Synchrony levels during evoked seizure-like bursts in mouse neocortical slices

Slices (n = 45) from the somatosensory cortex of mouse (P8-13) generated spontaneous bursts of activity (0.10 +/- 0.05 Hz) that were recorded extracellularly. Multiunit action potential (AP) activity was integrated and used as an index of population activity. In this experimental model, seizure-like activity (SLA) was evoked with bicuculline (5-10 microM) or N-methyl-d-aspartate (NMDA, 5 microM). SLA was an episode with repetitive bursting at a frequency of 0.50 +/- 0.06 Hz. To evaluate whether SLA was associated with a change in synchrony, we obtained simultaneous intracellular and extracellular recordings (n = 40) and quantified the relationship between individual cells and the surrounding population of neurons. During the SLA there was an increase in population activity and bursting activity was observed in neurons and areas that were previously silent. We defined synchrony as cellular activity that is consistently locked with the population bursts. Signal-averaging techniques were used to determine this component. To quantitatively assess change in synchronous activity at SLA onset, we estimated the entropy of the single cell's spike trains and subdivided this measure into network burst-related information and noise-related entropy. The burst-related information was not significantly altered at the onset of NMDA-evoked SLA and slightly increased when evoked with bicuculline. The signal-to-noise ratio determined from the entropy estimates showed a significant decrease (instead of an expected increase) during SLA. We conclude that the increased population activity during the SLA is attributed to recruitment of neurons rather than to increased synchrony of each of the individual elements.     

Role of synaptic metabotropic glutamate receptors in epileptiform discharges in hippocampal slices

Application of group I metabotropic glutamate receptor (mGluR) agonists elicits seizure discharges in vivo and prolonged ictal-like activity in in vitro brain slices. In this study we examined 1) if group I mGluRs are activated by synaptically released glutamate during epileptiform discharges induced by convulsants in hippocampal slices and, if so, 2) whether the synaptically activated mGluRs contribute to the pattern of the epileptiform discharges. The GABA(A) receptor antagonist bicuculline (50 microM) was applied to induce short synchronized bursts of approximately 250 ms in mouse hippocampal slices. Addition of 4-aminopyridine (4-AP; 100 microM) prolonged these bursts to 0.7-2 s. The mGluR1 antagonist (S)-(+)-alpha-amino-4-carboxy-2-methylbenzeneacetic acid (LY 367385; 25-100 microM) and the mGluR5 antagonist 2-methyl-6-(phenylethynyl)pyridine (MPEP; 10-50 microM), applied separately, significantly reduced the duration of the synchronized discharges. The effects of these antagonists were additive when applied together, suggesting that mGluR1 and mGluR5 exert independent actions on the epileptiform bursts. In phospholipase C beta1 (PLCbeta1) knockout mice, bicuculline and 4-AP elicited prolonged synchronized discharges of comparable duration as those observed in slices from wild-type littermates. Furthermore, mGluR1 and mGluR5 antagonists reduced the duration of the epileptiform discharges to the same extent as they did in the wild-type preparations. The results suggest that mGluR1 and mGluR5 are activated synaptically during prolonged epileptiform discharges induced by bicuculline and 4-AP. Synaptic activation of these receptors extended the duration of synchronized discharges. In addition, the data indicate that the synaptic effects of the group I mGluRs on the duration of epileptiform discharges were mediated by a PLCbeta1-independent mechanism.     

Effect of eugenol on spreading depression and epileptiform discharges in rat neocortical and hippocampal tissues

Eugenol, an aromatic molecule derived from several plants, has been receiving examination for clinical relevance in epilepsy and headache. To investigate the neurophysiologic properties of the action of eugenol, its effects on epileptiform field potentials elicited by omission of extracellular Mg2+, spreading depression induced by KCl microinjection, electrically evoked field potentials, and long-term potentiation were tested in rat neocortical and hippocampal tissues. Eugenol (10-100 micromol/l) dose-dependently and reversibly suppressed both epileptiform field potentials and spreading depression Eugenol also reversibly decreased the amplitude of the field postsynaptic potentials evoked in CA1 area of hippocampus and the third layer of neocortex. Eugenol significantly reduced the long-term potentiation by approximately 30% compared with controls. Thus, eugenol can suppress epileptiform field potentials and spreading depression, likely via inhibition of synaptic plasticity. The results indicate the potential for eugenol to use in the treatment of epilepsy and cephalic pain.     

Contribution of L-type calcium channels to epileptiform activity in hippocampal and neocortical slices of guinea-pigs

The aim of the present investigation was to compare the antiepileptic efficacy of the specific L-type calcium channel blocker nifedipine in hippocampal and neocortical slice preparations in the Mg²⁺-free model of epilepsy. The main findings were as follows. (1) In hippocampal slices, in general, nifedipine (20–80 μmol/l) exerted a suppressive effect both on repetition rate and on area under epileptiform field potentials. This effect was clearly dose dependent. In the majority of cases, this suppression was preceded by an increase, which was transient in nature. Only in the lowest concentration (20 μmol/l) used, in normal K⁺, instead of a depression, a persistent increase occurred. (2) In neocortical slices, in the majority of experiments, nifedipine (20–80 μmol/l) showed a depressive action only on the area under the epileptiform field potentials. The depressive effect of nifedipine on the area was dose dependent, although to a lesser extent than in the hippocampus. In nearly half of the slices this suppression was preceded by a transient increase. By contrast, the repetition rate of epileptiform field potentials increased transiently in about 20% of the slices followed by a decrease. In the remaining 80% of the slices the repetition rate increased persistently. (3) An elevation of the K⁺ concentration accentuated the depressive actions of nifedipine only in the hippocampus. In contrast to elevated K⁺, in both the hippocampus and the neocortex, epileptiform field potentials were not suppressed in all experiments in normal K⁺. (4) The reversibility of the depressive effects of nifedipine was differential in the two tissue types. In the hippocampus, after suppression of epileptiform field potentials they reappeared in the overwhelming majority of slices. In the neocortex, this was the case in only one experiment.These findings may indicate the existence of L-type calcium channels with a differential functional significance for epileptogenesis and/or the existence of different forms of L-type channels in hippocampal and neocortical tissue. As a whole, the differential effects of L-type calcium channel blockade in the hippocampus and neocortex point to differences in the network properties of the two tissue types.     

Contribution of L-type calcium channels to epileptiform activity in hippocampal and neocortical slices of guinea-pigs

The aim of the present investigation was to compare the antiepileptic efficacy of the specific L-type calcium channel blocker nifedipine in hippocampal and neocortical slice preparations in the Mg2+-free model of epilepsy. The main findings were as follows. (1) In hippocampal slices, in general, nifedipine (20-80 micromol/l) exerted a suppressive effect both on repetition rate and on area under epileptiform field potentials. This effect was clearly dose dependent. In the majority of cases, this suppression was preceded by an increase, which was transient in nature. Only in the lowest concentration (20 micromol/l) used, in normal K+, instead of a depression, a persistent increase occurred. (2) In neocortical slices, in the majority of experiments, nifedipine (20-80 micromol/l) showed a depressive action only on the area under the epileptiform field potentials. The depressive effect of nifedipine on the area was dose dependent, although to a lesser extent than in the hippocampus. In nearly half of the slices this suppression was preceded by a transient increase. By contrast, the repetition rate of epileptiform field potentials increased transiently in about 20% of the slices followed by a decrease. In the remaining 80% of the slices the repetition rate increased persistently. (3) An elevation of the K+ concentration accentuated the depressive actions of nifedipine only in the hippocampus. In contrast to elevated K+, in both the hippocampus and the neocortex, epileptiform field potentials were not suppressed in all experiments in normal K+. (4) The reversibility of the depressive effects of nifedipine was differential in the two tissue types. In the hippocampus, after suppression of epileptiform field potentials they reappeared in the overwhelming majority of slices. In the neocortex, this was the case in only one experiment. These findings may indicate the existence of L-type calcium channels with a differential functional significance for epileptogenesis and/or the existence of different forms of L-type channels in hippocampal and neocortical tissue. As a whole, the differential effects of L-type calcium channel blockade in the hippocampus and neocortex point to differences in the network properties of the two tissue types.     

Interneuron and pyramidal cell interplay during in vitro seizure-like events

Excitatory and inhibitory (EI) interactions shape network activity. However, little is known about the EI interactions in pathological conditions such as epilepsy. To investigate EI interactions during seizure-like events (SLEs), we performed simultaneous dual and triple whole cell and extracellular recordings in pyramidal cells and oriens interneurons in rat hippocampal CA1. We describe a novel pattern of interleaving EI activity during spontaneous in vitro SLEs generated by the potassium channel blocker 4-aminopyridine in the presence of decreased magnesium. Interneuron activity was increased during interictal periods. During ictal discharges interneurons entered into long-lasting depolarization block (DB) with suppression of spike generation; simultaneously, pyramidal cells produced spike trains with increased frequency (6-14 Hz) and correlation. After this period of runaway excitation, interneuron postictal spiking resumed and pyramidal cells became progressively quiescent. We performed correlation measures of cell-pair interactions using either the spikes alone or the subthreshold postsynaptic interspike signals. EE spike correlation was notably increased during interneuron DB, whereas subthreshold EE correlation decreased. EI spike correlations increased at the end of SLEs, whereas II subthreshold correlations increased during DB. Our findings underscore the importance of complex cell-type-specific neuronal interactions in the formation of seizure patterns.     

Characteristics of plateau activity during the latent period prior to epileptiform discharges in slices from rat piriform cortex

The deep piriform region has an unusually high seizure susceptibility. Voltage imaging previously located the sites of epileptiform discharge onset in slices of rat piriform cortex and revealed the spatiotemporal pattern of development of two types of electrical activity during the latent period prior to discharge onset. A ramplike depolarization (onset activity) appears at the site of discharge onset. Onset activity is preceded by a sustained low-amplitude depolarization (plateau activity) at another site, which shows little if any overlap with the site of onset. Because synaptic blockade at either of these two sites blocks discharges, it was proposed that both forms of latent period activity are necessary for the generation of epileptiform discharges and that the onset and plateau sites work together in the amplification of electrical activity. The capacity for amplification was examined here by studying subthreshold responses in slices of piriform cortex using two different in vitro models of epilepsy. Under some conditions electrically evoked responses showed a nonlinear dependence on stimulus current, suggesting amplification by strong polysynaptic excitatory responses. The sites of plateau and onset activity were mapped for different in vitro models of epilepsy and different sites of stimulation. These experiments showed that the site of plateau activity expanded into deep layers of neighboring neocortex in parallel with expansions of the onset site into neocortex. These results provide further evidence that interactions between the sites of onset and plateau activity play an important role in the initiation of epileptiform discharges. The site of plateau activity showed little variation with different stimulation sites in the piriform cortex, but when stimulation was applied in the endopiriform nucleus (in the sites of onset of plateau activity), plateau activity had a lower amplitude and became distributed over a much wider area. These results indicate that in the initiation of epileptiform discharges, the location of the circuit that generates plateau activity is not rigidly defined but can exhibit flexibility.     

468例癫Xian患者睡眠期Xian样放电与睡眠结构变化分析

目的：观察癫Xian患者的睡眠时相与Xian样放电的关系,并初步探讨癫Xian异常脑波活动对睡眠的影响。方法：对468例癫Xian患者进行24小时动态脑电图(AEEG）监测,观察发作间期清醒与睡眠脑电图Xian样放电的发作频率,分析58例癫Xian患者及对照组睡眠脑电图中睡眠时程、觉醒次数、睡眠纺缍波的变化。结果：468例患者中出现Xian样放电362例,睡眠期Xian样放电检出率88％,觉醒期检出率58％。Xian样放电主要出现于NREM睡眠Ⅰ-Ⅱ期。与对照组比较,癫Xian组NREMⅠ-Ⅱ睡眠期延长,NREMⅢ-Ⅳ期缩短;觉醒次数增加,觉醒次数与Xian样放电频率呈正相关;并有睡眠纺锤波减少及不对称。结论：癫Xian患者的Xian样放电主要出现于NREM睡眠Ⅰ-Ⅱ期,癫Xian活动对睡眠有一定影响,癫Xian患者睡眠质量下降。     

Partial disinhibition is required for transition of stimulus-induced sharp wave-ripple complexes into recurrent epileptiform discharges in rat hippocampal slices

Sharp wave-ripple complexes (SPW-Rs) in the intact rodent hippocampus are characterized by slow field potential transients superimposed by close to 200-Hz ripple oscillations. Similar events have been recorded in hippocampal slices where SPW-Rs occur spontaneously or can be induced by repeated application of high-frequency stimulation, a standard protocol for induction of long-lasting long-term potentiation. Such stimulation is reminiscent of protocols used to induce kindling epilepsy and ripple oscillations may be predictive of the epileptogenic zone in temporal lobe epilepsy. In the present study, we investigated the relation between recurrent epileptiform discharges (REDs) and SPW-Rs by studying effects of partial removal of inhibition. In particular, we compared the effects of nicotine, low-dose bicuculline methiodide (BMI), and elevated extracellular potassium concentration ([K(+)](o)) on induced SPW-Rs. We show that nicotine dose-dependently transformed SPW-Rs into REDs. This transition was associated with reduced inhibitory conductance in CA3 pyramidal cells. Similar results were obtained from slices where the GABAergic conductance was reduced by application of low concentrations of BMI (1-2 μM). In contrast, sharp waves were diminished by phenobarbital. Elevating [K(+)](o) from 3 to 8.5 mM did not transform SPW-Rs into REDs but significantly increased their incidence and amplitude. Under these conditions, the equilibrium potential for inhibition was shifted in depolarizing direction, whereas inhibitory conductance was significantly increased. Interestingly, the propensity of elevated [K(+)](o) to induce seizure-like events was reduced in slices where SPW-Rs had been induced. In conclusion, recruitment of inhibitory cells during SPW-Rs may serve as a mechanism by which hyperexcitation and eventually seizure generation might be prevented.     

468例癫癎患者睡眠期癎样放电与睡眠结构变化分析

目的：观察癫 患者的睡眠时相与 样放电的关系,并初步探讨癫 异常脑波活动对睡眠的影响。方法：对４６８例癫　患者进行２４小时动态脑电图（ＡＥＥＧ）监测,观察发作间期清醒与睡眠脑电图　样放电的发作频率,分析５８例癫　患者及对照组睡眠脑电图中睡眠时程、觉醒次数、睡眠纺锤波的变化。结果：４６８例患者中出现　样放电３６２例,睡眠期　样放电检出率８８％,觉醒期检出率５８％。样放电主要出现于ＮＲＥＭ睡眠Ⅰ－Ⅱ期。与对照组比较,癫　组ＮＲＥＭ　Ⅰ－Ⅱ睡眠期延长,ＮＲＥＭ Ⅲ－Ⅳ期缩短;觉醒次数增加,觉醒次数与　样放电频率呈正相关;并有睡眠纺锤波减少及不对称。结论：癫　患者的　样放电主要出现于ＮＲＥＭ睡眠Ⅰ－Ⅱ期,癫　活动对睡眠有一定影响,癫　患者睡眠质量下降。     

Voltage imaging reveals the CA1 region at the CA2 border as a focus for epileptiform discharges and long-term potentiation in hippocampal slices

Voltage-sensitive-dye imaging was used to study the initiation and propagation of epileptiform activity in transverse hippocampal slices. A portion of the slices tested generated epileptiform discharges in response to electrical shocks under normal physiological conditions. The fraction of slices showing epileptiform responses increased from 44 to 86% when bathing [K+] increased from 3.2 to 4 mM. Regardless of stimulation site in the dentate gyrus and hippocampus, discharges generally initiated in the CA3 region. After onset, discharges abruptly appeared in the CA1 region, right at the CA2 border. This spread from the CA3 region to the CA1 region was saltatory, occurring before detectable activity in the intervening CA2 and CA3 regions. Discharges did eventually propagate smoothly through the intervening CA3 region into the CA2 region, but on a slower timescale. The surge in the CA1 region did not spread back into the CA2 region, but spread through the CA1 region toward the subiculum. Tetanic stimulation, theta bursts, and GABA(A) receptor antagonists failed to alter this characteristic pattern, but did reduce the latency of discharge onset. The part of the CA1 region at the CA2 border, where epileptic responses emerged with relatively short latency, also expressed stronger long-term potentiation (LTP) than the rest of the CA1 region. The CA2 region, where discharges had long latencies and low amplitudes, expressed weaker LTP. Thus the CA1 region at the CA2 border has unique properties, which make this part of the hippocampus an important locus for both epileptiform activity and plasticity.     

Periodicity and directionality in the propagation of epileptiform discharges across neocortex

1. The horizontal propagation of epileptiform discharges has been studied in slices of neocortex treated with high concentrations of bicuculline methiodide, an antagonist of the inhibitory transmitter gamma-aminobutyric acid (GABA). The cortical areas examined were: primary somatosensory (SmI) and motor (MI), and primary (area 17) and secondary (area 18) visual areas of rats, and area 17 of cats. In all of these areas an electrical stimulus evoked single, all-or-none paroxysmal field potentials (PFPs) that propagated across the entire width of the slice without decrement. 2. The velocity of PFP propagation was approximately 0.06-0.09 m/s when averaged over cortical distances of several millimeters. PFP propagation occurred equally well in both directions across a slice. 3. Measurement of PFP propagation at higher spatial resolution (100-180 micron intervals) revealed that velocity was not homogeneous within rat SmI, rat area 18 and cat area 17, but instead varied manyfold as horizontal position changed. In these areas of cortex, propagation patterns were spatially periodic; power spectra reveal that the dominant spatial frequencies were centered about 1 mm-1, with negligible contributions above 2 mm-1. Occasionally PFP propagation was discontinuous, skipping over a small region of cortex and arriving distally before propagating into the more proximal region. 4. In those cortices with periodic propagation patterns, PFP velocity was also strongly direction-dependent. Propagation patterns measured in opposite directions across the same strip of cortex displayed similar periodicities, but in many slices they were negatively correlated, i.e., the propagation pattern in one direction was antiphasic compared to that in the other direction. 5. In contrast, propagation velocity across the center of area 17 of the rat was relatively constant and not directional. Near the boundaries of areas 17 and 18, however, PFP velocity changed abruptly and became periodic within area 18. Similarly, velocity within rat MI was more constant and less directional than in the adjacent SmI. 6. The patterns of PFP propagation velocity are often spatially periodic, directionally asymmetric, and depend upon cortical area. We suggest that the periodic patterns reflect systematic variations in the length or density of horizontal excitatory connections. Alternatively, or concurrently, periodicities could arise from the patchy distributions of intrinsic connections that have been observed anatomically in many areas of neocortex.     

Suppression of epileptiform burst discharges in CA3 neurons of rat hippocampal slices by the organic calcium channel blocker,verapamil

Summary We studied the effects of the organic calcium channel blocker, verapamil, on spontaneous and bicuculline-induced epileptiform burst discharges in CA3 pyramidal cells of hippocampal slices. A transient increase of burst discharge rate was observed in most cells within 30 min after the addition of verapamil (100 M) to the perfusing medium. Prolonged verapamil perfusions gradually reduced the rate and duration of burst discharges, then abolished them in all tested slices (over periods of 50–150 min) without blocking synaptic transmission. Responses to intracellular injections of current pulses were also gradually affected by verapamil: Action potential amplitude was decreased, action potential duration increased, frequency adaptation increased, amplitude of the fast hyperpolarization following a single action potential decreased, and amplitude and duration of the slow afterhyperpolarization markedly reduced. The amplitude of calcium spikes elicited in slices perfused with tetrodotoxin-containing medium was not affected by verapamil, but the mean velocity of depolarization near the peak of the calcium spike was decreased. Membrane resting potential and input resistance were not affected by verapamil. These results confirm that verapamil is able to suppress epileptiform activity, but suggest that this effect is rather non-specific, due to inhibition of both postsynaptic sodium and calcium conductances.     

Effects of dendroaspis natriuretic peptide on calcium-activated potassium current and its mechanism

In this study, we sought to investigate the effect of dendroaspis natriuretic peptide (DNP) on calcium-activated potassium current (I K(Ca)) and its mechanism in gastric antral circular smooth muscle cells (SMCs) using the whole-cell patch-clamp technique. DNP concentration-dependently increased macroscopic I K(Ca) and spontaneous transient outward currents (STOCs) in freshly isolated guinea pig gastric antral circular SMCs. The effects of DNP on I K(Ca) and/or STOCs were not blocked by applying calcium-free bath solution or the ryanodine receptor (RyR) antagonist ryanodine (10 microM), but they were inhibited by the inositol triphosphate receptor (IP3R) inhibitor heparin or the guanylate cyclase inhibitor LY83583. Moreover, a DNP-induced increase in STOCs was potentiated by the cyclic guanosine monophosphate (cGMP)-sensitive phosphoesterase inhibitor zaprinast. In conclusion, our results suggest that DNP increases I K(Ca) in gastric antral circular SMCs by increasing cGMP production and activating IP3Rs.