Cyclothiazide induces robust epileptiform activity in rat hippocampal neurons both in vitro and in vivo

Stimulus effects of extremely low-frequency electric field exposure on calcium oscillations in a human cortical spheroid

High-intensity, low-frequency (1 Hz to 100 kHz) electric and magnetic fields (EF and MF) cause electrical excitation of the nervous system via an induced EF (iEF) in living tissue. However, the biological properties and thresholds of stimulus effects on synchronized activity in a three-dimensional (3D) neuronal network remain uncertain. In this study, we evaluated changes in neuronal network activity during extremely low-frequency EF (ELF-EF) exposure by measuring intracellular calcium ([Ca2+]i) oscillations, which reflect neuronal network activity. For ELF-EF exposure experiments, we used a human cortical spheroid (hCS), a 3D-cultured neuronal network generated from human induced pluripotent stem cell (hiPSC)-derived cortical neurons. A 50 Hz sinusoidal ELF-EF exposure modulated [Ca2+]i oscillations with dependencies on exposure intensity and duration. Based on the experimental setup and results, the iEF distribution inside the hCS was estimated using high-resolution numerical dosimetry. The numerical estimation revealed threshold values ranging between 255-510 V/m (peak) and 131-261 V/m (average). This indicates that thresholds of neuronal excitation in the hCS were equivalent to those of a thin nerve fiber.

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.

Anti-PD-1 treatment protects against seizure by suppressing sodium channel function

AIMS

Although programmed cell death protein 1 (PD-1) typically serves as a target for immunotherapies, a few recent studies have found that PD-1 is expressed in the nervous system and that neuronal PD-1 might play a crucial role in regulating neuronal excitability. However, whether brain-localized PD-1 is involved in seizures and epileptogenesis is still unknown and worthy of in-depth exploration.

METHODS

The existence of PD-1 in human neurons was confirmed by immunohistochemistry, and PD-1 expression levels were measured by real-time quantitative PCR (RT-qPCR) and western blotting. Chemoconvulsants, pentylenetetrazol (PTZ) and cyclothiazide (CTZ), were applied for the establishment of in vivo (rodents) and in vitro (primary hippocampal neurons) models of seizure, respectively. SHR-1210 (a PD-1 monoclonal antibody) and sodium stibogluconate (SSG, a validated inhibitor of SH2-containing protein tyrosine phosphatase-1 [SHP-1]) were administrated to investigate the impact of PD-1 pathway blockade on epileptic behaviors of rodents and epileptiform discharges of neurons. A miRNA strategy was applied to determine the impact of PD-1 knockdown on neuronal excitability. The electrical activities and sodium channel function of neurons were determined by whole-cell patch-clamp recordings. The interaction between PD-1 and α-6 subunit of human voltage-gated sodium channel (Nav1.6) was validated by performing co-immunostaining and co-immunoprecipitation (co-IP) experiments.

RESULTS

Our results reveal that PD-1 protein and mRNA levels were upregulated in lesion cores compared with perifocal tissues of surgically resected specimens from patients with intractable epilepsy. Furthermore, we show that anti-PD-1 treatment has anti-seizure effects both in vivo and in vitro. Then, we reveal that PD-1 blockade can alter the electrophysiological properties of sodium channels. Moreover, we reveal that PD-1 acts together with downstream SHP-1 to regulate sodium channel function and hence neuronal excitability. Further investigation suggests that there is a direct interaction between neuronal PD-1 and Nav1.6.

CONCLUSION

Our study reveals that neuronal PD-1 plays an important role in epilepsy and that anti-PD-1 treatment protects against seizures by suppressing sodium channel function, identifying anti-PD-1 treatment as a novel therapeutic strategy for epilepsy.

Deficit of PKHD1L1 in the dentate gyrus increases seizure susceptibility in mice

Epilepsy is a chronic neurological disorder featuring recurrent, unprovoked seizures, which affect more than 65 million people worldwide. Here, we discover that the PKHD1L1, which is encoded by polycystic kidney and hepatic disease1-like 1 (Pkhd1l1), wildly distributes in neurons in the central nervous system (CNS) of mice. Disruption of PKHD1L1 in the dentate gyrus region of the hippocampus leads to increased susceptibility to pentylenetetrazol-induced seizures in mice. The disturbance of PKHD1L1 leads to the overactivation of the mitogen-activated protein kinase (MAPK)/extracellular regulated kinase (ERK)-Calpain pathway, which is accompanied by remarkable degradation of cytoplasmic potassium chloride co-transporter 2 (KCC2) level together with the impaired expression and function of membrane KCC2. However, the reduction of membrane KCC2 is associated with the damaged inhibitory ability of the vital GABA receptors, which ultimately leads to the significantly increased susceptibility to epileptic seizures. Our data, thus, indicate for the first time that Pkhd1l1, a newly discovered polycystic kidney disease (PKD) association gene, is required in neurons to maintain neuronal excitability by regulation of KCC2 expression in CNS. A new mechanism of the clinical association between genetic PKD and seizures has been built, which could be a potential therapeutic target for treating PKD-related seizures.

Furosemide prevents membrane KCC2 downregulation during convulsant stimulation in the hippocampus

In adults, γ-aminobutyric acid (GABA) type A receptor (GABA_AR)-mediated inhibition depends on the maintenance of low intracellular chloride anion concentration through neuron-specific potassium-chloride cotransporter-2 (KCC2). KCC2 has been widely reported to have a plasticity change during the course of epilepsy development, with an early downregulation and late recovery in neuronal cell membranes after epileptic stimulation, which facilitates epileptiform burst activity. Furosemide is a clinical loop diuretic that inhibits KCC2. Here, we first confirmed that furosemide pretreatment could effectively prevented convulsant stimulation-induced neuronal membrane KCC2 downregulation in the hippocampus in both in vivo and in vitro cyclothiazide-induced seizure model. Second, we verified that furosemide pretreatment rescued KCC2 function deficits, as indicated by E _GABA depolarizing shift and GABA_AR inhibitory function impairment induced via cyclothiazide treatment. Further, we demonstrated that furosemide also suppressed cyclothiazide-induced epileptiform burst activity in cultured hippocampal neurons and lowered the mortality rate during acute seizure induction. Overall, furosemide prevents membrane KCC2 downregulation during acute seizure induction, restores KCC2-mediated GABA inhibition, and interrupts the progression from acute seizure to epileptogenesis.

Transient sublethal hypoxia in neonatal rats causes reduced dendritic spines, aberrant synaptic plasticity, and impairments in memory

Hypoxic/ischemic insult, a leading cause of functional brain defects, has been extensively studied in both clinical and experimental animal research, including its etiology, neuropathogenesis, and pharmacological interventions. Transient sublethal hypoxia (TSH) is a common clinical occurrence in the perinatal period. However, its effect on early developing brains remains poorly understood. The present study was designed to investigate the effect of TSH on the dendrite and dendritic spine formation, neuronal and synaptic activity, and cognitive behavior of early postnatal Day 1 rat pups. While TSH showed no obvious effect on gross brain morphology, neuron cell density, or glial activation in the hippocampus, we found transient hypoxia did cause significant changes in neuronal structure and function. In brains exposed to TSH, hippocampal neurons developed shorter and thinner dendrites, with decreased dendritic spine density, and reduced strength in excitatory synaptic transmission. Moreover, TSH-treated rats showed impaired cognitive performance in spatial learning and memory. Our findings demonstrate that TSH in newborn rats can cause significant impairments in synaptic formation and function, and long-lasting brain functional deficits. Therefore, this study provides a useful animal model for the study of TSH on early developing brains and to explore potential pharmaceutical interventions for patients subjected to TSH insult.

Activation of Kir2.3 Channels by Tenidap Suppresses Epileptiform Burst Discharges in Cultured Hippocampal Neurons

BACKGROUND & OBJECTIVE

Tenidap, a selective human inwardly rectifying potassium (Kir) 2.3 channel opener, has been reported to have antiepileptic effect in the pilocarpine temporal lobe epilepsy rat model in our previous study. However, the effect of tenidap on neurons and its relationship with the epileptiform bursting charges in neuron is still required to be explored.

METHODS

In this study, cyclothiazide (CTZ) induced cultured hippocampal neuron epileptic model was used to study the antiepileptic effect of tenidap and the relationship between Kir2.3 channel and the neuronal epileptiform burst.

RESULTS

Patch clamp recording showed that both acute (2h) and chronic (48h) CTZ pre-treatment all significantly induced robust epileptiform burst activities in cultured hippocampal neurons, and tenidap acutely application inhibited this highly synchronized abnormal activities. The effect of tenidap is likely due to increased activity of Kir2.3 channels, since tenidap significantly enhanced kir current recorded from those neurons. In addition, neurons overexpressing Kir2.3 channels, by transfection with Kir2.3 plasmid, showed a significant large increase of the Kir current, prevented CTZ treatment to induce epileptiform burst discharge.

CONCLUSION

Our current study demonstrated that over activation of Kir2.3 channel in hippocampal neurons could positively interference with epileptiform burst activities, and tenidap, as a selective Kir2.3 channel opener, could be a potential candidate for seizure therapy.

Gluconate suppresses seizure activity in developing brains by inhibiting CLC-3 chloride channels

Neonatal seizures are different from adult seizures, and many antiepileptic drugs that are effective in adults often fail to treat neonates. Here, we report that gluconate inhibits neonatal seizure by inhibiting CLC-3 chloride channels. We detect a voltage-dependent outward rectifying Cl⁻ current mediated by CLC-3 Cl⁻ channels in early developing brains but not adult mouse brains. Blocking CLC-3 Cl⁻ channels by gluconate inhibits seizure activity both in neonatal brain slices and in neonatal animals with in vivo EEG recordings. Consistently, neonatal neurons of CLC-3 knockout mice lack the outward rectifying Cl⁻ current and show reduced epileptiform activity upon stimulation. Mechanistically, we demonstrate that activation of CLC-3 Cl⁻ channels alters intracellular Cl⁻ homeostasis and enhances GABA excitatory activity. Our studies suggest that gluconate can suppress neonatal seizure activities through inhibiting CLC-3 Cl⁻ channels in developing brains.

Tarps differentially affect the pharmacology of ampakines

Transmembrane AMPA receptor regulatory proteins (TARPs) govern AMPA receptor cell surface expression and distinct physiological properties including agonist affinity, desensitization and deactivation kinetics. The prototypical TARP, STG or γ2 and TARPs γ3, γ4, γ7 and γ8 are all expressed to varying degrees in the mammalian brain and differentially regulate AMPAR gating parameters. Positive allosteric AMPA receptor modulators or ampakines alter receptor rates of agonist binding/unbinding, channel opening and can offset receptor desensitization and deactivation. The effects of the two ampakines, CX614 and cyclothiazide (CTZ) were evaluated on homomeric GluR1-flip receptors and GluR2-flop receptors expressed on HEK293 cells by transient transfection with or without different TARPs γ2, γ3, γ4 or γ8 genes. γ4 was the most robust TARP in increasing the affinities of CX614 and CTZ on GluR1-flip receptors, but had no such effect on GluR2-flop receptors. However, γ8 gave the most significant increases in affinities of CX614 and CTZ on GluR2-flop. These data show that TARPs differentially affect the surface expression and kinetics of the AMPA receptor, as well as the pharmacology of ampakines for the AMPA receptor. The modulatory effects of TARPs on ampakine pharmacology are complex, being dependent on both the TARP subtype and the AMPA receptor subtypes/isoforms.

SK channels participate in the formation of after burst hyperpolarization and partly inhibit the burst strength of epileptic ictal discharges

Epilepsy is a common disease of the central nervous system. Tetanic spasms and convulsions are the key symptoms exhibited during epileptic seizures. However, the majority of patients have a significant post-seizure silence following a serious seizure; the underlying molecular neural mechanisms in this burst interval are unclear. The aim of the present study was to reveal the effect and role of calcium-activated potassium channels during this seizure interval silence period. Cyclothiazide (CTZ) was used to establish the seizure model in rat hippocampal cultured neurons, then the after-burst hyperpolarization (ABH) activities were recorded using the patch clamp technique. By comparing the amplitude and duration of hyperpolarizations, the present study analyzed the association between epileptiform bursts and ABHs when treated with different concentrations of CTZ. In addition, apamin and iberiotoxin were used for pharmacological tests. An intracranial electroencephalogram (EEG) recording was also performed when the CTZ experiments were repeated on animals. The experimental results revealed that treatment with high levels of CTZ induced larger ABHs and was associated with stronger burst activities, which suggested a positive correlation between ABH and epileptiform burst. Apamin, an antagonist of small conductance calcium-activated potassium (SK) channels, decreased the amplitude of ABH; however, reduced ABH was associated with enhanced burst activity, in burst probability and burst strength. These results revealed an important role of SK channels in the formation of ABH and in the inhibition of burst activity. Iberiotoxin, an antagonist of big conductance calcium-activated potassium (BK) channels, had no significant effect on ABH and burst activity. In addition, a positive correlation was identified between burst duration and ABH parameters. An intracellular calcium chelator impaired the amplitude of ABH; however, it did not affect the burst parameters. The rat cortical EEG recordings also exhibited a similar positive correlation between the duration of epileptic burst and after burst depression. Collectively, the results indicate that ABH may serve in the physiological feedback system to reduce the strength of epileptic hyperexcitation, a process in which SK channels are important.

KCC2 downregulation facilitates epileptic seizures

GABAA receptor-mediated inhibition depends on the maintenance of low level intracellular [Cl-] concentration, which in adult depends on neuron specific K+-Cl- cotransporter-2 (KCC2). Previous studies have shown that KCC2 was downregulated in both epileptic patients and various epileptic animal models. However, the temporal relationship between KCC2 downregulation and seizure induction is unclear yet. In this study, we explored the temporal relationship and the influence of KCC2 downregulation on seizure induction. Significant downregulation of plasma membrane KCC2 was directly associated with severe (Racine Score III and above) behavioral seizures in vivo, and occurred before epileptiform bursting activities in vitro induced by convulsant. Overexpression of KCC2 using KCC2 plasmid effectively enhanced resistance to convulsant-induced epileptiform bursting activities in vitro. Furthermore, suppression of membrane KCC2 expression, using shRNAKCC2 plasmid in vitro and shRNAKCC2 containing lentivirus in vivo, induced spontaneous epileptiform bursting activities in vitro and Racine III seizure behaviors accompanied by epileptic EEG in vivo. Our findings novelly demonstrated that altered expression of KCC2 is not the consequence of seizure occurrence but likely is the contributing factor.

Estrogen suppresses epileptiform activity by enhancing Kv4.2-mediated transient outward potassium currents in primary hippocampal neurons

Catamenial epilepsy is a common phenomenon in female epileptic patients that is, in part, influenced by the 17-β-estradiol level during the menstrual cycle, which modulates the strength of the epileptic seizures. However, the underlying mechanism(s) for catamenial epilepsy remains unknown. In the present study, the effect of 17‑β‑estradiol on modulating epileptiform activities was investigated in cultured hippocampal neurons by focusing on the transient outward potassium current. Using the patch clamp technique, 17‑β‑estradiol was demonstrated to have a dose‑dependent U‑shape effect on epileptiform bursting activities in cultured hippocampal neurons; only the low dose (~0.1 ng/ml) of 17‑β‑estradiol had a suppressive effect on the epileptiform activities. The blockade effect of the low dose 17‑β‑estradiol could be suppressed by phrixotoxin2 (PaTx2), a selective channel blocker for voltage‑gated potassium channel type 4.2 (Kv4.2), which mediates the transient outward potassium current. Furthermore, the 17‑β‑estradiol bell‑shape‑like dose‑dependently enhanced the transient outward potassium current, which was inhibited by the estrogen receptor antagonist ICI 182,780. In conclusion, these results indicate that reduced activation of the transient outward potassium current by a high (or none) 17‑β‑estradiol level may enhance the epileptiform bursting activities in neurons, which may be one of the triggering causes for catamenial epilepsy, and therefore, maintaining a certain low 17‑β‑estradiol level may aid in the control of catamenial epilepsy.

Effects of 3-aminoglutarate, a "silent" false transmitter for glutamate neurons, on synaptic transmission and epileptiform activity

Pharmacological tools that interact with the mechanisms that regulate vesicular filling and release of the neurotransmitter L-glutamate would be of enormous value. In this study, we provide physiological evidence that the glutamate analog, 3-aminoglutarate (3-AG), acts as a false transmitter to reduce presynaptic glutamate release. 3-AG inhibits glutamate-mediated neurotransmission both in primary neuronal cultures and in brain slices with more intact neural circuits. When assayed with the low affinity glutamate receptor antagonist γ-DGG, we demonstrate that 3-AG significantly reduces the synaptic cleft glutamate concentration, suggesting that 3-AG may act as a false transmitter to compete with glutamate during vesicle filling. Furthermore, using three different epileptic models (Mg(2+)-free, 4-AP, and high K(+)), we demonstrate that 3-AG is capable of suppressing epileptiform activity both before and after its induction. Our studies, along with those of the companion paper by Foster et al. (2015) indicate that 3-AG is a "silent" false transmitter for glutamate neurons that is a useful pharmacological tool to probe the mechanisms governing vesicular storage and release of glutamate under both physiological and pathophysiological conditions. 3-AG may have potential therapeutic value in conditions where the glutamate neurotransmitter system is pathologically overactive.

The discovery and characterization of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor potentiator N-{(3S,4S)-4-[4-(5-cyano-2-thienyl)phenoxy]tetrahydrofuran-3-yl}propane-2-sulfonamide (PF-04958242)

A unique tetrahydrofuran ether class of highly potent α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor potentiators has been identified using rational and structure-based drug design. An acyclic lead compound, containing an ether-linked isopropylsulfonamide and biphenyl group, was pharmacologically augmented by converting it to a conformationally constrained tetrahydrofuran to improve key interactions with the human GluA2 ligand-binding domain. Subsequent replacement of the distal phenyl motif with 2-cyanothiophene to enhance its potency, selectivity, and metabolic stability afforded N-{(3S,4S)-4-[4-(5-cyano-2-thienyl)phenoxy]tetrahydrofuran-3-yl}propane-2-sulfonamide (PF-04958242, 3), whose preclinical characterization suggests an adequate therapeutic index, aided by low projected human oral pharmacokinetic variability, for clinical studies exploring its ability to attenuate cognitive deficits in patients with schizophrenia.

Proconvulsive effect of hydrochlorothiazide in an in vitro rat seizure model

OBJECTIVES

Protective effects of diuretics, particularly of hydrochlorothiazide (HCT), for the development of epilepsy have been described in vivo. However, its mechanism of action is unknown.

MATERIALS AND METHODS

Extracellular field potentials were recorded from the CA1- and CA3-subfields of the hippocampus of rats. Epileptiform discharges were induced by omission of Mg2+ from the artificial cerebrospinal fluid (ACSF). HCT was added to the ACSF at a concentration of 2 mmol/l, 0.2 mmol/l or 0.02 mmol/l. Frequency, amplitude and duration of the epileptiform discharges were evaluated. Long-term potentiation (LTP) was induced with and without the presence of HCT (n=6; 2 mmol/l). In addition, rats were injected with HCT (n=4) or saline (n=2), and the brain tissue was analyzed using HPLC.

RESULTS

Application of 0.02, 0.2, and 2 mmol/l HCT accelerated the frequency of discharges by 50%, 91%, and 100%, respectively. The amplitude of burst discharges also increased by 9%, 54%, and 300%, and the duration of epileptiform discharges increased by 10%, 30% and 120%. All parameters returned close to the basal levels after 60min washout of the substance. HCT increased the electrical evoked potentials but did not affect the LTP in hippocampal tissues. There was no evidence of HCT in the rat brain after intraperitoneal injection.

CONCLUSION

Exposure of hippocampal slices to HCT enhanced epileptiform activity in a dose-dependent manner. In addition, HCT does not seem to cross the blood brain barrier in rats. Thus, the anticonvulsive effect of HCT most likely is not through direct neuronal effect.

Activation of extrasynaptic GABA(A) receptors inhibits cyclothiazide-induced epileptiform activity in hippocampal CA1 neurons

Extrasynaptic GABA(A) receptors (GABA(A)Rs)-mediated tonic inhibition is reported to involve in the pathogenesis of epilepsy. In this study, we used cyclothiazide (CTZ)-induced in vitro brain slice seizure model to explore the effect of selective activation of extrasynaptic GABA(A)Rs by 4,5,6,7-tetrahydroisoxazolo[5,4-c] pyridine-3-ol (THIP) on the CTZ-induced epileptiform activity in hippocampal neurons. Perfusion with CTZ dose-dependently induced multiple epileptiform peaks of evoked population spikes (PSs) in CA1 pyramidal neurons, and treatment with THIP (5 μmol/L) significantly reduced the multiple PS peaks induced by CTZ stimulation. Western blot showed that the δ-subunit of the GABA(A)R, an extrasynaptic specific GABA(A)R subunit, was also significantly down-regulated in the cell membrane 2 h after CTZ treatment. Our results suggest that the CTZ-induced epileptiform activity in hippocampal CA1 neurons is suppressed by the activation of extrasynaptic GABA(A)Rs, and further support the hypothesis that tonic inhibition mediated by extrasynaptic GABA(A)Rs plays a prominent role in seizure generation.

Downregulated GABA and BDNF-TrkB pathway in chronic cyclothiazide seizure model

Cyclothiazide (CTZ) has been reported to simultaneously enhance glutamate receptor excitation and inhibit GABAA receptor inhibition, and in turn it evokes epileptiform activities in hippocampal neurons. It has also been shown to acutely induce epileptic seizure behavior in freely moving rats. However, whether CTZ induced seizure rats could develop to have recurrent seizure still remains unknown. In the current study, we demonstrated that 46% of the CTZ induced seizure rats developed to have recurrent seizure behavior as well as epileptic EEG with a starting latency between 2 weeks and several months. In those chronic seizure rats 6 months after the seizure induction by the CTZ, our immunohistochemistry results showed that both GAD and GAT-1 were significantly decreased across CA1, CA3, and dentate gyrus area of the hippocampus studied. In addition, both BDNF and its receptor TrkB were also decreased in hippocampus of the chronic CTZ seizure rats. Our results indicate that CTZ induced seizure is capable of developing to have recurrent seizure, and the decreased GABA synthesis and transport as well as the impaired BDNF-TrkB signaling pathway may contribute to the development of the recurrent seizure. Thus, CTZ seizure rats may provide a novel animal model for epilepsy study and anticonvulsant drug testing in the future.

Aggravation of seizure-like events by hydrogen sulfide: involvement of multiple targets that control neuronal excitability

AIMS

Epileptic seizures are well-known neurological complications following stroke, occurring in 3% of patients. However, the intrinsic correlation of seizures with stroke remains largely unknown. Hydrogen sulfide (H2 S) is a gas transmitter that may mediate cerebral ischemic injury. But the role of H2 S in seizures has not been understood yet. We examined the effect of H2 S on seizure-like events (SLEs) and underlying mechanisms.

METHODS AND RESULTS

Pentylenetetrazole (PTZ)- and pilocarpine-induced rat epileptic seizure models were tested. Low-Mg(2+) /high-K(+) - and 4-aminopyridine (4-AP)-induced epileptic seizure models were examined using patch-clamp recordings in brain slices. It was found that NaHS aggravated both PTZ- and pilocarpine-induced SLEs in rats, while both low-Mg(2+) /high-K(+) - and 4-AP-induced SLEs were also exacerbated by NaHS in brain slices, which may be due to its regulation on the voltage-gated sodium channel, N-methyl-D-aspartic acid receptor (NMDAR), and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) function. Furthermore, these effects were reversed by blocking voltage-gated sodium channel, NMDAR, and AMPAR.

CONCLUSIONS

These results suggest a pathological role of increased H2 S level in SLEs in vivo and in vitro. Enzymes that control H2 S biosynthesis could be interesting targets for antiepileptic strategies in poststroke epilepsy treatment.

Modulation of extracellular d-serine content by calcium permeable AMPA receptors in rat medial prefrontal cortex as revealed by in vivo microdialysis

In mammalian brains, d-serine has been shown to be required for the regulation of glutamate neurotransmission as an endogenous co-agonist for the N-methyl-d-aspartate type glutamate receptor that is essential for the expression of higher-order brain functions. The exact control mechanisms for the extracellular d-serine dynamics, however, await further elucidation. To obtain an insight into this issue, we have characterized the effects of agents acting at the α-amino-3-hydroxy-5-methyl-4-isoxazolepropioinic acid (AMPA) type glutamate receptor on the extracellular d-serine contents in the medial prefrontal cortex of freely moving rats by an in vivo microdialysis technique in combination with high-performance liquid chromatography with fluorometric detection. In vivo experiments are needed in terms of a crucial role of d-serine in the neuron-glia communications despite the previous in vitro studies on AMPA receptor-d-serine interactions using the separated preparations of neurons or glial cells. Here, we show that the intra-cortical infusion of (S)-AMPA, an active enantiomer at the AMPA receptor, causes a significant and concentration-dependent reduction in the prefrontal extracellular contents of d-serine, which is reversed by an AMPA/kainate receptor antagonist, 2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo[f]quinoxaline-7-sulfonamide disodium salt, and a calcium permeable AMPA receptor antagonist, 1-naphthyl acetyl spermine. The d-serine reducing effects of (S)-AMPA are augmented by co-infusion of cyclothiazide that prevents AMPA receptor desensitization. Our data support the view that a calcium permeable AMPA receptor subtype may exert a phasic inhibitory control on the extracellular d-serine release in the mammalian prefrontal cortex in vivo.

Regulation of epileptiform activity by two distinct subtypes of extrasynaptic GABAA receptors

Background

GABAergic deficit is one of the major mechanisms underlying epileptic seizures. Previous studies have mainly focused on alterations of synaptic GABAergic inhibition during epileptogenesis. Recent work suggested that tonic inhibition may also play a role in regulating epileptogenesis, but the underlying mechanism is not well understood.

Results

We employed molecular and pharmacological tools to investigate the role of tonic inhibition during epileptogenesis both in vitro and in vivo. We overexpressed two distinct subtypes of extrasynaptic GABA_A receptors, α5β3γ2 and α6β3δ receptors, in cultured hippocampal neurons. We demonstrated that overexpression of both α5β3γ2 and α6β3δ receptors enhanced tonic inhibition and reduced epileptiform activity in vitro. We then showed that injection of THIP (5 μM), a selective agonist for extrasynaptic GABA_A receptors at low concentration, into rat brain also suppressed epileptiform burst activity and behavioral seizures in vivo. Mechanistically, we discovered that low concentration of THIP had no effect on GABAergic synaptic transmission and did not affect the basal level of action potentials, but significantly inhibited high frequency neuronal activity induced by epileptogenic agents.

Conclusions

Our studies suggest that extrasynaptic GABA_A receptors play an important role in controlling hyperexcitatory activity, such as that during epileptogenesis, but a less prominent role in modulating a low level of basal activity. We propose that tonic inhibition may play a greater role under pathological conditions than in physiological conditions in terms of modulating neural network activity.

BDNF-TrkB signaling pathway is involved in pentylenetetrazole-evoked progression of epileptiform activity in hippocampal neurons in anesthetized rats

Pentylenetetrazole (PTZ) is a widely-used convulsant used in studies of epilepsy; its subcutaneous injection generates an animal model with stable seizures. Here, we compared the ability of PTZ via the intravenous and subcutaneous routes to evoke progressive epileptiform activity in the hippocampal CA1 neurons of anesthetized rats. The involvement of the BDNF-TrkB pathway was then investigated. When PTZ was given intravenously, it induced epileptiform bursting activity at a short latency in a dose-dependent manner. However, when PTZ was given subcutaneously, it induced a slowly-developing pattern of epileptogenesis; first, generating multiple population-spike peaks, then spontaneous interictal discharge-like spike, leading to the final ictal discharge-like, highly synchronized bursting fi ring in the CA1 pyramidal layer of the hippocampus. K252a, a TrkB receptor antagonist, when given by intracerebroventricular injection, significantly reduced the probability of multiple population spike peaks induced by subcutaneous injection of PTZ, delayed the latency of spontaneous spikes, and reduced the burst frequency. Our results indicate that PTZ induces a progressive change of neuronal epileptiform activity in the hippocampus, and the BDNF-TrkB signaling pathway is mainly involved in the early phases of epileptogenesis, but not the synchronized neuronal burst activity associated with epileptic seizure in the PTZ animal model. These results provide basic insights into the changing pattern of hippocampal neuronal activity during the development of the PTZ seizure model, and establish an in vivo seizure model useful for future electrophysiological studies of epilepsy.

U-shape suppressive effect of phenol red on the epileptiform burst activity via activation of estrogen receptors in primary hippocampal culture

Phenol red is widely used in cell culture as a pH indicator. Recently, it also has been reported to have estrogen-like bioactivity and be capable of promoting cell proliferation in different cell lines. However, the effect of phenol red on primary neuronal culture has never been investigated. By using patch clamp technique, we demonstrated that hippocampal pyramidal neurons cultured in neurobasal medium containing no phenol red had large depolarization-associated epileptiform bursting activities, which were rarely seen in neurons cultured in phenol red-containing medium. Further experiment data indicate that the suppressive effect of the phenol red on the abnormal epileptiform burst neuronal activities was U-shape dose related, with the most effective concentration at 28 µM. In addition, this concentration related inhibitory effect of phenol red on the epileptiform neuronal discharges was mimicked by 17-β-estradiol, an estrogen receptor agonist, and inhibited by ICI-182,780, an estrogen receptor antagonist. Our results suggest that estrogen receptor activation by phenol red in the culture medium prevents formation of abnormal, epileptiform burst activity. These studies highlight the importance of phenol red as estrogen receptor stimulator and cautions of careful use of phenol red in cell culture media.

Cyclothiazide-induced persistent increase in respiratory-related activity in vitro

Hypoglossal (XII) motoneurons (MNs) innervate the genioglossus muscle of the tongue, which plays an important role in maintaining upper airway patency, particularly during sleep, and modulating upper airway resistance. Discovering methods for inducing long-term increases in genioglossal motoneuronal excitability to AMPA-mediated drive may help in the development of therapeutics for upper airway motor disorders such as obstructive sleep apnoea. We show that the diuretic, anti-hypertensive, AMPA receptor modulator cyclothiazide (CTZ) induces a profound and long-lasting increase in the amplitude of respiratory-related XII nerve activity in rhythmically active neonatal rat medullary slices. Treatment of the slice with CTZ (90 μM) for 1 h increased the integrated XII ( XII) nerve burst amplitude to 262 ± 23% of pre-treatment control at 1 h post-treatment;much of this increase lasted at least 12 h. The amount of CTZ-induced facilitation (CIF) was dependent upon both CTZ dose and exposure time and was accompanied by a long-lasting increase in endogenous AMPA-mediated drive currents to XII MNs. CIF, however, is not a form of plasticity and does not depend on AMPA or NMDA receptor activation for its induction. Nor does it depend on coincident protein kinase A or C activity. Rather, measurement of mEPSCs along with mass spectrometric analysis of CTZ-treated slices indicates that the cause is prolonged bioavailability of CTZ. These results illustrate a latent residual capacity for potentiating AMPA-mediated inspiratory drive to XII MNs that might be applied to the treatment of upper airway motor deficits.

TrkB inhibition as a therapeutic target for CNS-related disorders

The interaction of brain-derived neurotrophic factor (BDNF) with its tropomyosin-related kinase receptor B (TrkB) is involved in fundamental cellular processes including neuronal proliferation, differentiation and survival as well as neurotransmitter release and synaptic plasticity. TrkB signaling has been widely associated with beneficial, trophic effects and many commonly used psychotropic drugs aim to increase BDNF levels in the brain. However, it is likely that a prolonged increased TrkB activation is observed in many pathological conditions, which may underlie the development and course of clinical symptoms. Interestingly, genetic and pharmacological studies aiming at decreasing TrkB activation in rodent models mimicking human pathology have demonstrated a promising therapeutic landscape for TrkB inhibitors in the treatment of various diseases, e.g. central nervous system (CNS) disorders and several types of cancer. Up to date, only a few selective and potent TrkB inhibitors have been developed. As such, the use of crystallography and in silico approaches to model BDNF-TrkB interaction and to generate relevant pharmacophores represent powerful tools to develop novel compounds targeting the TrkB receptor.

Magnolol, a major bioactive constituent of the bark of Magnolia officinalis, exerts antiepileptic effects via the GABA/benzodiazepine receptor complex in mice

BACKGROUND AND PURPOSE

The aim of this study was to evaluate the anti-convulsant effects of magnolol (6, 6', 7, 12-tetramethoxy-2, 2'-dimethyl-1-β-berbaman, C18H18O2) and the mechanisms involved.

EXPERIMENTAL APPROACH

Mice were treated with magnolol (20, 40 and 80 mg·kg(-1)) 30 min before injection with pentylenetetrazol (PTZ, 60 mg·kg(-1), i.p.). The anti-seizure effects of magnolol were analysed using seizure models of behaviour, EEG and in vitro electrophysiology and c-Fos expression in the hippocampus and cortex.

KEY RESULTS

Magnolol at doses of 40 and 80 mg·kg(-1) significantly delayed the onset of myoclonic jerks and generalized clonic seizures, and decreased the seizure stage and mortality compared with those of the vehicle-treated animals. EEG recordings showed that magnolol (40 and 80 mg·kg(-1)) prolonged the latency of seizure onset and decreased the number of seizure spikes. The anti-epileptic effect of magnolol was reversed by the GABA(A)/benzodiazepine receptor antagonist flumazenil. Pretreatment with flumazenil decreased the effects of magnolol on prolongation of seizure latency and decline of seizure stage. In a Mg(2+)-free model of epileptiform activity, using multi-electrode array recordings in mouse hippocampal slices, magnolol decreased spontaneous epileptiform discharges. Magnolol also significantly decreased seizure-induced Fos immunoreactivity in the piriform cortex, dentate gyrus and hippocampal area CA1. These effects were attenuated by pretreatment with flumazenil.

CONCLUSIONS AND IMPLICATIONS

These findings indicate that the inhibitory effects of magnolol on epileptiform activity were mediated by the GABA(A) /benzodiazepine receptor complex.

Anticonvulsant activity of BmK AS, a sodium channel site 4-specific modulator

The anticonvulsant activity of BmK AS, a sodium channel site 4-selective modulator purified from scorpion venom (Buthus martensi Karsch), was investigated in unanesthetized rats with acute pentylenetetrazole (PTZ)- and pilocarpine-induced seizures. Rats were microinjected in the CA1 region with either saline or BmK AS, followed by epileptogenic doses of PTZ or pilocarpine 30 minutes later. The anticonvulsant efficacy of BmK AS in PTZ- or pilocarpine-evoked seizure-like behavior and cortical epileptiform EEG activity was assessed. Intrahippocampal injections of BmK AS (0.05-1 μg in 1 μL) produced dose-dependent anticonvulsant activity in the PTZ model, suppressing seizure-associated behavior and reducing both the number and duration of high-amplitude, high-frequency discharges (HAFDs) on the EEG. In contrast, BmK AS did not affect the epileptiform EEG in the pilocarpine model over the same dose range, although it did increase the latency to status epilepticus onset and slightly, but significantly, reduced the seizure score. In summary, our results demonstrate that the sodium channel site 4-selective modulator BmK AS is an effective inhibitor of PTZ- but not pilocarpine-induced acute seizures. These results indicate that BmK AS may serve as a novel probe in exploring the role of different sodium channel subtypes in an epileptogenic setting and as a potential lead in developing antiepileptic drugs specifically for the therapy of sodium channel site 4-related epilepsy.

BDNF-TrkB signaling pathway mediates the induction of epileptiform activity induced by a convulsant drug cyclothiazide

Brain-derived neurotrophic factor (BDNF) and its receptor TrkB play an important function in neuronal development and synaptic plasticity. Recently we have established that cyclothiazide (CTZ) is a novel convulsant drug inducing robust epileptiform activity in hippocampal neurons both in vitro and in vivo. However, the molecular mechanisms underlying such convulsant action of CTZ are unknown. Here, we investigated potential roles of BDNF-TrkB signaling pathway in the CTZ-induction of epileptiform activity. In anaesthetized rats, CTZ dose-dependently induced epileptiform activity characterized by progressing of multiple peaks of population spikes, spontaneous spiking events, and synchronized epileptiform bursts. Pre-injection of a receptor tyrosine kinase inhibitor K252a or a specific antibody for TrkB receptors before intracerebroventricular injection of CTZ significantly suppressed the epileptiform activity induced by CTZ. Similarly, in cultured hippocampal pyramidal neurons, pre-treatment with CTZ together with K252a or TrkB-receptor antibody also inhibited the CTZ-induction of epileptiform activity. Furthermore, we demonstrated that acute application of K252a in hippocampal cultures inhibited epileptiform bursts and action potential firing. We conclude that activation of BDNF-TrkB signaling pathway is fundamentally important during the CTZ-induction of epileptiform activity both in vitro and in vivo.

AMPA receptor activation reduces epileptiform activity in the rat neocortex

We have previously reported that topical application of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) to the rat neocortex prevents the effects of a subsequent application of N-methyl-d-aspartic acid (NMDA). Activation of NMDA receptors is involved in the pathogenesis of epileptic activity. Therefore, we examined if topically applied AMPA could affect changes in the somatosensory evoked potentials (SEPs) and electrocorticogram (ECoG) epileptic spikes caused by bicuculline. AMPA (50 microM) prevented the epileptiform activity to a level that was comparable to that caused by diazepam (3 mg/kg i.p.) or clomethiazole (100 mg/kg i.p.). Also, the epileptiform activity was suppressed by the AMPAR antagonist, CNQX, or the blocker of AMPAR desensitization, cyclothiazide. In the hippocampal slice, bicuculline-induced changes in the population spike potentials recorded from the CA1 cells were not affected by AMPA. We conclude that in the complex neuronal network of the rat neocortex, epileptiform activity can be suppressed in a variety of strategies that target the AMPA receptors: (1) blocking AMPA receptors, (2) promoting an apparent desensitization of AMPA receptors (possibly on the pyramidal neurons) or (3) reducing an apparent desensitization of AMPA receptors (possibly on the inhibitory GABA-ergic interneurons).

Cyclothiazide Prolongs Low [Mg2+]–Induced Seizure-Like Events

Here we address the effects of cyclothiazide (CTZ), an allosteric inhibitor of α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor desensitization, on low [Mg2+]–induced seizure-like events (SLEs) recorded from the CA3 pyramidal layer of juvenile rat hippocampal slices. CTZ (100 μM) made the period of tonic-like discharges (161 ± 18% of control) and the whole SLE (151 ± 15% of control) longer (in 7 of 9 slices) or induced endless SLE by stabilizing clonic-like bursting (in 2 of 9 slices). CTZ (30 μM) had no significant effects on SLE dynamics ( n = 4), whereas 300 μM CTZ induced endless SLEs in four of eight slices. Coapplication of CTZ (100 μM) with 100 μM GYKI-52466, the allosteric inhibitor of AMPA receptor function, restrained the effects of CTZ and shortened SLEs and their tonic phases to 37 ± 4.2 and 47 ± 4.2% of the control, respectively. Effects of GYKI-52466 and GYKI-52466 with CTZ on SLE dynamics were indistinguishable. 4-aminopyridine (4-AP; 50 μM) alone ( n = 5) or in combination with CTZ ( n = 6) transformed recurrent SLE pattern into incessant epileptiform activity with patterns distinguishable from those under 100 μM CTZ application. The effect of 4-AP may suggest a role for facilitated presynaptic glutamate release in disrupting recurrent dynamics. In contrast, the self-similar slow-down of low [Mg2+]–induced SLE dynamics by CTZ indicate AMPA receptor desensitization as a parameter shaping SLEs.

The growth compromised HSV-2 mutant DeltaRR prevents kainic acid-induced apoptosis and loss of function in organotypic hippocampal cultures

We have previously shown that the HSV-2 anti-apoptotic protein ICP10PK is delivered by the replication incompetent virus mutant DeltaRR and prevents kainic acid (KA)-induced epileptiform seizures and neuronal cell loss in the mouse and rat models of temporal lobe epilepsy. The present studies used DeltaRR and the ICP10PK deleted virus mutant DeltaPK to examine the mechanism of neuroprotection. DeltaRR-infected neuronal cells expressed a chimeric protein in which ICP10PK is fused in frame to LacZ (p175) while retaining ICP10PK kinase activity. DeltaPK-infected neuronal cells expressed a mutant ICP10 protein that is deleted in the PK domain and is kinase negative (p95). p175 and p95 were expressed in CA3 (86+/-3%) and CA1 (69+/-7%) cells from DeltaRR or DeltaPK-infected organotypic hippocampal cultures (OHC) and 80-85% of the ICP10 positive cells co-stained with antibody to beta(III) Tubulin (neuronal marker). DeltaRR, but not DeltaPK, inhibited KA-induced cell death and caspase-3 activation in CA3 neurons, an inhibition seen whether DeltaRR was delivered 2 days before or 2 days after KA administration (95% neuroprotection). Neuroprotection was associated with ERK and Akt activation and was abrogated by simultaneous treatment with the MEK (U0126) and PI3-K (LY294002) inhibitors. DeltaRR-mediated neuroprotection was associated with increased expression of the anti-apoptotic protein Bag-1 and decreased expression of the pro-apoptotic protein Bad. The surviving neurons retained normal synaptic function potentially related to increased expression of the transcription factor CREB. The data indicate that DeltaRR is a promising platform for neuroprotection from excitotoxic injury.

Downregulation of tonic GABA currents following epileptogenic stimulation of rat hippocampal cultures

Deficits in GABAergic inhibitory transmission are a hallmark of temporal lobe epilepsy and have been replicated in animal and tissue culture models of epilepsy. GABAergic inhibition comprises phasic and tonic inhibition that is mediated by synaptic and extrasynaptic GABAA receptors, respectively. We have recently demonstrated that chronic stimulation with cyclothiazide (CTZ) or kainic acid (KA) induces robust epileptiform activity in hippocampal neurons both in vitro and in vivo. Here, we report a downregulation of tonic GABA inhibition after chronic epileptogenic stimulation of rat hippocampal cultures. Chronic pretreatment of hippocampal neurons with CTZ or KA resulted in a marked reduction in GABAergic inhibition, as shown by a significant decrease in whole-cell GABA currents and in the frequency of miniature inhibitory postsynaptic currents (mIPSCs). Interestingly, synaptically localized GABAA receptors remained relatively stable, as evidenced by the unaltered amplitude of mIPSCs, as well as the unchanged punctate immunoreactivity of gamma2 subunit-containing postsynaptic GABAA receptors. In contrast, tonic GABA currents, assessed either by a GABAA receptor antagonist bicuculline or a selective extrasynaptic GABAA receptor agonist THIP, were significantly reduced following epileptogenic stimulation. These results reveal a novel form of neural plasticity, that epileptogenic stimulation can selectively downregulate extrasynaptic GABAA receptors while leaving synaptic GABAA receptors unchanged. Thus, in addition to synaptic alteration of GABAergic transmission, regulation of tonic inhibition may also play an important role during epileptogenesis.