Biomedical subjects

Y Ben-Ari

Publications and source records attributed to Y Ben-Ari.

At least 181 records · Page 10Linked to original sources

PubMed1994

[NMDA receptor and long-term potentiation].

In order to evaluate the role of the NMDA receptor redox site in long-term potentiation (LTP), we have investigated the effects of two redox reagents, 5,5'-dithiobis-2-nitrobenzoic acid (DTNB) and tris(carboxyethyl)phosphine (TCEP) on the induction and expression of various forms of LTP. DTNB a thiol-oxidizing agent, irreversibly reduces by 50% NMDA receptor EPSP. In the presence of DTNB, the induction of tetanic and anoxic LTP are prevented. When tetanic or anoxic LTP were generated first, DTNB completely reverses the potentiation and TCEP a disulfide-reducing agent restores LTP to its initial level. These redox agents have no effect on AMPA synaptic transmission and did not significantly modify the induction and the expression of tetanic AMPA-LTP. These results suggest that thiol-oxidizing compounds might be useful for the treatment of cerebral ischemia.

Animals↗

PubMed1994

Complete sequence of rat MAP2d, a novel MAP2 isoform.

MAP2 proteins are among the major microtubule-associated proteins in the vertebrate nervous system. The high molecular weight proteins MAP2a, MAP2b and the low molecular weight protein MAP2c are encoded by distinct mRNAs generated by alternative splicing from the same primary transcript. MAP2c is primarily found in embryonic and neonatal brain. Using primers selected in the 5' and 3' non-coding regions of the rat MAP2c sequence and reverse transcription-coupled PCR from adult rat brain RNA, we have amplified and sequenced the entire coding region of a novel MAP2 isoform containing a 93 base pair insertion. Sequence analysis reveals that the additional exon encodes a domain that is highly homologous to repeats found in the 3' end of the coding region of MAP2, MAP4 and Tau mRNA sequences. In these microtubule-associated proteins, the domains encoded by the repeats are involved in microtubule binding and bundling.

Animals↗

PubMed1993

Riluzole prevents anoxic injury in cultured cerebellar granule neurons.

Glutamate release has been reported to be involved in the neuronal death following ischemic or anoxic injury. Riluzole (2-amino-6-trifluoromethoxy-benzothiazole) is a putative inhibitor of glutamate release. We investigated the effect of this drug on anoxic injury in vitro. Cerebellar granule cells grown in culture were exposed to an anoxic atmosphere for 16-20 h, Riluzole (100 microM) was found to prevent the degeneration of these neurons induced by anoxia.

Animals↗

PubMed1993

The hypoglycemic sulphonylurea tolbutamide increases N-methyl-D-aspartate- but not kainate-activated currents in hippocampal neurons in culture.

The effects of the hypoglycemic sulphonylurea tolbutamide, a marker of K(+)-ATP channels, on the N-methyl-D-aspartate- (NMDA) and kainate-activated currents were studied in rat hippocampal neurons in culture, using the patch-clamp technique in a whole-cell configuration. Tolbutamide (500 microM) reversibly increased the peak amplitude and the steady state level of NMDA- but not kainate-evoked currents. This effect was not glycine dependent as it was observed at low and saturated concentrations of glycine. The affinity of the NMDA receptor-channel complex for glycine did not change in the presence of tolbutamide. The action of tolbutamide on the NMDA-activated current was not mediated by K(+)-ATP channels since CsCl was added intracellularly at concentrations which completely blocked all K+ channels. Possible mechanisms explaining the effect of tolbutamide via the modulation of intracellular messengers are discussed.

Animals↗

PubMed1993

NCAM immunoreactivity on mossy fibers and reactive astrocytes in the hippocampus of epileptic rats.

Sprouting and synaptogenesis of mossy fibers develop in adult hippocampus after epilepsy. In control conditions, mossy fibers constitute the main afferent pathway to the Ammon's horn, where they mainly innervate CA3 pyramidal cells, but after treatment with the convulsant agent, kainate, mossy fibers also innervate granule cell dendrites generating recurrent excitatory circuits which may contribute to the maintenance of the epileptic condition. In the present study we show an enhanced immunoreactivity to neural cell adhesion molecules (NCAMs), a family of membrane glycoproteins involved in axonal growth. NCAM immunoreactivity is enriched on cytoplasmic membranes of axon shafts that are likely to be mossy fiber collaterals. NCAM immunoreactivity was also observed on the cytoplasmic membranes of reactive astrocytes, at the axon-glial contacts. Our results therefore suggest that there is an interaction of newly developed mossy fibers with other fibers and glial cells. This interaction may be mediated by NCAMs. Taking into account the trophic properties of NCAMs we suggest that they regulate the sprouting, growing and synaptogenesis of mossy fibers in epileptic conditions.

Afferent Pathways↗

PubMed1993

Mossy fiber sprouting in epileptic rats is associated with a transient increased expression of alpha-tubulin.

Kainate-induced seizures lead to marked increases of alpha-tubulin mRNA and protein immunoreactivity in the rat dentate gyrus. The increase in alpha-tubulin mRNA was restricted to the granule cell bodies. alpha-Tubulin immunoreactivity was enhanced in granule cell dendrites and axons (the mossy fibers), in the molecular layer. These changes peaked 6-12 days after kainate treatment and preceded the collateral sprouting of mossy fibers which occur 12 to 30 days after seizures. The present results suggest that microtubule formation contributes to the synaptic rearrangements which take place in the hippocampus after seizures.

Amygdala↗

PubMed1993

Metabotropic receptor stimulation coupled to weak tetanus leads to long-term potentiation and a rapid elevation of cytosolic protein kinase C activity.

We have previously shown that short-term potentiation (STP) inducing weak tetanus induces long-term potentiation (LTP) when it is coupled with activation of metabotropic glutamate (mGlu) receptors by trans-(+/-)-1-amino-1,3-cyclopentanedicarboxylic acid (t-ACPD) in rat CA1 slices. In the present study, we examined if this conversion of STP to LTP involves activation of protein kinase C (PKC). Two minutes but not 30 min after coupling, there was a significant increase in the activator-dependent PKC activity in the cytosolic fraction. STP induction or t-ACPD application did not change PKC activity. There was no activity increase in the membrane fraction. STP was also induced by a co-application of gamma-amino-3-hydroxy-5-methyllisoxazole-4-propionic acid (AMPA) and N-methyl-D-aspartic acid (NMDA). Coupling this STP with t-ACPD, however, did not result in an LTP or PKC activity increase, indicating a requirement for synaptic activity. A rapid and transient (< 5 min) increase in cytosolic PKC activity was also seen after the induction of LTP by stronger tetanic stimulation. No LTP tested in the present study was accompanied by activator-independent, persistent increases in PKC activity. STP induction depends on NMDA receptor activation, and the activation of mGlu receptors results in the production of intracellular second messengers. Our results therefore indicate that these separate components may add and bring about PKC activation and LTP.

Animals↗

PubMed1993

Effect of potassium channel modulators on the release of glutamate induced by ischaemic-like conditions in rat hippocampal slices.

The effects of the potassium channel openers lemakalim, RP 52891 and galanin and the potassium channel blockers glibenclamide and gliquidone were evaluated by the release of endogenous glutamate from rat hippocampal slices subjected to a brief period of ischaemia (2-10 min). Ischaemia was mimicked by incubating slices in a glucose free medium equilibrated with 95% N2/5% CO2. These conditions evoked a release of glutamate which was insensitive to tetrodotoxin and Ca2+ indicating a non-vesicular origin. The release of glutamate evoked by a 6- or 8-min period of ischaemia was reduced by 25-40% in the presence of lemakalim (10 microM), RP 52891 (10 microM) or galanin (0.3 microM), whereas it was enhanced by 60 to 100% in the presence of glibenclamide (1 microM) and gliquidone (2 microM). These observations suggest that cellular damage resulting from ischaemia induced excessive release of glutamate in the hippocampus may be partly reduced by potassium channel openers, and conversely increased by sulfonylureas.

Animals↗

PubMed1993

The NMDA receptor contributes to anoxic aglycemic induced irreversible inhibition of synaptic transmission.

Percent recovery of CA1 field EPSP amplitude following various anoxic aglycemic (AA) periods was examined in rat hippocampal slices superfused with MK-801 (0.1 microM, 1 microM, 10 microM) or Mg(2+)-free artificial cerebrospinal fluid. Slices treated with 0.1 microM MK-801 showed greater percent recuperation of EPSP amplitude following 3 min 30 s of AA (36 +/- 12% vs 6 +/- 4% in controls). Higher concentrations of MK-801 resulted in a greater recovery of EPSP amplitudes in more than one time period of AA, with 10 microM MK-801 providing protection in up to 4 min 30 s AA. Percent recuperation of EPSP amplitude was smaller in Mg(2+)-free slices following 2 min (34 +/- 15% vs 81 +/- 11% in controls) and 2 min 30 (25 +/- 14% vs 77 +/- 10% in controls) of AA. These results suggest that the activation of the N-methyl-D-aspartate (NMDA) receptor channel may contribute to irreversible AA induced synaptic failure in CA1.

Animals↗

PubMed1993

Involvement of GABAA receptors in the outgrowth of cultured hippocampal neurons.

Whereas GABA is a major inhibitory neurotransmitter in the adult central nervous system, recent experiments performed in our laboratory have shown that the activation of GABAA receptors in the hippocampus leads to excitatory effects during the early post-natal period. The possible consequence of a depolarizing effect of GABA was assessed on the neuritic outgrowth of embryonic hippocampal neurons in culture. No morphological alterations were observed when hippocampal neurons were cultured for three days in the presence of muscimol, a GABAA receptor agonist. In contrast, the neuritic outgrowth of cultured hippocampal neurons was profoundly affected by the presence of bicuculline in the culture medium. In the presence of this GABAA receptor antagonist neurons displayed a reduction in the number of primary neurites and branching points, resulting in a concomitant decrease of the total neuritic length. Thus, this study suggests that GABA, acting on GABAA subtype of receptors, is able to affect the development of the hippocampus.

Animals↗

PubMed1993

Galanin reduces release of endogenous excitatory amino acids in the rat hippocampus.

Galanin is a 29-amino acid peptide widely distributed in the central nervous system where it modulates the release of several neurotransmitters and neurohormones. Because previous data had postulated that galanin could inhibit the release of excitatory amino acids and protect hippocampal neurons against anoxia, we have investigated the effect of galanin on the release of endogenous glutamate and aspartate evoked by potassium depolarization in rat hippocampal slices. Galanin, added to a concentration of 0.3 microM, produced a 50-60% reduction in the release of endogenous glutamate and aspartate as evoked by 40 mM K+. This effect was concentration-dependent with half-maximal effective galanin concentrations (EC50) of 1.7 and 5.9 nM for glutamate and aspartate, respectively. Such an effect was found to occur preferentially in the ventral rather than in the dorsal region of the hippocampus. The inhibitory effect of galanin on the K(+)-evoked release of excitatory amino acids was reversed by the specific galanin antagonist M-15 (0.3 microM), and by the ATP-sensitive potassium channel blocker glibenclamide (10 microM). Furthermore, M-15 alone increased the basal and the K(+)-evoked release of glutamate and aspartate from hippocampal slices. It is concluded that galanin exerts a tonic inhibition of excitatory glutamate/aspartate neurotransmission in the rat ventral hippocampus. The efficacy of glibenclamide in antagonizing the effect of galanin suggests the involvement of ATP-sensitive or -insensitive potassium channels in such a regulation.

Animals↗

PubMed1993

Epilepsy induced collateral sprouting of hippocampal mossy fibers: does it induce the development of ectopic synapses with granule cell dendrites?

In the present study, using Golgi and electron microscopy techniques, experimentally induced epilepsy (kindling and kainate treatment) elicited collateral sprouting of mossy fibers in rat hippocampus. Collateral branches invade the hilus, cross the granule cell layer, and distribute throughout the inner third of the molecular layer. These newly developed collaterals may acquire the typical features of mossy fibers including giant fiber varicosities (mousses), although the mean surface of these mousses was thinner in these collaterals than in terminal branches. Granule cell dendrites may develop giant thorny excrescences, suggesting that the targets of these collaterals are granule cells. Giant synaptic boutons appear in the inner third of molecular layer of epileptic rats. These boutons acquire the morphological features of mossy fiber boutons and made multiple synaptic contacts with dendritic spines. The analysis of the profile types suggests that some of the newly developed collateral mossy fibers made hypotrophic synaptic contacts.

Animals↗

PubMed1993

Reactive astrocytes in the kainic acid-damage hippocampus have the phenotypic features of type-2 astrocytes.

Kainic acid treatment, a model of temporal lobe epilepsy, induces Ammon's horn sclerosis characterized by degeneration of CA3 pyramidal neurons and reactive gliosis. We now report that in kainic acid treated rats, reactive astrocytes in the hippocampus are A2B5 immunopositive and express GAP-43 immunoreactivity. A2B5 is a cell surface ganglioside selectively expressed in the glial O-2A lineage (oligodendrocytes and type-2 astrocytes in vitro). Since A2B5-positive cells were also GFAP immunoreactive, our observation suggest that hippocampal-reactive astrocytes in the epileptic process are type-2 astrocytes. GAP-43 is a membrane-associated phosphoprotein involved in neurite outgrowth. In vitro analysis showed that the glial O-2A lineage may express this phosphoprotein. In this study, we found that GAP-43 was coexpressed in astrocytes with A2B5 suggesting that in vivo as in vitro type-2 astrocytes express GAP-43.

Animals↗

PubMed1993

Alterations of the GluR-B AMPA receptor subunit flip/flop expression in kainate-induced epilepsy and ischemia.

In the hippocampus, glutamatergic pathways are altered following seizure activity or transient global ischemia, both pathological conditions leading to selective neuronal degeneration. Glutamatergic receptors, and notably alpha-amino-3-hydroxy-5-methyl-4-isoxazolopropionate (AMPA) receptors, a family of glutamate receptors involved in fast synaptic transmission and in the maintenance of synaptic potentiation may play an important role in the pathological outcome. AMPA receptors are assembled from GluR-A, GluR-B, GluR-C and GluR-D polypeptides which exist in flop and flip variants, the latter allowing larger glutamate responses. Using in situ hybridization techniques, we show that kainate-induced epilepsy provokes a rapid but transient increase (50%) of GluR-B flip mRNA levels in all subregions of the hippocampus (CA1, CA3, dentate gyrus). This early phase is followed by a second, persistent GluR-B flip increase in regions in which neurons are known to be seizure-resistant (i.e. CA1 an dentate gyrus) while a 35% decrease is observed in the vulnerable CA3 area. Following global ischemia, the levels of GluR-B flip and flop variants are dramatically reduced (90-100%), well before any morphological signs of cell death, in the subiculum and CA1, two areas known to be particularly sensitive to ischemic insult. In keeping with the properties of GluR flip variants, it is suggested that altered subunit stoichiometry may lead to long-lasting enhanced efficiency of fast synaptic transmission in the epileptic hippocampus. Since GluR-B containing receptors are Ca2+ impermeable, our results also suggest altered Ca2+ permeability in the vulnerable pyramidal neurons of areas CA3 and CA1 in the epileptic and ischemic hippocampi, respectively.

Animals↗

PubMed1993

Regional distribution of sulfonylurea receptors in the brain of rodent and primate.

Glibenclamide, one of the most potent antidiabetic sulfonylureas, inhibits the activity of ATP-sensitive K+ channels in the pancreas as well as in the brain through its binding to specific receptors. Quantitative autoradiography was used to localize such receptors in the brain of rat, mouse, guinea-pig and marmoset, using [3H]glibenclamide as radioligand. In all four species, specific glibenclamide binding sites were found to be heterogeneously distributed. The highest densities were in the cerebral cortex, the molecular layer of the cerebellar cortex, the thalamus and the caudate-putamen. The globus pallidus and the substantia nigra were highly labelled in rat and mouse but poorly labelled in guinea-pig and marmoset. The distribution of glibenclamide binding sites in the hippocampus was different between the rodents and marmoset; in rodents, most binding sites were distributed in the fascia dentata and the CA3-CA4 fields of Ammon's horn, contrasting with a very homogeneous distribution in all subfields of the marmoset hippocampus. In conclusion, we demonstrate that primate brain contains specific binding sites for [3H]glibenclamide with a distribution not exactly similar to that in rodent brain.

Animals↗

PubMed1993

Biochemical correlates of long-term potentiation in hippocampal synapses.

Figure 2 summarizes biochemical events which are currently known or hypothesized to participate in LTP induction/maintenance. Current evidence strongly suggests that postsynaptic Ca2+, both entered from the outside of cells and released from intracellular stores, is the initial key substance for the induction of LTP. A rise of [Ca2+]i triggers a variety of enzymatic reactions and initiates the enhancement of synaptic transmission. This first step may be achieved by direct/indirect phosphorylations of protein molecules in postsynaptic receptors/ion channels. This would result in an increase in receptor sensitivity. An immediate increase in the number of available postsynaptic receptors by modifications of spine morphology is another candidate. Such modifications may be accomplished by cytoskeleton rearrangements or changes in extracellular environments. A change in spine structure may also cause an increase in spine neck conductance. Although it is unknown to what extent the increase in [Ca2+]i affects cellular chemistry, Ca2+ probably also directly/indirectly stimulates cascades which exert effects more slowly. A delayed increase in metabotropic receptor sensitivity may occur. New synthesis of protein molecules may be involved in late periods of LTP by replacing turnovered molecules and/or by supplying new materials. Some of these chains of biochemical events may also apply to presynaptic terminals, although the existence of retrograde messenger substances must still be confirmed. In addition, interactions between different protein kinases and second messengers appear to occur to bring about final effects.

Animals↗

PubMed1993

Regional variability in DNA fragmentation after global ischemia evidenced by combined histological and gel electrophoresis observations in the rat brain.

We have studied whether the delayed cell death induced by transient forebrain ischemia is associated with an internucleosomal cleavage of DNA into oligonucleosome-sized fragments. The integrity of genomic DNA in various brain regions after a 20-min four-vessel ischemia was examined using gel electrophoresis. We found typical ladders of oligonucleosomal DNA fragments in the striatum and in the Ammon's horn. In the latter we also often found a random DNA degradation as a smear pattern. These findings were reinforced by a specific in situ labeling of DNA breaks in tissue sections. A dark staining of nuclei was observed in the cell bodies of neurons--in particular in the head of the caudate and in the vulnerable CA1 hippocampal area. With biochemical and histological approaches, there was no evidence of DNA degradation in regions that are resistant to the injury. We conclude that the association of multiple mechanisms of cell damage may occur after a global ischemia. The regional variability in DNA fragmentation stresses the importance of using histological approaches in parallel with gel electrophoresis.

Animals↗

PubMed1993

Glutamate-induced neuronal death is not a programmed cell death in cerebellar culture.

Activation of programmed cell death has recently been suggested to be involved in the delayed neuronal death of CA1 hippocampal neurons after global ischemia based on protection offered by protein synthesis inhibitors. Here, we studied the effects of transcriptional (actinomycin D) and translational (cycloheximide and anisomycin) inhibitors on glutamate-induced neuronal death in cerebellar granule cell cultures. The effects of aurintricarboxylic acid, an endonuclease inhibitor, were studied as well. No protection against glutamate toxicity could be observed with any of these inhibitors. We also analyzed the genomic DNA of glutamate-treated cells on agarose gel electrophoresis. No DNA degradation could be observed after glutamate exposure. We conclude that glutamate-induced neuronal death does not exhibit the features of apoptosis in cultured granule cells.

Animals↗