Neuromodulatory properties of inflammatory cytokines and their impact on neuronal excitability

Common Pathological Mechanisms and Risk Factors for Alzheimer's Disease and Type-2 Diabetes: Focus on Inflammation

BACKGROUND

Diabetes is considered as a risk factor for Alzheimer's Disease, but it is yet unclear whether this pathological link is reciprocal. Although Alzheimer's disease and diabetes appear as entirely different pathological entities affecting the Central Nervous System and a peripheral organ (pancreas), respectively, they share a common pathological core. Recent evidence suggests that in the pancreas in the case of diabetes, as in the brain for Alzheimer's Disease, the initial pathological event may be the accumulation of toxic proteins yielding amyloidosis. Moreover, in both pathologies, amyloidosis is likely responsible for local inflammation, which acts as a driving force for cell death and tissue degeneration. These pathological events are all inter-connected and establish a vicious cycle resulting in the progressive character of both pathologies.

OBJECTIVE

To address the literature supporting the hypothesis of a common pathological core for both diseases.

DISCUSSION

We will focus on the analogies and differences between the disease-related inflammatory changes in a peripheral organ, such as the pancreas, versus those observed in the brain. Recent evidence suggesting an impact of peripheral inflammation on neuroinflammation in Alzheimer's disease will be presented.

CONCLUSION

We propose that it is now necessary to consider whether neuroinflammation in Alzheimer's disease affects inflammation in the pancreas related to diabetes.

Classifying Intracortical Brain-Machine Interface Signal Disruptions Based on System Performance and Applicable Compensatory Strategies: A Review

Brain-machine interfaces (BMIs) record and translate neural activity into a control signal for assistive or other devices. Intracortical microelectrode arrays (MEAs) enable high degree-of-freedom BMI control for complex tasks by providing fine-resolution neural recording. However, chronically implanted MEAs are subject to a dynamic in vivo environment where transient or systematic disruptions can interfere with neural recording and degrade BMI performance. Typically, neural implant failure modes have been categorized as biological, material, or mechanical. While this categorization provides insight into a disruption's causal etiology, it is less helpful for understanding degree of impact on BMI function or possible strategies for compensation. Therefore, we propose a complementary classification framework for intracortical recording disruptions that is based on duration of impact on BMI performance and requirement for and responsiveness to interventions: (1) Transient disruptions interfere with recordings on the time scale of minutes to hours and can resolve spontaneously; (2) Reversible disruptions cause persistent interference in recordings but the root cause can be remedied by an appropriate intervention; (3) Irreversible compensable disruptions cause persistent or progressive decline in signal quality, but their effects on BMI performance can be mitigated algorithmically; and (4) Irreversible non-compensable disruptions cause permanent signal loss that is not amenable to remediation or compensation. This conceptualization of intracortical BMI disruption types is useful for highlighting specific areas for potential hardware improvements and also identifying opportunities for algorithmic interventions. We review recording disruptions that have been reported for MEAs and demonstrate how biological, material, and mechanical mechanisms of disruption can be further categorized according to their impact on signal characteristics. Then we discuss potential compensatory protocols for each of the proposed disruption classes. Specifically, transient disruptions may be minimized by using robust neural decoder features, data augmentation methods, adaptive machine learning models, and specialized signal referencing techniques. Statistical Process Control methods can identify reparable disruptions for rapid intervention. In-vivo diagnostics such as impedance spectroscopy can inform neural feature selection and decoding models to compensate for irreversible disruptions. Additional compensatory strategies for irreversible disruptions include information salvage techniques, data augmentation during decoder training, and adaptive decoding methods to down-weight damaged channels.

Drug Resistance in Epilepsy: Clinical Impact, Potential Mechanisms, and New Innovative Treatment Options

Epilepsy is a chronic neurologic disorder that affects over 70 million people worldwide. Despite the availability of over 20 antiseizure drugs (ASDs) for symptomatic treatment of epileptic seizures, about one-third of patients with epilepsy have seizures refractory to pharmacotherapy. Patients with such drug-resistant epilepsy (DRE) have increased risks of premature death, injuries, psychosocial dysfunction, and a reduced quality of life, so development of more effective therapies is an urgent clinical need. However, the various types of epilepsy and seizures and the complex temporal patterns of refractoriness complicate the issue. Furthermore, the underlying mechanisms of DRE are not fully understood, though recent work has begun to shape our understanding more clearly. Experimental models of DRE offer opportunities to discover, characterize, and challenge putative mechanisms of drug resistance. Furthermore, such preclinical models are important in developing therapies that may overcome drug resistance. Here, we will review the current understanding of the molecular, genetic, and structural mechanisms of ASD resistance and discuss how to overcome this problem. Encouragingly, better elucidation of the pathophysiological mechanisms underpinning epilepsies and drug resistance by concerted preclinical and clinical efforts have recently enabled a revised approach to the development of more promising therapies, including numerous potential etiology-specific drugs (“precision medicine”) for severe pediatric (monogenetic) epilepsies and novel multitargeted ASDs for acquired partial epilepsies, suggesting that the long hoped-for breakthrough in therapy for as-yet ASD-resistant patients is a feasible goal.

IL-6 Receptor Blockade by Tocilizumab Has Anti-absence and Anti-epileptogenic Effects in the WAG/Rij Rat Model of Absence Epilepsy

Increased expression of interleukin-6 (IL-6) both in cerebrospinal fluid (CSF) and plasma is closely associated with convulsive epilepsy and symptom severity of depression. By comparison, at present, little is known about the role of this cytokine in childhood (non-convulsive) absence epilepsy. The aim of this work was to investigate the potential effects of acute and chronic treatment with tocilizumab (TCZ, 10 and 30 mg/kg/day), on absence seizures, their development, and related psychiatric comorbidity in WAG/Rij rats. It is known that lipopolysaccharide (LPS)-induced changes in inflammatory processes increase absence epileptic activity. In order to study the central effects of TCZ, we investigated whether administration of this anti-IL-6R antibody could modulate the lipopolysaccharide (LPS) or IL-6-evoked changes in absence epileptic activity in WAG/Rij rats. Our results demonstrate that TCZ, at both doses, significantly reduced the development of absence seizures in adult WAG/Rij rats at 6 months of age (1 month after treatment suspension) compared with untreated controls, thus showing disease-modifying effects. Decreased absence seizure development at 6 months of age was also accompanied by reduced comorbid depressive-like behavior, whereas no effects were observed on anxiety-related behavior. Acute treatment with TCZ, at 30 mg/kg, had anti-absence properties lasting ~25 h. The co-administration TCZ with i.c.v. LPS or IL-6 showed that TCZ inhibited the worsening of absence seizures induced by both proinflammatory agents in the WAG/Rij rats, supporting a central anti-inflammatory-like protective action. These results suggest the possible role of IL-6 and consequent neuroinflammation in the epileptogenic process underlying the development and maintenance of absence seizures in WAG/Rij rats. Accordingly, IL-6 signaling could be a promising pharmacological target in absence epilepsy and depressive-like comorbidity.

The role of inflammation in epileptogenesis

Epilepsy is a chronic neurological disorder that has an extensive impact on a patient’s life. Accumulating evidence has suggested that inflammation participates in the progression of spontaneous and recurrent seizures. Pro-convulsant incidences can stimulate immune cells, augment the release of pro-inflammatory cytokines, elicit neuronal excitation as well as blood-brain barrier (BBB) dysfunction, and finally trigger the generation or recurrence of seizures. Understanding the pathogenic roles of inflammatory mediators, including inflammatory cytokines, cells, and BBB, in epileptogenesis will be beneficial for the treatment of epilepsy. In this systematic review, we performed a literature search on the PubMed database using the following keywords: “epilepsy” or “seizures” or “epileptogenesis”, and “immunity” or “inflammation” or “neuroinflammation” or “damage-associated molecular patterns” or “cytokines” or “chemokines” or “adhesion molecules” or “microglia” or “astrocyte” or “blood-brain barrier”. We summarized the classic inflammatory mediators and their pathogenic effects in the pathogenesis of epilepsy, based on the most recent findings from both human and animal model studies.

Mild inflammation causes a reduction in resting-state amplitude of low-frequency fluctuation in healthy adult males

Systemic inflammation has been associated with negative mood states and human sickness behaviour. Previous studies have shown an association between systemic inflammation and changes in task-related blood-oxygen-level-dependent activity and functional connectivity within large-scale networks. However, no study has examined the effect of inflammation on the magnitude of blood-oxygen-level-dependent low-frequency fluctuations at rest. We used a double-blind placebo-controlled crossover design to randomise 20 male subjects (aged 20-50 years) to receive either a Salmonella typhi vaccine or a placebo saline injection at two separate sessions. All participants underwent a resting-state functional magnetic resonance scan and a measure of inflammation (interleukin 6) and mood (Profile of Mood States) 3 h after injection. We compared the whole brain amplitude of low-frequency fluctuations between the vaccine and placebo conditions using a repeated measures design. Vaccine condition was associated with greater interleukin 6 levels (p < 0.001). Vaccine condition was also associated with lower amplitude of low-frequency fluctuations in the right and left frontal pole, superior frontal gyrus, paracingulate gyrus (Cluster 1) and the right mid and inferior frontal gyrus (Cluster 2) (p < 0.001, false discovery rate corrected). Lower amplitude of low-frequency fluctuations pertaining to first cluster correlated with greater total Profile of Mood States score (worse mood) (r = -0.38; p = 0.04). These results imply possible excitation/inhibition imbalance mechanisms during inflammation that may be a relevant target in psychiatric disease, especially mood disorders.

In vivo KPT-350 treatment decreases cortical hyperexcitability following traumatic brain injury

PRIMARY OBJECTIVE

We tested whether KPT-350, a novel selective inhibitor of nuclear export, could attenuate cortical network hyperexcitability, a major risk factor for developing post-traumatic epilepsy (PTE) following traumatic brain injury (TBI).

RESEARCH DESIGN

All mice in this study underwent TBI and were subsequently treated with either KPT-350 or vehicle during the post-injury latent period. Half of the animal cohort was used for electrophysiology while the other half was used for immunohistochemical analysis.

METHODS AND PROCEDURES

TBI was induced using the controlled cortical impact (CCI) model. Cortical network activity was recorded by evoking field potentials from deep layers of the cortex and analyzed using Matlab software. Immunohistochemistry coupled with fluorescence microscopy and Image J analysis detected changes in neuronal and glial markers.

MAIN OUTCOMES AND RESULTS

KPT-350 attenuated TBI-associated epileptiform activity and restored disrupted input-output responses in cortical brain slices. In vivo KPT-350 treatment reduced the loss of parvalbumin-(+) GABAergic interneurons after CCI but did not significantly change CCI-induced loss of somatostatin-(+) GABAergic interneurons, nor did it reduce reactivity of GFAP and Iba1 glial markers.

CONCLUSION

KPT-350 can prevent cortical hyperexcitability and reduce the loss of parvalbumin-(+) GABAergic inhibitory neurons, making it a potential therapeutic option for preventing PTE.

Endoplasmic reticulum stress increases inflammatory cytokines in an epilepsy mouse model Gabrg2+/Q390X knockin: A link between genetic and acquired epilepsy?

OBJECTIVE

Neuroinflammation is a major theme in epilepsy, which has been characterized in acquired epilepsy but is poorly understood in genetic epilepsy. γ-Aminobutyric acid type A receptor subunit gene mutations are significant causes of epilepsy, and we have studied the pathophysiology directly resulting from defective receptor channels. Here, we determined the proinflammatory factors in a genetic mouse model, the Gabrg2^+/Q390X knockin (KI). We have identified increased cytokines in multiple brain regions of the KI mouse throughout different developmental stages and propose that accumulation of the trafficking-deficient mutant protein may increase neuroinflammation, which would be a novel mechanism for genetic epilepsy.

METHODS

We used enzyme-linked immunosorbent assay, immunoprecipitation, nuclei purification, immunoblot, immunohistochemistry, and confocal microscopy to characterize increased neuroinflammation and its potential causes in a Gabrg2^+/Q390X KI mouse and a Gabrg2^+/- knockout (KO) mouse, each associated with a different epilepsy syndrome with different severities.

RESULTS

We found that proinflammatory cytokines such as tumor necrosis factor alpha, interleukin 1-beta (IL-1β), and IL-6 were increased in the KI mice but not in the KO mice. A major underlying basis for the discrepancy in cytokine expression between the two mouse models is likely chronic mutant protein accumulation and endoplasmic reticulum (ER) stress. The presence of mutant protein dampened cytokine induction upon further cellular stimulation or external stress such as elevated temperature. Pharmacological induction of ER stress upregulated cytokine expression in the wild-type and KO but not in the KI mice. The increased cytokine expression was independent of seizure occurrence, because it was upregulated in both mice and cultured neurons.

SIGNIFICANCE

Together, these data demonstrate a novel pathophysiology for genetic epilepsy, increased neuroinflammation, which is a common mechanism for acquired epilepsy. The findings thus provide the first link of neuroinflammation between genetic epilepsy associated with an ion channel gene mutation and acquired epilepsy.

Microglial phagocytosis dysfunction in the dentate gyrus is related to local neuronal activity in a genetic model of epilepsy

OBJECTIVE

Microglial phagocytosis of apoptotic cells is an essential component of the brain regenerative response during neurodegeneration. Whereas it is very efficient in physiological conditions, it is impaired in mouse and human mesial temporal lobe epilepsy, and now we extend our studies to a model of progressive myoclonus epilepsy type 1 in mice lacking cystatin B (CSTB).

METHODS

We used confocal imaging and stereology-based quantification of apoptosis and phagocytosis of the hippocampus of Cstb knockout (KO) mice, an in vitro model of phagocytosis and siRNAs to acutely reduce Cstb expression, and a virtual three-dimensional (3D) model to analyze the physical relationship between apoptosis, phagocytosis, and active hippocampal neurons.

RESULTS

Microglial phagocytosis was impaired in the hippocampus of Cstb KO mice at 1 month of age, when seizures arise and hippocampal atrophy begins. This impairment was not related to the lack of Cstb in microglia alone, as shown by in vitro experiments with microglial Cstb depletion. The phagocytosis impairment was also unrelated to seizures, as it was also present in Cstb KO mice at postnatal day 14, before seizures begin. Importantly, phagocytosis impairment was restricted to the granule cell layer and spared the subgranular zone, where there are no active neurons. Furthermore, apoptotic cells (both phagocytosed and not phagocytosed) in Cstb-deficient mice were at close proximity to active cFos⁺ neurons, and a virtual 3D model demonstrated that the physical relationship between apoptotic cells and cFos⁺ neurons was specific for Cstb KO mice.

SIGNIFICANCE

These results suggest a complex crosstalk between apoptosis, phagocytosis, and neuronal activity, hinting that local neuronal activity could be related to phagocytosis dysfunction in Cstb KO mice. Overall, these data suggest that phagocytosis impairment is an early feature of hippocampal damage in epilepsy and opens novel therapeutic approaches for epileptic patients based on targeting microglial phagocytosis.

Markers in Status Epilepticus Prognosis

Status epilepticus (SE) is a neurologic emergency with high morbidity and mortality. The assessment of a patient's prognosis is crucial in making treatment decisions. In this review, we discuss various markers that have been used to prognosticate SE in terms of recurrence, mortality, and functional outcome. These markers include demographic, clinical, electrophysiological, biochemical, and structural data. The heterogeneity of SE etiology and semiology renders development of prognostic markers challenging. Currently, prognostication in SE is limited to a few clinical scores. Future research should integrate clinical, genetic and epigenetic, metabolic, inflammatory, and structural biomarkers into prognostication models to approach "personalized medicine" in prognostication of outcomes after SE.

Immediate inhibition of spinal secretory phospholipase A2 prevents the pain and elevated spinal neuronal hyperexcitability and neuroimmune regulatory genes that develop with nerve root compression

Cervical nerve root injury induces a host of inflammatory mediators in the spinal cord that initiate and maintain neuronal hyperexcitability and pain. Secretory phospholipase A2 (sPLA2) is an enzyme that has been implicated as a mediator of pain onset and maintenance in inflammation and neural injury. Although sPLA2 modulates nociception and excitatory neuronal signaling in vitro, its effects on neuronal activity and central sensitization early after painful nerve root injury are unknown. This study investigated whether inhibiting spinal sPLA2 at the time of nerve root compression (NRC) modulates the pain, dorsal horn hyperexcitability, and spinal genes involved in glutamate signaling, nociception, and inflammation that are seen early after injury. Rats underwent a painful C7 NRC injury with immediate intrathecal administration of the sPLA2 inhibitor thioetheramide-phosphorlycholine. Additional groups underwent either injury alone or sham surgery. One day after injury, behavioral sensitivity, spinal neuronal excitability, and spinal cord gene expression for glutamate receptors (mGluR5 and NR1) and transporters (GLT1 and EAAC1), the neuropeptide substance P, and pro-inflammatory cytokines (TNFα, IL1α, and IL1β) were assessed. Treatment with the sPLA2 inhibitor prevented mechanical allodynia, attenuated neuronal hyperexcitability in the spinal dorsal horn, restored the proportion of spinal neurons classified as wide dynamic range, and reduced genes for mGluR5, substance P, IL1α, and IL1β to sham levels. These findings indicate spinal regulation of central sensitization after painful neuropathy and suggest that spinal sPLA2 is implicated in those early spinal mechanisms of neuronal excitability, perhaps via glutamate signaling, neurotransmitters, or inflammatory cascades.

Immunohistological and Ultrastructural Study of the Inflammatory Response to Perforated Polyimide Cortical Implants: Mechanisms Underlying Deterioration of Electrophysiological Recording Quality

The deterioration of field potential (FP) recording quality and yield by in vivo multielectrode arrays (MEA) within days to weeks of implantation severely limits progress in basic and applied brain research. The prevailing hypothesis is that implantation of MEA platforms initiate and perpetuate inflammatory processes which culminate in the formation of scar tissue (the foreign body response, FBR) around the implant. The FBR leads to progressive degradation of the recording qualities by displacing neurons away from the electrode surfaces, increasing the resistance between neurons (current source) and the sensing pads and by reducing the neurons’ excitable membrane properties and functional synaptic connectivity through the release of pro-inflammatory cytokines. Meticulous attempts to causally relate the cellular composition, cell density, and electrical properties of the FBR have failed to unequivocally correlate the deterioration of recording quality with the histological severity of the FBR. Based on confocal and electron microscope analysis of thin sections of polyimide based MEA implants along with the surrounding brain tissue at different points in time after implantation, we propose that abrupt FP amplitude attenuation occurs at the implant/brain-parenchyma junction as a result of high seal resistance insulation formed by adhering microglia to the implant surfaces. In contrast to the prevailing hypothesis, that FP decrease occurs across the encapsulating scar of the implanted MEA, this mechanism potentially explains why no correlations have been found between the dimensions and density of the FBR and the recording quality. Recognizing that the seal resistance formed by adhering-microglia to the implant constitutes a downstream element undermining extracellular FP recordings, suggests that approaches to mitigate the formation of the insulating glial could lead to improved recording quality and yield.

Microglial mTOR is Neuronal Protective and Antiepileptogenic in the Pilocarpine Model of Temporal Lobe Epilepsy

Excessive activation of mammalian target of rapamycin (mTOR) signaling is epileptogenic in genetic epilepsy. However, the exact role of microglial mTOR in acquired epilepsy remains to be clarified. In the present study, we found that mTOR is strongly activated in microglia following excitatory injury elicited by status epilepticus. To determine the role of microglial mTOR signaling in excitatory injury and epileptogenesis, we generated mice with restrictive deletion of mTOR in microglia. Both male and female mice were used in the present study. We found that mTOR-deficient microglia lost their typical proliferative and inflammatory responses to excitatory injury, whereas the proliferation of astrocytes was preserved. In addition, mTOR-deficient microglia did not effectively engulf injured/dying neurons. More importantly, microglial mTOR-deficient mice displayed increased neuronal loss and developed more severe spontaneous seizures. These findings suggest that microglial mTOR plays a protective role in mitigating neuronal loss and attenuating epileptogenesis in the excitatory injury model of epilepsy.SIGNIFICANCE STATEMENT The mammalian target of rapamycin (mTOR) pathway is strongly implicated in epilepsy. However, the effect of mTOR inhibitors in preclinical models of acquired epilepsy is inconsistent. The broad presence of mTOR signaling in various brain cells could prevent mTOR inhibitors from achieving a net therapeutic effect. This conundrum has spurred further investigation of the cell type-specific effects of mTOR signaling in the CNS. We found that activation of microglial mTOR is antiepileptogenic. Thus, microglial mTOR activation represents a novel antiepileptogenic route that appears to parallel the proepileptogenic route of neuronal mTOR activation. This may explain why the net effect of mTOR inhibitors is paradoxical in the acquired models of epilepsy. Our findings could better guide the use of mTOR inhibitors in preventing acquired epilepsy.

Role of Innate Immune Receptor TLR4 and its endogenous ligands in epileptogenesis

Understanding the interplay between the innate immune system, neuroinflammation, and epilepsy might offer a novel perspective in the quest of exploring new treatment strategies. Due to the complex pathology underlying epileptogenesis, no disease-modifying treatment is currently available that might prevent epilepsy after a plausible epileptogenic insult despite the advances in pre-clinical and clinical research. Neuroinflammation underlies the etiopathogenesis of epilepsy and convulsive disorders with Toll-like receptor (TLR) signal transduction being highly involved. Among TLR family members, TLR4 is an innate immune system receptor and lipopolysaccharide (LPS) sensor that has been reported to contribute to epileptogenesis by regulating neuronal excitability. Herein, we discuss available evidence on the role of TLR4 and its endogenous ligands, the high mobility group box 1 (HMGB1) protein, the heat shock proteins (HSPs) and the myeloid related protein 8 (MRP8), in epileptogenesis and post-traumatic epilepsy (PTE). Moreover, we provide an account of the promising findings of TLR4 modulation/inhibition in experimental animal models with therapeutic impact on seizures.

The Bidirectional Relationship Between Sleep and Inflammation Links Traumatic Brain Injury and Alzheimer's Disease

Traumatic brain injury (TBI) and Alzheimer's disease (AD) are diseases during which the fine-tuned autoregulation of the brain is lost. Despite the stark contrast in their causal mechanisms, both TBI and AD are conditions which elicit a neuroinflammatory response that is coupled with physical, cognitive, and affective symptoms. One commonly reported symptom in both TBI and AD patients is disturbed sleep. Sleep is regulated by circadian and homeostatic processes such that pathological inflammation may disrupt the chemical signaling required to maintain a healthy sleep profile. In this way, immune system activation can influence sleep physiology. Conversely, sleep disturbances can exacerbate symptoms or increase the risk of inflammatory/neurodegenerative diseases. Both TBI and AD are worsened by a chronic pro-inflammatory microenvironment which exacerbates symptoms and worsens clinical outcome. Herein, a positive feedback loop of chronic inflammation and sleep disturbances is initiated. In this review, the bidirectional relationship between sleep disturbances and inflammation is discussed, where chronic inflammation associated with TBI and AD can lead to sleep disturbances and exacerbated neuropathology. The role of microglia and cytokines in sleep disturbances associated with these diseases is highlighted. The proposed sleep and inflammation-mediated link between TBI and AD presents an opportunity for a multifaceted approach to clinical intervention.

Presynaptic L-Type Ca2+ Channels Increase Glutamate Release Probability and Excitatory Strength in the Hippocampus during Chronic Neuroinflammation

Neuroinflammation is involved in the pathogenesis of several neurologic disorders, including epilepsy. Both changes in the input/output functions of synaptic circuits and cell Ca²⁺ dysregulation participate in neuroinflammation, but their impact on neuron function in epilepsy is still poorly understood. Lipopolysaccharide (LPS), a toxic byproduct of bacterial lysis, has been extensively used to stimulate inflammatory responses both in vivo and in vitro LPS stimulates Toll-like receptor 4, an important mediator of the brain innate immune response that contributes to neuroinflammation processes. Although we report that Toll-like receptor 4 is expressed in both excitatory and inhibitory mouse hippocampal neurons (both sexes), its chronic stimulation by LPS induces a selective increase in the excitatory synaptic strength, characterized by enhanced synchronous and asynchronous glutamate release mechanisms. This effect is accompanied by a change in short-term plasticity with decreased facilitation, decreased post-tetanic potentiation, and increased depression. Quantal analysis demonstrated that the effects of LPS on excitatory transmission are attributable to an increase in the probability of release associated with an overall increased expression of L-type voltage-gated Ca²⁺ channels that, at presynaptic terminals, abnormally contributes to evoked glutamate release. Overall, these changes contribute to the excitatory/inhibitory imbalance that scales up neuronal network activity under inflammatory conditions. These results provide new molecular clues for treating hyperexcitability of hippocampal circuits associated with neuroinflammation in epilepsy and other neurologic disorders.SIGNIFICANCE STATEMENT Neuroinflammation is thought to have a pathogenetic role in epilepsy, a disorder characterized by an imbalance between excitation/inhibition. Fine adjustment of network excitability and regulation of synaptic strength are both implicated in the homeostatic maintenance of physiological levels of neuronal activity. Here, we focused on the effects of chronic neuroinflammation induced by lipopolysaccharides on hippocampal glutamatergic and GABAergic synaptic transmission. Our results show that, on chronic stimulation with lipopolysaccharides, glutamatergic, but not GABAergic, neurons exhibit an enhanced synaptic strength and changes in short-term plasticity because of an increased glutamate release that results from an anomalous contribution of L-type Ca²⁺ channels to neurotransmitter release.

Modulating neuroinflammation and oxidative stress to prevent epilepsy and improve outcomes after traumatic brain injury

Traumatic brain injury (TBI) is a leading cause of death and disability in young adults worldwide. TBI survival is associated with persistent neuropsychiatric and neurological impairments, including posttraumatic epilepsy (PTE). To date, no pharmaceutical treatment has been found to prevent PTE or ameliorate neurological/neuropsychiatric deficits after TBI. Brain trauma results in immediate mechanical damage to brain cells and blood vessels that may never be fully restored given the limited regenerative capacity of brain tissue. This primary insult unleashes cascades of events, prominently including neuroinflammation and massive oxidative stress that evolve over time, expanding the brain injury, but also clearing cellular debris and establishing homeostasis in the region of damage. Accumulating evidence suggests that oxidative stress and neuroinflammatory sequelae of TBI contribute to posttraumatic epileptogenesis. This review will focus on possible roles of reactive oxygen species (ROS), their interactions with neuroinflammation in posttraumatic epileptogenesis, and emerging therapeutic strategies after TBI. We propose that inhibitors of the professional ROS-generating enzymes, the NADPH oxygenases and myeloperoxidase alone, or combined with selective inhibition of cyclooxygenase mediated signaling may have promise for the treatment or prevention of PTE and other sequelae of TBI. This article is part of the special issue entitled 'New Epilepsy Therapies for the 21st Century - From Antiseizure Drugs to Prevention, Modification and Cure of Epilepsy'.

Anti-depression effects of ketogenic diet are mediated via the restoration of microglial activation and neuronal excitability in the lateral habenula

Depression is a severe neuropsychiatric disorder, of which the underlying pathological mechanisms remain unclear. The ketogenic diet (KD) has been reported to exhibit preventative effects on depressive-like behaviors in rodents. However, the therapeutic effects of KD on depressive-like behaviors have not been illustrated thus far. Here, we found that KD treatment dramatically ameliorated depressive-like behaviors in both repeated social defeat stress (R-SDS) and lipopolysaccharide (LPS) models, indicating the potential therapeutic effects of KD on depression. Our electrophysiological studies further showed that neuronal excitability was increased in the lateral habenula (LHb) of mice exposed to R-SDS or LPS, which can be reversed in the presence of KD treatment. Moreover, R-SDS and LPS were also found to induce robust microglial inflammatory activation in the LHb. Importantly, these phenotypes were rescued in mice fed with KD. In addition, we found that the protein level of innate immune receptor Trem2 in the LHb was significantly decreased in depression models. Specific knockdown of Trem2 in LHb microglia induced depressive-like behaviors, increased neuronal excitability as well as robust microglial inflammatory activation. Altogether, we demonstrated the therapeutic effects of KD on depressive-like behaviors, which are probably mediated via the restoration of microglial inflammatory activation and neuronal excitability. Besides, we also proposed an unrecognized function of Trem2 in the LHb for depression. Our study sheds light on the pathogenesis of depression and thereby offers a potential therapeutic intervention.

Neuroimmune Mechanisms and Sex/Gender-Dependent Effects in the Pathophysiology of Mental Disorders

Innate and adaptive immune mechanisms have emerged as critical regulators of CNS homeostasis and mental health. A plethora of immunologic factors have been reported to interact with emotion- and behavior-related neuronal circuits, modulating susceptibility and resilience to mental disorders. However, it remains unclear whether immune dysregulation is a cardinal causal factor or an outcome of the pathologies associated with mental disorders. Emerging variations in immune regulatory pathways based on sex differences provide an additional framework for discussion in these psychiatric disorders. In this review, we present the current literature pertaining to the effects that disrupted immune pathways have in mental disorder pathophysiology, including immune dysregulation in CNS and periphery, microglial activation, and disturbances of the blood-brain barrier. In addition, we present the suggested origins of such immune dysregulation and discuss the gender and sex influence of the neuroimmune substrates that contribute to mental disorders. The findings challenge the conventional view of these disorders and open the window to a diverse spectrum of innovative therapeutic targets that focus on the immune-specific pathophenotypes in neuronal circuits and behavior. SIGNIFICANCE STATEMENT: The involvement of gender-dependent inflammatory mechanisms on the development of mental pathologies is gaining momentum. This review addresses these novel factors and presents the accumulating evidence introducing microglia and proinflammatory elements as critical components and potential targets for the treatment of mental disorders.

Inflammation and Corticospinal Functioning in Multiple Sclerosis: A TMS Perspective

Transcranial magnetic stimulation (TMS) has been employed in multiple sclerosis (MS) to assess the integrity of the corticospinal tract and the corpus callosum and to explore some physiological properties of the motor cortex. Specific alterations of TMS measures have been strongly associated to different pathophysiological mechanisms, particularly to demyelination and neuronal loss. Moreover, TMS has contributed to investigate the neurophysiological basis of MS symptoms, particularly those not completely explained by conventional structural damage, such as fatigue. However, variability existing between studies suggests that alternative mechanisms should be involved. Knowledge of MS pathophysiology has been enriched by experimental studies in animal models (i.e., experimental autoimmune encephalomyelitis) demonstrating that inflammation alters synaptic transmission, promoting hyperexcitability and neuronal damage. Accordingly, TMS studies have demonstrated an imbalance between cortical excitation and inhibition in MS. In particular, cerebrospinal fluid concentrations of different proinflammatory and anti-inflammatory molecules have been associated to corticospinal hyperexcitability, highlighting that inflammatory synaptopathy may represent a key pathophysiological mechanism in MS. In this perspective article, we discuss whether corticospinal excitability alterations assessed with TMS in MS patients could be useful to explain the pathophysiological correlates and their relationships with specific MS clinical characteristics and symptoms. Furthermore, we discuss evidence indicating that, in MS patients, inflammatory synaptopathy could be present since the early phases, could specifically characterize relapses, and could progressively increase during the disease course.

Cancer Exacerbates Chemotherapy-Induced Sensory Neuropathy

For the constellation of neurologic disorders known as chemotherapy-induced peripheral neuropathy, mechanistic understanding and treatment remain deficient. Here, we present the first evidence that chronic sensory neuropathy depends on nonlinear interactions between cancer and chemotherapy. Global transcriptional profiling of dorsal root ganglia revealed differential expression, notably in regulators of neuronal excitability, metabolism, and inflammatory responses, all of which were unpredictable from effects observed with either chemotherapy or cancer alone. Systemic interactions between cancer and chemotherapy also determined the extent of deficits in sensory encoding and ion channel protein expression by single mechanosensory neurons, with the potassium ion channel Kv3.3 emerging as one potential contributor to sensory neuron dysfunction. Validated measures of sensorimotor behavior in awake, behaving animals revealed dysfunction after chronic chemotherapy treatment was exacerbated by cancer. Notably, errors in precise forelimb placement emerged as a novel behavioral deficit unpredicted by our previous study of chemotherapy alone. These original findings identify novel contributors to peripheral neuropathy and emphasize the fundamental dependence of neuropathy on the systemic interaction between chemotherapy and cancer. SIGNIFICANCE: These findings highlight the need to account for pathobiological interactions between cancer and chemotherapy as a major contributor to neuropathy and will have significant and immediate impact on future investigations in this field.

Potential Cytokine Biomarkers in Intellectual Disability

Intellectual disability (ID), previously called mental retardation, is the most common neurodevelopmental disorder characterized by life-long intellectual and adaptive functioning impairments that have an impact on individuals, families, and society. Its prevalence is estimated to 3% of the general population and its etiology is still insufficiently understood. Besides the involvement of genetic and environmental factors, immunological dysfunctions have been also suggested to contribute to the pathophysiology of ID. Over the years, immune biomarkers related to ID have gained significant attention and researchers have begun to look at possible cytokine profiles in individuals suffered from this disorder. In fact, in addition to playing crucial physiological roles in the majority of normal neurodevelopmental processes, cytokines exert an important role in neuroinflammation under pathological conditions, and interactions between the immune system and central nervous system have long been under investigation. Cytokine levels imbalance has been reported associated with some behavioral characteristics and the onset of some syndromic forms of ID. In this review, we will focus on immunological biomarkers, especially the cytokine profiles that have been identified in people with ID. Thus, data reported and discussed in the present paper may provide additional information to start further studies and to plan strategies for early identification and managing of ID.

Dexamethasone as Abortive Treatment for Refractory Seizures or Status Epilepticus in the Inpatient Setting

Refractory seizures or status epilepticus (RS/SE) continues to be a challenge in the inpatient setting. Failure to abort a seizure with antiepileptic drugs (AEDs) may lead to intubation and treatment with general anesthesia exposing patients to complications, extending hospitalization, and increasing the cost of care. Studies have shown a key role of inflammatory mediators in seizure generation and termination. We describe 4 patients with RS/SE that was aborted when dexamethasone was added to conventional AEDs: a 61-year-old female with temporal lobe epilepsy who presented with delirium, nonconvulsive status epilepticus, and oculomyoclonic status; a 56-year-old female with history of traumatic left frontal lobe hemorrhage who developed right face and hand epilepsia partialis continua followed by refractory focal clonic seizures; a 51-year-old male with history of traumatic intracranial hemorrhage who exhibited left-sided epilepsia partialis continua; and a 75-year-old female with history of breast cancer who manifested nonconvulsive status epilepticus and refractory focal clonic seizures. All patients continued experiencing RS/SE despite first- and second-line therapy, and one patient continued to experience RS/SE despite third-line therapy. Failure to abort RS/SE with conventional therapy motivated us to administer intravenous dexamethasone. A 10-mg load was given (except in one patient) followed by 4.0- 5.2 mg q6h. All clinical and electrographic seizures stopped 3-4 days after starting dexamethasone. When dexamethasone was discontinued 1-3 days after seizures stopped, all patients remained seizure-free on 2-3 AEDs. The cessation of RS/SE when dexamethasone was added to conventional antiseizure therapy suggests that inflammatory processes are involved in the pathogenesis of RS/SE.

Analysis of gut microbiome, nutrition and immune status in autism spectrum disorder: a case-control study in Ecuador

Most studies on autism spectrum disorder (ASD) risk factors have been conducted in developed countries where ethnicity and environment are different than in developing countries. We compared nutritional status, immune response and microbiota composition in mestizo children with ASD with matched controls in Ecuador. Twenty-five cases and 35 controls were matched by age, sex and school location. The prevalence of under- and overweight was higher in children with ASD. Nutritional differences were accompanied by abnormal food habits and more frequent gastrointestinal symptoms in children with ASD. Also, greater serum concentrations of TGF-β1 were observed in children with ASD. Finally, there was greater alpha diversity and abundance of Bacteroides (2 OTUs), Akkermansia, Coprococcus and different species of Ruminococcus in ASD children.

Microglia alterations in neurodegenerative diseases and their modeling with human induced pluripotent stem cell and other platforms

Microglia are the main innate immune cells of the central nervous system (CNS). Unlike neurons and glial cells, which derive from ectoderm, microglia migrate early during embryo development from the yolk-sac, a mesodermal-derived structure. Microglia regulate synaptic pruning during development and induce or modulate inflammation during aging and chronic diseases. Microglia are sensitive to brain injuries and threats, altering their phenotype and function to adopt a so-called immune-activated state in response to any perceived threat to the CNS integrity. Here, we present a short overview on the role of microglia in human neurodegenerative diseases and provide an update on the current model systems to study microglia, including cell lines, iPSC-derived microglia with an emphasis in their transcriptomic profile and integration into 3D brain organoids. We present various strategies to model and study their role in neurodegeneration providing a relevant platform for the development of novel and more effective therapies.

Remitted depression and cognition in HIV: The role of cortisol and inflammation

In major depressive disorder (MDD) and remitted MDD (rMDD) alterations in cortisol and inflammation are associated with cognitive difficulties, but these relationships have not been investigated in HIV. We used secondary data from a placebo-controlled, cross-over study of cognitive performance following a probe of the hypothalamic-pituitary-adrenal (HPA) axis (low dose hydrocortisone; LDH 10 mg) in 65 people with HIV (PWH; 36 women). Using placebo data, we examined sex-specific associations between two biomarkers - basal afternoon salivary cortisol and salivary inflammatory cytokines - cognition, and rMDD. Salivary cortisol and inflammatory biomarkers were sampled across the 5 -h study. The panel of inflammatory markers included interleukin (IL)-6, IL-8, IL-1β, tumor necrosis factor-(TNF)-α, CRP, interferon gamma-induced protein (IP-10), monocyte chemotactic protein (MCP)-1, monokine induced by interferon (MIG), matrix metalloproteinase MMP-9, and MMP-1. Learning, memory, attention/concentration, and executive function were assessed 30 min and 4 h after the placebo intervention; visuospatial ability was also assessed 30 min after the placebo intervention. For women but not men with HIV, basal cortisol concentrations were higher in rMDD versus noMDD groups, and related to poorer learning and memory. For men and women with HIV, basal inflammatory cytokines were higher in rMDD versus noMDD groups, but were negatively related to cognition independent of rMDD status. Cortisol and cytokines relate to cognition in PWH, but the associations depended on sex, rMDD status, and their interaction.

Minocycline prevents neuronal hyperexcitability and neuroinflammation in medial prefrontal cortex, as well as memory impairment caused by repeated toluene inhalation in adolescent rats

Toluene can be intentionally misused by adolescents to experience psychoactive effects. Toluene has a complex mechanism of action and broad behavioral effects, among which memory impairment is reported consistently. We have previously reported that repeated toluene inhalation (8000 ppm) increases layer 5 prelimbic pyramidal cells' excitability in the medial prefrontal cortex (mPFC) of adolescent rats. Toluene also produces reactive oxygen species (ROS), which activate glial cells. Here, we tested the hypothesis that the anti-inflammatory agent minocycline would decrease toluene's effects because it inhibits NF-κB (nuclear factor enhancer of the kappa light chains of activated B cells) and reduces pro-inflammatory cytokine and ROS production. Our results show that minocycline (50 mg/kg, ip, for 10 days) prevents the hyperexcitability of mPFC neurons observed after repeated 8000 ppm toluene exposure (30 min/day, 2×/day for 10 days). Minocycline prevents toluene-induced hyperexcitability by a mechanism that averts the loss of the slow calcium-dependent potassium current, and normalizes mPFC neurons' firing frequency. These effects are accompanied by significant decreased expression of astrocytes and activated microglia in the mPFC, reduced NLRP3 inflammasome activation and mRNA expression levels of the pro-inflammatory cytokine interleukin 1β (IL-1β), as well as increased mRNA expression of the anti-inflammatory cytokine transforming growth factor β (TGF-β). Minocycline also prevents toluene-induced memory impairment in adolescent rats in the passive avoidance task and the temporal order memory test in which the mPFC plays a central role. These results show that neuroinflammation produces several effects of repeated toluene administration at high concentrations, and minocycline can significantly prevent them.

Moderate to severe acute pain disturbs motor cortex intracortical inhibition and facilitation in orthopedic trauma patients: A TMS study

OBJECTIVE

Primary motor (M1) cortical excitability alterations are involved in the development and maintenance of chronic pain. Less is known about M1-cortical excitability implications in the acute phase of an orthopedic trauma. This study aims to assess acute M1-cortical excitability in patients with an isolated upper limb fracture (IULF) in relation to pain intensity.

METHODS

Eighty-four (56 IULF patients <14 days post-trauma and 28 healthy controls). IULF patients were divided into two subgroups according to pain intensity (mild versus moderate to severe pain). A single transcranial magnetic stimulation (TMS) session was performed over M1 to compare groups on resting motor threshold (rMT), short-intracortical inhibition (SICI), intracortical facilitation (ICF), and long-interval cortical inhibition (LICI).

RESULTS

Reduced SICI and ICF were found in IULF patients with moderate to severe pain, whereas mild pain was not associated with M1 alterations. Age, sex, and time since the accident had no influence on TMS measures.

DISCUSSION

These findings show altered M1 in the context of acute moderate to severe pain, suggesting early signs of altered GABAergic inhibitory and glutamatergic facilitatory activities.

Soluble ST2 Is Associated With New Epileptiform Abnormalities Following Nontraumatic Subarachnoid Hemorrhage

Background and Purpose- We evaluated the association between 2 types of predictors of delayed cerebral ischemia after nontraumatic subarachnoid hemorrhage, including biomarkers of the innate immune response and neurophysiologic changes on continuous electroencephalography. Methods- We studied subarachnoid hemorrhage patients that had at least 72 hours of continuous electroencephalography and blood samples collected within the first 5 days of symptom onset. We measured inflammatory biomarkers previously associated with delayed cerebral ischemia and functional outcome, including soluble ST2 (sST2), IL-6 (interleukin-6), and CRP (C-reactive protein). Serial plasma samples and cerebrospinal fluid sST2 levels were available in a subgroup of patients. Neurophysiologic changes were categorized into new or worsening epileptiform abnormalities (EAs) or new background deterioration. The association of biomarkers with neurophysiologic changes were evaluated using the Wilcoxon rank-sum test. Plasma and cerebrospinal fluid sST2 were further examined longitudinally using repeated measures mixed-effects models. Results- Forty-six patients met inclusion criteria. Seventeen (37%) patients developed new or worsening EAs, 21 (46%) developed new background deterioration, and 8 (17%) developed neither. Early (day, 0-5) plasma sST2 levels were higher among patients with new or worsening EAs (median 115 ng/mL [interquartile range, 73.8-197]) versus those without (74.7 ng/mL [interquartile range, 44.8-102]; P=0.024). Plasma sST2 levels were similar between patients with or without new background deterioration. Repeated measures mixed-effects modeling that adjusted for admission risk factors showed that the association with new or worsening EAs remained independent for both plasma sST2 (β=0.41 [95% CI, 0.09-0.73]; P=0.01) and cerebrospinal fluid sST2 (β=0.97 [95% CI, 0.14-1.8]; P=0.021). IL-6 and CRP were not associated with new background deterioration or with new or worsening EAs. Conclusions- In patients admitted with subarachnoid hemorrhage, sST2 level was associated with new or worsening EAs but not new background deterioration. This association may identify a link between a specific innate immune response pathway and continuous electroencephalography abnormalities in the pathogenesis of secondary brain injury after subarachnoid hemorrhage.

Seizure-induced neuroinflammation contributes to ectopic neurogenesis and aggressive behavior in pilocarpine-induced status epilepticus mice

Epilepsy is a chronic neurological disorder often associated with recurrent seizures. A growing body of evidence suggests that seizures cause structural and functional alterations of the brain. It is reported that behavioral abnormalities frequently occur in patients with epilepsy and experimental epilepsy models. However, the precise pathological mechanisms associated with these epilepsy comorbidities remain largely unknown. Neurogenesis persists throughout life in the hippocampal dentate gyrus (DG) to maintain proper brain function. However, aberrant neurogenesis usually generates abnormal neural circuits and consequently causes neuronal dysfunction. Neuroinflammatory responses are well known to affect neurogenesis and lead to aberrant reorganization of neural networks in the hippocampal DG. Here, in this study, we observed a significant increase in neuroinflammation and in the proliferation and survival of newborn granular cells in the hippocampus of pilocarpine-induced status epilepticus (SE) mice. More importantly, these proliferating and surviving newborn granular cells are largely ectopically located in the hippocampal DG hilus region. Our behavior test demonstrated that SE mice displayed severe aggressive behavior. Pharmacological inhibition of neuroinflammation, however, suppressed the ectopic neurogenesis and countered the enhanced aggressive behavior in SE mice, indicating that seizure-induced neuroinflammation may contribute to ectopic neurogenesis and aggressive behavior in SE mice. These findings establish a key role for neuroinflammation in seizure-induced aberrant neurogenesis and aggressive behavior. Suppressing neuroinflammation in the epileptic brain may reduce ectopic neurogenesis and effectively block the pathophysiological process that leads to aggressive behavior in TLE mice.

Pregabalin inhibits in vivo and in vitro cytokine secretion and attenuates spleen inflammation in Lipopolysaccharide/Concanavalin A -induced murine models of inflammation

Immune system alteration has been implicated in the pathogenesis of chronic pain conditions, epilepsy and generalized anxiety disorder. Targeting cytokines has recently been proposed for the management of such conditions. Pregabalin (PGB) is an antiepileptic agent used for the management of these conditions. However, little is known about its immunomodulatory effects on cytokine secretion in vivo and in vitro. Hence, a mitogen (Lipopolysaccharide [LPS] or Concanavalin A [ConA])-induced murine model of inflammation was used to investigate the effect of PGB on in vivo and in vitro IL-1β, IL-6, TNF-α and IL-2 cytokine secretion using ELISA. In addition, PGB effect on spleen histology, as a lymphoid organ, was examined. Our results revealed that PGB significantly inhibited the secretion of ConA-induced IL-6 secretion, basal and ConA-induced TNF-α and IL-2 secretion in splenocytes in vitro. In vivo, PGB inhibited basal and LPS/ConA-induced IL-6 and TNF-α secretion in addition to LPS-induced IL-1β and ConA-induced IL-2 secretion. Moreover, PGB attenuated mitogen-induced inflammatory changes in the spleen. These findings provide an evidence of the anti-inflammatory properties of PGB on cytokine secretion and lymphoid organ inflammation. This might give insights into the role of PGB in the management of the inflammatory state in PGB-indicated conditions.

Is cannabidiol a drug acting on unconventional targets to control drug-resistant epilepsy?

Cannabis has been considered as a therapeutic strategy to control intractable epilepsy. Several cannabis components, especially cannabidiol (CBD), induce antiseizure effects. However, additional information is necessary to identify the types of epilepsies that can be controlled by these components and the mechanisms involved in these effects. This review presents a summary of the discussion carried out during the 2nd Latin American Workshop on Neurobiology of Epilepsy entitled "Cannabinoid and epilepsy: myths and realities." This event was carried out during the 10th Latin American Epilepsy Congress in San José de Costa Rica (September 28, 2018). The review focuses to discuss the use of CBD as a new therapeutic strategy to control drug-resistant epilepsy. It also indicates the necessity to consider the evaluation of unconventional targets such as P-glycoprotein, to explain the effects of CBD in drug-resistant epilepsy.

Interferon-γ acutely augments inhibition of neocortical layer 5 pyramidal neurons

BACKGROUND

Interferon-γ (IFN-γ, a type II IFN) is present in the central nervous system (CNS) under various conditions. Evidence is emerging that, in addition to its immunological role, IFN-γ modulates neuronal morphology, function, and development in several brain regions. Previously, we have shown that raising levels of IFN-β (a type I IFN) lead to increased neuronal excitability of neocortical layer 5 pyramidal neurons. Because of shared non-canonical signaling pathways of both cytokines, we hypothesized a similar neocortical role of acutely applied IFN-γ.

METHODS

We used semi-quantitative RT-PCR, immunoblotting, and immunohistochemistry to analyze neuronal expression of IFN-γ receptors and performed whole-cell patch-clamp recordings in layer 5 pyramidal neurons to investigate sub- and suprathreshold excitability, properties of hyperpolarization-activated cyclic nucleotide-gated current (I_h), and inhibitory neurotransmission under the influence of acutely applied IFN-γ.

RESULTS

We show that IFN-γ receptors are present in the membrane of rat's neocortical layer 5 pyramidal neurons. As expected from this and the putative overlap in IFN type I and II alternative signaling pathways, IFN-γ diminished I_h, mirroring the effect of type I IFNs, suggesting a likewise activation of protein kinase C (PKC). In contrast, IFN-γ did neither alter subthreshold nor suprathreshold neuronal excitability, pointing to augmented inhibitory transmission by IFN-γ. Indeed, IFN-γ increased electrically evoked inhibitory postsynaptic currents (IPSCs) on neocortical layer 5 pyramidal neurons. Furthermore, amplitudes of spontaneous IPSCs and miniature IPSCs were elevated by IFN-γ, whereas their frequency remained unchanged.

CONCLUSIONS

The expression of IFN-γ receptors on layer 5 neocortical pyramidal neurons together with the acute augmentation of inhibition in the neocortex by direct application of IFN-γ highlights an additional interaction between the CNS and immune system. Our results strengthen our understanding of the role of IFN-γ in neocortical neurotransmission and emphasize its impact beyond its immunological properties, particularly in the pathogenesis of neuropsychiatric disorders.

Immune Challenges and Seizures: How Do Early Life Insults Influence Epileptogenesis?

The development of epilepsy, a process known as epileptogenesis, often occurs later in life following a prenatal or early postnatal insult such as cerebral ischemia, stroke, brain trauma, or infection. These insults share common pathophysiological pathways involving innate immune activation including neuroinflammation, which is proposed to play a critical role in epileptogenesis. This review provides a comprehensive overview of the latest preclinical evidence demonstrating that early life immune challenges influence neuronal hyperexcitability and predispose an individual to later life epilepsy. Here, we consider the range of brain insults that may promote the onset of chronic recurrent spontaneous seizures at adulthood, spanning intrauterine insults (e.g. maternal immune activation), perinatal injuries (e.g. hypoxic–ischemic injury, perinatal stroke), and insults sustained during early postnatal life—such as fever-induced febrile seizures, traumatic brain injuries, infections, and environmental stressors. Importantly, all of these insults represent, to some extent, an immune challenge, triggering innate immune activation and implicating both central and systemic inflammation as drivers of epileptogenesis. Increasing evidence suggests that pro-inflammatory cytokines such as interleukin-1 and subsequent signaling pathways are important mediators of seizure onset and recurrence, as well as neuronal network plasticity changes in this context. Our current understanding of how early life immune challenges prime microglia and astrocytes will be explored, as well as how developmental age is a critical determinant of seizure susceptibility. Finally, we will consider the paradoxical phenomenon of preconditioning, whereby these same insults may conversely provide neuroprotection. Together, an improved appreciation of the neuroinflammatory mechanisms underlying the long-term epilepsy risk following early life insults may provide insight into opportunities to develop novel immunological anti-epileptogenic therapeutic strategies.

Repeated stress induces a pro-inflammatory state, increases amygdala neuronal and microglial activation, and causes anxiety in adult male rats

A link exists between immune function and psychiatric conditions, particularly depressive and anxiety disorders. Psychological stress is a powerful trigger for these disorders and stress influences immune state. However, the nature of peripheral immune changes after stress conflicts across studies, perhaps due to the focus on few measures of pro-inflammatory or anti-inflammatory processes. The basolateral amygdala (BLA) is critical for emotion, and plays an important role in the effects of stress on anxiety. As such, it may be a primary central nervous system (CNS) mediator for the effects of peripheral immune changes on anxiety after stress. Therefore, this study aimed to delineate the influence of stress on peripheral pro-inflammatory and anti-inflammatory aspects, BLA immune activation, and its impact on BLA neuronal activity. To produce a more encompassing view of peripheral immune changes, this study used a less restrictive approach to categorize and group peripheral immune changes. We found that repeated social defeat stress in adult male Sprague-Dawley rats increased the frequencies of mature T-cells positive for intracellular type 2-like cytokine and serum pro-inflammatory cytokines. Principal component analysis and hierarchical clustering was used to guide grouping of T-cells and cytokines, producing unique profiles. Stress shifted the balance towards a specific set that included mostly type 2-like T-cells and pro-inflammatory cytokines. Within the CNS component, repeated stress caused an increase of activated microglia in the BLA, increased anxiety-like behaviors across several assays, and increased BLA neuronal firing in vivo that was prevented by blockade of microglia activation. Because repeated stress can trigger anxiety states by actions in the BLA, and altered immune function can trigger anxiety, these results suggest that repeated stress may trigger anxiety-like behaviors by inducing a pro-inflammatory state in the periphery and the BLA. These results begin to uncover how stress may recruit the immune system to alter the function of brain regions critical to emotion.

Altered plasma prostaglandin E2 levels in epilepsy and in response to antiepileptic drug monotherapy

Prostaglandin E₂ (PGE₂), a physiologically active lipid compound, is increased in several diseases characterized by chronic inflammation. To determine its significance in epilepsy-associated inflammation and response to antiepileptic drug (AED), we evaluated the plasma PGE₂ (median, pg/ml) levels in drug-free patients with epilepsy (N = 34) and patients receiving AED monotherapy (N = 55) in addition to that in healthy controls (N = 34). When compared to controls, plasma PGE₂ levels were significantly elevated in all drug-free patients independent of the type of epilepsy (137.2 versus 475.7 pg/ml, p < 0.0001). Among the patients receiving AED monotherapy, only valproate responders showed a significant decrease compared to both drug-free patients (232.1 versus 475.7 pg/ml, p < 0.01) as well as valproate non-responders (232.1 versus 611.9 pg/ml, p < 0.0001). Both responders and non-responders on phenytoin or carbamazepine monotherapy had elevated PGE₂ levels similar to drug-free patients. In addition, no difference was observed in plasma profiles of PGE₂ precursor, arachidonic acid among the groups. Our work presents the clinical evidence of the association between plasma PGE₂ levels and valproate efficacy in patients with epilepsy.

The prevalence, characteristics and outcome of seizure in tuberculous meningitis

Seizures are a common finding in patients with tuberculous meningitis (TBM), and associate with four times increased risk of death and neurological disability, especially in children. It has been reported that brain inflammation, diffuse neuronal injury, and reactive gliosis may all contribute to the pathogenesis of seizures in TBM. Early seizure onset may be associated with meningeal irritation and cerebral oedema; while, the late seizures are usually due to infarction, hydrocephalus, tuberculoma and paradoxical response. Moreover, recurrent uncontrolled seizures can evolve to status epileptics resulting in an increased risk of chronic epilepsy and poor prognosis. Therefore, this review aimed to assess the frequency of seizures in patients with TBM, and discuss the etiologies, mechanisms, and characteristics of seizures in TBM. Besides, we have searched the literature to identify the prognostic factors for chronic epilepsy after TBM.

Molecular alterations of the TLR4-signaling cascade in canine epilepsy

BACKGROUND

Cumulating evidence from rodent models points to a pathophysiological role of inflammatory signaling in the epileptic brain with Toll-like receptor-4 signaling acting as one key factor. However, there is an apparent lack of information about expression alterations affecting this pathway in canine patients with epilepsy. Therefore, we have analyzed the expression pattern of Toll-like receptor 4 and its ligands in brain tissue of canine patients with structural or idiopathic epilepsy in comparison with tissue from laboratory dogs or from owner-kept dogs without neurological diseases.

RESULTS

The analysis revealed an overexpression of Toll-like receptor-4 in the CA3 region of dogs with structural epilepsy. Further analysis provided evidence for an upregulation of Toll-like receptor-4 ligands with high mobility group box-1 exhibiting increased expression levels in the CA1 region of dogs with idiopathic and structural epilepsy, and heat shock protein 70 exhibiting increased expression levels in the piriform lobe of dogs with idiopathic epilepsy. In further brain regions, receptor and ligand expression rates proved to be either in the control range or reduced below control levels.

CONCLUSIONS

Our study reveals complex molecular alterations affecting the Toll-like receptor signaling cascade, which differ between epilepsy types and between brain regions. Taken together, the data indicate that multi-targeting approaches modulating Toll-like receptor-4 signaling might be of interest for management of canine epilepsy. Further studies are recommended to explore respective molecular alterations in more detail in dogs with different etiologies and to confirm the role of the pro-inflammatory signaling cascade as a putative target.

Microglial polarization in posttraumatic epilepsy: Potential mechanism and treatment opportunity

Owing to the complexity of the pathophysiological mechanisms driving epileptogenesis following traumatic brain injury (TBI), effective preventive treatment approaches are not yet available for posttraumatic epilepsy (PTE). Neuroinflammation appears to play a critical role in the pathogenesis of the acquired epilepsies, including PTE, but despite a large preclinical literature demonstrating the ability of anti-inflammatory treatments to suppress epileptogenesis and chronic seizures, no anti-inflammatory treatment approaches have been clinically proven to date. TBI triggers robust inflammatory cascades, suggesting that they may be relevant for the pathogenesis of PTE. A major cell type involved in such cascades is the microglial cells-brain-resident immune cells that become activated after brain injury. When activated, these cells can oscillate between different phenotypes, and such polarization states are associated with the release of various pro- and anti-inflammatory mediators that may influence brain repair processes, and also differentially contribute to the development of PTE. As the molecular mechanisms and key signaling molecules associated with microglial polarization in brain are discovered, strategies are now emerging that can modulate this polarization, promoting this as a potential therapeutic strategy for PTE. In this review, we discuss the relevant literature regarding the polarization of brain-resident immune cells following TBI and attempt to put into perspective a role in epilepsy pathogenesis. Finally, we explore potential strategies that could polarize microglia/macrophages toward a neuroprotective phenotype to mitigate PTE development.

Infantile Spasms: An Update on Pre-Clinical Models and EEG Mechanisms

Infantile spasms (IS) is an epileptic encephalopathy with unique clinical and electrographic features, which affects children in the middle of the first year of life. The pathophysiology of IS remains incompletely understood, despite the heterogeneity of IS etiologies, more than 200 of which are known. In particular, the neurobiological basis of why multiple etiologies converge to a relatively similar clinical presentation has defied explanation. Treatment options for this form of epilepsy, which has been described as “catastrophic” because of the poor cognitive, developmental, and epileptic prognosis, are limited and not fully effective. Until the pathophysiology of IS is better clarified, novel treatments will not be forthcoming, and preclinical (animal) models are essential for advancing this knowledge. Here, we review preclinical IS models, update information regarding already existing models, describe some novel models, and discuss exciting new data that promises to advance understanding of the cellular mechanisms underlying the specific EEG changes seen in IS—interictal hypsarrhythmia and ictal electrodecrement.

'Prototypical' proinflammatory cytokine (IL-1) in multiple sclerosis: role in pathogenesis and therapeutic targeting

Introduction: It has been recognized for about 20 years that interleukin (IL)-1 signaling is implicated in Multiple Sclerosis (MS), a disabling, chronic, inflammatory and neurodegenerative disease of the central nervous system (CNS). Only recently, multifaceted roles of IL-1 emerged in MS pathophysiology as a result of both clinical and preclinical studies. Notably, drugs that directly target the IL-1 system have not been tested so far in MS.Areas covered: Recent studies in animal models, together with the development of ex vivo chimeric MS models, have disclosed a critical role for IL-1 not only at the peripheral level but also within the CNS. In the present review, we highlight the IL-1-dependent neuropathological aspects of MS, by providing an overview of the cells of the immune and CNS systems that respond to IL-1 signaling, and by emphasizing the subsequent effects on the CNS, from demyelinating processes, to synaptopathy, and excitotoxicity.Expert opinion: Drugs that act on the IL-1 system show a therapeutic potential in several autoinflammatory diseases and preclinical studies have highlighted the effects of these compounds in MS. We will discuss why anti-IL-1 therapies in MS have been neglected to date.

Pharmacological Evaluation of Drugs in Animal Models of Tinnitus

Despite the pressing need for effective drug treatments for tinnitus, currently, there is no single drug that is approved by the FDA for this purpose. Instead, a wide range of unproven over-the-counter tinnitus remedies are available on the market with little or no benefit for tinnitus but with potential harm and adverse effects. Animal models of tinnitus have played a critical role in exploring the pathophysiology of tinnitus, identifying therapeutic targets and evaluating novel and existing drugs for tinnitus treatment. This review summarises and compares the studies on pharmacological evaluation of tinnitus treatment in different animal models based on the pharmacological properties of the drug and provides insights into future directions for tinnitus drug discovery.

The Interplay between the Endocannabinoid System, Epilepsy and Cannabinoids

Epilepsy is a neurological disorder that affects approximately 50 million people worldwide. There is currently no definitive epilepsy cure. However, in recent years, medicinal cannabis has been successfully trialed as an effective treatment for managing epileptic symptoms, but whose mechanisms of action are largely unknown. Lately, there has been a focus on neuroinflammation as an important factor in the pathology of many epileptic disorders. In this literature review, we consider the links that have been identified between epilepsy, neuroinflammation, the endocannabinoid system (ECS), and how cannabinoids may be potent alternatives to more conventional pharmacological therapies. We review the research that demonstrates how the ECS can contribute to neuroinflammation, and could therefore be modulated by cannabinoids to potentially reduce the incidence and severity of seizures. In particular, the cannabinoid cannabidiol has been reported to have anti-convulsant and anti-inflammatory properties, and it shows promise for epilepsy treatment. There are a multitude of signaling pathways that involve endocannabinoids, eicosanoids, and associated receptors by which cannabinoids could potentially exert their therapeutic effects. Further research is needed to better characterize these pathways, and consequently improve the application and regulation of medicinal cannabis.

Inflammation and reactive oxygen species in status epilepticus: Biomarkers and implications for therapy

Preclinical studies in immature and adult rodents and clinical observations show that neuroinflammation and oxidative stress are rapid onset phenomena occurring in the brain during status epilepticus and persisting thereafter. Notably, both neuroinflammation and oxidative stress contribute to the acute and long-term sequelae of status epilepticus thus representing potential druggable targets. Antiinflammatory drugs that interfere with the IL-1β pathway, such as anakinra, can control benzodiazepine-refractory status epilepticus in animals, and there is recent proof-of-concept evidence for therapeutic effects in children with Febrile infection related epilepsy syndrome (FIRES). Inhibitors of monoacylglycerol lipase and P2X7 receptor antagonists are also promising antiinflammatory drug candidates for rapidly aborting de novo status epilepticus and provide neuroprotection. Antiinflammatory and antioxidant drugs administered to rodents during status epilepticus and transiently thereafter, prevent long-term sequelae such as cognitive deficits and seizure progression in animals developing epilepsy. Some drugs are already in medical use and are well-tolerated, therefore, they may be considered for treating status epilepticus and its neurological consequences. Finally, markers of neuroinflammation and oxidative stress are measureable in peripheral blood and by neuroimaging, which offers an opportunity for developing prognostic and predictive mechanistic biomarkers in people exposed to status epilepticus. This article is part of the Special Issue "Proceedings of the 7th London-Innsbruck Colloquium on Status Epilepticus and Acute Seizures.

Brainstem serotonergic, catecholaminergic, and inflammatory adaptations during chronic hypercapnia in goats

Despite the prevalence of CO₂ retention in human disease, little is known about the adaptive neurobiological effects of chronic hypercapnia. We have recently shown 30-d exposure to increased inspired CO₂ (InCO₂) leads to a steady-state ventilation that exceeds the level predicted by the sustained acidosis and the acute CO₂/H⁺ chemoreflex, suggesting plasticity within respiratory control centers. Based on data showing brainstem changes in aminergic and inflammatory signaling during carotid body denervation-induced hypercapnia, we hypothesized chronic hypercapnia per se will lead to similar changes. We found that: 1) increased InCO₂ increased IL-1β in the medullary raphe (MR), ventral respiratory column, and cuneate nucleus after 24 h, but not after 30 d of hypercapnia; 2) the number of serotonergic and total neurons were reduced within the MR and ventrolateral medulla following 30 d of increased InCO₂; 3) markers of tryptophan metabolism were altered following 24 h, but not 30 d of InCO₂; and 4) there were few changes in brainstem amine levels following 24 h or 30 d of increased InCO₂. We conclude that these changes may contribute to initiating or maintaining respiratory neuroplasticity during chronic hypercapnia but alone do not account for ventilatory acclimatization to chronic increased InCO₂.-Burgraff, N. J., Neumueller, S. E., Buchholz, K. J., LeClaire, J., Hodges, M. R., Pan, L., Forster, H. V. Brainstem serotonergic, catecholaminergic, and inflammatory adaptations during chronic hypercapnia in goats.

Cyclooxygenase-2 (COX-2) inhibitors: future therapeutic strategies for epilepsy management

Epilepsy, a common multifactorial neurological disease, affects about 69 million people worldwide constituting nearly 1% of the world population. Despite decades of extensive research on understanding its underlying mechanism and developing the pharmacological treatment, very little is known about the biological alterations leading to epileptogenesis. Due to this gap, the currently available antiepileptic drug therapy is symptomatic in nature and is ineffective in 30% of the cases. Mounting evidences revealed the pathophysiological role of neuroinflammation in epilepsy which has shifted the focus of epilepsy researchers towards the development of neuroinflammation-targeted therapeutics for epilepsy management. Markedly increased expression of key inflammatory mediators in the brain and blood-brain barrier may affect neuronal function and excitability and thus may increase seizure susceptibility in preclinical and clinical settings. Cyclooxygenase-2 (COX-2), an enzyme synthesizing the proinflammatory mediators, prostaglandins, has widely been reported to be induced during seizures and is considered to be a potential neurotherapeutic target for epilepsy management. However, the efficacy of such therapy involving COX-2 inhibition depends on various factors viz., therapeutic dose, time of administration, treatment duration, and selectivity of COX-2 inhibitors. This article reviews the preclinical and clinical evidences supporting the role of COX-2 in seizure-associated neuroinflammation in epilepsy and the potential clinical use of COX-2 inhibitors as a future strategy for epilepsy treatment.