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J Bockaert

Publications and source records attributed to J Bockaert.

At least 19 recordsLinked to original sources
PubMed1992

Alternative splicing generates metabotropic glutamate receptors inducing different patterns of calcium release in Xenopus oocytes.

A splice variant of the metabotropic glutamate receptor (mGluR) 1a, named mGluR1c, was isolated. Compared to mGluR1a, the predicted mGluR1c protein is 302 amino acids shorter at its C-terminal end. Despite this difference, mGluR1c activates phospholipase C in Xenopus oocytes with a pharmacological profile identical to that of mGluR1a. However, in contrast to the large fast transient responses induced by mGluR1a, mGluR1c receptors elicit a small more slowly generated long-lasting oscillatory current, suggesting that these two receptors do not generate the same pattern of Ca2+ release in Xenopus oocytes. In situ hybridization data show that mGluR1c mRNA is expressed at a lower level than the other splice variants of mGluR1. Some differences in the regional distribution of these transcripts were observed in the cerebellum, the olfactory bulb, and the striatum.

Alternative Splicing↗
PubMed1992

Measurement of gamma-enolase release, a new method for selective quantification of neurotoxicity independently from glial lysis.

We have developed a sensitive enzymatic-immunoassay to quantify the level of gamma-enolase (a specific neuronal enzyme) which is released from cultured cells after exposure to various toxins. We show that this method can estimate selectively neuronal cell death without significantly interfering with glial cell death. Indeed, no gamma-enolase is released when glial cells are killed with free-radical producing agents. Experiments comparing the levels of neuronal cell death induced by NMDA or free-radical producing drugs, performed either by measuring gamma-enolase release or using the classical fluorescein diacetate method, yielded similar results. In addition to selectively follow neuronal death in a mixed population of neurons and glial cells, this method provides a way of determining the cell death kinetics from a single culture dish, since enolase can be measured on small samples taken from the culture medium. Finally, we propose these two methods as being complementary and useful neuronal and other cellular death indexes and also to understand the complex problem of glial influence on neuronal survival or death.

Animals↗
PubMed1992

Characterization of a metabotropic glutamate receptor: direct negative coupling to adenylyl cyclase and involvement of a pertussis toxin-sensitive G protein.

We have characterized a G-protein-coupled glutamate receptor in primary cultures of striatal neurons. Glutamate, quisqualate, or trans-1-aminocyclopentane-1,3-dicarboxylate inhibited by 30-40% either forskolin-stimulated cAMP production in intact cells or forskolin plus vasoactive intestinal peptide-activated adenylyl cyclase assayed in neuronal membrane preparations. These inhibitory effects were suppressed after treatment of striatal neurons with Bordetella pertussis toxin, suggesting the involvement of a heterotrimeric guanine nucleotide-binding protein (G protein) of the G(i)/G(o) subtype. The pharmacological profile of this glutamate receptor negatively coupled to adenylyl cyclase was different from that of the metabotropic Qp glutamate receptor coupled to phospholipase C in striatal neurons and from that of the recently cloned "mGluR2" glutamate receptor, which is negatively coupled to adenylyl cyclase when expressed in non-neuronal cells.

Adenylate Cyclase Toxin↗
PubMed1992

Trans-ACPD inhibits cAMP formation via a pertussis toxin-sensitive G-protein.

In primary cultured striatal neurons we found that (+-)-trans-1-amino-cyclopentyl-1,3-dicarboxylate (trans-ACPD) could inhibit forskolin-induced cAMP formation in a dose-dependent manner (EC50 156 +/- 38 microM, n = 5, maximal inhibition 37.8 +/- 1.2, n = 37). The trans-ACPD-induced inhibition was totally abolished in neurons preincubated with Bordetella pertussis toxin (1 microgram/ml), demonstrating the involvement of a G-protein. This is the first report in intact neurons of a glutamate metabotropic receptor negatively coupled to cAMP formation.

Animals↗
PubMed1992

Insulin releasing effects of mastoparan and amphiphilic substance P receptor antagonists on RINm5F insulinoma cells.

It has been proposed that mastoparan (INLKALAALAKKIL) and other mast cell secretagogues such as substance P (SP) or compound 48/80 act by direct activation of the pertussis toxin (PTX)-sensitive G-proteins in intact cells. Here we have investigated whether or not the antagonists of SP, [D-Trp7,9,10] SP1-11 and [D-Trp7,9,10, N-leu11]SP1-11, can similarly induce exocytosis from RINm5F cells. In intact cells mastoparan and the SP antagonists stimulated insulin release in a dose-dependent manner at concentrations ranging from 10 to 100 microM. The maximal effect on insulin release, of both mastoparan and the SP antagonists was comparable to that obtained with 100 microM forskolin. Pretreatment of the intact cells, for 18 h with PTX or 6 h with cholera toxin, did not change the responses induced by both mastoparan and the SP antagonists. This absence of PTX effect, despite the fact that the three PTX substrates at 41, 40 and 39 kDa were ADP ribosylated after pretreatment suggests intrinsic differences between mast and RINm5F cells. Thus the SP antagonists behave similarly to mastoparan in its ability to induce insulin release in RINm5F cells. However, the higher concentrations required with RINm5F cells compared to that needed for mast cells suggest differences either in G-proteins composition or in the phospholipid composition of the membranes.

Adenosine Diphosphate Ribose↗
PubMed1992

Differential coupling of 5-HT1A receptors occupied by 5-HT or 8-OH-DPAT to adenylyl cyclase.

Human serotonin (5-hydroxytryptamine, 5-HT)-1A receptors have been transfected in NIH-3T3 cells, and their coupling to adenylyl cyclase was analysed depending on 1) the number of receptor expressed, 2) the experimental conditions used, 3) the nature of the agonists. Two monoclonal cell lines were used, expressing low (45 fmol/mg) and high (500 fmol/mg) levels of 5-HT1A receptor. Two methods were tested to study the negative coupling of the transfected 5-HT1A receptors to adenylyl cyclase: 1) measurement of cAMP production in intact cells, 2) measurement of adenylyl cyclase activity in vitro on membrane preparations. Studies on intact cells revealed that an increase in the receptor concentration was followed by 1) an increase in the efficacies of 5-HT, 5-CT (5-carboxamidotryptamine) and 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), 2) a 2 to 3-fold increase in the potency of 5-CT and 8-OH-DPAT, but no change in the potency of 5-HT. In membrane preparations, 8-OH-DPAT dose-response curve was shifted leftwards when the receptor concentration became higher whereas the corresponding shift was smaller for 5-HT and absent for 5-CT. Surprisingly, on membrane preparations, 8-OH-DPAT was a partial agonist relative to 5-HT. The relative efficacy of 8-OH-DPAT was lower in the clone expressing the lowest level of receptor. This partial agonist behavior of 8-OH-DPAT could be modulated by the ionic conditions under which the adenylyl cyclase activity was measured.(ABSTRACT TRUNCATED AT 250 WORDS)

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1992

Long-term expression of the c-fos protein during the in vitro differentiation of cerebellar granule cells induced by potassium or NMDA.

Levels of the c-fos protein were assayed in mouse cerebellar granule cells during their in vitro development under different culture conditions. When grown in media favoring both their survival and differentiation, i.e. in the presence of 30 mM K+ or 12.5 mM K+ plus 100 microM N-methyl-D-aspartate (NMDA), the c-fos protein becomes detectable in the nucleus of granule cells on and after 6 days and persists to high levels until the culture begins to decline. The protein c-fos appears therefore after the critical period described for the survival effect of K+ depolarization or NMDA receptor stimulation which corresponds to days 2-5 after plating. The c-fos protein remains however scarcely detectable or undetectable throughout the life-span of cells cultured under conditions providing poor survival and differentiation, i.e. in the presence of low K+ (5 or 12.5 mM) alone or when the effect of NMDA is blocked by the NMDA receptor antagonist MK-801. Interestingly, in cortical and striatal neurons, the survival and differentiation of which being not affected by depolarizing media, no c-fos protein is detected whatever the culture conditions tested at least during the first 18 days in vitro. This suggests that long-term expression of the c-fos gene might be related to some aspect of the late in vitro differentiation process of cerebellar granule cells.

Animals↗
PubMed1992

Nitric oxide-induced blockade of NMDA receptors.

We studied the effects of nitric oxide (NO)-producing agents on N-methyl-D-aspartate (NMDA) receptor activation in cultured neurons. 3-Morpholino-sydnonimine (SIN-1) blocked both NMDA-induced currents and the associated increase in intracellular Ca2+. The actions of SIN-1 were reversible and suppressed by hemoglobin. A degraded SIN-1 solution that did not release NO was unable to block NMDA receptors. This showed that the SIN-1 effects were due to NO and not to another breakdown product. Similar results were obtained with 1-nitrosopyrrolidine (an NO-containing drug) and with NO released from NaNO2. Pretreatment with hemoglobin potentiated NMDA-induced effects, demonstrating that endogenous NO modulates NMDA receptors. Since NMDA receptor activation induces NO synthesis, these results suggest a feedback inhibition of NMDA receptors by NO under physiological condition.

Animals↗
PubMed1992

Differential G protein-mediated coupling of D2 dopamine receptors to K+ and Ca2+ currents in rat anterior pituitary cells.

In anterior pituitary cells, dopamine, acting on D2 dopamine receptors, concomitantly reduces calcium currents and increases potassium currents. These dopamine effects require the presence of intracellular GTP and are blocked by pretreatment of the cells with pertussis toxin, suggesting that one or more G protein is involved. To identify the G proteins involved in coupling D2 receptors to these currents, we performed patch-clamp recordings in the whole-cell configuration using pipettes containing affinity-purified polyclonal antibodies raised against either Go alpha, Gi3 alpha, or Gi1,2 alpha. Dialysis with Go alpha antiserum significantly reduced the inhibition of calcium currents induced by dopamine, while increase of potassium currents was markedly attenuated only by Gi3 alpha antiserum. We therefore conclude that in pituitary cells, two different G proteins are involved in the signal transduction mechanism that links D2 receptor activation to a specific modulation of the four types of ionic channels studied here.

Adenosine Diphosphate Ribose↗
PubMed1992

The metabotropic glutamate receptor (MGR): pharmacology and subcellular location.

A pharmacological characterization of the metabotropic glutamate receptor (MGR) was performed in striatal neurons. Among the excitatory amino acid receptor antagonists tested, only D, L-2-amino-3-phosphonopropionate (D, L-AP3) inhibited QA-induced inositol phosphate (InsP) formation in a competitive manner (mean pKi = 4.45 +/- 0.43, n = 4). However, this drug was a partial agonist of MGR since it stimulated the inositol-phosphate formation. We found that D, L-AP3 also inhibited NMDA-induced calcium increase, in a competitive manner (mean pIC50 = 4.34 +/- 0.22, n = 8, and mean pKi = 3.7 +/- 0.11 n = 5). 1 mM of the ionotropic agonists alpha-amino-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), kainate (KA) or domoate (DO) (100 microM or higher) induced a significant InsP formation in striatal neurons. The InsP responses induced by all these agonists were totally blocked by the phorbol ester phorbol-12,13-dibutyrate (PdBu), but not by atropine or prazosin. Agonist-induced increases of intracellular calcium concentrations ([Ca2+]i) were insensitive to PdBu, suggesting that all these substances were able to stimulate the MGR in striatal neurons. Trans-1-amino-cyclopentyl-1,3-dicarboxylate (trans-ACPD) evoked dose-dependent inositol phosphate formations with an EC50 of 29 microM but had no significant effect on NMDA or AMPA receptors, as measured by the patch clamp technique. In the presence of 30 microM of AMPA, trans-ACPD induced a significant release of arachidonic acid (AA) in striatal neurons. No important AA release was observed by any of these agonists alone. 56 mM K+ did not mimic AMPA in this associative ionotropic/metabotropic effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Activation of 5-HT1A receptors expressed in NIH-3T3 cells induces focus formation and potentiates EGF effect on DNA synthesis.

NIH-3T3 fibroblasts have been transfected with human serotonin 5-HT1A receptors. Clonal cell lines expressed between 40 and 500 fmol receptor/mg. 5-HT1A agonists strongly inhibited nonstimulated- as well as forskolin- or isoproterenol-stimulated adenylyl cyclase. The effects of 5-HT1A receptor activation on cell growth were investigated. 5-HT1A agonists accelerated cell division, generated foci, and increased DNA synthesis. The stimulation of [3H]thymidine incorporation was much stronger when tyrosine kinase receptors were activated concomitantly. Cyclic AMP (cAMP) elevating agents inhibited DNA synthesis induced by all mitogens tested. The mitogenic activity of 5-HT1A agonists did not seem to be linked to adenylyl cyclase inhibition because 1) we were not able to measure any decrease in intracellular cAMP levels under the conditions of DNA synthesis assay and 2) 2',5'-dideoxyadenosine, which strongly inhibited adenylyl cyclase, was not mitogenic and did not modify the mitogenic effects of 5-HT1A agonists. Pertussis toxin completely blocked potentiation of epidermal growth factor effect induced by 8-hydroxy-di-(n-propyl)aminotetralin, a 5-HT1A agonist, but only partially blocked the one induced by insulin. In conclusion, in transfected NIH-3T3 cells, transforming and mitogenic effects of 5-HT1A agonists involve a pertussis toxin-sensitive G protein but do not seem to be linked to adenylyl cyclase inhibition.

3T3 Cells↗
PubMed1992

Sodium nitroprusside blocks NMDA receptors via formation of ferrocyanide ions.

The effects of a nitric oxide (NO) donor, sodium nitroprusside (SNP), on N-methyl-D-aspartate (NMDA) receptors were assessed by optical measurements of intracellular calcium concentration ([Ca2+]i) and patch-clamp techniques in cultured central neurons. SNP selectively blocked NMDA-mediated currents and increases in [Ca2+]i. SNP inhibited the binding of [3H]-CGS 19755. The blockade of NMDA responses by SNP was prevented by CPP or APV which are selective competitive NMDA receptor antagonists. These effects were not necessarily mediated by NO, since they were mimicked by ferrocyanide ions, the NO companion photolysis product of SNP.

Animals↗
PubMed1992

A nitric oxide (NO) synthase inhibitor accelerates amygdala kindling.

In response to NMDA receptor activation, hippocampal, striatal and cerebellar neurons synthesize nitric oxide (NO), which in turn elevates cGMP levels via guanylate cyclase. NO is increasingly being considered as a transsynaptic retrograde messenger, involved in neuronal plasticity. The effect of an inhibitor of NO synthase, L-NG-nitroarginine (NOArg), was studied on amygdala kindling and on kindled seizures in rats. NOArg increased kindling rate, particularly in its initial period, but did not modify seizure severity in previously kindled rats, although we have no definitive explanation for this effect. However, an enhanced post-synaptic excitability could be attributed to the blockade of the negative feed-back exerted by NO on the NMDA receptor.

Amino Acid Oxidoreductases↗
PubMed1992

Chronic NO synthase inhibition fails to protect hippocampal neurones against NMDA toxicity.

Since nitric oxide (NO) is supposed to mediate excitotoxicity in various brain structures, the effects of two NO synthase inhibitors were studied on rat hippocampal lesions induced by the focal injection of N-methyl-D-aspartate (NMDA). Although both drugs (NG-nitro-L-arginine methyl ester: L-NAME and L-NG-nitroarginine: L-NOARG) were given twice daily for 4 days before NMDA injection, at doses which are known to profoundly inhibit NO synthase activity, no significant decrease of NMDA-induced damage could be observed. These results do not confirm the current hypothesis of a NO involvement in NMDA toxicity at least on hippocampal neurons, in vivo.

Amino Acid Oxidoreductases↗
PubMed1992

The 5-HT4 receptor subtype inhibits K+ current in colliculi neurones via activation of a cyclic AMP-dependent protein kinase.

1. The aim of the present study was to examine the effect of 5-hydroxytryptamine (5-HT) on K+ current in primary culture of mouse colliculi neurones and to identify the 5-HT receptor subtype that could be involved in this effect. 2. The voltage-activated K+ current of the neurones was partially blocked by 8-bromo adenosine 3':5'-cyclic monophosphate (8-bromo-cyclic AMP). This effect was mimicked by 5-HT and the action of 5-HT could be antagonized by H7, a non specific protein kinase inhibitor, and by PKI, the specific cyclic AMP-dependent protein kinase blocker. 3. A similar cyclic AMP-dependent blockade of the K+ current was found with renzapride (BRL 24,924) and other 5-HT4 receptor agonists such as cisapride, BIMU 8, zacopride and 5-methoxytryptamine (5-MeOT). ICS 205,930, the classical 5-HT4 receptor blocker, could not be used in this study because it inhibited the studied K+ current by itself. However, the novel 5-HT4 receptor antagonist, DAU 6285 blocked the effects of 5-HT and renzapride on the K+ current. 4. The current was insensitive to the 5-HT1 and 5-HT3 receptor agonists (8-hydroxy-2-(di-n-propylamino) tetralin, RU 24,969, carboxamidotryptamine, 2-CH3-5-HT) as well as to 5-HT1, 5-HT2 and 5-HT3 antagonists (methiothepin, ketanserin, ondansetron [GR 38,032]). Moreover, these antagonists did not affect the actions of the tested 5-HT4 receptor agonists. 5. The present results show that part of the voltage-activated K+ current in mouse colliculi neurones is cyclic AMP-sensitive and the blockade of the current by 5-HT involves the 5-HT4 receptor subtype.The putative implication of 5-HT4 receptors in neuronal plasticity, via a blockade of K+ channels, is discussed.

Animals↗
PubMed1992

Evidence for a glutamate receptor of the AMPA subtype which mediates insulin release from rat perfused pancreas.

1. The effect of L-glutamate has been studied on insulin secretion by the isolated perfused pancreas of the rat. The glutamate receptor subtype involved has been characterized. 2. In the presence of a slightly stimulating glucose concentration (8.3 mM), L-glutamate (5 x 10(-5)-4 x 10(-3) M) induced an immediate, transient and concentration-dependent insulin response. On the other hand, in the presence of a non stimulating glucose concentration (2.8 mM), L-glutamate (10(-3) M) did not modify the basal insulin secretion. 3. The three non-NMDA receptor agonists, kainate (10(-4)-10(-3) M), alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA, 5 x 10(-5)-10(-4) M) and quisqualate (5 x 10(-6)-5 x 10(-5) M) all provoked a transient and concentration-dependent insulin response from pancreas perfused with 8.3 mM glucose. Compared with glutamate, kainate exhibited a similar efficacy, whereas AMPA and quisqualate elicited only a 3 fold lower maximal insulin response. In contrast, NMDA (10(-4)-10(-3) M) was ineffective. 4. An antagonist of non-NMDA receptors, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; 5 x 10(-5) M) totally prevented the stimulatory effect of L-glutamate (4 x 10(-4) M) and kainate (2 x 10(-4) M). In contrast, the NMDA receptor antagonist, (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine ((+) MK801) was without effect. 5. The insulin secretory effect of glutamate (4 x 10(-4) M) was not affected by atropine (3 x 10(-7) M) or tetrodotoxin (3 x 10(-6) M). 6. Quisqualate at a high maximally effective concentration (4 x 10(-4) M) inhibited glutamate (10(-3) M) or kainate (4 x 10(-4) M)-induced insulin release. 7. This study shows that L-glutamate stimulates insulin secretion in rat pancreas, by acting on an excitatory amino acid receptor of the AMPA subtype.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1992

Dialysis of lactotropes with antisense oligonucleotides assigns guanine nucleotide binding protein subtypes to their channel effectors.

This article describes a new approach for determining the role of endogenous guanine nucleotide binding (G) protein subunits in signal transduction. Sequential patch-clamping was applied to BSA gradient-enriched cultured lactotropes from lactating rats, first to dialyze antisense oligodeoxyribonucleotides (AS) directed against G alpha protein mRNAs and 48 h later to record ion-current responses to the PRL release inhibitor, dopamine. The effectiveness and specificity of action of six types of AS were determined by their effects on the in vitro translation of alpha o, alpha i1, alpha i2, alpha i3, and alpha s. The specificity of AS could be enhanced by replacing guanine by cytosine bases within the center core of AS and by maximizing the number of mismatches against nontargeted mRNAs within the extremities of AS. A total of 59 out of 240 cells could be investigated using the sequential patch clamp procedure in the absence of antibiotics. The typical decrease of the voltage-activated calcium current in response to 10 nM dopamine was diminished or abolished by AS, in correlation with the inhibition of in vitro translation of the alpha o subunit. The typical increase of the voltage-activated potassium current in response to dopamine was abolished by AS directed against alpha i3 but not alpha o mRNA. Control experiments showed that culture conditions or loss of receptor affinity for dopamine were not responsible for the loss of response. The results suggest that dopamine D2 receptors are linked via alpha o to calcium channels and via alpha i3 to potassium channels.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗