Interleukin-1beta enhances GABAA receptor cell-surface expression by a phosphatidylinositol 3-kinase/Akt pathway: relevance to sepsis-associated encephalopathy

Glutathione in HIV-Associated Neurocognitive Disorders

A large portion of patients with Human Immunodeficiency Virus (HIV) have neurologic sequelae. Those with better-controlled HIV via antiretroviral therapies generally have less severe neurologic symptoms. However, for many patients, antiretrovirals do not adequately resolve symptoms. Since much of the pathogenesis of HIV/AIDS (Autoimmune Deficiency Syndrome) involves oxidative stress either directly, through viral interaction, or indirectly, through inflammatory mechanisms, we have reviewed relevant trials of glutathione supplementation in each of the HIV-associated neurocognitive diseases and have found disease-specific results. For diseases for which trials have not been completed, predicted responses to glutathione supplementation are made based on relevant mechanisms seen in the literature. It is not sufficient to conclude that all HIV-associated neurocognitive disorders (HAND) will benefit from the antioxidant effects of glutathione supplementation. The potential effects of glutathione supplementation in patients with HAND are likely to differ based on the specific HIV-associated neurocognitive disease.

IL-1β, the first piece to the puzzle of sepsis-related cognitive impairment?

Sepsis is a leading cause of death resulting from an uncontrolled inflammatory response to an infectious agent. Multiple organ injuries, including brain injuries, are common in sepsis. The underlying mechanism of sepsis-associated encephalopathy (SAE), which is associated with neuroinflammation, is not yet fully understood. Recent studies suggest that the release of interleukin-1β (IL-1β) following activation of microglial cells plays a crucial role in the development of long-lasting neuroinflammation after the initial sepsis episode. This review provides a comprehensive analysis of the recent literature on the molecular signaling pathways involved in microglial cell activation and interleukin-1β release. It also explores the physiological and pathophysiological role of IL-1β in cognitive function, with a particular focus on its contribution to long-lasting neuroinflammation after sepsis. The findings from this review may assist healthcare providers in developing novel interventions against SAE.

Altered DNA methylation underlies monocyte dysregulation and immune exhaustion memory in sepsis

Monocytes can develop an exhausted memory state characterized by reduced differentiation, pathogenic inflammation, and immune suppression that drives immune dysregulation during sepsis. Chromatin alterations, notably via histone modifications, underlie innate immune memory, but the contribution of DNA methylation remains poorly understood. Using an ex vivo sepsis model, we show altered DNA methylation throughout the genome of exhausted monocytes, including genes implicated in immune dysregulation during sepsis and COVID-19 infection (e.g., Plac8). These changes are recapitulated in septic mice induced by cecal slurry injection. Methylation profiles developed in septic mice are maintained during ex vivo culture, supporting the involvement of DNA methylation in stable monocyte exhaustion memory. Methylome reprogramming is driven in part by Wnt signaling inhibition in exhausted monocytes and can be reversed with DNA methyltransferase inhibitors, Wnt agonists, or immune training molecules. Our study demonstrates the significance of altered DNA methylation in the maintenance of stable monocyte exhaustion memory.

Interleukin-10 enhances activity of ventral tegmental area dopamine neurons resulting in increased dopamine release

Dopamine transmission from the ventral tegmental area (VTA) to the nucleus accumbens (NAc) regulates important aspects of motivation and is influenced by the neuroimmune system. The neuroimmune system is a complex network of leukocytes, microglia and astrocytes that detect and remove foreign threats like bacteria or viruses and communicate with each other to regulate non-immune (e.g neuronal) cell activity through cytokine signaling. Inflammation is a key regulator of motivational states, though the effects of specific cytokines on VTA circuitry and motivation are largely unknown. Therefore, electrophysiology, neurochemical, immunohistochemical and behavioral studies were performed to determine the effects of the anti-inflammatory cytokine interleukin-10 (IL-10) on mesolimbic activity, dopamine transmission and conditioned behavior. IL-10 enhanced VTA dopamine firing and NAc dopamine levels via decreased VTA GABA currents in dopamine neurons. The IL-10 receptor was localized on VTA dopamine and non-dopamine cells. The IL-10 effects on dopamine neurons required post-synaptic phosphoinositide 3-kinase activity, and IL-10 appeared to have little-to-no efficacy on presynaptic GABA terminals. Intracranial IL-10 enhanced NAc dopamine levels in vivo and produced conditioned place aversion. Together, these studies identify the IL-10R on VTA dopamine neurons as a potential regulator of motivational states.

Potential Neuroprotective Role of Melatonin in Sepsis-Associated Encephalopathy Due to Its Scavenging and Anti-Oxidative Properties

Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection. The brain is one of the organs involved in sepsis, and sepsis-induced brain injury manifests as sepsis-associated encephalopathy (SAE). SAE may be present in up to 70% of septic patients. SAE has a very wide spectrum of clinical symptoms, ranging from mild behavioral changes through cognitive disorders to disorders of consciousness and coma. The presence of SAE increases mortality in the population of septic patients and may lead to chronic cognitive dysfunction in sepsis survivors. Therefore, therapeutic interventions with neuroprotective effects in sepsis are needed. Melatonin, a neurohormone responsible for the control of circadian rhythms, exerts many beneficial physiological effects. Its anti-inflammatory and antioxidant properties are well described. It is considered a potential therapeutic factor in sepsis, with positive results from studies on animal models and with encouraging results from the first human clinical trials. With its antioxidant and anti-inflammatory potential, it may also exert a neuroprotective effect in sepsis-associated encephalopathy. The review presents data on melatonin as a potential drug in SAE in the wider context of the pathophysiology of SAE and the specific actions of the pineal neurohormone.

Systemic inflammation, neuroinflammation and perioperative neurocognitive disorders

Perioperative neurocognitive disorder (PND) is a common disorder following anesthesia and surgery, especially in the elderly. The complex cellular and molecular processes are involved in PND, but the underlying pathogenesis of which remains inconclusive due to conflicting data. A growing body of evidence has been shown that perioperative systemic inflammation plays important roles in the development of PND. We reviewed the relevant literature retrieved by a search in the PubMed database (on July 20, 2023). The search terms used were "delirium", "post operative cognitive dysfunction", "perioperative neurocognitive disorder", "inflammation" and "systemic", alone and in combination. All articles identified were English-language, full-text papers. The ones cited in the review are those that make a substantial contribution to the knowledge about systemic inflammation and PNDs. The aim of this review is to bring together the latest evidence for the understanding of how perioperative systemic inflammation mediates neuroinflammation and brain injury, how the inflammation is regulated and how we can translate these findings into prevention and/or treatment for PND.

Tetramethylpyrazine contributes to the neuroprotection in a rodent epileptic model of pentylenetetrazole-induced kindling

OBJECTIVES

In this study, tetramethylpyrazine (TMP) was evaluated for its therapeutic potential as an alternative therapy for epileptogenesis and its associated comorbidities in rats.

METHODS

The sub-convulsant dose of pentylenetetrazole (PTZ) (35 mg/kg, intraperitoneally) was injected on alternative days to produce kindling for 32 days and observed for seizure score percent of kindled animals in each group. After kindling, the animals were evaluated in models of anxiety, memory and predictive of depression. The neuroprotective effect of TMP was assessed by estimating the biochemical parameters in the cortex and hippocampus of the brain. Histopathological alterations were also observed in the cortex and hippocampus (CA1, CA3 and DG).

KEY FINDINGS

The administration of TMP reduced the seizure score and percentage of kindled animals dose-dependently. Furthermore, TMP significantly improved the behavioural parameters measured in the predictive models of depression but not in the anxiety and cognitive performances of the animals. The oxidative-nitrosative stress, excitotoxicity, neuroinflammation and histological alterations in the brain induced by PTZ were significantly mitigated by administering the TMP high dose of 60 mg/kg.

CONCLUSION

In conclusion, the TMP attenuated the depression behaviour in the PTZ-induced kindled rats, and reduced the oxidative-nitrosative stress, excitotoxicity, neuroinflammation and histological alterations of the brain.

Altered DNA methylation underlies monocyte dysregulation and innate exhaustion memory in sepsis

Innate immune memory is the process by which pathogen exposure elicits cell-intrinsic states to alter the strength of future immune challenges. Such altered memory states drive monocyte dysregulation during sepsis, promoting pathogenic behavior characterized by pro-inflammatory, immunosuppressive gene expression in concert with emergency hematopoiesis. Epigenetic changes, notably in the form of histone modifications, have been shown to underlie innate immune memory, but the contribution of DNA methylation to this process remains poorly understood. Using an ex vivo sepsis model, we discovered broad changes in DNA methylation throughout the genome of exhausted monocytes, including at several genes previously implicated as major drivers of immune dysregulation during sepsis and Covid-19 infection (e.g. Plac8 ). Methylome alterations are driven in part by Wnt signaling inhibition in exhausted monocytes, and can be reversed through treatment with DNA methyltransferase inhibitors, Wnt agonists, or immune training molecules. Importantly, these changes are recapitulated in septic mice following cecal slurry injection, resulting in stable changes at critical immune genes that support the involvement of DNA methylation in acute and long-term monocyte dysregulation during sepsis.

The possible role of gut microbiota dysbiosis in the pathophysiology of delirium in older persons

Delirium is a clinical syndrome characterized by an acute change in attention, awareness and cognition with fluctuating course, frequently observed in older patients during hospitalization for acute medical illness or after surgery. Its pathogenesis is multifactorial and still not completely understood, but there is general consensus on the fact that it results from the interaction between an underlying predisposition, such as neurodegenerative diseases, and an acute stressor acting as a trigger, such as infection or anesthesia. Alterations in brain insulin sensitivity and metabolic function, increased blood-brain barrier permeability, neurotransmitter imbalances, abnormal microglial activation and neuroinflammation have all been involved in the pathophysiology of delirium. Interestingly, all these mechanisms can be regulated by the gut microbiota, as demonstrated in experimental studies investigating the microbiota-gut-brain axis in dementia. Aging is also associated with profound changes in gut microbiota composition and functions, which can influence several aspects of disease pathophysiology in the host. This review provides an overview of the emerging evidence linking age-related gut microbiota dysbiosis with delirium, opening new perspectives for the microbiota as a possible target of interventions aimed at delirium prevention and treatment.

Microglial NLRP3 Inflammasome Induces Excitatory Synaptic Loss Through IL-1β-Enriched Microvesicle Release: Implications for Sepsis-Associated Encephalopathy

Acute cerebral dysfunction is a pathological state common in severe infections and a pivotal determinant of long-term cognitive outcomes. Current evidence indicates that a loss of synaptic contacts orchestrated by microglial activation is central in sepsis-associated encephalopathy. However, the upstream signals that lead to microglial activation and the mechanism involved in microglial-mediated synapse dysfunction in sepsis are poorly understood. This study investigated the involvement of the NLRP3 inflammasome in microglial activation and synaptic loss related to sepsis. We demonstrated that septic insult using the cecal ligation and puncture (CLP) model induced the expression of NLRP3 inflammasome components in the brain, such as NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3), apoptosis-associated speck-like protein containing a C-terminal caspase recruitment domain (ASC), caspase-1, and IL-1β. Immunostaining techniques revealed increased expression of the NLRP3 inflammasome in microglial cells in the hippocampus of septic mice. Meanwhile, an in vitro model of primary microglia stimulated with LPS exhibited an increase in mitochondrial reactive oxygen species (ROS) production, NLRP3 complex recruitment, and IL-1β release. Pharmacological inhibition of NLRP3, caspase-1, and mitochondrial ROS all decreased IL-1β secretion by microglial cells. Furthermore, we found that microglial NLRP3 activation is the main pathway for IL-1β-enriched microvesicle (MV) release, which is caspase-1-dependent. MV released from LPS-activated microglia induced neurite suppression and excitatory synaptic loss in neuronal cultures. Moreover, microglial caspase-1 inhibition prevented neurite damage and attenuated synaptic deficits induced by the activated microglial MV. These results suggest that microglial NLRP3 inflammasome activation is the mechanism of IL-1β-enriched MV release and potentially synaptic impairment in sepsis.

Identification of biomarkers and therapeutic targets related to Sepsis-associated encephalopathy in rats by quantitative proteomics

BACKGROUND

Sepsis-associated encephalopathy (SAE) is a common and severe complication of sepsis. While several studies have reported the proteomic alteration in plasma, urine, heart, etc. of sepsis, few research focused on the brain tissue. This study aims at discovering the differentially abundant proteins in the brains of septic rats to identify biomarkers of SAE.

METHODS

The Prague-Dawley rats were randomly divided into sepsis (n = 6) or sham (n = 6) groups, and then the whole brain tissue was dissected at 24 h after surgery for further protein identification by Quantitative iTRAQ LC-MS/MS Proteomics. Ingenuity pathway analysis, Gene ontology knowledgebase, and STRING database are used to explore the biological significance of proteins with altered concentration.

RESULTS

Among the total of 3163 proteins identified in the brain tissue, 57 were increased while 38 were decreased in the sepsis group compared to the sham group. Bioinformatic analyses suggest that the differentially abundant proteins are highly related to cellular microtubule metabolism, energy production, nucleic acid metabolism, neurological disease, etc. Additionally, acute phase response signaling was possibly activated and PI3K/AKT signaling was suppressed during sepsis. An interaction network established by IPA revealed that Akt1, Gc-globulin, and ApoA1 were the core proteins. The increase of Gc-globulin and the decrease of Akt1 and ApoA1 were confirmed by Western blot.

CONCLUSION

Based on the multifunction of these proteins in several brain diseases, we first propose that Gc-globulin, ApoA1, PI3K/AKT pathway, and acute phase response proteins (hemopexin and cluster of alpha-2-macroglobulin) could be potential candidates for the diagnosis and treatment of SAE. These results may provide new insights into the pathologic mechanism of SAE, yet further research is required to explore the functional implications and clinical applications of the differentially abundant proteins in the brains of sepsis group.

Beneficial effects of tannic acid on comorbid anxiety in cecal ligation and puncture-induced sepsis in rats and potential underlying mechanisms

Sepsis-associated encephalopathy (SAE), a neurological dysfunction caused by sepsis, is the most common complication among septic ICU patients. Given the major role of inflammation in the pathophysiology of sepsis-induced anxiety, an extreme and early manifestation of SAE, the present study examined whether tannic acid, as an anti-inflammatory agent, has anxiolytic effects in cecal ligation and puncture (CLP)-induced sepsis. Forty male Wistar rats were assigned to four groups: (1) sham; (2) sham + tannic acid; (3) sepsis and (4) sepsis + tannic acid. Sepsis was induced by cecal ligation and puncture model. Animals in the sham + tannic acid and sepsis + tannic acid groups received tannic acid (20 mg/kg, i.p.), 6, 12, and 18 h after the sepsis induction. Twenty-four hours after the sepsis induction, systolic blood pressure and sepsis score were assessed. Anxiety-related behaviors were evaluated using elevated plus-maze and dark-light transition tests. Moreover, inflammatory markers (TNF-α and IL-6) and oxidative stress parameters (MDA and SOD) were measured in the brain tissue while protein levels (GABAA receptors and IL-1β) were assessed in the hippocampus. Administration of tannic acid significantly improved sepsis score and hypotension induced by sepsis. Anxiety-related behaviors showed a significant decrease in the sepsis + tannic acid group compared to the sepsis group. Tannic acid caused a significant decrease in the brain inflammatory markers and a remarkable improvement in the brain oxidative status compared to the septic rats. Tannic acid prevented animals from decreasing GABAA receptors and increasing IL-1β protein levels in the hippocampus compared to the sepsis group. This study indicated that tannic acid mitigated anxiety-related behaviors through decreasing inflammation and oxidative stress and positively modifying IL-1β/GABAA receptor pathway. Therefore, tannic acid shows promise as an efficacious treatment for comorbid anxiety in septic patients.

Cognitive performance in multiple sclerosis: what is the role of the gamma-aminobutyric acid system?

Cognitive impairment occurs in 40-65% of persons with multiple sclerosis and may be related to alterations in glutamatergic and GABAergic neurotransmission. Therefore, the aim of this study was to determine how glutamatergic and GABAergic changes relate to cognitive functioning in multiple sclerosis in vivo. Sixty persons with multiple sclerosis (mean age 45.5 ± 9.6 years, 48 females, 51 relapsing-remitting multiple sclerosis) and 22 age-matched healthy controls (45.6 ± 22.0 years, 17 females) underwent neuropsychological testing and MRI. Persons with multiple sclerosis were classified as cognitively impaired when scoring at least 1.5 standard deviations below normative scores on ≥30% of tests. Glutamate and GABA concentrations were determined in the right hippocampus and bilateral thalamus using magnetic resonance spectroscopy. GABA-receptor density was assessed using quantitative [¹¹C]flumazenil positron emission tomography in a subset of participants. Positron emission tomography outcome measures were the influx rate constant (a measure predominantly reflecting perfusion) and volume of distribution, which is a measure of GABA-receptor density. Twenty persons with multiple sclerosis (33%) fulfilled the criteria for cognitive impairment. No differences were observed in glutamate or GABA concentrations between persons with multiple sclerosis and healthy controls, or between cognitively preserved, impaired and healthy control groups. Twenty-two persons with multiple sclerosis (12 cognitively preserved and 10 impaired) and 10 healthy controls successfully underwent [¹¹C]flumazenil positron emission tomography. Persons with multiple sclerosis showed a lower influx rate constant in the thalamus, indicating lower perfusion. For the volume of distribution, persons with multiple sclerosis showed higher values than controls in deep grey matter, reflecting increased GABA-receptor density. When comparing cognitively impaired and preserved patients to controls, the preserved group showed a significantly higher volume of distribution in cortical and deep grey matter and hippocampus. Positive correlations were observed between both positron emission tomography measures and information processing speed in the multiple sclerosis group only. Whereas concentrations of glutamate and GABA did not differ between multiple sclerosis and control nor between cognitively impaired, preserved and control groups, increased GABA-receptor density was observed in preserved persons with multiple sclerosis that was not seen in cognitively impaired patients. In addition, GABA-receptor density correlated to cognition, in particular with information processing speed. This could indicate that GABA-receptor density is upregulated in the cognitively preserved phase of multiple sclerosis as a means to regulate neurotransmission and potentially preserve cognitive functioning.

The biological alterations of synapse/synapse formation in sepsis-associated encephalopathy

Sepsis-associated encephalopathy (SAE) is a common complication caused by sepsis, and is responsible for increased mortality and poor outcomes in septic patients. Neurological dysfunction is one of the main manifestations of SAE patients. Patients may still have long-term cognitive impairment after hospital discharge, and the underlying mechanism is still unclear. Here, we first outline the pathophysiological changes of SAE, including neuroinflammation, glial activation, and blood-brain barrier (BBB) breakdown. Synapse dysfunction is one of the main contributors leading to neurological impairment. Therefore, we summarized SAE-induced synaptic dysfunction, such as synaptic plasticity inhibition, neurotransmitter imbalance, and synapses loss. Finally, we discuss the alterations in the synapse, synapse formation, and mediators associated with synapse formation during SAE. In this review, we focus on the changes in synapse/synapse formation caused by SAE, which can further understand the synaptic dysfunction associated with neurological impairment in SAE and provide important insights for exploring appropriate therapeutic targets of SAE.

Inhibiting peripheral and central MAO-B ameliorates joint inflammation and cognitive impairment in rheumatoid arthritis

Rheumatoid arthritis (RA) is an autoimmune disorder characterized by chronic inflammation and the destruction of joints and systemic organs. RA is commonly accompanied by neuropsychiatric complications, such as cognitive impairment and depression. However, the role of monoamine oxidase (MAO) and its inhibitors in controlling neurotransmitters associated with these complications in RA have not been clearly identified. Here, we report that peripheral and central MAO-B are highly associated with joint inflammation and cognitive impairment in RA, respectively. Ribonucleic acid (RNA) sequencing and protein expression quantification were used to show that MAO-B and related molecules, such as gamma aminobutyric acid (GABA), were elevated in the inflamed synovium of RA patients. In primary cultured fibroblast-like synoviocytes in the RA synovium, MAO-B expression was significantly increased by tumor necrosis factor (TNF)-α-induced autophagy, which produces putrescine, the polyamine substrate for GABA synthesis. We also observed that MAO-B-mediated aberrant astrocytic production of GABA was augmented by interleukin (IL)-1β and inhibited CA1-hippocampal pyramidal neurons, which are responsible for memory storage, in an animal model of RA. Moreover, a newly developed reversible inhibitor of MAO-B ameliorated joint inflammation by inhibiting cyclooxygenase (Cox)-2. Therefore, MAO-B can be an effective therapeutic target for joint inflammation and cognitive impairment in patients with RA.

Inhibiting an enzyme that is upregulated during joint inflammation may prove a valuable therapy for rheumatoid arthritis (RA). As well as causing considerable pain and discomfort in the joints, RA can also trigger neuropsychiatric problems including depression and memory impairment. The monoamine oxidase (MAO) enzyme family is involved in the control of neurotransmitters, and there is evidence that links MAO-B levels with systemic inflammation. C. Justin Lee at Center for Cognition and Sociality, Institute for Basic Science,, Daejeon, South Korea, and co-workers examined the role of MAO-B in RA using patient tissue samples and mouse models. MAO-B and related molecules were upregulated in patients’ inflamed joint tissues. In mice, elevated MAO-B triggered the inhibition of nerve cell activity related to memory storage. A novel drug that inhibits MAO-B reduced RA-related inflammation and cognitive impairment in mice, suggesting a promising approach to treatment.

FKBP51 mediates resilience to inflammation-induced anxiety through regulation of glutamic acid decarboxylase 65 expression in mouse hippocampus

Background

Inflammation is a potential risk factor of mental disturbance. FKBP5 that encodes FK506-binding protein 51 (FKBP51), a negative cochaperone of glucocorticoid receptor (GR), is a stress-inducible gene and has been linked to psychiatric disorders. Yet, the role of FKBP51 in the inflammatory stress-associated mental disturbance remained unclear.

Methods

Fkbp5-deficient (Fkbp5-KO) mice were used to study inflammatory stress by a single intraperitoneal injection of lipopolysaccharide (LPS). The anxiety-like behaviors, neuroimaging, immunofluorescence staining, immunohistochemistry, protein and mRNA expression analysis of inflammation- and neurotransmission-related mediators were evaluated. A dexamethasone drinking model was also applied to examine the effect of Fkbp5-KO in glucocorticoid-induced stress.

Results

LPS administration induced FKBP51 elevation in the liver and hippocampus accompanied with transient sickness. Notably, Fkbp5-KO but not wild-type (WT) mice showed anxiety-like behaviors 7 days after LPS injection (LPS-D7). LPS challenge rapidly increased peripheral and central immune responses and hippocampal microglial activation followed by a delayed GR upregulation on LPS-D7, and these effects were attenuated in Fkbp5-KO mice. Whole-brain [¹⁸F]-FEPPA neuroimaging, which target translocator protein (TSPO) to indicate neuroinflammation, showed that Fkbp5-KO reduced LPS-induced neuroinflammation in various brain regions including hippocampus. Interestingly, LPS elevated glutamic acid decarboxylase 65 (GAD65), the membrane-associated GABA-synthesizing enzyme, in the hippocampus of WT but not Fkbp5-KO mice on LPS-D7. This FKBP51-dependent GAD65 upregulation was observed in the ventral hippocampal CA1 accompanied by the reduction of c-Fos-indicated neuronal activity, whereas both GAD65 and neuronal activity were reduced in dorsal CA1 in a FKBP51-independent manner. GC-induced anxiety was also examined, which was attenuated in Fkbp5-KO and hippocampal GAD65 expression was unaffected.

Conclusions

These results suggest that FKBP51/FKBP5 is involved in the systemic inflammation-induced neuroinflammation and hippocampal GR activation, which may contribute to the enhancement of GAD65 expression for GABA synthesis in the ventral hippocampus, thereby facilitating resilience to inflammation-induced anxiety.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02517-8.

Pathogenesis of sepsis-associated encephalopathy: more than blood-brain barrier dysfunction

Sepsis-associated encephalopathy is a common neurological complication of sepsis and is responsible for higher mortality and poorer long-term outcomes in septic patients. Sepsis-associated encephalopathy symptoms can range from mild delirium to deep coma, which occurs in up to 70% of patients in intensive care units. The pathological changes in the brain associated with sepsis include cerebral ischaemia, cerebral haemorrhage, abscess and progressive multifocal necrotic leukoencephalopathy. Several mechanisms are involved in the pathogenesis of sepsis-associated encephalopathy, such as blood-brain barrier dysfunction, cerebral blood flow impairment, glial cell activation, leukocyte transmigration, and neurotransmitter disturbances. These events are interrelated and influence each other, therefore they do not act as independent factors. This review is focused on new evidence showing the pathological process of sepsis-associated encephalopathy.

Association of IL-1B rs16944 Polymorphism With Acute Encephalopathy With Biphasic Seizures and Late Reduced Diffusion Is Opposite to That of Febrile Seizures

Objective

Acute encephalopathy with biphasic seizures and late reduced diffusion (AESD) is a severe neurologic complication of febrile infectious diseases in children. At the onset, AESD is clinically manifested as febrile status epilepticus. Subsequent damage to the cerebral cortex is ascribed to neurotoxicity. The incidence of AESD is remarkably high in Japan, suggesting the involvement of genetic factors. The expression of interleukin 1 beta (IL-1β), a member of the cytokine family involved in the inflammatory response, is reportedly associated with rs16944, a polymorphism in the upstream region of the IL-1B gene, being higher in TT genotype. Previous association studies of rs16944 with febrile seizures (FS) have demonstrated a significant excess in the TT vs. CC + CT genotype in the Asian population. Here, we conducted a case-control association study of rs16944 in AESD.

Methods

We genotyped rs16944 by Sanger sequencing on 283 patients with AESD. As controls, we used genotyping data of 104 Japanese individuals obtained from the 1,000 Genomes Project. Then, we performed a case-control association study using the chi-square test.

Results

The ratio of individuals with TT vs. those with CC+CT genotype was significantly lower in AESD than in the controls [p-value 0.021, Odds Ratio (OR) 0.52]. This finding was opposite to that of a previously reported FS.

Conclusion

The AESD has a genetic background distinct from FS and is not a severe type of FS.

Yokukansan suppresses neuroinflammation in the hippocampus of mice and decreases the duration of lipopolysaccharide- and diazepam-mediated loss of righting reflex induced by pentobarbital

Neuroinflammation is associated with the development of hypoactive delirium, which results in poor clinical outcomes. Drugs effective against hypoactive sur have not yet been established. Yokukansan has an anti-neuroinflammatory effect, making it potentially effective against hypoactive delirium. This study aimed to examine the effect of Yokukansan on the pentobarbital-induced loss of righting reflex duration extended with lipopolysaccharide (LPS)-induced neuroinflammation and diazepam-induced gamma-aminobutyric acid receptor stimulation in a mouse model. The active ingredients in Yokukansan and its anti-neuroinflammatory effect on the hippocampus were also investigated. Furthermore, we examined the in vitro anti-inflammatory effects of Yokukansan on LPS-stimulated BV2 cells, a murine microglial cell line. Findings revealed that treatment with Yokukansan significantly decreased the duration of pentobarbital-induced loss of righting reflex by attenuating the LPS-induced increase in interleukin-6 and tumor necrosis factor-alpha levels in the hippocampus. Moreover, treatment with Yokukansan significantly decreased the number of ionized calcium-binding adapter molecule-1-positive cells in the hippocampal dentate gyrus after 24 h of LPS administration. In addition, glycyrrhizic acid, an active ingredient in Yokukansan, partially decreased the duration of pentobarbital-induced loss of righting reflex. Treatment with Yokukansan also suppressed the expression of inducible nitric oxide, interleukin-6, and tumor necrosis factor mRNA in LPS-stimulated BV2 cells. Thus, these findings suggest that Yokukansan and glycyrrhizic acid may be effective therapeutic agents for treating neuroinflammation-induced hypoactive delirium.

Interferon-γ enhances neocortical synaptic inhibition by promoting membrane association and phosphorylation of GABAA receptors in a protein kinase C-dependent manner

Interferon-γ (IFN-γ), an important mediator of the antiviral immune response, can also act as a neuromodulator. CNS IFN-γ levels rise acutely in response to infection and therapeutically applied IFN-γ provokes CNS related side effects. Moreover, IFN-γ plays a key role in neurophysiological processes and a variety of chronic neurological and neuropsychiatric conditions. To close the gap between basic research, behavioral implications and clinical applicability, knowledge of the mechanism behind IFN-γ related changes in brain function is crucial. Here, we studied the underlying mechanism of acutely augmented neocortical inhibition by IFN-γ (1.000 IU ml^-1) in layer 5 pyramidal neurons of male Wistar rats. We demonstrate postsynaptic mediation of IFN-γ augmented inhibition by pressure application of GABA and analysis of paired pulse ratios. IFN-γ increases membrane presence of GABA_AR γ₂, as quantified by cell surface biotinylation and functional synaptic GABA_AR number, as determined by peak-scaled non-stationary noise analysis. The increase in functional receptor number was comparable to the increase in underlying miniature inhibitory postsynaptic current (mIPSC) amplitudes. Blockage of putative intracellular mediators, namely phosphoinositide 3-kinase and protein kinase C (PKC) by Wortmannin and Calphostin C, respectively, revealed PKC-dependency of the pro-inhibitory IFN-γ effect. This was corroborated by increased serine phosphorylation of P-serine PKC motifs on GABA_AR γ₂ upon IFN-γ application. GABA_AR single channel conductance, intracellular chloride levels and GABA_AR driving force are unlikely to contribute to the effect, as shown by single channel recordings and chloride imaging. The effect of IFN-γ on mIPSC amplitudes was similar in female and male rats, suggesting a gender-independent mechanism of action. Collectively, these results indicate a novel mechanism for the regulation of inhibition by IFN-γ, which could impact on neocortical function and therewith behavior.

Neuropsychological Outcome of Critically Ill Patients with Severe Infection

Sepsis and septic shock represent important burdens of disease around the world. Sepsis-associated neurological consequences have a great impact on patients, both in the acute phase and in the long term. Sepsis-associated encephalopathy (SAE) is a severe brain dysfunction that may contribute to long-term cognitive impairment. Its pathophysiology recognizes the following two main mechanisms: neuroinflammation and hemodynamic impairment. Clinical manifestations include different forms of altered mental status, from agitation and restlessness to delirium and deep coma. A definite diagnosis is difficult because of the absence of specific radiological and biological criteria; clinical management is restricted to the treatment of sepsis, focusing on early detection of the infection source, maintenance of hemodynamic homeostasis, and avoidance of metabolic disturbances or neurotoxic drugs.

Cerebral dysfunctions caused by sepsis during ageing

Systemic inflammation elicited by sepsis can induce an acute cerebral dysfunction known as sepsis-associated encephalopathy (SAE). Recent evidence suggests that SAE is common but shows a dynamic trajectory over time. Half of all patients with sepsis develop SAE in the intensive care unit, and some survivors present with sustained cognitive impairments for several years after initial sepsis onset. It is not clear why some, but not all, patients develop SAE and also the factors that determine the persistence of SAE. Here, we first summarize the chronic pathology and the dynamic changes in cognitive functions seen after the onset of sepsis. We then outline the cerebral effects of sepsis, such as neuroinflammation, alterations in neuronal synapses and neurovascular changes. We discuss the key factors that might contribute to the development and persistence of SAE in older patients, including premorbid neurodegenerative pathology, side effects of sedatives, renal dysfunction and latent virus reactivation. Finally, we postulate that some of the mechanisms that underpin neuropathology in SAE may also be relevant to delirium and persisting cognitive impairments that are seen in patients with severe COVID-19.

In this Review, Manabe and Heneka examine how the systemic inflammation associated with sepsis can lead to acute cerebral dysfunction known as sepsis-associated encephalopathy (SAE). Moreover, they suggest that some of the mechanisms involved in SAE may be relevant for understanding the cognitive impairments that develop in some patients with COVID-19.

Synaptic Dysfunction in Multiple Sclerosis: A Red Thread from Inflammation to Network Disconnection

Multiple sclerosis (MS) has been clinically considered a chronic inflammatory disease of the white matter; however, in the last decade growing evidence supported an important role of gray matter pathology as a major contributor of MS-related disability and the involvement of synaptic structures assumed a key role in the pathophysiology of the disease. Synaptic contacts are considered central units in the information flow, involved in synaptic transmission and plasticity, critical processes for the shaping and functioning of brain networks. During the course of MS, the immune system and its diffusible mediators interact with synaptic structures leading to changes in their structure and function, influencing brain network dynamics. The purpose of this review is to provide an overview of the existing literature on synaptic involvement during experimental and human MS, in order to understand the mechanisms by which synaptic failure eventually leads to brain networks alterations and contributes to disabling MS symptoms and disease progression.

A Multi-Ligand Imaging Study Exploring GABAergic Receptor Expression and Inflammation in Multiple Sclerosis

PURPOSE

The γ-aminobutyric acid (GABA) is the main inhibitory neurotransmitter and essential for normal brain function. The GABAergic system has been shown to have immunomodulatory effects and respond adaptively to excitatory toxicity. The association of the GABAergic system and inflammation in patients with multiple sclerosis (MS) remains unknown. In this pilot study, the in vivo relationship between GABA_A binding and the innate immune response is explored using positron emission tomography (PET) with [¹¹C] flumazenil (FMZ) and [¹¹C]-PK11195 PET (PK-PET), a measure of activated microglia/macrophages.

PROCEDURES

Sixteen MS patients had dynamic FMZ-PET and PK-PET imaging. Ten age-matched healthy controls (HC) had a single FMZ-PET. GABA_A receptor binding was calculated using Logan reference model with the pons as reference. Distribution of volume ratio (VTr) for PK-PET was calculated using image-derived input function. A hierarchical linear model was fitted to assess the linear association between PK-PET and FMZ-PET among six cortical regions of interest.

RESULTS

GABA_A receptor binding was higher throughout the cortex in MS patients (5.72 ± 0.91) as compared with HC (4.70 ± 0.41) (p = 0.002). A significant correlation was found between FMZ binding and PK-PET within the cortex (r = 0.61, p < 0.001) and among the occipital (r = 0.61, p = 0.012), parietal (r = 0.49, p = 0.041), and cingulate (r = 0.32, p = 0.006) regions.

CONCLUSIONS

A higher GABA_A receptor density in MS subjects compared with HC was observed and correlated with innate immune activity. Our observations demonstrate that immune-driven GABAergic abnormalities may be present in MS.

Anesthesiology: Resetting Our Sights on Long-term Outcomes: The 2020 John W. Severinghaus Lecture on Translational Science

Anesthesiologists have worked relentlessly to improve intraoperative anesthesia care. They are now well positioned to expand their horizons and address many of the longer-term adverse consequences of anesthesia and surgery. Perioperative neurocognitive disorders, chronic postoperative pain, and opioid misuse are not inevitable adverse outcomes; rather, they are preventable and treatable conditions that deserve attention. The author's research team has investigated why patients experience new cognitive deficits after anesthesia and surgery. Their animal studies have shown that anesthetic drugs trigger overactivity of "memory-blocking receptors" that persists after the drugs are eliminated, and they have discovered new strategies to preserve brain function by repurposing available drugs and developing novel therapeutics that inhibit these receptors. Clinical trials are in progress to examine the cognitive outcomes of such strategies. This work is just one example of how anesthesiologists are advancing science with the goal of improving the lives of patients.

Energy management and mitochondrial dynamics in cerebral cortex during endotoxemia

Mitochondria play an essential role in inflammatory processes such as sepsis or endotoxemia, contributing to organ-cellular redox metabolism, emerging as the energy hub of the cell, and as an important center of action of second messengers. In this work, we aimed to elucidate the energy state, redox balance, and mitochondrial remodeling status in cerebral cortex in an experimental model of endotoxemia. Female Sprague-Dawley rats were subjected to a single dose of LPS (ip 8 mg kg^-1 body weight) for 6 h. State 3 O₂ consumption was observed increased, ATP production and P/O ratio were observed decreased, probably indicating an inefficient oxidative phosphorylation process. O₂^- production and both systemic and tissue NO markers were observed increased in treated animals. The existence of nitrated proteins suggests an alteration in the local redox balance and possible harmful effects over energetic processes. Increases in PGC-1α and mtTFA expression, and in OPA-1 expression, suggest an increase in de novo formation of mitochondria and fusion of pre-existing mitochondria. The observed elongation of mitochondria correlates with the occurrence of mild mitochondrial dysfunction and increased levels of systemic NO. Our work presents novel results that contribute to unravel the mechanism by which the triad endotoxemia-redox homeostasis-energy management interact in the cerebral cortex, leading to propose a relevant mechanism for future developing therapeutics with the aim of preserving this organ from inflammatory and oxidative damage.

Neuroinflammation in Sepsis: Molecular Pathways of Microglia Activation

Frequently underestimated, encephalopathy or delirium are common neurological manifestations associated with sepsis. Brain dysfunction occurs in up to 80% of cases and is directly associated with increased mortality and long-term neurocognitive consequences. Although the central nervous system (CNS) has been classically viewed as an immune-privileged system, neuroinflammation is emerging as a central mechanism of brain dysfunction in sepsis. Microglial cells are major players in this setting. Here, we aimed to discuss the current knowledge on how the brain is affected by peripheral immune activation in sepsis and the role of microglia in these processes. This review focused on the molecular pathways of microglial activity in sepsis, its regulatory mechanisms, and their interaction with other CNS cells, especially with neuronal cells and circuits.

High Mobility Group Box 1/Toll-like Receptor 4 Signaling Increases GABRB3 Expression in Alcohol Exposure

INTRODUCTION

Prefrontal cortex (PFC) and striatal neurotransmitter homeostasis is affected by alcohol dependence. In this study, the microarray dataset from the Gene Expression Omnibus (GEO) database were downloaded. The prefrontal and striatum data were cross-analyzed to reveal the co-effects of alcohol dependence on the two brain regions of mice.

METHODS

The GSE123114 microarray profile was downloaded from the GEO database, and differentially expressed genes (DEGs) between the two groups were acquired by GEO2R. KEGG analyses were performed to identify the pivotal pathways of these DEGs. Key differential gene expressions and their mechanism associated with alcohol exposure were investigated by an intraperitoneal alcohol model.

RESULTS

A total of 13 overlapping DEGs from the PFC and striatal datasets of the GSE123114 microarray profile were identified, and they were significantly enriched in the morphine addiction pathway. The transcript levels and protein expression of Gabrb3 were consistent with the microarray data both in the PFC and striatum. The transcript levels of HMGB1, TLR4, TNFα and IL-1β were upregulated in the PFC and striatum of mice in the alcohol group. The HMGB1 inhibitor decreased Gabrb3 transcript and protein levels as well as TNFα and IL-1β transcript levels both in the PFC and striatum in the intraperitoneal alcohol model mice.

DISCUSSION

Through the reanalysis of GSE123114 microarray profile, we found that Gabrb3 is a key gene associated with alcohol exposure. In further experiments, our findings suggest that alcohol exposure modulates Gabrb3 expression through the HMGB1/TLR4 pathway. Moreover, inflammation-associated factors, such as IL-1β and TNFα, may be related to the HMGB1/TLR4-mediated regulation of GABRB3 expression in alcohol exposure.

Delirium

Delirium, a syndrome characterized by an acute change in attention, awareness and cognition, is caused by a medical condition that cannot be better explained by a pre-existing neurocognitive disorder. Multiple predisposing factors (for example, pre-existing cognitive impairment) and precipitating factors (for example, urinary tract infection) for delirium have been described, with most patients having both types. Because multiple factors are implicated in the aetiology of delirium, there are likely several neurobiological processes that contribute to delirium pathogenesis, including neuroinflammation, brain vascular dysfunction, altered brain metabolism, neurotransmitter imbalance and impaired neuronal network connectivity. The Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM-5) is the most commonly used diagnostic system upon which a reference standard diagnosis is made, although many other delirium screening tools have been developed given the impracticality of using the DSM-5 in many settings. Pharmacological treatments for delirium (such as antipsychotic drugs) are not effective, reflecting substantial gaps in our understanding of its pathophysiology. Currently, the best management strategies are multidomain interventions that focus on treating precipitating conditions, medication review, managing distress, mitigating complications and maintaining engagement to environmental issues. The effective implementation of delirium detection, treatment and prevention strategies remains a major challenge for health-care organizations globally.

Monocyte chemotactic protein-inducing protein 1 negatively regulating asthmatic airway inflammation and mucus hypersecretion involving γ-aminobutyric acid type A receptor signaling pathway in vivo and in vitro

BACKGROUND

Mounting evidence, consistent with our previous study, showed that γ-aminobutyric acid type A receptor (GABAAR) played an indispensable role in airway inflammation and mucus hypersecretion in asthma. Monocyte chemotactic protein-inducing protein 1 (MCPIP1) was a key negative regulator of inflammation. Recent studies showed that inflammation was largely suppressed by enhanced MCPIP1 expression in many inflammatory diseases. However, the role and potential mechanism of MCPIP1 in airway inflammation and mucus hypersecretion in asthma were still not well studied. This study was to explore the role of MCPIP1 in asthmatic airway inflammation and mucus hypersecretion in both mice and BEAS-2B cells, and its potential mechanism.

METHODS

In vivo, mice were sensitized and challenged by ovalbumin (OVA) to induce asthma. Airway inflammation and mucus secretion were analyzed. In vitro, BEAS-2B cells were chosen. Interleukin (IL)-13 was used to stimulate inflammation and mucus hypersecretion in cells. MCPIP1 Lentiviral vector (LA-MCPIP1) and plasmid-MCPIP1 were used to up-regulate MCPIP1 in lung and cells, respectively. MCP-1, thymic stromal lymphopoietin (TSLP), mucin 5AC (MUC5AC), MCPIP1, and GABAARβ2 expressions were measured in both lung and BEAS-2B cells. Immunofluorescence staining was performed to observe the expression of GABAARβ2 in cells.

RESULTS

MCPIP1 was up-regulated by LA-MCPIP1 (P < 0.001) and plasmid-MCPIP1 (P < 0.001) in lung and cells, respectively. OVA-induced airway inflammation and mucus hypersecretion, OVA-enhanced MCP-1, TSLP, MUC5AC, and GABAARβ2 expressions, and OVA-reduced MCPIP1 were significantly blunted by LA-MCPIP1 in mice (all P < 0.001). IL-13-enhanced MCP-1, TSLP, MUC5AC, and GABAARβ2 expressions, and IL-13-reduced MCPIP1 were markedly abrogated by plasmid-MCPIP1 in BEAS-2B cells (all P < 0.001).

CONCLUSION

The results of this study suggested that OVA and IL-13-induced airway inflammation and mucus hypersecretion were negatively regulated by MCPIP1 in both lung and BEAS-2B cells, involving GABAAR signaling pathway.

Neuroimmune System as a Driving Force for Plasticity Following CNS Injury

Following an injury to the central nervous system (CNS), spontaneous plasticity is observed throughout the neuraxis and affects multiple key circuits. Much of this spontaneous plasticity can elicit beneficial and deleterious functional outcomes, depending on the context of plasticity and circuit affected. Injury-induced activation of the neuroimmune system has been proposed to be a major factor in driving this plasticity, as neuroimmune and inflammatory factors have been shown to influence cellular, synaptic, structural, and anatomical plasticity. Here, we will review the mechanisms through which the neuroimmune system mediates plasticity after CNS injury. Understanding the role of specific neuroimmune factors in driving adaptive and maladaptive plasticity may offer valuable therapeutic insight into how to promote adaptive plasticity and/or diminish maladaptive plasticity, respectively.

Septic-Associated Encephalopathy: a Comprehensive Review

Septic-associated encephalopathy (SAE) is a key manifestation of sepsis, ranging from delirium to coma and occurring in up to 70% of patients admitted to the ICU. SAE is associated with higher ICU and hospital mortality, and also with poorer long-term outcomes, including cognitive and functional outcomes. The pathophysiology of SAE is complex, and it may involve neurotransmitter dysfunction, inflammatory and ischemic lesions to the brain, microglial activation, and blood-brain barrier dysfunction. Delirium (which is included in the SAE spectrum) is mostly diagnosed with validated scales in the ICU population. There is no established treatment for SAE; benzodiazepines should generally be avoided in this setting. Nonpharmacological prevention and management is key for treating SAE; it includes avoiding oversedation (mainly with benzodiazepines), early mobilization, and sleep promotion.

Sepsis-induced encephalopathy impairs descending nociceptive pathways in rats

Sepsis-associated encephalopathy (SAE) is a significant problem in patients with sepsis, and it is associated with a decrease in cognitive and sensitivity capability induced by systemic inflammation. SAE is implicated in reversible brain damage of several regions related to cognition, emotion, and sensation; however, it is not well established if it could affect brain regions associated with nociceptive modulation. Here were evaluated the nociceptive thresholds in rats with systemic inflammation induced by cecal ligation puncture (CLP). After 24 h of CLP, it was observed an increase in nociceptive threshold in all tests. Periaqueductal gray, rostroventral medulla, critical regions for descending nociceptive modulation, were evaluated and showed enhanced pro-inflammatory cytokines as well as glial activation. These results suggest that systemic inflammation could compromise descending facilitatory pathways, impairing nociceptive sensory functioning.

Overinhibition mediated by parvalbumin interneurons might contribute to depression-like behavior and working memory impairment induced by lipopolysaccharide challenge

Systemic inflammation induces cognitive impairments via unclear mechanisms. Accumulating evidence has demonstrated that a subset of neurons that express parvalbumin (PV) play a critical role in regulation of cognitive and emotional behavior. Thus, the aim of the present study was to test whether disruption of PV interneuron mediates systemic inflammation-induced depression-like behavior and working memory impairment by lipopolysaccharide (LPS) challenge. Here we showed that LPS induces depression-like behavior and working memory impairment, coinciding with increased PV expression, enhanced GABAergic transmission, and impaired long-term potentiation (LTP) in the hippocampus. Notably, systemic administration of NMDA (N-methyl-D-aspartate) receptor (NMDAR) antagonist ketamine was able to interfere with PV expression and reverse depression-like behavior and working memory impairment, which is probably mediated by reversing impaired LTP. In addition, flumazenil, a competitive antagonist acting at the benzodiazepine binding site of the GABA_A receptor, also ameliorated these abnormal behaviors. Collectively, our study added growing evidence to the limited studies that overinhibition mediated by PV interneurons might play a critical role in LPS-induced depression-like behavior and working memory impairment.

The Delta-Subunit Selective GABA A Receptor Modulator, DS2, Improves Stroke Recovery via an Anti-inflammatory Mechanism

Inflammatory processes are known to contribute to tissue damage in the central nervous system (CNS) across a broad range of neurological conditions, including stroke. Gamma amino butyric acid (GABA), the main inhibitory neurotransmitter in the CNS, has been implicated in modulating peripheral immune responses by acting on GABA _A receptors on antigen-presenting cells and lymphocytes. Here, we investigated the effects and mechanism of action of the delta-selective compound, DS2, to improve stroke recovery and modulate inflammation. We report a decrease in nuclear factor (NF)-κB activation in innate immune cells over a concentration range in vitro. Following a photochemically induced motor cortex stroke, treatment with DS2 at 0.1 mg/kg from 1 h post-stroke significantly decreased circulating tumor necrosis factor (TNF)-α, interleukin (IL)-17, and IL-6 levels, reduced infarct size and improved motor function in mice. Free brain concentrations of DS2 were found to be lower than needed for robust modulation of central GABA _A receptors and were not affected by the presence and absence of elacridar, an inhibitor of both P-glycoprotein and breast cancer resistance protein (BCRP). Finally, as DS2 appears to dampen peripheral immune activation and only shows limited brain exposure, we assessed the role of DS2 to promote functional recovery after stroke when administered from 3-days after the stroke. Treatment with DS2 from 3-days post-stroke improved motor function on the grid-walking, but not on the cylinder task. These data highlight the need to further develop subunit-selective compounds to better understand change in GABA receptor signaling pathways both centrally and peripherally. Importantly, we show that GABA compounds such as DS2 that only shows limited brain exposure can still afford significant protection and promote functional recovery most likely via modulation of peripheral immune cells and could be given as an adjunct treatment.

Ethanol and Cytokines in the Central Nervous System

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

Molecular Mechanisms of Cancer-Induced Sleep Disruption

Sleep is essential for health. Indeed, poor sleep is consistently linked to the development of systemic disease, including depression, metabolic syndrome, and cognitive impairments. Further evidence has accumulated suggesting the role of sleep in cancer initiation and progression (primarily breast cancer). Indeed, patients with cancer and cancer survivors frequently experience poor sleep, manifesting as insomnia, circadian misalignment, hypersomnia, somnolence syndrome, hot flushes, and nightmares. These problems are associated with a reduction in the patients' quality of life and increased mortality. Due to the heterogeneity among cancers, treatment regimens, patient populations and lifestyle factors, the etiology of cancer-induced sleep disruption is largely unknown. Here, we discuss recent advances in understanding the pathways linking cancer and the brain and how this leads to altered sleep patterns. We describe a conceptual framework where tumors disrupt normal homeostatic processes, resulting in aberrant changes in physiology and behavior that are detrimental to health. Finally, we discuss how this knowledge can be leveraged to develop novel therapeutic approaches for cancer-associated sleep disruption, with special emphasis on host-tumor interactions.

Shared microglial mechanisms underpinning depression and chronic fatigue syndrome and their comorbidities

In 2011, it was reviewed that a) there is a strong co-occurrence between major depression and chronic fatigue syndrome (CFS), with fatigue and physio-somatic symptoms being key symptoms of depression, and depressive symptoms appearing during the course of CFS; and b) the comorbidity between both disorders may in part be explained by activated immune-inflammatory pathways, including increased translocation of Gram-negative bacteria and increased levels of pro-inflammatory cytokines, such as interleukin (IL)-1. Nevertheless, the possible involvement of activated microglia in this comorbidity has remained unclear. This paper aims to review microglial disturbances in major depression, CFS and their comorbidity. A comprehensive literature search was conducted using the PubMed / MEDLINE database to identify studies, which are relevant to this current review. Depressed patients present neuroinflammatory alterations, probably related to microglial activation, while animal models show that a microglial response to immune challenges including lipopolysaccharides is accompanied by depressive-like behaviors. Recent evidence from preclinical studies indicates that activated microglia have a key role in the onset of fatigue. In chronic inflammatory conditions, such as infections and senescence, microglia orchestrate an inflammatory microenvironment thereby causing fatigue. In conclusion, based on our review we may posit that shared immune-inflammatory pathways and especially activated microglia underpin comorbid depression and CFS. As such, microglial activation and neuro-inflammation may be promising targets to treat the overlapping manifestations of both depression and CFS.

Bicuculline Reduces Neuroinflammation in Hippocampus and Improves Spatial Learning and Anxiety in Hyperammonemic Rats. Role of Glutamate Receptors

Patients with liver cirrhosis may develop minimal hepatic encephalopathy (MHE) with mild cognitive impairment. Hyperammonemia is a main contributor to cognitive impairment in MHE, which is mediated by neuroinflammation. GABAergic neurotransmission is altered in hyperammonemic rats. We hypothesized that, in hyperammonemic rats, (a) enhanced GABAergic tone would contribute to induce neuroinflammation, which would be improved by reducing GABAergic tone by chronic bicuculline treatment; (b) this would improve spatial learning and memory impairment; and (c) modulation of glutamatergic neurotransmission would mediate this cognitive improvement. The aim of this work was to assess the above hypotheses. Bicuculline was administrated intraperitoneally once a day for 4 weeks to control and hyperammonemic rats. The effects of bicuculline on microglia and astrocyte activation, IL-1β content, on membrane expression of AMPA and NMDA glutamate receptors subunits in the hippocampus and on spatial learning and memory as well as anxiety were assessed. Treatment with bicuculline reduces astrocyte activation and IL-1β but not microglia activation in the hippocampus of hyperammonemic rats. Bicuculline reverses the changes in membrane expression of AMPA receptor subunits GluA1 and GluA2 and of the NR2B (but not NR1 and NR2A) subunit of NMDA receptors. Bicuculline improves spatial learning and working memory and decreases anxiety in hyperammonemic rats. In hyperammonemia, enhanced activation of GABAA receptors in the hippocampus contributes to some but not all aspects of neuroinflammation, to altered glutamatergic neurotransmission and to impairment of spatial learning and memory as well as anxiety, all of which are reversed by reducing activation of GABAA receptors with bicuculline.

HIV gp120 upregulates tonic inhibition through α5-containing GABAARs

HIV-Associated Neurocognitive disorder (HAND) affects nearly half of infected patients. The HIV envelope protein gp120 is shed by infected cells and is a potent neurotoxin in vitro that reproduces many aspects of HAND when expressed in vivo. Here, we show that HIV gp120 increases the amplitude of a tonic current mediated by γ-aminobutyric acid type-A receptors (GABA_ARs). Treating rat hippocampal cultures with 600 pM gp120_IIIB for 4 h increased a tonic bicuculline-sensitive current, which remained elevated for 24 h. The increased current resulted from upregulation of extrasynaptic α5-containing GABA_ARs, as indicated by inhibition with the selective inverse agonist basmisanil. Treatment with gp120 increased α5-GABA_AR immunoreactivity on the cell surface without new protein synthesis. The increase in tonic inhibition was prevented by a C-X-C chemokine receptor type 4 (CXCR4) antagonist or elimination of microglia from the culture. Treatment with interleukin-1β (IL-1β) increased the tonic current and an IL-1 receptor antagonist blocked the gp120-evoked response. Pharmacological or genetic inhibition of p38 mitogen-activated protein kinase (MAPK) prevented the gp120-evoked increase in tonic current and direct activation of a mutant form of p38 MAPK expressed in neurons increased the current. Collectively, these data show that gp120 activates CXCR4 to stimulate microglia to release IL-1β. Subsequent stimulation of IL-1 receptors activates p38 MAPK in neurons leading to the upregulation of α5-containing GABA_ARs. Increased tonic inhibition impairs neuroplasticity and inhibition of α5-containing GABA_ARs improves cognitive function in disease models. Thus, gp120-induced upregulation of α5-containing GABA_ARs presents a novel therapeutic target for HAND.

HIV gp120-induced neuroinflammation potentiates NMDA receptors to overcome basal suppression of inhibitory synapses by p38 MAPK

HIV-associated neurocognitive disorder affects about half of HIV-infected patients. HIV impairs neuronal function through indirect mechanisms mainly mediated by inflammatory cytokines and neurotoxic viral proteins, such as the envelope protein gp120. HIV gp120 elicits a neuroinflammatory response that potentiates NMDA receptor function and induces the loss of excitatory synapses. How gp120 influences neuronal inhibition remains unknown. In this study, we expressed a green fluorescent protein (GFP)-tagged recombinant antibody-like protein that binds to the post-synaptic scaffolding protein gephyrin to label inhibitory synapses in living neurons. Treatment with 600 pM gp120 for 24 h increased the number of labeled inhibitory synapses. HIV gp120 evoked the release of interleukin-1β (IL-1β) from microglia to activate IL-1 receptors on neurons. Subsequent activation of the tyrosine kinase Src and GluN2A-containing NMDA receptors increased the number of inhibitory synapses via a process that required protein synthesis. In naïve cultures, inhibition of neuronal p38 mitogen-activated protein kinase (p38 MAPK) increased the number of inhibitory synapses suggesting that p38 MAPK produces a basal suppression of inhibitory synapses that is overcome in the presence of gp120. Direct activation of a mutant form of p38 MAPK expressed in neurons mimicked basal suppression of inhibitory synapses. This study shows for the first time that gp120-induced neuroinflammation increases the number of inhibitory synapses and that this increase overcomes a basal suppression of synaptic inhibition. Increased inhibition may be an adaptive mechanism enabling neurons to counteract excess excitatory input in order to maintain network homeostasis. OPEN SCIENCE BADGES: This article has received a badge for *Open Materials* because it provided all relevant information to reproduce the study in the manuscript. The complete Open Science Disclosure form for this article can be found at the end of the article. More information about the Open Practices badges can be found at https://cos.io/our-services/open-science-badges/.

Acute transient cognitive dysfunction and acute brain injury induced by systemic inflammation occur by dissociable IL-1-dependent mechanisms

Systemic inflammation can impair cognition with relevance to dementia, delirium and post-operative cognitive dysfunction. Episodes of delirium also contribute to rates of long-term cognitive decline, implying that these acute events induce injury. Whether systemic inflammation-induced acute dysfunction and acute brain injury occur by overlapping or discrete mechanisms remains unexplored. Here we show that systemic inflammation, induced by bacterial LPS, produces both working-memory deficits and acute brain injury in the degenerating brain and that these occur by dissociable IL-1-dependent processes. In normal C57BL/6 mice, LPS (100 µg/kg) did not affect working memory but impaired long-term memory consolidation. However prior hippocampal synaptic loss left mice selectively vulnerable to LPS-induced working memory deficits. Systemically administered IL-1 receptor antagonist (IL-1RA) was protective against, and systemic IL-1β replicated, these working memory deficits. Dexamethasone abolished systemic cytokine synthesis and was protective against working memory deficits, without blocking brain IL-1β synthesis. Direct application of IL-1β to ex vivo hippocampal slices induced non-synaptic depolarisation and irreversible loss of membrane potential in CA1 neurons from diseased animals and systemic LPS increased apoptosis in the degenerating brain, in an IL-1RI-dependent fashion. The data suggest that LPS induces working memory dysfunction via circulating IL-1β but direct hippocampal action of IL-1β causes neuronal dysfunction and may drive neuronal death. The data suggest that acute systemic inflammation produces both reversible cognitive deficits, resembling delirium, and acute brain injury contributing to long-term cognitive impairment but that these events are mechanistically dissociable. These data have significant implications for management of cognitive dysfunction during acute illness.

Enhanced GABAergic Tonic Inhibition Reduces Intrinsic Excitability of Hippocampal CA1 Pyramidal Cells in Experimental Autoimmune Encephalomyelitis

Cognitive impairment (CI), a debilitating and pervasive feature of multiple sclerosis (MS), is correlated with hippocampal atrophy. Findings from postmortem MS hippocampi indicate that expression of genes involved in both excitatory and inhibitory neurotransmission are altered in MS, and although deficits in excitatory neurotransmission have been reported in the MS model experimental autoimmune encephalomyelitis (EAE), the functional consequence of altered inhibitory neurotransmission remains poorly understood. In this study, we used electrophysiological and biochemical techniques to examine inhibitory neurotransmission in the CA1 region of the hippocampus in EAE. We find that tonic, GABAergic inhibition is enhanced in CA1 pyramidal cells from EAE mice. Although plasma membrane expression of the GABA transporter GAT-3 was decreased in the EAE hippocampus, an increased surface expression of α5 subunit-containing GABA_A receptors appears to be primarily responsible for the increase in tonic inhibition during EAE. Enhanced tonic inhibition during EAE was associated with decreased CA1 pyramidal cell excitability and inhibition of α5 subunit-containing GABA_A receptors with the negative allosteric modulator L-655,708 enhanced pyramidal cell excitability in EAE mice. Together, our results suggest that altered GABAergic neurotransmission may underlie deficits in hippocampus-dependent cognitive function in EAE and MS.

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

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

Influence of lipopolysaccharide on diazepam-modified loss of righting reflex duration by pentobarbital treatment in mice

Benzodiazepine receptor agonists are widely prescribed therapeutic agents, alter gamma-aminobutyric acid (GABA)_A receptor function, and have hypnotic, anxiolytic, anticonvulsant, and antispastic effects. GABA_A receptor activity increases under systemic inflammatory conditions. We investigated the effect of benzodiazepine receptor agonists on pentobarbital-induced loss of righting reflex (LORR) duration using a mouse model of lipopolysaccharide (LPS)-induced inflammation. We assessed pentobarbital-induced LORR duration 24 h after LPS treatment in mice. Additionally, we examined the microglial response by immunohistochemistry and serum IL-6 and TNF-α concentrations in mice. LPS treatment significantly increased the duration of pentobarbital-induced LORR in mice treated with benzodiazepine receptor agonists (diazepam and brotizolam) and a GABA_A receptor agonist (muscimol) compared to that of mice treated with vehicle. These effects were blocked by bicuculline, a GABA_A receptor antagonist. LPS significantly increased the number of ionized calcium binding adapter molecule-1-positive hippocampal cells 2 and 24 h after treatment. The enhancing effect of diazepam in LPS-treated mice was significantly reduced by minocycline. These findings suggest that LPS enhances pentobarbital-induced LORR duration in mice treated with benzodiazepine via GABA_A receptor activity.

Delirium pathophysiology: An updated hypothesis of the etiology of acute brain failure

BACKGROUND

Delirium is the most common neuropsychiatric syndrome encountered by clinicians dealing with older adults and the medically ill and is best characterized by 5 core domains: cognitive deficits, attentional deficits, circadian rhythm dysregulation, emotional dysregulation, and alteration in psychomotor functioning.

DESIGN

An extensive literature review and consolidation of published data into a novel interpretation of known pathophysiological causes of delirium.

RESULTS

Available data suggest that numerous pathological factors may serve as precipitants for delirium, each having differential effects depending on patient-specific patient physiological characteristics (substrate). On the basis of an extensive literature search, a newly proposed theory, the systems integration failure hypothesis, was developed to bring together the most salient previously described theories, by describing the various contributions from each into a complex web of pathways-highlighting areas of intersection and commonalities and explaining how the variable contribution of these may lead to the development of various cognitive and behavioral dysfunctions characteristic of delirium. The specific cognitive and behavioral manifestations of the specific delirium picture result from a combination of neurotransmitter function and availability, variability in integration and processing of sensory information, motor responses to both external and internal cues, and the degree of breakdown in neuronal network connectivity, hence the term acute brain failure.

CONCLUSIONS

The systems integration failure hypothesis attempts to explain how the various proposed delirium pathophysiologic theories interact with each other, causing various clinically observed delirium phenotypes. A better understanding of the underlying pathophysiology of delirium may eventually assist in designing better prevention and management approaches.

Microglia permit climbing fiber elimination by promoting GABAergic inhibition in the developing cerebellum

Circuit refinement during postnatal development is finely regulated by neuron–neuron interactions. Recent studies suggest participation of microglia in this process but it is unclear how microglia cooperatively act with neuronal mechanisms. To examine roles of microglia, we ablate microglia by microglia-selective deletion of colony-stimulating factor 1 receptor (Csf1r) by crossing floxed-Csf1r and Iba1-iCre mice (Csf1r-cKO). In Csf1r-cKO mice, refinement of climbing fiber (CF) to Purkinje cell (PC) innervation after postnatal day 10 (P10)–P12 is severely impaired. However, there is no clear morphological evidence suggesting massive engulfment of CFs by microglia. In Csf1r-cKO mice, inhibitory synaptic transmission is impaired and CF elimination is restored by diazepam, which suggests that impairment of CF elimination is caused by a defect of GABAergic inhibition on PCs, a prerequisite for CF elimination. These results indicate that microglia primarily promote GABAergic inhibition and secondarily facilitate the mechanism for CF elimination inherent in PCs.

In the mammalian cerebellum, surplus synapses between climbing fibers (CF) and Purkinje cells (PC) are developmentally pruned. Here, Nakayama and colleagues show that ablation of microglia impairs pruning of CF-PC synapses because of dysfunction of GABAergic inhibition prerequisite for pruning.

Interaction of the α7-nicotinic subunit with its human-specific duplicated dupα7 isoform in mammalian cells: Relevance in human inflammatory responses

The α7 nicotinic receptor subunit and its partially duplicated human-specific dupα7 isoform are coexpressed in neuronal and non-neuronal cells. In these cells, α7 subunits form homopentameric α7 nicotinic acetylcholine receptors (α7-nAChRs) implicated in numerous pathologies. In immune cells, α7-nAChRs are essential for vagal control of inflammatory response in sepsis. Recent studies show that the dupα7 subunit is a dominant-negative regulator of α7-nAChR activity in Xenopus oocytes. However, its biological significance in mammalian cells, particularly immune cells, remains unexplored, as the duplicated form is indistinguishable from the original subunit in standard tests. Here, using immunocytochemistry, confocal microscopy, coimmunoprecipitation, FRET, flow cytometry, and ELISA, we addressed this challenge in GH4C1 rat pituitary cells and RAW264.7 murine macrophages transfected with epitope- and fluorescent protein-tagged α7 or dupα7. We used quantitative RT-PCR of dupα7 gene expression levels in peripheral blood mononuclear cells (PBMCs) from patients with sepsis to analyze its relationship with PBMC α7 mRNA levels and with serum concentrations of inflammatory markers. We found that a physical interaction between dupα7 and α7 subunits in both cell lines generates heteromeric nAChRs that remain mainly trapped in the endoplasmic reticulum. The dupα7 sequestration of α7 subunits reduced membrane expression of functional α7-nAChRs, attenuating their anti-inflammatory capacity in lipopolysaccharide-stimulated macrophages. Moreover, the PBMC's dupα7 levels correlated inversely with their α7 levels and directly with the magnitude of the patients' inflammatory state. These results indicate that dupα7 probably reduces human vagal anti-inflammatory responses and suggest its involvement in other α7-nAChR-mediated pathophysiological processes.