Search PubMed⌕ Search

Biomedical subjects

Y Ben-Ari

Publications and source records attributed to Y Ben-Ari.

At least 109 records · Page 6Linked to original sources
PubMed1997

Blocking GABA(A) inhibition reveals AMPA- and NMDA-receptor-mediated polysynaptic responses in the CA1 region of the rat hippocampus.

We have investigated the conditions required to evoke polysynaptic responses in the isolated CA1 region of hippocampal slices from Wistar adult rats. Experiments were performed with extracellular and whole cell recording techniques. In the presence of bicuculline (10 microM), 6-cyano-7-nitroquinoxaline-2-3-dione (10 microM), glycine (10 microM), and a low external concentration of Mg2+ (0.3 mM), electrical stimulation of the Schaffer collaterals/commissural pathway evoked graded N-methyl-D-aspartate (NMDA)-receptor-mediated late field potentials in the stratum radiatum of the CA1 region. These responses were generated via polysynaptic connections because their latency varied strongly and inversely with the stimulation intensity and they were abolished by a high concentration of divalent cations (7 mM Ca2+). These responses likely were driven by local collateral branches of CA1 pyramidal cell axons because focal application of tetrodotoxin (30 microM) in the stratum oriens strongly reduced the late synaptic component and antidromic stimulation of CA1 pyramidal cells could evoke the polysynaptic response. Current-source density analysis suggested that the polysynaptic response was generated along the proximal part of the apical dendrites of CA1 pyramidal cells (50-150 microm below the pyramidal cell layer in the stratum radiatum). In physiological concentration of Mg2+ (1.3 mM), the pharmacologically isolated NMDA-receptor-mediated polysynaptic response was abolished. In control artificial cerebrospinal fluid (with physiological concentration of Mg2+), bicuculline ( 10 microM) generated a graded polysynaptic response. Under these conditions, this response was mediated both by alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/NMDA receptors. In the presence of D-2-amino-5-phosphonovalerate (50 microM), the polysynaptic response could be mediated by AMPA receptors, although less efficiently. In conclusion, suppression of gamma-aminobutyric acid-A inhibition reveals glutamate receptor-mediated network-driven events in the isolated CA1 region. These polysynaptic responses are mediated by AMPA and/or NMDA receptors depending on the pharmacological conditions and the external concentration of Mg2+ used. We suggest that these responses are driven by local recurrent collaterals of CA1 pyramidal cells.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1997

Molecular and cellular cascades in seizure-induced neosynapse formation.

Limbic seizures induce in vulnerable structures, such as the hippocampal complex, morphologic changes that may contribute to the development of epilepsy. They include neuronal cell death, reactive gliosis, and neosynapse formation. In temporal lobe epilepsy patients, cell death develops in Ammon's horn and the hilus. This cell death involves both necrotic and apoptotic mechanisms and is likely responsible for the initiation of the glial reaction that consists of astroglial and macrophage proliferation and hypertrophy. Reactive astrocytes acquire the phenotypic properties of type 2 astrocytes and express trophic factors (e.g., bFGF), cell adhesion molecules (e.g., NCAM), and substrate molecules (e.g., tenascin-C). Seizures induce in the hippocampus a synaptic remodeling of mossy fibers. Mossy fiber collaterals innervate granule cell dendrites, creating recurrent excitatory circuits. We suggest that collateral branches of MF originate under the influence of trophic factors and as a consequence of an overproduction of tubulin polymers. In fact, seizures induce a transient increased expression of tubulin and microtubule-associated proteins in granule cells and mossy fibers. Navigation of mossy fiber growth cones may be facilitated by the interaction with astrocytes, which would exert this effect by producing and excreting cell adhesion and substrate molecules. In light of the results discussed here, one can suggest that in the adult brain, activated astrocytes could contribute to the process of axonal outgrowth and synaptogenesis.

Animals↗
PubMed1997

[Consequences of recurrent seizures during development].

While many children with recurrent seizures have a good prognosis, a small percentage of children with intractable epilepsy have a more ominous course with a gradual decline in cognitive abilities over time. While the reasons for this cognitive decline may be multifactorial, there is evidence both from human and animal studies that recurrent seizures may lead to gradual cognitive impairment in some children. Laboratory studies have also demonstrated that recurrent seizures can lead to deficits in learning and memory as well as structural changes in the brain. It is important for the clinical to be aware of gradual declines in intelligence that may occur over time.

Animals↗
PubMed1997

[Glutamatergic excitatory receptors and temporal lobe epilepsy].

Despite a considerable wealth of data, the mechanisms responsible for the generation of epileptic bursts in temporal lobe epilepsy (TLE) remain a mystery. Recently, research and therapy have focused on impairment of GABAergic inhibition in epilepsy. Several lines of evidence support this approach: 1-GABA is the main inhibitory neurotransmitter in the neuronal structures involved in TLE. 2-Enhancers of GABAergic inhibition (such as benzodiazepines or barbiturates) are commonly used as antiepileptic drugs. 3-Interictal discharges can be obtained following the pharmacological blockade of GABAA receptors. Since the axiom at the basis of epilepsy research states that the balance between inhibition and excitation is tipped toward excitation, we have addressed the following question: where are the loci most likely to be involved in such imbalance? We have limited our investigation to the excitatory side of the story. The main glutamatergic excitatory receptors (AMPA and NMDA) involved in TLE and their properties will be first addressed. We will focus on the excitatory synapses most likely involved in epileptogenesis. We have then specifically studied the effects of redox reagents on NMDA receptor-dependent epileptiform activity in a chronic animal model of TLE, the kainic acid lesioned rat hippocampus. We report that oxidizing drugs abolish evoked epileptiform discharges via a decrease by 50 p. 100 of NMDA receptor-mediated responses without affecting synaptic plasticity and thus memory and learning. The dormant cell hypothesis (i.e. the disconnection of inhibitory interneurons from their excitatory afferents) was also tested. We report that interneurons are not dormant in TLE and fire bursts of action potentials during spontaneous or evoked paroxismal activity.

Animals↗
PubMed1996

Bidirectional plasticity expressed by GABAergic synapses in the neonatal rat hippocampus.

1. Activity-dependent plasticity of GABAergic synaptic transmission was investigated in neonatal rat hippocampal slices obtained between postnatal day (P) 2-10 using intracellular recording techniques. In all experiments, AMPA receptors were blocked by continual application of CNQX (10 microM). 2. Between P2 and P4, tetanic stimulation (TS) evoked NMDA receptor-dependent long-term depression of monosynaptic GABAA EPSPS (LTDGABAA). In contrast, when NMDA receptors were blocked by D-AP5 (50 microM), the same TS evoke long-term potentiation of GABAA EPSPS (LTPGABAA). 3. Between P6 and P10, TS failed to produce either LTP or LTD or hyperpolarizing monosynaptic GABAA IPSPS under the same recording conditions. However, when GABAergic potentials were rendered depolarizing (KCl-filled electrode) Ts induced either LTPGABAA or LTDGABAA in the presence or absence of D-AP5, respectively. 4. Both LTPGABAA and LTDGABAA were specific to the conditioned pathway and could be sequentially expressed at the same synapses. Potentiation of GABAergic synaptic efficacy was induced more easily following previous induction of LTDGABAA than in naive slices. 5. In conclusion, early in development, bidirectional synaptic plasticity is expressed by GABAA receptors and the activation (or not) of NMDA receptors determines the induction of either LTPGABAA or LTDGABAA.

Animals↗
PubMed1996

NG-nitro-L-arginine methyl ester reduces necrotic but not apoptotic cell death induced by reversible focal ischemia in rat.

During cerebral ischemia, nitric oxide (NO) production via stimulation of NO synthase, is likely one of the major events leading to neuronal death. Recently, we have demonstrated that after reversible focal ischemia, apoptosis was implicated in the penumbra whereas necrosis was prominent in the ischemic core. We have now examined the effect of a non-specific inhibitor of NO synthase, NG-nitro-L-arginine methyl ester (L-NAME, 3 ing kg-1 i.p., 5 min and 3 h after the onset of ischemia), on the progress of apoptotic and necrotic nuclei following transient focal cerebral ischemia, using DNA electrophoresis and terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick-end labeling (TUNEL assay). Our results indicated that L-NAME prevented the loss of necrotic, but not apoptotic cells.

Animals↗
PubMed1996

Redox sites of NMDA receptors can modulate epileptiform activity in hippocampal slices from kainic acid-treated rats.

Using an animal model of temporal lobe epilepsy, the kainic acid lesioned rat hippocampus, we have evaluated the possibility of modulating glutamate N-methyl-D-aspartate (NMDA) receptor-dependent evoked epileptiform activity through the manipulation of NMDA receptor redox sites. Epileptiform activity was recorded extracellularly from hippocampal slices, in the stratum pyramidale of the CA1 area, and the effects of the oxidizing reagent 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB) and the reducing agent Tris(2-carboxy ethyl)phosphine (TCEP) on these responses were quantified. Epileptiform activity was substantially reduced in the presence of DTNB but was fully reinstated with the application of TCEP. The effects of both drugs persisted even after wash. Epileptiform activity was totally abolished in the presence of the NMDA receptor antagonist D-2-amino-5-phosphonovaleric acid. These results suggest that epileptiform activity can be controlled by manipulation of the redox sites of NMDA receptors and raise the possibility of developing new anticonvulsant drugs which do not fully block NMDA receptor-mediated synaptic transmission.

Animals↗
PubMed1996

The HIV-1 envelope protein gp120 induces neuronal apoptosis in hippocampal slices.

The HIV-1 envelope protein gp120 produces neuronal cell damage in primary cultures of a variety of cell types including hippocampal and retinal ganglion cell neurons. The properties of primary cell cultures are, however, often markedly different from those of cells living in their normal environment. We now report that gp120 induces widespread chromatin condensation and lesions in pyramidal granular neurones and in interneurones of rat hippocampal organotypic slice cultures. This damage is clearly of an apoptotic (programmed cell death) type. The use of an in vitro organized structure will enable the molecular and cellular mechanism of action of gp120 to be examined in conditions which are particularly suitable and relevant to the in vivo situation.

Animals↗
PubMed1996

Reactive glial cells express a vitronectin-like protein in the hippocampus of epileptic rats.

Injection of kainic acid into the amygdala induces in addition to a local cell loss a seizure related distal damage of the hippocampal complex, in particular in the CA3 field and hilus. This neuronal lesion is associated with hypertrophy and proliferation of astroglial cells which start around 3 days after kainate and peaks within 20 days of kainate. We now report that reactive astrocytes are labelled with antibodies against vitronectin in the CA3 field and hilus. In the present study we also exclude that the presence of vitronectin into the brain is due to an extravasation from serum throughout a blood brain barrier leakage. The present results constitute the first demonstration for a glial expression of vitronectin in vivo. Vitronectin is an extracellular matrix glycoprotein involved in axonal growth. The glial expression of vitronectin may therefore contribute to the synaptic remodeling of mossy fibers induced in the hippocampus by such treatment.

Amygdala↗
PubMed1996

Use of two-dimensional gel electrophoresis to characterize protein synthesis during neuronal death in cerebellar culture.

Two-dimensional gel electrophoresis was performed to further investigate the biochemical changes in protein synthesis observed in two neuronal death models, induced respectively by cytosine arabinoside and glutamate. These drugs induced, respectively, apoptotic and necrotic types of cell death in cerebellar cultures, as previously reported. Most of the proteins showed decreased labeling after toxic exposure, as expected, but some polypeptides showed increased labeling or appeared to be newly synthesized. The identification of these polypeptides and their implication in neuronal death are discussed.

Animals↗
PubMed1996

Transient increase of tenascin-C in immature hippocampus: astroglial and neuronal expression.

In the present report we describe the anatomical localization of cells expressing tenascin-C, an extracellular matrix glycoprotein, in the hippocampal complex of developing rats. We report a development-dependent down regulation of both tenascin-C protein and mRNA. The highest levels of expression of tenascin-C was observed in rat pups from embryonic day 18 to postnatal day 7. Double labelling experiments performed with a tenascin-C antibody or tenascin-C probes combined with specific markers of astrocytes (GFAP) or neurons (MAP2 and Tau) allowed us to demonstrate that tenascin-C is expressed by both immature astrocytes and neurons in immature hippocampus. The temporal and topographic distribution of cells expressing tenascin-C (in the hilus and the stratum oriens of CA3) correlate with the localization and period of migration and maturation of post-mitotic cells. In view of these data we discuss the hypothesis that tenascin-C, as a mediator of neuron-glia interactions, may contribute to the development of hippocampal cells.

Animals↗
PubMed1996

Seizures induce tenascin-C mRNA expression in neurons.

Tenascin-C, an extracellular matrix glycoprotein that exhibits both growth-promoting and growth-inhibiting properties, is produced in the CNS mainly by astrocytes. In the present study we show that kainate-induced seizures result in an increased expression of tenascin-C in rat brain. Tenascin-C mRNA was increased mainly in the granule cell layer of the hippocampal complex, but tenascin-C mRNA expression was also observed in the pyriform cortex and amygdalo-cortical nucleus. Double labelling experiments using tenascin-C probes and MAP2 (a neuronal microtubule associated protein) antibodies revealed many neurons in these layers that express tenascin-C mRNA. These results support our previous findings of an increased tenascin-C immunoreactivity associated with the axons of granule cells. Tenascin-C expression is rapidly induced by seizures (6 h), preceding any lesion and glial reaction. In this pathological condition tenascin-C appears to be produced by both glia and neurons. The functional repercussions on the scarring and remodelling processes are also discussed.

Animals↗
PubMed1996

Apoptotic features of selective neuronal death in ischemia, epilepsy and gp 120 toxicity.

The occurrence of physiological cell death has been known for decades, but interest in the subject was renewed in 1972 when Kerr, Wyllie and Currie described in detail the ultrastructural changes characteristic of dying cells and coined the term apoptosis to describe the process. Cells display a wide variety of morphological changes when dying during development or following a toxic insult. A binary classification scheme suggests that physiologically appropriate death is due to apoptosis and that pathological mechanisms involve necrosis. However, recent studies indicate a potential involvement of apoptotic cell death in ischemia, status epilepticus and HIV-1 infection.

Animals↗
PubMed1996

Apoptosis and necrosis after reversible focal ischemia: an in situ DNA fragmentation analysis.

Apoptosis is one of the two forms of cell death and occurs under a variety of physiological and pathological conditions. Cells undergoing apoptotic cell death reveal a characteristic sequence of cytological alternations including membrane blebbing and nuclear and cytoplasmic condensation. Early activation of an endonuclease has been previously demonstrated after a transient focal ischemia in the rat brain Charriaut-Marlangue C, Margaill I, Plotkine M, Ben-Ari Y (1995) Early endonuclease activation following reversible focal ischemia. J Cereb Blood Flow Metab 15:385-388). We now show that a significant number of striatal and cortical neurons, exhibited chromatin condensation, nucleus segmentation, and apoptotic bodies increasing with recirculation time, as demonstrated by in situ labeling of DNA breaks in cryostat sections. Apoptotic nuclei were also detected in the horizontal limb diagonal band, accumbens nucleus and islands of Calleja. Several necrotic neurons, in which random DNA fragmentation occurs, were also shown at 6 h recirculation, in the ischemic core. Further investigation with hematoxylin/eosin staining revealed that apoptotic nuclei were present in cells with a large and swelled cytoplasm and in cells with an apparently well-preserved cytoplasm. These two types of cell death were reminiscent of those described in developmental cell death. Our data suggested that apoptosis may contribute to the expansion of the ischemic lesion.

Animals↗
PubMed1996

Acidic calponin cloned from neural cells is differentially expressed during rat brain development.

Calponin is an actin-, tropomyosin- and Ca2+ calmodulin-binding protein that inhibits in vitro the actomyosin MgATPase. Basic and acidic variants of calponin have been described to date. Although the cerebral expression of calponin remained controversial for some time, transcripts encoding acidic calponin in the adult rat brain and in cultured cerebellar cells have been reported. In the present work, we report the expression of acidic calponin mRNAs and the isolation of cDNAs encoding the full-length acidic calponin in cultured neuronal and glial cells and in adult rat brain. Sequence analysis reveals that acidic calponin in the brain is identical to that previously described in rat aortic vascular smooth muscle. In situ hybridization shows that calponin is highly expressed during ontogenesis in granule cells of the dentate gyrus of the hippocampus, in all layers of the olfactory bulb and in cerebellar granule neurons of the external and internal layers. In the adult rat brain, calponin expression decreased in these fields, but increased in choroid plexus cells. Bergmann glial cells were also labelled by a calponin probe. The reverse transcription-coupled polymerase chain reaction confirms that calponin mRNA levels are highest in the early stages of hippocampal development and that expression levels are low in adult hippocampi. The developmental expression pattern of brain acidic calponin suggests that calponin could be involved in contractile activity associated with neural cell proliferation or neuronal migration.

Acids↗
PubMed1996

Intracellular injection of a Ca2+ chelator prevents generation of anoxic LTP.

1. The effects of intracellular injection of Ca2+ chelator 1,2-bis (2-aminophenoxy) ethane N,N,N',N'-tetra-acetic acid (BAPTA, 50 mM) on anoxia-aglycemia-induced long-term potentiation (LTP) were investigated in the CA1 region of hippocampal slices with the use of extra- and intracellular recording techniques. Experiments were performed in artificial cerebrospinal fluid (ACSF) containing 10 microM bicuculline and 10 microM 6-cyano-7-nitroquinoxaline- 2,3-dione (CNQX) to pharmacologically isolate N-methyl-D-aspartate (NMDA)-receptor-mediated responses. NMDA-receptor-mediated excitatory postsynaptic potentials (EPSPs) and field potentials were evoked by stimulation of the Schaffer collateral/commissural pathway in the presence of 0.3 mM MgCl2 and 10 microM glycine to promote NMDA-receptor-mediated responses. Under these conditions, application of 50 microM D-2-amino-phosphono-valerate (D-APV) abolished EPSPs and field potentials. 2. Anoxic-aglycemic (AA) episodes (duration 2-2.5 min) potentiated the initial slope (measured within 3 ms from the onset of the synaptic responses) of EPSPs by 108 +/- 14.3% (mean +/- SE, P = 0.0012, n = 7). We refer to this LTP of NMDA-receptor-mediated synaptic responses as anoxic LTP. 3. Intracellular injection of the Ca2+ chelator BAPTA (with the intracellular recording electrode filled with 50 mM BAPTA in 3 M KCl) prevented anoxic LTP. Thirty to 40 min after the AA episode, in BAPTA-loaded cells, the initial slope of the EPSPs was not significantly changed (+7.12 +/- 5%, P = 0.35, n = 5). In contrast, the initial slope of the field potentials, measured at the same time in the same slices, was persistently increased (+49 +/- 2.8%, P = 0.0022, n = 5). 4. High-frequency tetanic stimulation (100 Hz for 500 ms, 2 times, 30 s apart) of the Schaffer collateral/commissural pathway, applied > 0.5 h after the AA episode, induced an additional significant and persistent increase in the initial slope of the field potential (tetanic LTP, +35.4 +/- 9.8%, P = 0.012, n = 5). In BAPTA-loaded cells, there was no further change in the initial slope of the EPSP (+3.9 +/- 3.4%, P = 0.205, n = 5) after the tetanic stimulation. 5. We also report that AA episodes or tetanic stimulation induced a persistent increase in a late synaptic component that was blocked by 50 microM D-APV. This late component was mediated polysynaptically, because its time to peak decreased with increasing stimulation intensities and it was strongly reduced by high-divalent-cation superfusate (ACSF containing 7 mM Ca2+). This component, which had a delay of approximately 8-30 ms, contaminated mainly the peak amplitude and the decay of the monosynaptic response without affecting its initial slope. Thus the measure of the initial slope takes into account only the early phase of the monosynaptic response. 6. We conclude that 1) a rise in intracellular Ca2+ is necessary to generate anoxic LTP of NMDA-receptor-mediated responses, as is the case for tetanic LTP; and 2) in the presence of bicuculline and low extracellular Mg2+, AA episodes and tetanic stimulations induced a long-lasting enhancement of a polysynaptic component mediated or controlled by NMDA receptors.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1996

Spontaneous release of GABA activates GABAB receptors and controls network activity in the neonatal rat hippocampus.

1. We investigated the effects of the selective gamma-aminobutyric acid-B (GABAB) receptor antagonist, P-3 aminopropyl-P-diethoxymethyl phosphoric acid (CGP 35348), on spontaneous and evoked postsynaptic potentials (PSPs) and currents (PSCs) in CA3 pyramidal cells and interneurons of hippocampal slices obtained between postnatal day 3 and 7 with the use of intracellular and whole cell recording techniques. The intracellular pipette solution contained either 2 M CsCl or 50 mM 2(triethylamino)-N-(2,6-dimethylphenyl) acetamine (QX314) dissolved in 2 M KMeSO4. Cesium and QX314 block postsynaptic responses mediated by GABAB receptors. 2. Under control conditions, bath application of CGP 35348 (0.5-1 mM) progressively increased the duration of spontaneous and evoked polysynaptic giant GABAergic PSPs leading to the appearance of ictal-like discharges. The effects of CGP 35348 were dose dependent and voltage independent. 3. In CA3 pyramidal neurons, CGP 35348 (0.5 mM) had no effect on monosynaptic GABAergic inhibitory PSPs (IPSPs) that were isolated in the presence of ionotropic glutamate receptor antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 10 microM) and D(-)2-amino-5-phosphovaleric acid (D-APV, 50 microM). Similarly, CGP 35348 (0.5 mM) had no effect on monosynaptic glutamatergic excitatory PSPs (EPSPs) that were isolated in the presence of bicuculline (10 microM) and high divalent cation artificial cerebrospinal fluid (ACSF; 6 mM Mg2+/4 mM Ca2+). 4. In CA3 pyramidal neurons exposed to CNQX (20 microM) and D-APV (50 microM), application of the potassium channel blocker 4-aminopyridine (4-AP, 50 microM) generated synchronous giant GABAergic PSPS that were blocked in the presence of high divalent cation ACSF (6 mM Mg2+/4 mM Ca2+) or bicuculline (10 microM). The duration of these synchronous GABAergic PSPs was prolonged in the presence of CGP 35348 (0.5 mM) but did not lead to the appearance of ictal-like discharges. 5. In the presence of bicuculline, interictal giant glutamatergic potentials were observed in simultaneously recorded CA3 pyramidal cells and interneurons. CGP 35348 (0.5 mM) progressively increased the duration of these bicuculline-induced glutamatergic bursts leading to the simultaneous appearance of ictal discharges in both pyramidal cells and interneurons. 6. These results suggest that in the neonatal CA3 hippocampal region, when synchronous giant polysynaptic GABAergic PSPs are present (i.e., under basal, control conditions), spontaneously released GABA reaches a critical level and activates GABAB receptors on both pyramidal cells and interneurons thus regulating the level of glutamatergic and GABAergic activity in the CA3 neuronal network.

Animals↗