Effect of sodium ions on penicillin-induced epileptiform activity in vitro

Summary Intra- and extracellular recordings were obtained from the CA1 region of guinea pig hippocampal slices maintained in vitro. We studied the effect of reducing the extracellular sodium concentration on penicillin-induced epileptiform responses.In control experiments, Tris and choline were assayed as sodium substitutes. Choline was found unsuitable, since it induced repetitive firing in the absence of any convulsant agent. Replacement of 50% of the extracellular sodium ([Na⁺]_o) with Tris reduced the amplitude of the presynaptic fiber volley, the field EPSP, and the population spike. Intracellular studies showed that when [Na⁺]_o was lowered, action-potential amplitudes were reversibly depressed by an amount close to that predicted by the Nernst relation.Orthodromically elicited epileptiform discharges, induced by penicillin, were reduced in a low-sodium medium when constant stimulus currents were employed. If orthodromic stimulus strengths in normal and low-sodium states were equated on the basis of the field-EPSP amplitude, no significant diminution of the depolarizing-wave component of the epileptiform response was observed. These results suggest that a synaptic component underlies penicillin-induced epileptiform discharges.Supported by grants from the Norwegian Research Council for Science and the Humanities and by NIH grants NS 11535 and NS 15772     

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.     

FR, DRL, and discrimination learning in rats following aspiration lesions and penicillin injection into hippocampus

Rats with bilateral hippocampal destruction produced by aspiration, rats with injections of penicillin into hippocampus, rats with injections of sodium sulfadiazine into hippocampus, and control animals were tested on three operant tasks - auditory discrimination, fixed ratio (FR), and DRL 20 performance. The animals with penicillin injections were significantly impaired on higher FR schedules and DRL 20 performance. Hippocampal destruction produced by aspiration resulted in performance superior to control subjects on higher FR schedules and significantly impaired performance on the auditory discrimination and DRL 20 tasks. A hypothesis based upon these behavioral results is offered which predicts the behavioral tasks upon which subjects with penicillin injection to hippocampus are likely to be impaired.     

Simulation of the conduction velocity properties of nerve fibres by an electrical model

The paper presents a simple electrical circuit model from which the relationship between the diameter of the axon and its conduction velocity can be derived. The model is primarily intended for the larger myelinated fibres in peripheral nerves. However, a simplified model is also shown for nonmyelinated fibres, where the relationship is quite different. In the conclusion some qualitative considerations are presented for thin myelinated fibres with a slow velocity of conduction. The conduction velocity/diameter relationship of these fibres gradually approaches that for nonmyelinated fibres with decreasing diameter.     

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.     

Epileptiform lesions in rat hippocampus and acquisition of two-way avoidance

Three experiments were conducted to examine the effects on the acquisition of two-way active avoidance of implantation into the hippocampus of rats of two substances (aluminum hydroxide, penicillin) known to produce epileptogenic electrical discharges. In Experiment 1 bilateral deposits of aluminum hydroxide (ALOH) were placed in the hippocampus and the effects of this manipulation were compared to the effects of bilateral hippocampal aspiration. Sufficient postoperative time (130 days) was allowed such that epileptogenic discharges developed in the ALOH-implanted rats. Both bilateral hippocampal-ALOH deposits and bilateral hippocampal aspiration resulted in facilitated acquisition of the two-way avoidance. The results of Experiment 2 replicated this observation, but also indicated that bilateral hippocampal deposits of penicillin did not cause detectable effects on acquisition of the avoidance. Epileptiform activity produced by the penicillin was observed to disappear by postoperative Day 4. In Experiment 3 unilateral hippocampal aspiration was combined with contralateral implants of either ALOH or penicillin and avoidance training was begun 13 days postoperatively. Epileptiform activity was not observed in the ALOH-implanted rats and disappeared by postoperative Day 4 in the penicillin implanted rats. No significant changes were observed in the rate of acquisition of two-way active avoidance as a result of the manipulations done in Experiment 3. It is concluded that epileptiform discharge initiated focally within the hippocampus produces effects on the acquisition of two-way active avoidance which are similar to the effects produced by bilateral ablation.     

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.     

Propagation velocity and triggering threshold of retinal spreading depression are not correlated

Spreading depression (SD) is a pronounced but transient disturbance of cellular homeostasis in the neuropil of the central nervous system which spreads in a wave-like manner across the tissue. At the wavefront the cells depolarize and a distinct ion redistribution between intra- and extracellular space is observed. In the aftermath of SD the recovering tissue is refractory: during an early absolute refractory period no further SD can be triggered, during the subsequent relative refractory period SD waves spread at lower velocity than usual. In this paper we shall examine the influence of temperature on SD triggering and on SD propagation in the chicken retina (retinal spreading depression, rSD) and we shall examine rSD triggering and rSD propagation in the refractory period. It will be shown that cooling decreases the threshold of rSD triggering, i.e. it becomes easier to trigger rSD when the temperature is reduced. At the same time cooling slows rSD propagation. In contrast, during the relative refractory period triggering rSD is more difficult than usual while rSD propagation is also slowed. These results demonstrate that the propagation velocity of rSD is not correlated with the triggering threshold. In particular, the propagation velocity of rSD must not be used to predict the influence of experimental conditions on the triggering threshold.     

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.     

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.     

Involvement of non-NMDA receptors in picrotoxin-induced epileptiform activity in the hippocampus

The ability of the non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) to suppress picrotoxin-induced epileptiform burst activity was examined. Intracellular recordings were obtained from hippocampal CA1 and CA3 pyramidal neurons maintained in vitro. Bath application of CNQX (5 microM) significantly reduced or abolished evoked paroxysmal depolarizing shifts (PDSs) in all CA1 and CA3 neurons tested. In cells where a CNQX-insensitive component in the PDS was manifest, this remaining activity was abolished by the N-methyl-D-aspartate (NMDA) receptor antagonist D-2-amino-5-phosphonovaleric acid (20 microM), suggesting the existence of a NMDA-mediated synaptic potential. Our results indicate that non-NMDA receptor antagonists are capable of markedly reducing picrotoxin-induced epileptiform activity and that these receptors play an important role in generation of PDSs.     

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.     

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.     

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.     

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。     

神经传导速度对糖尿病周围神经病的诊断价值

目的 :探讨神经传导速度 (NCV)对糖尿病周围神经病 (DPN)的诊断价值。方法 :对 5 0例糖尿病患者分为有症状组和无症状组 ,进行周围神经NCV的测定 ,与健康人对照 ,同时行相关因素分析。结果 :糖尿病患者运动神经传导速度 (MCV)、感觉神经传导速度 (SCV)与健康人比较存在明显差异 ,且有症状组更显著 (P <0 0 5 ) ;患者的NCV与空腹血糖无明显相关 ,而与病程长短呈正相关。结论 :周围神经NCV的检测有助于DPN的早期诊断     

Melatonin reduces low-Mg2+ epileptiform activity in human temporal slices

Scizure susceptibility waxes and wanes in an apparently circadian manner in many epileptic patients. Fluctuations of melatonin concentration with highest levels during the night and lowest levels in the early morning could be involved in this phenomenon. Therefore, the action of melatonin on epileptic activity was tested. The experiments were carried out on human temporal neocortical slices cut from tissue resected for surgical treatment of epilepsy. Autoradiographic studies were performed on parallel slices with 100–120 pmol 2-[¹²⁵I]iodomelatonin/l in the absence or presence of unlabelled melatonin. High-affinity binding sites of melatonin could be demonstrated in layers II–V of the temporal cortex. The binding was saturable, specific and occurred with low capacity. In electrophysiological studies, epileptiform field potentials were elicited by omission of Mg²⁺ from the superfusate and recorded from layers II–V. The frequency of occurrence of epileptiform field potentials was reduced to 0.5 of the initial value with application of melatonin (10 and 100 nmol/l) in each case. This effect was reversible upon washing. The findings favour the hypothesis that melatonin depresses epileptiform neuronal activity through specific neocortical receptors.     

复合动作电位传播速度分布的复时谱估计方法的仿真研究

复合动作电位传播速度分布（ＰＶＤ）的估计，在神经电生理和病理学的基础研究和临床应用方面都具有重要的意义。但是，目前的方法存在许多问题，很少用于临床实践。本文提出了估计ＰＶＤ的复时谱分析方法，通过参考曲线的超前叠加以及尾部压缩，从很大程度上考虑了组成复合动作电位的单纤维动作电位的时程差异。因此得到了满意的结果，仿真研究表明，这个方法算法简单，结果可靠。但是，对于速度范围很宽的ＰＶＤ，估计误差将会增大     

Neural grafting to ischemic lesions of the adult rat hippocampus

Summary The purpose of this study was to examine the structural and connective integration of developing hippocampal neurons grafted to ischemic lesions of the adult rat hippocampus. The 4-vessel occlusion model was used to cause transient cerebral ischemia which damages CA1 pyramidal cells in the dorsal hippocampus, but spares nonpyramidal neurons and afferents in the area. One week later, cell suspensions were made from the CA1 region of fetal (E18-20) rats and injected stereotaxically into the lesion. The recipient brains were examined 6 weeks to 6 months later for survival, morphology, and intrinsic and extrinsic connections of the grafts. The methods used included cell stains, histochemical staining for acetylcholinesterease (AChE), immunocytochemical staining for neuropeptides (cholelecystokinin (CCK), somatostatin (SS), enkephalin (Enk) and an astrocytic marker, glial fibrillary acidic protein (GFAP), as well as tracing by retrograde axonal transport of fluorochromes and light and electron microscopy of anterograde axonal degeneration. The grafts survived well (80%) and were often quite large. They were well integrated in the lesioned host brain area, contained both pyramidal cells and neuropeptidergic neurons and displayed a near normal GFAP immunoreactivity for astrocytes. The latter contrasted the dense gliosis of the host ischemic lesion. Judged by the AChE staining the grafts were innervated by cholinergic host septohippocampal fibers. Ingrowth of host hippocampal commissural fibers was demonstrated by Fink-Heimer staining for degenerating nerve terminals following acute lesions of the hippocampal commissures. At the ultrastructural level degenerating, electron dense terminals of host commissural origin were found even deep inside the graft neuropil in synaptic contact with mainly dendritic spines. A transplant efferent connection to the host brain was demonstrated by retrograde fluorochrome tracing and consisted of a homotypic projection to more posterior levels of the ipsilateral host CA1 and subiculum. Minor abnormal, efferent projections to the host dentate molecular layer were shown in Timm staining. We conclude that fetal CA1 neurons grafted to one week old ischemic lesions of the dorsal CA1 in adult rats become structurally well incorporated and can establish nerve connections with the host brain.     

Ischemia-induced changes in the electrical activity of the hippocampus

Summary Consequences of transient (15–20 min) ischemia on the neuronal activity of the dentate gyrus and hippocampal CA 1 region were investigated in chronically implanted Sprague-Dawley rats. Forebrain ischemia was produced by occlusion of the carotids for 15 or 20 min, following cauterization of the vertebral arteries. Following the release of the carotids, both spontaneous and evoked activity showed a steady but partial recovery, reaching a maximum 12 to 24 h after the ischemic insult. From this plateau, both the power of rhythmic slow activity recorded during walking and the power of slow delta activity obtained during alert immobility decreased monotonically, with large changes occuring between postischemic days 2 and 4. The changes in spontaneous activity were accompanied by a decrease and eventual disappearance of the Schaffer collateral evoked responses in CA 1. Perforant path volleys were less efficient in activating the granule cells following ischemia compared to baseline levels. This decreased responsiveness was paralleled by a relative impairment of paired pulse depression. Neurophysiological signs of spontaneous or evoked neuronal hyperexcitability were not observed at any time point during the 8 postischemic days. Neuronal damage in the CA 1 region varied from moderate to complete loss of pyramidal cells. In addition, degenerating neurons were also observed in the hilus of the dentate gyrus. These findings do not support the overwork version of the excitoxic hypothesis of delayed neuronal damage and indicate that the cause of ischemic cell death should be sought in factors other than neuronal hyperactivity.