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Y Ben-Ari

Publications and source records attributed to Y Ben-Ari.

At least 55 records · Page 3Linked to original sources
PubMed1999

Calcium-dependent inactivation of the monosynaptic NMDA EPSCs in rat hippocampal neurons in culture.

The effects of increased dendritic calcium concentration ([Ca2+]i) induced by single action potentials on monosynaptic glutamatergic excitatory postsynaptic currents (EPSCs) were studied in cultured rat hippocampal neurons. To investigate the respective roles of pre- and postsynaptic elements in the depolarization-induced NMDAR inactivation, we have performed simultaneous paired whole-cell recordings from monosynaptically connected pre- and postsynaptic hippocampal neurons. We report that the single firing of the postsynaptic neuron did not result in inactivation of the NMDAR-EPSC, whereas a burst of depolarizing steps transiently depressed the NMDAR-EPSCs in both pyramidal cells and interneurons. This effect was mediated by postsynaptic voltage-gated Ca2+ influx, as it was prevented by: (i) buffering postsynaptic [Ca2+]i with 30 mM BAPTA; (ii) removing extracellular Ca2+; or (iii) applying Cd2+o (100 microM), a voltage-gated calcium channel blocker. It does not involve presynaptic mechanisms as it selectively affected NMDA but not alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptor-mediated EPSCs. These results suggest that inactivation of NMDAR-channels by voltage-gated Ca influx is a general property of hippocampal neurons, which may play an important role in reducing postsynaptic NMDAR Ca2+ influx that leads to plasticity or excitotoxicity during sustained neuronal activity.

Animals↗
PubMed1999

Acidic calponin immunoreactivity in postnatal rat brain and cultures: subcellular localization in growth cones, under the plasma membrane and along actin and glial filaments.

Acidic calponin, an F-actin-binding protein, is particularly enriched in brain, where calponin protein and mRNA are mainly expressed by neurons. The presence of calponin immunoreactivity in cultured astroglial cells has been reported, but the presence of acidic calponin in astrocytes in vivo appears equivocal. For the present study, we raised a specific polyclonal antibody against the 16-residue synthetic peptide covering the sequence E311-Q326 (EYPDEYPREYQYGDDQ) situated at the carboxy-terminal end of rat acidic calponin, and we investigated the cellular and subcellular localization of the protein in the developing central nervous system. Our results show that acidic calponin is particularly enriched in: (i) growth cones and submembranous fields of maturing cerebellar and cortical cells, where it codistributes with microfilaments and (ii) glial cells in vivo, including radial glia, glia limitans, Bergmann glia and mature astrocytes, and ex vivo, where acidic calponin strongly colocalizes with intermediate glial fibrillary acidic protein (GFAP) and vimentin filaments. Finally, up to four acidic calponin subtypes with different isoelectric point (pI) values were identified by two-dimensional gel electrophoresis of cerebellar and hippocampal extracts. The more acidic isoforms were developmentally regulated. As only one single mRNA for acidic calponin has been identified, these isoforms must reflect postsynthesis changes probably related to the particular functions of acidic calponin in maturing cells. Although brain acidic calponin's exact role remains uncertain, the present data suggest that it is involved in neuronal and glial plasticity.

Acids↗
PubMed1999

Maturation of kainate-induced epileptiform activities in interconnected intact neonatal limbic structures in vitro.

In vivo studies suggest that ontogenesis of limbic seizures is determined by the development of the limbic circuit. We have now used the newly-developed in vitro intact interconnected neonatal rat limbic structures preparation to determine the developmental profile of kainate-induced epileptiform activity in the hippocampus and its propagation to other limbic structures. We report gradual alterations in the effects of kainate during the first postnatal week on an almost daily basis; from no epileptiform activity at birth, through interictal seizures around postnatal day (P) 2 and ictal seizures by the end of the first week. The developmental profile of kainate-induced hippocampal seizures is paralleled by the expression of postsynaptic kainate receptor-mediated currents in CA3 pyramidal cells. Intralimbic propagation of the hippocampal seizures is also age-dependent: whereas seizures readily propagate to the septum and to the contralateral hippocampus via the commissures on P2, propagation to the entorhinal cortex only takes place from P4 onwards. Finally, repeated brief applications of kainate to the hippocampus induce recurrent spontaneous glutamatergic ictal and interictal discharges which persist for several hours after the kainate is washed away and which replace the physiological pattern of network activity. Paroxysmal activities are thus generated by kainate in the hippocampus at an early developmental stage and are initially restricted to this structure. Before the end of the first week of postnatal life, kainate generates the epileptiform activities that may perturb activity-dependent mechanisms that modulate neuronal development. Although at this stage neurons are relatively resistant to the pathological effects of kainate, the epileptiform activities that it generates will perturb activity-dependent mechanisms that modulate neuronal development.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1999

Late embryonic expression of AMPA receptor function in the CA1 region of the intact hippocampus in vitro.

Studies in slices suggest that alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor-mediated synaptic currents are not present in CA1 (Cornu ammonis) pyramidal neurons at birth (P0). We have re-examined this issue in the rat intact hippocampal formation (IHF) in vitro. Injections of biocytin or carbocyanine show that the temporo-ammonic, commissural and Schaffer collateral pathways are present at birth in the marginal zone of CA1. Electrical stimulation of these pathways evoked field excitatory postsynaptic potentials (fEPSPs) in the marginal zone of CA1 from embryonic day 19 (E19) to postnatal day 9 (P9). These fEPSPs are mediated by synaptic AMPA receptors as they are reduced or completely blocked by: (i) tetrodotoxin; (ii) high divalent cation concentrations; (iii) the adenosine A1 receptor agonist CPA; (iv) anoxic episodes; (v) the selective AMPA receptor antagonist 1-(4-aminophenyl)-3-methylcarbamyl-4-methyl-7, 8-methylenedioxy-3,4-dihydro-5H-2,3-benzodiazepine (GYKI-53655) or the mixed AMPA-kainate receptor antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and 6-nitro-7-sulphamoylbenzo[f]quinoxaline-2,3-dione (NBQX). The amplitude of the fEPSPs is also reduced by D(-)-2-amino-5-phosphonopentanoic acid (D-APV) and its duration is increased by bicuculline suggesting the participation of N-methyl-D-aspartate (NMDA) and GABAA (gamma-aminobutyric acid) receptors. Finally, AMPA receptor-mediated fEPSPs are also recorded in P0 slices, but they are smaller and more labile than in the IHF. Our results suggest that in embryonic CA1 neurons, glutamate acting on AMPA receptors already provides a substantial part of the excitatory drive and may play an important role in the activity-dependent development of the hippocampus. Furthermore, the IHF may be a convenient preparation to investigate the properties of the developing hippocampus.

2-Amino-5-phosphonovalerate↗
PubMed1999

Cortical malformations and epilepsy: new insights from animal models.

In the last decade, the recognition of the high frequency of cortical malformations among patients with epilepsy especially children, has led to a renewed interest in the study of the pathophysiology of cortical development. This field has also been spurred by the recent development of several experimental genetic and non-genetic, primarily rodent, models of cortical malformations. Epileptiform activity in these animals can appear as spontaneous seizure activity in vivo, in vitro hyperexcitability, or reduced seizure susceptibility in vitro and in vivo. In the neonatal freeze lesion model, that mimics human microgyria, hyperexcitability is caused by a reorganization of the network in the borders of the malformation. In the prenatal methylazoxymethanol model, that causes a diffuse cortical malformation, hyperexcitability is associated with alteration of firing properties of discrete neuronal subpopulations together with the formation of bridges between normally unconnected structures. In agreement with clinical evidence, these experimental data suggest that cortical malformations can both form epileptogenic foci and alter brain development in a manner that causes a diffuse hyperexcitability of the cortical network.

Abnormalities, Drug-Induced↗
PubMed1999

Consequences of cortical dysplasia during development in rats.

PURPOSE: To determine whether focal cortical dysplasia alters excitability in regions distant to the region of the dysplasia. METHODS: We studied the physiological consequences of cortical dysplasia induced by either one or three freeze lesions at birth. Seizure susceptibility was assessed at age 35 days by amygdala kindling. c-fos immunostaining was performed after kainic acid-induced seizures at 10, 20, or 30 days to evaluate the patterns of neuronal activation. RESULTS: Freeze lesions consistently produced uniform regions of dysplasia. No significant differences in seizure susceptibility, as measured by afterdischarge threshold and kindling rate, were seen between controls and rats receiving either one or three freeze lesions. c-fos activation after kainic acid injection was not observed in the region of the dysplasia. However, rats with freeze lesions at age 30 days demonstrated asymmetric c-fos staining with greater staining in CA1 ipsilateral, than contralateral, to the lesion. CONCLUSIONS: Focal cortical dysplasia results in enhancement of c-fos activation in regions outside the borders of the dysplasia. However, as indicated by kindling rate, the functional consequences of these alterations do not appear to be robust.

Amygdala↗
PubMed1999

Three-independent-compartment chamber to study in vitro commissural synapses.

We describe a novel chamber in which the two intact neonatal rat hippocampi and the commissural fibers are placed in three independent compartments separated by latex membranes and perfused selectively with different solutions. A set of control tests showed that the compartments are well isolated: 1) methylene blue or eosin applied to one compartment did not diffuse to other compartments when verified via the microscope, and spectrophotometry revealed that <1/10.000th of the dye diffuses to other compartments; 2) tetrodotoxin (1 microM) applied to the commissural compartment blocked the synaptic responses evoked contralaterally without affecting those evoked on the ipsilateral side. This chamber enables a wide range of experiments that cannot be performed in conventional chambers, e.g., to study the maturation and plasticity of the commissural connections, bilateral synchronization of the rhythmic activities in the limbic system, commissural propagation of the epileptiform activities, etc.

Animals↗
PubMed1999

Dual role of GABA in the neonatal rat hippocampus.

The effects of modulators of GABA-A receptors on neuronal network activity were studied in the neonatal (postnatal days 0-5) rat hippocampus in vitro. Under control conditions, the physiological pattern of activity of the neonatal hippocampal network was characterized by spontaneous network-driven giant depolarizing potentials (GDPs). The GABA-A receptor agonist isoguvacine (1-2 microM) and the allosteric modulator diazepam (2 microM) induced biphasic responses: initially the frequency of GDPs increased 3 to 4 fold followed by blockade of GDPs and desynchronization of the network activity. The GABA-A receptor antagonists bicuculline (10 microM) and picrotoxin (100 microM) blocked GDPs and induced glutamate (AMPA and NMDA)-receptor-mediated interictal- and ictal-like activities in the hippocampal slices and the intact hippocampus. These data suggest that at early postnatal ages GABA can exert a dual - both excitatory and inhibitory - action on the network activity.

Animals↗
PubMed1999

Abnormal connections in the malformed cortex of rats with prenatal treatment with methylazoxymethanol may support hyperexcitability.

Prenatal treatment with methylazoxymethanol (MAM) in rats generates animals with a diffuse cortical malformation associated with hyperexcitability. These alterations are reminiscent of the cortical malformations associated with epilepsy in children. We hypothesised that one of the mechanisms supporting hyperexcitability in MAM rats could be the presence of abnormal cortical connections in the malformed cortex. Using a variety of anatomical techniques, we provide evidences for three types of such abnormal connections: (i) tangential bundles of corticocortical fibres in and below the neocortical molecular layer; (ii) partial deafferentation of neocortical heterotopias by afferent cortical fibres whatever their location; (iii) exuberant innervation of hippocampal CA3 pyramidal cells by mossy fibres that form ectopic mossy boutons on their basal dendrites. We conclude that these abnormal intrinsic cortical connections may support the propagation of paroxymal activity in the neocortex of MAM-treated rats.

Abnormalities, Drug-Induced↗
PubMed1999

Inflammatory responses in the cerebral cortex after ischemia in the P7 neonatal Rat.

BACKGROUND AND PURPOSE: The contribution of inflammatory response to the pathogenesis of ischemic lesions in the neonate is still uncertain. This study described the chronological sequence of inflammatory changes that follow cerebral ischemia with reperfusion in the neonatal P7 rat. METHODS: P7 rats underwent left middle cerebral artery electrocoagulation associated with 1-hour left common carotid artery occlusion. The spatiotemporal pattern of cellular responses was characterized immunocytochemically with the use of antibodies against rat endogenous immunoglobulins to visualize the area of the breakdown of the blood-brain barrier. Infiltration of neutrophils and T lymphocytes was demonstrated by antibodies against myeloperoxidase and a pan-T cell marker, respectively. Antibodies ED1 and OX-42 were applied to identify microglial cells and macrophages. The response of astrocytes was shown with antibodies against glial fibrillary acidic protein. Cell survival was assessed by Bcl-2 expression. Cell death was demonstrated by DNA fragmentation with the use of the terminal deoxynucleotidyl transferase-mediated dUTP biotin nick end labeling (TUNEL) assay and Bax immunodetection. RESULTS: Endogenous immunoglobulin extravasation through the blood-brain barrier occurred at 2 hours of recirculation and persisted until 1 month after ischemia. Neutrophil infiltration began at 24 hours and peaked at 72 to 96 hours (30+/-3.4 neutrophils per 0.3 mm(2); P<0.0001), then disappeared at 14 days after ischemia. T cells were observed between 24 and 96 hours of reperfusion. Resident microglia-macrophages exhibited morphological remnants and expressed the cell death inhibitor Bcl-2 at 24 hours of recirculation. They became numerous within the next 48 hours and peaked at 7 days after ischemia. Phenotypic changes of resident astrocytes were apparent at 24 hours, and they proliferated between 48 hours and 7 days after ischemia. Progressively inflammatory cells showed DNA fragmentation and the cell death activator Bax expression. Cell elimination continued until there was a complete disappearance of the frontoparietal cortex. CONCLUSIONS: These data demonstrate that perinatal ischemia with reperfusion triggers acute inflammatory responses with granulocytic cell infiltration, which may be involved in accelerating the destructive processes.

Animals↗
PubMed1999

Epileptogenic action of caffeine during anoxia in the neonatal rat hippocampus.

Excessive maternal caffeine consumption can lead to fetal and neonatal pathology, but the underlying mechanisms have not been determined. Here, we report that low doses of caffeine generate seizures when applied in conjunction with brief anoxic episodes in the hippocampus of neonatal rats in vitro. In control conditions, brief (4-6 minutes) anoxic episodes reversibly depressed evoked synaptic responses and blocked the physiological pattern of network activity. In the presence of caffeine (50 microM), similar anoxic episodes generated ictal (29%) or interictal (33%) epileptiform activities often followed during reoxygenation by recurrent spontaneous seizure activity that persisted for several hours. These effects are likely mediated by a blockade of adenosine receptors by caffeine because (1) in control conditions, caffeine antagonized the inhibitory effect of selective A1 receptor agonist N6-cyclopentyladenosine on excitatory synaptic responses, and (2) epileptogenic effects of caffeine were reproduced by selective A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine and theophylline. Our findings suggest that endogenous adenosine released during anoxia acting via A1 receptors prevents seizures in the neonatal hippocampus and that the antagonism of these receptors by caffeine leads to epileptogenesis. This study suggests concerns about the safety of caffeine in the fetus and newborn.

Action Potentials↗
PubMed1999

GABA is the principal fast-acting excitatory transmitter in the neonatal brain.

gamma-aminobutyric acid (GABA) is the principal neurotransmitter of inhibition in the adult mammalian brain. However, at early stages of development, including the embryonic period and first week of postnatal life, GABA plays the role of main neurotransmitter of excitation. The paradoxical excitatory effect of GABA is caused by an inverted chloride gradient and, therefore, a depolarizing direction of GABA type A (GABAA) receptor mediated responses. In addition, another type of GABAergic inhibition mediated by postsynaptic GABA type B (GABAB) receptors is not functional at early stage of life. In the neonatal rat hippocampus, GABA, acting via GABAA receptors, activates voltage-gated sodium and calcium channels and potentiates the activity of N-methyl-D-aspartate (NMDA) receptors by reducing their voltage-dependent Mg2+ block. The temporal window when GABA exerts excitatory actions coincides with a particular pattern of activity of hippocampal neuronal network that is characterized by periodical giant depolarizing potentials (GDPs) reminiscent of interictal-like epileptiform discharges. Recent studies have shown that GDPs result from the synchronous discharge of GABAergic interneurons and principal glutamatergic pyramidal cells, and they are mediated by the synergistic excitatory actions of GABAA and glutamate receptors. GDPs provide synchronous intracellular Ca2+ oscillations and may, therefore, be implicated in hebbian modulation of developing synapses and activity-dependent formation of the hippocampal network.

Animals↗
PubMed1998

Decreased seizure threshold and more rapid rate of kindling in rats with cortical malformation induced by prenatal treatment with methylazoxymethanol.

In humans, cortical malformations are highly epileptogenic. In rats, prenatal treatment with methylazoxymethanol (MAM) cause a diffuse cortical malformation that is yet not associated with seizures. We performed rapid hippocampal kindling in MAM and control rats. We show that MAM rats present (i) a lower initial afterdischarge threshold; (ii) a more rapid progression to generalized seizures. We conclude that MAM rats may serve as models for human epileptogenic cortical malformations.

Abnormalities, Drug-Induced↗
PubMed1998

Neuronal migration disorders: heterotopic neocortical neurons in CA1 provide a bridge between the hippocampus and the neocortex.

Neuronal migration disorders have been involved in various pathologies, including epilepsy, but the properties of the neural networks underlying disorders have not been determined. In the present study, patch clamp recordings were made from intrahippocampal heterotopic as well as from neocortical and hippocampal neurons from brain slices of rats with prenatally methylazoxymethanol-induced cortical malformation. We report that heterotopic neurons have morphometrical parameters and cellular properties of neocortical supragranular neurons and are integrated in both neocortical and hippocampal networks. Thus, stimulation of the white matter induces both antidromic and orthodromic response in heterotopic and neocortical neurons. Stimulation of hippocampal afferents evokes a monosynaptic response in the majority of heterotopic neurons and a polysynaptic all-or-none epileptiform burst in the presence of bicuculline to block gamma-aminobutyric acid type A inhibition. Furthermore, hippocampal paroxysmal activity generated by bath application of bicuculline can spread directly to the neocortex via the heterotopia in methylazoxymethanol-treated but not in naive rats. We conclude that heterotopias form a functional bridge between the limbic system and the neocortex, providing a substrate for pathological conditions.

Action Potentials↗
PubMed1998

Giant depolarizing potentials: the septal pole of the hippocampus paces the activity of the developing intact septohippocampal complex in vitro.

In neonatal hippocampal slices, recurrent spontaneous giant depolarizing potentials (GDPs) provide neuronal synchronized firing and Ca2+ oscillations. To investigate the possible role of GDPs in the synchronization of neuronal activity in intact neonatal limbic structures, we used multiple simultaneous electrophysiological recordings in the recently described preparation of intact neonatal septohippocampal complex in vitro. Combined whole-cell (in single or pairs of cells) and extracellular field recordings (one to five simultaneous recording sites) from the CA3 hippocampal region and various parts of the septum indicated that spontaneous GDPs, which can be initiated anywhere along the longitudinal hippocampal axis, are most often initiated in the septal poles of hippocampus and propagate to medial septum and temporal poles of both hippocampi simultaneously. GDPs were abolished in the medial septum but not in the hippocampus after surgical separation of both structures, suggesting hippocampal origin of GDPs. The preferential septotemporal orientation of GDP propagation observed in the intact hippocampus was associated with a corresponding gradient of GDP frequency in isolated portions of hippocampus. Accordingly, most GDPs propagated in the septotemporal direction in both septal and temporal hippocampal isolated halves, and whereas GDP frequency remained similar in the septal part of hippocampus after its surgical isolation, it progressively decreased in more temporally isolated portions of the hippocampus. Because GDPs provide most of the synaptic drive of neonatal neurons, they may modulate the development of neuronal connections in the immature limbic system.

Animals↗
PubMed1998

Neocortex in the hippocampus: an anatomical and functional study of CA1 heterotopias after prenatal treatment with methylazoxymethanol in rats.

Migration disorders cause neurons to differentiate in an abnormal heterotopic position. Although significant insights have been gained into the etiology of these disorders, very little is known about the anatomy of heterotopias. We have studied heterotopic masses arising in the hippocampal CA1 region after prenatal treatment with methylazoxymethanol (MAM) in rats. Heterotopic cells were phenotypically similar to neocortical supragranular neurons and exhibited the same temporal profile of migration and neurogenesis. However, they did not express molecules characteristic of CA1 neurons such as the limbic-associated membrane protein. Horseradish peroxidase injections in heterotopia demonstrated labeled fibers not only in the neocortex and white matter but also in the CA1 stratum radiatum and stratum lacunosum. To study the pathophysiological consequences of this connectivity, we compared the effects of neocortical and limbic seizures on the expression of Fos protein and on cell death in MAM animals. After metrazol-induced seizures, Fos-positive cells were present in CA1 heterotopias, the only hippocampal region to be activated with the neocortex. By contrast, kainic acid-induced seizures caused a prominent delayed cell death in limbic regions and in CA1 heterotopias. Together, these results suggest that neocortical heterotopias in the CA1 region are integrated in both the hippocampal and neocortical circuitry.

Animals↗
PubMed1998

[Living-related liver transplantation--first experiences at Rabin Medical Center].

Our experience with living-related liver transplantation is described. In 2 boys and 1 girl, aged 4-4.5 years with acute, fulminating hepatitis A, the presence of very severe jaundice (bilirubin levels > 18 mg%) associated with severe coagulopathy (INR > 10) and encephalopathy indicated the need for urgent liver transplantation. In all 3 cases the left lateral hepatic segment of a matched blood type parent was transplanted. None of the donors suffered a serious complication postoperatively and all returned to full activity in 6-16 weeks. The post-transplantation course was uneventful in 1 child, but in the other 2 there was hepatic arterial thrombosis in 1 at 1 day and in the other at 8 days post-transplantation. Early detection of arterial thrombosis by Doppler sonography permitted salvage of the 2 hepatic grafts after thrombectomy and re-anastomosis. In 1 of these 2 children an anastomotic biliary stricture was found 2 months after transplantation. It was corrected at surgery and a percutaneous stent was inserted. All 3 children are alive with normal graft function at 2, 7 and 8 months post-transplantation, respectively. This initial experience indicates that living-related liver transplantation is feasible in Israel. The technique might help to solve our severe organ shortage for children awaiting liver transplantation.

Adult↗