Seizing Control of KCC2: A New Therapeutic Target for Epilepsy

Emergent epileptiform activity in spinal sensory circuits drives ectopic bursting in afferent axons and sensory dysfunction after cord injury

ABSTRACT

Spinal cord injury leads to hyperexcitability and dysfunction in spinal sensory processing. As hyperexcitable circuits can become epileptiform, we explored whether such activity emerges in a thoracic spinal cord injury (SCI) contusion model of neuropathic pain. Recordings from spinal sensory axons in multiple below-lesion segmental dorsal roots demonstrated that SCI facilitated the emergence of spontaneous ectopic burst spiking in afferent axons, which were correlated across multiple adjacent dorsal roots. Burst frequency correlated with behavioral mechanosensitivity. The same bursting events were recruited by afferent stimulation, and timing interactions with ongoing spontaneous bursts revealed that recruitment was limited by a prolonged post-burst refractory period. Ectopic bursting in afferent axons was driven by GABA A receptor activation, presumably by conversion of subthreshold GABAergic interneuronal presynaptic axoaxonic inhibitory actions to suprathreshold spiking. Collectively, the emergence of stereotyped bursting circuitry with hypersynchrony, sensory input activation, post-burst refractory period, and reorganization of connectivity represent defining features of an epileptiform network. Indeed, these same features were reproduced in naive animals with the convulsant 4-aminopyridine (fampridine). We conclude that spinal cord injury promotes the emergence of epileptiform activity in spinal sensory networks that promote profound corruption of sensory signaling. This includes hyperexcitability and bursting by ectopic spiking in afferent axons that propagate bidirectionally by reentrant central and peripheral projections as well as sensory circuit hypoexcitability during the burst refractory period. More broadly, the work links circuit hyperexcitability to epileptiform circuit emergence, further strengthening it as a conceptual basis to understand features of sensory dysfunction and neuropathic pain.

Bis-piperidine alkaloids from the peels of Areca catechu

Four new alkaloids, arecatines A-D (1-4), were isolated from the peels of Areca catechu. Compound 1 is an unusual piperidine-pyridine hybrid alkaloid, whereas compounds 2-4 feature bis-piperidine alkaloids. Their structures were elucidated by UV, IR, HRESIMS, and NMR spectra analysis. The molecular docking analysis indicated that compound 3 exhibited the best binding affinity with the GABAA receptor, indicating its potential anti-epilepsy activity.

GABA-Induced Seizure-Like Events Caused by Multi-ionic Interactive Dynamics

Experimental evidence showed that an increase in intracellular chloride concentration [Formula: see text] caused by gamma-aminobutyric acid (GABA) input can promote epileptic firing activity, but the actual mechanisms remain elusive. Here in this theoretical work, we show that influx of chloride and concomitant bicarbonate ion [Formula: see text] efflux upon GABA receptor activation can induce epileptic firing activity by transition of GABA from inhibition to excitation. We analyzed the intrinsic property of neuron firing states as a function of [Formula: see text] We found that as [Formula: see text] increases, the system exhibits a saddle-node bifurcation, above which the neuron exhibits a spectrum of intensive firing, periodic bursting interrupted by depolarization block (DB) state, and eventually a stable DB through a Hopf bifurcation. We demonstrate that only GABA stimuli together with [Formula: see text] efflux can switch GABA's effect to excitation which leads to a series of seizure-like events (SLEs). Exposure to a low [Formula: see text] can drive neurons with high concentrations of [Formula: see text] downward to lower levels of [Formula: see text], during which it could also trigger SLEs depending on the exchange rate with the bath. Our analysis and simulation results show how the competition between GABA stimuli-induced accumulation of [Formula: see text] and [Formula: see text] application-induced decrease of [Formula: see text] regulates the neuron firing activity, which helps to understand the fundamental ionic dynamics of SLE.

Human-Induced Pluripotent Stem Cell (iPSC)-Derived GABAergic Neuron Differentiation in Bipolar Disorder

Bipolar disorder (BP) is a recurring psychiatric condition characterized by alternating episodes of low energy (depressions) followed by manias (high energy). Cortical network activity produced by GABAergic interneurons may be critical in maintaining the balance in excitatory/inhibitory activity in the brain during development. Initially, GABAergic signaling is excitatory; with maturation, these cells undergo a functional switch that converts GABAA channels from depolarizing (excitatory) to hyperpolarizing (inhibitory), which is controlled by the intracellular concentration of two chloride transporters. The earliest, NKCC1, promotes chloride entry into the cell and depolarization, while the second (KCC2) stimulates movement of chloride from the neuron, hyperpolarizing it. Perturbations in the timing or expression of NKCC1/KCC2 may affect essential morphogenetic events including cell proliferation, migration, synaptogenesis and plasticity, and thereby the structure and function of the cortex. We derived induced pluripotent stem cells (iPSC) from BP patients and undiagnosed control (C) individuals, then modified a differentiation protocol to form GABAergic interneurons, harvesting cells at sequential stages of differentiation. qRT-PCR and RNA sequencing indicated that after six weeks of differentiation, controls transiently expressed high levels of NKCC1. Using multi-electrode array (MEA) analysis, we observed that BP neurons exhibit increased firing, network bursting and decreased synchrony compared to C. Understanding GABA signaling in differentiation may identify novel approaches and new targets for treatment of neuropsychiatric disorders such as BP.

The suppressive effect of the specific KCC2 modulator CLP290 on seizure in mice

Epilepsy is a chronic neurological disorder characterized by episodic dysfunction of central nervous system. The most basic mechanism of epilepsy falls to the imbalance between excitation and inhibition. In adults, GABAA receptor (GABAAR) is the main inhibitory receptor to prevent neurons from developing hyperexcitability, while its inhibition relies on the low intracellular chloride anion concentration ([Cl-]i). Neuronal-specific electroneutral K+-Cl- cotransporter (KCC2) can mediate chloride efflux to lower [Cl-]i for GABAAR mediated inhibition. Our previous study has revealed that the coordinated downregulation of KCC2 and GABAAR participates in epilepsy. According to a high-throughout screen for compounds that reduce [Cl-]i, CLP290 turns out to be a specific KCC2 functional modulator. In current study, we first confirmed that CLP290 could dose-dependently suppress convulsant-induced seizures in mice in vivo as well as the epileptiform burst activities in cultured hippocampal neurons in vitro. Then, we discovered that CLP290 functioned through preventing the downregulation of the KCC2 phosphorylation at Ser940 and hence the KCC2 membrane expression during convulsant stimulation, and consequently restored the GABA inhibition. In addition, while CLP290 was given in early epileptogenesis period, it also effectively decreased the spontaneous recurrent seizures. Generally, our current results demonstrated that CLP290, as a specific KCC2 modulator by enhancing KCC2 function, not only inhibits the occurrence of the ictal seizures, but also suppresses the epileptogenic process. Therefore, we believe KCC2 may be a suitable target for future anti-epileptic drug development.

Dissecting the networks underlying diverse brain disorders after prenatal glucocorticoid overexposure

New human life begins in the uterus in a period of both extreme plasticity and sensitivity to environmental disturbances. The fetal stage is also a vital period for central nervous system development, with experiences at this point profoundly and permanently shaping brain structure and function. As such, some brain disorders may originate in utero. Glucocorticoids, a class of essential stress hormones, play indispensable roles in fetal development, but overexposure may have lasting impacts on the brain. In this review, we summarize data from recent clinical and non-clinical studies regarding alterations in fetal brains due to prenatal glucocorticoid overexposure that are associated with nervous system disorders. We discuss relevant changes to brain structure and cellular functions and explore the underlying molecular mechanisms. In addition, we summarize factors that may cause differential outcomes between varying brain regions, and outline clinically feasible intervention strategies that are expected to minimize negative consequences arising from fetal glucocorticoid overexposure. Finally, we highlight the need for experimental evidence aided by new technologies to clearly determine the effects of excessive prenatal glucocorticoid exposure. This review consolidates diverse findings to help researchers better understand the relationship between the prenatal glucocorticoid overexposure and the effects it has on various fetal brain regions, promoting further development of critical intervention strategies.

GABA system as the cause and effect in early development

GABA is the primary inhibitory neurotransmitter in the adult brain and through its actions on GABAARs, it protects against excitotoxicity and seizure activity, ensures temporal fidelity of neurotransmission, and regulates concerted rhythmic activity of neuronal populations. In the developing brain, the development of GABAergic neurons precedes that of glutamatergic neurons and the GABA system serves as a guide and framework for the development of other brain systems. Despite this early start, the maturation of the GABA system also continues well into the early postnatal period. In this review, we organize evidence around two scenarios based on the essential and protracted nature of GABA system development: 1) disruptions in the development of the GABA system can lead to large scale disruptions in other developmental processes (i.e., GABA as the cause), 2) protracted maturation of this system makes it vulnerable to the effects of developmental insults (i.e., GABA as the effect). While ample evidence supports the importance of GABA/GABAAR system in both scenarios, large gaps in existing knowledge prevent strong mechanistic conclusions.

GABAergic system and chloride cotransporters as potential therapeutic targets to mitigate cell death in ischemia

Gamma aminobutyric acid (GABA) is a critical inhibitory neurotransmitter in the central nervous system that plays a vital role in modulating neuronal excitability. Dysregulation of GABAergic signaling, particularly involving the cotransporters NKCC1 and KCC2, has been implicated in various pathologies, including epilepsy, schizophrenia, autism spectrum disorder, Down syndrome, and ischemia. NKCC1 facilitates chloride influx, whereas KCC2 mediates chloride efflux via potassium gradient. Altered expression and function of these cotransporters have been associated with excitotoxicity, inflammation, and cellular death in ischemic events characterized by reduced cerebral blood flow, leading to compromised tissue metabolism and subsequent cell death. NKCC1 inhibition has emerged as a potential therapeutic approach to attenuate intracellular chloride accumulation and mitigate neuronal damage during ischemic events. Similarly, targeting KCC2, which regulates chloride efflux, holds promise for improving outcomes and reducing neuronal damage under ischemic conditions. This review emphasizes the critical roles of GABA, NKCC1, and KCC2 in ischemic pathologies and their potential as therapeutic targets. Inhibiting or modulating the activity of these cotransporters represents a promising strategy for reducing neuronal damage, preventing excitotoxicity, and improving neurological outcomes following ischemic events. Furthermore, exploring the interactions between natural compounds and NKCC1/KCC2 provides additional avenues for potential therapeutic interventions for ischemic injury.

The brain-specific kinase LMTK3 regulates neuronal excitability by decreasing KCC2-dependent neuronal Cl- extrusion

LMTK3 is a brain-specific transmembrane serine/threonine protein kinase that acts as a scaffold for protein phosphatase-1 (PP1). Although LMKT3 has been identified as a risk factor for autism and epilepsy, its physiological significance is unknown. Here, we demonstrate that LMTK3 copurifies and binds to KCC2, a neuron-specific K+/Cl- transporter. KCC2 activity is essential for Cl--mediated hyperpolarizing GABAAR receptor currents, the unitary events that underpin fast synaptic inhibition. LMTK3 acts to promote the association of KCC2 with PP1 to promote the dephosphorylation of S940 within its C-terminal cytoplasmic domain, a process the diminishes KCC2 activity. Accordingly, acute inhibition of LMTK3 increases KCC2 activity dependent upon S940 and increases neuronal Cl- extrusion. Consistent with this, LMTK3 inhibition reduced intrinsic neuronal excitability and the severity of seizure-like events in vitro. Thus, LMTK3 may have profound effects on neuronal excitability as an endogenous modulator of KCC2 activity.

Serine 937 phosphorylation enhances KCC2 activity and strengthens synaptic inhibition

The potassium chloride cotransporter KCC2 is crucial for Cl- extrusion from mature neurons and thus key to hyperpolarizing inhibition. Auditory brainstem circuits contain well-understood inhibitory projections and provide a potent model to study the regulation of synaptic inhibition. Two peculiarities of the auditory brainstem are (i) posttranslational activation of KCC2 during development and (ii) extremely negative reversal potentials in specific circuits. To investigate the role of the potent phospho-site serine 937 therein, we generated a KCC2 Thr934Ala/Ser937Asp double mutation, in which Ser937 is replaced by aspartate mimicking the phosphorylated state, and the neighbouring Thr934 arrested in the dephosphorylated state. This double mutant showed a twofold increased transport activity in HEK293 cells, raising the hypothesis that auditory brainstem neurons show lower [Cl-]i. and increased glycinergic inhibition. This was tested in a mouse model carrying the same KCC2 Thr934Ala/Ser937Asp mutation by the use of the CRISPR/Cas9 technology. Homozygous KCC2 Thr934Ala/Ser937Asp mice showed an earlier developmental onset of hyperpolarisation in the auditory brainstem. Mature neurons displayed stronger glycinergic inhibition due to hyperpolarized ECl-. These data demonstrate that phospho-regulation of KCC2 Ser937 is a potent way to interfere with the excitation-inhibition balance in neural circuits.

The dual role of microglia in neuropathic pain after spinal cord injury: Detrimental and protective effects

Spinal cord injury (SCI) is a debilitating condition that is frequently accompanied by neuropathic pain, resulting in significant physical and psychological harm to a vast number of individuals globally. Despite the high prevalence of neuropathic pain following SCI, the precise underlying mechanism remains incompletely understood. Microglia are a type of innate immune cell that are present in the central nervous system (CNS). They have been observed to have a significant impact on neuropathic pain following SCI. This article presents a comprehensive overview of recent advances in understanding the role of microglia in the development of neuropathic pain following SCI. Specifically, the article delves into the detrimental and protective effects of microglia on neuropathic pain following SCI, as well as the mechanisms underlying their interconversion. Furthermore, the article provides a thorough overview of potential avenues for future research in this area.

Acute neuroinflammation leads to disruption of neuronal chloride regulation and consequent hyperexcitability in the dentate gyrus

Neuroinflammation is a salient part of diverse neurological and psychiatric pathologies that associate with neuronal hyperexcitability, but the underlying molecular and cellular mechanisms remain to be identified. Here, we show that peripheral injection of lipopolysaccharide (LPS) renders the dentate gyrus (DG) hyperexcitable to perforant pathway stimulation in vivo and increases the internal spiking propensity of dentate granule cells (DGCs) in vitro 24 h post-injection (hpi). In parallel, LPS leads to a prominent downregulation of chloride extrusion via KCC2 and to the emergence of NKCC1-mediated chloride uptake in DGCs under experimental conditions optimized to detect specific changes in transporter efficacy. These data show that acute neuroinflammation leads to disruption of neuronal chloride regulation, which unequivocally results in a loss of GABAergic inhibition in the DGCs, collapsing the gating function of the DG. The present work provides a mechanistic explanation for neuroinflammation-driven hyperexcitability and consequent cognitive disturbance.

CDKL5-mediated developmental tuning of neuronal excitability and concomitant regulation of transcriptome

Cyclin-dependent kinase-like 5 (CDKL5) is a serine-threonine kinase enriched in the forebrain to regulate neuronal development and function. Patients with CDKL5 deficiency disorder (CDD), a severe neurodevelopmental condition caused by mutations of CDKL5 gene, present early-onset epilepsy as the most prominent feature. However, spontaneous seizures have not been reported in mouse models of CDD, raising vital questions on the human-mouse differences and the roles of CDKL5 in early postnatal brains. Here, we firstly measured electroencephalographic (EEG) activities via a wireless telemetry system coupled with video-recording in neonatal mice. We found that mice lacking CDKL5 exhibited spontaneous epileptic EEG discharges, accompanied with increased burst activities and ictal behaviors, specifically at postnatal day 12 (P12). Intriguingly, those epileptic spikes disappeared after P14. We next performed an unbiased transcriptome profiling in the dorsal hippocampus and motor cortex of Cdkl5 null mice at different developmental timepoints, uncovering a set of age-dependent and brain region-specific alterations of gene expression in parallel with the transient display of epileptic activities. Finally, we validated multiple differentially expressed genes, such as glycine receptor alpha 2 and cholecystokinin, at the transcript or protein levels, supporting the relevance of these genes to CDKL5-regulated excitability. Our findings reveal early-onset neuronal hyperexcitability in mouse model of CDD, providing new insights into CDD etiology and potential molecular targets to ameliorate intractable neonatal epilepsy.

Unilateral optogenetic kindling of hippocampus leads to more severe impairments of the inhibitory signaling in the contralateral hippocampus

The kindling model has been used extensively by researchers to study the neurobiology of temporal lobe epilepsy (TLE) due to its capacity to induce intensification of seizures by the progressive recruitment of additional neuronal clusters into epileptogenic networks. We applied repetitive focal optogenetic activation of putative excitatory neurons in the dorsal CA1 area of the hippocampus of mice to investigate the role of inhibitory signaling during this process. This experimental protocol resulted in a kindling phenotype that was maintained for 2 weeks after the animals were fully kindled. As a result of the different phases of optogenetic kindling (OpK), key inhibitory signaling elements, such as KCC2 and NKCC1, exhibited distinct temporal and spatial dynamics of regulation. These alterations in protein expression were related to the distinct pattern of ictal activity propagation through the different hippocampal sublayers. Our results suggest the KCC2 disruption in the contralateral hippocampus of fully kindled animals progressively facilitated the creation of pathological pathways for seizure propagation through the hippocampal network. Upon completion of kindling, we observed animals that were restimulated after a rest period of 14-day showed, besides a persistent KCC2 downregulation, an NKCC1 upregulation in the bilateral dentate gyrus and hippocampus-wide loss of parvalbumin-positive interneurons. These alterations observed in the chronic phase of OpK suggest that the hippocampus of rekindled animals continued to undergo self-modifications during the rest period. The changes resulting from this period suggest the possibility of the development of a mirror focus on the hippocampus contralateral to the site of optical stimulations. Our results offer perspectives for preventing the recruitment and conversion of healthy neuronal networks into epileptogenic ones among patients with epilepsy.

K+/Cl- cotransporter 2 (KCC2) and Na+/HCO3- cotransporter 1 (NBCe1) interaction modulates profile of KCC2 phosphorylation

K+/Cl- cotransporter 2 (KCC2) is a major Cl- extruder in mature neurons and is responsible for the establishment of low intracellular [Cl-], necessary for fast hyperpolarizing GABAA-receptor mediated synaptic inhibition. Electrogenic sodium bicarbonate cotransporter 1 (NBCe1) is a pH regulatory protein expressed in neurons and glial cells. An interactome study identified NBCe1 as a possible interaction partner of KCC2. In this study, we investigated the putative effect of KCC2/NBCe1 interaction in baseline and the stimulus-induced phosphorylation pattern and function of KCC2. Primary mouse hippocampal neuronal cultures from wildtype (WT) and Nbce1-deficient mice, as well as HEK-293 cells stably transfected with KCC2WT, were used. The results show that KCC2 and NBCe1 are interaction partners in the mouse brain. In HEKKCC2 cells, pharmacological inhibition of NBCs with S0859 prevented staurosporine- and 4-aminopyridine (4AP)-induced KCC2 activation. In mature cultures of hippocampal neurons, however, S0859 completely inhibited postsynaptic GABAAR and, thus, could not be used as a tool to investigate the role of NBCs in GABA-dependent neuronal networks. In Nbce1-deficient immature hippocampal neurons, baseline phosphorylation of KCC2 at S940 was downregulated, compared to WT, and exposure to staurosporine failed to reduce pKCC2 S940 and T1007. In Nbce1-deficient mature neurons, baseline levels of pKCC2 S940 and T1007 were upregulated compared to WT, whereas after 4AP treatment, pKCC2 S940 was downregulated, and pKCC2 T1007 was further upregulated. Functional experiments showed that the levels of GABAAR reversal potential, baseline intracellular [Cl-], Cl- extrusion, and baseline intracellular pH were similar between WT and Nbce1-deficient neurons. Altogether, our data provide a primary description of the properties of KCC2/NBCe1 protein-protein interaction and implicate modulation of stimulus-mediated phosphorylation of KCC2 by NBCe1/KCC2 interaction-a mechanism with putative pathophysiological relevance.

KCC2 reverse mode helps to clear postsynaptically released potassium at glutamatergic synapses

Extracellular potassium [K+]o elevation during synaptic activity retrogradely modifies presynaptic release and astrocytic uptake of glutamate. Hence, local K+ clearance and replenishment mechanisms are crucial regulators of glutamatergic transmission and plasticity. Based on recordings of astrocytic inward rectifier potassium current IKir and K+-sensitive electrodes as sensors of [K+]o as well as on in silico modeling, we demonstrate that the neuronal K+-Cl- co-transporter KCC2 clears local perisynaptic [K+]o during synaptic excitation by operating in an activity-dependent reversed mode. In reverse mode, KCC2 replenishes K+ in dendritic spines and complements clearance of [K+]o, therewith attenuating presynaptic glutamate release and shortening LTP. We thus demonstrate a physiological role of KCC2 in neuron-glial interactions and regulation of synaptic signaling and plasticity through the uptake of postsynaptically released K+.

Excitatory/inhibitory balance in epilepsies and neurodevelopmental disorders: Depolarizing γ-aminobutyric acid as a common mechanism

Epilepsy is one of the most common neurological disorders. Although many factors contribute to epileptogenesis, seizure generation is mostly linked to hyperexcitability due to alterations in excitatory/inhibitory (E/I) balance. The common hypothesis is that reduced inhibition, increased excitation, or both contribute to the etiology of epilepsy. Increasing evidence shows that this view is oversimplistic, and that increased inhibition through depolarizing γ-aminobutyric acid (GABA) similarly contributes to epileptogenisis. In early development, GABA signaling is depolarizing, inducing outward Cl- currents due to high intracellular Cl- concentrations. During maturation, the mechanisms of GABA action shift from depolarizing to hyperpolarizing, a critical event during brain development. Altered timing of this shift is associated with both neurodevelopmental disorders and epilepsy. Here, we consider the different ways that depolarizing GABA contributes to altered E/I balance and epileptogenesis, and discuss that alterations in depolarizing GABA could be a common denominator underlying seizure generation in neurodevelopmental disorders and epilepsies.

Emergent epileptiform activity drives spinal sensory circuits to generate ectopic bursting in intraspinal afferent axons after cord injury

Spinal cord injury ( SCI ) leads to hyperexcitability and dysfunction in spinal sensory processing. As hyperexcitable circuits can become epileptiform elsewhere, we explored whether such activity emerges in spinal sensory circuits in a thoracic SCI contusion model of neuropathic pain. Recordings from spinal sensory axons in multiple below-lesion segmental dorsal roots ( DRs ) demonstrated that SCI facilitated the emergence of spontaneous ectopic burst spiking in afferent axons, which synchronized across multiple adjacent DRs. Burst frequency correlated with behavioral mechanosensitivity. The same bursting events were recruited by afferent stimulation, and timing interactions with ongoing spontaneous bursts revealed that recruitment was limited by a prolonged post-burst refractory period. Ectopic bursting in afferent axons was driven by GABA A receptor activation, presumably via shifting subthreshold GABAergic interneuronal presynaptic axoaxonic inhibitory actions to suprathreshold spiking. Collectively, the emergence of stereotyped bursting circuitry with hypersynchrony, sensory input activation, post-burst refractory period, and reorganization of connectivity represent defining features of epileptiform networks. Indeed, these same features were reproduced in naïve animals with the convulsant 4-aminopyridine ( 4-AP ). We conclude that SCI promotes the emergence of epileptiform activity in spinal sensory networks that promotes profound corruption of sensory signaling. This corruption includes downstream actions driven by ectopic afferent bursts that propagate via reentrant central and peripheral projections and GABAergic presynaptic circuit hypoexcitability during the refractory period.

Semaphorin 4D induced inhibitory synaptogenesis decreases epileptiform activity and alters progression to Status Epilepticus in mice

Previously we demonstrated that intra-hippocampal infusion of purified, Semaphorin 4D (Sema4D) extracellular domain (ECD) into the mouse hippocampus rapidly promotes formation of GABAergic synapses and decreases seizure susceptibility in mice. Given the relatively fast action of Sema4D treatment revealed by these studies, we sought to determine the time course of Sema4D treatment on hippocampal network activity using an acute hippocampal slice preparation. We performed long-term extracellular recordings from area CA1 encompassing a 2-hour application of Sema4D and found that hippocampal excitation is suppressed for hours following treatment. We also asked if Sema4D treatment could ameliorate seizures in an acute seizure model: the kainic acid (KA) mouse model. We demonstrate that Sema4D treatment delays and suppresses ictal activity, delays the transition to Status Epilepticus (SE), and lessens the severity of SE. Lastly, we sought to explore alternative methods of Sema4D delivery to hippocampus and thus created an Adeno Associated Virus expressing the ECD of Sema4D. Our data reveal that virally delivered, chronically overexpressed Sema4D-ECD promotes GABAergic synapse formation and suppresses ictal activity and progression to SE. These results provide proof of concept that viral delivery of Sema4D is an efficacious and promising delivery method to abate epileptiform activity and progression to SE.

Alteration of GABAergic neurons and abnormality of NKCC1/KCC2 in focal cortical dysplasia (FCD) type Ⅱ lesions

BACKGROUND

The current conclusions of molecular genetics still cannot satisfactorily explain the pathogenesis of focal cortical dysplasia (FCD) and the reason for drug resistance. The interneurons of GABA deserve attention. To observe the distribution and changes of GABAergic neurons and to explore the expression of cation chloride cotransporter NKCC1/KCC2 in focal cortical dysplasia (FCD) type II lesions is a highly significant job.

METHODS

The expressions of GAD67(a marker of active GABAergic neuron), NKCC1 and KCC2 were detected by immunohistochemistry and immunohistochemistry double staining in 10 cases of FCD Ⅱa and 10 cases of FCD Ⅱb. The number of GAD67 positive neurons was counted, and the average absorbance (IA) of NKCC1 positive expression was measured, using Image Pro-Plus7.0 software. The data were statistically analyzed.

RESULTS

The density of GABAergic neuron in focal dysplastic regions was significantly lower than that in the histologically "normal" cerebral cortex, regions from the same specimen (p < 0.0001, t-test). Compared to the NKCC1 staining intensity of neurons in the control group (measuring 1000 cells each), the IA value of dysmorphic neurons was significantly increased (p < 0.05, t'-test Cochran & Cox method). Intracytoplasmic concentration of KCC2 was evident in dysmorphic neurons but not in the other mature neurons. Most of the balloon cells were negative for NKCC1, except for few balloon cells showing sparse colored particles. The expression of KCC2 was negative in all balloon cells.

CONCLUSIONS

The changes in the expression of NKCC1 and KCC2 may indicate that dysmorphic neurons were in a state similar to that of immature neurons. This state may be related to the abnormal electrophysiology of epilepsy. The difference between the number of GAD67 positive cells in the lesion site and the remote site of the same case may be an evaluation index of the effectiveness of surgery.

Degeneracy in epilepsy: multiple routes to hyperexcitable brain circuits and their repair

Due to its complex and multifaceted nature, developing effective treatments for epilepsy is still a major challenge. To deal with this complexity we introduce the concept of degeneracy to the field of epilepsy research: the ability of disparate elements to cause an analogous function or malfunction. Here, we review examples of epilepsy-related degeneracy at multiple levels of brain organisation, ranging from the cellular to the network and systems level. Based on these insights, we outline new multiscale and population modelling approaches to disentangle the complex web of interactions underlying epilepsy and to design personalised multitarget therapies.

TC-G 1008 facilitates epileptogenesis by acting selectively at the GPR39 receptor but non-selectively activates CREB in the hippocampus of pentylenetetrazole-kindled mice

The pharmacological activation of the GPR39 receptor has been proposed as a novel strategy for treating seizures; however, this hypothesis has not been verified experimentally. TC-G 1008 is a small molecule agonist increasingly used to study GPR39 receptor function but has not been validated using gene knockout. Our aim was to assess whether TC-G 1008 produces anti-seizure/anti-epileptogenic effects in vivo and whether the effects are mediated by GPR39. To obtain this goal we utilized various animal models of seizures/epileptogenesis and GPR39 knockout mice model. Generally, TC-G 1008 exacerbated behavioral seizures. Furthermore, it increased the mean duration of local field potential recordings in response to pentylenetetrazole (PTZ) in zebrafish larvae. It facilitated the development of epileptogenesis in the PTZ-induced kindling model of epilepsy in mice. We demonstrated that TC-G 1008 aggravated PTZ-epileptogenesis by selectively acting at GPR39. However, a concomitant analysis of the downstream effects on the cyclic-AMP-response element binding protein in the hippocampus of GPR39 knockout mice suggested that the molecule also acts via other targets. Our data argue against GPR39 activation being a viable therapeutic strategy for treating epilepsy and suggest investigating whether TC-G 1008 is a selective agonist of the GPR39 receptor.

The role of GPR39 zinc receptor in the modulation of glutamatergic and GABAergic transmission

BACKGROUND

Despite our poor understanding of the pathophysiology of depression, a growing body of evidence indicates the role of both glutamate and gamma-aminobutyric acid (GABA) signaling behind the effects of rapid-acting antidepressants (RAADs). GPR39 is a zinc-sensing receptor whose activation leads to a prolonged antidepressant-like response in mice. Both GPR39 and zinc can modulate glutamatergic and GABAergic neurotransmission, however, exact molecular mechanisms are still elusive. In this study, we aimed to research the role of glutamatergic and GABAergic system activation in TC-G 1008 antidepressant-like effects and the disruptions in this effect caused by a low-zinc diet.

METHODS

In the first part of our study, we investigated the role of joint administration of the GPR39 agonist (TC-G 1008) and ligands of the glutamatergic or GABAergic systems, in antidepressant-like response. To evaluate animal behaviour we used the forced swim test in mice. In the second part of the study, we assessed the effectiveness of TC-G 1008-induced antidepressant-like response in conditions of decreased dietary zinc intake and its molecular underpinning by conducting a Western Blot analysis of selected proteins involved in glutamatergic and GABAergic neurotransmission.

RESULTS

The TC-G 1008-induced effect was blocked by the administration of NMDA or picrotoxin. The joint administration of TC-G 1008 along with muscimol or SCH50911 showed a trend toward decreased immobility time. Zinc-deficient diet resulted in dysregulation of GluN1, PSD95, and KCC2 protein expression.

CONCLUSIONS

Our findings indicate the important role of glutamate/GABA signaling in the antidepressant-like effect of TC-G 1008 and imply that GPR39 regulates the balance between excitatory and inhibitory activity in the brain. Thus, we suggest the zinc-sensing receptor be considered an interesting new target for the development of novel antidepressants.

Direct activation of KCC2 arrests benzodiazepine refractory status epilepticus and limits the subsequent neuronal injury in mice

Hyperpolarizing GABAAR currents, the unitary events that underlie synaptic inhibition, are dependent upon efficient Cl- extrusion, a process that is facilitated by the neuronal specific K+/Cl- co-transporter KCC2. Its activity is also a determinant of the anticonvulsant efficacy of the canonical GABAAR-positive allosteric: benzodiazepines (BDZs). Compromised KCC2 activity is implicated in the pathophysiology of status epilepticus (SE), a medical emergency that rapidly becomes refractory to BDZ (BDZ-RSE). Here, we have identified small molecules that directly bind to and activate KCC2, which leads to reduced neuronal Cl- accumulation and excitability. KCC2 activation does not induce any overt effects on behavior but prevents the development of and terminates ongoing BDZ-RSE. In addition, KCC2 activation reduces neuronal cell death following BDZ-RSE. Collectively, these findings demonstrate that KCC2 activation is a promising strategy to terminate BDZ-resistant seizures and limit the associated neuronal injury.

Dexmedetomidine Pre-Treatment of Neonatal Rats Prevents Sevoflurane-Induced Deficits in Learning and Memory in the Adult Animals

Anesthetics have been shown to cause cytotoxicity, cell death, affect neuronal growth and connectivity in animal models; however, their effects on learning and memory remain to be fully defined. Here, we examined the effects of the inhalation anesthetic sevoflurane (SEV)-both in vivo by examining learning and memory in freely behaving animals, and in vitro using cultured neurons to assess its impact on viability, mitochondrial structure, and function. We demonstrate here that neonatal exposure to sub-clinically used concentrations of SEV results in significant, albeit subtle and previously unreported, learning and memory deficits in adult animals. These deficits involve neuronal cell death, as observed in cell culture, and are likely mediated through perturbed mitochondrial structure and function. Parenthetically, both behavioural deficits and cell death were prevented when the animals and cultured neurons were pre-treated with the anesthetic adjuvant Dexmedetomidine (DEX). Taken together, our data provide direct evidence for sevoflurane-induced cytotoxic effects at the neuronal level while perturbing learning and memory at the behavioural level. In addition, our data underscore the importance of adjuvant agents such as DEX that could potentially counter the harmful effects of commonly used anesthetic agents for better clinical outcomes.

TGF-β2 Regulates Transcription of the K+/Cl- Cotransporter 2 (KCC2) in Immature Neurons and Its Phosphorylation at T1007 in Differentiated Neurons

KCC2 mediates extrusion of K⁺ and Cl^- and assuresthe developmental "switch" in GABA function during neuronal maturation. However, the molecular mechanisms underlying KCC2 regulation are not fully elucidated. We investigated the impact of transforming growth factor beta 2 (TGF-β2) on KCC2 during neuronal maturation using quantitative RT-PCR, immunoblotting, immunofluorescence and chromatin immunoprecipitation in primary mouse hippocampal neurons and brain tissue from Tgf-β2-deficient mice. Inhibition of TGF-β/activin signaling downregulates Kcc2 transcript in immature neurons. In the forebrain of Tgf-β2^-/- mice, expression of Kcc2, transcription factor Ap2β and KCC2 protein is downregulated. AP2β binds to Kcc2 promoter, a binding absent in Tgf-β2^-/-. In hindbrain/brainstem tissue of Tgf-β2^-/- mice, KCC2 phosphorylation at T1007 is increased and approximately half of pre-Bötzinger-complex neurons lack membrane KCC2 phenotypes rescued through exogenous TGF-β2. These results demonstrate that TGF-β2 regulates KCC2 transcription in immature neurons, possibly acting upstream of AP2β, and contributes to the developmental dephosphorylation of KCC2 at T1007. The present work suggests multiple and divergent roles for TGF-β2 on KCC2 during neuronal maturation and provides novel mechanistic insights for TGF-β2-mediated regulation of KCC2 gene expression, posttranslational modification and surface expression. We propose TGF-β2 as a major regulator of KCC2 with putative implications for pathophysiological conditions.

Chloride imbalance in Fragile X syndrome

Developmental changes in ionic balance are associated with crucial hallmarks in neural circuit formation, including changes in excitation and inhibition, neurogenesis, and synaptogenesis. Neuronal excitability is largely mediated by ionic concentrations inside and outside of the cell, and chloride (Cl-) ions are highly influential in early neurodevelopmental events. For example, γ-aminobutyric acid (GABA) is the main inhibitory neurotransmitter of the mature central nervous system (CNS). However, during early development GABA can depolarize target neurons, and GABAergic depolarization is implicated in crucial neurodevelopmental processes. This developmental shift of GABAergic neurotransmission from depolarizing to hyperpolarizing output is induced by changes in Cl- gradients, which are generated by the relative expression of Cl- transporters Nkcc1 and Kcc2. Interestingly, the GABA polarity shift is delayed in Fragile X syndrome (FXS) models; FXS is one of the most common heritable neurodevelopmental disorders. The RNA binding protein FMRP, encoded by the gene Fragile X Messenger Ribonucleoprotein-1 (Fmr1) and absent in FXS, appears to regulate chloride transporter expression. This could dramatically influence FXS phenotypes, as the syndrome is hypothesized to be rooted in defects in neural circuit development and imbalanced excitatory/inhibitory (E/I) neurotransmission. In this perspective, we summarize canonical Cl- transporter expression and investigate altered gene and protein expression of Nkcc1 and Kcc2 in FXS models. We then discuss interactions between Cl- transporters and neurotransmission complexes, and how these links could cause imbalances in inhibitory neurotransmission that may alter mature circuits. Finally, we highlight current therapeutic strategies and promising new directions in targeting Cl- transporter expression in FXS patients.

Efficient Gene Expression in Human Stem Cell Derived-Cortical Organoids Using Adeno Associated Virus

Cortical organoids are 3D structures derived either from human embryonic stem cells or human induced pluripotent stem cells with their use exploding in recent years due to their ability to better recapitulate the human brain in vivo in respect to organization; differentiation; and polarity. Adeno-associated viruses (AAVs) have emerged in recent years as the vectors of choice for CNS-targeted gene therapy. Here; we compare the use of AAVs as a mode of gene expression in cortical organoids; over traditional methods such as lipofectamine and electroporation and demonstrate its ease-of-use in generating quick disease models through expression of different variants of the central gene—TDP-43—implicated in amyotrophic lateral sclerosis and frontotemporal dementia.

Analyzing the mechanisms that facilitate the subtype-specific assembly of γ-aminobutyric acid type A receptors

Impaired inhibitory signaling underlies the pathophysiology of many neuropsychiatric and neurodevelopmental disorders including autism spectrum disorders and epilepsy. Neuronal inhibition is regulated by synaptic and extrasynaptic γ-aminobutyric acid type A receptors (GABA _A Rs), which mediate phasic and tonic inhibition, respectively. These two GABA _A R subtypes differ in their function, ligand sensitivity, and physiological properties. Importantly, they contain different α subunit isoforms: synaptic GABA _A Rs contain the α1-3 subunits whereas extrasynaptic GABA _A Rs contain the α4-6 subunits. While the subunit composition is critical for the distinct roles of synaptic and extrasynaptic GABA _A R subtypes in inhibition, the molecular mechanism of the subtype-specific assembly has not been elucidated. To address this issue, we purified endogenous α1- and α4-containing GABA _A Rs from adult murine forebrains and examined their subunit composition and interacting proteins using liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) and quantitative analysis. We found that the α1 and α4 subunits form separate populations of GABA _A Rs and interact with distinct sets of binding proteins. We also discovered that the β3 subunit, which co-purifies with both the α1 and α4 subunits, has different levels of phosphorylation on serines 408 and 409 (S408/9) between the two receptor subtypes. To understand the role S408/9 plays in the assembly of α1- and α4-containing GABA _A Rs, we examined the effects of S408/9A (alanine) knock-in mutation on the subunit composition of the two receptor subtypes using LC-MS/MS and quantitative analysis. We discovered that the S408/9A mutation results in the formation of novel α1α4-containing GABA _A Rs. Moreover, in S408/9A mutants, the plasma membrane expression of the α4 subunit is increased whereas its retention in the endoplasmic reticulum is reduced. These findings suggest that S408/9 play a critical role in determining the subtype-specific assembly of GABA _A Rs, and thus the efficacy of neuronal inhibition.

Ionic Plasticity: Common Mechanistic Underpinnings of Pathology in Spinal Cord Injury and the Brain

The neurotransmitter GABA is normally characterized as having an inhibitory effect on neural activity in the adult central nervous system (CNS), which quells over-excitation and limits neural plasticity. Spinal cord injury (SCI) can bring about a modification that weakens the inhibitory effect of GABA in the central gray caudal to injury. This change is linked to the downregulation of the potassium/chloride cotransporter (KCC2) and the consequent rise in intracellular Cl- in the postsynaptic neuron. As the intracellular concentration increases, the inward flow of Cl- through an ionotropic GABA-A receptor is reduced, which decreases its hyperpolarizing (inhibitory) effect, a modulatory effect known as ionic plasticity. The loss of GABA-dependent inhibition enables a state of over-excitation within the spinal cord that fosters aberrant motor activity (spasticity) and chronic pain. A downregulation of KCC2 also contributes to the development of a number of brain-dependent pathologies linked to states of neural over-excitation, including epilepsy, addiction, and developmental disorders, along with other diseases such as hypertension, asthma, and irritable bowel syndrome. Pharmacological treatments that target ionic plasticity have been shown to bring therapeutic benefits.

Consequences: Bench to home

Seizure clusters (also referred to as acute repetitive seizures) consist of several seizures interspersed with brief interictal periods. Seizure clusters can break down γ-aminobutyric acidergic (GABAergic) inhibition of dentate granule cells, leading to hyperactivation. Functional changes to GABAA receptors, which play a vital neuroinhibitory role, can include altered GABAA receptor subunit trafficking and cellular localization, intracellular chloride accumulation, and dysregulation of proteins critical to chloride homeostasis. A reduction in neuroinhibition and potentiation of excitatory neurotransmission in CA1 pyramidal neurons represent pathological mechanisms that underlie seizure clusters. Benzodiazepines are well-established treatments for seizure clusters; however, there remain barriers to appropriate care. At the clinical level, there is variability in seizure cluster definitions, such as the number and/or type of seizures associated with a cluster as well as the interictal duration between seizures. This can lead to delays in diagnosis and timely treatment. There are gaps in understanding between clinicians, their patients, and caregivers regarding acute treatment for seizure clusters, such as the use of rescue medications and emergency services. This lack of consensus to define seizure clusters in addition to a lack of education for appropriate treatment can affect quality of life for patients and place a greater burden on patient families and caregivers. For patients with seizure clusters, the sense of unpredictability can lead to continuous traumatic stress, during which patients and families live with a heightened level of anxiety. Clinicians can affect patient quality of life and clinical outcomes through improved seizure cluster education and treatment, such as the development and implementation of a personalized seizure action plan as well as prescriptions for suitable rescue medications indicated for seizure clusters and instructions for their proper use. In all, the combination of targeted therapy along with patient education and support can improve quality of life.

Regulation of Potassium and Chloride Concentrations in Nervous Tissue as a Method of Anticonvulsant Therapy

Abstract

Under some pathological conditions, such as pharmacoresistant epilepsy, status epilepticus or certain forms of genetic abnormalities, spiking activity of GABAergic interneurons may enhance excitation processes in neuronal circuits and provoke the generation of ictal discharges. As a result, anticonvulsants acting on the GABAergic system may be ineffective or even increase seizure activity. This paradoxical effect of the inhibitory system is due to ionic imbalances in nervous tissue. This review addresses the mechanisms of ictal discharge initiation in neuronal networks due to the imbalance of chloride and potassium ions, as well as possible ways to regulate ionic concentrations. Both the enhancement (or attenuation) of the activity of certain neuronal ion transporters and ion pumps and their additional expression via gene therapy can be effective in suppressing seizure activity caused by ionic imbalances. The Na+–K+-pump, NKCC1 and KCC2 cotransporters are important for maintaining proper K+ and Cl– concentrations in nervous tissue, having been repeatedly considered as pharmacological targets for antiepileptic exposures. Further progress in this direction is hampered by the lack of sufficiently selective pharmacological tools and methods for providing effective drug delivery to the epileptic focus. The use of the gene therapy techniques, such as overexpressing of the KCC2 transporter in the epileptic focus, seems to be a more promising approach. Another possible direction could be the use of optogenetic tools, namely specially designed light-activated ion pumps or ion channels. In this case, photon energy can be used to create the required gradients of chloride and potassium ions, although these methods also have significant limitations which complicate their rapid introduction into medicine.

A personalizable autonomous neural mass model of epileptic seizures

Work in the last two decades has shown that neural mass models (NMM) can realistically reproduce and explain epileptic seizure transitions as recorded by electrophysiological methods (EEG, SEEG). In previous work, advances were achieved by increasing excitation and heuristically varying network inhibitory coupling parameters in the models. Based on these early studies, we provide a laminar NMM capable of realistically reproducing the electrical activity recorded by SEEG in the epileptogenic zone during interictal to ictal states. With the exception of the external noise input into the pyramidal cell population, the model dynamics are autonomous. By setting the system at a point close to bifurcation, seizure-like transitions are generated, including pre-ictal spikes, low voltage fast activity, and ictal rhythmic activity. A novel element in the model is a physiologically motivated algorithm for chloride dynamics: the gain of GABAergic post-synaptic potentials is modulated by the pathological accumulation of chloride in pyramidal cells due to high inhibitory input and/or dysfunctional chloride transport. In addition, in order to simulate SEEG signals for comparison with real seizure recordings, the NMM is embedded first in a layered model of the neocortex and then in a realistic physical model. We compare modeling results with data from four epilepsy patient cases. By including key pathophysiological mechanisms, the proposed framework captures succinctly the electrophysiological phenomenology observed in ictal states, paving the way for robust personalization methods based on NMMs.

NKCC1 and KCC2: Structural insights into phospho-regulation

Inhibitory neurotransmission plays a fundamental role in the central nervous system, with about 30–50% of synaptic connections being inhibitory. The action of both inhibitory neurotransmitter, gamma-aminobutyric-acid (GABA) and glycine, mainly relies on the intracellular Cl^– concentration in neurons. This is set by the interplay of the cation chloride cotransporters NKCC1 (Na⁺, K⁺, Cl^– cotransporter), a main Cl^– uptake transporter, and KCC2 (K⁺, Cl^– cotransporter), the principle Cl^– extruder in neurons. Accordingly, their dysfunction is associated with severe neurological, psychiatric, and neurodegenerative disorders. This has triggered great interest in understanding their regulation, with a strong focus on phosphorylation. Recent structural data by cryogenic electron microscopy provide the unique possibility to gain insight into the action of these phosphorylations. Interestingly, in KCC2, six out of ten (60%) known regulatory phospho-sites reside within a region of 134 amino acid residues (12% of the total residues) between helices α8 and α9 that lacks fixed or ordered three-dimensional structures. It thus represents a so-called intrinsically disordered region. Two further phospho-sites, Tyr⁹⁰³ and Thr⁹⁰⁶, are also located in a disordered region between the ß8 strand and the α8 helix. We make the case that especially the disordered region between helices α8 and α9 acts as a platform to integrate different signaling pathways and simultaneously constitute a flexible, highly dynamic linker that can survey a wide variety of distinct conformations. As each conformation can have distinct binding affinities and specificity properties, this enables regulation of [Cl^–]_i and thus the ionic driving force in a history-dependent way. This region might thus act as a molecular processor underlying the well described phenomenon of ionic plasticity that has been ascribed to inhibitory neurotransmission. Finally, it might explain the stunning long-range effects of mutations on phospho-sites in KCC2.

Molecular Mechanisms of Epilepsy: The Role of the Chloride Transporter KCC2

Epilepsy is a neurological disease characterized by abnormal or synchronous brain activity causing seizures, which may produce convulsions, minor physical signs, or a combination of symptoms. These disorders affect approximately 65 million people worldwide, from all ages and genders. Seizures apart, epileptic patients present a high risk to develop neuropsychological comorbidities such as cognitive deficits, emotional disturbance, and psychiatric disorders, which severely impair quality of life. Currently, the treatment for epilepsy includes the administration of drugs or surgery, but about 30% of the patients treated with antiepileptic drugs develop time-dependent pharmacoresistence. Therefore, further investigation about epilepsy and its causes is needed to find new pharmacological targets and innovative therapeutic strategies. Pharmacoresistance is associated to changes in neuronal plasticity and alterations of GABA_A receptor-mediated neurotransmission. The downregulation of GABA inhibitory activity may arise from a positive shift in GABA_A receptor reversal potential, due to an alteration in chloride homeostasis. In this paper, we review the contribution of K⁺-Cl^--cotransporter (KCC2) to the alterations in the Cl^- gradient observed in epileptic condition, and how these alterations are coupled to the increase in the excitability.

Brain-Derived Neurotrophic Factor Inhibits the Function of Cation-Chloride Cotransporter in a Mouse Model of Viral Infection-Induced Epilepsy

Well over 100 different viruses can infect the brain and cause brain inflammation. In the developing world, brain inflammation is a leading cause for epilepsy and often refractory to established anti-seizure drugs. Epilepsy generally results from an imbalance in excitatory glutamatergic and inhibitory GABAergic neurotransmission. GABAergic inhibition is determined by the intracellular Cl⁻ concentration which is established through the opposing action of two cation chloride cotransporters namely NKCC1 and KCC2. Brain-derived neurotrophic factor (BDNF) signaling is known to regulate expression of KCC2. Hence we hypothesized that viral induced epilepsy may result from aberrant BDNF signaling. We tested this hypothesis using a mouse model of Theiler’s murine encephalomyelitis virus (TMEV) infection-induced epilepsy. We found that BDNF levels in the hippocampus from TMEV-infected mice with seizures was increased at the onset of acute seizures and continued to increase during the peak of acute seizure as well as in latent and chronic phases of epilepsy. During the acute phase of epilepsy, we found significant reduction in the expression of KCC2 in hippocampus, whereas the level of NKCC1 was unaltered. Importantly, inhibiting BDNF using scavenging bodies of BDNF in live brain slices from TMEV-infected mice with seizures normalized the level of KCC2 in hippocampus. Our results suggest that BDNF can directly decrease the relative expression of NKCC1 and KCC2 such as to favor accumulation of chloride intracellularly which in turn causes hyperexcitability by reversing GABA-mediated inhibition. Although our attempt to inhibit the BDNF signaling mediated through tyrosine kinase B–phospholipase Cγ1 (TrkB-PLCγ1) using a small peptide did not change the course of seizure development following TMEV infection, alternative strategies for controlling the BDNF signaling could be useful in preventing seizure generation and development of epilepsy in this model.

Altered hippocampal GR/KCC2 signaling mediates susceptibility to convulsion in male offspring following dexamethasone exposure during pregnancy in rats

Epidemiological research suggests that convulsions may have an intrauterine developmental origin related to the application of dexamethasone, an artificially synthesized glucocorticoid. Here, using a rat animal model of prenatal dexamethasone exposure (PDE) we confirm that PDE can cause susceptibility to convulsions in male offspring and explore the epigenetic programming mechanism underlying this effect related to intrauterine type 2K⁺-Cl^- cotransporter (KCC2). Wistar rats were injected with dexamethasone (0.2mg/kg/d) subcutaneously during the gestational days (GD) 9-20 and part of the offspring was given lithium pilocarpine (LiPC) at postnatal week 10. Our results showed that male offspring of the PDE+LiPC group exhibited convulsions susceptibility, as well as increased hippocampal gamma-aminobutyric acid (GABA) and intracellular chloride ions level and decreased GABA receptor expression. The offspring also showed a decrease of hippocampal KCC2 H3K14ac levels and KCC2 expression. PDE male fetal rats (GD20) showed similar changes to male offspring after birth and exhibited an increased expression of glucocorticoid receptor (GR) and histone deacetylase type 2 (HDAC2). We observed effects consistent with those observed in PDE fetal rats following in vitro dexamethasone treatment of the fetal rat hippocampal neuron H19-7 cell line, and the effects could be reversed by treatment with a GR inhibitor (RU486) or HDAC2 inhibitor (romidepsin). Taken together, this study confirmed that PDE causes a reduction of H3K14ac levels in the KCC2 promoter region caused by activation of fetal hippocampal GR-HDAC2-KCC2 signaling. We proposed that this abnormal epigenetic modification is the mechanism underlying offspring convulsions susceptibility. CATEGORIES: mechanism of toxicity.

Why won't it stop? The dynamics of benzodiazepine resistance in status epilepticus

Status epilepticus is a life-threatening neurological emergency that affects both adults and children. Approximately 36% of episodes of status epilepticus do not respond to the current preferred first-line treatment, benzodiazepines. The proportion of episodes that are refractory to benzodiazepines is higher in low-income and middle-income countries (LMICs) than in high-income countries (HICs). Evidence suggests that longer episodes of status epilepticus alter brain physiology, thereby contributing to the emergence of benzodiazepine resistance. Such changes include alterations in GABA_A receptor function and in the transmembrane gradient for chloride, both of which erode the ability of benzodiazepines to enhance inhibitory synaptic signalling. Often, current management guidelines for status epilepticus do not account for these duration-related changes in pathophysiology, which might differentially impact individuals in LMICs, where the average time taken to reach medical attention is longer than in HICs. In this Perspective article, we aim to combine clinical insights and the latest evidence from basic science to inspire a new, context-specific approach to efficiently managing status epilepticus.

Striatal Chloride Dysregulation and Impaired GABAergic Signaling Due to Cation-Chloride Cotransporter Dysfunction in Huntington’s Disease

Intracellular chloride (Cl–) levels in mature neurons must be tightly regulated for the maintenance of fast synaptic inhibition. In the mature central nervous system (CNS), synaptic inhibition is primarily mediated by gamma-amino butyric acid (GABA), which binds to Cl– permeable GABAA receptors (GABAARs). The intracellular Cl– concentration is primarily maintained by the antagonistic actions of two cation-chloride cotransporters (CCCs): Cl–-importing Na+-K+-Cl– co-transporter-1 (NKCC1) and Cl– -exporting K+-Cl– co-transporter-2 (KCC2). In mature neurons in the healthy brain, KCC2 expression is higher than NKCC1, leading to lower levels of intracellular Cl–, and Cl– influx upon GABAAR activation. However, in neurons of the immature brain or in neurological disorders such as epilepsy and traumatic brain injury, impaired KCC2 function and/or enhanced NKCC1 expression lead to intracellular Cl– accumulation and GABA-mediated excitation. In Huntington’s disease (HD), KCC2- and NKCC1-mediated Cl–-regulation are also altered, which leads to GABA-mediated excitation and contributes to the development of cognitive and motor impairments. This review summarizes the role of Cl– (dys)regulation in the healthy and HD brain, with a focus on the basal ganglia (BG) circuitry and CCCs as potential therapeutic targets in the treatment of HD.

The Developmental Changes in Intrinsic and Synaptic Properties of Prefrontal Neurons Enhance Local Network Activity from the Second to the Third Postnatal Weeks in Mice

The prefrontal cortex (PFC) is characterized by protracted maturation. The cellular mechanisms controlling the early development of prefrontal circuits are still largely unknown. Our study delineates the developmental cellular processes in the mouse medial PFC (mPFC) during the second and the third postnatal weeks and characterizes their contribution to the changes in network activity. We show that spontaneous inhibitory postsynaptic currents (sIPSC) are increased, whereas spontaneous excitatory postsynaptic currents (sEPSC) are reduced from the second to the third postnatal week. Drug application suggested that the increased sEPSC frequency in mPFC at postnatal day 10 (P10) is due to depolarizing γ-aminobutyric acid (GABA) type A receptor function. To further validate this, perforated patch-clamp recordings were obtained and the expression levels of K-Cl cotransporter 2 (KCC2) protein were examined. The reversal potential of IPSCs in response to current stimulation was significantly more depolarized at P10 than P20 while KCC2 expression is decreased. Moreover, the number of parvalbumin-expressing GABAergic interneurons increases and their intrinsic electrophysiological properties significantly mature in the mPFC from P10 to P20. Using computational modeling, we show that the developmental changes in synaptic and intrinsic properties of mPFC neurons contribute to the enhanced network activity in the juvenile compared with neonatal mPFC.

Targeting ischemia-induced KCC2 hypofunction rescues refractory neonatal seizures and mitigates epileptogenesis in a mouse model

[Figure: see text].

Effects of in utero exposure to monosodium glutamate on locomotion, anxiety, depression, memory and KCC2 expression in offspring

In pregnancy, there is a significant risk for developing embryos to be adversely affected by everyday chemicals such as food additives and environmental toxins. In recent times, several studies have documented the detrimental effect of exposure to such chemicals on the behaviour and neurodevelopment of the offspring. This study evaluated the influence of the food additive, monosodium glutamate (MSG), on behaviour and development in mice. Pregnant dams were exposed to MSG 2 or 4 g/kg or distilled water from gestation day 10-20. On delivery, postnatal day 1 (PN 1), 3 pups were sacrificed and whole brain samples assayed for KCC2 expression by western blot. The remaining pups were housed until PN 43 before commencing behavioural assessment. Their weights were measured at birth and at 3 days intervals until PN 42. The impact of prenatal exposure to MSG on baseline exploratory, anxiety and depression behaviours as well as spatial and working memory was assessed. In utero exposure to 4 g/kg MSG significantly reduced exploratory drive and increased depression-like behaviours but did not exert any significant impact on anxiety-like behaviours (p < 0.01). Additionally, there was a two-fold increase in KCC2 expression in both 2 and 4 g/kg MSG-exposed offspring. CONCLUSION: This study indicates that, in utero exposure to MSG increases the expression of KCC2 and causes significant effect on locomotion and depression-like behaviours but only marginally affects memory function.

Toward Understanding the Diverse Roles of Perisomatic Interneurons in Epilepsy

Epileptic seizures are associated with excessive neuronal spiking. Perisomatic γ-aminobutyric acid (GABA)ergic interneurons specifically innervate the subcellular domains of postsynaptic excitatory cells that are critical for spike generation. With a revolution in transcriptomics-based cell taxonomy driving the development of novel transgenic mouse lines, selectively monitoring and modulating previously elusive interneuron types is becoming increasingly feasible. Emerging evidence suggests that the three types of hippocampal perisomatic interneurons, axo-axonic cells, along with parvalbumin- and cholecystokinin-expressing basket cells, each follow unique activity patterns in vivo, suggesting distinctive roles in regulating epileptic networks.

Inhibiting with-no-lysine kinases enhances K+/Cl- cotransporter 2 activity and limits status epilepticus

First-in-line benzodiazepine treatment fails to terminate seizures in about 30% of epilepsy patients, highlighting a need for novel antiseizure strategies. Impaired GABAergic inhibition is key to the development of such benzodiazepine-resistant seizures, as well as the pathophysiology of status epilepticus (SE). It is emerging that reduced or impaired neuronal K+/Cl- cotransporter 2 (KCC2) activity contributes to deficits in γ-aminobutyric acid (GABA)-mediated inhibition and increased seizure vulnerability. The with-no-lysine kinase (WNK)-STE20/SPS1-related proline/alanine-rich (SPAK) kinase signaling pathway inhibits neuronal KCC2 via KCC2-T1007 phosphorylation. A selective WNK kinase inhibitor, WNK463, was recently synthesized by Novartis. Exploiting WNK463, we test the hypothesis that pharmacological WNK inhibition will enhance KCC2 activity, increase the efficacy of GABAergic inhibition, and thereby limit seizure activity in animal models. Immunoprecipitation and Western blot analysis were used to examine WNK463's effects on KCC2-T1007 phosphorylation, in vitro and in vivo. A thallium (Tl+) uptake assay was used in human embryonic kidney (HEK-293) cells expressing KCC2 to test WNK463's effects on KCC2-mediated Tl+ transport. Gramicidin-perforated- and whole-cell patch-clamp recordings in cortical rat neurons were used to examine WNK463's effects on KCC2-mediated Cl- transport. In mouse brain slices (entorhinal cortex), field recordings were utilized to examine WNK463's effects on 4-aminopyridine-induced seizure activity. Last, WNK463 was directly deliver to the mouse hippocampus in vivo and tested in a kainic acid model of diazepam-resistant SE. WNK463 significantly reduces KCC2-T1007 phosphorylation in vitro and in vivo (mice). In human embryonic kidney 293 (HEK-293) cells expressing KCC2, WNK463 greatly enhanced the rates Tl+ transport. However, the drug did not enhance Tl+ transport in cells expressing a KCC2-phospho null T1007 mutant. In cultured rat neurons, WNK463 rapidly reduced intracellular Cl- and consequently hyperpolarized the Cl- reversal potential (EGABA). In mature neurons that were artificially loaded with 30 mM Cl-, WNK463 significantly enhanced KCC2-mediated Cl- export and hyperpolarized EGABA. In a 4-aminopyridine model of acute seizures, WNK463 reduced the frequency and number of seizure-like events (SLEs). Finally, in an in vivo kainic acid (KA) model of diazepam-resistant SE, WNK463 slowed the onset and reduced the severity of KA-induced status epilepticus. Last, WNK463 prevented the development of pharmaco-resistance to diazepam in drug-treated mice. Our findings demonstrate that acute WNK463 treatment potentiates KCC2 activity in neurons and limits seizure burden in two well-established models of seizures and epilepsy. Our work suggests that agents which act to increase KCC2 activity may be useful adjunct therapeutics to alleviate diazepam-resistant SE.

Developmental dysregulation of excitatory-to-inhibitory GABA-polarity switch may underlie schizophrenia pathology: A monozygotic-twin discordant case analysis in human iPS cell-derived neurons

Schizophrenia is a major psychiatric disorder, but the molecular mechanisms leading to its initiation or progression remain unclear. To elucidate the pathophysiology of schizophrenia, we used an in vitro neuronal cell culture model involving human induced pluripotent stem cells (hiPSCs) derived from a monozygotic-twin discordant schizophrenia pair. The cultured neurons differentiated from hiPSCs were composed of a mixture of glutamatergic excitatory neurons and gamma aminobutyric acid (GABA)ergic inhibitory neurons. In the electrophysiological analysis, a different pattern of spontaneous neuronal activity was observed under the condition without any stimulants. The frequency of spontaneous excitatory post-synaptic currents (sEPSCs) was significantly higher in the hiPSC-derived neurons of the patient with schizophrenia than in the control sibling at day-in-vitro 30. However, the synaptic formation was not different between the patient with schizophrenia and the control sibling during the same culture period. To explain underlying mechanisms of higher excitability of presynaptic cells, we focused on the potassium-chloride co-transporter KCC2, which contributes to excitatory-to-inhibitory GABA polarity switch in developing neurons. We also revealed the altered expression pattern of KCC2 in hiPSC-derived neurons from the patient with schizophrenia, which could contribute to understanding the pathology of schizophrenia in the developing nervous system.

Probing the polarity of spontaneous perisomatic GABAergic synaptic transmission in the mouse CA3 circuit in vivo

The hypothesis that reversed, excitatory GABA may be involved in various brain pathologies, including epileptogenesis, is appealing but controversial because of the technical difficulty of probing endogenous GABAergic synaptic function in vivo. We overcome this challenge by non-invasive extracellular recording of neuronal firing responses to optogenetically evoked and spontaneously occurring inhibitory perisomatic GABAergic field potentials, generated by individual parvalbumin interneurons on their target pyramidal cells. Our direct probing of GABAergic transmission suggests a rather anecdotal participation of excitatory GABA in two specific models of epileptogenesis in the mouse CA3 circuit in vivo, even though this does not preclude its expression in other brain areas or pathological conditions. Our approach allows the detection of distinct alterations of inhibition during spontaneous activity in vivo, with high sensitivity. It represents a promising tool for the investigation of excitatory GABA in different pathological conditions that may affect the hippocampal circuit.

Sleep, neuronal hyperexcitability, inflammation and neurodegeneration: Does early chronic short sleep trigger and is it the key to overcoming Alzheimer's disease?

Evidence links neuroinflammation to Alzheimer's disease (AD); however, its exact contribution to the onset and progression of the disease is poorly understood. Symptoms of AD can be seen as the tip of an iceberg, consisting of a neuropathological build-up in the brain of extracellular amyloid-β (Aβ) plaques and intraneuronal hyperphosphorylated aggregates of Tau (pTau), which are thought to stem from an imbalance between its production and clearance resulting in loss of synaptic health and dysfunctional cortical connectivity. The glymphatic drainage system, which is particularly active during sleep, plays a key role in the clearance of proteinopathies. Poor sleep can cause hyperexcitability and promote Aβ and tau pathology leading to systemic inflammation. The early neuronal hyperexcitability of γ-aminobutyric acid (GABA)-ergic inhibitory interneurons and impaired inhibitory control of cortical pyramidal neurons lie at the crossroads of excitatory/inhibitory imbalance and inflammation. We outline, with a prospective framework, a possible vicious spiral linking early chronic short sleep, neuronal hyperexcitability, inflammation and neurodegeneration. Understanding the early predictors of AD, through an integrative approach, may hold promise for reducing attrition in the late stages of neuroprotective drug development.

Non-Cell-Autonomous Regulation of Optic Nerve Regeneration by Amacrine Cells

Visual information is conveyed from the eye to the brain through the axons of retinal ganglion cells (RGCs) that course through the optic nerve and synapse onto neurons in multiple subcortical visual relay areas. RGCs cannot regenerate their axons once they are damaged, similar to most mature neurons in the central nervous system (CNS), and soon undergo cell death. These phenomena of neurodegeneration and regenerative failure are widely viewed as being determined by cell-intrinsic mechanisms within RGCs or to be influenced by the extracellular environment, including glial or inflammatory cells. However, a new concept is emerging that the death or survival of RGCs and their ability to regenerate axons are also influenced by the complex circuitry of the retina and that the activation of a multicellular signaling cascade involving changes in inhibitory interneurons - the amacrine cells (AC) - contributes to the fate of RGCs. Here, we review our current understanding of the role that interneurons play in cell survival and axon regeneration after optic nerve injury.