The effects of vitamin E on penicillin-induced epileptiform activity in rats

Epilepsy is a disorder characterized by recurrent seizures, which can increase the content of reactive oxygen in the brain. Active oxygen free radical scavengers such as ascorbic acid or α-tocopherol (vitamin E) might prevent epilepsy. A variety of animal seizure models exist which help to document the effects of vitamin E and specify its action. In this study, we have evaluated dose-dependent effect of α-tocopherol on penicillin-induced epileptiform activity, analyzed by electrocorticogram (ECoG). The epileptiform activity was induced by microinjection of penicillin into the left sensorimotor cortex. Thirty minutes after penicillin injection, 100, 300, or 500 mg/kg of α-tocopherol was administrated intramuscularly (i.m.). α-Tocopherol (100, 300, or 500 mg/kg) alone did not significantly change the spike amplitudes in non-penicillin pretreated control animals. α-Tocopherol of 300, or 500 mg/kg significantly decreased the frequency of epileptiform activity in the penicillin-pretreated animals. The low dose of α-tocopherol (100 mg/kg) did not significantly change either amplitude or frequency of epileptiform activity. α-Tocopherol of 500 mg/kg i.m. was the most effective dose in changing of frequency on penicillin-induced epileptiform activity. The anti-convulsant effects of α-tocopherol appeared 80, 60, 30 min after α-tocopherol injection in 300, 500, and 3 day vitamin E supplemented groups. These data indicate that α-tocopherol decreases the frequency of penicillin-induced epileptic activity.     

Propagation velocity of epileptiform activity in the hippocampus

Summary The propagation of epileptiform burst activity was investigated in the CA1 area of the in-vitro hippocampal slice preparation of the guinea pig. This activity was provoked by 0.1 mM 4-aminopyridine in the bathing medium and was recorded in the pyramidal layer with an array of eight electrodes. The delay between the first population spike of a burst recorded with different electrodes was calculated using the cross-correlation function. The propagation velocity was estimated from the delays and the electrode intervals. It was found that the velocity of spontaneous and evoked epileptiform bursts varies between 0.15 and 5 m/s and is not confined to the range of conduction velocities of the fibre systems in CA1 (0.3–0.55 and 1.0–1.8 m/s). Different velocities can be present in different parts of the CA1 area and the initiation of spontaneous bursts is not confined to the CA2–3 areas, but can also occur in CA1. Burst activity also propagated in a low calcium-high magnesium medium. Different mechanisms of propagation are discussed and it is argued that the propagation velocity due to ephaptic interaction may vary largely. It is concluded that epileptiform activity can be propagated not only by synaptic connections at or near the pyramidal layer, but also by way of electrical field effects of population spikes.     

Anticonvulsive effects of nimodipine on penicillin-induced epileptiform activity

The common features of all types of epilepsy are synchronized and uncontrolled discharges of nerve cell assemblies. It is believed that calcium ions play an important role in the generation of epileptic activity. Excessive calcium influx into neurons is the first step toward a seizure. The aim of the present study is to investigate whether the calcium channel blocker nimodipine has anticonvulsive effects. The left cerebral cortex was exposed by craniotomy in anaesthetized rats. An epileptic focus was produced by injection of penicillin G potassium (500 units) into the somatomotor cortex. After the epileptiform activity reached maximum frequency and amplitude; nimodipine was injected into the same area. Application of nimodipine caused an inhibition in the electrocorticograms (ECoG). Solvent alone did not affect the epileptiform activity. The results of this study indicate that nimodipine may have anticonvulsant effects.     

Expert system approach to detection of epileptiform activity in the EEG

An expert system for the automated detection of spikes and sharp waves in the EEG has been developed. The system consists of two distinct stages. The first is a feature extractor, written in the conventional procedural language Fortran, which uses parts of previously published spike-detection, algorithms to produce a list of all spike-like occurrences in the EEG. The second stage, written in the production system language OPS5, reads the list and uses rules incorporating knowledge elicited from an electroencephalographer (EEGer) to confirm or exclude each of the possible spikes. Information such as the time of occurrence, polarity and channel relationship are used in this process. A summary of thedetected epileptiform events is produced which is available to the EEGer in interpreting the EEG. The performance of the expert system is compared with an EEGer using a 320s segment from an EEG containing epileptiform activity. The system detected 19 events and missed seven (false negative) which the EEGer considered epileptiform. There were no false positive detections.     

马桑内酯致痫大鼠海马神经细胞外Na~ 、K~ 活度的变化

目的和方法 :应用Na 、K 选择性微电极检测马桑内酯致痫大鼠海马及海马脑片神经细胞外Na 、K 活度的改变。结果 :海马内注射马桑内酯 (5 μL ,5× 10 -4 mol/L)致痫大鼠 30s、1min和 2min后 ,海马神经细胞外Na 活度分别低于对照组 2 7 7mmol/L、5 0 3mmol/L和 5 7 8mmol/L ,而K 活度则分别高于对照组 2 3mmol/L、2 4mmol/L和 2 9mmol/L(P <0 0 1)。 3min后 ,K 活度基本恢复至对照水平 ,而Na 活度仍持续低于对照水平 (P <0 0 1)。海马脑片的实验结果与在体实验相似。结论 :海马神经细胞处于癫痫状态时 ,存在Na 内流、K 外流现象。     

马桑内酯致痫大鼠海马神经细胞外Na+、K+活度的变化

目的和方法：应用Na⁺、K⁺选择性微电极检测马桑内酯致痫大鼠海马及海马脑片神经细胞外Na⁺、K⁺活度的改变。结果：海马内注射马桑内酯（5 μL,5×10^-4 mol/L）致痫大鼠30 s、1 min和2 min后,海马神经细胞外Na⁺活度分别低于对照组27.7 mmol/L、50.3 mmol/L和57.8 mmol/L,而K活度则分别高于对照组2.3 mmol/L、2.4 mmol/L和2.9 mmol/L（P<0.01）。3 min后,K⁺活度基本恢复至对照水平,而Na⁺活度仍持续低于对照水平（P<0.01）。海马脑片的实验结果与在体实验相似。结论：海马神经细胞处于癫痫状态时,存在Na⁺内流、K⁺外流现象。     

The effect of neuronal population size on the development of epileptiform discharges in the low calcium model of epilepsy

The CA1 region of the rat hippocampal slice generates spontaneous electrographic seizures (field bursts) when exposed to ACSF containing < or = 0.2 mM calcium. It has been proposed that, particularly during the early part of a field burst, synchronised activity in small independent aggregates of neurons results in low amplitude irregular population spikes and subsequent fusion of aggregates generates high amplitude, regular discharging spikes. In the present experiments, we have tested the hypothesis that progression from aggregate formation to aggregate fusion requires a critical mass of participating neurons. We found that isolated CA1 segments >2 mm are still able to generate high amplitude, regular discharging population spikes, but when segment length is reduced to 1-2 mm, only 29% generate spikes with these characteristics; in the remainder, the field burst shows a DC shift+/-low amplitude irregular population spikes. No field bursts were seen in segments < 0.7 mm or in 50% of those 0.7-1 mm in length (in the remaining 50%, only the DC component of the field burst was present). Exposing 1-2 mm segments to hypo-osmolar perfusate induced a return of high amplitude rhythmic discharging population spikes in the field burst. We interpret these observations by indicating that progression from aggregate formation to aggregate fusion requires a critical neuronal mass and can be enhanced by reducing osmolarity of the perfusate.     

Anticholinesterase-induced epileptiform activity in immature rat piriform cortex slices, in vitro

Purpose: Acute in vitro brain slice models are commonly used to study epileptiform seizure generation and to test anti-epileptic drug action. Seizure-like activity can be readily induced by manipulating external ionic concentrations or by adding convulsant agents to the bathing medium. We previously showed that epileptiform bursting was induced in slices of immature (P14–28) rat piriform cortex (PC) by applying oxotremorine-M, a potent muscarinic receptor agonist. Here, we examined whether raising levels of endogenous acetylcholine (ACh) by exposure to anticholinesterases, could also induce epileptiform events in immature (P12–14) or early postnatal (P7–9) rat PC brain slices. Methods: The effects of anticholinesterases were investigated in rat PC neurons using both extracellular MEA (P7–9 slices) and intracellular (P12–14 slices) recording methods. Results: In P7–9 slices, eserine (20 μM) or neostigmine (20 μM) induced low amplitude, low frequency bursting activity in all three PC cell layers (I–III), particularly layer III, where neuronal muscarinic responsiveness is known to predominate. In P12–14 neurons, neostigmine produced a slow depolarization together with an increase in input resistance and evoked cell firing. Depolarizing postsynaptic potentials evoked by intrinsic fibre stimulation were selectively depressed although spontaneous bursting was not observed. Neostigmine effects were blocked by atropine (1 μM), confirming their muscarinic nature. We conclude that elevation of endogenous ACh by anticholinesterases can induce bursting in early postnatal PC brain slices, further highlighting the epileptogenic capacity of this brain region. However, this tendency declines with further development, possibly as local inhibitory circuit mechanisms become more dominant.     

Short-duration swimming exercise decreases penicillin-induced epileptiform ECoG activity in rats

The aim of the present study is to understand the basic relationship between swimming exercise and natural course of epilepsy in animals by performing an electrophysiological study. For this purpose, male Wistar rats were submitted to daily swimming exercise program of three different durations. Animals were swim-exercised for 90 days with either 15 minutes, 30 minutes or 60 minutes/day. Thereafter, the epileptiform activity was induced by a single microinjection of penicillin (500 units) into the left somatomotor cortex. Short-duration swimming exercise (15 min per day for 90 days) decreased the mean frequency and amplitude of penicillin-induced epileptiform activity in the 70 and 90 minutes after penicillin injection compared to penicillin administered group, respectively. Moderate-duration (30 min per day for 90 days) and long-duration (60 min per day for 90 days) swimming exercise did not alter either the frequency or amplitude of epileptiform activity. The results of the present study provide electrophysiologic evidence that short-duration swimming exercise partially inhibits penicillin-induced epileptiform activity. These data also suggest that moderate and long-duration swimming exercise do not increase either the frequency or severity of seizure in the model of penicillin-induced epilepsy.     

Regional and time dependent variations of low Mg2+ induced epileptiform activity in rat temporal cortex slices

Summary In order to study spatial interactions during low magnesium induced epileptiform activity, changes in extracellular potassium concentration ([K⁺]_o) and associated slow field potentials (f.p.'s) were recorded in thin rat temporal cortex slices (400 m) containing the neocortical temporal area 3 (Te3), the entorhinal cortex (EC) and the hippocampal formation with the dentate gyrus, area CA3 and CA1 and the subiculum (Sub). The epileptiform activity was characterized by short recurrent epileptiform discharges (40 to 80 ms, 20/min) in areas CA3 and CA1 and by interictal discharges and tonic and clonic seizure like events (SLE's) (13–88s) in the EC, Te3 and Sub. While interictal discharges occurred independent of each other in the different subfields, the three areas became synchronized during the course of a SLE. The EC, Te3 and Sub all could represent the focus for generation of the SLE's. This initiation site for SLE's sometimes changed from one area to another. The characteristics of the rises in [K⁺]_o and subsequent undershoots were comparable to previous observations in in vivo preparations. Interestingly, rises in [K⁺]_o could start before actual onset of seizure like activity in secondarily recruited areas. The epileptiform activity could change its characteristics to either a state of recurrent tonic discharge episodes or to a continuous clonic discharge state reminiscent of various forms of status epilepticus. We did not observe, in any of these states, active participation by area CA3 in the epileptiform activity of the EC in spite of clear projected activity to the dentate gyrus. Even after application of picrotoxin (20 M), area CA3 did not actively participate in the SLE's generated in the entorhinal cortex. When baclofen (2 M) was added to the picrotoxin containing medium, SLE's occurred both in the entorhinal cortex and in area CA3, suggesting that inhibition of inhibitory interneurons by baclofen could overcome the filtering of projected activity from the entorhinal cortex to the hippocampus.     

Calcium-dependent potassium current following penicillin-induced epileptiform discharges in the hippocampal slice

Summary Penicillin-induced paroxysmal depolarization shifts (PDS) are followed by prolonged afterhyperpolarizations of about 2 seconds duration. Intracellular injection of EGTA blocked a late component of the afterhyperpolarizations; an early one lasting up to one second was only slightly reduced by EGTA. It is concluded that afterhyperpolarizations following penicillininduced PDS comprise different components: an initial one lasting up to one second which is not Ca²⁺-dependent and a slow one lasting up to two seconds which is caused by a Ca²⁺-dependent K⁺ current.     

The interactions of nitric oxide and adenosine on penicillin-induced epileptiform activity in rats

In this study, the influence of nitric oxide (NO) and adenosine systems on penicillin-induced epileptiform activity was examined in rats. NO donor, sodium nitroprusside (SNP, 50 micrograms per rat, i.c.v.) reduced the frequency but not the amplitude of epileptiform discharges. Non-selective NOS inhibitor, N-omega-nitro-L-arginine methyl ester (L-NAME, 100 micrograms per rat, i.c.v.) practically did not exert any effect on the spike frequency and amplitude. Adenosine (100 micrograms per rat, i.c.) reduced spike frequency but not the amplitude, whereas theophylline (100 micrograms per rat, i.c.v.) increased the mean spike frequency and amplitude of penicillin-induced epileptiform discharges. Co-injection of theophylline and L-NAME did not cause a further increase in the epileptiform activity compared with theophylline. When NO production was blocked with L-NAME, the inhibitory effects of adenosine were lost. The obtained results suggest that NO and adenosine may decrease penicillin-induced epileptiform activity in rats and that NO, at least in part, may mediate the anticonvulsant effect of adenosine.     

Alkylxanthine adenosine antagonists and epileptiform activity in rat hippocampal slices in vitro

Despite its potent proconvulsant effects in vitro, the adenosine A1 receptor antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX) does not induce seizures when administered in vivo. This contrasts with the effects of less selective adenosine antagonists such as theophylline or cyclopentlytheophylline, and led us to reexamine the nature of DPCPX-induced epileptiform activity. In the present study, we report that proconvulsant effects of bath-applied DPCPX in rat hippocampal slices are only observed after a preceding stimulus such as NMDA receptor activation or brief tetanic stimulation. While this may be due to the absence of a basal “purinergic tone”, the relatively high interstitial concentrations of adenosine present in the slice suggest that access of the drug to A1 receptors may instead be prevented by tightly coupled endogenous adenosine, with the ternary adenosine-A1 receptor-G protein complex stabilised in the high-affinity conformation by a coupling cofactor. This implies that a substantial percentage of adenosine A1 receptors are inactive under physiological conditions, but that access of adenosine A1 receptor antagonists may be facilitated under pathological conditions. Once induced, DPCPX-evoked spiking persists for long periods of time. A “kindling” effect of A1 receptor blockade is unlikely, since persistent spiking is not usually observed with less selective A1 antagonists even after prolonged application. Alternatively, endogenous adenosine released during increased neuronal activity may activate A2 receptors during selective A1 blockade. The most important factor determining the duration of DPCPX-induced spiking, however, may be a persistence of the drug in the tissue and subsequent access to the A1 receptor via a membrane-delineated pathway, since DPCPX-induced spiking could be shown to decrease markedly after a transient superfusion of theophylline. This hypothesis, which implies that the apparent affinity of adenosine antagonists for the A1 receptor is in part a function of their membrane partitioning coefficient, is supported by a close correlation between alkylxanthine logP values obtained from the literature and theirK _i value at A1 receptors, but not at the enzyme phosphodiesterase, whose xanthine binding site is presented to the cytosol. The implications for the therapeutic value of purinergic drugs are discussed.     

Inhibitory mechanisms in epileptiform activity induced by low magnesium

In rat hippocampal slices epileptiform activity was induced by superfusion with Mg²⁺-free artificial cerebrospinal fluid (ACSF). Paroxysmal depolarization shifts (PDS) were evoked by electrical stimulation of Schaffer collaterals. To investigate the afterpotentials that follow PDS, intracellular recordings were made from CA1 pyramidal cells. The experiments revealed that several components are engaged in the generation of PDS afterpotentials in Mg²⁺-free ACSF. A long lasting component which determined the overall duration of the PDS afterhyperpolarization was blocked by intracellular application of ethylenebis(oxonitrilo)-tetraacetate (EGTA); concomitantly, the afterhyperpolarizations following depolarizing current injections were blocked. This indicated that the long lasting component was due to a slow Ca²⁺-activated K⁺ current. The block of Ca²⁺-activated K⁺ current uncovered a depolarizing PDS afterpotential with an N-shaped voltage dependence, suggesting that this depolarizing afterpotential component may be due to an N-methyl d-aspartate (NMDA) conductance. Intracellular injection of Cl^– revealed that the PDS were followed by Cl^– currents lasting about 500 ms. This component could be blocked by application of bicuculline suggesting that it is due to a synaptically GABA-mediated (i.e. -aminobutyric acid) Cl^– current. A comparison of PDS afterpotentials in Mg²⁺-free ACSF and those in other models of epileptiform activity suggests that similar sequences of inhibitory components are activated in spite of different pharmacological alterations of membrane conductances which induce the epileptiform discharges.     

Effect of magnesium and nickel ions on focal penicillin-induced epileptic activity in the rat cerebral cortex

Research Institute of General Pathology and Pathological Physiology, Academy of Medical Sciences, Moscow. Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 113, No. 4, pp. 347–349, April, 1992.     

The role of excitatory amino acid receptors in the propagation of epileptiform discharges from the entorhinal cortex to the dentate gyrus in vitro

Summary The relationship between epileptiform events in the medial entorhinal cortex (MEC) and the dentate gyrus was investigated using a slice preparation from rat brain. Simultaneous intracellular recordings were made from neurones in layer II of the MEC and neurones in the granule cell layer of the dentate gyrus (DGC). Epileptiform activity was induced by perfusion with Mg⁺⁺-free medium or GABA_A-receptor blockers. Epileptiform discharges in MEC cells were reflected on a one-to-one basis and at a latency of 1–3 ms by depolarizing events in DGC. The latter rarely gave rise to action potentials. Bath perfusion of the N-methyl-D-aspartate (NMDA) receptor blocker, 2-aminophosphonovalerate (2-AP5) abolished the Mg⁺⁺-free induced events in MEC cells and the corresponding depolarizations in the DGC but local application of 2-AP5 to the dentate gyrus only reduced the depolarizations. The non-NMDA-receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), whether bath applied or applied locally to the DG, had little effect on the cortical events but strongly reduced the depolarizations of the DGC. The discharges induced in MEC cells by GABA-blockers were reduced by bath applied 2-AP5 but abolished by CNQX. These effects were mirrored in the dentate gyrus by a reduction in the depolarizing events by 2-AP5 and their abolition by CNQX. Local application of either antagonist to the dentate gyrus reduced but did not abolish the depolarizations. Thus, Mg⁺⁺-free induced events in MEC depend mainly on enhanced NMDA-receptor activity, while events induced by bicuculline are primarily dependant on non-NMDA receptors. The depolarizing events in the DGC which reflect the activity in the EC are mediated by both types of receptor, although non-NMDA receptors play a much greater role.     

A novel method for automated classification of epileptiform activity in the human electroencephalogram-based on independent component analysis

Diagnosis of several neurological disorders is based on the detection of typical pathological patterns in the electroencephalogram (EEG). This is a time-consuming task requiring significant training and experience. Automatic detection of these EEG patterns would greatly assist in quantitative analysis and interpretation. We present a method, which allows automatic detection of epileptiform events and discrimination of them from eye blinks, and is based on features derived using a novel application of independent component analysis. The algorithm was trained and cross validated using seven EEGs with epileptiform activity. For epileptiform events with compensation for eyeblinks, the sensitivity was 65 ± 22% at a specificity of 86 ± 7% (mean ± SD). With feature extraction by PCA or classification of raw data, specificity reduced to 76 and 74%, respectively, for the same sensitivity. On exactly the same data, the commercially available software Reveal had a maximum sensitivity of 30% and concurrent specificity of 77%. Our algorithm performed well at detecting epileptiform events in this preliminary test and offers a flexible tool that is intended to be generalized to the simultaneous classification of many waveforms in the EEG.     

焦亚硫酸钠对大鼠海马CA1区神经元钠电流的影响

目的：探讨SO2 及其体内衍生物（亚硫酸盐和亚硫酸氢盐）对中枢神经元钠通道的影响。 方法: 采用全细胞膜片钳技术研究了焦亚硫酸钠（SMB）对大鼠海马CA1区神经元钠电流的影响及超氧化物歧化酶(SOD)、过氧化氢酶(CAT)及谷胱甘肽过氧化物酶(GPx)相应的保护作用。 结果： ① 焦亚硫酸钠可剂量依赖性地增大全细胞钠电流，剂量为2 μmol/L和20 μmol/L时，钠电流分别增大（22.36±3.28）% 和（65.05±5.75）%（n=10）。② 10　μmol/L的焦亚硫酸钠不影响钠电流的激活过程，却非常显著地影响其失活过程，使失活曲线显著右移，作用前后的半数失活电压分别为（-82.38±0.54）mV和（-69.39±0.41）mV (n=10, P<0.01), 但失活曲线的斜率因子未见改变。③ SOD(1×106 U/L)、CAT(2×106 U/L) 及GPx (1×104 U/L) 均可使SMB（10 μmol/L）增大的钠电流部分恢复。 结论： SMB增大钠电流并抑制其失活过程，从而影响神经细胞的兴奋性，这一效应可能与硫中心或氧中心自由基的损伤作用有关。     

癫痫患者痫样放电的压缩谱阵研究

目的评估ＣＳＡ对癫痫的检测价值，探讨痫样放电在ＣＳＡ上的特点。方法用脑电监护仪连续记录清醒与睡眠期脑电后，以２ｓ为单元作离线ＣＳＡ分析。结果ＣＳＡ可清晰地显示出清醒期与浅睡期的散在频发中高幅放电与１ｓ以上的阵发放电，而不能显示出散在性少量放电与低幅放电；不同的放电类型在ＣＳＡ上具有不同的特征。结论对于癫痫，ＣＳＡ能有效且应主要应用于放电频繁的癫痫或癫痫状态的监护，并对发作类型的判断有一定参考价值。     

发作期及发作间期痫性放电对癫痫的诊断价值

目的探讨发作期及发作间期脑电图对癫痫诊断的意义。方法对５６例癫痫患者常规脑电图（ＲＥＥＧ）与２４ｈ脑电图（ＡＥＥＧ）进行比较研究。结果①ＲＥＥＧ的阳性率为３０％，而ＡＥＥＧ的阳性率为８６％；②不同类型癫痫在发作期和发作间期大脑活动的规律和特点，ＲＥＥＧ无１例记录到癫痫发作，而ＡＥＥＧ有２７例（４８％）记录到癫痫发作全过程的大脑电活动变化。结论发作期的ＥＥＧ对确定癫痫类型有重要意义，全身性癫痫在发作的同时发作波在两侧半球同时出现，而部分性发作患者在临床发作的同时ＥＥＧ常局限在某一脑叶有单个棘波发放，此棘波处是癫痫的病灶的部位，这种局限棘波可扩散至全脑而临床出现全身阵挛发作，此类患者为部分性癫痫并非全身性癫痫。