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Biomedical subjects

Y Ben-Ari

Publications and source records attributed to Y Ben-Ari.

At least 73 records · Page 4Linked to original sources
PubMed1998

Glutamate receptors in dysplasic cortex: an in situ hybridization and immunohistochemistry study in rats with prenatal treatment with methylazoxymethanol.

Injection of the antimitotic drug methylazoxymethanol (MAM) in the pregnant rat at E14 leads in the offsprings to a severe malformation with microcephaly and cortical heterotopiae in the white matter and in the CA1 field of the hippocampus. These animals suffer cognitive and epileptic disorders. Since these pathologies have been associated with glutamatergic transmission abnormalities, we have examined by in situ hybridization and immunohistochemistry the distribution and expression levels of several glutamate receptors subunits in these rats. Examination of the GluR2 flip and flop, NR1, NR2A and NR2B subunit gene transcripts showed a qualitatively similar distribution in both the neocortex and hippocampus of MAM and control rats. Quantitative analysis revealed an altered proportion of the GluR2 flip and flop subunits in the CA1 region of MAM animals as compared to controls. Moreover, a 26% reduction in the expression of the NR1 subunit and a 40% increase in the expression of the GluR2 flip subunit were noted in cortical heterotopiae, as compared to the adjacent neocortex. Immunostaining for GluR2/3, NR1 or NR2 showed, in both MAM and control animals, that glutamate receptors were mainly concentrated in the soma and dendrites of neocortical and hippocampal pyramidal cells, including in heterotopiae, and in the apical dendrites of hippocampal granule cells. Abnormalities in the expression of glutamate receptor subtypes in cortical heterotopiae and in the hippocampal CA1 region could contribute to functional disorders previously reported in MAM animals such as memory impairments and epilepsy.

Animals↗
PubMed1998

Glutamate receptors in dysplasic cortex: an in situ hybridization and immunohistochemistry study in rats with prenatal treatment with methylazoxymethanol

Injection of the antimitotic drug methylazoxymethanol (MAM) in the pregnant rat at E14 leads in the offsprings to a severe malformation with microcephaly and cortical heterotopiae in the white matter and in the CA1 field of the hippocampus. These animals suffer cognitive and epileptic disorders. Since these pathologies have been associated with glutamatergic transmission abnormalities, we have examined by in situ hybridization and immunohistochemistry the distribution and expression levels of several glutamate receptors subunits in these rats. Examination of the GluR2 flip and flop, NR1, NR2A and NR2B subunit gene transcripts showed a qualitatively similar distribution in both the neocortex and hippocampus of MAM and control rats. Quantitative analysis revealed an altered proportion of the GluR2 flip and flop subunits in the CA1 region of MAM animals as compared to controls. Moreover, a 26% reduction in the expression of the NR1 subunit and a 40% increase in the expression of the GluR2 flip subunit were noted in cortical heterotopiae, as compared to the adjacent neocortex. Immunostaining for GluR2/3, NR1 or NR2 showed, in both MAM and control animals, that glutamate receptors were mainly concentrated in the soma and dendrites of neocortical and hippocampal pyramidal cells, including in heterotopiae, and in the apical dendrites of hippocampal granule cells. Abnormalities in the expression of glutamate receptor subtypes in cortical heterotopiae and in the hippocampal CA1 region could contribute to functional disorders previously reported in MAM animals such as memory impairments and epilepsy. Copyright 1997 Elsevier Science B.V.

Journal Article↗
PubMed1998

Consequences of neonatal seizures in the rat: morphological and behavioral effects.

Whereas neonatal seizures are a predictor of adverse neurological outcome, there is controversy regarding whether seizures simply reflect an underlying brain injury or can cause damage. We subjected neonatal rats to a series of 25 brief flurothyl-induced seizures. Once mature the rats were compared with control littermates for spatial learning and activity level. Short-term effects of recurrent seizures on hippocampal excitation were assessed by using the intact hippocampus formation preparation and long-term effects by assessing seizure threshold. Brains were analyzed for neuronal loss, sprouting of granule cell axons (mossy fibers), and neurogenesis. Compared with controls, rats subjected to neonatal seizures had impaired learning and decreased activity levels. There were no differences in paired-pulse excitation or inhibition or duration of afterdischarges in the intact hippocampal preparation. However, when studied as adults, rats with recurrent flurothyl seizures had a significantly lower seizure threshold to pentylenetetrazol than controls. Rats with recurrent seizures had greater numbers of dentate granule cells and more newly formed granule cells than the controls. Rats with recurrent seizures also had sprouting of mossy fibers in CA3 and the supragranular region. Recurrent brief seizures during the neonatal period have long-term detrimental effects on behavior, seizure susceptibility, and brain development.

Animals↗
PubMed1998

Apoptosis and programmed cell death: a role in cerebral ischemia.

Hypoxic-ischemic neuronal death has long been considered to represent necrosis, but it now appears that many brain neurons undergo apoptosis after either global or focal ischemic insults. Recent studies demonstrated: 1) DNA cleavage into oligonucleosome-sized fragments demonstrated by a typical ladder pattern; 2) early endonuclease activation, as demonstrated by the presence of high molecular weight DNA fragments (300 to 50 kbp); 3) chromatin condensation and apoptotic bodies formation; 4) activation of apoptosis-associated proteins. These results may indicate that apoptosis contributes to the development of the ischemic infarct and is probably substantially distinct from ischemia-triggered excitotoxicity, which tends to produce necrosis.

Animals↗
PubMed1998

Interneurones are not so dormant in temporal lobe epilepsy: a critical reappraisal of the dormant basket cell hypothesis.

One axiom at the basis of epilepsy research is that there exists an imbalance between excitation and inhibition. This abnormality can be achieved by an increase of excitation on principal cells, a decreased inhibition (i.e. disinhibition) or both. This review focuses on dysfunction of inhibition, and in particular on the 'dormant basket cell hypothesis'. This hypothesis states that, (1) interneurones are functionally disconnected from excitatory afferents, resulting in hyperexcitability of principal neurones and loss of paired pulse inhibition, (2) when properly activated, interneurones can still perform their task, i.e. suppress epileptiform activity and restore paired pulse inhibition. The aim of this review is to discuss the evidence in support of the 'dormant basket cell hypothesis'. We will first discuss the rationale underlying the hypothesis and the criteria needed to validate the hypothesis. We will then show that, (1) the key experimental data offered in support of the hypothesis (Bekenstein and Lothman, 1993. Dormancy of inhibitory interneurones in a model of temporal lobe epilepsy. Science 259, 97-100; Sloviter, 1991. Permanently altered hippocampal structure, excitability, and inhibition after experimental status epilepticus in the rat: the 'dormant basket cell' hypothesis and its relevance to temporal lobe epilepsy. Hippocampus 1, 41-66) are difficult to interpret, and (2) recent recordings from interneurones in epileptic tissue argue against the hypothesis. The 'dormant basket cell hypothesis' is then discussed in the broader context of disinhibition.

Afferent Pathways↗
PubMed1998

Ultrastructural morphology of neuronal death following reversible focal ischemia in the rat.

Electron microscopy and terminal deoxynucleotidyl transferase (TdT) mediated dUTP-biotin nick end-labelling (TUNEL) were used to illustrate the different stages and subcellular alterations of cell degeneration that occur in the striatum of the rat after transient focal ischemia. Degenerating neurons exhibited different morphological types: apoptosis Type 1 (aggregation of dense masses of chromatin beneath the 'intact' nuclear membrane) and Type 2 (high cytoplasmic vacuolization), and necrosis. These profiles were localized in different part of the striatum. Type 1 was found in the head of the caudate putamen, Type 2 in the middle part of the striatum and necrosis in the striatal core. These ultrastructural results demonstrated that apoptosis occurs in neurons following focal ischemia in the striatal penumbra. In contrast, necrosis can be observed in the ischemic core, the region maximally affected by the ischemia. Finally, the presence of astrocytes throughout both the penumbra and ischemic core displaying numerous cytoplasmic vacuoles suggested an activation of glial cells.

Journal Article↗
PubMed1998

GluR5 kainate receptor activation in interneurons increases tonic inhibition of pyramidal cells.

We studied the modulation of GABAergic inhibition by glutamate and kainate acting on GluR5-containing kainate receptors in the CA1 hippocampal region. Glutamate, kainate or ATPA, a selective agonist of GluR5-containing receptors, generates an inward current in inhibitory interneurons and cause repetitive action potential firing. This results in a massive increase of tonic GABAergic inhibition in the somata and apical dendrites of pyramidal neurons. These effects are prevented by the GluR5 antagonist LY 293558. Electrical stimulation of excitatory afferents generates kainate receptor-mediated excitatory postsynaptic currents (EPSCs) and action potentials in identified interneurons that project to the dendrites and somata of pyramidal neurons. Therefore glutamate acting on kainate receptors containing the GluR5 subunit may provide a protective mechanism against hyperexcitability.

Animals↗
PubMed1998

MAP2d mRNA is expressed in identified neuronal populations in the developing and adult rat brain and its subcellular distribution differs from that of MAP2b in hippocampal neurones.

The brain microtubule-associated protein MAP2 family is composed of high-molecular-weight (MAP2a and MAP2b) and low-molecular-weight (MAP2c and MAP2d) isoforms. The common C-terminal region of HMW MAP2 and MAP2c contains three repeated microtubule-binding domains while MAP2d comprises four repeats. MAP2c mRNA is known to be expressed at high levels in the immature brain. We show that in the brains of rat pups, MAP2c mRNAs are indeed expressed at high levels compared with MAP2d. However, in adult rat brains, MAP2d mRNA levels are higher than MAP2c. In order to identify the neural cells expressing MAP2d, we used in situ hybridization. In vivo, we show that MAP2d mRNA is expressed in well-identified neuronal populations of the brain. In primary cultures of hippocampal neurones, double-labelling experiments confirm that MAP2d is clearly expressed in neurones. We also evaluated in this study the subcellular distribution of the MAP2d mRNAs in cultured hippocampal neurones and we report that in contrast with MAP2b mRNAs, mostly localized in dendrites, MAP2d mRNAs are essentially located in neuronal cell bodies.

Animals↗
PubMed1998

Long-lasting enhanced expression in the rat hippocampus of NMDAR1 splice variants in a kainate model of epilepsy.

Chronic epilepsy is associated with increased excitability which may result from abnormal glutamatergic synaptic transmission involving altered properties of N-methyl-D-aspartate (NMDA) receptors. To date two gene families encoding NMDA receptor subunits have been cloned, NR1 and NR2. Eight NR1 mRNAs are generated by alternative splicing of exons 5, 21 and 22; the NR1-1 to NR1-4 C-terminal variants exist in the a or b version depending on the presence or absence of the domain encoded by exon 5. Epilepsy was induced in rats by unilateral intra-amygdalar injection of kainate and animals were killed from 6 h to 4 months following the injection. Increased NR1 mRNA levels were observed during status epilepticus (6-24 h after the injection), both psilateral and contralateral, while a second wave of NMDAR1 mRNA increase occurred in chronic epileptic animals, between 21 days and 4 months following kainate injection. Our data show: (i) a permanent increase of the NR1-2a and NR1-2b mRNA species (containing exon 22) in all hippocampal fields, both ipsilateral and contralateral, and (ii) an increase of the NR1-3 (a and b) mRNAs (containing exon 21) in the ipsilateral CA1, and NR1-3a mRNA in the ipsilateral dentate gyrus. No long-term changes were observed for the NR1-1 and NR14 splice variants. In the ipsilateral CA3 area a globally decreased mRNA expression was associated with neuronal loss. A possible contribution to the maintenance of the epileptic state by an increased expression of NMDA receptors is discussed.

Animals↗
PubMed1998

Nitric oxide production and perivascular tyrosine nitration following focal ischemia in neonatal rat.

Oxygen free radicals and nitric oxide (NO.) have been proposed to be involved in acute CNS injury produced by cerebral ischemia; however, controversy remains regarding how they cause injury. Because superoxide generation is triggered during reperfusion, the cytotoxic oxidant peroxynitrite could be formed, but it is not known if this occurs. Dot blot and immunohistochemistry studies were performed on the magnitude and time course of tyrosine nitration and inducible NO synthase (NOS2) in the postischemic rat pup brain. Neonatal ischemia was induced by permanent left middle cerebral artery occlusion in association with 1-h occlusion of the left common carotid artery in 7-day-old Wistar pups. Nitrotyrosine (NT) immunoreactivity was evident in the blood vessels close to the cortical infarct at 48-72 h of recovery, and T lymphocytes were involved with this production. NOS2 immunoreactivity was seen in neutrophils in the same vessels and in the parenchyma at 72 h of recirculation. Whereas NT staining decreased with time, NOS2-positive neutrophils could be still detected in arachnoid vessels at 14 days of recirculation. We conclude that perivascular reactions mediated by peroxynitrite are important in the cascade of events that lead to brain oxidative stress in neonatal ischemia. Moreover, NO-related species may serve as a signaling function instead of directly mediating toxicity.

Animals↗
PubMed1998

Ontogenesis of presynaptic GABAB receptor-mediated inhibition in the CA3 region of the rat hippocampus.

gamma-Aminobutyric acid-B(GABAB) receptor-dependent and -independent components of paired-pulse depression (PPD) were investigated in the rat CA3 hippocampal region. Intracellular and whole cell recordings of CA3 pyramidal neurons were performed on hippocampal slices obtained from neonatal (5-7 day old) and adult (27-34 day old) rats. Electrical stimulation in the hilus evoked monosynaptic GABAA postsynaptic currents (eIPSCs) isolated in the presence of the ionotropic glutamate receptor antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 10 microM) and D(-)2-amino-5-phosphovaleric acid (-AP5, 50 microM) with 2(triethylamino)-N-(2,6-dimethylphenyl) acetamine (QX314) filled electrodes. In adult CA3 pyramidal neurons, when a pair of identical stimuli was applied at interstimulus intervals (ISIs) ranging from 50 to 1,500 ms the amplitude of the second eIPSC was depressed when compared with the first eIPSC. This paired-pulse depression (PPD) was partially blocked by P-3-aminoprophyl -P-diethoxymethylphosphoric acid (CGP35348, 0.5 mM), a selective GABAB receptor antagonist. In neonates, PPD was restricted to ISIs shorter than 200 ms and was not affected by CGP35348. The GABAB receptor agonist baclofen reduced the amplitude of eIPSCs in a dose-dependent manner with the same efficiency in both adults and neonates. Increasing the probability of transmitter release with high Ca2+ (4 mM)/low Mg2+ (0.3 mM) external solution revealed PPD in neonatal CA3 pyramidal neurons that was 1) partially prevented by CGP35348, 2) independent of the membrane holding potential of the recorded cell, and 3) not resulting from a change in the reversal potential of GABAA eIPSCs. In adults the GABA uptake blocker tiagabine (20 microM) increased the duration of eIPSCs and the magnitude of GABAB receptor-dependent PPD. In neonates, tiagabine also increased duration of eIPSCs but to a lesser extent than in adult and did not reveal a GABAB receptor-dependent PPD. These results demonstrate that although GABAB receptor-dependent and -independent mechanisms of presynaptic inhibition are present onGABAergic terminals and functional, they do not operate at the level of monosynaptic GABAergic synaptic transmission at early stages of development. Absence of presynaptic autoinhibition of GABA release seems to be due to the small amount of transmitter that can access presynaptic regulatory sites.

2-Amino-5-phosphonovalerate↗
PubMed1998

A model of transient unilateral focal ischemia with reperfusion in the P7 neonatal rat: morphological changes indicative of apoptosis.

BACKGROUND AND PURPOSE: The mechanisms leading to delayed cell death after hypoxic-ischemic injury in the developing brain remain to be elucidated. The aim of this study was to develop a model of transient focal ischemia in the neonatal rat in an attempt to create a reperfusion phase since in the filament model of reversible middle cerebral artery occlusion, size limitations precluded performing this procedure before 14 to 18 days. We then analyze whether apoptosis or necrosis occurs in this model. METHODS: Seven-day-old Wistar rat pups (n = 96) underwent permanent left middle cerebral artery occlusion in association with 1-hour occlusion of the left common carotid artery. Evolution of the brain infarction was studied from 24 hours to 3 months on cresyl violet-stained coronal sections. Infarct volume was determined with the use of the mitochondrial stain 2,3,5-triphenyltetrazolium chloride. Neuronal death was demonstrated by the silver staining method of Gallyas et al (1980). Chromatin condensation was shown by DNA fragmentation assessed with the use of terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling (TUNEL) assay in cryostat sections and electron microscopic analysis. RESULTS: Almost all of the animals who survived had reproducible cortical infarcts. The mean infarct volume was 31+/-7 mm3 (mean+/-SD). The ipsilateral hemisphere showed a well-delineated lesion in the frontoparietal cortex at 3-month recovery. Argyrophilic (dying) neurons were observed a few hours after reperfusion and increased with time. Cells exhibiting DNA fragmentation were shown as early as 6 hours, increased up to and peaked at 24 to 96 hours, then progressively decreased and persisted for several days, suggesting an ongoing process. Electron microscopy analysis demonstrated high condensation and clumping of chromatin beneath nuclear membrane in shrunken neurons. CONCLUSIONS: Our study demonstrates the feasibility of performing ischemia-reperfusion in 7-day-old rats that develop progressive neuronal death with features characteristic of apoptosis. The reperfusion phase mimics events that occur during neonatal human hypoxic-ischemic encephalopathy at birth, since perinatal intensive care most often permits recirculation.

Animals↗
PubMed1997

Contributions of AMPA and GABA(A) receptors to the induction of NMDAR-dependent LTP in CA1.

The contributions of (+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) and gamma-aminobutyric acid (GABA[A]) receptors in the induction of long-term potentiation (LTP) have been studied in the CA1 region of the rat hippocampus. The results suggest that: (1) in physiological conditions, AMPARs are necessary for the induction of N-methyl-D-aspartate receptor (NMDAR)-dependent LTP since LTP cannot be elicited in the presence of the AMPAR antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). Although a NMDAR-dependent LTP occurs in the presence of a GABA(A) antagonist and high concentrations of divalents cations, blockade of AMPARs leads to a voltage-dependent calcium channels (VDCC)-dependent LTP since its induction is blocked by nifedipine and not by APV. (2) The bicarbonate-induced GABA(A) receptor-mediated depolarizing response is not necessary in the induction of NMDAR-dependent or VDCC-dependent LTP since induction of these two types of LTP were not blocked by acetazolamide or in a nominally bicarbonate-free solution.

2-Amino-5-phosphonovalerate↗
PubMed1997

Differential expression of fibronectin, tenascin-C and NCAMs in cultured hippocampal astrocytes activated by kainate, bacterial lipopolysaccharide or basic fibroblast growth factor.

Different reports demonstrated that reactive glial cells express increased amounts of adhesion and matrix molecules. Despite a wealth of information on the expression of these molecules during development and after lesion, very little is known of how this expression is regulated. In the present report we used Western blots and immunocytochemistry to investigate the expression of neural cell adhesion molecule (NCAM), fibronectin and tenascin-C in cultured astrocytes from rat hippocampus. The effects of three different extracellular signals were analyzed: the glutamatergic receptor agonist kainic acid, the basic fibroblast growth factor (bFGF) and the bacterial lipopolysaccharide. Each treatment had a specific pattern of glial activation and differentially modified the expression of these proteins. Treatment of astrocytes with kainic acid resulted in an increase of tenascin-C, a decrease of fibronectin and a shift of NCAMs isoforms: NCAM 140 and PSA-NCAM (polysialic acid-rich NCAMs) were increased while NCAM 120 was decreased, bFGF increased fibronectin, tenascin-C and NCAM 120, while decreasing PSA-NCAM. Finally, the treatment of astrocytes with lipopolysaccharide induced a significant increase of fibronectin, tenascin-C and NCAM 120 but did not modify the expression of NCAM 140 and PSA-NCAM. These data suggest different mechanisms for modulation of cell surface interactions. They suggest that glial activation by bFGF and lipopolysaccharide are associated with an increase of the adhesive properties, while kainate action is rather associated with a decrease of the adhesiveness of astrocytes.

Animals↗
PubMed1997

Operative GABAergic inhibition in hippocampal CA1 pyramidal neurons in experimental epilepsy.

Patch-clamp recordings of CA1 interneurons and pyramidal cells were performed in hippocampal slices from kainate- or pilocarpine-treated rat models of temporal lobe epilepsy. We report that gamma-aminobutyric acid (GABA)ergic inhibition in pyramidal neurons is still functional in temporal lobe epilepsy because: (i) the frequency of spontaneous GABAergic currents is similar to that of control and (ii) focal electrical stimulation of interneurons evokes a hyperpolarization that prevents the generation of action potentials. In paired recordings of interneurons and pyramidal cells, synchronous interictal activities were recorded. Furthermore, large network-driven GABAergic inhibitory postsynaptic currents were present in pyramidal cells during interictal discharges. The duration of these interictal discharges was increased by the GABA type A antagonist bicuculline. We conclude that GABAergic inhibition is still present and functional in these experimental models and that the principal defect of inhibition does not lie in a complete disconnection of GABAergic interneurons from their glutamatergic inputs.

Action Potentials↗