Neuronal hyperactivity recruits microglial processes via neuronal NMDA receptors and microglial P2Y12 receptors after status epilepticus

Ion Channels and Receptors as Determinants of Microglial Function

Microglia provide immune surveillance of the CNS. They display diverse behaviors, including nondirectional and directed motility of their processes, phagocytosis of targets such as dying neurons or superfluous synapses, and generation of reactive oxygen species (ROS) and cytokines. Many of these functions are mediated by ion channels and cell surface receptors, the expression of which varies with the many morphological and functional states that microglial cells can adopt. Recent progress in understanding microglial function has been facilitated by applying classical cell physiological techniques in situ, such as patch-clamping and live imaging, and cell-specific transcriptomic analyses. Here, we review the contribution of microglial ion channels and receptors to microglial and brain function.

Loss of Par1b/MARK2 primes microglia during brain development and enhances their sensitivity to injury

Background

Microglia, the resident immune cells of the brain, exhibit various morphologies that correlate with their functions under physiological and pathological conditions. In conditions such as aging and stress, microglia priming occurs, which leads to altered morphology and lower threshold for activation upon further insult. However, the molecular mechanisms that lead to microglia priming are unclear.

Methods

To understand the role of Par1b/MARK2 in microglia, we first expressed shRNA targeting luciferase or Par1b/MARK2 in primary microglial cells and imaged the cells using fluorescent microscopy to analyze for morphological changes. A phagocytosis assay was then used to assess functional changes. We then moved in vivo and used a Par1b/MARK2 knockout mouse model to assess for changes in microglia density, morphology, and phagocytosis using immunohistochemistry, confocal imaging, and 3D image reconstruction. Next, we used two-photon in vivo imaging in live Par1b/MARK2 deficient mice to examine microglia dynamics. In addition, a controlled-cortical impact injury was performed on wild-type and Par1b/MARK2-deficient mice and microglial response was determined by confocal imaging. Finally, to help rule out non-cell autonomous effects, we analyzed apoptosis by confocal imaging, cytokine levels by multiplex ELISA, and blood-brain barrier permeability using Evans Blue assay.

Results

Here, we show that loss of the cell polarity protein Par1b/MARK2 facilitates the activation of primary microglia in culture. We next found that microglia in Par1b/MARK2 deficient mice show increased density and a hypertrophic morphology. These morphological changes are accompanied with alterations in microglia functional responses including increased phagocytosis of neuronal particles early in development and decreased surveillance of the brain parenchyma, all reminiscent of a primed phenotype. Consistent with this, we found that microglia in Par1b/MARK2 deficient mice have a significantly lower threshold for activation upon injury.

Conclusions

Together, our studies show that loss of Par1b/MARK2 switches microglia from a surveillant to a primed state during development, resulting in an increased neuroinflammatory response to insults.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1390-3) contains supplementary material, which is available to authorized users.

ATP release during seizures - A critical evaluation of the evidence

That adenosine 5' triphosphate (ATP) functions as an extracellular signaling molecule has been established since the 1970s. Ubiquitous throughout the body as the principal molecular store of intracellular energy, ATP has a short extracellular half-life and is difficult to measure directly. Extracellular ATP concentrations are dependent both on the rate of cellular release and of enzymatic degradation. Some findings from in vitro studies suggest that extracellular ATP concentrations increase during high levels of neuronal activity and seizure-like events in hippocampal slices. Pharmacological studies suggest that antagonism of ATP-sensitive purinergic receptors can suppress the severity of seizures and block epileptogenesis. Directly measuring extracellular ATP concentrations in the brain, however, has a number of specific challenges, notably, the rapid hydrolysis of ATP and huge gradient between intracellular and extracellular compartments. Two studies using microdialysis found no change in extracellular ATP in the hippocampus of rats during experimentally-induced status epilepticus. One of which demonstrated that ATP increased measurably, only in the presence of ectoATPase inhibitors, with the other study demonstrating increases only during later spontaneous seizures. Current evidence is mixed and seems highly dependent on the model used and method of detection. More sensitive methods of detection with higher spatial resolution, which induce less tissue disruption will be necessary to provide evidence for or against the hypothesis of seizure-induced elevations in extracellular ATP. Here we describe the current hypothesis for ATP release during seizures and its role in epileptogenesis, describe the technical challenges involved and critically examine the current evidence.

Basic Concept of Microglia Biology and Neuroinflammation in Relation to Psychiatry

The hypothesis that the neuroimmune system plays a role in the pathogenesis of different psychiatric disorders, including schizophrenia, depression, and bipolar disease, has attained increasing interest over the past years. Previously thought to have the sole purpose of protecting the central nervous system (CNS) from harmful stimuli, it is now known that the central immune system is critically involved in regulating physiological processes including neurodevelopment, synaptic plasticity, and circuit maintenance. Hence, alterations in microglia - the main immune cell of the CNS - and/or inflammatory factors do not unequivocally connote ongoing neuroinflammation or neuroinflammatory processes per se but rather might signify changes in brain homoeostasis. Despite this, psychiatric research tends to equate functional changes in microglia or alterations in other immune mediators with neuroinflammation. It is the main impetus of this chapter to overcome some of the current misconceptions and possible oversimplifications with respect to neuroinflammation and microglia activity in psychiatry. In order to do so, we will first provide an overview of the basic concepts of neuroinflammation and neuroinflammatory processes. We will then focus on microglia with respect to their ontogeny and immunological and non-immunological functions presenting novel insights on how microglia communicate with other cell types of the central nervous system to ensure proper brain functioning. And lastly, we will delineate the non-immunological functions of inflammatory cytokines in order to address the possible misconception of equating alterations in central cytokine levels with ongoing central inflammation. We hereby hope to help unravel the functional relevance of neuroimmune dysfunctions in psychiatric illnesses and provide future research directions in the field of psychoneuroimmunology.

Physiology of Microglia

Microglia constitute the major immune cells that permanently reside in the central nervous system (CNS) alongside neurons and other glial cells. These resident immune cells are critical for proper brain development, actively maintain brain health throughout the lifespan and rapidly adapt their function to the physiological or pathophysiological needs of the organism. Cutting-edge fate mapping and imaging techniques applied to animal models enabled a revolution in our understanding of their roles during normal physiological conditions. Here, we highlight studies that demonstrate the embryonic yolk sac origin of microglia and describe factors, including crosstalk with the periphery and external environment, that regulate their differentiation, homeostasis and function in the context of healthy CNS. The diversity of microglial phenotypes observed across the lifespan, between brain compartments and between sexes is also discussed. Understanding what defines specific microglial phenotypes is critical for the development of innovative therapies to modulate their effector functions and improve clinical outcomes.

Microglia and the Purinergic Signaling System

Microglia are the main resident immune-competent cell type of the central nervous system (CNS); these cells are highly sensitive to subtle changes in the chemical environment of the brain. Microglia are activated during diverse conditions, such as apoptosis, trauma, inflammation, and infection. The specific activities of microglia result from the confluence of environmental stimuli and the cellular state. It is likely that several signaling systems with different biological functions operate in competition and/or synergy, thus regulating similar microglial behaviors. The purinergic system is one of the fundamental signaling systems that establish microglial behavior in a wide spectrum of conditions. Adenosine tri-phosphate (ATP) belongs to the purinergic signaling system, which includes P2X, P2Y, and P1 receptors, as well as other proteins participating in ATP secretion and extracellular ATP degradation, and molecules that recognize purines as a ligand. In this review, we focus on the latest pre-clinical and basic purinergic system and microglial research, with particular attention to data collected in vivo and ex vivo. This chapter is divided into sections related to microglial ATP release, ATP degradation, and ATP-related actions mediated by P2X and P2Y receptor activation.

3DMorph Automatic Analysis of Microglial Morphology in Three Dimensions from Ex Vivo and In Vivo Imaging

Microglia are dynamic immune cells of the central nervous system, and their morphology is commonly used as a readout of cellular function. However, current morphological analysis techniques rely on either tracing of cells or two-dimensional projection analysis, which are time-consuming, subject to bias, and may ignore important three-dimensional (3D) information. Therefore, we have created 3DMorph, a MATLAB-based script that analyzes microglial morphology from 3D data. The program initially requires input of threshold levels, cell size expectations, and preferred methods of skeletonization. This makes 3DMorph easily scalable and adaptable to different imaging parameters or cell types. After these settings are defined, the program is completely automatic and can batch process files without user input. Output data includes cell volume, territorial volume, branch length, number of endpoints and branch points, and average distance between cells. We show that 3DMorph is accurate compared to manual tracing, with significantly decreased user input time. Importantly, 3DMorph is capable of processing in vivo microglial morphology, as well as other 3D branching cell types, from mouse cranial windows or acute hippocampal slices. Therefore, we present a novel, user-friendly, scalable, and semiautomatic method of analyzing cell morphology in 3 dimensions. This method should improve the accuracy of cell measurements, remove user bias between conditions, increase reproducibility between experimenters and labs, and reduce user input time. We provide this open source code on GitHub so that it is free and accessible to all investigators.

Regulation of microglial process elongation, a featured characteristic of microglial plasticity

Microglia, a type of glia within the brain characterized by a ramified morphology, are essential for removing neuronal debris and restricting the expansion of a lesion site. Upon moderate activation, they undergo a transformation in morphology inducing beneficial responses. However, upon strong stimulation, they mediate neuronal damage via production of pro-inflammatory cytokines. The inhibition of this cascade is considered an effective strategy for neuroinflammation-associated disorder therapy. During this pathological activation microglia also undergo a shortening of process length which contributes to the pathogenesis of such disorders. Thus, microglial plasticity should be considered to have two components: one is the production of inflammatory mediators, and the other is the dynamic changes in their processes. The former role has been well-documented in previous studies, while the latter one remains largely unknown. Recently, we and others have reported that the elongation of microglial process is associated with the transformation of microglia from a pro-inflammatory to an anti-inflammatory state, suggesting that the shortening of process length would make the microglia lose their ability to restrict pathological injury, while the elongation of microglial process would help attenuate neuroinflammation. Compared with the traditional anti-neuroinflammatory strategy, stimulating elongation of microglial process not only reduces the production of pro-inflammatory cytokines, but restores the ability of microglia to scan their surrounding environments, thus rendering their homeostasis regulation more effective. In this review, we provide a discussion of the factors that regulate microglial process elongation in vitro and in vivo, aiming to further drive the understanding of microglial process plasticity.

Microglia mediate non-cell-autonomous cell death of retinal ganglion cells

Excitotoxicity is well known in the neuronal death in the brain and is also linked to neuronal damages in the retina. Recent accumulating evidence show that microglia greatly affect excitotoxicity in the brain, but their roles in retina have received only limited attention. Here, we report that retinal excitotoxicity is mediated by microglia. To this end, we employed three discrete methods, that is, pharmacological inhibition of microglia by minocycline, pharmacological ablation by an antagonist for colony stimulating factor 1 receptor (PLX5622), and genetic ablation of microglia using Iba1-tTA::DTA^tetO/tetO mice. Intravitreal injection of NMDA increased the number of apoptotic retinal ganglion cells (RGCs) followed by reduction in the number of RGCs. Although microglia did not respond to NMDA directly, they became reactive earlier than RGC damages. Inhibition or ablation of microglia protected RGCs against NMDA. We found up-regulation of proinflammatory cytokine genes including Il1b, Il6 and Tnfa, among which Tnfa was selectively blocked by minocycline. PLX5622 also suppressed Tnfa expression. Tumor necrosis factor α (TNFα) signals were restricted in microglia at very early followed by spreading into other cell types. TNFα up-regulation in microglia and other cells were significantly attenuated by minocycline and PLX5622, suggesting a central role of microglia for TNFα induction. Both inhibition of TNFα and knockdown of TNF receptor type 1 by siRNA protected RGCs against NMDA. Taken together, our data demonstrate that a phenotypic change of microglia into a neurotoxic one is a critical event for the NMDA-induced degeneration of RGCs, suggesting an importance of non-cell-autonomous mechanism in the retinal neuronal excitotoxicity.

Microglia Enhance Synapse Activity to Promote Local Network Synchronization

Microglia are highly motile immunoreactive cells that play integral roles in the response to brain infection and damage, and in the progression of various neurological diseases. During development, microglia also help sculpt neural circuits, via both promoting synapse formation and by targeting specific synapses for elimination and phagocytosis. Microglia are also active surveyors of neural circuits in the mature, healthy brain, although the functional consequences of such microglia-neuron contacts under these conditions is unclear. Using in vivo imaging of neurons and microglia in awake mice, we report here the functional consequences of microglia-synapse contacts. Direct contact between a microglial process and a single synapse results in a specific increase in the activity of that contacted synapse, and a corresponding increase in back-propagating action potentials along the parent dendrite. This increase in activity is not seen for microglia-synapse contacts when microglia are activated by chronic lipopolysaccharide (LPS) treatment. To probe how this microglia-synapse contact affects neural circuits, we imaged across larger populations of motor cortical neurons. When microglia were again activated by LPS (or partially ablated), there was a decrease in the extent to which neuronal activity was synchronized. Together, our results demonstrate that interactions between physiological or resting microglia and synapses in the mature, healthy brain leads to an increase in neuronal activity and thereby helps to synchronize local populations of neurons. Our novel findings provide a plausible physical basis for understanding how alterations in immune status may impact on neural circuit plasticity and on cognitive behaviors such as learning.

Region-Specific Phenotypes of Microglia: The Role of Local Regulatory Cues

Microglia are ubiquitous, macrophage like cells within the central nervous system (CNS) that play critical roles in supporting neuronal health and viability. They can also influence neuronal membrane properties and synaptic connectivity, positioning microglia as key cellular players in both physiological and pathological contexts. Microglia have generally been assumed to be equivalent throughout the CNS, but accumulating evidence indicates that their properties vary substantially across distinct CNS regions. In comparison to our understanding of neuronal diversity and its functional importance, our knowledge about causes and consequences of microglial regional heterogeneity is extremely limited. To fully understand how microglia influence the function of specific neuronal populations and shape heightened susceptibility of some neurons to damage and disease, greater focus on microglial heterogeneity is needed.

The Importance of Inter-Species Variation in Traumatic Brain Injury-Induced Alterations of Microglial-Axonal Interactions

Interactions between microglia and neuronal components are important for normal CNS function. They are also associated with neuroinflammation and many pathological processes and several studies have explored these interactions in terms of phagocytic engulfment. Much progress has also been made in understanding the consequences of chronic neuroinflammatory changes following trauma. However, little is known about acute alterations to these physical non-phagocytic microglial-neuronal interactions following traumatic brain injury (TBI), and particularly to what degree these post-injury interactions may be influenced by the animal species utilized in pre-clinical models of TBI. To investigate these problems, we evaluated the physical interactions between microglia and injured axons acutely (6 h and 1 day) following central fluid percussion injury (cFPI) in both rats and micro pigs. The physical interactions between Iba-1+ microglia and either normal MBP+ myelinated fibers or APP+ injured axonal swellings in the thalamus were assessed following injury or sham via quantitative image analysis of 3D confocal micrographs. The results indicated that the physical interactions between microglia and injured axonal swellings decreased by nearly half in rats 6 h following cFPI but was consistent with sham control at 1 day post-cFPI. This reduction was also observed in non-injured intact fibers at both timepoints following TBI in the rat. Microglial process interactions with injured axons in the micro pig, however, increased nearly 2-fold compared to interactions with intact axonal segments 1 day post-cFPI. This study shows that the species utilized for in vivo pre-clinical studies influences the manner in which microglial-axonal interactions change following TBI. These species differences can be leveraged to further our understanding of the mechanisms involved in microglial process convergence and how these neuro-immune interactions alter the progression of axonal injury following TBI.

Coupled Oscillators Model of Hyperexcitable Neuroglial Networks

Glial populations within neuronal networks of the brain have recently gained much interest in the context of hyperexcitability and epilepsy. In this paper, we present an oscillator-based neuroglial model capable of generating Spontaneous Electrical Discharges (SEDs) in hyperexcitable conditions. The network is composed of 16 coupled Cognitive Rhythm Generators (CRGs), which are oscillator-based mathematical constructs previously described by our research team. CRGs are well-suited for modeling assemblies of excitable cells, and in this network, each represents one of the following populations: excitatory pyramidal cells, inhibitory interneurons, astrocytes, and microglia. We investigated various pathways leading to hyperexcitability, and our results suggest an important role for astrocytes and microglia in the generation of SEDs of various durations. Analysis of the resultant SEDs revealed two underlying duration distributions with differing properties. Particularly, short and long SEDs are associated with deterministic and random underlying processes, respectively. The mesoscale of this model makes it well-suited for (a) the elucidation of glia-related hypotheses in hyperexcitable conditions, (b) use as a testing platform for neuromodulation purposes, and (c) a hardware implementation for closed-loop neuromodulation.

Microglia in the Retina: Roles in Development, Maturity, and Disease

Microglia, the primary resident immune cell type, constitute a key population of glia in the retina. Recent evidence indicates that microglia play significant functional roles in the retina at different life stages. During development, retinal microglia regulate neuronal survival by exerting trophic influences and influencing programmed cell death. During adulthood, ramified microglia in the plexiform layers interact closely with synapses to maintain synaptic structure and function that underlie the retina's electrophysiological response to light. Under pathological conditions, retinal microglia participate in potentiating neurodegeneration in diseases such as glaucoma, retinitis pigmentosa, and age-related neurodegeneration by producing proinflammatory neurotoxic cytokines and removing living neurons via phagocytosis. Modulation of pathogenic microglial activation states and effector mechanisms has been linked to neuroprotection in animal models of retinal diseases. These findings have led to the design of early proof-of-concept clinical trials with microglial modulation as a therapeutic strategy.

RNAseq analysis of hippocampal microglia after kainic acid-induced seizures

Microglia have been shown to be of critical importance to the progression of temporal lobe epilepsy. However, the broad transcriptional changes that these cells undergo following seizure induction is not well understood. As such, we utilized RNAseq analysis upon microglia isolated from the hippocampus to determine expression pattern alterations following kainic acid induced seizure. We determined that microglia undergo dramatic changes to their expression patterns, particularly with regard to mitochondrial activity and metabolism. We also observed that microglia initiate immunological activity, specifically increasing interferon beta responsiveness. Our results provide novel insights into microglia transcriptional regulation following acute seizures and suggest potential therapeutic targets specifically in microglia for the treatment of seizures and epilepsy.

Structure, Pharmacology and Roles in Physiology of the P2Y12 Receptor

P2Y receptors are G-protein-coupled receptors (GPCRs) for extracellular nucleotides. The platelet ADP-receptor which has been denominated P2Y₁₂ receptor is an important target in pharmacotherapy. The receptor couples to G_αi2 mediating an inhibition of cyclic AMP accumulation and additional downstream events including the activation of phosphatidylinositol-3-kinase and Rap1b proteins. The nucleoside analogue ticagrelor and active metabolites of the thienopyridine compounds ticlopidine, clopidogrel and prasugrel block P2Y₁₂ receptors and, thereby, inhibit ADP-induced platelet aggregation. These drugs are used for the prevention and therapy of cardiovascular events such as acute coronary syndromes or stroke. The recently published three-dimensional crystal structures of the human P2Y₁₂ receptor in complex with agonists and antagonists will facilitate the development of novel therapeutic agents with reduced adverse effects. P2Y₁₂ receptors are also expressed on vascular smooth muscle cells and may be involved in the pathophysiology of atherogenesis. P2Y₁₂ receptors on microglial cells operate as sensors for adenine nucleotides released during brain injury. A recent study indicated the involvement of microglial P2Y₁₂ receptors in the activity-dependent neuronal plasticity. Interestingly, there is evidence for changes in P2Y₁₂ receptor expression in CNS pathologies including Alzheimer's diseases and multiple sclerosis. P2Y₁₂ receptors may also be involved in systemic immune modulating responses and the susceptibility to develop bronchial asthma.

Neuroplasticity in stroke recovery. The role of microglia in engaging and modifying synapses and networks

Neuroplasticity after ischaemic injury involves both spontaneous rewiring of neural networks and circuits as well as functional responses in neurogenic niches. These events involve complex interactions with activated microglia, which evolve in a dynamic manner over time. Although the exact mechanisms underlying these interactions remain poorly understood, increasing experimental evidence suggests a determining role of pro- and anti-inflammatory microglial activation profiles in shaping both synaptogenesis and neurogenesis. While the inflammatory response of microglia was thought to be detrimental, a more complex profile of the role of microglia in tissue remodelling is emerging. Experimental evidence suggests that microglia in response to injury can rapidly modify neuronal activity and modulate synaptic function, as well as be beneficial for the proliferation and integration of neural progenitor cells (NPCs) from endogenous neurogenic niches into functional networks thereby supporting stroke recovery. The manner in which microglia contribute towards sculpting neural synapses and networks, both in terms of activity-dependent and homeostatic plasticity, suggests that microglia-mediated pro- and/or anti-inflammatory activity may significantly contribute towards spontaneous neuronal plasticity after ischaemic lesions. In this review, we first introduce some of the key cellular and molecular mechanisms underlying neuroplasticity in stroke and then proceed to discuss the crosstalk between microglia and endogenous neuroplasticity in response to brain ischaemia with special focus on the engagement of synapses and neural networks and their implications for grey matter integrity and function in stroke repair.

Microglial interactions with the neurovascular system in physiology and pathology

Microglia as immune cells of the central nervous system (CNS) play significant roles not only in pathology but also in physiology, such as shaping of the CNS during development and its proper maintenance in maturity. Emerging research is showing a close association between microglia and the neurovasculature that is critical for brain energy supply. In this review, we summarize the current literature on microglial interaction with the vascular system in the normal and diseased brain. First, we highlight data that indicate interesting potential involvement of microglia in developmental angiogenesis. Then we discuss the evidence for microglial participation with the vasculature in neuropathologies from brain tumors to acute injuries such as ischemic stroke to chronic neurodegenerative conditions. We conclude by suggesting future areas of research to advance the field in light of current technical progress and outstanding questions. © 2018 Wiley Periodicals, Inc. Develop Neurobiol 78: 604-617, 2018.

Notch Signaling Regulates Microglial Activation and Inflammatory Reactions in a Rat Model of Temporal Lobe Epilepsy

The inflammatory response mediated by microglia in the central nervous system is closely related to epilepsy. Notch signaling plays an important role in the microglial activation during hypoxia. This study aimed to investigate whether Notch signaling is involved in microglial activation and subsequent inflammation-related neuronal injury during the process of epileptogenesis in a rat model of temporal lobe epilepsy. By using western blotting, real-time quantitative PCR, immunohistochemistry and immunofluorescence labeling, we found that the expression of Notch signaling increased after status epilepticus and that a γ-secretase inhibitor could significantly inhibit the upregulation of Notch signaling, the activation of microglia, and the release of proinflammatory cytokines. Likewise, the neuronal apoptosis and loss in the hippocampus after SE were attenuated by the γ-secretase inhibitor. These results suggest that Notch signaling plays a key role in neuroinflammation and inflammation-related neuronal damage in epilepsy, and γ-secretase inhibitors may become a novel prospective therapeutic agent for epilepsy.

Genetic deletion of xCT attenuates peripheral and central inflammation and mitigates LPS-induced sickness and depressive-like behavior in mice

The communication between the immune and central nervous system (CNS) is affected in many neurological disorders. Peripheral injections of the endotoxin lipopolysaccharide (LPS) are widely used to study this communication: an LPS challenge leads to a biphasic syndrome that starts with acute sickness and is followed by persistent brain inflammation and chronic behavioral alterations such as depressive-like symptoms. In vitro, the response to LPS treatment has been shown to involve enhanced expression of system <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup><mml:mrow><mml:mi>x</mml:mi></mml:mrow> <mml:mrow><mml:mi>c</mml:mi></mml:mrow> <mml:mrow><mml:mo>-</mml:mo></mml:mrow> </mml:msubsup> </mml:math> . This cystine-glutamate antiporter, with xCT as specific subunit, represents the main glial provider of extracellular glutamate in mouse hippocampus. Here we injected male xCT knockout and wildtype mice with a single intraperitoneal dose of 5 mg/kg LPS. LPS-injection increased hippocampal xCT expression but did not alter the mainly astroglial localization of the xCT protein. Peripheral and central inflammation (as defined by cytokine levels and morphological activation of microglia) as well as LPS-induced sickness and depressive-like behavior were significantly attenuated in xCT-deficient mice compared with wildtype mice. Our study is the first to demonstrate the involvement of system <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup><mml:mrow><mml:mi>x</mml:mi></mml:mrow> <mml:mrow><mml:mi>c</mml:mi></mml:mrow> <mml:mrow><mml:mo>-</mml:mo></mml:mrow> </mml:msubsup> </mml:math> in peripheral and central inflammation in vivo and the potential therapeutic relevance of its inhibition in brain disorders characterized by peripheral and central inflammation, such as depression.

Microglia after Seizures and in Epilepsy

Microglia are the resident immune cells in the brain that constitute the brain’s innate immune system. Recent studies have revealed various functions of microglia in the development and maintenance of the central nervous system (CNS) in both health and disease. However, the role of microglia in epilepsy remains largely undiscovered, partly because of the complex phenotypes of activated microglia. Activated microglia likely exert different effects on brain function depending on the phase of epileptogenesis. In this review, we mainly focus on the animal models of temporal lobe epilepsy (TLE) and discuss the proepileptic and antiepileptic roles of activated microglia in the epileptic brain. Specifically, we focus on the roles of microglia in the production of inflammatory cytokines, regulation of neurogenesis, and surveillance of the surrounding environment in epilepsy.

The Metabotropic Purinergic P2Y Receptor Family as Novel Drug Target in Epilepsy

Epilepsy encompasses a heterogeneous group of neurological syndromes which are characterized by recurrent seizures affecting over 60 million people worldwide. Current anti-epileptic drugs (AEDs) are mainly designed to target ion channels and/or GABA or glutamate receptors. Despite recent advances in drug development, however, pharmacoresistance in epilepsy remains as high as 30%, suggesting the need for the development of new AEDs with a non-classical mechanism of action. Neuroinflammation is increasingly recognized as one of the key players in seizure generation and in the maintenance of the epileptic phenotype. Consequently, targeting signaling molecules involved in inflammatory processes may represent new avenues to improve treatment in epilepsy. Nucleotides such as adenosine-5′-triphosphate (ATP) and uridine-5′-triphosphate (UTP) are released in the brain into the extracellular space during pathological conditions such as increased neuronal firing or cell death. Once released, these nucleotides bind to and activate specific purinergic receptors termed P2 receptors where they mediate the release of gliotransmitters and drive neuronal hyperexcitation and neuroinflammatory processes. This includes the fast acting ionotropic P2X channels and slower-acting G-protein-coupled P2Y receptors. While the expression and function of P2X receptors has been well-established in experimental models of epilepsy, emerging evidence is now also suggesting a prominent role for the P2Y receptor subfamily in seizure generation and the maintenance of epilepsy. In this review we discuss data supporting a role for the P2Y receptor family in epilepsy and the most recent finding demonstrating their involvement during seizure-induced pathology and in epilepsy.

Role of microglia-neuron interactions in diabetic encephalopathy

In the central nervous system, the primary immune cells, the microglia, prevent pathogenic invasion as the first line of defense. Microglial energy consumption is dependent on their degree of activity. Microglia express transporters for the three primary energy substrates (glucose, fatty acids, glutamine) and regulate diabetic encephalopathy via microglia-neuron interactions. Microglia may play a sentry role for rapid protection or even ablation of impaired neurons. Neurons exhibit hyperactivity in response to hyperglycemia, hyperlipidemia, and neurotoxic factors and release potential microglial activators. Microglial activation is also regulated by proinflammatory factors, caspase-3 activity, P2X₇ receptor, interferon regulatory factor-8, and glucocorticoids. Modulation of microglia in diabetic encephalopathy may involve CX3CL1, p38 MAPK, purinergic, and CD200/CD200R signaling pathways, and pattern recognition receptors. The microglia-neuron interactions play an important role in diabetic encephalopathy, and modulation of microglial activation may be a therapeutic target for diabetic encephalopathy.

Cerebellar microglia are dynamically unique and survey Purkinje neurons in vivo

Microglia are the innate immune cells of the central nervous system and are also important participants in normal development and synaptic plasticity. Here, we demonstrate that the microglia of the mouse cerebellum represent a unique population compared to cortical microglia. Microglia are more sparsely distributed within the cerebellum and have a markedly less ramified morphology compared to their cortical counterparts. Using time-lapse in vivo imaging, we found that these differences in distribution and morphology ultimately lead to decreased parenchymal surveillance by cerebellar microglia. We also observed a novel form of somal motility in cerebellar microglia in vivo, which has not been described in cortical populations. We captured microglial interactions with Purkinje neurons in vivo. Cerebellar microglia interact dynamically with both the dendritic arbors and somas of Purkinje neurons. These findings suggest that cerebellar microglia are physiologically distinct from cortical populations and that these differences may ultimately alter how they could contribute to plasticity and disease processes in the cerebellum. © 2017 Wiley Periodicals, Inc. Develop Neurobiol 78: 627-644, 2018.

The GluN2A Subunit Regulates Neuronal NMDA receptor-Induced Microglia-Neuron Physical Interactions

Microglia are known to engage in physical interactions with neurons. However, our understanding of the detailed mechanistic regulation of microglia-neuron interactions is incomplete. Here, using high resolution two photon imaging, we investigated the regulation of NMDA receptor-induced microglia-neuron physical interactions. We found that the GluN2A inhibitor NVPAAM007, but not the GluN2B inhibitor ifenprodil, blocked the occurrence of these interactions. Consistent with the well-known developmental regulation of the GluN2A subunit, these interactions are absent in neonatal tissues. Furthermore, consistent with a preferential synaptic localization of GluN2A subunits, there is a differential sensitivity of their occurrence between denser (stratum radiatum) and less dense (stratum pyramidale) synaptic sub-regions of the CA1. Finally, consistent with differentially expressed GluN2A subunits in the CA1 and DG areas of the hippocampus, these interactions could not be elicited in the DG despite robust microglial chemotactic capabilities. Together, these results enhance our understanding of the mechanistic regulation of NMDA receptor-dependent microglia-neuronal physical interactions phenomena by the GluN2A subunit that may be relevant in the mammalian brain during heightened glutamatergic neurotransmission such as epilepsy and ischemic stroke.

Microglial modulation of neuronal activity in the healthy brain

Investigations on the role of microglia in the brain have traditionally been focused on their contributions to disease states. However, recent observations have now convincingly shown that microglia in the healthy brain are not passive bystanders, but instead play a critical role in both central nervous system development and homeostasis of synaptic circuits in the adult. Here, we review the various mechanisms by which microglia impact neuronal communication in the healthy adult brain, both by sensing nearby synaptic responses and by actively modulating neuronal function. © 2017 Wiley Periodicals, Inc. Develop Neurobiol 78: 593-603, 2018.

Status Epilepticus Triggers Time-Dependent Alterations in Microglia Abundance and Morphological Phenotypes in the Hippocampus

Status epilepticus (SE) is defined by the occurrence of prolonged “non-stop” seizures that last for at least 5 min. SE provokes inflammatory responses including the activation of microglial cells, the brain’s resident immune cells, which are thought to contribute to the neuropathology and pathophysiology of epilepsy. Microglia are professional phagocytes that resemble peripheral macrophages. Upon sensing immune disturbances, including SE, microglia become reactive, produce inflammatory cytokines, and alter their actin cytoskeleton to transform from ramified to amoeboid shapes. It is widely known that SE triggers time-dependent microglial expression of pro-inflammatory cytokines that include TNFα and IL-1β. However, less is known in regards to the spatiotemporal progression of the morphological changes, which may help define the extent of microglia reactivity after SE and potential function (surveillance, inflammatory, phagocytic). Therefore, in this study, we used the microglia/macrophage IBA1 marker to identify and count these cells in hippocampi from control rats and at 4 h, 3 days, and 2 weeks after a single episode of pilocarpine-induced SE. We identified, categorized, and counted the IBA1-positive cells with the different morphologies observed after SE in the hippocampal areas CA1, CA3, and dentate gyrus. These included ramified, hypertrophic, bushy, amoeboid, and rod. We found that the ramified phenotype was the most abundant in control hippocampi. In contrast, SE provoked time-dependent changes in the microglial morphology that was characterized by significant increases in the abundance of bushy-shaped cells at 4 h and amoeboid-shaped cells at 3 days and 2 weeks. Interestingly, a significant increase in the number of rod-shaped cells was only evident in the CA1 region at 2 weeks after SE. Taken together, these data suggest that SE triggers time-dependent alterations in the morphology of microglial cells. This detailed description of the spatiotemporal profile of SE-induced microglial morphological changes may help provide insight into their contribution to epileptogenesis.

Metyrapone prevents acute glucose hypermetabolism and short-term brain damage induced by intrahippocampal administration of 4-aminopyridine in rats

Intracerebral administration of the potassium channel blocker 4-aminopyridine (4-AP) triggers neuronal depolarization and intense acute seizure activity followed by neuronal damage. We have recently shown that, in the lithium-pilocarpine rat model of status epilepticus (SE), a single administration of metyrapone, an inhibitor of the 11β-hydroxylase enzyme, had protective properties of preventive nature against signs of brain damage and neuroinflammation. Herein, our aim was to investigate to which extent, pretreatment with metyrapone (150 mg/kg, i.p.) was also able to prevent eventual changes in the acute brain metabolism and short-term neuronal damage induced by intrahippocampal injection of 4-AP (7 μg/5 μl). To this end, regional brain metabolism was assessed by 2-deoxy-2-[¹⁸F]fluoro-d-glucose ([¹⁸F]FDG) positron emission tomography (PET) during the ictal period. Three days later, markers of neuronal death and hippocampal integrity and apoptosis (Nissl staining, NeuN and active caspase-3 immunohistochemistry), neurodegeneration (Fluoro-Jade C labeling), astrogliosis (glial fibrillary acidic protein (GFAP) immunohistochemistry) and microglia-mediated neuroinflammation (in vitro [¹⁸F]GE180 autoradiography) were evaluated. 4-AP administration acutely triggered marked brain hypermetabolism within and around the site of injection as well as short-term signs of brain damage and inflammation. Most important, metyrapone pretreatment was able to reduce ictal hypermetabolism as well as all the markers of brain damage except microglia-mediated neuroinflammation. Overall, our study corroborates the neuroprotective effects of metyrapone against multiple signs of brain damage caused by seizures triggered by 4-AP. Ultimately, our data add up to the consistent protective effect of metyrapone pretreatment reported in other models of neurological disorders of different etiology.

A microglia-cytokine axis to modulate synaptic connectivity and function

Microglia have recently been recognized as key regulators of synapse development, function, and plasticity. Critical to progressing the field is the identification of molecular underpinnings necessary for microglia to carry out these important functions within neural circuits. Here, we focus a review specifically on roles for microglial cytokine signaling within developing and mature neural circuits. We review exciting new studies demonstrating essential roles for microglial cytokine signaling in axon outgrowth, synaptogenesis and synapse maturation during development, as well as synaptic transmission and plasticity in adulthood. Together, these studies identify microglia and cytokines as critical modulators of neural circuits within the healthy brain, with implications for a broad range of neurological disorders with disruptions in synaptic structure and function.

Whole-cell Currents Induced by Puff Application of GABA in Brain Slices

Pharmacological administration is commonly used when conducting whole-cell patch-clamp recording in brain slices. One of the best methods of drug application during electrophysiological recording is the puff technique, which can be used to study the effect of pharmacological reagents on neuronal activities in brain slices. The greatest advantage of puff application is that the drug concentration around the recording site increases rapidly, thus preventing desensitization of membrane receptors. Successful use of puff application involves careful attention to the following elements: the concentration of the drug, the parameters of the puff micropipette, the distance between the tip of a puff micropipette and the neuron recorded, and the duration and pressure driving the puff (pounds per square inch, psi). This article describes a step-by-step procedure for recording whole-cell currents induced by puffing gamma-aminobutyric acid (GABA) onto a neuron of a prefrontal cortical slice. Notably, the same procedure can be applied with minor modifications to other brain areas such as the hippocampus and the striatum, and to different preparations, such as cell cultures.

Microglia emerge as central players in brain disease

There has been an explosion of new findings recently giving us insights into the involvement of microglia in central nervous system (CNS) disorders. A host of new molecular tools and mouse models of disease are increasingly implicating this enigmatic type of nervous system cell as a key player in conditions ranging from neurodevelopmental disorders such as autism to neurodegenerative disorders such as Alzheimer's disease and chronic pain. Contemporaneously, diverse roles are emerging for microglia in the healthy brain, from sculpting developing neuronal circuits to guiding learning-associated plasticity. Understanding the physiological functions of these cells is crucial to determining their roles in disease. Here we focus on recent developments in our rapidly expanding understanding of the function, as well as the dysfunction, of microglia in disorders of the CNS.

Purinergic Signalling: Therapeutic Developments

Purinergic signalling, i.e., the role of nucleotides as extracellular signalling molecules, was proposed in 1972. However, this concept was not well accepted until the early 1990's when receptor subtypes for purines and pyrimidines were cloned and characterised, which includes four subtypes of the P1 (adenosine) receptor, seven subtypes of P2X ion channel receptors and 8 subtypes of the P2Y G protein-coupled receptor. Early studies were largely concerned with the physiology, pharmacology and biochemistry of purinergic signalling. More recently, the focus has been on the pathophysiology and therapeutic potential. There was early recognition of the use of P1 receptor agonists for the treatment of supraventricular tachycardia and A2A receptor antagonists are promising for the treatment of Parkinson's disease. Clopidogrel, a P2Y12 antagonist, is widely used for the treatment of thrombosis and stroke, blocking P2Y12 receptor-mediated platelet aggregation. Diquafosol, a long acting P2Y2 receptor agonist, is being used for the treatment of dry eye. P2X3 receptor antagonists have been developed that are orally bioavailable and stable in vivo and are currently in clinical trials for the treatment of chronic cough, bladder incontinence, visceral pain and hypertension. Antagonists to P2X7 receptors are being investigated for the treatment of inflammatory disorders, including neurodegenerative diseases. Other investigations are in progress for the use of purinergic agents for the treatment of osteoporosis, myocardial infarction, irritable bowel syndrome, epilepsy, atherosclerosis, depression, autism, diabetes, and cancer.

An autocrine purinergic signaling controls astrocyte-induced neuronal excitation

Astrocyte-derived gliotransmitters glutamate and ATP modulate neuronal activity. It remains unclear, however, how astrocytes control the release and coordinate the actions of these gliotransmitters. Using transgenic expression of the light-sensitive channelrhodopsin 2 (ChR2) in astrocytes, we observed that photostimulation reliably increases action potential firing of hippocampal pyramidal neurons. This excitation relies primarily on a calcium-dependent glutamate release by astrocytes that activates neuronal extra-synaptic NMDA receptors. Remarkably, our results show that ChR2-induced Ca²⁺ increase and subsequent glutamate release are amplified by ATP/ADP-mediated autocrine activation of P2Y1 receptors on astrocytes. Thus, neuronal excitation is promoted by a synergistic action of glutamatergic and autocrine purinergic signaling in astrocytes. This new mechanism may be particularly relevant for pathological conditions in which ATP extracellular concentration is increased and acts as a major danger signal.

Microglia-mediated synaptic elimination in neuronal development and disease

It has recently become clear that microglia, the immune cells of the central nervous system, are far more active in the healthy brain than previously thought. Microglia facilitate many stages of brain development by shaping neuronal connectivity via synaptic elimination. Dysfunction of these same processes likely underlies a wide range of neurological and neurodevelopmental disorders.

Expression and function of the metabotropic purinergic P2Y receptor family in experimental seizure models and patients with drug-refractory epilepsy

OBJECTIVE

ATP is released into the extracellular space during pathologic processes including increased neuronal firing. Once released, ATP acts on P2 receptors including ionotropic P2X and metabotropic P2Y receptors, resulting in changes to glial function and neuronal network excitability. Evidence suggests an involvement of P2Y receptors in the pathogenesis of epilepsy, but there has been no systematic effort to characterize the expression and function of the P2Y receptor family during seizures and in experimental and human epilepsy.

METHODS

Status epilepticus was induced using either intra-amygdala kainic acid or pilocarpine to characterize the acute- and long-term changes in hippocampal P2Y expression. P2Y expression was also investigated in brain tissue from patients with temporal lobe epilepsy. Finally, we analyzed the effects of two specific P2Y agonists, ADP and UTP, on seizure severity and seizure-induced cell death.

RESULTS

Both intra-amygdala kainic acid and pilocarpine-induced status epilepticus increased the transcription of the uracil-sensitive P2Y receptors P2ry₂ , P2ry₄ , and P2ry₆ and decreased the transcription of the adenine-sensitive P2Y receptors P2ry₁ , P2ry₁₂ , P2ry₁₃ . Protein levels of P2Y₁ , P2Y₂ , P2Y₄ , and P2Y₆ were increased after status epilepticus, whereas P2Y₁₂ expression was decreased. In the chronic phase, P2ry₁ , P2ry₂ , and P2ry₆ transcription and P2Y₁ , P2Y₂ , and P2Y₁₂ protein levels were increased with no changes for the other P2Y receptors. In hippocampal samples from patients with temporal lobe epilepsy, P2Y₁ and P2Y₂ protein expression was increased, whereas P2Y₁₃ levels were lower. Demonstrating a functional contribution of P2Y receptors to seizures, central injection of ADP exacerbated seizure severity, whereas treatment with UTP decreased seizure severity during status epilepticus in mice.

SIGNIFICANCE

The present study is the first to establish the specific hippocampal expression profile and function of the P2Y receptor family after experimental status epilepticus and in human temporal lobe epilepsy and offers potential new targets for seizure control and disease modification.

Chemokine CCL2-CCR2 Signaling Induces Neuronal Cell Death via STAT3 Activation and IL-1β Production after Status Epilepticus

Elevated levels of chemokine C-C motif ligand 2 (CCL2) and its receptor CCR2 have been reported in patients with temporal lobe epilepsy and in experimental seizures. However, the functional significance and molecular mechanism underlying CCL2-CCR2 signaling in epileptic brain remains largely unknown. In this study, we found that the upregulated CCL2 was mainly expressed in hippocampal neurons and activated microglia from mice 1 d after kainic acid (KA)-induced seizures. Taking advantage of CX3CR1^GFP/+:CCR2^RFP/+ double-transgenic mice, we demonstrated that CCL2-CCR2 signaling has a role in resident microglial activation and blood-derived monocyte infiltration. Moreover, seizure-induced degeneration of neurons in the hippocampal CA3 region was attenuated in mice lacking CCL2 or CCR2. We further showed that CCR2 activation induced STAT3 (signal transducer and activator of transcription 3) phosphorylation and IL-1β production, which are critical for promoting neuronal cell death after status epilepticus. Consistently, pharmacological inhibition of STAT3 by WP1066 reduced seizure-induced IL-1β production and subsequent neuronal death. Two weeks after KA-induced seizures, CCR2 deficiency not only reduced neuronal loss, but also attenuated seizure-induced behavioral impairments, including anxiety, memory decline, and recurrent seizure severity. Together, we demonstrated that CCL2-CCR2 signaling contributes to neurodegeneration via STAT3 activation and IL-1β production after status epilepticus, providing potential therapeutic targets for the treatment of epilepsy.SIGNIFICANCE STATEMENT Epilepsy is a global concern and epileptic seizures occur in many neurological conditions. Neuroinflammation associated with microglial activation and monocyte infiltration are characteristic of epileptic brains. However, molecular mechanisms underlying neuroinflammation in neuronal death following epilepsy remain to be elucidated. Here we demonstrate that CCL2-CCR2 signaling is required for monocyte infiltration, which in turn contributes to kainic acid (KA)-induced neuronal cell death. The downstream of CCR2 activation involves STAT3 (signal transducer and activator of transcription 3) phosphorylation and IL-1β production. Two weeks after KA-induced seizures, CCR2 deficiency not only reduced neuronal loss, but also attenuated seizure-induced behavioral impairments, including anxiety, memory decline, and recurrent seizure severity. The current study provides a novel insight on the function and mechanisms of CCL2-CCR2 signaling in KA-induced neurodegeneration and behavioral deficits.

Microglia in steady state

Microglial cells are the resident tissue macrophages of the CNS and are widely recognized for their immune surveillance of the healthy CNS. In addition to this well-accepted function, recent findings point to major roles for microglia in instructing and regulating the proper function of the neuronal networks in the adult CNS, but these cells are also involved in creating neuronal networks by orchestrating construction of the whole network during development. In this Review, we highlight recent findings about the steady-state functions of microglial cells, the factors that are important for physiological microglial function, and how microglia help to maintain tissue homeostasis in the CNS.

What the Spectrum of Microglial Functions Can Teach us About Fetal Alcohol Spectrum Disorder

Alcohol exposure during gestation can lead to severe defects in brain development and lifelong physical, behavioral and learning deficits that are classified under the umbrella term fetal alcohol spectrum disorder (FASD). Sadly, FASD is diagnosed at an alarmingly high rate, affecting 2%–5% of live births in the United States, making it the most common non-heritable cause of mental disability. Currently, no standard therapies exist that are effective at battling FASD symptoms, highlighting a pressing need to better understand the underlying mechanisms by which alcohol affects the developing brain. While it is clear that sensory and cognitive deficits are driven by inappropriate development and remodeling of the neural circuits that mediate these processes, alcohol’s actions acutely and long-term on the brain milieu are diverse and complex. Microglia, the brain’s immune cells, have been thought to be a target for alcohol during development because of their exquisite ability to rapidly detect and respond to perturbations affecting the brain. Additionally, our view of these immune cells is rapidly changing, and recent studies have revealed a myriad of microglial physiological functions critical for normal brain development and long-term function. A clear and complete understanding of how microglial roles on this end of the spectrum may be altered in FASD is currently lacking. Such information could provide important insights toward novel therapeutic targets for FASD treatment. Here we review the literature that links microglia to neural circuit remodeling and provide a discussion of the current understanding of how developmental alcohol exposure affects microglial behavior in the context of developing brain circuits.

Enhanced classical complement pathway activation and altered phagocytosis signaling molecules in human epilepsy

Microglia-mediated neuroinflammation is widely associated with seizures and epilepsy. Although microglial cells are professional phagocytes, less is known about the status of this phenotype in epilepsy. Recent evidence supports that phagocytosis-associated molecules from the classical complement (C1q-C3) play novel roles in microglia-mediated synaptic pruning. Interestingly, in human and experimental epilepsy, altered mRNA levels of complement molecules were reported. Therefore, to identify a potential role for complement and microglia in the synaptodendritic pathology of epilepsy, we determined the protein levels of classical complement proteins (C1q-C3) along with other phagocytosis signaling molecules in human epilepsy. Cortical brain samples surgically resected from patients with refractory epilepsy (RE) and non-epileptic lesions (NE) were examined. Western blotting was used to determine the levels of phagocytosis signaling proteins such as the complements C1q and C3, MerTK, Trem2, and Pros1 along with cleaved-caspase 3. In addition, immunostaining was used to determine the distribution of C1q and co-localization to microglia and dendrites. We found that the RE samples had significantly increased protein levels of C1q (p=0.034) along with those of its downstream activation product iC3b (p=0.027), and decreased levels of Trem2 (p=0.045) and Pros1 (p=0.005) when compared to the NE group. Protein levels of cleaved-caspase 3 were not different between the groups (p=0.695). In parallel, we found C1q localization to microglia and dendrites in both NE and RE samples, and also observed substantial microglia-dendritic interactions in the RE tissue. These data suggest that aberrant phagocytic signaling occurs in human refractory epilepsy. It is likely that alteration of phagocytic pathways may contribute to unwanted elimination of cells/synapses and/or impaired clearance of dead cells. Future studies will investigate whether altered complement signaling contributes to the hyperexcitability that result in epilepsy.

Contribution of platelet P2Y12 receptors to chronic Complete Freund's adjuvant-induced inflammatory pain

Essentials The role of platelet P2Y12 receptors in the regulation of chronic inflammatory pain is unknown. Complete Freund's Adjuvant (CFA)-induced chronic inflammatory pain model was used in mice. Gene deficiency and antagonists of P2Y12 receptors attenuate hyperalgesia and local inflammation. Platelet P2Y12 receptors contribute to these effects in the chronic phase of inflammation.

SUMMARY

Background P2Y12 receptor antagonists are widely used in clinical practice to inhibit platelet aggregation. P2Y12 receptors are also known to regulate different forms of pain as well as local and systemic inflammation. However, it is not known whether platelet P2Y12 receptors contribute to these effects. Objectives To explore the contribution of platelet P2Y12 receptors to chronic inflammatory pain in mice. Methods Complete Freund's adjuvant (CFA)-induced chronic inflammatory pain was induced in wild-type and P2ry12 gene-deficient (P2ry12-/- ) mice, and the potent, direct-acting and reversible P2Y12 receptor antagonists PSB-0739 and cangrelor were used. Results CFA-induced mechanical hyperalgesia was significantly decreased in P2ry12-/- mice for up to 14 days, and increased neutrophil myeloperoxidase activity and tumor necrosis factor (TNF)-α and CXCL1 (KC) levels in the hind paws were also attenuated in the acute inflammation phase. At day 14, increased interleukin (IL)-1β, IL-6, TNF-α and KC levels were attenuated in P2ry12-/- mice. PSB-0739 and cangrelor reversed hyperalgesia in wild-type mice but had no effect in P2ry12-/- mice, and PSB-0739 was also effective when applied locally. The effects of both local and systemic PSB-0739 were prevented by A-803467, a selective NaV1.8 channel antagonist, suggesting the involvement of NaV1.8 channels in the antihyperalgesic effect. Platelet depletion by anti-mouse CD41 antibody decreased hyperalgesia and attenuated the proinflammatory cytokine response in wild-type but not in P2ry12-/- mice on day 14. Conclusions In conclusion, P2Y12 receptors regulate CFA-induced hyperalgesia and the local inflammatory response, and platelet P2Y12 receptors contribute to these effects in the chronic inflammation phase.

Sotalol enhances the anticonvulsant action of valproate and diphenylhydantoin in the mouse maximal electroshock model

BACKGROUND

Sotalol as a drug blocking β-receptors and potassium KCNH2 channels may interact with different substances that affect seizures. Herein, we present interactions between sotalol and four conventional antiepileptic drugs: carbamazepine, valproate, phenytoin and phenobarbital.

METHODS

Effects of sotalol and antiepileptics alone on seizures were determined in the electroconvulsive threshold test, while interactions between sotalol and antiepileptic drugs were estimated in the maximal electroshock test in mice. Motor coordination and long-term memory were evaluated, respectively, in the chimney test and passive-avoidance task. Brain concentrations of antiepileptics were determined by fluorescence polarization immunoassay.

RESULTS

Sotalol at doses up to 100mg/kg did not affect the electroconvulsive threshold. Applied at doses 60-100mg/kg, sotalol potentiated the antielectroshock action of valproate, while at doses 80-100mg/kg that of phenytoin. Sotalol (up to 100mg/kg) did not affect the action of carbamazepine or phenobarbital in the maximal electroshock. Sotalol alone and in combinations with antiepileptics impaired neither motor performance nor long-term memory in mice. Finally, sotalol did not change brain concentration of valproate and phenytoin, so pharmacokinetic interactions between the drugs are not probable.

CONCLUSIONS

As far as obtained data may be extrapolated into clinical conditions, sotalol may be considered as an arrhythmic drug that does not reduce the action of classical antiepileptic drugs and thereby can be used in epileptic patients with cardiac arrhythmias.

Role of Akt-independent mTORC1 and GSK3β signaling in sublethal NMDA-induced injury and the recovery of neuronal electrophysiology and survival

Glutamate-induced excitotoxicity, mediated by overstimulation of N-methyl-D-aspartate (NMDA) receptors, is a mechanism that causes secondary damage to neurons. The early phase of injury causes loss of dendritic spines and changes to synaptic activity. The phosphatidylinositol-4,5-bisphosphate 3-kinase/Akt/ mammalian target of rapamycin (PI3K/Akt/mTOR) pathway has been implicated in the modulation and regulation of synaptic strength, activity, maturation, and axonal regeneration. The present study focuses on the physiology and survival of neurons following manipulation of Akt and several downstream targets, such as GSK3β, FOXO1, and mTORC1, prior to NMDA-induced injury. Our analysis reveals that exposure to sublethal levels of NMDA does not alter phosphorylation of Akt, S6, and GSK3β at two and twenty four hours following injury. Electrophysiological recordings show that NMDA-induced injury causes a significant decrease in spontaneous excitatory postsynaptic currents at both two and twenty four hours, and this phenotype can be prevented by inhibiting mTORC1 or GSK3β, but not Akt. Additionally, inhibition of mTORC1 or GSK3β promotes neuronal survival following NMDA-induced injury. Thus, NMDA-induced excitotoxicity involves a mechanism that requires the permissive activity of mTORC1 and GSK3β, demonstrating the importance of these kinases in the neuronal response to injury.

The adenosine generating enzymes CD39/CD73 control microglial processes ramification in the mouse brain

Microglial cells invade the brain as amoeboid precursors and acquire a highly ramified morphology in the postnatal brain. Microglia express all essential purinergic elements such as receptors, nucleoside transporters and ecto-enzymes, including CD39 (NTPDase1) and CD73 (5'-nucleotidase), which sequentially degrade extracellular ATP to adenosine. Here, we show that constitutive deletion of CD39 and CD73 or both caused an inhibition of the microglia ramified phenotype in the brain with a reduction in the length of processes, branching frequency and number of intersections with Sholl spheres. In vitro, unlike wild-type microglia, cd39^-/- and cd73^-/- microglial cells were less complex and did not respond to ATP with the transformation into a more ramified phenotype. In acute brain slices, wild-type microglia retracted approximately 50% of their processes within 15 min after slicing of the brain, and this phenomenon was augmented in cd39^-/- mice; moreover, the elongation of microglial processes towards the source of ATP or towards a laser lesion was observed only in wild-type but not in cd39^-/- microglia. An elevation of extracellular adenosine 1) by the inhibition of adenosine transport with dipyridamole, 2) by application of exogenous adenosine or 3) by degradation of endogenous ATP/ADP with apyrase enhanced spontaneous and ATP-induced ramification of cd39^-/- microglia in acute brain slices and facilitated the transformation of cd39^-/- and cd73^-/- microglia into a ramified process-bearing phenotype in vitro. These data indicate that under normal physiological conditions, CD39 and CD73 nucleotidases together with equilibrative nucleoside transporter 1 (ENT1) control the fate of extracellular adenosine and thereby the ramification of microglial processes.