagonists may be able to mitigate the development of LID through the regulation of central neuroinflammation, thereby providing a new theoretical basis for finding new therapeutic targets for LID.

Neuroprotective Potential of L-Glutamate Transporters in Human Induced Pluripotent Stem Cell-Derived Neural Cells against Excitotoxicity

Human induced pluripotent stem cell (hiPSC)-derived neural cells have started to be used in safety/toxicity tests at the preclinical stage of drug development. As previously reported, hiPSC-derived neurons exhibit greater tolerance to excitotoxicity than those of primary cultures of rodent neurons; however, the underlying mechanisms remain unknown. We here investigated the functions of L-glutamate (L-Glu) transporters, the most important machinery to maintain low extracellular L-Glu concentrations, in hiPSC-derived neural cells. We also clarified the contribution of respective L-Glu transporter subtypes. At 63 days in vitro (DIV), we detected neuronal circuit functions in hiPSC-derived neural cells by a microelectrode array system (MEA). At 63 DIV, exposure to 100 μM L-Glu for 24 h did not affect the viability of neural cells. 100 µM L-Glu in the medium decreased to almost 0 μM in 60 min. Pharmacological inhibition of excitatory amino acid transporter 1 (EAAT1) and EAAT2 suppressed almost 100% of L-Glu decrease. In the presence of this inhibitor, 100 μM L-Glu dramatically decreased cell viability. These results suggest that in hiPSC-derived neural cells, EAAT1 and EAAT2 are the predominant L-Glu transporters, and their uptake potentials are the reasons for the tolerance of hiPSC-derived neurons to excitotoxicity.

Brain-derived neurotrophic factor (BDNF) has direct anti-inflammatory effects on microglia

Microglia are the primary immunocompetent cells that protect the brain from environmental stressors, but can also be driven to release pro-inflammatory cytokines and induce a cytotoxic environment. Brain-derived neurotrophic factor (BDNF) is important for the regulation of plasticity, synapse formation, and general neuronal health. Yet, little is known about how BDNF impacts microglial activity. We hypothesized that BDNF would have a direct modulatory effect on primary cortical (Postnatal Day 1-3: P1-3) microglia and (Embryonic Day 16: E16) neuronal cultures in the context of a bacterial endotoxin. To this end, we found that a BDNF treatment following LPS-induced inflammation had a marked anti-inflammatory effect, reversing the release of both IL-6 and TNF-α in cortical primary microglia. This modulatory effect was transferrable to cortical primary neurons, such that LPS-activated microglial media was able produce an inflammatory effect when added to a separate neuronal culture, and again, BDNF priming attenuated this effect. BDNF also reversed the overall cytotoxic impact of LPS exposure in microglia. We speculate that BDNF can directly play a role in regulating microglia state and hence, influence microglia-neuron interactions.

The Missing Piece? A Case for Microglia's Prominent Role in the Therapeutic Action of Anesthetics, Ketamine, and Psychedelics

There is much excitement surrounding recent research of promising, mechanistically novel psychotherapeutics - psychedelic, anesthetic, and dissociative agents - as they have demonstrated surprising efficacy in treating central nervous system (CNS) disorders, such as mood disorders and addiction. However, the mechanisms by which these drugs provide such profound psychological benefits are still to be fully elucidated. Microglia, the CNS's resident innate immune cells, are emerging as a cellular target for psychiatric disorders because of their critical role in regulating neuroplasticity and the inflammatory environment of the brain. The following paper is a review of recent literature surrounding these neuropharmacological therapies and their demonstrated or hypothesized interactions with microglia. Through investigating the mechanism of action of psychedelics, such as psilocybin and lysergic acid diethylamide, ketamine, and propofol, we demonstrate a largely under-investigated role for microglia in much of the emerging research surrounding these pharmacological agents. Among others, we detail sigma-1 receptors, serotonergic and γ-aminobutyric acid signalling, and tryptophan metabolism as pathways through which these agents modulate microglial phagocytic activity and inflammatory mediator release, inducing their therapeutic effects. The current review includes a discussion on future directions in the field of microglial pharmacology and covers bidirectional implications of microglia and these novel pharmacological agents in aging and age-related disease, glial cell heterogeneity, and state-of-the-art methodologies in microglial research.

Effect of Ouabain on Glutamate Transport in the Hippocampus of Rats with LPS-Induced Neuroinflammation

A lipopolysaccharide (LPS)-induced neuroinflammation rat model was used to study the effects of ouabain (OUA) at low concentrations, which can interact with the Na,K-ATPase, causing the modulation of intracellular signalling pathways in the Central Nervous System. Our study aimed to analyse the effects of OUA on glutamate transport in the hippocampus of rats with LPS-induced neuroinflammation. Adult male Wistar rats were divided into four groups: OUA (1.8 µg/kg), saline (CTR), LPS (200 µg/kg), and OUA + LPS (OUA 20 min before LPS). The animals were sacrificed after 2 h, and the hippocampus was collected for analysis. After treatment, we determined the activities of Na,K-ATPase and glutamine synthetase (GS). In addition, expression of the α1, α2, and α3 isoforms of Na,K-ATPase and the glutamate transporters, EAAT1 and EAAT2, were also analysed. Treatment with OUA caused a specific increase in the α2 isoform expression (~20%), whereas LPS decreased its expression (~22%), and treatment with OUA before LPS prevented the effects of LPS. Moreover, LPS caused a decrease of approximately 50% in GS activity compared with that in the CTR group; however, OUA pre-treatment attenuated this effect of LPS. Notably, it was found that treatment with OUA caused an increase in the expression of EAAT1 (~30%) and EAAT2 (~25%), whereas LPS caused a decrease in the expression of EAAT1 (~23%) and EAAT2 (~25%) compared with that in the CTR group. When treated with OUA, the effects of LPS were abrogated. In conclusion, the OUA pre-treatment abolished the effect caused by LPS, suggesting that this finding may be related to the restoration of the interaction between FXYD2 and the studied membrane proteins.

Gliovascular alterations in sporadic and familial Alzheimer's disease: APOE3 Christchurch homozygote glioprotection

In response to brain insults, astrocytes become reactive, promoting protection and tissue repair. However, astroglial reactivity is typical of brain pathologies, including Alzheimer's disease (AD). Considering the heterogeneity of the reactive response, the role of astrocytes in the course of different forms of AD has been underestimated. Colombia has the largest human group known to have familial AD (FAD). This group carries the autosomal dominant and fully penetrant mutation E280A in PSEN1, which causes early-onset AD. Recently, our group identified an E280A carrier who did not develop FAD. The individual was homozygous for the Christchurch mutation R136S in APOE3 (APOEch). Remarkably, APOE is the main genetic risk factor for developing sporadic AD (SAD) and most of cerebral ApoE is produced by astroglia. Here, we characterized astrocyte properties related to reactivity, glutamate homeostasis, and structural integrity of the gliovascular unit (GVU), as factors that could underlie the pathogenesis or protection of AD. Specifically, through histological and 3D microscopy analyses of postmortem samples, we briefly describe the histopathology and cytoarchitecture of the frontal cortex of SAD, FAD, and APOEch, and demonstrate that, while astrodegeneration and vascular deterioration are prominent in SAD, FAD is characterized by hyperreactive-like glia, and APOEch displays the mildest astrocytic and vascular alterations despite having the highest burden of Aβ. Notably, astroglial, gliovascular, and vascular disturbances, as well as brain cell death, correlate with the specific astrocytic phenotypes identified in each condition. This study provides new insights into the potential relevance of the gliovasculature in the development and protection of AD. To our knowledge, this is the first study assessing the components of the GVU in human samples of SAD, FAD, and APOEch.

Synapse Dysfunctions in Multiple Sclerosis

Multiple sclerosis (MS) is a chronic neuroinflammatory disease of the central nervous system (CNS) affecting nearly three million humans worldwide. In MS, cells of an auto-reactive immune system invade the brain and cause neuroinflammation. Neuroinflammation triggers a complex, multi-faceted harmful process not only in the white matter but also in the grey matter of the brain. In the grey matter, neuroinflammation causes synapse dysfunctions. Synapse dysfunctions in MS occur early and independent from white matter demyelination and are likely correlates of cognitive and mental symptoms in MS. Disturbed synapse/glia interactions and elevated neuroinflammatory signals play a central role. Glutamatergic excitotoxic synapse damage emerges as a major mechanism. We review synapse/glia communication under normal conditions and summarize how this communication becomes malfunctional during neuroinflammation in MS. We discuss mechanisms of how disturbed glia/synapse communication can lead to synapse dysfunctions, signaling dysbalance, and neurodegeneration in MS.

Increased Inflammation and Treatment of Depression: From Resistance to Reuse, Repurposing, and Redesign

Based on mounting clinical and translational evidence demonstrating the impact of exogenously administered inflammatory stimuli on the brain and behavior, increased endogenous inflammation has received attention as one pathophysiologic process contributing to psychiatric illnesses and particularly depression. Increased endogenous inflammation is observed in a significant proportion of depressed patients and has been associated with reduced responsiveness to standard antidepressant therapies. This chapter presents recent evidence that inflammation affects neurotransmitters and neurocircuits to contribute to specific depressive symptoms including anhedonia, motor slowing, and anxiety, which may preferentially improve after anti-cytokine therapies in patients with evidence of increased inflammation. Existing and novel pharmacological strategies that target inflammation or its downstream effects on the brain and behavior will be discussed in the context of a need for intelligent trial design in order to meaningfully translate these concepts and develop more precise therapies for depressed patients with increased inflammation.

The Autism Spectrum Disorder-Associated Bacterial Metabolite p-Cresol Derails the Neuroimmune Response of Microglial Cells Partially via Reduction of ADAM17 and ADAM10

The bacterial metabolite 4-methylphenol (para-cresol or p-cresol) and its derivative p-cresyl sulfate (pCS) are elevated in the urine and feces of children with autism spectrum disorder (ASD). It has been shown that p-cresol administration induces social behavior deficits and repetitive behavior in mice. However, the mechanisms of p-cresol, specifically its metabolite pCS that can reach the brain, in ASD remain to be investigated. The pCS has been shown to inhibit LPS-stimulated inflammatory response. A Disintegrin And Metalloprotease 10 (ADAM10) and A Disintegrin And Metalloprotease 17 (ADAM17) are thought to regulate microglial immune response by cleaving membrane-bound proteins. In the present study, a neuroinflammation model of LPS-activated BV2 microglia has been used to unveil the potential molecular mechanism of pCS in ASD pathogenesis. In microglial cells pCS treatment decreases the expression or maturation of ADAM10 and ADAM17. In addition, pCS treatment attenuates TNF-α and IL-6 releases as well as phagocytosis activity of microglia. In in vitro ADAM10/17 inhibition experiments, either ADAM10 or ADAM17 inhibition reduces constitutive and LPS-activated release of TNF-α, TNFR-1 and IL-6R by microglial cells, while it increases constitutive and LPS-activated microglial phagocytotic activity. The in vivo results further confirm the involvement of ADAM10 and ADAM17 in ASD pathogenesis. In in utero VPA-exposed male mice, elevated concentration in serum of p-cresol-associated metabolites pCS and p-cresyl glucuronide (pCG) is associated with a VPA-induced increased ADAM10 maturation, and a decreased ADAM17 maturation that is related with attenuated levels of soluble TNF-α and TGF-β1 in the mice brain. Overall, the present study demonstrates a partial role of ADAM10 and ADAM17 in the derailed innate immune response of microglial cells associated with pCS-induced ASD pathogenesis.

Activation of non-classical NMDA receptors by glycine impairs barrier function of brain endothelial cells

Blood–brain barrier (BBB) integrity is necessary to maintain homeostasis of the central nervous system (CNS). NMDA receptor (NMDAR) function and expression have been implicated in BBB integrity. However, as evidenced in neuroinflammatory conditions, BBB disruption contributes to immune cell infiltration and propagation of inflammatory pathways. Currently, our understanding of the pathophysiological role of NMDAR signaling on endothelial cells remains incomplete. Thus, we investigated NMDAR function on primary mouse brain microvascular endothelial cells (MBMECs). We detected glycine-responsive NMDAR channels, composed of functional GluN1, GluN2A and GluN3A subunits. Importantly, application of glycine alone, but not glutamate, was sufficient to induce NMDAR-mediated currents and an increase in intracellular Ca²⁺ concentrations. Functionally, glycine-mediated NMDAR activation leads to loss of BBB integrity and changes in actin distribution. Treatment of oocytes that express NMDARs composed of different subunits, with GluN1 and GluN3A binding site inhibitors, resulted in abrogation of NMDAR signaling as measured by two-electrode voltage clamp (TEVC). This effect was only detected in the presence of the GluN2A subunits, suggesting the latter as prerequisite for pharmacological modulation of NMDARs on brain endothelial cells. Taken together, our findings argue for a novel role of glycine as NMDAR ligand on endothelial cells shaping BBB integrity.

NF-κB and AP-1 are required for the lipopolysaccharide-induced expression of MCP-1, CXCL1, and Cx43 in cultured rat dorsal spinal cord astrocytes

TLR4 and Cx43 signaling in dorsal spinal cord has been shown to be involved in the development of neuropathic pain. However, it is not clear whether TLR4 signaling is associated with the expression of MCP-1, CXCL1, and Cx43 in LPS (lipopolysaccharide)-treated rat dorsal spinal cord astrocytes under in vitro condition. In the present study, we found that TLR4 antagonist TAK-242 significantly inhibited LPS-induced MCP-1, CXCL1, and Cx43 expression, suggesting the role of TLR4 in response to LPS in cultured dorsal spinal cord astrocytes. Application of TAK-242 significantly blocked LPS-induced NF-κB and AP-1 activity and the expression of MCP-1, CXCL1 and Cx43. Furthermore, NF-κB inhibitor PDTC and AP-1 inhibitor SR11302 significantly blocked LPS-induced MCP-1, CXCL1, and Cx43 expression. DNA-binding activity of NF-κB, its effect on MCP-1 expression was suppressed by PDTC and SR11302. On the other hand, DNA-binding activity of AP-1, its effect on CXCL1 or Cx43 expression was also suppressed by PDTC and SR11302. In addition, PDTC was found to inhibit the nuclear translocation of AP-1 and the expression of c-Jun induced by LPS, which suggested that NF-κBp65 is essential for the AP-1 activity. Similarly, SR11302 significantly blocked LPS-induced the nuclear translocation of NF-κBp65 and the expression of NF-κBp65 induced by LPS. Pretreatment with CBX, Gap26, or Gap19 (Cx43 blockers) significantly inhibited abnormal astrocytic hemichannel opening and chemokines (MCP-1 and CXCL1) release in LPS-stimulated astrocytes. In summary, cell culture experiments revealed that LPS stimulation could evoke TLR4 signaling with the subsequent activation of NF-κB and AP-1, resulting in the expression of MCP-1, CXCL1, and Cx43. TLR4 activation increased Cx43 hemichannel, but not gap-junction activities and induced the release of the MCP-1 and CXCL1 from astrocytes via Cx43 hemichannel. These findings may help us to understand the role of astrocytic signaling in inflammatory response within dorsal spinal cord tissue.

Neuroinflammation in Post-Traumatic Stress Disorder

Post-traumatic stress disorder (PTSD) is a well-known mental illness, which is caused by various stressors, including memories of past physical assaults and psychological pressure. It is diagnosed as a mental and behavioral disorder, but increasing evidence is linking it to the immune system and inflammatory response. Studies on the relationship between inflammation and PTSD revealed that patients with PTSD had increased levels of inflammatory cytokine biomarkers, such as interleukin-1, interleukin-6, tumor necrosis factor-α, nuclear factor-κB, and C-reactive protein, compared with healthy controls. In addition, animal model experiments imitating PTSD patients suggested the role of inflammation in the pathogenesis and pathophysiology of PTSD. In this review, we summarize the definition of PTSD and its association with increased inflammation, its mechanisms, and future predictable diseases and treatment possibilities. We also discuss anti-inflammatory treatments to address inflammation in PTSD.

Neurobiology of early life adversity: A systematic review of meta-analyses towards an integrative account of its neurobiological trajectories to mental disorders

Adverse childhood experiences (ACEs) may leave long-lasting neurobiological scars, increasing the risk of developing mental disorders in later life. However, no review has comprehensively integrated existing evidence across the fields: hypothalamic-pituitary-adrenal axis, immune/inflammatory system, neuroimaging, and genetics/epigenetics. We thus systematically reviewed previous meta-analyses towards an integrative account of ACE-related neurobiological alterations. Following Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline, a total of 27 meta-analyses until October 2021 were identified. This review found that individuals with ACEs possess blunted cortisol response to psychosocial stressors, low-grade inflammation evinced by increased C-reactive protein levels, exaggerated amygdalar response to emotionally negative information, and diminished hippocampal gray matter volume. Importantly, these alterations were consistently observed in those with and without psychiatric diagnosis. These findings were integrated and discussed in a schematic model of ACE-related neurobiological alterations. Future longitudinal research based on multidisciplinary approach is imperative for ACE-related mental disorders' prevention and treatment.

Dystrophin deficiency affects human astrocyte properties and response to damage

In addition to progressive muscular degeneration due to dystrophin mutations, 1/3 of Duchenne muscular dystrophy (DMD) patients present cognitive deficits. However, there is currently an incomplete understanding about the function of the multiple dystrophin isoforms in human brains. Here, we tested the hypothesis that dystrophin deficiency affects glial function in DMD and could therefore contribute to neural impairment. We investigated human dystrophin isoform expression with development and differentiation and response to damage in human astrocytes from control and induced pluripotent stem cells from DMD patients. In control cells, short dystrophin isoforms were up-regulated with development and their expression levels changed differently upon neuronal and astrocytic differentiation, as well as in 2-dimensional versus 3-dimensional astrocyte cultures. All DMD-astrocytes tested displayed altered morphology, proliferative activity and AQP4 expression. Furthermore, they did not show any morphological change in response to inflammatory stimuli and their number was significantly lower as compared to stimulated healthy astrocytes. Finally, DMD-astrocytes appeared to be more sensitive than controls to oxidative damage as shown by their increased cell death. Behavioral and metabolic defects in DMD-astrocytes were consistent with gene pathway dysregulation shared by lines with different mutations as demonstrated by bulk RNA-seq analysis. Together, our DMD model provides evidence for altered astrocyte function in DMD suggesting that defective astrocyte responses may contribute to neural impairment and might provide additional potential therapeutic targets.

Amino Acid Solute Carrier Transporters in Inflammation and Autoimmunity

The past decade exposed the importance of many homeostasis and metabolism related proteins in autoimmunity disease and inflammation. Solute carriers (SLCs) are a group of membrane channels that can transport amino acids, the building blocks of proteins, nutrients, and neurotransmitters. This review summarizes the role of SLCs amino acid transporters in inflammation and autoimmunity disease. In detail, the importance of Glutamate transporters SLC1A1, SLC1A2, and SLC1A3, mainly expressed in the brain where they help prevent glutamate excitotoxicity, is discussed in the context of central nervous system disorders such as multiple sclerosis. Similarly, the cationic amino acid transporter SLC7A1 (CAT1), which is an important arginine transporter for T cells, and SLC7A2 (CAT2), essential for innate immunity. SLC3 family proteins, which bind with light chains from the SLC7 family (SLC7A5, SLC7A7 and SLC7A11) to form heteromeric amino acid transporters, are also explored to describe their roles in T cells, NK cells, macrophages and tumor immunotherapies. Altogether, the link between SLC amino acid transporters with inflammation and autoimmunity may contribute to a better understanding of underlying mechanism of disease and provide novel potential therapeutic avenues. Significance Statement SIGNIFICANCE STATEMENT In this review, we summarize the link between SLC amino acid transporters and inflammation and immune responses, specially SLC1 family members and SLC7 members. Studying the link may contribute to a better understanding of related diseases and provide potential therapeutic targets and useful to the researchers who have interest in the involvement of amino acids in immunity.

Update on Statin Treatment in Patients with Neuropsychiatric Disorders

Statins are widely accepted as first-choice agents for the prevention of lipid-related cardiovascular diseases. These drugs have both anti-inflammatory and anti-oxidant properties, which may also make them effective as potential treatment marked by perturbations in these pathways, such as some neuropsychiatric disorders. In this narrative review, we have investigated the effects of statin therapy in individuals suffering from major depressive disorder (MDD), schizophrenia, anxiety, obsessive-compulsive disorder (OCD), bipolar disorder (BD), delirium, and autism spectrum disorders using a broad online search of electronic databases. We also explored the adverse effects of these drugs to obtain insights into the benefits and risks associated with their use in the treatment of these disorders. Lipophilic statins (including simvastatin) because of better brain penetrance may have greater protective effects against MDD and schizophrenia. The significant positive effects of statins in the treatment of anxiety disorders without any serious adverse side effects were shown in numerous studies. In OCD, BD, and delirium, limitations, and contradictions in the available data make it difficult to draw conclusions on any positive effect of statins. The positive effects of simvastatin in autism disorders have been evaluated in only a small number of clinical trials. Although some studies showed positive effect of statins in some neuropsychiatric disorders, further prospective studies are needed to confirm this and define the most effective doses and treatment durations.

Pathophysiological Ionotropic Glutamate Signalling in Neuroinflammatory Disease as a Therapeutic Target

Glutamate signalling is an essential aspect of neuronal communication involving many different glutamate receptors, and underlies the processes of memory, learning and synaptic plasticity. Despite neuroinflammatory diseases covering a range of maladies with very different biological causes and pathophysiologies, a central role for dysfunctional glutamate signalling is becoming apparent. This is not just restricted to the well-described role of glutamate in mediating neurodegeneration, but also includes a myriad of other influences that glutamate can exert on the vasculature, as well as immune cell and glial regulation, reflecting the ability of neurons to communicate with these compartments in order to couple their activity with neuronal requirements. Here, we discuss the role of pathophysiological glutamate signalling in neuroinflammatory disease, using both multiple sclerosis and Alzheimer's disease as examples, and how current steps are being made to harness our growing understanding of these processes in the development of neuroprotective strategies. This review focuses in particular on N-methyl-D-aspartate (NMDA) and 2-amino-3-(3-hydroxy-5-methylisooxazol-4-yl) propionate (AMPA) type ionotropic glutamate receptors, although metabotropic, G-protein-coupled glutamate receptors may also contribute to neuroinflammatory processes. Given the indispensable roles of glutamate-gated ion channels in synaptic communication, means of pharmacologically distinguishing between physiological and pathophysiological actions of glutamate will be discussed that allow deleterious signalling to be inhibited whilst minimising the disturbance of essential neuronal function.

IκB kinase inhibition remodeled connexins, pannexin-1, and excitatory amino-acid transporters expressions to promote neuroprotection of galantamine and morphine

Inflammatory pathway and disruption in glutamate homeostasis join at the level of the glia, resulting in various neurological disorders. In vitro studies have provided evidence that membrane proteins connexions (Cxs) are involved in glutamate release, meanwhile, excitatory amino-acid transporters (EAATs) are crucial for glutamate reuptake (clearance). Moreover, pannexin-1 (Panx-1) activation is more detrimental to neurons. Their expression patterns during inflammation and the impacts of IκB kinase (IKK) inhibition, morphine, and galantamine on the inflammatory-associated glutamate imbalance remain elusive. To investigate this, rats were injected with saline or lipopolysaccharide. Thereafter, vehicles, morphine, galantamine, and BAY-117082 were administered in different groups of animals. Subsequently, electroencephalography, enzyme-linked immunosorbent assay, western blot, and histopathological examinations were carried out and various indicators of inflammation and glutamate level were determined. Parallel analysis of Cxs, Panx-1, and EAAts in the brain was performed. Our findings strengthen the concept that unregulated expressions of Cxs, Panx-1, and EAATs contribute to glutamate accumulation and neuronal cell loss. Nuclear factor-kB (NF-κB) pathway can significantly contribute to glutamate homeostasis via modulating Cxs, Panx-1, and EAATs expressions. BAY-117082, via inhibition of IkK, promoted the anti-inflammatory effects of morphine as well as galantamine. We concluded that NF-κB is an important component of reshaping the expressions of Cxs, panx-1, and EAATs and the development of glutamate-induced neuronal degeneration.

Neuroinflammation in neurological disorders: pharmacotherapeutic targets from bench to bedside

Neuroinflammation is one of the host defensive mechanisms through which the nervous system protects itself from pathogenic and or infectious insults. Moreover, neuroinflammation occurs as one of the most common pathological outcomes in various neurological disorders, makes it the promising target. The present review focuses on elaborating the recent advancement in understanding molecular mechanisms of neuroinflammation and its role in the etiopathogenesis of various neurological disorders, especially Alzheimer's disease (AD), Parkinson's disease (PD), and Epilepsy. Furthermore, the current status of anti-inflammatory agents in neurological diseases has been summarized in light of different preclinical and clinical studies. Finally, possible limitations and future directions for the effective use of anti-inflammatory agents in neurological disorders have been discussed.

Cognitive Dysfunction After Analgesia and Sedation: Out of the Operating Room and Into the Pediatric Intensive Care Unit

In the midst of concerns for potential neurodevelopmental effects after surgical anesthesia, there is a growing awareness that children who require sedation during critical illness are susceptible to neurologic dysfunctions collectively termed pediatric post-intensive care syndrome, or PICS-p. In contrast to healthy children undergoing elective surgery, critically ill children are subject to inordinate neurologic stress or injury and need to be considered separately. Despite recognition of PICS-p, inconsistency in techniques and timing of post-discharge assessments continues to be a significant barrier to understanding the specific role of sedation in later cognitive dysfunction. Nonetheless, available pediatric studies that account for analgesia and sedation consistently identify sedative and opioid analgesic exposures as risk factors for both in-hospital delirium and post-discharge neurologic sequelae. Clinical observations are supported by animal models showing neuroinflammation, increased neuronal death, dysmyelination, and altered synaptic plasticity and neurotransmission. Additionally, intensive care sedation also contributes to sleep disruption, an important and overlooked variable during acute illness and post-discharge recovery. Because analgesia and sedation are potentially modifiable, understanding the underlying mechanisms could transform sedation strategies to improve outcomes. To move the needle on this, prospective clinical studies would benefit from cohesion with regard to datasets and core outcome assessments, including sleep quality. Analyses should also account for the wide range of diagnoses, heterogeneity of this population, and the dynamic nature of neurodevelopment in age cohorts. Much of the related preclinical evidence has been studied in comparatively brief anesthetic exposures in healthy animals during infancy and is not generalizable to critically ill children. Thus, complementary animal models that more accurately "reverse translate" critical illness paradigms and the effect of analgesia and sedation on neuropathology and functional outcomes are needed. This review explores the interactive role of sedatives and the neurologic vulnerability of critically ill children as it pertains to survivorship and functional outcomes, which is the next frontier in pediatric intensive care.

Amelioration of lipopolysaccharide-induced memory impairment in equilibrative nucleoside transporter-2 knockout mice is accompanied by the changes in glutamatergic pathways

Neuroinflammation has been implicated in cognitive deficits in neurological and neurodegenerative diseases. Lipopolysaccharide (LPS)-induced neuroinflammation and the breakdown of the blood-brain barrier can be attenuated in mice with equilibrative nucleoside transporter-2 (ENT2/Ent2) deletion. The present study was aimed to investigate the role of ENT2 in cognitive and neuronal functions under physiological and inflammatory conditions, in terms of behavioral performance and synaptic plasticity in saline- and LPS-treated Ent2 knockout (KO) mice and their wild-type (WT) littermate controls. Repeated administrations of LPS significantly impaired spatial memory formation in Morris water maze and hippocampal-dependent long-term potentiation (LTP) in WT mice. The LPS-treated WT mice exhibited significant synaptic and neuronal damage in the hippocampus. Notably, the LPS-induced impairment in spatial memory and LTP performance were attenuated in Ent2 KO mice, along with the preservation of neuronal survival. The beneficial effects were accompanied by the normalization of excessive extracellular glutamate and aberrant downstream signaling of glutamate receptor activation, including the upregulation of phosphorylated p38 mitogen-activated protein kinase and the downregulation of phosphorylated cyclic adenosine monophosphate-response element-binding protein. There was no significant difference in behavioral outcome and all tested parameters between these two genotypes under physiological condition. These results suggest that ENT2 plays an important role in regulating inflammation-associated cognitive decline and neuronal damage.

Alpha-Synuclein as a Prominent Actor in the Inflammatory Synaptopathy of Parkinson's Disease

Parkinson’s disease (PD) is considered the most common disorder of synucleinopathy, which is characterised by intracellular inclusions of aggregated and misfolded α-synuclein (α-syn) protein in various brain regions, and the loss of dopaminergic neurons. During the early prodromal phase of PD, synaptic alterations happen before cell death, which is linked to the synaptic accumulation of toxic α-syn specifically in the presynaptic terminals, affecting neurotransmitter release. The oligomers and protofibrils of α-syn are the most toxic species, and their overexpression impairs the distribution and activation of synaptic proteins, such as the SNARE complex, preventing neurotransmitter exocytosis and neuronal synaptic communication. In the last few years, the role of the immune system in PD has been increasingly considered. Microglial and astrocyte activation, the gene expression of proinflammatory factors, and the infiltration of immune cells from the periphery to the central nervous system (CNS) represent the main features of the inflammatory response. One of the actors of these processes is α-syn accumulation. In light of this, here, we provide a systematic review of PD-related α-syn and inflammation inter-players.

Ceftriaxone Reduces Waterpipe Tobacco Smoke Withdrawal-induced Anxiety in rats via Modulating the Expression of TNF-α/NFĸB, Nrf2, and GLT-1

Tobacco exposure has been linked to neuroinflammation and adaptive/maladaptive changes in neurotransmitter systems, including in glutamatergic systems. We examined the effects of waterpipe tobacco smoke (WTS) on inflammatory mediators and astroglial glutamate transporters in mesocorticolimbic brain regions including the prefrontal cortex (PFC), nucleus accumbens (NAc) and ventral tegmental area (VTA). The behavioral consequences of WTS exposure on withdrawal-induced anxiety-like behavior were assessed using elevated plus maze (EPM) and open field (OF) tests. Male Sprague-Dawley rats were randomly assigned to 3 experimental groups: a control group exposed only to standard room air, a WTS exposed group treated with saline vehicle, and a WTS exposed group treated with ceftriaxone. WTS exposure was performed for 2 h/day, 5 days/week, for 4 weeks. Behavioral tests (EPM and OF) were conducted weekly 24 h after WTS exposure, during acute withdrawal. During week 4, rats were given either saline or ceftriaxone (200 mg/kg i.p.) 30 min before WTS exposure. WTS increased withdrawal-induced anxiety, and ceftriaxone attenuated this effect. WTS exposure increased the relative mRNA levels for nuclear factor ĸB (NFĸB), tumor necrosis factor-α (TNF-α), and brain-derived neurotrophic factor (BDNF) in the PFC, NAc and VTA, and ceftriaxone treatment reversed these effects. In addition, WTS decreased the relative mRNA of nuclear factor erythroid 2 related factor 2 (Nrf2), glutamate transporter 1 (GLT-1) and cystine-glutamate transporter (xCT) in PFC, NAc and VTA, and ceftriaxone treatment normalized their expression. WTS caused neuroinflammation, alteration in relative mRNA glutamate transport expression, and increased anxiety-like behavior, and these effects were attenuated by ceftriaxone treatment.

Linking atypical depression and insulin resistance-related disorders via low-grade chronic inflammation: Integrating the phenotypic, molecular and neuroanatomical dimensions

Insulin resistance (IR) and related disorders, such as T2DM, increase the risk of major depressive disorder (MDD) and vice versa. Current evidence indicates that psychological stress and overeating can induce chronic low-grade inflammation that can interfere with glutamate metabolism in MDD as well as insulin signaling, particularly in the atypical subtype. Here we first review the interactive role of inflammatory processes in the development of MDD, IR and related metabolic disorders. Next, we describe the role of the anterior cingulate cortex in the pathophysiology of MDD and IR-related disorders. Furthermore, we outline how specific clinical features of atypical depression, such as hyperphagia, are more associated with inflammation and IR-related disorders. Finally, we examine the regional specificity of the effects of inflammation on the brain that show an overlap with the functional and morphometric brain patterns activated in MDD and IR-related disorders.

Appetite Regulation of TLR4-Induced Inflammatory Signaling

Appetite is the basis for obtaining food and maintaining normal metabolism. Toll-like receptor 4 (TLR4) is an important receptor expressed in the brain that induces inflammatory signaling after activation. Inflammation is considered to affect the homeostatic and non-homeostatic systems of appetite, which are dominated by hypothalamic and mesolimbic dopamine signaling. Although the pathological features of many types of inflammation are known, their physiological functions in appetite are largely unknown. This review mainly addresses several key issues, including the structures of the homeostatic and non-homeostatic systems. In addition, the mechanism by which TLR4-induced inflammatory signaling contributes to these two systems to regulate appetite is also discussed. This review will provide potential opportunities to develop new therapeutic interventions that control appetite under inflammatory conditions.

Dopamine and Neuroinflammation in Schizophrenia - Interpreting the Findings from Translocator Protein (18kDa) PET Imaging

Schizophrenia is a complex disease whose pathophysiology is not yet fully understood. In addition to the long prevailing dopaminergic hypothesis, the evidence suggests that neuroinflammation plays a role in the pathophysiology of the disease. Recent studies using positron emission tomography (PET) that target a 18kDa translocator protein (TSPO) in activated microglial cells in an attempt to measure neuroinflammation in patients have shown a decrease or a lack of an increase in TSPO binding. Many biological and methodological considerations have been formulated to explain these findings. Although dopamine has been described as an immunomodulatory molecule, its potential role in neuroinflammation has not been explored in the aforementioned studies. In this review, we discuss the interactions between dopamine and neuroinflammation in psychotic states. Dopamine may inhibit neuroinflammation in activated microglia. Proinflammatory molecules released from microglia may decrease dopaminergic transmission. This could potentially explain why the levels of neuroinflammation in the brain of patients with schizophrenia seem to be unchanged or decreased compared to those in healthy subjects. However, most data are indirect and are derived from animal studies or from studies performed outside the field of schizophrenia. Further studies are needed to combine TSPO and dopamine imaging to study the association between microglial activation and dopamine system function.

Brain Disorders and Chemical Pollutants: A Gap Junction Link?

The incidence of brain pathologies has increased during last decades. Better diagnosis (autism spectrum disorders) and longer life expectancy (Parkinson's disease, Alzheimer's disease) partly explain this increase, while emerging data suggest pollutant exposures as a possible but still underestimated cause of major brain disorders. Taking into account that the brain parenchyma is rich in gap junctions and that most pollutants inhibit their function; brain disorders might be the consequence of gap-junctional alterations due to long-term exposures to pollutants. In this article, this hypothesis is addressed through three complementary aspects: (1) the gap-junctional organization and connexin expression in brain parenchyma and their function; (2) the effect of major pollutants (pesticides, bisphenol A, phthalates, heavy metals, airborne particles, etc.) on gap-junctional and connexin functions; (3) a description of the major brain disorders categorized as neurodevelopmental (autism spectrum disorders, attention deficit hyperactivity disorders, epilepsy), neurobehavioral (migraines, major depressive disorders), neurodegenerative (Parkinson's and Alzheimer's diseases) and cancers (glioma), in which both connexin dysfunction and pollutant involvement have been described. Based on these different aspects, the possible involvement of pollutant-inhibited gap junctions in brain disorders is discussed for prenatal and postnatal exposures.

Neuron-Astrocyte Interactions in Parkinson's Disease

Parkinson’s disease (PD) is the second most common neurodegenerative disease. PD patients exhibit motor symptoms such as akinesia/bradykinesia, tremor, rigidity, and postural instability due to a loss of nigrostriatal dopaminergic neurons. Although the pathogenesis in sporadic PD remains unknown, there is a consensus on the involvement of non-neuronal cells in the progression of PD pathology. Astrocytes are the most numerous glial cells in the central nervous system. Normally, astrocytes protect neurons by releasing neurotrophic factors, producing antioxidants, and disposing of neuronal waste products. However, in pathological situations, astrocytes are known to produce inflammatory cytokines. In addition, various studies have reported that astrocyte dysfunction also leads to neurodegeneration in PD. In this article, we summarize the interaction of astrocytes and dopaminergic neurons, review the pathogenic role of astrocytes in PD, and discuss therapeutic strategies for the prevention of dopaminergic neurodegeneration. This review highlights neuron-astrocyte interaction as a target for the development of disease-modifying drugs for PD in the future.

Microglia alter the threshold of spreading depolarization and related potassium uptake in the mouse brain

Selective elimination of microglia from the brain was shown to dysregulate neuronal Ca²⁺ signaling and to reduce the incidence of spreading depolarization (SD) during cerebral ischemia. However, the mechanisms through which microglia interfere with SD remained unexplored. Here, we identify microglia as essential modulators of the induction and evolution of SD in the physiologically intact brain in vivo. Confocal- and super-resolution microscopy revealed that a series of SDs induced rapid morphological changes in microglia, facilitated microglial process recruitment to neurons and increased the density of P2Y12 receptors (P2Y12R) on recruited microglial processes. In line with this, depolarization and hyperpolarization during SD were microglia- and P2Y12R-dependent. An absence of microglia was associated with altered potassium uptake after SD and increased the number of c-fos-positive neurons, independently of P2Y12R. Thus, the presence of microglia is likely to be essential to maintain the electrical elicitation threshold and to support the full evolution of SD, conceivably by interfering with the extracellular potassium homeostasis of the brain through sustaining [K⁺]_e re-uptake mechanisms.

Blood glutamate scavengers and exercises as an effective neuroprotective treatment in mice with spinal cord injury

OBJECTIVE

Excitotoxicity due to neuronal damage and glutamate release is one of the first events that leads to the progression of neuronal degeneration and functional impairment. This study is based on a paradigm shift in the therapeutic approach for treating spinal cord injury (SCI). The authors tested a new treatment targeting removal of CNS glutamate into the blood circulation by injection of the blood glutamate scavengers (BGSs) recombinant enzyme glutamate-oxaloacetate transaminase (rGOT1) and its cosubstrate oxaloacetic acid (OxAc). Their primary objective was to investigate whether BGS treatment, followed by treadmill exercises in mice with SCI, could attenuate excitotoxicity, inflammation, scarring, and axonal degeneration and, at a later time point, improve functional recovery.

METHODS

A pharmacokinetic experiment was done in C57BL/6 naive mice to verify rGOT1/OxAc blood activity and to characterize the time curve of glutamate reduction in the blood up to 24 hours. The reduction of glutamate in CSF after BGS administration in mice with SCI was confirmed by high-performance liquid chromatography. Next, SCI (left hemisection) was induced in the mice, and the mice were randomly assigned to one of the following groups at 1 hour postinjury: control (underwent SCI and received PBS), treadmill exercises, rGOT1/OxAc treatment, or rGOT1/OxAc treatment followed by treadmill exercises. Treatment started 1 hour postinjury with an injection of rGOT1/OxAc and continued for 5 consecutive days. Starting 1 week after SCI, the exercises and the combined treatment groups recommenced the treadmill exercise regimen 5 days a week for 3 months. Locomotor function was assessed for 3 months using the horizontal grid walking test and CatWalk. Axonal anterograde and wallerian degenerations were evaluated using tetramethylrhodamine dextran. Tissue sections were immunofluorescently stained for Iba1, GFAP, GAP-43, synaptophysin, and NeuN.

RESULTS

BGS treatment decreased the CSF glutamate level up to 50%, reduced axonal wallerian degeneration, and increased axonal survival and GAP-43 expression in neuronal cells. Combined treatment reduced inflammation, scarring, and lesion size. Additionally, the combination of BGS treatment and exercises increased synapses around motor neurons and enhanced axonal regeneration through the lesion site. This resulted in motor function improvement 3 months post-SCI.

CONCLUSIONS

As shown by biochemical, immunohistochemical, and functional analysis, BGSs exhibit a substantial neuroprotective effect by reducing excitotoxicity and secondary damage after SCI. Furthermore, in combination with exercises, they reduced axonal degeneration and scarring and resulted in improved functional recovery.

Blocking glycine receptors reduces neuroinflammation and restores neurotransmission in cerebellum through ADAM17-TNFR1-NF-κβ pathway

BACKGROUND

Chronic hyperammonemia induces neuroinflammation in cerebellum, with glial activation and enhanced activation of the TNFR1-NF-kB-glutaminase-glutamate-GABA pathway. Hyperammonemia also increases glycinergic neurotransmission. These alterations contribute to cognitive and motor impairment. Activation of glycine receptors is reduced by extracellular cGMP, which levels are reduced in cerebellum of hyperammonemic rats in vivo. We hypothesized that enhanced glycinergic neurotransmission in hyperammonemic rats (1) contributes to induce neuroinflammation and glutamatergic and GABAergic neurotransmission alterations; (2) is a consequence of the reduced extracellular cGMP levels. The aims were to assess, in cerebellum of hyperammonemic rats, (a) whether blocking glycine receptors with the antagonist strychnine reduces neuroinflammation; (b) the cellular localization of glycine receptor; (c) the effects of blocking glycine receptors on the TNFR1-NF-kB-glutaminase-glutamate-GABA pathway and microglia activation; (d) whether adding extracellular cGMP reproduces the effects of strychnine.

METHODS

We analyzed in freshly isolated cerebellar slices from control or hyperammonemic rats the effects of strychnine on activation of microglia and astrocytes, the content of TNFa and IL1b, the surface expression of ADAM17, TNFR1 and transporters, the phosphorylation levels of ERK, p38 and ADAM17. The cellular localization of glycine receptor was assessed by immunofluorescence. We analyzed the content of TNFa, IL1b, HMGB1, glutaminase, and the level of TNF-a mRNA and NF-κB in Purkinje neurons. Extracellular concentrations of glutamate and GABA were performed by in vivo microdialysis in cerebellum. We tested whether extracellular cGMP reproduces the effects of strychnine in ex vivo cerebellar slices.

RESULTS

Glycine receptors are expressed mainly in Purkinje cells. In hyperammonemic rats, enhanced glycinergic neurotransmission leads to reduced membrane expression of ADAM17, resulting in increased surface expression and activation of TNFR1 and of the associated NF-kB pathway. This increases the expression in Purkinje neurons of TNFa, IL-1b, HMGB1, and glutaminase. Increased glutaminase activity leads to increased extracellular glutamate, which increases extracellular GABA. Increased extracellular glutamate and HMGB1 potentiate microglial activation. Blocking glycine receptors with strychnine or extracellular cGMP completely prevents the above pathway in hyperammonemic rats.

CONCLUSIONS

Glycinergic neurotransmission modulates neuroinflammation. Enhanced glycinergic neurotransmission in hyperammonemia would be due to reduced extracellular cGMP. These results shed some light on possible new therapeutic target pathways for pathologies associated to neuroinflammation.

Catastrophic consequences: can the feline parasite Toxoplasma gondii prompt the purrfect neuroinflammatory storm following traumatic brain injury?

Traumatic brain injury (TBI) is one of the leading causes of morbidity and mortality worldwide; however, treatment development is hindered by the heterogenous nature of TBI presentation and pathophysiology. In particular, the degree of neuroinflammation after TBI varies between individuals and may be modified by other factors such as infection. Toxoplasma gondii, a parasite that infects approximately one-third of the world’s population, has a tropism for brain tissue and can persist as a life-long infection. Importantly, there is notable overlap in the pathophysiology between TBI and T. gondii infection, including neuroinflammation. This paper will review current understandings of the clinical problems, pathophysiological mechanisms, and functional outcomes of TBI and T. gondii, before considering the potential synergy between the two conditions. In particular, the discussion will focus on neuroinflammatory processes such as microglial activation, inflammatory cytokines, and peripheral immune cell recruitment that occur during T. gondii infection and after TBI. We will present the notion that these overlapping pathologies in TBI individuals with a chronic T. gondii infection have the strong potential to exacerbate neuroinflammation and related brain damage, leading to amplified functional deficits. The impact of chronic T. gondii infection on TBI should therefore be investigated in both preclinical and clinical studies as the possible interplay could influence treatment strategies.

Microglial NMDA receptors drive pro-inflammatory responses via PARP-1/TRMP2 signaling

Chronic neuroinflammation driven by microglia is a characteristic feature associated with numerous neurodegenerative diseases. While acute inflammation can assist with recovery and repair, prolonged microglial pro-inflammatory responses are known to exacerbate neurodegenerative processes. Yet, detrimental outcomes of extended microglial activation are counterbalanced by beneficial outcomes including phagocytosis and release of trophic factors promoting neuronal viability. Our past work has shown that the nuclear enzyme poly(ADP-ribose) polymerase-1 (PARP-1) is a key signaling hub driving pro-inflammatory microglia responses, but the signaling pathway maintaining PARP-1 activation remains elusive. While best understood for its role in promoting DNA repair, our group has shown that PARP-1 activity can be stimulated via Ca²⁺ influx-dependent ERK1/2-mediated phosphorylation. However, to date, the route of Ca²⁺ entry responsible for stimulating PARP-1 has not been identified. A likely candidate is via Ca²⁺ -permeable transient receptor potential melastatin 2 (TRPM2) channels activated downstream of PARP-1 in a cascade that involves ADP-ribose (ADPR) production by poly(ADP-ribose) glycohydrolase (PARG). Here we demonstrate that NMDA receptor (NMDAR) stimulation in primary cultured microglia induces their proliferation, morphological activation and release of pro-inflammatory mediators. These responses were contingent on the recruitment of PARP-1, PARG and Ca²⁺ permeable TRPM2 channels. Furthermore, we show that Ca²⁺ influx is necessary to activate PARP-1/TRPM2 signaling, in an ERK1/2-dependent, but DNA damage independent, manner. Our findings, showing that PARP-1/TRPM2 mediate the pro-inflammatory effects of NMDAR stimulation, provides a unifying mechanism linking elevated glutamate levels to chronic neuroinflammation.

Paroxetine suppresses reactive microglia-mediated but not lipopolysaccharide-induced inflammatory responses in primary astrocytes

BACKGROUND

Astrocytes are the most abundant glial cells in a brain that mediate inflammatory responses and provide trophic support for neurons. We have previously disclosed that paroxetine, a common selective serotonin reuptake inhibitor, ameliorates LPS-induced microglia activation. However, it remains elusive for the role of paroxetine in astrocytic responses.

METHODS

Isolated primary astrocytes were pretreated with paroxetine and stimulated with different stimuli, lipopolysaccharide (LPS) or microglia conditioned medium pre-activated with LPS (M/Lps). Inflammatory and neurotrophic responses, underlying mechanisms and the impact on neuronal survival were assessed.

RESULTS

Paroxetine had no impact on LPS-stimulated iNOS, TNF-α, and IL-1β expression, but inhibited M/Lps-induced TNF-α and IL-1β expression in primary astrocytes. Paroxetine suppressed M/Lps- but not LPS-induced activation of NF-κB and had no impact on the activation of MAPKs and STAT3. Incubation with the resulted astrocyte conditioned media caused no change in the viability of SH-SY5Y cells. BDNF and MANF mRNA expressions were upregulated by M/Lps and paroxetine, respectively. However, M/Lps- or LPS-induced extracellular releases of NO, TNF-α, and/or BDNF in astrocytes were in minor amount compared to those by microglia.

CONCLUSIONS

Paroxetine ameliorates the reactive microglia-mediated inflammatory responses in astrocytes partially via inhibition of the NF-κB pathway but has no impact on LPS-stimulated astrocyte activation. While the effects of paroxetine on secondary astrocytic responses are not robust compared to its effect on the innate immune responses of microglia, the results together may implicate a therapeutic potential of paroxetine against neuroinflammation-associated neurological disorders such as Parkinson's disease.

Amyloid Fibril-Induced Astrocytic Glutamate Transporter Disruption Contributes to Complement C1q-Mediated Microglial Pruning of Glutamatergic Synapses

The complement C1q plays a critical role in microglial phagocytosis of glutamatergic synapses and in the pathogenesis of neuroinflammation in Alzheimer's disease (AD). We recently reported that upregulation of metabotropic glutamate receptor signaling is associated with increased synaptic C1q production and subsequent microglial phagocytosis of synapses in the rodent models of AD. Here, we explored the role of astrocytic glutamate transporter in the synaptic C1q production and microglial phagocytosis of hippocampal glutamatergic synapses in a rat model of AD. Activation of astrocyte and reduction glutamate transporter 1 (GLT1) were noted after bilateral microinjection of amyloid-beta (Aβ_1-40) fibrils into the hippocampal CA1 area of rats. Ceftriaxone is a β-lactam antibiotic that upregulates GLT1 expression. Bilateral microinjection of ceftriaxone recovered GLT1 expression, decreased synaptic C1q production, suppressed microglial phagocytosis of glutamatergic synapses in the hippocampal CA1, and attenuated synaptic and cognitive deficits in rats microinjected with Aβ_1-40. In contrast, artificial suppression of GLT1 activity by DL-threo-beta-benzyloxyaspartate (DL-TBOA) in naïve rats induced synaptic C1q expression and microglial phagocytosis of glutamatergic synapses in the hippocampal CA1 area, resulting in synaptic and cognitive dysfunction. These findings demonstrated that impairment of astrocytic glutamate transporter plays a role in the pathogenesis of AD.

Glutamate Chemical Exchange Saturation Transfer (GluCEST) Magnetic Resonance Imaging in Pre-clinical and Clinical Applications for Encephalitis

BACKGROUND

Encephalitis is a common central nervous system inflammatory disease that seriously endangers human health owing to the lack of effective diagnostic methods, which leads to a high rate of misdiagnosis and mortality. Glutamate is implicated closely in microglial activation, and activated microglia are key players in encephalitis. Hence, using glutamate chemical exchange saturation transfer (GluCEST) imaging for the early diagnosis of encephalitis holds promise.

METHODS

The sensitivity of GluCEST imaging with different concentrations of glutamate and other major metabolites in the brain was validated in phantoms. Twenty-seven Sprague-Dawley (SD) rats with encephalitis induced by Staphylococcus aureus infection were used for preclinical research of GluCEST imaging in a 7.0-Tesla scanner. For the clinical study, six patients with encephalitis, six patients with lacunar infarction, and six healthy volunteers underwent GluCEST imaging in a 3.0-Tesla scanner.

RESULTS

The number of amine protons on glutamate that had a chemical shift of 3.0 ppm away from bulk water and the signal intensity of GluCEST were concentration-dependent. Under physiological conditions, glutamate is the main contributor to the GluCEST signal. Compared with normal tissue, in both rats and patients with encephalitis, the encephalitis areas demonstrated a hyper-intense GluCEST signal, while the lacunar infarction had a decreased GluCEST signal intensity. After intravenous immunoglobulin therapy, patients with encephalitis lesions showed a decrease in GluCEST signal, and the results were significantly different from the pre-treatment signal (1.34 ± 0.31 vs 5.0 ± 0.27%, respectively; p = 0.000).

CONCLUSION

Glutamate plays a role in encephalitis, and the GluCEST imaging signal has potential as an in vivo imaging biomarker for the early diagnosis of encephalitis. GluCEST will provide new insight into encephalitis and help improve the differential diagnosis of brain disorders.

Decreased Plasma Levels of Growth Differentiation Factor 11 in Patients With Schizophrenia: Correlation With Psychopathology and Cognition

Schizophrenia is linked with abnormal neurodevelopment, on which growth differentiation factor 11 (GDF-11) has a great impact. However, a direct evidence linking GDF-11 to the pathophysiology of schizophrenia is still lacking. The current study aimed to investigate the relationship between plasma GDF-11 levels and both psychopathological symptoms and cognitive function in schizophrenia. Eighty-seven schizophrenia patients and 76 healthy controls were enrolled in the present study. The symptomatology of schizophrenia was evaluated using the Positive and Negative Syndrome Scale (PANSS). Cognitive function was assessed by Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) including twelve neurocognitive tests in five aspects of cognitive function. Plasma GDF-11 levels were determined by enzyme-linked immunosorbent assay (ELISA). We found that plasma levels of GDF-11 were significantly lower in schizophrenia patients relative to healthy controls. Correlation analysis showed significant negative correlations between the GDF-11 levels and the PANSS total score, the positive symptoms score, the negative symptoms score or the general score. Additionally, positive associations were observed between plasma GDF-11 levels and the visuospatial/constructional, attention, immediate memory, or delayed memory in patients. Partial correlation analysis showed that these correlations were still significant after adjusting for age, gender, education years, body mass index, duration of illness, and age of onset except for the visuospatial/constructional and attention index. Multiple regression analysis revealed that GDF-11 was an independent contributor to the immediate memory, delayed memory and RBANS total score in patients. Collectively, the correlations between plasma GDF-11 and psychopathological and cognitive symptoms suggest that abnormal GDF-11 signaling might contribute to schizophrenic psychopathology and cognitive impairments and GDF-11 could be a potential and promising biomarker for schizophrenia.