Epileptiform Activity In Slices Research Articles

Alarin potentiates ongoing epileptiform activity in rat brain slices: an in vitro electrophysiological study.

Alarin is a newly discovered neuropeptide that belongs to the galanin peptide family with a wide range of bioactivity in the nervous system. Its function in the brain's autonomic areas has been studied, and it has been reported that alarin is involved in the regulation of excitability in hypothalamic neurons. Its role in the regulation of excitability in the hippocampus, however, is unknown. In this study, we investigated if alarin induced any synchronous discharges or epileptiform activity, and if it had any effect on already initiated epileptiform discharges. We used thick acute horizontal hippocampal slices obtained from 30‑ to 35‑day‑old rats. Extracellular field potential recordings were evaluated in the CA1 region of the hippocampus. Our data demonstrated that, alarin application did not result in any epileptiform activity or abnormal discharges. 4‑aminopyridine was applied to induce epileptiform activity in the slices. We found that alarin increased the frequency of interictal‑like events and the mean power of local field potentials in the CA1 region of the hippocampus, which was induced by 4‑aminopyridine. These results demonstrated for the first time that alarin has a modulatory effect on synchronized neuronal discharges and showed the contribution of the neuropeptide alarin to epilepsy‑like conditions.

Epileptiform activity in mouse hippocampal slices induced by moderate changes in extracellular Mg2+, Ca2+, and K+

BackgroundRodent brain slices—particularly hippocampal slices—are widely used in experimental investigations of epileptiform activity. Oxygenated artificial cerebrospinal fluid (ACSF) is used to maintain slices in vitro. Physiological or standard ACSF containing 3–3.5 mM K+, 1–2 mM Mg2+, and 1–3 mM Ca2+ generally does not induce population epileptiform activity, which can be induced by ACSF with high K+ (8–10 mM), low Mg2+, or low Ca2+ alone or in combination. While low-Mg2+ ACSF without intentionally added Mg salt but with contaminating Mg2+ (≤ 50–80 µM) from other salts can induce robust epileptiform activity in slices, it is unclear whether such epileptiform activity can be achieved using ACSF with moderately decreased Mg2+. To explore this issue, we examined the effects of moderately modified (m)ACSF with 0.8 mM Mg2+, 1.3 mM Ca2+, and 5.7 mM K+ on induction of epileptiform discharges in mouse hippocampal slices.ResultsHippocampal slices were prepared from young (21–28 days old), middle-aged (13–14 months old), and aged (24–26 months old) C57/BL6 mice. Conventional thin (0.4 mm) and thick (0.6 mm) slices were obtained using a vibratome and pretreated with mACSF at 35–36 °C for 1 h prior to recordings. During perfusion with mACSF at 35–36 °C, spontaneous or self-sustained epileptiform field potentials following high-frequency stimulation were frequently recorded in slices pretreated with mACSF but not in those without the pretreatment. Seizure-like ictal discharges were more common in thick slices than in thin slices.ConclusionsProlonged exposure to mACSF by pretreatment and subsequent perfusion can induce epileptiform field potentials in mouse hippocampal slices.

Seizure-Induced Potentiation of AMPA Receptor-Mediated Synaptic Transmission in the Entorhinal Cortex.

Excessive excitation is considered one of the key mechanisms underlying epileptic seizures. We investigated changes in the evoked postsynaptic responses of medial entorhinal cortex (ERC) pyramidal neurons by seizure-like events (SLEs), using the modified 4-aminopyridine (4-AP) model of epileptiform activity. Rat brain slices were perfused with pro-epileptic solution contained 4-AP and elevated potassium and reduced magnesium concentration. We demonstrated that 15-min robust epileptiform activity in slices leads to an increase in the amplitude of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR)-mediated component of the evoked response, as well as an increase in the polysynaptic γ-aminobutyric acid (GABA) and N-methyl-D-aspartate (NMDA) receptor-mediated components. The increase in AMPA-mediated postsynaptic conductance depends on NMDA receptor activation. It persists for at least 15 min after the cessation of SLEs and is partly attributed to the inclusion of calcium-permeable AMPA receptors in the postsynaptic membrane. The mathematical modeling of the evoked responses using the conductance-based refractory density (CBRD) approach indicated that such augmentation of the AMPA receptor function and depolarization by GABA receptors results in prolonged firing that explains the increase in polysynaptic components, which contribute to overall network excitability. Taken together, our data suggest that AMPA receptor enhancement could be a critical determinant of sustained status epilepticus (SE).

Mild systemic inflammation and moderate hypoxia transiently alter neuronal excitability in mouse somatosensory cortex

During the perinatal period, the brain is highly vulnerable to hypoxia and inflammation, which often cause white matter injury and long-term neuronal dysfunction such as motor and cognitive deficits or epileptic seizures. We studied the effects of moderate hypoxia (HYPO), mild systemic inflammation (INFL), or the combination of both (HYPO+INFL) in mouse somatosensory cortex induced during the first postnatal week on network activity and compared it to activity in SHAM control animals. By performing in vitro electrophysiological recordings with multi-electrode arrays from slices prepared directly after injury (P8–10), one week after injury (P13–16), or in young adults (P28–30), we investigated how the neocortical network developed following these insults. No significant difference was observed between the four groups in an extracellular solution close to physiological conditions. In extracellular 8mM potassium solution, slices from the HYPO, INFL, and HYPO+INFL group were more excitable than SHAM at P8–10 and P13–16. In these two age groups, the number and frequency of spontaneous epileptiform events were significantly increased compared to SHAM. The frequency of epileptiform events was significantly reduced by the NMDA antagonist D-APV in HYPO, INFL, and HYPO+INFL, but not in SHAM, indicating a contribution of NMDA receptors to this pathophysiological activity. In addition, the AMPA/kainate receptor antagonist CNQX suppressed the remaining epileptiform activity.Electrical stimulation evoked prominent epileptiform activity in slices from HYPO, INFL and HYPO+INFL animals. Stimulation threshold to elicit epileptiform events was lower in these groups than in SHAM. Evoked events spread over larger areas and lasted longer in treated animals than in SHAM. In addition, the evoked epileptiform activity was reduced in the older (P28–30) group indicating that cortical dysfunction induced by hypoxia and inflammation was transient and compensated during early development.

Network excitability in a model of chronic temporal lobe epilepsy critically depends on SK channel-mediated AHP currents

Hippocampal CA1 pyramidal neurons generate an after-hyperpolarization (AHP) whose medium component is thought to be generated by small-conductance Ca2+-activated K+ channels (SK channels). Neuronal excitability is increased in epilepsy, and the AHP in turn is fundamentally involved in regulation of cellular excitability. We therefore investigated the involvement of the SK channel-mediated AHP in controlling cell and network excitability in the pilocarpine model epilepsy. Both acutely isolated CA1 pyramidal cells and isolated hippocampal slices were investigated in terms of the impact of SK channel-mediated AHP on hyperexcitability. Our findings show that pilocarpine-treated chronically epileptic rats exhibit significantly reduced SK channel-mediated hyperpolarizing outward current which was accompanied by a significant decrease in the somatic AHP. Paradoxically, inhibiting SK channels strongly exacerbated 0-Mg2+-induced epileptiform activity in slices from pilocarpine-treated animals, while having a significantly smaller effect in control tissue. This suggests that in chronically epileptic tissue, network excitability very critically depends on the remaining SK-channel mediated AHP. Additional real-time RT-PCR and semiquantitative Western blot experiments revealed that both the SK2 channel transcript and protein were significantly downregulated in the epileptic CA1 region. We conclude that SK2 channels are down-regulated in chronic epilepsy underlying the impaired SK channel function in CA1 pyramidal cells, and a further reduction of the remaining critical mass of SK channels results in an acute network decompensation.

Epileptiform activities in slices of hippocampus from mice after intra‐hippocampal injection of kainic acid

Intra-hippocampal kainate injection induces the emergence of recurrent seizures after a delay of 3-4 weeks. We examined the cellular and synaptic basis of this activity in vitro using extracellular and intracellular records from longitudinal hippocampal slices. These slices permitted recordings from the dentate gyrus, the CA3 and CA1 regions and the subiculum of both the injected and the contralateral non-injected hippocampus. A sclerotic zone was evident in dorsal regions of slices from the injected hippocampus, while ventral regions and tissue from the contralateral hippocampus were not sclerotic. Interictal field potentials of duration 50-200 ms were generated spontaneously in both ipsilateral and contralateral hippocampal slices, but not in the sclerotic region, at 3-12 months after injection. They were initiated in the CA1 and CA3 regions and the subiculum. They were blocked by antagonists at glutamatergic receptors and were transformed into prolonged epileptiform events by GABAergic receptor antagonists. The membrane potential and the reversal potential of GABAergic synaptic events were more depolarized in CA1 pyramidal cells from kainate-treated animals than in control animals. Ictal-like events of duration 8-80 s were induced by tetanic stimulation (50 Hz, 0.2-1 s) preferentially in dorsal contralateral and ventral ipsilateral slices. Similar events were initiated by focal application of a combination of high K(+) and GABA. These data show that both interictal and ictal-like activities can be induced in slices of both ipsilateral and contralateral hippocampus from kainate-treated animals and suggest that changes in cellular excitability and inhibitory synaptic signalling may contribute to their generation.

The effect of extracts of Searsia species on epileptiform activity in slices of the mouse cerebral cortex

Ethnopharmacological relevance Searsia dentata and Searsia pyroides are used in traditional South African medicine to treat convulsions and epilepsy. Previous studies have demonstrated that extracts of these plants comprise compounds that bind to the flumazenil-sensitive site on the GABA A receptor. However, their use as anticonvulsant medicinal plants cannot be adequately explained by these findings. Aims The aim of this study was to examine the possible involvement of the glutamatergic system of extracts from the plants. Materials and methods The mouse cortical wedge preparation was used for functional characterization of the extracts. The affinity towards the NMDA and the AMPA receptor was investigated using classical [ 3H]-GP39653 and [ 3H]-AMPA binding assays, respectively. Results The extracts of Searsia dentata and Searsia pyroides inhibited the spontaneous epileptiform discharges in mouse cerebral cortical slices with ED 50 of 0.62 and 1.67 mg dry extract/mL, respectively. Both extracts displaced [ 3H]-GP39653 binding and significantly inhibited the NMDA-induced response during co-administration in cortical slices. Conclusion In this study, the NMDA receptor antagonistic effect of the crude ethanolic extracts of these two South African medicinal plants was demonstrated.

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.

Layer I ectopias and increased excitability in murine neocortex.

Cortical dysplasias are associated with both epilepsy and cognitive impairments in humans. Similarly, several animal models of cortical dysplasia show that dysplasia causes increased seizure susceptibility and behavioral deficits in vivo and increased levels of excitability in vitro. As most current animal models involve either global disruptions in cortical architecture or the induction of lesions, it is not yet clear whether small spontaneous neocortical malformations are also associated with increased excitability or seizure susceptibility. Small groups of displaced neurons in layer I of the neocortex, ectopias, have been identified in patients with cognitive impairments, and similar malformations occur sporadically in some inbred lines of mice where they are associated with behavioral and sensory-processing deficits. In a previous study, we characterized the physiology of cells within neocortical ectopias, in one of the inbred lines (NXSM-D/Ei) and showed that the presence of multiple ectopias is associated with the generation of spontaneous epileptiform activity in slices. In this study, we use extracellular recordings from brain slices to show that even single-layer I ectopias are associated with higher excitability. Specifically, slices that contain single ectopias display epileptiform activity at significantly lower concentrations of the GABA(A) receptor antagonist bicuculline than do slices without ectopias (either from opposite hemispheres or animals without ectopias). Moreover, because removal of ectopias from slices does not restore normal excitability, enhanced excitability is not generated within the ectopia. Finally, we show that in vivo, mice with ectopias are more sensitive to the convulsant pentylenetetrazole than are mice without ectopias. Together these results suggest that alterations in cortical hemispheres containing focal layer I malformations increase cortical excitability and that even moderately small spontaneous cortical dysplasias are associated with increased excitability in vitro and in vivo.

Glutamate receptor involvement in dentate granule cell epileptiform activity evoked by mossy fiber stimulation

In many persons with temporal lobe epilepsy, dentate granule cells form an interconnected synaptic network. This recurrent mossy fiber circuit mediates reverberating excitation that may facilitate seizure propagation by synchronizing granule cell discharge. The involvement of specific glutamate receptors in granule cell epileptiform activity evoked by stimulating the mossy fibers was investigated with use of rat hippocampal slices superfused with bicuculline, with or without increasing [K +] o to 6 mM. The occurrence of short-latency mossy fiber-evoked granule cell epileptiform activity in slices from pilocarpine-treated rats correlated with the presence and extent of recurrent mossy fiber growth. Blockade of AMPA receptors nearly abolished the orthodromic component of the response; subsequent antagonism of kainate receptors as well appeared to have no further action. Antagonism of NMDA receptors reduced the duration of epileptiform discharge, but increased the amplitude of population spikes within the evoked burst. Thus AMPA and NMDA, but perhaps not kainate, receptors play an important role in this type of epileptiform activity. Activation of type II metabotropic glutamate receptors, which inhibits the release of glutamate from mossy fiber boutons, reduced the magnitude of epileptiform discharge. This action was reversed by a partial agonist of these receptors. However, neither an agonist nor an antagonist of type III metabotropic glutamate receptors significantly altered the response. Considering the importance of synchronous granule cell discharge for seizure propagation from the entorhinal cortex to the hippocampus, agonists of type II metabotropic glutamate receptors may be useful in suppressing such discharge both experimentally and clinically.

Modest increase in extracellular potassium unmasks effect of recurrent mossy fiber growth.

The recurrent mossy fiber pathway of the dentate gyrus expands dramatically in many persons with temporal lobe epilepsy. The new connections among granule cells provide a novel mechanism of synchronization that could enhance the participation of these cells in seizures. Despite the presence of robust recurrent mossy fiber growth, orthodromic or antidromic activation of granule cells usually does not evoke repetitive discharge. This study tested the ability of modestly elevated [K(+)](o), reduced GABA(A) receptor-mediated inhibition and frequency facilitation to unmask the effect of recurrent excitation. Transverse slices of the caudal hippocampal formation were prepared from pilocarpine-treated rats that either had or had not developed status epilepticus with subsequent recurrent mossy fiber growth. During superfusion with standard medium (3.5 mM K(+)), antidromic stimulation of the mossy fibers evoked epileptiform activity in 14% of slices with recurrent mossy fiber growth. This value increased to approximately 50% when [K(+)](o) was raised to either 4.75 or 6 mM. Addition of bicuculline (3 or 30 microM) to the superfusion medium did not enhance the probability of evoking epileptiform activity but did increase the magnitude of epileptiform discharge if such activity was already present. (2S,2'R,3'R)-2-(2',3'-dicarboxycyclopropyl)glycine (1 microM), which selectively activates type II metabotropic glutamate receptors present on mossy fiber terminals, strongly depressed epileptiform responses. This result implies a critical role for the recurrent mossy fiber pathway. No enhancement of the epileptiform discharge occurred during repetitive antidromic stimulation at frequencies of 0.2, 1, or 10 Hz. In fact, antidromically evoked epileptiform activity became progressively attenuated during a 10-Hz train. Antidromic stimulation of the mossy fibers never evoked epileptiform activity in slices from control rats under any condition tested. These results indicate that even modest changes in [K(+)](o) dramatically affect granule cell epileptiform activity supported by the recurrent mossy fiber pathway. A small increase in [K(+)](o) reduces the amount of recurrent mossy fiber growth required to synchronize granule cell discharge. Block of GABA(A) receptor-mediated inhibition is less efficacious and frequency facilitation may not be a significant factor.

Focal epileptogenesis in a rat model of polymicrogyria.

Polymicrogyria, a developmental cortical malformation associated with epilepsy, can be modeled in rats with a transcortical freeze lesion on the day of birth (P0) or P1. We have used field potential recordings to characterize the incidence, propagation patterns, and distribution of epileptiform activity in slices from rats with experimental microgyri. Interictal-like epileptiform activity was evoked in slices from 85% of freeze-lesioned rats aged P12-P118. These data show age-specific properties of epileptogenesis, including: a delay in onset, a decrease in the incidence of epileptiform activity in rats >P40 that was specific to those lesioned on P0 as opposed to P1, and a shift in the likely site of initiation to areas further from the microgyrus in mature animals. Several observations suggest that the area adjacent to the microgyrus, which appears histologically normal in Nissl stains, contains the necessary epileptogenic neuronal circuits: 1) in 78% of slices, epileptiform activity could be evoked only from a focal zone adjacent to the microgyrus (paramicrogyral zone) and not within the microgyrus proper; 2) epileptiform activity consistently originated from a particular site within this paramicrogyral zone, independent of the location of the stimulating electrode, suggesting that the generator is outside of the microgyrus; 3) evoked epileptiform activities in the paramicrogyral cortex were unaltered after separation of this zone from the microgyrus with a transcortical cut; and 4) the short-latency graded field potential evoked in the paramicrogyral zone contained an additional negativity not seen in control slices. The epileptiform activity was blocked reversibly by N-methyl--aspartate receptor antagonists in slices from mature as well as immature freeze-lesioned rats. These results suggest that aberrant synaptic connectivity develops in rat cortex surrounding the microgyrus and produces a focal epileptogenic zone whose capacity to generate epileptiform activities does not depend on connections with the malformation itself. We hypothesize that afferents, originating from cortical and extracortical sites, lose their targets in the region of the malformation and make appropriate laminar contacts in the cortex adjacent to the malformation, creating an overabundance of excitatory input to this cortical zone. Increased excitatory feedback onto specific cortical elements may be one factor involved in epileptogenesis in this model of a cortical malformation.

Voltage imaging of epileptiform activity in slices from rat piriform cortex: onset and propagation.

The piriform cortex is a temporal lobe structure with a very high seizure susceptibility. To investigate the spatiotemporal characteristics of epileptiform activity, slices of piriform cortex were examined by imaging electrical activity with a voltage-sensitive fluorescent dye. Discharge activity was studied for different sites of stimulation and different planes of slicing along the anterior-posterior axis. Epileptiform behavior was elicited either by disinhibition with a gamma-aminobutyric acid-A receptor antagonist or by induction with a transient period of spontaneous bursting in low-chloride medium. Control activity recorded with fluorescent dye had the same pharmacological and temporal characteristics as control activity reported previously with microelectrodes. Simultaneous optical and extracellular microelectrode recordings of epileptiform discharges showed the same duration, latency, and all-or-none character as described previously with microelectrodes. Under all conditions examined, threshold electrical stimulation applied throughout the piriform cortex evoked all-or-none epileptiform discharges originating in a site that included the endopiriform nucleus, a previously identified site of discharge onset. In induced slices, but not disinhibited slices, the site of onset also included layer VI of the adjoining agranular insular cortex and perirhinal cortex, in slices from anterior and posterior piriform cortex, respectively. These locations had not been identified previously as sites of discharge onset. Thus like the endopiriform nucleus, the deep agranular insular cortex and perirhinal cortex have a very low seizure threshold. Additional subtle differences were noted between the induced and disinhibited models of epileptogenesis. Velocity was determined for discharges after onset, as they propagated outward to the overlying piriform cortex. Propagation in other directions was examined as well. In most cases, velocities were below that for action potential conduction, suggesting that recurrent excitation and/or ephaptic interactions play a role in discharge propagation. Future investigations of the cellular and organizational properties of regions identified in this study should help clarify the neurobiological basis of high seizure susceptibility.

Spatio-temporal distribution of epileptiform activity in slices from human neocortex: recordings with voltage-sensitive dyes.

The spatio-temporal distribution of epileptiform activity was investigated in slices from human temporal neocortex resected during epilepsy surgery. Activity was recorded by use of a voltage-sensitive dye and an optical recording system. Epileptiform activity was induced with 10 microM bicuculline and electrical stimulation of layer I. In 10 slices from six patients investigated, epileptiform activity spread across most of the slice. Largest amplitudes were located in layer II/III. Epileptiform activity was characterized by long-lasting potentials with slow rising phases and a low velocity of spread in the horizontal direction (0.044 m/s). This spatio-temporal pattern of epileptiform activity in human slices was similar to that found previously in neocortical slices from guinea pigs with bicuculline. In four of nine human slices investigated under control bath conditions (in non-epileptogenic medium), the spatio-temporal activity patterns were similar to those of guinea pigs in non-epileptogenic medium. In the remaining five human slices, however, the spread in the horizontal direction was significantly larger (4188 microm) in non-epileptogenic medium than that found in slices from guinea pigs (2171 microm). Activity in human slices showing such 'wide spread' in control bath conditions occasionally had characteristic features of epileptiform activity. Further work will have to clarify whether these epileptiform features reflect intrinsic epileptiform properties in human tissue slices.

Changes in voltage‐operated calcium channels modify ethanol withdrawal hyperexcitability in mouse hippocampal slices

Measurements of hippocampal excitability were made from area CA1 of isolated mouse hippocampal slices, prepared after chronic ethanol treatment in vivo, and the effects of the stereoisomers of the dihydropyridine Bay K 8644, that act at calcium channels, were investigated. The decrease in the threshold stimulation required to produce a single population spike, the leftward shift in the population spike input-output curves, and the increase in population spike amplitude, that were seen during ethanol withdrawal, were all increased by the (-) isomer of Bay K 8644. This isomer has been shown to increase opening of calcium channels. These effects of ethanol withdrawal were decreased by the (+) isomer of Bay K 8644, that is a calcium channel blocker. In contrast, the increase in paired-pulse potentiation of the population spike, seen during the initial phase of ethanol withdrawal, was significantly decreased by both isomers of Bay K 8644. After the chronic ethanol treatment, single orthodromic stimuli produced epileptiform field potentials, consisting of two independent phases, a short latency series of multiple population spikes, superimposed upon the initial observed EPSP, and a longer latency train of spikes, occurring on a second EPSP, temporally distinct from the first. The (-) isomer of Bay K 8644 increased both these phases of epileptiform activity during ethanol withdrawal in a dose-dependent manner, while (+)-Bay K 8644 reduced the initial phase of multiple spiking and abolished the later phase. In slices from control animals, the higher concentration of (-)-Bay K 8644 (2 microM), but not the lower concentration (500 nM) decreased the stimulation required to produce multiple population spikes. Neither produced the long latency epileptiform activity. The (+) isomer of Bay K 8644 had no effect on control recordings. Lesioning the Schaffer collateral-commissural fibre pathway, or removing area CA3, in slices from ethanol-treated animals, abolished the later phase of epileptiform activity without affecting the initial multiple spiking. Intracellular recordings from area CA1 showed both the short latency and the longer latency epileptiform activities in slices from ethanol-treated mice and in control hippocampal slices after application of the (-) isomer of Bay K 8644, but these patterns of activity were not seen in control slices in the absence of Bay K 8644. Spontaneous activity during ethanol withdrawal was seen in intracellular recordings, but such activity was not seen in the field potential recordings.(ABSTRACT TRUNCATED AT 400 WORDS)

Local synaptic circuits and epileptiform activity in slices of neocortex from children with intractable epilepsy.

1. Single and dual intracellular recordings were performed in neocortical slices obtained from tissue samples surgically removed from children (8 mo to 15 yr) for the treatment of intractable epilepsy. Electrical stimulation and glutamate microapplication were used to study local synaptic inputs to pyramidal cells. 2. In recordings with potassium-acetate electrodes, activation of presynaptic neocortical neurons with glutamate microdrops did not elicit a clear increase in postsynaptic potentials (PSPs) but did suppress current-evoked repetitive spike firing in recorded neurons. Bicuculline (10 microM) blocked this effect, suggesting it was caused by the activation of presynaptic gamma-aminobutyric acid (GABA) cells. In recordings with KCl electrodes, glutamate microdrops elicited an increase in the frequency and amplitude of depolarizing PSPs. Bicuculline (5-10 microM) blocked the glutamate-evoked PSPs, suggesting they were reversed GABAA-receptor-mediated inhibitory postsynaptic potentials (IPSPs). In one cell recorded with a KCl electrode (total n = 8), current-evoked spike trains elicited afterdischarges of reversed IPSPs, thus revealing a recurrent inhibitory circuit. Therefore local inhibitory synaptic circuits were robust and could be observed in tissue from patients as young as 11 mo. 3. In addition to short-latency (10-25 ms), monosynaptic excitatory postsynaptic potentials (EPSPs), electrical stimulation at low intensities sometimes elicited delayed EPSPs (20-60 ms). When GABAA-receptor-mediated synaptic inhibition was partially reduced in bicuculline (5-10 microM), electrical stimulation evoked large EPSPs at long and variable latencies (100-300 ms). Glutamate microapplication caused an increase in the frequency and amplitude of EPSPs; preliminary results suggest that glutamate microdrops were less likely to evoke EPSPs in tissue from younger patients (8-12 mo) than in slices from patients greater than 4 yr. Evidence for local excitatory synaptic circuits was thus found when synaptic inhibition was partially reduced. 4. After further reduction of inhibition in bicuculline (5-50 microM), electrical stimulation elicited epileptiform bursts. In pairs of simultaneously recorded neurons, bursts were generated synchronously from long-latency EPSPs (100-300 ms) in slices from patients as young as 8 mo. Reflected EPSPs at very long and variable latencies (500-1,100 ms) and repetitive epileptiform bursts could be evoked synchronously in pairs of cells. Glutamate activation of local presynaptic neurons elicited robust epileptiform events in recorded cells. This was seen in slices from patients as young as 16 mo. 5. These data provide physiological evidence for the presence of local inhibitory and excitatory synaptic circuits in human neocortex at least as early as 11 and 8 mo, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)

Afterpotential generation in hippocampal pyramidal cells.

Afterpotential generation in hippocampal pyramidal cells.R K Wong, and D A PrinceR K Wong, and D A PrincePublished Online:01 Jan 1981https://doi.org/10.1152/jn.1981.45.1.86MoreSectionsPDF (2 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformation Cited ByThe Role of Canonical Transient Receptor Potential Channels in Seizure and Excitotoxicity9 April 2014 | Cells, Vol. 3, No. 2Recruiting Extrasynaptic NMDA Receptors Augments Synaptic SignalingAlexander Z. Harris, and Diana L. 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Miller1 October 2006 | Journal of Neurophysiology, Vol. 96, No. 4Sodium-activated potassium conductance participates in the depolarizing afterpotential following a single action potential in rat hippocampal CA1 pyramidal cellsBrain Research, Vol. 1023, No. 2Analysis of the influence of differences in somatic symmetry and sharpness on the firing rateNeurocomputing, Vol. 58-60Pacemaker potentials are the physiologic basis of epileptiform activity in the buccal ganglia of Helix pomatiaActa Biologica Hungarica, Vol. 55, No. 1-4Post-spike distance-to-threshold trajectories of neurones in monkey motor cortex9 March 2004 | The Journal of Physiology, Vol. 555, No. 3Modulation of afterpotentials and firing pattern in guinea pig CA3 neurones by group I metabotropic glutamate receptors12 January 2004 | The Journal of Physiology, Vol. 554, No. 2Different types of bursting calcium oscillations in non-excitable cellsChaos, Solitons & Fractals, Vol. 18, No. 4Endogenous pacemaker potentials develop into paroxysmal depolarization shifts (PDSs) with application of an epileptogenic drugBrain Research, Vol. 975, No. 1-2The influence of neuron shape changes on the firing characteristicsNeurocomputing, Vol. 52-54Intrinsic Bursting Alone Does Not Beget SeizuresEpilepsy Currents, Vol. 3, No. 1A new bursting model of CA3 pyramidal cell physiology suggests multiple locations for spike initiationBiosystems, Vol. 67, No. 1-3Long-lasting modification of intrinsic discharge properties in subicular neurons following status epilepticus9 August 2002 | European Journal of Neuroscience, Vol. 16, No. 2Temporal Interaction between Single Spikes and Complex Spike Bursts in Hippocampal Pyramidal CellsNeuron, Vol. 32, No. 1Ionic Mechanisms Underlying Burst Firing of Layer III Sensorimotor Cortical Neurons of the Cat: An In Vitro Slice StudyYoshihiro Nishimura, Masaru Asahi, Koichi Saitoh, Hirofumi Kitagawa, Yuichi Kumazawa, Kunio Itoh, Min Lin, Takanobu Akamine, Hiroshi Shibuya, Toshihiro Asahara, and Tetsuro Yamamoto1 August 2001 | Journal of Neurophysiology, Vol. 86, No. 2Electrophysiological Characterization of “Giant” Cells in Stratum Radiatum of the CA3 Hippocampal RegionNataša Savić, and Marina Sciancalepore1 May 2001 | Journal of Neurophysiology, Vol. 85, No. 5Seizure-like activity in the disinhibited CA1 minislice of adult guinea-pigs5 August 2004 | The Journal of Physiology, Vol. 532, No. 3Initiation of network bursts by Ca 2+ -dependent intrinsic bursting in the rat pilocarpine model of temporal lobe epilepsy5 August 2004 | The Journal of Physiology, Vol. 532, No. 1Suppression of epileptiform activity by high frequency sinusoidal fields in rat hippocampal slices5 August 2004 | The Journal of Physiology, Vol. 531, No. 1Dendritic Voltage-Gated Ion Channels Regulate the Action Potential Firing Mode of Hippocampal CA1 Pyramidal NeuronsJeffrey C. Magee, and Michael Carruth1 October 1999 | Journal of Neurophysiology, Vol. 82, No. 4Protein kinase C mediates muscarinic block of intrinsic bursting in rat hippocampal neurons8 September 2004 | The Journal of Physiology, Vol. 518, No. 1Voltage Imaging of Epileptiform Activity in Slices From Rat Piriform Cortex: Onset and PropagationRezan Demir, Lewis B. Haberly, and Meyer B. Jackson1 November 1998 | Journal of Neurophysiology, Vol. 80, No. 5Characterization of Carbachol-Induced Rhythmic Bursting Discharges in Neurons From Guinea Pig Lateral Septum SlicesBernard Carette1 September 1998 | Journal of Neurophysiology, Vol. 80, No. 3Analysis of a Class of Models of Bursting Electrical Activity in Pancreatic $\beta$-CellsSIAM Journal on Applied Mathematics, Vol. 58, No. 2Low-Voltage Activated T-Type Calcium Currents Are Differently Expressed in Superficial and Deep Layers of Guinea PigPiriform CortexJacopo Magistretti, and Marco de Curtis1 February 1998 | Journal of Neurophysiology, Vol. 79, No. 2Reduced outward K + conductances generate depolarizing after-potentials in rat supraoptic nucleus neurones30 September 2004 | The Journal of Physiology, Vol. 505, No. 1Spatiotemporal patterns of γ frequency oscillations tetanically induced in the rat hippocampal slice30 September 2004 | The Journal of Physiology, Vol. 502, No. 3Modulation of endogenous firing patterns 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No. 4The central nucleus of the rat amygdala: in vitro intracellular recordingsBrain Research, Vol. 604, No. 1-2Electrophysiology and burst-firing of rat subicular pyramidal neurons in vitro: a comparison with area CA1Brain Research, Vol. 600, No. 1Adenosine modulation of potassium currents in preganglionic nerve terminals of avian ciliary gangliaNeuroscience Letters, Vol. 137, No. 1Functional organization of the hippocampal CA3 region: implications for epilepsy, brain waves and spatial behaviour9 July 2009 | Network: Computation in Neural Systems, Vol. 3, No. 4Reopening of Ca2+ channels in mouse cerebellar neurons at resting membrane potentials during Recovery from InactivationNeuron, Vol. 7, No. 5Kindling-induced persistent alterations in the membrane and synaptic properties of CA1 pyramidal neuronsBrain Research, Vol. 561, No. 2Afterpotential characteristics and firing patterns in maturing rat hippocampal CA1 neurones in in vitro slicesDevelopmental Brain Research, Vol. 62, No. 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staggerer mutant miceBrain Research, Vol. 311, No. 1Synchronized afterdischarges in the hippocampus: Simulation studies of the cellular mechanismNeuroscience, Vol. 12, No. 4Intracellular recordings from rat dorsolateral septal neurons, in vitroBrain Research, Vol. 305, No. 2Excitatory projection of the rat subicular complex to the cingulate cortex and synaptic integration with thalamic afferentsBrain Research, Vol. 301, No. 1Extracellular fields influence transmembrane potentials and synchronization of hippocampal neuronal activityBrain Research, Vol. 294, No. 2Penicillin-induced epileptogenesis in immature rat CA3 hippocampal pyramidal cellsDevelopmental Brain Research, Vol. 12, No. 2Median raphe- and contralateral hippocampus-elicited EEG spikes which correspond to hyperpolarizations of pyramidal cells in the kindled hippocampus of the rabbitBrain Research, Vol. 278, No. 1-2Biochemical and immunohistochemical correlates of kindling-induced epilepsy: role of calcium binding proteinBrain Research, Vol. 278, No. 1-2Cellular bases of hippocampal EEG in the behaving ratBrain Research Reviews, Vol. 6, No. 2Hyperpolarization following long-lasting tetanic activation of hippocampal pyramidal cellsBrain Research, Vol. 275, No. 1Cellular and synaptic basis of kainic acid-induced hippocampal epileptiform activityBrain Research, Vol. 273, No. 1Development of calcium action potentials in mouse hippocampal cell culturesDevelopmental Brain Research, Vol. 8, No. 1Prolonged post-tetanic depolarization of frog dorsal root fibersNeuroscience, Vol. 9, No. 1Two types of interictal transients of reversed polarity in rat hippocampus during kindlingElectroencephalography and Clinical Neurophysiology, Vol. 55, No. 3Cellular mechanisms underlying the inhibitory surround of penicillin epileptogenic fociBrain Research, Vol. 261, No. 2Enkephalin inhibition of inhibitory input to CA1 and CA3 pyramidal neurons in the hippocampusBrain Research, Vol. 249, No. 2Cholinergic excitation of mammalian hippocampal pyramidal cellsBrain Research, Vol. 249, No. 2Variations in electrophysiological properties of hippocampal neurons in different subfieldsBrain Research, Vol. 242, No. 2Simulation of intrinsic bursting in CA3 hippocampal neuronsNeuroscience, Vol. 7, No. 5A physiological test for electrotonic coupling between CA1 pyramidal cells in rat hippocampal slicesBrain Research, Vol. 235, No. 2Learning and recall of temporal sequences in the network of CA3 pyramidal cells and a basket cell More from this issue > Volume 45Issue 1January 1981Pages 86-97 https://doi.org/10.1152/jn.1981.45.1.86PubMed6259299History Published online 1 January 1981 Published in print 1 January 1981 Metrics

Spatial divergence and temporal dispersion in primary olfactory nerve of cat.

Spatial divergence and temporal dispersion in primary olfactory nerve of cat.W J FreemanW J FreemanPublished Online:01 Nov 1972https://doi.org/10.1152/jn.1972.35.6.733MoreSectionsPDF (2 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Back to Top Next Download PDF FiguresReferencesRelatedInformationCited ByUltrastructural characteristics and conduction velocity of olfactory receptor neuron axons in the olfactory marker protein-null mouseBrain Research, Vol. 866, No. 1-2Voltage Imaging of Epileptiform Activity in Slices From Rat Piriform Cortex: Onset and PropagationRezan Demir, Lewis B. Haberly, and Meyer B. Jackson1 November 1998 | Journal of Neurophysiology, Vol. 80, No. 5A new method to estimate time delays between EEG signals applied to beta activity of the olfactory cortical areasElectroencephalography and Clinical Neurophysiology, Vol. 73, No. 3Petit mal seizure spikes in olfactory bulb and cortex caused by runaway inhibition after exhaustion of excitationBrain Research Reviews, Vol. 11, No. 3Periglomerular cell action on mitral cells in olfactory bulb shown by current source density analysisBrain Research, Vol. 308, No. 2Modelling compound action potentials of peripheral nerves in situ. I. Model description; evidence for a non-linear relation between fibre diameter and velocityElectroencephalography and Clinical Neurophysiology, Vol. 54, No. 4Slow potentials in the turtle olfactory bulb in response to odor stimulation of the nose and electrical stimulation of the olfactory nerveBrain Research, Vol. 128, No. 3Dispersion along fiber tracts and in the coupling between tracts and a cortical networkComputer Programs in Biomedicine, Vol. 4, No. 4Attenuation of transmission through glomeruli of olfactory bulb on paired shock stimulationBrain Research, Vol. 65, No. 1Relation of glomerular neuronal activity to glomerular transmission attenuationBrain Research, Vol. 65, No. 1Topographic organization of primary olfactory nerve in cat and rabbit as shown by evoked potentialsElectroencephalography and Clinical Neurophysiology, Vol. 36Average transmission distance from mitral-tufted to granule cells in olfactory bulbElectroencephalography and Clinical Neurophysiology, Vol. 36 More from this issue > Volume 35Issue 6November 1972Pages 733-44 https://doi.org/10.1152/jn.1972.35.6.733PubMed4654248History Published online 1 November 1972 Published in print 1 November 1972 Metrics