Lowering of the potassium concentration induces epileptiform activity in guinea-pig hippocampal slices

In vitro seizure like events and changes in ionic concentration

BACKGROUND

In vivo, seizure like events are associated with increases in extracellular K(+) concentration, decreases in extracellular Ca(2+) concentration, diphasic changes in extracellular sodium, chloride, and proton concentration, as well as changes of extracellular space size. These changes point to mechanisms underlying the induction, spread and termination of seizure like events.

METHODS

We investigated the potential role of alterations of the ionic environment on the induction of seizure like events-considering a review of the literature and own experimental work in animal and human slices.

RESULTS

Increasing extracellular K(+) concentration, lowering extracellular Mg(2+) concentration, or lowering extracellular Ca(2+) concentration can induce seizure like events. In human tissue from epileptic patients, elevation of K(+) concentration induces seizure like events in the dentate gyrus and subiculum. A combination of elevated K(+) concentration and 4-AP or bicuculline can induce seizure like events in neocortical tissue.

CONCLUSIONS

These protocols provide insight into the mechanisms involved in seizure initiation, spread and termination. Moreover, pharmacological studies as well as studies on mechanisms underlying pharmacoresistance are feasible.

Modulation of c-Fos and BDNF protein expression in pentylenetetrazole-kindled mice following the treatment with novel antiepileptic compound HHL-6

Brain-derived neurotrophic factor (BDNF) and c-Fos are shown to promote epileptogenesis and are taken as a marker of neuronal activity. The present study investigated the expression of BDNF and c-Fos in mice brain with pentylenetetrazol- (PTZ-) induced generalized seizure and evaluated the effect of novel tryptamine derivative HHL-6 on the expression of these two markers. The subconvulsive dose of PTZ (50 mg/kg) was administered on alternate days in the experimental groups until the seizure scores 4-5 developed in the PTZ-control group. At the end of each experiment, animals were sacrificed, brain samples were collected and cryosectioned, and immunohistochemical analysis of BDNF and c-Fos protein was performed. Data obtained from two sections per mouse (n = 12 animals/group) is presented as means ± S.E.M. The test compound HHL-6 demonstrated a potent anticonvulsant activity in the PTZ-induced seizure in mice. Significant reduction in the BDNF (P < 0.003) and c-Fos (P < 0.01) protein expression was observed in the HHL-6 treated group. Based on these results we suggest that one of the possible mechanisms of HHL-6 to inhibit epileptogenesis might be due to its controlling effect on the cellular and molecular expression of the factors that contribute to the development of epileptogenic plasticity in the CNS.

Characterizing the persistent CA3 interneuronal spiking activity in elevated extracellular potassium in the young rat hippocampus

Seizures coincide with an increase in extracellular potassium concentrations [K(+)](e) yet little information is available regarding this phenomenon on the firing pattern, frequency and neuronal properties of inhibitory neurons responsible for modulating network excitability. Therefore, we investigated the effects of elevating [K(+)](e) from 2.5 to 12.5mM on CA3 rat hippocampal interneurons in vitro using whole-cell patch-clamp recordings. We found that the majority of interneurons (21/25) in artificial cerebral spinal fluid (aCSF) exhibited spontaneous tonic spiking activity. As the [K(+)](e) increased to 12.5mM, interneurons exhibited a tonic, irregular, burst firing activity, or a combination of these. The input resistance decreased significantly to 59+/-18% at 7.5mM K(+) and did not further change at higher [K(+)](e) while the amount of K(+)-induced depolarization significantly increased from 5 to 12.5mM K(+) perfusion; a depolarization block occurred in 4 of the 12 interneurons at 12.5mM. Also, as [K(+)](e) increased, a transition from lower (1.3+/-0.6Hz) to higher dominant peak frequency (15.0+/-5.0Hz) was observed. We found that non-fast spiking (NFS) interneurons represented the majority of cells recorded and exhibited mostly tonic firing activity in raised K(+). Fast spiking (FS) interneurons predominately had a tonic firing pattern with very few exhibiting bursting activity in elevated K(+). In conclusion, we report that raised [K(+)](e) in amounts observed during seizures increases hippocampal CA3 interneuronal activity and suggests that a loss or impairment of inhibitory function may be present during these events.

Neocortical Microenvironment in Patients with Intractable Epilepsy: Potassium and Chloride Concentrations

PURPOSE

The regulation of extracellular ion concentrations plays an important role in neuronal function and epileptogenesis. Despite the many studies into the mechanisms of epileptogenesis in human experimental models, no data are available regarding the fluctuations of extracellular potassium ([K(+)](o)) and chloride ([Cl(-)](o)) concentrations, which could underlie seizure susceptibility in human chronically epileptic tissues in vivo.

METHODS

By using cerebral microdialysis during surgical resection of epileptic foci, the basic [K(+)](o) and [Cl(-)](o) as well as their changes after epicortical electric stimulation were studied in samples of dialysates obtained from 11 patients by ion-selective microelectrodes.

RESULTS

The mean basal values of [K(+)](o) and [Cl(-)](o) in all patients were 3.83 +/- 0.08 mM and 122.9 +/- 2.6 mM, respectively. However, significant differences were observed in the basal levels of both [K(+)](o) and [Cl(-)](o) between different patients. Statistically, no correlation was found between basal [K(+)](o) or [Cl(-)](o) and electrocorticogram (ECoG) spike activity, but in one patient, dramatically lowered baseline [Cl(-)](o) was accompanied by enhanced ECoG spike activity. Application of epicortical electrical stimulation increased [K(+)](o) but not [Cl(-)](o) in all cases. According to the velocity as well as spatial distribution of [K(+)](o) reduction to the prestimulation levels, three different types of responses were observed: slow decline, fast decline, and slow and fast declines at adjacent sites.

CONCLUSIONS

These data may represent abnormalities in ion homeostasis of the epileptic brain.

Association between variation in the human KCNJ10 potassium ion channel gene and seizure susceptibility

PURPOSE

Our research program uses genetic linkage and association analysis to identify human seizure sensitivity and resistance alleles. Quantitative trait loci mapping in mice led to identification of genetic variation in the potassium ion channel gene Kcnj10, implicating it as a putative seizure susceptibility gene. The purpose of this work was to translate these animal model data to a human genetic association study.

METHODS

We used single stranded conformation polymorphism (SSCP) electrophoresis, DNA sequencing and database searching (NCBI) to identify variation in the human KCNJ10 gene. Restriction fragment length polymorphism (RFLP) analysis, SSCP and Pyrosequencing were used to genotype a single nucleotide polymorphism (SNP, dbSNP rs#1130183) in KCNJ10 in epilepsy patients (n = 407) and unrelated controls (n = 284). The epilepsy group was comprised of patients with refractory mesial temporal lobe epilepsy (n = 153), childhood absence (n = 84), juvenile myoclonic (n = 111) and idiopathic generalized epilepsy not otherwise specified (IGE-NOS, n = 59) and all were of European ancestry.

RESULTS

SNP rs#1130183 (C > T) alters amino acid 271 (of 379) from an arginine to a cysteine (R271C). The C allele (Arg) is common with conversion to the T allele (Cys) occurring twice as often in controls compared to epilepsy patients. Contingency analysis documented a statistically significant association between seizure resistance and allele frequency, Mantel-Haenszel chi square = 5.65, d.f. = 1, P = 0.017, odds ratio 0.52, 95% CI 0.33-0.82.

CONCLUSION

The T allele of SNP rs#1130183 is associated with seizure resistance when common forms of focal and generalized epilepsy are analyzed as a group. These data suggest that this missense variation in KCNJ10 (or a nearby variation) is related to general seizure susceptibility in humans.

Effect of recurrent epileptiform discharges induced by magnesium-free treatment on developing cortical neurons in vitro

As seizures in infants and children often originate from the neocortex, neocortical epilepsy models may be appropriate for studying epileptiform activity and seizure-induced injury in the developing nervous system. However, the characterization of epileptiform activity or seizure-induced injury in cultured developing cortical neurons has seldom been reported. Therefore, We attempted to establish a cultured developing cortical neuronal epilepsy model, and to study the subsequent effect on neurons. Cultures were exposed to Mg(2+)-free media for 3 h, and then returned to regular media. Using whole-cell patch-clamp intracellular recording techniques, we found that spontaneously recurrent epileptiform discharges for at least 72 h could be induced after transient Mg(2+)-free treatment. Neuron morphology following Mg(2+)-free treatment demonstrated no prominent alterations. At different time points (6, 24 and 72 h) after Mg(2+)-free treatment, neuronal viability, identified by trypan blue staining and LDH activity, and apoptosis, measured by flow cytometry, showed modest but non-significant (P>0.05) changes compared with the age-matched control group after various culture periods (6 and 17 days) in vitro. Mitochondrial metabolic activity, measured by MTT assay, significantly decreased by 15% at 6 h after Mg(2+)-free treatment (P<0.05) in neurons cultured for 6 days, and at 24 h showed a 29% decrease in neurons cultured for 17 days (P<0.05). In conclusion, brief Mg(2+)-free treatment constitutes a cultured developing cortical neuron 'seizure' model, and can induce transient mitochondrial dysfunction without cell loss.

Background potassium concentrations and epileptiform discharges. I. Electrophysiological characteristics of neuronal activity

Intra- and extracellular recording techniques were used to study the epileptiform activity generated by guinea pig hippocampal slices perfused with free-magnesium artificial cerebrospinal fluid in the presence of physiologic (4 mM), reduced (2 mM) or elevated (8 mM) extracellular potassium concentrations ([K(+)](o)). Extracellular field potentials along with intracellular recordings were recorded in CA1 or CA3 region. Reduction of [K(+)](o) significantly increased the latency of epileptiform field potential (EFP) appearance as well as burst discharge duration and decreased EFP repetition rate. Depending on different background [K(+)](o), epileptiform burst discharges appeared in different patterns including varied types of paroxysmal depolarisation shifts and burst activity in CA1 and CA3 subfields. Comparison with physiological and increased [K(+)](o,) reduction of [K(+)](o) significantly increased the mean duration of bursts, mean amplitude of depolarisation, mean after-hyperpolarisation duration, and inter-spike intervals in both CA1 and CA3 areas. Three distinct patterns were distinguished on the basis of their evoked firing pattern in response to application of depolarising current pulses in the interval of epileptiform burst discharges. Neurons superfused with 2 mM [K(+)](o) presented fast adapting pattern while cells washed with 4 or 8 mM [K(+)](o) exhibited intrinsically bursting or slow adapting patterns. Comparing the groups with different background [K(+)](o), there is a more severe form of discharges in low K(+) and a subtle difference between 4 and 8 mM K(+). The data indicate the importance of background [K(+)](o) on epileptiform burst discharge pattern and characteristics.

Differential role of KIR channel and Na(+)/K(+)-pump in the regulation of extracellular K(+) in rat hippocampus

Little information is available on the specific roles of different cellular mechanisms involved in extracellular K(+) homeostasis during neuronal activity in situ. These studies have been hampered by the lack of an adequate experimental paradigm able to separate K(+)-buffering activity from the superimposed extrusion of K(+) from variably active neurons. We have devised a new protocol that allows for such an analysis. We used paired field- and K(+)-selective microelectrode recordings from CA3 stratum pyramidale during maximal Schaffer collateral stimulation in the presence of excitatory synapse blockade to evoke purely antidromic spikes in CA3. Under these conditions of controlled neuronal firing, we studied the [K(+)]o baseline during 0.05 Hz stimulation, and the accumulation and rate of recovery of extracellular K(+) at higher frequency stimulation (1-3 Hz). In the first set of experiments, we showed that neuronal hyperpolarization by extracellular application of ZD7288 (11 microM), a selective blocker of neuronal I(h) currents, does not affect the dynamics of extracellular K(+). This indicates that the K(+) dynamics evoked by controlled pyramidal cell firing do not depend on neuronal membrane potential, but only on the balance between K(+) extruded by firing neurons and K(+) buffered by neuronal and glial mechanisms. In the second set of experiments, we showed that di-hydro-ouabain (5 microM), a selective blocker of the Na(+)/K(+)-pump, yields an elevation of baseline [K(+)]o and abolishes the K(+) recovery during higher frequency stimulation and its undershoot during the ensuing period. In the third set of experiments, we showed that Ba(2+) (200 microM), a selective blocker of inwardly rectifying K(+) channels (KIR), does not affect the posttetanus rate of recovery of [K(+)]o, nor does it affect the rate of K(+) recovery during high-frequency stimulation. It does, however, cause an elevation of baseline [K(+)]o and an increase in the amplitude of the ensuing undershoot. We show for the first time that it is possible to differentiate the specific roles of Na(+)/K(+)-pump and KIR channels in buffering extracellular K(+). Neuronal and glial Na(+)/K(+)-pumps are involved in setting baseline [K(+)]o levels, determining the rate of its recovery during sustained high-frequency firing, and determining its postactivity undershoot. Conversely, glial KIR channels are involved in the regulation of baseline levels of K(+), and in decreasing the amplitude of the postactivity [K(+)]o undershoot, but do not affect the rate of K(+) clearance during neuronal firing. The results presented provide new insights into the specific physiological role of glial KIR channels in extracellular K(+) homeostasis.

Low concentration of DL-2-amino-5-phosphonovalerate induces epileptiform activity in guinea pig hippocampal slices

PURPOSE

The specific mechanisms by which low concentrations of cyclosporine induce seizures and low concentrations of phencyclidine provoke behavioral excitation remain to be elucidated. Both compounds block N-methyl-d-aspartate (NMDA) receptors. The aim of this study was to determine if low concentrations of the NMDA-receptor blockers increase the seizure susceptibility.

METHODS

Guinea pig hippocampal slices were exposed to artificial cerebrospinal fluid containing the NMDA blocker dl-2-amino-5-phosphono-valerate (APV; 0.1-10 microM). Extracellular field potentials were recorded from CA1 and CA3 regions.

RESULTS

Low concentrations of APV induced epileptiform burst discharges (0.1-0.25 microM), whereas higher doses failed to decrease the seizure threshold (1-10 microM).

CONCLUSIONS

The results indicate that the excitatory effect of low concentrations NMDA blockers may play a role in the neurotoxicity of aforementioned substances.

History of epilepsy in Medieval Iranian medicine

The history of epilepsy in Medieval Persian medicine is not well-known in the Western world. This article presents the clinical approaches according to which Medieval Iranian practitioners viewed epilepsy and dealt with its problems. The clinical viewpoints of epilepsy are collected from Medieval Persian scientific references. These describe clinical manifestations, basic mechanisms, etiologies, treatment and prognosis. Medieval Iranian practitioners provide detailed clinical information on epilepsy. They mention various forms and symptoms of epilepsy and its apparent causes and offer dietary and hygienic rules, as well as a long list of pharmacologic compounds for treating it. Their findings about epilepsy are very accurate and vivid and many of them are accepted even today.