Gliosis is a histopathological characteristic of epilepsy that comprises activated microglia and astrocytes. It is unclear whether or how crosstalk occurs between microglia and astrocytes in the ...evolution of epilepsy. Here, we report in a mouse model of status epilepticus, induced by intracerebroventricular injection of kainic acid (KA), sequential activation of microglia and astrocytes and their close spatial interaction in the hippocampal CA3 region. Microglial ablation reduced astrocyte activation and their upregulation of complement C3. When compared to wild‐type mice, both C3−/− and C3aR−/− mice had significantly less microglia–astrocyte interaction in response to KA‐induced status epilepticus. Additionally, KA‐injected C3−/− mice had significantly less histochemical evidence of neurodegeneration. The results suggest that the C3‐C3aR pathway contributes to KA‐induced neurodegeneration by mediating microglia–astrocyte communication. The C3‐C3aR pathway may prove to be a potential therapeutic target for epilepsy treatment.
Main Points
Microglia are required for astrocytes activation in experimental status epilepticus.
C3 from astrocytes activates microglia via C3a receptors.
Microglia–astrocyte interaction promotes gliosis and neuronal injury after seizures.
Cognition and behavior are tightly linked to synaptic function. A growing body of evidence suggests that aberrant neurotransmission, caused by changes in synaptic protein expression levels, may be a ...major cause underlying different brain disorders. These changes in expression result in abnormal synaptic organization or function, leading to impaired neurotransmission and unbalanced circuit operations. Here, we review the data supporting the involvement of mutations in genes coding for kainate receptor (KAR) subunits in the pathogenesis of psychiatric disorders and Down syndrome (DS). We show that most of these mutations do not affect the biophysical properties or the receptors, but rather alter subunit expression levels. On the basis of reports studying KAR genes mutations in mouse models of autism spectrum disorders and DS, we illustrate how deviations from the physiological regulatory role that these receptors play in neurotransmitter release and plasticity give rise to synaptic alterations that lead to behavioral and cognitive deficits underlying these disorders.
This article is part of the special Issue on ‘Glutamate Receptors – Kainate receptors’.
•Many cases of brain disorders are associated with changes in expression levels of synaptic proteins.•Mutations in KAR subunits are linked to psychiatric disorders and Down syndrome.•Dysregulation of KARs expression results in aberrant synaptic transmission.•Excess of KARs impair brain function and reproduce behaviours related to human diseases.
Although halogen radicals are recognized to form as products of hydroxyl radical (•OH) scavenging by halides, their contribution to the phototransformation of marine organic compounds has received ...little attention. We demonstrate that, relative to freshwater conditions, seawater halides can increase photodegradation rates of domoic acid, a marine algal toxin, and dimethyl sulfide, a volatile precursor to cloud condensation nuclei, up to fivefold. Using synthetic seawater solutions, we show that the increased photodegradation is specific to dissolved organic matter (DOM) and halides, rather than other seawater salt constituents (e.g., carbonates) or photoactive species (e.g., iron and nitrate). Experiments in synthetic and natural coastal and estuarine water samples demonstrate that the halide-specific increase in photodegradation could be attributed to photochemically generated halogen radicals rather than other photoproduced reactive intermediates e.g., excited-state triplet DOM (3DOM*), reactive oxygen species. Computational kinetic modeling indicates that seawater halogen radical concentrations are two to three orders of magnitude greater than freshwater •OH concentrations and sufficient to account for the observed halide-specific increase in photodegradation. Dark •OH generation by gamma radiolysis demonstrates that halogen radical production via •OH scavenging by halides is insufficient to explain the observed effect. Using sensitizer models for DOM chromophores, we show that halogen radicals are formed predominantly by direct oxidation of Cl⁻ and Br⁻ by ³DOM*, an •OH-independent pathway. Our results indicate that halogen radicals significantly contribute to the phototransformation of algal products in coastal or estuarine surface waters.
During neuronal development, AMPA receptors (AMPARs) and NMDA receptors (NMDARs) are important for neuronal differentiation. Kainate receptors (KARs) are closely related to AMPARs and involved in the ...regulation of cortical network activity. However, their role for neurite growth and differentiation of cortical neurons is unclear. Here, we used KAR agonists and overexpression of selected KAR subunits and their auxiliary neuropilin and tolloid-like proteins, NETOs, to investigate their influence on dendritic growth and network activity in organotypic cultures of rat visual cortex. Kainate at 500 nM enhanced network activity and promoted development of dendrites in layer II/III pyramidal cells, but not interneurons. GluK2 overexpression promoted dendritic growth in pyramidal cells and interneurons. GluK2 transfectants were highly active and acted as drivers for network activity. GluK1 and NETO1 specifically promoted dendritic growth of interneurons. Our study provides new insights for the roles of KARs and NETOs in the morphological and physiological development of the visual cortex.
Focused ultrasound (FUS) has potential utility for modulating regional brain excitability and possibly aiding seizure control; however, the duration of any beneficial effect is unknown. This study ...explores the efficacy and time course of a short series of pulsed FUS in suppressing EEG epileptiform spikes/bursts in a kainic acid (KA) animal model of temporal lobe epilepsy. Forty-four male Sprague–Dawley rats were recorded for 14 weeks with EEG while software calculated EEG numbers of epileptiform spikes and bursts (≥ 3 spikes/s). Four regimens of FUS given in a single session at week 7 were evaluated, with mechanical index (MI) ranging from 0.25 to 0.75, intensity spatial peak temporal average (
I
SPTA
) from 0.1 to 2.8 W per cm
2
, duty cycle from 1 to 30%, and three consecutive pulse trains for 5 or 10 min each. Controls included sham injections in four and KA without FUS in eleven animals. Histological analysis investigated tissue effects. All animals receiving KA evidenced EEG spikes, averaging 10,378 ± 1651 spikes per 8 h and 1255 ± 199 bursts per 8 h by weeks 6–7. The KA-only group showed a 30% of increase in spikes and bursts by week 14. Compared to the KA-only group, spike counts were reduced by about 25%, burst counts by about 33%, and burst durations by about 50% with FUS. Behavioral seizures were not analyzed, but electrographic seizures longer than 10 s declined up to 70% after some FUS regimens. Repeated-measure ANOVA showed a significant effect of higher intensity and longer sonication duration FUS treatment using 0.75-MI,
I
SPTA
2.8 W/cm
2
, 30% duty cycle for 10-min sonications (group effect,
F
(4, 15) = 6.321,
p
< 0.01; interaction effect,
F
(44, 165) = 1.726,
p
< 0.01), with the hippocampal protective effect lasting to week 14, accompanied by decreased inflammation and gliosis effect. In contrast, spike and burst suppression were achieved using an FUS regimen with 0.25-MI
I
SPTA
0.5 W/cm
2
, 30% duty cycle for 10-min sonications. This regimen reduced inflammation and gliosis at weeks 8–14 and protected hippocampal tissue. This study demonstrates that low-intensity pulsed ultrasound can modulate epileptiform activity for up to 7 weeks and, if replicated in the clinical setting, might be a practical treatment for epilepsy.
Objective
Pharmacoresistance and the lack of disease‐modifying actions of current antiseizure drugs persist as major challenges in the treatment of epilepsy. Experimental models of ...chemoconvulsant‐induced status epilepticus remain the models of choice to discover potential antiepileptogenic drugs, but doubts remain as to the extent to which they model human pathophysiology. The aim of the present study was to compare the molecular landscape of the intra‐amygdala kainic acid model of status epilepticus in mice with findings in resected brain tissue from patients with drug‐resistant temporal lobe epilepsy (TLE).
Methods
Status epilepticus was induced via intra‐amygdala microinjection of kainic acid in C57BL/6 mice, and gene expression was analyzed via microarrays in hippocampal tissue at acute and chronic time‐points. Results were compared to reference datasets in the intraperitoneal pilocarpine and intrahippocampal kainic acid model and to human resected brain tissue (hippocampus and cortex) from patients with drug‐resistant TLE.
Results
Intra‐amygdala kainic acid injection in mice triggered extensive dysregulation of gene expression that was ~3‐fold greater shortly after status epilepticus (2729 genes) when compared to epilepsy (412). Comparison to samples from patients with TLE revealed a particularly high correlation of gene dysregulation during established epilepsy. Pathway analysis found suppression of calcium signaling to be highly conserved across different models of epilepsy and patients. cAMP response element‐binding protein (CREB) was predicted as one of the main upstream transcription factors regulating gene expression during acute and chronic phases, and inhibition of CREB reduced seizure severity in the intra‐amygdala kainic acid model.
Significance
Our findings suggest the intra‐amygdala kainic acid model faithfully replicates key molecular features of human drug‐resistant TLE and provides potential rational target approaches for disease‐modification through new insights into the unique and shared gene expression landscape in experimental epilepsy.
The kainate receptors (KARs) are members of the ionotropic glutamate receptor family and assemble into tetramers from a pool of five subunit types (GluK1–5). Each subunit confers distinct functional ...properties to a receptor, but the compositional and stoichiometric diversity of KAR tetramers is not well understood. To address this, we first solve the structure of the GluK1 homomer, which enables a systematic assessment of structural compatibility among KAR subunits. Next, we analyze single-cell RNA sequencing data, which reveal extreme diversity in the combinations of two or more KAR subunits co-expressed within the same cell. We then investigate the composition of individual receptor complexes using single-molecule fluorescence techniques and find that di-heteromers assembled from GluK1, GluK2, or GluK3 can form with all possible stoichiometries, while GluK1/K5, GluK2/K5, and GluK3/K5 can form 3:1 or 2:2 complexes. Finally, using three-color single-molecule imaging, we discover that KARs can form tri- and tetra-heteromers.
Display omitted
•The cryo-EM structure of the GluK1 homomer•Complex co-expression patterns of two or more KAR subunit types across cell types•KAR di-heteromers can assemble with 3:1, 2:2, and 1:3 stoichiometries•KARs can assemble as tri-heteromers and tetra-heteromers
Selvakumar et al. use cryo-electron microscopy, single-cell RNA sequencing analysis, and single-molecule fluorescence techniques to investigate the stoichiometric and assembly diversity of kainate receptors (KARs). The work gives insight into KAR molecular diversity and expands the potential KAR subunit combinations to include a variety of di-, tri-, and tetra-heteromers.
Numerous rare variants that cause neurodevelopmental disorders (NDDs) occur within genes encoding synaptic proteins, including ionotropic glutamate receptors. However, in many cases, it remains ...unclear how damaging missense variants affect brain function. We determined the physiological consequences of an NDD causing missense mutation in the
kainate receptor (KAR) gene, that results in a single amino acid change p.Ala657Thr in the GluK2 receptor subunit. We engineered this mutation in the mouse
gene, yielding a GluK2(A657T) mouse, and studied mice of both sexes to determine how hippocampal neuronal function is disrupted. Synaptic KAR currents in hippocampal CA3 pyramidal neurons from heterozygous A657T mice exhibited slow decay kinetics, consistent with incorporation of the mutant subunit into functional receptors. Unexpectedly, CA3 neurons demonstrated elevated action potential spiking because of downregulation of the small-conductance Ca
activated K
channel (SK), which mediates the post-spike afterhyperpolarization. The reduction in SK activity resulted in increased CA3 dendritic excitability, increased EPSP-spike coupling, and lowered the threshold for the induction of LTP of the associational-commissural synapses in CA3 neurons. Pharmacological inhibition of SK channels in WT mice increased dendritic excitability and EPSP-spike coupling, mimicking the phenotype in A657T mice and suggesting a causative role for attenuated SK activity in aberrant excitability observed in the mutant mice. These findings demonstrate that a disease-associated missense mutation in
leads to altered signaling through neuronal KARs, pleiotropic effects on neuronal and dendritic excitability, and implicate these processes in neuropathology in patients with genetic NDDs.
Damaging mutations in genes encoding synaptic proteins have been identified in various neurodevelopmental disorders, but the functional consequences at the cellular and circuit level remain elusive. By generating a novel knock-in mutant mouse, this study examined the role of a pathogenic mutation in the GluK2 kainate receptor (KAR) subunit, a subclass of ionotropic glutamate receptors. Analyses of hippocampal CA3 pyramidal neurons determined elevated action potential firing because of an increase in dendritic excitability. Increased dendritic excitability was attributable to reduced activity of a Ca
activated K
channel. These results indicate that a pathogenic KAR mutation results in dysregulation of dendritic K
channels, which leads to an increase in synaptic integration and backpropagation of action potentials into distal dendrites.
The occurrence and seasonal variations of marine algal toxins in phytoplankton and oyster samples in Daya Bay (DYB), South China Sea were investigated. Two Dinophysis species, namely, D. caudata and ...D. acuminata complex, were identified as Okadaic acid (OA)/pectenotoxin (PTX) related species. Liquid chromatography with tandem mass spectrometry (LC-MS/MS) analysis demonstrated that 2.04–14.47 pg PTX2 per cell was the predominant toxin in single-cell isolates of D. caudata. D. acuminata was not subjected to toxin analysis. The occurrence of OAs in phytoplankton concentrates of net-haul sample coincided with the presence of D. accuminata complex, suggesting that this species is most likely an OA producer in this sea area. OA, dinophysistoxins-1 (DTX1), PTX2, PTX2sa, gymnodimine (GYM), homoyessotoxin (homoYTX), and domoic acid (DA) demonstrated positive results in net haul samples. To our best knowledge, this paper is the first to report the detection of GYM, DA, and homoYTX in phytoplankton samples in Chinese coastal waters. Among the algal toxins, GYM demonstrated the highest frequency of positive detections in phytoplankton concentrates (13/17). Five compounds of algal toxins, including OA, DTX1, PTX2, PTX2sa, and GYM, were detected in oyster samples. DA and homoYTX were not detected in oysters despite of positive detections for both in the phytoplankton concentrates. However, neither the presence nor absence of DA in oysters can be determined because extraction conditions with 100% methanol used to isolate toxins from oysters (recommended by the EU-Harmonised Standard Operating Procedure, 2015) would likely be unsuitable for this water-soluble toxin. In addition, transformation of DA during the digestion process of oysters may also be involved in the negative detections of this toxin. GYM exhibited the highest frequency of positive results in oysters (14/17). OAs were only detected in the hydrolyzed oyster samples. The detection rates of PTX and PTX2sa in oysters were lower than those in the net haul samples.
•D. caudata and D. acuminata complex were identified as Okadaic acid (OA)/pectenotoxin (PTX) related species.•PTX2 was the predominant toxin in D. caudata, while OAs were related with D. acuminata complex.•This paper is the first to report the detection of GYM, DA, and homoYTX in phytoplankton samples in Chinese coastal waters.•GYM exhibited the highest frequency of positive detections in phytoplankton concentrates (13/17) and oysters (14/17).
Our understanding of the molecular properties of kainate receptors and their involvement in synaptic physiology has progressed significantly over the last 30 years. A plethora of studies indicate ...that kainate receptors are important mediators of the pre- and postsynaptic actions of glutamate, although the mechanisms underlying such effects are still often a topic for discussion. Three clear fields related to their behavior have emerged: there are a number of interacting proteins that pace the properties of kainate receptors; their activity is unconventional since they can also signal through G proteins, behaving like metabotropic receptors; they seem to be linked to some devastating brain diseases. Despite the significant progress in their importance in brain function, kainate receptors remain somewhat puzzling. Here we examine discoveries linking these receptors to physiology and their probable implications in disease, in particular mood disorders, and propose some ideas to obtain a deeper understanding of these intriguing proteins.
Kainate receptors are important mediators of the actions of glutamate, but the mechanisms underlying their effects are often a topic of debate. Here, Lerma and Marques examine discoveries linking these receptors to physiology and consider their probable implications for disease.
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