NR2A contributes to genesis and propagation of cortical spreading depression in rats

Development of a Dihydroquinoline-Pyrazoline GluN2C/2D-Selective Negative Allosteric Modulator of the N-Methyl-d-aspartate Receptor

Subunit-selective inhibition of N-methyl-d-aspartate receptors (NMDARs) is a promising therapeutic strategy for several neurological disorders, including epilepsy, Alzheimer's and Parkinson's disease, depression, and acute brain injury. We previously described the dihydroquinoline-pyrazoline (DQP) analogue 2a (DQP-26) as a potent NMDAR negative allosteric modulator with selectivity for GluN2C/D over GluN2A/B. However, moderate (<100-fold) subunit selectivity, inadequate cell-membrane permeability, and poor brain penetration complicated the use of 2a as an in vivo probe. In an effort to improve selectivity and the pharmacokinetic profile of the series, we performed additional structure-activity relationship studies of the succinate side chain and investigated the use of prodrugs to mask the pendant carboxylic acid. These efforts led to discovery of the analogue (S)-(-)-2i, also referred to as (S)-(-)-DQP-997-74, which exhibits >100- and >300-fold selectivity for GluN2C- and GluN2D-containing NMDARs (IC50 0.069 and 0.035 μM, respectively) compared to GluN2A- and GluN2B-containing receptors (IC50 5.2 and 16 μM, respectively) and has no effects on AMPA, kainate, or GluN1/GluN3 receptors. Compound (S)-(-)-2i is 5-fold more potent than (S)-2a. In addition, compound 2i shows a time-dependent enhancement of inhibitory actions at GluN2C- and GluN2D-containing NMDARs in the presence of the agonist glutamate, which could attenuate hypersynchronous activity driven by high-frequency excitatory synaptic transmission. Consistent with this finding, compound 2i significantly reduced the number of epileptic events in a murine model of tuberous sclerosis complex (TSC)-induced epilepsy that is associated with upregulation of the GluN2C subunit. Thus, 2i represents a robust tool for the GluN2C/D target validation. Esterification of the succinate carboxylate improved brain penetration, suggesting a strategy for therapeutic development of this series for NMDAR-associated neurological conditions.

Testing the Role of Glutamate NMDA Receptors in Peripheral Trigeminal Nociception Implicated in Migraine Pain

The pro-nociceptive role of glutamate in the CNS in migraine pathophysiology is well established. Glutamate, released from trigeminal afferents, activates second order nociceptive neurons in the brainstem. However, the function of peripheral glutamate receptors in the trigeminovascular system suggested as the origin site for migraine pain, is less known. In the current project, we used calcium imaging and patch clamp recordings from trigeminal ganglion (TG) neurons, immunolabelling, CGRP assay and direct electrophysiological recordings from rat meningeal afferents to investigate the role of glutamate in trigeminal nociception. Glutamate, aspartate, and, to a lesser extent, NMDA under free-magnesium conditions, evoked calcium transients in a fraction of isolated TG neurons, indicating functional expression of NMDA receptors. The fraction of NMDA sensitive neurons was increased by the migraine mediator CGRP. NMDA also activated slowly desensitizing currents in 37% of TG neurons. However, neither glutamate nor NMDA changed the level of extracellular CGRP. TG neurons expressed both GluN2A and GluN2B subunits of NMDA receptors. In addition, after removal of magnesium, NMDA activated persistent spiking activity in a fraction of trigeminal nerve fibers in meninges. Thus, glutamate activates NMDA receptors in somas of TG neurons and their meningeal nerve terminals in magnesium-dependent manner. These findings suggest that peripherally released glutamate can promote excitation of meningeal afferents implicated in generation of migraine pain in conditions of inherited or acquired reduced magnesium blockage of NMDA channels and support the usage of magnesium supplements in migraine.

Src family kinases activity is required for transmitting purinergic P2X7 receptor signaling in cortical spreading depression and neuroinflammation

BACKGROUND

Purinergic P2X7 receptor plays an important role in migraine pathophysiology. Yet precise molecular mechanism underlying P2X7R signaling in migraine remains unclear. This study explores the hypothesis that P2X7 receptor transmits signaling to Src family kinases (SFKs) during cortical spreading depression (CSD) and neuroinflammation after CSD.

METHODS

CSD was recorded using electrophysiology in rats and intrinsic optical imaging in mouse brain slices. Cortical IL-1β and TNFα mRNA levels were detected using qPCR. Glutamate release from mouse brain slices was detected using glutamate assay.

RESULTS

The data showed that deactivation of SFKs by systemic injection of PP2 reduced cortical susceptibility to CSD in rats and CSD-induced IL-1β and TNF-α gene expression in rat ipsilateral cortices. Consistently, in mouse brain slices, inhibition of SFKs activity by saracatinib and P2X7 receptor by A740003 similarly reduced cortical susceptibility to CSD. When the interaction of P2X7 receptor and SFKs was disrupted by TAT-P2X7, a marked reduction of cortical susceptibility to CSD, IL-1β gene expression and glutamate release after CSD induction were observed in mouse brain slices. The reduced cortical susceptibility to CSD by TAT-P2X7 was restored by NMDA, and disrupting the Fyn-NMDA interaction using TAT-Fyn (39-57) but not disrupting Src-NMDA receptor interaction using TAT-Src (40-49) reduced cortical susceptibility to CSD. Furthermore, activation of P2X7 receptor by BzATP restored the TAT-Fyn (39-57)-reduced cortical susceptibility to CSD.

CONCLUSION

This study reveals that SFKs activity transmits P2X7 receptor signaling to facilitate CSD propagation via glutamatergic pathway and promote neuroinflammation, which is of particular relevance to migraine.

Cerebellar spreading depolarization mediates paroxysmal movement disorder

Paroxysmal kinesigenic dyskinesia (PKD) is the most common paroxysmal dyskinesia, characterized by recurrent episodes of involuntary movements provoked by sudden changes in movement. Proline-rich transmembrane protein 2 (PRRT2) has been identified as the major causative gene for PKD. Here, we report that PRRT2 deficiency facilitates the induction of cerebellar spreading depolarization (SD) and inhibition of cerebellar SD prevents the occurrence of dyskinetic movements. Using Ca²⁺ imaging, we show that cerebellar SD depolarizes a large population of cerebellar granule cells and Purkinje cells in Prrt2-deficient mice. Electrophysiological recordings further reveal that cerebellar SD blocks Purkinje cell spiking and disturbs neuronal firing of the deep cerebellar nuclei (DCN). The resultant aberrant firing patterns in DCN are tightly, temporally coupled to dyskinetic episodes in Prrt2-deficient mice. Cumulatively, our findings uncover a pivotal role of cerebellar SD in paroxysmal dyskinesia, providing a potent target for treating PRRT2-related paroxysmal disorders.

Updated review on the link between cortical spreading depression and headache disorders

INTRODUCTION

Experimental animal studies have revealed mechanisms that link cortical spreading depression (CSD) to the trigeminal activation mediating lateralized headache. However, conventional CSD as seen in lissencephalic brain is insufficient to explain some clinical features of aura and migraine headache.

AREAS COVERED

The importance of CSD in headache development including dysfunction of the thalamocortical network, neuroinflammation, calcitonin gene-related peptide, transgenic models, and the role of CSD in migraine triggers, treatment options, neuromodulation and future directions are reviewed.

EXPERT OPINION

The conventional understanding of CSD marching across the hemisphere is invalid in gyrencephalic brains. Thalamocortical dysfunction and interruption of functional cortical network systems by CSD, may provide alternative explanations for clinical manifestations of migraine phases including aura. Not all drugs showing CSD blocking properties in lissencephalic brains, have efficacy in migraine headache and monoclonal antibodies against CGRP ligand/receptors which are effective in migraine treatment, have no impact on aura in humans or CSD properties in rodents. Functional networks and molecular mechanisms mediating and amplifying the effects of limited CSD in migraine brain remain to be investigated to define new targets.

Inhibition of NR2A reduces calcitonin gene-related peptide gene expression induced by cortical spreading depression in rat amygdala

Despite robust evidence on the role of calcitonin gene-related peptide (CGRP) in migraine via both central and peripheral actions, relatively less is known about how CGRP in the limbic system is involved in migraine progression. This study investigated whether CGRP production machinery exists in the two key limbic regions including hippocampus and amygdala using cortical spreading depression (CSD) as a model of migraine and whether such alteration by CSD is sensitive to N-methyl-d-aspartate (NMDA) receptor regulation in rats. A single or repetitive CSD was induced by topical application of KCl and monitored using electrophysiological methods. The NR2A-containing NMDA receptor antagonist, NVP-AAM077, or its vehicle, was perfused into the contralateral cerebroventricular ventricle of rat. Quantitative PCR was used to measure CGRP mRNA levels in the ipsilateral and contralateral hippocampus and amygdala after CSD events and compared to respective sham treatments. The results showed that neither a single CSD nor repetitive CSD affected CGRP mRNA levels in both the contralateral and ipsilateral hippocampus at 24 h post CSD induction. Differently, significant elevation of CGRP gene expression was observed in the ipsilateral amygdala at 24 h post multiple CSD, but not contralateral side, and not post-single CSD. Further results showed that the CSD-induced CGRP gene expression in the amygdala was markedly reduced by NVP-AAM077 and this reduction corresponded to a reduced cortical susceptibility to CSD in rats. We conclude that repetitive CSD events induce CGRP gene expression in amygdala, which is sensitive to NR2A regulation.

Sarcoma Family Kinase-Dependent Pannexin-1 Activation after Cortical Spreading Depression is Mediated by NR2A-Containing Receptors

Cortical spreading depression (CSD) is a propagating wave of depolarization followed by depression of cortical activity. CSD triggers neuroinflammation via the pannexin-1 (Panx1) channel opening, which may eventually cause migraine headaches. However, the regulatory mechanism of Panx1 is unknown. This study investigates whether sarcoma family kinases (SFK) are involved in transmitting CSD-induced Panx1 activation, which is mediated by the NR2A-containing N-methyl-D-aspartate receptor. CSD was induced by topical application of K⁺ to cerebral cortices of rats and mouse brain slices. SFK inhibitor, PP2, or NR2A–receptor antagonist, NVP–AAM077, was perfused into contralateral cerebral ventricles (i.c.v.) of rats prior to CSD induction. Co-immunoprecipitation and Western blot were used for detecting protein interactions, and histofluorescence for addressing Panx1 activation. The results demonstrated that PP2 attenuated CSD-induced Panx1 activation in rat ipsilateral cortices. Cortical susceptibility to CSD was reduced by PP2 in rats and by TAT-Panx308 that disrupts SFK–Panx1 interaction in mouse brain slices. Furthermore, CSD promoted activated SFK coupling with Panx1 in rat ipsilateral cortices. Moreover, inhibition of NR2A by NVP–AAM077 reduced elevation of ipsilateral SFK–Panx1 interaction, Panx1 activation induced by CSD and cortical susceptibility to CSD in rats. These data suggest NR2A-regulated, SFK-dependent Panx1 activity plays an important role in migraine aura pathogenesis.

ROS/TRPA1/CGRP signaling mediates cortical spreading depression

Objectives

The transient receptor potential ankyrin A 1 (TRPA1) channel and calcitonin gene-related peptide (CGRP) are targets for migraine prophylaxis. This study aimed to understand their mechanisms in migraine by investigating the role of TRPA1 in cortical spreading depression (CSD) in vivo and exploring how reactive oxygen species (ROS)/TRPA1/CGRP interplay in regulating cortical susceptibility to CSD.

Methods

Immunohistochemistry was used for detecting TRPA1 expression. CSD was induced by K⁺ on the cerebral cortex, monitored using electrophysiology in rats, and intrinsic optical imaging in mouse brain slices, respectively. Drugs were perfused into contralateral ventricle of rats. Lipid peroxidation (malondialdehyde, MDA) analysis was used for indicating ROS level.

Results

TRPA1 was expressed in cortical neurons and astrocytes of rats and mice. TRPA1 deactivation by an anti-TRPA1 antibody reduced cortical susceptibility to CSD in rats and decreased ipsilateral MDA level induced by CSD. In mouse brain slices, H₂O₂ facilitated submaximal CSD induction, which disappeared by the antioxidant, tempol and the TRPA1 antagonist, A-967079; Consistently, TRPA1 activation reversed prolonged CSD latency and reduced magnitude by the antioxidant. Further, blockade of CGRP prolonged CSD latency, which was reversed by H₂O₂ and the TRPA1 agonist, allyl-isothiocyanate, respectively.

Conclusions

ROS/TRPA1/CGRP signaling plays a critical role in regulating cortical susceptibility to CSD. Inhibition ROS and deactivation of TRPA1 channels may have therapeutic benefits in preventing stress-triggered migraine via CGRP.

Positive and Negative Allosteric Modulators of N-Methyl-d-aspartate (NMDA) Receptors: Structure-Activity Relationships and Mechanisms of Action

Excitatory activity in the CNS is predominately mediated by l-glutamate through several families of l-glutamate neurotransmitter receptors. Of these, the N-methyl-d-aspartate receptor (NMDAR) family has many critical roles in CNS function and in various neuropathological and psychiatric conditions. Until recently, the types of compounds available to regulate NMDAR function have been quite limited in terms of mechanism of action, subtype selectivity, and biological effect. However, several new classes of NMDAR agents have now been identified that are positive or negative allosteric modulators (PAMs and NAMs, respectively) with various patterns of NMDAR subtype selectivity. These new agents act at several newly recognized binding sites on the NMDAR complex and offer significantly greater pharmacological control over NMDAR activity than previously available agents. The purpose of this review is to summarize the structure-activity relationships for these new NMDAR modulator drug classes and to describe the current understanding of their mechanisms of action.

Episodic Migraine With and Without Aura: Key Differences and Implications for Pathophysiology, Management, and Assessing Risks

PURPOSE OF REVIEW

To review the pathophysiologic, epidemiologic, and clinical evidence for similarities and differences between migraine with and without aura.

RECENT FINDINGS

The ICHD-3 has recently refined the diagnostic criteria for aura to include positive symptomatology, which better differentiates aura from TIA. Although substantial evidence supports cortical spreading depression as the cause of visual aura, the role (if any) of CSD in headache pain is not well understood. Recent imaging evidence suggests a possible hypothalamic origin for a headache attack, but further research is needed. Migraine with aura is associated with a modest increase in the risk of ischemic stroke. The etiology for this association remains unclear. There is a paucity of evidence regarding treatments specifically aimed at the migraine with aura subtype, or whether migraine with vs without aura responds to treatment differently. Migraine with typical aura is therefore often treated similarly to migraine without aura. Lamotrigine, daily aspirin, and flunarizine have evidence for efficacy in prevention of migraine with aura, and magnesium, ketamine, furosemide, and single-pulse transcranial magnetic stimulation have evidence for use as acute treatments. Although triptans have traditionally been contraindicated in hemiplegic migraine and migraine with brainstem aura, this prohibition is being reconsidered in the face of evidence suggesting that use may be safe. The debate as to whether migraine with and without aura are different entities is ongoing. In an era of sophisticated imaging, genetic advancement, and ongoing clinical trials, efforts to answer this question are likely to yield important and clinically meaningful results.

Systematic review of the pharmacological agents that have been tested against spreading depolarizations

Spreading depolarization (SD) occurs alongside brain injuries and it can lead to neuronal damage. Therefore, pharmacological modulation of SD can constitute a therapeutic approach to reduce its detrimental effects and to improve the clinical outcome of patients. The major objective of this article was to produce a systematic review of all the drugs that have been tested against SD. Of the substances that have been examined, most have been shown to modulate certain SD characteristics. Only a few have succeeded in significantly inhibiting SD. We present a variety of strategies that have been proposed to overcome the notorious harmfulness and pharmacoresistance of SD. Information on clinically used anesthetic, sedative, hypnotic agents, anti-migraine drugs, anticonvulsants and various other substances have been compiled and reviewed with respect to the efficacy against SD, in order to answer the question of whether a drug at safe doses could be of therapeutic use against SD in humans.

Sarcoma family kinase activity is required for cortical spreading depression

Objectives Sarcoma family kinase activity is associated with multiple diseases including ischemia and cancer; however, its role in the mechanism of migraine aura has been less well characterised. This study aims to investigate whether sarcoma family kinase is required for cortical spreading depression. Methods Cortical spreading depression was induced by topical application of K⁺ to the cerebral cortex and was monitored using electrophysiology in rats, and intrinsic optical signal in mouse brain slices. Drugs were perfused into the contralateral cerebral ventricle for pharmacological manipulations in rats. Western blot analysis was used for detecting the level of phosphorylated, and total, sarcoma family kinase in the ipsilateral cortex of rats. Key results The data demonstrate that a single cortical spreading depression in rats induced ipsilateral cortical sarcoma family kinase phosphorylation at the Y416 site. Deactivation of sarcoma family kinase by its inhibitor (3-(4-chlorophenyl) 1-(1,1-dimethylethyl)-1 H-pyrazolo[3,4- dpyrimidin-4-amine) suppressed the elevated enzyme activity and cortical susceptibility to cortical spreading depression. Interestingly, the inhibitory effect of the N-methyl-D-aspartate receptor antagonist NVP-AAM077 on cortical spreading depression was reversed by the sarcoma family kinase activator pYEEI (EPQY(PO₃H₂)EEEIPIYL), suggesting a link between this enzyme and N-methyl-D-aspartate receptors. Similarly, after deactivation of sarcoma family kinase, a reduction of sarcoma family kinase phosphorylation and cortical susceptibility to cortical spreading depression was observed with NVP-AAM077. Conclusions We conclude that activation of sarcoma family kinase is required for cortical spreading depression, and this process is regulated by recruiting N-methyl-D-aspartate receptors. This study provides novel insight for sarcoma family kinase function in the mechanism of migraine aura.

NMDA Receptors in the Central Nervous System

NMDA-type glutamate receptors are ligand-gated ion channels that mediate a major component of excitatory neurotransmission in the central nervous system (CNS). They are widely distributed at all stages of development and are critically involved in normal brain functions, including neuronal development and synaptic plasticity. NMDA receptors are also implicated in the pathophysiology of numerous neurological and psychiatric disorders, such as ischemic stroke, traumatic brain injury, Alzheimer's disease, epilepsy, mood disorders, and schizophrenia. For these reasons, NMDA receptors have been intensively studied in the past several decades to elucidate their physiological roles and to advance them as therapeutic targets. Seven NMDA receptor subunits exist that assemble into a diverse array of tetrameric receptor complexes, which are differently regulated, have distinct regional and developmental expression, and possess a wide range of functional and pharmacological properties. The diversity in subunit composition creates NMDA receptor subtypes with distinct physiological roles across neuronal cell types and brain regions, and enables precise tuning of synaptic transmission. Here, we will review the relationship between NMDA receptor structure and function, the diversity and significance of NMDA receptor subtypes in the CNS, as well as principles and rules by which NMDA receptors operate in the CNS under normal and pathological conditions.