Epileptiform Activity In Brain Slices Research Articles

High and Low-Frequency Stimulation Effect on Epileptiform Activity in Brain Slices.

Neurostimulation is one of the new therapeutic approaches in patients with drug-resistant epilepsy, and despite its high efficiency, its mechanism of action is still unclear. On the one hand, electrical stimulation in the human brain is immoral; on the other hand, the creation of the epilepsy model in laboratory animals affects the entire brain network. As a result, one of the ways to achieve the neurostimulation mechanism is to use epileptiform activity models In vitro. In vitro models, by accessing the local network from the whole brain, we can understand the mechanisms of action of neurostimulation. A literature search using scientific databases including PubMed, Google Scholar, and Scopus, using "Neurostimulation" and "epileptiform activity" combined with "high-frequency stimulation", " low-frequency stimulation ", and "brain slices" as keywords were conducted, related concepts to the topic gathered and are used in this paper. Electrical stimulation causes neuronal depolarization and the release of GABAA, which inhibits neuronal firing. Also, electrical stimulation inhibits the nervous tissue downstream of the stimulation site by preventing the passage of nervous activity from the upstream to the downstream of the axon. Neurostimulation techniques consisting of LFS and HFS have a potential role in treating epileptiform activity, with some studies having positive results. Further investigations with larger sample sizes and standardized outcome measures can be conducted to validate the results of previous studies.

Modulation of seizure-like events by the small conductance and ATP-sensitive potassium ion channels

Potassium ion channels are extensively involved in the regulation of epileptic seizures. The small conductance calcium-sensitive potassium channels (SK channels) and ATP-sensitive potassium (KATP) channels are activated by calcium ion entry and decrease ATP levels, respectively. These channels can underlie the post-burst afterhyperpolarization and be upregulated during seizures, providing negative feedback during epileptic activity. Using the whole-cell patch-clamp method in rat brain slices, we investigated the effect of SK- and KATP-affecting drugs on seizure-like events (SLEs) in the 4-aminopyridine model of epileptic seizures in vitro. We demonstrate that SK and KATP channels contribute to sustaining the high-frequency firing of the principal neurons in the deep layers of the entorhinal cortex during injections of depolarizing current and epileptiform discharges. Neither the pharmacological blockade nor the activation of these channels was able to prevent the epileptiform activity in brain slices. However, the blockade of KATP channels increases the SLE duration, suggesting that these channels may contribute to the termination of SLEs. Thus, KATP channels can be considered a promising target for pharmacological interventions for the treatment of epilepsy.

L-Theanine Reduces Epileptiform Activity In Brain Slices

L-Theanine Reduces Epileptiform Activity In Brain Slices ABSTRACT Objective: L-theanine is one of the main amino acid of tea plant which can cross the blood brain barrier. In the central nervous system, L-theanine has certain effects on a number of neurotransmitter systems. In this study we tested whether acute application of L-theanine could induce any seizure like or inhibitory activity in the brain slice. Materials and Methods: Effects of L-theanine on epileptiform activity were investigated in two different brain regions. Horizontal hippocampal-entorhinal cortex slices were obtained from 30-35 days old C57BL/6 mice. Extracellular field potentials were recorded from medial entorhinal cortex (EC) and CA3 region of hippocampus. Epileptiform activity was induced by application of 4 Aminopyridine (4AP, 100 µM) in the brain slices and 50 µM L-theanine was applied. From the recordings, the duration and frequencies of ictal like events as well as frequency and amplitude of inter-ictal like activities were calculated. Results: L-theanine alone did not initiate any synchronized activity. Although, bath application of L-theanine after 4AP induces epileptiform acitivities, did not significantly alter the duration and frequency of ictal discharges, L-theanine attenuated the interictal discharges. In EC the frequencies of interictal discharges were significantly decreased. In CA3, the amplitudes of interictal activities were significantly reduced. Conclusion: The present findings suggest that L-theanine do not induce any seizure like event but rather had a suppressive effect on ongoing epileptiform activity. Key Words: Theanine, 4 Aminopyridine, Brain Slice, Epileptiform activity, CA3, Entorhinal cortex

7,8-Dihydroxyflavone potentiates ongoing epileptiform activity in mice brain slices

In the central nervous system, Tropomyosin-receptor-kinase B (TrkB) signaling is involved in neuronal survival, differentiation as well as in regulation of synaptic transmission and excitability. As its powerful potential to modulate neuronal functions, TrkB pathway is an attractive target for novel drugs and treatment of common neurological disorders. 7,8-Dihydroxyflavone (DHF), a TrkB receptor agonist, has similar properties with neurotrophin Brain Derived Neurotropic Factor (BDNF). DHF is reported to have a number of beneficial effects in neuroprotection, against depression and improving learning and memory. However, the outcome of acute application of DHF on the excitability of neuronal circuits is not clear. Especially the effects of DHF on synchronized epileptiform activity are not known. In this study, we investigated whether DHF induces epileptiform activity in brain slices and DHF has any effect on already initiated epileptiform discharges. We used acute horizontal hippocampal-entorhinal cortex slices obtained from 30 to 35 days of mice. Extracellular field potential recordings were obtained from entorhinal cortex (EC) and hippocampus CA1 region. DHF did not initiate any epileptiform activity or abnormal discharges. However, DHF increased the frequency of 4 aminopyridine (4AP) induced ictal and interictal events in both EC and CA1. The duration of induced ictal charges were also prolonged upon DHF application. In a number of slices, both EC and CA1, DHF led to ictogenesis. These results suggest that the acute activation of TrkB by DHF has a powerful potential on synchronized neuronal discharges which should be considered in future therapeutical approaches.

Методика оценки вклада различных типов ионотропных рецепторов в постсинаптический ответ в ходе эпилептоподобных разрядов in vitro

Epileptiform activity in brain slices is the result of a complex integration of excitatory and inhibitory synaptic inputs. The temporal pattern of activation of various synaptic conductances during interictal discharges makes it possible to describe the neural network activity during seizures and to analyze the effect of different pharmacological agents on it. Existing methods of synaptic conductance estimation generally require an assumption of linearity of the current-voltage relationship (I-V relationship) of neuronal response and produce the estimates of only two types of conductances – excitatory and inhibitory, without isolating the contribution of specific types of postsynaptic receptors. This paper describes the theoretical basis for the assessment of postsynaptic conductances of three types of ionotropic receptors (AMPA, NMDA, and GABAa types) that are activated during the interictal discharges in the entorhinal cortex. The proposed algorithm utilizes the differences in the shape of the I-V relationships of these receptors to assess their contributions to the neuron response and requires the implementation of the whole-cell patch-clamp method in the voltage-clamp mode. The proposed method is demonstrated in three models of epileptiform activity in vitro. We compared the time course of synaptic conductances during interictal discharges generated with intact GABAa receptor-mediated transmission and when GABAa receptors are partially blocked by the antibiotic cefepime or by bicuculline. We demonstrated that even though cefepime is an antagonist of GABAa receptors, their total conductance during the late stages of interictal discharges is significantly increased when this antibiotic is applied, compared to the model in which these receptors were not blocked, or the one in which another competitive antagonist, bicuculline, was used. Thus, the proposed method allowed us to identify subtle differences in the temporal course of the three types of synaptic conductances and to demonstrate the differences in the proepileptic effects of GABAa receptor blockers.

Exploiting the Other Inhibitory Ion: KCNQ Potassium Channels and Regulation of Excitability in Developing and Mature Brain

Epileptiform Activity Induced by Pharmacologic Reduction of M-Current in the Developing Hippocampus In Vitro Pena F, Alavez-Perez N Epilepsia 2006;47(1):47–54 Purpose Benign familial neonatal convulsions (BFNCs), an inheritable epilepsy that occurs in neonates but not in adults, is caused by hypofunctional mutations in genes codifying for the M-type K+ current. In an attempt to develop an in vitro model of this disease, we tested whether blocking M-current with linopirdine induces epileptiform activity in brain slices from animals of different ages. Methods Horizontal hippocampus–entorhinal cortex slices were obtained from neonatal (1–2 weeks after birth) and adult (8–9 weeks after birth) rats. Extracellular field recordings of the CA1 region were performed. After recording control conditions, linopirdine was added to the bath, and field activity was recorded continuously for 3 hours. A drug 4-aminopyridine, commonly used to induce epileptiform activity in vitro, was used as a control for our experimental conditions. Results Bath perfusion of linopirdine induced epileptiform activity only in slices from neonatal rats. Epileptiform activity consisted of interictal-like and ictal-like activity. In slices from adult rats, linopirdine induced erratic interictal-like activity. In contrast, 4-aminopyridine was able to induce epileptiform activity in slices from both neonatal and adult rats. Conclusions We demonstrated that blockade of Mcurrent in vitro produces epileptiform activity with a developmental pattern similar to that observed in BNFCs. This could be an in vitro model that can be used to study the cellular mechanisms of epileptogenesis and the developmental features of BFNCs, as well as to develop some therapeutic strategies. Conditional Transgenic Suppression of M Channels in Mouse Brain Reveals Functions in Neuronal Excitability, Resonance and Behavior Peters HC, Hu H, Pongs O, Storm JF, Isbrandt D Nat Neurosci 2005;8(1):51–60 In humans, mutations in the KCNQ2 or KCNQ3 potassium-channel genes are associated with an inherited epilepsy syndrome. We have studied the contribution of KCNQ/M-channels to the control of neuronal excitability by using transgenic mice that conditionally express dominant-negative KCNQ2 subunits in brain. We show that suppression of the neuronal M current in mice is associated with spontaneous seizures, behavioral hyperactivity and morphological changes in the hippocampus. Restriction of transgene expression to defined developmental periods revealed that M-channel activity is critical to the development of normal hippocampal morphology during the first postnatal weeks. Suppression of the M current after this critical period resulted in mice with signs of increased neuronal excitability and deficits in hippocampus-dependent spatial memory. M-current-deficient hippocampal CA1 pyramidal neurons showed increased excitability, reduced spike-frequency adaptation, attenuated medium afterhyperpolarization and reduced intrinsic subthreshold theta resonance. M channels are thus critical determinants of cellular and neuronal network excitability, postnatal brain development and cognitive performance.

Epileptiform Activity Induced by Pharmacologic Reduction of M‐Current in the Developing Hippocampus in Vitro

Benign familial neonatal convulsions (BFNCs), an inheritable epilepsy that occurs in neonates but not in adults, is caused by hypofunctional mutations in genes codifying for the M-type K+ current. In an attempt to develop an in vitro model of this disease, we tested whether blocking M-current with linopirdine induces epileptiform activity in brain slices from animals of different ages. Horizontal hippocampus-entorhinal cortex slices were obtained from neonatal (1-2 weeks after birth) and adult (8-9 weeks after birth) rats. Extracellular field recordings of the CA1 region were performed. After recording control conditions, linopirdine was added to the bath, and field activity was recorded continuously for 3 h. 4-Aminopyridine, a drug commonly used to induce epileptiform activity in vitro, was used as a control for our experimental conditions. Bath perfusion of linopirdine induced epileptiform activity only in slices from neonatal rats. Epileptiform activity consisted of interictal-like and ictal-like activity. In slices from adult rats, linopirdine induced erratic interictal-like activity. In contrast, 4-aminopyridine was able to induce epileptiform activity in slices from both neonatal and adult rats. We demonstrated that blockade of M-current in vitro produces epileptiform activity with a developmental pattern similar to that observed in BNFCs. This could be an in vitro model that can be used to study the cellular mechanisms of epileptogenesis and the developmental features of BFNCs, as well as to develop some therapeutic strategies.

Low-calcium epileptiform activity in the hippocampus in vivo.

It has been clearly established that nonsynaptic interactions are sufficient for generating epileptiform activity in brain slices. However, it is not known whether this type of epilepsy model can be generated in vivo. In this paper we investigate low-calcium nonsynaptic epileptiform activity in an intact hippocampus. The calcium chelator EGTA was used to lower [Ca2+]o in the hippocampus of urethane anesthetized rats. Spontaneous and evoked field potentials in CA1 pyramidal stratum and in CA1 stratum radiatum were recorded using four-channel silicon recording probes. Three different types of epileptic activity were observed while synaptic transmission was gradually blocked by a decline in hippocampal [Ca2+]o. A short latency burst, named early-burst, occurred during the early period of EGTA application. Periodic slow-waves and a long latency high-frequency burst, named late-burst, were seen after synaptic transmission was mostly blocked. Therefore these activities appear to be associated with nonsynaptic mechanisms. Moreover, the slow-waves were similar in appearance to the depolarization potential shifts in vitro with low calcium. In addition, excitatory postsynaptic amino acid antagonists could not eliminate the development of slow-waves and late-bursts. The slow-waves and late-bursts were morphologically similar to electrographic seizure activity seen in patients with temporal lobe epilepsy. These results clearly show that epileptic activity can be generated in vivo in the absence of synaptic transmission. This type of low-calcium nonsynaptic epilepsy model in an intact hippocampus could play an important role in revealing additional mechanisms of epilepsy disorders and in developing novel anti-convulsant drugs.

Cesium induces spontaneous epileptiform activity without changing extracellular potassium regulation in rat hippocampus.

Cesium has been widely used to study the roles of the hyperpolarization-activated (I(h)) and inwardly rectifying potassium (K(IR)) channels in many neuronal and nonneuronal cell types. Recently, extracellular application of cesium has been shown to produce epileptiform activity in brain slices, but the mechanisms for this are not known. It has been proposed that cesium blocks the K(IR) in glia, resulting in an abnormal accumulation of potassium in the extracellular space and inducing epileptiform activity. This hypothesis has been tested in hippocampal slices and cultured hippocampal neurons using potassium-sensitive microelectrodes. In the present study, application of cesium produced spontaneous epileptiform discharges at physiological extracellular potassium concentration ([K(+)](o)) in the CA1 and CA3 regions of hippocampal slices. This epileptiform activity was not mimicked by increasing the [K(+)](o). The epileptiform discharges induced by cesium were not blocked by the N-methyl-D- aspartate (NMDA) receptor antagonist AP-5, but were blocked by the non-NMDA receptor antagonist CNQX. In the dentate gyrus, cesium induced the appearance of spontaneous nonsynaptic field bursts in 0 added calcium and 3 mM potassium. Moreover, cesium increased the frequency of field bursts already present. In contrast, ZD-7288, a specific I(h) blocker, did not cause spontaneous epileptiform activity in CA1 and CA3, nor did it affect the field bursts in the dentate gyrus, suggesting that cesium induced epileptiform activity is not directly related to blockade of the I(h). When potassium-sensitive microelectrodes were used to measure [K(+)](o), there was no significant increase in [K(+)](o) in CA1 and CA3 after cesium application. In the dentate gyrus, cesium did not change the baseline level of [K(+)](o) or the rate of [K(+)](o) clearance after the field bursts. In cultured hippocampal neurons, which have a large and relatively unrestricted extracellular space, cesium also produced cellular burst activity without significantly changing the resting membrane potential, which might indicate an increase in [K(+)](o). Our results suggest that cesium causes epileptiform activity by a mechanism unrelated to an alteration in [K(+)](o) regulation.

Prenatal morphine exposure alters ovarian steroid hormonal regulation of seizure susceptibility

The present study examined the ovarian hormonal regulation of seizure susceptibility in prenatally morphine- and saline-exposed adult female rats in the flurothyl seizure model in vivo, and in low-magnesium-induced epileptiform activity in brain slices, in vitro. All females were ovariohysterectomized (OVX); some received either estrogen (E) or progesterone (P) replacement, while others were injected with E+P sequentially. In prenatally saline-treated control females, there was an increase in the flurothyl-induced clonic seizure threshold (anticonvulsant effect) in the presence of both hormones (E+P) compared to OVX controls. In morphine-exposed females, there was an increase in the flurothyl-induced clonic seizure threshold after an E injection alone while there was a reduced tonic–clonic seizure threshold in the presence of both hormones (E+P) compared to the hormone treatment-matched group of saline-exposed females. In control females, in low magnesium medium in vitro, the development of two types of epileptiform activity (seizure-like events and status of short discharges) was not affected by the different hormonal conditions. However, prenatal morphine exposure suppressed the development of both types of epileptiform activity in the E-injected females compared to the E-injected, control females. The present data demonstrate that the anticonvulsant effects of P on seizure susceptibility requires the presence of E. Furthermore, prenatal morphine exposure alters ovarian steroid hormone-regulated seizure susceptibility.

Ictal epileptiform events induced by removal of extracellular magnesium in slices of entorhinal cortex are blocked by baclofen

Most manipulations employed to elicit epileptiform activity in brain slices result in brief, interictal-like events. In slices of the rat entorhinal cortex perfusion with a magnesium-depleted medium elicits prolonged seizure events which are more reminiscent of ictal activity. The interictal events in brain slice models are blocked by baclofen, but there is an indication from one study (H. S. Swartzwelder, D. V. Lewis, W. W. Anderson, and W. A. Wilson, 1987, Brain Res. 410: 362-366) that ictal events may not be affected by this drug. The present study examined the effects of baclofen on ictal events recorded in entorhinal cortex slices in magnesium-free medium. Simultaneous studies of effects of baclofen on interictal responses in the hippocampal region of the same slices were made on many occasions. The results show that both types of epileptiform activity are suppressed with a similar facility by baclofen.